48 research outputs found
A decade of solar Type III radio bursts observed by the Nancay Radioheliograph 1998-2008
Full text linkWe 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
Understanding CME and associated shock in the solar corona by merging multi wavelengths observation
Full text linkUsing 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
The adoption of open access scholarly communication in Tanzanian public universities: some Influencing factors
Get PDFOpen access is a means for free availability of scholarly content via the internet. It is an
emerging opportunity for wider and unlimited access to scholarly literature. Scholarly
communication, through open access journals and self-arching, are the two main
approaches of open access publishing. However, this mode of scholarly communication
is not widely utilised in developing countries such as Tanzania. This article discusses
the factors that influence the adoption of open access for scholarly communication
in Tanzanian public universities, based on a study conducted in 2008 using a survey
questionnaire. A sample of 544 researchers, selected through stratified random sampling
from a population of 1 088 researchers and 69 policymakers at six public universities in
Tanzania, provided their views. It was evident from the findings that researchers’ internet
usage skills and self-efficacy, social influence, performance expectancy, effort expectancy,
and the respondents’ general perceptions about open access were the positive factors likely
to facilitate open access adoption. The current poor research conditions and researchers’
low internet self-efficacy (such as inadequate information search skills) were cited as the
main hindrances for researchers to use open access outlets to access scholarly content. It is therefore recommended that university policies on scholarly communication should
be revised to incorporate the use of open access publishing. Furthermore, universities
should accelerate the establishment of institutional repositories, advocacy campaigns
and training directed at researchers, policymakers, readers and information managers of
scholarly content, and the improvement of internet speed through subscription to more
bandwidth, so as to meet the demand from the scholarly communit
A Decade of Solar Type III Radio Bursts Observed by the Nancay Radioheliograph 1998-2008
No full textInternational audienc
A Decade of Solar Type III Radio Bursts Observed by the Nancay Radioheliograph 1998-2008
No full textInternational audienc
A Decade of Solar Type III Radio Bursts Observed by the Nancay Radioheliograph 1998-2008
No full textInternational audienc
