Infrared observations of the jovian system from voyager 2

Infrared spectra obtainedfrom Voyager 2 have provided additional data on the Jovian system, complementing those obtained from Voyager 1. The abundance ratio of ethane to acetylene in Jupiter's atmosphere appears to be about three times larger in the polar regions than at lower latitudes. A decidedly hemispherical asymmetry exists, with somewhat higher ratios prevailing in northern latitudes. An overall increase in the abundance ratio by a factor of about 1.7 appears to have occurred between the Voyager 1 and 2 encounters. Global brightness temperature maps of Jupiter at 226 and 602 cm(-1) exhibit a large amount of local- and planetary-scale structure, as well as temporal variability. Although heterogeneous cloud structure and ammonia concentration in the lower troposphere may contribute to the appearance of the 226-cm(-1) map, the detail in the 602-cm(-1) maps probably represents the actual horizontal thermal structure near the tropopause and suggests that dynamical heating and cooling processes are important. Low-latitude surface temperatures on the Galilean satellites rangefrom approximately 80 K on the dark sides to 155 K at the subsolar point on Callisto. Below a thin insulating layer, the thermal inertia of Callisto is somewhat greater than that of Earth's moon. Upper limits on the infrared optical depth of the Jovian ring rangingfrom approximately 3 x 10(-4) at 250 cm(-1) to 3 x 10(-3) at 600 cm(-1) have been found.     

Wirkungen technogener Druckbelastung auf die Spannungsverteilung und das Bodengefüge einer Schwarzerde aus Löß

Effect of wheeling on stress distribution and changes in the macro- and microstructure of a cambic phaeozem derived from loess The determination of stress induced changes in the poresystem due to repeated wheeling of a cambic phaeozem derived from loess as well as in the aggregate size distribution, arrangement, and stage are reported. It could be shown, that repeated wheeling always results in a further stress distribution to deeper depths and that the vertical stresses dominate with repeated wheeling. Furthermore the octahedral shear stresses and mean normal stresses exceed the maximum strength defined by the Mohr Coulomb failure line and define a further soil deformation. The process of aggregate deterioration can be verified by radiographs from which not only the changes in bulk density on a mesoscale can be derived but from which also the crack patterns can be defined for the different stages of structure deterioration. Under the well known assumption that pore water pressure is increased due to wheeling, soil compaction and consecutive soil homogenisation by kneading can be differentiated. The consequences for ecological parameters will be discussed.     

The mechanical behavior of structured and homogenized soil under repeated loading

Soil deformation is increasingly important in crop production since nowadays weights of agricultural machines exceed the bearing capacity of most soils. Often this is counteracted by distributing the weight over more axles leading to an increase in wheeling frequency. Machine passages during one year can, depending on the crop and equipment used, range between two and five times for the majority of the field and up to twenty times and more for a wheeling track. These add up to hundreds of loading events for a crop‐rotation period. In this study, we investigated the effect of multiple loading with the same load in a cyclic‐compression test on soil‐pore‐volume change. The tests were conducted on homogenized soil samples with varying texture and undisturbed soil samples from a field experimental site comparing conventional and conservation‐tillage systems. Of particular interest was the question whether there is significant plastic soil deformation for soil stresses that remained sufficiently below the precompression stress, which is commonly neglected. Our results show that especially for cohesive soils, the assumption of fully elasticity in the recompression range may not be justified since those soils show distinct cyclic‐creep behavior. We found that deformation under cyclic loading follows a logarithmic law. We used the slope of the logarithmic fit of void‐ratio changes vs. loading cycles as a parameter to characterize the sensitivity of soils to cyclic compression. The results suggest that for characterizing the mechanical stability of soils that show cyclic creep, we have (with respect to long‐term deformation effects) to consider both precompression stress and cyclic compressibility.     

A dynamic method to determine the O2-partial pressure distribution within soil aggregates

During amperometric measurements of oxygen concentration an electrode itself consumes oxygen. To make sure that oxygen concentration at a soil microsite is not lowered by the measurement itself, but determines the in situ situation, the sensitive tip of the electrode should not be in a static position for a longer time than is necessary to reach equilibrium. If the electrode is moved stepwise through the soil aggregate and is allowed to reach equilibrium at every position, it is possible to measure profiles of oxygen partial pressure distribution from the surface to the center of single soil aggregates. We used a small electromotor attached to a micromanipulator to push the pO₂-sensitive microelectrode at a constant speed through the soil aggregate. As an advantage this ‘dynamic’ method needs no man power and gives continuous profiles of oxygen concentration from the surface to the center of the aggregate.     

Comparison of the prediction efficiency of two pedotransfer functions for soil cation‐exchange capacity

The aim of this study was to provide knowledge of the prediction efficiency of two pedotransfer functions for soil cation‐exchange capacity (CEC), i.e., the approaches of Krogh et al. (2000) and Scheinost (1995). Potential CEC, i.e., CEC at pH 8.1, was predicted for 30 samples of German soils showing a strong variation of soil organic C and clay content which are important soil characteristics for CEC. The results were compared to analyzed potential CEC of the samples by coefficient‐of‐efficiency (EC) criterion of Nash and Sutcliffe (1970). Significant deviations between observed and measured CEC were found for both functions. The approach of Scheinost (1995) showed a higher prediction efficiency (EC = 0.77 in comparison to EC = 0.26 for Krogh et al., 2000) and better results under extrapolative conditions.     

Aggregate characterization as compared to soil bulk properties

The aim of this paper is to clarify the effect of soil aggregation on the physical and chemical properties of structured soils and as compared with the homogenized material. Aggregation and aggregate strength do not only depend on biological activity and organic exudates, but also on the intensity, number and time of swelling, and drying events. Such aggregates are not only more dense than the structured bulk soil, the intra-aggregate pore distribution consists not only of finer pores, but they are also more tortuous. Thus, water and ion fluxes by mass flow as well as ion transportation by diffusion are delayed, whereby the length of the flow path in such tortuous finer pores further retards chemical exchange processes. Futhermore, the chemical composition of the percolating soil solution differs more from that of the corresponding homogenized material the stronger and denser the aggregates are. From the mechanical point of view, the strength of single aggregates, determined as the angle of internal friction and cohesion, depends on the number of contact points or the forces, which can be transmitted at each single contact point. However, internal soil parameters, like grain size distribution or chemical composition, further affect the strength. The more structured the soils are, the higher is the proportion of the effective stress on total stress, but even in single aggregates neutral stresses can be revealed. This is true because of the relationship to the smaller value of the hydraulic conductivity and higher tortuosity. Finally, some dynamic effects on aggregation and aggregate deterioration are discussed.     

Effects of land use and clay content on soil structure as measured by Fracture Surface Analysis

Soil clods were collected from the A horizons of six soils (3 Aqualfs and 3 Uderts) in the vicinity of Bayreuth in northern Bavaria. The soils had a range of clay contents and came from arable, meadow (pasture) and forest areas. The soils ranged in workability from easily workable to difficult to work. The clods, still moist as collected, were fractured into two parts by tensile stress and one part of each clod was embedded in polyester resin. The embedded clod parts were then sectioned to show profiles of the fracture surfaces. The profiles were digitized by a television scanner. Statistical measures of the roughness of the fracture surfaces were computed. Fracture surface roughness was strongly influenced by land use and soil clay content. Soil workability was related to fracture surface roughness and hence also to land use and soil clay content. Ease of soil working was mainly associated with the presence of soil structural features larger than 10 mm.