29 research outputs found
A study of BPS and near-BPS black holes via AdS/CFT
In the settings of various AdS/CFT dual pairs, we use results from supersymmetric localiza tion to gain insights into the physics of asymptotically-AdS, BPS black holes in 5 dimensions,
and near-BPS black holes in 4 dimensions.
We first begin with BPS black holes embedded in the known examples of AdS5/CFT4
dualities. Using the Bethe Ansatz formulation, we compute the superconformal index at large
N with arbitrary chemical potentials for all charges and angular momenta, for general N = 1
four-dimensional conformal theories with a holographic dual. We conjecture and bring some
evidence that a particular universal contribution to the sum over Bethe vacua dominates the
index at large N. For N = 4 SYM, this contribution correctly leads to the entropy of BPS
Kerr-Newman black holes in AdS5 × S
5
for arbitrary values of the conserved charges, thus
completing the microscopic derivation of their microstates. We also consider theories dual
to AdS5 × SE5, where SE5 is a Sasaki-Einstein manifold. We first check our results against
the so-called universal black hole. We then explicitly construct the near-horizon geometry
of BPS Kerr-Newman black holes in AdS5 × T
1,1
, charged under the baryonic symmetry
of the conifold theory and with equal angular momenta. We compute the entropy of these
black holes using the attractor mechanism and find complete agreement with field theory
predictions.
Next, we consider the 3d Chern-Simons matter theory that is holographically dual to
massive Type IIA string theory on AdS4 × S
6
. By Kaluza-Klein reducing on S
2 with a
background that is dual to the asymptotics of static dyonic BPS black holes in AdS4, we
construct a N = 2 supersymmetric gauged quantum mechanics whose ground-state degener acy reproduces the entropy of BPS black holes. We expect its low-lying spectrum to contain
information about near-extremal horizons. Interestingly, the model has a large number of
statistically-distributed couplings, reminiscent of SYK models
Approximate Primal-Dual Fixed-Point based Langevin Algorithms for Non-smooth Convex Potentials
The Langevin algorithms are frequently used to sample the posterior
distributions in Bayesian inference. In many practical problems, however, the
posterior distributions often consist of non-differentiable components, posing
challenges for the standard Langevin algorithms, as they require to evaluate
the gradient of the energy function in each iteration. To this end, a popular
remedy is to utilize the proximity operator, and as a result one needs to solve
a proximity subproblem in each iteration. The conventional practice is to solve
the subproblems accurately, which can be exceedingly expensive, as the
subproblem needs to be solved in each iteration. We propose an approximate
primal-dual fixed-point algorithm for solving the subproblem, which only seeks
an approximate solution of the subproblem and therefore reduces the
computational cost considerably. We provide theoretical analysis of the
proposed method and also demonstrate its performance with numerical examples
Boosting Adversarial Attack with Similar Target
Deep neural networks are vulnerable to adversarial examples, posing a threat
to the models' applications and raising security concerns. An intriguing
property of adversarial examples is their strong transferability. Several
methods have been proposed to enhance transferability, including ensemble
attacks which have demonstrated their efficacy. However, prior approaches
simply average logits, probabilities, or losses for model ensembling, lacking a
comprehensive analysis of how and why model ensembling significantly improves
transferability. In this paper, we propose a similar targeted attack method
named Similar Target~(ST). By promoting cosine similarity between the gradients
of each model, our method regularizes the optimization direction to
simultaneously attack all surrogate models. This strategy has been proven to
enhance generalization ability. Experimental results on ImageNet validate the
effectiveness of our approach in improving adversarial transferability. Our
method outperforms state-of-the-art attackers on 18 discriminative classifiers
and adversarially trained models
NF-ULA: Normalizing Flow-Based Unadjusted Langevin Algorithm for Imaging Inverse Problems
Bayesian methods for solving inverse problems are a powerful alternative to classical methods since the Bayesian approach offers the ability to quantify the uncertainty in the solution. In recent years, data-driven techniques for solving inverse problems have also been remarkably successful, due to their superior representation ability. In this work, we incorporate data-based models into a class of Langevin-based sampling algorithms for Bayesian inference in imaging inverse problems. In particular, we introduce NF-ULA (Normalizing Flow-based Unadjusted Langevin algorithm), which involves learning a normalizing flow (NF) as the image prior. We use NF to learn the prior because a tractable closed-form expression for the log prior enables the differentiation of it using autograd libraries. Our algorithm only requires a normalizing flow-based generative network, which can be pre-trained independently of the considered inverse problem and the forward operator. We perform theoretical analysis by investigating the well-posedness and non-asymptotic convergence of the resulting NF-ULA algorithm. The efficacy of the proposed NF-ULA algorithm is demonstrated in various image restoration problems such as image deblurring, image inpainting, and limited-angle X-ray computed tomography (CT) reconstruction. NF-ULA is found to perform better than competing methods for severely ill-posed inverse problems
NF-ULA: Langevin Monte Carlo with Normalizing Flow Prior for Imaging Inverse Problems
Bayesian methods for solving inverse problems are a powerful alternative to
classical methods since the Bayesian approach offers the ability to quantify
the uncertainty in the solution. In recent years, data-driven techniques for
solving inverse problems have also been remarkably successful, due to their
superior representation ability. In this work, we incorporate data-based models
into a class of Langevin-based sampling algorithms for Bayesian inference in
imaging inverse problems. In particular, we introduce NF-ULA (Normalizing
Flow-based Unadjusted Langevin algorithm), which involves learning a
normalizing flow (NF) as the image prior. We use NF to learn the prior because
a tractable closed-form expression for the log prior enables the
differentiation of it using autograd libraries. Our algorithm only requires a
normalizing flow-based generative network, which can be pre-trained
independently of the considered inverse problem and the forward operator. We
perform theoretical analysis by investigating the well-posedness and
non-asymptotic convergence of the resulting NF-ULA algorithm. The efficacy of
the proposed NF-ULA algorithm is demonstrated in various image restoration
problems such as image deblurring, image inpainting, and limited-angle X-ray
computed tomography (CT) reconstruction. NF-ULA is found to perform better than
competing methods for severely ill-posed inverse problems
NF-ULA: Normalizing Flow-Based Unadjusted Langevin Algorithm for Imaging Inverse Problems
Bayesian methods for solving inverse problems are a powerful alternative to classical methods since the Bayesian approach offers the ability to quantify the uncertainty in the solution. In recent years, data-driven techniques for solving inverse problems have also been remarkably successful, due to their superior representation ability. In this work, we incorporate data-based models into a class of Langevin-based sampling algorithms for Bayesian inference in imaging inverse problems. In particular, we introduce NF-ULA (Normalizing Flow-based Unadjusted Langevin algorithm), which involves learning a normalizing flow (NF) as the image prior. We use NF to learn the prior because a tractable closed-form expression for the log prior enables the differentiation of it using autograd libraries. Our algorithm only requires a normalizing flow-based generative network, which can be pre-trained independently of the considered inverse problem and the forward operator. We perform theoretical analysis by investigating the well-posedness and non-asymptotic convergence of the resulting NF-ULA algorithm. The efficacy of the proposed NF-ULA algorithm is demonstrated in various image restoration problems such as image deblurring, image inpainting, and limited-angle X-ray computed tomography (CT) reconstruction. NF-ULA is found to perform better than competing methods for severely ill-posed inverse problems
PlanarTrack: A Large-scale Challenging Benchmark for Planar Object Tracking
Planar object tracking is a critical computer vision problem and has drawn
increasing interest owing to its key roles in robotics, augmented reality, etc.
Despite rapid progress, its further development, especially in the deep
learning era, is largely hindered due to the lack of large-scale challenging
benchmarks. Addressing this, we introduce PlanarTrack, a large-scale
challenging planar tracking benchmark. Specifically, PlanarTrack consists of
1,000 videos with more than 490K images. All these videos are collected in
complex unconstrained scenarios from the wild, which makes PlanarTrack,
compared with existing benchmarks, more challenging but realistic for
real-world applications. To ensure the high-quality annotation, each frame in
PlanarTrack is manually labeled using four corners with multiple-round careful
inspection and refinement. To our best knowledge, PlanarTrack, to date, is the
largest and most challenging dataset dedicated to planar object tracking. In
order to analyze the proposed PlanarTrack, we evaluate 10 planar trackers and
conduct comprehensive comparisons and in-depth analysis. Our results, not
surprisingly, demonstrate that current top-performing planar trackers
degenerate significantly on the challenging PlanarTrack and more efforts are
needed to improve planar tracking in the future. In addition, we further derive
a variant named PlanarTrack for generic object tracking from
PlanarTrack. Our evaluation of 10 excellent generic trackers on
PlanarTrack manifests that, surprisingly,
PlanarTrack is even more challenging than several popular
generic tracking benchmarks and more attention should be paid to handle such
planar objects, though they are rigid. All benchmarks and evaluations will be
released at the project webpage.Comment: Tech. Repor
Superconformal indices at large N and the entropy of AdS5 x SE5 black holes
The large N limit of the four-dimensional superconformal index was computed and successfully compared to the entropy of a class of AdS5 black holes only in the particular case of equal angular momenta. Using the Bethe ansatz formulation, we compute the index at large N with arbitrary chemical potentials for all charges and angular momenta, for general four-dimensional conformal theories with a holographic dual. We conjecture and bring some evidence that a particular universal contribution to the sum over Bethe vacua dominates the index at large N. For SYM, this contribution correctly leads to the entropy of BPS Kerr-Newman black holes in AdS5 x S5 for arbitrary values of the conserved charges, thus completing the microscopic derivation of their microstates. We also consider theories dual to AdS5 x SE5, where SE5 is a Sasaki-Einstein manifold. We first check our results against the so-called universal black hole. We then explicitly construct the near-horizon geometry of BPS Kerr-Newman black holes in AdS5 T^{1,1}, charged under the baryonic symmetry of the conifold theory and with equal angular momenta. We compute the entropy of these black holes using the attractor mechanism and find complete agreement with the field theory predictions
Space advanced technology demonstration satellite
The Space Advanced Technology demonstration satellite (SATech-01), a mission for low-cost space science and new technology experiments, organized by Chinese Academy of Sciences (CAS), was successfully launched into a Sun-synchronous orbit at an altitude of similar to 500 km on July 27, 2022, from the Jiuquan Satellite Launch Centre. Serving as an experimental platform for space science exploration and the demonstration of advanced common technologies in orbit, SATech-01 is equipped with 16 experimental payloads, including the solar upper transition region imager (SUTRI), the lobster eye imager for astronomy (LEIA), the high energy burst searcher (HEBS), and a High Precision Magnetic Field Measurement System based on a CPT Magnetometer (CPT). It also incorporates an imager with freeform optics, an integrated thermal imaging sensor, and a multi-functional integrated imager, etc. This paper provides an overview of SATech-01, including a technical description of the satellite and its scientific payloads, along with their on-orbit performance