Sub-Nanowires Boost Superior Capacitive Energy Storage Performance of Polymer Composites at High Temperatures

Polymer dielectrics with high breakdown strength (E_b) and high efficiency are urgently demanded in advanced electrical and electronic systems, yet their energy density (U_e) is limited due to low dielectric constant (ε_r) and high loss at elevated temperatures. Conventional inorganic fillers with diameters from nano to micrometers can only increase ε_r at the cost of compromised E_b and U_e due to their poor compatibility with polymer matrix. Herein, hydroxyapatite (HAP) sub-nanowires with a diameter of ≈0.9 nm are incorporated in polyetherimide (PEI) matrix to form HAP/PEI sub-nanocomposites. ε_r and E_b of the composites are concomitantly enhanced with only 0.5 wt.% of HAP sub-nanowires, leading to high U_e of 5.14 (@150 °C) and 3.1 J cm⁻³ (@200 °C) with efficiency of 90% and high-temperature stability up to 3 × 10⁵ charge-discharge cycles at 200 °C. Microstructural analysis and molecular dynamics simulations indicate that the sub-nanowires with comparable diameter as polymer chains induce enormous interfacial area, substantially increase mobility of polymer chains and form dense traps for charge carriers. This work extends the current research scope of polymer-inorganics composite dielectrics to the sub-nano-level incorporation and provides a novel strategy for fabricating high performance polymer dielectrics at elevated temperatures.     

Optical Design of Silica Aerogels for On-Demand Thermal Management

Silica aerogels, a type of porous material featuring extra low density and thermal conductivity, have drawn increasing interest from both academia and industry owing to their excellent thermal insulation performance. However, thermal insulation is always the single consideration when silica aerogels are used for thermal management. In this study, the on-demand thermal management (ODTM) of silica aerogel with either passive thermal insulation, passive heating, or passive cooling in different environments is revealed. The ODTM behavior of silica aerogels can be simply fulfilled through their optical property variations such as solar light transparency and infrared emissivity, which are controllable via the microstructures of the building blocks and surface composition design. Robust solar heating of 25 °C higher than the ambient in the daytime and sub-ambient cooling of 7 °C at night is achieved with the traditional transparent silica aerogel. Interestingly, sub-ambient cooling of 5 °C in the daytime and a warmer state on cold nights is achieved by modifying its solar transmittance and infrared emissivity. This study guides a comprehensive understanding of the thermal management behavior of silica aerogels and leads to ODTM applications of silica aerogels by tailoring their optical and thermal conductivity properties.     

Transmission Scheme for 2D Antenna Array MIMO Systems with Limited Feedback

Three-dimensional (3D) multiple-input multiple-output (MIMO) systems exploit spatial richness and provide another degree of freedom to transmit signals and eliminate spatial interference. Currently, however, there is no 3D codebook for two-dimensional (2D) antenna array MIMO systems with limited feedback. In this paper, based on the existing 2D codebook, we present a limited feedback and transmission scheme for 2D antenna array MIMO systems. In this scheme, the mobile station (MS) has imperfect channel knowledge, and the base station (BS) only acquires partial information relating the channel instantiation. MS must feed back two channel state information (CSI) instances, i.e., the horizontal and vertical CSIs. After receiving the two CSI instances, the BS interpolates a new vertical precoding vector using the vertical CSI. Then, the BS re-constructs a 3D beamforming vector using horizontal and vertical precoding vectors and compensates the reported horizontal channel quality indicator. System level simulation is employed, and the simulation results show that the proposed method improves the system spectral efficiency and the cell-edge SE significantly.     

基于MPLS的PWE3实现研究

本文从较底层的角度，阐述了如何使用MPLS技术实现PWE3仿真业务的处理流程。首先简单的介绍了PWE3和MPLS的基本原理。然后重点放在了展示MPLS技术底层Label处理的大量细节。井以Ethernet和ATM的PWE3业务为例详细叙述了底层LSR上MPLS处理单元为实现PWE3功能而进行的各种操作。     

一种低抖动、宽调节范围的带宽自适应CMOS锁相环

提出了一种低抖动、宽调节范围的带宽自适应CMOS锁相环.由于环路带宽可根据输入频率进行自动调节,电路性能可在整个工作频率范围内得到优化.为了进一步提高电路的抖动特性,在电荷泵电路中采用匹配技术,并在压控振荡器中应用电压-电压转换电路以减小压控振荡器的增益.芯片采用SMIC 0.35μm CMOS工艺加工.测试结果表明该锁相环电路可在200MHz～1.1GHz的输出频率范围内保持良好的抖动性能.     

基于比特概率优化算法的分布式视频编码

分布式视频编码器中Turbo码纠错所需要的校验位数量直接决定整个编码器的率失真(RD,Rate-Distortion)性能.分析了传统算法的次优化问题,提出一种新的基于比特概率优化的信道似然值计算算法,该算法首先将原始像素进行比特面分解,然后分别对每个比特面进行独立Turbo码编码及联合解码.解码端在已知已解码比特面的条件下,计算当前解码比特面更准确的信道似然值作为Turbo码的解码输入,减少解码所需要传输的校验位数量,提高编码器RD性能.实验结果表明所提算法能明显提升编码系统的RD性能.     

532nm激光照射后的兔视网膜损伤修复

目的:观察532nm激光照射后的兔视网膜损伤和修复。方法:采用(光斑直径约为2mm、照射时间100s、能量密度200J/cm2、532nm)激光照射家兔视网膜后极部,连续观察1d、3d、7d、14d和28d后眼底及组织学改变。结果:照后1d可见明显水肿及出血。3d后凝固斑边界清晰,出血范围扩大,可见脉络膜成纤维细胞开始增生。14d后渗出和出血大部分吸收。28d后大量纤维组织增生及新生血管形成。结论:该照射剂量可以引起家兔视网膜较为严重的损伤,其修复存在一定的规律性。     

地形对基于波瓣分裂的米波雷达测高方法的影响

针对基于波瓣分裂的米波雷达“比相比幅”测高方法,研究地形对米波雷达测高的影响。说明不同介质的平坦地面反射系数,分析影响粗糙地面反射系数的各种因素,讨论不同地面反射系数对高度测量精度的影响。阐述地面几何反射点的计算方法,解释地面有效反射区的范围及其在测高中的应用,探讨漫反射信号产生原因及其对基于波瓣分裂测高方法的影响。     

大马士革镶嵌结构对Cu膜微结构及应力的影响

通过TEM、SEM、XRD和EBSD,观察了Cu互连线和平坦Cu膜的微观结构。采用薄膜应力测试分布仪和二维面探测器XRD,测量了平坦Cu膜和Cu互连线的应力,计算了Cu薄膜热应力的理论值。凹槽侧壁成为互连线新的形核区域,并且在平行于侧壁的方向形成较弱的(111)织构。与平坦膜相比,互连线晶粒尺寸明显变小(、111)织构较弱,且存在大量Σ3和Σ9晶界。平坦膜和互连线分别表现出压应力和张应力。降温过程产生的热应力为互连线的主要应力。     

一种集群计算并行I/O中启发式文件分类分配策略研究

提出了一种新的应用于集群计算环境的文件分配算法,即启发式文件分类分配算法(Heuristic FileSorted Assignment algorithm,HFSA),它在保证系统负载基本均衡的前提下,按相似的访问服务时间对每个待分配的数据文件进行磁盘分配.具体实现时,首先对待分配文件按它们的服务时间大小进行排序,然后从集群中选择一个结点的磁盘,将有序的若干文件连续地分配到该磁盘上,直接该磁盘达到最大负载时为止.通过对新策略与已有的贪婪文件分配法进行实验比较,结果表明:在访问响应时间方面,系统轻负载时,缩短了20.2%,系统重负载时,缩短了31.6%,并且数据访问的速率越高,由启发式文件分类分配策略所改善的性能就越明显.