短程及多跳的工业无线网络实时性和可靠性研究

无线通信技术极大地推动了科技发展和社会进步，已成为国际技术竞争的焦点和制高点之一。其中工业环境下无线网络技术的开发和应用，成为继模拟仪表控制系统、集散控制系统、现场总线控制系统之后，在过程控制和工业自动化领域拥有广阔市场前景的应用技术。随着无线通信技术的进一步发展，在未来的工业过程自动化领域，无线网络技术将会有更为广阔的应用前景。 工业无线网络技术的发展所面临的主要问题是：如何保证工业通信过程中的实时性和可靠性。本论文较为详尽地研究、探讨了工业无线网络中的实时性和可靠性问题，阐述了实时性和可靠性的涵义，分析了工业无线网络对实时性和可靠性的特殊需求，在借鉴已有研究成果并进行创新的基础上提出了问题解决方案。本文重点在网络的数据链路层和网络层展开了研究工作。主要的研究内容与创新点包括以下几个方面： 在数据链路层的媒体访问控制层，针对恶劣的工业环境对数据传输的实时性和可靠性的较高要求，和以往工业无线网络中采用的无线通信技术，如无线局域网、蓝牙和Zigbee等技术存在抗干扰能力差的严重缺陷的现实，本论文采用目前无线通信技术领域的热点技术——超宽带技术作为物理信道的通信介质，在对超宽带技术的特点和工业无线信道模型进行研究的基础上，充分利用超宽带技术抗干扰能力强的特点，采用跨层设计的思想——物理层和媒体访问控制层联合设计的方式，提出了基于信道状态的信道选择和速率自适应的多信道媒体访问控制协议，该协议一方面根据射频环境的动态变化，使用信道估计技术从多个可选数据信道中，选择可用的或者相对理想的信道用于数据的传输；另一方面在传输过程中，根据物理信道反馈的误码率值来判断当前的通信质量，可以要求物理层执行参数修改策略，实现发射速率的调整，解决由于多用户干扰、碰撞和工业环境干扰等因素造成的误码率增大问题，来满足工业无线网络的实时性和可靠性需求。该协议优于目前已有的协议，可以缓解干扰带来的延迟增大和吞吐量下降的问题，更好地满足工业通信的实时性和可靠性需求。 在数据链路层的逻辑链路控制子层，针对已有的无线网络缓存管理策略在通信中发生拥塞时，无法提供对实时数据的实时性保证，以及不适当的报文丢弃机制无法提供对非实时数据提供可靠性保证的问题，本文借鉴有线通信网络中缓存队列数据分组的动态概率丢弃思想，提出了一种适用于工业实时数据通信的超时早期检测机制，其基本思想在于节点的缓存队列在接纳新到的实时数据时，对其能否在规定的时延限制之内到达目的节点进行估计，并根据估计结果进行早期丢弃，防止无效的传输占用宝贵的无线资源；建立分别存储实时数据和非实时数据的双队列缓存管理策略，两类队列采用循环调度的方法实现数据传输的公平性，以保证数据传输的实时性和可靠性。本文提出的节点缓存管理策略有利于减小排队时延、降低后继分组超时丢弃和缓存队列拥塞发生的概率，与已有的无线网络缓存管理策略相比，可以提高实时数据传输的实时性和非实时数据传输的可靠性。 在网络层，本文重点在路由协议方面进行了研究，针对已有路由协议在工业无线网络应用中存在的不适用性问题，以及工业无线网络传输路径可靠性较差的特点，本文采用可靠性理论，对不相交和相交的多路径选择策略的可靠度进行了分析；针对工业无线网络对通信的可靠性和实时性的特殊需求，本文提出了路径可靠性评估模型。在对基于节点的邻居列表链路稳定性预测的基础上，通过路径的可靠性因子和延时因子的计算来建立可靠的多路径路由。在模拟了不稳定和不可预测的工业通信现场环境后，通过与传统的单路径路由协议和多路径路由协议性能的对比，验证了本文提出的多路径路由协议的有效性。在不稳定和不可预测的通信环境下，其可靠性和实时性性能优于已有的同类多路径路由协议。 针对已有无线网络路由协议由于对节点故障类型分析不充分，使得网络中的关键节点更新和路由重构次数增加，从而造成工业无线网络的可靠性和实时性难以得到满足的问题，本文借鉴D.Pradhan在经典理论文献中提出的系统可靠性性能改进的思想，根据工业无线网络的工作环境和特点，研究了分簇结构的工业无线网络中的关键节点——簇首节点的容错算法。本文根据对网络中簇首节点的故障类型的分类，提出了能够及时判断故障类型和有效解决相应故障的簇首容错算法，进而保证在簇首发生故障的情况下，使其能够得到及时的检测和恢复，从而满足工业无线网络的可靠性和实时性需求。本文提出的簇首容错算法在网络中的簇首节点发生故障或通信链路出现异常情况时，能够有效地提高数据发送和接收效率，降低通信延迟，其可靠性和实时性明显优于无容错机制的路由协议算法和已有节点容错机制的路由协议算法，因此本文提出的簇首容错算法更适用于环境恶劣的工业现场环境。

Characteristic Dimensionless Numbers in Multi-Scale and Rate-Dependent Processes

For this sake, the macroscopic equations of mechanics and the kinetic equations of the microstructural transformations should form a unified set that be solved simultaneously. As a case study of coupling length and time scales, the trans-scale formulation

Biological application of multi-component nanowires in hybrid devices powered by F-1-ATPase motors

In this paper, construction of hybrid device by integrating nanowires with F1-ATPase motors is described. The nickel nanowires and multi-segment nanowires, including gold and nickel, were fabricated by electrochemical deposition in nanoporous templates. The nickel nanowires functionalized by biotinylated peptide can be assembled directly onto F1-ATPase motors to act as the propellers. If the multicomponent nanowires, including gold and nickel, were selectively functionalized by the thiol group modified ssDNA and the synthetic peptide, respectively, the biotinylated F1- ATPase motors can be attached to the biotinylated peptide on nickel segment of the nanowires. Then, the multi-component nanowires can also be used as the propellers, and one may observe the rotations of the multi-component nanowires driven by F1-ATPase motors. Therefore, introduction of multiple segments along the length of a nanowire can lead to a variety of multiple chemical functionalities, which can be selectively bound to cells and special biomolecules. This method provides an insight for the construction of other hybrid devices with its controlling arrangement of different biomolecule on designed nanometer scale structures.

Synchronous Multi-Scale Observations on Rock Damage and Rupture

This paper reports a multi-scale study on damage evolution process and rupture of gabbro under uniaxial compression with several experimental techniques, including MTS810 testing machine, white digital speckle correlation method, and acoustic emission technique. In particular, the synchronization of the three experimental systems is realized for the study of relationship of deformation and damage at multiple scales. It is found that there are significant correlation between damage evolution at small and large length scales, and rupture at sample scale, especially it displays critical sensitivity at multiple scales and trans-scale fluctuations.

Analysis of residual stress gradient in MEMS multi-layer structure

Residual stress and its gradient through the thickness are among the most important properties of as-deposited films. Recently, a new mechanism based on a revised Thomas-Fermi-Dirac (TFD) model was proposed for the origin of intrinsic stress in solid film

Extended self-similar scaling law of multi-scale eddy structure in wall turbulence

The longitudinal fluctuating velocity of a turbulent boundary layer was measured in a water channel at a moderate Reynolds number. The extended self-similar scaling law of structure function proposed by Benzi was verified. The longitudinal fluctuating velocity, in the turbulent boundary layer was decomposed into many multi-scale eddy structures by wavelet transform. The extended self-similar scaling law of structure function for each scale eddy velocity was investigated. The conclusions are I) The statistical properties of turbulence could be self-similar not only at high Reynolds number, but also at moderate and low Reynolds number, and they could be characterized by the same set of scaling exponents xi (1)(n) = n/3 and xi (2)(n) = n/3 of the fully developed regime. 2) The range of scales where the extended self-similarity valid is much larger than the inertial range and extends far deep into the dissipation range,vith the same set of scaling exponents. 3) The extended selfsimilarity is applicable not only for homogeneous turbulence, but also for shear turbulence such as turbulent boundary layers.