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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.
171

As novas formas de controle em One Dimensional Man, de Herbert Marcuse

Jannarelli, Vicente Claudio 01 October 2010 (has links)
Made available in DSpace on 2016-04-27T17:26:52Z (GMT). No. of bitstreams: 1 Vicente Claudio Jannarelli.pdf: 396996 bytes, checksum: f73c91adbb40d28ab3983198884316c9 (MD5) Previous issue date: 2010-10-01 / One-Dimensonal Man deals with certain basic tendencies in contemporary industrial society which seem indicate a new phase of civilization. These tendencies have engendered a mode of thought and behavior which undermined the very foundations of the traditional culture. The main characteristic of this new mode of thought and behavior is the repression of all values, aspirations, and ideas which cannot be defined in terms of operations and attitudes validated by the prevailing forms of rationality. The consequence is the weakening and even the disappearance of all genuinely radical critique, the integration of all opposition in the established system. Herbert Marcuse develops, in One-Dimensional Man, a model both of his critical social theory and of his critical philosophy inspired by his philosophical studies and his work with the Frankfurt School. Also describes a the mechanisms through which the advanced industrial society integrates individuals into its world of thought and behavior. Identifying these mechanisms - the new forms of control , according to Marcuse - their origin, the relationship and synergy amongst themselves are the main scopes of this present job / One-Dimensional Man trabalha com certas tendências básicas da sociedade industrial avançada que parecem indicar uma nova fase de civilização. Tais tendências geraram uma forma de pensamento e comportamento que minou a base da cultura tradicional. A principal característica dessa nova forma de pensamento e de comportamento é a repressão de todos os valores, aspirações, e idéias que não podem ser definidas em termos de operações e atitudes validadas pelas formas prevalecentes de racionalidade. A conseqüência é o enfraquecimento e mesmo o desaparecimento de toda crítica genuinamente radical, a integração de toda oposição no sistema estabelecido. Herbert Marcuse desenvolve, em One-Dimensional Man, não apenas um modelo de crítica social, como também sua filosofia crítica inspirada por seus estudos filosóficos e por trabalho desenvolvido junto à Escola de Frankfurt. Descreve também os mecanismos através dos quais a sociedade industrial avançada integra indivíduos em seu mundo de pensamento e comportamento. Identificar esses mecanismos as novas formas de controle , conforme Marcuse sua origem, o relacionamento e sinergia entre eles são os principais objetivos da presente dissertação
172

Etude des propriétés mésoscopiques dans les systèmes quasi-unidimensionnels à onde de densité de charge

AYARI, Anthony 25 November 2002 (has links) (PDF)
Nous avons étudié les propriétés de transport des ondes de densité de charge dans le composé quasi-unidimensionnel NbSe3, à l'échelle micronique et submicronique (jusqu'à 300nm). Nous avons mis au point un process de salle blanche pour la réalisation de microstructures à onde de densité de charge, connectées électriquement par des contacts ohmiques. Cela nous permit de réaliser des expériences sur l'effet d'une force perpendiculaire au mouvement d'une onde de densité de charge et d'observer que la réduction du champ seuil de dépiégeage mesuré précédemment par un autre groupe était liée à des inhomogénéités d'injection de courant et non à une augmentation de l'effet de taille géométrique et de la gravure sur les propriétés des échantillons comme le champ seuil ou la température de transition. De plus, nous avons effectué des mesures couplées transport/rayons X à haute résolution à l'ESRF (European Synchrotron Radiation Facility). Nous avons observé un accroissement de la cohérence spatiale du condensat quand la cohérence temporelle augmente et nous avons étudié différents mécanismes d'interaction entre deux ondes de densité de charge.
173

Formation and Decomposition of Platinum–Thallium Bond, Kinetics and Mechanism. Structural Characterization of Some Metal Cyanides in the Solid State

Nagy, Péter January 2004 (has links)
The kinetic and mechanistic features of a new series ofplatinum-thallium cyano compounds containing a direct andunsupported by ligands metal-metal bond have been studied insolution, using standard mix–and–measurespectrophotometric technique and stopped–flow method.These reactions are interpreted as oxidative addition of the cspecies to the square planar Pt(CN)42-complex. Each of these processes was found to befirst-order in Pt(CN)42-, the corresponding TIIIIcomplex and a cyanide ion donating species whichacts as a catalyst. Both di- and trinuclear complexes werestudied, and the kinetically significant thallium complexes intheir formation and the catalytically active cyanide sourcesare as follows: [(CN)5PtTl(CN)3]3-: Tl(CN)4–(alkaline region), Tl(CN)3(slightly acidic region) and CN–; [(CN)5Pt–Tl(CN)]–: Tl(CN)2+and Tl(CN)2+; [(CN)5Pt–Tl–Pt(CN)5]3-: [(CN)5Pt–Tl(CN)]–and HCN. Appropriatemechanisms were postulated for the overall reactions in allcases, which include i) metal–metal bond formation stepand ii) coordination of an axial cyanide ion to the platinumcenter. Two experimentally indistinguishable kinetic modelswere proposed for the formation of the dinuclear complexeswhich are different in the sequence of the two steps. In thecase of the trinuclear complex, experimental evidence isavailable to exclude one of the alternative reaction paths, andit was proven that the metal–metal bond formation precedesthe axial cyanide coordination. The cyanide ligands coordinated to TIIIIin the Pt–Tl complexes could be replacedsuccessfully with aminopolycarboxylates e.g.: mimda2-, nta3-, edta4-. The [(CN)5Pt–Tl(edta)]4-complex, with a direct metal–metal bond hasbeen prepared in solution by two different reactions: a)dissolution of [(CN)5Pt–Tl](s) in an aqueous solution of edta, b)directly from Pt(CN)42-and Tl(edta)(CN)2-. The decomposition reaction is greatlyaccelerated by cyanide and significantly inhibited by edta. Itproceeds through the [(CN)5Pt–Tl(CN)3]3-intermediate. The formation of [(CN)5Pt–Tl(edta)]4-can proceed via two different pathways dependingon the ratio of the cyanide to the edta ligand concentrations.The’direct path’at excess of edta means theformation of intermediate[(CN)4Pt···Tl(CN)(edta)]4-, followed by a release of the cyanide from theTl–centre followed by coordination of a cyanide from thebulk to the Pt–centre of the intermediate. The’indirect path’dominates in the absence of extraedta and the formation of the Pt–Tl bond occours betweenPt(CN)42-and Tl(CN)4–. Homoligand MTl(CN)4(M = TlI, K, Na) and, for the first time, Tl(CN)3species have been synthesized in the solid stateand their structures solved by single crystal X–raydiffraction method. Interesting redox processes have been foundbetween TIIIIand CN–in non–aqueous solution and in Tl2O3-CN–aqueous suspension. In the crystal structureof Tl(CN)3·H2O, the thallium(III) ion has a trigonal bypiramidalcoordination geometry with three cyanides in the trigonalplane, while an oxygen atom of the water molecule and anitrogen atom from a cyanide ligand attached to a neighboringthallium complex, form a linear O–Tl–N fragment.Cyanide ligand bridges thallium units forming an infinitezigzag chain structure. Among the thallium(III) tetracyanocompounds, the isostructural M[Tl(CN)4](M = Tl and K) and Na[Tl(CN)4]·3H2O crystallize in different crystal systems, but thethallium(III) ion has in all cases the same tetrahedralgeometry in the [Tl(CN)4]–unit. Three adducts of mercury(II) (isoelectronic with TIIII) (K2PtHg(CN)6·2H2O, Na2PdHg(CN)6·2H2O and K2NiHg(CN)6·2H2O) have been prepared from Hg(CN)2and square planar transition metal cyanides MII(CN)42-and their structure have been studied by singlecrystal X–ray diffraction, XPS and Raman spectroscopy inthe solid state. The structure of (K2PtHg(CN)6·2H2O consists of strictly linear one dimensional wireswith PtIIand HgIIcenters located alternately, dHg–Pt= 3.460 Å. The structure of Na2PdHg(CN)6·2H2O and K2NiHg(CN)6·2H2O can be considered as double salts, the lack ofhetero–metallophilic interaction between both the HgIIand PdIIatoms, dHg–Pd= 4.92 Å, and HgIIand NiIIatoms, dNi–Pd= 4.60 Å, seems obvious. Electronbinding energy values of the metallic centers measured by XPSshow that there is no electron transfer between the metal ionsin all three adducts. In solution, experimental findingsclearly indicate the lack of metal–metal bond formation inall studied HgII–CN-–MII(CN)42-systems (M = Pt, Pd and Ni). It is in contrary tothe platinum–thallium bonded cyanides. KEYWORDS:metal–metal bond, platinum, thallium,kinetics, mechanism, stopped flow, oxidative addition, cyanocomplexes, edta, redox reaction, metal cyanides, X–raydiffraction, Raman, NMR, mercury, palladium, nickel, onedimensional wire
174

Limit theorems for a one-dimensional system with random switchings

Hurth, Tobias 15 November 2010 (has links)
We consider a simple one-dimensional random dynamical system with two driving vector fields and random switchings between them. We show that this system satisfies a one force - one solution principle and compute its unique invariant density explicitly. We study the limiting behavior of the invariant density as the switching rate approaches zero and infinity and derive analogues of classical probabilistic results such as the central limit theorem and large deviations principle.
175

Ultrafast Dynamics in Quasi-One-Dimensional Organic Molecular Crystals / Self-Assembled Monolayers of Photochromic Molecules / Ultraschnelle Dynamik in quasi-eindimensionalen organischen Molekülkristallen / Selbst-assemblierte Monoschichten photochromer Moleküle

Canzler, Tobias W. 16 September 2002 (has links) (PDF)
Der erste Teil der Arbeit beschäftigt sich mit ultraschnellen Relaxationsprozessen in quasi-eindimensionalen organischen Molekülkristallen. Als Modellsystem wird das Perylenderivat MePTCDI untersucht. Mit verschiedenen Methoden der optischen Ultrakurzzeit-Spektroskopie werden Prozesse der Exzitonen- und Phononenrelaxation in der Zeit-Domäne untersucht. Die dafür aufgebauten Experimente erreichen eine Zeitauflösung von 20 Femtosekunden. Durch optische Anregung der niedrigsten elektronischen Übergänge werden in einem organischen Molekülkristall freie Exzitonen mit Wellenvektor k=0 gebildet. Dabei werden gleichzeitig zahlreiche intramolekulare und intermolekulare Schwingungsfreiheitsgrade angeregt. Die Anregung mit fs-Laserpulsen führt zum Aufbau kohärenter Schwingungswellenpakete. Es werden sowohl hochenergetische Oszillationen intramolekularer Vibrationen beobachtet, als auch erstmalig niedrigenergetische Oszillationen, die von Gittervibrationen (Phononen) stammen. Die kohärenten Vibrationen im elektronischen Grundzustand klingen bei Raumtemperatur im Bereich einiger Pikosekunden ab. Durch die optische Anregung mit fs-Laserpulsen wird nicht nur phononische Kohärenz, sondern auch elektronische Kohärenz der optischen Übergänge induziert. Die elektronische Kohärenz klingt mit der Dephasierungszeit T2 ab. Trotz der hohen Zeitauflösung war es letztendlich nicht möglich, die Dephasierung des niedrigsten exzitonischen Übergangs zeitlich aufzulösen - sie liegt jedoch im Bereich 17fs < T2 < 52fs. Die energetische Relaxation der freien Exzitonen zu den relaxierten, emittierenden Exzitonenzuständen erfolgt mit einer Zeitkonstante von ca. 50fs. Von diesen relaxierten Zuständen erfolgt die energetische Abregung in den elektronischen Grundzustand im ns-Bereich. Im zweiten Teil der Arbeit werden Untersuchungen an selbst-assemblierten Monoschichten (SAM) photochromer Moleküle vorgestellt. Als Modellsystem dienen Azobenzen-funktionalisierte Thiole auf Gold (111). Es konnten hochgeordnete Monoschichten dieser photochromen Moleküle erzielt werden, allerdings sind die bisherigen Schichten aufgrund der dichten Packung nicht photoaktivierbar. Mit Hilfe von Raster-Mikroskopie und Infrarot-Spektroskopie werden diese ultradünnen Schichten strukturell untersucht. Es wird ein kommensurates Wachstum mit zwei Molekülen in der nahezu rechteckigen Einheitszelle beobachtet, wobei die laubbaumförmigen Moleküle nahezu senkrecht auf der Oberfläche stehen. Als weitere Methode wurde die Generation der zweiten Harmonischen (Second Harmonic Generation, SHG) angewendet. Diese Technik eröffnet prinzipiell die Möglichkeit, photostimuliertes Schalten der Schicht zeitaufgelöst zu untersuchen. / The first part of this thesis is devoted to ultrafast relaxation processes in quasi-one-dimensional organic molecular crystals. Crystalline samples of the perylene derivative MePTCDI are employed as a model system. Processes concerning the excitonic and phononic relaxation are investigated in time domain using various experimental techniques of optical ultrafast spectroscopy. The experimental setups attain a time-resolution of 20 femtoseconds. Free excitons at wavevector k=0 are formed in a molecular crystal by optical excitation of the lowest electronic transitions. Thereby, various intramolecular and intermolecular vibrational degrees of freedom are excited simultaneously. The excitation by fs-laser pulses results in the composition of coherent vibrational wave packets. Both, higher-energetic oscillations caused by intramolecular vibrations (internal phonons) and, for the first time in a quasi-one-dimensional organic system, lower-energetic modulations which are related to coherent lattice phonons (external phonons) are observed. The coherence of both types of phonons in the electronic ground state is damped at room temperature within a few ps. Besides phononic coherence, optical excitation by fs-laser pulses additionally induces electronic coherence of the optical transitions. The electronic coherence decays with the dephasing time T2. In spite of the high time-resolution, finally it was not possible to time resolve the dephasing of the lowest excitonic transition - however, we can estimated it to be in the range of 17fs < T2 < 52fs. The energetic relaxation of free excitons to the relaxed, emitting exciton states takes place with a time constant of approx. 50fs. The subsequent energetic relaxation to the electronic ground state occurs on a ns-time scale. In the second part, investigations of self-assembled monolayers (SAM) of photochromic molecules are presented. Azobenzene-functionalized thiols on gold (111) are employed as a model system. Highly ordered monolayers of these photochromic molecules could be realized. However, these layers are not photoactive because of dense packing. By use of scanning tunneling microscopy and infra-red spectroscopy the structural properties of these ultrathin layers are investigated. A commensurate growth, yielding a lattice with two molecules within the nearly rectangular unit cell is observed. The molecules, shaped like a broad-leafed tree, are found to stand nearly upright on the surface. Second harmonic generation (SHG) is applied as another experimental method. This technique allows to time resolve photo-stimulated conformational changes of the layers in principle.
176

Formation and Decomposition of Platinum–Thallium Bond, Kinetics and Mechanism. Structural Characterization of Some Metal Cyanides in the Solid State

Nagy, Péter January 2004 (has links)
<p>The kinetic and mechanistic features of a new series ofplatinum-thallium cyano compounds containing a direct andunsupported by ligands metal-metal bond have been studied insolution, using standard mix–and–measurespectrophotometric technique and stopped–flow method.These reactions are interpreted as oxidative addition of the cspecies to the square planar Pt(CN)<sub>4</sub><sup>2-</sup>complex. Each of these processes was found to befirst-order in Pt(CN)<sub>4</sub><sup>2-</sup>, the corresponding TI<sup>III</sup>complex and a cyanide ion donating species whichacts as a catalyst. Both di- and trinuclear complexes werestudied, and the kinetically significant thallium complexes intheir formation and the catalytically active cyanide sourcesare as follows: [(CN)<sub>5</sub>PtTl(CN)<sub>3</sub>]<sup>3-</sup>: Tl(CN)<sub>4</sub><sup>–</sup>(alkaline region), Tl(CN)<sub>3</sub>(slightly acidic region) and CN<sup>–</sup>; [(CN)<sub>5</sub>Pt–Tl(CN)]–: Tl(CN)<sub>2</sub><sup>+</sup>and Tl(CN)<sub>2</sub><sup>+</sup>; [(CN)<sub>5</sub>Pt–Tl–Pt(CN)<sub>5</sub>]<sup>3-</sup>: [(CN)<sub>5</sub>Pt–Tl(CN)]–and HCN. Appropriatemechanisms were postulated for the overall reactions in allcases, which include i) metal–metal bond formation stepand ii) coordination of an axial cyanide ion to the platinumcenter. Two experimentally indistinguishable kinetic modelswere proposed for the formation of the dinuclear complexeswhich are different in the sequence of the two steps. In thecase of the trinuclear complex, experimental evidence isavailable to exclude one of the alternative reaction paths, andit was proven that the metal–metal bond formation precedesthe axial cyanide coordination.</p><p>The cyanide ligands coordinated to TI<sup>III</sup>in the Pt–Tl complexes could be replacedsuccessfully with aminopolycarboxylates e.g.: mimda<sup>2-</sup>, nta<sup>3-</sup>, edta<sup>4-</sup>. The [(CN)<sub>5</sub>Pt–Tl(edta)]<sup>4-</sup>complex, with a direct metal–metal bond hasbeen prepared in solution by two different reactions: a)dissolution of [(CN)<sub>5</sub>Pt–Tl](s) in an aqueous solution of edta, b)directly from Pt(CN)<sub>4</sub><sup>2-</sup>and Tl(edta)(CN)<sup>2-</sup>. The decomposition reaction is greatlyaccelerated by cyanide and significantly inhibited by edta. Itproceeds through the [(CN)<sub>5</sub>Pt–Tl(CN)<sub>3</sub>]<sup>3-</sup>intermediate. The formation of [(CN)<sub>5</sub>Pt–Tl(edta)]<sup>4-</sup>can proceed via two different pathways dependingon the ratio of the cyanide to the edta ligand concentrations.The’direct path’at excess of edta means theformation of intermediate[(CN)4Pt···Tl(CN)(edta)]<sup>4-</sup>, followed by a release of the cyanide from theTl–centre followed by coordination of a cyanide from thebulk to the Pt–centre of the intermediate. The’indirect path’dominates in the absence of extraedta and the formation of the Pt–Tl bond occours betweenPt(CN)<sub>4</sub><sup>2-</sup>and Tl(CN)4<sup>–</sup>.</p><p>Homoligand MTl(CN)<sub>4</sub>(M = Tl<sup>I</sup>, K, Na) and, for the first time, Tl(CN)<sub>3</sub>species have been synthesized in the solid stateand their structures solved by single crystal X–raydiffraction method. Interesting redox processes have been foundbetween TI<sup>III</sup>and CN<sup>–</sup>in non–aqueous solution and in Tl<sub>2</sub>O<sub>3</sub>-CN<sup>–</sup>aqueous suspension. In the crystal structureof Tl(CN)<sub>3</sub>·H<sub>2</sub>O, the thallium(III) ion has a trigonal bypiramidalcoordination geometry with three cyanides in the trigonalplane, while an oxygen atom of the water molecule and anitrogen atom from a cyanide ligand attached to a neighboringthallium complex, form a linear O–Tl–N fragment.Cyanide ligand bridges thallium units forming an infinitezigzag chain structure. Among the thallium(III) tetracyanocompounds, the isostructural M[Tl(CN)<sub>4</sub>](M = Tl and K) and Na[Tl(CN)<sub>4</sub>]·3H<sub>2</sub>O crystallize in different crystal systems, but thethallium(III) ion has in all cases the same tetrahedralgeometry in the [Tl(CN)<sub>4</sub>]<sup>–</sup>unit.</p><p>Three adducts of mercury(II) (isoelectronic with TI<sup>III</sup>) (K<sub>2</sub>PtHg(CN)<sub>6</sub>·2H<sub>2</sub>O, Na<sub>2</sub>PdHg(CN)<sub>6</sub>·2H<sub>2</sub>O and K<sub>2</sub>NiHg(CN)<sub>6</sub>·2H<sub>2</sub>O) have been prepared from Hg(CN)<sub>2</sub>and square planar transition metal cyanides M<sup>II</sup>(CN)<sub>4</sub><sup>2-</sup>and their structure have been studied by singlecrystal X–ray diffraction, XPS and Raman spectroscopy inthe solid state. The structure of (K<sub>2</sub>PtHg(CN)<sub>6</sub>·2H<sub>2</sub>O consists of strictly linear one dimensional wireswith Pt<sup>II</sup>and Hg<sup>II</sup>centers located alternately, d<sub>Hg–Pt</sub>= 3.460 Å. The structure of Na<sub>2</sub>PdHg(CN)<sub>6</sub>·2H<sub>2</sub>O and K<sub>2</sub>NiHg(CN)<sub>6</sub>·2H<sub>2</sub>O can be considered as double salts, the lack ofhetero–metallophilic interaction between both the Hg<sup>II</sup>and Pd<sup>II</sup>atoms, d<sub>Hg–Pd</sub>= 4.92 Å, and Hg<sup>II</sup>and Ni<sup>II</sup>atoms, d<sub>Ni–Pd</sub>= 4.60 Å, seems obvious. Electronbinding energy values of the metallic centers measured by XPSshow that there is no electron transfer between the metal ionsin all three adducts. In solution, experimental findingsclearly indicate the lack of metal–metal bond formation inall studied Hg<sup>II</sup>–CN<sup>-</sup>–M<sup>II</sup>(CN)4<sup>2-</sup>systems (M = Pt, Pd and Ni). It is in contrary tothe platinum–thallium bonded cyanides.</p><p><b>KEYWORDS:</b>metal–metal bond, platinum, thallium,kinetics, mechanism, stopped flow, oxidative addition, cyanocomplexes, edta, redox reaction, metal cyanides, X–raydiffraction, Raman, NMR, mercury, palladium, nickel, onedimensional wire</p>
177

Zur Dynamik geometrisch nichtlinearer Balken

Weiß, Holger 07 January 2000 (has links)
Ziel der Arbeit ist es, die instationären zeitlichen und räumlichen Bewegungsabläufe stark deformierbarer eindimensionaler Kontinua durch ein allgemeines mechanisch-mathematisches Modell unter Berücksichtigung ihrer Biege- und Torsionssteifigkeit zu beschreiben und zu dessen Lösung geeignete numerische Verfahren zu testen und auszuwählen. Die entwickelten Algorithmen werden auf Aufgabenstellungen aus der Raumfahrt-, Meeres- und Textiltechnik angewendet. / It is the aim of this thesis to describe the instationary motion of flexible one-dimensional continua by a general mechanical-mathematical model, when bending and torsional stiffness is not negligible, and to test and select appropriate numerical solution methods. The developed algorithms are used to solve problems from space, marine and textil engineering.
178

Dielectric Formulation Of The One Dimensional Electron Gas

Tas, Murat 01 April 2004 (has links) (PDF)
The charge and spin density correlations in a one dimensional electron gas (1DEG) confined in a semiconductor quantum wire structure at zero temperature are studied. The dielectric formulation of the many--body problem is employed and the longitudinal dielectric function, local-field correction, static structure factor, pair correlation function, ground state energy, compressibility, spin-dependent effective interaction potentials, paramagnon dispersion and static spin response function of the 1DEG are computed within the self-consistent field approximations of Singwi et al., known as the STLS and SSTL. The results are compared with those of other groups, and those obtained for two-dimensional electron gas systems whenever it is possible. It is observed that the SSTL satisfies the compressibility sum rule better than the STLS. Calculating the ground state energy of the 1DEG in unpolarized and fully polarized states, it is shown that both STLS and SSTL predict a Bloch transition for 1DEG systems at low electron densities. Finally, the coupled plasmon-phonon modes in semiconductor quantum wires are calculated within the Fermi and Luttinger liquid theories. The coupling of electrons to bulk longitudinal optical phonons without dispersion and to acoustic phonons via deformation potential with a linear dispersion are considered. Using the dielectric formalism, a unified picture of the collective coupled plasmon-phonon modes is presented. Considerable differences between the predictions of the Fermi and Luttinger liquid approaches at large wave vector values, which may be observed experimentally, are found.
179

Radiative transfer in multiply layered media

De Lautour, N. J. (Nathaniel J.) January 2006 (has links)
The theory of radiative transfer is applied to the problem of multiple wave scattering in a one-dimensional multilayer. A new mathematical model of a multilayer is presented in which both the refractive index and width of each layer are randomized. The layer widths are generated by a new probability distribution which allows for strong layer width disorder. An expression for the transport mean free path of the multilayer is derived based on its single-scattering properties. It will be shown that interference between the field reflected from adjacent layer interfaces remains significant even in the presence of strong layer width disorder. It will be proven that even when the scattering is weak, the field in a random multilayer localizes at certain frequencies. The effect of increasing layer width randomization on this form of localization is quantified. The radiative transfer model of time-harmonic scattering in multilayers is extended to narrow-band pulse propagation in weakly scattering media. The tendency of pulses to broaden in this medium is discussed. A radiative transport model of the system is developed and compared to numerical solutions of the wave equation. It is observed that pulse broadening is not described by simple transfer theory. The radiative transfer model is extended by the addition of a Laplacian term in an attempt to model the effect of ensemble average pulse broadening. Numerical simulation results in support of this proposal are given, and applications for the theory suggested. Finally, the problem of acoustic wave scattering by planar screens is considered. The study was motivated by the idea that multiple scattering experiments may prove possible in a medium composed of such scatterers. Successful multiple scattering in a medium of planar scatterers will depend on the scattering cross-section at angles away from normal incidence. The scattering cross-section is calculated for a circular disc using a new technique for solving the acoustic wave equation on planar surfaces. The method is validated by comparison with available analytic solutions and the geometric theory of diffraction.
180

Radiative transfer in multiply layered media

De Lautour, N. J. (Nathaniel J.) January 2006 (has links)
The theory of radiative transfer is applied to the problem of multiple wave scattering in a one-dimensional multilayer. A new mathematical model of a multilayer is presented in which both the refractive index and width of each layer are randomized. The layer widths are generated by a new probability distribution which allows for strong layer width disorder. An expression for the transport mean free path of the multilayer is derived based on its single-scattering properties. It will be shown that interference between the field reflected from adjacent layer interfaces remains significant even in the presence of strong layer width disorder. It will be proven that even when the scattering is weak, the field in a random multilayer localizes at certain frequencies. The effect of increasing layer width randomization on this form of localization is quantified. The radiative transfer model of time-harmonic scattering in multilayers is extended to narrow-band pulse propagation in weakly scattering media. The tendency of pulses to broaden in this medium is discussed. A radiative transport model of the system is developed and compared to numerical solutions of the wave equation. It is observed that pulse broadening is not described by simple transfer theory. The radiative transfer model is extended by the addition of a Laplacian term in an attempt to model the effect of ensemble average pulse broadening. Numerical simulation results in support of this proposal are given, and applications for the theory suggested. Finally, the problem of acoustic wave scattering by planar screens is considered. The study was motivated by the idea that multiple scattering experiments may prove possible in a medium composed of such scatterers. Successful multiple scattering in a medium of planar scatterers will depend on the scattering cross-section at angles away from normal incidence. The scattering cross-section is calculated for a circular disc using a new technique for solving the acoustic wave equation on planar surfaces. The method is validated by comparison with available analytic solutions and the geometric theory of diffraction.

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