6,751 research outputs found
A decade of solar Type III radio bursts observed by the Nancay Radioheliograph 1998-2008
We present a statistical survey of almost 10 000 radio Type III bursts
observed by the Nancay Radioheliograph from 1998 to 2008, covering nearly a
full solar cycle. In particular, sources sizes, positions, and fluxes were
examined. We find an east-west asymmetry in source positions which could be
attributed to a 6(+/-)1 degree eastward tilt of the magnetic field, that source
FWHM sizes s roughly follow a solar-cycle averaged distribution dN/ds = 14
{\nu}^{-3.3} s^{-4} arcmin^{-1} day^{-1}, and that source fluxes closely follow
a solar-cycle averaged dN/dS_{\nu} = 0.34 {\nu}^{-2.9} S_{\nu}^{-1.7} sfu^{-1}
day^{-1} distribution (when {\nu} is in GHz, s in arcmin, and S_{\nu} in sfu).
Fitting a barometric density profile yields a temperature of 0.6 MK, while a
solar wind-like (\propto h^{-2}) density profile yields a density of 1.2x10^6
cm^{-3} at an altitude of 1 RS, assuming harmonic emission. Finally, we found
that the solar-cycle averaged radiated Type III energy could be similar in
magnitude to that radiated by nanoflares via non-thermal bremsstrahlung
processes, and we hint at the possibility that escaping electron beams might
carry as much energy away from the corona as is introduced into it by
accelerated nanoflare electrons.Comment: 22 pages, 18 figure
X-ray reflectivity, diffraction and grazing incidence small angle X-ray scattering as complementary methods in the microstructural study of sol–gel zirconia thin films
X-ray reflectometry, X-ray diffraction and grazing incidence small angle X-ray scattering have been complementary used to fully characterize zirconia (ZrO2) thin films obtained by the sol–gel route. The films were synthesized on various sapphire (Al2O3), silicon (Si) and glass mirrorpolished wafers by a dip-coating process in a zirconia precursor sol. Versus the synthesis parameters as alkoxide sol concentration, withdrawal speed and annealing temperature, the microstructure of the layer is managed and its different microstructural parameters such as thickness, mass density, crystalline phase, grain size and spatial arrangement have been determined. The as prepared layers are amorphous. During a thermal treatment at low temperature (<1000 -C), the layers thickness decreases while their mass density increases. Simultaneously the zirconia precursor crystallises in the zirconia tetragonal form and the coating is made of randomly oriented nanocrystals which self organise in a dense close-packed microstructure. At low temperature, this microstructural evolution is similar whatever the substrate. Moreover, the layer evolves as the corresponding bulk xerogel showing that the presence of the interface does not modify the thermal microstructure evolution of the layer which is controlled by a normal grain growth leading to relatively dense nanocrystalline thin films
Resampling technique applied to the characterization of microsegregation
Characterization of short-range chemical heterogeneities in metallic materials, such as the so-called microsegregation resulting from solidification, is most often performed using EDS or WDS spot measurements. The most usual way is to perform countings on points located along a regular grid. Due to experimental limitation, the grid step is generally of the same order of magnitude than the characteristic distance(s) of the chemical heterogeneities under investigation. In such a case, the measurements can not be assumed to be independent one from each other, and the resulting interferences (correlations) preclude application of simple statistics to the solute distribution obtained. In the present work, this is clearly shown by using a resampling technique applied to "chemical" images obtained by phase field modelling
Understanding CME and associated shock in the solar corona by merging multi wavelengths observation
Using multi-wavelength imaging observations, in EUV, white light and radio,
and radio spectral data over a large frequency range, we analyzed the
triggering and development of a complex eruptive event. This one includes two
components, an eruptive jet and a CME which interact during more than 30 min,
and can be considered as physically linked. This was an unusual event. The jet
is generated above a typical complex magnetic configuration which has been
investigated in many former studies related to the build-up of eruptive jets;
this configuration includes fan-field lines originating from a corona null
point above a parasitic polarity, which is embedded in one polarity region of
large Active Region (AR). The initiation and development of the CME, observed
first in EUV, does not show usual signatures. In this case, the eruptive jet is
the main actor of this event. The CME appears first as a simple loop system
which becomes destabilized by magnetic reconnection between the outer part of
the jet and the ambient medium. The progression of the CME is closely
associated with the occurrence of two successive types II bursts from distinct
origin. An important part of this study is the first radio type II burst for
which the joint spectral and imaging observations allowed: i) to follow, step
by step, the evolution of the spectrum and of the trajectory of the radio
burst, in relationship with the CME evolution; ii) to obtain, without
introducing an electronic density model, the B-field and the Alfven speed.Comment: 17 pages, 13 figure
Prior uncertainty investigation of density-viscosity dependent joint transport of heat and solute in alluvial sediments
Joint heat and solute tracer tests allow to add diffusion and conduction information to the solute advection-dispersion and help imaging preferential pathways in heterogeneous aquifers. We perform a joint interpretation of heat and solute tracer tests combining deterministic modeling and Bayesian Evidential Learning. The results show a strong influence of the water viscosity. The stochastic simulations highlight the influence of spatial and parameter uncertainty on the resulting breakthrough curves, stressing the need for realistic uncertainty quantification.Joint heat and solute tracer test inversion for imaging preferential pathway
Modeling a heat tracer test in alluvial sediments using Monte Carlo : on the importance of the prior
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