视觉光化学过程中的构象电子跃迁

本文应用构象电子跃迁理论讨论了视觉光化学过程中的构象电子跃迁,证明了维生素A从All—Trans构象到11—cis构象的跃迁几率大于到9—cis构象的跃迁几率2.8倍,与实验及自然界前者优于后者较好地符合。     

视黄醛分子光致构象跃迁

本文应用罗辽复提出的构象电子场理论,讨论了视黄醛分子的光致构象跃迁。计算得到的结果表明,视黄醛分子从all-trans构象到1l—cis构象的跃迁几率大于到9—cis构象的跃迁几率,两个几率的比值:10<ω_(11)/ω_9<100。与实验事实和自然界前者优于后者的事实较好地符合。     

ABEEMσπ-GB／SA方法计算6种氨基酸四肽溶剂化自由能

使用ABEEMσπ浮动电荷极化分子力场，在298 K ，NVT 系综下对5种构象的A la四肽水溶液进行了动力学模拟。计算了动力学平衡态下A la四肽中非氢原子的均方根偏差。结合广义玻恩模型（GB）计算了溶剂化自由能的极性部分，使用SA 方法计算了溶剂化自由能的非极性部分。溶剂化自由能的结果表明，A la四肽αR螺旋和β折叠构象容易在水溶液中存在。使用类似方法分别对Gly ，Leu ，Val ，Asn和Asp四肽的αL螺旋构象水溶液进行了动力学研究，计算了这5种四肽的溶剂化自由能。结果表明，A sp和A sn四肽亲水性较强，Leu、Val和Ala四肽疏水性较强，Gly 四肽居中，此结论与实际相符。该类研究为ABEEMσπ浮动电荷力场用于其他生物大分子体系奠定了很好的基础。     

线型聚合物链的三级相互作用对键构象几率的影响

本文采用旋转异构态模型的三级相互作用近似,计算了Polymethylene(PM)链键构象的几率,并与二级相互作用近似下键构象的几率作了比较,得到一些新的结果.     

18—冠醚—6及其Na^＋和K^＋络合物振动光谱的研究

通过对１８－冠醚－６的３种构象及其碱金属络合物的正则模计算，考察了构象与振动光谱分布间的关系，并把计算结果与实验进行了比较，结果表明，金属离子和溶剂都对１８－冠－６－分子振动光谱分布有较大的影响。     

18－冠醚－6及其Na~＋和K~＋络合物振动光谱的研究

通过对１８－冠醚－６的３种构象及其碱金属络合物的正则模计算，考察了构象与振动光谱分布间的关系，并把计算结果与实验进行了比较，结果表明，金属离子和溶剂都对１８－冠醚－６分子振动光谱分布有较大的影响     

正壬烷构象的振动光谱研究

对于含有一个gauche构象的正壬烷,包括全反式构象在内主要有四种稳定构象。为了得到各种构象与特征频率之间的对应关系,运用从头计算方法分别计算出了这四种构象的红外振动频率以及相应强度。根据其振动强度以及振动特征,特别是振动发生在gauche位置的振动模式,得到了各种构象在整个范围内的红外光谱特征峰以及相同振动模式随构象变化的规律。这不但弥补了正壬烷链构象实验研究的不足,而且还起到一定的理论指导作用。     

可视化分析四肽构象空间中的模式

用一种可视的方式分析四肽构象空间中的聚集情况,从而直观地建立了四肽结构类和二级结构之间的联系.据此给出了四肽构象类的一种划分方案,并将此方案应用于更长肽段构象模式的发现和评估其他方法对肽段构象分类的合理性.实验结果与其他方法相比更具有可解释性.     

关联色噪声对线性系统定态几率分布的影响

提出了一种将两个关联噪声分布化为两企我关联噪声线性组合的方法，讨论了在关联加性噪声和乘性噪声驱动下一线性系统的定态几率分布，数值计算表明，噪声间的关联参数对定态几率分布的峰值位置和形状有较大影响；且在完全负关联条件下，定态几率分布被锁定在某一固定位置上。     

无扰Polymethylene链反式键序列的几率

本文应用高分子链构象统计的旋转异构态二级相互作用模型,计算了Polymethylene(PM)链在不同温度下连续k个t态构象出现的几率P_(kt),得到150—500K温度范围内P_(kt)与温度T和连续t态键数k之间的函数关系式;分析了PM链反式键序列的几率的特性;讨论了聚乙烯单晶在稀溶液中形成时,旋转异构态二级相互作用模型适用的可能性,有助于对结晶理论的进一步研究。     

Study on properties of residue-residue contacts in protein

Residue-residue contacts are very important in forming protein structure. In this work, we calculated the average probability of residue-residue contacts in 470 globular proteins and analyzed the distribution of contacts in the different interval of residues using Contacts of Structural Units (CSU) and Structural Classification (SCOP) software. It was found that the relationship between the average probability PL and the residue distance L for four structural classes of proteins could be expressed as lgPL=a+b x L, where a and b are coefficients. We also discussed the connection between two aspects of proteins which have equal array residue number and found that the distribution probability was stable (or un-stable) if the proteins had the same (or different) compact (for example synthase) in the same structural class.     

Statistical analysis on protein-protein interface in crystals： Specific and non-specific interfaces are differentially distributed

The distribution of contact areas, or fractions of contacting, of protein-protein interfaces in crystals of pure polypeptides contains two components: a major exponential distribution and a minor flatter distribution. Suppose the two components belong to specific and non-specific contacts,respectively, then the probability of a contact with a givena rea, or fraction of contacting, can be estimated. By dividing the whole database into two sub-databases, one of them is known to contain more specific contacts than the other, this hypothesis is confirmed and it is also proved that the fraction of contacting is more effective than the contact area on discriminating specific and non-specific contacts in protein crystals.     

增强纤维复合材力学性能指标概率分布类型

为明确增强纤维复合材(FRP)力学性能指标的概率分布模型,通过收集整理近1 000份FRP材性试验样本,利用3种拟合优度检验方法口(x2检验、K-S检验、A-D检验)分析FRP极限拉伸强度、弹性模量、厚度的概率分布类型,并检验各指标间的相关性,基于Weibull分布函数重新定义FRP拉伸强度的标准值,将计算值与现行规范取值进行对比.研究结果表明:极限抗拉强度与弹性模量近似服从Weibull分布;厚度近似服从对数正态分布,同时3个指标间呈现一定的弱相关性.采用经验证的Weibull分布函数计算公式可较好估计材性标准值,计算结果较各规范更为合理、安全.     

从高分子构象与动力学到蛋白质折叠

针对作用在聚合物刷上的键拉力研究表明作用在接枝基面上的力随着聚合物刷接枝密度的增大反而减小,然而尾端单体上的拉伸张力并没有消失.高分子的构象和动力学转变决定了其物性和多种多样的应用,而生物大分子蛋白质作为由二十种不同属性的氨基酸构成的序列,更是具有由其序列所决定的特别的三维自然结构.本文就聚合物刷、聚合物纳米复合材料、聚合物网络等几种高分子体系的构象与动力学过程,及蛋白质构象和其折叠与去折叠的动力学过程做了介绍.特别是蛋白质的折叠与去折叠速率在单分子操纵实验中受到拉力的调控,通过测量这种拉力依赖的动力学过程、蛋白质的自由能曲面和折叠去折叠路径可以得到系统全面的研究.本文以肌肉蛋白titin的免疫球蛋白结构域I27为例对蛋白质折叠研究进行了阐述.     

区域导航技术下的平行航路侧向重叠概率的研究

着重对区域导航平行航路的侧向重叠概率的计算进行了研究。首先,通过数据统计,分析侧向重叠概率在平行航路安全性评估中的重要性;其次,利用双指数分布和分离的双指数分布对区域导航技术下的平行航路侧向重叠概率进行了计算;最后,通过仿真比较来确定最适合区域导航下的平行航路侧向重叠概率的计算方法。结果表明,用分离的双指数分布描述大偏航密度函数所得的侧向重叠概率更接近于实际情况。     

Statistical mechanics and topology of polymer chains.

The statistical-mechanical treatment of closed polymer chains based on algebraic topology is proposed. Using the Monte-Carlo method numerical results were obtained for the probability to knot formation during random closing of polymer chains of different length. For very rigid chains such as DNA double helix the probability of knot formation is rather great. Topological restrictions in a system of two polymer chains are shown to lead to a specific topological interaction between them.     

双门限协作能量检测性能分析

传统的单门限能量检测,如果有突发噪声或者其它因素,产生误检的概率会比较大。使用基于OR准则的双门限协作能量检测算法,检测时对每个用户设定两个判决门限,利用多个用户检测结果进行OR准则协作判决,提升检测性能。数值仿真结果表明,这一方法能够提高频谱检测概率、抑制漏检率。当信噪比较低、认知用户数N=5时,双门限性能最高要比单门限高出22％;认知用户数N=10时,双门限性能最高要比单门限高出17％。实际应用中,低信噪比的恶劣环境居多,因此双门限检测具有不可比拟的优势,应用空间非常广阔。     

Raman spectroscopic study of DNA photodamage sensitized by hypocrellin B and 5-brominated-hypocrellin B

Hypocrellin B (HB) is a highly effective photosensitizer. One of its derivatives, 5-brominated-hypocrellin B (5-Br-HB) has better photosensitive characterlstics than it. Using Raman spectroscopy, the microcosmic photodamage to DNA sensitized by HB and 5-Br-HB was studied at molecular level. The results showed that when HB and 5-Br-HB were added to the solution of DNA and irradiated, the characteristic Raman frequencies and intensities of DNA changed to various degrees. The photodamage occurred on the whole DNA molecule, including phosphate backbone, deoxyribose and four bases. Not only the conformation but also the configuration of DNA was photodamaged: breakage of some H-bonds, disappearance of B-form conformation, scission of double or single strand and serious damage of four bases. The damage to A-T pairs was stronger than that to C-G pairs and DNA became polynucleotides finally. The 5-Br-HB-photosensitized damage to DNA was stronger than HB, which suggested the better photosensitive characteristics of 5-Br-HB in bioactive environment. The molecular mechanisms of photodamage to DNA sensitized by 5-Br-HB and HB were also elucidated.     

The molten globule protein conformation probed by disulphide bonds

The molten globule is a compact protein conformation that has a secondary structure content like that of the native protein, but poorly defined tertiary structure. It is a stable state for a few proteins under particular conditions and could be a ubiquitous kinetic intermediate in protein folding. The extent to which native interactions, above the level of the secondary structure, are preserved in this conformation is not so far known. Here we report that alpha-lactalbumin can adopt a molten globule conformation when one of its four disulphide bonds is reduced. In this state, the three other disulphide bonds rearrange spontaneously, at the same rate as when the protein is fully unfolded, to a number of different disulphide bond isomers that tend to maintain the molten globule conformation. That the molten globule state is compatible with a variety of disulphide bond pairings suggests that it is unlikely to be stabilized by many specific tertiary interactions.     

Mechanical performance and texture characteristic of an IF steel containing Nb and Ti by double cold rolling

Single cold rolling and double cold rolling were applied to hot rolled strips with different reduction ratios. The evolutions of { 100}, { 111} and Goss face texture during double rolling were investigated by comparing the orientation distribution function (ODF) of the double rolled sample with that of the single rolled one. The double cold rolling texture is characterized by a higher γ-texture and a lower α-texture, and the { 111}〈112〉 component is improved remarkably. Based on the TEM observation and mechanical properties test, it is found that the reduction ratio assignment significantly affects the texture variation, as-annealing microstructures, and properties of the double cold rolled samples. These results may provide a theoretical guide for the industrial production of double cold rolled IF steel.