Дисертації з теми "Localization density"
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1
Lee, Chee Sing. "Simultaneous localization and mapping using single cluster probability hypothesis density filters." Doctoral thesis, Universitat de Girona, 2015. http://hdl.handle.net/10803/323637.
Анотація:
The majority of research in feature-based SLAM builds on the legacy of foundational work using the EKF, a single-object estimation technique. Because feature-based SLAM is an inherently multi-object problem, this has led to a number of suboptimalities in popular solutions. We develop an algorithm using the SC-PHD filter, a multi-object estimator modeled on cluster processes. This algorithm hosts capabilities not typically seen with feature-base SLAM solutions such as principled handling of clutter measurements and missed detections, and navigation with a mixture of stationary and moving landmarks. We present experiments with the SC-PHD SLAM algorithm on both synthetic and real datasets using an autonomous underwater vehicle. We compare our method to the RB-PHD SLAM, showing that it requires fewer approximations in its derivation and thus achieves superior performance.En aquesta tesis es desenvolupa aquest algoritme a partir d’un filtre PHD amb un únic grup (SC-PHD), una tècnica d’estimació multi-objecte basat en processos d’agrupació. Aquest algoritme té unes capacitats que normalment no es veuen en els algoritmes de SLAM basats en característiques, ja que és capaç de tractar falses característiques, així com característiques no detectades pels sensors del vehicle, a més de navegar en un entorn amb la presència de característiques estàtiques i característiques en moviment de forma simultània. Es presenten els resultats experimentals de l’algoritme SC-PHD en entorns reals i simulats utilitzant un vehicle autònom submarí. Els resultats són comparats amb l’algoritme de SLAM Rao-Blackwellized PHD (RB-PHD), demostrant que es requereixen menys aproximacions en la seva derivació i en conseqüència s’obté un rendiment superior.
2
Heinicke, Christiane. "Lithospheric-Scale Stresses and Shear Localization Induced by Density-Driven Instabilities." Thesis, Uppsala universitet, Geofysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183725.
Анотація:
The initiation of subduction requires the formation of lithospheric plates which mostly deform at their edges. Shear heating is a possible candidate for producing such localized deformation. In this thesis we employ a 2D model of the mantle with a visco-elasto-plastic rheology and enabled shear heating. We are able to create a shear heating instability both in a constant strain rate and a constant stress boundary condition setup. For the rst case, localized deformation in our specic setup is found for strain rates of 10-15 1/s and mantle temperatures of 1300°C. For constant stress boundaries, the conditions for a setup to localize are more restrictive. Mantle motion is induced by large cold and hot temperature perturbations. Lithospheric stresses scale with the size of these perturbations; maximum stresses are on the order of the yield stress (1 GPa). Adding topography or large inhomogeneities does not result in lithospheric-scale fracture in our model. However, localized deformation does occur for a restricted parameter choice presented in this thesis. The perturbation size has little effect on the occurrence of localization, but large perturbations shorten its onset time.
3
Torab, Leili. "The forward problem of EEG source localization using Current Density Imaging." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0020/MQ53445.pdf.
4
López, Villafuerte Freddy [Verfasser]. "Localization of wireless sensor nodes based on local network density / Freddy López Villafuerte." Berlin : Freie Universität Berlin, 2010. http://d-nb.info/1024104060/34.
5
De, Santis Lorenzo. "Theory of electron Localization Function and its Applications: Surfaces, Impurities and Enzymatic Catalysis." Doctoral thesis, SISSA, 1999. http://hdl.handle.net/20.500.11767/4428.
6
Mazzarello, Riccardo. "Localization and density of states of disordered low-dimensional systems in a magnetic field." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971652023.
7
Dihidar, Souvik. "Applications of Low Density Parity Check Codes for Wiretap Channels and Congestion Localization in Networks." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13969.
Анотація:
Error control coding in some form is present in virtually every communication system today. Recently, Low Density Parity Check (LDPC) codes have been proposed along with a simple iterative decoding algorithm. These codes have been demonstrated to perform very close to the Shannon Limit. The simplicity of LDPC codes have also led to many interesting asymptotic and finite-length properties of these codes. The techniques for designing good LDPC codes over a wide variety of channels have been studied. LDPC codes are being used in a wide variety of applications, such as fading channels, Orthogonal Frequency Division Multiplexing (OFDM) systems, source compression etc. This proposal investigates the use of LDPC codes in wiretap channel systems such as quantum key distribution and for congestion localization in large networks.
Quantum Key Distribution (QKD) is secure key exchange method where the two legitimate parties first transmit information over a quantum channel, which can be eavesdropped on by the eavesdropper. The QKD system can be modeled as a special case of an wiretap channel system. An wiretap chanel system is a broadcast system, where the sender has to send a message to a legitimate party over a main channel. The wiretapper also receives the message through another channel called the wiretap channel. The sender has to code the transmitted message in such a way so that the legitimate party is able to recover the message without errors, whereas the wiretapper essentially has no information about the message. As we will see, the encoder for such a system is stochastic as opposed to a deterministic encoder in error correction coding. In this research, we propose a coding scheme using LDPC codes for such systems.
Congestion in a network occurs when some nodes receive more traffic than they can process. It leads to dropping packets and thus lowering the throughput. On the contrary, if other nodes in the network are aware of the congested nodes, new packets can be dynamically routed through less congested routes. We developed a congestion detection mechanism wherein a few high priority probe packets are routed through the network. A central entity collects the contents of all the probe packets and estimates the state (congested or not) of every node in the network. One important parameter of congeston localization schemes is scalability, i.e. how the number of measurements scales with the size of network as the size of the network grows. We have shown that it is possible to do congestion detection using our scheme for a properly designed network with the number of measurements required growing linearly with the size of the network.
8
Elesev, Aleksandr. "Robot Localization Using Inertial and RF Sensors." Miami University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=miami1218571607.
9
Maffei, Renan de Queiroz. "Translating sensor measurements into texts for localization and mapping with mobile robots." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/158403.
Анотація:
Localização e Mapeamento Simultâneos (SLAM), fundamental para robôs dotados de verdadeira autonomia, é um dos problemas mais difíceis na Robótica e consiste em estimar a posição de um robô que está se movendo em um ambiente desconhecido, enquanto incrementalmente constrói-se o mapa de tal ambiente. Provavelmente o requisito mais importante para localização e mapeamento adequados seja um preciso reconhecimento de local, isto é, determinar se um robô estava no mesmo lugar em diferentes ocasiões apenas analizando as observações feitas pelo robô em cada ocasião. A maioria das abordagens da literatura são boas quando se utilizam sensores altamente expressivos, como câmeras, ou quando o robô está situado em ambientes com pouco ambiguidade. No entanto, este não é o caso, por exemplo, quando o robô equipado apenas com sensores de alcance está em ambientes internos estruturados altamente ambíguos. Uma boa estratégia deve ser capaz de lidar com tais ambientes, lidar com ruídos e erros nas observações e, especialmente, ser capaz de modelar o ambiente e estimar o estado do robô de forma eficiente. Nossa proposta consiste em traduzir sequências de medições de laser em uma representação de texto eficiente e compacta, para então lidar com o problema de reconhecimento de local usando técnicas de processamento lingüísticos. Nós traduzimos as medições dos sensores em valores simples computados através de um novo modelo de observação baseado em estimativas de densidade de kernel chamado de Densidade de Espaço Livre (FSD). Estes valores são quantificados permitindo a divisão do ambiente em regiões contíguas de densidade homogênea, como corredores e cantos. Regiões são representadas de forma compacta por simples palavras descrevendo o valor de densidade espacial, o tamanho e a variação da orientação daquela região. No final, as cadeias de palavras compõem um texto, no qual se buscam casamentos de n-gramas (isto é, sequências de palavras). Nossa técnica também é aplicada com sucesso em alguns cenários de operação de longo-prazo, onde devemos lidar com objetos semi-estáticos (i.e. que se movem ocasionalmente, como portas e mobílias). Todas as abordagens foram avaliadas em cenários simulados e reais obtendo-se bons resultados.Simultaneous Localization and Mapping (SLAM), fundamental for building robots with true autonomy, is one of the most difficult problems in Robotics and consists of estimating the position of a robot that is moving in an unknown environment while incrementally building the map of such environment. Arguably the most crucial requirement to obtain proper localization and mapping is precise place recognition, that is, determining if the robot is at the same place in different occasions just by looking at the observations taken by the robot. Most approaches in literature are good when using highly expressive sensors such as cameras or when the robot is situated in low ambiguous environments. However this is not the case, for instance, using robots equipped only with range-finder sensors in highly ambiguous indoor structured environments. A good SLAM strategy must be able to handle these scenarios, deal with noise and observation errors, and, especially, model the environment and estimate the robot state in an efficient way. Our proposal in this work is to translate sequences of raw laser measurements into an efficient and compact text representation and deal with the place recognition problem using linguistic processing techniques. First, we translate raw sensor measurements into simple observation values computed through a novel observation model based on kernel-density estimation called Free-Space Density (FSD). These values are quantized into significant classes allowing the division of the environment into contiguous regions of homogeneous spatial density, such as corridors and corners. Regions are represented in a compact form by simple words composed of three syllables – the value of spatial density, the size and the variation of orientation of that region. At the end, the chains of words associated to all observations made by the robot compose a text, in which we search for matches of n-grams (i.e. sequences of words), which is a popular technique from shallow linguistic processing. The technique is also successfully applied in some scenarios of long-term operation, where we must deal with semi-static objects (i.e. that can move occasionally, such as doors and furniture). All approaches were evaluated in simulated and real scenarios obtaining good results.
10
MERICO, DAVIDE. "Tracking with high-density, large-scale wireless sensor networks." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/7785.
Анотація:
Given the continuous technological advances in computing and communication, it seems that we are rapidly heading towards the realization of paradigms commonly described as ubiquitous computing, pervasive computing, ambient intelligence, or, more recently, "everyware". These paradigms envision living environments pervaded by a high number of invisible technological devices affecting and improving all aspects of our lives. Therefore, it is easy to justify the need of knowing the physical location of users. Outdoor location-aware applications are already widespread today, their growing popularity showing that location-awareness is indeed a very useful functionality.
Less obvious is how the growing availability of these locations and tracks will be exploited for providing more intelligent "situation-understanding" services that help people.
My work is motivated by the fact that, thanks to location-awareness systems, we are more and more aware of the exact positions of the users but unfortunately we are rarely capable of exactly understanding what they are doing. Location awareness should rapidly evolve and become "situation-awareness" otherwise the ubiquitous-computing vision will become impracticable.
The goal of this thesis is devising alternative and innovative approaches to the problem of indoor position estimation/assessment and evaluating them in real environments. These approaches are be based on: (i) a low-cost and energy-aware localization infrastructure; (ii) multi-sensor, statistically-based, localization algorithms; (iii) logic-based situation assessment techniques.
The algorithms and techniques that are the outcome of this thesis have all been tested by implementing them and measuring (both in a quantitative sense and in a qualitative sense) the performance in the field.
11
Tsevelnyam, Amgalanbayar. "Lokalizace zařízení pomocí BLE rámců." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-317135.
Анотація:
Master’s thesis is about indoor localization of objects or persons using Bluetooth Low Energy. The outcome of this work is determining the accuracy of a localization method One Nearest Zone on density of the localization network, implementing the Trilateration method and also determining the accuracy of this localization method on density of the localization network.
12
Cazé, Alexandre. "Emission, scattering and localization of light in complex structures : from nanoantennas to disordered media." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-00917876.
Анотація:
Utiliser des milieux nanostructurés pour confiner la lumière permet d'augmenter l'interaction entre un émetteur et le rayonnement électromagnétique. Dans cette thèse, nous utilisons un formalisme classique (présenté au Chap. 1) pour décrire cette interaction dans différents contextes, qui peuvent être regroupés en deux parties (respectivement Parties II et III). Dans un premier temps, nous étudions l'apparition de modes localisés en champ proche de structures complexes. Nous nous intéressons à deux différents types de structures: des nanoantennes d'or et des films d'or désordonnés. Nos résultats nous permettent de discerner les modes radiatifs et non-radiatifs. Nous introduisons le concept de Cross Density Of States (CDOS) pour décrire quantitativement la cohérence spatiale intrinsèque associée à la structure modale d'un milieu complexe. Nous démontrons ainsi une réduction de l'extention spatiale des modes au voisinage de la percolation électrique des films d'or désordonnés.
Nous nous intéressons ensuite à des milieux fortement diffusants. En éclairant de telles structures par une source cohérente, on obtient une figure d'intensité complexe appelée speckle. Nous utilisons une méthode diagrammatique pour démontrer une corrélation négative entre les figures de speckle réfléchie et transmise à travers une tranche dans le régime mésoscopique. Nous nous intéressons ensuite à la corrélation C0, qui apparait lorsque la source est enfouie dans le milieu. Nous proposons une démonstration générale de l'égalité entre la corrélation C0 et les fluctuations normalisées de la LDOS, et soulignons le rôle fondamental des interactions de champ proche. Finalement, nous observons numériquement le régime de couplage fort entre un diffuseur résonnant et un mode localisé d'Anderson au sein d'un milieu désordonné 2D.
13
Santana-Bonilla, Alejandro. "Density functional theory and model-based studies of charge transfer and molecular self-organization on surfaces:." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-222478.
Анотація:
Molecular-based quantum cellular automata (m-QCA), as an extension of quantum-dot QCAs, offer a novel alternative in which binary information can be encoded in the molecular charge configuration of a cell and propagated via nearest-neighbor Coulombic cell-cell interactions. Appropriate functionality of m-QCAs involves a complex relationship between quantum mechanical effects, such as electron transfer processes within the molecular building blocks, and electrostatic interactions between cells. In the first part of this document, the influence of structural distortions in single m-QCA is addressed within a minimal model using an diabatic-to-adiabatic transformation. Thus, it is shown that even small changes of the classical square geometry between driver and target cells, such as those induced by distance variations or shape distortions, can make cells respond to interactions in a far less symmetric fashion, modifying and potentially impairing the expected computational behavior of the m-QCA. The model has been further extended to consider time-dependent external electric fields in which a special emphasis is given to the profiles in which this external parameter can interact with the associated molecular complex. The results of the model have been validated by a direct comparison with first-principle calculations allowing to conclude the plausibility to induce the intra-molecular charge transfer process in a controllable manner via the interaction with the external electric field. The influence played by the electric field profile in the response of the molecular complex is also investigated. The results suggests a major role played by this variable in terms of the time length in which the intra-molecular charge transfer can be observed.
In the second part, first-principle theoretical calculations of the self-assembly properties and electronic structure of Ferrocene-functionalized complexes have been carried out. Hence, five different molecular complexes which offer a potential playground to realistic implement the m-QCA paradigm have been investigated. The main emphasis is given to study the interaction between localized charge-carrier molecular states and the delocalized surface states. The results of these calculations demonstrate the possibility to obtain real systems in which intra-molecular charge localization can be combined with self-assembly scaffolding and absorbed on either Highly oriented pyrolytic graphite (HOPG) or metallic-surfaces. Finally, the validation of these findings is carried out via comparison with accesible experimental results and opening the gate to plausible strategies where the paradigm can be implemented.
14
Burt, Jason Bryan. "A study of the crystal chemistry, electron density distributions, and hydrogen incorporation in the Al₂SiO₅ polymorphs." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27756.
Анотація:
The Al₂SiO₅ polymorphs have been examined to provide new insights into their chemical bonding, their crystal chemistry, their equations of state, and the incorporation of water in the form of hydroxyl in their structures. The Al₂SiO₅ polymorphs provide a unique structural assemblage for a crystal chemical examination due to the variation in Al coordination in the structures where Al is in 4-fold, 5-fold, and 6-fold in sillimanite, andalusite, and kyanite, respectively. Consequently, the Al₂SiO₅ polymorphs have been examined with a combination of experimental (high pressure X-ray diffraction and Polarized FTIR spectroscopy) and theoretical (VASP and Crystal 98) methods.
An experimental high pressure X-ray diffraction study on andalusite and sillimanite has constrained their equation of state and the pressure derivatives of their bulk modulus with pressure. Additionally, the effect of pressure on the crystal structures has been examined, where the main structural response is compression of the AlO₆ octahedra. Comparatively, compression of the AlO₆ octahedra in andalusite is more anisotropic, while the major direction of axial compressibility in both structures is dependent on the orientation of the AlO6 octahedra.
In order to better understand the crystal chemistry of the Al-O and Si-O bonds in the polymorphs, ELF isosurfaces were examined. ELF isosurfaces represent a graphical representation of the localized electron probability density. Six distinct types of ELF isosurfaces were observed in the Al₂SiO₅ polymorphs resulting from differences in the geometry, coordination, and coordinated cation atomic number surrounding the oxygens within the crystal structures. The ELF was also shown to be isostructurally related to electron density difference maps.
In a combined experimental and theoretical investigation of the Al₂SiO₅ polymorphs, potential protonation sites within the crystal structures were determined at an atomic level with polarized FTIR spectroscopy and analysis of (3,-3) critical points of the negative Laplacian. The polarized FTIR spectra indicate the orientation of the OH dipole in the three polymorphs and the (3,-3) critical points indicate regions of locally concentrated electron density. Potential protonation sites were determined based on the value of the negative Laplacian, the underbonded nature of the oxygens, and the number of surrounding cations.Ph. D.
15
Arias, Olivares David. "Relation Among Localization, Delocalization and Physicochemical Properties. From Electron Density Databases to Magnetic Properties Effects of the acceptor unit in dyes with acceptor–bridge–donor architecture on the electron photo-injection mechanism and aggregation in DSSCs The role of Cr, Mo and W in the electronic delocalization and the metal–ring interaction in metallocene complexes". Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS015.
Анотація:
Tout d'abord, nous évoquerons un aperçu général de l'analyse topologique basée sur la densité d'électronique, le trou d'échange-corrélation et la densité de paires. Une fois la densité électronique rappelée, l'analyse topologique de la densité électronique est expliquée, ainsi que la procédure de calcul des points critiques de la densité électronique, le calcul de la matrice hessienne de la densité électronique et la définition des points critiques à la surface. Tous ces outils topologiques permettent de caractériser la nature des liaisons chimiques parallèlement à l'indice basé sur la délocalisation. Afin de comprendre la nature des énergies et des interactions dans les systèmes, l'analyse d'interaction non covalente est expliquée et combinée à l'analyse de décomposition d?énergie. De plus, les états de transition seront étudiés en appliquant les orbitales naturelles pour la valence chimique (ETS-NOCV). Les concepts clés du magnétisme moléculaire sont abordés. Nous nous concentrons sur l'aimantation et la susceptibilité magnétique, les composants diamagnétiques et paramagnétiques provenant de toute réponse magnétique dans les systèmes. Les propriétés de champs magnétiques induits sont étudiés dans le but de comprendre l'aromaticité à travers de deux descripteurs, les déplacements chimiques indépendants du noyau et les densités de courant induit. En annexe à la théorie, l'interaction isotrope dans les composés dinucléaires est introduite pour expliquer et mesurer certaines erreurs trouvées dans la théorie de la fonctionnelle de densité (TFD). [...]The first property here analysed and related with electronic localization/delocalization is the aromaticity. Aromaticity is an important concept introduced by Kekulé; since then, theoreticians and experimentalist have tried to understand it in different groups of molecules analogues to benzene. The importance of this concept and how the aromaticity is affected by the chemical environment is important to understand and link some physicochemical properties. i.e., reactivity, stability, magnetic response. The physicochemical properties of interest are the electronic structure, the nature of bonds and organometallic interactions(differentiation between metallocenes and metallabencenes). Furthermore, the magnetic response and the study of building blocks as possible candidates to make nano-wires or new low-dimension magnetic materials. Finally, we try to understand the interaction and the errors involved in some properties theoretically computed like, the isotropic coupling between metals through aromatic (or organic) units that have become important benchmark molecules to study magnetic properties in inorganic as well as metal-organic systems [...]
16
Leseur, Olivier. "Diffusion, localisation et absorption de lumière en milieux désordonnés. Impact des corrélations spatiales du désordre." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066107/document.
Анотація:
Dans cette thèse, différents aspects de la propagation de lumière en milieux hétérogènes sont abordés. Dans un premier temps, les concepts et les outils fondamentaux de la propagation des ondes en milieux désordonnés sont rappelés.Ensuite, le régime de localisation d'Anderson est abordé pour des systèmes bidimensionnels ouverts. La localisation est mise en évidence de manière simple à partir du calcul de la figure de speckle transmis par une réalisation unique du désordre et en faisant varier les conditions d'illumination. Les régimes localisé et diffusif sont alors nettement différenciés, permettant d'introduire un nouveau critère pour la localisation.Puis, un régime dilué dans lequel les corrélations du désordre jouent un rôle important est étudié. En particulier, l'étude se concentre sur les milieux hyperuniformes, qui permettent de montrer de manière spectaculaire comment les corrélations peuvent changer les propriétés de diffusion d'un milieu jusqu'à le rendre totalement transparent. L'influence des corrélations du désordre sur le coefficient d'absorption d'un milieu désordonné est également envisagée, elle s'avère être modérée.La dernière partie s'intéresse aux fluctuations du taux d'émission d'un émetteur de type molécule fluorescente enfoui dans un milieu désordonné en fonction de sa position. Cette corrélation spatiale d'un nouveau genre permet d'obtenir de manière découplée des informations sur les détails microscopiques du milieu (corrélations) et l'environnement local de la sourceIn this thesis, different aspects of wave propagation in complex media are adressed. First, basicconcepts and tools of the propagation of waves in disordered media are reminded.Then, the Anderson localization regime is tackled for two-dimensional open systems. The localization is highlighted in a simple way from a calculation of the transmitted speckle pattern for a single configuration of the disorder with varying illumination conditions. Localized and diffused regimes are clearly differenciated, allowing to introduce a new critria for localization.Next, a weak scattering regime for which correlations of the disorder play a significant role is investigated. Namely, the study is focused on hyperuniform materials, where correlations are such that they are transparent compared with their uncorreleted equivalent. The influence of the correlations of the disorder on the absorption coefficient is also considered, but it is found to be moderated.The final part is dedicated to the fluctuations of the decay rate of an emitter, (e. g. fluorescentmolecule), embedded in a disordered medium as a function of its position. This new type of spatialcorrelation allows to extract information on the microscopic details of the medium (correlations) and the local environment of the source in an uncoupled way
17
Pincet, Lancelot. "Dynamic excitation systems for quantitative and super-resolved fluorescence microscopy." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP033.
Анотація:
La microscopie de localisation de molécule unique (SMLM) est une technique optique super-résolue permettant d'observer des échantillons biologiques marqués par des fluorophores avec une résolution bien inférieure à la limite de diffraction. La qualité de cette imagerie dépend fortement de la capacité à observer les molécules de manière individuelle, ce qui nécessite un contrôle précis de la photophysique des fluorophores pour qu'ils émettent de manière décalée dans l'espace et le temps. Jusqu'à présent, les méthodes d'excitation dynamique visaient à produire une illumination uniforme sur des champs larges (200 um x 200 um). Cependant, ces types d'illumination rencontrent des difficultés pour imager les échantillons biologiques denses, comme les neurones, où la diversité de la densité de fluorophores entrave la génération d'un régime de molécule unique de qualité uniforme sur toute la zone observée. Pour résoudre ce problème, je propose une nouvelle approche qui ajuste dynamiquement l'illumination en fonction de la densité de l'échantillon. Cette méthode combine un nouveau système optique d'excitation tri-dynamique avec une boucle de rétroaction basée sur l'analyse de densité, bénéficiant d'une étude approfondie de la photophysique des fluorophores. Le système d'imagerie intelligent, où le motif d'excitation varie dans le temps, intègre un système de balayage 2D, un système de zoom variable et un laser. Ceci permet de générer une variété de cartes d'éclairement dynamiques pour s'adapter à l'échantillon observé et à la densité de localisations détectées localement. Cette nouvelle approche a été validée sur différents échantillons biologiques. De plus, le système d’excitation dynamique a également permis d’explorer des modalités d'imagerie d'échantillons vivants, telles que le MSIM ou le FRAPSingle Molecule Localization Microscopy (SMLM) is a super-resolution optical technique enabling the observation of biological samples labeled with fluorescent dyes at resolutions well below the diffraction limit. The quality of this imaging heavily relies on the ability to observe molecules individually, requiring precise control of fluorescent dye photophysics for them to emit with a high sparsity in both space and time. Until now, dynamic excitation methods aimed to produce uniform illumination over large fields (200 um x 200 um). However, these types of illumination encounter difficulties in imaging dense biological samples, such as neurons, where the diversity in dye density prevented the generation of a uniform single molecule regime across the entire observed area. To address this issue, I propose a new approach that dynamically adjusts illumination based on sample density. This method combines a novel tri-dynamic optical excitation system with a feedback loop based on density analysis, benefiting from an in-depth study of fluorescent dye photophysics. The intelligent imaging system, where the excitation pattern varies over time, integrates a 2D scanning system, a variable zoom system, and a laser. This allows for the generation of a variety of dynamically changing illumination patterns to adapt to the observed sample and the density of locally detected localizations. This new approach has been validated on various biological samples. Additionally, the dynamic excitation system has also been explored for live samples imaging techniques, such as MSIM or FRAP
18
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.
Анотація:
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
19
Luo, Zhiming. "Traffic analysis of low and ultra-low frame-rate videos." Thèse, Université de Sherbrooke, 2017. http://hdl.handle.net/11143/11854.
Анотація:
Abstract: Nowadays, traffic analysis are relying on data collected from various traffic sensors. Among the various traffic surveillance techniques, video surveillance systems are often used for monitoring and characterizing traffic load. In this thesis, we focused on two aspects of traffic analysis without using motion features in low frame-rate videos: Traffic density flow analysis and Vehicle detection and classification. Traffic density flow analysis}: Knowing in real time when the traffic is fluid or when it jams is a key information to help authorities re-route vehicles and reduce congestion. Accurate and timely traffic flow information is strongly needed by individual travelers, the business sectors and government agencies. In this part, we investigated the possibility of monitoring highway traffic based on videos whose frame rate is too low to accurately estimate motion features. As we are focusing on analyzing traffic images and low frame-rate videos, traffic density is defined as the percentage of road being occupied by vehicles. In our previous work, we validated that traffic status is highly correlated to its texture features and that Convolutional Neural Networks (CNN) has the superiority of extracting discriminative texture features. We proposed several CNN models to segment traffic images into three different classes (road, car and background), classify traffic images into different categories (empty, fluid, heavy, jam) and predict traffic density without using any motion features. In order to generalize the model trained on a specific dataset to analyze new traffic scenes, we also proposed a novel transfer learning framework to do model adaptation. Vehicle detection and classification: The detection of vehicles pictured by traffic cameras is often the very first step of video surveillance systems, such as vehicle counting, tracking and retrieval. In this part, we explore different deep learning methods applied to vehicle detection and classification. Firstly, realizing the importance of large dataset for traffic analysis, we built and released the largest traffic dataset (MIO-TCD) in the world for vehicle localization and classification in collaboration with colleagues from Miovision inc. (Waterloo, On). With this dataset, we organized the Traffic Surveillance Workshop and Challenge in conjunction with CVPR 2017. Secondly, we evaluated several state-of-the-art deep learning methods for the classification and localization task on the MIO-TCD dataset. In light of the results, we may conclude that state-of-the-art deep learning methods exhibit a capacity to localize and recognize vehicle from a single video frame. While with a deep analysis of the results, we also identify scenarios for which state-of-the-art methods are still failing and propose concrete ideas for future work. Lastly, as saliency detection aims to highlight the most relevant objects in an image (e.g. vehicles in traffic scenes), we proposed a multi-resolution 4*5 grid CNN model for the salient object detection. The model enables near real-time high performance saliency detection. We also extend this model to do traffic analysis, experiment results show that our model can precisely segment foreground vehicles in traffic scenes.De nos jours, l’analyse de trafic routier est de plus en plus automatisée et s’appuie sur des données issues de senseurs en tout genre. Parmi les approches d’analyse de trafic routier figurent les méthodes à base de vidéo. Les méthodes à base de vidéo ont pour but d’identifier et de reconnaître les objets en mouvement (généralement des voitures et des piétons) et de comprendre leur dynamique. Un des défis parmi les plus difficile à résoudre est d’analyser des séquences vidéo dont le nombre d’images par seconde est très faible. Ce type de situation est pourtant fréquent considérant qu’il est très difficile (voir impossible) de transmettre et de stocker sur un serveur un très grand nombre d’images issues de plusieurs caméras. Dans ce cas, les méthodes issues de l’état de l’art échouent car un faible nombre d’images par seconde ne permet pas d’extraire les caractéristiques vidéos utilisées par ces méthodes tels le flux optique, la détection de mouvement et le suivi de véhicules. Au cours de cette thèse, nous nous sommes concentré sur l’analyse de trafic routier à partir de séquences vidéo contenant un très faible nombre d’images par seconde. Plus particulièrement, nous nous sommes concentrés sur les problème d’estimation de la densité du trafic routier et de la classification de véhicules. Pour ce faire, nous avons proposé différents modèles à base de réseaux de neurones profonds (plus particulièrement des réseaux à convolution) ainsi que de nouvelles bases de données permettant d’entraîner les dits modèles. Parmi ces bases de données figure « MIO-TCD », la plus grosse base de données annotées au monde faite pour l’analyse de trafic routier.
20
Huang, Henry. "Bearing-only SLAM : a vision-based navigation system for autonomous robots." Thesis, Queensland University of Technology, 2008. https://eprints.qut.edu.au/28599/1/Henry_Huang_Thesis.pdf.
Анотація:
To navigate successfully in a previously unexplored environment, a mobile robot must be able to estimate the spatial relationships of the objects of interest accurately. A Simultaneous Localization and Mapping (SLAM) sys- tem employs its sensors to build incrementally a map of its surroundings and to localize itself in the map simultaneously. The aim of this research project is to develop a SLAM system suitable for self propelled household lawnmowers. The proposed bearing-only SLAM system requires only an omnidirec- tional camera and some inexpensive landmarks. The main advantage of an omnidirectional camera is the panoramic view of all the landmarks in the scene. Placing landmarks in a lawn field to define the working domain is much easier and more flexible than installing the perimeter wire required by existing autonomous lawnmowers. The common approach of existing bearing-only SLAM methods relies on a motion model for predicting the robot’s pose and a sensor model for updating the pose. In the motion model, the error on the estimates of object positions is cumulated due mainly to the wheel slippage. Quantifying accu- rately the uncertainty of object positions is a fundamental requirement. In bearing-only SLAM, the Probability Density Function (PDF) of landmark position should be uniform along the observed bearing. Existing methods that approximate the PDF with a Gaussian estimation do not satisfy this uniformity requirement. This thesis introduces both geometric and proba- bilistic methods to address the above problems. The main novel contribu- tions of this thesis are: 1. A bearing-only SLAM method not requiring odometry. The proposed method relies solely on the sensor model (landmark bearings only) without relying on the motion model (odometry). The uncertainty of the estimated landmark positions depends on the vision error only, instead of the combination of both odometry and vision errors. 2. The transformation of the spatial uncertainty of objects. This thesis introduces a novel method for translating the spatial un- certainty of objects estimated from a moving frame attached to the robot into the global frame attached to the static landmarks in the environment. 3. The characterization of an improved PDF for representing landmark position in bearing-only SLAM. The proposed PDF is expressed in polar coordinates, and the marginal probability on range is constrained to be uniform. Compared to the PDF estimated from a mixture of Gaussians, the PDF developed here has far fewer parameters and can be easily adopted in a probabilistic framework, such as a particle filtering system. The main advantages of our proposed bearing-only SLAM system are its lower production cost and flexibility of use. The proposed system can be adopted in other domestic robots as well, such as vacuum cleaners or robotic toys when terrain is essentially 2D.
21
Huang, Henry. "Bearing-only SLAM : a vision-based navigation system for autonomous robots." Queensland University of Technology, 2008. http://eprints.qut.edu.au/28599/.
Анотація:
To navigate successfully in a previously unexplored environment, a mobile robot must be able to estimate the spatial relationships of the objects of interest accurately. A Simultaneous Localization and Mapping (SLAM) sys- tem employs its sensors to build incrementally a map of its surroundings and to localize itself in the map simultaneously. The aim of this research project is to develop a SLAM system suitable for self propelled household lawnmowers. The proposed bearing-only SLAM system requires only an omnidirec- tional camera and some inexpensive landmarks. The main advantage of an omnidirectional camera is the panoramic view of all the landmarks in the scene. Placing landmarks in a lawn field to define the working domain is much easier and more flexible than installing the perimeter wire required by existing autonomous lawnmowers. The common approach of existing bearing-only SLAM methods relies on a motion model for predicting the robot’s pose and a sensor model for updating the pose. In the motion model, the error on the estimates of object positions is cumulated due mainly to the wheel slippage. Quantifying accu- rately the uncertainty of object positions is a fundamental requirement. In bearing-only SLAM, the Probability Density Function (PDF) of landmark position should be uniform along the observed bearing. Existing methods that approximate the PDF with a Gaussian estimation do not satisfy this uniformity requirement. This thesis introduces both geometric and proba- bilistic methods to address the above problems. The main novel contribu- tions of this thesis are: 1. A bearing-only SLAM method not requiring odometry. The proposed method relies solely on the sensor model (landmark bearings only) without relying on the motion model (odometry). The uncertainty of the estimated landmark positions depends on the vision error only, instead of the combination of both odometry and vision errors. 2. The transformation of the spatial uncertainty of objects. This thesis introduces a novel method for translating the spatial un- certainty of objects estimated from a moving frame attached to the robot into the global frame attached to the static landmarks in the environment. 3. The characterization of an improved PDF for representing landmark position in bearing-only SLAM. The proposed PDF is expressed in polar coordinates, and the marginal probability on range is constrained to be uniform. Compared to the PDF estimated from a mixture of Gaussians, the PDF developed here has far fewer parameters and can be easily adopted in a probabilistic framework, such as a particle filtering system. The main advantages of our proposed bearing-only SLAM system are its lower production cost and flexibility of use. The proposed system can be adopted in other domestic robots as well, such as vacuum cleaners or robotic toys when terrain is essentially 2D.
22
Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812/document.
Анотація:
Dans une première partie nous explorerons les effets d'impuretés désordonnées et paramagnétiques sur l'effet spin-Hall intrinsèque dans un gaz d'électrons bi-dimensionnel avec un couplage spin-orbite de Rashba. A faible désordre, la conductivité de spin-Hall reste proche de sa valeur d'échantillon pur, comme le montrent un calcul analytique de réponse linéaire et une étude numérique. De fortes fluctuations sont toutefois observées, elles augmentent avec l'importance du désordre. Pour caractériser la dynamique d'un paquet d'onde sur un réseau, nous mesurons sa taille, le taux de participation inverse, et sa dimension de corrélation. Le système subit une transition de localisation à une valeur critique du désordre. Dans le régime localisé, la densité locale d'états n'est plus uniforme et ne coïncide plus avec la densité totale d'états. Une corrélation antiferromagnétique entre les impuretés et les électrons de conduction est observée. Après la transition de localisation, la conductivité de spin augmente significativement. La première correction quantique dans le formalisme de réponse linéaire, contribue positivement à la conductivité de spin-Hall. Dans une seconde partie, le modèle de Hubbard avec double échange avec corrélations électroniques est étudié par la méthode du champ moyen dynamique (DMFT) dans l'approximation de non-croisement pour la résolution du problème d'impureté (NCA). Autour du quart remplissage, un polaron orbital est observé et décrit à l'aide d'un Hamiltonien effectif. Le double échange dans les semi-conducteurs magnétiques dilués est étudié dans l'approximation du potentiel cohérent (CPA)Spintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
23
Poater, i. Teixidor Jordi. "Índexos de localització i deslocalització derivats de la densitat bielectrònica: anàlisi i aplicacions en estructura molecular, reactivitat química i aromaticitat." Doctoral thesis, Universitat de Girona, 2003. http://hdl.handle.net/10803/8029.
Анотація:
La present tesi doctoral s'emmarca dins el camp de la química teòrica icomputacional. El primer objectiu, que va ser el de partida, consistia a veure si els índexos
bielectrònics derivats de la teoria AIM podien ser útils per estudiar la reorganització
electrònica al llarg d'una reacció. De forma paral·lela es va plantejar un objectiu
metodològic, el càlcul dels índexos mencionats a altres nivells de teoria, com podia ser
DFT o CI. CI. Aquests dos objectius varen portar a molts d'altres, tot i que els principals són:
Objectiu 1. Estudi de la reorganització de parells d'electrons al llarg d'una
reacció.
Objectiu 2. Efecte de la solvatació sobre l'estructura de parells d'electrons d'una
molècula.
Objectiu 3. Càlcul dels índexos de localització i deslocalització als nivells de teoria
del funcional de la densitat i post-Hartree-Fock.
Objectiu 4. Caracterització de l'enllaç per pont d'hidrogen per mitjà de
l'estructura dels parells d'electrons.
Objectiu 5. L'índex de deslocalització: nou criteri electrònic d'aromaticitat.
24
Rojas, Molina Constanza. "Etude mathématique des propriétés de transport des opérateurs de Schrödigner aléatoires avec structure quasi-cristalline." Thesis, Cergy-Pontoise, 2012. http://www.theses.fr/2012CERG0565/document.
Анотація:
Cette thèse est consacrée à l'étude du transport électronique dans des modèles désordonnés non ergodiques, dans le cadre de la théorie des opérateurs de Schrödinger aléatoires.Pour commencer, nous reformulons l'outil principal pour notre étude, l'analyse multi-échelles, dans le cadre non ergodique. Nous établissons les conditions d'homogénéité que l'opérateur doit vérifier pour appliquer cette méthode. Ensuite, nous étudions les propriétés spectrales des opérateurs de Delone-Anderson non ergodiques. Ces systèmes modélisent l'énergie d'une particule en interaction avec un milieu dont la structure atomique est quasi-cristalline et la nature des impuretés est désordonnée. Dans le cas où les mesures de probabilité associées au potentiel de simple site sont régulières, en dimension 2 et sous l'effet d'un champ magnétique, nous établissons une transition métal-isolant et l'existence d'une énergie de mobilité qui sépare les régions de localisation et de délocalisation dynamiques. Pour des mesures de simple site régulières et celle de Bernoulli, nous démontrons la localisation dynamique en bas du spectre. De plus, nous obtenons une description quantitative de la région de localisation dynamique en termes de paramètres géométriques de l'ensemble de Delone de base.Nous concluons ce travail avec l'étude de la densité d'états intégrée pour des modèles de Delone-Anderson, en combinaison avec des outils de la théorie des systèmes dynamiques associés aux quasi-cristaux. Sous certaines conditions sur la géométrie de l'ensemble de Delone sous-jacent, nous montrons l'existence de la densité d'états intégrée. De plus, dans le cas d'une perturbation de Delone-Anderson du Laplacien libre, nous démontrons qu'elle a un comportement asymptotique de Lifshitz en bas du spectreHis thesis is devoted to the study of electronic transport in non ergodic disordered models, in the framework of random Schrödinger operators.We start by reformulating the main tool in our study, the multiscale analysis, in the non ergodic setting. We establish suitable homogeneity conditions on the operator, in order to apply this method.Next, we study the spectral properties of non ergodic Delone-Anderson operators. These models represent a particle interacting with a medium whose atomic structure is quasi-crystalline and the nature of its impurities is disordered. In the case where the probability measures associated to the single-site potential are regular, in dimension 2 and under the effect of a magnetic field, we establish a metal-insulator transition and the existence of a mobility edge that separates the localization and delocalization regions. In arbitrary dimension, for regular and for Bernoulli single-site measures, we show dynamical localization at the bottom of the spectrum. Moreover, we obtain a quantitative lower bound on the size of the localization region in terms of the geometric parameters of the underlying Delone structure.We conclude this essay by studying the integrated density of states for Delone-Anderson models, using tools from the theory of dynamical systems associated to quasicrystals. Under certain conditions on the geometry of the underlying Delone set, we show the existence of the integrated density of states. Furthermore, in the case of a Delone-Anderson perturbation of the free Laplacian, we show it exhibits Lifshitz tails at the bottom of the spectrum
25
Blanquer, Guillaume. "Étude de l’interaction rayonnement-matière en champ proche de nanostructures par microscopie de fluorescence super-résolue." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLET042.
Анотація:
Au cours de cette thèse nous nous sommes intéressés à l’interaction de la lumière avec l’environnement aux échelles nanométriques. Les candidats idéaux pour sonder cette interaction en nanophotonique sont les émetteurs fluorescents car leurs propriétés d’émission sont fortement dépendantes de l’environnement qui les entoure. Le taux d’émission spontanée de ces émetteurs donne notamment une mesure directe de la densité d’états électromagnétiques et constitue à ce titre le paramètre le plus adéquat pour rendre compte de ces interactions.Cette thèse est organisée en deux parties. La première porte sur le développement et l’utilisation d’une technique de microscopie super-résolue en champ large du taux de désexcitation de molécules uniques. Cette technique se base sur la mesure simultanée du taux de désexcitation de chaque molécule par une matrice linéaire de détecteurs de photons uniques et de leur position par une caméra amplifiée. Les résultats expérimentaux obtenus en champ proche d’un nanofil d’argent ont été analysés et comparés à des simulations numériques. Grâce à cette analyse, l’effet de mirage plasmonique induit par le nanofil a pu être mis en évidence. De plus, en effectuant une sélection sur le taux d’émission spontanée mesuré pour chaque molécule et la taille de la tache de diffraction correspondante, il a été possible de déduire l’orientation du moment dipolaire des molécules et leur position réelle sur l’échantillon.La seconde partie de cette thèse a été consacrée à l’étude de guides d’ondes optiques nanostructurés. En particulier, l’influence d’une nanofibre en silice sur la distribution d’un champ optique généré par un faisceau laser collimaté a été mise en évidence expérimentalement grâce à une sonde fluorescente à balayage. Les données recueillies sont en très bon accord avec des simulations basées sur la théorie de Mie. De plus, une structure de guide d’ondes hybride diélectrique/plasmonique a été étudiée. Cette structure a pour objectif d’optimiser le couplage de la fluorescence d’un émetteur fluorescent dans un guide d’onde optique diélectrique par l’intermédiaire d’une antenne plasmonique. Des simulations ont permis d’aboutir à un design ainsi qu’à la réalisation d’un premier échantillon. Une approche expérimentale est également proposée pour la caractérisation de ce dispositif optiqueIn this thesis we study the interaction of light with the environment at the nanoscale. Fluorescent emitters are ideal candidates to probe this interaction because their emission properties strongly depend on the surrounding environment. The emitters’ decay rate is directly linked to the local density of electromagnetic states, which is therefore the most appropriate parameter to quantify the interactions with the environment.This thesis is organized into two parts. The first one concerns the development and the implementation of a wide-field super-resolved lifetime microscopy technique at the single molecule level. This technique is based on the simultaneous measurement of single-molecules’ decay rate with a linear matrix of single photon detectors and of their position with an amplified camera. Experimental results obtained in the near-field of a silver nanowire are analyzed and compared with numerical simulations. Such comparison provides the evidence of the plasmonic mirage effect induced by the presence of the nanowire. Moreover we show that, by making a selection on the measured decay rate and on the size of the corresponding point spread function, it is possible to deduce the orientation of the molecular dipole moments and their real position on the sample.The second part of this thesis is focused on the study of nanostructured optical waveguides. We report on the measurement, performed with a fluorescent scanning near-field microscope, of the field generated around a tapered silica nanofiber by a collimated beam perpendicular to it. The results are in very good agreement with numerical simulations based on Mie theory. We also study a dielectric/plasmonic hybrid waveguide. A plasmonic nanoantenna fabricated on top of a dielectric optical waveguide enhances the coupling of the emission of a fluorescent emitter to the guided mode. The design and fabrication of an optimized device are achieved thanks to numerical simulations. An experimental approach is also proposed to characterize this device
26
Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés." Electronic Thesis or Diss., Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812.
Анотація:
Dans une première partie nous explorerons les effets d'impuretés désordonnées et paramagnétiques sur l'effet spin-Hall intrinsèque dans un gaz d'électrons bi-dimensionnel avec un couplage spin-orbite de Rashba. A faible désordre, la conductivité de spin-Hall reste proche de sa valeur d'échantillon pur, comme le montrent un calcul analytique de réponse linéaire et une étude numérique. De fortes fluctuations sont toutefois observées, elles augmentent avec l'importance du désordre. Pour caractériser la dynamique d'un paquet d'onde sur un réseau, nous mesurons sa taille, le taux de participation inverse, et sa dimension de corrélation. Le système subit une transition de localisation à une valeur critique du désordre. Dans le régime localisé, la densité locale d'états n'est plus uniforme et ne coïncide plus avec la densité totale d'états. Une corrélation antiferromagnétique entre les impuretés et les électrons de conduction est observée. Après la transition de localisation, la conductivité de spin augmente significativement. La première correction quantique dans le formalisme de réponse linéaire, contribue positivement à la conductivité de spin-Hall. Dans une seconde partie, le modèle de Hubbard avec double échange avec corrélations électroniques est étudié par la méthode du champ moyen dynamique (DMFT) dans l'approximation de non-croisement pour la résolution du problème d'impureté (NCA). Autour du quart remplissage, un polaron orbital est observé et décrit à l'aide d'un Hamiltonien effectif. Le double échange dans les semi-conducteurs magnétiques dilués est étudié dans l'approximation du potentiel cohérent (CPA)Spintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
27
Zemánek, Ondřej. "Počítání vozidel v statickém obraze." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2020. http://www.nusl.cz/ntk/nusl-417211.
Анотація:
Tato práce se zaměřuje na problém počítání vozidel v statickém obraze bez znalosti geometrických vlastností scény. V rámci řešení bylo implementováno a natrénováno 5 architektur konvolučních neuronových sítí. Také byl pořízen rozsáhlý dataset s 19 310 snímky pořízených z 12pohledů a zachycujících 7 různých scén. Použité konvoluční sítě mapují vstupní vzorek na mapu hustoty vozidel, ze které lze získat jejich počet a lokalizaci v kontextu vstupního snímku. Hlavním přínosem této práce je porovnání a aplikace dosavadních nejlepších řešení pro počítání objektů v obraze. Většina z těchto architektur byla navržena pro počítání lidí v obraze, proto musely být uzpůsobeny pro potřeby počítání vozidel v statickém obraze. Natrénované modely jsou vyhodnoceny GAME metrikou na TRANCOS datasetu a na velkém spojeném datasetu. Dosažené výsledky všech modelů jsou následně popsány a porovnány.
28
Trambly, de Laissardière Guy. "Etude théorique de la structure électronique des matériaux quasicristallins." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10075.
Анотація:
Les quasicristaux sont des solides ordonnes presentant une coherence orientationnelle a longue distance sans periodicite de translation. Leurs proprietes electroniques sont spectaculaires. Par exemple, la phase alpdre presente une resistivite de semi-conducteur (> 10 ohm. Cm a 4 k), bien que sa densite d'etats au niveau de fermi soit environ 1/10 de celle de l'aluminium pur. Une etude numerique de plusieurs alliages intermetalliques a base d'aluminium et d'approximants realistes de quasicristaux a permis de degager deux caracteristiques essentielles de leur structure electronique: un creusement important de la densite d'etats au niveau de fermi par rapport aux electrons libres, ce qui est attendu pour les alliages de hume-rothery, et une structure tres piquee dans la densite d'etats. Cette derniere propriete, specifique des quasicristaux, a ete correlee avec les proprietes de transport electroniques. Le role des metaux de transition a ete etudie par une generalisation du modele de l'etat lie virtuel en tenant compte de la specificite de ces alliages. Nous presentons, entre autre, une explication de la valence negative apparente des metaux de transition qui est evoquee depuis longtemps dans les intermetalliques. En outre, cette etude montre que les metaux de transition jouent un role important dans le creusement de la densite d'etats au niveau de fermi. Dans le cadre de la theorie de la diffusion, nous analysons la localisation des electrons par un agregat atomique dans une matrice metallique. Cette etude montre l'existence d'etats lies virtuels d'agregats qui peuvent expliquer la structure piquee de la densite d'etats et sont coherents avec la notion d'etats critiques generalement consideres pour decrire le spectre electronique des pavages quasiperiodiques. Cependant, la stabilite des agregats n'est pas due a cette localisation car leur energie de cohesion est la somme d'interactions de paires. Cela renforce l'image des quasicristaux comme des alliages de hume-rothery
29
Faggiani, Rémi. "Resonant nanophotonics : structural slow light and slow plasmons." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0396/document.
Анотація:
L'augmentation de l'interaction lumière-matière aux échelles micro et nanométriques est un des fers de lance de la nanophotonique. En effet, le contrôle de la répartition spatiale de la lumière grâce à l'interaction résonante entre nanostructures et ondes électromagnétiques a conduit aux développements de nombreuses applications dans des domaines variés tels que les télécommunications,la spectroscopie et la détection d'objets. Le ralentissement de la lumière, sujet de la thèse, obtenue grâces à l'interférence d'ondes contre-propageantes dans des milieux périodiques ou le confinement sub-longueur d'onde dans des guides d'ondes plasmoniques, est associé à une compression des pulses lumineux et une forte augmentation du champ électrique, deux phénomènes clés pour la miniaturisation de composées optiques et l'augmentation de l'interaction lumière matièreEnhancing light-matter interactions at micro and nanoscales is one of the spearheads of nanophotonics. Indeed, the control of the field distribution due to the resonant interaction of nanostructures with electromagnetic waves has prompted the development of numerous optical components for many applications in telecommunication, spectroscopy or sensing. A promising approach lies in the control of light speed in nanostructures. Light slowdown, obtained by wave interferences in periodic structures or subwavelength confinement in plasmonic waveguides, is associated to pulse compressions and large field enhancements,which are envisioned as key processes for the miniaturization of optical devices and the enhancement of light-matter interactions.The thesis studies both fundamental aspects and possible applications related to slow light in photonic and plasmonic nanostructures. In particular, we study the impact of periodic system sizes on the group velocity reduction and propose a novelfamily of resonators that implement slow light on very small spatial scales. We then investigate the role of fabrication disorder in slow periodic waveguides on light localization and demonstrate how modal properties influence the confinement of localized modes. Also we propose a new hollow-core photonic crystal waveguide that provides efficient and remote couplings between the waveguide and atoms thatare trapped away from it. Finally we demonstrate the important role played by slow plasmons on the emission of quantum emitters placed in nanogap plasmonic antennas and explain how large radiation efficiency can be achieved by overcoming quenching in the metal. Additionally, one part of the thesis is devoted to thederivation of a novel modal method to accurately describe the dynamics of plasmonic resonators under short pulse illumination
30
Teichert, Fabian. "Elektronischer Transport in defektbehafteten quasi-eindimensionalen Systemen am Beispiel von Kohlenstoffnanoröhrchen." Master's thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-139650.
Анотація:
Die vorliegende Arbeit beschäftigt sich mit den Transporteigenschaften defektbehafteter Kohlenstoffnanoröhrchen (CNTs). Als Beispiel werden dabei einfache und doppelte Fehlstellen betrachtet. Der Fokus liegt auf der Berechnung des Transmissionsspektrums und der Leitfähigkeit mit einem schnellen, linear skalierenden rekursiven Greenfunktions-Formalismus, mit dem große Systeme quantenmechanisch behandelt werden können. Als Grundlage wird ein dichtefunktionalbasiertes Tight-Binding-Modell verwendet. Der Einfluss der Defektdichte und des CNT-Durchmessers wird im Rahmen einer statistischen Analyse untersucht. Es wird gezeigt, dass im Grenzfall kleiner Transmission die Leitfähigkeit exponentiell mit der Defektanzahl skaliert. Das System befindet sich im Regime starker Lokalisierung, wobei die Lokalisierungslänge von der Defektdichte und dem CNT-Durchmesser abhängt.
31
Teichert, Fabian, Andreas Zienert, Jörg Schuster, and Michael Schreiber. "Electronic transport through defective semiconducting carbon nanotubes." IOP Publishing Ltd, 2018. https://monarch.qucosa.de/id/qucosa%3A32462.
Анотація:
We investigate the electronic transport properties of semiconducting (m, n) carbon nanotubes (CNTs) on the mesoscopic length scale with arbitrarily distributed realistic defects. The study is done by performing quantum transport calculations based on recursive Green's function techniques and an underlying density-functional-based tight-binding model for the description of the electronic structure. Zigzag CNTs as well as chiral CNTs of different diameter are considered. Different defects are exemplarily represented by monovacancies and divacancies. We show the energy-dependent transmission and the temperature-dependent conductance as a function of the number of defects. In the limit of many defetcs, the transport is described by strong localization. Corresponding localization lengths are calculated (energy dependent and temperature dependent) and systematically compared for a large number of CNTs. It is shown, that a distinction by (m − n)mod 3 has to be drawn in order to classify CNTs with different bandgaps. Besides this, the localization length for a given defect probability per unit cell depends linearly on the CNT diameter, but not on the CNT chirality. Finally, elastic mean free paths in the diffusive regime are computed for the limit of few defects, yielding qualitatively same statements.
32
Boujida, Mohamed. "Contribution à l'étude des propriétés de transport de quelques oxydes métalliques et supraconducteurs de basse dimensionnalité." Grenoble 1, 1988. http://www.theses.fr/1988GRE10157.
Анотація:
Les proprietes de transport (magnetoconductivite, effet hall, ondes de densite de charge, ondes de densite de spin, transitions supraconductrices) des oxydes metalliques et supraconducteurs quasi-bidimensionnels sont etudiees a basse temperature
33
Petit, Edwige. "Application des anticorps monoclonaux a l'etude de la conformation de l'apo a-i a la surface des lipoproteines de haute densite." Toulouse 3, 1987. http://www.theses.fr/1987TOU30095.
34
Berro, Soumaya. "Identification of muscle activation schemes by inverse methods applied on HD-sEMG signals." Electronic Thesis or Diss., Compiègne, 2022. http://www.theses.fr/2022COMP2708.
Анотація:
L'identification rapide ou en temps réel de l'activation spatio-temporelle des unités motrices (UM) qui représentent les unités fonctionnelles du système neuromusculaire est fondamentale dans les applications de contrôle des prothèses et en réhabilitation fonctionnelle. Cependant, cette procédure demande un temps de calcul énorme. Par conséquent, le travail de cette thèse a été consacré à fournir un algorithme permettant l'identification en temps réel des stratégies d'activation spatiale et temporelle des UMs en appliquant des méthodes inverses sur les signaux HD-sEMG (électromyogramme de surface à haute densité) à partir d'une grille placée sur le Biceps Brachial (BB). À cette fin, nous proposons une approche innovante, qui implique l'utilisation de la méthode inverse classique de minimisation de norme et une interpolation de courbe en 3D, à savoir l'approche est nommée CFB-MNE. Cette méthode, fondée sur l'identification inverse (estimation de la norme minimale) couplée à un dictionnaire des potentiels d'action des unités motrices simulées (MUAP) d'un modèle récent et testée sur des simulations, a permis la localisation en temps réel des unités motrices individuelles simulées. Une analyse de robustesse (modifications anatomiques, physiologiques et instrumentales) a ensuite été effectuée pour vérifier l'efficacité de l'algorithme proposé. Enfin, l'algorithme proposé a été testé sur des UMs avec des schémas de recrutement réalistes donnant des résultats prometteurs et encourageants en identification spatiale et temporelle sur trois scenarios. Pour conclure, en perspectives, les résultats prometteurs obtenus suggèrent l'utilisation de l'apprentissage automatique et de l'intelligence artificielle (IA) pour améliorer encore les performances de l'algorithme proposéFast or real-time identification of the spatiotemporal activation of Motor Units (MUs), functional units of the neuromuscular system, is fundamental in applications as prosthetic control and rehabilitation guidance but often dictates expensive computational times. Therefore, the thesis work was devoted to providing an algorithm that enables the real-time identification of MU spatial and temporal activation strategies by applying inverse methods on HD-sEMG (high-density surface electromyogram) signals from a grid placed over the Biceps Brachii (BB). For this purpose, we propose an innovative approach, that involves the use of the classical minimum norm inverse method and a 3D fitting curve interpolation, namely CFB-MNE approach. This method, based on inverse identification (minimum norm estimation) coupled to simulated motor unit action potential (MUAP) dictionary from a recent model and tested on simulations, allowed the real time localization of simulated individual motor units. A robustness analysis (anatomical, physiological, and instrumental modifications) was then performed to verify the efficiency of the proposed algorithm. Finally, the proposed algorithm was tested on MUs with realistic recruitment patterns giving promising results in both spatial and temporal identification. To conclude, a door to future perspectives was opened, according to the obtained promising results, suggesting the use of machine learning and artificial intelligence (AI) to further boost the performance of the proposed algorithm
35
Ben, Salem Azzedine. "Synthese et caracterisation physique et structurale des conducteurs unidimensionnels de type fe : :(1+x)nb::(3-x)se::(10)." Nantes, 1987. http://www.theses.fr/1987NANT2018.
Анотація:
Ce compose est le prototype d'une serie de formulation (mm')nb::(2)s::(10)(mm' = fe,v,cr,nb,ta) presentant une chaine trigonale prismatique |nbse::(3)| et une double chaine oelaedrique |(mm')se::(6)|. Ces composes ont une transition metal isolant vers 140 k. L'observation d'une onde de densite de charge aux caracteristiques identiques a celles de nbse::(3) indique que la chaine conductrice est la chaine trigonale prismatique |nbse::(3)|. La variation de la conductivite au voisinage de la transition indique un mecanisme de localisation d'anderson. Les proprietes physiques du compose ou se a ete substitue par s ont ete etudiees. L'etude de l'insertion par li a ete effectuee
36
Chu, Yan-Ling, and 朱艷伶. "Density-Adaptive Range-Free Localization in Large-Scale Sensor Networks." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/51897822631700103781.
Анотація:
碩士國立中央大學
軟體工程研究所
100
In recent years, a number of location-based services have been proposed, such as search, target tracking and rescue. An accurate and efficient localization algorithm is crucial in supporting all these services in wireless networks. There are many different localization algorithms proposed in the literature. Due to the cost and limitation of hardware on sensing nodes, range-free localization schemes are considered more practical. In this thesis, we propose the novel correction scheme, namly SHR Correction Scheme, for distance estimation and localization. Compared to other range-free distance estimation and localization methods, SCS reduces the range estimation and localization error significantly, especially when the number of anchors is low.
37
Wang, Yu-Ren, and 王毓仁. "Earthquake Localization in a High Density Seismic Sensor Network in Taiwan." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/55557955607990108509.
Анотація:
碩士國立臺灣科技大學
資訊工程系
102
Earthquakes have always been a major disaster in Taiwan, but due to our inability to accurately predict the occurrence of an earthquake, the concept and study of EEW (Earthquake Early Warning) emerged: when an earthquake occurs, if we can detect it and estimate its properties as soon as possible, we can send out warnings and let people prepare for the incoming disaster, indirectly reduces the damage of properties and losses of lives from an earthquake. This study created a novel EEW system utilizing the Palert network, a high density sensor network consisting of over 400 detection sites deployed across Taiwan. When we detect the first arrival wave with the STA/LTA triggers, we can determine whether an earthquake have occurred and locate the hypocenter. Unlike traditional locating problems, the position of the hypocenter is 3-dimensional. Thus, we created a scoring model that takes advantage of the different P-wave arrival time between detection sites, then divide the terrain into a 3-dimensional virtual grid based on longitude, latitude and depth. The virtual grid is composed of various cells, with each cell having a score under the scoring model. The higher the score, the more the cell fits into the known parameters of the hypocenter. In other words, the highest-scoring cell is the hypocenter, and we purpose a neighborhood method for finding this cell. In our experiments, we gathered every earthquakes occurred on 2013 in Taiwan or the surrounding sea with a magnitude greater than ML4.0, and we compare our method to an exhaustive method, a downscaling method and Geiger's method. From the results, our neighborhood method has the advantages of high speed, accurate location and stable results, proving that our method can be readily applied to EEW and disaster prevention.
38
k'ai, chung hung, and 鍾泓凱. "Parameterless density-based clustering for subcellular localization analysis of Achaea protein sequences." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/88489890499719445213.
Анотація:
碩士亞洲大學
生物資訊學系碩士班
94
Clustering analysis is a very useful tool for discovering unknown knowledgeform dataset because of there is no needed pre-knowledge for training instead offinding group in the dataset. According to the categories form research, there are threemajor clustering methods: Hierarchical clustering algorithms, Partition clustering algorithms and density based clustering algorithms, but the characteristic that make density based clustering algorithm is more powerful to the unknown dataset than others is automatic detect cluster number and shape detect form cluster. Although there are many algorithms for different kinds of clustering problem, but none can handle all in once, however input parameter is the common drawback of algorithms. Without any understanding about the dataset, try-and-error is the only way find out the input parameter which has great influence to clustering result. In this thesis, we consider all point in the dataset to finding an optimal parameter for describing point density in its position. Considering density as a continuing force field, combine density with minimum spanning tree which saves neighbors information form high dimensional space to one dimensional space can easily find out clusters. As the experiment result show, this automatic method none needed any parameter from user but still works well.
39
Rogers, Brandon Jeremy. "The Reliability of Signal Strength for Localization of High-Density ZigBee Wireless Networks." 2007. http://trace.tennessee.edu/utk_gradthes/199.
Анотація:
This thesis investigates the reliability of ZigBee signal strength within a high-density wireless network, specifically looking at the Link Quality Indicator (LQI) as provided by the physical layer and accessible at the networking and application layers within the stack protocol. It also investigates methods by which LQI can be used for discovery, identification, and localization of nodes within a ZigBee wireless network. The thesis concentrates on practical approaches specifically as it would pertain to commissioning a high-density network for an application such as lighting control in building automation. There are seven potential algorithms proposed using factors such as minimum distance error, perceived confidence, and triangulation. Experiments, which explore the reliability of signal strength indicators, reveal that the fluctuations of the signal strength indicate that a simple, inexpensive algorithm is insufficient. Simulations, which explore varying conditions such as network layouts, node-count, and node-density, reinforce this notion; however, this thesis also shows that more complicated and expensive methods do show promising results. Using the simplest of methodologies, the experiments and simulations result in 30-35% accuracy. However, with the more complicated methodologies (using techniques such as reiteration, emulation, and cooperation), the results reveal accuracies of 80-90%. This thesis concludes from these results that a simple algorithm and methodology may not be sufficient but that there are approaches that can improve the results. However, the cost of these approaches may be deemed too high for practical use. Further exploration in these methodologies, though, should show promise that more sufficient accuracies without sacrificing too much cost are attainable.
40
Lee, Chih-Yuan, and 李治原. "Abnormal Crowd Behavior Detection and Localization via Kernel Based Direct Density Ratio Estimation." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/95546677836042558374.
Анотація:
碩士國立臺灣科技大學
電子工程系
102
In this theme, we consider the analysis of abnormally behavior in surveillance system. To simplify the problem, we formalized it as an outlier detection problem. In our case, all behaviors in training data are normal. By creating a model by training data, we can define abnormalities whose probability is below a certain threshold under this model. Based on this, we use Kullback–Leibler importance estimation procedure (KLIEP) to compute the ratio of training data and testing data which we used as our inlier score. The KLIEP is a method to estimate the inlier score, not the probability densities themselves. This formulation allows us to avoid non-parametric density estimation, which is known to be a difficult task. After computing inlier score by KLIEP, we create a model by training data and testing data. According to this model, other testing data can also get a inlier score which can represent the degree of similarity between training data and testing data. Based on the concept of inlier-based outlier detection and normal score, we can determine an appropriate threshold and find which location at testing data is abnormal. In our evaluation we used PASCAL metric to evaluate our localization rate by ground truth. Through computer simulations, we find that our method has high accuracy of localization rate in UCSD dataset compared with previous works.
41
Huang, Wei-Li, and 黃偉立. "A Study of Indoor Localization Based on Multi-Dimension Kernel Density Estimation with Device Diversity." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/jrnauk.
Анотація:
碩士國立高雄應用科技大學
電機工程系博碩士班
102
Recently, the wireless network is widely used, wherever at home, office, shopping malls or airports are covered with the wireless network. So we can use the wireless signal intensity changes and characteristics to achieve a stable and accuracy indoor positioning system. During the past decades, many fingerprint-based indoor positioning systems have been proposed and achieved great progress. Typically, a fingerprint-based positioning system mainly relied on the concept of radio fingerprint for localization and assumed that received signal strength (RSS) has location singularity. However, the singularity may not be available in a real application, where the RSS at a location is variant owing to signal noise and dynamic obstacles such as moving people. To well represent RSS distribution and consider the effects above mentioned, the purpose of this study is to design a new RSS modeling method based on multi-dimension kernel density estimation (MD-KDE). Also, the new RSS modeling method allows our system to perform region-based target localization. Comparing with the conventional point-based method, our system can utilize more information for localization. Another important issue we will focus on is the device diversity problem where the device used to train the radio map and the device used to sense RSS for position query are difference. Due to device diversity, the sensed RSS would be away form the trained radio map and this leads to poor positioning accuracy. To compensate the device diversity effect, a linear transfer model was adopted in our system. In this paper we will design a landmark-based RSS compensation method. Based on the Wi-Fi landmarks, our system could automatically collect RSS pairs between two devices in order to train the transfer model.
42
Mazzarello, Riccardo [Verfasser]. "Localization and density of states of disordered low-dimensional systems in a magnetic field / vorgelegt von Riccardo Mazzarello." 2004. http://d-nb.info/971652023/34.
43
WU, HUI-LIN, and 吳慧琳. "Enucleation of deciduomal cells by density gradient centrifugation and its application to intracellular localization of unbound progesterone receptors." Thesis, 1990. http://ndltd.ncl.edu.tw/handle/06322568440837449580.
44
Santana-Bonilla, Alejandro. "Density functional theory and model-based studies of charge transfer and molecular self-organization on surfaces:: implications for molecular-based Quantum Cellular Automata." Doctoral thesis, 2016. https://tud.qucosa.de/id/qucosa%3A30246.
Анотація:
Molecular-based quantum cellular automata (m-QCA), as an extension of quantum-dot QCAs, offer a novel alternative in which binary information can be encoded in the molecular charge configuration of a cell and propagated via nearest-neighbor Coulombic cell-cell interactions. Appropriate functionality of m-QCAs involves a complex relationship between quantum mechanical effects, such as electron transfer processes within the molecular building blocks, and electrostatic interactions between cells. In the first part of this document, the influence of structural distortions in single m-QCA is addressed within a minimal model using an diabatic-to-adiabatic transformation. Thus, it is shown that even small changes of the classical square geometry between driver and target cells, such as those induced by distance variations or shape distortions, can make cells respond to interactions in a far less symmetric fashion, modifying and potentially impairing the expected computational behavior of the m-QCA. The model has been further extended to consider time-dependent external electric fields in which a special emphasis is given to the profiles in which this external parameter can interact with the associated molecular complex. The results of the model have been validated by a direct comparison with first-principle calculations allowing to conclude the plausibility to induce the intra-molecular charge transfer process in a controllable manner via the interaction with the external electric field. The influence played by the electric field profile in the response of the molecular complex is also investigated. The results suggests a major role played by this variable in terms of the time length in which the intra-molecular charge transfer can be observed.
In the second part, first-principle theoretical calculations of the self-assembly properties and electronic structure of Ferrocene-functionalized complexes have been carried out. Hence, five different molecular complexes which offer a potential playground to realistic implement the m-QCA paradigm have been investigated. The main emphasis is given to study the interaction between localized charge-carrier molecular states and the delocalized surface states. The results of these calculations demonstrate the possibility to obtain real systems in which intra-molecular charge localization can be combined with self-assembly scaffolding and absorbed on either Highly oriented pyrolytic graphite (HOPG) or metallic-surfaces. Finally, the validation of these findings is carried out via comparison with accesible experimental results and opening the gate to plausible strategies where the paradigm can be implemented.
45
Lee, Eric Jin Ser. "Ultrasound propagation through complex media with strong scattering resonances." 2014. http://hdl.handle.net/1993/23847.
Анотація:
The propagation of ultrasound through two- and three-dimensional strongly scattering media, with either random or ordered internal structures, has been investigated through experiments and finite element simulations. All media investigated have strong scattering resonances, leading to novel transport behaviour. The two-dimensional samples consist of nylon rods immersed in water. When the nylon rods are arranged in a triangular lattice to form two-dimensional phononic crystals, very unusual dispersion properties are observed when the lattice constant is adjusted so that Bragg and hybridization gaps overlap in frequency. This behaviour is attributed to the competition between two co-existing propagating modes, leading to a new method for tuning bandgap properties and adjusting the transmission by orders of magnitude. The scattering resonance of the nylon rods also leads to unusual Dirac cone properties at the K point of the triangular lattice. The three-dimensional media were fabricated by brazing aluminum beads together to form a disordered porous solid network, with either vacuum or air in the pores, depending on the experiment. This system is of particular interest because it has been shown to exhibit Anderson localization of ultrasound. Two experimental approaches were developed to investigate previously unstudied properties of this system. By directly counting the modes in the frequency domain, the density of states was measured. At intermediate frequencies, the density of states was found to be approximately independent of frequency, while at higher frequencies, the frequency dependence was consistent with traditional density-of-states models. The level statistics of the modes was also investigated to determine the conditions under which level repulsion occurs. By using a laser interferometer to measure the ultrasonic displacements on the surface of a large slab-shaped sample, sub-diffusive behaviour was observed, demonstrating the feasibility of using such measurements to investigate the transition to Anderson localization in these samples.
46
Teichert, Fabian. "Quantum transport in defective carbon nanotubes at mesoscopic length scales." 2018. https://monarch.qucosa.de/id/qucosa%3A34326.
Анотація:
This thesis theoretically investigates the electronic transport properties of defective carbon nanotubes (CNTs). For the defects the focus is set to vacancy types. The calculations are performed using quantum transport theory and an underlying density-functional-based tight-binding method. Two algorithmic improvements are derived, which accelerate the common methods for quasi one-dimensional systems for the specific case of (i) randomly distributed defects and (ii) long unit cells. With this, the transmission spectrum and the conductance is calculated as a function of the CNT length, diameter, chiral angle, defect type, defect density, defect fraction, and temperature. The diffusive and the localized transport regime are described by extracting elastic mean free paths and localization lengths for metallic and semiconducting CNTs. Simple analytic models for estimating or even predicting the conductance dependence on the mentioned parameters are derived. Finally, the formation of defect-induced long-range deformations and its influence on the conductance are studied.:1 Introduction
2 Fundamentals
2.1 Carbon nanotubes
2.1.1 Structure
2.1.2 Properties
2.1.3 Defects
2.1.4 Synthesis
2.1.5 Characterization
2.1.6 Applications
2.2 Electron structure theory
2.2.1 Introduction
2.2.2 Density functional theory
2.2.3 Density-functional-based tight binding
2.2.3.1 First-order expansion
2.2.3.2 Creation of the parameter set
2.2.3.3 Second-order expansion
2.2.3.4 Usage
2.3 Electron transport
2.3.1 Equilibrium Green’s-function-based quantum transport theory
2.3.2 Transport regimes
2.3.3 Classical derivation: drift-diffusion equation with a sink
2.3.4 Quantum derivation: Dorokhov-Mello-Pereyra-Kumar theory
A Improved recursive Green’s function formalism for quasi one-dimensional systems with realistic defects (J. Comput. Phys. 334 (2017), 607–619)
A.1 Introduction
A.2 Quantum transport theory
A.3 Recursive Green’s function formalisms
A.3.1 Forward iteration scheme
A.3.2 Recursive decimation scheme
A.3.3 Renormalization decimation algorithm
A.4 Improved RGF+RDA
A.5 Performance test
A.5.1 Random test matrix
A.5.2 Transport through carbon nanotubes
A.6 Summary and conclusions
B Strong localization in defective carbon nanotubes: a recursive Green’s function study (New J. Phys. 16 (2014), 123026)
B.1 Introduction
B.2 Theoretical framework
B.2.1 Transport formalism
B.2.2 Recursive Green’s function formalism
B.2.3 Electronic structure
B.2.4 Strong localization
B.3 Modeling details of the defective system
B.4 Results and discussion
B.4.1 Single defects
B.4.2 Randomly distributed defects
B.4.3 Localization exponent
B.4.4 Diameter dependence and temperature dependence of the localization exponent
B.5 Summary and conclusions
Supplementary material
C Electronic transport in metallic carbon nanotubes with mixed defects within the strong localization regime (Comput. Mater. Sci. 138 (2017), 49–57)
C.1 Introduction
C.2 Theoretical framework
C.3 Modeling details
C.4 Results and discussion
C.4.1 Conductance
C.4.2 Localization exponent
C.4.3 Influence of temperature
C.4.4 Conductance estimation
C.5 Summary and conclusions
D An improved Green’s function algorithm applied to quantum transport in carbon nanotubes (arXiv: 1806.02039)
D.1 Introduction
D.2 Electronic transport
D.3 Decimation technique and renormalization-decimation algorithm
D.4 Renormalization-decimation algorithm for electrodes with long unit cells
D.4.1 Surface Green’s functions
D.4.2 Bulk Green’s functions and electrode density of states
D.5 Complexity measure and performance test
D.6 Exemplary results
D.7 Summary and conclusions
E Electronic transport through defective semiconducting carbon nanotubes (J. Phys. Commun. 2 (2018), 105012)
E.1 Introduction
E.2 Theoretical framework
E.3 Modeling details
E.4 Results and discussion
E.4.1 Transmission and transport regimes
E.4.2 Energy dependent localization exponent and elastic mean free path
E.4.3 Conductance, effective localization exponent and effective elastic mean free path
E.5 Summary and conclusions
Supplementary material
F Influence of defect-induced deformations on electron transport in carbon nanotubes (J. Phys. Commun. 2 (2018), 115023)
F.1 Introduction
F.2 Theory
F.3 Results
F.4 Summary and conclusions
3 Ongoing work
4 Summary and outlook
4.1 Summary
4.2 Outlook
5 Appendix
5.1 Bandstructure of graphene
5.2 Quantum transport theory and Landauer-Büttiker formula
References
List of figures
List of tables
Acknowledgement
Selbstständigkeitserklärung
Curriculum vitae
List of publicationsDiese Dissertation untersucht mittels theoretischer Methoden die elektronischen Transporteigenschaften von defektbehafteten Kohlenstoffnanoröhren (englisch: carbon nanotubes, CNTs). Dabei werden Vakanzen als Defekte fokussiert behandelt. Die Berechnungen werden mittels Quantentransporttheorie und einer zugrunde liegenden dichtefunktionalbasierten Tight-Binding-Methode durchgeführt. Zwei algorithmische Verbesserungen werden hergeleitet, welche die üblichen Methoden für quasi-eindimensionale Systeme für zwei spezifische Fälle beschleunigen: (i) zufällig verteilte Defekte und (ii) lange Einheitszellen. Damit werden das Transmissionsspektrum und der Leitwert als Funktion von CNT-Länge, Durchmesser, chiralem Winkel, Defekttyp, Defektdichte, Defektanteil und Temperatur berechnet. Das Diffusions- und das Lokalisierungstransportregime werden beschrieben, indem die elastische freie Weglänge und die Lokalisierungslänge für metallische und halbleitende CNTs extrahiert werden. Einfache analytische Modelle zur Abschätzung bis hin zur Vorhersage des Leitwertes in Abhängigkeit besagter Parameter werden abgeleitet. Schlussendlich werden die Bildung einer defektinduzierten, langreichweitigen Deformation und deren Einfluss auf den Leitwert studiert.:1 Introduction 2 Fundamentals 2.1 Carbon nanotubes 2.1.1 Structure 2.1.2 Properties 2.1.3 Defects 2.1.4 Synthesis 2.1.5 Characterization 2.1.6 Applications 2.2 Electron structure theory 2.2.1 Introduction 2.2.2 Density functional theory 2.2.3 Density-functional-based tight binding 2.2.3.1 First-order expansion 2.2.3.2 Creation of the parameter set 2.2.3.3 Second-order expansion 2.2.3.4 Usage 2.3 Electron transport 2.3.1 Equilibrium Green’s-function-based quantum transport theory 2.3.2 Transport regimes 2.3.3 Classical derivation: drift-diffusion equation with a sink 2.3.4 Quantum derivation: Dorokhov-Mello-Pereyra-Kumar theory A Improved recursive Green’s function formalism for quasi one-dimensional systems with realistic defects (J. Comput. Phys. 334 (2017), 607–619) A.1 Introduction A.2 Quantum transport theory A.3 Recursive Green’s function formalisms A.3.1 Forward iteration scheme A.3.2 Recursive decimation scheme A.3.3 Renormalization decimation algorithm A.4 Improved RGF+RDA A.5 Performance test A.5.1 Random test matrix A.5.2 Transport through carbon nanotubes A.6 Summary and conclusions B Strong localization in defective carbon nanotubes: a recursive Green’s function study (New J. Phys. 16 (2014), 123026) B.1 Introduction B.2 Theoretical framework B.2.1 Transport formalism B.2.2 Recursive Green’s function formalism B.2.3 Electronic structure B.2.4 Strong localization B.3 Modeling details of the defective system B.4 Results and discussion B.4.1 Single defects B.4.2 Randomly distributed defects B.4.3 Localization exponent B.4.4 Diameter dependence and temperature dependence of the localization exponent B.5 Summary and conclusions Supplementary material C Electronic transport in metallic carbon nanotubes with mixed defects within the strong localization regime (Comput. Mater. Sci. 138 (2017), 49–57) C.1 Introduction C.2 Theoretical framework C.3 Modeling details C.4 Results and discussion C.4.1 Conductance C.4.2 Localization exponent C.4.3 Influence of temperature C.4.4 Conductance estimation C.5 Summary and conclusions D An improved Green’s function algorithm applied to quantum transport in carbon nanotubes (arXiv: 1806.02039) D.1 Introduction D.2 Electronic transport D.3 Decimation technique and renormalization-decimation algorithm D.4 Renormalization-decimation algorithm for electrodes with long unit cells D.4.1 Surface Green’s functions D.4.2 Bulk Green’s functions and electrode density of states D.5 Complexity measure and performance test D.6 Exemplary results D.7 Summary and conclusions E Electronic transport through defective semiconducting carbon nanotubes (J. Phys. Commun. 2 (2018), 105012) E.1 Introduction E.2 Theoretical framework E.3 Modeling details E.4 Results and discussion E.4.1 Transmission and transport regimes E.4.2 Energy dependent localization exponent and elastic mean free path E.4.3 Conductance, effective localization exponent and effective elastic mean free path E.5 Summary and conclusions Supplementary material F Influence of defect-induced deformations on electron transport in carbon nanotubes (J. Phys. Commun. 2 (2018), 115023) F.1 Introduction F.2 Theory F.3 Results F.4 Summary and conclusions 3 Ongoing work 4 Summary and outlook 4.1 Summary 4.2 Outlook 5 Appendix 5.1 Bandstructure of graphene 5.2 Quantum transport theory and Landauer-Büttiker formula References List of figures List of tables Acknowledgement Selbstständigkeitserklärung Curriculum vitae List of publications