415 research outputs found
Explosive events - swirling transition region jets
In this paper, we extend our earlier work to provide additional evidence for
an alternative scenario to explain the nature of so-called `explosive events'.
The bi-directed, fast Doppler motion of explosive events observed
spectroscopically in the transition region emission is classically interpreted
as a pair of bidirectional jets moving upward and downward from a reconnection
site. We discuss the problems of such a model. In our previous work, we focused
basically on the discrepancy of fast Doppler motion without detectable motion
in the image plane. We now suggest an alternative scenario for the explosive
events, based on our observations of spectral line tilts and bifurcated
structure in some events. Both features are indicative of rotational motion in
narrow structures. We explain the bifurcation as the result of rotation of
hollow cylindrical structures and demonstrate that such a sheath model can also
be applied to explain the nature of the puzzling `explosive events'. We find
that the spectral tilt, the lack of apparent motion, the bifurcation, and a
rapidly growing number of direct observations support an alternative scenario
of linear, spicular-sized jets with a strong spinning motion.Comment: 9 pages, 3 figures, accepted for publication in Solar Physic
Dynamics and plasma properties of an X-ray jet from SUMER, EIS, XRT and EUVI A & B simultaneous observations
Small-scale transient phenomena in the quiet Sun are believed to play an
important role in coronal heating and solar wind generation. One of them named
as "X-ray jet" is the subject of our study. We indent to investigate the
dynamics, evolution and physical properties of this phenomenon. We combine
spatially and temporally multi-instrument observations obtained simultaneously
with the SUMER spectrometer onboard SoHO, EIS and XRT onboard Hinode, and
EUVI/SECCHI onboard the Ahead and Behind STEREO spacecrafts. We derive plasma
parameters such as temperatures and densities as well as dynamics by using
spectral lines formed in the temperature range from 10 000 K to 12 MK. We also
use image difference technique to investigate the evolution of the complex
structure of the studied phenomenon. With the available unique combination of
data we were able to establish that the formation of a jet-like event is
triggered by not one but several energy depositions which are most probably
originating from magnetic reconnection. Each energy deposition is followed by
the expulsion of pre-existing or new reconnected loops and/or collimated flow
along open magnetic field lines. We derived in great detail the dynamic process
of X-ray jet formation and evolution. We also found for the first time
spectroscopically in the quiet Sun a temperature of 12~MK and density of 4
10^10~cm^-3 in a reconnection site. We raise an issue concerning an uncertainty
in using the SUMER Mg X 624.9 A line for coronal diagnostics. We clearly
identified two types of up-flow: one collimated up-flow along open magnetic
field lines and a plasma cloud formed from the expelled BP loops. We also
report a cooler down-flow along closed magnetic field lines. A comparison is
made with a model developed by Moreno-Insertis \etal\ (2008).Comment: 15 pages, 15 figure
2D and 3D Polar Plume Analysis from the Three Vantage Positions of STEREO/EUVI A, B, and SOHO/EIT
Polar plumes are seen as elongated objects starting at the solar polar
regions. Here, we analyze these objects from a sequence of images taken
simultaneously by the three spacecraft telescopes STEREO/EUVI A and B, and
SOHO/EIT. We establish a method capable of automatically identifying plumes in
solar EUV images close to the limb at 1.01 - 1.39 R in order to study their
temporal evolution. This plume-identification method is based on a multiscale
Hough-wavelet analysis. Then two methods to determined their 3D localization
and structure are discussed: First, tomography using the filtered
back-projection and including the differential rotation of the Sun and,
secondly, conventional stereoscopic triangulation. We show that tomography and
stereoscopy are complementary to study polar plumes. We also show that this
systematic 2D identification and the proposed methods of 3D reconstruction are
well suited, on one hand, to identify plumes individually and on the other
hand, to analyze the distribution of plumes and inter-plume regions. Finally,
the results are discussed focusing on the plume position with their
cross-section area.Comment: 22 pages, 10 figures, Solar Physics articl
Parasite avoidance behaviours in aquatic environments
Parasites, including macroparasites, protists, fungi, bacteria and viruses, can impose a heavy burden upon host animals. However, hosts are not without defences. One aspect of host defence, behavioural avoidance, has been studied in the terrestrial realm for over 50 years, but was first reported from the aquatic environment approximately 20 years ago. Evidence has mounted on the importance of parasite avoidance behaviours and it is increasingly apparent that there are core similarities in the function and benefit of this defence mechanism between terrestrial and aquatic systems. However, there are also stark differences driven by the unique biotic and abiotic characteristics of terrestrial and aquatic (marine and freshwater) environments. Here, we review avoidance behaviours in a comparative framework and highlight the characteristics of each environment that drive differences in the suite of mechanisms and cues that animals use to avoid parasites. We then explore trade-offs, potential negative effects of avoidance behaviour and the influence of human activities on avoidance behaviours. We conclude that avoidance behaviours are understudied in aquatic environments but can have significant implications for disease ecology and epidemiology, especially considering the accelerating emergence and re-emergence of parasites.peerReviewe
Enhanced thermal conductivity of carbon fiber/phenolic resin composites by the introduction of carbon nanotubes
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APPLIED PHYSICS LETTERS. 90(9):093125 (2007) and may be found at https://doi.org/10.1063/1.2710778 .ArticleAPPLIED PHYSICS LETTERS. 90(9):093125 (2007)journal articl
Parameters of the Magnetic Flux inside Coronal Holes
Parameters of magnetic flux distribution inside low-latitude coronal holes
(CHs) were analyzed. A statistical study of 44 CHs based on Solar and
Heliospheric Observatory (SOHO)/MDI full disk magnetograms and SOHO/EIT 284\AA
images showed that the density of the net magnetic flux, , does
not correlate with the associated solar wind speeds, . Both the area and
net flux of CHs correlate with the solar wind speed and the corresponding
spatial Pearson correlation coefficients are 0.75 and 0.71, respectively. A
possible explanation for the low correlation between and
is proposed. The observed non-correlation might be rooted in the structural
complexity of the magnetic field. As a measure of complexity of the magnetic
field, the filling factor, , was calculated as a function of spatial
scales. In CHs, was found to be nearly constant at scales above 2 Mm,
which indicates a monofractal structural organization and smooth temporal
evolution. The magnitude of the filling factor is 0.04 from the Hinode SOT/SP
data and 0.07 from the MDI/HR data. The Hinode data show that at scales smaller
than 2 Mm, the filling factor decreases rapidly, which means a mutlifractal
structure and highly intermittent, burst-like energy release regime. The
absence of necessary complexity in CH magnetic fields at scales above 2 Mm
seems to be the most plausible reason why the net magnetic flux density does
not seem to be related to the solar wind speed: the energy release dynamics,
needed for solar wind acceleration, appears to occur at small scales below 1
Mm.Comment: 6 figures, approximately 23 pages. Accepted in Solar Physic
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