David Attewell

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The surface reflectance of objects is highly variable, ranging between 4% for, say, charcoal and 90% for fresh snow. When stimuli are presented simultaneously, people can discriminate hundreds of levels of visual intensity. Despite this, human languages possess a maximum of just three basic terms for describing lightness. In English, these are white (or(More)
The statistics of natural images have often been used to account for various properties of animal visual systems. However, for most visual tasks, the images themselves are not important; it is the physical properties of the surfaces which generated them that guide behaviour. Here, we present statistical characterisations of the surface reflectances(More)
An analysis of large-area CO J=3-2 maps from the James Clerk Maxwell Telescope for 12 nearby spiral galaxies reveals low velocity dispersions in the molecular component of the interstellar medium. The three lowest luminosity galaxies show a relatively flat velocity dispersion as a function of radius while the remaining nine galaxies show a central peak with(More)
The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an H i-selected sample of 155 galaxies spanning all morphological types with distances less than 25 Mpc. We describe the scientific goals of the survey, the sample selection, and the observing strategy. We also present an atlas and analysis of the CO J=3-2 maps for the 47(More)
We present CO J=3→2 maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with CO J=1→0 data and find that the computed CO J=3→2 to CO J=1→0 line ratio (R31) agrees with values measured in other NGLS field galaxies. We(More)
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