880 research outputs found
Dynamic Planar Embeddings of Dynamic Graphs
We present an algorithm to support the dynamic embedding in the plane of a
dynamic graph. An edge can be inserted across a face between two vertices on
the face boundary (we call such a vertex pair linkable), and edges can be
deleted. The planar embedding can also be changed locally by flipping
components that are connected to the rest of the graph by at most two vertices.
Given vertices , linkable decides whether and are
linkable in the current embedding, and if so, returns a list of suggestions for
the placement of in the embedding. For non-linkable vertices , we
define a new query, one-flip-linkable providing a suggestion for a flip
that will make them linkable if one exists. We support all updates and queries
in O(log) time. Our time bounds match those of Italiano et al. for a
static (flipless) embedding of a dynamic graph.
Our new algorithm is simpler, exploiting that the complement of a spanning
tree of a connected plane graph is a spanning tree of the dual graph. The
primal and dual trees are interpreted as having the same Euler tour, and a main
idea of the new algorithm is an elegant interaction between top trees over the
two trees via their common Euler tour.Comment: Announced at STACS'1
Superconducting Vortices in Half-Metals
When the impurity mean free path is short, only spin-polarized Cooper pairs
which are non-locally and antisymmetrically correlated in time may exist in a
half-metallic ferromagnet. As a consequence, the half-metal acts as an
odd-frequency superconducting condensate. We demonstrate both analytically and
numerically that quantum vortices can emerge in half-metals despite the
complete absence of conventional superconducting correlations. Because these
metals are conducting in only one spin band, we show that a circulating spin
supercurrent accompanies these vortices. Moreover, we demonstrate that magnetic
disorder at the interfaces with the superconductor influences the position at
which the vortices nucleate. This insight can be used to help determine the
effective interfacial misalignment angles for the magnetization in hybrid
structures, since the vortex position is experimentally observable via
STM-measurements. We also give a brief discussion regarding which
superconducting order parameter to use for odd-frequency triplet Cooper pairs
in the quasiclassical theory.Comment: 9 pages, 8 figure
Planar Reachability in Linear Space and Constant Time
We show how to represent a planar digraph in linear space so that distance
queries can be answered in constant time. The data structure can be constructed
in linear time. This representation of reachability is thus optimal in both
time and space, and has optimal construction time. The previous best solution
used space for constant query time [Thorup FOCS'01].Comment: 20 pages, 5 figures, submitted to FoC
Probit Models with Binary Endogenous Regressors
Sample selection and endogeneity are frequent causes of biases in non-experimental empirical studies. In binary models a standard solution involves complex multivariate models. A simple approximation has been shown to work well in bivariate models. This paper extends the approximation to a trivariate model. Simulations show that the approximation outperforms full maximum likelihood while a least squares approximation may be severely biased. The methods are used to estimate the influence of trust in the parliament and politicians on voting- propensity. No previous studies have allowed for endogeneity of trust on voting and it is shown to severely affect the results.endogeneity; multivariate probit; approximation; Monte Carlo simulation
Faster Fully-Dynamic Minimum Spanning Forest
We give a new data structure for the fully-dynamic minimum spanning forest
problem in simple graphs. Edge updates are supported in
amortized time per operation, improving the amortized bound of
Holm et al. (STOC'98, JACM'01). We assume the Word-RAM model with standard
instructions.Comment: 13 pages, 2 figure
Sources of Regional Resilience in the Danish ICT Sector
In this paper the use of the term âresilienceâ is discussed and a definition for use in quantitative studies of industrial evolution is suggested. Resilience is the ability of an industry in a region to exploit the possibilities arising from external events and adapt to thrive under new selection environments. An econometric analysis is undertaken to uncover the effects of the change in selection environment that the ICT industry faced from the burst of the ICT bubble in the year 2000. It is shown that some characteristics of regional industry structure are associated with growth over the whole period while other characteristics have varying effects pre and post burst. Special attention is given to the responsiveness of growth to the evolution of sales of ICT goods and services in Denmark and it is found that the industry structures that restrain growth also are the ones, which make the regional industry better able to exploit changes in sales at the national level.Resilience; Business cycle; ICT sector; Regional growth
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