关键词： Metallic glass  

摘要： The introduction of a glass-glass interface is an effective way to improve the plasticity of metallic glass. However, the strength-plasticity trade-off has not still been effectively overcome. Here, the effect of the composition on the mechanical properties and deformation behavior of the CuZr nanoglass (NG) is investigated under tensile loading by a molecular dynamics simulation. The results indicate that high-performance NGs can be obtained by adjusting the percentage of Cu atoms. There is a critical Cu content (i.e., 75%), which makes the NGs have both high strength and high plasticity. The results show that with the increase in the Cu content, the deformation mechanism of the NGs changes from necking to uniform plastic deformation and then to the nucleation and the growth of the main shear band. Our results underscore the importance of the composition in the design and preparation of high-performance metallic glass.

关键词： Redox reactions   Kinetic parameters   Anions   Solvents   Kinetics  

摘要： Application of organometallic ruthenium(II) arene complexes has been successful for the modulation of cellular redox processes via their interaction with species such as formate to control the NAD(+)/NADH balance in cells. Here we present the first evidence that similar effects can be reached with the application of a nonorganometallic ruthenium(II) polypyridyl complex. Kinetic studies performed demonstrate the ability of [Ru-II(terpy)(en)(H2O/EtOH)](2+) in water/ethanol (1:9, v/v) solution, where terpy = 2,2':6',2 ''-terpyridine and en = ethylenediamine, to catalyze the reduction of the NAD(+) coenzyme to NADH in the presence of formate as hydride transfer source. In this case, terpy instead of arene is responsible for the labilization of coordinated solvent. The suggested catalytic cycle begins with the fast anation of the [Ru-II(terpy)(en)(H2O/EtOH)(2+) complex by formate. This is followed by the rate-determining formate-catalyzed decarboxylation of the generated ruthenium(II) formato complex to form [Ru-II(terpy)(en)H](+). Rapid hydride transfer to NAD(+) from [Ru-II(terpy)(en)H](+) to form NADH and to regenerate the starting ruthenium(II) solvato complex, closes the overall catalytic cycle.

关键词： Kinetics   2H-thiopyrano [2   3-b] quinoline   the UV-visible   dialkyl acetylenedicarboxylate   2-mercaptoquinoline-3-carbaldehyde and triphenylphosphine  

摘要： The main aim of full chemical-kinetics investigation in this work, was recognition of a different role of triphenylphosphine (TPP) in the reaction with dialkyl acetylenedicarboxylates [di-tert-butyl acetylenedicarboxylate (DTBAD), diethyl acetylenedicarboxylate (DEAD) or dimethyl acetylenedicarboxylate (DMAD)] in the presence of SH-acid such as 2-mercaptoquinoline-3-carbaldehyde for the generation of 2H-thiopyrano [2, 3-b] quinoline-2, 3-dicarboxylates. The unexpected and different kinetic results (in comparison with previous work in the presence of TPP) is confirmed by the UV/vis spectrophotometry technique which is accompanied by these results. (1) The reaction followed third-order kinetics. (2) Step(1), containing TPP and DTBAD (DEAD or DMAD), was a fast step (k(obs) = 84.61 ***(-1) ). (3) The rate of overall reaction (TPP, S-H acid and DTBAD) in the presence of dichloromethane solvent (DCM) at 13 degrees C is (5.87 ***(-1) ), approximately 14.4 times lesser than the fast step. (4) The proposed mechanism is consist of six steps, amongst them, intermediate I-3 in step(4) having a well sensitive part to any changes in the reaction environment because it is near the reaction center. Any changes in dialkyl acetylenedicarboxylates' structures can be influenced their inductive and steric effects, corresponding to remarkable changes in the rate of this step (4) (k(4) ). (4) For this reason, step(4) was recognized as a rate determining-step.

关键词： Redox reactions   Free energy   QM/MM   Genetics   Defects  

摘要： The redox properties of two large DNA fragments composed of 39 base pairs, differing only by an 8-oxoguanine (8oxoG) defect replacing a guanine (G), were investigated in physiological conditions using mixed quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations. The quantum region of the native fragment comprised 3 G-C base pairs, while one G was replaced by an 8oxoG in the defect fragment. The calculated values for the redox free energy are 6.55 +/- 0.28 eV and 5.62 +/- 0.30 eV for the native and the 8oxoG-containing fragment, respectively. The respective estimates for the reorganization free energy are 1.25 +/- 0.18 eV and 1.00 +/- 0.18 eV. Both reactions follow the Marcus theory for electron transfer. The large difference in redox potential between the two fragments shows that replacement of a G by an 8oxoG renders the DNA more easily oxidizable. This finding is in agreement with the suggestion that DNA fragments containing an 8oxoG defect can act as sinks of oxidative damage that protect the rest of the genome from assault. In addition, the difference in redox potential between the native and the defect DNA fragment indicates that a charge transfer-based mechanism for the recognition of DNA defects might be feasible, in line with recent suggestions based on experimental observations.

关键词： 机械通气   急性心肌梗死   心源性休克   介入治疗  

摘要： 目的探讨急性心肌梗死(AMI)合并心源性休克(CS)出现急性肺水肿接受急诊经皮冠状动脉介入治疗(PCI)时早期应用机械辅助肺通气对于住院期间死亡率及血流动力学的影响。方法入选2015年1月至2016年12月期间就诊于天津市胸科医院CCU病房的急性心肌梗死患者。所有入选患者接受急诊冠状动脉(冠脉)造影检查,并根据病变特点完成急诊PCI,根据应用辅助通气类型分为侵入性机械辅助通气(IMV)组和非侵入性辅助通气(NIV)组。调查两组患者的临床资料、血流动力学指标、住院期间死亡率,分析IMV对于临床预后的影响。结果在急性心肌梗死的患者中,心源性休克的发生率为8.2%,83.5%的CS合并急性肺水肿。接受IMV患者造影结果示TIMI血流0-1级的比例明显高于NIV(P<0.05),IMV组的Ph值、氧分压明显低于NIV组,乳酸水平高于NIV组(P<0.05);IMV组的IABP使用时间、辅助通气时间短于NIV组,差异有统计学意义(P<0.05)。IMV组与NIV组比较术后即刻中心静脉压(CVP)、肺动脉压(PAP)、肺毛细血管楔压(PCWP)、平均动脉压(MAP)值比较差异没有统计学意义(P>0.05);IMV组术后3 h、6 h、12 h、24 h CVP、PAP、PCWP均低于NIV患者(P<0.05);IMV组MAP术后3 h、6 h、12 h均高于NIV患者(P<0.05)差异比较有统计学意义。接受IMV死亡率33.33%,接受NIV死亡率40.7%,差异无统计学意义(χ^2=0.412,P=0.521)。Logistic回归分析提示FMC时间过长、肝功能衰竭、肾功能衰竭、术后TIMI血流<3级为AMI发生CS院内死亡的独立风险因素(P<0.05),而使用IMV未增加患者死亡风险(P=0.629,95%CI:0.117~34.837)。结论AMI合并CS出现急性肺水肿的患者,早期行急诊介入治疗,置入IABP的同时,在基础麻醉状态下予以气管插管,呼吸机辅助呼吸,采用中等水平的PEEP模式,可以明显增加患者的生存获益。

关键词： 系统动力学   地铁盾构施工   机械费用   设备选型   掘进参数  

摘要： 以某地铁施工项目为例,基于系统动力学理论,对盾构机、龙门吊、同步压降泵、灰浆搅拌机以及电动灌浆机等主要施工机械设备使用费用进行分析。结果表明:采用系统动力学进行盾构施工机械费用预测,与实际情况基本吻合。同时从机械单价、盾构直径以及掘进速度3个方面对地铁盾构施工机械费用影响进行了探讨分析,可为地铁盾构施工机械设备选型、盾构施工掘进参数设置提供借鉴。

关键词： 光伏电站   机械臂   静力学分析   动力学建模   动力学分析  

摘要： 针对光伏电站清灰设备现状和西北地区环境,在清灰设备机械臂三维模型基础上,对清灰设备机械臂进行静力学分析求解,得到其数学解析式。首先,采用拉格朗日平衡法对机械臂进行动力学建模,然后用机械系统动力学仿真分析软件(ADAMS)建立清灰设备机械臂虚拟样机模型,并对其进行动力学仿真分析,得到机械臂末端运动轨迹、各关节角速度、角加速度、力及力矩特性曲线,为机械臂结构优化设计提供了理论依据,最后用刷体清灰实验验证所选方法的有效性以及所建模型的正确性。

关键词： Molecular dynamics   Functionally graded material (FGM)   Nanowire   Micromechanical modeling   Beat vibration  

摘要： Functionally graded material (FGM) is a class of advanced materials, consisting of two (or more) different constituents, that possesses a continuously varying composition profile. With the advancement of nanotechnology, applications of FGMs have shifted from their conventional usage towards sophisticated micro and nanoscale electronics and energy conversion devices. Therefore, the study of mechanical and vibrational properties of different FGM nanostructures is crucial in exploring their feasibility for different applications. In this study, for the first time, we employed molecular dynamics (MD) simulations to investigate the mechanical and vibrational properties of radially graded Cu-Ni FGM nanowires (NW). Distribution of Cu and Ni along the radial direction follows power-law, exponential and sigmoid functions for FGM NWs under consideration. Our results demonstrate that distribution function parameters play an important role in modulating the mechanical (elastic modulus and ultimate tensile strength) and vibrational (natural frequency and quality factor) properties of FGM NWs. The study also suggests that elastic moduli of FGM NWs can be predicted with relatively good accuracy using Tamura and Reuss micromechanical models, regardless of NW diameter. We found that Euler-Bernoulli beam theory under-predicts the natural frequencies of FGM NWs, whereas He-Lilley model closely approximates the MD results. Interestingly, FGM NWs are always found to exhibit beat vibration because of their asymmetrical cross sections. Finally, this is the first atomistic scale study of FGMs that directly compares MD simulations with continuum theories and micromechanical models to understand the underlying mechanisms that govern the mechanical and vibrational properties of FGM NWs in nanoscale.