纳秒级气体火花开关的研制     

冯学斌  钱燕  张军晖  尹文庆 《南京农业大学学报》2012,35(1):125-129

为了研究高压脉冲电场对种子活性的影响,结合脉冲功率技术和计算机辅助设计技术,研制了满足最新高空核爆电磁脉冲模拟标准MIL-STD-461F的纳秒级气体火花开关。在分析开关放电原理的基础上,考虑火花隙电阻和开关结构电容的影响,基于Simulink建立了开关的动态放电模型,仿真分析了负载、开关电感、开关电容等因素对放电脉冲特性的影响,为开关的设计提供了参考。在此基础上,试制了纳秒级气体火花开关样品,在50Ω负载上输出脉冲峰值达到25 kV,上升时间2.5 ns,脉冲宽度18 ns,为进一步研究脉冲电场种子效应奠定了基础。  相似文献   

浅议修缮购置专项预算编制与会计核算问题     

黄振环 《农业科研经济管理》2012,(2):35-37

文章阐述了修购专项实施的重要意义;指出了修购专项在预算编制与会计核算中存在的问题;并提出了规范化建议:一是提高预算编制水平;二是规范会计核算,确保会计信息的准确完整;三是完善资产入账手续,确保资产不重不漏。  相似文献   

浅析修购专项对研究所发展的重要作用     

赵国辉 《农业科研经济管理》2012,(2):23-25

主要介绍了中国农业科学院哈尔滨兽医研究所获得修购专项的支持情况和管理情况,重点总结了修购专项对研究所发展的重要作用:一是改善了科研条件;二是打造了高水平的公共实验共享平台;三是培养了项目管理人才;四是完善了相关管理制度;五是取得了丰硕的科研成果。最后提出财政部门能给予持续、稳定的支持。  相似文献   

燕山山地油松人工林林隙大小对更新的影响   总被引：3，自引：0，他引：3  

李兵兵  秦琰  刘亚茜  刘相兵  黄选瑞 《林业科学》2012,48(6):147-151

林隙(gap)又称林窗,指森林群落中老龄树木死亡或偶然因素(如干旱、台风、火灾等)造成成熟阶段的优势种死亡,从而形成林冠空隙的现象(Watt,1947)。美国生态学家Runkle(1982)将林隙分为2种,一种是林冠空隙(canopy gap),指上方无树冠遮荫的部分,即太阳处于正中位置时无树冠遮荫的面积之和;另一种是扩展林隙(expanded gap),指形成该林隙周围树木基部所包围的面积(Runkle,1981)。本研究所指的林隙为应用最为广泛的扩展林隙。近年来的森林动态学研究表明:林隙在森林结构和多样性维持中起着重要的作用,已  相似文献   

Incidence, nature, and etiology of metabolic acidosis in dogs and cats     

K Hopper  SE Epstein 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2012,26(5):1107-1114

  相似文献   

开林窗与封禁对华北落叶松林下植被多样性的影响   总被引：1，自引：0，他引：1  

田军  孙海静  于树峰  隋玉龙  黄选瑞 《河北林果研究》2012,(3):260-264

以木兰林管局典型的华北落叶松林为研究对象,对其采取开林窗、封禁等改造措施,采用样方法进行野外调查,通过丰富度、生态优势度、多样性、均匀度指数,分析不同经营措施下的生物多样性及样地的物种组成。结果表明:开林窗面积中等及较小的样地各生物多样性指数均呈上升趋势,且高于对照,而开林窗面积较大样地的Pielou均匀度指数成降低趋势;封育区的Simpson和Shannon-Wiener多样性指数与均匀度指数均大于对照区,而封育区的Margalef丰富度指数虽然呈上升趋势,但仍小于对照区;该实验区林下植被的优势物种为乌苏里苔草。  相似文献   

Exploring the silvicultural and economic viability of gap cutting in Mediterranean softwood plantations     

Roberto MERCURIO  Raffaele SPINELLI 《中国林学(英文版)》2012,14(1):63-69

Gap cutting consists of the removal of all trees growing on a small surface,varying in size from 200 to 600 m 2.In Italy,gap cutting has been successfully tested for introducing the natural regeneration of native species into softwood plantations,thus accelerating the transition towards climax hardwood stands.Depending on plantation types and conditions,gap cutting should be started at an age between 70 and 80 years and the system should include at least 12 to 15 gaps,in order to produce enough wood to cover costs.Generally,natural regeneration is firmly established within 5-7 years from treatment.Gap cutting also offers superior results to selection thinning,the latter producing about 35% less value and incurring 25% to 30% more costs.As for all regeneration cuts,the success of gap cutting depends on wildlife control in order to prevent extensive damage to the regeneration.  相似文献   

雷州半岛高桥红树林内带林窗特征分析——以湛江市廉江高桥红树林保护小区为例   总被引：1，自引：0，他引：1  

黄剑坚  刘素青  韩维栋 《林业资源管理》2012,(5):46-50

对红树林林窗特征研究,是研究退化红树林生态系统恢复与重建、对次生红树林进行改造、科学管理红树林生态系统的基础。对雷州半岛廉江高桥红树林保护小区内带林窗特征进行了调查,分析林窗大小结构、形成方式、形成木特征等。调查发现:高桥红树林内带林窗主要以小面积林窗为主,分布在实际面积1～10 m2之间和扩展面积1～50 m2之间;林窗主要形成方式是枯死,其次是侧枝损坏;林窗形成木数量范围在1～6株之间,平均每个林窗有2.3株形成木;形成木种类是红海榄、桐花树、木榄、秋茄,各占总比例的5.4%,8.9%,60.7%,25.0%;形成木腐烂等级较高。  相似文献   

林窗理论在山地型城市森林建设中的应用前景     

宋聚学  马立辉  黄世友 《林业调查规划》2013,(4):107-110,122

从森林循环演替、森林特殊的生境、边缘效应、森林植被物种多样性及森林景观格局多样性等方面论述了林窗干扰作用,并讨论了林窗理论在山地型城市森林建设中森林动态管理、森林景观格局优化和林相改造等方面的应用前景。  相似文献   

Extract from the Zooxanthellate Jellyfish Cotylorhiza tuberculata Modulates Gap Junction Intercellular Communication in Human Cell Cultures     

Antonella Leone  Raffaella Marina Lecci  Miriana Durante  Stefano Piraino 《Marine drugs》2013,11(5):1728-1762

On a global scale, jellyfish populations in coastal marine ecosystems exhibit increasing trends of abundance. High-density outbreaks may directly or indirectly affect human economical and recreational activities, as well as public health. As the interest in biology of marine jellyfish grows, a number of jellyfish metabolites with healthy potential, such as anticancer or antioxidant activities, is increasingly reported. In this study, the Mediterranean “fried egg jellyfish” Cotylorhiza tuberculata (Macri, 1778) has been targeted in the search forputative valuable bioactive compounds. A medusa extract was obtained, fractionated, characterized by HPLC, GC-MS and SDS-PAGE and assayed for its biological activity on breast cancer cells (MCF-7) and human epidermal keratinocytes (HEKa). The composition of the jellyfish extract included photosynthetic pigments, valuable ω-3 and ω-6 fatty acids, and polypeptides derived either from jellyfish tissues and their algal symbionts. Extract fractions showed antioxidant activity and the ability to affect cell viability and intercellular communication mediated by gap junctions (GJIC) differentially in MCF-7and HEKa cells. A significantly higher cytotoxicity and GJIC enhancement in MCF-7 compared to HEKa cells was recorded. A putative action mechanism for the anticancer bioactivity through the modulation of GJIC has been hypothesized and its nutraceutical and pharmaceutical potential was discussed.  相似文献