Light Collimation and Focussing by a Thin Flat Metallic Slab

We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a punctual source. The effect is optimised when the radiation is around the bulk, not at the surface, plasma frequency. And the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of the Aluminium whose imaginary part of the permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.Comment: 6 pages, 3 figures. To be published on Optics Lette

Исследовании биомеханики дентальных имплантов методом конечных елементов

The complexity of the forces which act on the dental implant, in the stomathognatic system environment can have miscellaneous consequences on the periimplantar tissues, the implant length and diameter being mainly considered critical factors in achieving and maintaining osseointegration in optimal parameters. The finite element analysis technique purpose is to reveal the influence of the geometrical parameters and to establish which one ensures the most proper distribution of the stress over the implant-bone surface.The simulation was realized for cylindrical, solid and non-threaded implants made of titan. I have chosen three different lengths for the embeded endosseous implant and three different diameters The finite element technique indicates a more effective impact of the diameter in reducing the effects of the masticatory forces applied comparing to the length of the implant.Комплексные и атипичные силы которые взаимодействуют на импланты играют важную роль на пери- имплантарные ткани. Длинна и диаметр имплантов считаются как критические параметры, которые влияют на успешность остеоинтеграции в оптимальных параметрах. Роль анализа методом конечных елементов исследовать который из выше указанных параметров распостраняет более уравновестно силы и стрес на уровне костно-имплантатного соединения. Результаты показывают что диаметр имплантата имеет более уравновешенную способность распределения сил в отличии от длинны

The Finite Element Technique In The Analysys Of Implant Biomechanics

The complexity of the forces which act on the dental implant can have miscellaneous consequences on the periimplantar tissues. In this study we want to reveal the influence of two geometrical parameters, implant length and diameter, considered critical factors in achieving and maintaining osseointegration in optimal parameters. The analysis of the mechanical stress distribution over the implant bed was based on the finite element technique, using three-dimensional computerized models. The simulation was applied for cylindrical, solid and non-threaded implants made of titan. Three different lengths were chosen for the embedded endosseous implant, 8 mm, 10 mm. and 12 mm, all of them having the same diameter (3.75 mm.), respectively, three different diameters: 4 mm, 5 mm. and 6 mm, all of them having the same length (10 mm.). The implant with 8 mm length and 3.75 diameter (the smallest size used) produced not only a concentration of the strain on the cortical wall, but maximally values on the stressed area and a minimally strain dissipation on the bone adjacent to implant. When the length increase, maximally values decrease, being distribute on a smaller zone, and the residual stress dissipating on a larger area. The increases of the implant diameter significant reduce the strain on the bone adjacent to implant neck. This influence is more effective comparing with implant length, due to a more favorable distribution of the forces applied in our study. If the diameter increases with only 1 mm. it determines a significant strain reduction on the periimplantar bone, almost 50%, and may achieve till 60% (in case of more than 6 mm. diameter)