Numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere

Three-dimensional numerical simulations with CO5BOLD, a new radiation hydrodynamics code, result in a dynamic, thermally bifurcated model of the non-magnetic chromosphere of the quiet Sun. The 3-D model includes the middle and low chromosphere, the photosphere, and the top of the convection zone, where acoustic waves are excited by convective motions. While the waves propagate upwards, they steepen into shocks, dissipate, and deposit their mechanical energy as heat in the chromosphere. Our numerical simulations show for the first time a complex 3-D structure of the chromospheric layers, formed by the interaction of shock waves. Horizontal temperature cross-sections of the model chromosphere exhibit a network of hot filaments and enclosed cool regions. The horizontal pattern evolves on short time-scales of the order of typically 20 - 25 seconds, and has spatial scales comparable to those of the underlying granulation. The resulting thermal bifurcation, i.e., the co-existence of cold and hot regions, provides temperatures high enough to produce the observed chromospheric UV emission and -- at the same time -- temperatures cold enough to allow the formation of molecules (e.g., carbon monoxide). Our 3-D model corroborates the finding by Carlsson & Stein (1994) that the chromospheric temperature rise of semi-empirical models does not necessarily imply an increase in the average gas temperature but can be explained by the presence of substantial spatial and temporal temperature inhomogeneities.Comment: 18 pages, 13 figures, accepted by Astronomy & Astrophysics (30/10/03

g factor of lithiumlike silicon 28Si11+

The g factor of lithiumlike 28Si11+ has been measured in a triple-Penning trap with a relative uncertainty of 1.1x10^{-9} to be g_exp=2.0008898899(21). The theoretical prediction for this value was calculated to be g_th=2.000889909(51) improving the accuracy to 2.5x10^{-8} due to the first rigorous evaluation of the two-photon exchange correction. The measured value is in excellent agreement with the state-of-the-art theoretical prediction and yields the most stringent test of bound-state QED for the g factor of the 1s^22s state and the relativistic many-electron calculations in a magnetic field

Phosphat-Mobilisierung durch Haupt- und Zwischenfrüchte nach Düngung von weicherdigem Rohphosphat im ökologischen Landbau

Obwohl die agronomische Wirksamkeit von weicherdigem Rohphosphat gering ist, wird weicherdiges Rohphosphat im organischen Landbau gedüngt. Das Ziel des Projektes war es in Feld- und Gefäßversuchen in einer Fruchtfolge 2002/2003 und 2003/2004 zu prüfen, ob weicherdiges Rohphosphat von phosphataneignungseffizienten Pflanzen (Weißlupine und Ackerbohne) für phosphataneignungsineffiziente Pflanzen (Spinat und Mais) mobilisiert wird. Es zeigte sich, dass die P-Aufnahme von Spinat in einer Fruchtfolge mit Weißlupine und Ackerbohne höher war als in einer Fruchtfolge mit Sommerweizen. In Gefäßversuchen führte die Applikation von neuem Thomasphosphat (CaHPO4) zu einer höher Phosphataufnahme der Pflanzen als Rohphosphat