Visibility of Cold Atomic Gases in Optical Lattices for Finite Temperatures

In nearly all experiments with ultracold atoms time-of-flight pictures are the only data available. In this paper we present an analytical strong-coupling calculation for those time-of-flight pictures of bosons in an optical lattice in the Mott phase. This allows us to determine the visibility, which quantifies the contrast of peaks in the time-of-flight pictures, and we suggest how to use it as a thermometer.Comment: Author Information under http://www.theo-phys.uni-essen.de/tp/ags/pelster_dir

Nonparametric estimation of the volatility under microstructure noise: wavelet adaptation

We study nonparametric estimation of the volatility function of a diffusion process from discrete data, when the data are blurred by additional noise. This noise can be white or correlated, and serves as a model for microstructure effects in financial modeling, when the data are given on an intra-day scale. By developing pre-averaging techniques combined with wavelet thresholding, we construct adaptive estimators that achieve a nearly optimal rate within a large scale of smoothness constraints of Besov type. Since the underlying signal (the volatility) is genuinely random, we propose a new criterion to assess the quality of estimation; we retrieve the usual minimax theory when this approach is restricted to deterministic volatility.Adaptive estimation; diffusion processes; high-frequency data; microstructure noise; minimax estimation; semimartingales; wavelets.

Dynamics of thin-film spin-flip transistors with perpendicular source-drain magnetizations

A "spin-flip transistor" is a lateral spin valve consisting of ferromagnetic source drain contacts to a thin-film normal-metal island with an electrically floating ferromagnetic base contact on top. We analyze the \emph{dc}-current-driven magnetization dynamics of spin-flip transistors in which the source-drain contacts are magnetized perpendicularly to the device plane by magnetoelectronic circuit theory and the macrospin Landau-Lifshitz-Gilbert equation. Spin flip scattering and spin pumping effects are taken into account. We find a steady-state rotation of the base magnetization at GHz frequencies that is tuneable by the source-drain bias. We discuss the advantages of the lateral structure for high-frequency generation and actuation of nanomechanical systems over recently proposed nanopillar structures.Comment: Accepted by Phys.Rev.B as regular articl

Dynamic Fingerprints of Synthetic Antiferromagnet Nanostructures with Interfacial Dzyaloshinskii-Moriya Interaction

Synthetic antiferromagnet (SAF) nanostructures with interfacial Dzyaloshinskii-Moriya interaction can host topologically distinct spin textures such as skyrmions and thus are regarded as promising candidates for both spintronics and magnonics applications. Here, we present comprehensive micromagnetic simulations of such material systems and discuss the rich phase diagrams that contain various types of magnetic configurations. Aside from the static properties, we further discuss the resonant excitations of the calculated magnetic states which include individual skyrmions and skyrmioniums. Finally, the internal modes of SAF skyrmion clusters are studied and discussed in the context of magnetic sensing applications based on the dynamic fingerprint in broadband ferromagnetic resonance measurements.Comment: 9 pages, 5 figure

Towards a Theory of Explanation and Prediction for the Formation of Trust in IT Artifacts

In this paper we argue that the predominant trust conceptualization in IS has a major weakness when researching trust in IT artifacts and that a theory of explanation and prediction for the formation of trust in IT artifacts is necessary to face the upcoming challenges. Thus, we motivate a trust conceptualization from the HCI discipline, and develop a formative measurement model for trust in IT artifacts to achieve deeper insights on the formation of trust. The results of our pre-study with 102 undergraduate students suggest that the new conceptualization is valueable for creating the desired insights on the formation of trust in IT artifacts. In an upcoming field experiment with about 250 users we expect to gain more detailed and reliable insights in the formation of trust in IT artifacts allowing us to derive a first theory of explanation and prediction for the formation of trust in IT artifacts