37 research outputs found
A low density of 0.8 g/cc for the Trojan binary asteroid 617 Patroclus
The Trojan population consists of two swarms of asteroids following the same
orbit as Jupiter and located at the L4 and L5 Lagrange points of the
Jupiter-Sun system (leading and following Jupiter by 60 degrees). The asteroid
617 Patroclus is the only known binary Trojan (Merline et al. 2001). The orbit
of this double system was hitherto unknown. Here we report that the components,
separated by 680 km, move around the system centre of mass, describing roughly
a circular orbit. Using the orbital parameters, combined with thermal
measurements to estimate the size of the components, we derive a very low
density of 0.8 g/cc. The components of Patroclus are therefore very porous or
composed mostly of water ice, suggesting that they could have been formed in
the outer part of the solar system.Comment: 10 pages, 3 figures, 1 tabl
Nano-engineered electron–hole exchange interaction controls exciton dynamics in core–shell semiconductor nanocrystals
A strong electron–hole exchange interaction (EI) in semiconductor nanocrystals (NCs) gives rise to a large (up to tens of meV) splitting between optically active ('bright') and optically passive ('dark') excitons. This dark–bright splitting has a significant effect on the optical properties of band-edge excitons and leads to a pronounced temperature and magnetic field dependence of radiative decay. Here we demonstrate a nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. We show that the dark–bright splitting can be widely tuned by controlling the electron–hole spatial overlap in core–shell CdSe/CdS NCs with a variable shell width. In thick-shell samples, the EI energy reduces to <250 μeV, which yields a material that emits with a nearly constant rate over temperatures from 1.5 to 300 K and magnetic fields up to 7 T. The EI-manipulation strategies demonstrated here are general and can be applied to other nanostructures with variable electron–hole overlap
Optimization of end milling process of Oil Hardened Non-Shrinking Die Steel (OHNS) under different cutting environment using Taguchi and Response surface methodology (RSM) approach
Electrical Conductivity of Alkali-silicate Glass containing Fe_2O_3.
Electrical resistivity (ρ) of Alkali-Silicate glasses has been measured to find out the behavior of Fe-ion in these glasses. ρ depends mainly upon the Fe^<2+>/Fe total-ratio, and has the minimum peak. The behavior of Fe-ion at the minimum of ρ is discussed by the results of Mo^^¨ssbauer-spectra in terms of the oxygen-coordination number of Fe^<3+>-ion. The mechanism of electrical conductance in these glasses is assumed to be the valence electron transfer between Fe^<2+> and 6-fold oxygen Fe^<3+>