Structural evolution of alumina supported Mo-W carbide nanoparticles synthesized by precipitation from homogeneous solution

The synthesis of alumina-supported Mo-W carbide nanoparticles from the propane carburization of precursor metal sulphide, itself, obtained via precipitation from homogeneous solution (PFHS) has been investigated. Carburization temperature and time as well as the temperature-composition and time-temperature interaction effects were also found to be important determinants of the BET surface area, pore volume, surface chemical nature and extent of carburization. Thermogravimetry revealed that the metal sulphide conversion proceeds via a two-stage process involving substitutionary reaction in which S atom is replaced with carbon atom in the metal lattice. SEM images also confirmed that although temperature is detrimental to high surface area, the presence of spherical nanoagglomerates (25-35 nm) is indicative of the high dispersion offered by precipitation from homogeneous solution.     

Resonant cavity-enhanced mercury cadmium telluride detectors

The next-generation mercury cadmium telluride (HgCdTe) detectors will need to be able to spectrally resolve images to a degree far exceeding that currently available in two or even three color techniques. However, narrow, spectral pass bands will result in very low photon flux impinging on a detector. This paper investigates the use of resonant cavity-enhanced (RCE) detectors as a means of improving signal-to-noise performance of narrow spectral-width infrared (IR) detection systems.     

A PSpice circuit model for low-pressure gaseous discharge lampsoperating at high frequency

A simple, but accurate, PSpice circuit model simulating the electrical characteristics of low-pressure gaseous discharge lamp operating at high frequency is proposed. The model is constructed from a two-parameter equation and is suitable for computer simulation and analytic derivation in a preliminary design of electronic dimming ballasts. Simulated and measured results are used to verify the theoretical discussion     

Defects at center P underlie diabetes-associated mitochondrial dysfunction

Detailed respiration studies on isolated liver mitochondria from streptozotocin-induced diabetic Sprague-Dawley rats revealed a disease-associated decrease in the ADP/O ratio, a marker for mitochondrial ability to couple the consumption of oxygen to the phosphorylation of ADP. This decrease was observed following induction of respiration with glutamate/malate, succinate, or duroquinol, which enter the electron transport chain selectively at complexes I (NADH dehydrogenase), II (succinate dehydrogenase), or III (cytochrome bc1 complex), respectively. These data, coupled with studies using respiratory inhibitors (most importantly antimycin A and myxothiazol), localize at least a portion of this defect to a single site within the electron transport chain (center P in the Q-cycle portion of complex III). These results suggest that liver mitochondria from diabetic animals may generate increased levels of reactive oxygen species at the portion of the electron transport chain already established as the major site of mitochondrial free radical generation. The reduction in the ADP/O ratio occurred in mitochondria that do not have overt defects in the respiratory control ratio or in State 3 and State 4 respiration. The data in this paper suggest that defects in center P of the electron transport chain likely increase mitochondrial exposure to oxidants in the diabetic. This data may partially explain the evidence of altered exposure and/or response to reactive species in mitochondria from diabetics. This work thus provides further clues to the interaction between oxidative stress and diabetes-associated mitochondrial dysfunction.     

Influence of femoral lengthening on hip joint space in posttraumatic femoral shortening

AIMS: To objectively assess the psychological and psychosexual morbidity of patients with vulvar vestibulitis. METHODS: 30 patients with variable degrees of vulvar vestibulitis were recruited from a vulval clinic. Each patient underwent a detailed history and clinical examination. Friedrich's criteria were used for the diagnosis of vulvar vestibulitis. Standardised questionnaires to assess psychological and psychosexual function were completed by the patient before review. These questionnaires were the STAI and a modified psychosexual questionnaire introduced by Campion. RESULTS: Patients experienced considerable psychological dysfunction compared with controls. All aspects of psychosexual dysfunction were affected. CONCLUSIONS: When managing patients, psychosexual and psychological issues must be considered in addition to other conventional types of therapy. Vulvar vestibulitis may be a risk factor for developing psychosexual complications including vaginismus, low libido, and orgasmic dysfunction. Consideration of these factors must be an integral part of the management of patients with all chronic vulval conditions.     

Partial adaptive nulling on a monopulse phased array antenna system

A partial phase-only nulling (PPON) algorithm has been developed and evaluated on a 496-element monopulse phased array antenna system which employs five-bit phase shifters. Using this PPON algorithm allows nulls in the far-field pattern to be steered to the desired directions for a phased array equipped with low-resolution phase shifters to perform simultaneous nulling in the sum and two difference patterns in the environment of multiple jammers. Simulated and experimental patterns are illustrated     

ECVBA traffic‐smoothing scheme for VBR media streams

We propose an effective and efficient traffic‐smoothing called the efficient changes and variability bandwidth allocation (ECVBA) scheme. This algorithm not only minimizes the peak rate of a stream but also increases the likelihood of successful VBR stream transmission. The main benefit is that it can immediately release bandwidth to other sites in the network. Copyright © 2002 John Wiley & Sons, Ltd.     

Motionless mixers for the design of multitubular polymerization reactors

Experimental investigations of thermal bulk polymerization of styrene in pilot plants of different sizes have been performed. Each pilot plant is composed of a tubular recycle reactor, connected in series with a tubular reactor, both completely filled with Sulzer motionless mixers. Kinetic, reactor and viscosity models have been verified in a wide range of styrene conversions (up to 96%) temperatures (up to 210 °C) and polystyrene molar masses (up to 360 000). Scale-up studies were carried out which confirmed that multitubular reactors of special design can be applied for industrial polymerization process.     

A novel process for fabricating electrical contact SnO<Subscript>2</Subscript>/Ag composites by reciprocating extrusion

Reciprocating extrusion combined with simple powder compaction was used to produce electrical contact SnO₂/Ag composites from Ag and SnO₂ powders with improved properties. The SnO₂ particles were uniformly dispersed in the Ag matrix after 20 passes of extrusion. The hardness of the composites increased with extrusion passes and leveled off after ten passes, whereas the electrical conductivity decreased slowly after five passes. The variation of the coefficient of thermal expansion with temperature revealed that SnO₂/Ag interface strength increased with extrusion passes and was greatest after 20 passes. The SnO₂/Ag composites with 20 passes showed the best electrical contact properties in which there was no mass loss through mass transfer from cathode to anode during the make-break erosion test at both low and high current conditions. On the other hand, SnO₂/Ag composites with one pass and commercial SnO₂-In₂O₃/Ag specimens had an apparent mass loss under the same condition. Electrical contact composites produced by the present method are promising in electrical contact applications in consideration of cost and performance.