Thermal infrared spectra of experimentally shocked andesine anorthosite

Andesine-rich (An_36–46) anorthosite rocks experimentally shocked to high pressures (16–57 GPa) exhibit changes in spectral features with increasing pressure in laboratory thermal infrared emission spectra (250–1400 cm^?1). These results are similar to previous studies of shocked bytownite- and albite-rich rocks, albeit with differences in absorption band centers characteristic of mineralogy and composition. Typical spectral absorptions result from Si–O antisymmetric stretch motions of the silica tetrahedral (1000–1250 cm^?1) and weaker absorptions due to Si–O–Si octahedral bending vibrations (350–700 cm^?1). Many of these features persist to higher pressures in the andesine spectra compared to similar features in measurements of shocked bytownite. This is consistent with previous thermal infrared absorption studies of shocked feldspars and likely is related to differences in density, hardness, and Al content. A transparency feature at ～832 cm^?1 observed in powdered andesine spectra also degrades with increasing pressure, intermediate between the ～828 cm^?1 and ～855 cm^?1 transparency features in spectra of powders of shocked bytownite and albitite, respectively. These data can be incorporated into thermal infrared spectral analyses of cratered planetary surfaces (or laboratory spectra of shocked samples) to help constrain the occurrence and degree of shock in plagioclase feldspars.     

UV Capabilities to Probe the Formation of Planetary Systems: From the ISM to Planets

Planetary systems are angular momentum reservoirs generated during star formation. Solutions to three of the most important problems in contemporary astrophysics are needed to understand the entire process of planetary system formation: The physics of the ISM. Stars form from dense molecular clouds that contain ∼ 30% of the total interstellar medium (ISM) mass. The structure, properties and lifetimes of molecular clouds are determined by the overall dynamics and evolution of a very complex system – the ISM. Understanding the physics of the ISM is of prime importance not only for Galactic but also for extragalactic and cosmological studies. Most of the ISM volume (∼ 65%) is filled with diffuse gas at temperatures between 3000 and 300 000 K, representing about 50% of the ISM mass. The physics of accretion and outflow. Powerful outflows are known to regulate angular momentum transport during star formation, the so-called accretion–outflow engine. Elementary physical considerations show that, to be efficient, the acceleration region for the outflows must be located close to the star (within 1 AU) where the gravitational field is strong. According to recent numerical simulations, this is also the region where terrestrial planets could form after 1 Myr. One should keep in mind that today the only evidence for life in the Universe comes from a planet located in this inner disk region (at 1 AU) from its parent star. The temperature of the accretion–outflow engine is between 3000 and 10 ⁷ K. After 1 Myr, during the classical T Tauri stage, extinction is small and the engine becomes naked and can be observed at ultraviolet wavelengths. The physics of planet formation. Observations of volatiles released by dust, planetesimals and comets provide an extremely powerful tool for determining the relative abundances of the vaporizing species and for studying the photochemical and physical processes acting in the inner parts of young planetary systems. This region is illuminated by the strong UV radiation field produced by the star and the accretion–outflow engine. Absorption spectroscopy provides the most sensitive tool for determining the properties of the circumstellar gas as well as the characteristics of the atmospheres of the inner planets transiting the stellar disk. UV radiation also pumps the electronic transitions of the most abundant molecules (H ₂, CO, etc.) that are observed in the UV.Here we argue that access to the UV spectral range is essential for making progress in this field, since the resonance lines of the most abundant atoms and ions at temperatures between 3000 and 300 000 K, together with the electronic transitions of the most abundant molecules (H ₂, CO, OH, CS, S ₂, CO ₂ ⁺, C ₂, O ₂, O₃, etc.) are at UV wavelengths. A powerful UV-optical instrument would provide an efficient mean for measuring the abundance of ozone in the atmosphere of the thousands of transiting planets expected to be detected by the next space missions (GAIA, Corot, Kepler, etc.). Thus, a follow-up UV mission would be optimal for identifying Earth-like candidates.     

Forecasting vertical ground surface movement from shrinking/swelling soils with artificial neural networks

Artificial neural networks (ANNs) are used to estimate vertical ground surface movement when soils expand and contract due to changes in soil moisture content caused by changing climate conditions. Several counterpropagation ANN test cases were investigated to map climate data (i.e. temperature and rainfall) to vertical ground surface movement at field sites in Texas and Australia. Three of the four ANN test cases use a historical time series of climate data to forecast ground surface elevation relative to a specified datum. The fourth ANN test case predicts the rate of ground surface movement, and requires post‐processing of the predicted rates to calculate ground surface elevation relative to a specified datum. The counterpropagation network has demonstrated a successful mapping of temperature and rainfall data to vertical ground surface movement at a field site when it is trained with a subset of data from the same field site (test cases 1 and 2). The results of training an ANN on one field site and testing it on another field site (test cases 3 and 4) demonstrate the ability of the ANN to capture trends in vertical ground surface movement. When compared with the predictions from a physics‐based method (shrink test‐water content method) that requires measurements/estimates of changes in soil water content, the ANN‐based predictions (based on climatic changes) captured the trends in the field measurements of shrinking–swelling soil surface movements equally well. These findings are promising and merit further investigation with data from additional field sites. Copyright © 2007 John Wiley & Sons, Ltd.     

Future trends in transport and fate of diffuse contaminants in catchments,with special emphasis on stable isotope applications

A summary is provided of the first of a series of proposed Integrated Science Initiative workshops supported by the UNESCO International Hydrological Programme. The workshop brought together hydrologists, environmental chemists, microbiologists, stable isotope specialists and natural resource managers with the purpose of communicating new ideas on ways to assess microbial degradation processes and reactive transport at catchment scales. The focus was on diffuse contamination at catchment scales and the application of compound‐specific isotope analysis (CSIA) in the assessment of biological degradation processes of agrochemicals. Major outcomes were identifying the linkage between water residence time distribution and rates of contaminant degradation, identifying the need for better information on compound specific microbial degradation isotope fractionation factors and the potential of CSIA in identifying key degradative processes. In the natural resource management context, a framework was developed where CSIA techniques were identified as practically unique in their capacity to serve as distributed integrating indicators of process across a range of scales (micro to diffuse) of relevance to the problem of diffuse pollution assessment. Copyright © 2006 John Wiley & Sons, Ltd.     

Wetland nitrogen dynamics in an Adirondack forested watershed

Wetlands often form the transition zone between upland soils and watershed streams, however, stream–wetland interactions and hydrobiogeochemical processes are poorly understood. We measured changes in stream nitrogen (N) through one riparian wetland and one beaver meadow in the Archer Creek watershed in the Adirondack Mountains of New York State, USA from 1 March to 31 July 1996. In the riparian wetland we also measured changes in groundwater N. Groundwater N changed significantly from tension lysimeters at the edge of the peatland to piezometer nests within the peatland. Mean N concentrations at the peatland perimeter were 1·5, 0·5 and 18·6 µmol L^?1 for NH₄⁺, NO₃^? and DON (dissolved organic nitrogen), respectively, whereas peatland groundwater N concentration was 56·9, 1·5 and 31·6 µmol L^?1 for NH₄⁺, NO₃^? and DON, respectively. The mean concentrations of stream water N species at the inlet to the wetlands were 1·5, 10·1 and 16·9 µmol L^?1 for NH₄⁺, NO₃^? and DON, respectively and 1·6, 28·1 and 8·4 µmol L^?1 at the wetland outlet. Although groundwater total dissolved N (TDN) concentrations changed more than stream water TDN through the wetlands, hydrological cross‐sections for the peatland showed that wetland groundwater contributed minimally to stream flow during the study period. Therefore, surface water N chemistry was affected more by in‐stream N transformations than by groundwater N transformations because the in‐stream changes, although small, affected a much greater volume of water. Stream water N input–output budgets indicated that the riparian peatland retained 0·16 mol N ha^?1 day^?1 of total dissolved N and the beaver meadow retained 0·26 mol N ha^?1 day^?1 during the study period. Nitrate dominated surface water TDN flux from the wetlands during the spring whereas DON dominated during the summer. This study demonstrates that although groundwater N changed significantly in the riparian peatland, those changes were not reflected in the stream. Consequently, although in‐stream changes of N concentrations were less marked than those in groundwater, they had a greater effect on stream water chemistry—because wetland groundwater contributed minimally to stream flow. Copyright © 2004 John Wiley & Sons, Ltd.     

The Gas Production Rate and Coma Structure of Comet C/1995 O1 (Hale–Bopp)

The University of Wisconsin–Madison and NASA–Goddard conducted acomprehensive multi-wavelength observing campaign of coma emissionsfrom comet Hale–Bopp, including OH 3080 Å, [O I] 6300 Å H₂O⁺ 6158 Å, H Balmer-α 6563 Å, NH₂ 6330 Å, [C I] 9850 ÅCN 3879 Å, C₂ 5141 Å, C₃ 4062 Å,C I 1657 Å, and the UV and optical continua. In thiswork, we concentrate on the results of the H₂O daughter studies.Our wide-field OH 3080 Å measured flux agrees with other, similarobservations and the expected value calculated from published waterproduction rates using standard H₂O and OH photochemistry.However, the total [O I] 6300 Å flux determined spectroscopically overa similar field-of-view was a factor of 3-4 higher than expected.Narrow-band [O I] images show this excess came from beyond theH₂O scale length, suggesting either a previously unknown source of[O I] or an error in the standard OH + ν→ O(¹ D) + H branching ratio. The Hale–Bopp OH and[O I] distributions, both of which were imaged tocometocentric distances >1 × 10⁶ km, were more spatiallyextended than those of comet Halley (after correcting for brightnessdifferences), suggesting a higher bulk outflow velocity. Evidence ofthe driving mechanism for this outflow is found in the Hα lineprofile, which was narrower than in comet Halley (though likelybecause of opacity effects, not as narrow as predicted by Monte-Carlomodels). This is consistent with greater collisional coupling betweenthe suprathermal H photodissociation products and Hale–Bopp's densecoma. Presumably because of mass loading of the solar wind by ionsand ions by the neutrals, the measured acceleration of H₂O⁺ downthe ion tail was much smaller than in comet Halley. Tailwardextensions in the azimuthal distributions of OH 3080 Å,[O I], and [C I] , as well as a Doppler asymmetry in the[O I] line profile, suggest ion-neutral coupling. While thetailward extension in the OH can be explained by increased neutralacceleration, the [O I] 6300 Å and [C I] 9850 Å emissions show 13%and >200% excesses in this direction (respectively), suggesting anon-negligible contribution from dissociative recombination of CO⁺and/or electron collisional excitation. Thus, models including theeffects of photo- and collisional chemistry are necessary for the fullinterpretation of these data.