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Publications

2021

On the implementation of memory reclamation methods in a lock-free hash trie design

Authors
Moreno, P; Areias, M; Rocha, R;

Publication
JOURNAL OF PARALLEL AND DISTRIBUTED COMPUTING

Abstract
Hash tries are a trie-based data structure with nearly ideal characteristics for the implementation of hash maps. Starting from a particular lock-free hash map data structure, named Lock-Free Hash Tries, we focus on solving the problem of memory reclamation without losing the lock-freedom property. To the best of our knowledge, outside garbage collected environments, there is no current implementation of hash maps that is able to reclaim memory in a lock-free manner. To achieve this goal, we propose an approach for memory reclamation specific to Lock-Free Hash Tries that explores the characteristics of its structure in order to achieve efficient memory reclamation with low and well-defined memory bounds. We present and discuss in detail the key algorithms required to easily reproduce our implementation by others. Experimental results show that our approach obtains better results when compared with other state-of-the-art memory reclamation methods and provides a competitive and scalable hash map implementation, if compared to lock-based implementations.

2021

Exploiting the Potentials of HVAC Systems in Transactive Energy Markets

Authors
Nematkhah, F; Bahrami, S; Aminifar, F; Catalao, JPS;

Publication
IEEE TRANSACTIONS ON SMART GRID

Abstract
Transactive energy (TE) is a viable framework to tackle the load-generation mismatch in energy systems with high penetration of renewable energy resources (RERs). In this paper, we propose a TE framework for prosumers with heating, ventilation, and air conditioning (HVAC) systems to address real-time power shortage in a residential microgrid. Our framework consists of two phases. First, to mitigate load-generation mismatch, we develop an online appliance scheduling method to determine the optimal operation schedule of each prosumer's appliances. In particular, we apply receding horizon optimization (RHO) to tackle the load and renewable generation uncertainties and to better match the real-time power consumption of the appliances with the priorly-purchased power from the day-ahead market. Second, in case that there still exists power shortage at the microgrid level, a TE market based on pay-as-market clearing price (MCP) is proposed among prosumers to reduce the power consumption of their HVAC systems. We capture the competition among the participating prosumers as a non-cooperative game and develop an algorithm to achieve the Nash equilibrium, while considering prosumers' willingness to participate in the TE market. Extensive simulations are performed to demonstrate the efficiency of our proposed TE framework.

2021

Guest Editorial: BIOSIG 2020 special issue on trustworthiness of person authentication

Authors
Sequeira, AF; Gomez Barrero, M; Correia, PL;

Publication
IET BIOMETRICS

Abstract
[No abstract available]

2021

Multimodal Multi-tasking for Skin Lesion Classification Using Deep Neural Networks

Authors
Carvalho, R; Pedrosa, J; Nedelcu, T;

Publication
ADVANCES IN VISUAL COMPUTING (ISVC 2021), PT I

Abstract
Skin cancer is one of the most common types of cancer and, with its increasing incidence, accurate early diagnosis is crucial to improve prognosis of patients. In the process of visual inspection, dermatologists follow specific dermoscopic algorithms and identify important features to provide a diagnosis. This process can be automated as such characteristics can be extracted by computer vision techniques. Although deep neural networks can extract useful features from digital images for skin lesion classification, performance can be improved by providing additional information. The extracted pseudo-features can be used as input (multimodal) or output (multi-tasking) to train a robust deep learning model. This work investigates the multimodal and multi-tasking techniques for more efficient training, given the single optimization of several related tasks in the latter, and generation of better diagnosis predictions. Additionally, the role of lesion segmentation is also studied. Results show that multi-tasking improves learning of beneficial features which lead to better predictions, and pseudo-features inspired by the ABCD rule provide readily available helpful information about the skin lesion.

2021

Machine Learning automatic assessment for glaucoma and myopia based on Corvis ST data

Authors
Leite, D; Campelos, M; Fernandes, A; Batista, P; Beirão, J; Menéres, P; Cunha, A;

Publication
Procedia Computer Science

Abstract
Glaucoma is a silent disease characterized by progressive degeneration of retinal ganglion cells and, when not detected or treated early, can lead to blindness. Computer systems have demonstrated their efficiency in the medical decision-making process and Artificial Intelligence (AI) techniques have helped advances in ophthalmology, allowing for faster and more effective detection of glaucoma. Machine learning is a very promising subfield of AI that supports research in understanding the development, progression and treatment of glaucoma, identifying new risk factors and assessing the importance of existing ones. This study aims to test and analyze the results of different models of supervised machine learning in the detection and classification of ophthalmic diseases (Glaucoma, high myopia and low myopia) based on data from Corvis ST. The most important characteristics were selected based on a variance greater than 0.02. In terms of accuracy, the models that obtained the best results were Random Forrest 0.73, Stochastic Gradient Descent (SGD) 0.75, Gradient Boosting Classifier (GBC) 0.76 and K-Nearest Neighbors 0.71. The GBC model achieved the best results in accuracy, AUC, Recall and F1Score 76.00, 52.5, 78.00, 70.2 respectively.

2021

Linear Programming Meets Block-based Languages

Authors
da Giao, H; Cunha, J; Pereira, R;

Publication
2021 IEEE SYMPOSIUM ON VISUAL LANGUAGES AND HUMAN-CENTRIC COMPUTING (VL/HCC 2021)

Abstract
Linear programming is a mathematical optimization technique used in numerous fields including mathematics, economics, and computer science, with numerous industrial contexts, including solving optimization problems such as planning routes, allocating resources, and creating schedules. As a result of its wide breadth of applications, a considerable amount of its user base is lacking in terms of programming knowledge and experience and thus often resorts to using graphical software such as Microsoft Excel. However, despite its popularity amongst less technical users, the methodologies used by these tools are often ad-hoc and prone to errors. To counteract this problem we propose creating a block-based language that allows users to create linear programming models using data contained inside spreadsheets. This language will guide the users to write syntactically and semantically correct programs and thus aid them in a way that current languages do not.

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