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1.
The nature of chain folding in polymers and the determination of the chain length at which folding occurs have been central questions in polymer science. The study of the formation of lamellar polymer crystals through chain folding has received a new impetus as a result of the recent synthesis of normal alkanes of strictly uniform chain lengths up to C(390) H(782). Chain folding is found in all such paraffins starting with C(150)H(302). As with polyethylenes obtained by conventional polymerization, the fold length in the normal alkanes varies with crystallization temperature, but it is always an integral reciprocal of the full chain length. This behavior indicates that the methyl end groups are located at the lamellar surface and that the fold itself must be sharp and adjacently reentrant. 相似文献
2.
一株石油降解菌Lysinibacillus fusiformis 23-1的筛选鉴定及原油降解特性 总被引：1，自引：0，他引：1
石油泄露造成了严重的环境问题和重大经济损失,微生物修复是解决石油污染的最为有效的途径。从青藏高原石油污染土样筛选产生物表面活性剂的低温石油降解菌,并研究了该菌株对石油的乳化性能、降解特性、降解条件以及对不同碳链烃类的利用。本实验用血平板法分离到一株产表面活性剂石油降解菌23-1,形态学和16S rRNA基因序列分析鉴定其为纺锤形赖氨酸芽孢杆菌(Lysinibacillus fusiformis 23-1),比色法测定该菌株的乳化性能为19.6%,超声波法测定乳化稳定性为37.5%,表明其能够降低油水界面张力,具有增溶作用。质量法测定L. fusiformis 23-1对石油的降解率为57%,适宜降解条件为:初始pH为7.5,温度为25 ℃,培养8 d后获得最佳降解效果。GC-MS方法测定该菌株的石油降解特性,结果表明,该菌对石油中不同碳链的烃类降解能力不同。L. fusiformis 23-1能产表面活性剂,具有较强的降解石油能力,可用于石油污染修复。 相似文献
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Alkanes at the air-sea interface were analyzed in 118 surface samples collected at five different intervals over a 12-month period from Timbalier Bay (Louisiana), ogfshore Louiisiana, and offshore Florida. The alkanes were characterized by gas chromatography and mass spectrometry. Unexpectedly, methyl branched alkanes ranging in chain length froin C(15) to C(35) and cycloalkanes were frequently the predominant components. This suggests that the alkanes are produced by natural biological sources as well as human activities. 相似文献
4.
Aluminas and their surface chemistry play a vital role in many areas of modern technology. The behavior of adsorbed water is particularly important and poorly understood. Simulations of hydrated alpha-alumina (0001) surfaces with ab initio molecular dynamics elucidate many aspects of this problem, especially the complex dynamics of water dissociation and related surface reactions. At low water coverage, free energy profiles established that molecularly adsorbed water is metastable and dissociates readily, even in the absence of defects, by a kinetically preferred pathway. Observations at higher water coverage revealed rapid dissociation and unanticipated collective effects, including water-catalyzed dissociation and proton transfer reactions between adsorbed water and hydroxide. The results provide a consistent interpretation of the measured coverage dependence of water heats of adsorption, hydroxyl vibrational spectra, and other experiments. 相似文献
5.
以碳原子数Ｎ和Ｗｉｅｎｅｒ指数Ｗ,Ｐ为结构参数,建立了烷烃同分异构体的沸点与其分子结构间的定量关系式,用此式计算了７６个支链烷烃的沸点。结果表明,该式适用范围广泛,计算结果较准确,可用于预测烷烃同分异构体的沸 相似文献
6.
Solid friction between a charged polymer and fixed gel points can dramatically affect polymer mobility in gel electrophoresis. The effect is present when a polymer chain is entangled over many gel points along a portion of its length, leading to significantly different behavior than predicted by conventional theory: the mobility of the chain decreases and exhibits a stronger length dependence, which separates long linear charged polymers of different molecular weights. 相似文献
7.
Studt F Abild-Pedersen F Bligaard T Sørensen RZ Christensen CH Nørskov JK 《Science (New York, N.Y.)》2008,320(5881):1320-1322
The removal of trace acetylene from ethylene is performed industrially by palladium hydrogenation catalysts (often modified with silver) that avoid the hydrogenation of ethylene to ethane. In an effort to identify catalysts based on less expensive and more available metals, density functional calculations were performed that identified relations in heats of adsorption of hydrocarbon molecules and fragments on metal surfaces. This analysis not only verified the facility of known catalysts but identified nickel-zinc alloys as alternatives. Experimental studies demonstrated that these alloys dispersed on an oxide support were selective for acetylene hydrogenation at low pressures. 相似文献
8.
为研制氨吸附制冷用活性炭一膨胀石墨的混合吸附剂,选用椰壳活性炭和可膨胀石墨,初步分析了氨在膨胀石墨添加比率为50％的混合吸附剂上的吸附平衡．吸附剂试样首先经由77K液氮在其上吸附数据的结构表征,然后应用根据容积法原理建立的吸附平衡测试装置,在温度293．15～303．15K、压力0—1MPa,测试了氨在试样上的吸附平衡数据,并通过等量吸附线标绘和Dubinin—Astakhov方程的模型分析,研究了氨在混合吸附剂上的吸附平衡．结果表明,添加膨胀石墨减小了混合吸附剂的比表面积和微孔容积,Dubinin—Astakhov方程在平衡压力较高区域的预测精度可达到4％,氨在混合吸附剂上的等量吸附热为16．94～27．78kJ／mol．添加膨胀石墨必须兼顾混合吸附剂的吸附容量和传热传质性能． 相似文献
9.
[目的]选育能够高效降解石油烃的不动杆菌。[方法]采用低能N~+对不动杆菌菌株a8进行诱变,测量离子注入前后不动杆菌对石油烃的降解率,并研究其降解能力和降解机理。[结果]当N~+的注入能量和注入剂量分别为15 ke V和8.0×1015ions/cm~2时,不动杆菌的降解率可提高至95.03%;利用该注入参数对出发菌种a8进行3次连续诱变后,获得1株能有效降解59种烷烃的突变菌株AQ-15;结合分子生物学技术,对AQ-15降解长链石油烷烃的酶Alm A基因进行分析,发现酶结合位点之一的47th氨基酸由原来的天冬氨酸(Asp,D)变为甘氨酸(Gly,G),从而提高了酶的活性,达到了高效降解长链石油烷烃的效果,揭示了离子注入后不动杆菌降解率提高的机理。[结论]选育出1株能够高效降解石油烃的不动杆菌菌株AQ-15。 相似文献
10.
Two-dimensional molecular patterns were obtained by the adsorption of long-chain alkanes, alcohols, fatty acids, and a dialkylbenzene from organic solutions onto the basal plane of graphite. In situ scanning tunneling microscopy (STM) studies revealed that these molecules organize in lamellae with the extended alkyl chains oriented parallel to a lattice axis within the basal plane of graphite. The planes of the carbon skeletons, however, can be oriented either predominantly perpendicular to or predominantly parallel with the substrate surface, causing the lamellar lattice to be either in or near registry with the substrate (alkanes and alcohols) or not in registry (fatty acids and dialkylbenzenes). In the case of the alcohols and the dialkylbenzene the molecular axes are tilted by +30 degrees or -30 degrees with respect to an axis normal to the lamella boundaries, giving rise to molecularly well-defined domain boundaries. Fast STM image recording allowed the spontaneous switch between the two tilt angles to be observed in the alcohol monolayers on a time scale of a few milliseconds. 相似文献
11.
对上证指数对数收益率的长相依性进行了统计检验并完成了相应的统计建模以及参数估计. 通过选择分数布朗运动作为刻画股票投资回报的驱动过程, 并得到了此模型下股指收益的VaR计算的显式表达式. 数值分析的结果显示分数布朗运动模型下的VaR值要高于Black-Scholes模型下的VaR值, 这表明长相依性质对于股指风险有很大的影响, 在相关的金融风险产品的风险度量中应加以重视. 相似文献
12.
以碳原子数 N和 Wiener指数 W,P为结构参数 ,通过数学拟合的方法 ,建立了烷烃的折光率与其分子结构间的定量关系式 ,并计算了 1 0 1个烷烃的折光率。结果表明 ,该式计算结果较准确 ,应用该式可以预测烷烃的折光率 相似文献
13.
首先对高炉炉渣经过不同浓度硫酸处理后在不同pH条件下的除磷效果进行了研究;再通过等温吸附、动力学吸附和热力学吸附模拟实验,应用不同的吸附方程进行拟合,探讨了静态实验下高炉炉渣对磷的吸附特性。结果表明:高炉炉渣在经过2 mol/L硫酸处理后,在pH=9的条件下对磷具有最好的吸附性能;Langmuir等温吸附模型能较好地模拟高炉炉渣对磷的等温吸附过程;Lagergren一级吸附速率方程和Bangham动力学方程均能较好地描述高炉炉渣对磷的动力吸附,且前者更好。根据Gibbs自由能变(△G0<0)和标准反应焓变值(△H0>0)判断,该吸附是自发的、吸热的化学吸附反应。 相似文献
14.
A recently designed single-crystal surface calorimeter has been deployed to measure the energy difference between two solid surface structures. The clean Pt{100} surface is reconstructed to a stable phase in which the surface layer of platinum atoms has a quasi-hexagonal structure. By comparison of the heats of adsorption of CO and of C(2)H(4) on this stable Pt{100}-hex phase with those on a metastable Pt{100}-(1x1) surface, the energy difference between the two clean phases was measured as 20 +/- 3 and 25 +/- 3 kilojoules per mole of surface platinum atoms. 相似文献
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16.
Monoamines and diamines dissolved in cyclohexane solution reversibly enhance the band-edge photoluminescence (PL) intensity of immersed n-type cadmium sulfide (n-CdS) and n-type cadmium selenide (n-CdSe) substrates through adsorption. The magnitude of the PL increase is used to estimate amine-induced contractions in the semiconductor's depletion width, and the dependence of the PL intensity on amine concentration provides an estimate of the adduct formation constant. Two diamines, ethylenediamine and o-phenylenediamine, exhibit unusually low reductions in depletion width and substantially larger adduct equilibrium constants relative to the other amines studied, consistent with chelation to surface Cd(2+) ions. These studies demonstrate that PL can be used as a contactiess, in situ technique for characterizing the steric and electronic landscape of semiconductor surfaces and for correlating molecular and surface chemistry. 相似文献
17.
实验结果表明，在ｎｃ＝１０～１６范围内，烷基三甲基溴化铵表面活性剂在水溶液表面的吸附和在水溶液中的胶团化作用均随着其碳氢链长的增加而呈不同程度的增强．在实际应用中，结合使用效果和经济效益，当强调表面吸附时，以Ｃ１２ＴＡＢ较好；若希望利用其胶团性质，则应更多地使用价廉的Ｃ１６ＴＡＢ． 相似文献
18.
一种混沌系统的变结构同步控制方法 总被引：1，自引：0，他引：1
本文提出了一种变结构混沌同步控制方法,首先针对Lorenz系统设计了滑模变结构控制器,然后对所提出的方法进行了计算机仿真,仿真结果表明,该方法正确有效。 相似文献
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