1,771 research outputs found
Hilbert Statistics of Vorticity Scaling in Two-Dimensional Turbulence
In this paper, the scaling property of the inverse energy cascade and forward
enstrophy cascade of the vorticity filed in two-dimensional (2D)
turbulence is analyzed. This is accomplished by applying a Hilbert-based
technique, namely Hilbert-Huang Transform, to a vorticity field obtained from a
grid-points direct numerical simulation of the 2D turbulence with a
forcing scale and an Ekman friction. The measured joint probability
density function of mode of the vorticity and
instantaneous wavenumber is separated by the forcing scale into
two parts, which corresponding to the inverse energy cascade and the forward
enstrophy cascade. It is found that all conditional pdf at given
wavenumber has an exponential tail. In the inverse energy cascade, the
shape of does collapse with each other, indicating a
nonintermittent cascade. The measured scaling exponent is
linear with the statistical order , i.e., ,
confirming the nonintermittent cascade process.
In the forward enstrophy cascade, the core part of is changing
with wavenumber , indicating an intermittent forward cascade.
The measured scaling exponent is nonlinear with and
can be described very well by a log-Poisson fitting:
. However, the
extracted vorticity scaling exponents for both inverse
energy cascade and forward enstrophy cascade are not consistent with
Kraichnan\rq{}s theory prediction. New theory for the vorticity field in 2D
turbulence is required to interpret the observed scaling behavior.Comment: 13 pages with 10 figure
LGLG-WPCA: An Effective Texture-based Method for Face Recognition
In this paper, we proposed an effective face feature extraction method by
Learning Gabor Log-Euclidean Gaussian with Whitening Principal Component
Analysis (WPCA), called LGLG-WPCA. The proposed method learns face features
from the embedded multivariate Gaussian in Gabor wavelet domain; it has the
robust performance to adverse conditions such as varying poses, skin aging and
uneven illumination. Because the space of Gaussian is a Riemannian manifold and
it is difficult to incorporate learning mechanism in the model. To address this
issue, we use L2EMG to map the multidimensional Gaussian model to the linear
space, and then use WPCA to learn face features. We also implemented the
key-point-based version of LGLG-WPCA, called LGLG(KP)-WPCA. Experiments show
the proposed methods are effective and promising for face texture feature
extraction and the combination of the feature of the proposed methods and the
features of Deep Convolutional Network (DCNN) achieved the best recognition
accuracies on FERET database compared to the state-of-the-art methods. In the
next version of this paper, we will test the performance of the proposed
methods on the large-varying pose databases
The refined BPS index from stable pair invariants
A refinement of the stable pair invariants of Pandharipande and Thomas for
non-compact Calabi-Yau spaces is introduced based on a virtual
Bialynicki-Birula decomposition with respect to a C* action on the stable pair
moduli space, or alternatively the equivariant index of Nekrasov and Okounkov.
This effectively calculates the refined index for M-theory reduced on these
Calabi-Yau geometries. Based on physical expectations we propose a product
formula for the refined invariants extending the motivic product formula of
Morrison, Mozgovoy, Nagao, and Szendroi for local P^1. We explicitly compute
refined invariants in low degree for local P^2 and local P^1 x P^1 and check
that they agree with the predictions of the direct integration of the
generalized holomorphic anomaly and with the product formula. The modularity of
the expressions obtained in the direct integration approach allows us to relate
the generating function of refined PT invariants on appropriate geometries to
Nekrasov's partition function and a refinement of Chern-Simons theory on a lens
space. We also relate our product formula to wallcrossing.Comment: 60 pages, 1 eps figure; reference updated; minor typos correcte
Cross-frequency interactions during diffusion on complex brain networks are facilitated by scale-free properties
We studied the interactions between different temporal scales of diffusion
processes on complex networks and found them to be stronger in scale-free (SF)
than in Erdos-Renyi (ER) networks, especially for the case of phase-amplitude
coupling (PAC)-the phenomenon where the phase of an oscillatory mode modulates
the amplitude of another oscillation. We found that SF networks facilitate PAC
between slow and fast frequency components of the diffusion process, whereas ER
networks enable PAC between slow-frequency components. Nodes contributing the
most to the generation of PAC in SF networks were non-hubs that connected with
high probability to hubs. Additionally, brain networks from healthy controls
(HC) and Alzheimer's disease (AD) patients presented a weaker PAC between slow
and fast frequencies than SF, but higher than ER. We found that PAC decreased
in AD compared to HC and was more strongly correlated to the scores of two
different cognitive tests than what the strength of functional connectivity
was, suggesting a link between cognitive impairment and multi-scale information
flow in the brain.Comment: 38 pages, 8 figures, 3 supplementary figure
Learning Domain-Invariant Subspace using Domain Features and Independence Maximization
Domain adaptation algorithms are useful when the distributions of the
training and the test data are different. In this paper, we focus on the
problem of instrumental variation and time-varying drift in the field of
sensors and measurement, which can be viewed as discrete and continuous
distributional change in the feature space. We propose maximum independence
domain adaptation (MIDA) and semi-supervised MIDA (SMIDA) to address this
problem. Domain features are first defined to describe the background
information of a sample, such as the device label and acquisition time. Then,
MIDA learns a subspace which has maximum independence with the domain features,
so as to reduce the inter-domain discrepancy in distributions. A feature
augmentation strategy is also designed to project samples according to their
backgrounds so as to improve the adaptation. The proposed algorithms are
flexible and fast. Their effectiveness is verified by experiments on synthetic
datasets and four real-world ones on sensors, measurement, and computer vision.
They can greatly enhance the practicability of sensor systems, as well as
extend the application scope of existing domain adaptation algorithms by
uniformly handling different kinds of distributional change.Comment: Accepte
Dynamic SPECT reconstruction with temporal edge correlation
In dynamic imaging, a key challenge is to reconstruct image sequences with
high temporal resolution from strong undersampling projections due to a
relatively slow data acquisition speed. In this paper, we propose a variational
model using the infimal convolution of Bregman distance with respect to total
variation to model edge dependence of sequential frames. The proposed model is
solved via an alternating iterative scheme, for which each subproblem is convex
and can be solved by existing algorithms. The proposed model is formulated
under both Gaussian and Poisson noise assumption and the simulation on two sets
of dynamic images shows the advantage of the proposed method compared to
previous methods.Comment: 24page
Phase-error restraint with the empirical mode decomposition method in phase measurement profilometry
Harnessing Sparsity over the Continuum: Atomic Norm Minimization for Super Resolution
Convex optimization recently emerges as a compelling framework for performing
super resolution, garnering significant attention from multiple communities
spanning signal processing, applied mathematics, and optimization. This article
offers a friendly exposition to atomic norm minimization as a canonical convex
approach to solve super resolution problems. The mathematical foundations and
performances guarantees of this approach are presented, and its application in
super resolution image reconstruction for single-molecule fluorescence
microscopy are highlighted
Molecular access to multi-dimensionally encoded information
Polymer scientist have only recently realized that information storage on the molecular level is not only restricted to DNA-based systems. Similar encoding and decoding of data have been demonstrated on synthetic polymers that could overcome some of the drawbacks associated with DNA, such as the ability to make use of a larger monomer alphabet. This feature article describes some of the recent data storage strategies that were investigated, ranging from writing information on linear sequence-defined macromolecules up to layer-by-layer casted surfaces and QR codes. In addition, some strategies to increase storage density are elaborated and some trends regarding future perspectives on molecular data storage from the literature are critically evaluated. This work ends with highlighting the demand for new strategies setting up reliable solutions for future data management technologies
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