The Cosmogony of Super-Massive Black Holes

We summarize our recent results on the evolution of super-massive black holes in the cores of galaxies. Our models are based on the viscous, Eddington-limited evolution of self-gravitating accretion disks. We find that, within this framework, one can explain the growth time scales and the luminosities of individual objects as well as the variation of these quantities for AGN with different black hole masses

Konzeption, Implementation und Evaluation von Online-Seminaren in der universitären, erziehungswissenschaftlichen Ausbildung

Eine Vielzahl von Gründen sprechen für den Einsatz von Online-Seminaren in der universitären Lehre: Beispielsweise ermöglichen Online-Seminare eine Erweiterung des Veranstaltungsspektrums, eine Ausweitung der Wissensvermittlung sowie temporäre und örtliche Flexibilität. Daneben sollte darauf geachtet werden, dass die Didaktik, die diesen Seminaren zu Grunde liegt, einen Schwerpunkt im Entwicklungsprozess bildet. Im diesem Beitrag werden exemplarisch zwei Seminare aus dem Hochschulbereich dargestellt, die diesen Anforderungen in ihrem konzeptionellen Aufbau gerecht werden wollen und hinsichtlich ihrer Akzeptanz überprüft wurden

Formation of Super-massive Black Holes

We show that the rapid formation of super-massive black holes in quasars can indeed be understood in terms of major galaxy mergers followed by disk accretion. The necessary short disk evolution time can be achieved provided the disk viscosity is sufficiently large, which, for instance, is the case for hydrodynamic turbulence, unlimited by shock dissipation. We present numerical calculations for a representative case. This general picture can account for (a) the presence of highly luminous quasars at redshifts z > 6; (b) for the peak in quasar activity at z ~ 2; and (c) for a subsequent rapid disappearance of quasars at later epochs.Comment: 9 pages, 1 figure, to appear in the proceedings of the Xth Marcel Grossman Meeting, Rio de Janeiro, 200

Resonance fluorescence of a site-controlled quantum dot realized by the buried-stressor growth technique

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 110, 111101 (2017) and may be found at https://doi.org/10.1063/1.4978428.Site-controlled growth of semiconductor quantum dots (QDs) represents a major advancement to achieve scalable quantum technology platforms. One immediate benefit is the deterministic integration of quantum emitters into optical microcavities. However, site-controlled growth of QDs is usually achieved at the cost of reduced optical quality. Here, we show that the buried-stressor growth technique enables the realization of high-quality site-controlled QDs with attractive optical and quantum optical properties. This is evidenced by performing excitation power dependent resonance fluorescence experiments at cryogenic temperatures showing QD emission linewidths down to 10 μeV. Resonant excitation leads to the observation of the Mollow triplet under CW excitation and enables coherent state preparation under pulsed excitation. Under resonant π-pulse excitation we observe clean single-photon emission associated with g(2)(0) = 0.12 limited by non-ideal laser suppression.EC/FP7/615613/EU/External Quantum Control of Photonic Semiconductor Nanostructures/EXQUISIT

Two-photon interference from remote deterministic quantum dot microlenses

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 110, 011104 (2017) and may be found at https://doi.org/10.1063/1.4973504.We report on two-photon interference (TPI) experiments using remote deterministic single-photon sources. Employing 3D in-situ electron-beam lithography, we fabricate quantum-light sources at specific target wavelengths by integrating pre-selected semiconductor quantum dots within monolithic microlenses. The individual single-photon sources show TPI visibilities of 49% and 22%, respectively, under pulsed p-shell excitation at 80 MHz. For the mutual TPI of the remote sources, we observe an uncorrected visibility of 29%, in quantitative agreement with the pure dephasing of the individual sources. Due to its efficient photon extraction within a broad spectral range (>20 nm), our microlens-based approach is predestinated for future entanglement swapping experiments utilizing entangled photon pairs emitted by distant biexciton-exciton radiative cascades.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/FP7/615613/EU/External Quantum Control of Photonic Semiconductor Nanostructures/EXQUISIT

Strategies for the acquisition of geographica! knowledge and spatial images

In der vorliegenden Studie wurden vor dem Hintergrund der Theorien zur mentalen Repräsentation Annahmen zu entwicklungsbedingten Unterschieden der Verarbeitung und Abspeicherung topographischer Informationen überprüft. Zugleich wurden die Effekte unterschiedlicher Präsentationsmodi (ikonisch vs. sprachlich vs. ikonisch/sprachlich) sowie die Annahme einer Kongruenz zwischen Encodierungs- und Abrufmodus experimentell untersucht. Die Ergebnisse des Experimentes bestätigen die Hypothese entwicklungsbedingter Unterschiede in der Fähigkeit, geographische Information adäquat zu verarbeiten sowie die Wirksamkeit einer Kongruenz zwischen Präsentations- und Reproduktionmodus. Gleichfalls stützen die Befunde die Doppelcodierungstheorie, die von einer Überlegenheit einer Präsentation in zwei unterschiedlichen, sich ergänzenden Modi (Codes) ausgeht, und widerlegen die Hypothese, welche die Wirksamkeit einer Lehrstrategie annimmt, bei der die Rezipienten die Informationen von einer Modalität in eine andere transformieren. Insgesamt konnte die kognitionstheoretisch und didaktisch bedeutsame Funktion visueller Vorstellungen für den Erwerb geographischen Wissens nachgewiesen werden. (DIPF/Orig.)This study examines various assumptions concerning developmental differences in Processing and storing topographic Information on the basis of theories of mental representations. At the same time it experimentally tests the effects of different presentation modi (iconic vs. verbal vs. iconic/verbal) as well as the assumption of a congruence between the encoding and recalling modi. The results of this experiment confirm the hypothesis of developmental differences concerning the ability to adequately process geographical information as well as the effectiveness of a congruence between the presentation and reproduction modi. The results also Support the theory of double coding, which assumes the superiority of a presentation in two different, complementing modi (codes); they disprove the hypothesis which assumes the effectiveness of a teaching strategy in which the recipients transform information from one modality into another. On the whole it was possible to prove that visual images have an important function in the acquisition of geographical knowledge from the viewpoint of both cognition theory and didactics