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Publicações

Publicações por CTM

2008

3D object reconstruction from uncalibrated images using a single off-the-shelf camera

Autores
Azevedo, TCS; Tavares, JMRS; Vaz, MAP;

Publicação
COMPUTATIONAL VISION AND MEDICAL IMAGING PROCESSING

Abstract
Three-dimensional (3 D) objects' reconstruction using just bi-dimensional (21)) images has been a major research topic in Computer Vision. However, it is still a hard problem to solve, when automation, speed and precision are required and/or the objects present complex shapes and visual properties. In this paper, we compare two Active Computer Vision methods commonly used for the 3D reconstruction of objects from image sequences, acquired with a single off-the-shelf CCD camera: Structure From Motion (SFM) and Generalized Voxel Coloring (GVC) SFM recovers the 3D shape of an object using the camera(s)'s or object's movement, while VC is a volumetric method that uses photoconsistency measures to build a 31) model for the object. Both methods considered do not impose any kind of restrictions to the relative motion involved.

2008

A scalable and efficient approach for obtaining measurements in CAN-based control systems

Autores
Andersson, B; Pereira, N; Elmenreich, W; Tovar, E; Pacheco, F; Cruz, N;

Publicação
IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS

Abstract
The availability of small inexpensive sensor elements enables the employment of large wired or wireless sensor networks for feeding control systems. Unfortunately, the need to transmit a large number of sensor measurements over a network negatively affects the timing parameters of the control loop. This paper presents a solution to this problem by representing sensor measurements with an approximate representation-an interpolation of sensor measurements as a function of space coordinates. A priority-based medium access control (MAC) protocol is used to select the sensor messages with high information content. Thus, the information from a large number of sensor measurements is conveyed within a few messages. This approach greatly reduces the time for obtaining a snapshot of the environment state and therefore supports the real-time requirements of feedback control loops.

2008

Analyzing TDMA With Slot Skipping

Autores
Andersson, B; Pereira, N; Tovar, E;

Publicação
IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS

Abstract
Distributed real-time system, such as factory automation systems, require that computer nodes communicate with a known and low hound on the communication delay. This can be achieved with traditional time division multiple access (TDMA). But improved flexibility and simpler upgrades are possible through the use of TDMA with slot-skipping (TDMA/SS), meaning that a slot is skipped whenever it is not used and consequently the slot after the skipped slot starts earlier. We propose a schedulahility analysis for TDMA/SS. We assume knowledge of all message streams in the system, and that each node schedules messages in its output queue according to deadline monotonic. Firstly, we present a non-exact (but fast) analysis and then, at the cost of computation time, we also present an algorithm that computes exact queuing times.

2008

How a cyber-physical system can efficiently obtain a snapshot of physical information even in the presence of sensor faults

Autores
Andersson, B; Pereira, N; Tovar, E;

Publicação
PROCEEDINGS OF THE SIXTH INTERNATIONAL WORKSHOP ON INTELLIGENT SOLUTIONS IN EMBEDDED SYSTEMS

Abstract
We present a distributed algorithm for cyber-physical systems to obtain a snapshot of sensor data. The snapshot is an approximate representation of sensor data; it is an interpolation as a function of space coordinates. The new algorithm exploits a prioritized Medium Access Controll (MAC) protocol to efficiently transmit information of the sensor data. It scales to a very large number of sensors and it is able to operate in the presence of sensor faults.

2008

A simple mixture to enhance muscle transmittance

Autores
Oliveira, L; Lage, A; Clemente, MP; Tuchin, VV;

Publicação
OPTICAL TECHNOLOGIES IN BIOPHYSICS AND MEDICINE IX

Abstract
Skeletal muscle is a fibrous tissue composed by muscle fibers and interstitial fluid. Due to this constitution, the muscle presents a non uniform refractive index profile that origins strong light scattering. One way to improve tissue transmittance is to reduce this refractive index mismatch by immersing the muscle in an optical clearing agent. As a consequence of such immersion tissue also suffers dehydration. The study of the optical clearing effect created by a simple mixture composed by ethanol, glycerol and distilled water has proven its effectiveness according to the variations observed in the parameters under study. The effect was characterized in terms of its magnitude, time duration and histological variations. The applied treatment has created a small reduction of the global sample refractive index that is justified by the long time rehydration caused by water in the immersing solution. From the reduction in sample pH we could also identify the dehydration process created in the sample. The immersion treatment has originated fiber bundle contraction and a spread distribution of the muscle fiber bundles inside. New studies with the mixture used, or with other combinations of its constituents might be interesting to perform with the objective to develop new clinical procedures.

2007

Design of circuits and integrated systems

Autores
Teixeira, JP; Matos, JS; Tomas, J; Teixeira, IC;

Publicação
IET COMPUTERS AND DIGITAL TECHNIQUES

Abstract

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