Uncertainty in the determination of soil hydraulic parameters and its influence on the performance of two hydrological models of different complexity

Data of soil hydraulic properties forms often a limiting factor in unsaturated zone modelling, especially at the larger scales. Investigations for the hydraulic characterization of soils are time-consuming and costly, and the accuracy of the results obtained by the different methodologies is still debated. However, we may wonder how the uncertainty in soil hydraulic parameters relates to the uncertainty of the selected modelling approach. We performed an intensive monitoring study during the cropping season of a 10 ha maize field in Northern Italy. The data were used to: i) compare different methods for determining soil hydraulic parameters and ii) evaluate the effect of the uncertainty in these parameters on different variables (i.e. evapotranspiration, average water content in the root zone, flux at the bottom boundary of the root zone) simulated by two hydrological models of different complexity: SWAP, a widely used model of soil moisture dynamics in unsaturated soils based on Richards equation, and ALHyMUS, a conceptual model of the same dynamics based on a reservoir cascade scheme. We employed five direct and indirect methods to determine soil hydraulic parameters for each horizon of the experimental profile. Two methods were based on a parameter optimization of: a) laboratory measured retention and hydraulic conductivity data and b) field measured retention and hydraulic conductivity data. The remaining three methods were based on the application of widely used Pedo-Transfer Functions: c) Rawls and Brakensiek, d) HYPRES, and e) ROSETTA. Simulations were performed using meteorological, irrigation and crop data measured at the experimental site during the period June – October 2006. Results showed a wide range of soil hydraulic parameter values generated with the different methods, especially for the saturated hydraulic conductivity Ksat and the shape parameter a of the van Genuchten curve. This is reflected in a variability of the modeling results which is, as expected, different for each model and each variable analysed. The variability of the simulated water content in the root zone and of the bottom flux for different soil hydraulic parameter sets is found to be often larger than the difference between modeling results of the two models using the same soil hydraulic parameter set. Also we found that a good agreement in simulated soil moisture patterns may occur even if evapotranspiration and percolation fluxes are significantly different. Therefore multiple output variables should be considered to test the performances of methods and model

Investigation into Stability, Transition and Turbulence of Thermal Plumes

In this thesis, the stability, transition and turbulence of thermal plumes were investigated by numerical simulation. Experiments were also conducted, but only for the validation of the simulation code being used. The effect of variable transport properties on a large eddy simulation of a turbulent axisymmetric plume was examined, and it was shown that an in-house incompressible Navier-Stokes solver, which is based on a standard Smagorinsky LES model, with the effects of variable properties incorporated using a modified Sutherlands law, predicts the correct statistical behaviours of the turbulent plume. The near-field puffing instability in thermal planar plumes, which had received little attention in the literature, was investigated by direct numerical simulation. The associated lapping flow instability, forming bulge structures over a heated floor section, was studied using a channel flow model, which allows the lapping flow velocity to be varied. The parametric dependencies were found for the bulge formation and the oscillation frequencies in the lapping flow. Further, the Prandtl number dependent transitional behaviours in the near-field were investigated, and direct stability analysis was conducted to study the lapping flow and stem instabilities. Experiments using a shadowgraph technique and an in-house, two-dimensional, two-component particle image velocimetry, with water as the working fluid, provided validations for the near-field unsteady behaviours of thermal plumes. A ventilated filling box flow with a transitional planar plume was also investigated by direct numerical simulation. A mapping of transitional flow behaviours was obtained, and the parametric dependencies of turbulence statistics and mean flow characteristics were investigated. The three-dimensionality was shown to have only minor effects on the transitional ventilated filling box flows being considered

Eigenlevel statistics of the quantum adiabatic algorithm

We study the eigenlevel spectrum of quantum adiabatic algorithm for 3-satisfiability problem, focusing on single-solution instances. The properties of the ground state and the associated gap, crucial for determining the running time of the algorithm, are found to be far from the predictions of random matrix theory. The distribution of gaps between the ground and the first excited state shows an abundance of small gaps. Eigenstates from the central part of the spectrum are, on the other hand, well described by random matrix theory.Comment: 8 pages, 10 ps figure

Mg-Ni-H films as selective coatings: tunable reflectance by layered hydrogenation

Unlike other switchable mirrors, Mg2NiHx films show large changes in reflection that yield very low reflectance (high absorptance) at different hydrogen contents, far before reaching the semiconducting state. The resulting reflectance patterns are of interference origin, due to a self-organized layered hydrogenation mechanism that starts at the substrate interface, and can therefore be tuned by varying the film thickness. This tunability, together with the high absorptance contrast observed between the solar and the thermal energies, strongly suggests the use of these films in smart coatings for solar applications.Comment: Three two-column pages with 3 figures embedded; RevTE