1,191 research outputs found
MCMC based Generative Adversarial Networks for Handwritten Numeral Augmentation
This is the author accepted manuscript. The final version is available from Springer via the DOI in this record.In this paper, we propose a novel data augmentation framework for handwritten numerals by incorporating the probabilistic learning and the generative adversarial learning. First, we simply transform numeral images from spatial space into vector space. The Gaussian based Markov probabilistic model is then developed for simulating synthetic numeral vectors given limited handwritten samples. Next, the simulated data are used to pre-train the generative adversarial networks (GANs), which initializes their parameters to fit the general distribution of numeral features. Finally, we adopt the real handwritten numerals to fine-tune the GANs, which increases the authenticity of generated numeral samples. In this case, the outputs of the GANs can be employed to augment original numeral datasets for training the follow-up inference models. Considering that all simulation and augmentation are operated in 1-D vector space, the proposed augmentation framework is more computationally efficient than those based on 2-D images. Extensive experimental results demonstrate that our proposed augmentation framework achieves improved recognition accuracy.This work was supported by grants from the Chinese Scholarship Council (CSC) program
Anisotropy in the helicity modulus of a 3D XY-model: application to YBCO
We present a Monte Carlo study of the helicity moduli of an anisotropic
classical three-dimensional (3D) XY-model of YBCO in superconducting state. It
is found that both the ab-plane and the c-axis helicity moduli, which are
proportional to the inverse square of the corresponding magnetic field
penetration depth, vary linearly with temperature at low temperatures. The
result for the c-axis helicity modulus is in disagreement with the experiments
on high quality samples of YBCO. Thus we conclude that purely classical phase
fluctuations of the superconducting order parameter cannot account for the
observed c-axis electrodynamics of YBCO.Comment: 7 pages, 1 figur
Assessing the effects of foregrounds and sky removal in WMAP
Many recent analyses have indicated that large scale WMAP data display
anomalies that appear inconsistent with the standard cosmological paradigm.
However, the effects of foreground contamination, which require elimination of
some fraction of the data, have not been carefully investigated due to the
complexity in the analysis. Here we develop a general formalism of how to
incorporate these effects in any analysis of this type. Our approach is to
compute the full multi-dimensional probability distribution function of all
possible sky realizations that are consistent with the data and with the
allowed level of contamination. As an example we apply this method to compute
the joint probability distribution function for the possible realizations of
quadrupole and octopole using the WMAP data. This 12 dimensional distribution
function is explored using the Markov Chain Monte Carlo technique. The
resulting chains are used to asses the statistical significance of the low
quadrupole using frequentist methods, the quadrupole-octopole alignment using
several methods (angular momentum dispersion, multipole vectors and a new
method based of feature matching) and the quadrupole-octopole aligment with
ecliptic.Comment: 12 pages, 11 figures, 3 tables; replaced with the version accepted by
PRD. Added a few statistical tests and expanded discussion. Results
unchanged. Added acknowledgement in v3, clarified discussion of other work in
v
Projected single-spin flip dynamics in the Ising Model
We study transition matrices for projected dynamics in the
energy-magnetization space, magnetization space and energy space. Several
single spin flip dynamics are considered such as the Glauber and Metropolis
canonical ensemble dynamics and the Metropolis dynamics for three
multicanonical ensembles: the flat energy-magnetization histogram, the flat
energy histogram and the flat magnetization histogram. From the numerical
diagonalization of the matrices for the projected dynamics we obtain the
sub-dominant eigenvalue and the largest relaxation times for systems of varying
size. Although, the projected dynamics is an approximation to the full state
space dynamics comparison with some available results, obtained by other
authors, shows that projection in the magnetization space is a reasonably
accurate method to study the scaling of relaxation times with system size. The
transition matrices for arbitrary single-spin flip dynamics are obtained from a
single Monte-Carlo estimate of the infinite temperature transition-matrix, for
each system size, which makes the method an efficient tool to evaluate the
relative performance of any arbitrary local spin-flip dynamics. We also present
new results for appropriately defined average tunnelling times of magnetization
and compute their finite-size scaling exponents that we compare with results of
energy tunnelling exponents available for the flat energy histogram
multicanonical ensemble.Comment: 23 pages and 6 figure
Final State Interactions Effects in Neutrino-Nucleus Interactions
Final State Interactions effects are discussed in the context of Monte Carlo
simulations of neutrino-nucleus interactions. A role of Formation Time is
explained and several models describing this effect are compared. Various
observables which are sensitive to FSI effects are reviewed including
pion-nucleus interaction and hadron yields in backward hemisphere. NuWro Monte
Carlo neutrino event generator is described and its ability to understand
neutral current production data in GeV neutrino flux
experiments is demonstrated.Comment: 13 pages, 16 figure
Combination of improved multibondic method and the Wang-Landau method
We propose a method for Monte Carlo simulation of statistical physical models
with discretized energy. The method is based on several ideas including the
cluster algorithm, the multicanonical Monte Carlo method and its acceleration
proposed recently by Wang and Landau. As in the multibondic ensemble method
proposed by Janke and Kappler, the present algorithm performs a random walk in
the space of the bond population to yield the state density as a function of
the bond number. A test on the Ising model shows that the number of Monte Carlo
sweeps required of the present method for obtaining the density of state with a
given accuracy is proportional to the system size, whereas it is proportional
to the system size squared for other conventional methods. In addition, the new
method shows a better performance than the original Wang-Landau method in
measurement of physical quantities.Comment: 12 pages, 3 figure
Noisy Monte Carlo revisited
We present an exact Monte Carlo algorithm designed to sample theories where
the energy is a sum of many couplings of decreasing strength. Our algorithm,
simplified from that of L. Lin et al. hep-lat/9905033, avoids the computation
of almost all non-leading terms. We illustrate its use by simulating SU(2)
lattice gauge theory with a 5-loop action, and discuss further applications to
full QCD.Comment: latex, 8 page
Exact sampling from non-attractive distributions using summary states
Propp and Wilson's method of coupling from the past allows one to efficiently
generate exact samples from attractive statistical distributions (e.g., the
ferromagnetic Ising model). This method may be generalized to non-attractive
distributions by the use of summary states, as first described by Huber. Using
this method, we present exact samples from a frustrated antiferromagnetic
triangular Ising model and the antiferromagnetic q=3 Potts model. We discuss
the advantages and limitations of the method of summary states for practical
sampling, paying particular attention to the slowing down of the algorithm at
low temperature. In particular, we show that such a slowing down can occur in
the absence of a physical phase transition.Comment: 5 pages, 6 EPS figures, REVTeX; additional information at
http://wol.ra.phy.cam.ac.uk/mackay/exac
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