833,451 research outputs found
Strategy for reliable strain measurement in InAs/GaAs materials from high-resolution Z-contrast STEM images
Geometric phase analysis (GPA), a fast and simple Fourier space method for strain analysis, can give useful information on accumulated strain and defect propagation in multiple layers of semiconductors, including quantum dot materials. In this work, GPA has been applied to high resolution Z-contrast scanning transmission electron microscopy (STEM) images. Strain maps determined from different g vectors of these images are compared to each other, in order to analyze and assess the GPA technique in terms of accuracy. The SmartAlign tool has been used to improve the STEM image quality getting more reliable results. Strain maps from template matching as a real space approach are compared with strain maps from GPA, and it is discussed that a real space analysis is a better approach than GPA for aberration corrected STEM images
Surface-material maps of Viking landing sites on Mars
Researchers mapped the surface materials at the Viking landing sites on Mars to gain a better understanding of the materials and rock populations at the sites and to provide information for future exploration. The maps extent to about 9 m in front of each lander and are about 15 m wide - an area comparable to the area of a pixel in high resolution Viking Orbiter images. The maps are divided into the near and far fields. Data for the near fields are from 1/10 scale maps, umpublished maps, and lander images. Data for the far fields are from 1/20 scale contour maps, contoured lander camera mosaics, and lander images. Rocks are located on these maps using stereometric measurements and the contour maps. Frequency size distribution of rocks and the responses of soil-like materials to erosion by engine exhausts during landings are discussed
Adaptive binning of X-ray galaxy cluster images
We present a simple method for adaptively binning the pixels in an image. The
algorithm groups pixels into bins of size such that the fractional error on the
photon count in a bin is less than or equal to a threshold value, and the size
of the bin is as small as possible. The process is particularly useful for
generating surface brightness and colour maps, with clearly defined error maps,
from images with a large dynamic range of counts, for example X-ray images of
galaxy clusters. We demonstrate the method in application to data from Chandra
ACIS-S and ACIS-I observations of the Perseus cluster of galaxies. We use the
algorithm to create intensity maps, and colour images which show the relative
X-ray intensities in different bands. The colour maps can later be converted,
through spectral models, into maps of physical parameters, such as temperature,
column density, etc. The adaptive binning algorithm is applicable to a wide
range of data, from observations or numerical simulations, and is not limited
to two-dimensional data.Comment: 8 pages, 12 figures, accepted by MNRAS (includes changes suggested by
referee), high resolution version at
http://www-xray.ast.cam.ac.uk/~jss/adbin
Holomorphic discs with dense images
We prove that for any complex manifold X, the set of all holomorphic maps
from the unit disc to X whose images are everywhere dense in X forms a dense
subset in the space of all holomorphic maps from the disc to X. We show by an
example that this need not hold for maps from the disc to complex spaces with
singularities
o-minimal GAGA and a conjecture of Griffiths
We prove a conjecture of Griffiths on the quasi-projectivity of images of
period maps using algebraization results arising from o-minimal geometry.
Specifically, we first develop a theory of analytic spaces and coherent sheaves
that are definable with respect to a given o-minimal structure, and prove a
GAGA-type theorem algebraizing definable coherent sheaves on complex algebraic
spaces. We then combine this with algebraization theorems of Artin to show that
proper definable images of complex algebraic spaces are algebraic. Applying
this to period maps, we conclude that the images of period maps are
quasi-projective and that the restriction of the Griffiths bundle is ample.Comment: Comments welcome! v2: minor change
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