Path integral calculations of vacancies in solid Helium
We study properties of vacancies in solid 4He using Path Integral Monte Carlo. We find, in agreement with other calculations, that the energy to create a single vacancy is 11.5 K and is monotonic with the number of vacancies. If more then a few percent of the system becomes vacant, we find the system becomes unstable to melting. We show the number of exchanges in the system is increased by vacancies and how the underlying lattice is altered by the presence of a vacancy. We also examine the efficacy of using a tight binding Hamiltonian to describe the vacancy in the crystal, show that vacancies are attractive, and find values for the effective mass and inter-vacancy attraction.
Fate of vacancy-induced supersolidity in 4He.
The supersolid state of matter, exhibiting nondissipative flow in solids, has been elusive for 35 years. The recent discovery of a nonclassical moment of inertia in solid 4He by Kim and Chan provided the first experimental evidence, although the interpretation in terms of supersolidity of the ideal crystal phase remains a subject to debate. Using quantum Monte Carlo methods we investigate the long-standing question of vacancy-induced superflow and find that vacancies in a 4He crystal phase separate instead of forming a supersolid. On the other hand, nonequilibrium vacancies relaxing on defects of polycrystalline samples could provide an explanation for the experimental observations.
EVALUATION OF THE PLASMA CLEANED SURFACE OF A HERITAGE WOODEN PAINTING USING IQA METHODS
In this paper a new approach regarding the assessment of the visual efficiency of the plasma cleaning treatment applied in artwork restoration is discussed. The proposed method, which was tested in the case of a wooden painting, evaluates the competence of the cleaning process using image quality indexes based on structural similarity and metrics based on peak-signal-to-noise ratio (PSNR) combined with human visual system (HVS) properties. A systematic comparison between the effectiveness of these metrics and a discussion concerning their performances in the context of evaluating the plasma treatment were conducted.