• Volume 32, Issue 1

January 1989,   pages  1-97

• Fine-hyperfine structures of$$c\bar c$$ and$$b\bar b$$ systems in a non-relativistic Hulthen plus linear potentialsystems in a non-relativistic Hulthen plus linear potential

The heavy mesons of the charmonium and upsilon family are described in an alternative static potential model chosen in a combination of Hulthen and linear potential. We find that the quark-confining potential in the form of an equal admixture of vector and scalar parts successfully explains the fine-hyperfine structures of$$c\bar c$$ and$$b\bar b$$ systems in a flavour-independent manner. The leptonic decay widths of the vector mesons ofψ and γ families are calculated taking into account the Poggio-Schnitzer correction. We obtain some of the bound states of the yet-to-be observed$$t\bar t$$ system for thet-quark mass ranging from 50 to 200 GeV.

• Nucleon-nucleon interaction with tensor forces in the quark compound bag model

A model forN-N interaction proposed earlier by two of us (VSB and VKG), has been extended to incorporate the tensor component of the nuclear force. Based on the quark compound bag model (QCB), the nucleon-nucleon potential has a short range repulsive core which is non-local and has a characteristic energy dependence and is expressed in terms of the parameters relating to the six-quark compound bag. To account for the low energy properties, this repulsive core interaction is supplemented by a phenomenological non-local potential containing both central (S-wave) and tensor components and operates only outside the QCB. Using this model, we analyse and compare the results with the experimental data for the electromagnetic form factors of the deuteron, theD-state observables, such as the quadrupole moment, theD-state probability, and theD/S ratio along with then-p scattering phase shifts up to about 400 MeV.

• Influence of the laser field polarization on the electron impact ionization of hydrogen

The triple differential cross-sections for the ionization of hydrogen by electron impact in the presence of a laser field have been calculated in the coplanar asymmetric geometry by using the first Born approximation and the symmetric geometry by using the Coulomb-Born approximation at an incident electron energy of 250 eV. The variation of the triple differential cross-sections, for fixed values of the angles of scattering and ejection, is studied as a function of the linear polarization of the laser field. The changes are quite amenable to experimental investigation.

• Simulation of pressure-space-time history in underwater explosions

Pressure-space-time history of shock waves due to the detonation of explosive charge in water is obtained by simulating the numerical integration of shock trajectory with the variation of fluid parameters behind the shock front. Results are compared with those obtained experimentally elsewhere.

• Explosive compaction of superconducting powder

Superconducting powder, YBa2Cu3O7−x, with grains of size varying from 2 to 20μ and superconductivity up to 90°K was compacted to a uniform density of 6.2 g/cc (96% of theoretical maximum density) by explosive-shock loading in cylindrical configuration. A typical size of rod (3.76 mm diameter and 70 mm length) was fabricated using the present technique of explosive compaction. The compacted specimen shows levitation at the liquid nitrogen temperature.

• Universal scaling law for first order phase transformation: LiKSO4

We have measured the kinetics of phase transition in LiKSO4 (C66C3v4;Tc∼201 K) by monitoring the time-dependent change in Raman intensity of selected vibrational lines at various temperatures in the transformed phaseC3v4. We find that the observed growth curves for several temperatures display a nearly universal shape when plotted against a suitably scaled time parameter. We interpret our results in terms of a phenomenological model of nucleation and growth.

• Influence of donor-donor transport on excitation energy transfer

Energy migration and transfer from acriflavine to rhodamine B and malachite green in poly (methylmethacrylate) have been investigated using the decay function analysis. It is found that the influence of energy migration in energy transfer can be described quite convincingly by making use of the theories of Loring, Andersen and Fayer (LAF) and Huber. At high acceptor concentration direct donor-acceptor transfer occurs through Förster mechanism.

• A universal trend in the structural correlation with oxygen content in RBa2Cu3Ox systems

It is shown that the lattice parametersa, b andc in the superconducting perovskites RBa2Cu3Ox are inter-related and well correlated to the total oxygen content. The correlation shows a universal trend.

• On the perfect penrose tiling and its basic building blocks

We show that the basic building blocks of a perfect Penrose pattern (PPT) in two dimensions can be established by adding another condition to the Penrose’s original edge rules. The implications of this result are discussed in the context of recent papers by Onada, Jaric, Ronchetti and others concerning growth algorithm for PPT’s.

• X-ray diffraction analysis and occurrence of multiple phases in Bi-Sr-Ca-Cu-O superconductors

Starting composition 1112 for Bi-Sr-Ca-Cu-oxide yields multiphase super-conductors with the proportion of constituent phases depending sensitively on the annealing temperature. The R-T curves show zero resistivity and the transition corresponding toTc = 80 K phase prominently. However, indexing of X-ray diffraction peaks reveals presence of 80 K (lowTc) as well as 108 K (highTc) phase. The lowTc phase thus corresponds to the orthorhombic structure with a unit cell ofa = 5.4Å,b = 27 Å andc = 30.56 Å. This is further understood to be composed of a pseudotetragonal cell ofa =b = 5.41 Å. The highTc phase similarly pertains to the orthorhombic structure withc = 36 Å.

• Temperature-modified Coulomb potential for the electron-proton system

The finite-temperature Schrödinger equation, derived recently from the Bethe-Salpeter equation for the bound states of an electron and a proton interacting via the instantaneous Coulomb interaction, is studied in the coordinate space. An expression for the temperature-modified Coulomb potential is obtained and briefly discussed.

• On the consistent inference of probability distributions

We respond to criticism (Karbelkar 1986) concerning our approach to consistent inference of probabilities for reproducible experiments (Tikochinskyet al 1984).

• Pramana – Journal of Physics

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