29,250 research outputs found
Sampling the Probability Distribution of Type Ia Supernova Lightcurve Parameters in Cosmological Analysis
In order to obtain robust cosmological constraints from Type Ia supernova (SN
Ia) data, we have applied Markov Chain Monte Carlo (MCMC) to SN Ia lightcurve
fitting. We develop a method for sampling the resultant probability density
distributions (pdf) of the SN Ia lightcuve parameters in the MCMC likelihood
analysis to constrain cosmological parameters, and validate it using simulated
data sets. Applying this method to the Joint Lightcurve Analysis (JLA) data set
of SNe Ia, we find that sampling the SN Ia lightcurve parameter pdf's leads to
cosmological parameters closer to that of a flat Universe with a cosmological
constant, compared to the usual practice of using only the best fit values of
the SN Ia lightcurve parameters. Our method will be useful in the use of SN Ia
data for precision cosmology.Comment: 9 pages, 6 figures, 4 tables. Revised version accepted by MNRA
Regularized Wasserstein Means for Aligning Distributional Data
We propose to align distributional data from the perspective of Wasserstein
means. We raise the problem of regularizing Wasserstein means and propose
several terms tailored to tackle different problems. Our formulation is based
on the variational transportation to distribute a sparse discrete measure into
the target domain. The resulting sparse representation well captures the
desired property of the domain while reducing the mapping cost. We demonstrate
the scalability and robustness of our method with examples in domain
adaptation, point set registration, and skeleton layout
Supervised Attentions for Neural Machine Translation
In this paper, we improve the attention or alignment accuracy of neural
machine translation by utilizing the alignments of training sentence pairs. We
simply compute the distance between the machine attentions and the "true"
alignments, and minimize this cost in the training procedure. Our experiments
on large-scale Chinese-to-English task show that our model improves both
translation and alignment qualities significantly over the large-vocabulary
neural machine translation system, and even beats a state-of-the-art
traditional syntax-based system.Comment: 6 pages. In Proceedings of EMNLP 2016. arXiv admin note: text overlap
with arXiv:1605.0314
A modified lattice Bhatnagar-Gross-Krook model for convection heat transfer in porous media
The lattice Bhatnagar-Gross-Krook (LBGK) model has become the most popular
one in the lattice Boltzmann method for simulating the convection heat transfer
in porous media. However, the LBGK model generally suffers from numerical
instability at low fluid viscosities and effective thermal diffusivities. In
this paper, a modified LBGK model is developed for incompressible thermal flows
in porous media at the representative elementary volume scale, in which the
shear rate and temperature gradient are incorporated into the equilibrium
distribution functions. With two additional parameters, the relaxation times in
the collision process can be fixed at a proper value invariable to the
viscosity and the effective thermal diffusivity. In addition, by constructing a
modified equilibrium distribution function and a source term in the evolution
equation of temperature field, the present model can recover the macroscopic
equations correctly through the Chapman-Enskog analysis, which is another key
point different from previous LBGK models. Several benchmark problems are
simulated to validate the present model with the proposed local computing
scheme for the shear rate and temperature gradient, and the numerical results
agree well with analytical solutions and/or those well-documented data in
previous studies. It is also shown that the present model and the computational
schemes for the gradient operators have a second-order accuracy in space, and
better numerical stability of the present modified LBGK model than previous
LBGK models is demonstrated.Comment: 38pages,50figure
Volume-averaged macroscopic equation for fluid flow in moving porous media
Darcy's law and the Brinkman equation are two main models used for creeping
fluid flows inside moving permeable particles. For these two models, the time
derivative and the nonlinear convective terms of fluid velocity are neglected
in the momentum equation. In this paper, a new momentum equation including
these two terms are rigorously derived from the pore-scale microscopic
equations by the volume-averaging method, which can reduces to Darcy's law and
the Brinkman equation under creeping flow conditions. Using the lattice
Boltzmann equation method, the macroscopic equations are solved for the problem
of a porous circular cylinder moving along the centerline of a channel.
Galilean invariance of the equations are investigated both with the intrinsic
phase averaged velocity and the phase averaged velocity. The results
demonstrate that the commonly used phase averaged velocity cannot serve as the
superficial velocity, while the intrinsic phase averaged velocity should be
chosen for porous particulate systems
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