283 research outputs found
Critical cavity in the stretched fluid studied using square-gradient density-functional model with triple-parabolic free energy
The generic square-gradient density-functional model with triple-parabolic
free energy is used to study the stability of a cavity introduced into the
stretched liquid. The various properties of the critical cavity, which is the
largest stable cavity within the liquid, are compared with those of the
critical bubble of the homogeneous bubble nucleation. It is found that the size
of the critical cavity is always smaller than that of the critical bubble,
while the work of formation of the former is always higher than the latter in
accordance with the conjectures made by Punnathanam and Corti [J. Chem. Phys.
{\bf 119}, 10224 (2003)] deduced from the Lennard-Jones fluids. Therefore their
conjectures about the critical cavity size and the work of formation would be
more general and valid even for other types of liquid such as metallic liquid
or amorphous. However, the scaling relations they found for the critical cavity
in the Lennard-Jones fluid are marginally satisfied only near the spinodal.Comment: 10 pages, 6 figures, J. Chem. Phys. at pres
Exergy analysis:Tthe effect of relative humidity, air temperature and effective clothing insulation on thermal comfort
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Use of the q-Gaussian mutation in evolutionary algorithms
Copyright @ Springer-Verlag 2010.This paper proposes the use of the q-Gaussian mutation with self-adaptation of the shape of the mutation distribution in evolutionary algorithms. The shape of the q-Gaussian mutation distribution is controlled by a real parameter q. In the proposed method, the real parameter q of the q-Gaussian mutation is encoded in the chromosome of individuals and hence is allowed to evolve during the evolutionary process. In order to test the new mutation operator, evolution strategy and evolutionary programming algorithms with self-adapted q-Gaussian mutation generated from anisotropic and isotropic distributions are presented. The theoretical analysis of the q-Gaussian mutation is also provided. In the experimental study, the q-Gaussian mutation is compared to Gaussian and Cauchy mutations in the optimization of a set of test functions. Experimental results show the efficiency of the proposed method of self-adapting the mutation distribution in evolutionary algorithms.This work was supported in part by FAPESP and CNPq in Brazil and in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant EP/E060722/1 and Grant EP/E060722/2
Capillary pressure of van der Waals liquid nanodrops
The dependence of the surface tension on a nanodrop radius is important for
the new-phase formation process. It is demonstrated that the famous Tolman
formula is not unique and the size-dependence of the surface tension can
distinct for different systems. The analysis is based on a relationship between
the surface tension and disjoining pressure in nanodrops. It is shown that the
van der Waals interactions do not affect the new-phase formation thermodynamics
since the effect of the disjoining pressure and size-dependent component of the
surface tension cancel each other.Comment: The paper is dedicated to the 80th anniversary of A.I. Rusano
Surface Structure of Liquid Metals and the Effect of Capillary Waves: X-ray Studies on Liquid Indium
We report x-ray reflectivity (XR) and small angle off-specular diffuse
scattering (DS) measurements from the surface of liquid Indium close to its
melting point of C. From the XR measurements we extract the surface
structure factor convolved with fluctuations in the height of the liquid
surface. We present a model to describe DS that takes into account the surface
structure factor, thermally excited capillary waves and the experimental
resolution. The experimentally determined DS follows this model with no
adjustable parameters, allowing the surface structure factor to be deconvolved
from the thermally excited height fluctuations. The resulting local electron
density profile displays exponentially decaying surface induced layering
similar to that previously reported for Ga and Hg. We compare the details of
the local electron density profiles of liquid In, which is a nearly free
electron metal, and liquid Ga, which is considerably more covalent and shows
directional bonding in the melt. The oscillatory density profiles have
comparable amplitudes in both metals, but surface layering decays over a length
scale of \AA for In and \AA for Ga. Upon controlled
exposure to oxygen, no oxide monolayer is formed on the liquid In surface,
unlike the passivating film formed on liquid Gallium.Comment: 9 pages, 5 figures; submitted to Phys. Rev.
A New SU UMa-Type Dwarf Nova, QW Serpentis (= TmzV46)
We report on the results of the QW Ser campaign which has been continued from
2000 to 2003 by the VSNET collaboration team. Four long outbursts and many
short ones were caught during this period. Our intensive photometric
observations revealed superhumps with a period of 0.07700(4) d during all four
superoutbursts, proving the SU UMa nature of this star. The recurrence cycles
of the normal outbursts and the superoutbursts were measured to be 50
days and 240(30) days, respectively. The change rate of the superhump period
was -5.8x10^{-5}. The distance and the X-ray luminosity in the range of 0.5-2.4
keV are estimated to be 380(60) pc and log L_x = 31.0 \pm 0.1 erg s^{-1}. These
properties have typical values for an SU UMa-type dwarf nova with this
superhump period.Comment: 9 pages, 12 figures, to appear in the VSNET special issue of PAS
Nucleation and Bulk Crystallization in Binary Phase Field Theory
We present a phase field theory for binary crystal nucleation. In the
one-component limit, quantitative agreement is achieved with computer
simulations (Lennard-Jones system) and experiments (ice-water system) using
model parameters evaluated from the free energy and thickness of the interface.
The critical undercoolings predicted for Cu-Ni alloys accord with the
measurements, and indicate homogeneous nucleation. The Kolmogorov exponents
deduced for dendritic solidification and for "soft-impingement" of particles
via diffusion fields are consistent with experiment.Comment: 4 pages, 4 figures, accepted to PR
V5852 Sgr : an unusual nova possibly associated with the Sagittarius stream
We report spectroscopic and photometric follow-up of the peculiar nova V5852~Sgr (discovered as OGLE-2015-NOVA-01), which exhibits a combination of features from different nova classes. The photometry shows a flat-topped light curve with quasi-periodic oscillations, then a smooth decline followed by two fainter recoveries in brightness. Spectroscopy with the Southern African Large Telescope shows first a classical nova with an Fe II or Fe IIb spectral type. In the later spectrum, broad emissions from helium, nitrogen and oxygen are prominent and the iron has faded which could be an indication to the start of the nebular phase. The line widths suggest ejection velocities around 1000 km s-1. The nova is in the direction of the Galactic bulge and is heavily reddened by an uncertain amount. The V magnitude 16 days after maximum enables a distance to be estimated and this suggests that the nova may be in the extreme trailing stream of the Sagittarius dwarf spheroidal galaxy. If so it is the first nova to be detected from that, or from any dwarf spheroidal galaxy. Given the uncertainty of the method and the unusual light curve we cannot rule out the possibility that it is in the bulge or even the Galactic disk behind the bulge.Publisher PDFPeer reviewe
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