A computationally efficient method of evaluating Green's functionsfor 1-, 2-, and 3-D enclosures

A model-based parameter estimation (MBPE) technique is used to evaluate efficiently the Green's functions associated with parallel plates, rectangular waveguides, and cavities. The numerical model uses a novel approach to break the dyadic Green's function into simpler functions so that a set of regressed polynomials can reconstruct the function. Examples of method of moments calculations incorporating MBPE are presented to show the computational advantage as compared to the direct approach     

A multilevel formulation of the method of moments [EM scattering]

The modeling of electromagnetic scattering and radiation problems using the method of moments (MoM) is limited to resonant frequencies because of the extensive computational requirements of solving large matrix equations. In this study, a multilevel formulation of MoM which allows substantial computational savings and, thus, extends the application of MoM to higher frequencies is presented. Using a hierarchy of discretization levels, the multilevel technique extracts different modal components of the solution by focusing on a specific portion of the spectrum of the solution at a given level. The fundamental features of this process for the MoM solution of the electric field integral equation (EFIE) are developed and implemented. This multilevel MoM allows the rapid evaluation of the current distributions on a variety of 2-D scatterers with thousands of unknowns in fewer than ten cycles and in fractions of the normal CPU times. The method is stable, fast, suitable for multiple excitations, and adaptable as a `solve' module for almost any MoM code     

Accumulation of human immunodeficiency virus-specific cytotoxic T lymphocytes away from the predominant site of virus replication during primary infection

Down-regulation of the initial burst of viremia during primary human immunodeficiency virus (HIV) infection is thought to be mediated predominantly by HIV-specific CD8+ cytotoxic T lymphocytes (CTL). This response is associated with major perturbations in the T cell receptor (TCR) repertoire. To investigate the failure of the cellular immune response to adequately control viral spread and replication and to prevent establishment of HIV infection, changes in the TCR repertoire and in the distribution of virus-specific CTL between blood and lymph node were analyzed in three patients with primary infection. By the combined use of clonotype-specific polymerase chain reaction and analysis of the frequency of in vivo activated HIV-specific CTL, it was shown that HIV-specific CTL clones preferentially accumulated in blood as opposed to lymph node. Accumulation of HIV-specific CTL in blood occurred prior to effective down-regulation of virus replication in both blood and lymph node. These findings should provide new insights into how HIV, and possibly other viruses, elude the immune response of the host during primary infection.     

Anomalous behavior of near fields calculated by the method of moments

The method of moments can be used to find solutionsJof the equationX(J) = lambda R(J), whereRandXare the real and imaginary parts (respectively) of theZ(impedance) operator of a perfectly conducting body. These solutions, called the characteristic currents, are characterized by an important near-field feature-the resulting free-space electric fields tangential to the body are constant in phase over the entire body. Although the method of moments is often used to solve electromagnetic problems where the far radiation fields of the solution currents are of interest, general moment-method theory indicates that the technique should also yield current solutions exhibiting accurate near-field behavior as the dimension of the solution space is increased. The near-field phase characteristics of resonant thin-wire characteristic current distribution, as calculated by several familiar moment-methods schemes, are presented. The ensuing discussion reveals several anomalies concerning the near-field behavior of the fields resulting from these currents. These anomalies are then discussed in light of the basic rudiments of the method of moments.     

Reassessment of socially mediated learning in Siamese fighting fish (Betta splendens).

Seven experiments examined a previous report of Pavlovian conditioning of territorial behavior using a mirror unconditioned stimulus/stimuli (UCS) in Betta splendens. Control procedures omitted from the original research were included. Three studies failed to find that exposure to a mirror (UCS) in a colored tunnel conditioned stimulus/stimuli (CS+) produces learned approach to this tunnel. Instead, the fish exhibited unlearned green color preferences prior to mirror exposure and highly variable, random tunnel preferences after mirror exposure, One experiment provided evidence for an associative effect with the red CS+, but training with the green CS+ did not produce enhanced tunnel preferences. In contrast, spatial discrimination was shown in 2 experiments. The data, taken with other failures to replicate, raised questions about the biological preparedness of B. splendens to learn to associate agonistic responses with color features in the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cross-phase modulation in multispan WDM optical fiber systems

The spectral characteristics of cross-phase modulation (XPM) in multispan intensity-modulation direct-detection (IM-DD) optical systems are investigated, both experimentally and theoretically. XPM crosstalk levels and its spectral features are found to be strongly dependent on fiber dispersion and optical signal channel spacing. Interference between XPM-induced crosstalk effects created in different amplified fiber spans is also found to be important to determine the overall frequency response of XPM crosstalk effects. XPM crosstalk between channels with different data rates is evaluated. The crosstalk level between higher and lower bit rate channels is found to be similar to that between two lower bit rate channels. The effect of dispersion compensation on XPM crosstalk in multispan optical systems is discussed and per span dispersion compensation was found to be the most effective way to minimize the effect of XPM crosstalk     

Generation of ultrahigh-speed tunable-rate optical pulses usingstrongly gain-coupled dual-wavelength DFB laser diodes

A novel and simple method to generate a variable-rate, ultrahigh-speed optical pulse train is demonstrated using a dual-wavelength, strongly gain-coupled distributed-feedback laser diode. The repetition rate of the optical pulse train is continuously tunable from 25 to 80 GHz and no high-speed electronics are required in this method     

FDTD modeling of scatterers in stratified media

The FDTD technique is well suited for calculating the fields scattered by buried objects when the sources are close enough to the air/ground interface so that they can be incorporated into the solution space. Difficulties arise, however, when the sources are far from the interface since the total fields in the solution space are not all outgoing waves. Using well-known formulas for the fields transmitted and reflected by stratified media, this paper discusses a method whereby the fields scattered by a buried object can be easily calculated by the FDTD technique when the incident field is a plane wave     

An Optimum Combination of Power Levels and Combiner Weighting for Generating 64-QAM from Three 4-PSK Signals

64 state quadrature amplitude modulation (64-QAM) can be generated by combining three 4-PSK signals, thereby allowing nonlinear amplifiers with smaller power ratings to be used. An optimum combination of amplifier power levels and combiner weighting is described which results in no lost power when the peak power state of the 64-QAM signal is being keyed.