Combining classification and regression approaches for the quantification of highly overlapping capillary electrophoresis peaks by using evolutionary sigmoidal and product unit neural networks

This is a study of the potential of neural networks built by using different transfer functions (sigmoidal, product and sigmoidal–product units) designed by an evolutionary algorithm to quantify highly overlapping electrophoretic peaks. To test this approach, two aminoglycoside antibiotics, amikacin and paramomycin, were quantified from samples containing either only one component or mixtures of them though capillary zone electrophoresis (CZE) with laser‐induced fluorescence (LIF) detection. The three models assayed used as input data the four‐parameter Weibull curve associated with the profile of the electrophoretic peak and in some cases the class label for each sample estimated by cluster analysis. The combination of classification and regression approaches allowed the establishment of straightforward network topologies enabling the analytes to be quantified with great accuracy and precision. The best models for mixture samples were provided by product unit neural networks (PUNNs), 4:4:1 (14 weights) for both analytes, after discrimination by cluster analysis, allowing the analytes to be quantified with great accuracy: 8.2% for amikacin and 5.6% for paromomycin within the standard error of prediction for the generalization test, SEP_G. For comparison, partial least square regression was also used for the resolution of these mixtures; it provided a minor accuracy: SEP_G 11.8 and 15.7% for amikacin and paramomycin, respectively. The reduced dimensions of the neural networks models selected enabled the derivation of simple quantification equations to transform the input variables into the output variable. These equations can be more easily interpreted from a chemical point of view than those provided by other ANN models. Copyright © 2007 John Wiley & Sons, Ltd.     

Homological approximations for profinite and pro-p limit groups

Abstract

We study homological approximations of the profinite completion of a limit group (see Thm. A) and obtain the analogous of Bridson and Howie’s Theorem for the profinite completion of a non-abelian limit group (see Thm. B).     

A Mössbauer study of ultrathin Fe(110)/Ag(111) heterostructures grown by molecular beam epitaxy

We have grown good quality single crystal heterostructures of Fe(110) / Ag(111) with a high degree of epitaxy not previously achieved for films this thin. The iron-free mica substrates are transparent to gamma rays and aid in the epitaxial growth process. These films were characterized by reflection high-energy electron diffraction (RHEED), residual gas analysis (RGA), and transmission Mössbauer spectroscopy. The film with the thickest Fe component (8 monolayers) showed a hyperfine field comparable to bulk while the films with the thinnest Fe components (1.3 and 2.0 monolayers) showed an enhanced hyperfine field at 4.2 K. All the films were magnetically ordered at all the temperatures measured. Most importantly, and in contrast to other work, the direction of magnetization was in-plane for all of the films.     

Mean sample spacings, sample size and variability in an auction-theoretic framework

In terms of a standard model for English auctions and sealed-bid auctions, we study the impact of an increase in bidding competition and in variance of the distribution of valuations on the winner's expected rent using tools from order statistics and stochastic ordering.     

Ligand-controlled and nanoconfinement-boosted luminescence employing Pt(ii) and Pd(ii) complexes: from color-tunable aggregation-enhanced dual emitters towards self-referenced oxygen reporters

In this work, we describe the synthesis, structural and photophysical characterization of four novel Pd(ii) and Pt(ii) complexes bearing tetradentate luminophoric ligands with high photoluminescence quantum yields (Φ_L) and long excited state lifetimes (τ) at room temperature, where the results were interpreted by means of DFT calculations. Incorporation of fluorine atoms into the tetradentate ligand favors aggregation and thereby, a shortened average distance between the metal centers, which provides accessibility to metal–metal-to-ligand charge-transfer (³MMLCT) excimers acting as red-shifted energy traps if compared with the monomeric entities. This supramolecular approach provides an elegant way to enable room-temperature phosphorescence from Pd(ii) complexes, which are otherwise quenched by a thermal population of dissociative states due to a lower ligand field splitting. Encapsulation of these complexes in 100 nm-sized aminated polystyrene nanoparticles enables concentration-controlled aggregation-enhanced dual emission. This phenomenon facilitates the tunability of the absorption and emission colors while providing a rigidified environment supporting an enhanced Φ_L up to about 80% and extended τ exceeding 100 μs. Additionally, these nanoarrays constitute rare examples for self-referenced oxygen reporters, since the phosphorescence of the aggregates is insensitive to external influences, whereas the monomeric species drop in luminescence lifetime and intensity with increasing triplet molecular dioxygen concentrations (diffusion-controlled quenching).

Pt(ii) and Pd(ii) complexes with unprecedented photophysical properties were developed. Encapsulation in nanoparticles boosted their performance while rendering them as self-referenced oxygen sensors.     

Study of the reaction of complexation of penicillin V with cobalt(II) in methanolic medium

As shown by spectrophotometry, two specific complexes with stoichiometry 1:1 and 2:1 are formed when penicillin V reacts with cobalt(II) in a methanolic medium. Stability constants are determined at 20 degrees , as well as the molar absorptivities at 510 nm. The results obtained are: log beta(1:1) = 1.67 +/- 0.01 l.mole(-1) and log beta(2:1) = 5.76 +/- 1.01 l(2).mole(-2), (1:1) = 13.62 +/- 0.73 and (2:1) = 12.95 +/- 0.61 l.mole(-1).cm(-1).