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Publications

Publications by CTM

2009

3D Object Reconstruction from Uncalibrated Images Using an Off-the-Shelf Camera

Authors
Azevedo, TCS; Manuel, J; Tavares, RS; Vaz, MAP;

Publication
ADVANCES IN COMPUTATIONAL VISION AND MEDICAL IMAGE PROCESSING: METHODS AND APPLICATIONS

Abstract
Three-dimensional (3D) objects reconstruction using just bi-dimensional (2D) images has been a major research topic in Computer Vision. However, it is still a hard problem to address, when automation, speed and precision are required and/or the objects have complex shapes or image properties. In this paper, we compare two Active Computer Vision methods frequently 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 based on the relative motion involved, while VC is a volumetric method that uses photo-consistency measures to build the required 3D model. Both methods considered do not impose any kind of restrictions on the relative motion involved.

2009

High Glucose Changes Extracellular Adenosine Triphosphate Levels in Rat Retinal Cultures

Authors
Costa, G; Pereira, T; Neto, AM; Cristovao, AJ; Ambrosio, AF; Santos, PF;

Publication
JOURNAL OF NEUROSCIENCE RESEARCH

Abstract
Diabetic retinopathy (DR) is the leading cause of blindness in adults. In diabetes, there is activation of microglial cells and a concomitant release of inflammatory mediators. However, it remains unclear how diabetes triggers an inflammatory response in the retina. Activation of P2 purinergic receptors by adenosine triphosphate (ATP) may contribute to the inflammatory response in the retina, insofar as it has been shown to be associated with microglial activation and cytokine release. In this work, we evaluated how high glucose, used as a model of hyperglycemia, considered the main factor in the development of DR, affects the extracellular levels of ATP in retinal cell cultures. We found that basal extracellular ATP levels were not affected by high glucose or mannitol, but the extracellular elevation of ATP, after a depolarizing stimulus, was significantly higher in retinal cells cultured in high glucose compared with control or mannitol-treated cells. The increase in the extracellular ATP was prevented by application of botulinum neurotoxin A or by removal of extracellular calcium. In addition, degradation of exogenously added ATP was significantly lower in high-glucose-treated cells. It was also observed that, in retinal cells cultured under high-glucose conditions, the changes in the intracellular calcium concentrations were greater than those in control or mannitol-treated cells. In conclusion, in this work we have shown that high glucose alters the purinergic signaling system in the retina, by increasing the exocytotic release of ATP and decreasing its extracellular degradation. The resulting high levels of extracellular ATP may lead to inflammation involved in the pathogenesis of DR. (C) 2008 Wiley-Liss, Inc.

2009

Optimizing the pictorial compacted data detection process for working at the noisy environment, using reversible symmetrical codes

Authors
Shafafi K.; Samanfar A.; Saremian E.; Moradtalab O.;

Publication
2009 International Conference on Information and Multimedia Technology, ICIMT 2009

Abstract
Variable-length codes, using source statistical features, improve the encoding. However, using these codes can results in error propagation in bit string transmitted to noisy transmission environments. This paper has used reversible symmetrical codes in the bit string obtained from JPEG compressor in order to overcome this problem. several examples of reversible code design algorithm have been reviewed and a symmetrical code based on Huffman code has been analyzed and deigned for JPEG compressor Jpeg compressor has been simulated by Huffman standard code and by reversible symmetrical code and the amount of their compression has been compared for several pictures Also, optimization of detection trend in noisy condition has been displayed. © 2009 IEEE.

2009

Efficient Computation of Min and Max Sensor Values in Multihop Networks

Authors
Pereira, N; Andersson, B; Tovar, E; Carvalho, P;

Publication
Intelligent Technical Systems

Abstract
Consider a wireless sensor network (WSN) where a broadcast from a sensor node does not reach all sensor nodes in the network; such networks are often called multihop networks. Sensor nodes take individual sensor readings, however, in many cases, it is relevant to compute aggregated quantities of these readings. In fact, the minimum and maximum of all sensor readings at an instant are often interesting because they indicate abnormal behavior, for example if the maximum temperature is very high then it may be that a fire has broken out. In this context, we propose an algorithm for computing the min or max of sensor readings in a multihop network. This algorithm has the particularly interesting property of having a time complexity that does not depend on the number of sensor nodes; only the network diameter and the range of the value domain of sensor readings matter. © 2009 pringer Science+Business Media B.V.

2009

Using a Prioritized Medium Access Control Protocol for Incrementally Obtaining an Interpolation of Sensor Readings

Authors
Andersson, B; Pereira, N; Tovar, E; Gomes, R;

Publication
PROCEEDINGS OF THE SEVENTH INTERNATIONAL WORKSHOP ON INTELLIGENT SOLUTIONS IN EMBEDDED SYSTEMS

Abstract
This paper addresses sensor network applications which need to obtain an accurate image of physical phenomena and do so with a high sampling rate in both time and space. We present a fast and scalable approach for obtaining an approximate representation of all sensor readings at high sampling rate for quickly reacting to critical events in a physical environment This approach is an improvement on previous work in that after the new approach has undergone a startup phase then the new approach can use a very small sampling period.

2009

Improving the Reliability of WiDom in a Single Broadcast Domain

Authors
Pereira, N; Andersson, B; Tovar, E; Carvalho, P;

Publication
2009 IEEE INTERNATIONAL SYMPOSIUM ON INDUSTRIAL EMBEDDED SYSTEMS

Abstract
WiDom is a previously proposed prioritized medium access control protocol for wireless channels. We present a modification to this protocol in order to improve its reliability. This modification has similarities with cooperative relaying schemes, but, in our protocol, all nodes can relay a carrier wave. The preliminary evaluation shows that, under transmission errors, a significant reduction on the number of failed tournaments can be achieved.

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