002118   Sen D;Mahata T;Patra A K;Mazumder S;Sharma B P (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085) : Effect of porosity and pore morphology on the low-frequency dielectric response in sintered ZrO₂-8 mol% Y₂O₃ ceramic compact. Pramana J Phys 2004, 63(2), 309-14.

Effect of porosity and pore size distribution on the low-frequency dielectric response, in the range 0.01 - 100 kHz, in sintered ZrO₂-8 mol% Y₂O₃ ceramic compacts have been investigated. Small-angle neutron scattering (SANS) technique has been employed to obtain the pore characteristics like pore size distribution, specific surface area etc. It has been observed that the real and the imaginary parts of the complex dielectric permittivity, for the specimens, depend not only on the porosity but also on the pore size distribution and pore morphology significantly. Unlike normal Debye relaxation process, where the loss tangent vis-avis the imaginary part of the dielectric constant shows a pronounced peak, in the present case the same increases at lower frequency region and an anomalous non-Debye type relaxation process manifests.

2 illus, 1 table, 9 ref

002117   Sen A;Rao M N;Mittal R;Chaplot S L (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085) : Inelastic neutron scattering study of lattice dynamics in alpha-ZnCl₂. Pramana J Phys 2004, 63(2), 393-7.

Inelastic neutron scattering experiments have been carried out to measure the phonon density of states in polycrystalline alpha-ZnCl₂ at Dhruva, Trombay. Lattice dynamical calculations, based on an interatomic potential model, are accomplished to study phonons associated with this otherwise extremely hygroscopic compound. Our calculated data are found to be well-compatible with the available measured ones.

2 illus, 1 table, 11 ref

002116   Sekar R;Vaidyanathan G;Vasanthakumari R (Math Dep, Phys Dep, Pondicherry Engng Coll, Pondicherry-605 014) : Ferroconvection induced by point heat source. Indian J Engng Mater Sci 2004, 11(4), 331-7.

A mathematical model is proposed to study the onset of the free convection in ferrofluid at low Rayleigh number from an instantaneous point heat source. In this work, the leading term of series expansion of the dependent variable in terms of Rayleight number is considered and is valid in small Rayleigh number regime only. The rate of heat generation is assumed to be not very high, so that Stoke's flow approximation could be used. The flow field is explained by the streamlines at different times. In the absence of field, the results are compared for the thermal convection due to the instantaneous point heat source.

6 illus, 6 ref

002115   Scholten P C (Philips Res Lab, , Eindhoven, The Netherlands) : First century of colloid magneto-optics. Indian J Engng Mater Sci 2004, 11(4), 323-30.

Starting with the first report of a magneto-optical effect in a colloid by Grove in 1845 and the unsuccessful search by Farady, the various discoveries by Kerr, Majorana, Cotton and Mouton and others up to about 1940 are described. A survey of the development of the theoretical interpretation has as highlights Schmauss' idea of particle orientation, Cotton and Mouton realizing that thermal motion provided the opposing mechanism, and Langevin's statistical-mechanical treatment. This part ends with the expressions for the dichroism by Naik and Desai in 1964.

7 illus, 23 ref

002114   Sastry P U;Chitra R;Choudhury R R;Ramanadham M (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085) : Zinc (tris) thiourea sulphate (ZTS): a single crystal neutron diffraction study. Pramana J Phys 2004, 63(2), 257-61.

The crystal structure of ZTS has been determined by neutron diffraction with a final R-value of 0.026. Using the structural parameters, the contributions from the structural groups to the linear optical susceptibility and linear electro-optic coefficients have been evaluated. Results showed a significant contribution from the hydrogen bonds in the structure.

1 illus, 4 tables, 5 ref

002113   Saibabu G;Reddy A R;Srikanth D (Physics Dep, Railway College, Kazipet-506 003) : Study of effect of quenching and deformation on KCl: Cd<. Bull Mater Sci 2004, 27(5), 459-66.

The study of ionic conductivity vs reciprocal temperature of pure KCl and KCl crystal doped with 0.1, 0.3 and 0.5 mole% gadolinium has been carried out in as grown, quenched from elevated temperatures (100, 350 and 500°C) and annealed at various timings i.e. 2-3 h and deformed by different percentages. The plots exhibit three well-known regions, II, III and IV (extrinsic regions). The intrinsic region I was not observed in the plots as the conductivity measurements were taken up to 575°C. From the analysis of these plots, activation energies for the migration of cation vacancy and the association of gadolinium ion with cation vacancy in the lattice of KCl crystals are calculated. These values are compared with previously reported values. Further, an attempt is made to explain the existence of oxidation state of gadolinium ion in + 3 state rather than in + 2 state as reported earlier. The variation in conductivity with effect of concentration of impurity ion, quenching and annealing and deformation with various percentages are explained on the basis of formation of impurity vacancy dipoles, vacancy - vacancy pairs (which appear in the form of precipitation), storage of cation vacancies in the form of defects, introduction of fresh dislocations, etc.

4 illus, 26 ref

002112   Sahoo A;Sarkar S;Krishna P S R;Joarder R N (Phys Dep, Jadavpur Univ, Kolkata-700 032) : Temperature effects of the structure of liquid D-methanol through neutron diffraction. Pramana J Phys 2004, 63(2), 183-8.

The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these liquids at elevated temperatures through neutron diffraction. The liquid consists of deuterated methanol and neutron data was collected on the high-Q diffractometer at Dhruva, BARC. The corrected data at elevated temperatures (BP (boiling point) and double the BP) show that there is a large change in the H-bonded structure of this liquid. The pre-peak or hump, known to be signature of H-bonded clusters appears to be present at all the three temperatures studied. In the low-Q (scattering vector) data Ornstein Zernike (OZ) behaviour is also observed. It is however, seen that the intramolecular structure does not change very much at higher temperatures. A detailed model analysis is in progress and would be reported later.

5 illus, 1 table, 9 ref

002111   Saha S K (Gantala Road, Nabadwip, , Nadia W B -741 302) : Raman induced phase conjugation spectroscopy A quantitative analysis in benzene. J Optics 2003, 32(4), 197-201.

Raman Induced Phase conjugation spectroscopy (RIPCS) is a new form of Coherent Raman Spectroscopy (CRS) using non-degenerate four-wave mixing in a phase conjugation (PC) geometry. With this technique one can measure complete Raman spectra of transpaent media. Uses this technique to obtain Raman spectra of benzene in the vicinity of 992 cm^-1 Raman mode. Also analyses these spectra to determine the ration of the resonant and noneresonant components of the third-order nonlinear susceptibility.

^ssc2 illus, 1 table, 13 ref

002110   Rayaprol S;Parmar R;Kuberkar D G;Chakraborty K R;Krishna P S R;Ramanadham M (Phys Dep, Saurashtra Univ, Rajkot-360 005) : Neutron diffraction studies on La_2-xDy_xCa_2xBa₂Cu_4+2xO _z superconductors. Pramana J Phys 2004, 63(2), 213-9.

Structural studies on Dy-substituted La-2125 type superconductors have been carried out by neutron diffraction experiments at room temperature using a monochromatic neutron beam of wavelength (λ) = 1.249 Angstrom. A series of samples with La_2-xDy_xCa_2xBa₂Cu_4+2xO_z stoichiometric composition, for x = 0.1-0.5, have been studied for their structural properties. A tetragonal Y-123 unit cell was taken as the starting model for the Rietveld analysis. All the samples fit into the starting model, with no structural transition taking place with increasing dopant concentration. The results of Rietveld analysis and structural properties have been discussed in detail.

3 illus, 1 table, 11 ref

002109   Rao D V S;Balamuralikrishnan R;Muraleedharan K (Defence Metallurgical Reseach Laboratory, , Kanchanbagh PO, Hyderabad-500 058) : Accurate determination of the voltage of a transmission electronmicroscope (TEM) by <60>0 1 2<128><60> CBED-HOLZ analyses using GaAs crystal. Bull Mater Sci 2004, 27(5), 471-82.

Convergent beam electron diffraction(CBED) is a powerful technique to estimate lattice distortion and lattice strain in crystals. The positions of the higher-order Laue-zone (HOLZ) lines in the transmitted disc of CBED patterns are very sensitive to the lattice parameter, and can therefore be used to estimate changes in the lattice parameter. This offers the possibility to calculate lattice misfit and lattice strain. The positions of the HOLZ lines depend not only on the lattice parameter, but also on the operating voltage of the microscope. It is essential to know the actual voltage of the microscope. In the present work, (1 0 0) GaAs crystal has been used as a standard. Cross-sectional TEM specimens were prepared by argon ion beam thinning techique using a liquid nitrogen cold stage. <60> 1 2 <62>on-zone CBED technique has been used to estimate the actual voltage of the transmission electron microscope (Philips EM430T TEM), when the voltage was set at 250 kV. CBED-HOLZ simulation and analyses have been done, using JEMS software, to correlate with the experimental data. The methodolgies adopted for estimating the actual voltage of TEM are discussed in this paper. The studies have also been cross-checked using <60>0 1 2<62> and <60>2 3 3<62> zone axes using (1 0 0) silicon standard. The techniques established are found to be suitable for TEMs operating at a setting voltage of about 250 kV.

15 illus, 4 tables, 11 ref

002108   Raman R;Roy R M;Roy S K (NO, Bihar College of Enginering, Patna) : A study of lattice dynamics of a face centered cubic crystal (F C C C). Appl Sci Period 2004, 6(3), 155-64.

A new model has been developed for the analysis of lattice dynamics of NaCl crystal structure utilysing the valence force field approximation. This model is the modified model of rigidon model and hence is called as valence force field model which retains all the advantages of RIM and describes the lattice dynamics of NaCl crystal structures. The results obtained from this model agrees well with the experimental values available.

2 illus, 4 tables, 18 ref

002107   Rajput S S;Jamuar S S (Electrical Engng Dep, Indian Inst of Technol, New Delhi-110 016) : A CMOS operational floating conveyor. IETE Tech Rev 2003, 20(6), 507-15.

A CMOS realization for operational floating current conveyor (OFC), which can be reconfigured as various types of current conveyors, has been described. The proposed OFC has very lower power consumption and a bandwidth of 100 MHz. For ±2.5 V power supply, the voltage transfer takes place from -1V to 2V. P-Spice simulation confirms the high performance of the proposed circuit structures.

15 illus, 16 ref

002106   Raj K;Moskowitz B;Tsuda S (Ferrotec Corporation (USA, , Nashua, NH, USA) : New commercial trends of nanostructured ferrofluids. Indian J Engng Mater Sci 2004, 11(4), 241-52.

In the realm of nanotech materials, ferrofluids are unique in that their constituents are both liquid and solid. True microsystems based on hydrodynamic principles of ferrofluids may still be some years aways. However, ferrofluids are already contributing to nanotechnology, first as components of microproducts and second by their utilization in processes engaged in fabrication of nanostructured materials. Focuses on applications of ferrofluids, which are related to the derive towards the new technology.

12 illus, 3 tables, 18 ref

002105   Raikher Y L;Rasukov V V (Inst of continuous Media Mechanics, Ural Div of RAS, Perm, 614013, Russia) : Models for microrheology of complex magnetic fluids. Indian J Engng Mater Sci 2004, 11(4), 253-61.

A review of some aspects of orientational magnetodynamics of viscoelastic magnetic fluids and ferrogels is given. As an archetypal theoretical model we use an assembly of non-interacting dipolar Browninan nanoparticles embedded in and coupled to a matrix that possesses either a dynamic (Maxwellian) or a weak equilibrium (Hookean) elasticity or both. With regard to their magnetic properties, the particles are assumed to be rigid dipoles. In the mechanical aspect the particles are taken to be two-dimensional, i.e., are modeled by disks, either inertial or inertia-less. Two types of dissipative interaction between a particle and its environment - a simple Stokes viscous friction and a friction with a simple exponential memory (like in a Maxwellian fluid) - are analyzed. Using the linear response approach we find the equilibrium correlation functions and the dynamic magnetic susceptibilities of the media. For the case of inertia-less particles the kinetic equation of rotary diffusion is derived and certain peculiarities in its properties are discussed.

2 illus, 15 ref

002104   Pratap A;Lad K;Raval K G (Condensed Matter Phys Lab, Applied Phys Dep, Faculty of Technol and En, M S Univ of Baroda, Vadodara-390 001) : Structure factors and phonon dispersion in liquid Li_0.61Na_0.39 alloy. Pramana J Phys 2004, 63(2), 431-5.

The phonon spectra for liquid Li and Na have been computed through the phenomenological model of Bhatia and Singh for disordered systems like liquids and glasses and the obtained results have been compared with the available data obtained by inelastic neutron scattering (INS) and inelastic X-ray scattering (IXS) experiments. The effective pair potentials and their space derivatives are important ingredients in the computation of the dispersion curves. The pair potentials are obtained using the pseudo-potential theory. The empty core model proposed by Ashcroft is widely used for pseudo-potential calculations for alkali metals. But, it is thought to be unsuitable for Li because of its simple 1s electronic structure. However, it can be used with an additional term known as Born-Mayer (BM) core term. The influence of the BM core term on the phonon dispersion is discussed. The same pseudo-potential formalism has been employed to obtain the dispersion relation in liquid Li_0.61Na_0.39 alloy. Apart from the phonon spectra, the Ashcroft-Langreth structure factors in the alloy are derived in the Percus-Yevick approximation.

4 illus, 24 ref

002103   Patra A K;Ramanathan S;Sen D;Mazumder S (Solid State Phys Div, Materials Sci Div, Bhabha Atomic Res centre, Mumbai-400 085) : SANS investigation on evolution of pore morphology for varying sintering time in porous ceria. Pramana J Phys 2004, 63(2), 327-31.

Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine at 80°C. The precipitates were ground to fine particles of average size ~0.7 μm. Circular disks with 10 mm diameter, 2 and 3 mm thickness were prepared from the green compacts by sintering at 1300°C for three different sintering times. Evolution of the pore structures in these specimens with sintering time was investigated by small-angel neutron scattering (SANS). The results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones.

5 illus, 11 ref

002102   Parekh K;Upadhyay R V (Phys Dep, Bhavnagar Univ, Bhavnagar-364 002) : Characterization of transformer oil based magnetic fluid. Indian J Engng Mater Sci 2004, 11(4), 262-6.

In the present paper two different magnetic fluids synthesized earlier with transformer oil as carrier liquid are characterized. The magnetic properties of these fluids are studied using viscometry, magnetometer and Quincke's technique. The properties of the magnetic fluid are compared with those of the pure transformer oil and the results are discussed.

3 illus, 2 tables, 5 ref

002101   Pande S S;Borkar S P;Prafulla S;Srivastava V D;Behare, A;Mukhopadhyay P K;Ghodgaonkar M D;Kataria S K (Electronics Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: sspande@magnum.barc.ernet.in) : Instrumenttation for PSD-based neutron diffractometers at Dhruva reactor. Pramana J Phys 2004, 63(2), 459-63.

Linear position sensitive detectors (PSDs) are widely used to configure neutron diffractometers and other instruments. Necessary front-end electronics and a data acquisition system [1] is developed to cater to such instruments build around the Dhruva research reactor in BARC. These include three diffractometers with multiple PSDs and four with single PSD. The front-end electronics consists of high voltage units, preamplifiers [2], shaping amplifiers, ratio ADCs (RDC) [3]. The data acquisition system consists of an interface card and software. Commercially available hardware like temperature controller or stepper motor controller connected over GPIB or RS232 are also integrated in the data acquisition system. The data acquisition is automated so that it can continue unattended for control parameter like temperature, thus enabling optimum utilization of available beam time. The instrumentation is scalable and can be easily configured for various instrumental requirements. The front-end electronics and the data acquisition system are described.

2 illus, 4 ref

002100   Pal B;Raychaudhuri S (NO, , 1/AF, Badhannagar, Kolkata 700 064) : Ultrasonic pulse propagation in a linear dispersive medium. J pure appl Ultrasonics 2004, 26(2-3), 63-6.

Ultrasonic wave propagation in a linear dispersive medium has been studied numerically. Analytical expression for the particle displacement at a position x at a time t inside a medium bounded by two parallel planes at x=0 and x=1 due to ultrasonic pulse propagation along x-direction has been derived. Numerical evaluation of the analytical expression for the response shows the nature of distortion of the pulse caused by dispersion. It has been suggested that even if the pulse gets distorted, the ultrasonic propagation parameters can be determined from the Fourier spectrum of the responses observed at different positions in the medium by the method of computational analysis, provided the medium is linear.

5 illus, 6 ref

002099   Pal A;Kumar H (Department of Chemistry, Kurukshetra University, Kurukshetra 136 119) : Thermodynamic parameters of binary liquid mixtures of some n-alkoxyethanols and polyethers with 1-propanol at 298.15 K deduced from ultrasonic speed and viscosity data. J pure appl Ultrasonics 2004, 26(2-3), 67-78.

Thermodynamic functions like internal pressure, free-volume, energy of vaporization, heat of vaporization etc, for eight binary mixtures of some n-alkoxyethanols and polyethers with 1-propanol have been evaluated at 298.15 K from the experimentally determined values of density, viscosity, and ultrasonic speed. Corresponding excess functions have been computed. The results are explained on the basis of intermolecular interactions.

7 illus, 1 table, 27 ref

002098   Paikrao S S;Meena B L;Sharma S;Srivastava N; Singh V V P (Central Electronics Engng Res Inst (CEERI), , Pilani-333 031, Raj) : Results from a high dielectric electron emitter for use in electron tubes. Bull Indian Vacuum Soc 2004, 7(3), 23-7.

This paper present some results obtained for a high dielectric cathode (HDC) in vacuum. The cathode geometry has been simulated and analysed to study the influence of the thickness and dielectric constant of the dielectric material on the electric field produced at the tip of the metal, which emits the electron through field emission. A diode has been fabricated and used for the characterization of the cathode. Current density of the order of 150A/Cm² has been measured in vacuum. This cathode is being investigated for use as a trigger in a pseudospark switch (PSS) under development at CEERI.

7 illus, 1 table, 7 ref

002097   Nisha C K;Manorama S V;Maiti S;Jayachandran K N;Aswal V K;Goyal P S (Materials Sci Group, Indian Inst of Chem Technol, Hyderabad-500 007) : Small-angle neutron scattering studies on water soluble complexes of poly(ethylene glycol)-based cationic random copolymer and SDS. Pramana J Phys 2004, 63(2), 315-20.

The interaction of cationic random copolymers of methoxy poly (ethylene glycol) monomethacrylate and (3-(methacryloylamino)propyl) trimethylammonium chloride with oppositely charged surfactant, sodium dodecyl sulphate, and the influence of surfactant association on the polymer conformation have been investigated by small-angle neutron scattering. SANS data showed a positive indication of the formation of RCP-SDS complexes. Even though the complete structure of the polyion complexes could not be ascertained, the results obtained give the information on the local structure in these polymer-surfactant systems. The data were analysed using the log-normal distribution of the polydispersed spherical aggregate model for the local structure in these complexes. For all the systems the median radius and the polydispersity were found to be in the range of 20±2 Angstrom and 0.6±0.05, respectively.

2 illus, 12 ref

002096   Naik S S;Kotwal I;Chandak R M;Gaonkar V G (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: ssnaik@apsara.barc.ernet.in) : Data acquisition and instrument control system for neutron spectrometers. Pramana J Phys 2004, 63(2), 455-8.

A personal computer (PC)-based data aquisition and instrument control system has been developed for neutron spectrometers in Dhruva reactor hall and Guide. Tube laboratory. Efforts have been made to make the system versatile so that it can be used for controlling various neutron spectrometers using single end-on detector in step scan mode. Commercially available. PC add-on cards have been used for input-output and timer-counter operations. An interface card and DC motor driver card have been developed indigenously. Software for the system has been written in Visual C++ language using MS Windows operating system. This data acquisition and instrument control system is successfully controlling four spectrometers at Dhruva reactor.

2 illus, 2 ref

002095   Naidu P S;Prasad K R (Department of Physics, SVUPG Centre, Kavali 524 201) : Ultrasonic study of binary mixtures of insecticides in hexane at different temperatures. J pure appl Ultrasonics 2004, 26(2-3), 58-62.

Ultrasonic velocity, density and viscosity have been measured experimentally in solutions of fenvalerate and cypermethrin in the solvent hexane at four temperatures 30, 35,40 and 50°C. Various acoustical and other related parameters like adiabatic compressibility, internal pressure, apparent molar compressibility and volume and solvation numbers have been computed and discussed in the light of molecular interactions-solute and solute-solvent interactions in the solutions. In both the systems, solute-solvent interactions appear to be dominant.

3 tables, 14 ref

002094   Muraleedharan P M;Pankajakshan T;Harikrishnan M (National Inst of Oceanography, , Goa-403 004) : Validation of multi-channel scanning microwave radiometer on-board Oceansat-I. Curr Sci 2004, 87(3), 370-6.

Sea surface temperature (SST), sea surface wind speed (WS) and columnar water vapour (WV) derived from Multi-frequency Scanning Microwave Radiometer (MSMR) sensor on-board IRS-P4 (Oceansat-I) were validated against the in situ measurements from ship, moored buoy (MB), drifting buoy (DB) and autonomous weather station (AWS). About 1400 satellite in situ match-ups were used for the validation of SST and WS, while only 60 match-ups were available for the validation of WV. Therefore specific humidity, Q_a was used as a proxy for validating WV. The drifting buoy SSTs showed good correlation with the satellite values (r=0.84). The correlation of MB SSTs was better during night when the WS varied between 0 and 10 m/s. During the day, correlation peaked for higher wind speeds (<62> 10 m/s). MB (r<62>0.80) was relatively better than AWS ( r ~ 0.70) and ship (r <60>0.50) for validating satellite-derived WS. Daytime winds exhibited better correlation with satellite values when measured from ocean platforms (MB and ship), but the the winds measured from land-based platforms (AWS) were closer to satellite values during night time. Q_a values consistently showed higher correlation with satellite values during night-time. The low root mean square deviation (RMSD) of DB SST (1.17°C and MB WS (1.52 m s^-1) is within the achievable accuracy of the microwave sensor when validated with data collected over the tropical Indian Ocean. The RMSD of Q_a (1.81 g kg^-1), however, falls much beyond the attainable accuracy of the microwave sensor.

8 illus, 3 tables, 13 ref

002093   Mohanty B;Aswal V K;Goyal P S;Bohidar H B (Sch of Phys Sci, Jawaharlal Nehru Univ, New Delhi-110 067) : Small-angle neutron and dynamic light scattering study of gelatin coacervates. Pramana J Phys 2004, 63(2), 271-6.

3 illus, 2 ref

002092   Mittal R;Chaplot S L;Raj P;Shashikala K; Asthyamoorthy A (Solid State Phys Div, Novel Materials and Structural Chem Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: rmittal@apsara.barc.ernet.in) : Inelastic neutron scattering in Zr₂NiH_4.6. Pramana J Phys 2004, 63(2), 399-403.

In this paper we report the results obtained from inelastic neutron scattering measurements on Zr₂NiH_1.9 and Zr₂NiH_4.6 using triple-axis spectrometer at Dhruva reactor, Trombay. The spectrum up to 35 meV represents largely the lattice modes of Zr and Ni atoms. The vibrational frequencies of hydrogen atoms are expected predominantly at higher energies. The phonon spectra from 35-180 meV were recorded using a Be filter as analyser. In order to analyse the observed neutron spectra, we assume a set of Einstein modes due to the hydrogen atoms which are delta functons in energy. These delta functions are broadened by the resolution of the instrument. The vibrational frequencies obtined from the fitting of the observed phonon spectra have been assigned to various tetrahedral sites in both the compounds.

1 illus, 1 table, 15 ref

002091   Mittal R;Chaplot S L;Kolesnikov A I;Loong C K;Jayakumar O D;Kulshreshtha S K (Solid State Phys Div, Novel Materials and Structural Chem Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: rmittal@apsara.barc.ernet.in) : Inelastic neutron scattering and lattice dynamics of GaPO₄. Pramana J Phys 2004, 63(2), 405-8.

We report here mesurements of phonon spectrum and lattice dynamical calculations for GaPO₄. The measurements in low-cristobalite phase of GaPO₄ are carried out using high-resolution medium-energy chopper spectrometer at ANL, USA in the energy transfer range 0-60 meV. Semiempirical interatomic potential in GaPO₄, previously determined using ab-initio calculations have been widely used in studying the phase transitions among various polymorphs. The calculated phonon spectrum using the available potential show fair agreement with the experimental data. However, the agreement between the two is improved by including the polarisability of the oxygen atoms in the framework of the shell model. The lattice dynamical models are also exploited for calculations of various thermodynamic properties of GaPO₄.

2 illus, 12 ref

002090   Mitra S;Sumitra S;Umarji A M;Mukhopadhyay R; Yashonath S;Chaplot S L (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: smitra@apsara.barc.ernet.in) : Acetylene diffusion in Na-Y zeolite. Pramana J Phys 2004, 63(2), 449-53.

Study of diffusivity of acetylene adsorbed in Na-Y zeolite by quasi-elastic neutron scattering (QENS) measurements at temperatures of 300, 325 and 350 K is reported. A model in which the acetylene molecules undergo random-walk diffusion characterized by a Gaussian distribution of jump lengths inside zeolite cages describes the data consistently. The diffusion constant, residence time between jumps and root mean square jump length are determined.

2 illus, 1 table, 9 ref

002089   Mitra S;Pramanik A;Chakrabarty D; Mukhophadhyay R (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: smitra@apsara.barc.ernet.in) : Excess water dynamics in hydrotalcite: QENS study. Pramana J Phys 2004, 63(2), 437-41.

Results of the quasi-elastic neutron scattering (QENS) measurements on the dynamics of excess water in hydrotalcite sample with varied content of excess water are reported. Translational motion of excess water can be best described by random translation jimp diffusion model. The observed in translational diffusivity with increase in the amount of excess water is attributed to the change in binding of the water molecules to the host layer.

2 illus, 1 table, 11 ref

002088   Mitra S;Kamble V S;Tripathi A K;Gupta N M; Mukhopadhyay R (Solid State Phys Div, Applied Chem Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: smitra@apsara.barc.ernet.in) : Dynamics of different molecules adsorbed in porous media. Pramana J Phys 2004, 63(2), 443-8.

3 illus, 2 tables, 12 ref

002087   Misra S C K;Mathur P;Pant R P;Gupta A K (Engng Materials Div, Materials Characterization Div, National Physical Laboratory, New Delhi-110 012) : Nanocrystalline magnetic alloy thin films. Indian J Engng Mater Sci 2004, 11(4), 319-22.

In this communication the preparation and characterization of nanocrystalline magnetic thin films of MN doped Zn-Te alloys, prepared on various types of substrates by vacuum deposition techniques have been described. This technology is completely dry and suitable for making nanocrystalline device quality magnetic films on a complicated structure and is preferred for its simplicity. These magnetic thin films can be used as excellent recording media for information storage and handling.

6 illus, 15 ref

002086   Mishra R K;Agarwal Mishra R (Computer and I T Section, Tropical Forest Res Inst, P O RFRC, Jabalpur-482 021) : Unusually low/high-amplitude anisotropic wave train events in cosmic-ray intensity as an effect of interplanetary turbulences. J Indian Inst Sci 2003, 83(5-6), 107-16.

Using the ground-based neutron monitor data of Deep River we have studied the low- and high-amplitude anisotropic wave train events (LAE/HAE) in cosmic-ray intensity for different latitudes. The investigation has been made for both LAE and HAE during the period 1981-1994. It has been observed that the phase of diurnal anisotropy in the majority of HAE/LAE cases remains in the same co-rotational direction, but has shifted to later hours in some HAE cases and to early hours in some LAE cases. Further, for majority of HAE/LAE cases, the amplitude of semi-diurnal anisotropy remains statistically the same, while the phase for all HAE cases shifted to later hours. The HAE appears dominant during the declining phase of solar activity, whereas LAE appears dominant during minimum solar activity.

002085   Mathur P;Misra S C K;Kishore R;Upreti U C; Pandey J L (Engng Mat Div., Mat Characterization Div, National Phys Lab, New Delhi-110 012) : Preparation and characterization of vacuum deposited magnetic polyaniline thin films. Indian J Engng Mater Sci 2004, 11(4), 353-7.

Vacuum deposited polyaniline thin films have been found to exhibit excellent magneto-optic properties. The vacuum deposited thin films of doped polyaniline have been prepared on various substrates and their optical, electrical and magnetic characterization carried out. The thin films prepared on different substrate show a variety of surface topography and magnetic domains in crystalline phase. The crystallinity is induced by the influence of substrate on which the film is deposited. This technology establishes the feasibility of preparation of high-density disc storage magnetic recording media using vacuum deposited thin films. the advantage of these films is their magnetization and lower magnetic fields.

8 illus, 14 ref

002084   Manwar B G;Kavthia S H;Parsania P H (Department of Chemistry, Saurashtra University, Rajkot 360 005 Gujarat) : Ultrasonic velocity study of poly (R,R', 4,4'-cyclohexylidene diphenylene toluene-2, 4-disulfonates) solutions at 30°, 35° and 40°C. J pure appl Ultrasonics 2004, 26(2-3), 49-57.

Ultrasonic velocity (2 MHz) and acoustical parameters of poly (R, R', 4, 4'-cyclohexyli-dene diphenylene toluene 2-4-disulfonates) (PS-3: R=R'=Cl and PS-4: R=CH₃ and R'=Cl) solutions investigated to understand the effect of methyl and chlorine substituents on molecular interactions. The linear increase of ultrasonic velocity (U), acoustical impedance (Z), Rao's molar sound function (R), Van der Waals constant (b) and internal pressure (π); and nonlinear increase of classical absorption coefficient (α/f²)_Cl and viscous relaxation time (t) with C and decrease with T; and linear decrease of isentropic compressibility (k_s)relaxation strength (r), free length (L_f and free volume (V_f) (nonlinear) with concentration (C) and increase with temperature (T) suggested the existence of powerful molecular interactions and hence solvophilic nature of the polymers, which is supported by positive values of solvation number (S_n). Structural modification (entanglement) is found above 2% concentration in 1,2-dichloroethane and THF systems. The linear increase of S_n with C and T indicated the presenceof predominant polymer-solvent interactions over polymer-polymer interactions. The decrease of S_n with T is due to breaking of structure by predominant thermal energy over molecular interaction energy.

1 illus, 4 tables, 13 ref

002083   Kushwah V K;Singh B (Physics Dep, R B S College, Bichpuri, Agra 283 105) : Initial results of ultra low frequency magnetic field observations at Agra and their relation with seismic activities. Curr Sci 2004, 87(3), 332-9.

Employing search coil magnetometers (f=0.01-30 Hz) the ultra low frequency (ULF) magnetic field observations have been started at Agra since 13 September 2002. The analysis of first three months data shows that the amplitudes of the three components (Bx, By and Bz) are low between 0.01 and 0.30 nT normally, which increase to large values between 0.23 and 2.53 nT occasionally. Three cases of largest enhancements in amplitudes are selected and possible causes for the enhancements are examined in terms of magnetospheric ULF emissions (micropulsations) and ULF emissions associated with earthquakes using polarization parameter (Z/X) and magnetic storm index Kp variation. It has been shows that in the three selected cases the amplitude enhancements are associated with moderately large earthquakes that occurred in the neighbouring countries Pakistan and China. In two of the three cases, the recursory enhancements in amplitudes are identified clearly. The statistical analysis of the data using mean and standard deviation around the mean is carried out which supports the results satisfactorily. The propagation mechanism of the emissions between the source locations and observing sation at Agra is also discussed.

5 illus, 1 table, 29 ref

002082   Kumar S;Krishnamurthy A;Srivastava B;Das A; Paranjpe S K (Phys Dep, M L Sukhadia Univ, Udaipur-313 002) : Magnetization and neutron diffraction studies of feCrP. Pramana J Phys 2004, 63(2), 199-205.

Crystal structure and magnetic behaviour of FeCrP have been investigated using magnetization and neutron diffraction measurements. FeCrP crystallizes in orthorhombic FeZrP type structure (P_nma space group, Z=4) in which Cr atoms coccupy the pyramidal site and Fe atoms occupy the tetrahedral site with total preference. Structural parameters including positional parameters have been refined. The refined values of positional parameters for Fe and Cr are quite different from those in FeZrP. The nature of magnetization-temperature cure is suggestive of antiferromagnetic nature with T_N = 280 (±10) K. Preliminary analysis of neutron diffraction pattern at 13 K is indicative of a rather complicated magnetic structure.

4 illus, 1 table, 7 ref

002081   Kumar D;Kumar S (Physics Dep, Christ Church College, Kanpur-208 001) : Pre-exponential factor in a-Se₇₅In_25-xPb_x thin films. Bull Mater Sci 2004, 27(5), 441-4.

Temperature dependence of d.c. conductivity is studied in a-Se₇₅In_25-xPb_x thin films where x is varied from 0-10. From these measurements, the values of the pre-exponential factor (σ₀) and activation energy (ΔE) are calculated for each glassy alloy. An approximate linear dependence of In σ₀ on ΔE observed in this geassy system with good agreement between the expected and calucated to valus using Meyer-Neldu rule in case of amorphous materials indicates that the conduction band tails a finite energy distance towards the valence band and Fermi level is controlled by fixed dominant hole levels deeper in the gap.

2 illus, 2 tables, 25 ref

002080   Kumar A;Yusuf S M (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085) : Magnetic structure of molecular magnet Fe[Fe(CN)₆].4H₂O. Pramana J Phys 2004, 63(2), 239-44.

3 illus, 2 tables, 13 ref

002079   Kopcansky P;Potocova I;Koneracka M;Timko M; Jadzyn J;Czechowski G;Jansen A G M (Institute of Experimental Phys, Slovak Academy of Sci, Watsonova 47, 04353 Kosice, Slovakia) : Structural transitions in thermotropic ferronematics. Indian J Engng Mater Sci 2004, 11(4), 271-5.

The structural instabilities in ferronematics based on different types of liquid crystals, exposed to electric or magnetic fields oriented perpendicular (Fredericksz transition) and parallel to the initial director, were studied within the Buryloy and Raikher's theory. Using the capcitance measurements the critical electric (magnetic) fields E_FN(B_FN), corresponding to the Fredericksz transition, and fields E_max, (B_max), at which the initial perpendicularity between director n and magnetic moment m breaks-down in field parallel to the initial director, were found. These values were than used for the estimation of the surface density of the anchoring energy W of liquid crystal molecules on the magnetic particle surface.

5 illus, 3 tables, 13 ref

002078   Kolekar Y D;Kulkarni S B;Chakraborty K;Das A; Paranjpe S K;Joshi P B (Phsy Dep, Shivaji Univ, Kolhapur- 416 004) : Structural study and electrical properties of Zr-doped Nd₂Sn₂O₇ pyrochlore compounds. Pramana J Phys 2004, 63(2), 189-97.

Nd₂Sn₂O₇ pyrochlore with the substitution of Zr⁴⁺ were prepared by conventional ceramic double sintering technique. This single-phase formation was confirmed by X-ray diffraction and neutron diffraction techniques. Relative intensity calculations for X-ray diffraction analysis were performed for oxygen positional parameters x = 0.331 and 0.375, while Rietveld refinements were employed for neutron diffraction data. The neutron diffraction study revealed that there are only two anion sites with 48f and 8b positions. This indicates that the 8a site, i.e. O(3) sublattice, is completely vacant and the structure is a perfect cubic pyrochlore with space group Fd3m (O⁷_h). From the conductivity measurements, it is observed that the electronic conductivity dominates from room temperature up to about 525 K and for T<62> 525 K, the oxygen ion conduction dominates the charge transport in these compositions. Complex impedance spectroscopy indicates the existence of grain and grain boundary as two separate elements.

4 illus, 3 tables, 9 ref

002077   Kitano T;Hashmi S A R;Navin Chand (Regional Research Laboratory, , Hoshasngabad Road, Bhopal-462 026) : Influence of steady shear flow on dynamic viscoelastic properties of un-reinforced and Kevalar, glass fibre reinforced LLDPE. Bull Mater Sci 2004, 27(5), 409-15.

An experimental study was conducted to observe the effects of parallel-superposed flow condition on viscoelastic properties of LLDPE, Kevlar fibe reinforced LLDPE and hybrid of shoet glass fibre and Kevlar fibre reinforced LLDPE. Parallel-plate rheometer was employed for these tests. Rheological parameters such as loss modulus (G") and dynamic viscosity (η') do not vary significantly on superposing steady state shear with oscillatory shear in the studied range of experiment at 185° C in un-reinforced LLDPE. Kevlar fibre reinforced LLDPE and Kevlar/glass fibre reinforced LLDPE showed significant changes in the flow behaviour under various sets of superposed conditions. Storage modulus (G'), and G" become highly sensitive to low oscillatory angular frequencies (ω) under superposed conditions. These curves show two different regions with increased ω value. At low ω values, parameters G' and G" change sharply reachig a certain value, thereafter, changes are moderate with increased ω. In case of η' a maxima is observed, position of which, depends upon the value of steady shear rate. Maxima shifts towards higher frequencies with the increased steady shear rate.

12 illus, 15 ref

002076   Joshi N;Debnath A K;Aswal D K;Muthe K P;Gupta S K;Yakhmi J V (Technical Phys and Prototype Engng Div, Bhabha Atomic Res Centre, Mumbai-85) : Growth of Ag (100 nm)/ Al (10 nm) bilayer-structures by MBE and studies on surface segregation, morphology and transport properties. Bull Indian Vacuum Soc 2004, 7(3), 3-10.

The Ag (100nm)/ Al (10nm) bilayer-structures on (111) Si substrates have been grown using molecular beam epitaxy (MBE) to investigate their suitability for interconnect metallization in ULSI and GSI technologies. Grown Ag/Al bilayers were in-situ annealed at different temperatures between 25 and 500°C (under ~ 10^-8 torr vacuum), and characterized for morphological, structural, compositional and electrical transport properties. The X-ray photeelectron spectra, recorded as a function of annealing time, revealed that Al migrates to the top of the Ag layer, where it reacts with residual oxygen present in the chamber and forms Al₂O₃. The thickness of the so-formed Al₂O₃ overlayer is found to increase with logarithmic of annealing time, and would act as a passivation layer. X-ray diffrction results show that Ag/Al bilayer-structures have a preferred (111) texture. Atomic force microscopic studies show that Al diffusion primarily occurs through intercrystalline boundaries. The room temperature resistivity of Ag/Al bilayer-structures is found to increase monotonically upto an annealing temperature of 500°C; however for higher temperatures the resistivity reduced. This result is explained in terms of the disorder in Ag layer induced by Al. The bilayer structures annealed at 500°C showed an unusual metal-to-insulator transition at 130 K. This anomalous electrical property is explained using a thermally activated polaron hopping mechanism.

10 illus, 15 ref

002075   Jani K H;Upadhyay R V;Mehta R V (Phys Dep, Bhavnagr Univ, Bhavnagar-364 002) : Fabrication of an a.c. susceptometer to study the magnetic susceptibility in some ferro/ferrimagnetic materials/fluids. Indian J Engng Mater Sci 2004, 11(4), 349-52.

An a.c. susceptometer is fabricated to measure the a.c. susceptibility of variety of magnetic materials comprising magnetic fluids. The instrument is designed to work in the temperature range 77-300 K. It covers wide range of frequencies from 1 Hz to 5 kHz. The instrument is interfaced with a personal computer for data acquisition. A variety of magnetic samples have been characterized using the set-up.

4 illus, 3 tables, 5 ref

002074   Jain S K;Das A;Srivastava B K;Krishnamurthy A;Paranjpe S K (Phys Dep, Univ of Rajasthan, Jaipur-302 004) : Magnetic behaviour of (Fe_0.85Cr_0.15)₂As. Pramana J Phys 2004, 63(2), 207-12.

Magnetization and neutron diffraction measurements have been made on the title pseudo-binary of tetragonal anti-ferromagnets Fe₂As and Cr₂ As. In this system antiferromagnetic (AFM) ordering appears below 310 K. The moments are confined in the ab plane but unlike in the end members they are tilted off the α-axis. In addition to the AFM structure a weak ferromagnetic behaviour show up below ~ 80 K with a rather low moment of ~ 0.07 μB per formula unit at 5 K and under a field of 3 T.

5 illus, 7 ref

002073   Hangloo V;Bamzai K K;Kotru P N;Koul M L (Phys of Electron Dep, University of Jammu, Jammu-180 006) : Thermal characteristics of pure and substituted gel grown Gd-molybdate crystals. Bull Mater Sci 2004, 27(5), 395-401.

Polycrystalline spherulitic crystals of pure Gd-heptamolybdate and single and twinned crystals of substituted Gd-Ba-molybdate were grown by using gel encapsulation technique. The thermal behaviour of these crystals was studied using the thermoanalytical techniques, which included TG, DTA and DSC. Thermal analysis suggests decomposition of the materials in one or more than one stages. Results obtained on application of TG based models viz. Horowitz- Metzger, Coats-Redfern and Pilotyan-Novikovan, are reported. According to the results of the kinetics of thermal decomposition, the random nucleation model is shown to be the one that is relevant to the decomposition of single rare earth (Gd) containing material and contracting shpere to the decomposition of the substituted (Gd-Ba) one. The kinetic parameters viz. the order of reaction, frequency factor and energy of activation using the mentioned models, are computed and shown to bear reasonably good agreement.

10 illus, 4 tables, 16 ref

002072   Haldar J;Aswal V K;Goyal P S;Bhattacharya S (Organic Chem Dep, Indian Inst of Sci, Bangalore-560 012) : Small-angle neutron scattering study of aggregate structures of multi-headed pyridinium surfactants in aqueous solution. Pramana J Phys 2004, 63(2), 303-7.

The aggregate structures of a set of novel single-chain surfactants bearing one, two and three pyridinium headgroups have been studied using small-angle neutron scattering (SANS). It is found that the nature of aggregate structures of these cationic surfactants depend on the number of headgroups present in the surfactants. The single-headed pyridinium surfactant forms the lamellar structure, whereas surfactants with double and triple headgroups form micelles in water. The aggregates shrink in size with increase in the number of headgroups in the surfactants. The aggregation number (N) continually decreases and the fractional charge (α) increase with more number of headgroups on the surfactants. The semimajor axis (a) and semiminor axis (b = c) of the micelle also decrease with the increase in the numebr of headgroups in the surfactants. This indicates that hydrocarbon chains in such micelles prepared from multiheaded surfactants adopt bent conformation and no longer stay in extended conformation.

2 illus, 1 table, 8 ref

002071   Gupta S K;Pant R P;Arora M (Materials Characterization Div, National Phys Lab, Dr K S Krishnan Road, New Delhi-110 012) : Variable temperature electron paramagnetic resonance investigations of an ionic ferrofluid. Indian J Engng Mater Sci 2004, 11(4), 305-8.

An aqueous based ionic ferrofluid has been studied by EPR spectroscopy technique from room temperature to liquid nitrogen temperature. The line-width of EPR signal has been found to increase with decreasing temperature and this has been assigned to magnetic phase transition from ferromagnetic to a spin glass or cluster glass state mainly due to freezing of the carrier fluid. Line-width variation with temperature also suggests that bulk rotation mechanism is the dominant mode of relaxation. Any evidence of the presence of super-paramagnetism has not been observed.

3 illus, 16 ref

002070   Gupta A;Paramanik D;Varma S;Jacob C (Materials Science Centre, Indian Institute of Technology, Kharagpur-721 302) : CVD growth and characterization of 3C-SiC thin films. Bull Mater Sci 2004, 27(5), 445-51.

Cubic silicon carbide (3C-SiC) thin films were grown on (100) and (111) Si substrates by CVD technique using hexamethyldisilane (HMDS) as the source material in a resistance heated furnace. HMDS was used as the single source for both Si and C though propane was available for the preliminary carbonization. For selective epitaxial growth, patterned Si (100) substrates were used. The effect of different growth parameters such as substrate orientation, growth temperature, precursor concentration, etc on growth was examined to improve the film quality. The surface morphology, microstructure and crystallinity of grown films were studied using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS).

8 illus, 13 ref

002069   Goel P;Choudhury N;Chaplot S L (Solid State Phys Div, Bhabha Atomic Res Centre, Mumbai-400 085, Email: knp@apsara.barc.ernet.in) : Lattice dynamics of lithium oxide. Pramana J Phys 2004, 63(2), 409-12.

Li₂O finds several important technological applications, as it is used in solidstate batteries, can be used as a blanket breeding material in nuclear fusion reactors, etc. Li₂O exhibits a fast ion phase, characterized by a thermally induced dynamic disorder in the anionic sub-lattice of Li⁺, at elevated temperatures around 1200 K. Lattice-dynamical calculations of Li₂O have been carried out using a shell model in the quasi-harmonic approximation. The calculated phonon frequencies are in excellent agreement with the reported inelastic neutron scattering data. Thermal expansion, specific heat, elastic constants and equation of state have also been calculated which are in good agreement with the available experimental data.

4 illus, 1 table, 14 ref