Coarse-grained View Research Articles

Making fine-grained and coarse-grained sense distinctions, both manually and automatically

In this paper we discuss a persistent problem arising from polysemy: namely the difficulty of finding consistent criteria for making fine-grained sense distinctions, either manually or automatically. We investigate sources of human annotator disagreements stemming from the tagging for the English Verb Lexical Sample Task in the SENSEVAL-2 exercise in automatic Word Sense Disambiguation. We also examine errors made by a high-performing maximum entropy Word Sense Disambiguation system we developed. Both sets of errors are at least partially reconciled by a more coarse-grained view of the senses, and we present the groupings we use for quantitative coarse-grained evaluation as well as the process by which they were created. We compare the system's performance with our human annotator performance in light of both fine-grained and coarse-grained sense distinctions and show that well-defined sense groups can be of value in improving word sense disambiguation by both humans and machines.

Information granulation and rough set approximation

Information granulation and concept approximation are some of the fundamental issues of granular computing. Granulation of a universe involves grouping of similar elements into granules to form coarse-grained views of the universe. Approximation of concepts, represented by subsets of the universe, deals with the descriptions of concepts using granules. In the context of rough set theory, this paper examines the two related issues. The granulation structures used by standard rough set theory and the corresponding approximation structures are reviewed. Hierarchical granulation and approximation structures are studied, which results in stratified rough set approximations. A nested sequence of granulations induced by a set of nested equivalence relations leads to a nested sequence of rough set approximations. A multi-level granulation, characterized by a special class of equivalence relations, leads to a more general approximation structure. The notion of neighborhood systems is also explored. © 2001 John Wiley & Sons, Inc.

Maximum scales for preserving flux tube content in radial diffusion driven by interchange motions

Plasma in the inner magnetosphere of Jupiter is commonly assumed to be transported radially by fluctuating interchange motions, carrying, on the average, high‐density flux tubes outward and low‐density flux tubes inward. On a coarse‐grained view, this is a diffusion process; viewed on a sufficiently fine scale, high‐density outward‐diffusing tubes and low‐density inward‐diffusing tubes might be observable. However, the required fine scale is much smaller than the characteristic size of circulating eddies of the interchange motion; as a consequence of repeated bifurcations of the flow as the eddy pattern changes randomly, only flux tubes of cross‐sectional dimension smaller than a typical eddy size by the square of (eddy size divided by diffusion distance) have a reasonable chance of preserving their initial plasma content. Energy‐dependent guiding center drifts will randomize and smooth out density variations even on this fine scale if the plasma energy spectrum is wide enough; from a simple model of gradient drifts, the required energy width is proportional to the magnetic flux through a typical eddy divided by the diffusion time. The absence of fine‐grained density fluctuations in the Voyager plasma observations can be explained by such smoothing from gradient drifts, given the observed typical ion thermal energy spread of some 40 eV and the assumption that the typical eddy size is no larger than about 0.7 Jovian radii.