Actions and symmetries of NSR superstrings and D-strings

We present all NSR superstring and super-D-string actions invariant under a set of prescribed gauge transformations, and characterize completely their global symmetries. In particular we obtain locally supersymmetric Born-Infeld actions on general backgrounds in a formulation with extra target space dimensions. The nontrivial global symmetries of the superstring actions correspond to isometries of the background, whereas super-D-string actions can have additional symmetries acting nontrivially also on the coordinates of the extra dimensions.Comment: 4 pages, references added and errors correcte

Einfluss von Kernquadrupolmomenten auf die Amplitude von Polarisationsechose in amorphen Festkörpern

Die physikalischen Eigenschaften von amorphen Festkörpern werden unterhalb einiger Kelvin durch atomare Tunnelsysteme bestimmt. In diesem Temperaturbereich zeigen einige isolierende Multikomponentengläser magnetfeldabhängige Eigenschaften. Zur Erklärung dieser unerwarteten Magnetfeldeffekte in nominell unmagnetischen amorphen Systemen wurden in den letzten Jahren verschiedene Modelle entwickelt. Eines dieser Modelle setzt voraus, dass die Atomkerne der tunnelnden Teilchen ein elektrisches Kernquadrupolmoment besitzen. Mit dielektrischen Polarisationsechoexperimenten haben wir an amorphem Glycerin den Zerfall der Echoamplitude in Abhängigkeit des Magnetfelds untersucht. Durch partielles Deuterieren wurden gezielt Atome mit Kernquadrupolmoment und bekannter Quadrupolfrequenz in das System eingebracht. Der beobachtete Isotopeneffekt stützt die Erklärung der Magnetfeldeffekte basierend auf einem Kernquadrupolmoment. Auch die erstmals in Glycerin beobachtete Quantenschwebung im Zerfall von Zweipulsechos kann im Rahmen dieses Modells quantitativ erklärt werden

Familie - Generation - Institution : Generationenkonzepte in der Vormoderne

Dieser Band versammelt Beiträge zu Generationenbeziehungen und Generationenkonzepten in der Vormoderne, die auf eine Tagung des DFG-Graduiertenkollegs 'Generationenbewusstsein und Generationenkonflikte in Antike und Mittelalter' in Bamberg zurückgehen. Die behandelten Untersuchungsgegenstände reichen von den antiken Diadochenreichen über die ottonische Königsfamilie des 10. und 11. Jahrhunderts bis zum frühneuzeitlichen Landadel Westfalens. Dabei werden historische, literaturwissenschaftliche und soziologische Fragestellungen aufgegriffen, um den Erkenntniswert des Konzepts 'Generation' interdisziplinär zu diskutieren.This volume brings together contributions on generational relations and concepts of generation in Early Modernity given on the occasion of a conference organized at Bamberg by the Research Training Group of the German Research Foundation (DFG) 'Generational Awareness and Generational Conflicts in Antiquity and the Middle Ages'. The topics ranged from the ancient Diadoch kingdoms to the history of the Ottonian royal family of the 10th and 11th centuries and the early modern landed gentry in Westfalia. Addressing questions from historical, literary and social studies the validity of the concept of 'generation' was discussed among scholars and students from a variety of disciplines

N=2 central charge superspace and a minimal supergravity multiplet

We extend the notion of central charge superspace to the case of local supersymmetry. Gauged central charge transformations are identified as diffeomorphisms at the same footing as space-time diffeomorphisms and local supersymmetry transformations. Given the general structure we then proceed to the description of a particular vector-tensor supergravity multiplet of 24+24 components, identified by means of rather radical constraints

Recognizing Members of the Tournament Equilibrium Set is NP-hard

A recurring theme in the mathematical social sciences is how to select the "most desirable" elements given a binary dominance relation on a set of alternatives. Schwartz's tournament equilibrium set (TEQ) ranks among the most intriguing, but also among the most enigmatic, tournament solutions that have been proposed so far in this context. Due to its unwieldy recursive definition, little is known about TEQ. In particular, its monotonicity remains an open problem up to date. Yet, if TEQ were to satisfy monotonicity, it would be a very attractive tournament solution concept refining both the Banks set and Dutta's minimal covering set. We show that the problem of deciding whether a given alternative is contained in TEQ is NP-hard.Comment: 9 pages, 3 figure

A route for the top-down fabrication of ordered ultrathin GaN nanowires

Ultrathin GaN nanowires (NWs) are attractive to maximize surface effects and as building block in high-frequency transistors. Here, we introduce a facile route for the top-down fabrication of ordered arrays of GaN NWs with aspect ratios exceeding $10$ and diameters below $20\,$nm. Highly uniform thin GaN NWs are first obtained by using electron beam lithography to pattern a Ni/SiN$_x$ hard mask, followed by dry etching and wet etching in hot KOH. The SiN$_x$ is found to work as an etch stop during wet etching in hot KOH. Arrays with NW diameters down to $(33 \pm5)\,$nm can be achieved with a yield exceeding $99.9\,\%$. Further reduction of the NW diameter down to $5\,$nm is obtained by applying digital etching which consists in plasma oxidation followed by wet etching in hot KOH. The NW radial etching depth is tuned by varying the RF power during plasma oxidation. NW breaking or bundling is observed for diameters below $\approx 20\,$nm, an effect that is associated to capillary forces acting on the NWs during sample drying in air. This effect can be principally mitigated using critical point dryers. Interestingly, this mechanical instability of the NWs is found to occur at much smaller aspect ratios than what is predicted for models dealing with macroscopic elastic rods. Explicit calculations of buckling states show an improved agreement when considering an inclined water surface, as can be expected if water assembles into droplets. The proposed fabrication route can be principally applied to any GaN/SiN$_{x}$ nanostructures and allows regrowth after removal of the SiN$_{x}$ mask

High Temperature, Wireless Seismometer Sensor for Venus

Space agency mission plans state the need to measure the seismic activity on Venus. Because of the high temperature on Venus (462? C average surface temperature) and the difficulty in placing and wiring multiple sensors using robots, a high temperature, wireless sensor using a wide bandgap semiconductor is an attractive option. This paper presents the description and proof of concept measurements of a high temperature, wireless seismometer sensor for Venus. A variation in inductance of a coil caused by the movement of an aluminum probe held in the coil and attached to a balanced leaf-spring seismometer causes a variation of 700 Hz in the transmitted signal from the oscillator/sensor system at 426? C. This result indicates that the concept may be used on Venus