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Charnock, Gareth Trevor Patrick. "Computational spin dynamics and visualisation of large spin systems". Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601126.
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The thesis commences with a detailed review of the background theory of spin dynamics simulations. State space rest riction is introduced via a "top-down" approach. Common terms that make up the spin Hamiltonian are reviewed, and it is noted that the mathemat ical forms of these terms can be categorised in one of three ways. The review of the background theory complete, w::counts are given of the following four areas of research: 1. Formal conditions are established for the validity of state space restriction via spin order pruning, based on tracking the density matrix norm through spin order subspaces. The primary predictor for success is seen t o be the ratio of the largest eigenvalue to the relaxation rate. The lower this ratio; the fewer spin orders are required. 2. Software based around the Spin XML format , suitable for constructing and visualising large spin systems, is presented. Both a functional specification and a discussion of the internals are given. 3. A potential applicat ion of state space restriction, called "direct structure fitting" , (DSF) is explored. In DSF, a candidate chemical structure is optimised directly by minimising the difference between its predicted spectrum and an experimental spectrum. The following examples of successful fits are provided: cyanomethyl, propargyl, and tyrosyl radicals, in the liquid state, and, tyrosyl embedded in two ribonuclease reductase proteins in the powder state. 4. A new model of the pseudocontact shift, which assumes a delocalised electron, is presented. Mathematical subtleties are resolved that would otherwise lead to the failure of numerical evaluation if left untreated. Techniques to improve efficiency are discussed , and the resulting program runs comfortably on workstation-grade hardware on protein sized datasets. E. Coli DNA Polymerase III is investigated as an example, and evidence is presented that suggests that the new model would predict significant differences in structures if used in conjunction with molecular dynamics based structural refinement
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Zimmermann, Robert. "How large spheres spin and move in turbulent flows". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2012. http://tel.archives-ouvertes.fr/tel-00737746.
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Le but de ce travail de thèse est l'étude de la dynamique de sphères de grande taille dans un écoulement fortement turbulent. Pour ce faire, nous avons développé une nouvelle technique optique permettant de suivre la dynamique à 6 dimensions - position et orientation absolues - de plusieurs particules dans un écoulement complexe. Bien que la taille des particules soit comparable à l'échelle intégrale de l'écoulement, nous trouvons que sa dynamique de rotation et de translation est intermittente. De plus, nous observons que la translation et la rotation sont reliées par la force de Magnus. La répartition statistique de l'accélération n'est pas gaussienne et l'échange d'énergie avec le fluide est gouverné par la théorie mathématique des grandes déviations. Nous trouvons que le diamètre influence fortement la manière dont la particule explore l'écoulement. Nous avons ensuite appliqué le suivi de position et d'orientation à une particule instrumentée. Ce système mesure en permanence l'accélération lagrangienne qu'il subit via un accéléromètre embarqué et émet l'information à travers une électronique radio fréquence. L'orientation absolue est nécessaire pour exprimer les signaux de l'accéléromètre et ceux du suivi optique dans un repère commun; cela nous permet de comparer rigoureusement les mesures issues de ces deux techniques indépendantes. À partir de ces résultats nous avons développé des méthodes pour inférer des propriétés de l'écoulement à partir des signaux d'accélération de la particule instrumentée.
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Cho, HyungJoon Ph D. Massachusetts Institute of Technology. "Exploring large coherent spin systems with solid state NMR". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34432.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005.Includes bibliographical references (p. 119-124).
Solid state Nuclear Magnetic Resonance (NMR) allows us to explore a large coherent spin system and provides an ideal test-bed for studying strongly interacting multiple-spin system in a large Hilbert space. In this thesis, we experimentally investigate the spin dynamics in a rigid lattice of dipolarly coupled nuclear spins using multiple quantum NMR spectroscopy. Encoding multiple quantum coherences (MQC) in an arbitrary quantizing axis is developed. We utilized this method to encode coherence numbers in an orthogonal basis to Zeeman basis and showed that the dipolar-ordered state is a two spin correlated state, and confirmed the presence of the ... (flip-flop) terms in the experimentally prepared dipolar-ordered state. A new experimental investigation of the problem of the NM:R free induction decay (FID) in a lattice of spin 1/2 nuclei is presented to verify the multi-spin nature of the FID and the dominant role of the geometrical arrangement of the spins in the development of higher order correlations under the dipolar evolution. To study the dynamics and the controllability of these multiple spin correlations, effective decay times of individual coherence orders are measured under the dipolar interaction and under the control sequence that suppresses the dipolar evolution.
(cont.) It is seen that the decay time of each coherence order becomes shorter and more uniform among different coherence orders as the spin correlation size grows larger in both cases. Additional work has been done in this thesis, toward creating a pure state in solid state nuclear spins by transferring polarization from electron spins, i.e Dynamic Nuclear Polarization (DNP). A new cryogenic DNP probe was developed enabling multiple pulse irradiations at low temperature with enhanced polarization.
by HyungJoon Cho.
Ph.D.
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McNicholas, Stuart James. "Core optimisation in spin-coupled theory applied to large systems". Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387998.
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Wisniewski, Daniel. "Simulations of Dynamic Nuclear Polarization pathways in large spin ensembles". Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/39045/.
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Dynamic Nuclear Polarization (DNP) is a method for signal enhancement in NMR, with numerous applications ranging from medicine to spectroscopy. Despite the success of applications of DNP, the understanding of the underlying theory is still limited. Much of the work on the theory of DNP has been carried out on small spin systems; this is a restriction due to the exponential growth of the Liouville space in quantum simulations. In the work described in this thesis, a methodology is presented by which this exponential scaling can be circumvented. This is done by mathematically projecting the DNP dynamics at resonance onto the Zeeman subspace of the density operator. This has successfully been carried out for the solid effect, cross effect and recently for the Overhauser effect in the solid state (see appendix A.4). The results are incoherent state-dependent dynamics, resembling classical behaviour. Such form of effective dynamics allows the use of kinetic Monte Carlo algorithms to simulate polarization dynamics of very large spin systems; orders of magnitude larger than has previously been possible. We verify the accuracy of the mathematical treatment of SE-DNP and CE-DNP, and illustrate the insight large spin-system simulations provide into the mechanism of DNP. For SE-DNP the mechanism of polarization to the bulk of spin systems is determined to be spin diffusion, and we carried out studies into the efficiency and performance of radicals, with an outlook on radical design. We also show that the Zeeman projection can be applied to heteronuclear spin systems if the nuclear species are close in frequency, and we present a formalism for simulating C-13 nuclear spin systems based on a linear rate approach, enabling simulations of thousands of spins in a matter of minutes. A study into the scaling of the kinetic Monte Carlo algorithm error, and the simulation run time, with respect to an increasing number of spins is also presented. For CE-DNP the error analysis led to establishing a parameter regime in which the effective dynamics are accurate. We show that spin diffusion is the mechanism of transfer of polarization to bulk nuclei. We also show how the effective rates for CE-DNP can be used to understand the efficiency of bi-radicals, point to optimisation possibilities, and hold a potential to aid in bi-radical design. We finally show large scale simulations for CE-DNP bi-radical systems with improved parameters; leading to very rapid build-up of nuclear polarization.
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Chenattukuzhiyil, Safeer. "Study of domain wall dynamics in the presence of large spin orbit coupling : chiral damping and magnetic origami". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY080/document.
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La dynamique des parois de domaine magnétiques (DW) soulève actuellement un très fort intérêt à la fois du point de vue fondamental mais aussi en lien avec ses applications dans des dispositifs logique et mémoire. Des dispositifs nouveaux basés sur les DW ont déjà été proposés, par exemple présentant des très fortes densités de stockage et des taux de transfert élevés pour un remplacement des disques durs. De plus dans les Mémoires Magnétiques à Accès Aléatoire (MRAM), identifiées comme l'une des solutions les plus prometteuses pour le remplacement des DRAM et SRAM, le retournement de l'aimantation implique une propagation des DW. Le contrôle de la dynamique des DW sous courant est longtemps resté un challenge, principalement à cause d'imperfections dans les matériaux utilisés. Des déplacements rapides et contrôlé des DW au moyen d'un courant ont été reportés il y a quelques années seulement dans des multicouches présentant une asymétrie d'inversion (SIA). Plus récemment un mécanisme a été proposé basé sur la présence de couple de spin orbite (SOT) et de l'interaction Dzyaloshinskii-Moriya (DMI), tout deux trouvant leur origine dans l'interaction spin-orbite et nécessitant une SIA.Mon objectif initial était de tester ce modèle dans deux systèmes présentant différents SIA. Dans des multicouches Pt/Co/Pt à faible SIA, j'ai étudié la propagation des DW sous courant et sous champ et j'ai mis en évidence l'existence d'un amortissement chiral. Ce phénomène nouveau, pendant de DMI pour les mécanismes dissipatifs, influence à la fois la dynamique sous courant et sous champ et doit être pris en compte pour avoir une description complète des mécanismes. Dans des multicouches Pt/Co/AlOx à fort SIA, j'ai étudié de nouvelles géométries pour lesquelles le mouvement de la paroi de domaine et la direction du courant ne sont pas colinéaires. J'ai mis en évidence un déplacement asymétrique des DW en fonction de cette non-colinéarité qui ne peut pas être expliquée avec un modèle simple DMI+SOT. En se basant sur ces résultats expérimentaux, j'ai introduit un nouveau concept de dispositifs, appelé « origami magnétique » : la forme du dispositif gouverne le mécanisme de retournement. Ce concept apporte une grande flexibilité dans la construction de mémoires magnétiques non volatiles, rapides et peu gourmandes en énergie : des fonctionnalités différentes peuvent être obtenues sur un même wafer simplement par la maîtrise de la forme des différents éléments. Je montre la preuve de concept de deux dispositifsMagnetic domain wall (DW) dynamics is currently attracting tremendous interest both from a fundamental point of view as well as in relation with emerging magnetic memory and logic devices. New DW-based devices were recently proposed, for example to replace hard drive disks with higher density and faster date transfer. Moreover, in Magnetic Random Access Memory (MRAM), identified as one of the most promising candidate for DRAM and SRAM replacement, switching occurs through DW propagation. Control of current induced DW dynamics has long been a challenge mainly due to material imperfections. Only some years ago, fast and controllable motions were reported in multilayers presenting structural inversion asymmetry (SIA). More recently, a mechanism was proposed based on the presence of spin orbit torques and Dzyaloshinskii-Moriya interaction (DMI), both phenomena originating from the spin orbit interaction and needing (SIA).My initial objective was to test this model in two systems presenting different SIA. In Pt/Co/Pt multilayers with weak SIA, I studied both current and field induced DW motion and evidenced a chiral damping. This new phenomena, counterpart of the DMI for the dissipative aspects, influences both current and field induced dynamics and has to be taken into account for a complete picture of the mechanism. In Pt/Co/AlOx multilayers with strong SIA, I studied new geometries where the DW motion the and current flow are not collinear. I evidenced asymmetric DW motion as a function of this non-collinearity that cannot be explained with a simple SOT+DMI model. Based on these experimental results I introduce a new device concept named “magnetic origami”: the shape of the device governs the switching mechanism. This concept provides large flexibility to construct fast, low power non-volatile magnetic memory: different functionalities can be achieved on a wafer by simply mastering the shape of the different elements. I show the proof of concept of two such devices
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Zalma, Carre Alison. "Monitoring folding pathways for large RNAs using site-directed spin-labeling techniques". Thesis, Texas A&M University, 2005. http://hdl.handle.net/1969.1/4904.
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The function of biomolecules is very sensitive to structure. Folding in proteins and nucleic acids is a hierarchical process progressing from primary to secondary, then tertiary, and finally, quaternary structures. RNA in its folded form performs a variety of biological activities. Obtaining intramolecular distance measurements makes it possible to generate structural models along the folding pathway that may be related to the overall function of the molecule. Distances can be measured by Site-Directed Spin-Labeling (SDSL), in which nitroxyl spin-label probes are attached and observed by EPR spectroscopy. Spin-labels can provide information concerning structure and conformational changes because they are particularly sensitive to molecular motion and interspin distances. Continuous-wave EPR spectroscopy has been commonly applied to detect and monitor nitroxide spin-label probes within biological systems. A previous published SDSL study from this laboratory investigated a 10-mer RNA duplex model system with spin-label probe succinimdyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-carboxylate; however, an increased spin-labeling efficiency was observed with an isocyanate derivative of tetramethylpiperidyl-N-oxy (TEMPO). In this thesis, a 4-isocyano TEMPO spin-label probe replaced the previously used succinimdyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-carboxylate in 10-mer SDSL studies. The influence of labeling with the 4-iscocyano TEMPO spin-label in a 10-mer RNA model system was investigated with thermal denaturation, Matrix Assisted Laser Desorption Time of Flight Mass Spectrometry (MALDI-TOF-MS), Electron Paramagnetic Resonance (EPR) spectroscopy, and reverse phase high performance liquid chromatography (RP-HPLC). In the 10-mer RNA duplex model system a 4-isocyano TEMPO spin-label is individually attached to one strand and two strands are annealed to measure distances. This methodology is limited to systems in which two oligonucleotides are annealed together. To circumvent this limitation and also to explore single-strand dynamics a new methodology was implemented, double spin-labeling. Double spin-labeled single-stranded RNA was investigated as a single-strand and within a duplex via MALDI-TOF-MS, EPR spectroscopy and RP-HPLC. A double spin-labeling strategy in this work will be applicable to large complex RNAs like Group I intron of Tetrahymena thermophilia.
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Murch, Austin Matthew. "Aerodynamic Modeling of Post-Stall and Spin Dynamics of Large Transport Airplanes". Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/18855.
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This work addressed aerodynamic modeling methods for prediction of post-stall flight dynamics of large transport aircraft. This was accomplished by applying historically successful modeling methods used on high-performance military aircraft to a transport configuration. The overall research approach involved integrating forced oscillation and rotary balance wind tunnel data into an aerodynamic model using several methods of blending these data. The complete aerodynamic model was integrated into a six degree-of-freedom simulation. Experimental data from free-spin wind tunnel testing was used to validate the aerodynamic modeling methods by comparing aerodynamic force and moment coefficients and also to validate the simulation performance by comparing spin mode characteristics and time histories. The aerodynamic model prediction of spin dynamics was generally very good using all of the blending methods studied. In addition, key spin mode characteristics were predicted with a high degree of accuracy. Overall, using the Hybrid Kalviste method of blending forced oscillation and rotary balance data produced the closest match to the free-spin data when comparing aerodynamic coefficients and spin mode characteristics. Several issues were encountered with the blending methods that were exacerbated by nonlinearities and asymmetries in the dynamic aerodynamic data. A new method of looking up dynamic aerodynamic data was proposed to address shortcomings in the blending methods and recommendations were provided on addressing issues with the dynamic aerodynamic data.
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Kerzhner, Mark [Verfasser]. "Site-Directed Spin Labeling of Large Riboswitches Using Click Chemistry / Mark Kerzhner". Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1181855756/34.
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Brasil, Jader Eckert. "Probabilidades de spin quântico em temperatura positiva". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/177601.
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Nesta dissertação estudamos uma probabilidade obtida a partir de conceitos da Mecânica Estatística Quântica do ponto de vista da Teoria Ergódica. A probabilidade é obtida a partir de um estado KMS sobre um lattice unidimensional de spins quânticos. Mostramos que esta probabilidade é mixing para o shift. Além disso, mostramos que vale um princípio dos grandes desvios para uma certa classe de funções e exploramos algumas propriedades do Jacobiano. Iremos considerar o estado KMS associado a um certo Hamiltoniano específico agindo sobre o lattice de spins quânticos. Nas seções iniciais vamos apresentar alguns conceitos e prerequisitos básicos (como operadores densidade, produto tensorial, C*-algebras e estados KMS) para o entendimento do resultado principalIn this dissertation we study a probability derived from Quantum Statistical Mechanics through the viewpoint of Ergodic Theory. The probability is obtained from a KMS state acting on a one dimensional lattice of quantum spins. We show that this probability is mixing for the shift map. Moreover, we show that a large deviation principle is true for a certain class of functions and we explore some properties of the Jacobian. We will consider the KMS state associated to a certain specific Hamiltonian acting on the quantum spin lattice. In the initial sections we will present some concepts and prerequisites (such as density operators, tensor product, C*-algebras and KMS states) for the understanding of our main results.
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LONGO, EMANUELE MARIA. "HETEROSTRUCTURES BASED ON THE LARGE-AREA Sb2Te3 TOPOLOGICAL INSULATOR FOR SPIN-CHARGE CONVERSION". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/311358.
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I dispositivi elettronici che sfruttano proprietà legate allo spin elettronico costituiscono un settore molto promettente per lo sviluppo della nanoelettronica del futuro. Recentemente, gli isolanti topologici tridimensionali (IT-3D), quando posti a contatto con materiali ferromagnetici (FM), giocano un ruolo centrale nel contesto del miglioramento dell’efficienza di conversione tra spin e carica elettronici in eterostrutture di tipo FM/TI. L’oggetto principale di questa tesi è lo studio delle interazioni chimico-fisiche tra l’IT-3D Sb2Te3, nelle sue forme granulare ed epitassiale, con film di Fe e Co attraverso l’uso di tecniche di Diffrazione/Riflettività di raggi-X, spettroscopia di risonanza ferromagnetica (FMR) e pompaggio di spin in risonanza ferromagnetica (SP-FMR). In concomitanza con l’ottimizzazione delle proprietà dei materiali, un particolare interesse è stato rivolto verso l’impatto industriale della ricerca presentata. Per questo motivo, per la produzione di Sb2Te3 e di alcuni dei FM impiegati, sono state impiegate tecniche di deposizione di materiali su larga scala ( 4 pollici), quali la Metal Organic Chemical Vapor Deposition (MOCVD) e l’Atomic Layer Deposition (ALD) rispettivamente.
Una approfondita caratterizzazione chimica, strutturale e magnetica dell’interfaccia Fe/ Sb2Te3-granulare ha evidenziato un marcato intermixing tra i materiali e una generale tendenza degli atomi di Fe nel legare con l’elemento calcogenuro quando presente in un IT. Attraverso trattamenti termici rapidi e a bassa temperatura sottoposti sui film di Sb2Te3 granulare prima della crescita del Fe, l’interfaccia Fe/Sb2Te3-granulare è risultata morfologicamente più netta e chimicamente stabile. Lo studio di film sottili di Co cresciuti attraverso ALD su Sb2Te3 granulare ha permesso la produzione di interfacce Co/Sb2Te3-granulare di alta qualità, con la possibilità inoltre di modificare le proprietà magneto-strutturali dei film di Co attraverso una selezione appropriata di substrati.
Con l’obbiettivo di migliorare le proprietà dei film di Sb2Te3, dei trattamenti termici specifici sono stati condotti su Sb2Te3 granulare appena cresciuto, ottenendo film di Sb2Te3 altamente orientati con una qualità cristallina vicina al cristallo singolo di tipo epitassiale. Questi substrati di Sb2Te3 sono stati utilizzati per produrre eterostrutture di Au/Co/Sb2Te3-epitassiale e Au/Co/Au/Sb2Te3-epitassiale per studiare la loro risposta di FMR. I dati di FMR per il campione Au/Co/Sb2Te3-epitassiale sono stati interpretati considerando un contributo di Two Magnon Scattering (TMS) dominante, verosimilmente a causa della presenza di rugosità magnetica all’interfaccia Co/Sb2Te3-epitassiale. L’introduzione di un interlayer di Au per evitare il contatto diretto tra Co e Sb2Te3 si è dimostrato vantaggioso per la totale eliminazione del contributo di TMS.
Misure di SP-FMR sono state condotte sulla struttura ottimizzata Au/Co/Au/Sb2Te3-epitassiale, sottolineando il ruolo giocato dallo strato di Sb2Te3-epitassiale nel processo di SP. I segnali di SP ricavati da campioni di Au/Co/Au/Si(111) e Co/Au/Si(111) sono stati utilizzati per determinare l’efficienza di conversione spin-carica ottenuta dall’introduzione dello strato di Sb2Te3. L’efficienza estratta è stata calcolata interpretando i dati di SP-FMR attraverso i modelli di effetto Edelstein inverso ed effetto di Spin-Hall inverso, i quali hanno dimostrato che l’IT-3D Sb2Te3 è un candidato promettente per essere impiegato nella prossima generazione di dispositivi spintronici.Spin-based electronic devices constitute an intriguing area in the development of the future nanoelectronics. Recently, 3D topological insulators (TI), when in contact with ferromagnets (FM), play a central role in the context of enhancing the spin-to-charge conversion efficiency in FM/TI heterostructures. The main subject of this thesis is the study of the chemical-physical interactions between the granular and epitaxial Sb2Te3 3D-TI with Fe and Co thin films by means of X-ray Diffraction/Reflectivity, Ferromagnetic Resonance spectroscopy (FMR) and Spin Pumping-FMR. Beside the optimization of the materials properties, particular care was taken on the industrial impact of the presented results, thus large-scale deposition processes such as Metal Organic Chemical Vapor Deposition (MOCVD) and Atomic Layer Deposition (ALD) were adopted for the growth of the Sb2Te3 3D-TI and part of the FM thin films respectively. A thorough chemical, structural and magnetic characterization of the Fe/granular Sb2Te3 interface evidenced a marked intermixing between the materials and a general bonding mechanism between Fe atoms and the chalcogen element in chalcogenide-based TIs. Through rapid and mild thermal treatments performed on the granular Sb2Te3 substrate prior to Fe deposition, the Fe/granular-Sb2Te3 interface turned out to be sharper and chemically stable. The study of ALD-grown Co thin films deposited on top of the granular-Sb2Te3 allowed the production of high-quality Co/granular-Sb2Te3interfaces, with also the possibility to tune the magneto-structural properties of the Co layer through a proper substrate selection. In order to improve the structural properties of the Sb2Te3, specific thermal treatments were performed on the as deposited granular Sb2Te3, achieving highly oriented films with a nearly epitaxial fashion. The latter substrates were used to produce Au/Co/epitaxial-Sb2Te3 and Au/Co/Au/epitaxial-Sb2Te3 and the dynamic of the magnetization in these structures was investigated studying their FMR response. The FMR data for the Au/Co/Sb2Te3 samples were interpreted considering the presence of a dominant contribution attributed to the Two Magnon Scattering (TMS), likely due to the presence of an unwanted magnetic roughness at the Co/epitaxial-Sb2Te3 interface. The introduction of a Au interlayer to avoid the direct contact between Co and Sb2Te3 layers was shown to be beneficial for the total suppression of the TMS effect. SP-FMR measurements were conducted on the optimized Au/Co/Au/epitaxial-Sb2Te3 structure, highlighting the role played by the epitaxial Sb2Te3substrate in the SP process. The SP signals for the Au/Co/Au/Si(111) and Co/Au/Si(111) reference samples were measured and used to determine the effective spin-to-charge conversion efficiency achieved with the introduction of the epitaxial Sb2Te3 layer. The extracted SCC efficiency was calculated interpreting the SP-FMR data using the Inverse Edelstein effect and Inverse Spin-Hall effect models, which demonstrated that the Sb2Te3 3D-TI is a promising candidate to be employed in the next generation of spintronic devices.
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Zheng, Xiaochao 1977. "Precision measurement of neutron spin asymmetry An1 at large xBj using CEBAF at 5.7 GeV". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29310.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, February 2003.Includes bibliographical references (p. 263-276).
Nucleon spin structure has remained one of the key issues of hadronic physics since the 1980's. Among the unsolved questions, the neutron spin structure in the valence quark region (the large Bjorken variable XBj region) is of particular interest. The few data that existed in the large XBj region are very imprecise. Also, theoretical predictions based on Quantum Chromo-Dynamics (QCD) are difficult to carry out accurately in this non-perturbative region and having good experimental data is very important to test the models. Taking advantage of the polarized continuous-wave (CW) electron beam at Jefferson Laboratory (JLAB) and a high-density polarized 3He target in Hall A, we have measured the neutron spin asymmetry An1 and spin structure function gn1 to a good precision at three kinematics x = 0.33, 0.47 and 0.60, with Q2 = 2.7, 3.6 and 4.9 (GeV/c)2, respectively. The data at the two higher XBj points have improved the statistical accuracy of the world data by one order of magnitude. They show a zero crossing point around XBj = 0.47 and the datum at XBj = 0.60 is significantly positive. To determine An and g, cross sections and asymmetries of inclusive 3He(e,e') scattering have been measured in the deep-inelastic region. The transverse spin asymmetry An and structure function g were also extracted from data, though with less statistical precision. The asymmetries of pion photoproduction A[pi]⁻ were obtained as a byproduct.
(cont.) Combined with world fit of proton gP1/Ff1 data and the quark distribution ratio d/u, the polarized quark distributions ... have been obtained from gn1/Fn1 data. Results of ... at all three XBj points are negative, in disagreement with the predictions from pQCD based hadron helicity conservation. This dissertation will first give an introduction to the theories and formalism of polarized deep inelastic scattering and a review of the theories of An1. Next the experiment E99-117 at JLAB Hall A will be described, followed by the data analysis which yields results for ... The data presented greatly improve the current world fit of neutron polarized structure functions and provide valuable insight in the understanding of the neutron spin structure.
by Xiaochao Zheng.
Ph.D.
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Stumpf, Michael Peter Helmuth. "Interplay magnetism and temperature in the large-demensional limits of the Hubbard and t-J models". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299159.
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Trifa, Youssef. "Dynamiques de corrélations et d'intrication dans des gaz d'atomes froids". Electronic Thesis or Diss., Lyon, École normale supérieure, 2024. http://www.theses.fr/2024ENSL0018.
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Le problème quantique à N corps, notamment l’étude des propriétés dynamiques d’un système quantique composite est l’un des problèmes les plus durs de la physique moderne, car il y a peu de résultats analytiques et les méthodes numériques exactes requièrent des ressources numériques exponentielles en la taille du système. Dans cette thèse, nous avons étudié la mise en évidence de propriétés de corrélations et d’intrication pour des systèmes d’atomes magnétiques sur réseau, par exemple via la compression de spin. Pour cela nous avons mis au point de nouvelles méthodes numériques approchées, qui permettent de simuler des systèmes de grande taille. Cela nous a permis de proposer des protocoles qui permettent de générer de la compression de spin qui croit d’autant plus que le système est grand, ce qui a un double intérêt. D’une part, il s’agit d’un témoin d’intrication, qui permettrait donc de détecter de l’intrication dans un système d’atomes magnétiques, ce qui n’a pas encore été réalisée expérimentalement à ce jour. D’autre part la compression de spin présente un important intérêt métrologique, puisque les états comprimés permettent des mesures extrêmement précises de champs magnétiques par exemple, bien au-delà de ce qui est possible avec des atomes indépendants. Enfin, nous avons étudié la génération d’autres formes d'intrication, à savoir la compression à deux modes (de spin, ou d'impulsion), cette fois pour des systèmes d’atomes condensés. Connue dans le cas de condensats d’atomes de spin-1, nous avons proposé comment généraliser ce processus au cas de compression en impulsion, en utilisant un Hamiltonien modulé dans le temps. Les états intriqués ainsi produits sont potentiellement très intéressants dans la mesure à haute précision de forces inertiellesThe quantum many-body problem, and especially the study of dynamical properties of a multipartite quantum system, is one of the hardest problems of modern physics. There exist only a few analytical results and exact numerical simulations require an amount of resources that grow exponentially with the system size.In this thesis, we studied correlations and entanglement properties for systems composed of magnetic atoms on a lattice, for instance via the generation of spin squeezing. For this purpose we have developed new approximate numerical methods that allow us to study large system sizes. This enabled us to propose protocols to generate an amount of spin squeezing that scales with the system size. The advantage is twofold. Since spin squeezing is an entanglement witness, this would allow for entanglement detection in a system of magnetic atoms - which has yet to be realized experimentally. Moreover, spin squeezing offers an important metrological advantage, asspin-squeezed states can be used for extremely precise measurements of external magnetic fields, far beyond what one can achieve within dependent atoms.Finally, we studied the generation of other forms of entanglement, namely Dicke squeezing (of spin or momentum), in systems of Bose condensed atoms. This form of entanglement is well-known in spin-1 atomic condensates. Here, we propose a protocol to generalize it to the case of momentum modes, using a time-dependent Hamiltonian. The entangled states generated during the dynamics are potentially useful for the precision measurements of inertial forces
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Huang, Biao. "Exploring New Physics in Ultracold Quantum Gases: High Spin Fermions and Non-Trivial Background Manifolds". The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468280791.
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Ziaei, Vafa [Verfasser]. "Theoretical methods for studying charge and spin separation in excited states of large molecules and condensed phase / Vafa Ziaei". Bonn : Universitäts- und Landesbibliothek Bonn, 2018. http://d-nb.info/1154485943/34.
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Hollmann, Arne [Verfasser], Hendrik [Akademischer Betreuer] Bluhm i Dominique [Akademischer Betreuer] Bougeard. "Relaxation and decoherence of a 28Si/SiGe spin qubit with large valley splitting / Arne Hollmann ; Hendrik Bluhm, Dominique Bougeard". Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/122008252X/34.
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Lagarde, Delphine. "Dynamique de spin dans des structures semiconductrices à base de ZnO et de GaN". Toulouse, INSA, 2008. http://eprint.insa-toulouse.fr/archive/00000229/.
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Ce travail de thèse est une contribution à l'étude de la dynamique de spin des porteurs dans les structures semiconductrices de grande énergie de bande interdite à base de GaN et de ZnO. Nous avons mis en œuvre la technique de pompage optique orienté résolu en temps dans le domaine de l'ultra-violet pour mesurer les temps de relaxation de spin dans ces structures. Les propriétés de spin du trou et de l'exciton ont été analysées dans des couches épitaxiées de ZnO à partir des propriétés de polarisation de la photoluminescence issue des complexes d'excitons piégés sur des donneurs neutres. Nous avons mesuré à la fois le temps de relaxation de spin et le temps de cohérence de spin du trou localisé et avons mis en évidence le temps de relaxation de spin rapide de l'exciton libre. Nous avons également réalisé des études de pompage optique orienté sur des structures de GaN en phase cubique (blende de zinc), du matériau massif aux boîtes quantiques. Dans ces dernières, en analysant l'alignement optique de l'exciton dans des conditions d'excitation quasi-résonante, nous avons démontré le blocage de la relaxation de spin de l'exciton jusqu'à température ambianteThis thesis work is a contribution to the study of the spin dynamics of carriers in ZnO- or GaN-based wide bandgap semiconductor structures. We use time-resolved optical pumping experiments dedicated to the ultra-violet to measure spin relaxation times in those structures. The spin properties of hole and exciton in epitaxial layers of ZnO have been analysed from the polarization properties of the photoluminescence detected from neutral-donor bound exciton complexes. We measure both the localized hole spin relaxation time and spin decoherence time and have evidenced the fast spin relaxation time of the free exciton. We have also performed optical orientation experiments on cubic (zinc blende) GaN structures, from bulk material to quantum dots. In those, by studying the optical alignment of exciton spin under quasi-resonant excitation, we demonstrate the quenching of the exciton spin relaxation up to room temperature
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Müller, Patrick Erich [Verfasser]. "Limiting Properties of a Continuous Local Mean-Field Interacting Spin System : Hydrodynamic Limit, Propagation of Chaos, Energy Landscape and Large Deviations / Patrick Erich Müller". Bonn : Universitäts- und Landesbibliothek Bonn, 2016. http://d-nb.info/1122193866/34.
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Pacuski, Wojciech. "Spectroscopie optique de semi-conducteurs magnétiques dilués à large bande interdite, à base de ZnO et GaN". Phd thesis, Grenoble 1, 2007. http://www.theses.fr/2007GRE10310.
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Ce travail porte sur la spectroscopie magnéto-optique de semi-conducteurs magnétiques dilués (DMS) : ZnO et GaN dopés manganese, fer et cobalt. Les deux semi-conducteurs hôtes, ZnO et GaN ont une grande bande interdite, une structure wurtzite, une faible interaction spin - orbite et une forte interaction d'échange excitonique entre trous et électrons. En présence de champs magnétiques, les ions magnétiques induisent un effet Zeeman géant dont l'interprétation est complexe : les excitons s'anti-croisent et leurs énergies de transition et leurs forces d'oscillateur sont fortement influencées par l'effet Zeeman géant. On a mesuré expérimentalement le splitting Zeeman géant des excitons A et B avec des couches epitaxiées sur saphir (0001) et une propagation de la lumiere parallele a l'axe c du cristal et au champ magnétique (configuration Faraday). Le splitting Zeeman géant diminue avec la température et augmente non linéairement avec le champ magnétique en accord avec l'aimantation calculée des spins isolés. Une analyse quantitative nous a permis d'analyser les propriétés magnétiques et de mesurer les intégrales d'échange pour l'ensemble des matériaux étudiés. Pour des ions avec une configuration d5 (Mn2+ et Fe3+), l'aimantation suit une fonction de Brillouin, mais pour les configurations d7 et d4 (Co2+ ou Mn3+) l'interaction spin-orbite et le champ cristallin trigonal induisent une aimantation anisotrope, en accord avec l'analyse des transitions internes des ions mesurées en spectroscopie infrarouge. Pour (Ga,Mn)N, et (Ga,Fe)N, nous avons trouvé un signe positive pour l'intégrale d'échange entre trous et spins localisés (beta). En supposant une symétrie de la bande de valence dans ZnO correspondant a une interaction spin-orbite positive (Gamma_9, Gamma_7, Gamma_7), nous trouvons un signe négative de beta pour (Zn,Co)O, et beta est de pres de zéro pour (Zn,Mn)O. Toutefois, dans l'hypothese avec spin-orbite négative, nous trouvons un signe positif de beta. Les signes et les valeurs des intégrales d'échange déterminées a partir de nos mesures magnéto-optiques ne peuvent pas etre expliqués par des tendances matérielles et des modeles basés sur l'approximation de cristal virtuel. Ceci suggere que l'échange p-d en DMS a large bande interdite, soit dans le régime de couplage fort, et la nature de splitting Zeeman géant observé est différente qu'en semi-conducteurs magnétiques dilués classiquesThis work presents a magnetooptical study of diluted magnetic semiconductors (DMS) based on ZnO and GaN, doped with manganese, iron, and cobalt. Both host materials, ZnO and GaN, are wide band gap semiconductors with a wurtzite structure, a weak spin-orbit coupling and a strong electron-hole exchange interaction within the excitons. In the presence of a magnetic field, the magnetic ions induce in such materials a giant Zeeman effect with a complex behavior: excitons anti-cross, and not only the transition energies, but also the oscillator strengths are strongly affected by the giant Zeeman effect. On thin epitaxial layers grown on (0001) sapphire, we observed the giant Zeeman splitting of the A and B excitons, which are optically active in the Faraday configuration when the propagating light is parallel to the c-axis. The Zeeman splitting decreases with the temperature and increases non-linearly with the magnetic field, demonstrating a dependence on the magnetization of the localized spins. A quantitative analysis allows us to discuss the detailed behavior of the magnetization and to estimate the p-d exchange integral beta for the studied wide bandgap DMS. For the d^5 electronic configuration (Mn2+, and Fe3+) the magnetization follows a Brillouin function, whereas, for d7 or d4 of Co2+, and Mn3+, respectively, the spin orbit coupling and the trigonal crystal field lead to an anisotropic magnetization, consistent with that deduced independently from the analysis of intra-ionic optical transitions. We find a positive sign of beta for (Ga,Mn)N, and (Ga,Fe)N. In ZnO, the sign of the spin-orbit interaction, which determines the structure of the valence band, has been a matter of debate. Assuming that the valence band ordering in ZnO is Gamma_9, Gamma_7, Gamma_7 (this corresponds to usual, positive sign of the spin-orbit coupling), we find beta to be negative for (Zn,Co)O, and to be close to zero in (Zn,Mn)O. However, assuming the reversed valence band ordering, we find beta to be positive in both ZnO based DMS. The sign and the value of p-d exchange integrals determined from our magnetooptical measurements do not follow material trends in DMS and cannot be explained by models based on the virtual crystal approximation. This suggests that the p-d coupling in wide gap DMS is in the strong coupling regime, so that the nature of the observed giant Zeeman splitting is different from that in classical diluted magnetic semiconductors
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Pacuski, Wojciech. "Spectroscopie optique de semi-conducteurs magnétiques dilués à large bande interdite, à base de ZnO et GaN". Phd thesis, Université Joseph Fourier (Grenoble), 2007. http://tel.archives-ouvertes.fr/tel-00296634.
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Ce travail porte sur la spectroscopie magnéto-optique de semi-conducteurs magnétiques dilués (DMS) : ZnO et GaN dopés manganese, fer et cobalt. Les deux semi-conducteurs hôtes, ZnO et GaN ont une grande bande interdite, une structure wurtzite, une faible interaction spin - orbite et une forte interaction d'échange excitonique entre trous et électrons. En présence de champs magnétiques, les ions magnétiques induisent un effet Zeeman géant dont l'interprétation est complexe : les excitons s'anti-croisent et leurs énergies de transition et leurs forces d'oscillateur sont fortement influencées par l'effet Zeeman géant.On a mesuré expérimentalement le splitting Zeeman géant des excitons A et B avec des couches epitaxiées sur saphir (0001) et une propagation de la lumiere parallele a l'axe c du cristal et au champ magnétique (configuration Faraday). Le splitting Zeeman géant diminue avec la température et augmente non linéairement avec le champ magnétique en accord avec l'aimantation calculée des spins isolés. Une analyse quantitative nous a permis d'analyser les propriétés magnétiques et de mesurer les intégrales d'échange pour l'ensemble des matériaux étudiés. Pour des ions avec une configuration d5 (Mn2+ et Fe3+), l'aimantation suit une fonction de Brillouin, mais pour les configurations d7 et d4 (Co2+ ou Mn3+) l'interaction spin-orbite et le champ cristallin trigonal induisent une aimantation anisotrope, en accord avec l'analyse des transitions internes des ions mesurées en spectroscopie infrarouge. Pour (Ga,Mn)N, et (Ga,Fe)N, nous avons trouvé un signe positive pour l'intégrale d'échange entre trous et spins localisés (beta). En supposant une symétrie de la bande de valence dans ZnO correspondant a une interaction spin-orbite positive (Gamma_9, Gamma_7, Gamma_7), nous trouvons un signe négative de beta pour (Zn,Co)O, et beta est de pres de zéro pour (Zn,Mn)O. Toutefois, dans l'hypothese avec spin-orbite négative, nous trouvons un signe positif de beta. Les signes et les valeurs des intégrales d'échange déterminées a partir de nos mesures magnéto-optiques ne peuvent pas etre expliqués par des tendances matérielles et des modeles basés sur l'approximation de cristal virtuel. Ceci suggere que l'échange p-d en DMS a large bande interdite, soit dans le régime de couplage fort, et la nature de splitting Zeeman géant observé est différente qu'en semi-conducteurs magnétiques dilués classiques.
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Dall'Olio, Daniele. "Applicazione di un algoritmo d’apprendimento basato su sistemi fuori dall’equilibrio a dati di Genome Wide Association". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18499/.
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Il fenomeno dell’apprendimento può essere studiato attraverso metodiche di Meccanica Statistica. A partire dalle Neural Networks è possibile descrivere il problema dell'apprendimento mediante un sistema di spin interagenti. Usando una descrizione all’equilibrio del sistema e sotto opportune condizioni, tale problema si dimostra computazionalmente complesso. Tuttavia, esistono algoritmi euristici in grado di risolvere lo stesso problema efficacemente. Si dimostra che questa apparente inconsistenza è dovuta al fatto che lo spazio delle soluzioni degli algoritmi euristici non coincida con quello atteso all’equilibrio. Utilizzando una distribuzione fuori dall’equilibrio è possibile realizzare l’algoritmo replicated focusing Belief Propagation (rfBP), i cui risultati in termini di performance computazionali e di natura delle soluzioni sono in linea con i risultati degli algoritmi euristici. Questo lavoro evidenzia come l’utilizzo integrato di modelli a Spin-Glass, grafi e Neural Networks siano in grado di creare una base teorica solida per lo sviluppo di algoritmi di machine learning originali e innovativi.
Questo lavoro, inoltre, introduce una nuova libreria di C++ ottimizzata per il calcolo parallelo dell’algoritmo rfBP e applica tale algoritmo su dati di Genome Wide Association. Sono stati considerati campioni di genomi del batterio Salmonella, ospitati in diversi animali, ed è stato effettutato il training dell’algoritmo rfBP sull’insorgenza di mutazioni (Single Nucleotide Polymorphism, SNP), nel tentativo di determinare l’animale da cui essi sono stati ospitati. L’obiettivo di questa applicazione è capire come i genomi dei batteri siano influenzati dal proprio ospite animale e se è possibile evidenziare delle caratteristiche che permettano di risalire dalla sequenza di SNPs all’ospite. Questo lavoro mostra che l’algoritmo rfBP produce, su tali sequenze di SNPs, performance comparabili e superiori a quelli ricavati con le più comuni tecniche di Machine Learning.
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Sinha, Suddhasattwa. "Coherent control of dipolar coupled spins in large Hilbert spaces". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/41278.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006.Includes bibliographical references (p. 101-106).
Controlling the dynamics of a dipolar-coupled spin system is critical to the development of solid-state spin-based quantum information processors. Such control remains challenging, as every spin is coupled to a large number of surrounding spins. In this thesis, we primarily focus on developing coherent control techniques for such large spin systems. We start by experimentally simulating spin squeezing using a liquid-state NMR quantum information processor. We demonstrate that the precision of quantum control obtained using strongly modulating pulses was sufficient to reproduce the theoretically expected behavior of the spin observables and the associated entanglement measures among the underlying qubits. We then investigate coherent control in a more complex solid-state spin system consisting of an ensemble of spin pairs. Using pulse amplitude modulation techniques, we decouple the weaker interactions between different pairs and extend the coherence lifetimes within the two-spin system. This is achieved without decoupling the stronger interaction between the two spins within a pair. We thus demonstrated that it is possible to restrict the evolution of a dipolar coupled spin network to a much smaller subspace of the system Hilbert space which allows us to significantly extend the phase coherence times for selected states. Finally, we demonstrate the sensitivity of highly correlated multiple-quantum states to the presence of rare spin defects in a solid-state spin system.
(cont.) We design two multiple-pulse control sequences - one that suspends all spin interactions in the system including that of the defect spins, while the other selectively allows the defect spins to interact only with the abundant spins. By measuring the effective relaxation time of the rare spins, we demonstrate the efficiency of the two control sequences. Furthermore we observe that for small spin cluster sizes, the sensitivity of the highly correlated spin states to the spin defects depends on the coherence order of these correlated spin states. But beyond a certain cluster size, one observes a saturation effect as the higher coherence orders are no longer increasingly sensitive to the defect spin dynamics.
by Suddhasattwa Sinha.
Ph.D.
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Lange, Karsten [Verfasser]. "Two-mode entanglement in spin and spatial degrees of freedom / Karsten Lange". Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://d-nb.info/1166313921/34.
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Werner, Åström Petter. "Experimental study on innovative connections for large span structural timber trusses". Thesis, KTH, Byggnadsmaterial, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-256507.
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Large span timber trusses are usually built with glulam. One problem with large span glulam trusses is that the connections needed to transfer the load between truss members are often complex and expensive. Another issue is transportation. Building large span trusses out of structural timber instead, could be a way of simplifying the connections and at the same time increase the degree of on-site construction and thereby solving the transportation problem.In this study, a total of 18 laboratory tests were performed with the purpose of investigating the tensile strength and the load slip behavior of different connection designs for large span structural timber trusses. Six different test groups corresponding to six different connection designs were tested. The materials used include members made of C24 timber and gusset plates made of birch plywood, aluminum, and steel. Screws were used as fasteners for five test groups and adhesive was used for one group. The influence of different reinforcement techniques including reinforcement screws and added aluminum sheets was studied.The results showed a ductile failure behavior for all test groups except for the group where adhesive was used. However, a decrease of ductility was observed for groups were aluminum sheets were used on the outsides of the mid placed plywood gusset plate. A 12-17 % increase in capacity was observed due to the presence of aluminum sheets. The reinforcement screws had no significant effect on the capacity. However, the presence of reinforcement screws did lead to a reduction in scatter both regarding capacity and stiffness.
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Franzén, Daniel. "Large Swedish industrial companies : Farsightedness in business and sustainability strategies". Thesis, KTH, Organisation och ledning, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155175.
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Industry facilitates the economic development of nations and acquisition of human wealth. Parallel to the global spread of industry, the world is facing rapid population growth. Simultaneously, formerly impoverished populations are approaching middle class standards of living with corresponding increases in levels of consumption. If the populations and consumption levels of societies continue to grow at the expected pace we will face a future environmental crises in the long-term and the world’s environmental resources will not be adequate to meet coming needs. Societies, together with industry, must transform to become sustainable in order to tackle one of our world’s most pressing challenges.Governments and organizations are now pushing industrial companies to meet this challenge and integrate sustainability into their businesses in order to put the economy on the pathway to a sustainable transformation. The World Business Council for Sustainable Development has a vision with formulated conditions that must be met before year 2050 to meet this challenge. But in order to unlock the full potential of sustainable growth, one must also understand the farsightedness of company leaders. The aim of this study is to examine how farsighted Swedish industries are both related to business and sustainability strategies. The main questions for this thesis are: How farsighted are the longest-term strategies/tasks/visions of the Chief Executive Officers (CEOs)? How farsighted are the longest-term tasks that the CEO delegate to members of the management team? How farsighted are the longest-term sustainability strategy of the company? And finally, who in the organization is responsible for the longest-term sustainability strategy/task/vision?The thesis focuses on finding out if their farsightedness in sustainability strategies match with their other business strategies. Eight large Swedish industrial companies were investigated using interviews with their CEOs.The results show a very large difference between companies in the farsightedness measured with time-span of business strategy and sustainability strategy. The time-span of the tasks that the CEOs delegate to the management team also differ substantially between companies. Moreover, the study revealed that all of the studied companies place the ultimate responsibility for sustainability with the CEO and that the farsightedness in sustainability match with the companies’ business strategies. The research show that all eight companies do match their farsightedness in sustainability with business.
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Taleb, Bahaa. "Behavior of large-span metal and reinforced concrete culverts under earth and live loadings". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58239.pdf.
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Badoil, B. "CONTROLE SPECTROPHOTOMETRIQUE LARGE BANDE DE FILTRES INTERFERENTIELS EN COURS DE DEPOT". Phd thesis, Université Paul Cézanne - Aix-Marseille III, 2007. http://tel.archives-ouvertes.fr/tel-00472428.
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Les performances d'un filtre optique interférentiel sont directement liées à la qualité du contrôle optique implanté sur la machine de dépôt. Actuellement, les contrôles spectrophotométriques large bande se développent de plus en plus du fait de l'amélioration des détecteurs matriciels. Le système optique développé durant ce travail de thèse présente la particularité de mesurer simultanément les profils spectraux en transmission et en réflexion de l'échantillon traité en rotation au cours du dépôt, ceci sur une plage spectrale située entre 400 et 1000 nm. Un tel système couplé à un logiciel d'optimisation permet de compenser les éventuelles erreurs de dépôt en modifiant après la réalisation de chaque couche les épaisseurs de celles restant à déposer. Il permet également une caractérisation in situ des indices et épaisseurs de matériaux diélectriques ou absorbants.
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Johnson, Nathan Stuart. "Large-scale experimental and analytical seismic studies of a two-span reinforced concrete bridge system". abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3210946.
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Lemoult, Mélanie. "Contribution à l'étude et la modélisation du bruit à large bande à l'éjection des moteurs d'hélicoptères". Phd thesis, Ecole Centrale de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00625731.
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Le travail réalisé au cours de cette thèse, suite à l'initiative de Turbomeca, est une contribution à l'étude du bruit à large bande à l'échappement d'un turbomoteur d'hélicoptère, portant plus précisément sur la gamme de fréquences qui s'étend sur la gamme de fréquences qui s'étend de 100 à 5000 Hz. Contrairement au bruit à l'échappement des turboréacteurs d'avion sur lesquels le bruit de jet prédomine, ici ce dernier est négligeable en raison de la faible vitesse d'échappement des gaz. L'analyse des données disponibles à Turbomeca et une étude bibliographique approfondie ont permis de préciser la signature fréquentielle du bruit à large bande à l'échappement avec notamment trois contributions distinctes :- Le bruit de combustion direct généré au niveau de la chambre par la flamme (100-400 Hz)- Le bruit de la combustion indirect généré par la turbine haute-pression (500-800 Hz)- Le bruit de combustion indirect généré par la turbine libre (1-3 Hz)Le bruit de combustion indirect est issu de la déformation des perturbations tourbillonnaires et entropiques issues de la combustion lors de leur passage dans les turbines. Ce travail de thèse porte plus précisément sur ce mécanisme. Notamment, des essais sur une turbine industrielle ont été réalisés afin de mettre sa présence en évidence. En parallèle, un modèle analytique de type " disque d'action " (c'est-à-dire dans lequel la turbine est assimilée à une surface de discontinuité) a été développé. Ceci est justifié par le fait que les longueurs d'ondes (acoustique et aérodynamique) sont grandes devant les dimensions des aubes, notamment la corde axiale. On néglige ainsi la géométrie fine des aubes. Seule est prise en compte leur influence sur l'écoulement qui se traduit uniquement par l'accélération et/ou la déviation de ce dernier, et le changement des propriétés thermodynamiques correspondant. La difficulté de la modélisation réside dans l'écriture des relations de saut entre les grandeurs de l'écoulement en amont et en aval de la grille d'aubes.
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Reboul, Gabriel. "Modélisation du bruit à large bande de soufflantes de turboréacteurs". Phd thesis, Ecole Centrale de Lyon, 2010. http://tel.archives-ouvertes.fr/tel-00562647.
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Cette thèse propose différentes méthodologies de calcul du bruit à large bande générée par l'interaction rotor-stator d'une soufflante de turboréacteur et ce de la génération des sources acoustiques jusqu'au rayonnement en champ lointain. En premier lieu, le mécanisme d'interaction rotor-stator est étudié à travers une turbulence de grille homogène et isotrope (THI) impactant un profil isolé. Le cas de l'interaction rotor-stator en milieu guidé est ensuite traité et appliqué à une maquette de compresseur axial. Enfin, la dernière partie traite de la simulation du rayonnement aval en sortie de conduit. Dans chacune de ces parties, des approches analytiques et numériques sont proposées. Les méthodes analytiques permettentune prévision rapide du problème simplifié, et les méthodes numériques permettent de leverles hypothèses au prix d'un temps de calcul plus long.Le modèle d'Amiet est mis en œuvre pour simuler le bruit d'interaction THI-profil àtravers une expérience en soufflerie anéchoïque. Ce modèle simplifiant le profil en une plaque plane non portante, une approche numérique est également mise en place. La convection de perturbations de vitesse incidentes synthétisant une THI et impactant un profil isolé est simulée à l'aide d'un code CAA (Computational AeroAcoustics) résolvant les équations d'Euler en deux dimensions. Les différences de rayonnement entre une plaque plane et un profil cambré épais observées expérimentalement sont en partie retrouvées. Une simulation plus avancée d'un calcul LES (Large Eddy Simulation) 3D est également abordée.Dans la deuxième partie du mémoire, le modèle d'Amiet est étendu au problème de l'interaction rotor-stator en conduit. Différentes formulations sont proposées et discutées. Elles sont appliquées au cas d'un banc d'essai du DLR (centre de recherche aérospatiale allemand) avec des données d'entrée provenant d'un calcul RANS (Reynolds Averaged Navier-Stockes) ou bien directement de mesures. Les prévisions acoustiques ainsi obtenues sont satisfaisantes (+/-2 dB avec des données d'entrée expérimentales) compte tenu de la relative simplicité des modèles. Un calcul LES est exploité pour fournir directement les sources de bruit (fluctuations de pression pariétale). Les spectres obtenus montrent des tendances similaires à ceux issus du modèle d'Amiet malgré certains phénomènes non-physiques encore présents au niveau du calcul LES.Pour terminer, le rayonnement en champ libre est traité. Une manière simple et rapidede résoudre ce problème consiste à utiliser une intégrale de Kirchhoff, en supposant unécoulement moyen uniforme. Une comparaison avec une solution analytique (technique deWiener-Hopf) exacte pour les mêmes conditions montre que le rayonnement du bruit largebande est bien prévu par la méthode de Kirchhoff pour des angles de rayonnement inférieursà 90°. Cependant, pour prendre en compte la géométrie d'éjection de la nacelle et l'effet d'un écoulement hétérogène (cisaillement) sur le rayonnement en champ libre, une approche numérique est mise en place. Une technique permettant de simuler le caractère aléatoire des sources turbulentes ainsi que de satisfaire l'hypothèse de modes acoustiques incohérents est développée. Cette méthodologie est appliquée au cas simple du conduit semi-infini, puis à une tuyère réaliste. Les calculs sont validés à l'aide de solutions analytiques sur les configurations simplifiées. Une analyse critique des instabilités créées dans la couche de cisaillement et de leur influence sur les formulations intégrales couplées au calcul Euler pour obtenir le bruit en champ lointain complète ce dernier chapitre.
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Xiang, Shengqi [Verfasser], Markus [Akademischer Betreuer] Zweckstetter, Reinhard [Akademischer Betreuer] Lührmann, Ralf [Akademischer Betreuer] Ficner, Bert de [Akademischer Betreuer] Groot, Adam [Akademischer Betreuer] Lange i Lars Thorsten [Akademischer Betreuer] Kuhn. "Structural insights into Arginine-Serine rich proteins and N-H spin-spin coupling constants / Shengqi Xiang. Gutachter: Reinhard Lührmann ; Ralf Ficner ; Bert de Groot ; Adam Lange ; Lars Thorsten Kuhn. Betreuer: Markus Zweckstetter". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/1044871229/34.
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Kargarmoakhar, Ramtin. "Large-Scale Testing to Study the Effects of Critical Parameters on the Aerodynamic Behavior of Long Span Bridges". FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/1857.
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Long-span bridges are flexible and therefore are sensitive to wind induced effects. One way to improve the stability of long span bridges against flutter is to use cross-sections that involve twin side-by-side decks. However, this can amplify responses due to vortex induced oscillations.
Wind tunnel testing is a well-established practice to evaluate the stability of bridges against wind loads. In order to study the response of the prototype in laboratory, dynamic similarity requirements should be satisfied. One of the parameters that is normally violated in wind tunnel testing is Reynolds number. In this dissertation, the effects of Reynolds number on the aerodynamics of a double deck bridge were evaluated by measuring fluctuating forces on a motionless sectional model of a bridge at different wind speeds representing different Reynolds regimes. Also, the efficacy of vortex mitigation devices was evaluated at different Reynolds number regimes.
One other parameter that is frequently ignored in wind tunnel studies is the correct simulation of turbulence characteristics. Due to the difficulties in simulating flow with large turbulence length scale on a sectional model, wind tunnel tests are often performed in smooth flow as a conservative approach. The validity of simplifying assumptions in calculation of buffeting loads, as the direct impact of turbulence, needs to be verified for twin deck bridges. The effects of turbulence characteristics were investigated by testing sectional models of a twin deck bridge under two different turbulent flow conditions.
Not only the flow properties play an important role on the aerodynamic response of the bridge, but also the geometry of the cross section shape is expected to have significant effects. In this dissertation, the effects of deck details, such as width of the gap between the twin decks, and traffic barriers on the aerodynamic characteristics of a twin deck bridge were investigated, particularly on the vortex shedding forces with the aim of clarifying how these shape details can alter the wind induced responses.
Finally, a summary of the issues that are involved in designing a dynamic test rig for high Reynolds number tests is given, using the studied cross section as an example.
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Goméz, María Teresa. "El largo viaje the long journey : the cultural politics of the Communist Party of Spain, 1920-1939". Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36016.
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El largo viaje/The Long Journey deals with the cultural politics of the Communist Party of Spain from 1920, when Communism first emerged in the country, until 1939, when the Spanish Civil War ended. The aim of this dissertation is two-fold. On the one hand, by looking at the Party's cultural discourse, its attempts to provide the working class with a political education, and its relationship with communist intellectuals, it aims at explaining the Party's evolution from its original proletarian line in the early 1920s to its democratic line in the mid-1930s, after it joined the anti-fascist Popular Front alliance. On the other, it aims at investigating how, between the years of 1936 and 1938, the Communist Party ended up fulfilling the democratic revolutionary dream of the Spanish bourgeoisie. Through its work in the Ministry of Public Instruction, the Party brought back to life the cultural discourse and aspirations which the reformist and Republican bourgeoisie had been holding on to since the mid- and late nineteenth century. In doing that, Spanish Communists were using cultural practice to further advance the cause of the democratic revolution, and, perhaps more importantly, to make the Spanish people full participants in that revolution for the very first time.
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Sharples, Colin M. "Large- and small-scale factors influencing the population ecology of the European rabbit, Oryctolagus cuniculus L., in southern Spain". Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309906.
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Vedernikov, Ivan. "Seismic analysis of the roofing structural system of Adana stadium in Adana, Turkey". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
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The scope of the current thesis is the investigation of the seismic behavior of complex structures of soccer stadium in the city of Adana, Turkey. The main structural parts of the building of the stadium are reinforced concrete tribunes, steel façade and cable-stayed roof, resting on the structures of the façade.
The behavior of the coupled model in case of seismic excitation is studied. The coupled model is defined as a structural model that contains together all main structural parts: the tribunes, the façade and the roof.
In the engineering practice, a large-span roof and supporting substructures (façade, tribunes) are differentiated and analyzed separately. In case when the seismic analysis has to be done, the separated analysis has to be performed with caution and possible amplification effect of the seismic action for the structural model with all main structural blocks introduced has to be taken into account.
The amplification effect is defined as the increase of the displacements, total base shear and internal forces in the structural elements. To investigate the extent of the amplification effect, the results obtained from the analysis of coupled and uncoupled models were compared.
The results obtained from the modal spectral response analysis and nonlinear dynamic analysis of different structural models show a significant amplification of the displacements of the roof structure and façade bearing columns for a coupled model, with the subsequent increase of the total base shear transferred to the substructures form the roof and internal forces in the elements.
Methods of improving the structural behavior for the seismic excitation have been investigated. In particular, the effect of installation of seismic isolators for the roof structures has been studied. For the structural models with the isolated roof, the results of the analysis of both coupled and uncoupled models have been improved and all design requirements have been verified.
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Gómez, María Teresa. "El largo viaje/The long journey, the cultural politics of the Communist Party of Spain, 1920-1939". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ55335.pdf.
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Bories, Serge. "Conception et analyse des performances d'antennes pour les communications ultra large bande". Phd thesis, Paris 11, 2006. http://pastel.archives-ouvertes.fr/pastel-00002430.
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Le marché des radiocommunications de proximité évolue entre autres vers des applications soit à très basse consommation, soit à très haut débit. Bénéficiant d'une largeur de bande instantanée au moins cent fois plus grande que celle des systèmes large bande actuels, la technologie ultra large bande (ULB) se positionne naturellement sur ces deux créneaux. L'objectif de cette thèse est d'améliorer la compréhension et la performance des antennes ULB fonctionnant sur plusieurs gigahertz tout en répondant aux contraintes spécifiques des applications grand public. Dans un premier temps, la réduction de l'encombrement et du coût des antennes est le point de mire du travail de conception. Cependant ces réductions vont en général de pair avec une dégradation des performances qu'il faut pouvoir quantifier. Pour caractériser la performance de l'antenne sur une telle bande, les outils usuels (gain, phase) dans le domaine fréquentiel sont peu adaptés. Particulièrement pertinent pour le mode impulsionnel, des descripteurs temporels sont donc introduits. Entre autres, la distorsion de la forme d'onde rayonnée par l'antenne est étudiée. Elle permet d'analyser et de quantifier l'influence sur la qualité de la liaison, d'un comportement d'antenne variant en fonction de la fréquence. Dans un second temps, la distorsion qu'apporte l'antenne est mise en regard de celle apportée par les autres éléments de la chaîne de communication. Des campagnes de mesures du canal de propagation et de l'impact de l'intégration sur un terminal multimédia ont été réalisées.
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Ansari, Umair Azeem, i Syed Umair Ali. "Application of LEAN and BPR principles for Software Process Improvement (SPI) : A case study of a large software development organization". Thesis, Blekinge Tekniska Högskola, Institutionen för industriell ekonomi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-6085.
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Abstract ------------- Background ---------------- Like other businesses, the failures and problems faced by the software development industry over the time have motivated experts to look for software process improvement to create quality software rapidly, repeatedly, and reliably. Objective ------------ The purpose of this study is to evaluate if and how Lean thinking and principles primarily associated with auto manufacturing industry can be applied to software development lifecycle for Software Process Improvement (SPI). The secondary aim is to analyze how BPR can be integrated with Lean software development for process improvement. Method ---------- A derived Lean-BPR adoption pattern model is used as a theoretical framework for this thesis. The seven Lean software development principles along with four-step BPR process are selected as process improvement patterns, which effects the KPIs of a software organization. This research study incorporates both Qualitative and Quantitative methods and data to analyze the objectives of this study. The methodological framework of Plan-Do-Check-Act is used in the case study to implement process re-engineering incorporating Lean and BPR principles. The impact of adopting the Lean and BPR principles is assessed in terms of cost, productivity, quality of products and resource management. Results ---------- Application of Lean and BPR principles for software process improvement in the organization under study resulted in 79% improvement in test coverage, 60% reduction in time for test execution and analysis and 44% reduction in cost for fixing defects that were being passed to customer in past. Conclusion ------------- Based on case study results, it can be concluded that Lean, a bottom up approach, characterized by empowerment of employees to analyze and improve their own working process can be effectively combined with IT centric traditionally top down BPR approach for improving KPI’s and software processes.+45 40968458
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Perisse, Frédéric. "ETUDE ET ANALYSE DES MODES DE DEFAILLANCES DES CONDENSATEURS ELECTROLYTIQUES A L'ALUMINIUM ET DES THYRISTORS, APPLIQUEES AU SYSTEME DE PROTECTION DU LHC (LARGE HADRON COLLIDER)". Phd thesis, Université Claude Bernard - Lyon I, 2003. http://tel.archives-ouvertes.fr/tel-00268354.
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Le travail présenté porte sur l'étude et l'analyse des modes de défaillance des condensateurs électrolytiques à l'aluminium ainsi que sur les thyristors. Les composants étudiés sont des éléments principaux du système de protection des aimants supraconducteurs du LHC dont la fiabilité revêt est un aspect primordial. L'étude du vieillissement des condensateurs électrolytiques à l'aluminium à montré que leur fiabilité est fortement liée à leur caractéristique technologique. L'évolution de leur principal indicateur de vieillissement (ESR) peut être modélisée selon différente loi plus ou moins pessimiste choisis selon le mode d'utilisation de ceux-ci. Il apparaît que la prédiction de défaillance de ces composants autre que celle due à l'usure ne peut être que statistique compte tenu des nombreuses causes de défaillance entraînant divers modes de défaillance. Afin de pouvoir évaluer l'influence du vieillissement des condensateurs électrolytique à l'aluminium sur un système, des modèles simples prenant en compte ce paramètre ainsi que la température effective du composant sont proposés. Une précision acceptable compte tenu de la simplicité des modèles est obtenue. L'étude des thyristors à montré que ces composants ont peu de dérive de paramètres en vieillissement statique, par contre de nombreuses défaillances par court-circuit ont été observées. Ces défaillances ont toujours une origine locale due à des défauts du composant. La tenue en tension dépend fortement de la qualité du thyristor ainsi que de la technologie employée.
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Simon, Loïc. "Procedural reconstruction of buildings : towards large scale automatic 3D modeling of urban environments". Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00637638.
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This thesis is devoted to 2D and 3D modeling of urban environments using structured representations and grammars. Our approach introduces a semantic representation for buildings that encodes expected architectural constraints and is able to derive complex instances using fairly simple grammars. Furthermore, we propose two novel inference algorithms to parse images using such grammars. To this end, a steepest ascent hill climbing concept is considered to derive the grammar and the corresponding parameters from a single facade view. It combines the grammar constraints with the expected visual properties of the different architectural elements. Towards addressing more complex scenarios and incorporating 3D information, a second inference strategy based on evolutionary computational algorithms is adopted to optimize a two-component objective function introducing depth cues. The proposed framework was evaluated qualitatively and quantitatively on a benchmark of annotated facades, demonstrating robustness to challenging situations. Substantial improvement due to the strong grammatical context was shown in comparison to the performance of the same appearance models coupled with local priors. Therefore, our approach provides powerful techniques in response to increasing demand on large scale 3D modeling of real environments through compact, structured and semantic representations, while opening new perspectives for image understanding
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Bray, Matthew Robert. "The power of a single large shareholder in iberian firms: friend or foe?" reponame:Repositório Institucional do FGV, 2017. http://hdl.handle.net/10438/18022.
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Agency costs as a result of the separation of ownership and control within a firm can be a hurdle to the performance and profitability. It has been suggested that these costs can be reduced by the presence of a single large shareholder monitoring management and their decisions. On the contrary it has also been argued that a large shareholder negatively affects firm performance by deriving personal benefits from the firm and making suboptimal decisions. This research aims to investigate the relationship between the profitability of a firm and the level to which the shares of that firm are concentrated into a single shareholder. A random effects GLS panel regression is used to determine the effect of a large shareholder being present in Spanish and Portuguese firms by studying firms listed on these bourses over the period 2005 – 2014. The results show that a large shareholder has a negative influence in the Portuguese market, and no statistically significant effect in the Spanish market
Os custos de agência que resultam essencialmente da separação de poder e controlo de uma empresa, podem contribuir negativamente para a performance e rentabilidade desta. A literatura existente sugere que estes custos podem ser minimizados pela presença de um único grande accionista tendo em conta que pode monitorizar mais de perto os seus gestores e respectivas acções e decisões. Por outro lado, existem vários argumentos em estudos passados que defendem que um grande accionista pode afectar negativamente a performance de uma empresa, privilegiando a sua utilidade em detrimento de decisões que beneficiem a sociedade que controla. Este estudo tem por isso como objectivo investigar a relação entre a rentabilidade, lucro de uma empresa e proporção de acções que está concentrada num único accionista. Uma regressão de efeitos aleatórios de dados painel GLS é usada então para determinar o efeito da presença de grandes accionistas em empresas portuguesas e espanholas, listadas em bolsa no período 2005- 2014. Os resultados mostram que a presença de grandes accionistas tem um impacto negativo no mercado português, ao passo que não existe qualquer evidência significativa no caso espanhol.
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Pichatwatana, Kittitach. "Weather responsive internal roof shading systems for existing long-span glazed roof over large naturally ventilated and air-conditioned pedestrian concourses in the tropics". Thesis, Heriot-Watt University, 2016. http://hdl.handle.net/10399/3113.
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This research aims are to optimize weather responsive internal roof shading design systems and to recommend some design principles and guidelines for internal roof shading systems. Such systems would then provide a better building-centric thermal environment and energy performance, while maintaining adequate levels of natural lighting within the existing long-span glazed roofs over large naturally ventilated and air-conditioned pedestrian concourse in the tropics. Two shading configurations: low and high level shadings were tested both the physical indoor environment and energy performance using dynamic thermal and lighting models on the typical clear days and overcast day in summer and winter respectively. The thermal performance of these test cases was assessed using internal surface temperatures, air temperatures, mean radiant temperatures and operative temperatures. The energy performance of the tested cases was examined using solar heat gain and cooling loads as well as the visual performance using illuminance and daylight factors. These remedial solutions were also assessed the financial benefits using standard economic analysis methods to provide recommendation on the cost and payback periods. The predicted results of the large glazed naturally ventilated pedestrian concourse reveal that the internal roof shading device was very effective in reducing inner surface temperatures and consequently reducing radiant heat gain into the space. The low level shadings are more effective than the high level shadings in term of providing better energy, internal thermal and lighting performance. This configuration would reduce two third of the solar heat gain in the large glazed pedestrian concourse space. The predicted results of the large glazed air-conditioned pedestrian concourse reveal that only the low level shading can improve physical environment in terms of thermal, energy and lighting conditions. This configuration would reduce the ground floor heat gain and also the inner surface temperatures significantly. The buffer zone is a key reason that the low level shadings perform better than the high level shading. For the naturally ventilated case, creating a ventilated naturally thermal buffer space is critical to the design of an effective internal roof shading system. The large void space between the glazed roof and the low level shadings allows the free movement of the hot air to dissipate to the outdoors at a high level before it can enter the spaces below. For the air-conditioned case, a larger volume of air over the low level shadings allow for more accumulation of heat as compared to a smaller volume of air over the high shadings. In addition, high solar reflective property of the fabric decreases the solar heat by reflect a portion of the solar heat back out through the transparent roof, while some solar energy is also trapped within the air gap. According to the thermal environmental conditions required for comfort by the operative temperature recommended by ASHRAE (2004), the both shading options of the large glazed naturally ventilated case could only ease to some degree thermal discomfort. While the low level shading of the large glazed air-conditioned case also goes a long way to alleviating summer thermal discomfort. However the shadings could reduce the internal surface temperature significantly which are the main causes of the radiation heat gain in the large glazed naturally ventilated and air-conditioned pedestrian concourses. The visual performance results in both case studies reveal that the internal roof shading significantly reduced and maintained daylighting levels at an appropriate quality of light according to the CIBSE‘s recommendation only on hot clear days. Therefore retractable shading devices are recommended to provide sun screening only when required such as on summer clear days when solar gain is likely to result in overheating. Apart from the possible financial benefits with a present interest rate at 4.85% in China and 1.35% in Thailand over a life time of 30 years, the investment of the shading system could be financially beneficial due to the NPV > 0 and the IRR was greater than interest rate in both forms of long-span glazed roofs over large pedestrian concourses; natural ventilation and air-condition.
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Fang, Le. "Applying the Kolmogorov equation to the problem of subgrid modeling for Large-Eddy Simulation of turbulence". Phd thesis, Ecole Centrale de Lyon, 2009. http://tel.archives-ouvertes.fr/tel-00446447.
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The aim of the current work is to investigate a series of new subgrid models by employing the Kolmogorov equation of ltered quantities (KEF), which is an exact relation of turbulence in physical space. Different formulations of KEF are derived, including the forms in velocity eld (homogeneous isotropic turbulence, inhomogeneous anisotropic turbulence, homogeneous shear turbulence, homogeneous rotating turbulence), in scalar turbulence and in magnetohydrodynamic turbulence. The corresponding subgrid models are then formulated, for example: - The multi-scale improvement of CZZS model. - A new anisotropic eddy-viscosity model in homogeneous shear turbulence. - The improved velocity increment model (IVI). - The rapid-slow analysis and model application in inhomogeneous anisotropic scalar turbulence. - The attempt in magnetohydrodynamic (MHD) turbulence. Besides, there are also other important conclusions in this thesis: - The anisotropic effect of mean shear in physical space is analyzed. - Analytical corrections to the scaling of the second-order structure function in isotropic turbulence in introduced. - It is shown that the two-point distance of velocity increment must be much larger than the lter size, in order to satisfy the classical scaling law. Otherwise, the classical scaling law can not be directly applied in subgrid modeling. - A thought-experiment is described to analyse the time-reversibility problem of subgrid models. - A rapid algorithm for Tophat lter operator in discrete eld is introduced.
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Fedala, Djaafer. "Modélisation du bruit à large bande rayonné par un profil isolé : application aux turbomachines". Phd thesis, Paris, ENSAM, 2007. http://pastel.archives-ouvertes.fr/pastel-00003209.
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Les nuisances sonores sont devenues une importante préoccupation environnementale. L'accroissement des exigences de confort et le durcissement des réglementations européennes et mondiales ont rendu la réduction du bruit aérodynamique des turbomachines un enjeu primordial pour plusieurs industries. Ce travail a pour objectif principal le développement d'outils de modélisation de la composante à large bande du bruit des ventilateurs de façon à l'intégrer comme critère d'optimisation dès leur phase de conception. L'étude est concentrée sur les deux sources reconnues pour leurs contributions significatives dans le bruit rayonné : l'interaction des pales avec l'écoulement turbulent amont et la diffraction de la couche limite turbulente au niveau du bord de fuite. Dans un premier temps, une approche reposant sur la formulation analytique d'Amiet pour la prédiction du bruit d'un profil isolé disposé dans un écoulement turbulent est mise en oeuvre. L'effet de l'épaisseur n'est pas pris en compte dans la formulation initiale d'Amiet. Une correction gaussienne a été proposée sur la base des travaux de Gershfeld améliorant ainsi considérablement les résultats de calculs. Une extension vers la turbomachine est ensuite proposée et validée expérimentalement. Un ventilateur axial est disposé à l'amont de différents écoulements incidents turbulents générés par cinq dispositifs de contrôle de turbulence. La turbulence incidente est caractérisée par le modèle spectral de von Kármán à partir des mesures à fils chauds. La confrontation des spectres de puissance acoustique calculés à ceux mesurés donne un accord satisfaisant sur une large bande fréquentielle audible. Dans la deuxième partie, une modélisation hybride combinant des Simulations des Grandes Echelles avec une solution intégrale dans le domaine temporel de l'analogie de Ffowcs Willimas & Hawkings est développée. Une validation complétée par une étude des erreurs numériques du code acoustique développé sur la base de la formulation intégrale 1A de Farassat avec une surface perméable de Di Francescontonio a été réalisée. Les simulations LES bidimensionnelles de l'écoulement turbulent autour d'un profil ont reproduit la transition de la couche limite turbulente et le détachement tourbillonnaire au bord de fuite. L'analyse des spectres de pression pariétale a révélé que l écoulement amont a un important effet sur les fluctuations de pression pariétale et leurs localisations.
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Hurault, Jérémy. "Métrologie instationnaire embarquée pour la modélisation du bruit à large bande dans les turbomachines". Phd thesis, Paris, ENSAM, 2010. http://pastel.archives-ouvertes.fr/pastel-00005984.
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Les nuisances sonores sont devenues une importante préoccupation environnementale. L'accroissement des exigences de confort et le durcissement des réglementations tant européennes que mondiales ont rendu la réduction du bruit aérodynamique des turbomachines un enjeu primordial pour de nombreuses industries. Ce travail a pour objectif principal le développement d'outils de modélisation de la composante à large bande du bruit des ventilateurs de façon à l'intégrer comme critère d'optimisation dès leur phase de conception. L'empilement (dévers) étant connu pour avoir une influence sur les émissions acoustiques des ventilateurs, trois ventilateurs à empilements différents seront comparés tout au long de ce mémoire. Un banc d'essai permettant l'acquisition des pressions moyennes et instationnaires sur les pales des ventilateurs est conçu puis fabriqué. Ces données sont nécessaires comme entrées d'un modèle de prévision du bruit de bord de fuite. Les spectres de pressions mesurés sont comparés à différents modèles puis utilisés pour obtenir le spectre acoustique en champ lointain à partir du modèle d'Amiet de bord de fuite. Ce modèle prévu pour un profil fixe est adapté pour un ventilateur. Puis une simulation numérique RANS avec modèle de turbulence du deuxième ordre, de ces trois ventilateurs, est réalisée afin d'obtenir : les performances globales des ventilateurs à différents débits, la morphologie de l'écoulement notamment les profils des vitesses aval, les composantes du tenseur des contraintes de Reynolds, les champs de pression sur les pales et les variables de la couche limite. Toutes ces données sont comparées avec différentes mesures sur un banc normalisé permettant la mesure du débit de fonctionnement
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Lange, Florian [Verfasser], Holger [Akademischer Betreuer] Fehske, Holger [Gutachter] Fehske, Eric [Gutachter] Jeckelmann i Fabian [Gutachter] Heidrich-Meisner. "Density-matrix renormalization-group studies of spin, boson and fermion systems with symmetry-protected topological phases / Florian Lange ; Gutachter: Holger Fehske, Eric Jeckelmann, Fabian Heidrich-Meisner ; Betreuer: Holger Fehske". Greifswald : Universität Greifswald, 2019. http://d-nb.info/1199537756/34.
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Lange, Florian [Verfasser], Holger [Akademischer Betreuer] Fehske, Holger Gutachter] Fehske, Eric [Gutachter] Jeckelmann i Fabian [Gutachter] [Heidrich-Meisner. "Density-matrix renormalization-group studies of spin, boson and fermion systems with symmetry-protected topological phases / Florian Lange ; Gutachter: Holger Fehske, Eric Jeckelmann, Fabian Heidrich-Meisner ; Betreuer: Holger Fehske". Greifswald : Universität Greifswald, 2019. http://nbn-resolving.de/urn:nbn:de:gbv:9-opus-33484.
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Liang, Chenghua. "Caractérisations électriques de polymères conducteurs intrinsèques Polyaniline / Polyuréthane dans une large gamme de fréquence (DC à 20 GHz)". Phd thesis, Université du Littoral Côte d'Opale, 2010. http://tel.archives-ouvertes.fr/tel-00596089.
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L'objectif général de ce travail est d'accroître les connaissances fondamentales des Polymères Conducteurs Intrinsèques (PCI), et plus particulièrement de la Polyaniline (PANI) mélangée à du polyuréthane (PU), afin d'améliorer leurs propriétés électriques. Une étude morphologique montre que ces matériaux sont composés de chaines conductrices de type " spaghetti " mélangées dans une matrice isolante. Une première partie de ce travail est consacrée à la caractérisation diélectrique d'échantillons composés de 0.5%, 1%, 5% de PANI déposés sur de la fibre de verre dans une gamme de fréquence de 20 Hz à 20 GHz. Les résultats font apparaître une relaxation diélectrique qui évolue fortement avec la concentration du mélange. Ce phénomène est expliqué par un modèle théorique basé sur une distribution gaussienne des longueurs des îlots conducteurs. Une étude de vieillissement par voie thermique montre que les chemins de percolation finissent par se casser au cours du temps, ce qui entraine une diminution de la longueur moyenne des îlots et une dégradation des propriétés électriques des polymères conducteurs. La 2ème partie de ce travail concerne des mesures de bruit en 1/f sur des échantillons de 5%, 10%, 20%, 50% et 100% de PANI déposés en couche mince. Pour ces mesures, nous avons été amenés à mettre en place des méthodes utilisant des configurations spécifiques et à choisir la mieux adaptée à nos échantillons. Les résultats de cette étude montrent un fort excès de bruit en 1/f comparativement à ceux obtenus sur des matériaux homogènes. Ces excès de bruit sont expliqués par un modèle développé à partir de la morphologie de type " spaghetti ".
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Santos, Luciano Barbosa dos. "Contribuições ao estudo das cúpulas metálicas". Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-07112006-112533/.
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Este trabalho aborda, de uma forma geral, os sistemas estruturais normalmente adotados no projeto de cúpulas metálicas. Foi dado ênfase a um arranjo derivado do sistema Schwedler, recentemente utilizado em projetos desenvolvidos no interior do estado de São Paulo. O trabalho pode ser divido em duas partes, a primeira delas versando sobre as ligações que compunham o sistema estrutural estudado, e a segunda versando sobre a influência dessas ligações no comportamento da estrutura e sobre a influência da forma de contraventamento. As ligações foram estudadas sob dois aspectos diferentes, que foram: a) revisão e aperfeiçoamento dos critérios de dimensionamento adotados em algumas ligações, e b) proposição de modelos para descrição do comportamento momento-rotação de ligações com dupla tala de alma parafusada e de aparelhos de apoio. A influência do tipo de contraventamento e da rigidez das ligações foi investigada por meio do efeito exercido nos deslocamentos verticais e na distribuição de esforços internos da estrutura. Para tanto, foram utilizados programas computacionais de uso já consagrado, cujos resultados foram comparados entre si.In a general way, this work deals with structural systems usually adopted in the project of metallic domes. Emphasis was given to a derived arrangement derived of the Schwedler system, recently used in projects developed the state of São Paulo. The work can be divided in two parts, the first one is about the connections that compose the structural system studied, and second one treats the influence of those connections in the structure behavior and the influence in the brace configuration. The connections were studied under two different aspects, that were: a) revision and improvement of the design criteria adopted in some connections, and b) proposition of models for the momentrotation description for double plate connections of web. The influence of the brace type and of the rigidity of the connections were investigated by means of the effect in the vertical displacements and in the distribution of internal efforts of the structure. So, two commercial softwares were used, and the results were compared.