Rock thermal data at the grain scale: applicability to granular disintegration in cold environments     

Kevin Hall  Marie‐Franoise Andr 《地球表面变化过程与地形》2003,28(8):823-836

Consideration of the mechanisms associated with the granular disintegration of rock has been limited by available data. In most instances, both the size of the transducer and the nature of the study have negated any applicability of the resulting data to the understanding of grain‐to‐grain separation within rock. The application of microthermocouples (≤0·15 mm diameter) and high‐frequency logging (20 s intervals) at a taffoni site on southern Alexander Island and from a rock outcrop on Adelaide Island (Antarctica) provide new data pertaining to the thermal conditions, at the grain scale, of the rock surface. The results show that thermal changes (ΔT/t) can be very high, with values of 22 °C min^?1 being recorded. Although available data indicate that there can be differences in frequency and magnitude of ?uctuations as a function of aspect, all aspects experienced some large magnitude (≥2 °C min^?1) ?uctuations. Further, in many instances, large thermal changes in more than one direction could occur within 1 min or in subsequent minutes. These data suggest that the surface grains experience rapidly changing stress ?elds that may, with time, effect fatigue at the grain boundaries; albedo differences between grains and the resulting thermal variations are thought to exacerbate this. The available data failed to show any indication of water freezing (an exotherm) and thus it is suggested that microgelivation may not play as large a role in granular breakdown as is often postulated for cold regions, and that in this dry, Antarctic region thermal stress may play a signi?cant role. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Estimating monthly surface winds for Scania, southern Sweden, using geostrophic wind (1899–1997)     

Marie Ekström 《Geografiska Annaler: Series A, Physical Geography》2002,84(2):113-126

Wind direction conditions during the 20th century in Scania, southern Sweden, are investigated using an estimated series of monthly wind vector components (east–west u component and north–south v component). The series is developed from a regression relationship between pairwise (1973 to 1997) monthly averages of 10–m surface wind from Scania and a monthly geostrophic wind, based on mean sea level (MSL) pressure data from the National Center of Atmospheric Research (NCAR). The wind conditions during the 20th century are dominated by winds from southwesterly and westerly directions, particularly during summer and autumn. From the 1980s onwards, increased frequencies of westerly winds are evident in spring and summer; however, similarly large frequencies of westerly winds are also found during the early part of the 20th century. Analysis of the estimated wind series indicates large variation in wind direction during the investigated time period, particularly during 1930 to 1960 when large increases of easterly winds are evident in spring. Increased frequencies of easterly winds were also found in other months during this period but not to the same extent as during the spring season. Thus, the presence of periods with quite different wind characteristics suggests that the overall atmospheric circulation has experienced some shifts in this region during the 20th century.  相似文献   

Locating a Community Recycling Center within a Residential Area: A Belgian Case Study     

Benoît Flahaut  Marie‐Alexandre Laurent  Isabelle Thomas 《The Professional geographer》2002,54(1):67-82

This article demonstrates the operation of a simple optimal location‐allocation technique for solving the problem of locating one or several community recycling center(s) within a residential area. The article attempts to measure both transportation and externality costs in comparable units, and to incorporate them into the model. A sensitivity analysis of the results at the level of the nuisance provides further insight into the operation of the model and the relative importance of the quantification of pollution in applied location‐allocation problems.  相似文献   

Vertical accuracy evaluation of freely available latest high-resolution (30 m) global digital elevation models over Cameroon (Central Africa) with GPS/leveling ground control points.     

Loudi Yap  Ludovic Houetchak Kandé  Robert Nouayou  Nasser Abdou Ngouh  Marie Brigitte Makuate 《International Journal of Digital Earth》2019,12(5):500-524

Digital Elevation Models (DEMs) contain topographic relief data that are vital for many geoscience applications. This study relies on the vertical accuracy of publicly available latest high-resolution (30?m) global DEMs over Cameroon. These models are (1) the ALOS World 3D-30?m (AW3D30), (2) the Shuttle Radar Topography Mission 1 Arc-Second C-Band Global DEM (SRTM 1) and (3) the Advanced Spaceborne Thermal Emission and Reflection Global DEM Version 2 (ASTER GDEM 2). After matching their coordinate systems and datums, the horizontal positional accuracy evaluation was carried out and it shows that geolocation errors significantly influence the vertical accuracy of global DEMs. After this, the three models are compared among them, in order to access random and systematic effects in the elevation data each of them contains. Further, heights from 555 GPS/leveling points distributed all over Cameroon are compared to each DEM, for their vertical accuracy determination. Traditional and robust statistical measures, normality test, outlier detection and removal were used to describe the vertical quality of the DEMs. The test of the normality rejected the hypothesis of normal distribution for all tested global DEMs. Overall vertical accuracies obtained for the three models after georeferencing and gross error removal in terms of Root Mean Square (RMS) and Normalized Median Absolute Deviation (NMAD) are: AW3D30 (13.06?m and 7.75?m), SRTM 1 (13.25?m and 7.41?m) and ASTER GDEM 2 (18.87?m and 13.30?m). Other accuracy measures (MED, 68.3% quantile, 95% quantile) supply some evidence of the good quality of AW3D30 over Cameroon. Further, the effect of land cover and slope on DEM vertical accuracy was also analyzed. All models have proved to be worse in the areas dominated by forests and shrubs areas. SRTM 1 and AW3D30 are more resilient to the effects of the scattering objects respectively in forests and cultivated areas. The dependency of DEMs accuracy on the terrain roughness is evident. In all slope intervals, AW3D30 is performing better than SRTM 1 and ASTER GDEM 2 over Cameroon. AW3D30 is more representative of the external topography over Cameroon in comparison with two others datasets and SRTM 1 can be a serious alternative to AW3D30 for a range of DEM applications in Cameroon.  相似文献   

Modeling the early evolution of Vesta          下载免费PDF全文

Marie Weisfeiler  Donald L. Turcotte  Louise H. Kellogg 《Meteoritics & planetary science》2017,52(5):859-868

The early evolution of the asteroid Vesta has been extensively studied because of the availability of relevant data, especially important new studies of HED meteorites which originated from Vesta and the Dawn mission to Vesta in 2011–2012. These studies have concluded that an early melting episode led to the differentiation of Vesta into crust, mantle, and core. This melting episode is attributed to the decay of ²⁶Al, which has a half‐life of 7.17 × 10⁵ yr. This heating produced a global magma ocean. Surface cooling of this magma ocean will produce a solid crust. In this paper, we propose a convective heat‐transfer mechanism that effectively cools the asteroid when the degree of melting reaches about 50%. We propose that a cool solid surface crust, which is gravitationally unstable, will founder into the solid–liquid mix beneath and will very effectively transfer heat that prevents further melting of the interior. In this paper, we quantify this process. If Vesta had a very early formation, melting would commence at an age of about 1,30,000 yr, and solidification would occur at an age of about 10 Myr. If Vesta formed with a time delay greater than about 2 Myr, no melting would have occurred. An important result of our model is that the early melting episode is restricted to the first 10 Myr. This result is in good agreement with the radiometric ages of the HED meteorites.  相似文献   

Transitory Change of Bacterial Community Structure in Hot Water Biofilm: Effects of Anti‐Legionella Treatments          下载免费PDF全文

Maha Farhat  Marina Moletta‐Denat  Marie‐Cécile Trouilhé  Jacques Frère  Enric Robine 《洁净——土壤、空气、水》2018,46(6)

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Etude de l’évaporation de la nappe phréatique des zones arides: cas de Ouargla (Algérie)     

Myriam Marie El Fergougui  Djamel Boutoutaou  Noureddine Meza 《水文科学杂志》2017,62(7):1067-1077

La majorité des surfaces mises en valeur dans les zones arides et semi-arides de l’Algérie reposent sur des nappes phréatiques très minéralisées dont le niveau est proche de la surface du sol (0–1,5 m). En présence de conditions climatiques très sévères, le processus d’évaporation de ces nappes contribue en grande partie à la salinisation des terres et la dégradation du milieu. Les résultats de l’étude de l’évaporation de la nappe phréatique de la région de Ouargla montre que l’évaporation diminue au fur et à mesure que le niveau de la nappe s’éloigne de la surface du sol. L’évaporation de la nappe est maximale et égale à l’évaporation du plan d’eau lorsque le niveau de cette nappe est situé dans la couche 0–0,6 m et devient minimale au dessous de 1,7 m. Pour une meilleure mise en valeur des terres et une production agricole élevée, il est nécessaire de connaître la profondeur critique de la nappe phréatique, profondeur pour laquelle l’évaporation est faible et par conséquent le dépôt de sels est faible dans les sols à texture sableuse de la région aride de Ouargla.  相似文献   

Automated Analyte Separation by Ion Chromatography Using a Cobot Applied to Geological Reference Materials for Li Isotope Composition     

Marie L. Kuessner  Alkiviadis Gourgiotis  Gerard Manhs  Julien Bouchez  Xu Zhang  Jrme Gaillardet 《Geostandards and Geoanalytical Research》2020,44(1):57-67

The demand for large and reliable data sets on isotopic composition has increased in geochemistry and environmental sciences over recent years. We present an automated ion chromatographic separation method using a robotic pipetting arm, termed ‘ChemCobOne’, to reduce sample separation time. Its performance was tested for lithium isotope separation in geological reference materials using a single‐step separation with HCl (0.2 mol l^?1) and a 2 ml resin volume. This refined lithium purification method does not forfeit precision, accuracy or purity compared with manual sample processing. In addition, a δ⁷Li value for NASS‐6 of 30.99 ± 0.50‰ (2s) (95% CI = 0.14‰, n = 44) was determined and the first δ⁷Li values for the granite rock reference material GS‐N (?0.57 ± 0.25‰ (2s), 95% CI = 0.15‰, n = 15), and for the soil reference material NIST SRM 2709a (?0.37 ± 0.67‰ (2s), 95% CI = 0.15‰, n = 63) are proposed.  相似文献   

Local effects of blue mussels around turbine foundations in an ecosystem model of Nysted off-shore wind farm, Denmark     

Marie Maar  Karsten Bolding  Jens Kjerulf Petersen  Jrgen L.S. Hansen  Karen Timmermann 《Journal of Sea Research》2009,62(2-3):159

The development of off-shore wind farms along the coastline of north-west Europe is rapidly increasing; it is therefore important to study how this will affect the marine environment. The present study modelled the growth and feed-backs of blue mussels in natural beds and on turbine foundations in an off-shore wind farm (OWF) located in a shallow coastal ecosystem by coupling a dynamic energy budget (DEB) model to a small-scale 3D hydrodynamic–biogeochemical model. The model results showed that blue mussels located higher up in the water column on turbine pillars achieved a 7–18 times higher biomass than those located on the scour protection because the former experience an enhanced advective food supply. Secondly, the high biomasses of blue mussels on foundations created local ‘hot spots’ of biological activity and changed ecosystem dynamics due to their feed-backs e.g. ingestion of microplankton and copepods, excretion of ammonium and egestion of faecal pellets. The model results were supported by field measurements around foundations of Chl a concentrations and biomasses of the fauna community. Our study emphasised that OWFs seem to be particularly favourable for blue mussels in the western Baltic Sea and that the functioning of the OWFs as artificial reef ecosystems depends upon how the blue mussels interact with their local pelagic and benthic environment.  相似文献   

Upcoming International Events     

Annie Marie de Grosbois 《Environmental Geology》2007,53(2):471-476

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