64,524 research outputs found
Modeling incompressible thermal flows using a central-moment-based lattice Boltzmann method
In this paper, a central-moment-based lattice Boltzmann (CLB) method for
incompressible thermal flows is proposed. In the method, the incompressible
Navier-Stokes equations and the convection-diffusion equation for the
temperature field are sloved separately by two different CLB equations. Through
the Chapman-Enskog analysis, the macroscopic governing equations for
incompressible thermal flows can be reproduced. For the flow field, the tedious
implementation for CLB method is simplified by using the shift matrix with a
simplified central-moment set, and the consistent forcing scheme is adopted to
incorporate forcing effects. Compared with several D2Q5
multiple-relaxation-time (MRT) lattice Boltzmann methods for the temperature
equation, the proposed method is shown to be better Galilean invariant through
measuring the thermal diffusivities on a moving reference frame. Thus a higher
Mach number can be used for convection flows, which decreases the computational
load significantly. Numerical simulations for several typical problems confirm
the accuracy, efficiency, and stability of the present method. The grid
convergence tests indicate that the proposed CLB method for incompressible
thermal flows is of second-order accuracy in space
Provenance analysis for instagram photos
As a feasible device fingerprint, sensor pattern noise (SPN) has been proven to be effective in the provenance analysis of digital images. However, with the rise of social media, millions of images are being uploaded to and shared through social media sites every day. An image downloaded from social networks may have gone through a series of unknown image manipulations. Consequently, the trustworthiness of SPN has been challenged in the provenance analysis of the images downloaded from social media platforms. In this paper, we intend to investigate the effects of the pre-defined Instagram images filters on the SPN-based image provenance analysis. We identify two groups of filters that affect the SPN in quite different ways, with Group I consisting of the filters that severely attenuate the SPN and Group II consisting of the filters that well preserve the SPN in the images. We further propose a CNN-based classifier to perform filter-oriented image categorization, aiming to exclude the images manipulated by the filters in Group I and thus improve the reliability of the SPN-based provenance analysis. The results on about 20, 000 images and 18 filters are very promising, with an accuracy higher than 96% in differentiating the filters in Group I and Group II
Topological Anderson Insulator
Disorder plays an important role in two dimensions, and is responsible for
striking phenomena such as metal insulator transition and the integral and
fractional quantum Hall effects. In this paper, we investigate the role of
disorder in the context of the recently discovered topological insulator, which
possesses a pair of helical edge states with opposing spins moving in opposite
directions and exhibits the phenomenon of quantum spin Hall effect. We predict
an unexpected and nontrivial quantum phase termed "topological Anderson
insulator," which is obtained by introducing impurities in a two-dimensional
metal; here disorder not only causes metal insulator transition, as
anticipated, but is fundamentally responsible for creating extended edge
states. We determine the phase diagram of the topological Anderson insulator
and outline its experimental consequences.Comment: 4 pages, 4 figure
Supersymmetric QCD corrections to single top quark production at hadron colliders
We present the calculations of the supersymmetric QCD corrections to the
total cross sections for single top production at the Fermilab Tevatron and the
CERN Large Hadron Collider in the minimal supersymmetric standard model. Our
results show that for the s-channel and t-channel, the supersymmetric QCD
corrections are at most about 1%, but for the associated production process,
the supersymmetric QCD corrections increase the total cross sections
significantly, which can reach about 6% for most values of the parameters, and
the supersymmetric QCD corrections should be taken into consideration in the
future high precision experimental analysis for top physics.Comment: 33 pages, 19 figures, version to appear in Phys.Rev.
Using LIP to Gloss Over Faces in Single-Stage Face Detection Networks
This work shows that it is possible to fool/attack recent state-of-the-art
face detectors which are based on the single-stage networks. Successfully
attacking face detectors could be a serious malware vulnerability when
deploying a smart surveillance system utilizing face detectors. We show that
existing adversarial perturbation methods are not effective to perform such an
attack, especially when there are multiple faces in the input image. This is
because the adversarial perturbation specifically generated for one face may
disrupt the adversarial perturbation for another face. In this paper, we call
this problem the Instance Perturbation Interference (IPI) problem. This IPI
problem is addressed by studying the relationship between the deep neural
network receptive field and the adversarial perturbation. As such, we propose
the Localized Instance Perturbation (LIP) that uses adversarial perturbation
constrained to the Effective Receptive Field (ERF) of a target to perform the
attack. Experiment results show the LIP method massively outperforms existing
adversarial perturbation generation methods -- often by a factor of 2 to 10.Comment: to appear ECCV 2018 (accepted version
Finding diamonds in the rough: Targeted Sub-threshold Search for Strongly-lensed Gravitational-wave Events
Strong gravitational lensing of gravitational waves can produce duplicate
signals separated in time with different amplitudes. We consider the case in
which strong lensing produces identifiable gravitational-wave events and weaker
sub-threshold signals hidden in the noise background. We present a search
method for the sub-threshold signals using reduced template banks targeting
specific confirmed gravitational-wave events. We apply the method to all events
from Advanced LIGO's first and second observing run O1/O2. Using GW150914 as an
example, we show that the method effectively reduces the noise background and
raises the significance of (near-) sub-threshold triggers. In the case of
GW150914, we can improve the sensitive distance by . Finally,
we present the top possible lensed candidates for O1/O2 gravitational-wave
events that passed our nominal significance threshold of False-Alarm-Rate days
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