Mediterranean physical oceanography and biogeochemical cycles: General circulation and climate variability     

Joaquín Tintor  Guest Editors  Alberto Alvarez  Reiner Onken  Guest Editor 《Progress in Oceanography》2005,66(2-4):87

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Evolutionary path planning for autonomous underwater vehicles in a variable ocean   总被引：3，自引：0，他引：3  

Alvarez  A. Caiti  A. Onken  R. 《Oceanic Engineering, IEEE Journal of》2004,29(2):418-429

This paper proposes a genetic algorithm (GA) for path planning of an autonomous underwater vehicle in an ocean environment characterized by strong currents and enhanced space-time variability. The goal is to find a safe path that takes the vehicle from its starting location to a mission-specified destination, minimizing the energy cost. The GA includes novel genetic operators that ensure the convergence to the global minimum even in cases where the structure (in space and time) of the current field implies the existence of different local minima. The performance of these operators is discussed. The proposed algorithm is suitable for situations in which the vehicle has to operate energy-exhaustive missions.  相似文献   

Interplanetary dust between 1 and 5 AU     

John E. Stanley  S. Fred Singer  Jose M. Alvarez 《Icarus》1979,37(2):457-466

Analyses of the data from the Meteoroid Detection Experiment (MDE) and the Imaging Photopolarimeter (IPP) aboard Pioneer 10 and Pioneer 11 have led to contradictory conclusions. While the MDE indicates a significant particle environment in the outer solar system (out to at least 5 AU), the IPP sees no zodiacal light (therefore implying no small particles) past 3.3 AU. We reconcile the two results by noting that the spectral index, p [relating particle radius, s, and particle concentration, n(s), i.e., dn(s) = Cs^?pds], is not a constant in the solar system, but changes from p < 2 near 1 AU to p > 2.5 at 5 AU for particles in the range of 10 μm. The MDE value of p = 1.8 at 1 AU is in agreement with previous satellite measurements, while our earlier analysis of the Pioneer 10 Jovian encounter data indicated p > 2.5 at 5 AU. A joint analysis of the Pioneer 10 and Pioneer 11 MDE data also indicates that p > 2.5 in the outer solar system. We show that a varying spectral index violates a major assumption used in the interpretation of the IPP data, which in turn had led to the conclusion that zodiacal dust is absent beyond 3.3 AU. With p a function of solar distance, the MDE data is now consistent with the IPP data, thus indicating a significant particle concentration in the outer solar system.  相似文献   

Future changes of hot extremes in Spain: towards warmer conditions     

Lorenzo  M. N.  Alvarez  I. 《Natural Hazards》2022,113(1):383-402

Natural Hazards - One of the most relevant effects of climate change is its influence on the frequency and intensity of extreme events. The analysis and understanding of these events are of great...  相似文献   

S-Wave Velocities of the Lithosphere–Asthenosphere System in the Caribbean Region     

O’Leary F. González  José Leonardo Alvarez  Bladimir Moreno  Giuliano F. Panza 《Pure and Applied Geophysics》2012,169(1-2):101-122

An overview of the S-wave velocity (V _s) structural model of the Caribbean with a resolution of 2°?×?2° is presented. New tomographic maps of Rayleigh wave group velocity dispersion at periods ranging from 10 to 40?s were obtained as a result of the frequency time analysis of seismic signals of more than 400 ray-paths in the region. For each cell of 2°?×?2°, group velocity dispersion curves were determined and extended to 150?s by adding data from a larger scale tomographic study (Vdovin et al., Geophys. J. Int 136:324–340, 1999). Using, as independent a priori information, the available geological and geophysical data of the region, each dispersion curve has been inverted by the “hedgehog” non-linear procedure (Valyus, Determining seismic profiles from a set of observations (in Russian), Vychislitielnaya Seismologiya 4, 3–14. English translation: Computational Seismology (V.I. Keylis-Borok, ed.) 4:114–118, 1968), in order to compute a set of V _s versus depth models up to 300?km of depth. Because of the non-uniqueness of the solutions for each cell, a local smoothness optimization has been applied to the whole region in order to choose a three-dimensional model of V _s, satisfying this way the Occam's razor concept. Several known and some new main features of the Caribbean lithosphere and asthenosphere are shown on these models such as: the west directed subduction zone of the eastern Caribbean region with a clear mantle wedge between the Caribbean lithosphere and the subducted slab; the complex and asymmetric behavior of the crustal and lithospheric thickness in the Cayman ridge; the predominant oceanic crust in the region; the presence of continental type crust in Central America, and the South and North America plates; as well as the fact that the bottom of the upper asthenosphere gets shallower going from west to east.  相似文献   

Diagnosis, seismic analysis and reinforcement of an old building in El-Maleh, Algeria     

Nadir Boumechra  Fabio Casciati  Karim Hamdaoui 《地震工程与工程振动(英文版)》2010,9(4):577-586

The Northern part of Algeria is considered to be the most active seismogenic area in the Western Mediterranean region. This area has a rich history of seismicity and had experienced many destructive earthquakes such as the Chlef (1954), El-Asnam (1980), Beni-Chograne (1994), An-Temouchent (1999) and recently Boumerdes (2003) earthquakes. The earthquake of An-Temouchent on December 22, 1999, was of magnitude 5.7, killed at least 28 people and made thousands of families homeless. Consequent damage was seen in all the structures located in a radius of 30 km. In the city of El-Maleh, located 12 km northeast of An-Temouchent, the "The National Bank Branch" of El-Maleh suffered moderate damage, but enough to justify questions about its safety. The project of rehabilitating this building required a broad analysis of its static and dynamic, past and present behaviors. The study reported in this paper was a necessary preliminary step toward the development of an optimal retrofit solution.  相似文献   

Late Chiribaya agriculture and risk management along the arid Andean coast of southern Perú, A.D. 1200–1400     

Gregory Zaro  Adn Umire Alvarez 《Geoarchaeology》2005,20(7):717-737

Recent investigations at the coastal spring site of Wawakiki in southern Perú have identified an intensive, late pre‐Hispanic agricultural production strategy along a sea cliff some 30 km north of the Ilo River. Excavations identified buried stone‐faced agricultural terraces underlying Spanish colonial and post‐colonial furrows, and long irrigation canals that transported water along steep hill slopes from inland springs. Depositional patterns, cultural debris, and calibrated radiocarbon age ranges suggest the site was farmed most intensively between A.D. 1200 and 1400, a period characterized by prolonged highland drought and recurrent El Niño–induced floods in southern Perú. Farmers transformed this arid coastal promontory into a productive agricultural landscape by exploiting multiple spring sources, steep canals, and stone‐faced terraces in an area where water is a very limited commodity and steep barren hills are highly prone to erosion. Furthermore, high‐relief terrain left much of the agricultural infrastructure well protected from periodic floods. © 2005 Wiley Periodicals, Inc.  相似文献   

Benthic input rates predict seagrass (Posidonia oceanica) fish farm-induced decline     

Díaz-Almela E  Marbà N  Alvarez E  Santiago R  Holmer M  Grau A  Mirto S  Danovaro R  Petrou A  Argyrou M  Karakassis I  Duarte CM 《Marine pollution bulletin》2008,56(7):1332-1342

Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities.  相似文献   

Correlation of Filtration Resistance with Microbial Polymeric Substances Extracted from Membranes in a Submerged Membrane Bioreactor          下载免费PDF全文

Necati Kayaalp  Cumali Kinaci  Nadir Dizge  Nizamettin Hamidi 《洁净——土壤、空气、水》2014,42(12):1712-1720

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Evaluation of nitrate levels in groundwater under agricultural fields in two pilot areas in central Chile: A hydrogeological and geochemical approach   总被引：2，自引：0，他引：2       下载免费PDF全文

Emilio Fernández  Alejandro Grilli  Daniela Alvarez  Ramón Aravena 《水文研究》2017,31(6):1206-1224

The aim of this study is to evaluate the impact of the application of industrial fertilizers and liquid swine manure in groundwater in two pilot agricultural areas, San Pedro and Pichidegua, which have been under long‐term historic use of fertilizers. A comprehensive hydrogeological investigation was carried out to define the geology and the groundwater flow system. Chemical and isotopic tools were used to evaluate the distribution and behavior of the nitrate in the groundwater. The isotopic tools included δ¹⁸O, δ²H, and ³H, which provide information about the origin and residence time of the groundwater; δ¹⁵N‐NO₃^? and δ¹⁸O‐NO₃^?, which provide information about nitrate sources and processes that can affect nitrate along the groundwater flow system. The application rate of liquid manure and other fertilizers all together with land uses was also evaluated. The hydrogeological investigation identified the presence of a confined aquifer underneath a thick low‐permeability aquitard, whose extension covers most of the two study areas. The nitrate concentration data, excepting a few points in zones located near recharge areas in the upper part of the basins and lower areas at the valley outlets (San Pedro), showed nitrate concentration below 10 mgN/L at the regional scale. The isotope data for nitrate showed no influence of the liquid swine manure in the groundwater at the regional scale, except for the high part of the basins and the outlet of the San Pedro valley, which are areas fertilized by manure. This data showed that the regional aquifer on both pilot study areas is protected by the thick low‐permeability aquitard, which is playing an important role on nitrate attenuation. Evidence of denitrification was also found on both shallow and deep groundwater in the Pichidegua site. This study showed that a comprehensive hydrogeological characterization complemented by chemical and isotope data is key for understanding nitrate distribution and concentration in aquifers from areas with intensive agriculture activities.  相似文献