Quantitative High Resolution Electron Microscopy

 With the resolution becoming sufficient to reveal individual atoms, HREM is now entering the stage where it can compete with X-ray methods to quantitatively determine atomic structures of materials without much prior knowledge, but with the advantage of being applicable to aperiodic objects such as crystal defects. In our view the future electron microscope will be characterised by a large versatility in experimental settings under computer control such as the illumination conditions (TEM-STEM), CBED, detecting conditions (diffraction, image, ptychography) and many other tunable parameters such as focus (g), voltage, spherical aberration (C _s ), beam tilt, etc. Since modern detectors can detect single electrons, also the counting statistics is known. The only limiting factor in the experiment will be the total number of electrons that interact with the object during the experiment due to the limitations in the exposure time or in the object damage. However, instrumental potentialities will never be exploited fully if not guided by an experimental strategy. Here intuitive guidelines can be very deceptive. For instance an image made with the best electron microscope (C _s  = 0) at the best focus (g = 0) from the best object (phase object) would show no contrast at all. Hence, questions such as what is the best C _s , focus, object thickness, etc. can only be answered properly if done using a method of experiment design.     

集成滤波器在谱图信号除噪中的应用

本文提出了一种由神经元网络与线性自适应滤波器组成的集成滤波器的实现方法，用于谱图信号除噪处理。     

Steroid Cyclophanes as Artificial Cell-surface Receptors. Molecular Recognition and its Consequence in Signal Transduction Behavior

Steroid cyclophanes, bearing four bile acid moieties covalently placed on a tetraazaparacyclophane skeleton, were designed and synthesized as artificial cell-surface receptors. Guest-binding behavior of the steroid cyclophanes embedded in a bilayer membrane formed with a synthetic peptide lipid was clarified by means of fluorescence and circular dichroism spectroscopy. We found that the steroid cyclophane effectively bound aromatic guests in both bilayer membranes and aqueous solution. In addition, copper(II) ions acted as a guest species for the steroid cyclophane and a competitive inhibitor toward a NADH-dependent lactate dehydrogenase (LDH). On these grounds, we constituted a supramolecular assembly as an artificial signaling system in combination with the steroid cyclophane, a cationic peptide lipid, and LDH. As a consequence, the steroid cyclophane acted as an effective artificial cell-surface receptor being capable of transmitting an external signal to the enzyme in collaboration with copper(II) ions as a signal transmitter.     

分析信号处理方法的比较研究

研究了高效液相色谱－火焰原子吸收光谱联用系统分析信号处理方法，比较了各种处理方法的优缺点，用积分与适应平滑法综合处理色谱峰分析信号，不仅能有效地消除噪声，而且能使分析信号得到加强，以测定镍为例，经积分与适应平滑法综合处理后，检出限改善了２．７倍。     

Extrapolated Smoothing Descent Algorithm for Constrained Nonconvex and Nonsmooth Composite Problems*

In this paper, the authors propose a novel smoothing descent type algorithm with extrapolation for solving a class of constrained nonsmooth and nonconvex problems,where the nonconvex term is possibly nonsmooth. Their algorithm adopts the proximal gradient algorithm with extrapolation and a safe-guarding policy to minimize the smoothed objective function for better practical and theoretical performance. Moreover, the algorithm uses a easily checking rule to update the smoothing parameter to ensure that any accumulation point of the generated sequence is an (affine-scaled) Clarke stationary point of the original nonsmooth and nonconvex problem. Their experimental results indicate the effectiveness of the proposed algorithm.     

Elliptic Reconstruction and a Posteriori Error Estimates for Fully Discrete Semilinear Parabolic Optimal Control Problems

This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators.     

Fastiterative methods for least squares estimations

Least squares estimations have been used extensively in many applications, e.g. system identification and signal prediction. When the stochastic process is stationary, the least squares estimators can be found by solving a Toeplitz or near-Toeplitz matrix system depending on the knowledge of the data statistics. In this paper, we employ the preconditioned conjugate gradient method with circulant preconditioners to solve such systems. Our proposed circulant preconditioners are derived from the spectral property of the given stationary process. In the case where the spectral density functions() of the process is known, we prove that ifs() is a positive continuous function, then the spectrum of the preconditioned system will be clustered around 1 and the method converges superlinearly. However, if the statistics of the process is unknown, then we prove that with probability 1, the spectrum of the preconditioned system is still clustered around 1 provided that large data samples are taken. For finite impulse response (FIR) system identification problems, our numerical results show that annth order least squares estimator can usually be obtained inO(n logn) operations whenO(n) data samples are used. Finally, we remark that our algorithm can be modified to suit the applications of recursive least squares computations with the proper use of sliding window method arising in signal processing applications.Research supported in part by HKRGC grant no. 221600070, ONR contract no. N00014-90-J-1695 and DOE grant no. DE-FG03-87ER25037.     

基于双摄像头的心率测量系统的设计与改进

针对在外部干扰或昏暗环境下利用图像光电容积描记(image Photoplethysmography,iPPG)技术进行心率测量时准确度较差,提出了一种自适应心率提取算法,并在嵌入式硬件平台上进行了验证。算法根据图像中人脸与背景区域的色度关系来识别不同的场景并启动合适的摄像头进行图像采集及自适应映射,接着对提取出的信号进行滤波,在信号质量评估后输出结果。上述方法在Zynq平台上进行了验证,使用双摄像头实现实时心率测量,并对结果进行可视化输出。实验结果表明:优化后的算法在光照及运动的双重干扰下的测量误差从3.36BPM降至2.78BPM,准确率提升了17.3%。另外,所设计的系统能够实现在极端黑暗条件下的心率采集,平均误差约为2.39BPM。     

一种利用小波降噪的卫星导航信号并行捕获算法

针对全球定位系统（Global Positioning System,GPS）接收机传统捕获算法计算复杂度高、捕获灵敏度低等缺点,提出了一种可降噪的简化并行码相位捕获（Noise Reduction for Simplified Parallel Code Phase Acquisition,NR-SPCA）算法。该算法通过对信号降采样,利用小波变换对二次采样信号作降噪处理,提高了捕获灵敏度;利用GPS信号和C/A码互相关的稀疏性,并行计算降噪后的信号的相关值,提高了运算效率。仿真结果表明,在90%概率捕获成功的前提下,NR-SPCA算法比传统的PCA算法信噪比低1 dB,运算效率提升了100%。该算法还可应用于航天探测、自动驾驶等领域。     

带有前置EDFA卫星相干激光通信终端的信噪比分析

卫星激光通信链路是一项实现卫星大规模星座组网的关键技术。相干激光链路灵敏度高、抗背景干扰、速率升级空间大,在星间激光链路中应用广泛。文章建立了带有前置掺铒光纤放大器(EDFA)的卫星相干激光通信终端的信噪比分析模型,仿真分析了EDFA功率增益、EDFA噪声系数、本振光功率、信号光功率、光放后端光带宽、基带前端电带宽对终端输出信噪比的影响以及各种输出噪声功率占比的情况,得到了带有前置EDFA卫星相干激光通信终端的信噪比参数特性。