Scaling laws of solar and stellar flares

In this study we compile for the first time comprehensive data sets of solar and stellar flare parameters, including flare peak temperatures T_p, flare peak volume emission measures EM_p, and flare durations t_f from both solar and stellar data, as well as flare length scales L from solar data. Key results are that both the solar and stellar data are consistent with a common scaling law of EM_p ~ T_p^4.7, but the stellar flares exhibit ~250 times higher emission measures (at the same flare peak temperature). For solar flares we observe also systematic trends for the flare length scale L(T_p) ~ T_p^0.9 and the flare duration t_F(T_p) ~ T_p^0.9 as a function of the flare peak temperature. Using the theoretical RTV scaling law and the fractal volume scaling observed for solar flares, i.e., V(L) ~ L^2.4, we predict a scaling law of EM_p ~ T_p^4.3, which is consistent with observations, and a scaling law for electron densities in flare loops, n_p ~ T_p^2/L ~ T_p^1.1. The RTV-predicted electron densities were also found to be consistent with densities inferred from total emission measures, n_p=(EM_p/q_V*V)^1/2, using volume filling factors of q_V=0.03-0.08 constrained by fractal dimensions measured in solar flares. Our results affect also the determination of radiative and conductive cooling times, thermal energies, and frequency distributions of solar and stellar flare energies.Comment: 9 Figs., (paper in press, The Astrophsycial Journal

Comprehensive Simulation of Vertical Cavity Surface Emitting Lasers: Inclusion of a Many-Body Gain Model

This paper describes a comprehensive simulation technique for semiconductor lasers. In particular, a many-body calculation of optical gain for the quantum-well region is integrated into a multi-dimensional electro-opto-thermal simulator. Simulation results of material gain and DC device data of a commercial 850 nm Vertical Cavity Surface Emitting Lasers (VCSEL) are compared to measurements. They illustrate the validity of the approac

X-Ray Spectroscopy of Stars

(abridged) Non-degenerate stars of essentially all spectral classes are soft X-ray sources. Low-mass stars on the cooler part of the main sequence and their pre-main sequence predecessors define the dominant stellar population in the galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense, of X-ray spectra from the solar corona. X-ray emission from cool stars is indeed ascribed to magnetically trapped hot gas analogous to the solar coronal plasma. Coronal structure, its thermal stratification and geometric extent can be interpreted based on various spectral diagnostics. New features have been identified in pre-main sequence stars; some of these may be related to accretion shocks on the stellar surface, fluorescence on circumstellar disks due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot stars clearly dominate the interaction with the galactic interstellar medium: they are the main sources of ionizing radiation, mechanical energy and chemical enrichment in galaxies. High-energy emission permits to probe some of the most important processes at work in these stars, and put constraints on their most peculiar feature: the stellar wind. Here, we review recent advances in our understanding of cool and hot stars through the study of X-ray spectra, in particular high-resolution spectra now available from XMM-Newton and Chandra. We address issues related to coronal structure, flares, the composition of coronal plasma, X-ray production in accretion streams and outflows, X-rays from single OB-type stars, massive binaries, magnetic hot objects and evolved WR stars.Comment: accepted for Astron. Astrophys. Rev., 98 journal pages, 30 figures (partly multiple); some corrections made after proof stag

Optische Einrichtung, Kamera sowie Verfahren zur Verschiebung einer optischen Achse

Also published as: DE102013112357(A1)patent submitter:ZHAW Zürcher Hochschule für Angewandte WissenschaftenDie Erfindung betrifft eine optische Einrichtung, die derart ausgestaltet ist, dass die optische Achse einer Linseneinheit der optischen Einrichtung lateral versetzbar ist. Es ist erfindungsgemäss vorgesehen, dass die optische Einrichtung (1) eine Linseneinheit (20) sowie eine die Linseneinheit (20) in Richtung deren optischer Achse (21) stützende Axial-Lagerungseinrichtung (30) umfasst, die mit wenigstens einem elektroaktiven Materialbauteil (40) mechanisch gekoppelt ist, welches eine parallel zur optischen Achse (21) wirkende Kraftkomponente (Fz) in Richtung der Axial-Lagerungseinrichtung (30) realisiert, und mit welchem bei Variation der an ihm angelegten elektrischen Spannung auf Grund der dadurch erzeugten Form- und/ oder Längenänderung die Linseneinheit (20) translatorisch in einer Ebene, die im Wesentlichen senkrecht zur optischen Achse (21) der Linseneinheit (20); verläuft, bewegbar ist, wobei die Axial-Lagerungseinrichtung (30) eine Gegengraft (Fg) zu der von dem elektroaktiven Materialbauteil (40) parallel zur optischen Achse (21) aufgebrachten Kraftkomponente (Fz) realisiert. Die Axial-Lagerungseinrichtung (30) ist derart ausgestaltet, dass sie eine Verschiebung der Linseneinheit (20) und somit einen lateralen Versatz der optischen Achse (21) der Linseneinheit (20) ermöglicht. Des Weiteren betrifft die vorliegende Erfindung eine Kamera mit der erfindungsgemässen optischen Einrichtung sowie ein Verfahren zur Verschiebung einer optischen Achse einer Linseneinheit der erfindungsgemässen optischen Einrichtung

Comprehensive Simulation of Vertical Cavity Surface Emitting Lasers: Inclusion of a Many-Body Gain Model

ISSN:1569-8025ISSN:1572-813