Personalized automatic sleep staging with single-night data: a pilot study with Kullback-Leibler divergence regularization
PHYSIOLOGICAL MEASUREMENT
Authors: Huy Phan; Mikkelsen, Kaare; Chen, Oliver Y.; Koch, Philipp; Mertins, Alfred; Kidmose, Preben; De Vos, Maarten
Abstract
Objective: Brain waves vary between people. This work aims to improve automatic sleep staging for longitudinal sleep monitoring via personalization of algorithms based on individual characteristics extracted from sleep data recorded during the first night.Approach: As data from a single night are very small, thereby making model training difficult, we propose a Kullback-Leibler (KL) divergence regularized transfer learning approach to address this problem. We employ the pretrained SeqSleepNet (i.e. the subject independent model) as a starting point and finetune it with the single-night personalization data to derive the personalized model. This is done by adding the KL divergence between the output of the subject independent model and it of the personalized model to the loss function during finetuning. In effect, KL-divergence regularization prevents the personalized model from overfitting to the single-night data and straying too far away from the subject independent model.Main results: Experimental results on the Sleep-EDF Expanded database consisting of 75 subjects show that sleep staging personalization with single-night data is possible with help of the proposed KL-divergence regularization. On average, we achieve a personalized sleep staging accuracy of 79.6%, a Cohen's kappa of 0.706, a macro F1-score of 73.0%, a sensitivity of 71.8%, and a specificity of 94.2%.Significance: We find both that the approach is robust against overfitting and that it improves the accuracy by 4.5 percentage points compared to the baseline method without personalization and 2.2 percentage points compared to it with personalization but without regularization.
Adsorption mechanisms of crude oil onto polytetrafluoroethylene membrane: Kinetics and isotherm, and strategies for adsorption fouling control
SEPARATION AND PURIFICATION TECHNOLOGY
Authors: Zhang, Bing; Yu, Shuili; Zhu, Youbing; Shen, Yu; Gao, Xu; Shi, Wenxin; Tay, Joo Hwa
Abstract
In this work, a polytetrafluoroethylene (PTFE) membrane was experimentally studied to examine the mechanisms of adsorption fouling of crude oil on the microfiltration membrane. Isotherm and kinetics models were fit to the adsorption data. Scanning electron microscopy-energy dispersive spectroscopy and Fourier-transform infrared spectroscopy were conducted, and the effects of the initial concentration of crude oil, contact time, solution pH, ionic strength, and temperature were examined to understand the adsorption mechanism. Our results revealed that the Temkin model and pseudo-first-order model fit the adsorption data for crude oil on the PTFE membrane well, with R-2 values of > 0.98. The adsorption behavior was physical, as indicated by the value of the heat of adsorption B-T (0.0281c//mol) and Delta H-r(m)theta, (-16.24 kJ/mol). Moreover, the values of Delta H-r(m)theta, (4.21-6.31 kJ/mol), Delta H-r(m)theta (-16.24 kJ/mol), and Delta H-r(m)theta (-0.06981 kl/(mol:10) indicated that the adsorption followed a spontaneous, exo-. thermic, and less random process. Furthermore, the adsorption fouling was mitigated by slowing down the diffusion rate, decreasing the initial concentration of crude oil, reducing the adsorption time, increasing the solution temperature, and maintaining a pH value between 4.0 and 10.0. These results provide theoretical support for mitigating the adsorption fouling of the PTFE membrane during oily wastewater treatment.