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Numerical analysis of fluid flow in a vial
Žiga Časar, 2019, master's thesis

Abstract: Lyophilization or freeze-drying is a widely used process in the pharmaceutical and food industry. In the process the solvent will be removed under extreme conditions of low temperature and low system pressures, whereby sublimation happens, the transition from the solid phase to the gas phase, with skipping the liquid phase, which happens bellow the triple point. This study focuses on numerical modeling at the start of the process, the so called primary drying. For this stage the highest mass flow rates of vapor are typical, since the driving force of the process is the pressure difference between the sublimation front and surrounding area. In this stage the non-bonded solvent is removed. Because of the extreme conditions the typical computational fluid dynamics approach is not suitable anymore and has to be corrected. One way to do this is to use additional models for fluid behavior at the solid wall. The study focuses on the influence of different boundary conditions on the solid wall, No-Slip, Free Slip and Maxwell Slip, and their effect on fluid flow inside the vial. A quantitative and qualitative comparison of the results is presented.
Keywords: Lyophilization, Knudsen number, computational fluid dynamics, fluid flow, numerical modeling, slip boundary condition
Published: 09.07.2019; Views: 627; Downloads: 111
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Micro-scale responses of granular materials under different confining pressures using the discrete element method
Mahmud Sazzad, 2016, original scientific article

Abstract: Biaxial compression tests were carried out on assemblies of ovals to study the micro-scale responses of granular materials under different confining pressures using the discrete element method (DEM). A total of 8450 ovals were generated in a rectangular frame without any overlap. Four dense samples were prepared from the initially generated sparse sample under different confining pressures. The simulated results yield a stress-straindilatancy behaviour similar to that observed in sands under different confining pressures. The evolution of the different microparameters and their inter-relationships are established. When the confining pressure is relatively high, the difference between the coordination number and the effective coordination number is very small; however, the difference is apparent for a low confining pressure. The microtopology of the granular assembly at several important states of shear is also reported. It is noted that the topological distribution of the granular materials is confining- pressure dependent. The normalized void-cell number is a minimum under the lowest confining pressure, whereas the same number is a maximum under the highest confining pressure. A linear relationship is observed between the normalized void-cell number and the effective coordination number, regardless of the confining pressures. The evolution of the deviatoric fabric for different confining pressures is measured and the macro-micro relationship is presented.
Keywords: microstructures, confining pressure, fabric, microtopology, coordination number, macro-micro relationship
Published: 15.06.2018; Views: 573; Downloads: 43
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Fuzzy-sets decision-support system for geotechnical site soundings
Djemalddine M. Boumezerane, Smaïn Belkacemi, Bojan Žlender, 2011, original scientific article

Abstract: A geotechnical site investigation is an important and complex task that is generally carried out in two steps. The first step, consisting of preliminary soundings, guides the subsequent site characterization. The number of soundings required to adequately characterize a site is set on the basis of an engineering judgement following the preliminary investigation, this is affected by the geological context, the area topography, the project type, and the knowledge of the neighbouring areas. A fuzzy-sets decision-support system, considering parameters that affect the number of soundings required to adequately characterize a site, is proposed. Parameter uncertainties and a lack of information are also considered. On the basis of the available qualitative and quantitative information, the proposed fuzzy system makes it possible to estimate, for a common project, the number of site soundings required to adequately characterize the site. The cases presented show that a Fuzzy Inference System can be used as a systematic decision-support tool for engineers dealing with site characterizations.
Keywords: geotechnical investigation, soundings number, fuzzy sets, fuzzy inference, uncertainties
Published: 13.06.2018; Views: 335; Downloads: 44
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Analysis of personal income taxation determinants in Croatia in long run
Irena Palić, Ksenija Dumičić, Barbara Grofelnik, 2017, original scientific article

Abstract: Personal income taxation remains an ongoing issue in Croatia. It is used as an important instrument of income redistribution. Moreover, it directly affects purchasing power of the working population. Numerous changes have been made in this type of taxation since the establishment of Croatian tax system. The aim of this paper is to analyse possible determinants of personal income taxation in Croatia. After offering brief insight into public finance theory regarding personal income taxation, the structure of personal income taxation in Croatia is explained. The empirical analysis of the determinants of personal income taxation in Croatia is conducted using cointegration analysis. Economic conditions, average monthly wage, and number of taxpayers are used as determinants of personal income tax used in this research. The cointegration analysis is conducted using monthly data from January 2008 to February 2016. The results of the research show a statistically significant negative impact of economic conditions and statistically significant positive impact of average monthly wage and number of taxpayers on personal income taxation in long run, what is in line with economic and public finance theory.
Keywords: personal income taxation determinants, economic conditions, wages, number of taxpayers, johansen cointegration approach, Croatia
Published: 03.05.2018; Views: 509; Downloads: 110
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Roman domination number of the Cartesian products of paths and cycles
Polona Repolusk, Janez Žerovnik, 2012, original scientific article

Abstract: Roman domination is a historically inspired variety of general domination such that every vertex is labeled with labels from $\{0,1,2\}$. Roman domination number is the smallest of the sums of labels fulfilling condition that every vertex, labeled 0, has a neighbor, labeled 2. Using algebraic approach we give ▫$O(C)$▫ time algorithm for computing Roman domination number of special classes of polygraphs (rota- and fasciagraphs). By implementing the algorithm we give formulas for Roman domination number of the Cartesian products of paths and cycles ▫$P_n \Box P_k$▫, ▫$P_n \Box C_k$▫ for ▫$k \leq 8$▫ and ▫$n \in {\mathbb N}$▫ and for ▫$C_n \Box P_k$▫ and ▫$C_n \Box C_k$▫ for ▫$k \leq 5$▫, ▫$n \in {\mathbb N}$▫. We also give a list of Roman graphs among investigated families.
Keywords: graph theory, Roman domination number, Cartesian product, polygraphs, path algebra
Published: 23.08.2017; Views: 600; Downloads: 151
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Conduction and convection heat transfer characteristics of water-based Au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures
Primož Ternik, Rebeka Rudolf, 2014, original scientific article

Abstract: The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles' volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid's (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.
Keywords: natural convection, heat transfer, nanofluid, Nusselt number
Published: 07.07.2017; Views: 606; Downloads: 287
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Wiener numbers of pericondensed benzenoid hydrocarbons
Sandi Klavžar, Ivan Gutman, Amal Rajapakse, 1997, original scientific article

Abstract: Using a recently developed technique for the calculation of the Wiener number (W) of benzenoid systems, we determine explicit expressions for W for several homologous series of pericondensed benzenoid hydrocarbons. An elementary proof for the correctness of the used method is also included.
Keywords: mathematics, chemical graph theory, distance in graphs, Wiener number, benzenoids
Published: 05.07.2017; Views: 680; Downloads: 120
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Computing the weighted Wiener and Szeged number on weighted cactus graphs in linear time
Blaž Zmazek, Janez Žerovnik, 2003, original scientific article

Abstract: Cactus is a graph in which every edge lies on at most one cycle. Linear algorithms for computing the weighted Wiener and Szeged numbers on weighted cactus graphs are given. Graphs with weighted vertices and edges correspond to molecular graphs with heteroatoms.
Keywords: mathematics, graph theory, Wiener number, Szeged number, weighted cactus, linear algorithm
Published: 05.07.2017; Views: 343; Downloads: 69
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How long can one bluff in the domination game?
Boštjan Brešar, Paul Dorbec, Sandi Klavžar, Gašper Košmrlj, 2017, original scientific article

Abstract: The domination game is played on an arbitrary graph ▫$G$▫ by two players, Dominator and Staller. The game is called Game 1 when Dominator starts it, and Game 2 otherwise. In this paper bluff graphs are introduced as the graphs in which every vertex is an optimal start vertex in Game 1 as well as in Game 2. It is proved that every minus graph (a graph in which Game 2 finishes faster than Game 1) is a bluff graph. A non-trivial infinite family of minus (and hence bluff) graphs is established. Minus graphs with game domination number equal to 3 are characterized. Double bluff graphs are also introduced and it is proved that Kneser graphs ▫$K(n,2)$▫, za ▫$n \ge 6$▫, are double bluff. The domination game is also studied on generalized Petersen graphs and on Hamming graphs. Several generalized Petersen graphs that are bluff graphs but not vertex-transitive are found. It is proved that Hamming graphs are not double bluff.
Keywords: domination game, game domination number, bluff graphs, minus graphs, generalized Petersen graphs, Kneser graphs, Cartesian product of graphs, Hamming graphs
Published: 09.05.2017; Views: 624; Downloads: 357
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On Vizing's conjecture
Boštjan Brešar, 2001, original scientific article

Abstract: A dominating set ▫$D$▫ gor a graph ▫$G$▫ is a subset ▫$V(G)$▫ such that any vertex in ▫$V(G)-D$▫ has a neighbor in ▫$D$▫, and a domination number ▫$\gamma(G)$▫ is the size of a minimum dominating set for ▫$G$▫. For the Cartesian product ▫$G \Box H$▫ Vizing's conjecture states that ▫$\gamma(G \Box H) \ge \gamma(G)\gamma(H)$▫ for every pair of graphs ▫$G,H$▫. In this paper we introduce a new concept which extends the ordinary domination of graphs, and prove that the conjecture holds when ▫$\gamma(G) = \gamma(H) = 3$▫.
Keywords: mathematics, graph theory, graph, Cartesian product, domination number
Published: 31.03.2017; Views: 722; Downloads: 79
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