介孔SiO2薄膜增敏SERS基底在消逝波激励下的特性表征

采用溶胶-凝胶分子模板法在50 nm 厚金膜表面制备约40 nm 厚介孔二氧化硅(MPS)薄膜, 然后在MPS薄膜表面静电自组装金纳米粒子(GNP)单层膜, 形成的多层膜结构用作表面增强拉曼散射(SERS)基底.利用扫描电镜观测到MPS薄膜具有表面开口多孔结构, 有助于小分子向薄膜内快速扩散. 基于时域有限差分(FDTD)方法对电场分布的仿真结果指出, 在表面等离子体共振(SPR)条件下分布于金膜与GNP之间的消逝场显著增强. 由于空间重叠, 该增强场能够高效激发MPS内富集的小分子拉曼信号, 产生的拉曼信号还可免受金属作用的干扰. 利用Kretschmann 结构和尼罗蓝(NB)拉曼活性分子测试了Au/MPS/GNP基底在785 nm激发波长下的SERS效果, 并与Au/GNP基底进行了比较. 结果表明, 在SPR条件下, Au/MPS/GNP基底能够导致较强的定向和背向拉曼信号, 而且在586 cm^-1处的背向拉曼信号强度是Au/GNP基底的40 倍, 这归功于MPS薄膜. 进一步测试表明背向拉曼信号强度与NB浓度成正相关. 这意味着Au/MPS/GNP基底具有良好的半定量检测本领.     

基于谱技术的电流型CMOS乘法器

本文应用开关信号理论,建立了基于谱技术的对称二值逻辑的传输电流开关理论,该理论能从开关级指导设计基于谱技术的对称二值电流型CMOS电路．在基于谱技术的对称二值代数中,“负”,“线加”和“乘”运算构成完备集,因此,应用传输电流开关理论设计的对称二值电流型电流镜和乘法器电路可以实现任意对称二值函数．     

等衍射长度超短脉冲贝塞耳-高斯光束的传输特性

使用复解析信号法,研究了衍射长度与频率无关的超短脉冲贝塞耳－高斯光束在自由空间中的传输，推导出了解析表达式并进行了理论和计算分析.结果表明：在无衍射长度内，等衍射长度超短脉冲贝塞耳.高斯光束的横向光强分布扩展很小.在无衍射长度之外，横向光强分布有显著扩展.但是，在无衍射长度内轴上脉冲波形仍有展宽.随传输距离增加轴上蓝移单调增加逐渐达到一渐近值.随横向距离增加轴外光谱移动由蓝移变为红移.     

Effective SNR improvement using a high-power pulsed pump in an ytterbium-doped fiber amplifier

A high-power pulsed pump method is proposed to obtain a high-energy output with an improved signal- to-noise ratio （SNR） during pulse amplification. Based on numerical analysis, the ytterbium-doped fiber amplifiers are compared under different pumping conditions. At the same signal gain, the output using the high-power pulsed pump shows great SNR improvement and reduced output signal distortion, compared with a continuous-wave pump and a low-power pulsed pump. By adjusting the pump parameters, the amplifier can achieve the optimal output SNR without sacrificing the signal gain. We believe that the high-power pulsed pump scheme is very suitable for the high-energy nanosecond pulse amplification, which has a high SNR requirement.     

Fiber-based optical parametric amplifier for 40-Gb/s NRZ-DPSK signal transmission system employing QC-LDPC codes

In this letter, we investigate quasi-cyclic low-density parity-check （QC-LDPC） codes in a 40-Gb/s nonreturn-to-zero differential phase-shift keying （NRZ-DPSK） signal transmission system based on a fiber- based optical parametric amplifier （FOPA）. A constructed algorithm of QC-LDPC codes according to the optimizing set of shift vMues on the circulant permutation matrix （CPM） of the basis matrix is proposed. Simulation results prove that the coding gain in the encoded system can be realized at 10.2 dB under QC- LDPC codes with a code rate of 5/6 when the bit error rate （BER） is 10-9. In addition, the error-floor level originating from the uncoded system is suppressed.     

Real-time video signal transmission over a terahertz communication link

A 2.4-m communication link operating at 3.9 THz based on a terahertz quantum cascade laser and a terahertz quantum well photodetector （THz QWP） are introduced. The lumped electrical models of THz QWP for small signals are presented. A discussion of the bandwidth limit of the detecting circuit is presented. Using direct on off-keying modulation and intensity detection, the transmission of digital video signal with a data rate of 2.5 Mb/s is demonstrated. Pseudo-random binary sequences are transmitted to investigate the bit-error rate （BER） at different rates. Result shows the error free transmission when the rate is below 5 Mb/s.     

Markov transition probability-based network from time series for characterizing experimental two-phase flow

We generate a directed weighted complex network by a method based on Markov transition probability to represent an experimental two-phase flow. We first systematically carry out gas-liquid two-phase flow experiments for measuring the time series of flow signals. Then we construct directed weighted complex networks from various time series in terms of a network generation method based on Markov transition probability. We find that the generated network inherits the main features of the time series in the network structure. In particular, the networks from time series with different dynamics exhibit distinct topological properties. Finally, we construct two-phase flow directed weighted networks from experimental signals and associate the dynamic behavior of gas-liquid two-phase flow with the topological statistics of the generated networks. The results suggest that the topological statistics of two-phase flow networks allow quantitative characterization of the dynamic flow behavior in the transitions among different gas-liquid flow patterns.     

Comparative investigation of the resistance and ability to trigger high voltage discharge for single and multiple femtosecond filaments in air

A comparative investigation of the resistance and ability to trigger high voltage(HV) discharge for a single filament(SF) and multiple filaments(MFs) has been carried out.The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance,but this is not the case for the MF.The MF’s resistance is much smaller than the SF’s.However,the MF shows a slightly higher HV breakdown threshold than the SF.The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path.     

An improved deconvolution method for X-ray coded imaging in inertial confinement fusion

In inertial confinement fusion （ICF）, X-ray coded imaging is considered as the most potential means to diagnose the compressed core. The traditional Richardson-Lucy （RL） method has a strong ability to deblur the image where the noise follows the Poisson distribution. However, it always suffers from over-fitting and noise amplification, especially when the signal-to-noise ratio of image is relatively low. In this paper, we propose an improved deconvolution method for X-ray coded imaging. We model the image data as a set of independent Gaussian distributions and derive the iterative solution with a maximum-likelihood scheme. The experimental results on X-ray coded imaging data demonstrate that this method is superior to the RL method in terms of anti-overfitting and noise suppression.     

独立分量分析在爆破振动信号分离中的应用初探

综合运用小波分析和独立分量分析对实测的2孔微差爆破振动试验信号进行分离研究.采用小波分析分解滤去爆破振动信号能量比低的高频部分,提取主要特征所在的频段的重构信号,然后运用独立分量分析(independent component analysis,ICA)对其重构信号进行分离,初步成功获得了体现现场实际情况的分段震波,确...