Pollen record from red clay sequence in the central Loess Plateau between 8.10 and 2.60 Ma

The origin and development of Asian monsoon circula-tion, the desertification and aridification of Asian inland in relation to vegetation evolution and the soil erosion in northwest China have been more and more drawing inten-sive scientific and society attention. Recently the studiesof monsoon evolution from some Tertiary Red Clay sec-tions located at the central Loess Plateau in the eastern Liupan Mountains, based on chronology, dust flux, grains size, magnetic susceptibility, and rates o…     

临夏回族青少年头发和指甲微量元素含量对比分析

对500名(男246,女254)13～17岁临夏回族青少年头发和指甲中的Fe、Cu、Ni、Zn、Mn、Pb、Cd、Mo、Se和Ca元素的含量进行了对比分析。结果表明这十种元素在人体的头发和指甲中均存在,但男女之间有差异,其共同特点是头发中的Cu、Zn高于指甲,Cd、Mo和Se元素的含量男女均极少,且无差异(p>0.05),男女指甲中的Pb、Fe含量均高于头发(p<0.05);男性指甲中的Mn高于头发(p<0.05),而在女性无显著差异;Ca作为一种常量元素,男女指甲中的含量均极显著地高于头发(p<0.01)。证实测定人体微量元素时,只测定头发中的含量不能完全代表元素的分布特征和变化情况,指甲和头发对于研究人体微量元素具有同等重要的意义。     

MOCVD生长AlGaAs-GaAs DBR及其特性

本文报导了任意铝组分的AlGaAs材料的MOCVD外延生长和控制,解决了MOCVD生长高铝组分AIGaAs这一难题。国内首次运用MOCVD技术生长出高反射率的适合于垂直腔面发射激光器的AlGaAs-GaAs四分之一波长的分布布拉格反射镜(DBR)结构。用高分辨透射电镜观察得出,该DBR有良好的周期性、厚度均匀和界面平直。测得其反射率为94％,响应波长为820nm-868nm。     

A 1.5 Ma sporopollen record of paleoecologic environment evolution in the central Chinese Loess Plateau

A 1.5 Ma sporopollen record was obtained from a continuous loess-paleosol sequence at Chaona in the central Chinese Loess Plateau. It shows that (1) arid herbs of largely Artemisia and Chenopodiaceae and arbors of mainly Pinus, Betula and Quercus dominate loess and paleosol, respectively, reflecting cycles of cold-dry and warm-humid conditions of glaciation and interglaciation; (2) that similar vegetation pattern and cold-dry condition were found in times of unusual thick and coarse loesses L9 and L15, which have been regarded as two extremely cold and dry times as indicated by inorganic climatic proxies; and (3) that shifts of vegetations from earlier forest-steppe to open-forest and steppe and then to steppe were found at 0.95 and 0.5 Ma,implying a stepwise of drying of the Loess Plateau in the Quaternary.     

Fluorophotometric thin-layer chromatography of ginkgo terpenes by postchromatographic thermochemical derivatization and quality survey of commercial ginkgo products

Terpenoid lactones in Ginkgo biloba leaves are the main active constituents and the content of these terpenes is therefore the key factor for evaluating the quality of the leaves, the extract, and its preparations distributed on the market. The precleanup sample solutions were applied onto the silica gel plate modified with sodium acetate solution and developed with a solvent system of toluene-ethyl acetate-acetone-methanol, and a fluorescence chromatogram was generated by means of postchromatographic thermal chemical reaction. Fluorescence scanning was conducted quantitatively. The methodology validation confirmed that it is a practical alternative for routine quality control for ginkgo terpenes and the results are comparable with those obtained by high-performance liquid chromatography (HPLC). On the basis of the method established, a quality survey of the various commercial ginkgo products from different sources was undertaken. The obtained data demonstrated that the fluctuation of the content of individual terpene and/or the total terpenes among replicate samples is so significant as to cast doubts on the consistency of their pharmacological and clinical efficacy.     

辐照聚乙烯单晶的退火研究

用红外光谱、ＤＳＣ、ＳＡＸＳ和ＷＡＸＤ等方法考察了辐照５ＭＧｙ后的聚乙烯单晶在退火前后的结构变化，对比未辐照样品在同样条件下的变化，提出在９０℃以下和１０５℃聚乙烯有不同的退火机理，辐照引起的交联和晶区结构损伤，限制了退火对晶体结构的改善程度．     

气提浓缩仪分析水中痕量挥发性有机物研究

本文描述了气提浓缩仪的设计及操作程序用于对水中痕量挥发性有机物的测定。分析物被气提吸附于TenaxGC柱上,然后直接脱附到毛细管气相色谱柱上进行分析,并用FID或MS鉴定。本文除对色谱条件进行优化外,对气提时间和脱附温度等分析操作条件也进行了研究。检测下限为0.01-0.30PPb,峰面积检测精度优于6.9％,对16种化合物的回收率优于74％。     

河流崩岸防治的模袋排帘法及模型试验

为解决冲刷引起的崩岸问题,结合土力学和水力学两方面的原理,提出了崩岸防治新措施——模袋排帘。通过室内水槽模型的含沙水流试验,测量泥沙冲淤地形变化,对所提出的模袋排帘的功效进行了直观的验证。结果表明,模袋排帘结构形式能有效调整近岸坡水流结构;透沙窗的设置,适应河流悬沙分布特征,实现了局部淤积、稳定岸坡地形的目的;大大降低岸坡上的排体覆盖率,经济成本得到削减,且施工方便。     

不确定性信息的内涵与外延剖析

剖析了不确定性信息概念的内涵，给出了不确定性信息的外延概念：灰色信息、未确知信息、模糊信息、粗糙信息、随机信息与不确定性信息间的关系，为实现综合处理确定与不确定性信息奠定了理论基础。     

An ecological study on dynamics of toxic Microcystis blooms in a eutrophic park pond, Wuhan, China

The results of ecological investigation of Microcystis blooms and their toxicity in a eutrophic park pond ( where the annual average of total nitrogen and total phosphorus was 6.1 mg'L^-1 and 1. 79 mg'L^-1. respectively) are presented. The blooms were mainly contributed by M. aeruginosa occurring in the period from May to October when water temperature ranged from 16 to 33 °C . Three remarkable growth peaks of Microcystis during the period were observed with chlorophyll a level of 0. 73 mg*L^-1. 44 mg*L^-1. and 1. 30 mg'L^-1. respectively. The blooms were independent of phosphorus, but highly dependent on ammonium. A level of ammonium of 9. 5 mg'L^-1 could trigger the outbreak of the bloom, while that below 0. 89 mg'L^-1 could inhibit its formation. In other words, ammonium in higher concentrations could promote blooming, while that in lower concentrations could be inhibitory. Microcystis toxicity tended to increase with the blooming process, but the toxic peaks lagged behind their corresponding growth peaks.