Comparison of Sr Transport in Compacted Homoionous Na and Ca Bentonite Using a Planar Source Method Evaluated at Ideal and Non-Ideal Boundary Condition

With the aim to determine the influence of dominant interlayer cation on the sorption and diffusion properties of bentonite, diffusion experiments with Sr on the compacted homoionous Ca- and Na-forms of Czech natural Mg/Ca bentonite using the planar source method were performed. The bentonite was compacted to 1400 kg·m−3, and diffusion experiments lasted 1, 3 or 5 days. Two methods of apparent diffusion coefficient Da determination based on the analytical solution of diffusion equation for ideal boundary conditions in a linear form were compared and applied. The determined Da value for Ca-bentonite was 1.36 times higher than that for Na-bentonite sample. Values of Kd were determined in independent batch sorption experiments and were extrapolated for the conditions of compacted bentonite. In spite of this treatment, the use of Kd values determined by batch sorption experiments on a loose material for the determination of effective diffusion coefficient De values from planar source diffusion experiments proved to be inconsistent with the standard Fickian description of diffusion taking into account only the pore diffusion in compacted bentonite. Discrepancies between Kd and De values were measured in independent experiments, and those that resulted from the evaluation of planar source diffusion experiments could be well explained by the phenomenon of surface diffusion. The obtained values of surface diffusion coefficients Ds were similar for both studied systems, and the predicted value of total effective diffusion coefficient De(tot) describing Sr transport in the Na-bentonite was four times higher than in the Ca-bentonite.

Near-Field Resolution in Planar Source Reconstructions

<div>This paper deals with the classical question of estimating the achievable resolution in terms of the configuration parameters in inverse source problems. In particular, the study focuses on the case of a planar surface magnetic current which is to be reconstructed from near-field observed over a bounded rectangular aperture parallel to the source domain. Here, the plan is to work out a resolution estimation that precisely captures the spatially varying behaviour entailed by the near-field and aspect-limited configuration. To this end, the pertinent radiation operator is inverted by an adjoint inversion scheme (a backpropagation- like method) and the corresponding point-spread function is analytically estimated. Numerical examples show that the derived resolution estimation clearly points out the role of the geometrical parameters of the configuration and it is more accurate than other literature results.</div>

Near-Field Resolution in Planar Source Reconstructions

<div>This paper deals with the classical question of estimating the achievable resolution in terms of the configuration parameters in inverse source problems. In particular, the study focuses on the case of a planar surface magnetic current which is to be reconstructed from near-field observed over a bounded rectangular aperture parallel to the source domain. Here, the plan is to work out a resolution estimation that precisely captures the spatially varying behaviour entailed by the near-field and aspect-limited configuration. To this end, the pertinent radiation operator is inverted by an adjoint inversion scheme (a backpropagation- like method) and the corresponding point-spread function is analytically estimated. Numerical examples show that the derived resolution estimation clearly points out the role of the geometrical parameters of the configuration and it is more accurate than other literature results.</div>

Near-Field Warping Sampling Scheme for Broad-Side Antenna Characterization

In this paper the problem of sampling the field radiated by a planar source observed over a finite planar aperture located in the near-field is addressed. The problem is cast as the determination of the spatial measurement positions which allow us to discretize the radiation problem so that the singular values of the radiation operator are well-approximated. More in detail, thanks to a suitably warping transformation of the observation variables, the kernel function of the relevant operator is approximated by a band-limited function and hence the sampling theorem applied to achieved discretization. It results in the sampling points having to be non-linearity arranged across the measurement aperture and their number can be considerably lowered as compared to more standard sampling approach. It is shown that the proposed sampling scheme works well for measurement apertures that are not too large as compared to the source’s size. As a consequence, the method appears better suited for broad-side large antenna whose radiated field is mainly concentrated in front of the antenna. A numerical analysis is included to check the theoretical findings and to study the trade-off between the field accuracy representation (over the measurement aperture) and the truncation error in the estimated far-field radiation pattern.

Assessment of thermal water outflow plume in heterogeneous glaciofluvial deposits: a case study from Julian Alps, Slovenia

&lt;p&gt;In Alps, a number of thermal springs are known, which represent the outflow of thermal water from low temperature geothermal systems in fractured rocks. Such dynamics is usually characterized with convection flow, derived either by fault intersection or hydrogeological barrier where the thermal water is uprising due to hydraulic pressure imbalance. When the water is uprising due to convection, it is very likely that the mixing processes between the deep thermal component and the shallow fresh groundwater are established. In Bled case study in Slovenia, the thermal water with average temperature of 21.5 &amp;#176;C, which is around 12 &amp;#176;C higher than average annual air temperature, is discharging from fractured carbonate rocks into glacial Quaternary sediments. Since they have relatively higher but heterogeneous permeability, the uprising thermal water drains into these deposits and, consequently, forms thermal plume which is extending parallel to prevailing fresh groundwater flow direction. Knowing the extent of the thermal plume is of crucial importance for sustainable exploration of the geothermal resource, since it provides answers also to the key issues related to its geothermal and hydraulic characteristics and the dynamics of the regional flow of groundwater, including its recharge area. By approximating the thermal water outflow as a planar source (since we assume it springs out from a fault zone), a planar advective heat transport model (PAHM) was used to evaluate its geometry and quantify the rates. Nine scenarios were applied accounting for different dimensions of the heat source. Each scenario was verified by calculating relative error between the analytical model results and measured borehole temperatures. The PAHM proved to be a useful tool in applying heat transfer as a planar source in groundwater flow. Still, it is necessary to consider or to introduce relatively rough assumptions (e.g. simple model geometry) leading to a very conservative approach. The heterogeneity of the medium has a significant influence on the temperature distributions obtained with different simulation scenarios. Therefore, the calculated temperature distribution within a thermal plume is a subject to uncertainty. In addition, some small portion of a relative error can be attributed to Lake Bled, since the thermal plume is extending in the zone of lake water temperature fluctuation influence. Nevertheless, the analytical model can be used as a tool for simulating spatial distribution of the observed values acquired from field measurements and thus more correctly evaluating the average natural conditions.&lt;/p&gt;

Toward a better system for short range precision force measurements

Many precision experiments have been done in the Casimir regime and in short range gravity when the separation between the interacting bodies is in the sub-micron range. Experimental complexity is minimized when one of the bodies is a sphere and the other one is a plate, making the alignment between the two bodies ubiquitous. Our group has produced the most precise Casimir measurements, and the best limits on predicted Yukawa-like potentials by measuring a force between a [Formula: see text] sphere attached to a [Formula: see text] micro-mechanical oscillator and a planar source mass. By replacing the spherical surface with a fraction of a [Formula: see text] long cylinder with [Formula: see text]m, the force sensitivity can be greatly enhanced. Here, it is paramount to know the angular deviation between the long axis of the cylinder and both the axis of rotation of the oscillator and the plate. Tests between a cylinder and a structure etched into a silicon wafer show that deviations of [Formula: see text]rad are readily accessible. Additionally, a scaled up experiment is used to investigate if capacitance measurements can determine the orientation of the cylinder with respect to a plane with the required precision.