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Indian Journal of Pure and Applied Physics

 

 

 

 ISSN: 0019-5596

CODEN: IJOPAU 42 (9) 625-706

Volume 42

Number 9

SEPTEMBER 2004

 

CONTENTS

Atomic and Molecular Physics

 

Numerical evaluation of lead equivalence of patient and hardware materials in medical diagnostic X- ray shielding

Akintunde Akangbe Okunade

629

Fluorescence quenching of anthracene by aniline in different solvents

Annoji Reddy, J Thipperudrappa , D S Biradar, M T Lagare & S M Hanagodimath*

648

 

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

 

Optoelectronic properties of mercuric iodide crystals for radiation detection

S L Sharma*, G Anil Kumar & H N Acharya

653

 

Molecular interactions in binary mixtures of tetrahydrofuran with alkanols(C6, C8, C10): An ultrasonic and volumetric study

Anwar Ali*, Anil Kumar Nain , Vinod Kumar Sharma & Shakil Ahmad

666

 

Analysis of coupling characteristics of rectangular core optical waveguide coupler

D Engles & S S Malik*

674

 

Condensed Matter: Structural, Mechanical and Thermal Properties

 

 

Thermodynamic properties of some simple metals in liquid phase by pseudopotential theory

P B Thakor*, V N Patel, B Y Thakore, P N Gajjar & A R Jani

684

 

Statistical associating fluid theory-dimers of the solid phase of the pearl-necklace model

Vivek Kumar Singh & K N Khanna*

688

 

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

 

Depolarization studies of polyvinylidene fluoride foil electrets using thermally stimulated discharge

P K Khare, Devendra K Sahu , Ashutosh Verma & Rudra Kant Srivastava*

693

 

Interdisciplinary Physics and Related Areas of Science and Technology

 

Current-mode lowpass, bandpass and highpass biquads using a single current feedback amplifier

N A Shah*, M F Rather & S Z Iqbal

697

 

High input impedance allpass networks using four terminal floating nullor

N A Shah* & M A Malik

                 700

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

 

Indian Journal of Pure & Applied Physics

Vol. 42, September 2004, pp 629-647

 

Numerical evaluation of lead equivalence of patient and hardware materials in
medical diagnostic X-ray shielding

Akintunde Akangbe Okunade

 

Numerical comparison of attenuation and hardening properties of phantom (lucite, soft tissue, water) and hardware (aluminium and steel) materials with those of lead has been carried out. Results show that the shieldings that are affordable by lead attenuation equivalent thicknesses (LAE) and lead hardening equivalent thicknesses (LHE) are not strictly equivalent to those affordable by thickness of substitutes (phantom materials, aluminium and steel) when there are differences in attenuation and hardening properties. Even though beams through LAE that are not ‘exact’ have equal exposure values, the half value layers are higher than those through thickness of lead substitutes. Example calculations show that the use of lead thickness (LAE) that are not ‘exact’ to account for the shielding afforded by the thickness of patient (water phantom) produce lesser reduction of primary radiation level in the area marked for shielding. The ‘exact’ LAE that will reduce primary radiation level equally as the patient and radiographic table may be higher by close to 20 % or more of that which is not ‘exact’.

 

[Keywords: Attenuation properties, Hardening properties, Primary radiation level, Attenuation equivalent thicknesses, Hardening equivalent thicknesses]

IPC Code: G 01 L 1/25

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 648-652

 

Fluorescence quenching of anthracene by aniline in different solvents

Annoji Reddy, J Thipperudrappa, D S Biradar, M T Lagare &

S M Hanagodimath

 

Fluorescence quenching of anthracene by aniline in five different solvents has been carried out at room temperature with a view to understand the quenching mechanisms. Experimental results show positive deviation in the Stern-Volmer plots in all the solvents studied. In order to interpret these results the ground state complex and sphere of action static quenching models have been invoked. Using these models various rate parameters have been determined. Ground state complex formation model is found not to be applicable. Using sphere of action static quenching model various rate parameters have been determined. The magnitudes of these parameters imply that sphere of action static quenching model agrees well with the experimental results. Hence, the positive deviation in the S-V plots is attributed to the static and dynamic quenching. Further, with the use of finite sink approximation model it has been observed that these bimolecular reactions are diffusion limited. The dependence of Stern-Volmer constant on dielectric constant of the solvents suggests the charge transfer character of the excited complex.

 

[Keywords: Fluorescence quenching, Anthracene, Aniline, Stern-Volmer plots]

IPC Code: C 09K 9/00

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 653-665

 

Optoelectronic properties of mercuric iodide crystals for radiation detection

S L Sharma, G Anil Kumar & H N Acharya

 

Optoelectronic properties of some red mercuric iodide (a-HgI2) crystals have been studied for wavelengths 450-700 nm at temperatures 80-300 K. These crystals were grown (a) by solvent evaporation from a-HgI2-tetrahydrofurane saturated solution, (b) by hydration of a-HgI2-dimethyl sulphoxide-methanol saturated solution and (c) by polymer controlled growth (PCG) in vapour phase. Important aspects of optical generation of the charge carriers have been discussed. The measurements of thermally stimulated currents were also carried out in order to understand the temperature dependence of photocurrents in different wavelength regions. With the computer simulation of the photocurrent versus wavelength spectrum, the room temperature transport properties (the mobility-lifetime products and surface recombination velocities of the two charge carriers) for the crystals of three types have been estimated. For a typical electric field strength of about 2´103 V/cm, the electron drift lengths for the crystals of three types were found to be 1150, 1350 and 6500 mm, respectively, whereas the hole drift lengths were found to be 50, 50 and 150 mm, respectively. As the typical thickness of a-HgI2 photodetector for any scintillation spectrometer is about 300 mm, under the negative electrode illumination, all the three types of a-HgI2 crystals present high potential for their use as photodetectors in conjunction with most of the scintillators.

 

[Keywords: Mercuric iodide; Photoresponse; Radiation detector; Scintillation spectrometer]

IPC Code: H 01 J 49/00

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 666-673

 

Molecular interactions in binary mixtures of tetrahydrofuran with alkanols (C6,C8,C10) : An ultrasonic and volumetric study

Anwar Ali, Anil Kumar Nain, Vinod Kumar Sharma & Shakil Ahmad

 

The densities and ultrasonic speeds in binary mixtures of tetrahydrofuran (THF) with alkanols (1-hexanol, 1-octanol and 1-decanol) have been measured over the whole composition range at 35 °C. Isentropic compressibility, intermolecular free length, relative association, molecular association, acoustic impedance, excess compressibility, excess molar volume, excess acoustic impedance and excess partial molar volume of alkanols in THF were calculated using the values of density and ultrasonic speed. The variation of these parameters with composition indicates that the disruption of associated structure of alkanols on addition of THF dominates over that of weak interaction between unlike molecules in all the three systems investigated. Moreover, a comparison of theoretical ultrasonic speeds, calculated by using collision factor theory (CFT), free length theory (FLT), Nomoto’s empirical relation and Van Dael-Vangeel’s ideal mixing relation, with those obtained experimentally reveals that CFT, FLT and Nomoto’s relation predict the data well than ideal mixing relation.

 

[Keywords: Molecular interactions, Binary mixtures, Ultrasonic study, Tetrahydrofuran]

IPC Code: B 01 J 19/10

 

 

 

Indian Journal of Pure & Applied Physics

Vol. 42, September 2004, pp 674-683

 

Analysis of coupling characteristics of rectangular core optical waveguide coupler

D Engles* & S S Malik**

 

A theoretical formulism based on the boundary matching technique has been proposed to study the systematic of an asymmetric waveguide coupler. Same formulism is applicable to a symmetric coupler. The equivalent parallel coupling length to account for the coupling in the two S-shaped regions in the input and the output of the coupler is obtained from the coupler geometry and is dealt with more accurately and sensitively in our calculations. No fitting parameter is required for our calculation. The calculated characteristics of the asymmetric coupler are very close to those of experimental ones. Our model can aid in the design of diffused channel single mode rectangular core optical waveguide couplers.

 

[Keywords: Asymmetric couplers, Broadband couplers, Boundary matching technique]

IPC Code: H 01 P 3/20

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 684-687

 

Thermodynamic properties of some simple metals in liquid phase by pseudopotential theory

P B Thakor, V N Patel, B Y Thakore, P N Gajjar & A R Jani

 

The Gibbs-Bogoliubov (GB) variational method is applied to investigate the thermodynamic properties of some simple metals in liquid phase viz; Mg, Cd, Al, In, Tl and Pb using pseudopotential theory. For description of the structure, charged hard sphere (CHS) model is used as a reference system. Our well established model potential is used to describe the electron-ion interaction. The local field correction function proposed by Sarkar et al. Mod Phys Lett B, 12 (1998) 639 is applied for the first time to introduce the exchange and correlation effects in the study of thermodynamics of these metals. The comparison with the experimental findings establishes the use of Sarkar et al. screening function in such study.

 

[Keyword: Thermodynamic properties, Pseudopotential theory, Charged hard sphere model]

IPC Code: G 01 K

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 688-692

 

Statistical associating fluid theory-dimer of the solid phase of the pearl-necklace model

Vivek Kumar Singh & K N Khanna

 

Statistical associating fluid theory-Dimer (SAFT-D) of chain molecules for liquid phase is extended to model the solid phase of chains. The model of freely jointed chains of tangent hard spheres requires the equation of state of hard sphere monomers in solid phase and contact values of the radial distribution function of the dimer molecules for solid phase. The theoretical results for the equation of state and free energies for the chains up to 8 mers are compared with simulation results. The agreement between theory and simulation is improved over the recent results of Vega and MacDowell (Vega C and MacDowell L G, J Chem Phys, 114(2001) 10411) employing thermodynamics perturbation theory of first order (TPT-1).

 

[Keywords: Fluid theory, Dimer, Pearl- necklace model, Perturbation theory]

IPC Code: G 01 K

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 693-696

 

Depolarization studies of polyvinylidene fluoride foil electrets using thermally stimulated discharge

P K Khare1, Devendra K Sahu2, Ashutosh Verma3 & Rudra Kant Srivastava3

 

Thermally stimulated discharge current (TSDC) in foils of polyvinylidene fluoride (PVDF) was measured under various polarizing conditions. The TSDC thermograms were recorded by reheating the samples at a linear rate of 3 oC/min. It was found that samples give rise to a peak around (100 ± 10 oC). The peak position is not consistent with the polarization fields and temperatures. The activation energy associated with the peak is found to be ~ 0.62 eV. The dependence of TSD current and TSDC data on polarizing agents, i.e. field and temperature is explained on the basis of theoretical predictions. The space charge polarization contributes significantly to the polarization of the polymer.

 

[Keywords: Electrets, Thermally stimulated discharge, Polyvinylidene fluoride]

IPC Code: H 01 G 7/02

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 697-699

 

Current-mode lowpass, bandpass and highpass biquads using a single current feedback amplifier

N A Shah, M F Rather & S Z Iqbal

 

A novel current-mode second-order filtering configuration employing an inverting current feedback amplifier (CFA) and four passive elements is presented. The circuit can realize simultaneously lowpass (LP) and bandpass (BP) functions. The circuit supports realisation of highpass (HP) and bandpass (BP) filtering responses as well through RC : CR transformation. All passive sensitivities are low. The circuit has been simulated using Personal Computer-Simulation Programme with Integrated Circuit Emphasis (PSPICE) and simulation results are found to be in close conformity with the theoretical values.

 

[Keywords: Current feedback amplifier, Biquads, Current-mode lowpass]

IPC Code: H 03 K 3/00

 

 

 

Indian Journal of Pure & Applied Physics

 Vol. 42, September 2004, pp 700-702

 

High input impedance allpass networks using four terminal floating nullor

N A Shah & M A Malik

 

Two novel circuits to realize high input impedance voltage-mode allpass filter functions each using a single four terminal floating nullor (FTFN) and four passive components have been presented. The realizibility condition is simple and temperature invariant being in the form of resistor ratio. The phase besides being adjustable by the frequency of applied voltage signal can also be controlled by adjusting the values of passive components without disturbing the realizibility condition. Simulation results are also included.

 

[Keywords: Four terminal floating nullor, Allpass filters, High input impedance]

IPC Code: H 03 H1/00