10,866 research outputs found
When do finite sample effects significantly affect entropy estimates ?
An expression is proposed for determining the error caused on entropy
estimates by finite sample effects. This expression is based on the Ansatz that
the ranked distribution of probabilities tends to follow an empirical Zipf law.Comment: 10 pages, 2 figure
A method for filling gaps in solar irradiance and in solar proxy data
Data gaps are ubiquitous in spectral irradiance data, and yet, little effort
has been put into finding robust methods for filling them. We introduce a
data-adaptive and nonparametric method that allows us to fill data gaps in
multi-wavelength or in multichannel records. This method, which is based on the
iterative singular value decomposition, uses the coherency between simultaneous
measurements at different wavelengths (or between different proxies) to fill
the missing data in a self-consistent way. The interpolation is improved by
handling different time scales separately.
Two major assets of this method are its simplicity, with few tuneable
parameters, and its robustness. Two examples of missing data are given: one
from solar EUV observations, and one from solar proxy data. The method is also
appropriate for building a composite out of partly overlapping records.Comment: to appear in Astronomy & Astrophysics (2011
Non-Gaussian statistics in space plasma turbulence, fractal properties and pitfalls
Magnetic field fluctuations in the vicinity of the Earth's bow shock have
been investigated with the aim to characterize the intermittent behaviour of
strong plasma turbulence. The observed small-scale intermittency may be the
signature of a multifractal process but a deeper inspection reveals caveats in
such an interpretation. Several effects, including the anisotropy of the
wavefield, the violation of the Taylor hypothesis and the occasional occurrence
of coherent wave packets, strongly affect the higher order statistical
properties. After correcting these effects, a more Gaussian and scale-invariant
wavefield is recovered.Comment: 13 pages (including 13 postscript figures), to appear in Nonlinear
Processes in Geophysic
Stability of the quantum supermembrane in a manifold with boundary
We point out an effect which may stabilize a supersymmetric membrane moving
on a manifold with boundary, and lead to a light-cone Hamiltonian with a
discrete spectrum of eigenvalues. The analysis is carried out explicitly for a
closed supermembrane in the regularized matrix model version.Comment: 10 pages, harvmac (references added, minor changes
On The spectrum of a Noncommutative Formulation of the D=11 Supermembrane with Winding
A regularized model of the double compactified D=11 supermembrane with
nontrivial winding in terms of SU(N) valued maps is obtained. The condition of
nontrivial winding is described in terms of a nontrivial line bundle introduced
in the formulation of the compactified supermembrane. The multivalued
geometrical objects of the model related to the nontrivial wrapping are
described in terms of a SU(N) geometrical object which in the
limit, converges to the symplectic connection related to the area preserving
diffeomorphisms of the recently obtained non-commutative description of the
compactified D=11 supermembrane.(I. Martin, J.Ovalle, A. Restuccia. 2000,2001)
The SU(N) regularized canonical lagrangian is explicitly obtained. In the limit it converges to the lagrangian in (I.Martin, J.Ovalle,
A.Restuccia. 2000,2001) subject to the nontrivial winding condition. The
spectrum of the hamiltonian of the double compactified D=11 supermembrane is
discussed.
Generically, it contains local string like spikes with zero energy.
However the sector of the theory corresponding to a principle bundle
characterized by the winding number , described by the SU(N) model we
propose, is shown to have no local string-like spikes and hence the spectrum of
this sector should be discrete.Comment: 16 pages.Latex2
Corrosion of alloy 800H and the effect of surface-applied CeO2 in a sulphidizing/oxidizing/carburizing environment at 700°C
The corrosion behavior of a wrought austenitic Fe-20Cr-32Ni steel, Alloy 800H, was studied in a simulated coal-gasification atmosphere at 700°C for exposure times up to 2500 hr. The influence of preoxidation and CeO2-surface application followed by preoxidation on the corrosion resistance of this material was assessed. The improvement in the corrosion resistance due to preoxidation of the blank material was small, whereas the effect of the CeO2-treatment was significant. This difference is thought to be due to better scale adherence in the case of CeO2-surface application
M Theory As A Matrix Model: A Conjecture
We suggest and motivate a precise equivalence between uncompactified eleven
dimensional M-theory and the N = infinity limit of the supersymmetric matrix
quantum mechanics describing D0-branes. The evidence for the conjecture
consists of several correspondences between the two theories. As a consequence
of supersymmetry the simple matrix model is rich enough to describe the
properties of the entire Fock space of massless well separated particles of the
supergravity theory. In one particular kinematic situation the leading large
distance interaction of these particles is exactly described by supergravity .
The model appears to be a nonperturbative realization of the holographic
principle. The membrane states required by M-theory are contained as
excitations of the matrix model. The membrane world volume is a noncommutative
geometry embedded in a noncommutative spacetime.Comment: Typo and tex error corrected. 41 pages, harvma
- …