Browsing by Subject "computer simulation"
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Item Computer Simulation and Comparison of Proton and Carbon Ion Treatment of Tumor Cells Using Particle and Heavy Ion Transport Code System(2011-02-22) Curtis, Keel BrandonCharged particle beams are an increasingly common method of cancer treatment. Because of their Bragg peak dose distribution, protons are an effective way to deliver a dose to the tumor, while minimizing the dose to surrounding tissue. Charged particles with greater mass and higher charge than protons have an even sharper Bragg peak and a higher Relative Biological Effectiveness (RBE), allowing a greater dose to be delivered to the tumor and sparing healthy tissue. Since carbon ions are being implemented for treatment in Europe and Japan, this study will focus on carbon as the heavier ion of choice. Comparisons are drawn between moderated and unmoderated protons and carbon ions, all of which have a penetration depth of 10 cm in tissue. Scattering off the beam line, dose delivered in front of and behind the tumor, and overall dose mapping are examined, along with fragmentation of the carbon ions. It was found that fragmentation of the carbon ion beam introduced serious problems in terms of controlling the dose distribution. The dose to areas behind the tumor was significantly higher for carbon ions versus proton beams. For both protons and carbon ions, the use of a moderator increased the scattering off of the beam line, and slightly increased the dose behind the tumor. For carbon ions, the use of a moderator increased the degree of fragmentation throughout the beam path.Item Dose calculation methodology for irradiation treatment of complex-shaped foods(2009-06-02) Kim, JongsoonDose calculation methodology was developed for irradiation treatment of complex-shaped foods. To obtain satisfactory electron beam irradiation of food products, a strict process control is required to ensure that the dose delivered to all parts of the treated product falls within some specified range. The Monte Carlo electron transport simulation and computer tomography (CT) scan technology were used to predict the dose distribution in complex shaped foods, an apple phantom composed of paraffin wax, chloroform, and methyl yellow, and a chicken carcass. The Monte Carlo code used was successfully tested against the experimental data, resulting in less than 5% discrepancy between the simulated and measured data. For 1.35 MeV electron beam simulation of apple phantom, tilting and axial rotation ensures dose distribution of the entire surface of the phantom, even reaching the critical regions of the apple stem and calyx ends. For 1 and 5 MeV X-ray simulations, both depth-dose curves show exponential attenuation after a build-up region. The depth to peak for the former is shorter than that of the latter. For 1.35 MeV electron beam simulation of a chicken carcass, dose adsorption occurred up to 5-7 mm deep, resulting in surface irradiation of the carcass. For 10 MeV electron beam simulation, the doses within the carcass reached a peak of 1.2 times the incident dose with increasing depth. Two-sided X-ray (5 MeV) irradiation significantly improved the dose uniformity ratio, from 2.5 to 1.8. A web-based integrated system was developed for data manipulation and management for irradiation treatment of foods. Based on CT scan, three dimensional geometry modeling was used to provide input data to the general Monte Carlo N-Particle (MCNP) code. A web-based interface provided the on-line capability to formulate input data for MCNP and to visualize output data generated by MCNP. The integrated Matlab and Matlab Web Server programs automatically functions through the steps and procedures for data input and output during simulation. In addition, a database having D10 values (decimal reduction value), food nutrition composition, and qualities was integrated into the dose planning system to support food irradiation treatment.Item Extending and Formalizing the Energy Signature Method for Calibrating Simulations and Illustrating with Application for Three California Climates(Texas A&M University, 2004-11-15) Bensouda, NabilThis thesis extends and formalizes the energy signature method developed by Wei et al. (1998) for the rapid calibration of cooling and heating energy consumption simulations for commercial buildings. This method is based on the use of "calibration signatures" which characterize the difference between measured and simulated performance. By creating a library of shapes for certain known errors, clues can be provided to the analyst to use in identifying what simulation input errors may be causing the discrepancies. These are referred to as "characteristic signatures". In this thesis, sets of characteristic signatures are produced for the climates typified by Pasadena, Sacramento and Oakland, California for each of the four major system types: single-duct variable-air-volume, single-duct constant-volume, dual-duct variable-air-volume and dual-duct constant-volume. A detailed step-by-step description is given for the proposed methodology, and two examples and a real-world case study serve to illustrate the use of the signature method.Item Risk-Based Technology Assessment for Capital Equipment Acquisition Decisions in Small Firms(2013-08-06) Merriweather, Samuel P.Companies and organizations must make decisions concerning capital budgeting. Capital budgeting is a decision-making process that determines whether a firm should purchase equipment to be used on a long-term basis. The initial investment in the equipment is predicted to be returned through revenue gained by the use of the equipment over its lifetime. However, there is inherent risk associated with these investment decisions. Therefore, potential purchasers must decide whether the risk involved with investing in the equipment is justified. This dissertation addresses risk-based technology assessment for capital equipment acquisition decisions in small firms. Technology assessment, here, is concerned with understanding the uncertainty associated with assessing the value predicted in the capital budgeting process. When analyzing the risk for a given technology, we assign a probability law to its net present value. Our primary research contribution is providing an analytical framework together with a computational strategy to support capital equipment budgeting in firms where the value of candidate technologies can represent nearly all the firm?s value. Since small firms typically have limited budgets, spending for technology is always a difficult budgeting decision. The organization?s administration must decide which, if any, among the available technologies will be best for their operation. The process for acquiring technology in many small firms can be filled with challenges. Most important among them is that capital budgeting is typically a ?one-off? decision. These decisions are difficult since the candidate technologies may not have operational data available. Thus, decision makers need some means to predict how the proposed technology (e.g., equipment or machinery) will be used. Hence, firms should follow techniques and procedures based on appropriate normative principles and well-established theory. Senior company executives and/or governance boards are often authorized to approve capital equipment purchases. However, these company leaders may not have adequate expertise in the operations of candidate technologies or may lack the understanding necessary to determine how new technologies may impact other company operations. Appropriate financial evaluation measures and selection criteria that incorporate risk are critical to making sound, quantitative acquisition decisions. The research reported here offers an analytical framework for comparing different technology alternatives in capital budgeting decisions. Comparison is based on the expected net present value and the risk (i.e., probability law on net present value) associated with each decision alternative. To this end, the operational characteristics of each technology alternative are connected to their potential revenue and cost streams. The framework is embedded within a computational architecture that can be customized to account for operations and technologies in specific application scenarios. One major barrier addressed by this research is overcoming the fact that new technologies typically have no historical operational data. Therefore, characterizing the uncertainty of operations (e.g., distribution of the equipment lifetime) can be very difficult. Discrete- event simulation is used to generate potential revenue and cost estimates. We demonstrate the tractability and practicality of the analytical framework and computational architecture via a healthcare technology assessment decision. Data extracted from a published journal article detailing a hospital?s technology assessment decision are used to find the risk of the medical technology using the computational architecture developed. Widely-available, no-cost software tools are employed. Results of the health care example suggest that the financial analysis in the original technology assessment was in- adequate and simplistic. Small firms may find this research particularly beneficial because potential investments can be a significant portion of a small firm?s value.Item Structure of gas-liquid interface and hydrophobic interface for urea aqueous solution: a computer simulation study(2009-05-15) Yu, MengUrea aqueous solution is ubiquitously used to denature protein. Regardless of its extensive use, the mechanism is still unclear and remains an active field of study. There have been two proposed mechanisms, the direct and indirect. The indirect mechanism, which attributes the ability of urea of changing water structure, is susceptible since many research works show that there is little effect of urea on water structure. The current study provided evidence for the indirect mechanism by demonstrating that the introduction of urea slightly changes the water structure in the hydrophobic interfacial areas. In the current study, the urea aqueous solution systems with either gas-liquid or hydrophobic interface are studied by MD simulations, and the structures of water near the interfacial areas are analyzed in terms of density, orientation and number of hydrogen bonds. For each kind of interface, systems with four different urea concentrations are included, ranging from 0M to 8M. The results show slight change of water structure by the urea solute on the hydrophobic interface in terms of the orientation and number of hydrogen bonds per water molecule.