An evaluation of garnet-clinopyroxene geothermometry in granulites

Four new formulations of the garnet-clinopyroxene geothermometer (Ellis and Green 1979; Ganguly 1979; Saxena 1979; Dahl 1980) have been evaluated in the Adirondacks and five other granulite terranes using results from 94 mineral pairs. The Saxena and Ganguly formulations give temperatures that are generally 100–150° C above those constrained by phase equilibria and other independent thermometry while the empirical calibration of Dahl gives widely scattered, erratic results. Despite some scatter in the data, the Ellis and Green calibration appears to be more accurate and precise than the others and is the most useful garnet-clinopyroxene thermometer currently available for quantitative thermometry in granulites. All four formulations are sensitive to large variations (>70–80° C) in temperature suggesting that problems with accuracy and precision can be improved with further refinement of model-based aspects of the thermometers.     

Geochemistry and evolution of the fuego volcanic complex, Guatemala

Four closely spaced vents along a fissure make up the Fuego and Acatenango volcanic centers in western Guatemala. The Fuego complex is composed of the Fuego and Meseta vents, but historic activity has consisted exclusively of high-Al₂O₃ basalts from the Fuego vent. The Meseta vent is inactive and deeply exposed. Prehistoric lavas from Fuego and Meseta are generally more silicic than historic Fuego lavas, but all the rocks form a single coherent geochemical variation pattern. Major element chemistry of these rocks is consistent with plagioclase, olivine, augite, and magnetite (POAM) fractionating from high-Al₂O₃ basalt. Separate batches of magma can be recognized from trace-element data throughout the history of the Fuego complex. This suggests that closed-system, POAM fractionation of distinct magma bodies occurs at Fuego. Trace-element data requires that deep fractionation of olivine, clinopyroxene, and perhaps magnetite from primary olivine tholeiite occurs before arrival of new magma into the shallow (8–16 km) magma chamber at Fuego. Migration of activity from Meseta to Fuego along the fissure is correlated with the change towards more mafic compositions at Fuego. The shift of the vents may have resulted in shorter repose periods and less time for fractionation before eruption. A minimum age of 17,000 years was required to build the Fuego complex.The andesitic rocks from the adjacent, larger composite volcanoes of Acatenango and Agua have higher incompatible element concentrations, different incompatible element ratios, and lower CaO, Na₂O, and Al₂O₃ contents than Fuego's lavas. We believe the magmatic evolution of Acatenango and Agua is much more complex than Fuego.     

Cladding influence on dynamics response of tall buildings

Precast concrete panels form attractive facades for steel frame buildings and are generally regarded as non-structural by structural engineers. However, panels have been found to add lateral stiffness until their capacity or that of their connections is exceeded. Consequently, the computed dynamic response based on a model of the structural framing alone may be quite different from that experienced by the actual structure. As a case study, the influence of precast concrete panels on lateral and torsional stiffness of a 25-storey building was investigated. The effect of cladding on dynamic properties and linear seismic response was explored by varying panel stiffness. Cladding stiffness was added to the bare frame model until analytical frequency values matched vibration test results. Then, using the cladding stiffness values obtained, an accidental eccentricity between centres of mass and rigidity at each floor level was imposed and linear seismic response computed. Torsional response effects were increased substantially. Finally, a modified cladding panel connection was developed based on previously-reported studies for panelized construction. The influence of the proposed connection on overall structural response was determined for different ground motion inputs.     

Dissolved organic carbon in pore waters from a hypersaline environment

Pore waters were collected from a sea-marginal, hypersaline pond in the Sinai and analyzed for dissolved organic carbon (DOC). The pore water DOC values ranged from 121 to 818 mg 1⁻¹ with maxima between 15 and 54 cm deep. These values are some of the highest observed from recent sediments and probably reflect production via abiotic as well as biotic sources.     

Use of microbial enrichments for the study of the anaerobic degradation of cholesterol

To demonstrate the potential of model microbial assemblages in studies of the biogeochemistry of complex organic molecules, anaerobic microbial populations capable of degrading cholesterol (cholest-5-en-3β-ol) have been enriched from marine sediment sources. The bacterial enrichments actively mineralized the C-4 nucleus of the cholesterol ring system to carbon dioxide when nitrate was present as the terminal electron acceptor. Nitrite was found as an intermediate in the reduction of nitrate, indicating the presence of denitrifying bacteria in the enrichments. When sulfate was supplied as the sole electron acceptor, active dissimilation of cholesterol was not observed. In enrichments containing 5 mM nitrate, 95–98% of the added cholesterol was recovered as carbon dioxide (2–5%), transformation products (20–30%), or as the unmodified sterol (70–80%). Cholesterol transformation products thus far identified include 5α- and 5β-cholestan-3β-ol, cholest-4-en-3-one, 5α-androstan-3, 17-dione and androst-4-en-3, 17 dione.     

Big Data from the Ground Up: Mobile Maps and Geographic Knowledge

Consumer users of maps on mobile devices are producing noteworthy geographic knowledges in the contexts of their own lives that are distinct from those of professional data scientists. By leveraging the streaming nature of big data in mobile maps and zooming multiscalar views, consumer users' mobile map practices produce a popular, multiscalar form of visual geographic knowledge that is both enabled and limited by its big data assemblage and associated technologies. The first half of this article outlines the role of consumer user practices amidst spatial big data assemblages, not for volunteered geographic information or aggregate analysis but for contextual, everyday use. Consumer users and their knowledges are coconstituted through mobile map viewing and as materially limited technological practices. This article focuses specifically on the consumer users' concept of scale in this context, for Web-based maps' multiscalar views differentiate them from older maps. The second half analyzes mobile map consumer users' concepts of scale in a series of focus groups that involved both questions and observing participants' actions with maps on their own phones. Instead of passively accepting maps at predetermined optimized scales from the map application, consumer users actively viewed the map across scales while searching but not while navigating.     

A study on the motion characteristics and their impact on the wind measurement post-processing of the GPS dropwindsonde. Part II: impacts of post-processing/composition schemes

When the Global Positioning System dropwindsonde wind measurements are used, post-processing and composition approaches are necessary to calculate the vertical profiles of wind statistics. In order to understand the impacts of post-processing/composition schemes on the wind statistics calculated based on dropwindsonde measurements, various post-processing/composition schemes were utilized to post-process and to composite pseudo-dropsonde measurements resulting from numerical simulation of dropsonde motions in a pseudo-stochastic wind field. Since the wind statistics of the pseudo-stochastic wind field were specified, the comparison between wind statistics calculated based on pseudo-dropsonde measurements and the specified values provided some insights into the impacts of different post-processing/composition schemes. The post-processing/composition schemes investigated include the low-pass filter to reduce high-frequency dropsonde measurement noises, the finite difference scheme to calculate dropsonde accelerations, which is needed to dynamically correct dropsonde measurements and composition data size.