715,090 research outputs found
MOLECULAR LINE-SHAPE MODELING FROM FIRST PRINCIPLES
International audienceWe present an ab initio approach to spectral line-shape modeling and the comparison of the results with experimental data
Hierarchical Graphical Models for Multigroup Shape Analysis using Expectation Maximization with Sampling in Kendall's Shape Space
This paper proposes a novel framework for multi-group shape analysis relying
on a hierarchical graphical statistical model on shapes within a population.The
framework represents individual shapes as point setsmodulo translation,
rotation, and scale, following the notion in Kendall shape space.While
individual shapes are derived from their group shape model, each group shape
model is derived from a single population shape model. The hierarchical model
follows the natural organization of population data and the top level in the
hierarchy provides a common frame of reference for multigroup shape analysis,
e.g. classification and hypothesis testing. Unlike typical shape-modeling
approaches, the proposed model is a generative model that defines a joint
distribution of object-boundary data and the shape-model variables.
Furthermore, it naturally enforces optimal correspondences during the process
of model fitting and thereby subsumes the so-called correspondence problem. The
proposed inference scheme employs an expectation maximization (EM) algorithm
that treats the individual and group shape variables as hidden random variables
and integrates them out before estimating the parameters (population mean and
variance and the group variances). The underpinning of the EM algorithm is the
sampling of pointsets, in Kendall shape space, from their posterior
distribution, for which we exploit a highly-efficient scheme based on
Hamiltonian Monte Carlo simulation. Experiments in this paper use the fitted
hierarchical model to perform (1) hypothesis testing for comparison between
pairs of groups using permutation testing and (2) classification for image
retrieval. The paper validates the proposed framework on simulated data and
demonstrates results on real data.Comment: 9 pages, 7 figures, International Conference on Machine Learning 201
ELM triggering conditions for the integrated modeling of H-mode plasmas
Recent advances in the integrated modeling of ELMy H-mode plasmas are
presented. A model for the H-mode pedestal and for the triggering of ELMs
predicts the height, width, and shape of the H-mode pedestal and the frequency
and width of ELMs. Formation of the pedestal and the L-H transition is the
direct result of ExB flow shear suppression of anomalous transport. The
periodic ELM crashes are triggered by either the ballooning or peeling MHD
instabilities. The BALOO, DCON, and ELITE ideal MHD stability codes are used to
derive a new parametric expression for the peeling-ballooning threshold. The
new dependence for the peeling-ballooning threshold is implemented in the ASTRA
transport code. Results of integrated modeling of DIII-D like discharges are
presented and compared with experimental observations. The results from the
ideal MHD stability codes are compared with results from the resistive MHD
stability code NIMROD.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Factor price frontiers with international fragmentation of multistage production
This paper investigates international fragmentation in a modeling framework where the multi-stage nature of industrial production is made explicitly, and where the engineering sequence of stages is juxtaposed with a sequence of increasing economic incentive for international fragmentation. Assuming that there are two tradable goods sectors, a multi-stage sector amenable to international fragmentation and a standard sector where production is always fully integrated in the domestic economy, I first explore the nature and shape of the domestic factor price frontier, endogenously determining the margin of international fragmentation under given world prices for the two goods. I then explore the consequences of an exogenous change in the terms of trade on the margin of international fragmentation, and the implications of a fall in the cost of transport and communication that facilitates an increasing degree of international fragmentation.international fragmentation, multi-stage production, factor price frontiers
Sculpting multi-dimensional nested structures
Special Issue: Shape Modeling International (SMI) Conference 2013International audienceSolid shape is typically segmented into surface regions to define the appearance and function of parts of the shape; these regions in turn use curve networks to represent boundaries and creases, and feature points to mark corners and other shape landmarks. Conceptual modeling requires these multi-dimensional nested structures to persist throughout the modeling process, an aspect not supported, up to now, in free-form sculpting systems. We present the first shape sculpting framework that preserves and controls the evolution of such nested shape features. We propose a range of geometric and topological behaviors (such as rigidity or mutability) applied hierarchically to points, curves or surfaces in response to a set of typical free-form sculpting operations, such as stretch, shrink, split or merge. Our method is illustrated within a free-form sculpting system for self-adaptive quasi-uniform polygon meshes, where geometric and topology changes resulting from sculpting operations are applied to points, edges and triangular facets. We thus facilitate, for example, the persistence of sharp features that automatically split or merge with variable rigidity, even when the shape changes genus. Sculpting nested structures expands the capabilities of most conceptual design workflows, as exhibited by a suite of models created by our system
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