002268   Samanta C (NO, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700 064) : Physics with loosely bound nuclei. Pramana J Phys 2001, 57(2-3), 519-24.

Essential aspect of contemporary physics is to understand properties of nucleonic matter that constitutes the world around us. Over the years research in nuclear physics has provided strong guidance in understanding the basic principles of nuclear interactions. But, the scenario of nuclear physics changed drastically as the new generation of accelerations started providing more and more rare isotopes, which are away from the line of stability. These weakly bound nuclei are found to exhibit new forms of nuclear matter and unprecedented exotic behaviour. The low breakup thresholds of these rare nuclei are posing new challanges to both theory and experiments. Fortunately, nature has provided a few loosely bound stable nuclei that have been studied thoroughly for decades. Attempts are being made to find a consistent picture for the unstable nuclei starting from their stable counterparts. Some significant differences in the structure and reaction mechanisms are found.

3 illus, 16 ref

002267   Sakata H (Department of Applied Chemistry, Tokai University, 1117, Kitakaname, Hiratsuka, Kanagawa-259 1292) : Hopping conduction in vanadium and iron tellurite glasses. Indian J Phys-Pt A 2001, 75(4), 307-12.

Dc transport properties of vanadium and iron tellurite glasses are reviewed. Glasses of both systems exhibit small polaron hopping condition. Vanadium tellurite glasses indicate adiabatic and non-adiabatic small polaron hopping conduction, while iron tellurite glasses present only non-adiabatic small polaron hopping transport due to lower concentration of maximum Fe₂O₃ content for glass forming. The former produces variable-range hopping conduction depending on glass composition at temperatures lower than θ_D/4, but the latter provides no variable-range hopping transport in the measurable range of temperatures. The application of pressure on some glasses of both systems increases conductivity. Oxygen gassensing behaviour due to gas diffusion are found for both kinds of the glasses.

10 illus, 47 ref

002266   Roy A (NO, Nuclear Science Centre, Aruna Asaf Ali Marg, P O Box 10502, New Delhi-110 067) : Superconducting linac and associated accelerator development at NSC. Pramana J Phys 2001, 57(2-3), 659-63.

There has been significant progress in the programme to develop a superconducting linear accelerator as a booster for the Pelletron accelerator at the Nuclear Science Centre. Presents the current status of the development in all the major components of the accelerator.

1 illus

002265   Ray S C (Department of Physis, MCKV Institute of Engineering, 243, G T Road (North), Liluah, Howrah-711 204) : Preparation and study of Cu₂O thin films deposited by the dip technique. Indian J Phys-Pt A 2001, 75(4), 453-5.

Copper oxide films are prepared using methanolic solution of cupric chloride (CuCl₂, 2H₂O) by the dip-coating technique at different baking temperatures. XRD study confirms that the films are of Cu₂O phase when prepared at baking temperature of 360°C and CuO phase when prepared at 400°C or more than 400°C banking temperature. The optical band gap of the Cu₂O films calculated from optical absorption measurements is 1.85 eV which is quite comparable with the reported value.

4 illus, 1 table, 11 ref

002264   Rastogi R G (Department of Physics and Space Sciences, Gujarat University, Ahmedabad-300 009) : Disturbance time variation of geomagnetic vertical field in the Indian equatorial electrojet. Curr Sci 2001, 80(8), 1056-9.

The disturbance time variations of the vertical component (Z) of the geomagnetic field at stations in the Indian chain, following a sudden commencement storm show a spectacularly large decrease at only the electrojet stations, Thiruvananthapuram, Etaiyapuram, Kodaikanal and Annamalainagar. This decrease is not synchronous in time with the decrease of the horizontal (H) field. The peak depression of the Z field occurs about three hours before the time of peak decrease of H, i.e. during the middle of the main phase of the storm, when the ring current is developing at the fastest rate. This first clear description of Dst (Z) at Indian electrojet stations is further confirmation of the sub-surface conducting channel in Palk Strait, where currents are induced by the ionospheric source current, producing large decrease of Z field at ground level. Similar analysis of Dst(Z) at different equatorial stations around the world is recommended to understand the abnormal features of Indian equatorial electrojet.

1 illus, 1 table, 11 ref

002263   Ramanna R;Jain S R (NO, National Institute of Advanced Studies, Indian Institute of Science Ca, Bangalore-560 012) : Empirical approach to the theory of particle and nuclear phenomena: review and some new ideas. Pramana J Phys 2001, 57(2-3), 263-9.

Experimental data on masses and lifetimes of unstable particles falls into a pattern, a brief review of some interesting consequences is presented. From the experience in semiclassical methods and recent advances in quantum chromodynamics, it is proposed that an appropriate generalisation of the Gutzwiller trace formula for field theories may lead to a systematic semiclassical chromodynamics theory. The theory can be developed to get appropriate dynamics leading to an explanation of pattern discovered in the empirical data.

^iia2 illus, 18 ref

002262   Ram Swarup;Gupta A K (National Physical Laboratory, , Dr K s Krishna Road, New Delhi-110 012) : Granularity effect on microwave surface resistance in high-T_c YBa₂ Cu₃ O_7-x bulk and thin film superconductor. Indian J Phys-Pt A 2001, 75(4), 413-7.

Reports the effect of variation of Josephson coupling strength in YBa₂Cu₃O_7-x (YBCO) superconductor due to grain enlargement, grain orientation and magnetic field on microwave surface resistance (R_s). The coupling strength in the bulk samples has been increased by increasing the sample density from 4.4 to 5.3 g/cm³, whereas in thin films, the same could be increased by increasing the c-axis orientation of the grains. The value of R_s (10GHz, 65K) in bulk samples has been found to decrease from 52 to 4 mΩ with the increase of the coupling strength from 0.06 to 0.43 and in thin films from 930 to 600 μΩ with increase of the coupling strength from 0.92 to 2.43. The effect of grain decoupling on microwave surface resistance was studied under dc and microwave magnetic fields. The surface resistance increases gradually with the application of dc and microwave magnetic fields due to grain decoupling and finally gets saturated beyond a certain critical field.

4 illus, 1 table, 20 ref

002261   Ram S;Rana S (Materials Science Centre, Indian Institute of Technology, Kharagpur-721 302) : Phase transformations in porous Al₂O3 Ceramic nanoclusters. Indian J Phys-Pt A 2001, 75(4), 437-41.

Porous ceramic powder of Al₂O₃ nanoclusters is deduced by a controlled thermal decomposition of a porous AlO(OH)αH₂O powder (Porosity Φ = 18%), a precursor of alumina or sapphire, at selected temperatures in the 5---1500 K range. The precursor has been synthesized in a highly pure form using a new chemical method of an electrochemical surface hydrolysis of a thin Al-plate in water. The pores govern a controlled thermal decomposition of it at a molecular scale and result in a refined porous Al₂O₃ powder of an enhance Φ value up to 40% over the starting value. The sample appears in different polymorphic metastable forms at different temperatures. If compared to in a bulk Al₂O₃, the transformations occur at significantly reduced temperatures by the assistance of the pores. The results are discussed with microstructure and X-ray powder diffraction studies.

5 illus, 1 table, 17 ref

002260   Ram S (Materials Science Centre, Indian Institute of Technology, Kharagpur, Kharagpur-721 302) : Magnetism in a new series of high-energy-density magnetic materials of amorphous alloys. Indian J Phys-Pt A 2001, 75(4), 379-83.

Unusually, a high-energy-density (JH)_max as 10 to 20 kJ/m³ appears in amorphous R-Fe-Al alloys at room temperature. This is a new series of ferromagnets that presents a considerably high value of (JH)_max in an amorphous state. The (JH)_max value is comparable to that in well-known high-energy-density rare-earth (R) magnets of R₂Fe₁₄ B and similar intermetallics. In principle, a high value of (JH)_max occurs on a high value of coercivity H_c and/or remanence J_r. A primary source of H_c is the magnetocrystalline anisotropy H_a which appears in a crystalline ferromagnetic (or ferrimagnetic) material. It results in an optimal value of H_c in an assembly of single domain particles of size D <126> D_c, with D_c, with D_c, the critical value of D. As an amorphous material does not have H_a it is not expected to have a large value of H_c observed in this example. This is demonstrated with representative R-Fe-Al (R = Nd, Pr, or Er) amorphouse alloys. The values of H_c, J_r, Curie temperature , T_c, as well as (JH)_max are found to be optimal at an optimal Fe <126> 30 at % content over the series.

5 illus, 2 table, 16 ref

002259   Rai R (Theory Group, National Physical Laboratory, Dr K S Krishnan Marg, New Delhi-110 012) : Study of Jahn-Teller and vibronic mixing interactions in T_1u and T_1g levels of C<. Indian J Phys-Pt A 2001, 75(4), 419-21.

The Jahn-Teller problem of C^-₆₀ in icosahedral symmetry is studied. The Jahn-Teller interaction in both the low lying levels T_1u and T_1g are taken into account and also the vibronic mixing between the two under an odd vibrational mode τ_1u is considered. With respect to the involvement of τ_1u mode operators, the vibronic Hamiltonian is an antisymmetric matrix operator. It is shown that an exact solution of the Hamiltonian in an infinite coupling model can be evolved by using a canonical transformation of τ_1u mode operators.

15 ref

002258   Radha Krishna B;Subramanyam T K;srinivasulu Naidu B;Uthanna S (Department of Physics, Srivenkateswara University, Tirupati-517 502) : Characterization of dc magnetron sputtered indium oxide films. Indian J Phys-Pt A 2001, 75(4), 457-60.

Indium Oxie films were deposited by dc reactive magnetron sputtering from indium target on to glass substrates held at temperatures in the range 373-673 K in an oxygen partial pressure of 2 x 10^-4 mbar. The dependence of structure, electrical and optical properties of the films on the substrate temperature was systematically studied. The films prepared at 373 K were amorphous while those formed at temperatures ≥ 473 K were polycrystalline with cubic structure. The electrical resistivity of the films decreased from 2.4 x 10^-2 Ω cm to 1.3 x 10^-3 Ω cm and Hall mobility increased from 2.5 cm²/Vsec to 18 cm²/Vsec with the increase of substrate temperature from 373 K to 673 K due to the improvement in the crystallinity of the films. The temperature dependence of Hall mobility indicated that the grain boundary scattering of the charge carriers predominated in these films. The optical transmittance (at λ = 600 nm) increased from 68% to 85% and the optical band gap increased from 3.64 eV to 3.78 eV with the increase of the substrate temperature from 373 K to 673 K respectively.

5 illus, 21 ref

002257   Prasad P S R (Mineral Physics Group, National Geophysical Research Institute, Hyderabad-500 007) : In situ micro-Raman investigation of dehydration mechanism in natural gypsum. Curr Sci 2001, 80(9), 1203-7.

Stability of bassanite and the mechanism of dehydration of natural gypsum were investigated by in situ micro-Raman spectroscopy in the temperature range 300-380 K and 300-450 K. From the thermal evolution of the sulphate (940-1200 cm^-1) and water (3250-3750 cm^-1) molecular stretching (V₁ and V₃) modes, it was evident that the gypsum dehydrated irreversibly into bassanite at about 370 ± 5 K. Reports that this transformation was preceded by the soluble anhydrite phase, with a characteristic Raman shift for V₁(SO₄) to about 1026 cm^-1. From the Arrhenius-type variations in the reduced intrensities of V₁(SO₄) for bassanite and anhydrite at 1014 cm^-1 and 1026 cm^-1, respectively, the activation energy for bassanite to anhydrite was estimated to be 32.5 ± 6.6 kJ mol^-1

5 illus, 1 table, 25 ref

002256   Popov Y P (Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Moscow Region 141980, Russia) : Peculiarities of the modern neutron spectrometry. Pramana J Phys 2001, 57(2-3), 601-10.

Neutron spectrometry provides many branches of science and technology with the necessary data. Usually the main part of the data is supplied by powerful neutron time-of-flight spectrometers. Nevertheless there are many other very effective but simpler and cheaper neutron spectroscopy methods on accelerators, suitable for solution of plenty of scientific and applied problems (for example, in astrophysics and radioactive waste transmutation). The methods of slowing-down spectrometry in lead and graphite, generating of neutron spectra, characteristic for nucleosynthesis in the stars, and neutron spectrometry by means of primary γ-transition shift are discussed in the report.

5 illus, 12 ref

002255   Phatak S C (NO, Institute of Physics, Bhubaneswar-751 005) : Quark matter formation in dense stellar objects. Pramana J Phys 2001, 57(2-3), 325-35.

It is expected that at very large densities and/or temperatures a quark-hadron phase transition takes place. Lattice QCD calculations at zero baryon density indicate that the transition occurs at Tc <126> 150-170 MeV. The transition is likely to be second order or a cross over phenomenon. The matter densities in the interior of neutron stars being larger than the nuclear matter density, the neutron star cores may possibly consist of quark matter which may be formed during the collapse of supernova. Starting with the assumption that the quark matter, when formed consists of predominantly u and d quarks. Considers the evolution of s quarks by weak interactions in the work. The reaction rates and time required to reach the chemical equilibrium are computed here. Calculations show that the chemical equilibrium is reached in about 10^-7 seconds. Further more during the equilibrium process enormous amount of energy is released and copious numbers of neutrinos are produced. Implications of these on the evolution of supernovae will be discussed.

3 illus, 14 ref

002254   Paul G K;Bandyopadhyay S;Sen S K (Department of Materials Science, Indian Association for the Cultivation of Science, Calcutta) : Preparation of aluminum doped zinc oxide films by sol-gel method : thermoelectric power and hall voltage measurements. Indian J Phys-Pt A 2001, 75(4), 433-5.

Transparent and conducting aluminium-doped zinc oxide (ZnO) films were prepared by the sol gel technique on silica-glass substrates. A simple analog subtration circuit has been fabricated to measure the Seebeck coefficient of a specimen containing 1.7 at% A1 at room temperature under high vacuum. This is small and negative. X-ray diffractogram indicates that the film is polycrystalline and scanning electron microscopy confirms the polycrysta;llinity with a grain size of approximately 40 nm. The Hall voltage at room temperature is also found negative. An attempt has also been made to explain the two experimental data

4 illus, 4 ref

002253   Pant P C;Pandey V P;Rajput B S (Department of Physics, Kumaun University, Nainital-263 002) : Scattering of a dyon from a dyonium. Indian J Phys-Pt A 2001, 75(2), 181-7.

Investigating the behaviour of a dyon moving in the field of another dyon it has been demonstrated that angular momentum for this system is modified and it carries an extra residual angular momentum. Study of scattering of a dyon from a dyonium has also been undertaken and it has been demonstrated that scattering cross sections are modified from the usual scattering cross sections of quantum electrodynamics due to the presence of magnetic charge on dyon.

21 ref

002252   Palit N;Dasgupta A;Ray S;Chatterjee P (Energy Research Unit, Indian Association for the Cultivation of Science, Calcutta-700 032) : Carrier transport at the junction of tandem solar cells. Indian J Phys-Pt A 2001, 75(4), 371-4.

Computer simulation of experimental current - voltage and spectral response characteristics of an incomplete cell structure - p₁-i₁-n₁-p₂-has been used to understand the hole transport mechanisms at the n-p junction. Two types of p-layer at the junction have been studied : hydrogenated microcrystalline silicon (μc-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H). Case (i) shows a fairly high fill factor (FF) and conversion efficiency (η), as against a very low FF and η in case(ii). Modelling reveals that this difference is due to the much lower activation energy, hence, larger free hole population in p-<109>c-Si:H. Also learn that both tunnelling and diffusion help push holes produced in P₂ by the incident light, towards the recombination layer at the junction. Thus, to ensure high rate of diffusion of holes, p₂ should have a high free hole density, which in turn, leads to improved performance. Preformance. Preliminary studies on double junction solar cells reveal that a μc-Si:H p-layer at the junction results in an 8% improvement in FF.

5 illus, 1 table, 11 ref

002251   Ozawa A (NO, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan) : Recent radioactive ion beam program at RIKEN and related topics. Pramana J Phys 2001, 57(2-3), 525-33.

Recent experimental programs at RIKEN concerning RI beams are reviewed. RIKEN has the ring cyclotron (RRC) with high intense heavy-ion beams and large acceptance fragment separator, RIPS. The complex can provide high intense RI-beams. By using the high intense RI-beams, a variety of experiments have been done. Recently, nuclear structure for unstable nuclei has been paid much attention. IN special, disappearance and appearance of magic numbers are discussed experimentally and theoretically. Thus, in this review, related experiments concerning disappearance and appearance of magic numbers are described. Finally, future project in RIKEN, RI-beam factory, is introduced briefly.

13 ref

002250   Ostrovsky S M;Nag K;Haase W (Institute of Physical Chemistry, Darmstadt University of Technology, Petersenstrabe 20, D-64287 Darmstadt, Germany) : Electronic and vibronic interactions in the mixed valence dimers. Indian J Phys-Pt A 2001, 75(4), 301-5.

General overview of different electronic and vibronic interactions in the mixed valence dimeric compounds is presented. They are isotropic exchange interaction, double exchange and vibronic coupling (PKS and Piepho modes). The influence of these interactions on the properties of the dimeric complexes is discussed. As an example investigations of fully delocalized [L`Fe₂(μ-OAc)₂](CIO₄) iron dimer.

5 illus, 1 table, 18 ref

002249   Oset E et al (Departamento de Fisica Teorica and IFIC, Centro Mixto Universidad de Valencia-CSIC, Institutos de Investigacion, Apdo, correos 2085, 46071, Valencia, Spain) : Chiral unitary theory: application to nuclear problems. Pramana J Phys 2001, 57(2-3), 417-31.

Briefly describes some basic elements of chiral perturbation theory, <67>PT, and how the implementation of unitarity and other novel elements lead to a better expansion of the T-matrix for meson-meson and meson-baryon interactions. Applications are then done to the ππ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and K^- atoms, and how the φ meson properties are changed in a nuclear medium.

9 illus, 1 table, 57 ref

002248   Nayak T K (NO, Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata-700 064) : Multiplicity distributions and charged-neutral fluctuations. Pramana J Phys 2001, 57(2-3), 285-300.

Results from the multiplicity distributions of inclusive photons and charged particles, scaling of particle multiplicities, event-by-event multiplicity fluctuations, and charged-neutral fluctuations in 158A GeV Pb+Pb collisions are presented and discussed. A scaling of charged particle multiplicity as N^1.07±0.05part and photons as N^1.12±0.03part have been observed, indicating violation of naive wounded nucleon model. The analysis of localized charged-neutral fluctuation indicates a model-independent demonstration of non-statistical fluctuations in both charged particles and photons in limited azimuthal regions. However, no correlated charged-neutral fluctuations are observed.

10 illus, 1 table, 26 ref

002247   Narasimha Reddy S;Rao P S;Ravikumar R V S S N;Reddy B J (Department of Physics, S V Degree College, Cuddapah-516 003) : EPMA, OPTICAL, EPR and IR spectral studies of prehnite mineral. Indian J Phys-Pt A 2001, 75(4), 429-32.

Light apple - green mineral of Ireland donated by Musee De Mineralogie, Ecole Nationale Superier Des Mines, Paris, France, has been investigated by Electron Probe Micro Analysis (EPMA), Optical absorption, Electron Paramagnetic Resonance (EPR) and Infrared (IR) spectroscopy. The EPMA indicates the presence of iron as the major constitutent and titanium, manganese and nickel in traces. The optical absorption spectrum recorded at RT show eight bands at 9343, 10650, 19994, 22721, 15500, 23250, 24624 and 27710 cm^-1. The former four bands are attributed to Fe(III) and the rest to Fe(II). The crystal field parameters Dq, B and C evaluated for Fe (III) and Fe (II) are 694, 650, 2600 and 980, 885, 3800 cm^-1 respectively. The EPR resonances at g = 4.62, 4.34, 3.85 and 3.66 indicate the presence of Fe(III) in octahedral symmetry in the mineral. The presence of manganese is confirmed by the sextet at g = 2.00 in the EPR spectrum: The vibrational spectrum in IR region exhibited the characteristic bands of water and silicates. The splitting of the triply degenerate mode of SiO₄ indicates the deviation of symmetry from the ideal T₄ symmetry.

3 illus, 3 table, 11 ref

002246   Murali K R;Subramanian V;Chockalingam M J (NO, Central Electrochemical Research Institute, Karaikudi-630 006) : Studies on the spray pyrolised CuInS₂ films. Bull Electrochem 1998, 14(12), 476-80.

Electrical, optical and electrochemical properties of thin films of CuInS₂ prepared by spray pyrolysis using cuprous chloride, indium chloride and thiourea sprayed onto heated glass, conducting SnO₂: F and Ti substrates are reported. CuInS₂ is a promising semiconductor in the group of I-III-VI semiconductors for photoelectrochemical cells due to its high absorption coefficient (10⁴ cm^-1) and the optimum band gap (1.55 eV). Polycrystalline films spray pyrolysed at substrate temperatures in the range of 523-573 K were nearly stoichiometric as shown by auger electron spectroscopic studies. More reports are available on the preparation of `n' type CuInS<sub>2</sub>. Photoelectrochemical studies on spray pyrolysed `p' type CuInS₂ with vaccum annealing treatment has been reported. XRD studies indicated prominent peaks of CuInS₂ with a chalcopyrite structure. The films wee `p' type and their resistivities after vacuum annealing at 573 K WAS found to be 2 X 10^-3 ohm cm. The films were characterised by XRD, EPMA, AES, optical, SEM and photoelectrochemical studies. A substrate temperature of 573 K was found to be favourable for obtaining stoichiometric films. Hall measurement on the films indicated a resistivity around 10^-3 ohm cm, carrier concentration around 10¹⁸ cm^-3 and a mobility around 25 cm² V^-1 s^-1.

31 ref

002245   Mishra A;Pandey R K;Bisen D P;Chandra B P (Department of Post-Graduate Studies and Research in Physics and Elect, Rani Durgawati University, Jabalpur-428 001) : Up-conversion luminescence in Er<. Indian J Phys-Pt A 2001, 75(4), 335-8.

Studied up-conversion luminescence of Er³⁺ and Yb³⁺ doped YOCI phosphors for different concentrations of Er³⁺ and Yb³⁺ ions in which Er³⁺ acts as an activator and Yb³⁺ acts as coactivator. In the excitation spectra, as well as in the emission spectra, two effective peaks of high intensity are found at wavelengths 820 and 930 nm and 445 and 695 nm respectively. In YOCI:Er³⁺; Yb³⁺ doped phosphors, initially the intensity increases rapidly with increasing temperature from 30°C reaches a maximum at about 80°C and then decreases. In the excitation spectra, as well as in the emission spectra, initially the intensity increases with activator or sensitizer concentration, attains an optimum value and then it decreases with further increase in the activator or sensitizer concentration. This infrared to visible conversion phenomenon can be understood on the basis of the cooperative sequential sensitization model.

4 illus, 10 ref

002244   Mehata M S;Tripathi H B (Photophysics Laboratory, Department of Physics, DSB Campus, Kumaon University, Nainital-263 002) : Photophysics of 6-methoxyquinoline in Nafion® polymer matrix. Indian J Phys-Pt A 2001, 75(2), 189-92.

Fluorescence characteristics of 6-methoxyquinoline (6MQ) in Nafion® polymer have been reported. The spectral features as well as transient studies show a similarity for 6MQ in fluid media at low tempeature and in Nafion® matrix at ambient temperature. Excitation wavelength dependence of the fluorescence alongwith the decay measurements across the emission profile show the presence of various conformers in the form of monocations that assume different geometries in the polymer matrix and these conformers undergo excited state charge transfer process.

^ssc5 illus, 14 ref

002243   Majumdar C K (Physics and Applied Mathematics Unit, Indian Statistical Institute, 203 B. T. Road, Calcutta-700 035) : Magnetism department at IACS : Krishnan's creation. Indian J Phys-Pt A 2001, 75(4), 297-300.

Krishnan started his physics research in spectroscopy with C.V. Raman and did some pioneering work in Raman effect in solids. Later he developed precise experimental methods to measure magnetic anisotropy in crystals; These methods went by the names the oscillation method and the critical couple method. Some important results will be recalled. The work of Krishnan and his students and coworkers established the usefulness of magnetic methods as a supplement to X-ray methods for determining crystal structure. This led to the organisation of the Department of Magnetism in the Indian Association for the Cultivation of Science (I A C S). We shall examine some things which their work missed, and also subsequent developments in the field of magnetism.

16 ref

002242   Madhusudana N V (Raman Research Institute, C V Raman Avenue, Bangalore-560 080) : Recent advances in thermotropic liquid crystals. Curr Sci 2001, 80(8), 1018-25.

Liquid crystals are states of condensed matter whose symmetries lie between those of 3-dimensionally periodic crystals and isotropic liquids. Thermotropic liquid crystalline phases are exhibited by a large number of organic compounds whose molecules have anisotropy of shape. A typical intermolecular energy responsible for the stability of the relevant order in the medium is comparable to the thermal energy, and thus liquid crystals are soft materials. Relatively weak interactions like those between molecular dipoles or chiral centers of appropriate molecules can give rise to new types of liquid crystals. Now more than 35 types are known, and many more are likely to be discovered in the future.

14 illus, 32 ref

002241   Madare M A;Salvi S V (ICLES M J College of Arts, Science and Commerce, Sector 9A, A. Roye Road, VASHI, New Mumbai-400 703) : Investigation of electrical and dielectric properties of `modified' iron titanates. Indian J Phys-Pt A 2001, 75(4), 363-6.

Iron titanate is a pseudobrookite and exhibits spin glass behaviour, thermal cracking, magnetic texture, high resistivity and many other interesting properties. Hence polycrystalline iron titanate has multifaceted applications. This communication presents synthesis and investigation of electrical resistivity as a function of temperature and dielectric behaviour as a function of temperature as well as frequency (relaxation spectra) of `pure' and `modified' iron titanates. `Pure' iron titanate is synthesized by usual standard ceramic method using A.R. grade oxides. In `modified' iron titanates, the ionic pair of `lithium and aluminium' is incorporated by the ceramic technique. The percentage of lithium and aluminium in each sample is determined by chemical analyis using ICAP technique. The single phase formation is confirmed by XRD technique and structural information is obtained using XRD and FTIR techniques. Structurally, all samples remain pseudobrookite having orthorhombic cell. The analysis of relaxation spectra establishes the presence of space-charge, which decreases on incorporation of `LiAl' pair. The changes in resistivity, dielectric constant, dielectric loss are discussed and analysed on the basis of doping, impurity compensation and grain texture.

7 illus, 2 table, 21 ref

002240   Machner H (NO, , Email : h.machner@fz-juelichide) : Meson production in p + d reactions. Pramana J Phys 2001, 57(2-3), 399-416.

Total and differential cross sections for the reactions p + d → ³He + m⁰ with m = π, η and p + d → ³H+π⁺ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations. The aspect of isospin symmetry breaking is studied.

18 illus, 33 ref

002239   Longe P;Bose S M (Institut de Physique B5, Universite de Liege, Sart-Tilman, B-4000 lieg, , ) : Collective excitations in aligned carbon nanotube superlattices. Indian J Phys-Pt A 2001, 75(4), 327-33.

Collective electronic excitation (plasmon) modes of aligned carbon nanotube superlattices have been calculated. The nanotubes are described by two-dimensional electron gases (2DEG) confined on jollow cylindrical surfaces which are regularly aligned in a plane forming the 2D superlattice, or which form a hexagonal closed-pack structure producing the 3D superlattice. The series of modes obtained in the random phase approximation can be presented as combination of three contributions : a one-tubule contribution, a uniform 2D or 3D bulk contribution, and a contribution related to the lattice structure. For plasmon wavelengths small compared to the distance a between axes, these modes tend to be those of individual tubules, i.e. the one-tubule contribution is dominant for aq<62><62>1 (q=momentum). For large wavelengths, however, they tend to those of the 2D or 3D uniform electron gas, i.e. the bulk contributions dominate for aq <60><60> 1. The lattice contribution to plasmon frequency is most significant at intermediate wavelengths.

3 illus, 17 ref

002238   Ladgaonkar B P;Vasambekar P N;Vaingankar A S (Department of Electronics, Shivaji University, Kolhapur-416 004) : Cation distribution study of Nd<. Indian J Phys-Pt A 2001, 75(4), 351-5.

Assuming preferential distribution of magnesium ion among tetrahedral (A) and octahedral (B) site the cation distribution is predicted for Nd³⁺ substituted Zn-Mg ferrites. Cation distribution is investigated by a method wherein structural refinement is applied. The theoretical intensity of X-ray reflections, which found to depend on site occupancy, was calculated. The dependence of intensity of reflections against cation distribution parameter was studied which suggests that the intensity of (220) and (422) reflections are sensitive to A-site, whereas that of (222) and (400) to the B-site. ZClose agreement of the theoretically calculated and experimentally observed intensity supports the predicted cation distribution. To counter check, the simplified method wherein graph of theoretical intensity of (220) reflections is plotted against distribution parameter. By plotting observed intensity of the same plane the exact distribution parameter is decided with the help of this plot. The plot of reliability factor, R against distribution parameter shows deep near about exact distribution parameter, which supports the exactness of cation distribution. The investigated cation distribution reveals that zinc ion shows its strong occupancy on A-site and magnesium ion distributes partially among A and B sites indicating maximum occupancy on A site for X = 020. The substituted Nd³⁺ ion resides on B-site displacing proportional amount of magnesium from B site to A site.

3 illus, 1 table, 17 ref

002237   Kundu S K;Okabe E;Chaudhuri B K;Haase W (Solid State Physics Department, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-700 032) : Observation of successive phase transitions in ferroelectric liquid crystal (CS-1013) from dielectric measurements and a pseudospin type model for studying ferro and antiferroelectric behaviour. Indian J Phys-Pt A 2001, 75(2), 109-11.

From dielectric measurements, shown the appearance of successive phase transitions in a ferroelectric liquid crystal CS-1013. Between crystalline and isotropic phases, observed successive phase transitions viz. Cr - <126> 35° - SmC^* - 63°C - SmA - 70°C-N*-80°C-Iso. Both Goldstone mode (GM) and Soft mode (SM) are observed in the SmC^* phase. A theoretical pseudospin type model has been suggested for studying ferro and antiferroelectric phase transitions in liquid crystals.

3 illus, 15 ref

002236   Kubo K I (School of Science, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo 192-0397, Japan) : Nuclear and hadronic reaction mechanisms producting spin asymmetry. Pramana J Phys 2001, 57(2-3), 379-87.

Briefly reviews concept of the quark recombination (QRC) model and a general success of the model. To solve the existing problem, so called anomalous spin observables, in the high energy hyperon spin phenomena, proposes a meachanism; the primarily produced quarks, which are predominantly u and d quarks, act as the leading partons to form the hyperons. Extension of the quark recombination concept with this mechanism is successful in providing a good account of the anomalous spin observables. Another kind of anomaly, the non-zero analysing power and spin depolarization in the Λ hyperon productions, are also discussed and well understood by the presently proposed mechanism.

4 illus, 19 ref

002235   Krishnan R;Srivastava V (School of Physics, University of Hyderabad, Hyderabad-500 046) : Low temperature resistance of quasi one-dimensional wires. Indian J Phys-Pt A 2001, 75(4), 449-51.

The problem of the resistance of quasi one-dimensional (1D) wires is studied at temperatures low enough to preclude phonons. Localization becomes conspicuous at such temperatures. We have considered the inelastic scattering due to two level systems or tunneling states, which is dominant at low temperatures. Demonstrats that 1D localization is very sensitive to the frequency of inelastic scattering events. This calls for new experiments to investigate certain finer aspects of the 1D transport. Also expected to be relevant in connection with the current discussion on the saturation of the intrinsic decoherence time at ultra low temperatures in mesoscopic systems.

17 ref

002234   Kotecha M;Pandey L (Department of Physics, Rani Durgavati University, Jabalpur-482 001) : Nuclear spin-lattice relaxation of I = 3/2 quadrupolar spin-system due to domain-walls in order-disorder ferroelectrics. Indian J Phys-Pt A 2001, 75(2), 149-58.

A general theory is developed for the study of spin-lattice relaxation of I = 3/2 spins due to domain-walls in order-disorder ferroelectrics. It is assumed that the domain-wall structure is responsible for relaxation and the transfer of nuclear magnetization between the nuclei near the domain-walls and those deep inside the domain occurs through nearest neighbour interaction by spin-diffusion process. Rate equations are formed by representing the ferroelectric domains by a one-dimensional chain of equidistant spins having dipolar coupling. Spin-populations are calculated as a function of time for different ratios of quadrupolar to dipolar transition probabilities for a sample subjected to selective rf pulse. It is shown that for the situation where the centre line is initially saturated, the satellite population follows a power law dependence that can be approximated by C1(L/a)^p(1/Woo)^p/2 (t)^-p/2 for times greater than the domain-diffusion time L²/Wooa², where L,a and Woo are the domain width, internuclear spacing and dipolar transition probability respectively. The results are quite general and are found in qualitative agreement with the ²³Na relaxation behaviour at low temperature in ferroelectric NaNO2.

7 illus, 33 ref

002233   Kelkar N G;Jain B K (Nuclear Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085) : Hyperon production in pp collisions. Pramana J Phys 2001, 57(2-3), 389-97.

Reports on a study of the proton induced hyperon production reactions. Discusses the theoretical efforts made towards understanding the existing data and the uncertainties involved in the calculations. The calculations of the missing mass spectra for the pp → K⁺ Λp reaction which involve a proper coupled channel treatment of the final state Λp interaction are presented. Significant differences in the results using different models of the hyperon-nucleon interaction are found.

5 illus, 17 ref

002232   Karar M;Chaudhuri B K;Purohit T;Haase W (Department of Solid State Physics, I A C S, Calcutta-700 032) : On the deuteration induced phase transitions in (NH₄)₂ PbCl₆ type crystals with pseudospin-lattice coupled mode model and using statistical green's function technique. Indian J Phys-Pt A 2001, 75(4), 483-7.

Deuteration induced phase transitions (DIPT) occur in some H-bonded crystals like A₂MX_{6 (where A = NH4, X = Cl, Br, I etc. and M = Pb, Pt, Se etc.) showing one or no transition in the correspnding undeuterated phase. The hydrogen bonds in (NH4)2 PbCl6 type crystals of our present investigation is rather weak and hence simple spin (pseudo-spin) like ordering of the hydrogen bonds and tunneling mechanism are not sufficient to explain the DIPT or the two successive phase transitions occurring in some deuterated system. In the present paper, using two sublattice pseudospinlattice (phonon) coupled mode (PLCM) model, we have tried to explain the origin of single phase transition in a protonated system and a double phase transition in the corresponding deuterated system. Landau theory of phase transition also supports the concept of two phase transitions in such a system under certain conditions.}

25 ref

002231   Kar T;Choudhary R N P;Bera S (Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur-721 302) : Synthesis and characterisation of (Pb1-xBax) (Li1/4La1/4W1/2)O3 ceramics. Indian J Phys-Pt A 2001, 75(2), 131-4.

Polycrystalline samples of Ba-modified lead lithium lanthanum tungstate viz. (Pb1-xBax) (Li1/4La1/4W1/2)O3 (x = 0.00, 0.03, 0.07, 0.10) were prepared by solid-state reaction technique using high-purity ingredient oxides and carbonates. The formation of the compounds was checked by X-ray diffraction (XRD) technique. Measurements of polarisation, dielectric constant and loss, dc resistivity as function of temperature show that the ferroelectric property of the mother compounds (i.e., lead lithium lanthanum tungstate) vanishes with the increase of Ba²⁺ion concentration.

5 illus, 20 ref

002230   Kanchana G;Arivuoli D (Crystal Growth Centre, Anna University, Chennai-600 025) : Growth and characterization of antimony thiourea bromide (ATB). Indian J Phys-Pt A 2001, 75(2), 123-6.

Single crystals of the metal organic nonlinear optical material, antimony thiourea bromide (ATB) were grown from sodium meta silicate gel at ambient temperature. The conditions for the growth of large ATB single crystals of dimension 10 mm x 5 mm x 5 mm in gel were obtained. X-ray analysis confirmed the crystal structure to be orthorhombic with space group Cmc21. The grown crystals were characterized by EDAX, FTIR, TGA, DSC and Microhardness studies. Spectroscopic studies on ATB reveal the presence of sulphur-to-antimony bonds in the complex. Thermal analysis indicates that the material melts at 96°C.

5 illus, 11 ref

002229   Joshi V S;Joshi M J (Solid State Physics and Materials Science Laboratories, Department of, Saurashtra University, Rajkot-360 005) : FTIR spectroscopic and thermal studies of calcium tartrate trihydrate crystals grown by gel assistance. Indian J Phys-Pt A 2001, 75(2), 159-63.

Single crystals of calcium tartrate trihydrate were grown by using silica gel as a medium. The gel was set by acidification of sodium metasilicate solution by orthophosphric acid solution. The supernatant solution containing calcium chloride and tartaric acid was poured on the gel. However, this is in contrast to the usual growth technique for growing calcium tartrate crystals, where the gel is set with tartaric acid and calcium chloride is used as a supernatant solution. The crystal growth and the role played by gel is discussed. The crystals were characterized by FTIR spectroscopic technique and thermogravimetric analysis. A kinetics of dehydration was studied by using the Coast-Redfern, the Horowitz-Metzger and the Freeman - Carroll Relations.

8 illus, 21 ref

002228   Jana T;Dasgupta A;Ray S (Energy Research Unit, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-700 032) : P-type microcrystalline silicon films prepared by VHF-PECVD technique. Indian J Phys-Pt A 2001, 75(4), 409-12.

Very high Frequency Plasma Enhanced Chemical Vapour Deposition Technique (VHF-PECVD) is very much important for growth of microcrystalline silicon material at high deposition rate. p-type μc-Si:H films have been developed by VHF-PECVD technique at low substrate temperature (250°C) and low power (55 mW/cm²). The effect of plasma frequency on optoelectronic and structural properties have been studied. The size of crystallites developed in silicon matrix varies from 100 Angstrom to 500 Angstrom and the optical bandgap is 1.86 eV. The maximum conductivity of 35.7 Scm^-1 has been achieved with a high deposition rate (33.00 Angstrom/min) at 63.75 MHz plasma excitation frequency.

6 illus, 26 ref

002227   Jain S R (Nuclear Physics Division, Van de Graaf Building, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085) : Quantum chaos, thermalization and dissipation in nuclear systems. Pramana J Phys 2001, 57(2-3), 571-84.

Nuclei have complex energy-level sequence with statistical properties in agreement with canonical random matrix theory. This agreement appears when the one-particle one-hole states are mixed completely with two-particle two-hole states. In the transition, there is a new universality which is presented here, brining about a relation between dynamics and statistics. Summarizes also the role of chaos in thermalization and dissipation in isolated systems like nuclei. The methods used to bring forth this understanding emerge from random matrix theory, semiclassical physics, and the theory of dynamical systems.

40 ref

002226   Jain P;Ralston J P (Physics Department, Indian Institute of Technology, Kanpur-208 016) : Exclusive hadronic processes and color transparency. Pramana J Phys 2001, 57(2-3), 433-44.

Reviews the current status of high energy exclusive processes and color transparency.

^iia8 illus, 39 ref

002225   Jain A K;Amita (Department of Physics, University of Roorkee, Roorkee-247 667) : Magnetic rotation and chiral symmetry breaking. Pramana J Phys 2001, 57(2-3), 611-22.

Deformed mean field of neclei exhibits various geometrical and dynamical symmetries which manifest themselves as various types of rotational and decay patterns. Most of the symmetry operations considered so far have been defined for a situation wherein the angular momentum coincides with one of the principal axes and the principal axis cranking may be invoked. New possibilities arise with the observation of rotational features in weakly deformed nuclei andnow interpreted as magnetic rotational bands. More than 120 MR bands have now been identified by filtering the existing data. Presents a brief overview of these bands. The total angular momentum vector in such bands in tilted away from the principal axes. Such a situation gives rise to several new possibilities including breaking of chiral symmetry as discussed recently by Frauendorf. Presents the outcome of such symmetries and their possible experimental verification. Some possible examples of chiral bands are presented.

8 illus, 14 ref

002224   Hossain I;Ishii T;Ogawa M;Asai M;Shelley A; Makishima A (Department of Physics, Shahjalal University of Science and Technology, Sylhet, Bangladesh) : Yield of isomers in <. Indian J Phys-Pt A 2001, 75(2), 165-8.

Reports the yields and distribution of ns-μs isomers produced in ⁷⁶Ge (635 MeV) + ¹⁹⁸Pt deep-inelastic collision. The population yields of isomers evaluated for individual channel and compared with the relevant yields produced in ⁷⁶Ge (635 MeV) + ¹⁹⁸Pt and ⁷⁴Ge (550 MeV) + ¹⁹⁸Pt reaction. These comparisons reflect how isomer yield depends on beam energies and projectile mass in deep-inelastic collisions.

002223   Hirai M;Kumano S;Miyama M (Department of Physics, Saga University, Honjo-1, Saga 840-8502, Japan) : Parametrization of nuclear parton distributions. Pramana J Phys 2001, 57(2-3), 445-57.

Optimum nuclear parton distributions are obtained by analysing available experimental data on electron and muon deep inelastic scattering (DIS). The distributions are given at Q² = 1 GeV² with a number of parameters, which are determined by a <67>² analysis of the data. Valence-quark distributions are relatively well determined at medium x, but they are slightly dependent on the assumed parametrization form particularly at small x. Although anitquark distributions are shadowed at small x, their behavior is not obvious at medium x from the F2 data. The gluon distributions could not be restricted well by the inclusive DIS data; however, the analysis tends to support the gluon shadowing at small x. Provides analytical expressions and computer subroutines for calculating the nuclear parton distributions, so that other researchers could use them for applications to other high-energy nuclear reactions.

9 illus, 13 ref

002222   Gupta R K (Physics Department, Panjab University, Chandigarh-160 014) : Superheavy nuclei - cold synthesis and structure. Pramana J Phys 2001, 57(2-3), 481-92.

Quantum mechanical fragmentation theory (QMFT), given for the cold synthesis of new and superheavy elements, is reviewed and the use of radioactive nuclear beams (RNB) and targets (RNT) is discussed. The QMFT is a complete theory of cold nuclear phenomena, namely, the cold fission, cold fusion and cluster radioactivity. Also, the structure calculations based on the axially deformed relativistic mean field (DRMF) approach are presented which predict new regions of spherical magicity, namely Z = 120 and N = 172 or 184, for superheavy nuclei. This result is discussed in the light of recent experiments reporting the cold synthesis of Z = 118 element.

7 illus, 1 table, 23 ref

002221   Gupta C S (NO, College of Health Sciences, Ministry of Health, PO Box-12, State of Bahrain) : Effect of copper doping on phosphorescence of CaS : Er phosphors. Indian J Phys-Pt A 2001, 75(2), 135-41.

CaS phosphors doped with varying concentrations of Er and/or Cu (singly as well as doubly activated) were prepared. The phosphorescence have been studied with reference to the phosphorescence decay characteristics and the spectral distribution of luminescence emission. The study is confirmed to the effect of higher concentration of Cu (1% to 10^-2 %) on CaS phosphors activated with very low concentration of Er (10^-3 to 10^-9 %). The decay study reveals that the trap group corresponding to about 0.69 eV is independent of activator concentration and is characteristic of the host lattice itself. CaS : Er phosphor gives a characteristic band at 5750 Angstrom; while CaS:Cu gives two bands at 4440 and 5800 Angstrom. The phosphorescence spectra of doubly activated CaS:Er, Cu phosphors again give two bands at 4440 and 5800 Angstrom. Blue, green and red emission is of great interest for color displays, printing, opto-electronics, lasers, medical diagnosis and of therapeutical use.

7 illus, 2 table, 13 ref

002220   Goyal P S;Aswal V K (Inter-University Consortium for Department of Atomic Energy Facilities, , Mumbai Centre, R5-Shed, Bhabha Atomic Research Centre, Mumbai-400 085) : Micellar structure and inter-micelle interactions in micellar solutions: results of small angle neutron scattering studies. Curr Sci 2001, 80(8), 972-9.

Micelles are aggregates of surfactant molecules suspended in water. The structure (shape and size) of a micelle depends both on the architecture of the constituent surfactant molecule and the solution conditions such as temperature, presence of impurities, etc. The inter-particle interaction between micelles also depends on several different parameters. It is of interest to study the structure and intermicellar interactions in micellar solutions both from the point of view of basic research and the applications. It has been found that the technique of Small Angle Neutron Scattering (SANS) is ideally suited for the above studies. This paper gives an introduction to the technique of SANS and discusses the results of typical SANS studies dealing with the micellar structure and the inter-micellar interactions.

10 illus, 33 ref

002219   Ghosh T K (NO, Venderbit University, Nashville, TN37235, USA) : First results from RHIC-PHENIX. Pramana J Phys 2001, 57(2-3), 355-69.

PHENIX experiment consists of a large detector system located at the newly commissioned relativistic heavy ion collider (RHIC) at the Brookhaven National Laboratory. The primary goal of the PHENIX experiment is to look for signatures of the QCD prediction of a deconfined high-energy-density phase of nuclear matter quark plasma. PHENIX started data taking for Au+Au collisions at square root^sNN = 130 GeV in June 2000. The signals from the beam-beam counter (BBC) and zero degree calorimeter (ZDC) are used to determine the centrality of the collision. A Glauber model reproduces the ZDC spectrum reasonably well to determine the participants in a collision. Charged particle multiplicity distribution from the first PHENIX paper is compared with the other RHIC experiment and the CERN, SPS results. Transverse momentum of photons are measured in the electro-magnetic calorimeter (EMCal) and preliminary results are presented. Particle identification is made by a time of flight (TOF) detector and the results show clear separation of the charged hadrons from each other.

10 illus, 32 ref