9,424 research outputs found
Possession et exorcisme dans une Eglise pentecôtiste au Brésil
Les accusations lancées par le pentecôtisme contre les cultes de possession brésiliens ne doivent pas cacher l'influence des cultes sur les formes rituelles de ce mouvement religieux. Certaines Eglises pentecôtistes développent en effet des séances d'exorcisme où le démon habitant les possédés emprunte les traits des esprits que reçoivent les médiums dans les cultes. L'analyse d'une séance d'exorcisme dans le temple de l'Eglise universelle, récemment implantée dans la ville de Belém, révèle ainsi l'intégration d'éléments rituels, et des catégories qui leur sont associées, aux cérémonies pentecôtistes. Cette appropriation s'accompagne cependant d'une profonde transformation du dispositif de la possession et d'une altération de la condition de possédé : le lien avec le démon n'étant plus de l'ordre de l'alliance mais de l'entrave, le possédé subit désormais son état. (Résumé d'auteur
Understanding the production of dual BEC with sympathetic cooling
We show, both experimentally and theoretically, that sympathetic cooling of
Rb atoms in the state by evaporatively cooled atoms in the
state can be precisely controlled to produce dual or single
condensate in either state. We also study the thermalization rate between two
species. Our model renders a quantitative account of the observed role of the
overlap between the two clouds and points out that sympathetic cooling becomes
inefficient when the masses are very different. Our calculation also yields an
analytical expression of the thermalization rate for a single species.Comment: 3 figure
L\'evy-like behavior in deterministic models of intelligent agents exploring heterogeneous environments
Many studies on animal and human movement patterns report the existence of
scaling laws and power-law distributions. Whereas a number of random walk
models have been proposed to explain observations, in many situations
individuals actually rely on mental maps to explore strongly heterogeneous
environments. In this work we study a model of a deterministic walker, visiting
sites randomly distributed on the plane and with varying weight or
attractiveness. At each step, the walker minimizes a function that depends on
the distance to the next unvisited target (cost) and on the weight of that
target (gain). If the target weight distribution is a power-law, , in some range of the exponent , the foraging medium induces
movements that are similar to L\'evy flights and are characterized by
non-trivial exponents. We explore variations of the choice rule in order to
test the robustness of the model and argue that the addition of noise has a
limited impact on the dynamics in strongly disordered media.Comment: 15 pages, 7 figures. One section adde
Hydrodynamic reductions of the heavenly equation
We demonstrate that Pleba\'nski's first heavenly equation decouples in
infinitely many ways into a triple of commuting (1+1)-dimensional systems of
hydrodynamic type which satisfy the Egorov property. Solving these systems by
the generalized hodograph method, one can construct exact solutions of the
heavenly equation parametrized by arbitrary functions of a single variable. We
discuss explicit examples of hydrodynamic reductions associated with the
equations of one-dimensional nonlinear elasticity, linearly degenerate systems
and the equations of associativity.Comment: 14 page
Generating anisotropic fluids from vacuum Ernst equations
Starting with any stationary axisymmetric vacuum metric, we build anisotropic
fluids. With the help of the Ernst method, the basic equations are derived
together with the expression for the energy-momentum tensor and with the
equation of state compatible with the field equations. The method is presented
by using different coordinate systems: the cylindrical coordinates
and the oblate spheroidal ones. A class of interior solutions matching with
stationary axisymmetric asymptotically flat vacuum solutions is found in oblate
spheroidal coordinates. The solutions presented satisfy the three energy
conditions.Comment: Version published on IJMPD, title changed by the revie
Deeply subrecoil two-dimensional Raman cooling
We report the implementation of a two-dimensional Raman cooling scheme using
sequential excitations along the orthogonal axes. Using square pulses, we have
cooled a cloud of ultracold Cesium atoms down to an RMS velocity spread of
0.39(5) recoil velocity, corresponding to an effective temperature of 30 nK
(0.15 T_rec). This technique can be useful to improve cold atom atomic clocks,
and is particularly relevant for clocks in microgravity.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
The -structures on complex line bundles and explicit Riemannian metrics with SU(4)-holonomy
We completely explore the system of ODE's which is equivalent to the
existence of a parallel -structure on the cone over a 7-dimensional
3-Sasakian manifold. The one-dimensional family of solutions of this system is
constructed. The solutions of this family correspond to metrics with holonomy
SU(4) which generalize the Calabi metrics.Comment: 11 page
Mixed (open/closed) N=(2,2) string theory as an integrable deformation of self-duality
The exact effective field equations of motion, corresponding to the
perturbative mixed theory of open and closed (2,2) world-sheet supersymmetric
strings, are investigated. It is shown that they are only integrable in the
case of an abelian gauge group. The gravitational equations are then stationary
with respect to the Born-Infeld-type effective action.Comment: 9 pages, LaTe
A thick shell Casimir effect
We consider the Casimir energy of a thick dielectric-diamagnetic shell under
a uniform velocity light condition, as a function of the radii and the
permeabilities. We show that there is a range of parameters in which the stress
on the outer shell is inward, and a range where the stress on the outer shell
is outward. We examine the possibility of obtaining an energetically stable
configuration of a thick shell made of a material with a fixed volume
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