Trends in the magnetic properties of Fe, Co and Ni clusters and monolayers on Ir(111), Pt(111) and Au(111)

We present a detailed theoretical investigation on the magnetic properties of small single-layered Fe, Co and Ni clusters deposited on Ir(111), Pt(111) and Au(111). For this a fully relativistic {\em ab-initio} scheme based on density functional theory has been used. We analyse the element, size and geometry specific variations of the atomic magnetic moments and their mutual exchange interactions as well as the magnetic anisotropy energy in these systems. Our results show that the atomic spin magnetic moments in the Fe and Co clusters decrease almost linearly with coordination on all three substrates, while the corresponding orbital magnetic moments appear to be much more sensitive to the local atomic environment. The isotropic exchange interaction among the cluster atoms is always very strong for Fe and Co exceeding the values for bulk bcc Fe and hcp Co, whereas the anisotropic Dzyaloshinski-Moriya interaction is in general one or two orders of magnitude smaller when compared to the isotropic one. For the magnetic properties of Ni clusters the magnetic properties can show quite a different behaviour and we find in this case a strong tendency towards noncollinear magnetism

Differential response at the seafloor during Palaeocene and Eocene ocean warming events at Walvis Ridge, Atlantic Ocean (ODP Site 1262)

The Latest Danian Event (LDE, c. 62.1 Ma) is an early Palaeogene hyperthermal or transient (<200 ka) ocean warming event. We present the first deep-sea benthic foraminiferal faunal record to study deep-sea biotic changes together with new benthic (Nuttallides truempyi) stable isotope data from Walvis Ridge Site 1262 (Atlantic Ocean) to evaluate whether the LDE was controlled by similar processes as the minor early Eocene hyperthermals. The spacing of the double negative δ13C and δ18O excursion and the slope of the δ18O–δ13C regression are comparable, strongly suggesting a similar orbital control and pacing of eccentricity maxima as well as a rather homogeneous carbon pool. However, in contrast to early Eocene hyperthermals, the LDE exhibits a remarkable stability of the benthic foraminiferal fauna. This lack of benthic response could be related to the absence of threshold-related circulation changes or better pre-adaptation to elevated deep-sea temperatures, as the LDE was superimposed on a cooling trend, in contrast to early Eocene warming

Chemostratigraphy and stratigraphic distribution of keeled planktonic foraminifera in the Cenomanian of the North German Basin

The record of keeled planktonic foraminifera during the Cenomanian in boreal epicontinental basins is discontinuous. Micropalaeontologic and bulk carbonate carbon and oxygen isotope investigations from two cores in the centre of the North German Basin (NGB, Wunstorf, Lower Saxony) showed keeled praeglobotruncanids and rotaliporids to exclusively appear during three stratigraphic intervals of varying duration in the lower and middle Cenomanian. Our new highresolution carbon isotope (\u3b413Ccarb) composite curve shows that keeled foraminifera are absent during the Mid-Cenomanian Event (MCE) I. In the aftermath of MCE I, keeled planktonic foraminifera are present throughout. The data are correlated to previously published sequence stratigraphic models for the NGB. The presence/absence of keeled planktonic foraminifera in the epicontinental NGB is believed to be controlled by sea level and according environmental conditions in the epicontinental basin.In den Cenoman-zeitlichen Abfolgen der epikontinentalen Becken der borealen Kreide lassen sich gekielte planktonische Foraminiferen nicht durchgehend nachweisen. Neue Untersuchungen an zwei Bohrungen aus dem Norddeutschen Becken bei Wunstorf in Niedersachsen zeigen, dass sich die Vorkommen von gekielten Praeglobotruncanen und Rotaliporiden auf drei stratigraphisch klar abtrennbare Intervalle des Untercenomaniums und Mittelcenomaniums beschr\ue4nken. Die hier pr\ue4sentierte neue und hochaufl\uf6sende Kohlenstoffisotopenkurve (\u3b413Ccarb) belegt u ferdem ein Fehlen gekielter planktonischer Foraminiferen w\ue4hrend der positiven C-Isotopen-Exkursion des Mid-Cenomanian Event (MCE) I. Oberhalb des MCE I ist das Vorkommen gekielter planktonischer Foraminiferen kontinuierlich. Die Korrelation unserer Daten mit etablierten sequenzstratigraphischen Untergliederungen f\ufcr das Cenomanium Norddeutschlands weist auf einen Zusammenhang zwischen Meeresspiegelschwankungen und dem Vorkommen gekielter Formen hin. Offensichtlich erm\uf6glichten die Umweltbedingungen w\ue4hrend hoher Meeresspiegelst\ue4nde das Leben gekielter Formen in den Randbecken

Social Media in der akademischen Lehramtsausbildung:Gestaltungsgrundsätze für eine kompetenzorientierte Lehre mit Hilfe internetgestützter Kooperations- und Kolloborationsmedien

Die vorliegende Dissertation befasst sich mit dem Einsatz von Social Media in der Lehramtsausbildung. Gefragt wird, welche impliziten Annahmen zu den Usern und der hochschulischen Anwendbarkeit internetgestützter Kooperations- und Kollaborationsmedien existieren, die eine Entfaltung des didaktischen Potentials von Social Media beeinträchtigen können. Es werden hierfür Gestaltungsgrundsätze entwickelt, die Lehrenden eine Hilfestellung für die Planung und Durchführung eigener Social Media-gestützter Lernarrangements bieten. Insbesondere wird hierbei die Benotung von Lernendenleistungen Gegenstand der Untersuchung, da sie für den Einsatz von Social Media in formalen Bildungskontexten eine besondere Schwierigkeit darstellt. Mittels Peer Reviews, einem Verfahren wechselseitiger Begutachtung studentischer Eigenleistungen, wird versucht, eine Brücke zwischen den Anforderungen formaler Bildungsgänge und dem freiwilligen Austausch zu schlagen, der für den Einsatz von Social Media essentiell ist

Joint distribution of the first and second eigenvalues at the soft edge of unitary ensembles

The density function for the joint distribution of the first and second eigenvalues at the soft edge of unitary ensembles is found in terms of a Painlev\'e II transcendent and its associated isomonodromic system. As a corollary, the density function for the spacing between these two eigenvalues is similarly characterized.The particular solution of Painlev\'e II that arises is a double shifted B\"acklund transformation of the Hasting-McLeod solution, which applies in the case of the distribution of the largest eigenvalue at the soft edge. Our deductions are made by employing the hard-to-soft edge transitions to existing results for the joint distribution of the first and second eigenvalue at the hard edge \cite{FW_2007}. In addition recursions under $a \mapsto a+1$ of quantities specifying the latter are obtained. A Fredholm determinant type characterisation is used to provide accurate numerics for the distribution of the spacing between the two largest eigenvalues.Comment: 26 pages, 1 Figure, 2 Table