用3D-FDTD法分析用于近场光存储的光纤探针电磁波传输特性

提高近场光存储的存储信息密度的关键主要在于掌握近场存储光纤探针的透光率、近场光斑直径尺寸以及场梯度等近场物理量。采用三维时域有限差分 (3D FDTD)法分析了可用于近场光存储的光纤探针尖的光学性质 ,对不同类型光纤的近场光场分布进行了数值计算 ,给出结果并进行比较 ,从光学性质的角度对其在近场光存储中的应用加以讨论。完全镀膜光纤尖在极近场处的光斑可获得 10nm的尺寸 ,远小于传统光纤光学聚焦的光斑尺寸大小。     

A Multi-Radio Multi-Channel Assignment Algorithm Based on Topology Control and Link Interference Weight for a Power Distribution Wireless Mesh Network

Wireless Personal Communications - In this paper, a multi-radio multi-channel (MRMC) assignment algorithm based on topology control and link interference weight for power distribution wireless mesh...     

pin硅波导在1550 nm波段的光电流雪崩增强效应实验研究

The photocurrent effect in pin silicon waveguides at 1550 nm wavelength is experimentally investigated. The photocurrent is mainly attributed to surface-state absorption,defect-state absorption and/or two-photon absorption.Experimental results show that the photocurrent is enhanced by the avalanche effect.A pin silicon waveguide with an intrinsic region width of 3.4μm and a length of 2000μm achieves a responsivity of 4.6 mA/W and an avalanche multiplication factor of about five.     

On Analysis of the Contention Access Period of IEEE 802.15.4 MAC and its Improvement

The release of IEEE 802.15.4 medium access control (MAC) and physical layer specifications represents a significant milestone in promoting deployment of wireless sensor networks. This paper first analyzes the performance of the contention access period (CAP) specified in the IEEE 802.15.4 standard by integrating the discrete-time Markov chain models of the node states and the channel states. Then a modified CAP is analyzed, which could significantly improve the performance of the system. Based on the theoretical analysis of the CAP and the effect of the modification, we have that in the saturated network of IEEE 802.15.4, the collision probability is large, and the throughput is small. The main reasons are the employment of slotted carrier sense multiple access-collision avoidance and the mechanism that if a frame transmission cannot be completed before the end of the CAP, it has to wait until the start of the next CAP. Thus an enhanced collision-avoidance MAC protocol, which achieves a better performance and is compatible with the IEEE 802.15.4 standard, is proposed to improve the performance of the system. Extensive simulations validate our conclusions.     

CCD相机调制传递函数的测试分析

调制传递函数(MTF)是评价CCD相机成像系统质量的重要参数,它能真实地反映相机拍摄时的空间频率与图像对比度的关系。CCD相机的MTF测试中最关键的是靶标的选择,它决定了整个系统的测量精度和操作过程的复杂程度。理想的靶标函数是正弦函数,但制作光出射度随正弦波规律变化的分辨率板是非常困难的,因此利用明暗相间、相互平行的黑白条纹分辨率板来代替正弦波分辨率板,提出了测量MTF的方法。重点对CCD相机在奈奎斯特频率处的MTF测试结果进行了分析与评价。     

Congestion warning method based on the Internet of vehicles and community discovery of complex networks

The traffic congestion occurs frequently in urban areas, while most existing solutions only take effects after congesting. In this paper, a congestion warning method is proposed based on the Internet of vehicles(IOV) and community discovery of complex networks. The communities in complex network model of traffic flow reflect the local aggregation of vehicles in the traffic system, and it is used to predict the upcoming congestion. The real-time information of vehicles on the roads is obtained from the IOV, which includes the locations, speeds and orientations of vehicles. Then the vehicles are mapped into nodes of network, the links between nodes are determined by the correlations between vehicles in terms of location and speed. The complex network model of traffic flow is hereby established. The communities in this complex network are discovered by fast Newman(FN) algorithm, and the congestion warnings are generated according to the communities selected by scale and density. This method can detect the tendency of traffic aggregation and provide warnings before congestion occurs. The simulations show that the method proposed in this paper is effective and practicable, and makes it possible to take action before traffic congestion.     

High‐Strength and High‐Toughness Double‐Cross‐Linked Cellulose Hydrogels: A New Strategy Using Sequential Chemical and Physical Cross‐Linking

Polysaccharide‐based hydrogels have multiple advantages because of their inherent biocompatibility, biodegradability, and non‐toxicic properties. The feasibility of using polysaccharide‐based hydrogels could be improved if they could simultaneously fulfill the mechanical property and cell compatibility requirements for practical applications. Herein, the construction of double‐cross‐linked (DC) cellulose hydrogels is described using sequential chemical and physical cross‐linking, resulting in DC cellulose hydrogels that are mechanically superior to single‐cross‐linked cellulose hydrogels. The formation and spatial distribution of chemically cross‐linked domains and physically cross‐linked domains within the DC cellulose hydrogels are demonstrated. The molar ratio of epichlorohydrin to anhydroglucose units of cellulose and the concentration of the aqueous ethanol solution are two critical parameters for obtaining mechanically strong and tough DC cellulose hydrogels. The mechanical properties of the DC cellulose hydrogels under loading‐unloading cycles are described using compression and tension models. The possible toughening mechanism of double‐cross‐linking is discussed.     

容错同步设计

提出容错同步设计原则和设计方法，并用此方法设计声码器的同步方案。实际运行表明：此方法设计的同步稳定可靠、性能良好。     

CO_2激光切雕机及其加工工艺的研究

一种可用于雕刻和切割非金属的新型ＣＯ２激光设备。介绍了这套设备各部分的结构特点、工作原理以及计算机软件的工作原理。并简述了该设备进行雕刻和切割时的工艺参数。