Momentum and the growth-free segment of a population

In the scenario of a sudden drop in fertility to replacement level. Preston (1986) argued that the population segment under age T, the length of generation, remained growth-free. Here we first present a new relationship for the momentum of any observed population as the ratio of 1) the proportion of the observed population under the mean age at childbearing to 2) the proportion of its life table population under that mean age. We then use that relationship to demonstrate Preston's approximation. Growth factors for other population segments are also presented. When the initial population is stable, momentum can be approximated as a function of the net reproduction rate alone.     

Peer influence and drug use among adolescents in rural areas

A sample of 1,004 eighth and tenth grade students in twenty-three small Central/East Texas communities was assessed to determine 1) their perception of the number of their friends who use drugs, 2) the amount of information they received about drugs from their friends, and 3) the connection between those perceptions and drug use. A multiple regression model which included grade, gender, the degree to which friends are perceived to use drugs and the amount of information about drugs received from friends explained 39 percent of the variance in the degree to which rural adolescents were involved in drug use. An item specific analysis of the subcomponents of these composite variables explained 44 percent of the variance in the degree to which rural adolescents were involved in drug use. This same four-factor model accurately classified over 81 percent of non-drug-users and 67 percent of users using discriminant analysis. Students who perceived a higher degree of drug use among their friends and who received more information about drugs from their friends used drugs more frequently. Lower marijuana use in these rural areas as compared to the nation, both as a peer perception and as a fact, may protect these students to a degree from broader patterns of drug use. The findings of this study support the theory that peer pressure is related to drug abuse, even in rural areas.     

Union survival strategies for the twenty-first century

Clearly, the necessary changes in the law and culture will not come easily or quickly. But, transcending all forms of these labor market segments is a set of concerns that arguably should spur a search for common ground between labor and management. The proliferation of automated technologies, together with the continuing impact of foreign competition with cheap labor markets, has led some to predict that, over the next quarter century, we will witness the elimination of the blue-collar, mass assembly-line worker from the production process.¹⁴ Moreover, the theory that those losing jobs in the manufacturing sector will be generally absorbed into the service sector is losing currency as it is becoming clear that service jobs are, themselves, not invulnerable either to offshore outsourcing (e.g., telephone operators, data processors) or to automated technology (e.g., bank tellers, office secretaries). Nor is it realistic to expect the new “knowledge sector” to absorb more than a fraction of the unemployed and underemployed casualties of this transformation. As a result, the widening gap between the haves and have nots will only continue to grow. As the trend accelerates, certain possibilities for a labor-management accommodation emerge. For one thing, although corporations may be enjoying short-term gains from present wage stagnation, downsizing, outsourcing, and casting off of permanent employees, the longer term effects include a work force with considerably diminished consumer purchasing power. In some industries, corporations are already acknowledging the adverse effects of this trend. Furthermore, as employers are contributing into pension funds on behalf of fewer and fewer “employees,” the forced savings pool that has for many years constituted a primary financing source of capital investments in our economy, will gradually be depleted.¹⁵ At the same time as employers are coming face to face with the disadvantages of the union-free environment they have so long sought, employers are also rediscovering the contributions to productivity, quality, and efficiency that can be gained from a truly empowered work force with an independent voice in the workplace. All of this should lead an enlightened management to place less currency on resisting unionization and other legitimate forms of independent employee representation, and to join labor in advocating strong labor standards and effective labor law for all four of the labor market segments that exist today and will exist tomorrow. The authors wish to convey their deep appreciation for the invaluable contributions to this paper made by David Silberman of Bredhoff & Kaiser and Craig Becker, Associate General Counsel, Service Employees International Union. Another version of this paper was published in Labor Lawyer.     

Recognition of overlap graphs

Overlap graphs occur in computational biology and computer science, and have applications in genome sequencing, string compression, and machine scheduling. Given two strings \(s_{i}\) and \(s_{j}\) , their overlap string is defined as the longest string \(v\) such that \(s_{i} = uv\) and \(s_{j} = vw\) , for some non empty strings \(u,w\) , and its length is called the overlap between these two strings. A weighted directed graph is an overlap graph if there exists a set of strings with one-to-one correspondence to the vertices of the graph, such that each arc weight in the graph equals the overlap between the corresponding strings. In this paper, we characterize the class of overlap graphs, and we present a polynomial time recognition algorithm as a direct consequence. Given a weighted directed graph \(G\) , the algorithm constructs a set of strings that has \(G\) as its overlap graph, or decides that this is not possible.     

《阿Q正传》与《祝福》的整合意义

鲁迅小说的代表作《阿Q正传》和《祝福》的一个重要文学成就表现为两者是完美的合璧之作。小说中的主人公阿Q与祥林嫂分别是封建社会男性民众和女性民众的代表人物 ,两者交相辉映 ,具有整合封建社会民众生存状态本质和民众国民性本质的意义 ,开掘出鲁迅小说社会批判的深刻内涵     

我国实施项目资产证券化的可行性与影响因素

加入WTO意味着我国经济将更大程度地开放 ,在我国金融体系与国际接轨的过程中 ,资产证券化必然会成为金融改革深化的一个方向。我国发展资产证券化过程中 ,贷款项目、现实基础、信息交换等已具备一定的条件。但发展资产证券化要求一定制度基础和市场环境的全面支持 ,对信用支撑、法律建设、税收和会计制度、中介服务机构、有效灵活的监管、市场环境和人力资源以及技术水平等有较高的要求。由于我国在这方面尚未广泛进行实践 ,因此亟需建设完善的制度环境 ,消除资产证券化的障碍。该文着重对实施项目贷款证券化的可行性和影响因素进行了讨论     

History of sexual abuse and parental alcohol misuse: Risk,outcomes and protective factors in adolescents

This study examined the school performance, suicidal involvement, disordered eating behaviors, pregnancy risk and chemical use of teenagers with a history of sexual abuse or parental alcohol misuse and found that they had higher rates of these adverse outcomes than among a comparison group of teenagers without such background risk factors. Adolescents with dual-risk background reported higher levels of suicide risk, disordered eating, sexual behaviors and chemical abuse than teenagers with only one background risk factor. Among index group members, protective factors against these adverse outcomes included a high degree of religiosity and the ability to discuss problems with family or friends. Risk factors that increased the likelihood of adverse outcomes included depression, perceived substance use in school and worries about family financial security.The first author was supported in the preparation of this article by a grant from the Lois and Samuel Silberman Fund of New York.     

An Experimental Analysis of Children's Dislike of Aggressors and Victims

We experimentally examined social contextual factors that might moderate children's dislike for aggressors and for victims of aggression, by varying both the aggressor's behavior (aggressive toward multiple children versus aggressive only toward one child) and the victim's behavior (passive versus assertive). Children (117 male and female fourth to sixth graders) listened to one of four scenarios describing the experiences of boys at a summer camp and rated how much they liked the aggressor, the victim, and the other children in the scenario; children also reported how much they thought the aggressor, victim, and others liked each other. Overall, and consistent with previous research, children disliked aggressors the most, followed by victims and then by the other children in the scenarios. Importantly, children's liking was influenced by the social context in which the aggression occurred, particularly in regards to how the victim responded. Aggressors (general or focused) were liked more if their victim was assertive rather than nonassertive. Furthermore, children liked nonassertive victims less than assertive victims, particularly a nonassertive victim in response to a general aggressor. Inferred liking among the group members also was dependent on the social context of the provocation. This research highlights the need to consider aggression as more than a set of behaviors. Aggression is a social event embedded within a social context and interpersonal relationships must be considered.     

Estimation of long-term trends and variation in avian survival probabilities using random effects models

We obtained banding and recovery data from the Bird Banding Laboratory (operated by the Biological Resources Division of the US Geological Survey) for adults from 129 avian species that had been continuously banded for > 24 years. Data were partitioned by gender, banding period (winter versus summer), and by states/provinces. Data sets were initially screened for adequacy based on specific criteria (e.g. minimum sample sizes). Fifty-nine data sets (11 waterfowl species, the Mourning Dove and Common Grackle) met our criteria of adequacy for further analysis. We estimated annual survival probabilities using the Brownie et al. recovery model {St, ft} in program MARK. Trends in annual survival and temporal process variation were estimated using random effects models based on shrinkage estimators. Waterfowl species had relatively little variation in annual survival probabilities (mean CV = 8.7% and 10% for males and females, respectively). The limited data for other species suggested similar low temporal variation for males, but higher temporal variation for females (CV = 40%). Evidence for long-term trends varied by species, banding period and sex, with no obvious spatial patterns for either positive or negative trends in survival probabilities. An exception was Mourning Doves banded in Illinois/Missouri and Arizona/New Mexico where both males (slope = -0.0122, se = 0.0019 and females (slope = -0.0109 to -0.0128, se = 0.0018 -0.0032) exhibited declining trends in survival probabilities. We believe our approach has application for large-scale monitoring. However, meaningful banding and recovery data for species other than waterfowl is very limited in North America.