功率变换器肋片散热器的理论分析与优化设计

针对现有散热器模型的不足,建立了恒热流的边界条件下的散热器的数学模型,得到了散热器的温度分布公式。提出了散热器的优化方法,并利用Flux软件对现有功率变换器的散热器在自然空气冷却条件下进行优化。得到了两种优化方案,都在功率器件允许的温度范围内减小散热器的体积和质量,从而充分发挥了散热器的作用。     

Size Effects on the Mechanical Properties of Nanoporous Graphene Networks

It is essential to understand the size scaling effects on the mechanical properties of graphene networks to realize the potential mechanical applications of graphene assemblies. Here, a “highly dense‐yet‐nanoporous graphene monolith (HPGM)” is used as a model material of graphene networks to investigate the dependence of mechanical properties on the intrinsic interplanar interactions and the extrinsic specimen size effects. The interactions between graphene sheets could be enhanced by heat treatment and the plastic HPGM is transformed into a highly elastic network. A strong size effect is revealed by in situ compression of micro‐ and nanopillars inside electron microscopes. Both the modulus and strength are drastically increased as the specimen size reduces to ≈100 nm, because of the reduced weak links in a small volume. Molecular dynamics simulations reveal the deformation mechanism involving slip‐stick sliding, bending, buckling of graphene sheets, collapsing, and densification of graphene cells. In addition, a size‐dependent brittle‐to‐ductile transition of the HPGM nanopillars is discovered and understood by the competition between volumetric deformation energy and critical dilation energy.     

Broadband polarized photodetector based on p-BP/n-ReS2 heterojunction

Two-dimensional(2D) atomic crystals,such as graphene,black phosphorus(BP) and transition metal dichalcogenides(TMDCs) are attractive for use in optoelectronic devices,due to their unique crystal structures and optical absorption properties.In this study,we fabricated BP/ReS2 van der Waals(vdWs) heterojunction devices.The devices realized broadband photoresponse from visible to near infrared(NIR)(400–1800 nm) with stable and repeatable photoswitch characteristics,and the photoresponsivity reached 1.8 mA/W at 1550 nm.In addition,the polarization sensitive detection in the visible to NIR spectrum(532–1750 nm) was demonstrated,and the photodetector showed a highly polarization sensitive photocurrent with an anisotropy ratio as high as 6.44 at 1064 nm.Our study shows that van der Waals heterojunction is an effective way to realize the broadband polarization sensitive photodetection,which is of great significance to the realization and application of multi-functional devices based on 2D vdWs heterostructures.     

MPEG-2视频编码标准及CLM4400视频编码芯片简介

本文通过MPEG-2和MPEG-1在视频方面的比较，简略地介绍了MPEG-2视频标准，并附带介绍了C-CUBE公司的MPEG-2视频编码芯片CLM4400的功能和应用前景。     

传输故障处理经验总结

处理传输故障的关键是故障的准确定位。为了达到这个目标,需要在维护时清楚故障定位的原则、排查故障的可能原因,掌握一种高效的手段或方法来迅速处理可能遇到的各种故障。     

基于嵌入式的智能流速仪研制

流速仪为水工筑建设计提供准确的江河的流速值,随着应用需求的增加,原有的8位单片机控制系统不能完全满足现代水文测量的需要。本文研制了一种旋桨式传感器的智能流速仪,以AT91SAM9261为微处理器,采用CPLD芯片为流速数据采集接口,配以TFT-LCD显示屏,移植uClinux实时操作系统,具有测周、计数、双向测速等多种测量方式,可实现16个通道同步独立检测。系统测量方式灵活,测量时间短,测量精度高,稳定可靠等特点,广泛用于水文检验部门和科研设计院等单位。     

PLC提高性实验的实验教学改革探索

介绍PLC即可编程序控制器在实验教学中进行的提高性实验,提高性实验之一是PLC对三台鼠笼异步电动机的自动与手动控制,PLC指令的灵活应用及实现。     

Dopamine‐Modified Cationic Conjugated Polymer as a New Platform for pH Sensing and Autophagy Imaging

A dopamine‐modified conjugated polymer PFPDA is synthesized and characterized. At low pH, dopamine exists in its hydroquinone form and lacks the ability to quench fluorescence. At high pH, the proportion of the quinone form of dopamine increases due to its autooxidation, and efficient intramolecular electron transfer from the polymer main chain to quinone occurs, resulting in the quenching of the fluorescence of PFPDA. Thus, PFPDA exhibits a fluorescence “turn‐on” response at low pH. PFPDA possesses excellent photostability and exhibits no cytotoxicity, which makes it a good fluorescent material for pH sensing and cell imaging. A light‐induced hydroxyl anion emitter, MGCB, is also used to change the pH of the solution and thus regulate the fluorescence of PFPDA via remote control under light irradiation. Because the cytoplasm becomes acidic when cell autophagy occurs, PFPDA can also be used for autophagy imaging of HeLa cells with good selectivity.     

Toward Forty Thousand-Cycle Aqueous Zinc-Iodine Battery: Simultaneously Inhibiting Polyiodides Shuttle and Stabilizing Zinc Anode through a Suspension Electrolyte

Aqueous zinc-iodine (Zn-I₂) batteries are promising candidates for grid-scale energy storage due to their safety and cost-effectiveness. However, the shuttle effect of polyiodides, Zn corrosion, and accumulation of by-products restrict their applications. Herein, a simple vermiculite nanosheets (VS) suspension electrolyte is designed for simultaneous confinement of polyiodides and stabilization of Zn anode. It is found that the generation of I₅⁻ as dominant intermediate and the precipitation reaction between I₅⁻ and alkaline by-products should cause irreversible iodine species loss. Benefiting from the high binding energy between polyiodides and silica-oxygen bonds of VS, dissolved polyiodides are effectively anchored on the surface of VS suspended in the bulk electrolyte to suppress the shuttle effect, which is confirmed by in situ Raman, Ultraviolet-visible characterizations and theoretical calculations. Furthermore, the self-assembly VS interfacial layer on the surface of Zn anode hinders side reactions induced by polyiodides. Meanwhile, the interlayer and surface excess negative charges of VS tend to be compensated by Zn²⁺ from diffuse layer, which serves as ion accelerators for transferring Zn²⁺ at the interface immediately, rendering dendrite-free Zn plating/stripping behavior. Consequently, the Zn-I₂ battery with VS electrolyte achieves an ultra-long lifespan of 40000 cycles with a negligible capacity decay at 20 C.     

Virtual access network embedding in wireless mesh networks

Network virtualization of a wireless mesh network (WMN) is an economical way for different subscribers to customize their exclusive access networks through a common network infrastructure. The most critical task of network virtualization is virtual network embedding, which can be divided into two sub-problems: node mapping and link mapping. Although there exist approaches to virtual network embedding in wired networks, the characteristics of WMNs make virtual network embedding become a unique and challenging problem. In this paper, virtual access network embedding is studied for WMNs. To support flexible resource allocation in virtual access network embedding, each access node is designed based on orthogonal frequency division multiple access (OFDMA) dual-radio architecture. Through subcarrier allocation on each link, virtual access networks are gracefully separated from each other. To coordinate channel assignment across different links under the constraint of a limited number of orthogonal channels, a novel channel allocation algorithm is proposed to exploit partially-overlapped channels to improve resource utilization. Since the virtual access network embedding problem is NP-hard, a heuristic algorithm is developed based on an enhanced genetic algorithm to obtain an approximate but effective solution. Simulation results illustrate that the virtual access network embedding framework developed in this paper works effectively in WMNs.