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When different observers match the same color, using the same matching stimuli, it is found that there are slight differences in the amounts that they require to make up a match. The interpretation of color differences plays an important role in some cases, for example in color evaluation during print approval, when the designer has high requirements regarding the accuracy of color reproduction, for medical purposes, in the automotive or other industries. There are several tests for determining who is the best candidate for evaluating colors. One of the most convenient tests is the Farnsworth-Munsell 100 Hue Test. The main disadvantage of this and similar tests is that one can't straightforwardly connect perceptual interpretation of color differences with objective results done with instrumental measurement of color differences. The paper proposed a way to express in ΔE* units the results of testing the subject's sensitivity to color differences, and in that way to determine as precisely as possible the difference in color that an individual subject can perceive in some part of the colored space. By calculating the average value of ΔE* of the respondents for certain parts of the color space, a conclusion can be drawn about the general sensitivity of the respondents to differences in colors.

A series of bimetallic Sn-Pd catalysts were prepared by a template-free two step electrodeposition method. According to this method, Sn was electrodeposited firstly in potentiostatic or galvanostatic regime on Cu electrodes in the form of dendrites, then Pd was galvanostatically electrodeposited in the second step on the electrode with the electrodeposited Sn dendrites. The produced Sn-Pd electrocatalysts were compared with an electrocatalyst obtained by Pd electrodeposition on a bare Cu electrode. The morphological and elemental analysis of Sn-Pd and Pd electrocatalysts was performed by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) techniques. The dendrites of various shapes and degree of branching were obtained by Sn deposition depending on electrodeposition regime, while Pd was electrodeposited in a form of compact Pd islands on both Sn dendrites and the Cu electrode. Cyclic voltammetry (CV) was applied for the electrochemical examination of Sn-Pd and Pd catalysts towards the ethanol oxidation reaction (EOR) in the alkaline solution. The electrocatalyst Sn0.6-Pd0.4 with an atomic ratio of 60 at.% Sn-40 at.% Pd showed higher oxidation efficiency and better tolerance towards intermediate species in EOR than the other examined electrocatalysts . It was shown that the lower fraction of Pd, relative to Sn, was crucial to achieving optimal synergy of Sn with Pd thus contributing to enhanced electrochemical behavior regarding EOR. Серија на биметални катализатори со различни односи на Sn:Pd беа подготвени со методот на двостепена електродепозиција без користење шаблонски протокол. Според овој метод, прво Sn во форма на дендрити беше нанесен електрохемиски во потенциостатски или галваностатски режим врз површината на Cu-електроди. Потоа, во вториот чекор, Pd беше галваностатски нанесен на електродата врз нанесените дендрити од Sn. Вака добиените Sn:Pd-електрокатализатори беа споредени со електрокатализатори добиени со нанесување на Pd на чиста Cu електрода. Морфолошката и елементарната анализа на Sn:Pd и Pd-електрокатализаторите беше направена со помош на скенирачка електронска микроскопија (SEM) и со примена на рендгенска спектроскопија со енергетска дисперзија (EDS). Дендритите со различни форми и различен степен на разгранување беа добиени со нанесување Sn во зависност од режимот на електродепозиција, додека Pd беше нанесен во форма на компактни острови врз дендритите од Pd и Sn на површината на Cu-електродата. Цикличната волтаметрија (CV) беше применета за електрохемиското испитување на Sn:Pd и Pd-катализаторите во од аспект на оксидацијата на етанолот во алкална средина. Eлектрокатализаторот Sn0.6-Pd0,4 со атомски однос од 60 % Sn и 40 % Pd покажа поголема ефикасност на оксидација и поголема толеранција во однос на интермедијарните супстрати отколку другите испитани електрокатализатори. Се покажа дека помал удел на Pd во однос на Sn е еден од клучните фактори за обезбедување оптимална синергија на Sn со Pd, при што на овој начин беше забележана зголемена електрохемиска активност односно оксидацијата на етанолот.

In this study, Sn powders were electrodeposited from an alkaline electrolyte containing 20 g/l SnCl2 × 2H2O in 250 g/l NaOH at the room temperature by application of both potentiostatic and galvanostatic regimes of the electrolysis. Electrodeposition was performed at various cathodic potentials (−1185, – 1200, −1270, – 1400, – 1600 and – 1800 mV vs. Ag/AgCl), and at a current density outside the plateau of the limiting diffusion current density (−3.0 mA cm-2). Morphology of Sn particles is characterized by scanning electron microscope (SEM) and crystal structure by X-ray diffraction (XRD). Second International Conference on Electron Microscopy of Nanostructures ELMINA 2022, August 22nd-26th, 2022, Belgrade, Serbia.

Introduction: Bronchiolitis is an acute viral disease of lower respitatory pathways in children under 2 years of age. It is manifested by coughing, whistling and refusing food intake. The most common cause of bronchiolitis is a respiratory syncytial virus. Vitamin D is a steroid hormone which is synthesized in the skin after sun exposure or food intake. With discovery of Vitamin D receptors and hydroxylated enzymes in immune cells, a potential role for Vitamin D in maintaining immune homeostasis was seen. It has been established that Vitamin D induces a change of the antimicrobial polypeptide, cathelicidin, which has both antibacterial and antiviral roles. Objective: Determine whether the serum Vitamin D levels in acute viral bronchiolitis patients from Central Kosovo is lowered. Methods: This prospective study included 34 children aged up to 2 years, that have been diagnosed with the heavy form of acute viral bronchiolitis. Blood was drawn from all subjects to analyze serum Vitamin D levels. Results:Average levels of Vitamin D, measured in all subjects, was 35.5 ng/ml. After Vitamin D levels stratification, 62% of the subjects had normal levels of serum Vitamin D, while 38% of the subjects had lower levels of serum Vitamin D. 15% of children had lower levels than 20 ng/ml. With children of ages up to 12 months there was a statistical significance of negative direction between Vitamin D serum levels and body height (r=-0.683, p=0.010) and between Vitamin D serum levels and body weight (r=-0.725, p=0.005). With children of ages up to 24 months there was only a statistical significance of negative direction between Vitamin D levels and body height (r=-0.540, p=0.011). Conclusion: Our research confirmed that children with acute viral bronchiolitis have a significant deficiency of Vitamin D, although it's a required addition to nutrition for children under the age of 2 years.

Comparative analysis of morphological and structural features of copper dendrites obtained by potentiostatic and galvanostatic regimes of electrolysis was made. The 3D (three dimensional) pine-like dendrites composed from stalk and corncob-like forms as branches, with the sharp tips of both stalk and branches, were obtained by the potentiostatic regime of electrolysis with all analyzed amounts of passed electricity. On the other hand, with increasing the amount of the passed electricity the shape of 3D pine-line dendrites obtained by the galvanostatic regime of electrolysis changed than those with the sharp tips of stalk and branches to those which the tips finished globules. Comparing with Cu deposits obtained at overpotentials which belonged to different types of electrodeposition control, it is concluded that overpotential at the end of passed amount of the electricity plays crucial role in the final shape of galvanostatically produced Cu dendrites. Irrespective of the shape of Cu dendrites, crystallites of copper were random oriented in the both types of dendrites. Napravljena je uporedna analiza morfoloških i strukturnih karakteristika dendrita bakra dobijenih potenciostatskim i galvanostatskim režimima elektrolize. Trodimenzionalni (3D) dendriti nalik stablu bora izgrađeni od stabla i grana koje nalikuju klipovima kukuruza, sa oštrim vrhovima, su bili dobijeni potenciostatskim režimom elektrolize sa svim analiziranim količinama propuštenog naelektrisanja. Na drugoj strani, sa povećanjem količine propuštenog naelektrisanja oblik 3D dendrita dobijenih galvanostatskim režimom elektrolize se menjao od onih sa oštrim vrhovima i stalka i grana do onih čiji vrhovi su se završavali globulama. Poređenjem sa talozima bakra dobijenim na prenapetostima koje su pripadale različitim tipovima kontrole procesa elektrohemijskog taloženja, zaključeno je da prenapetost na kraju propuštene količine naelektrisanja igra presudnu ulogu u krajnjem obliku galvanostatski proizvedenih Cu dendrita. Bez obzira na oblik Cu dendrita, kristaliti bakra su bili slučajno orijentisani u oba tipa dendrita. XII YuCorr International Conference, September 13-16, 2021, Tara Mountain, Serbia, [http://sitzam.org.rs/YUCORR/]

Starting from the problems of bias and validation in combining different research methods and methodologies, the paper discusses the advantages and shortcomings of triangulation. The triangulation concept which involves the use of more than one method to obtain records from more than one source is critically analyzed, and particularly the justification of defining the goal of triangulation as a process that is used to better understand social phenomena by looking at them from more than one perspective. The author points out the importance of the awareness that triangulation does not necessarily lead to an attempt to support the findings, taking into account the four concepts: triangulation as validation check, continuous triangulation, triangulation as a search for the completeness of information/image and triangulation as epistemological dialogue. To solve the problem of the corresponding metaphor and analogy with the original meaning of triangulation, the author suggests an anamorphic paradigm: different methods are combined as a product of different theoretical traditions, and their combination can add depth and scope, but not accuracy; a clearer picture (and this is only possible to achieve, not accuracy) is obtained by choosing the appropriate perspective, angle, and point of view.

Lead and nickel powder particles were produced by the processes of electrolysis and characterized by scanning electron microscope (SEM). The X-ray diffraction (XRD) analysis of the produced particles was done. Morphologies of Pb and Ni particles were correlated with their crystal structure at the semi quantitative level by determination of 'Texture Coefficients' (TC) and 'Relative Texture Coefficient' (RTC). The two dimensional (2D) dendritic particles of lead of different degree of ramification were obtained by the potentiostatic regime of electrolysis from the nitrate, acetate and hydroxide electrolyte. The spongy-like particles of nickel constructed from holes formed of the detached hydrogen bubbles and surrounded by cauliflower-like agglomerates of approximately spherical grains (the honeycomb-like structure) were obtained by the galvanostatic regime of electrolysis from the chloride electrolyte. Although crystallites were dominantly oriented in the (111) plane in both Pb and Ni particles, analysis of the XRD data showed different preferred orientation of the formed particles. All types of Pb dendritic particles showed the strong (111) preferred orientation, while crystallites of Ni in the spongy-like particles were almost random oriented. The obtained results were discussed following Winand's classification of metals on the normal, intermediate and inert metals based on their values of the exchange current density, melting point and overpotential for hydrogen evolution reaction. Čestice praha olova i nikla proizvedene su procesima elektrolize i okarakterisane skenirajućim elektronskim mikroskopom. Urađena je i rendgeno-strukturna analiza dobijenih čestica. Morfologije čestica olova i nikla su korelisane sa njihovom kristalnom strukturom na polukvantitativnom nivou određivanjem 'Teksturnog koeficijenta' (TC) i 'Relativnog teksturnog koeficijenta' (RTC). Dvodimen- zionalne (2D) dendritične čestice olova različitog stepena razgranatosti dobijene su potenciostatskim režimom elektrolize iz nitratnog, acetatnog i hidroksilnog elektrolita. Čestice nikla sunđerastog oblika u čijoj strukturi se uočavaju rupe formirane odvajanjem mehurova vodonika okružene karfiolastim aglomeratima približno sferičnih zrna (struktura pčelinjeg saća) dobijene su galvanostatskim režimom elektrolize iz hloridnog elektrolita. Premda su kristaliti dominantno orijentisani u (111) ravni i u česticama praha olova i nikla, analiza rendgenograma je pokazala njihove različite dominantne orijentacije. Svi tipovi olovnih dendritičnih čestica su pokazali strogu (111) dominantnu orijentaciju, dok kristaliti nikla u sunđerastim česticama su bili skoro slučajno orijentisani. Dobijeni rezultati su diskuto- vani sledeći Vinjadovu klasifikaciju metala na normalne, intermedijalne i inertne, zasnovane na njihovim vrednostima gustine struje izmene, tačke topljenja i prenapetosti za reakciju izdvajanja vodonika.

Lead and nickel powder particles were produced by the processes of electrolysis and characterized by scanning electron microscope (SEM). The X-ray diffraction (XRD) analysis of the produced particles was done. Morphologies of Pb and Ni particles were correlated with their crystal structure at the semi quantitative level by determination of 'Texture Coefficients' (TC) and 'Relative Texture Coefficient' (RTC). The two dimensional (2D) dendritic particles of lead of different degree of ramification were obtained by the potentiostatic regime of electrolysis from the nitrate, acetate and hydroxide electrolyte. The spongy-like particles of nickel constructed from holes formed of the detached hydrogen bubbles and surrounded by cauliflower-like agglomerates of approximately spherical grains (the honeycomb-like structure) were obtained by the galvanostatic regime of electrolysis from the chloride electrolyte. Although crystallites were dominantly oriented in the (111) plane in both Pb and Ni particles, analysis of the XRD data showed different preferred orientation of the formed particles. All types of Pb dendritic particles showed the strong (111) preferred orientation, while crystallites of Ni in the spongy-like particles were almost random oriented. The obtained results were discussed following Winand's classification of metals on the normal, intermediate and inert metals based on their values of the exchange current density, melting point and overpotential for hydrogen evolution reaction.

in many historical and comparative overviews of the works, in which there is an analytical discussion of the dominant pedagogical theories in the twentieth century, John Dewey (Dewey, 1933) is referred to as the founder and creator of the concept of reflection (reflective thought and knowledge) in practice. Reflection as a concept is understood as the forms and the form of problem solving, as well as continuously thinking about the causes of problems in situations in situ, including active and systematically and consistently changing connecting ideas with solutions to the problems and situations that preceded them (Hatton & Smith, 1995). Reflective thinking is the most general level to tackle practical problems, allowing the ''recommended'' doubts and confusion before proposing possible solutions to the problem. Dewey wrote about a reflective action which refers to the use of solutions to the problem and to thinking through the course of the action. in later works of the authors who have dealt with this problem, an unambiguous link can be observed between the so-called ''professional'' action and the reflection on action which, in this cyclical relationship, leads to visible changes (Zeichner & Gore, 1984). Already at first glance, this implies a connection with experiential learning and adult position of observation and reflection in various models of experiential learning, which will be discussed later. it would be useful to compare this method with a cyclic action of routine as an expression of impulse, tradition and authority. Reflective action, as opposed to the routine, is a consistently and carefully thought-out action (practice reflection), which is an ''awakened'' knowledge and belief, and that is an expression of openness, accountability and commitment. We are ready for reflection, says Schon, when the ''knowledge-in-action'' - a kind of knowledge that professionals notice when it is acted spontaneously - occurs suddenly and unintentionally (Schon, 1987). This presents, almost unexpectedly and suddenly, two types of reflection (1) reflection on action which occurs during the action interrupting and interfering with it, and (2) reflections in action which appears in the action as well as in the disruption and interruption, so that we think about her and about how to reshape the action that takes place in the moments of reflection. The idea of reflective practitioners (educators, adult educators, sociologists, etc.), or a practitioner who thinks about his/her own practice and the practice of reflection draws on its theoretical origins that Schon develops almost like an original idea that became well-known. He assumes that the practice of practical activities (such as teaching, instruction, therapeutic work of doctors or therapists) constitutes an original and very specific epistemology. Contrary to the dominant technical rationality that underpins modern professional education, Schon believes that professional knowledge and competence includes the effect of successful practitioners (educators, adult educators, teachers, etc.), especially in reflection-in-action (''reflection of what we do while doing'') (Schon, 1986), which appears in problem situations. Hence, the practical education of the profession, according to the author, necessarily follows the model of learning by doing a particular kind of apprenticeship modelled on the training of musicians, artists and drama artists. In his second book (The Reflective Practitioner), Schon develops reflective practicum and confronts it with a dominant, normative curriculum, which constitutes the basis of theoretical knowledge to solve practical, instrumental problems. Practice, however, that is often characterized by uncertainty in this case does not become one solution, but the solution depends on the choice of the value of paragraph, depending on what aspect of the situation we pay more attention to. Schon distinguishes knowledge in action, what implicit knowledge is contained in intelligent actions that are difficult to explicate verbally, and theory of action, an attempt to describe the tacit knowledge based on observation and reflection (reflection). While knowledge is a dynamic action, the theories of action (descriptions of the operation and the strategies they use, rules, values and assumptions which we hold) are always a static structure. They are practical checks that are back in action. These checks are nothing but an evaluation of our theory and action based on the action, and self-evaluation practitioners. It is believed that only in an ironic sense and not as a pedeutological truism active and dynamic teaching situation can be treated as a non-susceptible reflective thinking of teachers. Advocates of this view argue that this is so because the teacher is in the midst of an activity, and cannot make a ' 'step back' ' nor the first rationalization of the various alternative courses of action in the immediate moment, but he then reflects on the consequences of the different alternatives. And even though he thinks very carefully about how to act in each moment and the situation that continues, he eventually has to admit to himself that he must determine on something that he does or does not do. Thus, a teacher who works is in a way still a dogmatist who can think of a rich range of possible actions and activities, while it may seem that he can do only one thing at a time. Proponents of this concept of critical reflexivity used to broad explanations of his criticism that are often based on a single act of the court action, which may not always be the argument of generalization. Notwithstanding the aforementioned arguments, finding that the teacher is an active teaching situation that is too busy to think reflectively, it does not mean that the teaching sentenced to life is a blind impulsivity and a conduct routine. Teachers feel that they can continue to operate keenly and dedicatedly. When you are in the classroom, good teachers act ''knowingly'' and often with a direct review or self­insight. As teachers, we are often like them in a position to find ourselves (beat out) in a situation that bites ''language''. On the other occasions, the situation and context tell us in which direction and how to act. Reflective thinking and actions of the teacher's centred and insufficiently treated pedeutological term should demand phenomenological, philosophical, conceptual and empirical research. in this short essay on reflective practicum teachers restrict to just thinking about distinctive phenomenological attitude and the importance of teaching practice as a reflective action. We may ask where and how does reflection affect pedagogical reality? is it in a way that reflectivity can be achieved through experience? How does this differ from conceptualizations that were made in literature? What kind of reflection and conscious and meaningful action can be achieved in the classroom? What are the forms of knowledge and skills that inform and constitute the practice? We know ad nauseam that beginning teachers (sometimes occurs and marks the induction of teachers) typically face a number of problems in the interactive reality of teaching. We will present, at the beginning, the ideal situation: thoroughly prepared new teachers, an expert in the field of science that teaches, successfully defeating the theory of developmental psychological characteristics of students working with them etc., an expert who becomes a connoisseur equipped with knowledge about successful models of teaching and school management, someone who successfully combines the practical and theoretical skills acquired in the training of team cooperation and through learning the exercises in observation of teaching, acquires and begins to develop a critical understanding of the philosophical, political and professional implications and issues of professional practice. Finally, regardless of the lack of experience, the teacher is willing to consciously and conscientiously "lead" students through innovative, well-structured, streamlined lectures and lessons. it is not unusual that, despite the excellent preparation, new teachers still do well in the conflict and confusion of the reality in the classroom: he is now "face to face" with students, faced with the risk of no illusions and self-delusion, and with all plans and no anticipation fit to the new reality. And somehow, by some chance, not all the hard-earned knowledge in the subject areas of science and teaching, teaching skills, teaching, and educational theory and knowledge of the characteristics of the curriculum are fulfilled nor they live the reality of the teaching situation.

The one of the main contributions of Belgrade Electrochemical School to the field of metal electrodeposition is investigation of a mechanism of formation and growth of the disperse deposits. Spongy-like, cauliflower-like, needle-like, carrot-like, dendrites of various shapes, etc. are the typical disperse forms obtained by the electrodeposition processes. From the electrochemical point of view, a dendrite, as the most significant disperse form, is defined as an electrode surface protrusion that grow under activation or mixed control, while deposition to the flat part of the electrode surface is under complete diffusion control. In this paper, all electrochemical aspects concerning mechanism of formation and growth of dendrites are reviewed. Jedan od glavnih doprinosa Beogradske elektrohemijske škole u polju elektrohemijskog taloženja metala je istraživanje mehanizma formiranja i rasta disperznih taloga. Sunđerasti, karfiolasti, nalik iglama i šargarepi, dendriti različitog oblika, itd. su tipične disperzne forme dobijene procesima elektrohemijskog taloženja metala. Sa elektrohemijske tačke gledišta, dendrit, kao najznačajnija disperzna forma, je definisan kao izbočina na elektrodnoj površini koja raste pod aktivacionom ili mešovitom kontrolom, dok je taloženje na ravnom delu elektrodne površine pod punom difuzionom kontrolom. U ovom radu prikazani su svi elektrohemijski aspekti koji se odnose na mehanizam formiranja i rasta dendrita.

The most of the air pollution originates from combustion processes, so it is important to make quantitative as well as qualitative analysis, as the sources of pollution can be stochastic - especially the road traffic. The goal of the study is to determine closer road traffic as one of the major sources of the pollution in the city of Niš. The analysis was performed on the vehicle fleet composition and the estimation of the annual mileage on the city territory. These data were used as the input for the COPERT methodology of air pollutant emissions calculation from road transport. Based on these data, annual emissions of CO2 and major pollutants were calculated, as well as the specific average emissions on roads.

This paper discusses the problem dialogicity in pedagogical relationship, the complex nature of stroke in pedagogical situations and atmosphere as well as space in which the active and specific pedagogical relationship develops. Status of pedagogical trueism, selfexpleined paradigms that do not need to explain and operationalize, the above phenomena are not justified deserved. Author has tried to depict the contours, offering a general overview of the issues pedagogical relationship as a phenomenon dialogicity. Tact and atmosphere here appear to be essential and intertwined phenomena. This is a unique, unpredictable and complex phenomena of the pedagogical relationship, almost beyond the reach of science, through which we can understand the educational situation in their immediate and full quality and capacity. Realized in the ability of teachers to 'read' pedagogical situation hic et nunc, the pedagogical skills-based activities that depend on the perspective of meaning that emerge from each situation and re-appear in it.

The author present, in chronological and distinctive review and comparative analysis, some of most important researchers of social pedagogy. Although on the margin of historical picture, in literature which lightens the strength of social pedagogy in its heights the author presents thoughts and ideas of Adolf Disterveg, Karl Mager and Paul Nathorp. Some attention and place was made for distinction of Paul Nathorp, neglected author and researcher of social pedagogy. His thoughts about relation between education, learning and community, step- -by-step learning community, basic function of social life fundamental levels of social activity and social pedagogical idea of state are specially highlighted. Review of contemporary influences of social pedagogy on science of education in 20. century shows valid arguments for statements that scientific imperialism is not the only reason for justification of interdisciplinary approach of phenomena which science interprets and explains.

The modern and rapidly developing paper and board industry requires more efficient agents for the surface of paper in order to improve the mechanical properties. The starch coating used for the reinforcement of schrenz (110g/m(2)) contained ultrasonicated nanoparticles of the mineral sepiolite. The viscosity of starch dispersions modified with different concentration of sepiolite was followed at the temperature of the coating on schrenz. The values of the breaking length, bursting strength and CMT-strength of the paper reinforced with modified starch were increased by up to 20%. The viscoelastic properties as storage modulus were increased, too. Scanning electron microscopy of the samples showed deagglomeration and homogeneity of the sepiolite nanoparticles.

The appearance of Moiré pattern can significantly affect the quality of offset reproduction. It is formed by superimposingof fine details of two or more structures.It appears in printing when: screen structures are misaligned because of misregistration (it is very difficult to predict it, because it is not visible on the proof), inappropriate combination of screen frequency and screen angles is used, an original halftone that contains patterned objects is scanned and exposed or when fine details of continuous tone original are superimposed whit input frequency of scanner or with CCD element structure of digital camera. The aim of this work is to investigate the influence of reproduction parameters, such as screen frequency, imaging resolution, register accuracy or input bit-map resolution to appearance of Moiré pattern. Tests will be done on a limited number of combinations of screen frequencies and input resolutions. The test result will be recommendations, which parameters combination should be avoided and which to use so that Moiré pattern could be minimized on the final printing product. Key words: Moiré, quality, reproduction, screening

U kompjuterskoj pripremi za štampanje važi preporuka da rezolucija bit mape za kvalitetnu reprodukciju treba da bude oko dva puta veća od linijature rastera kojim će se štampati, ukoliko se reprodukuje u izvornoj veličini. Često se dešava da operater pripreme nema na raspolaganju bit mapu odgovarajuće rezolucije, ili da se iz tehnoloških razloga nemoţe štampati rasterom visoke linijature. U ovom radu je tehnikom tabačne ofset štampe načinjeno više odštampanih uzoraka sa različitim kombinacijama rezolucije bit mape i linijature rastera kojim je štampano. Uzorci su ispitani objektivnom metodom - spektrofotometrijskim merenjem, i subjektivnom metodom - anketiranjem grupe posmatrača, u cilju utvrđivanja uticaja rezolucije i linijature na kvalitet reprodukcije, i utvrđivanja graničnih uslova koji daju još uvek prihvatljiv kvalitet reprodukcije za prosečnog posmatrača. Deo uzoraka je reprodukovan iz tif fajlova, a deo iz jpg, da bi se ispitalo da li prosečan posmatrač može da uoči razliku u kvalitetu. Ključne reči: kvalitet otiska, reprodukcija, linijatura, rezolucija

Fast social–political and economic changes European societies have been faced with in the last few decades have had a significant influence on educational changes, highlighting the needs for the reform of educational systems and their adapting to the new needs of economy and society. For this reason, more attention is paid to the issues of reform processes regarding the area of secondary vocational education in professional literature. Such practice is being conditioned by the fact that modernization of this important segment of educational system, having in mind its direct connection to economy and business world, presents a crucial assumption of an overall social and economic development of every country. For the reasons mentioned above, this paper deals with problems in the reform of vocational education in Serbia, and vocational education is being discussed from the context of economic growth and society development. The aim of this paper is to point out the importance of economic value of education as well as importance of investments in human resources. Theoretical elaboration and set tasks have forced the use of descriptive, comparative-historic and analytical-synthetic method, as well as the use of content analysis. Analysis results, however, indicate that even though today’s education economic value of education is undisputed, educational system in our country still faces a multitude of problems and challenges posed by modern society., Review Article

Lead electrodeposition processes from basic (nitrate) and complex (acetate) electrolytes were mutually compared by scanning electron microscopy and X-ray diffraction investigation of the produced powder particles. The shape of dendritic particles strongly depended on the type of electrolyte. Dendrites composed of a stalk and weakly developed primary branches (the primary type) were predominantly formed from the basic electrolyte. Ramified dendrites composed of a stalk and of both primary and secondary branches (the secondary type) were mainly formed from the complex electrolyte. In both types of powder particles, Pb crystallites were predominantly oriented in the (111) plane. The formation of powder particles of different shapes with strong (111) preferred orientation is discussed and explained by consideration of the general characteristics of the growth of crystals in electrocrystallization processes. Procesi elektrohemijskog taloženja olova iz osnovnog (nitratnog) i kompleksnog (acetatnog) elektrolita su bili međusobno upoređeni tehnikom skenirajuće elektronske mikroskopije i rendgensko-difrakcionom analizom proizvedenih čestica praha. Oblik dendritičnih čestica je snažno zavisio od tipa elektrolita. Dendriti sastavljeni od stabla i slabo razvijenih grana (primarni tip) su bili predominantno formirani iz osnovnog elektrolita. Razgranati dendriti sastavljeni od stabla i od primarnih i sekundarnih grana (sekundarni tip) su bili uglavnom formirani iz kompleksnog elektrolita. U oba tipa praškastih čestica kristaliti olova su bili dominantno orijentisani u (111) ravni. Formiranje praškastih čestica sa strogom (111) orijentacijom je bilo diskutovano i objašnjeno razmatranjem opštih karakteristika rasta kristala u procesima elektrokristalizacije.

The wetting solution plays significant role in offset printing process, helping in separation of printing from non-printing areas of the printing form. The wetting solution is characterized by the share of isopropyl alcohol, pH value, electrical conductivity, temperature and water hardness, which is a direct consequence of the presence of various salts in water. It is proved that setting the optimal total hardness of water, which is recommended to be kept from 8od to 12od of German hardness, could extend the service life of metal components and machine parts in contact with the wetting solution, because of reduced corrosion and lime scale sedimentation. It also extends the life of the rubber rollers in contact with the wetting solution. However, there is an issue of particular owner’s and management’s interest: would they get prints of higher quality if they install system for regulation of the water hardness? In this paper an attempt was made to determine the correlation between the total hardness of water and some characteristics of print quality (tone value increase, range of reproduced tonal values, maximum screen ruling at which it is possible to get a clear image without defects). In the experimental part a single color sheet fed offset printing machine will be used, on which all printing conditions will be kept constant, except the hardness of water to be used in the wetting solution. Soft, medium hard and hard water will be used. Key words: wetting solution, water hardness, print quality

In this study, electrodeposition of silver from nitrate solution at the high overpotentials was analyzed. Morphologies of silver deposits obtained at the different overpotentials and with the different electrodeposition times were examined using the technique of scanning electron microscopy (SEM). The different disperse morphological forms, such as granules, needle-like and spongy-dendritic ones were formed during silver electrodeposition from this solution. The size of granules decreased and their number increased with the increase of overpotential of electrodeposition. With the increasing overpotential, the induction time for the appearance of spongy-dendritic forms decreased with a tendency to increase their ramification. Mathematic model describing the mechanism of metal electrodeposition at the high overpotentials is proposed and discussed on the basis of the obtained silver surface morphology.

Savremena štamparija srednje veličine, koja kao osnovni postupak koristi tabačnu ofset štampu, danas mora da odgovori brojnim izazovima: tiraži se smanjuju, ali se povećavaju zahtevi klijenata u pogledu nivoa kvaliteta otiska ; zahtevi klijenata su sve veći i veći, ali sa druge strane, tržište diktira sve niže cene ; s obzirom da su tiraži sve manji, neophodno je skratiti trajanje pripreme fajlova za štampanje i trajanje podešavanja mašine za štampanje tiraža, da bi se povećao broj naloga koji se može odštampati u smeni ; došlo je do potpune demokratizacije pripreme za štampu, i štamparije sve češće od svojih klijenata dobijaju fajlove koji su, navodno, spremni za osvetljavanje, a u stvari u sebi sadrže elemente koji su potencijalno problemati ni za reprodukciju u ofsetu. Jedan od pristupa koji može da pomogne štampariji da uspešno odgovori na pomenute zahteve jeste uvođenje automatizacije u proces reprodukcije. Automatizovati se mogu mnogi delovi u procesu reprodukcije, među kojima su: pregled i korigovanje dobijenih fajlova, impozicija, podešavanje nanosa boje po zonama na štamparskoj mašini tokom podešavanja mašine za štampanje novog tiraža, kontrola i regulacija nanosa boje tokom štampanja tiraža i pretpodešavanje doradnih mašina. U ovom radu biće dat pregled mogućnosti automatizacije postojećeg radnog toka u jednoj tipičnoj štampariji koja kao osnovni postupak koristi tabačni ofset i proizvodi uglavnom razli ite akcidenične grafičke proizvode. Posebno će biti prikazani postupak i ostvareni efekti automatizacije podešavanja nanosa boje u fazi podešavanja mašine za štampanje novog tiraža, i kontrolisanja i regulacije nanosa boje tokom štampanja tiraža na tabačnoj štamparskoj mašini za ofset štampu. Ključne reči: Savremena štamparija, tabačni ofset, zahtevi, automatizacija, radni tok.

An approach based on the equations of electrochemical kinetics for the estimation of the current density distribution in electrochemical cells is presented. This approach was employed for a theoretical explanation of the phenomena of the edge and corner effects. The effects of the geometry of the system, the kinetic parameters of the cathode reactions and the resistivity of the solution are also discussed. A procedure for a complete analysis of the current distribution in electrochemical cells is presented. Prikazan je sažeti pregled ranijih rezultata i predstavljen je poboljšan pristup proceni raspodele struje u elektrohemijskim ćelijama. Ovaj pristup, zasnovan na jednačinama elektrohemijske kinetike, upotrebljen je za teorijsko objašnjenje ivičnih i ugaonih efekata. Takođe su diskutovani uticaji geometrije sistema, kinetičkih parametara katodnih reakcija i otpornosti rastvora. Predstavljena je procedura za kompletnu analizu raspodele struje u elektrohemijskim ćelijama.

Using the cyclic voltammetry, it has been shown that hydrogen evolution at a gold electrode is necessary in the electrochemical activation of azithromycin dihydrate and erythromycin A. After four hours of the potential holding at -1.2 V vs. SCE, the pH of the electrolyte has been changed from 8.40 to 8.96; from 8.40 to 8.77 in the presence of erythromycin A, and from 8.40 to 9.18 in the presence of azithromycin, indicating the reaction of the hydrogen species with antibiotics. This effect has been confirmed by using the phenolphthalein indicator and by analysing colours of the solutions by UV-Vis, as well as by FTIR spectroscopy. Under the identical experimental conditions at the gold electrode, in contrast to azithromycin dihydrate and erythromycin A, roxithromycin and midecamycin electroactivity promotion has been obtained during the first forward sweep starting from the area of a double layer region. Metodom ciklične voltametrije je pokazano da je izdvajanje vodonika na elektrodi od zlata neophodno za elektrohemijsku aktivaciju azitromicin-dihidrata i eritromicina A. Četiri sata držanja potencijala na vrednosti 1,2 V vs. SCE je rezultovalo u promeni pH elektrolita sa 8,40 na 8,96; sa 8,40 na 8,77 u prisustvu eritromicina A, i sa 8,40 na 9,18 u prisustvu azitromicina, ukazujući na reakciju čestica izdvojenog vodonika sa antibioticima. Efekat je potvrđen upotrebom fenolftalein indikatora i analizom boje elektrolita UV-Vis spektroskopijom, a molekula antibiotika FTIR spektroskopijom. Pod istim eksperimentalnim uslovima na elektrodi od zlata, u suprotnosti sa ponašanjem azitromicin-dihidrata i eritromicina A, elektroaktivnost roksitromicina i midekamicina je uočena počevši od oblasti formiranja dvojnog sloja, tj. bez ikakvog učešća čestica izdvojenog vodonika.

The effect of the concentration of the reacting ion on the nature of the control of the electrodeposition process was investigated by digital simulation of the polarization curve using the Newman form of the polarization curve equation and the Levich dependence of the limiting diffusion current density under natural convection conditions. A simple method for the determination of the exchange current density from polarization measurements is also proposed. The agreement with experiments was correct. U radu je ispitivan uticaj koncentracije reagujućeg jona na vrstu kontrole procesa elektrohemijskog taloženja. Primenjena je digitalna simulacija polarizacionih krivih na osnovu Newman-ovog oblika jednačine polarizacione krive i Levich-eve zavisnosti granične difuzione gustine struje u uslovima prirodne konvekcije. Predložen je jednostavan metod određivanja gustine struje izmene na osnovu polarizacionih merenja. Dobijena je zadovoljavajuća saglasnost sa eksperimentalno dobijenim vrednostima.

Digital simulation was employed for the solution of the general polarization curve equation of metal deposition processes. By approximating the dependence of the exchange current density on concentration with a linear function for one- and two-electron transfer processes, an error lower than 20% was obtained. Za rešavanje jednačine opšte polarizacione krive za proces taloženja metala primenjena je digitalna simulacija. Aproksimirajući zavisnost gustine struje izmene od koncentracije linearnom funkcijom, za procese sa jednoelektronskim i dvoelektronskim transferom dobijena je relativna greška koja ne prelazi 20%.

У расправама теоретичара из различитих научних области, тема интерпретације визуелног идентитета на новцу све је присутнија. Међу економистима и стручњацима из сродних дисциплина, наглашава се међусобни однос између културе, друштава и економије – „непоправљиво испреплетених неодвојивих области“–. Поједине представе на анализираним ликовним решењима, касније и на оптицајном новцу су истовремено допринеле изградњи перцепције становништва у различитим државним трансформацијама у Србији. Помирење дуалне природе новца тежак је задатак који захтева даља питања у вези са фундаменталним значењем новца. Које су се то поруке преносиле путем папирног и кованог новца и у којим је друштвено – економским праксама он циркулисао? Пропаганда ових симбола, кроз разне жанрове илуструје и конзервативну природу „монетарне културе“, што није велико изненађење, али указује и на начине на које је иконографија папирног и кованог новца учествовала у визуелној конструкцији и јачању друштвених идентитета и сврставњу Србије у Европске и светске токове. Дискусија о формирању „монетарне културе“, а уједно и њене безбедносне улоге, начину на који се креира, прво на ликовним решењима за новчанице, затим и на издатом новцу у истраженом периоду од 1868-2018, заснива се на њиховој усклађености и једнакости. Активности по питању обликовања, израде и борбе против фалсификовања новца у Србији су биле веома интензивне и оне представљају један од предмета истраживања у овом раду. У обновљеној Кнежевини Србији, затим, Краљевини Србији у оптицају је био страни новац све до 1868. године, када се појављује први бакарни српски новац кнеза Михаила Обреновића. Сребрни новац уведен је 1875, а златни 1879. године за време Милана Обреновића. Готово све стране монете (43 врсте) фалсификовале су се одмах по пуштању у оптицај. У Кнежевини Србији, у настојању да се оствари контрола технолошког поступка израде националне монете и истовремено спречи фалсификовање новца свих врста и порекла, именовани су „испитивачи руда и фаличног новца“, хемичар Михајло Рашковић, Сима Лозанић и касније Марко Леко од 1884. до 1920. године. Од оснивања Привилеговане народне банке Краљевине Србије (1884) у оптицају је и српски новац – валута динар. Посебно се истичу периоди када је Банка била, у својим почецима и раној фази, везана за стручњаке и гравере Banque de France и Banque nationale de Belgique. Временом је Народна Банка, мудрим укључивањем српских и југословенских научника и уметника успела да оствари визуелну самосталност и изразитост визуелног идентитета, који одражава и континуитет и данас. Томе је свакако допринело укључивање највећих стручњака за ликовну уметност у Управни одбор и Комисију за сарадњу са уметницима Народне банке – Михаила Валтровића, Уроша Предића, Ђорђа Ђоке Јовановића и Паје Јовановића, Рудолфа Арчибалда Рајса, Младена Јосића, Васе Поморишца и других, који су путем позива или конкурса укључили плејаду уметника и научника у рад за ликовна решења, а затим за оптицајни новац. У процесу развоја токова визуелног идентитета на новцу може се издвојити шест периода: крај XIX века и почетак XX века, период између два рата, период после Другог светског рата, период Социјалистичке изградње, Распад II Југославије и период од 2003. до 2018. године. У процесу развоја токова у оквиру визуелног идентитета, прати се хронолошки след догађаја у оквиру надлежности и функција Народне банке. Анализирана идејна решења за новчанице потичу из збирке Народне Банке Србије, односно из Завода за израду новчаница и кованог новца у Топчидеру. У овом раду се сагледавају уметничко-технолошки аспекти и токови развоја визуелног идентитета у служби заштите новца од фалсификовања. viii Поред тога, развој науке и технологије омогућавао је примену савременијих поступака производње и унапређење система заштите новца, а истовремено и веће техничко-технолошке могућности за израду фалсификата. У другом делу овог рада представљен је потенцијал примене Оптичке микроскопије и Раманове спектроскопије као недеструктивних форензичких метода у анализи историјских и оптицајних новчаница. Циљ истраживања јесте доказати да су Оптичка микроскопија и Раманова спектроскопија успешно примењиве у анализи новчаница. Утврђене су сигурносне технике штампе и сигурносни елементи у оквиру уобличавања визуелног идентитета, односно монетарне културе. Експериментални део рада извршен је на историјским новчаницама које су издате у периоду од 1893. до 2018. године. In discussions of theoreticians from various scientific fields, the issue of interpretation of visual identity on money is increasingly present. Economists and experts from similar disciplines are underlining the mutual relation between culture, societies and economy – “irreparably intertwined areas”–. Some illustrations on analysed design solutions, and later on circulating money, also helped build the perception of residents in various state transformations in Serbia. To reconcile the dual nature of money is a difficult task that requires further questions into the fundamental meaning of money. What are the messages that were conveyed by way of paper banknotes and coins, and in which socio-economic practices did such money circulate? The propaganda of these symbols through various genres also illustrates a conservative nature of the “monetary culture”, which is no big surprise, but it does indicate the ways in which the iconography of banknotes and coins participated in the visual construction and strengthening of social identities, and helped make Serbia part of European and global trends. The discussion about the formation of a “monetary culture”, and at the same time its security role, the manner of creation, first in artistic design solutions for banknotes and then on issued money in the researched period 1868–2018, is based on their harmonisation and equivalency. Activities in terms of shaping, producing and fighting against counterfeit money in Serbia were very intensive and are one of the topics of research in this paper. In the renewed Principality of Serbia, and later the Kingdom of Serbia, foreign money was in circulation until 1868, when the first copper Serbian money of Prince Mihailo Obrenović appeared. Silver money was introduced in 1875, and gold in 1879, during Milan Obrenović. Counterfeits of almost all foreign legal tenders (43 kinds) appeared immediately after money was released into circulation. In the Principality of Serbia, in an effort to establish control of the technological process of manufacturing a national legal tender and simultaneously prevent counterfeits of money of all kinds and origins, “examiners of ores and flawed money” were appointed – chemist Mihajlo Rašković, Sima Lozanić and later Marko Leko, from 1884 until 1920. Since the establishment of the Privileged National Bank of the Kingdom of Serbia (1884), Serbian money has also been in circulation – the dinar. Of particular significance are periods when in its beginnings and the early stage, the Bank had close ties with experts and engravers from Banque de France and Banque nationale de Belgique. Over time, by wisely involving Serbian and Yugoslav scientists and artists, the National Bank managed to achieve visual independence and a particular visual identity, which has been maintained in continuity to date. This was certainly facilitated by the involvement of major arts experts in the National Bank’s Governing Board and the Committee for Cooperation with Artists – Mihailo Valtrović, Uroš Predić, Đorđe Đoka Jovanović and Paja Jovanović, Rodolphe Archibald Reiss, Mladen Josić, Vasa Pomorišac and others. By invitation or a competition, these artists joined a plethora of other artists and scientists engaged in coming up with design solutions, and then in circulating money. The process to develop the trends of visual identity on money can be classified into six periods: the end of the 19th century and the beginning of the 20th century, the period between the two world wars, the period after World War II, the period of the Socialist construction, the Dissolution of Yugoslavia, and the period from 2003 until 2018. In the process to develop trends within visual identity, we monitor the chronological sequence of events under the competences and functions of the National Bank. The analysed design solutions for banknotes come from the collection of the National Bank of Serbia, i.e. the Institute for Manufacturing Banknotes and Coins in Topčider. This paper looks into the artistic-technological aspects and trends of developing a visual identity in the service of protecting money from counterfeiting. x In addition, the development of science and technology enabled the implementation of more modern manufacturing procedures and the improvement of the money protection system, while at the same time it made room for greater technical-technological possibilities for counterfeiting. In the second part of the paper, the authors present the potential for implementing optical microscopy and Raman spectroscopy as non-destructive forensic methods for analysing historical and circulating banknotes. The aim of the research was to prove that optical microscopy and Raman spectroscopy have been successfully applied in banknote analysis. Security printing techniques were defined, as well as security elements within the shaping of visual identity, i.e. monetary culture. The experimental part of the paper was conducted on historical banknotes issued between 1893 and 2018.

U okviru ove doktorske disertacije izvršeno je formiranje polietilenskih/polikaprolaktonskih (PE/PCL) hibridnih materijala na bazi nanoceluloze i metalnih oksida. Rad je podeljen na četiri celine. U prvoj je sintetisana i okarakterisana nanoceluloza NC i modifikovana nanoceluloza NCMA i formirani su kompoziti na bazi gvožđe oksida NC-Fe3O4 i NCMA-Fe3O4. U drugom delu su formirani i ispitani dvoslojni hibridni filmovi PE/PCL sa kompozitima NC-Fe3O4 i NCMA-Fe3O4 u polikaprolaktonskom sloju. U trećem delu je sintetisana i okarakterisana nanoceluloza NC i modifikovana nanoceluloza NCMA i formirani su kompoziti na bazi bakar (II) oksida NC-CuO i NCMA-CuO i u četvrtom su formirani i ispitani dvoslojni hibridni filmovi PE/PCL sa kompozitima NC-CuO i NCMA-CuO u polikaprolaktonskom sloju. U prvom delu disertacije su sintetisani kompoziti nanoceluloza-magnetit (NC-Fe3O4) i maleinskom kiselinom funkcionalizovana nanoceluloza/magnetit (NCMA-Fe3O4), a zatim upotrebljeni kao punioci u polikaprolaktonskom sloju (PLC) pri različitim koncentracijama (5, 10 i 15 mas%). Kompozitnim materijalima nanoceluloza-magnetit su najpre proučavane strukturne, morfološke i termalne karakteristike, a nakon toga su inkorporirani u PCL sloj. Strukturna analiza izvršena je na osnovu rezultata dobijenih primenom rendgenske difrakcione analize (XRD) i infracrvene spektroskopije sa Furijeovom transformacijom (FTIR). Morfološka svojstva su proučavana skenirajućom elektronskom mikroskopijom (SEM). Termička svojstva su ispitana primenom termogravimetrijske analize. U drugom delu disertacije, polikaprolaktonski sloj sa puniocima je nanet na površinu polietilenske folije i ispitana su barijerna svojstva dobijenih hibridnih dvoslojnih filmova. Dodatak filera (punilaca) ne narušava prvobitna svojstva polimernog sloja, naročito u pogledu njegovih barijernih svojstava... Synthesis and characterization of polyethylene/polycaprolactone-modified nanocellulose hybrid materials containing different metal oxides was performed. The work is divided into four parts, and the first is a synthesized and characterized NC nanocellulose and modified NCMA nanocellulose, and composites based on iron oxide NC-Fe3O4 and NCMA- Fe3O4 are formed. In the second part, two-layer hybrid PE/PCL films were formed and tested with NC- Fe3O4 and NCMA- Fe3O4 composites in a polycaprolactone layer. In the third part, NC nanocellulose NC and modified NCMA nanocellulose were synthesized and characterized by copper (II) oxide NC-CuO and NCMA-CuO composites, and in the fourth, two-layer hybrid PE/PCL films were formed with NC-CuO and NCMA-CuO in a polycrystalline layer. Nanonocelulose/magnetite (NC-Fe3O4) nanocomposite and maleic acid functionalized NC/magnetite (NCMA-Fe3O4) nanocomposite were prepared and used as filler at various concentrations (5, 10 and 15 wt. %) in polycaprolactone (PCL) layer. The structural, morphological and thermal properties were investigated, upon composite materials were incorporated in PCL layer. Structural properties of composites were investigated by using FT–IR (Fourier transform infrared spectroscopy) and XRD analysis. The morphological properties were investigated by SEM (scanning electron microscopy). The second part of the thesis was focused on characterization of hybrid multicomponent films containing Fe3O4 nanoparticles. Polycaprolactone filled with nanocellulose/magnetite composites were coated on LDPE layer and barrier properties of low-density polyethylene/polycaprolactone-modified nanocellulose hybrid materials were investigated...

Natural convection in enclosed spaces has been studied for quite a long time in energetics. It emerges in a wide range from the smallest scales (in pipelines, channels, tanks) to the largest ones (atmosphere, molten planet core). The occuring processes depend on geometric relations and temperature of respective surfaces, which defines the type of flow that would occur. A special group of these flows appears when the flow takes place between two parallel plates with different temperatures, most often when the lower plate temperature is higher than that of the upper – a well known case is that of the Rayleigh - Bénard convection. The given examples of natural convection are still based on the generalization of the plates confining the flow being unlimited. In engineering practice, this is surely not the case so that in the proposed research the influence of the side walls to the flow is done, with no idealization of the process and in the real three-dimensional domain. Natural convection has an undeniable effect on the thermal-flow processes in engineering practice. The tanks used in most mobile engineering systems are approximately of parallelopipedic shape. Such tanks may contain all kinds of hydraulic fluids, so that the research done within this dissertation has chosen water, diesel fluid, motor oil, alcohol and air that represent the majority of fluids that can be found in the given tanks. The research done within the dissertation will show the influence of external effects, most of all, of temperature changes upon thermal-flow processes taking place in the given tanks. The obtained results should more closely show the real flow regimes taking place in the given tanks as well as their influence upon the deposition of solid particles that can be found in the given tanks.

Predmet ove doktorske disertacije je proučavanje uticaja parametara sinteze na svojstva nanostrukturnih kompozita na bazi sepiolita u cilju dobijanja materijala poboljšanih svojstava, kao i proučavanje primene ovih materijala u industriji papira. Proučavanjem svojstava disperzija skroba sa nanočestičnim sepiolitom različitih koncentracija utvrđeno je da povećanje sadržaja sepiolita u disperziji skroba dovodi do promene prirode viskoznosti ove disperzije. Disperzija čistog skroba je nenjutnovski dilatantni fluid, a dodatkom ultrazvučno tretiranih nanočestica sepiolita postaje pseudoplastični fluid. Skenirajućom elektronskom mikroskopijom je pokazano homogeno dispergovanje nanovlakana sepiolita na uzorcima papira na kojima je nanešena disperzija na bazi skroba i sepiolita. Prisustvo sepiolita u disperzijama koje se koriste za ojačavanje papira značajno je uticalo na gramaturu, dužinu kidanja, otpornost na pritisak i otpornost na pucanje papira. Utvrđeno je da način pripreme disperzija sepiolita i skroba takođe utiče na mehanička svojstva papira. Uzorci papira na koje su nanešene ultrazvučno tretirane disperzije, a zatim pripremljene slično industrijskom postupku, su pokazale najbolja mehanička i viskoelastična svojstva. Proučavanjem svojstava nanostrukturnih premaza za papir na bazi sepiolita i polivinil butirala pokazano je da prisustvo nanočestica sepiolita ne utiče značajno na vrednost temperature transformacije, Tg. Dodatkom različitih količina sepiolita, vrednosti sile kidanja i apsorbovane zatezne energije su povećane do 10 % u odnosu na uzorke papira sa čistim PVB-em. Mehanička svojstva papira ojačanog kompozitom PVB/sepiolit su IV ispitana mikrokidalicom i nanoindentacijom. Obe metode su pokazale da uzorak papira ojačan sa PVB-em u kome je dispergovano 3 mas. % sepiolita ima najbolja mehanička svojstva, što je posledica sinergetskog dejstva čestica sepiolita i polimernog matriksa, polivinil butirala... The aim of this study was to investigate the influence of synthesis parameters on properties of sepiolite based nanostructered composite and their applications in paper industry. The investigation of the properties of starch dispersions with sepiolite nanoparticles different concentrations showed that increasing the sepiolite content led to a change of the nature of the viscosity. Pure starch dispersion is a non-Newtonian dilatant fluid; and the addition of ultrasonificated sepiolite nanoparticles transformed this dispersion into a pseudoplastic fluid. Scanning electron microscopy showed homogeneous sepiolite nanofibers dispersed on the paper samples. The presence of sepiolite influenced the paper grammage, breaking length, bursting strength and flat crush. Additionally, the preparation method of the sepiolite-starch dispersions influenced on the improvement of the mechanical properties of the paper. The papers coated with ultrasonificated dispersions followed by dilution, similar to the industry procedure, showed the highest values of the relevant mechanical and viscoelastic properties. The presence of sepiolite in PVB coating showed no significant influence on Tg values. The values of the break force and the tensile energy absorption of paper samples were increased by up to 10 %. The nanoindentation tests also showed increases in the hardness and modulus. The paper sample reinforced with nanocomposite PVB/3 wt. % sepiolite exhibited the best improvements of the mechanical properties measured by both methods...

The aim of this study was to investigate the influence of synthesis parameters on properties of sepiolite based nanostructered composite and their applications in paper industry. The investigation of the properties of starch dispersions with sepiolite nanoparticles different concentrations showed that increasing the sepiolite content led to a change of the nature of the viscosity. Pure starch dispersion is a non-Newtonian dilatant fluid; and the addition of ultrasonificated sepiolite nanoparticles transformed this dispersion into a pseudoplastic fluid. Scanning electron microscopy showed homogeneous sepiolite nanofibers dispersed on the paper samples. The presence of sepiolite influenced the paper grammage, breaking length, bursting strength and flat crush. Additionally, the preparation method of the sepiolite-starch dispersions influenced on the improvement of the mechanical properties of the paper. The papers coated with ultrasonificated dispersions followed by dilution, similar to the industry procedure, showed the highest values of the relevant mechanical and viscoelastic properties. The presence of sepiolite in PVB coating showed no significant influence on Tg values. The values of the break force and the tensile energy absorption of paper samples were increased by up to 10 %. The nanoindentation tests also showed increases in the hardness and modulus. The paper sample reinforced with nanocomposite PVB/3 wt. % sepiolite exhibited the best improvements of the mechanical properties measured by both methods... Predmet ove doktorske disertacije je proučavanje uticaja parametara sinteze na svojstva nanostrukturnih kompozita na bazi sepiolita u cilju dobijanja materijala poboljšanih svojstava, kao i proučavanje primene ovih materijala u industriji papira. Proučavanjem svojstava disperzija skroba sa nanočestičnim sepiolitom različitih koncentracija utvrđeno je da povećanje sadržaja sepiolita u disperziji skroba dovodi do promene prirode viskoznosti ove disperzije. Disperzija čistog skroba je nenjutnovski dilatantni fluid, a dodatkom ultrazvučno tretiranih nanočestica sepiolita postaje pseudoplastični fluid. Skenirajućom elektronskom mikroskopijom je pokazano homogeno dispergovanje nanovlakana sepiolita na uzorcima papira na kojima je nanešena disperzija na bazi skroba i sepiolita. Prisustvo sepiolita u disperzijama koje se koriste za ojačavanje papira značajno je uticalo na gramaturu, dužinu kidanja, otpornost na pritisak i otpornost na pucanje papira. Utvrđeno je da način pripreme disperzija sepiolita i skroba takođe utiče na mehanička svojstva papira. Uzorci papira na koje su nanešene ultrazvučno tretirane disperzije, a zatim pripremljene slično industrijskom postupku, su pokazale najbolja mehanička i viskoelastična svojstva. Proučavanjem svojstava nanostrukturnih premaza za papir na bazi sepiolita i polivinil butirala pokazano je da prisustvo nanočestica sepiolita ne utiče značajno na vrednost temperature transformacije, Tg. Dodatkom različitih količina sepiolita, vrednosti sile kidanja i apsorbovane zatezne energije su povećane do 10 % u odnosu na uzorke papira sa čistim PVB-em. Mehanička svojstva papira ojačanog kompozitom PVB/sepiolit su IV ispitana mikrokidalicom i nanoindentacijom. Obe metode su pokazale da uzorak papira ojačan sa PVB-em u kome je dispergovano 3 mas. % sepiolita ima najbolja mehanička svojstva, što je posledica sinergetskog dejstva čestica sepiolita i polimernog matriksa, polivinil butirala...

One of the most important characteristics of heat exchangers, besides thermal efficiency, is their compactness or surface area to volume ratio. The need to achieve high efficiency in a compact unit with high operating pressure has led to the development of heat exchangers with perforated plates or, as they are called in the literature, the Matrix Heat Exchangers (MHE). In this PhD thesis experimental and numerical research was undertaken to measure the thermal and flow characteristics of an assembly of perforated plates, in an effort to obtain indications for engineering calculations. The study was undertaken in the Laboratory for Thermal Engineering at the Faculty of Mechanical Engineering, Niš. In the experimental part of the study, packages of one, two and three 2 mm thick plates were used, with a porosity of 25.6% and a square arrangement of holes that were 2 mm in diameter. Water was used as the heating fluid, while the heated fluid was air. The package of plates was placed in the experimental chamber which had a fan as an inlet, with the ability to control the flow. The fluid flow rate, pressure drops and the temperatures of the fluids at the inlet and outlet of the chamber, as well as the temperature of air between the plates, were measured at the pre-defined locations in the perforated plate heat exchanger. Also, the pressure drop was measured for the perforated plate package with and without the water collector. In the numerical part of this research, the PHOENICS 2014 software package was used. In the first part of the numerical study the heat transfer from plates with the porosity from 10 to 50% was investigated. In the second part of the numerical study, a package of three plates was established and the effect of distance between the plates was also examined. Experimental results and the results of other authors were used to validate the numerical experiment. iv On the basis of experimental and numerical results, criterial equations for heat transfer and formulas for pressure drop equations were established.

The research presented in this PhD thesis is directly linked to the achievement of sustainable building development analysis of indoor environment quality. The indoor environment quality includes the achieved level of heat, air, light, noise and aesthetic comfort. In the presented PhD thesis, special attention was paid to thermal comfort. Fundamental processes of mass, momentum and heat transfer are used to describe the various mechanisms of sensible and latent heat transfer from the human being to the environment and vice versa. The investigations were conducted by experimental, numerical and statistical methods. While investigating within PhD thesis, the following scientific contributions have been made: - Concerning the two-equation turbulence models, special attention was paid to the influence of production and dissipation terms of turbulent kinetic energy due to the fluctuation of body forces. - Varying empirical constants containing modeled terms of the differential equation for ε, the modifications were proposed for the empirical constant C 3 in the way that its value is declared variable as a function of the ratio of flow velocity component in the direction of the gravity vector and lateral directions, and an expression for its determination is proposed. - Concerning the heat transfer radiation model, the new model of radiation have been proposed that treats air contaminated by carbon dioxide as a nontransparent medium, and an expression is proposed in order to determine the effective emissivity of contaminated air. The experimentally obtained values of the general thermal comfort indicators were the basis for the validation of the mathematical models proposed in the presented PhD dissertation. The proposed models are built into a numerical code of the commercial software PHOENICS, and parametric analysis was conducted through a series of six test cases, starting from the basic model, which is characterized by the fact that the turbulent model and heat transfer by radiation model are built-in, up to the case C_B which includes both modifications. In addition to the standard procedure of error analysis, statistical analysis of a complex array has been conducted, so additional statistical indicators have given the right information about the each model quality. Based on the results of the numerical experiments, it was shown that the model of radiation compared to the turbulence model in the distribution of thermal characteristics and general thermal comfort indicators has a dominant role.