• Journal of the Korea Furniture Society
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• v.11 no.1
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• pp.45-51
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• 2000

It was thought that the stiffness of a coated specimen became lower than that of the solid wood because the stiffness of the dried film of coating material is lower than that of the solid wood. The authors were trying to compare the effect of lacquer varnish and rhus lacquer on the resonant frequency of the solid woods for the violin, spruce and maple. Vibration modal shape of coated specimens were same to those of solid woods, but the frequency became lower at each mode as were expected regardless of coat. frequency decrement of coated specimen was getting larger at upper mode in both European violin woods, however, rhus lacquer coated spruce specimens were less affected than lacquer varnish coated specimens.

• The Journal of the Korea Contents Association
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• v.7 no.3
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• pp.60-67
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• 2007

This research studies and analyzes the current trends and the frequency allocation bands for digital cordless phone(DCP) in other country. From these results, we propose 1.7GHz & 2.4GHz as a effective candidate frequency band for domestic DCP. A proposed 1.7GHz is expected to introduce DECT system of Europe. Therefore it is necessary to make an analysis of interference between 1.7GHz band and an adjacent IMT-2000 band. In this paper, we proposed the allocation of channel for 1.7GHz on the basis of the analysis of frequency interference between 1.7GHz band and an adjacent IMT-2000 band.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.4
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• pp.348-351
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• 2007

Recently, Nanotechnology becomes a major issue in most part of industries. Nanotechnology is expected to develop various application products due to nano material mired composites is improved physical and electrical properties compared to conventional composites materials. Dielectric and insulation materials need to develop and improve like other field about nanotechnology. In this paper, we reported dielectric dispersion by size(no filler, $1.2{\mu}m$, 500 nm, 10 nm), frequencies(60, 120, 1 kHz), and temperatures($30{\sim}170^{\circ}C$). Dielectric constant of composites materials with filler shows higher than composites materials without filler and increased depending on rising temperatures in low frequency region. It was the effect that nano-filler and impurities in composites contributed to electrical conductivity. And dielectric properties depending on temperatures shows to change in low frequency region dramatically We analyzed interfacial polarization in low frequency region($10^{-2}$ Hz) and oriented polarization in high frequency region($10^{-5{\sim}6}$ Hz) on composites materials.

• Current Optics and Photonics
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• v.5 no.3
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• pp.213-219
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• 2021

We describe a single-channel rubidium (Rb) radio-frequency atomic magnetometer (RFAM) as a receiver that takes magnetic signal resonating with Zeeman splitting of the ground state of Rb. We optimize the performance of the RFAM by recording the response signal and signal-to-noise ratio (SNR) in various parameters and obtain a noise level of 159 $fT{\sqrt{Hz}}$ around 30 kHz. When a resonant radiofrequency magnetic field with a peak amplitude of 8.0 nT is applied, the bandwidth and signal-to-noise ratio are about 650 Hz and 88 dB, respectively. It is a good agreement that RFAM using alkali atoms is suitable for receiving signals in the very low frequency (VLF) carrier band, ranging from 3 kHz to 30 kHz. This study shows the new capabilities of the RFAM in communications applications based on magnetic signals with the VLF carrier band. Such communication can be expected to expand the communication space by overcoming obstacles through the high magnetic sensitive RFAM.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.2
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• pp.249-254
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• 2021

As the spreading speed of electric vehicles increases rapidly, those are expected to be able to use them as flexible resources in the power system beyond the concern for the supply of its charging power. Especially when the Renewable Energy sources (RES) which have no intrinsic control capability have replaced the synchronous generators more and more, the power system needs to secure the additional frequency control resources to ensure its stability. However, the feasibility of using electric vehicles as the frequency control resources should be analyzed from the perspective of the power system operation and it requires the existing simulation frameworks for the power system. Therefore, this paper proposes the grid connected modeling of the primary frequency control provided by electric vehicles which can be integrated into the existing power system model. In addition, the proposed model is implemented considering technical performances constrained by the characteristics of the Vehicle-Grid Integration (VGI) system so that the simulation results can be accepted by the power utilities operating the power system conservatively.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.3
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• pp.169-177
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• 2014

Operation and control system has been installed and tested to use energy storage system(ESS) for frequency regulation at 4MW class of ESS demonstration facility installed at Jeju island, Korea in 2013. Simulation tests were performed by programing language C# for power system of Jeju island to develop control algorithm. Site simulation tests were performed in control system itself without connecting power system and energy storage system. Control algorithm was coded, modified and tested to load to controller and communication system and human-machine interface were developed and tested in the process of simulation tests. After similar results to that of simulation tests by programing language were obtained, power system and energy storage system demonstration facility were connected to control system by communication system. Energy storage system for frequency regulation was tested for actual frequency and simulation frequency. The site tests showed the similar results to that of simulation tests and the control systems is possible to be operated for frequency regulation. Faster response of energy storage system for frequency regulation, less costs and less capacity of energy storage systems which cover for frequency regulation of power plants. It is expected that more studies for time-reduction and time-delay elements can make less capacity of energy storage system cover more role of frequency regulation of power plants.

• Korean Journal of Community Nutrition
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• v.14 no.5
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• pp.545-555
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• 2009

School foodservice customers are likely to be tired of repeated cycle menus and their satisfaction for meals offered in school is inclined to be low. The menu variety is an important factor in increasing customer satisfaction. The purpose of this study was to investigate customer perspectives for applying rice based bread menus in order to add menu variety and promote using rice processed products in school foodservice. The questionnaire was distributed to 760 parent samples in elementary schools and 520 student samples in middle/high schools and a total of 665 and 387 usable data were collected, respectively. Food habits such as preference for cooking method, menu preference, food allergy and nutritional perspectives for menu and customer perception for rice based bread like quality, reliability, price, and purchasing convenience were investigated using 7 Likert scale. Also expected menu types applying rice based bread and offering frequency of rice bread menu were examined. Preference level for bread-based meals were moderate and students' preferences were slightly higher than parents. Menu types applying rice bread expected by middle/high school students were western food (49.4%), spaghetti (28.4%), set menu (13.7%), noodle (17.6%), Korean food (11.1%), Chinese food (10.9%) and porridge (4.5%). The most occupied rate was once in a week for expected offering frequency. Most respondents perceived that rice bread was more nutritive and qualitative than the wheat based one.

• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.67-72
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• 2019

In this study, we investigate the echo reduction performance of miniaturinzed Helmholtz resonators using smaller than wavelength acoustic metamaterial structures. The Helmholtz resonators are formed using air structures which exhibit large impedance mismatch with the surrounding underwater environment. Using the multi-physics software package, we find that significant reduction in the sonar signature is expected and frequency tailoring is possible by controlling the degree of space coiling and inner volume of the resonators. We find that for the basic Helmholtz resonators, up to 7 dB reduction in echo is expected at 10,000 Hz while when the miniaturized Helmoholtz resonators are used, up to 14 dB reduction in echo is expected at 5,000 Hz. In addition, frequency tailoring is demonstrated by varying the internal volume of the Helmholtz resonators and broadband characteristic is shown using superposition of various degree of space coiled structures. Through this study we investigate the effectiveness of the miniaturized Helmholtz resonators formed using air structures and the echo reduction results show promisses in the application of achieving underwater stealth.

• Journal of Fashion Business
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• v.18 no.1
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• pp.22-36
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• 2014

The purpose of this study is to examine the influence of expected values for appearance management on interest in make-up and cosmetics evaluation criteria. Questionnaires are being administered to 244 college students from the Deagu Metropolitan City and Kyungbook province. The frequency, factor analysis, reliability analysis, regression analysis, and t-test are used for data analysis. Expected values of appearance management are categorized into pleasure/satisfaction, other-expectancy, power value and conformity. Interest in make-up factors are found to be leadership in make-up, others-oriented, and appearance satisfactions. Cosmetics evaluation criteria are categorized into 4 factors such as skin suitability, pursuit of utility, non-essential attributes and symbolism. Pleasure/satisfaction, and conformity are the sub-variables of expected values for appearance management and have significant effects on leadership in make-up and others-oriented sub-variables for interest in make-up. Pleasure/satisfaction, and conformity, being the sub-variables of expected values for appearance management, have significant effects on skin suitability, the sub-variables of cosmetics evaluation criteria. And conformity has significant effects on symbolism, the sub-variables of cosmetics evaluation criteria. This indicates that women show high conformity for expected values of appearance management, leadership in make-up and others-oriented sub-variables for interest in make-up, and skin suitability of cosmetics evaluation criteria.

• Journal of Korea Water Resources Association
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• v.47 no.5
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• pp.447-457
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• 2014

This research focuses on the changes of return period for nonstationary rainfall data in which exceedance or nonexceedance probability varies depending on time. We examined two definitions of return period under nonstationarity and also performed nonstationary frequency analysis using the nonstationary Gumbel model to investigate variations of return period in Korea. Seogwipo, Inje, Jecheon, Gumi, Mungyeong, and Geochang were selected as subject sites of application. These sites have a trend in rainfall data as well as having more than 30 years data. As the results of application, the return periods considering nonstationarity are different with those considering stationarity. The differences of return periods between nonstationarity and stationarity increase as growing return period increases. In addition, the return period using the expected waiting time method shows lower value than that using the expected number of event method.