连续采煤机截齿截割能力的分析

为了确定连续采煤机截齿截割能力和其对煤岩的适应性，由截割电动机的功率求得连续采煤机截齿的平均截割力，对镐形齿进行截割实验，然后比较截割力的实验测定值与理论值，给出了适于截齿截割煤岩的截割阻抗，并计算分析了滚筒直径、滚筒的转速、截割功率和同时工作齿数对单个截齿截割力的影响。     

基于Pro／TOOLKIT的截割头截齿及齿座虚拟装配

通过建立单个截齿及齿座的定位模型，应用PROE的二次开发工具包Pro／TOOLKIT、VC＋＋和数据库技术，开发出掘进机截割头截齿及齿座的虚拟装配程序。该程序只需输入所有截齿定位模型的参数数据，即可得到整个截割头截齿与齿座的装配体。由此装配体能确定各个齿座的安装平面。进而得到满足设计要求的截割头头体，实现整个截割头的虚拟装配。为质量高、性能好的掘进机截割头的研发提供了一种高效、快捷的途径。     

连续采煤机工作面硬质包裹体分布的模拟研究

短壁工作面上硬质包裹体的分布直接影响连续采煤机的截割阻力、机器振动、工作噪音和截割的经济效益。文章在假定包裹体的几何形状为旋转椭球体的情况下，对长轴尺寸服从均匀分布、正态分布、指数分布、威布尔分布、伽玛分布和贝塔分布下的硬质包裹体在煤层中的分布进行了计算机模拟，并分析了各种情况的特征，为了解连续采煤机工作面硬质包裹体的分布、研究其截割过程和机器的工作性能创造了条件。     

基于H-J-C本构模型的掘进机截齿破岩过程的数值模拟

针对掘进机实际外负载难以获取及其载荷特性难以正确把握的现状,提出了利用接触动力学、岩石力学和有限元法等理论和方法构建在显示动力学分析程序LS-DYNA环境下基于H-J-C本构模型的截齿与岩石的接触动力学模型数值模拟平台;利用该平台对掘进机镐形截齿的横摆破岩过程进行了数值模拟,得到了截齿受到的三向阻力曲线;通过载荷特性分析,验证了所得载荷曲线的准确性,并获得了某工况下截齿载荷的主要频率结构;分析了截齿的碎岩机理,发现岩石的破碎是与截齿直接接触的岩石的拉压应力和其周边的剪切应力集中综合作用的结果.     

掘进机截割硬岩时镐齿磨损特性试验研究

为了研究掘进机镐齿在截割时的磨损特性,开展独头掘进与诱导开挖下的掘进试验,对比分析不同工程条件下截齿的磨损失效情况。结果表明,在掘进机硬岩掘进过程中,由于截割头的形状导致截齿的受力状况不一样,截齿的磨损程度也不相同,处在圆角区的截齿磨损情况最严重,圆锥区的截齿受损最轻微;在诱导开挖条件下,截齿的质量磨损减小,截齿的使用寿命得到提高。     

掘进机截割头辅助设计软件的研究与开发

针对目前国内掘进机截割头设计大多凭经验进行以及截割负载的非线性、时变性和强耦合等特点，通过对纵轴式掘进机截割头的分析与研究，建立了截割头负载的瞬态动力学模型；基于VC＋＋和MATLAB联合开发了用于掘进机截割头设计和负载计算的计算机辅助设计软件。应用此软件可以获得截割头载荷波动曲线及波动系数、生成截割头瞬时负载的文本及截割头三维参数化实体模型，以评价截割头设计的合理性并进一步指导截割头的优化设计；解决了掘进机截割头设计中盲目缩放几何尺寸及其负载计算因人而异造成设计与计算结果迥异的问题；为新型截割头的研发及对现有机型的改进提供了新的方法和手段。软件界面友好、操作简单、方便实用，使基于科学方法的截割头计算机辅助设计在工程中的应用和推广成为可能。     

不同围压与不同截齿侵入角作用下镐形截齿破岩数值模拟分析

为分析围压、截齿侵入角等对镐形截齿破岩效果的影响,采用颗粒流离散元法对不同围压和截齿侵入角下的镐形截齿破岩进行数值仿真,研究不同围压与截齿侵入角下对应的岩石破碎模式、牵引力、切割力以及裂纹数目的变化。研究表明:随着围压与截齿侵入角的变化,截齿破岩时呈现3种破坏模式:当围压为0~20 MPa、截齿侵入角为45°~60°时,可以产生向岩石内部扩展的裂纹,最利于破岩;当围压一定,截齿的侵入角为45°左右时,切割力最大而需求的牵引力最小,且两者波动最小,切割岩石最稳定;当截齿的侵入角为45°时,破岩效果最好,侵入角为60°时,围压10~20 MPa左右破岩效果较好,当截齿的侵入角为90°时,围压对截齿破岩无影响,且切割效果差。通过模拟,得出合适的截齿破岩参数,为截齿参数的选择提供指导。     

基于ADAMS／VIBRATION的采煤机截割部振动特性研究

建立了采煤机截割部刚柔耦合虚拟样机的振动模型；利用ADAMS／VIBRATION模块对其振动特性开展了研究；确定了对系统整体性能不利的模态振型和频率，发现截割部电机对系统振动的影响较大；并找出了截割部高速端惰轮轴处轴承失效的主要原因；为有效地抑制采煤机截割部的振动和对其进行局部结构优化提供了理论依据，对全面掌握截割部系统的动态性能具有重要价值。     

掘进机截割部刚柔耦合动力学建模与仿真研究

将大位移运动与小变形刚-柔耦合体动力学的建模理论应用于掘进机截割部的动态特性研究，利用ANSYS把截割部的截割主轴和截割套筒生成模态中性文件，导入ADAMS中建立刚柔耦合虚拟样机并进行运动学和动力学仿真，研究柔性体对截割部的影响。通过与刚性体模型仿真结果对比，揭示了工作装置中柔性体与刚性体耦合时的运动学、动力学特性。仿真结果表明柔性耦合模型更加符合实际情况。     

采煤机截割部虚拟仿真中的关键技术研究

以某煤机公司的采煤机截割部可靠性研究项目为依托，研究了计算机虚拟仿真中的关键技术，提出了保证仿真精度、提高仿真速度、缩短仿真时间的具体措施，大大提高了Pro／E、MATLAB、ADAMS和ANSYS四款软件协同仿真的可操作性；发现了该采煤机截割部的薄弱环节，如行星架刚度不足、摇臂壳体出现局部应力集中等；在仿真的基础上对壳体结构进行了改进，得到了优化的采煤机截割部传动机构，保证了截割过程的可靠性，对降低研发成本，节省研制时间，提高产品质量具较强的实用价值。     

Myelin-associated proteins block the migration of olfactory ensheathing cells: an in vitro study using single-cell tracking and traction force microscopy

Newly generated olfactory receptor axons grow from the peripheral to the central nervous system aided by olfactory ensheathing cells (OECs). Thus, OEC transplantation has emerged as a promising therapy for spinal cord injuries and for other neural diseases. However, these cells do not present a uniform population, but instead a functionally heterogeneous population that exhibits a variety of responses including adhesion, repulsion, and crossover during cell–cell and cell–matrix interactions. Some studies report that the migratory properties of OECs are compromised by inhibitory molecules and potentiated by chemical gradients. Here, we demonstrated that rodent OECs express all the components of the Nogo receptor complex and that their migration is blocked by myelin. Next, we used cell tracking and traction force microscopy to analyze OEC migration and its mechanical properties over myelin. Our data relate the decrease of traction force of OEC with lower migratory capacity over myelin, which correlates with changes in the F-actin cytoskeleton and focal adhesion distribution. Lastly, OEC traction force and migratory capacity is enhanced after cell incubation with the Nogo receptor inhibitor NEP1-40.     

Microfabricated tissues for investigating traction forces involved in cell migration and tissue morphogenesis

Cell-generated forces drive an array of biological processes ranging from wound healing to tumor metastasis. Whereas experimental techniques such as traction force microscopy are capable of quantifying traction forces in multidimensional systems, the physical mechanisms by which these forces induce changes in tissue form remain to be elucidated. Understanding these mechanisms will ultimately require techniques that are capable of quantifying traction forces with high precision and accuracy in vivo or in systems that recapitulate in vivo conditions, such as microfabricated tissues and engineered substrata. To that end, here we review the fundamentals of traction forces, their quantification, and the use of microfabricated tissues designed to study these forces during cell migration and tissue morphogenesis. We emphasize the differences between traction forces in two- and three-dimensional systems, and highlight recently developed techniques for quantifying traction forces.     

E-cadherin plays an essential role in collective directional migration of large epithelial sheets

In wound healing and development, large epithelial sheets migrate collectively, in defined directions, and maintain tight cell-cell adhesion. This type of movement ensures an essential function of epithelia, a barrier, which is lost when cells lose connection and move in isolation. Unless wounded, epithelial sheets in cultures normally do not have overall directional migration. Cell migration is mostly studied when cells are in isolation and in the absence of mature cell-cell adhesion; the mechanisms of the migration of epithelial sheets are less well understood. We used small electric fields (EFs) as a directional cue to instigate and guide migration of epithelial sheets. Significantly, cells in monolayer migrated far more efficiently and directionally than cells in isolation or smaller cell clusters. We demonstrated for the first time the group size-dependent directional migratory response in several types of epithelial cells. Gap junctions made a minimal contribution to the directional collective migration. Breaking down calcium-dependent cell-cell adhesion significantly reduced directional sheet migration. Furthermore, E-cadherin blocking antibodies abolished migration of cell sheets. Traction force analysis revealed an important role of forces that cells in the leading rows exert on the substratum. With EF, the traction forces of the leading edge cells coordinated in directional re-orientation. Our study thus identifies a novel mechanism--E-cadherin dependence and coordinated traction forces of leading cells in collective directional migration of large epithelial sheets.     

Magnification: how to turn a spyglass into an astronomical telescope

According to the received view, the first spyglass was assembled without any theory of how the instrument magnifies. Galileo, who was the first to use the device as a scientific instrument, improved the power of magnification up to 30 times. How did he accomplish this feat? Galileo does not tell us what he did. We hold that such improvement of magnification is too intricate a problem to be solved by trial and error, accidentally stumbling upon a complex procedure. We construct a plausibility argument and submit that Galileo had a theory of the telescope. He could develop it by analogical reasoning based on the phenomenon of reflection in mirrors—as it was put to use in surveying instruments—and applied to refraction in sets of lenses. Galileo could appeal to this analogy and assume Della Porta’s theory of refraction. He could thus turn the spyglass into a revolutionary scientific instrument—the telescope.     

The platinum pyrometers of Louis Bernard Guyton de Morveau,F.R.S. (1737–1816)

As we have seen, it was clearly Guyton's intention, in 1808, to supply details of his improved platinum pyrometer, and he did submit a drawing of the instrument at the meeting of the Class in December 1810. It would seem that on that occasion he did not supply those details which are to be found in the fourth, unpublished, part of the ‘Essay’. The existence of a text fit to be sent to the printer, and the execution of a drawing relating to the improved version of his platinum pyrometer, might be taken as evidence that Guyton intended to publish. His paper of 1810 did not appear until 1814, however, so that publication of the fourth part of the ‘Essay’ could scarcely have occurred until 1815 or later. Guyton probably hoped to be able to read it to the Class of Physical and Mathematical Sciences before publishing it in the Annales de Chimie, but his death on 2 January 1816 robbed him of the opportunity.     

Selection of high-level abamectin resistance from field-collected house flies,Musca domestica

Summary Abamectin is a novel, highly promising insecticide with activity against many pests. To determine if resistance to abamectin could occur, we collected house flies from several New York dairies and selected them in the laboratory. Resistance developed repidly and to a high level (36 or>60,000-fold, depending upon test technique and/or adjuvant) that could not be overcome by the synergists piperonyl butoxide orS,S,S-tributylphosphorotrithioate. There was no increase in (cross)resistance to crotoxyphos, dichlorvos, dimethoate, tetrachlorvinphos, permethrin, dieldrin or lindane following abamectin selection. Our results suggest the potential for abamectin resistance is high, at least in house flies, and that the judicious use of abamectin will be needed to prolong its usefulness as an insecticide.     

牵引供电扩能系统仿真研究

改善电气化铁道牵引供电能力不足的有效措施之一是进行牵引供电扩能改造,应用综合补偿技术是牵引供电扩能的最佳方法.但其影响因素较多,且时变性和相关性强,不易建立精确的数学模型.本文采用基于列车牵引计算的仿真方法,针对增设不同的扩能补偿设备,结合半定量分析方法时补偿设备的安装位置和投切容量等参数选取、有效控制策略的选择等建立了牵引供电扩能仿真系统,通过分析列车的运行工况来评价投入不同补偿设备所达到的扩能效果,系统的应用结果表明该仿真模型是行之有效的.     

General mechanisms of drought response and their application in drought resistance improvement in plants

Plants often encounter unfavorable environmental conditions because of their sessile lifestyle. These adverse factors greatly affect the geographic distribution of plants, as well as their growth and productivity. Drought stress is one of the premier limitations to global agricultural production due to the complexity of the water-limiting environment and changing climate. Plants have evolved a series of mechanisms at the morphological, physiological, biochemical, cellular, and molecular levels to overcome water deficit or drought stress conditions. The drought resistance of plants can be divided into four basic types-drought avoidance, drought tolerance, drought escape, and drought recovery. Various drought-related traits, including root traits, leaf traits, osmotic adjustment capabilities, water potential, ABA content, and stability of the cell membrane, have been used as indicators to evaluate the drought resistance of plants. In the last decade, scientists have investigated the genetic and molecular mechanisms of drought resistance to enhance the drought resistance of various crops, and significant progress has been made with regard to drought avoidance and drought tolerance. With increasing knowledge to comprehensively decipher the complicated mechanisms of drought resistance in model plants, it still remains an enormous challenge to develop water-saving and drought-resistant crops to cope with the water shortage and increasing demand for food production in the future.     

CAS directly interacts with vinculin to control mechanosensing and focal adhesion dynamics

Focal adhesions are cellular structures through which both mechanical forces and regulatory signals are transmitted. Two focal adhesion-associated proteins, Crk-associated substrate (CAS) and vinculin, were both independently shown to be crucial for the ability of cells to transmit mechanical forces and to regulate cytoskeletal tension. Here, we identify a novel, direct binding interaction between CAS and vinculin. This interaction is mediated by the CAS SRC homology 3 domain and a proline-rich sequence in the hinge region of vinculin. We show that CAS localization in focal adhesions is partially dependent on vinculin, and that CAS–vinculin coupling is required for stretch-induced activation of CAS at the Y410 phosphorylation site. Moreover, CAS–vinculin binding significantly affects the dynamics of CAS and vinculin within focal adhesions as well as the size of focal adhesions. Finally, disruption of CAS binding to vinculin reduces cell stiffness and traction force generation. Taken together, these findings strongly implicate a crucial role of CAS–vinculin interaction in mechanosensing and focal adhesion dynamics.