• 센서학회지
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• 제10권5호
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• pp.320-328
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• 2001

PVDF(Polyvinylidene fluoride) 압전막을 이용하여 $8{\times}8$의 요소를 갖는 2차원 배열 수중청음기를 설계 제작하고. 그것을 이용하여 수 MHz$\sim$수십 MHz 대역의 초음파 음장을 측정하는 방법 및 측정시스템을 구축하였다 수중청음기의 설계에 있어서는 배면체의 종류에 따른 주파수 응답특성을 Mason 등가회로에 의해 해석하였고, 압전체 요소의 크기 및 간격, 스캐닝 스탭에 따른 음장 측정 정도를 검토하였다 2.25MHz의 원형평면 트랜스듀서가 만드는 수중 음장을 제작한 수중청음기 및 측정시스템으로 측정한 결과, 비교적 정밀한 측정이 가능함을 알았다.

• 한국운동역학회지
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• 제15권4호
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• pp.117-129
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• 2005

The purpose of this study was to characterize the impact shock wave and its attenuation, and the kinematic response of the lower extremity's joints to the impact shock during downhill running in which the lower extremity's extensor acts dominantly. For this study, fifteen subjects(mean age:$27.08{\pm}4.39$; mass:$76.30{\pm}6.60$; height:$177.25{\pm}4.11$) were required to run on the 0% grade treadmill and downhill grades of 7%, and 15% in random at speed of their preference. When the participant run, acceleration at the tibia and the sacrum and kinematic data of the lower extremity were collected for 20s so as to provide at least 5 strides for analysis at each grade. Peak impact accelerations were used to calculate shock attenuation between the tibia and sacrum in time domain at each grade. Fast Fourier transformation(FFT) and power spectral density(PSD) techniques were used to analyze impact shock factors and its attenuation in the frequency domain. Joint coordinate system technique was used to compute angular displacement of the ankle and knee joint in three dimension. The conclusions were drawn as fellows: 1. Peak impact accelerations of the tibia and sacrum in downhill run were greater than that of 0% grade run, but no significant between conditions. Peak shock of PSD resembled also in pattern of peak impact acceleration. The wave of impact shock attenuation between the tibia and sacrum decreased with increasing grade, but didn't find a significant difference between grade conditions. 2. Adduction/abduction, flexion/extention, and internal/external rotation of the ankle and knee joints at support phase between grade conditions didn't make much difference. 3. At grade of 7% and 15%, there were relationship between the knee of the flexion/extension movement and peak impact acceleration during heel strike and found also it in the ankle of plantar/dorsiflexion at grade of 15%.

• 한국인터넷방송통신학회논문지
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• 제10권3호
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• pp.131-137
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• 2010

UMSN (Ubiquitous Medical Sensor Network)은 실시간 객체식별과 센서 정보 수집으로 병원 등 의료시설의 u-Healthcare 시스템에 사용되고 있다. RF 무선 주파수로 리더기를 이용해 태그를 식별하는 RFID는 특히 환자 관리에 많이 쓰인다. 하지만 RFID 태그는 리더기의 질의에 항상 자신의 ID를 응답하기 때문에 불법적인 리더기에 ID를 전송하거나 불필요한 질의에 응답하여 도청, 스푸핑 등의 보안 취약점이 발생할 수 있다. 본 논문은 UMSN 기반의 환자관리 시스템에서 리더기가 환자, 의료기기, 의료진, 각종센서 등에 부착된 태그에 과도한 인증을 요청하여 발생할 수 있는 RFID Back-end Server의 트래픽을 줄이고 이 과정에서 발생 가능한 도청, 스푸핑 등의 보안 위협을 줄이기 위해 태그 ID 세분화 기법을 제안한다. 제안 기법은 환자의 태그 ID 문자열을 기준으로 환자를 분류하여 집단으로 구분하고 해당 집단에 인가된 리더기가 태그를 읽었을 때만 Back-end Server가 태그 인증절차를 수행하도록 하여 Back-end Server 트래픽과 보안 위협을 줄일 수 있다.

• 한국군사과학기술학회지
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• 제21권2호
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• pp.166-172
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• 2018

To develop and evaluate the real-time SAR(Synthetic Aperture Radar) motion measurement system, true antenna phase center(APC) positions during SAT(Synthetic Aperture Time) are needed. In this paper, CDGPS(Carrier phase Differential Global Positioning System) post processing method is proposed to get the true APC position for spotlight SAR image formation. The CDGPS position is smoothed to remove high frequency noise which exists inherently in the carrier phase measurement. This paper shows smoothed CDGPS data is enough to provide the true APC for high-quality SAR image formation through motion measurement result, phase error estimation and IRF(Impulse Response Function) analysis.

• Journal of Power Electronics
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• 제17권4호
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• pp.1048-1057
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• 2017

An indirect matrix converter (IMC) is a modern power generation system that enables a direct ac/ac conversion without the need for any bulky and limited lifetime electrolytic capacitor. This system also allows four-quadrant operation, generation of sinusoidal output voltage waveforms with variable frequency and amplitude, and control of input power factor. This study proposes a pulse-width modulation-based sliding-mode controller to achieve unity input-power factor operation of the IMC independently of the active power exchanged with the grid, as well as a fast dynamic response. The designed equivalent control law determines, at each sampling period, the appropriate q-axis component of the modulated input current to be injected into the grid through the LC input filter. An integral term of the error is included in the expression of the sliding surface to increase the accuracy of the control method. A double space vector modulation method is used to synthesize the direction of the space vector of the input currents as required by the sliding-mode controller and the space vectors of the target output voltages. Simulation and experimental results are provided to show the effectiveness and evaluate the performance of the proposed control method.

• 한국해양공학회지
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• 제27권5호
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• pp.63-69
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• 2013

The mooring lines of a floating type offshore plant are known to show wide banded and bimodal responses. These phenomena come from a combination of low and high frequency random load components, which are derived from the drift-restoring motion characteristic and wind- sea, respectively. In this study, fatigue models were applied to predict the fatigue damage of mooring lines under those loads, and the result were compared. For this purpose, seven different fatigue damage prediction models were reviewed, including mathematical formula. A FPSO (floating, production, storage, and offloading) with a $4{\times}4$ spread catenary mooring system was selected as a numerical model, which was already installed at an offshore area of West Africa. Four load cases with different combinations of wave and wind spectra were considered, and the fatigue damage to each mooring line was estimated. The rain flow fatigue damage for the time process of the mooring tension response was compared with the results estimated by all the fatigue damage prediction models. The results showed that both Benasciutti-Tovo and JB models could most accurately predict wide banded bimodal fatigue damage to a mooring system.

• 의학교육논단
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• 제24권3호
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• pp.205-214
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• 2022

The purpose of this study was to analyze the results of a study on the psychological state, lifestyle, self-management ability, and academic adaptation of medical students, and to present examples of improvement of a student support center based on the results. A medical school in Daegu has been surveying the living conditions of students every year for 6 years since 2016. More than 60% of medical students experienced depression and more than 70% experienced stress, but these rates have significantly improved over the past 5 years. There were many cases of drinking or smoking to relieve stress, but the frequency of drinking recently decreased substantially. Some students had difficulties in emotional regulation (11.5%) and time management (16.6%), and challenges in planning and self-management increased significantly during the coronavirus disease 2019 (COVID-19) pandemic. The satisfaction and adaptability of medical students are high, but the number of students who are not satisfied with but negative response rate is 2%-3% in every year. However, satisfaction has significantly increased in tandem with curriculum changes and COVID-19. Based on these data, the counseling system was reorganized to support psychological stability, the medical humanities curriculum was improved, and changes in actual quality of life were induced by developing and operating non-curricular programs. Furthermore, standardized questionnaires will be developed and data from many medical schools will be shared, which is expected to support medical students more effectively.

• 한국전기전자재료학회논문지
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• 제36권2호
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• pp.143-150
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• 2023

Underwater wireless communication is a challenging issue for realizing the smart aqua-farm and various marine activities for exploring the ocean and environmental monitoring. In comparison to acoustic and radio frequency technologies, the visible light communication is the most promising method to transmit data with a higher speed in complex underwater environments. To send data at a speedier rate, high-performance photodetectors are essentially required to receive blue and/or cyan-blue light that are transmitted from the light sources in a light-fidelity (Li-Fi) system. Here, we fabricated high-performance organic phototransistors (OPTs) based on P-type donor polymer (PTO2) and N-type acceptor small molecule (IT-4F) blend semiconductors. Bulk-heterojunction (BHJ) PTO2:IT-4F photo-active layer has a broad absorption spectrum in the range of 450~550 nm wavelength. Solution-processed OPTs showed a high photo-responsivity >1,000 mA/W, a large photo-sensitivity >10³, a fast response time, and reproducible light-On/Off switching characteristics even under a weak incident light. BHJ organic semiconductors absorbed photons and generated excitons, and efficiently dissociated to electron and hole carriers at the donor-acceptor interface. Printed and flexible OPTs can be widely used as Li-Fi receivers and image sensors for underwater communication and underwater internet of things (UIoTs).

• 산업진흥연구
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• 제8권4호
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• pp.131-137
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• 2023

본 연구는 군의 성범죄로 발생하는 문제점을 파악하고자 2019년 2월부터 2022년 5월28일까지 뉴스에서 다룬 군 성범죄 관련 기사를 수집하고 분석하였다. 언론에 보도된 군 성폭력 현황을 파악하고자 뉴스 빅 데이터 전문분석 시스템인 빅카인즈 (BIGKinds)를 활용하여 기사를 수집하였고, Textom 프로그램을 활용해 키워드를 대상으로 시기별 빈도 분석, 워드 클라우드, 의미 연결망 분석 기법을 활용하여 연구를 수행하였다. 데이터 분석 결과, 첫째, 군 내부의 성범죄에 대한 사건 관련 보도는 피해자에게 대중의 관심이 집중된 것을 확인할 수 있었다. 둘째, 성범죄에 대응하는 관련 당국의 미온적 시스템의 문제가 드러났다. 셋째, 성범죄 피해자에 대한 지원 부족이 나타났다.

• 한국학교보건학회지
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• 제2권1호
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• pp.48-57
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• 1989

To evaluate the college students' health status, the author distributed C.M.I. to 233 college students consisting of 102 males and 131 females who randomly selected from a college in seoul. The conclusion are as follow: 1. The mean of CMI scores for the male students was 32.84 and that for the female students was 43.25. Statistical significant difference was observed between the mean of CMI scores for male students and that for female students. 2. For male students, The CMI mean scores for the day students was 29.46 and for evening students was 35.85. There was no statistical significant difference the day students and that for the evening students. 3. For female students, the mean of CMI scores for day students was 42.40 and that for the evening students was 44.64. But there was no statistical significant difference between the mean CMI scores for the day students and that for the evening students. 4. In both female and male groups, the affirmative response rate of inadequacy, fatigability and eyes and ears are higher than any of the other items. 5. In comparing the CMI items of male students and female students, the significant differences cardiovascular system, musculoskeletal system, skin, nervous system, genitourinary system, fatigability, habits, inadequacy, depression and tension. The mean scores for female students, with the exception of habits, were higher than those for male students. 6. In comparing the CMI items of male day students and male evening students, there was significant difference in the items of the cardiovascular system, digestive tract, skin, genitourinary system, inadequacy, and anger : the mean scores of evening male students were higher than those of day students. 7. In the case of female students, the CMI mean scores of the evening students in the categories eyes and ears, cardiovascular system, digestive tract, musculoskeletal system, skin, genitourinary system, fatigability, inadequacy, depression, anxiety, and sensitivity were higher scores than those of the day students. However, the were no significant difference between both groups except in the cathgory of habits. 8. The frequency rate of neurotic students, who were identified by fukamachi's classification, were 12.5% in the day male students, 18.6% in th evening male students, 13.6% in the day female students, and 18.0% in the evening female students.