Deep seismic exploration of the Iberian Microplate     

Juvenal Andres  David Marti  Ignacio Marzan  Imma Palomeras  Puy Ayarz  Fernando Simancas  DavidMartinez-Poyatos  Antonio Azor  Francisco Gonzalez-Lodeiro?  Jordi Diaz  Ramon Carbonel 《《地质学报》英文版》2018,92(Z1):11-11

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Characterization and rehabilitation of the “Porta Férrea” stone materials,University of Coimbra,Portugal     

Lídia Catarino  Francisco P. S. C. Gil  Mário Quinta-Ferreira  Fernando Marques 《Environmental Earth Sciences》2018,77(11):416

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Multiple Scale Modeling of Geophysical Processes     

Eugénio M. Rocha  Francisco Curado 《Mathematical Geosciences》2018,50(5):491-493

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Palaeoceanographic changes in the North Atlantic during the Mid‐Pleistocene Transition (MIS 31–19) as inferred from planktonic foraminiferal and calcium carbonate records     

Iván Hernández‐Almeida  Francisco Javier Sierro  José‐Abel Flores  Isabel Cacho  Gabriel Michael Filippelli 《Boreas: An International Journal of Quaternary Research》2013,42(1):140-159

Marine sediments from the Integrated Ocean Drilling Project (IODP) Site U1314 (56.36°N, 27.88°W), in the subpolar North Atlantic, were studied for their planktonic foraminifera, calcium carbonate content, and Neogloboqudrina pachyderma sinistral (sin.) δ¹³C records in order to reconstruct surface and intermediate conditions in this region during the Mid‐Pleistocene Transition (MPT). Variations in the palaeoceanography and regional dynamics of the Arctic Front were estimated by comparing CaCO₃ content, planktonic foraminiferal species abundances, carbon isotopes and ice‐rafted debris (IRD) data from Site U1314 with published data from other North Atlantic sites. Site U1314 exhibited high abundances of the polar planktonic foraminifera N. pachyderma sin. and low CaCO₃ content until Marine Isotope Stage (MIS) 26, indicating a relatively southeastward position of the Arctic Front (AF) and penetration of colder and low‐salinity surface arctic water‐masses. Changing conditions after MIS 25, with oscillations in the position of the AF, caused an increase in the northward export of the warmer North Atlantic Current (NAC), indicated by greater abundances of non‐polar planktonic foraminifera and higher CaCO₃. The N. pachyderma sin. δ¹³C data indicate good ventilation of the upper part of the intermediate water layer in the eastern North Atlantic during both glacial and interglacial stages, except during Terminations 24/23, 22/21 and 20/1. In addition, for N. pachyderma (sin.) we distinguished two morphotypes: non‐encrusted and heavily encrusted test. Results indicate that increases in the encrusted morphotype and lower planktonic foraminiferal diversity are related to the intensification of glacial conditions (lower sea‐surface temperatures, sea‐ice formation) during MIS 22 and 20.  相似文献   

Nonlinear adaptive control of an underwater towed vehicle     

Francisco Curado Teixeira  António Pedro Aguiar 《Ocean Engineering》2010,37(13):1193-1220

This paper addresses the problem of simultaneous depth tracking and attitude control of an underwater towed vehicle. The system proposed uses a two-stage towing arrangement that includes a long primary cable, a gravitic depressor, and a secondary cable. The towfish motion induced by wave driven disturbances in both the vertical and horizontal planes is described using an empirical model of the depressor motion and a spring-damper model of the secondary cable. A nonlinear, Lyapunov-based, adaptive output feedback control law is designed and shown to regulate pitch, yaw, and depth tracking errors to zero. The controller is designed to operate in the presence of plant parameter uncertainty. When subjected to bounded external disturbances, the tracking errors converge to a neighbourhood of the origin that can be made arbitrarily small. In the implementation proposed, a nonlinear observer is used to estimate the linear velocities used by the controller thus dispensing with the need for costly sensor suites. The results obtained with computer simulations show that the controlled system exhibits good performance about different operating conditions when subjected to sea-wave driven disturbances and in the presence of sensor noise. The system holds promise for application in oceanographic missions that require depth tracking or bottom-following combined with precise vehicle attitude control.  相似文献   

Phytoplankton production and seasonal biomass variation of seagrass,Ruppia maritima L., in a tropical Mexican lagoon with an ephemeral inlet     

Francisco J. Flores-Verdugo  John W. Day  Laurence Mee  Raquel Briseño-Dueñas 《Estuaries and Coasts》1988,11(1):51-56

Plankton metabolism andRuppia maritima biomass were measured seasonally during 1982–83 in El Verde Lagoon, a small coastal lagoon with an ephemeral inlet on the Pacific Coast of Mexico. Total net aquatic primary production was 521 g C m^?2 y^?1. The water column was slightly heterotrophic, with an annual P/R ratio of 0.89. Our analysis indicates that tropical and subtropical coastal lagoons with restricted or seasonal inlets have generally higher net aquatic primary productivity levels than lagoons with permanently open inlets. We hypothesize that this is due to retention of nutrients and plankton stocks during the dry season. The seasonal pattern of water column metabolism was related to rainfall and riverflow, with higher values generally occurring during the wet season. Net production and respiration were about three times lower during the 1982 dry season as compared to the 1983 dry season which received considerable rains due to abnormal climatic conditions. The biomass ofR. maritima ranged from zero to 620 g dry wt m^?2. Growth occurred only during the dry season and there were two distinct biomass peaks representing two separate crops. The second crop was heavily epiphytized with nitrogen-fixing algae. There was an apparent succession in dominance of water column productivity over the year, withRuppia dominating during the dry season and phytoplankton more important during the wet season.  相似文献   

Recent accretion in mangrove ecosystems based on137Cs and210Pb     

James C. Lynch  John R. Meriwether  Brent A. McKee  Francisco Vera-Herrera  Robert R. Twilley 《Estuaries and Coasts》1989,12(4):284-299

Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated sites in Terminos Lagoon, Mexico, and a basin mangrove forest in Rookery Bay, Florida, USA. Accretion rates were determined using the radionuclides²¹⁰Pb and¹³⁷Cs. Consolidation-corrected accretion rates for the Rookery Bay cores, ranged from 1.4 to 1.7 mm yr^?1, with an average rate of 1.6 mm yr^?1. Rates at the Mexico sites ranged from 1.0 to 4.4 mm yr^?1, with an average of 2.4 mm yr^?1. Determination of rates in these mangrove forests was greatly affected by the consolidation corrections which decreased the apparent accretion rate by over 50% in one case. Accretion rates at basin sites compare favorably with a reported 1.4 to 1.6 mm yr^?1 rate of sea-level rise, indicating little or no subsidence at inland locations. Accretion rates in fringe sites are generally greater than basin sites, indicating greater subsidence rates in these sediments over longer time intervals.  相似文献   

Seismic activity related to the 1991 eruption of Colima Volcano,Mexico     

Francisco Núñez-Cornú  F. Alejandro Nava  Servando De la Cruz-Reyna  Zenón Jiménez  Carmen Valencia  Rosalía García-Arthur 《Bulletin of Volcanology》1994,56(3):228-237

Ten years after the last effusive eruption and at least 15 years of seismic quiescence, volcanic seismic activity started at Colima volcano on 14 February 1991, with a seismic crisis which reached counts of more than 100 per day and showed a diversity of earthquake types. Four other distinct seismic crises followed, before a mild effusive eruption in April 1991. The second crisis preceded the extrusion of an andesitic scoriaceous lava lobe, first reported on 1 March; during this crisis an interesting temporary concentration of seismic foci below the crater was observed shortly before the extrusion was detected. The third crisis was constituted by shallow seismicity, featuring possible mild degassing explosion-induced activity in the form of hiccups (episodes of simple wavelets that repeat with diminishing amplitude), and accompanied by increased fumarolic activity. The growth of the new lava dome was accompanied by changing seismicity. On 16 April during the fifth crisis which consisted of some relatively large, shallow, volcanic earthquakes and numerous avalanches of older dome material, part of the newly extruded dome, which had grown towards the edge of the old dome, collapsed, producing the largest avalanches and ash flows. Afterwards, block lava began to flow slowly along the SW flank of the volcano, generating frequent small incandescent avalanches. The seismicity associated with the stages of this eruptive activity shows some interesting features: most earthquake foci were located north of the summit, some of them relatively deep (7–11 km below the summit level), underneath the saddle between the Colima and the older Nevado volcanoes. An apparently seismic quiet region appears between 4 and 7 km below the summit level. In June, harmonic tremors were detected for the first time, but no changes in the eruptive activity could be correlated with them. After June, the seismicity decreasing trend was established, and the effusive activity stopped on September 1991.  相似文献   

Discrete models for vertical vibrations of surface and embedded foundations     

Francisco C. P. De Barros  J. Enrique Luco 《地震工程与结构动力学》1990,19(2):289-303

A five-parameter discrete model that approximates the dynamic force4isplacement relationship for rigid foundations undergoing vertical vibrations on a uniform elastic half-space is presented. The model involves a combination of two springs, two viscous dampers and a mass. Values of the parameters for circular, square and rectangular foundations placed on the surface or embedded in an elastic half-space are listed. The parameters are obtained by minimizing the discrepancy between the force4isplacement relation for the model and that obtained by solution of the mixed boundary-value problem of the rigid foundation on an elastic half-space. The definition of an appropriate input motion to represent wave excitation is also discussed. The input motion to the discrete model differs from the input motion that should be used in a continuum model.  相似文献   

Reply by authors to M. D. Trifunac     

Eduardo Reinoso  Mario Ordaz And  Francisco J. Sanchez-Sesma 《地震工程与结构动力学》1991,20(8):804-804

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