关键词： biopolymers and renewable polymers   crystallization   mechanical properties   morphology   thermal properties  

摘要： Poly(3-hydroxybutyrate) (PHB), is one important biopolymer and a promising alternative to petroleum-based plastics. In this article, formulations of PHB and triethyl citrate (TEC) as plasticizer were prepared by melt extrusion. The effect of TEC on the mechanical, thermal, and morphological properties of PHB was investigated by tensile tests, impact resistance, dynamic-mechanical analysis, differential scanning calorimetry, polarized optical microscopy, and small- and wide-angle X-ray scattering. TEC acted as an efficient plasticizer for PHB, imparting gradual changes in the properties as the mass fraction of TEC increased. A reduction in the elastic modulus, an increase in the intensity of beta relaxation indicated a higher capacity of mechanical energy dissipation for the formulations containing higher mass fractions of TEC. TEC reduced its glass transition and melting temperatures, contributing to the increase of the processing window of the temperature and minimizing thermal degradation of PHB. TEC had a strong influence on the kinetics of crystallization, the morphology of the spherulites, and the crystalline structural parameters, such as long period, crystalline lamella, and interlamellar amorphous region thicknesses. Our study clarifies how the morphology of the PHB crystalline phase evolves in the presence of the plasticizer and with the time of crystallization.

关键词： antiperovskite   formation energy   mechanical properties   phonon   p‐   type semiconductors   structural properties   thermoelectric properties  

摘要： We present a comparative study on the structural, electronic, elastic, and thermoelectric properties of the cubic inverse-perovskites A(3)OX (where A = Li, Na, K and X = Cl, Br, I) by density functional theory (DFT). The cohesive, formation, and elastic properties analysis indicates that all studied materials are chemically, thermodynamically, and mechanically stable. Electronic properties reveal that all the inverse A(3)OX perovskite are direct bandgap semiconductors except Li3OCl and Li3OBr with ionic nature which is confirmed by electron localization function (ELF) analysis. We have also calculated Debye temperature (Theta(D)) and Gruneisen parameter (gamma) to determine the lattice thermal conductivity for all the A(3)OX materials. Furthermore, thermoelectric (TE) properties are explored by calculating the Seebeck coefficient (S), electronic thermal conductivity, power factor (PF), electrical conductivity (sigma/tau), lattice thermal conductivity, and ZT value. Our investigated A(3)OX inverse-perovskites provide a fertile base that can improve the overall TE performance for TE applications and green energy production.

摘要： Modeling and simulations are a pillar in the development of complex technical systems. However, for time-critical applications a conduction of high-fidelity simulations is not always feasible. To mitigate this computational bottleneck model order reduction (MOR) can be applied. For nonlinear models, linear MOR approaches are only practicable to a limited extend. Nonlinear approaches, on the contrary, often require deep interventions in the used simulation code. If access is not possible, non-intrusive nonlinear model order reduction can be the key to success. The goal of this work is to implement a non-intrusive approach using classical model order reduction along with machine learning algorithms. It relies on the idea to learn the dynamics in the reduced space. The approach aims to learn the temporal evolution of the reduced dynamics of a system. By applying the method to a problem arising from the field of structural dynamics, accurate surrogate models are received. They can speed up the simulation time significantly, while still providing high-quality state approximations.

标准号: GB/T 39832-2021

摘要： 本标准给出了用于农业、园艺和区域维护(景观美化)的物料动力收集装置的设计和结构的安全要求和方法。本标准适用于园艺用悬挂式、半悬挂式或牵引式机械。本标准规定了物料收集系统按预定使用时排除和减少机械危险的方法。本标准不涉及环境危险，道路安全，电磁兼容性，动力输出轴(PTO)，动力输出传动轴防护装置或控制要求。

关键词： Ligands  

摘要： The reduction of An(vi) (An = U, Np, and Pu) to An(iv) significantly decreases its solubility and mobility. This reaction can be hindered by complexation with inorganic (e.g., carbonate) or organic ligands. Ethylenediaminetetraacetic acid (EDTA) is one such organic ligand that forms stable complexes with actinides. Therefore, it may enhance the mobility of actinides. However, the redox kinetics and mechanisms of actinyl (An(v/vi)O-2(+/2+))-EDTA are not well characterized yet and are thus studied here using quantum-mechanical calculations. The principle is to approach the actinyl-EDTA and Fe2+ (reductant) in small incremental steps and calculate the system energy at each distance. The overall reaction is then delineated into sub-processes (encounter frequency in bulk solution, formation of outer-sphere complex, transition from outer- to inner-sphere complex, and electron transfer), and reaction rates are determined for each sub-process. The formation of outer-sphere complexes occurs rapidly in microseconds to seconds over a wide range of actinyl concentrations (pM to mu M);in contrast, the transition to the inner-sphere complex is relatively slow (milliseconds to a few seconds). Immediate electron transfer to form the pentavalent actinide is observed along the reaction path for Np(vi) and Pu(vi), but not for U(vi). Surprisingly, in acidic conditions, one of the carboxylic groups gets protonated in EDTA of [UO2(edta)](2-) rather than one of the amino groups. This process-based series of calculations can be applied to any redox reaction and allows the prediction of changes to the rate law and rate-limiting step in a more fundamental way for different environments.

关键词： DFT   Ozanimod   TD-DFT   Non-covalent interactions   Molecular docking  

摘要： Ozanimod is a newly formulated drug used to manage relapsing multiple sclerosis. Here, we use computational chemistry tools to study the structure and various physio-chemical properties of the molecule. We applied the dispersion corrected omega B97XD functional with DGDZVP as a basis set and DEF2SV as a fitting set to determine the geometry of the molecule. Potential energy scan predicts that the most stable conformer is stable by 8.15 kcal/mol with respect to the eclipsed conformation. Time dependent density functional theory (TD-DFT) with CAM-B3LYP and the same basis sets were used to study the electronic spectra in methanol solvent. Non covalent interactions, average local ionization energy, and energy descriptors helped in predicting the reactivity and stability of the molecule. The compound also had excellent non-linear optical properties when compared to the standard material urea. Screening for biological activity followed by molecular docking studies suggested that ozanimod interacts with three proteins responsible for autoimmune disorders. (C) 2020 Elsevier B.V. All rights reserved.

关键词： GaAs nanowires   Nanomechanics   In-situ TEM mechanical Tests   Tensile deformation   Molecular dynamics simulation  

摘要： Nanowire-based devices have been widely applied in optoelectronics, sensors, generators and spectroscopy. These nanowires are typically subjected to mechanical conditions during manufacture or operation. Thus, a compressive understanding of nanowire mechanical properties is increasingly required. However, only limited results have been reported owing to the challenges inherent in nanomechanical testing, particularly for quantitative tensile deformation. Herein, taper-free zinc blende GaAs nanowires with a 120 nm diameter are grown along the [111]B direction using metalorganic vapor phase epitaxy. The mechanical properties and fracture mechanisms of these single-phase GaAs nanowires are explored by in-situ uniaxial tensile deformation inside a transmission electron microscope, followed by molecular dynamics simulations. Under tensile stress, GaAs nanowires deform overally elastically until sudden brittle fracture at 3.79% strain. The fracture strength and elastic modulus are experimentally determined as 4.0 and 109.5 GPa, respectively, which are much smaller than other reported results based on compression. The tensile deformation and fracture mechanisms are further explored using molecular dynamics simulations, and the effects of different crystal structures on the GaAs nanowire mechanical behavior are discussed. These results assess the mechanical behavior of single GaAs nanowires and present critical insights into the reliable design of engineering nanodevices.

关键词： 风电基础   ANSYS   Matlab/Simulink   黏性阻尼系数   刚度  

摘要： 采用Matlab/Simulink软件分别对机械振动激励和地震激励作用下的风电基础进行了动力仿真分析.基于有限元软件ANSYS对风电基础的动力学参数进行了计算.采用时程分析法对风电基础在输入机械振动激励和地震激励时的位移、速度和加速度时程曲线进行了仿真.研究了黏性阻尼系数和刚度对风电基础动力响应的影响.研究结果表明,风电基础的最终响应状态是由所输入的激励状态所决定,黏性阻尼系数的大小对风电基础的动力响应无明显影响,而刚度大小对其动力响应影响明显,在一定范围内,随着刚度的增加,风电基础的位移、速度时程曲线波动越大.

关键词： 专业学位研究生   专业课程   教学改革   实践能力  

摘要： 专业课程是专业学位硕士研究生培养重要一环,为了更好激发研究生创新能力和提高实践动手能力,本文对“动力机械测试技术”课程的教学内容、教学方法和教学手段等进行探索,以此提高专业学位硕士研究生的培养质量,同时为高校专业学位研究生课程综合改革提供借鉴。

关键词： 材料成型及控制工程   能源与动力工程   机械电子工程   卓越工程师教育培养计划   国家特色专业   机械设计制造及其自动化   三峡大学   核工程与核技术  

摘要： 2014年1月原机械与材料学院更名为机械与动力学院,学院现设有机械设计制造及其自动化、机械电子工程、材料成型及控制工程、工业工程、能源与动力工程、核工程与核技术六个本科专业,其中机械设计制造及其自动化为国家特色专业、第二批卓越工程师教育培养计划专业和省本科品牌专业,材料成型及控制工程为第三批卓越工程师教育培养计划专业。