An analytic satellite theory using gravity and a dynamic atmosphere

An analytical solution is given for the motion of an artifical Earth satellite under the combined influences of gravity and atmospheric drag. The gravitational effects of the zonal harmonicsJ ₂,J ₃, andJ ₄ are included, and the drag effects of any arbitrary dynamic atmosphere are included. By a dynamic atmosphere, we mean any of the modern empirical models which use various observed solar and geophysical parameters as inputs to produce a dynamically varying atmosphere model. The subtleties of using such an atmosphere model with an analytic theory are explored, and real world data is used to determine the optimum implementation. Performance is measured by predictions against real world satellites. As a point of reference, predictions against a special perturbations model are also given.     

Climatic Changes, Successions of Peatlands and Zonal Vegetation, and Peat Accumulation Dynamics in the Holocene (the West-Siberia Peat Profile ‘Vodorasdel’)

The developmental history of peatland and dry land vegetation within the Ob-Vasugan watershed of Western Siberia was characterized according to features of the plant communities and climatic changes which were revealed by stratigraphic, spore-pollen and C¹⁴ (carbon) data obtained from a vertical peat profile Vodorasdel. Changes in the paleoecological environment over the last 10000 years were divided into five periods. The climate was characterized in the Holocene according to these periods. At the watershed studied, peatland-forming processes started about 9510 years ago resulting in 550 cm of peat accumulation. The rate of peat accumulation within the watershed decreased over time from 1.9–0.3 mm year^{– 1}.     

Subsurface storm flow formation at different hillslopes and implications for the ‘old water paradox’

Although many studies over the past several decades have documented the importance of subsurface stormflow (SSF) in hillslopes, its formation is still not well understood. Therefore, we studied SSF formation in the vadose soil zone at four different hillslopes during controlled sprinkling experiments and natural rainfall events. Event and pre‐event water fractions were determined using artificially traced sprinkling water and ²²²Rn as natural tracer. SSF formation and the fraction of pre‐event water varied substantially at different hillslopes. Both intensity of SSF and fraction of pre‐event water depended on whether SSF in preferential flow paths was fed directly from precipitation or was fed indirectly from saturated parts of the soil. Soil water was rapidly mobilized from saturated patches in the soil matrix and was subsequently released into larger pores, where it mixed with event water. Substantial amounts of pre‐event water, therefore, were contained in fast flow components like subsurface storm flow and also in overland flow. This finding has consequences for commonly used hydrograph separation methods and might explain part of the ‘old water paradox’. Copyright © 2007 John Wiley & Sons, Ltd.     

Biogeochemistry of Ethanol and Acetaldehyde in Freshwater Sediments

This study reports the first ethanol and acetaldehyde measurements in sediment porewaters collected at multiple freshwater locations. Ethanol concentrations ranged from 11 to 2535 nM and acetaldehyde concentrations ranged from 6 to 320 nM. A significant positive correlation (p < 0.001) was observed between ethanol concentrations and the percent organic carbon content of sediments (TOC). Porewater depth profiles at two sites within the same lake indicated potential diffusion of ethanol into sediments from the overlying water at a lower TOC site and upwards diffusion from sediment into the water column at a higher TOC site. Diffusion of water column ethanol into sediments was observed at individual sites from October to January, whereas the opposite was true from June to August indicating the seasonal variability of ethanol flux from sediments. Changes in ethanol concentrations during a long-term sediment incubation experiment showed an inverse relation with acetaldehyde concentrations. The lack of a quantitative conversion was likely due to other sources and sinks that control their abundance. Our study provided new information on the biogeochemistry of ethanol in freshwater sediments and shed light on the potential role of ethanol in the global carbon cycle.     

A porous media finite element approach for soil instability including the second-order work criterion

This paper deals with the hydromechanical modelling of the initiation of failure in soils with particular reference to landslides. To this end, localized and diffused failure modes are simulated with a finite element model for coupled elasto-plastic variably saturated porous geomaterials, in which the material point instability is detected with the second-order work criterion based on Hill’s sufficient condition of stability. Three different expressions of the criterion are presented, in which the second-order work is expressed in terms of generalized effective stress, of total stress and thirdly by taking into account the hydraulic energy contribution for partially saturated materials. The above-mentioned computational framework has been applied to study two initial boundary value problems: shear failure of a plane strain compression test of globally undrained water-saturated dense sand (where cavitation occurs at strain localization) and isochoric grain matter, and the onset of a flowslide from southern Italy due to rainfall (Sarno-Quindici events, May 5–6 1998). It is shown that the second-order work criterion applied at the material point level detects the local material instability and gives a good spatial indication of the extent of the potentially unstable domains in both the localized and diffused failure mechanisms of the cases analyzed, is able to capture the instability induced by cavitation of the liquid water and gives results according to the time evolution of plastic strains and displacement rate.     

Reformulation of the Brouwer geopotential theory for improved computational efficiency

The theory, as derived by Brouwer and later modified by Lyddane, of the motion of an artificial Earth satellite perturbed by the first five zonal harmonics is reformulated in terms of an alternate set of variables. This alternate set of variables produces an equivalent solution, has no small eccentricity or small inclination restrictions, and allows calculation of position and velocity with considerably fewer algebraic and trigonometric operations. In addition, the alternate set of variables avoids one solution of Kepler's equation.     

A physical study of low-frequency dispersion of rock conductivity in time-domain electromagnetics

Most rocks display conductivity dispersion in the low-frequency range, when the usual displacement currents are neglected. The strong influence this low-frequency dispersion (LFD), including the response sign reversals, was revealed by field experiments with the coincident-loop configuration widely used in transient electromagnetics (EM). Mathematical modelling of LFD has been the subject of numerous studies. However, confirmation of the role of LFD or induced polarization (IP) by comparing mathematical modelling and field data is rather poor, because knowledge of the properties of rocks in the area of the field measurements is usually insufficient. For this reason physical modelling of LFD has been carried out at Moscow State Geological-prospecting Academy (Russia) in 1994-95. In order to observe criteria of similarity for both induction and polarization transients, a ring-shaped model was chosen and was represented by an electric circuit, consisting of lumped elements (real rock samples included). Qualitatively different transients for dispersive models and their non-dispersive ohmic equivalents were observed.