Optimization of nearest neighbor classifiers via metaheuristic algorithms for credit risk assessment

The classification problem consists of using some known objects, usually described by a large vector of features, to induce a model that classifies others into known classes. The present paper deals with the optimization of Nearest Neighbor Classifiers via Metaheuristic Algorithms. The Metaheuristic Algorithms used include tabu search, genetic algorithms and ant colony optimization. The performance of the proposed algorithms is tested using data from 1411 firms derived from the loan portfolio of a leading Greek Commercial Bank in order to classify the firms in different groups representing different levels of credit risk. Also, a comparison of the algorithm with other methods such as UTADIS, SVM, CART, and other classification methods is performed using these data.     

Global existence for parabolic systems by Lyapunov functions

We present a result on the global existence of classical solutions for quasilinear parabolic systems with homogeneous Dirichlet boundary conditions in bounded domains with a smooth boundary. Our method relies on the use of Lyapunov functions.     

Finite difference discretization of the Benjamin‐Bona‐Mahony‐Burgers equation

Numerical solutions of the Benjamin‐Bona‐Mahony‐Burgers equation in one space dimension are considered using Crank‐Nicolson‐type finite difference method. Existence of solutions is shown by using the Brower's fixed point theorem. The stability and uniqueness of the corresponding methods are proved by the means of the discrete energy method. The convergence in L^∞‐norm of the difference solution is obtained. A conservative difference scheme is presented for the Benjamin‐Bona‐Mahony equation. Some numerical experiments have been conducted in order to validate the theoretical results.© 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007     

Enhancement of Mobile Phase Velocity in TLC by Means of an External Alternating Electric Field

JPC – Journal of Planar Chromatography – Modern TLC - In normal TLC practice, migration of the mobile phase through the layer is controlled by capillary forces. Under these conditions...     

Memory effects and ergodicity for diffusion in spatially correlated velocity fields

We show that the process of diffusion in statistically homogeneous velocity fields with finite correlation range “remembers” the shape and the orientation of the source over hundreds of dimensionless times and behaves ergodically with respect to the one-particle dispersion only asymptotically. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Organophosphorus insecticides extraction and heterogeneous oxidation on column for analysis with an acetylcholinesterase (AChE) biosensor

This paper presents an analysis method for organophosphorus insecticides based on AChE biosensors coupled with a preconcentration and oxidation on a solid phase column. Three organic solvents, acetonitrile (ACN), ethanol and methanol were tested for their influence on AChE activity, insecticide inhibition and their ability to elute the adsorbed insecticides. Our results showed that ACN in a concentration of 5% (v/v) had the less negative effect on biosensor analysis and was the most appropriate organic solvent for the column elution. The presence of the organic solvent in the incubation media of the biosensor was found to induce a reduction of the inhibition percentages. The inhibition of the biosensors was performed in phosphate buffer with 5% (v/v) ACN, while the initial and remaining response of the biosensors were measured in PBS. In these conditions, the LODs of paraoxon and dichlorvos were measured with or without a preconcentration step. The LODs of the AChE biosensor without sample preconcentration were 8 × 10⁻⁸ M for paraoxon and 1 × 10⁻⁷ M dichlorvos and the LOD obtained after the preconcentration step were 2.5 × 10⁻⁸ M for paraoxon and 2.5 × 10⁻⁸ M for dichlorvos. Moreover, the use of the column allowed the heterogeneous oxidation of organophosphorus insecticides for improved LOD.     

Synthesis of poly(methyl methacrylate-co-styrene)-block-polysulfide-block-poly(methyl methacrylate-co-styrene) copolymers by free radical polymerization combined with oxidative coupling

Poly(methyl methacrylate-co-styrene)-block-polysulfide-block-poly(methyl methacrylate-co-styrene) triblock copolymers were synthesized for the first time by the free radical copolymerization of methyl methacrylate (MMA) and styrene (St) in the presence of a thiocol oligomer as a chain transfer agent, followed by chemical oxidation of the remaining SH-end groups. The apparent chain transfer constant of the thiocol SH groups in the copolymerization reaction was estimated from the rate of consumption of the thiol groups versus the overall rate of consumption of the monomers (C_T = 1.28). Based on this value, the chain transfer constant of the thiocol SH groups in St polymerization was calculated . The triblock copolymers synthesized were characterized by SEC and ¹H NMR measurements.     

Synthesis and X-ray structure of a new pyrrolo[1,2-b]-pyridazine derivative

The synthesis, characterization and X-ray crystal structure of 2-(4-chloro-phenyl)-7-methylpyrrolo[1,2-b]pyridazine are reported. The compound crystallizes in the space group P2(1)/c (No.14) with a =3.8568(1), b = 11.0690(3), c = 26.4243(7) A, beta =92.777(1) degrees and Z = 4. Accurate molecular parameters for the novel heterocyclic system were obtained from intensity data collected at 113K. The molecule assumes a planar conformation in the crystal and the packing is based on pi-pi stacking with interplanar spacing 3.400 ?, typical of aromatic molecules with potential for displaying useful optical properties.