• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 407
  • 160
  • 85
  • 44
  • 26
  • 13
  • 8
  • 7
  • 6
  • 5
  • 5
  • 5
  • 5
  • 5
  • 5
  • Tagged with
  • 901
  • 105
  • 91
  • 89
  • 81
  • 73
  • 62
  • 62
  • 53
  • 51
  • 51
  • 49
  • 48
  • 46
  • 46
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
541

Laserinduzierte Änderungen der elektronischen Transporteigenschaften von Manganaten / Laser-induced changes of electronic transport properties of manganites

Mchalwat, Manuel Mounir 09 May 2017 (has links)
No description available.
542

Excitation et détection optiques de la dynamique de l’aimantation dans le semi-conducteur ferromagnétique (Ga,Mn)(As,P) / Excitation and detection optical processes of the magnetization dynamic in the diluted magnetic-semiconductor (Ga,Mn)(As,P)

Shihab, Sylvain 15 December 2015 (has links)
Le développement des lasers impulsionnels a permis l’émergence de l’étude de la dynamique de l’aimantation dans le domaine temporel (fs-ns) par des techniques optiques. Dans les couches minces ferromagnétiques présentant une faible absorption optique les mécanismes de couplage de la lumière avec les propriétés magnétiques permettant l’excitation de la précession de l’aimantation et sa détection ne sont qu’imparfaitement connus. Pour développer leur compréhension il est nécessaire de faire varier les paramètres magnétiques. Les alliages semi-conducteurs ferromagnétiques sont pour cela des matériaux de choix du fait de leurs propriétés magnétiques aisément ajustables grâce au couplage entre les propriétés semi-conductrices et magnétiques. Les conditions pour une excitation optimale ont été précisées. L’excitation par une variation thermique transitoire des constantes d’anisotropie a été quantifiée. Le rôle de l’absorption et du déphasage optique dans la détection a été établi. L’observation de plusieurs ondes de spin a permis la détermination de la constante d’échange en fonction de la concentration en phosphore. J’ai montré que celle-ci variait peu, contrairement aux prédictions théoriques. / Development of impulsional laser enhanced the study of the magnetization dynamic in the temporal domain (fs-ns) with optical techniques. In thin ferromagnetic films with a weak optical absorption, excitation and optical mechanisms are not yet fully understood. To increase our understanding, variations of magnetic parameters are required. To that end, the magnetic semiconductor like (Ga,Mn)(As,P) are a good choice due to their magnetic properties easily adjustable thanks to the coupling between magnetic and semiconductor properties. In this thesis, conditions for optimal excitations were established. Supposing a thermal excitation origin, we assessed the transient change of temperature and anisotropy constant. I also established the role of the optical absorption and dephasing due to the finite magnetic layer thickness in the spin-waves detection process. The observation of several spin-waves gave me the opportunity to assess the spin-stiffness constant as a function of phosphorus. On the contrary of theoretical prediction, I showed that the spin-stiffness hardly vary with the phosphorus concentration.
543

Etude comparative de l'investissement psychique de l'habitat en France et aux Etats-Unis / Comparative study of psychic investment in housing in France and the United States

Mortet, Jérôme 10 February 2015 (has links)
En cette période de mondialisation des modes d’habitation et d’uniformisation desagencements de l’espace, est-ce qu’il subsiste des différences au niveau du fonctionnementfamilial dans les pays occidentaux ? Et si ces différences subsistent, comment se transposent-ellessur l’habitat réel ? Ainsi cette recherche universitaire propose une étude comparative del’investissement psychologique de l’habitat entre la France et les Etats-Unis. Le test projectifnommé « l’épreuve familiale de spatiographie projective » élaboré par Patrice Cuynet (1999-2000) a pour objectif de comprendre l’image du corps familial à travers l’analyse du dessincollectif de leur maison de rêve. Ce test a été administré à 30 familles françaises et 30familles américaines. Nous sommes partis du postulat que l’habitat est une enveloppe, unepeau réelle et fantasmée de la famille (A. Eiguer, 1983) qui fonctionne comme le Moi-peau(D. Anzieu, 1985). Grâce à cette méthodologie, nous allons pouvoir établir un diagnostic surla structuration familiale et comparer les résultats obtenus en France et aux Etats-Unis. / In this current period of globalization of the housing arrangements and of thestandardization in the space layouts, are some differences subsisting in the family functioningin western societies? And if these differences remain, how do they reflect on the real housingenvironment? This thesis will approach a comparative study of the psychological investmentof the housing environment between France and the United States. The projective test named" the family test of spatiography projective " developed by Patrice Cuynet (1999-2000) set outto gain a better understanding of the image of the family body through the analysis of thecollective drawing of their dream house. This test was assigned to 30 French families and 30American families. We started from the postulate that the housing environment is anenvelope, a real skin and fantasized over the family (In. Eiguer on 1983) which works as theEgo-skin (D. Anzieu on 1985). Thanks to this methodology, we are going to be able toestablish a diagnosis on the family structuring and compare the results obtained in Franceand in the United States.
544

Technical Feasibility Study of an IGBT-based Excitation System

Frisk, Johan January 2017 (has links)
This thesis aims to design a cabinet to house some of the required hardware to realize a 1000 A IGBT inverter controlled static excitation system. In the thesis practical design considerations are identified and solved. The suggested excitation system requires a cabinet to house the inverters. Together with inverter requirements stated by the inverter manufacturer and possible electromagnetic interference from switching of the IGBT:s, practical design considerations arise when realizing the system. Identified design considerations are heat dissipation, EMI, IP-code requirements and mechanical stresses at inverter connections. In this study, the design considerations are addressed and a cabinet design with required components inside is suggested. The suggested cabinet together with its components could fulfil the suggested system's- and the inverter's requirements. However, the IP-code allowed by the suggested EMC-seals might be lower than the IP54 required by the inverter. The cabinets EMC-properties will probably be lowered if regular rubber gaskets are used. The study suggests one possible configuration which is possible to realize. It is suggested that further consideration is dedicated to the EMI reducing properties of the cabinet if it is to be installed in an environment sensitive to EMI.
545

Otimização simultânea de posições e forças de amortecedores de vibração por atrito para controle de vibrações de estruturas

Ontiveros Pérez, Sergio Pastor January 2014 (has links)
A otimização de amortecedores é uma área nova que vem sendo explorada nos últimos anos. Existem vários métodos clássicos e outros mais recentes que estão disputando em confiabilidade, eficiência e rapidez na obtenção de um resultado ótimo. Os algoritmos de otimização são classificados em determinísticos, que utilizam a informação do gradiente, ou seja, usam os valores das funções e suas derivadas, e os meta-heurísticos são algoritmos aleatórios que são métodos probabilísticos não baseados em gradiente, utilizando somente a avaliação da função objetivo. O Firefly Algorithm é um algoritmo meta-heurístico relativamente recente inspirado no comportamento da luz dos vagalumes. Este trabalho propõe um método para a otimização de amortecedores por atrito utilizando algoritmo meta-heurístico. O método proposto é testado em dois edifícios, de nove e dezesseis andares, submetidos a duas excitações sísmicas cada. A otimização tem um objetivo principal: diminuir a resposta dinâmica em termos do deslocamento máximo no topo das estruturas obtido através de um algoritmo programado baseado no método das diferenças finitas centrais, otimizando o local de um número máximo de amortecedores e as forças de atrito dos mesmos. Para o caso da estrutura de nove andares o número máximo de amortecedores é de quatro e para o caso da estrutura de dezesseis andares o número máximo é seis. Os resultados demostraram que, para os dois casos estudados, o deslocamento no topo da estrutura diminui em mais de 50%, concluindo-se que o método programado é eficaz assim como o Firefly Algorithm é adequado para obter as posições e as forças de atrito ótimas. Portanto, acredita-se que o método proposto poderá ser utilizado como uma ferramenta útil para auxiliar no projeto de amortecedores por atrito. / The damper’s optimization is a new area that has been explored in recent years. There are several classics and newer methods that are competing in reliability, efficiency and speed in achieving a great result. The algorithms are classified as deterministic, using gradient information, or use the function values and their derivatives, and meta- heuristic optimization algorithms are random probabilistic methods that are not based on gradient using only the evaluation of the objective function. The Firefly Algorithm is a relatively new meta-heuristic algorithm inspired on the behavior of the light of fireflies. This work proposes a method for the friction damper’s optimization using meta-heuristic algorithm. The proposed method is tested in two structures: a nine story building and a sixteen story building. They were submitted to two seismic excitations each. The optimization has one main goal: to reduce the dynamic response in terms of the maximum displacement at the top of the structures obtained by a programmed algorithm based on the central finite difference method, optimizing the location of a maximum number of dampers and their friction’s forces. In the case of the nine story building, the maximum number of dampers is four, and in the case of the sixteen story building the maximum number is six. The results showed that for the two cases studied, the displacement at the top of the structure decreases by more than 50%, concluding that the programmed method is effective and the Firefly Algorithm is appropriate to get the positions and friction’s forces optimal. Therefore, it is believed that the proposed method can be used as a tool to aid in the design of friction dampers.
546

Studie magnonických krystalů ve frekvenční doméně / Study of magnonic crystals in a frequency domain

Turčan, Igor January 2017 (has links)
Popis magnetodynamických vlastností nanomagnetů a nanostrukturovaných magnetických materiálů vyžaduje metody vhodné pro zkoumání typické časové odezvy těchto systémů, tj. v řádu nanosekund a méně. Nedostatek technik, vhodných právě pro charakterizaci v časové doméně, je spojen s možnostmi současné elektroniky. Další možný přístup, jak popsat vlastnosti nanomagnetů, je charakterizace ve frekvenční doméně v pásmu GHz. Nejrozšířenější technikou charakterizace ve frekvenční doméně je měření feromagnetické rezonance (FMR). Ze spekter FMR lze získat cenné informace o systému: parametr tlumení, saturační magnetizace atd. Metoda, kterou využíváme k detekci excitací spinových vln, má za cíl zjednodušení charakterizace. Využíváme termoelektrickou detekci spinových vln v magnetických drátech prostřednictvím anomálního Nernstova jevu. Metoda je založena na disipaci tepla uvnitř magnetické vrstvy v důsledku útlumu spinových vln, a proto dochází k vytvoření teplotního gradientu směrem k substrátu (kolmo k povrchu). To vede k vytvoření elektrického pole kolmého jak na teplotní gradient, tak na směr magnetizace. Napětí je obvykle v řádu V, proto může být měřeno obvyklým laboratorním vybavením. Navzdory své jednoduchosti poskytuje tato metoda velmi zajímavé výsledky a může být použita pro charakterizaci magnonických vlnovodů, magnonických metamateriálů, emitorů spinových vln a dalších zařízení, pracujících se spinovými vlnami.
547

Algoritmy optimálního řízení pohonu se stejnosměrným motorem / DC Drive Optimal Control

Regent, David January 2008 (has links)
Master‘s thesis contains the issue of positional control of the separate exciting DC motor. In the work is the creation of mathematical model. Next theme of document are questions of optimal control and method of solution LQ controler. The work is also a proposal state observer.
548

Optické vlastnosti organických polovodičů / Organic semiconductors properties

Kočer, Martin January 2013 (has links)
This diploma thesis deals with optical properties of organic semiconductors and measuring method of absorption edge. Project is focused on absorption of light in organic semiconductors. This work also describes device for measuring of absorption edge.
549

Behavioral and synaptic consequences following removal of the Il1rapl1 gene in mice, a model of intellectual disability / Conséquences comportementales et synaptiques de l’absence de la protéine IL1RAPL1 chez la souris, un modèle de désordre intellectuel

Houbaert, Xander 28 November 2014 (has links)
Les désordres intellectuels (DI) comprennent une collection hétérogène de désordresneurodéveloppementaux qui émergent pendant l’enfance. Ils ont une incidence de 1 à 3% dansla population et sont associés avec des déficits dans les fonctions mentales et adaptives. Denombreuses mutations ont été identifiées dans des gènes codant pour des protéines quiremplissent des fonctions biologiques très diverses dans le cerveau. Parmi ces protéines,certaines sont enrichies à la synapse, supposant que les déficits cognitifs associés aux DIpourraient être reliés à des déficits synaptiques. L’objectif scientifique de notre équipe et decomprendre le rôle de certaines protéines dans la fonction synaptique et la cognition enutilisant des souris génétiquement modifiées portant des mutations dans le gènecorrespondant. Je me suis concentré sur Il1rapl1, un gène codant pour la protéine Interleukinreceptor-accessory-protein-like-1. Des mutations ou micro-délétions dans ce gène sont liés audéveloppement de DI chez l’homme. Dans les neurones, Il1rapl1 code pour une protéinetransmembranaire qui serait impliquée dans la formation et/ou la stabilisation de synapsesexcitatrices. Les conséquences de l’absence d’IL1RAPL1 à des niveaux plus intégrés restaientpeu étudiées lors du début de ma thèse. J’ai utilisé une souris déficiente pour IL1RAPL1 (KO) afinde comprendre le lien entre les déficits comportementaux et la fonction synaptique. Pour cela,j’ai soumis des souris KO à des taches comportementales de peur conditionnée. J’ai ensuiteutilisé une combinaison d’approches in vitro, ex vivo et in vivo afin de caractériser la fonctionsynaptique dans les circuits neuronaux dédiés : l’amygdale latérale et basolatérale. Desenregistrements electrophysiologiques ont montré une dérégulation de la balance entre latransmission inhibitrice et excitatrice (I/E) dans l’amygdale de souris Il1rapl1 KO, causant ainsides déficits dans la capacité d’acquérir et d’exprimer la mémoire de peur conditionnée. Lacorrection de ce déficit synaptique in vivo par pharmacologie ou par optogénétique a permis derestaurer le comportement chez les souris KO. / Intellectual disability (ID) comprises a highly heterogeneous collection of neurodevelopmentaldisorders that arise during childhood. They have an incidence of 1-3% in the population withimpairments in mental and adaptive functions. While the etiologies of IDs are thought to bevery heterogeneous, a significant proportion of ID has genetic origins. Mutations in single IDgenes lead to dysfunctions in proteins that fulfill highly different biological functions in thebrain. Interestingly, ID-related proteins are often found enriched at synapses, suggesting thatcognitive impairments defining ID could be related to alterations of synaptic function. The maingoal of our research team is to understand the role of ID-related proteins in synaptic functionand cognition using mouse models bearing gene mutations associated to ID in humans. Myresearch focused on the study of Il1rapl1, a gene coding for the Interleukin-receptor-accessoryprotein-like-1 protein. Micro-deletions or point mutations in this gene are directly linked to thedevelopment of ID and autism spectrum disorder in humans. In neurons, Il1rapl1 encodes atrans-membrane protein and several in vitro experiments point to its important role in thedifferentiation and formation/stabilization of excitatory synapses trough interactions withpresynaptic, trans-synaptic or postsynaptic partners. However, the consequences of Il1rapl1deficiency at more integrated levels remains poorly understood. The principal objective of mythesis is to explore the link between synaptic deficits and behavioral impairments in Il1rapl1-deficient mice. To achieve that, wild-type and mutant animals were first submitted to fearlearning tasks. I then used a combination of in vivo, ex vivo and in vitro functional essays tocharacterize synaptic functions in behaviorally relevant neuronal circuits. Ultimately, ourworking hypothesis were challenged in vivo by pharmacological and optogenetic approaches tonormalize behavioral deficits in Il1rapl1 KO mice. Altogether my work demonstrates thatInhibitory/Excitatory imbalances associated with the absence of Il1rapl1 impaired both thecapacity to form new memories as well as the expression of previously formed memories.
550

Odraz vibronické modulace ve dvoudimenzionálních elektronických spektrech malých molekulárních agregátů / Signatures of vibronic modulation of small molecular aggregates in two-dimensional electronic spectra

Perlík, Václav January 2019 (has links)
We studied the effects of underdamped vibrational modes on excitonic energy transfer in small molecular aggregates by means of ultrafast nonlinear spectroscopy. We developed a vibronic dynamical model to account for the interplay of electronic and vibrational coherence during excitation transport. Our model was aimed to simulate signals of a broad class of linear and third order spectroscopies (absorption, fluorescence, transient absorption (TA), transient grating (TG), two-dimensional spectroscopy (2D)) in the visible domain andaccounts for anharmonic vibrations, sub-exponential relaxation and nonlinear electron-vibrational coupling. We subsequently applied the model for several case studies, such as carotenoid to bacteriochlorophyll excitation transfer in light-harvesting 2 complex (LH2) of purple bacteria, excitation transfer in perylene dyads or vibrational dynamics in hypericin. We have paid particular attention for detailed interpretation of lineshapes of 2D spectrograms employing, e.g. phase analysis and center line (CL) slopes with emphasis to study interplay of electronic, vibrational modulations, or finite excitation pulse durations.

Page generated in 0.1892 seconds