2,384 research outputs found
Disconnected Skeleton: Shape at its Absolute Scale
We present a new skeletal representation along with a matching framework to
address the deformable shape recognition problem. The disconnectedness arises
as a result of excessive regularization that we use to describe a shape at an
attainably coarse scale. Our motivation is to rely on the stable properties of
the shape instead of inaccurately measured secondary details. The new
representation does not suffer from the common instability problems of
traditional connected skeletons, and the matching process gives quite
successful results on a diverse database of 2D shapes. An important difference
of our approach from the conventional use of the skeleton is that we replace
the local coordinate frame with a global Euclidean frame supported by
additional mechanisms to handle articulations and local boundary deformations.
As a result, we can produce descriptions that are sensitive to any combination
of changes in scale, position, orientation and articulation, as well as
invariant ones.Comment: The work excluding {\S}V and {\S}VI has first appeared in 2005 ICCV:
Aslan, C., Tari, S.: An Axis-Based Representation for Recognition. In
ICCV(2005) 1339- 1346.; Aslan, C., : Disconnected Skeletons for Shape
Recognition. Masters thesis, Department of Computer Engineering, Middle East
Technical University, May 200
Security Theorems via Model Theory
A model-theoretic approach can establish security theorems for cryptographic
protocols. Formulas expressing authentication and non-disclosure properties of
protocols have a special form. They are quantified implications for all xs .
(phi implies for some ys . psi). Models (interpretations) for these formulas
are *skeletons*, partially ordered structures consisting of a number of local
protocol behaviors. Realized skeletons contain enough local sessions to explain
all the behavior, when combined with some possible adversary behaviors. We show
two results. (1) If phi is the antecedent of a security goal, then there is a
skeleton A_phi such that, for every skeleton B, phi is satisfied in B iff there
is a homomorphism from A_phi to B. (2) A protocol enforces for all xs . (phi
implies for some ys . psi) iff every realized homomorphic image of A_phi
satisfies psi. Hence, to verify a security goal, one can use the Cryptographic
Protocol Shapes Analyzer CPSA (TACAS, 2007) to identify minimal realized
skeletons, or "shapes," that are homomorphic images of A_phi. If psi holds in
each of these shapes, then the goal holds
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