Properties of the Positronium Negative Ion Interacting with Exponential Cosine-Screened Coulomb Potentials

The positronium negative ion (Ps ⁻) in exponential cosine-screened Coulomb potentials (ECSCP) has been theoretically investigated. Using highly correlated wave functions with 525 terms we report binding energies, annihilation rates and several other parameters for various values of the screening parameter. Our reported results for the unscreened case are in nice agreement with some of the most accurate results in the literature. Further we make a comparative study of the properties of Ps ⁻ in ECSCP with the corresponding properties in screened Coulomb potential (SCP). To the best of our knowledge, such a study on Ps ⁻ in ECSCP is carried out for the first time in the literature.     

Extraction and recovery of lignosulfonate from its aqueous solution using bulk liquid membrane

The paper presents an experimental study on the coupled transport of lignosulfonate (LS) through bulk liquid membrane (BLM) and thereby to identify the best set of solvent, operating conditions and mode of transport that would yield optimum performance of the BLM. Trioctylamine (TOA) is used as carrier. Among various solvents, tested for the above purpose, dichloroethane is found to be the best. The effects of operating condition, viz. pH, temperature, and carrier concentration, on the equilibrium distribution of LS are investigated. The effects of temperature, stirring of aqueous and organic phases, stirring speed, carrier concentration, initial feed and strip phase concentration on the separation of LS using BLM are also studied. It is observed that transport of LS can be enhanced by increasing the temperature and stirring speed of feed phase. Stirring of strip phase has no appreciable effects on the transport of LS. With increase in initial feed concentration the initial rate of the transport of LS is higher but continues for a longer time. Recovery of LS is much higher in co-transport mode in comparison to counter transport mode. Application of 1.25 M NaOH as stripping solution gives high recovery (70%) and high strip flux (70% of feed flux).     

Autoionization states of the positronium negative ion in exponential cosine-screened Coulomb potentials

The 2s^2 1S^e2s^2~^1{\rm S}^e autoionization resonance states of the positronium negative ion (Ps^-) in exponential cosine-screened Coulomb potentials (ECSCP) are investigated using stabilization method. Highly correlated wave functions for Ps^- are used to take into account the correlation effect of the charged particles. Results for resonance energies and widths are reported for the screening parameter in the range 0.0-0.07 (in a₀ ^-1), to the best our knowledge, for the first time in the literature.     

Vertical Sediment Concentration Distribution in High-Concentrated Flows: An Analytical Solution Using Homotopy Analysis Method

Transport of suspended sediment in open channel flow has an enormous impact on real life situations, viz. control and management of reservoir sedimentation, geomorphic evolution such as dunes, rivers, and coastlines etc. Transport entails advection and diffusion. Turbulent diffusion is governed by the concept of Fick's law, which is based on the molecular diffusion theory, and the equation that represents the distribution of sediment concentration is the advection-diffusion equation. The study uses the existing governing equation which considers different phases for solid and fluid, and then couples the two phases. To deal with high-concentrated flow, sediment and turbulent diffusion coefficients are taken to be different from each other. The effect of hindered settling on sediment particles is incorporated in the governing equation, which makes the equation highly non-linear. This study derives an explicit closed-form analytical solution to the generalized one-dimensional diffusion equation representing the vertical sediment concentration distribution with an arbitrary turbulent diffusion coefficient profile. The solution is obtained by Homotopy Analysis Method, which does not rely on the small parameters present in the equation. Finally, the solution is validated by comparing it with the implicit solution and the numerical solution. A relevant set of laboratory data is selected to check the applicability of the model, and a close agreement shows the potential of the model in the context of application to high-concentrated sediment-laden open channel flow.     

Nonlinear Effects on Electrophoresis of a Soft Particle and Sustained Solute Release

A numerical study is made on the electrophoresis of a core-shell soft particle based on the first principle of electrophoresis. The soft particle consists of a charged rigid core coated with a polymer shell. Numerical computations for the electrophoretic velocity are obtained and compared with the existing analytical solution. The analytical solutions, based on the Boltzmann distribution of ions and the Debye–Huckel approximation, are valid for lower range of charge density, weak applied electric field and thin double layer. Discrepancy from the existing analytical solution is found when the Debye layer extends beyond the porous shell. This discrepancy becomes larger for higher values of the rigid core surface potential, fixed charge density of the soft shell and stronger imposed electric field. The double-layer polarization is found to have a strong impact when the shell thickness is lower than the Debye length. The electrophoretic velocity is found to vary nonlinearly with the imposed electric field when the imposed field strength is large enough to create a potential drop across the particle bigger than the thermal potential. We have also analyzed the mechanism of sustained solute release from the soft particle. Our results show that the rate of solute release is large compared to a pure diffusion dominated process.     

Positron scattering from hydrogen atom embedded in weakly-coupled plasmas

Elastic scattering of positrons from the hydrogen atoms in weakly-coupled plasmas has been studied using an expression for partial wave scattering amplitude that has been derived within the framework second order distorted wave Born approximation. The interactions among the charged particles in the plasma have been represented by Debye-Hückel potentials. A detailed study has been made on differential and total cross sections in the energy range 20–300 eV. To the best of our knowledge such a study on the differential and total cross sections for elastic positron-hydrogen collisions in a weakly-coupled plasma environment is reported for the first time in the literature.     

Process-dependent magnetic properties of Co-doped ZnO in bulk and thin film form

Structural, optical and magnetic studies of Co-doped ZnO have been carried out for bulk as well as thin films. The magnetic studies revealed the superparamagnetic nature for low-temperature synthesized samples, indicating the presence of cobalt metallic clusters, and this is supported by the optical studies. For the high-temperature sintered samples one obtains paramagnetism. The optical studies reveal the presence of Co²⁺ ions in the tetrahedral sites indicating proper doping. Interestingly, the films deposited by laser ablation from the paramagnetic target showed room temperature ferromagnetism. It appears that the magnetic nature of this system is process dependent.     

Protein Renaturation in the Gelatin Film Formation Process

The protein collagen is found in gelatin films in its native (crystalline) phase or in its denaturated (amorphous) phase. The denaturated collagen in gelatin undergoes partial renaturation during the process of film formation from solution at room temperature. It is of particular interest to identify the timescale when the structure of the native collagen is restored in the process of the film formation. The present study demonstrates that using nuclear magnetic resonance (NMR) and calorimetric methods in controlled stages of the film formation, it is possible to follow the renaturation transition of collagen during this process. The signature of the transition from the random coil to the collagen-like partial triple-helix structure is observed through the linewidth parameter of the NMR spectra which is further complemented by a differential scanning calorimetry study.     

Forbidden rotational transitions in symmetric top molecules

The intensities of the forbidden Δk = ±6 and ±4 transitions in symmetric top molecules arising from rotational intensity borrowing are reported. A perturbation theoretical approach has been used to study the mixing of wavefunctions produced by the additional splitting term in the rotational Hamiltonian of C_3v or C_4v-type molecules. Numerical values are presented for PH₃, PD₃, and BrF₅ molecules. The importance of these results in structural analysis and astrophysical studies is discussed.