Electro-optic scattering from nitrocellulose solutions

Measurements have been made of the light intensity scattered from dilute solutions of a sample of nitrocellulose ($\text{M}{}_{\mathrm{w}}\text{= 460,000}$) in acetone, both in the absence and presence of a.c. and d.c. electric fields. In an earlier study, owing to a mathematical slip and a false interpretation of an experimental parameter, other workers [5] interpreted similar measurements in terms of a freely rotating polar chain model. It is shown herein that this cannot be so and that the molecules of nitrocellulose of this order of molecular weight and in this type of solvent are better regarded as extremely stiff and extended.     

Numerical Optimization of an Active Voltage Controller for High-Power IGBT Converters

Feedback control of insulated gate bipolar transistors (IGBTs) in the active region can be used to regulate the device switching trajectory. This facilitates series connection of devices without the use of external snubber networks. Control must be achieved across the full active region of the IGBT and must balance a number of conflicting system goals including diode recovery. To date, the choice of control parameters has been a largely empirical process. This paper uses accurate device models and formalized optimization procedures to evaluate IGBT active voltage controllers. A detailed optimization for the control of IGBT turn-on is presented in this paper     

Factorizations of the Complete Graph into C 5-Factors and 1-Factors

In this paper, we show that K_10n can be factored into C₅-factors and 1-factors for all non-negative integers and satisfying 2+=10n–1.Research partially supported by an NSF-AWM Mentoring Travel Grant     

An indexed atlas of digital mammograms for computer-aided diagnosis of breast cancer

Computer-aided diagnosis (cad) systems are being developed to assist radiologists in the interpretation of ambiguous mammographic features corresponding to possible signs of early breast cancer. Databases of digital mammograms are needed for testing such systems; we present an overview of a few such databases. Most databases are limited to single-exam sets of two or four mammograms on which the diagnosis was made, some ground-truth information related to the position of diagnostically significant mammographic features, and the diagnosis. We propose the design of a comprehensive, indexed atlas of digital mammograms. The design of an appropriate indexing scheme facilitates the implementation of content-based retrieval techniques needed for efficient access to and retrieval of relevant cases from the atlas. We also propose the use of mobile software agents for facilitating remote consultation of the atlas. Mobile agents can move between data sources such as the atlas and hospital repositories, perform computational tasks at each site, and return only relevant data to the user. These features reduce the computational requirements of the local computer system, bandwidth requirements, and overall network traffic. Proposed applications of the atlas include research, remote consultation, teaching, evaluation ofcad systems, and self-evaluation by radiologists.     

Variable step length finite difference method for calculation of the 3-phase electromagnetic field in the long conductor approach

The original motivation of this research is to describe comprehensive solutions based on Finite Difference Method (FDM) together with its software implementation that can handle the infinity long conductor. This paper focuses on developing FDM procedures for solving the interface regions, defined as regions where the step sizes change. Attention has been paid in this problem for creating robust and efficient techniques for solving the complex electromagnetic field at long distance from the transmission line based on a variable step size for the grid of FDM. Reduction in memory requirements has been achieved in these approaches. The industry has identified that there is a pressing need for a comprehensive method together with its software implementation that can handle the infinity long conductor problem. The research results of the project have immediate and practical application to the power industries.     

Temperature dependence of Al/Ti-based Ohmic contact to GaN devices: HEMT and MOSFET

In this paper two types of Al/Ti-based Ohmic contacts to Gallium Nitride (GaN) based devices are presented; ImplantedN⁺GaN (like the ones found in the Source/Drain of GaN Metal Oxide Semiconductor Field Effect Transistors-MOSFET) and heterojunction (HJ) AlGaN/GaN contacts (Source/Drain of High Electron Mobility Transistors-HEMT). Sheet resistance (R_sh) and contact resistance (R_c) have been investigated in the temperature (T) range of 25-250 °C. It was found that the R_sh (850/700 Ω□) (25/250 °C) and R_c (2.2/0.7 Ωmm) decrease with T for ImplantedN⁺GaN contact and R_sh (400/850 Ω□) and R_c (0.2/0.4 Ωmm) (weakly for R_c) increase with T for HJAlGaN/GaN contact. Numerical computation based models are used to determine the theoretical R_sh and R_c behavior with T and to fit the experimental values.