Ausbreitung von Kältefahnen im Grundwasser bei Erdwärmesonden

Shallow geothermal energy installations, especially ground source heat pump (GSHP) systems are increasingly being used for air conditioning and temperature control in buildings. Heating applications, for example, result in cold temperature anomalies (cold plumes) in the subsurface. To avoid interactions between adjacent cold plumes, authorities recommend minimum distances of about 10 m between installations. The length of these plumes can be simulated analytically and numerically. The presented analytical solutions are valid for steady-state conditions and consider conduction, convection and dispersion. The results show that the length depends on different parameters, especially flow velocity. The plumes in gravel aquifers become temporarily longer than in less permeable aquifers. Even under average energy extraction rates, they can exceed 10 m in length after one heating period. In the presented example the plume has a length of 10 m after 100 days under a continuous energy extraction rate of 55 W?m^?1. However, these plumes can regenerate quickly. Finally, the analytical results are discussed in a legal context.     

On the influence of baseline startle reactivity on the indexation of prepulse inhibition.

Prepulse inhibition (PPI) of the startle reflex refers to the reduction of the reflexive startle response to an intense pulse stimulus when its presentation is shortly preceded by a weak prepulse stimulus. PPI is considered as a cross-species translational model of sensorimotor gating, and deficient PPI has been reported in a number of neuropsychiatric disorders. Although a part of the literature is based on the assumption that PPI is independent of the baseline startle reaction, there is accumulating evidence (Csomor et al., 2006; Sandner & Canal, 2007; Yee, Chang, Pietropaolo, & Feldon, 2005) that argues against such an independency. The authors systematically investigated whether PPI indexed as percentage or difference score is dependent on the magnitude of baseline startle reactivity in healthy human volunteers and in C57BL/6 mice. The results revealed that both indexations of PPI were affected by the magnitude of the baseline startle. The authors highlight the pitfalls of different methods to index PPI, especially when startle reactivity differs considerably between groups under comparison, and offer practical recommendations to satisfactorily deal with such baseline differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Correlations for the particle deposition rate accounting for lift forces and hydrodynamic mobility reduction

A numerical procedure is presented which allows one to predict the deposition rate of microparticles suspended in a liquid flow onto the confining walls. Particle transport is not only diffusive but also affected by hydrodynamically induced lift force and reduced particle mobility. An appropriate expression for the lift‐induced migration is introduced into the numerical procedure. Its results agree quanititatively with previously published experimental data showing a significant effect of lift‐induced particle transport. Based on the numerical results algebraic correlations are obtained, which enable to calculate the particle deposition rate in situations where lift forces and mobility reduction diminishes the particle deposition rate.     

Innovative Methoden zum Geschiebemonitoring am Beispiel der Donau

In this article, new and innovative methods for bedload transport monitoring and their application in the context of a restoration project on the Danube River are described. Using an adapted basket sampler, a first comprehensive monitoring campaign for measuring bedload transport on the Danube was conducted and the temporal and spatial variability was shown. The development of a methodology for tracing artificial pebbles made it possible to track 40 pebble tracers of three different sizes on the Danube over the course of an entire year. Combining the two methods it could be determined that bedload already moves at low flow conditions and that bedload transport only increases slightly or even remains constant after reaching bank-full discharge. The tracer study identified size-selective transport ?C larger sizes were moving less often and over shorter distances than smaller sizes ?C with a mean transport distance of 3?km per year for the current bed material at Bad Deutsch-Altenburg. Detailed bathymetry and the analysis of the layer succession of the riverbed using the Freeze Core methodology complemented the other insights into the processes of sediment transport on the Danube River. These methods successfully characterized gravel sheets and allowed us to make predictive statements about bed armoring. We were also able to confirm a mean bed degradation of 2?cm per year using a combination of methods.     

Combinatorial corrosion study of the passivation of aluminium copper alloys

An Al_96.1–Cu_3.9 to Al_51.4–Cu_48.6 material library was obtained by thermal co-deposition and characterized by EDX and XRD. The crystallographic data reveals the presence of Al₂Cu and pure aluminium depending on the film composition and following the stoichiometry. Utilizing a scanning droplet cell setup, the zero current potential for anodization, the oxide formation factor and the dielectric constant of the oxide formed are presented with high resolution along the composition gradient.While the dielectric constant of the oxide formed remains nearly unaffected by the increasing copper content of the base material along the composition gradient, the zero current potential shows well defined steps between 6.9 and 8.5 at.% as well as between 20.9 and 26.7 at.% copper indicating an increased thickness of the native oxide present on the film. Additionally, starting around 25 at.% copper, oxygen evolution gradually superimposes the oxide growth and in turn significantly reduces the current efficiency for anodization. The formation of the intermetallic phase Al₂Cu was linked to both phenomena as it promotes the growth of native oxides and current leakage by oxygen evolution.     

A dynamic mesh refinement technique for Lattice Boltzmann simulations on octree-like grids

In this contribution, we present our new adaptive Lattice Boltzmann implementation within the Peano framework, with special focus on nanoscale particle transport problems. With the continuum hypothesis not holding anymore on these small scales, new physical effects—such as Brownian fluctuations—need to be incorporated. We explain the overall layout of the application, including memory layout and access, and shortly review the adaptive algorithm. The scheme is validated by different benchmark computations in two and three dimensions. An extension to dynamically changing grids and a spatially adaptive approach to fluctuating hydrodynamics, allowing for the thermalisation of the fluid in particular regions of interest, is proposed. Both dynamic adaptivity and adaptive fluctuating hydrodynamics are validated separately in simulations of particle transport problems. The application of this scheme to an oscillating particle in a nanopore illustrates the importance of Brownian fluctuations in such setups.