16,870 research outputs found
Time for Cloud? Design and implementation of a time-based cloud resource management system
The current pay-per-use model adopted by public cloud service providers has influenced the perception on how a cloud should provide its resources to end-users, i.e. on-demand and access to an unlimited amount of resources. However, not all clouds are equal. While such provisioning models work for well-endowed public clouds, they may not always work well in private clouds with limited budget and resources such as research and education clouds. Private clouds also stand to be impacted greatly by issues such as user resource hogging and the misuse of resources for nefarious activities. These problems are usually caused by challenges such as (1) limited physical servers/ budget, (2) growing number of users and (3) the inability to gracefully and automatically relinquish resources from inactive users. Currently, cloud resource management frameworks used for private cloud setups, such as OpenStack and CloudStack, only uses the pay-per-use model as the basis when provisioning resources to users. In this paper, we propose OpenStack Café, a novel methodology adopting the concepts of 'time' and booking systems' to manage resources of private clouds. By allowing users to book resources over specific time-slots, our proposed solution can efficiently and automatically help administrators manage users' access to resource, addressing the issue of resource hogging and gracefully relinquish resources back to the pool in resource-constrained private cloud setups. Work is currently in progress to adopt Café into OpenStack as a feature, and results of our prototype show promises. We also present some insights to lessons learnt during the design and implementation of our proposed methodology in this paper
Inhomogeneous Neutrino Degeneracy and Big Bang Nucleosynthesis
We examine Big Bang nucleosynthesis (BBN) in the case of inhomogenous
neutrino degeneracy, in the limit where the fluctuations are sufficiently small
on large length scales that the present-day element abundances are homogeneous.
We consider two representive cases: degeneracy of the electron neutrino alone,
and equal chemical potentials for all three neutrinos. We use a linear
programming method to constrain an arbitrary distribution of the chemical
potentials. For the current set of (highly-restrictive) limits on the
primordial element abundances, homogeneous neutrino degeneracy barely changes
the allowed range of the baryon-to-photon ratio. Inhomogeneous degeneracy
allows for little change in the lower bound on the baryon-to-photon ratio, but
the upper bound in this case can be as large as 1.1 \times 10^{-8} (only
electron neutrino degeneracy) or 1.0 \times 10^{-9} (equal degeneracies for all
three neutrinos). For the case of inhomogeneous neutrino degeneracy, we show
that there is no BBN upper bound on the neutrino energy density, which is
bounded in this case only by limits from structure formation and the cosmic
microwave background.Comment: 6 pages, no figure
Inhomogeneous Big-Bang Nucleosynthesis in Light of Recent Observations
We consider inhomogeneous big bang nucleosynthesis in light of the present
observational situation. Different observations of He-4 and D disagree with
each other, and depending on which set of observations one uses, the estimated
primordial He-4 corresponds to a lower baryon density in standard big bang
nucleosynthesis than what one gets from deuterium. Recent Kamiokande results
rule out a favorite particle physics solution to this tension between He-4 and
D. Inhomogeneous nucleosynthesis can alleviate this tension, but the more
likely solution is systematics in the observations. The upper limit to Omega_b
from inhomogeneous nucleosynthesis is higher than in standard nucleosynthesis,
given that the distance scale of the inhomogeneity is near the optimal value,
which maximizes effects of neutron diffusion. Possible sources of baryon
inhomogeneity include the QCD and electroweak phase transitions. The distance
scale of the inhomogeneities arising from the electroweak transition is too
small for them to have a large effect on nucleosynthesis, but the effect may
still be larger than some of the other small corrections recently incorporated
to SBBN codes.Comment: 12 pages, 8 figures, REVTe
Skyrmions around Kerr black holes and spinning BHs with Skyrme hair
We study solutions of the Einstein-Skyrme model. Firstly we consider test
field Skyrmions on the Kerr background. These configurations -- hereafter
dubbed Skerrmions -- can be in equilibrium with a Kerr black hole (BH) by
virtue of a synchronisation condition. We consider two sectors for Skerrmions.
In the sector with non-zero baryon charge, Skerrmions are akin to the known
Skyrme solutions on the Schwarzschild background. These `topological'
configurations reduce to flat spacetime Skyrmions in a vanishing BH mass limit;
moreoever, they never become "small" perturbations on the Kerr background: the
non-linearities of the Skyrme model are crucial for all such Skerrmions. In the
non-topological sector, on the other hand, Skerrmions have no analogue on the
Schwarzschild background. Non-topological Skerrmions carry not baryon charge
and bifurcate from a subset of Kerr solutions defining an existence line.
Therein the appropriate truncation of the Skyrme model yield a linear scalar
field theory containing a complex plus a real field, both massive and
decoupled, and the Skerrmions reduce to the known stationary scalar clouds
around Kerr BHs. Moreover, non-topological Skerrmions trivialise in the
vanishing BH mass limit. We then discuss the backreaction of these Skerrmions,
that yield rotating BHs with synchronised Skyrme hair, which continously
connect to the Kerr solution (self-gravitating Skyrmions) in the
non-topological (topological) sector. In particular, the non-topological hairy
BHs provide a non-linear realisation, within the Skyrme model, of the
synchronous stationary scalar clouds around Kerr.Comment: 23 pages, 7 figures; to appear in JHE
Where clouds are made...
Where clouds are made... explored Didcot A Power station in the last few months of its active life as it approached itâs closure in 2013. This was a commissioned project, jointly funded by Npower and South Oxfordshire Council.
Through the project and exhibition we explored different types of physical and social relationships that people had with the power station over itâs working life. For our exhibition at Cornerstone Arts Centre, Didcot, we made a wooden scaffolding structure referencing part of the pre-fab construction process. It was made to the same scale as one of the cooling towers, but represented a fragment of the whole. The almost imperceptible arc across the gallery floor drew attention to the enormity of the whole and the difficulty of comprehending the scale. Seen through the construction, we made a series of laser-cut wall drawings playing with the 70âs language of dials and switches within the control room
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