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We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness. [ABSTRACT FROM AUTHOR]

Chondritic components such as chondrules and matrix are the key time capsules that can help us understand the evolution and dynamics of the protoplanetary disk from which the Solar System originated. Knowledge of where and how these components formed and to what extent they were transported in the gaseous disk provides major constraints to astrophysical models that investigate planet formation. Here, we explore whether chondrules and matrix are genetically related to each other and formed from single reservoirs per chondrite group or if every chondrite represents a unique proportion of components transported from a small number of formation reservoirs in the disk. These 'static versus dynamic disk' interpretations of cosmochemical data have profound implications for the accretion history of the planets in the Solar System. To fully understand the relationship between chondrules and matrix and their potential "complementarity", we dive into the petrological nature and origin of matrix, the chemical and isotopic compositions of chondrules and matrix and evaluate these data considering the effect of secondary alteration observed in chondrites and the potential complexity of chondrule formation. Even though we, the authors, have used different datasets and arrived at differing interpretations of chondrule-matrix relationships in the past, this review provides clarity on the existing data and has given us new directions towards future research that can resolve the complementarity debate. [ABSTRACT FROM AUTHOR]

Abundances, apparent sizes, and individual chemical compositions of chondrules, refractory inclusions, other objects, and surrounding matrix have been determined for Semarkona (LL3.00) and Renazzo (CR2) using consistent methods and criteria on X‐ray element intensity maps. These represent the non‐carbonaceous (NC, Semarkona) and carbonaceous chondrite (CC, Renazzo) superclans of chondrite types. We compare object and matrix abundances with similar data for CM, CO, K, and CV chondrites. We assess, pixel‐by‐pixel, the major element abundance in each object and in the entire matrix. We determine the abundance of "metallic chondrules" in LL chondrites. Chondrules with high Mg/Si and low Fe/Si and matrix carrying opposing ratios complement each other to make whole rocks with near‐solar major element ratios in Renazzo. Similar Mg/Si and Fe/Si chondrule–matrix relationships are seen in Semarkona, which is within 11% of solar Mg/Si but significantly Fe‐depleted. These results provide a robust constraint in support of single‐reservoir models for chondrule formation and accretion, ruling out whole classes of astrophysical models and constraining processes of chondrite component formation and accretion into chondrite parent bodies. [ABSTRACT FROM AUTHOR]

The 2021 Leonard Medal was awarded to Dr. Katharina Lodders, in person, at the 2021 Annual Meeting of the Meteoritical Society in Chicago, IL, USA. This is the citation presented for Dr. Lodders. [ABSTRACT FROM AUTHOR]

We studied a thin section of Lewis Cliff (LEW) 87223, an unusual EL3‐related, enstatite chondrite (EC) that has primary and secondary features not observed in other ECs. We studied its metal‐rich nodules, possible shock features, and chondrules, eight of which are Al‐rich chondrules (ARCs). LEW 87223 has petrologic and compositional features similar to EL3s. Enstatite is the dominant mineral; chondrule boundaries are well defined; Si content of metal (0.5–0.6 wt%) is consistent with typical EL3; it has Cr‐bearing troilite, oldhamite, and alabandite; and its O‐isotopic composition is similar to other ECs. However, metal abundance in LEW 87223 (~13 vol%) is slightly higher than in other EL3s and its metal nodules are texturally and mineralogically different from other ECs. Both high and low Ni metals are present, and its alabandite has higher Fe (27.8 wt% Fe) than in other EL3s. Silicates appear darkened in plane polarized light, largely due to reduction of Fe from silicate. A remarkable feature of LEW 87223 is the high abundance of ARCs, which contain Ca‐rich plagioclase and varying amounts of Na‐rich plagioclase along chondrule edges and as veins. This suggests Na metasomatism and the possibility of hydrothermal fluids, potentially related to an impact event. LEW 87223 expands the range of known EC material. It shows that ECs are more diverse and record a wider range of parent body processes than previously known. LEW 87223 is an anomalous EL3, potentially the first member of a new EC group should similar samples be discovered. [ABSTRACT FROM AUTHOR]

Within this work, we present the first true three‐dimensional (3D) analysis of chondrule size. Knowledge about the physical properties of chondrules is important for validating astrophysical theories concerning chondrule formation and their aggregation into the chondritic meteorites (known as chondrites) that contain them. The classification of chondrites into chemical groups also relies on chondrule properties, including their dimensions. Within this work, we quantify the diameters of chondrules in five ordinary chondrites (OCs; comprised of the H, L, and LL chondrites) and one low‐iron enstatite (EL) chondrite. To extract the chondrule size data, we use x‐ray computed microtomography to image small (~1–2 cm3) chondrite samples followed by manual digital segmentation to isolate chondrules within the volumes or subvolumes. Our data yield true 3D results without stereographic corrections necessary for two‐dimensional (2D) or petrographic thin section‐based determinations of chondrule sizes. Our results are completely novel, but are consistent with previous surface analysis (2D) data for OCs. Within our OC chondrule diameter data, we find the trend of mean chondrule diameters increasing in the order H < L < LL. We also present the first detailed EL chondrite chondrule size‐frequency distribution. Finally, we examine the shapes and collective orientations of the chondrules within the chondrites and show that chondrite petrofabrics can be explored with our methodology. Chondrule shape‐preferred orientations are identical to the orientations of the metal and sulfide grains in the chondrites and this is likely due to impact‐related compaction. Highlights: We present a first true three‐dimensional analysis of chondrule size.Our ordinary chondrite chondrule diameter data demonstrate the trend of mean chondrule diameters increasing in the order H chondrites < L chondrites < LL chondrites.We also present the first detailed low‐iron enstatite chondrite chondrule size‐frequency distribution.We examine the shapes and collective orientations of the chondrules and show that chondrite petrofabrics can be explored with our methodology. [ABSTRACT FROM AUTHOR]

NWA 8785 is a remarkable, recently identified, unequilibrated enstatite chondrite. It was classified as an EL3 but contains highly unusual characteristics not observed in any other EL3, including a high abundance of FeO‐rich matrix and metal‐rich nodules that are texturally and mineralogically different from those in other EL3s. We characterized the mineral assemblages and compositions of metal‐rich nodules in a thin section of NWA 8785 and compared them to nodules in other EL3s to evaluate models for formation of metal‐rich nodules in EL3s. Of a total of 40 metal‐rich nodules, 10 were selected for detailed study. These metal‐rich nodules vary in their physical structure, texture, and mineral assemblages. Some contain the rare Al‐poor, alkali‐rich silicate mineral roedderite, a first discovery in an EL3, as well as the Cl‐bearing sulfide djerfisherite. The diversity of metal‐rich nodules in NWA 8785 suggests each nodule formed independently and supports their origin by primary processes prior to accretion. The high abundance of FeO‐rich matrix and the unique qualities of its metal‐rich nodules call into question classification of NWA 8785 as an EL3, but the Si content in its kamacite and Cr and Ti content in its troilite, and the presence of alabandite, support its classification as an EL3; thus, it is an EL3‐anomalous. Although alternative hypotheses exist, the presence of roedderite, as well as a magnetite‐rich matrix and sodalite, may provide the first evidence of extensive metasomatic alteration on the EL3 parent body. [ABSTRACT FROM AUTHOR]

Opaque assemblages (OAs) are small (submillimeter) objects composed primarily of metals, sulfides, and oxides that exist in nearly all chondritic meteorite groups as discrete objects in the matrix or associated with chondrules. The size, morphology, and petrology of OAs vary greatly between different chondrite groups, with petrologic grade within a single group, and by their apparent textural setting. Two hypotheses may explain the formation of matrix OAs: (1) they were separated from chondrules via surface tension during heating events, or (2) they formed as free‐floating objects in the solar nebula; however, this is the first comprehensive study of the petrology of OAs in ordinary chondrites (OCs) as a group, which seeks to determine if one hypothesis is sufficient to explain all such objects. Here, we use a newly developed machine learning algorithm to show that all OAs from the least equilibrated OC, Semarkona (LL 3.01), are composed of kamacite, taenite, troilite, pentlandite, magnetite, and other minor phases. These OAs form two distinct groups based on their modal mineralogy: one group in and associated with chondrules, and the other group free‐floating in the matrix. Chondrule OAs exhibit a bimodal distribution between sulfide‐ and metal‐rich endmembers in agreement with previous findings. Matrix OAs cluster at roughly equal abundances of sulfides and metals and universally exhibit magnetite rims. The two populations of chondrule OAs cannot be combined to form the modal mineralogies observed in matrix OAs and some matrix OAs exhibit mineralogical layering consistent with fractional condensation. Both observations support the hypothesis that matrix OAs were not formed by expulsion from chondrules and instead formed as free‐floating objects in the solar nebula; however, chondrule OAs must have formed with their host chondrules during heating events. [ABSTRACT FROM AUTHOR]

The size distribution, abundance, and physical and chemical characteristics of chondritic inclusions are key features that define the chondrite groups. We present statistics on the size and abundance of the macroscopic components (inclusions) in the Murchison (CM2) and Allende (CV3) chondrites and measure their general chemical trends using established X‐ray mapping techniques. This study provides a fine‐scale assessment of the two meteorites and a semiquantitative evaluation of the relative abundances of elements and their distribution among meteorite components. Murchison contains 72% matrix and 28% inclusions; Allende contains 57% and 43%, respectively. A broad range of inclusion sizes and relative abundances has been reported for these meteorites, which demonstrates the necessity for a more standardized approach to measuring these characteristics. Nonetheless, the characteristic mean sizes of inclusions in Allende are consistently larger than those in Murchison. We draw two significant conclusions (1) these two meteorites sampled distinct populations of chondrules and refractory inclusions, and (2) complementary Mg/Si ratios between chondrules and matrix are observed in both Murchison and Allende. Both support the idea that chondrules and matrix within each chondrite group originated in single reservoirs of precursors with approximately solar Mg/Si ratios, providing a constraint on astrophysical models of the origin of chondrite parent bodies. [ABSTRACT FROM AUTHOR]

Dynamic models of the protoplanetary disk indicate there should be large-scale material transport in and out of the inner Solar System, but direct evidence for such transport is scarce. Here we show that the ε50Ti-ε54Cr-Δ17O systematics of large individual chondrules, which typically formed 2 to 3 My after the formation of the first solids in the Solar System, indicate certain meteorites (CV and CK chondrites) that formed in the outer Solar System accreted an assortment of both inner and outer Solar System materials, as well as material previously unidentified through the analysis of bulk meteorites. Mixing with primordial refractory components reveals a “missing reservoir” that bridges the gap between inner and outer Solar System materials. We also observe chondrules with positive ε50Ti and ε54Cr plot with a constant offset below the primitive chondrule mineral line (PCM), indicating that they are on the slope ∼1.0 in the oxygen three-isotope diagram. In contrast, chondrules with negative ε50Ti and ε54Cr increasingly deviate above from PCM line with increasing δ18O, suggesting that they are on a mixing trend with an ordinary chondrite-like isotope reservoir. Furthermore, the Δ17O-Mg# systematics of these chondrules indicate they formed in environments characterized by distinct abundances of dust and H2O ice. We posit that large-scale outward transport of nominally inner Solar System materials most likely occurred along the midplane associated with a viscously evolving disk and that CV and CK chondrules formed in local regions of enhanced gas pressure and dust density created by the formation of Jupiter. [ABSTRACT FROM AUTHOR]

This document contains suggestions for best practices by authors who refer to meteorites in publications. It can also be taken as a guide for publishers in establishing guidelines for authors. The following best practices are recommended in addition to acknowledging the loaning institution or loaning individual (unless required otherwise). The main motivations are to: help ensure that research on meteorites is reproducible, prevent confusion in the literature, and enhance tracking of specimens and related data. [ABSTRACT FROM AUTHOR]

X‐ray microcomputed tomography (μCT) is a useful means of characterizing cosmochemical samples such as meteorites or robotically returned samples. However, there are occasional concerns that the use of μCT may be detrimental to the organic components of a chondrite. Small organic compounds such as amino acids comprise up to ~10% of the total solvent extractable carbon in CM carbonaceous chondrites. We irradiated three samples of the Murchison CM carbonaceous chondrite under conditions akin to and harsher than those typically used during typical benchtop X‐ray μCT imaging experiments to determine if detectable changes in the amino acid abundance and distribution relative to a nonexposed Murchison control sample occurred. After subjecting three meteorite samples to ionizing radiation dosages between ~300 Gray (Gy) and 3 kGy with bremstrahlung X‐rays, we analyzed the amino acid content of each sample. Within sampling and analytical errors, we cannot discern differences in the amino acid abundances and amino acid enantiomeric ratios when comparing the control samples (nonexposed Murchison) and the irradiated samples. We conclude that a polychromatic X‐ray μCT experiment does not alter the abundances of amino acids to a degree greater than how well those abundances are measured with our techniques and therefore any damage to amino acids is minimal. [ABSTRACT FROM AUTHOR]

The radiation record of extraterrestrial rocks provides important insights into their thermal and radiation history. For meteorites this relates to their orbits, thermal history, terrestrial age, preatmospheric size and shape, and possibly cosmic ray exposure age. For meteorites from the Moon and Mars, the radiation record allows insights into transit times. For Martian surface samples, the radiation record enables estimates of their sedimentary age. Despite this, there is a growing tendency to artificially expose these samples to large radiation doses by the use of X‐ray computed tomography (CT) imaging, often as part of their initial examination. In order to understand the effect of synchrotron microCT on meteorites, we placed samples of the Bruderheim L6 chondrite in the CT imaging port of the Advanced Photon Source at the Argonne National Laboratory, Argonne, Illinois. Monoenergetic X‐ray beams of 25 and 46 keV and a high flux broad spectrum beam were used. The synchrotron CT procedure exposed the samples to radiation doses significantly higher than the natural doses observed for meteorites (1670 to ~10,000 Gyr, compared to ~1000 Gyr for natural samples). It is clear that CT imaging, whether using a laboratory system as in our previous report or using the synchrotron source, makes measurement of the natural radiation record of the samples impossible. Samples should not be placed in a CT scanner without due consideration of the loss of unique information for these valuable extraterrestrial samples. [ABSTRACT FROM AUTHOR]

Abstract: Meteoritical and astrophysical models of planet formation make contradictory predictions for dust concentration factors in chondrule‐forming regions of the solar nebula. Meteoritical and cosmochemical models strongly suggest that chondrules, a key component of the meteoritical record, formed in regions with solids‐to‐gas mass ratios orders above the solar nebula average. However, models of dust grain dynamics in protoplanetary disks struggle to surpass concentration factors of a few except during very short‐lived stages in a dust grain's life. Worse, those models do not predict significant concentration factors for dust grains the size of chondrule precursors. We briefly develop the difficulty in concentrating dust particles in the context of nebular chondrule formation and show that the disagreement is sufficiently stark that cosmochemists should explore ideas that might revise the concentration factor requirements downward. [ABSTRACT FROM AUTHOR]

Miller Range 07273 is a chondritic melt breccia that contains clasts of equilibrated ordinary chondrite set in a fine-grained (<5 μm), largely crystalline, igneous matrix. Data indicate that MIL was derived from the H chondrite parent asteroid, although it has an oxygen isotope composition that approaches but falls outside of the established H group. MIL also is distinctive in having low porosity, cone-like shapes for coarse metal grains, unusual internal textures and compositions for coarse metal, a matrix composed chiefly of clinoenstatite and omphacitic pigeonite, and troilite veining most common in coarse olivine and orthopyroxene. These features can be explained by a model involving impact into a porous target that produced brief but intense heating at high pressure, a sudden pressure drop, and a slower drop in temperature. Olivine and orthopyroxene in chondrule clasts were the least melted and the most deformed, whereas matrix and troilite melted completely and crystallized to nearly strain-free minerals. Coarse metal was largely but incompletely liquefied, and matrix silicates formed by the breakdown during melting of albitic feldspar and some olivine to form pyroxene at high pressure (>3 GPa, possibly to ~15-19 GPa) and temperature (>1350 °C, possibly to ≥2000 °C). The higher pressures and temperatures would have involved back-reaction of high-pressure polymorphs to pyroxene and olivine upon cooling. Silicates outside of melt matrix have compositions that were relatively unchanged owing to brief heating duration. [ABSTRACT FROM AUTHOR]

X-ray computed tomography has become a popular means for examining the interiors of meteorites and has been advocated for routine curation and for the examination of samples returned by missions. Here, we report the results of a blind test that indicate that CT imaging deposits a considerable radiation dose in a meteorite and seriously compromises its natural radiation record. Ten vials of the Bruderheim L6 chondrite were placed in CT imager and exposed to radiation levels typical for meteorite studies. Half were retained as controls. Their thermoluminescence (TL) properties were then measured in a blind test. Five of the samples had TL data unaltered from their original (~10 cps) while five had very strong signals (~20,000 cps). It was therefore very clear which samples had been in the CT scanner. For comparison, the natural TL signal from Antarctic meteorites is ~5000-50,000 cps. Using the methods developed for Antarctic meteorites, the apparent dose absorbed by the five test samples was calculated to be 83 ± 5 krad, comparable with the highest doses observed in Antarctic meteorites and freshly fallen meteorites. While these results do not preclude the use of CT scanners when scientifically justified, it should be remembered that the record of radiation exposure to ionizing radiations for the sample will be destroyed and that TL, or the related optically stimulated luminescence, are the primary modern techniques for radiation dosimetry. This is particularly important with irreplaceable samples, such as meteorite main masses, returned samples, and samples destined for archive. [ABSTRACT FROM AUTHOR]

We report on a suite of microchondrules from three unequilibrated ordinary chondrites ( UOCs). Microchondrules, a subset of chondrules that are ubiquitous components of UOCs, commonly occur in fine-grained chondrule rims, although may also occur within matrix. Microchondrules have a variety of textures: cryptocrystalline, microporphyritic, radial, glassy. In some cases, their textures, and in many cases, their compositions, are similar to their larger host chondrules. Bulk compositions for both chondrule populations frequently overlap. The primary material that composes many of the microchondrules has compositions that are pyroxene-normative and is similar to low-Ca-pyroxene phenocrysts from host chondrules; primary material rarely resembles olivine or plagioclase. Some microchondrules are composed of FeO-rich material that has compositions similar to the bulk submicron fine-grained rim material. These microchondrules, however, are not a common compositional type and probably represent secondary FeO-enrichment. Microchondrules may also be porous, suggestive of degasing to form vesicles. Our work shows that the occurrence of microchondrules in chondrule rims is an important constraint that needs to be considered when evaluating chondrule-forming mechanisms. We propose that microchondrules represent melted portions of the chondrule surfaces and/or the melt products of coagulated dust in the immediate vicinity of the larger chondrules. We suggest that, through recycling events, the outer surfaces of chondrules were heated enough to allow microchondrules to bud off as protuberances and become entrained in the surrounding dusty environment as chondrules were accreting fine-grained rims. Microchondrules are thus byproducts of cyclic processing of chondrules in localized environments. Their occurrence in fine-grained rims represents a snapshot of the chondrule-forming environment. We evaluate mechanisms for microchondrule formation and hypothesize a potential link between the emergence of type II chondrules in the early solar system and the microchondrule-bearing fine-grained rims surrounding type I chondrules. [ABSTRACT FROM AUTHOR]

8-year-olds', 10-year-olds', and adults' concepts of mental activities involved in acts of knowing were examined in an attempt to gain insight into developmental changes in underlying theories of mind. Subjects rated the similarity of how the mind is used in a variety of common activities, each of which primarily involved either memory, comprehension, attention, or inference. Analyses of conceptual structure revealed 2 developmental changes. Between 8 and 10 years of age, children came to see the most important relation among mental activities to be the degree to which they involved memory. Between 10 years of age and adulthood, Comprehension and Attention first appeared as distinct, coherent concepts. At all ages, Memory and Inference were seen as distinct types of mental activities. These findings suggested that a sophisticated understanding of the representational nature of the mind might not be acquired before the latter part of middle childhood and might be mediated by an understanding of the central role played by memory. [ABSTRACT FROM AUTHOR]

Serving in a major museum of natural history has provided me with extraordinary opportunities to educate the public through public programs, exhibitions like our Ross Hall of Meteorites, and the curation of a Hayden Planetarium space show. Thank you, President Ghiorso, Dr. Weisberg, and members of the Mineralogical Society of America. [Extracted from the article]

A section containing the Cretaceous/Paleogene (= Cretaceous/Tertiary) boundary in Monmouth County, New Jersey, preserves a record of ammonites extending from the end of the Cretaceous into possibly the beginning of the Danian. The section includes the upper part of the Tinton Formation and lower part of the Hornerstown Formation. The top of the Tinton Formation is represented by a richly fossiliferous unit (the Pinna Layer) that contains many bivalves in life position as well as ammonite jaws preserved inside body chambers. Ammonites include Pachydiscus (Neodesmoceras) mokotibensis, Sphenodiscus lobatus, Eubaculites carinatus, E. latecarinatus, Discoscaphites iris, D. sphaeroidalis, D. minardi, and D. jerseyensis. The Pinna Layer probably represents a relatively short interval of time lasting tens to hundreds of years; it is conformably overlain by the Burrowed Unit, which contains a single fragment of Discoscaphites sp. and several fragments of E. latecarinatus, as well as several isolated specimens of ammonite jaws including two of Eubaculites. Examination of the mode of preservation of the ammonites and jaws suggests that they were fossilized during deposition of the Burrowed Unit and were not reworked from older deposits. Based on the ammonites and dinoflagellates in the Pinna Layer and the Burrowed Unit, these strata traditionally would be assigned to the uppermost Maastrichtian, corresponding to calcareous nannofossil Subzone CC26b. However, a weak iridium anomaly (500-600 pg/g) is present at the base of the Pinna Layer, which presumably represents the record of the bolide impact. Correlation with the iridium layer at the Global Stratotype Section and Point at El Kef, Tunisia, would, therefore, imply that these assemblages are actually Danian, provided that the iridium anomaly is in place and the ammonites and dinoflagellates are not reworked. If the iridium anomaly is in place, or even if it has migrated downward from the top of the Pinna Layer, the ammonites would have survived the impact at this site for a brief interval of time lasting from a few days to hundreds of years. [ABSTRACT FROM AUTHOR]

- Here, we show that several geochemical indicators point to number densities during chondrule formation that were far higher than can be accounted for by known nebula processes. The number densities implied by compound chondrules and nonspherical chondrules are shown to be significantly higher than estimated in previous studies. At the implied chondrule number densities, if a chondrule formation region survived a formation event it would have been gravitationally bound and would have collapsed quite rapidly to form an asteroidal-sized body. The diversity of chondrule compositions and textures in a chondrite group could have formed in a single event in subvolumes of a formation region that were chemically isolated from one another because of slow diffusion in the gas. Within these subvolumes, equilibration between chondrules with different compositions would have been fairly rapid, although small isotopic mass fractionations in elements like Fe, Si, Mg, and O may persist. This could explain the existence of the small isotopic mass fractionations in these elements that have been observed in chondrules. However, the evidence for recycling of chondrules requires that there was more than one chondrule formation event prior to formation of a parent asteroid. Finally, we argue that OC and CO chondrule Mg-Al systematics are both consistent with single ages or narrow ranges of ages, and that the CO, and possibly the OC, ages date parent body alteration. This would resolve the conundrum of needing to preserve in a turbulent nebula physically and chemically distinct CO and OC chondrule populations for 1-2 Myr. [ABSTRACT FROM AUTHOR]

- The Stardust mission captured comet Wild 2 particles in aerogel at 6.1 km s−1. We performed high-resolution three-dimensional imaging and X-ray fluorescence mapping of whole cometary tracks in aerogel. We present the results of a survey of track structures using laser scanning confocal microscopy, including measurements of track volumes, entry hole size, and cross-sectional profiles. We compare various methods for measuring track parameters. We demonstrate a methodology for discerning hypervelocity particle ablation rates using synchrotron-based X-ray fluorescence, combined with mass and volume estimates of original impactors derived from measured track properties. Finally, we present a rough framework for reconstruction of original impactor size, and volume of volatilized material, using our measured parameters. The bulk of this work is in direct support of nondestructive analysis and identification of cometary grains in whole tracks, and its eventual application to the reconstruction of the size, shape, porosity, and chemical composition of whole Stardust impactors. [ABSTRACT FROM AUTHOR]

- Low-iron, manganese-enriched (LIME) olivine grains are found in cometary samples returned by the Stardust mission from comet 81P/Wild 2. Similar grains are found in primitive meteoritic clasts and unequilibrated meteorite matrix. LIME olivine is thermodynamically stable in a vapor of solar composition at high temperature at total pressures of a millibar to a microbar, but enrichment of solar composition vapor in a dust of chondritic composition causes the FeO/MnO ratio of olivine to increase. The compositions of LIME olivines in primitive materials indicate oxygen fugacities close to those of a very reducing vapor of solar composition. The compositional zoning of LIME olivines in amoeboid olivine aggregates is consistent with equilibration with nebular vapor in the stability field of olivine, without re-equilibration at lower temperatures. A similar history is likely for LIME olivines found in comet samples and in interplanetary dust particles. LIME olivine is not likely to persist in nebular conditions in which silicate liquids are stable. [ABSTRACT FROM AUTHOR]

- Northwest Africa 5492 is a new metal-rich chondrite breccia that may represent a new oxygen reservoir and new chondrite parent body. It has some textural similarities to CB and CH chondrites, but silicates are more reduced, sulfides are more common and not associated with metal, and metal compositions differ from CB and CH chondrites. Oxygen isotope ratios indicate that Northwest Africa (NWA) 5492 components (chondrules and lithic fragments) formed in at least two different oxygen reservoirs. The more common, and presumably host, component plots in a region above the terrestrial fractionation line, below ordinary chondrite compositions, and just above enstatite chondrites in 3-oxygen space. The only other chondritic materials that plot in this region are chondrules from the Grosvenor Mountains (GRO) 95551 ungrouped metal-rich chondrite. The other rare component plots near the CR, CB, and CH chondrites. Based on petrologic characteristics and oxygen isotopic compositions, NWA 5492 appears to be related to the ungrouped metal-rich GRO 95551 chondrite. [ABSTRACT FROM AUTHOR]

There are many situations where strengthening might be required for a nonprismatic reinforced concrete section (i.e., a beam or slab where the depth of the section varies along its length). For example, many bridges in the United Kingdom have inadequate capacity to carry accidental vehicle loads on verges. These shallow depth verges are often cantilevered from the much deeper main bridge deck. The cantilever might be strengthened by applying fiber-reinforced polymer (FRP) composites to the top surface of the cantilever, extending transversely onto the bridge deck. However, a problem may exist with such a situation due to the potential for a dramatic reduction in the degree of strengthening which is achievable. This is due to the effects of cracking, and longitudinal shear stresses. Tests presented in this paper demonstrate that in regions where little or no cracking occurs, local or global debonding of the external FRP may result. Therefore, the strength of some nonprismatic beams, as predicted by current design guidelines, is often shown to be overly conservative and, in one case significantly unconservative. However, more importantly, the predicted failure modes and FRP strains often do not correspond to those observed. Advice on the best approach for analyzing these beams is given. [ABSTRACT FROM AUTHOR]

Yield-line analysis is conventionally undertaken using collapse mechanisms that comprise rigid regions that intersect at yield lines, which behave in uniaxial bending only. It is well established that the flexural capacity of reinforced concrete (RC) slabs subjected to biaxial bending can be less than that when they are subjected to uniaxial bending. Concerns must therefore result regarding whether the inability of conventional yield-line mechanisms to model regions of biaxial bending could lead to significantly unsafe (upper bound) results. A simple method is presented to enable zones of biaxial bending to be taken into account in yield-line analysis. In this method 'wide' yield-line mechanisms are used which comprise rigid regions that are connected by 'yield lines' of finite and constant width and with uniform finite curvature over their area. Two examples of the method are presented. From the results, it appears unlikely that the reduced flexural capacity of RC slabs in biaxial bending will have a highly significant effect on their overall capacity in many cases. Perhaps of greater significance is the variation in ductility observed for different bending cases. [ABSTRACT FROM AUTHOR]

Tetrahedrite fahlores from the Galena Mine of the Coeur d'Alene Mining District (Wallace, Idaho) have been found to be enriched in Ag by the Ag-Cu exchange reaction: 1/10 Cu10(Zn,Fe)2Sb4S13 / Cu-fahlore + AgSbS2 / in galena + PbS / galena = CuPbSbS3 / bournonite + 1/10Ag10(Zn,Fe)2Sb4S13 / Ag-fahlore which occurred during cooling following fahlore mineralization. This solid-state reaction produced a distinct population of high-Ag fahlores found in galena-rich samples, quantitatively removed Ag (in an AgSbS2 component) from galena, and accounts for all of the bournonite mineralization. This reaction has produced the most argentian fahlore yet found [molar Ag/(Ag + Cu) = 0.443] in the district, and forms a secondary overprint on any primary fahlore zoning that may have existed. The results obtained here indicate that the galena and fahlore-siderite stages of mineralization were virtually synchronous, as this reaction has produced the same result despite the opposite relative age relationships of these mineralization stages exhibited in two of the mines studied. Multiple lines of evidence suggest a temperature between 320 and 350 °C for this "stage." Based on the Ag/(Ag + Cu) of fahlores and Fe-Zn partitioning between fahlore and sphalerite, we estimate that fahlore compositions were frozen in by about 235 °C, roughly 40 °C above corresponding temperatures obtained for the Gold Hunter vein of the Lucky Friday Mine. This result and the absence of readily detectable diaphorite (∼Pb2Ag3Sb3S8) in the Galena Mine sample containing the highest Ag fahlore indicate a faster cooling rate for the terrane in the vicinity of the Galena Mine. [ABSTRACT FROM AUTHOR]

The article presents benefits of advanced composite fibre-reinforced polymer (FRP) materials in concrete structures. The use of FRPs for strengthening concrete structures is a relatively new technique. The method involves the use of carbon, aramid or glass fibres combined with epoxy, vinyl ester, phenolic or isophthalic resin to form an FRP composite. The composite may be applied to concrete structures in order to strengthen them and increase their load-carrying capacity. Since 1990s, the number of strengthening applications has increased significantly as clients, contractors and designers began to appreciate the benefits of this cost-effective technique.