34 research outputs found
Striga : biology and control
Meeting: Workshop on the Biology and Control of Striga, 14-17 Nov. 1983, Dakar, SNPublished jointly with IDR
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
Analytic solutions to modelling exponential and harmonic functions using Chebyshev polynomials: fitting frequency-domain lifetime images with photobleaching
The transport of the cardiac glycoside ouabain by the Malpighian tubules of Zonocerus variegatus
Darwinâs progress and the problem of slavery
Legendary as a âgeniusâ out of time, Charles Darwin is said to have revolutionized our understanding of life on earth by explaining nature-history as the purposeless product of directionless variation naturally selected through a chancy struggle for existence. Yet, whatever may be deduced from his theory of natural selection as understood today, Darwin himself was not bound by any such conclusions. His vision of nature-history, for all its haphazardness, was directional, meliorative and hopeful. In the 1830s he went out of his way to develop privately a subversive theory of human evolution, and he pursued the subject with tenacity for three decades before publishing The descent of man in 1871. Underpinning his research was a belief in racial brotherhood rooted in the greatest moral movement of the age, for the abolition of slavery. Darwin extended the abolitionistsâ common-descent image to the rest of life, making not just the races, but all races, kin. Human slavery, however, did not evolve into or out of existence. To Darwin it was a âsinâ to âexpiateâ by moral action, and the Origin of species was written with a view towards undermining slaveryâs creationist ideologues, most notably the Harvard professor Louis Agassiz. Intractable slavery collided with Darwinâs post-Christian progressivism in the US Civil War, clouding his hopes for humanity, but the Northern victory in 1865 enabled him to carry âthe grand idea of God hating sin and loving righteousnessâ into The descent of man, where the driving of formerly enslaved races out of existence is naturalized as a byproduct of historical progress in which âvirtue will be triumphantâ at last