49,265 research outputs found
Location of leaks in pipelines using parameter identification tools
This work proposes an approach to locate leaks by identifying the parameters
of finite models associated with these fault events. The identification problem
is attacked by using well-known identification methods such as the Prediction
Error Method and extended Kalman filters. In addition, a frequency evaluation
is realized to check the conditions for implementing any method which require
an excitation condition.Comment: This paper has some error
On Chow Stability for algebraic curves
In the last decades there have been introduced different concepts of
stability for projective varieties. In this paper we give a natural and
intrinsic criterion of the Chow, and Hilbert, stability for complex irreducible
smooth projective curves .
Namely, if the restriction of the tangent bundle of
to is stable then is Chow stable,
and hence Hilbert stable. We apply this criterion to describe a smooth open set
of the irreducible component of the Hilbert scheme of
containing the generic smooth Chow-stable curve of genus
and degree Moreover, we
describe the quotient stack of such curves. Similar results are obtained for
the locus of Hilbert stable curves.Comment: Minor corrections and improvements to presentation. We add Theorem
4.
Primordial black hole production during preheating in a chaotic inflationary model
In this paper we review the production of primordial black holes (PBHs)
during preheating after a chaotic inflationary model. All relevant equations of
motion are solved numerically in a modified version of HLattice, and we then
calculate the mass variance to determine structure formation during preheating.
It is found that production of PBHs can be a generic result of the model, even
though the results seem to be sensitive to the values of the smoothing scale.
We consider a constraint for overproduction of PBHs that could uncover some
stress between inflation-preheating models and observations.Comment: 6 pages, 5 figures. Prepared for the conference proceedings of the
9th Mexican School on Gravitation and Mathematical Physics : Cosmology for
the XXI Century: Inflation, Dark Matter and Dark Energ
Genus and spot density in the COBE DMR first year anisotropy maps
A statistical analysis of texture on the {\it COBE}-DMR first year sky maps
based on the genus and spot number is presented. A generalized
statistic is defined in terms of ``observable'' quantities: the genus and spot
density that would be measured by different cosmic observers. This strategy
together with the use of Monte Carlo simulations of the temperature
fluctuations, including all the relevant experimental parameters, represent the
main difference with previous analyses. Based on the genus analysis we find a
strong anticorrelation between the quadrupole amplitude and the
spectral index of the density fluctuation power spectrum at recombination
of the form K for fixed
, consistent with previous works. The result obtained based on the spot
density is consistent with this relation. In addition to the
previous results we have determined, using Monte Carlo simulations, the minimum
uncertainty due to cosmic variance for the determination of the spectral index
with the genus analysis. This uncertainty is .Comment: 5 pages, uuencode file containing text and 1 figure. MNRAS in press
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