Mental workload assessment is essential for maintaining human health and preventing accidents. Most research on this issue is limited to a single task. However, cross-task assessment is indispensable for extending a pre-trained model to new workload conditions. Because brain dynamics are complex across different tasks, it is difficult to propose efficient human-designed features based on prior knowledge. Therefore, this study proposes a concatenated structure of deep recurrent and 3D convolutional neural networks (R3DCNN) to learn EEG features across different tasks without prior knowledge. First, this study adds frequency and time dimensions to EEG topographic maps based on a Morlet wavelet transformation. Then, R3DCNN is proposed to simultaneously learn EEG features from the spatial, spectral and temporal dimensions. The proposed model is validated based on EEG signals collected from twenty subjects. This study employs a binary classification of low and high mental workload across spatial n-back and arithmetic tasks. The results show that the R3DCNN achieves an average accuracy of 88.9%, which is a significant increase compared with that of the state-of-the-art methods. In addition, the visualization of the convolutional layers demonstrates that the deep neural network can extract detailed features. These results indicate that R3DCNN is capable of identifying the mental workload levels for cross-task conditions.

Remaining useful life (RUL) prediction is central to the prognostics and health management (PHM) of lithium-ion batteries. This paper proposes a novel RUL prediction method for lithium-ion batteries based on the Wiener process with measurement error (WPME). First, we use the truncated normal distribution (TND) based modeling approach for the estimated degradation state and obtain an exact and closed-form RUL distribution by simultaneously considering the measurement uncertainty and the distribution of the estimated drift parameter. Then, the traditional maximum likelihood estimation (MLE) method for population based parameters estimation is remedied to improve the estimation efficiency. Additionally, we analyze the relationship between the classic MLE method and the combination of the Bayesian updating algorithm and the expectation maximization algorithm for the real time RUL prediction. Interestingly, it is found that the result of the combination algorithm is equal to the classic MLE method. Inspired by this observation, a heuristic algorithm for the real time parameters updating is presented. Finally, numerical examples and a case study of lithium-ion batteries are provided to substantiate the superiority of the proposed RUL prediction method.

The effectiveness of wireless sensor networks (WSNs) depends on the coverage and target detection probability provided by dynamic deployment, which is usually supported by the virtual force (VF) algorithm. However, in the VF algorithm, the virtual force exerted by stationary sensor nodes will hinder the movement of mobile sensor nodes. Particle swarm optimization (PSO) is introduced as another dynamic deployment algorithm, but in this case the computation time required is the big bottleneck. This paper proposes a dynamic deployment algorithm which is named “virtual force directed co-evolutionary particle swarm optimization” (VFCPSO), since this algorithm combines the co-evolutionary particle swarm optimization (CPSO) with the VF algorithm, whereby the CPSO uses multiple swarms to optimize different components of the solution vectors for dynamic deployment cooperatively and the velocity of each particle is updated according to not only the historical local and global optimal solutions, but also the virtual forces of sensor nodes. Simulation results demonstrate that the proposed VFCPSO is competent for dynamic deployment in WSNs and has better performance with respect to computation time and effectiveness than the VF, PSO and VFPSO algorithms.

Non-intrusive load monitoring (NILM) can monitor the operating state and energy consumption of appliances without deploying sub-meters and is promising to be widely used in residential communities. With the rapid increase of electric loads in amount and type, constructing representative load signatures and designing effective classification models are becoming increasingly crucial for NILM. In this paper, temporal and spectral load signatures that preserve sufficient information are constructed from the monitored energy data. The fusion of these two types of load signatures can provide rich distinguishing features for improving the performance of appliance recognition in NILM. Benefiting from the development of deep learning, this study proposes the two-stream convolutional neural networks (TSCNN) to extract the features from the two types of load signatures and perform classification. Furthermore, this study introduces the affinity propagation clustering strategy to mitigate the negative impact of intra-class variety mainly caused by multi-state loads in appliance recognition. The experimental results on public NILM datasets demonstrate that the proposed method outperforms most of the existing methods based on the voltage-current trajectory or recurrence graph in the recognition accuracy of submetered and aggregated measurements.

People’s mental workload profoundly affects their work efficiency and health. Mental workload assessment can be used to effectively avoid serious accidents caused by excessive mental workload. Both electroencephalogram (EEG) spectral features and its temporal features have proven to be useful in addressing this problem. The fusion of the two types of features can provide rich distinguishing information for improving mental workload assessment. Benefiting from the progress of deep learning, this study proposes the two-stream neural networks (TSNN) for fusing the two types of EEG features. Compared with hand-crafted features, the TSNN can learn and fuse EEG features from the spectral and temporal dimensions automatically without prior knowledge. The TSNN includes a spectral stream and a temporal stream. Each stream consists of a convolutional neural network (CNN) and a temporal convolutional network (TCN) to learn spectral or temporal features from EEG topographic maps. To fuse the learned spectral and temporal information, we concatenate the output of the two streams prior to the fully connected layer. EEG data were collected from 17 subjects who performed n-back tasks with easy, medium and hard difficulty levels, leading to a three-class mental workload classification. The results show that the TSNN achieves an average accuracy of 91.9%, which is a significant improvement over baseline classifiers based on hand-crafted features. The TSNN also outperforms state-of-the-art deep learning methods developed for EEG classification. The results indicate that the proposed structure is promising for fusing spectral and temporal features for mental workload assessment. In addition, it provides a high-precision approach for potential applications during cognitive activities.