Analysis of repeated hashing

A performance analysis of an overflow handling method for hash files, here called repeated hashing, is reported. The basic idea of repeated hashing is to rehash the overflow records into a smaller separate storage area; the overflow records from this area are in turn hashed into a still smaller separate storage area, etc. The expected retrieval performance and the storage requirements are analysed, both for initial loading and steady state. The problem of optimally partitioning the total storage area is considered and the optimal solution is given. It is concluded, however, that the usefulness of repeated hashing is in doubt because there are methods having the same performance but requiring less maintenance.     

Bottleneck routing with elastic demands

Bottleneck routing games are a well-studied model to investigate the impact of selfish behavior in communication networks. In this model, each user selects a path in a network for routing her fixed demand. The disutility of a user only depends on the most congested link visited. We extend this model by allowing users to continuously vary the demand rate at which data is sent along the chosen path. As our main result we establish tight conditions for the existence of pure strategy Nash equilibria.     

基于重复混沌扩频序列的差分混沌键控系统

提出一种基于可重复混沌扩频序列的差分混沌键控保密通信系统, 并对该系统的误码率进行分析。通过复制差分混沌键控调制信号的参考信号产生重复的混沌扩频序列, 再和经串并转换后的部分数据流相乘, 其余并行数据流按照传统差分混沌键控进行调制, 两部分信号相加后发送到信道中进行传输。在接收端进行相关解调恢复出原信息。理论分析和仿真结果表明: 在多径衰落信道下, 该系统的误码率低于DCSK、CDSK和CD-DCSK系统, 且扩频因子越小, 误码率越低。信道中叠加服从高斯分布噪声时的系统误码率相比叠加服从瑞利分布噪声时的小。     

一种通用的复模态矩阵摄动法

对于非自伴随系统,提出了一种通用的复模态矩阵摄动法.该法能同时适用于孤立特征值,重特征值及密集(相近)特征值三种复特征值情况.由复特征子空间缩聚技术求解低阶摄动项,高阶摄动项则由逐次逼近过程求得.三个计算实例表明,该通用方法合理可靠,精度高.     

A Universal Matrix Perturbation Technique for Complex Modes

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Models with a Kronecker product covariance structure: Estimation and testing

In this article we consider a pq-dimensional random vector x distributed normally with mean vector θ and covariance matrix Λ assumed to be positive definite. On the basis of N independent observations on the random vector x, we want to estimate parameters and test the hypothesis H: Λ = Ψ ⊗ Σ, where Ψ = (ψ _ij ): q × q, ψ _qq = 1, and Σ = (σ _ij ): p × p, and Λ = (ψ _ij Σ), the Kronecker product of Ψ and Σ. That is instead of 1/2pq(pq + 1) parameters, it has only 1/2p(p + 1) + 1/2q(q + 1) − 1 parameters. A test based on the likelihood ratio is given to check if this model holds. And, when this model holds, we test the hypothesis that Ψ is a matrix with intraclass correlation structure. The maximum likelihood estimators (MLE) are obtained under the hypothesis as well as under the alternatives. Using these estimators the likelihood ratio tests (LRT) are obtained. One of the main objects of the paper is to show that the likelihood equations provide unique estimators.      

Fatigue strength of metals and composites under repeated high-cycle torsion

The limiting stresses are determined and constant fatigue life diagrams for high-cycle torsion with repeated stress cycle are plotted using the limiting-state models obtained based on the hypothesis of a unified constant-life diagram, which is invariant to the number of cycles to failure. The unified constant-life diagram is given by a transcendental power function whose exponent is an additional parameter characterizing the sensitivity of the material to the asymmetry of the stress cycle. The calculated results and experimental data for carbon and alloyed steels and composite materials are in good agreement __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 2, pp. 19–28, February 2008.     

多项式的重根判别式和代数基本定理的简证

运用齐次线性方程组的理论研究实数域上多项式根的问题,给出了n次实系数多项式在复数域上存在某种特殊非零重根的判别公式,同时给出了代数基本定理的一个简洁的代数证明.     

Single vehicle routing problems with a predefined customer sequence, compartmentalized load and stochastic demands

We consider the problem of finding the optimal routing of a single vehicle that delivers K different products to N customers according to a particular customer order. The demands of the customers for each product are assumed to be random variables with known distributions. Each product type is stored in its dedicated compartment in the vehicle. Using a suitable dynamic programming algorithm we find the policy that satisfies the demands of the customers with the minimum total expected cost. We also prove that this policy has a specific threshold-type structure. Furthermore, we investigate a corresponding infinite-time horizon problem in which the service of the customers does not stop when the last customer has been serviced but it continues indefinitely with the same customer order. It is assumed that the demands of the customers at different tours have the same distributions. It is shown that the discounted-cost optimal policy and the average-cost optimal policy have the same threshold-type structure as the optimal policy in the original problem. The theoretical results are illustrated by numerical examples.     

常重复合码的构造和界

摘要给出了一种Chebyshev距离下的常重复合码的构造,并在其基础上讨论了它的译码算法和优化处理.考虑了Chebyshev距离下的界及其改进.研究了具有Chebyshev距离和Hamming距离的常重复合码的构造,给出了Hamming距离为4的常重复合码的一个结论.