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Search Results: 1 - 10 of 241621 matches for " K. O. Rasmussen "
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Assessing impacts of climate change, sea level rise, and drainage canals on saltwater intrusion to coastal aquifer
P. Rasmussen, T. O. Sonnenborg, G. Goncear,K. Hinsby
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2013,
Abstract: Groundwater abstraction from coastal aquifers is vulnerable to climate change and sea level rise because both may potentially impact saltwater intrusion and hence groundwater quality depending on the hydrogeological setting. In the present study the impacts of sea level rise and changes in groundwater recharge are quantified for an island located in the Western Baltic Sea. The low-lying central area of the investigated part of the island was extensively drained and reclaimed during the second half of the 19th century by a system of artificial drainage canals that significantly affects the flow dynamics of the area. The drinking water, mainly for summer cottages, is abstracted from 11 wells drilled to a depth of around 20 m into the upper 5–10 m of a confined chalk aquifer, and the total pumping is only 5–6% of the drainage pumping. Increasing chloride concentrations have been observed in several abstraction wells and in some cases the WHO drinking water standard has been exceeded. Using the modeling package MODFLOW/MT3D/SEAWAT the historical, present and future freshwater-sea water distribution is simulated. The model is calibrated against hydraulic head observations and validated against geochemical and geophysical data from new investigation wells, including borehole logs, and from an airborne transient electromagnetic survey. The impact of climate changes on saltwater intrusion is found to be sensitive to the boundary conditions of the investigated system. For the flux-controlled aquifer to the west of the drained area only changes in groundwater recharge impacts the freshwater–sea water interface whereas sea level rise does not result in increasing sea water intrusion. However, on the barrier islands to the east of the reclaimed area, below which the sea is hydraulically connected to the drainage canals, and the boundary of the flow system therefore controlled, the projected changes in sea level, groundwater recharge and stage of the drainage canals all have significant impacts on saltwater intrusion and the chloride concentrations found in abstraction wells.
Assessing impacts of climate change, sea level rise, and drainage canals on saltwater intrusion to coastal aquifer
P. Rasmussen,T. O. Sonnenborg,G. Goncear,K. Hinsby
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2013, DOI: 10.5194/hess-17-421-2013
Abstract: Groundwater abstraction from coastal aquifers is vulnerable to climate change and sea level rise because both may potentially impact saltwater intrusion and hence groundwater quality depending on the hydrogeological setting. In the present study the impacts of sea level rise and changes in groundwater recharge are quantified for an island located in the Western Baltic Sea. The low-lying central area of the investigated part of the island was extensively drained and reclaimed during the second half of the 19th century by a system of artificial drainage canals that significantly affects the flow dynamics of the area. The drinking water, mainly for summer cottages, is abstracted from 11 wells drilled to a depth of around 20 m into the upper 5–10 m of a confined chalk aquifer, and the total pumping is only 5–6% of the drainage pumping. Increasing chloride concentrations have been observed in several abstraction wells and in some cases the WHO drinking water standard has been exceeded. Using the modeling package MODFLOW/MT3D/SEAWAT the historical, present and future freshwater-sea water distribution is simulated. The model is calibrated against hydraulic head observations and validated against geochemical and geophysical data from new investigation wells, including borehole logs, and from an airborne transient electromagnetic survey. The impact of climate changes on saltwater intrusion is found to be sensitive to the boundary conditions of the investigated system. For the flux-controlled aquifer to the west of the drained area only changes in groundwater recharge impacts the freshwater–sea water interface whereas sea level rise does not result in increasing sea water intrusion. However, on the barrier islands to the east of the reclaimed area, below which the sea is hydraulically connected to the drainage canals, and the boundary of the flow system therefore controlled, the projected changes in sea level, groundwater recharge and stage of the drainage canals all have significant impacts on saltwater intrusion and the chloride concentrations found in abstraction wells.
Assessing impacts of climate change, sea level rise, and drainage canals on saltwater intrusion to coastal aquifer
P. Rasmussen,T. O. Sonnenborg,G. Goncear,K. Hinsby
Hydrology and Earth System Sciences Discussions , 2012, DOI: 10.5194/hessd-9-7969-2012
Abstract: Groundwater abstraction from coastal aquifers is vulnerable to climate change and sea level rise because both may potentially impact saltwater intrusion and hence groundwater quality depending on the hydrogeological setting. In the present study the impacts of sea level rise and changes in groundwater recharge are quantified for an island located in the Western Baltic Sea. Agricultural land dominates the western and central parts of the island, which geologically are developed as push moraine hills and a former lagoon (later wetland area) behind barrier islands to the east. The low-lying central area of the island was extensively drained and reclaimed during the second half of the 19th century. Summer cottages along the beach on the former barrier islands dominate the eastern part of the island. The main water abstraction is for holiday cottages during the summer period (June–August). The water is abstracted from 11 wells drilled to a depth of around 20 m in the upper 5–10 m of a confined chalk aquifer. Increasing chloride concentrations have been observed in several abstraction wells and in some cases the WHO drinking water standard has been exceeded. Using the modeling package MODFLOW/MT3D/SEAWAT the historical, present and future freshwater–sea water distribution is simulated. The model is calibrated against hydraulic head observations and validated against geochemical and geophysical data from new investigation wells, including borehole logs, and from an airborne transient electromagnetic survey. The impact of climate changes on saltwater intrusion is found to be sensitive to the boundary conditions of the investigated system. For the flux-controlled aquifer to the west of the drained area only changes in groundwater recharge impacts the freshwater–sea water interface whereas sea level rise do not result in increasing sea water intrusion. However, on the barrier islands to the east of the reclaimed area below which the sea is hydraulically connected to the drainage canal, and the boundary of the flow system therefore controlled, the projected changes in sea level, groundwater recharge and stage of the drainage canal all have significant impacts on saltwater intrusion and hence the chloride concentrations found in the abstraction wells.
Origins of elastic properties in ordered nanocomposites
R. B. Thompson,K. O. Rasmussen,T. Lookman
Physics , 2004, DOI: 10.1021/nl048407f
Abstract: We predict a diblock copolymer melt in the lamellar phase with added spherical nanoparticles that have an affinity for one block to have a lower tensile modulus than a pure diblock copolymer system. This weakening is due to the swelling of the lamellar domain by nanoparticles and the displacement of polymer by elastically inert fillers. Despite the overall decrease in the tensile modulus of a polydomain sample, the shear modulus for a single domain increases dramatically.
Exact Solutions of the Saturable Discrete Nonlinear Schrodinger Equation
Avinash Khare,K. O. Rasmussen,M. R. Samuelsen,A. Saxena
Physics , 2004, DOI: 10.1088/0305-4470/38/4/002
Abstract: Exact solutions to a nonlinear Schr{\"o}dinger lattice with a saturable nonlinearity are reported. For finite lattices we find two different standing-wave-like solutions, and for an infinite lattice we find a localized soliton-like solution. The existence requirements and stability of these solutions are discussed, and we find that our solutions are linearly stable in most cases. We also show that the effective Peierls-Nabarro barrier potential is nonzero thereby indicating that this discrete model is quite likely nonintegrable.
Probing the mechanical unzipping of DNA
N. K. Voulgarakis,A. Redondo,A. R. Bishop,K. O. Rasmussen
Physics , 2005, DOI: 10.1103/PhysRevLett.96.248101
Abstract: A study of the micromechanical unzipping of DNA in the framework of the Peyrard-Bishop-Dauxois model is presented. We introduce a Monte Carlo technique that allows accurate determination of the dependence of the unzipping forces on unzipping speed and temperature. Our findings agree quantitatively with experimental results for homogeneous DNA, and for $\lambda$-phage DNA we reproduce the recently obtained experimental force-temperature phase diagram. Finally, we argue that there may be fundamental differences between {\em in vivo} and {\em in vitro} DNA unzipping.
Bubble Statistics and Dynamics in Double-Stranded DNA
B. S. Alexandrov,L. T. Wille,K. O. Rasmussen,A. R. Bishop,K. B. Blagoev
Physics , 2006, DOI: 10.1103/PhysRevE.74.050901
Abstract: The dynamical properties of double-stranded DNA are studied in the framework of the Peyrard-Bishop-Dauxois model using Langevin dynamics. Our simulations are analyzed in terms of two probability functions describing coherently localized separations ("bubbles") of the double strand. We find that the resulting bubble distributions are more sharply peaked at the active sites than found in thermodynamically obtained distributions. Our analysis ascribes this to the fact that the bubble life-times significantly afects the distribution function. We find that certain base-pair sequences promote long-lived bubbles and we argue that this is due to a length scale competition between the nonlinearity and disorder present in the system.
Theory of Bubble Nucleation and Cooperativity in DNA Melting
S. Ares,N. K. Voulgarakis,K. O. Rasmussen,A. R. Bishop
Quantitative Biology , 2004, DOI: 10.1103/PhysRevLett.94.035504
Abstract: The onset of intermediate states (denaturation bubbles) and their role during the melting transition of DNA are studied using the Peyrard-Bishop-Daxuois model by Monte Carlo simulations with no adjustable parameters. Comparison is made with previously published experimental results finding excellent agreement. Melting curves, critical DNA segment length for stability of bubbles and the possibility of a two states transition are studied.
Elevation correction of ERA-Interim temperature data in complex terrain
J. Rasmussen, T. O. Sonnenborg, S. Stisen, L. P. Seaby, B. S. B. Christensen,K. Hinsby
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2012,
Abstract: Climate changes are expected to result in a warmer global climate, with increased inter-annual variability. In this study, the possible impacts of these climate changes on irrigation and low stream flow are investigated using a distributed hydrological model of a sandy catchment in western Denmark. The IPCC climate scenario A1B was chosen as the basis for the study, and meteorological forcings (precipitation, reference evapotranspiration and temperature) derived from the ECHAM5-RACMO regional climate model for the period 2071–2100 was applied to the model. Two bias correction methods, delta change and Distribution-Based Scaling, were used to evaluate the importance of the bias correction method. Using the annual irrigation amounts, the 5-percentile stream flow, the median minimum stream flow and the mean stream flow as indicators, the irrigation and the stream flow predicted using the two methods were compared. The study found that irrigation is significantly underestimated when using the delta change method, due to the inability of this method to account for changes in inter-annual variability of precipitation and reference ET and the resulting effects on irrigation demands. However, this underestimation of irrigation did not result in a significantly higher summer stream flow, because the summer stream flow in the studied catchment is controlled by the winter and spring recharge, rather than the summer precipitation. Additionally, future increases in CO2 are found to have a significant effect on both irrigation and low flow, due to reduced transpiration from plants.
Comment on "Can one predict DNA Transcription Start Sites by Studying Bubbles?"
C. H. Choi,A. Usheva,G. Kalosakas,K. O. Rasmussen,A. R. Bishop
Physics , 2005, DOI: 10.1103/PhysRevLett.96.239801
Abstract: Comment on T.S. van Erp, S. Cuesta-Lopez, J.-G. Hagmann, and M. Peyrard, Phys. Rev. Lett. 95, 218104 (2005) [arXiv: physics/0508094].
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