Parallel fractional hot-deck imputation (P-FHDI (Yang et al. 2020)) is a general-purpose, assumption-free tool for handling item nonresponse in big incomplete data by combining the theory of FHDI and parallel computing. FHDI cures multivariate missing data by filling each missing unit with multiple observed values (thus, hot-deck) without resorting to distributional assumptions. P-FHDI can tackle big incomplete data with millions of instances (big-$n$) or 10,000 variables (big-$p$). However, handling ultra incomplete data (i.e., concurrently big-$n$and big-$p$) with tremendous instances and high dimensionality has posed problems to P-FHDI due to excessive memory requirement and execution time. To tackle the aforementioned challenges, we propose the ultra data-oriented P-FHDI (named UP-FHDI) capable of curing ultra incomplete data. In addition to the parallel Jackknife method, this paper enables a computationally efficient ultra data-oriented variance estimation using parallel linearization techniques. Results confirm that UP-FHDI can tackle an ultra dataset with one million instances and 10,000 variables. This paper illustrates the special parallel algorithms of UP-FHDI and confirms its positive impact on the subsequent deep learning performance.

Hearing aid devices have been around for decades, while most of them focus on sound amplification and SNR improvement. This paper proposes an artificial ear based on the vibrotactile feedback. The speech signal is converted into the vibrotactile devices placed around the subject’s ear through the speech recognition algorithm and pattern coding method. Preliminary experiments on the prototype consisting of six motors which has shown that the recognition accuracy of letters and daily sentences reached 90%. The learning time of interpreting the vibrotactile signals could be less than four times that in real-time conversation, proving the feasibility of the proposed device for real-life application.

Though physiological signal based human-machine interfaces (HMIs) have recently developed rapidly, their practical use is restricted by many real-world environmental factors, one of which is muscle fatigue. This paper explores the sensitivities between surface electromyography (sEMG) and A-mode ultrasound (AUS) sensing modalities subject to muscle fatigue in the context of hand gesture recognition tasks. Two metrics, mean classification accuracy ( mCA) and decline rate ( DR), are proposed to evaluate the accuracy and muscle fatigue sensitivity between sEMG and AUS based HMIs. Muscle fatigue inducing experiment was designed and eight subjects were recruited to participate in the experiment. The gesture recognition accuracies of sEMG and AUS under non-fatigue state and fatigue state are compared through Mahalanobis distance based classifier linear discriminant analysis (LDA). In addition, Mahalanobis distance based metrics, repeatability index ( RI) and separability index ( SI), are introduced to evaluate the changes in the feature distribution during muscle fatigue and reveal the cause of the fatigue sensitivity difference between sEMG and AUS signals. The experimental results demonstrate that the fatigue robustness of AUS signal is better than that of sEMG signal. Specifically, with the employment of the LDA classifier trained under non-fatigue state, the testing accuracy of the sEMG signal on the non-fatigue state is 94.96%, while reduce to 68.26% on the fatigue state. The testing accuracy of the AUS signal on the corresponding states is 99.68% and 91.24% respectively. AUS signal attains higher mCA and lower DR, indicating that it has advantages over sEMG signal in terms of both accuracy and muscle fatigue sensitivity. In addition, the RI and RI/SI analysis reveal that before and after muscle fatigue, the consistency of AUS feature distribution is better than that of sEMG. These research outcomes validate that AUS is more tolerant to feature migration caused by muscle fatigue than sEMG.

The fractional hot-deck imputation (FHDI) is a general-purpose, assumption-free imputation method for handling multivariate missing data by filling each missing item with multiple observed values without resorting to artificially created values. The corresponding R package FHDI J. Im, I. Cho, and J. K. Kim, “An R package for fractional hot deck imputation,”R J., vol. 10, no. 1, pp. 140–154, 2018 holds generality and efficiency, but it is not adequate for tackling big incomplete data due to the requirement of excessive memory and long running time. As a first step to tackle big incomplete data by leveraging the FHDI, we developed a new version of a parallel fractional hot-deck imputation (named as P-FHDI) program suitable for curing large incomplete datasets. Results show a favorable speedup when the P-FHDI is applied to big datasets with up to millions of instances or 10,000 of variables. This paper explains the detailed parallel algorithms of the P-FHDI for large instances (big-$n$) or high-dimensionality (big-$p$) datasets and confirms the favorable scalability. The proposed program inherits all the advantages of the serial FHDI and enables a parallel variance estimation, which will benefit a broad audience in science and engineering.

Multi-modal sensory fusion is believed to obtain higher accuracy in gesture recognition. Its difficulty lies in mining discriminative features and fusing features from different modalities. Surface electromyography(sEMG) and ultrasound signals are typical signal modalities in gesture recognition. It is expected that the fusion of them can take advantage of the complementarity of electrophysiological information and muscle morphology information. This paper proposed two kinds of feature fusion method. The one is concatenating the manual designed sEMG and ultrasound features, and the other is a convolutional neural network (CNN) based feature exaction and fusion method for sEMG and ultrasound signals. Eight able-bodied subjects were involved to participate in the experiments. In the experiments, four channels of sEMG and A-mode ultrasound signals corresponding to 20 gestures were collected synchronously to evaluate the proposed method. The experimental results demonstrated that the fusion sEMG-ultrasound feature always outperformed the separate sEMG or ultrasound feature regardless of the feature extraction method, and as for fusion sEMG-ultrasound feature, the CNN based method achieve a high accuracy (97.38±1.49%) in 20 gestures, which surpassed the method of concatenating the manual designed features and applying machine learning algorithm (LDA, KNN, SVM).

In broad engineering fields, missing data is a common issue which often causes undesired bias and sparseness impeding rigorous data analyses. To tackle this problem, many imputation theories have been proposed and widely used. However, prior methods often require distributional assumptions and prior knowledge regarding data which may cause some difficulty for engineering research. Essentially, the fractional hot-deck imputation (FHDI) is an assumption-free imputation method, holding broad applicability in the engineering domains. FHDIs internal parameters and impact on statistical and machine learning methods, however, have been rarely understood. Thus, this study investigates the behavior and impacts of FHDI on prediction methods including generalized additive model, support vector machine, extremely randomized trees, and artificial neural network, for which four practical datasets (appliance energy, air quality, phenotypes, and weather) are used. Results show that FHDI performs better for improving the prediction accuracy compared to a simple naive method which cures missing data using the mean value of attributes, and FHDI has an asymptotically positive effect on prediction accuracy with decreasing response rates. Regarding an optimal setting, 30 to 35 is recommended for the FHDIs internal categorization number while 5 is recommended for the FHDI donors, which is aligned with Rubins recommendation.

Artificial tactile sensation (ATS) is of great importance in diverse fields, especially for amputees to explore and interact with the world. Although prosthesis are dexterous nowadays, lack of tactile sensation is expected to result in a high rejection rate. Electrical stimulation offers the potential of creating ATS to restore tactile sensation. This paper proposed a portable wireless electrotactile stimulator, which can output common square wave (CSW), sine wave (SW) and time-varying pulse width square wave (TPSW), with a superior resolution. A preliminary experiment showed that the amplitude was easy to be distinguished compared to the frequency for all waveforms. The pulse width changing frequency of TPSW was more discernible than that of CSW and SW. Besides, the TPSW felt the most comfortable while the CSW felt the worst. Furthermore, the SW felt better compared with CSW, especially under the low-frequency and high-amplitude condition. Therefore, the method have a potential to alleviate the discomfort of electrotactile stimulation and achieve a smooth sensation.