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Min Wu

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54 papers
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54

AAAI Conference 2026 Conference Paper

A Unified Shape-Aware Foundation Model for Time Series Classification

  • Zhen Liu
  • Yucheng Wang
  • Boyuan Li
  • Junhao Zheng
  • Emadeldeen Eldele
  • Min Wu
  • Qianli Ma

Foundation models pre-trained on large-scale source datasets are reshaping the traditional training paradigm for time series classification. However, existing time series foundation models primarily focus on forecasting tasks and often overlook classification-specific challenges, such as modeling interpretable shapelets that capture class-discriminative temporal features. To bridge this gap, we propose UniShape, a unified shape-aware foundation model designed for time series classification. UniShape incorporates a shape-aware adapter that adaptively aggregates multiscale discriminative subsequences (shapes) into class tokens, effectively selecting the most relevant subsequence scales to enhance model interpretability. Meanwhile, a prototype-based pretraining module is introduced to jointly learn instance- and shape-level representations, enabling the capture of transferable shape patterns. Pre-trained on a large-scale multi-domain time series dataset comprising 1.89 million samples, UniShape exhibits superior generalization across diverse target domains. Experiments on 128 UCR datasets and 30 additional time series datasets demonstrate that UniShape achieves state-of-the-art classification performance, with interpretability and ablation analyses further validating its effectiveness.

EAAI Journal 2026 Journal Article

Autoencoder: An efficient inverse design method for gallium nitride high electron mobility transistor structures

  • Yan Pang
  • Meilan Hao
  • Shu Wei
  • Lina Yu
  • Jufeng Han
  • Min Wu
  • Hong Qin
  • Weijun Li

Autoencoders are artificial neural networks widely used for feature extraction and data reconstruction, and can also be leveraged for device and material structure design. In gallium nitride (GaN) high electron mobility transistor (HEMT) inverse design, the mapping from target radio-frequency (RF) metrics to geometric parameters is often non-unique, meaning that multiple distinct structures can achieve similar performance. This one-to-many nature makes deterministic inverse regression unstable. Motivated by this challenge, this paper presents an autoencoder-based inverse design approach for GaN HEMT structures that learns the relationship between device geometry and two key RF metrics: cut-off frequency ( f T ) and maximum oscillation frequency ( f max ). The proposed method enables efficient generation of candidate GaN HEMT designs that match specified RF targets, using technology computer-aided design (TCAD) simulations to generate and label the training data. The model predicts four structural parameters, including gate–source spacing, gate length, gate field-plate length, and passivation-layer thickness. Experimental results show that the proposed framework can reliably generate structures consistent with the target specifications. The average relative error is 2. 64% for f T and 2. 67% for f max. Compared with direct inverse regression baselines, the autoencoder-based framework exhibits more stable training behavior and alleviates slow convergence or training failures caused by the non-uniqueness of the inverse mapping. In our implementation, the method can generate a candidate structure for a given RF target within a few milliseconds (ms), substantially reducing computational cost and providing an effective route to accelerate GaN HEMT device design.

AAAI Conference 2026 Conference Paper

Efficiently Computing Compact Formal Explanations

  • Min Wu
  • Xiaofu Li
  • Haoze Wu
  • Clark Barrett

Building on VeriX (Verified eXplainability), a system for producing optimal verified explanations for machine learning models, we present VeriX+, which significantly improves both the size and the generation time of formal explanations. We introduce a bound propagation-based sensitivity technique to improve the size, and a binary search-based traversal with confidence ranking for improving time---the two techniques are orthogonal and can be used independently or together. We also show how to adapt the QuickXplain algorithm to our setting to provide a trade-off between size and time. Experimental evaluations on standard benchmarks demonstrate significant improvements on both metrics, e.g., a size reduction of 38% on the GTSRB dataset and a time reduction of 90% on MNIST. We demonstrate that our approach is scalable to transformers and real-world scenarios such as autonomous aircraft taxiing and sentiment analysis. We conclude by showcasing several novel applications of formal explanations.

AAAI Conference 2026 Conference Paper

Hierarchical Structure-Property Alignment for Data-Efficient Molecular Generation and Editing

  • Ziyu Fan
  • Zhijian Huang
  • Yahan Li
  • Xiaowen Hu
  • Siyuan Shen
  • Yunliang Wang
  • Zeyu Zhong
  • Shuhong Liu

Property-constrained molecular generation and editing are crucial in AI-driven drug discovery but remain hindered by two factors: (i) capturing the complex relationships between molecular structures and multiple properties remains challenging, and (ii) the narrow coverage and incomplete annotations of molecular properties weaken the effectiveness of property-based models. To tackle these limitations, we propose HSPAG, a data-efficient framework featuring hierarchical structure–property alignment. By treating SMILES and molecular properties as complementary modalities, the model learns their relationships at atom, substructure, and whole-molecule levels. Moreover, we select representative samples through scaffold clustering and hard samples via an auxiliary variational auto-encoder (VAE), substantially reducing the required pre-training data. In addition, we incorporate a property relevance-aware masking mechanism and diversified perturbation strategies to enhance generation quality under sparse annotations. Experiments demonstrate that HSPAG captures fine-grained structure–property relationships and supports controllable generation under multiple property constraints. Two real-world case studies further validate the editing capabilities of HSPAG.

AAAI Conference 2026 Conference Paper

Implicit Neural Representation with Multi-Scale Sine Activation

  • Jufeng Han
  • Shu Wei
  • Min Wu
  • Lina Yu
  • Weijun Li
  • Linjun Sun
  • Hong Qin
  • Yan Pang

Implicit Neural Representations (INRs) have become a powerful paradigm for modeling continuous signals in computer vision, graphics, and scientific computing. However, multilayer perceptrons (MLPs) generally suffer from severe spectral bias, which limits their ability to accurately model high-frequency details and multi-scale structures. To address this challenge, we propose a novel Multi-Scale Sine Activation (MSA), which explicitly introduces multi-scale frequency responses by incorporating multiple sets of sine activations with logarithmically spaced frequencies in parallel at each layer. MSA is further combined with an amplitude modulation mechanism to ensure numerical stability and robust optimization across different frequency channels. We conduct extensive experiments on a series of challenging tasks, including 1D multi-scale function fitting, image representation, video representation, 3D shape representation, and PDEs solving. Experimental results show that MSA outperforms existing state-of-the-art methods in terms of reconstruction accuracy, detail preservation, and training stability.

AAAI Conference 2026 Conference Paper

Light but Sharp: SlimSTAD for Real-Time Action Detection from Sensor Data

  • Wei Cui
  • Lukai Fan
  • Zhenghua Chen
  • Min Wu
  • Shili Xiang
  • Haixia Wang
  • Bing Li

Sensory Temporal Action Detection (STAD) aims to localize and classify human actions within long, untrimmed sequences captured by non-visual sensors such as WiFi or inertial measurement units (IMUs). Unlike video-based TAD, STAD poses unique challenges due to the low-dimensional, noisy, and heterogeneous nature of sensory data, as well as the real-time and resource constraints on edge devices. While recent STAD models have improved detection performance, their high computational cost hampers practical deployment. In this paper, we propose SlimSTAD, a simple yet effective framework that achieves both high accuracy and low latency for STAD. SlimSTAD features a novel Decoupled Channel Modeling (DCM) encoder, which preserves modality-specific temporal features and enables efficient inter-channel aggregation via lightweight graph attention. An anchor-free cascade predictor then refines action boundaries and class predictions in a two-stage design without dense proposals. Experiments on two real-world datasets demonstrate that SlimSTAD outperforms strong video-derived and sensory baselines by an average of 2.1 mAP, while significantly reducing GFLOPs, parameters, and latency, validating its effectiveness for real-world, edge-aware STAD deployment.

JBHI Journal 2026 Journal Article

Multimodal Fusion of Behavioral and Physiological Signals for Enhanced Emotion Recognition via Feature Decoupling and Knowledge Transfer

  • Hongxiang Gao
  • Zhipeng Cai
  • Xingyao Wang
  • Min Wu
  • Chengyu Liu

Multimodal emotion recognition has emerged as a promising direction for capturing the complexity of human affective states by integrating physiological and behavioral signals. However, challenges remain in addressing feature redundancy, modality heterogeneity, and insufficient inter-modal supervision. In this paper, we propose a novel Multimodal Disentangled Knowledge Distillation framework that explicitly disentangles modality-shared and modality-specific features and enhances cross-modal knowledge transfer via a graph-based distillation module. Specifically, we introduce a dual-stream representation learning architecture that separates common and unique subspaces across modalities. To facilitate effective information interaction, we design a directed and learnable modality graph, where each edge represents the semantic transfer strength from one modality to another. We validate our method on two benchmark datasets—MAHNOB-HCI and DEAP—for both regression and classification tasks, under subject-dependent and subject-independent protocols. Experimental results demonstrate that our method achieves state-of-the-art performance, with statistical significance confirmed by paired two-tailed $t$ -tests. In addition, qualitative analysis of the learned modality graph and t-SNE embeddings further illustrates the effectiveness of our feature disentanglement and dynamic knowledge transfer design. This work offers a unified, interpretable, and robust framework for multimodal emotion understanding and lays the foundation for affective computing in real-world human–machine interaction scenarios.

AAAI Conference 2026 Conference Paper

Parameterized Abstract Interpretation for Transformer Verification

  • Pei Huang
  • Dennis Wei
  • Omri Isac
  • Haoze Wu
  • Min Wu
  • Clark Barrett

Transformers based on the self-attention mechanism have become foundational models across a wide range of domains, thereby creating an urgent need for effective formal verification techniques to better understand their behavior and ensure safety guarantees. In this paper, we propose two parameterized linear abstract domains for the inner products in the self-attention module, aiming to improve verification precision. The first one constructs symbolic quadratic upper and lower bounds for the product of two scalars, and then derives parameterized affine bounds using tangents. The other one constructs parameterized bounds by interpolating affine bounds proposed in prior work. We evaluate these two parameterization methods and demonstrate that both of them outperform the state-of-the-art approach which is regarded as optimal with respect to a certain mean gap. Experimental results show that, in the context of robustness verification, our approach is able to verify many instances that cannot be verified by existing methods. In the interval analysis, our method achieves tighter results compared to the SOTA, with the strength becoming more pronounced as the network depth increases.

AAAI Conference 2026 Conference Paper

Tighter Truncated Rectangular Prism Approximation for RNN Robustness Verification

  • Xingqi Lin
  • Liangyu Chen
  • Min Wu
  • Min Zhang
  • Zhenbing Zeng

Robustness verification is a promising technique for rigorously proving Recurrent Neural Networks (RNNs) robustly. A key challenge is to over-approximate the nonlinear activation functions with linear constraints, which can transform the verification problem into an efficiently solvable linear programming problem. Existing methods over-approximate the nonlinear parts with linear bounding planes individually, which may cause significant over-estimation and lead to lower verification accuracy. In this paper, in order to tightly enclose the three-dimensional nonlinear surface generated by the Hadamard product, we propose a novel truncated rectangular prism formed by two linear relaxation planes and a refinement-driven method to minimize both its volume and surface area for tighter over-approximation. Based on this approximation, we implement a prototype DeepPrism for RNN robustness verification. The experimental results demonstrate that DeepPrism has significant improvement compared with the state-of-the-art approaches in various tasks of image classification, speech recognition and sentiment analysis.

EAAI Journal 2025 Journal Article

A hybrid prediction model for marine wind speed considering internal temporal features recombination and external variables association

  • Haoxian Wen
  • Sheng Du
  • Chengda Lu
  • Yawu Wang
  • Min Wu
  • Weihua Cao

Marine wind exists widely as a major environmental disturbance in the process of marine resource exploration. Accurate short-term prediction of marine wind speed can ensure the safety of offshore exploration operations. The current wind speed prediction model has prediction lag, and lacks consideration of chaotic characteristics and the influence of external variables. Analyzing the chaotic time series characteristics of marine wind speed and their causative correlations, a hybrid prediction model for marine wind speed is presented in this paper, which incorporates the recombination of internal temporal features and external variables association. Firstly, the marine wind speed is decomposed using the improved complete ensemble empirical mode decomposition with adaptive noise, with features recombined based on a comprehensive evaluation of multiple entropies and hierarchical clustering. Subsequently, for the chaotic components characterized by strong randomness and nonlinearity, successive variational mode decomposition is used for a secondary decomposition, with chaotic reconstruction based on their recurrence plot characteristics. Then, a hybrid prediction model for marine wind speed considering internal temporal features recombination and external variables association is proposed. Finally, experiments are performed by using actual data from a marine buoy. The result shows that the hybrid prediction model can accurately predict the marine wind speed for the next time step, providing advanced environmental perception for marine resource exploration.

EAAI Journal 2025 Journal Article

A transfer learning-based plate shape prediction model with limited samples for roller quenching process

  • Wen Zhang
  • Min Wu
  • Sheng Du
  • Luefeng Chen
  • Jie Hu
  • Naoyuki Kubota

Plate shape is an important indicator in roller quenching process and significantly affects the using performance of steel plates. However, due to the high cost of plate shape detectors, although plate shape detectors play a vital role, many roller quenching production lines still operate without them. This issue severely limits the effectiveness of plate shape control methods and indirectly leads to a decline in plate shape quality. To address this gap and enable automatic feedback in scenarios lacking such detectors, this paper analyzes the limitations in both the accuracy and quantity of samples, and proposes a transfer learning-based plate shape prediction model. Firstly, a data augmentation module is proposed, and a deep sets module is designed for initial feature extraction. Then, a multilayer perceptron module is designed for deep feature extraction, aiming to enhance the ability of the model to capture nonlinear relationships. Next, an improved residual network module is designed to predict the plate shape. Through the special design of the model structure, the problem of different representation methods of plate shape is addressed. Finally, a targeted transfer learning strategy is designed for the proposed model to improve the accuracy in the absence of plate shape detectors. The experimental results demonstrate that the proposed model and strategy achieve high-accuracy plate shape prediction with limited samples, providing a practical plate shape prediction approach tailored for production lines without plate shape detectors.

ICML Conference 2025 Conference Paper

Closed-form Solutions: A New Perspective on Solving Differential Equations

  • Shu Wei
  • Yanjie Li 0005
  • Lina Yu
  • Weijun Li 0002
  • Min Wu
  • Linjun Sun
  • Jingyi Liu
  • Hong Qin 0007

The quest for analytical solutions to differential equations has traditionally been constrained by the need for extensive mathematical expertise. Machine learning methods like genetic algorithms have shown promise in this domain, but are hindered by significant computational time and the complexity of their derived solutions. This paper introduces SSDE (Symbolic Solver for Differential Equations), a novel reinforcement learning-based approach that derives symbolic closed-form solutions for various differential equations. Evaluations across a diverse set of ordinary and partial differential equations demonstrate that SSDE outperforms existing machine learning methods, delivering superior accuracy and efficiency in obtaining analytical solutions.

EAAI Journal 2025 Journal Article

Extended multi-kernel relevance vector machine optimized Kriging interpolation for coal seam thickness prediction in coal-bearing strata

  • Luefeng Chen
  • Mingdi Ma
  • Min Wu
  • Witold Pedrycz
  • Kaoru Hirota

During the drilling process of a coal mine roadway drilling rig, coal seam thickness variation affects the efficiency of coal seam mining. However, the cost of geological drilling required for coal seam exploration in practical engineering is high, the sample size of the data is small and the distribution is discrete, and spatial interpolation is required for coal seam thickness prediction in unexplored coal seams. Therefore, this paper proposes an improved method of kriging spatial interpolation for small sample, acquired from geological drilling. Firstly, for the small sample problem, we use a Relevance Vector Machine (RVM) to reconstruct the variogram in kriging interpolation. Secondly, multi-kernel RVM (MKRVM) is used to improve the fitting effect in global and local, respectively. Finally, Particle Swarm Optimization (PSO) is used as an extension of MKRVM to optimize the hyperparameters in the multiple kernel functions and the weights among different kernel functions to improve the fitting effect of the overall model. Through a series of comparative experiments, the superiority of the extended multi-kernel RVM (EMKRVM) method proposed in this paper is verified. At the same time, the method is applied to a practical project, and the results illustrate that our method has lower error in the prediction of coal seam thickness variation in coal-bearing strata, which can provide a better reference basis for the subsequent adjustment of drilling speed, rotation speed, and drilling pressure.

NeurIPS Conference 2025 Conference Paper

Learning Pattern-Specific Experts for Time Series Forecasting Under Patch-level Distribution Shift

  • Yanru Sun
  • Zongxia Xie
  • Emadeldeen Eldele
  • Dongyue Chen
  • Qinghua Hu
  • Min Wu

Time series forecasting, which aims to predict future values based on historical data, has garnered significant attention due to its broad range of applications. However, real-world time series often exhibit heterogeneous pattern evolution across segments, such as seasonal variations, regime changes, or contextual shifts, making accurate forecasting challenging. Existing approaches, which typically train a single model to capture all these diverse patterns, often struggle with the pattern drifts between patches and may lead to poor generalization. To address these challenges, we propose TFPS, a novel architecture that leverages pattern-specific experts for more accurate and adaptable time series forecasting. TFPS employs a dual-domain encoder to capture both time-domain and frequency-domain features, enabling a more comprehensive understanding of temporal dynamics. It then performs subspace clustering to dynamically identify distinct patterns across data segments. Finally, these patterns are modeled by specialized experts, allowing the model to learn multiple predictive functions. Extensive experiments on real-world datasets demonstrate that TFPS outperforms state-of-the-art methods, particularly on datasets exhibiting significant distribution shifts. The data and code are available: https: //github. com/syrGitHub/TFPS.

AAAI Conference 2025 Conference Paper

MetaSymNet: A Tree-like Symbol Network with Adaptive Architecture and Activation Functions

  • Yanjie Li
  • Weijun Li
  • Lina Yu
  • Min Wu
  • Jingyi Liu
  • Shu Wei
  • Yusong Deng
  • Meilan Hao

Mathematical formulas are the language of communication between humans and nature. Discovering latent formulas from observed data is an important challenge in artificial intelligence, commonly known as symbolic regression(SR). The current mainstream SR algorithms regard SR as a combinatorial optimization problem and use Genetic Programming (GP) or Reinforcement Learning (RL) to solve the SR problem. These methods perform well on simple problems, but poorly on slightly more complex tasks. In addition, this class of algorithms ignores an important aspect: in SR tasks, symbols have explicit numerical meaning. So can we take full advantage of this important property and try to solve the SR problem with more efficient numerical optimization methods? Extrapolation and Learning Equation (EQL) replaces activation functions in neural networks with basic symbols and sparsifies connections to derive a simplified expression from a large network. However, EQL's fixed network structure can't adapt to the complexity of different tasks, often resulting in redundancy or insufficient, limiting its effectiveness. Based on the above analysis, we propose MetaSymNet, a tree-like network that employs the PANGU meta-function as its activation function. PANGU meta-function can evolve into various candidate functions during training. The network structure can also be adaptively adjusted according to different tasks. Then the symbol network evolves into a concise, interpretable mathematical expression. To evaluate the performance of MetaSymNet and five baseline algorithms, we conducted experiments across more than ten datasets, including SRBench. The experimental results show that MetaSymNet has achieved relatively excellent results on various evaluation metrics.

JBHI Journal 2025 Journal Article

MTSNet: Convolution-Based Transformer Network With Multi-Scale Temporal-Spectral Feature Fusion for SSVEP Signal Decoding

  • Zhen Lan
  • Zixing Li
  • Chao Yan
  • Xiaojia Xiang
  • Dengqing Tang
  • Min Wu
  • Zhenghua Chen

Improving the decoding performance of steady-state visual evoked (SSVEP) signals is crucial for the practical application of SSVEP-based brain-computer interface (BCI) systems. Although numerous methods have achieved impressive results in decoding SSVEP signals, most of them focus only on the temporal or spectral domain information or concatenate them directly, which may ignore the complementary relationship between different features. To address this issue, we propose a dual-branch convolution-based Transformer network with multi-scale temporal-spectral feature fusion, termed MTSNet, to improve the decoding performance of SSVEP signals. Specifically, the temporal branch extracts temporal features from the SSVEP signals using the multi-level convolution- based Transformer (Convformer) that can adapt to the dynamic fluctuations of SSVEP signals. In parallel, the spectral branch takes the complex spectrum converted from temporal signals by the zero-padding fast Fourier transform as input and uses the Convformer to extract spectral features. These extracted temporal and spectral features are then integrated by the multi-scale feature fusion module to obtain comprehensive features with different scale information, thereby enhancing the interactions between the features and improving the effectiveness and robustness. Extensive experimental results on two widely used public SSVEP datasets, Benchmark and BETA, show that the proposed MTSNet significantly outperforms the state-of-the-art calibration-free methods in terms of accuracy and ITR. The superior performance demonstrates the effectiveness of our method in decoding SSVEP signals, which may facilitate the practical application of SSVEP-based BCI systems.

ICML Conference 2024 Conference Paper

A Neural-Guided Dynamic Symbolic Network for Exploring Mathematical Expressions from Data

  • Wenqiang Li
  • Weijun Li 0002
  • Lina Yu
  • Min Wu
  • Linjun Sun
  • Jingyi Liu
  • Yanjie Li 0005
  • Shu Wei

Symbolic regression (SR) is a powerful technique for discovering the underlying mathematical expressions from observed data. Inspired by the success of deep learning, recent deep generative SR methods have shown promising results. However, these methods face difficulties in processing high-dimensional problems and learning constants due to the large search space, and they don’t scale well to unseen problems. In this work, we propose DySymNet, a novel neural-guided Dy namic Sym bolic Net work for SR. Instead of searching for expressions within a large search space, we explore symbolic networks with various structures, guided by reinforcement learning, and optimize them to identify expressions that better-fitting the data. Based on extensive numerical experiments on low-dimensional public standard benchmarks and the well-known SRBench with more variables, DySymNet shows clear superiority over several representative baseline models. Open source code is available at https: //github. com/AILWQ/DySymNet.

AAAI Conference 2024 Conference Paper

Fully-Connected Spatial-Temporal Graph for Multivariate Time-Series Data

  • Yucheng Wang
  • Yuecong Xu
  • Jianfei Yang
  • Min Wu
  • Xiaoli Li
  • Lihua Xie
  • Zhenghua Chen

Multivariate Time-Series (MTS) data is crucial in various application fields. With its sequential and multi-source (multiple sensors) properties, MTS data inherently exhibits Spatial-Temporal (ST) dependencies, involving temporal correlations between timestamps and spatial correlations between sensors in each timestamp. To effectively leverage this information, Graph Neural Network-based methods (GNNs) have been widely adopted. However, existing approaches separately capture spatial dependency and temporal dependency and fail to capture the correlations between Different sEnsors at Different Timestamps (DEDT). Overlooking such correlations hinders the comprehensive modelling of ST dependencies within MTS data, thus restricting existing GNNs from learning effective representations. To address this limitation, we propose a novel method called Fully-Connected Spatial-Temporal Graph Neural Network (FC-STGNN), including two key components namely FC graph construction and FC graph convolution. For graph construction, we design a decay graph to connect sensors across all timestamps based on their temporal distances, enabling us to fully model the ST dependencies by considering the correlations between DEDT. Further, we devise FC graph convolution with a moving-pooling GNN layer to effectively capture the ST dependencies for learning effective representations. Extensive experiments show the effectiveness of FC-STGNN on multiple MTS datasets compared to SOTA methods. The code is available at https://github.com/Frank-Wang-oss/FCSTGNN.

JBHI Journal 2024 Journal Article

Graph Convolutional Network With Connectivity Uncertainty for EEG-Based Emotion Recognition

  • Hongxiang Gao
  • Xingyao Wang
  • Zhenghua Chen
  • Min Wu
  • Zhipeng Cai
  • Lulu Zhao
  • Jianqing Li
  • Chengyu Liu

Automatic emotion recognition based on multichannel Electroencephalography (EEG) holds great potential in advancing human-computer interaction. However, several significant challenges persist in existing research on algorithmic emotion recognition. These challenges include the need for a robust model to effectively learn discriminative node attributes over long paths, the exploration of ambiguous topological information in EEG channels and effective frequency bands, and the mapping between intrinsic data qualities and provided labels. To address these challenges, this study introduces the distribution-based uncertainty method to represent spatial dependencies and temporal-spectral relativeness in EEG signals based on Graph Convolutional Network (GCN) architecture that adaptively assigns weights to functional aggregate node features, enabling effective long-path capturing while mitigating over-smoothing phenomena. Moreover, the graph mixup technique is employed to enhance latent connected edges and mitigate noisy label issues. Furthermore, we integrate the uncertainty learning method with deep GCN weights in a one-way learning fashion, termed Connectivity Uncertainty GCN (CU-GCN). We evaluate our approach on two widely used datasets, namely SEED and SEEDIV, for emotion recognition tasks. The experimental results demonstrate the superiority of our methodology over previous methods, yielding positive and significant improvements. Ablation studies confirm the substantial contributions of each component to the overall performance.

AAAI Conference 2024 Conference Paper

Graph-Aware Contrasting for Multivariate Time-Series Classification

  • Yucheng Wang
  • Yuecong Xu
  • Jianfei Yang
  • Min Wu
  • Xiaoli Li
  • Lihua Xie
  • Zhenghua Chen

Contrastive learning, as a self-supervised learning paradigm, becomes popular for Multivariate Time-Series (MTS) classification. It ensures the consistency across different views of unlabeled samples and then learns effective representations for these samples. Existing contrastive learning methods mainly focus on achieving temporal consistency with temporal augmentation and contrasting techniques, aiming to preserve temporal patterns against perturbations for MTS data. However, they overlook spatial consistency that requires the stability of individual sensors and their correlations. As MTS data typically originate from multiple sensors, ensuring spatial consistency becomes essential for the overall performance of contrastive learning on MTS data. Thus, we propose Graph-Aware Contrasting for spatial consistency across MTS data. Specifically, we propose graph augmentations including node and edge augmentations to preserve the stability of sensors and their correlations, followed by graph contrasting with both node- and graph-level contrasting to extract robust sensor- and global-level features. We further introduce multi-window temporal contrasting to ensure temporal consistency in the data for each sensor. Extensive experiments demonstrate that our proposed method achieves state-of-the-art performance on various MTS classification tasks. The code is available at https://github.com/Frank-Wang-oss/TS-GAC.

TMLR Journal 2024 Journal Article

Leveraging Endo- and Exo-Temporal Regularization for Black-box Video Domain Adaptation

  • Yuecong Xu
  • Jianfei Yang
  • Haozhi Cao
  • Min Wu
  • Xiaoli Li
  • Lihua Xie
  • Zhenghua Chen

To enable video models to be applied seamlessly across video tasks in different environments, various Video Unsupervised Domain Adaptation (VUDA) methods have been proposed to improve the robustness and transferability of video models. Despite improvements made in model robustness, these VUDA methods require access to both source data and source model parameters for adaptation, raising serious data privacy and model portability issues. To cope with the above concerns, this paper firstly formulates Black-box Video Domain Adaptation (BVDA) as a more realistic yet challenging scenario where the source video model is provided only as a black-box predictor. While a few methods for Black-box Domain Adaptation (BDA) are proposed in the image domain, these methods cannot apply to the video domain since video modality has more complicated temporal features that are harder to align. To address BVDA, we propose a novel Endo and eXo-TEmporal Regularized Network (EXTERN) by applying mask-to-mix strategies and video-tailored regularizations. They are the endo-temporal regularization and exo-temporal regularization, which are performed across both clip and temporal features, while distilling knowledge from the predictions obtained from the black-box predictor. Empirical results demonstrate the state-of-the-art performance of EXTERN across various cross-domain closed-set and partial-set action recognition benchmarks, which even surpasses most existing video domain adaptation methods with source data accessibility. Code will be available at https://xuyu0010.github.io/b2vda.html.

YNIMG Journal 2024 Journal Article

Multimodal acoustic-electric trigeminal nerve stimulation modulates conscious perception

  • Min Wu
  • Ryszard Auksztulewicz
  • Lars Riecke

Multimodal stimulation can reverse pathological neural activity and improve symptoms in neuropsychiatric diseases. Recent research shows that multimodal acoustic-electric trigeminal-nerve stimulation (TNS) (i.e., musical stimulation synchronized to electrical stimulation of the trigeminal nerve) can improve consciousness in patients with disorders of consciousness. However, the reliability and mechanism of this novel approach remain largely unknown. We explored the effects of multimodal acoustic-electric TNS in healthy human participants by assessing conscious perception before and after stimulation using behavioral and neural measures in tactile and auditory target-detection tasks. To explore the mechanisms underlying the putative effects of acoustic-electric stimulation, we fitted a biologically plausible neural network model to the neural data using dynamic causal modeling. We observed that (1) acoustic-electric stimulation improves conscious tactile perception without a concomitant change in auditory perception, (2) this improvement is caused by the interplay of the acoustic and electric stimulation rather than any of the unimodal stimulation alone, and (3) the effect of acoustic-electric stimulation on conscious perception correlates with inter-regional connection changes in a recurrent neural processing model. These results provide evidence that acoustic-electric TNS can promote conscious perception. Alterations in inter-regional cortical connections might be the mechanism by which acoustic-electric TNS achieves its consciousness benefits.

JBHI Journal 2024 Journal Article

Progressive Dual Priori Network for Generalized Breast Tumor Segmentation

  • Li Wang
  • Lihui Wang
  • Zixiang Kuai
  • Lei Tang
  • Yingfeng Ou
  • Min Wu
  • Tianliang Shi
  • Chen Ye

To promote the generalization ability of breast tumor segmentation models, as well as to improve the segmentation performance for breast tumors with smaller size, low-contrast and irregular shape, we propose a progressive dual priori network (PDPNet) to segment breast tumors from dynamic enhanced magnetic resonance images (DCE-MRI) acquired at different centers. The PDPNet first cropped tumor regions with a coarse-segmentation based localization module, then the breast tumor mask was progressively refined by using the weak semantic priori and cross-scale correlation prior knowledge. To validate the effectiveness of PDPNet, we compared it with several state-of-the-art methods on multi-center datasets. The results showed that, comparing against the suboptimal method, the DSC and HD95 of PDPNet were improved at least by 5. 13% and 7. 58% respectively on multi-center test sets. In addition, through ablations, we demonstrated that the proposed localization module can decrease the influence of normal tissues and therefore improve the generalization ability of the model. The weak semantic priors allow focusing on tumor regions to avoid missing small tumors and low-contrast tumors. The cross-scale correlation priors are beneficial for promoting the shape-aware ability for irregular tumors. Thus integrating them in a unified framework improved the multi-center breast tumor segmentation performance.

NeurIPS Conference 2024 Conference Paper

Reinforced Cross-Domain Knowledge Distillation on Time Series Data

  • Qing Xu
  • Min Wu
  • Xiaoli Li
  • Kezhi Mao
  • Zhenghua Chen

Unsupervised domain adaptation methods have demonstrated superior capabilities in handling the domain shift issue which widely exists in various time series tasks. However, their prominent adaptation performances heavily rely on complex model architectures, posing an unprecedented challenge in deploying them on resource-limited devices for real-time monitoring. Existing approaches, which integrates knowledge distillation into domain adaptation frameworks to simultaneously address domain shift and model complexity, often neglect network capacity gap between teacher and student and just coarsely align their outputs over all source and target samples, resulting in poor distillation efficiency. Thus, in this paper, we propose an innovative framework named Reinforced Cross-Domain Knowledge Distillation (RCD-KD) which can effectively adapt to student's network capability via dynamically selecting suitable target domain samples for knowledge transferring. Particularly, a reinforcement learning-based module with a novel reward function is proposed to learn optimal target sample selection policy based on student's capacity. Meanwhile, a domain discriminator is designed to transfer the domain invariant knowledge. Empirical experimental results and analyses on four public time series datasets demonstrate the effectiveness of our proposed method over other state-of-the-art benchmarks.

EAAI Journal 2024 Journal Article

Time series classification models based on nonlinear spiking neural P systems

  • Xin Xiong
  • Min Wu
  • Juan He
  • Hong Peng
  • Jun Wang
  • Xianzhong Long
  • Qian Yang

Reservoir computing (RC) is a novel class of recurrent neural networks (RNN) models. Nonlinear spiking neural P (NSNP) systems are neural-like computing models with nonlinear spiking mechanisms. By introducing NSNP systems as the reservoir, we propose a new RC model for time series classification task, termed TSC-NSNP model. However, due to the high-dimensional nature of the reservoir state space, the TSC-NSNP model, like existing RC models, will encounter some challenges. To address the challenges. we utilize the reservoir model space representation and dimensionality reduction method to propose two improved models, termed TSC-DR-NSNP model and TSC-RMS-NSNP model. The three RC models can be easily realized and learnt in the RC framework. The proposed three RC models are evaluated on 21 benchmark time series classification data sets, and are compared with 20 classification models. The comparisons demonstrate the effectiveness of the presented three RC models for time series classification tasks.

AAAI Conference 2024 Conference Paper

Towards Efficient Verification of Quantized Neural Networks

  • Pei Huang
  • Haoze Wu
  • Yuting Yang
  • Ieva Daukantas
  • Min Wu
  • Yedi Zhang
  • Clark Barrett

Quantization replaces floating point arithmetic with integer arithmetic in deep neural network models, providing more efficient on-device inference with less power and memory. In this work, we propose a framework for formally verifying the properties of quantized neural networks. Our baseline technique is based on integer linear programming which guarantees both soundness and completeness. We then show how efficiency can be improved by utilizing gradient-based heuristic search methods and also bound-propagation techniques. We evaluate our approach on perception networks quantized with PyTorch. Our results show that we can verify quantized networks with better scalability and efficiency than the previous state of the art.

NeurIPS Conference 2024 Conference Paper

Training Binary Neural Networks via Gaussian Variational Inference and Low-Rank Semidefinite Programming

  • Lorenzo Orecchia
  • Jiawei Hu
  • Xue He
  • Zhe Wang
  • Xulei Yang
  • Min Wu
  • Xue Geng

Current methods for training Binarized Neural Networks (BNNs) heavily rely on the heuristic straight-through estimator (STE), which crucially enables the application of SGD-based optimizers to the combinatorial training problem. Although the STE heuristics and their variants have led to significant improvements in BNN performance, their theoretical underpinnings remain unclear and relatively understudied. In this paper, we propose a theoretically motivated optimization framework for BNN training based on Gaussian variational inference. In its simplest form, our approach yields a non-convex linear programming formulation whose variables and associated gradients motivate the use of latent weights and STE gradients. More importantly, our framework allows us to formulate semidefinite programming (SDP) relaxations to the BNN training task. Such formulations are able to explicitly models pairwise correlations between weights during training, leading to a more accurate optimization characterization of the training problem. As the size of such formulations grows quadratically in the number of weights, quickly becoming intractable for large networks, we apply the Burer-Monteiro approach and only optimize over linear-size low-rank SDP solutions. Our empirical evaluation on CIFAR-10, CIFAR-100, Tiny-ImageNet and ImageNet datasets shows our method consistently outperforming all state-of-the-art algorithms for training BNNs.

IJCAI Conference 2023 Conference Paper

Distilling Universal and Joint Knowledge for Cross-Domain Model Compression on Time Series Data

  • Qing Xu
  • Min Wu
  • Xiaoli Li
  • Kezhi Mao
  • Zhenghua Chen

For many real-world time series tasks, the computational complexity of prevalent deep leaning models often hinders the deployment on resource limited environments (e. g. , smartphones). Moreover, due to the inevitable domain shift between model training (source) and deploying (target) stages, compressing those deep models under cross-domain scenarios becomes more challenging. Although some of existing works have already explored cross-domain knowledge distillation for model compression, they are either biased to source data or heavily tangled between source and target data. To this end, we design a novel end-to-end framework called UNiversal and joInt Knowledge Distillation (UNI-KD) for cross-domain model compression. In particular, we propose to transfer both the universal feature-level knowledge across source and target domains and the joint logit-level knowledge shared by both domains from the teacher to the student model via an adversarial learning scheme. More specifically, a feature-domain discriminator is employed to align teacher’s and student’s representations for universal knowledge transfer. A data-domain discriminator is utilized to prioritize the domain-shared samples for joint knowledge transfer. Extensive experimental results on four time series datasets demonstrate the superiority of our proposed method over state-of-the-art (SOTA) benchmarks. The source code is available at https: //github. com/ijcai2023/UNI KD.

JBHI Journal 2023 Journal Article

ECG-CL: A Comprehensive Electrocardiogram Interpretation Method Based on Continual Learning

  • Hongxiang Gao
  • Xingyao Wang
  • Zhenghua Chen
  • Min Wu
  • Jianqing Li
  • Chengyu Liu

The value of Electrocardiogram (ECG) monitoring in early cardiovascular disease (CVD) detection is undeniable, especially with the aid of intelligent wearable devices. Despite this, the requirement for expert interpretation significantly limits public accessibility, underscoring the need for advanced diagnosis algorithms. Deep learning-based methods represent a leap beyond traditional rule-based algorithms, but they are not without challenges such as small databases, inefficient use of local and global ECG information, high memory requirements for deploying multiple models, and the absence of task-to-task knowledge transfer. In response to these challenges, we propose a multi-resolution model adept at integrating local morphological characteristics and global rhythm patterns seamlessly. We also introduce an innovative ECG continual learning (ECG-CL) approach based on parameter isolation, designed to enhance data usage effectiveness and facilitate inter-task knowledge transfer. Our experiments, conducted on four publicly available databases, provide evidence of our proposed continual learning method's ability to perform incremental learning across domains, classes, and tasks. The outcome showcases our method's capability in extracting pertinent morphological and rhythmic features from ECG segmentation, resulting in a substantial enhancement of classification accuracy. This research not only confirms the potential for developing comprehensive ECG interpretation algorithms based on single-lead ECGs but also fosters progress in intelligent wearable applications. By leveraging advanced diagnosis algorithms, we aspire to increase the accessibility of ECG monitoring, thereby contributing to early CVD detection and ultimately improving healthcare outcomes.

NeurIPS Conference 2023 Conference Paper

Estimating Propensity for Causality-based Recommendation without Exposure Data

  • Zhongzhou Liu
  • Yuan Fang
  • Min Wu

Causality-based recommendation systems focus on the causal effects of user-item interactions resulting from item exposure (i. e. , which items are recommended or exposed to the user), as opposed to conventional correlation-based recommendation. They are gaining popularity due to their multi-sided benefits to users, sellers and platforms alike. However, existing causality-based recommendation methods require additional input in the form of exposure data and/or propensity scores (i. e. , the probability of exposure) for training. Such data, crucial for modeling causality in recommendation, are often not available in real-world situations due to technical or privacy constraints. In this paper, we bridge the gap by proposing a new framework, called Propensity Estimation for Causality-based Recommendation (PropCare). It can estimate the propensity and exposure from a more practical setup, where only interaction data are available without any ground truth on exposure or propensity in training and inference. We demonstrate that, by relating the pairwise characteristics between propensity and item popularity, PropCare enables competitive causality-based recommendation given only the conventional interaction data. We further present a theoretical analysis on the bias of the causal effect under our model estimation. Finally, we empirically evaluate PropCare through both quantitative and qualitative experiments.

NeurIPS Conference 2023 Conference Paper

Reinforcement-Enhanced Autoregressive Feature Transformation: Gradient-steered Search in Continuous Space for Postfix Expressions

  • Dongjie Wang
  • Meng Xiao
  • Min Wu
  • Pengfei Wang
  • Yuanchun Zhou
  • Yanjie Fu

Feature transformation aims to generate new pattern-discriminative feature space from original features to improve downstream machine learning (ML) task performances. However, the discrete search space for the optimal feature explosively grows on the basis of combinations of features and operations from low-order forms to high-order forms. Existing methods, such as exhaustive search, expansion reduction, evolutionary algorithms, reinforcement learning, and iterative greedy, suffer from large search space. Overly emphasizing efficiency in algorithm design usually sacrifice stability or robustness. To fundamentally fill this gap, we reformulate discrete feature transformation as a continuous space optimization task and develop an embedding-optimization-reconstruction framework. This framework includes four steps: 1) reinforcement-enhanced data preparation, aiming to prepare high-quality transformation-accuracy training data; 2) feature transformation operation sequence embedding, intending to encapsulate the knowledge of prepared training data within a continuous space; 3) gradient-steered optimal embedding search, dedicating to uncover potentially superior embeddings within the learned space; 4) transformation operation sequence reconstruction, striving to reproduce the feature transformation solution to pinpoint the optimal feature space. Finally, extensive experiments and case studies are performed to demonstrate the effectiveness and robustness of the proposed method. The code and data are publicly accessible https: //www. dropbox. com/sh/imh8ckui7va3k5u/AACulQegVx0MuywYyoCqSdVPa? dl=0.

JBHI Journal 2023 Journal Article

Remote Blood Oxygen Estimation From Videos Using Neural Networks

  • Joshua Mathew
  • Xin Tian
  • Chau-Wai Wong
  • Simon Ho
  • Donald K. Milton
  • Min Wu

Peripheral blood oxygen saturation (SpO $_{2}$ ) is an essential indicator of respiratory functionality and received increasing attention during the COVID-19 pandemic. Clinical findings show that COVID-19 patients can have significantly low SpO $_{2}$ before any obvious symptoms. Measuring an individual's SpO $_{2}$ without having to come into contact with the person can lower the risk of cross contamination and blood circulation problems. The prevalence of smartphones has motivated researchers to investigate methods for monitoring SpO $_{2}$ using smartphone cameras. Most prior schemes involving smartphones are contact-based: They require using a fingertip to cover the phone's camera and the nearby light source to capture reemitted light from the illuminated tissue. In this paper, we propose the first convolutional neural network based noncontact SpO $_{2}$ estimation scheme using smartphone cameras. The scheme analyzes the videos of an individual's hand for physiological sensing, which is convenient and comfortable for users and can protect their privacy and allow for keeping face masks on. We design explainable neural network architectures inspired by the optophysiological models for SpO $_{2}$ measurement and demonstrate the explainability by visualizing the weights for channel combination. Our proposed models outperform the state-of-the-art model that is designed for contact-based SpO $_{2}$ measurement, showing the potential of the proposed method to contribute to public health. We also analyze the impact of skin type and the side of a hand on SpO $_{2}$ estimation performance.

AAAI Conference 2023 Conference Paper

SEnsor Alignment for Multivariate Time-Series Unsupervised Domain Adaptation

  • Yucheng Wang
  • Yuecong Xu
  • Jianfei Yang
  • Zhenghua Chen
  • Min Wu
  • Xiaoli Li
  • Lihua Xie

Unsupervised Domain Adaptation (UDA) methods can reduce label dependency by mitigating the feature discrepancy between labeled samples in a source domain and unlabeled samples in a similar yet shifted target domain. Though achieving good performance, these methods are inapplicable for Multivariate Time-Series (MTS) data. MTS data are collected from multiple sensors, each of which follows various distributions. However, most UDA methods solely focus on aligning global features but cannot consider the distinct distributions of each sensor. To cope with such concerns, a practical domain adaptation scenario is formulated as Multivariate Time-Series Unsupervised Domain Adaptation (MTS-UDA). In this paper, we propose SEnsor Alignment (SEA) for MTS-UDA to reduce the domain discrepancy at both the local and global sensor levels. At the local sensor level, we design the endo-feature alignment to align sensor features and their correlations across domains, whose information represents the features of each sensor and the interactions between sensors. Further, to reduce domain discrepancy at the global sensor level, we design the exo-feature alignment to enforce restrictions on the global sensor features. Meanwhile, MTS also incorporates the essential spatial-temporal dependencies information between sensors, which cannot be transferred by existing UDA methods. Therefore, we model the spatial-temporal information of MTS with a multi-branch self-attention mechanism for simple and effective transfer across domains. Empirical results demonstrate the state-of-the-art performance of our proposed SEA on two public MTS datasets for MTS-UDA. The code is available at https://github.com/Frank-Wang-oss/SEA

ICLR Conference 2023 Conference Paper

Transformer-based model for symbolic regression via joint supervised learning

  • Wenqiang Li
  • Weijun Li 0002
  • Linjun Sun
  • Min Wu
  • Lina Yu
  • Jingyi Liu
  • Yanjie Li 0005
  • Songsong Tian

Symbolic regression (SR) is an important technique for discovering hidden mathematical expressions from observed data. Transformer-based approaches have been widely used for machine translation due to their high performance, and are recently highly expected to be used for SR. They input the data points, then output the expression skeleton, and finally optimize the coefficients. However, recent transformer-based methods for SR focus more attention on large scale training data and ignore the ill-posed problem: the lack of sufficient supervision, i.e., expressions that may be completely different have the same supervision because of their same skeleton, which makes it challenging to deal with data that may be from the same expression skeleton but with different coefficients. Therefore, we present a transformer-based model for SR with the ability to alleviate this problem. Specifically, we leverage a feature extractor based on pure residual MLP networks to obtain more information about data points. Furthermore, the core idea is that we propose a joint learning mechanism combining supervised contrastive learning, which makes features of data points from expressions with the same skeleton more similar so as to effectively alleviates the ill-posed problem. The benchmark results show that the proposed method is up to 25% higher with respect to the recovery rate of skeletons than typical transformer-based methods. Moreover, our method outperforms state-of-the-art SR methods based on reinforcement learning and genetic programming in terms of the coefficient of determination ($R^2$).

NeurIPS Conference 2023 Conference Paper

VeriX: Towards Verified Explainability of Deep Neural Networks

  • Min Wu
  • Haoze Wu
  • Clark Barrett

We present VeriX ( Veri fied e X plainability), a system for producing optimal robust explanations and generating counterfactuals along decision boundaries of machine learning models. We build such explanations and counterfactuals iteratively using constraint solving techniques and a heuristic based on feature-level sensitivity ranking. We evaluate our method on image recognition benchmarks and a real-world scenario of autonomous aircraft taxiing.

JBHI Journal 2022 Journal Article

Characterising Alzheimer’s Disease With EEG-Based Energy Landscape Analysis

  • Dominik Klepl
  • Fei He
  • Min Wu
  • Matteo De Marco
  • Daniel J. Blackburn
  • Ptolemaios G. Sarrigiannis

Alzheimer’s disease (AD) is one of the most common neurodegenerative diseases, with around 50 million patients worldwide. Accessible and non-invasive methods of diagnosing and characterising AD are therefore urgently required. Electroencephalography (EEG) fulfils these criteria and is often used when studying AD. Several features derived from EEG were shown to predict AD with high accuracy, e. g. signal complexity and synchronisation. However, the dynamics of how the brain transitions between stable states have not been properly studied in the case of AD and EEG. Energy landscape analysis is a method that can be used to quantify these dynamics. This work presents the first application of this method to both AD and EEG. Energy landscape assigns energy value to each possible state, i. e. pattern of activations across brain regions. The energy is inversely proportional to the probability of occurrence. By studying the features of energy landscapes of 20 AD patients and 20 age-matched healthy counterparts (HC), significant differences are found. The dynamics of AD patients’ EEG are shown to be more constrained - with more local minima, less variation in basin size, and smaller basins. We show that energy landscapes can predict AD with high accuracy, performing significantly better than baseline models. Moreover, these findings are replicated in a separate dataset including 9 AD and 10 HC above 70 years old.

AAAI Conference 2022 Conference Paper

Generalizing Reinforcement Learning through Fusing Self-Supervised Learning into Intrinsic Motivation

  • Keyu Wu
  • Min Wu
  • Zhenghua Chen
  • Yuecong Xu
  • Xiaoli Li

Despite the great potential of reinforcement learning (RL) in solving complex decision-making problems, generalization remains one of its key challenges, leading to difficulty in deploying learned RL policies to new environments. In this paper, we propose to improve the generalization of RL algorithms through fusing Self-supervised learning into Intrinsic Motivation (SIM). Specifically, SIM boosts representation learning through driving the cross-correlation matrix between the embeddings of augmented and non-augmented samples close to the identity matrix. This aims to increase the similarity between the embedding vectors of a sample and its augmented version while minimizing the redundancy between the components of these vectors. Meanwhile, the redundancy reduction based self-supervised loss is converted to an intrinsic reward to further improve generalization in RL via an auxiliary objective. As a general paradigm, SIM can be implemented on top of any RL algorithm. Extensive evaluations have been performed on a diversity of tasks. Experimental results demonstrate that SIM consistently outperforms the state-of-the-art methods and exhibits superior generalization capability and sample efficiency.

YNICL Journal 2022 Journal Article

Rhythmic musical-electrical trigeminal nerve stimulation improves impaired consciousness

  • Min Wu
  • Benyan Luo
  • Yamei Yu
  • Xiaoxia Li
  • Jian Gao
  • Jingqi Li
  • Bettina Sorger
  • Lars Riecke

Accumulating evidence shows that consciousness is linked to neural oscillations in the thalamocortical system, suggesting that deficits in these oscillations may underlie disorders of consciousness (DOC). However, patient-friendly non-invasive treatments targeting this functional anomaly are still missing and the therapeutic value of oscillation restoration has remained unclear. We propose a novel approach that aims to restore DOC patients' thalamocortical oscillations by combining rhythmic trigeminal-nerve stimulation with comodulated musical stimulation ("musical-electrical TNS"). In a double-blind, placebo-controlled, parallel-group study, we recruited 63 patients with DOC and randomly assigned them to groups receiving gamma, beta, or sham musical-electrical TNS. The stimulation was applied for 40 min on five consecutive days. We measured patients' consciousness before and after the stimulation using behavioral indicators and neural responses to rhythmic auditory speech. We further assessed their outcomes one year later. We found that musical-electrical TNS reliably lead to improvements in consciousness and oscillatory brain activity at the stimulation frequency: 43.5 % of patients in the gamma group and 25 % of patients in the beta group showed an improvement of their diagnosis after being treated with the stimulation. This group of benefitting patients still showed more positive outcomes one year later. Moreover, patients with stronger behavioral benefits showed stronger improvements in oscillatory brain activity. These findings suggest that brain oscillations contribute to consciousness and that musical-electrical TNS may serve as a promising approach to improve consciousness and predict long-term outcomes in patients with DOC.

JBHI Journal 2021 Journal Article

An Attention Based CNN-LSTM Approach for Sleep-Wake Detection With Heterogeneous Sensors

  • Zhenghua Chen
  • Min Wu
  • Wei Cui
  • Chengyu Liu
  • Xiaoli Li

In this article, we propose an attention based convolutional neural network long short-term memory (CNN-LSTM) approach for sleep-wake detection with heterogeneous sensor data, i. e. , acceleration and heart rate variability (HRV). Since the three-dimensional acceleration data was sampled with a high frequency, we firstly design a CNN-LSTM structure to effectively learn latent features from the acceleration. Meanwhile, considering the unique format of the HRV data, some effective features are extracted based on domain knowledge. Next, we design a unified architecture to efficiently merge the features learned by CNN-LSTM approach from the acceleration and the extracted features from the HRV, which enables us to make full use of all the available information from these two heterogeneous sources. Taking into consideration that these two heterogeneous sources may have distinct contributions for the sleep and wake states, we propose an attention network to dynamically adjust the importance of features from the two sources. Real-world experiments have been conducted to verify the effectiveness of the proposed approach for sleep-wake detection. The results demonstrate that the proposed method outperforms all existing approaches for sleep-wake classification. In the evaluation of leave-one-subject-out (LOSO) cross-validation which is more challenging and practical, the proposed method achieves remarkable improvements ranging from 5% to 46% over the benchmark approaches.

IJCAI Conference 2021 Conference Paper

Deep Reinforcement Learning Boosted Partial Domain Adaptation

  • Keyu Wu
  • Min Wu
  • Jianfei Yang
  • Zhenghua Chen
  • Zhengguo Li
  • Xiaoli Li

Domain adaptation is critical for learning transferable features that effectively reduce the distribution difference among domains. In the era of big data, the availability of large-scale labeled datasets motivates partial domain adaptation (PDA) which deals with adaptation from large source domains to small target domains with less number of classes. In the PDA setting, it is crucial to transfer relevant source samples and eliminate irrelevant ones to mitigate negative transfer. In this paper, we propose a deep reinforcement learning based source data selector for PDA, which is capable of eliminating less relevant source samples automatically to boost existing adaptation methods. It determines to either keep or discard the source instances based on their feature representations so that more effective knowledge transfer across domains can be achieved via filtering out irrelevant samples. As a general module, the proposed DRL-based data selector can be integrated into any existing domain adaptation or partial domain adaptation models. Extensive experiments on several benchmark datasets demonstrate the superiority of the proposed DRL-based data selector which leads to state-of-the-art performance for various PDA tasks.

JBHI Journal 2021 Journal Article

Modulation Model of the Photoplethysmography Signal for Vital Sign Extraction

  • Mingliang Chen
  • Qiang Zhu
  • Min Wu
  • Quanzeng Wang

This paper introduces an amplitude and frequency modulation (AM-FM) model to characterize the photoplethysmography (PPG) signal. The model indicates that the PPG signal spectrum contains one dominant frequency component - the heart rate (HR), which is guarded by two weaker frequency components on both sides; the distance from the dominant component to the guard components represents the respiratory rate (RR). Based on this model, an efficient algorithm is proposed to estimate both HR and RR by searching for the dominant frequency component and two guard components. The proposed method is performed in the frequency domain to estimate RR, which is more robust to additive noise than the prior art based on temporal features. Experiments were conducted on two types of PPG signals collected with a contact sensor (an oximeter) and a contactless visible imaging sensor (a color camera), respectively. The PPG signal from the contactless sensor is much noisier than the signal from the contact sensor. The experimental results demonstrate the effectiveness of the proposed algorithm, including under relatively noisy scenarios.

EAAI Journal 2021 Journal Article

Prediction model of burn-through point with fuzzy time series for iron ore sintering process

  • Sheng Du
  • Min Wu
  • Luefeng Chen
  • Witold Pedrycz

Burn-through point (BTP) is an essential parameter in the iron ore sintering process. Operators usually judge whether the current production is stable by monitoring the BTP. It comes with significant application prospects to predict the BTP accurately. A prediction model of the BTP with fuzzy time series is designed in this paper. First, the fuzzy time series prediction method with the Fuzzy C-Means clustering is presented as the core modeling method. A prediction model of the response is constructed to obtain a timely response to the current BTP. The prediction model of the difference is established to estimate the present unmeasurable disturbance on the BTP. Then, a hybrid prediction model is built, which realizes the composition of these two models by an adjustment factor. Finally, a series of experiments is carried out using the raw time series data from an iron and steel plant. The experimental result shows that the designed model has better prediction performance for the BTP than existing models, which is an advantage resulting from the hybrid structure and the fuzzy time series prediction model with the Fuzzy C-Means clustering. This prediction model of the BTP implies the foundation for the stable control of the iron ore sintering process.

JBHI Journal 2021 Journal Article

Prediction of Synthetic Lethal Interactions in Human Cancers Using Multi-View Graph Auto-Encoder

  • Zhifeng Hao
  • Di Wu
  • Yuan Fang
  • Min Wu
  • Ruichu Cai
  • Xiaoli Li

Synthetic lethality (SL) is a very important concept for the development of targeted anticancer drugs. However, experimental methods for SL detection often suffer from various issues like high cost and low consistency across cell lines. Hence, computational methods for predicting novel SLs have recently emerged as complements for wet-lab experiments. In addition, SL data can be represented as a graph where nodes are genes and edges are the SL interactions. It is thus motivated to design advanced graph-based machine learning algorithms for SL prediction. In this paper, we propose a novel SL prediction method using Multi-view Graph Auto-Encoder (SLMGAE). We consider the SL graph as the main view and the graphs from other data sources (e. g. , PPI, GO, etc.) as support views. Multiple Graph Auto-Encoders (GAEs) are implemented to reconstruct the graphs for different views. We further design an attention mechanism, which assigns different weights for support views, to combine all the reconstructed graphs for SL prediction. The overall SLMGAE model is then trained by minimizing both the reconstruction error and prediction error. Experimental results on the SynLethDB dataset show that SLMGAE outperforms state-of-the-arts. The case studies on novel predicted SLs also illustrate the effectiveness of our SLMGAE method.

EAAI Journal 2021 Journal Article

Semi-supervised support vector regression based on data similarity and its application to rock-mechanics parameters estimation

  • Xi Chen
  • Weihua Cao
  • Chao Gan
  • Yasuhiro Ohyama
  • Jinhua She
  • Min Wu

Rock-mechanics parameters such as Young’s modulus and Poisson’s ratio are critical to geomechanical analysis and resource exploration. Because these parameters come from laboratory measurement, they present some characteristics such as insufficient samples and contamination of outliers. In this paper, a novel semi-supervised support vector machine soft sensor is devised considering the characteristics of the parameters. First, it takes into account data similarity and selects labeled data set that are most similar to the continuous unlabeled data set at each iteration to improve estimation performance. Meanwhile, an outlier deletion algorithm is developed for a better similarity comparison. After that, a semi-supervised approach is presented for the estimation of rock-mechanics parameters, it can leverage continuous unlabeled data to train the model dynamically. Finally, the verification of our method is carried out on data set from UCI (University of California, Irvine) and several drilling sites. The results demonstrate that our method outperforms eight well-known methods in estimation accuracy.

IJCAI Conference 2021 Conference Paper

Time-Series Representation Learning via Temporal and Contextual Contrasting

  • Emadeldeen Eldele
  • Mohamed Ragab
  • Zhenghua Chen
  • Min Wu
  • Chee Keong Kwoh
  • Xiaoli Li
  • Cuntai Guan

Learning decent representations from unlabeled time-series data with temporal dynamics is a very challenging task. In this paper, we propose an unsupervised Time-Series representation learning framework via Temporal and Contextual Contrasting (TS-TCC), to learn time-series representation from unlabeled data. First, the raw time-series data are transformed into two different yet correlated views by using weak and strong augmentations. Second, we propose a novel temporal contrasting module to learn robust temporal representations by designing a tough cross-view prediction task. Last, to further learn discriminative representations, we propose a contextual contrasting module built upon the contexts from the temporal contrasting module. It attempts to maximize the similarity among different contexts of the same sample while minimizing similarity among contexts of different samples. Experiments have been carried out on three real-world time-series datasets. The results manifest that training a linear classifier on top of the features learned by our proposed TS-TCC performs comparably with the supervised training. Additionally, our proposed TS-TCC shows high efficiency in few-labeled data and transfer learning scenarios. The code is publicly available at https: //github. com/emadeldeen24/TS-TCC.

AAAI Conference 2021 Conference Paper

Two-Stream Convolution Augmented Transformer for Human Activity Recognition

  • Bing Li
  • Wei Cui
  • Wei Wang
  • Le Zhang
  • Zhenghua Chen
  • Min Wu

Recognition of human activities is an important task due to its far-reaching applications such as healthcare system, context-aware applications, and security monitoring. Recently, WiFi based human activity recognition (HAR) is becoming ubiquitous due to its non-invasiveness. Existing WiFibased HAR methods regard WiFi signals as a temporal sequence of channel state information (CSI), and employ deep sequential models (e. g. , RNN, LSTM) to automatically capture channel-over-time features. Although being remarkably effective, they suffer from two major drawbacks. Firstly, the granularity of a single temporal point is blindly elementary for representing meaningful CSI patterns. Secondly, the timeover-channel features are also important, and could be a natural data augmentation. To address the drawbacks, we propose a novel Two-stream Convolution Augmented Human Activity Transformer (THAT) model. Our model proposes to utilize a two-stream structure to capture both time-over-channel and channel-over-time features, and use the multi-scale convolution augmented transformer to capture range-based patterns. Extensive experiments on four real experiment datasets demonstrate that our model outperforms state-of-the-art models in terms of both effectiveness and efficiency 1.

TCS Journal 2020 Journal Article

A game-based approximate verification of deep neural networks with provable guarantees

  • Min Wu
  • Matthew Wicker
  • Wenjie Ruan
  • Xiaowei Huang
  • Marta Kwiatkowska

Despite the improved accuracy of deep neural networks, the discovery of adversarial examples has raised serious safety concerns. In this paper, we study two variants of pointwise robustness, the maximum safe radius problem, which for a given input sample computes the minimum distance to an adversarial example, and the feature robustness problem, which aims to quantify the robustness of individual features to adversarial perturbations. We demonstrate that, under the assumption of Lipschitz continuity, both problems can be approximated using finite optimisation by discretising the input space, and the approximation has provable guarantees, i. e. , the error is bounded. We then show that the resulting optimisation problems can be reduced to the solution of two-player turn-based games, where the first player selects features and the second perturbs the image within the feature. While the second player aims to minimise the distance to an adversarial example, depending on the optimisation objective the first player can be cooperative or competitive. We employ an anytime approach to solve the games, in the sense of approximating the value of a game by monotonically improving its upper and lower bounds. The Monte Carlo tree search algorithm is applied to compute upper bounds for both games, and the Admissible A⁎ and the Alpha-Beta Pruning algorithms are, respectively, used to compute lower bounds for the maximum safety radius and feature robustness games. When working on the upper bound of the maximum safe radius problem, our tool demonstrates competitive performance against existing adversarial example crafting algorithms. Furthermore, we show how our framework can be deployed to evaluate pointwise robustness of neural networks in safety-critical applications such as traffic sign recognition in self-driving cars.

IJCAI Conference 2019 Conference Paper

Global Robustness Evaluation of Deep Neural Networks with Provable Guarantees for the Hamming Distance

  • Wenjie Ruan
  • Min Wu
  • Youcheng Sun
  • Xiaowei Huang
  • Daniel Kroening
  • Marta Kwiatkowska

Deployment of deep neural networks (DNNs) in safety-critical systems requires provable guarantees for their correct behaviours. We compute the maximal radius of a safe norm ball around a given input, within which there are no adversarial examples for a trained DNN. We define global robustness as an expectation of the maximal safe radius over a test dataset, and develop an algorithm to approximate the global robustness measure by iteratively computing its lower and upper bounds. Our algorithm is the first efficient method for the Hamming (L0) distance, and we hypothesise that this norm is a good proxy for a certain class of physical attacks. The algorithm is anytime, i. e. , it returns intermediate bounds and robustness estimates that are gradually, but strictly, improved as the computation proceeds; tensor-based, i. e. , the computation is conducted over a set of inputs simultaneously to enable efficient GPU computation; and has provable guarantees, i. e. , both the bounds and the robustness estimates can converge to their optimal values. Finally, we demonstrate the utility of our approach by applying the algorithm to a set of challenging problems.

IJCAI Conference 2017 Conference Paper

Learning User Dependencies for Recommendation

  • Yong Liu
  • Peilin Zhao
  • Xin Liu
  • Min Wu
  • Lixin Duan
  • Xiao-li Li

Social recommender systems exploit users' social relationships to improve recommendation accuracy. Intuitively, a user tends to trust different people regarding with different scenarios. Therefore, one main challenge of social recommendation is to exploit the most appropriate dependencies between users for a given recommendation task. Previous social recommendation methods are usually developed based on pre-defined user dependencies. Thus, they may not be optimal for a specific recommendation task. In this paper, we propose a novel recommendation method, named probabilistic relational matrix factorization (PRMF), which can automatically learn the dependencies between users to improve recommendation accuracy. In PRMF, users' latent features are assumed to follow a matrix variate normal (MVN) distribution. Both positive and negative user dependencies can be modeled by the row precision matrix of the MVN distribution. Moreover, we also propose an alternating optimization algorithm to solve the optimization problem of PRMF. Extensive experiments on four real datasets have been performed to demonstrate the effectiveness of the proposed PRMF model.

EAAI Journal 2016 Journal Article

Modeling of complex industrial process based on active semi-supervised clustering

  • Qi Lei
  • Huiping Yu
  • Min Wu
  • Jinhua She

Since industrial processes have a wide range of operating conditions, it is difficult to build a single global model that describes a process. One solution that is widely used in control engineering practice is to combine multiple models based on collected process data. For this approach to be successful, it is important to cluster the data before the modeling. In this study, pairwise constraints and an active-learning method were incorporated into the affinity propagation algorithm, resulting in a new method called active semi-supervised affinity propagation (ASSAP) clustering. To apply ASSAP to the modeling of industrial processes, an active-learning strategy is firstly used to obtain constraints on data based on the angle of change between two data points and the probability of their belonging to the same class, and then the constraints are used to adjust the clustering process so as to improve the clustering precision. Finally, the least-squares-support-vector-machine (LS-SVM) is used to build a submodel for each cluster of data points, and then all the sub-models are integrated into a model for the whole data set. Verification of the ASSAP method was carried out on data from the UCI (University of California, Irvine) Machine Learning Repository and Olivetti dataset. In addition, ASSAP and LS-SVM are combined to be applied to the data of the combustion process of a coke oven. The result shows the effectiveness of the method of modeling of complex industrial process based on ASSAP.

EAAI Journal 2015 Journal Article

Coordinated learning based on time-sharing tracking framework and Gaussian regression for continuous multi-agent systems

  • Xin Chen
  • Penghuan Xie
  • Yong He
  • Min Wu

Applying multi-agent reinforcement learning (MARL) in continuous distributed control system is an attractive issue, because it entitles agents adaptively to construct a cooperative behavior, even if the dynamics of such distributed system is unknown a priori. However the implementation of MARL always suffers from dimension explosion, nonstationary learning, and generalization in continuous systems. This paper presents a continuous coordinated learning algorithm with time-sharing tracking framework (CCL-TT) to deal with these problems, in which the value function is dimension reduced to lighten dimension explosion, the time-sharing tracking framework (TTF) is developed to solve nonstationary learning, and Gaussian regression modeling is applied to realize generalization. With TTF, a macroscopic concurrent learning is set up to meet the requirements of temporal stationary condition in value learning and generalization. Finally the simulation illustrates how CCL-TT realizes cooperative learning without knowledge about the dynamics of the system, even with disturbance.

IROS Conference 2009 Conference Paper

Synthesis of output feedback control for motion planning based on LTL specifications

  • Min Wu
  • Gangfeng Yan
  • Zhiyun Lin
  • Ying Lan

In the paper, we study the motion planning problem of a mobile robot in the plane. The goal is to design output feedback control such that the resulting path of a mobile robot satisfies desired linear temporal logic (LTL) specifications. Our control strategy is divided into a local output feedback control problem and a supervisory control for LTL specifications. For the former one, we design output feedback control laws to ensure that output trajectories either remain in a simplex, or leave the simplex and enter an adjacent simplex in finite time. For the latter, we construct a transition system based on reachability and search for feasible paths that satisfy the LTL specifications. In this way, a piecewise affine output feedback control is obtained to solve the motion planning problem. A simulation result is presented to illustrate our approach.

EAAI Journal 2007 Journal Article

Nonlinear system modeling and robust predictive control based on RBF-ARX model

  • Hui Peng
  • Zi-Jiang Yang
  • Weihua Gui
  • Min Wu
  • Hideo Shioya
  • Kazushi Nakano

An integrated modeling and robust model predictive control (MPC) approach is proposed for a class of nonlinear systems with unknown steady state. First, the nonlinear system is identified off-line by RBF-ARX model possessing linear ARX model structure and state-dependent Gaussian RBF neural network type coefficients. On the basis of the RBF-ARX model, a combination of a local linearization model and a polytopic uncertain linear parameter-varying (LPV) model are built to approximate the present and the future system's nonlinear behavior, respectively. Subsequently, based on the approximate models, a min–max robust MPC algorithm with input constraint is designed for the output-tracking control of the nonlinear system with unknown steady state. The closed-loop stability of the MPC strategy is guaranteed by the use of parameter-dependent Lyapunov function and the feasibility of the linear matrix inequalities (LMIs). Simulation study to a NO x decomposition process illustrates the effectiveness of the modeling and robust MPC approaches proposed in this paper.

EAAI Journal 2001 Journal Article

An expert control system using neural networks for the electrolytic process in zinc hydrometallurgy

  • Min Wu
  • Jin-Hua She
  • Michio Nakano

The final step in zinc hydrometallurgy is the electrolytic process, which involves passing an electrical current through insoluble electrodes to cause the decomposition of an aqueous zinc sulfate electrolyte and the deposition of metallic zinc at the cathode. For the electrolytic process studied, the most important process parameters for control are the concentrations of zinc and sulfuric acid in the electrolyte. This paper describes an expert control system for determining and tracking the optimal concentrations of zinc and sulfuric acid, which uses neural networks, rule models and a single-loop control scheme. The system is now being used to control the electrolytic process in a hydrometallurgical zinc plant. In this paper, the system architecture, which features an expert controller and three single-loop controllers, is first explained. Next, neural networks and rule models are constructed based on the chemical reactions involved, empirical knowledge and statistical data on the process. Then, the expert controller for determining the optimal concentrations is designed using the neural networks and rule models. The three single-loop controllers use the PI algorithm to track the optimal concentrations. Finally, the results of actual runs using the system are presented. They show that the system provides not only high-purity metallic zinc, but also significant economic benefits.