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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
111

Výtvarná kultura Protektorátu Čechy a Morava / Fine Art in the Protectorate Bohemia and Moravia

Pech, Milan January 2012 (has links)
The thesis deals with fine arts in the Protectorate of Bohemia and Moravia. It analyzes Czech fine art during the Nazi occupation of World War Two, concentrating on its official component that has not yet been deeply researched. The author surveyed archives, press and literature of the period. The aim was to identify key themes in the public discussion about artistic issues and to trace developments in the legal status of Czech fine art under the occupation. First, a brief portrait of the historical context of 1938 to 1945, accompanied by identifying several pathological phenomena that occupation and the war brought to Czech society. Those that crept into the fine arts are interpreted from a psychoanalytic point of view. Next the author focuses on the official cultural policy of the Protectorate of Bohemia and Moravia. He notes the short and long-term objectives of Nazi policies and their impact on the workings of cultural life in Czech society. He speaks about radical conservative critiques of modern art, which accused the avant-garde of mercantilism, of politicizing art, of being foreign, and arbitrary. So-called "degenerate" art (Entartete Kunst) is also briefly mentioned. A term that was used to defame and denounce modern art. For the first time, an unknown list of Czech "degenerate" painters...
112

[en] EXISTENCE AND REGULARITY OF SOLUTIONS: NONLOCAL AND NONLINEAR MODELS / [pt] EXISTÊNCIA E REGULARIDADE DE SOLUÇÕES: MODELOS NÃO LOCAIS E NÃO LINEARES

EDISON FAUSTO CUBA HUAMANI 14 September 2021 (has links)
[pt] Estudamos duas classes de equações diferenciais parciais, nomeadamente: uma equação de transferência radiativa e uma equação do calor duplamente não-linear. O primeiro modelo envolve uma equação não-local, na presença de um operador de espalhamento. Estuda-se a boa colocação do problema no semi-plano, no regime peaked. Prova-se um lema de averaging, que produz regularidade interior para o problema, além de regularização fracionária para as derivadas temporais da solução. O segundo conjunto de resultados da tese trata de uma equação de Trudinger com graus de não-linearidade distintos. Aproxima-se este problema pela p-equação do calor e importa-se regularidade da última para a primeira. Como consequência, mostra-se um resultado de regularidade melhorada no contexto não homogêneo. / [en] We consider two classes of partial differential equations. Namely: the radiative transfer equation and a doubly nonlinear model. The former concerns a nonlocal problema, driven by a scattering operator. We study the well-posedness of solutions in the peaked regime, for the half-space. A new averaging lemma yields interior regularity for the solutions and improved fractional regularization for the time derivatives. The second model we examine is a Trudinger equation with distinct nonlinearities degrees. Inspired by ideas launched by L. Caffarelli, we resort to approximation methods and prove improved regularity results for the solutions. The strategy is to relate our equation with p-caloric functions.
113

[pt] DOIS TÓPICOS EM EQUAÇÕES ELÍPTICAS DEGENERADAS COM DEPENDÊNCIA DO GRADIENTE: EXISTÊNCIA DE SOLUÇÕES E ESTIMATIVAS A PRIORI / [en] TWO TOPICS IN DEGENERATE ELLIPTIC EQUATIONS INVOLVING A GRADIENT TERM: EXISTENCE OF SOLUTIONS AND A PRIORI ESTIMATES

DANIA GONZALEZ MORALES 04 February 2019 (has links)
[pt] Esta tese tem o intuito do estudo da existência, não existência e estimativas a priori de soluções não negativas de alguns tipos de problemas elípticos degenerados coercivos e não coercivos com um termo adicional dependendo do gradiente. Dentre outras coisas, obtemos condições integrais generalizadas tipo Keller-Osserman para a existência e não existência de soluções. Também mostramos que condições adicionais e diferentes são necessárias quando p é maior ou igual à 2 ou p é menor ou igual à 2, devido ao caráter degenerado do operador. As estimativas a priori são obtidas para super-soluções e soluções de EDPs elípticas superlineares o sistemas de tais tipos de equações em forma divergente com diferentes operadores e não linearidades. Além do mais, obtemos extensões até a fronteira de algumas desigualdades de Harnack fracas e lemas quantitativos de Hopf para operadores elípticos como o p-Laplaciano. / [en] This thesis concerns the study of existence, nonexistence and a priori estimates of nonnegative solutions of some types of degenerate coercive and non coercive elliptic problems involving an additional term which depends on the gradient. Among other things, we obtain generalized integral conditions of Keller-Osserman type for the existence and nonexistence of solutions. Also, we show that different conditions are needed when p is higher or equal to 2 or p is less than or equal to 2, due to the degeneracy of the operator. The uniform a priori estimates are obtained for supersolutions and solutions of superlinear elliptic PDE or systems of such PDE in divergence form that can contain different operators and nonlinearities. We also give full boundary extensions to some half Harnack inequalities and quantitative Hopf lemmas, for degenerate elliptic operators like the p-Laplacian.
114

Mixtures of ultracold gases: Fermi sea and Bose-Einstein condensate of Lithium isotopes

Schreck, Florian 21 January 2002 (has links) (PDF)
Cette thèse décrit l'étude des gaz de fermions $^6$Li et de bosons<br />$^7$Li dans le régime quantique à très basse température. Le<br />refroidissement est obtenu par évaporation du $^7$Li dans un piège<br />magnétique très confinant. Puisque le refroidissement évaporatif<br />d'un gaz de fermion polarisé est quasiment impossible, le $^6$Li<br />est refroidi sympathiquement par contact thermique avec le $^7$Li.<br />Dans une première série d'expériences, les propriétés des gaz<br />quantiques dans les états hyperfins les plus élevés, piégés<br />magnétiquement, sont étudiées. Un gaz de $10^5$ fermions a une<br />température de 0.25(5) fois la température de Fermi ($T_F$) est<br />obtenu. L'instabilité du condensat pour plus de 300 atomes<br />condensés, à cause des interactions attractives, limite la<br />dégénérescence que l'on peut atteindre. Pour s'affranchir de cette<br />limite, une autre série d'expérience est menée dans les états<br />hyperfins bas, piégeable magnétiquement, où les interactions entre<br />bosons sont faiblement répulsives. Les collisions<br />inter-isotopiques permettent alors la thermalisation du mélange.<br />Le mélange d'un condensat de Bose-Einstein (CBE) de $^7$Li et d'un<br />mer de Fermi de $^6$Li est produit. Le condensat est quasi<br />unidimensionnel et la fraction thermique peut être négligeable. La<br />dégénérescence atteinte correspond à $T/T_C=T/T_F=0.2(1)$. La<br />température est mesurée à partir de la fraction thermique des<br />bosons qui disparaît aux plus basses températures, et limite notre<br />précision de mesure. Dans une troisième série d'expérience, les<br />bosons sont transférés dans un piège optique, et placé dans l'état<br />interne $|F=1,m_F=1\rangle$, l'état fondamental pour les bosons.<br />Une résonance de Feshbach est repérée puis exploitée pour former<br />un condensai où les interactions sont ajustables. Quand les<br />interactions effectives entre les atomes sont attractives, on<br />observe la formation d'un soliton brillant de matière. La<br />propagation de ce soliton sans dispersion sur une distance de<br />$1.1\,$mm est observée.
115

Stabilised finite element approximation for degenerate convex minimisation problems

Boiger, Wolfgang Josef 19 August 2013 (has links)
Die Online-Version dieses Dokuments enthält Software, die unter den Bedingungen der GNU General Public License verbreitet wird, entweder gemäß Version 3 der Lizenz oder jeder späteren Version. Weitere Informationen über Autoren und Lizenzbedingungen befinden sich in Appendix B des Dokuments sowie in LICENSE.txt in der eingebetteten tar-Datei. Die tar-Datei kann mit geeigneter Software geöffnet werden, z.B. mit Acrobat Reader und 7-Zip, oder KDE Okular und GNU tar. / Infimalfolgen nichtkonvexer Variationsprobleme haben aufgrund feiner Oszillationen häufig keinen starken Grenzwert in Sobolevräumen. Diese Oszillationen haben eine physikalische Bedeutung; Finite-Element-Approximationen können sie jedoch im Allgemeinen nicht auflösen. Relaxationsmethoden ersetzen die nichtkonvexe Energie durch ihre (semi)konvexe Hülle. Das entstehende makroskopische Modell ist degeneriert: es ist nicht strikt konvex und hat eventuell mehrere Minimalstellen. Die fehlende Kontrolle der primalen Variablen führt zu Schwierigkeiten bei der a priori und a posteriori Fehlerschätzung, wie der Zuverlässigkeits- Effizienz-Lücke und fehlender starker Konvergenz. Zur Überwindung dieser Schwierigkeiten erweitern Stabilisierungstechniken die relaxierte Energie um einen diskreten, positiv definiten Term. Bartels et al. (IFB, 2004) wenden Stabilisierung auf zweidimensionale Probleme an und beweisen dabei starke Konvergenz der Gradienten. Dieses Ergebnis ist auf glatte Lösungen und quasi-uniforme Netze beschränkt, was adaptive Netzverfeinerungen ausschließt. Die vorliegende Arbeit behandelt einen modifizierten Stabilisierungsterm und beweist auf unstrukturierten Netzen sowohl Konvergenz der Spannungstensoren, als auch starke Konvergenz der Gradienten für glatte Lösungen. Ferner wird der sogenannte Fluss-Fehlerschätzer hergeleitet und dessen Zuverlässigkeit und Effizienz gezeigt. Für Interface-Probleme mit stückweise glatter Lösung wird eine Verfeinerung des Fehlerschätzers entwickelt, die den Fehler der primalen Variablen und ihres Gradienten beschränkt und so starke Konvergenz der Gradienten sichert. Der verfeinerte Fehlerschätzer konvergiert schneller als der Fluss- Fehlerschätzer, und verringert so die Zuverlässigkeits-Effizienz-Lücke. Numerische Experimente mit fünf Benchmark-Tests der Mikrostruktursimulation und Topologieoptimierung ergänzen und bestätigen die theoretischen Ergebnisse. / Infimising sequences of nonconvex variational problems often do not converge strongly in Sobolev spaces due to fine oscillations. These oscillations are physically meaningful; finite element approximations, however, fail to resolve them in general. Relaxation methods replace the nonconvex energy with its (semi)convex hull. This leads to a macroscopic model which is degenerate in the sense that it is not strictly convex and possibly admits multiple minimisers. The lack of control on the primal variable leads to difficulties in the a priori and a posteriori finite element error analysis, such as the reliability-efficiency gap and no strong convergence. To overcome these difficulties, stabilisation techniques add a discrete positive definite term to the relaxed energy. Bartels et al. (IFB, 2004) apply stabilisation to two-dimensional problems and thereby prove strong convergence of gradients. This result is restricted to smooth solutions and quasi-uniform meshes, which prohibit adaptive mesh refinements. This thesis concerns a modified stabilisation term and proves convergence of the stress and, for smooth solutions, strong convergence of gradients, even on unstructured meshes. Furthermore, the thesis derives the so-called flux error estimator and proves its reliability and efficiency. For interface problems with piecewise smooth solutions, a refined version of this error estimator is developed, which provides control of the error of the primal variable and its gradient and thus yields strong convergence of gradients. The refined error estimator converges faster than the flux error estimator and therefore narrows the reliability-efficiency gap. Numerical experiments with five benchmark examples from computational microstructure and topology optimisation complement and confirm the theoretical results.
116

Plasmonic properties and applications of metallic nanostructures

Zhen, Yurong 16 September 2013 (has links)
Plasmonic properties and the related novel applications are studied on various types of metallic nano-structures in one, two, or three dimensions. For 1D nanostructure, the motion of free electrons in a metal-film with nanoscale thickness is confined in its normal dimension and free in the other two. Describing the free-electron motion at metal-dielectric surfaces, surface plasmon polariton (SPP) is an elementary excitation of such motions and is well known. When further perforated with periodic array of holes, periodicity will introduce degeneracy, incur energy-level splitting, and facilitate the coupling between free-space photon and SPP. We applied this concept to achieve a plasmonic perfect absorber. The experimentally observed reflection dip splitting is qualitatively explained by a perturbation theory based on the above concept. If confined in 2D, the nanostructures become nanowires that intrigue a broad range of research interests. We performed various studies on the resonance and propagation of metal nanowires with different materials, cross-sectional shapes and form factors, in passive or active medium, in support of corresponding experimental works. Finite- Difference Time-Domain (FDTD) simulations show that simulated results agrees well with experiments and makes fundamental mode analysis possible. Confined in 3D, the electron motions in a single metal nanoparticle (NP) leads to localized surface plasmon resonance (LSPR) that enables another novel and important application: plasmon-heating. By exciting the LSPR of a gold particle embedded in liquid, the excited plasmon will decay into heat in the particle and will heat up the surrounding liquid eventually. With sufficient exciting optical intensity, the heat transfer from NP to liquid will undergo an explosive process and make a vapor envelop: nanobubble. We characterized the size, pressure and temperature of the nanobubble by a simple model relying on Mie calculations and continuous medium assumption. A novel effective medium method is also developed to replace the role of Mie calculations. The characterized temperature is in excellent agreement with that by Raman scattering. If fabricated in an ordered cluster, NPs exhibit double-resonance features and the double Fano-resonant structure is demonstrated to most enhance the four-wave mixing efficiency.

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