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121.
Ioannis Caragiannis Christos Kaklamanis Maria Kyropoulou 《Journal of Combinatorial Optimization》2013,26(2):292-309
We consider the frugal coverage problem, an interesting variation of set cover defined as follows. Instances of the problem consist of a universe of elements and a collection of sets over these elements; the objective is to compute a subcollection of sets so that the number of elements it covers plus the number of sets not chosen is maximized. The problem was introduced and studied by Huang and Svitkina (Proceedings of the 29th IARCS annual conference on foundations of software technology and theoretical computer science (FSTTCS), pp. 227–238, 2009) due to its connections to the donation center location problem. We prove that the greedy algorithm has approximation ratio at least 0.782, improving a previous bound of 0.731 in Huang and Svitkina (Proceedings of the 29th IARCS annual conference on foundations of software technology and theoretical computer science (FSTTCS), pp. 227–238, 2009). We also present a further improvement that is obtained by adding a simple corrective phase at the end of the execution of the greedy algorithm. The approximation ratio achieved in this way is at least 0.806. Finally, we consider a packing based algorithm that uses semi-local optimization, and show that its approximation ratio is not less than 0.872. Our analysis is based on the use of linear programs which capture the behavior of the algorithms in worst-case examples. The obtained bounds are proved to be tight. 相似文献
122.
David McGuire Thomas N. Garavan David O'Donnell Sudhir K. Saha Maria Cseh 《Human Resource Development International》2013,16(4):335-350
Few empirical studies have examined the effect of personal values on the importance attached by individuals to training and development in organizations. We argue that personal values play an important role in decision-making processes (i.e. commitment to training and development) and that such values are the product of socialization processes operating at an organizational and societal level. Questionnaire data were collected from 340 Irish and Canadian line managers to test the hypothesis that personal values affect the importance attached by respondents to training and development. Capability values were found to be a significant positive predictor of the perceived importance of training and development. The findings emphasize the need for simultaneously examining both personal values and organizational factors as predictors of training and development activity. 相似文献
123.
Abstract The 24-h dietary intake, nutritional status parameters and psychosomatic factors of two-shift, three-shift and day workers were compared. Estimations of the dietary intake (across a work cycle) were made by use of a nutrient database. No significant differences were found between the groups for a large number of nutritional variables: intake of energy; intake and percentage of energy from protein, fat, total carbohydrates and sucrose; intake of coffee; and intake and density of vitamins and minerals. Only minor differences were found between the groups with regard to the quantitative intake of alcohol and calcium, and with regard to the quality of the diet (percentage of energy from alcohol, density of calcium). The groups differed significantly with respect to attitude towards work hours (three-shift workers being most negative in their attitude) and sleep disturbances (shift workers being most negative). The three-shift workers were more evening-oriented and they had higher concentrations of glucose in their blood. It was concluded that work hours not related to nutritional intake—at least not when total amounts across time are considered. It was also concluded that work hours were not related to Body Mass Index or blood lipids: triglycerides, total cholesterol, LDL (low-density lipoprotein) cholesterol and HDL (high-density lipoprotein) cholesterol. 相似文献
124.
Martijn Bouwknegt Jack F. Schijven Johanna A.C. Schalk Ana Maria de Roda Husman 《Risk analysis》2013,33(7):1228-1236
Quantitative microbiological risk assessment was used to quantify the risk associated with the exposure to Legionella pneumophila in a whirlpool. Conceptually, air bubbles ascend to the surface, intercepting Legionella from the traversed water. At the surface the bubble bursts into dominantly noninhalable jet drops and inhalable film drops. Assuming that film drops carry half of the intercepted Legionella, a total of four (95% interval: 1–9) and 4.5×104 (4.4×104 – 4.7×104) cfu/min were estimated to be aerosolized for concentrations of 1 and 1,000 legionellas per liter, respectively. Using a dose‐response model for guinea pigs to represent humans, infection risks for active whirlpool use with 100 cfu/L water for 15 minutes were 0.29 (~0.11–0.48) for susceptible males and 0.22 (~0.06–0.42) for susceptible females. A L. pneumophila concentration of ≥1,000 cfu/L water was estimated to nearly always cause an infection (mean: 0.95; 95% interval: 0.9–~1). Estimated infection risks were time‐dependent, ranging from 0.02 (0–0.11) for 1‐minute exposures to 0.93 (0.86–0.97) for 2‐hour exposures when the L. pneumophila concentration was 100 cfu/L water. Pool water in Dutch bathing establishments should contain <100 cfu Legionella/L water. This study suggests that stricter provisions might be required to assure adequate public health protection. 相似文献
125.
Differences in Delaying Motherhood Across European Countries: Empirical Evidence from the ECHP 总被引:1,自引:0,他引:1
Motherhood postponement and fertility decline have been observed in almost all developed countries. In this article, we aim
to assess some of the potential determinants of first childbirth timing in Europe, in a comparative perspective, using data
from the European Community Household Panel Survey (ECHP). We estimate, separately by country, hazard rates for the timing
at first childbirth conditioning to education and work characteristics. Moreover, in order to explain differences between
European countries, we decompose the differences between rates in the part due to the national population composition by specific
characteristics and the part due to different propensities for women with given characteristics. 相似文献
126.
In this article we discuss some theoretical and methodological perspectives for studying children's neighbourhoods as a social‐pedagogical context. This social‐pedagogical perspective includes a focus in research on a reflective approach based on the acquisition of empirical indicators about the impact of the neighbourhood on children's socialisation. A research outline based on the idea of mapping children's neighbourhoods within their social and historical context is presented as one possible example of such an analysis. 相似文献
127.
Web 2.0, Library 2.0, and the Hyperlinked Library 总被引:3,自引:0,他引:3
Discussions surrounding the concepts of Web 2.0/Library 2.0 are increasing among the library community. This column outlines key principles behind Web 2.0 and provides a brief explanation of social tools, such as blogs, RSS feeds, podcasting, and wikis. The author also provides specific uses and applications of these tools within the library environment to illustrate the Library 2.0 concept. An open framework for library communication or hyperlinked library can result if Library 2.0 philosophies are fully utilized. 相似文献
128.
Hübner Maria Martha Costa Austin John Miguel Caio F. 《The Analysis of verbal behavior》2008,24(1):55-62
In the current study, tacts with positive qualifying autoclitics for reading were reinforced in order to determine if this procedure would increase the time spent reading by participants. Participants included 5 children, between 9–10 years old. Participants were individually exposed to 4 free operant sessions during which they were instructed to independently choose play activities. During pre- and post-treatment conditions, no consequences were provided for choosing reading. In addition, 4 treatment sessions were conducted on days separate from the free operant session days, during which the experimenter praised each positive reading-related statement emitted by the participant. Following treatment sessions, 4 out of 5 participants increased the time allocated to reading, suggesting that reading could be increased when praise is delivered contingent upon positive reading-related verbalizations. 相似文献
129.
130.
Given recent changes in the labor force participation and economic standing of women, we ask whether a woman's position in the labor market has become a more important determinant of her position in the marriage market. Unlike much prior research on trends over time in assortative mating, we take an individual‐level approach to the analysis and rely on improved measures of labor market position, such as measuring wives' wages before marriage and considering multiple indicators of husbands' longer term economic standing. Our analysis relies on data from the National Longitudinal Survey of Young Women (N = 759) and the National Longitudinal Survey of Youth (N = 767). Our results are consistent with growth over time in the importance of women's earnings potential in determining their marriage prospects. 相似文献