References of "Alvarez, A"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailHCMV seroprevalence and associated risk factors in pregnat women, Havana City, 2007 to 2008
Correa, C. B.; Kouri, V.; Verdasquera, D. et al

in Prenatal Diagnosis (2010), 30(9), 888-92

Objective To prenatally identify pregnant women at risk of developing congenital infection due to human cytomegalovirus (HCMV). Methods One thousand one hundred and thirty-one pregnant women from three ... [more ▼]

Objective To prenatally identify pregnant women at risk of developing congenital infection due to human cytomegalovirus (HCMV). Methods One thousand one hundred and thirty-one pregnant women from three municipalities from Havana City were serologically screened for HCMV infection (IgM/IgG, IgG avidity) from January 2007 to January 2008. Demographical, epidemiological, and clinical variables were correlated to serologic status to identify predictors of seroconversion in pregnancy. Results The majority of women were seropositive to HCMV (92.6%); 27 women (2.4%) developed HCMV active infection during pregnancy, defined by the detection of IgG+ and IgM+ (7 women), IgM+ and IgG− (2 women), and IgG seroconversion (18 women). Susceptibility of active HCMV infection during pregnancy was associated with maternal age <20 years and nulligravidity. Primary infection was detected in 20 pregnant women (1.8%), whereas 7 patients (0.6%) had active non-primary infection. Conclusion Although pregnant women in Cuba have high seroprevalence rates for HCMV, those younger than 20 years and nulligravidae are at risk of acquiring infection during pregnancy. [less ▲]

Detailed reference viewed: 18 (7 ULg)
See detailAssimilation of Sea Surface Temperature predicted by a satellite-based forecasting system in a doubly nested primitive equation model of the Ligurian Sea
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Alvarez, A. et al

Conference (2004)

Data assimilation is traditionally used to combine model dynamics and observations in a statistical optimal way. Assimilation of observations improves therefore hindcasts and nowcasts of the ocean state ... [more ▼]

Data assimilation is traditionally used to combine model dynamics and observations in a statistical optimal way. Assimilation of observations improves therefore hindcasts and nowcasts of the ocean state than otherwise obtained by the model alone. The observational constraints are necessary to reduce uncertainties and imperfections of the ocean model. Due to the obvious lack of future observations, the model forecast cannot be controlled by observations and the predictive skill degrades as the forecast time lag increases. The error grow is not only caused by the chaotic nature of the system but also by the biases and drifts of the model. The later part can be reduced by considering different models with different imperfections. Data assimilation provides the statistical frame for merging the different model results. A primitive equation model of the Mediterranean Sea (1/4° resolution) has been implemented with two successive grid refinements of the Liguro-Provençal Basin (1/20°) and the Ligurian Sea (1/60°) respectively (Barth et al, 2003). The dependence of the ``parent'' model and the embedded ``child'' model is bi-directional; it involves the exchange of boundary conditions and feedback between the models. Alvarez el al. (2004) developed a statistical predictor for forecasting the SST of the Ligurian Sea with a time lag of 7 days based on the previous remote sensed SST. The degrees of freedom of the SST are reduced by an Empirical Orthogonal Function (EOF) analysis. A genetic algorithm trained by the historical SST evolution in the Ligurian Sea is used to predict the EOF amplitudes. Observed and forecasted SST are assimilated in the hydrodynamic model and the results of this two experiments are compared to the model run without assimilation. The assimilation of the forecasted SST reduces the error of the model by an amount comparable to the assimilation of real SST, showing the potential of skill improvement of combining statistical and hydrodynamic models. [less ▲]

Detailed reference viewed: 15 (1 ULg)
Full Text
Peer Reviewed
See detailModel intercomparison in the Mediterranean: MEDMEX simulations of the seasonal cycle
Beckers, Jean-Marie ULg; Rixen, M.; Brasseur, P. et al

in Journal of Marine Systems (2002), 33

The simulation of the seasonal cycle in the Mediterranean by several primitive equation models is presented. All models were forced with the same atmospheric data, which consists in either a monthly ... [more ▼]

The simulation of the seasonal cycle in the Mediterranean by several primitive equation models is presented. All models were forced with the same atmospheric data, which consists in either a monthly averaged wind-stress with sea surface relaxation towards monthly mean sea surface temperature and salinity fields, or by daily variable European Centre for Medium Range Weather Forecast (ECMWF) reanalysed wind-stress and heat fluxes. In both situations models used the same grid resolution. Results of the modelling show that the model behaviour is similar when the most sensitive parameter, vertical diffusion, is calibrated properly. It is shown that an unrealistic climatic drift must be expected when using monthly averaged forcing functions. When using daily forcings, drifts are modified and more variability observed, but when performing an EOF analysis of the sea surface temperature, it is shown that the basic cycle, represented similarly by the models, consists of the seasonal cycle which accounts for more than 90% of its variability. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 53 (13 ULg)
Full Text
See detailResults on SSH neural network forecasting in the Mediterranean Sea
Rixen, M.; Beckers, Jean-Marie ULg; Alvarez, A. et al

in Bostater, Charles R. Jr; Santoleri (Eds.) Remote Sensing of the Ocean and Sea Ice 2001 Volume 4544 (2002)

Nowadays, satellites are the only monitoring systems that cover almost continuously all possible ocean areas and are now an essential part of operational oceanography. A novel approach based on artificial ... [more ▼]

Nowadays, satellites are the only monitoring systems that cover almost continuously all possible ocean areas and are now an essential part of operational oceanography. A novel approach based on artificial intelligence (AI) concepts, exploits pasts time series of satellite images to infer near future ocean conditions at the surface by neural networks and genetic algorithms. The size of the AI problem is drastically reduced by splitting the spatio-temporal variability contained in the remote sensing data by using empirical orthogonal function (EOF) decomposition. The problem of forecasting the dynamics of a 2D surface field can thus be reduced by selecting the most relevant empirical modes, and non-linear time series predictors are then applied on the amplitudes only. In the present case study, we use altimetric maps of the Mediterranean Sea, combining TOPEX-POSEIDON and ERS-1/2 data for the period 1992 to 1997. The learning procedure is applied to each mode individually. The final forecast is then reconstructed form the EOFs and the forecasted amplitudes and compared to the real observed field for validation of the method. [less ▲]

Detailed reference viewed: 5 (1 ULg)
See detailSoft project: a new ocean forecasting system based on satellite data
Pascual, A.; Orfila, A.; Alvarez, A. et al

Conference (2002)

The aim of the SOFT project is to develop a new ocean forecasting system by using a combination of satellite data, evolutionary programming and numerical ocean models. To achieve this objective two steps ... [more ▼]

The aim of the SOFT project is to develop a new ocean forecasting system by using a combination of satellite data, evolutionary programming and numerical ocean models. To achieve this objective two steps are proposed: (1) to obtain an accurate ocean forecasting system using genetic algorithms based on satellite data; and (2) to integrate the above new system into existing deterministic numerical models. Evolutionary programming will be employed to build "intelligent" systems that, learning from the past ocean variability (provided by satellite data) and considering the present ocean state, will be able to infer near future ocean conditions. Validation of the forecast skill will be carried out by comparing the forecasts fields with satellite and in situ observations. Validation with satellite observations will provide the expected errors in the forecasting system. Validation with in situ data will indicate the capabilities of the satellite based forecast information to improve the performance of the numerical ocean models. This later validation will be accomplished considering in situ measurements in a specific oceanographic area at two different periods of time. The first set of observations will be employed to feed the hybrid systems while the second set will be used to validate the hybrid and traditional numerical model results. Keywords: forecasting, satellite data, empirical orthogonal functions, numerical models, genetic algorithms, neural networks, Mediterranean Sea. [less ▲]

Detailed reference viewed: 18 (0 ULg)
Full Text
Peer Reviewed
See detailEffect of topographic stress on circulation in the Western Mediterranean
Alvarez, A.; Tintore, J.; Holloway, G. et al

in Journal of Geophysical Research (1994), 99(C8), 16053-16064

The interaction of eddies with seafloor topography can exert large systematic forces on ocean circulation. Using a statistical mechanics approach it is possible to obtain a parametrization of this effect ... [more ▼]

The interaction of eddies with seafloor topography can exert large systematic forces on ocean circulation. Using a statistical mechanics approach it is possible to obtain a parametrization of this effect (the Neptune effect) for application in large-scale ocean circulation models. Circulation of the western Mediterranean has been observed to follow a definite cyclonic path. Numerical models usually show good qualitative agreement for the large-scale circulation but show systematic deficiencies at a subbasin scale. We have tested the importance of the Neptune effect on the circulation of the western Mediterranean Sea. To perform this test, different numerical experiments on western Mediterranean circulation were done with and without eddy-topography interaction. As a first step we analyze the influence of the Neptune effect in an ideal western Mediterranean with closed straits. After these experiments the more realistic case of open straits is studied. All the experiments show that the Neptune effect may be a significant factor in the basin and subbasin scale circulation in the western Mediterranean Sea. [less ▲]

Detailed reference viewed: 30 (2 ULg)
Full Text
Peer Reviewed
See detailTopographic forcing of the circulation of LIW in the Western Mediterranean
Alvarez, A.; Tintoré, J.; Holloway, G. et al

in Coastal Estuarine Studies (1994), 46

Circulation of the Western Mediterranean has been inferred from tracer properties and is the object of numerical modelling studies (eg., Beckers, 1991). The path of the Levantine Intermediate Water (LIW ... [more ▼]

Circulation of the Western Mediterranean has been inferred from tracer properties and is the object of numerical modelling studies (eg., Beckers, 1991). The path of the Levantine Intermediate Water (LIW), thought o be a buoyancy forced flow, provides an indicator of mid-depth circulation (Millot, 1987b). However, modelling studies which include buoyancy forcing appear to misrepresent the flow of LIW. We have used the 'GFDL Modular Ocean Model' (MOM) to explore the suggestion of Holloway (1992) that subgridscale eddy-topography interaction may be responsible for such systematic defects. We have executed MOM with and without the parametrization of the eddytopography interaction. The different results are compared with circulation inferred from observational data. [less ▲]

Detailed reference viewed: 12 (5 ULg)