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排序方式: 共有163条查询结果,搜索用时 15 毫秒
91.
F. RIIS E. KALLESON H. DYPVIK S. O. KRØGLI O. NILSEN 《Meteoritics & planetary science》2011,46(5):748-761
Abstract– The Ritland structure is a newly discovered impact structure, which is located in southwestern Norway. The structure is the remnant of a simple crater 2.5 km in diameter and 350 m deep, which was excavated in Precambrian gneissic rocks. The crater was filled by sediments in Cambrian times and covered by thrust nappes of the Caledonian orogen in the Silurian–Devonian. Several succeeding events of uplift, erosion, and finally the Pleistocene glaciations, disclosed this well‐preserved structure. The erosion has exposed brecciated rocks of the original crater floor overlain by a thin layer of melt‐bearing rocks and postimpact crater‐filling breccias, sandstones, and shales. Quartz grains with planar deformation features occur frequently within the melt‐bearing unit, confirming the impact origin of the structure. The good exposures of infilling sediments have allowed a detailed reconstruction of the original crater morphology and its infilling history based on geological field mapping. 相似文献
92.
M. D. Reed D. M. Terndrup R. Østensen S. Geier J. Gilker P. G. Beck P. Degroote J. Vanautgaerden C. Waelkens 《Astrophysics and Space Science》2010,328(1-2):83-86
During our campaign of acquiring follow-up photometric data to resolve short period pulsating sdB (EC14026 or V361 Hya) stars, we obtained data on the known pulsator KUV 04421+1416 and discovered that it is also in a reflection-effect binary. Here we present preliminary results of the pulsation analysis and provide some constraints on the companion, which is most likely an MV star. This makes KUV 04421+1416 only the second known system with an EC14026-type pulsator in a reflection-effect binary. 相似文献
93.
Kristian Vasskog Øyvind Paasche Atle Nesje John F. Boyle H.J.B. Birks 《Quaternary Research》2012,77(1):192-204
We explore the possibility of building a continuous glacier reconstruction by analyzing the integrated sedimentary response of a large (440 km2) glacierized catchment in western Norway, as recorded in the downstream lake Nerfloen (N61°56’, E6°52’). A multi-proxy numerical analysis demonstrates that it is possible to distinguish a glacier component in the ~ 8000-yr-long record, based on distinct changes in grain size, geochemistry, and magnetic composition. Principal Component Analysis (PCA) reveals a strong common signal in the 15 investigated sedimentary parameters, with the first principal component explaining 77% of the total variability. This signal is interpreted to reflect glacier activity in the upstream catchment, an interpretation that is independently tested through a mineral magnetic provenance analysis of catchment samples. Minimum glacier input is indicated between 6700–5700 cal yr BP, probably reflecting a situation when most glaciers in the catchment had melted away, whereas the highest glacier activity is observed around 600 and 200 cal yr BP. During the local Neoglacial interval (~ 4200 cal yr BP until present), five individual periods of significantly reduced glacier extent are identified at ~ 3400, 3000–2700, 2100–2000, 1700–1500, and ~ 900 cal yr BP. 相似文献
94.
Elizabeth M. Green Keith Callerame Ivo R. Seitenzahl Brooke A. White Elaina A. Hyde Melissa Giovanni Mike Reed Gilles Fontaine Roy Østensen 《Astrophysics and Space Science》2003,284(1):65-68
During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, weserendipitously discovered a new class of multimode pulsators withperiods of the order of an hour. These periods are a factor of tenlonger than those of previously known multimode sdB pulsators (EC14026 stars), implying the new pulsations are due to gravity modes rather than pressure modes. The iron opacity instability that drives the short period EC 14026 stars is effective in hot sdB's. Thelong period pulsators are found only among cooler sdB stars, wherethey are surprisingly common. The mechanism responsible for excitingthe deeper g-modes in cool sdB's is currently unknown, but thetemperature and gravity range in which these stars occur must be animportant clue. We present the first observational results for thisnew class of pulsating sdB stars, and discuss some possible implications. 相似文献
95.
96.
Trond Reitan Asgeir Petersen-Øverleir 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(6):445-453
Practical application of the power-law regression model with an unknown location parameter can be plagued by non-finite least squares parameter estimates. This presents a serious problem in hydrology, since stream flow data is mainly obtained using an estimated stage–discharge power-law rating curve. This study provides a set of sufficient requirements for the data to ensure the existence of finite least squares parameter estimates for a power-law regression with an unknown location parameter. It is shown that in practice, these requirements act as necessary for having a finite least squares solution, in most cases. Furthermore, it is proved that there is a finite probability for the model to produce data having non-finite least squares parameter estimates. The implications of this result are discussed in the context of asymptotic predictions, inference and experimental design. A Bayesian approach to the actual regression problem is recommended. 相似文献
97.
98.
99.
Sensitivity of simulated wintertime Arctic atmosphere to vertical resolution in the ARPEGE/IFS model
The current state-of-the-art general circulation models, including several of those used by the IPCC, show considerable biases
in the simulated present day high-latitude climate compared to observations and reanalysis data. These biases are most pronounced
during the winter season. We here employ ideal vertical profiles of temperature and wind from turbulence-resolving simulations
to perform a priori studies of the first-order eddy-viscosity closure scheme employed in the ARPEGE/IFS model. This reveals
that the coarse vertical resolution (31 layers) of the model cannot be expected to realistically resolve the Arctic stable
boundary layer. The curvature of the Arctic inversion and thus also the vertical turbulent-exchange processes cannot be reproduced
by the coarse vertical mesh employed. To investigate how turbulent vertical exchange processes in the Arctic boundary layer
are represented by the model parameterization, a simulation with high vertical resolution (90 layers in total) in the lower
troposphere is performed. Results from the model simulations are validated against data from the ERA-40 reanalysis. The dependence
of the surface air temperature on surface winds, surface energy fluxes, free atmosphere stability and boundary layer height
is investigated. The coarse-resolution run reveals considerable biases in these parameters, and in their physical relations
to surface air temperature. In the simulation with fine vertical resolution, these biases are clearly reduced. The physical
relation between governing parameters for the vertical turbulent-exchange processes improves in comparison with ERA-40 data. 相似文献
100.
Inversion of inline and broadside marine controlled‐source electromagnetic data with constraints derived from seismic data 下载免费PDF全文
Torgeir Wiik Janniche Irén Nordskag Eirik Øverland Dischler Anh Kiet Nguyen 《Geophysical Prospecting》2015,63(6):1371-1382
We present a structural smoothing regularization scheme in the context of inversion of marine controlled‐source electromagnetic data. The regularizing hypothesis is that the electrical parameters have a structure similar to that of the elastic parameters observed from seismic data. The regularization is split into three steps. First, we ensure that our inversion grid conforms with the geometry derived from seismic. Second, we use a seismic stratigraphic attribute to define a spatially varying regularization strength. Third, we use an indexing strategy on the inversion grid to define smoothing along the seismic geometry. Enforcing such regularization in the inversion will encourage an inversion result that is more intuitive for the interpreter to deal with. However, the interpreter should also be aware of the bias introduced by using seismic data for regularization. We illustrate the method using one synthetic example and one field data example. The results show how the regularization works and that it clearly enforces the structure derived from seismic data. From the field data example we find that the inversion result improves when the structural smoothing regularization is employed. Including the broadside data improves the inversion results even more, due to a better balancing between the sensitivities for the horizontal and vertical resistivities. 相似文献