Volume 25, Issue 2
August 1985, pages 1-224
pp 1- August 1985 Letter
It has been established that quasicrystals with icosahedral point group symmetry occur in a rapidly solidified Mg32 (Al, Zn)49 alloy chosen on the basis of its equilibrium crystal structure. This alloy has a natural tendency to form icosahedral atomic clusters stabilised by size difference amongst constituent atoms. Results highlight the relationship between equilibrium crystal structure and the tendency to form quasicrystals.
pp 123-133 August 1985 Mathematical Physics
A virial theorem for solitons derived by Friedberg, Lee and Sirlin is used to reduce a system of second order equations to an equivalent first order set. It is shown that this theorem, when used in conjunction with our earlier observation that soliton-like solutions lie on the separatrix, helps in obtaining soliton-like solutions of theories involving coupled fields. The method is applied to a system of equations studied extensively by Rajaraman. The ’t-Hooft-Polyakov monopole equations are then studied and we obtain the well-known monopole solutions in the Prasad-Sommerfeld limit (λ=0); for the case λ≠0, we succeed in obtaining a non-trivial algebraic constraint between the fields of the theory.
pp 135-148 August 1985 Cosmology And Gravitation
We analyze the accretion of charged matter onto a rotating black hole immersed in an aligned dipolar magnetic field. We specialize to motion in the equatorial plane and calculate the ‘Keplerian’ angular momentum distribution, the marginally stable and marginally bound orbits, and the efficiency of mass-to-energy conversion as functions of the angular momentum of the black hole and of the product of the dipole moment and the charge of the infalling matter. Although the detailed results are quite different from those previously obtained in the case of an uniform magnetic field, the astrophysically relevant results are very similar; when hydrodynamical accretion is considered, these effects of the magnetic field are always very small. But for test particles the efficiency can be significantly increased for limited ranges of the parameters.
pp 149-156 August 1985 Particle Physics
The electromagnetic mass splittings of heavier hadrons are estimated in the framework of gauge theory model where ligher quarks are taken to behave relativistically and the spatial wave functions are described by the spin-spin interaction affected relative distances between quarks. The predictions for (Ξ−-Ξ0), (Σ*0−Σ*+), (Ξ*−-Ξ*0), (Dc+−Dc0) and (Dc*+−Dc*0) are in fair agreement with the experimental data available whereas those for (Db−−Db0) and (Db*−−Db*0) are in qualitative agreement with other theoretical estimates.
pp 157-163 August 1985 Particle Physics
The lowest momentum at which the total scattering cross-section data are available for Σ+p and Σ−p scattering is 145 MeV/c and 142.5 MeV/c respectively. Thus extracting low energy parameters amounts to extrapolating the data to still lower energies. Using the analytic structure of foward scattering amplitude to advantage a parameterization of theσT is presented which is hoped to be more reliable and stable for deriving results through extrapolation. The scattering lengths and effective ranges for the Σ+p and Σ−p are also estimated.
pp 165-173 August 1985 Nuclear Physics
The postulates of the double core model of binary fission are examined against the two well-known charge division mechanisms of fission, namelyucd andecd. An analytic expression of the modifieducd formula is obtained. Radiochemical distribution of mass and charge, formulated from the model, is found to agree satisfactorily with available experimental results. Finally, the most probable charge and mass values of the radiochemical heavy and light products, the average number of neutron andβ-emissions per fragment, are calculated, and found to agree with experimental observations.
pp 175-177 August 1985 Atomic And Molecular Physics
The effect of including distortion (with and without exchange) in the wavefunction for the continuum electron while calculating the probability of autoionization of 2s21S. 2s2p1,3P, 2p21D and 2p21S states of He and Li+ has been studied.
pp 179-186 August 1985 Atomic And Molecular Physics
Relative integrated intensities of the bands of theD1Π →X1Σ+ system of SnO have been measured by the technique of heterochromatic photographic photometry. Using the Rydberg-Klein-Rees Franck-Condon factors andr-centroids, the variation of electronic transition momentRe with the internuclear separationr is found to beRe(r)=const. (0.564r−1) in the range of 1.865 A≤r≤2.041A. The relative band strengths are derived. Effective vibrational temperature of the source is found to be 2559 K.
pp 187-190 August 1985 Atomic And Molecular Physics
Experimental potential energy curve for the X2Π state of AsS has been constructed using the method of Rydberg-Klein-Rees. The precise dissociation energy for the ground state has been estimated as 4.150±0.13 eV by the curve fitting procedure. The first ionization potential of the AsS molecule is found to be 8.66 eV.
pp 191-200 August 1985 Atomic And Molecular Physics
Supersonic expansion from a nozzle produces noble gas clusters under various source conditions. The characteristics of atoms and dimers in a nozzle beam are examined. A study of the dimer collision cross-section suggests the existence of a temperature-dependent limiting oven pressure (PL) for the observation of pure dimers. This is further supported by the dependence of the beam intensity on stagnation pressure. The reduced pressure-temperature coordinates for noble gas dimers behave in accordance with the model of corresponding jets. The velocity distribution of atoms and dimers in a beam corresponding to stagnation pressure on either side ofPL is measured to determine the effect of condensation on the distribution pattern.
pp 201-209 August 1985 Atomic And Molecular Physics
cndo/Force method is used to evaluate the redundancy free internal valence force fields for two conformers of nitromethane. The initial force field is set up by taking the interaction and bending force constants from this method and transferring the stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining the initial force field using vibrational frequencies of isotopic speciesviz CH3NO2, CD3NO2, CH315NO2 and CH3N18O2. The final force field thus obtained is reasonable on the basis of frequency fit and potential energy distribution. The barrier to internal rotation is found to be 0.048 kcal mol−1.
pp 211-215 August 1985 Solid State Physics
Electric field gradient (efg) is calculated at the centre of the cell in the simple tetragonal crystal. The method uses Euler-Maclaurin summation formula and makes the planewise summation in the direct crystal space without any special regrouping of charges in point charge model. The results are in fair agreement with previous results of de Wette on the same system using Fourier transform to reciprocal space.
pp 217-220 August 1985 Solid State Physics
tandel effect and second harmonic generation studies on ferroelectric solid solutions (lead, strontium) titanate and (lead, calcium) titanate were carried out near the Curie temperature. The generated second harmonics are linear for low biasing fields with a zero off-set, while they decrease sharply at higher biasing fields. In the autostabilized state, thetandel elements adjust their impedance against the variations of a.c. field. Zero off-set might have been caused due to the presence of delects giving rise to an internal bias which in turn generates second harmonic.
pp 221-222 August 1985 Comments
The recent claim that a black hole can be treated as a relativistic gas of micro black holes (planckions) is shown to be physically inconsistent and in fact is grossly in error. Any deductions made about black holes from such models must therefore be treated with caution.
pp 223-224 August 1985 Comments
Some clarifications about a model for the internal structure of black holes developed in an earlier paper are presented to remove confusion in the interpretation of certain results.
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