Research into the design of distributed directory services

Distributed, computer based communication is becoming established within many working environments. Furthermore, the near future is likely to see an increase in the scale, complexity and usage of telecommunications services and distributed applications. As a result, there is a critical need for a global Directory service to store and manage communication information and therefore support the emerging world-wide telecommunications environment. This thesis describes research into the design of distributed Directory services. It addresses a number of Directory issues ranging from the abstract structure of information to the concrete implementation of a prototype system. In particular, it examines a number of management related issues concerning the management of communication information and the management of the Directory service itself. The following work develops models describing different aspects of Directory services. These include data access control and data integrity control models concerning the abstract structure and management of information as well as knowledge management, distributed operation and replication models concerning the realisation of the Directory as a distributed system. In order to clarify the relationships between these models, a layered directory architecture is proposed. This architecture provides a framework for the discussion of directory issues and defines the overall structure of this thesis. This thesis also describes the implementation of a prototype Directory service, supported by software tools typical of those currently available within many environments. It should be noted that, although this thesis emphasises the design of abstract directory models, development of the prototype consumed a large amount of time and effort and prototyping activities accounted for a substantial portion of this research. Finally, this thesis reaches a number of conclusions which are applied to the emerging ISO/CCITT X. 500 standard for Directory services, resulting in possible input for the 1988-92 study period

Research into the design of distributed directory services

Distributed, computer based communication is becoming established within many working environments. Furthermore, the near future is likely to see an increase in the scale, complexity and usage of telecommunications services and distributed applications. As a result, there is a critical need for a global Directory service to store and manage communication information and therefore support the emerging world-wide telecommunications environment. This thesis describes research into the design of distributed Directory services. It addresses a number of Directory issues ranging from the abstract structure of information to the concrete implementation of a prototype system. In particular, it examines a number of management related issues concerning the management of communication information and the management of the Directory service itself. The following work develops models describing different aspects of Directory services. These include data access control and data integrity control models concerning the abstract structure and management of information as well as knowledge management, distributed operation and replication models concerning the realisation of the Directory as a distributed system. In order to clarify the relationships between these models, a layered directory architecture is proposed. This architecture provides a framework for the discussion of directory issues and defines the overall structure of this thesis. This thesis also describes the implementation of a prototype Directory service, supported by software tools typical of those currently available within many environments. It should be noted that, although this thesis emphasises the design of abstract directory models, development of the prototype consumed a large amount of time and effort and prototyping activities accounted for a substantial portion of this research. Finally, this thesis reaches a number of conclusions which are applied to the emerging ISO/CCITT X. 500 standard for Directory services, resulting in possible input for the 1988-92 study period

Herschel-ATLAS: The angular correlation function of submillimetre galaxies at high and low redshift

We present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 μm-selected sample we detect no significant clustering, consistent with the expectation that the 250 μm-selected sources are mostly normal galaxies at z <∼ 1. For our 350 μm and 500 μm-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1’, but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z ∼ 2−3 we detect significant strong clustering, leading to an estimate of r0 ∼ 7−11 h−1 Mpc. The slope of our clustering measurements is very steep, δ ∼ 2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxie

A New Era in Extragalactic Background Light Measurements: The Cosmic History of Accretion, Nucleosynthesis and Reionization

(Brief Summary) What is the total radiative content of the Universe since the epoch of recombination? The extragalactic background light (EBL) spectrum captures the redshifted energy released from the first stellar objects, protogalaxies, and galaxies throughout cosmic history. Yet, we have not determined the brightness of the extragalactic sky from UV/optical to far-infrared wavelengths with sufficient accuracy to establish the radiative content of the Universe to better than an order of magnitude. Among many science topics, an accurate measurement of the EBL spectrum from optical to far-IR wavelengths, will address: What is the total energy released by stellar nucleosynthesis over cosmic history? Was significant energy released by non-stellar processes? Is there a diffuse component to the EBL anywhere from optical to sub-millimeter? When did first stars appear and how luminous was the reionization epoch? Absolute optical to mid-IR EBL spectrum to an astrophysically interesting accuracy can be established by wide field imagingat a distance of 5 AU or above the ecliptic plane where the zodiacal foreground is reduced by more than two orders of magnitude.Comment: 7 pages; Science White Paper for the US Astro 2010-2020 Decadal Survey. If interested in further community-wide efforts on this topic please contact the first autho

Designing location based learning experiences for people with intellectual disabilities and additional sensory impairments

The research reported here is part of a larger project which seeks to combine serious games (or games based learning) with location based services to help people with intellectual disability and additional sensory impairments to develop work based skills. Specifically this paper reports on where these approaches are combined to scaffold the learning of new routes and ultimately independent travel to new work and educational opportunities. A phased development methodology is applied in a user sensitive manner, to ensure that user feedback drives the ongoing development process. Methods to structure this include group feedback on conceptual storyboards, expert review of prototypes using usability heuristics relating to the main system goals, and finally co-discovery methods with student pairs exploring all three modes of the system in real world contexts. Aspects of developmental and cognitive psychological theories are also reviewed and it is suggested that combining games based learning approaches with location based services is an appropriate combination of technologies for an application specifically designed to scaffold route learning for this target audience

Plasma Dynamics

Contains table of contents for Section 2 and reports on four research projects.National Science Foundation Grant ECS-89-02990U.S. Air Force - Office of Scientific Research Grant AFOSR 89-0082-CU.S. Army - Harry Diamond Laboratories Contract DAAL02-89-K-0084U.S. Army - Harry Diamond Laboratories Contract DAAL02-92-K-0037U.S. Department of Energy Contract DE-AC02-90ER-40591U.S. Navy - Office of Naval Research Grant N00014-90-J-4130Lawrence Livermore National Laboratories Subcontract B-160456National Aeronautics and Space Administration Grant NAGW-2048National Science Foundation Grant ECS-88-22475U.S. Department of Energy Grant DE-FG02-91-ER-5410

Origins Space Telescope: baseline mission concept

The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the Universe today? How do habitable planets form? How common are life-bearing worlds? To answer these alluring questions, Origins will operate at mid- and far-infrared (IR) wavelengths and offer powerful spectroscopic instruments and sensitivity three orders of magnitude better than that of the Herschel Space Observatory, the largest telescope flown in space to date. We describe the baseline concept for Origins recommended to the 2020 US Decadal Survey in Astronomy and Astrophysics. The baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. A mid-infrared instrument (Mid-Infrared Spectrometer and Camera Transit spectrometer) will measure the spectra of transiting exoplanets in the 2.8 to 20  μm wavelength range and offer unprecedented spectrophotometric precision, enabling definitive exoplanet biosignature detections. The far-IR imager polarimeter will be able to survey thousands of square degrees with broadband imaging at 50 and 250  μm. The Origins Survey Spectrometer will cover wavelengths from 25 to 588  μm, making wide-area and deep spectroscopic surveys with spectral resolving power R  ∼  300, and pointed observations at R  ∼  40,000 and 300,000 with selectable instrument modes. Origins was designed to minimize complexity. The architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch, while the cryothermal system design leverages James Webb Space Telescope technology and experience. A combination of current-state-of-the-art cryocoolers and next-generation detector technology will enable Origins’ natural background-limited sensitivity