Gravitational Mesoscopic Constraints in Cosmological Dark Matter Halos     

Christine C. Dantas  Fernando M. Ramos 《Celestial Mechanics and Dynamical Astronomy》2006,94(1):67-81

We present an analysis of the behaviour of the ‘coarse-grained’ (‘mesoscopic’) rank partitioning of the mean energy of collections of particles composing virialized dark matter halos in a Λ-CDM cosmological simulation. We find evidence that rank preservation depends on halo mass, in the sense that more massive halos show more rank preservation than less massive ones. We find that the most massive halos obey Arnold’s theorem (on the ordering of the characteristic frequencies of the system) more frequently than less massive halos. This method may be useful to evaluate the coarse-graining level (minimum number of particles per energy cell) necessary to reasonably measure signatures of ‘mesoscopic’ rank orderings in a gravitational system.  相似文献   

First results from the H i Jodrell All Sky Survey: inclination-dependent selection effects in a 21-cm blind survey     

Robert H. Lang  Peter J. Boyce  Virginia A. Kilborn  Robert F. Minchin  Michael J. Disney  Christine A. Jordan  Marco Grossi  Diego A. Garcia  Ken C. Freeman  Steven Phillipps  Alan E. Wright 《Monthly notices of the Royal Astronomical Society》2003,342(3):738-758

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Queen Alexandra Range 93148: A new type of pyroxene pallasite?     

Christine Floss 《Meteoritics & planetary science》2002,37(8):1129-1139

Abstract— Trace elements, including the rare earth elements, were measured in olivine and orthopyroxene from Queen Alexandra Range (QUE) 93148, and in olivine from two main group pallasites, Springwater and Mount Vernon. Although QUE 93148 was originally classified as a lodranite, a variety of data including oxygen isotopic compositions (Goodrich and Righter, 2000), preclude a genetic relationship with the acapulcoites/lodranites. Incompatible trace element (e.g., Ti, Zr) distributions in orthopyroxene do indicate large amounts of melting and are consistent with the ultramafic assemblage observed in this meteorite. Trace element abundances in olivine are consistent with suggestions that QUE 93148 may be related to the main group pallasites (Goodrich and Righter, 2000), although there are some inconsistencies. Its trace element distributions are most like those of the pyroxene pallasites, suggesting that it may have formed in a similar manner. QUE 93148 may represent a new type of pyroxene pallasite with links to the main group pallasites.  相似文献   

Calcification rate and temperature effects on Sr partitioning in coccoliths of multiple species of coccolithophorids in culture     

Heather M. Stoll  Christine M. Klaas  Ian Probert  Jorge Ruiz Encinar  J. Ignacio Garcia Alonso   《Global and Planetary Change》2002,34(3-4)

Five common placolith-bearing coccolithophorid algae—Gephyrocapsa oceanica, Coccolithus pelagicus, Calcidiscus leptoporus, Umbilicosphaera sibogae (var. sibogae and var. foliosa), and Emiliania huxleyi—were cultured to investigate controls on Sr partitioning in coccolith calcite. For identical temperature and media composition, Sr partitioning varies by more than 30% in exponential phase cultures of the five species and is linearly related to rates of calcite production/cell (ρ=0.91). Exponential phase culture experiments with three strains of C. leptoporus and six strains of G. oceanica at varying temperatures show variations in Sr partitioning of 20% and 30%, respectively. With C. leptoporus, Sr partitioning is equally correlated with temperature and calcification rate (ρ=0.8), which themselves are highly correlated; the slope of the relationship between D_Sr and calcification rate is comparable to that observed in all species at constant temperature. However, in G. oceanica, increased temperature appears to enhance Sr incorporation by up to 2% to 1.6% °C⁻¹ in the range of 15 to 30 °C. The strong influence of calcification rate on Sr partitioning may be useful for inferring past variations in coccolithophorid productivity from Sr partitioning in coccolith sediments if the influence of temperature on Sr partitioning can be resolved. Because the relationship between calcite production and Sr partitioning is linear, a proportional change in calcification should be expressed much more strongly in the Sr/Ca ratio of large species with rapid calcite production than in smaller species, which produce calcite more slowly. Consequently, it may be possible to separate temperature and calcification influences on coccolith Sr/Ca by separately analyzing Sr/Ca in species that produce calcite rapidly and those that produce calcite slowly, if both undergo comparable relative changes in calcification rates.  相似文献   

Petrology of silicate inclusions in the Sombrerete ungrouped iron meteorite: Implications for the origins of IIE‐type silicate‐bearing irons     

Alex Ruzicka  Melinda Hutson  Christine Floss 《Meteoritics & planetary science》2006,41(11):1797-1831

Abstract— The petrography and mineral and bulk chemistries of silicate inclusions in Sombrerete, an ungrouped iron that is one of the most phosphate‐rich meteorites known, was studied using optical, scanning electron microscopy (SEM), electron microprobe analysis (EMPA), and secondary ion mass spectrometry (SIMS) techniques. Inclusions contain variable proportions of alkalic siliceous glass (?69 vol% of inclusions on average), aluminous orthopyroxene (?9%, Wo_1–4Fs_25–35, up to ?3 wt% Al), plagioclase (?8%, mainly An_70–92), Cl‐apatite (?7%), chromite (?4%), yagiite (?1%), phosphate‐rich segregations (?1%), ilmenite, and merrillite. Ytterbium and Sm anomalies are sometimes present in various phases (positive anomalies for phosphates, negative for glass and orthopyroxene), which possibly reflect phosphate‐melt‐gas partitioning under transient, reducing conditions at high temperatures. Phosphate‐rich segregations and different alkalic glasses (K‐rich and Na‐rich) formed by two types of liquid immiscibility. Yagiite, a K‐Mg silicate previously found in the Colomera (IIE) iron, appears to have formed as a late‐stage crystallization product, possibly aided by Na‐K liquid unmixing. Trace‐element phase compositions reflect fractional crystallization of a single liquid composition that originated by low‐degree (?4–8%) equilibrium partial melting of a chondritic precursor. Compositional differences between inclusions appear to have originated as a result of a “filter‐press differentiation” process, in which liquidus crystals of Cl‐apatite and orthopyroxene were less able than silicate melt to flow through the metallic host between inclusions. This process enabled a phosphoran basaltic andesite precursor liquid to differentiate within the metallic host, yielding a dacite composition for some inclusions. Solidification was relatively rapid, but not so fast as to prevent flow and immiscibility phenomena. Sombrerete originated near a cooling surface in the parent body during rapid, probably impact‐induced, mixing of metallic and silicate liquids. We suggest that Sombrerete formed when a planetesimal undergoing endogenic differentiation was collisionally disrupted, possibly in a breakup and reassembly event. Simultaneous endogenic heating and impact processes may have widely affected silicate‐bearing irons and other solar system matter.  相似文献   

Petrology and chemistry of MIL 03346 and its significance in understanding the petrogenesis of nakhlites on Mars     

James M. D. Day  Lawrence A. Taylor  Christine Floss  Harry Y. Mcsween 《Meteoritics & planetary science》2006,41(4):581-606

Abstract— Antarctic meteorite Miller Range (MIL) 03346 is a nakhlite composed of 79% clinopyroxene, ?1% olivine, and 20% vitrophyric intercumulus material. We have performed a petrological and geochemical study of MIL 03346, demonstrating a petrogenetic history similar to previously discovered nakhlites. Quantitative textural study of MIL 03346 indicates long (>1 × 10¹ yr) residence times for the cumulus augite, whereas the skeletal Fe‐Ti oxide, fayalite, and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling, probably as a lava flow. From the relatively high forsterite contents of olivine (up to Fo₄₃) compared with other nakhlites and compositions of augite cores (Wo_38–42En_35–40Fs_22–28) and their hedenbergite rims, we suggest that MIL 03346 is part of the same or a similar Martian cumulate‐rich lava flow as other nakhlites. However, MIL 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date. Calculated trace element concentrations based upon modal abundances of MIL 03346 and its constituent minerals are identical to whole rock trace element abundances. Parental melts for augite have REE patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients. This parallelism reflects closed‐system crystallization for MIL 03346, where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization. A model for the petrogenesis of MIL 03346 and the nakhlites (Nakhla, Governador Valadares, Lafayette, Yamato‐000593, Northwest Africa (NWA) 817, NWA 998) would include: 1) partial melting and ascent of melt generated from a long‐term LREE depleted mantle source, 2) crystallization of cumulus augite (± olivine, ± magnetite) in a shallow‐level Martian magma chamber, 3) eruption of the crystal‐laden nakhlite magma onto the surface of Mars, 4) cooling, crystal settling, overgrowth, and partial equilibration to different extents within the flow, 5) secondary alteration through hydrothermal processes, possibly immediately succeeding or during emplacement of the flow. This model might apply to single—or multiple—flow models for the nakhlites. Ultimately, MIL 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks on Mars with analogous petrogenetic histories to pyroxene‐rich terrestrial lava flows and to komatiites.  相似文献   

SIMS studies of Allende projectiles fired into Stardust‐type aluminum foils at 6 km/sec     

Peter Hoppe  Frank J. Stadermann  Thomas Stephan  Christine Floss  Jan Leitner  Kuljeet K. Marhas  Friedrich Hrz 《Meteoritics & planetary science》2006,41(2):197-209

Abstract— We have explored the feasibility of C, N, and O isotopic measurements by NanoSIMS and of elemental abundance determinations by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) on residues of Allende projectiles that impacted Stardust‐type aluminum foils in the laboratory at 6 km/sec. These investigations are part of a consortium study aimed at providing the foundation for the characterization of matter associated with microcraters that were produced during the encounter of the Stardust space probe with comet 81P/Wild‐2. Eleven experimental impact craters were studied by NanoSIMS and eighteen by TOF‐SIMS. Crater sizes were between 3 and 190 μm. The NanoSIMS measurements have shown that the crater morphology has only a minor effect on spatial resolution and on instrumental mass fractionation. The achievable spatial resolution is always better than 200 nm, and C and O isotopic ratios can be measured with a precision of several percent at a scale of several 100 nm, which is the typical size of presolar grains. This clearly demonstrates that presolar matter, provided it survives the impact into the aluminum foil partly intact, is recognizable even if embedded in material of solar system origin. TOF‐SIMS studies are restricted to materials from the crater rim. The element ratios of the major rock‐forming elements in the Allende projectiles are well‐characterized by the TOF‐SIMS measurements, indicating that fractionation of those elements during impact can be expected to be negligible. This permits chemical information on the type of impactor material to be obtained. For any more detailed assignments to specific chondrite groups, however, information on the abundances of the light elements, especially C, is crucial. This information could not be obtained in the present study due to unavoidable contamination during impact experiments.  相似文献   

Modelled impact of global warming on ENSO-driven precipitation changes in the tropical Pacific     

Christine T. Y. Chung  Scott B. Power 《Climate Dynamics》2016,47(3-4):1303-1323

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Application of Genetic Algorithm (GA) in History Matching of the Vapour Extraction (VAPEX) Heavy Oil Recovery Process     

Suxin Xu  Min Zhang  Fanhua Zeng  Christine Chan 《Natural Resources Research》2015,24(2):221-237

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Local perceptions in climate change debates: insights from case studies in the Alps and the Andes     

Christine Jurt  Maria Dulce Burga  Luis Vicuña  Christian Huggel  Ben Orlove 《Climatic change》2015,133(3):511-523

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