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1
Tomlin, Toby-Daniel. "Analysis and modelling of jitter and phase noise in electronic systems : phase noise in RF amplifiers and jitter in timing recovery circuits." University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2004. http://theses.library.uwa.edu.au/adt-WU2004.0021.
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Timing jitter and phase noise are important design considerations in most electronic systems, particularly communication systems. The desire for faster transmission speeds and higher levels of integration, combined with lower signal levels and denser circuit boards has placed greater emphasis on managing problems related to phase noise, timing jitter, and timing distribution. This thesis reports original work on phase noise modelling in electronic systems. A new model is proposed which predicts the up-conversion of baseband noise to the carrier frequency in RF amplifiers. The new model is validated by comparing the predicted phase noise performance to experimental measurements as it applies to a common emitter (CE), bipolar junction transistor (BJT) amplifier. The results show that the proposed model correctly predicts the measured phase noise, including the shaping of the noise about the carrier frequency, and the dependence of phase noise on the amplifier parameters. In addition, new work relating to timing transfer in digital communication systems is presented. A new clock recovery algorithm is proposed for decoding timing information encoded using the synchronous residual time-stamp (SRTS) method. Again, theoretical analysis is verified by comparison with an experimental implementation. The results show that the new algorithm correctly recovers the source clock at the destination, and satisfies the jitter specification set out by the ITU-T for G.702 signals.
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Chun, Sungjun. "Methodologies for modeling simultaneous switching noise in multi-layered packages and boards." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/15452.
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Kumar, Neraj. "Detection of Variable Retention Time in DRAM." PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/2103.
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This thesis investigates a test method to detect the presence of Variable Retention Time (VRT) bits in manufactured DRAM. The VRT bits retention time is modeled as a 2-state random telegraph process that includes miscorrelation between test and use. The VRT defect is particularly sensitive to test and use conditions. A new test method is proposed to screen the VRT bits by simulating the use conditions during manufacturing test. Evaluation of the proposed test method required a bit-level VRT model to be parameterized as a function of temperature and voltage conditions. The complete 2-state VRT bit model combines models for the time-in-state and for the retention-time including miscorrelation. A copula is used to model the eect of miscorrelation between test and use. The proposed VRT test algorithm runtime is estimated as a function of VRT test coverage, test temperature and test voltage.
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Luo, Yan, and 罗妍. "Three essays on noise and institutional trading." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44549246.
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Taylor, Katherine P. "Noise models of A/D and D/A converters for determination of fundamental noise limitations." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/16910.
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Envia, Edmane. "Influence of vane sweep on rotor-stator interaction noise." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184609.
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In this dissertation the influence of vane sweep on rotor-stator interaction noise is investigated. In an analytical approach, the interaction of a convected gust, representing the rotor viscous wake, with a cascade of finite span swept airfoils, representing the stator, is analyzed. The analysis is based on the solution of the exact linearized equations of motion. High-frequency convected gusts for which noise generation is concentrated near the leading edge of the airfoils are considered. In a preliminary study, the problem of an isolated finite span swept airfoil interacting with a convected gust is analyzed. Using Fourier transform methods and the Wiener-Hopf technique, an approximate solution for this problem is developed. Closed form expressions for the acoustic farfield are obtained and used in a parametric study to assess the effect of airfoil sweep on noise generation. Results indicate that sweep can substantially reduce the farfield noise levels for a single airfoil. Utilizing the single airfoil model, an approximate solution to the problem of noise radiation from a cascade of finite span swept airfoils interacting with a convected gust is derived. Only upstream radiated noise is considered. Neglecting the weak coupling between the adjacent leading edges at high frequencies, the cascade solution is constructed as a superposition of acoustic farfields emanating from an infinite number of isolated airfoils. A parametric study of noise generated by gust-cascade interaction is then carried out to assess the effectiveness of vane sweep in reducing rotor-stator interaction noise. The results of the parametric study show that, over a fairly wide range of conditions, sweep is beneficial in reducing noise levels. One conclusion of particular importance is that rotor wake twist or circumferential lean substantially influences the effectiveness of vane sweep. The orientation of the vane sweep must be chosen to enhance the natural phase lag caused by wake lean, in which case rather small sweep angles substantially reduce the noise levels.
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Mackenzie, Neil C. "The independent quadratic optimisation algorithm for the active control of noise and vibration /." Title page, contents and abstract only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phm15742.pdf.
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DITOLLA, ROBERT JOHN. "RANDOM VIBRATION ANALYSIS BY THE POWER SPECTRUM AND RESPONSE SPECTRUM METHODS (WHITE NOISE, FINITE-ELEMENT, VANMARCKE, DENSITY, NASTRAN)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183836.
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Determination of the stresses and displacements which occur in response to random excitations cannot be accomplished by traditional deterministic analysis methods. As the specification of the excitation and the response of the structure become more complex, solutions by direct, closed-form methods require extensive computations. Two methods are presented which can be used in the analysis of structures which are subjected to random excitations. The Power Spectrum Method is a procedure which determines the random vibration response of the structure based upon a frequency response analysis of a structural model. The Response Spectrum Method is a method which is based upon specified forces or displacements as a function of time. A derivation of each of the methods is presented and followed by comparisons of the results which were obtained for single and multiple-degree-of-freedom systems. Assumptions and limitations of the methods are discussed as well as their accuracy over ranges of frequency, damping and loading specification. As a direct application and comparison of the two methods, an analysis of the support system for the primary mirror of the Space Infrared Telescope Facility (SIRTF) has been performed. In addition, a method for the evaluation of the critical damping in a single-degree-of-freedom structure is demonstrated.
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Hinkle, Adam R. "Tight-binding calculation of electronic properties of oligophenyl and oligoacene nanoribbons." Virtual Press, 2008. http://liblink.bsu.edu/uhtbin/catkey/1398716.
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Within recent years, allotropic structures of carbon have been produced in the forms of tubes and ribbons which offer the promise of extraordinary electronic and thermal properties. Here we present analyses of oligophenyl and oligoacene systems–infinite, one-dimensional chains of benzene rings linked along the armchair and zigzag directions. These one-dimensional structures, which are amenable to calculation by analytical means, exhibit features very similar to carbon nanotubes and nanoribbons. Using a tight-binding Hamiltonian we analytically determine the density of states, local density of states, and energy-band structure for the phenyl and the acene. We also examine the effect of disorder on the energies and the corresponding states.Department of Physics and Astronomy
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Adams, William Mark 1961. "APPLICATION OF THE VARIANCE-TO-MEAN RATIO METHOD FOR DETERMINING NEUTRON MULTIPLICATION PARAMETERS OF CRITICAL AND SUBCRITICAL REACTORS (REACTOR NOISE, FEYNMAN-ALPHA)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275438.
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Gómez, Bardón María del Rocío. "Mathematical models and simulations of complex social systems." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1287/.
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In this thesis we present two different models of Complex Social Systems. The first model represents a vector-borne disease that takes place in a heterogeneous environment composed of areas of different types. Two populations take part in the epidemic process: humans and vectors. The population of humans moves around the heterogeneous environment. The idea of this model is to understand how the movement of people in the heterogeneous environment can affect the dynamics of the disease. The second model represents a Susceptible-Infected-Susceptible process on a social network. The population is represented as nodes, and the edges represent the possible transmissions between two people. We investigate how different topologies in the network affect the spread of the disease in the system. We simulate both models, and we perform a mathematical analysis of both of them. For the mathematical analysis we use an adapted version of the Random Heuristic Search framework, which was originally used for the understanding of Genetic Algorithms. In this thesis we investigate the predictability power of the mathematical approach.
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Wang, Gang. "Study of a low-dispersion finite volume scheme in rotocraft noise prediction." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12395.
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Gutiérrez, Arenas Omar. "Sensitivity, noise and detection of enzyme inhibition in progress curves /." Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6886.
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Zhang, Yang, and 張陽. "Nonlinear circuits modeling and analysis by the associated transform of Volterra transfer functions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/197528.
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Model order reduction (MOR) is one of the general techniques in the fields of computeraided design (CAD) and electronic design automation (EDA) which accelerates the flow of electronic simulations and verifications. By MOR, the original circuit, which is described by a set of ordinary differential equations (ODEs), can be trimmed into a much smaller reduced-order model (ROM) in terms of the number of state variables, with approximately the same input-output (I/O) characteristics. Hence, simulations using this ROM will be much more efficient and effective than using the original system.
In this thesis, a novel and fast approach of computing the projection matrices serving high-order Volterra transfer functions in the context of weakly and strongly nonlinear MOR is proposed. The innovation is to carry out an association of multivariate Laplace-domain variables in high-order multiple-input multiple-output (MIMO) transfer functions to generate univariate single-s transfer functions. In contrast to conventional projection-based nonlinear MOR which finds projection subspaces about every si in multivariate transfer functions, only that about a single s is required in the proposed approach. This translates into much more compact nonlinear ROMs without compromising accuracy. Different algorithms and their extensions are devised in this thesis. Extensive numerical examples are given to prove and verify the algorithms.published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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Li, Xun. "Physical systems for the active control of transformer noise." Title page, contents and abstract only, 2000. http://hdl.handle.net/2440/37964.
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Traditional means of controlling sound radiated by electrical power transformers involve the construction of large expensive barriers or full enclosures, which cause maintainability and cooling problems. One promising alternative is to use active noise control to cancel the noise. This thesis is concerned with one of the many problems which need to be investigated to develop a practical active noise cancellation system for transformers. This work, in particular, is concerned with the physical system design which includes the selection of the control source types and the evaluation of the near-field sensing strategies. Loudspeakers have been widely used in the past as an acoustic source for canceling transformer noise. The principal disadvantage of using loudspeakers is that to achieve global noise control, a large number, driven by a multi-channel controller, are required. However, if large panels are used in place of loudspeakers as control sources, it is possible that the number of the control sources and complexity of the controller could be reduced substantially. In addition to reducing the number of control sources and simplifying their application, panel sound sources could also overcome some disadvantages of the loudspeakers, such as limited life and deterioration due to the weather. Thus, part of the work described in this thesis is concerned with the development of a resonant curved panel with a backing cavity as an acoustic type source. The advantages of using a curved panel rather than a flat panel are twofold: first a curved panel is more easily excited by the extensional motion of the piezoelectric patch actuators; and second, it is more difficult to adjust the resonance frequencies of the efficient modes of a flat panel than of a curved panel. The analytical models for the design of the panel cavity systems have been developed. As an example, a resonant curved panel with a backing cavity system was constructed and the sound radiation of the system was measured. Results show that a resonant panel-cavity sound source could be used as an alternative to a number of loudspeakers for active cancellation of electric power transformer noise. Due to the advantages of using the vibration type control sources, two types of vibration control sources (inertial electrodynamic shakers and piezoelectric patch actuators) were considered and the mechanical output of the inertial shakers has been compared with that of the piezoelectric actuators. In contrast with the piezoelectric actuators, the resonance frequencies of the inertial shakers can be tuned to the frequencies of interest using simple tuning procedures, so that the output efficiency of the shakers can be increased. The output performance was evaluated for two types of actuators by measuring the structural response of either a panel or a transformer when excited by the actuators at half their rated voltage input. Results demonstrated that a much larger output amplitude at the frequency of interest can be achieved by the tuned inertial type actuators. Two near-field sensing strategies, the minimization of the sum of the sound intensities and the minimization of the sum of the squared sound pressures, have been studied. A quadratic expression was derived for the minimization of the sum of the sound intensities in the near-field. To evaluate the control performances achieved using both sensing strategies, a flat-panel was modelled with a harmonic point force disturbance and several point force control sources. Simulation results show that the control performance could be improved by minimizing the sum of the sound intensities in the hydrodynamic near-field, provided that a very large number of error sensors were used, otherwise better results were achieved using near-field squared pressure sensing. Both sensing strategies were used to predict the noise reductions that resulted for the active noise control of a small transformer in the laboratory environment and for a large electrical power transformer on site. To optimize the locations of the control sources (for the large transformer on site) and the locations of the error sensors (for the small transformer in the laboratory environment), a genetic algorithm (GA), which is an evolutionary optimization technique, was employed as a search procedure to optimize the control source and error sensor locations. The results showed that the control source locations and/or the error sensor locations must be optimized to achieve the maximum sound reduction for either error sensing strategy, especially for the sound intensity minimization; otherwise, the sound field level may increase after control due to the character of the cost function (the sum of the sound intensities). The simulation results were experimentally validated for the small transformer in the laboratory environment. Due to the limitation of the number of controller channels, the control performance was only evaluated for squared pressure minimization. The results demonstrated that for the case of 8 control sources and 8 error sensors, at 100 Hz, an average sound pressure reduction of 15.8 dB was achieved when evaluated at 528 monitoring locations at 0.25 m intervals on a surface that surrounded the transformer.Thesis (Ph.D.)--Engineering (Department of Mechanical Engineering), 2000.
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Snyder, Scott D. "A fundamental study of active noise control system design /." Title page, contents and abstract only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phs675.pdf.
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Ma, Chunyan. "Mathematical security models for multi-agent distributed systems." CSUSB ScholarWorks, 2004. https://scholarworks.lib.csusb.edu/etd-project/2568.
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This thesis presents the developed taxonomy of the security threats in agent-based distributed systems. Based on this taxonomy, a set of theories is developed to facilitate analyzng the security threats of the mobile-agent systems. We propose the idea of using the developed security risk graph to model the system's vulnerabilties.
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Richard, John S. "Modeling of multiple layered piezoelectric actuators in active structural control." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-12052009-020234/.
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Mondraǵon, Palomino Octavio. "A numerical study of the effects of multiplicative noise on a supercritical delay induced Hopf bifurcation in a gene expression model /." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101627.
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In the context of gene expression, we proposed a nonlinear stochastic delay differential equation as a mathematical model to study the effects of extrinsic noise on a delay induced Hopf bifurcation. We envisaged its direct numerical resolution. Following the example of the noisy oscillator, we first solved a linearized version of the equation, close to the Hopf bifurcation. The numerical scheme used is a combination of a standard algorithm to solve a deterministic delay differential equation and a stochastic Euler scheme. From our calculations we verified that the deterministic behaviour is fully recovered. For the stochastic case, we found that our solution is qualitatively accurate, in the sense that the noise induced shift in the critical value a, follows the trend the known analytic results predict. However, our numerical solution systematically overestimates the value of the shift. This is explained because the accuracy in the numerical estimation of the decay rate of a solution towards the stationary state value is a function of the control parameter a. We believe the mismatch between the numerical solution and the analytic results is due to a lack of convergence of our scheme, rather than to lack of accuracy. As our numerical scheme is an hybrid, the convergence problem can be improved, both at the deterministic and at the stochastic parts of the scheme. In this work we left our numerical results on the nonlinear case out, because before proceeding to the investigation of the nonlinear equation, the convergence must be assured in the linear case.
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Coles, Richard A. "Theory of the electronic states of semiconductor heterostructures." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4495/.
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This thesis is concerned with theoretical calculations of the properties of electronic bound states in semiconductor heterostructures. The complex band structure empirical pseudopotential method (EPM) is used as the foundation of the work. Spin orbit coupling and strain effects (due to lattice mismatch) are included in familiar ways, as is the transfer matrix method, allowing the study of arbitrarily configured heterostructures. These techniques are used to investigate the unusually deep InAs/AlSb conduction band well. The strong possibility of intraband transitions at electro magnetic wavelengths around 1.55µm is predicted, with corresponding enhanced momentum matrix elements and joint density of states over interband transitions. An InAs/GaSb/AlSb asymmetric well is investigated, paying particular attention to the bound states in the vicinity of the InAs/GaSb band overlap. The electron-like states are found to cross with heavy hole and anti-cross with light hole-like states, as a function of heterostructure dimension or applied electrostatic field. This is analogous to the hybridisation of states in the in-plane band structure, except that for zero in-plane wave vector there can be no appreciable hybridisation of electron and heavy hole states. A technique is described that has been developed to extract envelope functions from heterostructure wavefunctions calculated using the realistic complex band structure EPM approach. These envelope functions conform to Burt’s theory (M. G. Burt, J. Phys.: Condens. Matt. 4, 6651 (1992)) in that they are uniquely defined, continuous and smooth over all space. Comparisons with traditional effective mass envelope functions are made. The extracted envelope functions are used to demonstrate conclusively Burt's predictions (M. G. Burt, Superlatt. Mi- crostruct. 17, 335 (1995)) concerning the inadequacy of certain approximations for the calculation of interband dipole matrix elements and charge oscillation. Finally, the issue of k • p operator ordering is convincingly settled, in favour of 'ordered' over 'symmetrised' Hamiltonians, by comparison to EPM calculations, and using EPM derived k • p parameters.
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Kaczorowski, Przemyslaw Robert. "Thermal-based multi-objective optimal design of liquid cooled power electronic modules." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16448.
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Deragisch, Patricia Amelia. "Electronic portfolio for mathematical problem solving in the elementary school." CSUSB ScholarWorks, 1997. https://scholarworks.lib.csusb.edu/etd-project/1299.
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Electronic portfolio for mathematical problem solving in the elementary school is an authentic assessment tool for teachers and students to utilize in evaluating mathematical skills. It is a computer-based interactive software program to allow teachers to easily access student work in the problem solving area for assessment purposes, and to store multimedia work samples over time.
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Dutta, Kaushik. "Applying optimization techniques to improve e-business performance." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/30404.
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Ko, Hung-Tse. "Distribution system meta-models in an electronic commerce environment." Ohio : Ohio University, 2001. http://www.ohiolink.edu/etd/view.cgi?ohiou1173977323.
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Lim, Teck-Bin. "A unified computational fluid dynamics-aeroacoustics analysis of high speed propeller." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/12064.
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Crane, Scott P. "Structural acoustic design optimization of cylinders using FEM/BEM." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/17699.
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Perrault-Joncas, Dominique C. "Linear stability of coaxial jets with application to aeroacoustics." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112343.
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Motivated by a practical interest in noise generated by turbofan engine, this thesis studies the stability of parallel coaxial jets with velocity and temperature profiles characteristic of the exhaust region of the engine. Because the bypass stream mixes with both the exhaust and the ambient air, these profiles contain thin layers in which the velocity and temperature may vary rapidly. As a consequence, multiple instability modes are possible. In accordance with Rayleigh's theorem for axisymmetric incompressible shear flows, it follows that there are three possible modes, only two of which are unstable. To complement the study of parallel flow stability, this thesis also includes the derivation of the amplitude evolution equation for slowly varying axisymmetric incompressible flows.
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Breen, Barbara J. "Computational nonlinear dynamics monostable stochastic resonance and a bursting neuron model /." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180036/unrestricted/breen%5Fbarbara%5Fj%5F200312%5Fphd.pdf.
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Li, Jiukun, and 李久坤. "Equilibrium models in supply chains." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38523589.
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SILVA, WANDERLEI M. da. "Contribuição ao modelamento e simulação de motores com imãs permanentes e comutação eletrônica de alta rotação." reponame:Repositório Institucional do IPEN, 1998. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11642.
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Dissertacao (Mestrado)
IPEN/D
Escola Politecnica, Universidade de Sao Paulo - POLI/USP
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Nayyar, Raman. "Performance Analysis of a Hierarchical, Cache-Coherent, Shared Memory Based, Multi-processor System." PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4695.
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We have conducted a performance analysis of a large scale multiprocessor system based on shared buses organized in a hierarchical fashion and employing an easy to implement snoopy cache protocol. · This arrangement, named TREEBUS [ 5], presents a logical extension path for multiprocessor systems based on a single shared bus whose scalability is limited by the available system bus bandwidth [26]. The multiple, independent, hierarchical buses overcome the bus bandwidth limitation and the architecture can scale to relatively large sizes. We have developed an easy to use, reasonably accurate and computationally efficient analytic model for analyzing the performance of the memory hierarchy. Our analysis presents a balanced view by incorporating cost and size of the memory subsystem, two parameters which can significantly impact the feasibility of this architecture. The results indicate that the TREEBUS can deliver high performance for a maximum of about 512 processors using available technology. For larger sizes, the problem is not the limited system bus bandwidth but the unmanageable size of the main memory and a deteriorating cost/performance ratio.
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Dunne, Rajiv Carl. "An integrated process modeling methodology and module for sequential multilayered high-density substrate fabrication for microelectronic packages." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17379.
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Kim, Injoong. "Development of a knowledge model for the computer-aided design for reliability of electronic packaging systems." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/22708.
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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.Committee Co-Chair: Peak, Russell; Committee Co-Chair: Sitaraman, Suresh; Committee Member: Paredis, Christiaan; Committee Member: Pucha, Raghuram; Committee Member: Wong, C.
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Farhoomand, Ali F. "A dynamic hierarchical structural model of information systems success : the case of electronic data interchange." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39305.
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The purpose of this dissertation is to explicate the meaning of information systems (IS) success in the realm of a dynamic hierarchical structure model of IS success. Through an empirical study of 382 firms using internal and Electronic Data Interchange (EDI) systems, different characteristics of this model are examined via four hypotheses.First, using linear structural modelling techniques, it is shown that successful information systems share certain properties common to all systems, in addition to certain properties specific to each class of systems. Four generic factors influencing IS success are identified as (i) output reliability, (ii) system's characteristics, (iii) efficiency outcomes, and (iv) users' requirements. Second, the role of time in the IS adoption and assessment process is explored. By comparing firms that have adopted EDI with those that have not adopted EDI, it is shown that the decision maker's perception of IS success changes during different stages of the adoption and assessment process. Third, the role of stakeholders in the assessment process is examined by comparing perceptions of different managerial groups based on their educational background, management echelon, and functional area. It is shown that different stakeholders evaluate the success of IS differently. Finally, through an examination of various types of evaluation functions, it is shown that IS success is a multi-dimensional construct.
Overall, cross-group comparisons of the dynamic hierarchical structural model of IS success provide sufficient evidence regarding the instability of IS success across time, type of system, and stakeholders involved in the evaluation process.
In addition to the major hypotheses, two corollaries have also been examined. It is shown that user involvement in an IS project has a positive effect on the system's success. Further, the results of the study indicate that respondents in smaller companies are more satisfied with the support and services of the MIS department than their counterparts in larger companies.
Finally, by comparing three versions of the questionnaire used in the study, it is shown that question order has a significant effect on responses. The implications of this finding for survey studies are discussed.
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Langat, Philip Kibet. "Power-line sparking noise characterisation in the SKA environment." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/17970.
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Thesis (PhD)--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The Square Kilometre Array (SKA) and its demonstrator MeerKAT are being designed to operate over a wide frequency range and are expected to achieve greater sensitivity and resolution than existing telescopes. The radio astronomy community is well aware of the negative impact that radio frequency interference (RFI) has on observations in the proposed frequency band. This is because weak radio signals such as those from pulsars and distant galaxies are difficult to detect on their own. The presence of RFI sources in the telescope’s operating area can severely corrupt observation data, leading to inaccurate or misleading results. Power-line interference and radiation from electric fences are examples of RFI sources. Mitigation techniques for these interference sources in the SKA system’s electromagnetic environment are essential to ensure the success of this project. These techniques can be achieved with appropriate understanding of the characteristics of the noise sources. Overhead power-line interference is known to be caused mainly by corona and gap-type (commonly known as sparking noise) discharges. Sparking noise is the dominant interference for the SKA. It is mainly encountered on wooden pole lines, which are usually distribution lines operated at up to 66 kV AC in the South African network. At this voltage level, the voltage gradients on the lines are insufficient to generate conductor corona. The power requirements for SKA precursors will be below this voltage level. The aim of the research in this dissertation is to evaluate the power line sparking characteristics through measurements and simulation of line radiation and propagation characteristics. An artificially made sparking noise generator, which is mounted on a power line, is used as noise source and the radiation characteristics are measured. Measurements were carried out in different environments, which included a high-voltage laboratory (HV-Lab), a 40m test-line, and another 22-kV test line of approximately 1.5 km. The key sparking noise parameters of interest were the temporal and spectral characteristics. The time domain features considered were the pulse shape and the repetition rate. The lateral, longitudinal and height attenuation profiles were also quantified. Since sparking noise current pulses are injected or induced onto power line conductors, the line will act as an unintentional antenna. The far-field radiation characteristics of the line were evaluated through measurements on physical scale-model structures and simulations. 1/120th and 1/200th scaled lines, using an absorbing material and metallic ground planes, respectively, were simulated in FEKO. The measurements of the constructed scale models were taken in the anechoic chamber. Both measurements and simulations showed that the line exhibits an end-fire antenna pattern mode. Line length, pulse injection point and line configuration were some of the parameters found to affect the radiation patterns. The findings from this study are used to determine techniques to identify the sparking noise, and locate and correct the sources when they occur on the line hardware. Appropriate equipment is recommended to be used for the location and correction of sparking noise.
AFRIKAANSE OPSOMMING: Die Vierkante Kilometer Reeks (SKA) en sy demonstrasie projek, die Karoo Reeks Teleskoop (KAT), word ontwerp om oor 'n wye frekwensie-bereik te funksioneer. Beide sal na verwagting beter sensitiwiteit en resolusie as bestaande radioteleskope he. Die radio-astronomie-gemeenskap is deeglik bewus van die negatiewe impak wat radio-frekwensie steurnisse (RFS) op waarnemings in die voorgestelde frekwensieband het. Die rede hiervoor is dat swak radio-seine soos die van pulsars en verafgelee sterrestelsels inherent moeilik is om te bepaal. Die teenwoordigheid van RFS bronne in die teleskoop se onmiddellike operasionele gebied kan waarnemings nadelig beinvloed. Dit lei uiteindelik tot onakkurate of misleidende resultate. Kraglyne en uitstralings van elektriese heinings is voorbeelde van RFS bronne. Metodes om die oorsake van die steurnisse van die SKA se elektromagnetiese omgewing te verminder is noodsaaklik om die sukses van hierdie projekt te verseker. Dit vereis egter deeglike begrip van die eienskappe van hierdie bronne. Steurnisse as gevolg van oorhoofse kraglyne word hoofsaaklik veroorsaak deur korona en gapingtipe ontladings (algemeen bekend as vonkontladings). Vonkontladings word hier beskou as die belangrikste oorsaak van steurnisse vir die SKA. Dit word in die Suid-Afrikaanse netwerk hoofsaaklik aangetref op houtpaal-installasies, wat gewoonlik bestaan uit distribusie lyne wat tot en met 66 kV wisselstroom (WS) bedryf word. By hierdie operasionele spanning is die spanningsgradient op die lyn onvoldoende om korona op te wek. Die kragvereistes vir die SKA se voorafgaande projekte sal sodanig wees dat hierdie spanningsvlak nie oorskry sal word nie. Die doel van die navorsing omskryf in hierdie proefskrif is om die eienskappe van vonkontladings rondom kraglyne te evalueer. Dit word gedoen met behulp van metings en simulasies van uitstralings- en voortplantingspatrone wat met 'n spesifieke lyn geassosieer kan word. 'n Kunsmatige vonkontladingsopwekker word op 'n kraglyn geplaas en dien as bron om die uitstralingspatrone te meet. Metings is uitgevoer in verskillende omgewings, insluitende 'n hoogspanningslaboratorium (HV-Lab), 'n 40 m toetslyn en 'n 22 kV WS toetslyn van ongeveer 1.5 km lank. Die hoof vonkontladings eienskappe van belang is die temporale en spektrale eienskappe. Die tydgebiedeienskappe wat ondersoek is, is die pulsvorm asook die pulsherhalingskoers. Die laterale, longitudinale en hoogte-attenuasie profiele word ook gekwantifiseer. Aangesien stroompulse deur vonkontladings op die kraglyn geplaas of geinduseer word, sal die lyn as 'n ongewenste antenna optree. Die ver-veld uitstralingskenmerke van die lyn is ook geëvalueer deur gebruik te maak van fisiese skaalmodelstrukture en -simulasies. 1/120ste en 1/200ste geskaleerde lynmodelle, wat onderskeidelik 'n absorberende- en metaalgrondvlak bevat, was gebruik om 'n 3 spanlengte kraglyn te simuleer met behulp van FEKO. Metings van die fisiese skaalmodel strukture is in 'n anegoise kamer geneem. Beide die metings en die simulasies toon dat die lyn 'n endpunt uitstralingspatroon het. Lynlengte, die opwekkingsposisie van die stroompuls en die lynkonfigurasie is 'n paar van die parameters wat die uitstralingpatroon beïnvloed, soos in die navorsing aangedui. Die bevindinge van hierdie studie word gebruik om steurnisse as gevolg van vonkontladings op die kraglyn te identifiseer, op te spoor en uiteindelik reg te stel. Toepaslike toerusting word voorgestel wat gebruik kan word vir die identifisering en opsporing van vonkontladings.
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Qian, Zhiguang. "Computer experiments [electronic resource] : design, modeling and integration /." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11480.
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The use of computer modeling is fast increasing in almost every
scientific, engineering and business arena. This dissertation
investigates some challenging issues in design, modeling and
analysis of computer experiments, which will consist of four major
parts. In the first part, a new approach is developed to combine
data from approximate and detailed simulations to build a
surrogate model based on some stochastic models. In the second
part, we propose some Bayesian hierarchical Gaussian process
models to integrate data from different types of experiments. The
third part concerns the development of latent variable models for
computer experiments with multivariate response with application
to data center temperature modeling. The last chapter is devoted
to the development of nested space-filling designs for multiple
experiments with different levels of accuracy.
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Xian, Lede. "Electronic structure and interlayer coupling in twisted multilayer graphene." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51811.
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It has been shown recently that high-quality epitaxial graphene (EPG) can be grown on the SiC substrate that exhibits interesting physical properties and has great advantages for varies device applications. In particular, the multilayer graphene films grown on the C-face show rotational disorder. It is expected that the twisted layers exhibit unique new physics that is distinct from that of either single layer graphene or graphite. In this work, by combining density functional and tight-binding model calculations, we investigate the electric field and doping effects on twisted bilayer graphene (TBG), multiple layer effects on twisted triple-layer graphene, and wave packet propagation properties of TBG. Though these studies, we obtain a comprehensive description of the interesting interlayer interaction in this twisted multilayer graphene system.
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Parr, David Michael. "A general theory of electronic parametric instability of relativistically intense laser light in plasma." Thesis, University of Essex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310043.
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黃新祥 and Sun-cheung Wong. "Ab initio calculations of silicon clusters." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B3122197X.
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Zhai, Yusheng. "Time series forecasting competition among three sophisticated paradigms /." Electronic version (Microsoft Word), 2005. http://dl.uncw.edu/etd/2005/zhaiy/yushengzhai.html.
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Weingartner, Stephan G. "System development : an algorithmic approach." Virtual Press, 1987. http://liblink.bsu.edu/uhtbin/catkey/483077.
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The subject chosen to develop this thesis project on is developing an algorithm or methodology for system selection. The specific problem studied involves a procedure to determine anion computer system alternative is the best choice for a given user situation.The general problem to be addressed is the need for one to choose computing hardware, software, systems, or services in a -Logical approach from a user perspective, considering cost, performance and human factors. Most existing methods consider only cost and performance factors, combining these factors in ad hoc, subjective fashions to react: a selection decision. By not considering factors treat measure effectiveness and functionality of computer services for a user, existing methods ignore some of the most important measures of value to the user.In this work, a systematic and comprehensive approach to computer system selection has been developed. Also developed were methods for selecting and organizing various criteria.Also ways to assess the importance and value of different service attributes to a end-user are discussed.Finally, the feasibility of a systematic approach to computer system selection has been proven by establishing a general methodology and by proving it through a demonstration of a specific application.
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Eberhart, Andreas Bernhard Georg. "Contention-free Scheduling of Communication Induced by Array Operations on 2D Meshes." PDXScholar, 1996. https://pdxscholar.library.pdx.edu/open_access_etds/5077.
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Whole array operations and array section operations are important features of many data-parallel languages. Efficient implementation of these operations on distributed- memory multicomputers is critical to the scalability and high-performance of data-parallel programs. This thesis presents an approach for analyzing communication patterns induced by array operations and for using run-time information to schedule the message flow. The distributed, dynamic scheduling algorithms guarantee link-contention-free data transfer and utilize network resources almost optimally. They incur little overhead, which is important in order not to reduce the speedup gained by the parallel execution. The algorithms can be used by compilers for the generation of efficient code for array operations. Implemented in a runtime library, they can derive a schedule depending on parameters passed by the parallel application. Simulation results demonstrate the algorithms' superiority to the asynchronous transfer mode that is commonly used for this type of communication.
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Clarke, Samuel R. (Samuel Robert). "Development of a FEM waveguide code, incorporating Fast Frequency Techniques, for numerical synthesis." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52762.
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Thesis (MScEng)--University of Stellenbosch, 2002.ENGLISH ABSTRACT: A computational tool for numerical synthesis via optimization is developed. Only two port waveguide devices are considered. The Finite Element Method (FEM) is used for the electromagnetic analysis. Specifically, the frequency domain electric field FEM is used with vector curl-conforming constant tangential/linear normal brick-shaped elements. Special boundary conditions are used at the ports. These boundary conditions only consider dominant mode propagation. The issues surrounding the implementation of this formulation are discussed. The results generated using this code compare favorably to examples from independent sources. A parametric mesher that is used in conjunction with the FEM is developed. This is done to eliminate the need for human intervention during each iteration of the synthesis procedure. Fast Frequency (FF) techniques are presented to reduce the computational requirements of the synthesis. FF techniques reduce the cost of calculating many frequency samples in a specified band and do not reduce the computational requirements of computing a FEM solution at a single frequency. The FF techniques presented are: Asymptotic Waveform Evaluation (AWE), Model Based Asymptotic Waveform Evaluation (MB-AWE) and Model Based Parameter Estimation (MBPE) . The results obtained using these techniques are compared and the most suitable technique for the synthesizer is selected. MBPE is selected as the most suitable technique for this application. An adaptive sampling algorithm for Model Based Parameter Estimation is presented. The algorithm relies on the difference between multiple models generated from the same samples to determine the sample locations. The use of this algorithm enables a model of a narrow band filter at X-band to be determined using only fourteen FEM solutions. The difference between the model- and the FEM solutions is less then -lOOdBacross the band. A sample synthesis using generalized simulated annealing is presented. A single pole filter in X-band waveguide is successfully synthesized to illustrate the usefulness of the code. The use of FF techniques results in a computational cost saving of a factor of forty times.
AFRIKAANSE OPSOMMING: 'n Rekenaar werktuig vir numeriese sintese deur middel van optimering word ontwikkel. Slegs twee-poort golfleierkomponente word beskou. Die Eindige Element-metode (EEM) word vir die elektromagnetiese analise gebruik. Meer spesifiek, die frekwensiegebied, elektriese-veld EE-formuleering word gebruik, met eurl-ondersteunende, konstant-tagensiaaljlineêr-normaal, baksteenvormige vektorelemente. Spesiale grensvoorwaardes word by die poorte gebruik. Hierdie grensvoorwaardes neem slegs voortplanting van die dominante modus in ag. Die kwessies rondom die implementering van hierdie EEM word bespreek. Resultate wat met hierdie kode verkry word, vergelyk goed met dié vanuit onafhanklike bronne. 'n Parametriese diskretisasie prosedure in ontwikkel, vir gebruik saam met die genoemde EEM, met die doelom menslike interaksie uit die weg te ruim, tydens die sintese proses. Vinnige Frekwensie (VF) tegnieke word beskryf, met die doelom die berekeningskoste van die sintese te verminder. VF tegnieke verminder die berekeningskoste verbonde aan 'n reeks EEM oplosings binne 'n gegewe frekwensieband, maar verminder nie die koste verbonde aan 'n enkel-frekwensie EEM oplossing nie. Die VF tegnieke wat beskryf word, is die volgende: Asimptotiese Golfvorm Evaluasie (AGE), Model Gebaseerder Asimptotiese Golfvormevaluasie (MGAGE) en Model- Gebaseerde Parameterekstraksie (MGPE). Die resultate wat met hierdie metodes verkry word, word vergelyk om sodoende die mees toepaslike VF tegniek te kies. MGPE word gekies as die mees toepaslike tegniek. 'n Aanpasbase monsteringsalgoritme vir MGPE word beskryf. Die algoritme berus op die verskil tussen twee modelle wat vanaf dieselfde stel punte geskep word, om monsterfrekwensiewaardes te bepaal. Die gebruik van hierdie algoritme lei tot 'n model van 'n nou-, X-band filter, vanuit slegs veertien EEM oplossings. Die verskil tussen hierdie model en enige EEM oplossings binne die band, is kleiner as -lOOdB. 'n Voorbeeld sintese, wat gebruik maak van veralgemeende, gesimuleerde versmelting, word beskryf. 'n Enkel-pool filter by X-band word suksesvol gesintetiseer om die bruikbaarheid van die kode te illustreer. 'n Faktor veertig vermindering III berekeningskostes word behaal deur gebruik te maak van VF tegnieke.
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Kelly, Allan D. "Dynamic finite element modeling and analysis of a hermetic reciprocating compressor." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-01242009-063231/.
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Todd, Stephen Mark. "Computer assisted molecular simulations of ferroelectric liquid crystals : prediction of structural and electronic properties." Thesis, University of Hull, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301497.
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Ruckman, Christopher E. "A regression-based approach for simulating feedfoward active noise control, with application to fluid-structure interaction problems." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-170941/.
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Yuan, Jiangchuan. "Risk diversification framework in algorithmic trading." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51905.
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We propose a systematic framework for designing adaptive trading strategies that minimize both the mean and the variance of the execution costs. This is achieved by diversifying risk over sequential decisions in discrete time. By incorporating previous trading performance as a state variable, the framework can dynamically adjust the risk-aversion level for future trading. This incorporation also allows the framework to solve the mean-variance problems for different risk aversion factors all at once. After developing this framework, it is then applied to solve three algorithmic trading problems. The first two are trade scheduling problems, which address how to split a large order into sequential small orders in order to best approximate a target price – in our case, either the arrival price, or the Volume-Weighed-Average-Price (VWAP). The third problem is one of optimal execution of the resulting small orders by submitting market and limit orders. Unlike the tradition in both academia and industry of treating the scheduling and order placement problems separately, our approach treats them together and solves them simultaneously. In out-of-sample tests, this unified strategy consistently outperforms strategies that treat the two problems separately.
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Britton, Matthew Scott. "Stochastic task scheduling in time-critical information delivery systems." Title page, contents and abstract only, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phb8629.pdf.
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"January 2003" Includes bibliographical references (leaves 120-129) Presents performance analyses of dynamic, stochastic task scheduling policies for a real- time-communications system where tasks lose value as they are delayed in the system.
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Sener, Emre. "Automatic Bayesian Segmentation Of Human Facial Tissue Using 3d Mr-ct Fusion By Incorporating Models Of Measurement Blurring, Noise And Partial Volume." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615091/index.pdf.
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Segmentation of human head on medical images is an important process in a wide array of applications such as diagnosis, facial surgery planning, prosthesis design, and forensic identification. In this study, a new Bayesian method for segmentation of facial tissues is presented. Segmentation classes include muscle, bone, fat, air and skin. The method incorporates a model to account for image blurring during data acquisition, a prior helping to reduce noise as well as a partial
volume model. Regularization based on isotropic and directional Markov Random Field priors are integrated to the algorithm and their effects on segmentation accuracy are investigated. The Bayesian model is solved iteratively yielding tissue class labels at every voxel of an image. Sub-methods as variations of the main method are generated by switching on/off a combination of the models. Testing of the sub-methods are performed on two patients using single modality three-dimensional (3D) images as well as registered multi-modal 3D images (Magnetic Resonance and Computerized Tomography). Numerical, visual and statistical
analyses of the methods are conducted. Improved segmentation accuracy is obtained through the use of the proposed image models and multi-modal data. The methods are also compared with the Level Set method and an adaptive Bayesiansegmentation method proposed in a previous study.
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Derry, Philip. "Quasiparticle interference in strongly correlated electronic systems." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:f487c821-dbbb-4ebe-8b05-c13807379c2c.
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We investigate the manifestation of strong electronic correlations in the quasiparticle interference (QPI), arising from the scattering of conduction electrons from defects and impurities in an otherwise translationally-invariant host. The QPI may be measured experimentally as the Fourier transform of the spatial modulations in the host surface density of states that result, which are mapped using a scanning tunnelling microscope. We calculate the QPI for a range of physically relevant models, demonstrating the effect of strong local electronic correlations arising in systems of magnetic impurities adsorbed on the surface of non-interacting host systems. In the first instance the effect of these magnetic impurities is modelled via the single Anderson impurity model, treated via numerical renormalization group (NRG) calculations. The scattering of conduction electrons, and hence the QPI, demonstrate an array of characteristic signatures of the many-body state formed by the impurity, for example due to the Kondo effect. The effect of multiple impurities on the QPI is also investigated, with a numerically-exact treatment of the system of two Anderson impurities via state-of-the-art NRG calculations. Inter-impurity interactions are found to result in additional scattering channels and additional features in the QPI. The QPI is then investigated for the layered transition metal oxide Sr2RuO4, for which strong interactions in the host conduction electrons give rise to an unconventional triplet superconducting state at Tc ∼ 1.5K. The detailed mechanism for this superconductivity is still unknown, but electron-electron or electron-phonon interactions are believed to play a central role. We simulate the QPI in Sr2RuO4, employing an effective parametrized model consisting of three conduction bands derived from the Ru 4d t2g orbitals that takes into account spin orbit coupling and the anisotropy of the Ru t2g orbitals. Signatures of such interactions in the normal state are investigated by comparing these model calculations to experimental results. We also calculate the QPI in the superconducting state, and propose how experimental measurements may provide direct evidence of the anisotropy and symmetry of the superconducting gap, and thus offer insight into the pairing mechanism and the superconducting state.