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In the first part of the paper, the continuity equation in the boundary layer for stationary two-dimensional flow is derived on the basis of the law of mass conservation. After that, using Newton's second law for control volume, the equation for the momentum was derived. Using the derived equations, the analysis was performed with respect to the influence of temperature. After that, on the basis of the energy balance, an energy equation was derived in which a viscous dissipation function was introduced, which enabled a wider application. At the end of the paper, the derived equations were applied to a specific calculation example from technical practice in the calculation of thermal quantities in a rectilinear sliding bearing, which was the aim of the work

Oxidation as an undesired phenomena particularly evident in and significant for low-carbon steel, occurs at elevated temperatures due to the chemical effects of the atmosphere. The exact information about the thickness of the oxidation layer has a great practical importance. The aim of this paper is to take the existing process for calculating the depth of oxidation, which is valid for a stationary area, and use it for a non-stationary area. The non-stationary area of the heating curve is devided into a number of segments in which medium temepratures are relevant. These medium temperatures were defined in the paper. In order to use the effect of oxidation of the previous segment on the proceeding segment, a fictitious time was introduced, considering the temperature of the next segment. In the process of calculating the main relation, the starting point were individual, specific solutions, based on which we obtained the general solutions for the problem. The proposed model was illustrated using a suitable example where the depth of oxidation was determined for a typical low-carbon steel under atmospheric conditions, both for the stationary and for the non-stationary area.

The paper shows an example of performed optimization of sizes in terms of welding costs in a characteristic loaded welded joint. Hence, in the first stage, the variables and constant parameters are defined, and mathematical shape of the optimization function is determined. The following stage of the procedure defines and places the most important constraint functions that limit the design of structures, that the technologist and the designer should take into account. Subsequently, a mathematical optimization model of the problem is derived, that is efficiently solved by a proposed method of geometric programming. Further, a mathematically based thorough optimization algorithm is developed of the proposed method, with a main set of equations defining the problem that are valid under certain conditions. Thus, the primary task of optimization is reduced to the dual task through a corresponding function, which is easier to solve than the primary task of the optimized objective function. The main reason for this is a derived set of linear equations. Apparently, a correlation is used between the optimal primary vector that minimizes the objective function and the dual vector that maximizes the dual function. The method is illustrated on a computational practical example with a different number of constraint functions. It is shown that for the case of a lower level of complexity, a solution is reached through an appropriate maximization of the dual function by mathematical analysis and differential calculus.

Starting from the fact that the problem of the loss of technical work of exit gases in a boiler stack involves the state of thermodynamic imbalance, this paper gives a derivation of a suitable analytic relation for determining the maximum technical work, or exergy, which is equivalent to the lost technical work in exit gases. This serves as the basis for solving the suitable equivalent thermodynamic process which confirms the premiss of the problem. In order to observe the problem in its full range, the process involved was represented both in a work p-v diagram, a heat T-s diagram, as well as in an h-s diagram. The exergy function analysis was conducted according to the most influential parameter, whereas flue gases (exit gases) were considered as semi-perfect, due to the fact that this definition corresponds better to the real situation. With the aim to give a full insight into the subject matter in the sense of quantity, in the end the authors determined the power of an imaginary reversible machine which would operate under the same conditions and parameters, and which would use these gases until they become balanced with the environment. The concept of exergy developed on the basis of a general model for determining the loss of technical work in exit gases of boiler stacks was illustrated by a practical calculation example.

The paper presents relation for maximal pressure-volume work for closed systems by using principles of I and II law of thermodynamics, used in reversible processes in which mechanical and thermal balance has been achieved. For full interpretation of this problem for two characteristic cases, graphical review in p-v diagram is given, where in an obvious way is noticed that maximal expansion work is composed of isentropic and isothermal work as well as work against pressure of environment. On basis of derived relation, by using appropriate thermodynamic relations, expression for specific maximal work is obtained which is suitable for the analysis. That expression was observed like two-dimensional problem i.e. as function of two variables: initial pressure and initial temperature as primary parameters. Using mathematical analysis is proven existence of minimum of this function, function as well as its graphical presentation in three-dimensional coordinate system. Detailed mathematical analysis is presented that in general case function of maximal geometric work is one concave area in space. For efficient solving and analysis of this problem, complex function of maximal work is observed as two functions with one variable i.e. from two-dimensional problem we will make two single-dimensional problems. It’s proven that in single-dimensional problems also exists point in which maximal work is minimal and different from zero. At the end of the paper, opportunities for usage of this complex issues of maximal work which refer to exergy analysis and optimization of thermodynamic processes, also the guidelines for future research for problems of other gases, half – ideal gases and Van der Waals’s gas. It can be claimed that the procedure of analyzing thermodynamic function of maximal work, showed in paper, isn’t common in literature. Keywords: analysis, maximal pressure-volume work, and thermodynamic system, work-diagram

U radu je, na osnovu relacije za maksimalan rad kod zatvorenih termodinamičkih sistema, izvedenopšti model za određivanje minimalne zapremine rezervoara za komprimovani vazduh. S obzirom,da u posmatranom sistemu postoji mehanička i termodinamička neravnoteža, ispunjeni su uslovi zadobijanje maksimalnog rada. Dobijena relacija, koja predstalja novi model, može se direktnokoristiti u tehničkoj praksi za slučaj da su poznati parametri koji definišu početno stanje urezervoaru, parametri okoline, kao i energija koju je potrebno dobiti od komprimovanog vazduha.Radi potpunijeg predstavljanja posmatranog procesa, isti je predstavljen u radnom p-v i toplotnomT-s dijagramu. Pored analitičkog, u radu je predstvljeno i grafičko rešenje postavljenog problema,koje može poslužiti i za kontrolu dobijenih rezultata. Takođe, ilustrovana je primena izvedenogmodela na praktičnom primeru, gdje je određena minimalna zapremina sfernog rezervoara u kojemse nalazi vazduh.

In a semi-ideal gas, entropy changes cannot be determined through the medium specific heat capacity in a manner as determined by the change of internal energy and enthalpy, i.e. the amount of heat exchanged. Taking this into account, the authors conducted two models through which it is possible to determine the change in the specific entropy of a semi-ideal gas for arbitrary temperature interval using the spread sheet method, using the mean values of the appropriate functions. The idea is to replace integration, which occurs here in evitably, with mean values of the previous functions. The models are derived based on the functional dependence of the actual specific heat capacity on the temperature. The theorem used is that of the mean value of a function as well as the mathematical properties of the definite integral. The mean value of a fractional function is determined via its integrand while the logarithmic functions were performed by applying a suitable transformation of the differential calculus. The relations derived relation, using the computer program, have enabled the design of appropriate thermodynamic tables through which it is possible to determine the change in entropy of arbitrary state changes in an efficient and rational manner, without the use of calculus or finished forms. In this way, the change in the entropy of a semi-ideal gas is determined for an arbitrary temperature interval using the method which is analogous to that applied in determining the change of internal energy and enthalpy or the amount of heat exchanged, which was the goal of the work. Verification of the proposed method for both the above functions was performed for a a few characteristic semi-ideal gases where change c(T) is significant, for the three adopted temperature intervals, for the characteristic change of state. This was compared to the results of the classical integral and the proposed method through the prepared tables. In certain or special cases, it is possible to apply the presented method also in determining the change in entropy of the real gas. Apart from that, the paper shows that the change in entropy for the observed characteristic case can be represented or graphically determined using the planimetric method of diagrams with suitably selected coordinates.

Starting from the expression for the thrust in the field of full utilization cross section scrapings and tool life, an expression is derived for the maximum required thrust of universal machine. Then, using a working diagram the analysis of the main features of the simultaneous utilization of machines was performed and determined the optimal area of its utilization for given optimal diameter of treatment. Based on this, the well-known machine using its structural details and the corresponding function workability, derived relations to determine the optimal coefficient slenderness of scrapings suitable for practical use. In this case we think that is known critical material for work piece. Considering the critical and authoritative material of the work piece, based on the expression for the cutting speed was determined by the characteristic constant workability as the basis for establishing optimum tool material which is adequate for optimum regime. Both obtained relation can be considered as general model that can be applied directly to solving setting problems. Also, given the possibilities of practical application of the presented relations, especially in the case of other typical kinds of treatment. Finally, the model is verified on a one calculation example from practice for a Specific machine tool, where certain important characteristics of the optimal treatment are defined.

In this paper for complex processes in the field of production mechanical engineering, that describes with the product of step and exponential functions, unknown parameters are calculated. The starting complex function is reduced by suitable method to linear form and then using Taylor's formula developed in series surrounding center point of the experiment. Mathematical model obtained without factors interaction was compared with a similar regression functions. After some mathematical transformations this model allows to determination unknown parameters in the starting function. To simplify the experimental determination of the coefficients of regression and to simplify the analysis, linear model of first order with interactions in coded form was used. Transformation to natural coordinates is performed by using adequate equations. Verification of the suggested method was performed using characteristic experiment in the field of metal deformation. For well-known law of resistance of metals at hot plastic deformation, as a function of influencing factors, all unknown parameters were determined in two ways: by comparing corresponding linear functions and using available derived models. The regression function of prior thermo mechanical process technology was determined experimentally using orthogonal multiple factor first order plan. Also, required statistical analysis and testing of this model were performed. With graphical interpretation of obtained results in logarithmic coordinates, well fittings models and experimental results were shown. Finally, some possibilities for practical application of the proposed methods and models in the field of production engineering, especially in the case of complex processes, were suggested. This method, compared to other methods used for solving setting problem, is faster, more efficient and more reliable.

In this paper, for the case of gas oscillator two characteristic thermodynamic change of state, and for them defined functional dependence of the force from moving the piston in a nonlinear form were considered. In this paper small oscillations are observed and the linearization is performed by neglecting nonlinear term as the small size at isothermal change and with development obtained function in Taylor series for adiabatic change. Based on the analysis of analog oscillator of mechanical system, or the equivalent scheme of problems, characteristics oscillation parameters and the motion law of the observed thermodynamic system are defined. With this procedure greatly simplifying for problem solution was achieved with respect to classical procedure. At the end of the paper, an analysis of the obtained results were done and appropriate electrical analogy was setting. This is used for the presentation of the problem through appropriate electric circuits and analogy mathematical relations, which involve voltage and electric currents as electric sizes. Also, it was shown that the electrical analogy can be used for all mechanical and thermodynamic processes which describes by homogeneous second-order differential equations which are the most common in technical practice.

Starting from the definition of the average specific heat capacity for chosen temperature range, the analytic dependence between the real and the mean specific heat capacities is obtained using differential and integral calculation. The obtained relation in differential form for the defined temperature range allows for the problem to be solved directly, without any special restrictions on its use. Using the obtained relation, a general model in the form of a polynomial of arbitrary degree in the function of temperature was derived, which has more suitable and faster practical application and is more general in character than the existing model. New graphical method for solving the problem is obtained based on differential geometry and using the derived equation. This may also have practical significance since many problems in thermodynamics are solved analytically and graphically. This result was used in order to obtain the amount of specific heat exchanged using an analytical model or a planimetric method. In addition, this graphical solution was used for the construction of the diagram showing the dependence between the specific heat exchanged and temperature. This diagram also gives a simple graphical procedure for the calculation of the real and the average specific heat capacity for arbitrary temperature or temperature interval. The confirmation for all graphic constructions is obtained using the differential properties between thermodynamic units. In order for the graphical solutions presented to be applicable in practice, suitable ratio coefficients have been determined for all cases. Verification of the model presented, as well as the possibilities of its application, were given using several characteristic examples of semi-ideal and real gas. Apart from linear and non-linear functions in the form of polynomials, the exponential function of the dependence between specific heat capacities and temperature was also analysed in this process.

Starting from the experimental concentration-time ( cA,t diagram this work gives the construction of the rate of reaction-time (rA,t diagram using the pure graphic method. The diagram was constructed based on the constructed tangents in arbitrary points of the starting diagram by drawing lines parallel to them in the predetermined pole. The evidence of the construction was derived using differential geometry, i.e. the main theorem of differential calculus. Differential properties between the observed values were used in the method. Starting from the analytic relations rA = rA(t) and cA = cA(t), which can be very complex (polynomes of the n-th order), and, eliminating time t in order to give a full description of the process, we obtain the analytical relation rA = rA(cA), which is then graphically represented. Hoewever, this elimination of time can also be done graphically, in a relatively simple way. After that, through the use of the integral calculus, it was shown that concentration increase in a time interval is proportional to the (rA,t) diagram surface area. Using a similar procedure, further in the paper, it was shown that the time increase is proportional to the (1/rA, cA) diagram surface area. In order for the method to be applicable in practice, we have derived relations for appropriate coefficients of proportionality. Verification of the method is illustrated by the two characteristic examples from chemical kinetics at different monotonies of the starting experimental functions.

s: In this paper the influence of carbon dioxide pressure on supercritical extraction of Salvia officinalis L. was investigated. Supercritical fluid extraction with carbon dioxide was done for pressures of 80, 100, 150, 200 and 300 bar. It was concluded that with increasing pressure from 80 to 300 the bar extraction yield enhanced. GC/MS and GC/FID methods were used for qualitative and quantitative analyses of obtained extracts and essential oils from extracts.

The subject of the paper is reliability design in polymerization processes that occur in reactors of a chemical industry. The designed model is used to determine the characteristics and indicators of reliability, which enabled the determination of basic factors that result in a poor development of a process. This would reduce the anticipated losses through the ability to control them, as well as enabling the improvement of the quality of production, which is the major goal of the paper. The reliability analysis and calculation uses the deductive method based on designing of a scheme for fault tree analysis of a system based on inductive conclusions. It involves the use standard logical symbols and rules of Boolean algebra and mathematical logic. The paper eventually gives the results of the work in the form of quantitative and qualitative reliability analysis of the observed process, which served to obtain complete information on the probability of top event in the process, as well as objective decision making and alternative solutions.

Starting from the fact that the real mechanism in a chemical equation takes places through a certain number of radicals which participate in simultaneous reactions and initiate chain reactions according to a particular pattern, the aim of this study is to determine their number in the first couple of steps of the reaction. Based on this, the numbers of radicals were determined in the general case, in the form of linear difference equations, which, by certain mathematical transformations, were reduced to one equation that satisfies a particular numeric series, entirely defined if its first members are known. The equation obtained was solved by a common method developed in the theory of numeric series, in which its solutions represent the number of radicals in an arbitrary step of the reaction observed, in the analytical form. In the final part of the study, the method was tested and verified using two characteristic examples from general chemistry. The study also gives a suggestion of a more efficient procedure by reducing the difference equation to a lower order.

The problem of calculating stoichiometric coefficients in a chemical equation can be solved by standard methods and the method of multidimensional vector space, but good knowledge of vector algebra is required. In this paper, the authors proposed a matrix method and other treatment of the problem was given as the authors' own interpretation. A matrix was formed in the form of base using all the elements which take place in a chemical reaction, after which the matrixes of all the chemical compounds were determined based on numerical indexes and element symbols. This approach enables the setting of a principal matrix equation based on a mathematical approach. The solutions of this matrix equation are the desired stoichiometric coefficients that form a balanced equation. A new approach to tabular solving is presented. This method, compared to existing standard methods, is faster, simpler, and more effective, especially for complex chemical equations. The method was tasted on examples from inorganic chemistry and metallurgy.

In this paper, for the universal machine tool for turning and function of the thrust of the cutting speed for blasting area efficiency and stability of the tool and sectional filings. These dependencies were used to determine the main characteristics of the optimal and maximum operating power equipment. Based on this, an analysis of the increase in operating power equipment in typical cases in order to adapt to the new needs of exploitation properties and improve productivity.Using the previous analysis, it was determined the best solution in terms of the rational design of machines, by ensuring the simultaneous use of the main features on the basis of the increase in speed with the use of tools and higher stability. In order to better display problems, an analysis of the appropriate diagrams P-V and V-D.On a typical example of the manufacturing practice at the end of the work, we demonstrate improvement of exploitation characteristics of a universal machine through appropriate calculations in terms of new needs adjustment feature, where it is expected that the reconstruction of the smallest machines. U radu je za univerzalnu mašinu alatku za obradu struganjem određena zavisnost pogonske snage od brzine rezanja za eksploatacijsku oblast iskorištenja postojanosti alatke i preseka stugotine. Ove zavisnosti su iskorišćene za utvrđivanje glavnih optimalnih karakteristika i maksimalne pogonske snage mašine. Na bazi ovoga, izvršena je analiza povećanja pogonske snage mašine za karakteristične slučajeve u cilju prilagođavanja eksploatacionih karakteristika novim potrebama odnosno poboljšanja proizvodnosti. Koristeći prethodnu analizu, određeno je najpovoljnije rešenje sa aspekta racionalnog projektovanja mašine, pri čemu je obezbeđeno istovremeno iskorišćenje glavnih karakteristika na bazi povećanja broja obrta, a uz primenu alata veće postojanosti. Radi potpunijeg prikaza problema, izvršena je analiza u pogodnim dijagramima P-V odnosno V-D. Na karakterističnom primeru iz proizvodne prakse, na kraju rada, dat je prikaz poboljšanja eksploatacijskih karakteristika jednog univerzalnog struga kroz odgovarajuće proračune sa aspekta prilagođavanja karakteristika novim potrebama, pri čemu se očekuje da će rekonstrukcija mašina biti najmanja.

In this paper, for characteristic polytropic change of state of ideal gas is given graphical planimetric graphical representation of the most important energy values in workplace and thermal diagram, trough the appropriate area. In this paper, we used differential forms of the First and Second law of thermodynamics and basic equation which define the observed change of state, written in a suitable form. The results for the polytropic change of state, are applied to the isobaric and isochoric change of state. It is shown that any of the energy values ( q12, w12, wt12, Dh12, Du12) can be present in both workplace (p, v) as well as thermal (T-s) diagram. Graphical solutions, compared to the analytical, provide efficient theoretical explain and presentation of various thermodynamic processes of ideal gas with different aspects and greatly assist a clearer view of the problem and enhance each other living arrangement. Graphical representation of external influences or energy values shown in the diagrams, make it possible to more clearly we see connection between these effects, change of state, as well as their each other relations. This is particularly evident in the case when there are (p, v) and (T-s) diagram for a par tic u lar ideal gas, which is common in technical practices (e. g., air as an ideal gas). U radu je za karakterističnu politropsku promenu stanja idealnog gasa dato grafičko planimetrijsko predstavljanje najvažnijih energetskih veličina u radnom i toplotnom dijagramu, preko odgovarajućih površina. Pri ovome korišćeni su diferencijalni oblici prvog i drugog zakona termodinamike, kao i osnovne relacije koje definišu posmatranu promenu stanja, napisane u pogodnom obliku. Dobijeni rezultati, za politropsku kao opštu promenu stanja, primenjeni su na izobarsku i izohorsku, kao karakteristične promene stanja. Pokazano je da bilo koju od energetskih veličina (q12, w12, wt12, Δh12, Δu12) moguće predstaviti kako u radnom (p-v), tako i u toplotnom (T-s) dijagramu. Prikazana grafička rešenja, u odnosu na analitička, omogućuju efikasnije teorijsko razmatranje i predstavljanje različitih termodinamičkih procesa idealnog gasa sa različitih aspekata i znatno pomažu jasnijem sagledavanju problema i poboljšavaju međusobno sporazumevanje. Grafički prikazi spoljnih uticaja, odnosno energetskih veličina u prikazanim dijagramima, omogućuju da se još jasnije uoči veza između tih uticaja, promena stanja, kao i njihovi međusobni odnosi. Ovo posebno dolazi do izražaja za slučaj kada postoji (p, v) i (T-s) dijagram za određeni idealni gas, što je čest slučaj u tehničkoj praksi (na primer za vazduh kao idealan gas).

U ovom radu, kao za karakterističan primer iz hemijske kinetike, za reakciju prvog reda, sistem složenih hemijskih jednačina matematičkim transformacijama sveden je na sistem homogenih i nehomogenih diferencijalnih jednačina prvog i drugog reda, koje su pogodne za predstavljanje preko električne analogije. Nakon toga, posmatrana su električna kola sa rednom i paralelnom vezom u kojima su prisutne sve tri karakteristične otpornosti i to sa i bez strujnog izvora. Primenom Kirhofovih zakona, izvedene su pogodne diferencijalne jednačine u zavisnosti od naelektrisanja, napona i jačine struje, a koje predstavljaju opšti model za uspostavljanje analogije sa ranije izvedenim sličnim hemijskim jednačinama za određivanje koncentracije jedinjenja, u kojima su uključene i konstante brzine reakcije. Na kraju, na primeru jedne od karakterističnih izvedenih električnih relacija u diferencijalnom obliku, dat je tabelarni prikaz analogije između električnih i veličina koje figurišu u hemijskim jednačinama, kao i neke mogućnosti primene prikazanih analogija.

Summary: In this paper, based on derived differential equation for the heat transfer and a suitable boundary condition (equation of heat exchange), the appropriate model of cooling of meat stakes in the form of a flat plate is set up. By using theory of similarity, Fourier and Biot criterion is defined, which allowed setting criterial equation of temperature field which included an unnamed temperature and geometric criterion. For solving the obtained criterial equation, existing diagrams of temperature functions were utilized, which were specified by analytical method for the core, the surface and the interior of the observed model. The proposed model is used for analytical solving of a number of practical problems in the cooling process of meat steaks in a gaseous environment. Particular focus has been on the temperature of the surface and core of steak as well as ambient temperature and cooling time. Also, it was shown that proposed model can be used to define temperatures or temperature field along the thickness of steak, depending on the distance from the central plane. Special possibility of applying the model is for the case of preventing freezing steaks, when their temperature is maintained within specified limits.

U teorijskoj organskoj hemiji, zakoni molekulsko – orbitalne teorije omogucuju da se odrede energetska stanja π – elektrona u konjugovanim (nezasicenim) jedinjenjima. Pri ovome energetski nivoi elektrona, dobijaju se razvijanjem odgovarajuce determinante koja se formira koristeci tri karakteristicne matrice po definiciji. Svakom jedinjenju, pri ovome pridružuje se odgovarajuci polinom, dok ce energetski nivoi zavisiti od njegovih nula. Kod velike vecine jedinjenja koja se susrecu u teoriji i praksi, dobijeni polinom uvek ima bar jednu racionalnu nulu pa se problem resava jednostavno metodom faktorizacije. Problem nastaje kada karakteristicni polinom nema ni jednu racionalnu nulu. U ovom slucaju moguca je primena gotovih matematickih formula koje su međutim nepodesne za prakticnu upotrebu. Isto tako moguca je i primena numerickih metoda, koje daju samo približno realno resenje koje nije pogodno za primenu s obzirom da se gotovo uvek traži tacno realno resenje. Uzimajuci u obzir predhodno, u radu bice dat predlog za resavanje gore navedenog problema na bazi formiranja ekvivalentnih jednacina preko odgovarajucih matematickih transformacija, koje omogucuju da se na relativno jednostavan nacin dobiju tacno sve realne nule polinoma. U prikazanom radu, resavanje matematickog problema bice ilustrovano na nekoliko karakteristicnih primera. Tacnost dobijenih rezultata prema predloženoj metodi bice izvedena poređenjem sa približnim numerickim resenjem koristeci odgovarajuci racunarski program, odnosno numericke metode.

U prvom delu rada, za karakterističan primer složene hemijske reakcije, proanalizirano je nekoliko matematičkih metoda za rešavanje sistema diferencijalnih jednačina kojima se opisuje proces, a koje se najčešće koriste u inženjerskoj teoriji i praksi. Analiza je izvršena sa aspekta neophodnog matematičkog znanja, potrebnog vremena za rešavanje problema, mogućnosti greške kao i kontrole dobijenih rezultata. U drugom delu rada, dat je predlog za efikasnije rešavanje posmatranog problema pri čemu je primenjen princip redukcije sistema na jednu diferencijalnu jednačinu, koju je najpogodnije posmatrati kao nehomogenu jednačinu I reda sa konstantnim koeficijentima, zavisnu od vremena. Pokazano je da je predložena metoda pogodnija u odnosu na postojeće, s obzirom da ima određene prednosti i može se koristiti kao alternativa istim.

The vehicle presents a dynamic system performing vibrations under the influence of certain stimulus. Information driver receives from the environment and the vehicle is: macro and micro texture of the road, vibrations and noise of the vehicle's subsystem and so on. The road is usually evaluated according to its macro and micro texture. Microroughness of the roads is of great importance for the study of vehicle's oscillatory movements, reliable computation of vehicle systems, safety etc. Therefore, a special attention must be given to them during the analysis of dynamics, strength and safety of the vehicle. Microroughness that characterize the microprofile of the road in longitudinal and transverse direction have random character and can be established by experimental study of the road with utilization of devices. Accordingly, a variety of devices have been developed for measurement of macro- and micro profiles of the road as well as numerous mathematical and experimental procedures, which with certain approximation satisfy the given requirements, and with the increasing use of computer technology.