3,841 research outputs found
Absolute radiometric calibration of the EUNIS-06 170-205 A channel and calibration update for CDS/NIS
The Extreme-Ultraviolet Normal-Incidence Spectrograph sounding-rocket payload
was flown on 2006 April 12 (EUNIS-06), carrying two independent imaging
spectrographs covering wave bands of 300-370 A in first order and 170-205 A in
second order, respectively. The absolute radiometric response of the EUNIS-06
long-wavelength (LW) channel was directly measured in the same facility used to
calibrate CDS prior to the SOHO launch. Because the absolute calibration of the
short-wavelength (SW) channel could not be obtained from the same lab
configuration, we here present a technique to derive it using a combination of
solar LW spectra and density- and temperature-insensitive line intensity
ratios. The first step in this procedure is to use the coordinated, cospatial
EUNIS and SOHO/CDS spectra to carry out an intensity calibration update for the
CDS NIS-1 waveband, which shows that its efficiency has decreased by a factor
about 1.7 compared to that of the previously implemented calibration. Then,
theoretical insensitive line ratios obtained from CHIANTI allow us to determine
absolute intensities of emission lines within the EUNIS SW bandpass from those
of cospatial CDS/NIS-1 spectra after the EUNIS LW calibration correction. A
total of 12 ratios derived from intensities of 5 CDS and 12 SW emission lines
from Fe Fe X - Fe XIII yield an instrumental response curve for the EUNIS-06 SW
channel that matches well to a relative calibration which relied on combining
measurements of individual optical components. Taking into account all
potential sources of error, we estimate that the EUNIS-06 SW absolute
calibration is accurate to about 20%.Comment: 11 pages, 10 figures, 4 tables. 2010, ApJ Suppl. In pres
Underflight calibration of SOHO/CDS and Hinode/EIS with EUNIS-07
Flights of Goddard Space Flight Center's Extreme-Ultraviolet Normal-Incidence
Spectrograph (EUNIS) sounding rocket in 2006 and 2007 provided updated
radiometric calibrations for SOHO/CDS and Hinode/EIS. EUNIS carried two
independent imaging spectrographs covering wavebands of 300-370 A in first
order and 170-205 A in second order. After each flight, end-to-end radiometric
calibrations of the rocket payload were carried out in the same facility used
for pre-launch calibrations of CDS and EIS. During the 2007 flight, EUNIS, SOHO
CDS and Hinode EIS observed the same solar locations, allowing the EUNIS
calibrations to be directly applied to both CDS and EIS. The measured CDS NIS 1
line intensities calibrated with the standard (version 4) responsivities with
the standard long-term corrections are found to be too low by a factor of 1.5
due to the decrease in responsivity. The EIS calibration update is performed in
two ways. One is using the direct calibration transfer of the calibrated
EUNIS-07 short wavelength (SW) channel. The other is using the insensitive line
pairs, in which one member was observed by EUNIS-07 long wavelength (LW)
channel and the other by EIS in either LW or SW waveband. Measurements from
both methods are in good agreement, and confirm (within the measurement
uncertainties) the EIS responsivity measured directly before the instrument's
launch. The measurements also suggest that the EIS responsivity decreased by a
factor of about 1.2 after the first year of operation. The shape of the EIS SW
response curve obtained by EUNIS-07 is consistent with the one measured in
laboratory prior to launch. The absolute value of the quiet-Sun He II 304 A
intensity measured by EUNIS-07 is consistent with the radiance measured by CDS
NIS in quiet regions near the disk center and the solar minimum irradiance
obtained by CDS NIS and SDO/EVE recently.Comment: 16 pages, 14 figures, 5 tables, accepted by ApJ Supplement (Sep.
2011
Evidence of Explosive Evaporation in a Microflare Observed by Hinode/EIS
We present a detailed study of explosive chromospheric evaporation during a
microflare which occurred on 2007 December 7 as observed with the EUV Imaging
Spectrometer (EIS) onboard Hinode. We find temperature-dependent upflows for
lines formed from 1.0 to 2.5 MK and downflows for lines formed from 0.05 to
0.63 MK in the impulsive phase of the flare. Both the line intensity and the
nonthermal line width appear enhanced in most of the lines and are temporally
correlated with the time when significant evaporation was observed. Our results
are consistent with the numerical simulations of flare models, which take into
account a strong nonthermal electron beam in producing the explosive
chromospheric evaporation. The explosive evaporation observed in this
microflare implies that the same dynamic processes may exist in events with
very different magnitudes.Comment: 14 pages, 8 figures. Accepted for publication in the Astrophysical
Journa
The problem of causality in cultivation research
This paper offers an up-to-date review of problems in determining causal relationships in cultivation research, and considers the research rationales of various approaches with special reference to causal interpretation. It describes in turn a number of methodologies for addressing the problem and resolving it as far as this is possible. The issue of causal inference arises not only in cultivation research, however, but is basic to all media effects theories and approaches primarily at the macro-level whose main methodology rests on correlational studies (agenda-setting, spiral of silence, knowledge gap hypothesis, etc.). We therefore first discuss problems of causal interpretation in connection with the cultivation hypothesis, and then sketch in summary how these problems arise with other media effects theories. We first set out the basic features of the cultivation approach, then consider the difficulties with correlational studies and discuss alternative research designs - designs which are not original to us, but have been adapted for cultivation research. These comprise laboratory experiments, sequential studies, social studies and time-series procedures. Finally, we argue for multiple approaches that complement one another's advantages and balance out their disadvantages
Spatially-Resolved Nonthermal Line Broadening During The Impulsive Phase of a Solar Flare
This paper presents a detailed study of excess line broadening in EUV
emission lines during the impulsive phase of a C-class solar flare. In this
work, which utilizes data from the EUV Imaging Spectrometer (EIS) onboard
Hinode, the broadened line profiles were observed to be co-spatial with the two
HXR footpoints as observed by RHESSI. By plotting the derived nonthermal
velocity for each pixel within the Fe XV and Fe XVI rasters against its
corresponding Doppler velocity a strong correlation (|r| > 0.59) was found
between the two parameters for one of the footpoints. This suggested that the
excess broadening at these temperatures is due to a superposition of flows
(turbulence), presumably as a result of chromospheric evaporation due to
nonthermal electrons. Also presented are diagnostics of electron densities
using five pairs of density-sensitive line ratios. Density maps derived using
the Mg XII and Si X line pairs showed no appreciable increase in electron
density at the footpoints, while the Fe XII, Fe XIII, and Fe XIV line pairs
revealed densities approaching 10^(11.5) cm^(-3). Using this information, the
nonthermal velocities derived from the widths of the two Fe XIV lines were
plotted against their corresponding density values derived from their ratio.
This showed that pixels with large nonthermal velocities were associated with
pixels of moderately higher densities. This suggests that nonthermal broadening
at these temperatures may have been due to enhanced densities at the
footpoints, although estimates of the amount of opacity broadening and pressure
broadening appeared to be negligible.Comment: 11 pages, 10 figures. Accepted to Ap
Non-linear model-predictive-control for thermomechanical ring rolling
he authors present a new ring rolling variant that combines a semi-warm forming process of a bearing ring with controlled cooling directly followed by a cold forming process. The aim is to produce near net shape rings with a selected microstructure and high strength without additional consecutive heat treatment. To achieve this, a new and fast control strategy is necessary that not only controls the geometrical forming of the ring, but also considers temperature development and microstructure formation. The proposed control strategy is based on the application of a fast semi-analytical simulation model with a very short response time in combination with a FE-analysis of the thermomechanical ring rolling process. The semianalytical model is used as a predictor and a parallel FEA or experimental results as a corrector for the control model. The aim is to correctly identify transient process parameters needed to achieve defined product properties as a basis for a later implementation in a non-linear modelpredictive-control of thermomechanical ring rolling. The new approach will be described in detail and demonstrated numerically and experimentally
A novel indicator for kinematic hardening effect quantification in deep drawing simulation
Deep drawing simulation techniques reduce tool design costs and improve tool performance and reliability. In terms of strain hardening, mixed models capturing the kinematic effect are sometimes more accurate than isotropic models. Indeed, nonlinearity in strain paths can lead to inconsistent simulation results. However, the use of such models requires a greater number of tests including strain path changes. Therefore, the use of such mixed models shall be required only if the simulation includes non-linear strain paths and the material exhibits a pronounced Bauschinger effect. New tools to help engineers choose between models could ease the spread of more advanced models in simulation of deep drawing processes when needed. With this in mind, an indicator predicting the influence of kinematic effects could help to select an adequate model. In this study, a new indicator is introduced with the idea of characterising strain path non-linearity in order to assess kinematic hardening influence. The indicator is computed using the forming history taken from a purely isotropic simulation – which is easier to set up and parametrise. The ability of the indicator to predict inconsistencies within the isotropic simulation is investigated using U-channel simulations
Emission lines of Fe XI in the 257--407 A wavelength region observed in solar spectra from EIS/Hinode and SERTS
Theoretical emission-line ratios involving Fe XI transitions in the 257-407 A
wavelength range are derived using fully relativistic calculations of radiative
rates and electron impact excitation cross sections. These are subsequently
compared with both long wavelength channel Extreme-Ultraviolet Imaging
Spectrometer (EIS) spectra from the Hinode satellite (covering 245-291 A), and
first-order observations (235-449 A) obtained by the Solar Extreme-ultraviolet
Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and 276.36 A
lines of Fe XI are detected in two EIS spectra, confirming earlier
identifications of these features, and 276.36 A is found to provide an electron
density diagnostic when ratioed against the 257.55 A transition. Agreement
between theory and observation is found to be generally good for the SERTS data
sets, with discrepancies normally being due to known line blends, while the
257.55 A feature is detected for the first time in SERTS spectra. The most
useful Fe XI electron density diagnostic is found to be the 308.54/352.67
intensity ratio, which varies by a factor of 8.4 between N_e = 10^8 and 10^11
cm^-3, while showing little temperature sensitivity. However, the 349.04/352.67
ratio potentially provides a superior diagnostic, as it involves lines which
are closer in wavelength, and varies by a factor of 14.7 between N_e = 10^8 and
10^11 cm^-3. Unfortunately, the 349.04 A line is relatively weak, and also
blended with the second-order Fe X 174.52 A feature, unless the first-order
instrument response is enhanced.Comment: 9 pages, 5 figures, 13 tables; MNRAS in pres
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