21,918 research outputs found
Footballs, Conical Singularities and the Liouville Equation
We generalize the football shaped extra dimensions scenario to an arbitrary
number of branes. The problem is related to the solution of the Liouville
equation with singularities and explicit solutions are presented for the case
of three branes. The tensions of the branes do not need to be tuned with each
other but only satisfy mild global constraints.Comment: 15 pages, Refs. added, minor changes. Typo in eq. 4.3 corrected.
Version to be published in PR
The density profile of equilibrium and non-equilibrium dark matter halos
We study the diversity of the density profiles of dark matter halos based on
a large set of high-resolution cosmological simulations of 256^3 particles. The
cosmological models include four scale-free models and three representative
cold dark matter models. The simulations have good force resolution, and there
are about 400 massive halos with more than 10^4 particles within the virial
radius in each cosmological model. Our unbiased selection of all massive halos
enables to quantify how well the bulk of dark matter halos can be described by
the Navarro, Frenk & White (NFW) profile which was established for equilibrium
halos. We find that about seventy percent of the halos can be fitted by the NFW
profile with a fitting residual dvi_{max} less than 30% in Omega_0=1 universes.
This percentage is higher in lower density cosmological models. The rest of the
halos exhibits larger deviations from the NFW profile for more significant
internal substructures. There is a considerable amount of variation in the
density profile even for the halos which can be fitted by the NFW profile (i.e.
dvi_{max}<0.30). The distribution of the profile parameter, the concentration
, can be well described by a lognormal function with the mean value \bar c
slightly smaller (15%) than the NFW result and the dispersion \sigma_c in \ln c
about 0.25. The more virialized halos with dvi_{max}<0.15 have the mean value
\bar c in good agreement with the NFW result and a slightly smaller dispersion
\sigma_c (about 0.2). Our results can alleviate some of the conflicts found
recently between the theoretical NFW profile and observational results.
Implications for theoretical and observational studies of galaxy formation are
discussed.Comment: The final version accepted for publication in ApJ; one figure and one
paragraph added to demonstrate that all the conclusions of the first version
are solid to the resoltuion effects; 19 pages with 6 figure
Security Evaluation of Microsoftâs Windows Under Cyber-Flood Attacks
Cyberattacks are quite common occurrences today as such can compromise entire networks producing collective vulnerabilities. As shown herein, manifold experimental findings exhibit ramifications for a cyberattack victim during multiple simulations. All experiments were conducted with Appleâs iMac, the victim system, and different editions of Microsoft Windows 10 and Windows 8.1.
Cyberattacks herein categorize as Distributed Denial of Service (DDoS) attacks including Smurf, Ping Flood, Transmission Control Protocol-Synchronize (TCP-SYN) Flood, and User Datagram Protocol (UDP) Flood attacks. Experimental results from each cyberattack are recordings of computer activities such as memory consumption, disk utilization, and overall processor utilization.
DDoS attack simulations include networks with over 65 thousand systems per network which generate attack traffic for the victim system. Likewise, simulated legitimate traffic attempts to connect with a victim system for further evaluation purposes. Experimental data analysis involves comparing impactful differences between cyberattacks, Microsoft Windows versions, and editions of both versions
The Galaxy Cluster Luminosity-Temperature Relationship and Iron Abundances - A Measure of Formation History ?
Both the X-ray luminosity-temperature (L-T) relationship and the iron
abundance distribution of galaxy clusters show intrinsic dispersion. Using a
large set of galaxy clusters with measured iron abundances we find a
correlation between abundance and the relative deviation of a cluster from the
mean L-T relationship. We argue that these observations can be explained by
taking into account the range of cluster formation epochs expected within a
hierarchical universe. The known relationship of cooling flow mass deposition
rate to luminosity and temperature is also consistent with this explanation.
From the observed cluster population we estimate that the oldest clusters
formed at z>~2. We propose that the iron abundance of a galaxy cluster can
provide a parameterization of its age and dynamical history.Comment: 13 pages Latex, 2 figures, postscript. Accepted for publication in
ApJ Letter
Brane Universes and the Cosmological Constant
The cosmological constant problem and brane universes are reviewed briefly.
We discuss how the cosmological constant problem manifests itself in various
scenarios for brane universes. We review attempts - and their difficulties -
that aim at a solution of the cosmological constant problem.Comment: corrected typos, added references, 13 pages, accepted by MPLA as
brief revie
The General Warped Solution with Conical Branes in Six-dimensional Supergravity
We present the general regular warped solution with 4D Minkowski spacetime in
six-dimensional gauged supergravity. In this framework, we can easily embed
multiple conical branes into the warped geometry by choosing an undetermined
holomorphic function. As an example, for the holomorphic function with many
zeroes, we find warped solutions with multi-branes and discuss the generalized
flux quantization in this case.Comment: 1+19 pages, no figure, JHEP style, version to appear in JHE
Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85
This work is part of a series of papers devoted to investigate the evolution
of cluster galaxies during their infall. In the present article we imaged in
NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z
= 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2
deeper than 2MASS. We use these images to unveil asymmetries in the outskirts
of a sample of bright galaxies and develop a new asymmetry index, alpha_An,
which allows to quantify the degree of disruption by the relative area occupied
by the tidal features on the plane of the sky. We measure the asymmetries for a
subsample of 41 large area objects finding clear asymmetries in ten galaxies,
most of them being in groups and pairs projected at different clustercentric
distances, some of them located beyond R500 . Combining information on the
Hi-gas content of blue galaxies and the distribution of sub-structures across
Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful
tool to confirm that tidal mechanisms are indeed present and are currently
affecting a fraction of galaxies in Abell 85. However, when comparing our deep
NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in
this cluster, we discard the presence of tidal 1 interactions down to our
detection limit. Our results suggest that ram-pressure stripping is at the
origin of such spectacular disruptions. We conclude that across a complex
cluster like Abell 85, environment mechanisms, both gravitational and
hydrodynamical, are playing an active role in driving galaxy evolution.Comment: 30 pages, 13 figures, Accepted for Publication in A
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Syk-dependent Phosphorylation of CLEC-2: A Novel Mechanism of Hem-Immunoreceptor Tyrosine-Based Activation Motif Signaling
The C-type lectin-like receptor CLEC-2 signals via phosphorylation of a single cytoplasmic YXXL sequence known as a hem-immunoreceptor tyrosine-based activation motif (hemITAM). In this study, we show that phosphorylation of CLEC-2 by the snake toxin rhodocytin is abolished in the absence of the tyrosine kinase Syk but is not altered in the absence of the major platelet Src family kinases, Fyn, Lyn, and Src, or the tyrosine phosphatase CD148, which regulates the basal activity of Src family kinases. Further, phosphorylation of CLEC-2 by rhodocytin is not altered in the presence of the Src family kinase inhibitor PP2, even though PLCÎł2 phosphorylation and platelet activation are abolished. A similar dependence of phosphorylation of CLEC-2 on Syk is also seen in response to stimulation by an IgG mAb to CLEC-2, although interestingly CLEC-2 phosphorylation is also reduced in the absence of Lyn. These results provide the first definitive evidence that Syk mediates phosphorylation of the CLEC-2 hemITAM receptor with Src family kinases playing a critical role further downstream through the regulation of Syk and other effector proteins, providing a new paradigm in signaling by YXXL-containing receptors
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