3,477 research outputs found
Security and Privacy Issues in Cloud Computing
Cloud computing transforming the way of information technology (IT) for consuming and managing, promising improving cost efficiencies, accelerate innovations, faster time-to-market and the ability to scale applications on demand (Leighton, 2009). According to Gartner, while the hype grew ex-ponentially during 2008 and continued since, it is clear that there is a major shift towards the cloud computing model and that the benefits may be substantial (Gartner Hype-Cycle, 2012). However, as the shape of the cloud computing is emerging and developing rapidly both conceptually and in reality, the legal/contractual, economic, service quality, interoperability, security and privacy issues still pose significant challenges. In this chapter, we describe various service and deployment models of cloud computing and identify major challenges. In particular, we discuss three critical challenges: regulatory, security and privacy issues in cloud computing. Some solutions to mitigate these challenges are also proposed along with a brief presentation on the future trends in cloud computing deployment
Radiative diagnostics for sub-Larmor scale magnetic turbulence
Radiative diagnostics of high-energy density plasmas is addressed in this
paper. We propose that the radiation produced by energetic particles in
small-scale magnetic field turbulence, which can occur in laser-plasma
experiments, collisionless shocks, and during magnetic reconnection, can be
used to deduce some properties of the turbulent magnetic field. Particles
propagating through such turbulence encounter locally strong magnetic fields,
but over lengths much shorter than a particle gyroradius. Consequently, the
particle is accelerated but not deviated substantially from a straight line
path. We develop the general jitter radiation solutions for this case and show
that the resulting radiation is directly dependent upon the spectral
distribution of the magnetic field through which the particle propagates. We
demonstrate the power of this approach in considering the radiation produced by
particles moving through a region in which a (Weibel-like) filamentation
instability grows magnetic fields randomly oriented in a plane transverse to
counterstreaming particle populations. We calculate the spectrum as would be
seen from the original particle population and as could be seen by using a
quasi-monoenergetic electron beam to probe the turbulent region at various
angles to the filamentation axis.Comment: 17 pages, 4 figures, submitted to Phys. Plasma
Diffusion of Elements in the Interstellar Medium in Early-Type Galaxies
We consider the role of diffusion in the redistribution of elements in the
hot interstellar medium (ISM) of early-type galaxies. It is well known that
gravitational sedimentation can affect significantly the abundances of helium
and heavy elements in the intracluster gas of massive galaxy clusters. The
self-similarity of the temperature profiles and tight mass--temperature
relation of relaxed cool-core clusters suggest that the maximum effect of
sedimentation take place in the most massive virialized objects in the
Universe. However, Chandra and XMM-Newton observations demonstrate more complex
scaling relations between the masses of early-type galaxies and other
parameters, such as the ISM temperature and gas mass fraction. An important
fact is that early-type galaxies can show both decreasing and increasing radial
temperature profiles. We have calculated the diffusion based on the observed
gas density and temperature distributions for 13 early-type galaxies that
belonging to the different environments and cover a wide range of X-ray
luminosities. To estimate the maximum effect of sedimentation and thermal
diffusion, we have solved the full set of Burgers' equations for a
non-magnetized ISM plasma. The results obtained demonstrate a considerable
increase of the He/H ratio within one effective radius for all galaxies of our
sample. For galaxies with a flat or declining radial temperature profile the
average increase of the helium abundance is 60\% in one billion years of
diffusion. The revealed effect can introduce a significant bias in the metal
abundance measurements based on X-ray spectroscopy and can affect the evolution
of stars that could be formed from a gas with a high helium abundance.Comment: 15 pages, 9 figures, 3 tables, published in Astronomy Letters, 2017,
Volume 43, Issue 5, pp.285-30
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