263 research outputs found
Towards a consistent eddy-covariance processing: An intercomparison of EddyPro and TK3
A comparison of two popular eddy-covariance software packages is presented,
namely, EddyPro and TK3. Two approximately 1-month long test data sets were
processed, representing typical instrumental setups (i.e., CSAT3/LI-7500
above grassland and Solent R3/LI-6262 above a forest). The resulting fluxes
and quality flags were compared. Achieving a satisfying agreement and
understanding residual discrepancies required several iterations and
interventions of different nature, spanning from simple software
reconfiguration to actual code manipulations. In this paper, we document our
comparison exercise and show that the two software packages can provide
utterly satisfying agreement when properly configured. Our main aim,
however, is to stress the complexity of performing a rigorous comparison of
eddy-covariance software. We show that discriminating actual discrepancies
in the results from inconsistencies in the software configuration requires
deep knowledge of both software packages and of the eddy-covariance method.
In some instances, it may be even beyond the possibility of the investigator
who does not have access to and full knowledge of the source code. Being the
developers of EddyPro and TK3, we could discuss the comparison at all levels
of details and this proved necessary to achieve a full understanding. As a
result, we suggest that researchers are more likely to get comparable
results when using EddyPro (v5.1.1) and TK3 (v3.11) – at least with the
setting presented in this paper – than they are when using any other pair of
EC software which did not undergo a similar cross-validation.
As a further consequence, we also suggest that, to the aim of assuring
consistency and comparability of centralized flux databases, and for a
confident use of eddy fluxes in synthesis studies on the regional,
continental and global scale, researchers only rely on software that have
been extensively validated in documented intercomparisons
How Does the Choice of the Lower Boundary Conditions in Large-Eddy Simulations Affect the Development of Dispersive Fluxes Near the Surface?
Large-eddy simulations (LES) are an important tool for investigating the longstanding energy-balance-closure problem, as they provide continuous, spatially-distributed information about turbulent flow at a high temporal resolution. Former LES studies reproduced an energy-balance gap similar to the observations in the field typically amounting to 10–30% for heights on the order of 100 m in convective boundary layers even above homogeneous surfaces. The underestimation is caused by dispersive fluxes associated with large-scale turbulent organized structures that are not captured by single-tower measurements. However, the gap typically vanishes near the surface, i.e. at typical eddy-covariance measurement heights below 20 m, contrary to the findings from field measurements. In this study, we aim to find a LES set-up that can represent the correct magnitude of the energy-balance gap close to the surface. Therefore, we use a nested two-way coupled LES, with a fine grid that allows us to resolve fluxes and atmospheric structures at typical eddy-covariance measurement heights of 20 m. Under different stability regimes we compare three different options for lower boundary conditions featuring grassland and forest surfaces, i.e. (1) prescribed surface fluxes, (2) a land-surface model, and (3) a land-surface model in combination with a resolved canopy. We show that the use of prescribed surface fluxes and a land-surface model yields similar dispersive heat fluxes that are very small near the vegetation top for both grassland and forest surfaces. However, with the resolved forest canopy, dispersive heat fluxes are clearly larger, which we explain by a clear impact of the resolved canopy on the relationship between variance and flux–variance similarity functions
Memristive operation mode of a site-controlled quantum dot floating gate transistor
The authors gratefully acknowledge financial support from the European Union (FPVII (2007-2013) under Grant Agreement No. 318287 Landauer) as well as the state of Bavaria.We have realized a floating gate transistor based on a GaAs/AlGaAs heterostructure with site-controlled InAs quantum dots. By short-circuiting the source contact with the lateral gates and performing closed voltage sweep cycles, we observe a memristive operation mode with pinched hysteresis loops and two clearly distinguishable conductive states. The conductance depends on the quantum dot charge which can be altered in a controllable manner by the voltage value and time interval spent in the charging region. The quantum dot memristor has the potential to realize artificial synapses in a state-of-the-art opto-electronic semiconductor platform by charge localization and Coulomb coupling.Publisher PDFPeer reviewe
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