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111.
Pigeons' keypecking was reinforced by food on baseline schedules of multiple variable interval (VI) x VI x and on contrast schedules of multiple VI x VI y. Deprivation of food was varied by maintaining subjects at 75%, 85%, and 95% (+/- 2%) of their free-feeding weights. Positive and negative behavioral contrast were observed. The size of the contrast was not systematically altered by changes in deprivation. Positive and negative contrast were both larger later in the session than they were earlier. Within-session decreases in responding were steeper for the baseline than for the contrast schedules for positive contrast. Within-session decreases were steeper for the contrast than for the baseline schedules for negative contrast. These results were predicted by the idea that different amounts of habituation to the reinforcer during the baseline and contrast schedules contribute to behavioral contrast. The results show that contrast occurs under conditions that reduce the effect of the following component. The results support the assumption that positive and negative contrast are produced by symmetrical theoretical variables. 相似文献
112.
伸展在晶格内的离子键很强,因此从晶格中移走离子是困难的。由于这个原因,离子型化合物具有较高的熔点和沸点。存在于共价型固体或液体中的分子间的作用力没有这样强(除1~2例外),使分子聚集在一起的作用力布遍于固体中也是不强的。考虑下列的气化热: 相似文献
113.
Diversity of Gram negative bacteria antagonistic against major pathogens of rice from rice seed in the tropic environment 总被引:2,自引:0,他引:2
INTRODUCTIONRiceseedharborsadozenofplantpathogen icbacteria (Gotoetal.,1 988;Xieetal.,1 998) .Thebacterialpathogenscausearangeofricediseases,someverydestructivewhileothershavenoeffectonricecropgrowth .Inthisstudy ,wefoundalargenumberofbacteriaasso ciatedw… 相似文献
114.
Peer relations across 2 contexts (in school and after school) were examined for 577 participants, approximately 12 years old, from 3 middle schools in Milan, Italy. The primary research questions were: Do peer networks from different contexts uniquely contribute to explaining variance in individual behavior? Do measures of peer preference and peer network inclusion across contexts uniquely contribute to explaining individual depressive symptoms? Structural equation models showed that both the in-school and the after-school peer networks uniquely contributed to explaining variance in 2 types of individual problem behavior (in-school problem behavior, after-school delinquency), and that similarity with the 2 peer networks varied according to behaviors specific to each context and across gender. Finally, both in-school and after-school peer network inclusion contributed to explaining variance in depressive symptoms, after controlling for classroom peer preference. 相似文献
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OBJECTIVE: This study compared recidivism rates for alleged maltreatment perpetrators whose initial report was substantiated and those whose initial report was not substantiated, to determine whether they returned to the child welfare system at differing rates. METHOD: Statewide administrative child welfare services data over a period of 4 1/2 years was analyzed. The sample included 31,531 perpetrators of intrafamilial maltreatment. Separate analyses were conducted for each type of maltreatment (sexual abuse, physical abuse, and neglect). RESULTS: Bivariate relationships (substantiation status and recidivism) were analyzed using survival curves, and the study found that recidivism patterns differed by type of maltreatment and by substantiation status at the index event. Multivariate analyses using Cox Proportional Hazards models found that bivariate relationships held true even when controlling for neighborhood mean income, ethnicity, and gender. CONCLUSIONS: The study's finding that perpetrators whose index event was not substantiated return to the child welfare system at a high rate suggests the need to learn how to discriminate those unsubstantiated alleged perpetrators who are most at risk for recidivism. The finding of frequent cross-type recidivism indicates that intervention should focus on common themes across maltreatment types. 相似文献
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