基于时频分析的裂纹转子碰摩故障特征研究

为研究转子系统耦合故障特性,采用有限元方法建立了含有横向裂纹、转静碰摩的非线性转子动力学模型。首先研究了不同转速下裂纹、碰摩单一故障下转子系统的振动响应,其次研究了两种故障耦合情况下系统的振动响应特征。采用波形图、FFT谱图、瞬时频率和Hilbert-Huang时频谱(HHS)相结合的方法对故障转子振动信号进行了分析。分析结果表明:运用多种时频分析相结合的方法可以较为全面地了解转子的故障特征,裂纹转子在1/5、1/3临界转速时会发生较为明显的5X、3X谐波,且裂纹的产生会导致响应幅值增大,从而引起更为严重的碰摩。      

加速平动非惯性系中单摆的周期公式

本文从加速平动非惯性系中质点的动力学方程出发，导出了这种参照系中单摆周期的一般计算公式．     

论《爵士乐》的后现代身份叙事

《爵士乐》中“痕迹”与“裂缝”的双重意象揭示了白人文化冲击下黑人身份的错位与缺失。在对黑人身份进行重新建构的过程中,作者莫里森将爵士乐即兴变奏的特点变为文本的一种叙事策略,凸显了后工业社会中个体身份的流动性和不确定性,也为少数族裔在面临被边缘化的危机中实现自身独特的身份认同指出了一条可行性道路。     

中国农民工城市居留形态塑造机制审视——评《在中国城市中争取公民权:农民工、国家与市场逻辑》

美国学者苏黛瑞的《在中国城市中争取公民权:农民工、国家与市场逻辑》一书,以公民权为切入点,揭示了在国家计划体制、市场与农村流动人口三方动态博弈过程中,农民工的流动路径、其城市居留形态的塑造及城市生存策略。作为一本美籍学者对当代中国流动人口的研究论著,对国内学界而言,其价值在于不仅提供了农民工研究的新视角,而且更新了流动人口的研究范式,对中国流动人口研究有相当的启发与借鉴意义。     

广西农村社会发展对出生人口性别的影响分析

人口性别结构失衡对社会稳定和可持续发展都有不利的影响.相对城镇而言,广西上世纪80年代以来农村出生人口性别结构失调尤为严重.占人口多数的农村是广西出生人口性别比失调的主要根源.要解决好农村的人口问题,除了认真落实计划生育政策外,还要改善农村的社会环境,包括提高农村人口的文化素质,促进农村经济的发展,这样才能使农村家庭从...     

裂纹扩展下J积分及施加撕裂模量的理论推导

Ｊ积分和施加撕裂模量是断裂力学中两个很重要的参量。本文根据Ｐａｒｉｓ的撕裂模量理论推导了裂纹扩展下Ｊ积分和施加撕裂模量的计算公式。     

CRACKED BABIES AND THE PARTIAL BIRTH OF A NATION: MILLENNIALISM AND FETAL CITIZENSHIP

This essay explores whether fetal protection cases concerning ‘partial birth’ and ‘crack babies’ reflect an undercurrent of millennialism that characterizes anti-abortion violence. Because the dichotomized millennialist worldview of pure and impure domains easily corroborates racialist ideas that there are pure and impure races, discussions of fetal protection may also accommodate race-specific assumptions or implications. Fetuses involved in ‘partial birth’ abortions are routinely portrayed as purely innocent, whole, and intact babies worthy of the privileges of citizenship that will save them from death. But ‘crack babies’, who are explicitly presumed to be black, are routinely portrayed as impure, tainted, and polluted babies who are a liability to society and from whom the tax-paying citizenry should be saved. Viewed comparatively, these legal disputes may be seen as unwittingly reinscribing the racialist tenets of far-right groups that consider abortion to be the apocalyptic end times of white America.     

A continuous latent spatial model for crack initiation in bone cement

Summary.  Hip replacements rovide a means of achieving a higher quality of life for individuals who have, through aging or injury, accumulated damage to their natural joints. This is a very common operation, with over a million people a year benefiting from the procedure. The replacements themselves fail mainly as a result of the mechanical loosening of the components of the artificial joint due to damage accumulation. This damage accumulation consists of the initiation and growth of cracks in the bone cement which is used to fixate the replacement in the human body. The data come from laboratory experiments that are designed to assess the effectiveness of the bone cement in resisting damage. We examine the properties of the bone cement, with the aim being to estimate the effect that both observable and unobservable spatially varying factors have on causing crack initiation. To do this, an explicit model for the damage process is constructed taking into account the tension and compression at different locations in the specimens. A gamma random field is used to model any latent spatial factors that may be influential in crack initiation. Bayesian inference is carried out for the parameters of this field and related covariates by using Markov chain Monte Carlo techniques.     

HIV risk behavior and drug use among heterosexual male crack users by prostitution involvement

Crack and prostitution, or sex exchange, have been linked to the heterosexual spread of HIV (e.g. Inciardi 1993, 1995). Previous studies have found that among female crack users there are subgroups who do and do not become involved in prostitution (e.g. Logan, Farabee & Leukefeld 1998; Logan & Leukefeld 1998). However, there has been little focus in the literature on subgroups of male heterosexual crack users who are or are not involved in prostitution. The purpose of this study was to examine differences in male heterosexual crack users who reported no involvement in prostitution as clients (n = 4,208), males who reported involvement in prostitution as clients but not in the month preceding the interview (n = 2,774), and males who reported involvement in prostitution as clients the month preceding the interview (n = 2,283) from a multi-site sample of male crack users who participated in the National Institute of Drug Abuse (NIDA) AIDS Cooperative Agreement Project from 20 sites across the nation. Results of the logistic regression indicated that having an STD three or more times and using drugs during sex were associated with ever being involved in prostitution as clients, while using drugs during sex and having 5 or more sexual partners the month preceding the interview were significantly associated with being involved in prostitution as clients at the time of the interview. Implications for interventions are discussed.     

盐水泥浆中碳钢的腐蚀疲劳断裂

钻井液中钻具因受到各种作用应力,加上井下高温高压的腐蚀环境,使其易发生腐蚀疲劳断裂。为探讨钻具的断裂过程以期能找到有效的防护措施,实验室内建立了模拟试验装置。针对盐水泥浆中45钢的腐蚀疲劳断裂行为,通过自制的旋转弯曲腐蚀疲劳试验机,模拟钻具的运转受力情况,研究了不同泥浆介质、应力、载荷频率和温度对45钢腐蚀疲劳断裂行为的影响,并结合动态腐蚀试验和断口分析,讨论了各影响因素的作用。结果表明,盐水泥浆的pH值、Cl-含量等对45钢的疲劳寿命有直接影响,腐蚀疲劳寿命与与局部腐蚀的程度大小有密切关系;随着加载频率的增大,45钢的腐蚀疲劳寿命有较大提高;在15~80℃温度范围内,45℃左右时45钢的腐蚀疲劳寿命最短。