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Publications

Publications by CTM

2023

Investigating the Accuracy of Autoregressive Recurrent Networks Using Hierarchical Aggregation Structure-Based Data Partitioning

Authors
Oliveira, JM; Ramos, P;

Publication
BIG DATA AND COGNITIVE COMPUTING

Abstract
Global models have been developed to tackle the challenge of forecasting sets of series that are related or share similarities, but they have not been developed for heterogeneous datasets. Various methods of partitioning by relatedness have been introduced to enhance the similarities of sets, resulting in improved forecasting accuracy but often at the cost of a reduced sample size, which could be harmful. To shed light on how the relatedness between series impacts the effectiveness of global models in real-world demand-forecasting problems, we perform an extensive empirical study using the M5 competition dataset. We examine cross-learning scenarios driven by the product hierarchy commonly employed in retail planning to allow global models to capture interdependencies across products and regions more effectively. Our findings show that global models outperform state-of-the-art local benchmarks by a considerable margin, indicating that they are not inherently more limited than local models and can handle unrelated time-series data effectively. The accuracy of data-partitioning approaches increases as the sizes of the data pools and the models' complexity decrease. However, there is a trade-off between data availability and data relatedness. Smaller data pools lead to increased similarity among time series, making it easier to capture cross-product and cross-region dependencies, but this comes at the cost of a reduced sample, which may not be beneficial. Finally, it is worth noting that the successful implementation of global models for heterogeneous datasets can significantly impact forecasting practice.

2023

Forecasting Seasonal Sales with Many Drivers: Shrinkage or Dimensionality Reduction?

Authors
Ramos, P; Oliveira, JM; Kourentzes, N; Fildes, R;

Publication
APPLIED SYSTEM INNOVATION

Abstract
Retailers depend on accurate forecasts of product sales at the Store x SKU level to efficiently manage their inventory. Consequently, there has been increasing interest in identifying more advanced statistical techniques that lead to accuracy improvements. However, the inclusion of multiple drivers affecting demand into commonly used ARIMA and ETS models is not straightforward, particularly when many explanatory variables are available. Moreover, regularization regression models that shrink the model's parameters allow for the inclusion of a lot of relevant information but do not intrinsically handle the dynamics of the demand. These problems have not been addressed by previous studies. Nevertheless, multiple simultaneous effects interacting are common in retailing. To be successful, any approach needs to be automatic, robust and efficiently scaleable. In this study, we design novel approaches to forecast retailer product sales taking into account the main drivers which affect SKU demand at store level. To address the variable selection challenge, the use of dimensionality reduction via principal components analysis (PCA) and shrinkage estimators was investigated. The empirical results, using a case study of supermarket sales in Portugal, show that both PCA and shrinkage are useful and result in gains in forecast accuracy in the order of 10% over benchmarks while offering insights on the impact of promotions. Focusing on the promotional periods, PCA-based models perform strongly, while shrinkage estimators over-shrink. For the non-promotional periods, shrinkage estimators significantly outperform the alternatives.

2023

Depletion Based Digital and Analogue Circuits with n-Channel IGZO Thin Film Transistors

Authors
Carvalho, G; Pereira, M; Kiazadeh, A; Tavares, VG;

Publication
2023 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS, ISCAS

Abstract
In this work, both analogue and digital depletionmode single channel transistor circuits are presented and are simulated using an n-channel IGZO technology with V-TH =-0.87V. A logic family is introduced, suppressing the need for an additional voltage level and level restoring circuitry. Furthermore, in the analogue domain, a depletion current mirror topology is presented with demonstrated small current error. Finally, the current mirror is used in the design of an OpAmp, achieving a simulated open-loop gain of 45 dB, CMRR of 58 dB, unity-gain frequency of 444 kHz and a phase margin of 71 degrees.

2023

Disentangled Representation Learning for Privacy-Preserving Case-Based Explanations

Authors
Montenegro, H; Silva, W; Cardoso, JS;

Publication
MEDICAL APPLICATIONS WITH DISENTANGLEMENTS, MAD 2022

Abstract
The lack of interpretability of Deep Learning models hinders their deployment in clinical contexts. Case-based explanations can be used to justify these models' decisions and improve their trustworthiness. However, providing medical cases as explanations may threaten the privacy of patients. We propose a generative adversarial network to disentangle identity and medical features from images. Using this network, we can alter the identity of an image to anonymize it while preserving relevant explanatory features. As a proof of concept, we apply the proposed model to biometric and medical datasets, demonstrating its capacity to anonymize medical images while preserving explanatory evidence and a reasonable level of intelligibility. Finally, we demonstrate that the model is inherently capable of generating counterfactual explanations.

2023

Multimodal Context-Aware Detection of Glioma Biomarkers Using MRI and WSI

Authors
Albuquerque, T; Fang, ML; Wiestler, B; Delbridge, C; Vasconcelos, MJM; Cardoso, JS; Schüffler, P;

Publication
MEDICAL IMAGE COMPUTING AND COMPUTER ASSISTED INTERVENTION - MICCAI 2023 WORKSHOPS

Abstract
The most malignant tumors of the central nervous system are adult-type diffuse gliomas. Historically, glioma subtype classification has been based on morphological features. However, since 2016, WHO recognizes that molecular evaluation is critical for subtyping. Among molecular markers, the mutation status of IDH1 and the codeletion of 1p/19q are crucial for the precise diagnosis of these malignancies. In pathology laboratories, however, manual screening for those markers is time-consuming and susceptible to error. To overcome these limitations, we propose a novel multimodal biomarker classification method that integrates image features derived from brain magnetic resonance imaging and histopathological exams. The proposed model consists of two branches, the first branch takes as input a multi-scale Hematoxylin and Eosin whole slide image, and the second branch uses the pre-segmented region of interest from the magnetic resonance imaging. Both branches are based on convolutional neural networks. After passing the exams by the two embedding branches, the output feature vectors are concatenated, and a multi-layer perceptron is used to classify the glioma biomarkers as a multi-class problem. In this work, several fusion strategies were studied, including a cascade model with mid-fusion; a mid-fusion model, a late fusion model, and a mid-context fusion model. The models were tested using a publicly available data set from The Cancer Genome Atlas. Our cross-validated classification models achieved an area under the curve of 0.874, 0.863, and 0.815 for the proposed multimodal, magnetic resonance imaging, and Hematoxylin and Eosin stain slide images respectively, indicating our multimodal model outperforms its unimodal counterparts and the state-of-the-art glioma biomarker classification methods.

2023

Deep Learning Strategies For Rare Drug Mechanism of Action Prediction

Authors
Ferreira, G; Teixeira, M; Belo, R; Silva, W; Cardoso, JS;

Publication
2023 INTERNATIONAL JOINT CONFERENCE ON NEURAL NETWORKS, IJCNN

Abstract
The application of machine learning algorithms to predict the mechanism of action (MoA) of drugs can be highly valuable and enable the discovery of new uses for known molecules. The developed methods are usually evaluated with small subsets of MoAs with large support, leading to deceptively good generalization. However, these datasets may not accurately represent a practical use, due to the limited number of target MoAs. Accurate predictions for these rare drugs are important for drug discovery and should be a point of focus. In this work, we explore different training strategies to improve the performance of a well established deep learning model for rare drug MoA prediction. We explored transfer learning by first learning a model for common MoAs, and then using it to initialize the learning of another model for rarer MoAs. We also investigated the use of a cascaded methodology, in which results from an initial model are used as additional inputs to the model for rare MoAs. Finally, we proposed and tested an extension of Mixup data augmentation for multilabel classification. The baseline model showed an AUC of 73.2% for common MoAs and 62.4% for rarer classes. From the investigated methods, Mixup alone failed to improve the performance of a baseline classifier. Nonetheless, the other proposed methods outperformed the baseline for rare classes. Transfer Learning was preferred in predicting classes with less than 10 training samples, while the cascaded classifiers (with Mixup) showed better predictions for MoAs with more than 10 samples. However, the performance for rarer MoAs still lags behind the performance for frequent MoAs and is not sufficient for the reliable prediction of rare MoAs.

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