Likelihood inference for lognormal data with left truncation and right censoring with an illustration

The lognormal distribution is quite commonly used as a lifetime distribution. Data arising from life-testing and reliability studies are often left truncated and right censored. Here, the EM algorithm is used to estimate the parameters of the lognormal model based on left truncated and right censored data. The maximization step of the algorithm is carried out by two alternative methods, with one involving approximation using Taylor series expansion (leading to approximate maximum likelihood estimate) and the other based on the EM gradient algorithm (Lange, 1995). These two methods are compared based on Monte Carlo simulations. The Fisher scoring method for obtaining the maximum likelihood estimates shows a problem of convergence under this setup, except when the truncation percentage is small. The asymptotic variance-covariance matrix of the MLEs is derived by using the missing information principle (Louis, 1982), and then the asymptotic confidence intervals for scale and shape parameters are obtained and compared with corresponding bootstrap confidence intervals. Finally, some numerical examples are given to illustrate all the methods of inference developed here.     

Impact of dependent left truncation in semiparametric competing risks methods: A simulation study

In this study, we investigated the robustness of the methods that account for independent left truncation when applied to competing risks settings with dependent left truncation. We specifically focused on the methods for the proportional cause-specific hazards model and the Fine–Gray model. Simulation experiments showed that these methods are not in general robust against dependent left truncation. The magnitude of the bias was analogous to the strength of the association between left truncation and failure times, the effect of the covariate on the competing cause of failure, and the baseline hazard of left truncation time.     

浅议农村留守老人养老问题

农村留守老人养老问题已成为学术界的一个研究热点。本文从研究农村留守老人养老的意义出发,着重分析了造成农村留守老人养老困难的原因,以及提出解决农村留守老人养老问题的建议。本文认为传统家庭养老功能的衰弱、农村社会保障机制不健全、老人负担增加、老人孤独感增强和他们自身一些问题等五个方面是农村留守老人养老的主要困难。     

Evolution and physiological consequences of de-alation in crickets

Wing shedding or de-alation is a common phenomenon among crickets. Its significance and effects on other traits were examined based on the results from experiments using artifical or natural de-alation. Artificial de-alation at adult emergence induces rapid egg production and flight muscle histolysis in several species examined. However, natural de-alation does not always shorten the pre-ovipositional period because it does not occur immediately after adult emergence and because oviposition starts before de-alation. In some cases, naturally de-alated females produce more eggs than to intact females during early adult life, but peak ovipositing activity occurs before de-alation. Therefore, retention of the hindwings does not suppress high ovipositing activity in such cases. It appears that de-alation is a result rather than a causal factor in ending migration. Ovarian development and flight muscle histolysis, which can be stimulated by de-alation, are controlled by the jevenile hormone, but the mechanism inducing de-alation remains unknown. The possible factors leading to the evolution of de-alation are discussed.     

英国新左派运动及其当代审视——迈克尔·肯尼教授访谈录

英国新左派运动发端于1956年,随后在20世纪60年代中期发生分裂,退化为一个团结在《新左派评论》杂志周围的知识分子小团体,并在20世纪70年代以后走向终结。虽然作为政治运动的新左派历时短暂,但它仍为当代英国政治留下了一些重要的间接遗产。20世纪90年代初期以来,对新左派历史的研究日渐兴起。     

后选举权初期美国右翼妇女参政研究——社会性别之视角

依据传统社会性别,美国妇女的社会身份是贤妻良母,参与政治活动的权利极其有限。选举权实质性拓展了妇女群体的参政空间,右翼妇女自然包括其中。在罗斯福“新政”和二战期间,右翼妇女以反共、反犹、反“新政”、倾纳粹为核心的思想极具时代特征。在上述思想驱动下,她们发起了声势浩大的反战运动,试图影响美国内政、外交政策的制定与实施。通过对右翼思想和反战行为的解读,可剖析右翼妇女参政对美国传统社会性别的颠覆与突破。     

从角色冲突视角看农村留守妻子

随着中国农民工族的日益壮大，农村留守妻子群体不断地扩张，她们所面临的一些问题也引起了人们的关注。本文主要从角色冲突的视角并结合案例分析以揭示我国农村留守妻子所承受的压力，而且提出了相应的对策和建议。     

小提琴学生音准能力的培养

音准是指我们唱出和拉出的音,要符合音响学原理的振动频率.有了音准概念,才有可能拉准音.要拉准音,要靠耳的听辩能力,手在琴上的触觉能力和迅速的纠错能力,三者相互配合才能做好.     

The physiological costs of flight capability in wing-dimorphic crickets

Nutritional indices, triglyceride levels and flight muscle developmental profiles were compared between long-winged (LW) and short-winged (SW; flightless) morphs of the cricketsGryllus rubens Scudder andG. firmus Scudder. This was done to identify potential physiological costs of flight capability in adults. The LW morph of each species converted a lower proportion of assimilated nutrients into biomass (reduced ECD) than did the SW morph. This documents increased respiratory metabolism in the LW morph. Triglyceride concentration was higher in LW vs. SW adults. This suggests that the elevated respiration in the LW morph may be at least partially due to the increased biosynthesis of this high energy substance. Preliminary data indicate higher respiration rates of LW functional vs. SW vestigial flight muscles. Collectively, these data suggest that the energetic cost of flight capability in adults results from biosynthesis of triglyceride flight fuel and flight muscle maintenance but not flight muscle growth. No flight muscle growth was observed in adults.     

CRITICAL EXPLORATIONS OF GENDER AND THE CARIBBEAN: TAKING IT INTO THE TWENTY-FIRST CENTURY

ABSTRACT

In the years after the Greek Junta, activists who had been involved in anti-dictatorship movements abroad returned as the country’s new pool of left-leaning, well-educated political actors. Drawing on interviews with former activists and borrowing from recent developments in cultural sociology, I analyse these returns as political projects fraught with moral conundrums. I argue that the contemporary crisis structure accounts of returns by placing speakers within what Boltanski and Thévenot call a ‘situation subject to the imperative of justification’. I make two arguments regarding the critiques and valuations used in accounts: First, the idealized political subject put forward by former activists promotes withdrawal over participation and silence over speech. Second, failure is valorized as a principled mode of self-exoneration. This article further demonstrates the importance of theorizing return migration within an ethnographic treatment of the present.