Global stability of centrifugal filtration convection

A nonlinear stability analysis is performed to study the onset of convection in a fluid saturated porous layer subject to alternating direction of the centrifugal body force. By introducing a suitable energy functional, the analysis is carried out for the Darcy and the Brinkman models of flow through porous media. The nonlinear result is unconditional and its sharpest limit is determined and is compared with the corresponding linear limit. The failure of linear theory in describing the instability is established in a certain region of the parameter space where possible subcritical instabilities may arise. The stability boundaries are discussed graphically for various values of the Darcy number and comparison is made with the available known results.     

Polarizable Continuum Studies on Methyl and Ethyl Substituted 2,4-Pentanedione

The polarizable continuum solvation model (PCM) is extended to the possible tautomer forms of the natural alkyl substituted 2,4-pentanediones. Solvation analysis has been carried out of all of the conformers of 3-methyl and 3-ethyl substituted 2,4-pentanediones in polar and non-polar solvents having a wide range of dielectric constants. The test set consists of water, ethyl alcohol, methyl alcohol, chlorobenzene, chloroform, benzene and carbon tetrachloride. The physical properties of the systems, such as Gibbs energies, electrostatic energies and induced dipole moments are discussed. Quantum mechanical self consistent fields explain the properties of the compounds satisfactorily.     

Dependence of NO<Subscript>2</Subscript> sensitivity on thickness of oxide-sensing electrodes for mixed-potential-type sensor using stabilized zirconia

The effect of thickness of oxide-sensing electrode (SE) on NO₂ sensitivity of the planar sensor based on yttria-stabilized zirconia (YSZ) was examined at high temperatures. The sensitivity of the sensor increased with decreasing thickness of SE, and the highest sensitivity was obtained by using the thinnest layer of Cr₂O₃–SE (2.7 μm) at 700 °C. In the case of NiO–SE, the highest sensitivity was observed for the sensor using the 4 μm-thick SE even at high temperature of 850 °C. Based on the results of the measurements for the complex impedances, the polarization curves, and the gas-phase NO₂ decomposition catalysis, it was confirmed that the catalytic activity to the gas-phase NO₂ decomposition on the oxide–SE matrix played an important role in determining the NO₂ sensitivity of the present sensors. This artice was accidentally published twice. This is the second publication, please cite only the authoritative first one which is available at . An additional erratum is available at . An erratum to this article can be found at     

Conjugated polymers with carbazole,fluorene, and ethylene dioxythiophene in the main chain and a pendant cyano group: Synthesis,photophysical, and electrochemical studies

Six new conjugated polymers comprising of carbazole, fluorene, and ethylene dioxythiophene (EDOT) moieties along the backbone with a pendant cyano group attached to the ethylene moiety have been designed and synthesized via Sonogashira coupling polymerization reaction. Optical and electrochemical characterizations have shown that the energy band gaps lie within the range of 2.35–2.44 eV. Additionally, the presence of carbazole and EDOT makes these polymers better hole transporting materials, which is reflected from their low oxidation potential peaks (0.55–1.11 V) in cyclic voltammograms. Furthermore, the aggregation enhanced emission (AEE) phenomenon resulted in a 2.6‐fold increase in fluorescence intensity in a 90:10 THF/water mixture in comparison to pristine THF. The AEE properties were further verified by DLS (dynamic light scattering) experiment and SEM (scanning electron microscopy) studies. Polymers in solution as well as in polystyrene matrix emit in the green region (quantum yield in solution state Φ_f =41–43%) with CIE values (0.25–0.36, 0.52–0.57). Excellent thermal stability is observed for the new polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2774–2784     

Temperature dependence of NO2 sensitivity of YSZ-based mixed potential type sensor attached with NiO sensing electrode

A mixed potential type yttria-stabilized zirconia-based sensor using NiO sensing electrode and Pt reference electrode was fabricated, and its NO₂ sensing characteristics were examined at various operating temperatures in the range of 700–950 °C. It was observed that the sensitivity to NO₂ strongly depends on the operating temperature of the sensor; the sensitivity decreases with increasing operating temperature, while the response/recovery rates increase. To rationalize this temperature dependence of NO₂ response, polarization curves and complex impedances of the sensor were measured in the base gas and in the sample gas (400 ppm NO₂?+?base gas) at various operating temperatures. It turned out that the operating temperature had a strong influence on the rate of anodic reaction of oxygen; the increased rate of anodic reaction leads to lower NO₂ sensitivity and quicker response/recovery at higher operating temperature.     

Chemoselective N‐Alkylation of Indoles in Aqueous Microdroplets

Many reactions show much faster kinetics in microdroplets than in the bulk phase. Most reported reactions in microdroplets mirror the products found in bulk reactions. However, the unique environment of microdroplets allows different chemistry to occur. In this work, we present the first chemoselective N‐alkylation of indoles in aqueous microdroplets via a three‐component Mannich‐type reaction without using any catalyst. In sharp contrast, bulk reactions using the same reagents with a catalyst yield exclusively C‐alkylation products. The N‐alkylation yield is moderate in microdroplets, up to 53 %. We extended the scope of the microdroplet reaction and obtained a series of new functionalized indole aminals, which are likely to have biological activities. This work clearly indicates that microdroplet reactions can show reactivity quite different from that of bulk‐phase reactions, which holds great potential for developing novel reactivities in microdroplets.     

Analyte-induced photoreduction method for visual and colorimetric detection of tyrosine

A new method based on photochemical formation of silver nanoparticles (AgNPs) was developed for detection of tyrosine (Tyr). To selectively detect Tyr and to simplify the detection procedure, the photoactivity of Tyr was utilized to trigger the photochemical reduction in production of AgNPs. The drastic change of solution color caused by the surface plasmon resonance (SPR) absorption band of the formed AgNPs was used to extract the quantitative information of Tyr. This developed method is simple in detection, while both the sensitivity and selectivity are significant improved. Meanwhile, the solution color was changed from colorless to dark yellow after the formation of AgNPs, which allows a much higher sensitivity in visual identification when compared with the SPR band shifting technique commonly, used in conventional colorimetric methods. To optimize the detection system and to understand the mechanism in this proposed method, parameters such as irradiation time, intensity of light source, and the concentration of Tyr were systematically examined. Results indicated that these factors mainly affected the reaction rate of photoreduction. The morphologies of the formed AgNPs were similar, but with small differences in particle sizes. In the examination of selectivity, sixteen other amino acids were examined. Results indicated that only amino acids of tryptophan, cysteine and histidine are photoactive and possess potential interferences in analysis of Tyr. Quantitative studies indicated that a linear response up to 10 μM with a detection limit of 100 nM could be obtained. For visually detection, color change could be observed with a concentration as low as 500 nM of Tyr.     

Linear and non-linear stability limits for centrifugal convection in an anisotropic layer

This paper finds stability limits for the onset of convection in a fluid saturated porous layer subject to alternating directions of centrifugal acceleration. The layer is homogeneous but mechanically and thermally anisotropic. The Brinkman equation is assumed to govern the momentum balance of the fluid flow. A linear analysis based on normal mode approach and a non-linear analysis based on energy method are made. The non-linear results are unconditional and their sharp limits are obtained. The numerical solutions predicted using the compound matrix method show that the anisotropy parameters and offset distances of the axis of rotation significantly affect the stability characteristics.     

Phosphonated mesoporous silica based composite membranes for high temperature proton exchange membrane fuel cells

Journal of Solid State Electrochemistry - Mesoporous Santa Barbara Amorphous (SBA-15) was synthesized, and it was grafted with phosphonate functionality using a simple two-step process involving...