Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 24 for “"Diffusion approximation"”.
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Radiative heat transfer from aluminum oxide in solid propellant flames
… was solved by both a two-flux method and a diffusion approximation. The two-flux method was used for analyzing the optically thin medium near the surface of the propellant. At distances farther from the propellant surface, where the medium became optically thick due to the Al$\sb2$O$\sb3$ …
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Photon migration in highly scattering media as a measurement technique on automated cow milking systems
… that quantitative measurements can be made. The diffusion approximation, a simplified version of transport theory, was selected. The derivation and the limitations of the diffusion approximation were discussed and noted in order to ensure that any subsequent measurements made with milk fell …
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Proximity effect in superconductors: Experimental and theoretical determination of the transition temperature
… consists of two parts: (1) an extension of the diffusion approximation theory due to de Gennes, Guyon and Werthamer; this theory is valid only when the mean free paths in the two metals are small compared to the respective coherence lengths, (ii) an extension, under certain restrictive …
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Exploring the optimality of various bacterial motility strategies : a stochastic hybrid systems approach
… their stationary distributions and also derive a diffusion approximation of the system that provides further insight into the performance of various strategies. By comparing general chemotactic strategies, we hypothesize why various strategies may be evolutionarily advantageous for particular …
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Transport of muonic atoms
… gaseous hydrogen and deuterium is studied in the diffusion approximation and by means of the multiple collision expansion. The diffusion coefficient is derived. Scattering kernels are computed from the kinematics of an inelastic binary collision. The effect of rotations of the target molecules is …
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Modeling and Simulation of Radiation from Electronic Transitions in Hypersonic Atmospheric Reentry Flow
… Rosseland is used in the “optically thick,” or “diffusion” approximation. Absorption and emission coefficients compared respectably with other published results, discrepancies attributable to differing sources of input spectral data. The computational module was implemented in an in-house …
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Modeling the operating voltage of liquid metal battery cells
… electrolyte was modeled using a boundary layer diffusion approximation. For the IR drop, the solution resistance was assumed to be constant. The predicted operating voltage for both the Mg-Sb and Li-Bi was consistent with experimental data.
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Stability analysis of spatially dependent nonlinear reactor systems
… distribution governed by nonlinear multigroup diffusion approximation is considered in this thesis. Stability criteria for equilibrium states of various reactor feedback models are determined by the methods of Liapunov, semigroup and comparison functions. Comparison of the three approaches are …
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The Nonisothermal Stage of Magnetic Star Formation
… elastic and inelastic collisions to ambipolar diffusion and Ohmic dissipation. The species abundances are calculated using an extensive chemical-equilibrium network. The thermal evolution of the protostellar core and its affect on the dynamics are followed by employing the grey flux-limited …
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Numerical simulations of mass outflows from star-forming regions
… from more commonly used methods based on the diffusion approximation. Particular care is taken to test all the algorithms used in the code extensively. Detailed descriptions of the setup and results for each test problem used for the HD, MHD, and RHD algorithms is provided.
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Optimization of luminescent solar concentrators
… computational modeling of LSC system based on Diffusion Approximation (DA). Then, the physics model is subjected to an optimization algorithm based on Globally Convergent Method of Moving Asymptotes (GCMMA). For this optimization, the objective function is the integrated flux on the solar cell …
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Purely optical tomography : atlas-based reconstruction of brain activation
… we outline the benefits and applicability of a Diffusion Approximation-based faster forward model solver. We also describe a new registration algorithm based on superficial landmarks which is an essential tool for the purely optical tomographic image process proposed here. A purely optical …
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Energy transmission through and along thin films mediated by surface phonon-polaritons
… theory-based calculation is performed using a diffusion approximation. These results are further confirmed by simulations using fluctuational electrodynamics. It was found that for amorphous silicon dioxide films tens of nanometers thick, the in-plane heat flux carried by surface …
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Isogeometric Approach to Optical Tomography
… applies the IGA method to solve the RTE with the diffusion approximation and studies its behavior in comparison to conventional FEM. The results show comparison of the IGA-based solution with analytical and conventional FEM solutions in terms of accuracy and efficiency. While both methods show …
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Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges
… vapor shield layer has been captured using the diffusion approximation for radiation heat transfer within the ET plasma source with simulated results matching experimental measurements. The relationship between source radius and peak current density inside ET plasma discharges has also been …
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Long-term variation in cosmic-ray modulation
… equation can be derived, namely the Convection-Diffusion and th Force-Field approximations. These approximations were implemented t account for heliospheric modulation only. Utilizing the Force-Fiel approximations, Usoskin et al. (2011) calculated the modulatio potentials between 1936 and 2009 …
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Computer simulation of high fluence ion beam surface modification processes
… lattice dilation or accommodation and diffusion as well. The model for preferential sputtering takes into account the depletion of the preferentially sputtered element at the surface and the atomic transport process that results from the concentration gradients caused by the depletion. …
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Policy robustness : robust stability of multiclass queueing networks
Robustness has been a prominent topic for decades in the optimization literature. However, it is only a few years that robust techniques have been imported and further developed for stochastic models, particularly stochastic processing networks. A reason for this late adoption might be that …
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Resource allocation in stochastic processing networks : performance and scaling
… As a corollary, we establish the validity of the diffusion approximation developed by Kang et al. [32], in steady state, for the case [alpha] = 1. Second, we consider the design of resource allocation policies in switched networks. At a high level, the central performance questions of interest …
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Queueing Models for Large Scale Call Centers
… first part of this thesis is to show that the diffusion scaled queue length process for the G/GI/N queue in the Halfin-Whitt regime converges to a limiting stochastic process which is driven by a Gaussian process and satisfies a stochastic convolution equation. We also show that a similar …
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