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M\"obius Invariants of Shapes and Images
Identifying when different images are of the same object despite changes
caused by imaging technologies, or processes such as growth, has many
applications in fields such as computer vision and biological image analysis.
One approach to this problem is to identify the group of possible
transformations of the object and to find invariants to the action of that
group, meaning that the object has the same values of the invariants despite
the action of the group. In this paper we study the invariants of planar shapes
and images under the M\"obius group , which arises
in the conformal camera model of vision and may also correspond to neurological
aspects of vision, such as grouping of lines and circles. We survey properties
of invariants that are important in applications, and the known M\"obius
invariants, and then develop an algorithm by which shapes can be recognised
that is M\"obius- and reparametrization-invariant, numerically stable, and
robust to noise. We demonstrate the efficacy of this new invariant approach on
sets of curves, and then develop a M\"obius-invariant signature of grey-scale
images
Could humans recognize odor by phonon assisted tunneling?
Our sense of smell relies on sensitive, selective atomic-scale processes that
are initiated when a scent molecule meets specific receptors in the nose.
However, the physical mechanisms of detection are not clear. While odorant
shape and size are important, experiment indicates these are insufficient. One
novel proposal suggests inelastic electron tunneling from a donor to an
acceptor mediated by the odorant actuates a receptor, and provides critical
discrimination. We test the physical viability of this mechanism using a simple
but general model. Using values of key parameters in line with those for other
biomolecular systems, we find the proposed mechanism is consistent both with
the underlying physics and with observed features of smell, provided the
receptor has certain general properties. This mechanism suggests a distinct
paradigm for selective molecular interactions at receptors (the swipe card
model): recognition and actuation involve size and shape, but also exploit
other processes.Comment: 10 pages, 1 figur
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