Complexity and inapproximability results for the Power Edge Set problem

We consider the single channel PMU placement problem called the Power Edge Set problem. In this variant of the PMU placement problem, (single channel) PMUs are placed on the edges of an electrical network. Such a PMU measures the current along the edge on which it is placed and the voltage at its two endpoints. The objective is to find the minimum placement of PMUs in the network that ensures its full observability, namely measurement of all the voltages and currents. We prove that PES is NP-hard to approximate within a factor (1.12)-\(\epsilon \), for any \(\epsilon > 0\). On the positive side we prove that PES problem is solvable in polynomial time for trees and grids.     

The Impact of Higher Fixed Pay and Lower Bonuses on Productivity

This study analyzes the effects of performance related pay on productivity exploiting a change in the payment structure of a large Dutch marketing company. Specifically, we investigate the consequences for company sales of higher fixed pay in combination with lower bonuses. Exploiting shift level data of individual workers we find that average productivity decreases when the pay structure shifts more to fixed pay. Further analysis shows that this drop in productivity is larger for older workers and for high-ability employees, while over time the negative effect of the new system becomes smaller.     

Newborns' Face Recognition: The Role of Facial Movement

This study investigates the role of dynamic information in identity face recognition at birth. More specifically we tested whether semi‐rigid motion, conveyed by a change in facial expression, facilitates identity recognition. In Experiment 1, two‐day‐old newborns, habituated to a static happy or fearful face (static condition) have been tested using a pair of novel and familiar identity static faces with a neutral expression. Results indicated that newborns manifest a preference for the familiar stimulus, independently of the facial expression. In contrast, in Experiment 2 newborns habituated to a semi‐rigid moving face (dynamic condition) manifest a preference for the novel face, independently of the facial expression. In Experiment 3, a multistatic image of a happy face with different degrees of intensity was utilized to test the role of different amount of static pictorial information in identity recognition (multistatic image condition). Results indicated that newborns were not able to recognize the face to which they have been familiarized. Overall, results clearly demonstrate that newborns' face recognition is strictly dependent on the learning conditions and that the semi‐rigid motion conveyed by facial expressions facilitates identity recognition since birth.     

Predictors of short-term decay of cell phone contacts in a large scale communication network

Under what conditions is an edge present in a social network at time t likely to decay or persist by some future time t + Δt? Previous research addressing this issue suggests that the network range of the people involved in the edge, the extent to which the edge is embedded in a surrounding structure, and the age of the edge all play a role in edge decay. This paper uses weighted data from a large-scale social network built from cell-phone calls in an 8-week period to determine the importance of edge weight for the decay/persistence process. In particular, we study the relative predictive power of directed weight, embeddedness, newness, and range (measured as outdegree) with respect to edge decay and assess the effectiveness with which a simple decision tree and logistic regression classifier can accurately predict whether an edge that was active in one time period continues to be so in a future time period. We find that directed edge weight, weighted reciprocity and time-dependent measures of edge longevity are highly predictive of whether we classify an edge as persistent or decayed, relative to the other types of factors at the dyad and neighborhood level.     

Value Creation and the Alliance Experiences of Dutch Companies

This paper examines the effect on the market valuation of large Dutch companies following the announcements of international strategic alliances during the period 1985–1992. The effects are distinguished by type of alliance and country of origin of the partnering firms. While international strategic alliances are generally found to have a positive effect on a company’s market value, strategically and culturally distant foreign partners generate a strong negative effect. The results underscore the importance of conducting a strategic, operational and cultural audit of the partnering companies and the envisaged partnership. The audit needs to be taken as a starting point in developing the essential co-operation skills to make the alliance work and should become integrated within a comprehensive performance scorecard.     

The Transformative Potential of Social Work's Evolving Practice in Dementia Care

Social workers in diverse service systems throughout the United States encounter many opportunities for improving quality of life for people with dementia and their families. Yet practice with this population is unclearly defined and a core set of competencies for such practice does not yet exist. Instead, it is shaped by roles within aging and health systems. These roles are informed by a biomedical disease model of dementia. This article examines social work practice and its connection to evolving views on aging and senility throughout the 20th century. New directions for practice are recommended to improve services for individuals with dementia.     

Minority Composition,Inequality and the Growth of Municipal Police Forces, 1960–71

Abstract

Recent studies, in finding that community variables such as percentage Black and income inequality have significant effects on police size and expenditures, call into question the findings of earlier research. However, these recent studies are themselves subject to serious methodological limitations and leave open the question of whether it is class or racial conflict which affects the deployment of police resources. In this study we estimate several simultaneous equation models of police size per capita in 1971 for 88 non-Southern cities. Bach of these models holds constant the effects of per capita police size in 1960. Racial composition and racial inequality are found to be the only significant predictors of the growth in the number of police per capita.     

The use of self-generated identification codes in longitudinal research

Longitudinal research designs involve data collection at multiple time points to measure change over time. Therefore, identification of the same respondents is essential at each time point so that data from the same respondents can be matched for comparison over time. Subject-generated identification codes permit an anonymous means to track respondents over multiple data collection points. This article describes the evolution of subject-generated identification codes, techniques to improve respondent match rates, and the authors' experience using this mechanism in a longitudinal study of staff registered nurses working in hospitals. Challenges, recommendations, and implications for using subject-generated identification codes are discussed.     

The association of multiple risk factors with fruit and vegetable intake among a nationwide sample of college students

Few college students meet fruit and vegetable intake recommended requirements, and most receive no information from their institutions about this issue. The avoidable disease burden among students is large, the necessary information infrastructure exists, and Healthy People 2010 objectives indicate efforts should be taken to increase intake. OBJECTIVE: The authors examined the association of high-risk behaviors and fruit and vegetable intake to inform design of multiple risk factor interventions. PARTICIPANTS AND METHODS: The authors obtained data from a sample of 40,209 18- to 25-year-old college students who completed the American College Health Association-National College Health Assessment during the spring 2002 and 2003 semesters. RESULTS: Predictors of high fruit and vegetable intake for men and women included better: seatbelt and helmet use, physical activity, perceived health, sleep, self-care behaviors, and grades. Other notable predictors of high intake were reduced likelihood of cigarette smoking, alcohol use, drinking and driving, and feeling hopeless in both sexes; reduced likelihood of drinking and driving among men; and a greater likelihood of anorexia among women. CONCLUSIONS: The authors discuss implications of these findings.