关键词： 机械化   模型   预测   劳动力   关系  

摘要： 该文提出并探讨了种植业机械化程度与劳动力需求关系问题。其目的旨在发展完善农业机械化理论,为科学估算种植业劳动力数量和农村剩余劳动力数量提供理论参考。该文首先分析指出了用同型号的机组替代种植业劳动力具有线性替代关系,指出了机械化程度具有可分性,并对其进行了证明。在此基础上,建立了种植业机械化程度与劳动力需求关系模型,利用该模型不仅能够计算某一地区目前种植业劳动力需求数量,而且通过对未来各种作物机械化程度和播种面积的预测,也可计算出未来各时刻的种植业劳动力需求数量。最后进行了示例计算。

关键词： 动力机械   创新   实验教学  

摘要： 本文探讨了动力机械学科进行试验教学改革的方式方法,综述了国内外在设计型创新型试验教学方面的现状,提出了建设基础型、设计创新型、提高型三个不同层次的实验教学平台的方案,在实践教学内容和方式上以培养能力为主要目的,不但能够求得知识,更重要的是运用知识,创造发展新的知识。在学科专业设置上不求最全,但求特色鲜明,能够适应培养面向机械、能源大类的宽口径人才要求的实验教学体系。

关键词： mechanical alloying   phase transformations   kinetics   thermodynamics  

摘要： Based on the data of X-ray diffraction analysis and Mossbauer spectroscopy, a comparative analysis of kinetic dependences of the processes of structure and phase formation upon mechanoactivation of model systems with different types of interaction has been conducted. As model systems, we used systems with both negative (Fe-Mn, Fe-Co, Fe-Ni) and positive (Fe-Cu) deviations of the heats of mixing of the components from ideality. Two main types of the kinetic dependence of the evolution of the phase composition upon mechanical alloying have been considered: a simple linear dependence (found for the Fe(70)Ni(30) and Fe(65)Co(35) compositions) and a two-stage one (found for Fe(10)Co(90), Fe(50)Mn(50), and Fe(86.5)Cu(13.5)). It has been established that a scheme considering mechanical alloying of metallic materials as a result of the action of two processes (deformation and relaxation of interphase boundaries) makes it possible to substantiate the experimentally observed sequence of phase transformations on the basis of the thermodynamic driving forces of the process. The model concepts developed adequately describe the results of experimental investigations and, in particular, allow one to qualitatively account for the two-stage character of dependences of the phase composition on the mechanoactivation time.

关键词： Magneto-mechanical system   MEMS   Microvalve   Active flow control  

摘要： Actuators based on micro-magneto-mechanical systems (MMMS) for active flow control are presented. A magnetodynamic microvalve of pulsed microjets providing 150 m/s jet velocities through submillimetric holes, and microactuators based on nanostructured magnetostrictive films with induced magnetic instability of spin reorientation transition type, providing high sensitivity to the driving magnetic field. (C) 2009 Elsevier B. V. All rights reserved.

关键词： intravascular stent   biocorrosion   magnesium   calcium   fluorine-fluoride  

摘要： Recently, corrodible magnesium-based alloys have been introduced for use as cardiovascular stents and orthopedic implants. However, rapid corrosion rates have raised questions about their biocompatibility. Therefore, we developed a binary fluoride-coated magnesium-calcium alloy with improved degradation kinetics. Biocompatibility of the alloys was evaluated with metabolic assays (color-metric WST-1 test). Furthermore, five different probes of magnesium-calcium alloys (MgCa 0.4, 0.6, 0.8, 1.2, and 2.0 wt %) were cocultivated with human smooth muscle cells and endothelial cells. To investigate the decomposition kinetics in a physiological environment the alloys were used untreated and fluoride coated (MgF2). Mg and Ca decreased the metabolic activity in vascular cells dose-dependently, with cytotoxic effects only at unphysiological concentrations. Uncoated magnesium alloys showed signs of decomposition after a short incubation time of 24 h in contrast to MgF2 coated alloys. After 10 days smooth muscle and endothelial cells around the alloys were still alive, whereas colonization of the surfaces was only observed for smooth muscle cells. The fluoride-coated MgCa alloys exhibited good results concerning mechanical properties, degradation kinetics, and biocompatibility in vitro. We conclude that a binary fluoride magnesium-calcium alloy is a promising candidate for the production of cardiovascular stents. (C) 2009 Wiley Periodicals, Inc. J Biomed Mater Res 93A: 763-775, 2010

关键词： iron-nickel alloy   intermetallic compounds   deformation   mechanical alloying   Mossbauer spectroscopy  

摘要： The strain-induced dissolution of Ni(3)Al intermetallic particles in the matrix of the aging Fe-35Ni-5Al alloy has been found to become more intense with increasing rate of deformation in rotating Bridgman anvils. This regularity has been presumably explained by a disbalance in the kinetics of the dual process of strain-induced dissolution and formation of phases owing to an increase in the number of interstitial atoms and a retardation of the development of an alternative process of the precipitation of second phases with increasing rate of deformation.

关键词： Mechanical seals   Gas lubrication   Surface texturing   Hydrodynamic effect  

摘要： A new type of hydrodynamic laser surface texturing gas seal with orientation ellipse dimples is introduced to improve hydrodynamic effect. Theoretical model is developed to study the hydrodynamic effect of this new gas seal. Then, a parametric investigation of the texturing parameters such as slender ratio, dimple inclination angle, dimple depth, and dimple area rate is presented for the presented gas seal under different operating parameters of rotation speed, seal pressure, and clearance. Results show that the orientation dimples can greatly improve hydrodynamic effect of laser surface texturing gas seals. Open force may be improved more than 20% greater by hydrodynamic effect in the analysis.

关键词： Acclimation   C2H2 zinc finger protein   diameter growth   mechanical stimulus   Populus   TOUCH genes  

摘要： During their development, plants are subjected to repeated and fluctuating wind loads, an environmental factor predicted to increase in importance by scenarios of global climatic change. Notwithstanding the importance of wind stress on plant growth and development, little is known about plant acclimation to the bending stresses imposed by repeated winds. The time-course of acclimation of young poplars (Populus tremula ***. alba L.) to multiple stem bendings is studied here by following diameter growth and the expression of four genes PtaZFP2, PtaTCH2, PtaTCH4, and PtaACS6, previously described to be involved in the mechanical signalling transduction pathway. Young trees were submitted either to one transient bending per day for several days or to two bendings, 1-14 days apart. A diminution of molecular responses to subsequent bending was observed as soon as a second bending was applied. The minimum rest periods between two successive loadings necessary to recover a response similar to that observed after a single bending, were 7 days and 5 days for growth and molecular responses, respectively. Taken together, our results show a desensitization period of a few days after a single transitory bending, indicating a day-scale acclimation of sensitivity to the type of wind conditions plants experience in their specific environment. This work establishes the basic kinetics of acclimation to low bending frequency and these kinetic analyses will serve as the basis of ongoing work to investigate the molecular mechanisms involved. Future research will also concern plant acclimation to higher wind frequencies

关键词： calcium   hydration temperature dependence   QMCF MD   classical molecular dynamics  

摘要： Simulations using ab initio quantum mechanical charge field molecular dynamics (QMCF MD) and classical molecular dynamics using two-body and three-body potentials were performed to investigate the hydration of the Ca2+ ion at different temperatures. Results from the simulations demonstrate significant effects of temperature on solution dynamics and the corresponding composition and structure of hydrated Ca2+. Substantial increase in ligand exchange events was observed in going from 273.15 K to 368.15 K. resulting in a redistribution of coordination numbers to lower values. The effect of temperature is also visible in a red-shift of the ion-oxygen stretching frequencies, reflecting weakened ligand binding. Even the moderate increase from ambient to body temperature leads to significant changes in the properties of Ca2+ in aqueous environment. (C) 2009 Wiley Periodicals, Inc. J Cowin Chem 31: 1195-1200, 2010

关键词： Cells  

摘要： Mechanotactic cell motility has recently been shown to be a key player in the initial aggregation of crawling cells such as leukocytes and amoebae. The effects of mechanotactic signaling in the early aggregation of amoeboid cells are here investigated using a general mathematical model based on known biological evidence. We elucidate the hydrodynamic fundamentals of the direct guiding of a cell through mechanotaxis in the case where one cell transmits a mechanotactic signal through the fluid flow by changing its shape. It is found that any mechanosensing cells placed in the stimulus field of mechanical stress are able to determine the signal transmission direction with a certain angular dispersion which does not preclude the aggregation from happening. The ubiquitous presence of noise is accounted for by the model. Finally, the mesoscopic pattern of aggregation is obtained which constitutes the bridge between, on one hand, the microscopic world where the changes in the cell shape occur and, on the other hand, the cooperative behavior of the cells at the mesoscopic scale.