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Understanding and reproducing complex human oculomotor behaviors using computational models is a challenging task. In this paper, two studies are presented, which focus on the development and evaluation of a computational model to show the influences of cyclic top-down and bottom-up processes on eye movements. To explain these processes, reinforcement learning was used to control eye movements. The first study showed that, in a picture-viewing task, different policies obtained from different picture-viewing conditions produced different types of eye movement patterns. In another visual search task, the second study illustrated that feedback information from each saccadic eye movement could be used to update the model's eye movement policy, generating different patterns in the following saccade. These two studies demonstrate the value of an integrated reinforcement learning model in explaining both top-down and bottom-up processes of eye movements within one computational model. Index Terms--Cognitive model, eye movement, queueing network model, reinforcement learning.

Power-line communications (PLC) is a field that has raised a lot of research in the past years. In this paper, we introduce array codes into the PLC environment and we study the channel's performance. In particular, generalized array codes (GAC), as well as row and column array codes (RAC) are applied. We examine their performance by obtaining three different code rates from each category. Therefore, the (8, 4, 4), (12, 7, 4) and (16, 11, 4) GAC codes as well as the (9, 4, 4), (12, 6, 4), and (15, 8, 4) RAC codes are used, meaning that we obtain code rates of (1/2), (7/12), (11/16), and (4/9), (6/12), (8/15) respectively. In addition, for reasons of completeness, convolutional codes are also being applied under the same channel conditions. Moreover, we suggest a hybrid coding technique, which combines the (8, 4, 4) GAC and the (15, 8, 4) RAC code in order to meet the requirements of the PLC time-varying channel and improve its performance. Concerning the system's design, we take into consideration Zimmermann's model for the PLC channel. We apply Middleton's model for the channel's background and impulsive noise, while we also introduce a novel way of estimating the system's impulsive noise. Finally, the well-known transmission technique of orthogonal frequency-division multiplexing is used. The channel's performance is evaluated in terms of the bit-error rate for different [E.sub.b]/[N.sub.o] values via computer simulations. Index Terms--Generalized array codes (GACs), impulsive noise, power-line communications (PLC), row column codes (RAC codes).

This paper presents a new architecture layout for a real-time power system simulator based on a distributed cluster of IBM PC-compatible desktop computers. A real-time network simulator based on a PC cluster can successfully cope with the size requirements of growing power systems and the computational demands of fast transient studies. A powerful product has been developed using off-the-shelf Pentium II 400-MHz workstations with a commercial real-time operating system, standard input/output (I/O) interfaces, and a multimachine networking scheme. Models based on the standard tool for power systems transients simulations, the Electromagnetic Transients Programs (EMTP) program, optimized for real-time performance ensure accurate simulation results. Index Terms--EMTP, OVNI, PC-cluster, power system simulator, real time.

This paper discusses different computer tools used to help deliver, administer, and teach the material covered in two basic undergraduate courses in electrical engineering. The computer facilities, programs, and tutorials developed are discussed; however, the paper concentrates more on analyzing the results of using these tools in the student learning process. The students' marks and the results of several student surveys, as well as the teaching staff's observations, are used to evaluate the usefulness of the different tools and determine their advantages and disadvantages. Some unexpected results regarding the actual students' use of these tools are also presented and thoroughly analyzed. Index Terms - Computer learning, computers in lectures, course administration, simulation programs, student response.

A system experiment and a computer simulation program help examine the large signal optical parametric amplification in type I beta-Ba2O4 optical crystals. Experimental results coincide with the computer simulations for 354.7 nanometer 30 picosecond laser pulses. The crystals have a linewidth below 0.5 nanometers, a tunable wavelength in the range of 420 to 2,800 nm, a peak power of 51 MW and a one-BBO-OPA energy conversion efficiency of 61%.

The timing budget for inter-chip electrical interconnect becomes tight as the clock frequency of a high performance digital system increases. To meet the timing specifications it is essential to analyze the propagation delay of the electrical interconnect accurately, which requires including the full driver and receiver model (circuit files) and adequate transmission line model in the timing analysis. A general circuit simulator is needed in order to include the driver and receiver circuits which, in general, contain nonlinear active circuit elements. We have implemented the wave separation type multiconductor transmission line model in Intel's in-house circuit simulator TIM. In this paper we will present the details of implementation as well as a description of the algorithm. We will also compare the wave separation model to the distributed-lumped model, and present results from a number of simulation cases.

A three dimensional computer simulation of the interaction of various heavy ion cosmic rays with silicon is presented. The initial ion strike is modeled by the Classical Trajectory Monte Carlo algorithm. Primary electrons produced by the CTMC code, along with their position and momenta, are entered into a non-relativistic Monte Carlo electron transport program. Both elastic and inelastic scattering events are considered in the simulation of the secondary electron cascade. Inelastic collisions include ionization of all shells. A prediction is made of the quantity and distribution of charge generated within silicon due to the cosmic ray ion strike.

In this paper we present a novel approach to the evaluation of the dc parameters of a semi-empirical MESFET model: starting from the analytical expression of the drain current derived from a physics-based model, previously proposed, we provide a method to calculate the empirical de parameters of the so called 'Raytheon' model. The comparison between computed and measured dc characteristics is quite satisfactory on GaAs microwave FET's of 1 [Mu]m or more gate length. By adding to the results, obtained in this work, an adequate model of the stray capacitances, the circuit performance can be optimized using the technological characteristics of active devices.

In an earlier paper, we analyzed and offered solutions to several discrepancies that often arise when students seek to understand and reconcile their hand calculations with SPICE simulation results. This paper presents several additional commonly encountered but quite unexpected problems that frustrate and confuse students. In particular, we discuss the difficulties that arise from the use of Miller compensation in the middle gain stage of a typical bipolar op amp, the discrepancies that occur when a transistor is operating in 'high level injection region,' the techniques for minimizing the voltage offsets when the input transistors match perfectly, and the difficulties in calculating CMRR caused by the difference between the ac and dc gains of current mirrors. Index Terms--Analog amplifiers, complex pole pairs, current mirrors, feedback, high-level injection, input offsets, SPICE simulation, stability.