1,391 research outputs found
Liquid-gas phase behaviour of an argon-like fluid modelled by the hard-core two-Yukawa potential
We study a model for an argon-like fluid parameterised in terms of a
hard-core repulsion and a two-Yukawa potential. The liquid-gas phase behaviour
of the model is obtained from the thermodynamically self-consistent
Ornstein-Zernike approximation (SCOZA) of Hoye and Stell, the solution of which
lends itself particularly well to a pair potential of this form. The
predictions for the critical point and the coexistence curve are compared to
new high resolution simulation data and to other liquid-state theories,
including the hierarchical reference theory (HRT) of Parola and Reatto. Both
SCOZA and HRT deliver results that are considerably more accurate than standard
integral-equation approaches. Among the versions of SCOZA considered, the one
yielding the best agreement with simulation successfully predicts the critical
point parameters to within 1%.Comment: 10 pages 6 figure
A liquid state theory that remains successful in the critical region
A thermodynamically self-consistent Ornstein-Zernike approximation (SCOZA) is
applied to a fluid of spherical particles with a pair potential given by a
hard-core repulsion and a Yukawa attractive tail . This
potential allows one to take advantage of the known analytical properties of
the solution to the Ornstein-Zernike equation for the case in which the direct
correlation function outside the repulsive core is given by a linear
combination of two Yukawa tails and the radial distribution function
satisfies the exact core condition for . The predictions for the
thermodynamics, the critical point, and the coexistence curve are compared here
to other theories and to simulation results. In order to unambiguously assess
the ability of the SCOZA to locate the critical point and the phase boundary of
the system, a new set of simulations has also been performed. The method
adopted combines Monte Carlo and finite-size scaling techniques and is
especially adapted to deal with critical fluctuations and phase separation. It
is found that the version of the SCOZA considered here provides very good
overall thermodynamics and a remarkably accurate critical point and coexistence
curve. For the interaction range considered here, given by , the
critical density and temperature predicted by the theory agree with the
simulation results to about 0.6%.Comment: Prepared for the John Barker festschrift issue of Molecular Physics.
22 pages Latex, 6 ps figure
Local search for stable marriage problems
The stable marriage (SM) problem has a wide variety of practical
applications, ranging from matching resident doctors to hospitals, to matching
students to schools, or more generally to any two-sided market. In the
classical formulation, n men and n women express their preferences (via a
strict total order) over the members of the other sex. Solving a SM problem
means finding a stable marriage where stability is an envy-free notion: no man
and woman who are not married to each other would both prefer each other to
their partners or to being single. We consider both the classical stable
marriage problem and one of its useful variations (denoted SMTI) where the men
and women express their preferences in the form of an incomplete preference
list with ties over a subset of the members of the other sex. Matchings are
permitted only with people who appear in these lists, an we try to find a
stable matching that marries as many people as possible. Whilst the SM problem
is polynomial to solve, the SMTI problem is NP-hard. We propose to tackle both
problems via a local search approach, which exploits properties of the problems
to reduce the size of the neighborhood and to make local moves efficiently. We
evaluate empirically our algorithm for SM problems by measuring its runtime
behaviour and its ability to sample the lattice of all possible stable
marriages. We evaluate our algorithm for SMTI problems in terms of both its
runtime behaviour and its ability to find a maximum cardinality stable
marriage.For SM problems, the number of steps of our algorithm grows only as
O(nlog(n)), and that it samples very well the set of all stable marriages. It
is thus a fair and efficient approach to generate stable marriages.Furthermore,
our approach for SMTI problems is able to solve large problems, quickly
returning stable matchings of large and often optimal size despite the
NP-hardness of this problem.Comment: 12 pages, Proc. COMSOC 2010 (Third International Workshop on
Computational Social Choice
Factors inhibiting local government engagement in environmental sustainability
The literature on local government management of the environment in Australia has been limited in that it has typically focused on the urban sphere. In contrast, this paper places rurality at the centre of its inquiry. It uses data from 15 case studies of rural local governments in Australia to identify the main factors that inhibit natural resource management by rural councils. These barriers mobilise around four key themes: capacity, commitment, co-ordination and community. While many of the issues raised in this study of non-urban shires have been described in previous research, the paper argues that the geographic location of the areas under investigation aggravates barriers to engaging sustainability initiatives. It is contended that rural local governments need to be resourced accordingly to ensure that natural resource management at the local government level in Australia is not compromised
Self-driven soft imaging in liquid by means of photothermal excitation
The use of a laser to induce oscillations of an atomic force microscopy cantilever provides a way to excite the dynamics of the system in a very controlled manner. This excitation scheme has been used to obtain reliable self-sustained oscillations, in air and in liquid environments, and to implement an additional control loop leading to a soft, low-interaction, working mode. The dynamics of the oscillating cantilever has been characterized, both theoretically and experimentally, and the effectiveness of the approach has been verified on a test sample. © 2011 American Institute of Physics.Peer Reviewe
Phase behavior of a fluid with competing attractive and repulsive interactions
Fluids in which the interparticle potential has a hard core, is attractive at
moderate separations, and repulsive at greater separations are known to exhibit
novel phase behavior, including stable inhomogeneous phases. Here we report a
joint simulation and theoretical study of such a fluid, focusing on the
relationship between the liquid-vapor transition line and any new phases. The
phase diagram is studied as a function of the amplitude of the attraction for a
certain fixed amplitude of the long ranged repulsion. We find that the effect
of the repulsion is to substitute the liquid-vapor critical point and a portion
of the associated liquid-vapor transition line, by two first order transitions.
One of these transitions separates the vapor from a fluid of spherical
liquidlike clusters; the other separates the liquid from a fluid of spherical
voids. At low temperature, the two transition lines intersect one another and a
vapor-liquid transition line at a triple point. While most integral equation
theories are unable to describe the new phase transitions, the Percus Yevick
approximation does succeed in capturing the vapor-cluster transition, as well
as aspects of the structure of the cluster fluid, in reasonable agreement with
the simulation results.Comment: 15 pages, 20 figure
Finite-size effects on the dynamic susceptibility of CoPhOMe single-chain molecular magnets in presence of a static magnetic field
The static and dynamic properties of the single-chain molecular magnet
[Co(hfac)NITPhOMe] are investigated in the framework of the Ising model
with Glauber dynamics, in order to take into account both the effect of an
applied magnetic field and a finite size of the chains. For static fields of
moderate intensity and short chain lengths, the approximation of a
mono-exponential decay of the magnetization fluctuations is found to be valid
at low temperatures; for strong fields and long chains, a multi-exponential
decay should rather be assumed. The effect of an oscillating magnetic field,
with intensity much smaller than that of the static one, is included in the
theory in order to obtain the dynamic susceptibility . We find
that, for an open chain with spins, can be written as a
weighted sum of frequency contributions, with a sum rule relating the
frequency weights to the static susceptibility of the chain. Very good
agreement is found between the theoretical dynamic susceptibility and the ac
susceptibility measured in moderate static fields ( kOe),
where the approximation of a single dominating frequency turns out to be valid.
For static fields in this range, new data for the relaxation time,
versus , of the magnetization of CoPhOMe at low temperature are
also well reproduced by theory, provided that finite-size effects are included.Comment: 16 pages, 9 figure
- …