4,621 research outputs found
Kinetic Ballooning Mode Under Steep Gradient: High Order Eigenstates and Mode Structure Parity Transition
The existence of kinetic ballooning mode (KBM) high order (non-ground)
eigenstates for tokamak plasmas with steep gradient is demonstrated via
gyrokinetic electromagnetic eigenvalue solutions, which reveals that eigenmode
parity transition is an intrinsic property of electromagnetic plasmas. The
eigenstates with quantum number for ground state and for
non-ground states are found to coexist and the most unstable one can be the
high order states (). The conventional KBM is the state. It is
shown that the KBM has the same mode structure parity as the
micro-tearing mode (MTM). In contrast to the MTM, the KBM can be driven
by pressure gradient even without collisions and electron temperature gradient.
The relevance between various eigenstates of KBM under steep gradient and edge
plasma physics is discussed.Comment: 6 pages, 6 figure
SoK: Certified Robustness for Deep Neural Networks
Great advances in deep neural networks (DNNs) have led to state-of-the-art
performance on a wide range of tasks. However, recent studies have shown that
DNNs are vulnerable to adversarial attacks, which have brought great concerns
when deploying these models to safety-critical applications such as autonomous
driving. Different defense approaches have been proposed against adversarial
attacks, including: a) empirical defenses, which can usually be adaptively
attacked again without providing robustness certification; and b) certifiably
robust approaches, which consist of robustness verification providing the lower
bound of robust accuracy against any attacks under certain conditions and
corresponding robust training approaches. In this paper, we systematize
certifiably robust approaches and related practical and theoretical
implications and findings. We also provide the first comprehensive benchmark on
existing robustness verification and training approaches on different datasets.
In particular, we 1) provide a taxonomy for the robustness verification and
training approaches, as well as summarize the methodologies for representative
algorithms, 2) reveal the characteristics, strengths, limitations, and
fundamental connections among these approaches, 3) discuss current research
progresses, theoretical barriers, main challenges, and future directions for
certifiably robust approaches for DNNs, and 4) provide an open-sourced unified
platform to evaluate 20+ representative certifiably robust approaches.Comment: To appear at 2023 IEEE Symposium on Security and Privacy (SP); 14
pages for the main text; benchmark & tool website:
http://sokcertifiedrobustness.github.io
Low-mass Active Galactic Nuclei on the Fundamental Plane of Black Hole Activity
It is widely known that in active galactic nuclei (AGNs) and black hole X-ray
binaries (BHXBs), there is a tight correlation among their radio luminosity
(), X-ray luminosity () and BH mass (\mbh), the so-called
`fundamental plane' (FP) of BH activity. Yet the supporting data are very
limited in the \mbh regime between stellar mass (i.e., BHXBs) and
10\,\msun\ (namely, the lower bound of supermassive BHs in common
AGNs). In this work, we developed a new method to measure the 1.4 GHz flux
directly from the images of the VLA FIRST survey, and apply it to the type-1
low-mass AGNs in the \cite{2012ApJ...755..167D} sample. As a result, we
obtained 19 new low-mass AGNs for FP research with both \mbh\ estimates (\mbh
\approx 10^{5.5-6.5}\,\msun), reliable X-ray measurements, and (candidate)
radio detections, tripling the number of such candidate sources in the
literature.Most (if not all) of the low-mass AGNs follow the standard
radio/X-ray correlation and the universal FP relation fitted with the combined
dataset of BHXBs and supermassive AGNs by \citet{2009ApJ...706..404G}; the
consistency in the radio/X-ray correlation slope among those accretion systems
supports the picture that the accretion and ejection (jet) processes are quite
similar in all accretion systems of different \mbh. In view of the FP relation,
we speculate that the radio loudness (i.e., the luminosity ratio
of the jet to the accretion disk) of AGNs depends not only on Eddington ratio,
but probably also on \mbh.Comment: ApJ accepte
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