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61.
62.
Emilio Rosenblueth 《地震工程与结构动力学》1979,7(1):49-61
In December 1976 the new version of Mexico's Federal District Building Code was officially approved. It differs from previous versions in several matters: design values are based on a probabilistic assessment of seismicity, on a more careful and better substantiated consideration of wave filtering through the peculiar lacustrine soil and on approximate design optimization; ductility receives explicit treatment; and there are significant improvements in the treatment of overturning moments, torques, etc. The paper discusses these matters and contains information on code evolution in Mexico and on the implementation in the Federal District. 相似文献
63.
With the aim of studying the interspectific differences in the bioaccumulation of a series of elements in six species of estuarine
macrophytes, we measured the concentrations of various metals (Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn), as well as C and N, in
several species of macroalgae and one species of seagrass in estuaries in northwest Spain. To facilitate the interpretation
of the results, we also determined the concentrations of the same metals in sediments. Contamination by particulate metal
did not appear to be important. The levels of Cu in the different species were generally high in comparison with those found
in similar studies; in contrast, the concentrations of Pb and Zn were relatively low. The metal concentrations showed greater
variability and a distibution that was further from normal than those of C and N. In general the highest concentrations of
elements were found inEnteromorpha spp. andZostera noltii, and the lowest occurred inUlva spp. There were several significant positive correlations among tissue concentrations of Cr, Cu, and Ni. There were also
significant correlations between tissue concentrations of N and Zn, suggesting possible synergetic effects between them. Cluster
analysis clearly revealed that the chemical composition ofZ. noltii differed from that of the macroalage. Macroalgae were not grouped according to their taxonomic position, therefore it appears
that the concentrations of the elements depended more on the ecological traits of the macroalgal species rather than on any
possible, physiological differences among different taxonomic groups. Of the species studied,Ascophyllum nodosum andEnteromorpha spp. appeared to be the best biomonitors of metal contamination. 相似文献
64.
William E. Brooks Jason C. Willett Jonathan D. Kent Victor Vasquez Teresa Rosales 《Landslides》2005,2(2):117-123
Debris flows caused by El Niño events, earthquakes, and glacial releases have affected northern Perú for centuries. The Muralla Pircada, a northeast-trending, 2.5 km long stone wall east of the Santa Rita B archaeological site (Moche-Chimú) in the Chao Valley, is field evidence that ancient Andeans recognized and, more importantly, attempted to mitigate the effects of debris flows. The Muralla is upstream from the site and is perpendicular to local drainages. It is 1–2 m high, up to 5 m wide, and is comprised of intentionally-placed, well-sorted, well-rounded, 20–30 cm cobbles and boulders from nearby streams. Long axes of the stones are gently inclined and parallel local drainage. Case-and-fill construction was used with smaller cobbles and pebbles used as fill. Pre-Muralla debris flows are indicated by meter-sized, angular boulders that were incorporated in-place into construction of the dam and are now exposed in breeches in the dam. Post-Muralla debris flows in the Chao Valley are indicated by meter-sized, angular boulders that now abut the retention dam. 相似文献
65.
Anisotropy of magnetic susceptibility (AMS) and paleomagnetic methods have been applied on the middle Miocene–Pleistocene sedimentary sequence in the Boso and Miura Peninsulas of central Japan in order to identify the invisible regional deformation sense as well as the intensity of deformation of sediments. The southern sequences of the two peninsulas were subjected to syn-sedimentary deformation of folding and faulting generated in compressional tectonics. A previous result of the AMS experiment on the sequences shows a development of a strong magnetic lineation. Thus, it is conceivable that the lineation had to be generated during the process of deformation, and in a direction perpendicular to the shortening. However, the orientation of the magnetic lineations is inconsistent among the different tectonic domains in the southern sequence. The paleomagnetic declination in each domain reveals a clockwise rotation in various degrees. Reconstructed directions of the magnetic lineations show a consistent pattern in the east–west direction, suggesting that the sedimentary sequence was subjected to a north-southward compression. In contrast, the compressive direction of the sediment cover on the Pliocene–Pleistocene sequence reveals a northwest direction. Our results suggest that the Philippine Sea Plate had been subducting northward during the middle Miocene–Pliocene, and changed its direction during the Pliocene. 相似文献
66.
Emilio F. Moran Ryan Adams Bryn Bakoyéma Stefano Fiorini T. Bruce Boucek 《Climatic change》2006,77(3-4):343-361
This article reports on findings of a research project examining farmers' coping strategies in the Brazilian Amazon in response to El Niño related weather events. We examine the extent of vulnerability of small and large farmers to these events in a tropical rainforest environment. Little attention has been given to the impact of ENSO events in Amazônia, despite evidence for devastating fires during ENSOs. Although we found a range of locally developed forecasting techniques and coping mechanisms, farmers have sustained significant losses, and we suggest that increased access to scientific forecasts would greatly enhance the ability of the farmers in our study area to cope with El Niño related weather events. In Amazônia the El Niño phase of the El Niño-Southern Oscillation (ENSO) climate pattern leads to an extended period of reduced rainfall (Hobbs et al., 1998). This period of reduced rainfall can result in significant agricultural losses for farmers and ranchers in the area and in increased forest flammability. We have found that the majority of our study population uses several methods of forecasting, coping with, and adapting to drought events – and they recognize the economic losses they can experience and the loss of forests through the accidental spread of fire. The poorest farmers in our study area experience El Niño related drought events as a serious threat to their livelihoods. Their vulnerability is heightened during extreme climate events and our observations revealed that all of the farmers in our study would benefit from increased availability of improved forecast information relevant to their locality and their current farming strategies. This paper examines the availability and use of forecasts, the occurrence of accidental fires and techniques to prevent fire related losses, and the coping mechanisms for dealing with El Niño related drought in the agricultural regions surrounding the cities of Altamira and Santarém, in Pará State, Brazil. Distribution of an El Niño Prediction Kit at the end of the study and a series of workshops may lead to better local information on rainfall variability and create a farmer-maintained grid of collecting stations to sensitize farmers to the variability of precipitation in the region, and on their property. 相似文献
67.
Spain is a relatively large European country (ca. 500,000 km2) with extensive semiarid areas in which there exists a large number of good aquifers. In some areas, these aquifers are intensively
developed and are the most important sources of fresh water. Nevertheless, groundwater development and protection has rarely
been duly considered by the Spanish Water Administration, despite the pressure to remedy this situation by various groups
of experts, some of them members of the Water Administration. The Spanish Committee of the International Association of Hydrogeologists
(IAH) has been very active during the last decade in promoting activities to spread groundwater science, technology, and management
in Spain and outside, mostly in Latin America, and in trying to orient water policy toward issues of groundwater. These activities
include mainly the organization of technical and scientific meetings on current topics such as groundwater in the new Water
Act, overexploitation, groundwater in water-resources planning, groundwater pollution, natural-recharge estimation and others.
The impact of these activities on the recent water policy of Spain seems significant, and the experience gained may be applicable
to other countries.
Received, February 1997 · Revised, July 1997 · Accepted, July 1997 相似文献
68.
Under thhe drought conditions that have occurred in Bulgaria during the last decade, agricultural use of non-conventional water may be an important resource. This is a specific case of simultaneous purification and utilisation by soil ecological systems. However, using non-conventional quality water presents a number of ecological and health risks and poses problems connected with soil and surface and ground water contaminated and with producing crops of acceptable quality. Bulgaria's municipal, industrial, and rural wastewater reclamation and reuse, in addition to other non conventional water resources as sea water, drainage water and mineralised groundwater, may be a reliable source even in drought years and thus is capable of replacing potable used in agriculture. This paper reviews the work of the authors and their colleagues in assessing the irrigation potentials of waste water in Bulgaria. 相似文献
69.
70.
Attention is first focused on the probability distributions of the exceedance rates of given earthquake magnitudes when the generation process is idealized as Poisson. But data on significant disturbances are always scarce. Local-seismicity assessment is hence guided by information from tectonically similar areas, but ordinarily the guidance is intuitive. Bayesian statistics constitute the tool to do this rationally. Two more alternatives are presented and illustrated here. The approach is extended to a generating process that includes the Poisson as a special case. 相似文献