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

Suppression of combustion oscillations with mechanical devices Interim report

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

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

Functional design for operational earth resources ground data processing

The author has identified the following significant results. Study emphasis was on developing a unified concept for the required ground system, capable of handling data from all viable acquisition platforms and sensor groupings envisaged as supporting operational earth survey programs. The platforms considered include both manned and unmanned spacecraft in near earth orbit, and continued use of low and high altitude aircraft. The sensor systems include both imaging and nonimaging devices, operated both passively and actively, from the ultraviolet to the microwave regions of the electromagnetic spectrum

A review of modular strategies and architecture within manufacturing operations

This paper reviews existing modularity and modularization literature within manufacturing operations. Its purpose is to examine the tools, techniques, and concepts relating to modular production, to draw together key issues currently dominating the literature, to assess managerial implications associated with the emerging modular paradigm, and to present an agenda for future research directions. The review is based on journal papers included in the ABI/Inform electronic database and other noteworthy research published as part of significant research programmes. The research methodology concerns reviewing existing literature to identify key modular concepts, to determine modular developments, and to present a review of significant contributions to the field. The findings indicate that the modular paradigm is being adopted in a number of manufacturing organizations. As a result a range of conceptual tools, techniques, and frameworks has emerged and the field of modular enquiry is in the process of codifying the modular lexicon and developing appropriate modular strategies commensurate with the needs of manufacturers. Modular strategies and modular architecture were identified as two key issues currently dominating the modular landscape. Based on this review, the present authors suggest that future research areas need to focus on the development and subsequent standardization of interface protocols, cross-brand module use, supply chain power, transparency, and trust. This is the first review of the modular landscape and as such provides insights into, first, the development of modularization and, second, issues relating to designing modular products and modular supply chains

The Nature of the H2-Emitting Gas in the Crab Nebula

Understanding how molecules and dust might have formed within a rapidly expanding young supernova remnant is important because of the obvious application to vigorous supernova activity at very high redshift. In previous papers, we found that the H2 emission is often quite strong, correlates with optical low-ionization emission lines, and has a surprisingly high excitation temperature. Here we study Knot 51, a representative, bright example, for which we have available long slit optical and NIR spectra covering emission lines from ionized, neutral, and molecular gas, as well as HST visible and SOAR Telescope NIR narrow-band images. We present a series of CLOUDY simulations to probe the excitation mechanisms, formation processes and dust content in environments that can produce the observed H2 emission. We do not try for an exact match between model and observations given Knot 51's ambiguous geometry. Rather, we aim to explain how the bright H2 emission lines can be formed from within the volume of Knot 51 that also produces the observed optical emission from ionized and neutral gas. Our models that are powered only by the Crab's synchrotron radiation are ruled out because they cannot reproduce the strong, thermal H2 emission. The simulations that come closest to fitting the observations have the core of Knot 51 almost entirely atomic with the H2 emission coming from just a trace molecular component, and in which there is extra heating. In this unusual environment, H2 forms primarily by associative detachment rather than grain catalysis. In this picture, the 55 H2-emitting cores that we have previously catalogued in the Crab have a total mass of about 0.1 M_sun, which is about 5% of the total mass of the system of filaments. We also explore the effect of varying the dust abundance. We discuss possible future observations that could further elucidate the nature of these H2 knots.Comment: 51 pages, 15 figures, accepted for publication in MNRAS, revised Figure 12 results unchange