160 research outputs found
Local structure of Liquid-Vapour Interfaces
The structure of a simple liquid may be characterised in terms of ground
state clusters of small numbers of atoms of that same liquid. Here we use this
sensitive structural probe to consider the effect of a liquid-vapour interface
upon the liquid structure. At higher temperatures (above around half the
critical temperature) we find that the predominant effect of the interface is
to reduce the local density, which significantly suppresses the local cluster
populations. At lower temperatures, however, pronounced interfacial layering is
found. This appears to be connected with significant orientational ordering of
clusters based on 3- and 5-membered rings, with the rings aligning
perpendicular and parallel to the interface respectively. At all temperatures,
we find that the population of five-fold symmetric structures is suppressed,
rather than enhanced, close to the interface.Comment: 10 pages, 8 figures, accepted for publication by Molecular Physic
Comment on "Conjectures on exact solution of three-dimensional (3D) simple orthorhombic Ising lattices" [arXiv:0705.1045]
It is shown that a recent article by Z.-D. Zhang [arXiv:0705.1045] is in
error and violates well-known theorems.Comment: LaTeX, 3 pages, no figures, submitted to Philosophical Magazine.
Expanded versio
Coarse-graining diblock copolymer solutions: a macromolecular version of the Widom-Rowlinson model
We propose a systematic coarse-grained representation of block copolymers,
whereby each block is reduced to a single ``soft blob'' and effective intra- as
well as intermolecular interactions act between centres of mass of the blocks.
The coarse-graining approach is applied to simple athermal lattice models of
symmetric AB diblock copolymers, in particular to a Widom-Rowlinson-like model
where blocks of the same species behave as ideal polymers (i.e. freely
interpenetrate), while blocks of opposite species are mutually avoiding walks.
This incompatibility drives microphase separation for copolymer solutions in
the semi-dilute regime. An appropriate, consistent inversion procedure is used
to extract effective inter- and intramolecular potentials from Monte Carlo
results for the pair distribution functions of the block centres of mass in the
infinite dilution limit.Comment: To be published in mol.phys(2005
Molecular Theory of Hydrophobic Effects: ``She is too mean to have her name repeated.''
This paper reviews the molecular theory of hydrophobic effects relevant to
biomolecular structure and assembly in aqueous solution. Recent progress has
resulted in simple, validated molecular statistical thermodynamic theories and
clarification of confusing theories of decades ago. Current work is resolving
effects of wider variations of thermodynamic state, e.g. pressure denaturation
of soluble proteins, and more exotic questions such as effects of surface
chemistry in treating stability of macromolecular structures in aqueous
solutionComment: submitted to Ann. Rev. Phys. Chem., 31 pages, 245 references, 2
figure
Wetting transitions of continuously varying or infinite order from a mean-field density-functional theory
Interfacial Tensions near Critical Endpoints: Experimental Checks of EdGF Theory
Predictions of the extended de Gennes-Fisher local-functional theory for the
universal scaling functions of interfacial tensions near critical endpoints are
compared with experimental data. Various observations of the binary mixture
isobutyric acid water are correlated to facilitate an analysis of the
experiments of Nagarajan, Webb and Widom who observed the vapor-liquid
interfacial tension as a function of {\it both} temperature and density.
Antonow's rule is confirmed and, with the aid of previously studied {\it
universal amplitude ratios}, the crucial analytic ``background'' contribution
to the surface tension near the endpoint is estimated. The residual singular
behavior thus uncovered is consistent with the theoretical scaling predictions
and confirms the expected lack of symmetry in . A searching test of
theory, however, demands more precise and extensive experiments; furthermore,
the analysis highlights, a previously noted but surprising, three-fold
discrepancy in the magnitude of the surface tension of isobutyric acid
water relative to other systems.Comment: 6 figure
Theoretical investigation of the phase behaviour of model ternary mixtures containing n
An extremely powerful long-lived superluminal ejection from the black hole MAXI J1820+070
Black holes in binary systems execute patterns of outburst activity where two
characteristic X-ray states are associated with different behaviours observed
at radio wavelengths. The hard state is associated with radio emission
indicative of a continuously replenished, collimated, relativistic jet, whereas
the soft state is rarely associated with radio emission, and never
continuously, implying the absence of a quasi-steady jet. Here we report radio
observations of the black hole transient MAXI J1820070 during its 2018
outburst. As the black hole transitioned from the hard to soft state we
observed an isolated radio flare, which, using high angular resolution radio
observations, we connect with the launch of bi-polar relativistic ejecta. This
flare occurs as the radio emission of the core jet is suppressed by a factor of
over 800. We monitor the evolution of the ejecta over 200 days and to a maximum
separation of 10, during which period it remains detectable due to in-situ
particle acceleration. Using simultaneous radio observations sensitive to
different angular scales we calculate an accurate estimate of energy content of
the approaching ejection. This energy estimate is far larger than that derived
from state transition radio flare, suggesting a systematic underestimate of jet
energetics
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