No description available.

No description available.

No description available.

No description available.

The performance of optical imaging systems relies on control of aberrations that can arise from limitations in the design, manufacture, or alignment. This dissertation addresses the form of aberrations that occur for misaligned reflective systems, such as telescopes. The relationship between a characteristic set of field-dependent aberrations and the misalignments that cause them is systematically explored. A comprehensive technique that quantifies field performance for a 5-mirror system is given, using Monte Carlo analysis to provide confidence levels of image quality as functions of manufacturing and alignment errors. This analysis is an example of the "forward problem"— determining optical performance of a system if the errors are assumed. The inverse problem — determining the state of alignment based on measurements of performance — is more difficult. The solution to the inverse problem for a multiple mirror system requires an understanding of the complex coupling between many degrees of freedom (tilt, decenter, despace, shape error) of the optical elements and field-dependent aberrations.This work builds on previous treatment of field dependent optical aberrations from Tessieres, Thompson, Shack, Buchroeder and others. A basis set of field-dependent aberrations orthogonal over both field and pupil are developed here and used to describe systems with misaligned and misshapen optics. This description allows complete representation of high order and non-linear effects. The functional form of aberrations that are characteristic of mirror tilt, shift, and deformation show some useful patterns that provide insight to the fundamental effects of misalignment.The use of singular value decomposition to create orthogonal combinations of the field dependent aberrations provides a powerful tool for evaluating a system and for estimating the state of alignment using wavefront measurements. The following optical systems are evaluated to investigate the linear coupling between misalignment and the resulting field dependent aberrations:* 2-mirror telescopes, evaluating well-understood effects for an axisymmetric system and developing the relationships for an unobscured system.* 4-mirror correctors for a spherical primary telescope.The tools and methods are applied to reflective optical systems for astronomical telescopes, but the methods are general and can be useful for any optical imaging system.

No description available.

Thesis (M.S.)--Ohio University, March, 2000. / Title from PDF t.p.

Thesis (Ph. D. (Physics and Electronics))--Rhodes University, 2005.

The long term isolated pulsar monitoring program, which commenced in 1984 using the 26 m radio telescope at the Hartebeeshoek Radio Astronomy Observatory (HartRAO), has produced high resolution timing residual data over long timespans. This has enabled the analysis of observed spin down behaviour for 27 braking pulsars, most of which have dataspans longer than 14 years. The phenomenology of observed timing residuals of certain pulsars can be explained by pseudo periodic effects such as precession. Analytic and numerical models are developed to study the kinematic and dynamic behaviour of isolated but torqued precessing pulsars. The predicted timing residual behaviour of the models is characterised, and confronted with timing data from selected pulsars. Cyclic variations in the observed timing residuals of PSR B1642-03, PSR B1323-58 and PSR B1557-50 are fitted with a torqued precession model. The phenomenology of the observed timing behaviour of these pulsars can be explained by the precession models, but precise model fitting was not possible. This is not surprising given that the complexity of the pulsar systems is not completely described by the model. The extension of the pulsar monitoring program at HartRAO is used as motivation for the design and development of a new low cost, multi-purpose digital pulsar receiver. The instrument is implemented using a hybrid filterbank architecture, consisting of an analogue frontend and digital backend, to perform incoherent dedispersion. The design of a polyphase filtering system, which will consolidate multiple processing units into a single filtering solution, is discussed for future implementation.

This thesis reports on the design, construction, testing and operation of the spectral line and continuum receivers built for the 22 GHz Radio Telescope. First results from 'the telescope were obtained and have been analysed to give an estimate of system efficiency. Tests have been performed on the front end and in particular on the 22 GHz mixer in order to determine the minimum detectable temperature. The Sun, Moon and major planets are sources suitable for antenna alignment and consequently a literature survey of emission at 22 GHz from elements of the Solar system has been made.