865 resultados para Hill, David B. (David Bennett), 1843-1910.


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Technology involving genetic modification of crops has the potential to make a contribution to rural poverty reduction in many developing countries. Thus far, insecticide-producing 'Bt' varieties of cotton have been the main GM crops under cultivation in developing nations. Several studies have evaluated the farm-level performance of Bt varieties in comparison to conventional ones by estimating production technology, and have mostly found Bt technology to be very successful in raising output and/or reducing insecticide input. However, the production risk properties of this technology have not been studied, although they are likely to be important to risk-averse smallholders. This study investigates the output risk aspects of Bt technology using a three-year farm-level dataset on smallholder cotton production in Makhathini flats, Kwa-Zulu Natal, South Africa. Stochastic dominance and stochastic production function estimation methods are used to examine the risk properties of the two technologies. Results indicate that Bt technology increases output risk by being most effective when crop growth conditions are good, but being less effective when conditions are less favourable. However, in spite of its risk increasing effect, the mean output performance of Bt cotton is good enough to make it preferable to conventional technology even for risk-averse smallholders.

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Technology involving genetic modification of crops has the potential to make a contribution to rural poverty reduction in many developing countries. Thus far, pesticide-producing Bacillus thuringensis (Bt) varieties of cotton have been the main GM crops under cultivation in developing nations. Several studies have evaluated the farm-level performance of Bt varieties in comparison to conventional ones by estimating production technology, and have mostly found Bt technology to be very successful in raising output and/or reducing pesticide input. However, the production risk properties of this technology have not been studied, although they are likely to be important to risk-averse smallholders. This study investigates the output risk aspects of Bt technology by estimating two 'flexible risk' production function models allowing technology to independently affect the mean and higher moments of output. The first is the popular Just-Pope model and the second is a more general 'damage control' flexible risk model. The models are applied to cross-sectional data on South African smallholders, some of whom used Bt varieties. The results show no evidence that a 'risk-reduction' claim can be made for Bt technology. Indeed, there is some evidence to support the notion that the technology increases output risk, implying that simple (expected) profit computations used in past evaluations may overstate true benefits.

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In recent years, in overall value, the EU has become a net importer of organic food to supply increasing demand. Financial support for farmers during the conversion period has been made to help expand organic production as this was seen as a barrier to conversion. Meanwhile, farmers have been marketing products produced in this conversion period and labelled as such, the extent to which is described here for the UK, Portugal, Denmark, Ireland and Italy. Consumers' attitudes towards, and willingness-to-pay for, conversion-grade food in these countries is examined. It was found that consumers would be prepared to pay a premium for conversion-grade produce of around half the premium for organic produce with vegetables attracting a higher premium than meat. Finally, the potential of policies for marketing conversion-grade products to encourage more conversion is examined, together with barriers to achieving this. It is concluded that barriers to marketing such products, particularly from retailers, will be formidable. Thus, alternative policies are suggested. (C) 2009 Elsevier Ltd. All rights reserved.

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JASMIN is a super-data-cluster designed to provide a high-performance high-volume data analysis environment for the UK environmental science community. Thus far JASMIN has been used primarily by the atmospheric science and earth observation communities, both to support their direct scientific workflow, and the curation of data products in the STFC Centre for Environmental Data Archival (CEDA). Initial JASMIN configuration and first experiences are reported here. Useful improvements in scientific workflow are presented. It is clear from the explosive growth in stored data and use that there was a pent up demand for a suitable big-data analysis environment. This demand is not yet satisfied, in part because JASMIN does not yet have enough compute, the storage is fully allocated, and not all software needs are met. Plans to address these constraints are introduced.

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bearb. von Sal. Lehr

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af A. A. Wolff

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geh. von T. Tal ... in Amsterdam

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Vorlage des Digitalisates aus der Hochschule für jüdische Studien Heidelberg

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In einem kurzen Überblick werden sowohl theoretische Erklärungsansätze als auch ausgewählte empirische Forschungsbefunde zum Themenfeld „Familie und Bildung“ dargelegt. Im Zentrum steht die Frage, inwiefern Familien für den Bildungserfolg verantwortlich sind und die Bildungschancen ihrer Kinder beeinflussen. Diese Frage wird vornehmlich aus der Perspektive des strukturell-individualistischen Erklärungsansatzes von Boudon (1974) erörtert, der die zwischen Sozialschichten differierenden Bildungschancen als Folge von sozialer Ungleichheit – bemessen an der Klassenlage des Elternhauses – begreift . Ausgehend von Erkenntnissen der Sozialisationsforschung werden zunächst Sozialisation und Erziehung im sozialen Kontext des Elternhauses thematisiert. Anschließend werden mit Bezug auf den strukturell-individualistischen Ansatz zur Erklärung von Bildungsungleichheiten die Zusammenhänge von sozialer Herkunft , schulischen Leistungen und Bildungsentscheidungen sowie ihre individuellen und gesellschaft lichen Folgen diskutiert. Bei der Darlegung des Forschungsstandes werden ebenfalls Arbeiten vorgestellt, welche die sozialen Kontexte von Familien fokussieren. Dabei stellt sich u. a. die Frage, ob Netzwerke nicht nur als Teil der familiären Ressourcenstruktur auf die Bildungserfolge von Kindern einwirken, sondern auch als sozialer Referenzrahmen bzw. als soziale Bezugsgruppen, die Bildungsentscheidungen über die Vermittlung von sozialen Erwartungen beeinflussen.

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von Sally Rosenfelder