Indian Journal of Pure and Applied Physics

Investigation of the equation of state of hot and cold neutron matter using Gogny D1 effective interaction is presented. The binding energy per particle, spin symmetry energy, free energy, pressure, entropy, sound velocity and magnetic susceptibility are calculated as a function of density r fm^-3. The calculations cover a wide range of densities and are discussed in comparison with the realistic interaction calculation of Friedman and Pandharipande [Nucl Phys A, 361 (1981) 502].

Titania films deposited by thermal evaporation as

humidity sensor

The humidity sensors based on optical methods are best suited for those situations where remote analysis capability, high sensitivity and compactness of the device are the criteria for the measurement of humidity levels. The sensing element of optical humidity sensors consists of a rutile structured TiO₂ thin film deposited on the base of an isosceles glass prism. Such a TiO₂film is porous and highly sensitive to humidity. Light from He-Ne laser source enters the prism from one of the isosceles faces of the prism, and then gets reflected from the glass film interface, before emerging out from the other isosceles face of the prism. The emergent beam is collected through an optical fiber, which is connected to an optical power meter for measurement. Variations in the intensity of light caused by changes in humidity lying in the range 5-95% have been recorded.

Ultrasonic study of some ophthalmic solutions in

aqueous medium

Seven ophthalmic systems belonging to one class, which reduce the intra-ocular pressure have been chosen for an ultrasonic study. These solutions have pilocarpine nitrate/pilocarpine hydrochloride/timolol maleate as major components. Ultrasonic velocity and density have been measured in the aqueous solutions of these ophthalmic systems at 308.15 K. The deviations in velocity and compressibility have been computed. The effect of these systems on the structure of water has also been analyzed, employing Jacobson’s theory of adiabatic compressibilities.

Ultrasonic studies on molecular interaction of certain carbonyl compounds in n-hexane and chloroform solutions

The ultrasonic velocities (U), densities (r), and viscosities (h) are measured in n-hexane and chloroform solutions of acetophenone, ethyl methyl ketone and benzaldehyde at 298 K, in the concentration range 0.05-1 M. The variation in ultrasonic velocity values indicate solute-solvent interactions in both the media and stronger interactions are observed in chloroform solutions. Acoustical parameters such as adiabatic compressibility (b), linear free length (L_f), relaxation time (t), absorption coefficient (a/f²), molecular interaction parameter (c), and solvation number (S_n) values are also calculated. These values indicate that, the carbonyl compounds are strongly attracted by chloroform molecules probably through inter molecular hydrogen bond.

Security holograms readable with an encoded key hologram

A simple and cost effective two-step method for making security holograms, which are readable with an encoded key hologram, has been presented. These security holograms contain an additional security feature which can be read only by using an encoded key hologram in the reading process. In the final reading process, the sharp focus spot emerges only when the security hologram is illuminated by the decoding, reconstructing beam generated from the encoded key hologram. Since the verification/identification pattern in these holograms is a sharp focus spot rather than an image pattern, this type of security holograms are suitable for both visual as well as machine inspection. They can also be used as security codes for better protection against counterfeiting in the embossed holograms. Experimental results achieved have been discussed.

Measurement of heat storage coefficient of
solid-solid-air mixtures at different pressures

Using a plane heat source technique, the heat storage coefficient (HSC) of some varieties of selected three phase systems (solid-solid-air mixture) like, loose cement dispersed with marble powder, aluminium powder and iron powder respectively, has been measured at varying interstitial air pressures. The behaviour of the HSC values with the variation of pressure between the range 0.1 to 760 mm of mercury has been discussed. There is a marked change in the values of HSC for increase or decrease in the pressure region from 0.1 to 760 mm of mercury.

Thermal evaporation of diglycine hydrogen fluoride crystals

Diglycine hydrogen fluoride crystals have been grown from aqueous solution by slow evaporation technique, at room temperature. Thermal evaporation at the surface of the crystal shows formation of boat-shaped pits, in accordance with the (100) symmetry of cleavage face, with density of pits concentrated in some regions. The sizes of the pits increase at the same sites on prolonged thermal etching and show correspondence of few pits on matched counterparts. The rare evidence of mismatch of new domains is detected. The presence of typical circular feature, pits formed on domains, thick and thin domain lines and the glide band due to thermal stresses are illustrated.

Frequency distribution function of phonons in
different layers of graphite

Variation in the phonon frequency distribution function has been computed, using recently suggested unfolding technique by the authors, from the temperature-dependent mean square displacement of a carbon atom on a graphite surface, when different number of graphite layers are added on either side of it, ranging from 3 to 13 and then to a very large number. The cross-over of the dynamics from nearly two-dimensional to quasi two-dimensional situation is thus studied.

Measurement of effective thermal conductivity and
thermal diffusivity for assessing the integrity of
fiber to matrix bond in natural fiber composite

Thermal conductivity and thermal diffusivity of pineapple leaf reinforced phenol formaldehyde composite have been studied with special reference to chemically treated fibers using the transient plane source (TPS) technique, at room temperature and normal pressure. All the composites were made of 40% fiber by weight. The fibers were treated with alkali, silane and toluene diisocyanate. It was found that, thermal conductivity and thermal diffusivity of the composites increase after chemical treatment. The thermal conductivity of alkali treated fiber was found to be maximum in the present study. The thermal conductivity of treated and untreated fibers was calculated theoretically by Bruggman's model. The results of model calculation showed an increase of thermal conductivity of treated fiber over the thermal conductivity of untreated fiber.

Temperature dependence of exciton life-time in
GaAs/AlGaAs quantum wells

In GaAs/AlGaAs quantum well structures, the confinement of electrons as well as, holes in GaAs well region causes enhancement of Coulomb interaction, which leads to formation of excitons with large binding energy, and, therefore, excitonic states persist even up to room temperature. The phenomenon of photoluminescence (PL) in such structures is dominated by radiative recombination of excitons. The PL and PL decay time is found to depend on temperature. At higher temperatures, thermal population of higher excitonic sub-bands and exciton ionization also need to be considered. The temperature dependence of radiative and non-radiative exciton life-times have been formulated. The nonlinear behaviour of temperature dependence of total life-time of exciton or the PL decay time has been indicated. At low temperatures, exciton decay is mainly due to radiative processes whereas at higher temperatures, it is by non-radiative channels. Therefore, the life-time of exciton, initially, increases with temperature, attains a maximum value and then decreases at high temperatures. The processes different from radiative free exciton recombination also play an important role and possibly, dominate the recombination mechanism as the temperature is raised.

Study of dark and photoconductivity of

Sb-doped CuInSe₂ thin films

Dark and photoconductivity measurements of un-doped and Sb-doped CuInSe₂ (CIS) films prepared by pulsed laser deposition technique, using ArF laser have been reported. The dark and photoconductivity of Sb-doped films have been found to be higher, compared to the un-doped CIS films. Recombination mechanism has also been discussed in the doped and un-doped films.

Charge imbalance in a non-equilibrium superconductor

A general formalism for charge imbalance in a non-equilibrium superconductor is obtained using x-integrated Green’s function, which is applicable at arbitrary temperature, even when the width of quasi-particle states is appreciable due to pair breaking processes and when strong coupling effects are significant.

Effect of charge transfer behaviour on the

dielectric and ac conductivity of Co-Zn ferrite

doped with rare earth element

The dielectric constant e¢ and ac conductivity were measured for the ferrite samples Co_1-xZn_xLa_0.25Fe_1.75O₄; 0.1≤x≤0.7 at different temperatures as a function of the applied frequency. The dielectric constant was interpreted on the basis of changing the enthalpy as well as the internal energy of the system. The orientational and rotational polarizations play a significant role in increasing the value of e¢ in the second temperature region. The conductivity results give more than one straight line, indicating the different conduction mechanisms. The electron hopping between the iron ions and the hole hopping between the cobalt ions are the main conduction processes in the investigated samples as it was enhanced from the drift mobility data. The values of the activation energy obtained, indicate the semiconducting behaviour of the samples.

ISSN: 0019-5596		CODEN:IJOPAU 41(9) 671-742(2003)
VOLUME 41	NUMBER 9	SEPTEMBER 2003