9,721 research outputs found
Parton Energy Loss and the Generalized Jet Transport Coefficient
We revisit radiative parton energy loss in deeply inelastic scattering (DIS)
off a large nucleus within the perturbative QCD approach. We calculate the
gluon radiation spectra induced by double parton scattering in DIS without
collinear expansion in the transverse momentum of initial gluons as in the
original high-twist approach. The final radiative gluon spectrum can be
expressed in terms of the convolution of hard partonic parts and unintegrated
or transverse momentum dependent (TMD) quark-gluon correlations. The TMD
quark-gluon correlation can be factorized approximately as a product of initial
quark distribution and TMD gluon distribution which can be used to define the
generalized or TMD jet transport coefficient. Under the static scattering
center and soft radiative gluon approximation, we recover the result by
Gylassy-Levai-Vitev (GLV) in the first order of the opacity expansion. The
difference as a result of the soft radiative gluon approximation is
investigated numerically under the static scattering center approximation.Comment: 33 pages in RevTeX with 30 figures, final version appeared in PRD
with additional typos correcte
Background Subtraction via Generalized Fused Lasso Foreground Modeling
Background Subtraction (BS) is one of the key steps in video analysis. Many
background models have been proposed and achieved promising performance on
public data sets. However, due to challenges such as illumination change,
dynamic background etc. the resulted foreground segmentation often consists of
holes as well as background noise. In this regard, we consider generalized
fused lasso regularization to quest for intact structured foregrounds. Together
with certain assumptions about the background, such as the low-rank assumption
or the sparse-composition assumption (depending on whether pure background
frames are provided), we formulate BS as a matrix decomposition problem using
regularization terms for both the foreground and background matrices. Moreover,
under the proposed formulation, the two generally distinctive background
assumptions can be solved in a unified manner. The optimization was carried out
via applying the augmented Lagrange multiplier (ALM) method in such a way that
a fast parametric-flow algorithm is used for updating the foreground matrix.
Experimental results on several popular BS data sets demonstrate the advantage
of the proposed model compared to state-of-the-arts
On the Convergence of the Self-Consistent Field Iteration in Kohn-Sham Density Functional Theory
It is well known that the self-consistent field (SCF) iteration for solving
the Kohn-Sham (KS) equation often fails to converge, yet there is no clear
explanation. In this paper, we investigate the SCF iteration from the
perspective of minimizing the corresponding KS total energy functional. By
analyzing the second-order Taylor expansion of the KS total energy functional
and estimating the relationship between the Hamiltonian and the part of the
Hessian which is not used in the SCF iteration, we are able to prove global
convergence from an arbitrary initial point and local linear convergence from
an initial point sufficiently close to the solution of the KS equation under
assumptions that the gap between the occupied states and unoccupied states is
sufficiently large and the second-order derivatives of the exchange correlation
functional are uniformly bounded from above. Although these conditions are very
stringent and are almost never satisfied in reality, our analysis is
interesting in the sense that it provides a qualitative prediction of the
behavior of the SCF iteration
Video Captioning via Hierarchical Reinforcement Learning
Video captioning is the task of automatically generating a textual
description of the actions in a video. Although previous work (e.g.
sequence-to-sequence model) has shown promising results in abstracting a coarse
description of a short video, it is still very challenging to caption a video
containing multiple fine-grained actions with a detailed description. This
paper aims to address the challenge by proposing a novel hierarchical
reinforcement learning framework for video captioning, where a high-level
Manager module learns to design sub-goals and a low-level Worker module
recognizes the primitive actions to fulfill the sub-goal. With this
compositional framework to reinforce video captioning at different levels, our
approach significantly outperforms all the baseline methods on a newly
introduced large-scale dataset for fine-grained video captioning. Furthermore,
our non-ensemble model has already achieved the state-of-the-art results on the
widely-used MSR-VTT dataset.Comment: CVPR 2018, with supplementary materia
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