• Earthquakes and Structures
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• 제3권2호
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• pp.169-180
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• 2012

The performance of pure friction isolation system with respect to the frequency bandwidth of excitation and the predominant frequency is investigated. A set of earthquake ground motions (artificial as well as recorded [with different combinations of magnitude-distance and local site geology]) is considered for investigating effectiveness of pure friction isolators. The results indicate the performance of pure friction base isolated system does not only depend upon coefficient of friction and mass ratio but the stick-slip behaviour depends upon the frequency content of the excitation as well. Slippage prevails if the excitation frequency lies in a suitable frequency range. This range widens with increasing mass ratio. For larger mass ratios, the sliding effect is more pronounced and the maximum acceleration response is further reduced in the neighbourhood of frequency ratio (${\omega}/{\omega}_n$) of unity. The pure friction isolation system is effective in the case of broadband excitations only and that too, in the acceleration sensitive range of periods. The pure friction system is not effective for protection against narrow band motions for which the system response is quasi-periodic.

• 제어로봇시스템학회논문지
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• 제14권12호
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• pp.1232-1237
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• 2008

This paper introduces an application of wavelet analysis to the sensor fusion of GPS/INS/baroaltimeter. Using wavelet analysis the baro-inertial altitude is decomposed into the low frequency content and the high frequency content. The high frequency components, 'details', represent the perturbed altitude change from the long time trend. GPS altitude is also broken down by a wavelet decomposition. The low frequency components, 'approximations', of the decomposed signal address the long-term trend of altitude. It is proposed that the final altitude be determined as the sum of both the details of the baro-inertial altitude and the approximations of GPS altitude. Then the final altitude exclude long-term baro-inertial errors and short-term GPS errors. Finally, it is shown from the test results that the proposed method produces continuous and sensitive altitude successfully.

• Structural Engineering and Mechanics
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• 제3권5호
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• pp.497-509
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• 1995

Effectiveness of multiple tuned mass dampers (MTMD) in suppressing the dynamic response of base excited structure for first mode vibration is investigated. The effectiveness of the MTMD is expressed by the ratio of the root mean square (RMS) displacement of the structure with MTMD to corresponding displacement without MTMD. The frequency content of base excitation is modelled as a broad-band stationary random process. The MTMD's with uniformly distributed natural frequencies are considered for this purpose. A parametric study is conducted to investigate the fundamental characteristics of the MTMD's and the effect of important parameters on the effectiveness of the MTMD's. The parameters include: the fundamental characteristics of the MTMD system such as damping, mass ratio, total number of MTMD, tuning frequency ratio, frequency spacing of the dampers and frequency content of the base excitation. It has been shown that MTMD can be more effective and more robust than a single TMD with equal mass and damping ratio.

• Corrosion Science and Technology
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• 제2권2호
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• pp.93-97
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• 2003

Fatigue crack growth test or low alloy steel was performed in high temperature water. Test parameters were dissolved oxygen content. loading frequency and R-ratio ($P_{min}/P_{max}$). Since the sulfur content or the steel was low, there were no environmentally assisted cracks (EAC) in low dissolved oxygen(DO) water. At high DO, the crack growth rate at R = 0.5 tests was much increased due to environmental effects and the crack growth rate depended on loading frequency and maximized at a critical frequency. On the other hand, R = 0.7 test results showed an anomalous decrease of the crack growth rate as much different behavior from the R = 0.5. The main reason of the decrease may be related to the crack tip closure effect. All the data could be qualitatively understood by effects of oxide rupture and anion activity at crack tip.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2022년도 봄 학술논문 발표대회
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• pp.61-62
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• 2022

The unit quantity is an important factor influencing the durability, workability, and quality of concrete. Methods for measuring the unit quantity include a high frequency heating method, a unit volume mass method, a capacitance method, and a microwave method. However, these methods have disadvantages of poor measurement method, time required, and accuracy, and a relatively experimental method compensating for these disadvantages was used to measure the unit quantity using a high frequency main sensor (FDR) capable of simple and fast measurement. In addition, the unit quantity was evaluated by analyzing the measurement data through deep learning.

• 한국멀티미디어학회논문지
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• 제21권10호
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• pp.1221-1235
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• 2018

This study aims to analyze the multicultural content of the Korean Elementary School Textbook revised in 2015. This study abstracted the framework of multicultural factors for analysis of multicultural contents from the research on "Revision Guidelines by Analysis of Multicultural Factors in Secondary Curriculum and Textbook". The analyzed textbook is the integrated winter textbooks for both the first and second grades revised curriculum in 2015. Several findings were represented as follows: first, the frequency of multicultural content displayed five times in first grade and nineteen times in second grade respectively. Second, the analyzed textbooks did not include contents directly associated with multiculturalism. Activities and experience is important in the acceptance of unfamiliar cultures Thus, multicultural contents' frequency of within textbooks is very crucial. Finally, the revised curriculum focused on activities and experiences about the theme and content in the textbook and was developed around block chassis. For teaching the textbook content, teachers must perfectly understand textbooks through teacher training. The textbooks of reflecting right values on multiculturalismIn. this respect, elementary school curriculum and textbook content should be improved by supplementary revision fitting for the growth of humanity in the multicultural era.

• 한국식품영양학회지
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• 제32권6호
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• pp.589-597
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• 2019

In this study, 70 kinds of nutritional composition for five bokkeumbap products(spicy chicken, shrimp(saeu), haemul, nakji, and barbecue bokkeumbap) in high-frequency processed foods were analyzed. Raw data of intake amounts were collected from the 7th Korea National Health and Nutrition Examination Survey. Regarding proximate composition, spicy chicken bokkeumbap had lower water content and higher carbohydrate content than other bokkeumbaps, resulting in the highest total calories. The proximate composition of other bokkeumbaps were all distributed within a similar range. Vitamin content differed according to ingredients added to the bokkeumbaps. Haemul bokkeumbap had high content of vitamins B₁ and B₂, nakji bokkeumbap had high content of vitamin C and β-carotene, and barbecue bokkeumbap had high content of total niacin, folic acid, and vitamin A. For mineral content, barbecue bokkeumbap showed the highest content distribution, while nakji bokkeumbap showed the lowest content distribution. Regarding fatty acid and fat content, the highest content of fatty acids, saturated fats, and trans fats was detected in shrimp(saeu) bokkeumbap. For amino acid content, barbecue bokkeumbap showed highest content distribution. These results can be used as salient basic data for a food nutrient composition database and to significantly contribute to consumers' health.

• 한국지반공학회논문집
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• 제18권6호
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• pp.129-139
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• 2002

최근 지반 특성과 지반 오염도의 조사를 위해 유전상수 측정기법을 적용하기 위한 연구가 활발히 진행되고 있다. 본 연구에서는 다양한 함수비와 건조단위중량을 갖는 화강풍화토와 주문진표준사의 유전상수를 75kHz～12MHz의 주파수 범위에서 측정하였다. 사질토의 유전상수는 주파수가 증가함에 따라 감소하는 분산거동을 보였다. 또한 함수 비나 건조단위중량이 증가함에 따라 배향분극에 기여하는 물분자의 양이 증가하고 유전상수가 1인 공기의 양이 감소하여 유전상수가 증가하였다. 흙의 유전특성은 함수비와 건조단위중량을 모두 고려한 수분밀도에 선형적으로 비례하는 경향을 나타내었다. Maxwell식, Topp식, CRIM식에 의한 계산값과 측정된 값을 비교한 결과 기존의 식은 유전상수의 분산거동을 고려하지 못하고 있기 때문에 저주파에서는 측정값과 차이를 나타내었다.

• Earthquakes and Structures
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• 제8권6호
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• pp.1463-1480
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• 2015

This research aims to develop an empirical model for simulation of time-varying frequency in earthquake ground motion so as to be used easily in engineering applications. Briefly, 10545 recordings of the Next Generation Attenuation (NGA) global database of accelerograms from shallow crustal earthquakes are selected and binned by magnitude, distance and site condition. Then the wavelet spectrum of each acceleration record is calculated by using one-dimensional continuous wavelet transform, and the frequencies corresponding to the maximum values of the wavelet spectrum at a series of sampling time, named predominant frequencies, are extracted to analyze the variation of frequency content of seismic ground motions in time. And the time-variation of the predominant frequencies of 178 magnitude-distance-site bins for different directions are obtained by calculating the mean square root of predominant frequencies within a bin. The exponential trigonometric function is then use to fit the data, which describes the predominant frequency of ground-motion as a function of time with model parameters given in tables for different magnitude, distance, site conditions and direction. Finally, a practical frequency-dependent amplitude envelope function is developed based on the time-varying frequency derived in this paper, which has clear statistical parameters and can emphasize the effect of low-frequency components on later seismic action. The results illustrate that the time-varying predominant frequency can preferably reflect the non-stationarity of the frequency content in earthquake ground motions and that empirical models given in this paper facilitates the simulation of ground motions.

• 한국결정성장학회지
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• 제8권3호
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• pp.396-400
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• 1998

KLN은 성장 결정 내의 $Nb_2O_5$함유량에 따라 물성이 크게 변화하므로 단결정의 조성제어가 매우 중요하다. 본 실험에서는 초기 KLN용액의 $Nb_2O_5$함량을 증가시켜 $Nb_2O_5$함유량이 높은 KLN단결정을 온도요동법과 TSSG법에 의해 성장시키고 성장된 KLN단결정인 $Nb_2O_5$증가량에 따른 격자결함의 유무를 관찰하고자 유전 및 광학 특성을 관찰하다. KLN 단결정 내에 격자결함의 증가에 의해 낮은 에너지로의 단락 frequency 이동과 DPT 특성을 보이는 넓은 Curie 범위가 관찰되었다.