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1
Kalikavunkal, Priya. "Development of EMT Simulation Model to Use RMS Control Model". Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187641.
Testo completoAbstract (sommario):
Evolution is continuous and as a result, developments in semiconductors are endless. This led to the Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) converter termed as HVDC light. HVDC light is quite preferable because of its pros in the technology used as well as the application it is used for. For instance, the VSC technology allows independent control of the real and reactive power and has reduced short circuit current. HVDC light are used in applications such as wind power integration, offshore power supply, underground transmission and in enhancing connected AC networks. It is vital that the control system in HVDC ensures the stability of the system and the power flow between the AC and DC systems. This is done by determining the instant at which the IGBT’s are fired in the converterstations (at both rectifier and inverter). ABB has developed RMS (using sequence components and phasors) control system based on the actual control system in a fully graphical programming language tool known as Hidraw. This RMS control has been implemented in other simulation software such as Netomac, Power factory and PSS/E. the RMS control Model is named by ABB as Common Component. The thesis aims at implementing an RMS control Model in an EMT (Electro Magnetic Transient Tools) simulation, carried out at the department of High Voltage Direct Current at ABB, Ludvika. The RMS control Model is a developed power system control and protection model which uses a simplified representation of areal time control system. When implemented, the RMS control model results are then compared with the detailed control representation implemented in PSCAD. The thesis is a result of ABB’s innovative ideas in implementing the RMS control model called Common Component into various other simulation tools of different compatibility that enables the control system to be exercised and exploited to its fullest. It also gives the prospect in developing the control system to ensure the electrical system is more efficient. The control system implemented in the EMT tool will enable developing better EMT models. The Common Component is developed but has not been implemented in PSCAD. There has been no reference to such work being carried out. Hence no reference has been referred to specific to the main work. Currently the EMT tool uses a detailed representation that shares the same code as the actual control system, MACHTM (Modular Advanced Control for HVDC) [9] control system. The implementation of Common Component in PSCAD requires an interface between them to pass the necessary parameters between them. The Common Component is developed in C++ and FORTRAN while PSCAD uses FORTRAN and hence proper interface in C++ is developed. Thereafter the electrical model representing one HVDC station (rectifier) is modelled in PSCAD. Four electrical models are implemented, described and evaluated to achieve proper control in the electrical system. The electrical models are operated in STATCOM (Static synchronous compensator) mode, where either reactive power or AC Voltage Control can be used. The model is run in reactive power control mode and the system is studied along with the control system for the required control. Model 4 gives more accurate results compared with the other models. There is better reactive power control in monitoring the PCC (point of common Coupling) and converter bus of the HVDC system. Since the Common Component is a simplified representation of the MACH [9] control system, it can behanded over to third parties without IP concerns. A simplified representation also gives the advantage of reduced simulation time. The electrical model can be further extended for both the converter stations and assessed for other control modes such as real power, dc voltage control and ac voltage control. Also the model needs to be further investigated on its behavior when subjected to faults.Utveckling är kontinuerlig och det betyder att även utvecklingen av halvledare är oändlig. Det har lett till att en Voltage Source Converter (VSC) baserad High Voltage Direct Current (HVDC) omvandlare som kallas HVDC Light har skapats. HVDC light är att föredra på grund av dess fördelar i den teknik som används samt applikationerna den används för. Till exempel så tillåter VSC tekniken oberoende kontroll av den verkliga och reaktiva effekten och har minskat kortslutningsströmen. HVDC Light används i applikationer så som vindkraftintegration, offshore strömförsörjning, markkabelöverföring och för att förbättra anslutna växelströmsnät. Styrsystemet i HVDC säkerställer stabiliteten i systemet och kraftflödet mellan AC- och DC-system. Detta görs genom att bestämma det ögonblick då IGBT tänds i strömriktarstationerna (både likriktare och växelriktare). ABB har utvecklat ett RMS (med sekvenskomponenter och fasvektorer) styrsystem baserat på det faktiska styrsystemet i ett helt grafiskt programmeringsverktyg som kallas Hidraw. Denna RMS-kontroll har implementerats i andra simuleringsprogram såsom Netomac, Powerfactory och PSS/E. ABB kallar sin RMS-kontroll för Common Component. Avhandlingen syftar till att implementera en RMS-styrsystemsmodell i en EMT (Electro Magnetic Transient Tools) simulering som utförs vid institutionen för högspänd likström vid ABB, Ludvika. RMS-styrsystemsmodellen är ett befintligt utvecklat styr- och skyddssystem som använder en förenklad representation av det verkliga styrsystemet. När det implementerats jämförs resultaten från RMS-modelen med detaljerade styrsystemsrepresentationer som genomförts i PSCAD. Avhandlingen är ett resultat av ABBs innovativa idéer att implementera Common Component i olika simuleringsverktyg, trots deras olikheter, vilket gör det möjligt att prova och utvärdera styrsystemet maximalt. Det ger också utvecklingspotential för effektiviteten i kraftnäten. Att implementera styrsystemet i ett EMT-verktyg ger även bättre kunskap om att utveckla bättre EMT modeller. Common Component är redan utvecklad men har inte blivit implementerad i PSCAD. Det finns inga referenser till att något sådant arbete har utförts. Därför har inga sådana referenser tagits upp i rapporten. För närvarande så använder EMT verktyget en detaljerad styrsystemsrepresentation som delar samma kodbas som det verkliga styrsystemet, MACHTM (Modular Advanced Control for HVDC) [9]. Implemeteringen av Common Component i PSCAD kräver att gränssnitt mellan de båda kan överföra nödvändiga parametrar. Common Component är utvecklat i C++ och FORTRAN, PSCAD använder FORTRAN. För att kommunikationen mellan de två verktygen ska fungera har ett gränssnitt utvecklats i C++. Den elektriska modell som representerar en HVDC station (likriktaren) har tagits fram i PSCAD. Totalt har fyra olika elektriska modeller implementerats, beskrivits och utvärderats för att hitta en optimal representation. Implemeteringen av Common Component i PSCAD kräver att gränssnitt mellan de båda kan överföra nödvändiga parametrar. Common Component är utvecklat i C++ och FORTRAN, PSCAD använder FORTRAN. För att kommunikationen mellan de två verktygen ska fungera har ett gränssnitt utvecklats i C++. Den elektriska modell som representerar en HVDC station (likriktaren) har tagits fram i PSCAD. Totalt har fyra olika elektriska modeller implementerats, beskrivits och utvärderats för att hitta en optimal representation.
2
Sénéchal, Dorothée. "DNS des écoulements turbulents compressibles : fluctuations de pression, de masse volumique et de température". Paris 6, 2009. http://www.theses.fr/2009PA066106.
Testo completoAbstract (sommario):
Cette thèse traite du développement de méthodes numériques d'ordre élevé possédant de bonnes propriétés de capture de choc pour la résolution directe des équations Navier-Stokes compressibles. Le solveur DNS implémenté utilise des reconstructions d'ordre élevé UW et WENO/M (UW17/WENOM17) et un solveur de Riemann approché faiblement diffusif HLLC. L'intégration temporelle est implicite, précise à l'ordre deux et utilise une procédure de pas de temps dual avec sous-itérations explicites. Les calculs DNS compressibles dans un canal plan 3-D ont permis d'évaluer la dissipation numérique des schémas UW et WENO/M et l'effet de la résolution du maillage sur la prédiction des statistiques turbulentes. De nouveaux schémas d'ordre élevé (WENOM17) ont été développés. Une analyse de l'effet de la taille de boîte du canal plan sur la prédiction du champ turbulent a été réalisée. La base de données DNS compressible a permis d'effectuer une analyse détaillée de l'évolution des quantités thermodynamiques fluctuantes (', p' et T'') qui sont fortement corrélées en présence de parois isothermes. Une modélisation tensorielle de l'équation de transport pour '_rms a été proposée et validée en a priori et a posteriori. Une décomposition des fluctuations de pression en cinq termes a été appliquée aux corrélations qui interviennent dans l'équation de transport des tensions de Reynolds des modèles RSM. Cette décomposition permettra d'évaluer séparement les parties homogène et inhomogène de la diffusion de pression et du tenseur de redistribution du transport des tensions de Reynolds.
3
Ostrovsky, Rafail. "Software protection and simulation on oblivious RAMs". Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/103684.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1992.Includes bibliographical references (p. 71-72).
by Rafail M. Ostrovsky.
Ph.D.
4
Ton, Cuong. "Radar cross section (RCS) simulation for wind turbines". Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/34754.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimitedWind-turbine power provides energy-independence and greenhouse-gas reduction benefits, but if wind turbines are built near military and commercial radar and communication installations, they can cause degradation in the systems performance. The purpose of this research is to study the radar cross section (RCS) of a wind turbine and assess its effect on the performance of radar and communication systems. In this research, some basic scattering characteristics of wind turbines are discussed. Several computational methods of RCS prediction are examined, citing their advantages and disadvantages. Modeling and computational issues that affect the accuracy and convergence of the simulation results are discussed. RCS simulation results for two wind turbine configurations are presented: a horizontal axis, three-blade design and a vertical axis helical design. Several methods of mitigating wind turbine clutter are discussed. Issues of RCS reduction and control for wind turbines are also addressed.
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Shao, Min 1975. "A study of RMF monitoring using DEVS simulation". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80119.
Testo completoAbstract (sommario):
Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (leaf 56).
by Min Shao.
S.B.and M.Eng.
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MORGAT, ANNE. "Contribution a l'etude structurale des p21 ras. Simulations par dynamique moleculaire de la p21 ha ras". Paris 11, 1991. http://www.theses.fr/1991PA112159.
Testo completoAbstract (sommario):
La connaissance structurale approfondie des proteines ras (p21 ras) permet une meilleur comprehension des mecanismes reactionnels regulant leur activite biologique (fixation des nucleotides gdp, gtp et hydrolyse du gtp, en presence d'un ion mg ii). L'etude des complexes p21. Gppnp et p21. Gdp dans leur environnement cristallin, associee a une etude de leur surface moleculaire a montre des sites potentiels d'interactions avec d'autres macromolecules. Les proprietes dynamiques de la p21 ras complexee a une molecule de gppnp et un ion mg ii ont ete etudiees par dynamique moleculaire (programme discover). Cette simulation a apporte une meilleure connaissance des interactions entre la proteine et son ligand. L'effet de certaines mutations a pu etre evalue. Cette etude a permis d'emettre des hypotheses sur les sites d'interactions avec la proteine gap et le facteur d'echange, ainsi que sur leurs mecanismes d'action
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Gualchieri, Leonardo. "Simulation of bistatic radar experiments with deep space missions". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9682/.
Testo completoAbstract (sommario):
L’obiettivo del lavoro esposto nella seguente relazione di tesi ha riguardato lo studio e la simulazione di esperimenti di radar bistatico per missioni di esplorazione planeteria. In particolare, il lavoro si è concentrato sull’uso ed il miglioramento di un simulatore software già realizzato da un consorzio di aziende ed enti di ricerca nell’ambito di uno studio dell’Agenzia Spaziale Europea (European Space Agency – ESA) finanziato nel 2008, e svolto fra il 2009 e 2010. L’azienda spagnola GMV ha coordinato lo studio, al quale presero parte anche gruppi di ricerca dell’Università di Roma “Sapienza” e dell’Università di Bologna.
Il lavoro svolto si è incentrato sulla determinazione della causa di alcune inconsistenze negli output relativi alla parte del simulatore, progettato in ambiente MATLAB, finalizzato alla stima delle caratteristiche della superficie di Titano, in particolare la costante dielettrica e la rugosità media della superficie, mediante un esperimento con radar bistatico in modalità downlink eseguito dalla sonda Cassini-Huygens in orbita intorno al Titano stesso.
Esperimenti con radar bistatico per lo studio di corpi celesti sono presenti nella storia dell’esplorazione spaziale fin dagli anni ’60, anche se ogni volta le apparecchiature utilizzate e le fasi di missione, durante le quali questi esperimenti erano effettuati, non sono state mai appositamente progettate per lo scopo. Da qui la necessità di progettare un simulatore per studiare varie possibili modalità di esperimenti con radar bistatico in diversi tipi di missione.
In una prima fase di approccio al simulatore, il lavoro si è incentrato sullo studio della documentazione in allegato al codice così da avere un’idea generale della sua struttura e funzionamento. È seguita poi una fase di studio dettagliato, determinando lo scopo di ogni linea di codice utilizzata, nonché la verifica in letteratura delle formule e dei modelli utilizzati per la determinazione di diversi parametri.
In una seconda fase il lavoro ha previsto l’intervento diretto sul codice con una serie di indagini volte a determinarne la coerenza e l’attendibilità dei risultati. Ogni indagine ha previsto una diminuzione delle ipotesi semplificative imposte al modello utilizzato in modo tale da identificare con maggiore sicurezza la parte del codice responsabile dell’inesattezza degli output del simulatore.
I risultati ottenuti hanno permesso la correzione di alcune parti del codice e la determinazione della principale fonte di errore sugli output, circoscrivendo l’oggetto di studio per future indagini mirate.
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Guduff, Ludmilla. "Ultrafast diffusion-ordered NMR analysis of mixtures". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS239/document.
Testo completoAbstract (sommario):
La spectroscopie de résonance magnétique nucléaire (RMN) est un outil puissant qui permet l’étude directe de mélanges de manière non destructive. Les spectres RMN de petites molécules en solution peuvent être différenciés grâce à la stratégie DOSY (diffusion-ordered spectroscopy), une méthode de ‘chromatographie virtuelle’ qui s’appuie sur la mesure de coefficients de diffusion translationnelle. Les principaux obstacles à l’utilisation de la DOSY sont liés à la piètre sensibilité de la RMN de manière générale mais aussi à la nécessité d’introduire une dimension temporelle supplémentaire d’acquisition, ce qui va augmenter de manière significative la durée de l’expérience. Ce travail de thèse a pour objectif de mettre au point des outils inédits de RMN plus rapides et plus adaptés à la caractérisation de mélanges peu concentrés de petites molécules. Dans un premier temps, le concept de codage spatial de la diffusion dans l’expérience DOSY a été généralisé. Mis à profit dans les méthodes RMN dites ‘ultrarapides’, l’utilisation d’une dimension spatiale plutôt que temporelle pour encoder le phénomène de diffusion permet une accélération des expériences de RMN multidimensionnelles de plusieurs ordres de grandeur. L’acquisition séquentielle de spectres est remplacée par une acquisition parallèle de ces spectres dans différentes parties de l’échantillon. L’étude poussée des méthodes de DOSY rapides s’est appuyée sur des outils de simulation numérique dans le but d’améliorer la résolution des spectres et la précision des résultats. Les problèmes de sensibilité ont été abordés via le couplage des méthodes DOSY rapides avec des méthodes d’hyperpolarisation qui permettent d’augmenter l’intensité du signal. La combinaison des méthodes de diffusion conventionnelles avec les méthodes avancées de RMN ultrarapide et d’hyperpolarisation permettront des avancées significatives pour l’analyse de mélanges, en particulier les mélanges dynamiquesNMR spectroscopy is a powerful tool that allows a direct study of mixtures in a non-invasive manner. The NMR spectra of molecular species in mixtures can be separated with diffusion-ordered spectroscopy (DOSY), a ‘virtual chromatography’ approach based on the measurement of translational diffusion coefficients. Major limitation of DOSY comes from the time-dependent diffusion dimension, which results in long experiment durations, and also from the low sensitivity of NMR. The present work aims to build an innovative tool for mixtures characterization that will be faster and more efficient for low concentrated samples. We first generalized the concept of nD spatially encoded (SPEN) DOSY experiments for the analysis of complex mixtures. As bring forward by the so-called “ultrafast NMR” (UF NMR), the use of a spatial dimension to encode diffusion can accelerate experiments by several orders of magnitude since it replaces the sequential acquisition of sub-experiments by a parallel acquisition in different slices of the sample. More advanced exploration of SPENDOSY were carried out using numerical simulations for purpose of resolution and accuracy improvement. To address sensitivity issues, we then demonstrated that SPENDOSY data can be collected for hyperpolarized substrates. This particular coupling between conventional diffusion-based method with advanced techniques such as ultrafast NMR and hyperpolarization should mark a significant progress for complex mixtures analysis especially for time-evolving processes
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Veitshans, Thomas. "Propriétés des réseaux permanents ou temporaires dans les polymères : gonflement ; RMN et simulation ; RMN et écoulement". Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10206.
Testo completoAbstract (sommario):
Sont presentes trois projets permettant de mieux comprendre la structure de systemes polymeres et les liens entre cette structure et les grandeurs de l'approche rmn. Dans la partie etude de gels bimodaux nous mettons en evidence une relation entre des parametres rmn et des moments de la distribution de la longueur des chaines entre deux nuds. Nous developpons en outre une version bimodale du theoreme c#* que nous verifions. Le deuxieme projet est intitule simulation de la relaxation de l'aimantation transversale d'une chaine gaussienne en solution diluee, fixee aux extremites. Nous creons un code de calcul adapte a cette premiere etude numerique dans le domaine de l'approche rmn aux systemes polymeres. Le potentiel de telles etudes est montre par une analyse de la relaxation de l'aimantation transversale m#x(t). La partie relaxation de l'aimantation transversale d'un fluide de polymeres enchevetres et soumis a un cisaillement concerne l'etude du reseau temporaire des enchevetrements. Nous presentons un dispositif original permettant d'observer par rmn des fluides cisailles. Nous avons observe qu'un cisaillement n'a pas d'influence sur la fonction m#x(t) d'une solution semi-diluee dans la gamme des taux de cisaillement etudies. Cette etude necessite d'etre completee par des etudes subsequentes que nous specifions. Par ailleurs, d'autres etudes consecutives aux trois projets de recherche sont proposees. En particulier, nous decrivons une etude qui mettrait en evidence l'objectif commun des trois projets : mieux comprendre la physique de systemes polymeres et cela grace aux moyens que nous donne l'approche rmn.
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Al-Asad, Zahir. "Implementation of NURBS Objects in a Ray TracingCode for RCS Simulation". Thesis, Högskolan i Gävle, Ämnesavdelningen för elektronik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-7713.
Testo completo
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Silva, Alessandro Alves da. "Efeitos topográficos em espectros RBS". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-09042008-142058/.
Testo completoAbstract (sommario):
A medida da rugosidade de uma superfície costuma produzir resultados que dependem da metodologia empregada. A microscopia eletrônica de varredura, SEM, a microscopia de força atômica, AFM e a perfilometria são algumas das técnicas costumeiramente empregadas na caracterização de superfícies rugosas. Esse trabalho explora a e desenvolve o uso da espectrometria de retroespalhamento Rutherford, RBS, para medir e quantificar a rugosidade de uma superfície. Quatro diferentes amostras com rugosidade periódica e controlada (duas retangulares e duas senoidais) com razão de aspecto suficientemente grande que produzam efeitos mensuráveis por RBS, foram produzidas por interferometria óptica. Os espectros RBS experimentais foram convertidos em rugosidade rms e comparados com resultados de SEM e AFM. Medir rugosidade através de RBS permite inspecionar uma área (da ordem de alguns mm2) e profundidades muito maiores que as acessíveis por AFM, apesar de ainda limitados pela resolução em energia intrínseca da metodologia RBS.Measuring the roughness of a surface use to produce results which depend on the employed methodology. Scanning Electronic Microscopy, Atomic Force Microscopy, profilometry, are some of the techniques used to characterize surface roughness. This work explores and develops the use of Rutherford Backscattering Spectrometry to measure and quantify the roughness of a surface. Four different samples with controlled and periodic surface profiles (two rectangular waved, and two sinusoidal), with enough aspect ratio to, give measurable effects in an RBS analysis, were produced by optical interferometry to test and verify the proposed methodology. The experimental RBS spectra were converted into rms roughness and compared to SEM and AFM measurements. Measuring roughness by RBS enables one to inspect a much bigger area (of the order of some mm2) and with more depth resolution, than by using an AFM, yet still limited by the experimental intrinsic energy resolution of the RBS methodology.
12
Chesneau, Erwan. "Développement d'une nouvelle approche pour la modélisation structurale de verres boratés : combiner Résonance Magnétique Nucléaire (RMN) et Dynamique Moléculaire". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLV058/document.
Testo completoAbstract (sommario):
Les verres sont des matériaux utilisés dans de très nombreux domaines. Cependant leur structure reste à ce jour peu connue du fait de l’absence d’ordre à longue distance rendant difficile la résolution de la structure à l’échelle atomique. Il est admis que les verres sont constitué d’un enchainement désordonné d’unités élémentaires par exemple des triangles et tétraèdres de bore dans le cas des verres de borates. La résonance magnétique nucléaire (RMN) a démontré être une technique de choix pour l’étude des verres, permettant de mesurer la proportion de chaque unités. Toutefois, la résolution structurale du verre reste aujourd’hui un enjeu scientifique majeur afin de mieux comprendre les relations propriétés-composition. Cette thèse a pour objectif de développer des méthodes combinant des expériences de RMN 1D et 2D avec des calculs DFT de paramètres RMN effectués sur des modèles numériques afin de caractériser la signature spectrale de l’ordre à moyenne distance. Sur une première série de verres de borates de sodium, il a été mis en évidence que seul la dynamique moléculaire (DM) ab-initio permet de reproduire des unités superstructurale telle que des anneaux, qui ont pu être caractérisées expérimentalement notamment grâce à la prise en compte fine des effet de distributions des paramètres RMN. La deuxième série sont des verres d’aluminoborate de lanthane pour laquelle les simulations par DM ne permettent pas un accord satisfaisant avec l’expérience. De ce fait, nous avons exploré une méthode par Reverse Monte Carlo contraintes par les données expérimentales. Cette méthode permet d’améliorer significativement l’accord des modèles avec l’expérience et reste donc à poursuivreGlasses are materials used in many fields. However, their structures still not well known because of the lack of long range order, making it difficult to extract the structural information of these materials. It is accepted that the glassy network is made of many elementary unit chains, being boron triangles and tetrahedron in the case of borate glasses. Nuclear magnetic resonance (NMR) has proven to be a vital characterization technique for the glasses study. It allows the measurement of proportion of each unit. The determination of the structural resolution of glasses remains a major scientific challenge for understanding of the relationship between the glass properties and it elemental compositions. This thesis aims to develop new NMR approach combining 1D, 2D and oxygen-17 NMR with DFT-GIPAW calculations on numerical models in order to characterize the intermediate ranger order NMR fingerprint. The first study is on sodium borate glasses. It highlighted that only ab-initio molecular dynamics (MD) can reproduce the boron rings, which have been confirmed by the NMR data, taking into account of the fine NMR parameters distributions effects. The second study is on aluminoborate glasses. Unlike the previous, the computed MD structures are not in agreement with NMR data. Thereby, a diferente stuctural simulation is applied. Refined models have been determined by Reverse Monte Carlo by constraining few experimental NMR data. This method allows to significantly improve the agreement between sumulated models and the experiment
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Klähn, Marco. "Untersuchung des intrinsischen GTPase-Mechanismus von Ras p21 mit Mitteln der Molekulardynamik-Simulation und QM/MM-Kraftfeld". [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969939345.
Testo completo
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Carof, Antoine. "Modélisation de la relaxométrie RMN pour des ions mono-atomiques quadrupolaires en phase condensée". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066244/document.
Testo completoAbstract (sommario):
L'interprétation des expériences de relaxométrie RMN nécessite une modélisation précise des interactions entre le noyau étudié et son environnement. Pour un noyau quadrupolaire, l'interaction entre le gradient du champ électrique (EFG) émis par l'environnement avec le quadruple électrostatique du noyau est prépondérante. Notre travail a porté sur le développement du calcul des temps de relaxation RMN pour ces noyaux par simulation moléculaire. Nous nous sommes intéressés à la relaxation d'ions mono-atomiques en phase condensée à travers deux systèmes simples et réalistes : des solutions aqueuses d'électrolytes et des verres de silicate de sodium. L'EFG dé aux électrons de l'ion est obtenu en calculant la réponse du nuage électronique grâce à des calculs quantiques combinés à une récente méthode pour reconstruire la contribution des électrons de cœur. L'EFG dû à l'environnement est obtenu à partir d'une simulation moléculaire où les interactions sont décrites par un champ de force polarisable nouvellement développé. Les temps de relaxation obtenus en combinant ces deux contributions reproduisent correctement les résultats expérimentaux. Les simulations moléculaires nous permettent aussi d'extraire les mécanismes microscopiques. Pour les ions dans l'eau à dilution infinie, nous avons étudié les propriétés statistiques et dynamiques des fluctuations de l'EFG. Nous avons montré en particulier le rôle fondamental des fluctuations de densité de l'eau dans la première sphère de solvatation de l'ion. Cette thèse ouvre la voie à une meilleur compréhension des processus de relaxation RMN des ions mono-atomiques quadrupolaires dans des systèmes simples ou complexesInterpreting NMR relaxometry experiments requires an accurate modeling of interactions between the nucleus under study and its environment. For a quadrupolar nucleus, the interaction between the electric field gradient (EFG) arising from the environment and the electrostatic quadrupole of the nucleus is preponderant. The present work deals with a new method to compute NMR relaxation times for such nuclei with molecular simulations. We consider the relaxation of monoatomic ions in condensed matter through two simple and realistic systems: aqueous electrolytes and sodosilicate glasses. The EFG due to electrons around the ion is obtained by computing the electronic response with quantum calculation combined with a new method to obtain the contribution of core electrons. The EFG due to the environment is obtained from a molecular simulation where interactions are described using a recently developed polarisable force field. NMR relaxation times obtained by combining both these contributions compare well with experimental data. Molecular simulations allow us to highlight the microscopic mechanisms. For ions in water at infinite dilution, we studied the statistical and dynamical properties of EFG fluctuations. We notably demonstrated the primary role of water density fluctuations in the first solvation shell around the ion. This thesis opens the way for a better understanding of the mechanism behind the NMR relaxation of monoatomic and quadrupolar ions in simple and complex systems
15
Abba, Omar Sabina. "Capability of CORDEX RCMs in simulating extreme rainfall events over South africa". Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/9103.
Testo completoAbstract (sommario):
Includes bibliographical references.In South Africa, extreme rainfall events often lead to widespread destruction, damage infrastructure, displace communities, strain water management and even destroy lives. Past studies have shown that reliable predictions of extreme rainfall events from regional climate models (RCMs) could help reduce the impact of these events. The present study evaluates the ability of nine RCMs in simulating extreme rainfall events over South Africa, focusing on the Western Cape (WC) and east coast (EC) areas. This study defines an extreme rainfall over a location as rainfall that is equal to or above the 95th percentile of the rainfall distribution at that location, and defines widespread extreme rainfall events (WEREs) over an area as events during which more than 50 of the grid-points in the area experience extreme rainfall. The 95th percentile threshold values were calculated over 11 years (1998-2008) of South Africa’s daily rainfall data from the nine RCMs (CCLM, REMO, PRECIS, CRCM5, ARPEGE, REGCM3, WRF, RACMO and RCA35), which participated in the Coordinated Regional Climate Downscaling Experiment (CORDEX) and used ERA-Interim (ERAINT) as their boundary forcing. The simulations were compared to two observation datasets (TRMM and GPCP), and to ERAINT rainfall data to understand whether these RCMs improve on the results from ERAINT. A self organizing map (SOM) was used to characterize WEREs identified in all the datasets into archetypal groups, and ERAINT data is used to describe the underlying circulations for each archetypal rainfall pattern. The number of WEREs mapped to each rainfall pattern for each dataset allows us to get an idea of whether certain RCMs are more likely to simulate certain rainfall patterns.
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Simon, Christian. "Etude du mélange 2HF/KF par dynamique moléculaire numérique". Paris 6, 2001. http://www.theses.fr/2001PA066227.
Testo completo
17
Negrevergne, C. "Controle quantique grâce aux méthodes de RMN. Application à la simulation de systèmes quantiques". Phd thesis, Université Sciences et Technologies - Bordeaux I, 2002. http://tel.archives-ouvertes.fr/tel-00004371.
Testo completoAbstract (sommario):
Manipuler l'information selon les lois de la physique quantique permet d'ameliorer l'efficacite avec laquelle on traite certains problemes.Les methodes de Resonance Magnetique Nucleaire en solution permettent d'initialiser, de manipuler et d'observer l'etat d'un systeme de spins 1/2 couples. ces methodes ont ete utilisees pour realiser experimentalement un petit processeur d'information quantique (QIP pour "Quantum Information processor") pouvant executer une centaine d'operations elementaires. un des themes principaux de ce travail a ete de concevoir, d'optimiser et de valiser des sequences d'impulsions necessaires pour "programmer" ce QIP.
ces techniques ont ete utilises pour executer un algorithme quantique de simulation des systemes anyoniques. des resultats experimentaux pour la determination des energies propres et de fonctions de correlation d'un systeme illustratif de fermions sur reseaux ont ete obtenus permettant de valider l'algorithme de simulation dans son principe et son execution experimentale.
18
Negrevergne, Camille. "Contrôle quantique grâce aux méthodes de RMN : application à la simulation de systèmes quantiques". Bordeaux 1, 2002. http://www.theses.fr/2002BOR12593.
Testo completoAbstract (sommario):
Manipuler l'information selon les lois de la physique quantique permet d'améliorer l'efficacité avec laquelle on traite certains problèmes. Les méthodes de Résonance Magnétique Nucléaire en solution permettent d'initialiser, de manipuler et d'observer l'état d'un système de spins 1/2 couplés. Ces méthodes ont été utilisées pour réaliser expérimentalement un petit processeur d'information quantique (QIP) pouvant exécuter une centaine d'opérations élémentaires. Un des thèmes principaux de ce travail a été de concevoir, d'optimiser et de valider des séquences d'impulsions nécessaires pour "programmer" ce QIP. Ces techniques ont été utilisées pour exécuter un algorithme quantique de simulation des systèmes anyoniques. Des résultats expérimentaux pour la détermination des énergies propres et de fonctions de corrélation d'un système illustratif de fermions sur réseaux ont été obtenus permettant de valider l'algorithme de simulation dans son principe et son exécution expérimentale.
19
Mondloch, Riley. "Characterization of agricultural floodplain scour using one-dimensional hydraulic simulation". Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/1487.
Testo completoAbstract (sommario):
The Iowa Flood Center (IFC), a unit of The University of Iowa's IIHR - Hydroscience & Engineering, and the Iowa Department of Natural Resources are developing a statewide floodplain boundary dataset to provide information that is critical to proper flood mitigation planning. During flooding, soil loss from agricultural land, in addition to inundation, can have a substantial economic impact on an agricultural state like Iowa. The ability to identify areas with a high potential to experience scour during flooding could assist farmers and land owners in making better land management decisions. Currently, the IFC statewide floodplain mapping program is creating annual exceedance probability floodplain data for all Iowa streams. The effort described herein has developed methods to take advantage of this large dataset, applying uniform open channel flow theory to spatially characterize scour potential using custom tools created with GIS model builder. The results of this thesis are being used by the Iowa Natural Heritage Foundation (INHF) and the IFC to develop a program through which certified crop consultants can help farmers make more informed land management decisions based on risk of flood related soil loss.
20
Ong, Lay Im. "Investigations into profile ring rolling of aluminium alloy bicycle wheel rims through experiments and numerical process simulations". Thesis, Brunel University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280726.
Testo completo
21
Davis, Mallory. "Numerical Simulation of Unsteady Hydrodynamics in the Lower Mississippi River". ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/1126.
Testo completoAbstract (sommario):
Alterations along the Mississippi River, such as dams and levees, have greatly reduced the amount of freshwater and sediment that reaches the Louisiana coastal area. Several freshwater and sediment diversions have been proposed to combat the associated land loss problem. To aid in this restoration effort a 1-D numerical model was calibrated, validated, and used to predict the response of the river to certain stimuli, such as proposed diversions, channel closures, channel modifications, and relative sea level rise. This study utilized HEC-RAS 4.0, a 1-D mobile-bed numerical model, which was calibrated using a discharge hydrograph at Tarbert Landing and a stage hydrograph at the Gulf of Mexico, to calculate the hydrodynamics of the river. The model showed that RSLR will decrease the capacity of the Lower Mississippi River to carry bed material. The stage at Carrollton Gage is not significantly impacted by large scale diversions
22
Enea, Gabriele. "Simulation-Based Study to Quantify Data-Communication Benefits in Congested Airport Terminal Area". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/31206.
Testo completoAbstract (sommario):
The scope of this study was to evaluate the impact of the air traffic controller-to-pilot communication standard known as CPDLC or Data-Communication on the future air traffic operations. The impact was evaluated from the double viewpoint of airport delays and air traffic controllersâ workload. RAMS simulation software is used to perform all the runs and from its output data the values of terminal area delays and controllers workload are obtained. The New York Metroplex terminal area was used as a case study. Because of its complexity, where three major airports (i.e. JFK, Newark, and La Guardia) interact and constraint each other, this area was particularly interesting to be studied and the data analyzed gave a valuable insight on the possible future impact of Data-Communication in congested terminal areas. The results of the study, based on some previous man-in-the-loop simulations performed by the FAA in the nineties, showed that significant potential benefits could be obtained with the complete implementation of such technologies in the workload experienced by air traffic controllers. Moreover some small but not negligible benefits were obtained in the total delays accrued by each airport studied. On the other hand, the simulations of the future demand predicted by the FAA demonstrated that without a significant increment in capacity or limitation on the traffic growth intolerable delays would be recorded across the NAS in the future. For the complexity of the simulation model calibration and for the very time-consuming run time not all the scenarios described in the methodology were tested, demonstrating the weakness of RAMS as a ground simulation model.Master of Science
23
OHASSAN, ABDELHAMID. "Synthese et analyse conformationnelle d'oligopeptides aromatiques par resonance magnetique nucleaire (rmn) et par simulation moleculaire (sm)". Paris 7, 1993. http://www.theses.fr/1993PA077290.
Testo completoAbstract (sommario):
L'objectif de ce travail est la synthese d'oligopeptides artificiels a degres de liberte reduits afin de pouvoir en predire la conformation dans le but d'acceder a des analogues d'enzymes. La premiere partie de ce travail a donc consiste en la synthese de deux familles d'oligopeptides metahydroxybenzamido, et metamethoxybenzamido-, par la methode classique pas a pas. Le dimere d'acide 3-(3-amino-5-hydroxybenzamido)-5-hydroxybenzoique a fait l'objet d'une analyse complete par modelisation moleculaire, et resonance magnetique nucleaire mono et bidimensionnelle. La modelisation moleculaire a permis de reproduire fidelement les temps de relaxation et les parametres geometriques deduits des observations rmn, et a montre que le dimere existe sous la forme de deux conformeres privilegies en solution en quantites approximativement egales. A partir de ces donnees, on a pu montrer que, pour une chaine constituee de ce monomere (acide 3-amino-5-hydroxybenzoique), differentes conformations etaient possibles, helicoidale, globulaire, ou fibreuses
24
Rodriguez-Vilca, Juliet, Jose Paucar-Vilcañaupa, Humberto Pehovaz-Alvarez, Carlos Raymundo, Nestor Mamani-Macedo e Javier M. Moguerza. "Method for the Interpretation of RMR Variability Using Gaussian Simulation to Reduce the Uncertainty in Estimations of Geomechanical Models of Underground Mines". Springer, 2020. http://hdl.handle.net/10757/656171.
Testo completoAbstract (sommario):
El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado.The application of conventional techniques, such as kriging, to model rock mass is limited because rock mass spatial variability and heterogeneity are not considered in such techniques. In this context, as an alternative solution, the application of the Gaussian simulation technique to simulate rock mass spatial heterogeneity based on the rock mass rating (RMR) classification is proposed. This research proposes a methodology that includes a variographic analysis of the RMR in different directions to determine its anisotropic behavior. In the case study of an underground deposit in Peru, the geomechanical record data compiled in the field were used. A total of 10 simulations were conducted, with approximately 6 million values for each simulation. These were calculated, verified, and an absolute mean error of only 3.82% was estimated. It is acceptable when compared with the value of 22.15% obtained with kriging.
25
Lindblad, Erik. "Designing a framework for simulating radiology information systems". Thesis, Linköping University, Department of Computer and Information Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15211.
Testo completoAbstract (sommario):
In this thesis, a very flexible framework for simulating RIS is designed to beused for Infobroker testing. Infobroker is an application developed by MawellSvenska AB that connects RIS and PACS to achieve interoperability by enablingimage and journal data transmission between radiology sites. To put the project in context, the field of medical informatics, RIS and PACS systems and common protocols and standards are explored. A proof-of-concept implementation of the proposed design shows its potential and verifies that it works. The thesis concludes that a more specialized approach is preferred.
26
Ssembatya, Martin. "PERFORMANCE EVALUATION OF A SOLAR COOLING SYSTEM IN UAE – RAS AL KHAIMAH BY BOTH EXPERIMENT AND SIMULATION". Thesis, Högskolan i Gävle, Akademin för teknik och miljö, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-14312.
Testo completoAbstract (sommario):
In United Arab Emirates (UAE), a huge proportion of electrical energy consumed in buildings is used to run air conditioning equipments. This is because UAE’s climate is characterized by very high ambient temperatures and high humidity, especially during summer periods. There is need to promote air conditioning systems that are run by renewable energy based power because of the environment threats and energy security negative issues associated with conventional fossil fuel – energy powered systems. The huge buildings’ cooling loads occur during periods of high solar insolation; this creates a huge potential of using solar powered cooling systems for air conditioning applications. However, the solar air conditioning systems still face a number of challenges in UAE which include; the availability of cheap electricity from fossil fuel resources and lack of government incentives to promote renewable energy resources. In order to understand the potential of applying solar cooling systems for air conditioning applications versus conventional systems, there was a need to experimentally and/or theoretically evaluate the performance of pilot solar cooling systems in UAE. In this project, the performance of a 10 TR solar cooling system in Ras Al Khaimah (RAK) Emirate of UAE was evaluated by both experiment and theoretical simulation. TRNSYS, a transient – systems simulation software that was developed by Solar Energy Laboratory – University of Winsconsin, was used for the purpose of the theoretical simulations of the system. The solar cooling absorption equipment used for this study is an R&D system that was developed by CSEM – uae in RAK for the purpose of assessing the potential of applying solar cooling systems in UAE. The solar cooling system is based on absorption chilling technology run by hot water produced by a field of evacuated tube solar collectors. Experimental results were compared with TRNSYS – theoretical simulations results and areas of possible improvements in the solar cooling system were recommended. Results of the study show that the solar cooling system runs with a COP in the range of 0.60 – 0.80, with an average COP of 0.70. It was also observed that the inlet cooling and hot water temperatures to the absorption chiller have a huge impact on the performance of the solar cooling system. A need to isolate the absorption chiller hot water circuit from the hot water stratified tank by incorporation of a heat exchanger between the chiller and the stratified tank was also identified. This will help to improve the degree of stratification during the operation of the solar cooling system. Theoretical performance evaluation of the system using a typical TMY2 weather data shows that the system can meet its cooling requirement for at least eight (8) months of the year. In conclusion, this study has indicated that solar cooling for air conditioning application in UAE has a huge potential. However, further research is necessary to enable improvement of the performance of solar cooling systems and to assess the possibility of commercialization of such systems.
27
Épouhé, Céline. "Contribution à l'élucidation structurale : simulation de comportements de sous-structures partiellement définies issues de la RMN-2D". Paris 7, 2002. http://www.theses.fr/2002PA077077.
Testo completo
28
Lindgren, Jonas. "Evaluation of CST Studio Suite for simulation of radar cross-section". Thesis, Umeå universitet, Institutionen för fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-187751.
Testo completoAbstract (sommario):
When designing military vehicles, it is of interest to make the vehicles difficult to detect using radar. The radar cross-section (RCS) property indicates how easily a vehicle is detected by radar and should thus be minimized. However, the RCS of a vehicle represents the cross-sectional area of a perfectly reflecting sphere that would produce the same reflection strength as the vehicle in question. Since this is extremely complicated to calculate as military vehicles are quite complex, these calculations are performed using computational simulations. BAE Systems Hägglunds is looking into changing from their current simulation software OPTISCAT to CST Studio Suite and thus want to know how CST performs and compares against OPTISCAT. In this work, we show that CST obtains results within 2% of theoretical data when simulating a sphere and a slab. When simulating vehicles, the RCS difference between the two software is from 3% to 55% while showing similar general behavior. Results indicate that CST performs well when simulating simple objects but deviates from OPTISCAT when simulating the vehicle. It is not surprising that the software does not match up perfectly since they use different theoretical approaches, OPTISCAT uses physical optics while CST an extension to physical optics called the Shooting Bouncing Ray method. Even though the software differs to this extent it is most likely possible that CST can be a suitable replacement for OPTISCAT. When looking at RCS the important part is the location of spikes and since they have similar general behavior, those spikes may still be possible to identify. This thesis will hopefully act as a starting point for further examination of CST as a software for simulating RCS, for example by comparing results from CST to experimentally measured data. Hopefully it will also be used to improve the design process of making military vehicles harder to detect.
29
Del, Riego Navarro Andrés, e Pérez Álvaro Rico. "Simulation-based multiobjective optimization and availability analysis of reconfigurable manufacturing systems". Thesis, Högskolan i Skövde, Institutionen för ingenjörsvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-20196.
Testo completoAbstract (sommario):
Due to the changes and improvements that have occurred over the years, the manufacturing sector has evolved. Companies in the 21st-century face changes in the marketplace that are difficult to predict due to international competition and the rapid emergence of new products. To cope, companies must reinvent themselves and design manufacturing systems that seek to produce quality and low-cost products, and respond to the changes that must be faced. These capabilities are encompassed in reconfigurable manufacturing systems (RMS), capable of dealing with uncertainties quickly and economically. On the other hand, production planning with this type of system presents a significant challenge. Although simulation-based optimization techniques have been applied to address certain RMS challenges, only a few studies have applied simulation-based multi-objective optimization to simultaneously address several conflicting design objectives, as is the case in this project. This project aims to investigate some aspects using SBMO that directly affect the performance of a plant and demonstrate the usefulness of the method.Det finns övrigt digitalt material (t.ex. film-, bild- eller ljudfiler) eller modeller/artefakter tillhörande examensarbetet som ska skickas till arkivet.
30
Gärtner, Johan, e Philip Johansson. "AN ADAPTIVE CONTROL SYSTEM BASED ON PID, I2PD AND RLS, A SIMULATED DESIGN FOR UAVS". Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-35614.
Testo completoAbstract (sommario):
During this master thesis an adaptive control system for angular velocity was developed. The approach focuses on radio controlled quadrotors and thereby targets a computational efficient solution. The adaptation is divided into two steps. First, an Integral Squared Plus Time Delay (I2PD) model estimation is done through the Recursive Least Squares (RLS) algorithm. Second, control parameters for the quadrotors Proportional Integral Derivative (PID) controller are found by using empirically modified Tuning Rules (TRs) which are based on the I2PD model. Simulation results show the benefits of an adaptive tuning algorithm in regards of the time consuming process of manually tuning a PID controller as well as robustness against both predictable and unpredictable system changes. This includes actuator degradation, battery consumption, changes in weight or inertia etc. However, it is apparent that the tuning algorithm demands an arbitrary initial approximation to be stable at initialization.
31
Brun, Sorribas Carlos. "A comprehensive methodology to predict forest res behavior using complementary models". Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/283359.
Testo completoAbstract (sommario):
Els incendis a gran escala suposen un gran repte degut a l'impacte que tenen en la societat a diversos nivells. Aquest fenomen físic és un problema multidisciplinar que requereix de l'esforç d'investigadors de diferents camps. Així doncs, predir el comportament dels incendis forestals i minimitzar els seus efectes són els principals objectius d'aquest treball. Un dels principals problemes d'aquests tipus de fenòmens és la incertesa i la imprecisió dels paràmetres d'entrada. Per abordar aquest problema, ens basem en una estratègia de predicció basada en tècniques de calibració, que tracten de sintonitzar aquests paràmetres per tal de proporcionar una predicció més precisa, i reduir la incertesa sobre els paràmetres. En aquest treball, proposem estratègies per resoldre certes restriccions associades a aquesta tècnica. La distribució espacial dels paràmetres ha estat considerada uniforme en tot el terreny, per la qual cosa s'introdueix un model complementari que simula l'efecte del vent sobre terrenys complexes, degut al paper fonamental del vent en la propagació del foc. A més a més, es suggereix acoblar un model meteorològic, per enriquir el coneixement del sistema sobre l'evolució temporal de les variables meteorològiques.
Tots aquests components s'integren en un entorn de simulació i predicció, i es defineix una metodologia per simular incendis forestals reals, en la qual s'especifiquen els passos, procediments, models i eines necessàries per a construir un sistema d'avaluació del risc d'incendis forestals a temps real. Aquest sistema utilitza recursos i paradigmes propis de la Computació d'Altes Prestacions per proporcionar una resposta en un temps acceptable, degut a l'elevat cost computacional de l'avaluació de múltiples escenaris i de la integració de models complementaris.Los incendios a gran escala suponen un gran reto debido al impacto que tienen en la sociedad a múltiples niveles. Este fenómeno físico es un problema multidisciplinar que requiere del esfuerzo de investigadores de campos diversos. Por lo tanto, predecir el comportamiento de los incendios forestales y minimizar sus efectos son las principales metas de este trabajo. Uno de los problemas principales de este tipo de fenómenos es la incertidumbre e imprecisión de los parámetros de entrada. Para abordar este problema, nos basamos en una estrategia de predicción basada en técnicas de calibración, que trata de sintonizar estos parámetros para proporcionar una predicción más certera, y reducir la incertidumbre sobre los parámetros. En este trabajo, proponemos estrategias para resolver ciertas restricciones asociadas a esta técnica. La distribución espacial de los parámetros ha sido considerada uniforme a lo largo del terreno, por lo que introducimos un modelo complementario para simular el efecto del viento sobre terrenos complejos, debido al papel fundamental del viento en la propagación del fuego. Además, se sugiere acoplar un modelo meteorológico para enriquecer el conocimiento del sistema sobre la evolución temporal de las variables meteorológicas. Todos estos componentes se integran en un entorno de simulación y predicción, y se define una metodología para simular incendios forestales reales donde se especifican los pasos, procedimientos, modelos, y herramientas necesarias para construir un sistema de evaluación del riesgo de incendios forestales en tiempo real. Este sistema se sirve de recursos y paradigmas propios de la Computación de Altas Prestaciones para proporcionar una respuesta en un tiempo aceptable debido al alto coste computacional de evaluar múltiples escenarios, e integrar modelos complementarios.
Large scale forest fires suppose a great challenge due to their impact on society on many levels. This physical phenomenon is an interdisciplinary problem that requires the efforts of researchers across various fields. Therefore, predicting the behavior of forest fires and minimizing the effects of this hazard is the main goal of this work. One of the major problems with this kind of hazard is the uncertainty and imprecision of the input parameters. We rely on a prediction strategy based on calibration techniques that try to tune these parameters to produce a more accurate prediction and reduce the uncertainty of the parameters. In this work, we propose strategies to solve some of the restrictions associated with this technique. The spatial distribution of the parameters has been considered uniform along the terrain, and we introduce a complementary model to simulate the wind behavior over complex terrains, due to the leading role of wind in fire spreading. We also suggest coupling a meteorological model to enrich the knowledge of the system of the temporal evolution of the weather variables. All these components are integrated in a simulation and prediction framework, and a methodology to simulate real forest fire scenarios is defined in which the steps, processes, models and tools to build an effective real-time forest fire assessment system are specified. This system relies on High Performance Computing resources and paradigms to provide a response in an acceptable time due to the high computational cost of evaluating several scenarios and integrating complementary models.
32
Hanslík, Radovan. "Odrazná plocha osobních automobilů". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2019. http://www.nusl.cz/ntk/nusl-400701.
Testo completoAbstract (sommario):
This diploma thesis is aimed at radar cross section of passenger cars. Basic scattering parameters of simple targets are described. Some numeric methods used for computing radar cross section are discussed. CST Microwave Studio is used for simulation of passenger car with two different solvers. For the results there are plots of radar cross section of a car for 1 GHz, 24.125 GHz and 33 GHz. There is a plot of visualized hotspots.
33
Harket, Mouna. "Analyse structurale de sucres par RMN ²⁹Si, ¹³C : utilisation de quelques séquences INEPT et d'un programme de simulation". Bordeaux 1, 1995. http://www.theses.fr/1995BOR10528.
Testo completoAbstract (sommario):
Une exploitation des proprietes de l'inept ²⁹si et ¹³c, appliquee aux sucres per-trimethylsilyles et permethyles, permet d'effectuer une analyse structurale. Les spectres experimentaux, souvent tres complexes, sont analyses par comparaison avec des spectres calcules. L'attribution des atomes de silicium ou de carbone d'environnement geometrique different est basee sur des proprietes de phase et d'intensite theoriquement previsibles
34
Pouységu, Laurent. "Détermination structurale de sucres par RMN 29Si,13C et 31P : expériences INEPT et DEPT associées à des simulations de spectres". Bordeaux 1, 1997. http://www.theses.fr/1997BOR10583.
Testo completoAbstract (sommario):
UNE METHODE GENERALE DE DETERMINATION STRUCTURALE DES SUCRES PAR RMN 29Si,13C et 31P A ETE DEVELOPPEE. L'EXPLOITATION DES PROPRIETES DES SEQUENCES INEPT (NON REFOCALISE, REFOCALISE-DECOUPLE 1D OU 2D) ET DEPT ETENDU PERMET DE REALISER L'ANALYSE CONFORMATIONNELLE D'HEXOPYRANOSES DIVERSEMENT SUBSTITUES. ASSOCIEES A DES SIMULATIONS DE SPECTRES, CES EXPERIENCES CONDUISENT A LA LOCALISATION DES SUBSTITUANTS SUR LE CYCLE PYRANOSIQUE, AINSI QU'A L'ATTRIBUTION DES ATOMES DE CARBONE CYCLIQUES. UNE PROPRIETE DE COUPLAGE HOMONUCLEAIRE 31P-31P (INTERACTION DE TYPE COORDINATIF) A EGALEMENT ETE OBSERVEE POUR LA PREMIERE FOIS LORS DE L'ANALYSE DE SUCRES PERPHOSPHITYLES.
35
Johnston, Michael. "Development of a molecular simulator and its application to the study of biomolecular dynamics". Doctoral thesis, Universitat Pompeu Fabra, 2009. http://hdl.handle.net/10803/7172.
Testo completoAbstract (sommario):
Aquesta tesi tracta de la creació d'un nou programari de codi obert i d'una interfície de programació (API) per realitzar simulacions (bio) moleculars, així com de a la seva aplicació posterior a problemes biològics. El nou programa, Adun, es focalitza en les àrees clau del càlcul d'energies lliures, el desenvolupament ràpid de programari i la productivitat d'alt rendiment. Mètodes com SCAAS, EVB i Born generalitzat han estat implementats per tal d'assolir el primer objectiu. La presencia d'aquestes tècniques, a m´es d'altres, mostra la velocitat de desenvolupament d'Adun. Totes les característiques s´on accessibles mitjanant una interfície gràfica d'usuari avançada que proveeix de noves capacitats, com el tractament de dades integrat o la compartició de dades i de càlculs distribuïts. La capacitat d'Adun de tractar problemes biològics és il·lustrada amb la investigació de la dinàmica de la proteïna Ras i el desenvolupament, implementació i demostració d'un nou mètode per a la determinació de camins de transició. A més, per tal de demostrar el potencial del programa Adun, aquests estudis també proporcionen una visió avançada sobre l'ús de la informació dinàmica en determinar la unció de les proteïnes. L'estat actual del programa i els resultats dels dos estudis és, doncs, discutit, i es donen indicacions dels objectius i direccions futurs. Finalment s'examina el paper dels científics computacionals com desenvolupadors d'eines, per a ells mateixos o per a tota la comunitat científica.This thesis deals with the creation of a new open-source program and API for biomolecular simulation and its subsequent application to biological problems. The program, Adun, focuses on the key areas of biological free-energy calculations, rapid development and highperformance productivity. Methods such as SCAAS, EVB and switched Generalised-Born have been implemented to realise the first aim. The presence of these techniques, along with a multitude of others, verifies Adun's rapid development potential. All these features are united by an advanced graphical user interface which provides novel capabilities such as inbuilt data management, and distributed datasharing and computation. Adun's ability to tackle biological problems is illustrated with an investigation of Ras dynamics and the development, implementation and testing of a novel method for determining transition paths. In addition to concretely demonstrating Adun's potential these studies also provide insight into the use of dynamic information in elucidating protein function. The current state of the program and the results of the two studies is discussed and indications of future aims and directions given. In addition the role of computational scientists as developers of tools, for themselves and the wider scientific community, is examined.
36
Salhani, Mohamad. "Modélisation et simulation des réseaux mobiles de 4ème [quatrième] génération". Phd thesis, Toulouse, INPT, 2008. http://oatao.univ-toulouse.fr/7725/1/salhani.pdf.
Testo completoAbstract (sommario):
Cette thèse porte sur l'interopérabilité et la qualité de service dans les réseaux de 4ème génération. En particulier, nous proposons des solutions d'intégration entre le réseau WiMAX et le système satellite DVB-RCS en s'appuyant sur le standard IEEE 802.21. Trois solutions peuvent être mises en place pour l'interconnexion de réseaux sans fil. Il s'agit de la technologie GAN soutenue par le 3GPP, du protocole FMIP proposé par l'IETF et du standard IEEE 802.21. Notre choix se porte sur ce denier standard car il propose un cadre générique pour l'interopérabilité des réseaux. En fait, nous proposons une architecture satellitaire à base de WiMAX, DVB-RCS et IEEE 802.21 et nous décrivons aussi la procédure de handover WiMAX/DVB-RCS. Par ailleurs, nous améliorons les performances des réseaux WiMAX en utilisant un handover horizontal avec un mécanisme de réservation de ressources. Ensuite, le réseau WiMAX est intégré dans un système satellite DVB-RCS afin d'étudier les performances de cette convergence avec une réservation de ressources. Les résultats obtenus montrent que les mécanismes de réservation améliorent les performances. Afin de permettre au trafic de passer d'un réseau à l'autre en garantissant une qualité de service, une mise en correspondance de la qualité de service entre les réseaux WiMAX et DVB-RCS est proposée. En outre, nous proposons un mécanisme d'admission de connexion CAC dans le cadre de l'interconnexion WiMAX/DVB-RCS. Plusieurs stratégies sont prises en compte afin de permettre une coopérative efficace entre les deux systèmes.
37
Mutisya, Sylvia Mueni. "Atomistic simulations of water confined in cement". reponame:Repositório Institucional da UFABC, 2018.
Cerca il testo completoAbstract (sommario):
Orientador: Prof. Dr. Caetano Rodrigues MirandaTese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, Santo André, 2018.
A pasta de cimento 'e um material complexo, heterog¿eneo e poroso com excelentes propriedades que o tornam um aglutinante adequado para aplica¸c¿oes em constru¸c¿oes. A qualidade e a durabilidade do cimento t¿em uma forte rela¸c¿ao com a 'agua contida nele. Embora uma boa compreens¿ao das intera¸c¿oes complexas entre os poros do cimento e os flu'ýdos confinados 'e necess'aria para resolver os atuais problemas de durabilidade, at'e ent¿ao nenhum modelo foi bem sucedido na captura de todos os processos e o papel da 'agua no cimento continua a ser uma 'area de pesquisa ativa. Com o intuito de contribuir para a compreens¿ao atual da estrutura do cimento, este trabalho se concentrou no estudo dos processos din¿amicos que acontecem na nanoescala da 'agua confinada em poros de cimento. Utilizamos simula¸c¿oes atom'ýsticas que v¿ao desde primeiros princ'ýpios at'e din¿amica molecular para estudar a principal fase de hidrata¸c¿ao, ou seja, hidrato de silicato de c'alcio (C¿S¿H), modelado por uma estrutura de tobermorita com defeitos. A partir de primeiros princ'ýpios, investigamos a morfologia da superf'ýcie da tobermorita a qual rege as intera¸c¿oes da 'agua com o modelo C-S-H. Demonstramos que a tobermorita forma cristais pseudo-hexagonais e a faceta mais est'avel 'e a (004). A fim de explorar sistemas maiores, checamos a transferabilidade do potencial cl'assico CLAYFF na descri¸c¿ao dos componentes do cimento atrav'es de um estudo comparativo entre simula¸c¿oes de mec¿anica molecular e DFT. Embora as frequ¿encias calculadas com DFT e CLAYFF sejam diferentes, as propriedades estruturais e termodinâmicas apresentam grande concord¿ancia, indicando que o potencial CLAYFF 'e adequado para nossos c'alculos. Um par¿ametro importante para quantificar a din¿amica da 'agua no nanoconfinamento 'e o tempo de relaxa¸c¿ao T2. Para validar a metodologia implementada na determina¸c¿ao te'orica do tempo de relaxa¸c¿ao T2, realizamos simula¸c¿oes para a 'agua confinado dentro de nanoporos de calcita (1¿6 nm). Observamos que a din¿amica translacional 'e a principal respons'avel pela relaxa¸c¿ao de spin das mol'eculas de 'agua pr'oximas 'a superf'ýcie. O tempo de relaxa¸c¿ao T2 para mol'eculas de 'agua adsorvidas na superf'ýcie 'e menor e independente do tamanho de poro, no entanto, uma relaxa¸c¿ao de spin do tipo bulk 'e observada no centro dos poros maiores que 3 nm. Buscando elucidar as diversas propriedades da 'agua nanoconfinada em poros C¿S¿H, dividimos nosso estudo em tr¿es partes. Inicialmente, nos dedicamos a compreender os efeitos de confinamento da 'agua entre camadas (< 1 nm) e poros de gel (1¿5 nm) do modelo C-S-H, assim como suas influ¿encias nas intera¸c¿oes de superf'ýcie. A natureza hidrof'ýlica da superf'ýcie C¿ S¿H 'e evidenciada pela din¿amica lenta da 'agua que interage diretamente com a superf'ýcie. Entre as camadas, a 'agua se encontra praticamente im'ovel e exibe propriedades similares aquelas observadas em 'agua super-resfriada. Na sequ¿encia, investigamos o transporte da 'agua dentro da pasta de cimento implementando a relaxa¸c¿ao de troca do tipo 2D T2¿T2 RMN entre poros de gel com 1 nm e 4 nm conectados entre si. Nossos resultados mostraram que h'a trocas de mol'eculas de 'agua entre poros com um tempo caracter'ýstico de troca de 18 ns. Finalmente, conclu'ýmos nossos estudos considerando a natureza particulada do C¿S¿H a fim de estabelecer uma conex¿ao entre os fen¿omenos observados nas escalas nano e meso. Demonstramos que a 'agua confinada dentro do ambiente C¿S¿H edge-edge apresenta uma din¿amica semelhante ao caso das superf'ýcies planares.
Cement paste is a complex, heterogeneous and porous material with outstanding properties that make it a suitable binder for construction applications. The quality and durability of cement have a strong relationship with the water contained in it. While a good understanding of the complex interactions between the cement pores and the confined fluids is necessary to solve the current durability issues, no single model has been successful in capturing all the processes so far and the role of water in cement still remains an area of active research. To contribute to the current understanding of cement structure, this work has focused on studying the dynamical processes happening at the nanoscale of water confined in cement pores. We employ atomistic simulations ranging from first principles to molecular dynamics to study the main hydration phase, i.e calcium silicate hydrate (C¿S¿H), modeled by a defected tobermorite structure. Starting from first principles, the surface morphology of tobermorite which governs the interactions of water with the C¿S¿H model was investigated. It was shown that tobermorite forms pseudohexagonal crystals and the most stable facet is the (004). To upscale the calculations, the transferability of CLAYFF in the description of cementitious materials was tested through a comparative molecular mechanics and DFT study. Although the frequencies calculated with DFT and CLAYFF differ, the structures and thermodynamic quantities agree quite well, making CLAYFF a reasonable potential for our cement calculations. An important parameter to quantify water dynamics in nanoconfinement is NMR T2 relaxation time. To underpin the implemented methodology for theoretical determination of T2 relaxation time, simulations were performed for water confined within calcite nanopores (1¿6 nm). It was revealed that translational dynamics are the main contribution to spin relaxation of near surface water molecules. The T2 relaxation time for water molecules directly adsorbed on the surface is short and pore size independent, however a bulk¿like spin relaxation is observed at center of pores larger than 3 nm. To disentangle the diverse properties of water nanoconfined in C¿S¿H pores, the study of water within C¿S¿H was subdivided into three parts. The first part was dedicated to understanding the relative effect of the C¿S¿H surface and progressive confinement to water confined in the interlayer (< 1 nm) and gel pores (1¿5 nm) of C¿S¿H model. The hydrophilic nature of the C¿S¿H surface is evidenced by the slow dynamics for the water interacting directly with the surface. Within the interlayer, water is highly immobile and exhibits similar properties as those observed in supercooled water. Next, transport within cement paste was investigated by implementing 2D T2¿T2 NMR exchange relaxation between a 1 nm and 4 nm gel connected pores. We showed that there is water exchange in gel pores quantified by an exchange time of 18 ns. Lastly, the particulate nature of C¿S¿H is taken into consideration to facilitate bridging the gap between the atomistic and the mesoscale cement understanding. It was shown that water confined within the C¿S¿H edge¿edge environment portrays similar dynamics as in the C¿S¿H planar surfaces.
38
Hajjar, Redouane. "RMN de l'interaction quadripolaire au second ordre d'un solide en rotation : théorie, simulation et application du MQMAS aux catalyseurs solides". Paris 6, 2007. http://www.theses.fr/2007PA066614.
Testo completoAbstract (sommario):
L’objectif de cette thèse est l’étude de l’interaction quadripolaire en RMN et l’application de la spectroscopie haute résolution MQMAS (Multiple Quantum Magic Angle Spinning) à des matériaux catalytiques. Nous avons mis au point des feuilles de calcul MATHEMATICA qui déterminent de façon automatique les expressions analytiques des tenseurs sphériques V(2,0), W(2,0) et W(4,0) du gradient de champ électrique. Puis nous avons également mis au point des feuilles de calcul pour simuler l’intensité d’une cohérence donnée d’un spin I demi-entier dans un solide (statique ou en rotation MAS) et excité par une impulsion ou par une séquence MQMAS. Nous avons mené une étude par simulation et une autre expérimentale pour éclaircir la différence dans la littérature sur les phases de la troisième impulsion de la séquence SPAM (Soft Pulse Added Mixing). Cette séquence (en particulier la séquence SPAM tronquée) et sa variante Multiplex augmentent nettement le rapport S/B en MQMAS. Nous avons appliqué des séquences MQMAS aux noyaux quadripolaires (27Al et 51V) dans des matériaux catalytiques (Al-SBA-15 et Vx-SiBEA) et nous avons montré l’intérêt d’une part des cohérences 5Q et d’autre part celui du cyclage de phase Multiplex.
39
Henzel, Norbert. "Développement d'un nouvel outil d'analyse spectrale et d'estimation des paramètres de signaux RMN 13C". Nancy 1, 1997. http://www.theses.fr/1997NAN10020.
Testo completoAbstract (sommario):
Une nouvelle méthodologie d'analyse spectrale de signaux constitués de sinusoïdes amorties dans du bruit blanc ou coloré est présentée. Ce type de signaux (processus de type AR bruités, modélisables sous la forme d'un ARMA) se rencontre fréquemment, et en particulier en spectroscopie RMN. Premièrement, après présentation des bases de la RMN, le signal RMN est modélisé comme une somme d'exponentielles complexes amorties plus un bruit blanc. Ensuite, une comparaison des performances de quelques estimateurs spectraux reposant sur la séparation des sous-espaces signal et bruit, est présentée. Cette étude, effectuée en simulation et sur signaux réels, prend en compte l'influence des paramètres suivants : ordre, nombre d'observations, rapport signal sur bruit, nombre de composantes. Il en ressort que, quelque soit l'estimateur, l'amélioration de la résolution fréquentielle suppose une augmentation conjointe du nombre d'observations et de l'ordre. Pour des moyens informatiques courants et un temps de calcul raisonnable, la résolution est donc rapidement limitée, et reste insuffisante pour des signaux RMN de complexité moyenne. Les méthodes étudiées jusqu'ici reposent sur une approximation AR d'un ARMA. Une approche reposant sur l'estimation de la partie AR du processus ARMA, soit par une méthode de variable instrumentale, soit par l'approche Yule-Walker d'ordre élevé (YWOE) est alors étudiée. Les résultats des tests sur signaux réels montrent que ces méthodes permettent de diminuer le nombre de paramètres, par rapport aux méthodes précédents. Ceci permet d'augmenter les ordres et le nombre d'observations, sans toutefois permettre d'atteindre la résolution fréquentielle requise sur des signaux RMN complexes. Finalement, une méthodologie d'analyse en sous-bandes est présentée. L’utilisation de filtres rif nous permet d'assurer l'adéquation entre le modèle après filtrage/décimation et l'estimateur (YWOE). Les principaux avantages d'une analyse en sous-bandes, (augmentation de la résolution, possibilité de diminuer les ordres, augmentation de la précision), sont confirmés en simulation. L’efficacité de cette approche sur des signaux RMN de forte complexité est illustrée
40
Ledieu, Aurélien. "Altération par l'eau des verres borosilicatés : expériences, modélisation et simulations Monte Carlo". Phd thesis, Ecole Polytechnique X, 2004. http://tel.archives-ouvertes.fr/tel-00008627.
Testo completoAbstract (sommario):
Cette these s'interesse au comportement en presence d'eau de poudres de verres borosilicates de composition variable. L'originalit´e de ces travaux reside dans la complementariteentre experiences et simulations num´eriques. Ils s'inscrivent plus generalement dans la problematique du comportement a long terme des verres de confinement des dechets nucleaires.
Dans un premier temps, nous avons etudie des verres contenant uniquement un melange d'oxydes de silicium, de bore et de sodium. Les cinetiques d'alteration montrent que la vitesse et le degre final de l'alteration dependent de la teneur initiale en bore selon un mecanisme de percolation. Il a ete observe qu'une pellicule se forme a la surface du verre et que, pour certaines compositions, celle-ci est responsable d'un arret de l'extraction des especes solubles (bore et sodium). Ce < gel d'alteration > est caracterise par resonance magnetique nucleaire (RMN) et diffusion des rayons X aux petits angles (SAXS).
D'autres elements ont ensuite ete ajoute a la composition borosilicatee initiale. Nous montrons ainsi que la presence d'oxydes de calcium, de zirconium et d'aluminium perturbe
fortement la vitesse et le degre final d'alteration et qu'il n'est plus possible d'interpreter le comportement de ces verres par la seule percolation du bore. En parallele, nous avons developpe un modele theorique, base sur la dissolution-recondensation des especes peu solubles, pour decrire l'alteration par l'eau des verres borosilicates. L'utilisation de simulations num´eriques de type Monte Carlo sur reseau teste
les concepts de percolation du sous-reseau de bore, de reactivite locale des elements peu solubles, ainsi que de murissement de la texture poreuse du gel. Ce modele est valide explicitement
sur les verres a trois oxydes (Si, B et Na) par confrontation directe avec les experiences. Il est ensuite etendu au cas des verres de composition plus complexe (verres au zirconium et a l'aluminium). Au moyen d'hypotheses simples, nous parvenons alors a interpreter qualitativement le comportement paradoxal de ces verres a quatre oxydes.
Ces travaux montrent principalement qu'il est possible d'expliquer le comportement en presence d'eau d'un verre de composition donnee par la competition entre deux mecanismes
primordiaux, qui sont l'extraction des elements solubles et la reconstruction du gel d'alteration.
41
Smaldone, Saverio. "Analyse numérique et simulations de problèmes couplés pour le système cardiovasculaire". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066505.
Testo completoAbstract (sommario):
Dans cette thèse, nous proposons l'analyse numérique et le développement d'algorithmes partitionnés pour coupler l'écoulement du sang dans différents comparti- ments cardiovasculaires (3D-3D, 3D-0D) Dans une première partie, un problème couplé fluide-fluide est introduit. Sur l'interface qui sépare les domaines, des conditions aux limites de type Robin-Robin dérivées de la formulation d'interface de Nitsche sont considérées. Nous proposons différents schémas explicites dont la stabilité est analysée dans la norme de l'énergie. Des simulations numé- riques illustrent le potentiel des méthodes présentées. La deuxième partie propose des applications cardiovasculaires plus réalistes. Tout d'abord, un modèle d'ordre réduit pour les valves cardiaques est décrit. Sans traiter l'inter- action fluide-structure avec le sang, les valves sont remplacées par des surfaces agissant comme des résistances immergées dans le fluide. Des simulations numériques montrent l'efficacité et la robustesse de ce modèle. Pour finir, une formulation ALE est utilisée pour la résolution d'un modèle fluide sur un domaine mobile. Nous montrons qu'en ajoutant un terme consistent, une inégalité d'éner- gie stable peut être obtenue sans considérer aucune hypothèse de Loi de Conservation Géométrique. Le travail se termine avec des simulations numériques sur la dynamique du sang dans le ventricule gauche, couplé avec l'écoulement du sang dans l'aorteIn this thesis we present the numerical analysis and the development of parti- tioned algorithms in order to couple the blood dynamics in different cardiovascular compart- ments (3D-3D, 3D-0D). In the first part a fluid-fluid coupled problem is introduced. On the interface between the domains Robin-Robin boundary conditions, derived from the interface Nitsche’s formulation, are considered. We suggest different staggered explicit schemes whose stability is analyzed in the energy norm. Extensive numerical experiments illustrate the accuracy of the methods presented. The second part deals with more realistic cardiovascular applications. First a reduced order model for the heart valves is described. Without dealing with fluid-structure interaction with the blood flow, the valves are replaced by immersed surfaces acting as resistances on the fluid. Numerical simulations show the efficiency and the robustness of this model in the framework of a fluid-fluid interaction scheme. In the end, an ALE formulation is used to solve a fluid model in a moving domain. We show that adding a suitable consistent term, a stable energy inequality can be obtained without considering any Geometric Conservation Laws. The work ends with numerical sim- ulations on blood dynamics in the left ventricle coupled with the blood flowing in the aorta
42
Dang, Phuc Hung. "Développement d’aimant bas champ pour RMN Portable : Conception et construction". Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0007/document.
Testo completoAbstract (sommario):
Les travaux menés au cours de cette thèse porté sur le développement d’un aimant pour système de RMN portable. Une homogénéité élevée a été recherchée tout en maintenant le champ magnétique statique B0 aussi élevé que possible (100ppm, 0.12T). Les dimensions de l’aimant sont prédéfinies ainsi que celles de la zone d'intérêt fonction de la taille des aimants permanents utilisés. Ce type de système est dédié à la recherche biomédicale et agroalimentaire. Les travaux présentés ont consisté, à discuter dans un premier temps un certain nombre des paramètres des matériaux magnétiques essentiels à la construction d’aimants de RMN portables. Plus particulièrement le choix des aimants permanents, utilisant un matériau tels que le NdFeB a été justifié. Une combinaison entre portabilité, prix et sensibilité a abouti à la conception d’un prototype d’aimant portable pour appareil RMN à partir d’un système simple d’arrangement de 24 aimants permanents. Le champ magnétique et l'homogénéité de ce système ont été calculés et simulés à l’aide du logiciel Ansys puis les résultats obtenus ont été vérifiés avec le logiciel Radia. Une nouvelle méthode de shim pour augmenter l'homogénéité et corriger les imperfections du champ B0 a été aussi introduite. La position des aimants de shim a fait l’objet d’une optimisation avec le logiciel Radia. Sur la base de ces résultats, un prototype a été réalisé. Les résultats des mesures de champ magnétique et de l'homogénéité sont en bonne corrélation avec les résultats obtenus par simulation. Les erreurs de mesure ont été estimées et une précision suffisante a été atteinte compte tenu des tolérances portant à la fois sur les caractéristiques et sur la fabrication des aimants. Un autre aimant basé sur la configuration Mandhalas (Magnet Arrangement for Novel Discrete Halbach Layout) a fait l’objet d’une étude comparative, portant sur deux configurations utilisant des aimants de formes circulaires et de formes carrés, a été effectuée par simulation 2D (sur la base de trois critères : la masse, l'homogénéité et l'intensité du champ magnétique). Les Mandhalas fabriqués à partir d’aimants circulaires permettent d’avoir de meilleurs résultats (0.32T, 178ppm). D’autre part, la simulation 3D a été faite afin d’évaluer la totalité du système. A partir des résultats obtenus, un système de shim passif a été aussi utilisé dans ce cas et a permis l’augmentation de la zone d'homogénéité de manière significativeThis thesis focuses on the development of a magnet system for NMR applications with high homogeneity while maintaining the static magnetic field B0 as high as possible (100 ppm, 0.12T). Due to the application goals, the magnet dimensions are predefined as well as those of the region of interest according to the size of the used permanent magnets. Such system is dedicated to biomedical and agroalimentary applications. The goal of this research has been firstly, the discussion of parameters of magnetic materials which are essential to the construction of portable NMR magnets, and then the choice of the permanent magnet material the “NdFeB” that was explained. A compromise between the portability, price and the sensitivity has led to the design of a prototype of portable NMR magnet with a simple system of arrangement of 24 permanent magnets. The magnetic field and the homogeneity of the system were calculated and simulated by using ANSYS software and these results were correlated to those obtained by the Radia software. A new shim method has been used to increase the homogeneity and correct the field B0 imperfection. Based on these results, a prototype was realized. The results of the magnetic field strength and homogeneity obtained by measurements are in good correlation with the results obtained by simulation. Sufficient accuracy was reached to take into account and correct errors due to manufacturing tolerances of the magnets. Another magnet system based on Mandhalas configuration (Magnet Arrangement for Novel Discrete Halbach Layout) was studied. The comparison between two configurations made from circle and square magnets was performed by 2D simulation (using three criteria: mass, homogeneity and the magnetic field strength). The Mandhalas made from circle magnets give better results (0.32 T, 178 ppm). The 3D simulation was carried out to evaluate the total system. From these results, a passive shim system was also used in this case and the homogeneity significantly increases
43
Khan, Abdul Kareem. "Electrostaticanalisys the Ras active site". Doctoral thesis, Universitat Pompeu Fabra, 2009. http://hdl.handle.net/10803/7161.
Testo completoAbstract (sommario):
La preorganització electrostàtica del centre actiu s'ha postulat com el mecanisme genèric de l'acció dels enzims. Així, alguns residus "estratègics" es disposarien per catalitzar reaccions interaccionant en una forma més forta amb l'estat de transició, baixant d'aquesta manera el valor de l'energia dactivació g cat. S'ha proposat que aquesta preorientació electrostática s'hauria de poder mostrar analitzant l'estabilitat electrostàtica de residus individuals en el centre actiu.Ras es una proteïna essencial de senyalització i actúa com un interruptor cel.lular. Les característiques estructurals de Ras en el seu estat actiu (ON) són diferents de les que té a l'estat inactiu (OFF). En aquesta tesi es duu a terme una anàlisi exhaustiva de l'estabilitat dels residus del centre actiu deRas en l'estat actiu i inactiu.
The electrostatic preorganization of the active site has been put forward as the general framework of action of enzymes. Thus, enzymes would position "strategic" residues in such a way to be prepared to catalyze reactions by
interacting in a stronger way with the transition state, in this way decreasing the activation energy g cat for the catalytic process. It has been proposed that
such electrostatic preorientation should be shown by analyzing the electrostatic stability of individual residues in the active site.
Ras protein is an essential signaling molecule and functions as a switch in the
cell. The structural features of the Ras protein in its active state (ON state) are different than those in its inactive state (OFF state). In this thesis, an exhaustive analysis of the stability of residues in the active and inactive Ras active site is performed.
44
Fossat, Martin. "Étude de la thermodynamique et de la coopérativité du repliement des protéines par haute pression". Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT326/document.
Testo completoAbstract (sommario):
Ce travail de thèse ce concentre sur l’étude des protéines par l’usage de haute pression. Les articles présentés ici sont précéder d’une introduction présentant les différents modèles physiques utilisés pour décrire le repliement des protéines, une introduction posant les bases de la thermodynamique, ainsi que l’origine de la stabilité thermodynamique des protéines dans leur état plies. Il y a trois sujets principaux aborder dans ce mémoire. Le premier est l’étude de la coopérativité du repliement et du paysage de repliement de la protéine à répétition PP32 (Anp32a) a travers l’utilisation de la pression a différentes températures. La seconde étude concerne l’investigation de l’origine de l’expansivité thermique des protéines pliées grâce à l’utilisation de RMN haute pression et de la protéine très bien caractérisée Staphylococcal Nuclease (SNase) et de certaine de ses mutantes. Finalement, un dernier article sur la stabilité sous pression de la variant TC5b de la mini protéine model tryptophan-cage grâce une combinaison de RMN et de simulations moléculaires tout-atomes en « replica exchange »This thesis work focuses on the study of protein though the use of high pressure. There are three main points subject that are being inquired here. The first is the study of cooperativity and folding landscape of a repeat protein (Anp32a) though the use high pressure denaturation at different temperatures. The second concerns the investigation of the determinant of thermal expansivity in the folded state of protein using high pressure NMR, and the well characterized Staphylococcal Nuclease (SNase) and some of its mutants. Finally, a last article on the pressure stability of the model mini protein Tryptophan cage variant Tc5b by a combination of high pressure NMR and full atomic replica exchange simulations
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Justina, Hellen Mathei Della. "Interação entre as áreas funcionais do sistema visual e do sistema vestibular: estudo com RMF e EGV". Universidade Tecnológica Federal do Paraná, 2014. http://repositorio.utfpr.edu.br/jspui/handle/1/850.
Testo completoAbstract (sommario):
CAPES, CNPqO equilíbrio estático corporal é comandado por três sistemas sensoriais: o sistema vestibular, responsável pelas informações sobre a posição e os movimentos da cabeça; o sistema visual, que informa a posição espacial dos objetos em relação ao nosso corpo; e o sistema proprioceptivo, que controla a postura e a movimentação corporal. Estes três sistemas devem funcionar sempre em sintonia, caso contrário, o indivíduo apresentará problemas de equilíbrio. Dessa forma, é importante caracterizar as regiões corticais, bem como suas interações, envolvidas neste processo. Para isto, é necessário a utilização de técnicas de neuroimagem funcional, sendo a ressonância magnética funcional (RMf) uma das técnicas mais utilizadas neste campo nos dias de hoje. Entretanto, uma grande parte dos experimentos de RMf requer o uso de aparelhos eletrônicos para produzir estimulações somatosensoriais no corpo humano, onde a principal dificuldade é o seu ambiente hostil aos circuitos eletrônicos. A estimulação galvânica vestibular é um dos métodos mais utilizados para estimular o sistema vestibular. Esta consiste em fornecer uma corrente de baixa amplitude diretamente nas aferências vestibulares, a qual atua no disparo dos neurônios vestibulares primários atingindo principalmente as aferências otolíticas e as fibras dos canais semicirculares. O objetivo deste trabalho é analisar e avaliar as áreas cerebrais envolvidas com as estimulações visual e galvânica vestibular e suas interações, utilizando a técnica de RMf e um estimulador galvânico vestibular. Para tanto, como primeira etapa desta pesquisa, validou-se in vivo um estimulador galvânico vestibular. O estimulador elétrico não interferiu de forma significativa na qualidade das imagens de ressonância magnética e pode ser utilizado com segurança nos experimentos de RMf. Testes foram realizados para determinar um eletrodo suficientemente confortável para o voluntário durante a estimulação galvânica vestibular e que não causasse artefato nas imagens. Após estas etapas concluídas, 24 voluntários foram selecionados para realizarem três tarefas: uma puramente visual (um tabuleiro de xadrez piscante no centro da tela), uma puramente vestibular (pela aplicação da estimulação galvânica vestibular) e uma simultânea, com a apresentação em conjunto dos estímulos visual e vestibular. A estimulação puramente visual mostrou ativação dos córtices visual primário e associativo, enquanto que a estimulação puramente vestibular levou a ativação das principais áreas envolvidas com a função multimodal do sistema vestibular, como o córtex parietoinsular vestibular, o lóbulo parietal inferior, o giro temporal superior, o giro pré-central e o cerebelo. A estimulação simultânea dos sistemas visual e vestibular resultou na ativação dos giros frontal médio e inferior. Além do padrão de interação visual-vestibular inibitório recíproco ter sido mais evidente durante a condição simultânea, observou-se que as regiões frontais (córtex dorsomedial pré-frontal e giro frontal superior) estão envolvidas com o processamento da função executiva quando existem informações conflitantes dos sistemas visual e vestibular.
The static body equilibrium is controlled by three sensory systems: the vestibular system, responsible for informing the position and the movements of the head; the visual system, which informs the spatial objects position relative to the body; and the proprioceptive system, which controls posture and body movements. These three systems must always work in harmony, otherwise the individual will present balance problems. Thus, it is important to characterize the cortical regions, as well as their interactions, involved in this process. For this it is necessary to use functional neuroimaging techniques, the functional magnetic resonance imaging (fMRI) is one of the most used techniques in this field nowadays. However, a large fMRI experiments require the use of electronic devices for producing somatosensory stimulation in the human body, where the main difficulty is its hostile environment for electronic circuits. The galvanic vestibular stimulation is one of the most used methods to stimulate the vestibular system. This stimulation consist of applying a low current amplitude directly on vestibular afferents, which acts firing the primary vestibular neurons, affecting the otolithic afferents and the semicircular canals fibers. The objective of this work is to evaluate and analyze the brain areas involved with visual and galvanic vestibular stimulations and their interactions using fMRI. Therefore, as a first step of this research, a galvanic vestibular stimulator was validated in vivo. The electrical stimulator did not interfere in a significance way on magnetic resonance images quality and could be safely used in fMRI experiments. Tests were performed to select an electrode sufficiently comfortable for the volunteer during the galvanic vestibular stimulation and that do not cause artifacts in the images. After completed these steps, 24 subjects were selected to perform three tasks: a purely visual (a flashing checkerboard in the center of the screen), a purely vestibular (with application of galvanic vestibular stimulation) and a simultaneous, presenting the visual and vestibular stimuli together. The purely visual stimulation showed activation of the primary and associative visual cortices, while the purely vestibular stimulation led to activation of areas involved in multimodal function of the vestibular system, such as the parieto-insular vestibular cortex, the inferior parietal lobe, the superior temporal gyrus, the precentral gyrus and the cerebellum. The simultaneous stimulation of visual and vestibular systems resulted in activation of the middle and inferior frontal gyri. In addition to the reciprocal inhibitory visualvestibular interaction pattern had been more evident during the simultaneous condition, it was observed that frontal regions (dorsomedial prefrontal cortex and superior frontal gyrus) are involved with the executive function processing when there is conflicting information of visual and vestibular systems.
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Kadjo, Aziz. "Micro-capteurs implantables : étude des critères de performance en vue de l'optimisation des acquisitions par spectroscopie RMN in vivo". Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10179.
Testo completoAbstract (sommario):
L’objectif de la présente thèse est d’évaluer les performances des micro-antennes, en cas d’emploi en spectroscopie in vivo et de prévoir les éventuelles améliorations, tout en respectant les contraintes en termes d’encombrement et de biocompatibilité imposées par des applications cérébrales sur modèle animal. Par conséquent, dans ce travail, il fallait également évaluer la sensibilité tout en comprenant le fonctionnement particulier de ces micro-capteurs, points qui n’avaient pas encore été explorés. Ce document est organisé en cinq chapitres, le Premier est un aperçu sur la situation du sujet par rapport à l’existant et un rappel technique sur les travaux déjà effectués en matière de réalisation et en rapport avec les différents métabolites «cibles». Le Chapitre II présente les développements instrumentaux entrepris en vue de l’amélioration des conditions de détection: optimisation de l’adaptation en puissance et de l’adaptation en bruit à l’entrée du spectromètre prise aussi en considération. La difficulté du maintien du modèle dans un espace restreint est solutionnée en proposant différents montages de réglages déportés. L’introduction d’un préamplificateur à faible bruit est également étudiée et réalisée sur la micro-antenne et une antenne de surface fait maison. La question importante de la limite de détection est abordée sous un angle théorique et expérimental dans le Chapitre III. L’intérêt de cette analyse est l’évaluation des performances de la micro-antenne, on verra que cette nouvelle notion permet également de qualifier une installation de spectroscopie (capteur associé à un spectromètre pour une expérience donnée). Une étude d’amélioration apportée sur la limite de détection (LOD) par la technique de pondération sera traitée et validée sur des acquisitions spectroscopiques. Le Chapitre IV est destinée dans un première partie, à travers les modélisations, à discuter les variations de la limite de détection pour certains changements structurels (la dimension et le positionnement de la micro-bobine). Dans la deuxième partie, une mise en application de la limite de détection, à travers les expériences spectroscopiques sera présentée dans le but de comparer les performances de capteurs existants: principalement une antenne commerciale, la micro-antenne et une antenne fait maison. La question de la biocompatibilité de ces microantennes implantables est traitée dans le Chapitre V. La réalisation de cette étude a été effectuée en amont des travaux théoriques et instrumentaux et a permis leurs développements avec une démarche plus pragmatiqueThe objective of this thesis is to evaluate the micro-coil performance, in spectroscopy in vivo and provide any improvements, while respecting the constraints in terms of obstruction and biocompatibility imposed by applications on brain of animal models. Therefore, this work had also to assess the sensitivity understanding of these particular micro-sensors, a notion that has not yet been explored. This document is organized into five chapters: the first one is an "overview" of state of art techniques and a reminder of the work already done in terms of production and in relation to different metabolite "targets". Chapter II presents the instrumental developments undertaken to improve the detection: optimization of adaptation in power and noise matching at the spectrometer input, were also taken into account. The difficulty of maintaining the animal model in a reduced space is solved by providing different configurations of remote settings. The introduction of a low-noise preamplifier is also studied and implemented. The important question of the limit of detection is approached from a theoretical point of view in Chapter III. The interest of this analysis is to assess the performance of micro-coil, we will point out that this new concept enables to describe a spectroscopy facility (sensor associated with a spectrometer for a given experiment). A study of enhancement of the limit of detection by the apodization technique will be addressed and validated on spectroscopy acquisitions. Chapter IV is an implementation in the first part, through modelling, to discuss changes in the limit of detection for some structural changes (size and positioning of the micro-coil). In the second part, an implementation of the limit of detection through spectroscopic experiments will be presented in order to compare the performance of existing coils: a commercial coil and a micro-coil. The biocompatibility of implantable micro-coil treated in Chapter V. The completion of this study was carried out upstream of the theoretical and instrumental aspects in chapter III and IV and that helped their development with a more pragmatic approach
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Ferreira, Marcelo José Pena. "Análise espectral, geração de estrutura e simulação de dados de RMN 13C". Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/46/46135/tde-20032018-142649/.
Testo completoAbstract (sommario):
O sistema especialista SISTEMAT tem por objetivo auxiliar pesquisadores da área de produtos naturais no processo de determinação estrutural de substâncias. Para tanto, utilizando dados provenientes de várias técnicas espectrométricas e espectroscópicas, principalmente RMN 13C, inúmeros programas foram desenvolvidos com a finalidade de propor o provável esqueleto de uma substância. Essa informação, juntamente com as substruturas apresentadas a partir de um conjunto de dados, é utilizada por geradores estruturais como grandes restrições, a fim de impedir a explosão combinatória e a geração de propostas estruturais incompatíveis com produtos naturais, além de reduzir o elevado tempo computacional gasto durante uma análise. Esse trabalho descreve o desenvolvimento e utilização dos módulos de reconhecimento de esqueletos, determinação e geração estrutural e simulação de dados de RMN 13C de esteróides. Assim, foi elaborada uma base de dados com 1436 substâncias distribuídas entre 119 tipos de esqueletos provenientes das mais diversas fontes naturais. Vários testes foram realizados e bons percentuais de acerto foram obtidos para o reconhecimento de esqueletos e geração de propostas estruturais através da sobreposição dos tipos de anéis encontrados em esqueletos de esteróides. Para validar as propostas estruturais apresentadas pelo gerador, bem como para prever os dados de deslocamentos químicos de novos esteróides, o simulador de dados de RMN 13C foi usado e, quando comparado a um programa comercial de mesma finalidade, apresentou maior exatidão na previsão dos dados.The aim of the expert system SISTEMAT is to aid natural product researchers in the process of structural determination of organic substances. For that, using data from various spectrometric and spectroscopic techniques, mainly 13C NMR, countless programs were developed to propose the most probable skeleton of a substance. This information together with the substructures shown from the data set are utilized by structural generators as important constraints in order to avoid the combinatorial explosion problem and the generation of incompatible structural proposals for natural products, besides reducing the computational time spent during the analysis. This work describes the development and use of the modules of skeleton identification, structural determination and generation, and the 13C NMR data prediction of steroids. Thus, was built a database containing 1436 steroids distributed in 119 different skeletons originated from the most varied natural sources. Several tests were performed, wherein good hit percentuals were obtained for the skeleton identification and structural generation through the overlapping of the types of rings found in the steroid skeletons. For validation of the structural proposals shown by the generator as well as for prediction of the chemical shift data of new substances, the simulator of 13C NMR data was used and next compared with a commercial program of the same purpose, and exhibited higher accuracy in the data prediction.
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Hanslík, Radovan. "Odrazná plocha osobních automobilů". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2020. http://www.nusl.cz/ntk/nusl-412967.
Testo completoAbstract (sommario):
This diploma thesis is aimed at radar cross section of passenger cars. Basic scattering parameters of simple targets are described. Selected numeric methods used for computing radar cross section are discussed. Shape and size of simplified vehicle models is investigated. Simulations are verified by computing RCS of objects with well-known characteristics. Radar cross section of Skoda Octavia was simulated using selected numeric methods. Results of all performed simulations are shown in included graphs. Experimental measurment of radar cross section of a vehicle was performed so the measured data can be compared with the simulations.
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Jourdheuil, Gérard. "Approche topologique des deplacements chimiques **(1)h : application a la simulation spectrale". Paris 7, 1987. http://www.theses.fr/1987PA077214.
Testo completoAbstract (sommario):
Presentation du logiciel serp "simulation de l'ecran en resonance du proton". Il s'agit d'un module de simulation spectrale en rmn **(1)h permettant la construction du spectre attendu pour une structure donnee
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Cobo, Márcio Fernando. "Exploração de técnicas de RMN dipolar e aproximações analíticas no estudo de reorientações de segmentos moleculares". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-03022014-103352/.
Testo completoAbstract (sommario):
Neste trabalho exploramos o uso de sequências de pulsos de Ressonância Magnética Nuclear de Estado Sólido (RMN-ES) que utilizam o acoplamento dipolar magnético heteronuclear para o estudo de reorientações de segmentos moleculares no regime intermediário, testando-as em amostras modelo a fim de verificar suas eficiências. Paralelamente, simulações numéricas foram realizadas juntamente com cálculos analíticos para a melhor compreensão dos efeitos experimentais observados nessas sequências de pulsos. A primeira proposição, baseia-se no uso de Perfis de Hartmann-Hahn obtidos utilizando a Transferência de Polarização Cruzada (CPMAS) sob desacoplamento dipolar homonuclear Lee-Goldburg (LG), usando a interação dipolar heteronuclear como sonda do movimento molecular. A segunda proposição consiste em uma variação das técnicas DIPSHIFT e Time Constant recDIPSHIFT , o T2-recDIPSHIFT, segundo a qual, em condições favoráveis, é possível quantificar parâmetros dinâmicos relacionados aos movimentos moleculares no regime intermediário de sistemas fracamente acoplados pela interação dipolar magnética heteronuclear ou com geometrias de movimento de baixa amplitude. Por fim, propomos um novo método analítico para quantificação de parâmetros dinâmicos em experimentos de Separação de campo locais (SLF), baseado no método de Anderson-Weiss. Demonstramos a precisão do método analítico comparando curvas de Time Constant recDIPSHIFT para diversas taxas e geometrias de movimento obtidas pela aproximação analítica e pelo cálculo exato, além de efetuar um teste experimental em uma amostra modelo.In the present work we explore the use of Solid State Nuclear Magnetic Resonance (NMR) pulse sequences which use the heteronuclear dipolar magnetic coupling to study local rotations of molecular groups in the intermediate-regime of motion, testing them in standard samples in order to verify their efficiency. Simultaneously, numerical simulations and analytical calculations were performed to understand the experimental artifacts observed in these new pulse sequences. The first proposal, based on using Hartmann-Hahn matching profiles obtained by using the Cross Polarization transfer (CPMAS) under Lee-Goldburg homonuclear decoupling (LG), utilizing the heteronuclear dipolar interaction as probe of the molecular motion. The second proposal consists in a variation of DIPSHIFT and Time Constant recDIPSHIFT pulse sequences, dubbed T2 - recDIPSHIFT, whereby, in favorable conditions, it is possible to quantify molecular dynamic parameters of systems weakly coupled by heteronuclear dipolar interaction or to probe small-amplitude molecular motions. Finally, we proposed a new analytical method to describe Separated Local Field experiments (SLF), based upon the Anderson-Weiss approximation. We demonstrate the accuracy of the method comparing the Time Constant recDIPSHIFT curves for several rates and geometries of motion obtained by the analytical approximation and exact calculation, besides an experimental test has been performed in a model sample.