José A. Corrales

Combining GP operators with SA search to evolve fuzzy rule based classifiers

Abstract The genotype–phenotype encoding of fuzzy rule bases in GA, along with their corresponding crossover and mutation operators, can be used by other search schemes, improving the behavior of these last ones. As a practical consequence of this, a simulated annealing-based method for inducting both parameters and structure of a fuzzy classifier has been developed. The adjacency operator in SA has been replaced with a macromutation taken from tree-shaped genotype GAs. We will show that results of SA search are similar to those of GP in both the efficiency of the learned classifiers and in its linguistic interpretability, while the memory consumption of the learning process is lower.

Variations of the local anisotropy versus Tb content in amorphous CoZrTb thin films

The magnetic properties of rf sputtered amorphous (Co93Zr7)100−xTbx thin films were investigated as a function of Tb content for 0≤x≤2 by transverse biased initial susceptibility measurements. The deposition was performed in a magnetic field. This films exhibit a very well‐defined in‐plane anisotropy with negligible long‐range fluctuations and a small coercive field Hc, in accordance with the experimental data. The overall variations of the transverse susceptibility are related to the ripple, and the variations of the structure factor S with composition was measured. The local anisotropy Kloc, deduced from S, increases with the increasing amount of Tb in the layers. The results are discussed in terms of the single‐ion anisotropy of the rare earth.

Transverse susceptibility of nanoparticle systems: The effect of interaction, dispersion, and texture

The effect of texture, dispersion, and interaction on transverse susceptibility has been studied. We have developed a model based on the well-known Stoner-Wohlfarth model, by taking into account the texture, the anisotropy field value distribution, and the intergranular magnetic interactions. This model shows a good agreement with experimental measurements on granular FeCoV thin films and allows us to determine the mean value of the local magnetic anisotropy, intergrain interaction, and texture of these alloys.

TBIS measurements performed by MOKE for the study of soft ferromagnetic thin films and sandwiches: In-plane and biaxial anisotropies, local anisotropy and dispersion

Abstract Magneto-optic effects have been proved to be a premier tool for the study of magnetic thin films. In the case of films thinner than 1000 A and if there is no appreciable variation of the magnetic structure through the thickness, the magneto-optic effects provide complete information. It is noteworthy that transverse biased initial susceptibility (TBIS) measurement is very sensitive, for it allows a precise determination of the anisotropy field and, moreover, to quantify the anisotropy dispersion distinguishing between short- and long-range magnetization fluctuations in the plane of the film the origin of which is different. If the samples are deposited on glass substrates, by performing TBIS measurements with a magneto-optic transverse Kerr effect (MOKE) we can obtain information of the processes occurring at both film/air and glass/film interfaces, providing information of the variation of the magnetic properties through the thickness. We have successfully applied this technique for the study of thin films and sandwiches, focusing our attention on the following items: 1. (1) Uniaxial in-plane anisotropy, local anisotropy and anisotropy dispersion in transition metal-rare-earth thin films. We have investigated the dependence of the uniaxial anisotropy and its dispersion on the rare-earth substituted and on the composition. Using the ripple theory we have evaluated the local anisotropy as a function of the rare-earth content, and we have found a very nice correlation between macroscopic and local anisotropies, allowing us to establish the origin of the macroscopic anisotropy in these alloys. 2. (2) TBIS measurements can also be used as an alternative technique to measure perpendicular anisotropy. We have developed a theoretical model to explain the particular behaviour of TBIS curves in the most general case when both in-plane and perpendicular anisotropies are present (biaxial anisotropy). From the fit of the experimental curves to the theoretical model we can obtain the in-plane and the perpendicular anisotropy fields. 3. (3) When the samples are not magnetically homogeneous, they may present different magnetic phases which may be made evident by our technique. 4. (4) We recently extended this technique to the study of ferromagnetic double-layered and sandwiched films. In these systems the magnetic and magneto-optical properties are strongly influenced by the coupling at the interfaces. The high sensitivity of our procedure allowed us to distinguish between two contributions to the anisotropy dispersion in sandwiched films: a well-known term due to the in-plane anisotropy skew (long-range fluctuations of the in-plane easy axis) and a contribution due to the existence of a weak perpendicular anisotropy.

Effect of grain size on the soft magnetic properties of FeCoV∕CoNbZr multilayers

Experimental characterization of macroscopic effective anisotropy field and coercive field for nanocrystalline (FeCoV∕CoNbZr)16 multilayers was carried out with transverse susceptibility. The multilayer structure consisting of a FeCoV ferromagnetic nanogranular layer covered with a CoNbZr amorphous layer was prepared by rf sputtering. All multilayers had the same thickness of CoNbZr (3 nm) with FeCoV layer thickness varying between 6 and 30 nm. The properties of the optimized multilayer structured films are related to an appropriate grain size of FeCoV where the CoNbZr layer acts as a very effective grain refiner and reduces the average grain size. The experimental values of the coercive force and the macroscopic uniaxial anisotropy were related to the grain size. The values were analyzed according to a two dimensional random anisotropy model which takes into account the uniaxial anisotropy.

Induced and local anisotropies in amorphous CoZr–rare earth thin films containing Pr, Nd, and Tb

The induced in‐plane and local magnetic anisotropies of rf sputtered (Co93Zr7)100−xREx thin films were investigated as a function of RE content for RE=Pr, Nd, and Tb by transverse biased initial susceptibility measurements at both film/air and glass/film interfaces. The deposition was performed in a magnetic field. The films exhibit a very well defined in‐plane anisotropy with negligible long‐range fluctuations and a small coercive field Hc, in accordance with the experimental data. The overall variations of the transverse susceptibility are related to the ripple. The variations of the local anisotropy with composition were measured. Both the induced anisotropy Ku and the local anisotropy Kloc increase with the increasing amount of RE in the layers. A clear relationship between Ku and Kloc could be established. The results are discussed in terms of the single‐ion anisotropy of the rare earth. While the value of Ku is the same at both interfaces, the ripple constants were found to be slightly different. Th...

Using a Symbolic Model Checker for Verify Safety Properties in SA/RT Models

In this paper, structured methods are integrated with formal verification methods based on temporal logic. The goal is to use an operational method (SA/RT) for the system behavioural specification, and to complement this with safety properties expressed in a declarative style using temporal logic (CTL). These properties are checked against the operational specification using a model checker (SMV).

Use of Band Ratioing for Color Texture Classification

In the recent years, many authors have begun to exploit the extra information provided by color images to solve many computer vision problems. Among these problems, we find the texture classification field, which traditionally has used grayscale images, primarily due to the high hardware and processing costs. In this paper, a new approach for enhancing classical texture analysis methods is presented. By means of the band ratioing technique, we can extend any feature extraction algorithm to take advantage of color information and achieve higher classification rates. To prove this extreme, three standard techniques has been selected: Gabor filters, Wavelets and Cooccurrence Matrices. For testing purposes, 30 color textures have been selected from the Vistex database. We will perform a number of experiments on that texture set, combining different ways of adapting the former algorithms to process color textures and extract features from them.

Use of band ratioing for building illumination independent texture classification systems

When a researcher faces the problem of developing a computer vision application there are many problems that have to be solved. Among those problems, we find the study of the proper illumination conditions of the scene. The way the objects are illuminated is so critical that it affects all the elements in the analysis chain. Generally the lights are carefully chosen and adapted for the computer vision system, but in some cases the system will run under variable conditions. In those cases it will be necessary to improve the robustness of the algorithms in order to minimize the impact on the application. Texture classification systems are also vulnerable to this particularity. On such systems the effect of light changes on the measured features may eventually lead to texture misclassification and performance degradation. In this paper we present an approach that will be helpful to overcome such problems when the light comes from a directional source, such as halogen projectors, LED arrays, etc.

The role of local anisotropy in the origin of in-plane uniaxial anisotropy in amorphous CoZrNd thin films

The magnetic properties of rf-sputtered amorphous (Co93Zr7)100−xNdx thin films with 0 < x < 3.5 were investigated by transverse biased initial susceptibility (TBIS) measurements at both film/air and glass/film interfaces. The films exhibit a very well defined in-plane uniaxial anisotropy with negligible long-range fluctuations. A clear relationship could be established between Ku and Kloc, data which is discussed in terms of the single-ion anisotropy of the Nd ions. Although the value of Hk is the same at both interfaces, the as-determined ripple constants were found to be slightly different. This last result is believed to be related to some local defect, the origin of which is also advanced.