2,090 research outputs found
Constraining coherent low frequency radio flares from compact binary mergers
The presence and detectability of coherent radio emission from compact binary
mergers (containing at least one neutron star) remains poorly constrained due
to large uncertainties in the models. These compact binary mergers may
initially be detected as Short Gamma-ray Bursts (SGRBs) or via their
gravitational wave emission. Several radio facilities have developed rapid
response modes enabling them to trigger on these events and search for this
emission. For this paper, we constrain this coherent radio emission using the
deepest available constraints for GRB 150424A, which were obtained via a
triggered observation with the Murchison Widefield Array. We then expand this
analysis to determine the properties of magnetar merger remnants that may be
formed via a general population of binary neutron star mergers. Our results
demonstrate that many of the potential coherent emission mechanisms that have
been proposed for such events can be detected or very tightly constrained by
the complementary strategies used by the current generation of low-frequency
radio telescopes.Comment: 19 pages, submitted to MNRA
Wetting on Nanorough Surfaces
We present in this Letter a free-energy approach to the dynamics of a fluid
near a nanostructured surface. The model accounts both for the static phase
equilibrium in the vicinity of the surface (wetting angles, Cassie-Wenzel
transition) and the dynamical properties like liquid slippage at the boundary.
This method bridges the gap between phenomenological phase-field approaches and
more macroscopic lattice-Boltzmann models
Gas Enrichment at Liquid-Wall Interfaces
Molecular dynamics simulations of Lennard-Jones systems are performed to
study the effects of dissolved gas on liquid-wall and liquid-gas interfaces.
Gas enrichment at walls is observed which for hydrophobic walls can exceed more
than two orders of magnitude when compared to the gas density in the bulk
liquid. As a consequence, the liquid structure close to the wall is
considerably modified, leading to an enhanced wall slip. At liquid-gas
interfaces gas enrichment is found which reduces the surface tension.Comment: main changes compared to version 1: flow simulations are included as
well as different types of gase
Direct calculation of interfacial tensions from computer simulation: Results for freely jointed tangent hard sphere chains
We develop a methodology for the calculation of surface free energies based
on the probability distribution of a wandering interface. Using a simple
extension of the NpT sampling, we allow the interface area to randomly probe
the available space and evaluate the surface free energy from histogram
analysis and the corresponding average. The method is suitable for studying
systems with either continuous or discontinuous potentials, as it does not
require explicit evaluation of the virial. The proposed algorithm is compared
with known results for the surface tension of Lennard--Jones and Square Well
fluid, as well as for the interface tension of a bead--spring polymer model and
good agreement is found. We also calculate interfacial tensions of freely
jointed tangent hard sphere chains on athermal walls for a wide range of chain
lengths and densities. The results are compared with three different
theoretical approaches, Scaled Particle Theory, the Yu and Wu density
functional theory and an analytical approximation based on the latter approach.
Whereas SPT only yields qualitative results, the last two approaches are found
to yield very good agreement with simulations.Comment: 20 pages, 6 figures, Phys. Rev. E in press
[N]pT Monte Carlo Simulations of the Cluster-Crystal-Forming Penetrable Sphere Model
Certain models with purely repulsive pair interactions can form cluster
crystals with multiply-occupied lattice sites. Simulating these models'
equilibrium properties is, however, quite challenging. Here, we develop an
expanded isothermal-isobaric ensemble that surmounts this problem by
allowing both particle number and lattice spacing to fluctuate. We apply the
method with a Monte Carlo simulation scheme to solve the phase diagram of a
prototypical cluster-crystal former, the penetrable sphere model (PSM), and
compare the results with earlier theoretical predictions. At high temperatures
and densities, the equilibrium occupancy of
face-centered cubic (FCC) crystal increases linearly. At low temperatures,
although plateaus at integer values, the crystal
behavior changes continuously with density. The previously ambiguous crossover
around is resolved
Balancing Local Order and Long-Ranged Interactions in the Molecular Theory of Liquid Water
A molecular theory of liquid water is identified and studied on the basis of
computer simulation of the TIP3P model of liquid water. This theory would be
exact for models of liquid water in which the intermolecular interactions
vanish outside a finite spatial range, and therefore provides a precise
analysis tool for investigating the effects of longer-ranged intermolecular
interactions. We show how local order can be introduced through quasi-chemical
theory. Long-ranged interactions are characterized generally by a conditional
distribution of binding energies, and this formulation is interpreted as a
regularization of the primitive statistical thermodynamic problem. These
binding-energy distributions for liquid water are observed to be unimodal. The
gaussian approximation proposed is remarkably successful in predicting the
Gibbs free energy and the molar entropy of liquid water, as judged by
comparison with numerically exact results. The remaining discrepancies are
subtle quantitative problems that do have significant consequences for the
thermodynamic properties that distinguish water from many other liquids. The
basic subtlety of liquid water is found then in the competition of several
effects which must be quantitatively balanced for realistic results.Comment: 8 pages, 6 figure
Joint gravitational wave -- gamma-ray burst detection rates in the aftermath of GW170817
The observational follow-up campaign of the gravitational wave (GW)
multi-messenger event GW170817/GRB170817A has shown that the prompt
-rays are consistent with a relativistic structured jet observed from a
wide viewing angle \deg. We perform Bayesian inference using the
data from early and late EM observations to determine the jet profile of
GRB170817A assuming a structured jet model. We use the geometric dependence on
the burst luminosity to produce a short duration gamma-ray burst (sGRB)
efficiency function with redshift, which folded in with binary neutron star
detection rate, allows us to estimate the future joint GW/sGRB detection rates
for LIGO and Virgo detectors. We show that, if the jet structured profile of
GRB170817A is a relatively common feature of sGRBs, then there is a realistic
probability of another off-axis coincident detection during the third
aLIGO/Virgo observing run (O3). We also find that up to 4 yr joint
events may be observed during the advanced LIGO run at design sensitivity and
up to 10 yr by the upgraded advanced LIGO configuration A+. We show that
the detection efficiencies for wide-angled sGRB emissions will be limited by
GRB satellites as the GW detection range increases through proposed upgrades.
Therefore, although the number of coincident detections will increase with GW
detector sensitivity, the relative proportion of detected binary neutron stars
with -ray counterparts will decrease; 11\% for O3 down to 2\% during
A+.Comment: Updated to final accepted MNRAS versio
Mesoscopic model for the fluctuating hydrodynamics of binary and ternary mixtures
A recently introduced particle-based model for fluid dynamics with continuous
velocities is generalized to model immiscible binary mixtures. Excluded volume
interactions between the two components are modeled by stochastic multiparticle
collisions which depend on the local velocities and densities. Momentum and
energy are conserved locally, and entropically driven phase separation occurs
for high collision rates. An explicit expression for the equation of state is
derived, and the concentration dependence of the bulk free energy is shown to
be the same as that of the Widom-Rowlinson model. Analytic results for the
phase diagram are in excellent agreement with simulation data. Results for the
line tension obtained from the analysis of the capillary wave spectrum of a
droplet agree with measurements based on the Laplace's equation. The
introduction of "amphiphilic" dimers makes it possible to model the phase
behavior and dynamics of ternary surfactant mixtures.Comment: 7 pages including 6 figure
Isotropic-nematic interfacial tension of hard and soft rods: application of advanced grand canonical biased sampling techniques
Coexistence between the isotropic and the nematic phase in suspensions of
rods is studied using grand canonical Monte Carlo simulations with a bias on
the nematic order parameter. The biasing scheme makes it possible to estimate
the interfacial tension gamma in systems of hard and soft rods. For hard rods
with L/D=15, we obtain gamma ~ 1.4 kB T/L^2, with L the rod length, D the rod
diameter, T the temperature, and kB the Boltzmann constant. This estimate is in
good agreement with theoretical predictions, and the order of magnitude is
consistent with experiments.Comment: 10 pages, 10 figure
Scaling for Interfacial Tensions near Critical Endpoints
Parametric scaling representations are obtained and studied for the
asymptotic behavior of interfacial tensions in the \textit{full} neighborhood
of a fluid (or Ising-type) critical endpoint, i.e., as a function \textit{both}
of temperature \textit{and} of density/order parameter \textit{or} chemical
potential/ordering field. Accurate \textit{nonclassical critical exponents} and
reliable estimates for the \textit{universal amplitude ratios} are included
naturally on the basis of the ``extended de Gennes-Fisher'' local-functional
theory. Serious defects in previous scaling treatments are rectified and
complete wetting behavior is represented; however, quantitatively small, but
unphysical residual nonanalyticities on the wetting side of the critical
isotherm are smoothed out ``manually.'' Comparisons with the limited available
observations are presented elsewhere but the theory invites new, searching
experiments and simulations, e.g., for the vapor-liquid interfacial tension on
the two sides of the critical endpoint isotherm for which an amplitude ratio
is predicted.Comment: 42 pages, 6 figures, to appear in Physical Review
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