19,302 research outputs found
Model Independent Primordial Power Spectrum from Maxima, Boomerang, and DASI Data
A model-independent determination of the primordial power spectrum of matter
density fluctuations could uniquely probe physics of the very early universe,
and provide powerful constraints on inflationary models. We parametrize the
primordial power spectrum as an arbitrary function, and deduce its
binned amplitude from the cosmic microwave background radiation anisotropy
(CMB) measurements of Maxima, Boomerang, and DASI. We find that for a flat
universe with (scale-invariant) for scales h/Mpc, the
primordial power spectrum is marginally consistent with a scale-invariant
Harrison-Zeldovich spectrum. However, we deduce a rise in power compared to a
scale-invariant power spectrum for 0.001 h/{Mpc} \la k \la 0.01 h/{Mpc}. Our
results are consistent with large-scale structure data, and seem to suggest
that the current observational data allow for the possibility of unusual
physics in the very early universe.Comment: substantially revised and final version, accepted by Ap
Demonstration of fine pitch FCOB (Flip Chip on Board) assembly based on solder bumps at Fermilab
Bump bonding is a superior assembly alternative compared to conventional wire
bond techniques. It offers a highly reliable connection with greatly reduced
parasitic properties. The Flip Chip on Board (FCOB) procedure is an especially
attractive packaging method for applications requiring a large number of
connections at moderate pitch. This paper reports on the successful
demonstration of FCOB assembly based on solder bumps down to 250um pitch using
a SUESS MA8 flip chip bonder at Fermilab. The assembly procedure will be
described, microscopic cross sections of the connections are shown, and first
measurements on the contact resistance are presented.Comment: 4 pages, 8 figure
Planck priors for dark energy surveys
Although cosmic microwave background (CMB) anisotropy data alone cannot
constrain simultaneously the spatial curvature and the equation of state of
dark energy, CMB data provide a valuable addition to other experimental
results. However computing a full CMB power spectrum with a Boltzmann code is
quite slow; for instance if we want to work with many dark energy and/or
modified gravity models, or would like to optimize experiments where many
different configurations need to be tested, it is possible to adopt a quicker
and more efficient approach.
In this paper we consider the compression of the projected Planck CMB data
into four parameters, R (scaled distance to last scattering surface), l_a
(angular scale of sound horizon at last scattering), Omega_b h^2 (baryon
density fraction) and n_s (powerlaw index of primordial matter power spectrum),
all of which can be computed quickly. We show that, although this compression
loses information compared to the full likelihood, such information loss
becomes negligible when more data is added. We also demonstrate that the method
can be used for scalar field dark energy independently of the parametrisation
of the equation of state, and discuss how this method should be used for other
kinds of dark energy models.Comment: 8 pages, 3 figures, 4 table
Brane Inflation from Rotation of D4 Brane
In this paper, a inflationary model from the rotation of D4-brane is
constructed. We show that for a very wide rage of parameter, this model
satisfies the observation and find that regarded as inflaton, the rotation of
branes may be more nature than the distance between branes. Our model offers a
new avenue for brane inflation.Comment: 6 pages, no figure
Multiwavelength analysis of the young open cluster NGC 2362
We present a multiwavelength analysis of the young open cluster NGC 2362.
UBVRcIc CCD photometric observations, together with available data in the
Chandra data base, near infrared data from the Two Micron All Sky Survey
(2MASS), and recently published Halpha spectroscopy were used to get
information about the evolutionary stage of the cluster and the main physical
properties of its stellar content. Cluster membership is estimated for every
individual star by means of ZAMS and isochrone fitting. The cluster is
confirmed to host a richly populated pre-main sequence (PMS), and to contain a
large amount of X-ray emitting stars, which reach from the PMS members of GK
spectral type, up to the most luminous OB type main sequence (MS) members. The
PMS cluster members show no significant age spread, and the comparison to both
PMS and post-MS isochrones suggests a younger age for the more massive MS than
for lower mass PMS members. The analysis allows to asses the validity of
currently used pre-main sequence evolutionary models, and supports the
suggestion of a well defined positive correlation of the X-ray emission from
PMS stars with their bolometric luminosity. Clear differences are found on the
other hand, between the X-ray activity properties of MS and PMS cluster
members, both in the relation between X-ray luminosity and bolometric
luminosity, and in spectral properties as well.Comment: 1 gzipped file: 1 tex file with 9 pages text. 5 ps files with
figures. Submitted to Astrophysical Journa
Powerful High Velocity-Dispersion Molecular Hydrogen Associated with an Intergalactic Shock Wave in Stephan's Quintet
We present the discovery of strong mid-infrared emission lines of molecular
hydrogen of apparently high velocity dispersion (~870 km/s) originating from a
group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope
observations reveal emission lines of molecular hydrogen and little else. this
is the first time an almost pure H_2 line spectrum has been seen in an
extragalactic object. Along with the absence of PAH features and very low
excitation ionized gas tracers, the spectra resemble shocked gas seen in
Galactic supernova remnants, but on a vast scale. The molecular emission
extends over 24 kpc along the X-ray emitting shock-front, but has ten times the
surface luminosity as the soft X-rays, and about one-third the surface
luminosity of the IR continuum. We suggest that the powerful H_2 emission is
generated by the shock wave caused when a high-velocity intruder galaxy
collides with filaments of gas in the galaxy group. Our observations suggest a
close connection between galaxy-scale shock-waves and strong broad H_2 emission
lines, like those seen in the spectra of Ultraluminous Infrared Galaxies where
high-speed collisions between galaxy disks are common.Comment: 4 pages, 4 figures and 1 tabl
Shock wave propagation in vibrofluidized granular materials
Shock wave formation and propagation in two-dimensional granular materials
under vertical vibration are studied by digital high speed photography. The
steepen density and temperature wave fronts form near the plate as granular
layer collides with vibrating plate and propagate upward through the layer. The
temperature front is always in the transition region between the upward and
downward granular flows. The effects of driving parameters and particle number
on the shock are also explored.Comment: 9 pages, 4 figures, submitted to PR
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