26,884 research outputs found

    The Black and White Differences in First Marriage Propensity: Individual and Contextual Influences.

    Get PDF
    In the context of demographic, economic, and cultural perspectives of marriage, this dissertation attempts to identify causes of the black and white divergence in marriage propensity. The findings show a strong linkage between the social context and the marriage behavior of that person. This linkage provides a new angle from which the racial differences in marriage behavior are better understood. For females, the lower rate of marrying among black females, compared to white females, is due to poor marriage markets that black females are facing. The centrality of marriage in a social context, indicated by marriage rates and average age of first marriage, also plays a role in creating racial differences in the likelihood of marriage, although to a lesser degree. For males, the racial gap in marriage propensity is due to racial differentials in labor force participation and income at the individual level and to the differences in exposure to contextual influences. Since blacks are more likely than whites to live in a social context where the divorce rate is high but marriage and remarriage rates are low, and where the occurrence of female-headed households and illegitimacy are frequent, their attachment of marriage as an institution is weaker than whites. However, black males have more favorable marriage markets than white males. When this differential is adjusted, black males would have even lower odds for marriage than white males do. In sum, the social context pertaining to the importance of marriage and local availability for marriage are two important structural mechanisms that operate in the dynamic process of the racial divergence in the propensity for marriage. However, the way in which the two structural factors operate in the process is different for males and females. By adjusting for both factors, one observes a racial convergence in likelihood of marriage for females. By controlling for the same factors, however, one observes a mixed picture among males because the two factors counter-balance each other. Generally, the findings lend support to the notion that economic, demographic, and cultural factors have contributed to a declining propensity for marriage among black Americans

    Actively controlling the topological transition of dispersion based on electrically controllable metamaterials

    Full text link
    Topological transition of the iso-frequency contour (IFC) from a closed ellipsoid to an open hyperboloid, will provide unique capabilities for controlling the propagation of light. However, the ability to actively tune these effects remains elusive and the related experimental observations are highly desirable. Here, tunable electric IFC in periodic structure which is composed of graphene/dielectric multilayers is investigated by tuning the chemical potential of graphene layer. Specially, we present the actively controlled transportation in two kinds of anisotropic zero-index media containing PEC/PMC impurities. At last, by adding variable capacitance diodes into two-dimensional transmission-line system, we present the experimental demonstration of the actively controlled magnetic topological transition of dispersion based on electrically controllable metamaterials. With the increase of voltage, we measure the different emission patterns from a point source inside the structure and observe the phase-transition process of IFCs. The realization of actively tuned topological transition will opens up a new avenue in the dynamical control of metamaterials.Comment: 21 pages,8 figure
    • …
    corecore