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Search Results: 1 - 10 of 198126 matches for " N. Konz "
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Process identification of soil erosion in steep mountain regions
N. Konz, D. Baenninger, M. Konz, M. Nearing,C. Alewell
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2010,
Abstract: Mountainous soil erosion processes were investigated in the Urseren Valley (Central Switzerland) by means of measurements and simulations. The quantification of soil erosion was performed on hill slope scale (2·20 m) for three different land use types: hayfields, pastures with dwarf shrubs and pastures without dwarf shrubs with three replicates each. Erosion rates during growing season were measured with sediment traps between June 2006 and November 2007. Long-term soil erosion rates were estimated based on Cs- 137 redistribution. In addition, soil moisture and surface flow were recorded during the growing season in the field and compared to model output. We chose the WEPP model (Water Erosion Prediction Project) to simulate soil erosion during the growing season. Model parameters were determined in the field (slope, plant species, fractional vegetation cover, initial saturation level), by laboratory analyses (grain size, organic matter) and by literature study. The WEPP model simulates sheet erosion processes (interrill and splash erosion processes, please note that no rill erosion occurs at our sites). Model output resulted in considerable smaller values than the measured erosion rates with sediment traps for the same period. We attribute the differences to observed random gravity driven erosion of soil conglomerates. The Cs-137 measurements deliver substantially higher mean annual erosion rates, which are most likely connected to snow cover related processes such as snow gliding and avalanche activities.
Extending HELENA to incompressible plasma rotation parallel to the magnetic field
George Poulipoulis,George N. Throumoulopoulos,Christian Konz
Physics , 2015,
Abstract: Plasma rotation in connection to both zonal and mean (equilibrium) flows can play a role in the transitions to the advanced confinement regimes in tokamaks, as the L-H transition and the formation of Internal Transport Barriers. For incompressible rotation the equilibrium is governed by a generalized Grad-Shafranov (GGS) equation and a decoupled Bernoulli-type equation for the pressure. For parallel flow the GGS equation can be transformed to one identical in form with the usual GS equation. In the present study on the basis of the latter equation we have extended HELENA, an equilibrium fixed boundary solver. The extended code solves the GGS equation for a variety of the two free-surface-function terms involved for arbitrary Alfv\'en Mach and density functions. We have constructed diverted-boundary equilibria pertinent to ITER and examined their characteristics, in particular as concerns the impact of rotation on certain equilibrium quantities. It turns out that the rotation and its shear affect noticeably the pressure and toroidal current density with the impact on the current density being stronger in the parallel direction than in the toroidal one. Also, the linear stability of the equilibria constructed is examined by applying a sufficient condition.
Does WEPP meet the specificity of soil erosion in steep mountain regions?
N. Konz,D. B?nninger,M. Nearing,C. Alewell
Hydrology and Earth System Sciences Discussions , 2009,
Abstract: We chose the WEPP model (Water Erosion Prediction Project) to describe soil erosion in the Urseren Valley (central Switzerland) as it seems to be one of the most promising models for steep mountain environments. Crucial model parameters were determined in the field (slope, plant species, fractional vegetation cover, initial saturation level), by laboratory analyses (grain size, organic matter) or by the WEPP manual (rill- and interrill erodibility, effective hydraulic conductivity, cation exchange capacity). The quantification of soil erosion was performed on hill slope scale for three different land use types: meadows, pastures with dwarf shrubs and pastures without dwarf shrubs. Erosion rates for the vegetation period were measured with sediment traps between June 2006 and November 2007. Long-term soil erosion rates were estimated by measuring Cs-137 redistribution, deposited after the Chernobyl accident. In addition to the erosion rates, soil moisture and surface flow was additionally measured during the vegetation period in the field and compared to model output. Short-term erosion rates are simulated well whereas long term erosion rates were underestimated by the model. Simulated soil moisture has a parallel development compared to measured data from April onwards but a converse dynamic in early spring (simulated increase and measured decrease in March and April). The discrepancy in soil water during springtime was explained by delayed simulated snow cover melting. The underestimation of simulated long term erosion rates is attributed to alpine processes other than overland flow and splash. Snow gliding processes might dominate erosion processes during winter time. We assume that these differences lead to the general simulated underestimation of erosion rates. Thus, forcing erosion processes which dominate erosion rates in mountainous regions have to be implemented to WEPP for a successful application in the future.
Diabetische Polyneuropathie und das Risiko für ein diabetisches Fu syndrom
Konz K
Journal für Klinische Endokrinologie und Stoffwechsel , 2010,
Abstract: Die diabetische Polyneuropathie ist eine h ufige Folgeerkrankung und ein wesentlicher Wegbereiter für das diabetische Fu syndrom. Wie andere diabetische Folgekrankheiten beruht sie auf der Hyperglyk mie und dem daraus resultierenden vermehrten oxidativen Stress. Es existieren verschiedene klinische Erscheinungsformen der diabetischen Neuropathie. Sie muss differenzialdiagnostisch gegen andere h ufige Polyneuropathien abgegrenzt werden. Die Diagnostik obliegt in erster Linie dem diabetologisch t tigen Arzt. Nur bei differenzialdiagnostischen Problemen wird der Neurologe konsultiert. Bei diabetischem Fu syndrom ist eine angiologische Untersuchung obligat. Die kausalen und symptomatischen Therapieoptionen werden ausführlich dargestellt unter Berücksichtigung der Leitlinien der Deutschen Diabetes- Gesellschaft von 2009, insbesondere die Behandlung der schmerzhaften Verl ufe und des diabetischen Fu syndroms. Auf pr ventive Ma nahmen wird eingegangen.
An application of the HBV model to the Tamor Basin in Eastern Nepal
S Normand,M Konz,J Merz
Journal of Hydrology and Meteorology , 2010, DOI: 10.3126/jhm.v7i1.5616
Abstract: The semi-distributed, conceptual hydrological model HBV was applied to Tamor Nadi in order to estimate runoff at Tapethok, Taplejung, in Eastern Nepal. As there was no discharge data available for this particular location, the model was first calibrated and validated for the bigger, gauged basins at Mulghat and Majithar. However due to its structure HBV shows difficulties in modelling low and high flows correctly at the same time. Therefore two parameter sets were produced: one with focus on the model performance during low flows and the second one, on high flows. Those parameters were then applied to the basin at Tapethok. Generally HBV was able to correctly simulate low flows except for some sharp peaks due to isolated precipitation events. However, pre-monsoon discharge was overestimated while the runoff of the monsoon season were most of the time underestimated. The main reasons for this situation are: (1) HBV generates runoff from one single groundwater reservoir for the entire catchment, leading to sharp peaks with a rapid recession and therefore exaggerated reactions on precipitation during dry season; (2) during pre-monsoon snow and ice melt gain in importance and add to the mentioned problem; (3) due to the simplified representation of storages in the model structure the catchment area drains too quickly. Keywords: Tamor Basin DOI: http://dx.doi.org/10.3126/jhm.v7i1.5616 ? JHM 2010; 7(1): 49-58 ?
Dynamical evolution of high velocity clouds in the intergalactic medium
C. Konz,C. Bruens,G. T. Birk
Physics , 2002, DOI: 10.1051/0004-6361:20020863
Abstract: HI observations of high-velocity clouds (HVCs) indicate, that they are interacting with their ambient medium. Even clouds located in the very outer Galactic halo or the intergalactic space seem to interact with their ambient medium. In this paper, we investigate the dynamical evolution of high velocity neutral gas clouds moving through a hot magnetized ambient plasma by means of two-dimensional magnetohydrodynamic plasma-neutral gas simulations. This situation is representative for the fast moving dense neutral gas cloudlets in the Magellanic Stream as well as for high velocity clouds in general. The question on the dynamical and thermal stabilization of a cold dense neutral cloud in a hot thin ambient halo plasma is numerically investigated. The simulations show the formation of a comet-like head-tail structure combined with a magnetic barrier of increased field strength which exerts a stabilizing pressure on the cloud and hinders hot plasma from diffusing into the cloud. The simulations can explain both the survival times in the intergalactic medium and the existence of head-tail high velocity clouds.
Shear-Flow Driven Current Filamentation: Two-Dimensional Magnetohydrodynamic Simulations
C. Konz,H. Wiechen,H. Lesch
Physics , 2000, DOI: 10.1063/1.1322558
Abstract: The process of current filamentation in permanently externally driven, initially globally ideal plasmas is investigated by means of two-dimensional Magnetohydrodynamic (MHD)-simulations. This situation is typical for astrophysical systems like jets, the interstellar and intergalactic medium where the dynamics is dominated by external forces. Two different cases are studied. In one case, the system is ideal permanently and dissipative processes are excluded. In the second case, a system with a current density dependent resistivity is considered. This resistivity is switched on self-consistently in current filaments and allows for local dissipation due to magnetic reconnection. Thus one finds tearing of current filaments and, besides, merging of filaments due to coalescence instabilities. Energy input and dissipation finally balance each other and the system reaches a state of constant magnetic energy in time.
Implementation of a process-based catchment model in a poorly gauged, highly glacierized Himalayan headwater
M. Konz, S. Uhlenbrook, L. Braun, A. Shrestha,S. Demuth
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2007,
Abstract: The paper presents a catchment modeling approach for remote glacierized Himalayan catchments. The distributed catchment model TACD, which is widely based on the HBV model, was further developed for the application in highly glacierized catchments on a daily timestep and applied to the Nepalese Himalayan headwater Langtang Khola (360 km2). Low laying reference stations are taken for temperature extrapolation applying a second order polynomial function. Probability based statistical methods enable bridging data gaps in daily precipitation time series and the redistribution of cumulated precipitation sums over the previous days. Snow and ice melt was calculated in a distributed way based on the temperature-index method employing calculated daily potential sunshine durations. Different melting conditions of snow and ice and melting of ice under debris layers were considered. The spatial delineation of hydrological response units was achieved by taking topographic and physiographic information from maps and satellite images into account, and enabled to incorporate process knowledge into the model. Simulation results demonstrated that the model is able to simulate daily discharge for a period of 10 years and point glacier mass balances observed in the research area with an adequate reliability. The simple but robust data pre-processing and modeling approach enables the determination of the components of the water balance of a remote, data scarce catchment with a minimum of input data.
On the measurement of solute concentrations in 2-D flow tank experiments
M. Konz,P. Ackerer,E. Meier,P. Huggenberger
Hydrology and Earth System Sciences Discussions , 2007,
Abstract: In this study we describe and compare photometric and resistivity measurement methodologies to determine solute concentrations in porous media flow tank experiments. The first method is the photometric method, which directly relates digitally measured intensities of a tracer dye to concentrations without previously converting the intensities to optical densities. This enables an effective processing of a large amount of images to compute concentration time series at various points of the flow tank. Perturbations of the measurements are investigated and both lens flare effects and the image resolution turned out to be the major sources of error. An attached mask is able to minimize the lens flare effects. The second method for in situ measurement of salt concentrations in porous media experiments is the resistivity method. The resistivity measurement system uses two different input voltages at gilded electrode sticks to enable the measurement of salt concentrations from 0 to 300 g/l. Power laws are used to relate apparent resistivity values and salt concentrations. However, due to the unknown measurement volume of the electrodes, we consider the image analysis method more appropriate for intermediate scale laboratory benchmark experiments to evaluate numerical codes.
Tradeoffs for the implementation of a process-based catchment model in a poorly gauged, highly glacierized Himalayan headwater
M. Konz,S. Uhlenbrook,L. Braun,A. Shrestha
Hydrology and Earth System Sciences Discussions , 2006,
Abstract: The paper presents a catchment modeling approach for remote glacierized Himalayan catchments. The distributed catchment model TACD, which is widely based on the HBV model, was further developed for the application in highly glacierized catchments on a daily timestep and applied to the Nepalese Himalayan headwater Langtang Khola (360 km2). Low laying reference stations are taken for temperature extrapolation applying a second order polynomial function. Probability based statistical methods enable bridging data gaps in daily precipitation time series and the redistribution of cumulated precipitation sums over the previous days. Snow and ice melt was calculated in a distributed way based on the temperature-index method employing calculated daily potential sunshine durations. Different melting conditions of snow and ice and melting of ice under debris layers were considered. The spatial delineation of hydrological response units was achieved by taking topographic and physiographic information from maps and satellite images into account, and enabled to incorporate process knowledge into the model. Simulation results demonstrated that the model is able to simulate daily discharge for a period of 10 years and point glacier mass balances observed in the research area with an adequate reliability. The simple but robust data pre-processing and modeling approach enables the determination of the components of the water balance of a remote, data scarce catchment with a minimum of input data.
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