Optimization of heat‐transfer rate into time‐periodic two‐dimensional Stokes flows

The periodic boundary displacement protocol leading to the optimum wall‐to‐fluid heat‐transfer rate, or to the most efficient mixing rate, in 2‐D annular Stokes flows is determined by calculating the steady periodic velocity and temperature fields. To obtain the steady periodic state one usually solves the dynamical system obtained after the spatial coordinates have been discretized. Here, we calculate the steady periodic state using an implicit method based on the discretization of the time coordinate over a period and the asymptotic regime is enforced by the periodicity condition in the computed temperature field. The obtained system of equations is solved using a Newton‐type iterative algorithm with invariant Jacobian. At each iteration step, the sparse linearized system is solved using a multi‐grid algebraic technique of rapid convergence. From a computational point of view and for the problem considered here, this method is an order of magnitude faster than the one based on a spatial discretization. Copyright © 2006 John Wiley & Sons, Ltd.     

Cold plasma oscillations according to Weber's law. An unphysical result

Applying Weber's law to particle interactions in a uniform infinite cold plasma, a dispersion relation for longitudinal plasma oscillations is found. The classical result of plasma frequency oscillations is recovered for small wavelengths. Depending on the wavelength, the phase and group velocities may be singular. This unphysical result is due to the absence of transverse interaction in Weber's law.     

Study of semicarbazones and thiosemicarbazones derived from 1,2-naphthoquinone, as acid-base indicators: Evaluation of their transition limits through the chromaticity co-ordinates

The use of 1,2-naphthoquinone-2-semicarbazone, 1,2-naphthoquinone-2-semicarbzone-4-sulphonic acid and 1,2-naphthoquinone-2-thiosemicarbazone-4-sulphonic acid as acid—base indicators has been studied. The sharpness of the indicator transitions has been investigated by means of photometric titrations and the colour quality specified with the aid of the CIE chromaticity system. The results show that the three substances are satisfactory as neutralization indicators.     

Mobility of high-power solitons in saturable nonlinear photonic lattices

We theoretically study the properties of one-dimensional nonlinear saturable photonic lattices exhibiting multiple mobility windows for stationary solutions. The effective energy barrier decreases to a minimum in those power regions where a new intermediate stationary solution appears. As an application, we investigate the dynamics of high-power Gaussian-like beams finding several regions where the light transport is enhanced.     

Class formation in a social network with asset exchange

We study two kinds of economic exchanges, additive and multiplicative, in a system of N agents. The work is divided into two parts. In the first one, the agents are free to interact with each other. The system evolves to a Boltzmann-Gibbs distribution with additive exchange and condenses with a multiplicative one. If bankruptcy is introduced, both types of exchange lead to condensation. Condensation times have been studied. In the second part, the agents are placed in a social network. We analyze the behavior of wealth distributions in time, and the formation of economic classes is observed for certain values of network connectivity.     

Scalable, stereocontrolled total syntheses of (±)-axinellamines A and B

The development of a simple, efficient, scalable, and stereocontrolled synthesis of a common intermediate en route to the axinellamines, massadines, and palau'amine is reported. This completely new route was utilized to prepare the axinellamines on a gram scale. In a more general sense, three distinct and enabling methodological advances were made during these studies: (1) an ethylene glycol-assisted Pauson-Khand cycloaddition reaction, (2) a Zn/In-mediated Barbier-type reaction, and (3) a TfNH(2)-assisted chlorination-spirocyclization.     

Thermodynamics of axial substitution and kinetics of reactions with amino acids for the paddlewheel complex tetrakis(acetato)chloridodiruthenium(II,III)

The known paddlewheel, tetrakis(acetato)chloridodiruthenium(II,III), offers a versatile synthetic route to a novel class of antitumor diruthenium(II,III) metallo drugs, where the equatorial ligands are nonsteroidal anti-inflammatory carboxylates. This complex was studied here as a soluble starting prototype model for antitumor analogues to elucidate the reactivity of the [Ru(2)(CH(3)COO)(4)](+) framework. Thermodynamic studies on equilibration reactions for axial substitution of water by chloride and kinetic studies on reactions of the diaqua complexes with the amino acids glycine, cysteine, histidine, and tryptophan were performed. The standard thermodynamic reaction parameters ΔH°, ΔS°, and ΔV° were determined and showed that both of the sequential axial substitution reactions are enthalpy driven. Kinetic rate laws and rate constants were determined for the axial substitution reactions of coordinated water by the amino acids that gave the corresponding aqua(amino acid)-Ru(2) substituted species. The results revealed that the [Ru(2)(CH(3)COO)(4)](+) paddlewheel framework remained stable during the axial ligand substitution reactions and was also mostly preserved in the presence of the amino acids.     

Looking for the physiological role of anthocyanins in the leaves of Coffea arabica

The aim of this study was to determine which anthocyanins are related to the purple coloration of young leaves in Coffea arabica var. Purpurascens and assess their impact on photosynthesis as compared to C. arabica var. Catuaí, with green leaves. Two delphinidin glicosides were identified and histological cross-sections showed they were located throughout the adaxial epidermis in young leaves, disappearing as the leaves mature. Regardless the irradiance level, the photosynthetic performance of Purpurascens leaves did not differ from that observed in leaves of the Catuaí variety, providing no evidence that anthocyanins improve photosynthetic performance in coffee plants. To analyze the photoprotective action of anthocyanins, we evaluated the isomerization process for chlorogenic acids (CGAs) in coffee leaves exposed to UV-B radiation. No differences were observed in the total concentration of phenolic compounds in either variety before or after the UV treatment; however, we observed less degradation of CGA isomers in the Purpurascens leaves and a relative increase of cis-5-caffeoylquinic acid, a positional isomer of one of the most abundant form of CQA in coffee leaves, trans-5-caffeoylquinic acid, suggesting a possible protective role for anthocyanins in this purple coffee variety.     

An organophosphonate strategy for functionalizing silicon photonic biosensors

Silicon photonic microring resonators have established their potential for label-free and low-cost biosensing applications. However, the long-term performance of this optical sensing platform requires robust surface modification and biofunctionalization. Herein, we demonstrate a conjugation strategy based on an organophosphonate surface coating and vinyl sulfone linker to biofunctionalize silicon resonators for biomolecular sensing. To validate this method, a series of glycans, including carbohydrates and glycoconjugates, were immobilized on divinyl sulfone (DVS)/organophosphonate-modified microrings and used to characterize carbohydrate-protein and norovirus particle interactions. This biofunctional platform was able to orthogonally detect multiple specific carbohydrate-protein interactions simultaneously. Additionally, the platform was capable of reproducible binding after multiple regenerations by high-salt, high-pH, or low-pH solutions and after 1 month storage in ambient conditions. This remarkable stability and durability of the organophosphonate immobilization strategy will facilitate the application of silicon microring resonators in various sensing conditions, prolong their lifetime, and minimize the cost for storage and delivery; these characteristics are requisite for developing biosensors for point-of-care and distributed diagnostics and other biomedical applications. In addition, the platform demonstrated its ability to characterize carbohydrate-mediated host-virus interactions, providing a facile method for discovering new antiviral agents to prevent infectious disease.