The effects of the pretreatment of intravenous high dose methylprednisolone on Na(+)-K(+)/Mg(+2) ATPase and lipid peroxidation and early ultrastructural findings following middle cerebral artery occlusion in the rat

The sodium-potassium activated and magnesium dependent adenosine-5'-triphosphatase (Na(+)-K(+)/Mg(+2) ATPase EC.3.6.1.3.) activity and lipid peroxidation and early ultrastructural findings were determined in rat brain at the acute stage of ischaemia produced by permanent unilateral occlusion of the middle cerebral artery (MCA). The effects of the pretreatment with intravenous high-dose methylprednisolone (MP) on these biochemical indices and ultrastructural findings were also evaluated in the same model. The rats were divided into four groups. In group I, 10 rats were used to determine Na(+)-K(+)/Mg(+2) ATPase activity and the extent of lipid peroxidation by measuring the malondialdehyde (MDA) content and normal ultrastructural findings. In group II on 20 rats, only subtemporal craniectomy was done in order to determine the effects of the surgical procedure on these indices and findings. This group was treated intravenously with saline solution before occlusion. In group III with MCA occlusion, saline solution was administered intravenously to 20 rats in the same amount of methylprednisolone used in group IV, ten minutes before the occlusion. In Group IV, a single high-dose (30 mg/kg) of methylprednisolone was administered intravenously, ten minutes before occlusion in 20 rats. After occlusion of the middle cerebral artery, Na(+)-K(+)/Mg(+2) ATPase activity was decreased promptly in the first ten minutes in the ischaemic hemisphere and remained at a lower level than the contralateral hemispheres in the same group and the normal levels in group I, during 120 minutes of ischaemia. A single dose methylprednisolone pretreatment prohibited the inactivation of Na(+)-K(+)/Mg(+2) ATPase. On the other hand, there was significant difference in malondialdehyde content between group I and group III. Malondialdehyde levels were significantly increased following ischaemia and a non-significant increase was observed in the contralateral hemisphere. Methylprednisolone treatment significantly decreased malondialdehyde content on the side of the ischaemic hemisphere. We conclude that there is a positive relationship between membrane-bound enzyme Na(+)-K(+)/Mg(+2) ATPase activity, malondialdehyde content and early ultrastructural changes in the treated group with MP. These data suggest that the pretreatment injection of high doses (30 mg/kg) methylprednisolone contribute to the protection of the brain from ischaemia with stabilization of the cell membrane by effecting the lipid peroxidation and the activation of Na(+)-K(+)/Mg(+2) ATPase.     

Double necking in polymer tensile deformation

After initial necking of tensile polymer samples the deformation front moves along the gauge length at a stress which is smaller than the yield stress. The still undeformed parts of the sample are therefore subjected to conditions which favour deformation by a creep mechanism. If the extension rate is right, secondary necking becomes possible. Boundary conditions are discussed.     

综放面采空区遗煤自燃“三带”范围的预测

以峰峰矿区小屯矿14252综放面为研究对象,通过氧化热解实验测定煤样产生的气体成分;利用自制气体采样系统对采空区气体进行采集和分析,进而划分遗煤自燃"三带"范围。结果表明C2H2可作为该综放面煤炭自燃的预测指标,以C2H2浓度划分的采空区遗煤自燃"三带"范围为:散热带0~30m,自燃带30~127m,窒息带大于127m。     

葛洲坝500 kV开关站区域稳控装置的建立与应用

针对葛洲坝500kV开关站原有区域稳控装置存在的问题，通过对微机区域稳控装置设计目标、功能和基本控制原理的介绍，展示了一套全新的区域稳控装置：QWD系列区域稳控装置。该系列区域稳控装置已投运，为华中电网综合稳控装置的建立做好了前期的准备。     

省级电力行政交换网软交换改造方案研究

目前省级电力行政交换网大多采用程控交换设备组网,随着程控交换设备的逐步停产和电力系统业务多样化的发展需求,急需进行行政交换网升级改造工作。文章分析了软交换与IMS的商用情况,提出了近期省级电力行政交换网改造的技术体制选择建议、改造原则、建设模式、互联互通方案和下级站点典型接入方案。旨在为近期各省／市行政交换网改造提供方案参考。     

In situ characterization of solar flat plate collectors under intermittent operation

The Bayerisches Zentrum für angewandte Energieforschung Bayern (ZAE) performs an in situ test of eight different solar domestic hot water systems in Oberpfalz, Bayern. We present results of the evaluation of the collector loop from one system. This system has been chosen because due to the relatively low load the variability of the collector loop temperature is expected to be insufficient for testing purposes. The system under test consisted of the collector field and the piping from the cellar to the roof. First, we use a dynamic collector model which ignores the extra pipes and thus implicitly takes into account the pipes by modified parameter values. It is shown that this model can be inaccurate if the input data such as the irradiance and the inlet temperature do not vary sufficiently and independently from each other. Second, we use a model which explicitly takes into account the pipes, using the overall loss coefficient and the total specific heat capacity of the pipes as new parameters. It is shown that it is possible to identify the values of these additional parameters. The overall accuracy improves with the extended model. The models without and with pipes differ mainly in dynamic effects associated with the energy stored in the pipes during stops of the collector loop pump.