bluuebunny/crossref_metadata_2025 huggingface dataset:
The condensation with partial isolation (CWPI) model of condensation in the solar nebula
Authors: PETAEV MICHAIL I. , WOOD JOHN A.
Published: February 2010

Abstract— We have developed a nebular condensation model and a computational routine that potentially can account for the unequilibrated mineral assemblages in chondritic meteorites. The model assumes that as condensation proceeds, a specified fraction (called the isolation degree, ξ) of the existing condensate is steadily withdrawn from reactive contact with the residual gas, presumably as a result of the growth and aggregation of condensed mineral grains. The isolated condensates may remain in the condensing system as coarse inert objects; whereas, the mineral grains that are still in reactive contact with residual nebular gases are in the form of fine dust.

This paper describes the condensation with partial isolation (CWPI) model of condensation and uses it to study condensation in a nebula of solar composition at a total pressure of 10−5 bar. The systematic isolation of condensates from residual nebular gases has profound effects on the condensation sequence. At ξ values <0.2%, the condensation sequence is essentially independent of the isolation degree and identical to the classic condensation sequence. At ξ values >2.5%, the condensation sequence is also independent of the isolation degree and closely resembles the “inhomogeneous accretion model” or “chemical disequilibrium model” of condensation. In the intermediate range of ξ values, the character of the condensation sequence is very sensitive to the degree of chemical fractionation caused by condensate isolation.

The mineralogy of chondritic meteorites is not consistent with condensation sequences having ξ > 2.5; this is an upper limit on the ξ values that is characteristic of condensation in the solar nebula. The mineralogy and chemistry of carbonaceous and enstatite chondrites can be explained by accretion of isolated condensates formed at ξ values of ≤0.1% and 0.7–1.5%, respectively, providing that segregation of the inert coarse objects and fine reactive dust occurred in the nebula. Segregation of these two categories of condensate may have been responsible for the observed volatility‐based chemical fractionations among chondritic meteorites.
Nebular or parent body alteration of chondritic material: Neither or both?
Authors: SEARS DEREK W. G. , AKRIDGE D. GLEN
Published: February 2010

Abstract— Discussions of meteorite properties often concern whether they are the result of “nebular” or “parent body” processes, but several decades of research have not resolved the issue. Part of the problem is that any gas‐phase reaction involving meteoritic materials thought to have occurred is automatically assumed to be nebular, even though the most primitive solar system objects are water‐ and volatile‐rich and could easily generate vapors. Reactions important in meteorite genesis are those involving (1) oxidation of Fe, (2) oxidation of other cations, (3) reduction, (4) olivine‐pyroxene equilibria, and (5) hydration of silicates. The P‐T‐x conditions required are almost invariably incompatible with standard models for the early solar nebula, but clearly many of these reactions occurred prior to final agglomeration. Most of the reactions require high pressures (>10−3 atm) or, more importantly, major departures from cosmic composition, even though the final rocks are remarkably cosmic in elemental proportions. We suggest that most of these reactions occurred in a regolith rendered “dynamic” by the flow of copious volatiles. In such a scenario, liquid and gas phase reactions can occur at elevated temperatures and pressures relative to the nebula and with noncosmic gas phase compositions; but the system is “closed” to most components, so that cosmic proportions are essentially preserved.
Elemental redistribution in Tieschitz and the origin of white matrix
Authors: HUTCHISON ROBERT , ALEXANDER CONEL M.O'D. , BRIDGES JOHN C.
Published: February 2010

Abstract— Two types of mesostasis coexist within some porphyritic chondrules in Tieschitz. One type is smooth. The other, confined to chondrule margins, is blocky on a 5–10 μm scale. Mesostases in one porphyritic olivine‐pyroxene (POP) chondrule and one porphyritic olivine (PO) chondrule were analysed by scanning electron microscopy (SEM) and energy‐dispersive x‐ray spectrometry (EDS), as was white matrix nearby. Mesostases in the PO chondrule and in four others were analysed by ion probe. Pyroxene phenocrysts or dendrites extend across contacts between smooth and blocky mesostasis with no compositional change. Relative to smooth mesostasis, blocky mesostasis is enriched in Al, alkalis, Ba, F, and Cl but depleted in Si, Fe, and Ca. White matrix fills channels between the chondrules. It is physically and chemically similar to blocky mesostasis, but three ion probe analyses indicate that, unlike the mesostases, it is poor in Sc and has variable and fractionated rare earth elements (REEs).

Smooth mesostasis is interpreted as solidified primary chondrule liquid; whereas blocky mesostasis is its alteration product or, less likely, a precipitate replacing smooth mesostasis leached out by aqueous fluid. White matrix may have formed by secondary alteration or replacement of mesostases that had been expelled from chondrules during accretion, or as a precipitate filling interchondrule voids. Iron may have been lost from the bulk meteorite, but most other elements merely underwent internal redistribution. Disturbed isotopic systems indicate that aqueous fluid may have been active on the Tieschitz parent body only 2 Ga ago. If correct, this would be the first evidence that an ordinary chondrite parent body underwent internal reprocessing significantly later than 4.5 Ga ago.
Argon‐39‐argon‐40 “ages” and trapped argon in Martian shergottites, Chassigny, and Allan Hills 84001
Authors: BOGARD Donald D. , GARRISON Daniel H.
Published: February 2010

Abstract— Argon‐isotopic abundances were measured in neutron‐irradiated samples of Martian meteorites Chassigny, Allan Hills (ALH) 84001, ALH 77005, Elephant Moraine (EET) 79001, Yamato (Y) 793605, Shergotty, Zagami, and Queen Alexandra Range (QUE) 94201, and in unirradiated samples of ALH 77005. Chassigny gives a 39Ar‐40Ar age of 1.32 ± 0.07 Ga, which is similar to radiometric ages of the nakhlites. Argon‐39‐Argon‐40 data for ALH 84001 indicate ages between 3.9 and 4.3 Ga. A more precise definition of this age requires detailed characterization of the multiple trapped Ar components in ALH 84001 and of 39Ar recoil distribution. All six shergottite samples show apparent 39Ar‐40Ar ages substantially older than the ∼165–200 Ma range in ages given by other isotope dating techniques. Shergottites appear to contain ubiquitous Ar components acquired from the Martian atmosphere, the Martian mantle, and commonly terrestrial atmospheric contamination. Zagami feldspar also suggests inherited radiogenic 40Ar. These data analyses indicate that the recent Martian atmospheric component trapped in shergottites has a 40Ar/36Ar ratio possibly as low as ∼1750 and no greater than ∼1900. These ratios are less than the value of 3000 ± 500 reported by Viking. The 40Ar/36Ar ratio for the Martian mantle component is probably <500 but is poorly constrained. The correlation between trapped 40Ar/36Ar and 129Xe/132Xe ratios in shergottite impact glasses and unirradiated samples of ALH 77005 shows considerable scatter and suggests that the 36Ar/132Xe ratio in the Martian components may vary. Resolution of Martian atmospheric 40Ar/36Ar ratio at different time periods (i.e., at ∼4.0 and 0.2 Ga) is also difficult without an understanding of the composition of various trapped components.
Deficiencies in the classical model of s‐process nucleosynthesis
Authors: Laeter J. R. De , Rosman K. J. R.
Published: February 2010

Abstract— The classical model of s‐process nucleosynthesis, based on the concept of a steady neutron flux under astrophysical conditions pertaining to the He‐burning phase of red giant stars, has successfully described observed isotopic abundances and provided information on the physical conditions of the s‐process environment. Because most of the isotopes on the s‐process path are stable, their relevant nuclear parameters can be measured in the laboratory so that as more accurate elemental abundance and neutron capture cross‐section data have become available, the classical model has been tested under increasingly stringent conditions. Accurate determinations of the neutron capture cross sections at appropriate astrophysical conditions for the Ba isotopes have shown that the abundance of the s‐only isotope 136Ba is under‐produced by ∼20% according to the classical model. This paper describes the accurate assessment of the meteoritic abundance of Ba by the stable isotope dilution mass spectrometric technique, based on the Cl carbonaceous chondrites Orgueil and Ivuna. Repeated analyses of these two Cl chondrites give an abundance that is identical to the presently accepted solar system value for Ba within experimental errors, which indicates a deficiency in the classical model. When combined with similar data for the s‐only nuclides 116Sn and 142Nd, it is apparent that the classical model, having served a valuable function for many years, must be replaced by stellar models that more accurately reflect the dynamic nature of the He‐burning phase in red giant stars, in particular, during the thermal pulses of low‐mass asymptotic giant branch (AGB) stars.
Partial melting of the Indarch (EH4) meteorite: A textural, chemical, and phase relations view of melting and melt migration
Authors: McCoy Timothy J. , Dickinson Tamara L. , Lofgren Gary E.
Published: February 2010

Abstract—To test whether aubrites can be formed by melting of enstatite chondrites and to understand igneous processes at very low O fugacities, we have conducted partial melting experiments on the Indarch (EH4) chondrite at 1000–1500 °C. Silicate melting begins at 1000 °C, and Indarch is completely melted by 1500 °C. The metal‐sulfide component melts completely at 1000 °C. Substantial melt migration occurs at 1300–1400 °C, and metal migrates out of the silicate charge at 1450 °C and ∼50% silicate partial melting. As a group, our experiments contain three immiscible metallic melts (Si‐, P‐, and C‐rich), two immiscible sulfide melts (Fe‐ and FeMgMnCa‐rich), and silicate melt. Our partial melting experiments on the Indarch (EH4) enstatite chondrite suggest that igneous processes at lowfO2exhibit several unique features. The complete melting of sulfides at 1000 °C suggests that aubritic sulfides are not relics. Aubritic oldhamite may have crystallized from Ca and S complexed in the silicate melt. Significant metal‐sulfide melt migration might occur at relatively low degrees of silicate partial melting. Substantial elemental exchange occurred between different melts (e.g., S between sulfide and silicate, Si between silicate and metal), a feature not observed during experiments at higherfO2. This exchange may help explain the formation of aubrites from known enstatite chondrites.
Evidence for a very high carbon/iridium ratio in the Tunguska impactor
Authors: RASMUSSEN Kaare L. , OLSEN Hans J. F. , GWOZDZ Raymond , KOLESNIKOV Euginev M.
Published: February 2010

Abstract— We have measured excess Ir and depletion of 14C, two independent indicators of cosmic material, in peat cores from the central Tunguska impact site. Both Ir and 14C show pronounced anomalies in the same stratigraphical depth interval. We have estimated an integral deposition of nonradioactive cosmogenic C of 6.8 ± 1.0 mg C cm−2, and an integrated Ir deposition of 5.9 ± 1.2 pg Ir cm−2. The very high C/Ir ratio and a deduced δ13C value of +55 ± 10% relative to V Pee Dee Belemnite (VPDB) of the impactor material found in this study points towards a cometary type impactor, rather than a chondritic or achondritic asteroidal type impactor.
Variation of Leonid maximum times with location of observer
Authors: McNAUGHT R. H. , ASHER D. J.
Published: February 2010

Abstract— A time adjustment from the Earth's centre to the observer's location is quantified and shown to improve the residuals between the observed time of pronounced Leonid showers and the time calculated from perturbed dust trails. A correlation with the exact time of closest approach to the nominal dust trail orbit would allow a further improvement in the residuals. However, there is no evidence for such a correlation, which suggests that the dust trail cross section is substantially elongated within the orbital plane. These results indicate that approaches to dust trails within 0.0005 AU are predictable with an uncertainty of ∼5 min. Application of this correction to satellites confirms the utility of two strategies to minimise the impact risk. The time adjustment could be applied to any meteor stream.
The Tatahouine diogenite: Mineralogical and chemical effects of sixty‐three years of terrestrial residence
Authors: BARRAT J. A. , GILLET Ph. , LESOURD M. , BLICHERT‐TOFT J. , POUPEAU G. R.
Published: February 2010

Abstract— Comparison between clasts of the Tatahouine diogenite, collected the day of the fall in 1931 and 63 years later in 1994, allows the evaluation of mineralogical and chemical effects of terrestrial residence on meteorites. Secondary minerals are found in the 1994 samples: iron stains and carbonate rosettes. Major and trace element abundances have been determined on fallen and found clasts. No significant differences have been observed for most elements with the exception of Rb, Sr, and (in a single case) the light rare earth elements (LREE). In this case, the REE pattern of a 1994 clast displays a weak positive Ce anomaly, probably linked to the presence of iron hydroxide. The contents of Rb and Sr are significantly higher in the 1994 samples than in the 1931 clasts and reflect the formation of calcite inside some of the clast fractures. These results demonstrate that weathering processes may change the chemistry of meteorites in a very short time.
Concentrations of siderophile elements in nonmagnetic fractions of Antarctic H‐ and L‐chondrites: A quantitative approach on weathering effects
Authors: WELTEN K. C.
Published: February 2010

Abstract— The nonmagnetic separates of Antarctic H‐ and L‐chondrite finds from the Lewis Cliff stranding area are enriched in Fe and siderophile elements such as Ni, Co, Cu, As, Ir, and Au, relative to those of non‐Antarctic falls. The siderophile enrichments are caused by the oxidation of metallic Fe‐Ni to nonmagnetic hydrous Fe‐Ni oxides. The concentrations of Fe, Ni, and Co in each sample were used to calculate the amount of oxidized metal, which serves as a quantitative measure of the degree of weathering. The amount of oxidized metal is generally between 1–10 wt% and shows a rough correlation with the qualitative A‐B‐C‐weathering classification for increasing rustiness. No clear correlation was found between weathering and terrestrial age, although meteorites older than 0.2 Ma contain on the average ∼50% more oxidized metal. Also, no correlation was found between the degree of weathering and the natural thermoluminescence (TL) level, which is dominated by the thermal history in space rather than by the thermal history in or on the Antarctic ice. The only significant parameter for the degree of weathering seems to be the location of find, with the most weathered specimens being found in a part of the stranding area where melt‐water ponds are known to occur. This observation confirms that the occasional presence of liquid water plays an important role in the Antarctic weathering process and explains the poor correlation of the degree of weathering of Antarctic meteorites with terrestrial age and surface exposure age.
Distant ejecta from the Lockne marine‐target impact crater, Sweden
Authors: STURKELL Erik , ORMÖ Jens , NÕLVAK Jaak , WALLIN ÅSa
Published: February 2010

Abstract— The Lockne impact event took place in a Middle Ordovician (455 Ma) epicontinental sea. The impact resulted in an at least 13.5 km wide, concentric crater in the sea floor. Lockne is one of very few locations where parts of an ejecta layer have been preserved outside the crater structure. The ejecta from the Lockne impact rests on progressively higher stratigraphic levels with increasing distance from the crater, hence forming a slightly inclined discontinuity surface in the pre‐impact strata. We report on a ∼30 cm thick sandy layer at Hallen, 45 km south of the crater centre. This layer has a fining upward sequence in its lower part, followed by low‐angle cross‐laminations indicating two opposite current directions. It is rich in quartz grains with planar deformation features and contains numerous, up to 15 cm large, granite clasts from the crystalline basement at the Lockne impact site. The layer is within a sequence dated to the Baltoniodus gerdae conodont subzone. The dating is corroborated by chitinozoans indicating the latest Kukruse time below and the late Idavere above the impact layer. According to the chitinozoans biostratigraphy, some erosion may have occurred because of deposition of the impact layer. The Hallen outcrop, today 45 km from the centre of the Lockne crater, is at present the most distant accessible occurrence of ejecta from the Lockne impact. It is also the most distant location so far found where the resurge of water towards the crater has affected the bottom sediments.

A greater crater diameter than hitherto assumed, thus representing greater impact energy, might explain the extent of the ejecta blanket. Fluidisation of ejecta, to be expected at a marine‐target impact, might furthermore have facilitated the wide distribution of ejecta.
Interrelationships among meteoric metals, meteors, interplanetary dust, micrometeorites, and meteorites
Authors: RIETMEIJER Frans J. M.
Published: February 2010

Abstract— Meteor science, aeronomy, and meteoritics are different disciplines with natural interfaces. This paper is an effort to integrate the chemistry and mineralogy of collected interplanetary dust particles (IDPs), micrometeorites, and meteorites with meteoric data and with atmospheric metal abundances. Evaporation, ablation, and melting of decelerating materials in the Earth's atmosphere are the sources of the observed metal abundances in the upper atmosphere. Many variables ultimately produce the materials and phenomena we can analyze, such as different accretion and parent‐body histories of incoming extraterrestrial materials, different interactions of meteors with the Earth's middle atmosphere, meteor data reduction, and complex chemical interactions of the metals and ions with the ambient atmosphere. The IDP‐like and unequilibrated ordinary chondrite matrix materials are reasonable sources for observed meteoric and atmospheric metals. The hypothesis of hierarchical dust accretion predicts that low, correlated refractory element abundances in cometary meteors may be real. It implies that the CI or cosmic standard is not useful to appreciate the chemistry of incoming petrologically heterogeneous cometary matter. The quasi steady‐state metal abundances in the lower thermosphere and upper mesosphere are derived predominantly from materials with cometary orbital characteristics and velocities such as comets proper and near‐Earth asteroids. The exact influence of atmospheric chemistry on these abundances still needs further evaluation. Metal abundances in the lower mesosphere and upper stratosphere region are mostly from materials from the asteroidal belt and the Kuiper belt.
Space weathering on airless bodies: Resolving a mystery with lunar samples
Authors: PIETERS Carlé M. , TAYLOR Larry A. , NOBLE Sarah K. , KELLER Lindsay P. , HAPKE Bruce , MORRIS Richard V. , ALLEN Carl C. , McKAY David S. , WENTWORTH Susan
Published: February 2010

Abstract— Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe0) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe0, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S‐type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe0 on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.
Australasian microtektites in the South China Sea and the West Philippine Sea: Implications for age, size, and location of the impact crater
Authors: LEE Meng‐Yang , WEI Kuo‐Yen
Published: February 2010

Abstract— Microtektites from two deep‐sea cores in the South China Sea and the West Philippine Sea are identified as belonging to the Australasian tektite strewn field based on the morphology, chronostratigraphic occurrence, and geographical location of these microtektites. The higher concentrations of microtektites (>1000/cm2) in the marginal seas of the western Pacific, with the peak concentration in the South China Sea, support the hypothesis of a large impact crater in Indochina. These two new occurrences lead to a more precise dating of the impact event at 793 ka, whereas the size of the Australasian source crater on the Indochina Peninsula is estimated to be 90–116 km.
Bulk density of ordinary chondrite meteorites and implications for asteroidal internal structure
Authors: WILKISON Sarah L. , ROBINSON Mark S.
Published: February 2010

Abstract— The bulk densities of 82 samples of 72 ordinary chondrites (OCs) were measured to an accuracy of ∼1% using a modified Archimedian method. We found the average bulk density to be 3.44 ± 0.19 g/cm3 for the H group, 3.40 ± 0.15 g/cm3 for the L group, and 3.29 ± 0.17 g/cm3 for the LL group (± represent 1σ). Bulk density measurements of 11 pieces of one fall, Pultusk (H group), were also found to vary considerably (3.31 to 3.63 g/cm3). To investigate controls on bulk density within the OCs, we compared density with bulk chemical composition (the ratio of Fe metal to total Fe; the ratio of total Fe to SiO2; the ratio of FeO to total Fe and MgO). Within each OC group, bulk chemical composition is nearly invariant whereas bulk density varies from about 3.0 to 3.8 g/cm3. Slight but systematic differences in average density between the H, L, and LL groups presumably relate to differences in metallic Fe abundance. However, considerable overlap between OC groups and the wide range of bulk densities within each group suggest differences in porosity dominantly control variations of density within the OC subgroups.
Iron‐rich aureoles in the CM carbonaceous chondrites Murray, Murchison, and Allan Hills 81002: Evidence for in situ aqueous alteration
Authors: HANOWSKI Nicolaus P. , BREARLEY Adrian J.
Published: February 2010

Abstract— Iron‐rich aureoles in CM carbonaceous chondrites are previously unidentified domains of aqueously altered matrix material, whose FeO content may exceed that of the surrounding matrix by up to more than 15 wt%. We describe the petrography and mineralogy of these objects in the CM chondrites Murray, Murchison, and Allan Hills (ALH) 81002. The size of Fe‐rich aureoles ranges from a few hundred microns to several millimeters in diameter and appears to be a function of the degree of alteration of the host chondrite. The origin of Fe‐rich aureoles is related to the alteration of large metal grains that has resulted in the formation of characteristic PCP‐rich reaction products that are frequently observed at the centers of the aureoles. This suggests that Fe‐rich aureoles in CM chondrites are the result of the mobilization of Fe from altering metal grains into the matrix. The fact that Fe‐rich aureoles enclose numerous chondritic components such as chondrules, calcium‐aluminum‐rich inclusions (CAIs), and mineral fragments, as well as their radial symmetric appearance, are strong evidence that they formed in situ and that significant directional fluid flow was not involved in the alteration process. This and additional constraints, such as the distribution of S and other elements, as well as the inferred alteration conditions, are consistent with in situ parent‐body alteration. The observations are, however, entirely incompatible with preaccretionary alteration models in which the individual CM chondrite components have experienced diverse alteration histories. The presence of numerous intact aureoles in the brecciated CM chondrites Murray and Murchison further suggests that the alteration occurred largely after brecciation affected these meteorites. Therefore, the progressive aqueous alteration of CM chondrites may not be necessarily coupled to brecciation as has been previously proposed.
Formation of CmSn compounds by photopolymerization of CS2 in the atmosphere of Jupiter
Authors: Heymann Dieter , Cataldo Franco , Thiemens Mark h. , Fokkens Roelof , Nibbering Nico m. m. , Vis Ronald d.
Published: February 2010

Abstract— Toluene extracts from two (CSn)x photopolymers were examined with high‐performance liquid chromatography (HPLC), matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry, particle‐induced x‐ray emission (PIXE), and 12C(d,p)13C nuclear microprobing. the extracts contained elemental s and at least from 17 to 20 distinct cmsn compounds with m/z less than ∼500 amu. Whereas H2S is the dominant S‐bearing compound of the normal jovian atmosphere, elemental S, CS, and CS2 were observed at Shoemaker‐Levy 9 cometary impact sites and at altitudes of the transiently disturbed jovian atmosphere where photodissociation and photopolymerization occur. It is uncertain whether the CS2 molecular densities were sufficiently large for both to occur, but photopolymerization could have occurred during larger impacts of Jupiter's history. Because the known stable CmSn compounds are yellow, orange and deep red, they could contribute significantly to the colors of the jovian clouds.
Devri‐Khera: A new L6 chondrite
Authors: GHOSH S. , BANDYOPADHYAY T. K. , PANT N. C. , SHOME S. , SEN D. K. , RAJAWAT R. S.
Published: February 2010

Abstract— The Devri‐Khera meteorite fell on 1994 October 30 in the Jhalwar district of Rajasthan, northwestern India. The texture, mineralogy and mineral and bulk compositions show that Devri‐Khera is an L6 chondrite of shock facies S4.
Relationship between cooling rate and cooling age of a mineral: Theory and applications to meteorites
Authors: GANGULY Jibamitra , TIRONE Massimiliano
Published: February 2010

Abstract— We reviewed here the recent development on the mathematical formulation of closure temperature of a cooling geochronological system, which permits direct retrieval of cooling rate from cooling age when the diffusion parameters, grain size and initial temperature are known. This formulation is used to show how the cooling rate can be retrieved by comparing the core and bulk age of a mineral determined by a single decay system. The cooling rates of seven H chondrites of the metamorphic types H4, H5 and H6 were retrieved from the available data on the Pb‐Pb model ages of the phosphates and the diffusion kinetic data of Pb in apatite. The results are in excellent agreement with the metallographic cooling rates and show an inverse relation with the metamorphic grade of these chondrites. We also addressed the problem of ∼90 Ma younger Sm‐Nd mineral isochron age, defined by orthopyroxene, phosphate and plagioclase, of the Morristown mesosiderite compared to the Pb‐Pb age of the Estherville mesosiderite. It is shown that this younger age could have been a consequence of resetting during cooling instead of an “impulsive heating” event, as suggested earlier.
Silicate darkening in the Kobe CK chondrite: Evidence for shock metamorphism at high temperature
Authors: Tomeoka Kazushige , Ohnishi Ichiro , Nakamura Noboru
Published: February 2010

Abstract— The Kobe CK4 chondrite, like most metamorphosed CK chondrites, exhibits pronounced silicate darkening of matrix and chondrule mesostases. Our petrographic and scanning electron microscopic study reveals that the matrix of Kobe consists mostly of intermixtures of two types of fine‐grained olivine. One forms subhedral to anhedral normal crystals. The other fills interstices of the subhedral to anhedral olivine crystals, exhibiting a complex network of veinlets. The latter type of olivine contains high densities of small spherical vesicles (<0.05‐3 μm in diameter) and grains (<0.05‐5 μm) of magnetite and pentlandite as well as round to anhedral grains (1–10 μm) of plagioclase, low‐Ca pyroxene, diopside and chlorapatite. The vesicular olivine is particularly abundant in regions of matrix that exhibit a relatively high degree of darkening and commonly fills chondrule mesostases. The vesicular olivine is clearly the principal cause of the silicate darkening in Kobe. The internal texture of the vesicular olivine closely resembles those of local melts produced from the matrices of experimentally and naturally shocked carbonaceous chondrites. The occurrence and texture of the vesicular olivine suggest that it resulted from recrystallization of partially melted matrix olivine by shock.

Kobe exhibits light shock effects in olivine that are consistent with shock stage S2 that is too low to explain the occurrence of olivine melting. We suggest that the vesicular olivine in Kobe was produced by shock metamorphism at a relatively mild shock pressure (<25 GPa) and a high temperature (>600 °C). Thus, it is probable that the shock effects in olivine, manifest as fracturing and deformation, were relatively minor, but heating was strong enough to cause partial melting of matrix olivine.
Mineralogical interpretation of reflectance spectra of Eros from NEAR near‐infrared spectrometer low phase flyby
Authors: Mcfadden Lucy A. , Wellnitz Dennis D. , Schnaubelt Matthew , Gaffey Michael J. , Bell J. F. , Izenberg Noam , Murchie Scott , Chapman Clark R.
Published: February 2010

Abstract—High signal‐to‐noise near‐infrared spectrometer (NIS) spectra acquired during the low phase flyby of the near‐Earth asteroid rendezvous (NEAR) mission to 433 Eros are analyzed to determine mineral chemistry and proportions of mafic silicates across the asteroid's surface at 2.68 × 5.50 km spatial resolution. Spectral band parameters are derived, and compared with those of laboratory samples of known mineral composition, grain size distribution and terrestrial, meteoritic and lunar pyroxene spectral properties. The NIS derived band parameters are consistent with ordinary chondrite meteorites. We invoke the presence of a clinopyroxene component in the spectra, which is consistent with ordinary chondrite mineralogy and/or some degree of partial melting of ordinary chondritic material. Spectra measured across the surface of Eros can reveal small but real spectral variations. Most relative spectra are uniform to within 1–2%. Some areas suggest compositional variations of a few percent. Spectral slope variations of a few percent are seen indicating a non‐uniform distribution of materials affecting the slope parameter but with no resolved absorption bands. We find no correlation of slope with viewing geometry or compositional variation. The band parameter values do not consistently indicate a specific ordinary chondrite class but Eros is definitely undifferentiated with possible compositional variations of no more than 1–2%.
Cosmic‐ray exposure history of two Frontier Mountain H‐chondrite showers from spallation and neutron‐capture products
Authors: WELTEN K. C. , NISHIIZUMI K. , MASARIK J. , CAFFEE M. W. , JULL A. J. T. , KLANDRUD S. E. , WIELER R.
Published: February 2010

Abstract—We measured the concentrations of10Be,26Al,36Cl,41Ca and14C in the metal and/or stone fractions of 27 Antarctic chondrites from Frontier Mountain (FRO), including two large H‐chondrite showers. To estimate the pre‐atmospheric size of the two showers, we determined the contribution of neutron‐capture produced36Cl (half‐life = 3.01 times 105years) and41Ca (1.04 times 105years) in the stone fraction. The measured activities of neutron‐capture36Cl and41Ca, as well as spallation produced10Be and26Al, were compared with Monte Carlo‐based model calculations. The largest shower, FRO 90174, includes eight fragments with an average terrestrial age of (100 ± 30) × 103years; the neutron‐capture saturation activities extend to 27 dpm/kg stone for36Cl and 19 dpm/kg stone for41Ca. The concentrations of spallation produced10Be,26Al and36Cl constrain the radius (R) to 80–100 cm, while the neutron‐capture41Ca activities indicate that the samples originated from the outer 25 cm. With a pre‐atmospheric radius of 80–100 cm, FRO 90174 is among the largest of the Antarctic stony meteorites. The large pre‐atmospheric size supports our hypothesis that at least 50 of the ∼150 classified H5/H6‐chondrites from the Frontier Mountain stranding area belong to this single fall; this hypothesis does not entirely account for the high H/L ratio at Frontier Mountain. The smaller shower, FRO 90001, includes four fragments with an average terrestrial age of (40 ± 10) × 103years; they contain small contributions of neutron‐capture36Cl, but no excess of41Ca. FRO 90001 experienced a complex exposure history with high shielding conditions in the first stage (150 <R< 300 cm) and much lower shielding in the second stage (R< 30 cm), the latter starting ∼1.0 million years (Ma) ago. Based on the measured10Be/21Ne and26Al/21Ne ratios, the cosmic‐ray exposure ages of the two showers are 7.2 ± 0.5 Ma for FRO 90174 and 8 ± 1 Ma for FRO 90001. These ages coincide with the well‐established H‐chondrite peak and corroborate the observation that the exposure age distribution of FRO H‐chondrites is similar to that of non‐Antarctic falls. In addition, we found that corrections for neutron‐capture36Ar (from decay of36Cl) result in concordant21Ne and38Ar exposure ages.
Production rates of cosmogenic helium‐3, neon‐21, and neon‐22 in ordinary chondrites and the lunar surface
Authors: MASARIK J. , NISHIIZUMI K. , REEDY R. C.
Published: February 2010

Abstract— The production of 3He, 21Ne, and 22Ne in meteoroids of various sizes and in the lunar surface was investigated. The LAHET code system, a purely physical model for calculating cosmic‐ray particle fluxes, was used to simulate cosmic‐ray particle interactions with extraterrestrial matter. We discuss the depth and size dependence of the shielding parameter 22Ne/21Ne, which is used for reconstruction of pre‐atmospheric sizes, depth, and exposure histories. The 22Ne/21Ne ratio decreases with increasing depth or pre‐atmospheric size but then increases with depth in very large objects. This increase with depth in the 22Ne/21Ne ratio means that this ratio is a poor indicator of shielding in some large objects. The dependence of 3He/21Ne as function of 22Ne/21Ne was also calculated, and differences between the calculations and the Bern line are discussed.
Authors' Reply
Authors: Goiter J. D. , Glikson A. Y.
Published: February 2010

Abstract— Reimold et al. question our interpreted impact origin of the Fohn structure, Timor Sea, and criticise methodological aspects of the seismic reflection survey of Fohn structure and chemical analytical techniques. Our impact interpretation resulted from (1) remarkable analogies between the seismic structures of massive core‐annular trough structure of volcanic diatremes, and the syncline‐ringed central uplift of impact structures; (2) occurrence of Cretaceous microfossils in the drill chips, which suggested deep excavation; (3) lack of seismic evidence for volcanic feeders or conduits, and (4) the ultramafic chemistry of drill chips (Ni < 428 ppm; Co < 51 ppm; Cr < 518 ppm). Here we indicate that, since publication of our paper, we have uncovered in Fohn‐1 drill cuttings rare apatite‐rich lamproite mineral assemblages consisting of pseudomorphs of analcite after leucite, nontronite‐altered olivine, diopside, alkali pyroxene, Ti‐phlogopite, apatite, Mg‐ilmenite, priderite, rutile, and secondary barite. The new data explain the high gamma ray log anomalies in Fohn‐1 well and shed new light on the origin of the Fohn structure. Our error serves to clarify criteria for distinguishing between buried diatremes and impact structures.
Assessment of the interstellar processes leading to deuterium enrichment in meteoritic organics
Authors: SANDFORD Scott A. , BERNSTEIN Max P. , DWORKIN Jason P.
Published: February 2010

Abstract— The presence of isotopic anomalies is the most unequivocal demonstration that meteoritic material contains circumstellar or interstellar components. In the case of organic compounds in meteorites and interplanetary dust particles (IDPs), the most useful isotopic tracer has been deuterium (D). We discuss four processes that are expected to lead to D enrichment in interstellar materials and describe how their unique characteristics can be used to assess their relative importance for the organics in meteorites. These enrichment processes are low‐temperature gas phase ion‐molecule reactions, low‐temperature gas‐grain reactions, gas phase unimolecular photodissociation, and ultraviolet photolysis in D‐enriched ice mantles. Each of these processes is expected to be associated with distinct regiochemical signatures (D placement on the product molecules, correlation with specific chemical functionalities, etc.), especially in the molecular population of polycyclic aromatic hydrocarbons (PAHs). We describe these differences and discuss how they may be used to delineate the various interstellar processes that may have contributed to meteoritic D enrichments. We also briefly discuss how these processes may affect the isotopic distributions in C, O, and N in the same compounds.
A transmission electron microscope study of exsolution and coarsening in iron‐bearing clinopyroxene from synthetic analogues of chondrules
Authors: WEINBRUCH Stephan , MÜLLER Wolfgang F. , HEWINS Roger H.
Published: February 2010

Abstract— The microstructure of Fe‐rich clinopyroxene from synthetic analogues of chondrules was studied by transmission electron microscopy. The samples were cooled at various rates from 1455 °C to the quench temperature of 1000 °C. Slow cooling at rates below approximately 50–60 °C/h leads to the development of coherent pigeonite/augite exsolution lamallae on (001). A final wavelength of 19.6 ± 1.1 nm was obtained at a cooling rate of 10 °C/h, and 17.4 ± 2.4 ran at a cooling rate of 50 °C/h. Faster cooling at rates between approximately 50 and 450 °C/h yields only modulated structures with a wavelength on the order of 17–19 nm for the (001) orientation.

Coherent exsolution lamellae on (001) in clinopyroxene occur in chondrules of H, L, LL, and CV chondrites, indicating that slow cooling of chondrules at subsolidus temperatures is a widespread phenomenon. The variation of the lamellar wavelength observed in natural chondrules corresponds to a variation of the subsolidus cooling rates between ∼0.1 and 50 °C/h. The low cooling rates at subsolidus temperatures deduced from the microstructure of Fe‐rich clinopyroxene point to nonlinear cooling, with cooling rates decreasing with decreasing temperature.
Predicting the Sound Transmission Loss of Sandwich Panels by Statistical Energy Analysis Approach
Authors: Wang Tongan , Li Shan , Rajaram Shankar , Nutt Steven R.
Published: February 2010

A statistical energy analysis (SEA) approach is used to predict the sound transmission loss (STL) of sandwich panels numerically. Unlike conventional SEA studies of the STL of sandwich panels, which consider only the antisymmetric (bending) motion of the sandwich panel, the present approach accounts for both antisymmetric and symmetric (dilatational) motions. Using the consistent higher-order sandwich plate theory, the wave numbers of the waves propagating in the sandwich panel were calculated. Using these wave numbers, the wave speed of the propagating waves, the modal density, and the radiation efficiency of the sandwich panels were determined. Finally, the sound transmission losses of two sandwich panels were calculated and compared with the experimentally measured values, as well as with conventional SEA predictions. The comparisons with the experimental data showed good agreement, and the superiority of the present approach relative to other approaches is discussed and analyzed.
Rest-to-Rest Motion of an Experimental Flexible Structure Subject to Friction: Linear Programming Approach
Authors: Kased Rajaey , Singh Tarunraj
Published: February 2010

A linear programming approach designed to eliminate the residual vibration of the two-mass harmonic system subject to friction and undergoing a point-to-point maneuver is proposed and implemented on an experimental test bed. Techniques for design of positive pulse control profiles for nonrobust and robust open loop controller design are explored, where the positive pulses initiate motion and the friction force brings the system to rest. It is shown that consistent results can be obtained from experiments and the robustness against frequency uncertainty results in the reduction in residual vibration as well as steady-state error.
Nonlinear Model Based Estimation of Rigid-Body Motion Via an Indirect Measurement of an Elastic Appendage
Authors: Senesh M. , Wolf A. , Gottlieb O.
Published: February 2010

In this paper, we develop and implement a nonlinear model based procedure for the estimation of rigid-body motion via an indirect measurement of an elastic appendage. We demonstrate the procedure by motion analysis of a compound planar pendulum from indirect optoelectronic measurements of markers attached to an elastic appendage that is constrained to slide along the rigid-body axis. We implement a Lagrangian approach to derive a theoretical nonlinear model that consistently incorporates several generalized forces acting on the system. Identification of the governing linear and nonlinear system parameters is obtained by analysis of frequency and damping backbone curves from controlled experiments of the decoupled system elements. The accuracy of the proposed model based procedures is evaluated and its results are compared with those of a previously reported point cluster estimation procedure. Two cases are investigated to yield 1.7% and 3.4% errors between measured motion and its model based estimation for experimental configurations, with a slider mass to pendulum frequency ratios of 12.8 and 2.5, respectively. Motion analysis of system dynamics with the point cluster method reveals a noisy signal with a maximal error of 3.9%. Thus, the proposed model based estimation procedure enables accurate evaluation of linear and nonlinear system parameters that are not directly measured.
Steady-State Transverse Response in Coupled Planar Vibration of Axially Moving Viscoelastic Beams
Authors: Chen Li-Qun , Ding Hu
Published: February 2010

Steady-state periodical response is investigated for planar vibration of axially moving viscoelastic beams subjected external transverse loads. A model of the coupled planar vibration is established by introducing a coordinate transform. The model can reduce to two nonlinear models of transverse vibration. The finite difference scheme is developed to calculate steady-state response numerically. Numerical results demonstrate there are steady-state periodic responses in transverse vibration, and resonance occurs if the external load frequency approaches the linear natural frequencies. The effect of material parameters and excitation parameters on the amplitude of the steady-state responses are examined. Numerical results also indicate that the model of coupled vibration and two models of transverse vibration predict qualitatively the same tendencies with the changing parameters, and the two models of transverse vibration yield satisfactory results.
The Transmissibility of Vibration Isolators With a Nonlinear Antisymmetric Damping Characteristic
Authors: Peng Z. K. , Lang Z. Q. , Jing X. J. , Billings S. A. , Tomlinson G. R. , Guo L. Z.
Published: February 2010

In the present study, the concept of the output frequency response function, recently proposed by the authors, is applied to theoretically investigate the force transmissibility of single degree of freedom (SDOF) passive vibration isolators with a nonlinear antisymmetric damping characteristic. The results reveal that a nonlinear antisymmetric damping characteristic has almost no effect on the transmissibility of SDOF vibration isolators over the ranges of frequencies, which are much lower or higher than the isolator’s resonance frequency. On the other hand, the introduction of a nonlinear antisymmetric damping can significantly reduce the transmissibility of the vibration isolator over the resonance frequency region. The results indicate that nonlinear vibration isolators with an antisymmetric damping characteristic have great potential to overcome the dilemma encountered in the design of passive linear vibration isolators, that is, increasing the level of damping to reduce the transmissibility at the resonance could increase the transmissibility over the range of higher frequencies. These important theoretical conclusions are then verified by simulation studies.
Forced Response Analysis of Integrally Bladed Disks With Friction Ring Dampers
Authors: Laxalde Denis , Thouverez Fabrice , Lombard Jean-Pierre
Published: February 2010

This paper investigates a damping strategy for integrally bladed disks (blisks) based on the use of friction rings. The steady-state forced response of the blisk with friction rings is derived using the so-called dynamic Lagrangian frequency-time method adapted to cyclic structures with rotating excitations. In addition, an original approach for optimal determination of the number of Fourier harmonics is proposed. In numerical applications, a representative compressor blisk featuring several rings is considered. Each substructure is modeled using finite-elements and a reduced-order modeling technique is used for the blisk. The efficiency of this damping technology is investigated, and friction dissipation phenomena are interpreted with respect to frequency responses. It is shown that the friction damping effectiveness depends mainly on the level of dynamic coupling between blades and disk, and on whether the dynamics features significant alternating stick/slip phases. Through parameter studies, design guidelines are also proposed.