近20年青海三江源自然保护区植被生产力变化模拟

三江源保护区是我国最大的自然保护区,对我国的生态安全起着重要的保障作用。作为生态系统功能重要指标之一的净初级生产力的大小及其速率,一直是人们关心的问题。本文利用GLOPEM模型模拟得到的青海三江源地区1988-2008年的NPP数据,计算了三江源自然保护区内外1988-2008、1988-2004,以及2004-2008年3个时间段的NPP年际变化速率,比较了三江源保护区内外的NPP年际变化。同时对三江源各个下属保护区的NPP增长潜力进行了排序,结果认为,三江源地区自生态系统工程实施以来,NPP有了明显的回升,回升速率约为0.47gC/m2.a,其内部大多数子保护区的NPP也有了明显恢复,NPP回升的保护区占到总保护区数量的72%。

基于遥感与GIS的20世纪90年代中国城镇用地时空特征

文章利用20世纪90年代初期、中期和末期全国1∶100000土地利用动态变化数据提取城镇用地动态变化数据,利用单元自动机和人工神经网络模型对全国城镇用地进行了区划。在此基础上,研究了90年代两个阶段中国城镇用地时空格局。研究表明:90年代前5年东部沿海地区受经济高速发展和开放政策的影响,城镇用地扩展迅速,中西部地区城镇用地扩展较慢;90年代后5年国家加大了耕地资源保护力度,在政府宏观调控政策和耕地资源保护条例的影响下,东部沿海地区城镇用地扩展大幅回落,中部地区城镇扩展也有较大幅度回落,西部地区随着经济发展加快,城镇用地扩展回落较小。

20世纪90年代内蒙古自治区土地利用动态与风力侵蚀动态对比研究

内蒙古是我国风力侵蚀较为严重的地区之一,同时也是我国土地利用方式剧烈变化的地区之一。依据两期土地利用数据以及相应年代的土壤风力侵蚀数据,研究了20世纪90年代内蒙古自治区土地利用和风力侵蚀的静、动态格局。根据土地利用和风力侵蚀的空间分布及动态变化特点,设计了内蒙古土地利用—风力侵蚀动态区划,基于该区划详细讨论了内蒙古不同地区占主导地位的土地利用动态与风力侵蚀动态,由此揭示了两者之间存在的驱动——被驱动关系。研究发现,在过去10年里,内蒙古土地利用和风力侵蚀的基本格局没有太大变化,但风力侵蚀在总体上是增强了,而土地利用的变化主要反映为草地的退化和耕地的扩张。土地利用动态与风力侵蚀动态有着良好的时空对应关系草地的退化与耕地的扩张导致了显著的风力侵蚀增强,而草地的改善以及耕地的收缩对风力侵蚀的影响不是很大,这同时也表明了土地利用动态对风力侵蚀动态正、反向驱动力的不平衡性。

20世纪90年代LUCC过程对中国农田光温生产潜力的影响:基于气候观测与遥感土地利用动态观测数据

在20世纪90年代中国气候观测数据和遥感土地利用动态观测数据的支持下,计算了中国20世纪90年代农田光温生产潜力的变化.结果表明:20世纪90年代的LUCC过程直接导致了中国农田光温生产潜力总量和区域分布的变化,总体趋势是南减北增,总量净增加2622万吨;在各种土地利用类型之间的相互转变和转化过程中,耕地扩张和农田损失是导致全国农田光温生产潜力总量净变化的主要原因,耕地扩张使全国农田光温生产潜力总量净增加8335万吨,占全国农田光温生产潜力总量的3.50%,主要分布在东北、西北和华北等农林、农牧交错区和沙漠绿洲区,主要是由于该地区大面积的农田开垦所导致;农田损失使全国农田光温生产潜力总量净减少5713万吨,占全国农田光温生产潜力总量的2.40%,主要分布在黄淮海平原、长江三角洲、珠江三角洲、陇中、东南沿海、四川盆地东南部以及乌鲁木齐—石河子一带,主要是由于该区域经济发展较快,城市扩张明显,城乡建设用地大量侵占耕地的缘故.

温度对Ti_(45)Zr_(35)Ni_(20)合金电化学贮氢性能的影响

采用真空熔炼法制备了Ti45Zr35Ni20合金,研究了合金在不同温度下的电化学贮氢性能。结果表明,Ti45Zr35-Ni20电极的电化学性能随着温度而变化,温度从323 K升高到343 K时,电极的活化次数从22次减少到8次,放电容量从86.1 mAh/g增到135.0 mAh/g,快速放电能力也有所提高,然而,高温使电极的循环稳定性显著下降,自放电率增大。

Blends of Polypropylene and Syndiotactic 1,2-Polybutadiene: Morphology, Crystallization Behaviors and Mechanical Properties

Morphologies, crystallization behavior and mechanical properties of polypropylene(PP)/syndiotactic 1,2-polybutadiene(s-1,2 PB) blends were investigated. Morphology observation shows the well dispersed domains of s-1,2 PB in PP matrix with the rather small domain sizes from 0.1 to 0.5 mu m when the s-1,2 PB content increases from 5% to 20% (mass fraction) in the blends, and the phase structure tends to become co-continuous as s-1,2 PB content further increases.

The solid-liquid extraction of yttrium from rare earths by solvent (ionic liquid) impreganated resin coupled with complexing method

A kind of solvent (ionic liquid) impreganated resin (IL-SIR) was developed herein for ameliorating imidazolium-type IL-based liquid-liquid extraction of metal ions. In this study, [C(8)mim][PF6] containing Cyanex923 was immobilized on XAD-7 resin for solid-liquid extraction of rare earth (RE). The solid-liquid extraction contributed to ameliorating mass transfer efficiency, i.e. shortening equilibrium time from 40 min to 20 min, increasing extraction efficiency from 29% to 80%. In additional, the novel IL-SIR could separate Y(III) from Sc(III), Ho(III), Er(III), Yb(III) effectively by adding water-soluble complexing agent.

Alternating Copolymerization of Cyclohexene Oxide and Carbon Dioxide Catalyzed by Noncyclopentadienyl Rare-Earth Metal Bis(alkyl) Complexes

The syntheses of several dialkyl complexes based on rare-earth metal were described. Three beta-diimine compounds with varying N-aryl substituents (HL1 = (2-CH3O(C6H4))N=C(CH3)CH=C(CH3)NH(2-CH3O(C6H4)), HL2 = (2,4,6-(CH3)(3) (C6H2))N=C(CH3)CH=C(CH3)NH(2,4,6-(CH3)(3)(C6H2)), HL3 = PhN=C(CH3)CH(CH3) NHPh) were treated with Ln(CH2SiMe3)(3)(THF)(2) to give dialkyl complexes L(1)Ln (CH2SiMe3)(2) (Ln = Y (1a), Lu (1b), Sc (1c)), L(2)Ln(CH2SiMe3)(2)(THF) (Ln = Y (2a), Lu (2b)), and (LLu)-Lu-3(CH2SiMe3)(2)(THF) (3). All these complexes were applied to the copolymerization of cyclohexene oxide (CHO) and carbon dioxide as single-component catalysts.

Effect of substitution of chromium for nickel on structure and electrochemical characteristic of Ti0.26Zr0.07V0.24Mn0.1Ni0.33 multi-phase hydrogen storage alloy

Ti-Zr-V-Mn-Ni-based multi-component alloys demonstrate high discharge capacity in KOH electrolyte. However, the drastic decrease in their discharge capacities makes them unsuitable for use as negative electrode material in the Ni/MH battery. In present work, Ni is partially replaced by Cr in the Ti-Zr-V-Mn-Ni-based alloys to improve their cycle life. The effects of Cr substitution on microstructures and the electrochemical characteristics of the alloys are investigated. It is found that Cr substitution is very effective to improve the cyclic durability of the alloys although the discharge capacity decreases with changing x from 0.05 to 0.20. Some kinetic performances have been also investigated using electrochemical impedance spectroscopy (EIS) and potentiostatic discharge technique.

Synthesis and Crystal Structure of a New 3D Copper B-Paradodecatungstate Compound: [Na-2(H2O)(8)][Na-8(H2O)(20)][Cu(en)(2)][W12O42] center dot 3H(2)O

A new polyoxotungstate complex [Na-2(H2O)(8)][Na-8(H2O)(20)][Cu(en)(2)][W12O42] center dot 3 H2O (1) (en = ethylenediamine) has been synthesized in aqueous solution and characterized by elemental analysis, IR spectroscopy and TG analysis, together with a single crystal X-ray diffraction study. In compound 1, the Cu(en)(2)(2+) complex cation links the [W12O42](12-) anions to form a I D chain, and the ID chains are further interconnected with Na-8(H2O)(20)(8+) and Na-2(H2O)(8)(2+) cations to construct a new 3D framework.

Solvent effects on spectrophotometric titrations and vibrational spectroscopy of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin in aqueoius DMF

The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH)(1)PH2) is studied as a function of solvent composition of DMF-H2O binary solvent mixture ([OH-] = 0.04 M). Combining the structure changes of the porphyrin and the "four orbital" model of Gouterman, many features of the optical spectra of this deprotonated para-hydroxy-substituted tetraphenylporphyrin in different composition of binary solvent mixtures can be rationalized. In highly aqueous solvents, the changes of the titration curves are shown to be mainly due to hydrogen-bonding of the oxygen of the phenoxide anion group by the hydroxylic solvent, Which decreases the energy of the phenoxide anion pi orbital. Thus the phenoxide anion pi orbital cannot cross over the porphyrin Tr orbital being a different HOMO. However, its energy is close to that of the porphyrin pi orbitals. As a result, in the visible region, no charge-transfer band is observed, while in the visible-near region, the Soret peak split into two components. In nonaqueous solvents, the changes are mainly attributed to further deprotonation of pyrrolic-Hs of (OH) 1PH2 by NaOH and coordination with two sodium ions to form the sodium complex of (OH) 1PH2, which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH)(1)PH2 into three-banded spectra of regular metalloporphyrin.

Extraction kinetics of Sc(III), Y(III), La(III) and Gd(III) from chloride medium by Cyanex 302 in heptane using the constant interfacial cell with laminar flow

The extraction kinetics of Sc, Y, La and Gd(III) from the hydrochloric acid medium using Cyanex 302 (hereafter HL) in heptane solution have been measured by the constant interfacial cell with laminar flow. Reaction regions are explored at liquid-liquid interface. Extraction regimes are deduced to be diffusion-controlled for Sc(Ill) and mixed controlled for Y, La and Gd(Ill). Extraction mechanisms are discussed according to the dimeric model of Cyanex 302 in non-polar solution. From the temperature dependence of rate measurement, the values of E-a, Delta H-+/-, Delta S-+/- and Delta G(300)(+/-) are calculated and it is found that the absolute values of these parameters keep crescent trend for Sc, Y, La and Gd(III). At the same time, it is found that it can easily achieve the mutual separation among the Sc, Y and La(III) with kinetics extraction methods.

Phase transition and conformational variation of N-alkylated branched poly(ethyleneimine) comblike polymer

A series of branched poly(ethyleneimine) (PEI) derived polymers with different lengths of n-alkyl side chains, denoted as PEI(n)Cs (n = 12, 14, 16, 18, 20, number of carbon atoms in alkyl side group), have been prepared by a N-alkylation method, and systematically characterized by differential scanning calorimertry (DSC) and wide-angle X-ray diffraction (WARD) as well as Fourier transform infrared spectroscopy (FTIR). The side chains grafted on these comblike polymers are long enough to form crystalline phase composed of paraffin-like crystallites. The crystallization of the side chains forces the branched poly(ethyleneimine) molecules to pack into layered structure, between which the crystallites are located. The melting temperatures of the side chain crystallites increase from -12.36 to +51.49 degreesC with increasing the length of the side chains from n. = 12 to n = 20, which are a little bit lower than the corresponding pristine n-alkanes. PEI18C was taken as an example in this work for the investigation of phase transition and conformational variation of the side chains with temperature changing.

Crystallographic and electrochemical properties of ball-milled quasicrystalline Ti45Zr35Ni17Cu3 alloy with 20 mass% Ni

Icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder was ball-milled with 20 mass% Ni, and the effect of the ball-milling time (t) on crystallographic and electrochemical characteristics were investigated. The amounts of icosahedral quasicrystalline and Ni phases decreased when ball-milling time increased from 30 to 180 min. The powder consisted of amorphous and (Ni and Ti) phases after 360 min of ball-milling. The maximum discharge capacity of the powder electrodes first increased from 89 (t = 0 min) to 192 mAh g(-1) (t = 180 min), and then decreased to 138 mAh g(-1) (t = 360 min). The high-rate dischargeability and the discharge capacity after 15 cycles increased with increasing ball-milling time.

Synthesis and electrochemical characteristics of lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate

Four lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate were prepared and characterized by elemental analyses, LR, UV-Visible,H-1 NMR, XPS and molar conductance. The redox properties of the lutetium complex with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate in dichloromethane were studied by cyclic voltammetry.