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641.
Ramona K. Z. Heck 《Journal of Family and Economic Issues》1992,13(3):315-346
Using an ordinary least squares regression procedure and data from the NE-167 sample of home-based employment households, the effects of children on seven major home-based work dimensions, respectively, are estimated along with remaining work dimensions and a series of control variables. The findings show that having a child equal to or under 18 years of age reduces home-based work hours by 407 hours per year, which equates to 1 work day per week. The separate effect of a child under 6 years of age reduces work hours by 296 hours per year or about three-quarters of a work day per week. Being a male home-based worker offsets these children effects considerably compared with being a female home-based worker. Children in general are negatively related to large-scale businesses that hire employees or services. Younger children negatively affect the likelihood of being a home-based business owner and being involved in seasonal home-based employment.This article reports results from the Cooperative Regional Research Project, NE-167, entitled, At-Home Income Generation: Impact on Management, Productivity and Stability in Rural and Urban Families, partially supported by Cooperative States Research Service, U.S. Department of Agriculture, and the Experiment Stations at the University of Hawaii, Iowa State University, Lincoln University (Missouri), Michigan State University, Cornell University (New York), The Ohio State University, The Pennsylvania State University, Utah State University, and University of Vermont. Appreciation is expressed to You-Hyun Cho for the computer assistance needed to complete these analyses. Patsy Seilen and Justine Lynge were instrumental in formatting and stylizing this article to required guidelines.Her current research interests include household asset and debt formation, working families, and employers' benefits and home-based employment. She received her Ph.D. from Purdue University in 1978. 相似文献
642.
Ramona K. Z. Heck 《Journal of Family and Economic Issues》1991,12(3):217-233
The purpose of this research analysis is to investigate the factors that are associated with the likelihood of a worker choosing homebased employment. Using a sample of 6,744 employed men and women from the 1984 Panel Study of Income Dynamics, a logit estimation procedure is employed. Factors which decrease the likelihood of being a homebased worker include minority status, higher levels of total family labor income, a high school education or less, and longer working hours. Older workers, workers without children, workers with young children under age six, the self-employed, and farmers are all more likely to be involved in homebased employment.Ramona K.Z. Heck is an Associate Professor in the Department of Consumer Economics and Housing, 133 Martha Van Rensselaer Hall, Cornell University, Ithaca, N.Y. 14853. Her current research interests include: household asset and debt formation, working families and employers' benefits, and homebased employment. She received her Ph.D. from Purdue University in 1978.The analyses in this paper are related to work in progress under the Cooperative Regional Research Project, NE-167 entitled, At-Home-Income-Generation: Impact on Management, Productivity and Stability in Rural/Urban Families, partially supported by the stations of Hawaii, Iowa, Lincoln University (Missouri), Michigan, New York, Ohio, Pennsylvania, Utah, Vermont, and the U.S. Department of Agriculture. 相似文献
643.
This paper addresses the problem of improving the polyhedral representation of a certain class of machine scheduling problems. Despite the poor polyhedral representation of many such problems in general, it is shown that notably tighter linear programming representations can be obtained for many important models. In particular, we study the polyhedral structure of two different mixed-integer programming formulations of the flow shop scheduling problem with sequence-dependent setup times, denoted by SDST flow shop. The first is related to the asymmetric traveling salesman problem (ATSP) polytope. The second is less common and is derived from a model proposed by Srikar and Ghosh based on the linear ordering problem (LOP) polytope. The main contribution of this work is the proof that any facet-defining inequality (facet) of either of these polytopes (ATSP and LOP) induces a facet for the corresponding SDST flow shop polyhedron. The immediate benefit of this result is that all developments to date on facets and valid inequalities for both the ATSP and the LOP can be applied directly to the machine scheduling polytope. In addition, valid mixed-integer inequalities based on variable upper-bound flow inequalities for either model are developed as well. The derived cuts are evaluated within a branch-and-cut framework. 相似文献
644.
645.
A. Knight Z. Cheng S. S. Grewal K. R. Islam M. D. Kleinhenz P. S. Grewal 《Urban Ecosystems》2013,16(3):637-656
Urban agriculture offers a framework for local self-reliance and resilience in cities. However, there is a concern over the capacity of urban soil to provide sustainable and safe food production. We tested the effectiveness of several soil health indicators to predict food crop productivity and quality in vacant lots in a disadvantaged neighborhood in the city of Cleveland, Ohio. We defined soil health as a state of composite well being in terms of biological, chemical, and physical properties of the soil as they relate to crop productivity. Twelve city-owned vacant lots, three close to each of the four city schools, were selected for soil properties and plant growth analyses. Soil samples were analyzed for pH, moisture content (θv), soil texture, soil organic matter (SOM), active carbon (AC), ammonium (NH4-N), nitrate (NO3-N), microbial biomass N (MBN), and nematode community parameters including total (TNN), bacteria-feeding (BFN), fungal-feeding (FFN), and plant-parasitic (PPN) nematodes, number of nematode genera (NNG), and nematode food web enrichment index (EI) and structure index (SI). Lettuce was planted in the selected vacant lots and its growth was documented through measures of dry biomass, numbers of leaves/plant, and complementary subjective appearance scores related to physiological status. All measured parameters varied considerably among vacant lots except soil pH. Principal components analysis revealed that among the primary soil physical, chemical, and biological parameters, soil clay, NO3-N, MBN, SOM, AC, TNN, BFN, FFN, and PPN contributed most to the variance of the entire dataset. There were also several positive correlations among these key soil health predictor variables: AC was positively correlated with clay, SOM, MBN, TNN, BFN, FFN and PPN, and TNN was positively correlated with AC, SOM, MBN, BFN, FFN and PPN. Of the identified primary soil health indicators, only clay, SOM, and MBN positively correlated with lettuce dry biomass, which was also positively correlated with a secondary soil health indicator, the nematode food web EI. Lettuce leaf necrosis was negatively correlated with clay, AC, SOM, MBN, TNN, FFN, and PPN, and the proportion of withered leaves was negatively correlated only with SOM. It is concluded that AC, PPN, TNN, SOM, MBN, clay, and nematode food web EI can serve as important soil health indicators that have potential for predicting crop productivity and quality in urban soils. It is also concluded that lettuce can serve as an important indicator of soil health with respect to crop productivity and quality in vacant lots. 相似文献
646.
Christophe Z. Guilmoto 《Population and development review》2009,35(3):519-549
This article adopts a comparative perspective to review the recent increase in the sex ratio at birth (SRB) across Asia. It first describes and compares the most recent birth statistics in Asia in order to identify commonalities in the gradual rise of SRBs observed from Armenia to South Korea. This comparison provides the basis for identifying specific transition patterns in the changes in SRBs. Their recent rise is then interpreted in a social and historical framework borrowed from fertility decline and based on three preconditions: access to sex‐selection technology, preference for male births, and pressure from low fertility. On a broader plane, the process of growing imbalances in the sex composition of the population gives rise to a tragedy of the commons. This article indicates the factors that appear most likely to trigger a turnaround in this transitional demographic situation and to facilitate a return to biologically normal sex ratios in the future. 相似文献
647.
Stan Z. Li 《Journal of applied statistics》1998,25(3):425-443
A Bayesian approach to object matching is presented. An object and a scene are each represented by features, such as critical points, line segments and surface patches, constrained by unary properties and contextual relations. The matching is presented as a labeling problem, where each feature in the scene is assigned (associated with) a feature of the known model objects. The prior distribution of a scene's labeling is modeled as a Markov random field, which encodes the between-object constraints. The conditional distribution of the observed features labeled is assumed to be Gaussian, which encodes the within-object constraints. An optimal solution is defined as a maximum a posteriori estimate. Relationships with previous work are discussed. Experimental results are shown. 相似文献
648.
中国学者与日本学者就"亚洲传播研究的蓬勃发展及未来"这一问题进行对话,其中的问题包括:亚洲传播研究蓬勃发展的情况如何?为什么亚洲传播研究者尚未终止欧洲中心传播范式的统治?亚洲传播研究的目的与意义何在?哪些亚洲本土文化概念可以为亚洲传播理论的发展做出贡献?如何评价亚洲传播研究? 相似文献
649.
650.
This article tests the long-run neutrality of money proposition using quarterly U.S. data over the period from 1960:1 to 1996:2 and the methodology suggested by King and Watson (1997), paying particular attention to the integration and cointegration properties of the variables. Comparisons are made among simple sum, Divisia, and currency equivalent (CE) monetary aggregates using the Anderson et al. (1997a, 1997b) series of Divisia and CE monetary aggregates. 相似文献