Multi-path heuristic for redundancy allocation: the tree heuristic

A tree heuristic is presented for solving the general redundancy allocation problem in reliability optimization. The tree heuristic can obtain several local optima by branching off the main searching path when some criterions are satisfied. Then, the best local optima is selected for the final solution. The tree heuristic is a simple, efficient, iterative heuristic for any integer nonlinear programming problems with increasing constraint functions. Iterative heuristics are normally trapped in a local optimum. However, the tree heuristic can overcome local optima by branching the solution path. The experiments show that the proposed heuristic is very efficient in terms of solution quality, and computation time.     

Investigation of Stress Evolution Induced by Electromigration in Sn-Ag-Cu Solder Joints Based on an X-Ray Diffraction Technique

The critical current density and temperature endured by solder joints are identified as the two most important parameters that determine the occurrence of electromigration (EM). It is well known that movement of metal atoms/ions during current stressing can induce obvious stress concentrations at the anode and cathode interfaces of the solder joint. Therefore, the global average effects of EM on stress evolution at both the anode and cathode interfaces were investigated with different current densities by employing a nondestructive x-ray diffraction technique. The ultimate results indicated that the compressive stress increased gradually at the anode side under low current density. However, stress fluctuation could be observed under high current density due to an obvious Joule heating effect. For further understanding of the mechanism of stress evolution in the solder joint during current stressing, a four-stage model is considered. First, Cu expansion led to increase of the compressive stress at both electrodes. Second, stress relaxation compensated the compressive stress and caused it to decrease. Third, the EM effect promoted compressive stress and tensile stress at the anode and cathode, respectively. Finally, a steady state of stress was achieved at the anode, while the state of tensile stress at the cathode remained transient.     

High-performance polymer light emitting diodes with interface-engineered graphene anodes

Recently, graphene-based organic light emitting diodes (OLEDs) were successfully demonstrated using graphene as anodes. However, the graphene electrodes have not been utilized for polymer light emitting diodes (PLEDs) yet, although the simpler device structure and the solution-based fabrication process of PLEDs are expected to be more advantageous in terms of time and cost. Here we demonstrate high-performance polymer light emitting diodes (PLEDs) with simple two-layer structures using interface-engineered single-layer graphene films as anodes. The single-layer graphene synthesized by chemical vapor deposition methods was transferred onto a glass substrate utilizing an elastic stamp, and its work function was engineered by varying the duration and the power of ultraviolet ozone (UVO) treatment. Thus, we were able to optimize the contact between silver electrodes and the graphene anodes, leading to the considerable enhancement of light-emitting performance.     

Ku-band stop filter implemented on a high resistivity silicon with inverted microstrip line photonic bandgap (PBG) structure

We have developed the inverted microstrip line photonic bandgap (IML-PBG) structure using the surface micro-machining technology on the high resistivity silicon (HRS) substrate. Because, when the IML was fabricated, the holes for removing a sacrificial layer were necessary, we have introduced these holes into the PBG structure for the Ku-band stop filter (BSF). Rectangular spiral PBG structure showed the notch characteristics and the array with suitable distance showed the stop band with under -20 dB from 15 to 19 GHz and under -3 dB pass-band loss.     

Liquid Metal Based Island‐Bridge Architectures for All Printed Stretchable Electrochemical Devices

The adoption of epidermal electronics into everyday life requires new design and fabrication paradigms, transitioning away from traditional rigid, bulky electronics towards soft devices that adapt with high intimacy to the human body. Here, a new strategy is reported for fabricating achieving highly stretchable “island‐bridge” (IB) electrochemical devices based on thick‐film printing process involving merging the deterministic IB architecture with stress‐enduring composite silver (Ag) inks based on eutectic gallium‐indium particles (EGaInPs) as dynamic electrical anchors within the inside the percolated network. The fabrication of free‐standing soft Ag‐EGaInPs‐based serpentine “bridges” enables the printed microstructures to maintain mechanical and electrical properties under an extreme (≈800%) strain. Coupling these highly stretchable “bridges” with rigid multifunctional “island” electrodes allows the realization of electrochemical devices that can sustain high mechanical deformation while displaying an extremely attractive and stable electrochemical performance. The advantages and practical utility of the new printed Ag‐liquid metal‐based island‐bridge designs are discussed and illustrated using a wearable biofuel cell. Such new scalable and tunable fabrication strategy will allow to incorporate a wide range of materials into a single device towards a wide range of applications in wearable electronics.     

Chiral Stereoisomer Engineering of Electron Transporting Materials for Efficient and Stable Perovskite Solar Cells

A series of chiral stereoisomers of electron transporting materials with two chiral substituents is rationally designed and synthesized, and the influence of stereoisomerism on their physical and electronic properties is investigated to demonstrate highly efficient and stable perovskite solar cells (PSCs). Compared to mesomeric naphthalene diimide (NDI) derivatives, which have heterochiral side groups with centrosymmetric molecular packing of symmetric‐shaped conformers in the crystalline state, enantiomeric NDI derivatives have homochiral side groups that exhibit non‐centrosymmetric molecular packing of asymmetric‐shaped conformers in the crystalline state and exhibit better solution processability based on one order of magnitude higher solubility. A similar trend is observed in different rylene diimide stereoisomers based on larger semiconducting core perylene diimide. The PSCs based on NDI enantiomers with good film‐forming ability and a very high lowest phase transition temperature (T_lowest) of 321 °C exhibit a high and uniform average power conversion efficiency (PCE) of 19.067 ± 0.654%. These PSCs also have a high temporal device stability, with less than 10% degradation of the PCE at 100 °C for 1000 h without encapsulation. Therefore, chiral stereoisomer engineering of charge transporting materials is a potential approach to achieve high solution processability, excellent performance, and significant temporal stability in organic electronic devices.     

路由表快速查找算法

路由器中路由表查找速度是当前英特网发展的瓶颈之一。归纳了设计中路由表快速查找算法时需考虑的问题,分析并比较了各种典型算法的原理。     

主动网安全授权机制的设计

以可编程交换机方案＾「１」为基础,以主动网络的节点安全为出发点,设计了一种主动网安全授权机制。设计要点包括划资源对象,定义对象操作集,建立层次化授权与用户管理结构,实现权限分级与授仅自动委托以及利用加密、摘要与签名算法保证授权的正确性和守整性。     

Fuzzy sliding-mode controllers with applications

This paper concerns the design of robust control systems using sliding-mode control that incorporates a fuzzy tuning technique. The control law superposes equivalent control, switching control, and fuzzy control. An equivalent control law is first designed using pole placement. Switching control is then added to guarantee that the state reaches the sliding mode in the presence of parameter and disturbance uncertainties. Fuzzy tuning schemes are employed to improve control performance and to reduce chattering in the sliding mode. The practical application of fuzzy logic is proposed here as a computational-intelligence approach to engineering problems associated with sliding-mode controllers. The proposed method can have a number of industrial applications including the joint control of a hydraulically actuated mini-excavator as presented in this paper. The control hardware is described together with simulated and experimental results. High performance and attenuated chatter are achieved. The results obtained verify the validity of the proposed control approach to dynamic systems characterized by severe uncertainties