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.

The result of many years of international co-operation in video coding has been the development of algorithms that remove interframe redundancy, such that only changes in the image that occur over a given time are encoded for transmission to the recipient. The primary process used here is the derivation of pixel differences, encoded in a method referred to as Differential Pulse-Coded Modulation (DPCM)and this has provided the basis of contemporary research into low-bit rate hybrid codec schemes. There are, however, instances when the DPCM technique cannot successfully code a segment of the image sequence because motion is a major cause of interframe differences. Motion Compensation (MC) can be used to improve the efficiency of the predictive coding algorithm. This thesis examines current thinking in the area of motion-compensated video compression and contrasts the application of differing algorithms to the general requirements of interframe coding. A novel technique is proposed, where the constituent features in an image are segmented, classified and their motion tracked by a local search algorithm. Although originally intended to complement the DPCM method in a predictive hybrid codec, it will be demonstrated that the evaluation of feature displacement can, in its own right, form the basis of a low bitrate video codec of low complexity. After an extensive discussion of the issues involved, a description of laboratory simulations shows how the postulated technique is applied to standard test sequences. Measurements of image quality and the efficiency of compression are made and compared with a contemporary standard method of low bitrate video coding.

This thesis discusses the issues involving the support of Living Ontologies: collaborating in the construction and maintenance of ontologies using the Internet. Ontologies define the concepts used in describing a domain: they are used by knowledge engineers as reusable components of knowledge-based systems. Knowledge engineers create ontologies by eliciting information from domain experts. However, experts often have different conceptualisations of a domain and knowledge engineers often have different ways of formalising their conceptualisations. Taking a constructivist perspective, constructing ontologies from multiple conflicting conceptualisations can be seen as a design activity, in which knowledge engineers make choices according to the context in which the representation will be used. Based on this theory, a methodology for collaboratively constructing ontologies might involve comparing differing conceptualisations and using these comparisons to initiate discussion, changes to the conceptualisations and the development of criteria against which they can be evaluated. APECKS (Adaptive Presentation Environment for Collaborative Knowledge Structuring) is designed to support this methodology. APECKS aims not only to support the collaborative construction of ontologies but also to use ontologies to present information to its users adaptively within a virtual environment. It demonstrates a number of innovations over conventional ontology servers, such as prompted knowledge elicitation from domain experts, automated comparisons between ontologies, the creation of design rationales and change tracking. A small evaluation of APECKS has shown that it is usable by domain experts and that automated comparisons between ontologies can be used to initiate alterations, investigations of others' conceptualisations and as a basis for discussion. Possible future development of APECKS includes tighter integration with a virtual environment and with other networked knowledge-based tools. Further research is also needed to develop the methodology on which APECKS is based, by investigating ways of comparing, combining and discussing ontologies.

Modern wireless telecommunication devices (GSM Mobile system) (cellular telephones and wireless modems on laptop computers) have the potential to interfere with implantable medical devices/prostheses and cause possible malfunction. An implant of resonant dimensions within a homogeneous dielectric lossy sphere can enhance local values of SAR (the specific absorption rate). Also antenna radiation pattern and other characteristics are significantly altered by the presence of the composite dielectric entities such as the human body. Besides, the current safety limits do not take into account the possible effect of hot spots arising from metallic implants resonant at mobile phone frequencies. Although considerable attention has been given to study and measurement of scattering from a dielectric sphere, no rigorous treatment using electromagnetic theory has been given to the implanted dielectric spherical head/cylindrical body. This thesis aims to deal with the scattering of a plane electromagnetic wave from a perfectly conducting or dielectric spherical/cylindrical implant of electrically small radius (of resonant length), embedded eccentrically into a dielectric spherical head model. The method of dyadic Green's function (DGF) for spherical vector wave functions is used. Analytical expressions for the scattered fields of both cylindrical and spherical implants as well as layered spherical head and cylindrical torso models are obtained separately in different chapters. The whole structure is assumed to be uniform along the propagation direction. To further check the accuracy of the proposed solution, the numerical results from the analytical expressions computed for the problem of implanted head/body are compared with the numerical results from the Finite-Difference Time-Domain (FDTD) method using the EMU-FDTD Electromagnetic simulator. Good agreement is observed between the numerical results based on the proposed method and the FDTD numerical technique. This research presents a new approach, away from simulation work, to the study of exact computation of EM fields in biological systems. Its salient characteristics are its simplicity, the saving in memory and CPU computational time and speed.

No description available.

No description available.

In this study, two courses from the McGill Distance Education program with very different learning goals were examined to investigate the instructional role of two communication technologies (i.e., fax and e-mail) in distance education. The data set included verbatim e-mail and fax transcripts, instructor interviews, course syllabi and course assignments. Triangulation procedures were followed to examine the following within the context of two distance education courses with very different learning goals: (1) the general instructional purposes for which the technologies were used; (2) the levels of learning reflected in the mediated interactions; and (3) the relationship between the use of the technology, the instructors' perceptions of its use and the stated learning outcomes of the courses. / Electronic-mail provided the interaction necessary for encouraging discussions of course content in the Instructional Design course, whereas fax was used more for the transmission of knowledge in both courses. An examination of the relationship between course learning objectives, course transcripts, and instructor interviews indicated that the instructors were consistent in their view of the different communication technologies,. their purpose for using the chosen technology, and the way in which they used the specific communication technology. However, this consistency was not reflected in the students' use of the communication technologies since the students responded only at Bloom's lower levels of learning even though the instructors used all levels of learning. (Abstract shortened by UMI.)

Thesis (PhD)--University of South Australia, 1996

Thesis (M.Eng. in Electronic Engineering)--University of South Australia, 1995.

Large numbers of installed medium or high voltage power cables are now of advanced age and have gradual insulation deterioration problems. On-line Partial Discharge (PD) measurement has inherent advantages over the conventional off-line measurement, but it also suffers from a very significant Electro-Magnetic Interference (EMI) problem due to the small PD signal levels being monitored. The large magnitude EMI signal often completely swamps the smaller magnitude PD signal, making it difficult to monitor anything but extremely large PD activity. To monitor cable condition and to be able to assess insulation degradation trends requires advanced techniques. In this thesis, the issues of sensor selection, digital filtering, software based on-line differential technique and wavelet Transform (WT) de-noising techniques are studied. Their applicability, advantages and limitations are discussed with the simulation and high voltage measurement results. The High Frequency Current Transformer (HFCT) type PD sensor is selected after being compared with other sensor in term of sensitivity, universal applicability, frequency response and the installation difficulty. The sinusoidal noise frequency identification and application of the conventional digital filtering are studied. The Least Mean Square (LMS) and Recursive Least Square (RLS) algorithm digital adaptive filters are compared in detail and RLS adaptive filter is selected. Wavelet transform de-noising technique for on-line PD measurement is carefully studied and the applications of noise reduction are developed. A novel WT threshold value selection algorithm is presented in this thesis. The new WT algorithm is compared with the existing wavelet techniques using numerical simulation and laboratory high voltage testing data on cables. The results show that this new fully automatic WT de-noising method has achieved great progress with the capability of detection 30 pC PD signal during on-site on-line measurement where typical noise level is ten times higher in magnitude. On the basis of traditional off-line differential or balanced detection circuit, a software based on-line differential technique is proposed in this thesis. The novel method developed has the capability to process one whole AC cycle of PD data. It enables traditional q-?? and n-?? distributions to be obtained as well as PD repetition rates and the usual integrated PD parameters. These techniques are developed for the on-site on-line PD measurement in power cables, but they are not limited to cables. They can also be applied to other high voltage equipment with minor or without modification in the data acquisition procedure.