• Volume 14, Issue 5

      May 1980,   pages  321-423

    • Quantum beats from channeling relativistic electrons

      R Lal S K Joshi

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      Possibility has been explored of periodic time variation of intensity (quanturn beats) of radiation emitted from relativistic electrons channeling along the 〈110〉 axis of a crystal of f.c.c. (diamond) lattice structure.

    • Anharmonic oscillator model for first order structural phase transition

      Avinash Khare S N Behera

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      Exact solutions for the motion of a classical anharmonic oscillator in the potentialV(φ)=2 − |A|φ4 +6 are obtained in (1 + 1) dimensions. Instanton-like solutions in (imaginary time) which takes the particle from one maximum of the potential to the other are obtained in addition to the usual oscillatory solutions. The energy dependence of the frequencies of oscillation is discussed in detail. This can be used as a model for the first order structural phase transition in the mean field approximation. The high and low temperature behaviour of the static susceptibility is obtained. Finally, a qualitative explanation is offered for the observed central peak in ferroelectrics like SrTiO2.

    • Thermally stimulated current spectra in nitrogen implanted fluorinated ethylene propylene

      J P Jog S B Ogale S J Walzade A S Ogale S V Bhoraskar M R Bhiday V N Bhoraskar

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      Thermally stimulated current spectra of nitrogen implanted fluorinated ethylene propylene polymer foils have been studied. Two characteristic peaks have been obtained for samples implanted with nitrogen ions with energies ranging from 20 to 60 keV. The variations in the activation energies and relaxation times of charge carriers, as a function of implantation energy, have been attributed to the corresponding changes in the carrier distribution in the polymer. The carrier mobilities and mobility life-time products have also been estimated for the two characteristic peaks.

    • An automated high precision calorimeter for the temperature range 200 K–400 K. Part II. Design of temperature controllers

      H Heck I S Williams E S R Gopal S Jyothi

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      The design and construction of precision temperature controllers, capable of tracking the temperature of the samples to within 1 mK for ramp heating rates from 0.05 to 10 K per hour, are discussed. A tutorial section on the evolution of the control loop configuration is first given. This is followed by an outline of the refinements of the basic control loop desirable in the actual implementation of the electronic controller. The novel features of the present system and its performance are then briefly discussed. Finally the inadequacy of the conventional PID controllers for this application, the estimation of the time constants of the physical system needed in the design of the electronic controllers and the pitfalls in using a simple model of the heater plus thermometer assembly with a single pole are also discussed.

    • A solid state pulsed NMR spectrometer

      R K Shenoy J Ramakrishna K R Jeffrey

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      A 10 MHz pulsed NMR spectrometer, built using mostly solid state devices, is described. The pulse programmer provides 2-pulse, 3-pulse, saturation burst and Carr-Purcell sequences both in repetitive and manual modes of operation. The transmitter has a maximum power output of ∼ 2 kW with a 75 Ω output impedance termination. The total gain of the receiver system is around 120 dB with a minimum band width of 2 MHz. The recovery time of the receiver is ∼ 7 µsec. A two-channel boxcar integrator capable of working in the single channel, differential and double boxcar modes provides signal to noise ratio improvement. The sensitivity and the linearity of the boxcar integrator are ∼ 2 mV and ∼ 0.1% respectively.

    • Iteration approach to peratisation technique

      S V Kulkarni L K Sharma

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      Peratisation scheme normally used to obtain scattering lengtha(α) is through Born series. In this paper an iteration approach to this technique has been presented. This approach has also been applied to different potentials successfully.

    • High resolution spectrum of DyO molecule

      B R Yadav S B Rai D K Rai

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      Emission spectrum of DyO molecule has been photographed under high resolution in the wavelength region 5000 to 6300 A. The observed bands have been arranged into three different band systems. The rotational structure in the (0, 0) band of system I is partially resolved and analysed. Isotopic shifts have been calculated for various isotopic molecules and compared with observations. Electronic states involved in the transitions have been discussed.

    • Electronic spectra of parafluorobromobenzene

      Shashi K Singh K N Upadhya

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      The electronic absorption spectrum of parafluorobromobenzene is reported together with its band shape and molecular geometry. The electronic transition is found to be the 2900–2400 Å system and the analysis consistent with other paraheterohalogenated benzenes. The intense bands, including 0–0, are double headed and areB-type in nature.A-type vibronic bands are also observed although less intense than theB-type bands. In all 9 excited states and 5 ground state fundamentals could be assigned.

    • The electroweak mixing angle in unified gauge theories

      Jatinder K Bajaj G Rajasekaran

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      We study in detail the factors that influence the unification relations among the coupling parameters of strong and electroweak interactions. We find that the factor that decides the unification relations in a theory is the fermion content of the theory. The specific ‘observed’ group of strong and electroweak interactions used and the specific unification group in which these interactions are embedded are largely irrelevant. In particular, we find that the unification value of the electroweak mixing angle is the same for almost all models of interest. We also explicitly illustrate that the canonical value 3/8 of the mixing angle is a characteristic result of the currently popular sequential doublets scheme of fermions. Addition of extra fermion singlets reduces the mixing angle to 1/4. We propose this sequential triplets scheme of fermions as an interesting alternative to the current scheme.

    • The electroweak mixing angle in unified gauge theories—the renormalisation effects

      Jatinder K Bajaj G Rajasekaran

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      A general analysis of the renormalisation corrections to the unification results for the coupling constants of strong and electroweak interactions is attempted. In particular, the effects of introducing an energy scale intermediate between the unification energy and the low-energy regions are studied and found to be important. This analysis is applied to unification schemes of both kinds, namely, unification at superhigh energies, and unification at accessible energies.

    • Errata

      U C Naithani B S Semwal

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