[1] We develop a hydrological model of the Martian crust, including both ancient heavily cratered terrains and younger basaltic and sedimentary terrains. The porosity, permeability, and compressibility are represented as interdependent functions of the effective stress state of the aquifer, as determined by the combination of the lithostatic pressure and the fluid pore pressure. In the megaregolith aquifer model, the crust is modeled as a 2 km thick megaregolith, composed of lithified and fractured impact ejecta, overlying the impact-fractured and partially brecciated basement rock. The hydraulic properties depend primarily upon the abundance of breccia and the compressional state of the fractures. The porosity ranges from approximately 0.16 at the surface to 0.04 at a depth of 10 km, with a sharp discontinuity at the base of the regolith. The permeability varies from approximately 10 À11 m 2 at the surface to 10 À15 m 2 at depths of 5 km or more and is strongly dependent upon the fluid pore pressure. The hydrologic properties of basaltic and sedimentary aquifers are also considered. These parameters are used to model the fluid pressures generated beneath a thickening cryosphere during a postulated dramatic cooling of the climate at the end of the Noachian. As a result of a negative feedback between the fluid pore pressure and the permeability, it is more difficult than previously thought to generate pore pressures in excess of the lithostatic pressure by this mechanism. The production of the outflow channels as the result of such a climatic change is deemed unlikely.Citation: Hanna, J. C., and R. J. Phillips (2005), Hydrological modeling of the Martian crust with application to the pressurization of aquifers,

No abstract

[1] Mangala and Athabasca Valles are the type examples of a distinct class of outflow channels that debouch directly from extensional tectonic features. We here demonstrate that the tectonic events responsible for the formation of the graben and fissures at the sources of the channels would have likely resulted in a near-instantaneous pressurization of the surrounding aquifers. Subsequent drainage of the pressurized aquifers though the confining cryosphere to the surface along the tectonically generated faults and fissures would have produced the catastrophic floods responsible for forming the channels. The peak discharges and individual flood volumes would have been dependent upon the magnitude of the individual tectonic events at the source regions. We estimate that individual extensional tectonic events at the source regions of Mangala and Athabasca Valles would have resulted in flood volumes ranging from 3 to 300 km 3 and peak discharges ranging from 10 5 to 10 6 m 3 s À1. Our models further show that the entire extensional tectonic history of Athabasca Valles would have resulted in a total cumulative flood volume of 200-14,000 km 3 , whereas that at Mangala Valles would have resulted in a total flood volume of 3000-22,000 km 3 , both consistent with inferred flood volumes based on the geomorphology. Athabasca Valles in particular is of interest as it is the youngest of the outflow channels, demonstrating that this mechanism has brought substantial volumes of water to the surface in the present epoch.

Previous thermodynamic analyses of carbon formation in SOFCs assumed that graphite could be used to represent the properties of carbon formed in the anode. It is generally observed, however, that catalytically grown carbon nanofibers (CNF) are more likely to form in the SOFC anode with nickel catalysts. The energetic and entropic properties of CNF are different from those of graphite. We compare equilibrium results based on thermochemical properties for graphite, to new results based on a previously reported value of an empirically determined Gibbs free energy for carbon fibers grown on a nickel support (with fitted values of H°CNF = 54.46 kJ/mol and S°CNF = 68.90 J/mol/K for a nickel crystal size of 5.4 nm). There is little difference in predictions of carbon formation under open-circuit conditions between the two carbon types for methane mixtures, with graphite predicted to form at lower temperatures than CNF. There is a much bigger difference in predictions for methanol mixtures, especially at low steam-carbon ratios. The differences for propane are even more pronounced, and the improved predictions assuming CNF are in closer agreement with past observations. We show a strong dependence of CNF formation and “coking threshold” on nickel crystallite size, supporting previous reports that the nickel particle size is a dominating parameter for controlling filament growth. If both carbon types are included in the calculations, only the thermodynamically favored form (i.e., the type having the lowest formation energy) exists. Predicted Nernst potentials are more-or-less independent of the carbon type and in agreement with measured open-circuit voltages.

Interstitial collagenase activity stimulates bone resorption by mouse marrow osteoclasts [1]. Here, we show that collagenase activity promotes bone resorption by activating adherent osteoclasts to resorb bone. Inhibition of interstitial collagenase activity, either with peptidomimetic hydroxymates or with a specific anti-interstitial collagenase inhibiting antibody, reduced bone resorption by 73-92%. Equal numbers of osteoclasts adhered to bone in the presence of collagenase inhibitors and osteoclast survival was unaffected. In contrast, formation of actin rings and polarization of the vacuolar-H+-ATPase (V-ATPase) to ruffled membranes, two indicators of osteoclast activation, were decreased by inhibiting collagenase activity and stimulated in the presence of cleaved or heat-denatured type I collagen in proportion to increases and decreases of bone resorptive activity. Addition of excess recombinant osteoprotegerin-ligand to cultures did not restore bone resorption in the presence of interstitial collagenase inhibitors. These data support the hypothesis that cleaved collagen stimulates osteoclastic bone resorption by triggering cytoskeletal reorganization and transport of V-ATPase from cytoplasmic stores to ruffled membranes.