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991.
992.
Pierre Couture Simon A. Visser Raymond van Coillie Christian Blaise 《Aquatic Sciences - Research Across Boundaries》1985,47(2):127-158
The review focuses on the use of primary producers as a biological tool for evaluating the impact of damage by human activity (eutrophication, toxicity) on the aquatic environment. Studies are discussed following a reductionist approach by using algal bioassays (Selenastrum capricornutum). Variations of algal growth potential (AGP) within watersheds show the impact of human activities such as agriculture and urbanization, on water quality. The study of variation of the AGP in time allowed the investigation of the effect of abiotic (temperature, flow rate) and biotic factors (indigenous primary production) on the concentration of nutrients potentially available to phytoplankton. Seasonal changes of the AGP have further shown the impact of non-point (runoff) or point sources (sewage effluents) on the aquatic system. A staggered relationship was observed between AGP values and chlorophyll a content of indigenous phytoplankton. Values obtained in the laboratory by means of this type of approach would therefore appear to be transferably to natural systems. S. capricornutum was also used to identify toxic characteristics of substances (in pure form or used in formulations) and effluents released into the environment. It was shown that the user of bioassays should use care when evaluating results from tests requiring pretreatment such as storage, autoclaving and filtration. Cautious interpretation is also recommended in order to distinguish between effects of growth-limiting essential elements and the presence of toxic substances. In general it appears from this review that the AGP provides helpful information for a sound management of the aquatic environment. 相似文献
993.
Pierre Welander 《Dynamics of Atmospheres and Oceans》1982,6(4):233-242
A theoretical study is made of a simple mixed-layer model, in the form of a well-mixed constant-depth layer, forced from above by a heat flux kT(TA−T) and salinity flux kS(SA−S), where TA and SA are two reference values and T and S the temperature and salinity of the layer. The layer has a turbulent exchange of heat and salt with underlying water, kept at constant temperature and salinity, which is small in a statically stable case; large in a statically unstable case. If kT>kS, self-sustained oscillations may occur. In one cycle, a fast temperature rise, a slower salinity increase, and a final relaxation when the layer adjusts to the conditions of the underlying water, are observed. 相似文献
994.
Clinopyroxene composition as a method of identification of the magmatic affinities of paleo-volcanic series 总被引:3,自引:0,他引:3
Jacques Leterrier René C. Maury Pierre Thonon Danielle Girard Michèle Marchal 《Earth and Planetary Science Letters》1982,59(1):139-154
Uranium contents and234U/238U activity ratios have been determined for groundwaters from the Lincolnshire Limestone artesian aquifer in eastern England. Changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone. The western part of the aquifer, closest to recharge, is dominated by oxidising groundwaters which then enter a reducing zone towards the east, where there is an abrupt decrease in Eh and the chlorinity of the groundwaters begins to increase. Uranium contents in the oxidising zone range from 0.7 to 3.4 μg kg?1 and234U/238U activity ratio of this dissolved uranium is close to unity, the equilibrium value. The uranium content decreases abruptly when the grounwaaters enter the reducing zone, averaging 0.04 μg kg?1 east of the oxidation/reduction barrier. Simultaneously with the decrease in uranium content, there is an increase in234U/238U activity ratio and this ratio increases to a maximum within 7 km of the oxidation/reduction barrier. This increase in activity ratio is attributed to enhanced234U solution due to234Th recoil from uraniferous fissure surfaces east of the oxidising zone. The activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to234Th recoil from the oolith surfaces. However, the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium.234Th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium-bearing surfaces in the process of oolith cementation. 相似文献
995.
Vincent Renard Kazuaki Nakamura Jacques Angelier Jacques Azema Jacques Bourgois Christine Deplus Kantaro Fujioka Yozo Hamano Philippe Huchon Hajimu Kinoshita Pierre Labaume Yujiro Ogawa Tetsuzo Seno Akira Takeuchi Manabu Tanahashi Akinori Uchiyama Jean-Louis Vigneresse 《Earth and Planetary Science Letters》1987,83(1-4)
Leg 2 of the French-Japanese 1984 Kaiko cruise has surveyed the trench triple junction off central Japan, where the Japan, Izu-Bonin and Sagami Trenches intersect. The Izu-Bonin Trench is deeper than the Japan Trench and filled by a thick turbiditic series. Its anomalous depth is explained by the westward retreat of the edge of the northwestward moving Philippine Sea plate. On the contrary to what happens in the Japan Trench, horst and graben structures of the Pacific plate obliquely enters the Izu-Bonin Trench, suggesting that the actual boundary between these two trenches is located to the north of the triple junction. The inner wall of the Izu-Bonin Trench is characterized in the triple junction area by a series of slope basins whose occurrence is related to the dynamics of this area. The northernmost basin is overthrust by the edge of the fore-arc area of the Northeast Japan plate. The plate boundary is hardly discernible further east, which makes it impossible to locate precisely the triple junction itself. These features suggest that large intra-plate deformation occurs there due to the interaction of the plates involved in the triple junction and the weak mechanical strength of the wedge-shaped margin of the overriding plates. 相似文献
996.
Georges Boudon Michel P. Semet Pierre M. Vincent 《Journal of Volcanology and Geothermal Research》1987,33(4)
We recently reported (Boudon et al., 1984) on an eruption similar to that of May 18, 1980 at Mount St. Helens, that took place about 3100 years ago at la Soufrière, Guadeloupe. During the course of detailed geological mapping of the deposits of this event, older debris flow and blast deposits were recognized in the northern sector of the mapped area. Uncarbonized wood fragments in the debris flow have yielded ages ca. 11,500 y. B.P. The deposits extend from an amphitheater crater westward to the caribbean shore about 10 km downslope from the volcano. The deposits and crater structure suggest that they are the result of catastrophic flank failure like the event 3100 years ago. Unlike the latter activity, however, no magmatic component is found in the deposits. 相似文献
997.
998.
Helgard Boyer David C. Smith Christian Chopin Bernard Lasnier 《Physics and Chemistry of Minerals》1985,12(1):45-48
Raman microprobe (RMP) spectra of synthetic coesiste and three natural coesites from eclogite — facies rocks are provided and evaluated for characterisation purposes. The main coesite line lies at 521 cm?1 and the other characteristic lines attributed to coesite occur at 117, 177 and 271 cm?1. Two petrologically useful applications were (a) the confirmation of the coesite structure in very small natural crystals deduced to be coesite from petrographic observations only, and (b) the recognition of sub-microscopic crystallites of quartz in incipiently — transformed coesite in all the natural samples. 相似文献
999.
Inclusion of spherical charge relaxation in response to the long-range electrostatic potential (potential induced breathing, or PIB) gives improved results for the static and dynamic properties of oxides. PIB is a Gordon-Kim type model, in which the crystal charge density is estimated by overlapping ionic charge densities. No experimental data are used, except for the values of universal constants, and in this sense the results are from first principles. In contrast to earlier models which include some form of charge relaxation, we explicitly include the breathing effects on the self-energy and pair potentials in the model Hamiltonian. PIB is a many-body effect that couples the long-and short-range forces in a way that is not present in any other first principles or empirical models. It leads to the observed violations of the Cauchy relations for the elastic constants whereas central force rigid ion models cannot violate the Cauchy relations. PIB also reduces the predicted LO-TO splitting because the breathing effect introduces dynamical effective charges that are lower in magnitude than the ionic charges. Some results are shown and discussed for MgO (periclase), BeO (bromellite), Al2O3 (corundum), TiO2 (rutile) and SiO2 (quartz and stishovite). 相似文献
1000.
Pierre Dansereau 《Geoforum》1978,9(3):161-210
This paper attempts to place within an ecological framework the way in which man has appropriated and changed landscape. The ecosystem concept is used in order to facilitate a realistic examination of the ever changing relationship of man and nature. The resultant ecological grading of human settlements covers the full range of environments from “wild” to “urban”. It is hoped that such an approach will help to alert, educate, and instruct planners and decision makers as to the ecological cost of a number of problems which are normally viewed in economic, political, or social terms. 相似文献