Substrate surface atomic structure influence on the growth of InAlAs quantum dots

We have examined the influence of substrate surface orientation on self-assembled InAlAs/AlGaAs quantum dots grown on (0 0 1) and (n 1 1) A/B (n = 3, 5) GaAs substrates by molecular beam epitaxy (MBE). Preliminary characterizations have been performed using photoluminescence (PL) and transmission electron microscopy (TEM). The PL emission energies of quantum dots on high Miller index surface are found to be strongly dependent on the atomic-terminated surface (A or B surface) of the substrate. We observed that there were planar ordering larger islands on (3 1 1)B surface compared to (0 0 1) surface, in contrast, a rough interface and smaller "grains" on (3 1 1)A surface, this result is identical with PL emission energy from these islands. We propose that the rapid strain-induced surface "roughening" impedes the formation of 3D islands on A surface, and indicating that this is a promising approach of the realization of ordering distribution on (3 1 1)B plane for devices such as red-emitting semiconductor quantum dots lasers. (C) 1999 Elsevier Science B.V. All rights reserved.

Novel Sulfonated Polyimide Ionomers by Incorporating Pyridine Functional Group in the Polymer Backbone

A series of sulfonated polyimides (SPIs) containing pyridine ring in the polymer backbone were synthesized by the polycondensation of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTDA), 5-(2,6-bis(4-arninophenyl)pyridin-4-yl)-2-methoxy benzene sulfonic acid (SDAM), and 4,4'-diaminodiphenyl ether (ODA). Flexible, transparent, and tough membranes were obtained. Property study revealed that all the membranes displayed high thermal stability with the desulfonation and decomposition temperature higher than 290 and 540 degrees C, respectively, as well as good mechanical property with Young's modulus larger than 1.0 GPa, maximum strength (MS) on a scale of 60-80 MPa, and elongation at break (EB) ranged from 41.79 to 75.17%.

ELECTROCHEMICAL REACTION OF CYTOCHROME-C AT GOLD ELECTRODES MODIFIED WITH THIOPHENE CONTAINING ONE FUNCTIONAL-GROUP

The electrochemical reactions of cytochrome c were studied at a thiophene-modified gold electrode. It was demonstrated that thiophene is an effective promoter, although there is only one functional group in the molecule. Based on this result, the mechanis

PENDANT FUNCTIONAL-GROUP COPOLYETHER SULFONES .1. SYNTHESIS AND CHARACTERIZATION OF NEW COPOLYETHER SULFONES WITH PENDANT ALDEHYDE GROUPS MODIFIED INTO PHENOLIC AZOMETHINE GROUPS

New functional copolyether sulfones with pendant aldehyde groups were synthesized by the classical polycondensation reaction between 4,4' -dichlorodiphenyl sulfone (I) and various bisphenols such as 5,5'-methylene bis-salicylaldehyde (II-2), 2,2-bis( 4-hydroxyphenyl)propane (III), and 2,6-bis(4-hydroxybenzylidene)cyclohexanone (IV). Condensation reaction with 4-aminophenol led to pendant phenolic azomethine groups containing copolyether sulfones. The structures of the resulting polymers were confirmed by IR, H-1-NMR spectra, and elemental analyses. The polymers were characterized by reduced viscosity, solubility, thermal stability, DSC, and x-ray diffraction measurements.

The influence of the microstructure evolution on the surface morphology in the annealing process of helium-implanted spinel

Single-crystalline spinel (MgAl2O4) specimens were implanted with helium ions of 100 keV at three successively increasing fluences of (0.5, 2.0 and 8.0) x 10(16) ions/cm(2) at room temperature. The specimens were subsequently annealed in vacuum at different temperatures ranging from 500 to 1100 degrees C. Different techniques, including Fourier transformed infrared spectroscopy (FTIR), thermal desorption spectrometry (TDS), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the specimens, It was found that the absorbance peak in the FTIR due to the stretching vibration of the Al-O bond shifts to smaller wave numbers with increasing fluence, shifting back to larger wave numbers with an increase of annealing temperature. The absorbance peak shift has a linear relationship with the fluence increase in the as-implanted state, while it does not have a linear relationship with the fluence increase after the annealing process. Surface deformation occurred in the specimens implanted with fluences of 2.0 and 8.0 x 10(16) ions/cm(2) in the annealing process. The phenomena described above can be attributed to differences in defect formation in the specimens. (C) 2008 Elsevier B.V. All rights reserved.

Influence of Electrostatic Interaction on Fibrinogen Adsorption on Gold Studied by Imaging Ellipsometry Combined with Electrochemical Methods

Imaging ellipsometry was combined with electrochemical methods for studying electrostatic interactions of protein and solid surfaces. The potential of zero charge for gold-coated silicon wafer/solution interfaces wad determined by AC impedance method. The potential of the gold-coated silicon wafer was controlled at the potential of zero charge, and the adsorption of fibrinogen on the potential-controlled and non-controlled surfaces was measured in real time at the same time by imaging ellipsometry The effect of electrostatic interaction was studied by comparing the difference between the potential of controlled adsorption and the Potential of noncontrolled adsorption. It was shown that the rate of fibrinogen adsorption on the potentiostatic surface was faster than that on the nonpotentiostatic surface. The electrostatic influence on fibrinogen adsorption on the gold-coated silicon wafer was weak, so the hydrophobic interaction should be the major affinity.

Influence of buoyancy on floating-zone convection of small bond number

Gravity may influence the velocity and temperature distributions, bouyancy may induce Rayleigh instability and the instability may be excited due to the change of free surface shape associating with gravity in the thermocapillary convection. These effects have been studied in the present paper. The results show that gravity may have an important effect in thermocapillary oscillatory convection even for the cases of small Bond number experiments either on the ground or in space.

放牧对草原群落主要植物种和功能群水分来源与水分利用效率的影响

水分是半干旱草原生态系统植物多样性和初级生产力的限制因素。近年来由于人为干扰和气候干旱，特别是过度放牧，导致半干旱地区草原严重退化，草地生产利用和生态服务功能日益衰减，自然灾害频繁发生。草原退化演替主要表现为不同植物种的消长和替代过程。在内蒙古草原，过度放牧导致多年生根茎禾草和丛生禾草被豆科灌木或具根茎和不定根的杂类草替代，丰富的多年生杂类草被一、二年生植物替代。目前，对于上述功能群之间的替代机制，以及草原退化的机理尚不十分清楚。本研究在中国科学院内蒙古草原生态系统定位研究站选取了79年围封的大针茅(Stipa grandis)样地、其外围的自由放牧样地及中德合作项目“ Matter Fluxes in grassland of Inner Mongolia as influenced by stocking rate (MAGIM) ”的传统平地放牧处理小区为研究对象，从植物-水分关系的角度，利用氢和碳稳定性同位素技术，研究主要植物种和功能群水分来源和水分利用效率对放牧的响应，进而揭示放牧干扰下草原退化的机理。本研究取得了如下主要研究结果和结论： 1. 在干旱年份，雨水仅湿润了大针茅草原0-20cm的表层土壤。土壤中保存的冬季降水贡献了植物可利用水分的30%，而在正常年份只有10%。干旱季节羊草(Leymus chinensis)和大针茅能够利用土壤60cm以下保存的多年降水，而糙隐子草(Cleistogenes squarrosa)和冰草(Agropyron cristatum)只能利用生长季的雨水。长期过度放牧使冰草和糙隐子草的相对生物量和相对多度均显著增加，而羊草的相对生物量和相对多度显著降低。这种由放牧引起的群落结构与组成的改变，降低了植被对冬季降水的利用，加剧了干旱对生态系统的影响。 2. 依据羊草草原群落植物的生活型和光合类型划分为：C4禾草、C4杂类草、C4灌木、C3禾草、C3杂类草、C3鳞茎类植物和C3灌木七个功能群，各功能群间的水分利用效率差异显著。不同功能群植物在对土壤水分的利用上存在着明显的生态位分离。C4禾草和C3鳞茎类植物主要利用表层水分，而C4灌木则利用深层土壤水分，C3其它功能群介于二者之间。在无放牧和低载畜率下，各功能群植物均主要吸收浅层土壤水分，功能群间竞争相对强烈。在较高载畜率下，C3禾草转为利用深层土壤水分，功能群间出现水分生态位的分离，部分地缓解了植物对土壤表层水分的竞争。沿着载畜率梯度，群落对浅层土壤水分的利用呈现出先增加，尔后下降的趋势。 3. 在放牧干扰下，羊草草原群落中主要植物种稳定性碳同位素值的变化范围为-13.100/00~-27.590/00。不同功能群植物间的水分利用效率有着显著的差异：C4禾草> C4杂类草> C4灌木> C3禾草、C3杂类草> C3鳞茎类植物> C3灌木。C3鳞茎类植物和C4杂类草的水分利用效率随载畜率增加而降低。C3和C4禾草的水分利用效率随载畜率的增加表现为先增加，尔后下降的趋势。群落水平的水分利用效率主要由占生物量90%的禾草的水分利用效率决定。随着载畜率增加，群落水分利用效率有逐渐降低的趋势。

Variations and possible source of potentially available phosphorus in a Chinese shallow eutrophic lake

Surface, overlying, and interstitial waters were collected at monthly intervals at three experimental stations in a shallow Chinese eutrophic lake (Lake Donghu) to assess the occurrence, distribution, and status of UV-sensitive phosphorus compounds (UVSP) and phosphatase hydrolyzable phosphorus (PHP), coupled with kinetics of alkaline phosphatase activity (APA). Orthophosphate (o-P) concentrations were generally the highest at Station 1, where chlorophyll a (chl a) was a function of o-P at temporal scale. The V-max/K-m of APA obtained by Michaelis-Menten approach paralleled the chlorophyll data at two stations. These facts imply that the development of phytoplankton may be attributed to APA induced by PHP. The potentially available UVSP and PHP peaked in interstitial, overlying, and surface water simultaneously sometimes in 1995 to 1996 and 1997 to 1999. It is postulated that they may arise from the bottom. UVSP peaked in interstitial water at the 12-16 cm layers in sediment cores. Moreover, in interstitial water, UV irradiation resulted in an elevated o-P concentration and decreased APA in a timeseries analysis. Therefore, the mechanism that APA involved in the process of photorelease of o-P was not demonstrated. UVSP is most likely a functional group of labile phosphorus distinct from the enzymatic substrate in this shallow eutrophic lake.

Influence of interface modification on the performance of polymer/Bi2S3 nanorods bulk heterojunction solar cells

In this paper, bulk heterojunction photovoltaic devices based on the poly[2-methoxy-5-(3',7'-dimethyloctyloxy)- 1,4-phenylenevinylene] (MDMO-PPV):Bi2S3 nanorods hybrid material were present. To optimize the performance of the devices, the interface modification of the hybrid material that has a significant impact on the exciton dissociation efficiency was studied. An improvement in the device performance was achieved by modifying the Bi2S3 surface with a thin dye layer. Moreover, modifying the Bi2S3 surface with anthracene-9-carboxylic acid can enhance the performance further. Compared with the solar cells with Bi2S3 nanorods hybrid with the MDMO-PPV as the active layer, the anthracene-9carboxylic acid modified devices are better in performance, with the power conversion efficiency higher by about one order in magnitude.

2-C-支链-1,6-脱水吡喃葡萄糖的开环反应及吡喃烯糖的合成研究

在糖化学合成中，1,6-脱水吡喃糖不仅是合成具有生物活性低聚糖、糖共体、抗原、抗体以及天然产物等化合物重要原料，而且还是许多具有生物活性的天然产物的结构单元。同时，它还具有[3,2,1]的双环缩醛结构，使其在糖化学合成中具有高的立体选择性和区域选择性，同时减少了C-1 和C-6 位的保护和去保护的优点。此外，环内的缩醛开环后，又可以相应地在C-1 和C-6 位进行官能团转化以及糖苷化反应。 本文报道了一种新的1,6-脱水吡喃糖的合成方法，并设计合成了2-C-支链-1,6-脱水吡喃葡萄糖1-195、1-197、1-198 以及2-C-支链-6-硫代1,6-脱水吡喃葡萄糖1-225。到目前为止，1,6-脱水糖开环并进行糖苷化反应，存在选择性较差、产率低的缺点。我们发现，在乙腈做溶剂的条件下，NiCl5 能高立体选择性高产率地催化化合物1-195、1-197、1-198 开环并与ROH、RSH 发生糖苷化反应。在NiCl5-乙腈条件下，合成了一系列2-C-支链-α-糖苷和2-C-支链-β-硫代糖苷，并对2-C-支链1,6-脱水吡喃葡萄糖的生成机理以及开环机理进行了探讨。 烯糖在糖化学合成中是重要的起始原料，从Fischer 首次合成烯糖至今，一直不断地有新的合成方法出现。但目前文献报道的方法存在所用试剂有毒、价格贵和操作繁琐等缺点。我们对Fischer-Zach 方法进行了改进， 发现Zn-NaH2PO4-H2O 和Zn-PEG600-H2O 体系都能很好地合成烯糖。该方法具有条件温和、绿色环保、操作简单的优点。在Zn-NaH2PO4 溶液或Zn-PEG600 条件下，以溴代糖为原料，高产率地合成一系列的烯糖。 The 1,6-anhydrohexopyranoses are crucial subunits of myriad bioactive nature products, as well as important syntons of carbohydrate chemistry which have been extensively used to prepare the biologically potential oligosaccharides, glycoconjugates, antibiotics, and structurally varied nature products. Their particular [3.2.1] bicyclic skeleton makes them have high regio- and stereo-control in a variety of reactions, and such structure avoids protecting hydroxyl groups at C1 and C6.Additionally, the cleavage of the internal acetal under acidic conditions could be beneficial for further transformations of functional group and glycosylation of the corresponding pyranosyl sugar at the C6 or C1 site. Herein we developed a novel approach to prepare the 1,6-anhydrohexopyranose, and synthesized the 2-C-branched-1,6-anhydrohexopyranose 1-195, 1-197, 1-198 and 2-C-branched-6-thio-1,6-anhydrohexopyranose 1-225. Until now, glycosylation of 1,6-anhydrohexopyranoses has been limited because of the low yields and low stereoselectivity. In this paper, we found that NiCl5-MeCN system could selectively cleave the ring of 1,6-anhydrohexopyranoses with alcohols and thiols at room temperature in high yields. A series of 2-C-branched-α-glycosides and 2-C-branched-β-thioglycosides have been synthesized via NiCl5-catalyzed. Furthermore, we investigated the formation and ring-opening mechanism of 2-C-acetylmethyl-1,6-anhydrohexopyranose. Glycals are significant starting material in carbohydrate chemistry. After the Fischer-Zach method for forming glucal was reported for the first time, the numerous synthetic methods for glycals have been explored. However, there are several drawbacks in the existing methods, such as the usage of very expensive and toxic reagents, intricate operation, and the influence of acid-sensitive and base-sensitive functional group. We improved the Fischer-Zach method and developed a facile, mild and environmentally benign methodology towards the synthesis of the glycals in Zn-NaH2PO4-H2O or Zn-PEG600-H2O system. Our method involves the treatment of glycosyl bromides with Zn in NaH2PO4 aqueous solution or PEG600-H2O at room temperature, affording various glycals in excellent yields.

Stable Isotope Probing:Linking Functional Activity to Specific Members of Microbial Communities

Linking organisms or groups of organisms to specific functions within natural environments is a fundamental challenge in microbial ecology. Advances in technology for manipulating and analyzing nucleic acids have made it possible to characterize the members of microbial communities without the intervention of laboratory culturing. Results from such studies have shown that the vast majority of soil organisms have never been cultured, highlighting the risks of culture-based approaches in community analysis. The development of culture-independent techniques for following the flow of substrates through microbial communities therefore represents an important advance. These techniques, collectively known as stable isotope probing (SIP), involve introducing a stable isotope-labeled substrate into a microbial community and following the fate of the substrate by extracting diagnostic molecular species such as fatty acids and nucleic acids from the community and determining which specific molecules have incorporated the isotope. The molecules in which the isotope label appears provide identifying information about the organism that incorporated the substrate. Stable isotope probing allows direct observations of substrate assimilation in minimally disturbed communities, and thus represents an exciting new tool for linking microbial identity and function. The use of lipids or nucleic acids as the diagnostic molecule brings different strengths and weaknesses to the experimental approach, and necessitates the use of significantly different instrumentation and analytical techniques. This short review provides an overview of the lipid and nucleic acid approaches, discusses their strengths and weaknesses, gives examples of applications in various settings, and looks at prospects for the future of SIP technology.

Preparation and characterization of post-derivatives from functional polystyrene (ATRP) with p-nitroaniline-azomethine phenol and their thermal and optical study

The functional polystyrene, (Cl-PS)(2)-CHCOOCH2CH2OH ( designated as XPSt and coded P2) was prepared by ATRP at 130(0)C using CuCl and bipyridine as catalysts, 2,2-dichloro acetate-ethylene glycol (DCAG) as multifunctional initiator and THF as solvent. 4-Nitoroaniline azomethine-4' phenol (P1) as chromophores were covalently linked to the functional end groups of the polymer by using simple displacement reaction. The functional polystyrenes, namely XPSt (P2) and (PS)(2)-CHCOOCH2CH2OH, designated as X-PSt and coded P3 and their post-derivatives, namely, DXPSt (P4) and DX-PSt (P5) respectively were characterized by IR, NMR and UV spectroscopies, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), polarising optical microscopy (POM) and XRD studies. DSC showed that incorporation of chromophores in the side chains of polymers towards the polystyrene moiety increases the rigidity of the polymer and subsequently, its glass transition temperature; however the incorporation of side chain towards the alcoholic functional group decreases the glass transition temperature. The post derivatives do not play any significant role to increase the thermal stability ( TGA).

Effect of properties of active carbon supports on performance of Pt/C catalysts in polymer electrolyte membrane fuel cell

The Pt/C catalysts were prepared with pine active carbon and Vulcan XC-72 active carbon as the supports. The performances of the Pt/C catalysts in polymer electrolyte membrane fuel cell were compared. The result indicates that the performance of Pt/Vulcan XC-72 is better than that of Pt/pine. The physical and chemical properties of the two active carbons were measured using several analysis techniques. It was found that the pore size, specific conductivity and the surface function group significantly influence the performance of the electrocatalyst.