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U novome Nacionalnom kurikulumu predmeta Fizika stavlja se naglasak na istraživački usmjerenu nastavu, pri čemu je prednost dana eksperimentalnim istraživanjima koje učenik obavlja samostalno. Cilj ovog rada je odrediti koliki je utjecaj istraživački usmjerene nastave na usvajanje temeljnih fizikalnih koncepata, odnosno odgojno-obrazovnih ishoda. Sudionici istraživanja su učenici sedmih razreda osnovne škole. Kontrolna skupina sastoji se od učenika razrednog odjela kojima je nastava fizike održana kroz predavačku nastavu te rješavanje konceptualnih i numeričkih zadataka uz snimljene pokuse, računalne simulacije i demonstracijske pokuse. U eksperimentalnoj skupini su učenici drugog razrednog odjela kojima je nastava održana slično kao u eksperimentalnoj skupini, ali uz eksperimentalni istraživački rad učenika. Instrument istraživanja su konceptualni zadaci i anketa u kojoj učenici izražavaju svoje stavove o nastavi fizike. Obje skupine imaju istog učitelja fizike te dobivaju iste primjere zadataka i ankete, čiji se podaci obrađuju sa svrhom određivanja moguće razlike u postignutoj razini ostvarenosti odgojno-obrazovnih ishoda., In the new national curriculum for the subject of Physics, emphasis is placed on research-oriented teaching, whereby priority is given to experimental research that the students perform on their own. The goal of this paper is to determine the impact of research-oriented teaching on the understanding of fundamental physical concepts. The participants of the research are seventh-grade elementary school students. The control group consists of a class of students in which physics lessons were held through lectures and solving conceptual and numerical problems with recorded experiments, computer simulations and demonstration experiments. In the experimental group there are students of the another group of seventh-grade elementary school students, in which classes were held similarly, but with the experimental research work student did by themselves. The instruments of the research are conceptual questions and a survey in which students express their views on physics teaching. Both groups have the same physics teacher and receive the same examples of tasks and surveys, the data of which are processed for the purpose of determining possible differences in the achieved level of educational outcomes.

Dioba stanica složen je proces koji počinje formiranjem diobenog vretena koje razdvaja kromosome u dvije stanice kćeri na kraju mitoze. Diobeno vreteno je mikrostroj, sazdan od mikrotubula, koji pažljivo organizira sile koje generiraju motorni proteini, a njegova se funkcionalnost oslanja na preciznosti samoorganizacije vretena. Pogreške u samoorganizaciji vretena mogu dovesti do krive podjele kromosoma (missegregacije) koja rezultira nepravilnim brojem kromosoma u stanicama kćeri. Stanje s nepravilnim brojem kromosoma naziva se aneuploidija. Aneuploidija u kombinaciji s velikom učestalosti dobitka i gubitka kromosoma može stvoriti domino efekt koji dovodi do razvoja tumorskih tkiva. U ovoj doktorskoj tezi želimo razumjeti ključne procese koji stoje iza formiranja antiparalelnih svežnjeva diobenog vretena, kao i istražiti koje su posljedice grešaka tijekom stanične diobe nakon više generacija. Kako bismo razumjeli evoluciju tumora iz zdravih stanica, razvili smo "makrokariotip model" i pokazali da perturbiran broj kromosoma u tumorskim stanicama uglavnom proizlazi zbog brže diobe stanica koje karakterizira specifična kombinacija kromosoma ili zbog kombinacije brže diobe i nepravilne stanične smrti tih stanica. Ovaj teorijski rezultat objašnjava eksperimentalno opažene kombinacije kromosoma u različitim stadijima razvoja tumora, uključujući mali broj aneuploidnih stanica u predtumorskim stadijima, kao i visoko aneuploidne stanice u tumorskom stadiju. Također istražujemo samoorganizaciju mikrotubula u antiparalelne svežnjeve i u tu svrhu razvijamo matematički model koji uključuje dinamiku mikrotubula i motornih proteina. Rješavanjem modela pokazujemo da mikrotubuli sa svakog pola traže one sa suprotnog pola izvodeći nasumično kutno kretanje. Nakon kontakta, dva mikrotubula usmjereno klize bočno jedan duž drugoga prema antiparalelnoj konfiguraciji. Uvodimo duljinu konture mikrotubula kao mjeru aktivnosti motora koji pokreću usmjerenu rotaciju mikrotubula, što otkriva da usmjerenje motora prema minus kraju dovodi mikrotubule u antiparalelnu organizaciju. Zaključno, naš teorijski pristup pridonosi boljem razumijevanju složenog procesa stanične diobe i dugoročnih posljedica njezina neispravnog funkcioniranja te na taj način povezuje dvije različite vremenske skale relevantne za pravilno funkcioniranje stanice. Cell division is a complex process that starts with the formation of a mitotic spindle which segregates chromosomes into two daughter cells at the end of mitosis. The mitotic spindle is a microtubule based micro-machine that carefully orchestrates the forces generated by motor proteins and its functionality relies on the accuracy of spindle self-organization. Errors in spindle self-organization can lead to missegregation which produces aneuploidy, a state with irregular number of chromosomes. Aneuploidy in combination with propensity of gaining and losing chromosome with high frequency can create a domino effect which leads to the development of tumor tissues. In this thesis we aim to understand the key processes behind the formation of an antiparallel bundle of a mitotic spindle as well as explore what are the consequences of errors during cell division after multiple generations. To understand tumor evolution from healthy cells we develop a “macro-karyotype model” and show that the perturbed number of chromosomes in tumor cells arises predominantly from a faster division of cells characterized by a specific combination of chromosomes, or together with irregular cell death. This theoretical result explains experimentally observed combination of chromosomes in different stages of tumor development including a small number of aneuploid cells in pretumor stages as well as highly aneuploid cells in tumor stage. We also investigate the selforganization of microtubules into an antiparallel bundle and for that purpose develop a mathematical model that includes the dynamics of microtubules and motor proteins. By solving the model, we show that microtubules from each pole search for those from the opposite pole by performing a random angular movement. Upon contact, two microtubules slide sideways along each other in a directed manner toward the antiparallel configuration. We introduce the contour length of microtubules as a measure of the activity of motors that drives microtubule sliding, which reveals that minus-end-directed motility drives microtubules into an antiparallel organization. In conclusion, our theoretical approach contributes to a better understanding of the complex process of cell division and the long-term consequences of its malfunctioning and thereby connects two different timescales relevant for proper cell functioning.

Dvostruki beta raspadi (ββ) su relevantni u modernoj fizici jer bezneutrinski mod dvostrukog beta raspada (0νββ) predstavlja mogući signal fizike izvan standardnog modela i zbog važnosti za proučavanje neutrinskih masa. Dvoneutrinski mod (2νββ) je bitan za testiranje modela prije proširenja na 0νββ raspade. U ovom radu, koristeći relativistički energijski funkcional gustoće, nuklearni matrični elementi su istraženi za 2νββ raspad nuklida 48^Ca,76^Ge, 82^Se, 96^Zr, 100^Mo, 116^Cd, 128^Te, 130^Te, 136^Xe i 150^Nd i 0νββ raspad nuklida 76^Ge, 82^Se, 96^Zr, 100^Mo, 110^Pd, 116^Cd, 124^Sn, i 128^Te. Relativistički Hartree-Bardeen-Cooper-Schrieffer (RHBCS) model, odnosno relativistički Hartree-Bogoliubov (RHB) model, korišteni su za opis osnovnog stanja jezgara i proton-neutron relativistička aproksimacija slučajnih faza (PN-RQRPA) za opis relevantnih prijelaza s izmjenom naboja koji doprinose dvostrukim beta raspadima. Korištene su tri efektivne interakcije, interakcija s izmjenom mezona DD-ME2 i interakcije s točkastim vezanjem DD-PC1 i DD-PCX. Korelacije sparivanja su uzete u obzir u oba izospinska kanala koristeći separabilnu interakciju sparivanja. Određene su optimalne vrijednosti parametra snage izoskalarnog sparivanja u PN-RQRPA rezidualnoj interakciji iz prilagodbe poluživota jednostrukih beta raspada. Za 2νββ raspade, istraženi su relevantni faktori faznog prostora i pripadajuća vremena poluživota, i rezultati su uspoređeni s rezultatima prijašnjih istraživanja i eksperimentalnim vrijednostima. Dobiveni rezultati za 2νββ nuklearne matrične elemente su u većini slučajeva nešto manji od rezultata drugih modela, ali su za većinu jezgara blizu eksperimentalnim vrijednostima. Rezultati za 0νββ raspade su uglavnom manji od vrijednosti koje bi mogli očekivati na temelju rezultata drugih modela, pogotovo za interakcije s točkastim vezanjem. Ovaj rad predstavlja prvu primjenu relativističkog teorijskog okvira zasnovanog na PN-RQRPA na problem dvostrukih beta raspada. Osim toga, računi bezneutrinskih dvostrukih beta raspada uključuju puni relativistički operator prijelaza izveden bez nerelativističkih redukcija, što ovaj rad čini prvom implementacijom punog relativističkog operatora za bezneutrinske dvostruke beta raspade u računu temeljenom na QRPA. Postoji niz mogućih unaprijeđenja i proširenja modela, od kojih treba istaknuti uključivanje većeg broja multipola međujezgre, uključivanje kratkodosežnih korelacija i razvoj modela za deformirane jezgre. Double beta decays comprise decays of radioactive nuclei where two neutrons decay into two protons, or vice versa. Depending on whether neutrinos are emitted concurrently, the decays can be classified as two-neutrino (2νββ) or neutrinoless (0νββ). As second-order processes, the only situation in which double beta decays represent a significant decay branch is the decay of even-even nuclei[1], where a single beta decay of an even-even parent nucleus, stabilised by pairing, into a less stable odd daughter nucleus is forbidden[1]. This means that there is a small number of experimentally verified nuclides that decay through 2νββ decay and a small number of candidates for the experimentally unobserved 0νββ decay. Once considered of little significance[2], double beta decays have become an object of considerable theoretical interest in recent years[3, 4]. The revival of interest in the topic of double beta decays is chiefly due to the connection of the 0νββ decay mode to physics beyond the standard model, particularly to the question of the nature of the neutrino (namely whether the neutrino is a Majorana or a Dirac particle)[5]. This connection is proven to hold regardless of the underlying physics by the Schechter-Valle "black box" theorem [6]. Despite the importance of neutrinoless decays, the 2νββ remains important as the only double beta decay mode we have experimental evidence of, despite significant experimentalist effort to find a signal of neutrinoless double beta decay[7, 8, 9, 10, 11, 12, 13], and as such is indispensable for developing and benchmarking theoretical frameworks for double beta decay. The present work addresses both modes of double beta decay, in the framework of a protonneutron (or charge exchange) quasiparticle random-phase approximation (PN-RQRPA)[14] based on relativistic nuclear energy density functional[15, 16]. This work presents the first calculation of the nuclear properties of double beta decay based on the PN-RQRPA and as the first implementation of our theoretical framework represents a starting point for further studies within the relativistic framework. The most important quantity to be calculated, from a nuclear structure standpoint, is the nuclear matrix element. Within approaches based on the QRPA, this is achieved by using data (transition matrix elements, QRPA amplitudes, occupation numbers and energies) from two single beta decay calculations, starting from the initial and from the final nucleus. The difference in the final states for both, representing the intermediate nucleus, is taken into account with an overlap factor calculated from occupation factors and QRPA amplitudes for both single beta calculations. In the present work we use both the most widespread form for the overlap factor[17] and a more involved form due to Simkovic[18], however by comparing the overall values of the NME we find that the differences are small. The PN-RQRPA calculation is built on top of a relativistic mean-field theory, which in the present work is realised as either relativistic Hartree-BCS or relativistic Hartree-Bogoliubov model. The relativistic Lagrangians associated with the nuclear energy density functional include three density dependent interactions: the DD-ME2[19] meson-exchange interaction based on quantum hadrodynamics[20] and the point coupling interactions DD-PC1[21] and DD-PCX[22]. The use of different interactions allows us to estimate systematically the theoretical spread of values for the matrix elements in our framework. All of the calculations were maximally self-consistent, including quantities such as nuclear radii and Q-values derived directly from our relativistic mean-field calculations. The implementation of the relativistic mean field theory in the description of ground state properties is based on the DIRHB code for the relativistic Hartree-Bogoliubov model[23] and alternately the relativistic Hartree-BCS model[24] and the code for QRPA already in use at the University of Zagreb[25]. The relativistic charge-exchange QRPA (PN-RQRPA) allows us to calculate the states in the intermediate nuclei for both kinds of double beta decay as excitations from an even-even nucleus. For the calculation of the final nuclear matrix elements, custom code has been written that connects the outputs of the two QRPA calculations. The strength of the isoscalar pairing in the residual interaction of the PN-RQRPA, which we describe using a dimensionless parameter V_0pp, is a crucial parameter of our model. For the 2νββ decay mode, we show both the dependence of the nuclear matrix element on V_0pp and the values of the NME at optimal T=0 pairing strength. The optimal values of V_0pp were determined following the approach of Ref. [26, 27, 28], based on a global fit of the half-lives of single β decay to the experimental data. We use even-even nuclides spanning 8 ≤ Z ≤ 82, for which experimental data on single β decays are available, and where the effect of changing V_0pp on the relative change of T_1/2 is larger than 20%, and where T_1/2 < 103 s. The ansatz we work with depends on (N −Z), introducing an isotopic dependence on V_0pp. The optimal values of V_0pp obtained in this way are mostly clustered around 1.0, showing a very weak breaking of the isospin symmetry. As this is close to the so-called breaking point of the PN-RQRPA[29], where the lowest root of the PN-RQRPA equation becomes imaginary and a new mean field description is necessary, for most nuclides, it contributes to an additional and considerable lowering of the NME from the values at V_0pp = 0. The problem of the value of the axial coupling constant, gA, that is essential in weak processes, is briefly discussed in the work; more information can be found, e.g., in Ref.[3]. Concerning the value of the gA parameter in our work, we have decided not to use excessively quenched values below gA = 1.0, as sometimes used in QRPA calculations[3, 30]. We either use the vacuum value, gA = 1.27, or a reasonably quenched value of gA = 1.0. An argument in favour of the latter can be made as it has proven to be the case that some quenching is necessary in order to reproduce single beta decay half-lives[31]. In the case of 2νββ decay we show the results for both values, although we use gA = 1.0 in tables and in comparisons with the results of other theoretical approaches. In the case of 0νββ decays, our calculations use gA = 1.27 in order to facilitate comparison to the results of calculations of 0νββ nuclear matrix elements in other theoretical frameworks. As is known, the closure approximation is not appropriate for the treatment of 2νββ decays, so in all cases except when explicitly noted, the 2νββ nuclear matrix elements have been calculated using the full energy denominator. The only cases where the closure approximation was used was in comparison with the Interacting Boson Model (IBM) results[32] which were themselves calculated in the closure approximation. The energy denominator is taken from Ref. [33] and differs for each nucleus. The 0νββ results were calculated in the closure approximation, which is appropriate for this mode of decay[34]. The average closure energies were the same as those used in the 2νββ case. Our results for the nuclear matrix elements for the 2νββ mode are in general smaller than the results of other approaches[3, 30, 35, 36, 37, 38, 39]. However we argue they are just as good if not improved when compared to the experimental NMEs[40] for known double beta decays. The two nuclides whose NMEs diverge from the experimental results the most, 76Ge and 82Se, can be shown to display marked triaxiality[41], which means that a more successful description of their 2νββ decays might have to wait for the development of a deformed version of the PN-RQRPA code. In addition to the nuclear matrix elements, we calculate the phase space factors and the halflives for those 2νββ nuclides where the data about the optimal V_0pp is available. The calculation of the phase space factors follows the approach of Ref.[42, 33], although we report new values of the PSF that do not correspond entirely to the results in the works cited. The calculated halflives show variance from the experimental results, although most of them are within an order of magnitude from the experimental T_1/2. Concerning the calculations of 0νββ nuclear matrix elements, the main feature that distinguishes this work from previous studies of neutrinoless double beta decay is that, following recent work mostly in the framework of the generator coordinate method[43, 44, 45], we extend our calculations to also use the full relativistic transition operator in addition to the transition operator that arises from a nonrelativistic reduction of that operator. As a result, instead of grouping the contributions to our nuclear matrix element into distinct Fermi, Gamow-Teller and tensor terms, we can directly show the contributions of the operators containing vector-vector (VV), axial-vector-axial-vector (AA), axial-vector-pseudovector (AP), pseudoscalar-pseudoscalar (PP) and weak magnetic (MP) couplings to the final result. We obtain results consistent with the fact, already reported[44], that the AA operator contributes the most to the final value of the nuclear matrix element, with the other couplings contributing at most around 1% of the total absolute value to the 0νββ nuclear matrix element, whether the fully relativistic operator is used or not, except in 116^Cd where the contributions go up to 7%. Our calculations of the 2νββ nuclear matrix elements converged at a maximum pn pair energy of around 100 MeV. Unfortunately we find that the 0νββ matrix element converges much slower, and calculations need to be extended to higher energies. Therefore the calculation of 0νββ NMEs requires considerable computing power, which is exacerbated by the fact that we have to sum over a large number of JΠ states of the intermediate nucleus. Since this is the first application of the PN-RQRPA-based model, we have decided to limit ourselves to a maximum value of the multipole of the transition to the intermediate nucleus of 6+, and to disregard the weak magnetic contribution (which we expect to be low[44]) from the fully relativistic calculation. Furthermore we have been unable to implement an easy way to take short-range correlations[34] into account, particularly since our calculation of the 0νββ matrix elements proceeds in a novel way. These and other limitations still leave our work as proof of concept that 0νββ NMEs can be calculated by directly calculating the contributions of various coupling channels, without recoupling the result into a matrix element between two-neutron and two-proton states, as is commonly done in the relevant literature[46]. Finally, the nuclear matrix elements we obtain are almost systematically lower than those calculated in other theoretical approaches, even those based on the pn-QRPA. This was already the case for the 2νββ nuclear matrix elements we obtain, but is more pronounced in the 0νββ case. Of course, in the latter case we also do not have any experimental data to compare our results to. Calculating the 0νββ matrix elements for the case in which isoscalar pairing vanishes does not help much as the dependence of the nuclear matrix elements on the strength parameter for isoscalar pairing V_0pp is rather slight, as expected[47]. Only for the DD-ME2 results we obtain an appreciable enhancement of the 0νββ NMEs. In fact, our results for the 0νββ nuclear matrix elements are closer to those of the interacting shell model than most of those reported from the nonrelativistic QRPA approaches. Curiously, a similar Skyrme-based (the similarity of Skyrme and point coupling interactions has been noted[48]) QRPA calculation by Terasaki reported even lower values of the 0νββ NME, which was blamed on excessive correlations within the QRPA[48] and the high-momentum components of the interaction. However, we believe that the low value of our results for the 0νββ nuclear matrix elements points to a need to extend the calculation to cover transitions of higher multipolarity, and further developments of the model going beyond this study, especially the inclusion of nuclear deformation effects. The ratio of our results for the nuclear matrix elements obtained using the nonrelativistic reduction of the transition operator and the results obtained by using the full relativistic transition operator also needs to be noted. Previous work within the GCM reported these two as being very similar, and therefore the nonrelativistic approximation as justified[45, 43]. In contrast, for some nuclides we find a ratio of the result obtained with the nonrelativistically reduced operator to the one obtained using a fully relativistic transition operator as low as 5%, closer to what was reported in Ref. [44] as an anomalous result for 150Nd, raising the question of how anomalous this result truly is and if the nonrelativistic reduction of the transition operator is as justified as it first appears to be. As stated, this work represents the first implementation of the theoretical framework based on the PN-RQRPA in the study of double beta decays. The perspectives for future research as continuation of the present work are numerous. In the immediate aftermath, we will focus on extending our calculations of the 0νββ nuclear matrix elements in the sense of extending it to transitions of higher multipolarity and inclusion of nuclear deformation effects. In addition, we can consider other ways of finding the optimal value of the isoscalar pairing strength parameter V_0pp, for decays proceeding through both modes of double beta decay. Further extensions are possible. In order to implement a viable treatment of short-range correlations within our 0νββ decay study, we can extend our treatment of the ground state wavefunction to include a so-called unitary correlation operator. This procedure, consequently referred to as the Unitary Correlation Operator Method (UCOM)[49, 50], does not violate the normalisation of the wave functions as the simpler Jastrow function approach does[51] and might be more appropriate for our approach. The PN-RQRPA code we use is based on a code that is able to treat charge-exchange excitations at finite temperature. Double beta decay at finite temperature has only been sporadically mentioned in the literature, which means that the effects of finite temperature, while possibly small, mostly remain unexplored. By opening new charge-exchange transitions in nuclei at finite temperature, the NMEs could become larger. A further possibility is to extend our calculation to the case of deformed nuclei. As mentioned earlier, already in the case of 2νββ decays we have knowledge about the importance of triaxiality to some of the nuclei being studied, while others have deformations that could be approximated with axial symmetry. The theory framework for a deformed PN-RQRPA is under development at the University of Zagreb; once complete we will be able to use it to extend our study to the treatment of deformed nuclei as well, although this represents an increase in the computational complexity of the problem, particularly for 0νββ decays [47]. Such an extension would then represent the first QRPA calculation of deformed nuclei using the full relativistic operator.

Let u formaciji već je više od stotinu godina predmet istraživanja raznih znanstvenih disciplina te je do danas znanstveno dokazano da takva strategija letenja može dovesti do značajnih ušteda u potrošnji energije. Kako bi se ovaj potencijal u potpunosti iskoristio potrebno je unaprijediti postojeće sustave upravljanja letom, do razine djelomične ili potpune autonomije. Cilj istraživanja bio je unaprijediti model aerodinamičke interferencije pri letu u formaciji kojim se može pouzdanije simulirati složene aerodinamičke pojave u takvom letu. Ovo se ostvarilo sprezanjem nestacionarne metode vrtložne rešetke s 2D viskoznim optjecanjem profila te proširivanjem modela uvodenjem koncepta slobodnog traga. Razvijeni model validiran je u stacionarnim i nestacionarnim uvjetima strujanja. Primjenjiv je za proizvoljnu geometriju nosećih površina, pri različitim vrijednostima Reynoldsovog i Machovog broja te za veliki raspon napadnih kutova, uključujući i područje nakon pojave sloma uzgona. Glavna primjena modela razmatrana u ovom radu je primjena za let u formaciji, bez ograničenja na vrstu, broj članova, raznolikost letjelica ili na medusobni položaj letjelica u formaciji. Na primjeru leta složenom putanjom za dvije bespilotne letjelice u formaciji prikazane su mogućnosti razvijenog modela u nestacionarnom strujanju i pri prijelaznim režimima leta. Posebna pozornost pridana je numeričkoj efikasnosti te se procedura, uz nekoliko modifikacija, približila izvodenju simulacije u stvarnom vremenu. Formation flight has been a subject of research in various scientific fields for over a hun dred years, and it has already been scientifically proven that such strategy can result in significant energy savings. In order to take advantage of this potential, existing flight control systems need to be enhanced to the level of partial or full autonomy. The aim of the research was to improve the aerodynamic interference model of formation flight achieving more accurate simulation of the aerodynamic effects in a such flight. This was accomplished by coupling the unsteady vortex lattice method with 2D viscous flow aro und the airfoil and by extending the model with the free wake rollup model. Developed model was successfully validated for both steady and unsteady flow. It is applicable for arbitrary lifting surface geometry, for different Reynolds and Mach numbers, for large range of angle of attack including values beyond the stall angle. The main application of the developed model considered in this thesis was the formation flight, of any type, of any number of formation members, geometry diversity of formation members, or its mutual position in formation. Simulation of complex scenario of formation flight, that also included transient flight regimes, was successfully conducted. A special attention was given to the possibility of time effective calculation and a simulation close to the real time simulation was achieved with several adaptations of the procedure. The thesis is organized in six chapters as follows. First chapter presents relevance and motivation for this research, its goals, hypothesis and methodology. There is also an overview of the relevant literature defining the base ground and scope of the research described in this thesis. The essential aerodynamic model as described in chapter two is based on the poten tial flow and its elements are: standard vortex lattice method, unsteady vortex method method, and free-wake method. Standard vortex lattice method is based on vortex rings with extension for unsteady flow and extension for free wake rollup. Previously described model is extended with viscous effects of the airfoil as described in chapter three. This extension included coupled potential flow and 2D airfoil flow which included viscous and compressibility effects. This coupling was achieved with iterative process of correction of angle of attack for each section of discretized lifting surface. Developed model has a capability of application for arbitrary lifting surface geometry and for different flow parameters, both in steady and unsteady flow. Several examples were presented that validated the developed model in steady and unsteady flow. Fourth chapter introduces specifics of formation flight, and metrics for the evaluation of the formation flight efficiency as a whole but also for each aircraft in the formation. As a measure of formation efficiency a new parameter is introduced a formation drag ratio KDF , and a measure of efficiency of flight in formation for one formation member a formation member drag ratio kDF . These metric parameters can be used to evaluate formation performance, evaluate formation strategy and scenarios. An example of ap plication of the developed model for the analysis of close formation with two members is presented. In fifth chapter results of several numerical experiments for close echelon formations with two or more members with same geometry are presented. Example for the aircraft used in these experiments is unmanned aircraft Aerosonde, while its geometry and aerodynamic data are given in the Appendix. Numerical experiments in steady and unsteady conditions with main variable being a relative position of follower aircraft with respect to the leader. This analysis resulted in definition of optimal position of follower aircraft in the formation. This chapter also presents of two modification of the procedure that benefited of significantly shorter computation time. Sixth and last chapter briefly states main conclusion of the research described in this thesis, summarizing achieved scientific contributions, and discuses topics and tasks for future research work that would contribute to the further development of the model and its enhancements, offering its different potential applications.

U ovoj disertaciji predstavljeno je istraživanje fotokemije i ultrabrze dinamike kinon metida - međuprodukata sa potencijalnom primjenom u biologiji i medicini. Kinon metidi su važni međuprodukti u kemiji i fotokemiji fenola te su zanimljivi zbog svoje biološke aktivnosti i sve veće primjene u organskoj sintezi. Njihova biološka aktivnost temelji se na antiproliferativnom djelovanju zbog čega su primjenjivi u fotokemoterapiji. Upravo zbog procesa poput fotokemoterapije koji koriste biološku aktivnost kinon metida, od presudne važnosti je istraživanje puta fotokemijske reakcije njihovog nastajanja na ultrabrzim skalama. U svrhu provođenja istraživanja, na Institutu za fiziku u Zagrebu izgrađen je eksperimentalni postav za ultrabrzu tranzijentnu apsorpciju. Ostvarena je vremenska rezolucija od 200fs. Spektralni prozor probnog pulsa proteže se od 320nm do iznad 600nm što omogućava širokopojasno praćenje dinamike. Valnu duljinu pumpnog pulsa moguće je postaviti na jednu od harmonika: 267nm, 400nm, 800nm. Kao prekursori kinon metida odabrani su: adamantan fenol, adamantanski i neadamantanski derivat naftola te BODIPY-fenol. Kombiniranjem tranzijentne apsorpcije sa vremenski razlučivim mjerenjima fluorescencije te laserskom fotolizom otkriveno je kako kinon metid iz adamantan fenola nastaje u osnovnom stanju u ultrabrzoj reakciji fotodehidratacije preko konusnog presjeka sa vremenskom konstantom od 100fs. Uz stvaranje kinon metida, na različitim skalama dolazi i do stvaranja radikala i radikal kationa te tripletnog stanja prekursorske molekule. Kod derivata naftola uočeno je da se, iako molekule dijele kromoforu, reakcije uvelike razlikuju. Kod adamantan naftola, kinon metid također nastaje u osnovnom stanju fotodehidratacijom preko konusnog presjeka ali sporije, na nanosekundnoj skali, dok kod derivata naftola bez adamantanskog dijela isti nastaje nakon 40μs eliminacijom OHˑ skupine iz radikala prekursorske molekule koji nastaje ili iz radikal kationa eliminacijom protona ili iz S1 stanja prijenosom vodika. Vremenski razlučivim mjerenjima fluorescencije BODIPY-fenola potvrđena je anti-Kasha fizika uzorka. Naime, opažen je fluorescencijski pojas koji odgovara fluorescenciji iz viših pobuđenih singletnih stanja molekule iz kojih kreće reakcija stvaranja kinon metida. In this work, ultrafast photochemistry of short-lived and very reactive quinone methide intermediates is presented. Quinone methides were generated from 3 different precursors: adamantyl phenol and 2 naphthol derivatives and every photochemical reaction pathway was observed to be different. Main part of the experimental measurements was done using the ultrafast transient absorption setup built at the Institute of physics in Zagreb. Experimental setup has a possibility of wavelength choice between 800nm, 400nm, 267nm. A time resolution of 220 fs was achieved by the gradual inclusion of new experimental equipment and careful adjustments of the setup. Since for quinone methide application in chemistry, medicine or biology it is necessary to know the reaction pathway, this work’s goal was to elucidate the complete pathway of a few reactions of quinone methide generation. Experimental setup for ultrafast transient absorption at the Institute of physics opens up possibilities for further study of ultrafast photochemistry of various molecules as well as for research of a large number of interesting photoinduced processes important in chemistry, biology and medicine. Further improvement of the experimental setup can be started by connecting the homemade NOPA to the rest of the setup. In this way, it would be possible to select an excitation wavelength from spectral windows: 260-300nm and 500-670nm with a significantly shorter pulse duration of approximately 50fs. Additionally, by pumping the supercontinuum crystals with NOPA, the white light spectrum could be expanded to UV and the detection noise could be decreased with the use of cooled detectors.

Cilj: Cilj rada je predstaviti rezultate ispitivanja studentskih stavova o fizici i njihove povezanosti s usvajanjem koncepata u fizici. Ispitanici i metode: U istraživanju je sudjelovalo 89 studenata prve godine Preddiplomskog stručnog studija Fizioterapija, Fakulteta zdravstvenih studija Sveučilišta u Rijeci. Ovom istraživanju, prethodilo je ispitivanje učenika sedmih i osmih razreda jedne riječke osnovne škole (N = 92). Upitnik je sadržavao tvrdnje kojima su izražavani stavovi ispitanika studenata o fizici. Drugi dio upitnika činile su tvrdnje među kojima su bile i česte miskoncepcije u fizici. Miskoncepcije smo podijelili na one koje nastaju zbog jezičnog miješanja pojmova iz svakodnevnog života i znanosti, one koje proizlaze iz korištenja neispravnih pretpostavki za objašnjenje svakodnevnog iskustva te one koje se temelje na nerazumijevanju znanstvenih pojmova i koncepata. Rezultati: Studenti u najvećoj mjeri imaju neutralan stav prema fizici. Postoji statistički značajna razlika u zastupljenosti miskoncepcija prema uzroku njihova nastanaka (Hi-kvadrat; P < 0,001). Najzastupljenijima su se pokazale miskoncepcije nastale poistovjećivanjem izraza iz svakodnevnog života i znanosti, tzv. žargonske miskoncepcije (58 % slučajeva). Utjecaj studentskih stavova na učestalost miskoncepcija pokazao se statistički značajnim za stavove koji ukazuju na to da su ispitanici više usmjereni na memoriranje gradiva i kvantitativne manipulacije nego na uspješno usvajanje znanstvenih pojmova i koncepata. Zaključci: Primjena napredne tehnologije u terapiji i dijagnostici u okviru medicinske skrbi ukazuje na sve veću potrebu za znanjem iz fizike kod studenata zdravstvenih i medicinskih studija. Studenti shvaćaju važnost fizike u svojem obrazovanju i većinom ne iskazuju negativan stav prema fizici. Određene vrste miskoncepcija zadržavaju se tijekom čitavog obrazovnog procesa. Zato treba sprječavati nastanak neznanstvenih koncepata, odnosno ako oni već postoje, treba ih što ranije detektirati i aktivno raditi na njihovom uklanjanju., Objective: The aim of the paper is to present the results of the study of students’ attitudes towards physics and their relationship with the acquisition of concepts in physics. Subjects and Methods: Eighty-nine students of the first year of undergraduate studies in physiotherapy at the Faculty of Health Studies, University of Rijeka, participated in the study. This study was preceded by a survey of seventh and eighth grade students of an elementary school in Rijeka (N=92). The questionnaire contained statements expressing the attitude of the surveyed students towards physics. The second part of the questionnaire consisted of statements that included common misconceptions in physics. We divided the misconceptions into those that arise from the linguistic mixing of terms from everyday life and science, those that result from the use of incorrect assumptions to explain everyday experiences, and those that are based on a misunderstanding of scientific terms and concepts. Results: Students have predominantly neutral attitudes toward physics. There is a statistically significant difference in the prevalence of misconceptions according to the cause of their occurrence (chi-square; P

Male GTPaze iz obitelji Rho predstavljaju skupinu signalnih proteina odgovornih za regulaciju i koordinaciju brojnih staničnih aktivnosti vođenih aktinskim citoskeletom. Među eukariotskim stanicama, amebe Dictyostelium discoideum se najbrže spontano repolariziraju, te su sposobne u roku od 30 sekundi potpuno preokrenuti orijentaciju. Kao takve, one predstavljaju osnovni poligon za ispitivanje konceptualnih modela koji povezuju male GTPaze i njihove signalne puteve s morfodinamikom stanica tijekom migracije. U D. discoideum, aktivni Rac1 regulira aktinske polimeraze na prednjem kraju i proteine koji usnopljuju aktinske niti na zadnjem kraju polariziranih stanica. Dinamiku aktivnosti Rac1 pratili smo koristeći specifičnu fluorescentnu sondu, i uz nepravilne obrasce, također uočili pojavu pravilnih obrazaca, u obliku stabilne polarizacije, te putujućih i stojnih valova. Proveli smo sistematsku analizu reakcijsko-difuzijskih modela srednjeg polja čije reakcije slijede zakon o djelovanju masa, te identificirali minimalni model koji može reproducirati navedene pravilne obrasce. Odgovarajući model iskoristili smo za opis dinamike proteina Rac1 i njegove ciljne molekule DGAP1. Osim što je uspješno reproducirao pojedinačne značajke eksperimentalno opaženih dinamičkih obrazaca fluorescentno obilježenih Rac1 i DGAP1, model je također reproducirao predominantno negativnu prostorno-vremensku korelaciju između tih proteina. Uz spomenuti model srednjeg polja, također smo razvili odgovarajući stohastički model kako bismo proučili utjecaj nasumičnih fluktuacija na ponašanje ovog sustava, te smo ustanovili njihovu ključnu ulogu u spontanim prelascima između različitih tipova obrazaca promatranih proteina. Small GTPases from the Rho family represent a group of signaling proteins responsible for the regulation and coordination of numerous cellular activities guided by the actin cytoskeleton. Among eukaryotic cells, Dictyostelium discoideum amoebas are capable of the fastest reorganization of the actin network, and can reverse their polarity within one minute. As such, they represent a basic testing ground for conceptual models linking small GTPases and their signaling pathways to cell morphodynamics during migration. In D. discoideum, active Rac1 regulates actin polymerases at the leading edge and actin filament-bundling proteins at the trailing end of polarized cells. We monitored the spatio-temporal distribution of Rac1 activity using a specific fluorescent probe, and in addition to irregular patterns, we also observed the appearance of regular patterns, in the form of stable polarization, as well as traveling and standing waves. We conducted a systematic analysis of mean field reaction-diffusion models with reactions that follow the law of mass action, and identified a minimal model that can reproduce the observed regular patterns. We used a variant of this model to describe the dynamics of Rac1 GTPase and its effector protein DGAP1. Besides successfully reproducing individual features of the experimentally observed dynamic patterns of fluorescently labeled proteins, the model also reproduced the predominantly negative spatio-temporal correlation between Rac1 and DGAP1. In addition to the mean field model, we developed a stochastic model in order to analyze the impact of random fluctuations on the behavior of the system, and established their key role in spontaneous transitions between different types of protein patterns.

Ramanova spektroskopija metoda je karakterizacije i identifikacije materijala bazirana na neelastičnom Ramanovom raspršenju fotona svjetlosti na materijalu. Primjenjuje se u raznim znanstvenim i industrijskim područjima, od fizike, kemije, biologije, medicine, znanosti o materijalima, do kontrola sigurnosti, detekcije nedozvoljenih tvari i proučavanja umjetničkih dijela. Zbog neelastičnosti procesa, Ramanovo raspršenje daje vrlo slab signal, zbog čega su razvijene različite metode pojačanja. Jedna od novih metoda pojačanja, čije su prednosti jednostavnost i niska cijena primjene, neinvazivnost, reproducibilnost i stabilnost, temelji se na fotonskom nanomlazu koji nastaje obasjavanjem mikroleće svjetlošću. Odabirom pogodnih parametara, fotonski nanomlaz može imati izrazito visok intenzitet, usku širinu, ili veliku duljinu, zbog čega se osim za Ramanovu spektroskopiju, istražuje i za primjene u nanolitografiji, super-rezoluciji, optičkim silama, pohrani podataka i sličnim poljima. Trenutno, njegova primjena u Ramanovoj spektroskopiji nedovoljno je istražena, a i sama svojstva i uvjeti za njegov nastanak nerazjašnjeni su. Istraživanjima u sklopu ovog doktorskog rada unaprijeđena je metoda pojačanja, te su dobivena i nova saznanja o fotonskom nanomlazu općenito. Napravljen je računalni program temeljen na Generaliziranoj-Lorenz Mie teoriji, kojim je izračunat širok raspon različitih konfiguracija za fotonski nanomlaz iz dielektrične mikrosfere. Dobiven je sistematičan uvid u svojstva i ovisnost fotonskog nanomlaza o parametrima te uvid u promjene pojedinih ovisnosti u različitim uvjetima. Pokazana je kritična važnost parametra pozicije upadne zrake. Odabirom određene kombinacije parametara dobiven je izrazito intenzivan, vrlo uzak ili izrazito dug fotonski nanomlaz daleko izvan mikrosfere. Istraživanjem područja visokog indeksa loma mikrosfere, modeliranjem je pokazano da fotonski nanomlaz može nastati izvan mikrosfere i kada je indeks loma viši od 2, što je u dosadašnjoj literaturi bilo označeno kao gornja granica. Varijacijom eksperimentalnih parametara optimizirano je pojačanje. Pomoću vertikalnog ramanskog mapiranja određena je optimalna pozicija upadne zrake za pojačanje te je pokazana njezina važnost. Izmjerena je ovisnost pojačanja o kolekcijskom vlaknu, mikroskopskom objektivu i veličini mikrosfere. Diskutiran je mehanizam pojačanja, koji smo podijelili u dva doprinosa - od fotonskog nanomlaza, te od kolekcijskog sustava. Dobiveno je kombinirano pojačanje mikrosfere i plazmonskog pojačanja. Dizajniran je i testiran novi sustav za mehaničku kontrolu mikrosfere pod mikroskopskim objektivom, kojim je moguće iskoristiti pojačanje za svaku točku ramanskog mapiranja. Dobiveno je pojačanje intenziteta i rezolucije mapiranja. Raman spectroscopy is a method for characterization and identification of materials, which is widely used in a broad range of scientific and industrial fields, like materials science, physics, chemistry, biology, medicine, security control, substance control and art examination. It is based on Raman scattering of light on molecules and crystals. As opposed to its elastic counterpart - Rayleigh scattering, Raman scattering is inelastic, which means that the scattered photon has a different energy than the incident one. Because of this, Raman scattering has low probability of occurrence and the scattered Raman intensity is very low. For this reason, many methods for the enhancement of Raman scattering have been developed through the years. One of the new methods of enhancement is based on photonic nanojet, which is a concentrated beam of light emerging from the shadow side of an illuminated microlens. This method of enhancement is characterized by a low cost and a simple principle of implementation. It is a non-invasive, reproducible and reliable way of enhancement. By careful choice of parameters, photonic nanojet can have very high intensity, very narrow width, or very long length. This makes it suitable not only for Raman scattering enhancement, but also for applications in nanolithography, super resolution, optical forces, data storage and similar fields. Although being a promising technique, the role and usage of photonic nanojet in Raman spectroscopy is currently underexplored. Moreover, the properties and conditions for emergence of the photonic nanojet generally are still not clear. This PhD dissertation is a result of four years of research on photonic nanojet and its usage for Raman spectroscopy. It is based on four published papers [1, 2, 3, 4], one still unpublished body of work, and a patent application [5, 6]. This research has resulted not only in the improvement of the method of Raman enhancement, but also with new findings in the general field of photonic nanojet. The research was performed from two angles, experimental and computational. The series of computer codes were written in order to model the photonic nanojet in various conditions. The codes, based on Generalized Lorenz-Mie theory, calculate the electric field intensity from scattering of a Gaussian beam on a dielectric microsphere, upon which a photonic nanoi Extended abstract jet emerges. A large amount of configurations was calculated which provided a systematic overview of photonic nanojet properties and its dependence on parameters. Also, the change of dependencies is detected and investigated by variation of other parameters. The parameters which are varied are the incident Gaussian beam wavelength, position and waist radius, and the microsphere radius. The microsphere refractive index was taken to correspond to SiO2 material. The investigated properties of a photonic nanojet are its maximum intensity, position, width and length. The incident Gaussian beam position is shown to be of critical importance for photonic nanojet properties. Two types of photonic nanojet are identified: Type 1 has lower intensity, its position is further away from the microsphere and has larger dimensions, while Type 2 has higher intensity, it is positioned close to the microsphere edge, and has smaller dimensions. The size matching between the incident beam waist radius and microsphere radius is shown to improve the intensity of the photonic nanojet, but it is not the main contribution. Proper positioning of the incident beam, small waist radius and short wavelength are shown to be important for high intensity. It is also shown that all parameters are important in their absolute value, and that size parameter from Lorenz-Mie theory cannot be applied. Furthermore, parameter combinations for the photonic nanojet of extremely high intensity, very narrow width, or extremely long length with long working distance are determined. In some regimes, intensity oscillations are also detected, and they are identified as whispering-gallery modes and Mie interferences. The occurrence of the photonic nanojet is also investigated when a high refractive index microsphere is used. The investigation followed three theoretical levels: geometrical optics, ray transfer matrix analysis, and Generalized Lorenz-Mie theory. Geometrical optics show that divergent incident light rays can be focused outside a high refractive index microsphere. Ray transfer matrix analysis show that divergent cone of a Gaussian beam produces output beam with a waist outside a high refractive index microsphere. The mathematical condition for that occurrence is derived. Finally, the Generalized Lorenz-Mie theory calculations show that a photonic nanojet can emerge outside the microsphere even when the refractive index of a microsphere is higher than two, which was up to now considered a limit in literature. The calculations also show the difference in focusing of the incident beam based on the refractive index of the microsphere, which is confirmed by the vertical Raman mapping. The Raman enhancement is optimized by variation of experimental parameters. Optimal position of the incident laser beam is determined by vertical Raman mapping, and explained with ray transfer matrix analysis. Laser beam profiles under the microscope objective are determined by a knife-edge method. Antenna effect of the microsphere for the enhancement is detected. The dependence of the enhancement on the collection fiber diameter, microscope objective and microsphere size is determined. Two microsphere materials were used: SiO2 and barium tiii Extended abstract tanate glass. The dependence on microsphere radius shows different behaviors depending on the objective used. The calculations of a photonic nanojet intensity are compared with experimental values of the Raman enhancement, which suggest that the photonic nanojet is not the only contribution to the enhancement. The enhancement strongly lowers by increasing the numerical aperture of the objective. The highest enhancement of the silicon substrate, of 19.29× is achieved in configuration of barium titanate glass microsphere of radius of 4.5 μm and 10× NA 0.25 microscope objective. The mechanism of the enhancement is discussed, which is separated into two contributions. The first contribution comes from the photonic nanojet, and the second contribution comes from the collection system. The model of the effective numerical aperture of the microsphere-objective system is presented, and compared with the experimental results. The usage of the microsphere for the enhancement was further improved by designing the new system for mechanical control of the microsphere. The system is called two-stemmed microsphere and allows positioning of the microsphere under the laser beam of the microscope objective independently of the substrate position. This way, Raman mapping can be performed in which each point is enhanced. The system is tested on a silicon substrate with domains separated by visible borders. Raman mappings are compared with atomic force microscope measurements. With two-stemmed microsphere, the intensity enhancement is 4× and the estimated resolution enhancement is 3×. Combined enhancement of SERS (surface-enhanced Raman scattering) and microsphere is achieved. The SERS substrates which were used were non-uniform and uniform silver nanoislands. The used analytes were 4-mercaptophenylboronic acid or 4-mercaptobenzoic acid. The non-uniform substrates combined with the microsphere show higher but less reproducible enhancement than the uniform substrates with the microspheres.

Ubrzano širenje svemira jedno je od ključnih otkrića u modernoj kozmologiji. Iako se na tom problemu radi već dva desetljeća, još uvijek nema empirijski potvrđene teorije koja bi na zadovoljavajući način objasnila ovu pojavu. U ovom radu razvija se nova metodologija modeliranja tamne energije preko implicitne jednadžbe stanja kozmičkog fluida te modeliranja brzine zvuka kao funkcije parametra jednadžbe stanja kozmičkih fluida. Postupak se demonstrira na uspostavljanju novih i analizi postojećih modela. Ispituju se svojstva tamne materije i tamne energije poput tranzijentne tamne energije i budućih singulariteta u širenju svemira. Proučava se ujedinjenje tamne materije i tamne energije u dobivenih modelima i sukladnost s podacima iz kozmoloških i astrofizičkih opažanja. Uspoređuje se veći broj dosad uspostavljenih modela i parametrizacija tamne energije i provjerava sukladnost s osnovnim svojstvima barotropskog fluida. Povezuje se koncept k-esencije s predloženom metodologijom i analiziraju dobiveni rezultati. Na temelju orbitalnih brzina objekata u našoj galaksiji proučava se brzina zvuka kozmičkih fluida u ovisnosti o udaljenosti od središta galaksije i rezultati se uspoređuju s temeljnim postavkama barotropskog fluida. Accelerated expansion of the universe is one of key discoveries in modern cosmology. Even though the problem has been worked on for more than two decades, there is still no empirically confirmed theory that would sufficiently explain this phenomenon. In this work, a new methodology of modelling dark energy through implicit equation of state of cosmic fluid is developed: speed of sound is being modelled as a function of parameter w of the equation of state of cosmic fluids. The procedure is demonstrated through establishing new and analysis of already existing models. As can be seen in the equation of acceleration, value of component parameter of equation of state, w = p/ρ, is crucial for the behaviour of expansion of universe. If w > -1/3, the contribution to expansion is decelerating and if w < -1/3, the contribution to expansion is accelerating. The ΛCDM model presumes that w = -1 for dark energy throughout the history of the universe. This assumption, however, leads to some recently observationally established tensions, which is why a dynamic dark energy is investigated: several models and parametrizations are trying to establish a dynamic function where w changes with time. After the primary objective of this work, the development of new methodology, the secondary direction of this work is twofold. The first direction is investigating how much certain functions and parametrizations of w(a) yield results that conform with observation. The second is checking if dark energy in selected and also newly constructed models has the properties of barotropic fluid, i.e., if its pressure is the function of energy density only; also, this means verifying that the value of its speed of sound squared, cˇ2s is always between zero and speed of light squared. Methodology derived in this work will rely heavily on equations derived from the fluid continuity equation. Due to the nature of those equations, behaviour of parameter w around the value of -1 will be especially important because at that point cˇ2s, parameter w and/or other cosmic parameters often go through a singularity. In chapter 2 a model is presented that, in some cases, allows a smooth cosmological constant boundary crossing between areas w < -1 to w > -1. Some results of this model are then compared to observational data. Also, depending on model parameters, possible futures are discussed: Big Rip, Small Rip and transient dark energy. Some of the important parameter regimes show a wide range of scale factor a during which the parameter w is almost constant and close to -1, conforming to the current observational results. Another set of models introduced in this work is the one unifying dark matter and dark energy. Analytical function for c2s (w) yields results that describe behaviour of unified dark fluid that behaves like dark energy or dark matter through different stages of development of the universe: starting with dark matter stage, depending on model parameters, parameter w goes through the stage of dark energy to end up either as phantom energy (w < -1), dark energy with w asymptotically going to w* or shifting back into dark matter regime. The next part of the work deals with collecting around 40 models presented in literature and determining whether dark energy presented there has key properties of barotropic fluid. Analytical examination is performed in two cases and numerical analysis using two methods is performed in all of them, examining if speed of sound squared of the dark fluid remains between zero and speed of light squared for the whole interval of cosmic past (0 < a < a_0). Results show that many models developed since the discovery of accelerated expansion of the universe do not satisfy these conditions. Furthermore, newly constructed models of dark energy are examined through the model of purely kinetic k-essence, formulating it through Lagrange field theory which would connect cosmology with other areas of physics. In all introduced models there is a case of unification of dark matter and dark energy with w shifting from zero or near-zero (depending on model parameters) at a = 0 to w asymptotically going to -1 as a goes to infinity. Finally, observational data of orbital velocities of objects in Milky Way galaxy are examined and used to establish a method of checking if local dark fluid is in concord with properties of barotropic fluid. A model-independent method is derived for calculating speed of sound squared from the observed data using numerical calculation of first and second derivatives of orbital velocity on distance from the galaxy centre. The results mostly show the possibility of dark matter showing properties of barotropic fluid, however, there is significant room for improvement with regard to the accuracy of observed data.

Modificirana teorija gravitacije poznata kao f(T) gravitacija oslanja se na torziju kao temeljno svojstvo prostorvremena. Kako bi se istražila predviđanja ove teorije, ona je primijenjena na niz problema iz područja kozmologije, dok su njena predviđanja u području sferno simetričnih problema istražena u znatno manjoj mjeri. Predloženo istraživanje usredotočuje se na konstrukciju sfernosimetričnih rješenja i proučavanje njihovih svojstava u okviru tzv. kovarijantne inačice gravitacije tipa f(T) koja osigurava invarijantnost jednadžbi gibanja u odnosu na odabir tetrade. Izvest će se i analizirati modificirane Einsteinove jednadžbe u kovarijantnoj formulaciji f(T) teorije gravitacije te će se proučiti uloga Lorentzove (spinske) koneksije u njima. Istražit će se statična vakuumska rješenja kao i nevakuumska rješenja poput politropskih kompaktnih objekata i bozonskih zvijezda. Proučit će se i mogućnost nalaženja sfernosimetričnih rješenja ovisnih o vremenu, pri čemu će biti potrebno pronaći odgovarajuće tetrade i odgovarajući oblik Lorentzove (spinske) koneksije. Jednadžbe gibanja će se zbog svoje matematičke složenosti rješavati numeričkim postupcima. Rad ne sadrži sažetak na drugom jeziku.

U ovom radu opisan je Blender i sve simulacije koje dolaze u programskom paketu. Simulacije su testirane kako bi se uvidjela povezanost između parametara, složenosti scene, vrste simulacije i komponenata računala koje utječu na njihov rad. Vrste simulacija su protumačene i uspoređene na temelju njihove potrošnje resursa. Navedeni su i drugi alati za izradu simulacija čiji se pristup, korištene tehnologije i performanse znatno razlikuju od Blendera. This thesis describes Blender and all the simulations that come in the software package. Simulations were tested to see the relationship between parameters, complexity of the scene, type of simulation and the computer components that affect their operation. Simulations are interpreted and compared based on their resource consumption. Other tools for creating simulations are listed, whose approach, used technologies and performance are significantly different from Blender.

Fizikalni pokus treba biti dio svakog sata fizike. Postavlja se pitanje koje pokuse izabrati, koja je za to potrebna oprema i koliko vremena treba nastavniku za pripremu. Mikroračunala poput micro:bita omogućavaju relativno brzu konstrukciju pokusa u kome se koriste njegovi interni ili vanjski senzori. U ovom radu su dane smjernice za izvođenje nekoliko pokusa koji su vezani uz temu valova u fizici. Slično se može izvesti u brojnim drugim područjima fizike. Pri tome se uči osnove programiranja i upravljanje sa senzorima, prijenos i obrada podataka. Osim toga ideja je i učiniti fiziku zanimljiviju učenicima, potaknuti ih da samostalno istražuju kroz projekte, ali i izvode grupna istraživanja vezana uz važne teme današnjice. A physics experiment should be part of every physics lesson. The question arises as to which tests to choose, what equipment is needed and how much time the teacher needs to prepare. Microcomputers like the micro:bit enable relatively fast construction of experiments using its internal or external sensors. In this thesis, guidelines are given for performing several experiments related to the topic of waves in physics. The same can bed one in many other areas of physics. In doing so, several subject are connecter interdisciplinary, for example, physics with computer science and mathematics. In doing so, the basic of programming and sensor management, dana transmission and processing are learned. In addition, the idea is to make physics more interesting to students, to encourage them to independently research through projects, but also to carry out group research related to important topics of today.

U ovoj doktorskoj disertaciji pulsna laserska ablacija u vodi korištena je za sintezu nanočestica titanovog dioksida i cinkovog oksida koje imaju jaka fotokatalitička svojstva. U tu svrhu korišten je nanosekundni laser Nd:YAG osnovne valne duljine 1064 nm. Razne eksperimentalne tehnike (XRD, XPS, TEM/SEM, UV-Vis, Raman) su primijenjene za karakterizaciju dobivenih nanočestica kako bi se odredila njihova kristalna struktura, optička svojstva, oblik i distribucija po veličini. Razvijena je jednostavna metoda za određivanje koncentracije laserski sintetiziranih nanočestica u vodi, a u njoj se koriste podaci o volumenu ablacijskog kratera i raspodjela nanočestica po veličini. Metoda je testirana na nanočesticama titanovog dioksida i provjerena pomoću Beer-Lambertovog zakona. Pulsnom laserskom ablacijom titana su dobivene načestice titanovog dioksida, koje su, nakon zagrijavanja u vodi na 90°C, kristalizirale i pokazale jaču fotokatalitičku aktivnost s obzirom na UV i vidljivo zračenje nego P25 čestice. Fotokataličnost nanočestica određivana je mjerenjem brzine fotodegradacije raznih organskih otapala (Methylene Blue, Rhodamine B) pod UV ili vidljivim zračenjem u njihovoj prisutnosti. Mjerena je ovisnost fotokatalitičke aktivnosti nanočestica cinkovog oksida o njihovoj koncentraciji, početnoj koncentraciji i vrsti organskog bojila, a dobivene ovisnosti su teorijski objašnjene. Razvijena je metoda za sintezu dopiranih nanočestica pulsnom laserskom ablacijom u vodi, na način da se u njoj ablatira meta na koju je prethodno u pulsnoj laserskoj depoziciji naparen film materijala za dopiranje. Na taj način su dobivene nanočestice cinkovog oksida s različitim udjelima srebra i pojačanom fotokatalitičkom aktivnošću koja je najveća na izmjerenom optimalnom masenom udjelu srebra 0.32%. In this PhD thesis pulsed laser ablation in water is used for synthesis of titanium dioxide and zinc oxide nanoparticles with strong photocatalytic properties. For that purpose the nanosecond laser ND:Yag with basic wavelength at 1064 nm is used. Various experimental techniques (XRD, XPS, TEM/SEM, UV-Vis, Raman) are performed for the purpose of characterization of synthesized nanoparticles in order to determine their crystal structure, optical properties, shape and size distribution. The simple method for determination of laser synthesized nanoparticles concentration in water is developed, in which the ablation crater volume and nanoparticles size-distribution data are used. The method is tested for titanium dioxide nanoparticles and verified by using Beer-Lambert law. Titanium dioxide nanoparticles are synthesized by pulsed laser ablation of titanium target and it is shown that they crystallized after heating in water at 90°C and developed large photocatalytic activity in the presence of UV and visible light when compared with P25. Photocatalytic efficiency of nanoparticles was calculated by measuring the photodegradation rate of different dyes (Methylene Blue, Rhodamine B) under UV or visible light and in their presence. A dependence of zinc oxide nanoparticles photocatalytic efficiency on their concentration, initial dye concentration and dye type was measured, and obtained relations are theoretically explained. The method for laser synthesis of doped nanoparticles is developed, in which pulsed laser ablation in water is used for ablation of target that is previously coated by dopant material using pulsed laser deposition. In this way the zinc oxide nanoparticles with different silver ratios are synthesized, and they are shown to have improved photocatalytic efficiency, which is the largest at the measured optimal silver ratio 0.32 wt %.

U ovom radu predstavljen je rad na razvoju kapilarne mikroprobe za MeV TOF-SIMS s primjenom na analizu bioloških uzoraka. Za razliku od magnetskog fokusiranja, pomoću staklene kapilare moguće je kolimirati teške ionske snopove viših energija koji proizvede veći prinos sekundarnih iona težih molekula. Razvijena su dva načina okidanja startnog signala za mjerenje vremena proleta sekundarih iona, detekcijom primarnih iona pomoću čestičnog detektora za tanke uzorke i detekcijom sekundarnih elektrona pomoću elektronskog multiplikatora za uzorke proizvoljne debljine. Ostvarena je optimalna masena razlučivost od 2500 za masu 575 Da u prvom, i 1400 u drugom, preferiranom načinu rada, zbog većeg broja uzoraka koji je moguće analizirati, jednostavnije pripreme istih i smanjene pozadine u masenom spektru. Prinos sekundarnih iona mjeren na uzorku plavog ftalocijanina pokazuje pozitivnu korelaciju s energijom, elektronskom zaustavnom moći, brzinom i nabojem primarnih iona u mjerenom energijskom području (50 – 300 keV/u). Nakon odabira optimalnog primarnog snopa i mjerenja prostorne razlučivosti (5×12 μm^2) analizirani su odabrani uzorci u oba načina rada. Halo primarnog snopa, vidljiv i u izmjerenim energijskim spektrima nakon prolaska kroz konusnu kapilaru, smanjuje kontrast u molekularnim mapama i uvelike ograničava primjene ovakvog postava. Alternativno rješenje, kolimiranje kružnom aperturom, pokazuje se boljim za dobivanje jasnijih i pouzdanijih molekularnih mapa različitih uzoraka u vakuumu (otisak prsta, presjek tinti na papiru, presjek moždanog tkiva). In this work, development of MeV TOF SIMS capillary microprobe is presented. There are two modes of operation, depending on a start trigger for TOF measurement: transmission mode for thin targets, where the best-achieved mass resolution is 2500 for mass 575 Da, and electron start mode for any kind of samples, with the best mass resolution of 1400 for the same mass. Despite the lower mass resolution due to the more complex setup, the latter mode makes possible the analysis of a large variety of samples with simpler sample preparation and less background compared to the former. Secondary ion yield measured for different primary ion parameters shows a positive correlation with ion energy, electronic stopping, velocity and charge state in the analyzed energy range. The best achieved lateral resolution is 5×12 μm^2, limited by the primary beam divergence. Beam halo, unavoidable with conical capillaries, significantly reduces the contrast in molecular maps and limits the application of capillary collimation. A setup with a simple round aperture is implemented as an alternative, and molecular maps obtained with this setup show clear advantage to capillary collimation for in-vacuum applications. A major modification and improvement of the current setup would be the replacement of target voltage pulsing with constant extraction.

U ovoj disertaciji istraživani su perovskitni tanki filmovi na bazi formamidinija. Cilj rada je bio istražiti uvjete pripreme formamidinijevih perovskita, odrediti njihova strukturna, optička i električna svojstva te istražiti ulogu polivinilpirolidona kao aditiva kojim bi se postigla njihova okolišna stabilnost. Sinteza perovskitnih tankih filmova proučavana je na staklenim podlogama s ciljem razvijanja optimalnih uvjeta ponovljive sinteze funkcionalnih tankih filmova. Utvrđeni uvjeti sinteze korišteni su za pripremu perovskitnog sloja na tankim filmovima titanijeva dioksida i cinkova oksida s ciljem izrade perovskitnih fotonaponskih ćelija. Eksperimentalno dobivena fotonaponska ćelija korištena je za izradu računalnog modela simulirane fotonaponske ćelije pomoću programa SCAPS 1D. Cilj modeliranja bio je istražiti je li SCAPS prikladan program za simulaciju perovskitnih fotonaposkih ćelija te kroz računalni model procjeniti poluvodička svojstva dobivenog perovskitnog tankog filma. Polivinilpirolidon istražen je kao potencijalni aditiv perovskitnom tankom filmu sa ciljem postizanja stabilnosti filma u okolišnim uvjetima. Istraživani su uvjeti sinteze perovskitnih filmova uz dodatak polivinilpirolidona, njegov utjecaj na morfološka, optička i električna svojstva te je istraživan utjecaj aditiva na parametre fotonaponske ćelije. In this dissertation perovskite thin films based on formamidinium were investigated. The aim was to investigate formamidinium perovskite synthesis conditions, to determine their structural, optic and electronic properties and to investigate the role of polyvinylpirrolidone as an aditive for ambient stabilization of the material. The synthesis of perovskite thin films was investigated on glass substrates with the goal of developing an optimal and reproducible procedure for the preparation of functional thin films. Established synthesis conditions were used for the preparation of perovskite films on titanium dioxide and zinc oxide thin films to prepare perovskite photovoltaic cells. Obtained experimental photovoltaic devices were used to prepare a computer model of a simulated photovoltaic cell by using SCAPS 1D program with the aim to determine if SCAPS is a suitable program for the simulation of perovskite photovoltaic devices and to estimate the semiconducting properties of the perovskite thin film. Polyvinylpirrolidone was investigated as an aditive in the perovskite thin film to achieve the stability of the material in the ambient environment. The investigation included the analysis of synthesis conditions of perovskite films with the addition of polyvinylpirrolidone, its impact on the morphology, optic and electrical properties and its impact on photovoltaic parameters.

Multiferoici su materijali kod kojih istovremeno postoji više vrsta dugodosežnih uređenja. Najpoznatiji te najistraživaniji su magnetoelektrični multiferoici kod kojih se javlja magnetsko i električno uređenje, te vezanje među njima. Vezanje između uređenja omogućava mijenjanje magnetizacije električnim poljem, kao i polarizacije magnetskim poljem. Ovakvi materijali zanimljivi su zbog mogućnosti koje nude u tehnološkoj primjeni, kao na primjer u senzorima, feroelektričnim fotovoltaicima, spintronici i nanoelektronici. Osim tehnološke primjene multiferoici su značajni i za fundamentalna istraživanja međudjelovanja elektronskog naboja, spina, orbitalnih stupnjeva slobode i kristalne rešetke. U ovom radu bit će predstavljeni rezultati istraživanja metalo-organskih materijala dvodimenzionalne i trodimenzionalne perovskitne strukture kod kojih postoji mogućnost istovremene pojave električnog i magnetskog uređenja. Motivacija za istraživanje 2D perovskita temeljenih na tetraklorokupratima(II) bio je prethodno istraživan etilamonijev tetraklorokuprat(II), na kojem je utvrđeno istovremeno postojanje magnetskog i električnog uređenja. Da bi se utvrdio utjecaj sastava i strukture na vrstu i temperaturu magnetskog uređenja, nastavljena su istraživanja niza halogenokuprata(II) s različitim organskim aminima. Kod niza anisidinijevih tetraklorokuprata(II), s tri različite konfiguracije anisidinijevog iona pokazano je kako se kristalna struktura mijenja ovisno o geometriji i elektronskoj strukturi organskog kationa. Ovisno o konfiguraciji kationa, mijenja se način udruživanja tetraklorokupratnih(II) aniona, udaljenost između susjednih bakrovih iona unutar te naginjanje i Jahn-Teller distorzija oktaedara klorovih aniona koji okružuju bakrove katione. Sve ove promjene utječu na magnetsko ponašanje, pa su tako za para- i meta-anisidinijev tetraklorokuprat(II) utvrđeni magnetski fazni prijelazi na 9.4 K i 4.2 K, različitih karaktera, dok ortho spoj nema vidljiv prijelaz. Drugi niz proučavanih 2D spojeva obuhvatio je etilamonijev tetraklorokuprat(II) i njegove derivate, kod kojih okosnicu organskog sloja čine 2-kloretilamonijev, odnosno 2-brometilamonijev kation, dok anorganski sloj tvore tetraklorokupratni(II), odnosno tetrabromokupratni(II) anioni. Najveća promjena magnetskog ponašanja uočena je za (BrC_2H_4NH_3)_2CuBr_4 gdje je bromov ion uzrokovao promjenu osnovnog magnetskog stanja iz antiferomagnetskog u feromagnetsko. Istraživanje 3D perovskita C(NH_2)_3Cu(HCOO)_3 pokazalo je da se primjenom električnog polja može utjecati na magnetizaciju uzorka ispod temperature magnetskog faznog prijelaza, a primjenom magnetskog polja na iznos električne polarizacije u paramagnetskoj fazi. Uz zanimljivo magnetoelektrično ponašanje, ovaj spoj pokazuje i veliku magnetsku anizotropiju. Na kraju rada stavit ćemo rezultate u širi kontekst i pokazati perspektive daljnjeg istraživanja i razvoja ovakvih materijala. In this work, we will present the results of our research on metal-organic materials of two dimensional and three dimensional perovskite structures with the possibility of simultaneous appearance of electric and magnetic orders. The motivation for the investigation of the 2D tetrachlorocuprate perovskites was previously investigated ethylammonium tetrachlorocuprate(II), (C_2H_5NH_3)_2CuCl_4 on which existence of the magnetic and electric order was observed. A number of investigated 2D layered metal-organic perovskite materials, of the general chemical formula A2BX4, consisted of three isomers ortho-, meta- and para-anisidinium tetrachlorocuprate (II), and ethylammonium tetrachlorocuprate(II) - EA_2CuCl_4 and a series of its derivatives, ClEA_2CuCl_4, BrEA_2CuCl_4, ClEA_2CuBr_4 i BrEA_2CuBr_4.

Jedna od glavnih tema istraživanja u modernoj senzorici obuhvaća funkcionalizaciju nanostrukturiranih materijala u svrhu poboljšanja osjetljivosti i selektivnosti senzora. Eksperimentalni put prema unapređenju senzora uključuje izradu i karakterizaciju materijala velike specifične površine, njihovo tretiranje fizikalnim i kemijskim metodama, te ispitivanje njihovog odziva na pokusne agense. Doktorski rad će biti baziran na izradi nanostrukturiranog silicija, s naglaskom na porozni silicij dobiven elektrokemijskim jetkanjem. Fokus ovog rada je ispitati njegova senzorska svojstva, primarno spram para organskih otapala i plinova, te utjecaj funkcionalizacije kisikom na odziv takvog senzora. One of the main research topics in modern sensorics includes functionalisation of nanostructured materials with a goal of improving sensors’ sensitivity and selectivity. The experimental path leading to such improvement involves production and characterisation of materials with a large specific surface area, their physical and chemical treatment, and assessment of their response to test chemicals. The work of this thesis will be based on production of nanostructured silicon, with emphasis on porous silicon obtained by electrochemical etching. Focus of the thesis will be to explore the sensing properties of nanostructured silicon, primarily with respect to organic vapours and gases. Also, the effects of functionalisation and morphological characteristics on the sensor’s response will be studied.

Nanostrukture poluvodičkih materijala intenzivno se proučavaju dugi niz godina radi interesantnih svojstva koja se javljaju kada je dimenzionalnost sustava smanjena te se u poluvodički materijalima počinje javljati efekt kvantnog zatočenja. U nanostrukturiranim poluvodičkim materijalima Ge i Si uočena je fotoluminiscencija čiji mehanizmi nisu u potpunosti razjašnjeni. U tu svrhu napravljene su nanostrukture s germanijem tehnikom rasprašenja magnetronskog izvora čestica. Dobivene nanostrukture su istražene uz pomoć GIWAXS spektroskopije, FTIR spektroskopije, UV-Vis spektroskopije, fotoluminiscencije i vremenski razlučene fotoluminiscencije. Nanočestice nastale u 150 nm debelom sloju nastalom miješanjem SiO_2 i Ge u omjeru 50:50 pokazale su fotoluminiscentna svojstva koja su posljedica Si-NBOHC, Ge-NBOHC, Si-ODC defekata, te najintenzivniji doprinos koji je pripisan nakupinama germanija u SiO_2 matrici. Veličina nanočestica germanija je 5 nm te raste s temperaturom grijanja do 8 nm. U fotoluminiscentnom spektru nije uočen doprinos koji bi pripisali efektu kvantnog zatočenja. Stvaranjem višeslojnih uzoraka s debljinom sloja od 4 nm u kojem se nalazi poluvodič germanij ograničavamo veličinu nanočestice koja je između 4–5 nm, te se pojavljuje fotoluminiscentni doprinos koji bi mogao odgovarati efektu kvantnog zatočenja u nanočesticama germanija. Deformacija koju osjećaju kristaliti posljedica je istezanja, te je deformacija veća kod nanočestica većih dimenzija. U ovom radu uspješno su napravljene višeslojne poluvodičke nanostrukture Ge i Si koristeći se tehnikom naparavanja pomoću elektronskog snopa koja je nešto jednostavnija i manje zahtjevna. Fotoluminiscentni spektar pokazao je doprinos koji dolazi od Si-NBOHC i Si-ODC defekata, a najintenzivniji doprinos pripisan je nakupinama poluvodiča u amorfnoj SiO_2 matrici. U crvenom dijelu spektra nalaze se doprinosi koje pripisujemo nanočesticama poluvodiča. Naprezanje kristalita posljedica je istezanja kristalita germanija i silicija, jedino kod kristalita silicija na temperaturama ≤ 1000 °C posljedica deformacije je kompresija. Naprezanje je veće na većim kristalitima silicija i germanija. Today, significant research efforts are being invested in the miniaturization of basic logic circuits and the integration of optics with electronics. By reducing the dimensions of structures to nanometer sizes and low dimensionality, unique properties and quantum effects become relevant. Varying the size and shape of the nanoparticles modifies the electronic band structure and precisely defined optical and electronic properties can be obtained. Silicon semiconductor nanostructures have an advantage due to compatibility with existing technology, while germanium provides a greater possibility of changing the electronic structure around the energy gap compared to silicon. Despite many years of research and a large number of published papers, it is still not possible to reliably and economically produce nanostructures of certain dimensions and with a small number of defects. All the mechanisms of photoluminescence in semiconductor nanostructures have not yet been identified and the question of how individual mechanisms work remains open. In this dissertation, an attempt was made to identify all observed photoluminescent contribution. These contributions originate from defects in nanostructures and are result from quantum confinement. An effort was made to determine the locations of photoluminescent defects in the nanostructure and the size of the nano crystallites that develop in the nanostructures. Moreover, here is shown how different sample production techniques affect the quality of nanostructures, i.e., the photoluminescent properties of nanostructures. In a theoretical introduction, it is explained when quantum confinement occurs and how it manifests itself in semiconductors with an indirect energy gap. Various examples of theoretical and experimental research on how quantum confinement affects the energy gap in silicon and germanium semiconductor nanoparticles are described. A brief overview of the possible recombination mechanisms that occur when we excite a sample with a laser is written. Then, an overview of possible defects that occur in the dielectric matrix of silicon dioxide is given. In addition to the dielectric, defects also occur on the surface of nanoparticles, and the number of defects increases with the size of the nanoparticle. Due to the different structural parameters between the nanoparticles and the surrounding dielectric matrix, stress felt by the silicon nanoparticles where the optical properties can be affected. The properties of the matrix adjacent to the surface of the nanoparticle can significantly affect defects and luminescent mechanisms. At the end of the chapter, the connection of optical parameters, such as the coefficient of reflectivity and absorption, with the refractive index and the dielectric function is given. Next, experimental setup and measurement methods is explained. Firstly, the technique of creating the sample is described: scattering from a magnetron source of particles and evaporation using an electron beam. The structural properties were determined by xii investigation of X-ray diffraction at a small angle of incidence and the Scherrer formula was used to determine the crystallite size. In addition to the size of the crystallite, the effect of deformation on crystallites is observed by this technique, which is determined by the Williams-Hall method and determines inhomogeneous deformation. From optical methods, infrared spectroscopy with Fourier transform, ultraviolet and visible spectroscopy in which reflectance was measured, and photoluminescent measurements were performed. Stationary and time-resolved photoluminescence was performed and described in more detail. The tested samples are then described. The technique of magnetron sputtering is a standard technique and it is used to make two types of nanostructures with germanium and silicon dioxide. The first structure with a thickness of 150 nm was obtained by simultaneous deposition of two targets SiO_2 and Ge in a ratio of 50:50. The second structure was made as a multilayer structure in which the layers of SiO_2 dielectrics and the layer in which the mixture of SiO_2 and Ge was in a ratio of 50:50 and the thickness of each layer was 4 nm. In the case of the obtained structures, the influence of the annealing temperature and the deposition temperature on the development of the structures obtained by heating the samples and their structural and photoluminescent properties were examined. Nanostructures obtained by electron beam evaporation consist of a Ge or Si semiconductor contained in a SiO_2 matrix. The particle size was controlled via a deposited semiconductor layer thickness of 2 or 4 nm. The results of this work show that the deposition temperature has an effect on the size of the semiconductor crystallite. The influence is greater in structures formed as a mixture of SiO_2 and Ge. Germanium crystals grow from 5 nm to 8 nm with increasing temperature, in addition, the dimensions of the crystallites depend a greatly on the plane in which they grow. In multilayer nanostructures, the size of the formed crystallites is determined primarily by the thickness of the layer. The temperature of crystallite formation is lower in multilayer samples. The stress of the crystallite was mainly due to the stretching of the germanium and silicon crystallites, only in the case of silicon crystallites at temperatures ≤ 1000 °C the deformation results in compression. The stress is higher on larger crystals. When the stress becomes large enough, the semiconductor crystals disappear, leaving voids behind. After the germanium crystals disappear, the photoluminescent signal increases, which leads to the conclusion that photoluminescence arises from defects. Photoluminescence is very similar in all semiconductor nanostructures of germanium. The greatest contribution to photoluminescence comes from defects, and only in the case of multilayer samples is observed the contribution that is a possible consequence of quantum confinement. In this paper, the mechanisms of photoluminescence arising from Si-NBOHC, Ge-NBOHC, Si-ODC defects were identified, and the most intense photoluminescent peak at 2.4 eV, which is attributed to defects in semiconductor clusters to the amorphous SiO_2 matrix, was better investigated. Ge-NBOHC defect is present only in samples obtained by sputtering technique from a magnetron source. In the structure formed as a mixture of Ge and SiO_2, Ge-NBOHC defect is found only at temperatures at which germanium crystals are observed, while in multilayer samples this defect occurs at crystallite formation temperatures xiii and survives at all heating temperatures. Other defects are observed in all samples. Nanostructures with silicon crystals that are produced with electron beam evaporation have a more pronounced contribution in the red part of the spectrum than germanium crystals and this part of the spectrum is attributed to quantum effects on Si or Ge semiconductor nanoparticles. Ge nanoparticles show only one photoluminescent contribution while Si nanoparticles show two components in the red region. When we look at the overall results, we come to the conclusion that Ge-NBOHC defects are formed in the shell around germanium nanoparticles and only in samples obtained by the sputtering technique from a magnetron source of particles. In samples obtained by electron beam evaporation, the Ge-NBOHC defect is not visible. However, the higher proportion of Si- NBOHC defects in the total spectrum at the temperatures at which nanoparticle formation begins are noticeable. This defect is present in all samples and at all temperatures, which indicates that the defect is trapped in the dielectric matrix, but also around nanoparticles. The Si-ODC defect shows that it is related to the Si-NBOHC defect and their ratio is inversely proportional. The defect that is visible at 2.4-2.3 eV and is attributed to defects in semiconductor clusters that remained in the amorphous SiO_2 matrix. This photoluminescent contribution is described by a stretched exponential curve with a dispersion coefficient varying 0.4-0.7 and a lifetime of 100-500 ns, which depends a lot on the individual nanostructure. Due to the complexity of this contribution, the mechanisms of this breakdown are still unknown and there is still much to research.

U Sunčevom sustavu, osim Sunca i planeta, do danas je otkriveno gotovo milijun malih tijela Sunčevog sustava. Zbog njihovih malih dimenzija, oni spadaju u objekte čije istraživanje često zahtijeva teleskope velikih promjera ili primjenu suvremenih opažačkih metoda. Jedna od suvremenih opažačkih metoda određivanja fizikalnih karakteristika malih tijela Sunčevog sustava, koja dozvoljava razlučivosti veće od bilo koje druge zemaljske metode, jest metoda zvjezdanih okultacija. Mala tijela po sastavu i orbitalnim parametrima možemo klasificirati u asteroide i komete. Međutim, među asteroidima se pojavljuje malobrojna skupina objekata koji pokazuju aktivnosti slične kometskim. U doktorskom radu istražena je mikroaktivnost malog tijela 95P/(2060) Chiron. Zbog nedavne indikacije da bi Chiron mogao posjedovati prstenove, njegov mehanizam gubitka mase može biti objašnjen udarima krhotina iz Chironove orbite koje padaju na njegovu površinu. Opažanja su prikupljana na Španjolskoj zvjezdarnici Calar Alto, a za analizu su uglavnom korištene fotometrijske metode. Određivanjem Chironove rotacijske krivulje sjaja i njegove apsolutne zvjezdane veličine, potvrđena je pretpostavka da Chiron posjeduje prstenove. Kao primjer primjene metode zvjezdanih okultacija u svrhu istraživanja fizičkih karakteristika malih tijela Sunčevog sustava, opisano je određivanje veličine, oblika, albeda i gustoće patuljastog planeta Haumea, gornje granice Haumeine atmosfere, te otkriće i karakterizacija prstenova oko glavnog tijela Haumee. U svrhu poboljšanja vremenske razlučivosti opažanja zvjezdanih okultacija s malim tijelima, istražena je i opisana mogućnost primjene atmosferskih Čerenkovljevih teleskopa MAGIC. Njihovi veliki promjeri i osjetljivi fotomultiplikatorski detektori s visokim frekvencijama uzorkovanja, osim za unapređenje razlučivosti u određivanju fizičkih karakteristika malih tijela Sunčevog sustava, mogu biti korišteni za izravna mjerenja promjera zvijezda. U doktorskom radu opisana je metoda određivanja zvjezdanih promjera pomoću detekcije Fresnelovih difrakcijskih uzoraka, koji se mogu opaziti tijekom zvjezdanih okultacija. Detaljno je modeliran signal kakav bi bio opažen teleskopima MAGIC, uzevši u obzir karakteristike teleskopa i osjetljivost detektora. Kroz opažačke prijedloge ostvareno je teleskopsko vrijeme za opažanje zvjezdanih okultacija s MAGIC teleskopima. Extended abstract - Besides the Sun and the planets, our Solar System contains nearly 1 million discovered small Solar System bodies. Due to their small size, they belong to objects whose research often requires large-sized telescopes or the application of modern observation methods. One of today’s modern observational methods used for determining the physical characteristics of the small Solar System bodies, allowing several orders of magnitude better resolutions than any other Earth-based method, is the stellar occultations method. By composition and orbital parameters, small Solar System bodies can be classified into asteroids and comets. Nevertheless, there is a group of asteroid-like objects that show cometlike activities. This doctoral thesis consists of 3 parts. In part one, the observed micro activity of the small Solar System body 95P/(2060) Chiron was investigated. In part two, as an extensive example of the application of the stellar occultation method to investigate the physical characteristics of small Solar System bodies, the determination of the dwarf planet’s Haumea size, shape, albedo, and density was described. In part three, in order to improve the temporal resolution of observations of stellar occultations with small bodies, the potential of using the atmospheric Cherenkov telescopes MAGIC for observing stellar occultations was investigated. Activity of 95P/(2060) Chiron The minor planet 95P/(2060) Chiron belongs to the asteroid group of centaurs, which according to dynamic parameters belongs to asteroids. Chiron has an orbit far away from the Sun, in which sublimation of water ice is not considered as a possible cause for triggering mass loss mechanisms. The expected rate of collisions among small bodies in the region of centaurs is not expected to be high. Regardless of that, since its discovery, Chiron has repeatedly shown indications of cometary activity (Kowal et al. 1979; Tholen et al. 1988; Meech Belton 1990). In 2015, Ortiz et al. (2015) found indications that (2060) Chiron possesses rings. Motivated by these findings, additional observations and interpretations of the cause of its activity were made and described in this doctoral thesis (and published in Cikota et al., 2018). Observations were carried out in three different observation campaigns between 2014 and 2016, using three different instruments located at the Calar Alto Observatory (CAHA) in Almeria, Spain - 3.5 m MOSCA, 1.23 m DLR-MKIII and 2.2 m CAFOS. From the collected observations, amplitudes of Chiron’s rotational light curves and measurements of Chiron’s absolute magnitudes were determined. The measured amplitudes are consistent with the model proposed by Ortiz et al. (2015) which is taking into account both, Chiron’s triangular ellipsoid-like shape and the light contribution of rings around Chiron. Although the frequency of collisions among small bodies in the centaur region is very low, iv due to the recent indication that Chiron possesses rings, and assuming that there is debris orbiting around Chiron, it is well possible that some of this debris may be continually falling and impacting on its surface, producing outbursts and forming a bound or quasi-bound coma. Consequently, a dust release mechanism triggered by impacts should not be excluded as a possible cause for its activity. To study this hypothesis, the scatter in Chiron’s photometric data was compared to the scatter of comparison stars of similar brightness as Chiron. The scatter of Chiron’s photometric measurements for the observations carried out on July 23 and 24, 2014, with the DLR-MKIII 1.23 m CAHA telescope was found to be 0.027 mag, while the comparison star’s scatter is 0.014 mag. During the photometric campaign in 2015, containing data collected with CAFOS 2.2 m CAHA telescope on September 11 and September 13, the scatter of Chiron’s photometric measurements was determined to be 0.029 mag, while the comparison star’s scatter values were 0.018 mag. The noticeable difference between the comparison star’s and Chiron’s photometric scatter supports our hypothesis of continuous micro activity on Chiron. That mechanism could also be a plausible explanation for impulsive brightening on a timescale of hours that have been observed by Luu Jewitt (1990). We hypothesize that some activity outbursts on regular comets could also be triggered by collisions, either with debris orbiting them or with meteoroids. Additionally, the data collected with the CAFOS 2.2 m CAHA telescope over 3 nights between September 11 and September 14, 2015, was used to search for comet-like activity signs like coma or tail. The data was combined to a false-color image of Chiron that contains 95 integrations of 300 s each, resulting in a total integration time of 28500 s (475 min). The combined image of Chiron shows that the coma itself is not detectable, but a very faint asymmetric shape with a measured position angle of ∼ 87◦ was observed. The feature can be explained by a ∼5 arcsec long comet-like tail, of a determined surface brightness of 25.3 mag(R)/arcsec2. Determination of the dwarf planet Haumea’s physical characteristics - Five dwarf planets are currently known in our Solar system. (1) Ceres is the closest dwarf planet to us, and the only dwarf planet orbiting in the inner part of the Solar system, within the main belt of asteroids. Four dwarf planets - (134340) Pluto, (136199) Eris, (136108) Haumea, and (136472) Makemake, are members of the Kuiper belt, located in the outer part of the Solar system beyond Neptune’s orbit. Due to the large distances of dwarf planets in the outer Solar system, indirect observation methods are necessary to accurately determine their physical characteristics. Among trans-Neptunian objects, the dwarf planet Haumea stands out in its elongated shape and extremely short rotation period (Brown et al. 2005; Rabinowitz et al. 2006; Brown et al. 2007). Unlike other dwarf planets (Sicardy et al. 2011; Ortiz et al. 2012; Stern et al. v 2015), Haumea’s physical characteristics were not precisely determined. In this doctoral thesis, the determination of Haumea’s size, shape, albedo, and density was described, as well as the discovery and characterization of its rings (published in Ortiz et al. 2017). On January 21, 2017, a stellar occultation of the dwarf planet Haumea was observed. The occulted star URAT1 533-182543 with its apparent brightness of 𝑚𝑅 = 17.6 mag made it observable already for small- and mid-sized telescopes. Therefore, the occultation event was observed from many locations and resulted in 12 positive detections from 10 different sites across Europe. From the collected sequences of CCD images, photometric measurements of the synthetic aperture were performed. In the case of data collected from the Črni Vrh Observatory by the drift method, a special procedure of photometric analysis was applied to the stellar trail. By fitting a square well model to the collected photometric measurements, the times of the star’s disappearance and reappearance were determined, and occultation chords were generated for each observation location. To the chords in the projected plane, an elliptical limb was fitted by minimizing a 𝜒2 function. By that, the apparent edge of the shape of the ellipse, which represents the outline of Haumea’s shadow, was determined. The determined parameters of the major and minor axis of the ellipse are 1 704 ± 4 km and 1 138 ± 26 km respectively. The position angle of the minor axis is -76.3◦ ± 1.2◦. A search for an atmosphere was performed and the upper value of Haumea’s atmospheric pressure was determined by using the best available data set collected by the Asiago Observatory. From Haumea’s mass, and assuming that the body is in hydrostatic equilibrium, an average surface gravity of 0.39 ms−2 was determined. By comparing a modelled occultation light curve with the observed light curve, the upper value of Haumea’s pure isothermal global atmosphere of 𝑁2 in thermal equilibrium can be determined. Assuming a surface temperature of 40 K, we find a 1 𝜎 upper limit for 𝑝surface(𝑁2) = 3 nbar, and a 3 𝜎 upper limit for 𝑝surface(𝑁2) = 15 nbar. In addition to the main occultation, there are brief dimmings prior to and after the main event. These dips are consistently explained by a narrow and dense ring around Haumea that absorbed about 50% of the incoming stellar flux. A distinct cross-sectional profile of the rings collected in an observation with the 1 m telescope of the Konkoly Observatory reveals a radial ring width of 𝑊ring ≈ 74 km at the occultation ingress and 𝑊ring ≈ 44 km at the occultation egress, with corresponding apparent transparency of p’ = 0.55 and p’ = 0.56. The locations of twelve detected secondary events, projected in the sky plane, allow the retrieval of the full ring orbit, assuming an apparent elliptical shape, and using the same approach as used for fitting Haumea’s limb. The parameters of the elliptical fit to the rings are 𝑎0 ring = 2287+75 −45 km for the apparent semimajor axis, and 𝑏0 ring = 541 ± 23 km for a semiminor axis. The position angle of the minor vi axis is 𝑃ring = -74.3◦ ± 1.3◦. Assuming the rings are circular, it implies a radius of the ring of 𝑟ring = 2287+75 −45 km and an inclination angle of 𝐵ring = 13,8◦ ± 0.5◦. The circular ring assumption is supported by the fact that the center of the ring ellipse coincides with the order of uncertainty with the center of the limb of Haumea’s main body. The position angle of the ring minor axis 𝑃ring = -74.3◦ ±1.3◦ coincides with that of the limb minor axis 𝑃limb = -76.3◦ ± 1.2◦, which is another strong argument that we are observing a ring that settled into Haumea’s equatorial plane. Furthermore, it was found that the radius of the rings coincides with the area where 3:1 spin-orbit resonances are expected. From the determined parameters of Haumea’s limb, a three-dimensional shape and density of Haumea were determined. The obtained parameters of the triaxial ellipsoid a × b × c are (1 161 ± 30) km × (852 ± 2) km × (513 ± 16) km. The mean value of the Haumea density, determined through the parameters of the triangular ellipsoid, and the mass determined by the orbital period of the Hi’iake satellite, is 1 885 ± 80 kg m−3. The geometric albedo of Haumea determined by our observations is 0.51, which is significantly smaller than the value of 0.804, as available in the most recent literature (Fornasier et al. 2013). Application of the atmospheric Cherenkov telescopes MAGIC for observing stellar occultations - In order to accurately determine the physical characteristics of small bodies by using the occultation method, a high temporal resolution of the detector is required. In order to improve the observational methods of stellar occultations, the use of the MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes was considered. With its sensitive central pixel, the MAGIC-II telescope has shown to be an excellent instrument for detecting millisecond flashes in the visible spectra. Compared to any other optical telescope used for observing stellar occultations, its central pixel with a temporal resolution of 10 kHz, combined with a large 17 m aperture, the MAGIC-II telescope enables reaching two orders higher resolutions. However, some of its limiting characteristics are the inability to control the sampling frequency, sensitivity only in the visible spectrum between 300 and 400 nm, and a low angular resolution (due to physically large pixels) responsible for a limitation in the apparent brightness of m = 13.5 ± 0.6 mag. In addition to determining the physical characteristics of small bodies, using the stellar occultation method enables us to determine the angular sizes of the occulted stars. Since stars are not point sources (they have a finite angular diameter), during the occultation of a stellar disk, its light curve does not show a sharp brightness drop but describes a Fresnel interference pattern whose details depend on the angular diameter of the occulted star. High sampling rates make it possible to record these interference patterns. Therefore, the high temporal resolution vii of the detector is the key for direct measurements of stellar radii. In this doctoral thesis, the method of determining stellar radii by observing Fresnel diffraction patterns that can be detected during stellar occultations is described. Models of the expected signal were performed, taking into account the characteristics of the MAGIC telescopes and the sensitivity of its detectors. Through observational proposals, telescope time was granted and first observations of stellar occultations with the MAGIC telescopes were acquired. Additionally, the effects of limb darkening of stellar disks were investigated. It was found that diffraction patterns formed by occultations of large disks with angular diameters of 0.7 mas and high limb darkening factors of u = 1.0 deviate in intensity up to approximately 5% from diffraction patterns of homogeneously illuminated stellar disks (u = 0.0). For stellar disks of smaller diameters or smaller limb darkening factors, the intensity deviations are smaller. These deviations in the intensity of diffraction patterns are reflected in the determination of the angular diameters of stellar disks. It was found that the angular radius of a homogeneously illuminated stellar disk, compared to a disk with a limb darkening factor of u = 1.0 taken into account, deviates by approximately 12.4%. Taking the limb darkening factors into account contributes to the accuracy of measurements of the angular diameters of stellar disks, but to achieve this accuracy, photometric measurements with uncertainties below 5% are required. Historically, almost all measurements of the stellar radii smaller than ∼1 arc millisecond have been performed by interferometric measurements. Measurements of stellar radii by observing occultations with asteroids allow reaching angular resolutions up to 0.1 milliarcseconds, which is at least a factor of two larger than the one available through interferometric measurements, and a factor of 10 larger than what can be achieved by observing lunar occultations. Therefore, the asteroid occultation method is extremely useful for measuring the angular diameters of stars below 1 milliarcsecond. In the period from December 2017 to February 2020, a total of 6 occultation observations with the MAGIC-II telescope were scheduled. Four observations were not successfully acquired due to bad weather or technical reasons. Two occultation events, those by the small bodies (83) Beatrix and (28) Bellona, were successfully acquired but resulted in a negative detection. Although the occultation events of (83) Beatrix and (28) Bellona occurred over sufficiently bright sources, and their probability of observation was estimated at 99%, the negative detections can be explained by a too small brightness drops, ∼1.5 mag for the (83) Beatrix event (2.5 𝜎), and ∼0.9 mag for the (28) Bellona event (1.5 𝜎). Based on the analysis presented in this thesis, we expect that any event with a brightness drop larger than 1.8-3.0 mag (3-5 𝜎 above background noise) should be detected. Therefore, the observation campaign of occultations on MAGIC telescopes will be continued in the future.

U tekstu se govori o dvjema knjigama Carla Rovellija objavljenima na hrvatskom, Red vremena (2021.) i Na krilima leptira: postoje mjesta gdje je ljubaznost važnija od pravila i druge misli o filozofiji, fizici i svijetu (2022.).

Uključenost u učenje je multidimenzionalni konstrukt koji se, prema većini autora, sastoji od više aspekata: bihevioralnog (trud, pažnja, koncentracija), kognitivnog (učenje s razumijevanjem) i emocionalnog (pozitivne emocije nasuprot negativnima), a prema nekim autorima i proaktivnog koji se odnosi na samoinicijativno obogaćivanje procesa učenja (primjerice, postavljanje pitanja, davanja prijedloga za poboljšavanja procesa učenja). Iako su poznati brojni pozitivni obrazovni ishodi uključenosti u učenje, manje se zna o prirodi i dinamici samog koncepta predmetno specifične uključenosti u učenje fizike. Stoga je cilj ovog istraživanja bio ispitati obilježja te dinamiku različitih aspekata uključenosti u učenje fizike koje učitelji prepoznaju. Za teorijski okvir odabran je Model četiri međusobno povezana aspekta učeničke uključenosti u učenje (Reeve, 2013). Prema ovom modelu četiri aspekta uključenosti u učenje (bihevioralni, kognitivni, emocionalni i proaktivni) međusobno su u interakciji i dovode do pozitivnih ishoda poput veće kvalitete učenja, akademskog postignuća te razvoja vještina i talenata. U okviru kvalitativne metodologije provedeno je 12 dubinskih polustrukturiranih intervjua s učiteljima fizike iz 11 osnovnih škola (9 učiteljica). Primijenjen je fenomenološki pristup. Rezultati istraživanja su pokazali da učitelji fizike proaktivni aspekt prepoznaju kao pokazatelj kvalietetne uključenosti u učenje fizike. Opisana dinamika različitih aspekata uključenosti u učenje fizike pokazuje da su različiti aspekti uključenosti u složenom međuodnosu, u skladu s teorijskim okvirom, ali i da emocionalni aspekt ima važnu ulogu u poticanju ili blokiranju ostalih aspekata u uključenosti u učenje fizike.

Kroz višegodišnje je iskustvo u izvoženju nastave iz fizike na preddiplomskim i diplomskim studijima kod studenata uocen problem svladavanja apstraktnijeg gradiva iz podrucja fizike. Navedeno se uglavnom odnosi na razumijevanje rješenja složenijih zadataka. Kao primjeri se mogu navesti gibanje cestice u gravitacijskom polju uz otpor zraka i gibanje naboja u elektromagnetskim poljima. Iako razumijevanje nije kod svih studenata isto te ovisi o sposobnosti usvajanja i korištenja matematickih formula, postupak vizualizacije rješenja opcenito igra korisnu ulogu. To se posebice ocituje kod studenata koji su skloniji vizualnom tipu ucenja. Da bi se studentima olakšalo svladavanje gradiva sadržanog u studijima fizike, na Odjelu za fiziku, Sveucilišta Josipa Jurja Strossmayera u Osijeku, uveden je kolegij Vizualizacija fizikalnih problema 2017. godine. Ova knjiga služi da bi se studentima omogucilo lakše pracenje sadržaja kolegija te kao repozitorij riješenih primjera koristeci programski paket Octave.

Eksponencijalni razvoj fizike i njezina otkrića u 20. stoljeću utjecali su na sve aspekte ljudskoga života: ekonomske, društvene, političke filozofske pa i umjetničke. Početak stoljeća obilježile su teorija relativnosti i kvantna fizika koje su uvele revolucionarne promjene u poimanje prostora i vremena, prirodom određenih ograničenja mjerenja, sprege motritelja i sustava kojeg promatra te probabilističke prirode svemira. Tehnologije zasnovane na otkrićima fizike upotrijebljene su u oba svjetska rata, od kojih je kulminacija i završetak drugoga bio upotreba atomskog oružja s posljedicama bez presedana u ljudskoj povijesti. U drugoj polovini stoljeća razvija se „big science,“ a otkrića tranzistora, čipa i kasnije Interneta izazivaju digitalnu revoluciju. Pored fundamentalnih spoznaja iz kozmologije i astrofizike do kraja 20. stoljeća fizika je doprinijela istraživanju svemira, svemirskom programu, otkriću strukture DNK i revolucionarizirala medicinsku dijagnostiku otkrićima brojnih slikovnih tehnika., The twentieth century made the science go through exponential development, which consequently took over the dominance of the intellectual sphere and exerted a huge influence on the economy, the standard of living and the society in general. Physics is a fundamental natural science that, apart from exceptional theoretical and experimental discoveries in the 20th century, has a strong influence on the development of related natural sciences, chemistry and biology (the discovery of DNA structure by X-ray crystallography), technology (the conquest of space, new materials, diagnostic techniques in medicine, digital revolution), and thus the economy as well, and due to the use of nuclear weapons there was also the influence on the social sphere and politics unprecedented in history. The article provides with an overview on the most significant physical discoveries of the 20th century and aspects of their influence on society and historical events through quotes from the famous physicists and science historians.

U doktorskoj disertaciji su prikazani metoda i rezultati vrednovanja točnosti izračuna apsorbirane doze računalnih algoritama koji se primjenjuju u radijacijskoj onkologiji. Metoda se temelji na primjeni Monte Carlo (MC) simulacije i komplementarna je postojećoj eksperimentalnoj metodologiji. MC simulacija je provedena korištenjem programskog paketa Monte Carlo N-Particle (MCNP). Istraživanje je provedeno za računalni algoritam sustava Elekta Monaco (MCTPS) kao jedan od najnaprednijih algoritama koji se trenutno koriste za planiranje jakosno modulirane radioterapije. Taj algoritam izračun apsorbirane doze dijelom temelji na MC simulaciji. On izračunava apsorbiranu dozu u malom volumenu sredstva koji se nalazi u sredstvu (D_m,m) te pruža mogućnost izračuna apsorbirane doze u vodi (D_w,m). Vrednovanje je provedeno za oba načina izračuna. Da bi se pouzdano utvrdila točnost MCNP izračuna apsorbirane doze bilo je potrebno dozimetrijski vrednovati rezultate MCNP modela 6 MV X-zraka u vodenom fantomu. MCNP simulacije provedene su u 13 postava homogenih fantoma različitih gustoća u rasponu od 0,2 g/cm^3 do 2,17 g/cm^3. Dodatno, vrednovanje je provedeno u složenim geometrijama kojima se nastojalo simulirati stvarne situacije. U heterogenoj geometriji istraživanje je bilo ograničeno na tri materijala gustoća usporedivih s gustoćama pojedinih vrsta tkiva. Osmišljena i simulirana su 4 različita scenarija za ispitivanje utjecaja heterogenosti na točnost izračuna apsorbirane doze u MCTPS, za oba načina izračuna, D_m,m i D_w,m. Korišten je fantom istih dimenzija kao kod izračuna u homogenoj geometriji, s razlikom što su na različitim dubinama dodavani umeci različitih gustoća. Odstupanja su izračunata pomoću korijena srednje vrijednosti kvadrata odstupanja (engl. root mean square deviation, RMS) za krivulje ovisnosti doze o dubini (DD). DD krivulje su izračunate pomoću MCNP programskog paketa te uspoređene s MCTPS izračunima. Također, za svih trinaest materijala ispitivana je točnost uračunavanja doprinosa različitih vrsta međudjelovanja u MCTPS izračunu apsorbirane doze. Prema rezultatima istraživanja, MCTPS način izračuna apsorbirane doze u sredstvu pokazuje RMS odstupanja u odnosu na MCNP izračun manji od 3% za sve materijale, osim za materijal najmanje gustoće (RMS=4,8%). Analiza rezultata između izračuna doza u vodi, nastao pretvorbom iz izračuna doze u sredstvu, i MCNP simulacije izračuna doze u vodi, pokazuje znatna odstupanja za većinu korištenih materijala, do najviše vrijednosti RMS = 13,1% za materijal najveće gustoće. Utvrđeno je da se izračun doze u vodi (D_w,m) koji je nastao pretvorbom iz izračuna doze u sredstvu bitno razlikuje od izračuna doze u vodi (D_w,w) i da ih treba razlikovati. Također, utvrđeno je da za različite materijale apsorbirana doza izračunata kao doza u sredstvu pokazuje bolje slaganje s algoritmima koji izračunavaju apsorbiranu dozu primjenom koncepta Dw,w, pri čemu najveće RMS odstupanje iznosi 3,7% za materijal najveće gustoće. U području gustoća manjih od vode potrebna su poboljšanja izračuna doza u sredstvu (D_m,m) te je predložena korekcija HU-RED krivulje i na taj način je RMS odstupanje smanjeno s 4,8% na 2,8%. Nadalje, s porastom atomskog broja materijala (počevši od materijala gustoće 1,66 g/cm3) utvrđeno je odstupanje u uračunavanju doprinosa fotoelektričnog učinka kao i doprinosa tvorbe para elektron-pozitron. Odstupanja u uračunavanju doprinosa fotoelektričnog učinka u izračunu apsorbirane doze od 1,3% do 1,7% utvrđena su za materijale gustoće od 1,66 g/cm^3 do 2,17 g/cm^3 na dubini od 5 cm. Ispitivanje točnosti uračunavanja doprinosa tvorbe para elektronpozitron na dubini od 10 cm pokazuje trend povećanja odstupanja do maksimalnog odstupanja od 2,3% za materijal gustoće 2,0 g/cm^3. Prikazani rezultati upućuju da MCTPS izračun apsorbirane doze kao doza u sredstvu (D_m,m) predstavlja točniji način izračuna apsorbirane doze. The most advanced treatment planning systems (TPSs) in radiation oncology have Monte Carlo (MC) based algorithms which facilitate the most accurate calculation of absorbed dose distributions in (external beam) radiotherapy. Such algorithms inherently calculate absorbed dose as dose to medium in medium (D_m,m), but also provide the ability to calculate absorbed dose as dose to water in medium (D_w,m) by converting the calculation from D_m,m to D_w,m using Spencer-Attix's extension of Brag-Gray small cavity theory. According to published data, differences between these two calculation options are noted, particularly in bony structures. Unlike the generalized MC codes (MCNP, EGS, GEANT...) several approximations and simplifications were introduced in such algorithms to speed up the calculation time. Thus, additional validation of calculation accuracy for both abovementioned calculation options is required. This doctoral dissertation presents the method and the results of a verification, complementary to the existing experimental methodology, for the accuracy validation of such algorithms using MC simulations. It was performed using Monte Carlo N-Particle code® (MCNP) by which the transport of photons and electrons is simulated. Algorithms used in radiation oncology calculate the absorbed dose without knowledge of the material chemical composition. Therefore, the investigation of the impact of material chemical composition on calculation accuracy was performed using MCNP calculations. Furthermore, the majority of clinical experience is based on the dose to water in water (D_w,w) concept provided by analytical algorithms and it has represented the standard for dose calculation during the past several decades. Considering that, additional MCNP calculation was performed to simulate the D_w,w concept of absorbed dose calculation. Hence, the deviation between the D_w,w and both calculation options provided by the MC based algorithms was determined. Additionally, the influence of predefined probabilities for X-ray interaction mechanisms and its respective contributions to absorbed dose calculations was validated using MCNP. Futhermore, in order to improve the accuracy of absorbed dose calculation for the D_m,m MCTPS calculation option, a correction for the HU-RED curve was applied. The impact of the proposed corrections on the accuracy of the absorbed dose calculation was also validated. Materials and methods: The calculation algorithm for intensity modulated radiotherapy (IMRT) built in the Elekta Monaco TPS is based on MC simulation. Its absorbed dose calculation has three components: a virtual source model (VSM), a transmission filter, and a patient model. The MC simulation is applied only in the final part of the calculation using X-Ray Voxel Monte Carlo (XVMC). Absorbed dose is calculated as Dm,m, but the conversion from Dm,m to Dw,m is enabled as well. In order to investigate the MCTPS absorbed dose distribution calculation accuracy for 6MV photon beam in various geometries, MCNP simulation was performed. To determine the accuracy of the MCNP absorbed dose calculation in any geometry, it is necessary to dosimetrically validate the results of the MCNP 6 MV X-ray beam model with the values measured using an ionization chamber in a water phantom. A virtual phantom of the same dimensions, 30×30×30 cm^3, as for MCTPS calculations was used. Percentage depth dose curves and dose profiles for various field sizes were calculated at several depths and compared to the measured data. For all MCNP calculations, cut-off energies of 1 keV for electrons (E_CUT) and 1 keV for photons (P_CUT) were applied. Statistical uncertainty for MCNP calculations was less than 1%. The validation criterion was set on the central part of the beam where deviation between calculated and measured data less than 0.5% was taken as acceptable. Initially, comparisons between dose calculation options built in MCTPS and MCNP in 13 different materials with mass densities ranging from 0.2 g/cm^3 to 2.17 g/cm3^3 was performed. The MCNP calculations were performed by assigning elemental chemical composition and mass density (MCNP_MEDIUM) and the absorbed dose is calculated as D_m,m. Additional MCNP simulation was performed to simulate D_w,w absorbed dose calculation (MCNP_WATER). Thus, MC simulation was performed for non-standard conditions, where different materials were represented as water of different densities. Depth dose curves (DDs) calculated by MCNP were compared to D_m,m and D_w,m calculated data using Root Mean Square (RMS) deviation (further in text: deviation). Additionally, similar validation of accuracy of absorbed dose calculations was performed in heterogeneous phantoms. For that reason, 4 different scenarios were designed and simulated. Heterogeneous geometries were simulated by placing inserts of different densities (ρ=0,205 g/cm^3 and ρ=1,6 g/cm^3) at different positions in the virtual water phantom. In this part, the study is limited to three materials used to mimic soft tissue, lungs and bones, respectively. In addition, the influence of the position of the heterogenity in the calculation geometry on the calculation of the absorbed dose was investigated. Due to differences in determination of materials in the respective calculation systems the influence of the chemical composition on the calculation of the absorbed dose in the semi-anthropomorphic phantom was eximened. Potential reasons for deviations were investigated. An improvement of the MCTPS Dm,m calculation accuracy is proposed. Results and discussion: The absorbed dose calculation accuracy is related to the capability of the algorithm to calculate absorbed dose at any point of interest within the patient and correlate it to the beam calibration point dose considered as the reference absorbed dose. In the MCTPS dose calculation engine, the chemical composition of the materials is not taken into account, thus introducing additional uncertainty into the calculation of absorbed dose. Deviations between DDs, for Dm,m and Dw,m in different materials become largest for material of mass density 2.17 g/cm3, up to 13%. Comparison for Dm,m calculation option to the MCNPMEDIUM shows very good agreement, with the deviation less than 3% for the majority of examined materials except for the lowest mass density in this research (ρ=0,2 g/cm^3), where the deviation is 4.8%. For the D_w,m calculation option results are acceptable only in the mass density range from 0.5 g/cm^3 to 1.06 g/cm^3 with deviations less than 2.5%. For the rest of the examined materials, the deviation increases, with a maximal value of 12.4% for mass density 2.17 g/cm3. Absorbed dose calculation comparison between D_w,m and MCNP_WATER shows large deviations for the majority of used materials, up to 13.1% for mass density 2.17 g/cm^3. Deviations between the D_m,m calculation option and MCNP_WATER are lower than one might expect, e.g. for the largest mass density in this research the deviation is 3.7%. Furthermore, the assumption of small cavity conditions applied through stopping power ratios of water and different materials for D_w,m calculation was also validated. It could be an acceptable approximation when assumptions of the Bragg-Gray cavity theory are fulfilled. The most probable energy of the secondary electrons for a 6 MV photon beam is below 300 keV. Such electrons have a range of 0.0957 g/cm2, and consequently, the conditions for small cavity when the voxel size of 3×3×3 mm^3 is used, mainly cannot be fulfilled due to the secondary electron range for almost all materials used. To verify the results obtained in simplified geometry, additional validation was performed in more complex geometry. The validation of the MCTPS absorbed dose calculation was performed by comparison with MCNP_MEDIUM calculations, when the conditions for charged particles equilibrium are not met due to heterogeneity. Since the validation was performed in complex geometry, a validation criterion was applied according to which a deviation 1.66 g/cm^3) differences in the calculation of the contribution of the photoelectric effect as well as pair production were observed. Differences in the calculation of the contribution of the photoelectric effect in the calculation of the absorbed dose from 1.3% to 1.7% were determined for materials with densities 1.66 g/cm3-2.17 g/cm^3 at a depth of 5 cm. Within MCTPS, equal stopping powers for positron and electron are applied to electron-positron pair production. However, examination of the deviation in the calculation of the contribution of electronpositron pair production at a depth of 10 cm shows increase of the deviation to a maximum value of 2.3% for the material with a density of 2.0 g/cm^3. The mean free path length, which is one of the parameters defined within the MCTPS when the conditions are met for the electron positron pair production is not correctly defined for the positron within the MCTPS. Conclusion: This doctoral dissertation presents the results of the method for validation of the MC based algorithm calculation accuracy which may be complementary to existing experimental verification methodology. The validation was performed for both options, D_m,m and D_w,m, using MCNP simulations. Although, algorithm built in MCTPS do not take into account the chemical composition of the medium, D_m,m calculation option shows very good agreement with standard MCNP calculations except for low density medium. Furthermore, it is demonstrated that the D_w,m calculation option differs substantially from D_w,w. It was also found that for different materials, absorbed dose calculated as D_m,m shows better agreement to the algorithms that calculate absorbed dose using D_w,w approach. The HU-RED correction was proposed in order to improve the accuracy of D_m,m calculation option built in MCTPS in low density medium. The results indicate that the absorbed dose distribution calculation performed with D_m,m could be preferable in order to allow better consistency with clinical data based on D_w,w dose concept as well as reference dosimetry performed in water. Also, this doctoral dissertation provides additional insight regarding the dilemma which calculation option is more accurate for use in radiation oncology. The results obtained indicate that D_m,m could be regarded as the preferable dose calculation option.

Danas, u suvremenom obrazovanju koje stavlja naglasak na znanja i vještine za nova zanimanja 21. stoljeća, nastava fizike ima sve veći utjecaj i značaj. U ovome se radu naglasak stavlja na rano učenje fizike, već u nižim razredima osnovne škole. Brojna istraživanja pokazuju da je susretanje djece sa STEM područjima (prirodoslovlje, tehnologija, inženjerstvo i matematika) bitno za njihov daljnji interes i motivaciju prema tim područjima. Djeca su u ranoj dobi jako znatiželjna, postavljaju puno pitanja te je tada pravi trenutak da im se predstave poticajni fizikalni koncepti. Ključan segment u nastavi fizike je pokus. Pokusi u nastavi fizike omogućuju djeci samostalno istraživanje te kod djece potiču maštovitost, razvijanje kritičkog razmišljanja i zaključavanja. Isto tako, u suvremenoj nastavi fizike dobro je implementirati primjere iz svakodnevnog života koji pobuđuju dodatni interes za fiziku. Sport je praktična aktivnost u kojoj se primjenjuju brojne fizikalne zakonitosti. Kako bi ih bolje razumjeli, postoje dvije opcije: jedna je detaljno istraživati - mjeriti gibanja i druge fizikalne pojave u sportu, a druga je osmisliti i izvoditi pokuse kojima bi se prikazale pojedine zakonitosti koje se primjenjuju u sportu. U radu se obrađuje nekoliko odabranih i prilagođenih primjera koji se mogu implementirati u kurikulum u osnovnoj školi, ponajviše u razrednoj nastavi. Today, in modern education that places emphasis on knowledge and skills for new occupations of the 21st century, the teaching of physics has an increasing influence and importance. In this thesis, the emphasis is placed on early learning of physics, already in the lower grades of primary school. Numerous studies show that meeting children with STEM areas (science, technology, engineering and mathematics) is essential for their further interest and motivation towards these areas. Children at an early age are very curious, they ask a lot of questions and then it is the right time to introduce them to stimulating physical concepts. A key segment in physics teaching is experimentation. Experiments in physics teaching enable children to explore independently and encourage children's imagination, development of critical thinking and reasoning. Likewise, in modern physics teaching it is good to implement examples from everyday life that arouse additional interest in physics. Sport is a practical activity in which a number of physical laws are applied. To better understand them, there are two options, one is to investigate in detail - to measure movements and other physical phenomena in sports, and the other is to design and perform experiments to show the individual laws applied in sports. This thesis deals with several selected and adapted examples that can be implemented in the curriculum in primary school, mostly in the classroom teaching.

Istraživački usmjerena nastava fizike potiče razvoj znanstvenog razmišljanja i zaključivanja. Učenici kroz istraživački usmjerenu nastavu razvijaju kritičko mišljenje, aktivno sudjeluju u nastavi te stječu znanja o samoj prirodi znanosti. Veliku ulogu u istraživački usmjerenoj nastavi fizike predstavlja pokus. Pokus, osim što nastavu čini zanimljivijom i zabavnijom, pruža izravno iskustvo učenicima o fizičkim pojavama. Pomoću pokusa učenici upoznavaju i istražuju nove pojave, te uz pokus uočavaju zakonitosti i testiraju hipoteze. Pri samom izvođenju pokusa kvantitativno se mjere fizičke veličine pri čemu pomažu mjerni instrumenti. Micro:bit kao suvremeno mikroračunalo može zamijeniti veći broj instrumenata i tako riješiti problem nedostatka opreme za izvođenje pokusa. Upoznavanje fizike na zabavan, kreativan i interdisciplinaran način uz korištenje tehnologije uvedeno je pomoću STEM pristupa obrazovanju. Research-oriented teaching of physics encourages the development of scientific thinking and reasoning. Through research-oriented teaching, students develop critical thinking, actively participate in teaching, and acquire knowledge about the very nature of science. Experiment plays a major role in research-oriented teaching of physics. The experiment, in addition to making teaching more interesting and fun, provides students with a direct experience of physical phenomena. With the help of the experiment, students get to know new phenomena, research about the phenomena, and with the experiment they notice the laws and test the hypotheses. During the experiment, physical quantities are measured quantitatively with the help of measuring instruments. Micro:bit as a modern microcomputer can replace a larger number of instruments and thus solve the problem of lack of equipment for performing experiments. Getting to know physics in a fun, creative and interdisciplinary way with the use of technology was introduced using the STEM approach to education.

Kao jedan od glavnih procesnih uređaja, izmjenjivači topline predmet su intenzivnih istraživanja usmjerenih na različita područja interesa koji uključuju optimalan dizajn, poboljšanja strukture, poboljšanja prijenosa topline, dinamičko ponašanje, automatsko upravljanje, sintezu mreže, numeričku simulaciju, eksperimentalne metode, proizvodnju i razvoj novih vrsta površina za prijenos topline. U ovom radu se za zadanu ukupnu površinu izmjenjivača topline traži optimalno mjesto priključka dodatne struje, određenog protoka i temperature, iz dostupne mreže izmjenjivača topline kako bi se ispunila dva cilja: ostvarenje maksimalnog toplinskog toka kao prvi cilj te iznalaženje mjesta priključka dodatne struje za postizanje maksimalne entropije kao drugi cilj. Definirani su kriteriji koji određuju pri kojim uvjetima se lokalni maksimum toplinskog toka postiže za sve vrijednosti 3 značajke, pri kojim uvjetima se pojavljuje za neke vrijednosti te iste značajke te kada se maksimum ne pojavljuje. Razvijen je i algoritam za izračun generirane entropije te je istraženo pri kojim uvjetima se pojavljuje njezin maksimum. Rezultati istraživanja prikazani su u odgovarajućim dijagramima te su interpretirani, s posebnim osvrtom na slučajeve koji udovoljavaju kriteriju maksimalnog toplinskog toka za sve radne točke protusmjernog rekuperatora, odnosno za pojedine radne točke rekuperatora. Također su prikazani i interpretirani slučajevi kod kojih niti jedna radna točka rekuperatora neće udovoljiti postavljenoj hipotezi za realizaciju maksimalnog toplinskog toka. Dijagramski su prikazani te interpretirani rezultati bezdimenzijske generirane entropije te omjer bezdimenzijskog toplinskog toka i bezdimenzijske generirane entropije. U ovom radu provedeno je i eksperimentalno istraživanje s ciljem potvrde izvedenog matematičkog modela za ostvarenje maksimalnog toplinskog toka. Rezultati matematičkog modela uspoređeni su s eksperimentalnim rezultatima kojima su pridružene izračunate sastavljene standardne mjerne nesigurnosti. As one of the main process equipment, heat exchangers are the subject of intensive research focused on various areas of interest including optimal design, structure improvements, enhanced heat transfer techniques, dynamic response behavior, automatic control, network synthesis, numerical simulation, experimental methods, manufacturing, and development of new types of heat transfer surfaces. For the purpose of this thesis, a counterflow heat exchanger of a given total heat transfer area was selected, in which the required amount of heat load needs to be exchanged, having various mass flow rates and supply temperatures of the streams available from the heat exchanger network. Those inlet parameters are such that by connecting either only stream A or only stream B to the heat exchanger with a given surface it would not be possible to achieve the targeted heat flow rate. Thus, the question arises as to whether the targeted amount of exchanged heat flow rate can be achieved by the simultaneous action of both stream A and stream B on a given overall heat exchange area. This means that such simultaneous operation of both streams does not a priori allow greater exchanged heat flow rate than in the case where these streams act individually. This thesis aims to obtain the general criterion that needs to be met in order not only to achieve an increase in heat flow rate in such connected (networked) heat exchangers, but to maximize the exchanged heat flow rate. Fulfillment of this criterion means finding the optimal position on a heat exchanger for connection of the stream A, so that the maximum heat flow rate can be, along with the stream B, achieved in a single networked heat exchanger. In other words, within this mathematical model, the criterion of the existence of the maximum heat flow rate, as a local extreme, should be found, which is greater than the heat flow rate achieved only with stream A or stream B. Also, an algorithm for entropy generation in a heat exchanger network is developed. Entropy generation due to heat transfer between streams at finite temperature differences is considered in the model. Due to the complexity of the expression for the calculation of entropy generation, it was not possible to extract the analytical criteria for achieving the local maximum entropy, so it is necessary to determine the maximum of the function numerically, for each case separately. The research is based on the following hypotheses: maximum heat flow rate and maximum entropy generation is possible to achieve, as local extrema, if the criteria that can be written in explicit dimensionless form are fulfilled. The goal of this research is to obtain these criteria, which will contain the given overall surface of the heat flow rate, inlet temperatures of the weaker and stronger stream as well as the temperature of the weaker stream which is taken from the heat exchanger network. The first criterion must relate to maximum heat flow rate goal and the second to maximum entropy generation goal. A very important parameter M is formulated, representing the ratio between temperature difference of the weaker inlet connecting stream from heat exchanger network and inlet stronger stream and the temperature difference of the inlet weaker stream and inlet stronger stream of the observed (separated) counterflow heat exchanger. The results of the research are presented in related diagrams and interpreted, with special emphasis on cases fulfilling the maximum heat flow rate criterion for all operating points of the counterflow heat exchanger as well as for certain operating points of the counterflow heat exchanger. Cases where none of the operating points of heat exchanger will meet the hypothesis for achieving the maximum heat flow rate are also presented and interpreted. Finally, the results of dimensionless entropy generation and ratio between dimensionless heat flow rate and dimensionless entropy generation are presented in diagrams and interpreted. An experimental study was also conducted with the aim of confirming the derived mathematical model for developing the criterion for the maximum heat flow rate. The results of the mathematical model are compared with the experimental results with associated calculated composed standard uncertainties. The dissertation confirms the thesis regarding the existence or non-existence of operating parameters of a networked heat exchanger with the aim of achieving the desired maximum heat flow rate, maximum entropy or the desired maximum ratio between dimensionless heat flow rate and dimensionless entropy. For given available (specific) data on flows and stream temperatures as well as the overall exchange surface of the networked heat exchanger, using developed computer program it is possible to give a very quick and easy answer to given demands or criteria.

Kozmičkim zrakama naziva se sveukupni tok visokoenergetskih čestica koji dolazi iz svemira i dopire do Zemlje. Galaktičke kozmičke zrake (eng. Galactic Cosmic Rays, GCR) potječu izvan Sunčevog sustava i imaju najveće energije. Tok GCR-a moduliran je Sunčevom aktivnošću tako da pojačana Sunčeva aktivnost štiti Zemlju od GCR-a. Promatramo sporadične promjene toka GCR uzrokovane koroninim izbačajima (tzv. Forbusheva smanjenja) koje obično traju oko tjedan dana i imaju nagli nastanak i postupni oporavak. Najveća opažena Forbusheva smanjena, vezana uz koronine izbačaje s udarnim valom, odvijaju se u dva koraka. Prvi korak smanjenja posljedica je udarnog vala i trubulentnog magnetskog polja iza njega, a drugi korak nastaje zbog magnetske strukture koroninog izbačaja. Udarni val i turbulentno područje iza njega znatno se razlikuju po dimenzijama, ali i fizikalnim mehanizmima koji uzrokuju smanjenje toka čestica pa je važno razdvojiti njihov utjecaj i proučavati ih zasebno. Ovdje se detaljno razmatraju procesi koji se javljaju pri prolasku visoko-energetskih čestica kroz udarni val, te je predstavljen model temeljen na jednočestičnom pristupu koji je opravdan s obzirom na mali broj zastupljenih čestica. Udarni val modeliran je strukturom unutar koje se magnetsko polje linearno mijenja. Numerički izračunate putanje čestica pokazuju širok spektar ponašanja čestica ovisno o svojstvima udarnog vala (jakost magnetskog polja, kut između silnica magnetskog polja i normale udarnog vala te debljina udarnog vala) i karakteristika same čestice (energija čestice i upadni kut). Rezultati pokazuju da se čestice viših energija teže reflektiraju. S druge strane udarni valovi veće debljine i te oni s jačim magnetkim poljem lakše reflektiraju čestice. Osim udarnog vala, smanjenje toka GCR uzrokuje i sama magnetska struktura CME-a. U nastavku je proširen analitički difuzijsko-ekspanzijski model Forbushevog smanjenja, ForbMod, tako da u obzir uzima čestice energija u rasponu od 50 MeV do 100 GeV. Na temelju izmjerenih Forbushevih smanjenja i difuzijsko-ekspanzijskog modela određen je aksijalni magnetski tok u blizini Sunca za nekoliko događaja u periodu od travnja 2010. do svibnja 2014. godine. Galactic cosmic rays (GCR) consist of high-energy particles that originate far outside solar system and reach the Earth. Studies show that for every decrease in GCR intensity there is an increase in interplanetary magnetic field (IMF). Interplanetary magnetic field can be increased due to different phenomena in solar atmosphere, such as coronal mass ejections (CMEs) – phenomena driven by the energy released from magnetic field. Furthermore, for every increase in IMF there is a decrease in GCR intensity. Such a short-term depression in the GCR count is called Forbush decrease (FDs) and it is named after the American physicist Scott E. Forbush who discovered it in 1937. Forbush decreases can be observed by particle detectors several days after the CME. Forbush decreases caused by fast coronal mass ejections (CMEs) often show a two-step decrease where the first step is attributed to the shock/sheath region, while the second step is attributed to the closed magnetic structure. Since the difference in size of shock and sheath region is significant, and since there are observed effects that can be related to shocks and not necessarily to the sheath region we expect that the physical mechanisms governing the interaction with GCRs in these two regions are different. We therefore aim to analyse interaction of GCRs with heliospheric shocks only. First we study the role of two physical mechanisms that could directly affect the galactic cosmic ray (GCR) count rate in the shock-sheath region ahead of the CME. These are the magnetic mirror effect at the shock front and the magnetic field compression behind the shock. The effects of the mentioned two mechanisms for the shock-related phase of the FD are quantified by employing a simplified magnetic configuration that includes an oblique magnetohydrodynamical (MHD) fast-mode shock. Using the jump relations at the shock we determine the fraction of GCR particles that are mirrored at the shock, as well as the increase of the unit-area flux of the transmitted particles due to the compression of the magnetic field in the downstream region. A combination of these two effects results in a decrease of the GCR count rate. The calculated FD amplitudes attain values up to 45 %, which is much larger than are the observed amplitudes. This confirms that the magnetic mirror approximation is not a valid one which is already indicated by the fact that the shock thickness is much smaller than the gyro-radius of the GCR particle (proton). In the next step we approximate the shock by a structure where the magnetic field linearly changes with position within this structure. We assume protons of different energy, different pitch angle and different incoming direction and also vary the shock parameters such as the magnetic field strength and orientation, as well as the shock thickness. We solve the set of three differential equations to obtain proton trajectories for different initial speed components, i.e. different initial conditions. The results are in an agreement with observations and demonstrate that protons with higher energies are less likely to be reflected. Also, thicker shocks and shocks iv with stronger field reflect protons more efficiently. In the second part of this research we focus on the magnetic structure of the CME. We use the observationally obtained FD amplitude to determine the flux rope (FR) expansion parameters. We use the diffusion-expansion model, ForbMod (Dumbović et al., 2018). This model is based on the assumption that the FR is a long expanding cylinder and GCR particles enter the FR via perpendicular diffusion. In the original model it is assumed that all particles have the same energy, i.e. rigidity of 1 GV which corresponds to the most common energy in energy spectrum. Parameters of expansion can be analytically expressed according to Eq. (1) in Rodari et al. (2018). We compare the values obtained by this simple model with the values obtained numerically from the same model adjusted to include particles with energies ranging from 50 MeV to 100 GeV. In that case expansion parameters can not be expressed analytically and have to be calculated numerically. The values obtained both ways are then used to determine axial magnetic flux near the Sun. These values of magnetic flux are compared to the values obtained using Eq. (6) in Scolini et al., (2020). They use an independent method based on the connection between CME kinematics and magnetic reconnection during and immediately after the eruption. Results indicate that ForbMod model is not applicable for the events where the expansion speed is small or even negative. For these events, magnetic fluxes were several orders of magnitude larger than expected. The smallest discrepancies in results are found in the events where the power-law index of magnetic flux expansion are large.

Reduction of harmful impact on the environment caused by rapid development of a fossil fuel-powered society is one of the most significant global challenges. The combustion-related pollutants such as sulfur oxides and nitrogen oxides stand among the most harmful ones due to large amounts of emissions discharged globally. The advanced models that provide insight into pollutant production and removal processes can be useful in designing new, more sustainable technology. Numerical models presented in this work aim to improve the calculation accuracy and efficiency for complex physicochemical processes of nitrogen oxides formation during the combustion of pulverised fuels, as well as the calculation of sulfur dioxide removal from flue gases by seawater absorption in spray droplets and liquid wall film. The chemical processes of absorption in droplets were modelled for pure water by a simplified chemical model accounting for the reactions in the aqueous phase, and additionally for seawater, by introducing the influence of alkalinity that increases the absorption potential. The second part of absorption modelling is the mass transfer dynamics, and it was described by two film theory. It separates the influence of resistances for the interface’s liquid and gas side. For droplets falling in the stream of rising gases, determining the mass transfer can be an issue, and the penetration theory was selected as the most suitable among the implemented models for the dominant liquid side mass transfer coefficient. Furthermore, to account for all of the relevant processes, the absorption of sulfur dioxide in wetted walls was also modelled by adopting an analogous approach. The main difference is in the implementation of the mass transfer model, as the hydrodynamic processes influencing the liquid wall film are different. The used approach is based on dimensionless parameters and hydrodynamic characteristics of wall film. The developed and implemented models were validated against experimental data obtained in the literature for simplified geometries and industrial cases. The comparison showed that the model is capable of replicating experimental results for different geometries, range of sulfur dioxide concentrations and liquid-to-gas ratios. Additionally, the nitrogen oxides’ formation was modelled with the aim of accurately predicting their concentrations in pulverised solid fuel combustion systems. The Euler-Lagrangian approach was also used for describing the multiphase flow of fuel particles, and the combustion model was augmented by addition of a nitrogen oxides’ production model. Thermal and fuel production pathways were included, but the fuel nitrogen pathway was modified by the addition of partitioning factor that accounted for changing influences of different pathways. Then, the experimental analysis of bituminous coal was performed on a TG-MS system and by applying a derived method for quantifying the fuel nitrogen partitioning. Finally, the obtained experimental data was used in numerical simulations of a drop tube test, resulting in nitrogen oxides’ concentrations comparable with the ones reported in the literature. Zaustavljanje štetnog utjecaja na okoliš i uklanjanje posljedica nastalih zbog neodrživog rasta ljudske civilizacije jedan je od najvažnijih ciljeva današnjice. To je razlog zašto se nameću sve stroža ograničenja po pitanju emisija polutanata ispuštenih u okoliš, a za poštivanje tih ograničenja bit će potrebno razviti i konstruirati nova i efikasnija tehnološka rješenja, a stara zamijeniti održivijima. Korištenje naprednih alata za razvoj proizvoda bit će neizostavno za postizanje tih održivih ciljeva, a jedan od alata jest i računalna dinamika fluida. Plinovite emisije dušikovih i sumporovih oksida spadaju me đu najznačajnije polutante nastale izgaranjem fosilnih goriva zbog njihovog štetnog utjecaja na zdravlje ljudi, nastanak kiselih oborina i troposferskog smoga, ali i zbog – u apsolutnom mjerilu – značajnih količina ispuštenih u okoliš. Stoga su numerički modeli koji opisuju ponašanje tih onečišćujućih tvari važni za njihovo smanjenje i kontrolu. Dušikovi i sumporovi oksidi nastaju pri izgaranju fosilnog goriva zbog njegovog sastava ili parametara izgaranja, a pri njihovom nastanku, širenju ili uklanjanju odvijaju se kompleksni kemijski i fizikalni procesi. Jedan od često korištenih pristupa za smanjenje emisija sumporovog dioksida u dimnim plinovima je mokro odsumporavanje, gdje se struja onečišćenih plinova dovodi u kontakt s kapljevinom s apsorbirajućim kapacitetom. Scrubberi su takvi kontaktori u kojima se ostvaruje velika specifična površina izme đu faza, često ubrizgavanjem spreja apsorbirajuće kapljevine. I obična voda ima svojstvo apsorpcije sumporovog dioksida, ali lužnate otopine povećavaju kapacitet. Morska se voda, zbog blago lužnate pH vrijednosti i prirodnog alkaliteta, može koristiti kao apsorbirajuća kapljevina, što omogućava primjene u brodskim i priobalnim aplikacijama. Za opis ovog procesa bitno je točnim modelom obuhvatiti kemijske reakcije u vodenoj fazi, kao i fizikalni prijenos mase preko granice sustava. Kemijske reakcije mogu biti opisane sustavom jednadžbi za sve reaktivne vrste, čije rješenje daje vrijednosti ravnotežnih koncentracija. One zapravo pokazuju potencijal za apsorpcijom, a da bismo izračunali dinamiku uklanjanja sumporovog dioksida, potrebno je modelom opisati prijelaz mase izme đu faza. U okvir modela dvofaznog strujanja implementiran je model dvaju filmova, koji otpor prijelazu mase dijeli na utjecaj plinovite i kapljevite faze. Ispitani su i implementirani modeli za računanje koeficijenta prijelaza mase, a za kapljevitu stranu koja je dominantna korištena je penetracijska teorija. Predstavljeni model validiran je prvo za slučaj jedne kapljice, a zatim i prema eksperimentalnim podacima za pojednostavljenu geometriju scrubbera. Rezultati simulacija su pokazali veoma dobro slaganje s eksperimentom, kako za običnu, tako i za morsku vodu. Za slučaj industrijske geometrije s velikim omjerom toka kapljevine u odnosu na dimne plinove, rezultati simulacija se nisu poklapali s eksperimentalnim rezultatima iznad 90%, što je objašnjeno značajnijim utjecajem filma kapljevine na stijenci. Stoga je implementiran i ispitan model analogan prijašnjem, samo prilago đen računanju prijelaza mase u film kapljevine prema drugačijim hidrodinamičkim parametrima. Kad je model apsorpcije u film bio uključen, rezultati su bili u boljem slaganju s eksperimentalnim podacima za slučaj industrijskog scrubbera. S druge strane, smanjenje dušikovih oksida često se pokušava ostvariti modifikacijama sustava izgaranja, tako da se postignu uvjeti koji su nepovoljni za njihov nastanak. Zbog toga je detaljniji uvid u kemijske reakcije i puteve nastanka izuzetno koristan, jer omogućava smanjenje polutanata tijekom njihovog nastanka. U sustavima izgaranja praškastog goriva, čestice koje ulaze u komoru izgaranja prolaze kroz složene transformacije, ugrubo podijeljene na zagrijavanje, sušenje, devolatilizaciju, te zapaljenje hlapljivih kemijskih vrsta i preostale ča đe. Njihovo gibanje opisuje se Euler-Lagrangeovim pristupom za dvofazno strujanje, a izgaranje čestica opisano je izmjenom mase i kinetikom kemijskih reakcija. Na taj numerički okvir za modeliranje izgaranja nadograđen je numerički model nastajanja dušikovih oksida. Kemijske reakcije i mehanizmi nastanka dušikovih oksida kompleksni su i ne u potpunosti razjašnjeni procesi, a pokušaji predviđanja koncentracija polutanata na temelju sastava goriva ne daju zadovoljavajuće rezultate. Njihovo formiranje izrazito ovisi o uvjetima izgaranja kao što su temperatura, sastav plinovite faze i goriva, veličina čestica te pretičak zraka. Nastanak dušikovih oksida uglavnom se dijeli na tri mehanizma: termalni, promptni te NO iz goriva. Termalni NO nastaje pri visokim temperaturama uslijed disocijacije molekularnog dušika iz zraka te je značajan pri visokim temperaturama. Produkcija i destrukcija dušikovih oksida iz goriva još uvijek nije u potpunosti shvaćen fenomen, unatoč većem broju provedenih istraživanja, a u sustavima izgaranja praškastog goriva ima dominantni utjecaj. Postojeći model nastanka NO iz goriva unaprije đen je upotrebom faktora raspodjele dušika iz goriva prema načinu doprinosa sveukupnom NO. Tako imamo doprinos preko hlapljivih komponenata goriva ili preko oksidacije koksnog ostatka u heterogenim reakcijama na površini čestica. Također, dušik iz goriva dijeli se i prema posrednoj kemijskoj vrsti koja na kraju sudjeluje u nastanku NO, tako da su dvije najznačajnije posredne kemijske vrste HCN i NH3, a njihov omjer ovisi o parametrima poput temperature, vrste goriva i vrste komore izgaranja. Kako bi rezultati simulacija bili što točniji, napravljena su eksperimentalna istraživanja na ugljenu koja su pokazala da je omjer HCN i NH3 pri pirolizi u TG-MS sustavu otprilike jednak, ali da je utjecaj oksidacije koksnog ostatka značajno jači od utjecaja hlapljivih tvari za HCN. Za potrebe pribavljanja ovih rezultata, modificirana je i upotrijebljena metoda kvantificiranja kvalitativnih podataka iz signala masene spektroskopije. Ovi rezultati su spojeni s modificiranim modelom nastanka dušikovih oksida iz goriva te uspoređeni s eksperimentalnim istraživanjima, što je pokazalo da je korištenjem faktora raspodjele dušika iz goriva model unaprije đen te da sa zadovoljavajućom točnošću reproducira koncentracije NO u dimnim plinovima koji izlaze iz komore izgaranja. HIPOTEZE I CILJEVI Hipoteza ovog rada je da će novi i unaprijeđeni matematički modeli omogućiti detaljan i numerički učinkovit izračun kompleksnih fizikalno-kemijskih procesa nastanka dušikovih oksida pri procesu izgaranja krutog goriva te uklanjanja sumporovog dioksida iz dimnih plinova apsorpcijom u kapljicama i filmu morske vode na stijenci. Ciljevi istraživanja su unapre đenje i implementacija novih modela za nastanak dušikovih oksida pri procesu izgaranja krutog praškastog goriva te razvoj matematičkog modela apsorpcije sumporovih oksida u vodene kapljice i film kapljevine na stijenci, s krajnjim ciljem dobivanja sveobuhvatnog alata za istraživanje uklanjanja polutanata u realnim sustavima izgaranja. METODE I PREGLED DISERTACIJE Ovaj rad numerički opisuje fizikalne i kemijske procese vezane za nastanak dušikovih oksida pri izgaranju praškastog goriva, kao i modele uklanjanja sumporovih oksida iz dimnih plinova sustava za izgaranje apsorpcijom u kapljice spreja ili film kapljevine na stijenci. Matematičkom nadogradnjom postojećeg numeričkog okvira temeljenog na zakonima održanja fizikalnih veli čina postignuto je unapre đenje modela za opisivanje relevantnih procesa. Kapljice i čestice goriva su kao diskretna faza opisane korištenjem Lagrangeove formulacije, a plinovita se faza rješava Eulerovom formulacijom unutar komercijalnog programskog paketa za računalnu dinamiku fluida AVL FIRETM, baziranom na metodi kontrolnih volumena. Razvijeni matematički modeli implementirani su u programskom jeziku FORTRAN upotrebom korisničkih funkcija povezanih s glavnim rješavačem. Poveznica s ostalim transportnim jednadžbama, modelom izgaranja i spreja ostvarena je modifikacijom izvora i ponora fizikalnih veličina. Eksperimentalno istraživanje provedeno je s ciljem određivanja raspodjele dušika iz goriva na mehanizme nastajanja posrednih kemijskih vrsta i posljedično dušikovih oksida. Primijenjena je nova metoda kvantifikacije uzoraka prema kvalitativnim rezultatima simultane termogravimetrijske analize i masene spektrometrije, a navedeni modeli omogućuju detaljniji uvid u mehanizme nastanka dušikovih oksida i unapređenje numeričkih izračuna sustava za izgaranje. Konačni cilj rada bio je dobivanje sveobuhvatnih numeričkih modela koji sa zadovoljavajućom točnošću reproduciraju eksperimentalne podatke. U poglavlju 1 dan je pregled literature i motivacija za izradu rada, kao i uvid u recentna znanstvena istraživanja vezana za modeliranje onečišćujućih tvari. U poglavlju 2 izloženi su matematički modeli računalne dinamike fluida primijenjeni u ovom istraživanju, dajući tako kratak opis numeričkog okvira korištenog za implementaciju modela. Posebno su obra đeni Euler-Lagrangeov pristup te metoda diskretnih kapljica koje služe za opisivanje dvofaznog toka. Tako đer, obrazložena je prikladnost korištenja pristupa koncentriranih parametara za modeliranje spreja, kao i osnovne jednadžbe za modeliranje ponašanja kapljica. Poglavlje 3 usredotočeno je na razvoj modela apsorpcije sumporovog dioksida u običnoj i morskoj vodi, te izlaže temelje modeliranja kemijskih procesa u vodenim otopinama pod ravnotežnim uvjetima. Prikazani su sustavi kemijskih jednadžbi među kemijskim vrstama koje sadrže sumpor, kao i posebnosti pri modeliranju kemijskih reakcija u morskoj vodi. Nakon toga, fokus je prebačen na problematiku modeliranja prijenosa mase preko granice izme đu plinovite i kapljevite faze. Glavni fizikalni procesi koji utječu na prijenos mase su recirkulacija u kapljicama, turbulentno strujanje, oscilacije kapljica i rastezanje površine, što zajedno čini kompleksan skup faktora. Izloženi su pojednostavljeni modeli te su rezultati dobiveni njima uspore đeni na razini jedne kapljice. Kasnije su odabrani modeli za kapljevitu i plinovitu stranu primijenjeni na cijeli sprej te su validirani na pojednostavljenim i kompletnim trodimenzionalnim slučajevima s realnim graničnim uvjetima. U poglavlju 4 izložen je rad vezan za modeliranje nastanka polutanata pri izgaranju krutog goriva. Prikazan je pregled prijašnjih istraživanja i korištenih modela, kao i pregled uobičajenih pristupa modeliranju procesa nastanka dušikovih spojeva. Ovo poglavlje detaljno analizira mehanizam nastanka NO iz dušika sadržanog u gorivu te prikazuje kemijske reakcije i posredne vrste u kemijskom mehanizmu. Kako bi se zaobišla izrazita ovisnost mehanizma nastanka dušikovih oksida o vrsti izgaranja, temperaturi, vrsti ugljena i ostalim parametrima, napravljena je eksperimentalna analiza ugljena gdje su pribavljeni podaci o raspodjeli dušika sadržanog u gorivu na posredne kemijske vrste HCN i NH3, kao i na volatile i oksidaciju krutog ostatka. Primijenjena je nova metoda za kvantifikaciju raspodjele iz kvalitativnih rezultata pribavljenih vezanim sustavom simultane termogravimetrijske analize i masene spektrometrije (TG-MS). Konačno, ti eksperimentalni rezultati spojeni su s numeričkim modelom i iskorišteni pri provođenju numeričkih simulacija, a rezultati modela su validirani s eksperimentalnim rezultatima za koncentracije NO. U poglavlju 5 prikazan je zaključak na temelju dobivenih rezultata provedenog istraživanja, kao i smjernice te preporuke za daljnji rad. ZNANSTVENI DOPRINOS I ZAKLJUČAK Znanstveni doprinos rada vidljiv je u unapre đenju alata za modeliranje uklanjanja i nastajanja onečišćujućih tvari pri izgaranju goriva. Glavni dio istraživačkog rada fokusiran je na razvoj i unapređenje numeričkog modela odsumporavanja dimnih plinova i njegovu implementaciju u okvir računalne dinamike fluida, što će omogućiti lakši razvoj tehnoloških rješenja za uklanjanje sumporovog dioksida u brodskim i priobalnim primjenama. Drugi je dio rada usredotočen na modeliranje nastanka dušikovih oksida prilikom izgaranja praškastog goriva, gdje je mehanizam za opisivanje njihovog nastajanja unaprijeđen i modificiran ponderiranim faktorima prema eksperimentalnoj analizi goriva simultanom termogravimetrijskom analizom i masenom spektrometrijom. Pritom razvijeni model omogućuje detaljnije opisivanje nastanka dušikovih oksida i unapređenje sustava za izgaranje Znanstveni doprinosi istraživanja su sljedeći: - Razvoj i implementacija sveobuhvatnog modela apsorpcije sumporovog dioksida iz dimnih plinova u kapljice spreja i film kapljevine na stijenci za običnu i morsku vodu, upotrebljiv za unaprjeđenje procesa odsumporavanja u industrijskim primjenama. - Numerički model nastanaka dušikovog monoksida pri izgaranju praškastog goriva prilagođen korištenjem ponderiranih faktora utjecaja posrednih kemijskih vrsta u mehanizmu nastanka polutanata, dobivenih primjenom nove metode kvantifikacije rezultata simultane termogravimetrijske analize i masene spektrometrije.

Magnetska pobuđenja predstavljaju fundamentalnu vrstu prijelaza u atomskim jezgrama bitnu i u modeliranju astrofizičkih procesa. U ovom radu istraženi su magnetski dipolni (M1) i kvadrupolni (M2) prijelazi u okviru relativističkog nuklearnog energijskog funkcionala gustoće (RNEDF) sa kontaktnim međudjelovanjem nukleona. Za opis M1 i M2 pobuđenja, uspostavljena je relativistička kvazičestična aproksimacija slučajnih faza (RQRPA) s uključenom izovektor-pseudovektor interakcijom i korelacijama sparivanja. Nakon provjere analitičkog pravila sume za M1 prijelaze, analizirana su M1 pobuđenja u jezgrama 48^Ca i 208^Pb. Istražena je evolucija snage M1 prijelaza duž izotopnih lanaca 36−64^Ca, 100−140^Sn i izotona Z=10-24, N=20, koja varira ovisno o M1 aktivnim nukleonima i spin-orbit cijepanju relevantnih stanja. Nedavno izmjerene snage M1 prijelaza izotopa 112−124^Sn kvalitativno se slažu sa teorijskim proračunom. Reproducirana je funkcija odziva eksperimentalnog spektra s dva vrha, a rezultati upućuju na potrebu manjeg gušenja žiromagnetskih faktora nukleona u jezgri u odnosu na prethodne teorijske rezultate. Razmatrana je uloga korelacija sparivanja u M1 prijelazima i pokazano je da su nužne za opis dva dominantna vrha iz eksperimentalnog spektra 50^Ti. Raspodjela prijelazne snage kvadrupolnih (M2) prijelaza pokazuje znatno fragmentiraniji spektar u odnosu na M1, dok analiza parcijalnih snaga prijelaza omogućava uvid u kolektivnost M2 pobuđenja. Electromagnetic excitations in finite nuclei represent one of the most important probes of relevance in nuclear structure and dynamics, as well as in nuclear astrophysics. In particular, various aspects of magnetic dipole (M1) mode have been considered both in experimental and theoretical studies [1–8] due to its relevance for diverse nuclear properties associated e.g., to unnatural-parity states, spin-orbit splittings and tensor force effects. Specifically, M1 spin-flip excitations are analog of Gamow-Teller (GT) transitions, meaning that, at the operator level, the dominant M1 isovector component is the synonym to the zeroth component of GT transitions, and can serve as probe for calculations of inelastic neutrino-nucleus cross section [9, 10]. This process is hard to measure but it is essential in supernova physics, as well as in the r-process nucleosynthesis calculations [7, 8, 11, 12]. The isovector spin-flip M1 response is also relevant for applications related to the design of nuclear reactors [13], for the understanding of single-particle properties, spinorbit interaction, and shell closures from stable nuclei toward limits of stability [14–18], as well as for the resolving the problem of quenching of the spin-isopin response in nuclei that is necessary for reliable description of double beta decay matrix elements [19]. In deformed nuclei, another type of M1 excitations has been extensively studied, known as scissors mode, where the orbital part of M1 operator plays a dominant role in a way that protons and neutrons oscillate with opposite phase around the core [3, 20–28]. In any nuclei undergoing experimental investigation, there are simultaneously present Eλ and Mλ multipole excitations, where the electric dipole (E1) and electric quadrupole (E2) responses [29–34] dominate over M1 response [35–43]. Thus, it is a rather challenging task to measure M1-related observables in a whole energy range. Even for the nuclides accessible by experiments, their full information on the M1 response has not been complete. The M1 transitions have been studied in various theoretical approaches. Various aspects of the M1 mode have been investigated in the shell model [9, 12, 14, 15, 22, 44, 45], including, e.g., scissors and unique-parity modes [22], tensor-force effect [14], low-energy enhancement of radiation [44], and the analogy with neutrino-nucleus scattering [9, 12]. The M1 energy-weighted sum rule has been discussed from a perspective of the spin-orbit energy [46]. The Landau-Migdal interaction has been one of the relevant topics in studies of M1 excitations [47, 48]. In order to reproduce a large fragmentation of the experimental M1 strength, the importance of including complex couplings going beyond the RPA level has also been addressed [26, 47–50]. Recently, the M1 excitation has been investigated in the framework based on the Skryme functionals [16–18], also extended to include tensor effects [51]. It has been shown that the results for the spin-flip resonance obtained by using different parameterizations do not appear as convincing interpretation of the experimental results. Additional effects have been explored in order to resolve this issue, e.g., the isovector-M1 response versus isospin-mixed responses, and the role of tensor and vector spin-orbit interactions [16, 17]. In recent analysis in Ref. [52], based on the Skyrme functionals, it has been shown that while modern Skyrme parameterizations successfully reproduce electric excitations, there are difficulties to describe magnetic transitions. In addition, some Skyrme sets result in the ambiguity that, by the same parameterization, the model cannot simultaneously describe one-peak and two-peak data for closed and open shell nuclei [16]. Thus, further developments of the Skyrme functional in the spin channel are called for [52]. Simultaneously, it is essential to explore the M1 response from different theoretical approaches to achieve a complete understanding of their properties, as well as to assess the respective systematic uncertainties. In this work we have introduced a novel approach to describe M1, 0+ ground state to 1+ excited state, transitions in even-even nuclei, based on the RHB + RQRPA framework with the relativistic point-coupling interaction, supplemented with the pairing correlations described by the pairing part of the Gogny force. In addition to the standard terms of the point coupling model with the DD-PC1 parameterization, the residual R(Q)RPA interaction has been extended by the isovector-pseudovector (IV-PV) contact type of interaction that contributes to unnatural parity transitions. This pseudovector type of interaction has been modeled as a scalar product of two pseudovectors. The strength parameter for this channel, αIV-PV, is considered as a parameter, which is constrained by the experimental data on M1 transitions of selected nuclei. We note that the IV-PV term does not contribute in the RHB calculation of the ground state, thus its strength parameter cannot be constrained together with other model parameters on the bulk properties of nuclear ground state. The pseudovector type of interaction would lead to the parity-violating mean-field at the Hartree level for the description of the 0+ nuclear ground state, and it contributes only to the RQRPA equations for unnatural parity transitions, i.e. 1+ excitation of M1 type. The coupling strength parameter αIV-PV is determined by minimizing the standard deviation σΔ (αIV-PV), where Δ is the gap between the theoretically calculated centroid energy and experimentally determined dominant peak position of measured M1 transition strength in 208Pb [38] and 48Ca [37] nuclei. It turns out that the optimal parameter value is αIV-PV = 0.53 MeVfm3 and in this case the energy gap Δ is less than 1 MeV both for 208Pb and 48Ca. In this way all the parameters employed in the present analysis are constrained and further employed in the analysis of the properties of M1 excitations. A recently developed non-pairing M1 sum rule in core-plus-two-nucleon systems [29] has been used as a consistency check of the present theory framework. In Ref. [29], the non-energy weighted sum (mk=0) of the M1 excitation was evaluated for some specific systems, which consist of the core with shell-closure and additional two valence neutrons or protons, e.g., 18O and 42Ca. If the pairing correlations between the valence nucleons are neglected, one advantage of that sum rule is that its non-energy weighted sum-rule value (SRV) is determined analytically for the corresponding system of interest. The sum of the M1-transition strength for 18O and 42Ca accurately reproduced the sum rule value (SRV), thus validating the introduced formalism and its numerical implementation for further exploration of M1 transitions. The present framework is firstly benchmarked on M1 transitions for two magic nuclei, 48Ca and 208Pb. The response functions RM1(E) have been explored in details, including their isoscalar and isovector components, that relate to the electromagnetic probe, as well as contributions of the spin and orbital components of the M1 transition operator. It is confirmed that, in nuclei without deformation, the spin component of the M1 transition strength dominates over the orbital one. Due to the differences in the gyromagnetic ratios, the isovector M1 transition strength is significantly larger than the isoscalar one, and they interfere destructively. It is shown that the major peaks of isovector spin-M1 transitions are dominated mainly by a single ph configuration composed of spin-orbit partner states. One of our interests was to investigate the role of the pairing correlations on the properties of M1 response functions in open shell nuclei, that has been addressed in the study of 42Ca and 50Ti. The RQRPA calculations show a significant impact of pairing correlations on the major peak by shifting it to the higher energies, and at the same time, by reducing the transition strength. In the 50Ti case, this effect is essential to reproduce the two-peak structure measured in the experiment [53]. The main effect of the pairing correlations is observed at the level of the ground state calculation, while it is rather small in the particle-particle channel of the residual RQRPA interaction. The M1 transition strengths from the present study appear larger than the values obtained from the experimental data. Therefore, it remains open question whether some additional effects should be included at the theory side, or some strength may be missing in the experimental data. In addition, the M1-excitation energies of light systems, e.g. 48Ca still have some deviation from the reference data. Recently, an experimental study based on the inelastic proton scattering provided novel data on E1 and M1 strength distributions along the even-even 112−124Sn isotope chain [54]. The resulting photoabsorption cross sections derived from the E1 and M1 strength distributions showed significant differences when compared to those from previous (γ, xn) experiments [55, 56]. This new experimental research enables us to explore the properties on M1 excitations in a broad range of even-even Sn nuclides, and examine the model calculations in a view of the mentioned experimental data from Ref. [54]. The quenching factors can be obtained by normalizing the calculations on M1 transitions to the experimental data. Accordingly, the free value of the g-factor (gfree) is often considerably quenched, leading to its effective value that was previously reported mainly as geff/gfree ≈ 0.6-0.75 [16, 17, 55, 57–59]. Therefore, in view of the quenching of the g-factors in finite nuclei it is interesting to explore how the novel inelastic proton scattering data [54] compare to the results on M1 transitions in the framework of the relativistic energy density functional. As previously discussed, one of the most important mechanisms responsible for the quenching is mixing with higher order configurations [48, 57, 59–62]. Additional effects have been suggested to arise from the core excitation [63], and the meson-exchange current effect [64, 65]. However, in our recent work [66] is shown that the M1 transition strength distribution is characterized by an interplay between single and double-peak structures, which can be understood from the evolution of single-particle states, their occupations governed by the pairing correlations, and two-quasiparticle transitions involved. Comparison with available experimental data shows that independent neutron and proton spin-flip spectra are correctly identified, single and double-peaked distribution of response function RM1(E) is reasonably well reproduced. The calculated peak positions Eth. peak show 1-2 MeV discrepancy, that could be further fine-tuned through additional adjustments of the strength parameter in the isovector-pseudovector channel, αIV-PV. In addition, it is shown that strength is considerably reduced than previously known, the quenching of the g-factors for the free nucleons needed to reproduce the experimental data on M1 transition strength amounts geff/gfree=0.80-0.93. Since some of the B(M1) strength above the neutron threshold may be missing in the inelastic proton scattering measurement, further experimental studies are required to confirm if only small modifications of the bare g-factors are actually needed when applied in finite nuclei. These data could allow us to establish an essential link between the M1 observables and theoretical models and improve our understanding of the role of M1 transitions in modeling radiative neutron capture cross sections of relevance for nucleosynthesis. A major interest in magnetic transitions is strongly focused on dipole (M1) excitations which was subject of our interest as well in our earlier work [66] and references therein. However, higher multipole, particulary 0+ ground state to 2− excited state transitions known as giant-quadrupole resonances (GQR), denoted as M2, are almost uncharted area of both theoretical and experimental research. Several available experimental references [67– 78] have elaborated highly fragmented M2 structure whose strength ∑/E BM2(E) is strongly suppressed compared to the few theoretical results [68, 73, 79–86] provided either in shell model or random-phase approximation (RPA) framework [87]. M2 quenching/suppression has been considered as a very important component in heavy stars modeling at later stage and before supernova collapse [88, 89] and nucleosynthesis processes [90]. Theoretical models which investigate nuclear dynamics with their basis in fluid-dynamics [91–94] predic activation of so called "twist mode" also experimentaly explored in Ref. [95] where 2− excitation in spherical nuclei is attributed to the orbital transitions caused by an effective rotation operator arround z axsis, rotation angle ”zα” is proportional to the z axis itself. In such picture one can imagine nucleon orbitals as different fluid layers which rotate in oposite dirrections, namely for z > 0 layers rotate counterclockwise while for z < 0 layers rotate clockwise. Consistency check and comparison between different theoretical models can be done by usage, as analytical tool, several sum-rule approaches developed in Refs. [96–100]. Apart of M2, higher multipoles λ > 2 [101] like M8 [102] or even higher spin states like M12 and M14 in Refs. [103, 104] have been part of experimental investigation. Exploration of M2 excitations showed consistent results when compared with earlier RPA and shell-model theoretical research, in particular for 16O, 48Ca, and 208Pb systems where strength values ∑/E BM2(E) are higher compared with the recent measurements. However, systematic partial strength analysis of complicated M2 fragmentation structure, in particular for 16O and 208Pb, showed very good agreement with the data. Pairing effects, modelled by the Gogny interaction with finite range, have shown tremendeous impact on spectra for open-shell nuclei by reducing the strength and shifting the centroid energy to higher values. This evidence convinced us that the model introduced in this work can be used for further thorough studies of M2 and higher multipole excitations. However, very fragmented structure of M2 transitions can not be explained without introducting a more sophisticated and technically demanding 2p2h excitations. In order to resolve still open questions, further theoretical and experimental developments, are needed, e.g., resolving the quenching effects in g factors, meson exchange effects, couplings with complex configurations, etc. Due to its relation to the spin-orbit interaction, M1 excitations could also provide a guidance toward more advanced RNEDFs. Recently, a new relativistic energy density functional has been constrained not only by the ground state properties of nuclei, but also by using the E1 excitation properties (i.e. dipole polarizability) and giant monopole resonance energy in 208Pb [105]. Similarly, M1 excitation properties in selected nuclei could also be exploited in the future studies to improve the RNEDFs. While in the previous studies the calculated ∑/E BM1(E) transition strengths considerably overestimated the experimental values, comparison of the RQRPA results for the total ∑/E BM1(E) strength with the new data on 112−124Sn isotopes from inelastic proton scattering [54] shows that differences are smaller than previously understood. Our analysis showed that discrepancy between model calculations and experiment are considerably reduced, i.e., the quenching of the g-factors for the free nucleons needed to reproduce the experimental data amount geff/gfree=0.80-0.93. Considering the fact that some of the ∑/E BM1(E) strength above the neutron threshold may be missing in the proton scattering experiment due to the reported limitations in accuracy [54], our analysis provides an indication that future experimental studies could confirm that actually very small modifications of the gfree factor are needed when applied in the nuclear medium in finite nuclei. Therefore, it is expected that this work can serve as guidance and motivation for the experimental community to systematically explore M1 resonant excitations, and in particular to reduce the uncertainties above the neutron threshold. Finally, complete understanding of M1 transitions within the framework used in this study, will also allow systematic large-scale calculations for the radiative neutron capture cross sections of relevance for the nucleosynthesis.

Procjena dodatnog otpora broda na valovima od velike je važnosti s ekološkog i ekonomskog aspekta. Dodatni otpor uzrokuje pad brzine plovidbe te utječe na povećanje zahtijevane snage i potrošnje goriva broda, a samim time i emisije štetnih plinova. Međunarodna pomorska organizacija (engl. International Maritime Organization, IMO), uvodi sve strože propise za smanjenje i kontrolu emisije štetnih plinova u pomorskoj industriji. Tako novi brodovi moraju zadovoljiti tehničke mjere, a postojeći brodovi operativne mjere s ciljem povećanja energetske učinkovitosti brodova i smanjenja emisije CO2. Iz tog je razloga već u preliminarnoj fazi osnivanja broda vrlo važno procijeniti povećanje otpora uslijed plovidbe broda na valovima za stanja mora na kojima će brod tijekom službe ploviti. Dodatni otpor na valovima vremenski je osrednjena vrijednost sile drugog reda, koja nastaje uslijed interakcije nailaznih valova i valova generiranih odzivom broda. S obzirom na zanemarive učinke viskoznosti, dodatni otpor moguće je razmatrati kao neviskoznu pojavu što omogućuje primjenu metoda i rješavača temeljenih na teoriji potencijalnog strujanja idealnog fluida, ali i ekstrapolaciju rezultata s modela na brod bez utjecaja mjerila. Obzirom da pouzdano određivanje dodatnog otpora na valovima zahtijeva provođenje složenih hidrodinamičkih proračuna, u okviru doktorskog rada razvijen je numerički model, koji se temelji na rezultatima hidrodinamičkih proračuna i umjetnoj neuronskoj mreži. Jedna od prednosti umjetne neuronske mreže je mogućnost aproksimacije rješenja složenih nelinearnih i viševarijabilnih problema bez poznavanja fizikalnog modela. Kako bi osnovani numerički model osigurao rezultate zadovoljavajuće točnosti, proveden je proces učenja umjetne neuronske mreže na temelju rezultata hidrodinamičkih proračuna kontejnerskih brodova različitih formi i značajki te za različita stanja mora. Dodatni otpor broda na pravilnim valovima određen je metodom rubnih integralnih jednadžbi (engl. Boundary Integral Equation Method, BIEM), a primjenom spektralne analize energije nepravilnih morskih valova određene su srednje vrijednosti dodatnog otpora za različita stanja mora definirana sa značajnom valnom visinom i periodom vala. Također, proveden je postupak validacije i verifikacije dobivenih numeričkih rezultata. U radu je provedena analiza osjetljivosti dodatnog otpora na pravilnim i nepravilnim valovima na različite značajke broda, s ciljem definiranja varijabli ulaznog vektora umjetne neuronske mreže. Analizirane su različite strukture unaprijedne statičke umjetne neuronske mreže s povratnim prostiranjem pogreške i jednim skrivenim slojem, parametri te različiti algoritmi učenja mreže. Istražen je i utjecaj načina pripreme podataka za proces učenja mreže na dobivene rezultate te prednosti primjene analize glavnih komponenata kao i klasifikacije podataka za učenje. Osnovani numerički model od posebne je praktične koristi u preliminarnoj fazi projektiranja kontejnerskog broda, kako bi se u kratkom roku i s točnošću procijenio dodatni otpor broda na valovima ovisno o planiranoj ruti plovidbe za koju se brod projektira. Za postojeće kontejnerske brodove, osnovani numerički model moguće je koristiti za procjenu dodatnog otpora pri različitim brzinama plovidbe i za različita stanja mora te tako doprinijeti planiranju rute plovidbe, posebice za izraženija stanja mora, uz ograničenje valova direktno u pramac. Evaluation of the ship added resistance in waves has increased in importance, especially from an economic as well as from an environmental protection point of view. Ship added resistance in waves causes a reduction in ship speed and has an impact on the increase in the fuel consumption and CO2 emission. The International Maritime Organization, IMO subjected the emission of harmful gases to increasingly stringent regulations, via the introduction of mandatory technical measures for new ships and operational measures for existing ships, with the aim of increasing the energy efficiency of ships and reducing CO2 emissions. For that reason, it is very important to predict the increase in ship resistance due to waves and power required for the ship sailing at an actual sea state, already in the ship design phase and when planning the sailing route of existing ships. Added resistance in waves is a time-averaged second order force consisted of three parts. When sailing in waves, ship generates two systems of waves: waves due to sailing in calm water and waves caused by the ship response to incoming waves. The first and largest part of added resistance arises due to the interference of waves generated by the ship, i.e. radiation waves mainly due to heave and pitch motions, and incoming waves. It is often called the drift force, although the drift force in the longitudinal direction of a ship is equal to the added resistance in waves only in the case of zero speed. The ship relative motions become large when the length of the ship is approximately equal to the wavelength, which corresponds to peak value of added resistance. At very long waves, when relative motions are negligible, the wave force corresponds to Froude-Krylov force that would ideally act on the ship hull in the absence of a diffraction component. On the other hand, in short waves the diffraction of incoming waves on the ship hull increases the second part of added resistance, i.e. the diffraction force with emphasized nonlinear effects. The third component is related to the viscous damping of the heave and pitch motions of the ship and is negligible in relation to the hydrodynamic damping of the motions (radiation waves). Therefore, added resistance is considered as a non-viscous phenomenon, which allows the application of methods and solvers based on the potential flow theory, but also an extrapolation of the results from model scale to ship scale without the scale effects. Analytical methods, methods based on the potential flow theory and the ones based on viscous flow theory are used for the evaluation of the ship added resistance in waves. Since the determination of the ship seakeeping characteristics and added resistance in waves requires rather complex hydrodynamic calculations to ensure an acceptable accuracy of the results, within this research a model that allows simple but sufficiently accurate and reliable evaluation of the ship added resistance sailing at an actual sea state is developed. Such model can have a practical benefit both during the ship design phase or while planning a favourable sailing route of a ship in service. The basis of the developed model is the results of hydrodynamic calculations of added resistance in waves for various hull forms at different sea states and artificial neural network, which has the ability to learn from examples and to discover relationships between the input data and solutions to the nonlinear multivariable regression problems. Hull forms of modern container ships with different types of bow and stern, section type and block coefficient (prismatic coefficient) are generated in order to create a sufficiently large database for the training process. The original hull forms with different main characteristics are modified in order to extend the range of prismatic coefficients and to obtain different longitudinal positions of the center of buoyancy. The influence of the ship mass characteristics, i.e. the vertical position of the center of gravity and the pitch radius of inertia, on the added resistance in regular regular waves is investigated, while the ship design speed is determined based on the regression analysis results. The results of the regression analysis also defined the variation range of the prismatic coefficient, in respect to the limitations of the method used for the hull form modification. Hydrodynamic calculations are conducted using the Boundary Integral Equations Method, BIEM based on the potential flow theory. Generated hull forms are discretized by flat panels and hydrodynamic calculations of added resistance in regular waves are performed. The numerical results obtained using panel method are compared to the ones obtained using finite volume method, FVM based on the viscous flow theory for benchmark containership KCS. In the defined incoming wave frequency range, the sensitivity analysis is carried out in order to define the neural network input parameters. The most important parameters affecting the added resistance in waves are the ship geometry, response in waves and the characteristics of the incoming waves. Since the ship response to incoming waves is highly dependent on the hull geometry, and transfer functions are often unknown in the preliminary design phase, it is practical to define ship main characteristics as the input parameters of the neural network. The obtained numerical results are validated against the available experimental data and verified, i.e. the numerical uncertainty is assessed. Top container ship sailing routes are analyzed and sea states with the highest probability of occurrence for waves coming from all directions and head waves for a given route are extracted based on the global wave atlas (Global Wave Statistics). For the numerically obtained results of added resistance in regular waves, spectral analysis is performed using two-parameter theoretical wave energy spectra: Bretschneider spectrum for unlimited and JONSWAP spectrum for limited fetch. In this way, the results of added resistance in irregular waves, i.e. at different sea states that ship may encounter during lifetime, are obtained. Feedforward artificial neural network with error back propagation and one hidden layer of neurons is generated as the basis of the numerical model for the estimation of ship added resistance in waves. A possible significant advantage of neural networks is that they do not require a known physical model of the before mentioned complex hydrodynamic problem. Based on the analysis of different neural network architectures, i.e. by varying the number of neurons in the hidden layer, learning rate and momentum parameters, as well as by performing an analysis of the results obtained using different learning algorithms, an adequate artificial neural network is set. The training process is performed using the results of hydrodynamic calculations, which are adequately prepared and divided into data sets for learning, validation and testing. The evaluation of the accuracy and generalization property of the neural network is evaluated based on the normalized value of the root mean square error. A multivariable linear regression analysis is also performed as well as principal component analysis in order to represent the input variables of the neural network with linearly independent variables. The generalization properties of the neural network employed for the evaluation of added resistance in waves is also analyzed for different wave headings, which increases the complexity and nonlinearity of the given problem. The developed numerical model has 12 input variables, 65 neurons in one hidden layer and is based on Levenberg-Marquard learning algorithm with Bayesian regularization. The model incorporates three sub models based on the classification of data according to the wave zero crossing period.

Rad i energija su među ključnim konceptima u fizici i predstavljaju izazov u nastavi fizike u osnovnoj i srednjoj školi. Suvremeni pristup učenju fizike baziran je na učenicima zanimljivim pokusima i aktivnostima iz svakodnevnog života. U ovom radu izabran je konkretan primjer, olimpijski sportovi koji su izvrsna podloga za proučavanje koncepata rada i energije. Sport općenito je učenicima zanimljiv, a okvir u kojem se uči kako primjenom fizikalnih znanja poboljšati sportske rezultate predstavlja dodanu motivaciju u učenju fizike. U ovom radu kroz primjere iz konkretnih olimpijskih sportova i fizikalne pokuse dani su okviri kako ovaj pristup implementirati u okviru postojećih kurikuluma nastave fizike. Work and energy are among the key concepts in physics and present a challenge in physics education in primary and secondary schools. Modern approach to learning physics is based on interesting experiments and everyday activities which are interesting to students. In this work, specific example was chosen, Olympic sports which are a excellent base for studying concepts of work and energy. Sports in general are interesting to students, and the framework in which they study how to enhance sports results by applying physics knowledge presents additional motivation in physics learning. In this work, through examples from specific Olympic sports and physics experiments, frameworks are given on how to implement this approach within the given physics curricula.

U ovoj disertaciji istraživani su tanki filmovi ZnO, TiO2 te kompozita ZnO@TiO2. Cilj je bio pripraviti nanostrukturirane materijale pogodne za fotokatalitičke i fotonaponske primjene. Za provjeru uspješnost postizanja željenih svojstava navedenih mikrostrukturiranih i nanostrukturiranih materijala od ključne važnosti je određivanje morfoloških i strukturnih svojstava, što se postiglo korištenjem prvenstveno elektronske mikroskopije i Ramanove spektroskopije. Za potrebe priprave fotonaponskih ćelija u čvrstom stanju s nanostrukturiranim ZnO tankim filmovima kao slojevima za prijenos elektrona bilo je potrebno optimirati debljinu i sastav susjednih slojeva što je utjecalo na pojavu električne histereze u različitim razmjerima. Nanostrukturirani TiO2 filmovi dodatno su dekorirani sa česticama i spojevima baziranim na Ag ili Cu za potrebe primjene u fotokatalitičkim reaktorima. Tim procesom je poboljšana efikasnost razgradnje organskih onečišćivala. Ispitana je mogućnost priprave filmova kompozitnih ZnO@TiO2 nanostruktura korištenjem niza fizikalnih i kemijskih metoda nanošenja TiO2 na nanostrukture ZnO. Utvrđena je najveća uspješnost nanošenja kemijskim metodama, što je razvidno iz najvećih vrijednosti postignutih vodljivosti i transmisije filmova. Problematika razjašnjavanja određenih mikrostrukturnih specifičnosti kompozita ZnO@TiO2 ostaje izazov s ciljem daljnjeg poboljšavanje efikasnosti i stabilnosti fotonaponskih i fotokatalitičkih sustava. This dissertation investigates ZnO, TiO2 and ZnO@TiO2 composites thin films. The aim was to prepare nanostructured materials suitable for photocatalytic and photovoltaic applications. In order to validate the obtaining of microstructured and nanostructured materials with desired properties, it was necessary to optimise morphologic and structural properties, which was primarily achieved using electron microscopy and Raman spectroscopy. In order to prepare solid state solar cells with nanostructured ZnO thin films for transport of the charge carriers, it was necessary to optimise the thickness and the composition of the adjacent layers, which influenced the extent of the occurring electric hysteresis. For use in photocatalytic reactors, TiO2 nanostructures were additionally decorated with Ag particles or Cu compounds, which improved the decomposition rate and efficiency of organic pollutants. A possibility of preparing ZnO@TiO2 thin film composites using various physical and chemical methods of TiO2 layer deposition on ZnO nanostructures was investigated. Chemical methods rose above others since composite films obtained thereof displayed the highest conductivity and the highest transmission properties. The challenges related with clarifying microstructural particularities of the ZnO@TiO2 composites remain with the aim of further improvement of efficiency and stability of photovoltaic and photocatalytic systems.

U posljednjih se tridesetak godina u vjetroinženjerstvu sve više koriste metode računalne dinamike fluida za modeliranje kompleksnih pojava u atmosferskom strujanju. Stoga je u sklopu doktorskog istraživanja razvijen novi računalni model neutralno temperaturno stratificiranog, stacionarnog, homogenog i ravninskog atmosferskog graničnog sloja (inženjerskog atmosferskog graničnog sloja) u kojem je strujanje uzrokovano dodatnom masenom silom promjenjivom po visini. Dodatna masena sila, koja fizikalno predstavlja dodatnu silu gradijenta tlaka promjenjivu po visini, uvrštena je u jednadžbu količine gibanja, pri čemu joj je početna vrijednost određena derivacijom poznate raspodjele naprezanja. Kako bi se generirale raspodjele naprezanja u skladu s dostupnim atmosferskim ili eksperimentalnim podatcima, vrijednosti dodatne masene sile su tijekom računalne simulacije (koristeći tehniku domene preteče) korigirane primjenom korekcijske procedure ugrađene u računalni algoritam za modeliranje strujanja fluida otvorenog koda OpenFOAM®. Strujanje inženjerskog atmosferskog graničnog sloja modelirano je tehnikom domene sljednika i tehnikom domene preteče u praznoj dvodimenzionalnoj računalnoj domeni, koristeći pet različitih modela turbulencije temeljenih na rješavanju vremenski osrednjenih Navier−Stokesovih jednadžbi: standardni k−ε, RNG k−ε, realizable k−ε, Wilcoxov k−ω i Menterov k−ω SST. Generirani profili osrednjene brzine, kinetičke energije turbulencije i disipacije ili specifične disipacije kinetičke energije turbulencije potom su korišteni kao ulazni profili za računalno modeliranje opterećenja zgrada uslijed vjetra, strujanje u atmosferskom graničnom sloju iznad brda jednostavne geometrije i proračun brzine strujanja vjetra na visinama koje odgovaraju visinama pješaka u okolini uzdignute zgrade. Dobiveni rezultati pokazuju da je novim modelom moguće ostvariti karakteristike strujanja u skladu s atmosferskim i eksperimentalnim podatcima, prethodnim računalnim simulacijama, te već postojećim modelima atmosferskog graničnog sloja. Proper characterization of atmospheric flow is one of the most important tasks in wind engineering. This is because the characteristics of atmospheric flow may affect a wide range of human activities, such as the wind loading of structures, pedestrian wind comfort in urban areas, building and bridge aerodynamics, traffic safety, the dispersion of exhaust gases produced by industrial combustion or vehicles, the natural ventilation of buildings, structural aeroacoustics, the siting of wind farms, the aerodynamics of wind turbine rotors, and wind-induced vibrations. A good understanding of atmospheric flow characteristics may also prevent serious structural damage caused by the effects of strong winds, and may reduce the risk of human casualties. The main research tools in wind engineering are atmospheric on-site measurements, measurements in wind tunnels, and the computational modelling of atmospheric flows by using computational fluid dynamics (CFD). Although atmospheric and laboratory measurements are still an essential tool to investigate atmospheric flow characteristics, CFD has been increasingly used in the last 30 years to model complex atmospheric flows. When compared to atmospheric and laboratory techniques, CFD is nowadays usually a less expensive and more efficient research tool. It is also less time consuming and allows for the computational modelling of the entire flow fields, which is usually not possible when flow characteristics are measured on site or in wind tunnels. Moreover, the computational modelling technique allows for effective control of the inflow characteristics, such as inflow wind speed or turbulence intensity. The atmospheric boundary layer (ABL) is the lowest layer of the Earth’s atmosphere, whose characteristics are mainly affected by the Earth’s surface. Theoretical models and atmospheric measurements have shown that in strong wind conditions, the ABL flow might be modelled as neutrally stratified, stationary, homogeneous and unidirectional. As strong wind conditions are often most interesting for wind engineers, the neutrally stratified, stationary, homogeneous and unidirectional ABL is also referred to as engineering ABL. Although large-eddy simulations have been increasingly used for the computational modelling of atmospheric turbulence, steady RANS (Reynolds-Averaged Navier-Stokes) is still a widespread tool for the modelling of atmospheric turbulence. This is because it is not so time consuming when compared to large-eddy simulations, and consequently it allows for the faster generation of computational results. The engineering ABL flow in an empty computational domain is computationally modelled by using the precursor domain technique or the successor domain technique. The former ensures flow homogeneity inside the computational domain as the Neumann boundary condition is applied at the inlet and the outlet boundaries of the domain for all modelled quantities (e.g. mean velocity, turbulence kinetic energy), or because the inlet and the outlet boundaries are treated as periodic boundaries. Unlike the precursor domain technique, the successor domain technique does not a priori ensure the homogeneity of the flow because the inflow profiles for the modelled quantities are defined at the inlet boundary, and the Neumann boundary condition is applied at the outlet boundary. Accordingly, the pressure gradient that could occur in the computational domain modifies the inflow profiles along the computational domain. When the successor domain technique is used, the inlet boundary conditions for the modelled quantities must be implemented in the employed CFD algorithm. This is not the case with the precursor domain technique. However, the force (or the forces) that drive the flow throughout the computational domain need to be explicitly modelled when the precursor domain technique is employed. Hypothesis and research methodologies A novel computational model for engineering ABL simulation was developed. The flow generated by the presented model is driven by the additional body force that varies with the increase in height. The body force was implemented in the momentum equation and its initial value was determined by deriving the known targeted stress distribution. This body force was derived by analysing the realistic neutrally stratified, stationary and homogeneous ABL, where the flow veers with the increase in height due to the effects of the Coriolis force. By analysing the forces that drive and retard such flow, it was shown that the flow in the neutrally stratified, stationary and homogeneous ABL is driven by the pressure gradient force that varies with the increase in height. This pressure gradient force is at its maximum close to the ground, while it declines as the height increases until it vanishes at geostrophic height. The performed analysis confirmed that the engineering ABL flow may be generated by applying the additional body force that varies with the increase in height, in the same manner as the flow in the neutrally stratified, stationary and homogeneous ABL is driven by the pressure gradient force that varies as the height increases. The initial body force values were corrected during the performed precursor domain technique computation by the correction procedure implemented in the open-source CFD algorithm OpenFOAM®. This was done to ensure that the computationally modelled stress distribution matches the experimental or theoretical stress distribution. The research hypothesis are as follows: a) The appropriate stress, mean velocity, and turbulence kinetic energy profiles that agree with the theoretical distributions or the atmospheric and laboratory measurements may be generated by the computational modelling of the engineering ABL flow driven by the additional body force implemented in the momentum equation. The implemented body force varies with the increase in height. b) The new model for the engineering ABL computation may be used to computationally model the problems related to the environmental and structural aerodynamics. The new computational model was tested by the computational analysis of the engineering ABL flow in an empty computational domain. The engineering ABL was computationally modelled by using both the precursor and the successor domain techniques, together with the five various steady RANS turbulence models, i.e. standard k−ε, RNG k−ε, realizable k−ε, Wilcox's k−ω, and Menter's k−ω SST turbulence model. The generated computational results were also compared to the computational results generated by using the shear stress-driven and the pressure-driven engineering ABL models. The profiles of the mean velocity, turbulence kinetic energy and dissipation rate or specific dissipation rate generated by the precursor domain technique using the presented engineering ABL model driven by the body force that varies with the increase in height were subsequently used as the inflow profiles at the inlet boundary of the computational domain when specific problems related to the wind engineering were studied. This was done to investigate the ability of the presented computational model to determine wind loads on structures (the pressure coefficient distribution on the building model surfaces and the drag force coefficient of the building model) and the characteristics of the engineering ABL flow above hilly terrain (mean velocity speed-up at the hill crest, the positions of the separation and the reattachment of the flow, turbulence kinetic energy distribution in the wake region behind the hill), and to estimate pedestrian wind comfort in the vicinity of a lift-up building (mean velocities at pedestrian-level heights). Computational results The computational results generated by using the new model of the engineering ABL in combination with the precursor domain technique confirm that the obtained flow is homogeneous due to the Neumann boundary condition applied at the inlet and the outlet boundaries of the computational domain. The obtained results also indicate that the pressure gradient generated in the computational domain does not influence the flow. Moreover, the computationally generated flow is mostly driven by the additional body force that varies with the increase in height, whereas the pressure gradient actually represents the error of the calibrated body force calculated by the correction procedure implemented in the CFD algorithm. Computational modelling of the engineering ABL flows in an empty computational domain showed that inactive turbulence modelling is the main prerequisite to achieve distributions of the turbulence kinetic energy in agreement with the atmospheric and laboratory measurements. It was also demonstrated that appropriate distributions of the turbulence kinetic energy cannot be achieved when the standard values of the turbulence model constants are used, as calculated turbulence kinetic energy values are significantly lower than the values predicted by the measurements. On the contrary, the computational modelling of the engineering ABL flow above the hill showed that modification of the turbulence model constants may seriously affect the mean wind speed-up values near the crest of the hill, the locations of the separation and the reattachment of the flow, and may also affect the turbulence kinetic energy distributions in the wake region behind the hill. When compared to the experimental measurements, the best results were obtained using the standard values of the turbulence model constants, i.e. without inactive turbulence modelling. Computational modelling of the engineering ABL flow in an empty computational domain by using the shear stress-driven, pressure-driven and body force-driven ABL models showed that experimental stress values can be reproduced only by a new computational model based on the additional body force that varies with the increase in height. The stress and the turbulence kinetic energy profiles obtained using the shear-stress-driven ABL model remain constant with the increase in height, while they decrease linearly with the increase in height when the pressure-driven ABL model is employed. All three ABL models generated similar mean velocity profiles. The obtained mean velocity, stress and turbulence kinetic energy profiles indicated that the choice of the steady RANS turbulence model affects only the mean velocity profile results. It was also confirmed that the precursor domain technique produces results that agree well with the results obtained using the successor domain technique. When the profiles generated by using the precursor domain technique and the presented computational model based on the body force that varies with the increase in height are set at the inlet boundary, the flow generated by using the successor domain technique without the additional body force can be considered homogeneous (in comparison with the results obtained by using the successor domain technique with the applied additional body force). Computational modelling of the engineering ABL flow over the cubic building model by using the shear stress-driven, pressure-driven and the body force-driven models showed that the additional body force implemented in the momentum equation does not affect the computational pressure coefficient distributions on the cubic building surfaces. The pressure coefficient distributions on these surfaces and the total drag force of the building are primarily affected by the choice of the steady RANS turbulence model, while the obtained results indicate that the employed ABL model does not influence the wind loads on buildings. The computational results also confirmed the appearance of the stagnation pressure anomaly caused by high values of the modelled turbulent viscosity, which is a drawback of the steady RANS turbulence models. When the profiles generated by using the precursor domain technique and the new computational model based on the body force that varies with the increase in height are set at the inlet boundary, the profiles generated by using the successor domain technique without the additional body force agree well with the results obtained by using the successor domain technique with the applied additional body force. These results indicate that the additional body force implemented in the momentum equation does not influence the pressure coefficient distributions on the cubic building surfaces and the calculated drag force coefficient. The mean wind speed-up values at the crest of the hill, the locations of the separation and the reattachment of the flow and the turbulence kinetic energy distributions in the wake region behind the hill generated by the computational modelling of the engineering ABL flow above the hill are mostly affected by the inactive turbulence modelling. When compared to the laboratory measurements, the best results were obtained using the standard values of the turbulence model constants. The obtained results also indicate that the mean wind speed-up values at the crest of the hill, the locations of the separation and the reattachment of the flow and the turbulence kinetic energy distributions in the wake region behind the hill are affected by the roughness of the hill surface and the slope of the hill. Computationally modelled mean velocity values at pedestrian-level heights in the vicinity of a lift-up building by using the shear stress-driven, pressure-driven and body force-driven ABL models together with the five various steady RANS turbulence models showed that the choice of the ABL model does not influence the computational results. On the contrary, the obtained results indicate that the computationally modelled mean velocity values are mostly affected by the employed steady RANS turbulence model. When the profiles generated by using the precursor domain technique and the presented computational model based on the body force that varies with the increase in height are set at the inlet boundary, the mean velocity values generated by using the successor domain technique without the additional body force agree well with the mean velocity values obtained by using the successor domain technique with the applied additional body force. These results indicate that the additional body force implemented in the momentum equation does not influence the mean velocity results at pedestrian-level heights in the vicinity of a lift-up building. Conclusion and scientific contribution The novel computational model was developed for the computational modelling of the engineering ABL flow that is driven by the additional body force that varies with the increase in height. This additional body force is implemented in the momentum equation along the constant pressure gradient force. The implemented body force represents the additional pressure gradient force that varies with the increase in height, in the same manner as the pressure gradient force varies in the neutrally stratified, stationary and homogeneous ABL where the flow varies with the height due to the Coriolis force. The initial body force value was determined by deriving the known targeted stress distribution and was corrected during the computational analysis by the correction procedure implemented in the CFD algorithm. The computational results obtained by modelling the engineering ABL flow in an empty computational domain using the developed engineering ABL model showed that the presented model is capable of reproducing mean velocity, turbulence kinetic energy and stress profiles in agreement with the theoretical distributions and atmospheric or laboratory measurements. The obtained results also indicate that appropriate stress profiles can be computationally reproduced only when the flow is modelled by using the precursor domain technique and the new engineering ABL model driven by the body force that is calibrated during the computation using the correction procedure implemented in the CFD algorithm. The performed computational investigation also showed that the shear stress-driven, pressure-driven and body force-driven engineering ABL flow can be properly modelled by using the precursor domain technique. The pressure-driven engineering ABL flow was modelled for the first time in combination with the RNG k−ε and realizable k−ε turbulence models using the precursor domain technique. Computational simulations of wind loads on a cubic building, the engineering ABL flow above hilly terrain, and mean velocity values at pedestrian-level heights in the vicinity of the lift-up building showed that the developed model can be adopted for modelling common problems in environmental and structural aerodynamics, as the obtained results agree well with the available laboratory measurements or previous computational simulations. The computational modelling of the engineering ABL flow above hilly terrain confirmed that inactive turbulence modelling generates mean wind speed-up at the crest of the hill that does not agree with laboratory measurements and previous computational simulations. Inactive turbulence modelling also produces a large wake behind the hill and high turbulence kinetic energy in the wake. The performed computations confirm that the standard values of the steady RANS turbulence model constants need to be used to computationally model problems in environmental and structural aerodynamics.

U članku se predstavljaju dobitnici Nobelove nagrade za fiziku 2021. Članak opisuje kako su dobitnici nagrade objasnili kaotičnu prirodu vremena zbog koje je nemoguće napraviti pouzdane vremenske prognoze za desetak dana unaprijed, ali i kako su, unatoč tome, napravili prve klimatske projekcije za budućih nekoliko desetljeća i stotinu godina.

Cilj ovog doktorskog rada je razvoj konvertera za učinkovitu detekciju termalnih neutrona. Kao osnovni, aktivni materijal u poluvodičkom detektoru, koristi se širokopojasni 4H-SiC. S obzirom na to da se termalni neutroni ne mogu detektirati direktno s poluvodičkim, čvrstim, detektorom već preko nabijenih čestica koje nastaju interakcijom s drugim jezgrama, potreban je učinkovit konverter. Fokus istraživanja je na izotopima 6Li te 10B, koji u interakciji s termalnim neutronima emitiraju alfa-čestice (6Li(n,α)3H, 10B(n,α)7Li). U okviru istraživanja primijenjeno je nekoliko različitih metoda pripreme tankih filmova. Optimalna debljina tankog sloja filma određena je na temelju Monte Carlo simulacija, a očekivane vrijednosti su u granicama od 1 do 30 μm. Morfologija i struktura dobivenih filmova proučavane su mikroskopskim metodama. Učinkovitost dobivenih konvertera testirana je na nuklearnom reaktoru TRIGA Mark II Instituta Jožef Stefan u Ljubljani, Slovenija. Osim odziva detektora na termalne neutrone, obrađen je i odziv silicijeva karbida na druge izvore ionizirajućeg zračenja kao što su alfa-čestice i gama-zračenje. This thesis deals with development of a converter for efficient detection of thermal neutrons. A wide gap 4H-SiC is used here as a basic, active material in the semiconductor detector. It is not possible to detect thermal neutrons directly with solid semiconductor detector, but through charged particles generated by interaction with other cores. Thus, an efficient converter is needed. The focus of the research is on the isotopes of 6Li and 10B, which interact with the thermal neutrons emitting alpha particles (6Li(n,α)3H, 10B(n,α)7Li). Within the scope of the research, a range of techniques of thin film preparation was used. Optimal thin film thickness was determined using Monte Carlo simulation. The expected values are within the range of 1 to 30 μm. The morphology and structure of the obtained films was studied by means of microscopy methods. Efficiency of the obtained converters was tested on the TRIGA Mark II nuclear reactor of the Jožef Stefan Institute in Ljubljana, Slovenia. In addition to the detector response to thermal neutrons, this thesis covers the response of silicon carbide to other sources of ionizing radiation such as alpha particles and gamma radiation as well.

Ovim radom vrši se pregled dijela trenutno dostupnih mobilnih aplikacija za učenje fizike i izrade aplikacije „Fizika korak po korak“ za učenje fizike na hrvatskom jeziku. Osvrće se na poteškoće s kojima se susreću razvojni inženjeri koji se bave razvojem obrazovne programske podrške. Pregledat će se dio metoda razvoja programske podrške, pojasniti pravila i poželjnost pridržavanja istih za vrijeme razvoja i ukazati na potrebu za testiranjem i verzioniranjem programa u razvojnom ciklusu koji će se primjenjivati za vrijeme razvoja programske podrške. Detaljnije će se prikazati dobrobiti razvoja hibridnih mobilnih aplikacija te izložiti dobre strane razvoja aplikacija za pametne telefone u Xamarin razvojnom okruženju koje je odabrano za razvoj programske podrške „Fizika korak po korak“. Program postavlja dinamička pitanja korisniku i prati napredak kroz 3 razine.

Nastava fizike, kao jedno od temeljnih STEM područja, u suvremenom obrazovanju ima sve veći značaj. U ovome radu stavljamo naglasak na rano učenje fizike, osobito koncepte sile. Upoznavanjem djece s konceptima prirodnih znanosti u razrednoj nastavi, dajemo mogućnosti za istraživanje, postavljanje raznih pitanja. Mnoga istraživanja pokazuju da je rano upoznavanje djece sa STEM područjem ključno za njihovo daljnje napredovanje i usmjeravanje ka tim područjima. Nastava fizike u središtu ima fizikalni pokus, koji nam omogućuje zanimljiviji pristup učenicima, te mogućnost njihovog samostalnog istraživanja. Djeca u ranoj dobi su znatiželjna, postavljaju pitanja, stoga trebamo iskoristiti to razdoblje da ih izložimo zanimljivim konceptima sile i potaknemo suradnju i istraživanja. U sklopu ovoga rada pokazujemo kako fiziku možemo uvesti već u razrednoj nastavi kroz koncept sile. Ako se djeca s njima nisu prije susrela, iste pokuse bi bilo dobro izvoditi u okviru odgovarajućih tema u kurikulumu fizike. Physics teaching, as one of the fundamental STEM fields, has an increasing importance in modern education. In this diploma thesis we put emphasis on early learning of physics, especially the concepts of force. By introducing children to the concepts of natural sciences in lower elementary school teaching, we provide opportunities for inquiry and asking questions. Great deal of studies demonstrate that early introducing children to the STEM field is crucial to their further progress and guidance towards these areas. Physics teaching has a physical experiment as its focus, which allows more interesting approach to students, and the possibility for their independent research. Children at an early age are curious and ask questions, therefore, we should use this period to expose them to interesting concepts of force and encourage their collaboration and research. In this diploma thesis we show how physics can be introduced in lower elementary school already, through the concept of force. If children have not encountered them before, the same experiments would be good to perform within the framework of appropriate topics in the physics curriculum.

U tezi predstavljamo rezultate računa na razini teorije funkcionala gustoće za tri primjera van der Waalsovih heterostruktura. Prvo predstavljamo rezultate za 295 heterostruktura sastavljenih od dva 2D kristala. Izračunate energije, geometrijske strukture, gustoće stanja te kemijski potencijali bit će pohranjeni u bazu podataka, koja će biti javno dostupna. Analizom rezultata karakteriziramo vezanje heterostruktura te pokazujemo da je utjecaj ne fizikalne deformacije ćelija pri slaganju ulaznih struktura na izračune relativno velik. Pokazujemo i da se taj utjecaj donekle može ispraviti konstrukcijom jednostavnih modela. Potom analiziramo vezanje monosloja PtSe2 s Pt(111) radi određivanja dosad nejasne strukture tog kompleksa. Usporedbom izračunatih energija vezanja te geometrijskih i elektronskih struktura PtSe2 na čistoj i monoslojem Se prekrivenoj Pt(111) pokazujemo da je u prvoj od njih PtSe2 kemisorbiran, a u drugoj fizisorbiran. Kako temeljita eksperimentalna karakterizacija ovog kompleksa pokazuje da je PtSe2 fizisorbiran, zaključujemo da je potonja struktura točna. Naposljetku, promatramo elektronsku strukturu grafena (Gr) adsorbiranog na Co(0001) prekrivenoj monoslojem Au ili Pt. Pokazujemo da se u grafenu pojavljuje magnetizacija zbog magnetskog efekta blizine, koja se može mijenjati primjenom statičkog električnog polja. Dodatno su Co|Au|Gr te Co|Pt|Gr učinkovitiji za primjenu u spintronici od prije istraživanih Co|hBN|Gr te Co|Gr|Gr jer im za istu promjenu magnetizacije treba manje električno polje. Dodatno, u Co|Pt|Gr efekt električnog polja jako je izražen, što je posljedica spinski polariziranog površinskog stanja blizu Fermijevog nivoa. Također, pokazujemo da se promjenom pokrivenosti Co(0001) može fino upravljati magnetizacijom i osjetljivošću grafena. Rad ne sadrži sažetak na drugom jeziku.

Posljednjih nekoliko godina istraživači su pokazali ponovni interes za uspjeh u učenju. Naročito su na polju obrazovne psihologije provedena mnoga istraživanja kako bi se analiziralo kako na učenje i postignuća utječu motivacijski i kognitivni čimbenici (Krapp, 1999). Studije proceduralnog i konceptualnog učenja obično su usredotočene na uključene kognitivne procese, manje se pažnje posvećuje motivaciji učenika. Istraživanje motivacije uspostavilo je vezu s općim, školskim postignućima (Boden et al., 2017). Kako je fizika jedan od predmeta za koji su učenici najmanje zainteresirani uglavnom zbog njene nerazumljivosti, težine, povezanosti s matematikom te apstraktnosti (Jokić, 2013), jedan od glavnih ciljeva je postao identificiranje i bolje razumijevanje učeničkih problema prilikom učenja fizike. Prema Ćosiću (2015), u Hrvatskoj samo manjina učenika smatra fiziku interesantnom i zanimljivom, i vrlo malo ih je spremno studirati ju. Stoga je bitno sustavno raditi na motiviranju i poticanju osnovnoškolaca i srednjoškolaca za učenje fizike te razvijati pozitivan stav prema ovom nastavnom predmetu. Kako bismo odredili što je za učenike motivacija i koje sredstvo motivacije ili poticaja najbolje djeluje na učenje, provedeno je anketno istraživanje na dvadeset osam učenika sedmog razreda osnovne škole. U ovom radu raspravljamo o rezultatima navedene ankete.

Što napraviti kako bi obrazovni sustav što bolje pratio promjene u društvu i tehnologiji? Današnje doba je digitalno i jako ga je teško zamisliti bez primjene tehnologija. Ipak, ona nije na pravi način integrirana u školski sustav. Način učenja i poučavanja nije se bitno promijenio, ali životom uz tehnologiju promijenio se način razmišljanja. Učenje temeljeno na igrama metoda je poučavanja koja uravnotežuje obrazovne materijale sa strategijama, pravilima i socijalnim aspektima igranja igre. Mnoge edukativne igre izlažu učenike ciljanim sadržajima kroz stvarne situacije i pomažu učenicima da razviju ključne životne vještine [1]. Učenje temeljeno na igrama omogućava učenicima da se na razigran i dinamičan način bave standardnim konceptima. U ovom radu prikazani su rezultati primjene jednog takvog modela u kojem su učenici osmog razreda osnovne škole primjenjivali Microsoft Minecraft Education u nastavi fizike, u temi Gibanje i sila, kao i razlike u mogućnostima izmjene informacija te različitim vrstama kognitivnih sposobnosti eksperimentalne i kontrolne skupine. Učenici u jednom razredu (eksperimentalna skupina), koristili su materijale za učenje temeljene na igri Microsoft Minecraft Education ; učenici u drugom razredu (kontrolna skupina), koristili su materijale za učenje koji se ne temelje na igrama. Rezultati su otkrili da je eksperimentalna skupina imala veću mogućnost izmjene informacija o relevantnim sadržajima što je pozitivno utjecalo na učenike eksperimentalne skupine koja je bila znatno više zainteresirana, koncentrirana i sposobna kontrolirati svoje učenje. Rezultate primjene modela poučavanja temeljimo na provedenim anketama među učenicima te rezultatima provedenog formativnog i sumativnog vrednovanja.

Lebdeće čestice koje nastaju procesima obrade metala često postižu vrlo visoke koncentracije, a u svom sastavu imaju značajne količine teških metala koji mogu negativno utjecati na zdravlje radnika koji su im izloženi. Cilj ovog rada je utvrditi postoji li kod radnika u radionicama za obradu metala povećano opterećenje metalima u radnom prostoru i u biološkom materijalu uzetom od ispitanika (kosa i nokti) te po potrebi dati smjernice i preporuke za provođenje preventivnih mjera vezanih uz opterećenje metalima. Kako bi se procijenila izloženost lebdećim česticama radnika u radionicama za obradu metala, prikupljeni su uzorci finih lebdećih čestica (PM2,5) u šest radionica za obradu metala te u dva kontrolna prostora. U svakoj radionici uzorci su prikupljani na teflonskim filtrima tijekom tri radna dana, a u većini prostora prikupljani su i podaci optičkim brojačem čestica tijekom desetak dana. Elementna analiza uzoraka provedena je tehnikama XRF i PIXE, dok su ukupne koncentracije PM2,5 određene gravimetrijski. Kao prvi korak u procjeni mogućeg utjecaja lebdećih čestica na zdravlje radnika, prikupljeni su uzorci kose i noktiju 68 osoba, od kojih su 34 izložena radnika te 34 pripadnika kontrolne skupine. Na biološkim uzorcima je izvršena elementna analiza tehnikom ICP-MS, čime su određene koncentracije 12 elemenata. Koncentracije PM2,5 u radionicama za obradu čelika dosezale su do 2900 µg/m3, dok je Fe sačinjavalo oko 50 % ukupne mase čestica. U radionicama za obradu aluminija koncentracije PM2,5 su dosezale do 300 µg/m3, a procjenjuje se da su najzastupljenije bile čestice iz vanjskih izvora. U kontrolnim prostorima koncentracije PM2,5 nisu prelazile 9 µg/m3. Koncentracije Al, Ti, Mn, Fe i Pb u kosi radnika koji obrađuju čelik značajno su veće od koncentracija tih elemenata u kosi kontrolne skupine, dok uzorci kose radnika iz radionica za obradu aluminija nisu značajno različiti od kontrolnih uzoraka. U noktiju radnika izmjerene su značajno veće koncentracije Ti, Mn i Fe nego u noktima iz kontrolne skupine. U biološkim uzorcima radnika zabilježeno je deponiranje metala iako se koncentracije lebdećih čestica nisu ni približile graničnim vrijednostima propisanih regulativom. Potrebno je provesti dodatna istraživanja kojima bi se utvrdilo ukazuje li ovo deponiranje na zdravlje radnika te po potrebi izmijeniti regulativu. Particulate matter (PM) is a mixture of solid particles and liquid droplets suspended in the atmosphere and it stands as one of the most important air pollutants. Its fine fraction, PM2.5, which consists of particles less than 2.5 µm in diameter, is of special interest because it can easily enter human respiratory system and therefore can have adverse impact on human health. Many studies have been conducted to monitor PM outdoors, but since people spend most of their time indoors, it is especially important to monitor indoor pollution, both in homes and workplaces. Metal processing techniques such as welding, cutting, grinding, and polishing produce significant levels of PM in metal workshops. PM from these sources, especially from welding, is typically less than 2.5 µm in diameter, often even less than 1 µm in diameter, so it can easily enter human respiratory system. Moreover, it is rich with heavy metal components such as Mn and Zn, which can cause specific health problems such as manganism. It is, therefore, very important to monitor PM levels in metal workshops, but also to monitor health status of the workers exposed to high levels of PM. The aim of this study is to determine whether the exposure to metals of the workers in metal workshops in Croatia is elevated by evaluating the exposure to metals in particulate matter and by biological monitoring. This can possibly lead to new regulations in this area. In order to estimate the levels of exposure to PM, six metal workshops in the vicinity of the city of Rijeka, Croatia, were chosen to participate in the study. Two of them are dealing with the aluminium components and four of them are mainly dealing with the steel and stainless steel components. Three of the workshops (including aluminium workshops) are rather small, with the area of about 200 m2 , and the other three are located in bigger halls, with the area of 400 m2 or more. In the first workshop, two sampling campaigns were performed. In the first one, the PM2.5 samples were collected in a store-room. 12-h samples were taken through 13 days, so that the samples represent daily and weekly changes in PM2.5 levels. In the second campaign, the sampling was performed in the main working room and samples were taken at finer time resolution. During the working time, 1-h samples were taken and one single 12-h sample was taken during the rest of the day. The sampling was performed during three working days. Similar sampling regime was performed in other workshops. During the working time, 1-h or 2-h samples were taken, and during the non-working time 4-h or 8-h samples were taken. The sampling lasted for three working days in each workshop. Additional sampling with an optical particle counter was performed in most of the workshops, during about ten days at each. Additional sapling was performed at two control workplaces: one laboratory and one office at the University of Rijeka. Three consecutive 8-h samples of PM2.5 were taken in each workplace, while the optical particle counter was used over longer period of time. The samples of PM2.5 were collected on thin polytetrafluoroethylene (Teflon) filters with a cyclone sampler. Overall, 234 samples were collected on the filters, including 134 hourly samples, 26 2-h samples, 29 4-h samples, 15 8-h samples and 30 12-h samples. Mass concentrations were obtained gravimetrically and elemental analysis was performed with X-ray fluorescence (XRF) and particle induced X-ray emission (PIXE) techniques. Concentrations of Na, Mg, Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb and Bi were obtained. Additionally, an optical particle counter measured PM concentrations of 6 different fractions from 0.3 to 10 µm in diameter. About 1800 h of data were collected in this way. As a first step to estimate possible health impacts of PM, biological samples were taken from 34 workers who agreed to participate in the study. Samples of hair were analysed from 30 workers from all the workshops included in the study, while 8 samples of nails were analysed from the workers from the first workshop. Additionally, 34 unexposed persons were included in the control group, from which 32 hair samples and 9 nail samples were analysed. Elemental analysis of biological samples was performed with inductively coupled plasma mass spectrometry (ICPMS) and concentrations of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb were determined. In most of the workshops, PM2.5 and elemental concentrations showed a pattern clearly connected to the working activities. The highest concentrations of almost all elements were obtained for the first workshop, during the second sampling campaign. Hourly PM2.5 concentrations in this period were up to 2900 µg/m3 , while Mn and Fe hourly concentrations were up to 45 and 1400 µg/m3 , respectively. In this and other steel workshops, Fe was a predominant element, making up to 50 % of total mass. Mn was one of the most recognizable elements, being one of the main components of welding electrodes. In the aluminium workshops, the total concentrations were much lower and with much different elemental compositions. In the second workshop, the maximum hourly PM2.5 concentration was 300 µg/m3 , while in the third workshop the maximum PM2.5 concentration was only 38 µg/m3 . As expected, Fe was not the predominant element, but neither was Al, because aluminium parts were neither welded nor heated in any other way that could produce fine particles. Much lower PM2.5 concentrations were measured in control workplaces, where the maximum PM2.5 concentration was only 9 µg/m3 . Concentrations and composition of PM2.5 in control workplaces were comparable to the data obtained previously in the outdoor air in the Rijeka city centre. In the hair samples, significantly higher concentrations of Al, Ti, Mn, Fe and Pb were measured in samples of workers in steel workshops than in the control samples. The highest concentrations of these metals were found for samples of workers from the first, fourth and fifth workshop, were the highest PM2.5 concentrations were measured as well. Although a very small number of nail samples was analysed, higher concentrations of Ti, Mn and Fe in the samples of workers are clearly visible. This indicates that these metals were deposited in analyzed tissues after being inhaled as particulate matter. It should be further investigated if these metals are deposited in other tissues and organs, such as liver or brain and whether that causes health problems. The results of this investigation show that deposition of metals in tissues of workers occurs even under PM concentrations that are far below limit values. For possible revision of current limit values it is necessary to carry on with further research wchich would investigate health status of the workers.

Niskodimenzionalni kvantni magnetizam važna je grana istraživanja u fizici kondenzirane tvari. Materijali niskodimenzionalne magnetske strukture često imaju bogate fazne dijagrame kao posljedicu kvantnih fluktuacija i prostorne ograničenosti, te nude izvrsnu platformu za testiranje teorijskih predviđanja poput kvantno-kritičnih točaka i Bose-Einstein kondenzacije. U sklopu fizike niskih dimenzija proučavani su magnetski izolirani klasteri, jednodimenzionalni lanci poput Haldaneovog lanca, spinske ljestve i dvodimenzionalne ravnine, od kojih je možda najpoznatija grupa visokotemperaturnih supravodiča. Nuklearna magnetska rezonancija, uparena s nuklearnom kvadrupolnom rezonancijom, nezaobilazna je u razumijevanju fizike takvih materijala. Tim tehnikama dobiva se direktan uvid u magnetsko i električno polje u blizini atomske jezgre od interesa. Spektroskopska i relaksacijska mjerenja tih tehnika nam omogućuju uvid u statičku i dinamičku spinsku susceptibilnost. U ovom radu proučavat ćemo dvije niskodimenzionalne magnetske strukture: spinski klaster SeCuO_3 i Haldaneov lanac m-NO_2PhBNO tehnikama nuklearne magnetske i kvadrupolne rezonancije. S obzirom da su uzorci monokristali, u sklopu ovog rada izrađen je i goniometar koji omogućuje preciznu orijentaciju uzorka. Ovisnost o orijentaciji parametar je na koji je NMR tehnika osjetljiva, stoga je mogućnost ugađanja tog parametra vrijedan dodatak već postojećoj eksperimentalnoj tehnici. Oba spoja karakterizirana su rendgenskom difrakcijom i određen im je fazni dijagram mjerenjem toplinskog kapaciteta. Glavna saznanja dobivena tijekom istraživanja koje je rezultiralo ovim radom su dublji lokalni uvid u spinsku strukturu tetramera, s posebnim naglaskom da su središnji spinovi ti koji se singletno uređuju, što je direktno potvrđeno, te na snažne fluktuacije vanjskih spinova. Za haldane sustav potvrđena je izotropnost uzorka, te je mapiran fazni dijagram. Istraživanja u području Luttingerove tekućine pokazuju da se radi o privlačnoj interakciji, kao što je i predviđeno Haldaneovom teorijom. Low-dimensional quantum magnetism is an important branch of research in the condensed matter physics. Materials that have a low-dimensional magnetic structure often have rich phase diagrams as a consequence of quantum fluctuations and spatial constraints and offer an excellent platform for testing of the theoretical predictions. Quantum transitions between phases, which can be caused by mechanical or magnetic effects, deserve special mention since they are also the subject of a lot of research. In the vicinity of such a transition, quantum fluctuations determine the physical system, and the system behaves universally, independent of the chemical and other specifics of the system itself. As a part of the low-dimensional physics, magnetically isolated clusters like one-dimensional chains such as the Haldane chain, the spin ladders, and two-dimensional planes of which perhaps the most well-known is the group of high-temperature superconductors, have been studied. Nuclear magnetic resonance technique, paired with the Nuclear quadrupole resonance technique, is indispensable in understanding the physics of such materials. These techniques provide direct insight into the magnetic and electric field near the atomic nucleus of interest. The spectroscopic and relaxation measurements of these techniques allow insight into static and dynamic spin susceptibility. Using single crystal samples for the experiment is extremely beneficial, for the NMR technique can resolve angle, and thus provide angle-related information that is lost if the sample is in a powder form. However, to be able to use the single crystal samples, a goniometer must be able to orient the sample in the desired orientation. Thus, in the scope of this thesis, a goniometer was designed and manufactured. This goniometer proved to be very reliable, made to withstand high magnetic fields and to be able to rotate in the low temperature environment. This paper will present the study of two low-dimensional magnetic structures: the spin cluster SeCuO_3 and the Haldane chain m-NO_2PhBNO (BoNO) by nuclear magnetic and quadrupole resonance techniques. Spin clusters possess simple intracluster interactions that can be well described theoretically and confirmed experimentally. SeCuO_3 compound cluster is worth studying because of its elusive simplicity. It is characterized by a wide temperature range of low-dimensional physics, from 8 K when the antiferromagnetic phase arises, to the room temperature at which it still doesn't follow the Curie-Weiss magnetism model. The behavior of a compound over a wide temperature range, from the antiferromagnetic phase to the activation behavior within tetramer spins, will be studied in the scope of this thesis. The Haldane system m-NO2PhBNO is interesting because it is a good candidate for an ideal Haldane chain, given the complete isotropy of the spin. Previous realizations of the Haldane chain of integer spin have a large anisotropy because the spin carrier is an ion of a transition metal group. In contrast, this system is a completely organic compound, where the integer spin is achieved in a molecular electron orbital. In addition, the two critical magnetic fields at which the quantum phase transitions, characteristic of such systems, occur are relatively low, with the upper field at H_c2 ≤ 40 T. We have characterized the phase diagram of the system at low magnetic fields and studied the one-dimensional physics region of the phase diagram described by the Luttinger fluid. In the first chapter of this thesis, Introduction, a brief overview of the magnetism was presented, with special emphasis on low dimensional physics regarding magnetic interactions. Motivation is given for this thesis. In the second chapter, The NMR experiment, overview of the experimental setup is given - the physics of the NMR, electronics and different measurement techniques that were used during the experimental research that is described in this thesis. Design and manufacturing, as well as using the rotator is described in details there. Third and fourth chapters cover experimental research of the tetramer compound SeCuO_3 and Haldane chain system m-NO_2PhBNO, respectively. Structural overview is described at the beginning, followed by theoretical description of expected physics and previous measurements. Main part of these chapters is the presentation of the experimental data generated in the scope of this thesis and its analysis. A vast amount of data was gathered during this doctoral research. The SeCuO_3 was characterized and its orientation determined by the crystallographic X-ray measurements. Phase transition to 3D ordered state was mapped with respect to magnetic field using homemade heat capacity method. Nuclear quadrupolar resonance spectrum was measured in the ordered phase, as well as relaxations. Small magnetic field was used as a perturbation to the quadrupolar Hamiltonian to determine the spin site responsible for the resonance signal. Nuclear magnetic resonance measurements were conducted and line shift was taken. An effort was made to completely understand complicated NMR spectrum, but to no avail at the time of the writing of this thesis. For the m-NO2PhBNO, characterisation and orientation were also done by the crystallographic X-ray. Phase diagram was mapped with homemade heat capacity method at very low temperatures, T < 0.5 K. Nuclear magnetic resonance spectrum was measured, and used to determine the best possible NMR line to conduct relaxation measurements on. Relaxation measurements were conducted at varying magnetic fields and temperatures in the phase region of Luttinger-liquid physics. Fifth chapter is the conclusion and outlook of the entire thesis. Main findings regarding SeCuO_3 are determination of the critical exponent connected to phase transition into anti-ferromagnetic state, lack of the NQR signal for the Cu2 crystal position, determination of the Cu1 crystal position to the visible NQR signal and relaxation and line shift measurements that both provide irrefutable evidence of singlet pairing of the inner tetramer spins, and their activation as the temperature is raised. This activation energy is consistent with spin interaction determined from a non-local methods. For the BoNO compound, a plethora of characterisation methods has been done, including the cooperation with chemistry department and Ruđer Bošković Institute, but also the heat capacity measurement setup made in-house. In the scope of this thesis, Luttinger liquid region of the phase diagram has been studied. It was shown that inside the Luttinger liquid region of the phase diagram the interaction is attractive, as was theoretically predicted for the Haldane chain system. These findings will provide a good basis for the start of measurements at low temperature and high magnetic field facilities, required to fully understand this compound. Additionally, Appendix A contains specifics of the calculations for the eigenvalues and eigenstates for the SeCuO_3 tetramer model.

Istražena su svojstva interagirajućih ultrahladnih bozonskih sustava korištenjem kvantnih Monte Carlo simulacija. Ispitana je suprafluidnost i Bose-Einsteinova kondenzacija vrlo rijetkih dvokomponentnih bozonskih mješavina u ovisnosti o temperaturi. Ovisno o interakcijama, sustav može biti u tri različita režima: miješanom, separiranom u dvije nakupine i separiranom u ljuskastom režimu. Uočena je anizotropnost suprafluidnosti u slučaju separacije u obliku dviju nakupina. Također je uočen i prijelaz pri kojem udio suprafluida postaje manji od udjela Bose- Einsteinovog kondenzata za svaki režim. Nadalje smo istražili svojstva jednodimenzionalnih jakointeragirajućih bozonskih sustava u periodičnim potencijalima. Detaljno je prikazan prijelaz suprafluida u Mottov izolator u režimima robusnog i fragilnog suprafluida. Istražili smo prijelaz iz jednodimenzionalnog u dvodimenzionalni sustav helija-4 unutar nanopore. Analizirali smo skaliranje suprafluidnosti s umnoškom temperature i duljine simulacijske ćelije te slaganje rezultata s teorijskim opisom. Uočen je prijelaz sustava helija-4 iz jednodimenzionalnog u dvodimenzionalni s povećanjem linijske gustoće unutar nanopore radijusa R = 4 Å što je vidljivo u ponašanju korelacijskih funkcija i suprafluidnosti. The properties of interacting ultracold Bose systems were investigated using quantum Monte Carlo simulations. The superfluidity and Bose-Einstein condensation of very dilute two species trapped bosons mixtures as a function of temperature were investigated. Depending on the interactions, the system can be in three different modes: mixed, separated into two blobs, and separated in a shell regime. Anisotropy of superfluidity was observed in the case of two blobs. A transition was also observed in which the superfluidity fraction becomes smaller than the condensate fraction for each regime. We further investigated the properties of one dimensional strongly interacting bosonic systems in periodic potentials. The transition of the superfluid to the Mott insulator phase in the robust and fragile superfluid regimes is shown in detail. We investigated transition from a one-dimensional system to a two-dimensional one of helium-4 in the nanopore. We analyzed the scaling of the helium-4 superfluidity with the product of the temperature and the length of the simulation cell and the agreement of the results with the theoretical predictions. The transition of the helium-4 system from one-dimensional to two-dimensional with an increase in the linear density within the nanopores of radius R = 4 Å was observed, which is visible in the behavior of the correlation function and suprafluidity.