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271.
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 (Vs500 m/sec). The extent of the interaction effects are highly dependent on the characteristics of the seismic excitation. 相似文献
272.
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 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. XDFe-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
273.
A mathematical model to simulate stream/aquifer interactions in an unconfined aquifer subjected to time varying river stage was developed from the linearized Boussinesq equation using the principle of superposition and the concept of semigroups. The mathematical model requires an estimate of three parameters to simulate ground-water elevations; transmissivity, specific yield, and recharge. The solution has physical significance and includes terms for the steady-state water level, the steady-state water level as influenced by a change in river stage, a transient redistribution of water levels in the aquifer from the previous day, and a transient change in water level caused by a change in river stage. The mathematical model was tested using observed water table elevations at three locations across a 2-km-wide alluvial valley aquifer. The average absolute deviation between observed and simulated daily water levels was 0.09 m. The difference in river stage over the test year was 4.9 m. 相似文献
274.
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
275.
Food insecurity is a major concern in the United States, particularly in high-poverty areas and among households with children. Urban agriculture helps address food insecurity and promote recreation, aesthetics, biodiversity, and other benefits. This article reports a socioeconomic evaluation of ten different variables, including in situ analysis of healthy, nutritious food options, of a small, intensely urbanized city to identify neighborhoods that would benefit from urban agriculture. We produced a hierarchy of locations (using census block groups), from least to greatest socioeconomic need, for new urban agriculture sites. Our results found that one block group qualified in all ten variables and two-thirds demonstrated a need in at least half of the variables. The majority of these block groups were distributed within the middle of the city. 相似文献
276.
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
277.
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
278.
We have analyzed luminosity profiles of E galaxies studied by Strom and Strom in six clusters of galaxies. We have found a relationship between radius, luminosity, and surface brightness for galaxies in each of the clusters. A dependence of the zero point of the relation with the local projected density of galaxies is likewise found:r
e
proj
–0.14
L
0.445
I
e
–0.413
. This relationship implies (i) that there is not a universal luminosity profile for elliptical galaxies, (ii) the environmental variation of radius is larger than that produced by mergers of galaxies, (iii) distance to a galaxy can be estimated from apparent magnitude, surface brightness, angular size, and apparent local projected density of galaxies. 相似文献
279.
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
280.
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