• IE interfaces
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• v.13 no.4
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• pp.694-702
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• 2000

For the graceful transition from the analog to digital TV systems, a systematic frequency assignment scheme must be incorporated into the transition planning procedure. In this study, we have studied the frequency assignment methodology for the efficient management of the limited spectrum resources. By applying the graph-theoretic approach, this study developed a new solution method for additional frequency assignment problem whose objective is to assign available frequencies for newly generated requirements (digital TV stations) with minimum reassignment of the preassigned frequencies to LPTV stations while meeting the interference-related constraints. The proposed algorithm can be effectively applied not only to the current digital TV introduction phase but also to the development phase with some further development. This study can be utilized as the basis for the future study on frequency assignments that aims at graceful transition from analog TV to digital TV.

• Journal of the Korean Society of Physical Medicine
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• v.13 no.4
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• pp.67-74
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• 2018

PURPOSE: This study was conducted to investigate the effects of vibration frequency and amplitude on scapular winging during the knee push-up plus exercise. METHODS: A total of 26 female subjects with scapular winging were evaluated while performing the knee push-up plus exercise with no vibration, low-frequency/low-amplitude (5 Hz/3 mm) vibration, low-frequency/high-amplitude (5 Hz/9 mm) vibration, high-frequency/low-amplitude (15 Hz/3 mm) vibration, and high-frequency/high-amplitude (15 Hz/9 mm) vibration. The surface EMG of the serratus anterior (SA) muscle was compared between the vibration frequency and amplitude. The EMG amplitude was normalized using the maximal voluntary isometric contraction (MVIC). The statistical significance of the results was evaluated using one-way ANOVA. RESULTS: The SA muscle EMG values increased at low-frequency/low-amplitude vibration and at low-frequency/high-amplitude vibration compared to no vibration. Furthermore, the same values increased at high-frequency/low-amplitude vibration and high-frequency/high-amplitude vibration compared to no vibration. In general, a higher vibration frequency and amplitude was associated with higher EMG values of the SA muscle, with particularly greater increases observed during high-frequency/high-amplitude vibration. There was also a significant difference between each condition with a high-frequency/high-amplitude vibration (p<.05). CONCLUSION: This study suggests that there were remarkable clinical effect of the knee push-up plus exercise with vibration, which enhanced the SA muscle activation in persons with scapular winging. Furthermore, applying a higher vibration frequency and amplitude more effectively increased for increasing SA muscle activation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.7
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• pp.978-983
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• 2015

This paper presents Frequency Bias setting for the adequate AGC(Automatic Generator Control) operation based on the frequency response of power system in Korea. AGC frequency control recovers the frequency up to 60Hz following a primary control when the frequency suddenly drops due to a fault in power system. AGC can compensate an appropriate amount of generation by calculating ACE(Are Control Error) from the frequency deviation with the AGC frequency bias set from the actual frequency response in power systems. An appropriateness of the proposed AGC bias setting is verified through case studies employing the simulation model.

• Korean Journal of Applied Biomechanics
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• v.32 no.4
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• pp.141-146
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• 2022

Objective: The purpose of this study was to investigate the effects of different frequency on muscle function of the thigh in patients with degenerative knee arthritis during the functional electrical stimulation (FES). Method: For this study, 16 male participants over 65 who patients with degenerative knee arthritis were recruited as research participants. In this research, isokinetic muscular function, EMG, and joint position sensation were performed after FES treatment was applied for three conditions (FES 20, FES 50, and Without FES). For each dependent variable, one-way ANOVA with repeated measures was to determine whether there were significant differences among three different conditions (p<.05). When a significant difference was found, post hoc analyses were performed by using the contrast procedure. Results: When compared to FES 50 and without FES, FES 20 causes significant increase in isometric knee extension strength. No significant differences were found in EMG values across different EMS conditions. Conclusion: The present study examined isokinetic muscular function, EMG, and joint position sensation in order to investigate the effects of different frequency muscle function of knee extensors during the functional electrical stimulation. The results of this study showed that FES with 20 Hz frequency had positive effect on knee extensor. Based on the findings of the present study, FES with lower frequency may help the performer to focus on developing strength in knee extensor muscles.

• Journal of Environmental Health Sciences
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• v.45 no.6
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• pp.583-593
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• 2019

Objectives: The purpose of this study was to evaluate the relationship between the frequency score of wearing personal protective equipment (PPE) and concentration of urinary organophosphorus pesticide metabolites in farmers. Methods: The study was conducted in Chungcheongnam-do Province of South Korea. We collected urine samples from 308 farmers from September to December 2017 and May to July 2018. Among them, 17 farmers with urinary creatinine levels outside the normal range were excluded. Information on the frequency of wearing PPE was obtained from the farmers through face-to-face survey. Each frequency of wearing for seven types of PPE was converted into a score and expressed as a total score, which was divided into quartiles. Four types of urinary organophosphorus pesticide metabolites were analyzed using a gas chromatography mass selective detector. Multiple linear regression analysis was used to identify concentrations of urinary organophosphorus pesticide metabolites affected by the frequency of wearing PPE. Results: The average frequency score of wearing PPE was 8.0. The quartiles of frequency score of wearing PPE were divided as follows: 1st quartile (≤1), 2nd quartile (1-6), 3rd quartile (6-12), and 4th quartile (>12). Compared with subjects with a low frequency score of wearing PPE (reference), subjects with a high frequency score of wearing PPE (4th quartile) had lower concentrations of urinary diethyl phosphate (DEP) (p<0.01) and dialkyl phosphate (ΣDAP) (p<0.05), which is the sum of dimethyl phosphate (DMP), DEP, dimethyl thiophosphate (DMTP), and diethyl thiophosphate (DETP). Conclusion: Concentrations of urinary organophosphorus pesticide metabolites were associated with frequency score of wearing PPE. Particularly as the frequency score of wearing PPE increased, concentrations of urinary DMP, DEP, DETP, and ΣDAP significantly decreased. The findings of this study can contribute to the management of health effects among farmers working with pesticides.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.3
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• pp.355-363
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• 2024

Time synchronization is crucial for ensuring the reliable operation of modern economic and social infrastructures. Techniques such as Global Navigation Satellite System (GNSS)-based methods and Two-Way Satellite Time and Frequency Transfer (TWSTFT) play key roles in precise time comparison and synchronization. TWSTFT, in particular, is recognized for its ability to achieve sub-nanosecond accuracy in time transfer, making it indispensable in fields such as satellite navigation. This paper proposes a comprehensive performance evaluation method for TWSTFT modems, emphasizing pre-validation in controlled environments to mitigate operational challenges. Using the proposed evaluation method, the study presents the standard deviation of RTT according to C/N₀ and compares it with the datasheet of a commercial TWSTFT modem. Through this approach, the aim of this study is to enhance the reliability and accuracy of TWSTFT-based time synchronization across diverse applications.

• Journal of Acupuncture Research
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• v.18 no.1
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• pp.76-87
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• 2001

Objective : Zusanli(ST36) and Hoku(Li4) are analgesic acupuncture points frequently used for acupuncture in Oriental medicine. The present study was conducted to see the antinociceptive effects produced by electroacupuncture combined two frequencies(Low, High) and two different acupuncture points(LI4, ST36) in the rat tail flick test. Method : In this study the Rats (Sprague-Dawley, 250-300g) were partially anesthetized with thiopental sodium(40mg/kg, i.p.). The basal reaction time for the tail-flick was 3${\pm}$0.5 sec. Low frequency(3Hz, 5V, biphasic) and high frequency(100Hz, 5V, biphasic) were applied to the inserted needle for the period of insertion(twenty minutes). Experimental groups are divied as follow; a) electroacupuncture stimulation groups at Hoku with or high frequency(L-EA, H-EA), b) electroacupuncture stimulation groups at Zusanli with low or high frequency(1-EA, h-EA), c) low frequency at Hoku and Zusanli(LIEA), d) low frequency at Hoku and high frequency at Zusanli(LhEA), e) high frequency at Hoku and low frequency at Zusanli(HIEA), f) high frequency at Hoku and Zusanli(HhEA) Results : The individual stimulation at either Hoku or Zusanli with low frequency has stronger and longer analgesic effect than high frequency stimulation. In addition, the combined stimulation at Hoku and Zusanli with low frequency has superior effect to individual stimulation with low frequency. LhEA and LIEA have superior effect to other stimulation groups among the combined groups. In order to determine the involvement of opioid system on the different antinociceptive effects, Naloxone, an opioid antagonist, was used in the combined groups. LIEA is the most sensitive when naloxone was administrated among study groups. HhEA is the least sensitive in the administration of naloxone. Conclusion : From results, this study confirmed that the opioid system is involved in analgesic effect of low frequency stimulation of acupuncture point, and we also can suggest the stronger analgesic effect of combining stimulation points is due to the theory of spatial summation in the nervous system.

• Journal of Animal Science and Technology
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• v.65 no.1
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• pp.244-257
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• 2023

The study aimed to investigate the effect of low-frequency oscillations on the cow udder, milk parameters, and animal welfare during the automated milking process. The study's objective was to investigate the impact of low-frequency oscillations on the udder and teats' blood circulation by creating a mathematical model of mammary glands, using milkers and vibrators to analyze the theoretical dynamics of oscillations. The mechanical vibration device developed and tested in the study was mounted on a DeLaval automatic milking machine, which excited the udder with low-frequency oscillations, allowing the analysis of input parameters (temperature, oscillation amplitude) and using feedback data, changing the device parameters such as vibration frequency and duration. The experimental study was performed using an artificial cow's udder model with and without milk and a DeLaval milking machine, exciting the model with low-frequency harmonic oscillations (frequency range 15-60 Hz, vibration amplitude 2-5 mm). The investigation in vitro applying low-frequency of the vibration system's first-order frequencies in lateral (X) direction showed the low-frequency values of 23.5-26.5 Hz (effective frequency of the simulation analysis was 25.0 Hz). The tested values of the first-order frequency of the vibration system in the vertical (Y) direction were 37.5-41.5 Hz (effective frequency of the simulation analysis was 41.0 Hz), with higher amplitude and lower vibration damping. During in vivo experiments, while milking, the vibrator was inducing mechanical milking-similar vibrations in the udder. The vibrations were spreading to the entire udder and caused physiotherapeutic effects such as activated physiological processes and increased udder base temperature by 0.57℃ (p < 0.001), thus increasing blood flow in the udder. Used low-frequency vibrations did not significantly affect milk yield, milk composition, milk quality indicators, and animal welfare. The investigation results showed that applying low-frequency vibration on a cow udder during automatic milking is a non-invasive, efficient method to stimulate blood circulation in the udder and improve teat and udder health without changing milk quality and production. Further studies will be carried out in the following research phase on clinical and subclinical mastitis cows.

• Proceedings of the KSPS conference
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• 2006.11a
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• pp.99-108
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• 2006

Three experiments were conducted to determine the exact locus of the frequency effect in speech production. In Experiment 1. a picture naming task was used to replicate whether the word frequency effect is due to the processes involved in lexical access or not. The robust word frequency effect of 31ms was obtained. The question to be addressed in Experiment 2 is whether the word frequency effect is originated from the level where a lemma is selected. To the end, using a picture-word interference task, the significance of interactions between the effects of target frequency, distractor frequency and semantic relatedness were tested. Interaction between the distractor frequency and semantic relatedness variables was significant. And interaction between the target and distractor frequency variables showed a significant tendency. In addition, the results of Experiment 2 suggest that the mechanism underlying the word frequency effect is encoded as different resting activation level of lemmas. Experiment 3 explored whether the word frequency effect is attributed to the lexeme level where phonological information of words is represented or not. A methodological logic applied to Experiment 3 was the same as to Experiment 2. Any interaction was not significant. In conclusion, the present study obtained the evidence supporting two assumptions: (a) the locus of the word frequency effect exists in the processes involved in lemma selection, (b) the mechanism for the word frequency effect is encoded as different resting activation level of lemmas. In order to explain the word frequency effect obtained in this study, the core assumptions of current production models need to be modified.

• Journal of Korean Library and Information Science Society
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• v.44 no.1
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• pp.27-47
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• 2013

This study investigated the classification performance of a kNN classifier using the feature selection methods based on document frequency(DF) and collection frequency(CF). The results of the experiments, which used HKIB-20000 data, were as follows. First, the feature selection methods that used high-frequency terms and removed low-frequency terms by the CF criterion achieved better classification performance than those using the DF criterion. Second, neither DF nor CF methods performed well when low-frequency terms were selected first in the feature selection process. Last, combining CF and DF criteria did not result in better classification performance than using the single feature selection criterion of DF or CF.