1,234 research outputs found
Centaurus A as the Source of ultra-high energy cosmic rays?
We present numerical simulations for energy spectra and angular distributions
of nucleons above 10^{19} eV injected by the radio-galaxy Centaurus A at a
distance 3.4 Mpc and propagating in extra-galactic magnetic fields in the
sub-micro Gauss range. We show that field strengths B~0.3 micro Gauss, as
proposed by Farrar and Piran, cannot provide sufficient angular deflection to
explain the observational data. A magnetic field of intensity ~1 micro Gauss
could reproduce the observed large-scale isotropy and could marginally explain
the observed energy spectrum. However, it would not readily account for the
E=320 plusminus 93 EeV Fly's Eye event that was detected at an angle 136
degrees away from Cen-A. Such a strong magnetic field also saturates
observational upper limits from Faraday rotation observations and X-ray
bremsstrahlung emission from the ambient gas (assuming equipartition of
energy). This scenario may already be tested by improving magnetic field limits
with existing instruments. We also show that high energy cosmic ray experiments
now under construction will be able to detect the level of anisotropy predicted
by this scenario. We conclude that for magnetic fields B~0.1-0.5 micro Gauss,
considered as more reasonable for the local Supercluster environment, in all
likelihood at least a few sources within ~10 Mpc from the Earth should
contribute to the observed ultra high energy cosmic ray flux.Comment: 7 latex pages, 7 postscript figures included; for related numerical
simulations see also http://www.iap.fr/users/sigl/r2e.htm
The correlation between soft and hard X-rays component in flares: from the Sun to the stars
In this work we study the correlation between the soft (1.6--12.4 keV, mostly
thermal) and the hard (20--40 and 60--80 keV, mostly non-thermal) X-ray
emission in solar flares up to the most energetic events, spanning about 4
orders of magnitude in peak flux, establishing a general scaling law and
extending it to the most intense stellar flaring events observed to date. We
used the data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI) spacecraft, a NASA Small Explorer launched in February 2002. RHESSI
has good spectral resolution (~1 keV in the X-ray range) and broad energy
coverage (3 keV--20 MeV), which makes it well suited to distinguish the thermal
from non-thermal emission in solar flares. Our study is based on the detailed
analysis of 45 flares ranging from the GOES C-class, to the strongest X-class
events, using the peak photon fluxes in the GOES 1.6--12.4 keV and in two bands
selected from RHESSI data, i.e.20--40 keV and 60--80 keV. We find a significant
correlation between the soft and hard peak X-ray fluxes spanning the complete
sample studied. The resulting scaling law has been extrapolated to the case of
the most intense stellar flares observed, comparing it with the stellar
observations. Our results show that an extrapolation of the scaling law derived
for solar flares to the most active stellar events is compatible with the
available observations of intense stellar flares in hard X-rays.Comment: 9 pages, 10 figures. To be published in Astronomy and Astrophysic
Bose Einstein condensation on inhomogeneous amenable graphs
We investigate the Bose-Einstein Condensation on nonhomogeneous amenable
networks for the model describing arrays of Josephson junctions. The resulting
topological model, whose Hamiltonian is the pure hopping one given by the
opposite of the adjacency operator, has also a mathematical interest in itself.
We show that for the nonhomogeneous networks like the comb graphs, particles
condensate in momentum and configuration space as well. In this case different
properties of the network, of geometric and probabilistic nature, such as the
volume growth, the shape of the ground state, and the transience, all play a
role in the condensation phenomena. The situation is quite different for
homogeneous networks where just one of these parameters, e.g. the volume
growth, is enough to determine the appearance of the condensation.Comment: 43 pages, 12 figures, final versio
Numerical Simulation of Compressible Vortical Flows Using a Conservative Unstructured-Grid Adaptive Scheme
A two-dimensional numerical scheme for the compressible Euler equations is presented and applied here to the simulation of exemplary compressible vortical flows. The proposed approach allows to perform computations on unstructured moving grids with adaptation, which is required to capture complex features of the flow-field. Grid adaptation is driven by suitable error indicators based on the Mach number and by element-quality constraints as well. At the new time level, the computational grid is obtained by a suitable combination of grid smoothing, edge-swapping, grid refinement and de-refinement. The grid modifications-including topology modification due to edge-swapping or the insertion/deletion of a new grid node-are interpreted at the flow solver level as continuous (in time) deformations of suitably-defined node-centered finite volumes. The solution over the new grid is obtained without explicitly resorting to interpolation techniques, since the definition of suitable interface velocities allows one to determine the new solution by simple integration of the Arbitrary Lagrangian-Eulerian formulation of the flow equations. Numerical simulations of the steady oblique-shock problem, of the steady transonic flow and of the start-up unsteady flow around the NACA 0012 airfoil are presented to assess the scheme capabilities to describe these flows accurately
Pharmacokinetics and antinociceptive effects of tramadol and its metabolite O-desmethyltramadol following intravenous administration in sheep
Although sheep are widely used as an experimental model for various surgical procedures there is a paucity of data on the pharmacokinetics and efficacy of analgesic drugs in this species. The aims of this study were to investigate the pharmacokinetics of intravenously (IV) administered tramadol and its active metabolite O-desmethyltramadol (M1) and to assess the mechanical antinociceptive effects in sheep. In a prospective, randomized, blinded study, six healthy adult sheep were given 4 and 6\u2009mg/kg tramadol and saline IV in a cross-over design with a 2-week wash-out period. At predetermined time points blood samples were collected and physiological parameters and mechanical nociceptive threshold (MNT) values were recorded. The analytical determination of tramadol and M1 was performed using high performance liquid chromatography. Pharmacokinetic parameters fitted a two- and a non-compartmental model for tramadol and M1, respectively. Normally distributed data were analysed by a repeated mixed linear model. Plasma concentration vs. time profiles of tramadol and M1 were similar after the two doses. Tramadol and M1 plasma levels decreased rapidly in the systemic circulation, with both undetectable after 6\u2009h following drug administration. Physiological parameters did not differ between groups; MNT values were not statistically significant between groups at any time point. It was concluded that although tramadol and M1 concentrations in plasma were above the human minimum analgesic concentration after both treatments, no mechanical antinociceptive effects of tramadol were reported. Further studies are warranted to assess the analgesic efficacy of tramadol in sheep
A noncommutative Sierpinski gasket
A quantized version of the Sierpinski gasket is proposed, on purely topological grounds, as a C*-algebra A infinity with a suitable form of self-similarity. Several properties of A infinity are studied, in particular its nuclearity, the structure of ideals as well as the description of irreducible representations and extremal traces. A harmonic structure is introduced, giving rise to a self-similar Dirichlet form E. A spectral triple is also constructed, extending the one already known for the classical gasket, from which E can be reconstructed. Moreover we show that A infinity is a compact quantum metric space
Power Corrections in Charmless B Decays
In this paper, we focus on the role of power corrections in QCD
factorization(QCDF) method in charmless two-body nonleptonic meson decays.
We use the ratio of the branching fraction of to
that of , for which the theoretical uncertainties are
greatly reduced, to show clearly that the power corrections in charmless B
decays are probably large. With other similar ratios considered, for example,
for the decay, it is very likely that, among various
sources of power corrections, annihilation topology plays an indispensable role
at least for penguin dominated channels. We also consider some
selective ratios of direct CP asymmetries. Among these, we find that, if power
corrections other than the chirally enhanced power corrections and annihilation
topology were negligible, QCDF would predict the direct CP asymmetry of to be about 3 times larger than that of ,
with opposite sign. Experimentally any significant deviation from this
prediction would suggest either new physics or possibly the importance of
long-distance rescattering effects.Comment: references and note added, to appear in Phys. Rev.
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