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)