3,226 research outputs found
Fast Dictionary Learning for Sparse Representations of Speech Signals
© 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Published version: IEEE Journal of Selected Topics in Signal Processing 5(5): 1025-1031, Sep 2011. DOI: 10.1109/JSTSP.2011.2157892
Finding Young Stellar Populations in Elliptical Galaxies from Independent Components of Optical Spectra
Elliptical galaxies are believed to consist of a single population of old
stars formed together at an early epoch in the Universe, yet recent analyses of
galaxy spectra seem to indicate the presence of significant younger populations
of stars in them. The detailed physical modelling of such populations is
computationally expensive, inhibiting the detailed analysis of the several
million galaxy spectra becoming available over the next few years. Here we
present a data mining application aimed at decomposing the spectra of
elliptical galaxies into several coeval stellar populations, without the use of
detailed physical models. This is achieved by performing a linear independent
basis transformation that essentially decouples the initial problem of joint
processing of a set of correlated spectral measurements into that of the
independent processing of a small set of prototypical spectra. Two methods are
investigated: (1) A fast projection approach is derived by exploiting the
correlation structure of neighboring wavelength bins within the spectral data.
(2) A factorisation method that takes advantage of the positivity of the
spectra is also investigated. The preliminary results show that typical
features observed in stellar population spectra of different evolutionary
histories can be convincingly disentangled by these methods, despite the
absence of input physics. The success of this basis transformation analysis in
recovering physically interpretable representations indicates that this
technique is a potentially powerful tool for astronomical data mining.Comment: 12 Pages, 7 figures; accepted in SIAM 2005 International Conference
on Data Mining, Newport Beach, CA, April 200
Dimensionality reduction with image data
A common objective in image analysis is dimensionality reduction. The most common often used data-exploratory technique with this objective is principal component analysis. We propose a new method based on the projection of the images as matrices after a Procrustes rotation and show that it leads to a better reconstruction of images
Revisiting Resolution and Inter-Layer Coupling Factors in Modularity for Multilayer Networks
Modularity for multilayer networks, also called multislice modularity, is
parametric to a resolution factor and an inter-layer coupling factor. The
former is useful to express layer-specific relevance and the latter quantifies
the strength of node linkage across the layers of a network. However, such
parameters can be set arbitrarily, thus discarding any structure information at
graph or community level. Other issues are related to the inability of properly
modeling order relations over the layers, which is required for dynamic
networks.
In this paper we propose a new definition of modularity for multilayer
networks that aims to overcome major issues of existing multislice modularity.
We revise the role and semantics of the layer-specific resolution and
inter-layer coupling terms, and define parameter-free unsupervised approaches
for their computation, by using information from the within-layer and
inter-layer structures of the communities. Moreover, our formulation of
multilayer modularity is general enough to account for an available ordering of
the layers and relating constraints on layer coupling. Experimental evaluation
was conducted using three state-of-the-art methods for multilayer community
detection and nine real-world multilayer networks. Results have shown the
significance of our modularity, disclosing the effects of different
combinations of the resolution and inter-layer coupling functions. This work
can pave the way for the development of new optimization methods for
discovering community structures in multilayer networks.Comment: Accepted at the IEEE/ACM Conf. on Advances in Social Network Analysis
and Mining (ASONAM 2017
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