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Field observations and experimental evidence refute previous objections to the coral snake mimicry hypothesis. Concordant color pattern variation spanning hundreds of miles and several presumed venomous models strongly suggests that several harmless or mildly venomous colubrid snakes are indeed mimics of highly venomous elapids.  相似文献   

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The reaction of oxygen with protein diiron sites is important in bioorganic syntheses and biomineralization. An unusually short Fe-Fe distance of 2.53 angstroms was found in the diiron (mu-1,2 peroxodiferric) intermediate that forms in the early steps of ferritin biomineralization. This distance suggests the presence of a unique triply bridged structure. The Fe-Fe distances in the mu-1, 2 peroxodiferric complexes that were characterized previously are much longer (3.1 to 4.0 angstroms). The 2.53 angstrom Fe-Fe distance requires a small Fe-O-O angle (approximately 106 degrees to 107 degrees). This geometry should favor decay of the peroxodiferric complex by the release of H2O2 and mu-oxo or mu-hydroxo diferric biomineral precursors rather than by oxidation of the organic substrate. Geometrical differences may thus explain how diiron sites can function either as a substrate (in ferritin biomineralization) or as a cofactor (in O2 activation).  相似文献   

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Mayer SE  Jencks C 《Science (New York, N.Y.)》1989,243(4897):1441-1445
This article is a review of research on how much the life chances of children are affected by the socioeconomic and racial mix of their schools and neighborhoods. The social mix of a high school has little effect on students' chances of attending college or on white students' academic achievement. Evidence about the effect of the socioeconomic mix of schools or neighborhoods on achievement of elementary school students, on graduation rates of high school students, on teenage crime, and on early labor market experience is weak. Growing up in poor neighborhoods seems to increase black teenage pregnancy rates.  相似文献   

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This paper provides a conceptual framework to explain why disparities may exist in food safety code compliance by food stores in different neighborhoods. Explanations include market dynamics, community characteristics, retailer attributes, inspector characteristics, and enforcement approaches, and interactions among the factors. A preliminary and limited empirical test of some of these relationships in Detroit, Michigan shows a higher rate of food safety violations by stores in poorer neighborhoods and in neighborhoods with higher concentrations of African-American residents. Stores inspected by female inspectors also scored higher numbers of critical violations, suggesting a need for greater examination of the social relations associated with enforcement interactions in food safety studies.
Kameshwari PothukuchiEmail:

Kameshwari Pothukuchi   PhD, is Associate Professor of Urban Planning at Wayne State University. She conducts research on issues related to urban food security, including grocery stores, community gardens, and community and regional food planning. A policy guide on community and regional food planning, co-authored by her, was recently adopted by the American Planning Association (). Rayman Mohamed   PhD, is Assistant Professor of Urban Planning at Wayne State University. He conducts research on land use and environmental planning. His recent articles examine decision making by developers, the economics of conservation subdivisions, and the relationship between sprawl and the costs of infrastructure. David A. Gebben   is a graduate student of agricultural economics and a research assistant in the Global Urban Studies Program at Michigan State University.  相似文献   

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Eisner R 《Science (New York, N.Y.)》1987,237(4822):1577-1582
Government deficits and debt are surpluses and assets of the private sector of the economy that stimulate private spending. Official measures of deficits are misleading, however, for failing to distinguish public investment from current spending and for failing to adjust for inflation. Correctly measured real deficits have contributed to the growth of gross national product, consumption, and imports, and to investment as well. Optimal policy consistent with balanced growth calls not for elimination of the nominal deficit but rather for prudent deficit reduction accompanied by and stemming at least partly from sufficient monetary stimulus to achieve and sustain relatively full employment.  相似文献   

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