Point defects in epitaxial GaN and ZnSe semiconductor layers have been studied using a low-energy positron beam. Ga vacancies are found to be present in n-type GaN grown by metal organic chemical vapor deposition, where the conductivity is due to residual oxygen. When n-type silicon impurity doping is done, clearly less vacancies are observed. In Mgdoped p-type and semi-insulating materials the...

Vacancies play a pivotal role in affecting ferroelectric polarization and switching properties, and there is a possibility that ferroelectricity may be utterly eliminated when defects render the system metallic. However, sufficient quantitative understandings of the subject have been lacking for decades due to the fact that vacancies in ferroelectrics are often charged and polarization in charg...

The enthalpy and entropy of vacancy creation in solid argon are re-evaluated using the two-body force approximation. At the triple point, the resulting vacancy free energy is g, = 1900 -4.0 RTcaljmole vat. This does not agree well with previous calculations of g,, but agrees well with experimental values of g, obtained from the argon specific heat”’ C, (but not with the questionable values obta...

Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H2 production under visible light were evaluated by gas chromatograph,...

For a benzenelike ring of six carbon atoms the dissipation of localized electron vacancies of TI and of a symmetry is calculated. The vacancies are described by Wannier sums. The calculation yields lifetimes of localization of about 10~16 s in both cases. These values are shorter by two orders of magnitude than any period of molecular vibrations. Therefore such transiently localized vacancies, ...

We consider the electronic structure near vacancies in the half-filled honeycomb lattice. It is shown that vacancies induce the formation of localized states. When particle-hole symmetry is broken, localized states become resonances close to the Fermi level. We also study the problem of a finite density of vacancies, obtaining the electronic density of states, and discussing the issue of electr...

In this paper torsion of hollow Poroelastic shaft with Elliptical section is developed. Using the boundary equation scheme. It looks for a stress function where satisfied Poisson equation and vanishes on boundary. It also analyzed stress function and warping displacement for the hollow elliptical section in Poroelastic shaft. At the end, the result of elastic and poroelastic shaft in warping di...

In this paper, numerical simulation for a two-dimensional viscous and incompressible flow past the elliptical airfoil is presented by Random Vortex Blob (RVB). RVB is a numerical technique to solve the incompressible, two-dimensional and unsteady Navier-Stocks equations by converting them to rotational non-primitive formulations. In this method, the velocity vector at a certain point can be cal...

To date, elliptical gear has been commonly used in automobile, automatic machinery, pumps, flow meters and printing presses for its particular non-uniform rotation. However, the dynamic characteristics of elliptical gears have not been clarified yet. In this study, The calculation as well as the experiment of two elliptical gears, which are a single elliptical gear and a double elliptical gear,...