The effect of distribution of iron-oxyhydroxide grain coatings on the transport of bacterial cells in porous media

 Among the demonstrated processes influencing the transport of bacteria through aquifers, the deposition of cells on mineral surfaces is one of the most important. For example, understanding the transport of introduced bacteria through aquifers is essential to designing some in situ bioremediation schemes. The impact of the presence and distribution of Fe(III)-oxyhydroxide-coated sand grains on bacterial transport through porous media was evaluated in column experiments in which bacteria (short rods; 1.2 μm length) were eluted through columns of quartz sand (0.5–0.6 mm in diameter) for several conditions of chemical heterogeneity of mineral substrate. Fe(III)-oxyhydroxide-coated sand was present as 10% of the mass, and it was arranged in three treatments: (1) homogeneously distributed, and present as a discrete layer (2) at the top and (3) at the bottom of 14-cm-long sand columns. A pulse input of 10⁸ cells ml^–1 was introduced in an artificial groundwater solution flowing at 14 cm h^–1 through the column, and eluted cells were counted. Peak breakthrough occurred at 1.0 pore volume. A large proportion of cells were retained; 14.7–15.8% of the cells were recovered after three pore volumes of solution had eluted through clean quartz sand, and only 2.1–4.0% were recovered from the Fe(III)-oxyhydroxide-coated sand mixtures. The three physical arrangements of the chemical heterogeneity resulted in essentially the same breakthrough of cells, indicating that the spatial distribution of iron coating does not affect the transport of bacteria. The results of the column transport experiments, which mimic hydrogeological conditions encountered in field problems, are consistent with our mechanistic understanding of bacterial sorption. Received: 10 April 1996 · Accepted: 17 February 1997     

The geochemical environment

Much of the assessment of high-level radioactive waste repositories will be accomplished through the application of geochemical models. Such models will be used to understand geochemical processes in the repository and the surrounding environment. The purpose of this paper is to review the nature of the currently available geochemical models. The kinds of calculations that a number of these models perform include aqueous speciation, mineral solubility, and mass transfer reactions. Presently, there are limitations on the success of calculation of adsorption reactions and rate-limited reactions. Ongoing development of geochemical models requires that more work be done to compile thermodynamic and kinetic data, incorporate additional geochemical processes and parameters into existing codes, and assess the accuracy of all simulations through validation studies and sensitivity analyses.     

Hydraulic Properties of Stony Vadose Zonesa

Hydraulic properties of saturated and unsaturated stony soils were studied on a 3.35 m long column, 1.24 m in diameter, filled with alternating sand and boulder layers. The boulders averaged 6.2 × 15 × 20 cm in size and were laid down on their flat side. Tensiometers and a neutron probe access tube were placed in the column for measuring pressure heads and water contents, respectively. Saturated conditions were obtained by ponding the column. The resulting hydraulic conductivity K was 5.1 m/day. This value could also be calculated from the measured K for the sand alone on separate samples, using a simple equation that takes into account the void ratio of the sand alone and that of the boulder-sand mixture. Unsaturated K was determined by applying water at less than ponded infiltration rates. Resulting relations between the unsaturated K and water content or negative pressure head could also be estimated from the relation between unsaturated K and pressure head for the sand alone and the calculated saturated K of the boulder-sand mixture. The method of Millington and Quirk for calculating the relation between unsaturated K and water content also gave reasonable results. The dispersivity of the boulder-sand column was 18 times that of the sand alone. Pore velocity was accurately estimated as the Darcy velocity divided by the volumetric water content. Hydraulic properties of stony vadose zones are difficult to determine. This work shows that they can be estimated from K relations measured in the laboratory on samples of the soil between the rocks. Knowledge of hydraulic properties of vadose zones is important in predicting movement of water and pollutants to the underlying ground water.     

Photometry of Venus: III. Interpretation of brightness distributions over the disk

A series of solar brightness distributions observed over the Venus disk at several wavelengths is analyzed. A single absorption mechanism is assumed, the main localization of which is varied within the clouds, in different models. An attempt is made to retrieve all of the observations from one or more of the models. From the ultraviolet observations, models in which the absorption is highly localized give a better fit although better measurements are needed before a definite conclusion may be drawn. Isophote maps in visible light disagree with the theoretical predictions of all the models, suggesting that a second absorption mechanism (perhaps the ground) ought to be called for in this spectral region.     

Assessment of the Kraków inhabitants’ health risk caused by the exposure to inhalation of outdoor air contaminants

Health risk associated with the exposure to the polluted atmospheric air inhalation was estimated for the residents of Kraków, Poland. The air pollution concentration data were obtained from the air-quality monitoring system of the city in 2007–2016. The carcinogenic risk of the studied subpopulations was not acceptable under the formula of C₆H₆ > BaP > As(PM10) > Cd(PM10) > Pb(PM10) > Ni(PM10). The total carcinogenic risk (Rt) amounted to 3.04E?04 for children, 2.22E?04 for infants, 1.45E?04 for women, and 1.22E?04 for men. The same risk was calculated for the top three locations of the monitoring stations in this respect, within the city of Kraków: Kurdwanów Housing Estate, Nowa Huta district, and Krasińskiego Av. Non-carcinogenic risk in the case of all six monitoring stations and in respect of all the studied subpopulations, resulting from the exposure to PM10 and for NO₂ for all stations in case of children and infants, as well as, for adults at Krasińskiego Av. and Dietla Str. stations was rated medium. For C₆H₆ in the case of adults, children, and infants the risk was rated low. The total risk (HI) of non-carcinogenic pollution was rated medium and ranged as follows: 6.53 for children, 4.70 for infants, 3.19 for women, and 2.67 for men. That type of risk was decreasing at the station locations as follows: Krasińskiego Av. > Dietla Str. > Nowa Huta district > Kurdwanów Housing Estate > Z?oty Róg Str. > Piastów Housing Estate.     

Transformed equations of motion for underwater vehicles

A method for dynamics investigation and coupling detection between velocities of autonomous underwater vehicles (AUVs) is presented in this paper. The method is based on transformation of equations of motion, which are usually used for an underwater vehicle, into equations with a diagonal mass matrix. The obtained equations contain quasi-velocities and allow one to give a further insight into the AUV dynamics especially for an underactuated system. Some advantages of the proposed approach are discussed, too. An analytical example for a 3-DOF AUV shows possible application of the transformed equations. Moreover, the given approach is validated via simulation on a 6-DOF vehicle.     

Decoupled PD set-point controller for underwater vehicles

A set-point controller for autonomous underwater vehicles (AUVs) is proposed in this paper. The controller is expressed in transformed equations of motion with a diagonal inertia matrix. It takes into account the dynamics of the system and it can be applied for fully actuated AUVs. The stability of the designed control law is demonstrated by means of a Lyapunov-based argument. Some advantages arising from the use of the controller are considered too. The performance of the proposed controller is validated via simulation on a 6-DOF underwater vehicle.