Surface electronic states of meteoritic nanodiamonds     

A. J. Laurence GARVIE 《Meteoritics & planetary science》2006,41(5):667-672

Abstract— The C K edge of Orgueil nanodiamonds (Cδ diamonds) was acquired by electron energy‐loss spectroscopy (EELS), with an energy resolution of 300 meV. The spectra show peaks at 282.5, 284.7, and 286.4 eV, which occur in the band gap below the main diamond edge and are absent from the bulk diamond spectrum. These peaks are attributed to transitions from C 1s surface core levels to unoccupied surface states, and arise from single and π‐bonded dangling bonds and C‐H bonds. A shoulder to the main absorption edge at 287.8 eV may correspond to hydrocarbon adsorbates. These results can be used to further our understanding of Cδ diamond structure and may reveal the presence of a fullerene‐like surface. The unique surface electronic states of the Cδ diamond surfaces are expected to affect their optical properties, which are dependent on features such as extent of H coverage, particle size, and surface structure.  相似文献   

Are the circular, dark features on Comet Borrelly's surface albedo variations or pits?     

Robert M Nelson  Laurence A Soderblom 《Icarus》2004,167(1):37-44

The highest resolution images of Comet 19P/Borrelly show many dark features which, upon casual inspection, appear to be low albedo markings, but which may also be shadows or other photometric variations caused by a depression in the local topography. In order to distinguish between these two possible interpretations we conducted a photometric analysis of three of the most prominent of these features using six of the highest quality images from the September 22, 2001 Deep Space 1 (DS1) flyby. We find that: 1. The radiance in the darkest parts of each feature increases as phase angle decreases, similarly to the radiance behavior of the higher albedo surrounding terrain. The dark features could be either fully illuminated low albedo spots or, alternatively, they could be depressions. No part of any of the three regions was in full shadow. 2. One of the regions has a radiance profile consistent with a rimmed depression, the second, with a simple depression with no rim, and the third with a low albedo spot. 3. The regolith particles are backscattering and carbon black is one of the few candidate regolith materials that might explain this low albedo. We conclude that Borrelly's surface is geologically complex to the limit of resolution of the images with a combination complex topography, pits, troughs, peaks and ridges, and some very dark albedo markings, perhaps a factor of two to three darker than the average 3-4% albedo of the surrounding terrains. Our technique utilizing measured radiance profiles through the dark regions is able to discriminate between rimmed depressions, rimless depressions and simple albedo changes not associated with topography.  相似文献   

Sutter's Mill dicarboxylic acids as possible tracers of parent‐body alteration processes     

Sandra Pizzarello  Laurence A. J. Garvie 《Meteoritics & planetary science》2014,49(11):2087-2094

Dicarboxylic acids were searched for in three Sutter's Mill (SM) fragments (SM2 collected prerain, SM12, and SM41) and found to occur almost exclusively as linear species of 3‐ to 14‐carbon long. Between these, concentrations were low, with measured quantities typically less than 10 nmole g^?1 of meteorite and a maximum of 6.8 nmole g^?1 of meteorite for suberic acid in SM12. The SM acids' molecular distribution is consistent with a nonbiological origin and differs from those of CMs, such as Murchison or Murray, and of some stones of the C2‐ungrouped Tagish Lake meteorite, where they are abundant and varied. Powder X‐ray diffraction of SM12 and SM41 show them to be dominated by clays/amorphous material, with lesser amounts of Fe‐sulfides, magnetite, and calcite. Thermal gravimetric (TG) analysis shows mass losses up to 1000 °C of 11.4% (SM12) and 9.4% (SM41). These losses are low compared with other clay‐rich carbonaceous chondrites, such as Murchison (14.5%) and Orgueil (21.1%). The TG data are indicative of partially dehydrated clays, in accordance with published work on SM2, for which mineralogical studies suggest asteroidal heating to around 500 °C. In view of these compositional traits and mineralogical features, it is suggested that the dicarboxylic acids observed in the SM fragments we analyzed likely represent a combination of molecular species original to the meteorite as well as secondary products formed during parent‐body alteration processes, such as asteroidal heating.  相似文献   

The Meteoritical Bulletin,No. 100, 2014 June     

Alex Ruzicka  Jeffrey N. Grossman  Laurence Garvie 《Meteoritics & planetary science》2014,49(8):E1-E101

Meteoritical Bulletin 100 contains 1943 meteorites including 8 falls (Boumdeid [2011], Huaxi, Ko?ice, Silistra, So?tmany, Sutter's Mill, Thika, Tissint), with 1575 ordinary chondrites, 139 carbonaceous chondrites, 96 HED achondrites, 25 ureilites, 18 primitive achondrites, 17 iron meteorites, 15 enstatite chondrites, 11 lunar meteorites, 10 mesosiderites, 10 ungrouped achondrites, 8 pallasites, 8 Martian meteorites, 6 Rumuruti chondrites, 3 enstatite achondrites, and 2 angrites, and with 937 from Antarctica, 592 from Africa, 230 from Asia, 95 from South America, 44 from North America, 36 from Oceania, 6 from Europe, and 1 from an unknown location. This will be the last Bulletin published in the current format. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available online at http://www.lpi.usra.edu/meteor/  相似文献   

An old galaxy group: Chandra X-ray observations of the nearby fossil group NGC 6482     

Habib G. Khosroshahi  Laurence R. Jones  Trevor J. Ponman 《Monthly notices of the Royal Astronomical Society》2004,349(4):1240-1250

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Spitzer imaging of i'-drop galaxies: old stars at z≈ 6     

Laurence P. Eyles  rew J. Bunker  Elizabeth R. Stanway  Mark Lacy  Richard S. Ellis  Michelle Doherty 《Monthly notices of the Royal Astronomical Society》2005,364(2):443-454

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Heights of formation of non-magnetic solar lines suitable for velocity studies     

Richard C. Altrock  Laurence J. November  George W. Simon  Robert W. Milkey  Simon P. Worden 《Solar physics》1975,43(1):33-37

Heights of formation of lines that do not exhibit Zeeman splitting are calculated using an LTE, partial non-LTE, and full non-LTE approach. Non-magnetic (g=0) lines are valuable for velocity investigations in quiet-Sun magnetic field regions, and a knowledge of their formation heights is useful for obtaining three dimensional velocity profiles in these regions. Presently at Sacramento Peak Observatory. Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

Post-starburst galaxies: more than just an interesting curiosity     

Vivienne Wild  C. Jakob Walcher  Peter H. Johansson  Laurence Tresse  Stéphane Charlot  Agnieszka Pollo  Olivier Le Fèvre  Loic de Ravel 《Monthly notices of the Royal Astronomical Society》2009,395(1):144-159

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From the Editor of the Meteoritical Bulletin     

Laurence A. J. GARVIE 《Meteoritics & planetary science》2012,47(11):1887-1887

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Scanning electron microscopical and cross sectional analysis of extraterrestrial carbonaceous nanoglobules     

Laurence A. J. GARVIE  Grant BAUMGARDNER  Peter R. BUSECK 《Meteoritics & planetary science》2008,43(5):899-903

Abstract— Carbonaceous nanoglobules are ubiquitous in carbonaceous chondrite (CC) meteorites. The Tagish Lake (C2) meteorite is particularly intriguing in containing an abundance of nanoglobules, with a wider range of forms and sizes than encountered in other CC meteorites. Previous studies by transmission electron microscopy (TEM) have provided a wealth of information on chemistry and structure. In this study low voltage scanning electron microscopy (SEM) was used to characterize the globule forms and external structures. The internal structure of the globules was investigated after sectioning by focused ion beam (FIB) milling. The FIB‐SEM analysis shows that the globules range from solid to hollow. Some hollow globules show a central open core, with adjoining smaller cores. The FIB with an SEM is a valuable tool for the analysis of extraterrestrial materials, even of sub‐micron‐sized “soft” carbonaceous particles. The rapid site‐specific cross‐sectioning capabilities of the FIB allow the preservation of the internal morphology of the nanoglobules, with minimal damage or alteration of the unsectioned areas.  相似文献