NOPR Collection:

Nonlinear dynamics in proton-noble gas atom collisions

1992-08-01T00:00:00Z

Title: Nonlinear dynamics in proton-noble gas atom collisions Authors: Deb, B M Abstract: Some recent works from our laboratory on time-dependent (TD) quantum-fluid density-functional studies of high-energy (25 keV) proton-neon and proton-helium atom collisions have been reviewed. These results in two generalized non-linear Schrodinger equations (GNLSE), depending on the forms of the various density functionals employed. The numerical solutions of these equations yield various time dependent quantities in three-dimensional space, e.g., electronic charge density, current density, difference density, effective potential surface as well as TD induced dipole moment, dipole polarizability, etc. The approach enables one to follow a collision process from start to finish, in course of time, thereby providing fresh insights into the mechanism of a collision process and identifying the non-linear features, if any, of the process which permits excitation but not ionization. One of the most interesting observations in this study is a natural partitioning of the collision process into approach, encounter and, departure regimes. Our approach has involved a simultaneous consideration of three crucial problems in density-functional theory, namely, time-dependence, excited states and a satisfactory kinetic energy density functional. Further, the phase associated with the hydrodynamic "wave function" has been related to Berry's geometrical phase in quantum mechanics. Page(s): 483-491

Design of molecular species for synthesis of advanced ceramic materials

1992-08-01T00:00:00Z

Title: Design of molecular species for synthesis of advanced ceramic materials Authors: Mehrotra, Ram C Abstract: In view of their solubility in organic solvents, case of purification due to their volatility and facile hydrolysability, alkoxides of metals have bee gaining increasing importance as precursors for the preparation of oxide ceramic materials by the sol-gel process. Synthesis and characterization of a number of soluble volatile bi- and poly-metallic alkoxides in the author's laboratories have added a new facet to the chemistry of metal alkoxides as these provide unique examples of coordination species stabilised by bridging alkoxy bonds between different metals. Molecular design of extraordinary homogeneous advanced ceramics has become a distinct possibility by employing a prefabricated volatile heterometal alkoxide, with a composition suited to that of the targeted material as a precursor in the sol-gel process. Care is required in some cases to introduce less hydrolysable auxiliary ligands like β-diketones at the metal centres at which hydrolysis rates tend to faster. The high over-all purity, with sometimes desired limits of impurities, is a dominant factor in attaining the predicted functionality of a product and it is possible to control this factor using the metal al oxide route. Page(s): 492-494

Synthesis and electron microscopic characterisation of Tl(Bi )-Sr-Ca-Cu-O high temperature superconductort

1992-08-01T00:00:00Z

Title: Synthesis and electron microscopic characterisation of Tl(Bi )-Sr-Ca-Cu-O high temperature superconductort Authors: Verma, G D; Ramakrishna, K; Srivastava, O N Abstract: The HTSC materials of Tl(Bi)-Sr-Ca-Cu-O system, corresponding to nominal compositions TI_2-XBi_XSr₂Ca₂Cu₃O₁₀(x=0.2, 0.4, 0.6 and 1.0) and with Tc in the range ~77 to ~106 K, have been synthesized. The electron microscopic explorations of the synthesized HTSC materials show curious structural characteristics. The transmission electron microscopic (TEM) investigations have revealed the presence of a new disordered superstructure (a ≈ 4.2 Ǻ, C ≈ 15.26 Ǻ). The origin of disorder is thought to be germane to the presence of lone pairs on Bi³⁺. It has also been suggested that substitution of Bi³⁺ at TI site in TI-Sr-Ca-Cu-O system optimises the carrier concentration (hole) leading to increase in Tc. Page(s): 495-499

Some aspects of photophysics of dyes and self-aggregation phenomenon in solution

1992-08-01T00:00:00Z

Title: Some aspects of photophysics of dyes and self-aggregation phenomenon in solution Authors: Rohatgi-Mukherjee, K K Page(s): 500-511