Browsing by Subject "DES"

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Advances in Selective Area Laser Deposition of Silicon Carbide
(1994) Tompkins, J.V.; Laabi, R.; Birmingham, B.R.; Marcus, H.L.
Selective Area Laser Deposition (SALD) is a Solid Freeform Fabrication (SFF) technique which uses a scanning laser beam to produce solid material by locally decomposing a gas precursor. In this work, a focused C02 laser beam strikes a substrate in the presence oftetramethylsilane (TMS) or diethylsilane (DES), producing silicon carbide objects with high density and no binder phase. Recent investigation has yielded growth rates up to 2.7mlnJmin in the beam area, and has eliminated previously noted contamination ofthe optics by a byproduct which mass spectroscopy identifies as silicon dioxide. This paper reviews a cause of non-uniform growth and delTIOnstrates the addition of hydrogen and reduced scan speeds to lTIake lTIultilayer parts. In addition, it presents a lTIethod for in-situ measurement of height of deposited material.
Distributed Current Feed and Distributed-Energy-Storage Railguns
(IEEE, 1983-10) Holland, L. D.;
Distributed-type railguns are combinations of power supplies and railguns designed to maintain a nearly constant current in the armature of a railgun and to overcome the accelerator length limitations of simple breech-fed railguns. This limitation arises from the increasing resistance and inductance of the rails with increasing railgun length. The energy efficiency of a railgun system from the primary energy store to the kinetic energy of the projectile can be improved as compared to the simple railgun in some applications. This is accompli shed by a reduction of the stored magnetic field energy in the bore of the railgun at the end of a shot and reduction of the resistive losses in the rails. The improved system performance of the distributed railguns over the simple breech-fed railguns is achieved at the expense of greater system complexity. The only distributed-type railguns that have been built to date are distributed-energy-store (DES) railguns. These systems presently use capacitors as the primary energy store, which allows the use of closing switches to initiate current from each of the stores. In this paper a new type of railgun, the distributed-current-feed (DCF) railgun, is presented. The DCF railgun system is a compromise in system complexity and efficiency between the DES rail guns and the simple breech-fed railguns. Also, the DCF railgun utilizes closing switches in such a manner as to allow the use of a variety of primary power supplies, including homopolar generators (HPGs), for such electromagnetic propulsion tasks as space launches.
Modeling food deserts : devising an adaptable framework to test built environment disruptors in urban food deserts
(2018-12) Abel, Kelsey Christina; Faust, Kasey M.
Food Deserts are an expansive problem with cascading effects on quality of life, equity, and health outcomes for FD residents. Within urban FDs, a disconnect exists between the built environment and stakeholder populations, which exacerbates access issues. Modeling food access within FDs could help decision makers and urban planners devise and test solutions to increase access and mitigate negative effects on FD residents. The devised framework provides an adaptable model that can be applied to any FD and then used to simulate the impact of a variety of disruptors. The framework leverages Object-Oriented Programming and combines Agent-Based Modeling, Geographic Information Systems, and Discrete Event Simulation. To test its functionality, this framework was applied to a case study region in Austin, Texas. Results indicate that all modeled disruptors improve food access in the case study region, but efficacy is dependent on disruptor location and the distance residents are willing to walk to reach a store or bus stop (referred to as WTWS and WTWB, respectively). Most significantly, this work demonstrates and discusses how simulation modeling can be used to (1) inexpensively test proposed solutions to food access issues before large-scale capital investments are made; (2) identify emergent behavior and confounding variables that might increase or decrease a disruptor’s efficacy if leveraged correctly; and (3) identify unique, area-specific solutions to food access issues within FDs to achieve more sustainable improvements in food access among underserved populations. The practical application of this work is its ability to provide decision makers with data on what built environment disruptors would be most effective at improving food access in FDs. Future iterations of this work may be used to recommended courses of action to engineers and decision makers about how to address food access in underserved regions from both a policy and a built environment perspective