Showing papers by "Indian Association for the Cultivation of Science published in 1979"

On the hierarchy equations of the wave-operator for open-shell systems

Abstract: Starting with the open-shell analogue of the Gell Mann-Low theorem of many-body perturbation theory, a non-perturbative linear operator equation is derived for the linked part of the wave-operatorW for open-shell systems. It is shown that, for a proper treatment of the linked nature of the wave-operator, a separation into its connected and disconnected components has to be made, and this leads to a hierarchy of equations for the various connected components. It is proved that the set of equations can be cast into a form equivalent to the non-perturbative equations of the wave-operator recently derived by Mukherjee and others in a coupled-cluster or exp(T) type formalism if a consistent use is made of a ‘core-valence separability’ condition introduced earlier. A comparison of the coupled-cluster representation ofW with the perturbative representation reveals that various alternative forms ofW in the coupled-cluster representation are possible and these reflect alternative ways of realising the core-valence expansion of the wave-operator. In particular it is emphasised how the use of Mandelstam block-ordering simplifies the coupled-cluster theories to a considerable extent and a comparison is made with coupled-cluster methods for open-shells put forward very recently by Ey and Lindgren. Finally, it is shown how difference energies of interest may be derived in a compact manner using the Mandelstam block-ordering of the wave-operator.

Rearrangement collisions in highly excited states of atomic hydrogen

Abstract: A new straightforward method for the evaluation of the rearrangement-scattering amplitude has been proposed to study the following reactions: ${\mathrm{H}}^{+}+\mathrm{H}(1s)\ensuremath{\rightarrow}\mathrm{H}(\mathrm{nlm})+{\mathrm{H}}^{+}$; ${e}^{+}+\mathrm{H}(1s)\ensuremath{\rightarrow}({e}^{+}{e}^{\ensuremath{-}})(\mathrm{nlm})+{\mathrm{H}}^{+}$, $2\ensuremath{\le}n\ensuremath{\le}\ensuremath{\infty}$ and $l=0,1$, in the first Born approximation embodying the full interacting potential. A contour-integral representation has been used for the Laguerre polynomial that occurs in the final-state wave function. The amplitude containing only the electron-nucleus interaction has been evaluated analytically. But the amplitude for the projectile nucleus interaction involves a contour integration on a circular path, and this integral can easily be evaluated numerically. To provide an estimate of the asymptotic cross section, expressions for the transition amplitudes when $n\ensuremath{\rightarrow}\ensuremath{\infty}$ have also been given. It is shown explicitly that the charge-exchange cross sections asymptotically obey the inverse $n$-cube law irrespective of the incident energy. In proton-hydrogen collisions our computed results for the low-lying discrete states show excellent agreement with the earlier theoretical values of Mapleton and those of Band as well. For positronium (Ps) formation all the reported results, except for the $2s$ excitation, are quite new. Zeros of the angular distributions are seen to be almost independent of the principal quantum number $n$, but dependent only on the projectile energy. ${n}^{3}\ensuremath{\sigma}$ shows regular smooth behavior with increasing $n$, and the results for $n=18$ and $n\ensuremath{\rightarrow}\ensuremath{\infty}$ agree within 0.5% throughout the energy range considered.

The diffusion of nickel into copper and copper—nickel alloys

Abstract: The diffusion of nickel into copper and copper–nickel alloys are investigated in the temperature range of 780 to 1037 °C by the resistometric method and the diffusion coefficients and activation energies are obtained. The nickel diffusion in copper is compared with the previous studies. For the diffusion of nickel into copper–1.08 at% nickel and copper–2.81 at% nickel alloys no such comparison can be made as there are no data available in this dilution range. The diffusion coefficients of the systems studied show a strong dependence on the alloy composition. It is also observed that addition of nickel into copper retards the diffusivity. The data obtained from the studies are analysed in the light of the theories of LeClaire and Neumann and Hirschwald.

Dissociative Recombination of H+2, HD+ and D+2 Molecular Ions

Abstract: An ab initio calculation of the cross-sections of dissociative recombination (DR) in H + 2 , HD + and D + 2 has been made using the projection operator technique. A single-configuration molecular orbital wavefunction has been used for the molecular resonance state, although the applicability of such a simple wavefunction has not been fully tested. The decay width has been calculated in the “local” approximation. Comparison with experiment shows that for H + 2 the calculated results can fully account for the total DR cross-section in the low and intermediate energy regions, and that the local approximation is sufficiently accurate to account for the undulatory structure in the energy dependence of the DR cross-section. A similar structure is also obtained for D + 2 , although here the agreement with experiment is less marked. For HD + no particular heteronuclearity effect is observed.

Lepton-hadron relation and the inclusive production of low-p T charged secondaries at ISR energies in pp scattering

Abstract: Some of the most important characteristics of the inclusive production of charged secondaries at small transverse momenta and high energies in pp scattering have been explained in the light of a new model of hadrons. The model suggests that Feynman scaling is not exact, but may be taken to be approximately valid in the ISR energy range. The inclusive distributions as well asx(dσ/dx) for pp→pX,\(pp \to \pi ^ \pm X\), pp→K±X and\(pp \to \bar pX\) have been evaluated which are found to be in excellent agreement with experiments. The model also explains the preponderance of positively charged particles over negatively charged particles and offers some predictions for various types of inclusive reactions which may be taken up for verification in future experiments.

Thermal investigations of the calcium salts of monocarboxylic aliphatic fatty acids

Abstract: Calcium salts of acetic and mono, di and trichloroacetic acids were investigated with respect to their dehydration and decarboxylation, using a derivatograph. A phase transition was noticed only in the case of calcium acetate. Effects of crucible and diluent on the thermal behaviour of the above salts were also studied. The decomposition products were investigated qualitatively, and from these gaseous products and also from the residue after pyrolysis the probable mechanisms of decompositions have been suggested. Activation energies for the decarboxylation processes were evaluated from the TG curves.

Electronic structure and optical properties of AlP, AlAs, and AlSb

Abstract: The composite wave variational version of the APW method is used in conjunction with the semiempirical tight-binding interpolation scheme to obtain the electronic band structure and optical absorption characteristics of the compounds AlP, AlAs, and AlSb. The results show that all these materials are indirect band gap semiconductors. The overall feature of the energy bands and the optical characteristics agree fairly well with existing theoretical and experimental results. The implication of the interpolation parameters is also emphasised. Es wird die Variationsmethode zusammengesetzter Wellen der APW-Methode zusammen mit dem halbempirischen „tight-binding” Interpolationsschema benutzt, um die elektronische Bandstruktur und die optischen Absorptionscharakteristiken der Verbindungen AlP, AlAs und AlSb zu erhalten. Die Ergebnisse zeigen, das alle diese Materialien indirekte Halbleiter sind. Der Gesamtverlauf der Energiebander und der optischen Charakteristiken stimmen gut mit den existierenden theoretischen und experimentellen Ergebnissen uberein. Der Einflus der Interpolationsparameter wird ebenfalls diskutiert.

(±)-Des-N-Morphinan: a Unique Bridged Hydrocarbon Attractant for the Rhinoceros Beetle, Oryctes rhinoceros; and Development of an Olfactometer

Abstract: An olfactometer designed for Oryctes rhinoceros (L.) is described and its effectiveness demonstrated by a comparison of results with field tested chemicals. Using the olfactometer, (±)-Des-N-morphinan, but not its stereoisomer was found to be a strong attractant for adult rhinoceros beetles. This is the 1st synthetic bridged hydrocarbon found to be an insect attractant.

Grain-boundary scattering in aluminium films deposited on to calcite substrate

Abstract: Electrical resistivity and temperature coefficient of resistivity of polycrystalline aluminium films deposited onto calcite substrates have been measured in situ. It was observed that films deposited at 130° C substrate temperature show reversible and reproducible behaviour with thermal cycling. The grain-boundary scattering theory of Mayadas and Shatzkes reproduces the experimental observations quite faithfully with the coefficient of specular reflection p=0 and grain-boundary reflection coefficient R=0.38 indicating that the grain-boundary scattering plays a significant role in electron transport in aluminium film deposited on to calcite substrate.

Calculations of proton-impact excitation of helium using the Glauber approximation

Abstract: Cross sections for the 1 /sup 1/S ..-->.. n /sup 1/S (n = 2,3,4) excitations of atomic helium under proton impact are calculated with incident energy ranging from 25 to 1000 keV employing the Glauber approximation. A properly orthogonalized set of He wave functions are used. The generalized oscillator strengths for 1 /sup 1/S ..-->.. 2 /sup 1/S and 1 /sup 1/S ..-->.. 3 /sup 1/S excitations are also calculated with these wave functions, and the results are compared with the existing theoretical and experimental data. The full Glauber scattering amplitude is separated into single and double-scattering parts. The single-scattering amplitude is evaluated from a closed-form expression. A numerical method is employed to calculate some integrals occuring in the double-scattering amplitude. At incident energies above 500 keV, the single-scattering contribution is found to dominate the Glauber result. The effect of the double-scattering term is appreciable at intermediate energies, where it substantially lowers the cross sections from the corresponding single-scattering result. The Glauber result at intermediate energies also underestimates most of the existing theoretical and experimental cross sections, which already show a wide variation among themselves in absolute values. However, the functional dependence of the Glauber cross sections on energy ismore » similar to that depicted by other calculations and measurements. Furthermore, the average ratio of the Glauber cross sections for 3 /sup 1/S and 4 /sup 1/S excitations at high energies show reasonable agreement with those obtained from other theories, as also the n/sup -3/ law of cross sections.« less