摘要： Radical pair recombination reactions are known to be sensitive to extremely weak magnetic fields and can therefore be said to function as molecular magnetoreceptors. The classic example is a carotenoid-porphyrin-fullerene (C center dot+PF center dot-) radical pair that has been shown to provide a "proof-of-principle" for the operation of a chemical compass [K. Maeda et al., Nature 453, 387 (2008)]. Previous simulations of this radical pair have employed semiclassical approximations, which are routinely applicable to its 47 coupled electronic and nuclear spins. However, calculating the exact quantum mechanical spin dynamics presents a significant challenge and has not been possible until now. Here, we use a recently developed method to perform numerically converged simulations of the C center dot+PF center dot- quantum mechanical spin dynamics, including all coupled spins. A comparison of these quantum mechanical simulations with various semiclassical approximations reveals that, while it is not perfect, the best semiclassical approximation does capture essentially all of the relevant physics in this problem.

标准号: GB/T 19725.2-2020

摘要： GB/T 19725的本部分规定了以内燃机为动力源并将机械动力传递至切割附件的便携式背负动力割灌机和割草机的设计、结构和使用方面的安全要求及其试验方法。本部分提出了消除或减少使用整机所产生的各种危害的方法，规定了由生产厂家提供的安全操作方面有关资料的要求。本部分和第1部分的相关章节（见4.1）涉及了在正常使用以及合理的、制造商可预见的误用整机时所有与整机相关的严重危险、危险情况及严重危害事件，背负式动力装置引起的全身振动危害除外。

标准号: GB/T 20888.1-2020

摘要： GB/T 20888的本部分规定了以内燃机为动力源经传动轴传递动力至切割附件的杆式侧挂式动力修枝锯（以下简称侧挂式修枝锯）的设计、结构和使用方面的安全要求及其试验方法。本部分中切割附件是指锯链及做往复运动或旋转运动的外径不大于205 mm的锯片。本部分提出了消除或减少使用以内燃机为动力的侧挂式修枝锯所产生的各种危害的方法，规定了由生产厂家提供的有关安全操作方面的资料要求。本部分涉及了与侧挂式修枝锯相关的，正常使用时以及合理的、可预见误用时的所有的重要危害，但没有涉及在操作手册中已经提出警告的架空电缆引起的电击危害。

标准号: GB/T 19725.1-2020

摘要： GB/T 19725的本部分规定了以内燃机为动力源并将机械动力传递至切割附件的便携式侧挂动力割灌机和割草机（以下简称整机）的设计、结构和使用方面的安全要求及其试验方法。本部分提出了消除或减少在使用割灌机和割草机过程中所产生的各种危害的方法，规定了由生产厂商提供的有关安全操作方面资料的要求。本部分涉及了在正常使用以及合理的、生产厂家可预见的误用整机时所有与整机相关的严重危险、危险情况及严重危害事件。

标准号: GB/T 20888.2-2020

摘要： GB/T 20888的本部分规定了具有背负式动力装置且动力源经传动轴传递动力至切割部件的杆式背负式动力修枝锯（以下简称“背负式修枝锯”）的设计和结构方面的安全要求及其试验方法。本部分中切割部件是指锯链及做往复运动或旋转运动的锯片。本部分提出了消除或减少使用背负式修枝锯所产生的各种危害的方法，规定了由生产厂家提供的有关安全操作方面的资料要求。本部分和GB/T 20888的第1部分的相关章节涉及了与背负式修枝锯相关的，正常使用时以及合理的、可预见误用时的所有的严重危害，但没有涉及接触架空电缆引起的电击危害（使用说明书中包含的警告和建议除外）和背负式动力装置引起的全身振动危害。

关键词： Geopolymer   Aluminosilicate powder   SiO2/Al2O3 ratio   Molecular dynamics simulation   Structural properties   Mechanical properties  

摘要： In this study, the impacts of different SiO2/Al2O3 ratio on the molecular structural and mechanical properties of geopolymer were investigated by molecular dynamics and experiment. Complex composition of raw materials may affect the analysis of geopolymer gels. Therefore, pure aluminosilicate powder with different SiO2/Al2O3 ratio were synthesized by sol-gel method firstly. Then the prepared powder mixed with the activating agent of NaOH and sodium silicate to prepare geopolymer. After 28d curing age, chemical composition and crystalline phase of geopolymer were characterized by X-ray fluorescence (XRF) and X-ray Diffraction (XRD) respectively. Based on the above characterization results of geopolymer gel, different SiO2/Al2O3 ratio of molecular models were built. Finally, molecular dynamics were performed on the molecular models to study energy and temperature, simulated XRD, radial distribution function (RDF), distribution of bond length and bond angle and elastic modulus. Results showed that with the increases of SiO2/Al2O3 ratio, both stability of molecular structure and mechanical properties of geopolymer were decreased. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Carbon dioxide  

摘要： In this work, the first investigation of the structural, dynamical and thermodynamical properties of solvated CO2 in liquid ammonia using a recently developed Quantum Mechanical/Molecular Mechanical Molecular Dynamics Thermodynamic Integration (QM/MM MD TI) approach has been carried out. The correlated resolution-of-identity Moller-Plesset Perturbation Theory (RI-MP2) ab initio level of theory has been applied to treat CO2 and its entire first solvation shell. In contrast to aqueous CO2, a negative value for the absolute solvation free energy of -25.9 +/- 1.5 kJ/mol was found. This latter value reflects that the solute-solvent interaction is more favorable in liquid ammonia solution. In order to obtain a detailed structural characterisation of solvated CO2, the evaluation of radial distribution functions was performed in conically restricted regions with respect to the main axis of the CO2 molecule. The presented data provides detailed information on the solvation properties of CO2 in pure liquid ammonia. Since knowledge about the latter is a key prerequisite to understand CO2-capture in ammonia solutions, the simulation results can be expected to act as a valuable reference. In addition, the detailed analysis of the individual QM/MM energy contributions showed that the overall potential energy is not affected by artificial contributions, which might influence the determination of solvation free energy. (C) 2020 Published by Elsevier B.V.

关键词： Adsorption   MOFs   PBA/GO   Ciprofloxacin   Kinetics and thermodynamic studies  

摘要： Water as a universal solvent has well-documented for its ability to dissolve various substances leading to water pollution. Metal organic frameworks (MOFs) have been proved to have interesting properties for the adsorptive removal of pollutants from water. In this work, Mn-PBA (Mn[Fe(CN)(6)]) and Mn-PBA/GO composite have been developed using simple and facile method for the adsorption of ciprofloxacin (CIP). The adsorption kinetic performance of as-synthesized composite for CIP is justified by applying pseudo-second order (R-2 = 0.99638) and liquid-film diffusion model (R-2 = 0.91603), whereas for the Mn-PBA, pseudo-second order (R-2 = 0.99951) and intra-particle model (R-2 = 0.80577) is well-fitted. The adsorption isotherm data of Mn-PBA/GO composite for CIP is fitted using Langmuir model (R-2 = 0.99994) and adsorption capacity (1826.64 mg/g) is observed higher than previous reports. The relative correlation coefficient value is calculated by using Tampkin model (R-2 = 0.62798), which indicated electrostatic relationship between Mn-PBA/GO and ciprofloxacin (CIP). Adsorption of CIP on the Mn-PBA/GO takes place according to endothermic and spontaneous processes (Delta H = +16.94 kj/mol, Delta G = -9.25 kj/mol). The composite has well retained its reusability and the removal efficiency is reduced only 5% after several cycles. Further, the influence of various factors (pH, contact time, adsorbent dose, adsorbate quantity, temperature and ionic strength) on adsorptive removal of CIP is also discussed.

关键词： Thermomechanical properties   BxCyNz heteronanotubes   NiTMTAA   Adsorption   Molecular dynamics simulation  

摘要： In this study, the adsorption characteristics together with the modified thermomechanical properties of stable BxCyNz heteronanotubes, i.e. BC2N, BC3, and NC3, in ambient conditions have been explored under the adsorption of NiTMTAA molecules (NiTMTAA/heteronanotube). Employing molecular dynamics study, it is observed that pi-pi stacking interaction plays a major role in the adsorption of NiTMTAA. The radius of gyration and circumferential distribution along the axis of NTs demonstrate the higher agglomeration of molecules near the wall of CNT and BC3 than that of other NTs. Moreover, it is observed that CNT and BNNT possess the highest Young's modulus and thermal conductivity than those of heteronanotubes. According to the results, the adsorption of NiTMTAA molecules reduces thermal conductivity. Unlikely, Young's modulus of NiTMTAA/heteronanotubes for small weight percentage of NiTMTAA molecules (< similar to 20%) is slightly higher than pure heteronanotubes. Furthermore, it is shown that for more than 20%, the thermomechanical properties are approximately converged to the slightly lower value than that of pure heteronanotubes. Finally, it is demonstrated that the presence of both boron (B) and nitrogen (N) atoms in heteronanotubes, i.e. BC2N, results in higher thermomechanical properties than the individual presence of B and N.

关键词： Molecular dynamics   Diamond   Nanotribology   Sliding   Rolling   Oscillating  

摘要： Molecular dynamics simulation is employed to analyze the effect of sliding, rolling and oscillating movements on nanotribology properties of a diamond abrasive on a silicon substrate. The abrasive oscillating mechanism is achieved by simulating megasonic vibration-assisted on the planarization process. In this paper, the effects of abrasive size, sliding velocity, depths of polishing, rolling velocity, rolling direction, oscillating amplitude and oscillating frequency on material removal are considered. The results showed that the rolling mechanism reaches the highest number of atoms removed while the suitable oscillating mechanism gains the lowest height of asperity. The oscillating movement has remarkable results in wiping out the asperity atoms, although at a high amplitude and a low frequency causing some atoms from the flat substrate stuck to the abrasive and left some surface defects. Moreover, a multi-asperities model is set up to simulate the global-scale ability of sliding, oscillating and rolling mechanisms on polishing. This model indicates the saturated behavior of the rolling mechanism, while the lowest value of the surface roughness attained by the sliding mechanism. Combining three types of removing mechanisms could create a smooth surface with a high effective removal rate on both local and global-scales.