24,475 research outputs found
Minimax Estimation of Large Precision Matrices with Bandable Cholesky Factor
Last decade witnesses significant methodological and theoretical advances in
estimating large precision matrices. In particular, there are scientific
applications such as longitudinal data, meteorology and spectroscopy in which
the ordering of the variables can be interpreted through a bandable structure
on the Cholesky factor of the precision matrix. However, the minimax theory has
still been largely unknown, as opposed to the well established minimax results
over the corresponding bandable covariance matrices. In this paper, we focus on
two commonly used types of parameter spaces, and develop the optimal rates of
convergence under both the operator norm and the Frobenius norm. A striking
phenomenon is found: two types of parameter spaces are fundamentally different
under the operator norm but enjoy the same rate optimality under the Frobenius
norm, which is in sharp contrast to the equivalence of corresponding two types
of bandable covariance matrices under both norms. This fundamental difference
is established by carefully constructing the corresponding minimax lower
bounds. Two new estimation procedures are developed: for the operator norm, our
optimal procedure is based on a novel local cropping estimator targeting on all
principle submatrices of the precision matrix while for the Frobenius norm, our
optimal procedure relies on a delicate regression-based thresholding rule.
Lepski's method is considered to achieve optimal adaptation. We further
establish rate optimality in the nonparanormal model. Numerical studies are
carried out to confirm our theoretical findings
Fermions tunnelling with quantum gravity correction
Quantum gravity correction is truly important to study tunnelling process of
black hole. Base on the generalized uncertainty principle, we investigate the
influence of quantum gravity and the result tell us that the quantum gravity
correction accelerates the evaporation of black hole. Using corrected Dirac
equation in curved spacetime and Hamilton-Jacobi method, we address the
tunnelling of fermions in a 4-dimensional Schwarzschild spacetime.
After solving the equation of motion of the spin 1/2 field, we obtain the
corrected Hawking temperature. It turns out that the correction depends not
only on the mass of black hole but aslo on the mass of emitted fermions. In our
calculation, the quantum gravity correction accelerates the increasing of
Hawking temperature during the radiation explicitly. This correction leads to
the increasing of the evaporation of black hole.Comment: 5page
No-go theorem and optimization of dynamical decoupling against noise with soft cutoff
We study the performance of dynamical decoupling in suppressing decoherence
caused by soft-cutoff Gaussian noise, using short-time expansion of the noise
correlations and numerical optimization. For the noise with soft cutoff at high
frequencies, there exists no dynamical decoupling scheme to eliminate the
decoherence to arbitrary orders of the short time, regardless of the timing or
pulse shaping of the control under the population conserving condition. We
formulate the equations for optimizing pulse sequences that minimizes
decoherence up to the highest possible order of the short time for the noise
correlations with odd power terms in the short-time expansion. In particular,
we show that the Carr-Purcell-Meiboom-Gill sequence is optimal in short-time
limit for the noise correlations with a linear order term in the time
expansion.Comment: 11 pages, 3 figure
Backlund transformations for Burgers Equation via localization of residual symmetries
In this paper, we obtained the non-local residual symmetry related to
truncated Painlev\'e expansion of Burgers equation. In order to localize the
residual symmetry, we introduced new variables to prolong the original Burgers
equation into a new system. By using Lie's first theorem, we got the finite
transformation for the localized residual symmetry. More importantly, we also
localized the linear superposition of multiple residual symmetries to find the
corresponding finite transformations. It is interesting to find that the nth
Backlund transformation for Burgers equation can be expressed by determinants
in a compact way
New interaction solutions of Kadomtsev-Petviashvili equation
The residual symmetry coming from truncated Painleve expansion of KP equation
is nonlocal, which is localized in this paper by introducing multiple new
dependent variables. By using the standard Lie group approach, the symmetry
reduction solutions for KP equation is obtained based on the general form of
Lie point symmetry for the prolonged system. In this way, the interaction
solutions between solitons and background waves is obtained, which is hard to
study by other traditional methods
New symmetry reductions related with the residual symmetry of Boussinesq equation
The Backlund transformation related symmetry is nonlocal, which is hardly to
apply in constructing solutions for nonlinear equations. In this paper, we
first localize nonlocal residual symmetry to Lie point symmetry by introducing
multiple new variables and obtain new Baaklund transformation. Then, by solving
out the general form of localized the residual symmetry, we reduce the enlarged
system by classical symmetry approach and obtain the corresponding reduction
solutions as well as related reduction equations. The localization procedure
provides a new way to investigate interaction solutions between different
waves
Residual Symmetry Reductions and Interaction Solutions of (2+1)-Dimensional Burgers Equation
The (2+1)-dimensional Burgers equation has been investigated first from
prospective of symmetry by localizing the nonlocal residual symmetries and then
studied by a simple generalized tanh expansion method. New symmetry reduction
solutions has been obtained by using the standard Lie point symmetry group
approach. A new B\"{a}klund transformation for Burgers equation has been given
with the generalized tanh expansion method . From this BT, interactive
solutions among different nonlinear excitations which is hard to obtain by
other methods has also been obtained easily
WiFE: WiFi and Vision based Intelligent Facial-Gesture Emotion Recognition
Emotion is an essential part of Artificial Intelligence (AI) and human mental
health. Current emotion recognition research mainly focuses on single modality
(e.g., facial expression), while human emotion expressions are multi-modal in
nature. In this paper, we propose a hybrid emotion recognition system
leveraging two emotion-rich and tightly-coupled modalities, i.e., facial
expression and body gesture. However, unbiased and fine-grained facial
expression and gesture recognition remain a major problem. To this end, unlike
our rivals relying on contact or even invasive sensors, we explore the
commodity WiFi signal for device-free and contactless gesture recognition,
while adopting a vision-based facial expression. However, there exist two
design challenges, i.e., how to improve the sensitivity of WiFi signals and how
to process the large-volume, heterogeneous, and non-synchronous data
contributed by the two-modalities. For the former, we propose a signal
sensitivity enhancement method based on the Rician K factor theory; for the
latter, we combine CNN and RNN to mine the high-level features of bi-modal
data, and perform a score-level fusion for fine-grained recognition. To
evaluate the proposed method, we build a first-of-its-kind Vision-CSI Emotion
Database (VCED) and conduct extensive experiments. Empirical results show the
superiority of the bi-modality by achieving 83.24\% recognition accuracy for
seven emotions, as compared with 66.48% and 66.67% recognition accuracy by
gesture-only based solution and facial-only based solution, respectively. The
VCED database download link is https://github.com/purpleleaves007/WIFE-Dataset.Comment: error in experiment result
Fixed-time consensus of multiple double-integrator systems under directed topologies: A motion-planning approach
This paper investigates the fixed-time consensus problem under directed
topologies. By using a motion-planning approach, a class of distributed
fixed-time algorithms are developed for a multi-agent system with
double-integrator dynamics. In the context of the fixed-time consensus, we
focus on both directed fixed and switching topologies. Under the directed fixed
topology, a novel class of distributed algorithms are designed, which guarantee
the consensus of the multi-agent system with a fixed settling time if the
topology has a directed spanning tree. Under the directed periodically
switching topologies, the fixedtime consensus is solved via the proposed
algorithms if the topologies jointly have a directed spanning tree. In
particular, the fixed settling time can be off-line pre-assigned according to
task requirements. Compared with the existing results, to our best knowledge,
it is the first time to solve the fixed-time consensus problem for
double-integrator systems under directed topologies. Finally, a numerical
example is given to illustrate the effectiveness of the analytical results
BeSense: Leveraging WiFi Channel Data and Computational Intelligence for Behavior Analysis
The ever evolving informatics technology has gradually bounded human and
computer in a compact way. Understanding user behavior becomes a key enabler in
many fields such as sedentary-related healthcare, human-computer interaction
(HCI) and affective computing. Traditional sensor-based and vision-based user
behavior analysis approaches are obtrusive in general, hindering their usage in
realworld. Therefore, in this article, we first introduce WiFi signal as a new
source instead of sensor and vision for unobtrusive user behaviors analysis.
Then we design BeSense, a contactless behavior analysis system leveraging
signal processing and computational intelligence over WiFi channel state
information (CSI). We prototype BeSense on commodity low-cost WiFi devices and
evaluate its performance in realworld environments. Experimental results have
verified its effectiveness in recognizing user behaviors.Comment: 11 pages accepted by IEEE Computational Intelligence Magazin
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