Search results for "Graph theory"
showing 10 items of 784 documents
Understanding seismic path biases and magmatic activity at Mount St Helens volcano before its 2004 eruption
2020
SUMMARY In volcanoes, topography, shallow heterogeneity and even shallow morphology can substantially modify seismic coda signals. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independently from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. Here, we apply the Multiple Lapse Time Window Analysis (MLTWA) to measure the relative importance of scattering attenuation vs absorption at Mount St Helens volcano before its 2004 eruption. The results show the characteristic dominance of scattering attenuation in volcanoes at lower frequencies (3–6 Hz), while absorption is the primary atte…
Description of Dynamic Structured Scenes by a SOM/ARSOM Hierarchy
2001
A neural architecture is presented, aimed to describe the dynamic evolution of complex structures inside a video sequence. The proposed system is arranged as a tree of self-organizing maps. Leaf nodes are implemented by ARSOM networks as a way to code dynamic inputs, while classical SOM's are used to implement the upper levels of the hierarchy. Depending on the application domain, inputs are made by suitable low level features extracted frame by frame of the sequence. Theoretical foundations of the architecture are reported along with a detailed outline of its structure, and encouraging experimental results.
Semi-automatic registration of retinal images based on line matching approach
2013
Accurate retinal image registration is essential to track the evolution of eye-related diseases. We propose a semiautomatic method based on features relying upon retinal graphs for temporal registration of retinal images. The features represent straight lines connecting vascular landmarks on the retina vascular tree: bifurcations, branchings, crossings, end points. In the built retinal graph, one straight line between two vascular landmarks indicates that they are connected by a vascular segment in the original retinal image. The locations of the landmarks are manually extracted to avoid the information loss due to errors in a retinal vessels segmentation algorithms. A straight line model i…
<title>Restoration of a short-exposure image sequence degraded by atmospheric turbulence</title>
2000
This paper deals with the restoration of the shape of an object observed with a high-resolution infrared imaging device, through atmospheric turbulence. The propagation path is quite long (a few tenth kilometer) and the image is thus disturbed. A sequence of short-exposure images of the interesting object is recorded. We can see that the object shape fluctuates randomly during the sequence, but that its edges remain sharp, thanks to the very short exposure time. A bayesian analysis of the Fourier descriptors associated to the edges shows that the optimal shape is the one corresponding to the mean Fourier descriptors. We thus propose two ways to estimate this shape. The first one consists in…
Computer-aided synthesis of complex pump and valve operations
1988
Abstract Process plant operators often have to synthesize sequences of valve and pump operations. On large plants there may be so many possible pipe routes and vessels that it is not practical to provide a priori computer support for every possible operation. The paper describes a program that could form the basis of an operator aid to synthesize appropriate operations from a knowledge of the plant layout and existing pumping operations. The paper concentrates on finding paths through the pipework and on generating a sequence of operations that establishes the path whilst simultaneously satisfying other safety and operating constraints. The paper includes two example problems which were use…
Quantifying the complexity of short-term heart period variability through K nearest neighbor local linear prediction
2008
The complexity of short-term heart period (HP) variability was quantified exploiting the paradigm that associates the degree of unpredictability of a time series to its dynamical complexity. Complexity was assessed through k-nearest neighbor local linear prediction. A proper selection of the parameter k allowed us to perform either linear or nonlinear prediction, and the comparison of the two approaches to infer the presence of nonlinear dynamics. The method was validated on simulations reproducing linear and nonlinear time series with varying levels of predictability. It was then applied to HP variability series measured from healthy subjects during head-up tilt test, showing that short-te…
On the packing sums of pairs
1993
Abstract This paper is concerned with the determination of the length of the largest interval of consecutive integers of the set hA k , where A k is a sequence of integers which is a B h -sequence.
Heuristics for the bi-objective path dissimilarity problem
2009
In this paper the path dissimilarity problem is considered. The problem has previously been studied within several contexts, the most popular of which is motivated by the need to select transportation routes for hazardous materials. The aim of this paper is to formally introduce the problem as a bi-objective optimization problem, in which a single solution consists of a set of p different paths, and two conflicting objectives arise, on one hand the average length of the paths must be kept low, and on the other hand the dissimilarity among the paths in the set should be kept high. Previous methods are reviewed and adapted to this bi-objective problem, thus we can compare the methods using th…
Left-to-right tree pattern matching
1991
We propose a new technique to construct left-to-right matching automata for trees. Our method is based on the novel concept of prefix unifcation which is used to compute a certain closure of the pattern set. From the closure a kind of deterministic matching automaton can be derived immediately. We also point out how to perform the construction incrementally which makes our approach suitable for applications in which pattern sets change dynamically, such as in the Knuth-Bendix completion algorithm.
Scatter Search and Path-Relinking: Fundamentals, Advances, and Applications
2010
Scatter search is an evolutionary metaheuristic that explores solution spaces by evolving a set of reference points, operating on a small set of solutions while making only limited use of randomization. We give a comprehensive description of the elements and methods that make up its template, including the most recent elements incorporated in successful applications in both global and combinatorial optimization. Path-relinking is an intensification strategy to explore trajectories connecting elite solutions obtained by heuristic methods such as scatter search, tabu search, and GRASP. We describe its mechanics, implementation issues, randomization, the use of pools of high-quality solutions …