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排序方式: 共有347条查询结果,搜索用时 15 毫秒
191.
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193.
Frédéric Thomas Jérôme Fauchier Kevin D. Lafferty 《Behavioral ecology and sociobiology》2002,51(3):296-301
Microphallus papillorobustus is a manipulative trematode that induces strong behavioural alterations in the gamaridean amphipod Gammarus insensibilis, making the amphipod more vulnerable to predation by aquatic birds (definitive hosts). Conversely, the sympatric nematode Gammarinema gammari uses Gammarus insensibilis as a habitat and a source of nutrition. We investigated the conflict of interest between these two parasite species by studying the consequences of mixed infection on amphipod behaviour associated with the trematode. In the field, some amphipods infected by the trematode did not display the altered behaviour. These normal amphipods also had more nematodes, suggesting that the nematode overpowered the manipulation of the trematode, a strategy that would prolong the nematode's life. We hypothesize that sabotage of the trematode by the nematode would be an adaptive strategy for the nematode consistent with recent speculation about co-operation and conflict in manipulative parasites. A behavioural test conducted in the laboratory from naturally infected amphipods yielded the same result. However, exposing amphipods to nematodes did not negate or decrease the manipulation exerted by the trematode. Similarly, experimental elimination of nematodes from amphipods did not permit trematodes to manipulate behaviour. These experimental data do not support the hypothesis that the negative association between nematodes and manipulation by the trematode is a result of the "sabotage" hypothesis. 相似文献
194.
本文介绍了构建在法国国家气象业务中心的自动化气象灾害查询系统.该系统在UNIX环境下采用PROC语言、GrADS的SCRIPT语言、SHELL语言混和编程,通过计算机网络从两类ORACLE大型数据库中,以SQL语言筛选相关资料,并组织成GrADS文件以图形方式提供给气象业务人员.系统从软件工程学原则出发,在保障运行稳定、可靠、方便、易维护及程序设计关键SCEM;GrADS;气象灾害评估;业务系统设计技术等方面采取了一系列措施,保证了业务运行需求. 相似文献
195.
196.
Allan G. Sangster Lewis Ling Frédéric Gérard Martin J. Hodson 《Water, Air, & Soil Pollution: Focus》2007,7(1-3):143-149
Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] shoots from mature trees were collected from two sites of contrasting soil pH: the Glendon campus of York
University in Toronto, Canada (pH 6.7 at 40 cm) designated Can.; and Breuil Forest, Morvan, France (pH 4 to 4.5) designated
Fr.. Needles were removed from the shoots, frozen in liquid nitrogen, and kept in a cryo-biological storage system prior to
X-ray microanalysis on the cold stage (−170°C) of a cryo-SEM. Four elements detected, potassium, phosphorus, sulphur and chlorine,
were ubiquitous in the needle tissues from both sites. Manganese was infrequently found in needle tissues from the Fr. site.
Calcium was localized most heavily in the outer tangential wall of the hypodermis and also in the epidermal walls. Silicon
(Si) concentrations were higher in the Fr. site than in the Can. site. The epidermis, hypodermis and mesophyll of needles
from the Fr. site exhibited the highest Si content, with greater amounts in the tip and middle of the needle than in the base.
Aluminium was distributed fairly evenly throughout the tissues, and there were few major sites of concentration. 相似文献
197.
Frédériqu Larrarte 《Environmental Fluid Mechanics》2008,8(3):249-261
A precise determination of the pollutant loads processed through the sewer networks is required for legal, environmental and
management reasons. Such a determination requires a good evaluation of concentrations, which is not an easy task because samplers
or sensors can perform measurements in a cross-sectional area of only a few locations, and this local information must then
be extrapolated across the whole cross-sectional area of the sewer network. This latter step is problematical. A great deal
of attention must be given to suspended solids because they are prone to settle and display heterogeneous concentration patterns.
A two-dimensional sampler has been designed to measure the variation of suspended solids concentration throughout a cross-sectional
area. This paper presents the principles upon which the conception of this experimental device was based and the building
process. Experimental results are presented and discussed. 相似文献
198.
Biodiversity monitoring surveys are rarely optimised statistically before being initiated. Here, we optimised the monitoring
of plants in a temperate forest. The total inventory cost, the number and size of quadrats were optimised to detect a 10%
change in species richness over 5 years with α = β = 0.05, using data from ongoing long-term floristic monitoring programs. The procedure showed that the inventory cost would
be ca 15% lower using 100-, 200-m2 quadrats instead of 300- or 400-m2 quadrats. Despite the cost associated with the optimisation (e.g. gathering preliminary data) and the imprecise estimates
(due to the typically small sample size of the pilot studies), optimisation would often be a better option than expert opinion
when designing a monitoring survey. 相似文献
199.
Many environmental problems are linked to multiphase flows encompassing ecological issues, chemical processes and mixing or
diffusion, with applications in different engineering fields. The transition from a supercritical flow to a subcritical motion
constitutes a hydraulic jump. This flow regime is characterised by strong interactions between turbulence, free surface and
air–water mixing. Although a hydraulic jump contributes to some dissipation of the flow kinetic energy, it is also associated
with increases of turbulent shear stresses and the development of turbulent eddies with implications in terms of scour, erosion
and sediment transport. Despite a number of experimental, theoretical and numerical studies, there is a lack of knowledge
concerning the physical mechanisms involved in the diffusion and air–water mixing processes within hydraulic jumps, as well
as on the interaction between the free-surface and turbulence. New experimental investigations were undertaken in hydraulic
jumps with Froude numbers up to Fr = 8.3. Two-phase flow measurements were performed with phase-detection conductivity probes.
Basic results related to the distributions of void fraction, bubble frequency and mean bubble chord length are presented.
New developments are discussed for the interfacial bubble velocities and their fluctuations, characterizing the turbulence
level and integral time scales of turbulence representing a “lifetime” of the longitudinal bubbly flow structures. The analyses
show good agreement with previous studies in terms of the vertical profiles of void fraction, bubble frequency and mean bubble
chord length. The dimensionless distributions of interfacial velocities compared favourably with wall-jet equations. Measurements
showed high turbulence levels. Turbulence time scales were found to be dependent on the distance downstream of the toe as
well as on the distance to the bottom showing the importance of the lower (channel bed) and upper (free surface) boundary
conditions on the turbulence structure. 相似文献
200.
Lopareva-Pohu A Verdin A Garçon G Lounès-Hadj Sahraoui A Pourrut B Debiane D Waterlot C Laruelle F Bidar G Douay F Shirali P 《Environmental pollution (Barking, Essex : 1987)》2011,159(6):1721-1729
Due to anthropogenic activities, large extends of soils are highly contaminated by Metal Trace Element (MTE). Aided phytostabilisation aims to establish a vegetation cover in order to promote in situ immobilisation of trace elements by combining the use of metal-tolerant plants and inexpensive mineral or organic soil amendments. Eight years after Coal Fly Ash (CFA) soil amendment, MTE bioavailability and uptake by two plants, Lolium perenne and Trifolium repens, were evaluated, as some biological markers reflecting physiological stress. Results showed that the two plant species under study were suitable to reduce the mobility and the availability of these elements. Moreover, the plant growth was better on CFA amended MTE-contaminated soils, and the plant sensitivity to MTE-induced physiological stress, as studied through photosynthetic pigment contents and oxidative damage was lower or similar. In conclusion, these results supported the usefulness of aided phytostabilisation of MTE-highly contaminated soils. 相似文献