Study on Pollution Flashover Performance of Short Samples of Composite Insulators Intended for /spl plusmn/800 kV UHV DC

Based on the artificial pollution tests, the effects of pollution and high altitude on the flashover performance of short samples of five kinds of UHV/EHV dc composite long rod insulators are analyzed. The exponent characterizing the influence of salt deposit density on the flashover voltage is related with the profile and the material of the insulator shed. The values of the samples' exponents vary between 0.24 and 0.30, which are smaller than those of porcelain or glass cap-and-pin insulators, namely, the influence of the pollution on the composite long rod insulators is less, relatively. Thus, the composite insulators have certain advantages in severe pollution regions. The best ratio of the leakage distance to the arcing distance is about 3.35. The exponent characterizing the influence of air pressure on the flashover voltage is related with the profile and the material of the insulator shed and the pollution severity, the values of the samples' exponents vary between 0.6 and 0.8, which are larger than those of porcelain or glass cap-and-pin insulators. Therefore, the dc composite insulator used in high altitude regions should have enough arcing distance. Based on the test results, if insulator sample Type E is selected for the plusmn800 kV UHV dc transmission lines, the basic arcing distance should be no less than 8.16 m and the basic leakage distance no less than 30.2 m.     

Experimental study on the ion migration of rod samples for high voltage DC porcelain support insulators

The ion migration testing used for DC porcelain support insulators was carried out in this paper. Ten rod samples for DC porcelain support insulators were subjected to a long-term ion migration testing in our laboratory in accordance with the reported procedure of IEC. The changes of Na⁺ distribution along with the samples under the long-term testing were analyzed, compared to that of the untested samples. The mechanical performance of the tested samples was verified by using bending breakdown testing. The research findings indicate that the ion migration testing designed for support insulators does not cause Na⁺ ion apparent migration in the samples and does not influence the mechanical performance of the tested samples     

Novel synthesis of quaternary nanocomposites based on chemical vapor grown graphene for photocatalytic hydrogen evolution

Pd-Pt/graphene-TiO₂ nanocomposites were synthesized via a facile ultrasonic and hydrothermal method. For the functionalization of graphene, large area graphene obtained by chemical vapor deposition method was oxidized by 3-chloroperoxybenzoic acid. The functionalized graphene oxide was decorated with TiO₂. And then, Pt and Pd nanoparticles were dispersed on graphene surface, simultaneously. The characterizations of “as-prepared” samples were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), Raman, specific surface area (BET) and with energy dispersive X-ray (EDX). The photocatalytic activity of the Pd-Pt/graphene-TiO₂ nanocomposite catalyst was evaluated by H₂ evolution under UV light. Pd-Pt/graphene-TiO₂ (Pd-Pt/G-TiO₂) exhibited higher photocatalytic activities than control experimental group samples (TiO₂, G-TiO₂, Pd/G-TiO₂ and Pt/G-TiO₂) under UV light irradiation.     

Recent Advances in Conjugated Polymer Materials for Disease Diagnosis

The extraordinary optical amplification and light‐harvesting properties of conjugated polymers impart sensing systems with higher sensitivity, which meets the primary demands of early cancer diagnosis. Recent advances in the detection of DNA methylation and mutation with polyfluorene derivatives based fluorescence resonance energy transfer (FRET) as a means to modulate fluorescent responses attest to the great promise of conjugated polymers as powerful tools for the clinical diagnosis of diseases. To facilitate the ever‐changing needs of diagnosis, the development of detection approaches and FRET signal analysis are highlighted in this review. Due to their exceptional brightness, excellent photostability, and low or absent toxicity, conjugated polymers are verified as superior materials for in‐vivo imaging, and provide feasibility for future clinical molecular‐imaging applications. The integration of conjugated polymers with clinical research has shown profound effects on diagnosis for the early detection of disease‐related biomarkers, as well as in‐vivo imaging, which leads to a multidisciplinary scientific field with perspectives in both basic research and application issues.     

TiO2 Nanorod Array Constructed Nanotopography for Regulation of Mesenchymal Stem Cells Fate and the Realization of Location‐Committed Stem Cell Differentiation

As a physical cue for controlling the fate of stem cells, surface nanotopography has attracted much attention to improve the integration between implants and local host tissues and cells. A biocompatible surface TiO₂ nanorod array is proposed to regulate the fate of bone marrow derived mesenchymal stem cells (MSCs). TiO₂ substrates with different surface nanotopographies: a TiO₂ nanorod array and a polished TiO₂ ceramic are built by hydrothermal and sintering processes, respectively. The assessment of morphology, viability, gene expression, and protein characterization of the MSCs cultured on the different TiO₂ substrates proves that a TiO₂ nanorod array promotes the osteogenic differentiation of MSCs, while a TiO₂ ceramic with a smooth surface suppresses it. Periodically assembled TiO₂ nanorod array stripes on the smooth TiO₂ ceramic are constructed by a combination of microfabrication and a chemical synthesis process, which realizes the location‐committed osteogenic differentiation of MSCs. A route to control the differentiation of MSCs by a nanostructured surface, which can also control the location and direction of MSCs on the surface of biomaterials with micro‐nano scale surface engineering, is demonstrated.     

Binder‐Free and Carbon‐Free 3D Porous Air Electrode for Li‐O2 Batteries with High Efficiency,High Capacity,and Long Life

Pt‐Gd alloy polycrystalline thin film is deposited on 3D nickel foam by pulsed laser deposition method serving as a whole binder/carbon‐free air electrode, showing great catalytic activity enhancement as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium oxygen batteries. The porous structure can facilitate rapid O₂ and electrolyte diffusion, as well as forming a continuous conductive network throughout the whole energy conversion process. It shows a favorable cycle performance in the full discharge/charge model, owing to the high catalytic activity of the Pt‐Gd alloy composite and 3D porous nickel foam structure. Specially, excellent cycling performance under capacity limited mode is also demonstrated, in which the terminal discharge voltage is higher than 2.5 V and the terminal charge voltage is lower than 3.7 V after 100 cycles at a current density of 0.1 mA cm^?2. Therefore, this electrocatalyst is a promising bifunctional electrocatalyst for lithium oxygen batteries and this depositing high‐efficient electrocatalyst on porous substrate with polycrystalline thin film by pulsed laser deposition is also a promising technique in the future lithium oxygen batteries research.     

智能交流接触器温度补偿控制策略研究

环境温度及接触器频繁工作会导致线圈温度上升,对接触器吸合产生影响,针对此问题,基于带反馈控制的PWM(脉宽调整)型智能交流接触器系统结构、工作原理及其动态特性,提出一种基于智能交流接触器的温度补偿控制策略。智能控制系统采集实时的输入电压和线圈温度值作为反馈输出控制量,通过特性分析与实验建立动态控制表,根据电压与温度值查表计算输出最佳占空比及其强激磁时间的PWM波,控制接触器合闸。研究结果表明,通过此控制策略能使接触器在各工作温度及阈值电压范围内实现最优合闸,并保证在较高温度下可靠合闸,提高其工作性能、使用寿命和环境适用范围。     

基于GSM的双向汽车防盗系统的研究与设计

提出了一种基于GSM通信模块和无线射频模块双向通信的汽车防盗系统设计方案。该设计以GSM网络为通信媒介,将车载主控制器检测到的各种汽车状态传送至预先设定的车主手机中,实现了车主对汽车的跟踪及监控,可有效防止汽车盗窃事件的发生。     

Reliable stabilization of stochastic time-delay systems with nonlinear disturbances

This paper is concerned with the stabilization problem for a class of continuous stochastic time-delay systems with nonlinear disturbances, parameter uncertainties and possible actuator failures. Both the stability analysis and synthesis problems are considered. The purpose of the stability analysis problem is to derive easy-to-test conditions for the uncertain nonlinear time-delay systems to be stochastically, exponentially stable. The synthesis problem, on the other hand, aims to design state feedback controllers such that the closed-loop system is exponentially stable in the mean square for all admissible uncertainties, nonlinearities, time-delays and possible actuator failures. It is shown that the addressed problem can be solved in terms of the positive definite solutions to certain algebraic matrix inequalities. Numerical examples are provided to demonstrate the effectiveness of the proposed design method.