• Volume 73, Issue 4

October 2009,   pages  627-798

• Complexification of three potential models – II

A new kind of $\mathcal{PT}$ and non-$\mathcal{PT}$-symmetric complex potentials are constructed from a group theoretical viewpoint of the sl$(2, C)$ potential algebras. The real eigenvalues and the corresponding regular eigenfunctions are also obtained. The results are compared with the ones obtained before.

• Application of FIRE for the calculation of photon matrix elements

The next-to-next-to-leading order (the order $\alpha \alpha_{s}^{2}$ ) corrections to the first moment of the polarized virtual photon structure function $g_{1}^{\gamma} (x, Q^{2}, P^{2})$ are studied in perturbative QCD for the kinematical region $\Lambda^{2} \ll P^{2} Q^{2}$, where $−Q^{2} (−P^{2})$ is the mass square of the probe (target) photon and 𝛬 is the QCD scale parameter. In order to evaluate the two-loop Feynman diagrams for the photon matrix element of the gluon operator, I apply the recently developed algorithm FIRE which reduces a complicated sum of scalar Feynman integrals to a linear combination of a few master integrals. The details of the calculation are presented.

• Microscopic study of low-lying yrast spectra and deformation systematics in neutron-rich 98−106Sr isotopes

Variation-after-projection (VAP) calculations in conjunction with Hartree–Bogoliubov (HB) ansatz have been carried out for $A = 98–106$ strontium isotopes. In this framework, the yrast spectra with $J^{\Pi} \geq 10^{+}$ , $B(E2)$ transition probabilities, quadrupole deformation parameter and occupation numbers for various shell model orbits have been obtained. The results of the calculation for yrast spectra give an indication that it is important to include the hexadecapole–hexadecapole component of the two-body interaction for obtaining various nuclear structure quantities in Sr isotopes. Besides this, it is also found that the simultaneous polarization of $p_{3}/2$ and $f_{5}/2$ proton subshells is a significant factor in making a sizeable contribution to the deformation in neutron-rich Sr isotopes.

• Measurement and theoretical estimation of induced activity in $^{\text{nat}}$In by high energy neutrons

Induced radioactivity in natural indium ($^{\text{nat}}$In) foils by high energy neutrons was measured at the KENS Facility, KEK, Japan, where a 16.7 cm thick W target was bombarded by protons of 500 MeV. High energy neutrons consequently produced irradiated the In targets placed at different depths inside a 4 m thick concrete shield placed at the beam exit. The measured activities were compared with the results calculated using the nuclear reaction model codes ALICE-91 and EMPIRE-2.18. To estimate the induced activity, excitation functions of the various radionuclides were calculated using the two codes and folded with the appropriate neutron energy distribution at different depths of the concrete shield. The calculated excitation functions of a given nuclide were found to vary widely from one another in some cases. The performances of the codes for different input parameters like level densities and inverse cross-sections are reported in this paper. Our analysis shows that neither of the two codes reproduced all the measured activities satisfactorily, requiring further improvements in the models adopted.

• Multiplicity fluctuations of pions and protons at SPS energy – An in-depth analysis with factorial correlator

We compute the factorial correlators to study the dynamical fluctuations of pions and a combination of pions and protons (compound multiplicity) in 32S–AgBr interactions at 200 A GeV. The study reveals that for both pion and compound multiplicity the correlated moments increase with the decrease in bin–bin separation 𝐷, following a power-law, which suggests the self-similarity of multiplicity fluctuation in each case. The results of the analysis also show a consistency with the prediction of 𝛼-model for the existence of intermittency in both cases.

• Structures, energetics and magnetic properties of (NiSn)$_{n}$ clusters with $n = 1–6$

We report the results of calculations which were performed to investigate equilibrium structures, electronic and magnetic properties of stoichiometric (NiSn)$_{n}$ clusters with $n = 1–6$ within the framework of density functional theory. The calculated results show that the structural arrangement of (NiSn)$_{n}$ clusters is dominated by the Ni–Sn and Ni–Ni interactions. We find that these binary clusters show significant variation in the geometries as compared to that of the host nickel clusters. The preference for tetrahedron unit of Ni3 Sn is seen in the lowest-energy configuration of these clusters. The multi-centre bonding between Ni atoms play an important role in stabilizing the stoichiometric Ni–Sn clusters. Doping of Sn atoms enhances the binding energy and reduces the ionization potential of nickel clusters. These binary clusters prefer the lowest spin state. For (NiSn)6 the magnetic moment is 0 𝜇B. The complete quenching of the cluster magnetic moment appears to be due to the antiferromagnetic alignment of atomic spins as revealed by the spin density plots.

• Measurement of vacancy transfer probability from K to L shell using K-shell fluorescence yields

The vacancy transfer probabilities from K to L shell through radiative decay, 𝜂KL , have been deduced for the elements in the range $19 \leq Z \leq 58$ using K-shell fluorescence yields. The targets were irradiated with 𝛾 photons at 59.5 keV from a 75mCi 241Am annular source. The K X-rays from different targets were detected with a high resolution Si(Li) detector. The measurement of vacancy transfer probabilities are least-squared fitted to second-order polynomials to obtain analytical relations that represent these probabilities as a function of atomic number. The obtained results agree with theoretical and fitted values.

• A phase-matchable nonlinear optical crystal 4-amino-5-mercapto-3-[1-(4-isobutylphenyl)ethyl]- 1,2,4-triazole: Synthesis, crystal growth and characterization

In this paper, we report the synthesis, growth and characterization of a new organic NLO single crystal of 4-amino-5-mercapto-3-[1-(4-isobutylphenyl)ethyl]-1,2,4-triazole (AMIT). The title compound is synthesized and single crystals were grown by the slow evaporation technique at room temperature. The grown crystal was characterized by powder XRD, FTIR, UV–Vis. and microhardness studies. The thermal analysis of the crystal was carried out by TGA, DTA and DSC. From DSC, the melting point of the crystal is found to be 168°C. The scanning electron microscopy (SEM) provides information about the surface morphology of the crystal. The SHG efficiency has been estimated as 0.3 times that of KDP using Kurtz powder method and is found to be a phase-matchable NLO crystal.

• Measurement of refractive index of biaxial potassium titanyl phosphate crystal plate using reflection spectroscopic ellipsometry technique

The paper reports the measurement of refractive indices and anisotropic absorption coefficients of biaxial potassium titanyl phosphate (KTP) crystal in the form of thin plate using reflection ellipsometry technique. This experiment is designed in the Graduate Optics Laboratory of the Addis Ababa University and He–Ne laser ($\lambda = 632.8$ nm), diode laser ($\lambda = 670.0$ nm) and temperature-tuned diode laser ($\lambda = 804.4$ and 808.4 nm), respectively have been employed as source. The experimental data for $n_{x}$, $n_{y}$ are fitted to the Marquardt–Levenberg theoretical model of curve fitting. The obtained experimental data of refractive indices are compared with different existing theoretical and experimental values of KTP crystals and found to be in good agreement with them.

• Computer simulation of viscous fingering in a lifting Hele-Shaw cell with grooved plates

We simulate viscous fingering generated by separating two plates with a constant force, in a lifting Hele-Shaw cell. Variation in the patterns for different fluid viscosity and lifting force is studied. Viscous fingering is strongly affected by anisotropy. We report a computer simulation study of fingering patterns, where circular or square grooves are etched on to the lower plate. Results are compared with experiments.

• Terahertz oscillations in mercury cuprate superconductors

It has been recently reported that the three-dimensional Bose–Einstein condensation of the quasi-particles is valid for the mercury cuprates at liquid helium temperature. In this study, the validity of the interlayer theory in three dimensions has been investigated for optimally oxygen-doped mercury cuprates at the temperature interval of 0–15 K. Furthermore, some thermodynamic and electrodynamics parameters of mercury cuprates have been calculated for both the under-doped and the over-doped samples at the vicinity of 4.2 K. Moreover, it has been determined that the superconducting system behaves as a terahertz wave cavity regardless of the oxygen doping concentration.

• Structural and magnetic properties of size-controlled Mn0.5Zn0.5Fe2O4 nanoparticles and magnetic fluids

Mn0.5Zn0.5Fe2O4 ferrite nanoparticles with tunable Curie temperature and saturation magnetization are synthesized using hydrothermal co-precipitation method. Particle size is controlled in the range of 54 to 135 Å by pH and incubation time of the reaction. All the particles exhibit super-paramagnetic behaviour at room temperature. Langevin’s theory incorporating the interparticle interaction was used to fit the virgin curve of particle magnetization. The low-temperature magnetization follows Bloch spin wave theory. Curie temperature derived from magnetic thermogravimetric analysis shows that Curie temperature increases with increasing particle size. Using these particles magnetic fluid is synthesized and magnetic characterization is reported. The monolayer coating of surfactant on particle surface is confirmed using thermogravimetric measurement. The same technique can be extended to study the magnetic phase transition. The Curie temperature derived using this measurement complies with the low-temperature magnetic measurement. The room-temperature and high-temperature magnetization measurements are also studied for magnetic fluid systems. The magnetic parameters derived for fluid are in good agreement with those obtained for the particle system

• Hybrid synchronization of hyperchaotic Lu system

In this paper, we study the hybrid synchronization between two identical hyperchaotic Lu systems. Hybrid synchronization of hyperchaotic Lu system is achieved through synchronization of two pairs of states and anti-synchronization of the other two pairs of states. Active controls are designed to achieve hybrid synchronization between drive and response systems using the sum and difference of relevant variables of the chaotic systems. Numerical simulations are presented to evaluate the analysis and effectiveness of the controllers.

• Stimulated Brillouin scattering of an electromagnetic wave in weakly magnetized plasma with variably charged dust particles

We have investigated analytically the stimulated Brillouin scattering (SBS) of an electromagnetic wave in non-dissipative weakly magnetized plasma in the presence of dust particles with variable charge.

• Locally-rotationally-symmetric Bianchi type-V cosmology with heat flow

In this paper we present a spatially homogeneous locally-rotationally-symmetric (LRS) Bianchi type-V cosmological model with perfect fluid and heat flow. A general approach is introduced to solve Einstein’s field equations using a law of variation for the mean Hubble parameter, which is related to average scale factor of the model that yields a constant value for the deceleration parameter. Exact solutions that correspond to singular and non-singular models are found with heat flow. The physical constraints on the solution and, in particular, the thermodynamical laws that govern such solutions are discussed in some detail.

• Pramana – Journal of Physics

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