8,007 research outputs found
Principal -Blocks and Sylow -Subgroups
Let be a finite group with Sylow -subgroup .
Navarro-Tiep-Vallejo have conjectured that the principal -block of
contains exactly one irreducible Brauer character if and only if all odd-degree
ordinary irreducible characters in the principal -block of are fixed by
a certain Galois automorphism . Recent work of Navarro-Vallejo has
reduced this conjecture to a problem about finite simple groups. We show that
their conjecture holds for all finite simple groups, thus establishing the
conjecture for all finite groups.Comment: 12 page
The Fundamental Plane of Galaxy Clusters
Velocity dispersion , radius and luminosity of elliptical
galaxies are known to be related, leaving only two degrees of freedom and
defining the so-called ``fundamental plane". In this {\em Letter} we present
observational evidence that rich galaxy clusters exhibit a similar behaviour.
Assuming a relation , the best-fit values
of and are very close to those defined by galaxies. The
dispersion of this relation is lower than 10 percent, i.e. significantly
smaller than the dispersion observed in the and relations. We
briefly suggest some possible implications on the spread of formation times of
objects and on peculiar velocities of galaxy clusters.Comment: 11pp., 4 figures (available on request), LaTeX, BAP-04-1993-015-OA
On the arithmetic of Krull monoids with infinite cyclic class group
Let be a Krull monoid with infinite cyclic class group and let denote the set of classes containing prime divisors. We study under
which conditions on some of the main finiteness properties of
factorization theory--such as local tameness, the finiteness and rationality of
the elasticity, the structure theorem for sets of lengths, the finiteness of
the catenary degree, and the existence of monotone and of near monotone chains
of factorizations--hold in . In many cases, we derive explicit
characterizations
Scaling in Gravitational Clustering, 2D and 3D Dynamics
Perturbation Theory (PT) applied to a cosmological density field with
Gaussian initial fluctuations suggests a specific hierarchy for the correlation
functions when the variance is small. In particular quantitative predictions
have been made for the moments and the shape of the one-point probability
distribution function (PDF) of the top-hat smoothed density. In this paper we
perform a series of systematic checks of these predictions against N-body
computations both in 2D and 3D with a wide range of featureless power spectra.
In agreement with previous studies, we found that the reconstructed PDF-s work
remarkably well down to very low probabilities, even when the variance
approaches unity. Our results for 2D reproduce the features for the 3D
dynamics. In particular we found that the PT predictions are more accurate for
spectra with less power on small scales. The nonlinear regime has been explored
with various tools, PDF-s, moments and Void Probability Function (VPF). These
studies have been done with unprecedented dynamical range, especially for the
2D case, allowing in particular more robust determinations of the asymptotic
behaviour of the VPF. We have also introduced a new method to determine the
moments based on the factorial moments. Results using this method and taking
into account the finite volume effects are presented.Comment: 13 pages, Latex file, 9 Postscript Figure
Investigation of peak shapes in the MIBETA experiment calibrations
In calorimetric neutrino mass experiments, where the shape of a beta decay
spectrum has to be precisely measured, the understanding of the detector
response function is a fundamental issue. In the MIBETA neutrino mass
experiment, the X-ray lines measured with external sources did not have
Gaussian shapes, but exhibited a pronounced shoulder towards lower energies. If
this shoulder were a general feature of the detector response function, it
would distort the beta decay spectrum and thus mimic a non-zero neutrino mass.
An investigation was performed to understand the origin of the shoulder and its
potential influence on the beta spectrum. First, the peaks were fitted with an
analytic function in order to determine quantitatively the amount of events
contributing to the shoulder, also depending on the energy of the calibration
X-rays. In a second step, Montecarlo simulations were performed to reproduce
the experimental spectrum and to understand the origin of its shape. We
conclude that at least part of the observed shoulder can be attributed to a
surface effect
Design and fabrication of a radiative actively cooled honeycomb sandwich structural panel for a hypersonic aircraft
The panel assembly consisted of an external thermal protection system (metallic heat shields and insulation blankets) and an aluminum honeycomb structure. The structure was cooled to temperature 442K (300 F) by circulating a 60/40 mass solution of ethylene glycol and water through dee shaped coolant tubes nested in the honeycomb and adhesively bonded to the outer skin. Rene'41 heat shields were designed to sustain 5000 cycles of a uniform pressure of + or - 6.89kPa (+ or - 1.0 psi) and aerodynamic heating conditions equivalent to 136 kW sq m (12 Btu sq ft sec) to a 422K (300 F) surface temperature. High temperature flexible insulation blankets were encased in stainless steel foil to protect them from moisture and other potential contaminates. The aluminum actively cooled honeycomb sandwich structural panel was designed to sustain 5000 cycles of cyclic in-plane loading of + or - 210 kN/m (+ or - 1200 lbf/in.) combined with a uniform panel pressure of + or - 6.89 kPa (?1.0 psi)
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