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1.
2.
A large amount of interest has recently been expressed pertaining to the quantity of physically adsorbed water by the Martian regolith. Thermodynamic calculations based on experimentally determined adsorption and desorption isotherms and extrapolated to subzero temperatures indicate that physical adsorption of more than one or two monomolecular layers is highly unlikely under Martian conditions. Any additional water would find ice to be the state of lowest energy and therefore the most stable form. To test the validity of the thermodynamic calculations we have measured adsorption and desorption isotherms of sodium montmorillonite at ?5°C. To a first approximation it was found to be valid. 相似文献
3.
Landslides pose serious hazards in the Mercantour Massif and the French Riviera in southeastern France. The context for landslide development is a particularly favourable one, both in terms of the geomorphic and structural setting of this Alpine region, and of the climatic, hydrologic and seismic factors that trigger such failures. High mountain relief and steep slopes constitute a very favourable setting for failures affecting massive basement rocks and a very heterogeneous sedimentary cover whose resistance has been weakened by weathering, tectonic stresses, and cambering due to gravity. Among trigger factors, the important appears to be the precipitation regime. Rainfalls are commonly concentrated into short high-intensity downpours or into bursts of sustained falls over periods of several days, leading to soil saturation and lubrication of potential failure planes. Snowmelt also contributes to these lubrication processes. Earthquakes affecting this region are also a potentially important landslide trigger. However, while a lot of work has been done on the relationship between extreme climatic events and landslide activity, much less is known of the trigger effects of earthquakes.Both the background factors that promote landslide development and the factors that trigger such failures are discussed within a time frame of landslide development. Progressive changes in soil strength due to weathering, rock cambering and shattering processes lead to long-term reduction in resistance. Superimposed on these progressive changes are episodic triggerings related to rainfall and snowmelt episodes or earthquakes. Landslides may occur as shallow, low-volume “one-time” events or may be part of a progressive long-term failure. The former generally affect unconsolidated or clay-rich sedimentary rocks, especially on the coastal hillslopes of the French Riviera. A notable exception of a major, voluminous “one-time” event was the submarine landslide of the Var Delta in 1979. This landslide, like numerous other smaller subaerial landslides onland, was largely a result of human activities. This landslide occurred following extensive modification of the Var Delta and, notably, reclamation of the steep, fine-grained delta front. Deforestation, quarrying, urbanisation and road network developments are various ways in which human activity has destabilized the coastal hillslopes, favouring the development of numerous shallow landslides following each episode of heavy rainfall.Progressive landslides on the upper hillslopes of the Mercantour Massif have developed over long time spans (order of 101 to 105 yrs) and have involved more complex interactions between lithological controls, slope characteristics and trigger factors. The Collelongue and Bois de Malbosc landslides have evolved into now stable failures buttressed by resistant migmatitic diorites or amphibolites. The more voluminous and well monitored Clapière landslide is a relatively simple rotational landslide of the toe-failure type. This active landslide poses a serious to inhabitants and infrastructure in the Tinée Valley. The importance of continued field monitoring, modelling and mapping of landslides and their hazards is emphasised. 相似文献
4.
Wolfram Neutsch Herbert Kalisch Horst Fichtner S. Ranga Sreenivasan Maurice Shevalier 《Astrophysics and Space Science》2003,288(3):391-408
The study of the expansion of the solar wind out of a system of coronal holes is continued. To this end, we consider the numerical
integration of partial differential equations for problems with icosahedral symmetry, in general. First, employing Weyl theory,
orbifold coordinates are introduced. Second, the icosahedral coordinates are discussed in detail. Third, following an analysis
of the properties of these coordinates and the derivation of a few expressions useful for grid construction, various alternatives
for the distribution of lattice points required for numerical integration are considered. A comparison of these numerical
grids motivates the choice of a specific grid optimized for the numerical integration carried out in the accompanying paper
by Kalish et al.(2002).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Incoherent scatter radars are designed to detect scatter from thermalfluctuations in the ionosphere. These fluctuations contain, among other things,features associated with ion-acoustic waves driven by random motions within theplasma. The resulting spectra are generally broad and noisy, but neverthelessthe technique can, through a detailed analysis of spectra, be used to measure arange of physical parameters in the Earth's upper atmosphere, and provides apowerful diagnostic in studies of magnetosphere-ionosphere coupling,thermosphere dynamics and the geospace environment in general. In recent yearsthere has been much interest in naturally occurring (as opposed to artificiallystimulated) enhanced ion-acoustic spectra seen in the auroral zone andcusp/cleft region. A study of the plasma instability processes that lead tosuch spectra will help us to better understand auroral particle acceleration,wave-particle and wave-wave interactions in the ionosphere, and theirassociation with magnetospheric processes. There is now a substantial body ofliterature documenting observations of enhanced ion-acoustic spectra, but thereremains controversy over generation mechanisms. We present a review ofliterature documenting observations of naturally enhanced ion-acoustic spectra,observed mainly along the geomagnetic field direction, along with a discussionof the theories put forward to explain such phenomena. 相似文献
6.
Maurice H. P. M. van Putten Alok C. Gupta 《Monthly notices of the Royal Astronomical Society》2009,394(4):2238-2246
Rotating black holes can power the most extreme non-thermal transient sources. They have a long-duration viscous time-scale of spin-down, and produce non-thermal emissions along their spin-axis, powered by a relativistic capillary effect. We report on the discovery of exponential decay in Burst and Triensient Source Experiment (BATSE) light curves of long gamma-ray bursts (GRBs) by matched filtering, consistent with a viscous time-scale, and identify ultra-high energy cosmic rays (UHECRs) about the Greisen–Zatsepin–Kuzmin (GZK) threshold with linear acceleration of ion contaminants along the black hole spin-axis, consistent with black hole masses and lifetimes of Fanaroff–Riley type II (FR II) active galactic nuclei (AGN). We explain the absence of UHECRs from BL Lac objects due to UHECR emissions preferably at appreciable angles away from the black hole spin-axis. Black hole spin may be the key to unification of GRBs and their host environments, and to AGN and their host galaxies. Our model points to long-duration bursts in radio from long GRBs without supernovae and gravitational waves from all long GRBs. 相似文献
7.
Five fresh, two weathered, and two metamorphosed basalt pillows with a presently or originally glassy outermost layer, together with a weathered and a metamorphosed basalt fragment without an originally glassy layer, all from the Mid-Atlantic Ridge, were investigated in detail. Fresh pillows usually show only very slight compositional heterogeneity, except for the glassy outermost layer where the total iron and MgO contents are higher and the K2O content and the ratio are lower than the interior. In particular, the K2O content of the glassy outermost layer is only about a half of that of the core in some pillows. In weathered pillows the surface layer shows higher total iron, TiO2, P2O5 and H2O contents and a higher ratio and a much lower CaO content than the interior. Most of the compositional heterogeneity observed in metamorphosed pillows may be ascribed to chemical migration during weathering, though metamorphism also may cause considerable heterogeneity. 相似文献
8.
M.E. Stuart L. Maurice T.H.E. Heaton M. Sapiano M. Micallef Sultana D.C. Gooddy P.J. Chilton 《Applied Geochemistry》2010
The Maltese islands are composed of two limestone aquifers, the Upper and Lower Coralline Limestone separated by an aquitard, the ‘Blue Clay’. The Lower Coralline Limestone is overlain in part by the poorly permeable Globigerina Limestone. The upper perched aquifers are discontinuous and have very limited saturated thickness and a short water level response time to rainfall. Frequent detections of coliforms suggest a rapid route to groundwater. However, the unsaturated zone has a considerable thickness in places and the primary porosity of the Upper Coralline Limestone is high, so there is likely to be older recharge by slow matrix flow as well as rapid recharge from fractures. Measurement of SF6 from a pumping station in a deep part of one of the perched aquifers indicated a mean saturated zone age of about 15 a. The Main Sea Level aquifers (MSL) on both Malta and Gozo have a large unsaturated thickness as water levels are close to sea level. On Malta, parts of the aquifer are capped by the perched aquifers and more extensively by the Globigerina Limestone. The limited detection of coliform bacteria suggests only some rapid recharge from the surface via fractures or karst features. Transmissivity is low and 3H and CFC/SF6 data indicate that saturated zone travel times are in the range 15–40 a. On Gozo the aquifer is similar but is more-extensively capped by impermeable Blue Clay. CFC data show the saturated zone travel time is from 25 a to possibly more than 60 a. Groundwater age is clearly related to the extent of low-permeability cover. The δ13C signature of groundwater is related to the geochemical processes which occur along the flowpath and is consistent with residence time ages in the sequence; perched aquifers < Malta MSL < Gozo MSL. The 18O and 2H enriched isotopic signature of post 1983 desalinated water can be seen in more-modern groundwater, particularly the urbanized areas of the perched and Malta MSL aquifers. In all aquifers, movement of solutes from the surface travelling slowly through the matrix provide a long-term source of groundwater contaminants such as NO3. 相似文献
9.
Michaël Hermoso Laurence Le Callonnec Fabrice Minoletti Maurice Renard Stephen P. Hesselbo 《Earth and Planetary Science Letters》2009,277(1-2):194-203
The causes of the pronounced negative excursion in carbon-isotope values that was recorded during the Early Toarcian Oceanic Anoxic Event (T-OAE) are still under debate, particularly with regard to the local versus global pattern of the excursion, and the extent to which recorded signals are under a diagenetic control. In this study we employ a novel microseparation technique in order to investigate the isotopic and mineralogical characteristics of different size fractions of the carbonate content from a Toarcian section recovered from the Sancerre–Couy borehole, southern Paris Basin. Beyond the recognition of a ? 6‰ δ13C excursion in the bulk carbonate content, our data also demonstrate that biogenic particles (such as coccoliths) and inorganic grains precipitated as early diagenetic phases (including dolomite) both record the excursion with the same magnitude. Although several black shales occur through the Paris Basin Toarcian section, it is only that associated with the onset of the OAE that coincides with a large negative carbon-isotope excursion. Taken together these observations indicate that during this event, the entire water column was characterized by homogeneous carbon-isotope values; such a pattern is incompatible with the idea that the negative excursion was generated simply through the upwelling of bottom waters enriched in re-mineralized organic carbon (cf. “the Küspert model”), since this would have required a strong vertical gradient in the water column. Additionally, the Paris Basin data show that the decrease in carbonate δ13C values during the OAE occurred in several discrete steps (each of some ? 2‰), as has previously been found for organic carbon substrates in other European sections. The stepped nature of the isotopic profile, which is part of a stratigraphic signature previously ascribed to Milankovitch forcing, is compatible with regular pulsed input of light carbon into the whole atmosphere–ocean system from a climatically sensitive source such as gas hydrate, or from thermal methanogenesis of organic-rich sediments in the Karoo–Ferrar large igneous province. Contrasts in the amplitude of the negative carbon-isotope excursion on a regional scale remain an important unexplained aspect of the Toarcian record. 相似文献
10.