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Ghendrih Ph.,French Atomic Energy Commission | Norscini C.,French Atomic Energy Commission | Hasenbeck F.,French Atomic Energy Commission | Hasenbeck F.,Forschungszentrum Jlich GmbH | And 9 more authors.
Journal of Physics: Conference Series | Year: 2012

Edge plasma turbulence modelled with 2D interchange is shown to exhibit convective transport at the microscale level. This transport property is related to avalanche like transport in such a flux-driven system. Correlation functions and source modulation are used to analyse the transport properties but do not allow one to recover the Fick law that must characterise the system at large scales. Coarse graining is then introduced to average out the small scales in order to recover the Fick law. One finds that the required space averaging is comparable to the system size while the time averaging is comparable to the confinement time. The system is then reduced to a single reservoir such that transport is characterised by a single scalar, either the diffusion coefficient of the Fick law or a characteristic evolution time constant. © 2013 Published under licence by IOP Publishing Ltd. Source

Jadoon K.Z.,King Abdullah University of Science and Technology | Weihermuller L.,Forschungszentrum Jlich GmbH | McCabe M.F.,King Abdullah University of Science and Technology | Moghadas D.,Federal Institute for Geosciences and Natural Resources | And 2 more authors.
Remote Sensing | Year: 2015

We tested an off-ground ground-penetrating radar (GPR) system at a fixed location over a bare agricultural field to monitor the soil freeze-thaw cycles over a snow-covered surface. The GPR system consisted of a monostatic horn antenna combined with a vector network analyzer, providing an ultra-wideband stepped-frequency continuous-wave radar. An antenna calibration experiment was performed to filter antenna and back scattered effects from the raw GPR data. Near the GPR setup, sensors were installed in the soil to monitor the dynamics of soil temperature and dielectric permittivity at different depths. The soil permittivity was retrieved via inversion of time domain GPR data focused on the surface reflection. Significant effects of soil dynamics were observed in the time-lapse GPR, temperature and dielectric permittivity measurements. In particular, five freeze and thaw events were clearly detectable, indicating that the GPR signals respond to the contrast between the dielectric permittivity of frozen and thawed soil. The GPR-derived permittivity was in good agreement with sensor observations. Overall, the off-ground nature of the GPR system permits non-invasive time-lapse observation of the soil freeze-thaw dynamics without disturbing the structure of the snow cover. The proposed method shows promise for the real-time mapping and monitoring of the shallow frozen layer at the field scale. © 2015 by the authors. Source

Gerhards T.,Forschungszentrum Jlich GmbH | MacKfeld U.,Forschungszentrum Jlich GmbH | Bocola M.,RWTH Aachen | Lieres E.V.,Forschungszentrum Jlich GmbH | And 3 more authors.
Advanced Synthesis and Catalysis | Year: 2012

The asymmetric mixed carboligation of aldehydes with thiamine diphosphate (ThDP)-dependent enzymes is an excellent example where activity as well as changes in chemo- and stereoselectivity can be followed sensitively. To elucidate the influence of organic additives in enzymatic carboligation reactions of mixed 2-hydroxy ketones, we present a comparative study of six ThDP-dependent enzymes in 13 water-miscible organic solvents under equivalent reaction conditions. The influence of the additives on the stereoselectivity is most pronounced and follows a general trend. If the enzyme stereoselectivity in aqueous buffer is already >99.9% ee, none of the solvents reduces this high selectivity. In contrast, both stereoselectivity and chemoselectivity are strongly influenced if the enzyme is rather unselective in aqueous buffer. For the S-selective enzyme with the largest active site, we were able to prove a general correlation of the solvent-excluded volume of the additives with the effect on selectivity changes: the smaller the organic solvent molecule, the higher the impact of this additive. Further, a correlation to logP of the additives on selectivity was detected if two additives have almost the same solvent- excluded volume. The observed results are discussed in terms of structural, biochemical and energetic effects. This work demonstrates the potential of medium engineering as a powerful additional tool for varying enzyme selectivity and thus engineering the product range of biotransformations. It further demonstrates that the use of cosolvents should be carefully planned, as the solvents may compete with the substrate(s) for binding sites in the enzyme active site. Abbreviations: ApPDC: pyruvate decarboxylase from Acetobacter pasteurianus; DCM: dichloromethane; DIPE: diisopropyl ether; DMSO: dimethyl sulfoxide; ee: enantiomeric excess; EtOAc: ethyl acetate; EtOH: ethanol; GC: gas chromatography; HPLC: high-performance liquid chromatography; HPP: 2-hydroxy-1-phenylpropan-1-one; iProp: isopropyl alcohol; LlKdcA: branched-chain keto acid decarboxylase from Lactococcus lactis; MIBK: methyl isobutyl ketone; MTBE: methyl tert-butyl ether; MTHF: 2-methyltetrahydrofuran; PAC: 1-hydroxy- 1-phenylpropan-2-one; PfBAL: benzaldehyde lyase from Pseudomonas fluorescens; PpBFD: benzoylformate decarboxylase from Pseudomonas putida; rpd: relative product distribution; TCM: trichloromethane; THF; tetrahydrofuran. © 2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim. Source

Babcock E.,Forschungszentrum Jlich GmbH | Mattauch S.,Forschungszentrum Jlich GmbH | Ioffe A.,Forschungszentrum Jlich GmbH
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

Maintaining high levels of 3He polarization over long periods of time is important for many areas of fundamental and particle beam physics. Long measurement times are often required in such experiments, and the data quality is a function of the 3He polarization. This is the case for neutron scattering, where the 3He can be used to analyze the spin of a scattered neutron beam. For neutron scattering, the relatively small fluxes of polarized neutrons lead to experiment times longer than several days. Consequently, the Jlich Centre for Neutron Science (JCNS) is developing spin-exchange optical pumping (SEOP) systems capable of polarizing the 3He gas in place on a typical neutron instrument. With the polarizer we have constructed, a very high level of 3He polarization of 80.4%±1.5% was obtained and maintained with good time stability. Having such high levels of polarization that are stable over time will reduce the measurement times for such experiments and eliminate time-dependent data corrections. © 2010 Elsevier B.V. All rights reserved. Source

Rosezin R.,Solid Information Technology | Meier M.,Solid Information Technology | Breuer U.,Forschungszentrum Jlich GmbH | Kgeler C.,Solid Information Technology | Waser R.,Solid Information Technology
IEEE Transactions on Nanotechnology | Year: 2011

This paper reports on the resistance switching effect in silver-doped methylsilsesquioxane (MSQ) thin films with Pt top and bottom electrodes. Silver is thermally diffused into MSQ films for different times and the results prove that silver ions (or other oxidizable metal ions) are required in the system, but not necessarily as one of the two electrodes. SEM investigations at horizontal cells (gap width 15100 nm) show the formation of metallic agglomerations in the gap. The forming process is found to be electric-field driven and the filament resistance is determined to be 30 /nm. Under the assumption of conical-shaped filament growth, the diameter of a filament is calculated to 13.5 nm, which is in agreement with the SEM observations. Memory device related tests on 100 100 nm2 cross junctions show unipolar switching up to 2000 times and retention at 85C for at least 6 104 s. © 2006 IEEE. Source

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