Transfer Functions of the Slip-Controlled Induction Machine

The use of a feedback loop to regulate the slip frequency of an inverter-driven induction machine is viewed as replacing the normal independent control of stator frequency with independent control of slip frequency. For steady-state conditions the two modes of operation are shown to produce characteristics analogous to shunt and series dc machines. A method employing closed-form transfer functions, a reduced set of nondimensional parameters, and a general root locus diagram is used to present the dynamic characteristics of controlled slip frequency operation and to compare performance with conventional operation. The parameter range in the general diagram is sufficient to incorporate nearly all standard induction machines over a wide size and frequency range. The results demonstrate that the ratio K? of the rotor transient time constant to the static electromechanical time constant is a critical parameter in the comparison of the two modes. Since this parameter tends to increase with machine size, the relative advantages of slip frequency control are shown to be machine-size dependent. Inclusion of a speed-control loop regulating machine voltage is also Considered and shown to be described by the same general root loci. The performance of this closed-loop system is also shown to be very dependent on K? and hence on machine size.     

User Interfaces for Complex Engineering Software: Application of Virtual Reality

IT systems for engineers are becoming more numerous and complex and will further proliferate in the future. It is infeasible to expect users to be trained to work with a plethora of systems, especially as many of them will only see occasional use. Therefore, in the near future, systems will need user interfaces that allow intuitive access and usage. This paper examines a new style of user interface based on virtual reality.     

Raman line imaging for spatially and temporally resolved mole fraction measurements in internal combustion engines

An optical diagnostic system based on line imaging of Raman-scattered light has been developed to study the mixing processes in internal combustion engines. The system permits multipoint, single laser-shot measurements of CO(2), O(2), N(2), C(3)H(8), and H(2)O mole fractions with submillimeter spatial resolution. Selection of appropriate system hardware is discussed, as are subsequent data reduction and analysis procedures. Results are reported for data obtained at multiple crank angles and in two different engine flow fields. Measurements are made at 12 locations simultaneously, each location having measurement volume dimensions of 0.5 mm x 0.5 mm x 0.9 mm. The data are analyzed to obtain statistics of species mole fractions: mean, rms, histograms, and both spatial and cross-species covariance functions. The covariance functions are used to quantify the accuracy of the measured rms mole fraction fluctuations, to determine the integral length scales of the mixture inhomogeneities, and to quantify the cycle-to-cycle fluctuations in bulk mixture composition under well-mixed conditions.     

Free radicals in γ-irradiated PETN

An EPR investigation of-irradiated PETN (Pentaerythritol Tetranitrate) was conducted. Low temperature irradiation accumulates at least two different radicals. The more stable radical is the NO₂ radical presumably produced by photon cleavage of the NO₂ groups and/or by radical reactions in excited states resulting in detached NO₂. The spectrum of the more reactive radical is obtained by computer substraction. Decay kinetics are proposed for the NO₂ and the unknown highly reactive radical.     

"Productivity in publication and the quality of psychology departments": Reply to Schaeffer and Sulyma.

Responds to comments by D. L. Schaeffer and I. M. Sulyma (1979) on W. M. Cox and V. Catt's (see record 1978-21651-001) article on publication productivity by psychology departments. The article by Cox and Catt was an attempt to derive one index of productivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trajectories leading to school-age conduct problems.

The present study applied a semiparametric mixture model to a sample of 284 low-income boys to model developmental trajectories of overt conduct problems from ages 2 to 8. As in research on older children, 4 developmental trajectories were identified: a persistent problem trajectory, a high-level desister trajectory, a moderate-level desister trajectory, and a persistent low trajectory. Follow-up analyses indicated that initially high and low groups were differentiated in early childhood by high child fearlessness and elevated maternal depressive symptomatology. Persistent problem and high desister trajectories were differentiated by high child fearlessness and maternal rejecting parenting. The implications of the results for early intervention research are discussed, with an emphasis on the identification of at-risk parent-child dyads. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Three-Dimensional Modeling of Thermohydrodynamic Lubrication in Slider Bearings Using Streamline Upwind Petrov-Galerkin Method

A three-dimensional thermohydrodynamic lubrication model which couples the Reynolds and energy equations is developed in the finite-element program Sepran. The model uses the streamline upwind Petrov-Galerkin method. Model results indicate the peak temperature is not on the mid-plane surface. This position shifts toward the mid-plane as the width-to-length ratio is reduced from 10 to 1 as well as when pressure boundary conditions are altered in such a way that the inlet/outlet pressure is higher than the side pressure. The adiabatic temperature profiles of an infinite slider and a square slider are compared. The wider slider shows a higher peak temperature. The side flow plays a major role in determining the value and position of the peak temperature. Model results also indicate peak side flow at a width-to-length ratio of 2.     

High quality gate dielectrics formed by rapid thermal chemical vapor deposition of silane and nitrous oxide

In the present study, we have performed electrical characterization of oxides deposited via rapid thermal chemical vapor deposition using SiH₄ and N₂O. We have investigated the effect of temperature, pressure, and SiH₄ to N₂O ratio on the electrical and material properties of as-deposited films. We have found that as-deposited oxides deposited at low temperatures, low pressures, and with a low silane to nitrous oxide ratio of ～0.5% give good material and electrical properties. The as-deposited films are stoichiometric in nature and have high deposition rates. As-deposited films had very low D_it values, high breakdown fields, and excellent subthreshold swing. The leakage currents and metal oxide semiconductor field effect transistor current drive, although lower than thermal oxides, were found to be quite acceptable. We have also investigated the thickness dependence of the films and found that as the film thickness is reduced below 50Å, the reliability improves for all oxides including the silicon-rich deposited oxides.