Structural probing of D-fructose derived ligands for asymmetric addition of diethylzinc to aldehydes

A series of new chiral ligands derived from D-fructose have been synthesized and applied in the enantioselective addition of diethylzinc to aldehydes. Comparison of the enantioselectivities obtained with these ligands demonstrated that the catalytic properties are highly dependent upon the structure of ligands, a rational explanation of the structural effects on the catalytic properties is provided. (C) 2003 Elsevier Science Ltd. All rights reserved.

二恶英类物质检测分析技术进展

介绍了同位素稀释气相色谱质谱联用和生物快速检测法测定二恶英类化合物的技术进展,概述了国际通用的二恶英类标准分析方法体系,提出了各方法的适用范围,综述了我国二恶英类化合物分析研究现状并对我国二恶英分析检测提出了建议。

基于景观敏感度的猴石森林公园保护区划

基于GIS技术,选取坡度、相对景点距离、相对游道距离、景点视觉几率和游道视觉几率5个指标分别对猴石森林公园进行敏感度评价,并建立了综合敏感度评价模型,运用层次分析法(AHP)确定各指标权重,进而确定了公园内各区域的综合敏感度等级,将公园相应地划分为4个等级的敏感区.结果表明:研究区Ⅲ级敏感区的面积最大,为495.80hm2,占公园总面积的38.3%.这一区域在强调保护自然景观的同时,可进行适度开发,提倡利用人文景观美化和衬托自然景观.Ⅳ级敏感区的面积最小,为142.80hm2,占研究区总面积的11.0%.这一区域的开发潜力最大,可开展大规模的综合性旅游设施和游道布设.Ⅰ、Ⅱ级敏感区的面积依次为297.24和359.72hm2,分别占研究区总面积的22.9%和27.8%,Ⅰ级敏感区内景观应严格保护,禁止任何人为开发建设,维持自然景观的本色,Ⅱ级敏感区内除简易的林间小道和石阶山道外,严禁开山取石、破坏植被和水体.

科尔沁沙地不同密度小叶锦鸡儿灌丛水量平衡研究

根据沙地水分平衡理论推算了不同栽植密度下小叶锦鸡儿灌丛的蒸散量.结果表明,小叶锦鸡儿灌丛生长期土壤水分含量随着植被密度增加而降低,0.5 m×1 m、1 m×2 m密度植被区平均土壤含水量低于凋萎湿度(1.55%),2 m×2 m密度植被和天然小叶锦鸡儿植被平均土壤含水量保持在1.60%以上,能够满足植被生存和生长的水分需求.蒸散量随着植被密度增加而增大,以0.5 m×1 m密度灌丛区最高,为297.81 mm,占同期降水量的97.90%;2 m×2 m密度灌丛区最低,为279.71 mm,生长期末期土壤水分节余为24.49 mm.依据生长期土壤水分状况和水分平衡要求,科尔沁沙地小叶锦鸡儿灌丛适宜密度应为2 m×2 m.

牛蒡根际土壤致害菌Fusariumsolani分离鉴定

目的:探索牛蒡根际镰刀菌与牛蒡之间的相互关系。方法:从全国30个地区采集牛蒡根际土壤样品,进行了根际土壤真菌数量和群落的生态学研究,测定镰刀菌发酵液对牛蒡幼苗和牛蒡子萌发的影响,并对其中毒性最强的两株镰刀菌F130和F131进行了形态学和分子生物学的鉴定。结果:镰刀菌为牛蒡根际的最优势类群,贡献率为34.297%,其次为木霉,贡献率为22.519%;绝大多数镰刀菌对牛蒡有明显的毒性作用,其中F130和F131被鉴定为Fusarium solani。结论:Fusarium solani是牛蒡根际土壤中的致害菌。

a fuzzy-based method for evaluating the trustworthiness of software processes

University of Paderborn; Fraunhofer Inst. Exp. Softw. Eng. (IESE); Chinese Academy of Science (ISCAS)

Uncertainties in estimates of cropland area in China: a comparison between an AVHRR-derived dataset and a Landsat TM-derived dataset

The large uncertainties in estimates of cropland area in China may have significant implications for major cross-cutting themes of global environmental change-food production and trade, water resources, and the carbon and nitrogen cycles. Many earlier studies have indicated significant under-reporting of cropland area in China from official agricultural census statistics datasets. Space-borne remote sensing analyses provide an alternative and independent approach for estimating cropland area in China. In this study, we report estimates of cropland area from the National Land Cover Dataset (NLCD-96) at the 1:100,000 scale, which was generated by a multi-year National Land Cover Project in China through visual interpretation and digitization of Landsat TM images acquired mostly in 1995 and 1996. We compared the NLCD-96 dataset to another land cover dataset at I-km spatial resolution (the IGBP DIScover dataset version 2.0), which was generated from monthly Advanced Very High Resolution Radiometer (AVHRR)-derived Normalized Difference Vegetation Index (NDVI) from April, 1992 to March, 1993. The data comparison highlighted the limitation and uncertainty of cropland area estimates from the DIScover dataset. (C) 2003 Elsevier Science B.V. All rights reserved.

Metal-organic frameworks based on the pyridine-2,3-dicarboxylate and a flexible bispyridyl ligand: syntheses, structures, and photoluminescence

Three new metal-organic coordination polymers, [Cu(2,3-pydc)(bpp)]center dot 2.5H(2)O (1), [Zn(2,3-pydc)(bpp)]center dot 2.5H(2)O (2) and [Cd(2,3-pydc)(bpp)(H2O)]center dot 3H(2)O (3) (2,3-pydcH(2) = pyridine-2,3-dicarboxylic acid, bpp 1,3-bis(4-pyridyl)propane), have been synthesized at room temvperature. All complexes have metal ions serving as 4-connected nodes but represent two quite different structural motifs. Complexes 1 and 2 are isomorphous, both of which feature 2D -> 3D parallel interpenetration. Each two-dimensional (2D) layer with (4, 4) topology is interlocked by two nearest neighbours, one above and one below, thus leading to an unusual 3D motif. Complex 3 has a non-interpenetrating 3D CdSO4 framework with cavities occupied by uncoordinated water molecules.

Carbon deposition behavior over copper salts of molybdovanadophosphoric acid catalyst supported by magnesia

MgO supported copper salt of molybdovanadophosphoric acid H4PMo11VO40 catalysts were prepared in alcohol by impregnation and the carbon deposition over these catalysts during the n-hexanol oxidation reaction was studied. The coke predominantly deposited on the catalyst surface in the form of CH., and it was not found that it caused the deactivation of the catalyst. The XRD, IR, XPS characterizations reveal that the Keggin structure of the CPMV was unaffected by carbon deposition. Moreover, it was shown that the supported CPMVs over the MgO surface can be beneficial to eliminate the coke. The temperature programmed oxidation (TPO) study showed that coke was formed over the catalyst on two different sites: (1) deposited on the CPMVs which can be burn off at a low temperature; (2) deposited on the MgO which could only be removed at higher temperature. The coke content reached constant with the reaction time increasing.

Synthesis and luminescence properties of nanocrystalline Gd2O3 : Eu3+ by combustion process

The nanocrystalline Gd2O3:Eu3+ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 45, and 23 run for the precursor and samples annealed at 600, 700 and 800 degrees C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O-2-Eu3+ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu3+ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu3+, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu3+ ions.

Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3.5-x (Al0.5Mo0.5)(x) (x=0-0.8) hydrogen storage alloys

The crystal structure, hydrogen storage property and electrochemical characteristics of the La0.7Mg0.3Ni3.5-x(Al0.5Mo0.5), (x=0-0.8) alloys have been investigated systematically. It can be found that with X-ray powder diffraction and Rietveld analysis the alloys are of multiphase alloy and consisted of impurity LaNi phase and two main crystallographic phases, namely the La(La, Mg)(2)Ni-9 phase and the LaNi5 phase, and the lattice parameter and the cell volume of both the La(La, Mg)(2)Ni-9 phase and the LaNi5 phase increases with increasing A] and Mo content in the alloys. The P-C isotherms curves indicate that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x, and the equilibrium pressure decreases with increasing x. The electrochemical measurements show that the maximum discharge capacity first increases from 354.2 (v = 0) to 397.6 mAh g(-1) (x = 0.6) and then decreases to 370.4 mAh g(-1) (x= 0.8). The high-rate dischargeability of the alloy electrode increases lineally from 55.7% (x=0) to 73.8% (x=0.8) at the discharge current density of 1200 mA g(-1). Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x.

Solvent induced different morphologies of bis(propyl)triethoxysilane substituted perylenediimide and their optical properties

Nano/microstructure of bis(propyl)triethoxysilane substituted perylenediimide (1) with nanoparticle and twisted microrod morphologies were obtained by reprecipitation method induced by water and petroleum ether, respectively. It is believed that the different nucleation and growth processes involved are responsible for the formation of the nano/micro-structure With different morphologies of 1. UV-vis absorption and photoluminescence measurements show that their UV-vis absorption and photoluminescence properties are different from each other as well as their monomer mid bulk materials due to the different effects on the change transfer (CT) transition energy levels caused by their different aggregation behaviors.