In this thesis we examine methods for measuring entanglement entropy in spin-1/2 Heisenberg systems using quantum Monte Carlo in the valence bond basis. We begin by presenting the quantum Monte Carlo techniques used in this research. We then use these techniques to directly compare the recently proposed valence bond entanglement entropy to the standard definition of entanglement entropy: the von Neumann entanglement entropy. We find that the valence bond entanglement entropy does not give a bound on the von Neumann entanglement entropy, and that it exhibits a multiplicative logarithmic correction to the area law that is not present in the scaling of the von Neumann entanglement entropy. We then present a method to measure higher orders of the generalized Renyi entanglement entropies using valence bond quantum Monte Carlo, and show results for the second Renyi entropy. We find the results converge to the exact results for one dimensional Heisenberg spin-1/2 chains, and see that the scaling of the second Renyi entropy follows an area law in the two dimensional Heisenberg ground state.

The goal of this thesis was to explore the effects of dose resolution, respiratory variation and dose calculation method on dose accuracy. To achieve this, two models of lung were created. The first model, called TISSUE, approximated the connective alveolar tissues of the lung. The second model, called BRANCH, approximated the lungs bronchial, arterial and venous branching networks. Both models were varied to represent the full inhalation, full exhalation and midbreath phases of the respiration cycle.<p> To explore the effects of dose resolution and respiratory variation on dose accuracy, each model was converted into a CT dataset and imported into a Monte Carlo simulation. The resulting dose distributions were compared and contrasted against dose distributions from Monte Carlo simulations which included the explicit model geometries. It was concluded that, regardless of respiratory phase, the exclusion of the connective tissue structures in the CT representation did not significantly effect the accuracy of dose calculations. However, the exclusion of the BRANCH structures resulted in dose underestimations as high as 14\% local to the branching structures. As lung density decreased, the overall dose accuracy marginally decreased.<p> To explore the effects of dose calculation method on dose accuracy, CT representations of the lung models were imported into the Pinnacle$^3$ treatment planning system. Dose distributions were calculated using the collapsed cone convolution method and compared to those derived using the Monte Carlo method. For both lung models, it was concluded that the accuracy of the collapsed cone algorithm decreased with decreasing density. At full inhalation lung density, the collapsed cone algorithm underestimated dose by as much as 15\%. Also, the accuracy of the CCC method decreased with decreasing field size.<p> Further work is needed to determine the source of the discrepancy.

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We use Particle-in-Cell Method¡]PIC¡^and Monte-Carlo-Collision Method¡]MCC¡^to model a plasma colliding system .By this way¡Awe can realize the behaviors and effects in the motion of plasma collision . Our mainly discuss is that the system will produce a thin layer¡]Sheath¡^between plasma and a workpiece ¡Aand the effects of colliding phenomenon in this thin layer¡]Sheath¡^ .

Computer simulation is now increasingly being used for design and performance evaluation of communication systems. When simulating a mobile wireless channel for communication systems, it is usually assumed that the fading process is a random variate with Rayleigh distribution. The random variates of the fading process should also have other properties, like autocorrelation, spectrum, etc. At present, there are a number of methods to generate the Rayleigh fading process, some of them quite recently proposed. Due to the use of different Rayleigh fading generators, different simulations of the same communication system yield different results. Three methods, viz., the Jakes method, the IDFT method and the filtering WGN method, have been studied, simulated and compared based on the Rayleigh fading process' properties. Various communication systems have been simulated using the Rayleigh fading generators and the difference in the results, if any, have been analyzed. The research studies the different Rayleigh fading generators and compares them using the properties of the Rayleigh fading channel. It is found that the IDFT method and the filtering WGN method generate processes that have properties very close to the ideal Rayleigh fading process.

Doctoral dissertation--Institute of political science and sociology--Bonn--Rheinische Friedrich-Wilhelms-University, 2005. / Bibliogr. p. 243-271.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 111-119).

Akademisk avhandling--Göteborgs universitet, 2005. / Bilbiogr. p. 77-79.

Doktorafhandling--Københavns universitet, 2005. / Bibliogr. p. 47-51. Résumé en danois.

Habilitation à diriger des recherches : Informatique : Rennes 1 : 2003. / Bibliogr. p.103-113.