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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:
F. Hegeler, M. Partridge, E. Schamiloglu, C. T. Abdallah, and N. Islam,
"Experimental studies of the cross-excitation instability in a relativistic backward wave oscillator",
SPIE 2000, Orlando, FL, April 2000.
[pdf]
Abstract: Our group first reported the operation of a relativistic backward wave oscillator (BWO) in the so-called “cross-excitation”
regime in 1998. This instability, whose general properties were predicted earlier through numerical studies, was a
consequence of using a particularly shallow rippled-wall waveguide (slow wave structure – SWS) that was installed in the
experiment to diagnose pulse shortening in a long pulse electron beam-driven high power microwave (HPM) source. This
particular SWS was required to accommodate laser interferometry measurements during the course of microwave generation.
Since those early experiments we have further studied this regime in greater detail using two different SWS lengths. We
have invoked time-frequency analysis, the smoothed-pseudo Wigner-Ville distribution in particular, to interpret the
heterodyned signals of the radiated power measurements. These recent results are consistent with earlier theoretical
predictions for the onset, voltage scaling, and general behavior for this instability. This paper presents data for a relativistic
BWO operating in the single frequency regime for two axial modes, operating in the cross-excitation regime, and discusses
the interpretation of the data, as well as the methodology used for its analysis. Although operation in the cross-excitation
regime is typically avoided due to its poorer efficiency, we discuss how it may be exploited in HPM effects studies.
F.L. Lewis, B. Horne and C. T. Abdallah,
"On the Computational Complexity of teh Manufacturing Job Shop and Reentrant Flowline",
IEEE Transactions on Systems, Man, and Cybernetics Part A, Vol. 30, No.2, pp. 222-229, 2000.
[pdf] [ps]
Abstract:
This paper presents a comparison study of the computational complexity of the general job shop protocol and the flow line
protocol in a flexible manufacturing system. It is shown that a certain representative problem of finding resource invariants
is NPcomplete in the case of the job shop, while in the flow line case it admits a closedform solution. The importance of
correctly selecting part flow and job routing protocols in flexible manufacturing systems to reduce complexity is thereby
conclusively demonstrated.
G. L. Heileman, C. T. Abdallah, B.M.E. Moret and B. Smith,
"Dynamical System Representation of Open Address Hash Functions",
Accepted, SODA, 1998.
[pdf] [ps]
Abstract: Number theory and probabilistic analyses have typically been used to justify the use of
various probing strategies for open address hashing. For example, Guibas and Szemeredi [1], and later
Lueker and Molodowitch [3], have shown that double hashing offers a good approximation to uniform
hashing if the hash function is assumed to select table entries with equal probability. In this paper we use
an analysis based on nonlinear dynamical systems theory to provide a similar result, without making any
probabilistic assumptions about the data distribution. The key to our approach is the ability to express hash
functions as dynamical systems. Below we demonstrate for the first time how some important families of
hash functions can be expressed as dynamical systems. After this, we provide an analysis of linear double
hashing that demonstrates the potential usefulness of representing hash functions in this fashion.
A. Jadbabaie, C. T. Abdallah, M. Jamshidi and P. Dorato,
"Guaranteed-Cost Control of the Nonlinear Benchmark Problem Using Model-Based Fuzzy Systems",
Proceedings IEEE Conference of Control Applications, pp. 792-796, Trieste, Italy, 1998.
[pdf] [ps]
Abstract: In this paper we design a state-feedback controller for the nonlinear benchmark problem.
Our approach relies on the use of Takagi-Sugeno fuzzy models to approximate the nonlinear system. Once the fuzzy model is
obtained, we develop a guaranteed-cost framework to design the controller using Linear Matrix Inequality methods and recently
obtained relaxed stability conditions. We show that our proposed controller will not only stabilize the system, but also has
satisfactory disturbance attenuation properties.
A. Jadbabaie, C. T. Abdallah, and P. Dorato,
"Guaranteed-Cost Control of Polynomial Nonlinear Systems",
Proceedings IEEE Conference on Decision and Control, pp. 4100-4102, Tampa, FL, 1998.
[pdf] [ps]
Abstract: This paper deals with the control of a class of nonlinear systems which are affine in control
and the drift and control vector field are polynomials. The states are normalized in the closed interval [0, 1]. The normalized
system is then transformed to a Bernstein polynomial basis. Bernstien polynomials have this property that they form a partition
of unity, therefore the dynamics of the nonlinear system can be written as a Poly-topic Linear Differential Inclusion (PLDI).
Once the PLDI is obtained, gain-scheduled controllers are designed using a guaranteed cost framework. This methods is further
illustrated by a simple numerical example.
R.A. Luke, P. Dorato and C. T. Abdallah,
"A Reduction in Conservatism for Convex Linear-Quadratic Simultaneous Performance Design",
NASA University Research Centers Technical Advances in Education,
Aeronautics, Space, Autonomy, Earth and Environment, Vol. 1, Proceedings of
the NASA URC Technical Conference, pp. 477-482, Albuquerque, NM, February 16-19, 1997.
[pdf]
Abstract: In this paper a fixed state feedback control law which minimizes upper bounds on
linear-quadratic performance measures for m disctinct plants is studied. Previous work [8] by the authors
demonstarted a convex semidefinite programming solution thereby guaranteeing global optimality. The present work
extends that result by proposing an algorithm which reduces the conservatism of the minimum guaranteed-cost
upper bounds for each of the m performance measures.
B. Smith, G. L. Heileman and C. T. Abdallah,,
"An Exponential Open Hashing Function Based on Dynamical Systems Theory",
Pre COST #254 Workshop on Intelligent Methods in Signal Processing and Communication , pp.201-206, Bayona, Spain, 1996.
[pdf]
Abstract: In this paper an efficient open addressing hash function called exponential hashing
is developed using concepts from dynamical systems theory and number theory. A comparison of exponenetial hashing
versus a highly-used double hash function is performed using an analysis based on Lyapunov exponents and entropy.
Proofs of optimal table parameter choices are provided for a number of hash functions. We also demonstrate experimentally
that exponential hashing nearly matches the performance of an optimal double hash function for uniform data distributions,
and performs significantly better for nonuniform data distributions. We show that exponential hashing exhibits a higher
integer Lyapunov exponent and entropy than double hashing for initial data probes, which offers one explanation
for its improved performance on nonuniform data distributions.
F. Perez and C. T. Abdallah,
"Phase-Convex Arcs in Root Space and their Application to Robust SPR Problems",
Proceedings IEEE Conference on Decision and Control, pp.3729-3731, Orlando, FL, 1994.
[pdf] [ps]
Abstract: This paper considers the problem of identifying regions in the complex-plane, such that the phase of polynomials
having roots in those regions, is bounded by that of a few extreme polynomials. Applications of the results are also
described.
C. T. Abdallah, P. Dorato, and S. Karni,
"Continuous and Discrete Time SPR Design Using Feedback",
Proceedings of the American Control Conference, Boston, MA, pp.1742-1743, 1991.
[pdf] [ps]
Abstract: This paper presents necessary and sufficient conditions for the existence of a feedback
compensator that will render a given continuous-time or discrete-time linear system SPR. When these conditions hold, the
controller is explicitely found.
V.S. Soualian, G.T. Park, C. T. Abdallah, and E. Schamiloglu,
"Iterative Learning Control Applications to High Power Microwave Tubes"
[pdf] [ps]
Abstract: In this paper, we present a “smart” high-peak power microwave tube, by implementing iterative learning control methodologies
to control a repetitively-pulsed, high-power, backward wave oscillator. The learning control algorithm is used to drive
the error between the actual output and its desired value to zero. The desired output may be a given power level, a given
frequency, or a combination of both. The learning control methodology is then experimentally verified.
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