This paper presents a u‐p (displacement‐pressure) semi‐Lagrangian reproducing kernel (RK) formulation to effectively analyze landslide processes. The semi‐Lagrangian RK approximation is constructed based on Lagrangian discretization points with fixed kernel supports in the current configuration. As a result, it tracks state variables at discretization points while allowing extreme deformation and material separation that is beyond the capability of Lagrangian formulations. The u‐p formulation following Biot theory is incorporated into the formulation to describe poromechanics of saturated geomaterials. In addition, a stabilized nodal integration method to ensure stability of the domain integration and kernel contact algorithms to model contact between bodies are introduced in the u‐p semi‐Lagrangian RK formulation. The proposed method is verified with several numerical examples and validated with an experimental result and the field data of an actual landslide. 相似文献
This paper presents the results of pollen and charcoal analyses carried out in the sedimentary formation of Ponta da Passadeira, south of the Tejo River estuary, Portugal. The data provide information regarding the evolution of the coastline and ecosystem of the estuary during the mid and late Holocene. The study focuses on a group of upright woody fossilized tree remains that, together with those identified earlier by García‐Amorena et al. (2007), form part of the fossil forest of Ponta da Passadeira. Eight remains were identified as Pinus pinaster, four as Pinus pinea and one as Pinus sp. Two specimens of these species were dated to 6523 and 5805 cal. a BP. Pollen analysis was undertaken in a clay layer located at the same point as the fossil forest, which is currently below sea level; the base of the clay layer was dated to 4906 cal. a BP. The pollen spectra reflect the dynamics of the vegetation that grew on this deposit, whereas the sporopollinic input masks the contribution of the regional vegetation. Wood charcoal remains recovered at an adjacent Final Neolithic settlement were also analysed, and a Pinus sp. specimen was radiocarbon dated to 5050 cal. a BP. The correlation amongst the three records provides key ecological markers for the understanding of the evolution of coastline ecosystems, and helps to clarify and understand the Holocene sea rise on the Atlantic seaboard of Iberia. The geographical location of Ponta da Passadeira is strategic because it enables a more clear definition of the configuration of landscapes that show an inflection point in this area of central Portugal. 相似文献
Abstract— Previous Raman investigations on experimentally shocked ingle‐crystal olivine indicated that the olivine Raman bands seemingly shift to a higher wave number with increasing shock pressure. If this effect could be confirmed, Raman analysis of natural shock‐metamorphosed minerals could potentially provide an important shock barometric tool. We carried out a Raman spectroscopic study on olivine in a series of natural dunite samples experimentally shocked to pressures between 5 and 59 GPa. In addition, we analyzed olivine grains in a sample of the Cold Bokkeveld C1 meteorite. We studied samples of several dunites with olivine of 90.64–92.00 mole% Fo to determine Raman effects in the region from 200 to 900 cm?1. Several olivine grains per sample/shock pressure stage were analyzed. Raman analysis, however, showed little or no shift with increasing shock pressure. The shifts to higher or lower frequencies observed were not specific for a given pressure stage, with some grains within a sample showing more shift than others. This finding is unrelated to the crystallographic orientation of analyzed grains and cannot be related systematically to the different degrees of optically determined shock metamorphism of the analyzed grains. We identified an increase in full width at half maximum (FWHM) for the 824 cm?1 band with increased shock pressure in the shocked Åheim samples above 45 GPa and, to a lesser extent, for the 856 cm?1 band. Evaluation of band broadening of olivine in the Cold Bokkeveld meteorite showed FWHM values that were much greater (9–20 cm?1) than those of olivine in the shocked dunite samples (7–12 cm?1). We concluded that these differences in FWHM are due to differences in chemical composition between the meteoritic and the experimentally shocked olivine. Therefore, using Raman spectroscopy to detect small shifts in wave numbers to higher frequencies with increased shock pressure does not yield consistent effects for polycrystalline dunite. An extra band at 650 cm?1 was identified in the Raman spectra of the unshocked Mooihoek dunite and the Åheim dunite samples shocked to 5, 29.3, and 59 GPa, as well as another at 696 cm?1 in all the spectra of the 59 GPa Åheim sample. The cause of these extra bands is not known. Comparison of these results with Raman spectra of olivine from the Cold Bokkeveld C1 meteorite did not allow us to determine shock pressures for the meteoritic olivine. 相似文献
Abstract— Asteroids 387 Aquitania and 980 Anacostia are anomalous members of the S-class. Their reflectance spectra exhibit a strong broad absorption feature longwards of 1.5 μm and no significant feature near 1 μm. Their spectra indicate the presence of spinel, an aluminum-magnesium oxide mineral commonly present in inclusions in CV3 and CO3 meteorites. Spinel probably makes up only a small percentage of the surface assemblages of these asteroids, but its spectral effect may be enhanced by its presence in fine-grained white inclusions in immature asteroid regoliths. It is speculated that Aquitania and Anacostia represent material formed in the same nebular zone as the CV3 and CO3 chondrites but either: A) at an earlier time in the nebula when such inclusions might have been a relatively larger fraction of the nebular grain population, or B) in local regions where nebular processes (e.g., settling to the midplane) had concentrated such inclusions. The close similarity of two orbital elements (a, i) suggests that Aquitania and Anacostia may be members of a partially dispersed asteroid family produced by the early disruption of a spinel-bearing parent body. 相似文献
A new method for solving the transport equation and boundary condition describing diffusive shock acceleration for interplanetary corotating interaction regions is provided. It involves inverting a quindiagonal matrix. Application of this method to realistic parameters indicates that the parallel diffusion coefficient magnitude is critical in determining whether observed particle distribution functions are exponential or power law. 相似文献
Abstract— Magmatic sulfide mineralogy has been studied in 2 olivine‐phyric shergottites (DaG 476 and SaU 005) and 4 basaltic shergottites (Zagami, Shergotty, Los Angeles, and NWA 480). Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are high (0.16 to 0.53 area percent) and correlate positively with abundances of Fe‐Ti oxides. Sulfides are mesostasis minerals, being mostly interstitial grains or locally enclosed in post‐cumulus melt inclusions (e.g., SaU 005) in olivine. Sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of Cu sulfides (chalcopyrite and/or cubanite). Hot desert finds (e.g., DaG 476) show abundant fracture‐filling iron (oxy)hydroxides of probable terrestrial origin. Unaltered sulfides show metal‐rich hexagonal pyrrhotite compositions with metal/sulfur (M/S) ratio ranging between 0.936 ± 0.005 and 0.962 ± 0.01. This compositional range corresponds to the two‐phase structural domain 2C + nC of the Fe‐S system; however, the high‐temperature disordered hexagonal 1C pyrrhotite structure would be in better agreement with magnetic properties of shergottites. Ni contents in pyrrhotite increase from Los Angeles (<0.05 at%) to Shergotty, Zagami, and NWA 480 (0.2–0.5 at%), and DaG 476 and SaU 005 (up to 3 at%). The higher Ni values of pyrrhotite in olivine‐phyric shergottites correlate with the abundance of pentlandite exsolutions, both reflecting more primitive Ni‐rich sulfide liquids where abundant olivine crystallized. This result and the strong correlation between sulfide abundances and Fe‐Ti oxides argue for a primary magmatic origin of these sulfides. Although they reproduce the trend of magmatic oxygen fugacity conditions determined from Fe‐Ti oxide pairs, observed pyrrhotite compositions are systematically more metal‐deficient compared to those calculated from the Fe‐S‐O system. This suggests post‐magmatic oxidation during cooling on Mars, followed by terrestrial weathering for hot desert finds. 相似文献
Abstract— Fifty‐four fragments of ordinary chondrites from 50 finds representing all searched areas in central Oman and all weathering stages were selected to compare the physical, chemical, and mineralogical effect of terrestrial weathering with 14C terrestrial ages. 14C ages range from 2.0 to >49 kyr with a median value of 17.9 kyr. The peak of the age range, which is between 10–20 kyr, falls in an arid climate period. A comparison of the chemical composition of Omani chondrites with literature data for unweathered H and L chondrites demonstrates a strong enrichment in Sr and Ba, and depletion in S during weathering. Water contents in H chondrites increase with terrestrial age, whereas L chondrites show a rapid initial increase followed by nearly constant water content. Correlating Sr, Ba, and H2O with age indicates two absorption trends: i) an initial alteration within the first 20 kyr dominated by H2O uptake, mainly reflecting Fe‐Ni metal alteration, and ii) a second Ba‐and Sr‐dominated stage correlated with slower and less systematic weathering of troilite that starts after H2O reaches ?2 wt%. Sulfur released from troilite partly combines with Ba and Sr to form sulfate minerals. Other parameters correlated with 14C age are degree of weathering, color of powdered meteorites, and the Ni/Fe ratio. Chemical analyses of 145 soils show a high degree of homogeneity over the entire interior Oman Desert, indicating large‐scale mixing by wind. Soil samples collected from beneath meteorite finds typically are enriched in Ni and Co, confirming mobilization from the meteorites. High Cr and Ni concentrations in reference soil samples, which decrease from NE to SW, are due to detrital material from ultramafic rocks of the Oman Mountains. 相似文献
The thickest development of Carboniferous Limestone in Great Britain (about 1200 m) is in the Pembroke Peninsula of SW Wales. In various places, the regularity of the normally well‐stratified limestone is broken by zones of disturbance, which are spectacularly displayed in magnificent near‐vertical cliff sections. The zones generally occupy the whole of the 50 m‐high cliffs and are up to 300 m wide. The chief component of these zones is a chaotic, clast‐supported breccia, composed of angular limestone fragments welded together with varying degrees of firmness by sparry calcite veining or a normally sparse, red‐pink sandy or silty matrix. The breccias are very easy to distinguish and form a striking contrast to the grey cliff scenery hereabouts ( Figs 1, 2 ), yet they have not been discussed much—until now. Figure 1 Open in figure viewer PowerPoint Location map, showing localities mentioned in the text, the outcrop of the Carboniferous Limestone, the chief synclinal axes and the distribution envelope of the Gash Breccias (after Thomas 1971 ). 1. Flimston Bay; 2. Bullslaughter Bay (west); 3. Bullslaughter bay (east); 4. Trevallen; 5. Box Bay; 6. Draught; 7. Whitesheet Rock; 8. Lydstep Point; 9. St Margaret's Point; 10. Den Point; 11. Valleyfield Top; 12. Pembroke Castle. 相似文献
