37,308 research outputs found
Data Analysis and Neuro-Fuzzy Technique for EOR Screening : Application in Angolan Oilfields
This study is sponsored by the Angolan National Oil Company (Sonangol EP) and the authors are grateful for their support and the permission to use the data and publish this manuscriptPeer reviewedPublisher PD
Signal detection for spectroscopy and polarimetry
The analysis of high spectral resolution spectroscopic and
spectropolarimetric observations constitute a very powerful way of inferring
the dynamical, thermodynamical, and magnetic properties of distant objects.
However, these techniques are photon-starving, making it difficult to use them
for all purposes. One of the problems commonly found is just detecting the
presence of a signal that is buried on the noise at the wavelength of some
interesting spectral feature. This is specially relevant for
spectropolarimetric observations because typically, only a small fraction of
the received light is polarized. We present in this note a Bayesian technique
for the detection of spectropolarimetric signals. The technique is based on the
application of the non-parametric relevance vector machine to the observations,
which allows us to compute the evidence for the presence of the signal and
compute the more probable signal. The method would be suited for analyzing data
from experimental instruments onboard space missions and rockets aiming at
detecting spectropolarimetric signals in unexplored regions of the spectrum
such as the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) sounding
rocket experiment.Comment: 10 pages, 5 figures, accepted for publication in A&
A new view of the Lindemann criterion
The Lindemann criterion is reformulated in terms of the average shear modulus
of the melting crystal, indicating a critical melting shear strain which
is necessary to form the many different inherent states of the liquid. In glass
formers with covalent bonds, one has to distinguish between soft and hard
degrees of freedom to reach agreement. The temperature dependence of the
picosecond mean square displacements of liquid and crystal shows that there are
two separate contributions to the divergence of the viscosity with decreasing
temperature: the anharmonic increase of the shear modulus and a diverging
correlation length .Comment: 4 pages, 3 figure
Connection between electrical conductivity and diffusion coefficient of a conductive porous material filled with electrolyte
The paper focuses on the cross-property connection between the effective electrical conductivity and the overall mass transfer coefficient of a two phase material. The two properties are expressed in terms of the tortuosity parameter which generalized to the case of a material with two conductive phases. Elimination of this parameter yields the cross-property connection. The theoretical derivation is verified by comparison with computer simulation
On the inversion of Stokes profiles with local stray-light contamination
Obtaining the magnetic properties of non-resolved structures in the solar
photosphere is always challenging and problems arise because the inversion is
carried out through the numerical minimization of a merit function that depends
on the proposed model. We investigate the reliability of inversions in which
the stray-light contamination is obtained from the same observations as a local
average. In this case, we show that it is fundamental to include the covariance
between the observed Stokes profiles and the stray-light contamination. The
ensuing modified merit function of the inversion process penalizes large
stray-light contaminations simply because of the presence of positive
correlations between the observables and the stray-light, fundamentally
produced by spatially variable systematics. We caution that using the wrong
merit function, artificially large stray-light contaminations might be
inferred. Since this effect disappears if the stray-light contamination is
obtained as an average over the full field-of-view, we recommend to take into
account stray-light contamination using a global approach.Comment: 5 pages, 3 figures, accepted for publication in Ap
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