Suchergebnisse

Fewer young adults are engaging in casual sexual intercourse now than in the past, but the reasons for this decline are unknown. The authors use data from the 2007 through 2017 waves of the Panel Study of Income Dynamics Transition into Adulthood Supplement to quantify some of the proximate sources of the decline in the likelihood that unpartnered young adults ages 18 to 23 have recently had sexual intercourse. Among young women, the decline in the frequency of drinking alcohol explains about one quarter of the drop in the propensity to have casual sex. Among young men, declines in drinking frequency, an increase in computer gaming, and the growing percentage who coreside with their parents all contribute significantly to the decline in casual sex. The authors find no evidence that trends in young adults' economic circumstances, internet use, or television watching explain the recent decline in casual sexual activity.

ABSTRACTIn this paper, we consider the problem of generating a random vector whose joint distribution is characterized by a copula function and their marginal distribution functions. We propose a sequential acceptance‐rejection method, which avoids the inversion of both marginal distributions and conditional distributions of the copula function which are needed in traditional generation methods. In our method, we first generate samples based on the marginal distributions and then use an acceptance‐rejection procedure to construct samples with the desired dependence structure. The method is also applicable in generating time series random variables. We prove that the computational cost of our method only grows linearly to their dimensionality for several types of copulas. Finally, we provide extensive numerical experiments which show our method is quite efficient in comparison with traditional methods.

This bibliometric study examined the development of research on the learning and teaching of second language (L2) listening from 1948 to 2020 (73 years). Specifically, the study involved: (1) a search and analysis of all the noun phrases to identify important research topics in the abstracts of the published journal articles on L2 listening over the 73 years (divided into three periods) using self-made Python scripts and (2) three co-citation analyses of the references in these articles regarding highly cited authors, publications, and journals, respectively, via the VOSviewer program. The keyword/phrase analysis produced results that helped uncover and delineate the research trends in L2 listening across the three time periods. The co-citation analyses identified the most highly cited authors, publications, and journals as well as the interrelations among the most highly cited items in each of the three categories illustrated with network maps. The results of the analyses and their implications are discussed.

This paper uses China Health and Nutrition Survey (CHNS) data to analyze the effect of foreign direct investment (FDI) on nutrient intakes across various family roles to identify the different family roles' heterogeneous nutrition intake responses to economic openness. The empirical evidence shows that FDI enhances labor forces' calorie intake significantly, especially for rural households. The government should continue facilitating more FDI inflows, especially FDI in secondary industries for rural populations. However, the larger the family, the smaller the effect of FDI on nutrient intake for some family roles. The elderly and children may be weaker responders on nutrient intake than other family members in an open economy. This implies the existence of intra-household redistribution and that the level of effectiveness will decrease with family size. The results suggest that family members in rural areas can benefit more in terms of nutrient intake. Our empirical evidence also indicates that female family members' calorie intake from the FDI effect is higher than that of male family members (except for the granddaughter/grandson). Preferential policies should be provided for the FDI, flowing to rural areas and female dominant industries.

AbstractWe consider a parallel‐machine scheduling problem with jobs that require setups. The duration of a setup does not depend only on the job just completed but on a number of preceding jobs. These setup times are referred to as history‐dependent. Such a scheduling problem is often encountered in the food processing industry as well as in other process industries. In our model, we consider two types of setup times—a regular setup time and a major setup time that becomes necessary after several "hard‐to‐clean" jobs have been processed on the same machine. We consider multiple objectives, including facility utilization, flexibility, number of major setups, and tardiness. We solve several special cases assuming predetermined job sequences and propose strongly polynomial time algorithms to determine the optimal timing of the major setups for given job sequences. We also extend our analysis to develop pseudopolynomial time algorithms for cases with additional objectives, including the total weighted completion time, the total weighted tardiness, and the weighted number of tardy jobs. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012