Zusammensetzung und großflächige Entwicklung der Bodenkohlenstoffvorräte in Ober- und Unterböden degradierter Grasland-Ökosysteme des Tibetischen Plateaus

Die Tibetischen Grasländer speichern etwa 2% der globalen Bodenkohlenstoffvorräte. Etwa ein Fünftel dieser Grasländer ist von besonders beweidungsresistenter Kobresia pygmaea dominiert. Staatliche Siedlungsprogramme führen jedoch zunehmend zu einer ungleichmäßigen Nutzung der Grasländer. Während in siedlungsfernen Gebieten der Beweidungsdruck abnimmt, steigt die Beweidungsintensität und damit die Bodendegradation in Siedlungsnähe. Ziel dieser Studie war es Veränderungen in der Menge und Zusammensetzung (C/N, Anteil von Lignin, Cutin, Suberin, Neutral- und Aminozuckern) der organischen Bodensubstanz (OBS) mit zunehmender Degradation der Kobresia pygmaea Wurzelmatten zu erfassen. Hierzu wurden die sechs Degradationsstadien in drei Tiefenstufen (0-5, 5-15 und 15-35 cm) beprobt. Auf der Grundlage dieser punktuell erhobenen Daten und unter Einbeziehung von weiteren 79 unabhängig veröffentlichten Literaturstudien wurden mittels Metaanalyse die wichtigsten Einflussfaktoren auf den Bodenkohlenstoffgehalt ermittelt. Höhere Beiträge hydrolysierbarer Fettsäuren und Neutralzucker zur OBS im Unterboden während der fortschreitenden Degradation deuten auf eine Translokation von Oberbodenmaterial, sowie eine Zunahme des Abbauzustands der OBS hin. Eine signifikante Anreicherung von Lignin mit zunehmendem Degradationsstadium wurde nachgewiesen. Der Beitrag von Aminozuckern nahm dagegen in allen Tiefen mit zunehmender Degradation ab. Die Metaanalyse zeigte, dass die Einflussvariablen Bodentextur, Höhenlage, Beweidungsintensität/Degradationsstufe, und Profilmächtigkeit bis zu 60% der Bodenkohlenstoffvorräte in einem ersten ausgewählten Testgebiet erklären. Basierend auf diesen Ergebnissen werden die zu erwartende Freisetzung bzw. Zunahme der Bodenkohlenstoffvorräte unter verschiedenen Beweidungsszenarien für ausgewählte Teilgebiete des Tibetplateaus modelliert

Time‐dependent global MHD simulations of Cassini T32 flyby: From magnetosphere to magnetosheath

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95383/1/jgra19655.pd

Communications and Transport: The mobility of information, people and commodities

In a context where the study of communications tends to focus only on the mobility of information, to the neglect of that of people and commodities, this article explores the potential for a closer integration between the fields of communications and transport studies. Against the presumption that the emergence of virtuality means that material geographies are no longer of consequence, the role of mediated ‘technologies of distance’ is considered here in the broader contexts of the construction (and regulation) of a variety of physical forms of mobility and the changing modes of articulation of the virtual and material worlds

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Feedback and rotational stabilization of resistive wall modes in ITER

Different models have been introduced in the stability code MARS-F in order to study the damping effect on resistive wall modes (RWM) in rotating plasmas. Benchmarks of MARS-F calculations with RWM experiments on JET and DIII-D indicate that the semi-kinetic damping model is a good candidate for explaining the damping mechanisms. Based on these results, the critical rotation speeds required for RWM stabilization in advanced ITER scenarios are predicted. Active feedback control of the n = 1 RWM in ITER is also studied using the MARS-F code

Modeling of resistive wall mode and its control in experiments and ITER

Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved between MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut, Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits