Theoretical analysis of acceleration-induced central nervous systemischemia

The mechanism responsible for the +G(z)-induced loss of consciousness (G-LOC) experienced by fighter pilots is investigated. The nature of a G-LOC episode is described formcases of rapid onset. Evidence suggests that the G-LOC mechanism might be closely related to the mechanism for sleep. A theory of G-LOC that treats it as a protective physiological mechanism is proposed.     

Numerical evaluation of dyadic diffraction coefficients andbistatic radar cross sections for a perfectly conducting semi-infiniteelliptic cone

In this paper, the scattering of electromagnetic waves by a perfectly conducting semi-infinite elliptic cone is treated. The exact solution of this boundary value problem in problem-adapted spheroconal coordinates in the form of a spherical multipole expansion is of poor convergence if both the source point and the field point are far away from the cone's tip. Therefore, an appropriate sequence transformation of these series expansions (we apply the Shanks transformation) is necessary to numerically determine the dyadic diffraction coefficients and bistatic radar cross sections (RCS) for an arbitrary elliptic cone. Our far-field data for an elliptic cone, a circular cone, and a plane angular sector are compared with some other results obtained with the aid of quite different methods     

Encoded moire inspection based on a computer solid model

An investigation into a system linking a computer solid modeler to an active stereo imaging inspection station is presented. Given the computer solid model of a surface, a projected pattern can be encoded so that the reflections from the object's surface exhibit a uniformly simple pattern when the object's surface and the modeled surface are identical. Research concerning the method of generating projection patterns, as well as the sensitivity of the system, is discussed. A prototype system consisting of a computer graphics workstation; a flexible projector, and a machine vision system was used to inspect two different manufactured parts     

The free vibration of skew plates using the hierarchical finite element method

The hierarchical finite element method is used to determine the natural frequencies and modes of flat, isotropic skew plates. A number of such plates with different boundary conditions—including free edges and point supports—are considered in this paper. The dependence of frequency on skew angle, aspect ratio and Poisson's ratio is investigated, though succinctness prohibits a complete study exploring the full interrelation of these parameters. Extensive results are presented in diagrammatic, graphical, and tabular format; these are shown to be in very good agreement with the work of other investigators, and should prove a valuable source of data for use by engineers and scientists.     

Analytic physics-based expressions for the empirical parameters ofthe Statz-Pucel MESFET model

The authors present a novel approach to the evaluation of the DC parameters of a semiempirical MESFET model: starting from the analytical expression of the drain current derived from a previously proposed physics-based model, they provide a method to calculate the empirical DC parameters of the so-called Raytheon model. The comparison between computed and measured DC characteristics is quite satisfactory on GaAs microwave FETs of 1 μm 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     

Histologically confirmed changes on CT of reoperated low-grade astrocytomas

During a 15-year period 37 patients with primary low-grade astrocytoma have been operated upon twice in our institute. CT and histological data at the time of the first and second operations were compared. The majority of primary astrocytomas showed as a low-density area without contrast enhancement; minimal, mainly marginal enhancement was present in six cases. At reoperation 10 tumours were histologically unchanged; the corresponding CT studies displayed a nonenhancing lesion, although insignificant contrast uptake could be seen in three cases. There were 18 tumours which had transformed into anaplastic astrocytoma: CT before repeat surgery showed more or less marked enhancement. In all nine cases which progressed into glioblastoma multiforme strong contrast enhancement was seen on CT at the time of recurrence. Although the grade of contrast uptake varied, the appearance of or increase in enhancement was a sign of some degree of anaplastic change, particularly convincing in cases of dedifferentiated glioblastoma multiforme.