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1.
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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Changes in streamflow and water table elevation influence oxidation–reduction (redox) conditions near river–aquifer interfaces, with potentially important consequences for solute fluxes and biogeochemical reaction rates. Although continuous measurements of groundwater chemistry can be arduous, in situ sensors reveal chemistry dynamics across a wide range of timescales. We monitored redox potential in an aquifer adjacent to a tidal river and used spectral and wavelet analyses to link redox responses to hydrologic perturbations within the bed and banks. Storms perturb redox potential within both the bed and banks over timescales of days to weeks. Tides drive semidiurnal oscillations in redox potential within the streambed that are absent in the banks. Wavelet analysis shows that tidal redox oscillations in the bed are greatest during late summer (wavelet magnitude of 5.62 mV) when river stage fluctuations are on the order of 70 cm and microbial activity is relatively high. Tidal redox oscillations diminish during the winter (wavelet magnitude of 2.73 mV) when river stage fluctuations are smaller (on the order of 50 cm) and microbial activity is presumably low. Although traditional geochemical observations are often limited to summer baseflow conditions, in situ redox sensing provides continuous, high‐resolution chemical characterization of the subsurface, revealing transport and reaction processes across spatial and temporal scales in aquifers. 相似文献
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Jrme Gattacceca Francis M. Mccubbin Audrey Bouvier Jeffrey Grossman 《Meteoritics & planetary science》2020,55(2):460-462
Meteoritical Bulletin 107 contains 2714 meteorites including 16 falls (Aba Panu, Ablaketka, Andila, Gueltat Zemmour, Hamburg, Karimati, Mahbas Arraid, Mangui, Mazichuan, Mukundpura, Ozerki, Parauapebas, Renchen, San Pedro de Urabá, Sokoto, Tintigny), with 2226 ordinary chondrites, 168 HED achondrites, 132 carbonaceous chondrites (including 41 CM, 34 CV, 26 CO, 21 CK, 4 CR, 5 ungrouped), 43 ureilites, 30 iron meteorites (including 2 ungrouped), 29 lunar meteorites, 22 Martian meteorites, 16 primitive achondrites (including 3 brachinites), 12 Rumuruti chondrites, 9 enstatite chondrites, 7 ungrouped achondrites, 6 pallasites, 5 mesosiderites, 3 enstatite achondrites, 3 ungrouped chondrites, and 2 angrites. 1569 meteorites are from Antarctica, 835 from Africa, 206 from South America, 62 from Asia, 21 from North America, 11 from unknown locations, 8 from Europe (including one from Russia), and 1 from Oceania. 相似文献
4.
Chronology and stratigraphy of the Magdalen Islands archipelago from the last glaciation to the early Holocene: new insights into the glacial and sea‐level history of eastern Canada 下载免费PDF全文
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Bidong Zhang Yangting Lin Jialong Hao Devin L. Schrader Meenakshi Wadhwa Randy L. Korotev William K. Hartmann Audrey Bouvier 《Meteoritics & planetary science》2023,58(10):1540-1551
About half of the lunar meteorites in our collections are feldspathic breccias. Acquiring geochronologic information from these breccias is challenging due to their low radioactive-element contents and their often polymict nature. We used high-spatial-resolution (5 μm) NanoSIMS (nanoscale secondary ion mass spectrometry) U-Pb dating technique to date micro-zircons in the lunar feldspathic meteorites Dhofar 1528 and Dhofar 1627. Three NanoSIMS dating spots of two zircon grains from Dhofar 1528 show a discordia with an upper intercept at 4354 ± 76 Ma and a lower intercept at 332 ± 1407 Ma (2σ, MSWD = 0.01, p = 0.91). Three spots of two zircon grains in Dhofar 1627 define a discordia with an upper intercept at 3948 ± 30 Ma and a lower intercept at 691 ± 831 Ma (2σ, MSWD = 0.40, p = 0.53). Both samples likely experienced shock metamorphism caused by impacts. Based on the clastic nature, lack of recrystallization and the consistent U-Pb and Pb-Pb dates of the zircons in Dhofar 1528, the U-Pb date of 4354 Ma is interpreted as the crystallization age of its Mg-suite igneous precursor. Some of the Dhofar 1627 zircons show poikilitic texture, a crystallization from the matrix impact melt, so the U-Pb date of 3948 Ma corresponds to an impact event, likely the Imbrium basin-forming event. These data are the first radiometric ages for these two meteorites and demonstrate that in situ (high spatial resolution) U-Pb dating has potential for extracting geochronological information about igneous activities and impact events from lunar feldspathic and polymict breccias. 相似文献
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Water is an invaluable resource, and equitable access to it is a fundamental human right. Disenfranchised groups often lose access to water resources because their interests are not well represented by decision makers. Excluding these groups from resource management policy often results in myopic decisions that contribute to further ecosystem damage. We describe the ecological degradation of Lake Urmia in Iran, which has recently experienced increased salinity and declining water quantity. The lake is a UNESCO Biosphere Reserve and Ramsar site, and supports unique biodiversity in the region. The lake's decline is driven by the destruction of Zagros forests and the government's water policies, which diverted water to more politically connected agricultural land users, increasing social inequity and prompting more deforestation. The most straightforward restoration solution is to discontinue the diversions and allow critical inflows to recharge Lake Urmia, preserving the lake and wetlands for migratory birds, tourists, and local communities. 相似文献
9.
Models of the collapse of a protostellar cloud and the formation of the solar nebula reveal that the size of the nebula produced will be the larger of (where J, M, and cs are the total angular momentum, total mass, and sound speed of the protosetellar material; G is the gravitational constant; k is a number of order unity; and v is the effective viscosity in the nebula). From this result it can be deduced that low-mass nebulas are produced if P ≡ (RV/RCF)2 ? 1; “massive” nebulas result if P ? 1. Gravitational instabilities are expected to be important for the evolution of P ? 1 nebulas. The value of J distinguishes most current models of the solar nebula, since P ∝ J?4. Analytic expressions for the surface density, nebular mass flux, and photospheric temperature distributions during the formation stage are presented for some simple models that illustrate the general properties of growing protostellar disks. It does not yet seem possible to rule out either P ? 1 or P < 1 for the solar nebula, but observed or possible heterogeneities in composition and angular-momentum orientation favor P < 1 models. 相似文献
10.
The photometric method detects planets orbiting other stars by searching for the reduction in the light flux or the change in the color of the stellar flux that occurs when a planet transits a star. A transit by Jupiter or Saturn would reduce the stellar flux by approximately 1% while a transit by Uranus or Neptune would reduce the stellar flux by 0.1%. A highly characteristic color change with an amplitude approximately 0.1 of that for the flux reduction would also accompany the transit and could be used to verify that the source of the flux reduction was a planetary transit rather than some other phenomenon. Although the precision required to detect major planets is already available with state-of-the-art photometers, the detection of terrestrial-sized planets would require a precision substantially greater than the state-of-the-art and a spaceborne platform to avoid the effects of variations in sky transparency and scintillation. Because the probability is so small of observing a planetary transit during a single observation of a randomly chosen star, the search program must be designed to continuously monitor hundreds or thousands of stars. The most promising approach is to search for large planets with a photometric system that has a single-measurement precision of 0.1%. If it is assumed that large planets will have long-period orbits, and that each star has an average of one large planet, then approximately 104 stars must be monitored continuously. To monitor such a large groups of stars simultaneously while maintaining the required photometric precision, a detector array coupled by a fiber-optic bundle to the focal plane of a moderate aperture (≈ 1 m), wide field of view (≈50°) telescope is required. Based on the stated assumptions, a detection rate of one planet per year of observation appears possible. 相似文献