Finding cyclic redundancy check polynomials for multilevel systems

This letter describes a technique for finding cyclic redundancy check polynomials for systems for transmission over symmetric channels which encode information in multiple voltage levels, so that the resulting redundancy check gives good error protection and is efficient to implement. The codes which we construct have a Hamming distance of 3 or 4. We discuss a way to reduce burst error in parallel transmissions and some tricks for efficient implementation of the shift register for these polynomials. We illustrate our techniques by discussing a particular example where the number of levels is 9, but they are applicable in general     

Representing and using legal knowledge in integrated decision support systems: DataLex WorkStations

There is more to legal knowledge representation than knowledge-bases. It is valuable to look at legal knowledge representation and its implementation across the entire domain of computerisation of law, rather than focussing on sub-domains such as legal expert systems. The DataLex WorkStation software and applications developed using it are used to provide examples. Effective integration of inferencing, hypertext and text retrieval can overcome some of the limitations of these current paradigms of legal computerisation which are apparent when they are used on a stand-alone basis. Effective integration of inferencing systems is facilitated by use of a (quasi) natural language knowledge representation, and the benefits of isomorphism are enhanced. These advantages of integration apply to all forms of inferencing, including document generation and casebased inferencing. Some principles for development of integrated legal decision support systems are proposed.     

Observation and Modeling of a Room-Temperature Negative Characteristic Temperature 1.3-μm p-Type Modulation-Doped Quantum-Dot Laser

A room-temperature negative characteristic temperature (T₀ ) and ultralow threshold current density (J_th) of 48 Amiddotcm^-2 are demonstrated for a 1.3-mum InAs quantum dot laser. These characteristics are obtained by combining a high-growth-temperature GaAs spacer layer with p-type modulation doping of the quantum dots in multiple layer dot-in-a-well structures. Through a comparison of p-doped and undoped devices, a photon coupling mechanism is proposed to account for the different temperature dependences of Jth for the two devices. Numerical simulations based on a rate equation model, which includes photon coupling between ground and excited quantum dot states, are performed. The simulations are able to account for the very different temperature-dependent Jth behavior of the doped and undoped device     

Recombination and loss mechanisms in low-threshold InAs-GaAs 1.3-/spl mu/m quantum-dot lasers

We show that even in quantum-dot (QD) lasers with very low threshold current densities (J/sub th/=40--50 A/cm/sup 2/ at 300 K), the temperature sensitivity of the threshold current arises from nonradiative recombination that comprises /spl sim/60% to 70% of J/sub th/ at 300 K, whereas the radiative part of J/sub th/ is almost temperature insensitive. The influence of the nonradiative recombination mechanism decreases with increasing hydrostatic pressure and increasing band gap, which leads to a decrease of the threshold current. We also studied, for the first time, the band gap dependence of the radiative part of J/sub th/, which in contrast increases strongly with increasing band gap. These results suggest that Auger recombination is an important intrinsic recombination mechanism for 1.3-/spl mu/m lasers, even in a very low threshold QD device, and that it is responsible for the temperature sensitivity of the threshold current.     

Labs of the World, Unite!!!

eScience is rapidly changing the way we do research. As a result, many research labs now need non-trivial computational power. Grid and voluntary computing are well-established solutions for this need. However, not all labs can effectively benefit from these technologies. In particular, small and medium research labs (which are the majority of the labs in the world) have a hard time using these technologies as they demand high visibility projects and/or high-qualified computer personnel. This paper describes OurGrid, a system designed to fill this gap. OurGrid is an open, free-to-join, cooperative Grid in which labs donate their idle computational resources in exchange for accessing other labs’ idle resources when needed. It relies on an incentive mechanism that makes it in the best interest of participants to collaborate with the system, employs a novel application scheduling technique that demands very little information, and uses virtual machines to isolate applications and thus provide security. The vision is that OurGrid enables labs to combine their resources in a massive worldwide computing platform. OurGrid is in production since December 2004. Any lab can join it by downloading its software from .     

Local government and state control: Municipalising the Northern Territory land councils

If implemented, the recommendations of a recent review of the Aboriginal Land Rights (Northern Territory) Act 1976 would see relatively strong provisions for Aboriginal people to obtain and manage their traditional lands abolished. A centrally regulated and assimilationist system of local governance would be substituted. The neo-colonial implications of the proposals are masked by liberal rhetoric of community and local democracy.     

Book reviews

TOWARDS COSMOPOLIS: Planning for Multicultural Cities. Leonie Sandercock. John Wiley & Sons, Chichester, UK, 1998. ISBN 0471971987 (paperback). 258 pp.; bibliography. RRP $41.15.

THE MYTH OF THE POWERLESS STATE: Governing the Economy in a Global Era. Linda Weiss. Polity/Blackwell, Cambridge, 1998. ISBN 0745615821 (paperback). 260 pp.; index and bibliography. RRP $37.95.

SOCIAL CHANGE, SUBURBAN LIVES: An Australian Newtown 1960s to 1990s. Lois Bryson and Ian Winter. Allen & Unwin, Sydney, 1998. ISBN 1864486996 (paperback). 238 pp.; index and bibliography. RRP $29.95.

CONTESTING THE AUSTRALIAN WAY: States, Markets and Civil Society. Paul Smyth and Bettina Cass (eds). Cambridge University Press, Cambridge, 1998. ISBN 0521633060 (hardback). 280 pp.; bibliography and index. RRP $90.00.

THE ECOLOGICAL CITY AND THE CITY EFFECT: Essays on the Urban Planning Requirements for the Sustainable City. Franco Archibugi. Ashgate, Aldershot, UK, 1997. ISBN 1859726534 (hardback). 243 pp.; bibliography and index. RRP $96.50.

CITIES FOR TOMORROW: Integrating Land Use, Transport and the Environment. Hans L. Westerman. Austroads, Sydney, 1998. ISBN 0855885033 (paperback). Resource Document 202 pp.; Better Practice Guide. 394 pp.; index. RRP $180.00.

EAST WEST PERSPECTIVES ON 21ST CENTURY URBAN DEVELOPMENT: Sustainable Eastern and Western Cities in the New Millennium. John Brotchie, Peter Newton, Peter Hall and John Dickey (eds). Ashgate, Aldershot, UK, 1999. ISBN 1840143177 (hardback). 432 pp.; bibliography and index. RRP $122.00.

MADE IN LANCASHIRE: A History of Regional Industrialisation. Geoffrey Timmins. Manchester University Press, Manchester, 1998. ISBN 0719045398. 334 pp.; bibliography and index. RRP $145.00.     

Philosophically Based Limitations to Freedom of Speech in Virtual Communities

This paper applies political philosophy to the question of freedom of speech in virtual communities. It takes as its starting point the philosophical justifications given for freedom of speech in (Greenawalt, in Computers, Ethics and Social Values, Prentice-Hall, 1995). For each of these justifications I discuss the types of speech to which they apply, and implications for virtual communities. The justifications imply several limitations to freedom of speech within a well-run virtual community. I give some examples in which the existence of virtual communities can be used to reflect on extant philosophical arguments and practices. By applying the list of steps for thinking about systems given in (Churchman, in The Systems Approach, New York: Dell Publishing Co., Inc., 1968), I obtain a classification framework for thinking about the merits and demerits of a particular speech act, and describe a justification for freedom of speech, missing from Greenawalt's list, that this classification helped me to identify. I give a summary of practical suggestions for administrators of virtual communities. Finally, I discuss why I consider the question of how to regulate speech in virtual communities matters, from a global perspective.