Universal scaling at non-thermal fixed points of a two-component Bose gas

Quasi-stationary far-from-equilibrium critical states of a two-component Bose gas are studied in two spatial dimensions. After the system has undergone an initial dynamical instability it approaches a non-thermal fixed point. At this critical point the structure of the gas is characterised by ensembles of (quasi-)topological defects such as vortices, skyrmions and solitons which give rise to universal power-law behaviour of momentum correlation functions. The resulting power-law spectra can be interpreted in terms of strong-wave-turbulence cascades driven by particle transport into long-wave-length excitations. Scaling exponents are determined on both sides of the miscible-immiscible transition controlled by the ratio of the intra-species to inter-species couplings. Making use of quantum turbulence methods, we explain the specific values of the exponents from the presence of transient (quasi-)topological defects.Comment: 13 pages, 12 figure

Non-Thermal Fixed Point in a Holographic Superfluid

We study the far-from-equilibrium dynamics of a (2+1)-dimensional superfluid at finite temperature and chemical potential using its holographic description in terms of a gravitational system in 3+1 dimensions. Starting from various initial conditions corresponding to ensembles of vortex defects we numerically evolve the system to long times. At intermediate times the system exhibits Kolmogorov scaling the emergence of which depends on the choice of initial conditions. We further observe a universal late-time regime in which the occupation spectrum and different length scales of the superfluid exhibit scaling behaviour. We study these scaling laws in view of superfluid turbulence and interpret the universal late-time regime as a non-thermal fixed point of the dynamical evolution. In the holographic superfluid the non-thermal fixed point can be understood as a stationary point of the classical equations of motion of the dual gravitational description.Comment: 37 pages, 10 figures; v2: discussion and figures added, matches published version; movies and additional material at http://www.thphys.uni-heidelberg.de/holographic-superflui

Multisensor Poisson Multi-Bernoulli Filter for Joint Target-Sensor State Tracking

In a typical multitarget tracking (MTT) scenario, the sensor state is either assumed known, or tracking is performed in the sensor's (relative) coordinate frame. This assumption does not hold when the sensor, e.g., an automotive radar, is mounted on a vehicle, and the target state should be represented in a global (absolute) coordinate frame. Then it is important to consider the uncertain location of the vehicle on which the sensor is mounted for MTT. In this paper, we present a multisensor low complexity Poisson multi-Bernoulli MTT filter, which jointly tracks the uncertain vehicle state and target states. Measurements collected by different sensors mounted on multiple vehicles with varying location uncertainty are incorporated sequentially based on the arrival of new sensor measurements. In doing so, targets observed from a sensor mounted on a well-localized vehicle reduce the state uncertainty of other poorly localized vehicles, provided that a common non-empty subset of targets is observed. A low complexity filter is obtained by approximations of the joint sensor-feature state density minimizing the Kullback-Leibler divergence (KLD). Results from synthetic as well as experimental measurement data, collected in a vehicle driving scenario, demonstrate the performance benefits of joint vehicle-target state tracking.Comment: 13 pages, 7 figure

Taxes and Mergers in Sweden

This paper studies the relative importance of tax incentives as merger motives in the Swedish industry during the period 1983-1987. Several econometric models are estimated and statistical tests performed. The tax-hypothesis is contrasted with an alternative hypothesis, suggested by Jensen, which explains mergers as a way for independent managers to increase their personal power. Neither hypothesis get any strong support in this study, the evidence is somewhat stronger in favor of Jensen's theory however

Microdeflectometry - a novel tool to acquire 3D microtopography with nanometer height resolution

We introduce "microdeflectometry", a novel technique for measuring the microtopography of specular surfaces. The primary data is the local slope of the surface under test. Measuring the slope instead of the height implies high information efficiency and extreme sensitivity to local shape irregularities. The lateral resolution can be better than one micron whereas the resulting height resolution is in the range of one nanometer. Microdeflectometry can be supplemented by methods to expand the depth of field, with the potential to provide quantitative 3D imaging with SEM-like features.Comment: 3 pages, 11 figures, latex, zip-file, accepted for publication at Optics Letter

Efficiency and Ownership Structure – The Case of Poland

We examine the effects of foreign entry on productive efficiency during the Polish investment liberalization. The performance of foreign acquisitions is compared to foreign firms entering the market through greenfield entry, as well as domestic acquisitions of privatized firms, domestic greenfields and remaining state-owned (non-privatized) firms during the period 1995-2000. We find that foreign privatized firms have realized larger productivity gains than all types of domestic firms and that this is not due to higher price-cost margins, which is consistent with the idea that foreign firms bring in firm-specific knowledge. Foreign greenfields have the highest average labour productivity, while foreign privatizations show the largest productivity increase.Privatizations; M As; FDI; Foreign Ownership; Productivity

Optimizing the internal electric field distribution of alternating current driven organic light-emitting devices for a reduced operating voltage

This work was funded with financial means of the European Social Fund and the Free State of Saxony through the OrthoPhoto project.The influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage of p-i-n based alternating current driven organic light-emitting devices (AC-OLEDs) is investigated. A three-capacitor model is employed to predict the basic behavior of the devices, and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3-3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. AC-OLEDs with optimized thickness of the insulating and intrinsic layers show a reduction in the driving voltage required to reach a luminance of 1000 cd/m2 of up to 23% (8.9 V) and a corresponding 20% increase in luminous efficacy.Publisher PDFPeer reviewe