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- Nathan Cole, Heidi Jo Newberg, +9 authors James Wisniewski
- 2007

We present a maximum likelihood method for determining the spatial properties of tidal debris and of the Galactic spheroid. With this method we characterize Sagittarius debris using stars with the colors of blue F turnoff stars in SDSS stripe 82. The debris is located at (α, δ, R) = (31.37 ± 0.26, 0.0, 29.22 ± 0.20 kpc), with a (spatial) direction given by… (More)

Data from the Sloan Digital Sky Survey has given evidence of structures within the Milky Way halo from other nearby galaxies. Both the halo and these structures are approximated by densities based on geometric objects. A model of the data is formed by a mixture of geometric densities. By using an EM-style algorithm, we optimize the parameters of our model… (More)

- Malik Magdon-Ismail, Jonathan T. Purnell
- 2011 IEEE Third Int'l Conference on Privacy…
- 2011

Clustering social networks is vital to understanding online interactions and influence. This task becomes more difficult when communities overlap, and when the social networks become extremely large. We present an efficient algorithm for constructing overlapping clusters, (approximately linear). The algorithm first embeds the graph and then performs a… (More)

- Malik Magdon-Ismail, Jonathan T. Purnell
- IJDMMM
- 2010

Covariance matrices capture correlations that are invaluable in modeling real-life datasets. Using all d elements of the covariance (in d dimensions) is costly and could result in over-fitting; and the simple diagonal approximation can be over-restrictive. In this work, we present a new model, the Low-Rank Gaussian Mixture Model (LRGMM), for modeling data… (More)

Clustering social networks is vital to understanding online interactions and influence. This task becomes more difficult when communities overlap, and when the social networks become extremely large. We present an efficient algorithm for constructing overlapping clusters, roughly linear in the size of the network. The algorithm first embeds the graph and… (More)

- Sibel Adali, Xiaohui Lu, Malik Magdon-Ismail, Jonathan T. Purnell
- ICWSM
- 2011

We study prominence ranking in heterogeneous social networks with actors who collaborate to create artifacts which display some homophily based community structure (Figure 1). For example, a paper is an artifact and multiple authors may collaborate on the paper. Papers appear in venues, which are communities containing papers on similar topics and of… (More)

Covariance matrices capture correlations that are invaluable in modeling real-life datasets. Using all d elements of the covariance (in d dimensions) is costly and could result in over-fitting; and the simple diagonal approximation can be over-restrictive. We present an algorithm that improves upon the diagonal matrix by allowing a low rank perturbation.… (More)

- Jonathan T. Purnell, Malik Magdon-Ismail
- 2009 International Conference on Machine Learning…
- 2009

Accent identification has grown over the past decade. There has been decent success when a priori knowledge about the accents is available. A typical approach entails detection of certain syllables and phonemes, which in turn requires phoneme-based models. Recently, Gaussian Mixture Models (GMMs) have been used as an unsupervised alternative to these… (More)

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