二恶英物质的结构性质分析

利用商业化的分子模拟软件,在分子力学计算的基础上,对二恶英分子的最稳定构型、最高占据轨道、电荷密度分布图和溶剂可及表面等进行了研究,并给出了二恶英的VRML分子模型,计算出分子的物理化学性质.对二恶英分子物质结构性质的分析将有助于从理论上寻找控制与治理二恶英污染的技术手段和方法.

应用反向传播神经网络预测化合物脑血分配系数

选用27种三维结构性质描述符对脑血分配系数预测建立神经网络模型.网络模型选用典型的适合函数逼近的两层结构神经网络对脑血分配系数(lgBB,BB为脑血浓度比)进行预测,计算中采用的模型具有一个双曲正切型激活函数的隐含层和一个线性激活函数的输出层.计算表明,使用小心选择的反向传播神经网络模型对化合物脑血分配系数具有较好的预测能力.

Translocation of Polymer Chains Through a Channel with Complex Geometries

The elastic behavior of a single chain transporting through complex channel which can be seen as the combination of three different channels （left channel, middle channel, and right channel, respectively） is investigated using the new pruned-enriched Rosenbluth method with importance sampling. The elastic force during the translocation process is calculated. At the entrance into the middle channel, there is the first plateau in the curve of the elastic force f （f〉0） versus x, here x represents the position of the first monomer along the x-axis direction. When the first monomer moves to a certain position, a second plateau is observed with the elastic force f〈0, which represents spontaneous translocation. The free energy difference between the subchain in the right channel and the subchain in the left channel may drive the transloeation. The influence of chain length and width of the left and right channels on the translocation process are also investigated. From the simulation results, more detailed explanations for the reason why the component translocation time is not the same for different channels can be presented.

Theoretical Study of the AIEt3-Promoted Tandem Reductive Rearrangement of Epoxides

The AIEt3-promoted tandem reductive rearrangement reactions of epoxides was studied at B3LYP/6- 31C（d,p） level. For the model compound α-hydroxy epoxides, two possible reaction pathways Ⅰ and Ⅱ were calculated. The main difference is the order of ethylene release and six- to five-member ring rearrangement. The ring contraction rearrangement in pathway Ⅰ is the first step and this step is the rate controlling step with a free energy barrier of 116.62 kJ/mol. For pathway Ⅱ, the ethylene release occurs first, and is followed by a six-member ring opening reaction which is the rate controlling step, and the barrier is 251.38 kJ/mol. The reason for such high barrier is that the ethylene release results in the following reaction being more difficult. The results show that pathway Ⅰ （C-C rearrangement and then ethylene release） is more favorable, which is consistent with experimental results.

Ab initio Study on Structures and Isomerization of Magnesium Fluorosilylenoid H2SiFMgF

The structures and isomerization of magnesium fluorosilylenoid H2SiFMgF were investigated by ab initio molecular orbital theory. Four equilibrium structures and three isomeric transition states were located and fully optimized at the B3LYP/6-31G（d,p） and G3MP2B3 levels, respectively. Based on the B3LYP/6- 31G（d,p） optimized geometries, harmonic frequencies of various structures were obtained and 29Si chemical shifts were calculated. The solvent effects were investigated by means of the polarizable continuum model using THF as a solvent at B3LYP/6-31G（d,p） level. Isomerization paths for isomers were confirmed by intrinsic reaction coordinate calculations. The calculated results show that tetrahedral structure has the lowest energy and is the most stable; tetrahedral, three-membered ring, and p-complex structures are suggested to be the experimentally detectable ones; and a-complex structure has the highest energy and will not exist.

Application of Characteristics of Seismogenic Structures in the Determination of Parameter of Potential Seismic Source Areas

The characteristics of seismogenic structures are an important basis for delineating the potential seismic source areas and determining the annual occurrence rate of earthquakes. The potential seismic source area does not only have the intension that “this area has the possibility for destructive earthquakes to occur in the future" but also means that earthquakes of high magnitude interval have the characteristics of similar recurrence. When determining the seismic activity parameters of a statistical unit, some active tectonic blocks in the unit may have different background earthquakes. In order to better reflect the heterogeneity in space of seismic activities, it is necessary to divide the potential seismic source areas into three orders. By analyzing the recurrence characteristics of earthquakes of high magnitude interval in the potential source area and calculating the occurrence probability of earthquakes of high magnitude interval in the potential seismic source area in the time window for prediction, the average annual occurrence rate of earthquakes can be obtained by the method of probability equivalent conversion in the time window for prediction. This would be helpful for considering the recurrence characteristics of strong earthquakes in potential source areas within the framework of seismic risk analysis of China. Besides, the insufficient frequency of characteristic earthquakes of the next high magnitude interval in the potential source area and the heterogeneity of strong earthquakes on seismogenic structures are analyzed to see their application in seismic risk analysis.

Structures and magnetic properties of several novel lanthanide coordination polymers based on thiophene-2,5-dicarboxylic acid

Eight novel lanthanide complexes： {Ln（TDA）I.5（H20）2 },, （Ln = Pr（la）, Nd（2a）） and { Ln（TDA）（Ac）（H2O）}n （Ln = Pr（1）, Nd（2） Eu（3）, Gd（4）, Tb（5）, Dy（6）; TDA = Thiophene-2,5-dicarboxylic acid anion） have been constructed by hydrothermal reaction. Structural analyses reveal that complexes Ia and 2a belong to the space group C2/c, exhibiting three-dimensional （3D） frame- works. Complexes 1-6 with P2t/c space group were prepared in the presence of excessive ammonium acetate, giving rise to interesting 3D frameworks different from those of la and 2a. Magnetic property studies of 4-6 reveal the weak antiferromag- netic interaction exists between adjacent Gd3＋ in 4. The complex 6 displays rather rare slow magnetization relaxation behavior in 3D frameworks.

Rare-earth-regulated Ru–O interaction within the pyrochlore ruthenate for electrocatalytic oxygen evolution in acidic media

Ruthenium-based catalyst is one of the most active catalysts for oxygen evolution reaction(OER)in acid media.However,the strong bonding between the Ru sites and oxygen intermediates leads to high overpotential to trigger the OER process.Hence,pyrochlore rare-earth ruthenate(RE_(2)-Ru_(2)O_(7))structures with a series of rare-earth elements(Nd,Sm,Gd,Er,and Yb)were constructed to tune the electronic structure of the Ru sites.Surface structure analysis indicated that the increase of the radius of the rare-earth cations resulted in higher content of defective oxygen(the percentage of the defective oxygen increased from 29.5% to 49.7%) in the RE_(2)Ru_(2)O_(7) structure due to the weakened hybridization of the Ru-O bond.This reduced the valence states of the Ru sites and enlarged the gap between the 4d band center and the Fermi level(E_(F))of Ru,resulting in the weakened adsorption of oxygen intermediates and the improved OER performance in acid media.Among the as-prepared ruthenium pyrochlores,Nd_(2)Ru_(2)O_(7) displayed the lowest OER onset overpotential(210 mV)and Tafel slope(58.48 mV dec^(-1)),as well as 30 times higher intrinsic activity and much higher durability than the state-of-art RuO_(2) catalyst.

Finite element method for viscoelastic medium with damage and the application to structural analysis of solid rocket motor grain

This paper studies the damage-viscoelastic behavior of composite solid propellants of solid rocket motors(SRM).Based on viscoelastic theories and strain equivalent hypothesis in damage mechanics,a three-dimensional(3-D)nonlinear viscoelastic constitutive model incorporating with damage is developed.The resulting viscoelastic constitutive equations are numerically discretized by integration algorithm,and a stress-updating method is presented by solving nonlinear equations according to the Newton-Raphson method.A material subroutine of stress-updating is made up and embedded into commercial code of Abaqus.The material subroutine is validated through typical examples.Our results indicate that the finite element results are in good agreement with the analytical ones and have high accuracy,and the suggested method and designed subroutine are efficient and can be further applied to damage-coupling structural analysis of practical SRM grain.