Dissertations / Theses: 'Time reversal of diffusion'

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Roelly, Sylvie, and Michèle Thieullen. "Duality formula for the bridges of a Brownian diffusion : application to gradient drifts." Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2006/671/.

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In this paper, we consider families of time Markov fields (or reciprocal classes) which have the same bridges as a Brownian diffusion. We characterize each class as the set of solutions of an integration by parts formula on the space of continuous paths C[0; 1]; R-d) Our techniques provide a characterization of gradient diffusions by a duality formula and, in case of reversibility, a generalization of a result of Kolmogorov.

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Blondel, Thibaud. "Approche Matricielle de l'Imagerie Sismique." Thesis, Paris Sciences et Lettres (ComUE), 2019. https://pastel.archives-ouvertes.fr/tel-03174491.

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Le projet de thèse a pour objectif d'étendre à la géophysique et à l'imagerie sismique une méthode matricielle de propagation des ondes dans les milieux hétérogènes. Cette méthode consiste à extraire la contribution de diffusion simple dans des données où la diffusion multiple prédomine, permettant ainsi d'améliorer l'imagerie dans ce type de milieux. L'approche a été mise au point en imagerie acoustique à l'Institut Langevin, en utilisant des réseaux linéaires unidimensionnels de transducteurs ultrasonores. Elle consiste à exploiter la matrice des réponses impulsionnelles entre les éléments du réseau, qui contient toute l'information disponible sur le milieu étudié, en y appliquant une série d'opérations mathématiques à des fins de détection, d'imagerie, de caractérisation ou de monitoring. La méthode a été testée dans un contexte industriel sur des aciers, ce qui a permis d'améliorer significativement la détection de défauts. Il s'agira durant ce projet d'adapter la méthode à la géophysique, en ayant recours à des réseaux bidimensionnels irréguliers de capteurs passifs et non plus à des réseaux de transducteurs unidimensionnels périodiques et contrôlables. D'une part, le retournement temporel itératif et les techniques associées peuvent être utilisées pour contrer les effets d'aberration associés aux hétérogénéités étendues de la couche superficielle, conduisant à une image du sous-sol mieux contrastée et résolue [1-4]. D'autre part, une approche plus élaborée basée sur les matrices aléatoires peut être utilisée dans les zones où des hétérogénéités de petites taille sont fortement diffusantes et/ou concentrées [5-7]. Dans ce régime, les méthodes d'imagerie conventionnelle souffrent de la diffusion multiple qui conduit à une image de speckle, sans lien direct avec la réflectivité du milieu. Dans le cas de capteurs purement passifs tels que les géophones habituellement utilisés en sismologie, la matrice de réponse du milieu sera obtenue de manière passive par corrélations croisées des bruits ambiants mesurés par les capteurs, tel que cela a été rigoureusement établi par des travaux innovants à ISTERRE [8]. L'objectif principal est de s'affranchir de la diffusion multiple et de repousser la profondeur limite des techniques d'imagerie existantes. De plus, l'étude de la contribution de diffusion multiple peut aussi être utile à des fins de caractérisation. Des paramètres de transport tels que les libres parcours moyens de diffusion ou de transport peuvent fournir des informations capitales sur la concentration ou la taille des inhomogénéités. References : [1] C. Prada and M. Fink, Wave Motion 20, 151 (1994). [2] C. Prada, S. Manneville, D. Spoliansky, and M. Fink, J. Acoust. Soc. Am. 99, 2067 (1996). [3] J-L. Robert, PhD dissertation on “Evaluation of Green's functions in complex media by decomposition of the Time Reversal Operator: Application to Medical Imaging and aberration correction “, Université Paris VII, 2008. [4] G. Montaldo, M. Tanter, and M. Fink, Phys. Rev. Lett. 106, 054301, 2011. [5] A. Aubry, A. Derode, Phys. Rev. Lett. 102, 084301, 2009. [6] A. Aubry, A. Derode, J. Appl. Phys. 106, 044903, 2009. [7] S. Shahjahan, A. Aubry, F. Rupin, B. Chassignole, and A. Derode, Appl. Phys. Lett. 104, 234105, 2014. [8] Campillo, M., P. Roux, and N.M. Shapiro (2011), Using seismic noise to image and to monitor the Solid Earth, in Encyclopedia of Solid Earth Geophysics, Gupta, Harsh K. (Ed.), 1230-1235, Springer, 2011
The project aims at extending to geophysical and seismic imaging a matrix approach of wave propagation in heterogeneous media. The method aims at separating single-scattering from multiple-scatterings contribution in a data set, thus allowing us to improve imaging in heterogeneous media, as if we could see through thick fog. The idea was successfully developed in the ultrasound imaging context at the Langevin Institute, restricted so far to 1-D linear arrays of ultrasonic sources/receivers. It consists in exploiting the set of inter-element impulse responses associated to an array of sensors. This response matrix contains all the information available on the scattering medium under investigation. A set of matrix operations can then be applied whether it be for detection, imaging, characterization or monitoring purposes. The method was tested on actual coarse-grain materials like steel, and was found to improve defect detection very significantly. The adaptability of the method in geophysics (with 2-D unevenly distributed passive sensors as opposed to controllable and periodic 1-D ultrasonic arrays) is to be investigated in this project. On the one hand, iterative time reversal and related techniques can be taken advantage of to overcome aberration effects associated to long-scale inhomogeneities of the superficial layer, leading to a better constrast and resolution of the subsoil image [1-4]. On the other hand, a more sophisticated random matrix approach can be used in areas where short-scale inhomogeneities are strongly scattering and/or concentrated [5-7]. In this regime, conventional imaging methods suffer from the multiple scattering of waves that results in a speckle image, with no direct connection with the medium's reflectivity. In the case of purely passive sensors such as classical geophones, the response matrix will be obtained passively from cross-correlation of ambient noise, as was thoroughly established by pioneer works at ISTERRE [8]. The main objective is to get rid of multiple scattering and push back the imaging-depth limit of existing imaging techniques. In addition, the study of the multiple scattering contribution can also be useful for characterization purposes. Transport parameters such as the scattering or transport mean free paths can actually yield key information about the concentration and the size of the inhomogeneities. References: [1] C. Prada and M. Fink, Wave Motion 20, 151 (1994). [2] C. Prada, S. Manneville, D. Spoliansky, and M. Fink, J. Acoust. Soc. Am. 99, 2067 (1996). [3] J-L. Robert, PhD dissertation on “Evaluation of Green's functions in complex media by decomposition of the Time Reversal Operator: Application to Medical Imaging and aberration correction “, Université Paris VII, 2008. [4] G. Montaldo, M. Tanter, and M. Fink, Phys. Rev. Lett. 106, 054301, 2011. [5] A. Aubry, A. Derode, Phys. Rev. Lett. 102, 084301, 2009. [6] A. Aubry, A. Derode, J. Appl. Phys. 106, 044903, 2009. [7] S. Shahjahan, A. Aubry, F. Rupin, B. Chassignole, and A. Derode, Appl. Phys. Lett. 104, 234105, 2014. [8] Campillo, M., P. Roux, and N.M. Shapiro (2011), Using seismic noise to image and to monitor the Solid Earth, in Encyclopedia of Solid Earth Geophysics, Gupta, Harsh K. (Ed.), 1230-1235, Springer, 2011

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Yang, Yougu. "Propagation des ondes acoustiques dans les milieux granulaires confinés." Phd thesis, Université Paris-Est, 2013. http://tel.archives-ouvertes.fr/tel-01037954.

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Ce travail de thèse est l'étude expérimentale de la propagation des ondes acoustiques dans un milieu granulaire sec et confiné. Ces ondes permettent de sonder de manière non invasive les propriétés viscoélastiques et la structure hétérogène du milieu, mais peuvent aussi être utilisées comme perturbation contrôlée pour étudier le réarrangement des réseaux des forces. Dans une première partie, nous nous intéressons à la propagation des ondes cohérentes dans les empilements des billes de verre et aussi dans ceux des grains irréguliers (sable). En régime linéaire, un très bon accord est retrouvé entre les vitesses d'onde de compression mesurées et celles prédites par la théorie des milieux effectifs, ce qui permet d'accéder au nombre de coordinance Z. En régime non linéaire, nous observons à la fois un softening et un hardening de la vitesse d'onde de compression à cause du changement de Z induit pat la forte vibration. La deuxième partie étudie la propagation des ondes multiplement diffusées. Nous montrons que le transport de ces ondes dans un milieu granulaire peut être décrit par le modèle de diffusion. Le coefficient de diffusion et l'absorption inélastique sont déterminés en fonction de la contrainte de confinement et de la fréquence d'onde incidente. Le libre parcours moyen versus la longueur d'onde relèvent deux régimes distincts du transport des ondes diffusées à basse et à haute fréquence. De plus, une décroissance non exponentielle est observée sur le profile d'intensité des ondes diffusées à temps long lorsque la fréquence de l'onde incidente devient importante. Une étude paramétrique basée sur la renormalisation du coefficient de diffusion est effectuée pour comprendre l'origine de ce transport diffusif anomal. Enfin, nous développons un dispositif (MRT) pour effectuer l'opération du retournement temporel dans un milieu granulaire. En régime linéaire, la recompression temporelle et la refocalisation spatiale sont vérifiées. Cependant, en régime non linéaire, nous observons que le processus du retournement temporel est brisé par l'interaction irréversible onde-matière, dû au changement ou réarrangement des réseaux des forces

4

Stephens, Edmund. "Time reversal violation in atoms." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334916.

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Lopez-Castellanos, Victor. "Ultrawideband Time Domain Radar for Time Reversal Applications." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1301040987.

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Naguleswaran, Siva. "Time reversal symmetry in nonlinear optics." Thesis, University of Canterbury. Physics, 1998. http://hdl.handle.net/10092/8166.

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Results following from time reversal symmetry are developed for those nonlinear optical processes where a statistical average is required. This extends results found in Rayleigh (and Raman) scattering to nonlinear optical processes of arbitrary order, and generalises those few analyses specific to nonlinear optics. For example, Onsager relations for self-conjugate nonlinear optical processes (when input and output photons form degenerate pairs) are derived, and associated reversality relations generalised. In the nonresonant limit magnetic dipole but not electric quadrupole terms in coherent processes are suppressed. For this and other selection rules a careful treatment is required to obtain gauge invariant conclusions since the relevant electronic operators in multipolar and Coulomb gauges have differing time reversal signatures. For general processes purely electric dipole contributions to natural optical activity are possible when intermediate resonances are present; strong resonances are not required for the domination of this contribution over the traditional contribution. Time reversal symmetry may be used to show the prescription for assigning signs to phenomenological damping factors that is usually associated with the optical susceptibility formalism is incorrect. An experimental test based on electrooptic rotation in fluid media is proposed which may distinguish between this incorrect prescription and the correct prescription. The role time reversal symmetry plays in restricting the number of parameters in Judd-Ofelt theory is elucidated.

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O'Donoughue, Nicholas A. "Stochastic Time Reversal for Radar Detection." Research Showcase @ CMU, 2011. http://repository.cmu.edu/dissertations/178.

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Time Reversal is an adaptive waveform transmission technique particularly suited to dispersive or non-homogenous media that focuses energy on a desired point in space. Early work concentrated on optical and acoustic/ultrasonic applications, followed more recently by applications in the electromagnetic domain. Time Reversal has been used for single- and multi-antenna detection, imaging, communications, non-destructive testing, and beam steering, among other applications. This thesis develops Time Reversal detection algorithms for randomly varying targets embedded in randomly varying clutter. We model the target and clutter as independent complex Gaussian random variables and consider both single-antenna and multi-antenna detection scenarios. We derive the optimal Time-Reversal Likelihood Ratio Test (TR-LRT) for the single-antenna case, as well as a sub-optimal Time Reversal-Linear Quadratic (TR-LQ) detector that allows for a priori threshold and performance computation. These detectors are compared against a benchmark Weighted Energy Detector (WED). For the multi-antenna scenario, we present the Time Reversal MIMO (TR-MIMO) detector and compare its performance to a conventional Spatial MIMO (S-MIMO) radar. We show that, for both scenarios, the relative performance of Time Reversal detection methods depends on the coherence of the channel between the forward and TR transmission stages. We discuss the potential for detection gains with Time Reversal in single-antenna and multi-antenna systems. We discuss lower and upper bounds on gain and show that Time Reversal provides a useful and computationally simple approximation to the optimal transmit signal. To compute the optimal hypothesis test for a Blind TR detection system, we derive a new statistical distribution, the Complex Double Gaussian distribution, which characterizes the complex product Z = XY of independent complex Gaussian random variables X and Y . We also apply this new probability distribution to analyze the performance of M-ary Phase Shift Keying (MPSK) communication systems, showing its applicability well beyond the realm of Time Reversal problems.

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Edelmann, Geoffrey F. "Underwater acoustic communications using time reversal /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3099539.

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Johnsson, Mattias Torbjörn. "Time reversal symmetry and the geometric phase." Thesis, University of Canterbury. Physics, 1998. http://hdl.handle.net/10092/8171.

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This thesis examines the quantum-mechanical geometric phase with a view toward time reversal symmetry considerations. The idea of time reversal in quantum mechanics is investigated, disagreements and inconsistencies in the literature are examined, and the action of the time reversal operator is extended to time-dependent Hamiltonians. With this background, and using a definition of time reversal symmetry based on the evolution operator, I demonstrate that the existence of a non-zero geometric phase can in all cases be attributed to a breakdown of time reversal symmetry in some form. This result holds for both adiabatic and nonadiabatic evolutions, and for arbitrary dimensional parameter spaces. I explore the role of the geometric phase in a two-level Kramers system described by a parameter-dependent Hamiltonian such that the two levels can become degenerate for some value of the parameters, and discuss, from a mathematical point of view, the monopole geometric potential that results. I then extend this analysis by considering a pair of Kramers doublets, each doublet degenerate due to time reversal symmetry, where the parameters can be chosen so that each of the pair of doublets becomes degenerate with the other. I find the explicit functional forms for the two resulting nonabelian geometric gauge potentials and show that they can be identified exactly with the only two gauge-inequivalent SU(2) monopole potentials of Yang. Furthermore, following a conformal transformation these potentials can be mapped to those of the SU(2) instanton/anti-instanton pair. Finally I examine the relevance of the geometric phase to the molecular physics of time-odd systems. Time-odd coupling in molecular physics is a much under-studied area, with many potentially interesting results. Specifically I study time-odd coupling in Jahn-Teller systems under the Born-Oppenheimer approximation, where the electronic position states are coupled to the lattice momentum rather than the usual time-even lattice position. As an example I solve the E ⊗ (b₁ ⊕ b₂ ⊕ a₂) Jahn-Teller system exactly, showing that once again monopole-like geometric potentials arise, and comment on how this affects the angular momentum of the lattice subsystem.

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Liddy, David W. Holmes John F. "Acoustic room de-reverberation using time-reversal acoustics /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA374579.

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Thesis (M.S. in Applied Physics) Naval Postgraduate School, September 1999.
"September 1999". Thesis advisor(s):, Andrés Larraza, Bruce C. Denardo. Includes bibliographical references (p. 49). Also available online.

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AHMAD, FAHEEM, and PRAMOD KAKKERLA. "FOCUSING OF UWB RADAR SIGNALS USING TIME REVERSAL." Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-15500.

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Focusing techniques and detection of targets is usually associated to defense and military use. However in recent past things have moved ahead. Now target detection using UWB radars is being done in many industries and corporations. Radarbolaget AB is one of them; one of their projects uses UWB radars to detect steel strips inside a furnace. This research solves a potential problem of detecting middle steel strip out of total three strip edges which can be seen by radar placed on the front. For better understanding of the reader, existing system and introductory UWB radar principles are discussed. As there can be many solutions to focusing of targets here (steel strip edge detection). Available focusing techniques have been discussed in detail along with the possible physical and simulation setups. Later in the document, detection methods have been proposed. UWB time reversed signal detection is a fairly new method and a very limited research has been done so far. PRBS sequence has been focused on in detection mechanism. Results section show that the pulse of the PRBS works better and produces more promising results rather than a repetitive signal. Time reversal methods for locating the target have been used to find the approximate location of the target. Manual distance calculations from target to the transmitter and receiver have been done. Comparison of actual distance from target to the transmitter is compared with simulation results. Different model simulation setups and their results have proved that using UWB Time reversed signals; a still or moving target can be detected with centimeter window precision.

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Liddy, David W., and John F. Holmes. "Acoustic room de-reverberation using time-reversal acoustics." Thesis, Monterey, California: Naval Postgraduate School, 1999. http://hdl.handle.net/10945/13698.

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This thesis probes the performance of one-channel time-reversal acoustics in a chamber in terms of the geometry of the cavity. In particular, a rectangular chamber is compared to an enclosure that has a stadium shape. The mode structure in the rectangular cavity is highly symmetric, while it is highly irregular in the stadium-shaped cavity. Time- reversal acoustic techniques produce an improved focus in the latter. The focusing quality is determined as a function of frequency, time-reversal window size, and spatial extent. A scheme for encrypted acoustic communication, both in air and underwater, that uses multiple broadband signals with identical bandwidth, Hanning window source spectra, and center frequencies separated by half the bandwidth, allowing for null detection between adjacent signals, is successfully investigated.

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Raghukumar, Kaustubha. "Pressure sensitivity kernels applied to time-reversal acoustics." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3359854.

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Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed July 23, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

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Hockings, William Hill. "Time Reversal Violation in Nuclear Effective Field Theory." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/196076.

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The lack of invariance with respect to time reversal (T) of the weak interactions has long been known. However, T violation has yet to be observed from flavor-diagonal sources, where the primary quantities of interest are electric dipole moments (EDMs). Weak T violation gives EDMs that are far too small, but strong T violation via flavor-diagonal sources could give EDMs strong enough to be detected in the near future. It is thus important to understand precisely how various quark-level sources of T violation manifest themselves in hadronic physics.A useful technique for dealing with low-energy phenomena involving nucleons, nuclei, and various mesons, is effective field theory (EFT). The formalism and methodology of EFT are presented, followed by an introduction to the construction of chiral Lagrangians.A motivation for the study of T violation beyond the weak interactions is then given, with brief introductions to the most important sources of T violation.The QCD theta term is looked at using two differentapproaches. First, enforcing vacuum stability at quark level, a series of T-violating interactions ensue. Second, enforcing vacuum stability at hadronic level via field redefinitions, spurious interactions are demonstrated to be avoidable. Both approaches involve a constraining relationship between theta-term T violation and up-down quark-mass-difference isospin violation. The quark chromo-EDMs are shown to be identical to the theta term in their chiral symmetry properties. The quark EDMs and Weinberg operator,conversely, are shown to generate new interactions in addition to those generated by the theta term, differing nucleon EDM contributions in particular.The electric dipole form factor (EDFF) of the nucleon, with a theta term source, is calculated in both leading and subleading orders in chiral perturbation theory, with the momentum dependence at both orders given entirely by contributions from the pion cloud. Theleading result is purely isovector, while an isoscalar result appears in subleading order. The isoscalar EDM is used as a lower-bound estimate of the deuteron EDM. The momentum dependence of the EDFF for small momentum transfer is related to the electromagnetic nucleonSchiff moment, which is computed to subleading order.

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Vallon, Henri. "Focusing high-power electromagnetic waves using time-reversal." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC006/document.

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L'objectif de la thèse a été de mettre en place dans un premier temps des modèles analytiques et statistiques permettant d'évaluer les performances d'un système à retournement temporel de fortes-puissances puis de les vérifier grâce à des mesures.Des campagnes de mesures ont alors permis de vérifier les modèles. Des simulations numériques ont aussi montrées les possibilités offertes par un tel système.En parallèle, des travaux sur l'impact des antennes dans une chambre réverbérantes ont été menés afin d'évaluer les performances d'un système ayant plusieurs sorties.Les résultats de thèses ont permis l'élaboration de nouvelles métriques des performances du système.Le développement d'un prototype a nécessité la conception et la réalisation de chacune des branches du système complet.Les premières campagnes de mesures ont permis la validation complète des modèles
A main aspect of this work has been to develop analytical and statistical models of the power efficiency of a time-reversal amplification system (TRAS).It is also important to evaluate the efficiency of a reverberation chamber. This allows quantifying the power received by one or more antenna when the reverberation chamber is excited. This factor is important when considering construction of the most efficient chamber for time-reversal amplification.Measurements assessing the loading effect of antennas in reverberation chambers when the field can be considered diffused were also undertaken. The study focuses on the evaluation of the varying quality factor when adding loaded antennas in the chamber.Another focus of this work is to evaluate the ratios between signals during calibration and focusing phase. An important aspect of the studies presented in this work thus concerns evaluation of the maximum value of the impulse response in a complex propagation system.We also present the power gain of time-reversal techniques and its statistical advantages compared to a classic use of a reverberation chamber.The development of a prototype required the design and implementation of each of the branches of the complete systems.The first measurement campaigns allowed the complete validation of the models

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Rane, Swati. "Diffusion tensor imaging at long diffusion time." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29708.

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Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Hu, Xiaoping; Committee Member: Brummer, Marijn; Committee Member: Duong, Tim; Committee Member: Keilholz, Shella; Committee Member: Schumacher, Eric. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Wang, Daniel Y. "Spatiotemporal processing and time-reversal for underwater acoustic communications." Thesis, Massachusetts Institute of Technology, 2005. http://handle.dtic.mil/100.2/ADA455115.

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Norville, Pelham D. "Time-Reversal Techniques in Seismic Detection of Buried Objects." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14475.

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An investigation is presented of the behavior of time-reversal focusing in soils. Initial numerical models demonstrate time-reversal focusing to be effective in elastic media, including when a large number of scattering objects were present in the medium. When scattering objects are present, time-reversal focusing demonstrates superior focusing ability when compared to other excitation methods such as uniform excitation or time-delay focusing. Multiple experimental investigations of experimental time-reversal focusing performed in sand evaluate time-reversal focusing effectiveness when multiple near-surface scattering objects are present in the medium. Experimental results demonstrate that time-reversal focusing is effective in the experimental context as well as the numerical models. Further experiments examine time-reversal focusing in more extreme cases where the entire ballistic wave is blocked, and the only energy reaching the focus point is reflected from scattering objects in the medium. A comparison to other focusing methods demonstrates that under these conditions, most focusing attempts with traditional methods will fail completely while time-reversal focusing does not. Additional configurations of time-reversal focusing examine its effectiveness when scattering is caused by an asymmetrical surface layers. The impact of an asymmetrical or non-uniform excitation array is also examined for time-reversal focusing in the presence of scattering objects. An investigation of the effects of scattering object geometry on focusing resolution in time-reversal focusing is also presented. Scattering object field density is found to have a strong, but diminishing effect on focusing resolution as the scattering object field density increased. Loss of surface wave energy available for focusing due to mode-conversion is found to be correlated with the density of the scattering object field. The impact of the weak non-linear nature of the soil on time-reversal focusing is examined through a study of time-reversal focusing behavior for a variety of amplitudes that generate different levels of non-linearity in the soil. This study of nonlinearity is coupled with a study of the impact of noise on time-reversal focusing. It appears that both non-linearity and noise have an impact on time-reversal focusing effectiveness. Further, the loss from these mechanisms seems to be interrelated. Noise seems to enhance non-linear loss in the soil.

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Glotov, Petr. "Time Reversal of Electromagnetic Waves in Randomly Layered Media." NCSU, 2006. http://www.lib.ncsu.edu/theses/available/etd-02272006-183752/.

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Time reversal is a general technique in wave propagation in inhomogeneous media when a signal is recorded at points of a device called time reversal mirror, gets time reversed and radiated back in the medium. The resulting field has a property of refocusing. Time reversal in acoustics has been extensively studied both experimentally and theoretically. In this thesis we consider the problem of time reversal of electromagnetic waves in inhomogeneous layered media. We use Markov process model for the medium parameters which allows us to exploit diffusion approximation theorem. We show that the field generated by the time reversal mirror focuses at a point of initial source inside of the medium. The size of the focusing spot is of the kind that it is smaller than the one that would be obtained if the medium were homogeneous meaning that the super resolution phenomenon is observed.

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Hofer, Stephen. "Time reversal symmetry breaking in 4f-doped Topological Insulators." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/theses/2400.

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Time-Reversal Symmetry (TRS) is a hallmark of Topological Insulator (TI) systems. TRS in conjuction with the strong Spin-Orbit Coupling (SOC) present in Bismuth Selenide is responsible for the uniquely robust surface states shown in this material. Breaking TRS in these systems in order to achieve gapped surface states requires the presence of a magnetic field throughout the material. We achieve this effect by doping the system with 4f elements whereby the magnetic field is provided by the local magnetic moments of the dopants manifesting ferromagnetic behavior. Through this spontaneous gap opening in the surface states in is expected that the Quantum Anomalous Hall Effect is present in the system. This thesis provides experimental evidence of good candidate materials for measuring the Quantum Anomalous Hall Effect. By combining X-ray Diffraction to ensure good crystal growth, Angle-resolved Photoemission Spectroscopy probe to the evolution of the bandstructure as an effect of doping and Density Functional Theory to support the experimental data it is shown in this work that Samarium doped Bismuth Selenide is a prime candidate for displaying the Quantum Anomalous Hall Effect.

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Brevis, Vergara Rodrigo Ignacio. "Source time reversal methods for acoustic and elastic waves." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/152342.

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Tesis para optar al grado de Doctor en Ciencias de la Ingeniería, Mención Modelación Matemática
Esta tesis estudia la detección y reconstrucción del término espacial de una fuente de variables separables en problemas de onda acústica y elástica. Para esto, estudiamos el método time-reversal mirror, el cual explota una invariancia intrínseca de la física a nivel microscópico que se observa también a nivel macroscópico en las ecuaciones de ondas. Esto significa que es posible recuperar la condición inicial de una ecuación de ondas homogénea revirtiendo la onda a través del tiempo. Para localizar y reconstruir el término espacial de la fuente, desarrollamos un método llamado source time reversal. La aplicación subyacente aquí es la detección de fuentes sísmicas en la minería. Es sabido que la actividad minera induce temblores dentro de las minas [50]. Esto se vuelve bastante peligroso si no se toman las precauciones adecuadas. Conocer sobre el origen de las actividades sísmicas puede ser utilizado para reducir el peligro de derrumbes y mejorar la seguridad dentro de las minas. Este trabajo se divide en tres capítulos; cada uno de ellos constituye un documento autocontenido para ser presentado como artículo. El primer capítulo aborda el problema de reconstrucción de fuente para ondas acústicas. Para esto introducimos el método source time reversal, la cual reconstruye el término espacial de una fuente de la forma f(x)g(t), donde f(x) entrega la forma y g(t) representa la distribución en tiempo de la fuente. Además, presentamos una estimación del error de la reconstrucción para el caso cuando f es una función de cuadrado integrable. Aquí, proponemos un método de regularización para implementar la reconstrucción de la fuente numéricamente. Adicionalmente, analizamos las principales características y limitaciones del método propuesto cuando se aplica a ondas acústicas. El capítulo dos estudia el problema de reconstrucción de fuente para ondas elásticas. Extendemos el método source time reversal para problemas elásticos. Además, introducimos un nuevo método de regularización para implementar la reconstrucción del término espacial de la fuente numéricamente para grandes volúmenes de datos. El nuevo método de regularización elimina las altas frecuencias presentes en la señal procesada, lo que permite utilizar mallas numéricas más gruesas y reduce el costo computacional. Finalmente, este capítulo presenta diversos experimentos numéricos para probar que el método es válido en el caso elástico. El último capítulo analiza un problema de reconstrucción de fuente diferente. Aquí consideramos una fuente compuesta por una suma finita de funciones de variable separable, donde cada término temporal de la fuente es una función delta de Dirac actuando a un tiempo diferente. Basado en una propiedad de tiempo reverso, la fuente puede ser localizada observando el desplazamiento y la velocidad de desplazamiento en el problema reverso [31]. Nosotros extendemos esta idea a sistemas de ondas elásticas. Adicionalmente, proponemos un algoritmo para la implementación numérica.
CONICYT, CMM - Conicyt PIA AFB170001 y el proyecto GEAGAM

22

Oborn, Jeremy Michael. "Time Reversed Smoke Simulation." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/7218.

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Physics-based fluid simulation often produces unpredictable behavior that is difficult for artists to control. We present a new method for art directing smoke animation using time reversed simulation. Given a final fluid configuration, our method steps backward in time generating a sequence that, when played forward, is visually similar to traditional forward simulations. This will give artists better control by allowing them to start from any timestep of the simulation. We address a number of challenges associated with time reversal including generating a believable final configuration and reversing entropy.

23

Schlegel, Marc. "Time reversal odd effects in semi-inclusive deep inelastic scattering." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981070086.

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Ravaine, Boris. "Violation of parity and time-reversal in atoms and molecules." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3258941.

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Root, Joseph Andrew. "Capabilities of an underwater acoustic volumetric array using time-reversal." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/18944.

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Mellars, Ehren Axel. "Time-reversal symmetry and topology in one-dimensional Josephson junctions." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8739/.

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We explore the roles of topology and time-reversal symmetry in one-dimensional superconducting systems. Specifically, we examine junctions involving time-reversal-invariant topological superconductors, which are characterised by the emergence of zero-energy Majorana- Kramers pairs at their boundaries. For Josephson junctions composed of these superconductors, we obtain, through a scattering matrix technique valid in a regime where the junction length is much shorter than the superconducting coherence length, exact analytical and numerical results for the Josephson current in terms of a small number of independently measurable junction parameters. The current is found to have a number of prominent and robust features which indicate the underlying symmetries and the nontrivial topology inherent in these systems. The most remarkable of these features occurs in the form of switches in the Josephson current, where the sign of the current reverses as a consequence of crossings between energy levels in the subgap spectrum. By utilising a quantum master equation approach, we establish general conditions under which these switches manifest in relation to a phenomenological relaxation rate and a voltage applied across the junction. Our findings enable quantitative predictions for such junctions, potentially assisting in experimental directions regarding the detection of Majorana- Kramers pairs in mesoscopic Josephson systems.

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He, Jiaze. "Time-reversal Based Array Damage Imaging in Structural Health Monitoring." Thesis, North Carolina State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10110540.

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Composite materials are receiving increasing attention and broadly used in aerospace industry due to their superior strength-to-weight ratio, corrosion resistance and design flexibility. The need for rapid nondestructive evaluation (NDE) techniques for composites is growing rapidly as the complexity and dimensions of the structures are increasing significantly. Structural health monitoring (SHM) has been attracting much attention as a means of providing in-service and in-situ monitoring of various critical structures. Due to their capability of long-range and through-the-thickness interrogation of the structures for small defects, guided waves have been studied extensively in damage detection for plate-like structures.

However, a few challenges exist when Lamb wave-based SHM/NDE techniques are employed. For example, the dispersion effect decreases the accuracy of many damage imaging algorithms; damage severity quantification is always a difficult problem. To provide possible solutions to above challenges, two damage imaging algorithms were developed and utilized for Lamb-wave based damage imaging.

The first algorithm is reverse-time migration (RTM), which was first used in geophysics to provide proper solutions to complex wave phenomena. The traditional imaging condition utilized in SHM is called excitation-time imaging condition, which used ray tracing and group velocity corresponding to the center frequency of the input signal. Due to the dispersion effect, the time-of-flight (ToF) estimation cannot always be accurate, especially for the situations that the Lamb waves propagate for a long distance. In this thesis, new imaging conditions are proposed to form enhanced zero-lag cross-correlation reverse-time migration (E-CCRTM) techniques. The proposed damage imaging technique takes into account the amplitude, phase, and all the frequency content of the Lamb waves propagating in the plate; thus, the severity of multiple sites of damage can be non-biasedly imaged regardless of the damage locations in comparison with using existing imaging conditions. The other imaging algorithm is called ‘DORT-MUSIC’. A Lamb wave-based, subwavelength imaging algorithm is developed for damage imaging in large-scale, plate-like structures based on a decomposition of the time-reversal operator (DORT) method combined with the multiple signal classification (MUSIC) algorithm in the space-frequency domain. The physics of wave propagation, reflection, and scattering that underlies the response matrix in the DORT method is mathematically formulated in the context of guided waves. Singular value decomposition (SVD) is then employed to decompose the experimentally measured response matrix into three matrices, detailing the incident wave propagation from the linear actuator array, reflection from the damage, and followed by scattering waves toward the linear sensing array for each small damage. The SVD and MUSIC-based imaging condition enable quantifying the damage severity by a ‘reflectivity’ parameter and super-resolution imaging.

The two algorithms were also integrated with a hybrid system mainly comprised piezoelectric actuators mounted onto the structure and a laser Doppler vibrometer (LDV) for reception. The flexibility of the proposed system was used for inspection of various plate-like structures. The experimental results show that the 2-D E-CCRTM has robust performance to image and quantify multiple sites of damage in large area of the plate using a single PZT actuator with a nearby areal scan using LDV, and the DORT-MUSIC (TR-MUSIC) imaging technique can provide rapid, highly accurate imaging results as well as damage quantification with unknown material properties.

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Mumm, Hans Pieter. "A test of time reversal violation in neutron beta decay /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9802.

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Denison, Michael Hunter. "Image Source Modeling of Time Reversal for Room Acoustics Applications." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7449.

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Time Reversal (TR) is a technique that may be used to focus an acoustic signal at a particular point in space. While many variables contribute to the quality of TR focusing of sound in a particular room, the most important have been shown to be the number of sound sources, signal bandwidth and absorption properties of the medium [Ribay et al., J. Acoust. Soc. Am. 117(5), 2866-2872 (2005)]. However, the effect of room size on TR focusing has not been explored. Using the image source method algorithm proposed by Allen and Berkley [J. Allen and D. A. Berkley, J. Acoust. Soc. Am. 65(4), 943-950 (1979)], TR focusing was simulated in a variety of rooms with different absorption and volume properties. Experiments are also conducted in a couple rooms to verify the simulations. The maximum focal amplitude, the temporal focus quality, and the spatial focus clarity are defined and calculated for each simulation. The results are used to determine the effects of absorption and room volume on TR. Less absorption increases the amplitude of the focusing and spatial clarity while decreasing temporal quality. Dissimilarly, larger volumes decrease focal amplitude and spatial clarity while increasing temporal quality. This thesis also explores the placement of individual transducers within a room. It also compares the layout of several source transducers used for a reciprocal time reversal process. Maximum focal amplitude and spatial clarity are found to increase when the focus location is dual coplanar to the source location while temporal quality is found to decrease in comparison to the case when source and focal location share only one plane. Maximum focal amplitude is found to be at a minimum when the focus location is at the critical distance and increases closer and farther away from the source, while temporal quality steadily decreases and spatial clarity steadily increases farther from the source. The maximum focal amplitude and the temporal quality are not greatly affected by the type of array layout, but a circular array is ideal for maximizing spatial clarity.

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Phung, Huong Thi Hoai. "Imaging of seismic and hum sources by time reversal method." Paris 7, 2010. http://www.theses.fr/2010PA077169.

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Etudier et comprendre les tremblements de terre est le but de beaucoup de chercheurs. De nos jours, avec le développement de la FDSN (Fédération of Digital Seismometers Networks), les sismogrammes contenant à la fois de l'information sur la source sismique et sur l'effet de propagation (structure), sont enregistrés en permanence. On peut facilement localiser un tremblement de terre par les méthodes classiques en utilisant les sismogrammes. Néanmoins, pour avoir un résultat plus précis sur la source sismique (tenseur des moments, fonction temporelle de la source), on a besoin de résoudre le problème inverse. La méthode du Renversement Temporel a permis la mise au point de nombreuses applications en contrôle non destructif, diagnostic médical et domotique dans le domaine des ondes acoustiques. Elle permet aussi de localiser les tremblements de terre et les tremblements glaciaires dans le domaine des ondes sismiques. Dans ce travail de thèse, on présente des applications du principe de retournement temporel aux sources sismiques virtuelles. Ensuite, on montre la localisation en temps et en espace, ainsi que la reconstruction du mécanisme au foyer du tremblement de terre du Haiti le 12 janvier 2010 en appliquant la méthode du renversement temporel aux sismogrammes complets et "one-bit". Le niveau d'excitation du bourdonnement (seismic hum) de la Terre est bien observé. Cependant, son origine n'est pas encore claire. L'idée est d'essayer de localiser sa source. On suppose que sa source est peut-être localisée en espace mais pas en temps. Nous concluons que la source du "hum" n'est pas locale mais au moins régionale
Studies of earthquake sources is one of purpose of many scientists. Today, with the development of FDSN (Federation of Digital Seismometers Networks), the seismograms are continuously recorded. They provide information on seismic source and on propagation (related to earth structure) effect. We can easily locate an earthquake by applying the classical methods on seismograms. However, to have a more accurate result on seismic source (seismic moment tensor, source time function), we need to solve an inverse problem. Time-reversal (hereafter referred to as TR) method has been successfully applied for acoustic waves in many fields such as imaging, underwater acoustics, non destructive testing, and for seismic waves in seismic earthquake location, and glacial earthquake imaging. In this thesis , we present the application of TR method to synthetic seismograms due to virtual earthquakes. We show the focusing of January 12th 2010 Haiti earthquake in space and time and the reconstructed focal mechanism by applying the TR method to complete and one-bit seismograms. The level of oscillation of seismic "hum" is well observed. However, the spatial and temporal origin of "hum" is still uncertain, and the idea is to use the advantage focusing source of the TR method to locate it. We assume that this source may be located in space, not in time. We show that hum source is not local but might be distributed in a very large region

31

Ilg, Matthias. "An investigation of spatially bounded, time independent quantum systems." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/28046.

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32

Dumont, Elisabeth M. M. "Unconventional vortex dynamics in superconducting states with broken time reversal symmetry /." [S.l.] : [s.n.], 2000. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13938.

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Graziani, Filippo. "Modulazioni "Time-reversal" con codifiche a bassa profondità per comunicazioni ultrasoniche." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/22625/.

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Nel presente elaborato viene affrontata la tematica relativa alla comunicazione mediante onde ultrasoniche guidate. Nel dettaglio, l'attenzione viene rivolta alla propagazione delle onde di Lamb, le quali sono in grado di propagarsi su strutture molto sottili con bassa attenuazione, dando luogo alla possibilità di realizzare questo schema di comunicazione. La tecnica "time-reversal" sfrutta le proprietà di queste onde, ovvero la focalizzazione spaziale e temporale, per portare dei picchi accentuati al ricevitore in corrispondenza dell'informazione utile. Questa tecnica, accoppiata con la Pulse Position Modulation, consente la realizzazione di sistemi di comunicazione con più nodi sensori contemporaneamente attivi in trasmissione e uno o più nodi sensori in ricezione. Viene inoltre considerata la possibilità di sfruttare algoritmi di quantizzazione, intesa come capacità di generazione del segnale in uscita su un numero limitato di livelli, al fine di rendere il sistema di comunicazione semplice ed economico. Le prestazioni del sistema sono verificate mediante simulazioni, realizzate in ambiente di sviluppo Matlab.

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Trung, Kien-Nguyen [Verfasser]. "Time reversal transmission approach for ultra wideband communications / Trung Kien Nguyen." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2011. http://d-nb.info/1017987165/34.

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Ogawa, Kazuhisa. "Optical Interferometric Measurements Inspired by Time-Reversal Symmetry of Quantum Mechanics." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/202718.

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36

Twengström, Mikael. "Time-reversal symmetry breaking and mixed coherence lengths in multicomponent superconductors." Thesis, KTH, Fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-138163.

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Reis, Itamar. "Axion term in topological insulators with broken time reversal and parity." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46360.

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The main subject of this work is the axion term in the effective electromagnetic action of topological insulators, which is responsible for the special electromagnetic properties of these materials. The axion term is characterized by a parameter θ, which can only take the values of 0, for regular insulators, or π, for topological insulators, respecting at least one of the time reversal or parity symmetries. A non zero axion term leads to a variety of measurable phenomena, generally referred to as the magneto-electric effects. We focus our interest on the value the parameter θ takes for a topological insulator, when both time reversal and parity are broken. In this case θ no longer must be quantized to 0 or π. We use a lattice model for a topological insulator, and introduce a symmetry breaking term in the Hamiltonian. We numerically find the value of θ in this case using calculations of the magnitude of various magneto-electric effects. The results are compared to the theoretical prediction. We find that θ is no longer quantized when a specific symmetry breaking term is introduced.

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Nguyen, Linh V., and Leonid A. Kunyansky. "A Dissipative Time Reversal Technique for Photoacoustic Tomography in a Cavity." SIAM PUBLICATIONS, 2016. http://hdl.handle.net/10150/622000.

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We consider the inverse source problem arising in thermo-and photoacoustic tomography. It consists in reconstructing the initial pressure from the boundary measurements of the acoustic wave. Our goal is to extend versatile time reversal techniques to the case when the boundary of the domain is perfectly reflecting, effectively turning the domain into a reverberant cavity. Standard time reversal works only if the solution of the direct problem decays in time, which does not happen in the setup we consider. We thus propose a novel time reversal technique with a nonstandard boundary condition. The error induced by this time reversal technique satisfies the wave equation with a dissipative boundary condition and, therefore, decays in time. For larger measurement times, this method yields a close approximation; for smaller times, the first approximation can be iteratively refined, resulting in a convergent Neumann series for the approximation.

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Odedo, Victor. "High resolution time reversal (TR) imaging based on spatio-temporal windows." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/high-resolution-time-reversal-tr-imaging-based-on-spatiotemporal-windows(f0589f73-901f-4de2-9886-7045b7f6cfd4).html.

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Through-the-wall Imaging (TWI) is crucial for various applications such as law enforcement, rescue missions and defense. TWI methods aim to provide detailed information of spaces that cannot be seen directly. Current state-of-the-art TWI systems utilise ultra-wideband (UWB) signals to simultaneously achieve wall penetration and high resolution. These TWI systems transmit signals and mathematically back-project the reflected signals received to image the scenario of interest. However, these systems are diffraction-limited and encounter problems due to multipath signals in the presence of multiple scatterers. Time reversal (TR) methods have become popular for remote sensing because they can take advantage of multipath signals to achieve superresolution (resolution that beats the diffraction limit). The Decomposition Of the Time-Reversal Operator (DORT in its French acronym) and MUltiple SIgnal Classification (MUSIC) methods are both TR techniques which involve taking the Singular Value Decomposition (SVD) of the Multistatic Data Matrix (MDM) which contains the signals received from the target(s) to be located. The DORT and MUSIC imaging methods have generated a lot of interests due to their robustness and ability to locate multiple targets. However these TR-based methods encounter problems when the targets are behind an obstruction, particularly when the properties of the obstruction is unknown as is often the case in TWI applications. This dissertation introduces a novel total sub-MDM algorithm that uses the highly acclaimed MUSIC method to image targets hidden behind an obstruction and achieve superresolution. The algorithm utilises spatio-temporal windows to divide the full-MDM into sub-MDMs. The summation of all images obtained from each sub-MDM give a clearer image of a scenario than we can obtain using the full-MDM. Furthermore, we propose a total sub-differential MDM algorithm that uses the MUSIC method to obtain images of moving targets that are hiddenbehind an obstructing material.

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Ash, Jason Travis. "Time Reversal and Applications in Solid-State NMR of Quadrupolar Nuclei." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1213361614.

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Winter, Thomas A. "Examination of time-reversal acoustic application to shallow water active sonar systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA378874.

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Xia, Jing. "Optical studies of broken time-reversal symmetry in solids using Sagnac interferometry /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

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Kandler, Anne, and James Steele. "Innovation diffusion in time and space." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-188644.

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In this paper we consider the spread of modern technological innovations. We contrast social learning and threshold heterogeneity models of innovation diffusion, and show how the typical temporal evolution of the distribution of adopters may be consistent with either explanation. Noting the likelihood that each model contains some useful independent explanatory power, we introduce a combined model. We also consider a spatially-structured population in which the spread of an innovation by social influence is modelled as a reaction-diffusion system, and show that the typical spatiotemporal evolution of the distribution is also consistent with a heterogeneity explanation. Additional contextual information is required to estimate the relative importance of social learning and of economic inequalities in observed adoption lags.

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Traytak, Sergey D. "Time-dependent competition effects in diffusion-limited crystal growth: Time-dependent competition effects in diffusion-limitedcrystal growth." Diffusion fundamentals 6 (2007) 47, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14226.

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Falcetelli, Francesco. "Modelling of Pencil-Lead Break Acoustic Emission Sources using the Time Reversal Technique." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16554/.

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In Acoustic Emissions (AE), Hsu-Nielsen Pencil-Lead Breaks (PLB) are used to generate sound waves enabling the characterization of acoustic wave speed in complex structures. The broadband signal of a PLB represents a repeatable emission, which can be applied at different regions of the structure, and therefore can be used to calibrate the localization algorithms of the AE system. In recent years, the use of Finite Element Method (FEM) has flourished for modelling acoustic Lamb wave propagation, which is present in thin plate-like structures. The primary challenge faced by the AE community is the lack of a well-known mathematical function of a PLB signal that can be applied in numerical simulations. This study makes use of a Time Reversal (TR) approach to identify the emission source of the PLB on a 7075-T651 aluminum plate. An ABAQUS CAETM model with piezoelectric actuators and sensors was developed. In order to avoid edge reflections, absorbing boundaries based on the Stiffness Reduction Method (SRM) were considered. The captured PLB signals were used as input to the FEM and was time-reversed. Furthermore, a band-limited white noise signal was used to calibrate the contribution of the broadband frequencies found in the transmitted wave packet. Preliminary results indicate that the TR approach can be used to understand the shape and function of the original transmitted signal.

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Abrantes, António Adolfo Mendes. "Examination of time-reversal acoustics in shallow water and applications to underwater communications /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA368422.

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Thesis (M.S. in Engineering Acoustics and Electrical Engineering) Naval Postgraduate School, June 1999.
"June 1999". Thesis advisor(s): Kevin B. Smith, Andrés Larraza, Monique P. Fargues. Includes bibliographical references (p. 75-77). Also available online.

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Heinemann, Michael Gerhard. "Experimental studies of applications of time-reversal acoustics to non-coherent underwater communications." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/.

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Thesis (M.S. in Engineering Acoustics and M.S. in Applied Physics) Naval Postgraduate School, March 2000.
Thesis advisor(s): Larraza, Andrès ; Smith, Kevin B. "March 2000." Includes bibliographical references (p. 59-60). Also available online.

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Stokely, John P. "Experimental studies of two-way single element time reversal in a noisy waveguide." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA393134.

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Yavuz, Mehmet Emre. "Time reversal based signal processing techniques for ultrawideband electromagnetic sensing in random media." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1198770526.

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Abboud, Layane. "Time Reversal techniques applied to wire fault detection and location in wire networks." Phd thesis, Supélec, 2012. http://tel.archives-ouvertes.fr/tel-00771964.

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In this thesis we present new approaches in the domains of soft fault detection and location in complex wire networks, based on the properties of time reversal. When addressing the detection of soft faults, the idea is to adapt the testing signal to the network under test, instead of being predefined for all the tested networks, as opposed to standard reflectometry techniques. We prove that this approach, which we name the Matched Pulse approach (MP), is beneficial whenever the system is more complex, i.e., its response is richer in echoes, which is opposed to common understanding. The MP analysis is conducted via a formal mathematical analysis, followed by simulation and experimental results validating the proposed approach. In the domain of soft fault location, and based on the DORT (Décomposition de l'Opérateur de Retournement Temporel) properties, we derive a distributive non-iterative method able to synthesize signals that focus on the fault position. Through a statistical study we analyze some of the influencing parameters on the performance of the method, and then simulation and experimental results show that the method is able to synthesize signals directly focalizing on the soft fault position, without the need for iterations.

Dissertations / Theses on the topic 'Time reversal of diffusion'

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