13,545 research outputs found
Characteristics of Precession Electron Diffraction Intensities from Dynamical Simulations
Precession Electron Diffraction (PED) offers a number of advantages for
crystal structure analysis and solving unknown structures using electron
diffraction. The current article uses many-beam simulations of PED intensities,
in combination with model structures, to arrive at a better understanding of
how PED differs from standard unprecessed electron diffraction. It is shown
that precession reduces the chaotic oscillatory behavior of electron
diffraction intensities as a function of thickness. An additional
characteristic of PED which is revealed by simulations is reduced sensitivity
to structure factor phases. This is shown to be a general feature of dynami-cal
intensities collected under conditions in which patterns with multiple incident
beam orienta-tions are averaged together. A new and significantly faster method
is demonstrated for dynami-cal calculations of PED intensities, based on using
information contained in off-central columns of the scattering matrix.Comment: 20 pages, 7 Figure
Does use of touch screen computer technology improve classroom engagement in children?
Many studies have shown that the use of technology in the classroom may influence pupil
engagement. Despite the recent widespread use of tablet technology, however, very little research has
been carried out into their use in a primary school setting. We investigated the use of tablet computers,
specifically Apple’s ‘iPad’, in an upper primary school setting with regard to children’s engagement.
Cognitive, emotional and general engagement was higher in lessons based on iPads than those which
were not. There was no difference in behavioral engagement. Of particular significance was the increase
in engagement seen in boys, which resulted in their engagement levels increasing to levels comparable
to those seen in girls. These findings suggest that tablet technology has potential as a tool in the
classroom setting
YF-12 cooperative airframe/propulsion control system program, volume 1
Several YF-12C airplane analog control systems were converted to a digital system. Included were the air data computer, autopilot, inlet control system, and autothrottle systems. This conversion was performed to allow assessment of digital technology applications to supersonic cruise aircraft. The digital system was composed of a digital computer and specialized interface unit. A large scale mathematical simulation of the airplane was used for integration testing and software checkout
Molecular dynamics simulations of lead clusters
Molecular dynamics simulations of nanometer-sized lead clusters have been
performed using the Lim, Ong and Ercolessi glue potential (Surf. Sci. {\bf
269/270}, 1109 (1992)). The binding energies of clusters forming crystalline
(fcc), decahedron and icosahedron structures are compared, showing that fcc
cuboctahedra are the most energetically favoured of these polyhedral model
structures. However, simulations of the freezing of liquid droplets produced a
characteristic form of ``shaved'' icosahedron, in which atoms are absent at the
edges and apexes of the polyhedron. This arrangement is energetically favoured
for 600-4000 atom clusters. Larger clusters favour crystalline structures.
Indeed, simulated freezing of a 6525-atom liquid droplet produced an imperfect
fcc Wulff particle, containing a number of parallel stacking faults. The
effects of temperature on the preferred structure of crystalline clusters below
the melting point have been considered. The implications of these results for
the interpretation of experimental data is discussed.Comment: 11 pages, 18 figues, new section added and one figure added, other
minor changes for publicatio
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