816 research outputs found
Multi-strand coronal loop model and filter-ratio analysis
We model a coronal loop as a bundle of seven separate strands or filaments.
Each of the loop strands used in this model can independently be heated (near
their left footpoints) by Alfv\'en/ion-cyclotron waves via wave-particle
interactions. The Alfv\'en waves are assumed to penetrate the strands from
their footpoints, at which we consider different wave energy inputs. As a
result, the loop strands can have different heating profiles, and the
differential heating can lead to a varying cross-field temperature in the total
coronal loop. The simulation of TRACE observations by means of this loop model
implies two uniform temperatures along the loop length, one inferred from the
171:195 filter ratio and the other from the 171:284 ratio. The reproduced flat
temperature profiles are consistent with those inferred from the observed EUV
coronal loops. According to our model, the flat temperature profile is a
consequence of the coronal loop consisting of filaments, which have different
temperatures but almost similar emission measures in the cross-field direction.
Furthermore, when we assume certain errors in the simulated loop emissions
(e.g., due to photometric uncertainties in the TRACE filters) and use the
triple-filter analysis, our simulated loop conditions become consistent with
those of an isothermal plasma. This implies that the use of TRACE/EIT triple
filters for observation of a warm coronal loop may not help in determining
whether the cross-field isothermal assumption is satisfied or not
Multi-strand coronal loop model and filter-ratio analysis
We model a coronal loop as a bundle of seven separate strands or filaments.
Each of the loop strands used in this model can independently be heated (near
their left footpoints) by Alfv\'en/ion-cyclotron waves via wave-particle
interactions. The Alfv\'en waves are assumed to penetrate the strands from
their footpoints, at which we consider different wave energy inputs. As a
result, the loop strands can have different heating profiles, and the
differential heating can lead to a varying cross-field temperature in the total
coronal loop. The simulation of TRACE observations by means of this loop model
implies two uniform temperatures along the loop length, one inferred from the
171:195 filter ratio and the other from the 171:284 ratio. The reproduced flat
temperature profiles are consistent with those inferred from the observed EUV
coronal loops. According to our model, the flat temperature profile is a
consequence of the coronal loop consisting of filaments, which have different
temperatures but almost similar emission measures in the cross-field direction.
Furthermore, when we assume certain errors in the simulated loop emissions
(e.g., due to photometric uncertainties in the TRACE filters) and use the
triple-filter analysis, our simulated loop conditions become consistent with
those of an isothermal plasma. This implies that the use of TRACE/EIT triple
filters for observation of a warm coronal loop may not help in determining
whether the cross-field isothermal assumption is satisfied or not
Spectroscopic Observations of Propagating Disturbances in a Polar Coronal Hole: Evidence of Slow Magneto-acoustic Waves
We focus on detecting and studying quasi-periodic propagating features that
have been interpreted both in terms of slow magneto-acoustic waves and of high
speed upflows. We analyze long duration spectroscopic observations of the
on-disk part of the south polar coronal hole taken on 1997 February 25 by the
SUMER spectrometer aboard SOHO. We calibrated the velocity with respect to the
off-limb region and obtain time--distance maps in intensity, Doppler velocity
and line width. We also perform a cross correlation analysis on different time
series curves at different latitudes. We study average spectral line profiles
at the roots of propagating disturbances and along the propagating ridges, and
perform a red-blue asymmetry analysis. We find the clear presence of
propagating disturbances in intensity and Doppler velocity with a projected
propagation speed of about km s and a periodicity of
14.5 min. To our knowledge, this is the first simultaneous detection
of propagating disturbances in intensity as well as in Doppler velocity in a
coronal hole. During the propagation, an intensity enhancement is associated
with a blue-shifted Doppler velocity. These disturbances are clearly seen in
intensity also at higher latitudes (i.e. closer to the limb), while
disturbances in Doppler velocity becomes faint there. The spectral line
profiles averaged along the propagating ridges are found to be symmetric, to be
well fitted by a single Gaussian, and have no noticeable red-blue asymmetry.
Based on our analysis, we interpret these disturbances in terms of propagating
slow magneto-acoustic waves.Comment: accepted for publication by A&
Upflows in the upper transition region of the quiet Sun
We investigate the physical meaning of the prominent blue shifts of Ne VIII,
which is observed to be associated with quiet-Sun network junctions (boundary
intersections), through data analyses combining force-free-field extrapolations
with EUV spectroscopic observations. For a middle-latitude region, we
reconstruct the magnetic funnel structure in a sub-region showing faint
emission in EIT-Fe 195. This funnel appears to consist of several smaller
funnels that originate from network lanes, expand with height and finally merge
into a single wide open-field region. However, the large blue shifts of Ne VIII
are generally not associated with open fields, but seem to be associated with
the legs of closed magnetic loops. Moreover, in most cases significant upflows
are found in both of the funnel-shaped loop legs. These quasi-steady upflows
are regarded as signatures of mass supply to the coronal loops rather than the
solar wind. Our observational result also reveals that in many cases the
upflows in the upper transition region (TR) and the downflows in the middle TR
are not fully cospatial. Based on these new observational results, we suggest
different TR structures in coronal holes and in the quiet Sun.Comment: 4 pages, 4 figures, will appear in the Proceedings of the Solar wind
12 conferenc
Kinetic Signatures and Intermittent Turbulence in the Solar Wind Plasma
A connection between kinetic processes and intermittent turbulence is
observed in the solar wind plasma using measurements from the Wind spacecraft
at 1 AU. In particular, kinetic effects such as temperature anisotropy and
plasma heating are concentrated near coherent structures, such as current
sheets, which are non-uniformly distributed in space. Furthermore, these
coherent structures are preferentially found in plasma unstable to the mirror
and firehose instabilities. The inhomogeneous heating in these regions, which
is present in both the magnetic field parallel and perpendicular temperature
components, results in protons at least 3-4 times hotter than under typical
stable plasma conditions. These results offer a new understanding of kinetic
processes in a turbulent regime, where linear Vlasov theory is not sufficient
to explain the inhomogeneous plasma dynamics operating near non-Gaussian
structures.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Understanding Needs Embodiment: A Theory-Guided Reanalysis of the Role of Metaphors and Analogies in Understanding Science
Many authors stress the importance of basing teaching on students' prior knowledge. To build a bridge between students' everyday knowledge and scientific concepts, the role of metaphors and analogies came into the focus of the science education community during the past two decades. Approaches using metaphor-based teaching strategies often regard metaphors and analogies as teaching tools that can be adopted by a teacher. On the basis of the theoretical framework of experientialism, we argue that not only teaching but also thinking about and understanding science without metaphors and analogies is not possible. An analysis of studies dealing with metaphors and analogies in science education shows that instructional analogies and metaphors are often not understood as intended or not used by students in their own explanations. By reanalyzing 199 instructional metaphors and analogies on the basis of a metaphor analysis, we show that it takes more than making a connection to everyday life to communicate science fruitfully. We show that good instructional metaphors and analogies need embodied sources. These embodied sources are everyday experiences conceptualized in, for example, schemata such as containers, paths, balances, and up and down. For the analysis, we introduce the concept of conceptual metaphors for analyzing metaphors as well as analogies
COMPARISON OF ORTHODOX WITH FIBREOPTIC OROTRACHEAL INTUBATION UNDER TOTAL I.V. ANAESTHESIA
Fibreoptic orotracheal intubation was compared with orthodox laryngoscopy and tracheal intubation using a total i.v. technique with propofol in 60 ASA I and II patients. There was no significant difference between the two techniques in haemodynamic profile (before, during and following the intubation procedure) and incidence of postoperative sore throat. Minimal oxygen saturation was 96% during the study; maximal end-tidal PCO2 after intubation was 5.4 kPa. Intubation time was faster (P < 0.01) in the orthodox group (30.7 (SEM 2.3) s) than in the fibreoptic group (52.7 (4.8) s
Rank-ordered Multifractal Spectrum for Intermittent Fluctuations
We describe a new method that is both physically explicable and
quantitatively accurate in describing the multifractal characteristics of
intermittent events based on groupings of rank-ordered fluctuations. The
generic nature of such rank-ordered spectrum leads it to a natural connection
with the concept of one-parameter scaling for monofractals. We demonstrate this
technique using results obtained from a 2D MHD simulation. The calculated
spectrum suggests a crossover from the near Gaussian characteristics of small
amplitude fluctuations to the extreme intermittent state of large rare events.Comment: 4 pages, 5 figure
Temperature anisotropy and differential streaming of solar wind ions -- Correlations with transverse fluctuations
We study correlations of the temperature ratio (which is an indicator for
perpendicular ion heating) and the differential flow of the alpha particles
with the power of transverse fluctuations that have wave numbers between 0.01
and 0.1 (normalized to , where is the proton inertial length).
We found that both the normalized differential ion speed, (where is the Alfv\'en speed) and the proton
temperature anisotropy, , increase when the
relative wave power is growing. Furthermore, if the normalized differential ion
speed stays below 0.5, the alpha-particle temperature anisotropy, , correlates positively with the relative power of
the transverse fluctuations. However, if is higher
than 0.6, then the alpha-particle temperature anisotropy tends to become lower
and attain even values below unity despite the presence of transverse
fluctuations of relatively high amplitudes. Our findings appear to be
consistent with the expectations from kinetic theory for the resonant
interaction of the ions with Alfv\'en/ion-cyclotron waves and the resulting
wave dissipation.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics journa
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