Generation of evenly-spaced pressure-solution seams during (late) diagenesis: A kinetic theory     

Enrique Merino  Peter Ortoleva  Peter Strickholm 《Contributions to Mineralogy and Petrology》1983,82(4):360-370

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Temporal development of fabric in uniaxially stressed polycrystalline media—A theory     

Enrique Merino  Peter Ortoleva 《Contributions to Mineralogy and Petrology》1980,71(4):429-435

We present a kinetic theory for the development of lattice-preferred orientation in a uniaxiallystressed aggregate consisting of elastically uniaxial crystals. The fabric is brought about by grain-boundary migration alone; other fabric-producing mechanisms, such as plastic deformation, syntectonic recrystallization, and dissolution/reprecipitation, are specifically excluded from the theory. The formulation statistically averages the mass transfer between a typical crystal and its adjacent neighbors over all the possible crystallographic orientations of these neighbors and over all the possible orientations of the interfaces between the neighbors and the crystal of interest. The rate of mass exchange between two adjacent crystals is proportional (1) to the difference between chemical potentials and (2) to the surface area common to them. With these assumptions we find an equation for the massfraction density of crystals that have a given orientation (with respect to the stress) at any given time. The theory predicts that beyond a certain time a gap develops in the distribution of crystal orientations allowed: the only crystals that continue to exist are those for which the c-axis is within a certain, timedependent range about the stress.  相似文献   

Soil-structure interaction effects on the seismic response of tall chimneys     

J. Enrique Luco 《Soil Dynamics and Earthquake Engineering》1986,5(3)

The effects of soil-structure interaction on the seismic response of tall (>100m) steel and reinforced concrete chimneys are described. Detailed models of a 130m high steel chimney and a 150m high reinforced concrete chimney are used as structural models. The foundations are represented as rigid blocks resting on a uniform viscoelastic soil model. Perfect bonding between the foundation and the soil is assumed. Parametric studies of the interaction effects on the magnitude and distribution of bending moments and shear forces include four soil rigidities and two seismic excitations characterized by very different frequency contents. The results obtained indicate strong interaction effects for intermediate and soft soils (V_s500 m/sec). The extent of the interaction effects are highly dependent on the characteristics of the seismic excitation.  相似文献   

Luna 20 pyroxenes: exsolution and phase transformation as indicators of petrologic history     

Subrata Ghose  I.Stewart McCallum  Enrique Tidy 《Geochimica et cosmochimica acta》1973,37(4):831-839

Pyroxenes from our sample of Luna 20 soil are predominantly orthopyroxene with subordinate pigeonite. The orthopyroxenes are chromium-rich bronzites and contain submicroscopic lamellae of augite in a twinned orientation exsolved on (100). These lamellae have a composition close to the diopside-hedenbergite join. Asymmetric diffuse streaks parallel to $\text{a}{}^1$ indicate stacking faults parallel to (100) and possibly very thin (10–20 Å) lamellae of clinobronzite parallel to (100). Pigeonite crystals are very complex crystallographically and chemically, with optically visible (001) augite exsolution lamellae and two sets of chromite exsolution lamellae. In addition, there are submicroscopic (100) augite lamellae and a second generation of clinohypersthene lamellae which appear to have exsolved from the (001) augite lamellae. The clinohypersthene host, which has a large number of stacking faults parallel to (100), has partially inverted to hypersthene of the same composition. The hypersthene occurs as very fine lamellae (less than 1000 Å) parallel to the (100) plane of the clinohypersthene. X_D^Fe-Mg values for five host-lamellae pairs in pigeonite K-4 indicate a significant amount of subsolidus readjustment. We tentatively conclude that many of the bronzite and pigeonite crystals were derived from rocks crystallized from a high level magma chamber in the lunar highland crust.  相似文献   

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy   总被引：5，自引：1，他引：4  

Enrique Romero  Paul H. Simms 《Geotechnical and Geological Engineering》2008,26(6):705-727

With the advent of modern microstructural testing techniques and microstructure based constitutive models the microstructural characterisation of soils is gaining prominence. This paper reviews the history of microstructure investigation in unsaturated soils and discusses the engineering significance of this research to date. After a brief overview of the main microstructural techniques, the paper focuses on the evaluation of the current state of use and the development of two widely used techniques to study the microstructure of partially saturated soils, namely mercury intrusion porosimetry and the environmental scanning electron microscopy. The details of these techniques, their advantages and limitations, are first covered, followed by the presentation of selected test results. These results highlight the use of these techniques for understanding different hydro-mechanical behavioural features observed at macroscopic scale. Specifically, the paper shows the use of these techniques to explore the fundamental properties of water retention characteristics, water permeability, and micro and macrostructural interactions along different hydro-mechanical paths.  相似文献   

Resource partitioning among air‐breathing marine predators: are body size and mouth diameter the major determinants?          下载免费PDF全文

Fabiana Saporiti  Stuart Bearhop  Damián G. Vales  Laura Silva  Lisette Zenteno  Mauricio Tavares  Enrique A. Crespo  Luis Cardona 《Marine Ecology》2016,37(5):957-969

Although the body size of consumers may be a determinant factor in structuring food webs, recent evidence indicates that body size may fail to fully explain differences in the resource use patterns of predators in some situations. Here we compared the trophic niche of three sympatric and sexually dimorphic air‐breathing marine predators (the South American sea lion, Otaria flavescens, the South American fur seal, Arctocephalus australis, and the Magellanic penguin, Spheniscus magellanicus) in three areas of the Southwestern Atlantic Ocean (Río de la Plata and adjoining areas, Northern Patagonia and Southern Patagonia), in order to assess the importance of body size and mouth diameter in determining resource partitioning. Body weight and palate/bill breadth were used to characterize the morphology of each sex and species, whereas the trophic niche was assessed through the use of stable isotope ratios of carbon and nitrogen. The quantitative method Stable Isotope Bayesian Ellipses in R (SIBER) was used to compute the area of the Bayesian ellipses and the overlap of the isotopic niches. The results showed that morphological similarity was significantly correlated with isotopic distance between groups within the δ¹³C–δ¹⁵N bi‐plot space in the Río de la Plata area, but not in Northern and Southern Patagonia. Furthermore, resource partitioning between groups changed regionally, and some morphologically distinct groups exhibited a large trophic overlap in certain areas, such as the case of male penguins and male sea lions in Southern Patagonia. Conversely, female sea lions always overlapped with the much larger males of the same species, but never overlapped with the morphologically similar male fur seals. These results indicate that body size and mouth diameter are just two of the factors involved in resource partitioning within the guild of air‐breathing predators considered here, and for whom – under certain environmental conditions – other factors are more important than morphology.  相似文献   

Talus Instability in a Recent Deglaciation Area and Its Relationship to Buried Ice and Snow Cover Evolution (Picacho Del Veleta, Sierra Nevada, Spain)     

Antonio Gómez  David Palacios  Enrique Luengo  Luis M. Tanarro  Lothar Schulte  Miguel Ramos 《Geografiska Annaler: Series A, Physical Geography》2003,85(2):165-182

The southernmost glacier in Europe formed during the Little Ice Age at the foot of the north wall of Picacho del Veleta (3 398 m) in Sierra Nevada, in the southeast region of the Iberian Peninsula (lat. 37δ03‘N, long. 3δ22‘W). The glacier gradually retreated during the last century, leaving a large talus slope at the base of the wall. The unconsolidated material covering the ice masses acted as a thermal insulator. Recent bottom temperature of snow (BTS) analyses and drillings indicate that the ice still exists within the talus. Evidence from field observations made during the period 1995–2001, revealed that large mass movements occurred during the driest summers (1998 and especially, 1999 and 2000) when the talus was snow free. These conditions suggest a direct relationship between talus stability and thermal insulation from the snow cover in areas where buried ice or decaying marginal permafrost exists.  相似文献   

Downward particle fluxes in the Guadiaro submarine canyon depositional system (north-western Alboran Sea), a river flood dominated system     

Albert Palanques  Mohamed El Khatab  Pere Puig  Pere Masqu    Joan Albert S  nchez-Cabeza  Enrique Isla 《Marine Geology》2005,220(1-4):23-40

Three moorings equipped with sediment traps were deployed in the north-western Alboran continental margin to study downward particle fluxes in the Guadiaro submarine canyon depositional system. This area is located close to the Strait of Gibraltar and is influenced by the upwelling induced by the Atlantic Jet and by episodic flood events from the Guadiaro River. Sediment traps were installed in the Guadiaro Canyon, in the Guadiaro Channel and in the adjacent continental slope. The overall duration of the deployment was 12 months (from November 1997 to October 1998). Time-series of downward particle fluxes, major constituents (organic carbon, nitrogen, biogenic opal, calcium carbonate and lithogenics) and ²¹⁰Pb were determined near the surface at mid-depths and near the bottom. Total mass fluxes (TMF) in this area fluctuated more than two orders of magnitude and showed an important seasonal variability with higher fluxes in winter. Increases in TMF and lithogenics together with decreases in ²¹⁰Pb, organic carbon and opal were recorded in all traps coinciding with river floods, indicating a direct response of the system to these events and a rapid offshore transport of suspended matter affecting the entire water column. The channel site received similar particle fluxes to the western open slope site, indicating that this channel did not act as a preferential sediment conduit during the deployment period. In the Guadiaro Canyon, TMF were more than one order of magnitude higher, ²¹⁰Pb concentration was lower (one half) and organic matter was more degraded than at the channel site during spring and summer, as a consequence of receiving particles resuspended by internal waves and occasionally by trawling activities. These particles were mainly retained in the canyon, which works as a trap. Also, during spring and summer, the opal and organic carbon percentages increased in all traps both in magnitude and variability, and peaks seem to be associated with biological blooms.  相似文献   

Seasonal variation and structure of a decapod (Crustacea) assemblage living in a Caulerpa prolifera meadow in Cádiz Bay (SW Spain)     

Inmaculada Lpez De La Rosa  Antonio Rodríguez  J. Enrique García Raso 《Estuarine, Coastal and Shelf Science》2006,66(3-4):624-633

The decapod taxocoenosis living in shallow muddy bottoms with the green algae Caulerpa prolifera was studied monthly between February 1994 and January 1996 in the Inner Bay of Cádiz (SW Spain). More than 32,000 specimens belonging to 35 species were collected. Six species were dominant (representing the 85.8% of the total number of specimens), but the structure of the taxocoenosis was regulated by the Hippolyte species, Sicyonia carinata, Palaemon adspersus and Liocarcinus arcuatus. There was no significant qualitative difference between years. There was no clear change in the dominance of groups of species during the year, as happened in the outer Bay. This is probably due to the sheltered character of the area and the more stable and dense vegetal cover, but some seasonal differences were found.The benthic characteristics of the Inner Bay of Cádiz, such as shallow soft bottoms of fine and muddy sediments and the presence of macrophytes (seagrasses and seaweeds) might be key factors influencing the composition and structure of the general and seasonal decapod assemblage. In spite of human impacts on the bay (e.g. aquaculture activities, sewage), the values of the diversity, equitability and richness indexes appeared stable over time (higher than those found in outer adjacent areas) and no significant differences between years were found.  相似文献   

Reply to “Discussion of “From saturated to unsaturated conditions and vice versa” by M. Lloret-Cabot et al. (DOI 10.1007/s11440-017-0577-6)” by S. Qi et al. (DOI 10.1007/s11440-017-0625-2)     

Martí Lloret-Cabot  Simon J. Wheeler  Jubert A. Pineda  Enrique Romero  Daichao Sheng 《Acta Geotechnica》2018,13(2):493-495

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