• Volume 33, Issue 5

      November 1989,   pages  1-614

    • Photoacoustic detection of two photon absorption in formaldehyde using pulsed dye laser

      A V Ravi Kumar G Padmaja V P N Nampoori C P G Vallabhan

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      Absorption spectra of formaldehyde molecule in the gas phase have been recorded using photoacoustic (PA) technique with pulsed dye laser at various power levels. The spectral profiles at higher power levels are found to be different from that obtained at lower laser powers. Two photon absorption (TPA) is found to be responsible for the photoacoustic signal at higher laser power while the absorption at lower laser power level is attributed to one photon absorption (OPA) process. Probable assignments for the different transitions are given in this paper.

    • A microprocessor based autoscanner for electromigration studies in thin films

      M Dhanabalan Y Syamasundara Rao K V Reddy

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      Mass transport due to electromigration can be estimated if the diffusion coefficientD and the electromigration effective charge numberZ* are known. Neutron activated tracer scanning method determine the radioactivity at different positions. An automatic scanning system for determining the radioactive concentration profiles developed using a microprocessor is described in this paper. Using the radioactive concentration profiles the electromigration shift is determined. From this shift the electromigration effective charge numberZ* is calculated. The system developed was tested for tin thin films.

    • On the Higgs feature of gravity

      G Sardanashvily O Zakharov

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      The gauge gravitation theory, based on the equivalence principle besides the gauge principle, is formulated in the fibre bundle terms. The correlation between gauge geometry on spinor bundles describing Dirac fermion fields and space-time geometry on a tangent bundle is investigated. We show that field functions of fermion fields in presence of different gravitational fields are always written with respect to different reference frames. Therefore, the conventional quantization procedure is applicable to fermion fields only if gravitational field is fixed. Quantum gravitational fields violate the above mentioned correlation between two geometries.

    • Bounds on non-leading QCD effects in a quark model for inclusive reactions

      D K Choudhury R C Goswami

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      We study the possible effect of QCD in the proton wave function in a quark model for inclusive processesA+B→C+X pursued by us. The assumption is the validity of the conjecture of Lepage and Brodsky in QCD on such effects. Our results obey the perturbative expectation, |Rg tan2φ|<1. Symmetric version of the model is, however, found to be at variance with most of the inclusive data as well as with some known phenomenology. If the dynamics of the underlying theory generate Regge-like symmetry breaking approximately, the model is phenomenologically viable, and the non-leading QCD effects become reasonable in size. Phenomenological necessity of the admixtures of (56, 0+)*, (70, 0+) and (56, 2+) in the nucleon wave function is also discussed in the present analysis.

    • Parity mixing in deformed Hartree-Fock approximation in A ≈ 70 mass region

      C R Praharaj

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      Parity mixing in deformed Hartree-Fock orbits preferentially lowers the energies of prolate deformed shapes and leads to a consistent description of the shapes of A ≈ 70 nuclei.

    • On the non-radiating motion of a charged particle

      N D Sen Gupta

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      The most general class of the electric and magnetic fields such that a charged particle moving in this field will not radiate is obtained. Apart from suitably orientated constant fields, it includes some special varying (but steady) fields.

    • Heat conduction and moisture migration in unsaturated soils under temperature gradients

      Ashok K Singh Ramvir Singh D R Chaudhary

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      An experimental study has been done to investigate the heat conduction and moisture distribution through the different layers of unsaturated soil. The soil is taken in the form of cylindrical columns in vertical and horizontal positions. The two ends of the cylindrical column were maintained at different constant temperature. The effective thermal conductivity was measured by dynamical method after achieving steady state. The distribution of moisture in the soil column was determined by gravimetric technique. The effective thermal conductivity (ETC) has also been predicted by temperature dependent model developed by Singhet al (1988). A close agreement has been found in experimental and predicted values of ETC.

    • Phonon density of states of tetracyanoethylene from coherent inelastic neutron scattering at Dhruva reactor

      S L Chaplot R Mukhopadhyay P R Vijayaraghavan A S Deshpande K R Rao

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      Inelastic neutron scattering experiments to determine phonon density of states of coherent scattering samples of polycrystalline complex solids are generally intensity-limited and therefore are feasible only at high flux facilities. Phonon density of states of the monoclinic phase of tetracyanoethylene at 300 K, obtained using the medium resolution triple axis spectrometer at the new Indian medium flux reactor Dhruva are reported here. The raw data is converted to the “neutron weighted” phonon density of states by applying suitable corrections. Comparison made with results from a theoretical calculation based on a semirigid molecule model of lattice dynamics is fair. Results from Dhruva are also consistent with that obtained (to be published) at the high flux pulsed neutron source (ISIS) of the Rutherford Appleton Laboratory in United Kingdom.

    • Soft mode dynamics of perovskite type crystals

      N S Panwar T C Upadhyay B S Semwal

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      The soft mode dynamics and related properties of perovskite, ABO3-type crystals have been studied using the operator form of the model Hamiltonian proposed by Pytte. The correlations have been evaluated using the double time thermal Green’s function technique and Dyson’s equation. Without any decoupling, the higher order correlations, appearing in the dynamical equation, have been evaluated using the renormalized Hamiltonian. The dielectric properties are directly related to the optical soft mode. The phonon width and shift have been calculated for different structural phases. The analysis of the temperature dependence of microwave loss tangent and dielectric constant explains the experimental results.

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