关键词： 急性肺损伤   潮气量   呼气末正压   血气   血流动力学  

摘要： 目的观察不同潮气量(Vt)联合呼气末正压(PEEP)机械通气(MV)对油酸型急性肺损伤(ALI)犬血气与血流动力学的影响。方法用油酸静脉注射法制备犬ALI模型,造模成功后随机分为不同Vt组行机械通气4h:小Vt组(A组,n=6),Vt为6mL/kg;大Vt组(B组,n=6):Vt为20mL/kg,PEEP均为10cmH2O(1cmH2O=0.098kPa)。观察动脉血气、血流动力学的变化。结果各组犬pH持续降低,但A组pH显著低于B组水平(P<0.01);PaO2、SO2造模后下降、MV后升高;B组PaCO2波动不大,而A组PaCO2在MV后上升,组间差异有显著性(P<0.01)。各组犬PAP水平在ALI后较前升高(P<0.05),而MV后继续升高(P<0.05);而各组CO水平在ALI时、MV1h后较前显著降低(P<0.05);但A组犬在MV4h时较MV2h时上升(P<0.05),且机械通气4h时较B组升高(P<0.05)。结论PEEP=10cmH2O机械通气可改善油酸型ALI犬的氧合状况但影响血流动力学;小Vt机械通气可导致高碳酸血症的同时升高CO。

关键词： 计算流体动力学   浮选机   数值计算   内部流场  

摘要： 利用计算流体动力学分析软件Fluent模拟计算机械搅拌式浮选机的内部流场。计算结果标明,矿浆在槽体内螺旋上升和螺旋下降的循环流动,存在流动死区和短路现象,湍流强度分布呈现对称性,最大湍流强度出现在叶片流道内,进出口对其影响不大。

关键词： 动力机械   江苏   机械行业   国有资本   管理部门   新加坡   路面  

摘要： 新加坡国有资本开始进入我国路面机械行业,由新加坡新科动力有限公司投资5000万美元完成两家公司的控股收购——经国家工商管理部门批准,江苏华通动力重工有限公司、江苏华伦动力机械有限公司正式成立。

关键词： 事故预防   阻升   切削工具   定义   耐久性   英语   林业   林业设备   林业机械   高速切削装置   手动装置   内燃机   处理   惰性气体铠装电弧焊   作标记   机械性能   机械测试   机械试验   电动的   噪声测量   操作说明书   便携的   动力传动系统   危险防护   修枝剪刀   安全装置   安全装置   安全要求   锯   规范(验收)   试验   测试   痕量元素分析   用户信息   林地培育   木材加工   工作场所安全  

标准号: NF U34-135-2009

关键词： steered molecular dynamics simulation   ubiquitin family   mechanical unfolding   unfolding intermediate   origin of mechanical stability  

摘要： Like the muscle protein Titin, proteins of the ubiquitin family exhibit a parallel strand arrangement, but otherwise having a distinctly different fold and not involved in an obvious load-bearing function, exhibit high resistance to mechanical unfolding. We have applied all-atom molecular dynamics simulation technique in implicit solvent to present a deep insight into the force-induced unfolding pathway of three proteins-ubiquitin, NEDD8, and SUMO-2-all having almost similar structural features. Two intermediates evolve in the unfolding pathway of each of the three proteins. The first intermediate, which has already been identified in case of ubiquitin by earlier simulation results, is similar for ubiquitin and NEDD8, but different in SUMO-2. We have found a new intermediate with beta 3-beta 4 hairpin and some residual alpha-helical character;and this intermediate is common for all the three proteins. Thus, proteins of the ubiquitin family pass through a we defined conformation in their force-induced unfolding pathway. Reason behind the higher mechanical stability of the proteins with parallel strand structures like Titin has also been identified.

关键词： Electrostatic force   mechanical shock   microelectromechanical systems (MEMS)   microstructure   printed circuit board (PCB)   reliability   squeeze film damping (SQFD)  

摘要： We present a theoretical and experimental investigation into the effect of the motion of a printed circuit board (PCB) on the response of microelectromechanical systems (MEMS) devices to shock loading. For the theoretical part, a 2-DOF model is used, where the first degree of freedom accounts for the PCB. The second degree of freedom represents the motion of the MEMS microstructure. Low-g acceleration pulses are applied to the MEMS-PCB assembly base to simulate shock pulses generated from a drop-table test. Simulation data are presented to show the effects of the natural frequency of the PCB, the natural frequency of the microstructure, and the shock pulse duration. Universal 3-D spectra representing the effect of these parameters are presented. It is found that neglecting the PCB effect on the design of MEMS devices under shock loads can lead to undesirable motion of their microstructures. The effects of electrostatic force and squeeze film damping are investigated. It is found that the amplification of motion due to the PCB can cause early pull-in instability for MEMS devices implementing electrostatic forces. The effect of higher order modes of a microbeam is studied through a continuous beam model coupled with a lumped model of the PCB. The limitations of the 2-DOF model are discussed. An experimental investigation is conducted to verify the theoretical results using a capacitive accelerometer. Experimental data for the response of the accelerometer while it is mounted on two representative PCBs due to different low-g shock conditions are shown. [2008-0026]

关键词： PACS62.20.Qp   81.65.Ps   83.10.Rs   85.30.De  

摘要： Chemical mechanical polishing (CMP) technology, being the mainstream technique of acquiring global planarization and nanometer level surface, has already become an attractive research item. In the case of CMP process, the indentation depth lies in the range of nanometer or sub-nanometer, huge hydrostatic pressure induced in the local deformation area which makes the material removal and surface generation process different from traditional manufacturing process. In order to investigate the physical essence of CMP technique, the authors carry out molecular dynamics (MD) analysis of chemical mechanical polishing of a silicon wafer. The simulation result shows that huge hydrostatic pressure is induced in the local area and leads to the silicon atom transform from the classical diamond structure (alpha silicon) to metal structure (beta silicon). This important factor results in the ductile fracture of silicon and then in the acquisition of a super-smooth surface.

关键词： Molecular biomechanics   Entropic spring   Bioinformatics   Worm-like chain   Molecular motor   Microtubule  

摘要： The 14- to 18-amino acid kinesin neck linker domain links the core motor to the coiled-coil dimerization domain. One puzzle is that the neck linker appears too short for the 4-nm distance each linker must stretch to enable an 8-nm step-when modeled as an entropic spring, high inter-head forces are predicted when both heads are bound to the microtubule. We addressed this by analyzing the length of the neck linker across different kinesin families and using molecular dynamics simulations to model the extensibility of Kinesin-1 and Kinesin-2 neck linkers. The force-extension profile from molecular dynamics agrees with the worm-like chain (WLC) model for Kinesin-1 and supports the puzzling prediction that extending the neck linker 4 nm requires forces multiple times the motor stall force. Despite being three amino acids longer, simulations suggest that extending the Kinesin-2 neck linker by 4 nm requires similarly high forces. A possible resolution to this dilemma is that helix alpha-6 may unwind to enable the two-head bound state. Finally, simulations suggest that cis/trans isomerization of a conserved proline residue in Kinesin-2 accounts for the differing predictions of molecular dynamics and the WLC model, and may contribute to motor regulation in vivo.

关键词： Echocardiography   Hemodynamics   Prothesis  

摘要： Objectives: In this prospective randomized trial, we compared tilting disc medtronic hall valve with bileaflet valves St. Jude and ATS valve for Hemodynamic Performance in the early post-operative period. Methods: Between December, 2007 and January 2009, 85 patients were randomized to undergo Mitral Valve Replacement with or without aortic valve replacement with either medtronic hall tilting disc valve or St. Jude or ATS bileaflet valve. Echocardiography was used to compare the hemodynamic performance (transvalvular mean diastolic gradient and in-vivo valve area) in the early post-operative period. The two groups were not significantly different with respect to age, sex, New York Heart Association (NYHA) Class, Left Ventricular ejection fraction, incidence and severity of mitral stenosis or insufficiency and preservation of subvalvular apparatus. Results: Comparison of echocardiographic hemodynamic parameters obtained at the time of discharge from hospital demonstrated no significant differences between the prosthesis with valve size greater than or equal to 25mm. However, for small size mitral prosthesis 23mm mean diastolic pressure gradients were less in bileaflet St. Jude Valve and effective orifice area was also larger. Conclusions: Both tilting disc (Medtronic hall) and bileaflet valves (St. Jude Medical, ATS) give equally good results for large size valves. But in case of small size valves (23mm). Bileaflet St. Jude mitral valve gave better results in terms of large effective orifice area and less gradient across the valve.

关键词： Metallic glasses   Powder metallurgy   Kinetics   Calorimetry  

摘要： Al70Y16Ni10Co4 glassy powder was produced by mechanical alloying of elemental powder mixtures and the thermal stability as well as the crystallization kinetics was investigated using differential scanning calorimetry in both isochronal and isothermal modes. The isochronal and isothermal activation energies have a similar value (similar to 280 kJ/mol). Similar activation energy was obtained for the process from the viscosity measurements. In addition, JMA analysis shows that the transformation is diffusion controlled three-dimensional process and the crystallization proceeds with increasing nucleation rate at annealing temperatures within the supercooled liquid region. while it proceeds with decreasing nucleation rate at temperatures below the glass transition temperature. Metal matrix composites were synthesized through powder metallurgy methods by hot extrusion of commercial 6061 Al alloy powder blended with different amounts of Al70Y16Ni10Co4 metallic glass reinforcement. The mechanical properties of the 6061 matrix are remarkably improved by the addition of the glass reinforcements. The ultimate compressive strength increases from 260 MPa for the 6061 alloy to 350 MPa for the composite with 50 vol.% of glassy phase. (C) 2008 Elsevier B.V. All rights reserved.