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Search Results: 1 - 10 of 1035 matches for " Brenda Kahl "
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Dependently-Typed Formalisation of Typed Term Graphs
Wolfram Kahl
Electronic Proceedings in Theoretical Computer Science , 2011, DOI: 10.4204/eptcs.48.6
Abstract: We employ the dependently-typed programming language Agda2 to explore formalisation of untyped and typed term graphs directly as set-based graph structures, via the gs-monoidal categories of Corradini and Gadducci, and as nested let-expressions using Pouillard and Pottier's NotSoFresh library of variable-binding abstractions.
Structure Factor and Electronic Structure of Compressed Liquid Rubidium
Chihara,Kahl
Physics , 1998, DOI: 10.1103/PhysRevB.58.5314
Abstract: We have applied the quantal hypernetted-chain equations in combination with the Rosenfeld bridge-functional to calculate the atomic and the electronic structure of compressed liquid-rubidium under high pressure (0.2, 2.5, 3.9, and 6.1 GPa); the calculated structure factors are in good agreement with experimental results measured by Tsuji et al. along the melting curve. We found that the Rb-pseudoatom remains under these high pressures almost unchanged with respect to the pseudoatom at room pressure; thus, the effective ion-ion interaction is practically the same for all pressure-values. We observe that all structure factors calculated for this pressure-variation coincide almost into a single curve if wavenumbers are scaled in units of the Wigner-Seitz radius $a$ although no corresponding scaling feature is observed in the effective ion-ion interaction.This scaling property of the structure factors signifies that the compression in liquid-rubidium is uniform with increasing pressure; in absolute Q-values this means that the first peak-position ($Q_1$) of the structure factor increases proportionally to $V^{-1/3}$ ($V$ being the specific volume per ion), as was experimentally observed by Tsuji et al.
Relative directed homotopy theory of partially ordered spaces
Thomas Kahl
Mathematics , 2006,
Abstract: Algebraic topological methods have been used successfully in concurrency theory, the domain of theoretical computer science that deals with parallel computing. L. Fajstrup, E. Goubault, and M. Raussen have introduced partially ordered spaces (pospaces) as a model for concurrent systems. In this paper it is shown that the category of pospaces under a fixed pospace is both a fibration and a cofibration category in the sense of H. Baues. The homotopy notion in this fibration and cofibration category is relative directed homotopy. It is also shown that the category of pospaces is a closed model category such that the homotopy notion is directed homotopy.
An euclidean affine invariant of quadrilaterals
Helmut Kahl
Mathematics , 2010,
Abstract: A certain real number, depending on two neighbouring sides of a quadrilateral and the diagonal meeting these two sides at their common point, is shown to be invariant under affinity. As an application we demonstrate a nice formula for the area of a finite sector at centre of a planar quadric with point symmetry.
Measuring quadric sectors at centre
Helmut Kahl
Mathematics , 2010,
Abstract: Sectors at centre of affine quadrics with point symmetry are investigated over arbitrary fields of characteristic different from two. As an application we demonstrate nice formulas for the area and the volume of such planar and spatial sectors, respectively, in euclidean space. It seems that up to now there has been atmost little research in this field up to very special cases.
The area of a sector at centre of a planar quadric
Helmut Kahl
Mathematics , 2009,
Abstract: Three linearly dependent and pairwise linearly independent vectors of an euclidian space uniquely determine a planar quadric with symmetry centre in the origin. A rather simple formula for the area of an arbitrary sector at centre of such a quadric will be shown by classical methods. The formula describes that area in dependence of 1. the lengths of the two straight lines that bound the sector at two sides, 2. the length of an arbitrary straight line from the centre to the quadric arc that bounds the sector at the third side, 3. the two angles in between these three straight lines.
Weak morphisms of higher dimensional automata
Thomas Kahl
Mathematics , 2013,
Abstract: We introduce weak morphisms of higher dimensional automata and use them to define preorder relations for HDAs, among which homeomorphic abstraction and trace equivalent abstraction. It is shown that homeomorphic abstraction is essentially always stronger than trace equivalent abstraction. We also define the trace language of an HDA and show that, for a large class of HDAs, it is invariant under trace equivalent abstraction.
Symmetric Matrices: Theory and Applications
Helmut Kahl
Mathematics , 2014,
Abstract: This text is a survey on symmetric matrices. It serves as a script for a module taught at university.
Relative directed homotopy theory of partially ordered spaces
Thomas Kahl
Mathematics , 2006,
Abstract: Algebraic topological methods have been used successfully in concurrency theory, the domain of theoretical computer science that deals with distributed computing. L. Fajstrup, E. Goubault, and M. Raussen have introduced partially ordered spaces (pospaces) as a model for concurrent systems. In this paper it is shown that the category of pospaces under a fixed pospace is both a fibration and a cofibration category in the sense of H. Baues. The homotopy notion in this fibration and cofibration category is relative directed homotopy. It is also shown that the category of pospaces is a closed model category such that the homotopy notion is directed homotopy.
Some collapsing operations for 2-dimensional precubical sets
Thomas Kahl
Mathematics , 2010,
Abstract: In this paper, we consider 2-dimensional precubical sets, which can be used to model systems of two concurrently executing processes. From the point of view of concurrency theory, two precubical sets can be considered equivalent if their geometric realizations have the same directed homotopy type relative to the extremal elements in the sense of P. Bubenik. We give easily verifiable conditions under which it is possible to reduce a 2-dimensional precubical set to an equivalent smaller one by collapsing an edge or eliminating a square and one or two free faces. We also look at some simple standard examples in order to illustrate how our results can be used to construct small models of 2-dimensional precubical sets.
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