基于最大似然频率精细估计的载波捕获算法

深空通信中,星上对载波的主动捕获主要利用频率估计的方法。在实际载波捕获电路中,精确的频率估计值导入锁相环,使得锁相环捕获带余量充足。在锁相环带宽一定的情况下,估计精度的提高可以减少FFT实现点数。在FFT频率粗估计的基础上,通过频率精细估计算法可提高估计精度。为获得估计精度更高的频率精细估计算法,利用最大似然泛函不变性推导了频率精细估计的最大似然算法。载噪比在5 dB时,估计精度可以提高到FFT分辨率的10-4。仿真结果表明,该算法估计性能优于其他频率精细估计算法。     

多技术状态产品性能可靠性仿真评估方法研究

针对某产品空投试验时多状态、小样本的特点,提出了一种基于正态环境因子的性能可靠性仿真评估方法。运用仿真技术获得了环境因子的仿真结果,利用环境因子将分散在不同空投条件下的试验数据折算到某一典型工况下,得到了较客观的产品入水可靠性评估结果。     

PCB企业知识管理实施浅析

分析了PCB企业知识管理的必要性,它是PCB企业迎接挑战、提升竞争力的必然选择。进而分析了PCB企业知识的特点和PCB企业知识管理现状,在此基础上提出了PCB企业知识管理实施的关键因素包括领导、文化与制度三个方面,同时对PCB企业知识管理实施的步骤做了初步的探讨。     

Highly Reproducible and Regulated Conductance Quantization in a Polymer‐Based Atomic Switch

A detailed understanding of the conductance quantization and resistive switching phenomena in redox‐based memories is crucial for realizing atomic‐scale memory devices and for finding the adequate design principles on which they can be based. Here, the emergence of quantized conductance states and their correlation with resistive switching characteristics in polymer‐based atomic switches are investigated using combinations of current–voltage measurements and first‐principles density functional theory (DFT) simulations. Various conductance states, including integer and half‐integer multiples of a single atomic point contact and fractional conductance variations, are observed in an Ag/polyethylene oxide/Pt device under sweeping of bias voltage. Moreover, highly controllable and reproducible quantized conductance behaviors by tuning the voltage sweep rate and the sweep voltage range, suggesting well‐controlled formation of the atomic point contact, are demonstrated. The device also exhibits longer retention times for higher conductance states. The DFT simulations reveal the transmission eigenstate of geometrically optimized atomic point contact structures and the impact of the atomic configurations and structural stability on the conductance state, which also explains their resistive switching behaviors. The well‐defined, multiple quantized conductance states observed in these polymer‐based atomic switches show promise for the development of new multilevel memory devices.     

Flexible Piezoelectric Touch Sensor by Alignment of Lead‐Free Alkaline Niobate Microcubes in PDMS

A highly sensitive, lead‐free, and flexible piezoelectric touch sensor is reported based on composite films of alkaline niobate K_0.485Na_0.485Li_0.03NbO₃ (KNLN) powders aligned in a polydimethylsiloxane (PDMS) matrix. KNLN powder is fabricated by solid‐state sintering and consists of microcubes. The particles are dispersed in uncured PDMS and oriented by application of an oscillating dielectrophoretic alignment field. The dielectric constant of the composite film is almost independent of the microstructure, while upon alignment the piezoelectric charge coefficient increases more than tenfold up to 17 pC N^?1. A quantitative analysis shows that the origin is a reduction of the interparticle distance to under 1.0 µm in the aligned bicontinuous KNLN chains. The temperature stable piezoelectric voltage coefficient exhibits a maximum value of 220 mV m N^?1, at a volume fraction of only 10%. This state‐of‐the‐art value outperforms bulk piezoelectric ceramics and composites with randomly dispersed particles, and is comparable to the values reported for the piezoelectric polymers polyvinylidenefluoride and its random copolymer with trifluoroethylene. Optimized composite films are incorporated in flexible piezoelectric touch sensors. The high sensitivity is analyzed and discussed. As the fabrication technology is straightforward and easy to implement, applications are foreseen in flexible electronics such as wireless sensor networks and biodiagnostics.     

Unusual Twisting Phonons and Breathing Modes in Tube‐Terminated Phosphorene Nanoribbons and Their Effects on Thermal Conductivity

By studying tube‐terminated phosphorene nanoribbons (PNRs), it is found that unusual phonon and thermal properties can emerge from topologically new edges. The lattice dynamics calculations show that in tube‐terminated PNRs, the breaking of rotation symmetry suppresses the degeneracy of phonon modes, causing the emergence of twisting mode. An anomalous change of an out‐of‐plane acoustic mode to breathing modes with nonzero energy at the center of Brillouin zone occurs when the phosphorene sheet is converted into a tube‐terminated PNR. These unusual twisting and breathing modes provide a larger phase space for scattering phonons, thus explaining the low thermal conductivity of tube‐terminated PNRs revealed by molecular dynamics calculations. Due to the change in the stress field distribution caused by the tube edge, a nearly strain‐independent thermal conductivity in tube‐terminated PNRs is observed, which is in contrast to the apparent enhancement of thermal conductivity in pristine and dimer‐terminated PNRs under tensile strain. The work reveals intriguing phononic and thermal behaviors of tube‐terminated 2D materials.     

太赫兹滤波器

太赫兹技术在生物、国防以及基础研究等方面有重要的应用,要实现对太赫兹波技术的实际有效的应用,与之相关的太赫兹传导、滤波器件等功能器件至关重要.目前太赫兹滤波器结构主要基于二维光子晶体、超颖材料、表面等离子体等结构.就太赫兹滤波器的研究进展进行了总结,并对其今后的研究发展方向进行了分析.     

基于AM-OLED基板的拓展多晶硅薄膜功能层的研究

在有源寻址有机发光二极管(active matrix organic light emitting diode,AM-OLED)显示基板中,将电学功能层--薄膜晶体管(thin film transistor,TFT)有源层材料p型掺杂金属诱导晶化(metal induced crystallized,MIC)多品硅(p+-MIC poly-Si)薄膜的版图适当延伸,来充当OLED的阳极,由于它具有低方块电阻、高功函数的电学特性和半反半透、低吸收率的光学特性.与OLED的金属铝阴极形成了微腔器件,成功地形成了显示基板上的多晶硅薄膜的光学功能层.对这一功能层的厚度进行了优化,比较了不同厚度下TFT器件的电学特性和OLED的光学特性.当其厚度为40nm时为最佳厚度,此时,TFT器件场迁移率、阈值电压、亚阈值幅摆、电流开关比和栅压诱导漏极漏电等性能为最佳,且红光微腔式OLED(microcavity-OLED,MOLED)的出光强度增大,光谱窄化,电流效率与功率效率均有所提高.这不仅使器件的性能有所提高,而且大大地简化了AM-OLED基板的制备流程.     

Bacteria-Responsive Self-Assembly of Antimicrobial Peptide Nanonets for Trap-and-Kill of Antibiotic-Resistant Strains

Bacterial trapping using nanonets is a ubiquitous immune defense mechanism against infectious microbes. These nanonets can entrap microbial cells, effectively arresting their dissemination and rendering them more vulnerable to locally secreted microbicides. Inspired by this evolutionarily conserved anti-infective strategy, a series of 15 to 16 residue-long synthetic β-hairpin peptides is herein constructed with the ability to self-assemble into nanonets in response to the presence of bacteria, enabling spatiotemporal control over microbial killing. Using amyloid-specific K114 assay and confocal microscopy, the membrane components lipoteichoic acid and lipopolysaccharide are shown to play a major role in determining the amyloid-nucleating capacity as triggered by Gram-positive and Gram-negative bacteria respectively. These nanonets displayed both trapping and killing functionalities, hence offering a direct improvement from the trap-only biomimetics in literature. By substituting a single turn residue of the non-amyloidogenic BTT1 peptide, the nanonet-forming BTT1-3A analog is produced with comparable antimicrobial potency. With the same sequence manipulation approach, BTT2-4A analog modified from BTT2 peptide showed improved antimicrobial potency against colistin-resistant clinical isolates. The peptide nanonets also demonstrated robust stability against proteolytic degradation, and promising in vivo efficacy and biosafety profile. Overall, these bacteria-responsive peptide nanonets are promising clinical anti-infective alternatives for circumventing antibiotic resistance.     

无外触发的激光扫描仪的时间同步方法研究

采用硬件和软件相结合的方法将sick激光扫描仪和惯性导航装置的数据采集时间统一到GPS的时间下,以GPS时间作为数据开始采集和数据融合的基准时间,通过后期算法实现了Sick激光扫描系统各传感器之间数据的同步融合.根据系统时间同步修正前与修正后的点云对比图详细分析了系统时间同步误差的因素,为以后此类型激光扫描仪在车载激光扫描系统中的应用奠定基础,也为同类设备时间同步方法的实现提供了参考.