1,219 research outputs found

    All-Pairs Shortest Path Algorithms Using CUDA

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    Utilising graph theory is a common activity in computer science. Algorithms that perform computations on large graphs are not always cost effective, requiring supercomputers to achieve results in a practical amount of time. Graphics Processing Units provide a cost effective alternative to supercomputers, allowing parallel algorithms to be executed directly on the Graphics Processing Unit. Several algorithms exist to solve the All-Pairs Shortest Path problem on the Graphics Processing Unit, but it can be difficult to determine whether the claims made are true and verify the results listed. This research asks "Which All-Pairs Shortest Path algorithms solve the All-Pairs Shortest Path problem the fastest, and can the authors' claims be verified?" The results we obtain when answering this question show why it is important to be able to collate existing work, and analyse them on a common platform to observe fair results retrieved from a single system. In this way, the research shows us how effective each algorithm is at performing its task, and suggest when a certain algorithm might be used over another

    Simulation and experimental study of the multichanneling rimfire gas switch

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    The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file viewed on (July 10, 2006)Includes bibliographical references.Thesis (M.S.) University of Missouri-Columbia 2005.Dissertations, Academic -- University of Missouri--Columbia -- Electrical engineering.Since 1985, the Rimfire switch has been used extensively in accelerators at Sandia National Laboratories. Demands for increased future accelerator performance require improvements to the Rimfire switch. This thesis is both a theoretical and experimental study of this switch. Theoretical study was achieved utilizing an advanced circuit model. Through this model, insight was gained into some of the intricacies of switch operation. In addition, past models were verified and extended. Utilizing the University of Missouri Terawatt Test Stand, experiments were conducted studying the multichanneling cascade section of the switch. The electrical affects of multichanneling and a method to force multichanneling was presented. In addition, an objective curve fitting method was used to deduce switch inductance from the measured data. Many conclusions were made with regard to the Rimfire switch. Specific topics included advanced triggering schemes, immersion dielectric changes, jitter reduction, electrical affects of multichanneling, factors effecting multichanneling, and switch impedance calculations

    The ferroelectric plasma thruster

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    The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file (viewed on June 9, 2009)Vita.Thesis (Ph. D.) University of Missouri-Columbia 2008.Micropropulsion is an enabling technology for microspacecraft. As requirements for microspacecraft missions become more demanding, so do the requirements for micropropulsion. Therefore, existing technologies require improvement, or new technologies need to be developed. The Ferroelectric Plasma Thruster (FEPT) is a new technology for microspacecraft propulsion. This dissertation is a demonstration of this technology and its characteristics. To produce thrust, the FEPT produces a plasma and a beam of ions. The acceleration of these ions away from the thruster is the mass-transfer mechanism of the thruster. Plasma parameters were measured such as average ion current, ion energy, ion species, and average power dissipated. Photography was performed including open-shutter photography and framing photography. These measured parameters were used to make a calculation of the thrust due to ions.For a more direct measurement of thrust, a micro-thrust stand was designed, built, and characterized. In addition, the mass flow rate from the thruster was measured by weighing the FEPT before and after operation. Combining these two measurements leads to a calculation of the specific impulse. Measured parameters include a thrust of [approximately] 70[micro]N, specific impulse of [approximately] 400 s, average power of [approximately] 6 W, and impulse bits of [less than] 1 nN [multiple] s. Advantages of the FEPT include its small mass of less than 6 g and its inherent simplicity. Only a single, low-power rf power supply is needed to form plasma and accelerate particles. Also, electrons are also expelled from the thruster which potentially removes the necessity of a separate neutralizer. Finally, the impulse bits delivered by the FEPT are extremely small which leads to very fine control of microspacecraft attitude.Includes bibliographical reference

    Transport of charged aerosol OT inverse micelles in nonpolar liquids

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    Surfactants such as Aerosol OT (AOT) are commonly used to stabilize and electrically charge nonpolar colloids in devices such as electronic ink displays. The electrical behavior of such devices is strongly influenced by the presence of charged inverse micelles, formed by excess surfactant that does not cover the particles. The presence of charged inverse micelles results in increased conductivity of the solution, affecting both the energy consumption of the device and its switching characteristics. In this work, we use transient current measurements to investigate the electrical properties of suspensions of the surfactant Aerosol OT in dodecane. No particles are added, to isolate the effect of excess surfactant. The measured currents upon application of a voltage step are found to be exponentially decaying, and can be described by an analytical model based on an equivalent electric circuit. This behavior is physically interpreted, first by the high generation rate of charged inverse micelles giving the suspension resistor like properties, and second by the buildup of layers of charged inverse micelles at both electrodes, acting as capacitors. The model explains the measurements over a large range of surfactant concentrations, applied voltages, and device thicknesses

    Charging dynamics of aerosol OT inverse micelles

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    Aerosol OT (AOT) is a commonly used surfactant and charging agent in nonpolar liquids. Properties such as the conductivity of AOT suspensions in nonpolar liquids and the behavior of charged AOT inverse micelles at interfaces have been studied recently, but still little is known about the generation dynamics of charged AOT inverse micelles. In this article, the generation dynamics of charged AOT inverse micelles in dodecane are investigated with transient current measurements. At low applied voltages, the generation rate is sufficiently fast to maintain the equilibrium concentration of charged inverse micelles, such that the current scales proportionally with the applied voltage. However, above a threshold voltage the current becomes limited by the generation of charged inverse micelles. Al2O3‑coated electrodes are used to achieve these high-voltage current measurements while reducing surface generation currents. The dependency of the resulting generation-limited currents with the micelle concentration and the liquid volume is compatible with a bulk disproportionation mechanism. The measured currents are analyzed using a model based on drift, generation, and recombination of charged inverse micelles and the corresponding generation and recombination rates of charged AOT inverse micelles have been determined

    Investigation of various types of inverse micelles in nonpolar liquids using transient current measurements

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    Transient current measurements are used to characterize a wide variety of charge carriers in nonpolar liquids. The transient current method allows us to obtain both the concentration and mobility of charge carriers and therefore also the hydrodynamic radius using Stokes' law. In this article, five different surfactants in dodecane are investigated: OLOA11K, Solsperse13940, Span80, Span85, and AOT. We show that different types of currents are observed depending on the size of the inverse micelles. For large inverse micelles such as for OLOA11K, Solsperse13940, and Span80, the measurement of the transient current is straightforward because of the low steady-state current level. However, for small inverse micelles such as AOT and Span85, the current from the generation of charges is much larger such that high voltages, a small distance between the electrodes, and dielectric coatings on the electrodes are required to measure the signal related to the initially present charged inverse micelles. The estimated hydrodynamic radii of AOT and Span85, the two smallest inverse micelles, are in good agreement with the values reported in the literature. The comparison of the transient currents with simulations indicates that the dynamics of the charge transport are well-understood

    Reduced glycogen availability is associated with increased AMPKα2 activity, nuclear AMPKα2 protein abundance, and GLUT4 mRNA expression in contracting human skeletal muscle

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    Glycogen availability can influence glucose transporter 4 (GLUT4) expression in skeletal muscle through unknown mechanisms. The multisubstrate enzyme AMP-activated protein kinase (AMPK) has also been shown to play an important role in the regulation of GLUT4 expression in skeletal muscle. During contraction, AMPK [alpha]2 translocates to the nucleus and the activity of this AMPK isoform is enhanced when skeletal muscle glycogen is low. In this study, we investigated if decreased pre-exercise muscle glycogen levels and increased AMPK [alpha]2 activity reduced the association of AMPK with glycogen and increased AMPK [alpha]2 translocation to the nucleus and GLUT4 mRNA expression following exercise. Seven males performed 60 min of exercise at ~70% [VO.sub.2] peak on 2 occasions: either with normal (control) or low (LG) carbohydrate pre-exercise muscle glycogen content. Muscle samples were obtained by needle biopsy before and after exercise. Low muscle glycogen was associated with elevated AMPK [alpha]2 activity and acetyl-CoA carboxylase [beta] phosphorylation, increased translocation of AMPK [alpha]2 to the nucleus, and increased GLUT4 mRNA. Transfection of primary human myotubes with a constitutively active AMPK adenovirus also stimulated GLUT4 mRNA, providing direct evidence of a role of AMPK in regulating GLUT4 expression. We suggest that increased activation of AMPK [alpha]2 under conditions of low muscle glycogen enhances AMPK [alpha]2 nuclear translocation and increases GLUT4 mRNA expression in response to exercise in human skeletal muscle. <br /

    Ultra-Wideband Antenna

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