לוח שנה משולב

What is an optimal particle shape for scattering, e.g., shape causing minimal extinction among those of equal volume and randomly oriented? Guided by the isoperimetric property of a sphere, relevant in the geometrical optics limit of scattering by large particles, we examine an analogous question in the low frequency (induced dipole moment) approximation, seeking to disentangle electric and geometric contributions. To that end, a simple proof is supplied of spherical optimality for a coated ellipsoidal particle and a monotonic increase with asphericity is shown in the low frequency regime for orientation-averaged induced dipole moments and scattering cross-sections. Physical insight is obtained from the Rayleigh-Gans (transparent) limit and eccentricity expansions. We propose linking low and high frequency regime in a single sweeping minimum principle valid for all size parameters, provided that reasonable size distributions wash out the Mie resonances. This proposal is further supported by the sum rule for integrated extinction. Implications for environmental remote sensing are discussed throughout the talk.

Spin based properties, applications, and devices are commonly related to magnetic effects and to magnetic materials. However, we established that chiral organic molecules can act as spin filters for photoelectrons transmission, in electron transfer, and in electron transport. The new effect, termed Chiral Induced Spin Selectivity (CISS), has interesting implications for the production of new types of spintronics devices and on electron transfer in biological systems.
The basic effect, and its applications and implications, will be presented.