http://hdl.handle.net/2160/283 Sun, 19 May 2013 23:48:03 GMT 2013-05-19T23:48:03Z http://hdl.handle.net/2160/12463 Are solar maximum fan streamers a consequence of twisting sheet structures? Morgan, H.; Habbal, S. R. Fan streamers are often observed at low to mid latitudes in the corona at solar maximum, appearing narrow in latitudinal extent near the Sun, and fanning out with height, adopting an approximately linear, but not necessarily radial, configuration above ~3 Rȯ. Aims: We offer arguments to support the conjecture that such structures may sometimes consist of high density, non-uniform sheets, viewed edge-on near the Sun, and twisting to a more face-on alignment by 3 Rȯ. Methods: EUV and white light observations of a fan streamer observed on 2000/12/05 are analyzed. A simple 3D density model is used to recreate the streamer structure. Results: EIT images show a thin bright sheet at the base of the streamer. The continuation of this structure through the EIT, MLSO MKIV coronameter, and LASCO C2 fields of view, suggests that this sheet is formed mostly of open magnetic field lines. The overall large-scale appearance of the streamer is well simulated by a simple model of a twisting high-density sheet. If the twisting-sheet conjecture is valid, there is a correlation between the distribution of enhanced rays within the streamer viewed in white light, and the distribution of small regions of enhanced brightness seen on the disk in EIT 171 Å at the position of the streamer base. Conclusions: .We suggest that the apparent poleward divergence of equatorial coronal rays, or threads, seen during solar maximum above active regions, may sometimes be a consequence of such a twisting sheet topology. Morgan, H.; Habbal, S. R., Morgan, Are solar maximum fan streamers a consequence of twisting sheet structures?, Astronomy & Astrophysics, 465, L47, 2007 Tue, 03 Apr 2007 00:00:00 GMT http://hdl.handle.net/2160/12463 2007-04-03T00:00:00Z http://hdl.handle.net/2160/7904 Noncommutative independence in the infinite braid and symmetric group Köstler, Claus; Gohm, Rolf This is an introductory paper about our recent merge of a noncommutative de Finetti type result with representations of the infinite braid and symmetric group which allows to derive factorization properties from symmetries. We explain some of the main ideas of this approach and work out a constructive procedure to use in applications. Finally we illustrate the method by applying it to the theory of group characters. Gohm, R., Köstler, C. (2012). Noncommutative independence in the infinite braid and symmetric group. Banach Center Publications, 96 pp. 193-206. Wed, 07 Nov 2012 00:00:00 GMT http://hdl.handle.net/2160/7904 2012-11-07T00:00:00Z http://hdl.handle.net/2160/7901 Transfer Functions for Pairs of Wandering Subspaces Gohm, Rolf Arendt, Wolfgang; Ball, Joseph; Behrndt, Jussi; Foerster, Karl-Heinz; Mehrmann, Volker; Trunk, Carsten To a pair of subspaces wandering with respect to a row isometry we associate a transfer function which in general is multi-Toeplitz and in interesting special cases is multi-analytic. Then we describe in an expository way how characteristic functions from operator theory as well as transfer functions from noncommutative Markov chains fit into this scheme. Gohm, R. (2012)., Transfer functions for pairs of wandering subspaces, In: Spectral Theory, Mathematical System Theory, Evolution Equations, Differential and Difference Equations, 221, pp.385-398 21st International Workshop on Operator Theory and Applications, Berlin, July 2010. Arendt, W., Ball, J. A., Behrndt, J., Forster, K-H., Mehrmann, V., Trunk, C. (eds.) Wed, 07 Nov 2012 00:00:00 GMT http://hdl.handle.net/2160/7901 2012-11-07T00:00:00Z http://hdl.handle.net/2160/7640 Characteristic Functions of Liftings Gohm, R.; Dey, S. We introduce characteristic functions for certain contractive liftings of row contractions. These are multi-analytic operators which classify the liftings up to unitary equivalence and provide a kind of functional model. The most important cases are subisometric and coisometric liftings. We also identify the most general setting which we call reduced liftings. We derive properties of these new characteristic functions and discuss the relation to Popescu's definition for completely non-coisometric row contractions. Finally we apply our theory to completely positive maps and prove a one-to-one correspondence between the fixed point sets of completely positive maps related to each other by a subisometric lifting. Gohm, R. (2011). Characteristic functions of liftings. Journal of Operator Theory, 65, 17-45. Mon, 31 Oct 2011 00:00:00 GMT http://hdl.handle.net/2160/7640 2011-10-31T00:00:00Z