26,552 research outputs found
Bipartite graph partitioning and data clustering
Many data types arising from data mining applications can be modeled as
bipartite graphs, examples include terms and documents in a text corpus,
customers and purchasing items in market basket analysis and reviewers and
movies in a movie recommender system. In this paper, we propose a new data
clustering method based on partitioning the underlying bipartite graph. The
partition is constructed by minimizing a normalized sum of edge weights between
unmatched pairs of vertices of the bipartite graph. We show that an approximate
solution to the minimization problem can be obtained by computing a partial
singular value decomposition (SVD) of the associated edge weight matrix of the
bipartite graph. We point out the connection of our clustering algorithm to
correspondence analysis used in multivariate analysis. We also briefly discuss
the issue of assigning data objects to multiple clusters. In the experimental
results, we apply our clustering algorithm to the problem of document
clustering to illustrate its effectiveness and efficiency.Comment: Proceedings of ACM CIKM 2001, the Tenth International Conference on
Information and Knowledge Management, 200
Understanding the white-light flare on 2012 March 9 : Evidence of a two-step magnetic reconnection
We attempt to understand the white-light flare (WLF) that was observed on
2012 March 9 with a newly constructed multi-wavelength solar telescope called
the Optical and Near-infrared Solar Eruption Tracer (ONSET). We analyzed WLF
observations in radio, H-alpha, white-light, ultraviolet, and X-ray bands. We
also studied the magnetic configuration of the flare via the nonlinear
force-free field (NLFFF) extrapolation and the vector magnetic field observed
by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). Continuum emission enhancement clearly appeared at the 3600
angstrom and 4250 angstrom bands, with peak contrasts of 25% and 12%,
respectively. The continuum emission enhancement closely coincided with the
impulsive increase in the hard X-ray emission and a microwave type III burst at
03:40 UT. We find that the WLF appeared at one end of either the sheared or
twisted field lines or both. There was also a long-lasting phase in the H-alpha
and soft X-ray bands after the white-light emission peak. In particular, a
second, yet stronger, peak appeared at 03:56 UT in the microwave band. This
event shows clear evidence that the white-light emission was caused by
energetic particles bombarding the lower solar atmosphere. A two-step magnetic
reconnection scenario is proposed to explain the entire process of flare
evolution, i.e., the first-step magnetic reconnection between the field lines
that are highly sheared or twisted or both, and the second-step one in the
current sheet, which is stretched by the erupting flux rope. The WLF is
supposed to be triggered in the first-step magnetic reconnection at a
relatively low altitude.Comment: 4 pages, 4 figures, published in A&A Lette
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