寿命分布NBUE性质的一个新刻画及应用

本文介绍绝对连续型NBUE寿命分布的一个新的刻画：一个寿命分布具有NBUE性当且仅当它随机地大于具有相应的平衡分布的随机变量。讨论了此刻画在可靠性与寿命检验中的应用，并建立了严格NBUE性的一个非参数检验方法。     

Comparison of hypothesis testing techniques for markov processes estimated from micro versus macro data

We estimate the parameters of a Markov chain model using two types of simulated data: micro, or actual interstate transition counts, and macro aggregate frequency. We compare, by means of Monte Carlo experiments, the validity and power for micro likelihood ratio tests with their macro counterparts, previously developed by the authors to complement standard least-squares point estimates. We consider five specific null hypotheses, including parameter stationarity, entity homogeneity, a zero-order process, a specified probability value, and equal diagonal probabilities. The results from these micro-macro comparisons should help to indicate whether micro panel data collection is justified over the use of simpler state frequency counts.     

基于无线通信基站的室内三维定位问题研究

对基于无线通信基站的室内三维定位问题进行了研究,建立了测量误差模型和终端定位模型.建立了TOA测量误差模型和基于测量误差估计的终端定位模型,提出了基于空间几何约束和测量噪声抑制的定位算法;分别在相对时间误差、最大时延、最小时延和随机法四种基站筛选方案下,分析了不同基站数目对定位精度的影响;利用轨迹上相近点的信道状态信息的相关性,采用Kalman滤波算法计算了终端运动轨迹;基于假设性检验,通过递减迭代搜索算法,得到了可定位终端数;建立了基站不同覆盖范围下,终端连接度数与定位精度之间关系的分析模型.     

PERSISTENCE AND EXTINCTION OF A STOCHASTIC SIS EPIDEMIC MODEL WITH DOUBLE EPIDEMIC HYPOTHESIS

In this paper, we aim at dynamical behaviors of a stochastic SIS epidemic model with double epidemic hypothesis. Sufficient conditions for the extinction and persistence in mean are derived via constructing suitable functions. We obtain a threshold of stochastic SIS epidemic model, which determines how the diseases spread when the white noises are small. Numerical simulations are used to illustrate the efficiency of the main results of this article.     

Estimation and detection of high-variable functions from Sloan—Woźniakowski space

The major difficulty arising in statistics of multi-variable functions is “the curse of dimensionality”: the rates of accuracy in estimation and separation rates in detection problems behave poorly when the number of variables increases. This difficulty arises for most popular functional classes such as Sobolev or Hölder balls.In this paper we consider functional classes of a new type, first introduced by Sloan and Wo?niakowski in 1998. We consider balls F _σ,s in a “Sloan—Wo?niakowski” or “weighted Sobolev” space characterized by two parameters: σ > 0 is a “smoothness” parameter, and s > 0 determines the weight sequence which describes “importance” of the variables. Previously Kuo and Sloan [18] used the spaces of similar structure to address the problem of numerical integration.For the classes F _σ,s we show that in the white Gaussian noise model, the separation rates in detection are similar to those for one-variable functions of smoothness σ* = min(s,σ) regardless of the original problem dimension; thus the curse of dimensionality is “lifted”. Similar results hold for the estimation problem.The studies are based on known results for estimation and detection problems for ellipsoids. Using these results, the asymptotics in the problems are determined by asymptotics of “distribution of coefficients” of ellipsoids. The key point of the paper is the study of these asymptotics for the balls F _σ,s .     

Flame propagation in a small-scale parallel flow

We consider the propagation of laminar premixed flames in the presence of a parallel flow whose scale is smaller than the laminar flame thickness. The study addresses fundamental aspects with relevance to flame propagation in narrow channels, to the emerging micro-combustion technology, and to the understanding of the effect of small scales in a (turbulent) flow on the flame structure. In part, the study extends the results of a previous analytical study carried out in the thick flame asymptotic limit which has in particular addressed the validity of Damköhler's second hypothesis in the context of laminar steady parallel flows. Several new contributions are made here.

Analytical contributions include the derivation of an explicit formula for the effective speed of a premixed flame U _T in the presence of an oscillatory parallel flow whose scale ? (measured with the laminar flame thickness δ _L ) is small and amplitude A (measured with the laminar flame speed U _L ) is (1). The formula shows a quadratic dependence on both the amplitude and the scale of the flow. The validity of the formula is established analytically in two distinguished limits corresponding to (1) frequencies of oscillations (measured with the natural frequency of the flame U _L /δ _L ), and to higher frequencies of (A/?) (the natural frequency of the flow). The analytical study yields partial support of Damköhler's second hypothesis in that it shows that the flame behaves as a planar flame (to leading order) with an increased propagation speed which depends on both the scale and amplitude of the velocity fluctuation. However our formula for U _T contradicts the formula given by Damköhler in his original paper where U _T has a square root dependence on the scale and amplitude.

Numerical contributions include a significant set of two-dimensional calculations which determine the range of validity of the asymptotic findings. In particular, these account for volumetric heat loss and differential diffusion effects. Good agreement between the numerics and asymptotics is found in all cases, both for steady and oscillatory flows, at least in the expected range of validity of the asymptotics. The effect of the frequency of oscillation is also discussed. Additional related aspects such as the difference in the response of thin and thick flames to the combined effect of heat loss and fluid flow are also addressed. It is found for example that the sensitivity of thick flames to volumetric heat loss is negligibly affected by the parallel flow intensity, in marked contrast to the sensitivity of thin flames. Interestingly, and somewhat surprisingly, thin flames are found to be more resistant to heat loss when a flow is present, even for unit Lewis number; this ceases to be the case, however, when the Lewis number is large enough.     

Complementation and decompositions in some weakly Lindelöf Banach spaces

Let Γ denote an uncountable set. We consider the questions if a Banach space X of the form C(K) of a given class (1) has a complemented copy of c₀(Γ) or (2) for every c₀(Γ)⊆X has a complemented c₀(E) for an uncountable E⊆Γ or (3) has a decomposition X=A⊕B where both A and B are nonseparable. The results concern a superclass of the class of nonmetrizable Eberlein compacts, namely Ks such that C(K) is Lindelöf in the weak topology and we restrict our attention to Ks scattered of countable height. We show that the answers to all these questions for these C(K)s depend on additional combinatorial axioms which are independent of ZFC ± CH. If we assume the P-ideal dichotomy, for every c₀(Γ)⊆C(K) there is a complemented c₀(E) for an uncountable E⊆Γ, which yields the positive answer to the remaining questions. If we assume ♣, then we construct a nonseparable weakly Lindelöf C(K) for K of height ω+1 where every operator is of the form cI+S for c∈R and S with separable range and conclude from this that there are no decompositions as above which yields the negative answer to all the above questions. Since, in the case of a scattered compact K, the weak topology on C(K) and the pointwise convergence topology coincide on bounded sets, and so the Lindelöf properties of these two topologies are equivalent, many results concern also the space Cp(K).     

Accounting of ligand–receptor interactions to explore and design novel architecture for PTP 1B inhibition: a legitimate approach

Computer‐aided drug design was performed on a diverse set of 103 biphenyl derivatives that demonstrated antidiabetic activity by restraining the protein tyrosine phosphatase 1B (PTP 1B) receptor. A four‐point pharmacophore hypothesis using the PHASE module of Schrödinger suite with one hydrogen bond acceptor (A) and three aromatic rings (R) as pharmacophoric features was generated. The hypothesis, ARRR.2, considered the best hypothesis in the present study is characterized by survival score (3.553), cross‐validated r² (Q²) (0.722), regression coefficient (0.949), Pearson R (0.867), and F value (492.6). The developed pharmacophore model was externally validated by predicting the activity of test set molecules. Docking algorithm combined with the drug–receptor binding free energetic and pharmacokinetic drug profile envisaged a novel concept, which may provide structural insights for the development of potential PTP 1B inhibitors. The study also provided a valid rapport between pharmacophore drug mapping, atom‐based three‐dimensional quantitative structure–activity relationship, molecular docking, sitemap, molecular simulations, and pharmacokinetic prediction approaches demonstrating the trends in activity. The results of these ligand–receptor relationship studies may account to design a legitimate template for the development and optimization of highly selective and potent PTP 1B inhibitors. Copyright © 2012 John Wiley & Sons, Ltd.     

Are the native states of proteins kinetic traps?

Four proteins were selected to represent each of the four different CATH classes and, for each protein, three decoys were constructed with structures totally alien to the native state. The decoys were scored against the native state with the help of the AMBER force field, using three measures: the average energy, the average fluctuation and the resistance to a heat pulse. Two sets of simulations were performed, one with explicit solvent and the other with implicit solvent. The overall conclusion is that, of these three measures, the most successful in picking out the native states was the last one, since the native structures take a consistently longer time to be destabilized in this manner. However, the general conclusion is also that none of the measures is completely effective in discriminating all the decoys, a result that supports other studies, according to which the native state is reached by a kinetic step.     

On the Weyl curvature hypothesis

The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity.