关键词： Electrochemical discharge phenomenon   Hysteresis   Bistability   Anode/cathode effect   Gas film life-time  

摘要： A model for the prediction of the current-voltage characteristics of a two electrodes cell incorporating the dynamics of the gas film formed during the electrochemical discharge phenomenon is developed. In its mean-field version, the model presents good qualitative agreement but overestimates the hysteresis effect and predicts too large current densities for the cell operation once the gas film is formed. An improved stochastic model, which assumes gas film departures from the electrode surface according to a Poisson process, addresses these issues and gives significantly better predictions. Two relations are presented which allow estimating the mean gas film detachment time and its variance from the experimental study of the hysteresis in the forward and reverse scan of a two electrode cell operated at high current densities.

关键词： Kinetics   Treatment plants   kinetic model   Volatile Solids   Reaction rates   model parameters   Environmental conditions   composting   optimum moisture content   Refuse composting  

摘要： This study focuses on the investigation of the kinetics of municipal solid waste composting in three full-scale mechanical-biological treatment (MBT) plants. The aims were to test a kinetic model based on volatile solids (VS) content change for describing the composting process in MBT plants, and to identify the model parameters that affected the estimation of the reaction rate constant most. To achieve this, VS content and several environmental conditions, namely temperature, moisture content, oxygen concentration and total bulk density were monitored throughout the composting process. Experimental data was fitted with a first-order kinetic model, and a rate constant (k) characteristic of composting under optimum environmental conditions was obtained. The kinetic model satisfactorily described the experimental data for the three MBT plants. k values ranged from 0.043 +/- 0.002 d(-1) to 0.082 +/- 0.011 d(-1). Sensitivity analysis showed that the model parameters that most affected the estimation of k were the initial biodegradable volatile solids content, the maximum temperature for biodegradation and the optimum moisture content. In conclusion, we show for the first time that full-scale MBT plants can be successfully modelled with a composting kinetic model. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Biomechanics   Biophysics/methods   Kinetics   Models, Molecular   Molecular Dynamics Simulation   Muscle Proteins/chemistry   Protein Kinases/chemistry   Protein Structure, Tertiary   Protein Unfolding   Ubiquitin/chemistry  

摘要： One of the applications of Molecular Dynamics (MD) simulations is to explore the energetic barriers to mechanical unfolding of proteins such as occurs in response to the mechanical pulling of single molecules in Atomic Force Microscopy (AFM) experiments. Although Steered Molecular Dynamics simulations have provided microscopic details of the unfolding process during the pulling, the simulated forces required for unfolding are typically far in excess of the measured values. To rectify this, we have developed the Pulsed Unconstrained Fluctuating Forces (PUFF) method, which induces constant-momentum motions by applying forces directly to the instantaneous velocity of selected atoms in a protein system. The driving forces are applied in pulses, which allows the system to relax between pulses, resulting in more accurate unfolding force estimations than in previous methods. In the cases of titin, ubiquitin and e2lip3, the PUFF trajectories produce force fluctuations that agree quantitatively with AFM experiments. Another useful property of PUFF is that simulations get trapped if the target momentum is too low, simplifying the discovery and analysis of unfolding intermediates.

关键词： chemical exchanges   diffusion   integral equations   molecular dynamics method   reaction kinetics   solvation   statistical mechanics  

摘要： Extraction of relaxation times, lifetimes, and rates associated with the transport of topological charge defects in hydrogen-bonded networks from molecular dynamics simulations is a challenge because proton transfer reactions continually change the identity of the defect core. In this paper, we present a statistical mechanical theory that allows these quantities to be computed in an unbiased manner. The theory employs a set of suitably defined indicator or population functions for locating a defect structure and their associated correlation functions. These functions are then used to develop a chemical master equation framework from which the rates and lifetimes can be determined. Furthermore, we develop an integral equation formalism for connecting various types of population correlation functions and derive an iterative solution to the equation, which is given a graphical interpretation. The chemical master equation framework is applied to the problems of both hydronium and hydroxide transport in bulk water. For each case it is shown that the theory establishes direct links between the defect's dominant solvation structures, the kinetics of charge transfer, and the mechanism of structural diffusion. A detailed analysis is presented for aqueous hydroxide, examining both reorientational time scales and relaxation of the rotational anisotropy, which is correlated with recent experimental results for these quantities. Finally, for OH(-)(aq) it is demonstrated that the "dynamical hypercoordination mechanism" is consistent with available experimental data while other mechanistic proposals are shown to fail. As a means of going beyond the linear rate theory valid from short up to intermediate time scales, a fractional kinetic model is introduced in the Appendix in order to describe the nonexponential long-time behavior of time-correlation functions. Within the mathematical framework of fractional calculus the power law decay similar to t(-sigma), where sigma is a paramet

关键词： SOLVATION   MOLECULAR dynamics   LIQUIDS   GEODESICS (Mathematics)   POTENTIAL energy surfaces   RELAXATION phenomena   CHEMICAL reactions  

摘要： It is not obvious that many-body phenomena as collective as solute energy relaxation in liquid solution should ever have identifiable molecular mechanisms, at least not in the sense of the well-defined sequence of molecular events one often attributes to chemical reactions. What can define such mechanisms, though, are the most efficient relaxation paths that solutions take through their potential energy landscapes. When liquid dynamics is dominated by slow diffusive processes, there are mathematically precise and computationally accessible routes to searching for such paths. We apply this observation to the dynamics of preferential solvation, the relaxation around a newly excited solute by a solvent composed of different components with different solvating abilities. The slow solvation seen experimentally in these mixtures stems from the dual needs to compress the solvent and to do solvent-solvent exchanges near the solute. By studying the geodesic (most efficient) paths for this combined process in a simple atomic liquid mixture, we show that the mechanism for preferential solvation features a reasonably sharp onset for slow diffusion, and that this diffusion involves a sequential, rather than concerted, series of solvent exchanges. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3481655]

关键词： H-2-storage properties of Mg   Addition of Ni and Fe2O3   Reactive mechanical grinding   Mg2Ni formation   Mg(OH)(2) formation  

摘要： The activated 76.5 wt%Mg-23.5 wt%Ni (Mg-Ni) has a lower hydriding rate, compared with Mg-23.5 wt%Ni heat-treated after melt spinning, due to the nonhomogeneous distribution of Ni particles in the mixture and the larger sizes of the particles. Among 76.5 wt%Mg-23.5 wt%Ni (Mg-Ni), 71.5 wt%Mg-23.5 wt%Ni-5 wt%Fe2O3(Mg-Ni-O), and 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe2O3(spray conversion) (Mg-Ni-Osc) samples, Mg-Ni-Osc has the highest hydriding and dehydriding rates. The reactive mechanical grinding of Mg with Ni, purchased Fe2O3 or Fe2O3(spray conversion) is considered to facilitate nucleation and shorten diffusion distances of hydrogen atoms. After hydriding-dehydriding cycling, all the samples contain Mg2Ni phase. The samples with Fe2O3 and Fe2O3(spray conversion) as starting materials contain Mg(OH)(2) phase after hydriding-dehydriding cycling as well as after reactive mechanical grinding. (C) 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

关键词： Li2MnO3   Li plus ionic duffusion   NMR  

摘要： XRD, Li-7 MAS NMR, and electrical resistivity measurements were carried out to probe the local structure and the Li+ ionic diffusion in lithium manganese oxide Li2MnO3 prepared by mechanical milling and solid state reaction. XRD profiles and NMR spectra remarkably changed as milling time increased, and it is suggested that a disordered frame structure consisting of Mn-O polyhedral blocks was produced. Such a precursor would enable one to synthesize Li-Mn-O compounds at relatively lower temperatures compared to the synthesis just by solid state reaction. The activation energy for the hopping of the Li+ ions in Li2MnO3 sintered at 900 degrees C was determined to be 0.46 eV from the analysis based on a simple Debye model of electrical resistivity. Changes in the NMR spectra and the electrical resistivities suggest that the Li+ ions begin to occupy available sites in the Mn-O block layer at low temperatures and located in those, forming the lithium layer sandwiched by oxygen layers, at high temperatures in Li2MnO3 prepared via mechanical milling. The establishment of the lithium layers plays an important role in a valid Li+ ionic conduction in layered Li2MnO3. (C) 2010 Elsevier B.V. All rights reserved.

关键词： 农机测试   田间试验   遥测   传感器  

摘要： 针对播种、收获、整地、植保等农业机械的研发需要依靠大量季节性田间试验,而相关试验检测手段却相对薄弱的现状,笔者研制了该系统。系统各传感器全面采用无线传输技术,上悬挂杆传感器和牵引拉力板分别配用角度传感器检测瞬时空间位置,并结合动态应变测试、嵌入式计算机等技术,在牵引车内无线实时接收机具扭矩、水平牵引力与垂直分力、机架载荷、转速等动力学信号,处理、分析并显示旋转功率、全功率等测试结果。同时,简单介绍了遥测系统的组成结构,对传感器电桥、应变片、电源、平衡元件等的参数选择进行了理论分析,介绍了电桥调零、正负极性判断、弹性元件材料确定、标定等采用的技术方法。最后,以动力输出轴一体化扭矩传感器为例详细阐述了农机测试专用传感器的设计与计算依据。

关键词： 肺泡表面活性物质(PS)   ARDS   机械通气   呼吸功能   血流动力学  

摘要： 目的探讨肺泡表面活性物质(PS)对ARDS机械通气危重患者呼吸功能及血流动力学的影响。方法对40例ARDS机械通气的危重患者,比较使用PS治疗前及治疗24h后动脉血气、呼吸力学及血流动力学参数的变化。结果 PS治疗后动脉血氧分压(PaO2)、氧合指数(PaO2/FiO2)、动脉血二氧化碳分压(PaCO2)及肺泡动脉血氧分压差(A-aDO2)较治疗前均有明显改善,P均<0.05;PS治疗后潮气量(Vt)、气道峰压(Ppeak)、平台压(Ppause)、心率(HR)、中心静脉压(CVP)、平均动脉压(MAP)较引流前均有明显改善(P均<0.05)。结论机械通气ARDS危重患者使用PS治疗可以明显改善通气和换气功能,并使患者的血流动力学趋于稳定。

关键词： 机械行业   变频器   C2000   绕线转子异步电动机   起重机行业   工业生产   起重运输设备   综合技术指标  

摘要： 起重运输设备作为国民工业生产特种设备，广泛应用到各种行业，随着工业生产对起重机调速性能要求的不断提高，常用传统的起重机调速方法由于其绕线转子异步电动机的集电环和电刷容易发生故障，再加上大量继电器和接触器的使用，致使现场维护量较大，调速系统的故障率较高，综合技术指标较差，已不能满足工业生产的特殊要求。近年来，随着变频技术的不断发展，变频器陛能日益提高，变频调速机械杼陛硬、凋速范围大、调速精度高、平稳胜好、易于控制和节能等特点，能够很好地满足起重设备安全平稳、可靠、操作性良好可靠、免维护等要求，迅速在起重机行业获得突破并广泛应用。