6,059 research outputs found
Vortices in condensate mixtures
In a condensate made of two different atomic molecular species, Onsager's
quantization condition implies that around a vortex the velocity field cannot
be the same for the two species. We explore some simple consequences of this
observation. Thus if the two condensates are in slow relative translation one
over the other, the composite vortices are carried at a velocity that is a
fraction of the single species velocity. This property is valid for attractive
interaction and below a critical velocity which corresponds to a saddle-node
bifurcation.Comment: 4 pages, 3 figure
Book Reviews
Reviews of the following books: Kiah Bayley: Founder of Maine Institutions by Arthur T. Hamlin; The French-Canadian Heritage of New England by Gerard J. Brault
Operator ordering in Two-dimensional N=1 supersymmetry with curved manifold
We investigate an operator ordering problem in two-dimensional N=1
supersymmetric model which consists of n real superfields. There arises an
operator ordering problem when the target space is curved. We have to fix the
ordering in quantum operator properly to obtain the correct supersymmetry
algebra. We demonstrate that the super-Poincar\'{e} algebra fixes the correct
operator ordering. We obtain a supercurrent with correct operator ordering and
a central extension of supersymmetry algebra.Comment: 7 page
Condensation of classical nonlinear waves
We study the formation of a large-scale coherent structure (a condensate) in
classical wave equations by considering the defocusing nonlinear Schr\"odinger
equation as a representative model. We formulate a thermodynamic description of
the condensation process by using a wave turbulence theory with ultraviolet
cut-off. In 3 dimensions the equilibrium state undergoes a phase transition for
sufficiently low energy density, while no transition occurs in 2 dimensions, in
analogy with standard Bose-Einstein condensation in quantum systems. Numerical
simulations show that the thermodynamic limit is reached for systems with
computational modes and greater. On the basis of a modified wave
turbulence theory, we show that the nonlinear interaction makes the transition
to condensation subcritical. The theory is in quantitative agreement with the
simulations
Jachère et systèmes agraires
Des espèces, essentiellement herbacées, sont utilisées par les paysans pour définir un itinéraire technique à appliquer aux parcelles en culture. L'abandon et la remise en culture d'une parcelle dépendraient donc de la germination de certaines plantes qui, pour le paysan, marquent des seuils dans l'évolution progressive ou régressive des terres. En effet, pour le paysan de la zone soudanienne, la "fertilité" d'une terre n'apparaît pas comme un vague concept, mais comme une réalité physique traduite par l'aspect du sol ou par sa production, mais comme une réalité physique traduite par l'aspect du sol ou par sa production, mais surtout par la présence d'une espèce végétale ou d'un groupe d'espèces végétales. Des enquêtes auprès des paysans de la zone soudanienne du Burkina Faso révèlent que la gestion du cycle culture-jachère repose sur la végétation à laquelle est accordée une valeur indicatrice. L'alternance culture-jachère n'est donc pas systématisée par le respect d'une durée fixe de culture ou d'abandon ; elle est plutôt dictée par la vitesse d'apparition de ces espèces. (Résumé d'auteur
Relationship between fibre orientation and tensile strength of natural collagen membranes for heart valve leaflets
Heart valve prostheses are used to replace native heart valves which that are damaged because of congenital diseases or due to ageing. Biological prostheses made of bovine pericardium are similar to native valves and do not require any anticoagulation treatment, but are less durable than mechanical prostheses and usually fail by tearing. Researches are oriented in improving the resistance and durability of biological heart valve prostheses in order to increase their life expectancy. To understand the mechanical behaviour of bovine pericardium and relate it to its microstructure (mainly collagen fibres concentration and orientation) uniaxial tensile tests have been performed on a model material made of collagen fibres. Small Angle Light Scattering (SALS) has been also used to characterize the microstructure without damaging the material. Results with the model material allowed us to obtain the orientation of the fibres, relating the microstructure to mechanical performanc
Quantization of the Riemann Zeta-Function and Cosmology
Quantization of the Riemann zeta-function is proposed. We treat the Riemann
zeta-function as a symbol of a pseudodifferential operator and study the
corresponding classical and quantum field theories. This approach is motivated
by the theory of p-adic strings and by recent works on stringy cosmological
models. We show that the Lagrangian for the zeta-function field is equivalent
to the sum of the Klein-Gordon Lagrangians with masses defined by the zeros of
the Riemann zeta-function. Quantization of the mathematics of Fermat-Wiles and
the Langlands program is indicated. The Beilinson conjectures on the values of
L-functions of motives are interpreted as dealing with the cosmological
constant problem. Possible cosmological applications of the zeta-function field
theory are discussed.Comment: 14 pages, corrected typos, references and comments adde
- …