Modelling sulphate stream concentrations in the Black Forest catchments Schluchsee and Villingen

International audienceThe sulphate (SO4) released by mineralisation and desorption from soil can play an important role in determining concentrations of SO4 in streams. The MAGIC model was calibrated for two catchments in the Black Forest, Germany (Schluchsee and Villingen) and SO4 concentrations in the streams for the years 2016 and 2030 were predicted. Special emphasis was placed on the dynamics of soil sulphur (S) pools. At Schluchsee, 90% of soil S is stored in the organic S (Sorg) pool, whereas at Villingen, 54% is in the inorganic (Sinorg) pool. The Villingen stream chemistry was modelled successfully by measured Langmuir isotherm parameters (LIPs) for Sinorg. Schluchsee data could not be modelled satisfactorily using measured or freely adapted LIPs only, as the Sinorg pool would have to be more than five times larger than what was measured. With 60.5 mmolc SO4 m-2 yr-1 as internal soil source by mineralisation and the measured LIPs, stream data was modelled successfully. The modelling shows that in these two catchments pre-industrial concentrations of SO4 in runoff can be reached in the next two decades if S deposition decreases as intended under currently agreed national and international legislation. Sorg is the most likely dominant source of SO4 released at Schluchsee. Mineralization from the Sorg pool must be included when modelling SO4 concentrations in the stream. As the dynamics and the controlling factors of S release by mineralisation are not yet clear, this process remains a source of uncertainty for predictions of SO4 concentrations in streams. Future research should concentrate on dynamics of S mineralisation in the field, such that mathematical descriptions of long-term S-mineralisation can be incorporated into biogeochemical models. Keywords: sulphate release, organic S, mineralisation, acidification, recovery, modelling, MAGIC, catchments, predictions, Germany, fores

GHz bandwidth electro-optics of a single self-assembled quantum dot in a charge-tunable device

The response of a single InGaAs quantum dot, embedded in a miniaturized charge-tunable device, to an applied GHz bandwidth electrical pulse is investigated via its optical response. Quantum dot response times of 1.0 \pm 0.1 ns are characterized via several different measurement techniques, demonstrating GHz bandwidth electrical control. Furthermore a novel optical detection technique based on resonant electron-hole pair generation in the hybridization region is used to map fully the voltage pulse experienced by the quantum dot, showing in this case a simple exponential rise.Comment: 7 pages, 4 figure

Micropatterned Electrostatic Traps for Indirect Excitons in Coupled GaAs Quantum Wells

We demonstrate an electrostatic trap for indirect excitons in a field-effect structure based on coupled GaAs quantum wells. Within the plane of a double quantum well indirect excitons are trapped at the perimeter of a SiO2 area sandwiched between the surface of the GaAs heterostructure and a semitransparent metallic top gate. The trapping mechanism is well explained by a combination of the quantum confined Stark effect and local field enhancement. We find the one-dimensional trapping potentials in the quantum well plane to be nearly harmonic with high spring constants exceeding 10 keV/cm^2.Comment: 21 pages, 6 figures, submitted to Phys. Rev.

Photocurrent and Photoconductance Properties of a GaAs Nanowire

We report on photocurrent and photoconductance processes in a freely suspended p-doped single GaAs nanowire. The nanowires are grown by molecular beam epitaxy (MBE), and they are electrically contacted by a focused ion beam (FIB) deposition technique. The observed photocurrent is generated at the Schottky contacts between the nanowire and metal source-drain electrodes, while the observed photoconductance signal can be explained by a photogating effect induced by optically generated charge carriers located at the surface of the nanowire. Both optoelectronic effects are sensitive to the polarization of the exciting laser field, enabling polarization dependent photodetectors

The problem of assessing the quality of health

This article analyzes the concept of "health" and the problem of assessing the quality of health

Architecture of soil microaggregates: Advanced methodologies to explore properties and functions

The functions of soils are intimately linked to their three-dimensional pore space and the associated biogeochemical interfaces, mirrored in the complex structure that developed during pedogenesis. Under stress overload, soil disintegrates into smaller compound structures, conventionally named aggregates. Microaggregates (<250 µm) are recognized as the most stable soil structural units. They are built of mineral, organic, and biotic materials, provide habitats for a vast diversity of microorganisms, and are closely involved in the cycling of matter and energy. However, exploring the architecture of soil microaggregates and their linkage to soil functions remains a challenging but demanding scientific endeavor. With the advent of complementary spectromicroscopic and tomographic techniques, we can now assess and visualize the size, composition, and porosity of microaggregates and the spatial arrangement of their interior building units. Their combinations with advanced experimental pedology, multi-isotope labeling experiments, and computational approaches pave the way to investigate microaggregate turnover and stability, explore their role in element cycling, and unravel the intricate linkage between structure and function. However, spectromicroscopic techniques operate at different scales and resolutions, and have specific requirements for sample preparation and microaggregate isolation; hence, special attention must be paid to both the separation of microaggregates in a reproducible manner and the synopsis of the geography of information that originates from the diverse complementary instrumental techniques. The latter calls for further development of strategies for synlocation and synscaling beyond the present state of correlative analysis. Here, we present examples of recent scientific progress and review both options and challenges of the joint application of cutting-edge techniques to achieve a sophisticated picture of the properties and functions of soil microaggregates

Functional Characterization of the HuR:CD83 mRNA Interaction

Maturation of dendritic cells (DC) is characterized by expression of CD83, a surface protein that appears to be necessary for the effective activation of naïve T-cells and T-helper cells by DC. Lately it was shown that CD83 expression is regulated on the posttranscriptional level by interaction of the shuttle protein HuR with a novel posttranscriptional regulatory RNA element (PRE), which is located in the coding region of the CD83 transcript. Interestingly, this interaction commits the CD83 mRNA to efficient nuclear export via the CRM1 pathway. To date, however, the structural basis of this interaction, which potentially involves three distinct RNA recognition motifs (RRM1–3) in HuR and a complex three-pronged RNA stem-loop element in CD83 mRNA, has not been investigated in detail. In the present work we analyzed this interaction in vitro and in vivo using various HuR- and CD83 mRNA mutants. We are able to demonstrate that both, RRM1 and RRM2 are crucial for binding, whereas RRM3 as well as the HuR hinge region contributed only marginally to this protein∶RNA interaction. Furthermore, mutation of uridine rich patches within the PRE did not disturb HuR:CD83 mRNA complex formation while, in contrast, the deletion of specific PRE subfragments from the CD83 mRNA prevented HuR binding in vitro and in vivo. Interestingly, the observed inhibition of HuR binding to CD83 mRNA does not lead to a nuclear trapping of the transcript but rather redirected this transcript from the CRM1- towards the NXF1/TAP-specific nuclear export pathway. Thus, the presence of a functional PRE permits nucleocytoplasmic trafficking of the CD83 transcript via the CRM1 pathway

Waveguide Coupled Resonance Fluorescence from On-Chip Quantum Emitter

Resonantly driven quantum emitters offer a very promising route to obtain highly coherent sources of single photons required for applications in quantum information processing (QIP). Realizing this for on-chip scalable devices would be important for scientific advances and practical applications in the field of integrated quantum optics. Here we report on-chip quantum dot (QD) resonance fluorescence (RF) efficiently coupled into a single-mode waveguide, a key component of a photonic integrated circuit, with a negligible resonant laser background and show that the QD coherence is enhanced by more than a factor of 4 compared to off-resonant excitation. Single-photon behavior is confirmed under resonant excitation, and fast fluctuating charge dynamics are revealed in autocorrelation g(2) measurements. The potential for triggered operation is verified in pulsed RF. These results pave the way to a novel class of integrated quantum-optical devices for on-chip quantum information processing with embedded resonantly driven quantum emitters