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31.
Mechanical property and deformation mechanism of gold nanowire with non-uniform distribution of twinned boundaries:A molecular dynamics simulation study 下载免费PDF全文
《中国物理 B》2021,30(5):56101-056101
The mechanical property and deformation mechanism of twinned gold nanowire with non-uniform distribution of twinned boundaries(TBs) are studied by the molecular dynamics(MD) method. It is found that the twin boundary spacing(TBS) has a great effect on the strength and plasticity of the nanowires with uniform distribution of TBs. And the strength enhances with the decrease of TBS, while its plasticity declines. For the nanowires with non-uniform distribution of TBs, the differences in distribution among different TBSs have little effect on the Young's modulus or strength, and the compromise in strength appears. But the differences have a remarkable effect on the plasticity of twinned gold nanowire. The twinned gold nanowire with higher local symmetry ratio has better plasticity. The initial dislocations always form in the largest TBS and the fracture always appears at or near the twin boundaries adjacent to the smallest TBS. Some simulation results are consistent with the experimental results. 相似文献
32.
针对水化硅酸钙纳米压痕模型忽视了压头与基底之间相互作用的问题,由尺寸差异引起的金刚石压头难以计算的问题,以及Wittmann模型无法得到实际接触面积的问题,提出了新的模型与计算方法.结合分子动力学方法,采用金刚石压头-Wittmann模型基底的组合方式构建无定形态水化硅酸钙纳米压痕试验模型.在建模阶段,考虑到压头模型与基底模型粒子间尺寸差异,提出了等比例替换模型,通过公式推导并就不同尺寸模拟结果验证了等比例替换模型的可行性.在计算阶段,提出了局部前处理的弛豫方法进行模拟.确定最大荷载位置处的接触面积为546 nm2,进而求出水化硅酸钙模型硬度H为0.84 GPa、折合模量Er为30.52 GPa.并通过纳米压痕试验,验证了模拟结果的准确性,证明了模型的科学性,对今后水化硅酸钙(C-S-H)纳米层面的模拟具有重要借鉴意义. 相似文献
33.
利用第一性原理对Li原子掺杂C28的分子器件的热自旋输运性质进行了计算。在不同的温度场下,上下自旋分别为Li原子掺杂C28的分子器件中的空穴和电子提供了输运通道,在MJ1和MJ3分子器件中,热自旋电流随着温度增加而增大,但在MJ2分子器件中,热自旋电流先增大再减小。三种分子器件都出现了自旋塞贝克效应,MJ2还出现了负微分电阻现象,利用费米-狄拉克分布和自旋输运谱对其物理机理进行了解释。根据Li掺杂C28的单分子器件的热自旋输运性质,可设计新的自旋纳米器件。 相似文献
34.
Tianyu Shan Liang Gao Xiaoqian Tong Qinqing Du Zhihang An Huiwen He Prof. Jiaping Lin Prof. Si Chen Prof. Xu Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(52):12098-12104
An amazing phenomenon of the relative magnitude of modulus of two liquid-crystal (LC) gels is found inverted under/above their phase transition temperature TLC-iso, which is further proved to be caused by their diverse morphology flexibility. By testing the polarity of two LCs, gelator POSS-G1-Boc (POSS=polyhedral oligomeric silsesquioxane) was discovered to self-assemble into more flexible structures in a relatively low polar LC, whereas more rigid ones are formed in higher polar LC. Hence, a fitting function to connect morphology flexibility with solvent polarity was established, which can even be generalized to a number of common solvents. Experimental observations and coarse-grained molecular dynamics simulations revealed that solvent polarity mirrors a “Morse code”, with each “code” corresponding to a specific morphology flexibility. 相似文献
35.
Michiel Janssen Prof. Dirk E. De Vos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10724-10734
The practical application of Shilov-type Pt catalysis to the selective hydroxylation of terminal aliphatic C−H bonds remains a formidable challenge, due to difficulties in replacing PtIV with a more economically viable oxidant, particularly O2. We report the potential of employing FeCl2 as a suitable redox mediator to overcome the kinetic hurdles related to the direct use of O2 in the Pt reoxidation. For the selective conversion of butyric acid to γ-hydroxybutyric acid (GHB), a significantly enhanced catalyst activity and stability (turnover numbers (TON)>30) were achieved under 20 bar O2 in comparison to current state-of-the-art systems (TON<10). In this regard, essential reaction parameters affecting the overall activity were identified, along with specific additives to attain catalyst stability at longer reaction times. Notably, deactivation by reduction to Pt0 was prevented by the addition of monodentate pyridine derivatives, such as 2-fluoropyridine, but also by introducing varying partial pressures of N2 in the gaseous atmosphere. Finally, stability tests revealed the involvement of PtII and FeCl2 in catalyzing the non-selective overoxidation of GHB. Accordingly, in situ esterification with boric acid proved to be a suitable strategy to maintain enhanced selectivities at much higher conversions (TON>60). Altogether, a useful catalytic system for the selective hydroxylation of primary aliphatic C−H bonds with O2 is presented. 相似文献
36.
Dr. Safaa M. Kishk Dr. Kirsty J. McLean Dr. Sakshi Sood Darren Smith Jack W.D. Evans Prof. Mohamed A. Helal Prof. Mohamed S. Gomaa Prof. Ismail Salama Prof. Samia M. Mostafa Dr. Luiz Pedro S. de Carvalho Colin W. Levy Prof. Andrew W. Munro Dr. Claire Simons 《ChemistryOpen》2019,8(7):995-1011
The emergence of untreatable drug-resistant strains of Mycobacterium tuberculosis is a major public health problem worldwide, and the identification of new efficient treatments is urgently needed. Mycobacterium tuberculosis cytochrome P450 CYP121A1 is a promising drug target for the treatment of tuberculosis owing to its essential role in mycobacterial growth. Using a rational approach, which includes molecular modelling studies, three series of azole pyrazole derivatives were designed through two synthetic pathways. The synthesized compounds were biologically evaluated for their inhibitory activity towards M. tuberculosis and their protein binding affinity (KD). Series 3 biarylpyrazole imidazole derivatives were the most effective with the isobutyl ( 10 f ) and tert-butyl ( 10 g ) compounds displaying optimal activity (MIC 1.562 μg/mL, KD 0.22 μM ( 10 f ) and 4.81 μM ( 10 g )). The spectroscopic data showed that all the synthesised compounds produced a type II red shift of the heme Soret band indicating either direct binding to heme iron or (where less extensive Soret shifts are observed) putative indirect binding via an interstitial water molecule. Evaluation of biological and physicochemical properties identified the following as requirements for activity: LogP >4, H-bond acceptors/H-bond donors 4/0, number of rotatable bonds 5–6, molecular volume >340 Å3, topological polar surface area <40 Å2. 相似文献
37.
利用ANSYS 对低活化铁素体马氏体(RAFM)钢进行非熔化极气体保护焊(TIG 焊)与电子束焊的抗疲劳模拟分析,再利用SDS200 电液伺服疲劳试验机对TIG 焊和电子束焊的两种RAFM 钢试件进行实验。通过施加相同梯度负荷对TIG 焊和电子束焊试件进行焊缝的疲劳性能实验。与实验结果对比分析,结果显示电子束焊优于 TIG 焊,但在一定负载下可以用TIG 焊代替电子束焊。 相似文献
38.
Two novel amino acids imine ligands (H2L1 and H2L2) have been synthesized using green condensation reaction from 2‐[3‐Amino‐5‐(2‐hydroxy‐phenyl)‐5‐methyl‐1,5‐dihydro‐[1, 2, 4]triazol‐4‐yl]‐3‐(1H‐indol‐3‐yl)‐propionic acid with benzaldehyde/p‐flouro benzaldehyde (1:1 molar ratio) in the presence of lemon juice as a natural acidic catalyst in aqueous medium. Their transition metal complexes have been prepared in a molar ratio (1:1). Characterization of the ligands and complexes using elemental analysis, spectroscopic studies, 1HNMR, 13CNMR, and thermal analysis has been reported. E*, ΔH*, ΔS* and ΔG* thermodynamic parameters, were calculated to throw more light on the nature of changes accompanying the thermal decomposition process of these complexes. The molar conductance measurement of metal complexes showed nonelectrolyte behavior. The metal complexes of the two ligands have tetrahedral geometry with a general molecular structure [M(H2L)Xn], where [(M = Mn (II), Co (II), Cu (II) and Zn (II), X = Cl, n = 2]; M = VO (II), X = SO4, n = 1] for H2L1. [M = Co (II), Cu (II), Zn (II)] for H2L2. Antibacterial activity of the complexes against (Bacillis subtilis, Micrococcus luteus, Escherichia coli), also antifungal activity against (Aspergillus niger, Candida Glabarta, Saccharomyces cerevisiae) have been screened. The results showed that all complexes have antimicrobial activity higher than free ligands. Molecular docking studies results showed that, all the synthesized compounds having minimum binding energy and have good affinity toward the active pocket, thus, they may be considered as good inhibitor of targeting PDB code: 1SC7 (Human DNA Topo‐isomerase I). 相似文献
39.
The radius of spatial analyticity for solutions of the KdV equation is studied. It is shown that the analyticity radius does not decay faster than as time t goes to infinity. This improves the works of Selberg and da Silva (2017) [30] and Tesfahun (2017) [34]. Our strategy mainly relies on a higher order almost conservation law in Gevrey spaces, which is inspired by the I-method. 相似文献
40.
Dr. Lan Hu Prof. Dr. Yan Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(32):7702-7710
Outcomes of chemical reactions are generally dominated by the intrinsic reactivities of reaction partners, but enzymes frequently override such constraints to transform less reactive molecules in the presence of more reactive ones. Despite the attractiveness of such catalysis, it is difficult to build synthetic catalysts with these features. Micellar imprinting is a powerful method to create template-complementary binding sites inside protein-sized water-soluble nanoparticles. When a photocleavable functional monomer was used to bind two phosphonate/phosphate templates as transition-state analogues, active sites with predetermined size and shape were formed inside doubly cross-linked micelles through molecular imprinting. Postmodification replaced the binding group with a catalytic pyridyl group, forming highly selective artificial esterases. The catalysts displayed enzyme-like kinetics and turnover numbers that were in the hundreds. The selectivity of the catalysts, derived from the substrate-complementary imprinted active sites, enabled transformation of less reactive esters in the presence of more reactive ones. 相似文献