Inference for step-stress accelerated life tests

In this paper we consider the more realistic aspect of accelerated life testing wherein the stress on an unfailed item is allowed to increase at a preassigned test time. Such tests are known as step-stress tests. Our approach is nonparametric in that we do not make any assumptions about the underlying distribution of life lengths. We introduce a model for step-stress testing which is based on the ideas of shock models and of wear processes. This model unifies and generalizes two previously proposed models for step-stress testing. We propose an estimator for the life distribution under use conditions stress and show that this estimator is strongly consistent.     

从配价理论看“N1是AV的N2”结构的歧义生成

从以往研究中可以发现,“N1是AV的N2”结构有些时候会存在歧义现象。以配价理论为基础,论证这类句子歧义的生成大多是由两种原因造成：一种是由于中心动词和与其共现的配价名词之间出现了复杂的语义关系;另一种是由于中心动词和隐省的配价名词之间出现了复杂的语义关系。     

超薄N6镍板焊接焊缝成形质量研究

当镍及镍基合金板材厚度小于l mm时,在焊接过程中容易出现烧穿、气孔和裂纹等缺陷,严重影响了焊接成形 质量。针对超薄镍及镍基合金的特殊性以及在焊接过程中易出现的问题,采用脉冲微束等离子弧方法焊接0.1 mm厚薄 镍板。文中分析了在一定占空比下,不同脉冲频率和不同基脉比对超薄N6镍板的焊缝成形质量的影响,得到合适的焊 接工艺参数。研究结果表明当基脉比为0.4,脉冲频率为500 Hz时,超薄N6板焊缝成形质量最好。通过该研究成功实 现了0.1 mm厚超薄N6的脉冲微束等离子弧焊接。     

Relative risk regression for current status data in case‐cohort studies

We propose using the weighted likelihood method to fit a general relative risk regression model for the current status data with missing data as arise, for example, in case‐cohort studies. The missingness probability is either known or can be reasonably estimated. Asymptotic properties of the weighted likelihood estimators are established. For the case of using estimated weights, we construct a general theorem that guarantees the asymptotic normality of the M‐estimator of a finite dimensional parameter in a class of semiparametric models, where the infinite dimensional parameter is allowed to converge at a slower than parametric rate, and some other parameters in the objective function are estimated a priori. The weighted bootstrap method is employed to estimate the variances. Simulations show that the proposed method works well for finite sample sizes. A motivating example of the case‐cohort study from an HIV vaccine trial is used to demonstrate the proposed method. The Canadian Journal of Statistics 39: 557–577; 2011. © 2011 Statistical Society of Canada     

Representations of moments using lower-order conditional moments

Moments and central moments of a random variable X   are expressed as integrals of functions of lower-order conditional moments and the cumulative distribution of X$X$. In particular, sample central moments of order 2k$2k$ are expressed as the sum of between groups variations, providing an analogue to the analysis of variance. Similar expressions are obtained for the expectations of real-valued and measurable functions of X$X$.     

The two-sample -test with a known ratio of variances

We consider the two-sample t-test where error variances are unknown but with known relationships between them. This situation arises, for example, when two measuring instruments average different number of replicates to report the response. In particular we compare our procedure with the usual Satterthwaite approximation in the two sample t-test with variances unequal. Our procedure uses the knowledge of a known ratio of variances while the Satterthwaite approximation assumes only that the two variances are unequal. Simulations show that our procedure has both better size and better power than the Satterthwaite approximation. Finally, we consider an extension of our results to the General Linear Model.     

Estimating the Lyapunov exponent from chaotic time series with dynamic noise

In this paper, we propose an estimator of the Lyapunov exponent of the skeleton for chaotic time series with dynamic noise and prove the consistency of the estimator under some assumptions.     

基于旋转变压器及TMS320F28035的伺服系统位置检测

为检测伺服系统位置信息,以旋转变压器作为位置传感器,设计了基于芯片AU6802N1的位置检测电路并在此基础上提出了一种仅利用TMS320F28035对旋转变压器转子位置直接解算的方法。该方法综合运用正弦峰值采样、CLA浮点数计算、误差校正等手段。实验表明,该方法在位置解算的速度和精度上可与AU6802N1芯片相比,节约了系统成本,具有一定的实用性。     

Semiparametric inference for survival models with step process covariates

The authors consider Bayesian methods for fitting three semiparametric survival models, incorporating time‐dependent covariates that are step functions. In particular, these are models due to Cox [Cox ( 1972 ) Journal of the Royal Statistical Society, Series B, 34, 187–208], Prentice & Kalbfleisch and Cox & Oakes [Cox & Oakes ( 1984 ) Analysis of Survival Data, Chapman and Hall, London]. The model due to Prentice & Kalbfleisch [Prentice & Kalbfleisch ( 1979 ) Biometrics, 35, 25–39], which has seen very limited use, is given particular consideration. The prior for the baseline distribution in each model is taken to be a mixture of Polya trees and posterior inference is obtained through standard Markov chain Monte Carlo methods. They demonstrate the implementation and comparison of these three models on the celebrated Stanford heart transplant data and the study of the timing of cerebral edema diagnosis during emergency room treatment of diabetic ketoacidosis in children. An important feature of their overall discussion is the comparison of semi‐parametric families, and ultimate criterion based selection of a family within the context of a given data set. The Canadian Journal of Statistics 37: 60–79; © 2009 Statistical Society of Canada     

Log‐rank permutation tests for trend: saddlepoint p‐values and survival rate confidence intervals

Suppose p + 1 experimental groups correspond to increasing dose levels of a treatment and all groups are subject to right censoring. In such instances, permutation tests for trend can be performed based on statistics derived from the weighted log‐rank class. This article uses saddlepoint methods to determine the mid‐P‐values for such permutation tests for any test statistic in the weighted log‐rank class. Permutation simulations are replaced by analytical saddlepoint computations which provide extremely accurate mid‐P‐values that are exact for most practical purposes and almost always more accurate than normal approximations. The speed of mid‐P‐value computation allows for the inversion of such tests to determine confidence intervals for the percentage increase in mean (or median) survival time per unit increase in dosage. The Canadian Journal of Statistics 37: 5‐16; 2009 © 2009 Statistical Society of Canada