15,483 research outputs found
The art of fitting p-mode spectra: Part II. Leakage and noise covariance matrices
In Part I we have developed a theory for fitting p-mode Fourier spectra
assuming that these spectra have a multi-normal distribution. We showed, using
Monte-Carlo simulations, how one can obtain p-mode parameters using 'Maximum
Likelihood Estimators'. In this article, hereafter Part II, we show how to use
the theory developed in Part I for fitting real data. We introduce 4 new
diagnostics in helioseismology: the echelle diagramme, the cross
echelle diagramme, the inter echelle diagramme, and the ratio cross spectrum.
These diagnostics are extremely powerful to visualize and understand the
covariance matrices of the Fourier spectra, and also to find bugs in the data
analysis code. These diagrammes can also be used to derive quantitative
information on the mode leakage and noise covariance matrices. Numerous
examples using the LOI/SOHO and GONG data are given.Comment: 17 pages with tex and ps files, submitted to A&A,
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The art of fitting p-mode spectra: Part I. Maximum Likelihood Estimation
In this article we present our state of the art of fitting helioseismic
p-mode spectra. We give a step by step recipe for fitting the spectra:
statistics of the spectra both for spatially unresolved and resolved data, the
use of Maximum Likelihood estimates, the statistics of the p-mode parameters,
the use of Monte-Carlo simulation and the significance of fitted parameters.
The recipe is applied to synthetic low-resolution data, similar to those of the
LOI, using Monte-Carlo simulations. For such spatially resolved data, the
statistics of the Fourier spectrum is assumed to be a multi-normal
distribution; the statistics of the power spectrum is \emph{not} a
with 2 degrees of freedom. Results for shows that all parameters
describing the p modes can be obtained without bias and with minimum variance
provided that the leakage matrix is known. Systematic errors due to an
imperfect knowledge of the leakage matrix are derived for all the p-mode
parameters.Comment: 13 pages, ps file gzipped. Submitted to A&
NIR Luminosity Function of Galaxies in Close Major-Merger Pairs and Mass Dependence of Merger Rate
A sample of close major-merger pairs (projected separation kpc, band magnitude difference mag) is selected from the matched 2MASS-2dFGRS catalog of Cole et al.
(2001). The pair primaries are brighter than mag. After
corrections for various biases, the comparison between counts in the paired
galaxy sample and counts in the parent sample shows that for the local `M*
galaxies' sampled by flux limited surveys, the fraction of galaxies in the
close major-merger pairs is 1.70. Using 38 paired galaxies in the
sample, a band luminosity function (LF) is calculated. This is the
first unbiased LF for a sample of objectively defined interacting/merging
galaxies in the local universe, while all previously determined LFs of paired
galaxies are biased by mistreating paired galaxies as singles. A stellar mass
function (MF) is translated from the LF. Compared to the LF/MF of 2MASS
galaxies, a differential pair fraction function is derived. The results suggest
a trend in the sense that less massive galaxies may have lower chance to be
involved in close major-merger pairs than more massive galaxies. The algorithm
presented in this paper can be easily applied to much larger samples of 2MASS
galaxies with redshifts in near future.Comment: Accepted by ApJL, 16 pages, 2 figure
Structural and optical properties of europium doped zirconia single crystals fibers grown by laser floating zone
Yttria stabilized zirconia single crystal fibers doped with europium ions were developed envisaging optical applications. The laser floating zone technique was used in order to grow millimetric high quality single crystal fibers. The as-grown fibers are completely transparent and inclusion free, exhibiting a cubic structure. Under ultraviolet (UV) excitation, a broad emission band appears at 551 nm. The europium doped fibers are translucent with a tetragonal structure and exhibit an intense red emission at room temperature under UV excitation. The fingerprint transition lines between the 5D0 and 7FJ(0â4) multiplets of the Eu3+ ions are observed with the main emission line at ⌠606ânm due to 5D0â7F2 transition. Photoluminescence excitation and wavelength dependent the photoluminescence spectra confirm the existence of different Eu3+ optical centers.
© 2011 American Institute of PhysicsFCT-PTDC/CTM/66195/2006FCT-SFRH/BD/45774/200
Perspectivas para o controle da broca da erva-mate Hedypathes betulinus (Klug, 1825) (Col.:Cerambycidae).
Development and exploratory cluster-randomised opportunistic trial of a theory-based intervention to enhance physical activity among adolescents
Peer reviewedPostprin
Combined grazing incidence RBS and TEM analysis of luminescent nano-SiGe/SiO2 multilayers.
Multilayer structures with five periods of amorphous SiGe nanoparticles/SiO2 layers with different thickness were deposited by Low Pressure Chemical Vapor Deposition and annealed to crystallize the SiGe nanoparticles. The use of grazing incidence RBS was necessary to obtain sufficient depth resolution to separate the signals arising from the individual layers only a few nm thick. The average size and areal density of the embedded SiGe nanoparticles as well as the oxide interlayer thickness were determined from the RBS spectra. Details of eventual composition changes and diffusion processes caused by the annealing processes were also studied. Transmission Electron Microscopy was used to obtain complementary information on the structural parameters of the samples in order to check the information yielded by RBS. The study revealed that annealing at 900 °C for 60 s, enough to crystallize the SiGe nanoparticles, leaves the structure unaltered if the interlayer thickness is around 15 nm or higher
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