6,695 research outputs found

    One Upper Estimate on the Number of Limit Cycles of Even Degree Li\'enard Equations in the Focus Case

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    We give an explicit upper bound for a number of limit cycles of the Li\'enard equation x˙=yF(x)\dot{x}=y-F(x), y˙=x\dot{y}=-x of even degree in the case its unique singular point (0,0)(0,0) is a focus.Comment: 10 pages, 1 figur

    Local seed systems and village-level determinants of millet crop diversity in marginal environments of India:

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    "In the subsistence-oriented, semi-arid production systems of Andhra Pradesh and Karnataka, India, the environment is marginal for crop growth and often there is no substitute for millet crops. Across communities, farmers grow thirteen different combinations of pearl millet, sorghum, finger millet, little millet, and foxtail millet varieties, but individual farmers grow an average of only two to three millet varieties per season. The notion of the seed system includes all channels through which farmers acquire genetic materials, outside or in interaction with the commercial seed industry. Data are compiled through household surveys and interviews with traders and dealers in village and district markets. Based on the concept of the seed lot, several characteristics of local seed markets are defined and measured by millet crop, including seed transfer rates for farmer-to-farmer transactions and seed replacement ratios. Most seed transactions appear to be based on money. Seed supply channels differ by improvement status of the genetic material. Econometric results indicate the significance of the seed replacement ratios and seed volumes traded in determining the levels of crop biodiversity managed by communities, in addition to the household, farm and other market-related factors identified by previous studies. These are interpreted as indicators of market strength." Authors' AbstractSeed systems, Crop diversity, Seed industry and trade, genetic variation,

    Farmer preferences for milpa diversity and genetically modified maize in Mexico: a latent class approach

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    Maize, the second most globally important staple crop after wheat, originated in Mexico, where it is typically grown as part of a set of associated crops and practices called the milpa system. This ancient mode of production is practiced today in ways that vary by cultural context and agro-environment. Milpas generate private economic value, in terms of food security, diet quality and livelihoods, for the twomillion farm households who manage them. Furthermore, milpas generate public economic value by conserving agrobiodiversity, especially that of maize landraces, which have the potential to contribute unique traits needed by plant breeders for future crop improvement. In this way, milpas contribute to global food security in maize. However, the sustainability of the milpa system has been threatened by offfarm employment opportunities, long-distance migration, the increasing commercialization and intensification of maize production. Most recently, the milpa system has been negatively impacted by the contamination of maize landraces by genetically modified (GM) maize, cultivation of which is currently prohibited in Mexico. Here, we employ a choice experiment to estimate Mexican farmers’ valuation of three components of agrobiodiversity (crop species richness, maize variety richness and maize landraces), and examine their interest in cultivating GM maize. Choice experiment data, household level social, economic and demographic data, community level economic development data, and information on milpa production characteristics, and farmers’ attitudes and perceptions with regards to GM food and crops were collected from 420 farm households across 17 communities in three states of Mexico. Using these data, we analyzed the heterogeneity of farmer preferences using a latent class model, which can be used to simultaneously identify sample segments having homogenous preferences for milpa attributes, as well as farmer characteristics affecting preferences. We further identified the characteristics of farmers who are most likely to continue growing maize landraces and managing milpa systems, as well as those least likely to accept GM maize. Specifically, we identified three distinct segments of farmers: (i) Landrace Conservationists derive the highest private economic value from continued management of landraces and the highest economic loss from the possible adoption of GM maize. These farmers are young, dislike GM foods and crops, and are mainly located at the Oaxaca site, where transgenic constructs have been found in maize landraces. (ii) Milpa Diversity Managers derive the highest economic value from managing all of the agrobiodiversity components of the milpa, and suffer fewer losses from management of GM maize. These are older farmers, who are curious and like to experiment with maize varieties. (iii) Marginalized Maize Producers derive little value from crop species and maize variety richness, receive minimal value from maize landraces, and also experience the smallest negative impact from the adoption of GM maize. These farmers are located in the most isolated communities, have the lowest level of productivity, and oversee the largest milpa areas. They are also the most tightly integrated into the maize output markets. These novel findings have implications for debates concerning the adoption of GM maize in Mexico and its associated costs and benefits, as well as for the design of targeted, cost-effective conservation programs on farms

    Maize in Eastern and Southern Africa: 'seeds' of success in retrospect

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    This synthesis revisits the “maize success story” in Sub-Saharan Africa, drawing selectively from an extensive published literature about maize seed technical change and related policies. The review focuses on the countries of Kenya, Zimbabwe, Zambia, and Malawi, where maize is most important in the food economy, and refers to the period when maize became a dominant food crop through the 1990s. The term “success” is equivocal in this case, both because of the difficult of establishing the appropriate counterfactual and because some of the policies that contributed to success in one period later led to decline. While the “seeds” themselves were the result of innovative, successful maize breeding, boom periods in maize production were episodic and the public investments in the controlled markets that bolstered them were not fiscally sustainable. Since maize will remain a crucial part of the food security equation even while the agricultural economies of the region diversify, continued investments in both maize research and market institutions, some of which must be public, are essential. The most vital question, however, is where the domestic political pressure to support these investments will originate an issue related to governance.Maize Africa, Southern., Seeds Technological innovations Africa., Food crops Africa, Eastern Marketing., Markets Prices., Food security Africa., Plant breeding Research., Investment of public funds.,