• Volume 27, Issue 5

      November 1986,   pages  1-712

    • Paramagnetic nematic liquid crystals

      S Chandrasekhar B K Sadashiva S Ramesha B S Srikanta

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      The paper reports new nematic liquid crystals that are paramagnetic.

    • The complex sine-Gordon theory: soliton solutions through the virial approach

      G P Malik K Sengupta

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      The one-soliton solutions found earlier through the inverse scattering method for the complex sine-Gordon theory by Lund (m2 < 0) and by Vega and Maillet (m2 > 0) are reobtained by using the virial theorem for solitons. An attempt is made to understand the physics of the virial approach.

    • On some operators in multichannel scattering

      S Mukherjee

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      We investigate the strong limit of an operator valued sequence used in other form in the nonrelativistic theory of multichannel scattering, and also some of its consequences.

    • Analogue of Aharonov-Bohm effect in spin gauge theory

      P C Naik

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      We predict the possibility of observing analogue of the Aharonov-Bohm effect due to long range interaction between spins originating in the framework of spin gauge theory developed earlier. The effect is predicted for both electrons (fermions) and photons. Appropriate experimental set-ups are suggested.

    • Spherically symmetric free fall collapse

      J Krishna Rao M Annapurna

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      The general dynamical equations for spherical gravitational collapse are derived by introducing the eigenvalue of the conformal Weyl tensor in the 2-2 component of the Einstein tensor and assuming the material content of the models to be a perfect fluid. Since this eigenvalue is coupled always with the material energy density, it has been interpreted as theenergy density of the free gravitational field whose presence is related with anisotropy and inhomogeneity. As a particular case, the collapse of a spherically symmetric dust (zero pressure) with vanishing radial acceleration (free fall collapse) is discussed. It is shown that the model is inhomogeneous with non-vanishing shear of the congruence of world lines of the dust particles. The model contains gravitational radiation by Szekere’s criterion since both shear invariant and the spatial gradient of density are non-vanishing. This is in contrast to the Oppenheimer-Synder model for which both the above mentioned characteristics are absent. A particular solution which is anisotropic and inhomogeneous has been given to prove the emission of gravitational radiation by the freely falling dust and in this case the energy density of the free gravitational field contains a typeN term superposed on the coulombian field.

    • Accurate measurement of thermal expansion of solids between 77 K and 350 K by 3-terminal capacitance method

      H N Subrahmanyam S V Subramanyam

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      The construction of a three-terminal capacitance cell and a bath type cryostat to measure thermal expansion of solids in the temperature range 77 K to 350 K is described. Calculation of the thermal expansion coefficients by using spline approximation is discussed along with the various errors involved in the measurement. The capacitance cell is calibrated by using aluminium and germanium as standard reference materials. The cell has an accuracy of 4% in the measurement of thermal expansion coefficient and a resolution of 1 Å change in length of sample of length 1 cm.

    • An X-band time domain electron paramagnetic resonance spectrometer

      Ranjan Das Balu Venkataraman Vinod R Bhagat Ajit S Ghangrekar Thomas Kuruvilla B K Chaturvedi G S Isola B M Marwaha P G Nair R S Parolia B K Sarkar

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      A computer-controlled X-band time domain electron paramagnetic resonance (EPR) spectrometer, with a time resolution of the order of 0.5μsec, has been constructed with many of the crucial microwave components designed and fabricated by the Microwave Engineering Group of TIFR. The spectrometer operates either in a microwave power pulsed mode for determination of spin-lattice relaxation times by the saturation recovery technique or in the kinetic mode for determination of the time dependence of EPR signal after laser excitation. It has an automatic frequency control, an automatic phase control and, most importantly, a field-frequency lock which ensures good stability of the EPR line positions enabling signal averaging for extended periods. The constructional details of the spectrometer and its performance in both the modes are described here by reporting results on certain typical systems.

    • Surface diffuseness of deformed and rotating nuclei

      Alok Saxena V S Ramamurthy

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      The surface diffuseness of deformed and rotating nuclei has been studied using the energy density formalism. It is shown that the surface diffuseness exhibits an anisotropy. This anisotropy in surface diffuseness can result in an anisotropic charged particle emission from highly spinning nuclei as has been seen in some recent experiments.

    • Theoretical study of the satellites and hypersatellites in the K-LL Auger spectrum of magnesium

      Lakshmi Natarajan A V Tankhiwale C Mande

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      This paper reports calculations of the energies of the satellite and hypersatellite lines in the K-LL Auger spectrum of magnesium. The results show that it may be possible to observe many more satellite and hypersatellite lines in the Auger spectrum which have not been hitherto reported experimentally.

    • Relative photodissociation cross-section of NaCs molecule, using argon ion laser lines

      A Sharma M N Dixit G L Bhale

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      Laser-induced photodissociation of NaCs molecule has been observed when a mixture of Na and Cs metal vapour in a glass cell was irradiated by most of the lines of an argon ion laser. The photodissociation results in the 3P state of Na atoms which is correlated with theF1Σ+ and G1π molecular states of NaCs. Distribution of photofragments over fine structure components 32P3/2 and 32P1/2 of Na has been studied. The ratio of intensity ofD2 line (5890 Å) toD1 line (5896 Å) of Na varies from around 2 at 5145 Å to about 3.5 at 4579 Å. The relative photodissociation cross-section increases monotonically as the wave-length of laser light decreases from 5145 Å to 4579 Å. It is seen that the 4579 Å photon is about 200 times more effective than the 5145 Å photon in causing the photoreaction NaCs + (Ar+ photon) → Na*(3P) + Cs(6S).

    • Calorimetric study of laser-irradiated thin foil targets

      T S Shirsat S Sharma H C Pant

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      Hydrodynmaic efficiency of laser-irradiated thin aluminum and gold-coated aluminum targets was experimentally determined using a specially designed cone calorimeter. Velocity of the accelerated target and ablation pressure were also estimated from the experimental data. The laser irradiance range used in the experiments was between 1012 and 1013 watts/cm2. Experiments indicate that the fall in the hydrodynamic efficiency due to gold coating on aluminum target is about 12% at an irradiance of 8 × 1012 W/cm2.

    • High pressure raman scattering in Pb5Ge3O11

      R K Soni K P Jain

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      The pressure dependence of various phonon modes has been investigated through the ferro-paraelectric phase transition. Most mode frequencies harden before levelling off above the phase transition. Mode Grüneisen parameters are estimated from the pressure dependence of phonon frequencies.

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