Search PubMed⌕ Search

Biomedical subjects

J W Frenken

Publications and source records attributed to J W Frenken.

5 recordsLinked to original sources
PubMed2001

How asymmetric islands become symmetric.

Scanning tunneling microscopy reveals that sputtering of the Au(110) surface results in the formation of vacancy islands with a broken mirror symmetry. These islands exhibit two types of steps on opposite sides: a lower energy (111) step and a higher energy (331) step. We analyze the thermal fluctuations and especially the kink distribution of such vacancy islands. Despite the broken symmetry, which they adopt internally, these islands show a symmetric average outer contour. Their coarsening proceeds via a variety of pathways, often leading to new, symmetric structures, with exclusively (111) steps. The lowest energy vacancy configuration is a bound pair of two vacancy lines or islands.

Journal Article↗
PubMed2001

Nothing moves a surface: vacancy mediated surface diffusion.

We report scanning tunneling microscopy observations, which imply that all atoms in a Cu(001) surface move frequently, even at room temperature. Using a low density of embedded indium "tracer" atoms, we visualize the diffusive motion of surface atoms. Surprisingly, the indium atoms seem to make concerted, long jumps. Responsible for this motion is an ultralow density of surface vacancies, diffusing rapidly within the surface. This interpretation is supported by a detailed analysis of the displacement distribution of the indium atoms, which reveals a shape characteristic for the vacancy mediated diffusion mechanism that we propose.

Journal Article↗
PubMed1998

Autotransplantation of premolars. A retrospective study.

The purpose of this clinical follow-up study was to evaluate the success rate of autotransplantation of human premolars. In the period between 1982 and 1994, 46 premolars in 31 patients were transplanted. A long-term success rate of 97.5% with a mean follow-up period of 3.5 years was achieved. It seems to be justified, therefore, in selected cases, to consider the possibility of autotransplantation as a good alternative to orthodontic or prosthetic treatment, including implant insertion, when closing a gap in the dental arch.

Adolescent↗