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Tesi sul tema "Spatial scattering"
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1
Susanto, Raden Dwi 1963. "Spatial coherence and rough bottom scattering in shallow water". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36003.
Testo completo
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Lim, Dong Sung. "Phase singularities and spatial-temporal complexity in optical fibres". Thesis, Heriot-Watt University, 1995. http://hdl.handle.net/10399/772.
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Morgan, Stephen P. "Continuous wave optical techniques for imaging through scattering media". Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319966.
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Hirst, Edwin. "Airborne particle shape and size classification from spatial light scattering profiles". Thesis, University of Hertfordshire, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332653.
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5
Ibison, Michael Craig. "Analytical studies of spatial and temporal confinement in stimulated Raman scattering". Thesis, University of Southampton, 1987. https://eprints.soton.ac.uk/396458/.
Testo completoAbstract (sommario):
The work presented in this thesis is a description of theoretical techniques for spatial and temporal confinement in the small signal regime of Stimulated Raman Scattering with a pump laser beam. The aim of this work is to provide where possible a mathematical model for the effects of confinement on both the pump, and the Raman generated Stokes fields, whilst at the same time to give some idea of the tools available to the theoretician pursuing this end. Particular attention has been paid to the (existing) domains over which relatively simple mathematical models are applicable, and also to provide bounds on the applicability of both original and existing results. Both the Maxwell and Lagrange formulation of the (electromagnetic) propagation problem are developed in this work. The paraxial ray equation which arises from the former is investigated in some detail; results are presented which give the full set of refractive index variations for which this equation is separable (and therefore potentially soluble) under an arbitrary transformation. The Lagrange formulation is employed to solve the spatial confinement problem which may arise from the use of a waveguide or a focussed pump beam. The traditional Maxwell formulation is used to provide the solutions to the temporal confinement problem. Where possible, results are presented which combine the solutions from both domains to obtain a model for simultaneous spatial and temporal confinement.
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Ille, Jean-Francois. "Interaction of spatial scales in acoustic radiation from hemi-capped cylinders". Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16091.
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Barton, John E. "Bioaerosol detection through simultaneous measurement of particle intrinsic fluorescence and spatial light scattering". Thesis, University of Hertfordshire, 2005. http://hdl.handle.net/2299/14272.
Testo completoAbstract (sommario):
Interest in the role and detection of airborne biological micro-organisms has increased dramatically in recent years, in part through heightened fears of bioterrorism. Traditional bio-detection methods have generally slow response times and require the use of reagents. Conversely, techniques based on light scattering phenomena are reagent-free and are able to operate in real-time. Previous research has established that classification of certain types of airborne particles on the basis of shape and size may be achieved through the analysis of the spatial light scattering patterns produced by individual particles. Similarly, other research has shown that the intrinsic fluorescence of particles excited by radiation of an appropriate wavelength can be used to establish the presence of biological particles, provided background particles with similar fluorescence properties are not present. This is often not the case. This thesis, therefore, describes the design, development, and testing of a new type of bioaerosol detection instrument in which the advantages of both particle spatial light scattering analysis and intrinsic fluorescence are exploited. The instrument, referred to as the Mult- Parameter Aerosol Monitor (MPAM), is unique in simultaneously recording data relating to the size, shape, and fluorescence properties of individual airborne particles at rates up to several thousand particles per second. The MPAM uses a continuous-wave frequency quadrupled Nd: YVO4 laser to produce both spatial scattering and fluorescence data from particles carried in single-file through the laser beam. This use of a CW laser leads to opto-mechanical simplicity and reduces fluorescence bleaching effects. A custom-designed multi-pixel Hybrid Photodiode (HPD) detector is used to record the spatial scattering data in forward scattering plane whilst particle fluorescence is recorded via a large solid-angle ellipsoidal reflector and single photomultiplier detector. Calibration tests and experimental trials involving a range of both biological and nonbiological aerosols have shown that the MPAM, when supported by appropriate data analysis algorithms, is capable of achieving enhanced levels of discrimination between biological and non-biological particles down to the submicrometre sizes and, in some cases, enhanced discrimination between classes of biological particle.
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Bagschik, Kai [Verfasser], e Hans Peter [Akademischer Betreuer] Oepen. "Coherent soft X-ray magnetic scattering and spatial coherence determination / Kai Bagschik ; Betreuer: Hans Peter Oepen". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2017. http://d-nb.info/1143868986/34.
Testo completo
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Mounaix, Mickaël. "Matricial approaches for spatio-temporal control of light in multiple scattering media". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066562/document.
Testo completoAbstract (sommario):
L’imagerie optique à travers des milieux diffusants, comme des milieux biologiques ou de la peinture blanche, reste un challenge car l’information spatiale portée par la lumière incidente est mélangée par les évènements multiples de diffusion. Toutefois, les modulateurs spatiaux de lumière (SLM) disposent de millions de degrés de liberté pour contrôler le profil spatial de la lumière en sortie du milieu, en forme de tavelure (speckle), avec des techniques de modulation du front d’onde. Cependant, si le laser génère une impulsion brève, le signal transmis s’allonge temporellement, car le milieu diffusant répond différemment pour les diverses composantes spectrales de l’impulsion. Nous avons développé, au cours de cette thèse, des méthodes de contrôle du profil spatiotemporel d’une impulsion brève transmise à travers un milieu diffusant. En mesurant la Matrice de Transmission Multi-Spectrale ou Résolue-Temporellement, la propagation de l’impulsion peut être totalement décrite dans le domaine spectral ou temporel. Avec des techniques de manipulation du front d’onde, les degrés de libertés spectraux/temporel peuvent être ajustés avec un unique SLM via la diversité spectrale du milieu diffusant. Nous avons démontré, de manière déterministe, la focalisation spatio-temporelle d’une impulsion brève après propagation dans un milieu diffusant, avec une compression temporelle proche de la durée initiale de l’impulsion, à différentes positions de l’espace-temps. Nous avons également démontré un façonnage contrôlé du profil temporel de l’impulsion, notamment avec la génération d’impulsions doubles. Nous exploitons cette focalisation spatio-temporelle pour exciter un processus optique non-linéaire, la fluorescence à deux photons. Cette approche ouvre des perspectives intéressantes pour le contrôle cohérent, l’étude de l’interaction lumière-matière ainsi que l’imagerie multi-photoniqueOptical imaging through highly disordered media such as biological tissue or white paint remains a challenge as spatial information gets mixed because of multiple scattering. Nonetheless, spatial light modulators (SLM) offer millions of degrees of freedom to control the spatial speckle pattern at the output of a disordered medium with wavefront shaping techniques. However, if the laser generates a broadband ultrashort pulse, the transmitted signal becomes temporally broadened as the medium responds disparately for the different spectral components of the pulse. We have developed methods to control the spatio-temporal profile of the pulse at the output of a thick scattering medium. By measuring either the Multispectral or the Time- Resolved Transmission Matrix, we can fully describe the propagation of the broadband pulse either in the spectral or temporal domain. With wavefront shaping techniques, one can control both spatial and spectral/temporal degrees of freedom with a single SLM via the spectral diversity of the scattering medium. We have demonstrated deterministic spatio-temporal focusing of an ultrashort pulse of light after the medium, with a temporal compression almost to its initial time-width in different space-time position, as well as different temporal profile such as double pulses. We exploit this spatio-temporal focusing beam to enhance a non-linear process that is two-photon excitation. It opens interesting perspectives in coherent control, light-matter interactions and multiphotonic imaging
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Franchi, Gianni. "Machine learning spatial appliquée aux images multivariées et multimodales". Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM071/document.
Testo completoAbstract (sommario):
Cette thèse porte sur la statistique spatiale multivariée et l’apprentissage appliqués aux images hyperspectrales et multimodales. Les thèmes suivants sont abordés :Fusion d'images :Le microscope électronique à balayage (MEB) permet d'acquérir des images à partir d'un échantillon donné en utilisant différentes modalités. Le but de ces études est d'analyser l’intérêt de la fusion de l'information pour améliorer les images acquises par MEB. Nous avons mis en œuvre différentes techniques de fusion de l'information des images, basées en particulier sur la théorie de la régression spatiale. Ces solutions ont été testées sur quelques jeux de données réelles et simulées.Classification spatiale des pixels d’images multivariées :Nous avons proposé une nouvelle approche pour la classification de pixels d’images multi/hyper-spectrales. Le but de cette technique est de représenter et de décrire de façon efficace les caractéristiques spatiales / spectrales de ces images. Ces descripteurs multi-échelle profond visent à représenter le contenu de l'image tout en tenant compte des invariances liées à la texture et à ses transformations géométriques.Réduction spatiale de dimensionnalité :Nous proposons une technique pour extraire l'espace des fonctions en utilisant l'analyse en composante morphologiques. Ainsi, pour ajouter de l'information spatiale et structurelle, nous avons utilisé les opérateurs de morphologie mathématiqueThis thesis focuses on multivariate spatial statistics and machine learning applied to hyperspectral and multimodal and images in remote sensing and scanning electron microscopy (SEM). In this thesis the following topics are considered:Fusion of images:SEM allows us to acquire images from a given sample using different modalities. The purpose of these studies is to analyze the interest of fusion of information to improve the multimodal SEM images acquisition. We have modeled and implemented various techniques of image fusion of information, based in particular on spatial regression theory. They have been assessed on various datasets.Spatial classification of multivariate image pixels:We have proposed a novel approach for pixel classification in multi/hyper-spectral images. The aim of this technique is to represent and efficiently describe the spatial/spectral features of multivariate images. These multi-scale deep descriptors aim at representing the content of the image while considering invariances related to the texture and to its geometric transformations.Spatial dimensionality reduction:We have developed a technique to extract a feature space using morphological principal component analysis. Indeed, in order to take into account the spatial and structural information we used mathematical morphology operators
11
Caplinger, James E. "ULTRAVIOLET RAYLEIGH SCATTER IMAGING FOR SPATIAL TEMPERATURE PROFILES IN ATMOSPHERIC MICRODISCHARGES". Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1401750986.
Testo completo
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Pollock, Tony Steven, e tony pollock@nicta com au. "On Limits of Multi-Antenna Wireless Communications in Spatially Selective Channels". The Australian National University. Research School of Information Sciences and Engineering, 2003. http://thesis.anu.edu.au./public/adt-ANU20050418.143712.
Testo completoAbstract (sommario):
Multiple-Input Multiple-Output (MIMO) communications systems using multiantenna arrays simultaneously during transmission and reception have generated significant interest in recent years. Theoretical work in the mid 1990?s showed the potential for significant capacity increases in wireless channels via spatial multiplexing with sparse antenna arrays and rich scattering environments. However, in reality the capacity is significantly reduced when the antennas are placed close together, or the scattering environment is sparse, causing the signals received by different antennas to become correlated, corresponding to a reduction of the effective number of sub-channels between transmit and receive antennas. By introducing the previously ignored spatial aspects, namely the antenna array geometry and the scattering environment, into a novel channel model new bounds and fundamental limitations to MIMO capacity are derived for spatially constrained, or spatially selective, channels. A theoretically derived capacity saturation point is shown to exist for spatially selective MIMO channels, at which there is no capacity growth with increasing numbers of antennas. Furthermore, it is shown that this saturation point is dependent on the shape, size and orientation of the spatial volumes containing the antenna arrays along with the properties of the scattering environment. This result leads to the definition of an intrinsic capacity between separate spatial volumes in a continuous scattering environment, which is an upper limit to communication between the volumes that can not be increased with increasing numbers of antennas within. It is shown that there exists a fundamental limit to the information theoretic capacity between two continuous volumes in space, where using antenna arrays is simply one choice of implementation of a more general spatial signal processing underlying all wireless communication systems.
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Fincke, Jonathan Randall. "Quantification of the spatial and temporal evolution of stratified shear instabilities at high Reynolds number using quantitative acoustic scattering techniques". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97855.
Testo completoAbstract (sommario):
Thesis: S.M., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 54-56).
The spatial and temporal evolution of stratified shear instabilities is quantified in a highly stratified and energetic estuary. The measurements are made using high-resolution acoustic backscatter from an array composed of six calibrated broadband transducers connected to a six-channel high-frequency (120-600 kHz) broadband acoustic backscatter system. The array was mounted on the bottom of the estuary and looking upward. The spatial and temporal evolution of the waves is described in terms of their wavelength, amplitude and turbulent dissipation as a function of space and time. The observed waves reach an arrested growth stage nearly 10 times faster than laboratory and numerical experiments performed at much lower Reynolds number. High turbulent dissipation rates are observed within the braid regions of the waves, consistent with the rapid transition to arrested growth. Further, it appears that the waves do not undergo periodic doubling and do not collapse once their maximum amplitude is reached. Under some conditions long internal waves may provide the perturbation that decreases the gradient Richardson number so as to initiate shear instability. The initial Richardson number for the observed instabilities is likely between 0.1 and 0.2 based on the slope and growth rate of the shear instabilities.
by Jonathan Randall Fincke.
S.M.
14
Martin, Martin Laura. "Numerical study of sound scattering by isolated elliptic vortices and turbulent jet shear layers". Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0025.
Testo completoAbstract (sommario):
Cette étude est consacrée à la diffusion d'ondes acoustiques par des tourbillons isolés et couches de cisaillement de jet turbulentes. Lorsque les ondes acoustiques traversent un volume de turbulence, les fluctuations de la turbulence modifient la direction de propagation des ondes. En outre, si la turbulence évolue dans le temps, le contenu spectral du son change également, ce qui entraîne un élargissement spectral. Afin de mieux comprendre ces phénomènes, une série d'analyses numériques a été réalisée. Pour ce faire, un code fourni par Siemens a été utilisé, dans lequel les Equations d'Euler Linéarisées sont résolues par la Méthode de Galerkin Discontinue. Il simule la propagation des ondes acoustiques sur un écoulement de base défini par l'utilisateur. Pour prendre en compte l'élargissement spectral, le code a été modifié pour pouvoir interpoler en temps et en espace des données externes dépendant du temps dans l’écoulement de base. L'interpolation a été testée par des différentes études de convergence du champ de pression diffusé par une couche de mélange bidimensionnelle. D'autres caractéristiques ont également été mises en œuvre pour faire face aux instabilités numériques causées par l'inhomogénéité de l’écoulement de base. Dans un premier temps, la diffusion des ondes acoustiques causée par un tourbillon elliptique de Kirchhoff isolé est étudiée. Lorsque le tourbillon est fixé dans l'espace, l'étude se concentre sur les effets de l'ellipticité, de l'orientation du tourbillon par rapport à la direction de propagation de l'onde acoustique incidente, de la vitesse tangentielle du tourbillon et de sa taille par rapport aux ondes acoustiques. La diffusion a été également étudiée lorsque le tourbillon est convecté. Une attention particulière a été accordée à son ellipticité et à la vitesse de convection. Les résultats montrent que l'ellipticité et surtout l'orientation du tourbillon jouent un rôle clé dans la diffusion. Enfin, l'étude de la diffusion du son par les couches de cisaillement des jets turbulents est menée, où la source acoustique est située à l'axe du jet. Pour cela, les données interpolées dans l'écoulement de base du code DGM appartiennent à une base de données externe de jets ronds simulés par LES. Ces jets ont des nombres de Mach variant entre 0,3 et 1,3, et leur température est 1, 1,5 ou 2,25 fois la température ambiante. Ces paramètres modifient les propriétés des fluctuations turbulentes. Le contenu spectral de ces fluctuations est donc comparé entre les jets. Ensuite, les champs de pression obtenus avec des écoulements de base moyens et des écoulements de base turbulents, ainsi que la différence entre eux, sont présentés. Leurs directivités sont également discutées, ainsi que les spectres du champ acoustique. Les spectres sont caractérisés par une tonalité centrale à la fréquence de la source et deux lobes latéraux. Ils sont symétriques pour des nombres de Mach élevés. La position des lobes latéraux se rapproche du ton central et leurs niveaux augmentent avec la température du jet pour des jets à nombre de Mach constant, ce qui peut s'expliquer par les changements subis par les fluctuations de la turbulenceThis study is consecrated to the scattering of acoustic waves by isolated vortices and turbulent jet shear layers. When the acoustic waves pass through a volume of turbulence, the fluctuations in the turbulence change the propagation direction of the waves. In addition, if the turbulence evolves in time, there is also a change in the sound spectral content, causing spectral broadening. In order to better understand these phenomena, a series of numerical analyses have been carried out. For this purpose, a code provided by Siemens has been used where the Linearised Euler Equations are solved by the Discontinuous Galerkin method. It simulates the acoustic wave propagation over a base flow defined by the user. To take into account the spectral broadening, the code has been modified to be able to interpolate time-dependent external data in time and space onto the base flow. The interpolation has been tested by different convergence studies of the pressure field scattered by a 2-dimensional mixing layer. Other features have been also implemented to cope with the numerical instability waves caused by the inhomogeneity of the base flow. Initially, the scattering of acoustic waves caused by an isolated Kirchhoff elliptic vortex is investigated. When the vortex is fixed in space, the study focuses on the effects of the ellipticity, the orientation of the vortex regarding the direction of propagation of the incident acoustic wave, the tangential velocity of the vortex and its size regarding the acoustic waves. The scattering has been investigated also when the vortex is convected. Special attention has been devoted to its ellipticity and the velocity convection. The results show that the ellipticity and especially the orientation of the vortex play a key role in the scattering. Finally, the study of the scattering of sound by turbulent jet shear layers is conducted, where the acoustic source is located at the jet axis. For that, the data interpolated in the base flow of the DGM code belong to an external database of round jets simulated by LES. These jets have Mach numbers varying between 0.3 and 1.3, and their temperature is 1, 1.5 or 2.25 times the ambience temperature. These parameters modify the properties of the turbulent fluctuations. Therefore, the spectral content of these fluctuations is compared between the jets. After that, the pressure fields obtained with mean base flows and turbulent base flows, and the difference between them are presented. Their directivities are also discussed, as well as the spectra of the acoustic field. The spectra are characterized by a central tone at the source frequency and two lateral lobes. They are symmetric for high Mach numbers. The position of the lateral lobes shifts closer to the central tone and their levels increase with the jet temperature for jets with constant Mach number, which can be explained by the changes undergone by the turbulence fluctuations
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McCall, David Samuel. "Measurement and modelling of light scattering by small to medium size parameter airborne particles". Thesis, University of Hertfordshire, 2011. http://hdl.handle.net/2299/6374.
Testo completoAbstract (sommario):
An investigation into the light scattering properties of Saharan dust grains is presented. An electrodynamic trap has been used to levitate single dust particles. By adjusting the trap parameters, partial randomisation of the particle orientation has been introduced. While levitated, the particles were illuminated by a laser, and a rotating half-wave retarder enabled selection of vertically or horizontally polarized incident light. A laser diffractometer and linear photodiode array have been used to measure intensity at scattering angles between 0.5° and 177°. Combining these measurements with Fraunhofer diffraction as calculated for a range of appropriately-sized apertures allows the calculation of the phase function and degree of linear polarization. The phase functions and degree of linear polarisation for four case study particles are presented - the phase functions are found to be featureless across most of the scattering region, with none of the halo features or rainbow peaks associated with regularly shaped particles such as hexagonal columns or spheres. Particle models comprised of large numbers of facets have been constructed to resemble the levitated particles. Utilizing Gaussian random sphere methods, increasing levels of roughness have been added to the surfaces of these models. A Geometric Optics model and a related model, Ray Tracing with Diffraction on Facets, have been modified to calculate scattering on these particle reconstructions. Scattering calculations were performed on each of these reconstructions using a range of refractive indices and two rotation regimes – one where the orientations of the reconstructed particle were limited to match those observed when the particle was levitated, and one where the orientation was not limited. Qualitative comparisons are performed on the phase functions and degree of linear polarization, where it is observed that the addition of roughness to the modelled spheroids causes the computed phase functions to increasingly resemble those from the levitated particles. Limiting the orientation of the particles does not affect the scattering noticeably. The addition of a very small absorption coefficient does not change the comparisons considerably. As the absorption coefficient is increased, however, the quality of the comparisons decreases rapidly in all cases but one. The phase functions are quantitatively compared using RMS errors, and further comparison is performed using the asymmetry parameter.
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Jáuregui, Sánchez Yessenia. "The nature of noise in single-pixel cameras and their application in imaging through scattering media". Doctoral thesis, Universitat Jaume I, 2019. http://hdl.handle.net/10803/667330.
Testo completoAbstract (sommario):
Imaging through scattering media has been a longstanding issue in many scientific fields and several optical techniques have emerged to retrieve the information of objects hidden in highly scattering media. Single-pixel imaging (SPI) techniques have proved to be a potential approach for imaging through scattering media. In this context, the objective of this thesis has been to study the nature of noise in SPI and to address the challenge of recovering the image of an object hidden behind a scattering media using visible and NIR light. In particular, we have developed a numerical model of a single-pixel camera (SPC) taking into account the properties of both the incident light and the photodiode. Moreover, we have proposed a novel approach for imaging through scattering media that combines SPI techniques with Fourier spatial filtering. Finally, we have studied the properties of a SPC in reflection configuration for imaging through scattering media.A pesar de los avances logrados en las últimas décadas, las técnicas convencionales de formación de imágenes aún fracasan al intentar adquirir la imagen de un objeto inmerso en un medio turbio. Sin embargo, las técnicas de imagen basadas en luz estructurada y detección con un solo píxel han probado ser una solución alternativa. El objetivo de esta tesis ha sido el estudio de la naturaleza del ruido de estas cámaras de un solo píxel y su aplicación en la formación de imágenes a través de un medio turbio empleando luz visible y radiación infrarroja. En particular, hemos desarrollado un modelo numérico para estas cámaras que tiene en cuenta tanto las propiedades de la iluminación como las del fotodiodo y hemos desarrollado una nueva cámara de un solo píxel basada en filtraje espacial de Fourier que mejora el contraste de las imágenes obtenidas a través de un medio turbio.
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Poon, Chien Sing. "Early Assessment of Burn Severity in Human Tissue with Multi-Wavelength Spatial Frequency Domain Imaging". Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1484582176416423.
Testo completo
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Безугла, Наталя Василівна. "Просторова фотометрія біологічних середовищ". Thesis, НТУУ "КПІ", 2016. https://ela.kpi.ua/handle/123456789/15918.
Testo completoAbstract (sommario):
Дисертаційна робота присвячена розробці методу фотометричного аналізу біологічних середовищ шляхом розширення простору визначення їх оптичних властивостей, що дозволило одночасно врахувати характеристики відбитого та пропущеного середовищем оптичного випромінювання в межах повного тілесного кута. У роботі розроблено методики реалізації математичного базису просторової фотометрії біологічних середовищ за принципами визначення інтенсивності розсіяння по паралелях (кільцевих смугах) та меридіанах (перетинах).
Запропоновані схемо-технічні рішення двох- та восьми-канальної інформаційно-вимірювальних систем для просторової фотометрії за перетинами, реалізовані на рівні експериментальних установок. Розроблено програмне забезпечення фотометричного паралельного аналізу, що дозволяє досліджувати індикатриси розсіяння за перетинами.
Проведено аналіз індикатрис розсіяння лазерного випромінювання товщинними зразками м’язових тканини на різних довжинах хвиль та з різним розміщенням волокон. Здійснено перехід від індикатриси розсіяння товщинними зразками до фактору анізотропії однократного розсіяння. Доведено ідентичність експериментально-визначених величин оптичних коефіцієнтів дифузного відбиття та повного пропускання та визначених за результатами Монте-Карло моделювання з використанням усередненої за перетинами величини фактору анізотропії однократного розсіяння.The thesis is devoted to developing the method of photometric analysis of biological media by expansion the space of definition their optical properties. That made possible the simultaneously consider the characteristics of the optical radiation, reflected and transmitted by biological media, within the full solid angle. In the work the main methods of solution the basic equation of radiative transfer theory in problems of optical biomedical diagnostics, were analyzed. Thus, the main attention focused on optical parameters of biological media: scattering (μs), absorption (μa) coefficients, and the anisotropy factor of single scattering (g), which are responsible for spatial distribution of scattered radiation by normal and pathology tissues or media (first order approximation, diffuse approximation, small angle approximation, flux models, Monte Carlo method). Conditions of use depending the type of biological media are described. The phase functions of single scattering (Mie, Henyey-Greenstein, Gegenbauer kernel, Delta-Eddington, Eddington), which used to describe the propagation the optical radiation in different types of biological media, were considered. Systematized the methods and tools of biophotonics with the possibilities of spatial-oriented analysis of radiation, scattered by sample of biological media, organs and body parts. Goniometric and spherical types of experimental setup are the most appropriated types that can used for spatial photometry. Photometric image of varying thickness samples of biological media by ellipsoidal reflectometry were received. Based on experimental research, the axial asymmetry of anisotropy of scattering by porcine and chicken muscle tissues of varying thickness in vitro at a wavelength of 632.8 nm was found. The influence of anisotropy of scattering on accuracy of determination the optical coefficients of diffuse reflection and total transmission by method Monte Carlo was demonstrated. Study of spatial anisotropy scattering by method of photometry was suggested. On this basis, has developed methods of implementing of the mathematical basis of spatial photometry of biological media by determining the scattering intensity along parallels (circular bands) and meridians (sections). The mechanism of the transition from experimentally determined indicatrix of scattering of thick sample to the anisotropy factor of single scattering by designed methods is proposed. The proposed scheme-technical versions of information-measurement system for spatial photometry along sections with two and eight channel, which were realized in experimental setups of goniometric and spherical type. The features of element synthesis, exploitation and calibration of setups are described. The interfaces and methods of application of developed software for parallel photometric analysis "IMSOB" and "IMSOB-2", to support research the scattering indicatrix along sections in reflected or transmitted light for two- and eight-channel systems respectively are given. The method of sample preparation of biological media and features of experiment for different experimental setups of spatial photometry are given. The methodology of preparation the biological samples used for research in this paper were detail described. The analysis of the indicatrix of laser light scattering by thick samples of muscle tissue at different wavelengths with transverse and longitudinal placement of fibers was made. The data obtained by method of spatial photometry, which realized the principle of analyses of the sections. Experimental studies conducted on goniometric type setup. For phase function of single scattering Henyey-Greenstein, modified by isotropic component in each sections, the transition from indicatrix scattering of thick sample to the single scattering anisotropy factor g was made. Identity of experimentally-determined values of the optical coefficients of diffuse reflection and total transmission and determined by the results of Monte Carlo simulation using the average values by sections of the anisotropy factor of single scattering are approved.
Диссертация посвящена разработке метода фотометрического анализа биологических сред путем расширения пространства определения их оптических свойств, что позволило одновременно учесть характеристики отраженного и пропущенного средой оптического излучения в пределах полного телесного угла. В работе разработаны методики реализации математического базиса пространственной фотометрии биологических сред по принципу определения интенсивности рассеяния по параллелям (кольцевым полосам) и меридианам (сечениям). Предложены схемотехнические решения двух- и восьмиканальной информационно-измерительных систем для пространственной фотометрии по сечениям, реализованные на уровне экспериментальных установок. Разработано программное обеспечение фотометрического параллельного анализа, позволяющее исследовать индикатрисы рассеяния по сечениям. Проведен анализ индикатрис рассеяния лазерного излучения толщинными образцами мышечных тканей на различных длинах волн и с разным размещением волокон. Осуществлен переход от индикатрисы рассеяния толщинных образцов к фактору анизотропии однократного рассеяния. Доказана идентичность экспериментально определенных величин оптических коэффициентов диффузного отражения и полного пропускания и определенных по результатам моделирования Монте-Карло с использованием усредненной по сечениям величины фактора анизотропии однократного рассеяния.
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Ocer, Nuri Erkin. "Parametric Investigation Of Spray Characteristics Using Interferometric Particle Imaging Technique". Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611397/index.pdf.
Testo completoAbstract (sommario):
Spray is an efficient tool in the usage whose primary objectives are to obtain droplets with increased liquid surface area and more dispersed liquid over a larger volume. The determination of spray characteristics has been a topic of extensive research recently. In the present investigation, the flow structure of a spray issuing from an oil burner nozzle was determined in a parametrical manner. The main tool in the experimental research is the Interferometric Particle Imaging (IPI) configuration. This method exploits the interference between light reflected from and refracted through individual transparent spray droplets which are illuminated by a laser light sheet in a wide angle forward-scatter region. Based on a scattering theory, the droplet diameter of spray particles can be related to the light pattern scattered from that particle. In addition, using double-framed images also enables the calculation of velocities associated with these particles. In this way, as a representation of spray structure, the droplet size and velocity distributions were obtained prior to a change in the primary parameters of liquid flow e.g. surface tension, viscosity, density and the injection pressure. The evolution of spray characteristics in space were also examined by conducting
measurements in different radial and axial locations relative to spray centerline.
20
Prevost, Florian. "Combinaison cohérente dans une fibre multicœurs pour des applications LIDAR". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLO003/document.
Testo completoAbstract (sommario):
Les Lidars cohérents permettent de mesurer la vitesse du vent à grande distance, en se basant sur le décalage en fréquence Doppler induit par la réflexion des aérosols. Le Lidar vent est composé d'un système MOPFA (Master Oscillator Power Fiber Amplifier), contenant un oscillateur continu, un modulateur d'intensité, et un amplificateur fibré. L'objectif principal de cette thèse est la réalisation d'un MOPFA pulsé de forte puissance crête à sécurité oculaire, en utilisant une fibre multicoeurs dopée erbium. L'impulsion mono-fréquence dans les fibres est limitée par les effets non-linéaire du au confinement du faisceau dans le coeur. Les fibres multicoeurs peuvent être vues comme des fibres à larges coeur. L'impulsion à amplifier est divisée et injectée dans tous les coeurs de la fibre amplificatrice à l'aide d'un modulateur spatial de lumière (SLM). A la sortie, les impulsions amplifiées sont recombinées par un élément optique de diffraction (EOD). La combinaison cohérente en sortie requière un contrôle indépendant des phases à l'injection qui est asservit par un algorithme basé sur la puissance de l'ordre zéro de l'EOD. La puissance crête après combinaison est alors la somme des puissances crêtes atteintes dans chacun des coeursCoherent Lidars can measure wind speed at long distance, using the Doppler frequency shift induced by the movement of the back reflecting aerosols. Wind Lidars usually include a MOPFA (Master Oscillator Power Fiber Amplifier) made of a continuous oscillator, an intensity modulator and a fiber amplifier. The main objective of this thesis is the realization of an eye-safe, high peak power, pulsed MOPFA using an erbium-doped multicore fiber. Single frequency pulse amplification in fibers is limited by nonlinear effects due to tight beam confinement in the core. Multicore fibers can be seen as a very large core fiber, thus mitigating the nonlinear effects. The pulse to be amplified is divided and injected into all cores of the amplifying fiber using a spatial light modulator (SLM). The amplified output pulses are then recombined at the fiber output by a diffractive optical element (DOE). The coherent combination at fiber output requires independent control of phases at injection provided by a feedback loop based on the DOE zero order power. The peak power after combination is the sum of the peak powers reached in each of the cores
21
Dutrion, Cécile. "Étude de faisabilité d'un revêtement élastique pour la furtivité acoustique". Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0011/document.
Testo completoAbstract (sommario):
Dans le cadre de certaines applications militaires ou méthodologiques, on peut chercher à rendre un objet « invisible » vis-à-vis des ondes acoustiques. Différentes méthodes passives ont été proposées ces dernières années pour éviter ou atténuer la diffraction d'ondes acoustiques sur des obstacles rigides. Ces techniques reposent sur des phénomènes purement acoustiques, avec par exemple la présence de multiples résonateurs ou d'objets diffractants. L'étude présentée ici s'intéresse pour sa part aux effets que l'on pourrait obtenir au moyen d'un revêtement multicouche élastique fixé à un cylindre que l'on souhaite rendre indétectable. Le comportement vibro-acoustique d'un tel revêtement est d'abord modélisé. Par optimisation, on détermine les caractéristiques mécaniques et dimensionnelles des couches permettant une atténuation omnidirectionnelle de la diffraction. Des configurations réalistes de revêtements composés d'une couche orthotrope et d'une couche isotrope sont dégagées dans le cas d'un milieu extérieur constitué d'air. On montre que de tels dispositifs permettent d'atténuer la diffraction à une fréquence donnée ou sur une bande de fréquence. Le problème de la caractérisation expérimentale de ces revêtements est également abordé. Dans un second temps, le cas d'un milieu extérieur constitué d'eau est étudié. On met alors en évidence une réduction de la diffraction avec des revêtements composés de deux couches isotropes. L'influence des différents paramètres de la couche intérieure est analysée. Enfin, des exemples montrent que la bande de fréquence sur laquelle a lieu l'atténuation de la diffraction peut être élargie en augmentant le nombre de couchesMaking an object invisible to acoustic waves could prove useful for military applications or measurements in confined space. Different passive methods have been proposed in recent years to avoid acoustic scattering from rigid obstacles.These techniques are exclusively based on acoustic phenomena, and use for instance multiple resonators or scatterers. This thesis deals with a different method and studies the effects in terms of scattering reduction of an elastic multi-layered coating fixed to the object to conceal. Vibrations of the coating subject to acoustic waves are first modelled to compute the scattered pressure in the external fluid. Mechanical and dimensional properties of the layers leading to omnidirectional scattering reduction are optimised. Considering an external fluid consisting of air, realistic configurations of coatings emerge, composed of a thick internal orthotopic layer and a thin external isotropic layer. These coatings are shown to enable scattering reduction at a precise frequency or on a larger frequency band. The problem of experimental characterisation is also addressed.The study then focuses on a cylinder immersed in water. Bi-layer isotropic coatings can be used in such configuration. A parametric study is led on the characteristics of the internal layer. Finally, significant scattering reduction is achieved for alarger frequency range by increasing the number of layers. Examples of four-layer isotropic coatings are presented to highlight this result
22
Bsaibes, Maroun. "Vers une meilleure compréhension des mécanismes de pertes et de couplages de modes dans les fibres optiques légèrement multimodes". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILR004.
Testo completoAbstract (sommario):
De nombreuses initiatives de recherche technologique ont été menées ces dernières années pour proposer des solutions à la saturation prochaine de la capacité des réseaux de télécommunications à base de fibres optiques monomodes. Dans ces conditions, alors que le multiplexage de l'information repose déjà sur l'utilisation simultanée de plusieurs dimensions physiques (longueur d'onde, polarisation, phase et temps), l'ajout d'une nouvelle dimension, à savoir l'espace, semble, la solution la plus prometteuse. Le multiplexage spatial des données (SDM) est alors possible via l'utilisation de fibres multicœurs (MCF) ou de fibres légèrement multimode (FMF) et la capacité devient alors proportionnelle au nombre de canaux spatiaux disponibles. Dans le cas des FMF, on parle de multiplexage modal (MDM), les canaux correspondants alors aux modes spatiaux guidés dans le cœur de la fibre. Les défis à relever pour aboutir à des transmissions à faible taux d'erreur sur des distances respectables sont nombreux sont cependant nombreux. Ainsi, la réduction de l'atténuation différentielle des modes (DMA) et du couplage entre modes sont deux obstacles à surmonter avant d'envisager transposer une telle technologie sur le terrain.Le premier objectif de cette thèse a été d'identifier et de quantifier la contribution des différentes sources de pertes à l'atténuation totale de chaque mode dans des FMF présentant des profils d'indice différents mais supportant le même nombre de modes. Le second objectif était d'établir et d'analyser le lien suspecté entre certains mécanismes d'atténuation, en l'occurrence ceux liés à la diffusion de la lumière, et le couplage entre les modes. A 1550 nm, il est connu que la diffusion de la lumière représente la plus grande source d'atténuation dans les fibres de silice. Elle est une combinaison de deux facteurs : la diffusion Rayleigh qui dépend des propriétés physico-chimiques du matériau utilisé pour créer la fibre, et la diffusion SALS (small angle light scattering), moins documenté dans la littérature, qui résulte des fluctuations de l'indice de réfraction dans le guide. Dans cette thèse, les coefficients de diffusion Rayleigh et SALS ont été quantifiés en mesurant la distribution angulaire de l'intensité diffusée de différents modes. En outre, l'atténuation par absorption (infrarouge et OH) a également été quantifiée. D'autre part, une méthode simple basée sur la réflectométrie optique (OTDR) a été appliquée pour comparer le coefficient de Rayleigh de mêmes modes se propageant dans deux FMFs différents. Parallèlement, des modèles théoriques ont été développés pour analyser les résultats obtenus, en particulier dans le cas du SALS. Les dépendances modales des coefficients de diffusion SALS de différentes fibres ont ainsi été qualitativement reproduites. Ce travail fournit des informations cruciales pour la compréhension de l'impact du profil d'indice du FMF sur les coefficients d'atténuation des modes, ce qui permet de mieux comprendre les limites des FMFs et les améliorations qui peuvent être apportées pour guider leur conceptionNumerous technological research initiatives have been conducted in recent years to propose solutions to the upcoming saturation of the capacity of single-mode optical fiber-based telecommunications networks. In these conditions, while information multiplexing is already based on the simultaneous use of several physical dimensions (wavelength, polarization, phase, and time), the addition of a new dimension, namely space, seems to be the most promising solution. Space division multiplexing (SDM) of the data is then possible through the use of multicore fibers (MCF) or few-mode fibers (FMF) and the capacity then becomes proportional to the number of spatial channels available. In the case of FMF, this is known as mode division multiplexing (MDM), with the channels corresponding to the spatial modes guided in the fiber core. However, there are many challenges to overcome in order to achieve low error rate transmissions over respectable distances. Thus, the reduction of the differential mode attenuation (DMA) and the coupling between modes are two obstacles to overcome before considering transposing such a technology to the field.The first objective of this thesis was to identify and quantify the contribution of the different loss sources to the total attenuation of each mode in FMFs with different index profiles but supporting the same number of modes. The second objective was to establish and analyze the suspected link between some attenuation mechanisms, in this case, those related to light scattering, and the coupling between modes. At 1550 nm, it is known that light scattering represents the largest source of attenuation in silica fibers. It is a combination of two factors: Rayleigh scattering which depends on the physico-chemical properties of the material used to create the fiber, and SALS (small angle light scattering), less documented in the literature, which results from fluctuations of the refractive index in the waveguide. In this thesis, the Rayleigh and SALS scattering coefficients were quantified by measuring the angular distribution of the scattered intensity of different modes. In addition, the absorption attenuation (infrared and OH) has also been quantified. On the other hand, a simple method based on optical reflectometry (OTDR) has been applied to compare the Rayleigh coefficient of the same modes propagating in two different FMFs. In parallel, theoretical models have been developed to analyze the obtained results, in particular in the case of SALS. The modal dependencies of the SALS scattering coefficients of different fibers have been qualitatively reproduced. This work provides crucial information for the understanding of the impact of the FMF index profile on the mode attenuation coefficients, leading to a better understanding of the limitations of FMFs and the improvements that can be made to guide their design
23
Fezzaa, Kamel. "Étude et applications de la cohérence à l'ESRF par interférométrie X". Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10051.
Testo completoAbstract (sommario):
Une specificite de la 3 eme generation des sources de rayonnement synchrotron (rs), telles que l'esrf, est leur grand flux coherent dans le domaine des rayons x. Outre le developpement d'une methode originale pour etudier la coherence du rs, notre but est d'ouvrir la voie pour les applications interferometriques ayant recours a 2 faisceaux x coherents. La 1 ere partie du memoire rassemble les connaissances generales utiles pour le traitement du sujet. Un rappel des proprietes du rs et des experiences qui, a l'esrf, utilisent sa coherence, est suivi d'une description de la ligne de lumiere id32 et d'un expose des bases de la theorie de la coherence partielle et de sa propagation. La 2 eme partie commence par la description de notre interferometre a 2 miroirs de fresnel independants en incidence rasante pour les x durs, avant d'en proposer la modelisation theorique. De la visibilite des franges de young sont deduites les longueurs transverses de coherence. Elle se termine par des applications consistant a observer des structures artificielles mesoscopiques, deposees sur un miroir. En introduisant un faisceau de reference, on obtient des hologrammes, directs ou de fourier. La reconstruction est faite dans des cas simples ; l'etape suivante serait de passer a des morphologies reelles plus complexes. La 3 eme partie donne une image temporelle de la coherence spatiale : la transition resonante de #5#7fe a 14. 4 kev excitee par une impulsion de rs genere une onde diffusee coherente de duree superieure a celle de l'excitation. Si la frequence de resonance varie avec la position des atomes diffuseurs, on pourra observer des battements temporels pourvu que le faisceau incident presente une coherence spatiale suffisante sur l'objet. Nous avons etudie et verifie ce phenomene quand le decalage est produit par effet doppler, et dans le cas de deux orientations magnetiques. Une perspective serait la mesure des longueurs de correlation des domaines magnetiques des echantillons.
24
Ghabbach, Ayman. "Métrologie de la polarisation de la lumière à l'échelle du grain de speckle : histogrammes du degré de polarisation, dépolarisation spatiale et repolarisation temporelle". Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4346.
Testo completoAbstract (sommario):
Les techniques polarimétriques ont connu un récent essor, notamment dans le domaine de l'imagerie satellitaire ou du biomédical. Ces techniques se sont étendues au cas des milieux désordonnés. Dans ce contexte, des théories unifiées sont apparues, mêlant cohérence temporelle et spatiale, dépolarisation...L'équipe CONCEPT de l'Institut Fresnel, est aujourd'hui étroitement impliquée dans l'étude de la polarisation dans le speckle de la lumière diffusée. Des résultats nouveaux ont été mis en évidence, comme la dépolarisation spatiale multi-échelle, les phénomènes de repolarisation temporelle, la dépolarisation spectrale. La prédominance de ces effets est naturellement liée à l'origine du speckle (surface, volume), mais aussi aux niveaux d'absorption et aux propriétés structurelles (rugosités, hétérogénéités) des milieux désordonnés.La plupart de ces études sont de nature théorique. Ce constat est lié à l'extrême difficulté de mesurer avec précision la polarisation de la lumière à l'échelle du grain de speckle. Les travaux réalisés dans le cadre de cette thèse avaient ainsi pour but de remédier à cette lacune, et nous ont amenés à développer une procédure optique pour extraire les états de polarisation, et le degré de polarisation (DOP), à l'échelle du grain de speckle. En conséquence la polarisation est ici extraite pour chaque pixel d'une matrice CCD, ce qui amène tout d'abord à mettre en évidence des nuages de points plus ou moins étendus sur la sphère de Poincaré. Les histogrammes de DOP sont ensuite utilisés comme véritables signatures des milieux désordonnésPolarimetric techniques knew a recent rise, especially in the field of satellite imaging andbiomedical, optics. These techniques are extended to the case of the disordered media, for applications related to the imaging scattering medium. In this context the unified theories appeared, combiningtemporal and spatial coherence, and depolarization...The team CONCEPT at Fresnel Institute, established in 2012, is now closely involved in the study of the polarization state of the scattered light within the speckle size. New results have been highlighted, such as the multi-scale spatial depolarization, the temporal enpolarization phenomena, and the spectral depolarization. The predominance of these effects is naturally related to the speckle origin (surface, bulk), but also to the absorption levels and the structural properties (roughness, heterogeneities) of disordered media.However, most of these studies are theoretical, and few experiments were previously able to reinforce the predictions. This statement is related to the extreme difficulty of accurately measuring the polarization of light across the speckle grain. Our thesis had the aim to address this gap in, and we were able to develop a procedure to extract the optical polarization states, and the degree of polarization (DOP), inside of the speckle grain.Consequently, the polarization is here extracted for each pixel of a CCD matrix, which leads first to highlight a cloud of points more or less extended on the Poincaré sphere. DOP histograms are then used as genuine signatures of disordered media
25
Nguyen, Linh Trung. "Estimation and separation of linear frequency- modulated signals in wireless communications using time - frequency signal processing". Queensland University of Technology, 2004. http://eprints.qut.edu.au/15984/.
Testo completoAbstract (sommario):
Signal processing has been playing a key role in providing solutions to key problems encountered in communications, in general, and in wireless communications, in particular. Time-Frequency Signal Processing (TFSP) provides eective tools for analyzing nonstationary signals where the frequency content of signals varies in time as well as for analyzing linear time-varying systems. This research aimed at exploiting the advantages of TFSP, in dealing with nonstationary signals, into the fundamental issues of signal processing, namely the signal estimation and signal separation. In particular, it has investigated the problems of (i) the Instantaneous Frequency (IF) estimation of Linear Frequency-Modulated (LFM) signals corrupted in complex-valued zero-mean Multiplicative Noise (MN), and (ii) the Underdetermined Blind Source Separation (UBSS) of LFM signals, while focusing onto the fast-growing area of Wireless Communications (WCom). A common problem in the issue of signal estimation is the estimation of the frequency of Frequency-Modulated signals which are seen in many engineering and real-life applications. Accurate frequency estimation leads to accurate recovery of the true information. In some applications, the random amplitude modulation shows up when the medium is dispersive and/or when the assumption of point target is not valid; the original signal is considered to be corrupted by an MN process thus seriously aecting the recovery of the information-bearing frequency. The IF estimation of nonstationary signals corrupted by complex-valued zero-mean MN was investigated in this research. We have proposed a Second-Order Statistics approach, rather than a Higher-Order Statistics approach, for IF estimation using Time-Frequency Distributions (TFDs). The main assumption was that the autocorrelation function of the MN is real-valued but not necessarily positive (i.e. the spectrum of the MN is symmetric but does not necessary has the highest peak at zero frequency). The estimation performance was analyzed in terms of bias and variance, and compared between four dierent TFDs: Wigner-Ville Distribution, Spectrogram, Choi-Williams Distribution and Modified B Distribution. To further improve the estimation, we proposed to use the Multiple Signal Classification algorithm and showed its better performance. It was shown that the Modified B Distribution performance was the best for Signal-to-Noise Ratio less than 10dB. In the issue of signal separation, a new research direction called Blind Source Separation (BSS) has emerged over the last decade. BSS is a fundamental technique in array signal processing aiming at recovering unobserved signals or sources from observed mixtures exploiting only the assumption of mutual independence between the signals. The term "blind" indicates that neither the structure of the mixtures nor the source signals are known to the receivers. Applications of BSS are seen in, for example, radar and sonar, communications, speech processing, biomedical signal processing. In the case of nonstationary signals, a TF structure forcing approach was introduced by Belouchrani and Amin by defining the Spatial Time- Frequency Distribution (STFD), which combines both TF diversity and spatial diversity. The benefit of STFD in an environment of nonstationary signals is the direct exploitation of the information brought by the nonstationarity of the signals. A drawback of most BSS algorithms is that they fail to separate sources in situations where there are more sources than sensors, referred to as UBSS. The UBSS of nonstationary signals was investigated in this research. We have presented a new approach for blind separation of nonstationary sources using their TFDs. The separation algorithm is based on a vector clustering procedure that estimates the source TFDs by grouping together the TF points corresponding to "closely spaced" spatial directions. Simulations illustrate the performances of the proposed method for the underdetermined blind separation of FM signals. The method developed in this research represents a new research direction for solving the UBSS problem. The successful results obtained in the research development of the above two problems has led to a conclusion that TFSP is useful for WCom. Future research directions were also proposed.
26
Nguyen, Linh-Trung. "Estimation and separation of linear frequency- modulated signals in wireless communications using time - frequency signal processing". Thesis, Queensland University of Technology, 2004. https://eprints.qut.edu.au/15984/1/Nguyen_Linh-Trung_Thesis.pdf.
Testo completoAbstract (sommario):
Signal processing has been playing a key role in providing solutions to key problems encountered in communications, in general, and in wireless communications, in particular. Time-Frequency Signal Processing (TFSP) provides eective tools
for analyzing nonstationary signals where the frequency content of signals varies in time as well as for analyzing linear time-varying systems. This research aimed at exploiting the advantages of TFSP, in dealing with nonstationary signals, into the fundamental issues of signal processing, namely the signal estimation and signal separation. In particular, it has investigated the problems of (i) the Instantaneous Frequency (IF) estimation of Linear Frequency-Modulated (LFM) signals corrupted in complex-valued zero-mean Multiplicative Noise (MN), and (ii) the Underdetermined Blind Source Separation (UBSS) of LFM signals, while focusing onto the fast-growing area of Wireless Communications (WCom).
A common problem in the issue of signal estimation is the estimation of the frequency of Frequency-Modulated signals which are seen in many engineering and real-life applications. Accurate frequency estimation leads to accurate recovery of the true information. In some applications, the random amplitude modulation
shows up when the medium is dispersive and/or when the assumption of point target is not valid; the original signal is considered to be corrupted by an MN process thus seriously aecting the recovery of the information-bearing frequency. The IF estimation of nonstationary signals corrupted by complex-valued zero-mean MN
was investigated in this research. We have proposed a Second-Order Statistics approach,
rather than a Higher-Order Statistics approach, for IF estimation using Time-Frequency Distributions (TFDs). The main assumption was that the autocorrelation function of the MN is real-valued but not necessarily positive (i.e. the spectrum of the MN is symmetric but does not necessary has the highest peak at zero frequency). The estimation performance was analyzed in terms of bias and variance, and compared between four dierent TFDs: Wigner-Ville Distribution, Spectrogram, Choi-Williams Distribution and Modified B Distribution. To further improve the estimation, we proposed to use the Multiple Signal Classification algorithm
and showed its better performance. It was shown that the Modified B Distribution performance was the best for Signal-to-Noise Ratio less than 10dB.
In the issue of signal separation, a new research direction called Blind Source Separation (BSS) has emerged over the last decade. BSS is a fundamental technique in array signal processing aiming at recovering unobserved signals or sources from observed mixtures exploiting only the assumption of mutual independence between the signals. The term "blind" indicates that neither the structure of the mixtures nor the source signals are known to the receivers. Applications of BSS are seen in, for example, radar and sonar, communications, speech processing, biomedical signal processing. In the case of nonstationary signals, a TF structure forcing
approach was introduced by Belouchrani and Amin by defining the Spatial Time- Frequency Distribution (STFD), which combines both TF diversity and spatial diversity. The benefit of STFD in an environment of nonstationary signals is the direct exploitation of the information brought by the nonstationarity of the signals.
A drawback of most BSS algorithms is that they fail to separate sources in situations where there are more sources than sensors, referred to as UBSS. The UBSS of nonstationary signals was investigated in this research. We have presented a new approach for blind separation of nonstationary sources using their TFDs. The
separation algorithm is based on a vector clustering procedure that estimates the
source TFDs by grouping together the TF points corresponding to "closely spaced"
spatial directions. Simulations illustrate the performances of the proposed method for the underdetermined blind separation of FM signals. The method developed in this research represents a new research direction for solving the UBSS problem.
The successful results obtained in the research development of the above two problems has led to a conclusion that TFSP is useful for WCom. Future research directions were also proposed.
27
Willman, Christopher. "Laser diagnostics for spatially resolved thermometry in combustion and flows". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:fc0cbf95-302f-4de7-9212-6afa2632c93a.
Testo completoAbstract (sommario):
The development of Laser-Induced Thermal Grating Spectroscopy (LITGS) for diagnostics of combusting and non-combusting flows is described. The first use of LITGS to provide in situ calibration of 2-Dimensional temperature distributions generated using Two-Colour Planar Laser-Induced Fluorescence (TC-PLIF) is reported. Time-resolved measurements of temperature distributions in a firing GDI optical engine obtained by TC-PLIF were made during the compression stroke and calibrated to the absolute temperature scale by simultaneous LITGS measurements. The accuracy and precision of the temperatures derived from LITGS data are evaluated using alternative methods of data analysis - Fast Fourier Transform and Fitting to theoretical models of the experimental data. The relative merits of the two methods are examined for analysis of weak LITGS signals obtained under engine conditions of low pressure and high temperature. The combined TC-PLIF and LITGS system was demonstrated by performing repeated single-shot measurements for 1 in every 10 four-stroke cycles showing excellent correlation of the temperatures derived from both techniques. Direct measurement of the effect of 'charge cooling', of order 5 K, for operation with direct injection is reported. Inhomogeneous temperature distributions were observed during the compression stroke for fired operation with Port Fuel Injection (PFI) and also with Gasoline Direct Injection (GDI). The effects of varying the relative concentrations of toluene and iso-octane in the two-component fuel were investigated. Extension of the LITGS technique to multi-point measurements along a 1-D line is described. By recording signals from 4 points on separate detectors using a fibre-coupled photodiode array the limitations of Streak Cameras used previously for 1-D LITGS measurements were overcome. Demonstration of principle experiments are reported in which simultaneous 4-point measurements were made with 1 mm spatial resolution and a precision of 0.7 % in temperature gradients in gas flows and in boundary layers at surfaces.
28
Bykov, A. (Alexander). "Experimental investigation and numerical simulation of laser light propagation in strongly scattering media with structural and dynamic inhomogeneities". Doctoral thesis, University of Oulu, 2010. http://urn.fi/urn:isbn:9789514261558.
Testo completoAbstract (sommario):
Abstract
Light scattering diagnostics of turbid media containing both structural and dynamic inhomogeneities is currently of significant importance. One of the important directions in modern light scattering diagnostics is the development of methods for probing biological media with visible- and near-infrared radiation allowing for visualization of the biotissue structure. Optical methods for studying the biotissue structure and characterization of its optical properties are very promising and have been rapidly developing during the past decade.
The present work is aimed at improving and discovering new potentials of currently existing methods of laser diagnostics of biological tissues containing both structural and dynamic inhomogeneities. In particular, the feasibilities of spatially resolved reflectometry and time-of-flight techniques for the problem of noninvasive determination of glucose level in human blood and tissues were examined both numerically and experimentally. The relative sensitivities of these methods to changes in glucose level were estimated. Time-of-flight technique was found to be more sensitive.
The possibilities of Doppler optical coherence tomography for imaging of dynamic inhomogeneities with high resolution were considered. This technique was applied for the first time for the imaging of complex autowave cellular motility and cytoplasm shuttle flow in the slime mold Physarum polycephalum. The effect of multiple scattering on the accuracy of the measured flow velocity profiles for the case of single flow and for the case of the flow embedded into the static medium with strong scattering was studied. It was shown that this effect causes significant distortion to the measured flow velocity profiles and it is necessary to take this into account while making quantitative measurements of flow velocities.
29
Gaudfrin, Florian. "Lidar supercontinuum pour la caractérisation spectrale des milieux diffusants à haute résolution spatiale : Étude numérique et développement instrumental". Thesis, Toulouse, ISAE, 2020. http://www.theses.fr/2020ESAE0007.
Testo completoAbstract (sommario):
Les méthodes de diagnostic par méthode lidar donnent des informations sur les paramètres optiques du milieu (coefficients de diffusion et d’absorption). Ces grandeurs dépendent des propriétés de la lumière (longueur d’onde, polarisation) et sont ensuite utilisées pour remonter aux propriétés microscopiques du milieu comme la distribution en taille, la morphologie, l’indice optique ou la concentration en particules. Cependant, les techniques lidar actuelles présentent des limitations. Les sources laser utilisées sont limitées à quelques longueurs d’onde visible ou proche infrarouge et l’identification des propriétés microphysiques nécessite une connaissance a priori du milieu diffusant. Des hypothèses sont formulées pour contraindre les méthodes d’inversion et remonter aux informations d’intérêt sur des aérosols naturels et anthropiques (particules carbonées, poussières désertiques, cendres volcaniques, etc.). En outre, les lidars actuels considèrent des portées kilométriques alors que de nouveaux besoins existent à courte distance : réalisation de mesures in situ en sortie de tuyères, contrôle local de panaches industriels à haute résolution spatiale… Les sources laser supercontinuum s’étendent du visible à l’infrarouge et offrent de nouvelles possibilités de mesures des propriétés optiques des aérosols sur un large domaine spectral continu. Leur utilisation dans les systèmes lidars est envisagée pour identifier les propriétés optiques du milieu sur toute une gamme continue de longueurs d’onde. L’un des objectifs majeurs de cette thèse est de démontrer la viabilité des lidars supercontinuum pour la caractérisation spectrale de cibles surfaciques et volumiques à haute résolution spatiale. Le premier axe concerne l’étude numérique du système avec le développement du simulateur PERFALIS. Le second axe se concentre sur la conception instrumentale d’un lidar appelé COLIBRIS. Il a permis de réaliser des mesures lidar à courte portée et à haute résolution spatiale (submétrique). Une première version a été proposée en analyse monochromatique et une seconde avec une analyse hyperspectrale de la lumière rétrodiffusée. Enfin, une nouvelle méthode d’inversion lidar nommée ST-LIM a été développée pour identifier les propriétés optiques d’un panache sans hypothèse a priori sur le rapport lidar (paramètre optique caractérisant le milieu sondé). La comparaison de mesures expérimentales avec les résultats de simulations valide le simulateur lidar dans ses deux modes de fonctionnement (monochromatique et hyperspectral). Les résultats montrent qu’il est important de considérer la forme réelle des impulsions laser lors de l’interaction lumière-matière dans le cas de sondages de panaches de faible épaisseur à haute résolution spatiale. À l’avenir, le simulateur lidar pourra être utilisé pour dimensionner de nouveaux instruments lidar supercontinuum ou monochromatiques et d’étudier leurs performances pour des versions embarquablesLidar diagnostic methods provide information on the optical parameters of the medium (scattering and absorption coefficients). These quantities depend on the properties of light (wavelength, polarization) and are then used to retrieve the microscopic properties of the medium such as size distribution, morphology, optical index or particle concentration. However, current lidar techniques have limitations. The laser sources used are limited to a few visible or near infrared wavelengths and the identification of the microphysical properties requires a priori knowledge of the scattering medium. Hypotheses are formulated to constrain the inversion methods and to provide information of interest on natural and anthropogenic aerosols (carbonaceous particles, desert dust, volcanic ash, etc.). In addition, current lidars consider kilometric ranges, whereas there are applications for those at short distances: in situ measurements at nozzle outlets, local control of industrial plumes with high spatial resolution, etc. Supercontinuum laser sources extend from the visible to the infrared and offer new possibilities for measuring the optical properties of aerosols over a wide continuous spectral range. Their use in lidar systems is considered to identify the optical properties of the medium over a wide and continuous range of wavelengths. A major objective of this thesis is to demonstrate the viability of supercontinuum lidars for the spectral characterization of surface and volume targets at high spatial resolution. The first axis concerns the numerical study of the system with the development of the PERFALIS simulator. The second axis focuses on the instrumental design of a lidar called COLIBRIS, allowing short-range lidar measurements with high spatial resolution (submetric). A first version was proposed in monochromatic analysis and a second one with a hyperspectral analysis of backscattered light. Finally, a new lidar inversion method named ST-LIM has been developed to identify the optical properties of a plume without any a priori hypothesis on the lidar ratio (optical parameter characterizing the surveyed medium). The comparison of experimental measurements with simulation results validates the lidar simulator in its two operating modes (monochromatic and hyperspectral). The results show the importance of considering the actual shape of the laser pulses during the light-matter interaction in the case of thin plume soundings with high spatial resolution. In the future, the lidar simulator may be used to design new supercontinuum or monochromatic lidar instruments and to study their performance for on-board versions
30
Watson, Francis Maurice. "Better imaging for landmine detection : an exploration of 3D full-wave inversion for ground-penetrating radar". Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/better-imaging-for-landmine-detection-an-exploration-of-3d-fullwave-inversion-for-groundpenetrating-radar(720bab5f-03a7-4531-9a56-7121609b3ef0).html.
Testo completoAbstract (sommario):
Humanitarian clearance of minefields is most often carried out by hand, conventionally using a a metal detector and a probe. Detection is a very slow process, as every piece of detected metal must treated as if it were a landmine and carefully probed and excavated, while many of them are not. The process can be safely sped up by use of Ground-Penetrating Radar (GPR) to image the subsurface, to verify metal detection results and safely ignore any objects which could not possibly be a landmine. In this thesis, we explore the possibility of using Full Wave Inversion (FWI) to improve GPR imaging for landmine detection. Posing the imaging task as FWI means solving the large-scale, non-linear and ill-posed optimisation problem of determining the physical parameters of the subsurface (such as electrical permittivity) which would best reproduce the data. This thesis begins by giving an overview of all the mathematical and implementational aspects of FWI, so as to provide an informative text for both mathematicians (perhaps already familiar with other inverse problems) wanting to contribute to the mine detection problem, as well as a wider engineering audience (perhaps already working on GPR or mine detection) interested in the mathematical study of inverse problems and FWI.We present the first numerical 3D FWI results for GPR, and consider only surface measurements from small-scale arrays as these are suitable for our application. The FWI problem requires an accurate forward model to simulate GPR data, for which we use a hybrid finite-element boundary-integral solver utilising first order curl-conforming N\'d\'{e}lec (edge) elements. We present a novel `line search' type algorithm which prioritises inversion of some target parameters in a region of interest (ROI), with the update outside of the area defined implicitly as a function of the target parameters. This is particularly applicable to the mine detection problem, in which we wish to know more about some detected metallic objects, but are not interested in the surrounding medium. We may need to resolve the surrounding area though, in order to account for the target being obscured and multiple scattering in a highly cluttered subsurface. We focus particularly on spatial sensitivity of the inverse problem, using both a singular value decomposition to analyse the Jacobian matrix, as well as an asymptotic expansion involving polarization tensors describing the perturbation of electric field due to small objects. The latter allows us to extend the current theory of sensitivity in for acoustic FWI, based on the Born approximation, to better understand how polarization plays a role in the 3D electromagnetic inverse problem. Based on this asymptotic approximation, we derive a novel approximation to the diagonals of the Hessian matrix which can be used to pre-condition the GPR FWI problem.
31
Baelde, Aurélien. "Propagation des ondes ultrasonores dans les alliages de titane à fort fibrage : cohérence spatiale et diffusion multiple". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066271/document.
Testo completoAbstract (sommario):
Le but de cette thèse est d'étudier la propagation des ondes ultrasonores dans les milieux présentant des diffuseurs allongés, et plus particulièrement les alliages de titane comportant des macrozones. Cette étude est menée à l'aide d'un dispositif expérimental constitué d'un transducteur multi-éléments linéaire en rotation autour de son axe, piloté par une électronique multivoie programmable. Le champ rétrodiffusé par un milieu à diffuseurs allongés présente une cohérence spatiale anisotrope et nous montrons que l'intensité rétrodiffusée par un tel milieu dépend de l'orientation du transducteur dans le plan perpendiculaire à la direction d'insonification. Cette dépendance permet de déterminer la direction d'élongation des macrozones, leur taille caractéristique, et de réduire le bruit de structure lors d'un contrôle ultrasonore. Une cartographie en trois dimensions de la direction locale des macrozones est ainsi réalisable en employant deux faisceaux ultrasonores focalisés en un même point selon deux directions différentes. Afin de déterminer le régime de diffusion aux fréquences usuelles de contrôle, nous avons développé, à partir des travaux de thèse d'Alexandre Aubry (UPMC 2008), un indicateur du niveau de diffusion multiple : l'estimateur de la proportion de diffusion simple. Il permet de démontrer que la diffusion multiple est importante dans les alliages de TA6V et Ti17. Nous avons de plus étendu cette méthode au cas d'interfaces eau/solide complexes suffisamment régulières. Enfin, nous proposons une nouvelle visualisation des résultats de simulations de forge permettant d'observer la direction réelle des macrozones et de mieux concevoir les plans de contrôleThis manuscript is devoted to the study of ultrasonic wave propagation in complex media composed of elongated scatterers, and specifically titanium alloys comprising macrozones. This study is carried out using a linear phased array probe rotating around its axis and driven by a multi-channel programmable amplifier. The ultrasonic field backscattered by elongated scatterers presents an anisotropic spatial coherence and we show that the intensity backscattered by such a medium depends on the angle between scatterers elongation direction and the orientation of the probe in the plane perpendicular to the insonified direction. This dependence allows to determine the macrozones elongation direction and size, and to reduce the structural noise during a non-destructive evaluation. A three dimensional cartography of local elongation direction of macrozones is achievable by using two beams focused at the same point but with different directions of incidence. In order to assess the scattering regime at conventional testing frequencies, we developed a multiple scattering measure: the single scattering proportion estimator, based on Alexandre Aubry’s PhD thesis (UPMC 2008). Applied on TA6V and Ti17 alloys, it showed strong multiple scattering. We further extended this estimator to the case of water/solid complex interfaces. Lastly, we proposed a new visualization of forging simulation results, allowing to directly observe the real macrozones elongation direction and to better design inspection procedures
32
Baelde, Aurélien. "Propagation des ondes ultrasonores dans les alliages de titane à fort fibrage : cohérence spatiale et diffusion multiple". Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066271.pdf.
Testo completoAbstract (sommario):
Le but de cette thèse est d'étudier la propagation des ondes ultrasonores dans les milieux présentant des diffuseurs allongés, et plus particulièrement les alliages de titane comportant des macrozones. Cette étude est menée à l'aide d'un dispositif expérimental constitué d'un transducteur multi-éléments linéaire en rotation autour de son axe, piloté par une électronique multivoie programmable. Le champ rétrodiffusé par un milieu à diffuseurs allongés présente une cohérence spatiale anisotrope et nous montrons que l'intensité rétrodiffusée par un tel milieu dépend de l'orientation du transducteur dans le plan perpendiculaire à la direction d'insonification. Cette dépendance permet de déterminer la direction d'élongation des macrozones, leur taille caractéristique, et de réduire le bruit de structure lors d'un contrôle ultrasonore. Une cartographie en trois dimensions de la direction locale des macrozones est ainsi réalisable en employant deux faisceaux ultrasonores focalisés en un même point selon deux directions différentes. Afin de déterminer le régime de diffusion aux fréquences usuelles de contrôle, nous avons développé, à partir des travaux de thèse d'Alexandre Aubry (UPMC 2008), un indicateur du niveau de diffusion multiple : l'estimateur de la proportion de diffusion simple. Il permet de démontrer que la diffusion multiple est importante dans les alliages de TA6V et Ti17. Nous avons de plus étendu cette méthode au cas d'interfaces eau/solide complexes suffisamment régulières. Enfin, nous proposons une nouvelle visualisation des résultats de simulations de forge permettant d'observer la direction réelle des macrozones et de mieux concevoir les plans de contrôleThis manuscript is devoted to the study of ultrasonic wave propagation in complex media composed of elongated scatterers, and specifically titanium alloys comprising macrozones. This study is carried out using a linear phased array probe rotating around its axis and driven by a multi-channel programmable amplifier. The ultrasonic field backscattered by elongated scatterers presents an anisotropic spatial coherence and we show that the intensity backscattered by such a medium depends on the angle between scatterers elongation direction and the orientation of the probe in the plane perpendicular to the insonified direction. This dependence allows to determine the macrozones elongation direction and size, and to reduce the structural noise during a non-destructive evaluation. A three dimensional cartography of local elongation direction of macrozones is achievable by using two beams focused at the same point but with different directions of incidence. In order to assess the scattering regime at conventional testing frequencies, we developed a multiple scattering measure: the single scattering proportion estimator, based on Alexandre Aubry’s PhD thesis (UPMC 2008). Applied on TA6V and Ti17 alloys, it showed strong multiple scattering. We further extended this estimator to the case of water/solid complex interfaces. Lastly, we proposed a new visualization of forging simulation results, allowing to directly observe the real macrozones elongation direction and to better design inspection procedures
33
Leedumrongwatthanakun, Saroch. "Quantum information processing with a multimode fibre". Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS526.
Testo completoAbstract (sommario):
Le transport à haut débit de données à travers des fibres optiques grâce au multiplexage spatial est en pratique limité par la diaphonie modale. Au lieu de considérer ce couplage modal comme une limitation, nous exploitons ici ce mélange de modes comme une ressource. Nous mettons en oeuvre un réseau optique linéaire programmable basé sur le concept de design photonique inverse, exploitant les techniques de mise en forme du front d’onde. Nous démontrons la manipulation d’interférences quantiques à deux photons sur divers réseaux linéaires, comprenant des degrés de liberté spatiaux et de polarisations. En particulier, nous vérifions expérimentalement la « zero transmission law » dans des interféromètres de Fourier et de Sylvester, permettant de quantifier le degré d’indiscernabilité d’un état d’entrée. De plus, grâce à la possibilité de mettre en oeuvre un réseau non unitaire, nous mettons en évidence l’anti-coalescence de photons dans toutes les configurations de sortie, et réalisons une expérience d’absorption cohérente. Nous démontrons ainsi l’aspect reconfigurable de l’implémentation de tels réseaux optiques linéaires dans des fibres multimodes. De plus, nous étudions les propriétés statistiques du speckle à un et à deux photons générés à partir de divers états d’entrée, après propagation dans une fibre multimode. Ces propriétés statistiques du speckle peuvent être utilisées pour extraire des informations sur la dimensionnalité, la pureté et l’indiscernabilité d’un état quantique inconnu, permettant ainsi leur classification. Ce travail met en évidence le potentiel du contrôle de front d’onde en milieux complexes pour le traitement quantique de l’informationTransport of information through a multimode optical fibre raises challenges when one wants to increase the data traffic using many spatial modes due to modal cross-talk and dispersion. Instead of considering those complex mixing of modes as a detrimental process, in this dissertation, we harness its mode mixing to process quantum optical information. We implement a reconfigurable linear optical network, a fundamental building block for scalable quantum technologies, based on an inverse photonic approach exploiting the technology of wavefront shaping. We experimentally demonstrate manipulation of two-photon quantum interference on various linear optical networks across both spatial and polarization degrees of freedom. In particular, we experimentally show the zero-transmission law in Fourier and Sylvester interferometers, which are used to certificate the degree of indistinguishability of an input state. Moreover, thanks to the ability to implement a non-unitary network, we observe the photon anti-coalescence effect in all output configurations, as well as the realization of a tunable coherent absorption experiment. Therefore, we demonstrate the reconfigurability, accuracy, scalability and robustness of the implemented linear optical networks for quantum information processing. Furthermore, we study the statistical properties of one-and two-photon speckles generated from various ground-truth states of light after propagating through a multimode fibre. These statistical properties of speckles can be used to extract information about the dimensionality, purity, and indistinguishability of an unknown input state of light, therefore allowing for state classification. Our results highlight the potential of complex media combined with wavefront shaping for quantum information processing
34
Croënne, C., J. O. Vasseur, Matar O. Bou, M. F. Ponge, P. A. Deymier, A. C. Hladky-Hennion e B. Dubus. "Brillouin scattering-like effect and non-reciprocal propagation of elastic waves due to spatio-temporal modulation of electrical boundary conditions in piezoelectric media". AMER INST PHYSICS, 2017. http://hdl.handle.net/10150/623049.
Testo completoAbstract (sommario):
The properties of a one-dimensional phononic crystal made of identical piezoelectric elements separated by thin metallic electrodes connected to the ground are studied theoretically for cases where the locations of the electrical connections change as a function of time with a specific speed. This spatio-temporal modulation of the electrical boundary conditions results in significant non-linear effects that are evidenced numerically. The interaction between an incident harmonic longitudinal wave and the time-dependent phononic crystal is shown to lead to frequency splitting analogous to Brillouin scattering. Moreover, the boundaries of the Bragg bandgaps are strongly affected, and for some specific modulation speed, one-way wave propagation can be achieved. Published by AIP Publishing.
35
Blanluet, Arthur. "Étude par acoustique large bande de la composition et de la distribution spatiale de couches diffusantes denses dans le golfe de Gascogne". Thesis, Rennes, Agrocampus Ouest, 2019. http://www.theses.fr/2019NSARH110.
Testo completoAbstract (sommario):
Les compartiments intermédiaires de l’écosystème pélagique (du mésozooplancton au micronecton) transfèrent l’énergie et la matière organique entre les producteurs primaires et un certain nombre d’espèces commerciales (anchois, sardines…). Certains de ces organismes produiraient des « couches diffusantes » (Sound Scattering Layers, SSLs) observés sur une large gamme d’échelles spatio-temporelles et de zones géographiques. Néanmoins, la composition taxonomique des SSLs reste encore en grande partie inconnue. L’objectif de cette thèse était de décrire la composition et la répartition de SSLs denses observées dans le golfe de Gascogne (GdG) au printemps à plusieurs échelles spatiales, en utilisant l’acoustique large bande, des filets et des outils vidéo. Dans le premier chapitre, nous avons montré que la largeur du faisceau d’un échosondeur avait peu d’impact sur les densités acoustiques de SSLs observées au printemps 2014, ce qui suggère que certaines SSLs du golfe de Gascogne pourraienten comparant la réponse acoustique large bande mesurée in situ aux prédictions de modèles de réflecteurs acoustiques paramétrées à l’aide des données d’échantillonnages biologiques. Nous avons déterminé que les réflecteurs dominant la réponse acoustique aux basses fréquences (18-150 kHz) étaient composés de siphonophores et de poissons mésopélagiques, tous porteurs d’inclusions gazeuses. La réponse acoustique aux plus hautes fréquences était dominée des organismes mésozooplanctoniques, dont de fortes densités de ptéropodes. Dans le troisième chapitre, nous avons appliqué des méthodes de clasIntermediate trophic components of pelagic ecosystem (from mesozooplakton to micronekton) funnel energy and organic matters from primary producers to many commercial species (anchovy, sardines…). Some of these organisms are supposed to be important contributors to the ubiquitous Sound Scattering Layers (SSLs) observed over a broad range of spatio-temporal scales and geographical areas. Yet, the SSLs taxonomic composition remains largely unknown. The aim of this PhD was to describe the composition and repartition of dense SSLs observed in the Bay of Biscay (France) in spring at several spatial scales, using broadband acoustics, nets and videos. In the first chapter, we showed that the echo sounder beam widths had few effect on the SSLs backscatter, suggesting those SSLs could be composed of unidentified small gaseous scatterers. In the second chapter we applied a forward approach to characterize the composition of SSLs sampled in spring 2016 at small scale,by comparing in situ frequency responses to predictions of scatterer models parameterized with biological sampling data. We determined that these SSLs were probably composed of gas-bearing siphonophores, who, together with mesopelagic fish, dominated the frequency spectra at low frequencies (18-150 kHz). The acoustic backscatter at higher frequencies was dominated by a mix of mesozooplankton organisms, including high densities of pteropods. In the third chapter we applied unsupervised classification methods and a supervised discriminant analysis to delineate the spatial distribution of a peculiar surface SSL composed of
36
Sankhe, Mamadou. "Caractérisations spatio-temporelles de milieux plasmagènes à haute énergie par diffusion laser". Thesis, Orléans, 2019. http://www.theses.fr/2019ORLE3028.
Testo completoAbstract (sommario):
Les milieux plasmagènes transitoires générés par décharge électrique pointe-pointe et par claquage laser sont utilisés dans des applications d’allumage de mélanges combustibles ou à des fins d’analyses telles que la spectroscopie de plasma induit par laser (LIBS). Parallèlement à leurs importants intérêts scientifiques et technologiques, ces milieux restent difficiles à appréhender en raison de leur caractère transitoire et des gradients importants qui les caractérisent. De plus, les hypothèses d’Équilibre Thermodynamique Local (ETL), souvent faites dans le cadre de leur étude, ne sont pas toujours vérifiées.Afin de mieux connaître ces milieux plasmagènes transitoires, deux techniques complémentaires de caractérisations spectroscopiques ont été mises en oeuvre : la Spectroscopie Optique d’Émission (SOE) et la Diffusion Thomson (DT).L’utilisation combinée de la SOE (fondée sur des hypothèses complémentaires validant l’ETL) et de la DT (supposant uniquement une distribution maxwellienne des vitesses translationnelles des particules), doit permettre de valider les conditions d’ETL dans les plasmas étudiés et de fournir des données d’entrée réalistes pour les modélisations.Dans le cadre de cette thèse, nous avons étudié une décharge électrique pointe-pointe, utilisée dans l’allumage de poudres métalliques, et des plasmas de claquage et d’ablation induits par laser, utilisés pour les applications LIBSThe transient plasmagenic media generated by tip-tip electric discharge and laser breakdown are used in fuel mixture ignition applications or for analytical purposes such as Laser-Induced Plasma Spectroscopy (LIBS). In addition to their important scientific and technological interests, these media are still difficult to grasp because of their transient nature and the important gradients that characterize them. In addition, the hypotheses of Local Thermodynamic Equilibrium (LTE), often made as part of their study, are not always verified.In order to better understand these transient plasmagenic media, two complementary spectroscopic characterization techniques have been implemented: Optical Emission Spectroscopy (OES) and Thomson Scattering (TS).The combined use of OES (based on complementary hypotheses validating LTE) and TS (assuming only a Maxwellian distribution of translational velocities of particles), should make it possible to validate the conditions of LTE in the plasmas studied and of provide realistic input data for modeling.In this manuscript, we studied a tip-tip electrical discharge, used in the ignition of metal powders, and laser-induced breakdown and ablation plasmas, used for LIBS applications
37
Brunet, Laurence. "Repartition spatiale de la densite electronique moleculaire en composantes atomiques in situ". Paris 6, 1987. http://www.theses.fr/1987PA066042.
Testo completoAbstract (sommario):
Modelisation originale de la densite electronique moleculaire par la superposition de densites atomiques spheriques, centrees sur les noyaux a partir de calculs d'orbitales moleculaires, avec trois invariants : la charge totale, le potentiel electrons-noyaux, le moment dipolaire. Description de la methode numerique pour determiner les densites associes aux atomes dans une base d'orbitales gaussiennes. Renseignements obtenus sur les modifications spatiales de la charge electronique par formation de liaisons, sur les facteurs de structure atomiques effectifs, apres transformation de fourier, en tenant compte de l'effet de l'environnement. Extension de la methode a la decomposition de la densite electronique moleculaire en densites composantes, autres qu'atomiques et non necessairement centrees sur les noyaux. Outre les applications a l'etude de la structure et des proprietes electroniques des molecules, proposition d'utilisation au calcul des polarisabilites optiques (lineaires ou non), a l'analyse des donnees cristallographiques obtenues par diffraction de rayon x et a la prevision de la structure des cristaux moleculaires
38
Rossi, Giuseppe Germano. "Etude de la réponse au rayonnement X entre 10KeV-100KeV des détecteurs à micro-pistes de germanium avec résolution spatiale et en énergie". Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10089.
Testo completoAbstract (sommario):
Dans le cadre d'un developpement d'un detecteur avec resolution spatiale et en energie pour comptage de photons dans des experiences de diffusion compton, nous avons etudie, au sein de l'esrf-grenoble, les performances de deux capteurs de germanium a micro-pistes. Ces deux detecteurs, issus de deux differentes technologies de fabrication, ont une resolution en energie associee a une resolution spatiale correspondante a leur pas de pistes de 200m. Nous avons valide l'utilisation d'une nouvelle plaquette multicouches connectante a tres haute densite les pistes du capteur meme, refroidi a l'azote liquide dans son cryostat, a l'electronique de lecture situee au plus proche a temperature ambiante. La resolution en position ainsi que la reponse en energie ont ete experimentalement caracterisees en balayant le detecteur avec un faisceau ponctuel monochromatique de lumiere de synchrotron de largeur 15m. Le systeme d'acquisition des donnees est base sur la mesure en coincidence de la reponse des pistes du capteur. A des energies plus basses que 15kev, nous trouvons que la region d'isolation entre deux pistes voisines est une source de piegeage de charge. Nous observons le phenomene de division de charge entre deux pistes a partir de 30kev. Cet effet, que nous lions au processus de diffusion des porteurs dans le volume du semi-conducteur, reduit considerablement la qualite des spectres d'energie ainsi que la resolution spatiale du capteur. Toutefois, apres traitement par un algorithme qui corrige la division de charge des donnees brutes tout en utilisant l'information des signaux mesures en coincidence, le phenomene de division dans les spectres est completement supprime. Nous avons mis au point a partir du code egs4, un programme de simulation de la reponse en energie comprenant le processus de diffusion des charges dans le volume du capteur. Les spectres en energie ainsi calcules reproduisent remarquablement les donnees experimentales et confirment le role critique de la diffusion de la charge dans la reponse des capteurs a micro-pistes. La conclusion de ce travail est que les detecteurs a micro-pistes de germanium fonctionnent dans la region d'energie 30-100kev avec une resolution en energie et position proche des limites physiques imposes par le processus d'absorption des photons et la diffusion des charges mobiles.
39
Böhm, Julian. "Phénomènes de transport originaux dans des expériences micro-ondes via la mise en forme spatiale et spectrale". Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4048/document.
Testo completoAbstract (sommario):
Le transport des ondes joue un rôle majeur dans les systèmes de communication comme le Wifi ou les fibres optiques. Les principaux problèmes rencontrés dans ces systèmes concernent la protection contre les intrusions, la consommation d’énergie et le filtrage modal. Nous proposons différentes expériences micro-ondes mettant toutes en œuvre une mise en forme des ondes, pour traiter ces problèmes. Dans une cavité micro-ondes, des états de diffusion particuliers sont générés en s’appuyant uniquement sur des mesures de transmission et sur le formalisme du temps de retard de Wigner-Smith. Ces états sont capables d’éviter une région déterminée de la cavité, de se concentrer sur un point particulier, ou de suivre une trajectoire d’une particule classique. Le filtrage de mode est mis en œuvre dans un guide d’ondes aux frontières ondulées et en présence de pertes dépendant de la position. Le profil du guide est choisi de façon à ce que les deux modes de Bloch qui se propagent encerclent un point exceptionnel. Cette trajectoire s’accompagne d’une transition non-adiabatique entre les deux modes et d'un filtrage asymétrique de ces modes. La thèse présente également des travaux liés à la problématique des algorithmes de « recherche quantique », notamment l’algorithme de Grover. Cette recherche est mise en œuvre dans un réseau en nid d’abeilles de résonateurs micro-ondes couplés, bien décrits par un modèle de liaisons fortes (le système constitue un analogue micro-ondes du graphène). Une expérience de preuve de principe propose la recherche de deux résonateurs distincts reliés au réseau. La loi d’échelle attendue pour cet algorithme est expérimentalement obtenue dans une chaîne linéaireTransport of waves plays an important role in modern communication systems like Wi-Fi or optical fibres. Typical problems in such systems concern security against possible intruders, energy consumption, time efficiency and the possibility of mode filtering. Microwave experiments are suited to study this kind of problems, because they offer a good control of the experimental parameters. Thus we can implement the method of wave shaping to investigate atypical transport phenomena, which address the mentioned problems. Wave front shaping solely based on the transmission together with the Wigner-Smith time delay formalism allows me to establish special scattering states in situ. These scattering states avoid a pre-selected region, focus on a specific spot or follow trajectories of classical particles, so called particle-like scattering states. Mode filtering is induced inside a waveguide with wavy boundaries and position dependent loss. The boundary profiles are chosen in such a way that the two propagating modes describe an encircling of an exceptional point in the Bloch picture. The asymmetric mode filtering is found due to the appearing non-adiabatic transitions. Another part of my work deals with Grover’s quantum search. I put such a search into practice in a two-dimensional graphene-lattice using coupled resonators, which form a tight-binding analogue. In this proof of principle experiment we search for different resonators attached to the graphene-lattice. Furthermore, the scaling behaviour of the quantum search is quantified for a linear chain of resonators
40
ROSATI, ROBERTO. "Microscopic modeling of energy dissipation and decoherence in nanoscale materials and devices". Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2599755.
Testo completoAbstract (sommario):
Primary goal of this thesis work is to develop and implement microscopic modeling strategies able to describe semiconductor-based nanomaterials and nanodevices, overcoming both the intrinsic limits of the semiclassical transport theory and the huge computational costs of non Markovian approaches.
The progressive reduction of modern optoelectronic devices space-scales, triggered by the evolution on semiconductor heterostructures at the nanoscale, together with the decrease of the typical time-scales involved, pushes device miniaturization toward limits where the application of the traditional Boltzmann transport theory becomes questionable, and a comparison with more rigorous quantum transport approaches is imperative. In spite of the quantum-mechanical nature of electron and photon dynamics in the core region of typical solid-state nanodevices, the overall behavior of such quantum systems is often governed by a highly non-trivial interplay between phase coherence and dissipation/dephasing. To this aim, the crucial step is to adopt a quantum mechanical description of the carrier subsystem; this can be performed at different levels, ranging from phenomenological dissipation/decoherence models to quantum-kinetic treatments. However, due to their high computational cost, non-Markovian Green’ s-function as well as density-matrix approaches like quantum Monte Carlo techniques or quantum-kinetics are currently unsuitable for the design and optimization of new-generation nanodevices. On the other end, the Wigner-function technique is a widely used approach which, in principle, is well suited to describe an interplay between coherence and dissipation: in fact it can be regarded both as a phase space formulation of the electronic density matrix and a quantum equivalent of the classical distribution function. The evolution of this quasi-distribution function is governed by the Wigner-equation, which is usually solved by applying local spatial boundary conditions. However, such a scheme has recently shown some intrinsic limits. In this thesis work we analyze both the reasons for these unphysical features –pointing out the needing of different and purely quantum approaches– and the limits in which they should not appear, thus justifying why these problems had not been encountered in numerous quantum-transport simulations based on this procedure.
For these reasons here we present a novel single-particle simulation strategy able to describe the interplay between coherence and dissipation/dephasing. In the presence of one- as well as two-body scattering mechanisms, we apply the mean-field approximation to the many-body Lindblad-type (hence, positive-definite) scattering superoperators provided by a recently proposed Markov approach, and we derive a closed equation of motion for the electronic single-particle density matrix. Although the resulting scattering superoperator turns out to be, at finite or high carrier densities, nonlinear and non-Lindblad, we prove that it is able to guarantee the positivity of the evolution (in striking contrast with conventional Markov approaches) independently of the scattering mechanisms, an essential prerequisite of any reliable kinetic treatment of semiconductor quantum devices; furthermore, it may be extended to the cases of quantum systems with open spatial boundaries (in this regard, it provides a formal derivation of a recently proposed Lindblad-like device-reservoir scattering superoperator). The proposed theoretical scheme is able, one the one hand, to recover the space-dependent Boltzmann equation and, on the other, to point out the regimes where a relevant role may be played by scattering-nonlocality effects, e.g. scattering-induced variations of the spatial charge-density which may not be provided by semiclassical treatments. Supplementing our analytical investigation with a number of simulated experiments in homogeneous as well as inhomogeneous GaN-based systems, we provide a rigorous treatment of scattering nonlocality in semiconductor nanostructures: in particular, we show how the scattering-nonlocality effects (i) are particularly significant in the presence of a carrier localization on the nanometric space scale, (ii) cause a speedup of the diffusion and (iii) in superlattice structures induce, with respect to scattering-free evolutions, a suppression of coherent oscillations between adjacent wells. These genuine quantum effects may be predicted also by other simplified treatments of the dissipation/decoherence like, e.g., the Relaxation Time Approximation: the latter however turns out to be, contrary to the proposed microscopic theoretical scheme, totally nonlocal, e.g. it is unable to recover the local character of the Boltzmann collision term in the semiclassical limit and it leads, especially for the case of quasielastic dissipation processes, to a significant overestimation of the diffusion speedup.
41
Lepcio, Petr. "Efekt submikrometrických rysů na reologii polymerních nanokompozitů". Doctoral thesis, Vysoké učení technické v Brně. CEITEC VUT, 2018. http://www.nusl.cz/ntk/nusl-391876.
Testo completoAbstract (sommario):
Polymerní nanokompozity (PNCs) mají slibnou budoucnost jako lehké funkční materiály zpracovatelné aditivními výrobními technologiemi. Jejich rychlému rozšíření však brání silná závislost jejich užitných vlastností na prostorovém uspořádání nanočástic (NP). Schopnost řídit disperzi nanočástic je tak klíčovým předpokladem pro jejich uplatnění ve funkčních kompozitech. Tato práce zkoumá přípravu polymerních nanokompozitů v modelové sklotvorné polymerní matrici roztokovou metodou, technikou schopnou vytvářet prostorové uspořádání nanočástic řízené strukturními a kinetickými parametry přípravného procesu. Prezentované výsledky popisují rozdíly mezi změnami rheologického chování roztoku polystyrenu při oscilačním smyku s vysokou amplitudou (LAOS) vyvolanými nanočásticemi. Výsledky vedou k závěru, že vysoce-afinní OP-POSS nanočástice při nízkých koncentracích dobře interagují s PS a tvoří tuhé agregáty, zatímco nízko-afinní OM-POSS nanočástice za těchto podmínek neovlivňují deformační chování polymerních řetězců. Dále byla pozornost zaměřena na vliv použitého rozpouštědla na uspořádání nanočástic v SiO2/PMMA a SiO2/PS nanokompozitech, který je v literatuře prezentován jako parametr řídící prostorové uspořádání nanočástic v pevném stavu. Důraz byl kladen na kvalitativní rozdíly mezi „špatně dispergovanými“ shluky nanočástic, které byly na základě rheologie a strukturální analýzy (TEM, USAXS) identifikovány jako polymerními řetězci vázané nanočásticové klastry a dva typy agregátů, jeden termodynamického a druhý kinetického původu. Jednotlivé druhy agregátů se vyznačují odlišnými kinetikami vzniku a rozdílnými vlastnostmi jak mezi sebou, tak v porovnání s dispergovanými nanočásticemi. Pozorované typy disperze nanočástic byly kvantitativně posouzeny podle svých rheologických vlastností během roztokové přípravy, podle kterých byla vyhodnocena míra adsorpce polymeru na povrch nanočástic a atrakce ve vypuzeném objemu. Výsledky byly porovnány s teorií PRISM. Důležitost uspořádání nanočástic byla demonstrována na porovnání teplot skelných přechodů různých struktur při stejném chemickém složení.
42
Golkin, Stanislav. "Simulation de la propagation d'ondes SH dans des structures périodiques et de la diffusion multiple d'ondes de volume en milieux aléatoires". Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR1A002/document.
Testo completoAbstract (sommario):
Cette thèse concerne l’étude de la propagation d’ondes acoustiques dans des structures hétérogènes. Le but essentiel de ces travaux est de confronter des résultats d’expériences numériques effectuées dans le domaine physique (espace, temps) à des prédictions analytiques pour la propagation des ondes de surface SH le long d’un demi-espace stratifié périodique produisant des spectres discontinus de dispersion pour les ondes, ainsi que pour la diffusion multiple dans des milieux aléatoires inclusionnaires (fissures, cavités). Le code numérique FDTD développé lors de cette étude a permis, en autres choses, de corroborer quantitativement les fenêtres spectrales théoriques d’existence des ondes de surface dans les demi-espaces périodiques,ainsi que de montrer des zones de validité fréquentielles des approches analytiques de diffusion multiple concernant les propriétés effectives de milieux aléatoiresThe study is concerned with acoustic waves in elastic media with a different nature of in homogeneity consisting in either periodically continuous or piece wise variation of material properties, or in random sets of defects embedded into a homogeneous matrix, with a given statistical distribution. The scope of problems is topical in non-destructive testing and other applications of ultrasound.Theoretical methods describing involved acoustic phenomena (complex dispersion features, coherent wave in random media, ensemble average techniques) often rely on certain a priori assumptions which render numerical verification especially important.The thesis presents results of analytical modelling of the propagation of surface acoustic waves along periodic half-space, for which the dispersion spectrum is rather complex (discontinuous spectrum of propagation for the surface waves). A 2nd order FDTD numerical code has been developed in order to perform numerical experiments in the space and time domains, and to corroborate the analytical predictions in the frequency domain. A good agreement of simulated results with analytical modelling demonstrates applicability and consistency of the numerical tool. Finally, the code has been used for extracting numerically the coherent wave regime (mean wave over ensemble averaging of the positions of scatterers) for the acoustic propagation in different types of populations of randomly distributed scatterers. The results indicate ranges of validity of some multiple scattering analytical techniques
43
Baba, Ibrahim El. "Contributions numériques en compatibilité électromagnétique impulsionnelle. Paradigme pour la caractérisation temporelle d'équipements". Thesis, Clermont-Ferrand 2, 2012. http://www.theses.fr/2012CLF22232/document.
Testo completoAbstract (sommario):
Le travail présenté dans cette thèse concerne la mise en oeuvre numérique de techniques temporelles pour des applications en compatibilité électromagnétique (CEM) impulsionnelle, essentiellement pour des études en chambre réverbérante à brassage de modes (CRBM). Prenant le contre-pied des approches fréquentielles, adaptées par nature aux études de cavités résonantes, l’idée directrice de ce mémoire a été d’étudier des moyens temporels originaux d’investigation de CRBM en vue de proposer de nouveaux paradigmes pour la caractérisation d’équipements. Originellement développé en acoustique, le processus de retournement temporel (RT) récemment appliqué aux ondes électromagnétiques permet une focalisation spatiale et temporelle de ces dernières d’autant meilleur que le milieu de propagation est réverbérant. Les chambres réverbérantes (CR) sont ainsi des endroits idéaux pour l’application du processus de RT. Après une nécessaire étude des nombreux paramètres qui gouvernent ce dernier couplée à la définition de méthodologies numériques spécifiques, les applications du RT en CRBM sont exposées. En particulier, l’intérêt d’une focalisation sélective pour des tests en susceptibilité rayonnée est démontré. L’importance des coefficients d’absorption et de diffraction des équipements en CRBM justifie leur caractérisation précise et efficace. À cette fin, la mise en oeuvre d’un calcul temporel de section efficace totale de diffraction (TSCS en anglais) est détaillée. L’application de cette nouvelle technique à différentes formes de brasseurs de modes permet au final de confronter ces résultats avec ceux obtenus à l’aide de tests normatifs CEMThe work presented in this thesis concerns the use of time techniques for impulsive ElectroMagnetic Compatibility (EMC) applications, mainly for Modes Stirred Reverberation Chamber (MSRC) studies. Contrary to approaches from frequency domain, obviously well-fitted for studies in resonant cavities, the main idea of this thesis was to study an original time method for MSRC investigation to propose new paradigms for equipment characterization. Originally developed in acoustics, the Time Reversal (TR) process recently applied to electromagnetic waves allows focusing it both in time and space. The process quality is even higher if the propagation environment is reverberant. Thus, the Reverberation Chambers (RC) are an ideal locations for TR implementation. After a study of parameters involved in the TR process coupled with the definition of specific numerical methods, the applications of TR in MSRC are exposed. In particular, the interest of selective focusing for radiated susceptibility tests is demonstrated. The importance of absorption and diffraction coefficients for MSRC equipment justifies their accurate and efficient characterization. To this end, the implementation of a temporal calculation of the Total Scattering Cross Section (TSCS) in RC is detailed. The application of this new technique to different forms of stirrers allows finally to face these results with those obtained from standard EMC test
44
Hunter, Brandon. "Channel Probing for an Indoor Wireless Communications Channel". BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/64.
Testo completoAbstract (sommario):
The statistics of the amplitude, time and angle of arrival of multipaths in an indoor environment are all necessary components of multipath models used to simulate the performance of spatial diversity in receive antenna configurations. The model presented by Saleh and Valenzuela, was added to by Spencer et. al., and included all three of these parameters for a 7 GHz channel. A system was built to measure these multipath parameters at 2.4 GHz for multiple locations in an indoor environment. Another system was built to measure the angle of transmission for a 6 GHz channel. The addition of this parameter allows spatial diversity at the transmitter along with the receiver to be simulated. The process of going from raw measurement data to discrete arrivals and then to clustered arrivals is analyzed. Many possible errors associated with discrete arrival processing are discussed along with possible solutions. Four clustering methods are compared and their relative strengths and weaknesses are pointed out. The effects that errors in the clustering process have on parameter estimation and model performance are also simulated.
45
Yeh, Po-Ting, e 葉柏廷. "Spatial and Temporal Characteristics of Light-Scattering Generated by Laser-Induced Breakdown". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/n93rt3.
Testo completoAbstract (sommario):
碩士國立交通大學
電子物理系所
106
The main goal of this research is to propose a new method of producing 3D visual image with high intensity 532 nm light source, and can be viewed from all 360 degrees. We use a high peak power, passively Q-switched flash-lamp laser and frequency-doubling technique, we can produce a 532 nm scattering light from laser-induced breakdown. We explore the consequence of 532 nm scattering and laser-induced breakdown by studying 90-degree spectrum and time-domain analysis. Further on, we discuss how different input energy, spot size and breakdown threshold affect focal point image and focal point image. These results show the possibility of visual-light 3D image by laser-induced breakdown.
46
Dama, Yousef A. S., Raed A. Abd-Alhameed, Dawei Zhou, Steven M. R. Jones, Mark B. Child e Peter S. Excell. "Calculation of the Spatial Envelope Correlation Between Two Antennas in Terms of the System Scattering Parameters Including Conducting Losses". 2010. http://hdl.handle.net/10454/4785.
Testo completoAbstract (sommario):
yesThe envelope correlation for a two-element antenna array may be calculated using the antenna radiation fields, or more simply from the scattering parameters of the system. The use of scattering parameters provides a major simplification over the direct use of field data. In this paper we propose a modification of the scattering parameter method which also includes the antenna losses. This approach has the advantage of simplifying the antenna design process, especially when low envelope correlations are needed. It also offers a better prediction of the spatial envelope correlation, and a good framework for understanding the effects of the mutual coupling. The accuracy of this proposed method is illustrated by two examples.
47
Pollock, Tony Steven. "On Limits of Multi-Antenna Wireless Communications in Spatially Selective Channels". Phd thesis, 2003. http://hdl.handle.net/1885/47999.
Testo completoAbstract (sommario):
Multiple-Input Multiple-Output (MIMO) communications systems using multiantenna arrays simultaneously during transmission and reception have generated significant interest in recent years. Theoretical work in the mid 1990?s showed the potential for significant capacity increases in wireless channels via spatial multiplexing with sparse antenna arrays and rich scattering environments. However, in reality the capacity is significantly reduced when the antennas are placed close together, or the scattering environment is sparse, causing the signals received by different antennas to become correlated, corresponding to a reduction of the effective number of sub-channels between transmit and receive antennas. ¶ By introducing the previously ignored spatial aspects, namely the antenna array geometry and the scattering environment, into a novel channel model new bounds and fundamental limitations to MIMO capacity are derived for spatially constrained, or spatially selective, channels. A theoretically derived capacity saturation point is shown to exist for spatially selective MIMO channels, at which there is no capacity growth with increasing numbers of antennas. Furthermore, it is shown that this saturation point is dependent on the shape, size and orientation of the spatial volumes containing the antenna arrays along with the properties of the scattering environment. ¶ This result leads to the definition of an intrinsic capacity between separate spatial volumes in a continuous scattering environment, which is an upper limit to communication between the volumes that can not be increased with increasing numbers of antennas within. It is shown that there exists a fundamental limit to the information theoretic capacity between two continuous volumes in space, where using antenna arrays is simply one choice of implementation of a more general spatial signal processing underlying all wireless communication systems.
48
Del, Bel Belluz Justin. "Spatial and temporal particulate variability at an integrated multi-trophic aquaculture (IMTA) site in Kyuquot Sound, British Columbia, using bio-optical methods". Thesis, 2014. http://hdl.handle.net/1828/5658.
Testo completoAbstract (sommario):
The goal of this thesis was to detail spatial and temporal organic particulate dynamics at an integrated multi-trophic aquaculture (IMTA) site on the west coast of Vancouver Island, Canada. To accomplish this goal, in-situ optical measurements of particulate scattering (bp), particulate backscattering (bbp) and the particulate backscattering ratio (bbp:bp) were collected in conjunction with discrete sampling for particulate organic carbon (POC) and chlorophyll a (chl a) concentrations. These measurements were performed over three seasons (autumn, winter and summer) at reference sites and at sites within and directly adjacent to the fish component of the IMTA system.
Chapter 2 of this thesis focused on the examination of bio-optical relationships over various timescales (seasonally, daily and within-day) to describe temporal and vertical particulate variability and to assess the effectiveness of bio-optical methods for environmental monitoring. Autumn showed low bio-optical magnitudes with distinct lower cage increases possibly attributable to aquaculture derived wastes. In spring, sampling was performed over diatom bloom conditions, dominating the bio-optical measurements. During summer, an Emiliania Huxleyi bloom likely occurred, strongly enhancing bbp and bbp:bp magnitudes in the thermally stratified upper water column. Throughout these conditions, bp was predominantly influenced by chl a suggesting sensitivity to phytoplankton concentrations. While bbp was conditioned by chl a during the diatom bloom, it was also highly sensitive to the presence of inorganic and likely detrital materials. Finally, bbp:bp was sensitive to particulate compositions, showing low values (< 0.010) in diatom dominated waters and high values when refractive coccoliths were likely present. Notably, in autumn, bbp:bp was conditioned by detrital particles and along with bbp, showed post-feeding lower cage increases suggesting that these parameters could be useful candidates for particulate waste tracking during low ambient particle conditions.
In chapter 3, the temporal, vertical and horizontal dispersion of the aquaculture derived particulate wastes are detailed. Autumn was the only period to show waste signals, likely due to their quick dilution into the particulate rich fields in spring/summer. During this period, post-feeding particulate waste increases were focused at the bottom of the cage with possible vertical sinking towards the seafloor. Minimal horizontal dispersion towards the scallop portion of the system was observed; however, more comprehensive sampling over differing hydrographic regimes is necessary to characterize waste dispersion. Based on our temporally limited autumn results, the most appropriate placement of uptake species for waste assimilation would be directly below the studied cage.
Our results highlight the need for high spatial and temporal resolution methods for particulate monitoring within IMTA settings as discrete sampling may miss “patchy” waste dispersal streams. The bio-optical measurements performed during this study could fill this need as they can provide high resolution information on particulate concentrations and compositions not achievable solely through the use of discrete water sampling. With further research, optical instrumentation could be incorporated into IMTA systems allowing for the near real time and continuous collection of data on particulate dynamics. This knowledge could greatly aid in the design and implementation of systems optimized for waste removal by uptake species.Graduate
0792
0768
0752
jdelbel@uvic.ca
49
Ren, Yu-Jiun, e 任宇駿. "Development of Hybrid Spatio-Temporl Radio Channel Model and Scattering Cluster Model for Macrocellular Environments". Thesis, 2002. http://ndltd.ncl.edu.tw/handle/94595107434883856712.
Testo completoAbstract (sommario):
碩士國立交通大學
電信工程系
90
This paper presents a new hybrid spatio-temporal radio channel model, which can characterize both the space-time property and the scatterer cluster effect well for macrocellular radio channel in urban environment. The hybrid model combines a site-specific model with a statistical model. The former model employs a deterministic approach to describe the direct wave, specular reflection wave and diffraction wave. The latter one employs a statistical approach to describe the scattered or diffused fields, which is due to the local scatterers around the mobile station, rough surface of dominant buildings, and multiple scattering effect of corners/edges of dominant buildings. It is found that the scattering or the diffused fields from each dominant building are arrived in groups in space-time domain, which can be modeled by applying the scatterer cluster. Here, a scatterer cluster is described by introducing randomly positioned scatterers in the associated “effective scattering zone”, which represents the effective diffused-reflection or -diffraction area of the buildings. The rules to determine the scattering zone size and the scatterer number are investigated by measurement-based method. By comparing the computed time of arrival, angle of arrival, r.m.s. angle spread and r.m.s. delay spread with the measured one, the hybrid model has been proved to be an effective and accurate spatio-temporal radio channel model.
50
Svetogorova, Elena. "Integral equation approach to reflection and transmission of a plane TE-wave at a (linear/nonlinear) dielectric film with spatially varying permittivity". Doctoral thesis, 2004. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2004110212.
Testo completoAbstract (sommario):
The reflection and transmission of an electromagnetic TE-polarized plane wave at a dielectric film between two linear semi-infinite media (substrate and cladding) is considered. All media are assumed to be homogeneous in x- and z- direction, isotropic, and non-magnetic. The permittivity of the film is assumed to be characterized by a continuously differentiable function of the transverse coordinate and the field. To obtain solutions of Maxwell´s equations that satisfy the boundary conditions the problem is reduced to a Helmholtz equation, which is transformed to a Volterra integral equation for the field intensity inside the film. The Volterra equation is solved by iteration subject to the appropriate boundary conditions. The (iteration) solutions for the linear case and for the nonlinear case are expressed in terms of a uniformly convergent series and a uniformly convergent sequence, respectively. The uniform convergence is proved using the Banach Fixed-Point Theorem. The condition for its applicability leads to a condition for the parameters of the problem. By iterating the Volterra equation an approximate solution for the intensity inside the film is presented. The mathematical basis of the procedure is outlined in detail. Using an approximate solution, the phase function,the phase shifts on reflection and transmission, the reflectivity and the absorptance are determined.Further iterations of the Volterra equation are possible.Semianalytical and numerical examples illustrate the main features of the approach. The method is succesfully applied to different permittivity functions (real, complex, Kerr-like and saturable nonlinear). The agreement between the approximate analytical solutions and numerical solutions is satisfactory. It seems that the method proposed can serve as a means to optimize certain parameters of the problem (material and/or geometrical) for particular purposes.