1,285 research outputs found
Interface Width and Bulk Stability: requirements for the simulation of Deeply Quenched Liquid-Gas Systems
Simulations of liquid-gas systems with extended interfaces are observed to
fail to give accurate results for two reasons: the interface can get ``stuck''
on the lattice or a density overshoot develops around the interface. In the
first case the bulk densities can take a range of values, dependent on the
initial conditions. In the second case inaccurate bulk densities are found. In
this communication we derive the minimum interface width required for the
accurate simulation of liquid gas systems with a diffuse interface. We
demonstrate this criterion for lattice Boltzmann simulations of a van der Waals
gas. When combining this criterion with predictions for the bulk stability we
can predict the parameter range that leads to stable and accurate simulation
results. This allows us to identify parameter ranges leading to high density
ratios of over 1000. This is despite the fact that lattice Boltzmann
simulations of liquid-gas systems were believed to be restricted to modest
density ratios of less than 20.Comment: 5 pages, 3 figure
Free induction decay of a superposition stored in a quantum dot
We study the free evolution of a superposition initialized with high fidelity
in the neutral-exciton state of a quantum dot. Readout of the state at later
times is achieved by polarized photon detection, averaged over a large number
of cycles. By controlling the fine-structure splitting (FSS) of the dot with a
dc electric field, we show a reduction in the degree of polarization of the
signal when the splitting is minimized. In analogy with the "free induction
decay" observed in nuclear magnetic resonance, we attribute this to hyperfine
interactions with nuclei in the semiconductor. We numerically model this effect
and find good agreement with experimental studies. Our findings have
implications for storage of superpositions in solid-state systems and for
entangled photon pair emission protocols that require a small value of the FSS
Limits on thermal variations in a dozen quiescent neutron stars over a decade
In quiescent low-mass X-ray binaries (qLMXBs) containing neutron stars, the
origin of the thermal X-ray component may be either release of heat from the
core of the neutron star, or continuing low-level accretion. In general, heat
from the core should be stable on timescales years, while continuing
accretion may produce variations on a range of timescales. While some quiescent
neutron stars (e.g. Cen X-4, Aql X-1) have shown variations in their thermal
components on a range of timescales, several others, particularly those in
globular clusters with no detectable nonthermal hard X-rays (fit with a
powerlaw), have shown no measurable variations. Here, we constrain the spectral
variations of 12 low mass X-ray binaries in 3 globular clusters over
years. We find no evidence of variations in 10 cases, with limits on
temperature variations below 11% for the 7 qLMXBs without powerlaw components,
and limits on variations below 20% for 3 other qLMXBs that do show non-thermal
emission. However, in 2 qLMXBs showing powerlaw components in their spectra
(NGC 6440 CX 1 & Terzan 5 CX 12) we find marginal evidence for a 10% decline in
temperature, suggesting the presence of continuing low-level accretion. This
work adds to the evidence that the thermal X-ray component in quiescent neutron
stars without powerlaw components can be explained by heat deposited in the
core during outbursts. Finally, we also investigate the correlation between
hydrogen column density (N) and optical extinction (A) using our sample
and current models of interstellar X-ray absorption, finding .Comment: 16 pages, 5 figures, MNRAS, in pres
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