1,036 research outputs found
Green Function Simulation of Hamiltonian Lattice Models with Stochastic Reconfiguration
We apply a recently proposed Green Function Monte Carlo to the study of
Hamiltonian lattice gauge theories. This class of algorithms computes quantum
vacuum expectation values by averaging over a set of suitable weighted random
walkers. By means of a procedure called Stochastic Reconfiguration the long
standing problem of keeping fixed the walker population without a priori
knowledge on the ground state is completely solved. In the model,
which we choose as our theoretical laboratory, we evaluate the mean plaquette
and the vacuum energy per plaquette. We find good agreement with previous works
using model dependent guiding functions for the random walkers.Comment: 14 pages, 5 PostScript Figures, RevTeX, two references adde
Temperature-extended Jarzynski relation: Application to the numerical calculation of the surface tension
We consider a generalization of the Jarzynski relation to the case where the
system interacts with a bath for which the temperature is not kept constant but
can vary during the transformation. We suggest to use this relation as a
replacement to the thermodynamic perturbation method or the Bennett method for
the estimation of the order-order surface tension by Monte Carlo simulations.
To demonstrate the feasibility of the method, we present some numerical data
for the 3D Ising model
Probability distributions for polymer translocation
We study the passage (translocation) of a self-avoiding polymer through a
membrane pore in two dimensions. In particular, we numerically measure the
probability distribution Q(T) of the translocation time T, and the distribution
P(s,t) of the translocation coordinate s at various times t. When scaled with
the mean translocation time , Q(T) becomes independent of polymer length,
and decays exponentially for large T. The probability P(s,t) is well described
by a Gaussian at short times, with a variance that grows sub-diffusively as
t^{\alpha} with \alpha~0.8. For times exceeding , P(s,t) of the polymers
that have not yet finished their translocation has a non-trivial stable shape.Comment: 5 pages, 4 figure
Vortex Particle-Mesh with Immersed Lifting Lines for Aerospace and Wind Engineering
AbstractWe present the treatment of lifting lines with a Vortex Particle-Mesh (VPM) methodology. The VPM method relies on the Lagrangian discretization of the Navier-Stokes equations in vorticity-velocity formulation. The use of this hybrid discretization offers several advantages. The particles are used solely for the advection, thereby waiving classical time stability constraints. They also exploit the compactness of vorticity support, leading to high computational gains for external flow simulations. The mesh, on the other hand, handles all the other computationally intensive tasks, such as the evaluation of the differential operators and the use of fast Fourier-based Poisson solvers, which allow the combination of unbounded directions and inlet/outlet boundaries. Both discretizations communicate through high order interpolation. The mesh and the interpolation also allow for additional advances; they are used to handle Lagrangian distortion by reinitializing the particle positions onto a regular grid. This crucial step, referred to as remeshing, guarantees the accuracy of the method. In addition, the resulting methodology provides computational efficiency and scalability to massively parallel architectures.Sources of vorticity are accounted for through a lifting line approach. This line handles the attached and shed vorticity contributions in a Lagrangian manner. Its immersed treatment efficiently captures the development of vorticity from thin sheets into a three-dimensional field. We apply this approach to the simulation of wake flows encountered in aeronautical and wind energy applications. An important aspect in these fields is the handling of turbulent inflows. We have developed a technique for the introduction of pre-computed or synthetic turbulent flow fields in vorticity form. Our treatment is based on particles as well and consistent with the Lagrangian character of the method. We apply here our method to the investigation of wind turbine wakes over very large distances, reaching cluster or wind farm sizes
Clustered Archimax Copulas
When modeling multivariate phenomena, properly capturing the joint extremal
behavior is often one of the many concerns. Archimax copulas appear as
successful candidates in case of asymptotic dependence. In this paper, the
class of Archimax copulas is extended via their stochastic representation to a
clustered construction. These clustered Archimax copulas are characterized by a
partition of the random variables into groups linked by a radial copula; each
cluster is Archimax and therefore defined by its own Archimedean generator and
stable tail dependence function. The proposed extension allows for both
asymptotic dependence and independence between the clusters, a property which
is sought, for example, in applications in environmental sciences and finance.
The model also inherits from the ability of Archimax copulas to capture
dependence between variables at pre-extreme levels. The asymptotic behavior of
the model is established, leading to a rich class of stable tail dependence
functions.Comment: 42 pages, 10 figure
The Random-bond Potts model in the large-q limit
We study the critical behavior of the q-state Potts model with random
ferromagnetic couplings. Working with the cluster representation the partition
sum of the model in the large-q limit is dominated by a single graph, the
fractal properties of which are related to the critical singularities of the
random Potts model. The optimization problem of finding the dominant graph, is
studied on the square lattice by simulated annealing and by a combinatorial
algorithm. Critical exponents of the magnetization and the correlation length
are estimated and conformal predictions are compared with numerical results.Comment: 7 pages, 6 figure
Probability distributions of the work in the 2D-Ising model
Probability distributions of the magnetic work are computed for the 2D Ising
model by means of Monte Carlo simulations. The system is first prepared at
equilibrium for three temperatures below, at and above the critical point. A
magnetic field is then applied and grown linearly at different rates.
Probability distributions of the work are stored and free energy differences
computed using the Jarzynski equality. Consistency is checked and the dynamics
of the system is analyzed. Free energies and dissipated works are reproduced
with simple models. The critical exponent is estimated in an usual
manner.Comment: 12 pages, 6 figures. Comments are welcom
Ignition and chemical kinetics of acrolein-oxygen-argon mixtures behind reflected shock waves
In order to address increasing greenhouse gas emissions, the future fossil fuel shortage and increasingly stringent pollutant emission regulations, a variety of biofuels are being progressively incorporated into conventional transportation fuels. Despite the beneficial impact of biofuels on most regulated pollutants, their combustion induces the increase of a variety of aldehydes that are being considered for specific regulations due to their high toxicity. One of the most hazardous aldehyde compounds is acrolein, C_2H_3CHO. Despite its high toxicity and increased formation during bioalcohol and biodiesel combustion, no experimental data are available for acrolein combustion. In the present study, we have investigated the ignition of acrolein–oxygen–argon mixtures behind reflected shock wave using three simultaneous emission diagnostics monitoring OH∗, CH∗ and CO_2∗. Experiments were performed over a range of conditions: Φ = 0.5–2; T_5 = 1178–1602 K; and P_5 = 173–416 kPa. A tentative detailed reaction model, which includes sub-mechanisms for the three measured excited species, was developed to describe the high-temperature chemical kinetics of acrolein oxidation. Reasonable agreement was found between the model prediction and experimental data
La iglesia de Montbrillant, en Ginebra
This church was built on sloping ground, and has two functional levels.
On the ground floor there is a church hall, with accommodation for 280 people, and a small annex with an additional chapel, a council chamber, parochial secretariat, offices and vestry.
Below there is a number of additional facilities, such as a parochial youth centre, and a covered court, which extends into the garden and serves in unsuitable weather to hold the activities that are normally practised out of doors.Construida sobre un terreno en declive, la iglesia de Montbrillant está organizada en dos niveles:
La planta superior, sita al nivel de la entrada, alberga el templo propiamente dicho con 280 asientos, pequeño local anexo dedicado al culto, sala de Consejo, secretariado parroquial, despachos para los pastores, vestuarios, etc.
En la planta inferior hay una serie de locales: centro parroquial de la juventud, servicios y un patio cubierto, prolongación del jardÃn, que sirve para poder celebrar, en caso de mal tiempo, las manifestaciones que normalmente se hacen al aire libre
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