Swapping trajectories: a new wall-induced cross-streamline particle migration mechanism in a dilute suspension of spheres

Binary encounters between spherical particles in shear flow are studied for a system bounded by a single planar wall or two parallel planar walls under creeping flow conditions. We show that wall proximity gives rise to a new class of binary trajectories resulting in cross-streamline migration of the particles. The spheres on these new trajectories do not pass each other (as they would in free space) but instead they swap their cross-streamline positions. To determine the significance of the wall-induced particle migration, we have evaluated the hydrodynamic self-diffusion coefficient associated with a sequence of uncorrelated particle displacements due to binary particle encounters. The results of our calculations quantitatively agree with the experimental value obtained by \cite{Zarraga-Leighton:2002} for the self-diffusivity in a dilute suspension of spheres undergoing shear flow in a Couette device. We thus show that the wall-induced cross-streamline particle migration is the source of the anomalously large self-diffusivity revealed by their experiments.Comment: submited to JF

The Perceived Impact of the In-Trust Agreements on CGIAR Germplasm Availability: An Assessment of Bioversity International's Institutional Activities

This study assesses the generation and consequences of the In-Trust Agreements (ITAs) that established the legal status of the CGIAR germplasm as freely available for the benefit of humanity under the auspices of FAO. The analysis looks at the history of the ITAs and focuses on the role of Bioversity International in research and other activities in influencing, facilitating and enabling the ITA negotiations. Results confirm the central role of Bioversity and policy research in the negotiations process. Concepts developed during the ITA negotiations contributed toward subsequent multilateral negotiations that eventually culminated in the International Treaty on Plant Genetic Resources

Is cryopreservation a viable method for long-term conservation of coffee biodiversity?

This brief summarizes the findings of the 2008 study carried out by Bioversity International and its partners that investigated two major issues relating to conservation of coffee germplasm: 1. What are the real threats to and losses of coffee germplasm held globally in field genebanks? 2. How do the costs of cryopreservation compare with those of maintaining coffee field collections for long-term conservation? The study shows that the costs of cryopreservation should not be considered prohibitive to establishing duplicate, back-up collections of coffee. If cryopreservation is adopted as a complement to field genebanks, the costs of cryopreservation must be added to existing costs of field conservation. However, field collections could be reduced and at least partly between cryopreservation and field collection to ensure the longterm, cost-efficient conservation of coffee genetic resources. This study investigated coffee as a test case, but the results are relevant to other species that are difficult to conserve using the traditional method of seed drying and low-temperature storage. The underlying objective of the study was to assess the potential impact of the widespread adoption of cryopreservation for more species and in more genebanks

Evaluating the impact of the Vavilov-Frankel Fellowship Programme

The Vavilov-Frankel Fellowship Programme awards two fellowships annually to young scientists from developing countries, to enable them to carry out innovative research on the conservation and use of plant genetic resources (PGR). Since 1994, 39 scientists from 24 countries have taken part in the programme. An evaluation of the impact of the Vavilov-Frankel Fellowships (VFF) reveals that overall the VFF Programme has met its stated goals of contributing to the scientific capacity of the Fellows and their home institutes, and of fostering the conservation and use of PGR. The evaluation also indicated ways in which the Fellowship Programme could be improved, and these are now being implemented

Medicinal and aromatic plants improve livelihoods in Yemen

The aim of this brief is to analyze the impact of a set of interventions related to conservation and use of neglected and underutilized species (NUS) on people’s livelihoods. Specifically a simultaneous three-equation model of households’ participation on undertulized crops conservation and income generation activities is applied to evaluate the outcome of a pilot research project implemented by Bioversity International in Yemen between 2002 and 2005. Results generated show a relation between project participation and the perceived yield increase demonstrating the importance for farmers to actively participate in the project’s activities and subsequently apply agronomic practices learnt to improve their livelihood. The generated benefits incentivized farmers to continue to apply the interventions beyond the lifetime of the project ensuring thus a sustainable process in which exogenous interventions, once adopted by farmers become integrant part of farmer’s agronomic practices

The Origin, Development And Structure Of Demand For Plant Genetic Resources. The Impact Of The In Trust Agreements To The CGIAR Collections Availability

The objective of this paper is to explore how the demand of germplasm held by CGIAR genebanks changed over time in order to assess the possible influence of the 1994 In Trust Agreements on germplasm demand. The proposed theoretic model motivates the realistic hypothesis that the consequences of the In-Trust Agreements lead to an enhancement of CGIAR germplasm utilization. Therefore the paper firstly examines the classical literature on biodiversity’s valuation and its recent developments and subsequently it investigates the origin of the agricultural biodiversity’s economic value, providing a basic conceptual framework to infer on factors determining the demand for germplasm. Two Bayesian estimation frameworks are applied to the IRRI accessions distribution’s time-series to provide formal evidence to the hypothesis, exploiting Markov Chain Monte Carlo methods, Gibbs sampling in particular. Evidence suggests that the demand variation implies a change in the genetic collections economic value, impacting therefore on their direct use search value.Crop genetic resources, germplasm collection, search theoretic framework, count data, changepoints, O19, Q18, Q57, C11,

The impact of diversity field forums: improving farmer management of millet and Sorghum in Mali

The brief summarizes an evaluation of the impact of one participatory research effort known as diversity field forums (DFFs). DFFs bear some similarities to farmer field schools - an approach to improving crop management practices that involves teaching groups of farmers how to solve problems, set priorities and conduct research through facilitated, handson sessions in fields allocated by the farming community. The Forums aim to strenghten the capacity of farmers to understand, analyse and manage their own plant genetic resources by creating a physical space that facilitates the exchange of ideas among farmers, extension agents and researchers and encourages farmers to experiment with different varieties and production approaches. The project, Empowering Sahelian farmers to leverage their crop diversity assets for enhanced livelihood strategies, was funded by the International Fund for Agricultural Development (IFAD) from 2005, coordinated by Bioversity International and implemented by a combination of local, national and international organizations. Villagers designed and conducted the field trials, with technical support from project staff, on land that they had set aside for the purpose. Farmers studied both modern varieties and landraces

The impact of the Musa International Transit Centre

This brief presents the findings of a study published in 2010 that documented and assessed the performance of the International Transit Centre for Musa germplasm (ITC) in terms of the conservation and distribution of Musa germplasm. It also analysed the costs of ITC operations, including possible future developments

The impact of organic bananas in Alto Beni, Bolivia

This Impact Brief reports on an assessment using an asset-based livelihoods approach and carried out in 2009, five years after the end of the project. Overall, about 85% of farm families in the region said their incomes had increased since the end of the project, and the community enterprise grew in terms of both sales and membership. The project clearly initiated and catalyzed the developments that resulted in these outcomes. The impact assessment also identified elements that could be used to strengthen any future similar projects; a greater ongoing investment in the community enterprise, particularly in social and human capital, and decentralization to meet farmers’ preferred methods of working are two examples