A Cooperative and Adaptive Variable Neighborhood Search for the Multi Depot Vehicle Routing Problem with Time Windows

In this paper we propose two cooperation schemes to compose new parallel variants of the Variable Neighborhood Search (VNS). On the one hand, a coarse-grained cooperation scheme is introduced which is well suited for being enhanced with a solution warehouse to store and manage the so far best found solutions and a self-adapting mechanism for the most important search parameters. This makes an a priori parameter tuning obsolete. On the other hand, a fine-grained scheme was designed to reproduce the successful properties of the sequential VNS. In combination with the use of parallel exploration threads all of the best solutions and 11 out of 20 new best solutions for the Multi Depot Vehicle Routing Problem with Time Windows were found.

Neighborhood Violence and Adolescent Friendships

This paper investigates the social consequences of neighborhood violence. Using ego-centered friendship network data from the National Longitudinal Study of Adolescent Health, a survey of adolescents in the United States in the mid-1990s, it examines the relationship between neighborhood violence and the quantity, closeness, and composition of adolescent same sex friendships. Though neighborhood violence is unrelated to quantity and closeness net of individual and family characteristics, it predicts boys’ friendships with individuals who no longer attend school (who are presumably older or have dropped out of school) and predicts boys’ and girls’ friendships with individuals who attend other schools. These results are consistent with the theory that violence and fear of victimization focus adolescents’ social attention on their neighborhoods and lead them to develop friendships with individuals who can help them to stay safe. By structuring who adolescents interact with, neighborhood violence may play a role in determining the cultural messages and ideals to which they are exposed.

Neighborhood Disadvantage and Birth Weight: The Role of Perceived Danger and Substance Abuse

In this analysis we connect structural neighborhood conditions to birth outcomes through their intermediate effects on mothers’ perceptions of neighborhood danger and their tendency to abuse substances during pregnancy. We hypothesize that neighborhood poverty and racial/ethnic concentration combine to produce environments that mothers perceive as unsafe, thereby increasing the likelihood of negative coping behaviors (substance abuse). We expect these behaviors, in turn, to produce lower birth weights. Using data from the Fragile Families and Child Wellbeing Study, a survey of a cohort mothers and children born between 1998 and 2000 in large cities in the United States, we find little evidence to suggest that neighborhood circumstances have strong, direct effects on birth weight. Living in a neighborhood with more foreigners had a positive effect on birth weight. To the extent that neighborhood conditions influence birth weight, the effect mainly occurs through an association with perceived neighborhood danger and subsequent negative coping behaviors. Poverty and racial/ethnic concentration increase a mother’s sense that her neighborhood is unsafe. The perception of an unsafe neighborhood, in turn, associates with a greater likelihood of smoking cigarettes and using illegal drugs, and these behaviors have strong and significant effects in reducing birth weight. However, demographic characteristics, rather than perceived danger or substance abuse, mediate the influence of neighborhood characteristics on birth weight.