Indian Journal of Pure and Applied Physics

 

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VOLUME 40                                                      NUMBER 3                                                        MARCH  2002

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CONTENTS

 

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

Effect of magnetic field dependent viscosity on ferroconvection in rotating medium

G Vaidyanathan*, R Sekar & A Ramanathan

 

 

 

159

Effect of magnetic field dependent viscosity on ferroconvection in sparsely distributed porous medium

      G Vaidyanathan*, A Ramanathan & S Maruthamanikandan

 

166

Rate intensification of mass transfer process using ferrofluids

      A K Suresh* & S Bhalerao

 

172

Couette flow of ferrofluid under spatially uniform sinusoidally time-varying magnetic fields

     S Jothimani* & S P Anjali Devi

185

Gauge interferometry-sans the use of expansion coefficient

      Mrityunjay Karfa

196

Condensed Matter: Structure, Mechanical and Thermal Properties

Properties of solids under the effect of high temperature and pressure-NaCl as an example

      Munish Kumar

 

 

 

202

Substitutional effects of La and Cr on CaFe12O19

      N Y Lanje, M Y Salunkhe & D K Kulkarni*

 

221

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

FT-IR analysis of Neyveli lignite and flyash samples

      R Venkatachalapathy*, C Manoharan, T Sridharan & C M Basilraj

 

 

207

Transition assignments to Lb1 satellites in X-ray emission spectra of first transition series

      S N Soni & S Poonia*

 

213

News Scan

Gravitation Sensors

      J B Dhawan

 

225

____________

*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, March  2002, pp. 150-165

Effect of magnetic field dependent viscosity on 

ferroconvection in rotating medium

G Vaidyanathan, R Sekar and A Ramanathan

 

In the present investigation, the authors have studied the effect of magnetic field dependent viscosity of ferrofluid inducing convection in a rotating medium. A linear stability analysis is used. Investigations are made for both stationary and oscillatory modes for various values of the Taylor number, magnetisation parameter and for different coefficient of viscosity. It is found that the field dependent viscosity delays the onset of convection. Numerical computations are made and illustrated graphically also.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 166-171

Effect of magnetic field dependent viscosity on ferroconvection in  sparsely distributed porous medium*

G Vaidyanathan, A Ramanathan & S Maruthamanikandan

The effect of magnetic field on viscosity of ferrofluid-inducing convection in a sparsely distributed porous medium heated from below has been studied. A linear stability analysis is carried out for both stationary and oscillatory modes. It is found that stationary mode alone is favourable when compared with oscillatory mode. The variation of heat dependent viscosity with respect to magnetic field tends to stabilize the system. Numerical results are obtained and are illustrated graphically for various permeability values.

 

Indian J Pure & Applied Physics

Vol. 40, March  2002, pp. 172-184

Rate intensification of mass transfer process using ferrofluids

A K Suresh & S Bhalerao

The rate of inter-phase mass transfer process is of central importance in several processes in the chemical industry. This rate depends on the mass transfer coefficient, which in turn is determined by molecular process taking place in a region close to the phase interface. The mass transfer coefficient is, therefore, not substantially influenced by the mixing processes taking place for away from the interface. In this study the authors present a novel stratagem for enhancement of mass transfer rates by employing ferrofluids in the ‘interfacial region’ and causing them to oscillate using a magnetic field external to the equipment. Taking a gas-liquid system as an example to illustrate the strategy, it is shown that 40-50% increase in mass transfer rates are easily achieved, and that the increase depends on the ferrofluid loading and the strength of the magnetic field employed. Some limitations of the methods employed in the present work are also discussed, and it is possible that much higher enhancements are potentially possible.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 185-195

Couette flow of ferrofluid under spatially uniform

sinusoidally time-varying magnetic fields

S Jothimani & S P Anjali Devi

The authors analysed the behaviour of Couette flow of a ferrofluid under spatially uniform sinusoidally time varying magnetic fields. The imposed magnetic field  ĤZ and magnetic flux density  are spatially uniform and are imposed on the system by external sources. The governing linear and angular momentum conservation equations are solved for flow and spin velocity distributions for zero and non-zero spin viscosities as a function of magnetic field strength, phase, frequency, direction coordinates along and transverse to the plates, as a function of pressure gradient along the plates, vortex viscosity, dynamic viscosity and ferrofluid magnetic susceptibility. Solutions for certain limiting cases are also given.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 196-201

Gauge interferometry-sans the use of expansion coefficient

Mrityunjay Karfa

 

In interferometric calibration of slip gauges, the temperature correction, the most dominant correction embraces two important parameters-one being the temperature itself and the other the coefficient of linear expansion a. In normal practice, for “00” grade slip gauge calibration, a values for all the individual slip gauges within the same set are assumed to be identical and unique which in fact is not true and naturally the follow up action based on this assumption will be error -inviting and accuracy of the calibration work will be the prime casualty. The best way to overcome this problem is to use the technique in such a way that the effect of a, the expansion coefficient, is nullified or neutralised. An approach based on graphical extrapolation technique has been suggested which not only eliminates the problem of using the value of a that one is apprehensive about, but also provides, as a by-product, a method to find the value of a for each and every individual slip gauge in conformity with the assumption that the a-values of individual slip gauges need not always be identical amongst themselves.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 202-206

Properties of solids under the effect of high temperature

and pressure - NaCl as an example

Munish Kumar

A simple theoretical method is used to investigate the properties of solids under varying conditions of temperature and pressure. The case of NaCl is discussed as an example for the entire range of temperature and pressure, viz. from room temperature up to the melting temperature (1000 K) at the pressures varying from atmospheric pressure (referred as P = 0) up to the structural transition pressure (P = 30 GPa). The results obtained for the temperature dependence of thermal expansivity are compared with those based on the widely used Suzuki equation. The results of the pressure dependence of thermal expansivity are compared with Anderson-Masuda relation. The results of Wang and Reeber [Phys Chem Miner, 23 (1996) 354] are also included for the sake of comparison. The good agreement with the available theoretical as well as experimental data, supports the simple method used in the present paper.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 221-224

NOTE

Substitutional effects of La and Cr on CaFe12O19

N Y Lanje, M Y Salunkhe & D K Kulkarni

 

A mixed oxide with chemical formula CaLaCr8Fe3O19 has been synthesized like CaFe12O19 by standard ceramic technique using proper stoichiometric proportions. Replacing nine Fe+3 ions by (La+3 + 8Cr+3) ions the twelve magnetic Fe+3 ions in CaFe12O19 are reduced to three. The compound now contains two types of magnetic ions, viz. 8Cr+3 and 3Fe+3. The formed sample is analyzed with the help of X-ray diffractometry. It is found to have hexagonal magnetoplumbite (M) structure with unit cell dimensions a = 5.74 Å, c = 21.88 Å and volume = 623.87 Å3 with a space group P63/mmc. The electrical conductivity and magnetic susceptibility measurements are carried out over a temperature range 300-800 K. It shows semiconducting behaviour with energy 0.28 eV for activation. The compound is paramagnetic in above temperature range with Curie molar constant (CM) 28.74, which is close to the expected value (28.12) based on stable valencies. Asymptotic Curie temperature is found to be 280 K. The ac magnetic susceptibility is also studied at room temperature and found to be 60.6 ´ 10-6 emu/Oe. The thermoelectric studies showed that the sample is p-type with Seebeck coefficient (S) as +293 mV/K. The compound can also be looked on the basis of substitutions of Cr+3 and La+3 in CaFe12O19.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 207-212

FT-IR analysis of Neyveli lignite and flyash samples

R Venkatachalapathy, C Manoharan, T Sridharan & C M Basilraj

Infrared spectroscopy has been recognised as a promising technique for the study of chemical structure and components present in the lignite samples. The extinction coefficient (K) values for aromatic-CH (3030 cm-1) and aliphatic -CH (2920 and 2850 cm-1) groups present in the lignite samples were calculated and compared with atomic H/C and O/C ratios. It is found that Neyveli lignite formation belongs to Tertiary period of very low rank coals. The probable period of formation is found to be miocene and oligocene-palaeocene period. The flyash spectrum reveals the removal of all organic compounds present in lignite and the presence of small amounts of refracting materials of inorganic nature like SiO2,FeO and FeS.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 213-220

Transition assignments to Lb1 satellites in X-ray emission spectra of first transition series

S N Soni and S Poonia

 

The X-ray satellite spectra arising due to  (x º s,p,d) transition array, in elements with Z = 26 to 30, have been calculated. The bar at the top denotes that these are the positions of ionization in the atom. While the energies of various transitions of the array have been determined by using available Hartree-Fock-Slater data on  and  Auger transition energies, their relative intensities have been estimated by considering cross-sections of singly ionized  (x º s,p) states and then of subsequent Coster Kronig and shake off processes. The calculated spectra have been compared with the measured satellite energies in Lb1 spectra. Their intense peaks have been identified as the observed satellite lines. The one-to-one correspondence between the peaks in calculated spectra and the satellites in measured spectra has been established on the basis of the agreement between the separations in the peak energies and those in the measured satellite energies. It has been established that two satellites observed in the Lb1 region of the X-ray spectra of the elements with Z = 26 to 30 and named b1I and b1II in order of increasing energy are mainly emitted by  transitions. The satellite b1I has been assigned to the superposition of the transitions 3F2-3F2, 3P2-3P2 and 3P2-3P1, contributing in order of decreasing intensity, and the line b1II, has been assigned to mainly the 3F3-3F3 transition. The possible contribution of other transitions of the  (x º s,p,d) array having appreciable intensities have also been discussed.

 

Indian Journal of Pure & Applied Physics

Vol. 40, March 2002, pp. 225-226

News Scan

Gravitation Sensors

The new state of matter, a Bose-Einstein condensate (BEC) consisting of super-cooled atoms all in the same quantum-mechanical state will serve as the basis for instruments of unprecedented sensitivity. For example, gravitation sensors using BEC interferometers may provide geologists, archeologists, and engineers with a powerful new tool for seeing beneath Earth’s surface: and BECs are already delivering new insights into the quantum effects that must be understood in fields such as nanotechnology and quantum computing.