The finite element method with continuity constraints for stair-step grids in geoscience     

T. P. Fries  M. Fücker  A. Kauerauf 《Computational Geosciences》2014,18(5):831-850

This work investigates the enforcement of continuity constraints on stair-step grids which are specialized grids for simulations in geosciences. They are rectilinear in horizontal directions but locally discontinuous (i.e., nonconforming) in the vertical direction. Furthermore, they allow for (partly) collapsed elements in order to model pinched-out layers. A robust and efficient algorithm for enforcing continuity is proposed which is tailored to the special properties of stair-step grids. A number of two- and three-dimensional finite element method (FEM) simulations on stair-step grids are conducted. Thereby, the Lagrange multiplier and penalty method with different ansatz spaces are studied for pointwise and averaged constraints. A particulary useful choice is the penalty method with continuous constraints and penalty parameters that depend on the element size.  相似文献   

A temperature-induced reversible transformation between paratacamite and herbertsmithite     

Mark D. Welch  Matthew J. Sciberras  Peter A. Williams  Peter Leverett  Jochen Schlüter  Thomas Malcherek 《Physics and Chemistry of Minerals》2014,41(1):33-48

The crystal chemistry of paratacamite has been re-evaluated by studying a crystal from the holotype specimen BM86958 of composition Cu_3.71Zn_0.29(OH)₆Cl₂ using single-crystal X-ray diffraction at 100, 200, 300, 353, 393 and 423 K. At 300 K paratacamite has space group $R\bar{3}$ with unit-cell parameters a 13.644 and c 14.035 Å and exhibits a pronounced subcell, a′ = ½a and c′ = c, analogous to that of the closely related mineral herbertsmithite, Cu₃Zn(OH)₆Cl₂. Between 353 and 393 K, paratacamite undergoes a reversible phase transformation to the herbertsmithite-like substructure, space group $R\bar{3}m$ , unit-cell parameters a 6.839 and c 14.072 Å (393 K). The transformation is characterised by a gradual reduction in intensity of superlattice reflections, which are absent at 393 and 443 K. On cooling from 443 to 300 K at ~10 K min^?1, the superlattice reflections reappear and the refined structures ( $R\bar{3}$ ) of the initial and recovered 300 K states are almost identical. The complete reversibility of the transformation establishes that paratacamite of composition Cu_3.71Zn_0.29(OH)₆Cl₂ is thermodynamically stable at ambient temperatures. The nature of the rhombic distortion of the M(2)O₆ octahedron is discussed by considering two possibilities that are dependent upon the nature of cation substitution in the interlayer sites.  相似文献   

The cosmic microwave background and the ionization history of the Universe     

Antony Lewis  Jochen Weller †  Richard Battye 《Monthly notices of the Royal Astronomical Society》2006,373(2):561-570

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Detection and rapid recovery of the Sutter's Mill meteorite fall as a model for future recoveries worldwide     

Marc Fries  Lucille Le Corre  Mike Hankey  Jeff Fries  Robert Matson  Jake Schaefer  Vishnu Reddy 《Meteoritics & planetary science》2014,49(11):1989-1996

The Sutter's Mill C‐type meteorite fall occurred on 22 April 2012 in and around the town of Coloma, California. The exact location of the meteorite fall was determined within hours of the event using a combination of eyewitness reports, weather radar imagery, and seismometry data. Recovery of the first meteorites occurred within 2 days and continued for months afterward. The recovery effort included local citizens, scientists, and meteorite hunters, and featured coordination efforts by local scientific institutions. Scientific analysis of the collected meteorites revealed characteristics that were available for study only because the rapid collection of samples had minimized terrestrial contamination/alteration. This combination of factors—rapid and accurate location of the event, participation in the meteorite search by the public, and coordinated scientific investigation of recovered samples—is a model that was widely beneficial and should be emulated in future meteorite falls. The tools necessary to recreate the Sutter's Mill recovery are available, but are currently underutilized in much of the world. Weather radar networks, scientific institutions with interest in meteoritics, and the interested public are available globally. Therefore, it is possible to repeat the Sutter's Mill recovery model for future meteorite falls around the world, each for relatively little cost with a dedicated researcher. Doing so will significantly increase the number of fresh meteorite falls available for study, provide meteorite material that can serve as the nuclei of new meteorite collections, and will improve the public visibility of meteoritics research.  相似文献   

Neutral hydrogen surveys for high-redshift galaxy clusters and protoclusters     

Richard A. Battye  Rod D. Davies  Jochen Weller 《Monthly notices of the Royal Astronomical Society》2004,355(4):1339-1347

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The Millennium Galaxy Catalogue: bulge–disc decomposition of 10 095 nearby galaxies     

Paul D. Allen  Simon P. Driver  Alister W. Graham  Ewan Cameron  Jochen Liske  Roberto De Propris 《Monthly notices of the Royal Astronomical Society》2006,371(1):2-18

We present near-infrared (NIR) adaptive optics-assisted spectroscopic observations of the  CO (Δμ= 2)  absorption bands towards the centre of the giant elliptical galaxy NGC 1399. The observations were made with NAOS-CONICA (on the European Southern Observatory's Very Large Telescope) and have a full width at half-maximum resolution of 0.15 arcsec (14 pc). Kinematic analysis of the observations reveals a decoupled core and strongly non-Gaussian line-of-sight velocity profiles in the central 0.2 arcsec (19 pc). NIR imaging also indicates an asymmetric elongation of the central isophotes in the same region.
We use spherical orbit-superposition models to interpret the kinematics, using a set of orthogonal 'eigen-velocity profiles' that allow us to fit models directly to spectra. The models require a central black hole of mass  1.2^+0.5_−0.6× 10⁹ M_⊙  , with a strongly tangentially biased orbit distribution in the inner 40 pc.  相似文献   

Preliminary evaluation of the occurrence of herbicides and PAHs in the Wet Tropics region of the Great Barrier Reef, Australia, using passive samplers   总被引：2，自引：0，他引：2  

Shaw M  Müller JF 《Marine pollution bulletin》2005,51(8-12):876-881

The proximity of the Great Barrier Reef (GBR) Marine Park to areas of intensive agriculture and increasing urbanisation places the park under potential threat of contamination by land-based pollutants. Passive samplers were deployed at inshore reef and river mouth sites in the Wet Tropics region of the GBR during a dry and a wet season to measure levels of land-based organic pollutants in this environment. Two types of passive sampling devices were deployed: (i) a polar sampler, which can be used to monitor polar herbicides and (ii) semipermeable membrane devices (SPMDs) which sequester more hydrophobic compounds (e.g. PAHs, chlorpyrifos). Herbicides (diuron, simazine, atrazine, hexazinone and/or flumeturon) were detected at low concentrations (ng L⁻¹) at all sites sampled and in both seasons. Chlorpyrifos was not detected while PAHs were present in SPMDs at levels below limits of detection. The results show that the GBR environment does contain low levels of organic pollutants and that passive sampling provides a sensitive monitoring tool for measuring waterborne organic pollutants.  相似文献   

Estimating reliability and resolution of probability forecasts through decomposition of the empirical score     

Jochen Br?cker 《Climate Dynamics》2012,39(3-4):655-667

Proper scoring rules provide a useful means to evaluate probabilistic forecasts. Independent from scoring rules, it has been argued that reliability and resolution are desirable forecast attributes. The mathematical expectation value of the score allows for a decomposition into reliability and resolution related terms, demonstrating a relationship between scoring rules and reliability/resolution. A similar decomposition holds for the empirical (i.e. sample average) score over an archive of forecast–observation pairs. This empirical decomposition though provides a too optimistic estimate of the potential score (i.e. the optimum score which could be obtained through recalibration), showing that a forecast assessment based solely on the empirical resolution and reliability terms will be misleading. The differences between the theoretical and empirical decomposition are investigated, and specific recommendations are given how to obtain better estimators of reliability and resolution in the case of the Brier and Ignorance scoring rule.  相似文献   

Capture effects in carbonaceous material: A Stardust analogue study     

Marc Fries  Mark Burchell  Anton Kearsley  Andrew Steele 《Meteoritics & planetary science》2009,44(10):1465-1474

Abstract— It is reasonable to expect that cometary samples returned to Earth by the Stardust space probe have been altered to some degree during capture in aerogel at 6.1 km/s. In order to help interpret the measured structure of these particles with respect to their original cometary nature, a series of coal samples of known structure and chemical composition was fired into aerogel at Stardust capture velocity. This portion of the study analyzed the surfaces of aerogel‐embedded particles using Raman spectroscopy. Results show that particle surfaces are largely homogenized during capture regardless of metamorphic grade or chemical composition, apparently to include a devolatilization step during capture processing. This provides a possible mechanism for alteration of some aliphatic compound‐rich phases through devolatilization of cometary carbonaceous material followed by re‐condensation within the particle. Results also show that the possibility of alteration must be considered for any particular Stardust grain, as examples of both graphitization and amorphization are found in the coal samples. It is evident that Raman G band (～1580 cm^?1) parameters provide a means of characterizing Stardust carbonaceous material to include identifying those grains which have been subjected to significant capture alteration.  相似文献   

The coating hypothesis for ammonia ice particles in Jupiter: Laboratory experiments and optical modeling     

Konstantinos S. Kalogerakis  Jochen Marschall  Patricia A. Engel  Rhiannon T. Meharchand  Michael H. Wong 《Icarus》2008,196(1):202-215

We report laboratory experiments and modeling calculations investigating the effect of a hydrocarbon coating on ammonia ice spectral signatures. Observational evidence and thermochemical models indicate an abundance of ammonia ice clouds in Jupiter's atmosphere. However, spectrally identifiable ammonia ice clouds are found covering less than 1% of Jupiter's atmosphere, notably in areas of strong vertical transport, indicating a short lifetime for the signature of ammonia absorption on condensed ammonia particles [Baines, K.H., Carlson, R.W., Kamp, L.W., 2002. Icarus 159, 74-94]. Current literature has suggested coating of ammonia ice particles by a hydrocarbon haze as a possible explanation for this paradox. The work presented here supports the inference of a coating effect that can alter or suppress ammonia absorption features. In the experiments, thin films of ammonia ices are deposited in a cryogenic apparatus, coated with hydrocarbons, and characterized by reflection-absorption infrared spectroscopy. We have observed the effects on the ammonia ice absorption features near 3 and 9 μm with coverage by thin layers of hydrocarbons. Modeling calculations of these multilayer thin films assist in the interpretation of the experimental results and reveal the important role of optical interference in altering the aforementioned ammonia spectral features. Mie and T-matrix scattering calculations demonstrate analogous effects for ammonia ice particles and investigate the relative effects of ammonia ice particle size, shape, and coating layer thickness on the ice particle spectral signatures.  相似文献