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排序方式: 共有203条查询结果,搜索用时 15 毫秒
61.
62.
Karim Benzerara Jennyfer Miot Guillaume Morin Georges Ona-Nguema Feriel Skouri-Panet Céline Férard 《Comptes Rendus Geoscience》2011,343(2-3):160-167
Microorganisms can mediate the formation of minerals by a process called biomineralization. This process offers an efficient way to sequester inorganic pollutants within relatively stable solid phases. Here we review some of the main mechanisms involved in the mediation of mineral precipitation by microorganisms. This includes supersaturation caused by metabolic activity, the triggering of nucleation by production of more or less specific organic molecules, and the impact of mineral growth. While these processes have been widely studied in the laboratory, assessment of their importance in the environment is more difficult. We illustrate this difficulty using a case study on an As-contaminated acid mine drainage located in the South of France (Carnoulès, Gard). In particular, we explore the potential relationships that might exist between microbial diversity and mineral precipitation. The present review, far from being exhaustive, highlights some recent advances in the field of biomineralogy and provides non-specialists an introduction to some of the main approaches and some questions that remain unanswered. 相似文献
63.
Samira Akhavan Sayed-Farhad Mousavi Jahangir Abedi-Koupai Karim C. Abbaspour 《Environmental Earth Sciences》2011,63(6):1155-1167
One of the major causes of groundwater pollution in Hamadan–Bahar aquifer in western Iran is a non-point source pollution
resulting from agricultural activities. Withdrawal of over 88% of drinking water from groundwater resources, adds urgency
to the studies leading to a better management of water supplies in this region. In this study, the DRASTIC model was used
to construct groundwater vulnerability maps based on the “intrinsic” (natural conditions) and “specific” (including management)
concepts. As DRASTIC has drawbacks to simulate specific contaminants, we conditioned the rates on measured nitrate data and
optimized the weights of the specific model to obtain a nitrate vulnerability map for the region. The performance of the conditioned
DRASTIC model improved significantly (R
2 = 0.52) over the intrinsic (R
2 = 0.12) and specific (R
2 = 0.19) models in predicting the groundwater nitrate concentration. Our study suggests that a locally conditioned DRASTIC
model is an effective tool for predicting the region’s vulnerability to nitrate pollution. In addition, comparison of groundwater
tables between two periods 30 years apart indicated a drawdown of around 50 m in the central plain of the Hamadan–Bahar region.
Our interpretation of the vulnerability maps for the two periods showed a polluted zone developing in the central valley requiring
careful evaluation and monitoring. 相似文献
64.
65.
The vulnerability of native rangeland plant species to global climate change in the West Asia and North African regions 总被引:1,自引:0,他引:1
This study aimed to evaluate the impact of climate change on the geographical distribution of selected native species from two areas from West Asia and North Africa. Three species representing two genera were selected for assessment of their vulnerability to climate change. The first species was Salsola vermiculata L. which is common to both study areas. The second genus was represented by two species, Haloxylon salicornicum (Moq.) Bunge from the Syrian rangelands and H. schmittianum Pomel from southern Tunisia. To assess the vulnerability of these species to climate change we used ecological-based models. The data inputs were composed of the species occurrence data and the environmental data which included eight climatic layers, three soil property layers in addition to an altitude layer. Since environmental parameters only enable assessing the sensitivity of target species to climate change, a grazing pressure layer was used to assess the species vulnerability. Only climatic parameters were considered as changing across three periods; current situation, 2020 and 2050. The main results indicated that threatened range species, such as S. vermiculata which were subjected to continuous grazing pressure, showed high vulnerability to climate change as expressed by the predicted decrease in the areas of their distribution. However, species with low palatability and broad ecological niches (i.e. H. salicornicum and H. schmittianum) had an advantage due to the reduced competition for water and nutrients. An adaptation strategy to increase the resilience of the most vulnerable species should involve management of grazing pressure and the establishment of other mitigation measures. 相似文献
66.
S.Z. Farooqui M. Karim N. Kawashima A. Qadir H. Rehman 《Astrophysics and Space Science》1997,258(1-2):221-235
The proposed ‘Gravitational-Wave Antenna Detector InteRferometer (GWADIR)’ will be a 3 km × 3 km Fabry-Perot type laser interferometer.
The laser oscillator to be used will be a DL excited Nd-YAG laser with a minimum output of 100 Watts. The optical system will
consist of 25 cm diameter Recycler, Beam Splitter, and Near/End Mirrors for each of two Ducts. The mirror system will be suspended
by fine wires to isolate the system from the seismic noises of the earth. The output light emerging from the interferometer
will be split into 8 beams and sent to 8 different interference detectors. These detectors will measure the interference intensities
for the recombined light from the separate legs of the interferometer. The effective amplification due to the interferometer
cavities will allow measurements of displacements to better than 10 times the wavelength of the laser light. A high vacuum
of 10-8 Torrs will be maintained throughout the system, using turbo-molecular and ion pumps. The detector is designed to reach
strain sensitivities from gravitational sources of h<10-23 (Hz)- 1/2 with a broad-band and narrow-band measurement capability
in the range of frequencies from 50 Hz to 10 4 Hz, thus allowing it to detect ‘standard’ signals from such sources as coalescing neutron stars or black-holes out to the
edge of the universe. If enough funding became available, the project is expected to complete by the middle of the next decade.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
Karim BENZERARA Virginie CHAPON David MOREIRA Purificacin L
PEZ‐GARCÍA Franois GUYOT Thierry HEULIN 《Meteoritics & planetary science》2006,41(8):1249-1265
Abstract— Biological processes can alter the chemistry and mineralogy of meteorites in a very short time, even in cold or hot deserts. It is thus important to assess the diversity of microorganisms that colonize meteorites in order to better understand their physiological capabilities. Microscopy observations of Tatahouine meteorite fragments that were exposed for 70 years in the Sahara desert showed that they were colonized by morphologically diverse biomorphs. A molecular diversity study based on 16S rRNA gene amplification of DNA supported the conclusion that a huge taxonomic diversity of prokaryotes colonized the Tatahouine meteorite in less than 70 years in the Tatahouine sand. Eleven different bacterial divisions were evidenced, among which Cytophaga‐Flexibacter‐Bacteroides (CFB), Cyanobacteria, and Alpha‐Proteobacteria were dominantly represented. Crenarcheota were also detected. Most of the Tatahouine meteorite phylotypes were related to sequences identified in the surrounding Tatahouine more generally to sequences detected in soils. Some of them, in particular many of the archaeal phylotypes, were detected in arid regions in association with desert varnish. The results suggest that the diversity of the clone library generated from the meteorite fraction was reduced compared with that of the Tatahouine sand clone library, which can be explained as the result of partial colonization of the meteorite and/or a specific selection of colonizing bacteria by the substrate. We discuss the possibility that several groups detected in this study may play a prominent role in the various alteration processes detected at the surface of the Tatahouine meteorite. 相似文献
68.
Karim Saheb Ettabaa Manel Ben Salem 《Journal of the Indian Society of Remote Sensing》2018,46(2):157-167
One of the challenging problems in processing high dimensional data, as hyperspectral images, with better spectral and temporal resolution is the computational complexity resulting from processing the huge amount of data volume. Various methods have been developed in the literature for dimensionality reduction, generally divided into two main techniques: data transformation techniques and features selection techniques. The feature selection technique is advantageous compared to transformation techniques in preserving the original data. However, deciding the appropriate number of features to be selected and choosing these features are very challenging since they require exhaustive researches. The progressive feature selection technique is a new concept recently introduced to address these issues based on priority criteria. However, this approach presents limits when these criteria are insufficient or depends on domain applications. In this paper, we present a new approach to improve the Progressive Feature Selection technique by adding new criteria that measure the amount of information present in each band. The endmembers extraction phase of the proposed approach includes both the N-FINDR and the ATGP algorithms. A case based reasoning system is used to choose the optimal criterion for the endmember extraction. The performances of this proposed approach were evaluated using AVIRIS hyperspectral image and the obtained results prove its effectiveness compared to other PBS techniques. 相似文献
69.
Zhong-Sen Li Assia Benchouk Feth-Ellah Mounir Derfouf Nabil Abou-Bekr Said Taibi Hanène Souli Jean-Marie Fleureau 《Acta Geotechnica》2018,13(1):51-71
The main objective of this paper is to examine how different engineering soils react to environmental variations and to provide correlations to characterize their behaviour under null external mechanical stress. Two French and two Algerian soils with liquid limits ranging from 36 to 112 were prepared under both slurry and Proctor compaction conditions, and then subjected to drying–wetting paths with suction controlled from several kPa to several hundreds of MPa. Experimental results are presented in five diagrams to show globally and simultaneously the shrinkage–swelling, saturation–desaturation and water retention characteristics. A reasonable consistency was observed between the oedometric and drying curves of slurry, confirming the equivalence between hydraulic loading (suction) and mechanical loading (consolidation stress) on the volume change behaviour of different soils. As an intrinsic parameter of soil nature, liquid limit was found to have a significant influence on the shrinkage limit, air-entry suction and compressibility of both slurry and compacted samples. For that reason, correlations between these characteristics and liquid limit were set up, providing a good basis for a first estimation of the drying–wetting curves. At the micro-scale, new experimental results were obtained: either on drying or wetting path, the micro-pores were almost unaffected, whereas, when matrix suction increased from 0.1 to 8 MPa, the volume of macro-pores decreased to quasi-closure. At last, the analogy between the compaction and drying–wetting curves, and the comparison of different methods to determine the water retention curve were addressed. Such analogies and comparisons contribute to a better understanding of the mechanisms of mechanical stress and suction. 相似文献
70.
Amel Dhib Mounir Ben Brahim Boutheina Ziadi Fourat Akrout Souad Turki Lotfi Aleya 《Marine pollution bulletin》2013
We studied the distribution of planktonic and epiphytic ciliates coupled with environmental factors and microalgae abundance at five stations in Ghar El Melh Lagoon (Tunisia). Planktonic ciliates were monitored for a year and epiphytic ciliates were sampled during summer 2011 in concordance with the proliferation of the seagrass Ruppia cirrhosa. Ciliate assemblage was largely dominated by Spirotrichea followed respectively by Tintinnida of and Strombidiida. No significant difference was found in the distribution of ciliate species among the stations. Redundancy analysis indicates that abiotic factors (temperature and nutriments) have a significant effect on the dynamics of certain ciliates. For epiphytic ciliates, 4 species were identified: Tintinnopsis campanula, Aspidisca sp., Strombidium acutum and Amphorides amphora. Based on PERMANOVA analyses, ciliates exhibit significant correlations among months and stations. According to ACP, epiphyte distribution follows roughly those of R. cirrhosa and pH. Significant correlations were found between harmful dinoflagellates and both planktonic and epiphytic ciliates. 相似文献