Solvent effect on DNA base stacked dimers: An isodensity polarizable continuum model approach

The role of solvent on the base stacking properties of various stacked dimers has been analyzed. Ab initio calculations have been performed on the various stacked dimers using the isodensity polarizable continuum model (IPCM), in the framework of the HF/6‐31G** level. It is observed that the stacked dimers undergo different levels of stabilization for different rotated conformations, and the total energy of stacked dimers depends on the twist angle. The results reveal that DNA stacked dimers prefer the twisted (rotated conformation) conformation in water environment, so as to escape from water, due to their hydrophobic nature. In addition, the presence of solvent stabilizes the stacking interaction between bases. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

层叠Blumlein线脉冲叠加特性

利用传输线等效放电模型对层叠Blumlein线的脉冲叠加特性进行了分析。结果表明:外部短路阻抗是降低层叠Blumlein线脉冲叠加效率的主要因素,其中,短路电感产生输出波形平顶的衰减,相对衰减量取决于叠加级数以及短路等效电感与传输线电感之比,短路电容产生输出波形前沿的慢化,前沿慢化的相对值取决于叠加级数以及短路等效电容与传输线等效电容之比;由于各级开关导通时间分散性的存在,输出波形的前沿及后沿皆呈阶段状,相当于产生了时间量等于开关导通分散性时间的前沿及后沿慢化现象。增加传输线外部的短路阻抗、减小多开关的导通分散性是提高层叠Blumlein线的脉冲叠加效率、改善输出波形的有效途径。     

DNA base stacking: The stacked uracil/uracil and thymine/thymine minima

The potential energy surfaces of stacked uracil dimer (U/U) and stacked thymine dimer (T/T) have been explored at the counterpoise (CP)‐corrected M06‐2X/6‐31+G(d) level of theory, in the gas phase and in solution (with water and, for U/U, 1,4‐dioxane as the solvents) modeled by a continuum solvent using the polarizable continuum model. Potential energy scans were created by rotation of one monomer around its center‐of‐mass, whereas the other monomer remained still. Both face‐to‐back (one molecule exactly on top of the other) and face‐to‐face (one base molecule flipped by 180°) structures were considered. Five or six (dependent on whether CP correction is included or not) stacked uracil dimer minima and six stacked thymine dimer minima were located. A number of transition states on the U/U and T/T potential energy surfaces were likewise identified. The general effect of the continuum solvent is a flattening of the potential energy surface. Comparison of the gas‐phase M06‐2X/6‐31+G(d) U/U interaction energies with estimated CCSD(T)/complete basis set values (where available) show the excellent performance of this functional for stacking energies. © 2012 Wiley Periodicals, Inc.     

二代高温超导带材耐高温性能研究

通过有限元软件对由20层高温超导带材所制成的超导叠带在覆铝时的温度分布进行模拟,模拟结果表明在覆铝过程中两侧带材均会经历420°C以上的高温.对几种高温超导带材在不同温度和持续时间下,对其ReBCO侧、哈氏合金侧和双侧分别加热进行高温实验,测试得出了各带材临界电流的退化情况.实验结果表明,高温对带材造成了性能退化,不同...     

Bonded excimer in stacked adenines:Semiclassical simulations

The nonradiative decay of a π-stacked pair of adenine molecules,one of which was excited by an ultrafast laser pulse,is studied by semiclassical dynamics simulations.This simulation investigation is focused on the effect of the formation of bonded excimer in stacked adenines on the mechanism of ultrafast decay.The simulation finds that the formation of the bonded excimer significantly lowers the energy gap between the LUMO and HOMO and consequently facilitates the deactivation of the electronically excited molecule.On the other hand,the formation of the chemical bond between two stacked adenines restricts the deformation vibration of the pyrimidine of the excited molecule due to the steric effect.This slows down the formation of the coupling between the HOMO and LUMO energy levels and therefore delays the deactivation process of the excited adenine molecule to the electronic ground state.     

准静态一维应变实验装置的设计与验证研究

准一维应变状态测试技术对混凝土等脆性材料的力学性能研究具有重要意义,而目前准一维应变实验装置设计单一、互换性较差,所以无法实现普及。针对上述情况,本文在套管围压装置的基础上进行叠加式设计与组合式分离设计,旨在建立一套结构简单、适用性广的准静态被动围压装置。基于数值模拟方法,本文对混凝土试样在一维应变状态与套管围压作用下的力学特性进行研究,从而分析混凝土试样在套管装置下能达到一维应变状态的程度;同时,对叠加式套管与整体式套管的性能进行比较,发现叠加式套管理论上能在准一维应变实验中很好地代替整体式套管。组合式分离设计的有效性最终通过相关实验得到验证。     

Complete and incomplete fusion studies in7Li and16O induced reactions on51V by measurement of excitation functions and recoil ranges

Excitation function and mean projected recoil ranges of nuclei produced in the⁷Li and¹⁶O induced reactions on⁵¹V target were measured by conventional stacked foil and thick-target thick-recoil-catcher technique for bombarding energiesE ≤ 50.0 MeV for⁷Li ions andE ≃ 60.0-96.0 MeV for the¹⁶O ions. The measured recoil ranges are converted to momentum transfer. The momentum transfer information was used to get clues about some aspects of the interaction such as complete and incomplete fusion reaction mechanism which correspond to full and reduced momentum transfer respectively. The measured excitation functions are compared with the calculation based on the statistical model which describes only equilibrium decay of the compound nucleus using the CASCADE code. The comparison of the CASCADE code with the measured excitation functions for the residue radioisotopes⁵¹Cr and⁵⁴Mn for the⁷Li +⁵¹V system indicates the reaction mechanisms is complete fusion of⁷Li with the target nucleus⁵¹V. Similarly the comparison of the CASCADE code with the measured excitation functions of the residue radioisotopes for the system¹⁶O +⁵¹ V indicates that the four reaction mechanisms (i) complete fusion of¹⁶O, (ii) incomplete fusion of¹²C, (iii) incomplete fusion of⁸Be and (iv) incomplete fusion of⁴He respectively with the target might be contributing to reaction cross sections.     

Excitation functions of alpha particle induced reactions on aluminium and copper

Cross-sections for the reactions with product nuclei²⁴Na,²²Na,⁶⁸Ga and⁶⁷Ga were investigated over the energy range of 30 to 75 MeV for alpha particle induced reactions on natural aluminium and copper, using stacked-foil activation technique. The measured excitation functions were analysed with special reference to their suitability for monitoring beam energy and intensity. The experimental results were compared with the predictions of hybrid model of Blann. The assumption of initial exciton numbern ₀=4(4p0h) best satisfies the measured excitation functions in the present work.     

Measurement and analysis of excitation functions for alpha induced reactions on iodine and cesium

The excitation functions for the reactions¹²⁷I(α, 2n)¹²⁹Cs,¹²⁷I(α, 4n)¹²⁷Cs,¹³³Cs(α, 2n)¹³⁵La and¹³³Cs(α, 4n)¹³³La have been measured up to ≈50 MeVα-particle energy using the stacked foil activation technique. Measured excitation functions are compared with pre-equilibrium geometry dependent hybrid model calculations. It has been found that theoretical calculations using an initial exciton numbern ₀=4 (2p+2n+0h) give good agreement with experimental excitation functions.     

WS2/MoS2 Heterostructures through Thermal Treatment of MoS2 Layers Electrostatically Functionalized with W3S4 Molecular Clusters

The preparation of 2D stacked layers combining flakes of different nature gives rise to countless numbers of heterostructures where new band alignments, defined at the interfaces, control the electronic properties of the system. Among the large family of 2D/2D heterostructures, the one formed by the combination of the most common semiconducting transition metal dichalcogenides, WS₂/MoS₂, has awakened great interest owing to its photovoltaic and photoelectrochemical properties. Solution as well as dry physical methods have been developed to optimize the synthesis of these heterostructures. Here, a suspension of negatively charged MoS₂ flakes is mixed with a methanolic solution of a cationic W₃S₄-core cluster, giving rise to a homogeneous distribution of the clusters over the layers. In a second step, a calcination of this molecular/2D heterostructure under N₂ leads to the formation of clean WS₂/MoS₂ heterostructures, where the photoluminescence of both counterparts is quenched, proving an efficient interlayer coupling. Thus, this chemical method combines the advantages of a solution approach (simple, scalable, and low-cost) with the good quality interfaces reached by using more complicated traditional physical methods.