Indian Journal of Pure and Applied Physics

 

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VOLUME 40 NUMBER 6 JUNE 2002

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CONTENTS

 

Atomic and Molecular Physics

Vibrational analysis of 2-chloroheptane

Neena Jaggi & RM P Jaiswal

 

385

Thomas-Fermi calculations for atoms in high magnetic field using realistic model

O H Mobarek* & E Al-Laheani

393

Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics and Fluid Dynamics

Ultrasonic pulse-broadening and attenuation in volcanic rock-A case study

M V M S Rao*, L P Sarma & K J Prasanna Lakshmi

 

396

Condensed Matter: Structure, Mechanical and Thermal Properties

Pair-breaking effects on charge imbalance in superconductors

B A Mattoo

402

Semimetal-semiconductor transition in Bi-In System

Sanjeeta Rani* & G K Chadha

407

Computation of thermodynamic functions of 2-and 4-phenylpyridine from vibrational spectra

M Isaq*, Sanjiv Arora & R S Kajal

417

Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties

Scattering characteristics of small particles in resonance region: Effect of shape

J J Joshi, H S Shah*, S K Sharma & RV Mehta

 

421

Dielectric relaxation in ternary mixtures of benzotrifluorides

G D Rewar & D Bhatnagar*

430

Temperature and frequency dependent dielectric constant/loss studies in pristine and high temperature

annealed poly (p-phenylene sulphide)

J K Quamara, N Singh & Azad Singh*

436

Interdisciplinary Physics and Related Areas of Science and Technology

Effective atomic number studies in different body tissues and amino acids

K Singh* & Gagandeep

 

442

News Scan

Fibre-optic telecommunications

J B Dhawan

 

450

Addendum

452

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*The corresponding author has been indicated by (*) mark in case of papers with more than one author

 

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 385-392

Vibrational analysis of 2-chloroheptane

*Neena Jaggi & R M P Jaiswal

Infrared and Raman spectra of 2-chloroheptane were recorded at ambient temperatures as pure liquid. Fundamental frequencies of 2-chloroheptane have been identified by carrying out the analysis of these spectra. Normal coordinate calculations have been made for the five probable conformations of the molecule by transferring force-constants from the studies of 2-chlorohexane. All the observed frequencies in the spectra could be assigned to the five conformations within an average frequency error 6.4 cm-1.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 393-395

Thomas-Fermi calculations for atoms in high magnetic field

using realistic model

O H Mobarek & E Al-Laheani

An approximate solution of the Thomas-Fermi equation for positive ions in a high magnetic field is obtained by making use of the variational principle. The radial wavefunctions of the hydrogen-like atom are used as the trial function that contains some variational parameters and satisfies the appropriate boundary and the normalization conditions. These parameters are determined by extemalizing the variational expression with respect to the parameters. These parameter values are then used to obtain the desired physical quantities. The initial slope of the variational trial function for several ions is obtained from which the energy and the ionization energy can be found. The results of the present calculation are in good agreement with those available in literature.

 

Indian J Pure & Applied Physics

Vol. 40, June 2002, pp. 396-401

Ultrasonic pulse-broadening and attenuation in

volcanic rock - A case study

M V M S Rao, L P Sarma & K J Prasanna Lakshmi

Ultrasonic pulse-broadening measurements at 1.0 MHz frequency have been carried out at the ambient conditions in a set of volcanic rocks of south-east Gujarat. The experimental data have been processed along with the results of P-wave velocity (Vp) measurements leading to the determination of internal friction (Qp-1) and attenuation (ap). The attenuation in rhyolites is relatively high (average Qp-1 = 0.0051, ap = 0.0330 dB/cm) compared to basalts (average Qp-1 = 0.0019, ap = 0.0100 dB/cm) which are fine-grained and well crystallized. The mineral composition, in particular, the volume percentage of ground mass in rhyolites is found to have a strong control on both the attenuation and velocity of the rock samples tested. The experimental method is briefly described and the results obtained are presented and discussed.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 402-406

Pair-breaking effects on charge imbalance in superconductors

B A Mattoo

Using quasi-classical Green function, a general formalism for calculating charge imbalance and its relaxation in non-equilibrium superconductors is presented. The formalism is applicable at arbitrary temperatures, under conditions when the width of quasi-particle state is appreciable due to pair breaking processes and when strong-coupling effects are significant. In the limit of small pair-breaking and for a weak coupling superconductor the collision term in the formalism reduces to the one in the quasi-particle Boltzmann equation.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 407-416

Semimetal-semiconductor transition in Bi-In system

Sanjeeta Rani &G K Chadha

Department of Physics and Astrophysics, Delhi University, New Delhi 110 007

Received 25 February 2002; accepted 18 April 2002

Semimetal-semiconductor transition in Bi-doped with 4 at. % In single crystal is reported for the first time. Resistivity and Hall coefficient measurements performed on single crystalline sample of Bi-In (4at.%) system for an extensive range of temperature from 4.2-300 K, reveal semiconducting behaviour explicitly in the range 30-130 K. Electronic parameters, i.e. carrier concentration and Hall mobility are calculated for the entire temperature range of 4.2-300 K. The pair of light mass bands at LC and Lv moves up relative to the TV band resulting in the disappearance of the overlap between the LC band and the TV band and an energy gap of the order of 37.3 MeV is introduced between the light electron (LC) and heavy hole (TV) band. Further, the direct band gap between Lc and Lv bands is narrowed to a value of 10.9 MeV in comparison to pure bismuth. An impurity level is also reported on account of doping corresponding to activation energy of 4.1 MeV. Results from microhardness measurements and XRD studies of pure Bi and Bi-In (4 at. %) alloy reveal that In makes complete solid solution with Bi and gains effective entry into the lattice, altering the periodicity of Bloch Potential and modifying the band structure of Bi. This seems to be the reason that the transition from semimetal to semiconductor takes place in the Bi-In alloy.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 417-420

Computation of thermodynamic functions of 2- and

4-phenylpyridine from vibrational spectra

M Isaq*, Sanjiv Arora & R S Kajal**

The complete assignments of the observed frequencies are used to compute the thermodynamic functions, namely, the entropy, heat capacity, enthalpy and the free energy of 2- and 4-phenylpyridine. These functions have been calculated by using standard expressions, at one atmospheric pressure in the temperature range 100-1500 K under the rigid rotator harmonic oscillator approximation.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 421-429

Scattering characteristics of small particles in resonance region:

Effect of shape

J J Joshi1, H S Shah2, S K Sharma3 & R V Mehta4

Scattering characteristics of spherical and nonspherical particles are studied using T-matrix method. Particle size is varied up to radius r = 0.3 micron. Computations are made for two chromatic pigments namely red and green with aspect ratio varying from 1 to 6 for three wavelengths l = 440, 560 and 680 nm used in colour calculations. Results show that the effect of shape is predominant on scattering characteristics of particles in resonance region. Scattering parameters are used to calculate reflectance of pigment system using many-flux multiple scattering theory. Results show that deviations in pigment shape from sphericity have remarkable effect on reflectance and hence on colour exhibited by pigment dispersions.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 430-435

Dielectric relaxation in ternary mixtures of benzotrifluorides

G D Rewar & D Bhatnagar

Dielectric relaxation in four ternary systems of benzotrifluorides consisting of benzotrifluoride, 2-chloro-benzotrifluoride and 2-amino-benzotrifluoride has been studied at 9.408 GHz over a temperature range 290-330 K. Static dielectric constant and refractive index of individual components of these benzotrifluorides and their mixture compositions have been measured. The measured dielectric data of these benzotrifluorides have been discussed in terms of distribution of relaxation time and its variation with temperature. The process of dipole orientation and viscous flow in these liquids has been discussed on the basis of rate theory. Various thermodynamical parameters viz. entropy, enthalpy and free energy of activation have been determined using measured dielectric data. These calculated thermo dynamical parameters for relaxation processes and viscous flow processes confirm existence of both inter-molecular and intra-molecular orientations in these substituted benzotrifluorides. These polar compounds under investigation have been used in pure form as dielectric samples. The methods used to obtain results presented in this paper are based on the measurement of standing wave pattern in a dielectric medium.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 436-441

Temperature and frequency dependent dielectric constant/loss studies in pristine and high temperature annealed poly (p-phenylene sulphide)

J K Quamara, N Singh1 & Azad Singh

Temperature and frequency dependent dielectric behaviour has been investigated for pristine and high temperature annealed poly p-phenylene sulphide (PPS) in the temperature range 30 to 250 C at frequencies 120 Hz, 1, 10 and 100 kHz. Samples used were in the form of pellets. A continuous decrease in dielectric constant from 30 to 140 C is according to Kirkwood model. A dipolar relaxation process (b-relaxation) associated with the newly formed cross-linked structure due to annealing and rigid amorphous phase (RAP) dipolar relaxation (d-relaxation) have been held responsible to dominate the dielectric behaviour in the temperature region 140 to 190 C and making e temperature independent in this temperature region. A dielectric loss maxima observed between 140 to 160 C confirms b-relaxation. Above 190 C, the crystalline-amorphous region with RAP as interface material leading to interfacial polarization (a-relaxation) has been held responsible for increasing the e value with temperature. The a-relaxation is confirmed through a dielectric loss peak in e-T curve around 230 C. The frequency dependent nature of the a-loss peak shows its distributive nature in relaxation time. A decrease in the a- and b-loss peak magnitudes in high temperature annealed samples is due to increase in crystallinity.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 442-449

Effective atomic number studies in different body tissues

and amino acids

K Singh* & Gagandeep

Effective atomic numbers (Zeff) of body tissues and amino acids have been calculated theoretically over a wide energy range from 10-3 to 105 MeV. The significant variations in Zeff due to composition of the material and domination of different interaction processes in different energy regions were observed.

 

Indian Journal of Pure & Applied Physics

Vol. 40, June 2002, pp. 450-451

News Scan

Fibre-optic telecommunications

Scientists engaged in R&D research are now underway to give birth to photonic crystal lasers, light-emitting diodes (LEDs), and photonic crystal thin films to serve as anti-counterfeit protection on credit cards. Ultimately, researchers hope to build diodes and transistors from this novel material that will one day enable the construction of an all-optical computer. It is possible to create energy levels in the photonic bandgap by introducing defects. For example, changing the size of a few of the holes in a photonic crystal is "equivalent to breaking the perfect periodicity of the silicon-crystal lattice", says Greg Parker, a professor of photonics at Southampton University in England. (Parker & Charlton, Physics World, (2000), p. 129). Thus, although perfect crystals are valuable for fabricating dispersive elements such as superprisms and three-dimensional (3-D) mirrors, those with defects enable researchers to custom- design photonic crystals that allow precise control of the frequencies and directions of propagating electromagnetic waves. This feature makes them especially useful in optical telecommunications and as laser sources. In this sense, the huge optical telecommunication market is close to reap the benefits of photonic crystals research.