1,422 research outputs found
The Wave Properties of Coronal Bright Fronts Observed Using SDO/AIA
Coronal bright fronts (CBFs) are large scale wavefronts that propagate though
the solar corona at hundreds of kilometers per second. While their kinematics
have been studied in detail, many questions remain regarding the temporal
evolution of their amplitude and pulse width. Here, contemporaneous high
cadence, multi-thermal observations of the solar corona from the Solar Dynamic
Observatory (SDO) and Solar TErrestrial RElations Observatory (STEREO)
spacecraft are used to determine the kinematics and expansion rate of a CBF
wavefront observed on 2010 August 14. The CBF was found to have a lower initial
velocity with weaker deceleration in STEREO observations compared to SDO (~340
km/s and -72 m/s/s as opposed to ~410 km/s and -279 m/s/s). The CBF kinematics
from SDO were found to be highly passband-dependent, with an initial velocity
ranging from 379+/-12 km/s to 460+/-28 km/s and acceleration ranging from
-128+/-28 m/s/s to -431+/-86 m/s/s in the 335A and 304A passbands respectively.
These kinematics were used to estimate a quiet coronal magnetic field strength
range of ~1-2 G. Significant pulse broadening was also observed, with expansion
rates of ~130 km/s (STEREO) and ~220 km/s (SDO). By treating the CBF as a
linear superposition of sinusoidal waves within a Gaussian envelope, the
resulting dispersion rate of the pulse was found to be ~8-13 Mm^2 s^-1. These
results are indicative of a fast-mode magnetoacoustic wave pulse propagating
through an inhomogeneous medium.Comment: 14 pages, 2 figures. Accepted for publication in The Astrophysical
Journal Letter
First SDO AIA Observations of a Global Coronal EUV "Wave": Multiple Components and "Ripples"
We present the first SDO AIA observations of a global coronal EUV disturbance
(so-called "EIT wave") revealed in unprecedented detail. The disturbance
observed on 2010 April 8 exhibits two components: one diffuse pulse
superimposed on which are multiple sharp fronts that have slow and fast
components. The disturbance originates in front of erupting coronal loops and
some sharp fronts undergo accelerations, both effects implying that the
disturbance is driven by a CME. The diffuse pulse, propagating at a uniform
velocity of 204-238 km/s with very little angular dependence within its extent
in the south, maintains its coherence and stable profile for ~30 minutes. Its
arrival at increasing distances coincides with the onsets of loop expansions
and the slow sharp front. The fast sharp front overtakes the slow front,
producing multiple "ripples" and steepening the local pulse, and both fronts
propagate independently afterwards. This behavior resembles the nature of real
waves. Unexpectedly, the amplitude and FWHM of the diffuse pulse decrease
linearly with distance. A hybrid model, combining both wave and non-wave
components, can explain many, but not all, of the observations. Discoveries of
the two-component fronts and multiple ripples were made possible for the first
time thanks to AIA's high cadences (10-20 s) and high signal-to-noise ratio.Comment: 7 pages, 5 figure
Deceleration and Dispersion of Large-scale Coronal Bright Fronts
One of the most dramatic manifestations of solar activity are large-scale
coronal bright fronts (CBFs) observed in extreme ultraviolet (EUV) images of
the solar atmosphere. To date, the energetics and kinematics of CBFs remain
poorly understood, due to the low image cadence and sensitivity of previous EUV
imagers and the limited methods used to extract the features. In this paper,
the trajectory and morphology of CBFs was determined in order to investigate
the varying properties of a sample of CBFs, including their kinematics and
pulse shape, dispersion, and dissipation. We have developed a semi-automatic
intensity profiling technique to extract the morphology and accurate positions
of CBFs in 2.5-10 min cadence images from STEREO/EUVI. The technique was
applied to sequences of 171A and 195A images from STEREO/EUVI in order to
measure the wave properties of four separate CBF events. Following launch at
velocities of ~240-450kms^{-1} each of the four events studied showed
significant negative acceleration ranging from ~ -290 to -60ms^{-2}. The CBF
spatial and temporal widths were found to increase from ~50 Mm to ~200 Mm and
~100 s to ~1500 s respectively, suggesting that they are dispersive in nature.
The variation in position-angle averaged pulse-integrated intensity with
propagation shows no clear trend across the four events studied. These results
are most consistent with CBFs being dispersive magnetoacoustic waves.Comment: 15 pages, 18 figure
First observations of a dome-shaped large-scale coronal EUV wave
We present first observations of a dome-shaped large-scale EUV coronal wave,
recorded by the EUVI instrument onboard STEREO-B on January 17, 2010. The main
arguments that the observed structure is the wave dome (and not the CME) are:
a) the spherical form and sharpness of the dome's outer edge and the erupting
CME loops observed inside the dome; b) the low-coronal wave signatures above
the limb perfectly connecting to the on-disk signatures of the wave; c) the
lateral extent of the expanding dome which is much larger than that of the
coronal dimming; d) the associated high-frequency type II burst indicating
shock formation low in the corona. The velocity of the upward expansion of the
wave dome ( km s) is larger than that of the lateral
expansion of the wave ( km s), indicating that the upward
dome expansion is driven all the time, and thus depends on the CME speed,
whereas in the lateral direction it is freely propagating after the CME lateral
expansion stops. We also examine the evolution of the perturbation
characteristics: First the perturbation profile steepens and the amplitude
increases. Thereafter, the amplitude decreases with r, the
width broadens, and the integral below the perturbation remains constant. Our
findings are consistent with the spherical expansion and decay of a weakly
shocked fast-mode MHD wave.Comment: Astrophysical Journal Letters, in pres
Does Every Quasar Harbor A Blazar?
Assuming there is a blazar type continuum in every radio-loud quasar, we find
that the free-free heating due to the beamed infrared continuum can greatly
enhance collisionally excited lines, and thus explain the stronger CIV
1549 line emission observed in radio loud quasars. We further predict
that the CIV line should show variability {\it not} associated with observed
continuum or Ly variability.Comment: 15 pages, 3 figures; to appear in Astrophys. J. Let
Investigation of the Formation and Separation of An EUV Wave from the Expansion of A Coronal Mass Ejection
We address the nature of EUV waves through direct observations of the
formation of a diffuse wave driven by the expansion of a coronal mass ejection
(CME) and its subsequent separation from the CME front. The wave and the CME on
2011 June 7 were well observed by Atmospheric Imaging Assembly onboard Solar
Dynamic Observatory. Following the solar eruption onset, marked by the
beginning of the rapid increasing of the CME velocity and the X-ray flux of
accompanying flare, the CME exhibits a strong lateral expansion. During this
impulsive expansion phase, the expansion speed of the CME bubble increases from
100 km s to 450 km s in only six minutes. An important finding is
that a diffuse wave front starts to separate from the front of the expanding
bubble shortly after the lateral expansion slows down. Also a type-II burst is
formed near the time of the separation. After the separation, two distinct
fronts propagate with different kinematic properties. The diffuse front travels
across the entire solar disk; while the sharp front rises up, forming the CME
ejecta with the diffuse front ahead of it. These observations suggest that the
previously termed EUV wave is a composite phenomenon and driven by the CME
expansion. While the CME expansion is accelerating, the wave front is cospatial
with the CME front, thus the two fronts are indiscernible. Following the end of
the acceleration phase, the wave moves away from the CME front with gradually
an increasing distance between them.Comment: 13 pages, 4 figures, accepted for publication in The Astrophysical
Journal Letter
The Drinfel'd twisted XYZ model
We construct a factorizing Drinfel'd twist for a face type model equivalent
to the XYZ model. Completely symmetric expressions for the operators of the
monodromy matrix are obtained.Comment: 15 pages, 4 figures, second preprint no. added, reference [14] added,
typos correcte
One-pot thiol–amine bioconjugation to maleimides: simultaneous stabilisation and dual functionalisation
Maleimide chemistry is widely used in the site-selective modification of proteins. However, hydrolysis of the resultant thiosuccinimides is required to provide robust stability to the bioconjugates. Herein, we present an alternative approach that affords simultaneous stabilisation and dual functionalisation in a one pot fashion. By consecutive conjugation of a thiol and an amine to dibromomaleimides, we show that aminothiomaleimides can be generated extremely efficiently. Furthermore, the amine serves to deactivate the electrophilicity of the maleimide, precluding further reactivity and hence generating stable conjugates. We have applied this conjugation strategy to peptides and proteins to generate stabilised trifunctional conjugates. We propose that this stabilisation-dual modification strategy could have widespread use in the generation of diverse conjugates
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