• Journal of the Optical Society of Korea
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• 제16권2호
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• pp.181-184
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• 2012

We report, for the first time, operation frequency dependence of current density-voltage ($J_{OLED}-V_{OLED}$) shift for multi-layer organic light-emitting diodes (OLEDs). When the OLEDs were electrically stressed for 21 hours with 50% duty voltage pulses at 60, 120, 240, and 360 Hz, the JOLED-VOLED shifts were suppressed by half for 360 Hz operation compared with 60 Hz operation, but with little change in emission efficiencies. This frequency dependent $J_{OLED}-V_{OLED}$ shift is believed to be commonly observed for typical multi-layer OLEDs and can be used to further improve lifetime of digitally-driven active-matrix OLED displays.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 A
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• pp.335-337
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• 2003

The protection against transient instability and consequent out-of-step condition is a major concern for the utility. The unstable system may cause serious damage to system elements such as generators and transmission lines. Therefore, out-of-step detection is essential to operate a system safely. This paper presents the Out-of-Step detection algorithm using voltage frequency variation. The digital filters based on Discrete Fourier Transforms (DFT) to calculate the frequency of a sinusoid voltage are used, and the generator angle is estimated using the variation of the calculated voltage frequency. The proposed out-of-step algorithm is based on the assessment of a transient stability using equal area criterion. The proposed out-of-step algorithm is verified and tested by using EMTP MODELS.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2016년도 추계학술대회
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• pp.700-702
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• 2016

나로우주센터에서는 우주발사체의 비행임무 초기구간 동안에 발사체의 거리 및 속도정보를 획득하기 위해서 광학추적장비에 거리측정 도플러 레이더를 탑재하여 운용하고 있다. 본 논문은 광학추적장비의 MFCW(Multi Frequency Continuous Wave)방식과 FMCW(Frequency Modulation Continuous Wave)방식 도플러 레이더 구성과 거리측정 방법을 기술하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1438-1445
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• 2008

The purpose of this study is to evaluate the fundamental frequency of the dam by the various methods using real microearthquake records which were measured on 'H' dam site and to compare each results. In this study, the fundamental frequency was evaluated by the frequency analysis of the microearthquake records which were measured on the dam crest, by the evaluation of acceleration amplification ratio between the foundation and the crest of dam, and by the evaluation of acceleration response spectrum ratio between the foundation and the crest of dam, respectively. Among these methods, it was found that the method by the evaluation of acceleration response spectrum ratio between the foundation and the crest of dam was the most effective method. But, if the simple engineering judgement can be considered, it was thought that the all three methods could reasonably evaluate the fundamental frequency of the dam.

• IEIE Transactions on Smart Processing and Computing
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• 제4권4호
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• pp.258-264
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• 2015

The first 77 GHz transceiver that applies a heterodyne structure-based linear frequency modulation-frequency shift keying (LFM-FSK) front-end module (FEM) is presented. An LFM-FSK waveform generator is proposed for the transceiver design to avoid ghost target detection in a multi-target environment. This FEM consists of three parts: a frequency synthesizer, a 77 GHz up/down converter, and a baseband block. The purpose of the FEM is to make an appropriate beat frequency, which will be the key to solving problems in the digital signal processor (DSP). This paper mainly focuses on the most challenging tasks, including generating and conveying the correct transmission waveform in the 77 GHz frequency band to the DSP. A synthesizer test confirmed that the developed module for the signal generator of the LFM-FSK can produce an adequate transmission signal. Additionally, a loop back test confirmed that the output frequency of this module works well. This development will contribute to future progress in integrating a radar module for multi-target detection. By using the LFM-FSK waveform method, this radar transceiver is expected to provide multi-target detection, in contrast to the existing method.

• Korea-Australia Rheology Journal
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• 제15권2호
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• pp.91-96
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• 2003

The sensitivity of the product to the ongoing sinusoidal disturbances of the process has been investigated in the film casting of viscoelastic polymer fluids using frequency response analysis. As demonstrated for fiber spinning process (Jung et al., 2002; Devereux and Denn, 1994), this frequency response analysis is useful for examining the process sensitivity and the stability of extensional deformation processes including film casting. The results of the present study reveal that the amplification ratios or gains of the process/product variables such as the cross-sectional area at the take-up to disturbances exhibit resonant peaks along the frequency regime as expected for the systems having hyperbolic characteristics with spilt boundary conditions (Friedly, 1972). The effects on the sensitivity results of two important parameters of film casting, i.e., the fluid viscoelasticity and the aspect ratio of the casting equipment have been scrutinized. It turns out that depending on the extension thinning or thickening nature of the fluid, increasing viscoelasticity results in enlargement or reduction of the sensitivity, respectively. As regards the aspect ratio, it has been found that an optimum value exists making the system least sensitive. The present study also confirms that the frequency response method produces results that corroborate well those by other methods like linear stability Analysis and transient solutions response. (Iyengar and Co, 1996; Silagy et al., 1996; Lee and Hyun, 2001).

• 대한한의학회지
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• 제28권3호통권71호
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• pp.289-298
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• 2007

Objectives : Electrical acupoint stimulation (EAS) has been used to treat motor dysfunction of stroke patients with reportedly effective results. The purpose of this study was to evaluate the efficacy of EAS with different frequencies in treating motor dysfunction of ischemic stroke patients. Methods : The subjects of this study were sixty-two ischemic stroke patients with motor dysfunction at Kyunghee Oriental Medicine Hospital who were hospitalized for one week to one month from onset. They were treated with 2Hz or 120Hz EAS for two weeks, and motor evoked potentials (MEP) were measured before and after EAS treatment. To compare the effect of 2Hz EAS with 120Hz, we measured latency, central motor conduction time (CMCT) and amplitude of MEP before and after EAS treatment. Results : After two weeks of treatment, we compared MEP data of the affected side between the 2Hz group and the 120Hz group. The 2Hz group showed more significant improvement than the 120Hz group in latency, CMCT and amplitude (P=0.008, 0.002, 0.002). In case of the affected side MEP data divided by normal side MEP data, the 2Hz group also showed improvement on latency, CMCT and amplitude with significant differences (P=0.003, 0.000, 0.008). Conclusions : These results suggest that low frequency EAS activates the central motor conduction system better than high frequency EAS, and it means that EAS with low frequency is more helpful for motor recovery after ischemic stroke than that with high frequency.

• 대한치과의사협회지
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• 제54권12호
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• pp.1024-1034
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• 2016

Purpose. The purpose of this study was to compare the type and frequency of prosthetic complications associated with attachment types for implant overdenture. Material and methods. In this retrospective study, 38 patients (mean age, 63.5 years) have been treated with implant overdentures from 2007 to 2014. Ten patients received a bar-clip attachment. Eleven patients had received a milled bar with Locator attachment. Seventeen patients had received a Locator attachment. The mean follow-up period was 36.9 months (range, 15-83 months). The type and frequency of prosthetic complications was recorded. The frequency was analyzed to determine the statistical difference among the 3 different attachments by using one-way ANOVA (${\alpha}=.05$) and Bonferroni post hoc method at a 5% level of significance. Results. The total number of prosthetic complications was higher in the bar-clip attachment (55 events) than in the milled bar with Locator attachment (39 events) and the Locator attachment (34 events). There were no statistically significant differences, and the most common prosthetic complication was the loss of retention. In the bar-clip attachment group, the average frequency of prosthetic complications was 3.0 events per prosthesis during the first year. In the milled bar with Locator attachment and Locator attachment groups, the average frequencies were 1.45 events and 2.35 events, respectively. Statistically significant differences were observed in the frequency of the complication. (p = .043) Conclusions. Compared to the bar-clip attachment, implant overdentures that use milled bars with the Locator attachment have a significantly lower incidence of prosthetic complications in the first year of follow-up after placement.

• 대한암한의학회지
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• 제21권2호
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• pp.63-74
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• 2016

Objective : The purpose of this study is to report the effects of radio-frequency hyperthermia cancer treatment in conjunction with Sorafenib on hepatocellular carcinoma patient. Method : The patient was diagnosed with hepatocellular carcinoma at S6/7 and treated with right posterior sectionectomy. After 4 months, tumor recurrence was found at S4, 5 and 8. After transarterial chemoembolization, the patient was prescribed Sorafenib (proprietary name $Nexavar^{(R)}$ ) as well as proceeding with radio-frequency hyperthermia. The clinical outcomes were measured by computed tomography, laboratory findings including tumor markers (AFP, PIVKA-II), natural killer (NK) cell activity, and numeric rating scales (NRS). Results : After the treatment, tumor size was decreased accompanying by reducing the level of tumor markers (AFP, PIVKA-II). Major clinical symptoms were improved with increasing NK cell activity. There were no adverse events based on National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. Conclusion : This case suggests that radio-frequency hyperthermia has synergistic effect for the treatment of hepatocellular carcinoma patient in conjunction with Sorafenib.

• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.87-93
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• 2013

In order to study the effect of the fluid-structure interaction (FSI) on the simulation results, the external characteristics and internal flow features of a diffuser pump were analyzed with a two-way flow solid coupling method. And the static and dynamic structure analysis of the blade was also caculated with the FEA method. The steady flow field is based on Reynolds Averaged N-S equations with standard $k-{\varepsilon}$ turbulent model, the unsteady flow field is based on the large eddy simulation, and the structure response is based on elastic transient structural dynamic equation. The results showed that the effect of FSI on the head prediction based on CFD really exists. At the same radius, the van mises stress on the nodes closed shroud and hub was larger than other nodes. A large deformation region existed near inlet side at the middle of blades. The strength of impeller satisfied the strength requirement with static stress analysis based on the fourth strength theory. The dynamic stress varied periodically with the impeller rotating. It was also found that the fundamental frequency of the dynamic stress is the rotating frequency and its harmonic frequency. The frequency of maximum stress amplitude at node 1626 was 7 times of the rotating frequency. The frequency of maximum stress amplitude at node 2328 was 14 times of the rotating frequency. No matter strength failure or fatigue failure, the root of blades near shroud is the key region to analyse.