**Indian Journal of Pure & Applied Physics**

**Vol. 40,
October 2002, pp. 683-689**

Effect of ammonium halides on the temperature of sound
velocity maximum of water

G
Venkata Ramana, E Rajagopal & N Manohara Murthy

Effect of ammonium halides on
the temperature of sound velocity maximum (TSVM) of water has been studied by
determining the ultrasonic velocity with an accuracy of ± 0.003 % using
single-crystal variable-path interferometer working at 3 MHz. The velocity
measurements were carried out at @ 2 °C intervals over a range
of 5 °C to either side of the TSVM of the solutions. The accuracy in fixing the
TSVM is ± 0.2 °C. The shift in TSVM of water due to the addition of the NH_{4}Cl,
D*T*_{obs}, is found to be positive up
to *w* @ 3.4 × 10^{-2} and
negative thereafter, where *w* represents weight fraction of the solute. The
shifts in TSVM of water due to the addition of the NH_{4}Br and NH_{4}I
are found to be negative throughout the concentration range. The structural
contribution to the shift in TSVM of water, D*T*_{str}, is found to be positive for
NH_{4}Cl and increases with increase in the concentration nonlinearly. D*T*_{str} for NH_{4}Br is
almost zero up to *w* @ 3 × 10^{-2} and
thereafter becomes negative. D*T*_{str} for NH_{4}I is found
to be negative throughout the concentration range. The results are explained in
terms of the structure, making and breaking nature of anions and cations
present in the solutions.

**Indian Journal of Pure & Applied Physics**

**Vol. 40,
October 2002, pp. 690-693**

Squeezed states in third harmonic generation

Jawahar Lal, R M P Jaiswal & B S Rajput

Field amplitude squeezing of
the third harmonic mode in a non-linear crystal has been investigated and it
has been shown that the squeezing occurs for selective phase values of the
fundamental mode of the incident light when calculated up to fourth power of the
interaction time. It is also shown that, the squeezing occurs with Poissonian
photon-statistics of the field.

**Indian J Pure & Applied Physics**

**Vol. 40,
October 2002, pp. 694-700**

Induced twist grain boundary phase in the binary mixtures of cholesteryl caprylate and nonyloxybenzoic acid

Ravindra
Dhar and A K
Srivastava & V K Agrawal^{}

Binary mixtures of
cholesteryl caprylate (ChC) and nonyloxybenzoic acid (NOBA) having different
mole ratios have been studied using differential scanning calorimeter (DSC) and
polarizing microscope (PM). ChC has monotropic chiral nematic (N*) mesophase in
the cooling cycle whereas, NOBA has enantiotropic nematic (N) and smectic C
(SmC) mesophases. Transition temperatures and enthalpies of these mixtures have
been determined with the help of DSC, whereas different mesophases have been
identified by their typical textures as viewed under polarizing microscope.
Addition of NOBA in ChC induces smectic A (SmA) and twist grain boundary A
(TGBA) phases between two critical concentrations.

**Indian Journal of Pure & Applied Physics**

**Vol. 40,
October 2002, pp. 701-708**

Field-dependent sound attenuation in barium titanate,
strontium titanate and potassium tantalate type perovskites

D S
Lingwal, U C Naithani & B S Semwal

A theoretical expression for attenuation constant in para-electric phase is described. Taking electric field as parameter, variation of attenuation constant with frequency and temperature is also discussed by considering third and fourth order anharmonic interactions. The attenuation constant increases with increasing temperature and frequency in presence of an electric field. In the vicinity of the Curie temperature, the attenuation constant increases anomalously. The results obtained are compared with the results of others.

**Indian Journal of Pure & Applied Physics**

**Vol. 40,
October 2002, pp. 709-713**

MHD free
convective flow through a porous medium

between two vertical parallel plates

Atul Kumar Singh

Free convective flow of a viscous, incompressible, electrically conducting fluid through a porous medium between two vertical parallel plates which are heated or cooled uniformly, under a pressure gradient in presence of uniform transverse magnetic field has been studied. The governing equations are solved to obtain approximate analytical solutions for velocity field and temperature distribution for small values of Rayleigh number, using regular perturbation technique. Two physical situations, namely, steady heating of ascending cold fluid (SHACF) and steady cooling of ascending hot fluid (SCAHF) have been investigated. The effect of various parameters on velocity field, temperature distribution, mass flow rate ratio, friction factor ratio and heat transfer rate has been discussed.

**Indian Journal of Pure & Applied Physics**

**Vol. 40,
October 2002, pp. 750-753**

NOTE

Design and development of an inexpensive, novel OTDR type
system for detection of fiber cracks and breaks

S Kher, S Chaubey, A L Chakraborty, V Bhanage & T P S Nathan

The optical time domain reflectometry signature of few fibers has been recorded using different lasers having different pulse energy. The signature corresponds to the light scattered back by the fiber towards the input end, versus time. One of the fiber signatures, obtained using nitrogen laser as light source, clearly displays few spikes corresponding to minor cracks in it. Suitability of this laser for OTDR applications has been tested.

**Indian Journal of Pure & Applied Physics**

**Vol. 40,
October 2002, pp. 714-719**

Lattice dynamics of thorium using semi-nonlocal pseudopotential

J K
Baria, P N Gajjar & A R Jani

A semi-nonlocal
pseudopotential is proposed to calculate lattice dynamics of fcc thorium. A unique
technique is suggested to determine the parameter of the potential. A new
criterion for the selection of screening function is suggested, for the first
time, to incorporate exchange and correlation effects in the pseudopotential
form factor. The present calculations have produced relatively better
theoretical values compared to earlier reports for phonon dispersion curves, *C*_{11},
*C*_{12}, *B* and the propagation velocities of elastic
waves.

**Indian Journal of Pure & Applied Physics**

Vol. 40, October 2002, pp. 720-725

Integrating
communication with sensing

**micro-bending
of multi-mode optical fibre**

H K
Sardana, Gaurav Julka & J K Chhabra

Environment perturbations on
a multi-mode fibre lead to changes in intensity at the output due to bending
induced losses. A carrier signal has been modulated in a form such that, the
amplitude of the light signal is not affected, which is left for sensing light
intensity variations due to micro-bending. Pulse frequency modulation has been
suggested for this purpose using a voltage-to-frequency converter. This
information is again decoded at the receiver end using frequency-to-voltage
conversion. In this manner, a fibre link, which is acting as a perturbation
sensor, also acts as a communication link without affecting the sensing
capability as long as the link is not damaged due to perturbation. It is known
that, the multi-mode fibre can be used to sense any form of environment
perturbation, such as strain, pressure, force, position, acceleration,
temperature etc^{1-3}. The proposed approach is applicable in all these
situations with integrated communication capability.

**Indian Journal of Pure & Applied Physics**

Vol. 40, October 2002, pp. 726-731

Electrical properties of boron delta-layers in silicon

M O
Hakim & M Mozibur Rahman

Electrical properties of MBE
grown boron d-layer in Si have been
investigated in the temperature range 10-300 K and a comparative study with
their uniform doping counterpart has been_{ }presented. Various boron
doping levels from 10^{12}-10^{14} cm^{-2} in the d-layer
show that, with the fall of temperature from 300 to 50 K, Hall mobility first
increases followed by a rapid decrease, and at temperature £50
K, it becomes almost constant. Higher doping level in the sample grossly lowers
the value of Hall mobility but its variations with temperature are almost
similar to each other. Existence of the dominant carrier scattering mechanism
has also been reported. In all the samples, freeze-out of carriers have been
clearly noticed below 100 K. Existence of a Mott metal-non-metal transition in
the sample has been observed at low temperature region when the doping
concentration exceeds a critical high value of 6´10^{13}_{ }cm^{-2},
and this has been found consistently with the other observations like zero
activation energy and negative TCR. The value of minimal metallic conductance
for the samples has also been reported.

**Indian Journal of Pure & Applied Physics**

**Vol. 40, October 2002, pp. 732-742**

Analytical models for the angular distributions of

filter-generated scatter in diagnostic radiology

A A Okunade, F O Ogundare & L A Hussain

Analytical models for
describing large volume of data on angular distributions of photons that have
undergone Compton & Rayleigh interactions while passing through spectrally
equivalent filter materials commonly considered useful in diagnostic radiology
have been developed. The comparison of the results of simulation of scatter data
from these filter materials, using Monte Carlo techniques with those from the
models developed, are in reasonable agreement.

**Indian Journal of Pure & Applied Physics**

**Vol. 40, October 2002, pp. 743-749**

**Empirical
scaling relationships between earthquake magnitudes, epicentral distances and
amplitudes of
radon anomalies in N-W Himalaya**

Vivek Walia, H S Virk & Puneet Kumar

Radon data accumulated during
the time-window (1992-1999) in the grid (30-34^{o}N, 74-78^{o}E)
in N-W Himalaya has been analysed vis-a-vis seismic data recorded in the same
area, supplied by Indian Meteorological Department (IMD) network. In general,
there is a positive correlation between total radon emission and the
micro-seismicity in the area under investigation. The earthquake magnitude has
moderate positive correlation with epicentral distance and low positive
correlation with amplitude of radon precursory signal, whereas, both show low
negative correlation between them. Empirical scaling relations are proposed
using the best-fit straight line from the log-linear graphs between magnitude
of the events (*M*) and log of the product of amplitude of radon anomaly (*A*)
and epicentral distance (*D*). The error between recorded and the
calculated magnitude is also taken into account. The number of points lying
within ± 25 % limit is 74 out of the
total 142 cases, on which the test is applied. The error range is higher at
lower epicentral distances and magnitudes, which shows that, the local geology
and tectonics have predominant influence on radon signals.

**Indian Journal of Pure & Applied Physics**

**Vol. 40, October 2002, pp. 754-754**

**News Scan**

**New
reliable sensors for magnetic field measurement using silver chalcogenides**

With the
advancement of technology, the demand of scientists entering new frontiers of
research such as, investigation of novel quantum states, magnetic resonance
imaging, etc., for a steady magnetic field of higher and yet higher value has
been realized. Today, compact magnets with a steady magnetic field of 20 T and
a pulsed field of 40 T, are routinely produced. Pulsed fields in the range
50-300 T from 10^{–8} to 10^{–6} s pulses have also been
achieved. The problem faced however is, measurement of such high magnetic
fields with accuracy and consistency, thus requiring a magnetic field sensor
that works over a wide range of magnetic field and is insensitive to
temperature