MICROSTRIP FILTERS USING DEFECTED GROUND STRUCTURE

Tato práce se zabývá možností využití narušené zemní plochy (DGS) při návrhu mikropáskových filtrů, založených na technologii nesymetrického mikropáskového vedení. Zemní rovina není (jako u klasického mikropáskového vedení) celistvá, ale odstraněním jejich částí vznikají struktury, vykazující rezonanční vlastnosti, kterých je využito při návrhu filtrů. Práci lze po věcné stránce rozdělit do tří částí. V první části (kapitola 4) jsou vlastnosti jednoho typu dolní propusti analyzovány pomocí simulací. Jedná se tedy o určitý experimentální úvod do problematiky DGS. V druhé části (kapitola 5) je prezentována nová výpočetní metoda pro návrh dolních propustí s DGS, jejíž funkčnost je ověřena simulacemi i realizací vzorků filtrů. Třetí část práce (kapitoly 7 a 8) pak pojednává o využití smyčkových rezonátorů tvořených štěrbinami v zemní rovině substrátu ve filtrech typu pásmová propust. Je uvažována i možnost kombinace těchto rezonátorů s rezonátory mikropáskovými. Několik filtrů tohoto typu je navrženo, simulováno a výsledky jsou ověřeny realizací vzorků.The thesis deals with the microstrip filter design using defected ground structure (DGS). The difference between standard asymmetric microstrip technique and DGS is in using the structures etched in the microwave substrate ground plane. The DGS resonant characteristics are then used in filter design. The thesis consists of three factual parts. The first one (chapter 4) introduces the use of the DGS resonators in the lowpass filter design. It involves experimental analysis of one type of the lowpass filter. The second part (chapter 5) deals with a novel microstrip lowpass filter design method using DGS. The proposed method is verified by simulations and several samples are realized and measured. Finally, the third part (chapters 7 and 8) deals with the bandpass filter design using specific defected ground structure as a resonator. The resonators are used in a coupled resonator structure. Filters of various orders and resonator configurations are designed and simulated. A combination of the DGS resonators and half-wavelength microstrip resonators is introduced as well. Selected samples are realized and measurement results are compared with simulations.

A multiscale thermodynamic generalization of Maxwell--Stefan diffusion equations and of the dusty gas model

Despite the fact that the theory of mixtures has been part of non-equilibrium thermodynamics and engineering for a long time, it is far from complete. While it is well formulated and tested in the case of mechanical equilibrium (where only diffusion-like processes take place), the question how to properly describe homogeneous mixtures that flow with multiple independent velocities that still possess some inertia (before mechanical equilibrium is reached) is still open. Moreover, the mixtures can have several temperatures before they relax to a common value. In this paper, we derive a theory of mixtures from Hamiltonian mechanics in interaction with electromagnetic fields. The resulting evolution equations are then reduced to the case with only one momentum (classical irreversible thermodynamics), providing a generalization of the Maxwell-Stefan diffusion equations. In a next step, we reduce that description to the mechanical equilibrium (no momentum) and derive a non-isothermal variant of the dusty gas model. These reduced equations are solved numerically, and we illustrate the results on effciency analysis, showing where in a concentration cell effciency is lost. Finally, the theory of mixtures identifies the temperature difference between constituents as a possible new source of the Soret coeffcient. For the sake of clarity, we restrict the presentation to the case of binary mixtures; the generalization is straightforward

A continuum model for yttria-stabilized zirconia incorporating triple phase boundary, lattice structure and immobile oxide ions

A continuum model for yttria-stabilized zirconia (YSZ) in the framework of non-equilibrium thermodynamics is developed. Particular attention is given to (i) modeling of the YSZ-metal-gas triple phase boundary, (ii) incorporation of the lattice structure and immobile oxide ions within the free energy model and (iii) surface reactions. A finite volume discretization method based on modified Scharfetter-Gummel fluxes is derived in order to perform numerical simulations. The model is used to study the impact of yttria and immobile oxide ions on the structure of the charged boundary layer and the double layer capacitance. Cyclic voltammograms of an air-half cell are simulated to study the effect of parameter variations on surface reactions, adsorption and anion diffusion. © 2019, The Author(s)

Dynamic maximum entropy reduction

Any physical system can be regarded on different levels of description varying by how detailed the description is. We propose a method called Dynamic MaxEnt (DynMaxEnt) that provides a passage from the more detailed evolution equations to equations for the less detailed state variables. The method is based on explicit recognition of the state and conjugate variables, which can relax towards the respective quasi-equilibria in different ways. Detailed state variables are reduced using the usual principle of maximum entropy (MaxEnt), whereas relaxation of conjugate variables guarantees that the reduced equations are closed. Moreover, an infinite chain of consecutive DynMaxEnt approximations can be constructed. The method is demonstrated on a particle with friction, complex fluids (equipped with conformation and Reynolds stress tensors), hyperbolic heat conduction and magnetohydrodynamics

Generalized Poisson--Nernst--Planck-based physical model of O2_2 I LSM I YSZ electrode

The paper presents a generalized Poisson-Nernst-Planck model of an yttria-stabilized zirconia electrolyte developed from first principles of nonequilibrium thermodynamics which allows for spatial resolution of the space charge layer. It takes into account limitations in oxide ion concentrations due to the limited availability of oxygen vacancies. The electrolyte model is coupled with a reaction kinetic model describing the triple phase boundary with electron conducting lanthanum strontium manganite and gaseous phase oxygen. By comparing the outcome of numerical simulations based on different formulations of the kinetic equations with results of EIS and CV measurements we attempt to discern the existence of separate surface lattice sites for oxygen adatoms and O2- from the assumption of shared ones. Furthermore, we discern mass-action kinetics models from exponential kinetics models

Quietly does it: questioning assumptions about class, sustainability and consumption

This paper questions assumptions about the relationship between class formation, sustainability and patterns of consumption. The empirical elements of the research are based upon qualitative and quantitative time-series research into food self-provisioning and 'quiet sustainability' in post socialist Central and Eastern Europe (Poland and the Czech Republic). It considers sustainable practices that are often considered to be taking place 'in the wrong place and the wrong time', i.e. they appear anomalous in terms of western expectations of patterns of development. We offer evidence of comparatively very high levels of food self-provisioning and sharing of the resulting produce amongst middle class Poles and Czechs. This evidence questions widely held assumptions about class, development and consumption. This evidence may be of significance for consideration of a much wider set of household practices/behaviours that are associated with the middle classes. Our explorations of the reasons for food self-provisioning throw new light on discussions of ethical consumption: ethics is lightly worn, even unacknowledged, amongst practitioners, but the commitments are widespread and robust. Our empirical findings, and the theoretical arguments we seek to test on the basis of them, are of particular significance in the context of rapid processes of rural and urban change in emerging economies

Scintillation detectors LaBr3(Ce) and LaCl3(Ce) applications in the gamma spectrometry and the environmental monitoring

V práci jsou popsány hlavní fyzikální a technické principy fungování anorganických scintilačních detektorů zejména s ohledem ke spektrometrii fotonového záření. Dále jsou uvedeny základní charakteristiky detektorů NaI(Tl), LaBr3(Ce) a LaCl3(Ce) a možnost jejich využití v monitorování životního prostředí. Nakonec je rozebrána spektrometrická trasa, vlastnosti a možnosti analýzy scintilačních spekter a metoda simulace jednoduchých scintilačních detektorů.In the thesis there are described main physical and technical principles of inorganic scintillators especially given to gamma-ray spectrometry. Next there are stated basic characteristics of detectors NaI(Tl), LaBr3(Ce), LaCl3(Ce) and their possible use in environmental monitoring. Finally there is analysis of spectrometry route, properties and possible analysis of scintillation spectrum and methods of simulation of simple scintillation detectors

Termodynamická analýza procesů v palivových článcích s pevnými oxidy

The fuel cells are the technology of the future. Although their discovery dates back to the 19th century the nature of how they work hasnt been adequately explained so far. This thesis focuses on description of solid oxides fuel cells (SOFC) for which ion conductive electrolyte and high operating temperature are distinctive. The mathematical model of SOFC developed in this thesis is formulated in terms of the mixture theory. The model development was constrained and simplified by isothermality, time-stationery and 1D approximation. The model equations characterize gas and ion transport and electric current flow in the fuel cell. Eventually comparison of the thesis model equations with the SOEC (solid oxides electrolysis cell) model developed at the Institute of Chemical Technology in Prague showed that both approaches lead to a similar conclusion. This thesis can be used as a basis for an experimental verification of the mixture theory.

Thermodynamic analysis of solid oxide cells

Thermodynamic analysis of solid oxide cells Petr Vágner The thesis deals with continuum thermodynamic modeling and analysis of phe- nomena in solid oxide electrochemical cells. A general description of the evo- lution of charged mixtures using partial mass densities, momentum density, entropy density, electric induction, magnetic field, polarization, and magnetiza- tion based on the GENERIC framework is formulated. The formulation is used to recover the Landau-Lifshitz magnetization relaxation model, the Single Re- laxation Time model for dielectrics, and the generalized Poisson-Nernst-Planck model. The latter model is consequently linked to the second part, where a novel double layer model of an yttria-stabilized zirconia interface is formulated within non-equilibrium thermodynamics. The model is solved for numerically in the time domain, and cyclic voltammetry of the system is analyzed. The last part of the thesis demonstrates the limits of Exergy Analysis on a simple solid oxide hydrogen fuel cell model with non-isothermal boundary. It is demon- strated that the minimization of entropy production does not necessarily lead to the maximization of the electric power for certain optimization scenarios. The thesis consists of a compilation of published and unpublished results of the author

Termodynamická analýza článků s pevnými oxidy

Termodynamická analýza článků s pevnými oxidy Petr Vágner Práce se zabývá modelováním článků s pevnými oxidy v rámci nerovnovážné ter- modynamiky. Nejprve je zformulován obecný popis evoluce směsi nabitých látek ve formalismu GENERIC pomocí parciálních hustot, hustoty hybnosti, hustoty entropie, pole elektrické indukce, magnetického pole, polarizace a magnetizace. Tato obecná formulace zahrnuje známé modely, jako jsou Landauova-Lifshitzova relaxace magnetizace, Single Relaxation Time model pro dielektrika a zobecněný Poissonův-Nernstův-Planckův model. Odvození poslední zmíněného modelu je dáno do souvislosti s druhou částí práce, ve které je zformulován nový model pro rozhraní článku s pevnými oxidy v rámci nerovnovážné termodynamiky. Numer- ické řešení evolučního modelu je využito k parametrické studii cyklické voltam- metrie rozhraní. Poslední část práce demonstruje limity Exergetické Analýzy pro zařízení s neizotermální hranici. Elektrický výkon zjednodušeného modelu vodíkového článku s pevnými oxidy je maximalizován v několika optimalizačních scénářích a je ukázáno, že minimalizace produkce entropie nutně nevede k max- imalizaci elektrického výkonu. Práce se sestává z kompilace publikovaných i...Thermodynamic analysis of solid oxide cells Petr Vágner The thesis deals with continuum thermodynamic modeling and analysis of phe- nomena in solid oxide electrochemical cells. A general description of the evo- lution of charged mixtures using partial mass densities, momentum density, entropy density, electric induction, magnetic field, polarization, and magnetiza- tion based on the GENERIC framework is formulated. The formulation is used to recover the Landau-Lifshitz magnetization relaxation model, the Single Re- laxation Time model for dielectrics, and the generalized Poisson-Nernst-Planck model. The latter model is consequently linked to the second part, where a novel double layer model of an yttria-stabilized zirconia interface is formulated within non-equilibrium thermodynamics. The model is solved for numerically in the time domain, and cyclic voltammetry of the system is analyzed. The last part of the thesis demonstrates the limits of Exergy Analysis on a simple solid oxide hydrogen fuel cell model with non-isothermal boundary. It is demon- strated that the minimization of entropy production does not necessarily lead to the maximization of the electric power for certain optimization scenarios. The thesis consists of a compilation of published and unpublished results of the author.Mathematical Institute of Charles UniversityMatematický ústav UKFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult