Analyses of the chondritic meteorite Orvinio (H6): Insight into the origins and evolution of shocked H chondrite material     

Jennifer A. GRIER  David A. KRING  Timothy D. SWINDLE  Andrew S. RIVKIN  Barbara A. COHEN  Daniel T. BRITT 《Meteoritics & planetary science》2004,39(9):1475-1493

Abstract— We have studied the petrography, reflectance spectra, and Ar‐Ar systematics of the Orivinio meteorite. Orvinio is an H chondrite not an L chondrite as sometimes reported. The material in the meteorite was involved in several impact events. One impact event produced large swaths of impact melt from H chondrite material surrounding relict clasts of chondrule‐bearing material. Not only were portions of a bulk H chondrite planestesimal melted during the impact event, but shock redistribution of metal and sulfide phases in the meteorite dramatically altered its reflectance spectra. Both the melt and relict clasts are darker than unshocked H chondrite material, bearing spectral similarities to some C‐class asteroids. Such shock metamorphism, which lowers the albedo of an object without increasing its spectral slope, may partially explain some of the variation among S‐class asteroids and some of the trends seen on asteroid 433 Eros. Noble gases record the evidence of at least two, and perhaps three, impact events in the meteorite and its predecessor rocks. The most significant evidence is for an event that occurred 600 Ma ago or less, perhaps ?325 Ma ago or less. There is also a signature of 4.2 Ga in the Ar‐Ar systematics, which could either reflect complete degassing of the rock at that time or partial degassing of even the most retentive sites in the more recent event.  相似文献   

The hydrocarbons in the Isla Vista marine seep environment     

Daniel H. Stuermer  Robert B. Spies  Paul H. Davis  Douglas J. Ng  Clarence J. Morris  Sharon Neal 《Marine Chemistry》1982,11(5):413-426

Hydrocarbon analyses on samples of sediment, interstitial water, and dissolved and particulate fractions of the water column from the vicinity of the Isla Vista seep near Santa Barbara, California, are presented. The results demonstrate that a very heterogeneous distribution of hydrocarbon composition and concentration exists in the seep environment and that the life-style and feeding habits of the organisms in this environment will have a dramatic effect on their hydrocarbon exposure.  相似文献   

Ultraluminous X-ray source 1E 0953.8+6918 (M81 X-9): an intermediate-mass black hole candidate and its environs     

Q.Daniel Wang 《Monthly notices of the Royal Astronomical Society》2002,332(3):764-768

We present a ROSAT and ASCA study of the Einstein source X-9 and its relation to a shock-heated shell-like optical nebula in a tidal arm of the M81 group of interacting galaxies. Our ASCA observation of the source shows a flat and featureless X-ray spectrum well described by a multicolour disc blackbody model. The source most likely represents an optically thick accretion disc around an intermediate-mass black hole  ( M ∼10² M_⊙)  in its high/soft state, similar to other variable ultraluminous X-ray sources observed in nearby disc galaxies. Using constraints derived from both the innermost stable orbit around a black hole and the Eddington luminosity, we find that the black hole is fast-rotating and that its mass is between ∼80 M_⊙–1.5×10² M_⊙. The inferred bolometric luminosity of the accretion disc is ∼(1.1×10⁴⁰ erg s⁻¹)/(cos  i ). Furthermore, we find that the optical nebula is very energetic and may contain large amounts of hot gas, accounting for a soft X-ray component as indicated by archival ROSAT PSPC data. The nebula is apparently associated with X-9; the latter may be powering the former and/or they could be formed in the same event (e.g. a hypernova). Such a connection, if confirmed, could have strong implications for understanding both the birth of intermediate-mass black holes and the formation of energetic interstellar structures.  相似文献   

An empirical calibration of star formation rate estimators     

Daniel Rosa&#;González  Elena Terlevich †  Roberto Terlevich ‡ 《Monthly notices of the Royal Astronomical Society》2002,332(2):283-295

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A PRINCIPAL AXIS SHIFT IN THE AMERICAN SPATIAL ECONOMY?*     

Daniel R. Vining  Joseph B. Dobronyi  Mark A. Otness  James E. Schwinn 《The Professional geographer》1982,34(3):270-278

Gottmann in his classic Megalopolis attributes the dominance of the Northeast to its function as the hinge region of the United States. In this paper, we show, via statistics on maritime trade and interregional freight traffic by rail, that Megalopolis is no longer the dominant “hinge” region. We present evidence that the Gulf region may be supplanting it in this function. Finally, we speculate on some of the reasons for the Gulf's rather sudden assumption of this role and its implications for the economic geography of the U.S.  相似文献   

The detection of the donor star in IY UMa     

Daniel J. Rolfe  Timothy M. C. Abbott  Carole A. Haswell 《Monthly notices of the Royal Astronomical Society》2002,334(3):699-704

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The MESSENGER mission to Mercury: scientific objectives and implementation     

Sean C. Solomon  Ralph L. McNutt  Jr.  Robert E. Gold  Mario H. Acua  Daniel N. Baker  William V. Boynton  Clark R. Chapman  Andrew F. Cheng  George Gloeckler  James W. Head III  Stamatios M. Krimigis  William E. McClintock  Scott L. Murchie  Stanton J. Peale  Roger J. Phillips  Mark S. Robinson  James A. Slavin  David E. Smith  Robert G. Strom  Jacob I. Trombka  Maria T. Zuber 《Planetary and Space Science》2001,49(14-15)

Mercury holds answers to several critical questions regarding the formation and evolution of the terrestrial planets. These questions include the origin of Mercury's anomalously high ratio of metal to silicate and its implications for planetary accretion processes, the nature of Mercury's geological evolution and interior cooling history, the mechanism of global magnetic field generation, the state of Mercury's core, and the processes controlling volatile species in Mercury's polar deposits, exosphere, and magnetosphere. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission has been designed to fly by and orbit Mercury to address all of these key questions. After launch by a Delta 2925H-9.5, two flybys of Venus, and two flybys of Mercury, orbit insertion is accomplished at the third Mercury encounter. The instrument payload includes a dual imaging system for wide and narrow fields-of-view, monochrome and color imaging, and stereo; X-ray and combined gamma-ray and neutron spectrometers for surface chemical mapping; a magnetometer; a laser altimeter; a combined ultraviolet–visible and visible-near-infrared spectrometer to survey both exospheric species and surface mineralogy; and an energetic particle and plasma spectrometer to sample charged species in the magnetosphere. During the flybys of Mercury, regions unexplored by Mariner 10 will be seen for the first time, and new data will be gathered on Mercury's exosphere, magnetosphere, and surface composition. During the orbital phase of the mission, one Earth year in duration, MESSENGER will complete global mapping and the detailed characterization of the exosphere, magnetosphere, surface, and interior.  相似文献   

A CAUTIONARY NOTE ON THE USE OF THE ALLOMETRIC FUNCTION TO ESTIMATE URBAN POPULATIONS     

Daniel R. Vining  Stephanus J. H. Louw 《The Professional geographer》1978,30(4):365-370

Use of the allometric function to estimate the number of inhabitants of urban areas, given knowledge of their land areas obtained through satellite photographs, rests as much on the stability of this function over time as on its goodness of fit to a cross section of cities at a single point in time. Using urban land and population data for four countries, the United States, Japan, Sweden, and Norway, this paper demonstrates that the function is not generally stable but rather has been subject to rapid upward shifts over the past 10 to 20 years.  相似文献   

COMPUTER-INTENSIVE SIGNIFICANCE-TESTING PROCEDURES*     

Daniel C. Knudsen 《The Professional geographer》1987,39(2):208-214

The role of statistics in geography is now widely recognized, yet there are continuing suspicions as to the appropriateness of traditional methods. I review three computer-intensive approaches to significance testing of sample data. Using these methods, one can virtually always make some statement about the significance of a measure for comparing samples. Yet each approach also yields slightly different information about the measure. This confusion may be lessened somewhat by adopting standard sets of significance-testing procedures.  相似文献   

On the detectability of H₂S in Jupiter     

Bruno Bézard  André Marten  Jean Paul Baluteau  Daniel Gautier  Jean-Marie Flaud  Claude Camy-Peyret 《Icarus》1983,55(2):259-271

The influence of hydrogen sulfide, a still-undetected key molecule for the Jovian atmospheric chemistry in the infrared spectrum, was investigated. Synthetic spectra including various vertical distribution profiles of H₂S have been computed and compared with observational data for Jupiter in the 2- to 15-cm^?1 and 1160- to 1200-cm^?1 spectral ranges. No firm conclusion about the presence of H₂S can be drawn from the latter spectral region because of large uncertainties in gaseous opacities. In the microwave range, H₂S is found to be a possible candidate to explain the measurements. Constraints to its vertical distribution which would imply a significant supersaturation in the troposphere are derived. Physical and chemical processes involving H₂S in the atmosphere are discussed in the light of this hypothesis.  相似文献