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201.
A method for the routine profiling of illicit heroin samples received in casework has been developed which depends on simple and straightforward sample pretreatment, followed by gas chromatography on a capillary column using flame-ionization detection. The factors affecting the choice of each aspect of the procedure are discussed, as are the statistical data for sampling and the chromatography. Components of illicit heroin derived from opium and other adulterants have been identified. The significance of data from samples examined in 1986 is discussed. 相似文献
202.
African agriculture is often dominated by smallholder farms composed of multiple plots. In policy circles it is often assumed that fragmentation coupled with small farm size is an impediment to increasing yields and thus decreasing poverty and food insecurity. There also exists an influential literature that explores the inverse relationship between farm size and yield. While there are many studies internationally, few have been conducted in Africa. Using an Ethiopian national survey, we explore the relationship between yield, farm size and fragmentation. We find an inverse relationship between farm size and yield, and a positive association between yield and land fragmentation. 相似文献
203.
Jason M. Newcomer Patti J. Clark Dixie K. Button Linda V. Weiland 《Journal of Gender Studies》2018,27(5):509-521
Certified aircraft mechanics represent the largest gender-based demographic disparity in aviation with a 49-to-1 male-to-female ratio. Recent research into women’s perspective on the aircraft mechanic career field revealed that a large majority of women felt unsure or negatively about their potential promotion opportunities and social acceptance. The purpose of this follow-on mixed-methods concurrent triangulation study was to explore the perspectives of men regarding the aforementioned topics to see if they differ from previously published research on women perceptions. A total of 587 men and 431 women completed an eight-question survey containing 5-point Likert-type and open-ended questions. The quantitative comparison consisted of the total 1018 responses, while only the survey responses from the 587 men were analysed for correlations and qualitative codes. Results indicated that there was a significant difference between the perceptions of men from those of the women regarding work environment safety and social acceptance. Additional correlation analysis revealed social acceptance to be a key variable when predicting career appropriateness, advancement opportunity and work environment safety. The 587 qualitative responses yielded results that differed from those of women, citing an assumption that women have the same advancement opportunities or be as socially accepted as men entering the field. 相似文献
204.
Christopher C. Weiss Brian V. Carolan E. Christine Baker-Smith 《Journal of youth and adolescence》2010,39(2):163-176
In an effort to increase both adolescents’ engagement with school and academic achievement, school districts across the United
States have created small high schools. However, despite the widespread adoption of size reduction reforms, relatively little
is known about the relationship between size, engagement and outcomes in high school. In response, this article employs a
composite measure of engagement that combines organizational, sociological, and psychological theories. We use this composite
measure with the most recent nationally-representative dataset of tenth graders, Educational Longitudinal Study: 2002, (N = 10,946, 46% female) to better assess a generalizable relationship among school engagement, mathematics achievement and
school size with specific focus on cohort size. Findings confirm these measures to be highly related to student engagement.
Furthermore, results derived from multilevel regression analysis indicate that, as with school size, moderately sized cohorts
or grade-level groups provide the greatest engagement advantage for all students and that there are potentially harmful changes
when cohorts grow beyond 400 students. However, it is important to note that each group size affects different students differently,
eliminating the ability to prescribe an ideal cohort or school size. 相似文献
205.
Nicole Leeper Piquero Kristan Fox Alex R. Piquero George Capowich Paul Mazerolle 《Journal of youth and adolescence》2010,39(4):380-392
Much of the prior work on General Strain Theory (GST) has focused on how strain and negative emotions interrelate to produce
criminal—especially violent—activity. Very little research has extended GST to examine other types of non-criminal, negative
behavior, such as self-harming behaviors associated with disordered eating, a traditionally female-specific self-directed
outcome. Using a sample of 338 young adults (54% female, 95% white), this article applies GST to disordered eating by examining
how strain and negative emotions relate to this particular outcome across gender. Findings indicate that two types of strain
measures predict depressive symptoms among males and females, that inequitable strainful experiences relate to disordered
eating among females but not males, that depressive symptoms but not anger increase disordered eating for both males and females,
and that membership in Greek organizations (sororities or fraternities) is associated with disordered eating but only for
males. Implications for theory and directions for future research are highlighted. 相似文献
206.
207.
Edmond P. Bowers Yibing Li Megan K. Kiely Aerika Brittian Jacqueline V. Lerner Richard M. Lerner 《Journal of youth and adolescence》2010,39(7):720-735
The understanding of positive development across adolescence rests on having a valid and equivalent measure of this construct across the breadth of this period of life. Does the Positive Youth Development (PYD) construct based on the Five Cs model have satisfactory psychometric properties for such longitudinal measurement invariance? Using longitudinal data derived from the 4-H Study of PYD, we assessed 920 youth (61.6% female) from a racially and ethically diverse sample (67.3% European American) who participated in three waves (Grades 8–10) of data collection. Building on prior findings that the Five Cs (i.e., Competence, Confidence, Connection, Character, and Caring) model of PYD was a robust measure that could be assessed comparably during early adolescence, we tested a hierarchy of second-order confirmatory factor analysis models to assess the extent to which PYD can be measured equivalently across middle adolescence. Evidence was found for strict measurement invariance across three measurement occasions, including equivalence of first-order and second-order factor loadings, equality of intercepts of observed variables, and equality of item uniqueness and disturbances of the first-order factors. These results suggest that PYD can be measured in the same way across measurement occasions, a prerequisite for the study of development. Implications for research and application of being able to measure PYD equivalently across adolescence are discussed. 相似文献
208.
Ellen H. O’Donnell Melissa Moreau Esteban V. Cardemil Alisha Pollastri 《Journal of youth and adolescence》2010,39(1):12-22
Research on the mechanisms by which interparental conflict (IPC) affects child depression suggests that both parenting and
children’s conflict appraisals play important roles, but few studies have explored the role of general cognitive style or
included both parenting and cognitions in the same design. Moreover, the effects of IPC on minority children are not well
understood. In this longitudinal study, parenting was examined as a mediator of the relation between increasing IPC and change
in depression. General cognitive style was included as a moderator. The combined influence of parenting and cognitions was
also explored. A racially and ethnically diverse sample of 88 fifth and sixth graders from two urban schools reported their
cognitive style, depressive symptoms, and perceptions of conflict and parenting at two time points separated by one year.
Parental warmth/rejection mediated the relation between IPC and depression, and general cognitive style acted as a moderator.
Parenting, cognitive style, and IPC did not significantly interact to predict change in depression over time. Findings indicate
that both parenting and children’s general cognitive style play a role in understanding the impact of increasing IPC on children’s
well-being. 相似文献
209.
The present study examined the longitudinal links between perceptions of family connectedness and body satisfaction in 1,774
(52% female) adolescents. Participants (10–15 years of age at Time 1) completed self-report measures at three measurement
occasions separated by 1 year each. Mean group difference results showed that both body satisfaction levels and perceived
levels of family connectedness decreased over 2 years for the whole sample. As expected, girls were generally less satisfied
with their bodies than boys, particularly in the older cohort. Structural equation modelling was used to assess stability
coefficients and cross-lagged effects, and longitudinal bidirectional effects between perceptions of family connectedness
and body satisfaction were found for girls, but not for boys. This result suggests that adolescent girls’ body satisfaction
is both affected by and a predictor of perceived family connectedness. 相似文献
210.
History is institutional memory writ large. One looks at economic history to see what problems recur, what causes them to recur, what solutions have worked best in the past, and which interventions have made the problems worse. The authors argue that a moderately complex interaction between the workings of the financial sector, the way in which the political system is organized, and the administration of regulation makes perfect regulation of the financial sector extremely unlikely. Many of these problems arise as a result of conflicting incentives for those participating in and regulating the financial field. The authors find that some proposed solutions have improved matters but have costs, and that some proposed solutions have actually worsened problems in the financial sector.
相似文献
Peoples and governments never have learned anything from history, or acted on principles deduced from it.
— Georg Wilhelm Friedrich Hegel, 1837