Optimal base-station locations in two-tiered wireless sensor networks

We consider generic two-tiered wireless sensor networks (WSNs) consisting of sensor clusters deployed around strategic locations, and base-stations (BSs) whose locations are relatively flexible. Within a sensor cluster, there are many small sensor nodes (SNs) that capture, encode, and transmit relevant information from a designated area, and there is at least one application node (AN) that receives raw data from these SNs, creates a comprehensive local-view, and forwards the composite bit-stream toward a BS. This paper focuses on the topology control process for ANs and BSs, which constitute the upper tier of two-tiered WSNs. Since heterogeneous ANs are battery-powered and energy-constrained, their node lifetime directly affects the network lifetime of WSNs. By proposing algorithmic approaches to locate BSs optimally, we can maximize the topological network lifetime of WSNs deterministically, even when the initial energy provisioning for ANs is no longer always proportional to their average bit-stream rate. The obtained optimal BS locations are under different lifetime definitions according to the mission criticality of WSNs. By studying intrinsic properties of WSNs, we establish the upper and lower bounds of maximal topological lifetime, which enable a quick assessment of energy provisioning feasibility and topology control necessity. Numerical results are given to demonstrate the efficacy and optimality of the proposed topology control approaches designed for maximizing network lifetime of WSNs.     

Constructing Internet coordinate system based on delay measurement

In this paper, we consider the problem of how to represent the locations of Internet hosts in a Cartesian coordinate system to facilitate estimation of network distances among arbitrary Internet hosts. We envision an infrastructure that consists of beacon nodes and provides the service of estimating network distance between pairs of hosts without direct delay measurement. We show that the principal component analysis (PCA) technique can effectively extract topological information from delay measurements between beacon hosts. Based on PCA, we devise a transformation method that projects the raw distance space into a new coordinate system of (much) smaller dimensions. The transformation retains as much topological information as possible and yet enables end hosts to determine their coordinates in the coordinate system. The resulting new coordinate system is termed as the Internet Coordinate System (ICS). As compared to existing work (e.g., IDMaps and GNP), ICS incurs smaller computation overhead in calculating the coordinates of hosts and smaller measurement overhead (required for end hosts to measure their distances to beacon hosts). Finally, we show via experiments with both real-life and synthetic data sets that ICS makes robust and accurate estimates of network distances, incurs little computational overhead, and its performance is not susceptible to the number of beacon nodes (as long as it exceeds a certain threshold) and the network topology.     

利用设计模式“类工厂”实现模板页面技术

主要介绍在Asp．net中利用设计模式的类工厂以及C#中类的继承，实现模板页面技术，达到页面级代码重用，解决在B／S项目开发中，相同相似功能页面存在的前台重复开发问题。提高开发效率，降低开发成本。     

Experimental investigation of hollow-core photonic crystal fibers with five photonic band-gaps

The hollow-core photonic crystal fibers （HC-PCFs） with integrity structure have been fabricated with an improved twice stack-and-draw technique. The transmission spectrum shows that five photonic band-gaps within 450-1100 nm have been obtained.And the green fight transmission in the HC-PCFs has been observed remarkably.     

光激发单极畴与耿氏偶极畴的物理机制比较

对比了半绝缘多能谷光电导开关中光激发单极畴和耿氏器件中偶极畴的物理机制. 从产生机理、电场分布、电子浓度、生长和演变过程等多角度阐述光激发单极畴的特性. 与偶极畴显著不同的是,光激发单极畴内仅有光生电子积累层,没有正离子层;光激发单极畴与光生空穴之间产生了一个与外加电场反向的电场,使畴前电场增强,畴头部电子浓度最高;光激发单极畴生长过程可以一直持续下去,终因电子碰撞电离演变为发光畴,如果碰撞电离达到雪崩强度,将演变为雪崩发光畴. 最后,本文用光激发单极畴模型解释了光电导开关非线性工作模式的超快上升沿、发光电流丝、电流锁定现象等重要实验现象.     

Hybrid Perovskite Quantum Dot/Non-Fullerene Molecule Solar Cells with Efficiency Over 15%

Organic-inorganic hybrid film using conjugated materials and quantum dots (QDs) are of great interest for solution-processed optoelectronic devices, including photovoltaics (PVs). However, it is still challenging to fabricate conductive hybrid films to maximize their PV performance. Herein, for the first time, superior PV performance of hybrid solar cells consisting of CsPbI₃ perovskite QDs and Y6 series non-fullerene molecules is demonstrated and further highlights their importance on hybrid device design. In specific, a hybrid active layer is developed using CsPbI₃ QDs and non-fullerene molecules, enabling a type-II energy alignment for efficient charge transfer and extraction. Additionally, the non-fullerene molecules can well passivate the QDs, reducing surface defects and energetic disorder. The champion CsPbI₃ QD/Y6-F hybrid device has a record-high efficiency of 15.05% for QD/organic hybrid PV devices, paving a new way to construct solution-processable hybrid film for efficient optoelectronic devices.     

一种新的克服OFDM技术中峰平比的方案

在OFDM技术中,PAPR(峰平比)过大的问题一直是人们研究的热点;作者利用一种新的CI/OFDM结构,通过选择合适的频率偏移,达到降低OFDM信号的峰平比的目的.通过对比分析了这种结构的可行性和有效性,并对其进行系统仿真.     

射频CO2激光陶瓷基板划片机

介绍了RFCO2 激光器及其对陶瓷基板划片的特点。分析了RFCO2 激光陶瓷基板划片的机理 ;给出了整机总体设计方案。对导光系统的激光束进行了模拟 ,给出了导光系统的光路图及聚焦镜焦平面处的光斑尺寸及能量分布图。整机性能指标达到国外进口机的水平     

使用EEG分析水平视差对3D图像舒适性的影响

水平视差是影响3D 图像舒适性的重要因素之一。采用不同等级水平视差的3D 图像作为刺激信号,通过记录被试者的EEG 反应信号,提取出被试者观看不同等级水平视差3D 图像的ERP 波形;同时记录被试观看这一系列3D 图像舒适性体验的行为数据,并计算其舒适性检测率。通过EEG信号分析可见,无论在交叉或者非交叉水平视差情况下,3D 图像水平视差舒适范围在45'以内;水平视差在45'~75'时,交叉视差3D 图像ERP 波形280 ms 附近的幅值与不舒适的程度相关,非交叉视差3D 图像ERP 波形250 ms 附近的幅值与不舒适程度相关;检测率曲线结果和主观评价结果显示:3D图像水平视差的舒适性范围在45'以内,水平视差在45'~75'时,3D 图像不舒适程度随着视差的增加而增大。结果表明:EEG 分析、检测率曲线和主观评价结论一致,因此,可以使用EEG 分析水平视差对3D 图像舒适性的影响。     

单壁碳纳米管和W针尖热处理时残气质谱

分别对W针尖上未组装和组装单壁纳米管理进行热处理,然后对所得残气质谱图进行记录和分析,发现在热处理过程中,脱附出一定量的原子C和原子O,然后结合成为CO和CO2被释放出来。