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- PostAnalysis of a pyramidal truss core structure using the finite element method and full scale experiments(1995) Ringsberg, Jonas; Lindqvist, Reine; Chalmers tekniska högskola / Institutionen för marin teknik; Chalmers University of Technology / Department of Naval Architecture and Ocean Engineering
- PostComputing with Memristor Networks(2014) Bennett, Christopher H.; Konkoli, Zoran; Chalmers tekniska högskola / Extern; Chalmers University of Technology / ExternalIt has been suggested that CMOS technologies will hit scaling limits due to fundamental design issues at the regime of molecular electronics. In this project, the memristor device has been evaluated as a candidate for building high-density, high-performance computers at such a scale. Although memristors are already under active research and development as random access memory, in this project, we evaluate their potential for neuromorphic (brain-inspired) information processing in the context of reservoir computing. We quantify a memristor network's capability to analyze sets of time-dependent input data for pattern recognition applications. We pose the following key question: given a network of a certain design, which signals might it be particularly adept at recognizing? To answer that question, a rigorous mathematical approach has been developed and implemented as computer software. Our preliminary results indicate that the conceptual approach that has been developed can be used to answer this question, and suggest that memristor networks are capable of real-time pattern recognition.
- PostEffects of electron trapping and ion collisions on electrostatic shocks(2018) Sundström, Andréas; Chalmers tekniska högskola / Institutionen för fysik, Subatomär fysik och plasmafysik (Chalmers); Chalmers University of Technology / Department of Physics, Subatomic and Plasma Physics (Chalmers)Electrostatic shocks in plasmas have been observed to be able to accelerate particles to twice the shock velocity with a very low energy spread. Shock phenomena are often modeled as exactly collisionless, which is a very good approximation for astrophysical shocks. However, collisions might play a role in shocks created in laboratory plasmas, since very sharp features of the ion distribution function develop due to ions being reflected at the shock front; this ion reflection results in empty regions of phase space with discontinuities at their boundaries. In this thesis the effects of a weak but finite ion collisionality are considered in a time dependent, semi-analytical treatment. The amplitude of the downstream potential oscillation is found to increase approximately as the square root of time as particles are scattered into the originally empty regions of phase space. The corresponding changes in the electrostatic potential lead to an increased size of the trapping regions in the ion phase space. This thesis also studies the effect of electron trapping in the potential oscillations downstream of the shockfront. Two model electron distributions, which are flat in the trapped regions of phase space, are considered. The two models only differ in where the potential threshold for trapping is set; one model allows for trapping at a freely set threshold in order to emulate the effects of far downstream behavior of the shock, while the other model only allows for trapping inside the downstream potential oscillation. In general the effects of electron trapping are to reduce the maximum electrostatic potential, but at the same time increase the range of shock propagation speeds for which electrostatic shock solutions exist. The second electron trapping model also exhibits multiple shock solutions for the same temperature ratio and Mach number in certain parameter regions.
- PostExperimentell undersökning av grunddammars och luftbubbelridåers reducerande effekt på ett kombinerat täthetsberoende och vindgenererat utbytesflöde(1967) Bergdahl, Lars; Asztély, Jan; Chalmers tekniska högskola / Extern; Chalmers University of Technology / ExternalA laboratory investigation of two methods to reduce the density driven and wind driven exchange flow in a narrow bay at Gunnarsö, Oskarshamn. The two methods are by a suberged dam or by an air-bubble curtain. The investigation was induced by the interest to prevent the water of this popular swimming bay to drop as much as 10 centigrades within a day.
- PostGPU Implementation of the Feynman Path-Integral Method in Quantum Mechanics(2011) Carlsson, Kristoffer; Gren, Martin; Bohlin, Gustav; Holmvall, Patric; Säterskog, Petter; Ahlén, Olof; Chalmers tekniska högskola / Extern; Chalmers University of Technology / ExternalThe Path-Integral Formulation of Quantum Mechanics is introduced along with a detailed mathematical description of how it is used in quantum computations. The important concept of the kernel is explained, along with the free particle and harmonic oscillator as examples. Furthermore, the method for calculating expectation values of quantum operators is explained. The expectation values are naturally calculated by importance sampled Monte Carlo integration and by use of the Metropolis algorithm. This is due to the discretization of the path integral results in an integral with a high number of integration variables. The mathematical concepts of this calculation are explained. Also, a method for obtaining the probability density of the treated system is presented. The calculations are performed by a GPU, due to its high capabilities for numerical operations. This requires the mathematical computations to be parallelized and is done by use of the free software PyOpenCL. A thorough introduction to these concepts are given. The resulting ground state energies and probability densities for many particle systems interacting with harmonic as well as attractive and repulsive gaussian potentials are presented. The calculations worked exceedingly well for many particle systems. Source code is available at https://sourceforge.net/projects/ feynmangpu/files/
- PostMakroglidning i plana skruvförband med kraftbetingad funktion(1986) Jacobson, Bengt; Chalmers tekniska högskola / Institutionen för maskin- och fordonskonstruktion; Chalmers University of Technology / Department of Machine and Vehicle Design
- PostOkonventionell beräkning(2015) Hakuni, Elias; Vesselényi, László Sall; Blomqvist, Viktor; Konkoli, Zoran; Chalmers tekniska högskola / Extern; Chalmers University of Technology / ExternalDetta litteraturbaserade arbete avser att ge en introduktion till fältet okonventionell beräkning. Okonventionell beräkning är ett begrepp och forskningsfält i gränslandet mellan matematik, datavetenskap, informationsteknik, filosofi och naturvetenskap. För arbetets syfte behöver det konventionella beräkningsgreppet först redogöras för. Konventionell beräkning kan ses som bestånde av två grenar: Dels en gren som utgörs av konventionella beräknare, den moderna digitala datorn; dels en som utgörs av konventionella beräkningsmodeller, turingmaskinen och Church-Turings hypotes. Turingmaskinen, utvecklad av Alan Turing på 1930-talet, är en formalisering av algoritmer. Church-Turings hypotes hävdar helt enkelt att turingmaskinen, och alla modeller ekvivalenta med densamma, kan beräkna alla funktioner som är beräkningsbara av en människa med penna och papper följandes en algoritm. Bakgrunden till dessa två resultat är den stora frågan: ”Vad går att beräkna?” Bryggan från konventionell beräkning till okonventionell beräkning är en breddning av beräkningsgreppet: en process som övergår från ett ursprungstillstånd till ett sluttillstånd. Med denna bredare definition öppnas ett större fält av beräkningar, beräknare och beräkningsmodeller än vad som ryms inom den rådande konventioner. Denna definition innefattar inte längre bara beteendet hos en digital dator eller en människa med papper och penna utan potentiellt allt från kvantfysiska fenomen och kemiska reaktioner till betraktelsen av en sten över tid och universums samlade företeelser. Implicit eller explicit är denna breda definition central för okonventionell beräkning, och viktiga frågor blir därför: ”Vad kan beräkna?”; ”Vilka kriterier behövs för en beräknare?”; och en återkoppling till den konventionella frågan: ”Vad kan beräknas?” Introduktionen av okonventionell beräkning slutförs genom exempel på tre olika okonventionella beräknare och beräkningsmodeller: Artificella neuronnät, kvantberäknare och reaktions-diffusionsberäknare. Beräknarnas och beräkningsmodellernas egenskaper, svagheter och eventuella användnings- och tillämpningsområden presenteras, såväl som hur de anses vara okonventionella.
- PostSOFC Modeling in Femlab(2003) Nordelöf, Anders; Salsing, Christofer; Chalmers tekniska högskola / Institutionen för experimentell fysik; Chalmers University of Technology / Department of Experimental PhysicsThis report describes a graduate thesis project for the Master of Science diploma from the Engineering Physics program at Chalmers University of Technology. It has been performed at Volvo Technology Corporation with the primary aim to model a given Solid Oxide Fuel Cell design, the Rutquist cell, in Femlab. The model is intended to provide information on current-voltage characteristics, power development and the temperature profile, both during startup and operation. The secondary purpose was to evaluate the suitability of Femlab for this kind of task. The project was initiated with a bibliographic research, which gave several theories and parameters useful for modeling the different processes in the SOFC design. These models were then implemented in Femlab. Two separate modes were created where the startup and the operation of the cell respectively, were simulated. The cell was assumed to be a part of a larger system and receive hot gases from a fuel reformer. The heating in the startup process was achieved by letting warm gas, 1073 K, enter the electrodes via the gas channels. The chemical reactions were assumed to begin when all parts of the structure had reached 1023 K. The calculations showed that the heating to this temperature takes about one minute, and that most of the heat exchange takes place in the electrodes. The resulting temperature profiles from the operation mode model demonstrate that the temperature is in the same range as other SOFC structures and that the design is very compact. The dimensions of a cubic stack developing 10 kW at maximum power would be less than one cubic decimeter. The computational software Femlab has advantages, but also several shortcomings. Among the advantages are the flexibility in the module based system and the short learning period needed for solving simple problems. The weaknesses include the necessity of good knowledge of numerical solution methods, since many settings have to be adjusted when the models become more complex; especially the error report system is poor and occasionally even missing. The report also presents the theory of the physical and chemical processes ceramic fuel cells. Suggestions for improvements and the effects of the delimitations and approximations used in the modeling work are discussed. Finally, recommendations for future work are put forward.