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排序方式: 共有215条查询结果,搜索用时 15 毫秒
191.
A. Kudo J. Zheng R.M. Koerner D.A. Fisher D.C. Santry Y. Mahara M. Sugahara 《Journal of environmental radioactivity》1998,40(3):263
Recent advancements in analytical technology make it possible for artificial radionuclides released from nuclear explosions to be detected in Arctic ice core layers. The fission product, 137Cs, and the unexpended fission material, 239+240Pu, originating from the Nagasaki A-bomb of August 1945, were measured by collecting 10 ice cores on the Agassiz ice cap, Ellesmere Island, Canada. The deposition rates were 0·020 mBq cm-2 for 137Cs and 0·0016 mBq cm-2 for 239+240Pu, originating from Nagasaki. Assuming the radionuclides, excluding the amount fissioned from the explosion and deposi-ted as local fallout, are deposited evenly throughout the Northern Hemisphere, 67% of the expected amount of 137Cs reached the Arctic while 1·1% of 239+240Pu reached the Arctic. The results suggest that different transport mechanisms exist for various contaminants in the global transport system. 相似文献
192.
The influence of swimming speed on sustained swimming performance of late-stage reef fish larvae 总被引:3,自引:0,他引:3
Replicate clutches of larvae were swum in a swimming flume at 4, 7, 10, 13, and 16 cm s-1 and the time swum until exhaustion recorded. There was a significant relationship between sustained swimming time and swimming speed for both maximum (R2=0.77; P<0.05) and mean sustained swimming times (R2=0.78; P<0.05), with fish swimming at slower speeds swimming longer and covering greater total distances. The relationship observed agrees with theoretical principles relating increasing swimming speed with increasing drag. We used our data for Amphiprion melanopus, combined with published information, to predict the swimming speeds that other reef fish taxa should be able to maintain for significant lengths of time (12-48 h) using three different models. The results agree well with field estimates (R2 values from 0.45 to 0.84), suggesting that there may be underlying factors influencing swimming ability in reef fish larvae that can be used to predict swimming abilities of different taxa. These models suggest that sustained swimming behaviour by reef fish larvae could have a much greater impact on modifying larval dispersal than previously thought. 相似文献
193.
B.E.A. Fisher M.P. Ireland D.T. Boyland S.P. Critten 《Environmental Modeling and Assessment》2002,7(4):291-299
There has been some discussion within the UK modelling community regarding the preferred choice of dispersion model for assessing the air quality impact of elevated point sources, each of which is reported to perform better than the other in certain circumstances. Coupled to this is the growing acceptance within the modelling community to include some recognition of model uncertainty in its reporting. As computer processing speeds increase further, this paper considers the possibility of using more than one model and highlights some of the advantages in doing so. 相似文献
194.
195.
McGee BL Pinkney AE Velinsky DJ Ashley JT Fisher DJ Ferrington LC Norberg-King TJ 《Environmental monitoring and assessment》2009,156(1-4):51-67
The Sediment Quality Triad (SQT) consists of complementary measures of sediment chemistry, benthic community structure, and sediment toxicity. We applied the SQT at 20 stations in the tidal portion of the Anacostia River from Bladensburg, MD to Washington, DC to establish a baseline of conditions to evaluate the effects of management actions. Sediment toxicity was assessed using 10-day survival and growth tests with the freshwater amphipod, Hyalella azteca and the midge, Chironomus dilutus. Triplicate grabs were taken at each station for benthic community analysis and the Benthic Index of Biotic Integrity (B-IBI) was used to interpret the data. Only one station, #92, exhibited toxicity related to sediment contamination. Sediments from this station significantly inhibited growth of both test species, had the highest concentrations of contaminants, and had a degraded benthic community, indicated by a B-IBI of less than 3. Additional sediment from this station was tested and sediment toxicity identification evaluation (TIE) procedures tentatively characterized organic compounds as the cause of toxicity. Overall, forty percent of the stations were classified as degraded by the B-IBI. However, qualitative and quantitative comparisons with sediment quality benchmarks indicated no clear relationship between benthic community health and contaminant concentrations. This study provides a baseline for assessing the effectiveness of management actions in the Anacostia River. 相似文献
196.
Nicholas E. Manos M.A Gail F. Fisher M.A 《Journal of the Air & Waste Management Association (1995)》2013,63(1):5-11
Atmospheric pollution by sulfur oxides is discussed in terms of the sources of the pollutant and the possible methods of control. Possible approaches to control are classified in general categories, including fuel desulfurization, process modifications, and flue-gas desulfurization. Some of the more promising specific possibilities are discussed in relation to the organizations developing them. 相似文献
197.
G. E. Fisher T. A. Huls 《Journal of the Air & Waste Management Association (1995)》2013,63(10):666-671
The Saltzman Phenoldisulfonic Acid and Nondispersive Infrared methods have been compared for the determination of oxides of nitrogen in automobile exhaust. The main purpose of this investigation was to determine whether the Nondispersive Infrared method could be used as a possible replacement for the Saltzman method. Results show that the Nondispersive Infrared analyzer can be used to measure NOx in exhaust gases with advantages over both the Saltzman and Phenoldisulfonic Acid methods. These advantages include simplicity, speed, less complicated analytical technique, and the fact that it is better adapted to be carried out by technicians at the test site. 相似文献
198.
The Honorable Joseph L. Fisher 《Journal of the Air & Waste Management Association (1995)》2013,63(9):910-912
The subject of energy choices and public policy is one that has interested me at a professional level. The outlook for energy supply for Americans is uncertain. Will the OPEC crank the per barrel price of world oil up again this fall by three or four dollars? We don’t know. Will the cost of finding and developing new domestic oil reserves continue to rise, and will the domestic production continue to fall as it has been doing since 1970? We don’t know. Would regulating the price of old oil and natural gas entering into interstate commerce bring forth significantly increased supplies? We don’t know. The chances for reducing oil consumption—or at least checking the rate of increase—are equally uncertain. Will still higher prices, brought on by whatever means, cause people and industries to use less oil? We don’t know. Will demand shift away from oil and natural gas to cheaper, more plentiful energy sources? We don’t know. Will penalties, taxes, or exhortations get the motor vehicle industry to produce more gasoline efficient cars and trucks? We don’t know. We may not even get a chance to try. Will new, less energy intensive lifestyles take over? We don’t know. 相似文献
199.
The hydrothermal vent vestimentiferans Riftia pachyptila Jones, 1981 and Ridgeia piscesae Jones, 1985 live in habitats with different abundances of external CO2. R. pachyptila is found in areas with a high input of hydrothermal fluid, and therefore with a high [CO2]. R. piscesae is found in a range of habitats with low to high levels of hydrothermal fluid input, with a correspondingly broad range of
CO2 concentrations. We examined the strategies for dissolved inorganic carbon (DIC) use by the symbionts from these two species.
R. pachyptila were collected from the East Pacific Rise (9°50′N; 104°20′W) in March 1996, and R. piscesae were collected from the Juan de Fuca Ridge (47°57′N; 129°07′W) during September of 1996 and 1997. The differences in the
hosts' habitats were reflected by the internal pools of DIC in these organisms. The concentrations of DIC in coelomic fluid
from R. piscesae were 3.1 to 10.5 mM, lower than those previously reported for R. pachyptila, which often exceed 30 mM. When symbionts from both hosts were incubated at in situ pressures, their carbon fixation rates increased with the extracellular
concentration of CO2, and not HCO3
−, and symbionts from R. piscesae had a higher affinity for CO2 than those from R. pachyptila (K
1/2 of 7.6 μM versus 49 μM). Transmission electron micrographs showed that symbionts from R. piscesae lack carboxysomes, irrespective of the coelomic fluid [DIC] of their host. This suggests that the higher affinity for CO2 of R. piscesae symbionts may be their sole means of compensating for lower DIC concentrations. The δ13C values of tissues from R. piscesae with higher [DIC] in the coelomic fluid were more positive, opposite to the trend previously described for other autotrophs.
Factors which may contribute to this trend are discussed.
Received: 24 September 1998 / Accepted: 12 May 1999 相似文献
200.
It is possible to develop large quantities of energy by installing a comprehensive regional insulation program. This paper develops a computer model for examining the quantity of energy that may be saved in a region if such a program is undertaken. The program requires data on: number of houses, type of houses and present degree of insulation. The results indicate that in the region under consideration it is possible to make available more energy, far cheaper, through insulation than by the alternative of constructing a large power plant. 相似文献