Classical and quantum properties of a 2-sphere singularity

Recently Boehmer and Lobo have shown that a metric due to Florides, which has been used as an interior Schwarzschild solution, can be extended to reveal a classical singularity that has the form of a two-sphere. Here the singularity is shown to be a scalar curvature singularity that is both timelike and gravitationally weak. It is also shown to be a quantum singularity because the Klein-Gordon operator associated with quantum mechanical particles approaching the singularity is not essentially self-adjoint.Comment: 10 pages, 1 figure, minor corrections, final versio

Homogeneity and plane-wave limits

We explore the plane-wave limit of homogeneous spacetimes. For plane-wave limits along homogeneous geodesics the limit is known to be homogeneous and we exhibit the limiting metric in terms of Lie algebraic data. This simplifies many calculations and we illustrate this with several examples. We also investigate the behaviour of (reductive) homogeneous structures under the plane-wave limit.Comment: In memory of Stanley Hobert, 33 pages. Minor corrections and some simplification of Section 4.3.

Job Crafting via Decreasing Hindrance Demands:The Motivating Role of Interdependence Misfit and the Facilitating Role of Autonomy

Job crafting theory suggests that misalignment between an employee’s preferred and actual amount of job characteristics acts as a motivational trigger for job crafting. We test this unexplored, yet key proposition underlying job crafting theory. To do so, however, we take a more comprehensive misfit perspective than previously applied, evaluating person-job undersupply and oversupply. We propose that task interdependence misfit motivates a reductive form of job crafting, decreasing hindrance demands. We also propose that low autonomy mitigates the misfit to decreasing hindrance demands relationship. To empirically evaluate this direction, we employ moderated polynomial regression and response surface analysis. Study 1 (N = 159 English-speaking respondents) findings suggest that task interdependence misfit (both undersupply and oversupply) is positively related to decreasing hindrance demands. Study 2 (N = 363 Dutch-speaking respondents) findings replicate and support our misfit hypothesis. Further, as expected, low levels of autonomy neutralize the relationship between task interdependence misfit and decreasing hindrance demands. Theoretical and practical implications regarding the misfit-as-motivation hypothesis, and the simultaneous investigation of job crafting facilitators (i.e., autonomy) and motivators (i.e., misfit) are discussed

The link between ethnic segregation and socio-economic status : An activity space approach

The extent to which ethnic segregation results from differences in socio-economic factors remains a seminal topic of debate. The growing literature demonstrating the multifaceted phenomenon of segregation urges more focus on individuals' spatial and social interactions. We applied an activity space approach and considered ethnic differences in individuals' activity spaces as an indicator of spatial segregation. We used mobile phone and survey datasets in Estonia. We show that place-based segregation indices derived from both datasets indicate similar levels of ethnic segregation. From an activity space perspective, the results show that the main socio-economic factor affecting the extensity of activity spaces is self-estimated social status rather than education and income. Results show that ethnic inequality in spatial behaviour is not straightforward, but rather that it is linked to how individuals position themselves in society. We argue that socio-economic factors need to be controlled to examine ethnic segregation from activity space perspective.Peer reviewe

Quotients of AdS_{p+1} x S^q: causally well-behaved spaces and black holes

Starting from the recent classification of quotients of Freund--Rubin backgrounds in string theory of the type AdS_{p+1} x S^q by one-parameter subgroups of isometries, we investigate the physical interpretation of the associated quotients by discrete cyclic subgroups. We establish which quotients have well-behaved causal structures, and of those containing closed timelike curves, which have interpretations as black holes. We explain the relation to previous investigations of quotients of asymptotically flat spacetimes and plane waves, of black holes in AdS and of Godel-type universes.Comment: 48 pages; v2: minor typos correcte

Ethnicity, schooling, and merit in the Netherlands

We examine to what extent ethnicity affects academic ability measured in the first year of secondary school and secondary school type in the Netherlands. We focus on second-generation immigrants. The empirical results indicate that academic ability (both in mathematics and language) is not affected by ethnicity, independent of parents’ occupation, education, and resources. On a bivariate level, children of Turkish and Moroccan immigrants in the Netherlands are found relatively often in lower tracks in secondary school. This relationship is fully driven by social class and merit, operationalized as including ability and effort. Moreover, children of Turkish, Surinamese and Antillean migrants are, relative to Dutch children from similar backgrounds and merit, more often found in higher tracks in secondary school. However, given the very skewed distribution of educational attainment of immigrants, it is questionable whether ‘class versus ethnicity models’ can accurately compare achievements of native and immigrant children in the Netherlands

Organizational Adaptation to Changing Environments

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66531/2/10.1177_000276428502800507.pd

Group diversity and group identification:the moderating role of diversity beliefs

Research on diversity in teams and organizations has revealed ambiguous results regarding the effects of group composition on workgroup performance. The categorization—elaboration model (van Knippenberg et al., 2004) accounts for this variety and proposes two different underlying processes. On the one hand diversity may bring about intergroup bias which leads to less group identification, which in turn is followed by more conflict and decreased workgroup performance. On the other hand, the information processing approach proposes positive effects of diversity because of a more elaborate processing of information brought about by a wider pool and variety of perspectives in more diverse groups. We propose that the former process is contingent on individual team members' beliefs that diversity is good or bad for achieving the team's aims. We predict that the relationship between subjective diversity and identification is more positive in ethnically diverse project teams when group members hold beliefs that are pro-diversity. Results of two longitudinal studies involving postgraduate students working in project teams confirm this hypothesis. Analyses further reveal that group identification is positively related to students' desire to stay in their groups and to their information elaboration. Finally, we found evidence for the expected moderated mediation model with indirect effects of subjective diversity on elaboration and the desire to stay, mediated through group identification, moderated by diversity beliefs

Family-Friendly Management, Organizational Performance and Social Legitimacy

Research on family-friendly practices has concentrated on the predictors of their use, particularly from the perspective of either institutional theory or the high involvement or commitment management vogue. This paper first shows how such perspectives can be used to generate hypotheses about the link between family-friendly management and organizational performance. Second, the paper reports research designed to test these, using data from a national representative sample of workplaces across the British economy, the Workplace Employment Relations Survey of 2004 (WERS2004). The results support the high commitment thesis that family-friendly management will strengthen the relationship between commitment and key economic outcomes, as the relationships between workforce commitment and productivity or quality are stronger in organizations when friendly management is high, which is consistent with social exchange theory. Family-friendly management is not, however, related to the human resource outcomes of labour turnover and absenteeism. Nor does the study find support for the argument that its use in conjunction with high involvement management enhances the performance effects of both. Equally, there is no support for the hypothesis from the institutional thesis that family-friendly management has positive effects on the legitimacy of the organization