Induction of mosaic sex-linked recessive lethals in the different germ cell stages of Drosophila melanogaster by bleomycin

The dead-end filtration characteristics of the dimorphic yeast Kluyveromyces marxianus var. marxianus (formerly fragilis) NRRLy2415 were investigated for a range of mean cell morphologies, ranging from predominantly yeast-like to predominantly filamentous. Semiautomated image analysis was used to measure the mean cell specific surface area, Sv, and the mean ratio of cell length to equivalent cylindrical diameter, Ldm, in each broth. The method of Ju and Ho (Biotechnol. Bioeng. 1988, 32, 95-99) was used to show that for broths with Ldm values between 1.72 and 10.03, the voidage of cell pellets formed by centrifugation increased with increasing Ldm. In the pressure range 30-180 kPa, the specific filter cake resistance, alpha, was found to be related to pressure, DeltaP, through the equation alpha = alpha0(1 + kcDeltaP). The dependence of alpha0/Sv2 on Ldm was found to be qualitatively consistent with the pellet voidage data and the Carman-Kozeny equation. Considerably better agreement with the experimental data was obtained when the Kozeny constant, K, was treated as variable and related to Ldm through the equation K = 4.83 + 7.08 log10 Ldm. The cake compressibility constant, kc, was found to increase with increasing Ldm, a phenomenon consistent with the wide range of voidages that can be displayed by beds of long cylinders.     

卫星通信技术的新进展

本文对国内外卫星通信的最新发展作了详尽论述;并综合概括了未来卫星通信技术的发展趋势;最后,对卫星通信市场进行了预测。     

低轨小型卫星的发展和应用

本文介绍低轨小卫星的发展和应用前景。低轨小卫星,体积和重量小,轨道低,功能单一,智能化,制造和发射都很容易,投资费用低,受到用户的普遍欢迎,有广阔的发展和应用前景。 小卫星在近几年发展迅速,应用广泛,已经受到世界各国的重视。在许多方面,已经应用小卫星和计划中应用小卫星的例子很多,本文只作简要介绍,目的在于引起人们的重视,发展我国的小卫星事业。     

海湾战争后防空系统及雷达电子设备的新发展

本文针对海湾战争后的新形势,介绍了战略防御的新构想、战术防空导弹系统及21世纪的防空概念,论述了AEW、AWACS、战场监视目标攻击雷达及其它雷达的最新发展情况,此外,还对国外的反隐身技术进展情况作了介绍。     

Inhibition of acid rock drainage from uranium ore waste using a conventional neutralization and precipitation treatment

Glass columns (length 50 cm, i.d. 4 cm) containing 900 g of uranium ore waste were subjected to a three-step process: (1) acid drainage generation, (2) neutralization and precipitation treatment and, again, (3) acid drainage generation. In the first acid generation step, lasting about one year, different variables (pyrite addition, inoculation and irrigation solution) were tested by measuring effluent pH, redox potential, total iron and sulphate. Conditions of acid generation were satisfactorily reproduced, reaching stable pH values around 2.0 that were determined mainly by pyrite addition and the type of irrigation solution used (distilled water or ferrous sulphate). The neutralization and precipitation treatment consisted of alternating irrigations of a neutralizing solution (CaO saturated plus NaOH) and a precipitating solution (ferric sulphate saturated). This treatment caused accumulation of basic iron sulphate and iron oxide precipitates according to SEM studies. After this treatment, the barrier effect created by the reaction products was checked, using irrigation solutions similar to the first step. The effluents collected showed higher pH and lower redox potential, total iron and sulphate values than those observed before the treatment, evidencing inhibition of acid drainage generation.     

Trends in Hydrological Parameters of a Southern Brazilian Watershed and its Relation to Human Induced Changes

The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km², the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of São Paulo city.     

Glomerular tip lesions--a newly described glomerular change

Glomerular tip lesion is a newly described histopathological lesion characterized by a focal and segmental widening of the mesangial matrix without hypercellularity together with capillary dilatation, hyaline exudation on the inside of capillary walls and occurrence of vacuolized cells, localized to the peripheral segments of the glomerular tuft. Clinically, these patients have a pronounced nephrotic syndrome with slightly reduced renal function, but terminal renal failure is seldom seen, even after many years of disorder. Two characteristic case histories are presented. The classification of this lesion among the glomerular disorders is at present uncertain. It may represent a transitional form between minor lesion nephritis and focal segmental sclerosis, a separate disorder, or a functional lesion associated with high proteinuria.     

Quenching of chlorophyll fluorescence by quinones

Obese (Lepr(fa)/Lepr(fa)) Zucker rats have a missense mutation in the leptin receptor gene. One amino acid substitution in the extracellular domain common to all known leptin receptor proteins results from this mutation. Obese Zucker rats are unable to respond behaviorally to leptin which is peripherally administered. However, conflicting reports exist on whether obese Zucker rats can respond to centrally administered leptin. The purpose of this study was to determine whether obese Zucker rats responded behaviorally and metabolically to intracerebroventricularly (i.c.v.) administered leptin and to compare the responses of lean and obese Zucker rats. We found that both lean and obese Zucker rats had similar body weight and food intake responses when administered a single i.c.v. leptin injection in a range of doses (1.25, 2.5, 5, and 10 microg), as well as daily i.c.v. administered leptin for five consecutive days. Both single and daily leptin administration also decreased respiratory quotient (RQ) similarly in lean and obese Zucker rats, indicating mobilization of fat as an energy source for leptin-treated rats. After withdrawal of daily leptin treatment, lean and obese Zucker rats exhibited different recovery responses. It is concluded that obese Zucker rats can respond to exogenous leptin when leptin is delivered into the brain ventricles.     

Absence of tolerance to the aversive stimulus properties of ethanol following oral ethanol self-administration

Aluminum has been reported to inhibit long-term potentiation (LTP) following in vivo administration and decrease glutamate release following in vitro exposure. Because glutamate release is critical for synaptic transmission and the development and maintenance of LTP in the hippocampus, we examined the effects of aluminum chloride (AlCl3) on depolarization-induced glutamate release and LTP in rat hippocampal slices. The effects of AlCl3 on [14C]glutamate release were examined by incubation of slices in depolarizing (56 mM)K+ buffer solution in the absence or presence of 2 mM CaCl2. After 15 min depolarization, AlCl3 (100-1000 microM) did not significantly affect Ca(2+)-dependent [14C]glutamate release from slices, whereas a known Ca2+ channel blocker (100 microM CdCl2) decreased Ca(2+)-dependent [14C]glutamate release by approximately 50%. In contrast to a previous report, acute exposure to AlCl3 was without effect on depolarization-dependent glutamate release. LTP of the population spike (PS) in CA1 of hippocampus was induced by the delivery of stimulus trains to the stratum radiatum. LTP of the PS was observed in both control slices and slices bathed in solution containing 100 microM AlCl3. Neither the magnitude nor longevity (measured up to 1 h posttrain) of LTP distinguished control from aluminum-exposed slices. The lack of sensitivity in rat to the encephalopathic changes induced by aluminum, or methodological differences in exposure conditions may account for the lack of effect of aluminum on in vitro LTP in rat hippocampus.     

方兴未艾的智能网技术

智能网(IN)的概念于1984年一被提出,便在世界范围内迅速掀起了IN研究的热潮,虽然至今已有十个年头,但仍可以说,IN技术的发展才刚刚起步。本文就是基于当前国际上对IN的研究,来介绍智能网的基本概念和结构,进而阐述其设计思想及主要特征,并对IN的未来发展趋势进行了探讨,最后为我国发展IN技术提出了可行建议。