Techniques for minimizing the input current distortion ofcurrent-controlled single-phase boost rectifiers

Techniques for minimizing the input current distortion of current-controlled single-phase boost rectifiers are described. The switching patterns of several boost rectifiers are examined to identify the nature of their input current waveforms. This analysis is used to examine the low-frequency current distortion levels, and hence the power quality, associated with the rectifiers. A PWM (pulse width modulation) strategy that selectively switches between positive unipolar PWM and negative unipolar PWM, called phase-adjusted unipolar PWM, is shown to produce the lowest current distortion levels. A novel two-switch asymmetrical half-bridge rectifier is presented that draws an input current at a unity fundamental power factor and with the same low distortion as obtained with the four-switch H-bridge rectifier. The operation of the various rectifiers is examined with reference to theoretical predictions, circuit simulations, and experimental results. This analysis is used to compare the performances of the various rectifier switching patterns     

The influence of gastrin and/or cholecystokinin antagonists on the proliferation of three human astrocytic tumor cell lines

We have investigated the potential role of gastrin in the regulation of cell growth in human astrocytic tumors. To this end we have used synthetic analogs of gastrin and cholecystokinin (CCK) which behave as gastrin and/or CCK antagonists, e.g. compounds JMV-97, JMV-209 and JMV-179. Their effects on astrocytic tumor cell proliferation was investigated by the use of the colorimetric MTT assay. The in vitro biological models used in the present study included the SW1088, U87 and U373 astrocytic tumor cell lines. The results demonstrated marked influence of gastrin and CCK antagonists in the regulation of astrocytic tumor growth. This suggests that gastrin and/or CCK antagonists might be tested in experimental glioblastoma.     

Optimizing glutaraldehyde crosslinking of collagen: effects of time,temperature and concentration as measured by shrinkage temperature

Glutaraldehyde (GA) crosslinking (fixation) of collageneous tissues is a widely used method for the preparation of implantible tissues to be used as biomaterials. In an attempt to optimize the fixation process, experiments were carried out with two types of collagen (native collagen membrane and synthetic collagen sheet) to study the effect on crosslinking of temperature, GA concentration and fixation time. Secondly, stimulation of GA diffusion was studied and finally, a procedure of low T-presoaking followed by brief exposure to high temperatures was investigated. As a measure of the degree of crosslinking the shrinkage temperature (T _s) was determined. Temperature (20°C or 45°C), concentration (0.1% or 1.0%) or fixation time (4 or 24 h) were found to be positively correlated with the T _s of the collagen sheets. Whereas untanned collagen exhibits a T _s of around 60°C, short-term (1 or 5 min), high-temperature (50°C) fixation with a 0.1% GA solution caused the shrinkage temperature to increase to 72°C and 85.1°C, respectively. Fixation with 0.01% GA for 5 min at 50°C appeared equally effective as 1 min with 0.1% GA (T _s=70°C). Microwave irradiation showed to be slightly more effective in enhancing the crosslinking process compared with conventional heating. Surprisingly, at any combination of temperature, concentration and fixation periods of 4 h or 24 h, an increased T _s towards the central regions of the collagen was observed. Soaking the samples at 20°C (1 h) or at 0°C (3 h) with subsequent short-time heating to 45°C caused an almost equal rise in T _s throughout the collagen samples and is therefore recommended for preparing implantable tissues.     

Vulcan--A versatile high-power glass laser for multiuser experiments

This paper reports the design and characterization of the newly upgraded Nd:glass laser facility at the Rutherford Laboratory. Emphasis is placed on the unusual aspects consequent on its role as a multiuser facility, where reliability and flexibility are of paramount importance. The basic facility configuration is of two high-power laser systems in parallel-a six-beam laser for implosion experiments and a separate high-power single beamline for either X-ray backlighting diagnostics of implosion experiments or use in a separate single-beam target area. Additional flexibility is provided by remotely controlled changeover mirrors enabling groups of amplifiers to be used in different combinations for various energies and shot repetition rates. Either a mode-locked or aQ-switched oscillator can be selected to provide a range of pulse durations from 50 ps to many nanoseconds. Harmonic generation is used routinely to give a choice of wavelengths for different experiments. The six-beam system is normally run at the second harmonic, although the fundamental wavelength is also available, while the single-beam target area can use fundamental, second, or third harmonics.     

Double blind study of vitamin E compared to placebo in the prevention of anemia in the low birth weight infant during the 7th week of life: therapeutic study

Sephadex G-25 (Kernlute test) yields satisfactory results for the identification of infants at risk for BE and for estimation of the bilirubin binding capacity of the serum. In the presence of more than 2 mg/100 ml of conjugated bilirubin, the interpretation of the Sephadex G-25 test requires caution. Gel filtration through Sephadex LH-20 and chloroform elution of the free unconjugated bilirubin not bound to albumin seems to be a useful tool for eliminating interference by conjugated bilirubin, which is not chloroform-extractable.     

IT2000: A critical appraisal of Singapore's state-wide strategic planning process for information technology

In April 1992, the Singapore Government announced its information technology (IT) vision and plan for the next 15 years to turn Singapore into ‘an intelligent island’, providing a strategic regional switching centre for expertise, goods, services and information. At the heart of this plan is a national information infrastructure that would capitalize on information as a key factor of production and an important ingredient for enhancing the quality of life of its people. Code named ‘IT2000’, the plan was developed by 60 senior managers at the National Computer Board in 1991 with participation and inputs from about 200 business and industry leaders, domain experts and academics. This paper describes the background of Singapore's drive into the information age, the IT2000 planning process, the roles of various participants and the main recommendations of the plan. An evaluation of IT2000 is made in terms of its objectives, its unanticipated results and its impacts on industry participants. Implications and lessons are drawn for strategic IT planning at the national or sectoral level.     

Semantic homophone priming in patients with dementia of the Alzheimer's type.

To examine the role of semantic processes in the verbal priming deficits of patients with dementia of the Alzheimer type (DAT), 15 DAT patients, 8 amnesic patients, and 12 controls were administered a homophone spelling bias task. Ss' spellings were biased against their previously preferred homophone spellings by presenting the homophones aurally in a semantically related context. The results showed that DAT patients were not significantly different from controls or amnesic patients on the immediate priming measure. However, both patient groups' semantic priming effects decayed more rapidly and their recognition performance was significantly impaired in relation to those for control Ss. These results suggest that DAT patients can perform normally on some semantic priming tasks if the task demands are within the capacity of the patients' remaining intact semantic structure and if the delay between presentations is brief. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The impact of river regulation on invertebrate communities in the U.K.

The impact of river regulation on invertebrates has received comparatively little attention in the U.K., with most studies concentrating on the effects of impoundment. During dam construction invertebrate diversity and abundance decreases. Longer term alterations in community structure (which usually extend for a relatively short distance downstream) reflect changes in flow, substrate, temperature, and water quality. In particular adverse effects on invertebrates have been attributed to a reduction in substrate heterogeneity together with an accumulation of sediment. Responses to impoundment within and between taxonomic groups are highly variable. In general Ephemeroptera and Coleoptera are reduced. Of the Plecoptera the Perlodidae and Chloroperlidae are more likely to be adversely affected than the Nemouridae or Leuctridae. The impact of impoundment on net-spinning Trichoptera varies with reductions in some populations and enhancement in others. Simuliids are usually restricted, probably because of a lack of suitable oviposition or attachment sites. Freshets released from reservoirs increase the level of invertebrate drift. However, the full consequences of impoundment on drift, recolonization, and upstream migration have yet to be assessed. There is some evidence that modified temperature regimes cause extended egg hatching periods and alter larval growth rates but further studies are needed. Little is known of the effects of inter-river transfers on invertebrates, but it has been suggested that changes in flow velocity, water chemistry, suspended solids, and temperature together with translocation of organisms are all likely to be important. The limited information available for groundwater schemes indicates that they are not detrimental to invertebrates. Their impact, however, is dependent upon factors such as the extent and timing of flow augmentation. It is suggested that there is scope for positive management of invertebrate communities through river regulation, although at present attitudes and practices do not encourage this. Many gaps in our knowledge still remain and these are discussed in relation to future research needs.