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Publications

1999

An overview of Controller Area Network

Authors
Farsi, M; Ratcliff, K; Barbosa, M;

Publication
COMPUTING & CONTROL ENGINEERING JOURNAL

Abstract
The Controller Area Network is a well-established networking system specifically designed with real-time requirements in mind. Developed in the 1980s by Robert Bosch, its ease of use and low cost has led to its wide adoption throughout the automotive and automation industries. However, for the beginner using CAN may seem somewhat bewildering. This article goes some way into explaining how CAN is used both at the hardware and the software levels.

1999

Eliminating synchronization overhead in automatically parallelized programs using dynamic feedback

Authors
Diniz, PC; Rinard, MC;

Publication
ACM Transactions on Computer Systems

Abstract
This article presents dynamic feedback, a technique that enables computations to adapt dynamically to different execution environments. A compiler that uses dynamic feedback produces several different versions of the same source code; each version uses a different optimization policy. The generated code alternately performs sampling phases and production phases. Each sampling phase measures the overhead of each version in the current environment. Each production phase uses the version with the least overhead in the previous sampling phase. The computation periodically resamples to adjust dynamically to changes in the environment. We have implemented dynamic feedback in the context of a parallelizing compiler for object-based programs. The generated code uses dynamic feedback to automatically choose the best synchronization optimization policy. Our experimental results show that the synchronization optimization policy has a significant impact on the overall performance of the computation, that the best policy varies from program to program, that the compiler is unable to statically choose the best policy, and that dynamic feedback enables the generated code to exhibit performance that is comparable to that of code that has been manually tuned to use the best policy. We have also performed a theoretical analysis which provides, under certain assumptions, a guaranteed optimality bound for dynamic feedback relative to a hypothetical (and unrealizable) optimal algorithm that uses the best policy at every point during the execution.

1999

Continuous frequency control from 5 to 10 GHz of an optical oscillator

Authors
Frazao, O; Tavares, P; Cunha, AF; Ribeiro, L; Ferreira da Rocha, J;

Publication
Proceedings of the Annual IEEE International Frequency Control Symposium

Abstract
An experimental set-up configuration, which allows the self-pulsation frequency of an optical oscillator to be modified by simply adjusting the bias current between 25 and 100 mA, is presented. For lower currents, the self-pulsation frequency is near 6 GHz and the device is stable. For higher currents, the self-pulsation frequency increases to near 11 GHz.

1999

Experimental results on high bit rate optical synchronization of RZ soliton type signals

Authors
Tavares, P; Frazao, O; Cunha, A; Ribeiro, LB; da Rocha, JF;

Publication
18TH CONGRESS OF THE INTERNATIONAL COMMISSION FOR OPTICS: OPTICS FOR THE NEXT MILLENNIUM, TECHNICAL DIGEST

Abstract
We report the development of a lab prototype for all optical synchronization at 10GHz. Adjusting the distance between the AR coated facet of the MQW semiconductor laser and the ferrule it was possible to induce the self-pulsation needed for correct operation. In the presence of optical RZ signals, the device leaves is natural pulsation frequency synchronizing with the input data.

1999

Poster session

Authors
Baquero, C;

Publication
OBJECT-ORIENTED TECHNOLOGY

Abstract
Report on the poster exhibition that took place at ECOOP'99.

1999

An instrument for measurement of induction motor drives based on phasor and modelling techniques

Authors
Araujo, RE; Freitas, DS; Goncalves, JJ;

Publication
IEEE TRANSACTIONS ON ENERGY CONVERSION

Abstract
This paper describes a practical instrument for realtime visualization of the necessary quantities for analysis, diagnosis and investigations of AC machine drives on an oscillographic display. The instrument needs no shaft position or speed sensor, it uses exclusively the acquired stator currents and voltages and provides information, in electrical and visual form, of: starer and rotor flux, torque, reactive power, torque current, flux current, torque angle and slip frequency. In the present version, the instrument circuitry is based on analogue signal processing techniques. The theoretical basis is a continuous-time machine model defined by a pair of simultaneous complex-coefficient differential equations. A formalization of the various calculation methods for the signal estimation is presented as well as one interpretative computer simulation for the stator current pattern. Practical results obtained with the device when applied to test and measure a real motor drive are presented and some conclusions are drawn. Main fields of application of the calculator include: monitoring systems, control units, research tools for induction motor drives, and test shops.

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