Fe isotopic composition of Martian meteorites and some terrestrial analogues

We report Fe isotopic composition of seven martian meteorites and other terrestrial materials that may be considered Martian analogues

Microbial D/H fractionation in extraterrestrial materials: application to micrometeorites and Mars

High D/H terrestrial alteration of micrometeorites is described and suggested to be a result of microbial isotopic fractionation by methanogens. Applications to other planetary materials, including martian meteorites, are also considered

Cryptoendolith alteration of Antarctic sandstone substrates: pioneers or opportunists?

The cryptoendolithic habitat of the Antarctic Dry Valleys has been considered a good analogy for past Martian ecosystems, if life arose on the planet. Yet cryptoendoliths are thought to favor the colonization of rocks that have a preexisting porous structure, e. g., sandstones. This may weaken their significance as exact analogues of potential rock-colonizing organisms on Mars, given our current understanding of the dominant volcanic nature of Martian geology. However, the production of oxalic acid, by these lichendominated communities, and its weathering potential indicate that it could be an aid in rock colonization, enabling endoliths to inhabit a wider variety of rock types. Utilizing ICP-AES and scanning electron microscope techniques, this study investigates elemental and mineralogical compositions within colonized and uncolonized layers in individual sandstone samples. This is in order to determine if the weathering of mineral phases within the colonized layers causes an increase in the amount of pore space available for colonization. The results show that colonized layers are more weathered than uncolonized, deeper portions of the rock substrate. Layers within uncolonized samples have uniform compositions. Differences between the colonized and uncolonized layers also occur to varying extents within colonized rocks of different mineralogical maturities. The results confirm that cryptoendoliths modify their habitat through the production of oxalic acid and suggest that over time this directly increases the porosity of their inhabited layer, potentially increasing the biomass it can support

Cryptoendolith colonization of diverse substrates (1): cultivation and characterization

We are investigating whether cryptoendolithic microorganisms are able to colonize diverse substrates through biogenic weathering. This first part of the study involves the cultivation and characterization of microbial consortia from Antarctic sandstone habitats

A Study of Different Modeling Choices For Simulating Platelets Within the Immersed Boundary Method

The Immersed Boundary (IB) method is a widely-used numerical methodology for the simulation of fluid-structure interaction problems. The IB method utilizes an Eulerian discretization for the fluid equations of motion while maintaining a Lagrangian representation of structural objects. Operators are defined for transmitting information (forces and velocities) between these two representations. Most IB simulations represent their structures with piecewise-linear approximations and utilize Hookean spring models to approximate structural forces. Our specific motivation is the modeling of platelets in hemodynamic flows. In this paper, we study two alternative representations - radial basis functions (RBFs) and Fourier-based (trigonometric polynomials and spherical harmonics) representations - for the modeling of platelets in two and three dimensions within the IB framework, and compare our results with the traditional piecewise-linear approximation methodology. For different representative shapes, we examine the geometric modeling errors (position and normal vectors), force computation errors, and computational cost and provide an engineering trade-off strategy for when and why one might select to employ these different representations.Comment: 33 pages, 17 figures, Accepted (in press) by APNU

Mineralogy and Geochemistry of Shergottite RBT 04262

This abstract presents mineralogical and geochemical data on newly discovered shergottite RBT 04262 and compares it with other known shergottites

To what distances do we know the confining potential?

We argue that asymptotically linear static potential is built in into the common procedure of extracting it from lattice Wilson loop measurements. To illustrate the point, we extract the potential by the standard lattice method in a model vacuum made of instantons. A beautiful infinitely rising linear potential is obtained in the case where the true potential is actually flattening. We argue that the flux tube formation might be also an artifact of the lattice procedure and not necessarily a measured physical effect. We conclude that at present the rising potential is known for sure up to no more than about 0.7 fm. It may explain why no screening has been clearly observed so far for adjoint sources and for fundamental sources but with dynamical fermions. Finally, we speculate on how confinement could be achieved even if the static potential in the pure glue theory is not infinitely rising.Comment: 16 pages, 5 figures. Additional arguments presented, a new figure and references adde