关键词： 农机总动力   灰色理论   预测  

摘要： 农业机械总动力预测是农业机械化科学管理的重要内容。为此,运用灰色系统理论GM(1,1)模型,对1998-2008年陕西省农业机械总动力进行了相关检验,模拟了陕西省农机总动力发展情况,相对误差均小于3%,平均误差为1.01%,模型可用于农机总动力预测。预测结果表明:2011-2015年陕西农业机械总动力分别为19 570,21 687,2 3932,26 315,28 843kW,呈直线上升趋势,年平均递增率为9.48%。

关键词： 机械动力学   学术会议   中国   征文   工程学   振动  

摘要： 由中国振动工程学学会主办的“2011中国机械动力学学术会议”将于2011年7月29—31日在杭州召开。

关键词： atomic force microscopy   dielectric polarisation   electric domain walls   ferroelectric switching   lead compounds   nanostructured materials   nucleation  

摘要： The local dynamics of ferroelectric domain polarization are uniquely investigated with sub-20-nm resolved maps of switching times, growth velocities, and growth directions. This is achieved by analyzing movies of hundreds of consecutive high speed piezo force microscopy images, which record domain switching dynamics through repeatedly alternating between high speed domain imaging and the application of 20-nanosecond voltage pulses. Recurrent switching patterns are revealed, and domain wall velocities for nascent domains are uniquely reported to be up to four times faster than for mature domains with radii greater than approximately 100 nm. Switching times, speeds, and directions are also shown to correlate with local mechanical compliance, with domains preferentially nucleating and growing in compliant sample regions while clearly shunting around locations with higher stiffness. This deterministic switching behavior strongly supports a defect-mediated energy landscape which controls polarization reversal, and that can therefore be predicted, modeled, and even manipulated through composition, processing, and geometry. Such results have important implications for the practical performance of ferroelectric devices by enabling guided optimization of switching times and feature densities, while the methods employed provide a new means to investigate and correlate dynamic functionality with mechanical properties at the nanoscale. (C) 2011 American Institute of Physics. [doi:10.1063/1.3581205]

关键词： 工程机械行业   东方红柴油机   动力元件   上海新国际博览中心   宝马   展放   品牌   亚太地区  

摘要： “上海宝马工程机械展”是世界最大的工程机械展bauma在中国的延伸，同时也是2010年亚太地区最具影响力的国际性行业博览会。bauma China2010暨第5届中国国际工程机械、建材机械、工程车辆及设备博览会于2010年11月23—26日在上海新国际博览中心召开。

关键词： Oxygen   Diffusion   Oxidation kinetics   Ascorbic acid   Mechanistic model   Sensitivity study  

摘要： A mechanistic model was developed taking into account both oxygen and ascorbic acid transfer phenomena and oxidation reaction of ascorbic acid. Studied system was cylindrical agar gel initially spiked with ascorbic acid and exposed to air on one face. This model describes oxygen and ascorbic acid diffusion (using Fick's law) and ascorbic acid oxidation rate. A sensitivity study showed that partial order of reaction with respect to oxygen was the critical factor in this model coupling transfer and reaction phenomena. This model has been validated at 20 degrees C using local measurements of ascorbic acid and oxygen contents in agar gels, and also using average ascorbic acid content, both type of data having been measured at different sampling times. It was shown that the reaction occurred at a significant extent only near from the interface air/gel, i.e. the part of the gel near from the interface air/gel contained high level of oxygen and low level of ascorbic acid, whilst the part near the other extremity of the gel contained high level of ascorbic acid and low level of oxygen. This model could be a useful tool to precisely locate the zone in a solid food submitted to oxidation, to determine which reactant and which phenomenon (diffusion and/or reaction) is rate limiting and consequently to assess better designs for strategies of protection against oxidation. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Thermoelectric materials   skutterudites   mechanical properties   surface effect   molecular dynamics  

摘要： Molecular dynamics simulations of the structural and mechanical properties of single-crystalline CoSb3 have been carried out at room temperature. Special emphasis was given to the surface effect. Four different boundary conditions were applied to represent a wide range of surface-atom fractions. The LAMMPS program in conjunction with a multibody potential was employed. First, free relaxation was performed to obtain the corresponding stable configurations. The atomic rearrangements and energy distributions were observed. Then, uniaxial tensile deformation was simulated at a constant strain rate. The stress-strain responses and structural evolutions were examined during the process. Comparison of simulation results between different boundary conditions was carefully made. It was found that, when the scale of the single-crystalline CoSb3 model becomes nanometric and the fraction of the surface atoms increases, the mechanical performance becomes substantially worse. Nonetheless, the deformation mechanism and intrinsic mechanical nature are very similar.

关键词： Labial interruption   Mechanical interruption   Subglottal pressure   Laryngeal airflow   Laryngeal resistance  

摘要： Objectives/Hypothesis. To directly compare the mechanical and labial interruption techniques of measuring subglottal pressure (P(s)), mean flow rate (MFR), and laryngeal resistance (R(L)). Methods. Thitty-four subjects performed 10 trials with both mechanical and labial interruption. P(s) and MFR were recorded, whereas R(L) was calculated by dividing P(s) by MFR. Coefficients of variation were calculated to compare intrasubject precision. A subset of 10 subjects performed the tasks twice with 30 minutes between sessions. Bland-Altman plots were used to determine intrasubject repeatability for each of the methods. Results. Mechanical interruption produced coefficients of variation for P(s), MFR, and R(L) of 0.0995, 0.127, and 0.129, respectively. Labial interruption produced coefficients of variation of 0.102, 0.147, and 0.169, respectively. P values were 0.824 for P(s), 0.159 for MFR, and 0.043 for R(L). The Bland-Altman plots revealed comparable repeatability between the two methods. The 95% confidence intervals of the Bland-Altman plots for mechanical interruption were (-0.050, 0.072), (-0.543, 1.832), and (-2.498, 10.528) for MFR, P(s), and R(L). Confidence intervals for labial interruption were (-0.018, 0.031) (0.057, 2.442), and (-3.267, 10.595) for MFR, P(s) and R(L). Conclusions. Mechanical interruption produced higher precision when measuring R(L) because of more reliable airflow measurements. Mechanical and labial interruption showed comparable repeatability. Further research into using mechanical interruption clinically is warranted.

关键词： hydrogen storage   lithium amide   magnesium hydride   isothermal kinetics   oxide  

摘要： The destabilized complex hydride system composed of LiNH2:MgH2 (1:1 molar ratio) is one of the leading candidates of hydrogen storage with a reversible hydrogen storage capacity of 8.1 wt%. A low sorption enthalpy of similar to 32 kJ/mole H-2 was first predicted by Alapati et al. utilizing first principle density function theory (DFT) calculations and has been subsequently confirmed empirically by Lu et al. through differential thermal analysis (DTA). This enthalpy suggests that favorable sorption kinetics should be obtainable at temperatures in the range of 160 degrees C to 200 degrees C. Preliminary experiments reported in the literature indicate that sorption kinetics are substantially lower than expected in this temperature range despite favorable thermodynamics. Systematic isothermal and isobaric sorption experiments were performed using a Sievert's apparatus to form a baseline data set by which to compare kinetic results over the pressure and temperature range anticipated for use of this material as a hydrogen storage media. Various material preparation methods and compositional modifications were performed in attempts to increase the kinetics while lowering the sorption temperatures. This paper outlines the results of these systematic tests and describes a number of beneficial additions which influence kinetics as well as NH3 formation.

关键词： Zinc   Peptides and proteins   QM/MM   Ions   Inhibitors  

摘要： Angiotensin-converting enzyme (ACE) is an important zinc-dependent hydrolase responsible for converting the inactive angiotensin I to the vasoconstrictor angiotensin II and for inactivating the vasodilator bradykinin. However, the substrate binding mode cif ACE has not been completely understood. In this work, we propose a model for an ACE Michaelis complex based on two known X-ray structures of inhibitor-enzyme complexes. Specifically, the human testis angiotensin-converting enzyme (tACE) complexed with two clinic drugs were first investigated using a combined quantum mechanical and molecular mechanical (QM/MM) approach. The structural parameters obtained from the 550 ps molecular dynamics simulations are in excellent agreement with the X-ray structures, validating the QM/MM approach. Based on these structures, a model for the Michaelis complex was proposed and simulated using the same computational protocol. Implications to ACE catalysis are discussed.

关键词： MOLECULAR dynamics   SIMULATION methods & models   MATERIALS -- Mechanical properties   CARBON nanotubes   FULLERENES   TEMPERATURE effect   ELASTICITY   STRENGTH of materials   DEFORMATIONS (Mechanics)  

摘要： The mechanical characteristics of a single-walled carbon nanotube (SWCNT) filled with C-60 fullerene subject to nanoindentation is studied using molecular dynamics (MD) simulations. The effects of temperature, indentation velocity, adhesion, and tip sizes were evaluated. The simulated results clearly show that the exerted load, Young's modulus, elastic energy, and plastic energy decrease significantly with increasing temperature and decreasing indentation velocity and tip size. C-60 fullerenes can effectively increase the mechanical strength of a SWCNT because they act as a "barrier" to resist the radial deformation, as well as an inner wall in a double-walled carbon nanotube. With the same indentation depth, the ratio of elastic energy to plastic energy for a material gradually increases with the increase in the radius of the tip. This indicates that the elastic recovery of a material is better when the tip has a larger radius. (C) 2011 Elsevier Ltd. All rights reserved.