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.     

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.     

基于改进零树编码的图像联合压缩加密算法

在认真研究算术编码和算术加密的基础上,提出了一种基于改进零树编码的图像联合压缩加密算法.使用密钥对图像压缩产生的原始上下文和原始判决进行修正,实现了图像联合加密.阐述了上下文修正和判决修正算法的规则,对其安全性进行分析.结合比特平面编码技术,可以使用不同密钥对不同小波分辨率的系数分别加密,实现分辨率选择性加密,以满足不同应用需求.对零树编码进行改进,加入自适应算术编码,并对联合压缩加密算法进行仿真.结果表明:相对原始图像压缩算法而言,所提出的图像联合压缩加密算法具有基本相当的压缩效率;相对区间分裂的联合加密算法而言,所提出算法具有更好的安全性.     

强噪声下三轴磁力计正交及增益误差校正及其测量实验

提出了适用于强测量噪声情况下的三轴磁力计正交及增益误差建模及校正方法,详细推导了磁力计测量误差模型,给出了误差参量辨识及校正算法,仿真证明了在强噪声情况下算法仍具有良好的收敛性,给出了不同信噪比条件下误差校正精度与采样点个数的关系,证实了算法能应用在磁力计测量噪声较强场合,并将其实现地磁场强度测量实验,获得了令人满意的结果。     

方差分析在乙型流感病毒灭活疫苗试验设计中的应用北大核心

摘.要:SARS,流感,乙肝,结核等生物疾病严重威胁人类的健康,为了应对病毒的入侵,必须研究应对病毒的灭活疫苗.而在众多的试验疫苗中,如何选择出最有效的病毒灭活疫苗进行推广,使其发挥最大的作用.下面结合多元统计中的一些方法,介绍如何利用方差分析这种统计方法进行试验设计,分析应对常见的乙型流感病毒的不同疫苗间是否有显著差异,从而找出最佳试验点,即最优的乙型流感病毒灭活疫苗.     

On optimality of the barrier strategy for the classical risk model with interest

In this paper, we consider the optimal dividend problem for a classical risk model with a constant force of interest. For such a risk model, a sufficient condition under which a barrier strategy is the optimal strategy is presented for general claim distributions. When claim sizes are exponentially distributed, it is shown that the optimal dividend policy is a barrier strategy and the maximal dividend-value function is a concave function. Finally, some known results relating to the distribution of aggregate dividends before ruin are extended.     

Optimal investment and excess of loss reinsurance with short-selling constraint

This paper considers the optimal control problem with constraints for an insurance company. The risk process is assumed to be a jump-diffusion process and the risk can be reduced through an excess of loss (XL) reinsurance. In addition, the surplus can be invested in the financial market. In the financial market, the short-selling constraint is one of the main factors which make models more realistic. Our goal is to find the optimal investment-reinsurance policy without short-selling, which maximizes the expected exponential utility of the terminal wealth. By solving the corresponding Hamilton-Jacobi-Bellman equation, the value function and the optimal investment-reinsurance policy are given in a closed form.     

First passage models for denumerable semi-Markov decision processes with nonnegative discounted costs

This paper considers a first passage model for discounted semi-Markov decision processes with denumerable states and nonnegative costs.The criterion to be optimized is the expected discounted cost incurred during a first passage time to a given target set.We first construct a semi-Markov decision process under a given semi-Markov decision kernel and a policy.Then,we prove that the value function satisfies the optimality equation and there exists an optimal(or e-optimal) stationary policy under suitable conditions by using a minimum nonnegative solution approach.Further we give some properties of optimal policies.In addition,a value iteration algorithm for computing the value function and optimal policies is developed and an example is given.Finally,it is showed that our model is an extension of the first passage models for both discrete-time and continuous-time Markov decision processes.     

细菌模型的非协调有限元分析

将非协调元应用于描述细菌传播的反应扩散方程组的初边值问题.借助单元的一些特性和非协调误差估计技巧,分别在半离散和全离散有限元格式下,研究了其数值解与精确解的误差估计,得到了最优的误差估计以及超逼近结果.     

Dynamics about Neural Array with Simple Lateral Inhibitory Connections

Lateral inhibitory effect is a well-known feature of information processing in neural systems. This paper presents a neural array model with simple lateral inhibitory connections. After detailed examining into the dynamics of this kind of neural array, the author gives the sufficient conditions under which the outputs of the network will tend to a special stable pattern called spatial sparse pattern in which if the output of a neuron is 1, then the outputs of the neurons in its neighborhood are 0. This ability called spatial sparse coding plays an important role in self-coding, self-organization and associative memory for patterns and pattern sequences. The main conclusions about the dynamics of this kind of neural array which is related to spatial sparse coding are introduced.