6,663 research outputs found
Limiting Weak Type Estimate for Capacitary Maximal Function
A capacitary analogue of the limiting weak type estimate of P. Janakiraman
for the Hardy-Littlewood maximal function of an L1-function is discovered.Comment: 9 page
Isocapacity Estimates for Hessian Operators
Through a new powerful potential-theoretic analysis, this paper is devoted to
discovering the geometrically equivalent isocapacity forms of Chou-Wang's
Sobolev type inequality and Tian-Wang's Moser-Trudinger type inequality for the
fully nonlinear Hessian operators.Comment: 23 pages, 5 figure
Poor man's holography: How far can it go?
One of the most exciting things in recent theoretical physics is the
suspicion that gravity may be holographic, dual to some sort of quantum field
theory living on the boundary with one less dimension. Such a suspicion has
been supported mainly by a variety of specific examples from string theory.
This paper is intended to purport the holographic gravity from a different
perspective. Namely we propose that such a holography can actually be observed
within the context of Einstein's gravity, where neither is spacetime required
to be asymptotically AdS nor the boundary to be located at conformal infinity.
We show that our holography works remarkably well at least at the level of
thermodynamics and hydrodynamics. In particular, a perfect matching between the
bulk gravity and boundary system is found not only for the equilibrium
variation but also for the non-equilibrium entropy production, where a method
of conserved current is seen to be efficient in relating the black hole
perturbation in the bulk gravity and the non-equilibrium thermodynamics on the
boundary.Comment: This essay received an honorable mention in the 2012 Essay
Competition of the Gravity Research Foundation. 12 pages, revtex4; v2: slight
improvement on presentation in section 3, typos fixed; v3: holographic
derivation of the first law of thermodynamics in section 2 is clarified and
strengthene
Generalized Kerr/CFT correspondence with electromagnetic field
The electrovac axisymmetric extreme isolated horizon/CFT correspondence is
considered. By expansion techniques under the Bondi-like coordinates, it is
proved that the near horizon geometry of electrovac axisymmetric extreme
isolated horizon is unique. Furthermore, explicit coordinate transformation
between the Bondi-like coordinates and the Poincare-type coordinates for the
near horizon metric of the extreme Kerr-Newmann spacetime is found. Based on
these analyses and the thermodynamics of the isolated horizon, then, the
Kerr/CFT correspondence is generalized to nonstationary extreme black holes
with electromagnetic fields.Comment: 14 page
Entropy of isolated horizon from surface term of gravitational action
Starting from the surface term of gravitational action, one can construct a
Virasoro algebra with central extension, with which the horizon entropy can be
derived by using Cardy formula. This approach gives a new routine to calculate
and interpret the horizon entropy. In this paper, we generalize this approach
to a more general case, the isolated horizon, which contains non-stationary
spacetimes beyond stationary ones. By imposing appropriate boundary conditions
near the horizon, the full set of diffeomorphism is restricted to a subset
where the corresponding Noether charges form a Virasoro algebra with central
extension. Then by using the Cardy formula, we can derive the entropy of the
isolated horizon.Comment: 11 page
A Survey of Distributed Consensus Protocols for Blockchain Networks
Since the inception of Bitcoin, cryptocurrencies and the underlying
blockchain technology have attracted an increasing interest from both academia
and industry. Among various core components, consensus protocol is the defining
technology behind the security and performance of blockchain. From incremental
modifications of Nakamoto consensus protocol to innovative alternative
consensus mechanisms, many consensus protocols have been proposed to improve
the performance of the blockchain network itself or to accommodate other
specific application needs.
In this survey, we present a comprehensive review and analysis on the
state-of-the-art blockchain consensus protocols. To facilitate the discussion
of our analysis, we first introduce the key definitions and relevant results in
the classic theory of fault tolerance which help to lay the foundation for
further discussion. We identify five core components of a blockchain consensus
protocol, namely, block proposal, block validation, information propagation,
block finalization, and incentive mechanism. A wide spectrum of blockchain
consensus protocols are then carefully reviewed accompanied by algorithmic
abstractions and vulnerability analyses. The surveyed consensus protocols are
analyzed using the five-component framework and compared with respect to
different performance metrics. These analyses and comparisons provide us new
insights in the fundamental differences of various proposals in terms of their
suitable application scenarios, key assumptions, expected fault tolerance,
scalability, drawbacks and trade-offs. We believe this survey will provide
blockchain developers and researchers a comprehensive view on the
state-of-the-art consensus protocols and facilitate the process of designing
future protocols.Comment: Accepted by the IEEE Communications Surveys and Tutorials for
publicatio
A statistical study towards the high-mass BGPS clumps with the MALT90 survey
In this work, we perform a statistical investigation towards 50 high-mass
clumps using the data from the Bolocam Galactic Plane Survey (BGPS) and the
Millimetre Astronomy Legacy Team 90-GHz survey (MALT90). Eleven dense molecular
lines (NH(1-0), HNC(1-0), HCO(1-0), HCN(1-0), HNC(1-0),
HCO(1-0), CH(1-0), HCN(10-9), SiO(2-1), CS(2-1) and
HNCO are detected. NH and HNC are shown to be good
tracers for clumps in virous evolutionary stages since they are detected in all
the fields. And the detection rates of N-bearing molecules decrease as the
clumps evolve, but those of O-bearing species increase with evolution.
Furthermore, the abundance ratios [NH]/[HCO] and
Log([HCN]/[HCO]) decline with Log([HCO]) as two linear functions,
respectively. This suggests the transformation of NH and HCN to
HCO as the clumps evolve. We also find that CH is the most abundant
molecule with an order of . Besides, three new infall candidates
G010.214-00.324, G011.121-00.128, and G012.215-00.118(a) are discovered to have
large-scaled infall motions and infall rates in the magnitude of
M yr.Comment: 40 pages, 14 figures, 6 table
The Petrov-like boundary condition at finite cutoff surface in Gravity/Fluid duality
Previously it has been shown that imposing a Petrov-like boundary condition
on a hypersurface may reduce the Einstein equation to the incompressible
Navier-Stokes equation, but all these correspondences are established in the
near horizon limit. In this note, we remark that this strategy can be extended
to an arbitrary finite cutoff surface which is spatially flat, and the
Navier-Stokes equation is obtained by employing a non-relativistic
long-wavelength limit.Comment: 17 pages, no figures, published in PR
Improving Robustness of ML Classifiers against Realizable Evasion Attacks Using Conserved Features
Machine learning (ML) techniques are increasingly common in security
applications, such as malware and intrusion detection. However, ML models are
often susceptible to evasion attacks, in which an adversary makes changes to
the input (such as malware) in order to avoid being detected. A conventional
approach to evaluate ML robustness to such attacks, as well as to design robust
ML, is by considering simplified feature-space models of attacks, where the
attacker changes ML features directly to effect evasion, while minimizing or
constraining the magnitude of this change. We investigate the effectiveness of
this approach to designing robust ML in the face of attacks that can be
realized in actual malware (realizable attacks). We demonstrate that in the
context of structure-based PDF malware detection, such techniques appear to
have limited effectiveness, but they are effective with content-based
detectors. In either case, we show that augmenting the feature space models
with conserved features (those that cannot be unilaterally modified without
compromising malicious functionality) significantly improves performance.
Finally, we show that feature space models enable generalized robustness when
faced with a variety of realizable attacks, as compared to classifiers which
are tuned to be robust to a specific realizable attack.Comment: 1. v5.0; 2. To appear at the 28th USENIX Security Symposium, 201
Sonic velocity in holographic fluids and its applications
Gravity/fluid correspondence becomes an important tool to investigate the
strongly correlated fluids. We carefully investigate the holographic fluids at
the finite cutoff surface by considering different boundary conditions in the
scenario of gravity/fluid correspondence. We find that the sonic velocity of
the boundary fluids at the finite cutoff surface is critical to clarify the
superficial similarity between bulk viscosity and perturbation of the pressure
for the holographic fluid, where we set a special boundary condition at the
finite cutoff surface to explicitly express this superficial similarity.
Moreover, we further take the sonic velocity into account to investigate a case
with more general boundary condition. In this more general case, two parameters
in the first order stress tensor of holographic fluid cannot be fixed, one can
still extract the information of transport coefficients by considering the
sonic velocity seriously.Comment: 13 pages; version accepted by Chinese Physics
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