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Each type of particle, by definition, is special. The special property of neutrinos is that they are penetrating. This has made their discovery and the understanding of their properties elusive, but it has also made them a useful tool in the study of particles and their interactions. In astrophysics, on account of this property, neutrinos provide an important means for energy transfer and permit insight into the interior of stars hidden to other radiation. The special conditions in space permit, in turn, the study of neutrino properties not possible in the laboratory.  相似文献   

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The quantity and physical state of methane and nitrogen in the atmosphere of Neptune's satellite Triton and on the surface are evaluated by means of new telescopic data and laboratory measurements of these volatiles. Methane ice is seen in some spectral regions, indicating that the atmosphere is sufficiently transparent to permit sunlight penetration to the surface. Some of the molecular nitrogen absorption occurs in the atmosphere, though some must occur in condensed nitrogen (liquid or solid) on Triton's surface, or in a thin cloud of condensed nitrogen. The Voyager spacecraft cameras should see the surface of Triton.  相似文献   

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Much is being made of local food. It is at once a social movement, a diet, and an economic strategy—a popular solution—to a global food system in great distress. Yet, despite its popularity or perhaps because of it, local food (especially in the US) is also something of a chimera if not a tool of the status quo. This paper reflects on and contrasts aspects of current local food rhetoric with Dalhberg’s notion of a regenerative food system. It identifies three problematic emphases—the locavore emphasis, the Wal-Mart emphasis, and the Pollan emphasis—and argues that they are shifting local food (as a concept and a social movement) away from the deeper concerns of equity, citizenship, place-building, and sustainability. It is suggested that local food activists and advocates might consider the use of multiple methodologies and forms of expression to explore the integration and reintegration of local food into diverse and redundant place-based practice. A short case study of a low-income, urban neighborhood in Lansing, Michigan, illustrates the value of contextual analysis for more fully enabling the local food movement and a regenerative food system.  相似文献   

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The pheromone-mediated flight behavior of male Oriental fruit moths was observed in the field to test the hypothesis that male activation far downwind of a female is initiated by the major, or most abundant, component of the pheromone blend. Males responded at significantly greater distances to the three-component pheromone blend produced by females than to the major component alone or to either binary mixture containing the major component and one minor component. These results support the alternative hypothesis that the active space of a multicomponent pheromone is a function of male perception of the female-released blend of components, rather than of the major component alone, and that so-called minor components have a greater impact on male behavior farther downwind of a female than previously thought.  相似文献   

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This paper argues that the new biotechnologies will affect the natural environment primarily in two ways: by bringing relatively wild areas, such as forests and estuaries, under domestication, and by forcing areas now domesticated, such as farms, out of production, because of surpluses. The problem of the safety of biotechnology—the risk of some inadvertent side-effect—seems almost trivial in relation to the social and economic implications of these intentional uses. The paper proposes that we should be more concerned about the successful uses of biotechnology than about the possible mishaps or failures.Mark Sagoff is Senior Research Associate and Acting Director of the Institute for Philosophy and Public Policy at the University of Maryland. His book,The Economy of the Earth: Philosophy, Law and the Environment (Cambridge University Press, 1988), deals with normative and conceptual issues in environmental law. Sagoff's work in ethical issues in biotechnology has received support from the National Science Foundation.  相似文献   

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Recent progress in the science of aging is driven largely by the use of model systems, ranging from yeast and nematodes to mice. These models have revealed conservation in genetic pathways that balance energy production and its damaging by-products with pathways that preserve somatic maintenance. Maintaining genome integrity has emerged as a major factor in longevity and cell viability. Here we discuss the use of mouse models with defects in genome maintenance for understanding the molecular basis of aging in humans.  相似文献   

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The authors make the case that population growth can lead to increases in agricultural output per head on a sustainable basis. This argument, originally developed by E. Boserup, is "illustrated by a study of Machakos District, Kenya during 1930-1960, which shows that, if policies are supportive, agricultural and non-farm incomes grow faster than even the rapid population growth rate experienced in Africa. Land use capability is not fixed, but can be transformed by investment, new technologies and good management. Lack of investment and consequent degradation are most likely at low population densities. While the study cannot foretell the future, Java illustrates a similar theme at even higher densities."  相似文献   

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Lost at sea: where is all the plastic?   总被引:10,自引:0,他引:10  
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