• Volume 1, Issue 2

      August 1973,   pages  61-116

    • Ferromagnetic behaviour of interacting superparamagnetic particle aggregates in basaltic rocks

      C Radhakrishnamurty N P Sastry E R Deutsch

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      Studies on two rare cases of magnetic behaviour in basaltic rocks are reported. In both the cases a peak in susceptibility occurs at −160°C. However, one sample shows only normal hysteresis loops at low temperatures in a wide range of fields, while the other sample shows a constricted hysteresis loop in 1000 Oe at −190°C. Both types of behaviour can occur as a result of differing states of aggregation of interacting superparamagnetic particles in the respective samples.

    • Scaling in prong-number distribution in$$\bar pp$$ collisionscollisions

      I Rama Rao K V L Sarma

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      The prong-number distributions in$$\bar pp$$ collisions at relatively low laboratory momenta (≾7 GeV/c) exhibit the same type of scaling which has been observed in pp and π-N collisions at momenta ≿ 50 GeV/c.

    • Electromagnetic properties of low lying levels in75As

      R C Chopra P N Tandon

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      Theg-factors of the 265 and 280 keV levels have been measured to be 0.61±0·16 and 0·30±0·05 respectively. The PAC technique was used for the measurements. In addition, the half-life of the 280 keV level has been remeasured to beT1/2=0·32±0·02 ns using γ-γ delayed coincidences. Electromagnetic properties of the various levels calculated on the core-particle coupling model agree with the experimental results. The results are compared with other existing theoretical calculations.

    • Photoelasticity in polycrystalline aggregates

      G S Ranganath S Ramaseshan

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      A theory for the photoelastic behaviour of transparent polycrystalline aggregates consisting of randomly oriented anisotropic crystallites has been developed. Such an aggregate is isotropic but it becomes birefringent under the influence of a uniaxial load. The photoelastic constants of the aggregate are given by the components of the spatial average of the photoelastic tensor of the single crystal, and are worked out by assuming either the strain to be continuous (Voigt approximation) or the stress to be continuous (Reuss approximation). The components of the average photoelastic tensor are very different for these two limits. The elastic and the photoelastic constants of alkali halide aggregates have been evaluated for both the stress continuity and the strain continuity conditions. The maximum variation of the elastic constants in going from the Voigt to the Reuss condition is 50 per cent while the photoelastic birefringence can vary by as much as 300 per cent in alkali halides. In the case of KI and rubidium halides even the sign of the photoelastic birefringence is different for the two limits.

    • Stimulated emission of x-rays from plasmas generated by short-pulse-laser-heating of solid targets

      Sudhanshu S Jha

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      The problem of heating of a solid target to generate a nonequilibrium plasma by subnanosecond laser pulses is considered. For an appreciable absorption of energy from a Nd-glass laser, the critical density of the electrons in the plasma turns out to be 1021 cm−3. These electrons can be heated up to 107 K or more by using pulses of about 10 picosecond duration and absorbed energy flux of the order of 1021 erg cm−2 sec−1. Starting from neutral atoms in a solid with a high atomic number, e.g., Z=26, for times in the picosecond regime the relevant rate equations are solved analytically to predict densities of the atoms at different ionization levels. It is shown that during such a short time the population density of the ions isoelectronic to neon builds up to a very large amount. This in turn leads to the population inversion in the 4s → 3p soft x-ray laser transition, via the electron-impact excitation of the 4s level of the isoelectronic neon ion. For the effective pumping times of the order of 5 picoseconds, a gain of the order of 102 db cm−1 is predicted for the laser transition in Fe XVII, Co XVIII or Cu XX.

    • A three dimensional ferromagnetic Ising ‘fluid’ model

      N Kumar K B Athreya

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      The three dimensional ferromagnetic spin-half Ising model with an arbitrary external magnetic field is considered in the spatial continuum limit and under a certain tempering condition to be imposed on the pair-wise spin-spin interaction. An expression for the partition function has been obtained for a tempered RKKY type interaction. The solution predicts the classical mean-field behaviour above a critical temperature below which the spontaneous magnetization jumps discontinuously from zero to the saturation value.

    • Determination of bond lengths in some compounds of rhenium from the x-ray LIII absorption discontinuity

      A V Pendharkar Chintamani Mande

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      The shapes and the fine structure of the x-ray LIII absorption discontinuity of rhenium have been studied in seven octahedral (K2ReCl6, K2ReBr6, (pyH)2ReCl6, (dipyH)2ReCl6, Re(dipy)Cl4, K3ReO2(CN)4 and ReO3) and three tetrahedral (KReO4, NH4ReO4 and NaReO4) compounds. The bond lengths in these compounds have been determined by applying Levy’s theory to the data on the fine structure associated with the edge beyond the molecular orbital region.

    • The law of rectilinear diameter for the liquid-gas phase transition

      A C Biswas

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      A rigorous semi-microscopic derivation of the law of rectilinear diameter for the liquid-gas phase transition has been provided.

    • Characteristics of a neutron moisture gauge with a solid state detector

      M K Nagpal P P Mehta K K Nagpaul Rama

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      The development of a neutron moisture gauge, using Cf252 as a source of fast neutrons and muscovite as a detector of thermal-neutron-induced-fission in Pu239 target, is reported. The laboratory and the field calibrations of the instrument reveal a linear relation between track count rate and the moisture volume fraction.

      Low cost, low weight, simplicity of operation, thermal stability and elimination of electronic gadgets and power supplies are the attractive features of this instrument. The main drawback is its poor detection efficiency for thermal neutrons and the consequent unsuitability as a routine logging instrument. Its special features make it particularly suited to deep bore hole logging such as in oil exploration.

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