Modeling long-range interactions across the visual field in stereo correspondence

When the eyes are converged, most objects in the visual scene will have a significant vertical disparity as measured at the retina. The pattern of vertical disparity across the retina is largely independent of object depth, depending mainly on the particular eye position adopted. Recently, Phillipson and Read (2010, European Journal of Neuroscience, doi:10.1111/j.1460-9568.2010.07454.x) showed that humans are better at achieving stereo correspondence when the vertical disparity field indicated infinite viewing distance, even when the physical viewing distance was just 30cm. They interpreted this as indicating that disparity encoding is optimized for long viewing distances, and is not updated to reflect changes in eye posture. Their results also indicated a significant effect of the visual periphery. Performance was better when the vertical disparity across the entire visual field was consistent with a given binocular eye position – even when this was not the eye position actually adopted – than when the vertical disparity beyond 20o eccentricity indicated a different eye position than that within 20o eccentricity. This is a surprising result, since (i) the task was to detect a target 8o in diameter, extending from 10o to 18o eccentricity, so information beyond 20o was completely irrelevant to the task, and (ii) many previous results indicate that the visual system detects and uses vertical disparity in local regions, even when the global vertical disparity field is not consistent with any single binocular eye position. Here, I show that this effect can be explained by a template-matching model in which the response of a population of disparity-detectors is compared with stored templates of the response expected to stimuli of known disparity

Active Galaxies and the Study of Black Hole Demographics

We discuss the critical importance of black hole mass indicators based on scaling relations in active galaxies. We highlight outstanding uncertainties in these methods and potential paths to substantial progress in the next decade.Comment: 4 pages, 1 figure, Invited review to appear in PAS

A wind tunnel investigation into the effects of roof curvature on the aerodynamic drag experienced by a light goods vehicle

Roof curvature is used to increase ground vehicle camber and enhance rear-body boat-tailing to reduce aerodynamic drag. Little aerodynamic data is published for light goods vehicles (LGVs) which account for a significant proportion of annual UK licensed vehicle miles. This paper details scale wind tunnel measurements at Re = 1.6 × 106 of a generic LGV utilising interchangeable roof panels to investigate the effects of curved roof profile on aerodynamic drag at simulated crosswinds between -6° and 16°. Optimum magnitudes of roof profile depth and axial location are suggested and the limited dataset indicates that increasing roof curvature is effective in reducing drag over a large yaw range, compared to a flat roof profile. This is primarily due to increased base pressure, possibly from enhanced mixing of longitudinal vortices shed from the rear-body upper side edges and increased turbulent mixing in the near-wake due to the increased effective boat-tail angle

X-ray Properties of Intermediate-mass Black Holes in Active Galaxies. III. Spectral Energy Distribution and Possible Evidence for Intrinsically X-ray-weak AGNs

We present a systematic X-ray study, the third in a series, of 49 active galactic nuclei with intermediate-mass black holes (IMBH; ~10^5-10^6 M_sun) using Chandra observations. We detect 42 out of 49 targets with a 0.5-2 keV X-ray luminosity 10^41-10^43 erg/s. We perform spectral fitting for the 10 objects with enough counts (>200), and they are all well fit by a simple power-law model modified by Galactic absorption, with no sign of significant intrinsic absorption. While we cannot fit the X-ray spectral slope directly for the rest of the sample, we estimate it from the hardness ratio and find a range of photon indices consistent with those seen in more luminous and massive objects. The X-ray-to-optical spectral slope (alphaox) of our IMBH sample is systematically flatter than in active galaxies with more massive black holes, consistent with the well-known correlation between alphaox and UV luminosity. Thanks to the wide dynamic range of our sample, we find evidence that alphaox increases with decreasing M_BH as expected from accretion disk models, where the UV emission systematically decreases as M_BH decreases and the disk temperature increases. We also find a long tail toward low alphaox values. While some of these sources may be obscured, given the high L_bol/L_Eddington values in the sample, we argue that some may be intrinsically X-ray-weak, perhaps owing to a rare state that radiates very little coronal emission.Comment: 13 pages (double columns), 2 tables, 9 figures, ApJ accepte

Investigation of the aerodynamic characteristics of a lifting body in ground proximity

The use of cambered hull shapes in the next generation of lighter-than-air vehicles to enhance aerodynamic performance, together with optimized take-off manoeuvre profiles, will require a more detailed understanding of ground proximity effects for such aircraft. A series of sub-scale wind tunnel tests at Re = 1.4 x 106 on a 6:1 prolate spheroid are used to identify potential changes in aerodynamic lift, drag and pitching moment coefficients that are likely to be experienced on the vehicle hull in isolation when in close ground proximity. The experimental data is supported by a preliminary assessment of surface pressure changes using a high order panel method (PANAIR) and RANS CFD simulations to assess the flow structure. The effect of ground proximity, most evident when non-dimensional ground clearance (h/c) < 0.3, is to reduce lift coefficient, increase drag coefficient and increase the body pitching moment coefficient