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91.
92.
Jean-Alix Barrat Akira Yamaguchi Richard C. Greenwood Claire Bollinger Marcel Bohn Ian A. Franchi 《Geochimica et cosmochimica acta》2009,73(19):5944-5958
The howardite–eucrite–diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired.The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body. 相似文献
93.
Bačík Peter Dikej Jakub Fridrichová Jana Miglierini Marcel Števko Martin 《Mineralogy and Petrology》2017,111(4):609-624
Mineralogy and Petrology - Tourmaline-supergroup minerals are common gangue minerals in Sb-hydrothermal veins on Betliar – Straková, Čučma – Gabriela and... 相似文献
94.
Studying the winter survival of forage grasses under a changing climate requires models that can simulate the dynamics of soil conditions at low temperatures. We developed a simple model that simulates depth of snow cover, the lower frost boundary of the soil and the freezing of surface puddles. We calibrated the model against independent data from four locations in Norway, capturing climatic variation from south to north (Arctic) and from coastal to inland areas. We parameterized the model by means of Bayesian calibration, and identified the least important model parameters using the sensitivity analysis method of Morris. Verification of the model suggests that the results are reasonable. Because of the simple model structure, some overestimation occurs in snow and frost depth. Both the calibration and the sensitivity analysis suggested that the snow cover module could be simplified with respect to snowmelt and liquid water content. The soil frost module should be kept unchanged, whereas the surface ice module should be changed when more detailed topographical data become available, such as better estimates of the fraction of the land area where puddles may form. 相似文献
95.
Marcel Kornfeld George C. Frison Mary Lou Larson James C. Miller Jan Saysette 《Geoarchaeology》1999,14(7):655-674
The Upper Twin Mountain Site, located within a geologic slump scar at 2548 m altitude, provides significant information on Paleoindian bison procurement. As the highest known Paleoindian bison bone bed, the site contained the partial skeletal remains of at least 15 adult Late Pleistocene bison (B. antiquus), Goshen projectile points, and debitage. Radiocarbon dates of 10,240±70 and 10,470±50 yr B.P. place Upper Twin Mountain midway between the northern Plains Goshen and southern Plains Plainview sites. With a late fall or early winter mortality of the bison and the presence of only local stone, year round occupation of Middle Park is indicated. Analysis of the geology, soil, and pollen, from the archaeological and nonarchaeological deposits at the Upper Twin Mountain and elsewhere in the region are used to describe the paleoenvironmental conditions in Middle Park. © 1999 John Wiley & Sons, Inc. 相似文献
96.
Marcel Liedermann Philipp Gmeiner Andrea Kreisler Michael Tritthart Helmut Habersack 《地球表面变化过程与地形》2018,43(2):514-523
A comprehensive monitoring programme focusing on bedload transport behaviour was conducted at a large gravel‐bed river. Innovative monitoring strategies were developed during five years of preconstruction observations accompanying a restoration project. A bedload basket sampler was used to perform 55 cross‐sectional measurements, which cover the entire water discharge spectrum from a 200‐year flood event in 2013 to a rare low flow event. The monitoring activities provide essential knowledge regarding bedload transport processes in large rivers. We have identified the initiation of motion under low flow conditions and a decrease in the rate of bedload discharge with increasing water discharge around bankfull conditions. Bedload flux strongly increases again during high flood events when the entire inundation area is flooded. No bedload hysteresis was observed. The effective discharge for bedload transport was determined to be near mean flow conditions, which is therefore at a lower flow discharge than expected. A numerical sediment transport model was able to reproduce the measured sediment transport patterns. The unique dataset enables the characterisation of bedload transport patterns in a large and regulated gravel‐bed river, evaluation of modern river engineering measures on the Danube, and, as a pilot project has recently been under construction, is able to address ongoing river bed incision, unsatisfactory ecological conditions for the adjacent national park and insufficient water depths for inland navigation. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
97.
Marcel J. M. Reichert 《Journal of Sea Research》1998,40(3-4)
Fringed flounder, Etropus crossotus, a small flatfish common along the southeastern coast of the US, were collected along the South Carolina coast in the fall of 1992, and in the North Inlet estuary from August 1992 until July 1994. Standard length was 82% of total length and the relationship between standard length and wet weight showed near-isometric growth with no significant differences between males and females. Dry weight was 21% of wet weight and ash-free dry weight 14% of wet weight with no significant differences between sexes. Daily increments in the sagittal otoliths were used for age determination. No annual structures could be identified. The maximum age was about 14.5 months. Age-at-length was not different between the sexes. The relationship between age and length was exponential, with age (in days) equalling an e power of 4.242 + 0.135 × standard length (in cm). Back-calculated hatch dates and catches of early juveniles indicated a spawning season that lasted from March to October. Females started to be sexually mature at 7 to 7.5 cm standard length, but 50% maturity was reached at 8 to 8.5 cm. Females could grow to that size within one spawning season. Individuals hatched early in the spawning season could produce eggs in the latter portion of that season's spawning period. 相似文献
98.
A new process-based approach is introduced for a more efficient computation of the overflow-induced growth of an erosional channel in a non-cohesive homogeneous narrow landmass such as the breach growth in a sand-dike. The approach is easy to incorporate in a 1D/2DV morphodynamic model to compute the channel growth both vertically and laterally. 相似文献
99.
100.
The present paper extends the analysis by Sakurai, Goossens, and Hollweg (1991) on resonant Alfvén waves in nonuniform magnetic flux tubes. It proves that the fundamental conservation law for resonant Alfvén waves found in ideal MHD by Sakurai, Goossens, and Hollweg remains valid in dissipative MHD. This guarantees that the jump conditions of Sakurai, Goossens, and Hollweg, that connect the ideal MHD solutions for
r
, andP across the dissipative layer, are correct. In addition, the present paper replaces the complicated dissipative MHD solutions obtained by Sakurai, Goossens, and Hollweg for
r
, andP in terms of double integrals of Hankel functions of complex argument of order
with compact analytical solutions that allow a straightforward mathematical and physical interpretation. Finally, it presents an analytical dissipative MHD solution for the component of the Lagrangian displacement in the magnetic surfaces perpendicular to the magnetic field lines which enables us to determine the dominant dynamics of resonant Alfvén waves in dissipative MHD. 相似文献