Microscopic observation of laser glazed yttria-stabilized zirconia coatings

Thermal barrier coatings (TBCs) are frequently used as insulation system for hot components in gas-turbine, combustors and power plant industries. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Glazing the top coat by laser beam is advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. Plasma-sprayed yttria-stabilized zirconia (YSZ) coating was glazed with Nd-YAG laser at different operating conditions. The surface morphologies, before and after laser treatment, were investigated by scanning electron microscopy. Laser beam assisted the densification of the surface by remelting a thin layer of the exposed surface. The laser glazing converted the rough surface of TBCs into smooth micron-size grains with size of 2-9 μm and narrow grain boundaries. The glazed surfaces showed higher Vickers hardness compared to as-sprayed coatings. The results revealed that the hardness increases as the grain size decreases.     

Hamiltonian nature of monopole dynamics

Classical electromagnetism with magnetic monopoles is not a Hamiltonian field theory because the Jacobi identity for the Poisson bracket fails. The Jacobi identity is recovered only if all of the species have the same ratio of electric to magnetic charge or if an electron and a monopole can never collide. Without the Jacobi identity, there are no local canonical coordinates or Lagrangian action principle. To build a quantum field of magnetic monopoles, we either must explain why the positions of electrons and monopoles can never coincide or we must resort to new quantization techniques.     

Generalization of the Kelvin equation for arbitrarily curved surfaces

Capillary condensation, which takes place in confined geometries, is the first-order vapor-to-liquid phase transition and is explained by the Kelvin equation, but the equation's applicability for arbitrarily curved surface has been long debated and is severe problem. Recently, we have proposed generic dynamic equations for moving surfaces. Application of the equations to the vapor/fluid interfaces in chemical equilibrium conditions nearly trivially solves the generalization problem for the Kelvin equation. The equations are universally true for any surfaces: atomic, molecular, micro or macro scale, real or virtual, Riemannian or pseudo-Riemannian, active or passive.     

Freudenthal duality and generalized special geometry

Freudenthal duality, introduced in Borsten et al. (2009) [1] and defined as an anti-involution on the dyonic charge vector in d=4 space-time dimensions for those dualities admitting a quartic invariant, is proved to be a symmetry not only of the classical Bekenstein-Hawking entropy but also of the critical points of the black hole potential.Furthermore, Freudenthal duality is extended to any generalized special geometry, thus encompassing all N>2 supergravities, as well as N=2 generic special geometry, not necessarily having a coset space structure.     

Characterization of laser sealed coatings of yttria partially stabilized zirconia

The present paper reports an experimental investigation based on X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and wavelength dispersive spectroscopy (WDS) analyses of phases formed after laser sealing of plasma sprayed coatings of 8.5 wt% yttria partially stabilized zirconia (YPSZ). X-ray diffraction and X-ray step-scanning analyses showed that the plasma sprayed and sealed coatings consisted mainly of t′ phase with a very small amount of monoclinic phase (m phase) in the plasma sprayed coatings. It was also found that the small amounts of m and cubic phases (c phase) present in the sealed coatings were dependent on laser processing specific energies (specific energy is equal to laser power/traverse speed x beam diameter). It was also found that rhombohedral (r) phase formed after laser sealing of coatings at higher specific energies. A direct relationship between c/a ratio of transformable tetragonal phase (t phase) produced by thermal treatment of sealed coatings and nontransformable tetragonal phase (t′ phase) and the amount of Yttria was obtained. A new equation was derived, which describes the relationship between Yttria concentration and the c/a ratio of tetragonal phases (t or t′).     

Surface characterization of plasma deposited nano-structured fluorocarbon coatings for promoting in vitro cell growth

Nano-structured “teflon-like” coatings characterized by highly-fluorinated, random, ribbon-shaped, micrometers-long structures were deposited on polyethylenetherephtalate (PET) substrates by plasma enhanced-chemical vapour deposition (PE-CVD) using modulated radiofrequency (RF, 13.56 MHz) glow discharges fed with C₂F₄ in modulated discharge (MD) and continuous wave (CW) regimes. Surfaces obtained in this way featured identical chemical composition and different roughness in the nanometric scale. Water contact angle (WCA) measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were utilized to characterize the surfaces. A positive relationship was shown to exist between the WCA value and the mean nano-structure height and the area root-mean-square (RMS) roughness of coatings. The possibility of obtaining coatings of varying nano-structure height, i.e., roughness, in a nanometric scale represents a promising result for further use of these surfaces as substrates for experiments on cell adhesion, proliferation and growth.     

Enhancement of soft X-ray emission from a pinch plasma using a rotating plasma for pre-ionization

An experimental study on the enhancement of soft X-ray emission from a pinch plasma has been carried out by using a rotating plasma for pre-ionization. The rotating plasma is produced by a pulsed J×B cross-field discharge between coaxial electrodes, and subjected to a pinch discharge. Under an optimized discharge condition, it has been observed that UV emission of 251.6 nm (Ar III) soft X-ray intensity increases with increasing applied axial magnetic field B. At 400 G, the X-ray intensity is enhanced by a factor of 3 compared to that without the rotating plasma. It is considered that this result is due to the improved characteristics of the pre-ionization rotating plasma, which influences the uniformity and stability of subsequent pinch plasma.     

Geometry and Physics Today

“Geometry,” in the sense of the classical differential geometry of smooth manifolds (CDG), is put under scrutiny from the point of view of Abstract Differential Geometry (ADG). We explore potential physical implications of viewing things under the light of ADG, especially matters concerning the “gauge theories” of modern physics, when the latter are viewed (as they are actually regarded currently) as “physical theories of a geometrical character.” Thence, “physical geometry,” in connection with physical laws and the associated with them, within the background spacetime manifoldless context of ADG, “differential” equations, are also being discussed.     

Stimulated infrared emission under excitation of condensed molecular dielectrics with giant pulses of a ruby laser

Stimulated infrared (IR) emission from a condensed dielectric medium under exposure to a giant pulse of a ruby laser is reported. This effect was predicted in the theoretical paper [1]. Experimental studies were carried out for a number of molecular liquids in two experimental geometries. In the first case (“in transmission” geometry) the propagation direction of the detected IR radiation coincided with that of the exciting radiation. In the second case IR radiation generated was detected in the opposite direction. The angle of divergence of IR radiation was found to be of 10⁻² rad, while the conversion efficiency with respect to the pumping intensity depended on the type of molecular liquid and varied in the range of 0.05–0.6%. Possible microscopic mechanisms of generation of IR radiation under pumping of the dielectric medium with visible or ultraviolet (UV) radiation are analyzed.     

Langmuir probe and spectroscopic studies of RF generated helium-nitrogen mixture plasma

This paper reports the effect of helium percentage variation in a capacitive RF helium-nitrogen mixture plasma on various plasma parameters and concentration of nitrogen active species (N₂(C³Π _u) and N₂ ⁺(B²Σ _u ⁺)). Langmuir probe is used for determination of electron energy distribution functions, effective electron temperature, plasma potential and electron density. Optical emission spectroscopy is used for determination of electron temperature from Boltzmann's plot of He–I lines and the relative changes in the concentration of active species by measuring the emission intensities of nitrogen (0-0) bands of the second positive and the first negative systems. The results demonstrate that electron temperature, electron density and concentration of active species increase significantly with increase in helium percentage in the mixture and RF power.