关键词： Adenosine Triphosphate/metabolism   Hydrolysis   Kinesin/metabolism   Kinetics   Microtubules/metabolism   Models, Biological   Probability  

摘要： Motivation: Kinesin is a smart motor protein that steps processively forward and backward along microtubules (MTs). The mechanical kinetics of kinesin affecting its stepping behavior is not fully understood. Here, we propose a mathematical model to study the mechanical kinetics of forward and backward stepping of kinesin motor based on the four-state discrete stochastic model of the motor. Results: Results show that the probabilities of forward and backward stepping can be modeled using the mean probabilities of forward and backward kinetic transitions, respectively. We show that the backward stepping of kinesin motor starts when the probability of adenosine diphosphate (ADP) binding to the motor is much higher than that of adenosine triphosphate (ATP) binding. Furthermore, our results indicate that the backward stepping is related to both ATP hydrolysis and synthesis with rate limiting factor being ATP synthesis. Low rate of ATP synthesis under high backward loads above 10 pN is also suggested as a reason for the detachment of kinesin motor from MT in the kinetic state ***.P-i.

关键词： 动力机械   维护   保养   检查  

摘要： 我国的动力机械在不断的进步,不仅提高了生产效率,同样也适应了社会经济发展的趋势。但是有一些实际操作者缺乏对动力机械的维护和保养意识,在使用过程中出现大量的违规操作,大大减少了动力的使用寿命。本文重点对动力机械如何进行合理使用时应注意的事项进行了分析,并提出了对动力机械维护以及保养方面的几点体会。

关键词： Mechanical alloying   Glassy powder   Crystallization   Thermal stability  

摘要： Al76Ni8Ti8Zr4Y4 glassy powder was produced by mechanical alloying process. The phase structure and the crystallization kinetics as well as the thermal stability were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC) in non-isothermal mode. The glassy alloy powder shows a distinct one-stage crystallization process with a wide supercooled liquid region. Crystallization occurs by the precipitation and growth of FCC-Al, with intermetallic compound AlTi, AlTi3, Al2Y and Al3Zr. The non-isothermal crystallization kinetics is analyzed by the modified Johnson-Mehl-Avrami (JMA) equation. The values of the Avrami exponent imply that the dominating crystallization mechanism of the present glassy powder is two- or three-dimensional nucleation and growth controlled by diffusion of atoms. The present glass powder has a large supercooled liquid region (SLR) Delta T-x value (86 K) and the apparent activation energy for crystallization is as high as 316 kJ/mol. The thermal stability was also evaluated by continuous transformation diagram (CHT) obtained by the extended Kissinger equation. To convince the thermal stability for a very long period of time, a quick annealing of the glassy powder at 700 K for 24 h was conducted and the related result was discussed. (C) 2013 Elsevier B.V. All rights reserved.

关键词： 农业机械总动力   预测   时间序列   ARIMA  

摘要： 运用黑龙江省1980-2011年的统计数据,建立了黑龙江省农业机械总动力的ARIMA模型,并进行了预测分析。结果表明:黑龙江省农业机械总动力是非平稳的时间序列,ARIMA模型的拟合效果良好;应用ARIMA(0,2,1)模型进行预测,1980-2011年预测值与实际值之间的平均相对误差为2.87%,可用于今后黑龙江省农业机械总动力的预测与分析。

关键词： Micro-mechanics   Apple   Enzyme degradation   Kinetics   Diffusion  

摘要： The enzymatic texture loss during apple maceration was studied by two micro-mechanical techniques. The first technique consisted of a 5% strain compression cycles at a strain rate of 4.5 x 10(-4) s(-1). The second technique consisted on micro-puncture of the apple parenchyma with a small needle. The first technique led to the peripheral tissues degradation modelling with a first order kinetic reaction or a more pertinent Weibull function. The second technique evidenced that the jagged part of the load vs penetration curve corresponded to an interaction between the needle tip and the turgescent apple texture and the fractal dimension of this jagged part was chosen as the texture parameter. Modelling the enzyme diffusion phenomenon with the second Fick's law and taking into account the model previously established on peripheral tissues allowed the estimation of an equivalent enzyme diffusivity through the apple parenchyma varying between 3.5 x 10(-11) and 5.5 x 10(-11) m(2) s(-1). (c) 2013 Published by Elsevier Ltd.

关键词： mechanical properties   molecular dynamics   nanowires   SiGe   vibrational properties  

摘要： In this work, we examine the vibrational and mechanical properties of clamped-clamped rectangular SixGe1-x and Si/SixGe1-x nanowires (NWs) using molecular dynamics simulations. A virtual atomic force microscope nanotip is used to drive the vibration. The frequency response, the beat vibration phenomenon and the calculation of mechanical properties such as quality factor Q and Young's modulus E are thoroughly analyzed. The influence of added mass and hydrogen passivation on the NW resonator performance is also demonstrated. The decreasing frequency trend with increasing Ge concentration was different for binary alloys and alloy superlattices, while it remained unaffected by the superlattice period. The beat vibration phenomenon driven by a single excitation was observed at elevated temperatures for all studied configurations. The resonance frequency decreases linearly with increasing temperature whereas the Q-factor follows a power law decrease. The Young's modulus E obtained through stress-strain computational experiments is found to be overestimated compared to the classical beam theory. Frequency decreases linearly as more atoms are added to the resonator. For low temperatures, the quality factor of composite Si/Ge resonators increased from 10(4) to 10(5) at T=23K, after performing hydrogen passivation on the NW free surfaces. The frequency shift due to the change in stoichiometry in a Si NW, alongside with representative snapshots of the vibrational behavior.

关键词： POLYAMIDES   NANOCOMPOSITE materials   RESEARCH   TITANIUM dioxide   POLYMERIC nanocomposites   NANOPARTICLE research   DIFFERENTIAL scanning calorimetry   NUCLEATION   CRYSTALLIZATION  

摘要： Titanium dioxide (TiO2) nanoparticles were pretreated with excessive toluene-2,4-diisocyanate (TDI) to synthesize TDI-functionalized TiO2 (TiO2-NCO), and then polymeric nanocomposites consisting of polyamide 6 (PA6) and functionalized-TiO2 nanoparticles were prepared via a melt compounding method. The interfacial interaction between TiO2 nanoparticles and polymeric matrix has been greatly improved due to the isocyanate (NCO) groups at the surface of the functionalized-TiO2 nanoparticles reacted with amino groups (NH2) or carboxyl (COOH) groups of PA6 during the melt compounding and resulted in higher tensile and impact strength than that of pure PA6. The nonisothermal crystallization kinetics of PA6/functionalized TiO2 nanocomposites was investigated by differential scanning calorimetry (DSC). The nonisothermal crystallization DSC data were analyzed by the modified-Avrami (Jeziorny) methods. The results showed that the functionalized-TiO2 nanoparticles in the PA6 matrix acted as effective nucleation agents. The crystallization rate of the nanocomposites obtained was faster than that of the pure PA6. Thus, the presence of functionalized-TiO2 nanoparticles influenced the mechanism of nucleation and accelerated the growth of PA6 crystallites. POLYM. COMPOS., 35:294-300, 2014. (c) 2013 Society of Plastics Engineers

关键词： Polyoxymethylene   recycled carbon fibre   composites   reinforcement   mechanical properties   crystallization kinetics  

摘要： Recycled carbon fibre was employed as a reinforcing material to prepare polyoxymethylene?based composites through a simple melting extrusion. An effective approach was developed to clean and modify the surface of as-received recycled carbon fibre with nitric acid and then with a silane-coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for polyoxymethylene/recycled carbon fibre composites due to the improved interfacial adhesion between fibres and the matrix. The thermal stabilities of the composites were also improved in the presence of recycled carbon fibre. The morphological observation of impact fracture surfaces indicated a good interfacial boding between fibres and matrix. The studies on nonisothermal and isothermal crystallization behaviors showed that recycled carbon fibre acted as a nucleation agent for the crystallization of polyoxymethylene domain in composites; therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of recycled carbon fibre. These crystallization features may be advantageous for the enhancement of mechanical performance and processability of polyoxymethylene?based composites. Derived from a combination of polyoxymethylene and recycled carbon fibre, this study may provide a development guide for sustainable engineering materials with a great potential as well as a low cost for industrial and civil applications.

关键词： Spatial ecology   Patchy landscape   Model reduction   Reaction-diffusion equation   Patch model  

摘要： Reaction-diffusion models for the dynamics of a biological population in a fragmented landscape can incorporate detailed descriptions of movement and behavior, but are difficult to analyze and hard to parameterize. Patch models, on the other hand, are fairly easy to analyze and can be parameterized reasonably well, but miss many details of the movement process within and between patches. We develop a framework to scale up from a reaction-diffusion process to a patch model and, in particular, to determine movement rates between patches based on behavioral rules for individuals. Our approach is based on the mean occupancy time, the mean time that an individuals spends in a certain area of the landscape before it exits that area or dies. We illustrate our approach using several different landscape configurations. We demonstrate that the resulting patch model most closely captures persistence conditions and steady state densities as compared with the reaction-diffusion model.

关键词： Nanocomposites   Plant polymer   Flammability   Thermal stability   Activation energy  

摘要： Melamine formaldehyde-furfuryl alcohol copolymer was impregnated into softwood in combination with 1,3-dimethylol-4,5-dihydroxy ethyleneurea, a crosslinking agent, nanoclay, and a renewable polymer, collected as gum from a local plant (Moringa oleifera) under vacuum condition and polymerized by catalyst heat treatment. Fourier-transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy were used to characterize the nanocomposites. Transmission electron microscopy showed uniform distribution of nanoclay in the composites. The mechanical properties were improved after the addition of plant polymer. The plant polymer had a marked influence on the flammability and thermal stability of the prepared composites. The apparent activation energy was determined by Ozawa-Flynn-Wall's and Vyazovkin methods. The activation energy of the composites decreased up to a certain decomposed fraction thereafter it remained constant. Higher the plant polymer content higher was the activation energy of the prepared composites which indicated a better interfacial adhesion and thermal stability.