Steady filtration problems with seawater intrusion: macro‐hybrid penalized finite element approximations

Macro‐hybrid penalized finite element approximations are studied for steady filtration problems with seawater intrusion. On the basis of nonoverlapping domain decompositions with vertical interfaces, sections of coastal aquifers are decomposed into subsystems with simpler geometries and small scales, interconnected via transmission conditions of pressure and flux continuity. Corresponding local penalized formulations are derived from the global penalized variational formulation of the two‐free boundary flow problem, with continuity transmission conditions modelled variationally in a dual sense. Then, macro‐hybrid finite element approximations are derived for the system, defined on independent subdomain grids. Parallel relaxation penalty‐duality algorithms are proposed from fixed‐point problem characterizations. Numerical experiments exemplify the macro‐hybrid penalized theory, showing a good agreement with previous primal conforming penalized finite element approximations (Comput. Methods Appl. Mech. Engng. 2000; 190 :609–624). Copyright © 2005 John Wiley & Sons, Ltd.     

Alpha4/3 conotoxins: phylogenetic distribution, functional properties, and structure-function insights

This review examines the alpha4/3 conotoxins as an example of molecular diversity in a class of compounds that have evolved in a group of closely related species in a single phylogenetic lineage. The species examined belong to Stephanoconus, a clade of Conus, a genus that contains 500-700 different species of carnivorous marine snails. We examine earlier work that describes the identification and characterization of alpha-ImI, the founding alpha4/3 toxin, and two other alpha4/3 toxins, alpha-ImII and alpha-RgIA. These three toxins all inhibit nicotinic acetylcholine receptors (nAChRs) belonging to a subset of nAChRs that are composed of only alpha subunits; they are, however, diverse in terms of the all-alpha subtype they preferentially antagonize and the receptor site that they bind to. We thus speculate that the alpha4/3 toxins may be a rich source of functionally diverse all-alpha subunit nAChR inhibitors. We review extensive work that has established a detailed model for alpha-ImI binding to one of its preferred nAChR subtypes (the alpha7 nAChR) and, by comparing the alpha-ImI, alpha-ImII and alpha-RgIA sequences demonstrate how structural features of alpha4/3 peptides that account for their diverse functional properties can be identified. This approach is extended to derive models of receptor-toxin binding that may account for the different subtype specificities of alpha4/3 peptides. We also speculate on how rational modification of alpha4/3 toxins may allow engineering of ligands with desired subtype specificities. The chemical diversity produced by the closely related animals in Stephanoconus is thus functionally differentiated, although structurally homologous.     

ESR of γ-irradiated DI-, TRI- and poly-glycin

The effects of γ radiation on glycylglycine, triglycine, and polyglycine have been studied using ESR spectroscopy. The radiation exposures have been performed under vacuum at room temperature. All those irradiated substances show a doublet absorption signal often ascribed to a radical formed on the α carbon of the peptide chain. The magnetic susceptibility has been found to depend on temperature according to the Curie-Weiss law. The radio-sensitivity parameter G_r , the hyperfine splitting constant A_h and the spectroscopic factor g nave been determinated as well as θ which is the temperature corresponding to the Curie temperature of the irradiated substance. The results on C_r , θ and A_h for all peptides studied here agree with the assumption of radiation induced free radicals located at the α carbon of the peptide chain, leading to conclude that the degree of delocalization of the unpaired electron increases for increasing number of glycine units in the peptide. Finally, from negative θ values obtained, a conclusion has been reached on the antiferromagnetic nature of the interaction between unpaired spins.     

Characterization and X-ray crystal structure of butanoylsalophencobalt(III)

The synthesis and characterization of the pentacoordinated butanoylsalophencobalt(III) compound, including X-ray analysis, are described. The chemical shift in the ¹³C-n.m.r. of the carbonyl carbon was determined by means of an HMBC experiment. Collision induced dissociation (CID) and high resolution mass spectrometry were used to establish the fragmentation pattern of the CoC₂₄H₂₁N₂O₃ compound. X-ray diffraction analysis shows the presence of two conformations for the acylsalophen ligand system in the same monocrystal, as well as two different OH–C hydrogen bonds with unusual interactions.     

On the effect of the local exchange in calculations of the hyperfine interaction parameters p(0) and (r−3)

The total electronic density at the nucleus for several configurations of Ru, and values of (r^?3) for the different orbitals of Fe and Ir in several configurations, calculated by the Xα and Hartree-Fock methods, are compared. The effect of variations of the parameter α on the results obtained is discussed.     

Carbochlorination of samarium sesquioxide

The chlorination of Sm₂O₃ in the presence of carbon using the gaseous mixture Cl₂(g)+Ar(g) has been studied by thermogravimetry. The effects of both the temperature between 200 and 950 °C and the total gas flow rate between 2.1 and 7.9 l h⁻¹ on the reaction rate were analyzed. The starting temperature of reaction, the stoichiometry and kinetic regimes of the reaction were obtained. Reactants and products were analyzed by X-ray diffraction (XRD) and electronic dispersive spectroscopy (EDS). The temporal evolution of the solid microstructure was followed by scanning electron microscopy (SEM).     

Individual and simultaneous fluorimetric determination of glycine and cysteine by flow injection analysis

A dual-channel flow injection configuration is proposed for individual and simultaneous determinations of glycine and cysteine (based on their reaction with phthaldialdehyde) in the range 1 × 10⁻⁷ – 1.5 × 10⁻⁵ M, with relative standard deviations of ± 1.7 and ± 1.3%, respectively, and a sampling frequency of 75–80 hr⁻¹ for both analytes. The inclusion of a selecting valve in the configuration allows the simultaneous determination of these analytes in the concentration range achieved in their individual determinations. The resolution of mixtures is feasible with average errors of ± 2.2%.     

Study of the Chemical Space of Selected Bacteriostatic Sulfonamides from an Information Theory Point of View

The relative structural location of a selected group of 27 sulfonamide‐like molecules in a chemical space defined by three information theory quantities (Shannon entropy, Fisher information, and disequilibrium) is discussed. This group is composed of 15 active bacteriostatic molecules, 11 theoretically designed ones, and para‐aminobenzoic acid. This endeavor allows molecules that share common chemical properties through the molecular backbone, but with significant differences in the identity of the chemical substituents, which might result in bacteriostatic activity, to be structurally classified and characterized. This is performed by quantifying the structural changes on the electron density distribution due to different functional groups and number of electrons. The macroscopic molecular features are described by means of the entropy‐like notions of spatial electronic delocalization, order, and uniformity. Hence, an information theory three‐dimensional space (IT‐3D) emerges that allows molecules with common properties to be gathered. This space witnesses the biological activity of the sulfonamides. Some structural aspects and information theory properties can be associated, as a result of the IT‐3D chemical space, with the bacteriostatic activity of these molecules. Most interesting is that the active bacteriostatic molecules are more similar to para‐aminobenzoic acid than to the theoretically designed analogues.     

Electrochemical Immunosensors: The Evolution from Elisa to EμPADs

Electrochemical immunosensors comprise the merging of two different disciplines: molecular biology and electrochemistry. This review explains in depth the main parts of electrochemical immunosensors and how the enzyme-linked immunosorbent assay (ELISA) has been integrated into sophisticated “lab-on-a-chip” and “point-of-care” devices. It also reviews how nanotechnology has been a powerful tool for achieving lower detection limits, more signal amplification, and constructing label-free devices. It finally explores the new perspectives on electrochemical immunosensors to integrate them in novel paper microfluidic devices called EμPADs. Colleagues introducing themselves to the topic for the first time will find in this review a comprehensive revision of how the basics of the technology have given rise to the emerging topic of EμPADs.