434 research outputs found
Energy loss and inelastic diffraction of fast atoms at grazing incidence
The diffraction of fast atoms at grazing incidence on crystal surfaces
(GIFAD) was first interpreted only in terms of elastic diffraction from a
perfectly periodic rigid surface with atoms fixed at equilibrium position.
Recently, a new approach have been proposed, referred here as the quantum
binary collision model (QBCM). The QBCM takes into account both the elastic and
inelastic momentum transfer via the Lamb-Dicke probability. It suggests that
the shape of the inelastic diffraction profiles are log-normal distributions
with a variance proportional to the nuclear energy loss deposited on the
surface. For keV Neon atoms impinging the LiF surface, the predictions of the
QBCM in its analytic version are compared with numerical trajectory
simulations. Some of the assumptions such as the planar continuous form, the
possibility to neglect the role of lithium atoms and the influence of
temperature are investigated. A specific energy loss dependence is identified in the quasi-elastic regime merging
progressively to the classical onset . The ratio of
these two predictions highlight the role of quantum effects in the energy loss.Comment: 9 pages 8 figures paper prepared for IISC-2
Micro-Sigmoids as Progenitors of Coronal Jets - Is Eruptive Activity Self-Similarly Multi-Scaled?
Observations from the X-ray telescope (XRT) on Hinode are used to study the
nature of X-ray bright points, sources of coronal jets. Several jet events in
the coronal holes are found to erupt from small-scale, S-shaped bright regions.
This finding suggests that coronal micro-sigmoids may well be progenitors of
coronal jets. Moreover, the presence of these structures may explain numerous
observed characteristics of jets such as helical structures, apparent
transverse motions, and shapes. In analogy to large-scale sigmoids giving rise
to coronal mass ejections (CMEs), a promising future task would perhaps be to
investigate whether solar eruptive activity, from coronal jets to CMEs, is
self-similar in terms of properties and instability mechanisms.Comment: 8 pages, 5 figures, 1 tabl
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