bluuebunny/crossref_metadata_2025 huggingface dataset:
Nebular shock waves generated by planetesimals passing through Jovian resonances: Possible sites for chondrule formation
Authors: HOOD Lon L. , CIESLA Fred J. , ARTEMIEVA Natalia A. , MARZARI Francesco , WEIDENSCHILLING Stuart J.
Published: January 2010

Abstract— The primordial asteroid belt contained at least several hundred and possibly as many as 10,000 bodies with diameters of 1000 km or larger. Following the formation of Jupiter, nebular gas drag combined with passage of such bodies through Jovian resonances produced high eccentricities (e = 0.3‐0.5), low inclinations (i < 0.5°), and, therefore, high velocities (3–10 km/s) for “resonant” bodies relative to both nebular gas and non‐resonant planetesimals. These high velocities would have produced shock waves in the nebular gas through two mechanisms. First, bow shocks would be produced by supersonic motion of resonant bodies relative to the nebula. Second, high‐velocity collisions of resonant bodies with non‐resonant bodies would have generated impact vapor plume shocks near the collision sites. Both types of shocks would be sufficient to melt chondrule precursors in the nebula, and both are consistent with isotopic evidence for a time delay of ˜1‐1.5 Myr between the formation of CAIs and most chondrules. Here, initial simulations are first reported of impact shock wave generation in the nebula and of the local nebular volumes that would be processed by these shocks as a function of impactor size and relative velocity. Second, the approximate maximum chondrule mass production is estimated for both bow shocks and impact‐generated shocks assuming a simplified planetesimal population and a rate of inward migration into resonances consistent with previous simulations. Based on these initial first‐order calculations, impact‐generated shocks can explain only a small fraction of the minimum likely mass of chondrules in the primordial asteroid belt (˜1024‐1025g). However, bow shocks are potentially a more efficient source of chondrule production and can explain up to 10–100 times the estimated minimum chondrule mass.
Thermal histories of IVA iron meteorites from transmission electron microscopy of the cloudy zone microstructure
Authors: GOLDSTEIN J. I. , YANG J. , KOTULA P. G. , MICHAEL J. R. , SCOTT E. R. D.
Published: January 2010

Abstract— We have measured the size of the high‐Ni particles in the cloudy zone and the width of the outer taenite rim in eight low shocked and eight moderately to heavily shocked IVA irons using a transmission electron microscope (TEM). Thin sections for TEM analysis were produced by a focused ion beam instrument. Use of the TEM allowed us to avoid potential artifacts which may be introduced during specimen preparation for SEM analysis of high Ni particles <30 nm in size and to identify microchemical and microstructural changes due to the effects of shock induced reheating. No cloudy zone was observed in five of the eight moderately to highly shocked (>13 GPa) IVA irons that were examined in the TEM. Shock induced reheating has allowed for diffusion from 20 nm to 400 nm across kamacite/taenite boundaries, recrystallization of kamacite, and the formation, in Jamestown, of taenite grain boundaries. In the eleven IVA irons with cloudy zone microstructures, the size of the high‐Ni particles in the cloudy zone increases directly with increasing bulk Ni content. Our data and the inverse correlation between cooling rate and high‐Ni particle size for irons and stony‐irons show that IVA cooling rates at 350‐200 °C are inversely correlated with bulk Ni concentration and vary by a factor of about 15. This cooling rate variation is incompatible with cooling in a metallic core that was insulated with a silicate mantle, but is compatible with cooling in a metallic body of radius 150 ± 50 km. The widths of the tetrataenite regions next to the cloudy zone correlate directly with high‐Ni particle size providing another method to measure low temperature cooling rates.
Druse clinopyroxene in D'Orbigny angritic meteorite studied by single‐crystal X‐ray diffraction, electron microprobe analysis, and Mössbauer spectroscopy
Authors: ABDU Yassir A. , SCORZELLI Rosa B. , VARELA Maria E. , KURAT Gero , AZEVEDO Izabel de Souza , STEWART Silvana J. , HAWTHORNE Frank C.
Published: January 2010

Abstract— The crystal structure of druse clinopyroxene from the D'Orbigny angrite, (Ca0.944 Fe2+0.042 Mg0.010Mn0.004) (Mg0.469Fe2+0.317Fe3+0.035Al0.125Cr0.010Ti0.044) (Si1.742Al0.258) O6, a = 9.7684(2), b = 8.9124(2), c = 5.2859(1) Å, β = 105.903(1)°, V = 442.58 Å3, space group C2/c, Z = 2, has been refined to an R1 index of 1.92% using single‐crystal X‐ray diffraction data. The unit formula, calculated from electron microprobe analysis, and the refined site scattering values were used to assign site populations. The distribution of Fe2+and Mg over the M1 and M2 sites suggests a closure temperature of 1000 °C. Mössbauer spectroscopy measurements were done at room temperature on a single crystal and a powdered sample. The spectra are adequately fit by a Voigt‐based quadrupole‐splitting distribution model having two generalized sites, one for Fe2+with two Gaussian components and one for Fe3+with one Gaussian component. The two ferrous components are assigned to Fe2+at the M1 site, and arise from two different next‐nearest‐neighbor configurations of Ca and Fe cations at the M2 site: (3Ca,0Fe) and (2Ca,1Fe). The Fe3+/Fetot ratio determined by Mössbauer spectroscopy is in agreement with that calculated from the electron microprobe analysis. The results are discussed in connection with the redox and thermal history of D'Orbigny.
The fine‐grained matrix of the Semarkona LL3.0 ordinary chondrite: An induced thermoluminescence study
Authors: CRAIG Jonathan P. , SEARS Derek W. G.
Published: January 2010

Abstract— To investigate the nature, origin, and history of the fine‐grained matrix in Semarkona and develop techniques suitable for small samples, we have measured the induced thermoluminescence properties of six matrix samples 10 μm to 400 μm in size. The samples had TL sensitivities comparable with 4 mg of bulk samples of type 3.2–3.4 ordinary chondrites, which is very high relative to bulk Semarkona. The other induced TL properties of these samples, TL peak temperatures, and TL peak widths distinguish them from other ordinary chondrite samples where the TL is caused by feldspar. Cathodoluminescence images and other data suggest that the cause of the luminescence in the Semarkona fine‐grained matrix is forsterite. In some respects the matrix TL data resemble that of Semarkona chondrules, in which the phosphor is forsterite and terrestrial forsterites from a variety of igneous and metamorphic environments. However, differences in the TL peak temperature versus TL peak width relationship between the matrix samples and the other forsterites suggest a fundamentally different formation mechanism. We also note that forsterite appears to be a major component in many primitive materials, such as nebulae, cometary dust, and Stardust particles.
Outward transport of CAIs during FU‐Orionis events
Authors: WURM Gerhard , HAACK Henning
Published: January 2010

Abstract— Evidence from meteorites shows that the first solids to form in the solar system, calcium‐aluminum‐rich inclusions (CAIs), were transported outward from the Sun by several AU in the early solar system. We introduce a new concept of levitation and outward transport of CAIs at the surface of protoplanetary disks. Thermal radiation from the disk and the Sun can cause particles to levitate above the disk and drift outward through a process known as photophoresis. During normal conditions this process only works for dust‐sized particles but during high luminosity events like FU‐Orionis outbursts, the process can provide an efficient lift and transport of CAIs from within the inner 1 AU to a distance of several AU from the Sun. This might explain why CAIs, believed to have formed close to the Sun, are common in meteorites believed to come from the outer asteroid belt but are rare or absent in samples from the inner solar system. Since the process only works during the FU‐Orionis event and only for particles up to cm‐size, it may also explain why the CAIs we find in meteorites appear to have formed within a short period of time and why they rarely exceed cm size.
On the origin of shocked and unshocked CM clasts in H‐chondrite regolith breccias
Authors: RUBIN Alan E. , BOTTKE William F.
Published: January 2010

Abstract— CM chondrite clasts that have experienced different degrees of aqueous alteration occur in H‐chondrite and HED meteorite breccias. Many clasts are fragments of essentially unshocked CM projectiles that accreted at low relative velocities to the regoliths of these parent bodies. A few clasts were heated and dehydrated upon impact; these objects most likely accreted at higher relative velocities. We examined three clasts and explored alternative scenarios for their formation. In the first scenario, we assumed that the H and HED parent bodies had diameters of a few hundred kilometers, so that their high escape velocities would effectively prevent soft landings of small CM projectiles. This would imply that weakly shocked CM clasts formed on asteroidal fragments (family members) associated with the H and HED parent bodies. In the second scenario, we assumed that weakly shocked CM clasts were spall products ejected at low velocities from larger CM projectiles when they slammed into the H and HED parent bodies. In both cases, if most CM clasts turn out to have ancient ages (e.g., ˜3.4‐4.1 Ga), a plausible source for their progenitors would be outer main belt objects, some which may have been dynamically implanted 3.9 Ga ago by the events described in the so‐called “Nice model.” On the other hand, if most CM clasts have recent ages (<200 Ma), a plausible source location for their parent body would be the inner main belt between 2.1–2.2 AU. In that case, the possible source of the CM‐clasts' progenitors' parent fragments would be the breakup ˜160 Ma ago of the parent body 170 km in diameter of the Baptistina asteroid family (BAF).
Expanding the application of the Eu‐oxybarometer to the lherzolitic shergottites and nakhlites: Implications for the oxidation state heterogeneity of the Martian interior
Authors: McCANTA Molly C. , ELKINS‐TANTON Linda , RUTHERFORD Malcolm J.
Published: January 2010

Abstract— Experimentally rehomogenized melt inclusions from the nakhlite Miller Range 03346 (MIL 03346) and the lherzolitic shergottite Allan Hills 77005 (ALH 77005) have been analyzed for their rare earth element (REE) concentrations in order to characterize the early melt compositions of these Martian meteorites and to calculate the oxygen fugacity conditions they crystallized under. D(Eu/Sm)pyroxene/melt values were measured at 0.77 and 1.05 for ALH 77005 and MIL 03346, respectively. These melts and their associated whole rock compositions have similar REE patterns, suggesting that whole rock REE values are representative of those of the early melts and can be used as input into the pyroxene Eu‐oxybarometer for the nakhlites and lherzolitic shergottites. Crystallization fO2 values of IW + 1.1 (ALH 77005) and IW + 3.2 (MIL 03346) were calculated. Whole rock data from other nakhlites and lherzolitic shergottites was input into the Eu‐oxybarometer to determine their crystallization fO2 values. The lherzolitic shergottites and nakhlites have fO2 values that range from IW + 0.4 to 1.6 and from IW + 1.1 to 3.2, respectively. These values are consistent with some previously determined fO2 estimates and expand the known range of fO2 values of the Martian interior to four orders of magnitude. The origins of this range are not well constrained. Possible mechanisms for producing this spread in fO2 values include mineral/melt fractionation, assimilation, shock effects, and magma ocean crystallization processes. Mineral/melt partitioning can result in changes in fO2 from the start to the finish of crystallization of 2 orders of magnitude. In addition, crystallization of a Martian magma ocean with reasonable initial water content results in oxidized, water‐rich, late‐stage cumulates. Sampling of these oxidized cumulates or interactions between reduced melts and the oxidized material can potentially account for the range of fO2 values observed in the Martian meteorites.
40Ar‐39Ar ages of H‐chondrite impact melt breccias
Authors: SWINDLE Timothy D. , ISACHSEN Clark E. , WEIRICH John R. , KRING David A.
Published: January 2010

Abstract— 40Ar‐39Ar analyses of a total of 26 samples from eight shock‐darkened impact melt breccias of H‐chondrite affinity (Gao‐Guenie, LAP 02240, LAP 03922, LAP 031125, LAP 031173, LAP 031308, NWA 2058, and Ourique) are reported. These appear to record impacts ranging in time from 303 ± 56 Ma (Gao‐Guenie) to 4360 ± 120 Ma (Ourique) ago. Three record impacts 300–400 Ma ago, while two others record impacts 3900–4000 Ma ago. Combining these with other impact ages from H chondrites in the literature, it appears that H chondrites record impacts in the first 100 Ma of solar system history, during the era of the “lunar cataclysm” and shortly thereafter (3500–4000 Ma ago), one or more impacts ˜300 Ma ago, and perhaps an impact ˜500 Ma ago (near the time of the L chondrite parent body disruption). Records of impacts on the H chondrite parent body are rare or absent between the era of planetary accretion and the “lunar cataclysm” (4400‐4050 Ma), during the long stretch between heavy bombardment and recent breakup events (3500‐1000 Ma), or at the time of final breakup into meteorite‐sized bodies (<50 Ma).
The plausible source(s) of 26Al in the early solar system: A massive star or the X‐wind irradiation scenario?
Authors: SAHIJPAL S. , GUPTA G.
Published: January 2010

Abstract— A quantitative analysis is presented for the irradiation contributions of the short‐lived nuclides, specifically 26Al, by the X‐wind scenario in the early solar system. The analysis is based on the comprehensive numerical simulations of the scenario that involves thermal processing of protoCAIs during the decades long X‐wind cycle. It would be difficult to explain the canonical value of 26Al/27Al in Ca‐Al‐rich inclusions on the basis of its inferred irradiation yields. Hence, the bulk inventory of 26Al in the early solar system was not produced by the X‐wind scenario. We suggest the predominant occurrence of gradual flares compared to impulsive flares in the early solar system as in the case of the modern solar flares. One tenth of the bulk 26Al was only produced by irradiation in case the entire solar inventory of 10Be was produced by local irradiation. The bulk 26Al inventory along with 60Fe was probably synthesized by a massive star. We present a qualitative model of the astrophysical settings for the formation of the solar system on the basis of a survey of the presently active star forming regions. We hypothesize that the formation of the solar system could have occurred almost contemporaneously with the formation of the massive star within a single stellar cluster. As the massive star eventually exploded as supernova Ib/c subsequent to Wolf‐Rayet stages, the short‐lived nuclides were probably injected into the solar proto‐planetary disc. The dynamically evolving stellar cluster eventually dispersed within the initial ˜10 million years prior to the major planetary formation episodes.
Labile trace elements in basaltic achondrites: Can they distinguish between meteorites from the Moon, Mars, and V‐type asteroids?
Authors: WOLF Stephen F. , WANG Ming‐Sheng , LIPSCHUTZ Michael E.
Published: January 2010

Abstract— We report data for 14 mainly labile trace elements (Ag, Au, Bi, Cd, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U, and Zn) in eight whole‐rock lunar meteorites (Asuka [A‐] 881757, Dar al Gani [DaG] 262, Elephant Moraine [EET] 87521, Queen Alexandra Range [QUE] 93069, QUE 94269, QUE 94281, Yamato [Y‐] 793169, and Y‐981031), and Martian meteorite (DaG 476) and incorporate these into a comparative study of basaltic meteorites from the Moon, Mars, and V‐type asteroids. Multivariate cluster analysis of data for these elements in 14 lunar, 13 Martian, and 34 howardite, eucrite, and diogenite (HED) meteorites demonstrate that materials from these three parents are distinguishable using these markers of late, low‐temperature episodes. This distinguishability is essentially as complete as that based on markers of high‐temperature igneous processes. Concentrations of these elements in 14 lunar meteorites are essentially lognormally distributed and generally more homogeneous than in Martian and HED meteorites. Mean siderophile and labile element concentrations in the 14 lunar meteorites indicate the presence of a CI‐equivalent micrometeorite admixture of 2.6% When only feldspathic samples are considered, our data show a slightly higher value of 3.4% consistent with an increasing micrometeorite content in regolith samples of higher maturity. Concentrations of labile elements in the 8 feldspathic samples hint at the presence of a fractionated highly labile element component, possibly volcanic in origin, at a level comparable to the micrometeorite component. Apparently, the process(es) that contributed to establishing lunar meteorite siderophile and labile trace element contents occurred in a system open to highly labile element transport.
The Carancas meteorite impact crater, Peru: Geologic surveying and modeling of crater formation and atmospheric passage
Authors: KENKMANN T. , ARTEMIEVA N. A. , WÜNNEMANN K. , POELCHAU M. H. , ELBESHAUSEN D. , PRADO H. NÚÑEZ del
Published: January 2010

Abstract— The recent Carancas meteorite impact event caused a worldwide sensation. An H4–5 chondrite struck the Earth south of Lake Titicaca in Peru on September 15, 2007, and formed a crater 14.2 m across. It is the smallest, youngest, and one of two eye‐witnessed impact crater events on Earth. The impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters. Fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight. The small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters. The Carancas cratering event, however, demonstrates that meter‐sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances. We present results of a detailed geologic survey of the crater and its ejecta. To constrain the possible range of impact parameters we carried out numerical models of crater formation with the iSALE hydrocode in two and three dimensions. Depending on the strength properties of the target, the impact energies range between approximately 100–1000 MJ (0.024–0.24 t TNT). By modeling the atmospheric traverse we demonstrate that low cosmic velocities (12–14 kms−1) and shallow entry angles (<20 °) are prerequisites to keep aerodynamic stresses low (<10 MPa) and thus to prevent fragmentation of stony meteoroids with standard strength properties. This scenario results in a strong meteoroid deceleration, a deflection of the trajectory to a steeper impact angle (40–60 °), and an impact velocity of 350–600 ms−1, which is insufficient to produce a shock wave and significant shock effects in target minerals. Aerodynamic and crater modeling are consistent with field data and our microscopic inspection. However, these data are in conflict with trajectories inferred from the analysis of infrasound signals.
Three‐dimensional textural and compositional analysis of particle tracks and fragmentation history in aerogel
Authors: Ebel Denton S. , Greenberg Michael , Rivers Mark L. , Newville Matthew
Published: January 2010

Abstract— We report analyses of aerogel tracks using (1) synchrotron X‐ray computed microtomography (XRCMT), (2) laser confocal scanning microscopy (LCSM), and (3) synchrotron radiation X‐ray fluorescence (SRXRF) of particles and their paths resulting from simulated hypervelocity impacts (1–2), and a single ∼1 mm aerogel track from the Stardust cometary sample collector (1–3). Large aerogel pieces can be imaged sequentially, resulting in high spatial resolution images spanning many tomographic fields of view (‘lambda‐tomography’). We report calculations of energy deposited, and tests on aromatic hydrocarbons showing no alteration in tomography experiments. Imaging at resolutions from ∼17 to ∼1 micron/pixel edge (XRCMT) and to <100 nm/pixel edge (LCSM) illustrates track geometry and interaction of particles with aerogel, including rifling, particle fragmentation, and final particle location. We present a 3‐D deconvolution method using an estimated point‐spread function for aerogel, allowing basic corrections of LCSM data for axial distortion. LCSM allows rapid, comprehensive, non‐destructive, high information return analysis of tracks in aerogel keystones, prior to destructive grain extraction. SRXRF with LCSM allows spatial correlation of grain size, chemical, and mineralogical data. If optical methods are precluded in future aerogel capture missions, XRCMT is a viable 3D imaging technique. Combinations of these methods allow for complete, nondestructive, quantitative 3‐D analysis of captured materials at high spatial resolution. This data is fundamental to understanding the hypervelocity particle‐aerogel interaction histories of Stardust grains.
Pyroxenes microstructure in comet 81P/Wild 2 terminal Stardust particles
Authors: Jacob Damien , Stodolna Julien , Leroux Hugues , Langenhorst Falko , Houdellier F.
Published: January 2010

Abstract— We report the examination by transmission electron microscopy (TEM) of four Stardust terminal particles extracted from two neighboring tracks (32 an 69). The particles are made of well‐preserved crystalline grains dominated by low‐Ca pyroxene ranging from nearly pure enstatite to pigeonite. Some olivine grains are also found, in chemical equilibrium with the surrounding pyroxenes. Various microstructures are observed, as a function of the composition of the grains. They include (100)‐twinned pigeonite, clino/ortho domains in enstatite and exsolution in a Ca‐rich grain. The microstructures are mostly consistent with a formation by cooling from high‐temperature phases, which could be associated to igneous processes. Some dislocations in glide configuration are also present, probably attesting for small intensity shocks. Possible effects of the rapid heating/cooling stage and thermal shock associated to the collect are discussed. It appears that most of the microstructural features reported here are plausibly pristine.
Along‐track compositional and textural variation in extensively melted grains returned from comet 81P/Wild 2 by the Stardust mission: Implications for capture‐melting process
Authors: Velbel Michael A. , Harvey Ralph P.
Published: January 2010

Abstract— Five amorphous (extensively melted) grains from Stardust aerogel capture Track 35 were examined by transmission electron microscopy (TEM); two from the bulb, two from near the bulb‐stylus transition, and one from near the terminal particle. Melted grains consist largely of a texturally and compositionally heterogeneous emulsion of immiscible metal/sulfide beads nanometers to tens of nanometers in diameter in a silica‐rich vesicular glass. Most metal/sulfide beads are spherical, but textures of non‐spherical beads indicate that some solidified as large drops during stretching and breaking while in translational and rotational motion, and others solidified from lenses of immiscible liquid at the silicate‐melt/vesicle (vapor) interface.

Melted grains appear to become richer in Fe relative to Mg, and depleted in S relative to Fe and Ni with increasing penetration distance along the aerogel capture track. Fe/S ratios are near unity in grains from the bulb of Track 35, consistent with the dominance of Fe‐monosulfide minerals inferred by previous research on Stardust materials. Near‐stoichiometric Fe/S in melted grains from the bulb suggests that Fe‐sulfides in the bulb were dispersed and melted during formation of the bulb but did not lose S. Along‐track increases in Fe/S in melted grains from the bulb through the bulb‐stylus transition and continuing into the stylus indicate that S initially present as iron monosulfide may have been progressively partially volatilized and lost from the melted grains with greater penetration of the grains deeper into the aerogel during capture‐melting of comet dust. Extensively melted grains from the bulbs of aerogel capture tracks may preserve better primary compositional information with less capture‐related modification than grains from farther along the same capture tracks.
Rietveld analysis of X‐ray powder diffraction patterns as a potential tool for the identification of impact‐deformed carbonate rocks
Authors: Huson Sarah A. , Foit Franklin F. , Watkinson A. John , Pope Michael C.
Published: January 2010

Abstract— Previous X‐ray powder diffraction (XRD) studies revealed that shock deformed carbonates and quartz have broader XRD patterns than those of unshocked samples. Entire XRD patterns, single peak profiles and Rietveld refined parameters of carbonate samples from the Sierra Madera impact crater, west Texas, unshocked equivalent samples from 95 miles north of the crater and the Mission Canyon Formation of southwest Montana and western Wyoming were used to evaluate the use of X‐ray powder diffraction as a potential tool for distinguishing impact deformed rocks from unshocked and tectonically deformed rocks. At Sierra Madera dolostone and limestone samples were collected from the crater rim (lower shock intensity) and the central uplift (higher shock intensity). Unshocked equivalent dolostone samples were collected from well cores drilled outside of the impact crater. Carbonate rocks of the Mission Canyon Formation were sampled along a transect across the tectonic front of the Sevier and Laramide orogenic belts.

Whereas calcite subjected to significant shock intensities at the Sierra Madera impact crater can be differentiated from tectonically deformed calcite from the Mission Canyon Formation using Rietveld refined peak profiles, weakly shocked calcite from the crater rim appears to be indistinguishable from the tectonically deformed calcite. In contrast, Rietveld analysis readily distinguishes shocked Sierra Madera dolomite from unshocked equivalent dolostone samples from outside the crater and tectonically deformed Mission Canyon Formation dolomite.
Incompletely compacted equilibrated ordinary chondrites
Authors: Sasso Matthew R. , Macke Robert J. , Boesenberg Joseph S. , Britt Daniel T. , Rivers Mark L. , Ebel Denton S. , Friedrich Jon M.
Published: January 2010

Abstract— We document the size distributions and locations of voids present within five highly porous equilibrated ordinary chondrites using high‐resolution synchrotron X‐ray microtomography (μCT) and helium pycnometry. We found total porosities ranging from ∼10 to 20% within these chondrites, and with μCT we show that up to 64% of the void space is located within intergranular voids within the rock. Given the low (S1‐S2) shock stages of the samples and the large voids between mineral grains, we conclude that these samples experienced unusually low amounts of compaction and shock loading throughout their entire post accretionary history. With Fe metal and FeS metal abundances and grain size distributions, we show that these chondrites formed naturally with greater than average porosities prior to parent body metamorphism. These materials were not “fluffed” on their parent body by impact‐related regolith gardening or events caused by seismic vibrations. Samples of all three chemical types of ordinary chondrites (LL, L, H) are represented in this study and we conclude that incomplete compaction is common within the asteroid belt.
Cosmogenic and trapped noble gases in individual chondrules: Clues to chondrule formation
Authors: Das J. P. , Murty S. V. S.
Published: January 2010

Abstract— We studied the elemental and isotopic abundances of noble gases (He, Ne, Ar in most cases, and Kr, Xe also in some cases) in individual chondrules separated from six ordinary, two enstatite, and two carbonaceous chondrites. Most chondrules show detectable amounts of trapped 20Ne and 36Ar, and the ratio (36Ar/20Ne)t (from ordinary and carbonaceous chondrites) suggests that HL and Q are the two major trapped components. A different trend between (36Ar/20Ne)t and trapped 36Ar is observed for chondrules in enstatite chondrites indicating a different environment and/or mechanism for their formation compared to chondrules in ordinary and carbonaceous chondrites. We found that a chondrule from Dhajala chondrite (DH‐11) shows the presence of solar‐type noble gases, as suggested by the (36Ar/20Ne)t ratio, Ne‐isotopic composition, and excess of 4He.

Cosmic‐ray exposure (CRE) ages of most chondrules are similar to their host chondrites. A few chondrules show higher CRE age compared to their host, suggesting that some chondrules and/or precursors of chondrules have received cosmic ray irradiation before accreting to their parent body. Among these chondrules, DH‐11 (with solar trapped gases) and a chondrule from Murray chondrite (MRY‐1) also have lower values of (21Ne/22Ne)c, indicative of SCR contribution. However, such evidences are sporadic and indicate that chondrule formation event may have erased such excess irradiation records by solar wind and SCR in most chondrules. These results support the nebular environment for chondrule formation.
Chemical identification of comet 81P/Wild 2 dust after interacting with molten silica aerogel
Authors: Rietmeijer Frans J. M.
Published: January 2010

Abstract— Flight aerogel in Stardust allocation C2092,2,80,47,6 contains percent level concentrations of Na, Mg, Al, S, Cl, K, Ca, Cr, Mn, Fe, and Ni that have a distinctive Fe‐ and CI‐normalized distribution pattern, which is similar to this pattern for ppb level chemical impurities in pristine aerogel. The elements in this aerogel background were assimilated in non‐vesicular and vesicular glass with the numerous nanometer Fe‐Ni‐S compound inclusions. After correction for the background values, the chemical data show that this piece of comet Wild 2 dust was probably an aggregate of small (<500 nm) amorphous ferromagnesiosilica grains with many tiny Fe,Ni‐sulfide inclusions plus small Ca‐poor pyroxene grains. This distinctive Fe‐ and CI‐normalized element distribution pattern is found in several Stardust allocations. It appears to be a common feature in glasses of quenched aerogel melts but its exact nature is yet to be established.
Collisional modification of the acapulcoite/lodranite parent body revealed by the iodine‐xenon system in lodranites
Authors: Crowther S. A. , Whitby J. A. , Busfield A. , Holland G. , Busemann H. , Gilmour J. D.
Published: January 2010

Abstract—The I‐Xe system of three lodranites has been investigated. Samples of Gibson yielded no isochrons, and late model ages are attributed to late addition of iodine. Two metal and one silicate separate from the transitional lodranite Graves Nunataks (GRA) 95209 gave ages that are consistent with each other and with the literature I‐Xe age of Acapulco feldspar. These yield a mean closure age 4.19 ± 0.53 Ma after the Shallowater enstatite reference age (4562.3 ± 0.4 Ma). Such identical I‐Xe ages from distinct phases imply that the parent material underwent a period of rapid cooling, the absolute age of this event being 4558.1 ± 0.7 Ma. Such rapid cooling indicates an increase in the rate at which heat could be conducted away, requiring a significant modification of the parent body. We suggest the parent body was modified by an impact at or close to the time recorded by the I‐Xe system.

An age of 10.4 ± 2.3 Ma after Shallowater has been determined for one whole‐rock sample of Lewis Cliff (LEW) 88280. Since the release pattern is similar to that of GRA 95209 this hints that the larger grain size of this sample may reflect slower cooling due to deeper post impact burial.
Three‐dimensional structures and elemental distributions of Stardust impact tracks using synchrotron microtomography and X‐ray fluorescence analysis
Authors: Tsuchiyama A. , Nakamura T. , Okazaki T. , Uesugi K. , Nakano T. , Sakamoto K. , Akaki T. , Iida Y. , Kadono T. , Jogo K. , Suzuki Y.
Published: January 2010

Abstract— Three‐dimensional structures and elemental abundances of four impact tracks in silica aerogel keystones of Stardust samples from comet 81P/Wild 2 (bulbous track 67 and carrot‐type tracks 46, 47, and 68) were examined non‐destructively by synchrotron radiation‐based microtomography and X‐ray fluorescence analysis. Track features, such as lengths, volumes and width as a function of track depth, were obtained quantitatively by tomography. A bulbous portion was present near the track entrance even in carrot‐type tracks. Each impact of a cometary dust particle results in the particle disaggregated into small pieces that were widely distributed on the track walls as well as at its terminal. Fe, S, Ca, Ni, and eight minor elements are concentrated in the bulbous portion of track 68 as well as in terminal grains. It was confirmed that bulbous portions and thin tracks were formed by disaggregation of very fine fragile materials and relatively coarse crystalline particles, respectively. The almost constant ratio of whole Fe mass to track volume indicates that the track volume is almost proportional to the impact kinetic energy. The size of the original impactor was estimated from the absolute Fe mass by assuming its Fe content (CI) and bulk density. Relations between the track sizes normalized by the impactor size and impact conditions are roughly consistent with those of previous hypervelocity impact experiments.
Penetration tracks in aerogel produced by Al2O3 spheres
Authors: Hörz Friedrich , Cintala Mark J. , See Thomas H. , Nakamura‐Messenger Keiko
Published: January 2010

Abstract— We conducted impact experiments into SiO2‐based aerogel of uniform density (0.02 g cm−3) with spherical corundum projectiles. The highly refractory nature and mechanical strength of corundum minimizes projectile deformation and continuous mass loss by ablation that might have affected earlier experiments with soda‐lime glass (SLG) impactors into aerogel targets. We find that corundum is a vastly superior penetrator producing tracks a factor of 2.5 longer, yet similar in diameter to those made by SLG. At velocities <4 km s−1 a cylindrical “cavity” forms, largely by melting of aerogel. The diameter and length of this cavity increase with velocity and impactor size, and its volume dominates total track volume. A continuously tapering, exceptionally long and slender “stylus” emerges from this cavity and makes up some 80–90% of the total track length; this stylus is characterized by solid‐state deformations. Tracks formed below 4 km s−1 lack the molten cavity and consist only of a stylus. Projectile residues recovered from a track's terminus substantially resemble the initial impactors at V > 4 km s−1, yet they display two distinct surfaces at higher velocities, such as a blunt, forward face and a well‐preserved, hemispherical trailing side; a pronounced, circumferential ridge of compressed and molten aerogel separates these two surfaces. Stringers and patches of melt flow towards the impactor's rear where they accumulate in a characteristic melt tip. SEM‐EDS analyses indicate the presence of Al in these melts at velocities as low as 5.2 km s−1, indicating that the melting point of corundum (2054 °C) was exceeded. The thermal model of aerogel impact by Anderson and Cherne (2008) suggests actual aerogel temperatures <5000 K at comparable conditions. We therefore propose that projectile melting occurs predominantly at those surfaces that are in contact with this very hot aerogel, at the expense of viscous heating and associated ablation. Exposure to superheated aerogel may be viewed as extreme form of “flash heating.” This seems consistent with observations from the Stardust mission to comet Wild 2, such as relatively pristine interiors of rather large, terminal particles, yet total melting of most fine‐grained dust components.
The Meteoritical Bulletin, No. 96, September 2009
Authors: Weisberg Michael K. , Smith Caroline , Benedix Gretchen , Herd Christopher D. K. , Righter Kevin , Haack Henning , Yamaguchi Akira , Aoudjehane Hasnaa Chennaoui , Grossman Jeffrey N.
Published: January 2010

Abstract— The Meteoritical Bulletin No. 96 contains a total of 1590 newly approved meteorite names with their relevant data. These include 12 from specific locations within Africa, 76 from northwest Africa, 9 from the Americas, 13 from Asia, 1 from Australia, 2 from Europe, 950 from Antarctica recovered by the Chinese Antarctic Research Expedition (CHINARE), and 527 from the American Antarctic program (ANSMET). Among these meteorites are 4 falls, Almahata Sitta (Sudan), Sulagiri (India), Ash Creek (United States), and Maribo (Denmark). Almahata Sitta is an anomalous ureilite and is debris from asteroid 2008 TC3 and Maribo is a CM2 chondrite. Other highlights include a lunar meteorite, a CM1 chondrite, and an anomalous IVA iron.
Moduli spaces of irreducible symplectic manifolds
Authors: Gritsenko V. , Hulek K. , Sankaran G. K.
Published: January 2010

We study the moduli spaces of polarised irreducible symplectic manifolds. By a comparison with locally symmetric varieties of orthogonal type of dimension 20, we show that the moduli space of polarised deformation K3[2]manifolds with polarisation of degree 2dand split type is of general type ifd≥12.
The disposition index: adjustment for peripheral vs. hepatic insulin sensitivity?
Authors: Færch K. , Brøns C. , Alibegovic A. C. , Vaag A.
Published: January 2010

The assessment of pancreatic β cell function in humans is challenging because of a complex interplay between insulin secretion, insulin sensitivity and hepatic insulin extraction. Simplified, the relationship between insulin secretion and insulin sensitivity can be described by an approximate hyperbola with the product of the two variables being constant for individuals with the same degree of glucose tolerance (the disposition index). Strengths and limitations of the disposition index have been widely debated in the literature. In this review we will focus on another and until recently unrecognized dimension of the disposition index, namely the issue of adjusting insulin secretion for hepatic versus peripheral insulin sensitivity. An underlying assumption of this issue is that the liver as compared to muscle plays a different role in the regulation of in vivo insulin secretion.
Scaling relations in nonlinear viscoelastic behavior of aqueous PEO solutions under large amplitude oscillatory shear flow
Authors: Cho Kwang Soo , Song Ki-Won , Chang Gap-Shik
Published: January 2010

We have found empirical scaling relations in nonlinear viscoelasticity of poly(ethylene oxide) (PEO) solutions under large amplitude oscillatory shear flow. The scaling relations superpose dimensionless nonlinear viscoelastic functions, such as the normalized amplitudes of elastic and viscous stresses and normalized Fourier intensities, measured at different strain amplitudes and frequencies on a single curve irrespective of the molecular weight and the concentration of the polymer solutions. The scaling relations reveal that the nonlinear viscoelastic functions are functions of dimensionless variable ζ≡γo cos δ(ω), where δ is the phase lag of linear viscoelasticity. The validity of our superposition was checked for PEO aqueous solutions under the conditions that concentration:3<c/ce<7; molecular weight: 400 kg/mol<M<1000kg/mol; τmω<10. We suggest some material parameters, which are expected to indicate chain architecture as well as to measure the strength of nonlinearity because the parameters are independent of the test conditions and compositions of the polymer solutions.
A Crucial Role for RACK1 in the Regulation of Glucose-Stimulated IRE1α Activation in Pancreatic β Cells
Authors: Qiu Yifu , Mao Ting , Zhang Yongliang , Shao Mengle , You Jia , Ding Qiurong , Chen Yan , Wu Dongmei , Xie Dong , Lin Xu , Gao Xiang , Kaufman Randal J. , Li Wenjun , Liu Yong
Published: January 2010

RACK1 dictates the response of the intracellular stress sensor IRE1α to different extracellular stimuli.
NK Cells Attack Pancreatic Beta Cells
Authors: Adler Elizabeth M.
Published: January 2010

The natural killer cell NKp46 receptor recognizes a ligand on pancreatic beta cells and may provide a therapeutic target against development of type 1 diabetes.
Garnering Information on Granulomas
Authors: Hurtley Stella
Published: January 2010

Epithelial cells play a role in tubercular granuloma formation and mycobacterial virulence.
Miniature Transport Engineers
Authors: Ray L. Bryan
Published: January 2010

Human municipal transportation engineers might learn design strategies from the lowly slime mold.
Science Signaling
Podcast: 26 January 2010
Authors: Lafon Monique , VanHook Annalisa M.
Published: January 2010

A single amino acid substitution in a viral protein is sufficient to attenuate rabies virulence.
High Diversity of Extended-Spectrum β-Lactamases in
Escherichia coli
Isolates from Italian Broiler Flocks
Authors: Bortolaia Valeria , Guardabassi Luca , Trevisani Marcello , Bisgaard Magne , Venturi Luciano , Bojesen Anders Miki
Published: January 2010

We characterized 67
Escherichia coli
isolates with reduced susceptibility to cefotaxime or ceftiofur obtained from healthy broilers housed in five Italian farms. The
bla
CTX-M-1
,
bla
CTX-M-32
and
bla
SHV-12
β-lactamase genes were identified on IncI1, IncN, or IncFIB plasmids. Considerable genetic diversity was detected among the extended-spectrum β-lactamase (ESBL)-producing isolates, and we identified indistinguishable strains in unrelated farms and indistinguishable plasmids in genetically unrelated strains. The detection of highly mobile plasmids suggests a potential animal reservoir for β-lactamase genes.
Roles of Calcineurin and Crz1 in Antifungal Susceptibility and Virulence of
Candida glabrata
Authors: Miyazaki Taiga , Yamauchi Shunsuke , Inamine Tatsuo , Nagayoshi Yosuke , Saijo Tomomi , Izumikawa Koichi , Seki Masafumi , Kakeya Hiroshi , Yamamoto Yoshihiro , Yanagihara Katsunori , Miyazaki Yoshitsugu , Kohno Shigeru
Published: January 2010

A
Candida glabrata
calcineurin mutant exhibited increased susceptibility to both azole antifungal and cell wall-damaging agents and was also attenuated in virulence. Although a mutant lacking the downstream transcription factor Crz1 displayed a cell wall-associated phenotype intermediate to that of the calcineurin mutant and was modestly attenuated in virulence, it did not show increased azole susceptibility. These results suggest that calcineurin regulates both Crz1-dependent and -independent pathways depending on the type of stress.
Activity of the Investigational Fluoroquinolone Finafloxacin against Ciprofloxacin-Sensitive and -Resistant
Acinetobacter baumannii
Isolates
Authors: Higgins Paul G. , Stubbings Will , Wisplinghoff Hilmar , Seifert Harald
Published: January 2010

This study compared the activity of finafloxacin, a novel fluoroquinolone which shows enhanced activity under acidic pH, and that of ciprofloxacin against
Acinetobacter baumannii
under standard conditions (pH 7.2) and at a pH of 5.8. Overall, finafloxacin demonstrated superior activity to ciprofloxacin under acidic conditions. Furthermore, finafloxacin showed comparable activity to ciprofloxacin at pH 7.2. Hence, finafloxacin could be a promising new antimicrobial agent for the treatment of
A. baumannii
infections at acidic body compartments.
Broad-Spectrum Activity against Bacterial Mastitis Pathogens and Activation of Mammary Epithelial Cells Support a Protective Role of Neutrophil Cathelicidins in Bovine Mastitis
Authors: Tomasinsig Linda , De Conti Gennyfer , Skerlavaj Barbara , Piccinini Renata , Mazzilli Maria , D'Este Francesca , Tossi Alessandro , Zanetti Margherita
Published: January 2010

Cathelicidins are peptide components of the innate immune system of mammals. Apart from exerting a direct antibiotic activity, they can also trigger specific defense responses in the host. Their roles in various pathophysiological conditions have been studied, but there is a lack of published information on their expression and activities in the context of mastitis. The aims of this study were to investigate the expression of the bovine cathelicidins BMAP-27, BMAP-28, Bac5, and indolicidin in healthy and infected mammary tissue and in lipopolysaccharide (LPS)-treated cells, to determine their activities against bacteria isolated from bovine mastitis, and to examine their potentials to trigger defense responses in bovine mammary cells. The genes were found to be upregulated in LPS-stimulated neutrophils, but not in infected quarters or epithelial cells. All peptides showed a variably broad spectrum of activity against 28 bacterial isolates from bovine mastitis (MIC values, 0.5 to 32 μM), some of which were antibiotic resistant. The activity of each peptide was significantly enhanced when it was pairwise tested with the other peptides, reaching the synergy threshold when indolicidin was present. The bactericidal activity was sensitive to milk components; BMAP-27 and -28 were highly effective in mastitic bovine milk and inhibited in milk from healthy cows. Both peptides were also active in whey and in blood serum and triggered the expression of tumor necrosis factor alpha (TNF-α) in bovine mammary epithelial cells. Our results indicate multiple roles for the bovine cathelicidins in mastitis, with complementary and mutually enhanced antimicrobial activities against causative pathogens and the capacity to activate host cells.
Pseudomonas aeruginosa
Cytotoxin ExoU Is Injected into Phagocytic Cells during Acute Pneumonia
Authors: Diaz Maureen H. , Hauser Alan R.
Published: January 2010

ExoU, a cytotoxin translocated into host cells via the type III secretion system of
Pseudomonas aeruginosa
, is associated with increased mortality and disease severity. We previously showed that impairment of recruited phagocytic cells allowed survival of ExoU-secreting
P. aeruginosa
in the lung. Here we analyzed types of cells injected with ExoU
in vivo
using translational fusions of ExoU with a β-lactamase reporter (ExoU-Bla). Cells injected with ExoU-Bla were detectable
in vitro
but not
in vivo
, presumably due to the rapid cytotoxicity induced by the toxin. Therefore, we used a noncytotoxic ExoU variant, designated ExoU(S142A)-Bla, to analyze injection
in vivo
. We determined that phagocytic cells in the lung were frequently injected with ExoU(S142A). Early during infection, resident macrophages constituted the majority of cells into which ExoU was injected, but neutrophils and monocytes became the predominant types of cells into which ExoU was injected upon recruitment into the lung. We observed a modest preference for injection into neutrophils over injection into other cell types, but in general the repertoire of injected immune cells reflected the relative abundance of these cells in the lung. Our results indicate that phagocytic cells in the lung are injected with ExoU and support the hypothesis that ExoU-mediated impairment of phagocytes has a role in the pathogenesis of pneumonia caused by
P. aeruginosa
.