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51.
José J. del Alonso Rosario M. Arias Ballesteros P. Villares Durán 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(3):259-272
The generation of internal lee waves (ILW) in the Strait of Gibraltar takes place in the main sill where the tidal flow interacts
with a submarine obstacle. The tidal flow is perturbed by subinertial phenomena of different nature summarized in the subinertial
currents that can inhibit the ILW generation. The authors present an attempt to randomize the problem by the introduction
of a Gaussian noise in the Taylor–Goldstein equation. The random number sets are generated from the statistical distribution
of the previously isolated random part of the subinertial currents from experimental data taken in the area during the Gibraltar
Experiment 94–96. The effect of the noise is translated into a continuous spreading of the spectrum around the solution of
the noise-free problem. A stability analysis is carried out in order to determine the single neutral modes of oscillations
and the phase space is divided onto regions of stability and instability as a function of the inflowing subinertial current.
The methodology and results could be useful for the design and timing of oceanographic surveys in straits where the ILWs occur. 相似文献
52.
Fernando Jesús Ballesteros Roselló 《Astrophysics and Space Science》2001,276(1):291-298
-ray telescopes based on coded-mask techniques does not give adirect image of the sky sources but its correlation with the mask responsefunction. To obtain an image of the sky sources one has to treatmathematically the detected image, usually by correlating it with areconstruction array (correlation methods). Unfortunately this kindof methods, although quite fast, have some limitations in the reconstructedimage and in handling the real telescope response.To improve these results, several reconstruction methods have been developedand used. In the case of LEGRI (a -ray coded-mask telescopedeveloped for the University of Valencia) we have used the EM algorithm,an iterative maximum likelihood algorithm with very good response andwith good handling of the telescope response. 相似文献
53.
When using γ-ray coded-mask cameras, one does not get a direct image as in classical optical cameras but the correlation of
the mask response with the source. Therefore the data must be mathematically treated in order to reconstruct the original
sky sources. Generally this reconstruction is based on linear methods, such as correlating the detector plane with a reconstruction
array, or non-linear ones such as iterative or maximization methods (i.e. the EM algorithm). The latter have a better performance
but they increase the computational complexity by taking a lot of time to reconstruct an image. Here we present a method for
speeding up such kind of algorithms by making use of a neural network with a back-propagation learning rule.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
54.
José Albaladejo Alberto Notario Carlos A. Cuevas Bernabé Ballesteros Ernesto Martínez 《Journal of Atmospheric Chemistry》2003,45(1):35-50
Absolute rate coefficient measurements have been carried out for the reactions of Cl atoms with propene and a series of 3-halopropenes, at room temperature (298 ± 2) K using a newly constructed laser photolysis-resonance fluorescence (PLP-RF) system. The rate coefficients obtained (in units of cm3 molecule–1 s–1) are: propene (1.40± 0.24) ×10–10, 3-fluoropropene (4.92 ± 0.42) ×10–11, 3-chloropropene (7.47 ± 1.50) × 10–11, 3-bromopropene (1.23± 0.14) ×10–10 and 3-iodopropene (1.29± 0.15) ×10–10. In order to test this new system, the reactions of Cl atoms with acetone and isoprene have also been studied and compared with data previously reported. The rate coefficients determined at room temperature for these last two reactions are (2.93 ± 0.20) ×10–12 cm3 molecule–1 s– 1 and (3.64± 0.20)×10–10 cm3 molecule–1 s–1, respectively. The measured values were independent of pressure over the range 20–200 Torr. The influence of the different halogen atoms substituents on the reactivity of these alkenes with Cl atoms as well as the atmospheric implications of these measurements are studied and discussed for the first time in this work and compared with the reactivity with NO3 and OH radicals. 相似文献
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Claudio Lo Iacono Jorge Guillén Pere Puig Marta Ribó Maria Ballesteros Albert Palanques Marcel lí Farrán Juan Acosta 《Continental Shelf Research》2010
High-resolution multibeam swath-bathymetry and sediment samples were collected across the outer shelf region of the Columbretes Islands (southern Ebro continental shelf, western Mediterranean Sea). Bathymetric data from the submerged part of the Columbretes volcanic system revealed the presence of three main relict sand bodies along the outer shelf, at 80–116 m depth range, above which asymmetric and slightly asymmetric large and very large 2D and 3D subaqueous dunes were observed. These bed features were recognized, mapped and quantified with the aim of evaluating their potential formation mechanisms in relation to the local hydrodynamic and morphologic settings of the area. Dunes range from 150 to 760 m in wavelength and from tens of centimeters to 3 m in height, and are among the longest ever recognized in an outer shelf region. These bedforms are mostly composed of medium-sized sandy sediments, presumably coming from the degraded relict sand bodies on top of which they have developed, mixed with fine fractions from the recent draping holocenic sediments. The orientation of the dunes is SSW, progressively turning W towards the southernmost sector of the area, following the trend of the shelf-edge. Contemporary hydrodynamic measurements at the Ebro continental shelf-edge show that recorded currents are insufficient to form the observed bedforms and that stronger currents are required for sediment mobilization and dune formation. Based on their morphology and orientation, it is proposed that these bedforms are produced by the action of the southward-flowing Liguro-Provençal-Catalan (LPC) geostrophic current. The LPC probably reaches high near-bottom currents during energetic hydrodynamic events through interactions with the seafloor morphology of the study area. Subaqueous dunes are expected to be basically inactive features with respect to present-day processes, although they can be reactivated during high-energy events. The small Δh/λ ratio measured in the dune fields of the Columbretes shelf revealed that the dune heights fall below the values predicted by the Flemming (1988) global equation, as observed in other outer shelf settings also dominated by unidirectional flows. This may suggest a different morphodynamic character of large dunes formed on outer shelves in a micro-tidal regime. 相似文献
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Jesús Rodrigo-Comino Mauro Ponsoda-Carreres David Salesa Enric Terol Yeboah Gyasi-Agyei Artemi Cerdà 《Singapore journal of tropical geography》2020,41(1):120-135
Persimmons (Diospyros kaki) are trees cultivated under subtropical environmental conditions but are also found in other regions such as the Mediterranean. However, no research has been conducted to investigate soil erosion processes under Mediterranean soil management systems characterized by flood irrigation and/or tillage. The Improved Stock Unearthing Method (ISUM) for assessing long-term soil mobilization was applied to two fields, one under tillage and the other under no-till with herbicide within a 25-year old Mediterranean persimmon plantation. Replicating methods used in vineyard studies, graft unións on persimmon plants were used as passive bio-indicators of soil surface changes in this study. The tilled field showed a total soil mobilization volume of 48.4 m3 on a 408.5 m2 plot, representing a total soil loss of 52.6 Mg ha-1 yr-1. For the plot (468 m2) managed with no-till and herbicide, the results indicated total soil mobilization of 33.6 m3 which translates to 31.9 Mg ha-1 yr-1. It is concluded that flood irrigation is able to modify the runoff pathways and landforms in Mediterranean persimmon plantations, and the flood impact is more extensive when combined with tillage. For the first time, ISUM has been successfully applied to estimate soil erosion in a plantation under flood irrigation. 相似文献