New insights into aggregation and conformational behaviour of humic substances: Application of high resolution ultrasonic spectroscopy

The potential of high resolution ultrasonic analysis (HRUS) in humic acid colloidal properties research has been demonstrated. Sodium salts of humic acids from soil and lignite showed similar behaviour, supporting the hypothesis that, at both neutral and alkaline pH, they aggregate from very low concentration. The same conclusion can be reached for solutions at high ionic strength. We tried to apply the same procedure as used for the study of micellization and determination of critical micelle concentration of common surfactants. As expected, our experiments did not show the same break as demonstrated on the HRUS records for sodium dodecyl sulfate, at least in the range of measured concentration (i.e. from 0.001 up to 10 g L⁻¹). The colloidal state of humic acids in aqueous solution is very sensitive to the presence of other, both charged and neutral, molecules. Aggregation of humic acids can be disturbed or promoted, depending on the concentration, by electrostatic or other weak interactions with extraneous molecules. Structures of varying mechanical strength (rigidity) can be formed in solutions of the same components but at different concentration. Such behaviour reflects mechanisms which occur during the sequestration of hydrophobic organic compounds and has several implications for the protection/transportation of labile structures and contaminants which are hypothesized to be encapsulated within hydrophobic pockets of soluble humic aggregates.     

Three-dimensional velocity model of the crust of the Bohemian Massif and its effects on seismic tomography of the upper mantle

We have compiled a representative three-dimensional P-velocity model of the crust of the Bohemian Massif (BM) to provide a basis for removing effects of the crustal structure in teleseismic tomography of the upper mantle. The model is primarily based on recently published 2D velocity models from findings of wide-angle refraction and near-vertical reflection seismic profiles of CELEBRATION 2000, ALP 2002, and SUDETES 2003 experiments. The best fitting 3D model of the BM crust (NearNeighbour model) is complemented by velocities according to the reference Earth model at sites where data are sparse, which precludes creating artificial heterogeneities that are products of interpolation method. To test the model, we have performed tomographic inversions of the P-wave travel times measured during the BOHEMA II experiment and compared the results obtained with and without crustal corrections. The tests showed that the presented crustal model decreases magnitudes of velocity perturbations leaking from the crust to the mantle in the western part of the BM. The tomographic images also indicated a highvelocity anomaly in the lower crust or just beneath the crust in the Brunovistullian unit. Such anomaly is not described by our model of the crust since no seismic profile intersects this part of the unit. The tests also indicated that crustal corrections are of the great importance especially for interpretations of the uppermost mantle down to depths of about 100 km.     

Experimental study of fly-ash migration by using magnetic method

Several studies have shown that magnetic measurements can be used in assessing soil contamination due to atmospheric deposition of pollutants. Reliable spatial mapping of magnetic susceptibility of soils assumes high temporal stability of deposited particles, accumulated in top-soil horizons. One of the main methodological concerns is whether the migration of deposited anthropogenic ferrimagnetic particles may bias the measured values. Measurements carried out on high-porosity (sandy) soils, or on soils with a very variable water regime may yield inconsistent values of top-soil magnetic susceptibility as the indicator of contamination. This study focuses on the laboratory examination of migration of fly ashes from a coal-burning power plant in sands of different porosity and under a simulated rain regime. Columns of sand of different grain sizes, placed in plastic cylinders, were contaminated on the surface by the fly ash. The vertical migration of magnetic particles was monitored using measurements of magnetic susceptibility with an SM400 Kappameter. Calibration measurements in the water environment showed an erroneous performance and resulted in the technical improvement of the used susceptibility meter (Model 2009). Our results show that the vertical distribution of flyash particles deposited on fine sand is very stable even after repeated rain simulation. The peak value of magnetic susceptibility is located in a stable position a few millimeters under the surface. Hence, standard top-soil magnetic mapping is in such a case reliable and fully representative. Contrary to that, in case of coarse sand, the peak value of magnetic susceptibility migrates by more than 10 cm. The results will be further used for numerical modeling of contaminant transport in porous media.     

Geoid and topography of Venus in various thermal convection models

Important though indirect information about the internal structure of Venus is provided by its topography and geoid. In the last decades this information has been used to constrain the Venus mantle viscosity structure and its dynamic regime. Recently, the geodynamic inversion of the Venus?? geoid and topography resulted in a group of best fitting viscosity profiles. We use these viscosity models here as an input to our mantle convection code. We carry out simulations of the Venus?? mantle evolution in a 3D spherical shell with depth dependent viscosity and check whether the character of the dynamic topography and the geoid represented by their power spectra fits the observed quantities. We compare the results with several other models obtained for different viscosity stratifications (constant, constant with highly viscous lithosphere, linear increase of viscosity). Further, we estimate the effect of other factors such as internal heating and varying Rayleigh number. We use a 2D spherical axisymmetric convection code to study the effect of lateral viscosity variations. In these 2D models we monitor the topography and the geoid developing above the axisymmetric plume and compare them with the observed elevations of Venus?? geoid and topography in several Regia. Though none of the models fits observed data perfectly, we can generally conclude, that the best fit between the observed and predicted quantities is reached for viscosity profiles with 200 km thick lithosphere followed by a gradual increase of viscosity with depth and with the upper mantle viscosity of 2 × 10 ²¹ Pa s. For all viscosity profiles the predicted geoid and topography spectra match the observed ones only up to the degree 40, thus indicating other than dynamic origin of these quantities for higher degrees.     

Design response spectra for Aqaba City–Jordan

Strong motion records for earthquakes epicentred in the Gulf of Aqaba during swarms in August 1993 and November 1995 are studied. These recordings are made at two sites in the City of Aqaba, one near the seashore and the other inland. The former site has deep alluvial profile with low shear-wave velocity, while the latter's soil profile is constituted of shallow stiff alluvium overlaying rock. The magnitudes of these events range from 4·8 to 6·2 on the Richter scale. Ground motion on the seashore site is much greater than the inland site. Response spectra are derived for each of the available accelerograms. Thirteen records at the inland site are statistically treated to arrive at mean response spectrum using 5 per cent damping. The derived spectra are found to be sharp with small plateau, this is associated with small peak displacement. Empirical site-dependent response spectra are also derived based on recent research and on recommendations of the UBC'97. Comparison is made between the empirical and measured spectra. These were found to be quite close for the inland site but data are not sufficient for the seashore site to make a conclusive comparison. Copyright © 1999 John Wiley & Sons, Ltd.     

Effect of a Viscosity Interface at 1000 km Depth on Mantle Circulation

We present the preliminary results of axisymmetric numerical simulations of thermal convection in the mantle with a phase transition boundary at 660 km depth and a viscosity interface at 1000 km depth. The results, obtained for Ra = 2 × 10 ⁶ , are compared with the case when both the phase and the viscosity boundaries are located at the same depth of 660 km.     

Trends in impact of acidification on groundwater bodies in the Czech Republic; an estimation of atmospheric deposition at the horizon 2015

The acidification of surface and groundwaters is a long standing issue in the Czech Republic which culminated in the second half of the last century by mass extinction of forest cover in many mountainous regions. The total deposition of sulfur at that time was reaching as much as about 108 kg/ha/year. This resulted in a decrease of alkalinity in groundwaters, decrease of pH and on the other hand an increase in concentration of nitrates, sulfates, berylium and aluminium. Desulfurization of power plants and attenuation of heavy industry leads to a decrease in sulfur deposition down to the present mean values around 16.5 kg/ha/year. It is expected that around the year 2010 the sulfur deposition should not have a substantial impact on the environment providing the similar trend would continue. However, a reverse trend can be observed in deposition of nitrogen. The growth of road traffic and more frequent use of earth gas for heating lead to a dramatic rise in nitrogen throughfall of which mean value increased from 15.4 kg/ha/year in 1990 up to 25.7 kg/ha/year in 2001. If such trend continues in future, then the mean values of nitrogen throughfall would attain 37.8 kg/ha/year in 2015, so that the nitrogen would take over the role of sulfur in acidification. Therefore, the problem of acidification in Central Europe is by no means resolved, only the structure of acidification input has been changed.