13,693 research outputs found
Efficient generic calibration method for general cameras with single centre of projection
Generic camera calibration is a non-parametric calibration technique that is applicable to any type of vision sensor. However, the standard generic calibration method was developed with the goal of generality and it is therefore sub-optimal for the common case of cameras with a single centre of projection (e.g. pinhole, fisheye, hyperboloidal catadioptric). This paper proposes novel improvements to the standard generic calibration method for central cameras that reduce its complexity, and improve its accuracy and robustness. Improvements are achieved by taking advantage of the geometric constraints resulting from a single centre of projection. Input data for the algorithm is acquired using active grids, the performance of which is characterised. A new linear estimation stage to the generic algorithm is proposed incorporating classical pinhole calibration techniques, and it is shown to be significantly more accurate than the linear estimation stage of the standard method. A linear method for pose estimation is also proposed and evaluated against the existing polynomial method. Distortion correction and motion reconstruction experiments are conducted with real data for a hyperboloidal catadioptric sensor for both the standard and proposed methods. Results show the accuracy and robustness of the proposed method to be superior to those of the standard method
Segre maps and entanglement for multipartite systems of indistinguishable particles
We elaborate the concept of entanglement for multipartite system with bosonic
and fermionic constituents and its generalization to systems with arbitrary
parastatistics. The entanglement is characterized in terms of generalized Segre
maps, supplementing thus an algebraic approach to the problem by a more
geometric point of view.Comment: 16 pages, the version to appear in J. Phys. A. arXiv admin note: text
overlap with arXiv:1012.075
Superconformal Field Theories for Compact G_2 Manifolds
We present the construction of exactly solvable superconformal field theories
describing Type II string models compactified on compact G_2 manifolds. These
models are defined by anti-holomorphic quotients of the form (CY*S^1)/Z_2,
where we realize the Calabi-Yau as a Gepner model. In the superconformal field
theory the Z_2 acts as charge conjugation implying that the representation
theory of a W(2,4,6,8,10) algebra plays an important role in the construction
of these models. Intriguingly, in all three examples we study, including the
quintic, the massless spectrum in the Z_2 twisted sector of the superconformal
field theory differs from what one expects from the supergravity computation.
This discrepancy is explained by the presence of a discrete NS-NS background
two-form flux in the Gepner model.Comment: 35 pages, TeX, harvmac, references added, typos corrected, extended
discussion in section
Coset Realization of Unifying W-Algebras
We construct several quantum coset W-algebras, e.g. sl(2,R)/U(1) and
sl(2,R)+sl(2,R) / sl(2,R), and argue that they are finitely nonfreely
generated. Furthermore, we discuss in detail their role as unifying W-algebras
of Casimir W-algebras. We show that it is possible to give coset realizations
of various types of unifying W-algebras, e.g. the diagonal cosets based on the
symplectic Lie algebras sp(2n) realize the unifying W-algebras which have
previously been introduced as `WD_{-n}'. In addition, minimal models of WD_{-n}
are studied. The coset realizations provide a generalization of
level-rank-duality of dual coset pairs. As further examples of finitely
nonfreely generated quantum W-algebras we discuss orbifolding of W-algebras
which on the quantum level has different properties than in the classical case.
We demonstrate in some examples that the classical limit according to Bowcock
and Watts of these nonfreely finitely generated quantum W-algebras probably
yields infinitely nonfreely generated classical W-algebras.Comment: 60 pages (plain TeX) (final version to appear in Int. J. Mod. Phys.
A; several minor improvements and corrections - for details see beginning of
file
On the probabilistic logical modelling of quantum and geometrically-inspired IR
Information Retrieval approaches can mostly be classed into probabilistic, geometric or logic-based. Recently, a new unifying framework for IR has emerged that integrates a probabilistic description within a geometric framework, namely vectors in Hilbert spaces. The geometric model leads naturally to a predicate logic over linear subspaces, also known as quantum logic. In this paper we show the relation between this model and classic concepts such as the Generalised Vector Space Model, highlighting similarities and differences. We also show how some fundamental components of quantum-based IR can be modelled in a descriptive way using a well-established tool, i.e. Probabilistic Datalog
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