Field emission vacuum power switch using vertically aligned carbon nanotubes

The best field emission properties from carbon nanotube cathodes were obtained when their heights, diameters and spacings were optimized. Field emission currents as high as 10 mA were obtained from 1 cm × 1 cm vertically aligned CNT cathode with optimized parameters grown using dc plasma CVD in situ. It was found that in order to obtain large emission current of >10 mA, space charge effects within the electron beam must be taken into account.

罗汉松科胚胎学与系统学研究

本文回顾了罗汉松科的研究历史，对一些属种的叶表皮形态、种子蛋白和同工酶及胚胎发育等进行了实验，结合分类学的文献资料和标本的查阅，对本科各属的形态特征进行了考察，探讨了罗汉松科的演化趋势、系统位置及其范围和属间关系。主要结论如下： 1．形态特征雄球花在本科内形式一致，小孢子叶螺旋状排列于轴上，其背面基部两侧着生两个花粉囊．雌性生殖器官上可育和不育苞片数目缩减，肉质鳞被逐渐缩减直至退化，生殖枝极度缩短． 2．胚胎发育罗汉松科胚胎发育为标准型，即原胚由三层组成：上层为开放层(U-tier)，中层为原胚柄层(PS)，下层为胚层细胞(E-cells)。融合核经四次分裂产生16个核，然后形成原胚，是罗汉松科的一个基本规律。融合核行五次分裂产生32个游离核的现象，只在少数属种中才能见到．原胚胚层细胞经历了一个双核时期，持续较长时间，直至胚柄极度伸长之后，才告结束，这一特征将罗汉松科与其它松杉类植物区别开来．原胚胚层细胞数目减少和所有胚层细胞趋于同层排列是罗汉松科植物胚胎发育的两个进化趋势． 3．叶表皮微形态特征在属间差异较为明显，在每个种中都有稳定的特征． 4．种子蛋白和酶电泳资料支持竹柏属(Nageia)和鸡毛松属(Dacrycarpus)从广义罗汉松属(Podocarpus s.l.)中分出．酶电泳资料的遗传分析显示竹柏属和罗汉松属的亲缘关系较近，与鸡毛松属的关系较远一些．种子蛋白在种内保持着很高的一致度，属间种子蛋白图谱表现出各自的专一性，属间差异明显，属内种间的种子蛋白图谱表现出较显著的相似性． 5．根据形态特征、胚胎学证据和酶电泳资料，认为竹柏属做为罗汉松科的成员更合适一些，并且它与罗汉松属的亲缘关系较近． 6．罗汉松科处于松杉类中较为进化的位置上，同红豆杉科一起组成红豆杉目，与松杉目并列，共置于松杉纲中．

Growth, recruitment, and abundance of juvenile striped mullet (Mugil cephalus) in South Carolina estuaries

Growth, recruitment, and abundance of young-of-the-year (YOY) striped mullet (Mugil cephalus L.) in estuarine habitats in South Carolina from 1998 to 2000 were examined and compared to historical data (1986–91) of growth, recruitment, and abundance. Daily growth increments from the sagittal otoliths of juvenile striped mullet were validated by using fish immersed in oxytetracycline hydrochloride (OTC) for five hours from the Charleston Harbor Estuary system. The distribution of back-calculated birthdates indicated that striped mullet spawn from October to late April and estuarine recruitment occurs from January through May. Juveniles were more abundant in mesohaline and polyhaline salinity regimes but were found throughout the estuary. Juvenile growth after recruitment into the estuary can be described by the relationship Total length (mm) = 0.341 (Age)1.04 (r2=0.741, P=0.001). Growth of juveniles according to the analysis of size-frequency data from historical surveys (1986 to 1991) in the same estuaries gave the relationship Total length (mm) = 8.77 (month)1.12 (r2=0.950, P=0.001). The similarity in the growth curves for both groups of fish suggests that juvenile striped mullet in South Carolina have consistent annual growth during the first year of life.