A planar integrated RCD snubber/voltage clamp

In order to reduce the cost, size, and weight of power electronic systems, it has become necessary to integrate electromagnetic structures, which until now have been constructed with discrete components. This approach not only reduces the component count, but also gives much greater control over parasitic elements. In this article, the authors describe an electromagnetically integrated resistor-capacitor-diode (RCD) snubber/voltage clamp that uses a planar construction technique. The design and construction are described and the performance is verified experimentally. Some advantages of the integrated component over its discrete counterpart are also given     

Bestimmung der Abtragungsraten von Zirconium,Tantal und der Legierung Tantal-40Niob in fluoridhaltiger azeotroper Salpetersäure mit Hilfe der Radiotracer-Methode

The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10^?6 to 5 · 10^?4 mm/y, for tantalum: 10^?8 to 4 · 10^?6 mm/y, and for the Ta-40Nb alloy: 2 · 10^?7 to 8 · 10^?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F^? and at a temperature of 108°C, corrosion rates between 5.3 · 10^?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10^?3 mm/y at 50°C/280 ppm F^? and 1.4 · 10^?2 mm/y at 110°C/320 ppm F^?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing.     

Primary prevention of malignant melanoma in the Stockholm Cancer Prevention Programme

The relation between intracoronary thrombus and endothelin-1 (ET-1) was studied. In a canine model, acute myocardial infarction (MI) was induced by coronary occlusive thrombus produced at a mock atheromatous plaque. Blood samples were collected from the aorta (A) and coronary vein (V). Twenty-eight open-chest dogs divided into three groups were studied. Group I (n = 15): acute MI was induced by coronary occlusive thrombus, and thrombolysis was obtained by urokinase two hours after MI. Group II (n = 8): nonocclusive thrombus was produced without inducing MI. Group III (n = 5): coronary artery was ligated for two hours and reperfused by release of ligation. In Group I, ET-1 was significantly increased after MI in A and V, and ET-1 in V was significantly more elevated than in A during thrombolysis, suggesting ET-1 production in the coronary vessels by thrombolysis. In Group II, ET-1 increased slightly during thrombus formation, but there was no difference in A and V. In Group III, ET-1 was elevated significantly after MI without A and V difference. These results indicate that there is no detectable ET-1 production with coronary thrombus formation, whereas coronary ET-1 production is detected during thrombolysis, most probably because resolved thrombus releases a more potent stimulus to ET-1 production.     

Non-invasive assessment of magnitude and dispersion of atrial cycle length during chronic atrial fibrillation in man

AIMS: Atrial fibrillation cycle lengths can be assessed from right precordial ECG leads and the unipolar oesophageal ECG using a non-invasive method called Frequency Analysis of Fibrillatory ECG. The purpose of this report is to present the results from application of this method in a large group of patients with long-term atrial fibrillation and to examine the differences between patients with 'coarse' and 'fine' atrial fibrillation. METHODS AND RESULTS: Simultaneous 15 min recordings from V1, V2 and an oesophageal lead at a position behind the posterior atrium were obtained in 28 patients, aged 41 to 78 years, with long-term (> 1 month) atrial fibrillation. In each lead, using the time averaging technique, the QRST complexes were suppressed. Thereafter, the frequency distribution of the residual ECG was estimated by means of Fast Fourier Transform. In the 3-12 Hz range of each lead, the dominant atrial cycle length, the power maximum and the spectral width were calculated. In 26 patients (93%), frequency spectra in the 3-12 Hz range could be obtained. The dominant atrial cycle length ranged from 120 to 175 ms, mean 150+/-16 (SD) ms in V1, and from 120 to 190 ms, mean 150+/-16 in an oesophageal lead (ns). The absolute difference in the dominant atrial cycle length between V1 and the oesophageal lead was 10.4+/-7.7 ms. There was no significant difference in the dominant atrial cycle length in V1 between patients with coarse and fine atrial fibrillation. The power maximum in V1 was significantly greater in patients with coarse compared to fine atrial fibrillation (P=0.01). The spectral widths ranged from 10 to 55 ms and demonstrated significantly higher mean values in lead V2 compared to V1 (P=0.001). Compared to V1, the mean values tended to be smaller in the oesophageal lead (P=0.05). CONCLUSIONS: Using the Frequency Analysis of Fibrillatory ECG method, the dominant atrial cycle length, power maximum and spectral width can be estimated from the frequency spectra in the majority of patients with atrial fibrillation. Spatial dispersion of the dominant atrial cycle length occurs in some patients and may be an important proarrhythmic marker. The distinction between coarse and fine atrial fibrillation cannot be used as a marker of the atrial cycle length.     

Evaluation of the clinical impact of endoscopic ultrasonography in gastrointestinal disease

A total of 120 gastro-intestinal tracts and 960 faecal samples were examined to assess the prevalence and seasonal changes in the gastro-intestinal helminth parasites of Red Sokoto (maradi) goats slaughtered at Ibadan between May 1991 and April 1992. Egg types of strongyles, Strongyloides, Trichuris, Skrjabinema, Dicrocoelium and Moniezia were encountered in 93%, 83%, 44%, 0.9%, 2.3% and 31% of the faecal samples respectively. However, only strongyle, Strongyloides and Trichuris eggs occurred in large numbers and were more common during the rainy season than in the dry season. The parasites recorded and their prevalences were Haemonchus contortus (90.0%), H. ovis (5.0%), Strongyloides papillosus (80.8%), Trichostrongylus colubriformis (78.3%), T. axei (69.2%), Trichuris ovis (72.5%), T. globulosa (38.3%), Oesophagostomum columbianum (67.5%), Cooperia curticei (58.3%) Gaigeria pachyscelis (40.8%), Skrjabinema ovis (5.0%), Nematodirus battus (5.8%), Moniezia expansa (29.2%), M. benedeni (10.0%), Paramphistomum spp. (5.0%) and Cysticercus tenuicollis (33.3%). Haemonchus ovis is reported for the first time in Nigeria. Mixed infections were most prevalent. Young goats were more commonly infected and had higher worm counts than adult goats. Only Haemonchus, Trichostrongylus, Strongyloides and Cooperia spp. occurred in large numbers. Irrespective of the age of the goats, higher worm counts were generally encountered during the rainy season than in the dry season. The results are discussed in relation to the control of helminthiasis in grazing animals in Nigeria.     

Single photon emission computed tomographic blood flow and magnetic resonance volume imaging of basal ganglia in Huntington''s disease

During oogenesis in Drosophila, germ cells appear in sequential clusters of 16 interconnected cells. The events surrounding the differentiation of these cells are not fully understood. Here we present genetic and morphological analysis of mutations in the gene stand still (stil). Through complementation analyses we have refined the location of this gene to cyological region 49B-C. Our analyses of ovaries from ethylmethane sulfonate (EMS)-induced mutant alleles of this gene suggest that mutations in the stil gene produce a wide range of phenotypic abnormalities, from the absence of germ cells in the most severe alleles, to egg chambers with cytoskeletal defects in the less severe alleles. Our results suggest a role for this gene in specifying or maintaining a cytoskeletal component, with consequences during oogenesis and possibly during germ line sex determination.