4,022 results for 1990

  • Images may show start of European-Africa plate collision

    Mascle, J; Hughen, C; Benkhelil, J; Chamot-Rooke, N; Chaumillon, E; Foucher, JP; Griboulard, R; Kopf, A; Lamarche, Geoffroy; Volkonskaia, A; Woodside, J; Zitter, T (1999)

    Journal article
    The University of Auckland Library

    View record details
  • SunOS Minix: a tool for use in Operating System Laboratories

    Ashton, Paul; Ayers, Daniel; Smith, Peter (1993)

    Doctoral thesis
    University of Canterbury Library

    Laboratory work is an essential part of the learning experience in many areas of Computer Science, and this is particularly true in the area of operating systems. To support laboratory work in operating systems, we have created SunOS Minix, a version of the Minix operating system that runs as a process under Sun Unix (SunOS). To date, projects for two advanced classes on operating systems have involved extensive work with the SunOS Minix source code. Also, we are in the process of developing a novel graphical monitoring and control interface that will make SunOS Minix a powerful tool for use in introductory operating system laboratories.

    View record details
  • A Case Study in Specifying and Testing Architectural Features

    Krishnan, Padmanabhan (1993)

    Doctoral thesis
    University of Canterbury Library

    This paper studies the speci cation and testing of two main architectural features. We consider restricted forms of instruction pipelining and parallel memory models present in the SPARC speci cation. The feasibility of using an automatic tool, the concurrency work bench, has been demonstrated.

    View record details
  • A Generator of Pseudo-Random Self-Similar Sequences Based on SRA

    Jeong, H. D. J.; McNickle, D.; Pawlikowski, K. (1998)

    Doctoral thesis
    University of Canterbury Library

    It is generally accepted that self-similar (or fractal) processes may provide better models for teletraffic in modern computer networks than Poisson processes. If this is not taken into account, it can lead to inaccurate conclusions about performance of computer networks. Thus, an important requirement for conducting simulation studies of telecommunication networks is the ability to generate long synthetic stochastic self-similar sequences. A generator of pseudo-random self-similar sequences, based on the SRA method [5], is implemented and analysed in this report. Properties of this generator were experimentally studied in the sense of its statistical accuracy and the time required to produce sequences of a given (long) length. This generator shows acceptable level of accuracy of the output data (in the sense of relative accuracy of the Hurst parameter) and is fast. The theoretical algorithmic complexity is O(n) [20].

    View record details
  • Towards Computer-Supported Collaborative Software Engineering

    Cook, Carl (1993)

    Doctoral thesis
    University of Canterbury Library

    Software engineering is a fundamentally collaborative activity, yet most tools that support software engineers are designed only for single users. There are many foreseen benefits in using tools that support real time collaboration between software engineers, such as avoiding conflicting concurrent changes to source files and determining the impact of program changes immediately. Unfortunately, it is difficult to develop non-trivial tools that support real time Collaborative Software Engineering (CSE). Accordingly, the few CSE tools that do exist have restricted capabilities. Given the availability of powerful desktop workstations and recent advances in distributed computing technology, it is now possible to approach the challenges of CSE from a new perspective. The research goal in this thesis is to investigate mechanisms for supporting real time CSE, and to determine the potential gains for developers from the use of CSE tools. An infrastructure, Caise, is presented which supports the rapid development of real time CSE tools that were previously unobtainable, based on patterns of collaboration evident within software engineering. In this thesis, I discuss important design aspects of CSE tools, including the identification of candidate patterns of collaboration. I describe the Caise approach to supporting small teams of collaborating software engineers. This is by way of a shared semantic model of software, protocol for tool communication, and Computer Supported Collaborative Work (CSCW) facilities. I then introduce new types of synchronous semantic model-based tools that support various patterns of CSE. Finally, I present empirical and heuristic evaluations of typical development scenarios. Given the Caise infrastructure, it is envisaged that new aspects of collaborative work within software engineering can be explored, allowing the perceived benefits of CSE to be fully realised.

    View record details
  • MLSE Receiver for the Dispersive Rayleigh Fading Channel

    Leon, Wing Seng; Taylor, Desmond P. (1997)

    Doctoral thesis
    University of Canterbury Library

    A maximum likelihood sequence estimator for the dispersive Rayleigh fading channel is developed. Following [1, 2], the MLSE uses a Kalman based channel estimator to acquire the channel parameters necessary to formulate the maximum likelihood metric. However, unlike the MLSE receiver presented in [1, 2], the proposed receiver uses the f-power series channel model [3, 4] to formulate the ML metric and the state space representation of the channel and the received samples. For channels with small delay spreads, this approach is advantageous because only a small number of parameters are required to be estimated by the Kalman channel estimator. Simulation results are presented for various channel parameters.

    View record details
  • DPSK Receiver with Implicit Diversity Gain for the Linearly Frequency-Selective Rayleigh Fading Channel

    Leon, Wing Seng; Taylor, Desmond P. (1999)

    Doctoral thesis
    University of Canterbury Library

    This paper presents a simple DPSK receiver for the frequency-selective fading channel. The channel is modelled as an f-power series truncated to the first two terms [1,2]. Two time invariant receiver filters are used to remove the channel induced ISI and to separate the two implicit diversity branches. The received samples from each branch are then differentially decoded and combined. Analytical and simulation results for binary DPSK show that this receiver outperforms the conventional receiver using matched filtering and a product demodulator.

    View record details
  • Equalization of Linearly Frequency-Selective Fading Channels

    Leon, W. S.; Mengali, U.; Taylor, D. P. (1997)

    Doctoral thesis
    University of Canterbury Library

    A simple technique for removing intersymbol interference (ISI) introduced by "linearly frequency-selective" fading channels is presented. The technique involves the optimization of the overall impulse response of the transmit and receive filters and effectively reduces the channel to one which is flat fading. Computer simulation results show that this equalization method works for channels with small delays.

    View record details
  • On Differentially Demodulated CPFSK

    Griffin, Anthony; Taylor, Desmond P. (1996)

    Doctoral thesis
    University of Canterbury Library

    This paper develops a differential encoder for differentially demodulated continuous phase frequency shift keying (CPFSK). CPFSK schemes with modulation index , where and are relatively prime positive integers, can be represented by a decomposed model consisting of a continuous phase encoder (CPE) and a memoryless modulator (MM). The differential encoder is shown to fit well with the CPE and form a decomposed model of differentially encoded CPFSK (DCPFSK). A basic receiver structure for differentially demodulating DCPFSK is presented along with simulation results. An exact formula for the minimum squared Euclidean distance (MSED) of differentially demodulated DCPFSK is also given.

    View record details
  • An Adaptive Receiver for the Time- and Frequency-Selective Fading Channel

    Leon, W. S.; Taylor, D. P. (1997)

    Doctoral thesis
    University of Canterbury Library

    An adaptive receiver is presented in this paper for the reception of linearly modulated signals transmitted over a time- and frequency-selective fading channel. The channel is modelled as a truncated power series [1] which represents the dispersive fading channel as a sum of three elementary flat-fading channels. The proposed receiver consists of a sequence estimator with a parallel channel estimator. The channel estimator recovers the instantaneous fading processes associated with each elementary channel and filters them to generate one-step predictions of each fading process. Some implementation difficulties and solutions are also discussed. Computer simulations using quadrature phase-shift keying (QPSK) and channels with moderate delay spreads and fade rates have been used to evaluate the performance of the receiver. The results show that our technique has potential in channels with delay spread of about 20%, signal-to-noise ratio (SNR) greater than 15dB, and applications requiring bit-error rates (BER's) less than 10-2.

    View record details
  • A Complete Optical Music Recognition System: Looking to the future

    Bainbridge, David (1994)

    Doctoral thesis
    University of Canterbury Library

    Reading music is something a child can learn, and once understood, it becomes such a natural process that it is no longer a conscious efforE If we were to dissect this •natural process,' we might hypothesise that reading music is demmposed into tux:) parts: the visual recognition of graphical shapes; and the application of our musical knowledge to derive its meaning A computer paradigm that models this structure would be a v:sxon system connected to a knowledge base Imagine an Optical Music Recognition (ONIR) system where the user describes the simple graphical shapes found in music using a customised drawing package, and expresses the musical knowledge necessary to correctly interpret these simple graphical shapes, using a specially designed musical language Such a system would capture the essence of reading music, forming a versatile foundation Music is rich in its diversity of notatiom instruments include specialised markings in a score, for example bowing information for a violinist, and in extreme situations a score is presented using a substantially different notation style, for example guitar tablature Moreover, music notation is evolving, so even if were possible to completely capture all the primitive shapes used in music today, the set uould eventually become incomplete Such attributes emphasize the dynamic nature of the problem domain of OMR The describes] system meets such demands by allowing the user to specify 'what makes up music' Consequently the system is itself dynamie Let us now consider the proposed system in more detail, by studying the roles of the customised drawing package and specially designed musical language in turn Reading music is something a child can learn, and once understood, it becomes such a natural process that it is no longer a conscious efforE If we were to dissect this •natural process,' we might hypothesise that reading music is demmposed into tux:) parts: the visual recognition of graphical shapes; and the application of our musical knowledge to derive its meaning A computer paradigm that models this structure would be a v:sxon system connected to a knowledge base Imagine an Optical Music Recognition (ONIR) system where the user describes the simple graphical shapes found in music using a customised drawing package, and expresses the musical knowledge necessary to correctly interpret these simple graphical shapes, using a specially designed musical language Such a system would capture the essence of reading music, forming a versatile foundation Music is rich in its diversity of notatiom instruments include specialised markings in a score, for example bowing information for a violinist, and in extreme situations a score is presented using a substantially different notation style, for example guitar tablature Moreover, music notation is evolving, so even if were possible to completely capture all the primitive shapes used in music today, the set uould eventually become incomplete Such attributes emphasize the dynamic nature of the problem domain of OMR The describes] system meets such demands by allowing the user to specify 'what makes up music' Consequently the system is itself dynamie Let us now consider the proposed system in more detail, by studying the roles of the customised drawing package and specially designed musical language in turn

    View record details
  • Akaroa2: Exploiting Network Computing by Distributing Stochastic Simulation

    Ewing, G.; Pawlikowski, K.; McNickle, D. (1998)

    Doctoral thesis
    University of Canterbury Library

    In this paper we discuss an application of network computing in the area of stochastic simulation. We focus on main programming issues associated with designing of the latest version of AKAROA2, a simulation package in which network computing is applied in a practical and user-friendly way. This implemention is based on Multiple Replications In Parallel (MRIP) scenario of distributed simulation, in which multiple computers of a network operate as concurrent simulation engines generating statistically equivalent simulation output data, and submitting them to global data analysers responsible for analysis of the final results and for stopping the simulation. The MRIP scenario can achieve speedup equal to the number of processors used. Keywords: distributed computing, distributed simulation, stochastic simulation

    View record details
  • A Comparative Study of Generators of Synthetic Self-Similar Teletraffic

    Jeong, H.-D. J.; McNickle, D.; Pawlikowski, K. (1998)

    Doctoral thesis
    University of Canterbury Library

    It is generally accepted that self-similar (or fractal) processes may provide better models for teletraffic in modern telecommunication networks than Poisson processes. If this is not taken into account, it can lead to inaccurate conclusions about performance of telecommunication networks. Thus, an important requirement for conducting simulation studies of telecommunication networks is the ability to generate long synthetic stochastic self-similar sequences. Three generators of pseudo-random self-similar sequences, based on the FFT [19], RMD [12] and SRA method [5], [10], are compared and analysed in this paper. Properties of these generators were experimentally studied in the sense of their statistical accuracy and times required to produce sequences of a given (long) length. While all three generators show similar levels of accuracy of the output data (in the sense of relative accuracy of the Hurst parameter), the RMD- and SRA-based generators appear to be much faster than the generator based on FFT. Our results also show that a robust method for comparative studies of self-similarity in pseudo-random sequences is needed.

    View record details
  • Visualisation Techniques for Collaborative GIS Browsers

    Churcher, Neville; Prachuabmoh, Parames; Churcher, Clare (1997)

    Doctoral thesis
    University of Canterbury Library

    Visual information overload is a serious problem for users of geographical information systems (GIS), or other applications with complex displays, where the requirements of access to both local detail and wider context conflict. This problem is compounded for users of real-time groupware applications by the need to maintain awareness information about other users and their actions. In this paper, we describe our use of fisheye views to assist with visual information overload management in GROUPARC, a lightweight real-time groupware application for browsing and annotating GIS data.

    View record details
  • An Interaction Network Monitor For Amoeba

    Ashton, Paul (1995)

    Doctoral thesis
    University of Canterbury Library

    The interaction network has been proposed as a way of representing interactive processing in a distributed system, and an interaction network monitor for SunOS was developed in earlier work. This paper describes development of an interaction network monitor for Amoeba, the first interaction network monitor for a distributed operating system. Case studies are used to show some of the types of information the monitor can capture, and to show that the monitor is a valuable tool for monitoring complex modern systems.

    View record details
  • A Calculus Based on Absence of Actions

    Krishnan, Padmanabhan (1995)

    Doctoral thesis
    University of Canterbury Library

    In this article we present a process algebra where the behaviour can be specified when certain actions cannot be exhibited. This is useful in specifying time outs, interrupts etc. We present a few properties which form the basis for a sound and complete axiomatisation of a bisimulation equivalence relation. A comparison with other approaches is presented.

    View record details
  • The NTP subnet in New Zealand

    Ashton, Paul (1999)

    Doctoral thesis
    University of Canterbury Library

    The contents of this work reflect the views of the authors who are responsible for the facts and accuracy of the data presented. Responsibility for the application of the material to specific cases, however, lies with any user of the report and no responsibility in such cases will be attributed to the author or to the University of Canterbury. This technical report contains a research paper, development report or tutorial article which has been submitted for publication in a journal or for consideration by the commissioning organisation. We ask you to respect the current and future owner of the copyright by keeping copying of this article to the essential minimum. Any requests for further copies should be sent to the author.

    View record details
  • An Intelligent SQL Tutor on the Web

    Mitrovic, Antonija; Hausler, Kurt (1997)

    Doctoral thesis
    University of Canterbury Library

    We present SQLT-Web, a Web-enabled intelligent teaching system for the SQL database language. The system observes students’ actions and adapts to their knowledge and learning abilities. Constraint-Based Modelling is used to model students. We describe the system's architecture in comparison to architectures of other existing Web-enabled tutors. All tutoring functions are performed on the server side, and we explain how SQLT-Web deals with multiple students. An initial evaluation of SQLT-Web has been done in a database course in May 1999. The students have enjoyed the system’s adaptability and found it a valuable asset to their learning.

    View record details
  • A Survey of Confidence Interval Formulae for Coverage Analysis

    Lee, Jong-Suk Ruth; McNickle, Donald; Pawlikowski, Krzysztof (1998)

    Doctoral thesis
    University of Canterbury Library

    Confidence interval estimators for proportions using normal approximation have been commonly used for coverage analysis of simulation output even though alternative approximate estimators of confidence intervals for proportions were proposed. This is because the normal approximation was easier to use in practice than the other approximate estimators. Computing technology has no problem with dealing these alternative estimators. Recently, one of the approximation methods for coverage analysis which is based on arcsin transformation has been used for estimating proportion and for controlling the required precision in [Raa95]. In this report, we compare three approximate interval estimators, based on a normal distribution approximation, an arcsin transformation and an F-distribution approximation, of a single proportion. These have application in sequential coverage analysis, conducted for assessing the quality of methods used in simulation output data analysis.

    View record details
  • The Design and Evolution of TurboTurtle, a Collaborative Microworld for Exploring Newtonian Physics

    Cockburn, Andy; Greenberg, Saul (1995)

    Doctoral thesis
    University of Canterbury Library

    TurboTurtle is a dynamic multi-user microworld for the exploration of Newtonian physics. With TurboTurtle, students can alter the attributes of the simulation environment, such as gravity, friction, and presence or absence of walls. Students explore the microworld by manipulating a variety of parameters, and learn concepts by studying the behaviours and interactions that occur. TurboTurtle has evolved into a ``group--aware'' system where several students, each on their own computer, can simultaneous control the microworld and gesture around the shared display. TurboTurtle's design rationale includes concepts such as equal opportunity controls, simulation timing, concrete versus abstract controls, recoverability, and how strictly views should be shared between students. Teachers can also add structure to the group's activities by setting the simulation environment to an interesting state, which includes a set of problems and questions. Observations of pairs of young children using TurboTurtle highlight extremes in collaboration styles, from conflict to smooth interaction. Finally, the technical work in making TurboTurtle group-aware is slight, primarily because it was built with a groupware toolkit called GroupKit.

    View record details