18,375 research outputs found
Equation of state of metallic hydrogen from Coupled Electron-Ion Monte Carlo simulations
We present a study of hydrogen at pressures higher than molecular
dissociation using the Coupled Electron-Ion Monte Carlo method. These
calculations use the accurate Reptation Quantum Monte Carlo method to estimate
the electronic energy and pressure while doing a Monte Carlo simulation of the
protons. In addition to presenting simulation results for the equation of state
over a large region of phase space, we report the free energy obtained by
thermodynamic integration. We find very good agreement with DFT calculations
for pressures beyond 600 GPa and densities above . Both
thermodynamic as well as structural properties are accurately reproduced by DFT
calculations. This agreement gives a strong support to the different
approximations employed in DFT, specifically the approximate
exchange-correlation potential and the use of pseudopotentials for the range of
densities considered. We find disagreement with chemical models, which suggests
a reinvestigation of planetary models, previously constructed using the
Saumon-Chabrier-Van Horn equations of state.Comment: 9 pages, 7 figure
Atypical late-time singular regimes accurately diagnosed in stagnation-point-type solutions of 3D Euler flows
We revisit, both numerically and analytically, the finite-time blowup of the
infinite-energy solution of 3D Euler equations of stagnation-point-type
introduced by Gibbon et al. (1999). By employing the method of mapping to
regular systems, presented in Bustamante (2011) and extended to the
symmetry-plane case by Mulungye et al. (2015), we establish a curious property
of this solution that was not observed in early studies: before but near
singularity time, the blowup goes from a fast transient to a slower regime that
is well resolved spectrally, even at mid-resolutions of This late-time
regime has an atypical spectrum: it is Gaussian rather than exponential in the
wavenumbers. The analyticity-strip width decays to zero in a finite time,
albeit so slowly that it remains well above the collocation-point scale for all
simulation times , where is the singularity time.
Reaching such a proximity to singularity time is not possible in the original
temporal variable, because floating point double precision ()
creates a `machine-epsilon' barrier. Due to this limitation on the
\emph{original} independent variable, the mapped variables now provide an
improved assessment of the relevant blowup quantities, crucially with
acceptable accuracy at an unprecedented closeness to the singularity time:
$T^*- t \approx 10^{-140}.
Nonequilibrium Phase Transitions in Directed Small-World Networks
Many social, biological, and economic systems can be approached by complex
networks of interacting units. The behaviour of several models on small-world
networks has recently been studied. These models are expected to capture the
essential features of the complex processes taking place on real networks like
disease spreading, formation of public opinion, distribution of wealth, etc. In
many of these systems relations are directed, in the sense that links only act
in one direction (outwards or inwards). We investigate the effect of directed
links on the behaviour of a simple spin-like model evolving on a small-world
network. We show that directed networks may lead to a highly nontrivial phase
diagram including first and second-order phase transitions out of equilibrium.Comment: 4 pages, RevTeX format, 4 postscript figs, uses eps
Wave-unlocking transition in resonantly coupled complex Ginzburg-Landau equations
We study the effect of spatial frequency-forcing on standing-wave solutions
of coupled complex Ginzburg-Landau equations. The model considered describes
several situations of nonlinear counterpropagating waves and also of the
dynamics of polarized light waves. We show that forcing introduces spatial
modulations on standing waves which remain frequency locked with a
forcing-independent frequency. For forcing above a threshold the modulated
standing waves unlock, bifurcating into a temporally periodic state. Below the
threshold the system presents a kind of excitability.Comment: 4 pages, including 4 postscript figures. To appear in Physical Review
Letters (1996). This paper and related material can be found at
http://formentor.uib.es/Nonlinear
The modular method: Milkfish pond culture
The modular method of milkfish culture (Chanos chanos) described in the manual is an improvement over the traditional extensive method. The manual is intended for the use of fish farmers and aquaculturists, extensionists, and students of aquaculture not only in the Philippines, but also in other milkfish-producing countries in Southeast Asia and the world. It covers the following: Interesting facts about milkfish -- biological characteristics, artificial breeding of milkfish; Design and operation of modular pond system -- pond preparation, stocking in the nursery or transition ponds, stocking in the rearing ponds, care of stock, pond utilization and production schedule, harvest and post-harvest; and, Economics and costing
Mudcrab, Scylla spp, production in brackishwater ponds
This manual covers the specifics of grow-out operation — site selection, pond specification, pond preparation, source of juveniles, transport and stocking, care of pond and stock, feeds and feeding, harvest, postharvest.
Also includes costs-and-benefits analysis and a list of useful references.Mudcrab (Scylla spp) production in brackishwater ponds is now gaining popularity, especially in communities that need to supplement their income. The manual covers the following: Distribution; Grow-out operation in ponds - site selection, pond specification, pond preparation, source of juveniles, transport and stocking of juveniles, care of pond and stock, feeds and feeding, harvest, post-harvest; Production and profits; Cost and analysis. It is hoped that the manual will be of use to fishfarmers and aquaculturists, extensionists, and students of aquaculture not only in the Philippines but also in other mudcrab producing countries in Southeast Asia
Analytical study of tunneling times in flat histogram Monte Carlo
We present a model for the dynamics in energy space of multicanonical
simulation methods that lends itself to a rather complete analytic
characterization. The dynamics is completely determined by the density of
states. In the \pm J 2D spin glass the transitions between the ground state
level and the first excited one control the long time dynamics. We are able to
calculate the distribution of tunneling times and relate it to the
equilibration time of a starting probability distribution. In this model, and
possibly in any model in which entering and exiting regions with low density of
states are the slowest processes in the simulations, tunneling time can be much
larger (by a factor of O(N)) than the equilibration time of the probability
distribution. We find that these features also hold for the energy projection
of single spin flip dynamics.Comment: 7 pages, 4 figures, published in Europhysics Letters (2005
Divergent Time Scale in Axelrod Model Dynamics
We study the evolution of the Axelrod model for cultural diversity. We
consider a simple version of the model in which each individual is
characterized by two features, each of which can assume q possibilities. Within
a mean-field description, we find a transition at a critical value q_c between
an active state of diversity and a frozen state. For q just below q_c, the
density of active links between interaction partners is non-monotonic in time
and the asymptotic approach to the steady state is controlled by a time scale
that diverges as (q-q_c)^{-1/2}.Comment: 4 pages, 5 figures, 2-column revtex4 forma
Conservation laws for the voter model in complex networks
We consider the voter model dynamics in random networks with an arbitrary
distribution of the degree of the nodes. We find that for the usual node-update
dynamics the average magnetization is not conserved, while an average
magnetization weighted by the degree of the node is conserved. However, for a
link-update dynamics the average magnetization is still conserved. For the
particular case of a Barabasi-Albert scale-free network the voter model
dynamics leads to a partially ordered metastable state with a finite size
survival time. This characteristic time scales linearly with system size only
when the updating rule respects the conservation law of the average
magnetization. This scaling identifies a universal or generic property of the
voter model dynamics associated with the conservation law of the magnetization.Comment: 5 pages, 4 figures; for related material please visit
http://www.imedea.uib.e
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