增长曲线模型（一般协方差结构）的Bayes影响分析

本文讨论具有一般协方差结构的增长曲线模型中未知参数矩阵的Ｂａｙｅｓ影响分析问题．在无信息先验分布假设下,Ｋ－Ｌ距离被用来评估指定响应阵对参数矩阵的后验分布的影响程度．     

Numerical Aspects in Estimating the Parameters of a Mixture of Normal Distributions

Abstract

Mixtures of normal distributions arise naturally in robustness analyses when distributional assumptions are not met and with the analysis of contaminated data. Typically these analyses involve substantial computational problems. We present some simulation procedures that address these difficulties.     

MRI检查无责任病灶脑后循环缺血患者的CT灌注成像研究

目的探讨MRI检查显示无责任病灶的脑后循环缺血(PCI)患者的局部脑血流灌注情况,探索PCI患者早期诊断的有效方法.方法选取符合PCI临床诊断的24例患者行头颅MRI检查,对未发现责任病灶的患者进一步行CT灌注成像(CTPI)检查.在CTPI图像上手绘感兴趣区域(ROI),记录病灶区与对照区的灌注参数,包括局部脑血流量(rCBF)、局部脑血容量(rCBV)、平均通过时间(MTT)和达峰时间(TTP).结果 CTPI检查发现异常灌注18例(阳性率75%),缺血灶共26处,其中小脑10处(38.5%),枕叶7处(26.9%),颞叶3处(11.5%),脑干6处(23.1%).TTP发现异常15例,且均与临床症状相对应,rCBF发现异常13例,rCBV发现异常8例.脑梗死前期分期:玉1期4例,玉2期1例,域1期5例,域2期8例.病灶区的rCBF、rCBV、MTT及TTP与对照区相比较,差异均有统计学意义(P<0.01或0.05).结论 CTPI检查通过对PCI患者进行ROI半定量分析,可客观评价脑后循环脑血流灌注情况,发现头颅MRI检查所未能发现的缺血灶,为临床诊治PCI提供依据.     

Consistency of spike and slab regression

Spike and slab models are a popular and attractive variable selection approach in regression settings. Applications for these models have blossomed over the last decade and they are increasingly being used in challenging problems. At the same time, theory for spike and slab models has not kept pace with the applications. There are many gaps in what we know about their theoretical properties. An important property known to hold in these models is selective shrinkage: a unique property whereby the posterior mean is shrunk toward zero for non-informative variables only. This property has been shown to hold under orthogonality for continuous priors under the modified class of rescaled spike and slab models. In this paper, we extend this result to the general case and prove an oracle property for the posterior mean under a discrete two-component prior. An immediate consequence is that a strong selective shrinkage property holds. Interestingly, the conditions needed for our result to hold in the non-orthogonal setting are more stringent than in the orthogonal case and amount to a type of enforced sparsity condition that must be met by the prior.     

A posterior preference articulation approach to multiresponse surface optimization

In multiresponse surface optimization (MRSO), responses are often in conflict. To obtain a satisfactory compromise, the preference information of a decision maker (DM) on the tradeoffs among the responses should be incorporated into the problem. In most existing work, the DM expresses a subjective judgment on the responses through a preference parameter before the problem-solving process, after which a single solution is obtained. In this study, we propose a posterior preference articulation approach to MRSO. The approach initially finds a set of nondominated solutions without the DM’s preference information, and then allows the DM to select the best solution from among the nondominated solutions. An interactive selection method based on pairwise comparisons made by the DM is adopted in our method to facilitate the DM’s selection process. The proposed method does not require that the preference information be specified in advance. It is easy and effective in that a satisfactory compromise can be obtained through a series of pairwise comparisons, regardless of the type of the DM’s utility function.     

Skew normal measurement error models

In this paper we define a class of skew normal measurement error models, extending usual symmetric normal models in order to avoid data transformation. The likelihood function of the observed data is obtained, which can be maximized by using existing statistical software. Inference on the parameters of interest can be approached by using the observed information matrix, which can also be computed by using existing statistical software, such as the Ox program. Bayesian inference is also discussed for the family of asymmetric models in terms of invariance with respect to the symmetric normal distribution showing that early results obtained for the normal distribution also holds for the asymmetric family. Results of a simulation study and an analysis of a real data set analysis are provided.     

重力坝坝基沿软弱结构面滑动失稳的非线性机制

对于存在单组软弱结构面的坝基深层抗滑问题,考虑了坝基软弱结构面介质在不同环境因素条件下的复杂弹脆性(应变硬化)和应变软化属性,用突变论建立了坝基沿单软弱结构面滑动的尖点突变模型。通过建立的模型分析,发现坝基滑动失稳主要取决于软弱面上复杂弹脆性介质和应变软化介质在应变软化拐点处的刚度比k、材料的均匀性指标m及几何—力学参数ξ;并给出了发生突变失稳的充分力学判据,指出传统的刚体极限平衡分析法存在一定的缺陷。指出库水水位上升还存在一种降低介质材料刚度比k的新机制,从理论上阐明,坝基滑动突变失稳的发生相应于水位峰值,在时间上可能具有滞后性;而工程处理措施的实施除提高坝基软弱结构面抗滑能力外,还具有一种增大材料刚度比k的新效应,使得滑动失稳更不易发生。     

Glottal closure, transglottal airflow, and voice quality in healthy middle-aged women

Seventeen healthy women, 45 to 61 years old, were examined using videofiberstroboscopy during phonation at three loudness levels. Two phoniatricians evaluated glottal closure using category and ratio scales. Transglottal airflow was studied by inverse filtering of the oral airflow signal recorded in a flow mask (Glottal Enterprises System) during the spoken phrase /ba:pa:pa:pa:p/ at three loudness levels. Subglottal pressure was estimated from the intraoral pressure during p occlusion. Running speech and the repeated /pa:/ syllables were perceptually evaluated by three speech pathologists regarding breathiness, hypo-, and hyperfunction, using continuous scales. Incomplete glottal closure was found in 35 of 46 phonations (76%). The degree of glottal closure increased significantly with raised loudness. Half of the women closed the glottis completely during loud phonation. Posterior glottal chink (PGC) was the most common gap configuration and was found in 28 of 46 phonations (61%). One third of the PGCs were in the cartilaginous glottis (PGCc) only. Two thirds extended into the membranous portion (PGCm); most of these occurred during soft phonation. Peak flow, peak-to-peak (AC) flow, and the maximum rate of change for the flow in the closing phase increased significantly with raised loudness. Minimum flow decreased significantly from normal to loud voice. Breathiness decreased with increased loudness. The results suggest that the incomplete closure patterns PGCc and PGCm during soft phonation ought primarily to be regarded as normal for Swedish women in this age group.