ON STABILITY AND PERFORMANCE OF INDUCTION MOTOR SPEED DRIVES WITH SLIDING MODE CURRENT CONTROL

A novel inner loop sliding mode current control scheme for induction motor speed drives is proposed in this paper. The controller design is based on the nonlinear mathematical model of an induction motor in a coordinate system oriented along the rotor flux. The parameters of the PI speed controller are taken into consideration in the inner loop sliding mode current control. Rigorous stability verification for the overall system is provided in this paper. The chattering in sliding mode control is attenuated using the reaching law design method. The experimental results show that the proposed approach exhibits robust tracking performance in the presence of motor parameter variations and load disturbances.     

Expectancy factors in the treatment of fear: Methodological and theoretical issues.

Critically reviews the literature assessing the importance of Ss' expectation of therapeutic gain in facilitating fear reduction. Reviewed studies fall into 2 major categories: those that compare the relative efficacy of systematic desensitization and placebos and those that attempt to manipulate Ss' expectation of therapeutic gain within a particular technique (e.g., systematic desensitization). The methodological problems with this research include the failure of investigators to evaluate the experiential impact of expectancy-inducing instructions, the use of unconvincing placebo manipulations, and the predominant employment of mildly fearful, poorly motivated Ss. In spite of these problems, it is tentatively concluded that expectancy manipulations are important change mediators. Several mechanisms may explain how expectancy mediates change, including increased compliance with real treatment procedures; increased tendency to test reality after having undergone an "effective" therapy, with subsequent fear extinction and self-reinforcement for behavioral improvement; modification of demand characteristics after treatment; and modification of cognitive events controlling fear responding. (71 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of strip-fed cavity-backed slots

The use of strip-fed cavity-backed slots is an attractive approach for compact conformal antenna arrays. This configuration also offers greater potential than traditional designs for additional antenna functions demanded by high-performance system requirements. As with previous approaches, it is desirable to avoid costly, time-consuming empirical design techniques, which in turn requires highly accurate analytic/numerical models. A full-wave integral equation analysis is presented, which by using the dyadic Green's functions for multilayered substrates, models this array element with a high degree of accuracy. Using a previously presented Green's function for a grounded slab, the analysis also accounts for dielectric-covered slots. Comparisons are made with measurements to validate the results     

Expectancies in therapy research: Interpretive artifact or mediating mechanism?

W. Wilkins (see record 1980-01498-001), in his critique of client expectancy, concludes that expectancy is a questionable interpretive artifact for the effectiveness of therapy. The authors disagree with much of Wilkins's analysis, which they say confuses attempts to demonstrate effectiveness with attempts to explore theoretical mechanisms. It is their view that expectancy is a viable alternative explanation for the effectiveness of therapy. Contrary to Wilkins's assertion, it is argued that systematic desensitization, as an exemplar of therapy, has not been demonstrated to be superior to equally credible, observable manipulations of expectancy. Further contributions to treatment technology will require a detailed analysis of how expectancy manipulations mediate improvement. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

External validity of laboratory fear assessment: Implications from two case studies.

Exposed 1 snake-phobic woman and 1 spider-phobic woman to a live snake or spider after they received systematic desensitization. In one assessment condition the 2 Ss were asked to approach and handle a caged snake or spider as in the traditional behavioral approach test, whereas in the other condition the Ss were exposed to the uncaged phobic stimuli. Both Ss manifested substantially greater physiological and cognitive distress while looking at the uncaged stimuli from a distance of 30 ft than when actually touching the caged snake or spider. Although both Ss were able to touch the caged snake or spider, they still reported being unable to engage in behaviors that were previously inhibited because of their phobia. Both Ss emphasized the importance of feeling in control when the phobic stimulus was caged but feeling out of control when the phobic stimulus was uncaged. Implications for the external validity of the behavioral approach test are discussed. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relaxation training and attention placebo in the treatment of severe insomnia.

Compared the effectiveness of progressive relaxation training with and without a supplementary relaxation recording, which Ss played at home, and an attention placebo manipulation in the modification of severe insomnia. Ss were 40 29-72 yr old insomniacs recruited through newspaper ads. Assessment measures included sleep postcards mailed in by the Ss, the MMPI Pt , D , and K scales, ratings of the therapist by Ss, and physiological recordings (EKG, skin conductance, and respiration). The relaxation training procedures were significantly more effective than placebo and no-treatment controls in modifying several parameters of sleeping behavior, reducing consumption of sleep-inducing medication, and influencing self-reports of anxiety. The supplementary relaxation tape did not increase the effectiveness of relaxation training conducted in the clinic, and there was no difference in the efficacy of the placebo and no-treatment conditions. Physiological data gathered during the last treatment session indicated few significant correlations between reductions in arousal associated with relaxation training and treatment outcome. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Wave Action and Bottom Shear Stresses in Lake Erie

For Lake Erie, the amplitudes and periods of wind-driven, surface gravity waves were calculated by means of the SMB hindcasting method. Bottom orbital velocities and bottom shear stresses were then calculated using linear wave theory and Kajiura's (1968) turbulent oscillating boundary layer analysis. These calculations were made for south-west and north wind directions and a steady wind speed of 40 km hr^?1. Calculated bottom shear stresses are related to the textural properties of surficial Lake Erie sediments as determined by Thomas et al. (1976). The bottom shear stresses, especially under prevailing southwest wind conditions, control the textural characteristics of surface sediments in Lake Erie. In particular, wave-induced bottom shear stresses are probably the most important energy source for sediment entrainment.     

Application of variable‐structure system in dc‐motor velocity‐control

Abstract

The most important characteristic of variable‐structure system (VSS) is its insensitivity to parameter variations in the sliding mode. In this paper three methods of VSS are used to implement DC‐motor velocity‐control. The conventional VSS uses only a sliding line. The adaptive VSS uses multiple switching lines. The modern method uses a sliding curve. The modern method makes a system trajectory following the sliding curve which has been set up in the controller from the initial state to the origin in the phase plane. Hence it is insensitive to parameter variations from the initial state to the steady state. If parameter variations are the most critical factors, then the modern VSS is the right method to be considered to overcome the problem of parameter variations.     

Torn ascending aorta missed by transesophageal echocardiography

Transesophageal echocardiography has become a commonly used screening tool for traumatic tears of the descending aorta. The role of transesophageal echocardiography for ascending aortic tears is not yet well-defined. We report an ascending aortic tear imaged by aortography but missed on transesophageal echocardiography.     

The Catalytic Activity of Co/ZrO2 for NO Reduction with Propane in O2 Presence

The selective catalytic reduction (SCR) of NO by propane in the presence of excess oxygen was studied on a Co/ZrO₂ catalyst. This system is present as active for the NO reduction to N₂. It was found that the addition of Co could improve the activity and selectivity of propane towards NO_x reduction. The activity depends strongly on the space velocity (GHSV) when the system works with low oxygen concentration and it is independent of the space velocity when the system operates with excess oxygen. The water vapor present in the feed produces deactivation in the catalyst as well as in the support.