Ahyoung Choi - Academia.edu (original) (raw)

Papers by Ahyoung Choi

Frontiers in Physiology, 2018

Journal of Healthcare Engineering, 2019

With the advent of smart sensing technology, environmental context and user context is widely dep... more With the advent of smart sensing technology, environmental context and user context is widely deployed by the context awareness middleware developers and application developers. This environment leverages to utilize the abundant resources of information. In this paper, we present the principles of context based physiological signal analysis in a ubiquitous VR environment. Ultimate goal of this work is building the principles of physiological signal analysis with the knowledge of unknown control variables such as environmental condition and user characteristics.

IEEE Access, 2020

This research is about new advances in the application of remote bio-signal monitoring technology... more This research is about new advances in the application of remote bio-signal monitoring technology. An unobtrusive IoT bio-signal measurement system is attached to a bed using a very thin strip sensor, then the user's sleep efficiency and respiration rate can be measured with accuracy similar to that of an existing FDA-approved sleep tracker. In particular, in this study, we propose a ubiquitous central monitoring system that links an existing, personal use, unobtrusive measurement system to cloud-based systems via WiFi transmission. The proposed monitoring system simultaneously collects, stores, and displays the data from multiple devices using a web server as well as PC and mobile platforms such as personal smart devices. In this study, we implemented a system for the real-time transmission and display of data from multiple unobtrusive systems and validated that there were no problems associated with sending and receiving data at distances of 300 km with around a one-second delay. In addition, we evaluated the tele-monitoring system's data processing time, CPU usage, and memory usage as the number of users was increased. Each user transmits an average of 810 bytes of data including information such as user id, time stamp, data for each channel, respiration rate and sleep status. We observed that the average data processing time was 0.15 seconds, average CPU usage was 5.01%, average memory usage was 0.1% assuming 10 users connected simultaneously. These results are expected to be useful in guiding future similar personal, public, and clinical applications of this technology. INDEX TERMS Biomedical monitoring, biomedical telemetry, health information management, Internet of Things, remote monitoring. HANGSIK SHIN (Member, IEEE) received the B.S. and M.S. degrees and the Ph.D. degree in electrical and electronic engineering from the

Proceedings of the 19th International Conference on Information Integration and Web-based Applications & Services, 2017

In 2015, the Korean government launched a major software education initiative. The urgency to ral... more In 2015, the Korean government launched a major software education initiative. The urgency to rally the nation around the 4th Industrial Revolution is the driving force. It consists of two major components. One is to enhance software (computer science) education in universities, and another is to make coding education mandatory in elementary and middle schools. The Korean Ministry of Science and ICT (MSIT) launched National Programs of Excellence in Software to innovate and expand software education in universities. The Ministry of Education, in collaboration with the MSIT, has required all middle schools and elementary schools to include mandatory coding courses, starting in 2018 and 2019, respectively, and started training teachers. In this article, we will discuss the background of the MSIT software initiative, and software education innovation by the Gachon University National Program of Excellence in Software. We will also briefly discuss the looming mandatory coding education ...

Mixed Reality (MR) is defined as the merging of real and virtual worlds on virtuality continuum [... more Mixed Reality (MR) is defined as the merging of real and virtual worlds on virtuality continuum [1], also shown in Figure 1. In other words, it includes Augmented Reality (AR) and Augmented Virtuality where real and virtual objects co-exist and interact in real time. MR contents are necessary elements to build Mixed Reality applications and real and virtual world information should be synchronized and co-exist or connected in the both world.

There is a tradeoff between user’s privacy and utility of context-aware services in ubiquitous co... more There is a tradeoff between user’s privacy and utility of context-aware services in ubiquitous computing environments. Many privacy models have been proposed to support the disclosure of personal information at different levels of detail, in ubiquitous computing environments. However, most of these models do not allow for explicit criteria to assess the benefit users are likely to reap by disclosing their personal information. In this paper, we propose an automated decision making mechanism that evaluates the “benefit of disclosure” for the users based on trust relationships between users and information requesters and manages the disclosure of user’s personal information accordingly. Unlike other trust models, we do not regard the reputation of an information requester as sufficient to determine his/her trustworthiness. Instead, we represent trustworthiness as a function of information requester’s reputation in the eyes of the user and his/her competence in a given context. To vali...

J. Univers. Comput. Sci., 2018

Recently, many studies have been conducted on how to manage and analyze various types of health d... more Recently, many studies have been conducted on how to manage and analyze various types of health data such as clinical data, genomic data, and wirelessly collected multiple sensory data. In this paper, we propose a web-based healthcare data integration and management platform that collects heterogeneous types of health-related medical record as well as real-time lifelogging data. This platform provides flexible architecture to different types of data exchanges. The platform manages real-time data such as heart rate, blood pressure, and activity information extracted from various healthcare devices and provides functions to transmit them to the server. Then it analyses the risk based on a domain knowledge and individual differences by applying machine learning tools, then visualizes the result to the patient and doctor dynamically based on information simplification method. It also controls the data access authority concerning the level of expertise and role. For evaluation of integra...

ˇˇWith the advent of light-weight daily physiological signal monitoring sensors, intelligent infe... more ˇˇWith the advent of light-weight daily physiological signal monitoring sensors, intelligent inference and analysis method for physiological signal monitoring application, commercialized products and services are released. However, practical constraints still remain for daily physiological signal monitoring. Most devices provide rough health check function and analyze with randomly sampled measurements. In this work, we propose the probabilistic modeling of physiological signal analysis. This model represent the relationship between previous user measurement (history), other group`s type, model and current observation. From the experiment, we found that the personalized analysis with long term regular data shows reliable result and reduces the analyzing errors. In addition, participants agree that the personalized analysis shows reliable and adaptive information than other standard analysis method. ↲ 핵심어: Physiological signal analysis, Personalized analysis, Context awareness 본 연구는 ...

In this paper, we present a lifelong learning AR agent that provides the customized assistance wi... more In this paper, we present a lifelong learning AR agent that provides the customized assistance with a mobile user at anywhere, anytime, anything. The agent infers a user's characteristics, e.g., preference and personality, based on the context history in environments. It generates the personalized assistance by reflecting the user's characteristics. The agent also shows appropriate responses to environmental conditions where the user actually exists. To show potentials of our agent, we have developed applicable applications how we could apply it to enhance the user's learning experience in smart home environments. Therefore, we expect possibilities for the proposed lifelong learning AR agent to be used as a personalized assistant in edutainment systems 1 . Keywords-lifelong learning AR agent, personalized AR assis- tant, situated assistance augmentation I. INTRODUCTION

2017 International Symposium on Ubiquitous Virtual Reality (ISUVR)

In this work, we proposed a virtual companion based interface that simplifies the smartphone inte... more In this work, we proposed a virtual companion based interface that simplifies the smartphone interface for the elderly. This interface displays menus according to the situation and users' request via a virtual agent and animates information in a 3-dimensional manner. We applied speech recognition technology from mobile and wearable devices to receive input from users. Virtual avatars were selected to visualize appropriate behavior based on user input. We expect that this mobile interface could be a future of next smartphone user interface.

IEEE Access

Typically, the pulse transit time (PTT) is extracted as a discrete value per heartbeat: it is cal... more Typically, the pulse transit time (PTT) is extracted as a discrete value per heartbeat: it is calculated as the time difference between specific points of the pulse waveforms measured at two different sites. However, this is not a perfect representation because a pulse wave propagates continuously. In this study, we propose a method to determine the continuous PTT (CPTT) by calculating consecutive time delays of photoplethysmography (PPG) waveforms measured at the fingers and toes of 14 young, healthy volunteers. The proposed CPTT is calculated as the average time delay determined by moving the segmented PPGs and has a correlation of 0.744 with conventional PTT. In addition, the proposed CPTT showed a-0.712 correlation coefficient (P < 0.001) with the continuous pulse-wave velocity derived from the continuous blood pressure waveform. These results suggest that the proposed CPTT is a promising indicator for pulse-wave velocity estimation. INDEX TERMS Blood pressure, photoplethysmography, pulse transit time, pulse-wave velocity.

Sensors

Recently, studies that analyze emotions based on physiological signals, such as electroencephalog... more Recently, studies that analyze emotions based on physiological signals, such as electroencephalogram (EEG), by applying a deep learning algorithm have been actively conducted. However, the study of sequence modeling considering the change of emotional signals over time has not been fully investigated. To consider long-term interaction of emotion, in this study, we propose a long short-term memory network to consider changes in emotion over time and apply an attention mechanism to assign weights to the emotional states appearing at specific moments based on the peak–end rule in psychology. We used 32-channel EEG data from the DEAP database. Two-level (low and high) and three-level (low, middle, and high) classification experiments were performed on the valence and arousal emotion models. The results show accuracies of 90.1% and 87.9% using the two-level classification for the valence and arousal models with four-fold cross validation, respectively. In the case of the three-level clas...

Physiological Measurement

In his Comment, Hejjel argued that some contents previously published by us were inappropriate fo... more In his Comment, Hejjel argued that some contents previously published by us were inappropriate for the statistical analysis of pulse rate variability due to high inter-individual dispersion. He also claimed that data collection over 5 min for short-term HRV analysis and data collection for an abnormal range of people were required. In order to give our perspective on these issues, we will discuss and clarify some of the existing literature and our own work on this subject, underlining the difference between electrocardiogram and photoplethysmogram.

2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2015

Quantification of energy storage is essential in understanding energy balance and can be determin... more Quantification of energy storage is essential in understanding energy balance and can be determined by bioelectrical impedance analysis (BIA). Here, we have developed a smartphone form factor multi-frequency BIA device that incorporates an analog front end for body composition measurements. The device was compared against a reference gel-electrode based BIA system in a clinical trial of 311 subjects for predicting BIA equations by calibrating the impedance index to body composition data from dual energy X-ray absorptiometry (DXA). Strong correlations were observed between DXA-based lean soft tissue and the impedance index generated at 50 KHz (R(2)=0.87; p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;;0.001). A similar trend was also evident at higher frequencies which matched results from the reference gel-electrode BIA device. The findings support the role of our consumer-oriented mobile Health initiative for multi-frequency BIA assessments to aid weight management.

IEEE Pulse, 2015

Clinical validation of Samsung's pocket-based bioelectrical impedance analyzers may increase cons... more Clinical validation of Samsung's pocket-based bioelectrical impedance analyzers may increase consumer interest in personal health management.

Sensors, 2015

Current bioelectric impedance analysis (BIA) systems are often large, cumbersome devices which re... more Current bioelectric impedance analysis (BIA) systems are often large, cumbersome devices which require strict electrode placement on the user, thus inhibiting mobile capabilities. In this work, we developed a handheld BIA device that measures impedance from multiple frequencies (5 kHz~200 kHz) with four contact electrodes and evaluated the BIA device against standard body composition analysis systems: a dual-energy X-ray absorptiometry (DXA) system (GE Lunar Prodigy, GE Healthcare, Buckinghamshire, UK) and a whole-body BIA system (InBody S10, InBody, Co. Ltd, Seoul, Korea). In the study, 568 healthy participants, varying widely in body mass index, age, and gender, were recruited at two research centers: the Samsung Medical Center (SMC) in South Korea and the Pennington Biomedical Research Center (PBRC) in the United States. From the measured impedance data, we analyzed individual body fat and skeletal muscle mass by applying linear regression analysis against target reference data.

Journal of the HCI Society of Korea, 2008

Recently researchers have studied mobile physiological sensing device. However, previous works fo... more Recently researchers have studied mobile physiological sensing device. However, previous works focused on multiple and real time physiological sensing method, instead of aesthetic shape of sensing devices, sensing comfort during monitoring and sensing reliability against the hand motion artifact. In this work, we propose a stone shaped physiological sensing device to monitor the physiological status in a daily life which maximize the aesthetic feeling and sensing comfort and sensing reliability. We proposed stepwise user centered design process for user centric physiological sensing device and evaluated appropriate sensing positions against the hand motion artifacts and pressure from sensors. From the usability test and experiments, we verified the proposed sensing device provides the aesthetic appeals, sensing comfort and sensing reliability. We expect that this work can be applied in the various health care applications in near future.

Lecture Notes in Computer Science, 2008

Recently there has been increasing research into mobile physiological sensing devices to explore ... more Recently there has been increasing research into mobile physiological sensing devices to explore the benefits in the areas of monitoring health and well-being. However, previous works have mainly focused on functionality, and less so on affective shape, comfort use, and stable sensing. In this work, we propose a stone-type physiological sensing device for general users, rather than professional experts. We found that our device was comfortable, stable and had aesthetic appeal for users during monitoring. To develop an affective shape, and to increase comfort, we applied a user-centered design process. We also used context-based physiological signal analysis to obtain stable analysis results according to individual users. As an application, we developed a rainbow ambient display to give visual feedback to users. We expect that this product can be applied in various healthcare applications.

Communications in Computer and Information Science, 2009

With the advent of lightweight , high-performance sensing and processing technology, a pervasive ... more With the advent of lightweight , high-performance sensing and processing technology, a pervasive physiological sensing device has been actively studied. However, a pervasive sensing device is easily affected by the external factors and environmental changes such as noise, temperature or weather. In addition, it is hard to deal with the internal factors of a user and personal differences based on physiological characteristics while measuring physiological signal with a pervasive sensing device. To address these issues, we propose a context-based decision making method considering pervasive sensing environments in which it concerns users' age, gender and sensing environments for detecting normal physiological condition of a user. From the research conducted, we found that the context-based physiological signal analysis for multiple users' regular data showed reliable results and reduced errors.