1. The nerves supplying the distal colon have been divided singly or in combination.
2. The effect of these lesions on the distal colon has been studied by radiograms. The results have been summarised above.
3. The histology of the nerves, before and after section, is described.
4. The hypogastric nerves in the cat are composed solely of fibres descending to the pelvic plexus.
Two-pass migration refers to the method of migrating a three-dimensional data set using only 2D migration routines. The data are migrated twice; once each along two orthogonal axes. The method is easily implemented with any 2D migration code, and in the case of Kirchhoff migration, is far less computationally expensive than one-pass 3D migration. As computing power continues to increase, this savings in computation cost becomes less relevant. However, we maintain that the method, primarily due to availability of 2D migration codes and ease of implementation, holds significant utility in shallow geophysics, and ground-penetrating radar in particular. We review two-pass migration through simple synthetic examples and demonstrate that for a constant velocity medium, it is equivalent to full 3D migration. Then, through a series of test pit studies and a field example, we demonstrate that the method provides results comparable to one-pass 3D migration for a variety of applications and velocity profiles typical of GPR imaging problems.
The ability of the human eye to perceive depth was measured using a specially designed instrument. Visual acuity and both monocular and binocular stereoacuity were measured when viewing the instrument directly and via a videoconferencing link. Ten subjects with an average age of 32.5 years (range 24-50) took part in the study. The group mean visual acuity using both eyes under normal test conditions was -0.04 logMAR (Snellen 6/5) compared with 0.18 logMAR (Snellen 6/10) for the video-link. The mean stereoacuity using both eyes was 37" (SD 18") under normal test conditions. When a videoconferencing link was used, the mean stereoacuity fell to 1218" (SD 1203") using one eye and to 1651" (SD 1419") using both eyes. The ability to perceive depth remotely via a video-link was significantly decreased compared with normal test conditions.
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