14,765 research outputs found
Heterogeneous aggregation in binary colloidal alloys
Molecular dynamics (MD) simulation has been employed to study the
nonequilibrium structure formation of two types of particles in a colloidal
suspension, driven by type-dependent forces. We examined the time evolution of
structure formation as well as the structural properties of the resulting
aggregation by studying the radial distribution function (RDF). The resulting
aggregation is well described by a binary colloidal gelation. We compared the
structural properties to those for one type of particles. From the MD results,
it is evident that there are significant differences between the RDF's of the
two cases. Moreover, we found that the average coordination number is generally
larger in the monodisperse case for all area fractions considered. Thus, by
means of heterogeneous aggregation, it is possible to obtain a wide variety of
structures while more close-packed structures are formed for monodisperse
colloidal aggregation.Comment: 15 pages, 5 eps figures; preliminary results have been reported at
the APS March Meeting 2002; accepted by Physica
Estimating the heterogeneous relationship between peer drinking and youth alcohol consumption in Chile using propensity score stratification
When estimating the association between peer and youth alcohol consumption, it is critical to account for possible differential levels of response to peer socialization processes across youth, in addition to variability in individual, family, and social factors. Failure to account for intrinsic differences in youth's response to peers may pose a threat of selection bias. To address this issue, we used a propensity score stratification method to examine whether the size of the association between peer and youth drinking is contingent upon differential predicted probabilities of associating with alcohol-consuming friends. Analyzing a Chilean youth sample (N = 914) of substance use, we found that youths are susceptible to the detrimental role of peer drinkers, but the harmful relationship with one's own drinking behavior may be exacerbated among youth who already have a high probability of socializing with peers who drink. In other words, computing a single weighted-average estimate for peer drinking would have underestimated the detrimental role of peers, particularly among at-risk youths, and overestimated the role of drinking peers among youths who are less susceptible to peer socialization processes. Heterogeneous patterns in the association between peer and youth drinking may shed light on social policies that target at-risk youths.We are extremely grateful to the youth and their families in Santiago, Chile for taking the time to participate in this study. This study received support from U.S. National Institute on Drug Abuse (R01 DAD21181), National Institute of Child Health and Human Development (R01-HD-074603-01), and the Vivian A. and James L. Curtis School of Social Work Research and Training Center, University of Michigan. (R01 DAD21181 - U.S. National Institute on Drug Abuse; R01-HD-074603-01 - National Institute of Child Health and Human Development; Vivian A. and James L. Curtis School of Social Work Research and Training Center, University of Michigan
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