Brownian dynamics simulation of the crystallization dynamics of charged colloidal particles

Crystal formation process of charged colloidal particles is investigated using Brownian dynamics (BD) simulations. The particles are assumed to interact with the pair-additive repulsive Yukawa potential. The time evolution of crystallization process and the crystal structure during the simulation are characterized by means of the radial distribution functions (RDF) and mean square displacement (MSD). The simulations show that when the interaction is featured with long-range, particles can spontaneously assemble into body-centered-cubic (BCC) arrays at relatively low particle number density. When the interaction is short-ranged, with increasing the number density particles become trapped into a stagnant disordered configuration before the crystallization could be actualized. The simulations further show that as long as the trapped configurations are bypassed, the face-centered-cubic (FCC) structures can be achieved and are actually more stable than BCC structures. (C) 2010 Elsevier Inc. All rights reserved.

青海湖地区普氏原羚的种群结构

普氏原羚是中国的特有动物。1986年在青海湖地区仅发现350 只普氏原羚, 分布于鸟岛、湖东2克图和元者3 个种群之中。1996～1998 年7 月至8 月, 我们沿设定的10 条样线对青海湖地区的普氏原羚进行了考察。调查样线总长度为37.55 km。观察记录距样线两侧100 m 以内普氏原羚足迹链和狼足迹链、粪堆和尿迹。同时记录观察样线两侧600 m 以内的普氏原羚个体, 记录群体大小、性别和年龄, 然后, 计算单位样带面积上普氏原羚和狼的密度。1997 年湖东2克图种群雄羚占29 %、雌羚占50 %和幼羚占21 %; 元者种群雄羚占29 %、雌羚占43 %和幼羚占27 %。狼捕食是1997 年湖东-克图种群数量下降的主要原因。在湖东-克图沙漠中, 1996 年普氏原羚群体大小为9.0 ±6.9 只(平均数±方差) , 密度为3.19 ±3.59 只/ km2 , 而1997 年为4.2 ±3.9 只/ km2 , 密度为1.14 ±1.09 只/ km2 。1997 年冬季猎狼后, 湖东-克图种群数量回升到2.14 ±3.13 只/ km2 , 幼羚占群体的27 %。

Energy transfer between silicon-oxygen-related defects and Yb3+ in transparent glass ceramics containing Ba2TiSi2O 8 nanocrystals

We report on the conversion of near-ultraviolet radiation of 250-350 nm into near-infrared emission of 970-1100 nm in Yb3+-doped transparent glass ceramics containing Ba2TiSi2O8 nanocrystals due to the energy transfer from the silicon-oxygen-related defects to Yb3+ ions. Efficient Yb3+ emission (F-2(5/2)-> F-2(7/2)) was detected under the excitation of defects absorption at 314 nm. The occurrence of energy transfer is proven by both steady state and time-resolved emission spectra, respectively, at 15 K. The Yb2O3 concentration dependent energy transfer efficiency has also been evaluated, and the maximum value is 65% for 8 mol % Yb2O3 doped glass ceramic. These materials are promising for the enhancement of photovoltaic conversion efficiency of silicon solar cells via spectra modification.

2-氨基-6-乙氧基苯并噻唑类偶氮染料及其金属鏊合物的合成及光学热学性能研究

合成了2-（2-氨基-6-乙氧基苯并噻唑基偶氮）-5-（N,N-二乙基氨基）三氟甲基磺酰苯胺偶氮染料（EBTDATFS）及其与乙酸镍、乙酸钴、乙酸铜、乙酸锌等金属盐鏊合的金属鏊合物。通过红外光谱、紫外-可见吸收光谱和MALDI质谱等对染料及其金属鏊合物进行了结构表征;使用旋涂方法在K9玻璃和抛光的单晶硅基片上制备薄膜;研究了镍金属鏊合物的热学性能;使用椭偏仪研究了Ni和Zn鏊合物的光学常数。结果表明：4种金属鏊合物薄膜最大吸收光谱为621-629nm,且长波边吸收峰陡峭;TGA-DSC测试结果表明镍金属鏊

Zn~(2+)浓度对固氮鱼腥藻(Anabaena azotica Ley)光能转化特性的影响

本实验对在不同Zn2+浓度条件下培养的固氮鱼腥藻(Anabaena azoticaLey)的生长、光合放氧速率和叶绿素荧光参数Fv/Fm进行了测定.结果表明,当Zn2+浓度为1.0μmol/L时,其比生长速率(Specific growth rate)最大,光合放氧速率和Fv/Fm值最高.当Zn2+浓度大于等于5.0μmol/L时会抑制A.azotica Ley的生长和光合作用.对在0μmol/L和5.0μmol/L Zn2+浓度下生长的藻细胞藻胆体-类囊体膜复合物吸收光谱的比较和对与5.0μmol/L

350-450nm范围的氧离子激发光谱的实验测量

在2×1.7串列加速器上,利用装有CCD的Spectrapro-500i光谱单色仪的测量装置,采用束-箔方法,在2 MeV束能下研究350-450 nm波长范围的离化态氧原子光谱。本文报道在350-450 nm范围已确定的182条光谱线,这些谱线大都属于O II到O IV原子的n、1能级间的跃迁的弱谱线。实验结果与现有的一些理论一致。实验发现,有28条谱线在以前的文献中没有报道。

Molybdenum L-shell X-ray production by 350-600 keV Xeq+ (q=25-30) ions

Molybdenum L-shell X-rays were produced by Xeq+ (q = 25-30) bombardment at low energies from 2.65 to 4.55 keV/amu (350-600 keV). We observed a kinetic energy threshold of Mo L-shell ionization down to 2.65-3.03 keV/amu (350-400 keV). The charge state effect of the incident ions was not observed which shows that the ions were neutralized, reaching an equilibrium charge state and losing their initial charge state memory before production of L-shell vacancies resulted in X-ray production. The experimental ionization cross sections were compared with those from Binary Encounter Approximation theory. Taking into account projectile deflection in the target nuclear Coulomb field, the ionization cross section of Mo L-shell near the kinetic energy threshold was well described. (C) 2010 Published by Elsevier B.V.

Fabrication, patterning and luminescence properties of X-2-Y2SiO5 : A (A = Eu3+, Tb3+, Ce3+) phosphor films via sol-gel soft lithography

X-2-y(2)SiO(5):A (A = Eu3+, Tb3+, Ce3+) phosphor films and their patterning were fabricated by a sol-gel process combined with a soft lithography. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), scanning electron microscopy (SEM) optical microscopy and photoluminescence (PL) were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 900 degreesC with X-1-Y2SiO5, which transformed completely to X-2-Y2SiO5 at 1250 degreesC. Patterned thin films with different band widths (5 pin spaced by 5 pm and 16 pm spaced by 24 pm) were obtained by a soft lithography technique (micromoulding in capillaries, MIMIC). The SEM and AFM study revealed that the nonpattemed phosphor films were uniform and crack free, and the films mainly consisted of closely packed grains with an average size of 350 run. The doped rare earth ions (A) showed their characteristic emissions in X-2-Y2SiO5 phosphor films, i.e., D-5(0)-F-7(J) (J = 0, 1, 2,3,4) for Eu3+, D-5(3), (4)-F-7(J) (J = 6, 5, 4, 3) for Tb3+ and 5d (D-2)-4f (F-2(2/5),(2/7)) for Ce3+, respectively. The optimum doping concentrations for EU3+, Tb3+ were determined to be 13 and 8 mol% of Y3+ in X-2-Y2SiO5 films, respectively.

A new hydrometallurgical process for extracting rare earths from apatite using solvent extraction with P-350

In this paper, a new process is proposed to recover rare earths from nitric acid leaching of apatite without interfering with the normal route for fertilizer production using solvent extraction with dimethyl heptyl methyl phosphonate CH3P(O)(OC8H17)(2) (P-350, B). In the present work, the leaching conditions are studied. In selected condition, apatite was dissolved in 20% (v/v) nitric acid solution at 60-70 degrees C while agitating. The most suitable acidity for extraction is 0.4 M HNO3. More than 98% of rare earths in apatite can be recovered using countercurrent extraction process with six stages when phase ratio = 0.5, and defluorination is unnecessary. The influences of phase ratio, stage number, acidity and salting-out agent on extractabilities Of P-350 are studied. The results show that rare earths can be separated with P-350 from Ca, P, Fe and other impurities. Mixed rare earth oxides (REO) of which purity is more than 95% with yield over 98% can be obtained.

Dissolved oxygen and O-2 flux across the water-air interface of the Changjiang Estuary in May 2003

The field observation of this study was carried out in the Changjiang Estuary from May 19 to 26,2003, just a few days before the Three Gorges Dam began to store water. A total of 29 stations, including 2 anchor stations, were distributed through almost the whole salinity gradient Based on the data gained from these stations, the biogeochemical characteristics of dissolved oxygen (DO) were examined. Spatial distribution of DO concentrations showed the pattern that it increased in a downriver direction. DO concentration generally varied within a narrow range of 733-8.10 mg l(-1) in the freshwater region and the west part of the mixed water region, and after that it increased rapidly. In vertical direction, the differences in DO concentrations between surface and 2 m above the bottom were big at the stations with water depths exceeding 20 m; DO concentration up to 14.88 mg l(-1) was recorded at the sea surface, while at 2 m above the bottom its concentration was only about 4 mg l(-1). The fluctuation in DO concentrations was small during a period of 48 h in the mixed water region and 2 m above the bottom of the seawater region; while it was large during the same period in the seawater region for surface and 5 m below the surface layer, and a maximum variation from 8.77 to 12.66 mg l(-1) in 4 h was recorded. Oxygen fluxes also showed a marked spatio-temporal variation. As a whole, the freshwater region and mixed water region were an oxygen sink while the seawater region was a source. Relationships between dissolved oxygen and some biogeochemical parameters which could markedly influence its spatio-temporal distribution were discussed in this paper. (C) 2008 Elsevier B.V. All rights reserved.

Determination of heat capacities and thermodynamic properties of 2-(chloromethylthio)benzothiazole by an adiabatic calorimeter

The molar heat capacities of 2-(chloromethylthio)benzothiazole (molecular formula C8H6ClNS2, CA registry no. 28908-00-1) were measured with an adiabatic calorimeter in the temperature range between (80 and 350) K. The construction and procedures of the calorimeter were described in detail. The performance of the calorimetric apparatus was evaluated by heat capacity measurements on alpha-Al2O3. The deviation of experiment heat capacities from the corresponding smoothed values lies within 0.3%, whereas the uncertainty is within +/-0.5%, compared with that of the recommended reference data over the whole experimental temperature range. A fusion transition was found from the C-p-T curve of 2-(chloromethylthio)benzothiazole. The melting temperature and the molar enthalpy and entropy of fusion of the compound were determined to be T-m = (315.11 +/- 0.04) K, Delta(fus)H(m) = (17.02 +/- 0.03) kJ(.)mol(-1), and Delta(fus)S(m) = (54.04 +/- 0.05) J(.)mol(-1.)K(-1), respectively. The thermodynamic functions (H-T - H-298.15) and (S-T - S-298.15) were also derived from the heat capacity data. The molar fraction purity of the 2-(chloromethylthio)benzothiazole sample used in the present calorimetric study was determined to be 99.21 by fraction melting.