6,470 research outputs found
Break junctions of the heavy-fermion superconductors
Mechanical-controllable break junctions of the heavy-fermion superconductors
can show Josephson-like superconducting anomalies. But a systematic study on
the contact size demonstrates that these anomalies are mainly due to Maxwell's
resistance being suppressed in the superconducting heavy-fermion phase. Up to
day, we could not find any superconducting features by vacuum-tunnelling
spectroscopy, providing further evidence for the pair-breaking effect of the
heavy-fermion interfaces.Comment: 5 pages, EPS figures included, REVTeX, to be published in Physica B
9
Determination of [S,S′]-Ethylenediaminedisuccinic Acid by High-Performance Liquid Chromatography
A new high-performance liquid chromatography (HPLC) method for the determination of ethylenediaminedisuccinic acid (EDDS) is presented. Free EDDS4- and EDDS complexes with divalent metals undergo conversion to the Fe(III) complex in the presence of Fe(III)Cl3. Fe(III)EDDS is separated by HPLC on an ion exchange column using (NH4)2SO4 eluent with detection at 258 nm. The detection limit is 0.01µM. The method is applied to natural waters and soil solution samples. A background of natural water results in a reduction in EDDS peak area. The method is suited for EDDS analysis in samples with well-defined, simple matrices such as those used in laboratory experiments or biodegradation studie
Spatial and temporal variation in organic acid anion exudation and nutrient anion uptake in the rhizosphere of Lupinus albus L
We investigated in situ the temporal patterns and spatial extent of organic acid anion exudation into the rhizosphere solution of Lupinus albus, and its relation with the nutrient anions phosphate, nitrate and sulfate by means of a rhizobox micro suction cup method under P sufficient conditions. We compared the soil solution in the rhizosphere of cluster roots with that in the vicinity of normal roots, nodules and bulk soil. Compared to the other rhizosphere and soil compartments, concentrations of organic acid anions were higher in the vicinity of cluster roots during the exudative burst (citrate, oxalate) and nodules (acetate, malate), while concentrations of inorganic nutrient anions were highest in the bulk soil. Both active cluster roots and nodules were most efficient in taking up nitrate and phosphate. The intensity of citrate exudation by cluster roots was highly variable. The overall temporal patterns during the lifetime of cluster roots were overlaid by a diurnal pattern, i.e. in most cases, the exudation burst consisted of one or more peaks occurring in the afternoon. Multiple exudation peaks occurred daily or were separated by 1 or 2days. Although citrate concentrations decreased with distance from the cluster root apex, they were still significantly higher at a distance of 6 to 10mm than in the bulk soil. Phosphate concentrations were extremely variable in the proximity of cluster roots. While our results indicate that under P sufficient conditions cluster roots take up phosphate during their entire life time, the influence of citrate exudation on phosphate mobilization from soil could not be assessed conclusively because of the complex interactions between P uptake, organic acid anion exudation and P mobilization. However, we observed indications of P mobilization concurrent with the highest measured citrate concentrations. In conclusion, this study provides semiquantitative in situ data on the reactivity of different root segments of L. albus L. in terms of root exudation and nutrient uptake under nutrient sufficient conditions, in particular on the temporal variability during the lifetime of cluster root
Seismic modeling using the frozen Gaussian approximation
We adopt the frozen Gaussian approximation (FGA) for modeling seismic waves.
The method belongs to the category of ray-based beam methods. It decomposes
seismic wavefield into a set of Gaussian functions and propagates these
Gaussian functions along appropriate ray paths. As opposed to the classic
Gaussian-beam method, FGA keeps the Gaussians frozen (at a fixed width) during
the propagation process and adjusts their amplitudes to produce an accurate
approximation after summation. We perform the initial decomposition of seismic
data using a fast version of the Fourier-Bros-Iagolnitzer (FBI) transform and
propagate the frozen Gaussian beams numerically using ray tracing. A test using
a smoothed Marmousi model confirms the validity of FGA for accurate modeling of
seismic wavefields.Comment: 5 pages, 8 figure
CMS Software Distribution on the LCG and OSG Grids
The efficient exploitation of worldwide distributed storage and computing
resources available in the grids require a robust, transparent and fast
deployment of experiment specific software. The approach followed by the CMS
experiment at CERN in order to enable Monte-Carlo simulations, data analysis
and software development in an international collaboration is presented. The
current status and future improvement plans are described.Comment: 4 pages, 1 figure, latex with hyperref
An oversimplification of physiological principles leads to flawed macroecological analyses
Macrophysiological analyses are useful to predict current and future range limits and improve our understanding of endotherm macroecology, but such analyses too often rely on oversimplifications of endothermic thermoregulatory and energetic physiology, which lessens their applicability. We detail some of the major issues with macrophysiological analyses based on the classic Scholander–Irving model of endotherm energetics in the hope that it will encourage other research teams to more appropriately integrate physiology into macroecological analyses
Verification and intercomparison of reactive transport codes to describe root-uptake
Several mathematical models have been developed to simulate processes and interactions in the plant rhizosphere. Most of these models are based on a rather simplified description of the soil chemistry and interactions of plant roots in the rhizosphere. In particular the feedback loops between exudation, water and solute uptake are mostly not considered, although their importance in the bioavailability of mineral elements for plants has been demonstrated. The aim of this work was to evaluate three existing coupled speciation-transport tools to model rhizosphere processes. In the field of hydrogeochemistry, such␣computational tools have been developed to␣describe acid-base and redox reactions, complexation and ion exchange, adsorption and precipitation of chemical species in soils and aquifers using thermodynamic and kinetic relationships. We implemented and tested a simple rhizosphere model with three geochemical computational tools (ORCHESTRA, MIN3P, and PHREEQC). The first step was an accuracy analysis of the different solution strategies by comparing the numerical results to the analytical solution of solute uptake (K or Ca) by a single cylindrical root. All models are able to reproduce the concentration profiles as well as the uptake flux. The relative error of the simulated concentration profile decreases with increasing distance from the root. The uptake flux was simulated for all codes with less than 5% error for K and less than 0.4% for Ca. The strength of the codes presented in this paper is that they can also be used to investigate more complex and coupled biogeochemical processes in rhizosphere models. This is shown exemplarily with simulations involving both exudation and uptake and the simultaneous uptake of solute and wate
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