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排序方式: 共有392条查询结果,搜索用时 15 毫秒
271.
Michel Potier Jocelyne Cousineau Lorraine Michaud Max Zolinger Serge B. Melançon Louis Dallaire 《黑龙江环境通报》1986,6(6):429-436
The intestinal microvilli of fetal origin in human amniotic fluid were purified by Ca2+ precipitation of contaminating organelles followed by differential centrifugation of microvillar membranes. In the purified preparation, the specific activity of the microvillar marker-enzymes maltase and sucrase increased about 77-fold over that in cell-free amniotic fluid. Significant contamination of the purified preparation by endoplasmic reticulum (microsomes) and lysosomes was ruled out on the basis of a low content of the marker enzymes glucose-6-phosphatase (microsomes) and acid phosphatase (lysosomes). Amniotic fluid microvilli contain typical enzymes of the fetal intestine including maltase, sucrase, trehalase, alkaline phosphatase and γ-glutamyltransferase, and their morphology by electron microscopy resembles that of vesiculated intestinal microvilli. Prenatal detection of genetic diseases due to a deficiency of a protein expressed in these membranes or associated to abnormal microvilli seems feasible. 相似文献
272.
Michel Jan Niklas Cathy Trudinger Jason Lowe Ben Matthews Brd Romstad Christiano Pires de Campos Natalia Andronova 《Environmental Science & Policy》2005,8(6):614
This paper evaluates the influence of different policy-related and scientific choices on the calculated regional contributions to global climate change (the “Brazilian Proposal”). Policy-related choices include the time period of emissions, the mix of greenhouse gases and different indicators of climate change impacts. The scientific choices include historical emissions and model representations of the climate system. We generated and compared results of several simple climate models. We find that the relative contributions of different nations to global climate change—from emissions of greenhouse gases alone—are quite robust, despite the varying model complexity and differences in calculated absolute changes. For the default calculations, the average calculated contributions to the global mean surface temperature increase in 2000 are about 40% from OECD, 14% from Eastern Europe and Former Soviet Union, 24% from Asia and 22% from Africa and Latin America. Policy-related choices, such as time period of emissions, climate change indicator and gas mix generally have larger influence on the results than scientific choices. More specifically, choosing a later attribution start date (1990 instead of 1890) for historical emissions, decreases the contributions of regions that started emitting early, such as the OECD countries by 6 percentage points, whereas it increases the contribution of late emitters such as Asia by 8 percentage points. However, only including the fossil CO2 emissions instead of the emissions of all Kyoto gases (fossil and land use change), increases the OECD contributions by 21 percentage points and decreases the contribution of Asia by 14 percentage points. 相似文献
273.
274.
de Bonis L Peigné S Likius A Mackaye HT Vignaud P Brunet M 《Die Naturwissenschaften》2007,94(7):575-580
We report on the oldest fox (Canidae) ever found in Africa. It is dated to 7 Ma based on the degree of evolution of the whole
fauna. It belongs to a new species. Its overall size and some morphological characteristics distinguish the Chadian specimen
from all the other foxes. The presence of Vulpes and of the genus Eucyon in slightly younger African locality, as well as in southwestern Europe in the late Miocene, may indicate that canids migrated
in Europe from Africa through a trans-Mediterranean route. 相似文献
275.
Municipal wastewaters are major sources of pollution for the aquatic biota. The purpose of this study was to determine the levels of some pharmaceutical products and the immunotoxic potential of a municipal wastewater aeration lagoon for the treatment of the domestic wastewaters of a small town with wastewater inputs from a 400-bed hospital complex. Endemic mussels were collected, caged and placed in the final aeration lagoon and at sites 1 km upstream and 1 km downstream of the effluent outfall in the receiving river for a period of 14 days. The results showed that the final aeration lagoon contained high levels of total coliforms, conductivity and low dissolved oxygen (2.9 mg/L) as well as detectable amounts of trimethoprim, carbamazepine, gemfibrozil, and norfloxacin at concentrations exceeding 50 ng/L. The lagoon effluent was indeed toxic to the mussel specimens, as evidenced by the appearance of mortality after 14 days (10% mortality), decreased mussel weight-to-shell-length ratio and loss of hemocyte viability. The number of adhering hemocytes, phagocytic activity, total nitrite levels and arachidonic cyclooxygenase activity were significantly higher in mussels placed in the final aeration lagoon. A multivariate analysis also revealed that water pH, conductivity, total coliforms and dissolved oxygen were the endpoints most closely linked with phagocytic activity, the amount of adhering hemocytes and loss of hemocyte viability. In conclusion, exposure of mussels to treated aerated lagoon wastewater is deleterious to freshwater mussels where the immune system is compromised. 相似文献
276.
Soizic Le Fur Emmanuel Fara Hassane Taïsso Mackaye Patrick Vignaud Michel Brunet 《Die Naturwissenschaften》2009,96(5):565-574
Characterizing the paleoenvironmental context of the first hominids is a key issue for understanding their behavioral and
morphological evolution. The present study aims at reconstructing the paleoenvironment of the TM266 vertebrate assemblage
(Toros-Menalla, Northern Chad) that yielded the earliest known hominid Sahelanthropus tchadensis (7 Ma). For the first time, a quantitative analysis is carried out on the fossil mammal assemblage associated with that hominid.
Two complementary approaches were applied: (1) the analysis of the relative abundances of taxa and their habitat preferences;
and (2) the study of the distribution of taxa within three meaningful ecovariables: locomotion, feeding preferences, and body
mass. The resulting taxonomic and paleoecological structures are used to reconstruct the diversity and the relative extent
of the habitats in that part of northern Chad seven million years ago. The paleoenvironment was composed of open areas with
dry and humid grasslands, prevailing over wooded habitats. Water was also widely available as freshwater bodies and certainly
swamps. It appears that the high habitat diversity of the landscape is a common feature among paleoenvironments associated
with early hominids. 相似文献
277.
Andries F. Hof Kelly C. de Bruin Rob B. Dellink Michel G.J. den Elzen Detlef P. van Vuuren 《Environmental Science & Policy》2009,12(7):832-843
Recent proposals at the UNFCCC meeting in Bali in December 2007 suggest that a 2% levy on the CDM could finance adaptation costs in developing regions. Other proposals include extending the scope of the levy to emissions trading. This study applies an Integrated Assessment Model to gain insight in the interactions between adaptation costs, residual damages and mitigation costs and to analyse the effectiveness of a 2% levy on both the CDM and emissions trading from developing countries. We show that adaptation is especially important in lower income regions where damages are higher. The revenues of a 2% levy strongly depend on both the climate mitigation target and the burden-sharing regime. A more stringent climate mitigation target results in more emissions trade and, in the longer run, less need for adaptation. Both factors increase the share of adaptation costs that can be funded. The burden-sharing regime strongly affects the revenues of a 2% levy as well: relatively more stringent targets for developed countries increase the revenues of a 2% levy. However, in the next two decades the share of adaptation that can be financed remains well below 20% in most cases. Additional funding mechanisms are therefore necessary to substantially finance adaptation costs in developing countries. 相似文献
278.
Christian Hermans Ann C. Vandaele Michel Carleer Sophie Fally Réginald Colin Alain Jenouvrier Bernard Coquart Marie-France Mérienne 《Environmental science and pollution research international》1999,6(3):151-158
Absorption spectroscopy, which is widely used for concentration measurements of tropospheric and stratospheric compounds,
requires precise values of the absorption cross-sections of the measured species. NO2, O2 and its collision-induced absorption spectrum, and H2O absorption cross-sections have been measured at temperature and pressure conditions prevailing in the Earth’s atmosphere.
Corrections to the generally accepted analysis procedures used to resolve the convolution problem are also proposed. 相似文献
279.
Julio César Marín Leal Stanislas Dubois Francis Orvain Robert Galois Jean-Louis Blin Michel Ropert Marie-Paule Bataillé Alain Ourry Sébastien Lefebvre 《Marine Biology》2008,153(4):673-688
Food sources for cultivated marine bivalves generally are not well identified, although they are essential for a better understanding
of coastal ecosystems and for the sustainability of shellfish farming activities. In addition to phytoplankton, other organic
matter sources (OMS), such as microphytobenthos and detritus (of terrestrial or marine origins), can contribute significantly
to the growth of marine bivalves. The aim of this study was to identify the potential food sources and to estimate their contributions
to the growth of the Pacific oyster (Crassostrea gigas) in two contrasting trophic environments of Normandy (France): the Baie des Veys (BDV) and the Lingreville area (LIN). Two
sites were studied in the BDV area (BDV-S and BDV-N) and one in the LIN area. To estimate the contribution of each type of
OMS, we used a combination of stable natural isotope composition (δ13C, δ15N) analysis of OMS and oyster tissue together with a modelling exercise. Field sampling was conducted every 2 months over
1 year. The sampled sources were suspended particulate organic matter from marine (PhyOM) and terrestrial (TOM) origins, microphytobenthos
(MPB), detrital organic matter from the superficial sediment (SOM), and macroalgae (Ulva sp., ULV). A statistical mixing model coupled to a bioenergetic model was used to calculate the contributions of each different
source at different seasons. Results showed that isotopic composition of the animal flesh varied with respect to the potential
OMS over the year within each ecosystem. Significant differences were also observed among the three locations. For instance,
the δ13C and δ15N values of the oysters ranged from −20.0 to −19.1‰ and from 6.9 to 10.8‰ at BDV-S, from −19.4 to −18.1‰ and from 6.4 to 10.0‰
at BDV-N, and from −21.8 to −19.4‰ and from 6.3 to 8.3‰ at LIN. The contributions of the different sources to oyster growth
differed depending on the ecosystem and on the period of the year. Phytoplankton (PhyOM) predominated as the principal food
source for oysters (particularly in the LIN location). MPB, TOM, and ULV detritus also possibly contributed to oysters’ diet
during summer and autumn at the BDV-S and BDV-N sites. SOM was not considered an OMS because it was already a mix of the other
four OMS, but rather a trophic reservoir that potentially mirrored the trophic functioning of marine ecosystems. 相似文献
280.
ebnem Andreani-Aksoyolu Johannes Keller Carlos Ordez Michel Tinguely Martin Schultz Andr S.H. Prvt 《Ecological modelling》2009,217(3-4):209
In this study, we investigated the effect of numerous regulations enforced since 1985 to improve air quality on ozone in Europe with the focus on Switzerland, using the Comprehensive Air Quality Model with Extensions (CAMx) for a specific summer period. Several emission scenarios for the year 2010 were also considered. The model results suggest that the emission reductions of ozone precursors should have been effective to reduce ozone production between 1985 and 2000 in northern Switzerland. However, observations do not indicate any significant change in surface ozone levels since early 1990s, except in the region of Zurich where there is a small negative trend. On the other hand, the model predictions match very well the spatial variability of the trends but the calculated trends are around 0.5 ppb year−1 lower than those observed. This difference is similar to the background ozone increase as suggested by the long-term observations at the high Alpine station Jungfraujoch. These results support the hypothesis that the decrease in local ozone production due to emission reductions might have been partly or completely compensated by the simultaneous increase in the background ozone. In 2010, a strict application of the Gothenburg Protocol in Europe would lead to a decrease in peak ozone concentrations by about 5% in Switzerland under the meteorological conditions applied. Our calculations also indicated that emission controls only in Switzerland would not be very effective to improve the air quality in the future. The further development of the background ozone will in any case be very important for the tropospheric ozone levels. 相似文献