• Volume 24, Issue 6

      June 1985,   pages  813-916

    • Photon emission from non-oriented spin systems

      G Ramachandran V Ravishankar

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      A method is suggested to determine experimentally whether the state of a spin system is oriented or non-oriented by measuring the angular distribution,I and the circular polarization asymmetry,Ac of the photons emitted by the system. These also provide enough data to determine the density matrix completely.

    • Tachyons in general relativity

      V S Gurin

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      The tachyonic version of the Schwarzschild (bradyonic) gravitational field within the framework of extended relativity is considered. The metric of a tachyonic black hole is obtained through superluminal transformations from a bradyonic metric. The extended space-time manifold of this geometry which includes both black and white tachyonic holes is analysed, and the differences between the tachyonic and bradyonic versions are noted. It is shown that the meanings of black holes, tachyons and bradyons depend on the character of the reference frame and are not absolute.

    • A high pressure-high temperature cell for electrical resistivity studies

      Mohammad Yousuf P Ch Sahu K Govinda Rajan

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      A high pressure-high temperature cell which permitsin-situ pressure and temperature calibration is described. The cell is in an opposed anvil configuaration, and houses two samples with four probes each along with a miniature furnace and a thermocouple. The pressure and temperature capability of the cell are 100 kbar and 1000°C respectively. This cell was developed to study the electrical resistivity of metals and alloys at high pressure and high temperature. Bismuth was used to calibrate the cell. We report in this paper the design details and the performance of this cell. Ni has been chosen as a test problem and the observed behaviour is indicated to show the quality of data.

    • Classical solitons with no quantum counterparts and their supersymmetric revival

      R K Kaul R Rajaraman

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      We demonstrate the phenomenon stated in the title, using for illustration a two-dimensional scalar-field model with a triple-well potential {fx837-1}. At the classical level, this system supports static topological solitons with finite energy. Upon quantisation, however, these solitons develop infinite energy, which cannot be renormalised away. Thus this quantised model has no soliton sector, even though classical solitons exist. Finally when the model is extended supersymmetrically by adding a Majorana field, finiteness of the soliton energy is recovered.

    • Some consequences of global horizontal symmetry

      V Gupta

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      It is pointed out that the present SU(3)c×SU(2)L×U(1) gauge interactions with three families have a global horizontal symmetry (denoted hereby SU(3)H) which is broken only by the weak charged hadron currentJh. Also, with (u, c), (d, s), (ve, {ie437-1}) and (e,μ) as doublets of SU(2)H (subgroup of SU(3)H),Jh has simple transformation properties under this subgroup. Amplitude relations, using SU(2)H symmetry, for hadronic leptonic and semileptonic decays are given.

    • Bosonic loops and gluon condensate

      S Misra B B Deo

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      Contributions to the vacuum polarisation inQCD are calculated separately with fermion as well as boson loops to have an idea of results expected for possible supersymmetric extension. It is found that the results are not altered in any significant way.

    • Inner shell structure of heavy atoms

      M P Das P Nayak

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      The inner-shell structure of some heavy atoms is examined using a self-consistent relativistic local density method. Ar(K), Kr(K) and Xe (K,L1,L2 andL3) binding energies and {ie863-1} (hyper-satellite) energies of Tl, Hg and Tm are calculated. The results are compared with available experimental data.

    • EXAFS study of intermetallics of the type RGe2 (R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Y) Part II: Determination of Ge-R distances

      A R Chourasia V D Chafekar C Mande

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      The extended x-ray absorption fine structure (EXAFS) associated with the GeK x-ray absorption discontinuity in pure germanium and in the intermetallics RGe2 (R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Y) has been studied. The Ge-R distances in these compounds have been determined by comparing the experimental phase shifts with the theoretical ones. The Ge-R distances in the compounds TbGe2, HoGe2 and ErGe2 are being reported for the first time in this work.

    • Focussing and defocussing of ballistic phonons in diamond and Nb3Sn

      A Pushpahasan K S Viswanathan

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      The ballistic propagation of phonons in diamond and Nb3Sn at 40 and at 4.2 K is examined. The nature of variation of the phonon magnification factor has been analysed both in the wave vector as well as group velocity spaces. Using the Polar Schmidt-net with Pole at (π/2,π/2), the mappings of phonon focussing and defocussing are made. It is shown that the mapping for theFTA mode for Nb3Sn exhibits islands acting as impenetrable barriers for phonon propagation.

    • Indentation studies of alkali halides at elevated temperatures

      K Kishan Rao D B Sirdeshmukh

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      The hardness of NaCl and KCl crystals has been estimated from the lengths of dislocation rosette formed around indentation at various temperatures up to 400°C. The hardness decreases with increasing temperature. This is due to the softening of the crystals at elevated temperatures which results in the easy movement of dislocations. The results are discussed using a few available relations which connect hardness to temperature. Arms of indentation dislocation rosette are well defined up to 300°C but around 400°C the rosette pattern is spread over a circular region. A possible mechanism is discussed.

    • Electrical and photoelectrical studies of plasma polymerized acrylonitrile

      Sujata B Dake S V Bhoraskar

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      The electrical and photoelectrical properties of plasma polymerized acrylonitrile (PAN) are reported. The polymer films were studied in silver-PAN-silver systems. Electrical conductivity at room temperature was of the order of 10−11 ohm−1 cm−1. The space charge limited current (SCLC) studies at room temperature and thermally stimulated current studies (TSC) over a temperature range of 290–500°K led to a clear understanding of carrier concentration, carrier mobility, trapping levels and activation energies. Photoelectric measurements were used to draw a band picture in plasma depositedPAN.

    • Plasmon dispersion and linewidth in aluminium

      R K Pal D N Tripathy

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      Plasmon dispersion in Al is estimated using the expression for the dynamic structure function,Spl(K,ω), corresponding to the plasmon excitations in a many-electron system derived earlier. An evaluation of its plasmon linewidth is also presented. It is observed that for Al both the dispersion and linewidth agree fairly well with experiments.

    • Dielectric relaxation of some heterocyclic compounds in highly viscous media

      Rajni Misra Amar Singh J P Shukla M C Saxena

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      Dielectric measurements on three heterocyclic compounds namely pyrrolidine, piperidine and 2-acetylpyridine in paraffin oil and paraffin oil + cyclohexane mixtures over the temperature range (294–318 K) at 9.8 GHz have been made. The data have been analysed using the method of Higasiet al and their dependence on macroscopic viscosity has been examined. The effect of solvent viscosity on the dipolar rotational process of the molecules in highly viscous media is also discussed.

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