559 research outputs found
Solar Flare Impulsive Phase Emission Observed with SDO/EVE
Differential emission measures (DEMs) during the impulsive phase of solar
flares were constructed using observations from the EUV Variability Experiment
(EVE) and the Markov-Chain Monte Carlo method. Emission lines from ions formed
over the temperature range log T = 5.8 - 7.2 allow the evolution of the DEM to
be studied over a wide temperature range at 10s cadence. The technique was
applied to several M- and X-class flares, where impulsive phase EUV emission is
observable in the disk-integrated EVE spectra from emission lines formed up to
3 - 4 MK, and we use spatially-unresolved EVE observations to infer the thermal
structure of the emitting region. For the nine events studied the DEMs
exhibited a two component distribution during the impulsive phase, a low
temperature component with peak temperature of 1 - 2 MK, and a broad high
temperature one from 7 - 30 MK. A bimodal high temperature component is also
found for several events, with peaks at 8 and 25 MK during the impulsive phase.
The origin of the emission was verified using AIA images to be the flare
ribbons and footpoints, indicating that the constructed DEMs represent the
spatially-average thermal structure of the chromospheric flare emission during
the impulsive phase.Comment: 18 pages, 6 figures, accepted for publication in Ap
Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9
We investigated the response of the solar atmosphere to non-thermal electron
beam heating using the radiative transfer and hydrodynamics modelling code
RADYN. The temporal evolution of the parameters that describe the non-thermal
electron energy distribution were derived from hard X-ray observations of a
particular flare, and we compared the modelled and observed parameters. The
evolution of the non-thermal electron beam parameters during the X1.5 solar
flare on 2011 March 9 were obtained from analysis of RHESSI X-ray spectra. The
RADYN flare model was allowed to evolve for 110 seconds, after which the
electron beam heating was ended, and was then allowed to continue evolving for
a further 300s. The modelled flare parameters were compared to the observed
parameters determined from extreme-ultraviolet spectroscopy. The model produced
a hotter and denser flare loop than that observed and also cooled more rapidly,
suggesting that additional energy input in the decay phase of the flare is
required. In the explosive evaporation phase a region of high-density cool
material propagated upward through the corona. This material underwent a rapid
increase in temperature as it was unable to radiate away all of the energy
deposited across it by the non-thermal electron beam and via thermal
conduction. A narrow and high-density ( cm) region at
the base of the flare transition region was the source of optical line emission
in the model atmosphere. The collision-stopping depth of electrons was
calculated throughout the evolution of the flare, and it was found that the
compression of the lower atmosphere may permit electrons to penetrate farther
into a flaring atmosphere compared to a quiet Sun atmosphere.Comment: 12 pages, 12 figure
Mapping Lyman Continuum escape in Tololo 1247-232
Low redshift, spatially resolved Lyman continuum (LyC) emitters allow us to
clarify the processes for LyC escape from these starburst galaxies. We use
Hubble Space Telescope (HST) WFC3 and ACS imaging of the confirmed low-redshift
LyC emitter Tol 1247-232 to study the ionization structure of the gas and its
relation to the ionizing star clusters. We perform ionization parameter mapping
(IPM) using [O III]4959, 5007 and [O II]3727 imaging as the high- and
low-ionization tracers, revealing broad, large-scale, optically thin regions
originating from the center, and reaching the outskirts of the galaxy,
consistent with LyC escape. We carry out stellar population synthesis modeling
of the 26 brightest clusters using our HST photometry. Combining these data
with the nebular photometry, we find a global LyC escape fraction of f_esc =
0.12, with uncertainties also consistent with zero escape and with all measured
f_esc values for this galaxy. Our analysis suggests that, similar to other
candidate LyC emitters, a two-stage starburst has taken place in this galaxy,
with a 12 Myr old, massive, central cluster likely having pre-cleared regions
in and around the center, and the second generation of 2 - 4 Myr old clusters
dominating the current ionization, including some escape from the galaxy.Comment: Accepted for publication in Ap
Development of a Wiki to Promote Financial Research Collaboration at the Financial University under the Government of the Russian Federation
The International Financial Laboratory of Financial University, Moscow sought to improve long distance research collaboration among its many branches throughout Russia. Our team planned to implement online software suitable to the Financial LaboratoryÂ’s needs. We researched the benefits of working online, alongside collaborative technologies. Based on our research, we used MediaWiki to develop finlabwiki.org, an environment for the creation and storage of research projects. Finlabwiki.org connects students with similar interests and aids them in the achievement of research goals
Observational Evidence for Gentle Chromospheric Evaporation During the Impulsive Phase of a Solar Flare
Observational evidence for gentle chromospheric evaporation during the
impulsive phase of a C9.1 solar flare is presented using data from the Reuven
Ramaty High-Energy Solar Spectroscopic Imager and the Coronal Diagnostic
Spectrometer on board the Solar and Heliospheric Observatory. Until now,
evidence for gentle evaporation has often been reported during the decay phase
of solar flares, where thermal conduction is thought to be the driving
mechanism. Here we show that the chromospheric response to a low flux of
nonthermal electrons (>=5x10^9 ergs cm^-2 s^-1) results in plasma upflows of
13+/-16, 16+/-18, and 110+/-58 km s^-1 in the cool He I and O V emission lines
and the 8 MK Fe XIX line. These findings, in conjunction with other recently
reported work, now confirm that the dynamic response of the solar atmosphere is
sensitively dependent on the flux of incident electrons.Comment: 5 page
Mycobacterium abscessus: Shapeshifter of the Mycobacterial World
In this review we will focus on unique aspects of Mycobacterium abscessus (MABS) which we feel earn it the designation of “shapeshifter of the mycobacterial world.” We will review its emergence as a distinct species, the recognition and description of MABS subspecies which are only now being clearly defined in terms of pathogenicity, its ability to exist in different forms favoring a saprophytic lifestyle or one more suitable to invasion of mammalian hosts, as well as current challenges in terms of antimicrobial therapy and future directions for research. One can see in the various phases of MABS, a species transitioning from a free living saprophyte to a host-adapted pathogen
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