排序方式： 共有29条查询结果，搜索用时 15 毫秒
1.
2.
T. Kohout A. Kallonen J.‐P. Suuronen P. Rochette A. Hutzler J. Gattacceca D. D. Badjukov R. Skála V. Böhmová J. Čuda 《Meteoritics & planetary science》2014,49(7):1157-1170
X‐ray microtomography (XMT), X‐ray diffraction (XRD), and magnetic hysteresis measurements were used to determine micrometeorite internal structure, mineralogy, crystallography, and physical properties at μm resolution. The study samples include unmelted, partially melted (scoriaceous), and completely melted (cosmic spherules) micrometeorites. This variety not only allows comparison of the mineralogy and porosity of these three micrometeorite types but also reveals changes in meteoroid properties during atmospheric entry at various velocities. At low entry velocities, meteoroids do not melt and their physical properties do not change. The porosity of unmelted micrometeorites varies considerably (0–12%) with one friable example having porosity around 50%. At higher velocities, the range of meteoroid porosity narrows, but average porosity increases (to 16–27%) due to volatile evaporation and partial melting (scoriaceous phase). Metal distribution seems to be mostly unaffected at this stage. At even higher entry velocities, complete melting follows the scoriaceous phase. Complete melting is accompanied by metal oxidation and redistribution, loss of porosity (1 ± 1%), and narrowing of the bulk (3.2 ± 0.5 g cm?3) and grain (3.3 ± 0.5 g cm?3) density range. Melted cosmic spherules with a barred olivine structure show an oriented crystallographic structure, whereas other subtypes do not. 相似文献
3.
Corrigendum
Corrigendum 相似文献4.
Virginie Guemas David Salas-Mélia Masa Kageyama Hervé Giordani Aurore Voldoire Emilia Sanchez-Gomez 《Climate Dynamics》2010,34(4):527-546
This study aims at understanding the summer ocean-atmosphere interactions in the North Atlantic European region on intraseasonal
timescales. The CNRMOM1d ocean model is forced with ERA40 (ECMWF Re-Analysis) surface fluxes with a 1-h frequency in solar
heat flux (6 h for the other forcing fields) over the 1959–2001 period. The model has 124 vertical levels with a vertical
resolution of 1 m near the surface and 500 m at the bottom. This ocean forced experiment is used to assess the impact of the
North Atlantic weather regimes on the surface ocean. Composites of sea surface temperature (SST) anomalies associated with
each weather regime are computed and the mechanisms explaining these anomalies are investigated. Then, the SST anomalies related
to each weather regime in the ocean-forced experiment are prescribed to the ARPEGE Atmosphere General Circulation Model. We
show that the interaction with the surface ocean induces a positive feedback on the persistence of the Blocking regime, a
negative feedback on the persistence of the NAO-regime and favours the transition from the Atlantic Ridge regime to the NAO-regime
and from the Atlantic Low regime toward the Blocking regime. 相似文献
5.
Aurore E. Sibois Shailen D. Desai Willy Bertiger Bruce J. Haines 《Journal of Geodesy》2017,91(8):965-983
We present results from the generation of 10-year-long continuous time series of the Earth’s polar motion at 15-min temporal resolution using Global Positioning System ground data. From our results, we infer an overall noise level in our high-rate polar motion time series of 60 \(\upmu \hbox {as}\) (RMS). However, a spectral decomposition of our estimates indicates a noise floor of 4 \(\upmu \hbox {as}\) at periods shorter than 2 days, which enables recovery of diurnal and semidiurnal tidally induced polar motion. We deliberately place no constraints on retrograde diurnal polar motion despite its inherent ambiguity with long-period nutation. With this approach, we are able to resolve damped manifestations of the effects of the diurnal ocean tides on retrograde polar motion. As such, our approach is at least capable of discriminating between a historical background nutation model that excludes the effects of the diurnal ocean tides and modern models that include those effects. To assess the quality of our polar motion solution outside of the retrograde diurnal frequency band, we focus on its capability to recover tidally driven and non-tidal variations manifesting at the ultra-rapid (intra-daily) and rapid (characterized by periods ranging from 2 to 20 days) periods. We find that our best estimates of diurnal and semidiurnal tidally induced polar motion result from an approach that adopts, at the observation level, a reasonable background model of these effects. We also demonstrate that our high-rate polar motion estimates yield similar results to daily-resolved polar motion estimates, and therefore do not compromise the ability to resolve polar motion at periods of 2–20 days. 相似文献
6.
Uncertainty assessment of ephemeral gully identification,characteristics and topographic threshold when using aerial photographs in agricultural settings 
下载免费PDF全文
下载免费PDF全文 Alexandre Maugnard Hélène Cordonnier Aurore Degre Pierre Demarcin Nathalie Pineux Charles L. Bielders 《地球表面变化过程与地形》2014,39(10):1319-1330
Manual digitizing on aerial photographs is still commonly used for characterizing gully erosion over large areas. Even when automated detection procedures are implemented, manual digitizing is frequently being resorted to in order to constitute reference datasets used for training and validation. In both cases, manual digitizing entails some subjective decisions on behalf of the operator, which introduces uncertainty into the resulting datasets. To assess the magnitude of this uncertainty, 11 experienced operators were asked to digitize and classify ephemeral gullies (EGs) on cropland following a standardized methodology. The resulting 11 datasets were compared in terms of number, type and location of EGs. Furthermore, for EGs located on a well‐defined runoff flow concentration axis, the slope versus contributing area topographic thresholds required for initiating gully channels were assessed using four thresholding methods, and compared across the 11 datasets. The operators identified 259 different EGs. However, the number (52–139) and sum total length (8.9–23.7 km) of EGs varied widely across operators. Only 34% of the EGs were digitized by more than half of the operators, and 7% were identified by all. Identification of EGs located on a well‐defined flow concentration axis proved least subjective. The longer the EG and the more fields the EG crossed, the larger the number of operators that were able to identify it. EGs were also most easily identified when located in sugar beet fields as compared to other crops. EG classification and topographic threshold lines were also found to be strongly operator‐dependent. Quantile regression appeared to be one of the most robust thresholding methods. Operator subjectivity when digitizing EGs on orthophotographs introduces uncertainty that should be taken into account in future remote sensing‐based studies of EG erosion whenever they rely, in part or in full, on manual photograph interpretation. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
Mathieu Causse Aurore Laurendeau Matthieu Perrault John Douglas Luis Fabian Bonilla Philippe Guéguen 《Bulletin of Earthquake Engineering》2014,12(2):755-768
Nonlinear dynamic analysis of existing or planned structures often requires the use of accelerograms that match a target design spectrum. Here, our main concern is to generate a set of motions with a good level of fit to the Eurocode 8 design spectra for France. Synthetic time series are generated by means of a non-stationary stochastic method. To calibrate the input parameters in the stochastic approach, we select a reference set of accelerograms for a Eurocode 8 type B site category from the PEER Ground-Motion Database, which are then adjusted to the target spectrum through wavelet addition. Then, we compute nonlinear seismic responses of a soil column, including pore pressure effects, and brittle and ductile structures to the stochastic time-series, the natural accelerograms and time-series generated using stationary stochastic approaches. The results of these calculations reveal considerable variability in response despite the similarities in terms of spectral acceleration. 相似文献
8.
Vincent Cantreul Nathalie Pineux Gilles Swerts Charles Bielders Aurore Degré 《地球表面变化过程与地形》2020,45(6):1376-1391
Intensive agricultural practices on sensitive soils induce high erosion rates in central Belgium. Expert-rules models quantify runoff and erosion at catchment scale, avoiding over-parameterization, and can include some direct or indirect connectivity features. The aim of this article is to test the ability of an expert-based model, LandSoil, to quantify runoff and to locate erosion and sedimentation areas in a small cultivated loamy catchment in Belgium during the years 2014, 2015 and 2016. Spatialized data are important for assessing model outputs and the erosive response. Measurements of runoff and observation of spatial erosion/deposition patterns, especially around major connectivity points, permitted an assessment of the reliability of the model results. Runoff modelling gave contrasting results (good linear adjustment at the outlet of the 83 ha sub-catchment (point 1): r2 of 0.96, Nash–Sutcliffe criterion of 0.95; less good at the outlet of the 3.9 ha sub-catchment (point 2): r2 of 0.28, Nash–Sutcliffe criterion of –0.47). For point 2 the poor results are explained by the very few runoff events observed, a scaling effect and the small area with a single land use. Graduated rulers demonstrate that the model is able to provide a coherent pattern of erosion/deposition. The study highlights great sensitivity to the effect of land use, land allocation, landscape design and slope gradients. Grass strips induce deposition of eroded particles when slopes are gentle (< 2%). Woodland strips decrease connectivity by being in the stream but deposit thinner sediment layers. Field boundaries have a role in the transport, but not really the quantity, of sediments. This model validation in the Belgian loess context allows us to use LandSoil in other similar environments in order to estimate the effects of landscape management scenarios. © 2020 John Wiley & Sons, Ltd. 相似文献
9.
Numerical model simulations of sea-breeze circulations in the presence of idealized topography are subjected to dimensional
analysis in order to capture the dynamics of the sea-breeze circulation combined with an upslope-flow circulation. A secondary
objective is to reconcile previous results based on observations. The analysis is based on a scaling analysis of sea-breeze
speed, depth and volume flux. This study is motivated by the fact that the literature of sea breezes interacting with upslope
flows is generally qualitative. Results show clear scaling regimes and strong interaction between the two thermally driven
circulations. We distinguish three regimes, depending on slope length, slope angle, stability and surface heat flux. The first
and third regimes obey the scaling laws of pure sea-breeze scaling. The second regime shows a significant decrease in the
scaled volume flux relative to pure sea-breeze scaling. Dynamical relations in the second regime show a strong influence on
the circulation of upslope stable air advection. 相似文献
10.