Water Drainage in Double-Porosity Soils: Experiments and Micro–Macro Modeling

This paper presents the experimental validation of a macroscopic model of unsaturated flow in double-porosity soils, which was developed using the asymptotic homogenization method. The model was implemented into a code which enables micro–macro coupled calculations of macroscopically one-dimensional and microscopically three-dimensional problems. A series of drainage experiments were carried out in a column filled with a double porosity medium. The porous medium is composed of Hostun sand and porous spheres made of sintered clay, periodically distributed in the sand. The characteristic pores sizes of the two media differ by two orders of magnitude. During the experiments the water content evolution inside the column, the capillary pressure, and the flux at the bottom of the column were measured. The numerical simulations results showed a good agreement with the experimental data, confirming the predictive ability of the model. The experimental and numerical evidence of the influence of the microporous inclusions on the flow dynamics (flux retardation, water retention in the microporosity), is clearly shown.     

A modified oddball paradigm for investigation of neural correlates of attention: a simultaneous ERP–fMRI study

Introduction

The objective of the presented study was to develop and evaluate a P300 experimental protocol for simultaneous registration of event-related potentials (ERPs) and functional MRI (fMRI) data with continuous imaging. It may be useful for investigating attention and working memory processes in specific populations, such as children and neuropsychiatric patients.

Materials and methods

Eleven children were investigated with simultaneous ERP–fMRI. To fulfill requirements of both BOLD and electroencephalographic signal registration, a modified oddball task was used. To verify the ERP–fMRI protocol we also performed a study outside the scanner using a typical two-stimuli oddball paradigm.

Results

Localization of the P300 component of ERPs partially corresponded with fMRI results in the frontal and parietal brain regions. FMRI activations were found in: middle frontal gyrus, insula, SMA, parietal lobule, thalamus, and cerebellum. Our modified oddball task provided ERP–fMRI results with high level of significance (EEG SNR = 35, fMRI p < 0.05–Bonf.). ERPs obtained in the scanner were comparable with those registered outside the scanner, although some differences in the amplitude were noticed, mainly in the N100 component.

Conclusion

In our opinion the presented paradigm may be successfully applied for simultaneous ERP–fMRI registration of neural correlates of attention in vulnerable populations.