Robust Torque Control of Switched-Reluctance Motors Without a Shaft-Position Sensor

This paper describes a technique for stabilizing the operation of variable-reluctance stepping-motor drives operating without a shaft-position sensor. In such systems there is a trade-off between the system efficiency and the torque margin (or pull-out torque) which depends on the width of the phase conduction pulse width. The scheme described in the paper permits the motor to run in the steady state with both narrow conduction pulse widths and high efficiency. Under transient or overload conditions the conduction pulse width is increased in response to a change in the dc link current, providing an increase in available torque. Tests on a small motor drive have produced a steady-state torque margin of over 300 percent and of 200 percent under step-change conditions.     

High-gain, V-band, low-noise MMIC amplifiers usingpseudomorphic MODFETs

State-of-the-art, 60-GHz, low-noise MMICs based on pseudomorphic modulation-doped FETs, with 0.25-μm×60-μm gates offset 0.3 μm from the source ohmic, are discussed. Single-state low-noise amplifiers (LNAs) exhibited minimum noise figures of 2.90 dB with 4.1 dB of associated gain at 59.25 GHz. Dual-state MMICs had minimum noise figures of 3.5 dB and 10.8 dB of associated gain at 58.50 GHz. Cascaded four-stage LNAs (two dual-stage MMICs) had minimum noise figures of 3.7 dB and over 20.7 dB of associated gain at 58.0 GHz. Finally, when biased for maximum gain, the four-stage amplifier exhibited over 30.4 dB of gain at 60.0 GHz     

A narrow-channel, 0.2-μm gate-length, double-quantum-wellpseudomorphic MODFET with high power gain at millimeter-wave frequencies

State-of-the-art pseudomorphic MODFETs were developed with metallurgical gate lengths between 0.22 and 0.25 μm, very short source-to-drain spacings of 0.7 μm, and a double-quantum-well material structure. S-parameter measurements were performed on these 60-μm gate-width devices up to 40 GHz. From these S-parameter measurements, an extrapolated value of 82 GHz was estimated for F_t. Modeling of the power gain as a function of frequency indicates that F_max may be as high as 305 GHz     

Role of a Historian in a Database Management System

Traditionally, a database manager tracks only transactions — an insufficient way to maintain a complete history. This multilevel system tracks three history levels: character, transaction, and global action.     

Dynamic analysis of a crack-arrest specimen

Under pressurized thermal shock (PTS) loading conditions arrest of running cracks at temperatures that range up to or above those corresponding to the onset of Charpy upper shelf is of particular interest. Only few crack arrest toughness (K_Ia) data above 200 MPa√m obtained from rather expensive PTS-experiments and wide-plate tests are available. In the present paper the capabilities of a relatively small panel crack arrest specimen for yielding K_Ia data in excess of 200 MPa√m under conditions of a rising K_I-field are investigated. For this purpose static and dynamic finite element analyses are performed. It is shown that dynamic effects cannot be neglected for this specimen type and K_Ia-values up to about 300 MPa√m can be expected from measurements in suitably conducted experiments.     

Predicting unit performance by assessing transformational and transactional leadership.

How do leadership ratings collected from units operating under stable conditions predict subsequent performance of those units operating under high stress and uncertainty? To examine this question, the authors calculated the predictive relationships for the transformational and transactional leadership of 72 light infantry rifle platoon leaders for ratings of unit potency, cohesion, and performance for U.S. Army platoons participating in combat simulation exercises. Both transformational and transactional contingent reward leadership ratings of platoon leaders and sergeants positively predicted unit performance. The relationship of platoon leadership to performance was partially mediated through the unit's level of potency and cohesion. Implications, limitations, and future directions for leadership research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanism of brain protection by nitroxide radicals in experimental model of closed-head injury

Reactive oxygen-derived species were previously implicated in mediation of post-traumatic brain damage; however, the efficacy of traditional antioxidants in preventing/reversing the damage is sometimes limited. The present work focused on the mechanisms underlying the neuroprotective activity of cell permeable, nontoxic, antioxidants, namely stable nitroxide radicals in an experimental model of rat closed-head injury. Brain damage was induced by the weight-drop method and the clinical status was evaluated according to a neurological severity score at 1 h and 24 h, where the difference between these scores reflects the extent of recovery. The metal chelator deferoxamine as well as three nitroxide derivatives, differing in hydrophilicity and charge, and one hydroxylamine (a reduced nitroxide) facilitated the clinical recovery and decreased the brain edema. The nitroxides, but neither the hydroxylamine nor deferoxamine, protected the integrity of the blood-brain barrier. Superoxide dismutase also improved the clinical recovery but did not affect brain edema or the blood-brain barrier. The results suggest that by switching back and forth between themselves, the nitroxide and hydroxylamine act catalytically as self-replenishing antioxidants, and protect brain tissue by terminating radical-chain reactions, oxidizing deleterious metal ions, and by removal of intracellular superoxide.     

Celiac disease

Celiac disease, or gluten-sensitive enteropathy, classically presents as diarrhea and weight loss in childhood, but it may also have protean manifestations and appear well into adult life. The increasing availability of noninvasive blood tests that are highly sensitive and specific for celiac disease enables primary care physicians to recognize the disorder in a wide variety of clinical situations. The authors believe that the disease is more common than supposed and thus offer this diagnostic review to increase awareness.     

Terminology and classification of UHF installations (under discussion)

Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 1, pp. 9–10, January, 1990.