Thermal Non-equilibrium Heat Transfer and Entropy Generation due to Natural Convection in a Cylindrical Enclosure with a Truncated Conical,Heat-Generating Porous Bed

Natural convection in enclosures driven by heat-generating porous media has diverse applications in fields like geothermal, chemical, thermal and nuclear energy. The present article focuses on heat transfer and entropy generation characteristics of a heat-generating porous bed, placed centrally within a fluid-filled cylindrical enclosure. Pressure drop and heat transfer in the porous bed are modelled using the Darcy–Brinkmann–Forchheimer approximation and the local thermal non-equilibrium model, respectively. Energy flux vectors have been utilised for visualising convective energy transfer within the enclosure. The study of a wide range of Rayleigh number (\(10^{7}\)–\(10^{11}\)) and Darcy number (\(10^{-6}\)–\(10^{-10}\)) reveals that heat transfer in the porous region can be classified into conduction-dominated and convection-dominated regimes. This is supplemented with an entropy generation analysis in order to identify and characterise the irreversibilities associated with the phenomenon. It is observed that entropy generation characteristics of the enclosure closely follow the above-mentioned regime demarcation. Numerical computations for the present study have been conducted using ANSYS FLUENT 14.5. The solid energy equation is solved as a user-defined scalar equation, while data related to energy flux vectors and entropy generation are obtained using user-defined functions.     

Surface enhanced Raman scattering of 2,2' biquinoline adsorbed on colloidal silver particles

Surface enhanced Raman scattering (SERS) in silver sol and normal Raman spectra in the bulk and in solution of 2,2' biquinoline (BQ) molecule have been investigated. The observed Raman bands along with their corresponding FTIR bands have been assigned based on the established assignments of the vibrational bands of the parent napthalene and quinoline molecules. Existence of both the cis and trans form of the BQ molecule in solution and in the bulk are inferred from the normal Raman and FTIR spectra, whereas SERS study reveal that in the surface adsorbed state the molecule exists in the cis form. Definite evidence of the charge transfer interaction to the overall contribution in the SER enhancement have been reported. The excitation profile also supports the CT interaction. Estimated enhancement factor of the principal SERS bands indicate that the molecule is adsorbed on the silver surface through both the nitrogen atoms with the molecular plane almost perpendicular to the surface. This preferred orientation of the molecule is in conformity with its existence in the cis form in the surface adsorbed state.     

Displacement of aqua ligands from the hydroxopentaaquarhodium(III) ion by pyridine-2-aldoxime: A kinetic and mechanistic approach

Summary The kinetics of anation of the hydroxopentaaqua-rhodium(III) ion by pyridine-2-aldoxime have been studied spectrophotometrically as a function of pH, substrate concentration, entering ligand, temperature and solvent polarity. The reaction rate increases with an increase in pH, temperature and ligand concentration, and reaches a limiting value at high ligand concentration. The activation parameters (H ^# = 87.5 kJ mol^–1 and S = –52.3 JK^–1 mol^–1) have been calculated from an Eyring plot and are compared with aqua exchanges in other systems. All the experimental facts lead to an associative interchange (I _a) mechanism with the prior formation of an outer-sphere association complex. Solvent polarity effects lead to the same conclusion.     

Role of positional isomers on receptor-anion binding and evidence for resonance energy transfer

New urea-based sensors show a strong affinity for F⁻, CH₃COO⁻, and H₂PO₄⁻ with an appreciable color change in the presence of excess F⁻. The position of the nitro group in the urea derivative influences the relative affinity toward anionic analytes. Spectral and ab initio studies showed the difference in the deprotonation sites for the ortho- and meta/para-isomers in these cases. Photophysical studies confirmed the resonance energy transfer in the case of the ortho-isomer. The ortho-isomer can act as a dual emission probe for F⁻.     

Inhibition of phosphatase activity by positively-charged cyclodextrins

[formula: see text] Aminocyclodextrins are known to bind phosphate esters such as phosphotyrosine and p-nitrophenyl phosphate. This paper describes the inhibition of phosphate ester hydrolysis, as catalyzed by lambda-protein phosphatase and acid phosphatase, that is caused by such binding interactions. ROESY studies provide structural information about the cyclodextrin-aryl phosphate complexes. In addition, these experiments are used to generate approximations of the rates of dissociation of the noncovalent complexes.