215 research outputs found
WIKINGER – Wiki Next Generation Enhanced Repositories
The regular indexing of text documents is based on the textual representation and does not evaluate the actual document content. In the semantic web approach, human-authored text documents are transformed into machine-readable content data which can be used to create semantic relations among documents. In this paper, we present on-going work in the WIKINGER project which aims to build a web-based system for semantic indexing of text documents by evaluating manual and semi-automatic annotations. A particular feature is the continuous refinement of the automatically generated semantic network by considering community feedback. The feasibility of the approach will be validated in a pilot application
Nonnegatively curved homogeneous metrics obtained by scaling fibers of submersions
We consider invariant Riemannian metrics on compact homogeneous spaces G/H
where an intermediate subgroup K between G and H exists, so that the
homogeneous space G/H is the total space of a Riemannian submersion. We study
the question as to whether enlarging the fibers of the submersion by a constant
scaling factor retains the nonnegative curvature in the case that the
deformation starts at a normal homogeneous metric. We classify triples of
groups (H,K,G) where nonnegative curvature is maintained for small
deformations, using a criterion proved by Schwachh\"ofer and Tapp. We obtain a
complete classification in case the subgroup H has full rank and an almost
complete classification in the case of regular subgroups.Comment: 23 pages; minor revisions, to appear in Geometriae Dedicat
On the total curvatures of a tame function
Given a definable function f, enough differentiable, we study the continuity
of the total curvature function t --> K(t), total curvature of the level {f=t},
and the total absolute curvature function t-->|K| (t), total absolute curvature
of the level {f=t}. We show they admits at most finitely many discontinuities
Exploiting symmetries in SDP-relaxations for polynomial optimization
In this paper we study various approaches for exploiting symmetries in
polynomial optimization problems within the framework of semi definite
programming relaxations. Our special focus is on constrained problems
especially when the symmetric group is acting on the variables. In particular,
we investigate the concept of block decomposition within the framework of
constrained polynomial optimization problems, show how the degree principle for
the symmetric group can be computationally exploited and also propose some
methods to efficiently compute in the geometric quotient.Comment: (v3) Minor revision. To appear in Math. of Operations Researc
Decomposable representations and Lagrangian submanifolds of moduli spaces associated to surface groups
In this paper, we construct a Lagrangian submanifold of the moduli space
associated to the fundamental group of a punctured Riemann surface (the space
of representations of this fundamental group into a compact connected Lie
group). This Lagrangian submanifold is obtained as the fixed-point set of an
anti-symplectic involution defined on the moduli space. The notion of
decomposable representation provides a geometric interpretation of this
Lagrangian submanifold
From ductile to brittle: evolution and localization of deformation below a crustal detachment (Tinos, Cyclades, Greece)
International audienceThe Cycladic Oligo-Miocene detachment of Tinos island is an example of a flat-lying extensional shear zone evolving into a low-angle brittle detachment. A clear continuum of extensional strain from ductile to brittle regime is observed in the footwall. The main brittle structures marking extension are shallow- and steeply dipping normal faults associated with subvertical extensional joints and veins. The earliest brittle structures are lowangle normal faults which commonly superimpose on, and reactivate, earlier (precursory) ductile shear bands, but newly formed low-angle normal faults could also be observed. Low-angle normal faults are cut by late steeply dipping normal faults. The inversion of fault slip data collected within, and away from, the main detachment zone shows that the direction of the minimum stress axis is strictly parallel to the NE-SW stretching lineation and that the maximum principal stress axis remained subvertical during the whole brittle evolution, in agreement with the subvertical attitude of veins throughout the island. The high angle of s1 to the main detachment suggests that the detachment was weak. This observation, together with the presence of a thick layer of cataclasites below the main detachment and the kinematic continuum from ductile to brittle, leads us to propose a kinematic model for the formation of the detachment. Boudinage at the crustal scale induces formation, near the brittle-ductile transition, of ductile shear zones near the edges of boudins. Shear zones are progressively exhumed and replaced by shallowdipping cataclastic shear zones when they reached the brittle field. Most of the displacement is achieved through cataclastic flow in the upper crust and only the last increment of strain gives rise to the formation of brittle faults. The formation of the low-angle brittle detachment is thus ''prepared'' by the ductile shear zone and the cataclasites and favored by the circulation of surface-derived fluids in the shear zone
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