A simple one-dimensional model for the explanation and analysis of GaAs MESFET behavior

The explanation of GaAs metal-semiconductor field effect transistor (MESFET) operation often involves the use of simplistic analytical formulae, which serve to obscure the more subtle physics of device action. The authors consider here a simple one-dimensional (1-D) model for GaAs MESFETs, which avoids more confusing numerical modeling schemes, yet still facilitates an analysis of the physical functionality of the device. The model takes into account current saturation due to either velocity saturation or channel pinch-off, the modulation of effective gate length and the series resistance of the regions beyond the gate. The results of the model have been compared to experimental data readily obtained from the literature, and the agreement has been shown to be goo

Novel nonalloyed thermally stable Pd/Sn and Pd/Sn/Au ohmic contacts for the fabrication of GaAs MESFETs

GaAs metal-semiconductor field-effect transistors (MESFETs) have been fabricated utilizing thermally stable Pd/Sn and Pd/Sn/Au ohmic contacts for the first time. MESFETs with Pd/Ge ohmic contacts are fabricated for comparison. The thermal stability of the Pd/Sn, Pd/Ge and Pd/Sn/Au ohmic contacts is also presente

Space station attitude disturbance arising from internal motions

A source of space station attitude disturbances is identified. The attitude disturbance is driven by internal space station motions and is a direct result of conservation of angular momentum. Three examples are used to illustrate the effect: a planar three link system, a rigid carrier body with two moveable masses, and a nonplanar five link system. Simulation results are given to show the magnitude of the attitude change in each example. Factors which accentuate or attenuate this disturbance effect are discussed

Optimization models and system dynamics simulations to improve military manpower systems

textManpower policy decisions are an extension of traditional operations management problems. Manpower policies strive to place the appropriate and accurate numbers of the correct types of people in the right jobs at the necessary time. Managers create inventory by hiring new workers, either in entry level or more senior positions. Over time, managers promote workers to satisfy demand for more advanced positions. Managers face the challenge of determining the number of people to hire into entry level positions, the number of people already in the work force to promote to more senior level positions, and in some open systems when and how many experienced employees to hire into these senior positions. This dissertation studies and develops three different methods and approaches to provide improved decision support to a healthcare organization’s manpower system. Our research goal is to design models of the organization’s manpower system to improve human resource operations. The healthcare system of interest is the United States Army’s Medical Department (AMEDD). The research will be arranged in three sections. We explore current practices and build improved optimization manpower system models. We use multi objective decision analysis techniques to enhance the optimization models. Lastly, we construct a system dynamics simulation model of the manpower system to address the limitations in the optimization models. There are three main contributions of this dissertation to the operations management literature. First, the development of improved manpower optimization models can be extended to other manpower systems. Second, we develop a technique to assess the manpower system value based on a series of value scoring transformation functions and weighting the over two hundred sub objectives in the optimization manpower system’s objective function. This application of multiple objective decision analysis makes it possible to compare different manpower systems. The system dynamics simulation of a military manpower system is new to the operations management literature as is how we use the system dynamics simulation to update optimization model parameters to construct a more realistic manpower system model.Information, Risk, and Operations Management (IROM

Comprehensive investigation of Ge-Si bonded interfaces using oxygen radical activation

In this work, we investigate the directly bonded germanium-silicon interfaces to facilitate the development of high quality germanium silicon hetero integration at the wafer scale. X-ray photoelectron spectroscopy data is presented which provides the chemical composition of the germanium surfaces as a function of the hydrophilic bonding reaction at the interface. The bonding process induced long range deformation is detected by synchrotron x-ray topography. The hetero-interface is characterized by measuring forward and reverse current, and by high resolution transmission electron microscopy. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3601355