关键词： 高速电主轴   木工机械   动力学分析  

摘要： 本文通过分析高速加工技术的特点,以及结合木材适宜的加工方式分析,对高速电主轴在木工机械中的关键技术进行分析,同时对高速电主轴在木工机械中的应用进行设计,最后利用MATLAB软件对木工机械中的高速电主轴进行动力学分析。

关键词： SEMICONDUCTOR nanowires   CARBON nanotubes   YOUNG'S modulus   MOLECULAR dynamics   VELOCITY  

摘要： Semiconductor nanowires are potential candidates for applications in quantum information processing, Josephson junctions, and field-effect transistors. Therefore, this study focused on the effects of covering a germanium nanowire (GeNW) with a single wall carbon nanotube (CNT) on the stress-strain diagram, failure points, and Young's modulus using molecular dynamics simulations. To describe the interactions between atoms in the system, we used Tersoff potential. Also, a Nose-Hoover thermostat was employed to control temperature of the system. The stress-strain curves of GeNW and GeNW inside CNT (CNT-GeNW) were obtained at various temperatures, radii, and strain velocities. It was found that coverage of GeNW with CNT led to 2-6 fold improved Young's modulus. It was also determined that a significant part of the Young's modulus in CNT-GeNW is due to the presence of CNT. Moreover, we defined the behavior of Young's modulus of GeNW as well as CNT-GeNW in the [100], [110], and [111] crystallography direction and found that Young's modulus decreased with increasing temperature. In addition, by increasing strain velocity, Young's modulus decreased for GeNW but increased for CNT-GeNW. Finally, we observed that when a GeNW is covered by a CNT, its failure point increased as compared with GeNW. Published by AIP Publishing.

关键词： PrMg12 alloy   Mechanical milling   Activation energy   Hydrogen storage kinetics  

摘要： In this paper, the nanocrystalline and amorphous PrMg11Ni + x wt.% Ni (x =100, 200) alloys were synthesized by mechanical milling. The gaseous and electrochemical hydrogen storage performances were studied in detail. The results reveal that increasing Ni content facilitates the glass forming of the alloys, and it significantly improves the gaseous and electrochemical hydrogen storage kinetics performance. Furthermore, milling time varying significantly affects the hydrogen storage properties of the alloys. The hydrogen capacity of the alloys first increases and then decreases with milling time prolonged. The hydriding rate and high-rate discharge ability (HRD) of the as-milled alloys have maximum values with milling time varying. But dehydriding rate always increases with milling time prolonged. The improved gaseous hydrogen storage kinetics of alloys are convinced to be ascribed to a reduction in hydrogen desorption activation energy caused by increasing Ni content and prolonging milling time. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： NdMg12 alloy   Mechanical milling   Activation energy   Hydrogen storage kinetics  

摘要： The nanocrystalline/amorphous NdMg11Ni + x wt.% Ni (x = 100, 200) composite hydrogen storage alloys were synthesized by ball milling, and the effects of Ni content and milling time on the hydrogen storage thermodynamics and dynamics of the alloys were systematically investigated. The results reveal that the variation of the Ni content has a slight effect on the thermodynamic properties of the alloys, but it significantly improves their absorption and desorption kinetics performance. The variation of the milling time clearly affects the hydrogen storage properties of the alloys. Hydrogen absorption capacity and hydrogen absorption saturation ratio have maximum values with milling time varying. But hydrogen desorption ratio always increases with milling time prolonging. It is found that the hydrogen desorption activation energy of the alloys clearly decreases with increasing Ni content and milling time, which is responsible for the improved hydrogen desorption kinetics of the alloys. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Gallic acid   Atrial natriuretic peptide   Protein kinase C   Phospholipase C   Mechanical dynamics  

摘要： Aims: Gallic acid (GA) protects against myocardial ischemia-reperfusion (I/R) injury, prevents cardiac hypertrophy and fibrosis, and has anti-inflammatory activity in the heart. However, its effects in regulating atrial natriuretic peptide (ANP) secretion are unknown. The aim of this study was to determine the function of GA in regulating ANP secretion and atrial dynamics in rat atria. Key findings: GA (0.01, 0.05, and 0.1 mu mol/L) significantly increased atrial ANP secretion and induced positive inotropy dose-dependently. GA (0.1 mu mol/L) also increased plasma level of ANP and hemodynamics in rats. These effects were accompanied by upregulation of atrial protein kinase C subtypes beta and epsilon (PKC beta and PKC epsilon), which was completely blocked by LY333531 and EAVSLKPT, antagonists of protein PKC beta and PKC epsilon, respectively. GA-induced ANP secretion was also attenuated by Go6983 but not rottlerin, antagonists of PKC alpha and PKC delta, and the positive inotropy was reversed by Go6983. U-73122, a phospholipase C (PLC) antagonist, mitigated the effects of GA on ANP secretion and mechanical dynamics and downregulated Phospho-PLC beta at Ser537 (pPLC(beta) S537), Phospho-PLC beta at Ser1105 (pPLC(beta) S1105), PKC beta and PKC epsilon levels, whereas KN62, an inhibitor of Ca2+/calmodulin-dependent kinase II, was not modified the GA-induced ANP secretion and suppressed GA-induced mechanical dynamics. Significance: GA promotes ANP secretion and effects positive inotropy with regard to mechanical dynamics through the activation of PLC-PKC signaling in rat atria. (C) 2017 Elsevier Inc. All rights reserved.

关键词： Cement   Hydration kinetics   Sugar   CaSO4   Heat release   Aluminate ferrite hydrates   Hydration products  

摘要： This article aims to study the hydration kinetics of cements containing sugars. The effects of Portland cement constituents (including aluminate and ferrite phases and CaSO4 content), and a sugar (glucose) on the hydration kinetics, microstructure and mechanical properties, were evaluated. The heat release during the hydration was analysed using an isothermal calorimeter. The reaction's products, gel structure and microstructure at different hydration times were analysed by the analytical methods XRD, FTIR and SEM. Furthermore, mortars and wood-wool cement composites were designed to validate the present findings. It is concluded that the newly derived binder can overcome retarding effects and result in wood-wool cement composites with excellent performance. (C) 2017 Elsevier Ltd. All rights reserved.

摘要： Bacteriophage T4 infects the bacterial host (Escherichia coli) using an efficient genomic delivery machine that is driven by elastic energy stored in a contractile tail sheath. Although the atomic structure of T4 is largely known, the dynamics of its fascinating injection machinery is not understood. This article contributes, to our knowledge, the first predictions of the energetics and dynamics of the T4 injection machinery using a novel dynamic model. The model employs an atomistic (molecular dynamics) representation of a fraction of the sheath structure to generate a continuum model of the entire sheath that also couples to a model of the viral capsid and tail tube. The resulting model of the entire injection machine reveals estimates for the energetics, timescale, and pathway of the T4 injection process as well as the force available for cell rupture. It also reveals the large and highly nonlinear conformational changes of the sheath whose elastic energy drives the injection process.

关键词： 毕业生   考研   就业   创业  

摘要： 随着高校扩招的进一步延伸,一方面意味着中国公民受教育的程度越来越高,为国家提前进入教育强国走出了重要一步,另一方面也说明中国传统的精英化教育转向了大众化教育,使得出现了越来越多的知识分子,导致人才市场饱和,越来越多的本科毕业生在毕业后因为找工作而伤透了脑筋,同时由于创业政策的支持,也让毕业生有了更多其他出路的选择,因此,本科毕业生在考研、就业、创业三方面有了更加多样化的抉择。

关键词： nucleic acid mechanical properties   twist-stretch coupling   DNA   RNA   molecular dynamics  

摘要： Multiple biological processes involve the stretching of nucleic acids (NAs). Stretching forces induce local changes in the molecule structure, inhibiting or promoting the binding of proteins, which ultimately affects their functionality. Understanding how a force induces changes in the structure of NAs at the atomic level is a challenge. Here, we use all-atom, microsecond-long molecular dynamics to simulate the structure of dsDNA and dsRNA subjected to stretching forces up to 20 pN. We determine all of the elastic constants of dsDNA and dsRNA and provide an explanation for three striking differences in the mechanical response of these two molecules: the threefold softer stretching constant obtained for dsRNA, the opposite twist-stretch coupling, and its nontrivial force dependence. The lower dsRNA stretching resistance is linked to its more open structure, whereas the opposite twist-stretch coupling of both molecules is due to the very different evolution of molecules' interstrand distance with the stretching force. A reduction of this distance leads to overwinding in dsDNA. In contrast, dsRNA is not able to reduce its interstrand distance and can only elongate by unwinding. Interstrand distance is directly correlated with the slide base-pair parameter and its different behavior in dsDNA and dsRNA traced down to changes in the sugar pucker angle of these NAs.

关键词： 碰振系统   周期运动   分岔   混沌  

摘要： 首先建立了一类三自由度碰振系统的理论模型,利用模态矩阵法推导出系统周期运动的周期解及系统在不动点处Poincaré映射的雅克比矩阵;再通过碰振系统的边界条件,分析系统周期运动的稳定性;最后通过MATLAB进行数值仿真,根据Poincaré截面图揭示了系统由分岔通向混沌的道路,为机械系统的优化设计提供了理论参考。