Sewers are aging, expensive assets that attract public attention only when they fail. Sewer operators are under increasing pressure to minimise their maintenance costs, while preventing sewer failures. Inspection can give early warning of failures and allow economical repair under noncrisis conditions. Current inspection techniques are subjective and detect only gross defects reliably. They cannot provide the data needed to confidently plan long-term maintenance. This paper describes PIRAT, a quantitative technique for sewer inspection. PIRAT measures the internal geometry of the sewer and then analyses these data to detect, classify, and rate defects automatically using artificial intelligence techniques. We describe the measuring system and present and discuss geometry results for different types of sewers. The defect analysis techniques are outlined and a sample defect report presented. PIRAT's defect reports are compared with reports from the conventional technique and the discrepancies discussed. We relate PIRAT to other work in sewer robotics.
A novel type of neutron interferometer was constructed and tested employing a split cylindrical zone plate with neutrons of 20 A wavelength. Its performance and relative merits are discussed.PACS numbers: 07.90. + C, 29.40.-n, 41.80.-y The highly successful perfect-crystal neutron interferometer of the type first developed by Bonse and Rauch 1 exhibits interference by amplitude division. It relies on dynamical Bragg diffraction in a highly perfect single crystal to provide the beam splitting. This type of interferometer, topologically analogous to the Mach-Zehnder interferometer of classical optics, has been employed in a variety of interesting experiments with use of thermal neutrons. 2 Its shortcomings, however, are its extreme sensitivity to mechanical and thermal disturbances, and its applicability only to wavelengths shorter than the Bragg cutoff (6.27 A in silicon).In this paper we discuss an alternative class of neutron interferometers, namely those that work by division of the wavefront, and report on recent experiments with one such device.Interference by division of the wavefront, analogous to Young's experiment, has been demonstrated with thermal and cold neutrons in several different ways. The very first neutron interferometer, 3 built by Maier-Leibnitz and Springer in 1962, was of this type; an adaptation of the Fresnel biprism with use of quartz prisms as ref ract-959 ing elements for cold neutrons. The experiments of Klein and Qpat 4 on Fresnel diffraction of neutrons by domain walls in ferromagnetic foils are also examples of interference of spatially separated parts of a wavefront, as is the case for the high-precision Fresnel diffraction experiments carried out more recently at the high-flux reactor of the Institut Laue-Langevin in Grenoble, France. 5 ' 6 One of these was, in fact, an exact version of the classical two-slit experiment. 6 Following the successful demonstration of the use of Fresnel zone plates as focusing and imaging elements for slow neutrons, 7 we recently carried out experiments on a split-lens interferometer, based on the classical model of Billet. 8 It is particularly applicable to cold and very cold neutrons and presents certain advantages, to be discussed later.The basic layout of a Billet split-lens interferometer is shown in Fig. 1(a). The points S 1 and S 2 mark the positions of two coherent real images of a primary source S, produced by the two halves of the split lens L x and L 2 . Nonlocalized interference fringes are produced in the region of overlap of the cones diverging from these
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