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Conference Papers-Various
Note: The papers on this website may differ from the published versions, both in format and in content.
Various:
E. Schamiloglu, C. T. Abdallah, G.T. Park, and V.S. Soualian,
"Inital Engineering Design for the Implementation of a "Smart Tube" Frequency Agile, High Power BWO"
[pdf]
Abstract: Recent work at the University of New Mexico (UNM) by
Morelan, et al. (1) has demonstrated how finite length effects in a high power vacuum backward wave oscillator
(BWO) can be exploited to achieve frequency agility for constant beam and magnetic field parameters. This
enhanced band~vidtll is obtained through the axial displacement of the slow wave structure with respect to
the cutoff neck “inlet” to the electrodynamics system. This paper describes the initial engineering design for
accomplishing this displacement automatically to facilitate the incorporation of a robust controller, as
proposed by Abdallah, et al. (2). The purpose of this controller is to demonstrate a “smart tube” where a
variety of objectives, such as i) maximizing the frequency bandwidth for a given constant power output, ii)
maximizing the radiated peak prover at a given frequency, or iii) maximizing the beam-to-microwave
power conversion efllciency, can be achieved automatically.
C. T. Abdallah, C. T. Abdallah, B.M Moret and B. Smith,
"Dynamical Systems Theory and Hashing"
[pdf] [ps]
Abstract: Number theory and statistics have been used to justify the use of various probing strategies for
hashing with open addressing. We show how measures from nonlinear dynamical systems theory can be used to analyze the behavior of
different probing strategies. The usefulness of this approach is demonstrated on a number of widely used hash functions.
An important connection we make between hashing and nonlinear dynamics is that many of the properties of a good probe sequence
are precisely those that define a chaotic dynamical system. As a specific example, we show that double hashing can be described
as chaotic discretetime dynamical systems and use nonlinear dynamical systems theory to quantify how well double hashing can be
expected to perform.
The dynamical systems approach to the analysis of hash functions has also proven useful as a design tool. We derive a new family
of hash functions, called exponential hashing, from this perspective and show that it improves on conventional double hashing.
Theoretical results are supported by experimentation which demonstrates that, for uniform data distributions, exponential hashing
matches the performance of double hashing, but that, for nonuniform data distributions (the more likely to be encountered in
practice), exponential hashing suffers none of the performance peaks and valleys that affect double hashing. Finally, we briefly
describe how this same approach could be used to derive random number generators with very fast mixing properties.
M. Jacobus, M. Jamshidi, C. T. Abdallah,
P. Dorato, D. Bernstein, "Design of Strictly Positive Real, Fixed-Order
Dynamic Compenstaors", Proceedings of the 29th Conference on Decision and Control, pp. 3492-3495, Honolulu, HI, December 1990.
[pdf]
Abstract: This paper presents sufficient conditions for the design of strictly positive real (SPR), fixed-order
dynamic compensators. The primary motivation for designing SPR compensators is for application to positive real (PR) plants. When an SPR
compensator is connected to a PR plant in a negative feedback configuration, the closed loop is guaranteed stable for arbitrary plant variations
as long as the plant remains PR. This paper gives equations that are a modified from the optimal projection equations,
with the separation principle not holding in either the full- or reduced-order case. A solution to the design equations is shown to
exist when the plant is PR (or just stable). Finally, the closed loop system consisting of a PR plant and an SPR compensator is shown
to be S-structured Lyapunov stable.
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