45,211 research outputs found
Rough interfaces, accurate predictions: The necessity of capillary modes in a minimal model of nanoscale hydrophobic solvation
Modern theories of the hydrophobic effect highlight its dependence on length
scale, emphasizing in particular the importance of interfaces that emerge in
the vicinity of sizable hydrophobes. We recently showed that a faithful
treatment of such nanoscale interfaces requires careful attention to the
statistics of capillary waves, with significant quantitative implications for
the calculation of solvation thermodynamics. Here we show that a coarse-grained
lattice model in the spirit of those pioneered by Chandler and coworkers, when
informed by this understanding, can capture a broad range of hydrophobic
behaviors with striking accuracy. Specifically, we calculate probability
distributions for microscopic density fluctuations that agree very well with
results of atomistic simulations, even many standard deviations from the mean,
and even for probe volumes in highly heterogeneous environments. This accuracy
is achieved without adjustment of free parameters, as the model is fully
specified by well-known properties of liquid water. As illustrative examples of
its utility, we characterize the free energy profile for a solute crossing the
air-water interface, and compute the thermodynamic cost of evacuating the space
between extended nanoscale surfaces. Together, these calculations suggest that
a highly reduced model for aqueous solvation can serve as the basis for
efficient multiscale modeling of spatial organization driven by hydrophobic and
interfacial forces.Comment: 14 pages, 7 figure
Ansatz of Hans Bethe for a two-dimensional Bose gas
The method of q-oscillator lattices, proposed recently in [hep-th/0509181],
provides the tool for a construction of various integrable models of quantum
mechanics in 2+1 dimensional space-time. In contrast to any one dimensional
quantum chain, its two dimensional generalizations -- quantum lattices -- admit
different geometrical structures. In this paper we consider the q-oscillator
model on a special lattice. The model may be interpreted as a two-dimensional
Bose gas. The most remarkable feature of the model is that it allows the
coordinate Bethe Ansatz: the p-particles' wave function is the sum of plane
waves. Consistency conditions is the set of 2p equations for p one-particle
wave vectors. These "Bethe Ansatz" equations are the main result of this paper.Comment: LaTex2e, 12 page
Lattice Gas Automata for Reactive Systems
Reactive lattice gas automata provide a microscopic approachto the dynamics
of spatially-distributed reacting systems. After introducing the subject within
the wider framework of lattice gas automata (LGA) as a microscopic approach to
the phenomenology of macroscopic systems, we describe the reactive LGA in terms
of a simple physical picture to show how an automaton can be constructed to
capture the essentials of a reactive molecular dynamics scheme. The statistical
mechanical theory of the automaton is then developed for diffusive transport
and for reactive processes, and a general algorithm is presented for reactive
LGA. The method is illustrated by considering applications to bistable and
excitable media, oscillatory behavior in reactive systems, chemical chaos and
pattern formation triggered by Turing bifurcations. The reactive lattice gas
scheme is contrasted with related cellular automaton methods and the paper
concludes with a discussion of future perspectives.Comment: to appear in PHYSICS REPORTS, 81 revtex pages; uuencoded gziped
postscript file; figures available from [email protected] or
[email protected]
The cold atom Hubbard toolbox
We review recent theoretical advances in cold atom physics concentrating on
strongly correlated cold atoms in optical lattices. We discuss recently
developed quantum optical tools for manipulating atoms and show how they can be
used to realize a wide range of many body Hamiltonians. Then we describe
connections and differences to condensed matter physics and present
applications in the fields of quantum computing and quantum simulations.
Finally we explain how defects and atomic quantum dots can be introduced in a
controlled way in optical lattice systems.Comment: Review article, 31 pages, 14 figures, to be published in Annals of
Physic
Quantum algorithm for Bose-Einstein condensate quantum fluid dynamics
The dynamics of vortex solitons in a BEC superfluid is studied. A quantum
lattice-gas algorithm (localization-based quantum computation) is employed to
examine the dynamical behavior of vortex soliton solutions of the
Gross-Pitaevskii equation (phi^4 interaction nonlinear Schroedinger equation).
Quantum turbulence is studied in large grid numerical simulations: Kolmogorov
spectrum associated with a Richardson energy cascade occurs on large flow
scales. At intermediate scales a k^{-6} power law emerges, in a
classical-quantum transition from vortex filament reconnections to Kelvin
wave-acoustic wave coupling. The spontaneous exchange of intermediate vortex
rings is observed. Finally, at very small spatial scales a k^{-3} power law
emerges, characterizing fluid dynamics occurring within the scale size of the
vortex cores themselves, a characteristic Kelvin wave cascade region. Poincare
recurrence is studied: in the free non-interacting system, a fast Poincare
recurrence occurs for regular arrays of line vortices. The recurrence period is
used to demarcate dynamics driving the nonlinear quantum fluid towards
turbulence, since fast recurrence is an approximate symmetry of the nonlinear
quantum fluid at early times. This class of quantum algorithms is useful for
studying BEC superfluid dynamics over a broad range of wave numbers, from
quantum flow to a pseudo-classical inviscid flow regime to a Kolmogorov
inertial subrange.Comment: 10 pages, 6 figure
Quartic Parameters for Acoustic Applications of Lattice Boltzmann Scheme
Using the Taylor expansion method, we show that it is possible to improve the
lattice Boltzmann method for acoustic applications. We derive a formal
expansion of the eigenvalues of the discrete approximation and fit the
parameters of the scheme to enforce fourth order accuracy. The corresponding
discrete equations are solved with the help of symbolic manipulation. The
solutions are explicited in the case of D3Q27 lattice Boltzmann scheme. Various
numerical tests support the coherence of this approach.Comment: 23 page
Topological Phases: An Expedition off Lattice
Motivated by the goal to give the simplest possible microscopic foundation
for a broad class of topological phases, we study quantum mechanical lattice
models where the topology of the lattice is one of the dynamical variables.
However, a fluctuating geometry can remove the separation between the system
size and the range of local interactions, which is important for topological
protection and ultimately the stability of a topological phase. In particular,
it can open the door to a pathology, which has been studied in the context of
quantum gravity and goes by the name of `baby universe', Here we discuss three
distinct approaches to suppressing these pathological fluctuations. We
complement this discussion by applying Cheeger's theory relating the geometry
of manifolds to their vibrational modes to study the spectra of Hamiltonians.
In particular, we present a detailed study of the statistical properties of
loop gas and string net models on fluctuating lattices, both analytically and
numerically.Comment: 38 pages, 22 figure
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