019891   Rajesh Singh;Singh A K;Singh R P (Physics Dep, Atmospheric Research Laboratory, Banaras Hindu University, Varanasi-221 005) : Synchronized whistlers recorded at Varanasi. Pramana J Phys 2003, 60(6), 1273-7.

Some interesting events of synchronized whistlers recorded at low latitude station Varanasi during magnetic storm period of the year 1977 are presented. The dynamic spectrum analysis shows that the component whistlers are Echersley whistlers having dispersion 10 s^1/2 and 30 s^1/2. An attempt has been made to explain the dynamic spectra using lightning discharge generated from magnetospheric sources.

2 illus, 18 ref

019890   Paul S N;Chattopadhyaya S;Bhattacharya S K; Bera B (Faculty of Science Dep, Serampre Girl's College, Hooghly-712 201) : On the study of ion-acoustic solitary waves and double-layers in a drift multicomponent plasma with electron-inertia. Pramana J Phys 2003, 60(6), 1217-33.

Using the pseudopotential method, theoretical investigation has been made on the first order Korteweg-de Vries ion-acoustic solitons in a multicomponent plasma consisting of warm positive ions, negative ions and isothermal electrons. The effects of electron-inertia and drift motion of the ions of the amplitudes and widths of the solitons have been studied in a plasma having (H⁺, CI⁺), (H⁺, O^-), (He⁺m H^-) and (He⁺, O^-) ions. Ion-acoustic double-layers have also been investigated for such plasmas. It has been found that drift velocity and electron-inertia have significant contribution on the formation of double-layers in multicomponent plasma.

8 illus, 4 tables, 31 ref

019889   Mondal S;Singh R K;Shanker R (Physics Atomic Physics Laboratory Dep, Banaras Hindu University, Varanasi-221 005) : Energy and angular distributions of electrons ejected from CH₄ and C₃H₈ under 16.0 keV electron impact. Pramana J Phys 2003, 60(6), 1203-15.

Relative cross sections, differential in energy and angle, for electrons ejected from CH₄ and C₃H₈ molecules under 16.0 keV electron impact have been measured. Electrons were analyzed by a 45° parallel plate electrostatic analyzer at emission angles varying from 60° to 135° with energies from 50 eV to 1000 eV. The angular distributions of electrons exhibit strucutres which are found to arise from Coulomb and non-Coulomb interactions. Furthermore, the double differential cross sections of electrons ejected from C₃H₈ molecule are found to be higher in magnitude than those from CH₄. Also, the angular distributions of C-K-shell Auger electrons emitted from the target molecules have been studied and shown to be isotropic within the experimental uncertainly.

8 illus, 24 ref

019888   Mahapatra S;Nag J (Physics Dep, Nuclear and Particle Physics Research Centre Jadavpur University, Kolkata-700 032) : Ground state structure of some double-μ hypernucleus by a three-body model using a simple corrdinate space approach. Pramana J Phys 2003, 60(6), 1179-85.

New experimental data on the binding energy Bμμof μμ⁶He, reported very recently, come up with the values Bμμ = 7.25±0.14 MeV and ΔBμμ = 1.01±0.2 MeV which are substantially lower than the old data Bμμ =10.9± MeV and ΔBμμ = 4.7±1.0 MeV in use in literature since 1966. In view of the new data we decided to undertake a re-study of the μμ⁶ He hypernucleus being the same three-body model (β-μ-μ) with a simple coordinate space variational approach which was employed earlier with the old data on μμ⁶He. After fitting different μ-μ potentials to the new data of μμ⁶He was have applied method to study some double-μ hypernuclei in light, medium and heavy mass regions and have determined the structural quantities like Bμμ, the r.m.s. values of core-μ (<60>r_core-μ>) and μ-μ (<60>rμ-μ) distances theoretically. The core-μ interaction considered is of Woods-Saxon type. The strength and the range of the core-μ potential have been adjusted to reproduce the μ-binding energy (Bμ). These are in good agreement with the relativistic mean field (RMF) results. Our study shows that the μ-μ bonding energy ΔBμμ decreases with increasing mass number from μ¹⁰μ Be to μ²¹⁰μPb of a double-μ hypernucleus.

1 illus, 3 tables, 17 ref

019887   Kalita P K (Physics Dep, Guwahati College, Guwahati-781 021) : Temperature dependence of dc photoconductivity in CdTe thin films. Pramana J Phys 2003, 60(6), 1247-57.

The temperature dependence of dc photoconductivity in the measuring range 303-417 K has been studied in CdTe thin films having thickness t < 4000

7 illus, 2 tables, 23 ref

019886   Jana D C;Prashan S S (Physics and Technologies Dep, Vidyasagar University, Paschim Midnapur-721 102) : On the effect of a longitudinal magnetic field on oscillatory characterisitics of a subnormal region in discharge in argon. Pramana J Phys 2003, 60(6), 1279-86.

Oscillating nature of current pulses under d.c. excitation in subnormal region with longitudinal magnetic field at pressure range 0.20 torr to 0.85 torr have been studied. The frequency, bandwidth, peak-peak voltage, cut-off current and rise time of the current pulses have been observed with pressure, average tube current and magnetic field. A study of these oscillograms in magnetic field, average tube current and pressure are presented. The probable mechanism for the generation of oscillation based on space-charge field modification with magnetic field is discussed.

8 illus, 3 tables, 7 ref

019885   Jain K K;Anil Kumar S K;Poddar H N P (Force and Hardness Standards, National Physical Laboratory, Dr K S Krishnan Marg, New Delhi-110 012) : A newly developed 5 kN dead weight force machine for reference calibration. MAPAN 2002, 17(4), 147-56.

Describes the salient features and the results of metrological performance of a newly developed 5 kN dead weight force machine that would serve as force reference calibration machine at NPL (India). Two well characterized strain gauge force transfer gauges of 2 kN and 5 kN full scale with a repeatability better than ± 0.0002% were used in compression mode to derive the best measurement capability of the machine. The derived best measurement capability of the machine is ± 50 ppm (k=2).

4 illus, 3 tables, 14 ref

019884   Jagdish Prashad (Chem Dep, Meerut Colege, Meerut-250 001) : Joshi effect in mercury vapour with a triode under various modes of detection mechanism. Asian J Chem 2003, 15(2), 1037-44.

Production of Joshi effect ±Δi in mercury vapour excited by a transformer discharge in the range 0.48 kV to 1.00 kV, 50 Hz has been studied with triode 30 coupled resistively with L.T. line using it is anode bend (α) and grid leak β detectors. The observations of i_D,L are taken in plate as well as in grid currents. For the observations in grid currents, at a given applied potential, i_D and -Δi are in the order β<62>α at lower values of the resistance R; at its higher values, they ae in the order α<62>β. The corresponding -%Δi is, however, in the order αΔβ for lower values of R, and in the order β<62>α for the higher values of R. For the observations in grid current, at a given applied potential, i_D is in the order α<62>β; the corresponding-Δo amd -%Δi are in the order β<62>α.

2 illus, 11 ref

019883   George J;Paul I;Varughese P A;Varghese G (Crystal Phyiscs Division Dep, Christian College, Chengannur-689 122) : Rhythmic patern formations in gels and matalon-packter law: a fresh perspective. Pramana J Phys 2003, 60(6), 1259-71.

The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law, spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure on the initial concentrations of the reactants is derived. Matalon-Packter law, which relates the spacing coefficient with the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems.

4 illus, 41 ref

019882   Choubisa R;Bhullar A S;Sud K K (Physics Dep, College of Science Campus, M.L.S. University, Udaipur-313 002) : Coplanar (e,3e) different cross-section of He atom. Pramana J Phys 2003, 60(6), 1187-1201.

Presents the results of calculation of five-fold different cross-section (FDCS) for (e,3e) process on He atom in low momentum transfer and high electron impact energy in shake-off mechanism. The formalism has been developed in Born approximation using plane waves, Byron and Joachain as well as Le Sech and correlated BBK-type wave functions respectively for incident and scattered, bound and ejected electrons. The angular distribution of FDCS of calculation is presented in various modes of coplanar calculation is able to reproduce the trend of the experimental data. However, it differs in magnitude from the experiment. The theory does not predict four-peak structure in summed mutual angle for lower excess ejected electron energies. Also discusses the importance of momentum transfer, post-collision interaction (PCI) and ion participation in the (e, 3e) process in constant θ₁₂ mode.

7 illus, 27 ref

019881   Chaudhary K P;Sharma R;Farid N;Singhal R P (National Physical Laboratory, , Dr K S Krishnan Marg, New Delhi-110 012) : Calibration of step gauge by substitution method on coordinate measuring machine and evaluation of uncretainly of measurement. MAPAN 2002, 17(2), 67-74.

In dimensional metrology, derived standards of length can be calibrated on displacement comparators. Substitution method is applied for calibration of step gauge. Precision 3D coordinate measuring machine (CMM) is used as a comparator to measure the pitch of the Koba step gauge by comparing it with a reference standard Koba step gauge having international traceability. Reference standard and the gauge under calibration have the same geometry and length. Measurements have ben carried out in the identical environmental conditions on the reference Koba step gauge and the step gauge under calibration. The measured values of step gauge under calibration are corrected with respect to the known values of reference Koba step gauge. Uncertainty of measurement using CMM as comparator has been evaluated taking into account all the factors that contribute to uncertainty significantly and uncertainty budget prepared. The uncertainty of measurement for calibration of step gauge is ±(0.3 + 0.9L)μm, where L is the length in metre. This is better uncertainty than the uncertainty achieved by performing calibration, using CMM alone, Calibration results, uncertainty budget, and calibration method are presented.

2 illus, 3 tables, 13 ref

019880   Bhagat L S (Physics Dep, Dr Ambedkar College, Nagpur-440 010) : Infrared spectra of Fe₂O₃-Li₂O-B₂O₃-MoO_{3 glasses.} Asian J Chem 2003, 15(2), 1173-7.

Changes in network structures of lithium-molybdenum-iron-borate glasses were investigated by means of infrared spectroscopy and X-ray analysis. Analysis of the network structures were carried out based on a networks unmodified by MoO₃ and Fe₂O₃-modified network. The unmodified networks are made by three dimensional array of clusters with unmodified BO₃ and BO₄ groups. MoO₃ reduction and Fe₂O₃ addition both gives contribution to four coordinated boron which governs the glass structure.

^ssc3 illus, 1 table, 12 ref

019879   Baria J K;Jani A R (Physics Dep, Sardar Patel University, Vallabh Vidyanagar-388 120) : Lattice mechanical properties of some fcc f-shell metals. Pramana J Phys 2003, 60(6), 1235-46.

A pseudopotential depending on an effective core redius is proposed to study the binding energy, equation of state, ion-ion interaction, phenon dispersion curves (q-space and r-space analysis), mode Gruneisen parameters and dynamical elastic constants of some fcc f-shell metals La, Yb, Ce and Th. The contribution of the s-like electrons is calculated in the second-order perturbation theory for the potential while d- and f-like electrons is taken into account by introducing repulsive short-range-Mayer term. The parameter of the potential is evaluated by zero pressure condition. An excellent agreement between theoretical investigations and experimental findings is achieved which confirms the present formalism.

12 illus, 2 tables, 35 ref

019878   Askerzade I N (Physics Dep, Ankara Univeristy, Tandogan-016 00, Ankara, Turkey) : Influence of the interplay between helicoidal magnetic ordering and superconductivity on the differential conductance in HoNi₂B₂C/Ag junctions. Pramana J Phys 2003, 60(6), 1282-91.

The point contact spectra of magnetic superconductor HoNi₂B₂C/Ag-based junctions is analysed in the framework of Blonder-Tinkham-Klapwijk (BTK) theory. The anomalous behavior in the dl/dV curves above the Neel temperature (T_N~5 K) is attempted to be explained by the partial suppression of superconducting gap parameter of the prevailing helical incommensurate structure.

20 ref

019877   Arun K G;Joy M;Kuriakose V C (Physics Dep, Cochin University of Science and Technology, Cochin-682 022) : Renormalized energy-momentum tensor of μΦ<. Pramana J Phys 2003, 60(6), 1161-9.

Considers a scalar field with quartic self-coupling in a spatially flat (3+1)-dimensinal Robertson-Walker space-time, having arbitrary mass and coupled to gravity. As special cases, energy-momentum tensor for conformal and minimal coupling are also obtained. The energy-momentum tensor is observed to exhibit trace anomaly in curved space-time.

17 ref

019876   Arun K G;Joy M;Kuriakose V C (Physics Dep, Cochin University of Science and Technology, Cochin-682 022) : Renormalized energy-momentum tensor of λΦ<. Pramana J Phys 2003, 60(6), 1161-9.

Divergenceless expression for teh energy-momentum tensor of scalar field is obtianed using the momentum cut-off regularization technique. Considers a scalar field with quartic self coupling in a spatially flat (3+1)-dimensional Robertson-Walker space-time, having arbitrary mass and coupled to gravity. As special cases, enery-momentum tensor for conformal and minimal coupling are also obtianed. The energy-momentum tensor is observed to exhibit trace anomaly in cruved space-time.

17 ref

019875   Ansari A;Yadav H L;Kaushik M;Jakhar U R (NO, Institute of Physics, Sachivalaya Marg, Bhubaneswar-751 005) : High-spin structure of neutron-rich Dy isotopes. Pramana J Phys 2003, 60(6), 1171-8.

In view of recent experimental progress on production and spectroscopy of neutron-rich isotopes of Dy with mass number A= 166 and 168, made theoretical investigations on the structure of high spin states of ^164-170 Dy isotopes in the cranked Hartree-Fock-Bogoliubov (CHFB) theory exploying a pairing+quadrupole+hexadecapole model interaction. With the increase of neutrom number the rotation alignment of the proton orbitals dominates the structure at high spins, which is clearly reflected in the spin dependence of the rotational g-factors. A particularly striking feature is the difference in the spin-dependent properties of ¹⁶⁶ as compared to that of ¹⁶⁴ Dy.

4 illus, 2 tables, 17 ref

018848   Zhou H;Zhang Y;Yang Z C O (Institute of Theoretical Physics, The Chinese Academy of Sciences, P O Box 2735, China) : The elastic theory of a single DNA molecule. Pramana J Phys 2003, 61(2), 353-60.

Studies the elastic responses of double- (ds) and single-stranded (ss) DNA at external forcefields. A double-strand-polymer elastic model is constructed and solved by path integral methods and Monte Carlo simulations to understand the entropic elasticity, Cooperative extensibility, and supercoiling property of dsDNA. The good agreement with experiments indicates that shortranged base-pair stacking interaction is crucial for the stability and the high deformability of dsDNA. Hairprin-coil transition in ssDNA is studied with generating function method. A threshold force is needed to pull the ssDNA hairpin patterns, stabilized by base pairing and base-pair stacking, into random coils. this transition is predicted to be of first order for stacking potential higher higher than some critical level, in accordance with experimental observation.

3 illus, 22 ref

018847   Vyas P R;Joshi T R (NO, Government Polytechnic, Chhotaudepur, Vadodara-391 165) : Some thermoluminescence properties of synthetic quartz and its potential as high level gamma radiation thermoluminescence dosimeter material. Indian J Phys-Pt A 2003, 77(3), 285-7.

Reports the thermoluminescence (TL) glow curves observed in powder of 230-350 mesh grain size of synthetic (laboratory made) quartz crystals with the without gamma irradiation. It is found that the specimen does not exhibit natural thermoluminescence (NTL). The excitation of the material at room temperature with gamma radiation induces TL peaks at 110°C[peak-I], 210°C[peak-II] and 340°C[peak-III] temperatures.Among them, peak-I is found sensitive tolow gamma doses and found absent in higher doses. In contrast to this, peak-II appears only at higher doses [70Gy-6kGy]. The examination of various dosimetric properties encourages the authors to suggest that peak-II present in synthetic quartz can be of use in the estimation of the higher-level-gamma doses used in radiation processing applications [100Gy-6kGy].

3 illus, 12 ref

018846   Virk H S;Chandi P S;Srivastava A K (Phys Dep, guru Nanak dev Univ, Amritsar-143 005) : Physical and chemical response of 70 MeV carbon ion irradiated kapton-H polymer. Bull Mater Sci 2001, 24(5), 529-34.

Physical and chemical responses of 70 MeV carbon ion irradiated Kapton-H polymer were studied by using UV-visible, FTIR and XRD techniques. The ion fluences ranging form 9.3 x 10¹¹-9 x 10¹³ ions cm^-2 were used. Recorded UV-visible spectra clearly showed a decrease in absorption initially with fluence, but for the higher fluences it showed a recovery characteristic. A decrease in band-gap energy of 0.07 eV was observed. The FTIR analysis indicated the high resistance to radiation induced degradation of polymer. The diffraction pattern of Kapton-H indicates that this polymer is semi-crystalline in its nature. In case of irradiated one, there was an average increase of crystallite size by 20%, but diffuse pattern indicates that there was a decrease in crystallinity, which may be attributed to the formation of complex structure induced by the cross-linking of the polymeric chains.

4 illus, 4 table, 21 ref

018845   Udayashankar N K;Bhat H L (Phys Dep, Karanataka Regional Engineering College, Surathkal, Srinivasnagar-574 157) : Growth and characterization of indium antimonide and gallium antimonide crystals. Bull Mater Sci 2001, 24(5), 445-53.

Indium antimonide and gallium antimonide were synthesized from the respective component elements using an indigenously fabricated synthesis unit. Bulk crystals of indium antimonide and gallium antimonide were grown using both the vertical and horizontal Bridgman techniques. Effect of ampoule shape and diameters on the crystallinity and homogeneity was studied. The grown crystals were characterized using X-ray analysis, EDAX, chemical etching, Hall effect and conductivity measurements. In the case of the gallium antimonide, effect of dopants (Te and In) on transport and photoluminescence properties was investigated.

13 illus, 2 tables, 46 ref

018844   Tschierske C;Dantlgraber G (Institute of Organic Chem, Martin-Luther-Univ Halle-Wittenberg, Kurt-Mothes Str.2, D-06120 Halle (Saale), Germany) : From antiferroeletricty to ferroelectricity in smectic mesophases formed by bent-core molecules. Pramana J Phys 2003, 61(2), 455-81.

This contribution gives an overview of ferroelectric switching liquid crystalline phases formed by bent-core molecules. First a descripition of some general principles behind the mesophase formation within bent-core systems are given, followed by a short review of the mesophase structures formed bty such molecules. Then, different classes of ferroelectric switching bent-coremesogens have been described. This type of switching behaviour has been reported for several subtypes of polar smectic phases (B2, B5, B7 and SmC_G) and recently for columnar mesophases. Particular attention is made to polyphilic bent-core molecules, composed of three incompatible units, a bent aromatic core, alkyl chains and an oligosiloxane unit. the importance of the decoupling of the layers into microsegregated sublayers for the ferroelectric organisation is discussed. Many of the ferroelectric switching mesophases show dark textures with distinct regions of opposite chirality in their ground states. It is discussed that this might be due to a helical superstructure formed as a result of an escape from macroscopic polar order. Hence, the materials themselves are not ferroelectric in the ground state, but upon alignment within an electric field in the measuring cells the ferroelectric states are stabilised by surface interactions, leading to a ferroelectric switching system. The designing principle has been extended to mesogenic dimers with bent-core structural units.

21 illus, 1 table, 69 ref

018843   Torgova S I;Geivandova T A;Frances cangeli O; Strigazzi A (FSUE `NIOPIK', Organic Intermediates and Dyes Institute, B.Sadovaya 1/4, Moscow 123995, Russia) : Banana-shaped 1,2,4-oxadiazoles. Pramana J Phys 2003, 61(2), 239-48.

3,5-Disubstituted 1,2,4-oxadiazoles are new type of liquid crystalline (LC) compounds with asymmetrical five-membered heterocycles as a central unit. They have a bent shape and are very convenient model-compounds for studying the dependence of the LC properties on the molecular design. Synthesizes and investigates `banana-shaped' 1,2,4-oxadiazoles using the ester groups as the linkage units. The new compounds exhibit spontaneous polarization in the smectice phase, even if there is no chiral group in the molecules. Preliminary experimental data suggest the presence of spontaneous polarization int eh nematic phase as well. In order to study the structural properties of the LC phases, X-ray diffraction (XRD) measurements on powder samples have been carried out. Based on the XRD data, a model of the structural arrangement of the bent molecules in the smectic phase is provided, which accounts for the macroscopic spontaneous polarization as well as the ferroelectric switching behavior.

1 illus, 2 tables, 22 ref

018842   Suri K;Annapoorni S;Tandon R P (Phys and astrophysics Dep, Univ of Delhi, Delhi-110 007) : Phase change induced by polypyrrole in iron-oxide polypyrrole nanocomposite. Bull Mater Sci 2001, 24(6), 563-7.

Nanocomposites of polypyrrole and iron oxide were prepared using simultaneous gelation and polymerization processes. Varied amounts of pyrrole monomer were added to a solution containing iron nitrate as precursor and 2-methoxy ethanol as solvent. The presence of oxide and polypyrrole was confirmed by using X-ray and FTIR techniques. Some of these nanocomposites exhibited magnetic behaviour. SEM studies of powder indicated presence of nanosized particles. Electrical conductivity studies of powders showed a slight variation in conductivity for lower concentration of pyrrole, with a sudden increase in conductivity at 15% of pyrrole concentration. a transition from a nonmagnetic to magnetic phase was also observed at the same concentration.

4 illus, 1 table, 22 ref

018841   Suresh K V (Raman Research Institute, , C V Raman Avenue) : Viscoelastic modes in chiral liquid crystals. Pramana J Phys 2003, 61(2), 297-312.

11 illus, 3 tables, 31 ref

018840   Srideshmukh D B;Sirdeshmukh L;Subhadra K G; Kishan Rao K;Bal Laxman S (Phys Dep, Kakatiya Univ, Warangal-506 009) : Systematic hardness measurements on some rare earth garnet crystals. Bull Mater Sci 2001, 24(5), 469-73.

Mircohardness measurements were undertaken on twelve rare earth garnet crystals. In yttrium aluminium garnet and gadolinium gallium garnet, there was no measureable difference in the hardness values of pure and nominally Nd-doped crystals. The hardness values were correlated with the lattice and elastic constants. An analysis of hardness data in terms of the interatomic binding indicated a high degree of covalency.

2 illus, 2 tables, 25 ref

018839   Singh N;Singh Y (Department of Physics, Banaras Hindu Univ, Varanasi-221 005) : Statistical mechanics of thermal denaturation of DNA oligomers. Pramana J Phys 2003, 61(2), 345-52.

Double stranded DNA chain is known to have non-trivial elasticity. Studies the effect of this elasticity on the denaturation profile of DNA oligomer by constraining one base pair at one end of the oligomer to remain in unstretched (or intract) state. The effect of this constraint on the denaturation profile of the oligomer has been calculated using the Peyrad-Bishop Hamiltonian. The denaturation profile is found to be very different from the free (i.e. without the constraint) oligomer. Also examines how this constraint affects the denaturation profile of the oligomer having a segment of defect sites located at different parts of the chain.

5 illus, 15 ref

018838   Shitole S J;Saraf K B (P G Dep of Phys, Pratap College, Amalner-425 401) : Growth and study of some gel grown group II single crystals of iodate. Bull Mater Sci 2001, 24(5), 461-8.

Single crystals of calcium iodate and barium iodate were grown by simple gel technique by single diffusion method. The optimum conditions were established by varying various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of the reactants etc. Crystals having different morphologies and habits were obtained. Prismatic, dendritic crystals of barium iodate and prismatic, needle shaped, hopper crystals of calcium iodate were obtained. Some of them were transparent, some transluscent, and few others were opaque. Both the crystals were studied using XRD, FT-IR, and thermal analysis. The crystals were doped by iron impurity. The effect of doping was studied using IR spectroscopy and thermal analysis.

11 illus, 4 tables, 10 ref

018837   Sharma H;Prakash S (Department of Physics, Punjab University, Chandigarh-160 014) : Strain field due to transition metal impurityies in Cu. Indian J Phys-Pt A 2003, 77(3), 247-53.

The strain field due to substitutional transition metal impurities in Cu metal are investigated using the discrete lattice model using Kanzaki lattice static method. The effective ion-ion interaction potential due to Wills and Harrison is used to evaluate dynamical matrix and the impurity-induced forces. The results for atomic displacements due to 3d , 4d and 5d impurities (Co, Ni, Pd, Ag, Pt and Au) in Cu are given up to 20 NN's of impurity and these are compared with the available experimental data which are found in agreement. The lattice shows expansion due to Co, Pd, Ag, Pt and Au impurities and contraction due to Ni impurity. the maximum displacements of 2.3% of 1 NN distance are found for CuAu alloy, while the minimum displacements of 0.43%of 1 NN distance are foun for CuNi alloy respectively. The relaxation energies for Ni and Pd impurities are found less than others impurities in Cu, therefore theses impurities may easily be solvable in Cu.

3 illus,5 tables,11 ref

018836   Sawadh P S;Kulkarani D K (Phys Dep, B D College of Engineering, Wardha-442 001) : Structural and magnetic properties of CaMa₂Fe₁₆O₂₇. Bull Mater Sci 2001, 24(1), 47-50.

A new compound, CaMg₂Fe₁₆O₂₇, is synthesized for the first time, in polycrystalline form, using stoichiometric mixture of oxides with standard ceramic technique and characterized by X-ray diffraction. It is found to have a hexagonal W-type structure with lattice parameter a= 5.850 A and c = 33.156 A. Electrical studies show that the compound is a semiconductor with energy of activation. ΔE=0.56 eV. Electrical conductivity results show a transition in the conductivity vs temperature plot ner the Curie temperature. The activation energy value obtained for the paramagnetic phase is found to be higher than that of the ferrimagnetic phase. The molar magnetic susceptibility was measured in the temperature range 300-850 K and the results show that the compound is ferrimagnetic at room temperature. The compound also shows hysteresis at 300 K. Paramagnetic nature of the sample above Curie temperature is also studied. The curie molar constant C_M calculated from the plot of 1/X_M vs T(K) is found to be nearly in agreement with the expected value.

5 illus, 1 tables, 10 ref

018835   Saravanan P;Jose T A;John Thomas P;Kulkarni G U (Chem and Phys of Mater Unit, Jawaharlal Nehru Centre for Advanced Scientific Res, Bangalore-560 064) : Submicron particles of Co, Ni and Co-Ni alloys. Bull Mater Sci 2001, 24(5), 515-21.

Magnetic sub-micron sized particles (with diameters in the range 100-600 nm) of Co, Ni and Co-Ni alloys, protected with polyvinylpyrrolidone have been prepared in gram quantities using the polyol process. Experiments carried out with different metal precursors and starting compositions have yielded reliable routes to produce particles of the desired diameters in the 100-600 nm range. The particles were characterized with X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, thermogravimetric analysis and magnetic measurements. The particles are found to be stable under ambient conditions indefinitely. The coercivity values of the Co and Ni particles are ~ 50% higher compared to the corresponding bulk values. The alloy particles follow and trend similar to the bulk alloys.

6 illus, 2 tables, 20 ref

018834   Sadashiva B K;Raghunathan V A (Raman Research Institute, , C V Raman Avenue, Bangalore-560 080) : Columnar phases exhibited by some polycatenear ligands and a few related metal complexes. Pramana J Phys 2003, 61(2), 219-29.

The synthesis and characterization of some polycatenar ligands which exhibit hexagonal columnar and cubic phases are reported. A pentacatenar with only four phenyl rings in the core and exhibiting a mesophase is also reported. A few copper (II) and palladium (II) complexes have been synthesized using these ligands and the mesomorphic properties exhibited by them are described. The hexagonal columnar phase exhibited by some of the complexes can be cooled down to room temperature. The mesophases have been characterized using a combination of polarized light microscopy, differential scanning calorimetry and X-ray diffraction methods.

8 illus, 3 tables, 12 ref

018833   Ruckmongathan T N (Raman Res Inst, , C V Raman Avenue, Bangalore-560 080) : Displaying gray shades in liquid crystal displays. Pramana J Phys 2003, 61(2), 313-29.

Quality of image in a display depends on the contrast, colour, resolution and the number of gray shades. A large number of gray shades in necessary to display images without any contour lines. These contours are due to limited number of gray shades in the display causing abrupt changes in grayness of the image, while the original image has a gradual change in brightness. Amplitude modulation has the capability to display a large number of gray shades with minimum number of time intervals [1,2]. Covers the underlaying principle of amplitude modulation, some variants and its extension to multi-line addressing. Other techniques for displaying gray shades in passive matrix displays are reviewed for the sake of comparison.

14 illus, 9 ref

018832   Ribeiro A C;Sebastiao P J;Cruz C (Centro de Fisica da Materia Condensada (UL), , Prof. Gama Pinto 2, 1699 Lisboa Cedex, Portugal IST (UTL), Av. Rovisco Pais, 1049-001 Lisboa, Portugal) : Contribution of proton NMR relaxation to the investigation of molecular dynamics in columnar mesophases of discotic and polycatenar molecules. Pramana J Phys 2003, 61(2), 205-18.

Presents a review concerning wide frequency range T₁ proton NMR relaxation studies performed in compounds exhibiting columnar mesophases, namely the Col_ho mesophase in the case of a liquid crystal of discotic molecules and the φ_h mesophase in the case of a liquid crystal of biforked molecules. These NMR relaxation studies were performed combining conventional and fast field cycling NMR techniques in a frequency range between 100 Hz and 300 MHz. The possibility of probing such a large frequency range has provided a way to effectively distinguish the influence, on the T₁ relaxation profiles, of the different molecular movements observed in this type of mesophases. In addition presents a comparison between the molecular dynamics in columnar (<102>_h) and lamellar (SmC) mesophases exhibited by the same biforked compound.

10 illus, 29 ref

018831   Reddy R R;Nazeer Ahammed Y;Abdul Azeem P;Rama Gopal K;Sasikala Devi B;Rao T V R (Department of Physics, Marathwada University, Aurungabad-431 004) : Interatomic force constants, ionicity and microhardness of binary tetrahedral semiconductors. Indian J Phys-Pt A 2003, 77(3), 237-41.

A simple relation between lattice energy (U), bond stretching and bond bending force constants (α,β), ionicity (f_i) and microhardness (H) developed for A^IIB^IV and A^IIIB^V semiconductors. The results are in excellent agreement with the values reported by different investigators.

4 illus, 3 tables, 24 ref

018830   Ravinder D;Vijaya Kumar K (Phys Dep, Osmania Univ, Hyderabad-500 007) : Dielectric behaviour of erbium substituted Mn-Zn ferrites. Bull Mater Sci 2001, 24(5), 505-09.

Dielectric properties such as dielectric constant (ε') and dielectric loss tangent (tan (δ) of mixed Mn-Zn-Er ferrites having the compositional formula Mn_0.58Zn_0.37Fe_2.05Er_xO₄ ( where x=0.2, 0.4, 0.6, 0.8 and 1.0) were measured at room temperature int eh frequency range 1-13 MHz using a HP 4192A impedance analyser. Plots of dielectric constant (ε') vs frequency show a normal dielectric behaviour of spinel ferrites. The frequency dependence of dielectric loss tangent (tan δ) was found to be abnormal, giving a peak at certain frequency for all mixed Mn-Zn-Er ferrites. a qualitative explanation is given for the composition and frequency dependence of the dielectric constant and dielectric loss tangent. Plots of dielectric constant vs temperature have shown a transition near the Curie temperature for all the samples of Mn-Zn-Er ferrites. However, Mn_0.58Zn_0.37Fe_1.05O₄ does not show a transition. On the basis of these results an explanation for the dielectric mechanism in Mn-Zn-Dr ferrites is suggested.

4 illus, 3 tables, 20 ref

018829   Ratnakaram Y C;Viswanadha Reddy A (Phys dep, S V Univ PG Centre, Kavali-524 201) : Correlation of radiative properties of rare earth ion (Pr 3+) in chlorophosphate glasses - 0.1 and 0.5 mol per cent concentations. Bull Mater Sci 2001, 24(5), 539-45.

Optical properties of chlorophosphate glasses of the type 50P_{2O5-30Na2HPO4-20RCl (R = potassium and lead) activated by 0.1 and 0.5 mol% of Pr³⁺ and Nd³⁺ have been investigated. Optical band graps (Eopt) have been reported for 0.1 and 0.5 mol% concentration of Pr³⁺ and Nd³⁺ doped potassium and lead chlorophosphate glasses. Energy levels and optical transitions of Pr³⁺ and Nd³⁺ and Nd³⁺ are assigned. Spectroscopic parameters (E¹, E², E³ξ4f and α), spectral intensities (↵expt), Judd-Ofelt intensity parameters (Ω2, Ω4 and Ω6) and radiative lifetimes (TR) are correlated for 0.1 and 0.5 mol% concentration of these two ions in potassium and lead chlorophosphate glasses.}

5 illus, 4 tables, 25 ref

018828   Ramanathan K V;Sinha N (Sophisticated Instruments Facility, Physics Dep, Indian Institute of Science, Bangalore-560 012) : Ordering in nematic liquid crystals from NMR cross-polarization studies. Pramana J Phys 2003, 61(2), 249-62.

The measurement of dipolar couplings between nuclei is a convenient way of obtatining directly liquid crystalline ordering through NMR since the coupling is dependent on the average orientation of the dipolar vector in the magnetic field which also aligns the liquid crystal. However, measurement of the dipolar coupling between a pair of selected nuclei is beset with problems that require special solutions. The use of cross polarization for measureing dipolar couplings in liquid crystals is illustrated. Transient oscillations observed during cross polarization provide the dipolar couplings between essentially isolated nearest neighbour spins which can be extracted for several sites simultaneously by employing two-dimensional NMR techniques. The use of the method for obtaining heteronuclear dipolar couplings and hence the order parameters of liquid crystals is presented. Several modifications to the basic experiment are considered and their utility illustrated. A method for obtaining proton-proton dipolar couplings, by utilizing cross polarization from the dipolar reservoir, is also presented.

11 illus, 32 ref

018827   Priya M;Padma C M;Freeda T H;Mahadevan C; Balasingh C (Phys dep, S T Hindu College, Nagercoil-629 002) : Electrical conductivity measurements on gel grown KDP crystals added with urea and thiourea. Bull Mater Sci 2001, 24(5), 511-14.

Pure and impurity added (with urea and thiourea) KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and prependicular directions at various temperatures ranging from 30 to 140°C by the conventional two-probe method. Study shows that the conductivity in KDP crystals, for both the impurities considered, in creases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.

4 illus, 2 tables, 11 ref

018826   Pratibha R;Madhusudana N V;Sadashiva B K (Raman Research Institute, , C V Raman Avenue, Bangalore-560 080) : On some liquid crystalline phases exhibited by compounds made of bent-core molecules and their mixtures with rod-like molecules. Pramana J Phys 2003, 61(2), 405-15.

In most homologous series of compounds made of bent-core (BC) molecules, the B2, B₁ and B₆ phases occur as the chain length decreases. Studies binary mixtures of the compound 1,3-phenylene bis[4-3-methylbenzoyloxy)]4'-n-dodecylbiphenyl 4'-carboxylate (BC12) which exhibits the B₂ phase with the compound 4-biphenylyl 4"-n-undecyloxybenzoate (BO11) mode of rod-lile (R) molecules. Finds the above sequency of occurrence of the B phases with increasing concentration of BO11. Describes the physical origin for the formation of these phases in both pure compounds and in the mixtures. Also finds the occurrence of the biaxial smectic A phase when the BO11 concentration is increased to 87-95.5 mol%. Report on another binary system composed of BC12 and 4-n-octyloxy 4'-cyanobiphenyl (80CB) made of R molecules. This system exhibits the biaxial smectic A phase down to 30°C. Using polarized infrared spectroscopy finds that the mutual orientation of the R and BC molecules in the SmA_db liquid crystal is such that the arrow axes of the BC molecules are along the layer normal of the partial bilayer smectic structure formed by the rods. Also describes unusual growth patterns obtained when the nematic phase transforms to the SmA_db phase in a mixture with 24 mol% of BC12.