Particle acceleration broadening

It is easily shown that for gravitational settling this Pe-number lies well above 1 for almost the complete colloidal size range (i.e. 1 pm), which means that diffusion does matter. In centrifugal fields, the critical particle size is shifted to lower values, yet even for centrifugal accelerations of 10 xg this value would remain above 10 nm. The particle diffusion broadens the sedimentation profiles and leads to an overestimation of the distribution width, if not properly accounted for in data analysis. However, its influence on the concentration profiles is decreasing with ongoing sedimentation (Fig. 2.8) because the diffusive particle displacement... 

A gamma-ray line at 0.511 MeV results from the mutual annihilation of an electron and a positron, a particle-antiparticle pair. A number of radioactive decay chains (see Table I) result in the emission of a positron as a decay product, which will annihilate upon first encounter with an electron. Also of astrophysical importance is the production of electrons and positrons via the photon-photon pair-creation process. Such pair plasmas are found in the vicinity of compact objects, such as neutron stars and black holes, that are associated with heated accretion disks and relativistic flows and jets, within which particle acceleration is known to occur. Thus, relatively narrow lines of 0.511-MeV annihilation radiation are expected to arise in the interstellar medium through the decay of dispersed, nucleosynthetic radionuclides, while broadened, Doppler-shifted, and possibly time-variable lines may occur in the high-energy and dense environments associated with compact objects. 

Demonstration of levitation of micron-sized latex particles by radiation pressure dates back to 1970 in the experiments reported by Ashkin [Ashkin 1970]. The average force accelerating (or slowing down) atoms in a laser field was derived by A.Kazantsev in 1972 [Kazantsev 1974]. Later in 1972-1974 he classified the optical forces as spontaneous, induced and mixed. In particular, it was he who first presented the dipole potentials for velocity broadened lines of resonance atoms in the logarithmic form... 

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