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The demand for energy services is growing rapidly in developing countries. Low levels of energy efficiency in electric power supply and in energy use mean that the energy sector threatens to absorb an intolerably high share of available financial resources. Energy inefficiency also contributes to local and global environmental problems. A strategy of vigorously improving energy efficiency is thus a key element of a sustainable development path. Results reported in this paper show that there is considerable room for efficiency improvement in both existing and new capital stocks, but a much larger effort than presently underway is essential if the potential is to be realized. Assistance from the industrialized countries can play a major role in such an effort.  相似文献   
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Total fatty acid compositions of colonies of two hermatypic, reef-building corals collected during the day-time over a depth range of 21 m were determined to assess the effect of depth-related environmental factors upon the lipid content of these organisms. No systematic changes were found, suggesting a steady-state balance between algal and animal lipogenesis in these symbiotic partnerships. Stephanocoenia michelinii, a day and night feeder, contained lipids indicative of external dietary sources such as copepods, whereas Montastrea annularis, a night feeder, did not.  相似文献   
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Ornaments are believed to signal an individual's ability to reproduce successfully and/or survive. Since an individual's fitness is often influenced by multiple traits (e.g. number of copulations, ability to acquire nest sites or to escape predators), which are difficult to quantify simultaneously, we examine performance traits (bite force, jumping performance) believed to be relevant to an individual's fitness. Specifically, we ask whether variation in dewlap size is related to variation in body size, bite force and jumping ability in the lizard Anolis carolinensis. Our results show that dewlap size is correlated with jumping capacity across all individuals, whereas the relationships between dewlap size, body size and bite force differ depending on sex/age class. We argue that selection against relatively large dewlaps at the transition between small mature and large mature males might be responsible for the lack of a relationship within large males. The absence or presence of a correlation between dewlap size and bite force, on the other hand, might be explained by differences in behaviour, such as territory establishment, anti-predator tactics, and/or mate choice. Our work thus suggests that selective forces influencing the evolution of ornaments may operate differently on different sexes and life-history stages.  相似文献   
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Transvaginal chorionic villus sampling (CVS) using concurrent transabdominal ultrasound guidance was performed in six women who desired CVS but could not be offered transcervical or transabdominal approaches because of uterine position and placental location. Satisfactory amounts of chorionic villi were obtained in all six cases with no maternal discomfort, an occurrence that contrasts with our experience in transvaginal CVS using endovaginal ultrasound guidance. We believe that transvaginal CVS using concurrent transabdominal ultrasound guidance warrants consideration as an alternative technique for first-trimester CVS in selected patients.  相似文献   
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Uptake and localisation of lead in the root system of Brassica juncea   总被引:1,自引:0,他引:1  
The uptake and distribution of Pb sequestered by hydroponically grown (14days growth) Brassica juncea (3days exposure; Pb activities 3.2, 32 and 217microM) was investigated. Lead uptake was restricted largely to root tissue. Examination using scanning transmission electron microscopy-energy dispersive spectroscopy revealed substantial and predominantly intracellular uptake at the root tip. Endocytosis of Pb at the plasma membrane was not observed. A membrane transport protein may therefore be involved. In contrast, endocytosis of Pb into a subset of vacuoles was observed, resulting in the formation of dense Pb aggregates. Sparse and predominantly extracellular uptake occurred at some distance from the root tip. X-ray photoelectron spectroscopy confirmed that the Pb concentration was greater in root tips. Heavy metal rhizofiltration using B. juncea might therefore be improved by breeding plants with profusely branching roots. Uptake enhancement using genetic engineering techniques would benefit from investigation of plasma membrane transport mechanisms.  相似文献   
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Examination of the benthic nematode fauna of the soft surface sediments of a turtle grass (Thalassia testudinum König) bed in Biscayne Bay (Miami, Florida) has revealed a high degree of homogeneity exemplified by the dominance of four species out of approximately 100 nematode taxa from the area. The dominant species, Metoncholaimus scissus, Theristus fistulatus, Spirinia parasitifera and Gomphionema typica, regularly comprised between 87 and 95% of the total number of nematodes present in samples collected during the winter and spring of 1966. T. fistulatus showed an abundance of 56% over the course of the study, i.e., 160 samples collected over a period of 14 months. Maximal peaks in population densities were noted and correlated with physiographic alterations in the environment. The M. scissus population declined concurrent with changes in the community; at the same time, with accumulation of sediment, the Terschellingia longicaudata population increased. Ratios of species, and especially shifts in the dominantforms present, with repeated collections, are extremely useful indicators of important biological and physical changes in a particular environment. Analysis of distributional data on dominant species in 64 samples from eight closely approximated positions showed that observed temporal and spatial variations were not significant statistically at the 5% level. It is concluded that erroneous observations can be made from ecological studies based on field data derived without proper replication or consideration of seasonal factors. The latter as well as intrinsic variability within the particular locality itself contribute to the basic faunistic composition of benthic communities.This work was supported by Grant 12482 from the National Institute of Health to the Institute of Marine Science, University of Miami, and is a contribution (No. 819) from the Institute of Marine Science and from the Nematology Section, Entomology Research Institute, Research Branch, Canada Department of Agriculture, Ottawa.  相似文献   
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In 2004 and 2005, the East Tennessee Ozone Study (ETOS) enhanced its regional measurement program with annular denuder systems to quantify sulfur dioxide (SO2) and PM2.5 sulfate (SO42?) at five sampling sites that were representative of the complex terrain and physiographic features of East Tennessee. Intersite spatial variability was more defined for SO2 than for SO42?, which showed a fairly uniform structure in both daytime and nighttime measurements. Pollution roses indicated that two sites may have been influenced by the proximity of SO2 emission sources. The data suggest that SO2 is affected by nearby sources in the study area while the sources of SO42? are regionally distributed.  相似文献   
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