Are protein folds atypical?

Protein structures are a very special class among all possible structures. It has been suggested that a "designability principle" plays a crucial role in nature's selection of protein sequences and structures. Here, we provide a theoretical base for such a selection principle, using a simple model of protein folding based on hydrophobic interactions. A structure is reduced to a string of 0s and 1s, which represent the surface and core sites, respectively, as the backbone is traced. Each structure is therefore associated with one point in a high dimensional space. Sequences are represented by strings of their hydrophobicities and thus can be mapped into the same space. A sequence that lies closer to a particular structure in this space than to any other structures will have that structure as its ground state. Atypical structures, namely those far away from other structures in the high dimensional space, have more sequences that fold into them and are thermodynamically more stable. We argue that the most common folds of proteins are the most atypical in the space of possible structures.     

Mast cells mediate acute inflammatory responses to implanted biomaterials

Implanted biomaterials trigger acute and chronic inflammatory responses. The mechanisms involved in such acute inflammatory responses can be arbitrarily divided into phagocyte transmigration, chemotaxis, and adhesion to implant surfaces. We earlier observed that two chemokines-macrophage inflammatory protein 1alpha/monocyte chemoattractant protein 1-and the phagocyte integrin Mac-1 (CD11b/CD18)/surface fibrinogen interaction are, respectively, required for phagocyte chemotaxis and adherence to biomaterial surfaces. However, it is still not clear how the initial transmigration of phagocytes through the endothelial barrier into the area of the implant is triggered. Because implanted biomaterials elicit histaminic responses in the surrounding tissue, and histamine release is known to promote rapid diapedesis of inflammatory cells, we evaluated the possible role of histamine and mast cells in the recruitment of phagocytes to biomaterial implants. Using i.p. and s. c. implantation of polyethylene terephthalate disks in mice we find: (i) Extensive degranulation of mast cells, accompanied by histamine release, occurs adjacent to short-term i.p. implants. (ii) Simultaneous administration of H1 and H2 histamine receptor antagonists (pyrilamine and famotidine, respectively) greatly diminishes recruitment and adhesion of both neutrophils (<20% of control) and monocytes/macrophages (<30% of control) to implants. (iii) Congenitally mast cell-deficient mice also exhibit markedly reduced accumulation of phagocytes on both i.p. and s.c implants. (iv) Finally, mast cell reconstitution of mast cell-deficient mice restores "normal" inflammatory responses to biomaterial implants. We conclude that mast cells and their granular products, especially histamine, are important in recruitment of inflammatory cells to biomaterial implants. Improved knowledge of such responses may permit purposeful modulation of both acute and chronic inflammation affecting implanted biomaterials.     

Roles of solution conductivity mismatch in transient current and fluid transport in electrolyte displacement by electro-osmotic flow

Electro-osmotically driven displacement between two solutions having a conductivity mismatch is theoretically examined. Internal pressures induced by the conductivity mismatch can affect the propagation of the solution interface and the behavior of the transient current. Combining Ohm’s law and fluid mass conservation, we derive a coupled set of length-averaged equations accounting for how the electric current and the traveling distance of the solution interface vary with time, electric field, and the solution conductivities. Extension to successive displacements involving multiple solution zones is made to reveal non-monotonic and stagewise changes in transient currents. For the first time, critical roles of surface conductance on displacements in highly charged channels are unraveled. We show that if the lower conductivity solution has a greater valence than the higher one, the effective conductivity of the former can exceed that of the latter when the channel height is below some critical value. The resulting transient current behavior can turn opposite to that usually observed in the large-channel case, offering a new paradigm for gauging the importance of surface conductance in submicron charged channels. Possible impacts of diffusion smearing and hydrodynamic dispersion are also discussed by including the additional mixing zone into the analysis. Having shown good agreement with the existing experimental data, our analysis not only captures the natures of solution displacement by electro-osmotic flow (EOF), but also extends the applicability of the current monitoring method for measuring surface zeta potentials of microchannels.     

Supporting rapid design and evaluation of pervasive applications: challenges and solutions

Along with the improvement of the key technologies for pervasive computing, the design of applications itself has emerged as a notable research area. A design should decide which features go into the application of supporting its context-awareness and ascertaining how well those features add value for users with an acceptable user experience. This paper initially identifies the challenges in designing and evaluating pervasive applications. It then presents a condensed survey of prototyping techniques and existing toolkits with the aim of understanding how the design issues have been addressed by research prototypes. At the end, we describe various open issues with suggestions of possible ways to extend the capabilities of current prototyping toolkits.     

基于机器视觉的高密度电路板缺陷检测系统

为减少高密度电路板的缺陷误报率,研究一种新型自动光学检测系统(AOI);系统采用自行研制的多色LED照明系统,利用机器视觉获取被测PCB的图像,通过图像处理软件系统快速准确地识别出各种缺陷;系统利用获取的彩色图像信息,根据各种缺陷的特征信息不同,采用OPENCV对各种缺陷的检测算法进行改进,使得系统性能有很大改进;对30块同类HDI型PCB的36300个检测点进行测试,测试结果证明,系统PCB缺陷的检出率高达99.87%,误报率只有0.32%。     

面向数据包丢失补偿的网络化广义预测控制

针对网络化控制系统中存在的数据包丢失,考虑了基于状态空间模型的网络化广义预测控制问题;在假设反馈通道和控制通道的数据包丢失过程确定可知的情况下,提出了一种采用预测器和预测控制器分别补偿反馈通道和控制通道的数据包丢失对系统性能影响的方法,通过把广义预测控制问题转化为滚动线性二次型最优跟踪问题,基于动态规划给出了网络化广义预测控制器的设计方法,并基于Ricoati差分方程非负定解的单调性,给出了末端加权矩阵保证系统稳定性的充分条件,最后通过仿真验证了所提出方法的有效性.     

网络控制系统中不同节点驱动方式的时延研究

在建立网络控制系统模型时,节点驱动方式的不同,对整个系统的实时性、稳定性以及鲁棒性等理论研究产生很大影响;通过分析网络节点在四种驱动方式下的动作时序和数学模型,用MATLAB/TrueTime仿真工具箱仿真测试了不同驱动方式在不同延时条件下所表现的特性:小时延情况下,事件驱动的网络控制系统性能优于时钟驱动的网络控制系统性能,而当网络负荷较重,尤其出现大时延时,采用时钟驱动的网络控制系统配合先进预估控制策略,将会得到较好的系统性能。     

嵌入式VxWorks系统下的CPCI设备驱动程序开发

具体分析了VxWorks下PCI总线的配置空间结构和地址映射,并采用CPCI9054芯片,结合一个信号产生、数据采集处理系统的工程实例,详细阐述了VxWorks下CPCI设备驱动程序的开发实现方法和具体步骤,并给出了部分关键代码.应用结果表明,该方法可移植性较高,可操作性强,对于了解和开发CPCI驱动程序具有一定的参考...     

Design reuse oriented partial retrieval of CAD models

As a huge number of 3D CAD models is generated each year, retrieval of 3D CAD models is becoming more and more important for achieving design reuse. However, the existing methods for partial retrieval of 3D CAD models are very few and far from the requirements of design reuse. In this paper, we present an approach to partial retrieval of 3D CAD models for design reuse. The criteria for determining whether a subpart of 3D CAD models is reusable for design is defined first. Based on the criteria defined, all the design reusable subparts involved in the 3D CAD models in the library are automatically extracted and stored in the library as reference models. Moreover, each design reusable subpart in the library is represented by all its local matching regions in a hierarchical way so as to support multi-mode partial retrieval. In our approach, three partial retrieval modes including normal retrieval, exact retrieval and relaxed retrieval are defined to meet various partial retrieval requirements of design reuse such as the incomplete and vague queries during the early design stage. And the multi-mode partial retrieval is achieved by performing multi-mode matching and similarity assessment between the query and the design reusable subparts in the library indexed by bitmap. Experimental results are presented to demonstrate the effectiveness of the approach.