Repositório RCAAP

Denote by X and Y two sets and consider u function f defined on X and with values in Y. Let U be a proper subset of X. Consider the set C of all pairs wx,f{ x)\}$ such that xeX \U. What does C imply about F? Under what circumstances does C determine F? (...)

This work refers to the application of adaptive techniques to automatic control problems. In many cases, the plant has a difficult to describe or unpredictable dynamic behaviour. Therefore, different methods for system identification are also presented, along with the available techniques and methodologies for the implementation of control functions. (...)

This thesis deals with symbol synchronization problems in additive Gaussian channels and channels with data dependent noise, this last point being motivated by optical communications. (...)

In this work, a possible solution to the problem of integrating a microwave power amplifier and its linearizer, is presented.The most common techniques of power amplifier linearization are reviewed, and its major drawbacks identified. (...)

Let H be the transfer function of a strictly stable, causal, and, linear system, and let h be its impulse response. If one does not assume a specific form for H, or, what is the same, a specific model for the system, the question arises as how to approximate that transfer function by another with a known form. (...)

The tomographic modalities that exist nowadays are important tools used to elaborate and/or consolidate a certain diagnosis, conduct a therapy, or to perform a surgical study. The tomographic modalities have specfic programs to reconstruct, visualize and analyze the data produced in a circular multiple view basis. Only recently, with the advent and popularity of powerful workstations, have the 3D reconstruction schemes of the anatomical structures under study been exploited. (...)

The clinical classification of focal epileptic patients depends greatly on the fuci localization and is determinant to the correct choice of therapy. Consequently, the well-being of the patient is also dependent on the foci localization methodology used in each case. (...)

This thesis studies infrared wireless local area networks, considering simultuneously the physical link and medium access aspects. A general description of free-space infrared physical links is carried out, with the main purpose of characterising and comparing quasi-diffuse and diffuse cells (in quasi-diffuse cells the optical connection between stations is through a single reflector while in the diffuse cells the optical connection is through the different reflecting surfaces of the propagation environment). (...)

The work to be presented was motivated by a contribution to the design of an optical receiver for use in an all-optical cable television distribution network, and evolves over the field of Linearization of amplifiers based on GaAs MESFET devices. (...)

The Olympus Satellite propagation package, comprising two vertical polarized beacons (12.5 and 30 GHz.) and a dual polarized one at 30 GHZ, is presented and the opportunities offered to characterise the propagation channel discussed. This subject, after a survey of that shows almost no available data and studies are available, is elected as a the main investigation topic of the thesis. (...)

The Hardware C++ language (HC++) was developed to explore the object-oriented paradigm in the multilevel specification of digital systems. The main motivation for its development was the verification that present hardware description languages do not fully support the object oriented approach and the need for object-oriented technology in hardware description languages in order to face the increasing complexity hardware systems. (...)

In this thesis, methods to detect frequency modulated digital signals are studied. In order to accomplish that goal, accurate models are developed for lasers based in bulk semiconductors and with quantum wells. The accuracy of these models is verified by comparison with measurements performed on lasers of experimental systems. (...)

In today's developed societies, the number of people affected by sleep disorders is growing by the day. To handle a growing number of patients, there has been a steady growth in the number of sleep analysis clinics and laboratories. Human sleep stages are hand-scored by an expert and this is a laborious, time consuming and difficult task. (...)

In this thesis we address the problem of edge detection. The fundamental idea that motivated the work is related to the philosophy with which the problem is addressed. Our line of work was in the direction of investigating methods that could be able to design specialized edge detectors, instead of general purpose operators. (...)

This thesis deals with wide-band propagation channel mollelling in the millimetre-wave band and its impact on the transmission performance of a mobile radio communication system intended to support the range of services envisioned for the B-ISDN. First, it is identified the appropriate frequency band to implement a mobile broadband system and/or a broadband wireless access for indoor environments. (...)

This thesis studies the performance of wireless in-house transmission systems using infrared optical signals. These studies focus in the physical layer of the transmission systems. (...)

This thesis reflects the experience carried out with the work developed during the last years in the Electronics and Telecommunications Department of the University of Aveiro with the participation in several national and international projects covering the hypermedia and computer supported collaborative work fields. (...)

In most hospitals, storage, distribution and presentation of medical images is based upon X-ray film. It allows a high quality image although cost and volume lead to conditioning it's use in storage and distribution of images. (...)

No summary/description provided

The scientific community has dedicated a lot of effort to the development and improvement of error-less methods for signal restoration. These methods are based on a priori knowledge of some characteristics of the signal, such as frequency band limitations, amplitude maxima and minima, time/space duration, etc. (...)