微重力细胞生物学实验地面模拟技术研究

<正>微重力对细胞的影响是空间生命科学研究的重要环节,(哺乳动物)细胞感受重力变化的机制是其中的一个基本问题。由于空间实验机会稀少且成本昂贵,必须辅助以相关的地面微重力效应模拟方法。旋转培养器在微重力细胞生物学实验中一直是模拟微重力效应的主要手段,其前提假设是,旋转可以"迷惑"细胞对固定重力方向的感知,并且重力方向改变的速度快于细胞对重力方向感知的响应时间阈值。严格上说旋

遮阴对黄波罗幼苗的光合特性及光能利用效率的影响

一直以来黄波罗(Phellodendron amurense)被认为是不耐阴树种,然而引入美国纽约后,发现它具有一定的耐阴性,在全光和林下均能更新,在纽约已经成为生物入侵种。为了探讨黄波罗的耐阴性问题,通过设置自然光与遮阴(15%自然光)两种光环境,观测了三年生黄波罗幼苗(遮阴1a后)光合生理参数、光能利用效率、叶绿素和比叶重的变化。结果表明,与自然光处理相比,遮阴处理的黄波罗幼苗最大光合速率、表观量子效率和暗呼吸速率略有下降,但差异不显著(p>0.05),光补偿点下降显著(p<0.05);同时,单位面积叶绿素含量无显著差异(p>0.05),而单位干重叶绿素含量显著升高,比叶重显著下降,叶面积显著增大(p<0.05)。上述结果说明:遮阴的黄波罗幼苗通过降低光补偿点和暗呼吸速率利用环境中的弱光,同时通过减小比叶重、增大叶面积和提高叶绿素b相对含量来增强对光的捕获,使其在弱光时的光能利用效率提高。由此推断,黄波罗幼苗能适应一定程度的遮阴。

基于县域要素的三江源地区旅游扶贫模式探讨

随着我国旅游业的兴起,人们越来越认识到旅游在消除贫困上的潜力和能力,然而,要让旅游真正朝着有利于消除贫困的方向发展,必须对旅游的发展方式加以调整,因地制宜地选择旅游扶贫的模式。本文构建了三江源地区各县贫困程度和旅游资源禀赋评价指标体系,定量测度了各评价区的贫困度和旅游资源禀赋综合得分,并采用四象限法划分出资高贫低、双高、双低、资低贫高4种旅游扶贫类型区,在此基础上,提出适用于整个三江源地区的旅游扶贫基本模式为政府主导模式,以及各类型区的旅游扶贫辅助模式,即资高贫低区的政企合作模式,双高区的项目推动模式,双

超细Ir催化剂对氨氧化的电催化性能

报道了一种新型的、用NH4F作络合剂的络合还原法制备的Ir催化剂及其对氨氧化的电催化性能.结果表明,由于溶液中的Ir3+和NH4F形成络合物,因此用这种络合法制得Ir催化剂中Ir粒子的平均粒径为2.8nm,要比不加络合剂时制得的Ir催化剂中Ir粒子的平均粒径(7.5nm)小很多.所以,用络合还原法制得的Ir催化剂对氨氧化的电催化活性和稳定性都比不加络合剂时制得的Ir催化剂好很多.且该制备方法简单、实用,适用于催化剂的实际生产.

The influence of arrangement of St in MBS on the properties of PVC/MBS blends

Three series of MBS core-shell impact modifiers were prepared by grafting styrene and methyl methacrylate onto PB or SBR seed latex in emulsion polymerization. All the MBS modifiers were designed to have the same total chemical composition, and MMA/Bd/St equals 30/42/28, which is a prerequisite for producing transparent blends with PVC. Under this composition, there were three different ways of arrangement for styrene in MBS, which led to the different structure of MBS modifier. The concentration of MBS in PVC/MBS blends was kept at a constant value of 20 wt.%. The effects of arrangement of St in MBS on the mechanical and optical properties of PVC/MBS blends were studied. The notched Izod impact test results showed that the MBS with a PB homopolymer core grafted with St had a lowest brittle-ductile transition (BDT) temperature and BDT temperature increased with the amount of St copolymerized with Bd in the core of MBS. The transparency of blends also increased with the amount of St copolymerized with Bd in the core. TEM results showed that the arrangement of St in MBS influenced the deformation behavior. Two deformation modes were observed in the blends: cavitation and shear yielding.

Amperometric tyrosinase biosensor based on a sol-gel-derived titanium oxide-copolymer composite matrix for detection of phenolic compounds

A new type of tyrosinase biosensor was developed for the detection of phenolic compounds, based on the immobilization of tyrosinase in a sol-gel-derived composite matrix that is composed of titanium oxide sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine. Tyrosinase entrapped in the composite matrix can retain its activity to a large extent owing to the good biocompatibility of the matrix. The parameters of the fabrication process and the variables of the experimental conditions for the enzyme electrode were optimized. The resulting sensor exhibited a fast response (20 s), high sensitivity (145.5 muA mmol(-1) 1) and good storage stability. A detection limit of 0.5 muM catechol was obtained at a signal-to-noise ratio of 3.

Novel poly(aryl ether ketone)s containing various pendant groups .2. Gas-transport properties

The gas transport of hydrogen, oxygen, nitrogen, carbon dioxide, and methane gases in a series of poly(aryl ether ketone)s was examined. These polymer membranes have a wide range of permeability coefficients and permselectivity coefficients, showing excellent gas-transport properties. The enhanced interchain interaction in the polymers due to intermolecular hydrogen bonds and ionic bonds results in a considerable increase in permselectivity but a decrease in permeability. On the contrary, the polymers with bulky arkyl substituents show significantly increased permeability. The causes of this trend are interpreted in terms of the free volume, interchain distance, and glass transition temperature together with the respective contribution of gas solubility and diffusivity to the overall permeability. Of interest is the observation that the ionomer IMPEK-K+, which simultaneously contains bulky isopropyl substituents and pendant carboxylate groups, exhibits over twice higher CO2 permeability and 15% higher CO2/CH4 permselectivity than those of bisphenol-A p'olysulfone (PSF). The possibility of using the new synthesized poly(aryl ether ketone)s in gas separation membrane application is also discussed. (C) 1997 John Wiley & Sons, Inc.

Characterization of degQ(Vh), a serine protease and a protective immunogen from a pathogenic Vibrio harveyi strain

Vibrio harveyi is an important marine pathogen that can infect a number of aquaculture species. V. harveyi degQ (degQ(Vh)), the gene encoding a DegQ homologue, was cloned from T4, a pathogenic V. harveyi strain isolated from diseased fish. DegQ(Vh) was closely related to the HtrA family members identified in other Vibrio species and could complement the temperature-sensitive phenotype of an Escherichia coli strain defective in degP. Expression of degQVh in T4 was modulated by temperature, possibly through the sigma(E)-like factor. Enzymatic analyses demonstrated that the recombinant DegQVh protein expressed in and purified from E. coli was an active serine protease whose activity required the integrity of the catalytic site and the PDZ domains. The optimal temperature and pH of the recombinant DegQVh protein were 50 C and pH 8.0. A vaccination study indicated that the purified recombinant DegQVh was a protective immunogen that could confer protection upon fish against infection by V. harveyi. In order to improve the efficiency of DegQVh as a vaccine, a genetic construct in the form of the plasmid pAQ1 was built, in which the DNA encoding the processed DegQVh protein was fused with the DNA encoding the secretion region of AgaV, an extracellular beta-agarase. The E.coli strain harboring pAQ1 could express and secrete the chimeric DegQVh protein into the culture supernatant. Vaccination of fish with viable E. coli expressing chimeric degQ(Vh) significantly (P < 0.001) enhanced the survival of fish against V. harveyi challenge, which was possibly due to the relatively prolonged exposure of the immune system to the recombinant antigen produced constitutively, albeit at a gradually decreasing level, by the carrier strain.

Isolation and mapping of telomeric pentanucleotide (TAACC)(n) repeats of the pacific whiteleg shrimp, Penaeus vannamei, using fluorescence in situ hybridization

To develop genetic and physical maps for shrimp, accurate information on the actual number of chromosomes and a large number of genetic markers is needed. Previous reports have shown two different chromosome numbers for the Pacific whiteleg shrimp, Penaeus vannamei, the most important penaeid shrimp species cultured in the Western hemisphere. Preliminary results obtained by direct sequencing of clones from a Sau3A-digested genomic library of P. vannamei ovary identified a large number of (TAACC/GGTTA)-containing SSRs. The objectives of this study were to (1) examine the frequency of (TAACC)(n) repeats in 662 P. vannamei genomic clones that were directly sequenced, and perform homology searches of these clones, (2) confirm the number of chromosomes in testis of P. vannamei, and (3) localize the TAACC repeats in P. vannamei chromosome spreads using fluorescence in situ hybridization (FISH). Results for objective I showed that 395 out of the 662 clones sequenced contained single or multiple SSRs with three or more repeat motifs, 199 of which contained variable tandem repeats of the pentanucleotide (TAACC/GGTTA),, with 3 to 14 copies per sequence. The frequency of (TAACC)n repeats in P. vannamei is 4.68 kb for SSRs with five or more repeat motifs. Sequence comparisons using the BLASTN nonredundant and expressed sequence tag (EST) databases indicated that most of the TAACC-containing clones were similar to either the core pentanucleotide repeat in PVPENTREP locus (GenBank accession no. X82619) or portions of 28S rRNA. Transposable elements (transposase for Tn1000 and reverse transcriptase family members), hypothetical or unnamed protein products, and genes of known function such as 18S and 28S rRNAs, heat shock protein 70, and thrombospondin were identified in non-TAACC-containing clones. For objective 2, the meiotic chromosome number of P. vannamei was confirmed as N = 44. For objective 3, four FISH probes (P1 to P4) containing different numbers of TAACC repeats produced positive signals on telomeres of P. vannamei chromosomes. A few chromosomes had positive signals interstitially. Probe signal strength and chromosome coverage differed in the general order of P1 > P2 > P3 > P4, which correlated with the length of TAACC repeats within the probes: 83, 66, 35, and 30 bp, respectively, suggesting that the TAACC repeats, and not the flanking sequences, produced the TAACC signals at chromosome ends and TAACC is likely the telomere sequence for P. vannamei.