Diffraction-limited CCD imaging with faint reference stars

By selecting short exposure images taken using a CCD with negligible readout noise we obtained essentially diffraction-limited 810 nm images of faint objects using nearby reference stars brighter than I=16 at a 2.56 m telescope. The FWHM of the isoplanatic patch for the technique is found to be 50 arcseconds, providing ~20% sky coverage around suitable reference stars.Comment: 4 page letter accepted for publication in Astronomy and Astrophysic

The development and interchange of navigational information and technology between the maritime communities of Iberia, North-Western Europe and Asia, 1500-1620

This thesis examines the development of navigational technology and its subsequent transmission through various means to the emergent maritime powers of Northwestern Europe. Since the fifteenth century the Portuguese, and to a lesser extent the Castillians had sought to impose a bureaucratic system of commercial security to prevent the exploitation by foreigners of the technical and cartographic knowledge available within their hydrographical agencies, navigation schools, and official trading monopolies. Some controversies over this are reviewed, but it is concluded that the most important feature of this technology was its international nature, even though until the 1540's this was disguised by Iberian security. This meant Portuguese sailors could share in a productive series of technical interchanges with Asian mariners after 1500.Possibly by the late sixteenth century they had come to rely too heavily on Asian information, Luso-Asian cartographers, and Asian pilots. This meant that once Northern Europe; powers had obtained translations of Iberian navigation manuals, and taken Iberian experts into their service, they could quickly attain such proficiency as to sail directly into Asian or Pacific waters and themselves participate in similar interchanges. This proved significant technically and politically because the Iberians were unable to place an effective security blanket on the interchange of navigational information in Asia. Asian waters had been typified by some long -standing traditions of relatively free interchange of such technology between seamen of different civilisations. Just as this mutually enriched Asian traditions, so it was also exploited by the Iberians and later European rivals. These interchanges are examined in chapters on the Arab, Indian, Indonesia, Pacific, Chinese, and Japanese interchanges. They hastened the development of a world economy, and the decline of the sixteenth century Portuguese Empire and monopoly of Asia's oceanic trade

Measurements of some parameters of thermal sparks with respect to their ability to ignite aviation fuel/air mixtures

A method used to generate thermal sparks for experimental purposes and methods by which parameters of the sparks, such as speed, size, and temperature, were measured are described. Values are given of the range of such parameters within these spark showers. Titanium sparks were used almost exclusively, since it is particles of this metal which are found to be ejected during simulation tests to carbon fiber composite (CFC) joints. Tests were then carried out in which titanium sparks and spark showers were injected into JP4/(AVTAG F40) mixtures with air. Single large sparks and dense showers of small sparks were found to be capable of causing ignition. Tests were then repeated using ethylene/air mixtures, which were found to be more easily ignited by thermal sparks than the JP4/ air mixtures

Suppression of combustion oscillations with mechanical devices Interim report

Static rocket thrust chamber simulator for cylindrical cold flow-type apparatus desig