• Volume 50, Issue 1

      January 1998,   pages  1-93

    • Universality in the effective pair interaction ofd-shell metals — Compressibility and vacancy formation energy of 3d-liquid metals

      A K Karmakar R N Joarder

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      Like liquid alkali metalsd-shell liquid metals show scaling behaviour in structure and interaction potentials. A realistic interaction potential model, properly parametrized can reasonably describe the universality in the isothermal compressibility and vacancy formation energy of 3d-liquid metals in electron ion plasma model.

    • Evidence of polaronic charge carriers in oxide superconductors

      C M Srivastava

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      The analysis of photoemission and femtosecond optical absorption spectroscopy in oxide superconductors supports the view that the charge carriers are polaronic in nature. These carriers are found to exist in the (Ba/Sr)-O planes and are coupled toB1g vibrations of the apical oxygen.

    • Electrical properties of a-antimony selenide

      Sanjeev Gautam D K Shukla Shelly Jain N Goyal

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      This paper reports conduction mechanism in a-Sb2Se3 over a wide range of temperature (238 to 338 K) and frequency (5 Hz to 100 kHz). The d.c. conductivity measured as a function of temperature shows semiconducting behaviour with activation energy ΔE=0.42 eV. Thermally induced changes in the electrical and dielectric properties of a-Sb2Se3 have been examined. The a.c. conductivity in the material has been explained using modified CBH model. The band conduction and single polaron hopping is dominant above room temperature. However, in the lower temperature range the bipolaron hopping dominates.

    • Monte-Carlo optimization of correlated helium wave function

      Sabyasachi Kar Puspajit Mandal

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      A new type of correlated wave function for the normal helium is proposed in the form:ψ(r1, r2)=Σcmφm withφm=exp]−α(r1+r2)]/(br12+a)m wherea, b, α are non-linear variational parameters. Optimizing these parameters by the Monte-Carlo technique, an energy eigen-value of −2.903645(a.u.) is obtained withonly three terms in the basis expansion alongwith satisfactory cusp condition, compared to the essentially exact non-relativistic value of −2.903724 as given by Freundet al (Phys. Rev.A29, 980 (1984)).

    • Total electron scattering cross-sections for nitrous oxide at low electron energies

      P Rawat K P Subramanian Vijay Kumar

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      Absolute total electron scattering cross sections for nitrous oxide have been measured at low electron energies using a photoelectron source. The measurements have been carried out at 19 electron energies varying from 0.73–9.14 eV with an accuracy of ±3%. The cross sections obtained in the present experiment have been compared with other measurements.

    • Hyperspherical calculation for electron hydrogen atom ionization collisions in a symmetric form

      J N Das

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      The hyperspherical partial wave method (Das [7]) has been presented here in a symmetric form so that effects of coupling among different partial waves may be included in a systematic way. It is also outlined here how to solve the relevant coupled set of radial wave equations numerically. Some preliminary results are presented forS, P andD waves in the low energy domain of 30–50 eV for the incident electron. In this calculation only two important partial waves are included in each channel. The results are compared with experimental ones and appear very encouraging.

    • Numerical modeling of laser matter interaction in the presence of an ambient gas

      A Neogi R K Thareja

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      A one dimensional numerical model to simulate the laser matter interaction in the presence of an ambient gas is presented. The model is developed by making appropriate modifications in MEDUSA, a one dimensional Lagrangian computer code, which simulates laser plasma interaction in vacuum. Various parameters of the plasma such as velocity, electron temperature, ion temperature, density, pressure, shock wave intensity of the plasma as it expands into a background gas are simulated. The results are compared with the experimental observations.

    • Absence of neutron emission during interaction of deuterium with metal at low energies

      A Shyam T C Kaushik

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      Technique and instrumentation to detect reliably, multiplicity of neutrons emitted in sharp bursts (≤100 µs) has been developed where a burst of as low as 15 neutrons and continuous emission of ⋍10−1 neutron/s may be detected. Using this technique, attempts were made to detect neutron emission from various experiments in which anomalous nuclear effects (or what is commonly referred to as cold fusion) may be expected to occur. No neutrons, above our detection threshold, were detected in the recent series of experiments.

    • Use of spherical gratings in a toroidal grating mount for vuv-soft x-ray synchrotron radiation

      K J S Sawhney A I Munshi R V Nandedkar

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      A toroidal grating monochromator (TGM) based beamline was designed earlier and it is being setup on the 450 MeV Indus-1 synchrotron radiation source. This beamline operates in 40–1000 Å wavelength range and gives a moderate resolution (∼500) at high throughput. Now-a-days, spherical gratings are giving very high resolution in some complex monochromators. We have evaluated the use of spherical gratings in the simple rotation mount of a TGM. The motivation has been to evaluate if the existing TGM beamline, without any hardware changes, can be used with the much cheaper spherical gratings. The two monochromators, employing toroidal and spherical gratings respectively, have been compared by performing detailed ray tracing calculations. Our study shows that, with the same mechanical hardware, a real spherical grating monochromator gives better performance compared to the conventional TGM with respect to the spectral resolution and the flux. Furthermore, for moderate resolution this improvement is realized even when the exit slit is not moved to keep the spherical grating in-focus.

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