排序方式: 共有91条查询结果,搜索用时 312 毫秒
81.
Elisa Camatti Alessandra Comaschi Alessandra De Olazabal Serena Fonda Umani 《Marine Ecology》2008,29(3):387-398
Mesozooplankton community composition at the species/taxa level was investigated from January to December 2001, at eight stations in the northern Adriatic Sea. Annual dynamics, taxonomic composition and spatial diversity in relation to different trophic conditions are discussed as related to previous studies and to different conditions, such as the presence of mucilage events. Zooplankton communities all over the northern sub‐basin were dominated by the cladoceran Penilia avirostris in summer, and by the calanoids Paracalanus parvus, Acartia clausi and the poecilostomatoids Oncaea spp. during the rest of the year. Whereas coastal communities were more variable with time and location, we were able to identify a group of offshore stations with a similar species/taxa composition and annual dynamics. Comparing the present results with previous studies, we observed significant changes in community composition in the time scale of 20 years, mostly due to a general decrease of A. clausi as the dominant species, being replaced by P. parvus. Also, P. avirostris swarms appear to have extended their temporal occurrence, and were present for longer periods of time when compared to past records. These changes might be related to the observed general increase of the average sea water temperature in the northern Adriatic Sea. 相似文献
82.
Terlizzi A Bevilacqua S Scuderi D Fiorentino D Guarnieri G Giangrande A Licciano M Felline S Fraschetti S 《Marine pollution bulletin》2008,56(7):1303-1309
The exploitation of fossil fuels in the Mediterranean Sea will likely lead to an increase in the number of offshore platforms, a recognized threat for marine biodiversity. To date, in this basin, few attempts have been made to assess the impact of offshore gas and oil platforms on the biodiversity of benthic assemblages. Here, we adopted a structured experimental design coupled with high taxonomic resolution to outline putative effects of gas platforms on soft-bottom macrofauna assemblages in the North Ionian Sea. The analysis was based on a total of 20,295 specimens of 405 taxa, almost entirely identified at species level. Multivariate and univariate analyses showed idiosyncratic patterns of assemblage change with increasing distance from the platforms. Potential reasons underlying such inconsistency are analyzed and the view that structured experimental monitoring is a crucial tool to quantify the extent and magnitude of potential threats and to provide sound baseline information on biodiversity patterns is supported. 相似文献
83.
Maurice Aubert Serena Diliberto Anthony Finizola Yashmin Chébli 《Bulletin of Volcanology》2008,70(6):743-751
Soil-temperature measurements can provide information on the distribution of degassing fissures, their relationship to the
internal structure of the volcano, and the temporal evolution of the system. At Vulcano Island (Italy), heat flux from a <3
km-deep magma body drives a hydrothermal system which extends across the main Fossa crater. This heat flux is also associated
with variable magmatic gas flow. A high-density map of soil-temperatures was made in 1996 at a constant depth of 30 cm on
the central and southern inner flanks of the Fossa crater. These measurements extended over an area covering about 0.04 km2, across which the heat flux is predominantly associated with a shallow boiling aquifer. The map shows that hot zones relate
to structures of higher permeability, mainly associated with a fissure system dating from the last eruptive cycle (1888–1890).
From 1996 to January 2005, we studied the evolution of the heat flux for the high temperature part of the map, both by repeating
our measurements as part of 14 visits, during which temperatures were measured at a constant depth, and using data from permanent
stations which allowed soil-temperatures to be continuously measured for selected vertical profiles. These data allowed us
to calculate the heat flux, and its variation, with good precision for values lower than about 100 W m−2, which is generally the case in the study area. Above 100 W m−2, although the heat flux value is underestimated, its variations are recorded with an error less than 10%. During the period
1996–2004, two increases in the thermal flux were recorded. The first one was related to the seismic crisis of November 1998
which opened existing or new fissures. The second, in November 2004, was probably due to magma migration, and was associated
with minor seismic activity. 相似文献
84.
Bruno M. Henriques Serena Bertone Peter A. Thomas 《Monthly notices of the Royal Astronomical Society》2008,383(4):1649-1654
We present results for a galaxy formation model that includes a simple treatment for the disruption of dwarf galaxies by gravitational forces and galaxy encounters within galaxy clusters. This is implemented a posteriori in a semi-analytic model by considering the stability of cluster dark matter subhaloes at z = 0 . We assume that a galaxy whose dark matter substructure has been disrupted will itself disperse, while its stars become part of the population of intracluster stars responsible for the observed intracluster light. Despite the simplicity of this assumption, our results show a substantial improvement over previous models and indicate that the inclusion of galaxy disruption is indeed a necessary ingredient of galaxy formation models. We find that galaxy disruption suppresses the number density of dwarf galaxies by about a factor of 2. This makes the slope of the faint end of the galaxy luminosity function shallower, in agreement with observations. In particular, the abundance of faint, red galaxies is strongly suppressed. As a result, the luminosity function of red galaxies and the distinction between the red and the blue galaxy populations in colour–magnitude relationships are correctly predicted. Finally, we estimate a fraction of intracluster light comparable to that found in clusters of galaxies. 相似文献
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86.
Marlène Jobard Serena Rasconi Télesphore Sime-Ngando 《Aquatic Sciences - Research Across Boundaries》2010,72(3):255-268
Fungi are a highly complex group of organisms of the kingdom Eumycota (i.e. the true-fungi) and other fungus-like organisms
traditionally studied by mycologists, such as slime molds (Myxomycota) and oomycota (Straminopiles or Heterokonts). They constitute
a significant proportion of the as yet undiscovered biota that is crucial in ecological processes and human well-being, through
at least three main trophic modes: saprophytism, parasitism, or symbiosis. In addition to direct benefit (sources of antibiotics)
or adverse effects (agents of disease), fungi can impact many environmental processes, particularly those associated with
the decomposition of organic matter. They are present in almost all regions and climates, even under extreme conditions. However,
studies have focussed mostly on economically interesting species, and knowledge of their diversity and functions is mainly
restricted to soil, rhizosphere, mangrove, and lotic ecosystems. In this study, we review the diversity and potential functions
of microscopic fungi in aquatic ecosystems, with focus on the pelagic environments where they often are regarded as allochthonous
material, of low ecological significance for food-web processes. Recent environmental 18S rDNA surveys of microbial eukaryotes
have (1) unveiled a large reservoir of unexpected fungal diversity in pelagic systems, (2) emphasized their ecological potentials
for ecosystem functioning, and (3) opened new perspectives in the context of food-web dynamics. In spite of persisting methodological
difficulties, we conclude that a better documentation of the diversity and quantitative and functional importance of fungi
will improve our understanding of pelagic processes and biogeochemical cycling. 相似文献
87.
Hugh R. A. Jones Yakiv Pavlenko Serena Viti R. J. Barber Larisa A. Yakovina David Pinfield Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2005,358(1):105-112
We compare high-resolution infrared observations of the CO 2–0 bands in the 2.297–2.310 μm region of M dwarfs and one L dwarf with theoretical expectations. We find a good match between the observational and synthetic spectra throughout the 2000–3500 K temperature regime investigated. None the less, for the 2500–3500 K temperature range, the temperatures that we derive from synthetic spectral fits are higher than expected from more empirical methods by several hundred kelvin. In order to reconcile our findings with the empirical temperature scale, it is necessary to invoke warming of the model atmosphere used to construct the synthetic spectra. We consider that the most likely reason for the back-warming is missing high-temperature opacity due to water vapour. We compare the water vapour opacity of the Partridge–Schwenke line list used for the model atmosphere with the output from a preliminary calculation by Barber & Tennyson. While the Partridge–Schwenke line list is a reasonable spectroscopic match for the new line list at 2000 K, by 4000 K it is missing around 25 per cent of the water vapour opacity. We thus consider that the offset between empirical and synthetic temperature scales is explained by the lack of hot water vapour used for computation of the synthetic spectra. For our coolest objects with temperatures below 2500 K, we find best fits when using synthetic spectra which include dust emission. Our spectra also allow us to constrain the rotational velocities of our sources, and these velocities are consistent with the broad trend of rotational velocities increasing from M to L. 相似文献
88.
Susan Henrico Serena Coetzee Antony Cooper Victoria Rautenbach 《Transactions in GIS》2021,25(1):468-490
Geospatial information and technologies are widely used in South Africa, initially mostly with proprietary software but today, mature, open source alternatives such as QGIS are available. We wanted to find out if and why South African users accepted QGIS, globally the most widely used free and open source GIS. We adapted the extended unified theory of acceptance and use of technology model to test several hypotheses regarding the acceptance and use of QGIS in South Africa. 205 registered members of the Geo‐Information Society of South Africa completed a structured questionnaire. Results show that habit has the most significant influence on behavioural intention to use QGIS, followed by facilitating conditions, price value and social influence. Performance expectancy, effort expectancy, hedonic motivation and access to source code played no significant role. The findings show that adoption of QGIS in South Africa is not primarily influenced by benefits attributed to open source software, such as cost benefits, customizability, improved reliability, quality and security. The results are useful for developers of any GIS product and for choosing a GIS product for an organization, because they provide insight into the behavioural intentions of users. 相似文献
89.
Regional landslide susceptibility zoning with considering the aggregation of landslide points and the weights of factors 总被引:4,自引:0,他引:4
In this paper, we propose a methodology for landslide susceptibility assessment at a regional scale in Yunnan, southwestern province of China. A landslide inventory map including 3,242 landslide points was prepared for the study area. Five factors recognized as correlated to landslide (namely, lithology, relative relief, tectonic fault density, rainfall, and road density) were analyzed and mapped in geographic information system. An index expressing the correlation between each factor and landslides [called class landslide susceptibility index (CLSI)] was proposed in the study. While analyzing landslide distribution in a large area, point aggregation might be expected. To quantify the uncertainty caused by aggregation, class landslide aggregation index was proposed. To account for the importance of each of the factors in the landslide susceptibility assessment, some weights were calculated by means of analytic hierarchy process. We propose a weighted class landslide susceptibility model (WCLSM), obtained by the combination of CLSI values of each factor with the correspondent weight. WCLSM performance in the study area was evaluated comparing the results obtained by first modeling all landslides and then by performing a time partition. The model was run including only landslides that occurred before 2009 and then validated with respect to landslides that occurred after 2009. The prediction–rate curve shows that the WCLSM model provides a good prediction for the study area. Of the study area, 21.4 % shows very high and high susceptibility and includes the 87.7 % of the number of landslides that occurred after 2009. 相似文献
90.