Dissertations / Theses on the topic 'Wave localization'
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1
Rimal, Nischal. "Impact Localization Using Lamb Wave and Spiral FSAT." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1388672483.
2
Vidiyala, Sai Krishna. "Simultaneous localization and mapping with radio signals." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24138/.
Abstract:
Simultaneous localization and mapping is a concept that originated in the robotics area, where robots are traditionally equipped with a laser sensor and can navigate and map an unknown surrounding environment. High-definition distance estimates and very narrow steering beams are provided
by high-accuracy SLAM technologies based on laser and mechanical steering devices. Unfortunately, these technologies are prohibitively expensive and cumbersome, and they cannot be integrated into mobile devices. This Thesis investigates millimeter wave (mmWave) radar technology to solve a SLAM problem. The technologies used are consistent with the concept of a personal mobile radar and they can be considered a proof-of-concept for further development of this concept.
3
Lotti, Marina, and Marina Lotti. "Experimental characterization of millimeter-wave radars for mapping and localization." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/19891/.
Abstract:
L’attività di tesi è inquadrata nell’ambito del progetto europeo PRIMELOC (Personal Radars for Radio Imaging and Infrastructure-less Localization) il cui scopo è quello di validare il concetto di radar personale per fornire servizi automatici di localizzazione e di mappatura degli ambienti indoor, evitando l’introduzione di infrastrutture ad hoc. Per far ciò, si vogliono sfruttare i dispositivi di future generazioni wireless che usano onde millimetriche, per costruire mappe di luoghi indoor. Le mappe sono ottenute scannerizzando l’ambiente circostante attraverso l’uso di massive antenna arrays ad onde millimetriche e di particolari algoritmi per la localizzazione e il mapping simultanei (simultaneous localization and mapping - SLAM). Per la validazione sperimentale del concetto di Personal Radar è fondamentale l’esecuzione di diverse campagne di misura in ambienti realistici. I dati raccolti da esse devono essere valutati e processati al fine di renderli adatti come input degli algoritmi di SLAM.
4
Woolard, Americo Giuliano. "Supplementing Localization Algorithms for Indoor Footsteps." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78698.
Abstract:
The data rich nature of instrumented civil structures has brought attention to alternative applications outside of the traditional realm of structural health monitoring. An interest has been raised in using these vibration measurements for other applications such as human occupancy. An example of this is to use the vibrations measured from footsteps to locate occupants within a building. The localization of indoor footsteps can yield several benefits in areas such as security and threat detection, emergency response and evacuation, and building resource management, to name a few. The work described herein seeks to provide supplementary information to better define the problem of indoor footstep localization, and to investigate the use of several localization techniques in a real-world, operational building environment. The complexities of locating footsteps via indoor vibration measurements are discussed from a mechanics perspective using prior literature, and several techniques developed for localization in plate structures are considered for their applicability to indoor localization. A dispersion compensation tool is experimentally investigated for localization in an instrumented building. A machine learning approach is also explored using a nearest neighbor search. Additionally, a novel instrumentation method is designed based on a multi-point coupling approach that provides directional inference from a single point of measurement. This work contributes to solving the indoor footstep localization problem by consolidating the relevant mechanical knowledge and experimentally investigating several potential solutions.Ph. D.
5
Bordiga, Giovanni. "Homogenization of periodic lattice materials for wave propagation, localization, and bifurcation." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/259019.
Abstract:
The static and dynamic response of lattice materials is investigated to disclose and control the connection between microstructure and effective behavior. The analytical methods developed in the thesis aim at providing a new understanding of material instabilities and strain localizations as well as effective tools for controlling wave propagation in lattice structures.
The time-harmonic dynamics of arbitrary beam lattices, deforming flexurally and axially in a plane, is formulated analytically to analyze the influence of the mechanical parameters on the dispersion properties of the spectrum of Floquet-Bloch waves. Several forms of dynamic localizations are shown to occur for in-plane wave propagation of grid-like elastic lattices. It is demonstrated that lattices of rods, despite being `simple' structures, can exhibit a completely different channeled response depending on the characteristics of the forcing source (i.e. frequency and direction) as well as on the slenderness of the elastic links. It is also shown how the lattice parameters can be tuned to attain specific dispersion properties, such as flat bands and sharp Dirac cones.
In the research field of material instabilities, a key result proposed in this thesis is the development of both static and dynamic homogenization methods capable of accounting for second-order effects in the macroscopic response of prestressed lattices. These methods, the former based on an incremental strain-energy equivalence and the latter based on the asymptotic analysis of lattice waves, allow the identification of the incremental constitutive operator capturing the macroscopic incremental response of arbitrary lattice configurations. The homogenization framework has allowed the systematic analysis of prestress-induced phenomena on the incremental response of both the lattice structure and its `effective' elastic solid, which in turn has enabled the identification of the complex interplay between microstructure, prestress, loss of ellipticity (shear band formation) and short-wavelength bifurcations.
Potential new applications for the control of wave propagation are also shown to be possible by leveraging the inclusion of second-order terms in the incremental dynamics. In particular, the tunability of the prestress state in a square lattice structure has been exploited to obtain dynamic interfaces with designable transmission properties. The interface can be introduced in a material domain by selectively prestressing the desired set of ligaments and the prestress level can be tuned to achieve total reflection, negative refraction, and wave channeling.
The obtained results open new possibilities for the realization of engineered materials endowed with a desired constitutive response, as well as to enable the identification of novel dynamic material instabilities.
6
Bordiga, Giovanni. "Homogenization of periodic lattice materials for wave propagation, localization, and bifurcation." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/259019.
Abstract:
The static and dynamic response of lattice materials is investigated to disclose and control the connection between microstructure and effective behavior. The analytical methods developed in the thesis aim at providing a new understanding of material instabilities and strain localizations as well as effective tools for controlling wave propagation in lattice structures.
The time-harmonic dynamics of arbitrary beam lattices, deforming flexurally and axially in a plane, is formulated analytically to analyze the influence of the mechanical parameters on the dispersion properties of the spectrum of Floquet-Bloch waves. Several forms of dynamic localizations are shown to occur for in-plane wave propagation of grid-like elastic lattices. It is demonstrated that lattices of rods, despite being `simple' structures, can exhibit a completely different channeled response depending on the characteristics of the forcing source (i.e. frequency and direction) as well as on the slenderness of the elastic links. It is also shown how the lattice parameters can be tuned to attain specific dispersion properties, such as flat bands and sharp Dirac cones.
In the research field of material instabilities, a key result proposed in this thesis is the development of both static and dynamic homogenization methods capable of accounting for second-order effects in the macroscopic response of prestressed lattices. These methods, the former based on an incremental strain-energy equivalence and the latter based on the asymptotic analysis of lattice waves, allow the identification of the incremental constitutive operator capturing the macroscopic incremental response of arbitrary lattice configurations. The homogenization framework has allowed the systematic analysis of prestress-induced phenomena on the incremental response of both the lattice structure and its `effective' elastic solid, which in turn has enabled the identification of the complex interplay between microstructure, prestress, loss of ellipticity (shear band formation) and short-wavelength bifurcations.
Potential new applications for the control of wave propagation are also shown to be possible by leveraging the inclusion of second-order terms in the incremental dynamics. In particular, the tunability of the prestress state in a square lattice structure has been exploited to obtain dynamic interfaces with designable transmission properties. The interface can be introduced in a material domain by selectively prestressing the desired set of ligaments and the prestress level can be tuned to achieve total reflection, negative refraction, and wave channeling.
The obtained results open new possibilities for the realization of engineered materials endowed with a desired constitutive response, as well as to enable the identification of novel dynamic material instabilities.
7
Reinwald, Michael. "Wave propagation in mammalian skulls and its contribution to acoustic source localization." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS244.
Abstract:
La précision avec laquelle le dauphin localise les sources sonores est excellente, que les sources soient situées dans le plan médial ou dans le plan transverse. Cette faculté est contre-intuitive étant donné que les dauphins n’ont pas d’oreille externe (pavillon), qui joue un rôle important chez les autres mammifères pour la localisation de sources en élévation. Dans cette thèse, des simulations tridimensionnelles ont été réalisées pour déterminer l’influence de la conduction osseuse du son dans le crâne d’un dauphin commun à bec court sur la pression acoustique au voisinage de l’oreille. La modalisation n’a pas permis de mettre en évidence d’encoches spectrales telles que celles créées par le pavillon de l’oreille externe des humains et qui codent chez celui-ci l’élévation de la source sonore. Une série d’expériences sur un crâne de dauphin, immergé dans une piscine, a permis de mesurer directement la conduction osseuse dans la mandibule. Les formes d’ondes complètes des sons reçus aux récepteurs fixés sur la mandibule, et particulièrement la coda du signal, a pu être utilisée avec succès pour obtenir la position de sources en utilisant un algorithme de corrélation. Ce résultat, qui devra être conforté par la réalisation d’autres expériences, suggère que le système auditif du dauphin pourrait utiliser la coda des signaux reçus lors de l’écholocation. Enfin, des simulations 2D ont permis de mettre en évidence le potentiel bénéfice du couplage de la conduction osseuse du son avec la propagation dans des structures graisseuses de la tête du dauphinThe spatial accuracy of source localization by dolphins has been observed to be equally accurate independent of source azimuth and elevation. This ability is counter-intuitive if one considers that humans and other species have presumably evolved pinnae to help determine the elevation of sound sources, while cetaceans have actually lost them. In this work, 3D numerical simulations are carried out to determine the influence of bone-conducted waves in the skull of a short-beaked common dolphin on sound pressure in the vicinity of the ears. The skull is not found to induce any salient spectral notches, as pinnae do in humans, that the animal could use to differentiate source elevations in the median plane. Experiments are conducted in a water tank by deploying sound sources on the horizontal and median plane around a skull of a dolphin and measuring bone-conducted waves in the mandible. Their full waveforms, and especially the coda, can be used to determine source elevation via a correlation-based source localization algorithm. While further experimental work is needed to substantiate this speculation, the results suggest that the auditory system of dolphins might be able to localize sound sources by analyzing the coda of biosonar echoes. 2D numerical simulations show that this algorithm benefits from the interaction of bone-conducted sound in a dolphin's mandible with the surrounding fats
8
LaPenta, Jason Michael. "Real-time 3-d localization using radar and passive surface acoustic wave transponders." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41738.
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2007.Includes bibliographical references (p. 141-150).
This thesis covers ongoing work into the design, fabrication, implementation, and characterization of novel passive transponders that allow range measurements at short range and at high update rates. Multiple RADAR measurement stations use phase-encoded chirps to selectively track individual transponders by triangulation of range and/or angle measurements. Nanofabrication processes are utilized to fabricate the passive surface acoustic wave transponders used in this thesis. These transponders have advantages over existing solutions with their small size (mm x mm), zero-power, high-accuracy, and kilohertz update rates. Commercial applications such as human machine interfaces, virtual training environments, security, inventory control, computer gaming, and biomedical research exist. A brief review of existing tracking technologies including a discussion of how their shortcomings are overcome by this system is included. Surface acoustic wave (SAW) device design and modeling is covered with particular attention paid to implementation of passive transponders. A method under development to fabricate SAW devices with features as small as 300nm is then covered in detail. The electronic design of the radar chirp transmitter and receiver are covered along with the design and implementation of the test electronics. Results from experiments conducted to characterize device performance are given.
by Jason Michael LaPenta.
S.M.
9
Kondrath, Andrew Stephen. "Frequency Modulated Continuous Wave Radar and Video Fusion for Simultaneous Localization and Mapping." Wright State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=wright1347715085.
10
Cheung, Sai-Kit. "The study of weak localization effects on wave dynamics in mesoscopic media in the diffusive regime and at the localization transition /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202006%20CHEUNG.
11
Evers, Martin [Verfasser]. "Two antagonizing aspects of spin transport : spin-wave localization and spin superfluidity / Martin Evers." Konstanz : KOPS Universität Konstanz, 2019. http://d-nb.info/1230323309/34.
12
Hanley, Thomas Harry. "On the exploitation of mode localization in surface acoustic wave MEMS for sensing applications." Thesis, University of Newcastle upon Tyne, 2017. http://hdl.handle.net/10443/3711.
Abstract:
Mode localization refers to the spatial trapping of energy in a coupled oscillatory system that occurs when a disorder is introduced into a previously ordered system. This thesis explores the exploitation of this phenomenon in surface acoustic wave (SAW) devices for sensing applications. The sensing application of primary focus within this work is a magnetic field sensor, wherein the strength of mode localization changes in proportion to an external magnetic field. In addition, application as a bio-mass sensor is suggested and briefly discussed. Utilisation of mode localization as a sense mechanism involves the use of changes in the normalised mode shape of a weakly-coupled two degree-of-freedom system as the sensor output. This is in contrast to the use of shifts in frequency, phase or amplitude as is commonplace in resonant micro-electromechanical systems (MEMS) sensor technology. The theory and principles of device operation are introduced utilising a discretised model. In particular, the use of a periodic array to couple the sensors’ two degrees-of-freedom is investigated. A generalised geometry of the SAW device is introduced, consisting of a pair of acoustically-coupled cavities. An analytical solution is found for the displacement fields within the cavities. The solution is achieved by coupling the internal cavity solutions using a ray tracing method. The results of the analytical solution are compared to a numerical solution found using commercial finite element analysis (FEA) software; good agreement is observed. The model is subsequently used to analyse and discuss device performance in the presence of noise; expressions are presented describing device operation and performance, and a case study is outlined evaluating use as a MEMS magnetometer. Finally, the design, manufacture and testing of a prototype design is discussed.
13
Park, Won Hyun, and Won Hyun Park. "Acoustic Source Localization in an Anisotropic Plate Without Knowing its Material Properties." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/622963.
Abstract:
Acoustic source localization (ASL) is pinpointing an acoustic source. ASL can reveal the point of impact of a foreign object or the point of crack initiation in a structure. ASL is necessary for continuous health monitoring of a structure. ASL in an anisotropic plate is a challenging task. This dissertation aims to investigate techniques that are currently being used to precisely determine an acoustic source location in an anisotropic plate without knowing its material properties. A new technique is developed and presented here to overcome the existing shortcomings of the acoustic source localization in anisotropic plates. It is done by changing the analysis perspective from the angular dependent group velocity of the wave and its straight line propagation to the wave front shapes and their geometric properties when a non-circular wave front is generated. Especially, 'rhombic wave front' and 'elliptical wave front' are dealt with because they are readily observed in highly anisotropic composite plates. Once each proposed technique meets the requirements of measurement, four sensor clusters in three different quadrants (recorded by 12 sensors) for the rhombus and at least three sensor clusters (recorded by 9 sensors) for the ellipse, accurate Acoustic Source Localization is obtained. It has been successfully demonstrated in the numerical simulations. In addition, a series of experimental tests demonstrate reliable and robust prediction performance of the developed new acoustic source localization technique.
14
Chen, Xin. "Load-enhanced lamb wave methods for the in situ detection, localization and characterization of damage." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54859.
Abstract:
A load-enhanced methodology has been proposed to enable the in situ detection, localization, and characterization of damage in metallic plate-like structures using Lamb waves. A baseline-free load-differential method using the delay-and-sum imaging algorithm is proposed for defect detection and localization. The term “load-differential” refers to the comparison of recorded ultrasonic signals at various levels of stress. Defect characterization is achieved by incorporating expected scattering information of guided waves interacting with defects into the minimum variance imaging algorithm, and a method for estimating such scattering patterns from the measurements of a sparse transducer array is developed. The estimation method includes signal preprocessing, extracting initial scattering values from baseline subtraction results, and obtaining the complete scattering matrix by applying radial basis function interpolation. The factors that cause estimation errors, such as the shape parameter used to form the basis function and the filling distance used in the interpolation, are discussed.
The estimated scattering patterns from sparse array measurements agree reasonably well with laser wavefield data and are further used in the load-enhanced method. The results from fatigue tests show that the load-enhanced method is capable of detecting cracks, providing reasonable estimates of their localizations and orientations, and discriminating them from drilled holes, disbonds, and fastener tightness variations.
15
Samarawickrama, Mahendra. "Acceleration Techniques for Sparse Recovery Based Plane-wave Decomposition of a Sound Field." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17302.
Abstract:
Plane-wave decomposition by sparse recovery is a reliable and accurate technique for plane-wave decomposition which can be used for source localization, beamforming, etc. In this work, we introduce techniques to accelerate the plane-wave decomposition by sparse recovery. The method consists of two main algorithms which are spherical Fourier transformation (SFT) and sparse recovery. Comparing the two algorithms, the sparse recovery is the most computationally intensive. We implement the SFT on an FPGA and the sparse recovery on a multithreaded computing platform. Then the multithreaded computing platform could be fully utilized for the sparse recovery. On the other hand, implementing the SFT on an FPGA helps to flexibly integrate the microphones and improve the portability of the microphone array. For implementing the SFT on an FPGA, we develop a scalable FPGA design model that enables the quick design of the SFT architecture on FPGAs. The model considers the number of microphones, the number of SFT channels and the cost of the FPGA and provides the design of a resource optimized and cost-effective FPGA architecture as the output. Then we investigate the performance of the sparse recovery algorithm executed on various multithreaded computing platforms (i.e., chip-multiprocessor, multiprocessor, GPU, manycore). Finally, we investigate the influence of modifying the dictionary size on the computational performance and the accuracy of the sparse recovery algorithms. We introduce novel sparse-recovery techniques which use non-uniform dictionaries to improve the performance of the sparse recovery on a parallel architecture.
16
Chan, Man Leong. "Optimization of electromagnetic follow up observations and localization of gravitational wave signals from compact binary coalescences." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/31007/.
Abstract:
Many gravitational wave sources will produce electromagnetic signals as they emit gravitational waves. An important example is binary neutron star mergers. The joint observations and discoveries of the electromagnetic signatures of these gravitational wave sources can produce substantial scientific benefits in physics, astrophysics and cosmology. To maximize the scientific outcomes of such gravitational events as much as possible, the detections of their electromagnetic signatures are necessary. The first detection of the inspiral signals from binary neutron stars by LIGO and VIRGO, and the observations of the associated electromagnetic counterparts throughout the electromagnetic spectrum have served an excellent example. These detections and discoveries have also ushered in a new era of both gravitational wave astronomy and multi-messenger astronomy. However, using gravitational wave interferometric detectors, the sky location estimates of the gravitational wave signals from binary neutron star can span a few hundreds square degrees, unless there are three or more detectors observing the event simultaneously. The large sky localization error poses a challenge for astronomers scanning the localization error to look for the electromagnetic signals of these gravitational wave events. The electromagnetic counterparts may also not be readily detectable depending on the distance and orientation of the sources, which presents further difficulties in detecting their signals. To alleviate the situation, we develop an algorithm to maximize the detection probability of the electromagnetic counterparts of gravitational wave events. The algorithm we develop is able to generate an observing strategy that optimizes the probability of successful electromagnetic follow-up observations given limited observational resources. This is achieved by using a greedy algorithm for tiling the sky location error and Lagrange multiplier for assigning observation times to observation fields. The analysis with the algorithm also allows an estimate of the detection probability. In Chapter 3, we present a proof-of-concept demonstration of this algorithm to four telescopes Subaru-HyperSuprimeCam, CTIO-Dark Energy Camera, Palomar Transient Factory and Pan-Starrs, for three different simulated binary neutron star events, assuming kilonova to be the target electromagnetic counterpart. By applying the algorithm to telescopes with arbitrary field of view and sensitivity within a range, we provide an insight into the potential of future telescopes and other telescopes not directly included in our analysis. Moreover, the algorithm is applied to the design of a space based mission, the Einstein Probe, to find the optimal combination of the size of field of view and the sensitivity. The localization of gravitational wave sources, which is determined both by the gravitational wave signals and the detectors, is an important factor to the success of electromagnetic follow-up observations. We investigate the localization of binary neutron star mergers detected with the Einstein Telescope and Cosmic Explorer. Compared to the existing detectors, the improvement in the sensitivity of the Einstein Telescope and Cosmic Explorer in the low frequency band has many important implications. One of them is the considerable increase in the length of the in-band of the signals from binary neutron stars, which is useful in localizing the sources. In Chapter 4, using a Fisher matrix approach, we estimate the sky localization error of binary neutron stars as a population and distributed at various distances. As the extended in-band duration of signals also increases the possibility of identifying and releasing the presence of a signal prior to merger, known as early warning, we investigate the prospect for early warning of binary neutron star merger events with these detectors. While the Einstein Telescope and Cosmic Explorer hold promising future for gravitational wave astronomy, they are not likely to be operative until the 2030s. In the literature, detectors designed with more advanced technologies than LIGO and VIRGO are proposed to fill the gap in time. We estimate the localization of binary black holes with two such detectors in Australia and China and seconds generation detectors such as LIGO, LIGO India, VIRGO and KAGRA. In chapter 5, we study electromagnetic observations of binary neutron star mergers with the Large Synoptic Survey Telescope. The Large Synoptic Survey Telescope is a telescope designed with large size of field of view and excellent sensitivity in its observing bands. Such a telescope provides a promising prospect for multimessenger astronomy with gravitational waves. With its sensitivity and field of view, the telescope is expected to enable electromagnetic follow-up observations with shorter exposure time and fewer observation fields than many existing telescopes. We define a simple procedure for electromagnetic follow-up observations triggered by gravitational waves using the telescope. Taking advantages of the Fisher matrix approach in Chapter 4 for the sky location estimates, we quantify the observation time necessary for the telescope to perform electromagnetic follow-up observation of binary neutron star mergers detected with different networks of gravitational wave detectors.
17
Ghatak, Gourab. "Millimeter wave multi-RAT small cells for heterogeneous mobile services : performance analysis and optimization." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLT010/document.
Abstract:
Les futures applications sans fil anticipent une explosion de la pléthore de cas d'utilisation et de services, qui ne peut être soutenue par des améliorations incrémentielles des schémas de communication existants. Pour cela, deux axes de recherche sont particulièrement intéressants: la densification du réseau à l'aide de petites cellules et la communication par ondes millimétriques (ondes millimétriques). Dans cette thèse, nous modélisons et évaluons des réseaux cellulaires constitués de petites cellules à ondes millimétriques utilisant la technique d'accès multi-radio (RAT) déployées au-dessus de la macro-architecture existante. Premièrement, nous modélisons mathématiquement un déploiement homogène de petites cellules multi-RAT et caractérisons les performances de l'utilisateur et du réseau en termes de probabilité de couverture signal sur brouillage plus rapport de bruit (SINR), de débit descendant et de probabilité de surcharge de cellule. Ensuite, nous étudions l'association des utilisateurs à différents niveaux et la sélection optimale de différents RAT, de manière à optimiser ces mesures de performance. En règle générale, les modèles de réseau cellulaire qui supposent des déploiements homogènes de petites cellules ne tiennent pas compte des nuances des caractéristiques de blocage urbain. Pour résoudre ce problème, nous modélisons les emplacements de petites cellules le long des routes d'une ville, puis nous prenons en compte les blocages de signaux dus à la construction d'immeubles ou au déplacement de véhicules sur les routes. Sur ce réseau, nous supposons que l’opérateur prend en charge trois types de services v.i.z., les communications ultra-fiables à faible temps de latence (URLLC), les communications massives de type machine (mMTC) et le haut débit mobile amélioré (eMBB) avec des besoins différents. En conséquence, nous étudions la sélection optimale de RAT pour ces services avec divers blocages de véhicules. Enfin, sur la base du modèle de déploiement sur route de petites cellules à ondes millimétriques, nous étudions un réseau conçu pour prendre en charge simultanément des services de positionnement et de données. Nous caractérisons la précision du positionnement en fonction des limites de la localisation, puis étudions des stratégies optimales de partitionnement des ressources et de sélection de la largeur de faisceau afin de répondre à diverses exigences de positionnement et de débit de donnéesFuture wireless applications anticipate an explosion in the plethora of use-cases and services, which cannot be sustained by incremental improvements on the existing communication schemes. For this, two research directions are particularly attractive: network densification using small cells and millimeter wave (mm-wave) wave communications. In this thesis, we model and evaluate cellular networks consisting of multi-radio access technique (RAT) mm-wave small cells deployed on top of the legacy macro-architecture. First, we mathematically model a homogeneous deployment of multi-RAT small cells and characterize the user and network performance in terms of signal to interference plus noise ratio (SINR) coverage probability, downlink throughput, and the cell overloading probability. Then, we study users association to different tiers and optimal selection of different RATs, so as to optimize these performance metrics. Generally, cellular network models that assume homogeneous deployments of small cells fail to take into account the nuances of urban blockage characteristics. To address this, we model the small cell locations along the roads of a city, and subsequently, we take into consideration the signal blockages due to buildings or moving vehicles on the roads. In this network, we assume that the operator supports three types of services v.i.z., ultra-reliable low-latency communications (URLLC), massive machine-type communications (mMTC), and enhanced mobile broadband (eMBB) with different requirements. Consequently, we study the optimal RAT selection for these services with varying vehicular blockages. Finally, based on the on-road deployment model of mm-wave small cells, we study a network designed to support positioning and data services simultaneously. We characterize the positioning accuracy based on the localization bounds and then study optimal resource partitioning and beamwidth selection strategies to address varied positioning and data-rate requirements
18
Khames, Imene. "Nonlinear network wave equations : periodic solutions and graph characterizations." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMIR04/document.
Abstract:
Dans cette thèse, nous étudions les équations d’ondes non-linéaires discrètes dans des réseaux finis arbitraires. C’est un modèle général, où le Laplacien continu est remplacé par le Laplacien de graphe. Nous considérons une telle équation d’onde avec une non-linéarité cubique sur les nœuds du graphe, qui est le modèle φ4 discret, décrivant un réseau mécanique d’oscillateurs non-linéaires couplés ou un réseau électrique où les composantes sont des diodes ou des jonctions Josephson. L’équation d’onde linéaire est bien comprise en termes de modes normaux, ce sont des solutions périodiques associées aux vecteurs propres du Laplacien de graphe. Notre premier objectif est d’étudier la continuation des modes normaux dans le régime non-linéaire et le couplage des modes en présence de la non-linéarité. En inspectant les modes normaux du Laplacien de graphe, nous identifions ceux qui peuvent être étendus à des orbites périodiques non-linéaires. Il s’agit des modes normaux dont les vecteurs propres du Laplacien sont composés uniquement de {1}, {-1,+1} ou {-1,0,+1}. Nous effectuons systématiquement une analyse de stabilité linéaire (Floquet) de ces orbites et montrons le couplage des modes lorsque l’orbite est instable. Ensuite, nous caractérisons tous les graphes pour lesquels il existe des vecteurs propres du Laplacien ayant tous leurs composantes dans {-1,+1} ou {-1,0,+1}, en utilisant la théorie spectrale des graphes. Dans la deuxième partie, nous étudions des solutions périodiques localisées spatialement. En supposant une condition initiale de grande amplitude localisée sur un nœud du graphe, nous approchons l’évolution du système par l’équation de Duffing pour le nœud excité et un système linéaire forcé pour le reste du réseau. Cette approximation est validée en réduisant l’équation φ4 discrète à l’équation de Schrödinger non-linéaire de graphes et par l’analyse de Fourier de la solution numérique. Les résultats de cette thèse relient la dynamique non-linéaire à la théorie spectrale des graphesIn this thesis, we study the discrete nonlinear wave equations in arbitrary finite networks. This is a general model, where the usual continuum Laplacian is replaced by the graph Laplacian. We consider such a wave equation with a cubic on-site nonlinearity which is the discrete φ4 model, describing a mechanical network of coupled nonlinear oscillators or an electrical network where the components are diodes or Josephson junctions. The linear graph wave equation is well understood in terms of normal modes, these are periodic solutions associated to the eigenvectors of the graph Laplacian. Our first goal is to investigate the continuation of normal modes in the nonlinear regime and the modes coupling in the presence of nonlinearity. By inspecting the normal modes of the graph Laplacian, we identify which ones can be extended into nonlinear periodic orbits. They are normal modes whose Laplacian eigenvectors are composed uniquely of {1}, {-1,+1} or {-1,0,+1}. We perform a systematic linear stability (Floquet) analysis of these orbits and show the modes coupling when the orbit is unstable. Then, we characterize all graphs for which there are eigenvectors of the graph Laplacian having all their components in {-1,+1} or {-1,0,+1}, using graph spectral theory. In the second part, we investigate periodic solutions that are spatially localized. Assuming a large amplitude localized initial condition on one node of the graph, we approximate its evolution by the Duffing equation. The rest of the network satisfies a linear system forced by the excited node. This approximation is validated by reducing the discrete φ4 equation to the graph nonlinear Schrödinger equation and by Fourier analysis. The results of this thesis relate nonlinear dynamics to graph spectral theory
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Blomqvist, Anneli. "Millimeter Wave Radar as Navigation Sensor on Robotic Vacuum Cleaner." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-288146.
Abstract:
Does millimeter-wave radar have the potential to be the navigational instrument of a robotic vacuum cleaner in a home? Electrolux robotic vacuum cleaner is currently using a light sensor to navigate through the home while cleaning. Recently Texas Instruments released a new mmWave radar sensor, operating in the frequency range 60-64 GHz. This study aims to answer if the mmWave radar sensor is useful for indoor navigation. The study tests the sensor on accuracy and resolution of angles and distances in ranges relevant to indoor navigation. It tests if various objects made out of plastic, fabric, paper, metal, and wood are detectable by the sensor. At last, it tests what the sensor can see when it is moving while measuring. The radar sensor can localize the robot, but the ability to detect objects around the robot is limited. The sensor’s absolute accuracy is within 3° for the majority of angles and around 1dm for most distances above 0.5 m. The resolution for a displacement of one object is 1°, respectively 5 cm, and two objects must be located at least 14° or 15 cm apart from each other to be recognized. Future tasks include removing noise due to antenna coupling to improve reflections from within 0.5 meter and figure out the best way to move around the sensor to improve the resolution.Har radar med millimetervågor förutsättningar att vara navigationsutrustning för en robotdammsugare i ett hem? Electrolux robotdammsugare använder för närvarande en ljussensor för att navigera genom hemmet medan den städar. Nyligen släppte Texas Instruments en ny radarsensor med vågor i frekvensområdet 60-64 GHz. Denna studie syftar till att svara om radarsensorn är användbar för inomhusnavigering. Studien testar sensorn med avseende på noggrannhet och upplösning av vinklar och avstånd i områden som är relevanta för inomhusnavigering. Den testar om olika föremål tillverkade av plast, tyg, papper, metall och trä kan detekteras av sensorn. Slutligen testas vad sensorn kan se om den rör sig medan den mäter. Radarsensorn kan positionera roboten, men hinderdetektering omkring roboten är begränsad. För det mesta ligger sensorns absoluta noggrannhet inom 3° för vinklar och omkring 1dm för avstånd över 0,5 m. Upplösningen för en förflyttning av ett objekt är 1° respektive 5 cm, och två objekt måste placeras minst 14° eller 15 cm ifrån varandra för att båda kunna upptäckas. Kommande utmaningar är att ta bort antennstörningar som ger sämre reflektioner inom 0,5 meter och ta reda på det bästa sättet att förflytta sensorn för att förbättra upplösningen.
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Ghatak, Gourab. "Millimeter wave multi-RAT small cells for heterogeneous mobile services : performance analysis and optimization." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLT010.
Abstract:
Les futures applications sans fil anticipent une explosion de la pléthore de cas d'utilisation et de services, qui ne peut être soutenue par des améliorations incrémentielles des schémas de communication existants. Pour cela, deux axes de recherche sont particulièrement intéressants: la densification du réseau à l'aide de petites cellules et la communication par ondes millimétriques (ondes millimétriques). Dans cette thèse, nous modélisons et évaluons des réseaux cellulaires constitués de petites cellules à ondes millimétriques utilisant la technique d'accès multi-radio (RAT) déployées au-dessus de la macro-architecture existante. Premièrement, nous modélisons mathématiquement un déploiement homogène de petites cellules multi-RAT et caractérisons les performances de l'utilisateur et du réseau en termes de probabilité de couverture signal sur brouillage plus rapport de bruit (SINR), de débit descendant et de probabilité de surcharge de cellule. Ensuite, nous étudions l'association des utilisateurs à différents niveaux et la sélection optimale de différents RAT, de manière à optimiser ces mesures de performance. En règle générale, les modèles de réseau cellulaire qui supposent des déploiements homogènes de petites cellules ne tiennent pas compte des nuances des caractéristiques de blocage urbain. Pour résoudre ce problème, nous modélisons les emplacements de petites cellules le long des routes d'une ville, puis nous prenons en compte les blocages de signaux dus à la construction d'immeubles ou au déplacement de véhicules sur les routes. Sur ce réseau, nous supposons que l’opérateur prend en charge trois types de services v.i.z., les communications ultra-fiables à faible temps de latence (URLLC), les communications massives de type machine (mMTC) et le haut débit mobile amélioré (eMBB) avec des besoins différents. En conséquence, nous étudions la sélection optimale de RAT pour ces services avec divers blocages de véhicules. Enfin, sur la base du modèle de déploiement sur route de petites cellules à ondes millimétriques, nous étudions un réseau conçu pour prendre en charge simultanément des services de positionnement et de données. Nous caractérisons la précision du positionnement en fonction des limites de la localisation, puis étudions des stratégies optimales de partitionnement des ressources et de sélection de la largeur de faisceau afin de répondre à diverses exigences de positionnement et de débit de donnéesFuture wireless applications anticipate an explosion in the plethora of use-cases and services, which cannot be sustained by incremental improvements on the existing communication schemes. For this, two research directions are particularly attractive: network densification using small cells and millimeter wave (mm-wave) wave communications. In this thesis, we model and evaluate cellular networks consisting of multi-radio access technique (RAT) mm-wave small cells deployed on top of the legacy macro-architecture. First, we mathematically model a homogeneous deployment of multi-RAT small cells and characterize the user and network performance in terms of signal to interference plus noise ratio (SINR) coverage probability, downlink throughput, and the cell overloading probability. Then, we study users association to different tiers and optimal selection of different RATs, so as to optimize these performance metrics. Generally, cellular network models that assume homogeneous deployments of small cells fail to take into account the nuances of urban blockage characteristics. To address this, we model the small cell locations along the roads of a city, and subsequently, we take into consideration the signal blockages due to buildings or moving vehicles on the roads. In this network, we assume that the operator supports three types of services v.i.z., ultra-reliable low-latency communications (URLLC), massive machine-type communications (mMTC), and enhanced mobile broadband (eMBB) with different requirements. Consequently, we study the optimal RAT selection for these services with varying vehicular blockages. Finally, based on the on-road deployment model of mm-wave small cells, we study a network designed to support positioning and data services simultaneously. We characterize the positioning accuracy based on the localization bounds and then study optimal resource partitioning and beamwidth selection strategies to address varied positioning and data-rate requirements
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Kiorpelidis, Ioannis-Markos. "Wave phenomena in one-dimensional space or time varying media." Electronic Thesis or Diss., Le Mans, 2023. https://cyberdoc-int.univ-lemans.fr/Theses/2023/2023LEMA1032.pdf.
Abstract:
L'interaction des ondes avec des milieux possédant des fluctuations spatiales et/ou temporelles conduit à une phénoménologie intéressante. Dans ce cadre, dans la présente thèse quatre phénomènes ondulatoires sont étudiés: deux se produisant dans des milieux variant dans l’espace et deux dans des milieux variant dans le temps. Nous commençons par explorer la diffusion des ondes par une configuration spatialement périodique finie sujette à des perturbations. Nous nous concentrons sur les résonances de transmission parfaite (PTR) et nous développons une méthode pour les préserver sous des perturbations asymétriques. L'analyse effectuée révèle une connexion par paire entre les PTR d'une configuration de diffusion spatialement périodique avec des cellules à symétrie miroir. Dans le même contexte de milieux variant spatialement, nous calculons la longueur de localisation des modes de bord topologiques qui sont supportés dans une chaîne mécanique masse-ressort possédant des fluctuations aléatoires de ses paramètres de rigidité. En présence d'un fort désordre chiral, la longueur de localisation diverge, ce qui implique une transition de phase topologique induite uniquement par le désordre. Dans une prochaine étape, nous considérons le cas où les couplages de la chaîne masse-ressort mécanique varient avec le temps de manière déterministe. Ce système variable dans le temps peut alors servir de plate-forme pour transférer un mode de bord topologique. Au-delà de la limite adiabatique, nous concevons un protocole pour les couplages variables dans le temps qui aboutit à un transfert rapide et robuste et conduit encore plus à une amplification du mode de bord transféré. Pour éclairer le phénomène d'amplification dans une plateforme variable dans le temps, nous explorons la propagation d'une onde dans un milieu à indice de réfraction périodique et dont la dynamique des ondes est régie par l'équation de Mathieu. L'onde présente une amplification transitoire en raison de la nature non normale de la matrice de propagation et nous fournissons la preuve numérique que les caractéristiques d'amplification globales sont fournies simplement par la matrice de monodromieThe interaction of waves with media possessing spatial or/and temporal fluctuations leads tointeresting phenomenology. Within this framework, in the present thesis four wave phenomena arestudied: two occurring in spatially-varying media and two in time-varying media. We begin byexploring wave scattering by a finite spatially-periodic setup that is subject to perturbation. Ourfocus is on perfect transmission resonances (PTRs) and we develop a method for preserving themunder asymmetric perturbations. The performed analysis reveals a pairwise connection betweenPTRs of a spatially-periodic scattering setup with mirror symmetric cells. In the same contextof spatially varying media, we compute the localization length of the topological edge modes thatare supported in a mechanical mass-spring chain possessing random fluctuations of its stiffnessparameters. In the presence of strong chiral disorder the localization length diverges, implying atopological phase transition that is induced purely by disorder. As a next step we consider thecase where the couplings of the mechanical mass-spring chain vary with time in a deterministicway. Then this time-varying system can serve as a platform for transferring a topological edgemode. Going beyond the adiabatic limit, we design a protocol for the time-varying couplingsthat results in a fast and robust transfer and even more leads to amplification of the transferrededge mode. To shed light into the phenomenon of amplification in a time-varying platform, weexplore the propagation of a wave in a medium with time-periodic refractive index and with wavedynamics governed by the Mathieu equation. The wave exhibits transient amplification due to thenon normal nature of the propagator matrix and we provide numerical evidence that the globalamplifying features are provided merely by the monodromy matrix
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Obeidat, Huthaifa A. N. "Investigation of Indoor Propagation Algorithms for Localization Purposes: Simulation and Measurements of Indoor Propagation Algorithms for Localization Applications using Wall Correction Factors, Local Mean Power Estimation and Ray Tracing Validations." Thesis, University of Bradford, 2018. http://hdl.handle.net/10454/17385.
Abstract:
The objective of this work is to enhance the awareness of the indoor propagation behaviour, by a set of investigations including simulations and measurements. These investigations include indoor propagation behaviour, local mean power estimation, proposing new indoor path loss model and introducing a case study on 60 GHz propagation in indoor environments using ray tracing and measurements.
A summary of propagation mechanisms and manifestations in the indoor environment is presented. This comprises the indoor localization techniques using channel parameters in terms of angle of arrival (AOA), time of arrival (TOA) and received signal strength (RSS). Different models of path loss, shadowing and fast fading mechanisms are explored. The concept of MIMO channels is studied using many types of deterministic channel modelling such as Finite Difference Time Domain, Ray tracing and Dominant path model.
A comprehensive study on estimating local average of the received signal strength (RSS) for indoor multipath propagation is conducted. The effect of the required number of the RSS data and their Euclidian distances between the neighbours samples are investigated over 1D, 2D and 3D configurations. It was found that the effect of fast fading was reduced sufficiently using 2D horizontal’s arrangement with larger spacing configuration.
A modified indoor path loss prediction model is presented namely effective wall loss model (EWLM). The modified model with wall correction factors is compared to other indoor path loss prediction models using simulation data (for 2.4, 5, 28, 60 and 73.5 GHz) and real-time measurements (for 2.4 and 5 GHz). Different operating frequencies and antenna polarizations are considered to verify the observations. In the simulation part, EWLM shows the best performance among other models. Similar observations were recorded from the experimental results.
Finally, a detailed study on indoor propagation environment at 60 GHz is conducted. The study is supported by Line of Sight (LoS) and Non-LoS measurements data. The results were compared to the simulated ones using Wireless-InSite ray tracing software. Several experiments have confirmed the reliability of the modelling process based on adjusted material properties values from measurements.
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Kim, Hyunki. "Spatial variability in soils stiffness and strength /." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-07132005-194445/.
Abstract:
Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.Mayne, Paul, Committee Member ; Frost, David, Committee Member ; Santamarina, Carlos, Committee Chair ; Rix, Glenn, Committee Member ; Ruppel, Carolyn, Committee Member.
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El, Khatib Muammar. "Characterization of metallic and insulating properties of low-dimensional systems." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30198/document.
Abstract:
Dans cette thèse nous avons étudié des indicateurs visant à caractériser les propriétés métalliques ou isolantes de systèmes de basse dimensionnalité à partir de calculs théoriques basés sur la fonction d'onde. Ces systèmes sont intéressants car ils permettent une compréhension en profondeur des phénomènes physiques qui peuvent ensuite être extrapolés à des systèmes plus étendus. Afin de réaliser cette étude nous avons utilisé un nouvel outil basé sur la théorie de la conductivité de Kohn : le tenseur de délocalisation total ou total position spread-tensor (TPS). Ce tenseur est défini comme le second cumulant de l'opérateur position : ? = - 2. Divisé par le numéro des électrons, il diverge quand la fonction d'onde est fortement délocalisée (forte fluctuation de la position des électrons) et converge vers une valeur finie dans le cas contraire. Ainsi, la conductivité est relié à la délocalisation de la fonction d'onde. Dans ce travail, deux définitions du TPS ont été abordées : une quantité sommée sur le spin (spin-summed TPS, SS-TPS) d'une part, et une décomposition selon le spin (spin-partitioned TPS, SSP-TSP) d'autre part. Cette dernière s'est avérée être un outil très efficace pour l'étude de systèmes fortement corrélés. Au cours de la thèse, nous avons commencé par étudier plusieurs systèmes diatomiques présentant des liaisons de natures différentes à l'aide de calculs d'interaction de configurations totale (FCI). Le TPS présente alors un maximum dans une zone précédant la rupture de liaison avant de converger asymptotiquement vers les valeurs atomiques, comme la consistance de taille du tenseur le laissait présager. Dans le cas de systèmes pour lesquels l'état électronique présente un croisement évité, le TPS diverge, mettant ainsi en évidence la forte délocalisation de la fonction d'onde. Le SS-TPS est donc un indicateur de choix pour suivre la nature de la liaison chimique. Nous avons ensuite considéré des systèmes à valence mixte de type II pour lesquels l'état fondamental présente un double-puits de potentiel avec un croisement évité avec le premier état excité. Il est donc nécessaire ici d'utiliser un traitement multi-configurationnel. Deux systèmes modèles ont ainsi été étudiés : i) deux di- mères H2 en interaction faible au niveau FCI et ii) un composé du type spiro au niveau CAS-SCF (à l'aide d'un code que nous avons implémenté dans Molpro). Dans les deux cas, le TPS présentait un maximum très marqué dans la région du croisement évité, signature d'une forte mobilité électronique. Nous nous sommes également intéressés à trois types de chaines d'atomes d'hydrogène : i atomes équidistants ii) chaines dimérisées à longueur de liaison H2 fixée et iii) chaines dimérisées. Tant le SS-TPS que le SP-TPS montrent des comportements différents selon le type de chaine considérée. Les premières ont un caractère métallique et une délocalisation de spin prononcée dans le régime fortement corrélé. Les secondes sont de nature isolante avec une délocalisation limitée. Les chaines dimérisées, quant à elle, dissocient très rapidement vers un état isolant mais avec une forte délocalisation de spin. Ces chaines demi-remplies ont aussi été traitées à l'aide d'hamiltonien de Hubbard et de Heisenberg. Nous avons ainsi pu rationaliser le comportement des SS-TPS et SP-TPS en variant le rapport de l'intégrale de saut et de la répulsion électron- électron (-t/U) entre sites adjacents. Le caractère ferromagnétique/anti-ferromagnétique a également pu être suivi en modifiant la valeur de la constante de couplage J dans le cas fortement corrélé. Finalement, ces indicateurs ont été mis en oeuvre pour des polyacenes cycliques. Dans ce cas, le TPS a permis de comprendre la nature des fonctions d'onde de l'état fondamental obtenues au niveau CAS-SCF et NEVPT2I carried out a theoretical study to characterize metallic and insulating properties of low-dimensional systems using wave function methods. Low-dimensional systems are particularly important because they allow an understanding that can be extrapolated to higher dimensional systems. We have employed a new tool based on the theory of conductivity of Kohn that we have named: total position-spread tensor (TPS). The TPS is defined as the second moment cumulant of the total position operator: ? = - 2 . The tensor divided by the number of electrons diverges when the wave function is delocalized (high fluctuation of electrons' positions), and it takes finite values for localized ones. In this way, the electrical conductivity is related to the proper delocalization of the wave function. In addition, the tensor can be divided in spin-summed (SS-TPS) and spin-partitioned tensors (SP-TPS). The latter one becomes a powerful tool to the study of strongly correlated systems. In this dissertation, we started to investigate at full configuration interaction (FCI) level diatomic molecules showing different types of bond. The TPS presented a marked maximum before the bond was broken and in the asymptotic limit one recovers the TPS values of isolated atoms (size consistency). For the case of diatomic systems showing avoided-crossing electronic states, the TPS diverges evidencing the high delocalization of the wave function. Therefore, the SS-TPS is capable of monitoring and characterizing molecular wave functions. We considered mixed-valence systems that are often distinguished by a double-well potential energy surface presenting an avoided-crossing. Thus, such a configuration possesses a strongly multireference nature involving at least two states of the same symmetry. Two different systems were investigated: i) two weakly interacting hydrogen dimers that were investigated at Full CI level, and ii) a spiro like molecule where the TPS tensor was evaluated in a CAS-SCF state-averaged wave function using our implementation of the SS- TPS formalism in MOLPRO. We found that the tensor's component in the direction of the electron transfer (ET) shows a marked maximum in the avoided-crossing region, evidencing the presence of a high electron mobility. The formalisms of the SS- and SP-TPS was applied to one dimensional systems composed by three types of half-filled hydrogen chains: i) equally-spaced chains, ii) fixed-bond dimerized chains, and iii) homothetic dimerized chains. Both the SS- and SP-TPS showed different signatures associated to the three types of systems. Equally-spaced chains have metallic wave functions and a high spin delocalization in the strongly correlated regime. In contrast, fixed-bond dimerized chains have an insulating character and a restricted spin delocalization. Finally, homothetic dimerized chains dissociate very quickly which renders them in the insulating state but with a high spin delocalization. We also studied half-filled chains by using the Hubbard and the Heisenberg Hamiltonians. On the one hand, we were able to depict the response of the SS- and SP-TPS by varying the ratio between the hopping and electron-electron repulsion (-t/U parameter) of topological connected sites. On the other hand, the ferromagnetic and anti-ferromagnetic character of the wave functions were evaluated by varying the coupling constant (J) in the strongly correlated systems. A theoretical study of closed polyacenes (PAH) structures was performed at CAS-SCF and NEVPT2 level. Our methodology for choosing the active space using the Hückel Hamiltonian was able to characterize the ground state of the systems that indeed fulfilled the Ovchinnikov rule. Finally, we applied the SS-TPS to understand the nature of the wave functions of these PAHs
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Denechaud, Vincent. "Vers une étude spectroscopique de la transition d'Anderson." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLO002/document.
Abstract:
Ce mémoire résume les travaux d'une thèse portant sur le transport et la localisation d'Anderson d'ondes de matière ultra-froide en milieu désordonné. C'est un travail expérimental visant à l'étude de la transition d'Anderson séparant les états d'énergie d'une particule quantique placée dans un potentiel désordonné selon deux phases : des états localisés, et des états diffusifs.Dans un premier temps, on rappellera les concepts fondamentaux permettant de comprendre les effets de localisation des ondes, et notamment leur interprétation en terme d'interférences. Ensuite, on donnera une description globale du dispositif expérimental permettant de préparer les nuages d'atomes ultra-froids servant de source d'ondes quantiques de matière, et de générer la figure de tavelures optique (speckle en anglais) jouant le rôle de potentiel désordonné pour les atomes.A l'issue de ce travail introductif, les notions de localisation introduites précédemment seront appliquées au transport d'atomes froids dans un speckle. Un bref état de l'art des expériences d'atomes froids portant sur la transition d'Anderson permettra de dessiner les limites en terme de contrôle de l'énergie des états peuplés par les atomes. Ces limitations permettront alors de motiver la mise en place d'une nouvelle méthode expérimentale dite "spectroscopique" permettant un contrôle complet par un opérateur extérieur de l'énergie des atomes placés le désordre.Le concept de fonction spectrale sera alors présenté comme outil fondamental permettant de caractériser les états d'énergie et de calibrer la fiabilité en énergie de la méthode spectroscopique. Enfin, des résultats expérimentaux portant sur la mesure de fonctions spectrales par cette nouvelle méthode spectroscopique viendront attester qu'il serait effectivement possible d'étudier la transition d'Anderson avec une résolution en énergie bien supérieure aux expériences précédentesThis manuscript summarizes the work of a thesis on Anderson's localization and transport of ultra-cold matter waves in disordered media. This is an experimental work aiming to study the Anderson transition separating the energy states of a quantum particle placed in a disordered potential into two phases: localized states and diffusive states.First, we will recall some fundamental concepts about wave localization and how such phenomenon is linked with some interference effects. Then, we will give a global description of the experimental set-up allowing to prepare the ultra-cold atomic samples used as a source of quantum matter waves, and to generate the speckle field used as disordered potential for the atoms.At the end of this introductory work, the concepts of localization introduced previously will be applied to the transport of cold atoms in a speckle field. A brief state of the art of cold-atom experiments dealing with the Anderson transition will allow us to set the limits of these works in terms of energy control on the atomic states. These limitations will then motivate the implementation of a new experimental "spectroscopic" method allowing a complete control of the energy of the atoms placed in disorder.The concept of spectral function will then be presented as a fundamental tool for characterizing energy states and for calibrating the energy reliability of the spectroscopic method. Finally, the experimental results on the measurement of spectral functions by this new spectroscopic method will show that it would be indeed possible to study the Anderson transition with a much higher energy resolution than the previous experiments
26
Amiot, Nicolas. "Design of simulation platform joigning site specific radio propagation and human mobility for localization applications." Phd thesis, Université Rennes 1, 2013. http://tel.archives-ouvertes.fr/tel-00971809.
Abstract:
This thesis focuses on the development of tools and methods dedicated for ultra wide band (UWB) localization systems in indoor environment. The thesis work was conducted within the European FP7 project Where2, about the cooperative localization in cellular networks. Data from a measurement campaign conduct during the project are used to validate the proposed algorithms. This thesis is divided in four parts : The first part is focused on the description of an original raytraing tool based on a graph description. In order to be compliant with the requirement of a mobile simulation, a new concept of rays signature enabling incremental computation, and a vectorized formalism for processing rays are described and implemented. The second part is focused on the indoor localization techniques, where a novel technique based on interval analysis approaches is presented and compared to alternative techniques. Advantageously using this approach, a specific processing based on an hypothesis testing method using received power observations to resolve ambiguities appearing in under determined localization problems is described. A third part describes different aspects of the dynamic platform. In particular a realistic mobility model based on ''steering behaviors'', a graph description of the network scene and an inter agents communication protocol are detailed. The fourth section uses measured data obtained from an heterogeneous measurement campaign to validate both the developed software platform and the proposed localization algorithms.
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Hildebrand, William Kurt. "Ultrasonic waves in strongly scattering disordered media: understanding complex systems through statistics and correlations of multiply scattered acoustic and elastic waves." American Physical Society, 2014. http://hdl.handle.net/1993/30843.
Abstract:
Ultrasonic wave transport in strongly scattering, disordered media is investigated via analysis of the multiply-scattered transmitted field. Measurements of transverse confinement, statistics, and correlations of the intensity were performed on an aluminum mesoglass, where aluminum beads were brazed together to form a porous slab sample. Comparison of the transverse confinement measurements with the self-consistent theory of localization was used to identify and locate a mobility edge in the sample at f = 1.1011 MHz, enabling a measurement of the critical exponent nu characterizing the Anderson transition, nu ~ 1.6–2. Infinite-range C0 correlations were observed, and observed to grow dramatically near the mobility edge, along with the C2 and C3 correlations. Measurements of the multifractal exponent Delta_2 were able to confirm the link between C0 correlations and Anderson localization. Experiments using the aluminum mesoglass with ethanol-filled pores showed evidence of two nearly-independent propagating modes, one of which appears to be characterized by a strongly renormalized diffusion coefficient. The density of states and level spacing statistics were investigated using a different mesoglass, constructed by sintering glass beads percolated on a random lattice. Direct measurements of these quantities were obtained by cutting small samples of this mesoglass, allowing individual vibrational modes to be resolved. The density of states showed a plateau extending well into the expected Debye regime, and evidence of a Boson peak was observed at low frequencies. The level spacing statistics indicated that transport in the frequency ranges measured was on the diffusive side of the mobility edge, showing agreement with the predictions of the GOE from random matrix theory. The dynamics of a suspension of bubbles were investigated using phase-based Diffusing Acoustic Wave Spectroscopy, where phase correlations were found to give additional information beyond traditional field- and intensity-based correlation measurements.October 2015
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Rodrigues, Cunha Leandro. "Robust bandgaps for vibration control in periodic structures." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD060.
Abstract:
Dans cette thèse, une méthodologie simple pour trouver des bandes interdites robustes est présentée. Quatre cellules unitaires différentes sont utilisées comme exemples numériques pour des modèles infinis et finis. Les deux premiers sont liés aux zones d'atténuation créées pour les ondes longitudinales en utilisant des cellules unitaires de masse et ressort et de barres. La méthode Matrice de Transfert est utilisée pour modéliser la cellule unitaire. Avec cette méthode, il est possible d'obtenir les réponses en fréquence, en utilisant une méthode spectrale, et des constantes de dispersion, en résolvant un problème a valeur propre. Les paramètres physiques et géométriques les plus influents sont déterminés en effectuant une analyse de sensibilité aux dérivées partielles et aux différences finies à travers un modèle infini. Dans ce cas, pour le deuxième exemple, la section de la demi-cellule est considérée comme une variable stochastique, représentée par une fonction densité de probabilité pour une analyse probabiliste. Le troisième exemple concerne les bandes interdites pour les ondes de flexion utilisant des cellules unitaires de poutres. Dans ce cas, la méthode habituelle de Matrice de Transfert ne peut pas être utilisée pour obtenir une réponse de structures finies en basse fréquence en raison de la présence de matrices mal conditionnées. Par conséquent, une méthode récursive est utilisée pour éviter la multiplication de matrices. Une analyse expérimentale est également réalisée pour ce cas, mais considérant que la longueur de la moitié des cellules unitaire comme incertaine. Le dernier exemple est un treillis périodique considérée avec et sans propriétés intelligentes. La cellule unitaire de cette structure en treillis peut avoir des membres passifs et actifs. À cause de la complexité de ce type de cellule, la méthode des éléments finis est utilisée. Cependant, ce type de structure ne présente pas de ruptures d'impédance suffisamment fortes pour ouvrir des bandes interdites même avec la présence de sous-structures répétitives. En vertu de cela, huit scénarios sont étudiés en considérant l'introduction de masse concentrée dans les articulations et les actionneurs piézoélectriques dans les circuits shunt résonants qui sont considérés comme stochastiques pour des cas spécifiques. À la fin, les résonances internes sont analysées à l'aide d'un modèle plus précis. Pour chaque modèle de structure, une simulation de Monte Carlo avec Latin Hypercube est effectuée, les distinctions entre les zones d'atténuation incertaines correspondantes pour les modèles finis et infinis sont exposées et la relation avec les modes localisés est clarifiée. Ces résultats suggèrent que les modèles finis ont une bande interdite plus large que les modèles infinis en considérant les incertitudes. En d'autres termes, les incertitudes entre les cellules voisines se compensent et les structures finies sont naturellement plus robustes. Enfin, l'effet de l'augmentation du niveau d'incertitude, en faisant varier un coefficient stochastique, est analysé et le concept de bande interdite robuste est présentéIn this thesis, a simple methodology to find robust bandgaps is presented. Four different periodic structures are used as numerical examples for infinite and finite models. The first two are related to attenuation zones created for longitudinal waves using spring-mass and stepped rod unit cells. The Transfer Matrix method is used to model the unit cell. With this method, it is possible to obtain the frequency responses, using a spectral method, and dispersion constants, solving an eigenvalue prob-lem. The most influential physical and geometrical parameters are determined by performing partial derivative and finite difference sensitivity analysis through an infinite model. Therein, for the second example, the cross-section area of half-cell is considered as a stochastic variable represented by a probability density function with specific deviation properties for a probabilistic analysis. The third example concerns the bandgaps for flexural waves using stepped beams unit cells. For this case, the classical Transfer Matrix method cannot be used to obtain finite structures response in low frequency because of the presence of ill-conditioned matrices. Therefore, a recursive method termed Translation Matrix, which avoid matrix multiplication, is used and the corresponding probabilistic analysis is per-formed using the half-cell thickness as a random variable. An experimental analysis is also performed for this case, but considering half-cell length as uncertain. The last example is a periodic truss that is considered with and without smart components. The unit cell of this lattice structure can present pas-sive and active members. As long as the type of unit cell is more complex, the finite element method is used. However, this kind of structure does not have impedance mismatches strong enough to open bandgaps although the presence of repetitive substructures. In virtue of this, eight scenarios are inves-tigated considering the introduction of concentrated mass on joints and piezoelectric actuators in reso-nant shunt circuit which are considered as stochastic for specific cases. For each structure model, a Monte Carlo Simulation with Latin Hypercube sampling is carried out, the distinctions between the corresponding uncertain attenuation zones for finite and infinite models are exposed and the relation with localized modes is clarified. These results lead to conclude that the finite models present a larger stop zone considering stochastic parameters than infinite models. In other words, the uncertainties be-tween neighbors’ cells compensate each other and the finite structures is naturally more robust. Final-ly, the effect of increasing the uncertainty level, by varying a stochastic coefficient, is analyzed and the concept of robust band gap is presented
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Prat, Tony. "Localisation d'Anderson avec des atomes froids : dynamique dans le désordre et perspectives avec des modèles chaotiques." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066232/document.
Abstract:
Dans cette thèse, nous étudions théoriquement plusieurs effets liés à la localisation d'Anderson, dans le contexte des atomes froids. Dans les systèmes d'atomes froids, le désordre est généralement créé à l'aide d'une figure de tavelure optique. Dans la première partie de la thèse, nous discutons des spécificités de ces potentiels optiques, et nous nous intéressons en particulier aux propriétés spectrales. Les expériences usant de l'interaction lumière-matière offrent d'intéressantes possibilités. Dans ce cadre, nous considérons dans une deuxième partie de la thèse l'étalement d'un paquet d'ondes atomique, initialement lancé avec une vitesse non nulle dans un potentiel désordonné. Nous trouvons qu'après un mouvement balistique, le centre de masse du paquet subit une rétro-réflection et retourne lentement à sa position initialle, se comportant comme un boomerang. Nous introduisons ensuite les interactions inter-atomiques dans une troisième partie. Nous considèrons des gaz dilués de bosons condensés, et traitons les interactions au niveau champ moyen. Plusieurs situations sont étudiées numériquement, en particulier le boomerang quantique, et l'étalement dynamique -- à la fois en impulsion et en énergie -- d'ondes de matière préparées en ondes planes. Dans la dernière partie de la thèse, nous montrons que des modèles chaotiques offrent des perspectives intéressantes pour l'étude de la localisation d'Anderson. D'une part, nous présentons des éléments probants en faveur d'un kick rotor sans spin dans l'ensemble symplectique. D'autre part, le réexamen de modèles communément étudiés de kick rotors quasi-périodiques révèle des résultats intrigantsThis thesis theoretically investigates several effects related to Anderson localization, focusing on the context of disordered and chaotic cold-atomic systems. In cold-atomic systems, optical speckle patterns are often used to create the disorder. The resulting potentials felt by the atoms differ from Gaussian random potentials, commonly assumed in the description of condensed-matter systems. In the first part of the thesis, we discuss their specificities, with an emphasis on the spectral properties. Atom-optics experiments offer interesting possibilities, such as the possibility to directly probe the atoms inside the disordered potential. In view of these possibilities, we consider in the second part of the thesis the spreading of matter wave packets initially launched with a non-zero velocity. We find that after an initial ballistic motion, the packet center-of-mass experiences a retroreflection and slowly returns to its initial position, mimicking a boomerang. Atom-atom interactions are then introduced in a third part. We consider dilute condensed bosonic gases, and treat the interactions at the mean-field (Gross-Pitaevskii) level. Various situations are studied numerically, in particular the quantum boomerang scenario, and the dynamical spreading both in momentum and energy of matter waves prepared as plane waves. In the last part, we show that chaotic models offer interesting prospects for the study of Anderson localization. On the one hand, we present strong evidences in favor of a spinless kicked rotor in the sympletic ensemble. On the other hand, a second look at a commonly studied quasi-periodically modulated kicked rotor reveals intriguing results
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Koirala, Remun. "Fonctions conjointes de localisation et de communication dans les réseaux 5G en bandes millimétriques." Thesis, Rennes 1, 2020. http://www.theses.fr/2020REN1S005.
Abstract:
Dans ce travail de thèse, on se proposait d’explorer les synergies inhérentes entre services de radiolocalisation et de communication au sein de systèmes sans fil en bandes millimétriques (mm-Wave). Ces derniers sont actuellement pressentis pour couvrir les besoins de la cinquième génération (5G) de réseaux en termes de débits et de charges utiles. Un objectif général consistait alors à montrer comment ces deux fonctions pouvaient s’avérer mutuellement bénéfiques. Tout d'abord, nous avons étudié comment la formation de faisceau (au sens du pré-codage) pouvait contribuer à améliorer les performances de localisation, pour des systèmes multi-porteuses mono- et multi-utilisateurs. En particulier, en s’appuyant sur les performances théoriques de localisation au sens de la limite inférieure de Cramér-Rao (CRLB), nous avons montré qu'il était possible, au moyen d’une formation de faisceau optimisée, d’améliorer l'estimation de variables radio intermédiaires, telles que le délai, l'angle de départ (AoD) et/ou l'angle d'arrivée (AoA) du signal transmis, et in fine, l’estimation de la position et/ou de l’orientation du mobile. Nous avons ensuite considéré le problème de la coexistence des deux services, en envisageant différentes stratégies de budgétisation et de partage de ressources, en temps et en fréquence. A cette occasion, nous avons illustré la présence de compromis non-triviaux entre les performances de localisation et de communication. Nous avons alors proposé des schémas d’allocation de ressources et d’optimisation des faisceaux (en termes de largeur et/ou d’alignement), permettant d’assurer conjointement le meilleur niveau de performances pour les deux services. Nous avons enfin étudié la possibilité d’exploiter explicitement l’information de localisation ainsi acquise, en particulier pour l'accès initial, l’estimation de canaux multi-trajets, ou encore la localisation et la cartographie simultanées (SLAM). En comparaison d’approches plus conventionnelles, nous avons montré comment les performances de telles applications pouvaient être améliorées en termes de précision, de latence et/ou de complexité calculatoireIn this thesis, we investigate different facets of localization and communication services motivated by the symbiosis between them in the millimeter wave (mm-Wave) context for the fifth generation (5G) of wireless communications. Our aim is twofold: first, show that this duality is mutually beneficial to both services, and second, aim towards a co-existence to capture these benefits in order to bring forth mm-Wave as a strong contender for 5G. First, we look into how beamforming, an integral part of mm-Wave communications, can aid in improving the localization performance. After characterizing the localization performance in terms of Cramer-Rao lower bound (CRLB), we show that with optimized beamforming, the estimation of localization variables (delay, angle of departure (AoD) and angle of arrival (AoA)) improves. Then we consider the problem of co-existence of the two services together in the same system while sharing time and frequency resources. We study the non-trivial trade-off between the performances of the two services during this resource budgeting. Then, relying on this trade-off, we design an optimal resource allocation scheme while also optimizing the beamwidth in order to ascertain high performance in terms of both localization and communication. In the same context, we also look into different applications of this improved location information namely initial access, channel estimation and simultaneous localization and communication (SLAM). We show that the related performances improve in terms of quality, latency and/or complexity in comparison to the conventional methods
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Costa, Alex Emanuel Barros. "Deslocalização de ondas acústicas em sistemas unidimensionais não periódicos." Universidade Federal de Alagoas, 2011. http://www.repositorio.ufal.br/handle/riufal/1663.
Abstract:
In this master degree thesis we numerically study the propagation of acoustic waves in one-dimensional non-periodic medium. We focus on two kinds of medium: (1) a media with scale-free long-range correlated elasticity distribution and (2) medium with an aperiodic pseudo-random elasticity distribution. In the first case, the random elasticity distribution is assumed to have a power spectrum S (k) ~ 1 / kª. By using a transfer matrix method we solve the discrete version of the scalar wave equation and comput the location length. In addition, we apply a second-order infinite-difference method for both the time and spatial variables and study the nature of the waves that propagate in the chain. Our numerical data indicate the presence of extended acoustic waves for high degree of correlations. In contrast with local correlation, we numerically demonstrated that scale-free correlations promote a stable phase of free acoustic waves in the thermodynamic limit. In the another case, elasticity distribution was generated by using a sinusoidal function whose phase varies as a power law, φ α nv, where n labels the positions along the media. By considering again a discrete one-dimensional version of the wave equation and a matrix recursive reformulation we compute the location length within the band of allowed frequencies. Our numerical data indicates the presence of extended acoustic waves with non-zero frequency for a sufficient degree of aperiodicity.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Nesta dissertação de mestrado estudamos numericamente a propagação de ondas acústicas em meios não periódicos unidimensionais. Nós nos concentramos em dois tipos de meios: (1) com distribuição da elasticidade possuindo correlação de longo alcance e (2) com distribuição aperiódica pseudo-aleatória. No primeiro caso, a elasticidade da distribuição aleatória é assumida ter um espectro de potência S(k)~1/kª. Usando o método de matriz de transferência resolvemos a versão discreta da equação da onda escalar e calculamos o comprimento de localização. Além disso, aplicamos o método de diferença infinita de segunda ordem para as variáveis temporal e espacial e estudamos a natureza das ondas que se propagem na cadeia. Nossos dados numéricos indicam a presença de ondas acústicas estendidas para alto grau de correlação. Em contraste com correlação local, demonstramos numericamente que correlações de livre-escala promovem uma fase estável com ondas acústicas livres no limite termodinâmico. No outro caso, a distribuição das constantes elásticas foram geradas usando uma função senoidal cuja faze varia como uma lei de potência, ϕ α nv , onde n rotula as posições ao longo da rede. Ao considerar novamente uma versão unidimensional discretizada da equação de onda e uma reformulação da matriz recursiva nós calculamos o comprimento de localização dentro da faixa de frequências permitidas. Nossos dados indicam a presença de ondas acústicas propagantes com frequência diferente de zero para um suficiente grau de aperiodicidade.
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Rüdiger, Benz. "Localization of notches with lamb waves." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/21510.
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Razo, López Luis Alberto. "Localisation des ondes électromagnétiques au-delà d'Anderson : rôle des corrélations, des symétries et de la topologie." Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ5013.
Abstract:
Au sens large, le terme de localisation ondulatoire fait référence à un phénomène où les ondes sont spatialement confinées dans de petites régions de l'espace sans la contrainte de barrières matérielles. Dans cette thèse, nous étudions (analytiquement, numériquement et expérimentalement) différents mécanismes physiques collectifs pour localiser spatialement, et donc pour contrôler les ondes électromagnétiques. En particulier, nous nous concentrons sur le rôle des potentiels non corrélés et corrélés, ainsi que sur des effets topologiques pour réaliser le confinement des ondes. Les études analytiques et numériques sont réalisées dans le cadre d'une approche récente de la modélisation de la localisation d'Anderson appelée théorie du paysage de localisation. D'autre part, des expériences sont réalisées à l'aide d'une plate-forme micro-ondes composée de petits cylindres diélectriques placés à l'intérieur d'une cavité constituée de deux plaques métalliques. La cavité met en œuvre un système d'ondes propagatives, où nous pouvons contrôler efficacement la permittivité locale au moyen des cylindres agissant comme des diffuseurs, ou comme un système de de liaison forte analogique, où, dans ce cas, les cylindres diélectriques jouent le rôle de résonateurs. Dans un premier temps, nous étendons le champ d'application de l'approche du paysage de localisation à une large classe de systèmes de liaison forte unidimensionnels et bidimensionnels en présence d'un désordre non corrélé, où des fonctions propres localisées apparaissent en bord de bande. Nous démontrons comment la théorie du paysage de localisation est capable de prédire avec précision non seulement les emplacements, mais aussi les énergies des fonctions propres localisées dans les régimes de basse et de haute énergie. Ensuite, en utilisant notre cavité expérimentale comme système de propagation, nous réalisons des expériences de transport de micro-ondes dans des réseaux planaires bidimensionnels. Les expériences sont réalisées sur un réseau désordonné et sur une spirale de Vogel apériodique à partir de laquelle nous caractérisons les structures modales électromagnétiques dans l'espace réel. Nos résultats révèlent que les systèmes apériodiques possèdent une grande variété de modes à longue durée de vie - avec des décroissances spatiales gaussiennes, exponentielles et en loi de puissance - qui sont capables de survivre même dans un environnement tridimensionnel. Ceci est confirmé par différentes quantités de transport telles que la densité d'états, le temps de décroissance caractéristique et la conductance de Thouless qui sont également accessibles expérimentalement. À l'inverse, nous montrons que les états propres dans les milieux désordonnés traditionnels sont toujours limités à des décroissances radiales exponentielles avec d'importantes fuites dès que les systèmes ne sont plus bidimensionnels. Enfin, nous utilisons la configuration expérimentale de liaison forte pour étudier la propagation des états hélicoïdaux topologiques. En particulier, nous analysons expérimentalement un ensemble de structures en nid d'abeille construites à l'aide d'un réseau triangulaire avec une cellule unitaire hexagonale, qui sont caractérisées par l'invariant topologique Z_2. En accédant à la structure modale dans l'espace réel et à la densité d'états, nos résultats révèlent la possibilité d'ouvrir une bande interdite topologique, peuplée d'états de bord localisés en bordure de la structure. Nous démontrons la nature unidirectionelle de la propagation de ces états de bord hélicoïdaux contre-propagatifs. Dans l'ensemble, nos résultats démontrent qu'il est possible de modéliser, de contrôler et de localiser les ondes électromagnétiques non seulement du point de vue d'Anderson, mais aussi au-delà. Grâce aux différents jalons que nous avons posés, nous ouvrons une voie vers l'hypothétique localisation d'Anderson des ondes électromagnétiques tridimensionnellesIn a broad sense, the term wave localization refers to a phenomenon where waves are spatially confined in small regions of the space without any bounding material barriers.In this Thesis, we investigate (analytically, numerically and experimentally) different physical collective mechanisms to spatially localize, and therefore, to control electromagnetic waves. Specifically, we focus on the role of uncorrelated and correlated potentials, as well as of topological effects to achieve wave confinement. Analytical and numerical studies are accomplished in the framework of a recent approach in the modeling of Anderson localization called localization landscape theory. On the other hand, experiments are performed using a microwave platform composed by small dielectric cylinders placed inside a cavity made of two metallic plates. The cavity implements a propagative wave system, where we can efficiently control the local permittivity by means of the cylinders acting as scatterers, or as an analogic tight-binding system, where, in this case, the dielectric cylinders play the role of resonators.First, we extend the scope of the localization landscape approach to a wide class of one and two dimensional tight-binding systems in the presence of uncorrelated disorder, where localized eigenfunctions appear in both band-edges. We demonstrate how the landscape theory is able to predict accurately not only the locations, but also the energies of localized eigenfunctions in the low- and high-energy regimes. Later, by using our experimental cavity as a propagative system, we perform microwave transport experiments in two dimensional planar arrays. Experiments are carried out on a disordered lattice and on an aperiodic Vogel spiral from where we characterize the electromagnetic modal structures in real space. Our results reveals that aperiodic systems can carry a rich variety of long-lived modes—with Gaussian, exponential, and power law spatial decays—which are able to survive even in a three-dimensional environment. This is supported by different transport quantities such as the density of states, the characteristic decay time, and the Thouless conductance that are also experimentally accessible. On the contrary, we show that the eigenstates in traditional disordered media are always limited to exponential radial decays with leaking features beyond two-dimensions.Finally, we use the experimental tight-binding configuration to investigate the propagation of topological helical states. Particularly, we experimentally analyze a set of honeycomb-like structures built using a triangular lattice with an hexagonal unit cell, which are characterized by the Z_2 topological invariant. By recovering the modal structure in real space and the density of states, our results reveal the possibility to open a topological gap, dwelt by edge states that lives in the border of the structure.We demonstrate the unidirectional counterpropagative features of such helical edge states.Taken together, our results demonstrate that it is possible to model, control and localize electromagnetic waves not only within, but beyond Anderson's conception. Thanks to the crossroads we have taken, we have mapped out an itinerary that brings us closer to the main avenue leading perhaps to Anderson localization of three dimensional electromagnetic waves
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Agred, Kahina. "Localisation automatique des aciers et caractérisation de la teneur en eau du béton armé par radar double-offset à grand rendement." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30194/document.
Abstract:
Les budgets destinés à l'entretien et à la réparation du patrimoine bâti étant très élevés, il est primordial de mettre en place des techniques fiables de suivi et de diagnostic des ouvrages pour réduire ces dépenses. Il existe de nombreuses techniques de contrôle non destructif (CND) employant différentes technologies à des coûts plus ou moins abordables. Elles permettent la détermination des propriétés du matériau renseignant sur l'état de l'ouvrage, et la détection d'inclusions ou de défauts dans le béton. Ces techniques sont connues pour leur rapidité de mise en œuvre et leur grand rendement sur site, mais aussi par leur caractère non intrusif qui permet de limiter le nombre de prélèvements. Cela les rend pertinentes pour la surveillance et l'inspection du patrimoine bâti, puisqu'elles peuvent fournir des informations liées à l'état d'un ouvrage sans l'endommager. Dans un ouvrage en béton armé, la couche d'enrobage des armatures est la plus sujette à de multiples agressions. C'est dans cette couche qu'ont lieu la majorité des réactions chimiques qui causent la dégradation de l'ouvrage, puisqu'avec la présence d'eau cet enrobage est considéré comme la zone de pénétration, de transfert et de fixation des agents agressifs présents dans l'environnement de l'ouvrage, favorisant par exemple la corrosion des armatures. La teneur en eau du béton est considérée comme un facteur très important dans le diagnostic des structures en béton armé, puisqu'elle conditionne le développement de la plupart des pathologies liées à la dégradation des structures affectant ainsi la durabilité du béton. La localisation avec précision des aciers de renforcement est également un élément primordial pour le diagnostic, mais également pour vérifier la conformité des dispositions constructives par rapport aux plans d'exécution. Dans ces travaux de recherche, nous utilisons la technologie radar pour la caractérisation géométrique et physique des éléments en béton armé, cela par le développement d'un algorithme automatique, rapide et sans prérequis. Les objectifs de cette étude sont : de localiser en surface et en profondeur les aciers du premier lit d'armatures, et de déterminer la vitesse de propagation des ondes électromagnétiques dans le béton d'enrobage pour estimer sa teneur en eauSince budgets for the maintenance and repair of built heritage structures are very high, it is essential to implement reliable techniques for monitoring and diagnosis of structures to reduce these costs. There are many non-destructive testing (NDT) methods employing different technologies which are more or less expensive. The NDT methods allow the determination of the properties of the material giving also information about the condition of the structure, and the detection of inclusions or defects in the concrete. These techniques are known for their fast implementation and their high performance in-situ, but also by their non-intrusive nature, which makes it possible to limit the number of samples for destructive assessment. This makes them relevant for the monitoring and inspection of built heritage, since they can provide information related to the condition of a structure without any damage. In a reinforced concrete structure, the concrete cover is the most prone to multiple aggressions. The majority of the chemical reactions which cause the degradation of the structure occur in this layer, since with the presence of water this coating is considered as the penetration, transfer and fixing zone of aggressive agents present in the environment of the structure, thus enhancing for example the corrosion of the reinforcements. The water content of concrete is considered as a very important factor in the diagnosis of reinforced concrete structures, since it conditions the development of most pathologies related to structural degradation, thus affecting the durability of concrete. The precise location of the reinforcement in the construction is also an essential element for the diagnosis, but also to check the conformity of the constructive dispositions with the execution plans. In this research, we use GPR technology for the geometrical and physical characterization of reinforced concrete elements, through the development of an automatic algorithm, fast and without pre-requisites. The objectives of this study are to locate the rebars of the first reinforcing layer in the plane and depth and to determine the propagation velocity of the electromagnetic waves in the coating layer to estimate the water content of concrete
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Laptyeva, Tetyana V. "Nonlinear waves in random lattices: localization and spreading." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-107881.
Abstract:
Heterogeneity in lattice potentials (like random or quasiperiodic) can localize linear, non-interacting waves and halt their propagation. Nonlinearity induces wave interactions, enabling energy exchange and leading to chaotic dynamics. Understanding the interplay between the two is one of the topical problems of modern wave physics. In particular, one questions whether nonlinearity destroys localization and revives wave propagation, whether thresholds in wave energy/norm exist, and what the resulting wave transport mechanisms and characteristics are. Despite remarkable progress in the field, the answers to these questions remain controversial and no general agreement is currently achieved.
This thesis aims at resolving some of the controversies in the framework of nonlinear dynamics and computational physics. Following common practice, basic lattice models (discrete Klein-Gordon and nonlinear Schroedinger equations) were chosen to study the problem analytically and numerically. In the disordered linear case all eigenstates of such lattices are spatially localized manifesting Anderson localization, while nonlinearity couples them, enabling energy exchange and chaotic dynamics. For the first time we present a comprehensive picture of different subdiffusive spreading regimes and self-trapping phenomena, explain the underlying mechanisms and derive precise asymptotics of spreading. Moreover, we have successfully generalized the theory to models with spatially inhomogeneous nonlinearity, quasiperiodic potentials, higher lattice dimensions and arbitrary nonlinearity index.
Furthermore, we have revealed a remarkable similarity to the evolution of wave packets in the nonlinear diffusion equation. Finally, we have studied the limits of strong disorder and small nonlinearities to discover the probabilistic nature of Anderson localization in nonlinear disordered systems, demonstrating the finite probability of its destruction for arbitrarily small nonlinearity and exponentially small probability of its survival above a certain threshold in energy. Our findings give a new dimension to the theory of wave packet spreading in localizing environments, explain existing experimental results on matter and light waves dynamics in disordered and quasiperiodic lattice potentials, and offer experimentally testable predictions.
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Grataloup, Géraldine Léonie 1979. "Localization of nonlinear water waves over a random bottom." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/16918.
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003.Includes bibliographical references (p. 87-90).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
by Géraldine Léonie Grataloup.
S.M.
37
Larcher, Marco. "Localization and spreading of matter waves in disordered potentials." Doctoral thesis, Università degli studi di Trento, 2013. https://hdl.handle.net/11572/367883.
Abstract:
In this thesis we address relevant problems of the physics of quantum disordered systems from a numerical and theoretical point of view, with specific attention to the connection of our findings with ultracold atomic gases experiments. We concentrate on two main issues: the interplay between localization and interaction in disordered systems and the problem of localization in correlated random potentials.
The first problem is investigated considering the expansion of a weakly interacting Bose gas in a bichromtic optical lattice. We observe that interaction has a destructive effect on the disorder-induced localization and leads to a subdiffusive expansion of the atomic gas. By comparing three characteristic energy scales of the system one can identify three different spreading regimes: weak chaos, strong chaos and self-trapping. The spreading behaviour in these regimes is predicted theoretically and verified numerically. We also interpreted existing experimental data on the basis of our findings and showed that there is a qualitative agreement between our numerical simulations and experiments.
The second problem is investigated proposing a new model of correlated disorder that can be implemented experimentally using ultracold dipolar gases. We show that this model is characterized by the presence of both short and long range correlations. We study the localization properties of the model and highlight the role played by short and long range correlations in the determination of those properties. In particular we show that when short-range correlations are dominant, extended states can appear in the spectrum. The effect of long-range correlations is instead to restore localization over the whole spectrum and lead to counterintuitive behaviours of the localization length. More precisely, depending on the localization regime they can enhance or reduce the localization length at the centre of the band.
38
Larcher, Marco. "Localization and spreading of matter waves in disordered potentials." Doctoral thesis, University of Trento, 2013. http://eprints-phd.biblio.unitn.it/889/2/Thesis_Larcher.pdf.
Abstract:
In this thesis we address relevant problems of the physics of quantum disordered systems from a numerical and theoretical point of view, with specific attention to the connection of our findings with ultracold atomic gases experiments. We concentrate on two main issues: the interplay between localization and interaction in disordered systems and the problem of localization in correlated random potentials.
The first problem is investigated considering the expansion of a weakly interacting Bose gas in a bichromtic optical lattice. We observe that interaction has a destructive effect on the disorder-induced localization and leads to a subdiffusive expansion of the atomic gas. By comparing three characteristic energy scales of the system one can identify three different spreading regimes: weak chaos, strong chaos and self-trapping. The spreading behaviour in these regimes is predicted theoretically and verified numerically. We also interpreted existing experimental data on the basis of our findings and showed that there is a qualitative agreement between our numerical simulations and experiments.
The second problem is investigated proposing a new model of correlated disorder that can be implemented experimentally using ultracold dipolar gases. We show that this model is characterized by the presence of both short and long range correlations. We study the localization properties of the model and highlight the role played by short and long range correlations in the determination of those properties. In particular we show that when short-range correlations are dominant, extended states can appear in the spectrum. The effect of long-range correlations is instead to restore localization over the whole spectrum and lead to counterintuitive behaviours of the localization length. More precisely, depending on the localization regime they can enhance or reduce the localization length at the centre of the band.
39
Podbielski, Jan. "Localization, coupling and interference of spin waves in ferromagnetic nanostructures." München Verl. Dr. Hut, 2008. http://d-nb.info/988228904/04.
40
Lyu, Pengfei. "Numerical and Experimental Indoor Channel Analysis for LOS-NLOS Identification at 60 GHz." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS186.
Abstract:
Avec l’émergence des objets connectés, les applications potentielles requérant la localisation indoor ou la continuité de localisation réapparaissent et suscitent, depuis quelques années déjà, de nombreuses études et recherches. La norme IEEE 802.11ad, opérant autour de 60 GHz, est un candidat potentiel pour résoudre le problème de localisation tout en permettant une communication très haut débit. Cette norme prometteuse pose toutefois un problème lié au caractère directionnel de la propagation, particulièrement sujette au blocage des ondes directes. En effet aucun calcul de coordonnées spatiales ne peut être entrepris si les signaux traités ne proviennent pas d’une propagation en ligne directe (LOS). Cette limitation induit par conséquent une nouvelle problématique qui consiste à s’assurer, dans les signaux en jeu, de la présence du LOS. Cela revient aussi à identifier les composantes NLOS issues des réflexions multiples. L'identification des trajets NLOS fait appel aux méthodes d’apprentissage de faisceaux qui permettent d’accéder au spectre angulaire d’un canal. Une première classification, par cluster est d’abord opérée, puis une analyse statistique utilisant les moments d’ordre 4 est conduite sur chaque cluster. L’exploitation de cette signature « kurtosis » permet une seconde classification discriminant les clusters issus de contributions LOS ou NLOSWith the emergence of connected objects, potential applications requiring indoor location or location continuity have reappeared and have been the subject of numerous studies and researches for several years now. The IEEE 802.11ad standard, operating around 60 GHz, is a potential candidate to solve the localization problem while allowing high data rate communication. However, this promising standard is particularly subject to blockage of direct waves. Indeed, no calculation of spatial coordinates can be undertaken if the processed signals do not come from a line of sight propagation (LOS). This limitation consequently induces a new problem which consists in ensuring, in the signals of interest, the presence of the LOS contribution. It also comes down to identifying the NLOS components brought by the multipath phenomenon. NLOS path identification uses beam-learning methods that provide access to the angular spectrum of a channel. A first classification, by clusters, is carried out, then a statistical analysis using the fourth standardized moment, is conducted on each cluster. The use of this "kurtosis" signature allows a second classification discriminating clusters induced by LOS contributions from those induced by NLOS contributions
41
Torrents, Verdaguer Genís. "New insights into holography from supersymmetric localization." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/398760.
Abstract:
Maldacena's conjecture, often known as the holographic duality or the AdS/CFT correspondence, proposes an equivalence between gravitational theories in a hyperbolic space of a certain dimensionality and gauge theories living on its boundary. The manner in which this connection is established makes the duality specially remarkable: both sides are thought to describe the very same string theoretic physics, but the validity regimes of the two descriptions are disjoint, and one expects either framework to be in its regime of validity the appropriate way to effectively reexpress the physics of the other. The nonintersection of these applicability regimes makes the duality very useful, but also very hard to verify and materialize.
Notice the potential implications of this framework for theoretical physics: one direction, strongly coupled quantum field theories become in a certain regime describable as semiclassical gravitational spacetimes, while on the other direction certain string theories without semiclassical background obtain a clean and workable definition as gauge field theories. As a consequence of these facts, holography has played a central role in research since its appearance, almost two decades ago.
However, despite numerous efforts devoted to its characterization, general understanding of the duality has only been majoritarely achieved around the regimes where the gravitational description becomes semiclassical. Consequently, the gauge-to-gravity direction of the duality is far less exploited than the opposite one, despite its conceptual relevance.
Having available results for strongly coupled gauge theories would be of a great help in addressing holography in this comparatively underdevelopped direction, and they would set a fertile ground to test, refine and understand the holographic conjecture. These type of predictions are hard to come by, but not inexistent: non-renormalized magnitudes constitute their most paradygmatical example, and recently different techniques have obtained exact results at arbitrary coupling for specific obserable sectors.
This thesis studies specifically one of these techniques, known as supersymmetric localization, and its role in shoring AdS/CFT. In particular, it restricts its analysis to a specific type of theory: Lagrangian N. = 2 SYM, and for specific results: half-BPS Wilson circular loops. Several interesting insights are put forward by its results.
A first observation is that the exact functional dependence we obtain from localization offer a guide on how to extend holographic predictions from their validity regime to a finite gauge range which produces plausible results, although a great care has to be taken in this process.
Complementarily, the study of this parametrical dependence for gauge N. = 4 theories with gauge Lie algebras presents two suggestive patterns: On the one hand, 't Hooft's topological expansion presents, at least for charges in fundamental representations, an underlying structure that relates sectors with different number of crosscaps among themselves. On the other hand, the matrix model structure obtained in the localization process can be interpreted in terms of a fermionic quantum mechanics, which at the 't Hooft limit matches the "bubbling geometry" structure of Lin, Lunin and Maldacena, but which persists at finite gauge group range.
Finally, the comparison of localization results within a more general type of construction is pre-sented. The specific set of theories considered contains both examples with semiclassical holographic duals and examples where this type of geometry is precluded. Supersymmetric field predictions in this case differentiate both groups with qualitatively different behaviours in the matrix model. This suggests a possible connection between the matrix model structure and the semiclassical spacetime codification in the dual field theory. Similar observations have been made in the literature.
This thesis, therefore, explicits a wide list of suggestions for holography that are motivated by lo-calization results in different regimes, even though the latter have been severely restricted to particular examples.Aquesta tesi estudia les lliçons que hom pot extreure, des del punt de vista de la dualitat hologràfica, de l'anomenada localització supersimètrica. La conjunció d'aquests dos formalismes ha estat utilitzada anteriorment per verificar els resultats del primer, però aquesta tesi va un pas més enllà i qüestiona fins a quin punt els resultats exactes oferts per la localització poden ser útils per extendre l'aplicabilitat de l'holografia gravitatòria. L'anàlisi d'aquests resultats en diferents règims posa de relleu diversos aspectes d'interès. Una primera observació és que la dependència funcional exacta que hom pot llegir dels resultats de la localització ofereixen, quan són utilitzats amb cura, una guia per estendre les prediccions holgràfiques des del seu règim de validesa a un rang de gauge finit mitjançant la qual es pot obtenir resultats plausibles. Complementàriament, l'estudi d'aquesta dependència paramètrica per teories maximalment super-simètriques amb grups de Lie clàssics presenta dos patrons suggerents: d'una banda, el desenvolupa-ment de 't Hooft té, almenys per càrregues en representació fonamental, una estructura subjacent que relaciona els sectors amb diferent nombre d'inversions topològiques entre ells. De l'altra, l'estructura dels models de matrius obtinguts en localitzar pot ésser interpretada en termes d'una mecànica quàntica de fermions, que encaixa amb l'estructura dels "universos de bombolles" de Lin, Lunin i Maldacena al límit de 't Hooft, però que manté la seva forma a qualsevol rang finit. Per últim, es compara resultats de localització entre ells en un marc de teories més generals, en què algunes admeten dual semiclàssic i d'altres no és d'esperar que ho facin. Les prediccions supersimètriques en aquest cas presenten diferències qualitatives que permeten distingir aquests dos grups de teories, suggerint una possible connexió entre la codificació de l'estructura gravitatòria a la teoria de camps i el model de matrius que s'obté en localitzar que complementa altres indicis en el mateix sentit obtinguts a la literatura. En definitiva, doncs, es posa de manifest en aquesta tesi que, tot i haver restringit l'anàlisi a sectors i observables específics, els resultats obtinguts per mitjà de la localització supersimètrica ofereixen una rica gamma de suggeriments sobre l'estructura hologràfica.
42
Glaister, A. J., Amri R. Al, and David P. Spicer. "Talent management: managerial sense making in the wake of Omanization." Routledge, 2018. http://hdl.handle.net/10454/17818.
Abstract:
YesWe examine how managers in Oman make sense of localization policies (Omanization) through their use of talent management (TM). Through an institutional logics (IL) lens, it is possible to examine how organizations confront institutional complexity and understand the interplay between state, market and societal logics. The paper analyses twenty-six interviews with managers in the Petroleum and Banking sector and is the first to examine TM within the context of Omanization using a layered, IL perspective. The paper finds that punitive state logics encourage organizations to focus on the societal wellbeing of their TM measures and inspires a sense of corporate social responsibility. Yet, the market logic dictates a stratified and differentiated approach that manages impressions of inclusivity while safeguarding organizational interests.
43
Draper, Brandon J. "Long-range outdoor monocular localization with active features for ship air wake measurement." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122504.
Abstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 85-87).
Monocular pose estimation is a well-studied aspect of computer vision with a wide array of applications, including camera calibration, autonomous navigation, object pose tracking, augmented reality, and numerous other areas. However, some unexplored areas of camera pose estimation remain academically interesting. This thesis provides a detailed description of the system hardware and software that permits operation in one application area in particular: long-range, precise monocular pose estimation in feature-starved environments. The novel approach to pose extraction uses special hardware, including active LED features and a bandpass-interference optical filter, to significantly simplify the image processing step of the Perspective-n-Point (PnP) problem. The PnP problem describes the calculation of pose from n extracted image points corresponding to n known 3D world points. The proposed application method operates in tandem with a tethered unmanned aerial vehicle (UAV) and mobile ground control station (GCS). The integrated localization and flight system serves as a platform for future U.S. Navy air flow research. Indoor tests at the RAVEN flight space of MIT's Aerospace Controls Lab and outdoor tests at a grass strip runway demonstrate the system's efficacy in providing an accurate and precise pose estimate of the UAV relative to the mobile GCS.
"Sources of funding for the project and my educational pursuits at MIT: Creare, LLC., the Small Business Technology Transfer (STTR), and the Office of Naval Research"--Page 5
by Brandon J. Draper.
S.M.
S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics
44
Kuehnert, Julian. "Simulation of High Frequency Seismic Waves generated by Rockfalls on Real Topography." Thesis, Université de Paris (2019-....), 2019. https://theses.md.univ-paris-diderot.fr/KUEHNERT_Julian_va2.pdf.
Abstract:
Les risques d'éboulements doivent être évalués et surveillés afin de prévenir les pertes de vies humaines et dommages aux infrastructures. A cet égard, il est important de créer des catalogues d'événements et de comprendre la dynamique des éboulements. Les ondes sismiques peuvent être utiles à cette fin, car elles transmettent des informations précieuses sur l'événement. Elles sont générées lorsque des éboulements touchent le sol et peuvent être utilisées pour détecter, classer et localiser des événements. Plus encore, on peut déduire des propriétés des éboulements telles que leur volumes et leur comportement dynamique. Cependant, les signaux sismiques hautes fréquences (>1Hz) sont mal compris. En effet, ils sont associés à des sources sismiques complexes qui sont réparties dans l'espace et peuvent varier rapidement dans le temps. De plus, les ondes sismiques hautes fréquences sont susceptibles d'être diffusées et diffractées en raison des interactions avec les hétérogénéités du sol ou la topographie de surface. Cette thèse franchit une étape importante dans la compréhension des signaux sismiques hautes fré-quences des éboulements en simulant la propagation des ondes sismiques en utilisant la méthode des éléments spectraux (SEM) avec des profils de vitesse réalistes et des topographies de surface 3D. L'influence de la topographie sur le champ des ondes sismiques est étudiée. On constate que l'ampli-fication induite par la topographie est sensiblement différente entre les sources situées en profondeurs et celles situées en surface. En effet, les ondes de surface générées par des sources peu profondes sont exposées à une diffusion et à une diffraction constantes lorsqu'elles se déplacent le long de la surface. La désintégration de l'énergie le long de la surface est étudiée pour différents modèles de vitesse et des équations sont dérivées pour calculer rétroactivement l'énergie sismique totale rayonnée par la source. Ceci est intéressant du fait du lien entre l'énergie sismique et le volume d'éboulement. Afin de tenir compte des effets topographiques, il est proposé un facteur de correction qui peut être introduit dans le calcul de l'énergie. Les signaux sismiques générés par les éboulements du cratère Dolomieu du Piton de la Fournaise, à La Réunion, sont analysés. Les sismogrammes synthétiques sont utilisés pour identifier et interpréter les signaux observés qui sont générés par des impacts uniques. L'influence de la topographie sur les formes d'onde est démontrée et la sensibilité avec l'emplacement et la direction de la source est évaluée. Les caractéristiques du signal telles que les amplitudes et le contenu fréquentiel sont expliquées sur la base de la théorie du contact de Hertz. De plus, les rapports spectraux entre stations, calculés à partir des signaux sismiques d'éboulement, sont considérés comme caractéristiques de la position de la source. La comparaison avec les rapports spectraux simulés suggère qu'ils sont dominés par la propagation le long de la topographie plutôt que par le mécanisme de la source. Sur la base de ces résultats, une méthode est proposée pour la localisation des éboulements à l'aide de rapports énergétiques simulés entre stations. La méthode est appliquée pour localiser les éboulements dans le cratère de Dolomieu. La mise en œuvre de la méthode implique une fenêtre temporelle glissante qui permet une application simple sur des signaux sismiques continus. L'accent est mis sur la capacité de la méthode à surveiller l'activité des éboulements en temps réelRockfall hazard has to be evaluated and monitored in order to prevent loss of life and infrastructure. In this regard it is important to create event catalogs and understand rockfall dynamics. Seismic waves can help for this purpose as they carry valuable information of the event. They are generated when rockfalls impact the ground and can be used to detect, classify and locate events. Beyond that, rockfall properties such as their volume and their dynamic behavior can be inferred. Yet, high frequency seismic signals (>1Hz) are poorly understood. This is because they are associated to complex seismic sources which are spatially distributed and can rapidly vary over time. On top of this, high frequency seismic waves are prone to be scattered and diffracted due to interactions with soil heterogeneities or surface topography. This thesis takes an important step forward to enhance understanding of high frequency rockfall seismic signals by simulating seismic wave propagation on domains with realistic velocity profiles and 3D surface topographies using the Spectral Element Method (SEM). The influence of the topography on the seismic wave field is investigated. It is found that topography induced amplification is substantially different between deep sources and sources located at the surface. This is because surface waves generated by shallow sources are exposed to constant scattering and diffraction when traveling along the surface. The energy decay along the surface is investigated for different velocity models and equations are derived to back-calculate the total seismic energy radiated by the source. This is of interest as the rockfall seismic energy is related to the rockfall volume. In order to account for topography effects, a correction factor is proposed which can be introduced in the energy calculation. Observed seismic signals generated by rockfall at Dolomieu crater on Piton de la Fournaise volcano, La Réunion, are analyzed. Synthetic seismograms are used to identify and interpret observed signals generated by single impacts. The influence of topography on the waveforms is demonstrated and the sensitivity on source location as well as source direction is evaluated. Signal characteristics such as amplitudes and frequency content are explained based on Hertz contact theory. Additionally, inter-station spectral ratios computed from rockfall seismic signals are shown to be characteristic of the source position. Comparison with simulated spectral ratios suggest that they are dominated by the propagation along the topography rather than the mechanism of the source. Based on these findings, a method is proposed for the localization of rockfalls using simulated inter-station energy ratios. The method is applied to localize rockfalls at Dolomieu crater. The implementation of the method involves a sliding time window which allows a straightforward application on continuous seismic signals. The potential of the method to monitor rockfall activity in real-time is emphasized
45
Harley, Joel B. "Data-Driven, Sparsity-Based Matched Field Processing for Structural Health Monitoring." Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/392.
Abstract:
This dissertation develops a robust, data-driven localization methodology based on the integration of matched field processing with compressed sensing ℓ1 recovery techniques and scale transform signal processing. The localization methodology is applied to an ultrasonic guided wave structural health monitoring system for detecting, locating, and imaging damage in civil infrastructures. In these systems, the channels are characterized by complex, multi-modal, and frequency dispersive wave propagation, which severely distort propagating signals. Acquiring the characteristics of these propagation mediums from data represents a difficult inverse problem for which, in general, no readily available solution exists. In this dissertation, we build data-driven models of these complex mediums by integrating experimental guided wave measurements with theoretical wave propagation models and ℓ1 sparse recovery methods from compressed sensing. The data-driven models are combined with matched field processing, a localization framework extensively studied for underwater acoustics, to localize targets in complex, guided wave environments. The data-driven matched field processing methodology is then refined, through the use of the scale transform, to achieve robustness to environmental variations that distort guided waves. Data-driven matched field processing is experimentally applied to an ultrasound structural health monitoring system to detect and locate damage in aluminum plate structures.
46
Kotol, Martin. "Neuronové modelování elektromegnetických polí uvnitř automobilů." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2018. http://www.nusl.cz/ntk/nusl-390291.
Abstract:
Disertační práce se věnuje využití umělých neuronových sítí pro modelování elektromagnetických polí uvnitř automobilů. První část práce je zaměřena na analytický popis šíření elektromagnetických vlny interiérem pomocí Nortonovy povrchové vlny. Následující část práce se věnuje praktickému měření a ověření analytických modelů. Praktická měření byla zdrojem trénovacích a verifikačních dat pro neuronové sítě. Práce se zaměřuje na kmitočtová pásma 3 až 11 GHz a 55 až 65 GHz.
47
Rayanov, Kristian. "Coherence of Matter and Light Waves in Localizing Media." Master's thesis, Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-88015.
Abstract:
The phenomena of coherence and localization have gained enormous research interest during the past decades. Theoretical predictions of localization have been confirmed recently in a variety of experiments in the fields of condensed matter physics and optics. We consider the widely employed model of the one-dimensional discrete nonlinear Schrödinger equation which allows for the investigation of localization of linear and nonlinear waves. We establish a generic connection between coherence and localization by showing that localized solutions are necessarily coherent. The effects of a loss of coherence are investigated numerically by applying random dephasing. The onset of a diffusive spreading regime is observed as a generic feature for persistent dephasing, which eventually destroys localization. After finite integration times maximal delocalization is achieved for a certain rate and strength of dephasing, resulting from the competition between destroying the initial wave packet on the one hand and not suppressing spreading too much on the other. When dephasing is switched off at a certain time, a loss or gain of coherence in linear wave packets directly corresponds to delocalization or stronger localization. This leads to stable partially coherent wave packets. In contrast, localization of nonlinear waves after dephasing is connected to the efforts of establishing complete coherence, at least for asymptotically long times. On intermediate time scales, however, various interesting partially coherent regimes can be observedDie Phänomene von Kohärenz und Lokalisierung haben sich in den letzten Jahrzehnten zum Schwerpunkt zahlreicher Forschungsinteressen entwickelt. Erst kürzlich wurden theoretische Vorhersagen von Lokalisierung in verschiedensten Experimenten in den Bereichen der Festkörperphysik und Optik bestätigt. In dieser Arbeit wird das häufig angewendete Modell der eindimensionalen diskreten nichtlinearen Schrödingergleichung betrachtet, welches die Untersuchung der Lokalisierung von linearen und nichtlinearen Wellen ermöglicht. Eine generelle Verbindung zwischen Kohärenz und Lokalisierung wird gezeigt, wonach lokalisierte Lösungen notwendigerweise kohärent sind. Die Auswirkungen eines Verlustes von Kohärenz werden numerisch durch Anwendung unterschiedlicher Methoden eines zufälligen Dephasierens untersucht. Ein permanentes Dephasieren führt stets zum Auftreten eines diffusiven Regimes, welches letztlich die Zerstörung von Lokalisierung bedingt. Nach einer endlichen Integrationszeit wird jedoch eine maximale Delokalisierung nur durch eine bestimmte Rate und Stärke des Dephasierens bewirkt, resultierend aus einem Wettstreit zwischen möglichst schneller Zerstörung des ursprünglichen Wellenpaketes auf der einen Seite und nicht zu starker Behinderung des Zerfließens auf der anderen. Wird das Dephasieren nach einer bestimmten Zeit abgeschaltet, so entspricht ein folglicher Verlust oder Zugewinn an Kohäarenz in einem linearen Wellenpaket direkt einem Verlust oder Zugewinn von Lokalisierung. Dabei treten im allgemeinen stabile teil-kohärente Wellenpakete auf. Im Gegensatz dazu ist Lokalisierung nichtlinearer Wellenpakete stets mit den Bemühungen verbunden, vollständige Kohärenz wiederherzustellen, zumindest für asymptotisch lange Zeiten. Auf mittleren Zeitskalen können jedoch verschiedene interessante teil-kohärente Strukturen beobachtet werden
48
Carrara, Matteo. "Fourier-based design of acoustic transducers." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54925.
Abstract:
The work presented in this thesis investigates novel transducer implementations that take advantage of directional sensing and generation of acoustic waves. These transducers are conceived by exploiting a Fourier-based design methodology. The proposed devices find application in the broad field of Structural Health Monitoring (SHM), which is a very active research area devoted to the assessment of the structural integrity of critical components in aerospace, civil and mechanical systems. Among SHM schemes, Guided Waves (GWs) testing has emerged as a prominent option for inspection of plate-like structures using permanently attached piezoelectric transducers.
GWs-based methods rely on the generation and sensing of elastic waves to evaluate structural integrity. They offer an effective method to estimate location, severity and type of damage. It is widely acknowledged among the GWs-SHM community that effective monitoring of structural health is facilitated by sensors and actuators designed with ad hoc engineered capabilities. The objective of this research is to design innovative piezoelectric transducers by specifying their electrode patterns in the Fourier domain. Taking advantage of the Fourier framework, transducer design procedures are outlined and tailored to relevant SHM applications, such as (i) directional actuation and sensing of GWs, (ii) simultaneous sensing of multiple strain components with a single device, and (iii) estimation of the location of impact sites on structural components. The proposed devices enable significant reductions in cost, hardware, and power requirements for advanced SHM schemes when compared to current technologies.
49
Schulte, Walter B. III. "The frequency response, impulse response, and transfer function of an ocean waveguide." Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1516.
Abstract:
Approved for public release, distribution is unlimitedIn this thesis, the ocean was modeled as a waveguide with an ideal pressure - release surface, and an ideal rigid bottom. The ocean waveguide was then treated as a linear, time - invariant, space - variant (TISV) filter or communication channel. The filter is time - invariant because no motion was modeled and because the properties of the ocean were assumed to be constant. The filter is space - variant because of the presence of the two boundaries, that is, the ocean surface and ocean bottom. This thesis investigates the ocean as a linear TISV filter by evaluating 1) the complex frequency response, 2) the impulse response, and 3) the transfer function of the ocean with respect to depth. It is shown that the TISV impulse response of the ocean contains information that can be used to help localize a target in range and whether the target is above or below the receiver. Computer simulation results were obtained by evaluating the three filter functions for several different test cases.
Ensign, United States Navy
50
Stellin, Filippo. "Anderson localization in interacting quantum systems." Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7004.
Abstract:
Dans cette thèse nous étudions au niveau théorique le comportement des particules quantiques (électrons, atomes, photons, etc.) se mouvant dans un milieu désordonné et sujets à la localisation d’Anderson. Pour des particules non interagissantes, le spectre de l’énergie peut posséder un ou plus points critiques, où les fonctions d’onde étendues deviennent localisées, en donnant lieu à une transition de phase métal-isolant connue comme Transition d’Anderson.Une question fondamentale est si et comment les transitions d’Anderson survivent dans des systèmesquantiques interagissants. Dans cet ouvrage, nous étudions un modèle simple décrivant le cas de deux particules dans un réseau désordonné et sujettes à des interactions mutuelles à courte portée. En combinant des simulations numériques sur une grande échelle avec des techniques à la fonction de Green, nous montrons que les transitions d’Anderson à deux particules se produisent en trois dimensions et explorons le diagramme de phase dans l’espace de l’énergie, du désordre et de l’interaction.Cette dernière présente une structure riche, caractérisée par un double renfoncement de la limite de phase, engendrée par la compétition entre les états de diffusion et les états liés de la paire. Nous prouvons aussi que les annonces précédentes concernant l’apparition de transitions d’Anderson en deux dimensions étaient essentiellement dues à des effets de taille finie.Un deuxième problème que nous abordons dans cette thèse est celui de l’occurrence de transitions métal-isolant en deux dimensions pour une particule en la présence d’un potentiel spatialement corrélé et sujette à des interactions spin-orbite, modélisées par les couplages Rashba-Dresselhaus. On éclaire que, indépendamment des propriétés du désordre, il y a un régime où l’énergie critique dépend linéairement du paramètre de désordre. La pente et l’intercepte sont étudiées en voisinage du point de symétrie spin-hélice persistant, dans lequel la symétrie SU(2) est restaurée et la transition métal-isolant disparaîtIn this thesis we theoretically investigate the behaviour of quantum particles (electrons, atoms, photons, etc.) moving in a random medium and undergoing Anderson localization. For noninteractingparticles, the energy spectrum can possess one or more critical points, where the nature of the single-particle wavefunctions changes from extended to localized leading to a undergoes a metal-insulator phase transition, also known as Anderson transition.A fundamental question is whether and how Anderson transitions survive in interacting quantum systems. Here we study a minimal model of two particles moving in a disordered lattice and subject to short-range mutual interactions. By combining large-scale numerics with Green’s functions techniques, we show that two-particle Anderson transitions do occur in three dimensions and explore the phase diagram in the space of energy, disorder and interaction strength. The latter presents a rich structure, characterized by a doubly reentrant behavior, caused by the competition between scattering and bound states of the pair. We also show that previous claims of 2D Anderson transitions of the pair are essentially due to finite-size effects.A second problem that we address in this thesis is the occurrence of 2D metal-insulator transitions for a single particle in the presence of a spatially correlated potential and subject to spin-orbit interactions, described by Rashba-Dresselhaus couplings. We illustrate that, irrespective of the properties of the disorder, there is a regime where the critical energy depends linearly on the disorder strength. The slope and the intercept are studied in the vicinity of the spin-helix point, where the SU(2) symmetry is restored and the 2D metal-insulator transition disappears