Instant Messaging (IM) is becoming increasingly popular in social as well as workplace environments. In fact, many employees use the same IM client to communicate with both colleagues and social contacts. Thus, there are valid concerns about the impact of IM on employee productivity. One of the major advantages of IM over other workplace communication tools such as e-mail and the telephone is the implementation of presence information. In particular, presence awareness is used to determine the avail- ability and willingness of a contact to engage in communication. A current problem with IM is the one-for-all approach to presence: all contacts receive the same set of presence information. However, presence is rooted in social psychology where it is known that the awareness of another person changes the behavior of oneself. Therefore the identity of a contact affects the availability and willingness directed towards that contact. In order for presence information to be provided to contacts, it must be represented in some type of data format. The Internet Engineering Task Force (IETF) has done much work in standardizing IM and presence systems. In particular their data format for presence describes a rich set of presence information including, but not limited to, location, activity, awareness, and mood information. Such information may be sensitive and access to it needs to be controlled to ensure privacy. As with access control policies, managing the information as the number of contacts increases becomes cumbersome and complex. This dissertation draws on the theoretical foundations of presence, current standards in the domain of IM, and lessons from access control to present an enhanced presence handling model for IM. The model is developed in stages, with each stage providing a specific improvement. The first stage of the model is grounded on the current work of the IETF. As such it distributes presence on a per-watcher basis. In the second stage of the model watchers fulfill a specific role and based on this role they receive only the entrusted presence information. In practice, it implies that a "friend" may get more (or less) information than a "colleague". The third stage of the model introduces the concept of availability profiles by drawing on social awareness principles. Availability profiles add the ability to transform presence and change the presentity's behavior to incoming messages according to the provided presence information. Finally the dissertation reports on the development of the RoBIM (Role- Based Instant Messenger) prototype. RoBIM is a standards-based IM system that conforms to the IETF SIMPLE protocol and provides various standard IM features. Here, RoBIM serves as a proof-of-concept for the proposed model. This study contributed to the domain of IM and presence by addressing some of the current presence handling issues. Most importantly, the proposed model takes into account the interpersonal effects of individualizing presence information for different contacts. Thus, the model challenges conventional thought and implementation of presence in IM.

The probability of undetected error P[formula omitted](є) for the primitive triple-error-correcting BCH codes of blocklength 2[formula omitted]  1, used solely for error detection on a binary symmetric channel with crossover probability є ≤ 1/2, is examined. It is shown that for odd values of m, P[formula omitted(є) increases monotonically with є. For even values of m, this is not necessarily true. However, for a fixed є, as m increases, P[formula omitted](є) approaches 2‾[formula omitted] where p is the number of parity bits. The extended double and triple-error-correcting primitive BCH codes are also examined. The undetected error probability of these codes is shown to have similar characteristics as the non-extended cases. An improved upper bound on the probability of undetected error which is valid for any linear code is derived. Comparison of this improved upper bound with the Kasami upper bound for some classes of codes is shown. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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[pt] O crescimento constante da demanda de energia elétrica está tornando necessário o aproveitamento, cada vez maior, dos potenciais hidroelétricos existentes em diversos pontos do País. O grande porte de algumas das futuras usinas hidroelétricas bem como o seu afastamento dos principais centros de consumo, tornará necessária a construção de extensa linha de transmissão em extra alta tensão. As características elétricas destas linhas, especialmente quando se usa compensação série, introduzem muitos problemas que tornam difícil ou em alguns casos impossível, a aplicação de esquemas convencionais de proteção por relés. O sistema de transmissão de Itaipu, atualmente em fase de projeto e que deverá entrar em funcionamento na década de 1980 na região sudeste do País, prevê a transmissão de cerca de 10.000 MW através de uma de aproximadamente 900 KM, numa faixa de tensão de 750 a 800kV. O presente trabalho, utilizando como exemplo um estudo preliminar das características elétricas deste sistema, analisa especificamente os problemas relacionados com a proteção de linhas dotadas de compensação série e apresenta ferramentas computacionais para a análise detalhada do comportamento de sistemas compensados em condições de curto-circuito bem como para a avaliação do desempenho de diversos esquemas de proteção. / [en] The Constant growth of the demand for electrical energy in Brazil is leading to an increased use of the country’s vast hydro potencial. The great size of the hydroelectric plants being planned for the near future, as well as their distance from the main load centers, will make it necessary to transmit vast amounts of power over long EHV lines. The electrical characteristics of some of these lines, specially those using series capacitores. Make it difficult, and in some cases impossible, to apply conventional protection schemes. This paper, using as an example a preliminary study of the above mentioned system, analyses specifically the problems related to the protection of series compensated transmission lines and describes two series computer programs suitable for circuit for short circuit studies and the evaluation of various protection schemes.

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This report presents an initial design effort for a high-speed, constant Frequency data extractor, which can be used to identify and track a particular constant frequency signal in the presence of other signals. Several factors must be included in the design considerations. The detection and acquisition of the correct signal should be accomplished at high speed to remain as close as possible to real time. Once detection has occurred, the system should generate a track-predict gate signal that enables the input line only when the real input pulse is expected. If track is lost, which happens whenever the track-predict gate and input pulse do not occur simultaneously, the initial detection method must be re-entered. The detectable frequency should be selectable over a wide range of values. Furthermore, the system should be able to detect and acquire the desired signal in the presence of large numbers of interfering signals, yet be flexible enough to adapt easily to other pulse modulation methods. Because of the above design factors as well as speed, size, and cost, a high-speed bipolar microprocessor was selected for this system implementation. A microprocessor allows most of the detection and acquisition to be accomplished in the software, thus making the system very adaptable to the host system's requirements.