The presolar grain inventory of fine‐grained chondrule rims in the Mighei‐type (CM) chondrites     

Jan Leitner  Knut Metzler  Christian Vollmer  Christine Floss  Pierre Haenecour  Jnos Kodolnyi  Dennis Harries  Peter Hoppe 《Meteoritics & planetary science》2020,55(6):1176-1206

We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine‐grained chondrule rims in six Mighei‐type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM‐related carbonaceous chondrite Sutter's Mill. Sixteen O‐anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix‐normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O‐rich grains are enriched in ¹⁷O, and could originate from low‐mass asymptotic giant branch stars. One grain is enriched in ¹⁷O and significantly depleted in ¹⁸O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core‐collapse supernova origin showing enhanced ¹⁸O/¹⁶O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O‐anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O‐rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe‐rich silicates, one forsterite‐like Mg‐rich silicate, two Al‐oxides with spinel‐like compositions, and one Fe‐(Mg‐)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (Ca₂Mg[Si₂O₇]) or a an åkermanite‐diopside (MgCaSi₂O₆) intergrowth.  相似文献   

Characteristics of surface ozone in Agra,a sub-urban site in Indo-Gangetic Plain     

Nidhi Verma  Aparna Satsangi  Anita Lakhani  K Maharaj Kumari 《Journal of Earth System Science》2018,127(3):42

In the present study, measurements of surface ozone (\(\hbox {O}_{3}\)) and its precursors (NO and \(\hbox {NO}_{2}\)) were carried out at a sub-urban site of Agra (\(27{^{\circ }}10'\hbox {N}\), \(78{^{\circ }}05'\hbox {E}\)), India during May 2012–May 2013. During the study period, average concentrations of \(\hbox {O}_{3}\), NO, and \(\hbox {NO}_{2}\) were \(39.6 \pm 25.3\), \(0.8 \pm 0.8\) and \(9.1 \pm 6.6 \, \hbox {ppb}\), respectively. \(\hbox {O}_{3}\) showed distinct seasonal variation in peak value of diurnal variation: summer \({>}\) post-monsoon \({>}\) winter \({>}\) monsoon. However, \(\hbox {NO}_{2}\) showed highest levels in winter and lowest in monsoon. The average positive rate of change of \(\hbox {O}_{3}\) (08:00–11:00 hr) was highest in April (16.3 ppb/hr) and lowest in August (1.1 ppb/hr), while average negative rate of change of \(\hbox {O}_{3}\) (17:00–19:00 hr) was highest in December (–13.2 ppb/hr) and lowest in July (–1.1 ppb/hr). An attempt was made to identify the \(\hbox {VOC--NO}_{\mathrm{x}}\) sensitivity of the site using \(\hbox {O}_{3}/\hbox {HNO}_{3}\) ratio as photochemical indicator. Most of the days this ratio was above the threshold value (12–16), which suggests \(\hbox {NO}_{\mathrm{x}}\) sensitivity of the site. The episodic event of ozone was characterized through meteorological parameters and precursors concentration. Fine particles (\(\hbox {PM}_{2.5}\)) cause loss of ozone through heterogeneous reactions on their surface and reduction in solar radiation. In the study, statistical analyses were used to estimate the amount of ozone loss.  相似文献   

Piping dynamics in mid‐altitude mountains under a temperate climate: Bieszczady Mountains,eastern Carpathians          下载免费PDF全文

Anita Bernatek‐Jakiel  Michał Jakiel  Kazimierz Krzemień 《地球表面变化过程与地形》2017,42(9):1419-1433

Piping has been recognized as an important geomorphic, soil erosion and hydrologic process. It seems that it is far more widespread than it has often been supposed. However, our knowledge about piping dynamics and its quantification currently relies on a limited number of data for mainly loess‐derived areas and marl badlands. Therefore, this research aimed to recognize piping dynamics in mid‐altitude mountains under a temperate climate, where piping occurs in Cambisols, not previously considered as piping‐prone soils. It has been expressed by the estimation of erosion rates due to piping and elongation of pipes in the Bere?nica Wy?na catchment in the Bieszczady Mountains, eastern Carpathians (305 ha, 188 collapsed pipes). The research was based on the monitoring of selected piping systems (1971–1974, 2013–2016). Changes in soil loss vary significantly between different years (up to 27.36 t ha^?1 yr^?1), as well as between the mean short‐term erosion rate (up to 13.10 t ha^?1 yr^?1), and the long‐term (45 years) mean of 1.34 t ha^?1 yr^?1. The elongation of pipes also differs, from no changes to 36 m during one year. The mean total soil loss is 48.8 t ha^?1 in plots, whereas in the whole studied catchment it is 2.0 t ha^?1. Hence, piping is both spatially and temporally dependent. The magnitude of piping in the study area is at least three orders of magnitude higher than surface erosion rates (i.e. sheet and rill erosion) under similar land use (grasslands), and it is comparable to the magnitude of surface soil erosion on arable lands. It means that piping constitutes a significant environmental problem and, wherever it occurs, it is an important, or even the main, sediment source. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Best practices for the use of meteorite names in publications     

Philipp R. Heck  Christopher Herd  Jeffrey N. Grossman  Dmitry Badjukov  Audrey Bouvier  Emma Bullock  Hasnaa Chennaoui‐Aoudjehane  Vinciane Debaille  Tasha L. Dunn  Denton S. Ebel  Ludovic Ferrire  Laurence Garvie  Jrme Gattacceca  Matthieu Gounelle  Richard Herd  Trevor Ireland  Emmanuel Jacquet  Robert J. Macke  Tim McCoy  Francis M. McCubbin  Takashi Mikouchi  Knut Metzler  Mathieu Roskosz  Caroline Smith  Meenakshi Wadhwa  Linda Welzenbach‐Fries  Toru Yada  Akira Yamaguchi  Ryan A. Zeigler  Michael Zolensky 《Meteoritics & planetary science》2019,54(7):1397-1400

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The Allende multicompound chondrule (ACC)—Chondrule formation in a local super‐dense region of the early solar system          下载免费PDF全文

Addi Bischoff  Gerhard Wurm  Marc Chaussidon  Marian Horstmann  Knut Metzler  Mona Weyrauch  Julia Weinauer 《Meteoritics & planetary science》2017,52(5):906-924

In Allende, a very complex compound chondrule (Allende compound chondrule; ACC) was found consisting of at least 16 subchondrules (14 siblings and 2 independents). Its overall texture can roughly be described as a barred olivine object (BO). The BO texture is similar in all siblings, but does not exist in the two independents, which appear as relatively compact olivine‐rich units. Because of secondary alteration of pristine Allende components and the ACC in particular, only limited predictions can be made concerning the original compositions of the colliding melt droplets. Based on textural and mineralogical characteristics, the siblings must have been formed on a very short time scale in a dense, local environment. This is also supported by oxygen isotope systematics showing similar compositions for all 16 subchondrules. Furthermore, the ACC subchondrules are isotopically distinct from typical Allende chondrules, indicating formation in or reaction with a more ¹⁶O‐poor reservoir. We modeled constraints on the particle density required at the ACC formation location, using textural, mineral‐chemical, and isotopic observations on this multicompound chondrule to define melt droplet collision conditions. In this context, we discuss the possible relationship between the formation of complex chondrules and the formation of macrochondrules and cluster chondrites. While macrochondrules may have formed under similar or related conditions as complex chondrules, cluster chondrites certainly require different formation conditions. Cluster chondrites represent a mixture of viscously deformed, seemingly young chondrules of different chemical and textural types and a population of older chondrules. Concerning the formation of ACC calculations suggest the existence of very local, kilometer‐sized, and super‐dense chondrule‐forming regions with extremely high solid‐to‐gas mass ratios of 1000 or more.  相似文献   

Neon produced by solar cosmic rays in ordinary chondrites   总被引：1，自引：0，他引：1       下载免费PDF全文

Antoine S. G. Roth  Reto Trappitsch  Knut Metzler  Beda A. Hofmann  Ingo Leya 《Meteoritics & planetary science》2017,52(6):1155-1172

Solar‐cosmic‐ray‐produced Ne (SCR‐Ne), in the form of low cosmogenic ²¹Ne/²²Ne ratios (²¹Ne/²²Ne_cos <0.8), is more likely to be found in rare meteorite classes, like Martian meteorites, than in ordinary chondrites. This may be the result of a sampling bias: SCR‐Ne is better preserved in meteorites with small preatmospheric radii and these specimens are often only studied if they belong to unusual or rare classes. We measured He and Ne isotopic concentrations and nuclear tracks in 25 small unpaired ordinary chondrites from Oman. Most chondrites have been intensively heated during atmospheric entry as evidenced by the disturbed track records, the low ³He/²¹Ne ratios, the low ⁴He concentrations, and the high peak release temperatures. Concentration depth profiles indicate significant degassing; however, the Ne isotopes are mainly undisturbed. Remarkably, six chondrites have low ²¹Ne/²²Ne_cos in the range 0.711–0.805. Using a new physical model for the calculation of SCR production rates, we show that four of the chondrites contain up to ~20% of SCR‐Ne; they are analyzed in terms of preatmospheric sizes, cosmic ray exposure ages, mass ablation losses, and orbits. We conclude that SCR‐Ne is preserved, regardless of the meteorite class, in specimens with small preatmospheric radii. Sampling bias explains the predominance of SCR‐Ne in rare meteorites, although we cannot exclude that SCR‐Ne is more common in Martian meteorites than it is in small ordinary chondrites.  相似文献   

Protracted storage of CR chondrules in a region of the disk transparent to galactic cosmic rays          下载免费PDF全文

Antoine S. G. Roth  Knut Metzler  Lukas P. Baumgartner  Beda A. Hofmann  Ingo Leya 《Meteoritics & planetary science》2017,52(10):2166-2177

Renazzo‐type carbonaceous (CR) chondrites are accretionary breccias that formed last. As such they are ideal samples to study precompaction exposures to cosmic rays. Here, we present noble gas data for 24 chondrules and 3 dark inclusion samples (DIs) from Shi?r 033 (CR2). The meteorite was selected based on the absence of implanted solar wind noble gases and an anomalous oxygen isotopic composition of the DIs; the oxygen isotopes match those in CV3 and CO3 chondrites. Our samples contain variable mixtures of galactic cosmic ray (GCR)‐produced cosmogenic noble gases and trapped noble gases of presolar origin. Remarkably, all chondrules have cosmogenic ³He and ²¹Ne concentrations up to 4.3 and 7.1 times higher than the DIs, respectively. We derived an average ³He‐²¹Ne cosmic ray exposure (CRE) age for Shi?r 033 of 2.03 ± 0.20 Ma (2 SD) and excesses in cosmogenic ³He and ²¹Ne in chondrules (relative to the DIs) in the range (in 10^?8 cm³STP/g) 3.99–7.76 and 0.94–1.71, respectively. Assuming present‐day GCR flux density, the excesses translate into average precompaction ³He‐²¹Ne CRE ages of 3.1–27.3 Ma depending on the exposure geometry. The data can be interpreted assuming a protracted storage of a single chondrule generation prior to the final assembly of the Shi?r 033 parent body in a region of the disk transparent to GCRs.  相似文献   

Measuring long-run economic effects of natural hazard     

Robert McComb  Young-Kyu Moh  Anita R. Schiller 《Natural Hazards》2011,58(1):559-566

This paper studies the long-run economic effects of severe weather on regional economies. A catastrophic event, such as a hurricane, will have an effect on both the directly impacted region and adjacent regions. With dramatically increasing damage from catastrophic weather events over the past few decades, comprehensive assessment of the long-run economic impact of natural disasters across the broader region becomes more important than ever for planning for post-disaster recovery. We estimate the long-run effect of Hurricane Katrina on the unemployment rate of Houston, TX by employing time-series and fixed-effect models. Using Dallas as a control, we find that Katrina is associated with a higher long-run unemployment rate in Houston than would otherwise have been expected. This implies that the hurricane-generated adverse relative effects on Houston. Our findings suggest that areas that are geographically proximate to the directly impacted region can sustain lasting negative economic consequences.  相似文献   

Professionalization of the shipping industry via postgraduate education     

Adolf K.Y. Ng  Anita C. Koo  Athanasios A. Pallis 《Ocean & Coastal Management》2011,54(5):364-373

The paper investigates the roles and nature of postgraduate education on the professionalization of the shipping industry. The recent growth of postgraduate education is marked by the massive expansion of professional programmes on disciplines which traditionally emphasized non-academic, apprentice-style learning approach, including shipping business and management. The reasons behind such growth of demands, however, have remained scarce and empirically under-researched. Understanding this deficiency, in this study, we have undertaken a questionnaire survey completed by students/graduates who are pursuing/have recently pursued masters' programmes in shipping-related business and management offered by six Asian and European universities. Specifically, we analyze student motivations, considerations, and sources of information before enrolling such programmes, the extent that the shipping industry or other forces act as driving forces towards such enrollment, as well as students' evaluation of the postgraduate programmes that they are pursing/have pursued. Integrated in these discussions are comparative analyses of the data provided by different student groups based on their professional experiences and cultural backgrounds. We believe that this study has provided the lacking empirical inputs essential for achieving the sustainable development of postgraduate education in shipping business and management.  相似文献   

The chemical characterization of the thermal waters in Budapest,Hungary by using multivariate exploratory techniques     

Judit Déri-Takács  Anita Erőss  József Kovács 《Environmental Earth Sciences》2015,74(12):7475-7486

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