Fòlaga: A low-cost autonomous underwater vehicle combining glider and AUV capabilities     

A. Alvarez  A. Caiti  G. Casalino  L. Gualdesi  R. Viviani 《Ocean Engineering》2009,36(1):24-38

The paper describes the current developments of a class of low-cost, light-weight autonomous underwater vehicles for coastal oceanographic applications; the vehicle class is named Fòlaga, the Italian name of an aquatic bird that swims on the water surface and dives to catch fish. The main design characteristics of the most recent vehicle of the class, the Fòlaga III, are reviewed. Navigation and control system design are discussed, with particular attention to the diving phase, which is accomplished as in oceanographic gliders by varying the vehicle buoyancy and attitude. Experimental results show that the PID robust controllers implemented are effective in the diving control phase. Finally, a distributed cooperation algorithm to be applied by a team of Fòlaga-like vehicles in adaptive oceanographic sampling applications is described. The algorithm optimizes area coverage while taking into account the accuracy in the reconstruction of the oceanographic field and inter-vehicle communication through a range constraint. The resulting dynamic programming algorithm can be implemented in a distributed fashion among the team components.  相似文献   

Modelling of Seismic Ground Motion in Santiago de Cuba City from Earthquakes in Oriente Fault Seismic Zone     

L. Alvarez  G. F. Panza  F. Vaccari  B. E. González 《Pure and Applied Geophysics》2001,158(9-10):1763-1782

— We present the results of complete P-SV and SH waves modelling, up to a maximum frequency of 1?Hz, along two profiles in Santiago de Cuba city. The seismic sources are located in the depth range from 10 to 40?km on the Oriente fault zone at distances of several tens of kilometres from the city. The calculation has been made by a hybrid method: Modal summation in the regional anelastic model (one-dimensional) where the source is buried, and finite differences in the local sedimentary anelastic models (two-dimensional). The analysis of the influence of the depth and of the distance of the source on the site effects shows that standard traditional methods, based on the deconvolution analysis of the rock outcrop motion, can lead to erroneous results.  相似文献   

Time series of multivariate data in aquatic ecology     

Miguel Alvarez Cobelas  María Verdugo  Carmen Rojo 《Aquatic Sciences - Research Across Boundaries》1995,57(3):185-198

Coupling of multivariate methods and time series analysis can be ueful for studying dynamics of aquatic communities. This is demonstratred with a data set from the pelagic area of an oligo-mesotrophic lake in Central Spain during 61 consecutive days of Autumn overturn. Abiotic variables, phytoplankton species and their total biomass were traced. Species abundance and specific biomass were considered as indices of community structure and resource partitioning, respectively. Abiotic and algal data sets were subjected to factor analyses of cases separately. Atmospheric forcing and nitrogen could be considered as the main (2) driving variables of the abiotic matrix. The coupling of motile abilities and cell size was associated to the main factors of the community structure matrix whereas phosphorus limitation and species responses to buoyancy represented the main factors of the biomass matrix. Coordinates of the two first factors could be used to mimic the trajectories in the data space. Significant short term lags (1–4 days) were found in most time series. Lagged responses of atmospheric forcing and nitrogen on phytoplankton community structure and resource partitioning at scales of 1–7 days were also shown. Overall phytoplankton biomass did not show significant delayed responses, thereby suggesting that it might be resulting from the interplay of other non-studied factors.  相似文献   

Evidence for a Neoproterozoic carbonate ramp on the northern edge of the Central African craton: relations with late Proterozoic intracratonic troughs     

Philippe Alvarez 《International Journal of Earth Sciences》1995,84(3):636-648

During Late Proterozoic times, the Archaean Central African craton was affected by trough faulting which led to the formation of grabens, the Sangha aulacogen being the main structure of this type in the studied area. This transverse basin connects with other basins on the northern and south-western borders of the craton. During the Cryogenian, this network of basins was filled with fluvio-deltaic and lacustrine periglacial deposits. The glacio-eustatic transgression in Neoproterozoic III (end-Proterozoic) times flooded extensive areas of shelf on the northern edge of the craton, leading to the development of carbonate sedimentation in a broad outer shelf environment associated with nearshore barriers and evaporitic lagoons. These facies are similar to those developed in the West Congolian Schisto-calcaire (shale-limestone) ramp succession. The North-Central African ramp succession (sediment slope) contains an example of tidal rhythmites in vertical accretion, which occurs beneath the barrier deposits on the subtidal outer shelf. Mathematical analysis of the bedding pattern yields a period of 29–30 days for the lunar month, a result which is in agreement with astrophysical evidence for this epoch (i.e. 650 Ma ago). Major subsidence and seismic activity on this gently sloping platform, associated with the proximity of the Sangha aulacogen, caused the triggering of carbonate turbidites and mass flow deposits. The proliferation of microbial mats under euphotic conditions on an extensive shelf led to the build-up of a carbonate platform. During early Neoproterozoic III times, the West Congolian and North-Central African ramps prograded northwards and southwards, respectively, into the Sangha aulacogen. The sea at that time was restricted to a long graben-like basin, while a remaining area of marine sedimentation persisted into the Palaeozoic. Thus the pattern of end-Proterozoic carbonate sedimentation on the borders of the Central African craton can be interpreted in terms of an overall gently sloping ramp model with progradation converging towards the Sangha aulacogen.  相似文献   

Permafrost: Relation between ice content and dielectric losses at 100°K     

Romn Alvarez 《Earth and Planetary Science Letters》1973,20(3):409-414

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Electrical conductivity of igneous rocks: Composition and temperature relations     

R. Alvarez  J. Perez Reynoso  L. Javier Alvarez  M. Lopez Martinez 《Bulletin of Volcanology》1978,41(4):317-327

The conductivity of four igneous rocks with, 49, 65, 77, and 84% SiO₂ was measured as a function of temperature in the interval from 20° to 1280°C; measurements were made in a vacuum of 10^?3 torr. No simple relationships were found between conductivity and SiO₂ content or versus major element groupings such as Na₂O=K₂O=CaO and TiO₂=Cr₂O₃=Al₂O₃=Fe₂O₃=FeO. An analytical expression was obtained between conductivity and the albite-quartz ratio, valid for temperatures between 300° and 1200°C. It was necessary to compute the CIPW norm in order to obtain the albite and quartz percentages. The onset of melting apparently occurred between 600° and 700°C. Petrography performed on two samples after cooling showed 70 and 85% partial melting. Three conduction regions were identified: 1) below 300°C, 2) between 300°C and 600°C, and 3) above 600°C. Different activation energies obtained for the heating and cooling intervals confirm that the sample undergoes textural changes in the heating-cooling cycle. Activation energy increments of 0.1 and 0.2 eV per decade of albite-quartz ratio were obtained.  相似文献   

New Activity of Chiron: Results from 5 Years of Photometric Monitoring     

René DuffardDaniela Lazzaro  Sandro PintoJorge Carvano  Claudia AngeliAlvaro Alvarez Candal  Silvia Fernández 《Icarus》2002,160(1):44-51

The results of photometric observations of Centaur object Chiron carried out at the Observatório do Pico dos Dias (OPD, Brazil), the Estación Astrof?́sica de Bosque Alegre (EABA, Argentina), and Complejo Astronómico El Leoncito (CASLEO, Argentina) from 1997 to 2001 are presented here. The analysis of the photometric data shows that the brightness of Chiron reached a minimum value in 1999 and began increasing again in 2000. The absolute magnitude, H_V, varied from 7.26 in June 1999 to 5.78 in April 2001. The data tend to indicate that Chiron is starting a new outburst of activity which is compatible with a sporadic cometary behavior not related to heliocentric distance.  相似文献   

Caution Against the Inappropriate Use of Analytical Fate and Transport Models to Estimate the Age and Risk of Petroleum Product Releases     

Pedro J. J. Alvarez 《Ground Water Monitoring & Remediation》1996,16(2):72-76

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Structural study of a semiductile strike-slip system in the Central Iberian Zone (Variscan Fold Belt,Spain): structural controls on gold deposits     

E. Gonzalez-Clavijo  M. A. Diez-Balda  F. Alvarez 《International Journal of Earth Sciences》1993,82(3):448-460

The Villalcampo shear system is a regional dextral strike-slip fault zone that affects Late Variscan granites and their metamorphic country rocks over an area of about 150 km². The detailed geometry of this subvertical north-west—south-east shear zone is outlined. The system forms an extensional fan to the northwest and extends to the south-east as a broad extensional duplex. Particular attention is focused on the distribution of fault rocks and associated veins in its north-west splay. A structural study of the shear bands (encompassing both geometric and kinematic criteria) and a microscopic study of the fault rocks has led to the interpretation of the system as a brittle—ductile shear zone. Calculations give a shear strain value of = 1.5 and a minimum displacement of s = 3700 m. The localization of gold mineralization in mylonite-filled subvertical extensional veins is a product of the formation of the Villalcampo shear system. The subvertical faults and veins underwent a process of cyclical sealing and reopening. As such they acted as valves controlled by fluid pressure regulating fluid—rock interactions and gold deposition. Conditions favouring these processes occur near the base of the seismogenic zone in the vicinity of the frictional—quasi-plastic transition at mid-greenschist metamorphic conditions (T = 350°C and 10–15 km depth).  相似文献   

Large Scale Rockfall Reach Susceptibility Maps in La Cabrera Sierra (Madrid) performed with GIS and Dynamic Analysis at 1:5,000   总被引：1，自引：0，他引：1  

Ayala-Carcedo  Francisco J.  Cubillo-Nielsen  Silvia  Alvarez  Ana  Domínguez  María J.  Laín  Luis  Laín  Ricardo  Ortiz  Guillermo 《Natural Hazards》2003,29(3):325-340

For the testing of the effect on the tsunami prevention facilities, a simplified methodfor tsunami risk assessment was suggested without wave run-up analysis. This methodis proposed using calculated offshore tsunami waveform and field reconnaissance suchas the seawall height, time necessary for residents' evacuation and tsunami warninginsurance. Then, two normalized values are evaluated; one is the ratio of calculatedmaximum tsunami height to seawall height, the other is the ratio of time betweentsunami over-topping and evacuation completion to total time required for evacuation.These two values are used to qualitatively estimate the safety of residents and the effectof tsunami prevention facilities, eliminating the necessity to compute complicatedtsunami run-up onshore.  相似文献