• Volume 55, Issue 3

September 2000,   pages  361-469 and L471-L478

• Rotating cylindrically symmetric Kaluza-Klein fluid model

Kaluza-Klein field equations for stationary cylindrically symmetric fluid models in standard Einstein theory are formulated and a set of physically viable solutions is reported. This set is believed to be the first such Kaluza-Klein solutions and it includes the Kaluza-Klein counterpart of Davidson’s solution describing spacetime of a perfect fluid in rigid rotation about a regular axis.

• Non-static local string in Brans-Dicke theory

A recent investigation showed that a local gauge string with a phenomenological energy momentum tensor, as prescribed by Vilenkin, is inconsistent in Brans-Dicke theory. In this work it has been shown that such a string is indeed consistent if one introduces time dependences in the metric. A set of solutions of full non-linear Einstein’s equations for the interior region of such a string are presented.

• Exotic decay in Ba isotopes via 12C emission

Considering Coulomb and proximity potentials as barriers, we have calculated the half lives for 12C emission from various Ba isotopes using different mass tables. The half life for 112Ba isotope calculated by us is 6.020×103 s which is comparable with the experimental value 5.620×103 s. From our study it is found that 114Ba is the good parent for 12C emission whose emission rate is favorable for measurement. The half lives predicted by us lie very close to those reported by Shanmugam et al using their cubic plus Yukawa plus exponential model. It is observed that inclusion of proximity potential does not produce significant deviation from the linear nature of the Geiger-Nuttall plots. Also it is found that the neutron excess in the parent nuclei slows down the exotic decay process.

• Variable operator technique and the min-max theorem

We investigate a variation method where the trial function is generated from the application of a variable operator on a reference function. Two conditions are identified, one for obtaining a maximum and another for a minimum. Although the conditions are easy to understand, the overall formulation is somewhat unusual as each condition gives rise to a two-step variation process. As an example, projection operators are used to form the variable operator, and by this tactics one obtains the new interpretation that the pseudopotential formalism is in fact equivalent to a minimax procedure.

The two-step variational process is nevertheless more flexible than the pseudopotential formalism, for it can also be used when the variable operator is not manifestly expressed in terms of projectors. This is illustrated by a comparison of the two-step method with the variational solution of Dirac’s relativistic electron equation. The same comparison leads to an alternative proof that the process of maximizing energy by varying the u–l coupling operator eliminates all negative-energy contributions from a trial spinor. The latter observation is crucial for the derivation of the min-max theorem in relativistic quantum mechanics.

• Comparison between Weber’s electrodynamics and classical electrodynamics

We present the main aspects of Weber’s electrodynamics and of Maxwell’s equations. We discuss Maxwell’s point of view related to Weber’s electrodynamics. We compare Weber’s force with Lorentz’s force. We analyse the relation between Weber’s law and Maxwell’s equations. Finally, we discuss some experiments performed and proposed with which we can distinguish Weber’s force from Lorentz’s one.

• Third harmonic generation of CO2 laser radiation in AgGaSe2 crystal

Generation of third harmonic of CO2 laser radiation has been obtained in a type-II, ϑ=57° cut 9 mm thick AgGaSe2 crystal for the first time by sum-frequency-mixing of the fundamental with its second harmonic, the latter being obtained using another type-I, ϑ=55° cut 11 mm thick AgGaSe2 crystal. The energy conversion efficiencies obtained for second harmonic and third harmonic generations are 6.3% and 2.4% respectively with the input fundamental pump power density of 5.9 MW/cm2 only. The wavelength of the fundamental CO2 laser radiation used for the generation of harmonics is 10.6 µm, P(20) line. A compact TEA CO2 laser source has been built in the laboratory.

• Generation of ultraviolet radiation with wide angular tolerance in cesium lithium borate crystal

Tangential phase-matching has been realised in cesium lithium borate (CLBO) crystal for the first time for the generation of fourth harmonic (266 nm) of Nd:YAG and third harmonic (226.7 nm) of a dye laser radiation by second harmonic generation and sum-frequency mixing with the angular tolerance as large as 22 mrad and 21 mrad respectively, over one of the interacting beams. An energy conversion efficiency of 15% for fourth harmonic generation is obtained with a 5.5 mm thick crystal and with the average pump powers only 170 and 70 mW. A set of Sellmeier dispersion equations for the CLBO crystal have also been formulated.

• Dynamics of self-focusing and self-phase modulation of elliptic Gaussian laser beam in a Kerr-medium

Using a direct variational technique involving elliptic Gaussian laser beam trial function, the combined effect of non-linearity and diffraction on wave propagation of optical beam in a homogeneous bulk Kerr-medium is presented. Particular emphasis is put on the variation of beam width and longitudinal phase delay with the distance of propagation. It is observed that no stationary self-trapping is possible. The regularized phase is also seen to be always negative.

• Non-linearity parameter B/A of binary liquid mixtures at elevated pressures

When sound waves of high amplitude propagate, several non-linear effects occur. Ultrasonic studies in liquid mixtures provide valuable information about structure and interaction in such systems. The present investigation comprises of theoretical evaluation of the acoustic non-linearity parameter B/A of four binary liquid mixtures using Tong and Dong equation at high pressures and T=303.15 K. Thermodynamic method has also been used to calculate the non-linearity parameter after making certain approximations.

• Crystal and molecular structure of N-(p-nitrobenzylidene)-3-chloro-4-fluoroaniline

The crystal structure of N-(p-nitrobenzylidene)-3-chloro-4-fluoroaniline (II) has been determined by X-ray structure analysis. This belongs to a class of benzylidene anilines. The structure was solved by direct method. The molecular packing of the non-planar molecules are held by Van der Waals and F…H7, O…Cl, F…F and N…H interactions.

• Electron impact single ionization of copper

Electron impact single ionization cross sections of copper have been calculated in the binary encounter approximation using accurate expression for σΔE as given by Vriens and Hartree-Fock momentum distribution for the target electron. The BEA calculation based on the usual procedure does not show satisfactory agreement with experiment in this case but a striking modification is found to be successful in explaining the experimental observations. The discrepancy is linked with the ionization of the 3d10 electrons and probably effective single ionization does not take place from 3d shell of copper leading to smaller values of experimental cross sections.

• Annealing effect on transport properties of Nd0.67Sr0.33MnO3 thin films

Annealing dependence of the lattice parameter, resistivity, magnetoresistance and thermopower have been studied on Nd0.7-Sr0.33MnO3 thin films deposited on LaAlO3 and alumina substrates by pulsed laser ablation. Upon annealing at 800°C and 1000°C the lattice constant of the LaAlO3 film tends toward that of the bulk target due to reduction in oxygen vacancies. This results in a metal-insulator transition at temperatures which increase with progressive annealing along with a decrease in the observed low temperature MR. Using a magnon scattering model we estimate the eg bandwidth of the film annealed at 1000°C and show that the magnon contribution to the resistivity is suppressed in a highly oxygen deficient film and gains prominence only upon subsequent annealing. We also show that upon annealing, the polaron concentration and the spin cluster size increases in the paramagnetic phase, using an adiabatic polaron hopping model which takes into account an exchange dependent activation energy above the resistivity peak.

• High spin states in 63Cu

Excited states of 63Cu were populated via the $^{52}{\rm Cr} + {}^{16}{\rm O}$ (65 MeV) reaction using the gamma detector array equipped with charged particle detector array for reaction channel separation. On the basis of $\gamma-\gamma$ coincidence relations and angular distribution ratios, a level scheme was constructed up to $E_{x} = 7$ MeV and $J^{\pi} = 23/2^{(+)}$. The decay scheme deduced was interpreted in terms of shell model calculations, with a restricted basis of the $f_{5/2}$, $p_{3/2}$, $p_{1/2}$, $g_{9/2}$ orbitals outside a $^{56}_{28}$Ni core.

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