018815   Mansour N A;Diab A M (Physics Dep, Faculty of Science, Zagazing University, Zagazig, Egypt) : Study of shape of the yrast line and deformation changes in gadolinium isotopes. Indian J Phys-Pt A 2003, 77(3), 289-91.

The Gamma ray studies of <6>147Gd nucleur had been performed previously on the basis of gamma-gamma coincidence, angular distribution and excitation function measurements. In this nucleus (N=83), two values for the effective moment of inertia are suggested which reproduced the energies of the non-yrast states, that are populated in the decay of the isomer. A comparison of the energy level patterns for the even gadolinium isotopes have been done by studying the changes in deformation the so-called Gauge plots.

2 illus,2 tables, 14 ref

018814   Malhotra B D;Singhal R (Biomolecular Electronics and Conducting Polymer Research Group, National Physical Laboratory, Dr.K S Krishnan Road, New Delhi-110 012) : Conducting polymer based biomolecular electronic devices. Pramana J Phys 2003, 61(2), 331-43.

Biomolecular electronics is rapidly evolving from physics, chemistry, biology, electronics and information technology. Organic materials such as proteins, pigments and conducting polymers have been considered as alternatives for carrying out the functions that are presently being performed by semiconductor silicon. Conducting polymers such as polypyrroles, polythiophenes and polyanilines have been projected for applications for a wide range of biomolecular electronic devices such as optical, electronic, drug-delivery, memory and biosensing devices. Reviews of some of the results obtained at our laboratory in the area of conducting polymer biomolecular electonics.

11 illus, 53 ref

018813   Lavrentovich O D (Chem Physics Interdisciplinary Program and Liquid Crystal Instt, Kent State Univ, Kent, Ohio 44242, USA) : Fluorescence of confocal polarizing microscopy: Three-dimensional imaging of the director. Pramana J Phys 2003, 61(2), 373-84.

Much of the modern understanding of orientational order in liquid crystals (LCs) is based on polarizing microscopy (PM). A PM image bears only two-dimensional (2D) information, integrating the 3D pattern of optical birefringence over the path of light. Recently. Proposed a technique to image 3D director patterns by fluorescence confocal polarizing microscopy (FCPM). The technique employes the property of LC to orient the fluorescent dye molecules of anisometric shape, added in small quantities to the LC. In LC, smooth director deformations do not alter mass density of the material. thus the density of dye is also uniform across the sample, except, perhaps, near the surface or at the cores of topological defects. In polarized light, the measured fluorescence signal is determined by the spatial orientation of the molecules rather than by dye concentration (as in regular biological samples stained with tissue-specific dyes). The contrast is enhanced when both excitation and detection of fluorescence light are performed in polarized in polarized light. Describes the essence of FCPM technique and illustrates some of its applications, including imaging of Frederiks electric-field induced effect in a nematic LC and defects such as dislocations in cholesteric LCs.

8 illus, 36 ref

018812   Lakshminarayanan V;Sur U K (Raman Res Institute, , C V Raman Avenue, Bangalore-560 080) : Hydrophobicity-induced drying transition in alkanethiol self-assembled monolayer-water interface. Pramana J Phys 2003, 61(2), 361-72.

Explains the phenomenon for the alkanethiol monolayer-aqueous electrolyte interface, in which the extremely hydophobic alkanethiol film repels water molecules adjacent to it and in the process creates a shield between the monolayer film and water. This effectively increases the overall thickness of the dielectric layer that is manifested as an abnormally low value of interfacial capacitance. This behaviour is very much akin to the `drying transition' proposed by Lum, Chandler and Weeks in their theory of length scale dependent hydrophobicity. For small hydrophobic units consisting of apolar solutes, the water molecules can reorganize around them without sacrificing their hydrogen bonds. since for an extended hydrophobic unit, the existence of hydrogen bonded water structure close to it is geometrically unfavourable, there is a net depletion of water molecules in the vicinity leading to the possible creation of a hydrophobic interfacial gap.

5 illus, 1 table, 35 ref

018811   Kumar S (Centre of Liquid Crystal Research, , O O Box 1329, Jalahalli, Bangalore-560 013) : Molecular engineering of discotic nematic liquid crystals. Pramana J Phys 2003, 61(2), 199-203.

Connecting two columnar phase forming discotic mesogens via a short rigid spacer leads to the formation of a π-conjugated discotic dimer showing discotic nematic (N_D) phase. Attaching branched-alkyl chains directly tothe core in hexaalkynylbenzene resulted in the stabilisation of N_D phase at ambient temperature. Pentalkynylbenzene derivatives possessing a combinating of normal and branched-alkoxy chains display a very broad N_D phase which is stable well below and above the room temperature.

3 illus, 13 ref

018810   Krishnaswamy R;Raghunathan V A;Sood A K (Raman Research Institute, , C V Raman Avenue, Bangalore-570 080) : Structures of some surfactant-polyelectrolyte complexes. Pramana J Phys 2003, 61(2), 447-54.

Structures of complexes formed in aqueous solutions by some anionic polyelectrolytes (double and single stranded (ds and ss) DNA, poly(vinyl sulfonate) (PVS), and poly(styrene sulfonate) (PSS)) with a cationic surfactant system consisting of cetyltrimethylammonium bromide (CTAB) and sodium 3-hydroxy-2-naphthoate (SHN) have been determined using small angle X- ray diffraction. all complexes are found to have a two-dimensional (2-D) hexagonal structure at low SHN concentrations. analysis of the diffraction data shows that the ds DNA-CTAB complex has an intercalated structure, with each DNA strand surrounded by three cylindrical micelles. On increasing SHN concentration, DNA-CTAB-SHN complexes exhibit a hexagonal-to-lamellar transition, whereas PVS complexes show a hexagonal → centered rectangular → lamellar transition. PSS complexes show yet another sequence of structures. These results indicate the significant influence of the chemical nature of the polyelectrolyte on the structure of the complex.

9 illus, 15 ref

018809   Krishnamurthy K S;Balakrishnan R (Allied Sci Dep, Faculty of Electrical and Machanical Engg, College of Military Engg, Pune-411 031) : Electric field generated solitons, disclinations and vortical flows in freely suspended nematic 8 CB. Pramana J Phys 2003, 61(2), 263-75.

Presents the results of optical studies on the instabilities in a substrate-free nematic 8CB film, subject to an in-plane electric field. The initial director field involves a - 1/2 strength disclination loop, separating the central pseudoisotropic zone from the splay-bend (SB) birefringent boundary. Three regimes of samples thickness are distinguishable on the basis of field-induced instabilities. Thick (~ 75μm) film display growth of SB zones (independently of disclination movement), wall-formation, and reversible transition between walls and disclinations. Moderately thick films, a few μm in the central part, exhibit distinctive undulations at the border of advancing SB layers. Submicron thin films, with smectic-like homeotripic central plateau, show spectacular isotropic vortex-pairs at either end of this plateau. further, the end regions of the birefringent zone exhibit both electro-convective flows and reorientational effects. The latter are associated with the formation of open and closed walls, and loop-wall emission. the final high field instability involves jet-like flows at the two ends of the film.

16 illus, 16 ref

018808   Krishan Rao K;Surender V (Phys Dep, Kakatiya Univ, Warangal-506 009) : Surface studies on As-grown (111) faces of sodium bromate crystals. Bull Mater Sci 2001, 24(6), 665-9.

Single crystals of sodium bromate are grown at various supersaturations ranging from 3% to 8%. Surface studies have been carried out on as-grown and etched (III) faces of these crystals. Typical and systematically oriented growth hillocks are observed almost on all the faces. Further dislocation studies are made to understand the growth history of these crystals. These studies suggest that the crystals grow by 2D-growth mechanism. In addition to this, studies are also conducted on the formation of overgrowths and inclusions in these crystals.

5 illus, 10 ref

018807   Kalita P K;Sarma B K;Das H L (Department of Physics, Gauhati University, Guwahati-781 014 Assam) : Structural and photoelectronic properteis of vaccume evaporated CdSe thin films. Indian J Phys-Pt A 2003, 77(3), 225-31.

Thermally evaporated CdSe thin films deposited at high substrate temperature T_s≥473 K are found to be polyerystalline with hexagonal ZnS type structure. The grain size increases with T. Film crystallinity shows the most preferential orientation along [002] reflection. The sublinear behaviour of photocurrent - light intensity characteristics, measured at different experimental condition for the films deposited at different T_S and t, clearly confirms the defect controlled photoconductivity in CdSe films. Activation energies in dark and under illuminations are calculated from the temperature dependence of dc conductivity of the films. The reduction of activation energy under illumination is explained on the basis of the grain boundary effect.The photocurrent in the films increases whereas the photosensitivity decrease exponentially with therise of ambient temperature within the range 303-403 K which is attributed to the effect of different types of scattering on carrier mobility. Spectral response shows a direct transition at 725 nm with an additional absorption around 975 nm which also confirms the existence of inherent defect states in CdSe films.

8 illus, 26 ref

018806   Janossy I (Research Institute for Solid State Physics and Optics, , H-1525, P O Box 49, Budapest, Hungary) : Photo-orientation at liquid crystal-polymer interfaces. Pramana J Phys 2003, 61(2), 435-445.

It is suggested that liquid crystal-polymer interfaces are coupled systems, in which the components mutually influence the orientational state of each other. The photo-orientation process at liquid crystal-polymer interfaces provides a striking example of such a coupling. Experiments show that the anisotropic structure generated by polarised light at a polymer surface is strongly affected by the phase of the liquid crystal covering the polymer. Photo-orientation is significantly more efficient when the liquid crystal is in the isotropic phase than when it exhibits orientational order. The observations are interpreted by assuming that in the smectic and nematic phases the liquid crystal stabilises to a large extent polymer chain-segments aligned parallel to the diretor, while it blocks the photo-induced formation of chain-segments in the perpendicular direction. Other situations, in which the coupling between the liquid crystal and the polymer can be important, are also discussed briefly.

5 illus, 17 ref

018805   Jain R;Bhandari D;Saxena N S;Sharma S K; Tripathi A (Physics Dep, Univ of Rajasthan, Jaipur-302 004) : Effect of high-energy heavy ion irradiation on the crystallization kinetics of co-based metallic glasses. Bull Mater Sci 2001, 24(1), 27-33.

Differential scanning calorimeter (DSC) is employed to study the crystallization kinetics of irradiated (at three different fluences with high-erergy heavy ion; Ni¹¹⁺ of 150 MeV) specimens of two Co-based metallic glasses. It is found that the crystallization process in both the glasses in completed in two phases. The DSC data have been analysed in terms of kinetic parameters viz. activation energy (E_c), Avrami exponent (n), dimensionality of growth (m), using two different theoretical models. The results obtained have been compared with that of virgin samples. The lower activation energy in case of second crystallization occurring at higher temperature indicates the easier nucleation of second phase. The abnormally high value of Avrami exponent in Co-Ni glass indicates very high nucleation rate during first crystallization.

10 illus, 3 tables, 15 ref

018804   Hatwalne Y;Madhusudana N V (Raman Research Institute, , C V Raman Avenue, Bangalore-560 080) : The cone phase of liquid crystals: triangular lattice of double-tilt cylinders. Pramana J Phys 2003, 61(2), 277-83.

Predictes the existence of a new defect-lattice phase near the nematic-smectic-C (NC) transition. This tilt-analogue of the blue phase in a lattice of double-tilt cylinders which are disclination lines in the smectic layer normal as well as the c-filed. Discusses the structure and stability of the cone phase. Suggests that many `nematics' exhibiting short range layering and tilt order may in fact be in the molten cone phase, which is a line liquid.

3 illus, 19 ref

018803   Haase W;Wrobel S;Falk K (Eduard-Zintl Institute of Inorganic and Physical Chem, Darmstadt Univ of Tech, Petersenstr 20, 64287 Darmstadt, Germany) : Recent results on some colomnar paramagnetic metallomesogens. Pramana J Phys 2003, 61(2), 189-98.

The liquid crystalline and selected physical properties of some vanadyl and manganese(III)-porphyrin-TCNE complexes are discussed. These materials form linear chains from a magnetic point of view and columnar discotic LC phases. Some of the manganese complexes exhibit and bulk magnetic phase below ~ 20 K. The discussed materials are studied by means of DSC, X-ray powder diffraction, dielectric spectroscopy, reversal current characterization and magnetic susceptibility measurements. A broader view on some physical properties of columnar paramagnetic metallomesogens is given.

9 illus, 24 ref

018802   Giri R;Singh H K;Tiwari R S;Srivastava O N (Phys Dep, Banaras Hindu Univ, varanasi-221 005) : Effect of cationic size in Hg(Tl/Bi)Ba2Ca2Cu3O8+ on superconducting and microstructural characteristics. Bull Mater Sci 2001, 24(5), 523-8.

Investigations on the effect of simultaneous substitution of Bi and Tl at the Hg site in the oxygen deficient HgO_δ layer of HgBa₂Ca₂Cu₃O_8=δ cuprate superconductor. Bulk polycrystalline samples have been prepared by the two-step solid state reaction process (precursor route). It has been observed that the as grown HgBi_0.2-xTl_xBa₂Ca₂Cu₃O_8=<100> (with x = 0.00, 0.05, 0.10, 0.15, 0.20) corresponds of the 1223 phase. It has been found that the T_c varies with the average cationic size <60>R_d<60> of the dopant cations. The optimum T_c of ~ 131 K has been found for the composition HgBi_0.15Tl_0.05Ba₂Ca₂Cu₃O_8=<100> has been found to be most dense and this phase exhibits the highest stability. The J_c of the optimum material HgBi_0.15Tl_0.05Ba₂Ca₂Cu₃O_8=<100> is found to be ~ 1.29 x 10³ x 10³ A/cm² at 77 K.

4 illus, 1 table, 13 ref

018801   Ghosh D;Deb A;Bhattacharyya S;Ghosh J (Department of Physics, Nuclear and Particle Physics Research Centre, Jadavpur University, Kolkata-700 032) : Azimuthal angle dependence of two and three particle dynamical correlation among target fragments in <. Indian J Phys-Pt A 2003, 77(3), 255-60.

Reports an investigation on the two particle and three particle short range dynamical angular correlation in emission angle space among the target fragments produced in ²⁸Si-AgBr interactions at 14.5 AGeV on different range of azimuthal angles 0°≤ϕ≤9 0°, 90°≤ϕ≤ 180<144>F255>≤ϕ≤ 360°. The experimental data have been compared with the Monte Carlo simulated events to extract dynamical correlation. The analysis reveals that both two and three particle dynamical correlation among target fragments depend on the azimuthal angle space.

2 illus, 28 ref

018800   Gadkari D B;Shashidharan P;Lal K B;Arora B M (Phys Dep, Mithibai College, Mumbai-400 056) : Influence of crystal-melt interface shape on self-seeding and single crystalline quality. Bull Mater Sci 2001, 24(5), 475-82.

The growth of Sb-based crystals (InSb, GaSb etc) was undertaken using resistive heater furnace by vertical directional solidification (VDS) technique. Crystal-melt interface shape during the growth was shown to convert from concave to convex along the crystal axiz of the ingots. Many antimodine (Sb) crystals of 8 mm to 18 mm diameter were grown by optimized growth parameters. The forced convenction and absence of conducting support to ampoule showed improvement in crystal quality of as grown ingots. Crystals showed preferred orientation and self-seeding. Results on interface shape and crystallinity of ingots were found to be in good agreement with the experiments.

6 illus, 22 ref

018799   Dixit V K;Rodrigues B V;Bhat H L (Phys Dep, Indian Institute of Sci, Bangalore-560 012) : Experimental setup for rapid crystallization using favoured chemical potential and hydrodynamic condition. Bull Mater Sci 2001, 24(5), 455-9.

The rapid crystallization of KH₂PO₄ (KDP) from solution is demonstrated at a rate up to = 7.5 mm/day along [100] and 22 mm/day along [001] in a crystallizer of 51 capacity, using accelerated crucible rotation technique (ACRT) and simulated platform geometry for controlling the hydrodynamic conditions. On an experimental basis crystals up to 40 x 43 x 66 mm^{3 size in about 3 days. Comparative analysis of the main structural and optical properties of crystals grown by conventional and rapid crystallization technique, is discussed.}

7 illus, 1 table, 12 ref

018798   Awasthi S K;Bajpai R (Deparment of Post-Graduate Studies and Research in Physics, Rani Durgawati University, Jabalpur-482 001) : Studies on microhardness, compatibility and thermal stability of poly (ethylmethacrylate) (PEMA) and poly (ethyleneoxide) (PEO) polyblens. Indian J Phys-Pt A 2003, 77(3), 233-6.

Microhardness study on polyblends of poly(ethylmethacrylate) (PEMA) and poly(ethyleneoxide)(PEO) is carried out by Vicker's microhardness testing.Thermal stability of this blend is investigated by Thermogravimetric analysis (TGA) and Differential thermal analysis (DTA). The decrease in the value of surface microhardness with increasing content of PEO in the blend reveals plasticization effect. The variation in thermal stability with increasing content of PEO is observed by TGA. The variation in compatibility and crystallinity of blend with increasing content of PEO is observed by DTA. Attempts have been made to correlate the results of microhardness and TGA-DTA.

5 illus,17 ref

018797   Asthana A;Srivastava O N (Phys Dep, Banaras Hindu Univ, Varanasi-221 005) : Observation of curious spiral growth features in Tl doped Hg bearing high temperature superconducting tapes. Bull Mater Sci 2001, 24(6), 595-601.

Synthesis of Hg(Tl)Ba₂Ca₂Cu₃O_8+δ superconducting tapes have been accomplished by annealing the precursor tape, Ba₂Ca₂Cu₃O_y (fabricated by doctor blade tape casting technique) in an environment of Hg(Tl) vapour. Characterization of superconducting HTSC tape sample was carried out through XRD, TEM, SEM and R-T measurements. Surface morphological investigations of the as-synthesized Hg(Tl)Ba₂Ca₂Cu₃O_8+δ HTSC tapes by scanning electron microscope have shown the occurrence of curious growth characteristics resembling spiral like features. These growth spirals encompass nearly the whole grain suggesting that spiral growth led to the formation of small crystal like grains of superconducting materials Hg(Tl)Ba₂Ca₂Cu₃O_8+δ. The likely mechanism for the generation of these screw dislocations has been elucidated in terms of incoherent coalescence of growth fronts formed from Hg(Tl):1223 and Hg(Tl):1234 nuclei.

6 illus, 27 ref

018796   Aparna M;Bhimasankaram T;Suryanarayana S V; Prasad G;Kumar G S (Phys Dep, Osmania Univ, Hyderabad-500 007) : Effect of lanthanum doping on electrical and electromechanical properties of Ba1-xLa xTi). Bull Mater Sci 2001, 24(5), 497-504.

The effect of lanthanum doping is studied on ferroelectric properties of Ba_1-xLa_xTiO₃ with x=0.0005, 0.001, 0.003 prepared through solid state sintering route. Dielectric and impedance spectroscopic studies have been carried out. The tetragonal distortion on the unit cell decreased and ferroelectric transition temperature, T_c increased with the increase of lanthanum content. Combined impedance and admittance spectroscopy was used to analyse impedance data. The electromechanical parameters were calculated from the resonant and anti-resonant frequencies from vector admittance plots. The electromechanical coefficients for Ba_1-xLa_xTiO₃ with x = 0.003 were found to be much larger than that of pure barium titanate.

8 illus, 3 tables, 16 ref

018795   Anusionwu B C;Ogundare F O;Orji C E (NO, Abdus Salam International Centre for Theoretical Physics, Trieste, Italy) : Thermodynamic investigation of persistent complexes in Si-P melts. Indian J Phys-Pt A 2003, 77(3), 275-9.

The Si-P alloy forms compounds SiP, SiP₂ in its solid phase. A statistical mechanical theory based on complex formation has been used to predict the possible compounds that could persist from the solid to the liquid state of Si-P melt at about 1750 K.The results show that Si₂P will exist in the liquid phase at lower concentrations of phosphorus. It also predicts the presence of Si₃P₂ which is strong and probably exists throughout the whole concentration range.

4 illus, 12 ref

018794   Anantharaman M R;Malini K A;Sindhu S;Mohammed E M;Date S K;Kulkarni S D;Kurian P (Phys Dep, Dept of Polymer Sci and Rubber Tech, Cochin Univ of Sci and Tech, Cochin-682 002) : Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites. Bull Mater Sci 2001, 24(6), 623-31.

Rubber ferrite composites containing vrious mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verifed and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.

11 illus, 19 ref

018793   Ananda Kumari R;Chandramani R (Department of Physics, , Bangalore University) : Evaluation of lattice parameter and defect related studies of (KBr)_x(NaBr)_1-x mixed crystals grown from aqueous solution. Indian J Phys-Pt A 2003, 77(3), 219-24.

Mixed crystals of KBr-NaBr of different compositions were grown by slow evaporation technique.Crystals were doped with gold. Both the undoped crystals were γ-irradiated using ⁶⁰Co source.All the irradiated samples were subjected to thermoluminescence, optical obsorption and ESR studies.The study shows the composition dependence of the parameters and enhancement in the luminescence intensity as well as the absorption coefficient with gold doping. For the non-irradiatedsamples, lattice parameter determination, microhardness and dielectric studies have been carried out. Results of the studies are reported.

9 illus,5 tables,18 ref

018792   Alam M K;Islam M N;Zaman M A;Ali M Y (NO, Institute of Nuclear Science & Technology, Atomic Energy Research Est, P.O.Box-3787, Dhaka-1000 Bangladesh) : Optical model studies for elastic scattering of protons. Indian J Phys-Pt A 2003, 77(3), 261-6.

The angular distribution of protons elastically scattered from ¹²C, ¹⁶O,²⁷Al, ²⁸, Si, ⁴⁰Ca, ^58,60,62,64Ni, ^63,64,65Cu, ^64,66,68Zn, ⁹⁰Zr, ¹⁰⁸Ag, ¹¹⁶Sn, ¹⁹⁷Au, ²⁰⁸Pb at different energies ranging from 28 MeV to 61.4 MeV, have been analyzed in terms of the spherical optical model. Independent energy search at each energy and common geometry optical model calculations ahve been performed. An over all satisfactory agreement has been obtained. The best fit parameter values of the depth, radius and diffusivity of all the real, imaginary and spin orbit parts of the potential are obtained by the method of least square. Systematic trends of variation of different potential depths are investigated. Imperical formula have been developed for the real potential depths of the proton scattering.

6 illus, 2 tables, 16 ref

018791   Acharya B R;Primak A;Dingemans T J;Samulski E;Kumar S (Phys Dep, Kent State Univ, Kent, Ohio 44242, USA) : The elusive thermotropic biaxial nematic phase in rigid bent-core molecules. Pramana J Phys 2003, 61(2), 231-7.

The biaxial nematic liquid crystalline phase was predicted several decades ago. Several vigorous attempts to find it in various systems resulted in mis-identifications. The results of X-ray diffraction and optical texture studies of the phases exhibited by rigid bent-core molecules derived from 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole reveal that the biaxial nematic phase is formed by three compounds of this type. X-ray diffraction studies reveal that the nematic phase of these compounds has the achiral symmetry D_2h, in which the overall long axes of the molecules are oriented parallel to each other to define the major axis of the biaxial phase. The apex of the bent-cores defines the minor axis of this phase along which the planes containing the bent-cores of neighboring molecules are oriented parallel to each other.

5 illus, 17 ref

017942   Zou B;Wang J;El-Sayed M A (Institute of Physics, Chinese Academy of Sciences, Beijing-100 080, China) : The correlation between emission in freshly prepared porous silicon and the carrier density in silicon wafer. Asian J Spectrosc 2002, 6(1), 9-15.

The emission, and Fourier transform infrared spectra of freshly prepared porous silicon (PS) and the silicon wafer are examined. Increasing the temperatures leads to a general decrease in the emission intensities of PS samples, however, the emission of freshly prepared samples show an unusually large and sudden increase in its intensity at the specific temperature at which the hydrogen ion conductivity in the silicon wafer increases. The temperature dependence of the O-H vibration intensity of silicon wafer shows a sudden decrease at the same temperature. These results are consistent with a model in which the luminescence in PS may come from the carrier-bound exciton in the confirmed nanostructure.

4 illus, 25 ref

017941   Zou B (Institute of Physics, Chinese Academy of Science, Beijing-100 080, China) : Interfacial polaron in quantum dots and stearate coated TiO₂ nanopartical. Asian J Spectrosc 2002, 6(1), 1-7.

Quantum confinement of carriers leads to the absorption band-edge red-shift and discrete levels in Quantum dots. Polaronic effect is found to be important in QD recently. A model about the "confirmed polaron" for strong coupling of carrier-phonon, their size dependent formation possibilities and energy variation in different QDs systems, and an indication of contribution from both intrinsic and/or extrinsic phonons has been reported. The spectroscopic characteristics of stearate coated TiO₂ nanoparticles are revisited by the above model. This model is useful to understand the luminescence phenomena of many QD systems.

4 illus, 16 ref

017940   Zoliana B;Pachuau Z;Zadeng L;Patra P K; Khathing D T;Thapa R K (Physics Dep, Condensed Matter Theory Research Group, Pachhunga University College,, Aizawl, Mizoram-796 001) : Photoemission studies of metal by using mathieu potential. Indian J Phys-Pt A 2003, 77(4), 393-6.

Photocurrent results from ferromagnetic materials Fe and Ni and D-band metals Pd and Cr is duscussed which is calculated by using the Mathieu for the crystal. A local dielectric functions have been used to calculate the electromagnetic field for the bulk, surface and vacuum regions of the metals.

4 illus, 12 ref

017939   Yadan S;Agarwal R;Bandyopadhyay A K;Sharma D R;Gupta A C (National Physical Laboratory, , Dr. K.S. Krishnan Marg, New Delhi - 110 012) : Modern instrumentation techniques in pressure.. metrology under static conditions. MAPAN 2003, 18(2), 57-82.

13 illus, 2 tables, 123 ref

017938   Wang D-S (NO, Institute of Physics, Chinese Academy of Science, Beijing-100 080, China) : Linear and nonlinear optical properties of borate crystals as calculated from the first principles. Bull Mater Sci 2003, 26(1), 159-63.

With the development of the state-of-are band calculation scheme andmassively parallel processing in the high performance compution it is now possible to calculate all important physical properties, including the nonlinear susceptibility, the multiphoton absorption rate, the birefringence adn the energy gap, from the first principles for complex practical nonlinear optical crystals, such as the borate crystal series, with an accuracy acceptable for materials development/design, and answer the questions often reaised by the material scienstists.

4 tables, 23 ref

017937   Vora A M;Patel M H;Gajjar P N;Jani A R (Dep of Physics, Sardar Patel Univ, Vallabh Vidyanagar-388 120) : Superconducting state parameters of indium based binary alloys. Pramana J Phys 2002, 58(5-6), 849-53.

Investigates the superconducting state parameters viz; electron-phonon coupling strength λ, Coulomb pseudopotential μ^*, transition temperature Tc, isotope effective exponent α and interaction strength N₀V for the In_1-xZn_x and In_1-xSn_x binary alloys. Incorporates six different types of local field correction functions, proposed by Hartree, Taylor, Vashistha-Singwi, Ichimaru-Utsumi, Farid et al and Sarkar et al to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of the various exchange and correlation functions is concluded from the study. The comparison with other such theoretical values is encouraging, which confirms the applicability of our model potential in explaining the superconducting state parameters of binary mixture.

12 ref

017936   Viswanadham C;Puthran G P;Jayaprakash D; Mishra R L (Accelerator and Pulse Power Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085) : Niobium sputter deposition on quarter wave resonators. Bull Indian Vacuum Soc 2003, 6(2), 3-15.

Niobium sputter deposition on quarter wave copper R. F. resonators, have been taken up in the laboratory. An ultra high vacuum system was made for this purpose. Niobium exhibits super-conducting properties at liquid Helium temperature. A uniform coating of about 1.5 μm of Niobium on the internal surfaces of the copper resonant cavities is desired. Power dissipation in the resonators can be greatly reduced by making the internal surfaces of the R. F. cavity super conducting.

10 illus, 3 ref

017935   Vijayan V (NO, Institute of Physics, Bhubaneswar-751 005) : Radiological impact from atmospheric releases of <. Indian J envir Prot 2001, 21(5), 425-7.

In order to assess radiological impact of the thermal power plant, the measurements were carried out using a gamma - ray spectrometer for estimating the natural radionuclides in flyashes from thermal power plants at Angul and Talcher in India. It is estimated that on an average about 1012 MBq of ²²⁶Ra per GW per year are discharge to the atmosphere from these two power plants at the Angul-Talcher area. The collective dose equivalent to lung tissues resulting from the atmospheric release of ²²⁶Ra is also discussed.

1 table, 8 ref

017934   Vijay Kumar (NO, Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai-980 8577, Japan) : Novel caged clusters of silicon: fullerenes, frank-kasper polyhedron and cubic. Bull Mater Sci 2003, 26(1), 109-14.

Recent findings of metal (M) encapsulated caged clusters of Si and Ge obtained from computer experiments based on an ab initio pseudopotential method. It is shown that one M atom changes drastically teh properties of Si and Ge clusters and that depending have been never used upon the size of the M atom, cages of 14, 15, and 16 Si as well as Ge atoms are formed. In particular M@Si₁₆ silicon fullerene has been obtained for M=Zr and Hf, while a Frank-Kasper polyhedron has been obtained for M@X₁₆, X=Si and Ge. These clusters show high stability and large highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) gaps which are likely to make these species strongly abundant. A regular icosahedral M@X₁₂ cluster has also been obtained for X = Ge and Sn by doping a divalent M atom. Interactions between clusters are rather weak. This is attractive for developing self-assembled cluster materials.

5 illus, 2 tables, 14 ref

017933   Verma A K;Ravindran P;Rao R S;Godwal B K; Jeanloz R (High Pressure Physics Division Dep, Bhabha Atomic Research Centre, Mumbai-400 085) : On the stability of rhenium up to 1TPa pressure against transition to the bcc structure. Bull Mater Sci 2003, 26(1), 183-7.

Electronic structure total energy calculations were carried out close packed (hcp) and body centred cubic (bcc) phases, by the full potential linear muffin-tin orbital method, in order to verify the stability of the ambient pressure hcp phase against transition to the bcc structure at high pressures. As per the results, no hcp to bcc structural transition can occur up to 1 TPa pressures. Moreover, Bain path calculations show that face centred cubic and body centred teragonal structures are also not energetically preferred over hcp in this pressure range. The axial ration (c/a) of Re changes by less than 0.33% in the pressure range studied.

5 illus, 20 ref

017932   Upadhye K V;Ganesh Kumara K;Purandare S C;Pai S P;Pinto R (Phys Dep, Indian Instt of Tech, Powai, Mumbai-400 076) : Direct injection of spin-polarized carriers across. Pramana J Phys 2002, 58(5-6), 1199-1201.

Reports here injection of spin-polarized carried from a half-metallic La_0.3-Ca_0.7MnO₃ (LCMO) colossal magnetoresistive (CMR) thin film into a high-temperature superconducting YBa₂Cu₃O_7-δ (YBCO) thin film studied using a micro-bridge. The LCMO and YBCO films were grown on (100) LaAlO₃ (LAO) substrate sequentially using pulsed laser deposition (PLD), I-V measurements carried out at 77 K show that while normal critical current, I^N_c, of the micro-bridge is 80 mA, the critical current, I^p_c, through the micro-bridge when injected from the CMR layer is 38 mA. This clearly shows that spin-polarized quasiparticles injected from the CMR layer into the YBCO layer suppress the critical current of the superconductor via the pair-breaking phenomena.

017931   Tulapurkar A A;Grover A K;Ramakrishnan S; Niazi A;Rastogi A K (Tata Institute of fundamental Res, , Homi Bhabha Road, Mumbai-400 005) : Peak effect studies in single crystals CeRu2 and 2H-NbS2. Pramana J Phys 2002, 58(5-6), 975-8.

Studies the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu₂ and 2H-NbS₂. 2H-NbS₂ is iso-structural and iso-electronic to 2H-NbSe₂, whose wimilarity with CeRu₂ as regards the PE representing the order-to disorder transformation of the flux line lattice was claimed some time ago. Reports on the step change in equilibrium magnetization across the peak effect in CeRu₂. Also presents the vortex phase diagrom of 2H-NbS₂ obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS₂ and 2H-NbSe₂.

3 illus, 6 ref

017930   Trivedi U N;Modi K B;Joshi H H (Dep of Phys, Saurashtra Univ, Rajkot-360 005) : Magnetic behavior of the oxide spinels. Pramana J Phys 2002, 58(5-6), 1031-4.

The effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al_{xCrxFe2.5-2xO4 (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mossbauer spectra (X<62>0.5>).}

1 illus, 1 table, 14 ref

017929   Tonouchi M (Res Centre for superconductor Photonics, Oska Univ and PRESTO/CREST, Uapan Sci and Tech Corp (JST), 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan) : Optical magnetic flux generation in superconductor. Pramana J Phys 2002, 58(5-6), 1153-7.

The generation of the magnetic flux quanta inside the superconductors is studied as a new effect to destroy superconductivity using femtosecond (fs) laser. The vortices are successfully generated in the YBa₂Cu₃O_7-δ thin film striplines by the fs laser. It is revealed that the vortex distribution in the strip reflects the fs laser beam profile.

4 illus, 12 ref

017928   Tomy C V;Pal D;Banerjee S S;Ramakrishnan S; Grover A K;Bhattacharya S;Higgins M J;Balakrishnan G;Paul M K (Dep of Phys, Indian Institute of Tech, Powai, Mumbai-400 076) : Study of the peak effect phenomenon in single crystals of 2H-NbSe2. Pramana J Phys 2002, 58(5-6), 925-35.

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase bundaries of the possible order-disorder transformations in the vortex matter. Presents a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. Sketches the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. Also establishes the connection between the metastability effects and pinning.

8 illus, 13 ref

017927   Thaker C M;Rayaprol S;Mavani K;Rana D S; Sahasrabudhe M S;Patil S I;Kuberkar D G (Dep of Phys, Saurashtra Univ, Rajkot-360 005) : Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO 3 perovskite. Pramana J Phys 2002, 58(5-6), 1035-9.

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1-2xPr_xCa_x)MnO₃ (LPCMO) type CMR material. It is reported that, with the increase in x (for x = 0.1), 0.15, 0.2), the T_c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance in crease with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. the results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for under standing the structural, transport and magnetic properties are discussed in detail.

4 illus, 1 table, 9 ref

017926   Suresh K G;Radha S;Nigam A K (dep of Physics, Indian Instutite of Technology, Mumbai-400 076) : Metamagnetism in Ce(Ga,Al)2. Pramana J Phys 2002, 58(5-6), 769-71.

Effect of al substitution on the magnetic properties of Ce(Gaal_x)₂ (x=0, 0.1 and 0.5) system has been studied. the magnetic state of CeGa₂ is found to be FM with a Tc of 8 K, whereas the compounds with x = 0.1 and 0.5 are AFM and possess T_N of about 9 K. These two compounds undergo metamagnetic transition and the critical fields are about 1.2 T and 0.5 T, respectively at 2 K. these variations are exp;ained on the basis of helical spin structure in these compounds.

1illus, 4 ref

017925   Sundrananjam R;Jayanthi S;Suganthi S K (Civil Engineering Dep, Government College of Technology, Coimbatore-641 013) : Kinetic analysis on anaerobic digestion of source - sorted organic fractions of municipal solid waste and domestic sewage. Indian J envir Prot 2001, 21(5), 416-19.

Kinetic study using Chen and Hashimoto model on anaerobic digestion of source - sorted organic fractions of municipal solid waste (SSORMSW) and domestic sewage was done in a laboratory scale biodigester, operated in semi - continuous mode, at ambient temperature at an organic loading rate of 1 kg VS/m³ day at different hydraulic retention times in day. Specific gas yield was 0.62 m³/kg VS. Using Chen and Hashimoto model the kinetic parameters, such as ultimate methane production rate (B⁰) of 0.75 maximum specific groth rate μ^m of 0.10 dimensionless kinetic parameter k = 1.0 methane production rate was 0.45.

2 illus, 5 tables, 7 ref

017924   Srivastava V (Microwave Tube Area, Central Electronics Engineering Research Institute, Pilani (Rajasthan)-333 031) : Sputter deposition of textured carbon on copper collector surface for a high efficiency space TWT. Bull Indian Vacuum Soc 2003, 6(2), 17-22.

High collector efficiency is a very important aspect of a space TWT. A four-stage depressed collector was successfully designed and jointly developed with BEL, Bangalore, for recovering minimum 80% energy of the spent electron beam for a C-band 60 W space TWT. The four electrodes of the depressed collector were made of OFHC copper. Because of the high secondary electrons emission from the copper surface, the collector electrodes were surface treated for supression of secondary electrons emission for achieving high collector efficiency. In the present prototypes of the C-band 60 W space TWT, Titanium carbide (TiC) of thickness about 10 microns was deposited on the copper collector surface using sputtering technique. Collector efficiency better than 75% was achieved with back streaming of electron beam (mainly caused by secondary electrons) less than 2 mA. It is expected that the sputter deposition of textured carbon on the copper electrode surface may improve collector efficiency upto 85% and may further reduce back streaming of electron beam. It is planned to develop an experimental set up for the sputter deposition of textured carbon on the copper collector for a high efficiency TWT.

3 illus, 1 table, 9 ref

017923   Srinivas K;Sarah P;Suryanarayana S V (Physics Dep, CVR College of Engineering, Mangalpalli, RR (Dist.)501 510) : Impedance spectroscopy study of polycrystalline Bi₆Fe₂Ti₃O₁₈. Bull Mater Sci 2003, 26(2), 247-53.

The electrical properties of polycrystalline Bi₆Fe₂Ti₁₃O₁₈ are investigated by impedance spectroscopy in the temperature range 30-550°C. The imaginary part of impedance as a function of frequency shows Debye like rexation. Impedance data are presented in the Nyquist plot which is used to identify an equivalent circuit and the fundamental circuit parameters are determined at different temperatures. The grain and grain-boundary contributions are estimated. The results of bulk a.c. conductivity as a function of temperature adn frequency are presented. The activation energies for the a.c. conductivity are calculated. The polaron hopping frequencies are estimated from the a.c. conductivity data.

8 illus, 15 ref

017922   Soibel A;Banerjee S S;Mayasoedov Y;Rappaport M L;Zeldov E;OOi S;Tamegai T (Dep of Condensed Matter Phys, The Weizmann Institute of Sci, rehovot 76100, Israel) : Investigating the vortex melting phenomenon in BSCCO crystals using magneto-optical imaging technique. Pramana J Phys 2002, 58(5-6), 893-8.

Using a novel differential magneto-optical imaging technique we investing the phenomenon of vortex lattic melting in crystals of Bi_{2Sr2CaCu2O8 (BSCCO). the images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface with varying field (H)/temperature (T). Believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across the sample, which create fluctuations in teh local melting temperature or field value. To study the fluctuations in the local melting temperature/field, Constructes maps of the melting landscape Tm(H, r), viz., the melting temperature (Tm) at a given location (r) in the sample at a given field (H). a study of these melting landscape is not fixed, but changes rather dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale and shape of the landscape result from the competing contributions of different type of quenched disorder which have opposite effects on the local melting transition.}

2 illus, 16 ref

017921   Sirdeshmukh D B;Kumara Swamy T;Geeta Krishna P;Subhadra K G (Physics Dep, Kakatiya University, Warangal-506 009) : Systematic hardness measurements on mixed and doped crystals of rubidium halides. Bull Mater Sci 2003, 26(2), 261-5.

Efforts are made to improve the hardness of rubidium halide crystals by solid solution hardening and impurity hardening. Systematic measurements have been made on rubidium halide mixed crystals (Rb br-Rbl and KI-RbI) and rubidium halide crystals doped with Sr²⁺ ions. The composition dependence of the hardness of mixed crystals follows the law ΔH_v=K x (1-x), where ΔHv is the enhancement in hardness, K a constant and x and (1-x) the concentration of the first and second component of the mixed crystals, respectively. The hardness of doped crystals increase with the concentration Cof the dopant according to the law, ΔHv=k C^m, where k and m are constants. The relative efficacy of the two methods of hardening is discussed.

3 illus, 4 tables, 18 ref

017920   Singh R J;Sharma P K;Khan S (Phys Dep, aligarh Muslim Unit, Aligarh-202 002) : EPR study of deoxygenated high temperature superconductors. Pramana J Phys 2002, 58(5-6), 843-8.

7 illus, 17 ref

017919   Singh P P (Physics Dep, Indian Institute of Technology, Mumbai-400 076) : Theoretical study of superconductivity in MgB₂ and its alloys. Bull Mater Sci 2003, 26(1), 131-5.

Using density-functional-based methods the fully-relaxed, full-potential electronic structure of the newly discovered superconductor, MgB₂, and AIB₂. The results, described in terms of total density of states (DOS) and the partial DOS around the Fermi energy, E_F, clearly show the importance of B p-electrons for superconductivity. For BeB₂ and NaB₂, the results indicate qualitative similarities byt significant quantitatives differnces in their electronic strucutre due to differences in the number of valence electrons and the lattic constants a and c. Also Mg_1-xM_xB₂ (M≡Al, Li or Zn) alloys have been studied using coherent-potential to describe disorder, Gaspari-Gyorffy appoach to evaluate, electron-phonon coupling, and Allen-Dynes equation to calculate the superconducting transition temperature, T_c. It has been found that in Mg_1-xM_xB₂ alloys the way T_c changes depends on the location of the added/modified k-resolved states on the Fermi surface and the variation of T_c as a function of concentration is dictated by the B p DOS.

5 illus, 29 ref

017918   Singh M P (Physics Dep, G.B. Pant University of Agriculture and Technology, Pantnagar-263 145, Uttaranchal) : Temperature dependence of junction voltage in bilayer cuprate superconductors. Indian J Phys-Pt A 2003, 77(4), 365-9.

Deals with the study of junction voltage as a function of temperature various microscopic interactions that exist in bilayer high temperature cuprate superconductors. For this purpose, a tight binding bilayer Hubbard Hamiltonian has been, considered that includes the in-plane (wihtin CuO₂ plane) and out-of-plane interactions. The situation for bilayered cuprates considered here is equivalent to a Josephson's coupled SIS junction. Relies on the Green's function equations of motion approach within simple BCS formalism and derive the expressions for superconducting order parameter, carrier density and junction voltage. The numerical analysis shows that in bilayer cuprates, the junction voltage depends on various in-plane contributions as well as on temperature. Finally, compares our theoretical results on junction voltage with that of existing experimental results and found to be in qualitative agreement.

2 illus, 20 ref