适合SMPS应用的thinQ碳化硅肖特基二极管

极管的反向恢复电荷相比,位移电流传递的电荷QC很小。QC和碳化硅肖特基二极管的开关损耗非常低,而且与超快硅二极管损耗大大依赖dI/dt、电流和温度相比,碳化硅二极管基本上与这些因素无关(见图2和3)。与这些参数的关系与硅二极管相比不在一个尺度上。这是由于这种器件的反向电容性特性。应用下面将讨论两个应用实例,主要关注由SiC二极管替代传统二极管所带来的效率和系统优越性。开关电源中的功率因数校正(升压变换器)由于各地制定相应的功率因数标准,世界上对功率因数校正器的需求快速增长。升压变换器通常用来实现功率因数校正,可以工…     

Hydrazidation of fibres based on acrylonitrile copolymers

Conclusions A scheme has been suggested for the catalytic effect of carboxyl groups on the conversion of -CN groups in acrylonitrile copolymers in modification with hydrazine hydrate.It has been shown that the hydrazidation of acrylonitrile copolymers is accompanied by the appearance of stable free radicals, the rate of formation of these correlating with the rate of nitrile group conversion.The suggestion has been made that a three-dimensional chemical network which is formed during hydrazidation aids in stabilizing the radicals.A chemisorptive fibre with anion-exchange groups has been prepared, which has satisfactory physico-mechanical and sorptive properties.Translated from Khimicheskie Volokna, No. 4, pp. 10–12, July–August, 1988.     

Characterization of the large (L) RNA of peanut bud necrosis tospovirus

The nucleocapsids purified from peanut plants systemically infected with peanut bud necrosis virus (PBNV), a member of the genus Tospovirus, contained both viral(v) and viral complementary(vc) sense L RNAs. Defective forms of L RNA containing 'core polymerase region' were observed. The full length L RNA of PBNV was sequenced using overlapping cDNA clones. The 8911 nucleotide L RNA contains a single open reading frame (ORF) in the vc strand, and encodes a protein of 330 kDa. At the 5' and 3' termini of the v sense RNA there were 247 and 32 nt untranslated regions, respectively, containing an 18 nt complementary sequence with one mismatch. Comparisons of the predicted amino acid sequence of the L protein of PBNV with other members of Bunyaviridae suggest that the L protein of PBNV is a viral polymerase. The L protein had highest identity in the 'core-polymerase domain' with the corresponding regions of other tospoviruses, tomato spotted wilt virus and impatiens necrotic spot virus.     

Malignant tumors of the small intestine

Primary malignant tumors of the small intestine are uncommon. The average annual incidence rate over a period of 30 years in Saskatchewan was 0.7 and 0.6 per 100,000 for male and females, respectively. The 209 patients who comprise the series represent 1.6% of the total number who had gastrointestinal cancers over the same period. The distribution of the tumors by site and histologic type is described. Both carcinoid and adenocarcinomatous tumors of the small intestine are associated with a high incidence of primary malignant neoplasms in other sites (17.0 and 20.3%, respectively). One patient with Peutz-Jeghers syndrome is of interest because of the malignant change which occurred in more than one of the small bowel polyps and because of consequent liver metastases. The reason for the poor prognosis in noncarcinoid small bowel malignant neoplasms is probably due to late diagnosis. The five-year disease-free survival in these tumors was 22.5%. Malignant carcinoids had a better overall five-year survival rate of 64%. For those confined to the bowel wall, the five-year survival rate was 73%, compared to 59% for those extending to nodes or metastasizing to distant organs.     

Retrograde nontransseptal balloon mitral valvuloplasty: immediate results and intermediate long-term outcome in 441 cases--a multicenter experience

OBJECTIVES: Our aim was to present the immediate and intermediate long-term results of the application of retrograde nontransseptal balloon mitral valvuloplasty (RNBMV) in four cooperating centers from Greece and India. BACKGROUND: RNBMV is a purely transarterial method of balloon valvuloplasty, developed with the aim to avoid complications associated with transseptal catheterization. Only single-center experience with RNBMV has been previously reported. METHODS: The procedure was attempted in 441 patients with symptomatic mitral stenosis (320 women, 121 men, mean age [+/-SD] 44+/-11 years, mean echocardiographic score [+/-SD] 7.7+/-2.0) from 1988 to 1996. Three hundred eighty-five patients with successful immediate outcome were followed clinically for a mean [+/-SD] of 3.5+/-1.9 (range, 0.5-9.1) years. RESULTS: A technically successful procedure was achieved in 388 (88%) cases. The echocardiographic score (p < 0.001), male gender (p=0.005), preprocedural mitral regurgitation (p=0.007) and previous surgical commissurotomy (p=0.029) were unfavorable predictors of immediate outcome. Complications included death (0.2%), severe mitral regurgitation (3.4%) and injury of the femoral artery (1.1%). Event-free (freedom from cardiac death, mitral valve surgery, repeat valvuloplasty and NYHA class > II symptoms) survival rates (+/-SEM) were 100%, 96.9+/-0.9%, 89.8+/-1.9% and 75.5+/-5.5% at 1, 2, 4 and 9 years, respectively. The echocardiographic score (p < 0.001), NYHA class (p=0.008) and postprocedural mitral valve area (p=0.009) were significant independent predictors of intermediate long-term outcome. CONCLUSIONS: Multicenter experience indicates that RNBMV is a safe and effective technique for the treatment of symptomatic mitral stenosis. As with the transseptal approach, patients with favorable mitral valve anatomy derive the greatest immediate and intermediate long-term benefit from this procedure.     

Effect of stretching temperature on structure and properties of polyethylene terephthalate (lavsan) fibre

Conclusions 1. With an increase in the stretching temperature up to a definite limit (170°C) the tensile strength of PETP and other fibres from crystalline polymers increases. However, at higher temperatures (230°C) the strength diminishes. This is evidently due to a reduction in the density of the intercrystallite regions of the fibrils, in which there is greater probability of polymer failure originating. Such behaviour of fibre made from PETP at elevated stretching temperatures is evidently associated both with the polymer structure and with its low molecular weight.2. For the preparation of a PETP fibre with high mechanical strength high orientation is a necessary but not sufficient condition; the fibre must be strengthened at these temperatures in order to form dense intercrystallite regions in the fibre fibrils together with a high degree of orientation.May we express our gratitude to Yu. A. Zubov and V. I. Selkhova (L. Ya. Karpov Physico-Chemical Scientific Research Institute) for the x-ray determination of the structure of the fibres investigated and also for the interest shown in discussions on the present.All-Union Synthetic Fibre Research Institute. Translated from Khimicheskie Volokna, No. 3, pp. 43–45, May–June, 1969.