143 research outputs found
Superfluid transitions in bosonic atom-molecule mixtures near Feshbach resonance
We study bosonic atoms near a Feshbach resonance, and predict that in
addition to a standard normal and atomic superfluid phases, this system
generically exhibits a distinct phase of matter: a molecular superfluid, where
molecules are superfluid while atoms are not. We explore zero- and
finite-temperature properties of the molecular superfluid (a bosonic,
strong-coupling analog of a BCS superconductor), and study quantum and
classical phase transitions between the normal, molecular superfluid and atomic
superfluid states.Comment: 4 revtex pages, 3 eps figures; submitted to PR
Phase Control of Nonlinear Breit-Wheeler Pair Creation
Electron-positron pair creation occurs throughout the universe in the
environments of extreme astrophysical objects, such as pulsar magnetospheres
and black hole accretion disks. The difficulty of emulating these environments
in the laboratory has motivated the use of ultrahigh-intensity laser pulses for
pair creation. Here we show that the phase offset between a laser pulse and its
second harmonic can be used to control the relative transverse motion of
electrons and positrons created in the nonlinear Breit-Wheeler process.
Analytic theory and particle-in-cell simulations of a head-on collision between
a two-color laser pulse and electron beam predict that with an appropriate
phase offset, the electrons will drift in one direction and the positrons in
the other. The resulting current may provide a collective signature of
nonlinear Breit-Wheeler, while the spatial separation resulting from the
relative motion may facilitate isolation of positrons for subsequent
applications or detection.Comment: 8 pages, 5 figure
Differential regulation of TNF-α and IL-1β production from endotoxin stimulated human monocytes by phosphodiesterase inhibitors
The effect of selective PDE-I (vinpocetine), PDE-III (milrinone, CI-930), PDE-IV (rolipram, nitroquazone), and PDE-V (zaprinast) isozyme inhibitors on TNF-α and IL-1β production from LPS stimulated human monocytes was investigated. The PDE-IV inhibitors caused a concentration dependent inhibition of TNF-α production, but only partially inhibited IL-1β at high concentrations. High concentrations of the PDE-III inhibitors weakly inhibited TNF-α, but had no effect on IL-1β production. PDE-V inhibition was associated with an augmentation of cytokine secretion. Studies with combinations of PDE isozyme inhibitors indicated that PDE-III and PDE-V inhibitors modulate rolipram's suppression of TNF production in an additive manner. These data confirm that TNF-α and IL-1β production from LPS stimulated human monocytes are differentially regulated, and suggest that PDE-IV inhibitors have the potential to suppress TNF levels in man
Equilibrium solutions of the shallow water equations
A statistical method for calculating equilibrium solutions of the shallow
water equations, a model of essentially 2-d fluid flow with a free surface, is
described. The model contains a competing acoustic turbulent {\it direct}
energy cascade, and a 2-d turbulent {\it inverse} energy cascade. It is shown,
nonetheless that, just as in the corresponding theory of the inviscid Euler
equation, the infinite number of conserved quantities constrain the flow
sufficiently to produce nontrivial large-scale vortex structures which are
solutions to a set of explicitly derived coupled nonlinear partial differential
equations.Comment: 4 pages, no figures. Submitted to Physical Review Letter
Renormalization Group for Large N Strongly Commensurate Dirty Boson Model
The large N sigma model, in D<4 space-time dimensions, with disorder a
function of d space dimensions, is analyzed via a renormalization group
treatment. Critical exponents for average quantities are calculated, first to
lowest order and then to all orders, in . In particular, it
is found that . When D=d+1, this model is equivalent to a large N
limit of the strongly commensurate dirty boson problem.Comment: 16 pages, 4 figures, to be published in PR
Dirty Bosons: Twenty Years Later
A concise, somewhat personal, review of the problem of superfluidity and
quantum criticality in regular and disordered interacting Bose systems is
given, concentrating on general features and important symmetries that are
exhibited in different parts of the phase diagram, and that govern the
different possible types of critical behavior. A number of exact results for
various insulating phase boundaries, which may be used to constrain the results
of numerical simulations, can be derived using large rare region type
arguments. The nature of the insulator-superfluid transition is explored
through general scaling arguments, exact model calculations in one dimension,
numerical results in two dimensions, and approximate renormalization group
results in higher dimensions. Experiments on He-4 adsorbed in porous Vycor
glass, on thin film superconductors, and magnetically trapped atomic vapors in
a periodic optical potential, are used to illustrate many of the concepts.Comment: 26 pages, 9 figures, submitted to Modern Physics Letters B (Brief
Reviews
Analytic pulse technique for computational electromagnetics
Numerical modeling of electromagnetic waves is an important tool for
understanding the interaction of light and matter, and lies at the core of
computational electromagnetics. Traditional approaches to injecting and
evolving electromagnetic waves, however, can be prohibitively expensive and
complex for emerging problems of interest and can restrict the comparisons that
can be made between simulation and theory. As an alternative, we demonstrate
that electromagnetic waves can be incorporated analytically by decomposing the
physics equations into analytic and computational parts. In particle-in-cell
simulation of laser--plasma interaction, for example, treating the laser pulse
analytically enables direct examination of the validity of approximate
solutions to Maxwell's equations including Laguerre--Gaussian beams, allows
lower-dimensional simulations to capture 3-D--like focusing, and facilitates
the modeling of novel space--time structured laser pulses such as the flying
focus. The flexibility and new routes to computational savings introduced by
this analytic pulse technique are expected to enable new simulation directions
and significantly reduce computational cost in existing areas.Comment: 26 pages, 9 figure
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