651 research outputs found
Economic exchanges in a stratified society: End of the middle class?
We study the effect of the social stratification on the wealth distribution
on a system of interacting economic agents that are constrained to interact
only within their own economic class. The economical mobility of the agents is
related to its success in exchange transactions. Different wealth distributions
are obtained as a function of the width of the economic class. We find a range
of widths in which the society is divided in two classes separated by a deep
gap that prevents further exchange between poor and rich agents. As a
consequence, the middle wealth class is eliminated. The high values of the Gini
indices obtained in these cases indicate a highly unequal society. On the other
hand, lower and higher widths induce lower Gini indices and a fairer wealth
distribution.Comment: 7 pages, 2 figures, 1 table, to appear in Physica
Correlation between Risk Aversion and Wealth distribution
Different models of capital exchange among economic agents have been proposed
recently trying to explain the emergence of Pareto's wealth power law
distribution. One important factor to be considered is the existence of risk
aversion. In this paper we study a model where agents posses different levels
of risk aversion, going from uniform to a random distribution. In all cases the
risk aversion level for a given agent is constant during the simulation. While
for a uniform and constant risk aversion the system self-organizes in a
distribution that goes from an unfair ``one takes all'' distribution to a
Gaussian one, a random risk aversion can produce distributions going from
exponential to log-normal and power-law. Besides, interesting correlations
between wealth and risk aversion are found.Comment: 8 pages, 7 figures, submitted to Physica A, Proceedings of the VIII
LAWNP, Salvador, Brazil, 200
Health systems’ responses to the roll-out of antiretroviral therapy (ART) in India: a comparison of two HIV high-prevalence settings
The government of India launched the free anti-retroviral therapy (ART) initiative in 2004 and the programme has since scaled up expansion in a phased manner. Programme authorities acknowledge problems in scale-up, yet discussions have been restricted to operational constraints, with little consideration for how local health system responses to HIV/AIDS influence the delivery of ART. This paper draws on the perspectives of key informants and people living with HIV (PLHIV) to compare delivery of ART in two ART centres in the States of Maharashtra and Andhra Pradesh at two distinct points of time. In 2005, data were collected through key informant interviews (KIIs) using interview guides and a survey of PLHIV using a semi-structured interview schedule. Differences were observed in the functioning and resources of the two centres, indicating different levels of preparedness which in turn influenced PLHIV's pathways in accessing ART. We examine these differences in the light of programme leadership, ownership and the roles of public, private and non-governmental organisation actors in HIV care. KIIs conducted during a follow-up visit in 2009 focused on changes in ART delivery. Many operational problems had been resolved; however, new challenges were emerging as a result of the increased patient load. An understanding of how ART programmes evolve within local health systems has bearing on future developments of the ART programme and must include a consideration of the wider socio-political environment within which HIV programmes are embedded
Dobiński relations and ordering of boson operators
We introduce a generalization of the Dobiński relation, through which we define a family of Bell-type numbers and polynomials. Such generalized Dobiński relations are coherent state matrix elements of expressions involving boson ladder operators. This may be used in order to obtain normally ordered forms of polynomials in creation and annihilation operators, both if the latter satisfy canonical and deformed commutation relations
Coloured peak algebras and Hopf algebras
For a finite abelian group, we study the properties of general
equivalence relations on G_n=G^n\rtimes \SG_n, the wreath product of with
the symmetric group \SG_n, also known as the -coloured symmetric group. We
show that under certain conditions, some equivalence relations give rise to
subalgebras of \k G_n as well as graded connected Hopf subalgebras of
\bigoplus_{n\ge o} \k G_n. In particular we construct a -coloured peak
subalgebra of the Mantaci-Reutenauer algebra (or -coloured descent algebra).
We show that the direct sum of the -coloured peak algebras is a Hopf
algebra. We also have similar results for a -colouring of the Loday-Ronco
Hopf algebras of planar binary trees. For many of the equivalence relations
under study, we obtain a functor from the category of finite abelian groups to
the category of graded connected Hopf algebras. We end our investigation by
describing a Hopf endomorphism of the -coloured descent Hopf algebra whose
image is the -coloured peak Hopf algebra. We outline a theory of
combinatorial -coloured Hopf algebra for which the -coloured
quasi-symmetric Hopf algebra and the graded dual to the -coloured peak Hopf
algebra are central objects.Comment: 26 pages latex2
The iron limitation mosaic in the California Current System: Factors governing Fe availability in the shelf/near-shelf region
The California Current System is a productive eastern boundary region off the coasts of Washington, Oregon, and California. There is strong seasonality to the region, with high levels of rainfall and river input to the coastal ocean during the winter season, and coastal and Ekman upwelling during the spring and summer. Iron (Fe) input to the coastal ocean during the winter months can be stored in the continental shelf mud belts and then be delivered to the surface ocean by upwelling in the spring and summer. There have been a number of studies providing strong evidence of Fe-limitation of diatom growth occurring in regions of the California Current System off of California, and the occurrence of Fe-limitation has been linked with narrow continental shelf mud belt width and low river input. We provide evidence for potential Fe-limitation of diatoms off the southern coast of Oregon in July 2014, just off the shelf break near Cape Blanco in a region with moderate shelf width and river input. Since eastern boundary regions account for a disproportionally large amount of global primary production, this observation of potential Fe-limitation in an unexpected near-shore region of the California Current System has implications for global models of primary productivity. In order to re-evaluate the factors impacting Fe availability, we utilize satellite imagery to compare with historical datasets, and show that unexpected levels of Fe can often be explained by eddies, plumes of upwelled water moving offshore, or lack of recent upwelling
Basic kinetic wealth-exchange models: common features and open problems
We review the basic kinetic wealth-exchange models of Angle [J. Angle, Social
Forces 65 (1986) 293; J. Math. Sociol. 26 (2002) 217], Bennati [E. Bennati,
Rivista Internazionale di Scienze Economiche e Commerciali 35 (1988) 735],
Chakraborti and Chakrabarti [A. Chakraborti, B. K. Chakrabarti, Eur. Phys. J. B
17 (2000) 167], and of Dragulescu and Yakovenko [A. Dragulescu, V. M.
Yakovenko, Eur. Phys. J. B 17 (2000) 723]. Analytical fitting forms for the
equilibrium wealth distributions are proposed. The influence of heterogeneity
is investigated, the appearance of the fat tail in the wealth distribution and
the relaxation to equilibrium are discussed. A unified reformulation of the
models considered is suggested.Comment: Updated version; 9 pages, 5 figures, 2 table
Professionalism, Golf Coaching and a Master of Science Degree: A commentary
As a point of reference I congratulate Simon Jenkins on tackling the issue of professionalism in coaching. As he points out coaching is not a profession, but this does not mean that coaching would not benefit from going through a professionalization process. As things stand I find that the stimulus article unpacks some critically important issues of professionalism, broadly within the context of golf coaching. However, I am not sure enough is made of understanding what professional (golf) coaching actually is nor how the development of a professional golf coach can be facilitated by a Master of Science Degree (M.Sc.). I will focus my commentary on these two issues
Hopf algebras and Markov chains: Two examples and a theory
The operation of squaring (coproduct followed by product) in a combinatorial
Hopf algebra is shown to induce a Markov chain in natural bases. Chains
constructed in this way include widely studied methods of card shuffling, a
natural "rock-breaking" process, and Markov chains on simplicial complexes.
Many of these chains can be explictly diagonalized using the primitive elements
of the algebra and the combinatorics of the free Lie algebra. For card
shuffling, this gives an explicit description of the eigenvectors. For
rock-breaking, an explicit description of the quasi-stationary distribution and
sharp rates to absorption follow.Comment: 51 pages, 17 figures. (Typographical errors corrected. Further fixes
will only appear on the version on Amy Pang's website, the arXiv version will
not be updated.
- …