Band 75, Heft 6

It is important to construct the correct formula for alpha decay half-lives. The present work verifies the validity of Geiger–Nuttall law (GNL) for actinides and hence presenting the simple empirical formula for alpha decay energies and halflives for actinides based on the available experimental results. We have studied the variation of logarithmic halflives with ZdnQ−1/2${Z}_{d}^{n}{Q}^{-1/2}$ for different values of n (0.2–1). The variation of logarithmic halflives with ZdnQ−1/2${Z}_{d}^{n}{Q}^{-1/2}$ is found to be linear for which n  = 0.6. The values produced by the present formula compared with that of experiments. The present formulae successfully produces the alpha decay half-lives and Q -value in the actinide region. This formula is specially for actinide parent nuclei only.

Presently, nerve pulse propagation is understood to take place by electric action pulses. The theoretical description is given by the Hodgkin-Huxley model. Recently, an alternative model was proclaimed, where signaling is carried out by acoustic solitons. The solitons are built by a local phase transition in the lyotropic liquid crystal (LLC) of a biologic membrane. We argue that the crystal structure arranging hydrogen bonds at the membrane surface do not allow such an acoustic soliton model. The bound water is a component of the LLC and the assumed phase transition represents a negative entropy step.

The main aim of this paper is, to obtain the analytical solution of the Riemann problem for a quasi-linear system of equations, which describe the one-dimensional unsteady flow of an ideal polytropic dusty gas in magnetogasdynamics without any restriction on the initial data. By using the Rankine-Hugoniot (R-H) and Lax conditions, the explicit expressions of elementary wave solutions (i. e., shock waves, simple waves and contact discontinuities) are derived. In the flow field, the velocity and density distributions for the compressive and rarefaction waves are discussed and shown graphically. It is also shown how the presence of small solid particles and magnetic field affect the velocity and density across the elementary waves. It is an interesting fact about this study that the results obtained for the Riemann problem are in closed form.

We perform a detailed study of the integrability of the Hořava-Lifshitz scalar field cosmology in a Friedmann-Lemaître-Robertson-Walker background space-time. The approach we follow to determine the integrability is that of singularity analysis. More specifically, we test whether the gravitational field equations possess the Painlevé property. For the exponential potential of the scalar field, we are able to perform an analytic explicit integration of the field equations and write the solution in terms of a Laurent expansion and more specifically write the solution in terms of right Painlevé series.

The influence of concentration of solute particles on squeeze film lubrication between two poroelastic surfaces has been analyzed using a mathematical model. Newtonian viscous fluid is considered as a lubricant whose viscosity varies linearly with concentration of suspended solute particles. Convection-diffusion model is proposed to study the concentration of solute particles and is solved using finite difference method of Crank–Nicolson scheme. An iterative procedure is used to get the solution for concentration, pressure and velocity components in film region. It has been observed that load carrying capacity decreases as the concentration of solute particles in the fluid film decreases. Further, the concentration of suspended solute particles decreases as the permeability of the poroelastic plate increases and these results may be useful in understanding the mechanism of human joint.

Full-potential augmented plane waves (FP-APW) method is applied to determine the electronic band profiles and magneto-electronic properties of XCu 2 P 2 (X = Ca, Sr) compounds. We have adopted Perdew, Burke and Ernzerhof's generalized gradient approximation (PBE-GGA) along with GGA plus Hubbard U parameter method (GGA+ U ) as exchange correlation potentials. The physical properties of interest for XCu 2 P 2 (X = Ca, Sr) compounds were analyzed for the first time in the Zintl phase of tetragonal structure with space group I4/mmm (No. 139). From the structural parameters we have found that ferromagnetic phase is more stable as compared to paramagnetic and antiferromagnetic phase. Electronic band profiles predict the metallic nature of these compounds in FM phase. The projected densities of states computed in this work recognize that the bonding is accomplished through hybridization of Cu-3 d with P- p states. The evaluated magnetic moments support weak ferromagnetism in these compounds. The compounds of interest are thermodynamically stable. In addition, the cohesive energies and Curie temperatures of the studied compounds were also predicted. Metallic and ferromagnetic nature of XCu 2 P 2 (X = Ca, Sr) compounds predict the important of these compounds in spintronic devices.

Gallium nitride nanocrystals as a wide bandgap semiconductor material for optoelectronic applications can be synthesized using chemical methods. In this research using co-precipitation and nitridation processes gallium nitride nanocrystals have been synthesized, and by tuning pH of the synthesis solution at the co-precipitation step, crystal quality and optical property of the resultant gallium nitride nanocrystals have been enhanced. Gallium nitride nanocrystal samples were synthesized using solutions with pH values of 2.1, 4.8, 7.8, and 9.0, and then nitridation at 950 °C under the flow of ammonia gas. The synthesized nanocrystal samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and photoluminescence techniques. The XRD data show that the nanocrystals have hexagonal wurtzite crystal structure, and using Scherer’s equation the sizes of the synthesized nanocrystals are 23.6, 26.6, 19.7, and 10.4 nm for the samples synthesized using the solutions with pH values of 2.1, 4.8, 7.8, and 9.0 respectively. The sizes of the nanocrystals obtained from SEM images are larger than the values obtained using Scherer’s equation, due to the aggregation of nanocrystals. EDX spectra show that pH of the synthesis solution affects the elemental stoichiometry of the gallium nitride nanocrystals. We obtained better stoichiometry for the nanocrystal sample synthesized using solution with the pH of 4.8. Photoluminescence spectra show that for this sample the emission intensity is higher than the others.

A new organic non-centrosymmetric nonlinear optical (NLO) material, p-nitrobenzylidene-p-phenylamineaniline (PNBPDA) was synthesized and single crystals of PNBPDA were grown from ethanol solution by slow evaporation solution growth technique. Single crystal X-ray diffraction (XRD) and powder XRD data confirm that PNBPDA crystallizes in monoclinic system with non-centrosymmetric space group Cc.Various characterizations like PXRD, fourier transform infrared (FT-IR) spectroscopy, thermal analysis and micro hardness test have been conducted. Optical studies have been done for evaluating the transparency range and the luminescence property of the grown single crystals of PNBPDA. Dielectric studies have carried out to investigate the electronic polarizability within the grown crystal. The frequency conversion efficiency of the grown crystal was determined using Kurtz Perry powder technique and second harmonic generation (SHG) was found to be 6 times that of standard Potassium Dihydrogen Phosphate (KDP). Z-Scan technique was performed to determine the third order non-linear optical properties of the grown crystal of PNBPDA. The optical limiting property and the laser damage threshold value reflect the practical applicability of PNBPDA crystal for photonic applications. Additionally, the theoretical background of PNBPDA was carved out using Density Functional Theory (DFT) by evaluating the geometrical and electronic structural properties from Frontier Molecular Orbital (FMO) analysis, Molecular Electrostatic Potential (MESP) analysis and non-linear features from dipole moment, polarizability and hyperpolarizability properties embedded within the PNBPDA molecule. The calculated first order hyperpolarizability ( β ) value of the molecule was found to be 14 times that of the standard urea molecule.

Hydrogen as a clean and abundant energy source with high energy density is considered as a promising solution to future energy crisis, although storage of hydrogen is still challenging. Lithium hydride can be an alternative for hydrogen storage because of its small volume and high storage capacities, although this material is unsuitable as hydrogen reservoir because of its high dehydriding temperature. The density functional theory calculations based on the first principle are applied to study the physical properties of LiH without and with different metal M (M=Al, Fe, and Ru). The M-substituted systems exhibit lower dehydriding temperatures than the pure LiH, and Li 1− x Al x H may be the most suitable candidate for hydrogen reservoir owing to the high hydrogen content and low dehydriding temperature. The stability and thermodynamic properties for hydrogen storage are discussed for these systems. The kinetics and the optical activity in the visible and infrared regions are enhanced by the metal dopants, characterized by the M impurity bands in the band gaps of the doped systems.