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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
361

Programovn­ mikrokontrol©r c2000 v programu MATLAB/Simulink / MATLAB/Simulink Model Based Design Using C2000 Microcontrollers

oupal, Ondej January 2020 (has links)
The aim of this thesis is to explore possibilities of rapid control prototyping, describe the concept of creating the software application in MATLAB/Simulink environment with use for development kit Texas instruments LaunchPad and create an application for DC and induction motor control in this environment. This work describes the application for unipolar/bipolar control H-Bridge of power converter for DC motor, measurement of output currents, speed and its displaying in real time using serial control interface. This thesis also desribes scalar and vector control of induction motor. All software applications with measurements are created in MATLAB/Simulink and attached to the thesis.
362

Atomistic simulations of competing influences on electron transport across metal nanocontacts

Dednam, Wynand 14 June 2019 (has links)
In our pursuit of ever smaller transistors, with greater computational throughput, many questions arise about how material properties change with size, and how these properties may be modelled more accurately. Metallic nanocontacts, especially those for which magnetic properties are important, are of great interest due to their potential spintronic applications. Yet, serious challenges remain from the standpoint of theoretical and computational modelling, particularly with respect to the coupling of the spin and lattice degrees of freedom in ferromagnetic nanocontacts in emerging spintronic technologies. In this thesis, an extended method is developed, and applied for the first time, to model the interplay between magnetism and atomic structure in transition metal nanocontacts. The dynamic evolution of the model contacts emulates the experimental approaches used in scanning tunnelling microscopy and mechanically controllable break junctions, and is realised in this work by classical molecular dynamics and, for the first time, spin-lattice dynamics. The electronic structure of the model contacts is calculated via plane-wave and local-atomic orbital density functional theory, at the scalar- and vector-relativistic level of sophistication. The effects of scalar-relativistic and/or spin-orbit coupling on a number of emergent properties exhibited by transition metal nanocontacts, in experimental measurements of conductance, are elucidated by non-equilibrium Green’s Function quantum transport calculations. The impact of relativistic effects during contact formation in non-magnetic gold is quantified, and it is found that scalar-relativistic effects enhance the force of attraction between gold atoms much more than between between atoms which do not have significant relativistic effects, such as silver atoms. The role of non-collinear magnetism in the electronic transport of iron and nickel nanocontacts is clarified, and it is found that the most-likely conductance values reported for these metals, at first- and lastcontact, are determined by geometrical factors, such as the degree of covalent bonding in iron, and the preference of a certain crystallographic orientation in nickel. / Physics / Ph. D. (Physics)
363

Operators for Multi-Resolution Morse and Cell Complexes / Оператори за мулти-резолуционе комплексе Морза и ћелијске комплексе / Operatori za multi-rezolucione komplekse Morza i ćelijske komplekse

Čomić Lidija 03 March 2014 (has links)
<p>The topic of the thesis is analysis of the topological structure of scalar fields and<br />shapes represented through Morse and cell complexes, respectively. This is<br />achieved by defining simplification and refinement operators on these<br />complexes. It is shown that the defined operators form a basis for the set of<br />operators that modify Morse and cell complexes. Based on the defined<br />operators, a multi-resolution model for Morse and cell complexes is constructed,<br />which contains a large number of representations at uniform and variable<br />resolution.</p> / <p>Тема дисертације је анализа тополошке структуре скаларних поља и<br />облика представљених у облику комплекса Морза и ћелијских комплекса,<br />редом. То се постиже дефинисањем оператора за симплификацију и<br />рафинацију тих комплекса. Показано је да дефинисани оператори чине<br />базу за скуп оператора на комплексима Морза и ћелијским комплексима.<br />На основу дефинисаних оператора конструисан је мулти-резолуциони<br />модел за комплексе Морза и ћелијске комплексе, који садржи велики број<br />репрезентација униформне и варијабилне резолуције.</p> / <p>Tema disertacije je analiza topološke strukture skalarnih polja i<br />oblika predstavljenih u obliku kompleksa Morza i ćelijskih kompleksa,<br />redom. To se postiže definisanjem operatora za simplifikaciju i<br />rafinaciju tih kompleksa. Pokazano je da definisani operatori čine<br />bazu za skup operatora na kompleksima Morza i ćelijskim kompleksima.<br />Na osnovu definisanih operatora konstruisan je multi-rezolucioni<br />model za komplekse Morza i ćelijske komplekse, koji sadrži veliki broj<br />reprezentacija uniformne i varijabilne rezolucije.</p>
364

Intégrabilité et superintégrabilité de deuxième ordre dans l'espace Euclidien tridimensionel

Abdul-Reda, Hassan 02 1900 (has links)
L'article "A systematic search for nonrelativistic systems with dynamical symetries, Part I" publié il y a à peu près 50 ans a commencé une classification de ce qui est maintenant appelé les systèmes superintégrables. Il était dévoué aux systèmes dans l'espace Euclidien ayant plus d'intégrales de mouvement que de degrés de liberté. Les intégrales étaient toutes supposées de second ordre en quantité de mouvement. Dans ce mémoire, sont présentés de nouveaux résultats sur la superintégrabilité de second ordre qui sont pertinents à l'étude de la superintégrabilité d'ordre supérieur et de la superintégrabilité de systèmes ayant des potentiels vecteurs ou des particules avec spin. / The article "A systematic search for nonrelativistic systems with dynamical symetries, Part I" published about 50 years ago started the classification of what is now called superintegrable systems. It was devoted to systems in Euclidean space with more integrals of motion than degrees of freedom. The integrals were all assumed to be second order polynomials in the particle momentum. Here we present some further results on second order superintegrability that are relevant for studies of higher order superintegrability and for superintegrability for systems with vector potentials or for particles with spin.
365

Search for heavy Higgs bosons A/H decaying to a top-quark pair in pp collisions at \sqrt(s)=8 TeV with the ATLAS detector

Stănescu-Bellu, Mădălina 30 April 2021 (has links)
In dieser Dissertation wird die Suche nach schweren neutralen pseudoskalaren A und skalaren H Higgs-Bosonen vorgestellt, die in gg-Fusionen erzeugt werden, und in ein Top-Antitop-Quark-Paar zerfallen. Gesucht wurde im vollständigen Datensatz von Proton–Proton-Kollisionen bei einer Schwerpunktsenergie von 8 TeV die vom ATLAS-Detektor am Large Hadron Collider aufgezeichnet wurde und einer integrierten Luminosität von 20.3 fb−1 entspricht. Der Signalprozess und der Haupthintergrund aus der Top-Quark-Paar-Produktion über starke gg-Fusionen-Prozesse, interferieren heftig, was zu einer Verzerrung des reinen Breit-Wigner-Resonanzpeak in eine Peak-Dip-Struktur führt. Diese Analyse ist die erste am LHC, die die Interferenz zwischen Signal und Hintergrundprozessen vollständig berücksichtigt. Die Suche stützt sich auf die statistische Analyse des invarianten Top-Quark-Paar-Massenspektrum, welches aus Ereignissen mit einem Elektron oder Myon mit hohem Transversalimpuls, einer hohen fehlenden Transversalenergie von dem nicht detektierten Neutrino und mindestens vier Jets rekonstruiert wird. In den Daten wird keine signifikante Abweichung vom erwarteten Standardmodell-Hintergrund beobachtet. Die Ausschließungsgrenzen wurden abgeleitet im Kontext des Typ II Two-Higgs-Doublet Model, für Higgs-Bosonen mit einer Masse von 500 und 750 GeV und mit niedrigerem tan(\beta)-Parameter, bei der tan(\beta) das Verhältnis der Vakuumerwartungswerte der beiden Higgs-Dublett-Felder ist. Diese Parameterregionen sind weitgehend unerforscht in Untersuchungen von beliebigen Endzuständen. / In this thesis a search is presented for heavy neutral pseudoscalar A and scalar H Higgs bosons, produced in gg fusion and decaying into a top-antitop quark pair. The search is conducted on the full proton-proton collisions dataset recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass collision energy of 8 TeV and corresponding to an integrated luminosity of 20.3 fb−1. The signal process and the main background from top quark pair production via the gg fusion strong process, interfere heavily, distorting the signal shape from the pure Breit-Wigner resonance peak to a peak-dip structure. This analysis is the first one at the LHC that fully takes into account the interference between a signal and the background processes. The search relies on the statistical analysis of the top quark pair invariant mass spectrum, which is reconstructed in signal candidate events with a high-transverse momentum electron or muon, large missing transverse energy from the undetected neutrino and at least four jets. No significant deviation from the expected SM background is observed in data. Exclusion limits are derived in the context of the type-II Two-Higgs-Doublet Model, for Higgs boson masses of 500 and 750 GeV and in the low tan(\beta) parameter region, where tan(\beta) is the ratio of the vacuum expectation values of the two Higgs doublet fields. These parameter regions have been largely unexplored by searches in any final state.
366

Twisted K-theory with coefficients in a C*-algebra and obstructions against positive scalar curvature metrics / Getwistete K-Theorie mit Koeffizienten in einer C*-Algebra und Obstruktionen gegen positive skalare Krümmung

Pennig, Ulrich 31 August 2009 (has links)
No description available.
367

Převod trojúhelníkových polygonálních 3D sítí na 3D spline plochy / 3D Triangles Polygonal Mesh Conversion on 3D Spline Surfaces

Jahn, Zdeněk Unknown Date (has links)
In computer graphics we can handle unstructured triangular 3D meshes which are not too usable for processing through their irregularity. In these situations it occurs need of conversion that 3D mesh to more suitable representation. Some kind of 3D spline surface can be proper alternative because it institutes regularity in the form of control points grid and that's why it is more suitable for next processing. During conversion, which is described in this thesis, quadrilateral 3D mesh is constructed at first. This mesh has regular structure but mainly the structure corresponds to structure of control points grid of resulting 3D spline surface. Created quadrilateral 3D mesh can be saved and consequently used in specific modeling applications for T-spline surface creation.
368

Application of the Duality Theory

Lorenz, Nicole 15 August 2012 (has links) (PDF)
The aim of this thesis is to present new results concerning duality in scalar optimization. We show how the theory can be applied to optimization problems arising in the theory of risk measures, portfolio optimization and machine learning. First we give some notations and preliminaries we need within the thesis. After that we recall how the well-known Lagrange dual problem can be derived by using the general perturbation theory and give some generalized interior point regularity conditions used in the literature. Using these facts we consider some special scalar optimization problems having a composed objective function and geometric (and cone) constraints. We derive their duals, give strong duality results and optimality condition using some regularity conditions. Thus we complete and/or extend some results in the literature especially by using the mentioned regularity conditions, which are weaker than the classical ones. We further consider a scalar optimization problem having single chance constraints and a convex objective function. We also derive its dual, give a strong duality result and further consider a special case of this problem. Thus we show how the conjugate duality theory can be used for stochastic programming problems and extend some results given in the literature. In the third chapter of this thesis we consider convex risk and deviation measures. We present some more general measures than the ones given in the literature and derive formulas for their conjugate functions. Using these we calculate some dual representation formulas for the risk and deviation measures and correct some formulas in the literature. Finally we proof some subdifferential formulas for measures and risk functions by using the facts above. The generalized deviation measures we introduced in the previous chapter can be used to formulate some portfolio optimization problems we consider in the fourth chapter. Their duals, strong duality results and optimality conditions are derived by using the general theory and the conjugate functions, respectively, given in the second and third chapter. Analogous calculations are done for a portfolio optimization problem having single chance constraints using the general theory given in the second chapter. Thus we give an application of the duality theory in the well-developed field of portfolio optimization. We close this thesis by considering a general Support Vector Machines problem and derive its dual using the conjugate duality theory. We give a strong duality result and necessary as well as sufficient optimality conditions. By considering different cost functions we get problems for Support Vector Regression and Support Vector Classification. We extend the results given in the literature by dropping the assumption of invertibility of the kernel matrix. We use a cost function that generalizes the well-known Vapnik's ε-insensitive loss and consider the optimization problems that arise by using this. We show how the general theory can be applied for a real data set, especially we predict the concrete compressive strength by using a special Support Vector Regression problem.
369

Elliptic Curve Cryptography for Lightweight Applications.

Hitchcock, Yvonne Roslyn January 2003 (has links)
Elliptic curves were first proposed as a basis for public key cryptography in the mid 1980's. They provide public key cryptosystems based on the difficulty of the elliptic curve discrete logarithm problem (ECDLP) , which is so called because of its similarity to the discrete logarithm problem (DLP) over the integers modulo a large prime. One benefit of elliptic curve cryptosystems (ECCs) is that they can use a much shorter key length than other public key cryptosystems to provide an equivalent level of security. For example, 160 bit ECCs are believed to provide about the same level of security as 1024 bit RSA. Also, the level of security provided by an ECC increases faster with key size than for integer based discrete logarithm (dl) or RSA cryptosystems. ECCs can also provide a faster implementation than RSA or dl systems, and use less bandwidth and power. These issues can be crucial in lightweight applications such as smart cards. In the last few years, ECCs have been included or proposed for inclusion in internationally recognized standards. Thus elliptic curve cryptography is set to become an integral part of lightweight applications in the immediate future. This thesis presents an analysis of several important issues for ECCs on lightweight devices. It begins with an introduction to elliptic curves and the algorithms required to implement an ECC. It then gives an analysis of the speed, code size and memory usage of various possible implementation options. Enough details are presented to enable an implementer to choose for implementation those algorithms which give the greatest speed whilst conforming to the code size and ram restrictions of a particular lightweight device. Recommendations are made for new functions to be included on coprocessors for lightweight devices to support ECC implementations Another issue of concern for implementers is the side-channel attacks that have recently been proposed. They obtain information about the cryptosystem by measuring side-channel information such as power consumption and processing time and the information is then used to break implementations that have not incorporated appropriate defences. A new method of defence to protect an implementation from the simple power analysis (spa) method of attack is presented in this thesis. It requires 44% fewer additions and 11% more doublings than the commonly recommended defence of performing a point addition in every loop of the binary scalar multiplication algorithm. The algorithm forms a contribution to the current range of possible spa defences which has a good speed but low memory usage. Another topic of paramount importance to ECCs for lightweight applications is whether the security of fixed curves is equivalent to that of random curves. Because of the inability of lightweight devices to generate secure random curves, fixed curves are used in such devices. These curves provide the additional advantage of requiring less bandwidth, code size and processing time. However, it is intuitively obvious that a large precomputation to aid in the breaking of the elliptic curve discrete logarithm problem (ECDLP) can be made for a fixed curve which would be unavailable for a random curve. Therefore, it would appear that fixed curves are less secure than random curves, but quantifying the loss of security is much more difficult. The thesis performs an examination of fixed curve security taking this observation into account, and includes a definition of equivalent security and an analysis of a variation of Pollard's rho method where computations from solutions of previous ECDLPs can be used to solve subsequent ECDLPs on the same curve. A lower bound on the expected time to solve such ECDLPs using this method is presented, as well as an approximation of the expected time remaining to solve an ECDLP when a given size of precomputation is available. It is concluded that adding a total of 11 bits to the size of a fixed curve provides an equivalent level of security compared to random curves. The final part of the thesis deals with proofs of security of key exchange protocols in the Canetti-Krawczyk proof model. This model has been used since it offers the advantage of a modular proof with reusable components. Firstly a password-based authentication mechanism and its security proof are discussed, followed by an analysis of the use of the authentication mechanism in key exchange protocols. The Canetti-Krawczyk model is then used to examine secure tripartite (three party) key exchange protocols. Tripartite key exchange protocols are particularly suited to ECCs because of the availability of bilinear mappings on elliptic curves, which allow more efficient tripartite key exchange protocols.
370

Application of the Duality Theory: New Possibilities within the Theory of Risk Measures, Portfolio Optimization and Machine Learning

Lorenz, Nicole 28 June 2012 (has links)
The aim of this thesis is to present new results concerning duality in scalar optimization. We show how the theory can be applied to optimization problems arising in the theory of risk measures, portfolio optimization and machine learning. First we give some notations and preliminaries we need within the thesis. After that we recall how the well-known Lagrange dual problem can be derived by using the general perturbation theory and give some generalized interior point regularity conditions used in the literature. Using these facts we consider some special scalar optimization problems having a composed objective function and geometric (and cone) constraints. We derive their duals, give strong duality results and optimality condition using some regularity conditions. Thus we complete and/or extend some results in the literature especially by using the mentioned regularity conditions, which are weaker than the classical ones. We further consider a scalar optimization problem having single chance constraints and a convex objective function. We also derive its dual, give a strong duality result and further consider a special case of this problem. Thus we show how the conjugate duality theory can be used for stochastic programming problems and extend some results given in the literature. In the third chapter of this thesis we consider convex risk and deviation measures. We present some more general measures than the ones given in the literature and derive formulas for their conjugate functions. Using these we calculate some dual representation formulas for the risk and deviation measures and correct some formulas in the literature. Finally we proof some subdifferential formulas for measures and risk functions by using the facts above. The generalized deviation measures we introduced in the previous chapter can be used to formulate some portfolio optimization problems we consider in the fourth chapter. Their duals, strong duality results and optimality conditions are derived by using the general theory and the conjugate functions, respectively, given in the second and third chapter. Analogous calculations are done for a portfolio optimization problem having single chance constraints using the general theory given in the second chapter. Thus we give an application of the duality theory in the well-developed field of portfolio optimization. We close this thesis by considering a general Support Vector Machines problem and derive its dual using the conjugate duality theory. We give a strong duality result and necessary as well as sufficient optimality conditions. By considering different cost functions we get problems for Support Vector Regression and Support Vector Classification. We extend the results given in the literature by dropping the assumption of invertibility of the kernel matrix. We use a cost function that generalizes the well-known Vapnik's ε-insensitive loss and consider the optimization problems that arise by using this. We show how the general theory can be applied for a real data set, especially we predict the concrete compressive strength by using a special Support Vector Regression problem.

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