On the solution of the number-projected Hartree-Fock-Bogolyubov equations

The numerical solution of the recently formulated number-projected Hartree-Fock-Bogolyubov (HFB) equations is studied in an exactly solvable cranked-deformed shell-model Hamiltonian. It is found that the solution of these number-projected equations involves similar numerical effort as that of bare HFB. We consider that this is significant progress in the mean-field studies of quantum many-body systems. The results of the projected calculations are shown to be in almost complete agreement with the exact solutions of the model Hamiltonian. The phase transition obtained in the HFB theory as a function of the rotational frequency is shown to be smeared out with the projection.     

Heterogeneous kinetic studies of the hydrogen peroxide decomposition with some transition metal‐heterocyclic complexes

The heterocyclic compounds piperidine (Pip), piperazine (Pz), morpholine (Morph), and N‐methyl piperazine (N‐MPz) were used as ligands to form transition metal complexes with Ni(II), Cu(II), and Co(II) ions. These complexes were supported on Dowex‐50W resin so as to form new potential active catalysts for H₂O₂ decomposition in an aqueous medium. In all cases the reaction showed a first‐order kinetics with respect to H₂O₂ concentration, except with Co(II) complexes, the reaction showed a second‐order kinetics with 2% divinyl benzene (DVB) (50–100 mesh and 200–400 mesh). The rate constant k (per gram dry resin) was evaluated with a resin of cross‐linkage 2 and 8% DVB (50–100 mesh) and 2% DVB (200–400 mesh) over temperature range 25–40°C. With a given resin cross‐linkage, the rate constant has the following order: Ni(II) complexes < Co(II) complexes < Cu(II) complexes. With Pz ligand, k increased in the following sequence: Ni(II) complexes < Cu(II) complexes < Co(II) complexes. The reaction mechanisms of the first‐ and second‐order kinetics were discussed and the activation parameters were deduced. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 617–624, 2001     

Improving performance of FxRLS algorithm for active noise control of impulsive noise

Active noise control (ANC) systems employing adaptive filters suffer from stability issues in the presence of impulsive noise. New impulsive noise control algorithms based on filtered-x recursive least square (FxRLS) algorithm are presented. The FxRLS algorithm gives better convergence than the filtered-x least mean square (FxLMS) algorithm and its variants but lacks robustness in the presence of high impulsive noise. In order to improve the robustness of FxRLS algorithm for ANC of impulsive noise, two modifications are suggested. First proposed modification clips the reference and error signals while, the second modification incorporates energy of the error signal in the gain of FxRLS (MGFxRLS) algorithm. The results demonstrate improved stability and robustness of proposed modifications in the FxRLS algorithm. However, another limitation associated with the FxRLS algorithm is its computationally complex nature. In order to reduce the computational load, a hybrid algorithm based on proposed MGFxRLS and normalized step size FxLMS (NSS-FXLMS) is also developed in this paper. The proposed hybrid algorithm combines the stability of NSS-FxLMS algorithm with the fast convergence speed of the proposed MGFxRLS algorithm. The results of the proposed hybrid algorithm prove that its convergence speed is faster than that of NSS-FxLMS algorithm with computational complexity lesser than that of FxRLS algorithm.     

Thermodynamic and kinetic studies of the retro-Diels-Alder reaction of 1,4-cyclohexadiene, 4H-pyran 4H-thiopyran, 1,4-dioxine,and 1,4-dithiine: a theoretical investigation

Theoretical studies of the retro-Diels-Alder reaction of 1,4-cyclohexadiene, 4H-pyran 4H-thiopyran, 1,4-dioxine, and 1,4-dithiine in the gas phase were carried out using DFT methods at the B3LYP/6–311?+?G(d,p) levels of theory. The barrier height (ΔE^?) and thermodynamic parameters (ΔG^? and ΔH^?) were estimated. The progress of the reactions was followed by means of the Wiberg bond indices. The synchronicity values of the reactions were calculated. The kinetic parameters were calculated for both reactions in 300–1200-K temperature range. Also, fitted equations to the gas phase Arrhenius equation were determined. Effect of the character and number of heteroatoms were illustrated on the thermodynamic and kinetic parameters.

     

Applications of enzyme-catalysed reactions in trace analysis-VII Determination of lead and indium by their inhibition of isocitrate dehydrogenase

The inhibition of isocitrate dehydrogenase by lead, indium and calcium has been studied. Methods for the determination of 0.024-1 mug of lead and indium, based on this inhibition, are outlined. Lead may be separeted from some interfering ions by extraction with tributyl phosphate in isobutyl methyl ketone, before application of the enzymic reaction.     

Application of fluid dynamic gauging to annular test apparatuses for studying fouling and cleaning

Fluid dynamic gauging (FDG) is a non-contact technique for measuring the thickness and strength of fouling layers immersed in liquid in situ. Its application to an annular geometry across a range of possible flow conditions, from stagnant to turbulent flow regimes (annulus Reynolds number ∼29,000), is demonstrated. Two modes of measurement are demonstrated: in the first, the pressure drop across the nozzle is fixed and the mass flow rate of liquid withdrawn through the gauge is measured. In the second, the mass flow rate of liquid is fixed and the pressure drop measured: the latter is a new mode of measurement and it is shown to perform equally well, with advantages for particular applications. The results were not affected significantly by the surface under study being heated, indicating that the technique is suitable for measuring deposit thicknesses insitu during fouling and cleaning experiments in annular devices which are commonly used in deposition studies. Computational fluid dynamics (CFD) simulations, which afford detailed information about the flow patterns and shear stresses imposed on the surface, showed good agreement with experimental data for tests in the laminar regime: simulation of the transitional and turbulent regimes was not attempted. A short study of whey protein fouling recorded mixed success owing to the softness of the deposit, but demonstrated the scope for FDG to monitor the development of fouling layers in these geometries.     

Modulation of aggregation behavior of amphiphilic drug AMT under the influence of polymer molecular weight and composition

The purpose of this study was to determine the aggregation behavior of amphiphilic drug amitriptyline hydrochloride (AMT) and to search for means which boost/suppress the aggregation behavior. Polyethylene glycols (PEGs) nonionic polymers (which are used as pharmaceutical excipients) of varying molecular weights from 400 to 35,000 were tested. To know their effect on the micellization and interfacial behavior of the drug, the critical micelle concentration (CMC) and critical aggregation concentration (CAC) were determined in presence of various polymers by tensiometric and conductivity methods. The CAC values were found to decrease while the CMC values increased with increase in the polymer concentration. The thermodynamic parameters were evaluated where ΔG°(mic) and ΔG°(agg) are found to be negative, confirming the feasibility of interaction between AMT and polymers.