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1.
Maud W. Makemson 《Earth, Moon, and Planets》1971,2(3):293-308
The systematic examination of lunar surface characteristics is entering a new phase requiring detailed measurements of position for purposes of cartography, surface and near-surface navigation, and correlation and data reduction of scientific experiments, such as gravimetry, active seismology, geological sampling, etc.A method of obtaining selenographic positions is described in this paper, and an example of the technique is presented. 相似文献
2.
Maud Cottet Xavier de Montaudouin Hugues Blanchet Pascal Lebleu 《Estuarine, Coastal and Shelf Science》2007,71(3-4):629-640
The cordgrass Spartina anglica is an introduced species that tends to invade sheltered sand and mudflats, at the upper low marsh level. In Arcachon Bay, a lagoon in South West of France, the cordgrass can also replace Zostera noltii beds. The consequence of cordgrass presence on macrobenthic fauna was estimated and compared to adjacent habitats (bare sands, Z. noltii sea grass beds) during one year. The communities of the three habitats were characterised by low species richness, low abundance and biomass (when Hydrobia ulvae, 90% of abundance, is not considered) and high seasonal stability. The infaunal assemblages were particularly homogeneous between habitats without any characteristic species.Cordgrass eradication experiments were performed and zoobenthic recolonisation was observed the following year. Modifications in benthic fauna were observed on epifauna only.These results highlight the limited structuring effect of habitat heterogeneity at high tidal levels and in soft-bottom sediments where desiccation becomes the dominant factor determining infauna community structure. 相似文献
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Received: 15 June 1999 · Accepted: 30 August 1999 相似文献
4.
Yasin Makhloufi Elme Rusillon Maud Brentini Andrea Moscariello Michel Meyer Elias Samankassou 《Swiss Journal of Geoscience》2018,111(3):475-500
The Upper Jurassic carbonates represent important potential targeted reservoirs for geothermal energy in the Geneva Basin (Switzerland and France). Horizons affected by dolomitization, the focus of the present study, are of particular interest because they proved to be productive in time-equivalent deposits currently exploited in Southern Germany. The study is based on sub-surface samples and outcrops in the Geneva Basin. Petrographic analyses allowed to constrain the paragenesis of the Upper Jurassic units prior to discussing the cause(s) and effect(s) of dolomitization. Data reveal that the facies are affected by early and late diagenesis. All samples show at least two stages of burial blocky calcite cementation with the exception of those from the sub-surface, which display an incomplete burial blocky cementation preserving primary intercrystalline porosity. Dolomitization affected all units. The results point to an early dolomitization event, under the form of replacement dolomite. Dedolomitization, through calcitization and/or dissolution, is an important process, creating secondary pore space. Results of the present study favor a reflux model for dolomitization rather than the mixing-zone model suggested in earlier work. However, considering the geodynamic context, other dolomitization models cannot be excluded for the subsurface. The presence of secondary pore space might contribute to the connectivity of the porous network providing enhanced reservoir properties. These results are a first step towards a better understanding of the diagenetic history of the Upper Jurassic in the Geneva Basin. Moreover, it provides a reasonable framework for further geochemical analyses to constrain the nature and timing of fluid migration. The paragenesis and the dolomitization model hold the potential to help in ongoing exploration for geothermal energy beyond the Geneva Basin. 相似文献
5.
Abigail Amissah-Arthur Bernard Mougenot Maud Loireau 《International journal of geographical information science》2013,27(6):583-599
Through the integration of SPOT HRV, biophysical and socioeconomic information, the study identified population carrying capacities and their vulnerability to land degradation. Land use intensification on the landscapes was quantified into expansion, early and late phases based on the Ruthenberg index calculated using a biennial series of SPOT images for the period 1986-96. Subsequently, farmland dynamic on different landscapes was calculated while observed patterns were linked with agricultural intensification and population carrying capacity. Results show a pattern of agricultural land degradation due to increasing pressure of population and agricultural intensification within a system characterised by little or no use of inputs. Fifty-six percent of the study area supports a population density higher than the carrying capacity (≤ 15 pers/km-2). Sixty-three percent of the study area is under early to late phases of agricultural intensification. Between 1986-96, cultivation declined 2-3% annually on landscapes with Low risk of degradation but increased by 1-2% on those with Average/Extreme risks. This emphasises the process of land abandonment as farmers move on to cultivating marginal lands despite above normal seasonal rainfalls observed during most of the period. By 1996, cultivation tended to include fields much farther away from the vicinity of villages, compared with 10 years earlier. Furthermore, by 1996, farmlands in the zones of late intensification declined from 12 to 4% and increased from 6 to 11% in the zone under the expansion phase. Indicating that by 1996 substantial amount of the land area required increasing lengths of fallowing. The spatial GIS modelling approach allowed not only identification of zones but synthesis of the observed pattern of landscape degradation. The paper highlights the need for combining remote sensing, biophysical and socio-economic data in environmental degradation studies in developing countries with their poor data availability. The role of developing countries scientists is stressed in taking the forefront to tackle environmental problems, which affect their region. The paper calls for increased co-operation between these scientists and regional and international data providers to overcome data availability problems and pave the way for better local and regional studies on environmental degradation. 相似文献
6.
Land clearance and hydrological change in the Sahel: SW Niger 总被引：1，自引：0，他引：1
Marc J. Leblanc Guillaume Favreau Sylvain Massuel Sarah O. Tweed Maud Loireau Bernard Cappelaere 《Global and Planetary Change》2008,61(3-4):135-150
In the West African semiarid belt of the Sahel, for the second half of the XXth century, lasting droughts (1970s–1980s) and one of the World's highest population growths have resulted in major land cover and hydrological changes that can be quantified using aerial photographs. This paper aims to provide one of the longest combined observations of land cover and hydrological changes for semiarid areas using a time series of normalised mosaics of aerial photographs dating back from 1950, field inquiries, and updated groundwater data. The 500 km2 study area in southwest Niger was chosen (i) for its rural environment representative of the rain-fed agriculture belt of the Sahel and (ii) to encompass the main hydrological study sites investigated in this region over the past two decades (Hapex-Sahel and AMMA experiments, 1990–2000s). Results have significant implications for future freshwater availability and food security in the Sahel.Between 1950 and 1992, 80% of the study area has been cleared, firstly to open new areas for agriculture and secondly for firewood supply (59% of the plateaux, 42% of the valley bottoms, and 87% of the hillslopes). Intermediate aerial photograph surveys (1960, 1975) attest an accelerated loss in the woody savannah that could not be recovered on the short term. A strong, indirect impact of land clearance is observed on the water resources. Land clearance has resulted in a modification of the soil properties and infiltration capacity and has led to an increase in Hortonian runoff collected in numerous gullies and ponds. Between 1950 and 1992, aerial photographs show a 2.5 fold increase of the drainage density with the development of large drainage systems and new ponds. Groundwater data also indicate a continuous rise in the water table, mostly noticeable since the 1980s with a mean groundwater level rise of 4 m for the 1963–2005 period (+ 15% in aquifer reserves). The relatively short 30 year time-lag between the onset of land clearance and the beginning of the water table rise is linked to the process of indirect groundwater recharge and is timed with the connectivity of the drainage network and the formation of new ponds. Finally, the sustained increase in surface runoff and groundwater recharge during the past four decades indicates that the indirect impact of land clearance on the terrestrial water balance has been stronger than that of the long-lasting Sahelian drought. As the rate of land clearance increased for the past century in semiarid Africa, its main hydrological effects may not yet be fully perceptible. 相似文献
7.
F. Albarède Philippe Telouk Maud Boyet Bruce Nelson 《Geochimica et cosmochimica acta》2004,68(12):2725-2744
New techniques of isotopic measurements by a new generation of mass spectrometers equipped with an inductively-coupled-plasma source, a magnetic mass filter, and multiple collection (MC-ICPMS) are quickly developing. These techniques are valuable because of (1) the ability of ICP sources to ionize virtually every element in the periodic table, and (2) the large sample throughout. However, because of the complex trajectories of multiple ion beams produced in the plasma source whether from the same or different elements, the acquisition of precise and accurate isotopic data with this type of instrument still requires a good understanding of instrumental fractionation processes, both mass-dependent and mass-independent. Although physical processes responsible for the instrumental mass bias are still to be understood more fully, we here present a theoretical framework that allows for most of the analytical limitations to high precision and accuracy to be overcome. After a presentation of unifying phenomenological theory for mass-dependent fractionation in mass spectrometers, we show how this theory accounts for the techniques of standard bracketing and of isotopic normalization by a ratio of either the same or a different element, such as the use of Tl to correct mass bias on Pb. Accuracy is discussed with reference to the concept of cup efficiencies. Although these can be simply calibrated by analyzing standards, we derive a straightforward, very general method to calculate accurate isotopic ratios from dynamic measurements. In this study, we successfully applied the dynamic method to Nd and Pb as examples. We confirm that the assumption of identical mass bias for neighboring elements (notably Pb and Tl, and Yb and Lu) is both unnecessary and incorrect. We further discuss the dangers of straightforward standard-sample bracketing when chemical purification of the element to be analyzed is imperfect. Pooling runs to improve precision is acceptable provided the pooled measurements are shown to be part of a single population. Second-order corrections seem to be able to improve the precision on 143Nd/144Nd measurements. Finally, after discussing a number of potential pitfalls, such as the consequence of peak shape, correlations introduced by counting statistics, and the effect of memory on double-spike methods, we describe an optimal strategy for high-precision and accurate measurements by MC-ICPMS, which involves the repetitive calibration of cup efficiencies and rigorous assessment of mass bias combined with standard-sample bracketing. We suggest that, when these simple guidelines are followed, MC-ICPMS is capable of producing isotopic data precise and accurate to better than 15 ppm. 相似文献
8.
Maud Leriche R. Lyana Curier Laurent Deguillaume Dimitri Caro Karine Sellegri Nadine Chaumerliac 《Journal of Atmospheric Chemistry》2007,57(3):281-297
The Model of Multiphase Cloud Chemistry M2C2 has recently been extended to account for nucleation scavenging of aerosol particles in the cloud water chemical composition. This extended version has been applied to multiphase measurements available at the Puy de Dôme station for typical wintertime anthropogenic air masses. The simulated ion concentrations in cloud water are in reasonable agreement with the experimental data. The analysis of the sources of the chemical species in cloud water shows an important contribution from nucleation scavenging of particles which prevails for nitrate, sulphate and ammonium. Moreover, the simulation shows that iron, which comes only from the dissolution of aerosol particles in cloud water, has a significant contribution in the hydroxyl radical production. Finally, the simulated phase partitioning of chemical species in cloud are compared with measurements. Numerical results show an underestimation of interstitial particulate phase fraction with respect to the measurements, which could be due to an overestimation of activated mass by the model. However, the simulated number scavenging efficiency of particles agrees well with the measured value of 40% of total number of aerosol particles activated in cloud droplets. Concerning the origin of chemical species in cloud water, the model reproduces quite well the contribution of gas and aerosol scavenging estimated from measurements. In addition, the simulation provides the contribution of in-cloud chemical reactivity to cloud water concentrations. 相似文献
9.
Landslides associated with the colluvial soils overlying the Natal Group in the greater Durban region of Natal, South Africa 总被引：3，自引：1，他引：2
In the last 25 years, many of the landslides that have occurred in the greater Durban region have been associated with the
colluvial soils overlying the Natal Group, most of which occurred during the very heavy rains of September 1987. Subsequently,
a very heavy rainfall event in February 1999 also gave rise to landslides. In fact, prior to 1987 these colluvial soils were
considered relatively stable. A critical precipitation coefficient has been developed which included the cumulative precipitation
up to a landslide event. In addition, an attempt has been made to establish a threshold value for triggering of landslides
for the colluvial soils from a study of pluviometric data. The results indicate that when a rainfall event exceeds 12% of
the mean annual rainfall, small-scale landslides are likely to occur. When a rainfall event is greater than 16% of the mean
annual rainfall, a moderate number of landslides take place. Major landslides are associated with rainfall events with intensities
in excess of 20% of the mean annual precipitation. An example of a landslide which occurred on the Natal Group due to construction
operations is provided, as well as an account of those which took place during September 1987. In the latter case, most of
the slides took the form of mudflows and were responsible for some of the worst damage which has occurred in the Durban region.
The colluvial soils involved were relatively thin and therefore became quickly saturated by the heavy rainfall. In some places
the situation was further aggravated by liquefaction of the soils.
Received: 15 June 1999 · Accepted: 30 August 1999 相似文献
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