443 research outputs found
A burst with double radio spectrum observed up to 212 GHz
We study a solar flare that occurred on September 10, 2002, in active region
NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the
radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha.
Solar Submillimeter Telescope observations, in addition to microwave data give
us a good spectral coverage between 1.415 and 212 GHz. We combine these data
with ultraviolet images, hard and soft X-rays observations and full-disk
magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic
Imaging data are used to identify the locations of X-ray sources at different
energies and to determine the X-ray spectrum, while ultra violet images allow
us to characterize the coronal flaring region. The magnetic field evolution of
the active region is analyzed using Michelson Doppler Imager magnetograms. The
burst is detected at all available radio-frequencies. X-ray images (between 12
keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate
the radio source position, show a single compact source displaced by 25" from
one of the hard X-ray footpoints. We model the radio spectra using two
homogeneous sources, and combine this analysis with that of hard X-rays to
understand the dynamics of the particles. Relativistic particles, observed at
radio wavelengths above 50 GHz, have an electron index evolving with the
typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure
Minimum mass of galaxies from BEC or scalar field dark matter
Many problems of cold dark matter models such as the cusp problem and the
missing satellite problem can be alleviated, if galactic halo dark matter
particles are ultra-light scalar particles and in Bose-Einstein condensate
(BEC), thanks to a characteristic length scale of the particles. We show that
this finite length scale of the dark matter can also explain the recently
observed common central mass of the Milky Way satellites ()
independent of their luminosity, if the mass of the dark matter particle is
about .Comment: 10 pages, 1 figure, accepted in JCA
An Extended Zel'dovich Model for the Halo Mass Function
A new way to construct a fitting formula for the halo mass function is
presented. Our formula is expressed as a solution to the modified Jedamzik
matrix equation that automatically satisfies the normalization constraint. The
characteristic parameters expressed in terms of the linear shear eigenvalues
are empirically determined by fitting the analytic formula to the numerical
results from the high-resolution N-body simulation and found to be independent
of scale, redshift and background cosmology. Our fitting formula with the
best-fit parameters is shown to work excellently in the wide mass-range at
various redshifts: The ratio of the analytic formula to the N-body results
departs from unity by up to 10% and 5% over 10^{11}<= M/(M_sun/h)<= 5x10^{15}
at z=0,\ 0.5 and 1 for the FoF-halo and SO-halo cases, respectively.Comment: Accepted for publication in JCAP; 19pages, 9 figures, significantly
revised, discussion on the limitation of our model adde
Agro-materials : a bibliographic review
Facing the problems of plastic recycling and fossil resources exhaustion, the use of biomass to conceive new materials appears like a reasonable solution. Two axes of research are nowadays developed : on the one hand the synthesis of biodegradable plastics, whichever the methods may be, on the other hand the utilization of raw biopolymers, which is the object of this paper. From this perspective, the âplasticâ properties of natural polymers, the caracteristics of the different classes of polymers, the use of charge in vegetable matrix and the possible means of improving the durability of these agro-materials are reviewed
Coalescence of nanoscale metal clusters: Molecular-dynamics study
We study the coalescence of nanoscale metal clusters in an inert-gas
atmosphere using constant-energy molecular dynamics. The coalescence proceeds
via atomic diffusion with the release of surface energy raising the
temperature. If the temperature exceeds the melting point of the coalesced
cluster, a molten droplet forms. If the temperature falls between the melting
point of the larger cluster and those of the smaller clusters, a metastable
molten droplet forms and freezes.Comment: 5 figure
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
Phantom Divide Crossing with General Non-minimal Kinetic Coupling
We propose a model of dark energy consists of a single scalar field with a
general non-minimal kinetic couplings to itself and to the curvature. We study
the cosmological dynamics of the equation of state in this setup. The coupling
terms have the form and
where
and are coupling parameters and their dimensions depend on the type
of function . We obtain the conditions required for phantom divide
crossing and show numerically that a cosmological model with general
non-minimal derivative coupling to the scalar and Ricci curvatures can realize
such a crossing.Comment: 12 pages, 4 figures. Accepted for publication in Gen. Rel. Grav.
arXiv admin note: substantial text overlap with arXiv:1105.4967,
arXiv:1201.1627, and with arXiv:astro-ph/0610092 by other author
Observation of hard scattering in photoproduction events with a large rapidity gap at HERA
Events with a large rapidity gap and total transverse energy greater than 5
GeV have been observed in quasi-real photoproduction at HERA with the ZEUS
detector. The distribution of these events as a function of the
centre of mass energy is consistent with diffractive scattering. For total
transverse energies above 12 GeV, the hadronic final states show predominantly
a two-jet structure with each jet having a transverse energy greater than 4
GeV. For the two-jet events, little energy flow is found outside the jets. This
observation is consistent with the hard scattering of a quasi-real photon with
a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil
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