Clasificación y su implementación en R

La clasificación de datos es un proceso de aprendizaje estadístico que trata de agrupar en categorías conocidas los diferentes casos considerados buscando alguna relación entre las características de individuos de la misma clase. A lo largo de este trabajo serán descritos tanto la construcción como el funcionamiento de algunas de las técnicas más habituales para abordar un problema de clasificación desarrolladas durante el siglo XX. Los clasificadores considerados estarán divididos en lineales, no lineales o árboles de clasificación. Para cada clasificador se realizará un ejemplo utilizando el paquete informático R con diferentes conjuntos de datos a fin de mostrar su implementación y ver las ventajas o desventajas del uso de cada uno de ellos. En dichos ejemplos veremos que esta clase de problemas se pueden encontrar en diversos ámbitos de estudio lo cual remarca la utilidad de este proceso.Classification is a statistical learning process which tries to group the different cases in known categories searching for a relationship between the features of the same class. Throughout this paper it will be described how to build a classifier and the performance of several of the most popular techniques developed during the 20th century. These classifiers could be linear, nonlinear or classification trees. For every classifier there will be an example with different data set using the R software in order to show the implementation of these algorithms and the advantages and disadvantages of every one. These examples demonstrate that this kinds of problems could be found in various fields of study which indicates how useful this process is.Universidad de Sevilla. Grado en Matemática

Dissolution and phosphate-induced transformation of ZnO nanoparticles in synthetic saliva probed by AGNES without previous solid-liquid separation. Comparison with UF-ICP-MS

The variation over time of free Zn2+ ion concentration in stirred dispersions of ZnO nanoparticles (ZnO NPs) prepared in synthetic saliva at pH 6.80 and 37 degrees C was followed in situ (without solid liquid separation step) with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). Under these conditions, ZnO NPs are chemically unstable due to their reaction with phosphates. The initial stage of transformation (around 5-10 h) involves the formation of a metastable solid (presumably ZnHPO4), which later evolves into the more stable hopeite phase. The overall decay rate of ZnO NPs is significantly reduced in comparison with phosphate-free background solutions of the same ionic strength and pH. The effective equilibrium solubilities of ZnO (0.29-0.47 mg.L-1), as well as conditional excess-ligand stability constants and fractional distributions of soluble Zn species, were determined in the absence and presence of organic components. The results were compared with the conventional ultrafiltration and inductively coupled plasma-mass spectrometry (UF-ICP-MS) methodology. AGNES proves to be advantageous in terms of speed, reproducibility, and access to speciation information. KeywordsThis work was supported by the Spanish Ministry MINECOunder Grant No. CTM2016-78798 and European UnionSeventh Framework Programme FP7-NMP.2012.1.3-3 underGrant No. 310584 (NANoREG). FQ gratefully acknowledgesa grant from AGAUR

Dynamics of trace metal sorption by an ion-exchange chelating resin described by a mixed intraparticle/film diffusion transport model. The Cd/Chelex case

The time-evolution of Cd2+ ion sorption by Chelex 100 resin was studied in batch experiments as a function of time, pH, ionic strength, stirring rate, mass of resin and initial metal ion concentration. In the experimental conditions, the amount of resin sites are in excess with respect to the amount of metal ion, leading to extensive depletion of metal in bulk solution when equilibrium is reached. The data were described using a mixed control mass transport model in finite volume conditions (MCM) that includes explicitly both intraparticle and film diffusion steps. Exact numerical computations and a new approximate analytical expression of this model are reported here. MCM successfully predicts the influence of pH and ionic strength on the experimental Cd(II)/Chelex kinetic profiles (which cannot be justified by a pure film diffusion controlled mechanism) with a minimum number of fitting parameters. The overall diffusion coefficient inside the resin was modelled in terms of the Donnan factor and the resin/cation binding stability constant. The values of the latter coefficient as a function of pH and ionic strength were estimated from the Gibbs-Donnan model. Even though MCM is numerically more involved than models exclusively restricted to film or intraparticle diffusion control, it proves to be accurate in a wider range of values of the mass transfer Biot number and solution/resin metal ratios.The authors gratefully acknowledge support for this research from the Spanish Ministry MINECO (Projects CTM2013-48967 and CTM2016-78798) and by the “Comissionat d'Universitats i Recerca de la Generalitat de Catalunya” (2014SGR1132). FQ acknowledges a grant from AGAUR

Gibbs-Donnan and specific ion interaction theory descriptions of the effect of ionic strength on proton dissociation of alginic acid

The apparent proton dissociation constants of a commercial alginic acid have been obtained in KNO3 and NaCl at concentrations ranging between 0.01 and 2 mol·L-1. An analysis of the dependence on the ionic strength at a constant value of the dissociation degree was done by means of empirical functions derived from the Gibbs-Donnan formalism for polyelectrolytes and a specific ion interaction theory (SIT). Both functions were able to fit the experimental data, although SIT yielded rather high errors in the fitted parameters due to a problem of multicollinearity, in contrast to the function derived from the Gibbs-Donnan approach.This work was funded by the projects BQU2002-02133 (from the Ministerio de Ciencia y Tecnología of Spain) and PGDIT02TAM10302PR (from the Xunta de Galicia). C.R.C. benefited from a FPU grant of the Ministerio de Educación, Cultura y Deporte of Spain

Removal of Inorganic Mercury From Aqueous Solutions by Biomass of the Marine Macroalga Cystoseira Baccata

[Abstract] The ability of Cystoseira baccata algal biomass to remove Hg(II) from aqueous solutions is investigated. The mercury biosorption process is studied through batch experiments at 25ºC with regard to the influence of contact time, initial mercury concentration, solution pH, salinity and presence of several divalent cations. The acid-base properties of the alga are also studied, since they are related to the affinity for heavy metals. The studies of the pH effect on the metal uptake evidence a sharp increasing sorption up to a pH value around 7.0, which can be ascribed to changes both in the inorganic Hg(II) speciation and in the dissociation state of the acid algal sites. The sorption isotherms at constant pH show uptake values as high as 178 mg.g-1 (at pH 4.5) and 329 mg.g-1 (at pH 6.0). The studies of the salinity influence on the Hg(II) sorption capacity of the alga exhibit two opposite effects depending on the electrolyte added; an increase in concentration of nitrate salts (NaNO3, KNO3) slightly enhances the metal uptake, on the contrary, the addition of NaCl salt leads to a drop in the sorption. The addition of different divalent cations to the mercury solution, namely Ca2+, Mg2+, Zn2+, Cd2+, Pb2+ and Cu2+, reveals that their effect on the uptake process is negligible. Finally, the equilibrium sorption results are compared with predictions 1 obtained from the application of a simple competitive chemical model, which involves a discrete proton binding constant and three additional constants for the binding of main neutral inorganic Hg(II) complexes, Hg(Cl) HgOHCl and Hg(OH)2, to the algal surface sites

Dealing with long-range interactions in the determination of polyelectrolyte ionization properties. Extension of the transfer matrix formalism to the full range of ionic strengths

The ionization state of charged macromolecules in solution is usually determined by the extent of the binding processes. These processes are very sensitive to the ionic strength of the medium, which are of long-range nature. The ionization properties of weak polyelectrolytes can be described by means of Ising-type models, which is only feasible when long-range interactions are neglected. Here, this formalism is extended to include long-range interactions by introducing a modified free energy involving only effective short-range interaction parameters. These parameters can be systematically calculated by using the Gibbs-Bogoliubov variational principle. The technique is illustrated with the calculation of titration curves of homogeneous and heterogeneous polyelectrolytes in a wide range of ionic strengths. The correction of the site protonation free energy (first order correction) is enough to obtain an excellent agreement between theory and Monte Carlo simulations. Corrections to other cluster parameters (higher order corrections) are also implemented. In general, the correction to a particular parameter represents the average change in the long-range energy when a new interaction is created in the polyelectrolyte. The method presented here represents an improvement in the description of the ionization state of polyelectrolytes that can be relevant in a wide range of areas.represents the average change in the long range energy when a new interaction (of the type described by the cluster parameter), is created in the polyelectrolyte. The method presented here represents an improvement in the description of the ionization state of charged macromolecules that can be relevant in a wide range of areas such as biochemistry, environmental chemistry, materials science, etc

IR characterization of Ln2−xSrxCoO4 (x≥1; Ln=La, Nd) oxides

[Abstract] We have recorded the FTIR spectra of powder samples of Ln2−xSrxCoO4 (Ln=La, Nd) at room temperature. We have identified the infrared active modes (3A2u+4Eu), and analyzed how they change as a function of Ln and the Sr doping. We correlate the obtained results with structural data obtained from powder X-ray diffraction studies and with the electronic properties displayed by these samples