• Economic and Environmental Geology
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• v.28 no.5
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• pp.481-485
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• 1995

This paper presents a new approaching method to determine the velocity and geometry of shallow subsurface from seismic refraction events. After picking the first breaks from seismic refraction data, we assume that field refraction seismogram can be replaced by the unit delta function having time shift of first break. Time curves are generated by shooting ray tracing. The partial derivatives seismogram for a damped least squares method is computed analytically at each step of the forward ray tracing. The technique is successfully tested on synthetic and real data. It has the advantage of real full waveform inversion, which is robust at low frequency band even if the initial guess is far from the true model.

• PNF and Movement
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• v.6 no.2
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• pp.11-18
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• 2008

Purpose : The purpose of this study was to identify that the effect of hold-relax and active stretching on recoveries of upper trapezius and sternocleidomastoid muscle fatigue after computer work. Methods : This study was conducted by 30 volunteer at the age of 23~33(resting group=10, hold-relax group=10, active stretching group=10). The muscle fatigue measured by tracing the median frequency(MDF) decrement from power spectrum analyses of EMG signals and the data were analyzed repeated ANOVA. Result : In case of upper trapezius, there was significant difference in group I,II and group II, III. In case of sternocleidomastoid, there was significant difference in group I,II and group I,III. Conclusion : The active stretching was effective for sternocleidomastoid and the hold-relax was effective for upper trapezius and sternocleidomastoid. The hold-relax was effective better than active stretching on recoveries of muscle fatigue.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.525-530
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• 2008

There are a few core technologies to enable high-performance $4^{th}$ generation (4G) broadband wireless communication system. A multiple input multiple output (MIMO) provides high-rate transmission through expended channels by multiple array antennas in both sender and receiver side. Also orthogonal frequency division multiplexing (OFDM) is well-known as the most appropriate technique for high data rate transmission such as Mobile WiMAX and WLAN. Efficient decrease of inter-carrier interference (ISI) and inter-carrier interference (ICI) are the reasons for why OFDM is suitable for high-performance transmission, 4G mobile communication. In this paper, we mainly focus on two of objects, combination between MIMO and OFDM, and OFDM channel simulator using Ray-tracing algorithm. The results of this paper can be used implementation of a Wireless Software Platform for 4G Mobile Communication Systems.

• Child Health Nursing Research
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• v.26 no.4
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• pp.393-401
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• 2020

Purpose: This pilot study aimed to describe children's social contact patterns and to analyze factors related to their social contacts. Methods: The participants were 30 children aged ≥13 months to <7 years, whose teachers at childcare centers and parents at home were asked to maintain diaries of their social contacts prospectively for 24 hours. Data were collected from November 30, 2018, to January 7, 2019. Results: The 30 participating children were in contact with 363 persons in a 24-hours period (mean, 12.1±9.1). The number of contacts showed significant relationships with day of the week (p<.001), number of family members/cohabitants (p=.015), area of residence (p=.003), and type of housing (p=.002). A multiple regression model showed significantly higher numbers of contacts on weekdays (B=10.64, p=.010). Physical versus non-physical types of contact showed significant differences in terms of duration, location, and frequency (p<.001). The duration of contacts showed significant relationships with their location and frequency (p<.001), while the frequency of contacts was significantly related to their location (p<.001). Conclusion: This is the first survey describing the characteristics of Korean preschool children's social contacts. Further large-scale social contact studies of children should be conducted.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2070-2078
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• 2014

In this work, the frequency response of gate-all-around (GAA) Ge/GaAs heterojunction tunneling field-effect transistor (TFET) with hetero-gate-dielectric (HGD) and pnpn channel doping profile has been analysed by technology computer-aided design (TCAD) device-circuit mixed-mode simulations, with comparison studies among ppn, pnpn, and HGD pnpn TFET devices. By recursive tracing of voltage transfer curves (VTCs) of a common-source (CS) amplifier based on the HGD pnpn TFET, the operation point (Q-point) was obtained at $V_{DS}=1V$, where the maximum available output swing was acquired without waveform distortion. The slope of VTC of the amplifier was 9.21 V/V (19.4 dB), which mainly resulted from the ponderable direct-current (DC) characteristics of HGD pnpn TFET. Along with the DC performances, frequency response with a small-signal voltage of 10 mV has been closely investigated in terms of voltage gain ($A_v$), unit-gain frequency ($f_{unity}$), and cut-off frequency ($f_T$). The Ge/GaAs HGD pnpn TFET demonstrated $A_v=19.4dB$, $f_{unity}=10THz$, $f_T=0.487$ THz and $f_{max}=18THz$.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.562-575
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• 2023

In an effort to improve water quality, the South Korean government has implemented measures to increase seawater circulation in Saemangeum Lake. We analyzed the effect of increasing the frequency of seawater circulation based on salinity levels and bottom water exchange in the lake, using an environmental fluid dynamics code model. When the sluice gate opening and shutting frequency increased from once to twice per day, the internal water level of Saemangeum Lake increased by up to ~0.7 m. The salinity increased by 2.12 psu near the western breakwater and decreased by 1.18 psu near the freshwater inlet. We analyzed the extent of bottom water exchange using a particle tracing method and observed that the residual rate of particles shallower than 5 m in water depth decreased by 2.52% in Case 2 (opening and shutting twice per day) compared to Case 1 (opening and shutting once per day). This indicates that increasing the frequency of sluice gate opening and shutting would promote enhanced bottom water exchange. Consequently, the increased salinity and bottom water exchange associated with increased seawater circulation are expected to improve water quality in Saemangeum Lake.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.10
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• pp.901-908
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• 2012

In an intelligent automated manufacturing environment, an administrator may use M2M (Machine-to-Machine) communication to recognize machine movement and the environment, as well as to respond to any potential dangers. However, commonly used wireless protocols for this purpose such WLAN (Wireless Local Area Network), ZigBee, and Bluetooth use the same ISM (Industrial Science Medical) band, and this may cause frequency interference among different devices. Moreover, an administrator is frequently exposed to dangerous conditions as a result of being surrounded by densely distributed moving machines. To address this issue, we propose in this paper to employ a location-based frequency interference management using fingerprinting scheme in industrial environments and its advanced localization schemes based on k-NN (Nearest Neighbor) algorithms. Simulation results indicate that the proposed schemes reduce distance error, frequency interference, and any potential danger may be responded immediately by continuous tracing of the locations.

• Journal of the Korea Society of Computer and Information
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• v.26 no.7
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• pp.57-64
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• 2021

In this paper, we propose and test the efficacy of an easy-to-use user location certification system for public places that relies on frequencies outside the audible range for humans. The inaudible frequencies come in signal frequency between 18-20 kHz and are generated by general audio speaker. After an individual's smart device detects the signal frequency, it sends the frequency value, user's personal ID, and user's location to a system server that certifies the user's visit location currently. The system server then saves a user visit record and categorizes it by individual. To show the usefulness of this proposed system, we developed a user visit certification application for smart devices linked to a system server. We then conducted a user visit certification experiment using the proposed system, with the result showing 99.6% accuracy. For a comparison, we then held a user visit certification experiment using a QR code, which confirmed that our proposed system performs better than QR code location certification. This proposed system can thus provide restaurants and other facilities reliable user contact tracing and electronic visitor access lists in the age of COVID-19.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.1003-1013
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• 2009

In the domestic environments, there are many tunnels since most of terrains have mountains. To ensure the quality of wireless network service in NLOS environment like tunnels which differ from indoor or outdoor wireless channels, researches on wave-propagation characteristics. through such channel are necessary. Especially, in such environment the ground repeater called Gap-Fillers are usually used for satellite mobile services. To make sure that mobile service using satellites in tunnels is available, the research about Gap Filling method is essential. This research is focus on the characterising the wave-propagation through tunnels, to find the appropriate frequency, HPBW of the Gap-Filler antennas, the number of Gap-Fillers, etc. In this paper, we present the effective Gap Filling method in tunnels for ISM band, based on analysis of ray tracing and measurement results.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.578-581
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• 2007

For tracing tag locations, a trajectories should be modeled and indexed in radio frequency identification (RFID) systems. The trajectory of a tag can be represented as a line that connects two spatiotemporal locations captured when the tag enters and leaves the vicinity of a reader. If a tag enters but does not leave a reader, its trajectory is represented only as a point captured at entry. Because the information that the tag stays in the reader is missing from the trajectory represented only as a point, we should extend the region of a query to find the tag that remains in a reader. In this paper, we propose an interval data model of tag's trajectory in order to solve the problem. Trajectories of tags are represented as two kinds of intervals; dynamic intervals which are time-dependent lines and static intervals which are fixed lines. We also show that the interval data model has better performance than others with a cost model