94 research outputs found
Exact -cosmological model coming from the request of the existence of a Noether symmetry
We present an -cosmological model with an exact analytic solution,
coming from the request of the existence of a Noether symmetry, which is able
to describe a dust-dominated decelerated phase before the current accelerated
phase of the universe.Comment: 4 pages, 2 figures, Contribution to the proceedings of Spanish
Relativity Meeting 2008, Salamanca, Sapin, 15-19 September 200
Chinese Internet AS-level Topology
We present the first complete measurement of the Chinese Internet topology at
the autonomous systems (AS) level based on traceroute data probed from servers
of major ISPs in mainland China. We show that both the Chinese Internet AS
graph and the global Internet AS graph can be accurately reproduced by the
Positive-Feedback Preference (PFP) model with the same parameters. This result
suggests that the Chinese Internet preserves well the topological
characteristics of the global Internet. This is the first demonstration of the
Internet's topological fractality, or self-similarity, performed at the level
of topology evolution modeling.Comment: This paper is a preprint of a paper submitted to IEE Proceedings on
Communications and is subject to Institution of Engineering and Technology
Copyright. If accepted, the copy of record will be available at IET Digital
Librar
Local temperature for dynamical black holes
A local Hawking temperature was recently derived for any future outer
trapping horizon in spherical symmetry, using a Hamilton-Jacobi tunneling
method, and is given by a dynamical surface gravity as defined geometrically.
Descriptions are given of the operational meaning of the temperature, in terms
of what observers measure, and its relation to the usual Hawking temperature
for static black holes. Implications for the final fate of an evaporating black
hole are discussed.Comment: 7 pages, contribution to Proceedings of ERE200
The heat flux from a relativistic kinetic equation with a simplified collision kernel
We show how using a special relativistic kinetic equation with a BGK- like
collision operator the ensuing expression for the heat flux can be casted in
the form required by Classical Irreversible Thermodynamics. Indeed, it is
linearly related to the temperature and number density gradients and not to the
acceleration as the so-called "first order in the gradients theories" contend.
Here we calculate explicitly the ensuing transport coefficients and compare
them with the results obtained by other authors.Comment: 4 pages, one figure. To appear in the AIP conference proceedings of
the XXXI Spanish Relativity Meeting: Physics and Mathematics of Gravitation.
Salamanca Spain, 15-19 September 200
A Prato Tour on Carbon Nanotubes: Raman Insights
The functionalisation of carbon nanotubes has been instrumental in broadening its application field, allowing especially its use in biological studies. Although numerous covalent and non-covalent functionalisation methods have been described, the characterisation of the final materials has always been an added challenge. Among the various techniques available, Raman spectroscopy is one of the most widely used to determine the covalent functionalisation of these species. However, Raman spectroscopy is not a quantitative technique, and no studies are reported comparing its performance when the same number of functional groups are added but using completely different reactions. In this work, we have experimentally and theoretically studied the functionalisation of carbon nanotubes using two of the most commonly used reactions: 1,3-dipolar cycloaddition of azomethylene ylides and diazonium-based radical addition. The number of groups introduced onto the tubes by these reactions has been determined by different characterisation techniques. The results of this study support the idea that data obtained by Raman spectra are only helpful for comparing functionalisations produced using the same type of reaction. However, they should be carefully analysed when comparing functionalisations produced using different reaction types.The functionalisation of carbon nanotubes using Prato reaction and diazonium-based radical addition has been studied. The results support the idea that data obtained by Raman spectroscopy are only helpful for comparing functionalisations produced using the same type of reaction. However, they should be carefully analysed when comparing different reaction types.imag
Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at √s=7 TeV
Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected
by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the
form of an enhancement of pairs of like-sign charged pions with small four-momentum
difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source
is investigated, determining both the correlation radius and the chaoticity parameter. The
measured correlation radius is found to increase as a function of increasing charged-particle
multiplicity, while the chaoticity parameter is seen to decreas
Energy dependence of ϕ meson production at forward rapidity in pp collisions at the LHC
The production of mesons has been studied in pp collisions at LHC energies with the ALICE detector via the dimuon decay channel in the rapidity region . Measurements of the differential cross section are presented as a function of the transverse momentum () at the center-of-mass energies , 8 and 13 TeV and compared with the ALICE results at midrapidity. The differential cross sections at and 13 TeV are also studied in several rapidity intervals as a function of , and as a function of rapidity in three intervals. A hardening of the -differential cross section with the collision energy is observed, while, for a given energy, spectra soften with increasing rapidity and, conversely, rapidity distributions get slightly narrower at increasing . The new results, complementing the published measurements at and 7 TeV, allow one to establish the energy dependence of meson production and to compare the measured cross sections with phenomenological models. None of the considered models manages to describe the evolution of the cross section with and rapidity at all the energies.publishedVersio
ϒ production in p–Pb collisions at sNN=8.16 TeV
ϒproduction in p–Pbinteractions is studied at the centre-of-mass energy per nucleon–nucleon collision √sNN=8.16TeV with the ALICE detector at the CERN LHC. The measurement is performed reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals 2.03 <3.53and −4.46 <−2.96, down to zero transverse momentum. In this work, results on the ϒ(1S) production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the ϒ(1S) yields with respect to ppcollisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the ϒ(2S) nuclear modification factor is evaluated, suggesting a suppression similar to that of the ϒ(1S). A first measurement of the ϒ(3S) has also been performed. Finally, results are compared with previous ALICE measurements in p–Pbcollisions at √sNN=5.02TeV and with theoretical calculations
Circulation of antibodies against yellow fever virus in a simian population in the area of Porto Primavera Hydroelectric Plant, São Paulo, Brazil
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