Página 1 dos resultados de 1776 itens digitais encontrados em 0.033 segundos

## Condensed phases of gases inside nanotube bundles

Calbi, M. Mercedes; Cole, Milton W.; Gatica, Silvina M.; Bojan, Mary J.; Stan, George
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/03/2001
Relevância na Pesquisa
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An overview is presented of the various phases predicted to occur when gases are absorbed within a bundle of carbon nanotubes. The behavior may be characterized by an effective dimensionality, which depends on the species and the temperature. Small molecules are strongly attracted to the interstitial channels between tubes. There, they undergo transitions between ordered and disordered quasi-one dimensional (1D) phases. Both small and large molecules display 1D and /or 2D phase behavior when adsorbed within the nanotubes, depending on the species and thermodynamic conditions. Finally, molecules adsorbed on the external surface of the bundle exhibit 1D behavior (striped phases), which crosses over to 2D behavior (monolayer film) and eventually 3D behavior (thick film) as the coverage is increased. The various phases exhibit a wide variety of thermal and other properties that we discuss here.; Comment: 12 fig., submitted to Review of Modern Physics Colloquia

## The rich behavior of the Boltzmann equation for dissipative gases

Ernst, M. H.; Trizac, E.; Barrat, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/09/2006
Relevância na Pesquisa
491.0433%
Within the framework of the homogeneous non-linear Boltzmann equation, we present a new analytic method, without the intrinsic limitations of existing methods, for obtaining asymptotic solutions. This method permits extension of existing results for Maxwell molecules and hard spheres to large classes of particle interactions, from very hard spheres to softer than Maxwell molecules, as well as to more general forcing mechanisms, beyond free cooling and white noise driving. By combining this method with numerical solutions, obtained from the Direct Simulation Monte Carlo (DSMC) method, we study a broad class of models relevant for the dynamics of dissipative fluids, including granular gases. We establish a criterion connecting the stability of the non-equilibrium steady state to an exponentially bound form for the velocity distribution $F$, which varies depending on the forcing mechanism. Power laws arise in marginal stability cases, of which several new cases are reported. Our results provide a minimal framework for interpreting large classes of experiments on driven granular gases.

## The equation of state for almost elastic, smooth, polydisperse granular gases for arbitrary density

Luding, S.; Strauss, O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/03/2001
Relevância na Pesquisa
498.04664%
Simulation results of dense granular gases with particles of different size are compared with theoretical predictions concerning the pair-correlation functions, the collison rate, the energy dissipation, and the mixture pressure. The effective particle-particle correlation function, which enters the equation of state in the same way as the correlation function of monodisperse granular gases, depends only on the total volume fraction and on the dimensionless width A of the size-distribution function. The ''global equation of state'' is proposed, which unifies both the dilute and the dense regime. The knowledge about a global equation of state is applied to steady-state situations of granular gases in the gravitational field, where averages over many snapshots are possible. The numerical results on the density profile agree perfectly with the predictions based on the global equation of state, for monodisperse situations. In the bi- or polydisperse cases, segregation occurs with the heavy particles at the bottom.; Comment: 21 pages, 11 figures

## Physical replicas and the Bose-glass in cold atomic gases

Morrison, S.; Kantian, A.; Daley, A. J.; Katzgraber, H. G.; Lewenstein, M.; Büchler, H. P.; Zoller, P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
594.84953%
We study cold atomic gases in a disorder potential and analyze the correlations between different systems subjected to the same disorder landscape. Such independent copies with the same disorder landscape are known as replicas. While in general these are not accessible experimentally in condensed matter systems, they can be realized using standard tools for controlling cold atomic gases in an optical lattice. Of special interest is the overlap function which represents a natural order parameter for disordered systems and is a correlation function between the atoms of two independent replicas with the same disorder. We demonstrate an efficient measurement scheme for the determination of this disorder-induced correlation function. As an application, we focus on the disordered Bose-Hubbard model and determine the overlap function within perturbation theory and a numerical analysis. We find that the measurement of the overlap function allows for the identification of the Bose-glass phase in certain parameter regimes.; Comment: 17 pages, 6 figures, updated and added several references, other minor changes and corrections

## Fluctuations of the Condensate in Ideal and Interacting Bose Gases

Xiong, Hongwei; Liu, Shujuan; Huang, Guoxiang; Xu, Zhijun; Zhang, Cunyuan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
491.0433%
We investigate the fluctuations of the condensate in the ideal and weakly interacting Bose gases confined in a box of volume V within canonical ensemble. Canonical ensemble is developed to describe the behavior of the fluctuations when different methods of approximation to the weakly interacting Bose gases are used. Research shows that the fluctuations of the condensate exhibit anomalous behavior for the interacting Bose gas confined in a box.; Comment: RevTex, 4 Figs,E-mail:hwxiong@sohu.com, corrected typos

## Thermodynamics of sustaining gases in the roughness of submerged superhydrophobic surfaces

Patankar, Neelesh A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/05/2015
Relevância na Pesquisa
496.82562%
Rough surfaces submerged in a liquid can remain almost dry if the liquid does not fully wet the roughness and gases are sustained in roughness grooves. Such partially dry surfaces can help reduce drag or enhance boiling. Gases sustained in roughness grooves would be composed of air and the vapor phase of the liquid itself. The thermodynamics of sustaining vapor was considered in a prior work [Patankar, Soft Matter, 2010, 6:1613]. Here, the thermodynamics of sustaining gases (e.g. air) is considered. Governing equations are presented along with a solution methodology to determine a critical condition to sustain gases. The critical roughness scale to sustain gases is estimated for different degrees of saturation of gases dissolved in the liquid. It is shown that roughness spacings of less than a micron are essential to sustain gases on surfaces submerged in water at atmospheric pressure. This is consistent with prior empirical data.; Comment: 15 pages, 6 figures

## The Gross-Pitaevskii equations and beyond for inhomogeneous condensed bosons

Angilella, G. G. N.; Bartalini, S.; Cataliotti, F. S.; Herrera, I.; March, N. H.; Pucci, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
577.93152%
A simple derivation of the static Gross-Pitaevskii (GP) equation is given from an energy variational principle. The result is then generalized heuristically to the time-dependent GP form. With this as background, a number of different experimental areas explored very recently are reviewed, in each case contact being established between the measurements and the predictions of the GP equations. The various limitations of these equations as used on dilute inhomogeneous condensed Boson atomic gases are then summarized, reference also being made to the fact that there is no many-body wave function underlying the GP formulation. This then leads into a discussion of a recently proposed integral equation, derived by taking the Bogoliubov-de Gennes equation as starting point. Some limitations of the static GP differential equation are thereby removed, though it is a matter of further study to determine whether a correlated wave function exists as underpinning for the integral equation formulation.; Comment: To appear in "Trends in Boson Research", edited by A. V. Ling (Nova Science, New York, ISBN 1594545219). Better quality figures available upon request

## Non-BCS superfluidity in trapped ultracold Fermi gases

Jensen, L. M.; Kinnunen, J.; Torma, P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
491.0433%
Superconductivity and superfluidity of fermions require, within the BCS theory, matching of the Fermi energies of the two interacting Fermion species. Difference in the number densities of the two species leads either to a normal state, to phase separation, or - potentially - to exotic forms of superfluidity such as FFLO-state, Sarma state or breached pair state. We consider ultracold Fermi gases with polarization, i.e. spin-density imbalance. We show that, due to the gases being trapped and isolated from the environment in terms of particle exchange, exotic forms of superfluidity appear as a shell around the BCS-superfluid core of the gas and, for large density imbalance, in the core as well. We obtain these results by describing the effect of the trapping potential by using the Bogoliubov-de Gennes equations. For comparison to experiments, we calculate also the condensate fraction, and show that, in the center of the trap, a polarized superfluid leads to a small dip in the central density difference. We compare the results to those given by local density approximation and find qualitatively different behavior.; Comment: Extended and revised, 13 pages, 13 figures

## Spin Diffusion in Trapped Gases: Anisotropy in Dipole and Quadrupole Modes

Mullin, W. J.; Ragan, R. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/06/2006
Relevância na Pesquisa
491.0433%
Recent experiments in a mixture of two hyperfine states of trapped Bose gases show behavior analogous to a spin-1/2 system, including transverse spin waves and other familiar Leggett-Rice-type effects. We have derived the kinetic equations applicable to these systems, including the spin dependence of interparticle interactions in the collision integral, and have solved for spin-wave frequencies and longitudinal and transverse diffusion constants in the Boltzmann limit. We find that, while the transverse and longitudinal collision times for trapped Fermi gases are identical, the Bose gas shows unusual diffusion anisotropy in both dipole and quadrupole modes. Moreover, the lack of spin isotropy in the interactions leads to the non-conservation of transverse spin, which in turn has novel effects on the hydrodynamic modes.; Comment: 18 pages, 9 figures

## Angular Fulde-Ferrell-Larkin-Ovchinnikov state in cold fermion gases in a toroidal trap

Yanase, Youichi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
494.2404%
We study the possibility of angular Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in which the rotation symmetry is spontaneously broken, in population imbalanced fermion gases near the BCS-BEC crossover. We investigate the superfluid gases at low temperatures on the basis of the Bogoliubov-de Gennes equation, and examine the stability against thermal fluctuations using the T-matrix approach beyond the local-density approximation (LDA). We find that the angular FFLO state is stabilized in the gases confined in the toroidal trap but not in the harmonic trap. The angular FFLO state is stable near the BCS-BEC crossover owing to the formation of pseudogap. Spatial dependences of number density and local population imbalance are shown for an experimental test.; Comment: final version for publication in Phys. Rev. B Rapid Communication

## Making, probing and understanding ultracold Fermi gases

Ketterle, Wolfgang; Zwierlein, Martin W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/01/2008
Relevância na Pesquisa
491.0433%
A review on superfluidity and the BEC-BCS crossover in ultracold Fermi gases.; Comment: Long review article, 206 pages, 74 figures, to appear in Ultracold Fermi Gases, Proceedings of the International School of Physics "Enrico Fermi", Course CLXIV, Varenna, 20 - 30 June 2006, edited by M. Inguscio, W. Ketterle, and C. Salomon (IOS Press, Amsterdam) 2008

## Paired states in spin-imbalanced atomic Fermi gases in one dimension

Kakashvili, Paata; Bolech, C. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/12/2008
Relevância na Pesquisa
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A growing expertise to engineer, manipulate and probe different cold-atom analogs of electronic condensed matter systems allows to probe properties of exotic pairing. We study paired states of spin-imbalanced ultracold atomic system of fermions with attractive short-range interactions in one-dimensional traps. Calculations are done using the Bethe Ansatz technique and the trap is incorporated into the solution via a local density approximation. The thermodynamic-Bethe-Ansatz equations are solved numerically and different local density profiles are calculated for zero and finite temperatures. A procedure to identify the homogeneous-system phase diagram using local density profiles in the trap is also proposed. Such scheme would be immediately useful for the experiments.; Comment: 4 pages, 2 figures

## Two-dimensional delta potential wells and condensed-matter physics

de Llano, M.; Salazar, A.; Solis, M. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
675.9297%
It is well-known that a delta potential well in 1D has only one bound state but that in 3D it supports an {\it infinite} number of bound states with {\it infinite} binding energy for the lowest level. We show how this also holds for the less familiar 2D case, and then discuss why this makes 3D delta potential wells unphysical as models of interparticle interactions for condensed-matter many-body systems. However, both 2D and 3D delta wells can be regularized'' to support a single bound level which in turn renders them conveniently simple single-parameter interactions, e.g., for modeling the pair-forming dynamics of quasi-2D superconductors such as the cuprates, or in 3D of other superconductors and of neutral-fermion superfluids such as ultra-cold trapped Fermi gases.; Comment: 19 pages including 5 figures

## Velocity Distributions of Granular Gases with Drag and with Long-Range Interactions

Kohlstedt, K.; Snezhko, A.; Sapozhnikov, M. V.; Aranson, I. S.; Olafsen, J. S.; Ben-Naim, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/07/2005
Relevância na Pesquisa
491.0433%
We study velocity statistics of electrostatically driven granular gases. For two different experiments: (i) non-magnetic particles in a viscous fluid and (ii) magnetic particles in air, the velocity distribution is non-Maxwellian, and its high-energy tail is exponential, P(v) ~ exp(-|v|). This behavior is consistent with kinetic theory of driven dissipative particles. For particles immersed in a fluid, viscous damping is responsible for the exponential tail, while for magnetic particles, long-range interactions cause the exponential tail. We conclude that velocity statistics of dissipative gases are sensitive to the fluid environment and to the form of the particle interaction.; Comment: 4 pages, 3 figures

## Shock-Like Dynamics of Inelastic Gases

Ben-Naim, E.; Chen, S. Y.; Doolen, G. D.; Redner, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/09/1999
Relevância na Pesquisa
491.0433%
We provide a simple physical picture which suggests that the asymptotic dynamics of inelastic gases in one dimension is independent of the degree of inelasticity. Statistical characteristics, including velocity fluctuations and the velocity distribution are identical to those of a perfectly inelastic sticky gas, which in turn is described by the inviscid Burgers equation. Asymptotic predictions of this continuum theory, including the t^{-2/3} temperature decay and the development of discontinuities in the velocity profile, are verified numerically for inelastic gases.; Comment: 4 pages, 5 figures, revtex

## Condensed matter physics with trapped atomic Fermi gases

Stoof, H. T. C.; Houbiers, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/08/1998
Relevância na Pesquisa
588.0553%
We present an overview of the various phase transitions that we anticipate to occur in trapped fermionic alkali gases. We also discuss the prospects of observing these transitions in (doubly) spin-polarized Li-6 and K-40 gases, which are now actively being studied by various experimental groups around the world.; Comment: 18 pages of LaTeX and 2 postscript figures. Contribution to the international summer school `Enrico Fermi' on Bose-Einstein condensation in atomic gases, Varenna 1998

## Long-time tails in freely cooling granular gases

Hayakawa, Hisao; Otsuki, Michio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
491.0433%
The long-time behavior of the current auto-correlation functions for the velocity, the shear stress and the heat flux is investigated in freely cooling granular gases. It is found that the correlation functions for the velocity and the shear stress have the long-time tails obeying $\tau^{-d/2}$, while the correlation function of heat flux decays as $\tau^{-(d+2)/2} \exp(-\zeta^* \tau)$ with the dimensionless cooling rate $\zeta^*$, the spatial dimension $d$ and the scaled time $\tau$ in terms of the collision frequency. The result of our numerical simulation of the freely cooling granular gases is consistent with the theoretical prediction.; Comment: 26 pages, 5 figures

## Anomalous velocity distributions in inelastic Maxwell gases

Brito, R.; Ernst, M. H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
569.7446%
This review is a kinetic theory study investigating the effects of inelasticity on the structure of the non-equilibrium states, in particular on the behavior of the velocity distribution in the high energy tails. Starting point is the nonlinear Boltzmann equation for spatially homogeneous systems, which supposedly describes the behavior of the velocity distribution function in dissipative systems as long as the system remains in the homogeneous cooling state, i.e. on relatively short time scales before the clustering and similar instabilities start to create spatial inhomogeneities. This is done for the two most common models for dissipative systems, i.e. inelastic hard spheres and inelastic Maxwell particles. In systems of Maxwell particles the collision frequency is independent of the relative velocity of the colliding particles, and in hard sphere systems it is linear. We then demonstrate the existence of scaling solutions for the velocity distribution function, $F(v,t) \sim v_0(t)^{-d} f((v/v_0(t))$, where $v_0$ is the r.m.s. velocity. The scaling form $f(c)$ shows overpopulation in the high energy tails. In the case of freely cooling systems the tails are of algebraic form, $f(c)\sim c^{-d-a}$, where the exponent $a$ may or may not depend on the degree of inelasticity...

## Transition from 3D to 1D in Bose Gases at Zero Temperature

Salasnich, L.; Parola, A.; Reatto, L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/04/2004
Relevância na Pesquisa
492.2326%
We investigate the effects of dimensional reduction in Bose gases induced by a strong harmonic confinement in the transverse cylindric radial direction. By using a generalized Lieb-Liniger theory, based on a variational treatment of the transverse width of the Bose gas, we analyze the transition from a 3D Bose-Einstein condensate to the 1D Tonks-Girardeau gas. The sound velocity and the frequency of the lowest compressional mode give a clear signature of the regime involved. We study also the case of negative scattering length deriving the phase diagram of the Bose gas (uniform, single soliton, multi soliton and collapsed) in toroidal confinement.; Comment: 5 pages, 5 figures, to be published in Phys. Rev. A

## Two-dimensional delta potential wells and condensed-matter physics

de Llano,M.; Salazar,A.; Solís,M.A.
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2005 EN
Relevância na Pesquisa
675.9297%
It is well-known that a delta potential well in 1D has only one bound state but that in 3D it supports an infinite number of bound states with infinite binding energy for the lowest level. We show how this also holds for the less familiar 2D case, and then discuss why this makes 3D delta potential wells unphysical as models of interparticle interactions for condensed-matter, many-body systems. However, both 2D and 3D delta wells can be "regularized" to support a single bound level which in turn renders them conveniently simple single-parameter interactions, e.g., for modeling the pair-forming dynamics of quasi-2D superconductors such as the cuprates, or in 3D of other superconductors and of neutral-fermion superfluids such as ultra-cold trapped Fermi gases.