Analysis of combined conduction and radiation heat transfer in presence of participating medium by the development of hybrid method

The current study addresses the mathematical modeling aspects of coupled conductive and radiative heat transfer in the presence of absorbing, emitting and isotropic scattering gray medium within two-dimensional square enclosure. A blended method where the concepts of modified differential approximation employed by combining discrete ordinate method and spherical harmonics method, has been developed for modeling the radiative transport equation. The gray participating medium is bounded by isothermal walls of two-dimensional enclosure which are considered to be opaque, diffuse and gray. The effect of various influencing parameters i.e., radiation-conduction parameter, surface emissivity, single scattering albedo and optical thickness has been illustrated. The adaptability of the present method has also been addressed.     

0+ analogue state in 118Sb from 117Sn(p,nγ) reaction

The analogue of the 0⁺ ground state in ¹¹⁸Sn has been observed in the compound nucleus ¹¹⁸Sb through ¹¹⁷Sn(p,n γ) ¹¹⁷Sb reaction. The neutron decays of this analogue resonance have been studied from the deexciting γ-rays of the residual nucleus ¹¹⁷Sb. From off resonance excitation functions, spin assignments have been made to states in ¹¹⁷Sb, on the basis of Hauser-Feshbach formalism. The resonance parameters of the isobaric analogue resonance have been determined, including the total, proton and neutron decay widths.     

Solubilization Site of Organic Perfume Molecules in Sodium Dodecyl Sulfate Micelles: New Insights from Proton NMR Studies

The site of incorporation of solubilizates in sodium dodecyl sulfate (SDS) micellar systems has been investigated by proton NMR spectroscopy. The solubilizate molecules chosen for the present study are phenol, 4-methylphenol, 4-allyl-2-methoxyphenol, anisole, 4-methylanisole, 4-propenylanisole, 1,8-cineole, and limonene. These molecules possess a wide variety of functional groups with different degrees of hydrophilic/hydrophobic character and are thereby solubilized at different micellar locations. Aromatic compounds, especially those having a phenolic-OH group, showed a large upfield shift of SDS methylene protons that are closely linked to the terminal sulfate groups. Additionally, in the case of phenolic compounds, the unresolved signals of the nine straight-chain bulk methylene protons of SDS are split into a broad doublet with uneven intensity. This splitting of methylene protons was found to be dependent on the concentration of the substrate. Based on these observations, probable solubilization sites and orientation of the substrate molecule within the micelles are discussed. Phenolic compounds, being the most hydrophilic among the present set, reside at the hydrophilic/hydrophobic boundary of micelle-water interface and thus influence the resonances of SDS protons the most. Aromatic methoxy and aliphatic compounds, being relatively more hydrophobic in nature, reside inside the micellar core and thereby result in smaller shifts. Copyright 2000 Academic Press.     

Remarkable impact of intermode couplings on multimode vibronic dynamics: the photoelectron spectrum of CH3F

Electronic and nuclear motions on intersecting potential energy surfaces are often intricately mixed and the spectrum can become very complex. Here we choose the strongly coupled Jahn-Teller system CH3F+ as a prototype example, and establish the importance of intermode coupling terms on multimode vibronic dynamics. The theoretical approach consists of a full second-order diabatic vibronic Hamiltonian, constructed from high-quality electronic structure calculations. Our results compare amazingly well with the experimental data. This highlights the success of the present theoretical approach in explaining the complex structure of vibronic spectra, ubiquitous in molecular systems.     

Intramolecular nitrone cycloaddition reaction on carbohydrate-based precursors: application in the synthesis of spironucleosides and spirobisnucleosides

A simple synthesis of chiral spironucleosides and spirobisnucleosides is described. Intramolecular 1,3-dipolar nitrone cycloaddition reaction of d-glucose-derived precursors having olefin at C-3 and nitrone at C-5, C-1, or C-2 (in nor-series) furnished bisisoxazolidinospirocycles 4-7, 11, and 12 in good yields. Reductive ring opening of the isoxazolidine moieties in 4-6 followed by construction of a nucleoside base upon the generated amino groups smoothly yielded spirobisnucleosides 17 and 18 and spironucleosides 20 and 21.     

Removal of Cr(VI) from Aqueous Solution Using Activated Cow Dung Carbon

Removal of hexavalent chromium from aqueous medium by using activated cow dung carbon was studied. Cow dung was carbonized and activated by treating with concentrated H(2)SO(4) followed by heating for 24 h at 120 degrees C. The extent of adsorption was studied as a function of pH, contact time, amount of adsorbent, concentration of adsorbate, and temperature. At lower pH (<3.5), the prepared sorbent was capable of removing approximately 90% Cr(VI) at 5 ppm concentration from aqueous synthetic solution. The dynamics of migration of the sorbate ions from the bulk onto the sorbent surface was studied and the results obtained under various experimental conditions were found to follow standard adsorption isotherms. The reaction kinetics was found to be of first order. Copyright 2000 Academic Press.     

On the (Emultiply sign in circlee)-Jahn-Teller conical intersections in the 3p(E') and 3d(E") Rydberg electronic states of triatomic hydrogen

The static and dynamic aspects of the Jahn-Teller (JT) interactions in the 3p(E') and 3d(E") Rydberg electronic states of H3 are analyzed theoretically. The static aspects are discussed based on recent ab initio quantum chemistry results, and the dynamic aspects are examined in terms of the vibronic spectra and nonradiative decay behavior of these states. The adiabatic potential-energy surfaces of these degenerate electronic states are derived from extensive ab initio calculations. The calculated adiabatic potential-energy surfaces are diabatized following our earlier study on this system in its 2p(E') ground electronic state. The nuclear dynamics on the resulting conically intersecting manifold of electronic states is studied by a time-dependent wave-packet approach. Calculations are performed both for the uncoupled and coupled state situations in order to understand the importance of nonadiabatic interactions due to the JT conical intersections in these excited Rydberg electronic states.     

Kinetics and Mechanism of the Reactions of Picolinic Acid with Dichloro-{1-alkyl-2-(arylazo)imidazole}palladium(II) Complexes

The reaction between Pd(N,N′)Cl₂ [N,N′ ≡ 1-alkyl-2-(arylazo)imidazole (N,N′) and picolinic acid (picH) have been studied spectrophotometrically at λ = 463 nm in MeCN at 298 K. The product is [Pd(pic)₂] which has been verified by the synthesis of the pure compound from Na₂[PdCl₄] and picH. The kinetics of the nucleophilic substitution reaction have been studied under pseudo-first-order conditions. The reaction proceeds in a two-step-consecutive manner (A → B → C); each step follows first order kinetics with respect to each complex and picH where the rate equations are: Rate 1 = {k′₀ + k′₂[picH]₀} × [Pd(N,N′)Cl₂] and Rate 2 = {k′′₀ + k′′₂[picH]₀}[Pd(N,O)(monodentate N,N′)Cl₂] such that the first step second order rate constant (k′₂) is greater than the second step second order rate constant (k′′₂). External addition of Cl⁻ (as LiCl) suppresses the rate. Increase in π-acidity of the N,N′ ligand, increases the rate. The reaction has been studied at different temperatures and the activation parameters (Δ^‡H° and Δ^‡S°) were calculated from the Eyring plot.