bluuebunny/crossref_metadata_2025_split huggingface dataset:
Testing an integrated chronology: I‐Xe analysis of enstatite meteorites and a eucrite
Authors: BUSFIELD A. , TURNER G. , GILMOUR J. D. 
Published: January 2010

Abstract— We have determined initial 129I/127I ratios for mineral concentrates of four enstatite meteorites and a eucrite. In the case of the enstatite meteorites the inferred ages are associated with the pyroxene‐rich separates giving pyroxene closure ages relative to the Shallowater standard of Indarch (EH4, 0.04 ± 0.67 Ma), Khairpur (EL6, −4.22 ± 0.67 Ma), Khor Temiki (aubrite, −0.06 Ma), and Itqiy (enstatite achondrite, −2.6 ± 2.6 Ma), negative ages indicate closure after Shallowater. No separate from the cumulate eucrite Asuka (A−) 881394 yielded a consistent ratio, though excess 129Xe was observed in a feldspar separate, suggesting disturbance by thermal metamorphism within 25 Ma of closure in Shallowater.Iodine‐129 ages are mapped to the absolute Pb‐Pb time scale using the calibration proposed by Gilmour et al. (2006) who place the closure age of Shallowater at 4563.3 ± 0.4 Ma. Comparison of the combined 129I‐Pb data with associated 53Mn ages, for objects that have been dated by both systems, indicates that all three chronometers evolved concordantly in the early solar system. The enstatite chondrites are offset from the linear array described by asteroid‐belt objects when 53Mn ages are plotted against combined 129I‐Pb data, supporting the suggestion that 53Mn was radially heterogeneous in the early solar system.
Yellow impact glass from the K/T boundary at Beloc (Haiti): XANES determination of the Fe oxidation state and implications for formation conditions
Authors: GIULI Gabriele , EECKHOUT Sigrid Griet , KOEBERL Christian , PRATESI Giovanni , PARIS Eleonora 
Published: January 2010

Abstract— We determined the iron oxidation state and coordination number in five samples of yellow impact glass from the Cretaceous‐Tertiary (K/T) boundary section at Beloc, Haiti, which formed as the result of impact melting during the Chicxulub impact event. The samples were analyzed by Fe K‐edge XANES spectroscopy and the results were compared with published data on eight black impact glasses and one high Si‐K impact spherule from the same impact layer. The pre‐edge peak of our high‐resolution XANES spectra displays evident variations indicative of significant changes in the Fe oxidation state, spanning a wide range from about 75 to 100 mole% Fe3+. Yellow K/T glasses have significantly higher Fe3+/(Fe2+ + Fe3+) ratios compared to black K/T impact glasses (from 20 to 75 mole% Fe3+) and high Si‐K glass (20 mole% Fe3+). In particular, all the pre‐edge peak data on these three types of impact glasses plot between two mixing lines joining a point calculated as the mean of a group of tektites studied so far (consisting of [4]Fe2+ and [5]Fe2+) to [4]Fe3+ and [5]Fe3+, respectively. Thus, the XANES spectra of the yellow K/T glasses can be interpreted as a mixture of [4]Fe2+, [5]Fe2+, [4]Fe3+, and [5]Fe3+.Our observations can be explained by a very large range of oxygen fugacity conditions during melt formation. Furthermore, there is a clear positive relationship between the Fe3+/(Fe2+ + Fe3+) ratio and the Ca content of these glasses, suggesting that the Fe oxidation state was influenced by the relative contribution of Ca‐sulfate‐ and Ca‐carbonate‐bearing sedimentary rocks at the impact site.
Shergottites Dhofar 019, SaU 005, Shergotty, and Zagami: 40Ar‐39Ar chronology and trapped Martian atmospheric and interior argon
Authors: KOROCHANTSEVA Ekaterina V. , TRIELOFF Mario , BUIKIN Alexei I. , HOPP Jens 
Published: January 2010

Abstract— We report a high‐resolution 40Ar‐39Ar study of mineral separates and whole‐rock samples of olivine‐phyric (Dhofar 019, Sayh al Uhaymir [SaU] 005) and basaltic (Shergotty, Zagami) shergottites. Excess argon is present in all samples. The highest (40Ar/36Ar)trapped ratios are found for argon in pyroxene melt inclusions (˜1500), maskelynite (˜1200), impact glass (˜1800) of Shergotty and impact glass of SaU 005 (˜1200). A high (40Ar/36Ar)trapped component‐usually uniquely ascribed to Martian atmosphere‐can also originate from the Martian interior, indicating a heterogeneous Martian mantle composition. As additional explanation of variable high (40Ar/36Ar)trapped ratios in shocked shergottites, we suggest argon implantation from a “transient atmosphere” during impact induced degassing.The best 40Ar‐39Ar age estimate for Dhofar 019 is 642 ± 72 Ma (maskelynite). SaU 005 samples are between 700–900 Ma old. Relatively high 40Ar‐39Ar ages of melt inclusions within Dhofar 019 (1086 ± 252 Ma) and SaU 005 olivine (885 ± 66 Ma) could date entrapment of a magmatic liquid during early olivine crystallization, or reflect unrecognized excess 40Ar components. The youngest 40Ar‐39Ar age of Shergotty separates (maskelynite) is ˜370 Ma, that of Zagami is ˜200 Ma.The 40Ar‐39Ar chronology of Dhofar 019 and SaU 005 indicate >1 Ga ages. Apparent ages uncorrected for trapped (e.g., Martian atmosphere, mantle) argon components approach 4.5 Ga, but are not caused by inherited 40Ar, because excess 40Ar is supported by 36Artrapped. Young ages obtained by 40Ar‐39Ar and other chronometers argue for primary rather than secondary events. The cosmic ray exposure ages calculated from cosmogenic argon are 15.7 ± 0.7 Ma (Dhofar 019), 1.0–1.6 Ma (SaU 005), 2.1–2.5 Ma (Shergotty) and 2.2–3.0 Ma (Zagami).
The Obolon impact structure, Ukraine, and its ejecta deposits
Authors: GUROV Eugene , GUROVA Elena , CHERNENKO Yuri , YAMNICHENKO Anatoly 
Published: January 2010

Abstract— The Obolon impact structure, 18 km in diameter, is situated at the northeastern slope of the Ukrainian Shield near its margin with the Dnieper‐Donets Depression. The crater was formed in crystalline rocks of the Precambrian basement that are overlain by marine Carboniferous and continental Lower Triassic deposits. The post‐impact sediments comprise marine Middle Jurassic (Bajocian and Bathonian) and younger Mesozoic and Cenozoic deposits. Today the impact structure is buried beneath an about 300‐meter‐thick sedimentary rock sequence.Most information on the Obolon structure is derived from two boreholes in the western part of the crater. The lowest part of the section in the deepest borehole is composed by allogenic breccia of crystalline basement rocks overlain by clast‐rich impact melt rocks and suevites. Abundant shock metamorphic effects are planar deformation features (PDFs) in quartz and feldspars, kink bands in biotite, etc. Coesite and impact diamonds were found in clast‐rich impact melt rocks. Crater‐fill deposits are a series of sandstones and breccias with blocks of sedimentary rocks that are covered by a layer of crystalline rock breccia.Crystalline rock breccias, conglomeratic breccias, and sandstones with crystalline rock debris have been found in some boreholes around the Obolon impact structure to a distance of about 50 km from its center. Those deposits are always underlain by Lower Triassic continental red clay and overlain by Middle Jurassic marine clay. The K‐Ar age of impact melt glasses is 169 Ma, which corresponds to the Middle Jurassic (Bajocian) age. The composition of crater‐fill rocks within the crater and sediments outside the Obolon structure testify to its formation under submarine conditions.
Predictions for the LCROSS mission
Authors: KORYCANSKY D. G. , PLESKO Catherine S. , JUTZI Martin , ASPHAUG Erik , COLAPRETE Anthony 
Published: January 2010

Abstract— We describe the results of a variety of model calculations for predictions of observable results of the LCROSS mission to be launched in 2009. Several models covering different aspects of the event are described along with their results. Our aim is to bracket the range of expected results and produce a useful guide for mission planning. In this paper, we focus on several different questions, which are modeled by different methods. The questions include the size of impact crater, the mass, velocity, and visibility of impact ejecta, and the mass and temperature of the initial vapor plume. The mass and velocity profiles of the ejecta are of primary interest, as the ejecta will be the main target of the S‐S/C observations. In particular, we focus on such quantities as the amount of mass that reaches various heights. A height of 2 km above the target is of special interest, as we expect that the EDUS impact will take place on the floor of a moderate‐sized crater ˜30 km in diameter, with a rim height of 1–2 km. The impact ejecta must rise above the crater rim at the target site in order to scatter sunlight and become visible to the detectors aboard the S‐S/C. We start with a brief discussion of crater scaling relationships as applied to the impact of the EDUS second stage and resulting estimated crater diameter and ejecta mass. Next we describe results from the RAGE hydrocode as applied to modeling the short time scale (t 0.1 s) thermal plume that is expected to occur immediately after the impact. We present results from several large‐scale smooth‐particle hydrodynamics (SPH) calculations, along with results from a ZEUS‐MP hydrocode model of the crater formation and ejecta mass‐velocity distribution. We finish with two semi‐analytic models, the first being a Monte Carlo model of the distribution of expected ejecta, based on scaling models using a plausible range of crater and ejecta parameters, and the second being a simple model of observational predictions for the shepherding spacecraft (S‐S/C) that will follow the impact for several minutes until its own impact into the lunar surface.For the initial thermal plume, we predict an initial expansion velocity of ˜7 km s−1, and a maximum temperature of ˜1200 K. Scaling relations for crater formation and the SPH calculation predict a crater with a diameter of ˜15 m, a total ejecta mass of ˜106kg, with ˜104kg reaching an altitude of 2 km above the target. Both the SPH and ZEUS‐MP calculations predict a maximum ejecta velocity of ˜1 km s−1. The semi‐analytic Monte Carlo calculations produce more conservative estimates (by a factor of ˜5) for ejecta at 2 km, but with a large dispersion in possible results.
Tellurium isotope compositions of calcium‐aluminum‐rich inclusions
Authors: FEHR Manuela A. , REHKÁMPER Mark , HALLIDAY Alex N. , HATTENDORF Bodo , GÜNTHER Detlef 
Published: January 2010

Abstract— A method for the precise and accurate determination of the tellurium (Te) isotope compositions of calcium‐aluminum‐rich inclusions (CAIs) has been developed. The technique utilizes multiple‐collector inductively coupled plasma‐mass spectrometry (MC‐ICPMS) with either Faraday detectors or a dual ion‐counting system. The external reproducibility (2s̀) for 126Te/125Te was ?15%0 and ?2%0 when 3 pg and 65 pg of Te were analyzed with the electron multipliers. Measurements performed on 200 pg of Te using Faraday detectors and time‐resolved software displayed an external reproducibility of ?8%0 for 126Te/124Te, whereas 3 ng Te could be measured to a precision of about 0.6%0.Analyses of five CAIs from the Allende chondrite yielded Te concentrations that range from 12 to 537 ppb and the inclusions are therefore depleted in Te relative to bulk Allende by factors of about 2 to 86. The Sn/Te ratios of the CAIs are also fractionated compared to bulk Allende (which displays 124Sn/128Te ??0.1) with 124Sn/128Te ratios of about 0.1 to 2.5. The Te isotope measurements for these refractory inclusions yielded no 126Te excesses from the decay of the short‐lived radionuclide 126Sn (ɛ1/2 = 234,500 years) and the most precise analysis provided a ɛ126Te value of 1 ±?6 (ɛ126Te = 126Te/124Te normalized to 122Te/124Te = 0.53594 and reported relative to the JMC Te standard). Minor differences in the Te isotope composition of the CAIs relative to the terrestrial standard and bulk Allende hint at the presence of small deficits in r‐process Te isotopes or excess of s‐process Te, but these nucleosynthetic anomalies are barely resolvable given the analytical uncertainties. Hence, it is also conceivable that these effects reflect small unresolved analytical artifacts.
Nuclear field shift effect as a possible cause of Te isotopic anomalies in the early solar system—An alternative explanation of Fehr et al. (2006 and 2009)
Authors: Moynier Frédéric , Fujii Toshiyuki , Albarède Francis 
Published: January 2010

Abstract— We explore the possibility that Te isotopic anomalies measured in Ca‐Al‐rich inclusions (Fehr et al. 2009) and in leachates of carbonaceous chondrites (Fehr et al. 2006) may be due to mass‐independent effects controlled by nuclear field shift rather than to nucleosynthetic processes. Fehr et al.'s spectrum of mass‐independent anomalies of Te isotopes shows a smooth correlation with mass number and nuclear charge distribution. Ratios of even to odd isotopes, as the 125Te/126Te ratio used by these authors for normalization are particularly prone to nuclear field shift effects. We show that the alternative normalization of isotopic ratios to 130Te/126Te strongly reduces the trend of isotopic fractionation with mass number, leaving only 125Te as truly anomalous.For both normalizations (125Te/126Te and 130Te/126Te), Fehr et al.'s results fit the theory of Bigeleisen (1996), which suggests that the nuclear field shift effect can potentially account for the observed Te isotope abundances, as an alternative to nucleosynthetic processes.We propose that these mass‐independent effects may be acquired during accretion of sulfides from the solar nebula.
K-theory Schubert calculus of the affine Grassmannian
Authors: Lam Thomas , Schilling Anne , Shimozono Mark 
Published: January 2010

AbstractWe construct the Schubert basis of the torus-equivariantK-homology of the affine Grassmannian of a simple algebraic groupG, using theK-theoretic NilHecke ring of Kostant and Kumar. This is theK-theoretic analogue of a construction of Peterson in equivariant homology. For the case whereG=SLn, theK-homology of the affine Grassmannian is identified with a sub-Hopf algebra of the ring of symmetric functions. The Schubert basis is represented by inhomogeneous symmetric functions, calledK-k-Schur functions, whose highest-degree term is ak-Schur function. The dual basis inK-cohomology is given by the affine stable Grothendieck polynomials, verifying a conjecture of Lam. In addition, we give a Pieri rule inK-homology. Many of our constructions have geometric interpretations by means of Kashiwara’s thick affine flag manifold.
Conjecture de monodromie-poids pour quelques variétés de Shimura unitaires
Authors: Boyer Pascal 
Published: January 2010

AbstractIn Boyer [Monodromy of perverse sheaves on vanishing cycles on some Shimura varieties, Invent. Math. 177 (2009), 239–280 (in French)], a sheaf version of the monodromy-weight conjecture for some unitary Shimura varieties was proved by giving explicitly the monodromy filtration of the complex of vanishing cycles in terms of local systems introduced in Harris and Taylor [The geometry and cohomology of some simple Shimura varieties (Princeton University Press, Princeton, NJ, 2001)]. The main result of this paper is the cohomological version of the monodromy-weight conjecture for these Shimura varieties, which we prove by means of an explicit description of the groups of cohomology in terms of automorphic representations and the local Langlands correspondence.
Activity of Linezolid in anIn VitroPharmacokinetic-Pharmacodynamic Model Using Different Dosages andStaphylococcus aureusandEnterococcus faecalisStrains with and without a Hypermutator Phenotype
Authors: Ba Boubakar B. , Arpin Corinne , Bikie Bi Nso Branly , Dubois Véronique , Saux Marie-Claude , Quentin Claudine 
Published: January 2010

ABSTRACTThe influence of antibiotic dosages and bacterial mutator phenotypes on the emergence of linezolid-resistant mutants was evaluated in anin vitropharmacokinetic-pharmacodynamic model. A twice-daily 0.5-h infusion of a 200-, 600-, or 800-mg dose for 48 h was simulated against four strains (MIC, 2 μg/ml):Staphylococcus aureusRN4220 and its mutator derivative MutS2,Enterococcus faecalisATCC 29212, and a mutator clinical strain ofE. faecalis, Ef1497. The peak concentrations (4.38 to 4.79, 13.4 to 14.6, and 19.2 to 19.5 μg/ml) and half-lives at β-phase (5.01 to 6.72 h) fit human plasma linezolid pharmacokinetics. Due to its bacteriostatic property, the cumulative percentages of the dosing interval during which the drug concentration exceeded the MIC (T> MIC), 66.6 and 69.1% of the dosing interval, were not significant, except for Ef1497, with an 800-mg dose and aT> MIC of 80.9%. At the standard 600-mg dosage, resistant mutants (2- to 8-fold MIC increases) were selected only with Ef1497. A lower, 200-mg dosage did not select resistant mutants ofE. faecalisATCC 29212, but a higher, 800-mg dosage against Ef1497 did not prevent their emergence. For the most resistant mutant (MIC, 16 μg/ml), characterization of 23S rRNA genes revealed the substitution A2453G in two of the four operons, which was previously described only inin vitromutants of archaebacteria. Nevertheless, this mutant did not yield further mutants under 600- or 200-mg treatment. In conclusion, linezolid was consistently efficient againstS. aureusstrains. The emergence of resistantE. faecalismutants was probably favored by the rapid decline of linezolid concentrations against a strong mutator, a phenotype less exceptional inE. faecalisthan inS. aureus.
Tat Pathway-Mediated Translocation of the Sec Pathway Substrate Protein MexA, an Inner Membrane Component of the MexAB-OprM Xenobiotic Extrusion Pump in
Pseudomonas aeruginosa
Authors: Yoneyama Hiroshi , Akiba Keiji , Hori Hatsuhiro , Ando Tasuke , Nakae Taiji 
Published: January 2010

ABSTRACT

Pseudomonas aeruginosa
is equipped with the Sec and Tat protein secretion systems, which translocate the xenobiotic transporter MexAB-OprM and the pathogenic factor phospholipase C (PlcH), respectively. When the signal sequence of MexA was replaced with that of PlcH, the hybrid protein was successfully expressed and recovered from the periplasmic fraction, suggesting that the hybrid protein had been translocated across the inner membrane. MexA-deficient cells harboring the plasmid carrying the
plcH
-
mexA
fusion gene showed antibiotic resistance comparable to that of the wild-type cells. This result suggested that MexA secreted via the Tat machinery was properly assembled and functioned as a subunit of the MexAB-OprM efflux pump. A mutation was introduced into the chromosomal
tatC
gene encoding an inner membrane component of the Tat protein secretion machinery in
mexA
-deficient cells, and they were transformed with the plasmid carrying the
plcH-mexA
fusion gene. The transformants showed antibiotic susceptibility comparable to that of
mexA
-deficient cells, indicating that the hybrid protein was not transported to the periplasm. Whole-cell lysate of the
mexA
-
tatC
double mutant harboring the
plcH-mexA
plasmid produced mainly unprocessed PlcH-MexA. The periplasmic fraction showed no detectable anti-MexA antibody-reactive material. On the basis of these results, we concluded that MexA could be translocated across the inner membrane through the Tat pathway and assembled with its cognate partners, MexB and OprM, and that this complex machinery was fully functional. This hybrid protein translocation system has the potential to be a powerful screening tool for antimicrobial agents targeting the Tat system, which is not present in mammalian cells.
Both Hemolytic Anemia and Malaria Parasite-Specific Factors Increase Susceptibility to NontyphoidalSalmonella entericaSerovar Typhimurium Infection in Mice
Authors: Roux Christelle M. , Butler Brian P. , Chau Jennifer Y. , Paixao Tatiane A. , Cheung Kong Wai , Santos Renato L. , Luckhart Shirley , Tsolis Renée M. 
Published: January 2010

ABSTRACTSevere pediatric malaria is an important risk factor for developing disseminated infections with nontyphoidalSalmonellaserotypes (NTS). While recent animal studies on this subject are lacking, early work suggests that an increased risk for developing systemic NTS infection during malaria is caused by hemolytic anemia, which leads to reduced macrophage microbicidal activity. Here we established a model for oralSalmonella entericaserotype Typhimurium challenge in mice infected withPlasmodium yoelii nigeriensis. Initial characterization of this model showed that 5 days after coinoculation,P. yoelii nigeriensisinfection increased the recovery ofS. Typhimurium from liver and spleen by approximately 1,000-fold. The increased bacterial burden could be only partially recapitulated by antibody-mediated hemolysis, which increased the recovery ofS. Typhimurium from liver and spleen by 10-fold. These data suggested that both hemolysis andP. yoelii nigeriensis-specific factors contributed to the increased susceptibility toS. Typhimurium. The mechanism by which hemolysis impaired resistance toS. Typhimurium was further investigated.In vitro,S. Typhimurium was recovered 24 h after infection of hemophagocytic macrophages in 2-fold-higher numbers than after infection of mock-treated macrophages, making it unlikely that reduced macrophage microbicidal activity was solely responsible for hemolysis-induced immunosuppression during malaria. Infection withP. yoelii nigeriensis, but not antibody-mediated hemolysis, reduced serum levels of interleukin-12p70 (IL-12p70) in response toS. Typhimurium challenge. Collectively, studies establishing a mouse model for this coinfection suggest that multiple distinct malaria-induced immune defects contribute to increased susceptibility toS. Typhimurium.
Clumping Factor A Interaction with Complement Factor I Increases C3b Cleavage on the Bacterial Surface ofStaphylococcus aureusand Decreases Complement-Mediated Phagocytosis
Authors: Hair Pamela S. , Echague Charlene G. , Sholl Amber M. , Watkins Justin A. , Geoghegan Joan A. , Foster Timothy J. , Cunnion Kenji M. 
Published: January 2010

ABSTRACTThe human complement system is important in the immunological control ofStaphylococcus aureusinfection. We showed previously thatS. aureussurface protein clumping factor A (ClfA), when expressed in recombinant form, bound complement control protein factor I and increased factor I cleavage of C3b to iC3b. In the present study, we show that, compared to the results for the wild type, when isogenic ClfA-deficientS. aureusmutants were incubated in serum, they bound less factor I, generated less iC3b on the bacterial surface, and bound fewer C3 fragments. It has been shown previously that two amino acids in ClfA (P336and Y338) are essential for fibrinogen binding. However,S. aureusexpressing ClfA(P336A Y338S) was less virulent than ClfA-deficient strains in animal models. This suggested that ClfA contributed toS. aureusvirulence by a mechanism different than fibrinogen binding. In the present study, we showed thatS. aureusexpressing ClfA(P336A Y338S) was more susceptible to complement-mediated phagocytosis than a ClfA-null mutant or the wild type. Unlike ClfA, ClfA(P336A Y338S) did not enhance factor I cleavage of C3b to iC3b and inhibited the cofactor function of factor H. Fibrinogen enhanced factor I binding to ClfA and theS. aureussurface. Twenty clinicalS. aureusstrains all expressed ClfA and bound factor I. High levels of factor I binding by clinical strains correlated with poor phagocytosis. In summary, our results suggest that the interaction of ClfA with factor I contributes toS. aureusvirulence by a complement-mediated mechanism.