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Accounting for Uncertainty in Machine Learning Surrogates: A Gauss-Hermite Quadrature Approach to Reliability Analysis

arXiv.org Artificial Intelligence

Machine learning surrogates are increasingly employed to replace expensive computational models for physics-based reliability analysis. However, their use introduces epistemic uncertainty from model approximation errors, which couples with aleatory uncertainty in model inputs, potentially compromising the accuracy of reliability predictions. This study proposes a Gauss-Hermite quadrature approach to decouple these nested uncertainties and enable more accurate reliability analysis. The method evaluates conditional failure probabilities under aleatory uncertainty using First and Second Order Reliability Methods and then integrates these probabilities across realizations of epistemic uncertainty. Three examples demonstrate that the proposed approach maintains computational efficiency while yielding more trustworthy predictions than traditional methods that ignore model uncertainty.


SaGess: Sampling Graph Denoising Diffusion Model for Scalable Graph Generation

arXiv.org Artificial Intelligence

Over recent years, denoising diffusion generative models have come to be considered as state-of-the-art methods for synthetic data generation, especially in the case of generating images. These approaches have also proved successful in other applications such as tabular and graph data generation. However, due to computational complexity, to this date, the application of these techniques to graph data has been restricted to small graphs, such as those used in molecular modeling. In this paper, we propose SaGess, a discrete denoising diffusion approach, which is able to generate large real-world networks by augmenting a diffusion model (DiGress) with a generalized divide-and-conquer framework. The algorithm is capable of generating larger graphs by sampling a covering of subgraphs of the initial graph in order to train DiGress. SaGess then constructs a synthetic graph using the subgraphs that have been generated by DiGress. We evaluate the quality of the synthetic data sets against several competitor methods by comparing graph statistics between the original and synthetic samples, as well as evaluating the utility of the synthetic data set produced by using it to train a task-driven model, namely link prediction. In our experiments, SaGess, outperforms most of the one-shot state-of-the-art graph generating methods by a significant factor, both on the graph metrics and on the link prediction task.


Understanding and Bridging the Modality Gap for Speech Translation

arXiv.org Artificial Intelligence

How to achieve better end-to-end speech translation (ST) by leveraging (text) machine translation (MT) data? Among various existing techniques, multi-task learning is one of the effective ways to share knowledge between ST and MT in which additional MT data can help to learn source-to-target mapping. However, due to the differences between speech and text, there is always a gap between ST and MT. In this paper, we first aim to understand this modality gap from the target-side representation differences, and link the modality gap to another well-known problem in neural machine translation: exposure bias. We find that the modality gap is relatively small during training except for some difficult cases, but keeps increasing during inference due to the cascading effect. To address these problems, we propose the Cross-modal Regularization with Scheduled Sampling (Cress) method. Specifically, we regularize the output predictions of ST and MT, whose target-side contexts are derived by sampling between ground truth words and self-generated words with a varying probability. Furthermore, we introduce token-level adaptive training which assigns different training weights to target tokens to handle difficult cases with large modality gaps. Experiments and analysis show that our approach effectively bridges the modality gap, and achieves promising results in all eight directions of the MuST-C dataset.


Reinforcement Learning-Based Cooperative P2P Power Trading between DC Nanogrid Clusters with Wind and PV Energy Resources

arXiv.org Artificial Intelligence

Abstract-- In replacing fossil fuels with renewable energy resources for carbon neutrality, the unbalanced resource production of intermittent wind and photovoltaic (PV) power is a critical issue for peer-to-peer (P2P) power trading. To address this issue, a reinforcement learning (RL) technique is introduced in this paper. For RL, a graph convolutional network (GCN) and a bi-directional long short-term memory (Bi-LSTM) network are jointly applied to P2P power trading between nanogrid clusters, based on cooperative game theory. The flexible and reliable DC nanogrid is suitable for integrating renewable energy for a distribution system. Each local nanogrid cluster takes the position of prosumer, focusing on power production and consumption simultaneously. For the power management of nanogrid cluster, multi-objective optimization is applied to each local nanogrid cluster with the Internet of Things (IoT) technology. Charging/discharging of an electric vehicle (EV) is executed considering the intermittent characteristics of wind and PV power production. RL algorithms, such as GCN-convolutional neural network (CNN) layers for deep Q-learning network (DQN), GCN-LSTM layers for deep recurrent Q-learning network (DRQN), GCN-Bi-LSTM layers for DRQN, and GCN-Bi-LSTM layers for proximal policy optimization (PPO), are used for simulations. Power management of nanogrid clusters with P2P power trading is simulated on a distribution test feeder in real time, and the proposed GCN-Bi-LSTM-PPO technique achieving the lowest electricity cost among the RL algorithms used for comparison reduces the electricity cost by 36.7%, averaging over nanogrid clusters. Keywords: Deep reinforcement learning, P2P power trading, Nanogrid, Power management, Renewable energy I.INTRODUCTION The widespread use of distributed energy resources (DERs) has significantly altered how energy is generated, transported, and used along the energy pipeline. A more decentralized and open electrical network is made possible with increased number of prosumers--individuals who produce and consume energy simultaneously. As a result of this context, new opportunities and difficulties for power systems have emerged. Peer-to-peer (P2P) power trading is a novel paradigm of distribution systems with a utility grid (UT) related to carbon neutrality and renewable energy generation [1]. P2P power trading has become a viable alternative for prosumers looking to actively participate in the energy market. Moreover, P2P trading gives end users more flexibility, increases possibilities to use clean energy, and aids in the transition to a low-carbon energy system. In addition to this, the other participants in the power market can also profit by lowering the peak electricity demand, lowering operating and maintenance expenses, and enhancing the dependability of the electrical system.


How AI can help the move to a low-carbon future

#artificialintelligence

There's a dire need to speed the planet's shift to clean energy - and the power of Artificial Intelligence can help. The world has gone through a number of energy transformations – from wood to coal, then to oil, gas and (partly) nuclear. These shifts were gradual and contingent on economic conditions. Now major efforts are under way to reform the global energy sector to make it low-carbon, non-nuclear and climate-compatible. But, unlike the previous transformations, the ongoing restructuring process is driven by elevated awareness of the disastrous consequences of climate change. Notwithstanding the global efforts made to revolutionise the energy business (to make it capable of coping with the variability inherent in most renewable energy generation technologies), there is still a dire need to speed up the shift to clean energy solutions.