Coverage with k-transmitters in the presence of obstacles

For a fixed integer k≥0, a k-transmitter is an omnidirectional wireless transmitter with an infinite broadcast range that is able to penetrate up to k “walls”, represented as line segments in the plane. We develop lower and upper bounds for the number of k-transmitters that are necessary and sufficient to cover a given collection of line segments, polygonal chains and polygons.     

Sex-Role Stereotyping and Social Work Education

The article presents the results of a nationwide study that examined the written criteria that is currently being used by graduate schools of social work for the appointment, retention, and promotion of their faculties. A content analysis of the study is discussed, and a unique behavioral model for the evaluation of faculty competence is offered.     

Preface

No abstract available for this article.     

Writing a Book Review for JFSW

ABSTRACT

For children in foster care, continued contact with biological parents may have significant implications. This article seeks to synthesize literature examining attachment theory and visitation between children in foster care and their parents. The results of the research synthesis indicate that although the exploration of attachment theory began over 40 years ago, the questions regarding the implications of foster care visitation and attachment continuation surprisingly remain unanswered.     

Cumulative Risk,Negative Emotionality,and Emotion Regulation as Predictors of Social Competence in Transition to School: A Mediated Moderation Model

The goals of this study were to examine the additive and interactive effects of cumulative risk and child negative emotionality on children's social competence in the transition from preschool to school and to test whether these associations were mediated by child emotion regulation within a sample of 310 low‐income, ethnically diverse boys. Multiple informants and methods were used to measure contextual risk factors and negative emotionality at the ages of 1.5 and two, emotion dysregulation at the age of 3.5, and social competence in the home at the age of five and in school at the age of six. Results indicated that the relation between cumulative risk and emotion dysregulation was amplified for children with higher levels of negative emotionality. In turn, emotion dysregulation predicted lower social competence across both the home and the school contexts. This study represents an early effort to develop an integrative model of social competence by considering joint contributions of contextual risk, negative emotionality, and emotion regulation.     

Probabilistic Assessment of the Failure Risk of the Europa Clipper Spacecraft due to Radiations

The Europa mission approved in 2019 is still in the development phase. It is designed to conduct a detailed reconnaissance of that moon of Jupiter as it could possibly support life as we know it. This article is based on a top-down approach (mission → system → subsystems → components) to model the probability of mission failure. The focus here is on the case where the (uncertain) radiation load exceeds the (uncertain) capacity of critical subsystems of the spacecraft. The model is an illustrative quantification of the uncertainties about (1) the complex external radiation environment in repeated exposures, (2) the effectiveness of the shielding in different zones of the spacecraft, and (3) the components’ capacities, by modeling all three as dynamic random variables. A simulation including a sensitivity analysis is used to obtain the failure probability of the whole mission in forty-five revolutions around Jupiter. This article illustrates how probabilistic risk analysis based on engineering models, test results and expert opinions can be used in the early stages of the design of space missions when uncertainties are large. It also describes the optimization of the spacecraft design, taking into account the decisionmakers’ risk attitude and the mission resource constraints.     

Asteroid Risk Assessment: A Probabilistic Approach

Following the 2013 Chelyabinsk event, the risks posed by asteroids attracted renewed interest, from both the scientific and policy‐making communities. It reminded the world that impacts from near‐Earth objects (NEOs), while rare, have the potential to cause great damage to cities and populations. Point estimates of the risk (such as mean numbers of casualties) have been proposed, but because of the low‐probability, high‐consequence nature of asteroid impacts, these averages provide limited actionable information. While more work is needed to further refine its input distributions (e.g., NEO diameters), the probabilistic model presented in this article allows a more complete evaluation of the risk of NEO impacts because the results are distributions that cover the range of potential casualties. This model is based on a modularized simulation that uses probabilistic inputs to estimate probabilistic risk metrics, including those of rare asteroid impacts. Illustrative results of this analysis are presented for a period of 100 years. As part of this demonstration, we assess the effectiveness of civil defense measures in mitigating the risk of human casualties. We find that they are likely to be beneficial but not a panacea. We also compute the probability—but not the consequences—of an impact with global effects (“cataclysm”). We conclude that there is a continued need for NEO observation, and for analyses of the feasibility and risk‐reduction effectiveness of space missions designed to deflect or destroy asteroids that threaten the Earth.