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191.
In this paper, the pull-out performance of an innovative system for soil anchoring is mechanically interpreted on the basis of a preliminary finite element investigation. The system consists of a tie rod equipped with thick steel sockets, extruding into the soil to increase the overall pull-out bearing capacity. The effectiveness of the anchorage is shown to be mainly due to the steel sockets, producing two correlated strength mechanisms: a direct one, associated with the shear/flexural strength of the sockets themselves; and an indirect one, in the form of a remarkable increase in the normal confinement on the tie rod and hence in the mobilizable shear stresses. The numerical results are finally exploited to conceive a simplified mechanical model for the interpretation/prediction of the pull-out anchor performance. 相似文献
192.
Claudio Di Celma Gino Cantalamessa Walter Landini Luca Ragaini 《Sedimentary Geology》2010,223(1-2):162-179
Shelf-indenting canyons and their tributary systems are fairly common constituents of Quaternary shelves of active continental margins, but they have been rarely reported from older successions. Recognition of these prominent geomorphologic features in the ancient record has important implications not only for a proper understanding of shoreface-to-shelf depositional systems, but also from a petroleum exploration standpoint as they represent efficient conduits for moving coarse-grained river- and nearshore-borne sediments to the adjacent slope even during periods of relative rise in sea level.Coastal exposures of the lower Pliocene Súa Member in the surroundings of Súa (northwest Ecuador), preserve the unusual juxtaposition of incising submarine channels onto nearshore deposits. This succession accumulated along a narrow, active continental margin during tectonically induced transgression and affords a rare opportunity to evaluate the stratigraphic evolution of such systems from an outcrop perspective. A comprehensive facies characterization combined with application of sequence stratigraphic concepts has led to definition of the following physical surfaces and stratal units in ascending order. (i) A polygenetic, regionally extensive erosional surface resulting from the superposition of the wave ravinement surface onto the previous subaerial sequence boundary (SB/wRS). (ii) A nearshore, sand-prone lithofacies succession comprising a condensed basal shellbed deepening upwards through lower-shoreface bioturbated silty sandstones, into inner shelf sandy mudstones. (iii) Two steep, U-shaped erosional features (turbidite shelf-entrenchment surfaces), interpreted as shelf channels, deeply incised into the subjacent nearshore sediments and marking an abrupt deepening of facies. (iv) A thick, fining-upward sedimentary succession laid down within the confines of the channels by high- and low-density turbidity currents and including both bed-load (traction) and suspended-load deposits; the overall fining- and thinning-upward character exhibited by the infill of these channels is thought to reflect decreasing flow energies and is consistent with the gradual cut-off of clastic influx to their upper reaches in response to progressive detachment from an adjacent coastal source during relative rise in sea level.Based on detailed analysis of facies and a sequence stratigraphic interpretation of outcrop data, this study contributes to extend the existing sequence stratigraphic schemes, further attesting that shelf-sediment bypass and deep-water sedimentation can take place at sea levels other than lowstand. 相似文献
193.
A bacterial copper-resistant strain was isolated from a hatchery-conditioned adult of the scallop Argopecten purpuratus and was identified as Vibrio sp. according to its physiological characteristics. The lowest concentration of Cu2+ required for its complete inhibition in VNSS medium was 50 microg ml(-1). The Vibrio strain was found to accumulate copper, exhibiting cellular and loosely bound copper levels of 201.14 and 493.21 microg g(-1) dry weight, respectively, after 24 h of incubation in VNSS medium supplemented with 15 microg ml(-1) of Cu2+, with cellular concentration factors of 10.17 and 14.35 after 12 and 24 h of exposure. When a scallop larvae culture was exposed to a concentration of 6.46 x 10(2) CFU ml(-1) of Cu-enriched Vibrio, they accumulated 20.42 +/- 1.12 and 30.96 +/- 1.85 microg Cu2+ g(-1) dry weight after 12 and 24 h, respectively. This study suggests that bacterial copper accumulation could be very active in marine environments increasing the occurrence of copper transfer to marine food chains. 相似文献
194.
Ken O’Hara-Dhand Richard L. S. Taylor Ian James Smalley David H. Krinsley Claudio Vita-Finzi 《Central European Journal of Geosciences》2010,2(1):45-51
Impact between windblown quartz grains as a source of desert dust is consistent with laboratory abrasion experiments and has received some field confirmation in the Negev. The suggestion is that an important process on Mars now gains support from laboratory studies; even though their geochemical interpretation is controversial, they show that dust generation by impact is tenable even for quartz. A simple mechanism for small dust production from sand seas is proposed; internal stresses can be mobilized by impact energy. A speculative mechanism (the andesite scenario) is proposed for fine particle production by particle impact on Mars. The internal stress range in terrestrial sand grains may vary, depending on the nature of the source rock, and this may influence particle production by impact processes. 相似文献
195.
Claudio Tomasi Stefano Marani Vito Vitale Frank Wagner Alessandra Cacciari Angelo Lupi 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):734-749
Measurements of direct solar irradiance were taken employing 4 different sun‐photometers at near infrared wavelengths, suitable for use in atmospheric hygrometry. This technique utilising a set of spectral ratios, in and out of selected water vapour absorption bands, was applied to the measurements to obtain accurate evaluations of precipitable water. For all the hygrometric ratios given by the 4 sun‐photometers used at the 3 stations of Sagres, Monchique and Mt. Foia, during the CLEARCOLUMN experiment, we determined the calibration curves by correcting them for the Rayleigh scattering effects and, then, plotting the natural logarithms of such corrected ratios versus the square root of the water vapour mass present along the atmospheric slant path. The regression lines drawn for the various scatter diagrams were estimated to give evaluations of precipitable water with an uncertainty of less than 5%, 3% and 10% at the 3 stations, respectively. The calibration curves of the sun‐photometer located at the Sagres station were determined using the precipitable water evaluations obtained from the local radiosounding measurements taken on 5 clear‐sky days. Those of the sun‐photometers used at the Monchique and Mt. Foia stations were instead determined through intercomparison between subsets of measurements simultaneously taken with various instruments at Sagres and Mt. Foia. Using these calibration curves, we examined all the field measurements determining the time‐patterns of precipitable water at the 3 stations. During the period from 16 June to 25 July 1997, precipitable water was found to vary between 1.1 and 3.7 g cm−2 at the Sagres station (with an accuracy within ±13%), between 1.0 and 2.8 g cm−2 at Monchique (±11%) and between 0.8 and 3.0 g cm−2 at the top of Mt. Foia (±26%). 相似文献
196.
197.
Manuela Cecconi Antonio DeSimone Claudio Tamagnini Giulia M.B. Viggiani 《国际地质力学数值与分析法杂志》2002,26(15):1531-1560
A constitutive model for granular materials is developed within the framework of strain–hardening elastoplasticity, aiming at describing some of the macroscopic effects of the degradation processes associated with grain crushing. The central assumption of the paper is that, upon loading, the frictional properties of the material are modified as a consequence of the changes in grain size distribution. The effects of these irreversible microscopic processes are described macroscopically as accumulated plastic strain. Plastic strain drives the evolution of internal variables which model phenomenologically the changes of mechanical properties induced by grain crushing by controlling the geometry of the yield locus and the direction of plastic flow. An application of the model to Pozzolana Nera is presented. The stress–dilatancy relationship observed for this material is used as a guidance for the formulation of hardening laws. One of the salient features of the proposed model is its capability of reproducing the stress–dilatancy behaviour observed in Pozzolana Nera, for which the minimum value of dilatancy always follows the maximum stress ratio experienced by the material. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
198.
Role of the backstop-to-cover thickness ratio on vergence partitioning in experimental thrust wedges
The ratio between the thickness of the sedimentary sequences offscraped from the subducting plate ( H c ) and the average thickness of the backstop ( H b ) is expected to significantly influence vergence partitioning in thrust wedges. A series of simple sandbox experiments was performed to study the role of the H c / H b ratio in model thrust wedges. The results obtained show that thrust wedges with H c / H b values lower than 1 are essentially pro-ward verging, with minor retro-ward faulting; H c / H b values greater than 1 imply an increase of vergence partitioning. When a threshold value is exceeded, fully partitioned, doubly vergent thrust wedges develop. Comparison with natural submarine thrust wedges suggests that these experimental results may provide useful insights on the evolution of structural architecture at convergent margins. 相似文献
199.
Claudio Codella Rafael Bachiller Milena Benedettini Paola Caselli 《Astrophysics and Space Science》2003,287(1-4):171-174
The preliminary results from a multiline mm-wave survey of H2S and SO2 emission towards the Cepheus A star forming region are presented. Large scale maps (? 5'×4') and high-resolution line profiles which clearly indicate the occurrence of multiple H2S and SO2 outflows are reported. In particular, a 0.6 pc long outflow flowing towards South from the CepA-East position has been discovered. In addition, besides the well known regions CepA-East and CepA-West other four clumps of shocked gas have been detected. These clumps exhibit distinct H2S/SO2 ratios, suggesting different chemical compositions for different regions and show that in Cepheus A the mass loss has strongly modified the chemistry of the quiescent gas. 相似文献
200.