• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.6
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• pp.21-27
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• 2009

As portable electronic systems being used more often, it becomes a more important issue to lengthen the lifetime of the power battery of the system, for instance, by developing batteries of a higher efficiency. A simple as well as practical method to lengthen the lifetime is to use multiple batteries that are connected in parallel. But in this paper we present a new idea in using multiple batteries, with which the residual energy of the battery can be used in the sense of recycling. The idea is based on a usual phenomenon that a battery cell that has been used until its voltage has dropped below a reference level may still have some residual energy, due to which the voltage can recover when the cell takes a rest for a while. As a practical realization scheme of this idea, a multi-cell configuration method with a cell selection switch is introduced, and its feasibility has been examined by performing experimental observations on the behavior of battery discharge. It has been found that the lifetime of an Alkaline primary battery cell can be lengthened approximately by one or two hours with the proposed method.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.6
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• pp.25-32
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• 2011

This paper proposes high efficiency current-mode DC-DC buck converter that are suitable for portable devices. The current-mode DC-DC buck converter using adjustable Dead-time control method improves the power efficiency 2~5%. The buck converter has been implemented with a standard 0.35${\mu}m$ CMOS process. The size of this chip is 0.97$mm^2$. The input range of the fabricated DC-DC buck converter is 2.5V~3.3V, and the output is 1.8V. The maximum loading current of the converter is 500mA and the peak efficiency is 93% at 200mA loads.

• The Journal of the Convergence on Culture Technology
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• v.6 no.4
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• pp.797-802
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• 2020

Over the past few years, smart devices, including smartphones, have been continuously required by users based on portability. The performance is improving. Ubiquitous computing environment and sensor network are also improved. Due to various network connection technologies, mobile terminals are widely used. Smart terminals need technology to make energy monitoring more detailed for more stable operation during use. The smart terminal which is light in small size generates the power shortage problem due to the various multimedia task among the terminal operation. Various estimation hardwares have been developed to prevent such situation in advance and to operate stable terminals. However, the method and performance of estimating the remaining amount are not relatively good. In this paper, we propose a method for estimating the remaining amount of smart terminals. The Capacity Estimation of lithium ion cells for stable operation was estimated based on machine learning. Learning the characteristics of lithium ion cells in use, not the existing hardware estimation method, through a map learning algorithm using machine learning technique The optimized results are estimated and applied.

• Communications of Mathematical Education
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• v.23 no.3
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• pp.863-885
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• 2009

In the era of wireless internet, we are apt to use a mobile phone for learning mathematics, besides the pc computer and the notebook computer. This study was to investigate the effect of M-learning when students were given a wireless mobile phone in terms of their perspectives towards the use of a mobile phone, achievement and attitudes towards mathematics. They were the 3th grader in a high school, who were expected to take Aptitude Test for the entrance of the university level. The most students who took an ubiquitous environment of M-learning showed it as a benefit for learning mathematics and did not spend time at other activities such as listening to music, sending text-message, playing games, etc, but at the M-learning activities. The students who engaged in the M-learning activities were improved a significantly higher score at Aptitude Test than the students who took the make-up courses in the school and also did a significantly higher disposition towards mathematics which was caused by curiosity among 7 components of the mathematical disposition.

• The KIPS Transactions:PartC
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• v.18C no.4
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• pp.199-206
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• 2011

Removable Storage provides the excellent portability with light weight and small size which fits in one's hand, many users have recently turned attention to the high-capacity products. However, due to the easy of portability for Removable Storage, Removable Storage are frequently lost and stolen and then many problems have been occurred such as the leaking of private information to the public. The advent of remote storage services where data is stored throughout the network, has allowed an increasing number of users to access data. The main data of many users is stored together on remote storage, but this has the problem of disclosure by an unethical administrator or attacker. To solve this problem, the encryption of data stored on the server has become necessary, and a searchable encryption system is needed for efficient retrieval of encrypted data. However, the existing searchable encryption system has the problem of low efficiency of document insert/delete operations and multi-keyword search. In this paper, an efficient searchable encryption system is proposed.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.11
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• pp.47-54
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• 2015

The number of users of SNS such as Twitter and Facebook increases due to the development of internet and the spread of supply of mobile devices such as smart phone. Moreover, there are also an increasing number of content pollution problems that pollute SNS by posting a product advertisement, defamatory comment and adult contents, and so on. This paper proposes an improved method of extracting the feature of content polluter for detecting a content polluter in SNS. In particular, this paper presents a method of extracting the feature of content polluter on the basis of incremental approach that considers only increment in data, not batch processing system of entire data in order to efficiently extract the feature value of new user data at the stage of predicting and classifying a content polluter. And it comparatively assesses whether the proposed method maintains classification accuracy and improves time efficiency in comparison with batch processing method through experiment.

• The Journal of the Korea Contents Association
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• v.21 no.7
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• pp.119-126
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• 2021

Recently OTT video service has grown rapidly and has a negative impact on the growth of pay-TV subscribers. Consequently the substitution of OTT services for pay-TV services will begin. This study explores OTT usage patterns, dividing into three sectors (OTT service use, OTT usage volume, and paid-OTT service use), by considering users' demographice factors, smart device ownership, pay-TV subscription, and bundle service use, by employing the Mediapanel dataset. The results showed that age, income, smartTV usage, market size, cable/satellite subscribers, TV VOD expenses, movie VOD expenses, and mobile bundle use are associated with OTT service use. The results also showed that age, household sizes, tablePC usgage, cable/satellite subscribers, TV VOD expenses, other VOD expenses, and unlimited data plans are associated with OTT usage volume. Lastly the results showed that age, gender, income, tabletPC usage, cable subscribers, other VOD expenses, mobile bundle usage, and unlimited data plans are associated with paid-OTT service use.

• Journal of the Institute of Convergence Signal Processing
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• v.22 no.1
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• pp.20-29
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• 2021

This study developed a smartwatch and a wind speed system in accordance with the necessity of a device that provides the information required in marine leisure. Based on a marine leisure smartwatch with a multi-sensor, a gyro box, and a wind speed system, external data such as GPS, motion, humidity, temperature, air pressure, and heart rate can be collected. In addition, the collected external environment data can be managed through an application on a smartphone, which is an Android-based mobile device. The developed smartwatch and wind speed system are expected to contribute to increasing accessibility and revitalization of the marine leisure industry. In addition, in terms of safety and education, the need for a device that provides marine information is large, so it is expected to increase the possibility of entering the high value-added market and improve the product localization rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2442-2450
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• 2010

Using sensor devices applied to various objects will be needed wireless network that it is easy to install in them. Tiny devices configured to processor that bas comparatively low computing ability are inappropriate to use devices that are wireless LAN, etc. In result, network devices needed to not only have simple communication protocol, but have Plug and Play function that it works as soon as it connects without installing any device driver. it also will industrially have both low power and low cost because of mobility of it. From IEEE 802.11 standard, WPAN(Wireless Personal Area Network) included in LAN is being developed by WPAN WG(Working Group) on area with low power consumption and low complexity. In addition to, it is standardizing MAC and PRY of the standard that is expected to wirelessly communicate within 10m. WPAN will be used generally in the more near future because of both low power and low cost of Zigbee. In this paper we designed zigbee based user authentication module for a automotive smart-key system.

• Journal of the HCI Society of Korea
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• v.11 no.3
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• pp.23-30
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• 2016

The landscape of the current fitness trackers is not only limited to the aerobic exercises but also the weight training is comparatively excluded. Recently, a few weight training fitness tracker was released, human-computer interaction was not well designed due to the lack of considering the context. Because body movement would be intense while doing exercises, having exercise performers hold or operate a device makes a negative experience. As the wearable device is always inseparable to body, it could provide effective feedback because holding or operating a device is not necessary. Therefore, this study aims to make the exercise performers feel a natural feedback through the wearable device to do effective exercises. As a result, this study identified three findings. First, the information which exercise performers most needed was 'during exercise.' and the most necessary information for exercise performers through wearable device's sensory feedback was about 'pace control' with counting and motivation. Second, the order of the most preferred presentation type of sensory feedback was auditory feedback, haptic feedback and visual feedback. Third, the satisfaction, utility, usefulness score of sensory feedback as same as the personal trainer's feedback. In conclusion, this study illustrated the feedback design implications using a wearable device while doing weight training and the possibilities that wearable device could be substitute for personal trainer.