1,641 research outputs found
Detection of advanced persistent threat using machine-learning correlation analysis
As one of the most serious types of cyber attack, Advanced Persistent Threats (APT) have caused major concerns on a global scale. APT refers to a persistent, multi-stage attack with the intention to compromise the system and gain information from the targeted system, which has the potential to cause significant damage and substantial financial loss. The accurate detection and prediction of APT is an ongoing challenge. This work proposes a novel machine learning-based system entitled MLAPT, which can accurately and rapidly detect and predict APT attacks in a systematic way. The MLAPT runs through three main phases: (1) Threat detection, in which eight methods have been developed to detect different techniques used during the various APT steps. The implementation and validation of these methods with real traffic is a significant contribution to the current body of research; (2) Alert correlation, in which a correlation framework is designed to link the outputs of the detection methods, aims to identify alerts that could be related and belong to a single APT scenario; and (3) Attack prediction, in which a machine learning-based prediction module is proposed based on the correlation framework output, to be used by the network security team to determine the probability of the early alerts to develop a complete APT attack. MLAPT is experimentally evaluated and the presented sy
TASTE. III. A homogeneous study of transit time variations in WASP-3b
The TASTE project is searching for low-mass planets with the Transit Timing
Variation (TTV) technique, by gathering high-precision, short-cadence light
curves for a selected sample of transiting exoplanets. It has been claimed that
the "hot Jupiter" WASP-3b could be perturbed by a second planet. Presenting
eleven new light curves (secured at the IAC80 and UDEM telescopes) and
re-analyzing thirty-eight archival light curves in a homogeneous way, we show
that new data do not confirm the previously claimed TTV signal. However, we
bring evidence that measurements are not consistent with a constant orbital
period, though no significant periodicity can be detected. Additional dynamical
modeling and follow-up observations are planned to constrain the properties of
the perturber or to put upper limits to it. We provide a refined ephemeris for
WASP-3b and improved orbital/physical parameters. A contact eclipsing binary,
serendipitously discovered among field stars, is reported here for the first
time.Comment: 10 pages, 6 figures, 4 tables; accepted for publication in A&
Strong subadditivity and the covariant holographic entanglement entropy formula
Headrick and Takayanagi showed that the Ryu-Takayanagi holographic
entanglement entropy formula generally obeys the strong subadditivity (SSA)
inequality, a fundamental property of entropy. However, the Ryu-Takayanagi
formula only applies when the bulk spacetime is static. It is not known whether
the covariant generalization proposed by Hubeny, Rangamani, and Takayanagi
(HRT) also obeys SSA. We investigate this question in three-dimensional
AdS-Vaidya spacetimes, finding that SSA is obeyed as long as the bulk spacetime
satisfies the null energy condition. This provides strong support for the
validity of the HRT formula.Comment: 38 page
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XIII. ACS/WFC Parallel-Field Catalogues
As part of the Hubble Space Telescope UV Legacy Survey of Galactic Globular
Clusters, 110 parallel fields were observed with the Wide Field Channel of the
Advanced Camera for Surveys, in the outskirts of 48 globular clusters, plus the
open cluster NGC 6791. Totalling about square degrees of observed sky,
this is the largest homogeneous Hubble Space Telescope photometric survey of
Galalctic globular clusters outskirts to date. In particular, two distinct
pointings have been obtained for each target on average, all centred at about
arcmin from the cluster centre, thus covering a mean area of about
for each globular cluster. For each field, at least one
exposure in both F475W and F814W filters was collected. In this work, we
publicly release the astrometric and photometric catalogues and the
astrometrised atlases for each of these fields.Comment: 30 pages, 23 figures. Accepted by MNRA
Blue Stragglers in Galactic Open Clusters and the Integrated Spectral Energy Distributions
Synthetic integrated spectral properties of the old Galactic open clusters
are studies in this work, where twenty-seven Galactic open clusters of ages >=
1Gyr are selected as the working sample. Based on the photometric observations
of these open clusters, synthetic integrated spectrum has been made for the
stellar population of each cluster. The effects of blue straggler stars (BSSs)
on the conventional simple stellar population (SSP) model are analyzed on an
individual cluster base. It is shown that the BSSs, whose holding positions in
the color-magnitude diagrams (CMDs) cannot be predicted by the current
single-star evolution theory, present significant modifications to the
integrated properties of theoretical SSP model. The synthesized integrated
spectral energy distributions (ISEDs) of our sample clusters are dramatically
different from the SSPs based on isochrone only. The BSSs corrected ISEDs of
stellar populations show systematic enhancements towards shorter wavelength in
the spectra. When measured with wide-band colors in unresolvable conditions,
the age of a stellar population can be seriously under-estimated by the
conventional SSP model. Therefore, considering the common existence of BSS
component in real stellar populations, a considerable amount of alternations on
the conventional ISEDs should be expected when applying the technique of
evolutionary population synthesis (EPS) to more complicated stellar systems.Comment: 45 pages, 21 figures Accepted for publication in ApJ (Feburary 1,
2005 issue
A digital-based integrated methodology for the preventive conservation of cultural heritage: the experience of HeritageCare project
A sustainable conservation strategy for cultural heritage protection is not feasible without a systematic documentation, registration and management of the information. The adoption of integrated inspection protocols and regular tracking processes, based on standardized procedures and uniform criteria, are the basis to successfully replace actual curative strategies with proactive conservation approaches. The opportunities brought by the digital tools can offer tremendous advantages in this regard. This paper explores the leading role that digitization is assuming in the context of heritage conservation through the experience of the HeritageCare project - Monitoring and preventive conservation of historic and cultural heritage" (SOE1/P5/P0258). The project has developed a digital-based integrated methodology aimed at providing enhanced tools and services to properly document cultural heritage buildings and engage directly owners in the conservation process of their legacy. The structured digital workflow on which the HeritageCare protocol relies is described in detail, encompassing different levels of information. Finally, the full application of the protocol is presented with reference to one of the most emblematic case studies of the project, the Ducal Palace of Guimaraes, Portugal.- This work was partly financed by FEDER funds through the Competitiveness Factors Operational Programme (COMPETE) and by national funds through the Foundation for Science and Technology (FCT) within the scope of project POCI-01-0145-FEDER-007633
Genotype-by-Environment Interaction in Interspecific \u3cem\u3eUrochloa\u3c/em\u3e Hybrids Using Factor Analytic Models
Environmental factors can influence plant phenotypes shaping the expression of pastures. The ability to test genotypes in multiple environments is critical in a breeding program because important traits are heavily influenced by the environment. Nutritional quality is critical in forage breeding because it affects the rate of live weight gain in livestock as well as the quality of end products such as milk and meat. However, there is not much information on the environmental effect on agronomic and nutritional quality traits in tropical forages. For this reason, the objective of the present study was to investigate the genotype-by-environment interaction in a breeding population of interspecific Urochloa hybrids evaluated for agronomic and nutritional quality traits across four locations in Colombia, using factor analytic mixed models. Phenotypic correlations among traits ranged from 0.26 (plant area vs dry weight) to 0.93 (fresh weight vs dry weight), indicating a strong interaction in some traits. Genetic correlations among environments showed different ranges depending on the variable evaluated. For example, plant height genetic correlations among environments ranged from 0.16 to 0.9, indicating high genotype-byenvironment interaction. The factor analytic analysis revealed that two factors explained more than 60% of the genetic variance in all traits evaluated and that 80% of the environments were clustered in the first factor. Factor analytic biplot indicates that Llanos location differed strongly from other locations evaluated. Based on the results obtained, the factor analytic analysis is a useful tool to stratify environments and identify Urochloa cultivars adapted to different ecological niches
Fast Scramblers, Horizons and Expander Graphs
We propose that local quantum systems defined on expander graphs provide a
simple microscopic model for thermalization on quantum horizons. Such systems
are automatically fast scramblers and are motivated from the membrane paradigm
by a conformal transformation to the so-called optical metric.Comment: 22 pages, 2 figures. Added further discussion in section 3. Added
reference
The Chemical Enrichment History of the Large Magellanic Cloud
Ca II triplet spectroscopy has been used to derive stellar metallicities for
individual stars in four LMC fields situated at galactocentric distances of
3\arcdeg, 5\arcdeg, 6\arcdeg\@ and 8\arcdeg\@ to the north of the Bar. Observed
metallicity distributions show a well defined peak, with a tail toward low
metallicities. The mean metallicity remains constant until 6\arcdeg\@
([Fe/H]-0.5 dex), while for the outermost field, at 8\arcdeg, the mean
metallicity is substantially lower than in the rest of the disk
([Fe/H]-0.8 dex). The combination of spectroscopy with deep CCD
photometry has allowed us to break the RGB age--metallicity degeneracy and
compute the ages for the objects observed spectroscopically. The obtained
age--metallicity relationships for our four fields are statistically
indistinguishable. We conclude that the lower mean metallicity in the outermost
field is a consequence of it having a lower fraction of intermediate-age stars,
which are more metal-rich than the older stars. The disk age--metallicity
relationship is similar to that for clusters. However, the lack of objects with
ages between 3 and 10 Gyr is not observed in the field population. Finally, we
used data from the literature to derive consistently the age--metallicity
relationship of the bar. Simple chemical evolution models have been used to
reproduce the observed age--metallicity relationships with the purpose of
investigating which mechanism has participated in the evolution of the disk and
bar. We find that while the disk age--metallicity relationship is well
reproduced by close-box models or models with a small degree of outflow, that
of the bar is only reproduced by models with combination of infall and outflow.Comment: 45 pages, 10 figures, accepted for publication in Astronomical
Journa
Flux and Instanton Effects in Local F-theory Models and Hierarchical Fermion Masses
We study the deformation induced by fluxes and instanton effects on Yukawa
couplings involving 7-brane intersections in local F-theory constructions. In
the absence of non-perturbative effects, holomorphic Yukawa couplings do not
depend on open string fluxes. On the other hand instanton effects (or gaugino
condensation on distant 7-branes) do induce corrections to the Yukawas. The
leading order effect may also be captured by the presence of closed string
(1,2) IASD fluxes, which give rise to a non-commutative structure. We check
that even in the presence of these non-perturbative effects the holomorphic
Yukawas remain independent of magnetic fluxes. Although fermion mass
hierarchies may be obtained from these non-perturbative effects, they would
give identical Yukawa couplings for D-quark and Lepton masses in SU(5) F-theory
GUT's, in contradiction with experiment. We point out that this problem may be
solved by appropriately normalizing the wavefunctions. We show in a simple toy
model how the presence of hypercharge flux may then be responsible for the
difference between D-quarks and Lepton masses in local SU(5) GUT's.Comment: 84 pages, 1 figure. v2: minor corrections and references adde
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