2,329 research outputs found
An assessment of Fe XX - Fe XXII emission lines in SDO/EVE data as diagnostics for high density solar flare plasmas using EUVE stellar observations
The Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics
Observatory obtains extreme-ultraviolet (EUV) spectra of the full-disk Sun at a
spectral resolution of ~1 A and cadence of 10 s. Such a spectral resolution
would normally be considered to be too low for the reliable determination of
electron density (N_e) sensitive emission line intensity ratios, due to
blending. However, previous work has shown that a limited number of Fe XXI
features in the 90-60 A wavelength region of EVE do provide useful
N_e-diagnostics at relatively low flare densities (N_e ~ 10^11-10^12 cm^-3).
Here we investigate if additional highly ionised Fe line ratios in the EVE
90-160 A range may be reliably employed as N_e-diagnostics. In particular, the
potential for such diagnostics to provide density estimates for high N_e
(~10^13 cm^-3) flare plasmas is assessed. Our study employs EVE spectra for
X-class flares, combined with observations of highly active late-type stars
from the Extreme Ultraviolet Explorer (EUVE) satellite plus experimental data
for well-diagnosed tokamak plasmas, both of which are similar in wavelength
coverage and spectral resolution to those from EVE. Several ratios are
identified in EVE data which yield consistent values of electron density,
including Fe XX 113.35/121.85 and Fe XXII 114.41/135.79, with confidence in
their reliability as N_e-diagnostics provided by the EUVE and tokamak results.
These ratios also allow the determination of density in solar flare plasmas up
to values of ~10^13 cm^-3.Comment: 7 pages, 3 figures, 2 tables, MNRAS in pres
RHESSI and SOHO/CDS Observations of Explosive Chromospheric Evaporation
Simultaneous observations of explosive chromospheric evaporation are
presented using data from the Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) and the Coronal Diagnostic Spectrometer (CDS) onboard SOHO. For
the first time, co-spatial imaging and spectroscopy have been used to observe
explosive evaporation within a hard X-ray emitting region. RHESSI X-ray images
and spectra were used to determine the flux of non-thermal electrons
accelerated during the impulsive phase of an M2.2 flare. Assuming a
thick-target model, the injected electron spectrum was found to have a spectral
index of ~7.3, a low energy cut-off of ~20 keV, and a resulting flux of
>4x10^10 ergs cm^-2 s^-1. The dynamic response of the atmosphere was determined
using CDS spectra, finding a mean upflow velocity of 230+/-38 km s^-1 in Fe XIX
(592.23A), and associated downflows of 36+/-16 km s^-1 and 43+/-22 km s^-1 at
chromospheric and transition region temperatures, respectively, relative to an
averaged quiet-Sun spectra. The errors represent a 1 sigma dispersion. The
properties of the accelerated electron spectrum and the corresponding
evaporative velocities were found to be consistent with the predictions of
theory.Comment: 5 pages, 4 figures, ApJL (In Press
A Si IV/O IV electron density diagnostic for the analysis of IRIS solar spectra
Solar spectra of ultraviolet bursts and flare ribbons from the Interface
Region Imaging Spectrograph (IRIS) have suggested high electron densities of
cm at transition region temperatures of 0.1 MK, based on
large intensity ratios of Si IV 1402.77 to O IV 1401.16. In
this work a rare observation of the weak O IV 1343.51 line is reported
from an X-class flare that peaked at 21:41 UT on 2014 October 24. This line is
used to develop a theoretical prediction of the Si IV 1402.77 to O IV
1401.16 ratio as a function of density that is recommended to be used
in the high density regime. The method makes use of new pressure-dependent
ionization fractions that take account of the suppression of dielectronic
recombination at high densities. It is applied to two sequences of flare kernel
observations from the October 24 flare. The first shows densities that vary
between to cm over a seven minute
period, while the second location shows stable density values of around
cm over a three minute period.Comment: 12 pages, 5 figures, submitted to Ap
Laser aiming simulation /LASIM/ Final report, Feb. 1967 - May 1968
Laser aiming simulation models for synchronous satellite optical communication system
Metal-insulator transition in a doped semiconductor
Millikelvin measurements of the conductivity as a function of donor density and uniaxial stress in bulk samples of phosphorus-doped silicon establish that the transition from metal to insulator is continuous, but sharper than predicted by scaling theories of localization. The divergence of the dielectric susceptibility as the transition is approached from below also points out problems in current scaling theories. The temperature dependence of the conductivity and the magnetoresistance in the metal indicate the importance of Coulomb interactions in describing the behavior of disordered systems
Opioid peptides promote cholera-toxin-catalysed ADP-ribosylation of the inhibitory guanine-nucleotide-binding protein (Gi) in membranes of neuroblastoma x glioma hybrid cells
Transnasal humidified rapid-insufflation ventilatory exchange ('THRIVE') in the coronavirus disease 2019 pandemic
Plasma Diagnostics of Active Region Evolution and Implications for Coronal Heating
A detailed study is presented of the decaying solar active region NOAA 10103
observed with the Coronal Diagnostic Spectrometer (CDS), the Michelson Doppler
Imager (MDI) and the Extreme-ultraviolet Imaging Telescope (EIT) onboard the
Solar and Heliospheric Observatory (SOHO). Electron density maps formed using
Si X (356.03A/347.41A) show that the density varies from ~10^10 cm^-3 in the
active region core, to ~7x10^8 cm^-3 at the region boundaries. Over the five
days of observations, the average electron density fell by ~30%. Temperature
maps formed using Fe XVI(335.41A)/Fe XIV(334.18A) show electron temperatures of
\~2.34x10^6 K in the active region core, and ~2.10x10^6 K at the region
boundaries. Similarly to the electron density, there was a small decrease in
the average electron temperature over the five day period. The radiative,
conductive, and mass flow losses were calculated and used to determine the
resultant heating rate (P_H). Radiative losses were found to dominate the
active region cooling process. As the region decayed, the heating rate
decreased by almost a factor of five between the first and last day of
observations. The heating rate was then compared to the total unsigned magnetic
flux (Phi_tot), yielding a power-law of the form P_H ~ Phi_tot^(0.81 +/- 0.32).
This result suggests that waves rather than nanoflares may be the dominant
heating mechanism in this active region.Comment: 9 pages, 11 figures. MNRAS, In Pres
Fe XI emission lines in a high resolution extreme ultraviolet spectrum obtained by SERTS
New calculations of radiative rates and electron impact excitation cross
sections for Fe XI are used to derive emission line intensity ratios involving
3s^23p^4 - 3s^23p^33d transitions in the 180-223 A wavelength range. These
ratios are subsequently compared with observations of a solar active region,
obtained during the 1995 flight Solar EUV Research Telescope and Spectrograph
(SERTS). The version of SERTS flown in 1995 incorporated a multilayer grating
that enhanced the instrumental sensitivity for features in the 170 - 225 A
wavelength range, observed in second-order between 340 and 450 A. This
enhancement led to the detection of many emission lines not seen on previous
SERTS flights, which were measured with the highest spectral resolution (0.03
A) ever achieved for spatially resolved active region spectra in this
wavelength range. However, even at this high spectral resolution, several of
the Fe XI lines are found to be blended, although the sources of the blends are
identified in the majority of cases. The most useful Fe XI electron density
diagnostic line intensity ratio is I(184.80 A)/I(188.21 A). This ratio involves
lines close in wavelength and free from blends, and which varies by a factor of
11.7 between N_e = 10^9 and 10^11 cm^-3, yet shows little temperature
sensitivity. An unknown line in the SERTS spectrum at 189.00 A is found to be
due to Fe XI, the first time (to our knowledge) this feature has been
identified in the solar spectrum. Similarly, there are new identifications of
the Fe XI 192.88, 198.56 and 202.42 A features, although the latter two are
blended with S VIII/Fe XII and Fe XIII, respectively.Comment: 21 pages, 9 gigures, accepted for publication in the Astrophysical
Journa
Structural relationships of actin, myosin, and tropomyosin revealed by cryo-electron microscopy.
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