排序方式： 共有109条查询结果，搜索用时 31 毫秒
41.
Miroslav Gačić Vedrana Kovačević Simone Cosoli Andrea Mazzoldi Jeffrey D. Paduan Isaac Mancero-Mosquera Sadegh Yari 《Estuarine, Coastal and Shelf Science》2009
Surface patterns of the low-frequency current in a 20 × 30 km region in front of the Venice Lagoon were analysed from a 13-month-long HF radar data set. Surface circulation was related to prevalent wind regimes in the area and to the tidal flow through the lagoon inlet. Three different categories of wind-forcing were defined: bora (NE wind), sirocco (SE wind), and finally the category containing all other wind directions and calms (winds lower than 3 m/sec). Mean flow and vorticity spatial distributions were discussed for different wind conditions. The coastal area about 5 km wide is characterized by a flow field with maximum vorticity. Outside the coastal boundary layer the interior flow is part of the Adriatic basin-wide cyclonic circulation. Two counter-rotating vortices of the dimension of about 4–5 km were evidenced in the average flow field in front of the lagoon inlet (Malamocco inlet) in all situations except for the bora. The vortex-pair is probably associated with the tidal flow through the inlet. The bora wind induces a strong southward coastal jet detached from the coast by about 5 km homogenizing the flow and eliminating the dipole. The average coastal flow pattern in calm wind conditions was also analysed as a function of the strong inflow/outflow (currents in the inlet > 0.7 m s−1) from the lagoon inlet. In both cases the vorticity pattern is similar, with the negative vorticity to the left of the inlet and positive to the right looking seaward. 相似文献
42.
Mohsen Maghrebi Roohollah Noori Mojtaba Sadegh Fereshteh Sarvarzadeh Aliasghar Erfanian Akbarzadeh Fatemeh Karandish Reza Barati Hamid Taherpour 《Ground water》2023,61(1):139-146
Qanat is an ancient underground structure to abstract groundwater without the need for external energy. A recognized world heritage, Qanat has enabled civilization in arid and semi-arid regions that lack perennial surface water resources. These important structures, however, have faced significant challenges in recent decades due to increasing anthropogenic pressures. This study uses remote sensing to investigate land-use changes and the loss of 15,983 Qanat shafts in the Mashhad plain, northeast of Iran, during the past six decades. This entails obtaining a rare aerial imagery from 1961, as well as recent satellite imagery, over a region with the highest density of Qanats in Iran, the birthplace of Qanat. Results showed that only 5.59% of the Qanat shafts in 1961 remained intact in 2021. The most prominent Qanat-impacting land-use changes were agriculture and urban areas, that accounted for 42.93 and 31.81% Qanat shaft destruction in the study area, respectively. This study also showed that groundwater table decline, demographic changes, and reduction in the appeal of working in the Qanat maintenance and construction industry among the new generation are existential threats to Qanats, and may result in the demise of these ancient structures in the future. Findings of this study can be used for urban planning in arid and semi-arid areas with the aim of protecting these historic water structures. 相似文献
43.
Rahimi Leila Malekmohammadi Bahram Yavari Ahmad Reza 《Natural Resources Research》2020,29(6):3701-3718
Natural Resources Research - Understanding the spatial–temporal dynamics of wetland land cover (LC) changes and their impacts on ecosystem services (ESs) is essential for wetland conservation... 相似文献
44.
The main goal of the proposed work is to delineate structural boundaries in a very complex geology environment using the spatial
and statistical properties of the potential field data. The analysis is performed using magnetic anomaly of the total field
data over In Ouzzal, an Archaean north–south elongated block belonging to the Hoggar (Algeria). This region is geologically
and geophysically very poorly known except some localized areas. The intrinsic properties of high-frequency signals and the
related causative sources are explored, thanks to two-dimensional continuous wavelet transform. The obtained results, represented
by spatial distribution of the maxima of the modulus of the wavelet transform at each scale, clearly show that the major magnetic
singularities of the field may be related to geological features. Comparison with the Euler’s deconvolution solutions exhibits
a very good correlation. Even though where geological structures are known, our method shows better resolution and accuracy.
The proposed multiscale method proves to be more powerful, easy to use, and versatile where classical methods of potential
field interpretation fail or are very constraining. However, work is still ongoing to try to better and fully characterize
the causative sources of the potential fields. 相似文献
45.
46.
Mehdi A. Guemache Jean-Luc Chatelain Djamel Machane Sihem Benahmed Leila Djadia 《Journal of African Earth Sciences》2011,59(4-5):349-358
The goal of this paper is to document causes of the failure of stabilization measures undertaken for stabilizing a complex landslide threatening the Sidi Rached viaduct in Constantine, Algeria. Since the first instabilities, documented in 1910 during its construction, significant disturbances have been regularly observed on its eastern part and reinforcements carried out were only temporarily effective. Observed disturbances are inherently related to the fact that the eastern abutment and the three subsequent piers are built on unstable Maastrichtian marls whereas the remainder of the viaduct rests on stable Turonian limestone. The five main factors controlling the activation of the failure process are reviewed: (1) geomorphology, (2) geology, (3) human activities, (4) climate, and (5) seismicity. Data interpretation of two inclinometer surveys carried out close to the eastern abutment shows that the unstable mass moves westward, towards the Rhumel gorges. The main slip surface is located in the Maastrichtian schistose marl, at a depth ranging from about 8 m (west) to about 30 m (east). This translational slide is associated with a settling phenomenon due to the petrophysical properties of the unstable marl. 相似文献
47.
We use semi-analytical modelling of galaxy formation to predict the mix of elliptical galaxies with boxy and disky isophotes,
assuming they originated from major mergers of different mass ratios. Numerical simulations of merging spiral galaxies indicate
equal mass mergers leading to boxy and merger with a mass ratio of 3:1 to disky ellipticals. Assigning isophotal shapes to
elliptical galaxies in our model we find bright disky ellipticals being as frequent or more frequent as bright boxy ellipticals,
in contrast to observations which indicate that most of the bright ellipticals should be boxy. The precursors of bright ellipticals
in our model are mainly also ellipticals which merge with each other later. Assuming that the merger of two ellipticals results
in boxy ellipticals increases the fraction of bright boxy ellipticals. By defining a disky as a bulge dominated galaxy with
an additional disk mass of more than 20% the total baryonic mass, increases the fraction of low mass disky ellipticals and
reproduces the observed trend of a steep increase in the fraction of low mass disky ellipticals.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
48.
The response surface methodology involving the five‐level central composite design (CCD) was employed to model and optimize the Cr(VI) immobilization process in a Cr‐spiked soil using starch‐stabilized zerovalent iron nanoparticles (ZVIn). ZVIn were synthesized via a borohydride reduction method and characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). All Cr(VI) immobilization experiments were conducted in a batch system. The variables for the CCD optimization were the ZVIn dosage (% w/w), reaction time (min), and initial Cr(VI) concentration in soil (mg/kg). The predicted response values by the second‐order polynomial model were found to be in good agreement with experimental values (R2 = 0.968 and adj‐R2 = 0.940). The optimization result showed that the Cr(VI) immobilization efficiency presented the maximal result (90.63%) at the following optimal conditions: ZVIn dosage of 1.5% w/w, reaction time of 60 min, and an initial Cr(VI) concentration of 400 mg/kg. 相似文献
49.
Detecting hydro-climatic change using spatiotemporal analysis of rainfall time series in Western Algeria 总被引：1，自引：0，他引：1
Leila Hamlaoui-Moulai Mohammed Mesbah Doudja Souag-Gamane Abderrahmane Medjerab 《Natural Hazards》2013,65(3):1293-1311
The knowledge of the climatic behavior especially that one of semi-arid regions is required to optimize the management of water resources. Here climate variability is directly related to water resources that are of a high socio-economic and environmental significance. This work deals mainly with a statistical analysis of the precipitation regime to assess its spatial distribution and temporal variation in north-western Algeria. For this, a time series and a principal component analysis are performed on rainfall series representing annual precipitations of twenty-one meteorological stations for the period 1914 to 2004, the most complete and longest of West Algeria, in order to detect patterns and trends in the region. A spectral analysis of the time series revealed the existence of a period of roughly 30 years for all stations. Furthermore, the trend of a wide part of the obtained spectra suggests the existence of another period longer than the samples size. 相似文献
50.
Sid-Ali Ouadfeul Mohamed Hamoudi Leila Aliouane Said Eladj 《Arabian Journal of Geosciences》2013,6(6):1669-1680
In this paper, we have analyzed the geomagnetic anomaly field reduced to the pole by the 2D directional continuous wavelet transform (DCWT). The objective is to identify geological contacts. The proposed idea has been applied firstly at a synthetic model, the obtained results showed the robustness of the proposed technique, after that the synthetic data has been noised; analysis shows that contacts identified by DCWT are affected by noise. To resolve this problem, we have proposed an algorithm to reduce the noise effect in the contacts model. Application on the real geomagnetic data of In Ouzzal area located in the West of Hoggar (Algeria) shows clearly the robustness of the proposed method. Comparison with the analytic signal solutions exhibits a difference between the two models of contacts. Our method gives results that are accurate with the structural geological map. 相似文献