• Wind and Structures
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• 제20권5호
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• pp.661-682
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• 2015

This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent "structures" of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent "events" and the "coherent structure" of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a "modified" complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

• Journal of Biosystems Engineering
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• 제23권1호
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• pp.57-66
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• 1998

This study was conducted to investigate the relationships between parameters affecting internal quality of watermelon and its acoustic characteristics. The measuring and analyzing system was established to study the acoustic characteristics of watermelon. Algorithms for analyzing sound signals were developed. Sound signals which was detected with the microphone were filtered, and their spectrum was computed by means of the Fast Fourier Transform. As watermelon changed from the unripe stage to ripe, acoustic waves in time domain became complicated, and several components appeared in frequency domain. The correlationship was investigated between some parameters affecting internal quality of the watermelon and several peak frequencies. Results indicated that weight, density and sugar content had high correlations with several frequencies(the first peak frequency, the second peak frequency, and the third peak frequency). And the sugar content and the volume of the watermelon were highly correlated with the third peak frequency.

• Journal of Nutrition and Health
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• 제21권4호
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• pp.223-231
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• 1988

This study was disigned to observe the pattern of food preference, desire, and intake frequency of children in Pusan area to establish basic data for school lunch program. The children in a public school with school lunch program in Pusan area, were asked the food preference, desire, and intake frequency of the 30 food items given on questinnarie. The subjects also recorded the food intake for 3 days with the mother's help. The results of this study are summarized as follows. 1) The total numbers of items taken per day per children were increased with advancing grades. The numbers were 27, 33 and food items for 2nd, 4th and 6th grade respectively. 2) The degree of preference, desire and intake frequency were also increased with higher grades for most given foods except cakes, seaweeds and beans. 3) Boys showed the higher intake frequency than girls for most food items. The girls, however, showed higher preference for cakes and cookies than boys. 4) There was a significant positive correlation between food preference and desire, however, a significant correlation was not found between preference and intake frequency, and between intake frequency and desire.

• 음성과학
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• 제8권3호
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• pp.51-73
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• 2001

This study starts with an investigation of the frequency of allophones from the narrowly transcribed data of (1) most frequently used 2000 words and (2) some passages of standard Seoul Korean. Consequently this entails the investigation of the frequency of phonemes by adding the number of allophones. These two investigations are conducted for the first time in the study of Korean phonology. Previous studies on the reported 'frequency of phoneme' are in fact studies on the 'frequency of letters' and the critical difference between these two types of studies has yet to be clarified accurately. This paper also reveals the proportional distribution of natural classes among Korean phonemes and letters.

• 한국환경과학회지
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• 제8권4호
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• pp.431-441
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• 1999

In this study, the regional frequency analysis is used to determine each subbasin drought frequency with reliable monthly precipitation and the L-Moments method which is almost unbiased and has very nearly a normal distribution is used for the parameter estimation of monthly precipitation time series in Nakdong river basin. As the result of this study, the duration of '93-'94 is most severe drought year than any other water year and the drought frequency is established as compared the regional frequency analysis result of cumulative precipitation of 12th duration months in each subbasin with that of 12th duration months in the major drought duration. The Linear regression equation is induced according to linear regression analysis of drought frequency between Nakdong total basin and each subbasin of the same drought duration. Therefore, as the foundation of this study, it can be applied proposed method and procedure of this study to the water budget analysis considering safety standards for the design of impounding facilities large-scale river basin and for this purpose, above all, it is considered that expansion of reliable preciptation data is needed in watershed rainfall station.

• 전력전자학회논문지
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• 제10권5호
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• pp.457-467
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• 2005

본 논문은 해남에서 제주로 연결되어 운전중인 HVDC 시스템의 새로운 주파수 제어기에 대하여 연구하였다. 연구의 첫 번째 목적은 현재의 동기조상기를 제거하기 위하여 새로운 주파수 제어기를 개발하고, 평가를 수행하는 것이다. 모의실험 케이스를 만들기 위하여 PSCAD/EMTDC와 PSS/E를 혼합하여 사용하였고 주 시스템 연구는 과도상태 분석을 위하여 PSCAD/EMTDC을 사용하였다. 연구 케이스는 3상과 1상 지락 그리고 부하탈락에 대한 사고를 모의하였고 연구결과를 나타내었다. 결론적으로 AC 네트워크로부터 검출되는 새로운 주파수 측정 방법은 유효한 주파수 제어와 동적 성능을 나타냄을 알 수 있었다.

• 한국응급구조학회지
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• 제26권1호
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• pp.129-138
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• 2022

Purpose: To analyze the frequency of emergency room visits according to socioeconomic factors of emergency room visitors. Methods: In this study, frequency analysis, percentage analysis, and x² test were performed using the SPSS 23.0 program based on the 2018 data from the Korea Health Panel. Results: Among 1,648 participants included in this study, 1,279 visited the emergency room only once in the past year, while 369 visited the emergency room more than once. The relationship between frequency of emergency room visits and socioeconomic factors was analyzed using x² test, and no statistically significant relationship was noted between emergency room visits and education, economic activity, insurance type, and individual quartile income. However, a significant relationship was noted between emergency room visits and being handicap and living in households with quintile income. Conclusion: The study determined the relationship between frequency of emergency room visits and socioeconomic factors. A follow-up study analyzing socioeconomic factors of outpatient departments, 119 ambulance transport services, and frequency of emergency room visits among chronically ill patients is needed to provide basic data for establishing health policies among different socioeconomic strata.

• 한국운동역학회지
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• 제33권1호
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• pp.17-24
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• 2023

Objective: The purpose of this study was to investigate the effects of different frequency on of knee extensors muscle function during electrical muscle stimulation (EMS). Method: In this research, 40 subjects who have no musculoskeletal disorder, and less than a year workout experience were recruited in order to analyze effects of EMS with different stimulus frequency. Forty subjects were randomly divided into four groups of ten subjects in each group. A EMS training program with different frequencies (without EMS [WE], EMS with frequency 30 Hz [E30], EMS with frequency 60 Hz [E60], EMS with frequency 90 Hz [E90]) was assigned to each group. Throughout eight weeks of training, test subjects were simultaneously carried out knee extension exercises such as squat, leg extension, and leg-press while using EMS with different frequency (20 min, pulse width 250 ㎲, on-off ratio 1:1). Isokinetic knee extension strength, muscle activity of the rectus femoris (RF), the vastus medialis (VM), and the vastus lateralis (VL), and the median frequency of the RF, the VM, and the VL were collected and compared between pre and post training in order to find effects of applying EMS with different frequencies. For each dependent variable, a one-way ANOVA was to determine whether there were significant differences among four different conditions (p<.05). When a significant difference was found, post hoc analyses were performed using the contrast procedure. Results: When compared to WE and E90, E30 causes significant increase in isokinetic knee extension strength. No significant differences were found in EMG values across different EMS conditions. However, the median frequency of the VM in E30 was significantly increased than the corresponding value for WE. Conclusion: The results of this study showed that EMS training with 30 Hz frequency had positive effect on knee extensor. Based of the findings of the present study, EMS training with lower frequency may help the performer to focus on developing strength in knee extensor muscles.

• Journal of Biosystems Engineering
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• 제36권6호
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• pp.476-483
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• 2011

The aerial application using an unmanned helicopter has been already utilized and an attitude controller would be developed to enhance the operational convenience and safety of the operator. For a preliminary study of designing flight controller, a state space model for an RC helicopter would be identified. Frequency sweep flight tests were performed and time history data were acquired in the previous study. In this study, frequency response of the flight test data of a small unmanned helicopter was analyzed by using the CIFER software. The time history flight data consisted of three replications each for collective pitch, aileron, elevator and rudder sweep inputs. A total of 36 frequency responses were obtained for the four control stick inputs and nine outputs including linear velocities and accelerations and angular velocities in 3-axis. The results showed coherence values higher than 0.6 for every primary control inputs and corresponding on-axis outputs for the frequency range from 0.07 to 4 Hz. Also the analysis of conditioned frequency response showed its effectiveness in evaluating cross coupling effects. Based on the results, the dynamic characteristics of the model helicopter can further be analyzed in terms of transfer functions and the undamped natural frequency and damping ratio of each critical mode.

• Human Ecology Research
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• 제56권4호
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• pp.361-375
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• 2018

This study recognizes the changes of the father's role and the importance of family mealtimes as well as examines the individual, family and social contexts surrounding the father's family mealtime. This study analyzed the trend of the father's family mealtime frequency and factors affecting them in order to explore the current conditions of their father's work and family balance through family mealtimes. Data from 492 fathers who have school aged children were collected through an online survey. The overall trend of the frequency of father's family meals showed an average of 2.4 breakfasts and an average of 3.2 dinners per week. The frequency of the father's family meals showed statistically significant differences according to the father's age, children's school age, dual income, weekly working hours, working flexibility, leaving on-time and the priority of work and family. The analysis of hierarchical linear regressions was conducted to determine factors affecting the frequency of father's family mealtime to show that the frequency of father's family mealtime was best explained by father's working conditions and perception variables. Working conditions such as working hours, leaving work on time, working flexibility were significant variables in regards to the father's family mealtime frequency. The father's perception towards parental efficacy, wife's support, and work-family priority were significant factors in regards to the father's family mealtime frequency. This study is meaningful in that it provides basic data on policy making for the compatibility of the father's work and family.