Standstill frequency response testing and modeling of salient-polesynchronous machines

Standstill frequency response (SSFR) testing and modeling of salient-pole synchronous machines are presented for two machines with integral and nonintegral numbers of stator slots per pole per phase. Frequency responses at different rotor positions have been investigated to explore the effects of rotor position in a machine with a fractional slot winding, as the electromagnetic fields and the armature magnetomotive forces do not precisely repeat every pole. The test results do not show any significant differences for various direct and quadrature axes rotor positions. The authors obtained a negative value of differential leakage inductance as theoretically postulated in the literature. The pertinent features of testing and modeling of salient-pole synchronous machines are described to point out the differences with SSFR testing of round rotor turbogenerators extensively published in the literature     

Simulation of the Viscous Sintering of Two Particles

The viscous sintering of two initially spherical particles is modeled as creeping flow in response to surface tension. The governing equations are solved using the finite-element method. The condensed results of this simulation, the center-to-center approach velocity, and the rate of change of contact area were presented earlier. Some details of the flow field during sintering and the evolution of the neck geometry in the early stages of sintering are presented here. Important numerical issues are detailed.     

Short-wavelength GaInNAs/GaAs semiconductor disk lasers

The use of GaInNAs/GaAs as an alternative active material to InGaAs/GaAs for semiconductor disk lasers with Watt-level emission in the 1160?1210 nm wavelength range is reported.     

Empirical issues in theoretical psychology: Comment on Kukla.

It is far from clear that A. Kukla's (see record 1989-24526-001) vision of a discipline concerned with the rigorous development and analysis of psychological theory could be realized in a completely nonempirical theoretical psychology. This issue is discussed in terms of Kukla's treatment of artificial intelligence and his call for the development of theoretical and empirical psychology as distinct disciplines. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

High-temperature electron mobilities in LPE-Grown GaP

We report measurements to 500°C of resistivity and Hall mobility in Sn-doped, n-type GaP grown by liquid phase epitaxy. Samples with room-temperature carrier densities between 1 × 10¹⁶ and 1 × 10¹⁸cm⁻³ were studied. Mobilities were in the range 100–180 cm²/V-sec at room temperature and in the range 27–35 cm²/V-sec at 400°C. Carrier densities increased by only about a factor of two with increasing temperature. Theoretical fits to the mobility data were made by considering contributions from intervalley, polar-optic, acoustic-deformation-potential, and ionlzed-impurity scattering mechanisms. Our results confirm the utility of GaP for high-temperature device applications and provide important information on electrical parameters needed for device modeling and design.     

Hypervelocity penetration of concrete

Experiments have been conducted with 6.25 mm diameter tungsten rods striking concrete at 2.2 km/s. Three concretes were used—one was 2.35 g/cm³ and the other two were 2.27 g/cm³. The erosion rates were measured to be T/ΔL = 2.4–3.1 depending on the density of the concrete. This is greater than the hydrodynamic value, which shows that the strength of the penetrator is affecting the penetration. The cratering efficiency was computed (which included surface spall) and was found to be commensurate with the strength of the concrete, 28–34 MPa. CTH calculations were conducted using the brittle fracture kinetics (BFK) and Holmquist–Johnson–Cook (HJC) material models for concrete. Density in the calculations was 2.25 g/cm³. It was not possible to match erosion rates at 2.2 km/s, which were too high in the calculations. Also, computed crater volumes were much too small, mainly due to spall in the experiments that was not shown in the computations. Another significant inaccuracy of the calculations was the damage extent, which became unrealistically widespread as time increased in the BFK model.     

Continuously synchronised growth

The advent of cell synchrony as a refinement in technique for cultivating microbes has given new dimensions to the study of microbial growth. By wedding synchrony to continuous culture, it becomes possible to convert and resolve the invariant (steady state) performance of asynchronous growth in a chemostat into a recognisable pattern of (cell cycle) activity, which repeats continually and occupies the mean doubling time periods of the cells growing in synchrony in a continuously synchronised culture. In this way, microbial growth and metabolism in a culture can be considered in terms of the individual cell instead of being related to the statistical mean of the cell population. Growth, continuous growth and continuously synchronised growth are considered in relation to these developments and an approach is made to account for the “physiological state”.     

A simple model for determining effects of negative differential mobility and magnitude of saturated velocity on the performance of Schottky-barrier field effect transistors

The effects of nonuniform fields in the channel of GaAs MESFETs, and the resulting range of velocities with which carriers drift, are here considered using a simple model in order to determine the effects of negative differential mobility and saturated velocity on the performance of these devices, and of devices made of other materials. On the basis of the equilibrated velocity-field ν(E) characteristic for GaAs, carriers in short-channel FETs drift over much of the source to drain length with the saturated high field velocity, i.e. a velocity about half that used in most previous analytical solutions for GaAs FETs, and one about equal to the maximum carrier velocity in Si. Neglecting transient effects in electron transport, fields at which a negative differential mobility occurs exist over only a very small portion of the channel. The value of low field mobility of the MESFET material is therefore important primarily in determining source resistance.