916 research outputs found
The Relationship of Coronal Mass Ejections to Streamers
We have examined images from the Large Angle Spectroscopic Coronagraph
(LASCO) to study the relationship of Coronal Mass Ejections (CMEs) to coronal
streamers. We wish to test the suggestion (Low 1996) that CMEs arise from flux
ropes embedded in a streamer erupting, thus disrupting the streamer. The data
span a period of two years near sunspot minimum through a period of increased
activity as sunspot numbers increased. We have used LASCO data from the C2
coronagraph which records Thomson scattered white light from coronal electrons
at heights between 1.5 and 6R_sun. Maps of the coronal streamers have been
constructed from LASCO C2 observations at a height of 2.5R_sun at the east and
west limbs. We have superposed the corresponding positions of CMEs observed
with the C2 coronagraph onto the synoptic maps. We identified the different
kinds of signatures CMEs leave on the streamer structure at this height
(2.5R_sun). We find four types of CMEs with respect to their effect on
streamers:
1. CMEs that disrupt the streamer 2. CMEs that have no effect on the
streamer, even though they are related to it. 3. CMEs that create streamer-like
structures 4. CMEs that are latitudinally displaced from the streamer.
This is the most extensive observational study of the relation between CMEs
and streamers to date. Previous studies using SMM data have made the general
statement that CMEs are mostly associated with streamers, and that they
frequently disrupt it. However, we find that approximately 35% of the observed
CMEs bear no relation to the pre-existing streamer, while 46% have no effect on
the observed streamer, even though they appear to be related to it. Our
conclusions thus differ considerably from those of previous studies.Comment: Accepted, Journal of Geophysical Research. 8 figs, better versions at
http://www.science.gmu.edu/~prasads/streamer.htm
STEREO and Wind observations of a fast ICME flank triggering a prolonged geomagnetic storm on 5-7 April 2010
On 5 April 2010 an interplanetary (IP) shock was detected by the Wind
spacecraft ahead of Earth, followed by a fast (average speed 650 km/s) IP
coronal mass ejection (ICME). During the subsequent moderate geomagnetic storm
(minimum Dst = -72 nT, maximum Kp=8-), communication with the Galaxy 15
satellite was lost. We link images from STEREO/SECCHI to the near-Earth in situ
observations and show that the ICME did not decelerate much between Sun and
Earth. The ICME flank was responsible for a long storm growth phase. This type
of glancing collision was for the first time directly observed with the STEREO
Heliospheric Imagers. The magnetic cloud (MC) inside the ICME cannot be modeled
with approaches assuming an invariant direction. These observations confirm the
hypotheses that parts of ICMEs classified as (1) long-duration MCs or (2)
magnetic-cloud-like (MCL) structures can be a consequence of a spacecraft
trajectory through the ICME flank.Comment: Geophysical Research Letters (accepted); 3 Figure
A Double‐Blind Randomized Placebo‐Controlled Trial of Oral Naltrexone for Heavy‐Drinking Smokers Seeking Smoking Cessation Treatment
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137315/1/acer13396.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137315/2/acer13396_am.pd
Structure-Function Relationships of the Neisserial EptA Enzyme Responsible for Phosphoethanolamine Decoration of Lipid A: Rationale for Drug Targeting
Bacteria cause disease by two general mechanisms: the action of their toxins on host cells and induction of a pro-inflammatory response that can lead to a deleterious cytokine/chemokine response (e.g., the so-called cytokine storm) often seen in bacteremia/septicemia. These major mechanisms may overlap due to the action of surface structures that can have direct and indirect actions on phagocytic or non-phagocytic cells. In this respect, the lipid A (endotoxin) component of lipopolysaccharide (LPS) possessed by Gram-negative bacteria has been the subject of literally thousands of studies over the past century that clearly identified it as a key virulence factor in endotoxic shock. In addition to its capacity to modulate inflammatory responses, endotoxin can also modulate bacterial susceptibility to host antimicrobials, such as the host defense peptides termed cationic antimicrobial peptides. This review concentrates on the phosphoethanolamine (PEA) decoration of lipid A in the pathogenic species of the genus Neisseria [N. gonorrhoeae and N. meningitidis]. PEA decoration of lipid A is mediated by the enzyme EptA (formerly termed LptA) and promotes resistance to innate defense systems, induces the pro-inflammatory response and can influence the in vivo fitness of bacteria during infection. These important biological properties have driven efforts dealing with the biochemistry and structural biology of EptA that will facilitate the development of potential inhibitors that block PEA addition to lipid A
Can Streamer Blobs prevent the Buildup of the Interplanetetary Magnetic Field?
Coronal Mass Ejections continuously drag closed magnetic field lines away
from the Sun, adding new flux to the interplanetary magnetic field (IMF). We
propose that the outward-moving blobs that have been observed in helmet
streamers are evidence of ongoing, small-scale reconnection in streamer current
sheets, which may play an important role in the prevention of an indefinite
buildup of the IMF. Reconnection between two open field lines from both sides
of a streamer current sheet creates a new closed field line, which becomes part
of the helmet, and a disconnected field line, which moves outward. The blobs
are formed by plasma from the streamer that is swept up in the trough of the
outward moving field line. We show that this mechanism is supported by
observations from SOHO/LASCO. Additionally, we propose a thorough statistical
study to quantify the contribution of blob formation to the reduction of the
IMF, and indicate how this mechanism may be verified by observations with
SOHO/UVCS and the proposed NASA STEREO and ESA Polar Orbiter missions.Comment: 7 pages, 2 figures; accepted by The Astrophysical Journal Letters;
uses AASTe
Double Penguins and the Contribution of Vector Meson--like States to the Decays
Using perturbative QCD, the contribution at the leading twist, leading
level, of charm and up quark loops to the decays and is presented. In the case of , the relative importance of these contributions depend
upon the unknown CKM matrix elements and .
Assuming that the ratio is bounded
between as is suggested by the Particle Data Group, the
error in extracting by these decays is estimated.Comment: 4 double column pages, revtex, 3 figures attached, 2 figures added
indicating less optimism concerning the accuracy at which
can be extracted: to appear in PR
Plasmoid-Induced-Reconnection and Fractal Reconnection
As a key to undertanding the basic mechanism for fast reconnection in solar
flares, plasmoid-induced-reconnection and fractal reconnection are proposed and
examined. We first briefly summarize recent solar observations that give us
hints on the role of plasmoid (flux rope) ejections in flare energy release. We
then discuss the plasmoid-induced-reconnection model, which is an extention of
the classical two-ribbon-flare model which we refer to as the CSHKP model. An
essential ingredient of the new model is the formation and ejection of a
plasmoid which play an essential role in the storage of magnetic energy (by
inhibiting reconnection) and the induction of a strong inflow into reconnection
region. Using a simple analytical model, we show that the plasmoid ejection and
acceleration are closely coupled with the reconnection process, leading to a
nonlinear instability for the whole dynamics that determines the macroscopic
reconnection rate uniquely. Next we show that the current sheet tends to have a
fractal structure via the following process path: tearing, sheet thinning,
Sweet- Parker sheet, secondary tearing, further sheet thinning... These
processes occur repeatedly at smaller scales until a microscopic plasma scale
(either the ion Larmor radius or the ion inertial length) is reached where
anomalous resistivity or collisionless reconnection can occur. The current
sheet eventually has a fractal structure with many plasmoids (magnetic islands)
of different sizes. When these plasmoids are ejected out of the current sheets,
fast reconnection occurs at various different scales in a highly time dependent
manner. Finally, a scenario is presented for fast reconnection in the solar
corona on the basis of above plasmoid-induced-reconnection in a fractal current
sheet.Comment: 9 pages, 11 figures, with using eps.sty; Earth, Planets and Space in
press; ps-file is also available at
http://stesun8.stelab.nagoya-u.ac.jp/~tanuma/study/shibata2001
Relationship between X-ray and ultraviolet emission of flares from dMe stars observed by XMM-Newton
We present simultaneous ultraviolet and X-ray observations of the dMe-type
flaring stars AT Mic, AU Mic, EV Lac, UV Cet and YZ CMi obtained with the
XMM-Newton observatory. During 40 hours of simultaneous observation we identify
13 flares which occurred in both wave bands. For the first time, a correlation
between X-ray and ultraviolet flux for stellar flares has been observed. We
find power-law relationships between these two wavelength bands for the flare
luminosity increase, as well as for flare energies, with power-law exponents
between 1 and 2. We also observe a correlation between the ultraviolet flare
energy and the X-ray luminosity increase, which is in agreement with the
Neupert effect and demonstrates that chromospheric evaporation is taking place.Comment: 8 pages, 4 figures, 3 tables, accepted by A&A (30 Sept. 2004
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