Detrital zircon SHRIMP U-Pb age study of the Cordillera Darwin Metamorphic Complex of Tierra del Fuego : sedimentary sources and implications for the evolution of the Pacific margin of Gondwana

The Cordillera Darwin Metamorphic Complex in the southernmost Andes includes a basement of probable Palaeozoic age, a mid-Jurassic and younger volcano-sedimentary cover, and a suite of Jurassic granites, all of which were jointly metamorphosed during the Cretaceous. Detrital zircon ages presented here show that some of the amphibolite-facies metamorphic rocks previously mapped as basement have a Jurassic protolith. Overall the detrital zircon age patterns for samples of the Cordillera Darwin basement differ from those of the Madre de Dios Terrane of the western Patagonian Andes with which they had been correlated; instead, they are more comparable with those from the Eastern Andes Metamorphic Complex, which apparently developed in a passive margin setting. The paucity of Cambrian detrital zircons indicates that the meta-igneous basement of the Magallanes foreland basin of central and northern Tierra del Fuego was not the main source of detritus for the protolith of the Cordillera Darwin Metamorphic Complex. The possibility is envisaged that the Magallanes Fagnano transform fault boundary between the Scotia and South America plates resulted from reactivation of an older, pre-Jurassic suture zone between the basement terranes of north–central Tierra del Fuego and Cordillera Darwin

Phase separation in hydrogen-helium mixtures at Mbar pressures

The properties of hydrogen-helium mixtures at Mbar pressures and intermediate temperatures (4000 to 10000 K) are calculated with first-principles molecular dynamics simulations. We determine the equation of state as a function of density, temperature, and composition and, using thermodynamic integration, we estimate the Gibbs free energy of mixing, thereby determining the temperature, at a given pressure, when helium becomes insoluble in dense metallic hydrogen. These results are directly relevant to models of the interior structure and evolution of Jovian planets. We find that the temperatures for the demixing of helium and hydrogen are sufficiently high to cross the planetary adiabat of Saturn at pressures around 5 Mbar; helium is partially miscible throughout a significant portion of the interior of Saturn, and to a lesser extent in Jupiter.Comment: 6 pages, 7 figures. Published in "Proceedings of the National Academy of Sciences USA

Comparative Evolution of Jupiter and Saturn

We present evolutionary sequences for Jupiter and Saturn, based on new nongray model atmospheres, which take into account the evolution of the solar luminosity and partitioning of dense components to deeper layers. The results are used to set limits on the extent to which possible interior phase separation of hydrogen and helium may have progressed in the two planets. When combined with static models constrained by the gravity field, our evolutionary calculations constrain the helium mass fraction in Jupiter to be between 0.20 and 0.27, relative to total hydrogen and helium. This is in agreement with the Galileo determination. The helium mass fraction in Saturn's atmosphere lies between 0.11 and 0.25, higher than the Voyager determination. Based on the discrepancy between the Galileo and Voyager results for Jupiter, and our models, we predict that Cassini measurements will yield a higher atmospheric helium mass fraction for Saturn relative to the Voyager value.Comment: 18 pages, LaTeX, 4 figures. submitted to ``Planetary and Space Science.'

A Comparison of the Interiors of Jupiter and Saturn

Interior models of Jupiter and Saturn are calculated and compared in the framework of the three-layer assumption, which rely on the perception that both planets consist of three globally homogeneous regions: a dense core, a metallic hydrogen envelope, and a molecular hydrogen envelope. Within this framework, constraints on the core mass and abundance of heavy elements (i.e. elements other than hydrogen and helium) are given by accounting for uncertainties on the measured gravitational moments, surface temperature, surface helium abundance, and on the inferred protosolar helium abundance, equations of state, temperature profile and solid/differential interior rotation.Comment: 25 pages, 6 tables, 10 figures Planetary and Space Science, in pres

An introduction to the indirect exposure assessment approach: modeling human exposure using microenvironmental measurements and the recent National Human Activity Pattern Survey.

Indirect exposure approaches offer a feasible and accurate method for estimating population exposures to indoor pollutants, including environmental tobacco smoke (ETS). In an effort to make the indirect exposure assessment approach more accessible to people in the health and risk assessment fields, this paper provides examples using real data from (italic>a(/italic>) a week-long personal carbon monoxide monitoring survey conducted by the author; and (italic>b(/italic>) the 1992 to 1994 National Human Activity Pattern Survey (NHAPS) for the United States. The indirect approach uses measurements of exposures in specific microenvironments (e.g., homes, bars, offices), validated microenvironmental models (based on the mass balance equation), and human activity pattern data obtained from questionnaires to predict frequency distributions of exposure for entire populations. This approach requires fewer resources than the direct approach to exposure assessment, for which the distribution of monitors to a representative sample of a given population is necessary. In the indirect exposure assessment approach, average microenvironmental concentrations are multiplied by the total time spent in each microenvironment to give total integrated exposure. By assuming that the concentrations encountered in each of 10 location categories are the same for different members of the U.S. population (i.e., the NHAPS respondents), the hypothetical contribution that ETS makes to the average 24-hr respirable suspended particle exposure for Americans working their main job is calculated in this paper to be 18 microg/m3. This article is an illustrative review and does not contain an actual exposure assessment or model validation

MATCH: An atom‐typing toolset for molecular mechanics force fields

We introduce a toolset of program libraries collectively titled multipurpose atom‐typer for CHARMM (MATCH) for the automated assignment of atom types and force field parameters for molecular mechanics simulation of organic molecules. The toolset includes utilities for the conversion of multiple chemical structure file formats into a molecular graph. A general chemical pattern‐matching engine using this graph has been implemented whereby assignment of molecular mechanics atom types, charges, and force field parameters are achieved by comparison against a customizable list of chemical fragments. While initially designed to complement the CHARMM simulation package and force fields by generating the necessary input topology and atom‐type data files, MATCH can be expanded to any force field and program, and has core functionality that makes it extendable to other applications such as fragment‐based property prediction. In this work, we demonstrate the accurate construction of atomic parameters of molecules within each force field included in CHARMM36 through exhaustive cross validation studies illustrating that bond charge increment rules derived from one force field can be transferred to another. In addition, using leave‐one‐out substitution it is shown that it is also possible to substitute missing intra and intermolecular parameters with ones included in a force field to complete the parameterization of novel molecules. Finally, to demonstrate the robustness of MATCH and the coverage of chemical space offered by the recent CHARMM general force field (Vanommeslaeghe, et al., J Comput Chem 2010, 31, 671), one million molecules from the PubChem database of small molecules are typed, parameterized, and minimized. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/88100/1/JCC_21963_sm_SuppInfo.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/88100/2/21963_ftp.pd

Validity of the uniform mixing assumption: determining human exposure to environmental tobacco smoke.

When using the mass balance equation to model indoor air quality, the primary assumption is that of uniform mixing. Different points in a single compartment are assumed to have the same instantaneous pollutant concentrations as all other points. Although such an assumption may be unrealistic, under certain conditions predictions (or measurements) of exposures at single points in a room are still within acceptable limits of error (e.g., 10%). In this article, three studies of the mixing of environmental tobacco smoke (ETS) pollutants are reviewed, and data from several other ETS field studies are presented. Under typical conditions for both short sources (e.g., 10 min) and the continuous sources of ETS in smoking lounges, I find that average exposure concentrations for a single point in a room represent the average exposure across all points in the room within 10% for averaging times ranging from 12 to 80 min. I present a method for determining theoretical estimates of acceptable averaging times for a continuous point source

Electronic and structural properties of vacancies on and below the GaP(110) surface

We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and electronic structure of neutral surface and subsurface vacancies at the GaP(110) surface. The cation as well as the anion surface vacancy show a pronounced inward relaxation of the three nearest neighbor atoms towards the vacancy while the surface point-group symmetry is maintained. For both types of vacancies we find a singly occupied level at mid gap. Subsurface vacancies below the second layer display essentially the same properties as bulk defects. Our results for vacancies in the second layer show features not observed for either surface or bulk vacancies: Large relaxations occur and both defects are unstable against the formation of antisite vacancy complexes. Simulating scanning tunneling microscope pictures of the different vacancies we find excellent agreement with experimental data for the surface vacancies and predict the signatures of subsurface vacancies.Comment: 10 pages, 6 figures, Submitted to Phys. Rev. B, Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm