1,720,982 research outputs found
On the creation of quantized vortex lines in rotating He II
No full textIn this paper we present some hydrodynamical consequences of a previously proposed stochastic model for superfluid4He. We discuss in particular the possibility of time-dependent evolutions which, starting from a rotational initial state, lead to asymptotic stationary solutions where the vorticity is concentrated in singular regions. An example of such asymptotic stationary solutions is the quantized vortex line solution. We also recall the concept of quantum critical slipping velocity and investigate some possible consequences on the spin-up problem and on the creation of systems of vortex lines
Lagrangian variational principle in stochastic mechanics: gauge structure and stability
No full textThe Lagrangian variational principle with the classical action leads, in stochastic mechanics, to Madelung’s fluid equations, if only irrotational velocity fields are allowed, while new dynamical equations arise if rotational velocity fields are also taken into account. The new equations are shown to be equivalent to the (gauge invariant) system of a Schrödinger equation involving a four‐vector potential (A,Φ) and the coupled evolution equation (of magnetohydrodynamical type) for the vector field A. A general energy theorem can be proved and the stability properties of irrotational and rotational solutions investigated
Stochastic mechanics and superfluidity in He4: rotation paradox and transition to turbulence
No full textSelf-consistent hydrodynamical model for He II near absolute zero in the framework of stochastic mechanics
No full textWorking in the framework of stochastic mechanics we propose a simple model, based on the hard-sphere gas approximation, for He II at T=0. The model seems to describe correctly the peculiar hydrodynamical behavior of He II near absolute zero and also provides good estimates for the critical velocities and the kinematic viscosity
Stochastic Quantization for a System of N Identical Interacting Bose Particles
No full textWe apply stochastic quantization to a system of N interacting identical bosons in an external potential Φ, by means of a general stationary-action principle. The collective motion is described in terms of a Markovian diffusion on , with joint density and entangled current velocity field , in principle of non-gradient form, related to one another by the continuity equation. Dynamical equations relax to those of canonical quantization, in some analogy with Parisi–Wu stochastic quantization. Thanks to the identity of particles, the one-particle marginal densities ρ, in the physical space , are all the same and it is possible to give, under mild conditions, a natural definition of the single-particle current velocity, which is related to ρ by the continuity equation in . The motion of single particles in the physical space comes to be described in terms of a non-Markovian three-dimensional diffusion with common density ρ and, at least at dynamical equilibrium, common current velocity v. The three-dimensional drift is perturbed by zero-mean terms depending on the whole configuration of the N-boson interacting system. Finally, we discuss in detail under which conditions the one-particle dynamical equations, which in their general form allow rotational perturbations, can be particularized, up to a change of variables, to the Gross–Pitaevskii equations
Stochastic quantization for a system of N identical Bose particles
No full textWe apply Stochastic Quantization to a system of N interacting identical Bosons in an external potential Phi, by means of a general stationary-action principle. The collective motion is described in terms of a Markovian diffusion on R^(3N), with joint density Rho and entangled current velocity field V, in principle of non-gradient form, related one to the other by the continuity equation. Dynamical equations relax to those of canonical quantization, in some analogy with Parisi-Wu stochastic quantization. Thanks to the identity of particles, the one-particle marginal densities rho, in the physical space R^3, are all the same and it is possible to give, under mild conditions, a natural definition of the single-particle current velocity, which is related to rho by the continuity equation in R^3. The motion of single particles in the physical space comes to be described in terms of a non-Markovian three-dimensional diffusion with common density rho and, at least at dynamical equilibrium, common current velocity v. The three-dimensional drift is perturbed by zero-mean terms depending on the whole configuration of the N-bosons interacting system. Finally we discuss in detail under which conditions the one-particle dynamical equations, which in their general form allow rotational perturbations, can be particularized, up to a change of variables, to Gross-Pitaevskii equations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Addendum to "A stochastic algorithm to compute optimal probabilities in the chaos game": a new convergence criterium
No full textWe propose a new convergence criterion for the stochastic algorithm for the optimization of probabilities (SAOP) described in an earlier paper. The criterion is based on the dissection principle for irreducible finite Markov chain
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