25,537 research outputs found
Convex subquivers and the finitistic dimension
Let \cQ be a quiver and a field. We study the interrelationship of
homological properties of algebras associated to convex subquivers of \cQ and
quotients of the path algebra K\cQ. We introduce the homological heart of
\cQ which is a particularly nice convex subquiver of \cQ. For any algebra
of the form K\cQ/I, the algebra associated to K\cQ/I and the homological
heart have similar homological properties. We give an application showing that
the finitistic dimension conjecture need only be proved for algebras with path
connected quivers
Stratifying systems over hereditary algebras
This paper deals with stratifying systems over hereditary algebras. In the
case of tame hereditary algebras we obtain a bound for the size of the
stratifying systems composed only by regular modules and we conclude that
stratifying systems can not be complete. For wild hereditary algebras with more
than 2 vertices we show that there exists a complete stratifying system whose
elements are regular modules. In the other case, we conclude that there are no
stratifing system over them with regular modules. In one example we built all
the stratifying systems, with a specific form, having maximal number of regular
summads
-Koszul algebras, 2- determined algebras and 2--Koszul algebras
The relationship between an algebra and its associated monomial algebra is
investigated when at least one of the algebras is -Koszul. It is shown that
an algebra which has a reduced \grb basis that is composed of homogeneous
elements of degree is -Koszul if and only if its associated monomial
algebra is -Koszul. The class of 2--determined algebras and the class
2--Koszul algebras are introduced. In particular, it shown that
2--determined monomial algebras are 2--Koszul algebras and the structure
of the ideal of relations of such an algebra is completely determined
Efficient tensor completion for color image and video recovery: Low-rank tensor train
This paper proposes a novel approach to tensor completion, which recovers
missing entries of data represented by tensors. The approach is based on the
tensor train (TT) rank, which is able to capture hidden information from
tensors thanks to its definition from a well-balanced matricization scheme.
Accordingly, new optimization formulations for tensor completion are proposed
as well as two new algorithms for their solution. The first one called simple
low-rank tensor completion via tensor train (SiLRTC-TT) is intimately related
to minimizing a nuclear norm based on TT rank. The second one is from a
multilinear matrix factorization model to approximate the TT rank of a tensor,
and is called tensor completion by parallel matrix factorization via tensor
train (TMac-TT). A tensor augmentation scheme of transforming a low-order
tensor to higher-orders is also proposed to enhance the effectiveness of
SiLRTC-TT and TMac-TT. Simulation results for color image and video recovery
show the clear advantage of our method over all other methods.Comment: Submitted to the IEEE Transactions on Image Processing. arXiv admin
note: substantial text overlap with arXiv:1601.0108
Concatenated image completion via tensor augmentation and completion
This paper proposes a novel framework called concatenated image completion
via tensor augmentation and completion (ICTAC), which recovers missing entries
of color images with high accuracy. Typical images are second- or third-order
tensors (2D/3D) depending if they are grayscale or color, hence tensor
completion algorithms are ideal for their recovery. The proposed framework
performs image completion by concatenating copies of a single image that has
missing entries into a third-order tensor, applying a dimensionality
augmentation technique to the tensor, utilizing a tensor completion algorithm
for recovering its missing entries, and finally extracting the recovered image
from the tensor. The solution relies on two key components that have been
recently proposed to take advantage of the tensor train (TT) rank: A tensor
augmentation tool called ket augmentation (KA) that represents a low-order
tensor by a higher-order tensor, and the algorithm tensor completion by
parallel matrix factorization via tensor train (TMac-TT), which has been
demonstrated to outperform state-of-the-art tensor completion algorithms.
Simulation results for color image recovery show the clear advantage of our
framework against current state-of-the-art tensor completion algorithms.Comment: 7 pages, 6 figures, submitted to ICSPCS 201
Spherically-symmetric solutions in general relativity
We present a tetrad-based method for solving the Einstein field equations for
spherically-symmetric systems and compare it with the widely-used
Lema\^itre-Tolman-Bondi (LTB) model. In particular, we focus on the issues of
gauge ambiguity and the use of comoving versus 'physical' coordinate systems.
We also clarify the correspondences between the two approaches, and illustrate
their differences by applying them to the classic examples of the Schwarzschild
and Friedmann-Robertson-Walker spacetimes. We demonstrate that the tetrad-based
method does not suffer from the gauge freedoms inherent to the LTB model,
naturally accommodates non-zero pressure and has a more transparent physical
interpretation. We further apply our tetrad-based method to a generalised form
of 'Swiss cheese' model, which consists of an interior spherical region
surrounded by a spherical shell of vacuum that is embedded in an exterior
background universe. In general, we allow the fluid in the interior and
exterior regions to support pressure, and do not demand that the interior
region be compensated. We pay particular attention to the form of the solution
in the intervening vacuum region and verify the validity of Birkhoff's theorem
at both the metric and tetrad level. We then reconsider critically the original
theoretical arguments underlying the so-called cosmological model,
which has recently received considerable attention. These considerations in
turn illustrate the interesting behaviour of a number of 'horizons' in general
cosmological models.Comment: 21 pages, 3 figures, submitted to Physical Review
Tracking objects using 3D object proposals
3D object proposals, quickly detected regions in a 3D scene that likely
contain an object of interest, are an effective approach to improve the
computational efficiency and accuracy of the object detection framework. In
this work, we propose a novel online method that uses our previously developed
3D object proposals, in a RGB-D video sequence, to match and track static
objects in the scene using shape matching. Our main observation is that depth
images provide important information about the geometry of the scene that is
often ignored in object matching techniques. Our method takes less than a
second in MATLAB on the UW-RGBD scene dataset on a single thread CPU and thus,
has potential to be used in low-power chips in Unmanned Aerial Vehicles (UAVs),
quadcopters, and drones.Comment: 4 pages, 4 figures, published in APSIPA 201
Correlating Cellular Features with Gene Expression using CCA
To understand the biology of cancer, joint analysis of multiple data
modalities, including imaging and genomics, is crucial. The involved nature of
gene-microenvironment interactions necessitates the use of algorithms which
treat both data types equally. We propose the use of canonical correlation
analysis (CCA) and a sparse variant as a preliminary discovery tool for
identifying connections across modalities, specifically between gene expression
and features describing cell and nucleus shape, texture, and stain intensity in
histopathological images. Applied to 615 breast cancer samples from The Cancer
Genome Atlas, CCA revealed significant correlation of several image features
with expression of PAM50 genes, known to be linked to outcome, while Sparse CCA
revealed associations with enrichment of pathways implicated in cancer without
leveraging prior biological understanding. These findings affirm the utility of
CCA for joint phenotype-genotype analysis of cancer.Comment: To appear at IEEE International Symposium on Biomedical Imaging
(ISBI) 201
An alternative approach to modelling a cosmic void and its effect on the cosmic microwave background
We apply our tetrad-based approach for constructing spherically-symmetric
solutions in general relativity to modelling a void, and compare it with the
standard Lema\^itre-Tolman-Bondi (LTB) formalism. In particular, we construct
models for the void observed in the direction of Draco in the WISE-2MASS galaxy
survey, and a corresponding cosmic microwave background (CMB) temperature
decrement in the Planck data in the same direction. We find that the
present-day density and velocity profiles of the void are not well constrained
by the existing data, so that void models produced from the two approaches can
differ substantially while remaining broadly consistent with the observations.
We highlight the importance of considering the velocity as well as the density
profile in constraining voids.Comment: 12 pages, 14 figures, submitted to MNRA
Light curves of a shock-breakout material and a relativistic off-axis jet from a Binary Neutron Star system
Binary neutron star mergers are believed to eject significant masses with a
diverse range of velocities. Once these ejected materials begin to be
decelerated by a homogeneous medium, relativistic electrons are mainly cooled
down by synchrotron radiation, generating a multiwavelength long-lived
afterglow. Analytic and numerical methods illustrate that the outermost matter,
the merger shock-breakout material, can be parametrized by power-law velocity
distributions .
Considering that the shock-breakout material is moving on-axis towards the
observer and the relativistic jet off-axis, we compute the light curves during
the relativistic and the lateral expansion phase. As a particular case, we
successfully describe the X-ray, optical and radio light curves alongside the
spectral energy distribution from the recently discovered gravitational-wave
transient GW170817, when the merger shock-breakout material moves with mildly
relativistic velocities near-Newtonian phase and the jet with relativistic
velocities. Future electromagnetic counterpart observations of this binary
system could be able to evaluate different properties of these light curves.Comment: 19 pages, 8 figures and one table. The model of an off-axis jet was
introduced to fit the multiwavelength data. Accepted for publication in Ap
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