26,411 research outputs found
Recommended from our members
Smart Computer Security Audit: Reinforcement Learning with a Deep Neural Network Approximator
A significant challenge in modern computer security is the growing skill gap as intruder capabilities increase, making it necessary to begin automating elements of penetration testing so analysts can contend with the growing number of cyber threats. In this paper, we attempt to assist human analysts by automating a single host penetration attack. To do so, a smart agent performs different attack sequences to find vulnerabilities in a target system. As it does so, it accumulates knowledge, learns new attack sequences and improves its own internal penetration testing logic. As a result, this agent (AgentPen for simplicity) is able to successfully penetrate hosts it has never interacted with before. A computer security administrator using this tool would receive a comprehensive, automated sequence of actions leading to a security breach, highlighting potential vulnerabilities, and reducing the amount of menial tasks a typical penetration tester would need to execute. To achieve autonomy, we apply an unsupervised machine learning algorithm, Q-learning, with an approximator that incorporates a deep neural network architecture. The security audit itself is modelled as a Markov Decision Process in order to test a number of decisionmaking strategies and compare their convergence to optimality. A series of experimental results is presented to show how this approach can be effectively used to automate penetration testing using a scalable, i.e. not exhaustive, and adaptive approach
Typical AGN at intermediate redshifts
We study the host galaxies and black holes of typical X-ray selected AGN at
intermediate redshifts (z~0.5-1.4). The AGN are selected such that their
spectral energy distributions are dominated by stellar emission, i.e., they
show a prominent 1.6micron bump thus minimizing the AGN emission contamination.
This AGN population comprises approximately 50% of the X-ray selected AGN at
these redshifts. AGN reside in the most massive galaxies at the redshifts
probed here, with characteristic stellar masses that are intermediate between
those of local type 2 AGN and high redshift (z~2) AGN. The inferred black hole
masses of typical AGN are similar to those of optically identified quasars at
similar redshifts. Since the AGN in our sample are much less luminous than
quasars, typical AGN have low Eddington ratios. This suggests that, at least at
intermediate redshifts, the cosmic AGN 'downsizing' is due to both a decrease
in the characteristic stellar mass of the host galaxies, and less efficient
accretion. Finally there is no strong evidence in AGN host galaxies for either
highly suppressed star formation, expected if AGN played a role in quenching
star formation, or elevated star formation when compared to mass selected
galaxies of similar stellar masses and redshifts.Comment: Conference proceedings of the meeting "Observational Evidence for
Black Holes" held in Calcutta, Feb 2008. Paper will be published by AI
Near-infrared K-band Spectroscopic Investigation of Seyfert 2 Nuclei in the CfA and 12 Micron Samples
We present near-infrared K-band slit spectra of the nuclei of 25 Seyfert 2
galaxies in the CfA and 12 micron samples. The strength of the CO absorption
features at 2.3-2.4 micron produced by stars is measured in terms of a
spectroscopic CO index. A clear anti-correlation between the observed CO index
and the nuclear K-L color is present, suggesting that a featureless hot dust
continuum heated by an AGN contributes significantly to the observed K-band
fluxes in the nuclei of Seyfert 2 galaxies. After correction for this AGN
contribution, we estimate nuclear stellar K-band luminosities for all sources,
and CO indices for sources with modestly large observed CO indices. The
corrected CO indices for 10 (=40%) Seyfert 2 nuclei are found to be as high as
those observed in star-forming or elliptical (=spheroidal) galaxies. We combine
the K-band data with measurements of the L-band 3.3 micron polycyclic aromatic
hydrocarbon (PAH) emission feature, another powerful indicator for
star-formation, and find that the 3.3 micron PAH to K-band stellar luminosity
ratios are substantially smaller than those of starburst galaxies. Our results
suggest that the 3.3 micron PAH emission originates in the putative nuclear
starbursts in the dusty tori surrounding the AGNs, because of its high surface
brightness, whereas the K-band CO absorption features detected at the nuclei
are dominated by old bulge (=spheroid) stars, and thus may not be a powerful
indicator for the nuclear starbursts. We see no clear difference in the
strength of the CO absorption and PAH emission features between the CfA and 12
micron Seyfert 2s.Comment: 28 pages, 6 figures, accepted for publication in ApJ (10 October
2004, v614 issue
Angular Momenta and Spin-Orbit Interaction of Nonparaxial Light in Free Space
We give an exact self-consistent operator description of the spin and orbital
angular momenta, position, and spin-orbit interactions of nonparaxial light in
free space. Both quantum-operator formalism and classical energy-flow approach
are presented. We apply the general theory to symmetric and asymmetric Bessel
beams exhibiting spin- and orbital-dependent intensity profiles. The exact wave
solutions are clearly interpreted in terms of the Berry phases, quantization of
caustics, and Hall effects of light, which can be readily observed
experimentally.Comment: 8 pages, 3 figure
Kink fluctuation asymptotics and zero modes
In this paper we propose a refinement of the heat kernel/zeta function
treatment of kink quantum fluctuations in scalar field theory, further
analyzing the existence and implications of a zero energy fluctuation mode.
Improved understanding of the interplay between zero modes and the kink heat
kernel expansion delivers asymptotic estimations of one-loop kink mass shifts
with remarkably higher precision than previously obtained by means of the
standard Gilkey-DeWitt heat kernel expansion.Comment: 21 pages, 8 figures, to be published in The European Physical Journal
- …