Von Bremen über Bologna nach Bremen – Zur Neustrukturierung der LehrerInnenbildung an der Universität Bremen

Mit Blick auf die Bremer LehrerInnenbildung (… gibt der Autor) zunächst einen knappen Überblick über deren universitäre Strukturen (…), um dann den erziehungswissenschaftlichen Anteil – den sogenannten Professionalisierungsbereich Erziehungswissenschaft – in den Studiengängen zu erläutern. Da seit wenigen Monaten aus guten Gründen eine neuerliche Reform der Struktur der LehrerInnenbildung ansteht, (… werden) anschließend die gemachten guten Erfahrungen ebenso wie die Schwierigkeiten und Fehler skizziert und durch bisher diskutierte Reformperspektiven ergänzt (…), bevor ein kurzer bilanzierender Ausblick die Überlegungen beschließt. (DIPF/ Orig.

A Relativistic Quark Model for Mesons with an Instanton-Induced Interaction

We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation. Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with a natural solution of the $U_A(1)$ problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this paper, we will also discuss our results concerning numerous meson decay properties. For processes like $\pi^+/K^+\to e^+\nu_e\gamma$ and $0^-\to\gamma\gamma$ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors of the $K_{\ell 3}$ decay and on the decay constants of the $\pi$, $K$ and $\eta$ mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged $\pi$ and $K$ mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data.Comment: 30 pages including 10 tables and 16 figures; submitted to Eur. Phys. J. A; misprints correcte

"Freude aus Verunsicherung ziehn - wer hat uns das denn beigebracht!" (Christa Wolf). Über den Zusammenhang von Negativität und Macht

Der zweite Teil des Bandes präsentiert "Analysen zum Verhältnis von Macht und Negativität". Der Autor untersucht Zusammenhänge zwischen "Negativität und Macht", welche auf Beziehungen zwischen "Kritik und Negativität" verweisen. In einer "kleinen Topographie der Negativität" deutet er Negativität mit Kierkegaard als eine "Wunde", in der unterschiedliche Denkformen zusammentreffen. Diese weisen Beziehungen zu Machtgefügen auf, in denen Macht weder kausal noch intentional, sondern in Wechselwirkung mit Freiheit als eine "ambivalente Strategie gleichzeitiger Affirmation und Negation" auftritt. Der Beitrag schließt mit Hinweisen auf "Aspekte einer pädagogischen Praxis der Negativität" und macht auf das Fehlen einer "Fehlerkultur", die Erschwerung einer "solidarischen Sozialisierung" durch "wechselseitige Konkurrenz" und die "Immunisierung gegen andere und anderes", aber auch auf einen kritischen und widerständigen Umgang mit diesen Sachverhalten aufmerksam. (DIPF/Orig.

Weak Decays Of Heavy Mesons In A Covariant Quark Model

In this paper we investigate weak decays of heavy mesons in the framework of a covariant quark model, which is based on the Bethe-Salpeter equation in instantaneous approximation. Apart from a phenomenological confinement potential, a residual interaction induced by instantons is adopted. Masses and many decay observables of light mesons have already been described successfully in this model. An appropiate extension allows a unified description of light and heavy systems. Using a set of parameters which are fixed by the mass spectra, we evaluate the form factors of semileptonic decays of charmed and bottom mesons. In the heavy quark limit these can be reduced to the Isgur-Wise function, which is calculated. Finally the form factors are used to determine the non-leptonic decay rates of B mesons in the factorization approximation.Comment: 20 pages including 13 tables and 6 figures; Corrected typo

Aufbau, Charakterisierung und Inbetriebnahme des 1.4 THz Kanals des Heterodyn-Empfängers GREAT

This thesis describes the characterisation and commissioning of the heterodyne receiver "German REceiver for Astronomy at Terahertz frequencies" (GREAT) aboard of the airborne "Stratospheric Observatory For Infrared Astronomy" (SOFIA). GREAT is a modular dual-channel-receiver designed for frequencies between 1.25 and 4.7 THz. Currently three single-pixel frequency channels are available. A fourth one is currently under construction and two multi-pixel systems are planned for 2014. In the frequency range observable with GREAT one can find a lot of transitions of molecules, such as rotational transitions of CO, and of atoms and ions, e.g the fine structure lines of C+ and O. Line emission of these transitions is often observed in photon-dominated regions (PDR) in space. These regions form at the edges of denser clouds of the interstellar medium which are illuminated by strong UV fields, e.g. of nearby OB-""stars. The UV-radiation heats up the gas and dust of the cloud and dissociates and ionizes the gas particles. These reactions depend on the intensity of the UV field, which drops down with increasing depth inside the clouds, and the density, which rises, leading to a characteristic stratification of the ions, atoms and molecules. After two short introductory chapters describing astronomy and receivers in the THz regime and especially the GREAT receiver and the SOFIA observatory, this thesis starts with a description of the build-up of the local oscillator (LO) for the L#1-channel (1.25-1.5 THz) of GREAT. This includes the design of a cross-channel LO housing and its certification by NASA and FAA. Then the used frequency multiplier chains, manufactured by Virginia Diodes Inc., are characterised. Afterwards the developed control electronics and security circuits for these chains are presented. The next chapter is dedicated to the commissioning of GREAT on SOFIA. GREAT's configuration during the first flights consisted of the L#1- and L#2-channel (1.82-1.92 THz). A short note on the adjustment of the cross-channel common optics is given. Then, the text presents a description of the developed alignment procedures and methods to derive the positions of the GREAT beam in SOFIA's focal plane and on its sub-reflector. Final values for pointing, telescope coupling and co-alignment between the two channels measured before the first and second flight series (April and July 2011) are given. The sensitivity and stability of the GREAT system are investigated. Noise temperatures of the L#1-channel lie in the range of 1200-1400 K, for the L#2-channel in the range of 1300-1800 K. The spectroscopic Allan times are above 100 seconds. The fifth chapter of this thesis presents results of the Cepheus B (CepB) project, one of the first observed with GREAT on SOFIA. CepB is part of a giant molecular cloud and shows sequential star formation. The UV radiation of a nearby OB star cluster illuminates the cloud surface, thereby creating several PDRs and possibly triggering new star formation processes. The existence of several embedded stars, including a luminous B-star, inside CepB is known. The aim of this project is to measure the dynamics of the triggering of star formation by UV radiation. [CII] and high rotational transitions of CO are used to trace the hot gas in CepB. A velocity resolved map containing the embedded star, two PDRs and two dense clumps was observed. Integrated-intensity maps are presented showing emission which is consistent with previous radio continuum and 13CO observations. A global velocity gradient across the map is visible in the velocity channel maps of [CII]. A value of (3.6 +/- 0.6) * 10^{-3} km/s*arcsec^{-1} was calculated which is consistent with former observations of Beuther et al. (2000). [CII] and CO(11-10) observations show a localized inversion of this gradient between the positions of two CO(11-10) emission maxima. Three possible scenarios are proposed for this discovery and further high resolution CO and [NII] observations to clarify this situation are suggested. Together with 13CO observations of Mookerjea et al. (2006), a clear stratification, consistent with the expected emission pattern of a simple 1-dimensional PDR, in a region of the map near the embedded star was observed. The embedded star is found to be the source of the UV radiation creating this PDR. The distances between the emission maxima were measured and compared with model calculations. The results are consistent with Mookerjea's and constrain the surface density of the PDR to 10^4 - 10^6 cm^{-3}

The Meson Spectrum in a Covariant Quark Model

Within the framework of the instantaneous Bethe-Salpeter equation, we present a detailed analysis of light meson spectra with respect to various parameterizations of confinement in Dirac space. Assuming a linearly rising quark-antiquark potential, we investigate two different spinorial forms (Dirac structures), namely {1/2}(\Id\otimes\Id - \gamma^0\otimes\gamma^0) as well as the $U_A(1)$-invariant combination {1/2}(\Id\otimes\Id - \gamma^5\otimes\gamma^5 - \gamma^\mu\otimes\gamma_\mu), both providing a good description of the ground state Regge trajectories up to highest observed angular momenta. Whereas the first structure is slightly prefered concerning numerous meson decay properties (see \cite{pap41}), we find the $U_A(1)$-invariant force to be much more appropriate for the description of a multitude of higher mass resonances discovered in the data of the {\sc Crystal Barrel} collaboration during the last few years. Furthermore, this confinement structure has the remarkable feature to yield a linear dependence of masses on their radial excitation number. For many experimental resonances such a trajectory-like behaviour was observed by Anisovich {\it et al.} We can confirm that almost the same slope occurs for all trajectories. Adding the $U_A(1)$-breaking instanton induced 't Hooft interaction we can compute the pseudoscalar mass splittings with both Dirac structures and for the scalar mesons a natural mechanism of flavour mixing is achieved. [...]Comment: 32 pages including 19 figures and 3 tables; submitted to Eur. Phys.

Virtual smarts - optimizing the coalescing of people for collective action within urban communities

Despite the importance of individuals coming together for social group-activities (e.g., pick-up volleyball), the process by which such groups coalesce is poorly understood, and as a consequence is poorly supported by technology. This is despite the emergence of Event-Based Social Network (EBSN) technologies that are specifically designed to assist group coalescing for social activities. Existing theories focus on group development in terms of norms and types, rather than the processes involved in initial group coalescence. This dissertation addresses this gap in the literature through four studies focusing on understanding the coalescing process for interest-based group activities within urban environments and a design of a mobile user interface aimed at increasing collective action initiation. Study One examined how well people\u27s needs for social group activity engagement are being met in the context of an urban university. The analysis of 60 interviews highlighted how participants considered activity leadership a burden, where it took too much time and was difficult to find others. Study Two (a mixed methods study of 763 Meetup.com groups in the NY/NJ/CT Tri-State) and Study Three (A survey of 511 students at an urban university) corroborated results that attendance and participation at the first meeting determined long-term success by giving the organizer belief that their group would be successful. Study Four involved the design and testing of a mobile group coalescing user-interface (UI) that featured several lightweight coalescing features hypothesized to reduce the challenges to organizing. Results from the 2000 participant study indicated that the UI increased the likelihood non-leaders would initiate collective action. The models generated from the study data suggested that a new theory is required to understand the role of critical mass in collective action. The combination of these investigations into interest-based group activity coalescing uncovered important gaps in the current knowledge of interest-based group activity coalescing and collective action initiation. This work extends our knowledge about how to improve coalescing support and encourage non-leaders to initiate activity coalescing, which will lead to a greater number of activities forming. Finally, this research uncovers the need to redefine collective action and critical mass models to include motivation to organize and its moderators

Semileptonic decays of baryons in a relativistic quark model

We calculate semileptonic decays of light and heavy baryons in a relativistically covariant constituent quark model. The model is based on the Bethe-Salpeter-equation in instantaneous approximation. It generates satisfactory mass spectra for mesons and baryons up to the highest observable energies. Without introducing additional free parameters we compute on this basis helicity amplitudes of electronic and muonic semileptonic decays of baryons. We thus obtain form factor ratios and decay rates in good agreement with experiment.Comment: 8 pages, 10 figures, 2 tables, typos remove

Strong Two--Body Decays of Light Mesons

In this paper, we present results on strong two-body decay widths of light $q\bar q$ mesons calculated in a covariant quark model. The model is based on the Bethe-Salpeter equation in its instantaneous approximation and has already been used for computing the complete meson mass spectrum and many electroweak decay observables. Our approach relies on the use of a phenomenological confinement potential with an appropriate spinorial Dirac structure and 't Hooft's instanton--induced interaction as a residual force for pseudoscalar and scalar mesons. The transition matrix element for the decay of one initial meson into two final mesons is evaluated in lowest order by considering conventional decays via quark loops as well as Zweig rule violating instanton--induced decays generated by the six--quark vertex of 't Hooft's interaction; the latter mechanism only contributes if all mesons in the decay have zero total angular momentum. We show that the interference of both decay mechanisms plays an important role in the description of the partial widths of scalar and pseudoscalar mesons.Comment: 35 pages, 7 figure