Scattering by spherically stratified microwave lens antennas

A comprehensive treatment of scattering by sources in the region of a spherically stratified object composed of discrete shells is presented and compared with measured results. The work encompasses the developments necessary for a thorough understanding of the focusing mechanism of a spherical lens. The method used is a modal technique that employs separation of variables in order to determine an eigenfunction representation of the incident and scattered fields. This formulation provides the Green's function required for the calculation of the scattering from a multiple layered sphere excited by an infinitesimal current element. The algorithm allows both near- and far-field predictions. The scattering by more complicated source field distributions is modeled by applying superposition with the appropriate coordinate transformations. From a practical standpoint, the present analysis allows the limitations of spherical lenses to be determined while providing the information required to optimize the lens design. A system was built based on the new design data, and its measured radiation characteristics are compared to the theoretical predictions. Excellent agreement is observed in most cases     

Combined statistical study of joint angles and ground reactionforces using component and multiple correspondence analysis

The purpose of this research is to propose a general methodology to draw gait patterns when including hip, knee and ankle angle excursions in the sagital plane and the three components of the ground reaction force. The multidimensional signal analysis procedure is divided into three main stages: 1) describing the six signals of each step through sliding averages computed for successive time windows, 2) analyzing separately the six step-by-window tables obtained for each signal through principal component analysis to reduce the excessive quantity of data, and 3) analyzing the most informative time windows of the six signals at the same time. To emphasize both linear and nonlinear relationships between the respective time windows, the signal range within a window is cut into fuzzy modalities such as, “low” “medium” and “large.” The resulting table is investigated using multiple correspondence analysis. The outcomes are gait patterns combining both time and space aspects. The factor planes obtained from multiple correspondence analysis constitute initial data models so that new data obtained from pathological gait can be directly projected onto them. Such an operation can be used to show how the rehabilitation of a particular subject evolves in relation to normal gait patterns     

Experiments on hot electron noise in semiconductor materials forhigh-speed devices

Experimental results on noise temperature and spectral density of current fluctuations (electron diffusion) at high electric fields in silicon, gallium arsenide, and indium phosphide are presented. The dominant noise sources are discussed in their relation to electron scattering mechanisms. Physical backgrounds of high speed-low noise performance (noise-speed tradeoff) are considered. Suppression in short samples of the fluctuations having long correlation time constant and (or) high threshold energy is discussed     

Dielectric measurements using a rational function model

A recently proposed rational function model for the aperture admittance of 50 ohm Teflon filled coaxial lines in contact with a homogeneous dielectric is experimentally validated. A calibration technique of the automatic network analyzer utilizing standard terminations and time domain gating is used. Uncertainties in the dielectric properties of reference liquids do not enter the calibration procedure. Experimental results for water and methanol are compared with estimated values. A model expression for the sensitivity of the probe is validated. The sensitivities of two coaxial line probes for the measurements made are determined. Results obtained using the new model are compared with those of other workers     

The effect of compensating faults models on NMR system reliability

Realistic estimates of the reliability of systems with N-tuple modular redundancy (NMR), must consider the effect of compensation of logic faults. Earlier analyses that include compensating faults are impractical to use, yield very complex mathematical formulas for reliability indices, and/or concern the simplest triple modular redundancy (TMR) system only. This paper gives a general approach to the problem. Two models of compensating faults are considered. For either model the lower and upper bounds on frequency of compensating faults are found. By applying some results of NMR system evaluation, the new estimates of upper and lower bounds of NMR system reliability with respect to compensating faults are derived. A simple algebraic form of the final results makes them useful     

Describing collaborative forms: a profile of the team-writingprocess

The paper examines collaborative writing practices students in the Air Force Institute of Technology's Graduate School of Logistics and Acquisition Management use to produce team-authored theses. In analyzing how student writing teams plan, execute, and assess writing activities, the researchers identify and describe some of the forms that collaboration takes, thereby successfully connecting their work within a broader research continuum concerning collaborative writing, particularly when applied in academic settings     

Traffic routing in the Warsaw metropolitan network: a deploymentstrategy

The Warsaw metropolitan network is undergoing a radical architectural and technological transformation. The transformation, forced by the large unrealized demand for telephone stations, and structural traffic bottlenecks, is based on the installation of eight digital transit switches of high capacity. The so-formed upper transit layer gives an opportunity for the deployment of an efficient traffic routing system, for carrying the growing traffic well beyond the year 2000 without additional investments. A step-wise strategy is presented far the deployment of a modern traffic routing system in the Warsaw network, adapted to, and taking advantage of the fast transformation of the network. The choice of the strategy is based on a case study of the traffic handling efficiency of various routing systems in a model of the Warsaw metropolitan network