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Aberration correctors using hexapole fields have proven useful to
correct for the spherical aberration in electron microscopy. We
investigate the limits of the present design for the hexapole corrector
with respect to minimum probe size for the scanning transmission electron
microscope and discuss several ways in which the design could be improved
by rather small and incremental design changes for the next generation of
advanced probe-forming systems equipped with a gun monochromator.
Planar defects in a polycrystalline diamond film were studied by
high-resolution transmission electron microscopy (HRTEM) and
high-resolution scanning transmission electron microscopy (STEM). In both
modes, sub-Ångström resolution was achieved by making use of
two aberration-corrected systems; a TEM and a STEM
CS-corrected microscope, each operated at 300 kV. For
the first time, diamond in 〈110〉 zone-axis orientation was
imaged in STEM mode at a resolution that allows for resolving the atomic
dumbbells of carbon at a projected interatomic distance of 89 pm. Twin
boundaries that show approximately the Σ3 CSL structure reveal at
sub-Ångström resolution imperfections; that is, local
distortions, which break the symmetry of the ideal Σ3 type twin
boundary, are likely present. In addition to these imperfect twin
boundaries, voids on the atomic level were observed. It is proposed that
both local distortions and small voids enhance the mechanical toughness of
the film by locally increasing the critical stress intensity factor.
Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.
Over 25 implementations of different functional languages are benchmarked using the same program, a floating-point intensive application taken from molecular biology. The principal aspects studied are compile time and execution time for the various implementations that were benchmarked. An important consideration is how the program can be modified and tuned to obtain maximal performance on each language implementation. With few exceptions, the compilers take a significant amount of time to compile this program, though most compilers were faster than the then current GNU C compiler (GCC version 2.5.8). Compilers that generate C or Lisp are often slower than those that generate native code directly: the cost of compiling the intermediate form is normally a large fraction of the total compilation time. There is no clear distinction between the runtime performance of eager and lazy implementations when appropriate annotations are used: lazy implementations have clearly come of age when it comes to implementing largely strict applications, such as the Pseudoknot program. The speed of C can be approached by some implementations, but to achieve this performance, special measures such as strictness annotations are required by non-strict implementations. The benchmark results have to be interpreted with care. Firstly, a benchmark based on a single program cannot cover a wide spectrum of ‘typical’ applications. Secondly, the compilers vary in the kind and level of optimisations offered, so the effort required to obtain an optimal version of the program is similarly varied.
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