18,022,848 research outputs found
Observation of the TeV gamma-ray source MGRO J1908+06 with ARGO-YBJ
The extended gamma ray source MGRO J1908+06, discovered by the Milagro air
shower detector in 2007, has been observed for about 4 years by the ARGO-YBJ
experiment at TeV energies, with a statistical significance of 6.2 standard
deviations. The peak of the signal is found at a position consistent with the
pulsar PSR J1907+0602. Parametrizing the source shape with a two-dimensional
Gauss function we estimate an extension \sigma = 0.49 \pm 0.22 degrees,
consistent with a previous measurement by the Cherenkov Array H.E.S.S.. The
observed energy spectrum is dN/dE = 6.1 \pm 1.4 \times 10^-13 (E/4 TeV)^{-2.54
\pm 0.36} photons cm^-2 s^-1 TeV^-1, in the energy range 1-20 TeV. The measured
gamma ray flux is consistent with the results of the Milagro detector, but is
2-3 times larger than the flux previously derived by H.E.S.S. at energies of a
few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable
excess rate observed by ARGO-YBJ along 4 years of data taking support the
identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula
of PSR J1907+0602, with an integrated luminosity above 1 TeV about 1.8 times
the Crab Nebula luminosity.Comment: 6 pages, accepted for pubblication by ApJ. Replaced to correct the
author lis
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at = 2.76 TeV
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb
collisions at TeV at the Large Hadron Collider is
presented. We observe a growing trend with energy now not only for the
longitudinal and the outward but also for the sideward pion source radius. The
pion homogeneity volume and the decoupling time are significantly larger than
those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/388
Identification of the TeV Gamma-ray Source ARGO J2031+4157 with the Cygnus Cocoon
The extended TeV gamma-ray source ARGO J2031+4157 (or MGRO J2031+41) is
positionally consistent with the Cygnus Cocoon discovered by -LAT at GeV
energies in the Cygnus superbubble. Reanalyzing the ARGO-YBJ data collected
from November 2007 to January 2013, the angular extension and energy spectrum
of ARGO J2031+4157 are evaluated. After subtracting the contribution of the
overlapping TeV sources, the ARGO-YBJ excess map is fitted with a
two-dimensional Gaussian function in a square region of , finding a source extension =
1.80.5. The observed differential energy spectrum is
photons cm
s TeV, in the energy range 0.2-10 TeV. The angular extension is
consistent with that of the Cygnus Cocoon as measured by -LAT, and the
spectrum also shows a good connection with the one measured in the 1-100 GeV
energy range. These features suggest to identify ARGO J2031+4157 as the
counterpart of the Cygnus Cocoon at TeV energies. The Cygnus Cocoon, located in
the star-forming region of Cygnus X, is interpreted as a cocoon of freshly
accelerated cosmic rays related to the Cygnus superbubble. The spectral
similarity with Supernova Remnants indicates that the particle acceleration
inside a superbubble is similar to that in a SNR. The spectral measurements
from 1 GeV to 10 TeV allows for the first time to determine the possible
spectrum slope of the underlying particle distribution. A hadronic model is
adopted to explain the spectral energy distribution.Comment: 16 pages, 3 figures, has been accepted by ApJ for publicatio
Intermittency and regularity issues in 3D Navier-Stokes turbulence
Two related open problems in the theory of 3D Navier-Stokes turbulence are
discussed in this paper. The first is the phenomenon of intermittency in the
dissipation field. Dissipation-range intermittency was first discovered
experimentally by Batchelor and Townsend over fifty years ago. It is
characterized by spatio-temporal binary behaviour in which long, quiescent
periods in the velocity signal are interrupted by short, active `events' during
which there are violent fluctuations away from the average. The second and
related problem is whether solutions of the 3D Navier-Stokes equations develop
finite time singularities during these events. This paper shows that Leray's
weak solutions of the three-dimensional incompressible Navier-Stokes equations
can have a binary character in time. The time-axis is split into `good' and
`bad' intervals: on the `good' intervals solutions are bounded and regular,
whereas singularities are still possible within the `bad' intervals. An
estimate for the width of the latter is very small and decreases with
increasing Reynolds number. It also decreases relative to the lengths of the
good intervals as the Reynolds number increases. Within these `bad' intervals,
lower bounds on the local energy dissipation rate and other quantities, such as
\|\bu(\cdot, t)\|_{\infty} and \|\nabla\bu(\cdot, t)\|_{\infty}, are very
large, resulting in strong dynamics at sub-Kolmogorov scales. Intersections of
bad intervals for are related to Scheffer's potentially singular set
in time. It is also proved that the Navier-Stokes equations are conditionally
regular provided, in a given `bad' interval, the energy has a lower bound that
is decaying exponentially in time.Comment: 36 pages, 3 figures and 6 Table
Investigation of a Protein Complex Network
The budding yeast {\it Saccharomyces cerevisiae} is the first eukaryote whose
genome has been completely sequenced. It is also the first eukaryotic cell
whose proteome (the set of all proteins) and interactome (the network of all
mutual interactions between proteins) has been analyzed. In this paper we study
the structure of the yeast protein complex network in which weighted edges
between complexes represent the number of shared proteins. It is found that the
network of protein complexes is a small world network with scale free behavior
for many of its distributions. However we find that there are no strong
correlations between the weights and degrees of neighboring complexes. To
reveal non-random features of the network we also compare it with a null model
in which the complexes randomly select their proteins. Finally we propose a
simple evolutionary model based on duplication and divergence of proteins.Comment: 19 pages, 9 figures, 1 table, to appear in Euro. Phys. J.
Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at TeV
Inclusive transverse momentum spectra of primary charged particles in Pb-Pb
collisions at = 2.76 TeV have been measured by the ALICE
Collaboration at the LHC. The data are presented for central and peripheral
collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross
section. The measured charged particle spectra in and GeV/ are compared to the expectation in pp collisions at the same
, scaled by the number of underlying nucleon-nucleon
collisions. The comparison is expressed in terms of the nuclear modification
factor . The result indicates only weak medium effects ( 0.7) in peripheral collisions. In central collisions,
reaches a minimum of about 0.14 at -7GeV/ and increases
significantly at larger . The measured suppression of high- particles is stronger than that observed at lower collision energies,
indicating that a very dense medium is formed in central Pb-Pb collisions at
the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98
On the One-dimensional Stability of Viscous Strong Detonation Waves
Building on Evans function techniques developed to study the stability of
viscous shocks, we examine the stability of viscous strong detonation wave
solutions of the reacting Navier-Stokes equations. The primary result,
following the work of Alexander, Gardner & Jones and Gardner & Zumbrun, is the
calculation of a stability index whose sign determines a necessary condition
for spectral stability. We show that for an ideal gas this index can be
evaluated in the ZND limit of vanishing dissipative effects. Moreover, when the
heat of reaction is sufficiently small, we prove that strong detonations are
spectrally stable provided the underlying shock is stable. Finally, for
completeness, the stability index calculations for the nonreacting
Navier-Stokes equations are includedComment: 66 pages, 7 figure
Application of the Two-Scale Model to the HERMES Data on Nuclear Attenuation
The Two-Scale Model and its improved version were used to perform the fit to
the HERMES data for (the virtual photon energy) and z (the fraction of
carried by hadron) dependencies of nuclear multiplicity ratios for
and mesons electro-produced on two nuclear targets (N
and Kr). The quantitative criterium was used for the first
time to analyse the results of the model fit to the nuclear multiplicity ratios
data. The two-parameter's fit gives satisfactory agreement with the HERMES
data. Best values of the parameters were then used to calculate the - and
- dependencies of nuclear attenuation for , K, K and
produced on Kr target, and also make a predictions for ,
z and the Q (the photon virtuality) - dependencies of nuclear attenuation
data for those identified hadrons and nuclea, that will be published by HERMES
The high-energy hadron spin-flip amplitude at small momentum transfer and new AN data from RHIC
In the case of elastic high-energy hadron-hadron scattering, the impact of
the large-distance contributions on the behaviour of the slopes of the
spin-non-flip and of the spin-flip amplitudes is analysed. It is shown that the
long tail of the hadronic potential in impact parameter space leads to a value
of the slope of the reduced spin-flip amplitude larger than that of the
spin-non-flip amplitude. This effect is taken into account in the calculation
of the analysing power in proton-nucleus reactions at high energies. It is
shown that the preliminary measurement of AN obtained by the E950 Collaboration
indeed favour a spin-flip-amplitude with a large slope. Predictions for AN at
pL = 250 GeV/c are given.Comment: 16 pages, 5 figures, a few typos fixed in v.
Tajikistan: Almost Two Thousand Mosques Closed in 2017
Tajikistan has claimed to have closed almost 2,000 mosques in 2017. Officials claimed they were closed at the request of local residents, but have not been able to explain why they only allow mosques with a capacity far below the possible numbers of worshippers
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