005226   Pradhan B;Rout G C;Behera S N (Department of Physics, Government Science College, Nuapada 766 105) : Model study of interplay of superconductivity and magnetism in cuprate superconductors. Indian J Phys 2004, 78(8), 781-7.

The compitition magnetism and superconductivity is investigated in cuprate superconductors of type R_1-xM_xCuO₄ {R=La, Nd; M=Sr,Ba, Ce}. The anti-ferromagnetic long range ordering and the superconducting ordering are associated witht the same conduction electrons and hence there is strong interplay between the two phenomena. A model is proposed for the interplay of the two types of orderings. Zubarev's double time Green's function technique and equations of motion method is used to evaluate the superconducting gap and anti-ferromagnetic staggered field. The interplay is studied by varying the coupling parameters, the postion of the f-level and the hybridisation. The results are discussed.

5 illus, 11 ref

005225   Parhi N;Routt G C;Behera S N (P G Department of Physics, M P C College (Autonomous) Baripada 757 001, Orissa, ) : Effect of charge density wave (CDW) on magnetization in manganite systems. Indian J Phys 2004, 78(8), 705-11.

The manganite system exhibits colossal magneto-resistance which is presumed to be explained by the lattice distortion in addition to the double exchange mechanism. In the present communication we consider a simple Hamiltonian consisting of the hopping term arising due to the itinerant electronso f Mn atom in presence of Charge-Density-Ware (CDW) distortion and the external magnetic field in the e_g band. The nested pieces of the Fermi surface with strong electron-phonon interaction brings about the formation of a CDW with an accompanying periodic lattice distortion. The induced feromagnetism in the e_g band originates due to the more localized (t_2g electrons. The appropriate electron Green's functions are calculated leading to the calculation of the magnetization and CDW gap. The magnetization and CDW gap are solved numerically and self-consistently. The results are discussed taking into account different model parametrs of the system.

5 illus, 17 ref

005224   Panigrahi S;Waugh S;Rout S K;Hassan A K;Ray A K (Department of Physics, National Institute of Technology, Rourkela 769 008, Orissa) : Study of spin coated organic thin film under spectrophotometer. Indian J Phys 2004, 78(8), 823-6.

Thin films of organic compound Calix resorcinarene are deposited by spin coating method at different spinning speed and different concentrations. Films are studied under UV double beam spectrophotometer. Film thickness data are estimated from absorption spectra which peaks around 454 nm. Peak absorbances are found to be in consistent with spinning speed and solution concentration. The relation between film thickness h and spin speed ω obey power law relationof the form h αω^3/2. This is in agreement with the theoretical model of spin coating mechanism. Increasing solution concentration results in thicker film. This is presumably because of increased fluid viscosity.

4 illus, 9 ref

005223   Ojha M S;Rout G C;Behera S N (Condensed Matter Physics Group, Government Science College, Chatrapur 761 020, Orissa) : Theoretical study of velocity of sound in heavy fermion superconductors. Indian J Phys 2004, 78(8), 789-95.

The microscopic theory of the temperature dependance of velocity of sound in superconducting heavy fermion system is reported. The Periodic Anderson Model Hamiltonian in presence of phonon interaction with the hybridisation between f-electron and conduction electrons as well as with bare f-electron is taken for calculation. BCS type Cooper pairing is taken into consideration. The phonon Green's function is calculated exactly in closed form using the Green's function technique fo Zubarev in the limit of zero wave vector and finite temperature. The variation of velocity with temperature is calculated numerically and studied for different model phonon parameters and electronic parameters of the atomic subsystem.

5 illus, 22 ref

005222   Mitra M;Sreeram P A;Dattagupta S (S N Bose National Centre for Basic Sciences, , JD Block, Sector III, Salt Lake City, Kolkata 700 098) : Quantum treatment of the anderson-hasegawa model-superexchange and polaronic heat capacity. Indian J Phys 2004, 78(8), 719-24.

Revisits the Auderson-Hasegawa double-exchange model and critically examine its exact solution when the core spins are treated quantum mechanically. Shows that the quantum effects, in the presence of an additional superexchange interaction between the core spins, yield a term, the significance of which has been hitherto ignored. The quantum considerations further lead to new results when polaronic effects, believed to be ubiquitous in manganites due to electron-phonon coupling, are included. The consequence of these results for the magnetic phase diagrams and the thermal heat capacity are analysed.

5 illus, 12 ref

005221   Mandal S;Roy S K (Department of Physics, Visva-Bharati, Santiniketan 731 235, West Bengal) : On the biological pattern formation from model calculations. Indian J Phys 2004, 78(8), 681-4.

Reviews some calculations to demonstrate the basic properties of biological pattern formation obtained from some models. Asuming a shallow gradient of source distribution, one can show that a striking patern of activator concentration may be obtained with a maximum at the terminal of high source density for three models viz. depletion model, activator-inhibitor model assuming common sources and that with different sources.

1 illus, 6 ref

005220   Maity R;Knndoo S;Chattopadhyay K K (Department of Physics, Jadavpur University, Kolkata 700 032) : Electro-optical properties of ZnO: Al thin films produced by sol-gel route. Indian J Phys 2004, 78(8), 837-40.

Both undoped and aluminium doped ZnO thin films of high quality were prepared by sol-gel route on glass substrates.Zinc acetate and isopropyl alcohol were taken as precursor materials. The conditions for preparations were optimized. Aluminium nitrate (Al(NO₃)₃-9H₂O) was doping material for aluminium doping and Zn/Al ratio was varied in the solution to vary doping concentration in the film. Structural characterizations were performed by XRD and TEM studies. The optical and electrical propertiesof the films were studied in detail and they were correlated with the doping concentrations and preparations conditions. The films deposited at optimized conditions on glass substrates showed electrical conductivity ~1.39 (Ωcm)^-1 and a transmission of about 90% in the visible region. Electrical properties were studied in detailed which indicated that the films showed activated electronic conduction and the activation energies were found to depend on the doping concentrations in the films. Room temperature Seebeck co-efficient was obtained -91.65 μV/K in optimized condition.

5 illus, 1 table, 18 ref

005219   Maitra M;Tarafdar S;Middya T R;De U (Condensed Matter Physics Research Centre, Department of Physics, Jadavpur University, Kolkata 700 032) : Impedance spectroscopy studies in polymer salt complex films with varying concentrations. Indian J Phys 2004, 78(8), 767-70.

Presents some results based on impedance spectroscopy and morphology studies on SPE (Solid Polymer Electrolyte). Host material is polyethylene oxide completed with ammonium perchlorate {PEO (1-x)-NH₄CIO₄(x)} where x denotes the weight fraction. The Cole-Coleplot shows a semi circle and a spike. The spike is not vertical and may have a curvature. The real part of conductivity shows a power law variation with frequency. This is characteristic of disordered structures, which may also be fractal.

5 illus, 8 ref

005218   Mahato M C (Department of Physics, North-Eastern Hill University, Shillong 793 022, Meghalaya) : Mobility of a forced brownian particle. Indian J Phys 2004, 78(8), 693-5.

Studies the mobility of a underdamped Brownian particle in a washboard (inclined `periodic') potential system with a similarly periodic space dependent friction coefficient. We find that dependingon the phase difference between the potential function and the friction coefficient the average mobility of the particle differswith respect to the sign of the slope of the washboard potential. Discussed the possible implications of the result.

3 illus, 10 ref

005217   Kundoo S;Saha P;Chattopadhyay K K (Department of Physics, Jadavpur University, Kolkata 700 032) : Investigation of tin-incorporated nanocomposite diamond like carbon film. Indian J Phys 2004, 78(8), 733-7.

Semiconducting Sn-incorporated nanocomposite diamond like carbon (Sn-DLC) films were synthesized by DC plasma enhanced chemical vapour deposition (PECVD) method using SnCl₂-2H₂O salt dissolved in methanol solution as the doping source and acetylene as the carrier gas. Fourier transform infrared spectroscopy (FTIR) measurements showed different vibrational modes of tetrahedrally bonded carbon and also some small peaks due to Sn-C bonding vibrations. Transmission electron microscopy (TEM) image and electron diffraction pattern also confirmed the incorporation of nanocrystalline Sn particles into the amorphous DLC matrix. Due tot presence of Sn clusters optical band gap of the films decreased sharply compared to the intrinsic material. It was found that resistivity of Sn-incorporated DLC films decreased drastically by eight orders of magnitude than than of the undoped DLC film. Also films exhibited good field emission properties at lower turn-on field.

6 illus, 13 ref

005216   Krishan R;Dan D;Jayannavar A M (INstitute of Physics, , Bhubaneswar 751 005) : Transport coherence in frictional ratchets. Indian J Phys 2004, 78(8), 747-50.

Studies the phenomena of noise induced transport in frictional ratchet systems. A Brownian particle moving in a space dependent frictional medium in the presence of external white noise fluctuations was considerd. To get the directed transport, unlike in other ratchet models like flashing or rocking ratches etc., do not require the potential experienced by the particle to be asymmetric nor do requires the external fluctuations to be correlated. Obtaineds analytical expressions for current and the diffusion coefficient. Shows that the frictional ratchets do not exhibit a pronounced coherence in the transport in that the diffusion spread overshadows the accompanying directed transport in system with finite spatial extensions.

3 illus, 16 ref

005215   Khan J A;Shahabuddin M (Department of Physics, Jamia Millia Islamia, Jamia Nagar) : Simulation of I-V characteristics of Josephson junctions array: magnetic field effect. Indian J Phys 2004, 78(8), 841-4.

The I-V characteristic of the Intrinsic stacked Josephson junctions (ISJJ) as a function of magnetic field are simulated.ISJJ has been modelled as one dimensional series array of Josephson junction. Each Josephson junction of the series is considered as resistively shunted junction model in which the effect of capacitance, inductance and a current source producing white noise are included. The critical currents of the ISJJ as functionof magnetic field shows Fraunhoffer like pattern. The simulated results have been compared with the T12212 mesas experimental results. It has been found that the simulated results are in good agreement with the experimental one.

6 illus, 10 ref

005214   Karki B P;Sinha S K (Department of Physics, L S College, B B A Bihar University, Muzaffarpur 842 001, Bihar) : Simple equilibrium statistical mechanical theory of hard non-sphere fluid mixtures. Indian J Phys 2004, 78(8), 757-61.

Using the physical interpretation of the reciprocal of activity, an expression is derived for the equation of state of hard convex body fluid mixtures. The theory is applied to calculate the equation of state of the fluid mixture of hard dumbbells and fluid mixturesof hard spheres and prolate spherocylinder with y=2. In all these cases, the agreement with the simulation data is fairly good.

4 tables, 4 ref

005213   Kar S;Bandyopadhyay S;Ray K K;Lahiri A K; Maiti A K;Goswami K (Department of Physics, Jadavpur University, Kolkata 700 032) : Thermal effect on mobility of colour centers in alkali halide crystals. Indian J Phys 2004, 78(8), 861-3.

Electron injection has been carried out in single crystal of pure KCl and KBr under constant field for different temperatures. The injection current and optical density as a function of time are measured for both growth and decay process to estimate the mobility of colour center. The activation energy for bleaching of trapped centers and corresponding dissociation energy have been calculated.

4 illus, 8 ref

005212   Jana D;Ghosh S;Das D (Department of Physics, University College of Science and Technology, 92 A P C Road, KOlkata 700 009) : Universal diamagnetism: a diagnostic test for spinless bosonic excitations. Indian J Phys 2004, 78(8), 713-18.

It is well known that classical gas of point charged particles do not show any effect of magnetic field in thermal equilibrium. Magnetism is truly a quantum phenomenon. Demonstrates explicitly that diamagnetism is a robust property of charged spinless bose systems. It will be shown that diamagnetism is a universal phenomenon of spinless bose systems at finite temperature regardless of their interactions. Starting from a single particle, the discussion will go on to N particles system and finally, end on to an interacting field theory in an arbitrary spatial dimension d. Present an exact and non-pertubative result of the theory which is an interesting feature from the field theory aspect. In thsi theory, as a byproduct, develops a novel regularization scheme, particularly useful for magnetic field problems.

20 ref

005211   Gupta S J;Das R (Phys Dep, Univ of Mumbai, Mumbai-400 098) : Hybrid theory for one-dimensional binary alloys with local environment disorder. Indian J pure appl Phys 2003, 41(1), 15-20.

The vibrational frequency spectra of the random one-dimensional binary alloys A_cB_1-c have been accurately predicted by a hybrid theory which combines the single-site coherent potential approximation (CPA) with the statistical theory of small clusters embedded in a defect lattice potential. It takes advantage of the assests of both the numerical calculations of Dean^1,2 [Rev Mod Phys, 44 (1972) 127; Proc Roy Soc A, 260 (1961) 263] and the statistical-analytical approaches of meanfield approximations. It uses the fundmental properties of finite clusters of atoms in order to properly determine the shortranged correlations in atomic motions. The local environment effects on the density of states are included, by considering the system as a multi-component system with different neighbour compositions. The theory of the authors is an alternative to multi-site CPA and the embedded cluster theory.

1 illus, 14 ref

005210   Gupta K K;Bansal A K;Singh P J;Sharma K S (Phys Dep, M S J Coll, Bharatpur-321 001) : Temperature dependence of dielectric relaxation of rigid polar molecules acetophenone, pyridine and their mixtures in dilute solutions of benzene. Indian J pure appl Phys 2003, 41(1), 57-63.

The dielectric absorption studies of acetophenone, pyridine and their binary mixtures, both consisting of rigid molecules, have been studied at 8.93 GHz in the dilute solutions of benzene at different temperatures. The relaxation times, dipole moments, thermodynamical parameters, viz. free energy, enthalpy and entropy of activation have been calculated from the dielectric data. The relaxation time (t₀) of the single component agrees well with literature values. The experimental values of relaxation time (t₀) of the dipolar mixture have been compared with the theoretical values obtained by employing different methods. The non-linear behaviour of μ² versus mole fraction is explained of the basis of solutesolute molecular association between these two-polar rigid molecules. The values of the molar entropy for the relaxation process indicate that, the cooperative orientation of the molecules in the single component system is retained in the mixture also.

3 illus, 4 tables, 18 ref

005209   Ghosh S (DSA Laboratory, Department of Physics, University of Calcutta, 92, A P C Road, Kolkata 700 009) : Positron annihilation studies on Li_0.25Mg_0.5Mn_0.1Fe_2.15-xIn_x< B>O₄ series. Indian J Phys 2004, 78(8), 771-4.

Positron annihilation spectroscopy is a well known technique for probing the electronic properties and defects in solids. The positrons coming out from the radioactive source ²²Na while entering a material thermalized within 1 to 10 ps giving rise to different components of lifetime. Investigation has been done to observe the effect of diamagnetic In³⁼ ions in the Li_0.25Mg_0.5Mn_0.1Fe_2.15-xIn_xO₄ series (with x = 0, 0.3, 0.6, 0.9) by positron annihilation lifetime spectroscopy. Variations in positron lifetime components and their corresponsing intensities have been discussed on the basis of In³⁼ion substitution in place of Fe³⁼ion.

5 illus, 7 ref

005208   Ghosh S (Department of Physics, University of Calcutta, 92, A P C Road, Kolkata 700 009) : Enhancement in resistivity with annealing temperature in the nanoparticles of Li-Mg ferrite thin films. Indian J Phys 2004, 78(8), 729-31.

Nanocrystalline thin films of Li_0.25Mg_0.5Mn_0.1Fe_2.15O₄ have been prepared by R F magnetron sputtering technique using Si (100) as substrate. These thin films have been annealed under oxygen atmosphere at 650°C, 700°C, 800°C and 900°C. X-ray diffraction measurement reveals variation in grain sizes proportional to the annealing remperatures. Resistivities of the films have been measured by two-probe method. Interestingly it is observed that resistivity of this ferrite system increases with increase in grain size. Variation in resistivity is explained from the viewpoint of the combining effect of crystal growth and electron-phonon interaction in small volumes.

005207   Gajjar P N;Vora A M;Jani A R (Department of Physics, Sardar Patel University, Vallabh Vidyanagar 388 120) : Superconducting state parameters of metals. Indian J Phys 2004, 78(8), 775-80.

The theoretical investigation of five superconducting state parameters (SSP) viz. electron-phonon coupling strength λ, Coulomb pseudopotential μ*. transition temperature T_C, isotope effective exponent α and interaction strength N_oV of five monovalent (Li, Na, K, Rb and Cs), two divalent (Mg and Zn) and five polyvalent (In, Tl, Sn, Pb and Bi) metals have been carried out by well-recognized and recently proposed model pseudopotential. Employed five different types of local field correction functions proposed by Hartree Taylor, Ichimaru-Utsumi, Farid et al and Sarkar et al to study the exchange and correlation effects on the present computations. The recent local field correction functions due to Ichimaru-Utsumi, Farid et al and Sarkar et al have been employed for the first time in the study of SSP of metals. A very strong influence of all the exchange and correlation functions is found in the present study. Results are in fair agreement with other available theoretical as well as experimental data. A strong dependency of the SSP of metals on the valency Z is found.

tables, ref

005206   Dubey R N;Qureshi M S;Singh V;Tiwari M;Dhoble S J (Phys Dep, Maulana Azad Coll of Technol, Bhopal-462 007) : Dielectric behaviour and trapping in praseodymium doped calcium sulphide phophors. Indian J pure appl Phys 2003, 41(1), 40-5.

Loss tangent, loss capacitance and relaxation times are generally evaluated by simultaneous measurement of acconductance and ac capacitance for dielectrics and semiconductors in different shapes, sizes and states. Here, a new method is suggested to evaluate all the above parameter using Debye equations and measureing capacitance of phosphor cells at different autio frequencies. Relaxation time at room temperature comes out to be in microseconds. This may be due to electron traps 0.7 eV below the conduction band. This dielectric study leads to the same trap level position as found by many workers in thermally stimulated luminescence (TSL) and thermally stimulated conductivity (TSC) as well as phosphorescence decay mechanism.

2 illus, 2 tables, 16 ref

005205   Dey T K;Karki S S;Sinha S K (Department of Physics, L S College, B B A Bihar University, Muzaffarpur 842 001, Bihar) : Simple equalibrium theory for equation of state of hard convex body fluids. Indian J Phys 2004, 78(8), 751-5.

Using the physical interpretation of the reciprocal of activity, an expression is derived for the equation of state of hard convex body fluids. The theory is applied to evaluate the equation of state of hard ellipsoid of revolution, hard dumbells and prolate hard spherocylinders. In all these cases, the agreement with simulation is fairly good.

4 tables, 3 ref

005204   Dey P;Nath T K (Department of Physics & Meteorology, Indian Institute of Technology, Kharagpur 721 302, West Bengal) : Strain modification of La_{0.67Sr0.33MnO3 CMR thin films using structural transitions of ferroelectric (001) BaTiO3 substrate.} Indian J Phys 2004, 78(8), 833-6.

Effects of drastic change of 3-dimensional film lattice strain associated with Jahn-Teller strain by substrate structural transformations, on the transport and magnetic properties of tensile strained epitaxial rf-sputtered 500 A La_{0/67Sr0.33MnO3 thin film have been studied using BaTiO3 as the template. A change of 10-12% in the resistivity of LSMO around the structural phase changes of BTO is observed, whereas a sudden change of 15-70% is found in case of magnetization. Application of high magnetic field (50kOe) suppresses both the electrical transport and magnetization jumps to a large extent. The magneto-transport studies, with magnetic field along longitudinal, transverse and perpendicular to the film plane, have been carried out at several temperature down to 4 K in the magnetic field range of 6T-OT-6T. Maximum CMR effect is observed around 32% at 300 K. The magnetization loop measured below the transition temperature (282 K) is nearly square and has well-defined saturation and coercive fields, consistent with behaviour along magnetic easy axis, while the behaviour above the transition (290 K) exhibits much higher saturation field and nearly zero remanence indicating hard aixs.}

5 illus, 8 ref

005203   Deshmukh C C;Doshi A G;Deshmukh C M (Vidyabharti Inst of Res and Post Graduate Studies in Sci and Manageme, , Amravati) : Ultrasonic behaviour of substituted acrylo phenone and its complexes. Indian J pure appl Phys 2003, 41(1), 21-3.

Ultrasonic velocity and density measurements on 3-(2-hydroxy-3-nitro-5-chlorophenyl)-5-(2-furyl)-Δ^{2< D>-pyrazoline and its complexes with Fe(II), Ni(II), Co(II), Cu(II), Mn(II) and Cr(II) in acetone as a solvent, have been carried out at 298.5 K. Different acoustic properties like apparent molar volume, apparent molar compressibility, inter-molecular free-length, etc. have been determined. the parameters so obtained have been interpreted in terms of solute-solvent and solute solute interactions.}

2 illus, 1 table, 12 ref

005202   Das A;Chakrabarti B K;Dutta A (Saha Institute of Nuclear Physics, , 1-AF Bidhannagar, Kolkata 700 064) : Quantum spin glass phase boundary in transverse field ising systems. Indian J Phys 2004, 78(8), 685-7.

Studies zero temperature quantum phase transition driven by the transverse field for random ±J Ising model on chain and square lattice. Presents some analytical results for one dimension and some numerical results for very small square lattice under periodic boundary condition. The numerical results are obtained employing exact diagonalization technique following Lanczos method.

3 illus, 8 ref

005201   Chankaya G;Ucar N (Ataturk Univ, Faculty of Sci and Arts, Physics Dep, Erzurum, Turkey) : Effect of hydrostatic pressure on series resistance of Au/n-GaAs schootky diodes. Indian J pure appl Phys 2003, 41(1), 36-9.

Au/n-GaAs Schottky barrier diodes have been fabricated. The series resistance has been measured as a function of hydrostatic pressure using the current-voltage (I-V) technique. It has been found that the series resistance increases with increasing hydrostatic pressure.

2 illus, 32 ref

005200   Chakraborty S;Mukhopadhyay A;Roy S K (Department ofPhysics, Jadavpur University, Kolkata 700 032) : Order parameter from birefringence studies of two mesogens: 4-propyl paraethoxy phenyl cyclohexyl carboxylate and 4-butyl paraethoxy phenyl cyclohexyl carboxylate desire. Indian J Phys 2004, 78(8), 763-6.

Texture and optical studies as a function of temperature have been conducted on two mesogenic members: code names D302 and D402 of the alkyl phenyl cyclohexyl carboxylates series to study the effect of increasing chain length. The transition temperatures of the two members were confirmed from texture studies. From birefringence studies, the refractive indices n, and n_o were determined and density measurements were made to obtain the orientational order parameter at various temperatures. The effect of increasing chain length of the molecules on the optical properties and thereupon on the OOP has been discussed. Comparison of experimentally obtained values has been made with the theoretical values obtained from Maier-Saupe theory.

6 illus, 8 ref

005199   Bishoyi K C;Rout G C;Behera S N (P G Department of Physics, F M College (Autonomous), Balasore 756 001, Orissa) : The spin-density-wave (SDW) in quaternary borocarbide superconductors. Indian J Phys 2004, 78(8), 809-14.

A large family of quaternary borocarbides RNi2B₂C (R = Lu, Y, Ho, Dy) was discovered which have separate phase of antiferromagnetism (AFM), superconductivity (SC) and co-existent anti-ferromagnetic superconductivity. Proposed a spin-density-wave (SDW) state as a possible mechanism of the anomalours anti-ferromagnetism in the borocarbide superconductors. In this SDW state, the electron-hole pair amplitude changes its sign in the momentum space. The BCS type mean field superconductivity and a mean field SDW in Hubbard model are considered. The superconducting gap and SDW gap are calculated by Zubarev's technique of equationof motion method and are solved self-consistently for different model parameters. The co-existenceof superconductivity and anti-ferromagnetism for both of the case i.e. T_c<62> T_N and T_c<60> T_N are explained.

8 illus, 23 ref

005198   Bhat R K;Rani Devi;Khosa S K (Phys and Elect Dep, Univ of Jammu, Jammu-180 006) : Study of neodymium mass chain in the vriation after projection framework. Indian J pure appl Phys 2003, 41(1), 5-14.

Variation after projection (VAP) calculations in conjunction with Hartree Bogoliubov (HB) ansatz have been carried out for ^128-154Nd mass chain. In this framework, the yarst spectra, B(E2) transition probabilities and occupation numbers for various shell model orbits have been obtained. The observed shape transition encountered in going from ¹⁴⁸Nd to ^150-154Nd is seen to arise due to enhanced occupation of low k-components of (h_11/2)_π orbit, increased polarization of (d_5/2)_π orbit and increase in the occupation of (i_13/2)_v and h_11/2)_v orbits.

2 illus, 4 tables, 52 ref

005197   Behera D;Mohapatra U K;Mishra N C (Department of Physics, Utkal University, Bhubaneswar-751 004, Orissa) : Magnetic field induced excess conductivity in Y_1-xCa_xBa2Cu₃O_7-y/Ag composite superconductors. Indian J Phys 2004, 78(8), 803-8.

Temperature dependent electrical resistivity has been studied in a set of Y_1-xCa_xBa2Cu₃O_7-y/Ag composite bulk samples. Partial doping of Ca and composite formation with Ag modifies the microstructure and enhances the conductivity of the system. These two aspects one modifying the intragranular and the other modifying the intergranular properties of the YBCO superconductor have a profound influence on SCOPF region. In the present work fluctuation induced excess conductivity in presence of magnetic field has been calculated from p vs T data in the framework of Aslamazov and Larkin (AL) and Lawrence and Doniach (LD) theories. In addition to the 3D Gaussian fluctuation on approaching the transition temperature from higher side, we observed a genuine critical regime which is consistent with the predictions of the full dynamic 3D-XY universality class with model-E dynamics. Still closer to T_c^mf, when magnetic field is applied, evidence is found for a fluctuation regime beyond 3D-XY which can be interpreted as the occurrenceof ultimate first order character of the superconducting transition. In contrast to the 3D-XY model, the samples showed a reduced critical exponent on applicationof magnetic field. Attribute the reduction of the critical exponent at higher magnetic field to an enlarged or extended critical region.

6 illus, 30 ref

005196   Baral P C;Rout G C (Department of Physics, Government College, Phulbani 762 001, Orissa) : Interplay of kondo effect and superconducting gap in heavy fermion system. Indian J Phys 2004, 78(8), 797-801.

The heavy fermion system in superconducting state is described by the Hamiltonian containing the conduction electron term, oil-site f-electron term besides the Kondo interaction and the Heisenberg interaction. The Hamiltonian is treated in mean-field approximation to find simultaneously the Knodo singlet term and antiferromagnetic correlation. The Kondo singlet parameter λ=<193>f_i,of_i,o<193> and f-electron correlation parameter λ= <193>f_i,of_{j,o<193> (nearest neighbours) are calculated by minimizing total energy of the system. In addition to this, a BCS type phonon mediated Cooper pairing is considered to find the superconducting gap equation. In this communication, interplay of Kondo effect and superconducting gap of the heavy fermion system is studied through the self-consistent solution of these two parameters.}

5 illus, 11 ref

004288   Yadav B C;Shukla R K (Opto-Electronics Research Laboratory, Phys Dep, University of Lucknow-226 007, ) : Titania films deposited by thermal evaporation as humidity sensor. Indian J pure appl Phys 2003, 41(9), 681-5.

The humidity sensors based on optical methods are best suited fir 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 TiO₂₂ film 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 chages in humidity lying in the range 5-95% have been recorded.

6 illus, 12 ref

004287   Varghese T (Physics Dep, Nirmala College, Muvattupuzha, Kerala 686 661) : Compton profiles of praseodymium and gadolinium. Indian J pure appl Phys 2004, 42(4), 239-42.

The Compton profiles of rare earth elements Pr and Gd were measured using IGC HPGe detector. The target atoms were excited by means of 59.54 keV gamma rays from Am-241 radioactive source of strength 300 mCi. Elemental foils of uniform aerial density, and purity better than 99.9% were used as targets. The data were recorded and analyzed using a 4K multichannel analyzer. The present experimental Compton profiles of Pr and Gd constitute the first measurement. The results are compared with theoretical Hartree-Fock free atom profiles.

2illus, 2 tables, 11 ref

004286   Tewari S P;Silotia P;Saxena A (Phys and Astrophysics Dep, University Delhi-110 007, ) : Frequency distribution function of phonons in different layers of graphite. Indian J pure appl Phys 2003, 41(9), 707-11.

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.

5 illus, 10 ref

004285   Suman C K;Prasad K ;Choudhary R N P (University Physics Dep, T.M. Bhagalpur University, Bhagalpur-812 007) : Impedance analysis of Pb₂Sb₃LaTi₅O₁₈ ceramic. Bull Mater Sci 2004, 27(6), 547-53.

Polycrystalline sample of Pb₂Sb₃LaTi₅O₁₈, a member of tungsten-bronze (TB) family, was prepared using a high temperature solid-state reaction technique. XRD analysis indicated the formation of a singlephase orthorombic structure. The dielectric studies revealed the diffuse phase transition and the transition temperature was found to be at 52°C. Limpedance plots were used as tools to analyse the sample behaviour as a function of frequency. Cole-Cole plots showed Debye relaxation. The activation energy was estimated to be 0.634 eV from the temperature variation of d.c. conductivity. The nature of variation of d.c. conductivity with temperature suggested NTCR behaviour.

12 illus, 1 table, 36 ref

004284   Srivastava K S;Husain M;Srivastava S (Physics Department, Lucknow University, Lucknow and Jamia Millia Islamia, Jamia Nagar, New Delhi) : High energy plasmon satellites in auger spectra of 4d transition metals. Indian J pure appl Phys 2004, 42(4), 302-3.

Theory of plasma oscillations in solids has been used to calculate the energy separation and relative intensity of plasmon satellites of Ag, Pd, Rh, Ru, Mo and Nb. The calculated values of energy separation and relative intensity agree well with the estimated values of energy separation and relative intensity of second satellites on the high energy side of the main line in the L₃M_4,5M_4,5Auger spectra observed by Landers et al.J.Electron Spect & Related Phenom, 72 (1995) 211.

2 tables, 14 ref

004283   Sreekumar K;Vaidyan V K (Department of Physics, University of Kerala, Thiruvananthapuram 695 581) : Dual phase wide band lock-in amplifier for linear and non-linear photo-thermal signal processing. Indian J pure appl Phys 2004, 42(4), 258-64.

A dual phase lock-in amplifier has been designed and developed for the processing of photo-thermal signals in 1 Hz to 110 kHz frequency range, with automatic frequency tracking over the entire bandwidth. The low power consumption of about 3.5 W of the unit ensures an eficient support in experiments of long duration like photothermal microscopy and subssurface imaging. The system accepts reference signals of any wave shape and synthesizes corresponding sine wave for fundamental only response. Second harmonic detection scheme has been incorporated for applications in non-linear photothermal experiments up to 55kHz. At 1 kHz, the measured common mode rejection ratio of the differential front end is about 70 dB, input voltage noise is about 25 nVl √Hz and current noise is about. 1 pA/√Hz. The sensitivity is 200 nV and the maximum possible dynamic reserve is 54 dB. The full-scale sensitivity is adjustable from 2 μ V to 200 mV and time constant from 1 ms to 50s.Optional notch filters are included for line frequency and its second harmonic. The phase stability, output offset drift and the total output error have been analyzed. The unit has been employed in laser-photoacoustic imaging for detecting a subsurface hole in an aluminium block and photothermal radiometry of a silicon wafer and the results have been presented. Though developed for photothermal applications, care has been taken to make it a low cost general-purpose instrument.

7 illus, 9 ref

004282   Sharma G D;Sharma S K;Roy M S (Physics Dep, Jai Narain Vyas University, Jodhpur, Rajasthan-342 005) : Photovoltaic properties of schottky device based on dye sensitized poly (3-phenyl azo methine thiophene) thin film. Thin Solid Films 2004, 468(1-2), 208-215.

004281   Sharma A;Gupta V P;Virdi A (Department of Physics, University of Jammu, Jammu-Tawi 180 006) : RHF and DFT based study of the structure, thermodynamic properties and electronic specture of methacryloyl halides. Indian J pure appl Phys 2004, 42(4), 251-7.

Advanced level theoretical studies using Functionals Theory (DFT) and Hartree-Fock (HF) methods involving extended basis sets with the inclusion of polarization and correlational effects have been attempted for understanding the conformational peculiarities of methacryloyl halides (F, Cl, Br), in their electronic ground (S_o) and first excited (S₁) states and to determine their thermodynamic and physico-chemical parameters. Potential energy curves for the S_o and S₁ states of the molecules have been plotted for studying rotational isomerism. Two stable conformers s-trans and s-cis have been identified, with the former being more stable than the latter, thus excluding the possibility of the higher energy gauche conformer reported in some experimental measurements, A complete interpretation of the electronic spectra in terms of the energy levels, frequency, intensity and nature of transition has been made for the stable conformers on the basis of Cl level calculations involving singly excited states.

2 illus, 5 tables, 21 ref

004280   Shah N A;Iqbal S Z;Parveen B (Department of Electronics & Instrumentation Technology, The University of Kashmir, Srinagar 190 006) : Minimum component current-mode universal filter. Indian J pure appl Phys 2004, 42(4), 296-8.

A novel curent-mode (CM) universal filter based on and employing only one second generation curent conveyor (CCII+), two operational transconductance amplifiers (OTAs), and three grounded capacitors is presented. The grounded capacitor configuration of the proposed circuit is beneficial to an integrated circuit (IC) implementation. Three types of current-transfers lowpass (LP), highpass (HP), and bandpass (BP) can be achieved simultaneously while other filtering responses allpass (AP) and notch can be obtained by summing the appropriate node curents without any change to be induced in the filter structure and/or employment of additional components. The transconductance gains of OTAs are used to tune the filter characteristics electronically in an orthogonal manner. The structure is devoid of resistors and enjoys low sensitivity performance. The experimental results are included.

^ssc4 illus, 15 ref

004279   Ravindra Prasad K;Subramanyam Naidu P (Phys Dep, SVUPG Centre, Kavali(AP) 524 201) : Ultrasonic study of some ophthalmic solutions in aqueous medium. Indian J pure appl Phys 2003, 41(9), 686-9.

Seven ophthalmic systems belonging to one class, which reduced 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.

5 illus, 10 ref

004278   Ramadan K A;Mansour H M M (Physics Dep, Faculty of Science, Cairo University, Giza, Egypt) : Thermodynamical properties of neutron matter using gogny effective interaction. Indian J pure appl Phys 2003, 41(9), 675-80.

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 ρ fm^-3. The calculations cover a wide range of densities and are discussed in comparison with the realistic interaction calculation of Friedman and Pandharipande.

7 illus, 17 ref

004277   Rakesh Kumar;Padha N;Shishodia P K;Mehra R M (Phys & Electronics Dep, University of Jammu, Jammu (J & K)-180 004) : Study of dark and photoconductivity of Sb-doped CuInSe₂ thin films. Indian J pure appl Phys 2003, 41(9), 723-6.

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.

5 illus, 11 ref

004276   Rajpurt N;Tiwari S;Chandra B P (Post Graduate Studies and Research in Physics and Electronics, Rani Durgawati University, Jabalpur-482 001) : Temperature dependence of pulse-induced mechanolouminescence excitation in coloured alkali halide crystals. Bull Mater Sci 2004, 27(6), 505-9.

The relative efficiencies of different crystals are often determined under identical conditions of temperature and excitation. If the temperature of a crystal is increased ior decreased with respect to room temperature, luminescence efficiency may get increased or decreased according to the composition of the crystal. When coloured crystals of NaCl, NaBr, KCl and KBr are excited by pulse-induced excitation at different temperatures, the mechanoluminescene (ML) intensity increases with temperature. The ML intensity of first peak, I_m1, second peak, I_m2 and the total ML intensity, I_T, initially increase with temperature and then tend to attain an optimum value for a particular temperature of crystals. The ratio, I_m2/I_m1, is found to increase with increasing temperature of the crystals. The expression derived on the basis of rate equations, are able to explain the temperature dependence of ML intensity on several parameters.

7 illus, 11 ref

004275   Pandey S K;Ramrakhiani M;Chandra B P (NO, Govt Model Science College, Jabalpur) : Temperature dependence of exciton life-time in GaAs/AlGaAs quantum wells. Indian J pure appl Phys 2003, 41(9), 719-22.

In GaAs/AlGaAs quantum well structures, the confinement of electrons as well as, holes in GaAs well region causes enhancement of Coulomb interaction, which leadd 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 in dominated by radiative recombination of excitons. The PL and PL decay time is found to depend on temperature. At higher temperature, 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, intially, 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.

4 illus, 12 ref

004274   Pal S;Jacob C (Materials Science Centre, Indian Institute of Technology, Kharagpur-721 302) : Silicon - a new substrate for GaN growth. Bull Mater Sci 2004, 27(6), 501-4.

Generally, GaN-based devices are grown on silicon carbide or sapphire substrates. But these substrates are costly and insulating in nature and also are not availalble in large diameter. Silicon can meet the requirements for a low cost and conducting substrate and will enable integration of optoelectronic or high power electronic devices with Si based electronics. But the main problem that hinders the rapid development of GaN devices based on siliconis the thermal mismatch of GaN and Si, which generates creacks. In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is comparable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on the market. Latest developments in GaN based devices on silicon have been reviewed.

43 ref

004273   Painuli C P;Bhatt R M;Raiwani Y P;Srivastava S;Gairola S C;Gairola R P;Indu B D;Tiwari M D (Journalism Department, H N B Narwhal University, Srinagar 246 174 Uttranchal) : Electronic heat capacity of crystalline solids. Indian J pure appl Phys 2004, 42(4), 288-93.

The expressions for the electron density of states (EDOS) and electronic heat capacity (EHC) have been obtained for an isotopically disordered anharmonic crystal. The quantum dynamics of the crystal has been discussed in the light of an almost complete Hamiltonian consisting of (i) harmonic and anharmonic phonon fields, (ii) electrons, (iii) electron-phonon interaction and (iv) localized fields. It is observed that the electron-phonon coupling plays a crucial role in determining EDOS and EHC. The temperature dependence of EDOS is the remarkable feature of the present formulation.

10 ref

004272   Nimal A T;Vijay Kumar;Gupta A K (National Physical Laboratory, , Dr K S Krishnan Road, New Delhi 110 012) : Superconducting transition edge bolometer based on single phase BPSCCO 2223 thick film. Indian J pure appl Phys 2004, 42(4), 275-8.

Single-phase Bi(pb)-Sr-Ca-Cu-O (BPSCCO) polycrystalline thick films on MgO substrates were used to realize superconductor bolometer, to detect infrared radiation. BPSCCO 2223 single-phase thick films were prepared by screenprinting technique with T_c(R=0)=107K. The film is patterned as a meander line to increase the length and the resistance of the detector. The patterned thick film mounted on a thermal insulator and maintained at mid point temperature of superconducting transition constitutes the bolometer. The bolometer is current biased and exposed to chopped IR radiation of wavelength 915 nm, and the output is measured as voltage. The bolometer response is studied for chopping frequencies in the range of 1 Hz to 1 kHz. Responsivity of 15 V/W has been achieved at chopping frequency of 2 Hz.

6 illus, 18 ref

004271   Mattoo B A (Phys Dep, S P College, Srinagar, Jammu & Kashmir-190 001) : Charge imbalance in a non-equilibrium superconductor. Indian J pure appl Phys 2003, 41(9), 727-30.

A general formalism for charge imbalance in a non-equilibrium superconductor is obtained using ξ-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.

9 ref

004270   Mangal R;Saxena N S;Joshi G P;Sreekala M S; Thomas S (Condensed Matter Physics Laboratory, Phys Dep, University of Rajasthan, Jaipur-302 004) : Measurement of effective thermal conductivity and thermal difusivity for assessing the integrity of fiber to matrix bond in natural fiber composite. Indian J pure appl Phys 2003, 41(9), 712-18.

Thermal conductivity and thermal diffusivity of pineapple leaf reinforced phenol formaldehydr 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.

11 illus, 1 table, 17 ref