Crises and collective socio-economic phenomena: simple models and challenges

Financial and economic history is strewn with bubbles and crashes, booms and busts, crises and upheavals of all sorts. Understanding the origin of these events is arguably one of the most important problems in economic theory. In this paper, we review recent efforts to include heterogeneities and interactions in models of decision. We argue that the Random Field Ising model (RFIM) indeed provides a unifying framework to account for many collective socio-economic phenomena that lead to sudden ruptures and crises. We discuss different models that can capture potentially destabilising self-referential feedback loops, induced either by herding, i.e. reference to peers, or trending, i.e. reference to the past, and account for some of the phenomenology missing in the standard models. We discuss some empirically testable predictions of these models, for example robust signatures of RFIM-like herding effects, or the logarithmic decay of spatial correlations of voting patterns. One of the most striking result, inspired by statistical physics methods, is that Adam Smith's invisible hand can badly fail at solving simple coordination problems. We also insist on the issue of time-scales, that can be extremely long in some cases, and prevent socially optimal equilibria to be reached. As a theoretical challenge, the study of so-called "detailed-balance" violating decision rules is needed to decide whether conclusions based on current models (that all assume detailed-balance) are indeed robust and generic.Comment: Review paper accepted for a special issue of J Stat Phys; several minor improvements along reviewers' comment

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Not AvailableCereals provide more than half of global human caloric intake. Though cereals are nutritious, their nutritional density, especially of micronutrients, is far below recommended level in the products we consume. Due to this, over three billion individuals are malnourished globally. About 45 micronutrients (required in μg to mg quantity) including some mineral elements, vitamins, essential amino acids and fatty acids are vital to human body. In addition, antinutrients in food staples, reduced accumulation by plants and low bioavailability of minerals contribute further to micronutrient deficiencies. Vitamin-A, iron and iodine deficiency disorders are the most common. Hence, there is a need to evolve viable strategies of micronutrient enrichment in dietary staples. Of the three major strategies viz., dietary diversification, supplementation and food fortification, agronomic and/or genetic fortification is the cost effective and sustainable way to address the problem of malnutrition. Considering the severity of malnutrition, the HarvestPlus initiated genetic biofortification program of staple food crops focusing on most limiting nutrients viz., iron, zinc, and vitamin A. Most of the HarvestPlus biofortified varieties are bred through conventional breeding. However, MAS and transgenics are also used to biofortify crops in the research programmes other than the HarvestPlus. More than 150 biofortified varieties of 10 crops have been released in 30 countries. More than 20 million people are consuming biofortified crops such as vitamin-A maize, iron pearl millet, zinc rice, zinc wheat, etc. Continuous efforts are needed still to biofortify staples and to encourage adoption further by farmers and consumers. With our present technological competence, multibiofortified staples can be developed by gene stacking. Much work on biofortification is still needed through collaborative and multi-sectoral approaches along with the strong policy support. In future, in addition to deployment of conventionally bred biofortified varieties, transgenic biofortified varieties may be approved and deployed.Not Availabl

Cosmic ray production in supernovae

International audienceWe give a brief review of the origin and acceleration of cosmic rays (CRs), emphasizing the production of CRs at different stages of supernova evolution by the first-order Fermi shock acceleration mechanism. We suggest that supernovae with trans-relativistic outflows, despite being rather rare, may accelerate CRs to energies above 10^{18}\mbox{ eV} over the first year of their evolution. Supernovae in young compact clusters of massive stars, and interaction powered superluminous supernovae, may accelerate CRs well above the PeV regime. We discuss the acceleration of the bulk of the galactic CRs in isolated supernova remnants and re-acceleration of escaped CRs by the multiple shocks present in superbubbles produced by associations of OB stars. The effects of magnetic field amplification by CR driven instabilities, as well as superdiffusive CR transport, are discussed for nonthermal radiation produced by nonlinear shocks of all speeds including trans-relativistic ones