5,453 research outputs found
Audio-visual multi-modality driven hybrid feature learning model for crowd analysis and classification
The high pace emergence in advanced software systems, low-cost hardware and decentralized cloud computing technologies have broadened the horizon for vision-based surveillance, monitoring and control. However, complex and inferior feature learning over visual artefacts or video streams, especially under extreme conditions confine majority of the at-hand vision-based crowd analysis and classification systems. Retrieving event-sensitive or crowd-type sensitive spatio-temporal features for the different crowd types under extreme conditions is a highly complex task. Consequently, it results in lower accuracy and hence low reliability that confines existing methods for real-time crowd analysis. Despite numerous efforts in vision-based approaches, the lack of acoustic cues often creates ambiguity in crowd classification. On the other hand, the strategic amalgamation of audio-visual features can enable accurate and reliable crowd analysis and classification. Considering it as motivation, in this research a novel audio-visual multi-modality driven hybrid feature learning model is developed for crowd analysis and classification. In this work, a hybrid feature extraction model was applied to extract deep spatio-temporal features by using Gray-Level Co-occurrence Metrics (GLCM) and AlexNet transferrable learning model. Once extracting the different GLCM features and AlexNet deep features, horizontal concatenation was done to fuse the different feature sets. Similarly, for acoustic feature extraction, the audio samples (from the input video) were processed for static (fixed size) sampling, pre-emphasis, block framing and Hann windowing, followed by acoustic feature extraction like GTCC, GTCC-Delta, GTCC-Delta-Delta, MFCC, Spectral Entropy, Spectral Flux, Spectral Slope and Harmonics to Noise Ratio (HNR). Finally, the extracted audio-visual features were fused to yield a composite multi-modal feature set, which is processed for classification using the random forest ensemble classifier. The multi-class classification yields a crowd-classification accurac12529y of (98.26%), precision (98.89%), sensitivity (94.82%), specificity (95.57%), and F-Measure of 98.84%. The robustness of the proposed multi-modality-based crowd analysis model confirms its suitability towards real-world crowd detection and classification tasks
Magnetic Control of Acoustic Resonators and Metamaterials
The magneto-elastic coupling between spin and acoustic excitations offers an excellent opportunity to combine, within the same signal processing devices, the magnetic tuneability and re-programmability inherent to magnonics with the energy efficiency of phononics. Relevant recent studies have focused on characterisation of the interaction strength in magnetoacoustic devices and on the excitation and detection of an acoustically induced magnetic signal. The work presented in this thesis focuses on the magnetic control of propagating acoustic waves, with the aim to reveal and to characterise the signatures of the magneto-elastic coupling in reflection and transmission of acoustic waves in magnetoacoustic metamaterials, and to explore their tuning using magnetic stimuli
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Fourth Order Dispersion in Nonlinear Media
In recent years, there has been an explosion of interest in media bearing quarticdispersion. After the experimental realization of so-called pure-quartic solitons, asignificant number of studies followed both for bright and for dark solitonic struc-tures exploring the properties of not only quartic, but also setic, octic, decic etc.dispersion, but also examining the competition between, e.g., quadratic and quarticdispersion among others.In the first chapter of this Thesis, we consider the interaction of solitary waves ina model involving the well-known φ4 Klein-Gordon theory, bearing both Laplacian and biharmonic terms with different prefactors. As a result of the competition ofthe respective linear operators, we obtain three distinct cases as we vary the modelparameters. In the first the biharmonic effect dominates, yielding an oscillatoryinter-wave interaction; in the third the harmonic effect prevails yielding exponen-tial interactions, while we find an intriguing linearly modulated exponential effectin the critical second case, separating the above two regimes. For each case, wecalculate the force between the kink and antikink when initially separated with suf-ficient distance. Being able to write the acceleration as a function of the separationdistance, and its corresponding ordinary differential equation, we test the corre-sponding predictions, finding very good agreement, where appropriate, with thecorresponding partial differential equation results. Where the two findings differ,we explain the source of disparities. Finally, we offer a first glimpse of the interplayof harmonic and biharmonic effects on the results of kink-antikink collisions andthe corresponding single- and multi-bounce windows.In the next two Chapters, we explore the competition of quadratic and quar-tic dispersion in producing kink-like solitary waves in a model of the nonlinearSchroedinger type bearing cubic nonlinearity. We present 6 families of multikink so-lutions and explore their bifurcations as a prototypical parameter is varied, namelythe strength of the quadratic dispersion. We reveal a rich bifurcation structure forthe system, connecting two-kink states with ones involving 4-, as well as 6-kinks.The stability of all of these states is explored. For each family, we discuss a “lowerbranch” adhering to the energy landscape of the 2-kink states (also discussed inthe previous Chapter). We also, however, study in detail the “upper branches”bearing higher numbers of kinks. In addition to computing the stationary statesand analyzing their stability at the PDE level, we develop an effective particle the-ory that is shown to be surprisingly efficient in capturing the kink equilibria and normal (as well as unstable) modes. Finally, the results of the bifurcation analysisare corroborated with direct numerical simulations involving the excitation of thestates in a targeted way in order to explore their instability-induced dynamics.While the previous two studies were focused on the one-dimensional problem,in the fourth and final chapter, we explore a two-dimensional realm. More specif-ically, we provide a characterization of the ground states of a higher-dimensionalquadratic-quartic model of the nonlinear Schr ̈odinger class with a combination of afocusing biharmonic operator with either an isotropic or an anisotropic defocusingLaplacian operator (at the linear level) and power-law nonlinearity. Examiningprincipally the prototypical example of dimension d = 2, we find that instabilityarises beyond a certain threshold coefficient of the Laplacian between the cubic andquintic cases, while all solutions are stable for powers below the cubic. Above thequintic, and up to a critical nonlinearity exponent p, there exists a progressivelynarrowing range of stable frequencies. Finally, above the critical p all solutionsare unstable. The picture is rather similar in the anisotropic case, with the dif-ference that even before the cubic case, the numerical computations suggest aninterval of unstable frequencies. Our analysis generalizes the relevant observationsfor arbitrary combinations of Laplacian prefactor b and nonlinearity power p.We conclude the thesis with a summary of its main findings, as well as with anoutlook towards interesting future problem
Ultrafast Optical Control of Order Parameters in Quantum Materials
Developing protocols to realize quantum phases that are not accessible thermally and to manipulate material properties on demand is one of the central problems of modern condensed matter physics. Impulsive electromagnetic stimulus provides an extensive playground not only to exert desired control over the material macroscopic properties but also to optically detect the underlying microscopic mechanisms. Two indispensable components form the cornerstone to realize these goals: a meticulous comprehension of light-induced phenomena and a suitable and versatile platform.
Abundant photoinduced phenomena emerge upon light irradiation. A collective oscillation of order parameter can be launched and probed in the weak perturbation regime; further increasing light intensity can transiently modulate the free-energy landscape, inducing a suppression, enhancement, reversal, and switch of order parameters; in the strong non-perturbative excitation regime, the system can be driven nonlinearly with microscopic coupling parameters modified. Understanding these light driven emergent phenomena lays the foundation of optical control and novel functionalities.
Quantum materials, embodying a large portfolio of topological and strongly correlated compounds, afford an exceptional venue to realize optical control. Owing to the complex interplay between the charge, spin, orbital, and lattice degrees of freedom, a rich phase diagram can be generated with various phases that are selectively and independently accessible via optical perturbations. They hence offer a wealth of opportunities to not only improve our comprehension of the underlying physics but also develop the next generation of ultrafast technologies.
In Chapter I of this thesis, I will first cover a multitude of light-induced emergent phenomena in quantum materials under the framework of time-dependent Landau theory, Keldysh theory, and Floquet theory, and then introduce several canonical microscopic models to quantitatively rationalize the intra- and interactions between different degrees of freedom in quantum materials. As the necessary theoretical background is established, three main experimental techniques that have been extensively utilized in my research: time-resolved reflectivity and Kerr effect, time-resolved second harmonic generation rotational anisotropy, and coherent phonon spectroscopy will be introduced in Chapter II. In Chapter III, I will demonstrate that a light-induced topological phase transition can be engendered concomitant with an inverse-Peierls structural phase transition in elemental Te. In Chapter IV, I will describe signatures of ultrafast reversal of excitonic order in excitonic insulator candidate Ta2NiSe5 and substantiate a manipulation of the reversal as well as the Higgs mode with tailored light pulses. In Chapter V, a light-induced switch of spin-orbit-coupled quadrupolar order in multiband Mott insulator Ca2RuO4 will be introduced. In Chapter VI, a Keldysh tuning of nonlinear carrier excitation and Floquet bandwidth renormalization in strongly driven Ca2RuO4 will be covered.</p
Linear and Nonlinear Kinetic Alfv\'en Wave Physics in Cylindrical Plasmas
Kinetic Alfv\'en Waves (KAWs) are generated in magnetized space and
laboratory plasmas due to a continuous shear Alfv\'en wave (SAW) spectrum and,
unlike SAWs, are characterized by microscale perpendicular structures of the
order of the thermal ion Larmor radius. This has important consequences on
heating, acceleration and transport processes connected with KAWs.
Historically, KAWs generation by mode conversion of SAWs in laboratory plasmas
and their strong damping/absorption right after SAW mode conversion have been
investigated for plasma heating. Here, we focus on the opposite limit: a mode
converted KAW weakly absorbed in a periodic magnetized plasma cylinder. We show
that a KAW may be excited as resonant cavity mode in the region between the
magnetic axis and the SAW resonant layer generated externally by an antenna
launcher; this process is qualitatively similar to mode converted electron
Bernstein waves. In this way, large amplitude KAWs may be generated time
asymptotically with relatively small coupled antenna power. This case has
little or no relevance for plasma heating but interesting nonlinear
implications for plasma equilibrium. In particular, we demonstrate that KAWs
may generate convective cells (CCs) by modulational instability, that a
consequence of plasma nonuniformity is the azimuthal symmetry breaking due to
plasma diamagnetic effects, that the modulational instability growth rate is
enhanced over the corresponding uniform plasma limit, that the unstable
parameter space is extended, and that the cylindrical geometry causes a complex
interplay between nonlinearity and nonuniformity. As a result, we show that it
is possible to control the CC radial structures and the corresponding parallel
electric field generation not only by means of the antenna frequency but also
by fine tuning of its amplitude.Comment: 117 pages, 42 figure
Feature Papers in Compounds
This book represents a collection of contributions in the field of the synthesis and characterization of chemical compounds, natural products, chemical reactivity, and computational chemistry. Among its contents, the reader will find high-quality, peer-reviewed research and review articles that were published in the open access journal Compounds by members of the Editorial Board and the authors invited by the Editorial Office and Editor-in-Chief
Modelling, Monitoring, Control and Optimization for Complex Industrial Processes
This reprint includes 22 research papers and an editorial, collected from the Special Issue "Modelling, Monitoring, Control and Optimization for Complex Industrial Processes", highlighting recent research advances and emerging research directions in complex industrial processes. This reprint aims to promote the research field and benefit the readers from both academic communities and industrial sectors
Efficient finite element methods for solving high-frequency time-harmonic acoustic wave problems in heterogeneous media
This thesis focuses on the efficient numerical solution of frequency-domain wave propagation problems using finite element methods. In the first part of the manuscript, the development of domain decomposition methods is addressed, with the aim of overcoming the limitations of state-of-the art direct and iterative solvers. To this end, a non-overlapping substructured domain decomposition method with high-order absorbing conditions used as transmission conditions (HABC DDM) is first extended to deal with cross-points, where more than two subdomains meet. The handling of cross-points is a well-known issue for non-overlapping HABC DDMs. Our methodology proposes an efficient solution for lattice-type domain partitions, where the domains meet at right angles. The method is based on the introduction of suitable relations and additional transmission variables at the cross-points, and its effectiveness is demonstrated on several test cases. A similar non-overlapping substructured DDM is then proposed with Perfectly Matched Layers instead of HABCs used as transmission conditions (PML DDM). The proposed approach naturally considers cross-points for two-dimensional checkerboard domain partitions through Lagrange multipliers used for the weak coupling between subproblems defined on rectangular subdomains and the surrounding PMLs. Two discretizations for the Lagrange multipliers and several stabilization strategies are proposed and compared. The performance of the HABC and PML DDM is then compared on test cases of increasing complexity, from two-dimensional wave scattering in homogeneous media to three-dimensional wave propagation in highly heterogeneous media. While the theoretical developments are carried out for the scalar Helmholtz equation for acoustic wave propagation, the extension to elastic wave problems is also considered, highlighting the potential for further generalizations to other physical contexts. The second part of the manuscript is devoted to the presentation of the computational tools developed during the thesis and which were used to produce all the numerical results: GmshFEM, a new C++ finite element library based on the application programming interface of the open-source finite element mesh generator Gmsh; and GmshDDM, a distributed domain decomposition library based on GmshFEM.Cette thèse porte sur la résolution numérique efficace de problèmes de propagation d'ondes dans le domaine fréquentiel avec la méthode des éléments finis. Dans la première partie du manuscrit, le développement de méthodes de décomposition de domaine est abordé, dans le but de surmonter les limitations des solveurs directs et itératifs de l'état de l'art. À cette fin, une méthode de décomposition de domaine sous-structurée sans recouvrement avec des conditions absorbante d'ordre élevé utilisées comme conditions de transmission (HABC DDM) est d'abord étendue pour traiter les points de jonction, où plus de deux sous-domaines se rencontrent. Le traitement des points de jonction est un problème bien connu pour les HABC DDM sans recouvrement. La méthodologie proposée mène à une solution efficace pour les partitions en damier, où les domaines se rencontrent à angle droit. La méthode est basée sur l'introduction de variables de transmission supplémentaires aux points de jonction, et son efficacité est démontrée sur plusieurs cas-tests. Une DDM sans recouvrement similaire est ensuite proposée avec des couches parfaitement adaptées au lieu des HABC (DDM PML). L'approche proposée prend naturellement en compte les points de jonction des partitions de domaine en damier par le biais de multiplicateurs de Lagrange couplant les sous-domaines et les couches PML adjacentes. Deux discrétisations pour les multiplicateurs de Lagrange et plusieurs stratégies de stabilisation sont proposées et comparées. Les performances des DDM HABC et PML sont ensuite comparées sur des cas-tests de complexité croissante, allant de la diffraction d'ondes dans des milieux homogènes bidimensionnelles à la propagation d'ondes tridimensionnelles dans des milieux hautement hétérogènes. Alors que les développements théoriques sont effectués pour l'équation scalaire de Helmholtz pour la simulation d'ondes acoustiques, l'extension aux problèmes d'ondes élastiques est également considérée, mettant en évidence le potentiel de généralisation des méthodes développées à d'autres contextes physiques. La deuxième partie du manuscrit est consacrée à la présentation des outils de calcul développés au cours de la thèse et qui ont été utilisés pour produire tous les résultats numériques : GmshFEM, une nouvelle bibliothèque d'éléments finis C++ basée sur le générateur de maillage open-source Gmsh ; et GmshDDM, une bibliothèque de décomposition de domaine distribuée basée sur GmshFEM
Continuous Lebesgue measure-preserving maps on one-dimensional manifolds: a survey
We survey the current state-of-the-art about the dynamical behavior of
continuous Lebesgue measure-preserving maps on one-dimensional manifolds
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