Molecular beam epitaxy

Molecular beam epitaxy is an ultrahigh vacuum technique for growing very thin epitaxial layers of semiconductor crystals. Because it is inherently a slow growth process, extreme dimensional control over both major compositional variations and impurity incorporation can be achieved. The result is that it has been possible, with one combination of lattice-matched semiconductors, GaAs and Alx-Gal-xAs, to demonstrate a large variety of novel single-crystal structures. These results have important implications for fundamental studies of the physics of thin-layered structures and for the development of new semiconductor electronic and optoelectronic devices.     

Molecular beam scattering from liquid surfaces

By means of controlled collisions of atoms and molecules with liquid surfaces, molecular beam experiments can be used to probe how gases stick to, rebound from, and exchange energy with molecules in the liquid phase. This report describes measurements of energy exchange in collisions between gases (neon, xenon, and sulfur hexafluoride) and polyatomic liquids (squalane and perfluoropolyether). Energy transfer depends critically on liquid composition and is more efficient for the hydrocarbon than for the perfluorinated ether.     

Molecular thermodynamics for chemical process design

Chemical process design requires quantitative information on the equilibrium properties of a variety of fluid mixtures. Since the experimental effort needed to provide this information is often prohibitive in cost and time, chemical engineers must utilize rational estimation techniques based on limited experimental data. The basis for such techniques is molecular thermodynamics, a synthesis of classical and statistical thermodynamics, molecular physics, and physical chemistry.     

Theoretical studies of the energetics and dynamics of chemical reactions

Computational studies of basic chemical processes not only provide numbers for comparison with experiment or for use in modeling complex chemical phenomena such as combustion, but also provide insight into the fundamental factors that govern molecular structure and change which cannot be obtained from experiment alone. We summarize the results of three case studies, on HCO, OH + H(2), and O + C(2)H(2), which illustrate the range of problems that can be addressed by using modern theoretical techniques. In all cases, the potential energy surfaces were characterized by using ab initio electronic structure methods. Collisions between molecules leading to reaction or energy transer were described with quantum dynamical methods (HCO), classical trajectory techniques (HCO and OH + H(2)), and statistical methods (HCO, OH + H(2), and O + C(2)H(2)). We can anticipate dramatic increases in the scope of this work as new generations of computers are introduced and as new chemistry software is developed to exploit these computers.     

Change in biogenic accumulative elementary pedogenic processes in zones with a different level of pollution by copper smelter emissions

It is shown that litter formation, humification, and the humus state of soils in zones at different distances from a smelter are determined by biotic and abiotic components of the ecological conditions of pedogenesis.     

Molecular self-assembly and nanochemistry: a chemical strategy for the synthesis of nanostructures

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.     

Molecular phylogenetical studies of the thermophilic spore-forming desulfotomaculum isolated from oil-field

A novel thermophilic and heterotrophic sulfate-reducing bacteria, strain CW-03, was isolated from crude oil well whose depth was 3.2 kilometer. The bacterium was strictly anaerobic; it does not endure acid and its maximum surviving temperature was 70℃. Many short chain organic compounds can be utilized as electron donors, which were acetate, formate, lactate, propionate, pyruvate, butyrate, succinate, malate, fumarate, valerate, caproate, heptanoate, octanoate, decanoate, tridecanoate, pentadecanoate, palmitate, heptadecanoate or ethanol, while sulfate and sulfite were used as electron acceptors. The following substrates were not utilized： benzoate undecanoate, dodecanoate, tetradecane, propanol, butanol, H2＋CO2 （80/20%; v/v） and acetate （1mM） ＋ H2. When lactate was used as electron donors, sulfite and thiosulfate, but not sulfer and nitrate, can be used as electron acceptors. Strain CW-03 was motile, curved rod, Gram-positive, pole flagellum and spore-forming. On the basis of 16S rRNA sequence alignment （accession numbers： AY703032）, CW-03 should be included in the genus Desulfotomaculum with BLAST analysis on line. However, some of its physiology and multiple sequence alignments were different from other members of this genus. Therefore, CW-03 should be recognized as a new species, for which we propose the name Desulfotomaculum chinamiddle （Bacteria, Firmicutes, Clostridia, Clostridiales, Peptococcaceae）.     

大叶胡颓子叶和茎化学成分预试的对比研究

采用化学成分系统预试法,对大叶胡颓子叶、茎的纯化水、石油醚及95%乙醇提取物进行研究,结果表明,大叶胡颓子叶、茎中均含有甾体或三萜类、酚类、鞣质、香豆素与萜类内酯、强心苷、有机酸、糖及其苷类、皂苷、氨基酸、多肽、蛋白质,叶中未检测到黄酮、蒽醌而茎的反应明显,茎中未检测到生物碱而叶的反应较明显。说明大叶胡颓子叶与茎含有多种药理活性成分,但在成分类型及其含量上存在着差异。     

龙眼花芽分化及其化学调控研究进展

从矿质营养、物质代谢、生殖生理、环境生理和化学物质调控等多方面对我国亚热带果树龙眼有关花芽分化期调控及其体内的物质代谢研究结果进行综述。     

瓜类性别分化的化学调控及作用机理研究进展

乙烯利、赤霉素、矮壮素、1-氨基环丙烷-1-羧酸等激素类型不同浓度对不同生长时期瓜类性别分化有不同程度的影响，了解其作用机理及研究进展，对瓜类的育种和栽培有较大应用价值。     

特色马铃薯有色物质的提取及相关性能的研究

文章重点研究了从特色马铃薯的皮和块茎中提取有色物质(紫红)的制备工艺。并对制备的有色物质的相关性能及结构进行了初步的探索。认为该天然提取物不但溶液鲜亮、自然、是不可多得的天然着色剂，而且，该有色物质对人红细胞白血病细胞株K562的生长显示了较为明显的体外抑制活性。植物提取物特色马铃薯色素，值得深入的研究和开发。     

Rates of elementary reactions: measurement and applications

Modern experimental techniques for measuring rate parameters of elementary reactions have transformed the field of gas-phase reaction kinetics from one of indirect inference to one of direct determination. Recent progress in the principal techniques is described, a few examples are given of the hundreds of elementary reactions for which rate information has become available, and comparison with reaction rate theory is briefly discussed. Some generalizations regarding the dependence of rate parameters on structure and thermodynamics are drawn, and successful applications to atmospheric and combustion modeling and measurement are presented.     

Ablation Thermal Protection Systems: Suitability of ablation systems to thermal protection depends on complex physical and chemical processes

The performance of ablation thermal protection systems is intimately related to the mass transfer, heat transfer, and chemical reactions which occur within the gas boundary layer. Production of a liquid layer and phase change or chemical reaction heat sinks greatly improve materials performance. Materials are available which achieve many goals for thermal protection. However, advanced materials which are now being developed provide hope of further reductions in the weight of heat-shielding structures.     

多效唑、缩节胺和矮壮素对花生化学调控效应的比较研究

【目的】筛选出适宜花生生长的植物生长调节剂及其最佳喷施浓度,为花生生产提供技术指导。【方法】以桂花771为试材,设不同浓度3种植物生长调节剂为处理,分别为多效唑（150、250、350、400mg/L）、缩节胺（200、250、300mg/L）和矮壮素（100、150、200mg/L）,调查花生农艺性状和产量。【结果】3种植物生长调节剂对花生植株生长的抑制程度顺序为：多效唑〉缩节胺〉矮壮素。多效唑、缩节胺和矮壮素分别在400、250和200mg/L时对花生植株生长的抑制程度最大。经多效唑处理的桂花771单株荚果数、单株生产力、产量分别较对照降低。250mg/L缩节胺处理花生单株生产力和产量均高于对照,但差异不显著。200mg/L矮壮素处理花生单株荚果数、单株生产力、产量达到最大值,分别比对照增加了15.7%、23.5%和17.0%。【结论】250mg/L缩节胺和100-200mg/L矮壮素可适当降低花生植株的伸长量,提高花生产量,其中200mg/L矮壮素对花生的化学调控增产效应最好。     

Comparison of RNA terminal sequences of phages f2 and Q-beta: chemical and sedimentation equilibrium studies

The terminal fragment obtained by hydrolysis with ribonuclease T(1) of the ribonucleic acid from the bacteriophage Qbeta has been isolated and purified. The results of chemical and enzymatic hydrolysis of this fragment and of the intact RNA itself indicate that the fragment has the composition (10 Cp, 4 Up), and that the RNA has the terminal sequence -GP(9 Cp, 4 Up) CpA. These conclusions are supported by the results of an application of the sedimentation-equilibrium method in which the molecular weight of the Qbeta fragment was compared with that of the corresponding fragment from f2 phage RNA for which the terminal sequence, -GpUpUpApCpCpApCpCpCpA had previously been determined.     

Experiments on the structure of an individual elementary particle

Research begun in the early 1970s on geonium is reviewed. Genoium is a man-made atom, created at liquid-helium temperature in ultrahigh vacuum from an individual electron in magnetic and electric trapping fields. For this atom the electron gyromagnetic ratio g = 2. 000 000 000 110(60) has been measured in microwave spectroscopy experiments after subtraction of quantum electrodynamics shifts. The g - g(Dirac) = 11 x 10(-11) excess over the value g(Dirac) = 2 for the theoretical Dirac point electron suggests for the electron of nature a corresponding excess radius R(e) - R(Dirac) over the Dirac radius R(Dirac) = 0 and a spatial structure. From a plot of measured g and R values for the near-Dirac particles electron, proton, triton, and helium-3 an electron radius R(e) approximately 10(-20) centimeter is extrapolated. In a speculation, the triton-proton-quark model has been extended to the electron, to a succession of subquarks, and finally to the "cosmon." Rapid decay of a cosmon-anticosmon pair created from the "nothing" state in a spontaneous quantum jump initiated the Big Bang.     

浅谈企业会计监督

会计监督包括内部会计监督和外部会计监督，面对企业现代化管理，规范会计行为，提高会计工作质量，维护经济秩序尤为重要。从会计监督现状看，急需进一步加强会计监督，强化会计监督就要有相应的对策，它是实现现代化企业制度不容忽视的重要问题。