36,091 research outputs found
Liquid-vapour asymmetry in pure fluids: A Monte Carlo simulation study
Monte Carlo simulations within the grand canonical ensemble are used to
obtain the joint distribution of density and energy fluctuations
for two model fluids: a decorated lattice gas and a polymer system. In the near
critical region the form of is analysed using a mixed field
finite-size-scaling theory that takes account of liquid-vapour asymmetry. Field
mixing transformations are performed that map onto the joint
distribution of critical scaling operators \ptMEstar\ appropriate to the Ising
fixed point. Carrying out this procedure permits a very accurate determination
of the critical point parameters. By forming various projections of \ptMEstar ,
the full universal finite-size spectrum of the critical density and energy
distributions of fluids is also obtained. In the sub-critical coexistence
region, an examination is made of the influence of field mixing on the
asymmetry of the density distribution.Comment: 19 pages Latex, 15 Figures available on request. Report Number
#IP-94.15
Accurate Measurements of the Chemical Potential of Polymeric Systems by Monte-Carlo Simulation
We present a new Monte-Carlo method for estimating the chemical potential of
model polymer systems. The method is based upon the gradual insertion of a
penetrable `ghost' polymer into the system and is effective for large chain
lengths and at high densities. Insertion of the ghost chain is facilitated by
use of an expanded ensemble in which weighted transitions are permitted between
states characterising the strength of the excluded volume and thermal
interactions experienced by the ghost chain. We discuss the implementation and
optimisation of the method within the framework of the bond fluctuation model,
and demonstrate its precision by a calculation of the finite-size corrections
to the chemical potential.Comment: 12 pages Latex, Report Number #IP-94.12
Concentration and energy fluctuations in a critical polymer mixture
A semi-grand-canonical Monte Carlo algorithm is employed in conjunction with
the bond fluctuation model to investigate the critical properties of an
asymmetric binary (AB) polymer mixture. By applying the equal peak-weight
criterion to the concentration distribution, the coexistence curve separating
the A-rich and B-rich phases is identified as a function of temperature and
chemical potential. To locate the critical point of the model, the cumulant
intersection method is used. The accuracy of this approach for determining the
critical parameters of fluids is assessed. Attention is then focused on the
joint distribution function of the critical concentration and energy, which is
analysed using a mixed-field finite-size-scaling theory that takes due account
of the lack of symmetry between the coexisting phases. The essential Ising
character of the binary polymer critical point is confirmed by mapping the
critical scaling operator distributions onto independently known forms
appropriate to the 3D Ising universality class. In the process, estimates are
obtained for the field mixing parameters of the model which are compared both
with those yielded by a previous method, and with the predictions of a mean
field calculation.Comment: 17 pages Latex, 9 figures appended as uuencoded .gz tar fil
The Lot of the Unemployed: A Time Use Perspective
This paper provides new evidence on time use and subjective well-being of employed and unemployed individuals in 14 countries. We devote particular attention to characterizing and modeling job search intensity, measured by the amount of time devoted to searching for a new job. Job search intensity varies considerably across countries, and is higher in countries that have higher wage dispersion. We also examine the relationship between unemployment benefits and job search.unemployment benefits, time use, job search, unemployment, inequality
New Two-Dimensional Models of Supernova Explosions by the Neutrino-Heating Mechanism: Evidence for Different Instability Regimes in Collapsing Stellar Cores
The neutrino-driven explosion mechanism for core-collapse supernovae in its
modern flavor relies on the additional support of hydrodynamical instabilities
in achieving shock revival. Two possible candidates, convection and the
so-called standing accretion shock instability (SASI), have been proposed for
this role. In this paper, we discuss new successful simulations of supernova
explosions that shed light on the relative importance of these two
instabilities. While convection has so far been observed to grow first in
self-consistent hydrodynamical models with multi-group neutrino transport, we
here present the first such simulation in which the SASI grows faster while the
development of convection is initially inhibited. We illustrate the features of
this SASI-dominated regime using an explosion model of a 27 solar mass
progenitor, which is contrasted with a convectively-dominated model of an 8.1
solar mass progenitor with subsolar metallicity, whose early post-bounce
behavior is more in line with previous 11.2 and 15 solar mass explosion models.
We analyze the conditions discriminating between the two different regimes,
showing that a high mass-accretion rate and a short advection time-scale are
conducive for strong SASI activity. We also briefly discuss some important
factors for capturing the SASI-driven regime, such as general relativity, the
progenitor structure, a nuclear equation of state leading to a compact
proto-neutron star, and the neutrino treatment. Finally, we evaluate possible
implications of our findings for 2D and 3D supernova simulations. Our results
show that a better understanding of the SASI and convection in the non-linear
regime is required.Comment: 12 pages, 13 figures; revised version accepted for publication in Ap
The Lot of the Unemployed: A Time Use Perspective
This paper provides new evidence on time use and subjective well-being of employed and unemployed individuals in 14 countries. We devote particular attention to characterizing and modeling job search intensity, measured by the amount of time devoted to searching for a new job. Job search intensity varies considerably across countries, and is higher in countries that have higher wage dispersion. We also examine the relationship between unemployment benefits and job search.unemployment, job search, time use, unemployment benefits, inequality
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