1,042 research outputs found
Inf-semilattice approach to self-dual morphology
Today, the theoretical framework of mathematical morphology is phrased in terms of complete lattices and operators defined on them. That means in particular that the choice of the underlying partial ordering is of eminent importance, as it determines the class of morphological operators that one ends up with. The duality principle for partially ordered sets, which says that the opposite of a partial ordering is also a partial ordering, gives rise to the fact that all morphological operators occur in pairs, e.g., dilation and erosion, opening and closing, etc. This phenomenon often prohibits the construction of tools that treat foreground and background of signals in exactly the same way. In this paper we discuss an alternative framework for morphological image processing that gives rise to image operators which are intrinsically self-dual. As one might expect, this alternative framework is entirely based upon the definition of a new self-dual partial ordering
Unraveling Coordination Problems
Strategic uncertainty complicates policy design in coordination games. To
rein in strategic uncertainty, the planner in this paper connects the problem
of policy design to that of equilibrium selection using a global games
approach. We characterize the subsidy scheme that induces coordination on a
given outcome of the game as its unique equilibrium. Optimal subsidies are
symmetric for identical players, continuous functions of model parameters, and
do not make the targeted strategies strictly dominant for any of the players;
these properties differ starkly from canonical results in the literature.
Uncertainty about payoffs impels policy moderation as aggressive intervention
might itself induce coordination failure.
JEL codes: D81, D82, D83, D86, H20.
Keywords: mechanism design, global games, contracting with externalities,
unique implementation
Cyclical patterns in risk indicators based on financial market infrastructure transaction data
Nanosecond repetitively pulsed discharges in N2-O2 mixtures: Inception cloud and streamer emergence
We evaluate the nanosecond temporal evolution of tens of thousands of positive discharges in
a 16 cm point-plane gap in high purity nitrogen 6.0 and in N2–O2 gas mixtures with oxygen
contents of 100 ppm, 0.2%, 2% and 20%, for pressures between 66.7 and 200 mbar. The
voltage pulses have amplitudes of 20 to 40 kV with rise times of 20 or 60 ns and repetition
frequencies of 0.1 to 10 Hz. The discharges first rapidly form a growing cloud around the tip,
then they expand much more slowly like a shell and finally after a stagnation stage they can
break up into rapid streamers. The radius of cloud and shell in artificial air is about 10% below
the theoretically predicted value and scales with pressure p as theoretically expected, while
the observed scaling of time scales with p raises questions. We find characteristic dependences
on the oxygen content. No cloud and shell stage can be seen in nitrogen 6.0, and streamers
emerge immediately. The radius of cloud and shell increases with oxygen concentration.
On the other hand, the stagnation time after the shell phase is maximal for the intermediate
oxygen concentration of 0.1% and the number of streamers formed is minimal; here the cloud
and shell phase seem to be particularly stable against destabilization into streamers
Image decompositions and transformations as peaks and wells
10 pages to be submitted to ISMM2011International audienceAn image may be decomposed as a difference between an image of peaks and an image of wells. Applying a morphological operator to these two components before reconstructing a final image produces interesting filters for grey tone or binary images. This decomposition depends upon the point of view from where the image is considered
Hierarchical characterization of complex networks
While the majority of approaches to the characterization of complex networks
has relied on measurements considering only the immediate neighborhood of each
network node, valuable information about the network topological properties can
be obtained by considering further neighborhoods. The current work discusses on
how the concepts of hierarchical node degree and hierarchical clustering
coefficient (introduced in cond-mat/0408076), complemented by new hierarchical
measurements, can be used in order to obtain a powerful set of topological
features of complex networks. The interpretation of such measurements is
discussed, including an analytical study of the hierarchical node degree for
random networks, and the potential of the suggested measurements for the
characterization of complex networks is illustrated with respect to simulations
of random, scale-free and regular network models as well as real data
(airports, proteins and word associations). The enhanced characterization of
the connectivity provided by the set of hierarchical measurements also allows
the use of agglomerative clustering methods in order to obtain taxonomies of
relationships between nodes in a network, a possibility which is also
illustrated in the current article.Comment: 19 pages, 23 figure
Multivariate risks and depth-trimmed regions
We describe a general framework for measuring risks, where the risk measure
takes values in an abstract cone. It is shown that this approach naturally
includes the classical risk measures and set-valued risk measures and yields a
natural definition of vector-valued risk measures. Several main constructions
of risk measures are described in this abstract axiomatic framework.
It is shown that the concept of depth-trimmed (or central) regions from the
multivariate statistics is closely related to the definition of risk measures.
In particular, the halfspace trimming corresponds to the Value-at-Risk, while
the zonoid trimming yields the expected shortfall. In the abstract framework,
it is shown how to establish a both-ways correspondence between risk measures
and depth-trimmed regions. It is also demonstrated how the lattice structure of
the space of risk values influences this relationship.Comment: 26 pages. Substantially revised version with a number of new results
adde
- …