1,029 research outputs found
Short-lived lattice quasiparticles for strongly interacting fluids
It is shown that lattice kinetic theory based on short-lived quasiparticles
proves very effective in simulating the complex dynamics of strongly
interacting fluids (SIF). In particular, it is pointed out that the shear
viscosity of lattice fluids is the sum of two contributions, one due to the
usual interactions between particles (collision viscosity) and the other due to
the interaction with the discrete lattice (propagation viscosity). Since the
latter is {\it negative}, the sum may turn out to be orders of magnitude
smaller than each of the two contributions separately, thus providing a
mechanism to access SIF regimes at ordinary values of the collisional
viscosity. This concept, as applied to quantum superfluids in one-dimensional
optical lattices, is shown to reproduce shear viscosities consistent with the
AdS-CFT holographic bound on the viscosity/entropy ratio. This shows that
lattice kinetic theory continues to hold for strongly coupled hydrodynamic
regimes where continuum kinetic theory may no longer be applicable.Comment: 10 pages, 2 figure
The Z-index: A geometric representation of productivity and impact which accounts for information in the entire rank-citation profile
We present a simple generalization of Hirsch's h-index, Z =
\sqrt{h^{2}+C}/\sqrt{5}, where C is the total number of citations. Z is aimed
at correcting the potentially excessive penalty made by h on a scientist's
highly cited papers, because for the majority of scientists analyzed, we find
the excess citation fraction (C-h^{2})/C to be distributed closely around the
value 0.75, meaning that 75 percent of the author's impact is neglected.
Additionally, Z is less sensitive to local changes in a scientist's citation
profile, namely perturbations which increase h while only marginally affecting
C. Using real career data for 476 physicists careers and 488 biologist careers,
we analyze both the distribution of and the rank stability of Z with
respect to the Hirsch index h and the Egghe index g. We analyze careers
distributed across a wide range of total impact, including top-cited physicists
and biologists for benchmark comparison. In practice, the Z-index requires the
same information needed to calculate h and could be effortlessly incorporated
within career profile databases, such as Google Scholar and ResearcherID.
Because Z incorporates information from the entire publication profile while
being more robust than h and g to local perturbations, we argue that Z is
better suited for ranking comparisons in academic decision-making scenarios
comprising a large number of scientists.Comment: 9 pages, 5 figure
A lattice Boltzmann study of non-hydrodynamic effects in shell models of turbulence
A lattice Boltzmann scheme simulating the dynamics of shell models of
turbulence is developed. The influence of high order kinetic modes (ghosts) on
the dissipative properties of turbulence dynamics is studied. It is
analytically found that when ghost fields relax on the same time scale as the
hydrodynamic ones, their major effect is a net enhancement of the fluid
viscosity. The bare fluid viscosity is recovered by letting ghost fields evolve
on a much longer time scale. Analytical results are borne out by
high-resolution numerical simulations. These simulations indicate that the
hydrodynamic manifold is very robust towards large fluctuations of non
hydrodynamic fields.Comment: 17 pages, 3 figures, submitted to Physica
Phase-field model of long-time glass-like relaxation in binary fluid mixtures
We present a new phase-field model for binary fluids exhibiting typical
signatures of self-glassiness, such as long-time relaxation, ageing and
long-term dynamical arrest. The present model allows the cost of building an
interface to become locally zero, while preserving global positivity of the
overall surface tension. An important consequence of this property, which we
prove analytically, is the emergence of compact configurations of fluid
density. Owing to their finite-size support, these "compactons" can be
arbitrarily superposed, thereby providing a direct link between the ruggedness
of the free-energy landscape and morphological complexity in configurational
space. The analytical picture is supported by numerical simulations of the
proposed phase-field equation.Comment: 5 Pages, 6 Figure
Hydrodynamic Model for Conductivity in Graphene
Based on the recently developed picture of an electronic ideal relativistic
fluid at the Dirac point, we present an analytical model for the conductivity
in graphene that is able to describe the linear dependence on the carrier
density and the existence of a minimum conductivity. The model treats
impurities as submerged rigid obstacles, forming a disordered medium through
which graphene electrons flow, in close analogy with classical fluid dynamics.
To describe the minimum conductivity, we take into account the additional
carrier density induced by the impurities in the sample. The model, which
predicts the conductivity as a function of the impurity fraction of the sample,
is supported by extensive simulations for different values of , the
dimensionless strength of the electric field, and provides excellent agreement
with experimental data.Comment: 19 pages, 4 figure
Derivation of the Lattice Boltzmann Model for Relativistic Hydrodynamics
A detailed derivation of the Lattice Boltzmann (LB) scheme for relativistic
fluids recently proposed in Ref. [1], is presented. The method is numerically
validated and applied to the case of two quite different relativistic fluid
dynamic problems, namely shock-wave propagation in quark-gluon plasmas and the
impact of a supernova blast-wave on massive interstellar clouds. Close to
second order convergence with the grid resolution, as well as linear dependence
of computational time on the number of grid points and time-steps, are
reported
Quaternionic Madelung Transformation and Non-Abelian Fluid Dynamics
In the 1920's, Madelung noticed that if the complex Schroedinger wavefunction
is expressed in polar form, then its modulus squared and the gradient of its
phase may be interpreted as the hydrodynamic density and velocity,
respectively, of a compressible fluid. In this paper, we generalize Madelung's
transformation to the quaternionic Schroedinger equation. The non-abelian
nature of the full SU(2) gauge group of this equation leads to a richer, more
intricate set of fluid equations than those arising from complex quantum
mechanics. We begin by describing the quaternionic version of Madelung's
transformation, and identifying its ``hydrodynamic'' variables. In order to
find Hamiltonian equations of motion for these, we first develop the canonical
Poisson bracket and Hamiltonian for the quaternionic Schroedinger equation, and
then apply Madelung's transformation to derive non-canonical Poisson brackets
yielding the desired equations of motion. These are a particularly natural set
of equations for a non-abelian fluid, and differ from those obtained by
Bistrovic et al. only by a global gauge transformation. Because we have
obtained these equations by a transformation of the quaternionic Schroedinger
equation, and because many techniques for simulating complex quantum mechanics
generalize straightforwardly to the quaternionic case, our observation leads to
simple algorithms for the computer simulation of non-abelian fluids.Comment: 15 page
Towards a unified lattice kinetic scheme for relativistic hydrodynamics
We present a systematic derivation of relativistic lattice kinetic equations
for finite-mass particles, reaching close to the zero-mass ultra-relativistic
regime treated in the previous literature. Starting from an expansion of the
Maxwell-Juettner distribution on orthogonal polynomials, we perform a
Gauss-type quadrature procedure and discretize the relativistic Boltzmann
equation on space-filling Cartesian lattices. The model is validated through
numerical comparison with standard benchmark tests and solvers in relativistic
fluid dynamics such as Boltzmann approach multiparton scattering (BAMPS) and
previous relativistic lattice Boltzmann models. This work provides a
significant step towards the formulation of a unified relativistic lattice
kinetic scheme, covering both massive and near-massless particles regimes
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