Concept of non-periodic metasurfaces based on positional gradients applied to IR-flat lenses

International audienceWe describe a theoretical study of gradient metasurfaces that – unlike most theoretical designs requiring advanced fabrication techniques – could easily be produced by a simple patterning method, templated microlens lithography (TEMPL). We show here that positional gradients of identical microstructures can lead to a gradient of phase lag across the metasurface. Using a radial gradient in the pitch of a hexagonal array of identical microfabricated resonators, one could thus produce gradient metasurfaces with the ability to focus infrared light. We provide illustrative examples of devices and compare their theoretical capabilities

Spectrométrie γ à l'aide de détecteurs Ge(Li) entre 0 et 14 MeV

Nous proposons une méthode de calibration en énergie entre 0 et 14 MeV, d'un dispositif de spectrométrie γ utilisant un détecteur Ge(Li). Nous exposons ensuite le principe d'une mesure de la variation de son efficacité de détection avec l'énergie, à l'aide de trois résonances de la réaction 27Al(p, γ)28Si, pour des protons de 655, 992 et 2 489 keV

On the computational complexity of algebraic numbers : the Hartmanis-Stearns problem revisited

International audience— We consider the complexity of integer base expansions of algebraic irrational numbers from a computational point of view. We show that the Hartmanis–Stearns problem can be solved in a satisfactory way for the class of multistack machines. In this direction, our main result is that the base-b expansion of an algebraic irrational real number cannot be generated by a deterministic pushdown automaton. We also confirm an old claim of Cobham proving that such numbers cannot be generated by a tag machine with dilation factor larger than one