1,175 research outputs found
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
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
Emission lines of Fe X in active region spectra obtained with the Solar Extreme-ultraviolet Research Telescope and Spectrograph
Fully relativistic calculations of radiative rates and electron impact
excitation cross sections for Fe X are used to derive theoretical emission-line
ratios involving transitions in the 174-366 A wavelength range. A comparison of
these with solar active region observations obtained during the 1989 and 1995
flights of the Solar Extreme-ultraviolet Research Telescope and Spectrograph
(SERTS) reveals generally very good agreement between theory and experiment.
Several Fe X emission features are detected for the first time in SERTS
spectra, while the transition at 195.32 A is identified for the first time (to
our knowledge) in an astronomical source. The most useful Fe X electron density
diagnostic line ratios are assessed to be 175.27/174.53 and 175.27/177.24,
which both involve lines close in wavelength and free from blends, vary by
factors of 13 between Ne = 1E8 and 1E13 cm-3, and yet show little temperature
sensitivity. Should these lines not be available, then the 257.25/345.74 ratio
may be employed to determine Ne, although this requires an accurate evaluation
of the instrument intensity calibration over a relatively large wavelength
range. However, if the weak 324.73 A line of Fe X is reliably detected, the use
of 324.73/345.74 or 257.25/324.73 is recommended over 257.25/345.74.Comment: 11 pages, 10 figures, MNRAS in pres
Novel Layers for Dies Used in Electromagnetic Sheet Metal Forming Processes
Due to the high forming velocities during electromagnetic sheet metal forming processes, a high impact force acts between workpiece and die. Here, the die surface sustains high damages shown by high wear and galling of the workpiece on the die surface. To enhance the die lifetime, a novel coating concept based on the PVD (physical vapour deposition) process was developed. In doing so, the hardness and the toughness of the designed layers were varied and adjusted to the demands of AlMg-sheet forming process
Process Analysis and Physical Simulation of Electromagnetic Joining of Thin-Walled parts
To avoid typical problems when connecting different metallic materials as aluminum and titanium as e.g. the formation of intermetallic phases, electromagnetic welding represents an alternative technology to conventional (i.e. usually thermal) joining processes. Although feasibility and potential of this technique are already proved, the fundamental correlations of part- and process-parameters have not yet been investigated systematically. As an approach to examine these, the performance of model experiments and supplementary technological tests is suggested. The resulting connection quality is evaluated using metallographic methods
Process Investigation of Tube Expansion by Gas Detonation
The present paper deals with the expansion of tubes by direct application of gas
detonation waves, i.e. the gas is both pressure medium and energy source. After an introduction to gas detonation forming, measurements of the motion process and the internal pressures are presented. Results of free expansion and of forming into a die are thoroughly studied and compared to the results of quasi-static burst tests and hydroforming. Using pure aluminum Al99.5 and a medium strength alloy AlMgSi1, expansions by 25 % and 20 % respectively are obtained. A simulation delivers details on the deformation process and specially prepared probes of high-speed tension tests give new insight into metallographic material behavior at different strain rates
Motivation to study in Higher Education:a comparison between Germany and Great Britain
This article deals with reasons for the motivation to study in higher education. To find out about motives, around 200 A-level students in Germany and Great Britain were asked about their plans for the time after completion of their A-levels. Through socio-demographic data the authors could deploy facts about social backgrounds and the affiliations to socio-economic classes. There are some expected findings (e.g., British A-level students are more likely to study than their German comrades) and some pretty unexpected results (e.g., social classes do not seem to divide students into choosing university or not)
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