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991.
Using the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we investigate the environmental dependence of stellar mass, star formation rate (SFR) and specific star formation rate (SSFR) of LRGs. It is found that stellar mass of LRGs nearly is independent of local environments, and that the environmental dependence of SFR and SSFR in the LRG sample is much weaker than the one in the Main galaxy sample. One possible explanation is that galaxy color and morphology are a pair of galaxy properties most predictive of local environments, while LRGs are a group of galaxies that are likely to be luminous, red and of early types (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
There is variability in the Mg isotopic composition that is a reflection of the widespread heterogeneity in the isotopic composition of the elements in the solar system at approximately 100 ppm. Measurements on a single calcium‐aluminum‐rich inclusion (CAI) gave a good correlation of 26Mg/24Mg with 27Al/24Mg, yielding an isochron corresponding to an initial (26Al/27Al)o = (5.27 ± 0.18) × 10?5 and an initial (26Mg/24Mg)o = ?0.127 ± 0.032‰ relative to the standard. This isochron is parallel to that obtained by Jacobsen et al. (2008) , but is distinctively offset. This demonstrates that there are different initial Mg isotopic compositions in different samples with the same 26Al/27Al. No inference about uniformity/heterogeneity of 26Al/27Al on a macro scale can be based on the initial (26Mg/24Mg)o values. Different values of 26Al/27Al for samples representing the same point in time would prove heterogeneity of 26Al/27Al. The important issue is whether the bulk solar inventory of 26Al/27Al was approximately 5 × 10?5 at some point in the early solar system. We discuss ultra refractory phases of solar type oxygen isotope composition with 26Al/27Al from approximately 5 × 10?5 to below 0.2 × 10?5. We argue that the real issues are: intrinsic heterogeneity in the parent cloud; mechanism and timing for the later production of 16O‐poor material; and the relationship to earlier formed 16O‐rich material in the disk. 26Al‐free refractories can be produced at a later time by late infall, if there is an adequate heat source, or from original heterogeneities in the placental molecular cloud from which the solar system formed. 相似文献
993.
Lewis R. DARTNELL Manish R. PATEL Michael C. STORRIE‐LOMBARDI John M. WARD Jan‐Peter MULLER 《Meteoritics & planetary science》2012,47(5):806-819
Abstract– Even in the absence of any biosphere on Mars, organic molecules, including polycyclic aromatic hydrocarbons (PAHs), are expected on its surface due to delivery by comets and meteorites of extraterrestrial organics synthesized by astrochemistry, or perhaps in situ synthesis in ancient prebiotic chemistry. Any organic compounds exposed to the unfiltered solar ultraviolet spectrum or oxidizing surface conditions would have been readily destroyed, but discoverable caches of Martian organics may remain shielded in the subsurface or within surface rocks. We have studied the stability of three representative polycyclic aromatic hydrocarbons (PAHs) in a Mars chamber, emulating the ultraviolet spectrum of unfiltered sunlight under temperature and pressure conditions of the Martian surface. Fluorescence spectroscopy is used as a sensitive indicator of remaining PAH concentration for laboratory quantification of molecular degradation rates once exposed on the Martian surface. Fluorescence‐based instrumentation has also been proposed as an effective surveying method for prebiotic organics on the Martian surface. We find the representative PAHs, anthracene, pyrene, and perylene, to have persistence half‐lives once exposed on the Martian surface of between 25 and 60 h of noontime summer UV irradiation, as measured by fluorescence at their peak excitation wavelength. This equates to between 4 and 9.6 sols when the diurnal cycle of UV light intensity on the Martian surface is taken into account, giving a substantial window of opportunity for detection of organic fluorescence before photodegradation. This study thus supports the use of fluorescence‐based instrumentation for surveying recently exposed material (such as from cores or drill tailings) for native Martian organic molecules in rover missions. 相似文献
994.
Alvaro P. CRÓSTA César KAZZUO‐VIEIRA Lidia PITARELLO Christian KOEBERL Thomas KENKMANN 《Meteoritics & planetary science》2012,47(1):51-71
Abstract– Vargeão Dome (southern Brazil) is a circular feature formed in lava flows of the Lower Cretaceous Serra Geral Formation and in sandstones of the Paraná Basin. Even though its impact origin was already proposed in the 1980s, little information about its geological and impact features is available in the literature. The structure has a rim‐rim diameter of approximately 12 km and comprises several ring‐like concentric features with multiple concentric lineaments. The presence of a central uplift is suggested by the occurrence of deformed sandstone strata of the Botucatu and Pirambóia formations. We present the morphological/structural characteristics of Vargeão Dome, characterize the different rock types that occur in its interior, mainly brecciated volcanic rocks (BVR) of the Serra Geral Formation, and discuss the deformation and shock features in the volcanic rocks and in sandstones. These features comprise shatter cones in sandstone and basalt, as well as planar microstructures in quartz. A geochemical comparison of the target rock equivalents from outside the structure with the shocked rocks from its interior shows that both the BVRs and the brecciated sandstone have a composition largely similar to that of the corresponding unshocked lithologies. No traces of meteoritic material have been found so far. The results confirm the impact origin of Vargeão Dome, making it one of the largest among the rare impact craters in basaltic targets known on Earth. 相似文献
995.
Guillermo M. MUÑOZ CARO Frans J. M. RIETMEIJER Virginia SOUZA‐EGIPSY Maria Pilar VALLES‐GONZÁLEZ 《Meteoritics & planetary science》2012,47(2):248-261
Abstract– We used a combination of different analytical techniques to study particle W7190‐D12 using microinfrared spectroscopy, micro‐Raman spectroscopy, and field emission scanning electron microscopy (FESEM) energy dispersive X‐ray spectroscopy (EDS). The particle consists mainly of hematite (α‐Fe2O3) with considerable variations in structural disorder. It further contains amorphous (Na,K)‐bearing Ca,Al‐silicate and organic carbon. Iron‐bearing spherules (<150 nm in diameter) cover the surface of this particle. At local sites of structural disorder at the hematite surface, the hematite spheres were reduced to FeO in the presence of organic carbons forming FeO‐spheres. However, metallic Fe spheres cannot be excluded based on the available data. To the best of our knowledge, this particle is the first detection of such spherules at the surface of a stratospheric dust particle. Although there is no definitive evidence for an extraterrestrial origin of particle W7190‐D12, we suggest that it could be an IDP that had moved away from the asteroid‐forming region of the early solar system into the outer solar system of the accreting Kuiper Belt objects. After it was released from a Jupiter family comet, this particle became part of the zodiacal cloud. Atmospheric entry flash‐heating caused (1) the formation of microenvironments of reduced iron oxide when indigenous carbon materials reacted with hematite covering its surface resulting in the formation of FeO‐spheres and (2) Na‐loss from Na,Al‐plagioclase. The particle of this study, and other similar particles on this collector, may represent a potentially new type of nonchondritic IDPs associated with Jupiter family comets, although an origin in the asteroid belt cannot be ignored. 相似文献
996.
Kana NAGASHIMA Masayuki NARA Jun‐ichi MATSUDA 《Meteoritics & planetary science》2012,47(11):1728-1737
Abstract– We performed micro‐Raman spectroscopic analyses of the carbon vein in five ureilites: Allan Hills (ALH) A77257, Northwest Africa (NWA) 3140, Shi?r 007, Yamato 790981 (Y‐790981), and Yamato 791538 (Y‐791538). The graphite peaks showed that the graphite structure in ureilite is well developed, especially compared with the carbonaceous material in carbonaceous chondrite. The domain sizes of the graphite were 45–110 Å. We observed shifts in the diamond peak positions to higher wave numbers with a large full width at half maximum (FWHM), especially for NWA 3140. Although the FWHM of a diamond peak is not a crucial diagnostic test for a chemical vapor deposition (CVD) origin of diamond, the shift of the diamond peaks to higher wave numbers could be a strong indicator that supports the CVD origin as these shifts have only been observed in CVD diamonds. We discuss the origin of diamond from various aspects, and confirm that the CVD model is the most plausible. We conclude that all carbon material (graphite, amorphous carbon, diamond, etc.) condensed on the early condensates in the primitive solar nebula. 相似文献
997.
Mirror mode waves in the solar wind are typically observed not as quasi-periodic sinusoidal signatures, but as trains of nonperiodic structures of two types: magnetic ??peaks?? and magnetic ??dips.?? Some trains of long durations have been called mirror mode storms. In this work we report mirror mode waves downstream of a stream interaction region (SIR) forward shock observed near 1?AU on 7?May 2007 with Solar Terrestrial Relations Observatory (STEREO) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. The high-resolution magnetic-field data (0.125-second resolution) from STEREO are scanned to search for magnetic dips and peaks (or upgoing magnetic ??mesas??) in the solar wind. STEREO-A observes a mirror mode storm: the appearance of mirror mode waves (mainly magnetic peaks and upgoing mesas) is simultaneous with the entry into a high-density, high-temperature, and high plasma ?? accompanied by a depressed field region; the magnetic dips survive in the lower plasma-?? region. STEREO-B observes mirror mode waves (mainly magnetic peaks) with different amplitudes and asymmetric forms, which can survive in a low plasma ?? region. THEMIS-D, which was located in the solar wind, also observes mirror mode waves (mainly magnetic peaks and upgoing mesas) as well as an enhanced ion temperature anisotropy (T ????3T ??). The enhanced ion temperature anisotropy and high plasma ?? satisfy the mirror-instability criterion. These observations of STEREO and THEMIS-D show that mirror mode waves can be excited downstream of a SIR forward shock near 1?AU. 相似文献
998.
999.
近年来,地磁谐波振幅比方法在国内得到较广泛的应用,并成为一种较为有效的地震预测方法。本文利用谐波振幅比方法,对2017年11月23日重庆武隆5.0级地震震中附近台站的地磁三分量数据进行计算,并分析了各台站10~60min周期谐波振幅比值异常特征。研究发现,异常台站几乎均位于震源机制解的拉张区(P波向下的区域),具有象限分布特征;异常台站NS向谐波振幅比值变化存在分层现象,短周期(浅部)的变化与长周期(深部)变化成相反相位,从电磁学机理看,浅部与深部之间存在EW向的面电流;近震中台站的异常低点时间存在由长周期(深部)向短周期(浅部)迁移的现象。 相似文献
1000.
In this article we use 1420 MHz data to demonstrate the likely reality of Galactic radio Loops V and VI. We further estimate distances and spectral indices for both these and the four main radio loops. In the cases of Loops I–IV, radio spectral indices are calculated from the mean brightnesses at 1420 and 820/404 MHz. The spectral indices of Loops V and VI are obtained from T –T plots between 1420 and 408 MHz. Using the supernova remnant (SNR) hypothesis for the origin of radio loops, distances are calculated from the surface brightnesses and the angular diameters at 1420 MHz. We also study how results for brightnesses and distances of radio loops agree with current theories of SNR evolution. For this purpose, the ambient density and initial explosion energy of the loops are discussed. We also discuss applications of different Σ–D relations. The results obtained confirm a non‐thermal origin and nearby locations for the Galactic radio loops. Therefore, we have indications that they are very old SNRs that evolve in low ambient densities, with high initial explosion energies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献