A. Uma Maheswari

Resonant states and transmission coefficient oscillations for potential wells and barriers

The oscillatory behavior of the transmission coefficient T as a function of energy is examined for an attractive square well and a rectangular barrier. We calculate T using resonant state boundary conditions and demonstrate that the maxima in T are correlated with the broad resonances generated by these potentials. For barrier potentials the maxima signify resonances occurring at energies above the barrier height. It is shown that the resonance position and width can also be generated from the complex poles of the amplitude of the transmitted plane wave. We also explain the relation between the positions of the resonances generated by the square well and the rectangular barrier to the energy eigenvalues of the corresponding rigid box with the same range. We show for a potential with an attractive well and a repulsive barrier that T exhibits oscillations when the particle energy is below the barrier, implying that in many cases the simple WKB type barrier penetration expression for T is not adequate. These...

Structural transformation of polymeric and cationic capped zirconia nanoparticles with temperature

The phase transformation mechanisms of zirconia nanocrystals obtained on thermal treatment of polyvinylpyrrolidone (PVP) and cetyltrimethylammoniumbromide (CTAB) capped hydrous amorphous zirconia (HAZ) on thermal treatment are investigated. In PVP assisted synthesis, tetragonal zirconia nanoparticles formation is the predominant one as compared to CTAB assisted synthesis. The decomposition of surfactants capped on HAZ with temperature (526°C for PVP and 466°C for CTAB) and subsequent interaction of the by-products with zirconia nanoparticles are responsible for tetragonal to monoclinic phase transformation. The decomposition temperature of capped surfactants is observed from thermogravimetric analysis (TGA) and subsequent interaction of by-products with zirconia nanoparticles at different temperatures is investigated from FTIR spectra. Further the structure of nanoparticles annealed at different temperatures is investigated using XRD, micro Raman and photoluminescence (PL) analysis.

Corrosion Resistance of 304L SS Spray Coated with Zirconia Nanoparticles

Influence of substrate temperature on corrosion (in 3.5% NaCl) and wear resistance of nanostructured zirconia thin film coated 304L SS substrates are studied by electrochemical and nano-indentation methods. This analysis shows 304L SS substrate spray coated with nanostructured zirconia at substrate temperature closer to the boiling point of the spray solvent ethanol exhibited good corrosion and wear resistance behaviour. This is because of the compressive stress developed during film fabrication at lower substrate temperature (~50 °C) and hence constrains the indentation plasticity, which leads to higher indentation load than the bare 304L SS.

Study on Vacancy Related Defects of CdS Nanoparticles by Heat Treatment

In this Work a Method of Incorporating Anion or Cation Vacancy during Synthesis Stage of CdS Nanoparticles to Induce Defect Level Emission Is Presented. Further the Influence of Temperature on this Vacancy Related Defects Is Also Studied. the as-Prepared Samples with Co-Precipitation Technique Were Heat Treated with Different Time Intervals at a Constant Temperature of 200 °C. From UV-Visible Absorption Spectra, the Band Gap of both the as-Prepared and Heat Treated Samples Are Calculated to Be 3.51 Ev Indicating that there Are No Significant Changes in the Size of Nanoparticles. The Photoluminescence Spectra of both Samples Showed Emission Bands Corresponding to Band Edge and Defect Levels. Further from the Spectra, it Was Observed that the Intensity of Band Edge Luminescence Decreases with Increase of Heat Treatment Duration. This Is due to the Fact that Induced Defects Have Reached the Surface of Nanoparticles.

Transmission and scattering by an absorptive potential

Transmission and scattering problems involving complex potentials are important in physics, in particular in describing nuclear collisions. We describe many pedagogical features of transmission in one dimension and scattering and absorption cross sections in three dimensions for a rectangular absorptive potential and compare the results with scattering from real barriers and a hard sphere. For a given energy in one dimension we show that the absorption reaches a maximum for a critical value of the absorption strength and then monotonically decreases with an increase in the absorption strength. An infinitely absorptive well becomes almost fully reflective and thus is similar to an infinitely high barrier. Similar results are found in three dimensions. We show that the absorption cross section in three dimensions diverges at a threshold energy, which is of critical importance for exothermic reactions.