1,021 research outputs found
Un cas de comparaison diférentielle. Catulle et Marguerite Yourcenar réécrivent le mythe d'Ariane
Physical properties of solar polar jets: A statistical study with Hinode XRT data
The target of this work is to investigate the physical nature of polar jets
in the solar corona and their possible contribution to coronal heating and
solar wind flow based on the analysis of X-ray images acquired by the Hinode
XRT telescope. We estimate the different forms of energy associated with many
of these small-scale eruptions, in particular the kinetic energy and enthalpy.
Two Hinode XRT campaign datasets focusing on the two polar coronal holes were
selected to analyze the physical properties of coronal jets; the analyzed data
were acquired using a series of three XRT filters. Typical kinematical
properties (e.g., length, thickness, lifetime, ejection rate, and velocity) of
18 jets are evaluated from the observed sequences, thus providing information
on their possible contribution to the fast solar wind flux escaping from
coronal holes. Electron temperatures and densities of polar-jet plasmas are
also estimated using ratios of the intensities observed in different filters.
We find that the largest amount of energy eventually provided to the corona
is thermal. The energy due to waves may also be significant, but its value is
comparatively uncertain. The kinetic energy is lower than thermal energy, while
other forms of energy are comparatively low. Lesser and fainter events seem to
be hotter, thus the total contribution by polar jets to the coronal heating
could have been underestimated so far. The kinetic energy flux is usually
around three times smaller than the enthalpy counterpart, implying that this
energy is converted into plasma heating more than in plasma acceleration. This
result suggests that the majority of polar jets are most likely not escaping
from the Sun and that only cooler ejections could possibly have enough kinetic
energy to contribute to the total solar wind flow.Comment: 21 pages, 10 figures, Submitted and accepted for publishing in
Astronomy and Astrophysics journa
Recent Results of non-accelarator-based neutrino experiments
Recent results of non-accelerator-based experiments, including those of
solar, atmospheric, and reactor neutrinos oscillations, neutrinoless
double-beta decays, and neutrino magnetic moments, are reviewed. Future
projects and their respective prospects are summarized.Comment: V.2, minor changes with one more reference added. Plenary talk given
at the "32nd International Conference on High Energy Physics", Aug. 16-22,
2004, Beijing, P.R. Chin
Neutrino texture saturating the CP asymmetry
We study a neutrino mass texture which can explain the neutrino oscillation
data and also saturate the upper bound of the CP asymmetry in the
leptogenesis. We consider the thermal and non-thermal leptogenesis based on the
right-handed neutrino decay in this model. A lower bound of the reheating
temperature required for the explanation of the baryon number asymmetry is
estimated as GeV for the thermal leptogenesis and GeV for
the non-thermal one.It can be lower than the upper bound of the reheating
temperature imposed by the cosmological gravitino problem. An example of the
construction of the discussed texture is also presented.Comment: 23 pages, 6 figure
S-particles at their naturalness limits
We draw attention on a particular configuration of supersymmetric particle
masses, motivated by naturalness and flavour considerations. All its relevant
phenomenological properties for the LHC are described in terms of a few
physical parameters, irrespective of the underlying theoretical model. This
allows a simple characterization of its main features, useful to define a
strategy for its discovery.Comment: 13 pages, 8 figures, added reference
The role of lateral magnetic reconnection in solar eruptive events
Abstract. On 10–11 December 2005 a slow CME occurred in between two coronal streamers in the Western Hemisphere. SOHO/MDI magnetograms show a multipolar magnetic configuration at the photosphere consisting of a complex of active regions located at the CME source and two bipoles at the base of the lateral coronal streamers. White light observations reveal that the expanding CME affects both of the lateral streamers and induces the release of plasma within or close to them. These transient phenomena are possibly due to magnetic reconnections induced by the CME expansion that occurs either inside the streamer current sheet or between the CME flanks and the streamer. Our observations show that CMEs can be associated to not only a single reconnection process at a single location in the corona, but also to many reconnection processes occurring at different times and locations around the flux rope. Numerical simulations are used to demonstrate that the observed lateral reconnections can be reproduced. The observed secondary reconnections associated to CMEs may facilitate the CME release by globally decreasing the magnetic tension of the corona. Future CME models should therefore take into account the lateral reconnection effect
A Comprehensive Study of the Initiation and Early Evolution of a Coronal Mass Ejection from Ultraviolet and White-Light Data
In this work we analyze simultaneous UV and white-light (WL) observations of a slow CME that occurred on 2000 January 31. Unlike most CMEs studied in the UV so far, this event was not associated with a flare or filament eruption. Based on vector magnetograph data and magnetic field models, we find that field disruption in an active region (AR) was driven by flux emergence and shearing motions, leading to the CME and to post-CME arcades seen in the EUV. WL images, acquired by the Mark IV coronagraph at the Mauna Loa Observatory, allowed us to identify the CME front, bubble, and core shortly (about 1 hr) after the CME ejection. From polarized brightness (pB) Mauna Loa data we estimated the mass and electron densities of the CME. The CME mass increases with time, indicating that about 2/3 of the mass originates above 1.6 R☉. Analysis of the UV spectra, acquired by the Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer (SOHO UVCS) at 1.6 and 1.9 R☉, allowed us to derive the electron temperature distribution across the CME. The temperature maximizes at the CME core and increases between 1.6 and 1.9 R☉. This event was unusual, in that the leading edge and the CME core were hotter than the ambient corona. We discuss magnetic heating and adiabatic compression as explanations for the high temperatures in the core and leading edge, respectively
A New Variety of Coronal Mass Ejection: Streamer Puffs from Compact Ejective Flares
We report on SOHO UVCS, LASCO, EIT, and MDI observations of a series of narrow ejections that occurred at the solar limb. These ejections originated from homologous compact flares whose source was an island of included polarity located just inside the base of a coronal streamer. Some of these ejections result in narrow CMEs ("streamer puffs") that move out along the streamer. These streamer puffs differ from "streamer blowout" CMEs in that (1) while the streamer is transiently inflated by the puff, it is not disrupted, and (2) each puff comes from a compact explosion in the outskirts of the streamer arcade, not from an extensive eruption along the main neutral line of the streamer arcade. From the observations, we infer that each streamer puff is produced by means of the inflation or blowing open of an outer loop of the arcade by ejecta from the compact-flare explosion in the foot of the loop. So, in terms of their production, our streamer puffs are a new variety of CME
Modeling UV and X-Ray Emission in a Post-CME Current Sheet
A post-CME current sheet (CS) is a common feature developed behind an
erupting flux rope in CME models. Observationally, white light observations
have recorded many occurrences of a thin ray appearing behind a CME eruption
that closely resembles a post-CME CS in its spatial correspondence and
morphology. UV and X-ray observations further strengthen this interpretation by
the observations of high temperature emission at locations consistent with
model predictions. The next question then becomes whether the properties inside
a post-CME CS predicted by a model agree with observed properties. In this
work, we assume that the post-CME CS is a consequence of Petschek-like
reconnection and that the observed ray-like structure is bounded by a pair of
slow mode shocks developed from the reconnection site. We perform
time-dependent ionization calculations and model the UV line emission. We find
that such a model is consistent with SOHO/UVCS observations of the post-CME CS.
The change of Fe XVIII emission in one event implies an inflow speed of ~10
km/s and a corresponding reconnection rate of M_A ~ 0.01. We calculate the
expected X-ray emission for comparison with X-ray observations by Hinode/XRT,
as well as the ionic charge states as would be measured in-situ at 1 AU. We
find that the predicted count rate for Hinode/XRT agree with what was observed
in a post-CME CS on April 9, 2008, and the predicted ionic charge states are
consistent with high ionization states commonly measured in the interplanetary
CMEs. The model results depend strongly on the physical parameters in the
ambient corona, namely the coronal magnetic field, the electron density and
temperature during the CME event. It is crucial to obtain these ambient coronal
parameters and as many facets of the CS properties as possible by observational
means so that the post-CME current sheet models can be scrutinized more
effectively
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