1,403 research outputs found
Critical swelling of particle-encapsulating vesicles
We consider a ubiquitous scenario where a fluctuating, semipermeable vesicle
is embedded in solution while enclosing a fixed number of solute particles. The
swelling with increasing number of particles or decreasing concentration of the
outer solution exhibits a continuous phase transition from a fluctuating state
to the maximum-volume configuration, whereupon appreciable pressure difference
and surface tension build up. This criticality is unique to
particle-encapsulating vesicles, whose volume and inner pressure both
fluctuate. It implies a universal swelling behavior of such vesicles as they
approach their limiting volume and osmotic lysis.Comment: 4 pages, 1 figur
Superfluid, Mott-Insulator, and Mass-Density-Wave Phases in the One-Dimensional Extended Bose-Hubbard Model
We use the finite-size density-matrix-renormalization-group (FSDMRG) method
to obtain the phase diagram of the one-dimensional () extended
Bose-Hubbard model for density in the plane, where and
are, respectively, onsite and nearest-neighbor interactions. The phase diagram
comprises three phases: Superfluid (SF), Mott Insulator (MI) and Mass Density
Wave (MDW). For small values of and , we get a reentrant SF-MI-SF phase
transition. For intermediate values of interactions the SF phase is sandwiched
between MI and MDW phases with continuous SF-MI and SF-MDW transitions. We
show, by a detailed finite-size scaling analysis, that the MI-SF transition is
of Kosterlitz-Thouless (KT) type whereas the MDW-SF transition has both KT and
two-dimensional-Ising characters. For large values of and we get a
direct, first-order, MI-MDW transition. The MI-SF, MDW-SF and MI-MDW phase
boundaries join at a bicritical point at (.Comment: 10 pages, 15 figure
Universal Magnetic Properties of at Intermediate Temperatures
We present the theory of two-dimensional, clean quantum antiferromagnets with
a small, positive, zero temperature () stiffness , but with the
ratio arbitrary. Universal scaling forms for the uniform
susceptibility (), correlation length(), and NMR relaxation rate
() are proposed and computed in a expansion and by Mont\'{e}-Carlo
simulations. For large , and asymptote
to universal values, while is nearly -independent. We find good
quantitative agreement with experiments and some numerical studies on
.Comment: 14 pages, REVTEX, 1 postscript figure appende
Nationally Representative Estimates of Serum Testosterone Concentration in Never-Smoking, Lean Men Without Aging-Associated Comorbidities
Context
Testosterone deficiency prevalence increases with age, comorbidities, and obesity.
Objective
To inform clinical guidelines for testosterone deficiency management and development of targets for nonpharmacologic intervention trials for these men, we determined serum testosterone in never-smoking, lean men without select comorbidities in nationally representative surveys.
Design Setting Participants
We used cross-sectional data for never-smoking, lean men ≥20 years without diabetes, myocardial infarction, congestive heart failure, stroke, or cancer, without use of hormone-influencing medications, and participated in morning sessions of National Health and Nutrition Examination Survey (NHANES) III (phase I 1988-1991) or continuous NHANES (1999-2004). By age, we determined median total testosterone (ng/mL) measured previously by a Food and Drug Administration-approved immunoassay and median estimated free testosterone concentration.
Results
In NHANES III, in never-smoking, lean men without comorbidities, median (25th, 75th percentile) testosterone was 4% to 9% higher than all men-20 to 39 years: 6.24 (5.16, 7.51), 40 to 59: 5.37 (3.83, 6.49), and ≥60: 4.61 (4.01, 5.18). In continuous NHANES, in never-smoking, lean men without comorbidities, levels were 13% to 24% higher than all men-20 to 39 years: 6.26 (5.32, 7.27), 40 to 59: 5.86 (4.91, 6.55), and ≥60: 4.22 (3.74, 5.73). In never-smoking, lean men without comorbidities, median estimated free testosterone was similar to (NHANES III) or slightly higher than (continuous NHANES) in all men.
Conclusions
These nationally representative data document testosterone levels (immunoassay) in never-smoking, lean men without select comorbidities 30 and 15 to 20 years ago. This information can be incorporated into guidelines for testosterone deficiency management and used to develop targets for nonpharmacologic intervention trials for testosterone deficiency
Environmental drivers of Culicoides phenology: how important is species-specific variation when determining disease policy?
Since 2006, arboviruses transmitted by Culicoides biting midges (Diptera: Ceratopogonidae) have caused significant disruption to ruminant production in northern Europe. The most serious incursions involved strains of bluetongue virus (BTV), which cause bluetongue (BT) disease. To control spread of BTV, movement of susceptible livestock is restricted with economic and animal welfare impacts. The timing of BTV transmission in temperate regions is partly determined by the seasonal presence of adult Culicoides females. Legislative measures therefore allow for the relaxation of ruminant movement restrictions during winter, when nightly light-suction trap catches of Culicoides fall below a threshold (the ‘seasonally vector free period’: SVFP). We analysed five years of time-series surveillance data from light-suction trapping in the UK to investigate whether significant inter-specific and yearly variation in adult phenology exists, and whether the SVFP is predictable from environmental factors. Because female vector Culicoides are not easily morphologically separated, inter-specific comparisons in phenology were drawn from male populations. We demonstrate significant inter-specific differences in Culicoides adult phenology with the season of Culicoides scoticus approximately eight weeks shorter than Culicoides obsoletus. Species-specific differences in the length of the SVFP were related to host density and local variation in landscape habitat. When the Avaritia Culicoides females were modelled as a group (as utilised in the SFVP), we were unable to detect links between environmental drivers and phenological metrics. We conclude that the current treatment of Avaritia Culicoides as a single group inhibits understanding of environmentally-driven spatial variation in species phenology and hinders the development of models for predicting the SVFP from environmental factors. Culicoides surveillance methods should be adapted to focus on concentrated assessments of species-specific abundance during the start and end of seasonal activity in temperate regions to facilitate refinement of ruminant movement restrictions thereby reducing the impact of Culicoides-borne arboviruses
Folding transitions of the triangular lattice with defects
A recently introduced model describing the folding of the triangular lattice
is generalized allowing for defects in the lattice and written as an Ising
model with nearest-neighbor and plaquette interactions on the honeycomb
lattice. Its phase diagram is determined in the hexagon approximation of the
cluster variation method and the crossover from the pure Ising to the pure
folding model is investigated, obtaining a quite rich structure with several
multicritical points. Our results are in very good agreement with the available
exact ones and extend a previous transfer matrix study.Comment: 16 pages, latex, 5 postscript figure
Monte Carlo simulation of a two-dimensional continuum Coulomb gas
We study the classical two-dimensional Coulomb gas model for thermal vortex
fluctuations in thin superconducting/superfluid films by Monte Carlo simulation
of a grand canonical vortex ensemble defined on a continuum. The
Kosterlitz-Thouless transition is well understood at low vortex density, but at
high vortex density the nature of the phase diagram and of the vortex phase
transition is less clear. From our Monte Carlo data we construct phase diagrams
for the 2D Coulomb gas without any restrictions on the vortex density. For
negative vortex chemical potential (positive vortex core energy) we always find
a Kosterlitz-Thouless transition. Only if the Coulomb interaction is
supplemented with a short-distance repulsion, a first order transition line is
found, above some positive value of the vortex chemical potential.Comment: 10 pages RevTeX, 7 postscript figures included using eps
Nature of the Low Field Transition in the Mixed State of High Temperature Superconductors
We have numerically studied the statics and dynamics of a model
three-dimensional vortex lattice at low magnetic fields. For the statics we use
a frustrated 3D XY model on a stacked triangular lattice. We model the dynamics
as a coupled network of overdamped resistively-shunted Josephson junctions with
Langevin noise. At low fields, there is a weakly first-order phase transition,
at which the vortex lattice melts into a line liquid. Phase coherence parallel
to the field persists until a sharp crossover, conceivably a phase transition,
near which develops at the same temperature as an infinite
vortex tangle. The calculated flux flow resistivity in various geometries near
closely resembles experiment. The local density of field induced
vortices increases sharply near , corresponding to the experimentally
observed magnetization jump. We discuss the nature of a possible transition or
crossover at (B) which is distinct from flux lattice melting.Comment: Updated references. 46 pages including low quality 25 eps figures.
Contact [email protected] or visit
http://www.physics.ohio-state.edu:80/~ryu/ for better figures and additional
movie files from simulations. To be published in Physical Review B1 01Jun9
Bulk and surface properties in the critical phase of the two-dimensional XY model
Monte Carlo simulations of the two-dimensional XY model are performed in a
square geometry with various boundary conditions (BC). Using conformal mappings
we deduce the exponent of the order parameter correlation
function and its surface analogue as a function of the temperature
in the critical (low-temperature) phase of the model.Comment: 26 pages, iop macro, one reference added, typos correcte
Quantum Computing and Quantum Simulation with Group-II Atoms
Recent experimental progress in controlling neutral group-II atoms for
optical clocks, and in the production of degenerate gases with group-II atoms
has given rise to novel opportunities to address challenges in quantum
computing and quantum simulation. In these systems, it is possible to encode
qubits in nuclear spin states, which are decoupled from the electronic state in
the S ground state and the long-lived P metastable state on the
clock transition. This leads to quantum computing scenarios where qubits are
stored in long lived nuclear spin states, while electronic states can be
accessed independently, for cooling of the atoms, as well as manipulation and
readout of the qubits. The high nuclear spin in some fermionic isotopes also
offers opportunities for the encoding of multiple qubits on a single atom, as
well as providing an opportunity for studying many-body physics in systems with
a high spin symmetry. Here we review recent experimental and theoretical
progress in these areas, and summarise the advantages and challenges for
quantum computing and quantum simulation with group-II atoms.Comment: 11 pages, 7 figures, review for special issue of "Quantum Information
Processing" on "Quantum Information with Neutral Particles
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