P. Villares

P. Villares
Universidad de Cádiz | UCA · Department of Applied Physics

PhD Physic

About

168
Publications
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2,350
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October 1969 - February 2014
Universidad de Cádiz
Position
  • Professor (Full)

Publications

Publications (168)
Article
Full-text available
A procedure has been developed for analyzing the evolution with temperature of the actual transformed volume fraction and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. By considering the assumptions of extended volume and spatially random nucleation, as well as, assuming th...
Article
Full-text available
Sea level anomaly maps from altimeter (AVISO) were retrieved for the Gulf of Cadiz (GoC) for the period 1997-2008, along with maps of Dynamic Atmospheric Correction (DAC), atmospheric pressure at sea level and satellite Sea Surface Temperature (SST). Data were averaged in time to obtain maps of monthly mean time series in order to analyze the seaso...
Article
Full-text available
Satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean; however, its use is still limited in shallow waters near the coast where two main issues still need a more detailed analysis. On one side, the local characteristics of each coastal region imply that certain corrections applied to the altimetry measureme...
Article
It is well known that in the study of the glass-crystal transformation kinetics, sometimes is necessary that both the nucleation frequency and the crystal growth rate depend on time as a power law. To explain the probable physical nature of this time dependence, the theoretical method developed (TMD) for non-isothermal processes, which we have publ...
Article
Full-text available
AVISO sea level anomaly weekely maps from radar altimetry were retrieved for the Gulf of Cadiz (GoC) (1997-2008), along with maps of Dynamic Atmospheric Correction (DAC), atmospheric pressure at sea level and satellite Sea Surface Temperature (SST). Data were averaged in time to obtain maps of monthly mean time series in order to analyze the season...
Chapter
Full-text available
This study analyses the spatio-temporal variability of satellite surface chlorophyll-a data (CHL) and Sea Level Anomaly (SLA) from altimetry data in order to characterize the influence of the regional circulation on the phytoplankton biomass in the Gulf of Cadiz (Southwestern coast of the Iberian Peninsula). A singular value decomposition (SVD) ana...
Article
This work analyzes the glass–crystal transformation kinetics of the Ag0.24As0.30Se0.46 glassy alloy, which presents two exothermic peaks, using differential scanning calorimetry (DSC) technique under non-isothermal conditions. The corresponding kinetic parameters are evaluated considering two different methods. On the one hand, the theoretical meth...
Article
Full-text available
Sea level anomaly maps from altimeter (AVISO) were retrieved for the Gulf of Cadiz (GoC) for the period 1997-2008, along with maps of Dynamic Atmospheric Correction (DAC), atmospheric pressure at sea level and satellite Sea Surface Temperature (SST). Data were averaged in time to obtain maps of monthly mean time series in order to analyze the seaso...
Article
Full-text available
Time series (1997-2008) of near-shore altimetry data and in-situ tide gauge records have been analyzed to investigate the seasonal variability of sea level along the Gulf of Cadiz. A high level of agreement was obtained between altimeter and in-situ observations, indicating that altimeter data can be a valuable tool to study the sea level seasonal...
Article
Full-text available
In this article, a theoretical procedure has been developed for the kinetic study of the glass-crystal transformations under continuous heating regime in materials involving formation and growth of nuclei, obtaining the corresponding parameters: kinetic exponent, activation energy, and pre-exponential frequency. It is an integral procedure, which i...
Article
A theoretical method, which we have published in two previous works, has been applied to the study of the glass-crystal transformation of the Ag0.16As0.38Se0.46 semiconductor glass under non-isothermal conditions. This method allows one to obtain an evolution equation with temperature for the actual volume fraction, to calculate the kinetic paramet...
Conference Paper
Full-text available
This paper presents the main results obtained from the application of synthetic aperture radar (SAR) sea surface image analysis to the validation of the baroclinic internal wave 3D modeling in the Strait of Gibraltar and Algeciras Bay. Appropriate SAR images, showing the occurrence of short-wavelength oscillations in the sea surface in this area, w...
Article
Full-text available
A theoretical procedure has been developed for the kinetic study of the glass–crystal transformation under continuous heating regime in materials involving formation and growth of nuclei. The quoted procedure obtains an evolution equation with the temperature for the actual volume fraction transformed at non-isothermal reactions. In this procedure...
Article
The water storage variations in lakes affect their physical, chemical and biological processes. Besides, the water masses of these waterbodies reflect the balance of the rainfall and evaporation with surface and ground waters. The lake’s water volume is estimated combining water level variations with accurate bathymetry and shore topography maps. L...
Article
Full-text available
Satellite altimetry has proved successful as a global tool for monitoring sea surface height, significant wave height and wind speed. Nevertheless, a global archive of 17 years of raw data from a series of missions is presently unexploited around the world coastline. This huge amount of unused data can be re-analyzed, improved and more intelligentl...
Article
A procedure has been developed to establish the thermal process type, to determine the dimensionality of the crystal growth and to evaluate the exponents of the power laws of the time-dependence both for the nucleation frequency and for the crystal growth rate in glass–crystal transformations under non-isothermal regime. To carry out the quoted pro...
Article
A procedure has been developed to obtain an evolution equation with the temperature for the actual transformed volume fraction under non-isothermal regime and to calculate the kinetic parameters in glassy solids. Once an extended volume of transformed material has been defined and spatially random transformed regions have been assumed, a general ex...
Article
A procedure has been developed to obtain an evolution equation with the temperature for the actual transformed volume fraction under non-isothermal regime, to calculate the kinetic parameters and to analyze the glass-crystal transformation mechanisms in solid systems where a large number of nuclei already exists and no other new nuclei are formed d...
Article
A theoretical method has been considered to determine the suitable form of the glass–crystal transformation function, and to calculate the kinetic parameters by using differential scanning calorimetry data, obtained from experiments carried out under non-isothermal regime. It is an integral method, which is based on a transformation rate independen...
Article
Full-text available
Fifteen years of global altimetry data over the coastal ocean lie, largely unexploited, in the data archives, simply because intrinsic difficulties in the corrections and issues of land contamination in the footprint. These data would be invaluable for studies of coastal circulation, sea level change and impact on the coastline. Amongst some initia...
Article
The surface extent of a lake reflects its water storage variations. This information has important hydrological and operational applications. However, there is a lack of information regarding this subject because the traditional methodologies for this purposes (ground surveys, aerial photos) requires high resources investments. Remote sensing techn...
Article
The use of remote sensing techniques in monitoring inland waters has become a powerful tool, considering the amount of ungauged waterbodies all over the world. The water mass balance is an essential subject to take into account in water management activities. The level changes of a lake surface are an indicator of the water mass balance of a basin...
Article
The Cramer-Rao lower bound (CRLB) for the estimations of the cosine and sine amplitudes of multi-tone sinusoidal model is derived and applied on TOPEX/Poseidon satellite altimetry data sets covering the Indian Ocean. The CRLB depends on the variance of the White Gaussian Noise that it is computed by Modern Parametric Autoregressive Adaptative Spect...
Article
Full-text available
It is well known that ocean-atmosphere dynamic affects the weather conditions over the continents and the ocean itself. The hydrologic cycle is driven by climatic parameters like precipitation, temperature, evaporation, winds and humidity. Hence, the river's water discharges and lake water level variations are impelled by climatic conditions also....
Article
Full-text available
The Cramer-Rao lower bound (CRLB) for the estimations of the cosine and sine amplitudes of multi-tone sinusoidal model is derived and applied on TOPEX/Poseidon satellite altimetry data sets covering the Indian Ocean. The CRLB depends on the variance of the White Gaussian Noise that it is computed by Modern Parametric Autoregressive Adaptative Spect...
Conference Paper
Full-text available
Drake Passage, the gap between South America and Antarctica, is a very energetic region, with strong currents and numerous eddies. These eddies are important for mixing waters across the main three fronts, and for affecting the biological productivity in the region. We use weekly maps of color images, sea level anomaly and geostrophic velocities to...
Article
Full-text available
The National Oceanography Centre (Southampton) retracking algorithm has been optimized to retrieve geophysical parameters from Envisat RA-2 18-Hz ocean averaged waveforms in an operational way. The retracking algorithm is based on Maximum Likelihood Estimation. In its linear form, it retrieves the significant wave height and the time origin. Extra...
Article
Full-text available
A procedure has been developed to determine the reliable form of the glass-crystal transformation function, and to deduce the kinetic parameters by using differential scanning calorimetry data, obtained from experiments performed under non-isothermal conditions. It is an integral method, which is based on a transformation rate independent of the th...
Article
Full-text available
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...
Article
A method has been developed for analyzing the non-isothermal glass-crystal transformation kinetics in materials for which the nucleation process takes place early in the transformation and the nucleation frequency is zero thereafter, the condition of “site saturation”. Under this condition the Johnson–Mehl–Avrami transformation rate equation can be...
Article
Full-text available
The National Oceanography Centre, Southampton retracking algorithm has been optimized to retrieve geophysical information from Envisat RA-2 18-Hz ocean averaged waveforms. The retracking algorithm is based on Maximum Likelihood Estimation. In its linear form, it retrieves the significant wave height and the epoch. Extra information can be retrieved...
Article
Full-text available
The interference modulated reflection spectra R(λ) at normal incidence for amorphous GeSe2 semiconducting films, deposited by thermal evaporation, were obtained in the spectral region from 400 nm to 2200 nm. The straightforward method proposed by Minkov, which is based on the use of the extrema of the interference fringes R(λ), has been applied in...
Article
A theoretical method is derived for the progress of a nucleation and growth-controlled reaction during heating at a constant rate. The kinetic parameters have been obtained assuming that the reaction rate constant is a time function through its Arrhenian temperature dependence. Besides, it has been shown that the different models, used in the liter...
Article
In the present work, a kinetic analysis on glass-crystal transformation from differential scanning calorimetry (DSC) data under non-isothermal condition is described. A method has been developed for analyzing the evolution with time of the volume fraction crystallized and for calculating the kinetic parameters at non-isothermal reactions in materia...
Article
Full-text available
The radar altimeter data sets are used to study several dynamical characteristic of the World's Oceans because the artificial satellites have a global coverage. One of the most important applications is related to the Mean Sea Level changes. The authors take into account the TOPEX/Poseidon data for the Mediterranean Sea and the Iberian Atlantic in...
Article
Full-text available
The glass-forming ability and devitrification of alloys in the Sb–As–Se system have been studied by differential scanning calorimetry (DSC). A comparison of various simple quantitative methods to assess the level of stability of glassy materials in the above-mentioned system is presented. All these methods are based on the characteristic temperatur...
Article
Full-text available
A procedure has been considered for analyzing the evolution with time of the volume fraction transformed and for calculating the kinetic parameters at nonisothermal reactions in materials involving formation and growth of nuclei. By assuming that the nucleation process takes place early in the transformation and the nucleation frequency is zero the...
Article
Full-text available
A procedure has been developed for analyzing the evolution with time of the actual volume fraction transformed, for calculating the kinetic parameters and for analyzing the glass–crystal transformation mechanisms in solid systems involving formation and growth of nuclei. By defining an extended volume of transformed material and assuming spatially...
Article
Full-text available
A method has been developed for analysing the evolution with time of the volume fraction transformed and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. By considering the assumptions of extended volume and random nucleation, a general expression of the fraction transformed a...
Article
Full-text available
The thermal stability and crystallization of alloys in the Ge–Sb–Se system were studied by differential scanning calorimetry (DSC). A comparison of various simple quantitative methods to assess the level of stability of the glassy materials in the above-mentioned system is presented. All of these methods are based on characteristic temperatures, ob...
Article
Full-text available
A procedure has been considered for analyzing the evolution with time of the volume fraction transformed and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. By assuming that the nucleation process takes place early in the transformation and the nucleation frequency is zero th...
Article
Full-text available
An analysis is carried out on two procedures which have been proposed for the determination of the temperature dependence of homogeneous crystal nucleation rates in glassy solids by using differential scanning calorimetry (DSC) measurements. The first procedure is based upon the hypothesis that the density of nucleated particles will increase monot...
Article
Full-text available
Present paper summarizes the capabilities of the ocean retracking model developed at the Southampton Oceanography Centre to retrieve geophysical parameters (mainly, significant wave height, backscatter power and range), using the RA-2 Envisat 18-Hz averaged waveforms. This model is based on the use of the Maximum Likelihood Estimation. One of the m...
Article
Full-text available
A theoretical method has been considered for deriving the evolution equation with time of the actual volume fraction transformed, for integrating the above mentioned equation under non-isothermal regime, and for deducing the kinetic parameters of the glass–crystal transformations in solid systems where a large number of nuclei already exists and no...
Article
Full-text available
Continuous heating differential scanning calorimetry is frequently employed to study the kinetics of transformation reactions and, in particular, the crystallization of the glassy alloys. Such data are analyzed by the Kissinger method, which was originally derived for the study of homogeneous reactions. Although the consensus in the literature, ove...
Article
Full-text available
A theoretical procedure has been developed for deriving the evolution equation with time of the actual volume fraction transformed, for integrating the above mentioned equation under non-isothermal regime, for deducing the kinetic parameters and for analyzing the glass-crystal transformation mechanisms in solid systems involving formation and growt...
Article
Full-text available
The real sea level response to atmospheric pressure variations is quantified and compared with the one deduced from the isostatic assumption, which is normally used to correct the effect of the atmospheric pressure oscillations in the ocean, the so-called Inverse Barometer Correction (IBC). We have analysed the first four years of ERS-2 altimetric...
Article
Full-text available
The exponential increase in the use of altimeter data in oceanographic studies in the past two decades has improved the knowledge of the processes that govern the interaction between the ocean and the atmosphere. One of these processes is the response of the ocean to atmospheric pressure variations, which has been deeply analysed in the past. That...
Article
Full-text available
A procedure has been developed for analyzing the evolution with time of the volume fraction crystallized and for calculating the kinetic parameters at non-isothermal reactions in materials involving growth of nuclei. By means of this method, and considering the assumptions of extended volume and randomly located nuclei, a general expression of the...
Article
Full-text available
A method has been developed for deriving the evolution equation with time of the volume fraction crystallized, for integrating the above-mentioned equation under non-isothermal conditions, and for deriving the kinetic parameters of the glass–crystal transformations in solid systems involving the formation and growth nuclei. By means of this method,...
Article
The glass formation and devitrification of alloys in the Sb–As–Se system were studied by differential scanning calorimetry. A comparison of various simple quantitative methods to assess the level of stability of the glassy materials in the above mentioned system is presented. All of these methods are based on characteristic temperatures, such as th...
Article
A procedure has been developed for analyzing the evolution with time of the volume fraction crystallized and for calculating the kinetic parameters at non-isothermal reactions in materials involving growth of nuclei. By means of this method, and considering the assumptions of extended volume and randomly located nuclei, a general expression of the...
Article
The variability of sea level and surface geostrophic currents in Atlantic Ocean is investigated using 333 cycles of altimeter information obtained by TOPEX-POSEIDON satellite. After the improvements of orbit accuracy, the most important concern to studies of sea level variability from altimeter height data are related with the formalism used for mo...
Conference Paper
Full-text available
We have used the first three years of ERS-2 altimeter data (May 1995 - June 1998) in order to analyse the space-temporal ocean response to atmospheric pressure variations in the three main ocean world basins: Atlantic, Indian and Pacific. We have also quantified the magnitude of the departures of this response from the hypothetical barometric facto...
Article
Full-text available
The ocean response to pressure variations is subtracted from altimeter records using the standard Inverse Barometer Correction (IBC), based on the hypothetical isostatic assumption. Previous analyses have demonstrated that this assumption has to be applied with care when the high frequency pressure variations are considered, as is the case of using...
Article
Full-text available
After leaving the Strait of Gibraltar the Mediterranean water outflow descends close to the bottom of the slopping topography towards the Gulf of Cadiz, being deflected to the right as a consequence of earth rotation effects, starting its mixes with its surrounding Atlantic waters. Consequently, the termohaline characteristics of the Mediterranean...
Article
The sea level response to fluctuations in barometric pressure is currently modelled by the inverted barometer (IB) approximation which implies a change of approximately 1 cm in sea level for 1 mb change in atmospheric pressure (isostatic assumption). Therefore, sea level gradients perfectly compensate the horizontal gradients in atmospheric pressur...
Article
Full-text available
The spatial and time variations of the Southern Ocean sea level and its possible relationship with the Antartic sea ice changes and surface geostrophic currents in the area are investigated using altimeter data sets from ERS-1, ERS-2 and Topex-Poseidon between 1992 and 1999. Altimeter data are analysed following an Empirical Orthogonal Function Dec...
Article
Full-text available
A procedure has been considered for analyzing the change with time of the volume fraction crystallized and for calculating the kinetic parameters (activation energy, kinetic exponent and frequency factor) of non-isothermal reactions in materials involving formation and growth of nuclei. By using the assumptions of extended volume and random nucleat...
Article
An alternative method is proposed for generalizing the Johnson–Mehl–Avrami equation, under restrictive assumptions for non-isothermal transformations on the basis of nucleation and crystal growth processes. An interesting result, according to literature, is that the Kissinger equation can be applied to the analysis of heterogeneous solid state tran...
Article
Full-text available
A procedure has been used for analyzing the evolution with time of the volume fraction crystallized and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. Considering the assumptions of extended volume and random nucleation, a general expression of the fraction crystallized has...
Article
Full-text available
A procedure has been developed for analyzing the evolution with time of the volume fraction crystallized and reaction mechanism and for calculating the kinetic parameters at non-isothermal transformations in materials involving formation and growth of nuclei. Considering the assumptions of extended volume and random nucleation, a general expression...
Article
A procedure has been developed for analyzing the evolution with time of the crystallized fraction and for calculating the kinetic parameters at non-isothermal reactions involving formation and growth of nuclei. Considering the assumptions of extended volume and random nucleation, a general expression of the transformed fraction as a function of tim...
Article
The techniques of differential thermal analysis are frequently employed to study the kinetics of the transformation reactions and, in particular, the crystallization of the glassy alloys. The corresponding thermal data can be analyzed by the Kissinger method, which was originally derived for the study of homogeneous reactions. The consensus in the...