4,007 research outputs found
The Poisson structure of the mean-field equations in the Phi^4 theory
We show that the mean-field time dependent equations in the Phi^4 theory can
be put into a classical non-canonical hamiltonian framework with a Poisson
structure which is a generalization of the standard Poisson bracket. The
Heisenberg invariant appears as a structural invariant of the Poisson tensor.
(To be pubished in Annals of Physics)Comment: 12 pages Te
Ground State Properties and Glueball Spectrum in SU(2) Yang-Mills Theory using Gauge Invariant Variables
We describe a nonperturbative calculation of the spectrum of SU(2) Yang-Mills
theory based on a Hamiltonian formulation. Our approach exploits gauge
invariant variables similar to those used in nuclear physics to describe
collective motion in nuclei.Comment: 18 pages Late
Exponential sums with reducible polynomials
International audienceHooley proved that if f â Z[X] is irreducible of degree â„ 2, then the fractions {r/n}, 0 < r < n with f (r) ⥠0 (mod n), are uniformly distributed in ]0, 1[. In this paper we study such problems for reducible polynomials of degree 2 and 3 and for finite products of linear factors. In particular, we establish asymptotic formulas for exponential sums over these normalized roots
Variational approximations for correlation functions in quantum field theories
Applying the time-dependent variational principle of Balian and V\'en\'eroni,
we derive variational approximations for multi-time correlation functions in
field theory. We assume first that the initial state is given and
characterized by a density operator equal to a Gaussian density matrix. Then,
we study the more realistic situation where only a few expectation values are
given at the initial time and we perform an optimization with respect to the
initial state. We calculate explicitly the two-time correlation functions with
two and four field operators at equilibrium in the symmetric phase.Comment: 60 pages, Latex, to be published in Annals of Physic
Asynchronous Changes in Vegetation, Runoff and Erosion in the Nile River Watershed during the Holocene
The termination of the African Humid Period in northeastern Africa during the early
Holocene was marked by the southward migration of the rain belt and the
disappearance of the Green Sahara. This interval of drastic environmental changes
was also marked by the initiation of food production by North African huntergatherer
populations and thus provides critical information on human-environment
relationships. However, existing records of regional climatic and environmental
changes exhibit large differences in timing and modes of the wet/dry transition at
the end of the African Humid Period. Here we present independent records of
changes in river runoff, vegetation and erosion in the Nile River watershed during
the Holocene obtained from a unique sedimentary sequence on the Nile River fan
using organic and inorganic proxy data. This high-resolution reconstruction allows
to examine the phase relationship between the changes of these three parameters
and provides a detailed picture of the environmental conditions during the
Paleolithic/Neolithic transition. The data show that river runoff decreased gradually
during the wet/arid transition at the end of the AHP whereas rapid shifts of
vegetation and erosion occurred earlier between 8.7 and ,6 ka BP. These
asynchronous changes are compared to other regional records and provide new
insights into the threshold responses of the environment to climatic changes. Our
record demonstrates that the degradation of the environment in northeastern Africa
was more abrupt and occurred earlier than previously thought and may have
accelerated the process of domestication in order to secure sustainable food
resources for the Neolithic African populations
Sophie Guérard de Latour, dir., Le multiculturalisme a-t-il un avenir ?
Partant du constat que « le multiculturalisme semble dĂ©sormais faire partie du paysage des dĂ©mocraties libĂ©rales », lâouvrage dirigĂ© par Sophie GuĂ©rard de Latour sur la dĂ©finition et Ă lâapplication du multiculturalisme dans ces dĂ©mocraties. ArticulĂ©es autour de trois axes, les contributions abordent diffĂ©rents points fondamentaux inhĂ©rents au multiculturalisme, envisagĂ© ici dans sa version libĂ©rale. La premiĂšre partie (« La culture, une catĂ©gorie piĂ©gĂ©e ? », pp. 27-134) sâapplique Ă redĂ©fin..
Les formations Ă lâadministration et Ă la gestion de la culture : bilan et perspectives
Les formations Ă la gestion et Ă lâadministration culturelles se sont multipliĂ©es en France depuis les annĂ©es 1980 avec le dĂ©veloppement du secteur culturel, la professionnalisation de lâemploi dans ce secteur mais aussi lâattrait pour la culture en gĂ©nĂ©ral. Ce sont prĂšs de 300 formations, majoritairement de niveau I sous forme de masters professionnels, qui ont pu ĂȘtre rĂ©pertoriĂ©es et caractĂ©risĂ©es (anciennetĂ©, nombre dâĂ©tudiants, domaine dâapplication et, le cas Ă©chĂ©ant, champ disciplinaire, types dâenseignement). Ces formations sont essentiellement universitaires mĂȘme si des Ă©coles de commerce consulaires ont pris position plus rĂ©cemment sur ce marchĂ©. Cette explosion du nombre de formations doit ĂȘtre resituĂ©e dans un double contexte : celui dâun espace europĂ©en des formations initiĂ© par le processus de Bologne et la rĂ©forme LMD, qui semblent avoir contribuĂ© Ă la multiplication de ces formations au sein de lâUniversitĂ© ; celui de la territorialisation des politiques de formation et dâune implication accrue du niveau rĂ©gional. LâintĂ©rĂȘt du secteur culturel comme des Ă©tudiants attirĂ©s par ces formations est que ce marchĂ© de lâemploi de gestion et dâadministration culturelles soit Ă la fois mieux apprĂ©ciĂ© quantitativement et mieux suivi qualitativement, et que les logiques respectives de lâenseignement supĂ©rieur et du marchĂ© de lâemploi se confrontent dans des pratiques rĂ©guliĂšres dâĂ©valuation, permettant ainsi de rapprocher offre et demande dâemploi dans une vĂ©ritable dĂ©marche de rĂ©gulation
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