• 한국환경보건학회지
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• 제28권2호
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• pp.183-192
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• 2002

Indoor air quality is affected by source strength of pollutants, ventilation rate, decay rate, outdoor level and so on. Although technologies exist to measure these factors directly, direct measurements of all factors are impractical in most field studies. The purpose of this study was to develop an alternative methods to estimate these factors by multiple measurements. Daily indoor and outdoor NO$_2$concentrations for 21 days in 20 houses in summer and winter, Seoul. Using a mass balance model and linear regression analysis, penetration factor (ventilation divided by sum of air exchange rate and deposition constant) and source strength factor(emission rate divided by sum of air exchange rate and deposition constant) were calculated. Subsequently, the ventilation and source strength were estimated. During sampling period, geometric mean of natural ventilation was estimated to be 1.10$\pm$1.53 ACH, assuming a residential NO$_2$decay rate of 0.8 hr$^{-1}$ in summer. In winter, natural ventilation was 0.75$\pm$1.31 ACH. And mean source strengths in summer and winter were 14.8ppb/hr and 22.4ppb/hr, respectively. Although the method showed similar finding previous studies, the study did not measure ACH or the source strength of the house directly. As validation of natural ventilations, infiltrations were measured with $CO_2$tracer gas in 18 houses. Relationship between ventilation and infiltration was statistically correlated (Pearson r=0.63, p=0.02).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.216.1-216.1
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• 2014

Closed drift ion source는 그 특성으로 인하여 강판 표면처리, 금속 표면 산화막 형성, 폴리머 혹은 기타 표면 개질 등 다양한 분야에서 사용이 되고 있다. 다양한 환경에서 사용 되는 소스의 특성으로 인하여 각기 다른 공정에 대한 최적의 특성이 요구 되며, 이러한 공정 환경에 맞춘 소스를 설계하기 위해서 ion source내 전극의 구조 및 자기장 세기 등 이온소스의 구조적 특성에 대한 연구가 필요하게 된다. 본 연구에서는 선형 이온소스의 구조 설계를 위한 실험을 소형(이온빔 인출 슬릿 직경: 60 mm) 이온빔 인출 장치를 제작하여 전극 구조에 따른 방전 특성을 우선적으로 평가를 실시하여 소형 이온빔 인출 장치에서 도출된 결과를 바탕으로 0.3 m급 linear closed drift ion source 설계에 대한 변수를 조사 하였다. 실험은 양극-음극(C-A) 간 간격 및 음극 슬릿(C-C) 간격 그리고 자기장 세기 조건에서 방전 전류 및 인출 이온빔 전류량 측정하였으며, 이 결과를 전산모사 결과와 비교 하였다. 방전전압 1~5 kV, 가스유량 10~50 sccm 조건에서 Ar 이온빔 방전 특성을 평가한 결과, 양극-음극(C-A) 간격이 넓을수록, 음극-음극(C-C) 간격이 좁을수록 방전 전류량이 증가함을 확인 하였다. 또한, 공정 가스 압력 및 자기장 세기 변화에 따른 1~5 kV의 방전 전압에 대한 방전 특성의 관찰 결과, 압력 및 자기장 변화에 따라서 방전 전류의 변화를 관찰 할 수 있었으며, 이에 대한 결과를 통하여 이온 소스 구조 내부에서의 방전 영역에 대한 압력과 자기장 세기에 대한 영향을 분석 할 수 있었다.

• 방송공학회논문지
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• 제21권2호
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• pp.169-179
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• 2016

오늘날 UHDTV (Ultra-High-Definition TV) 시대에 사용될 멀티미디어 부호화기로 MPEG-H에 대한 표준화가 진행되고 있다. 향후 방송용 오디오 콘텐츠는 채널 기반 오디오 콘텐츠에서 진화하여 객체 기반 오디오 콘텐츠까지도 포함하게 될 예정이다. 이에 따라, 채널 기반 오디오 콘텐츠의 객체 기반 오디오 콘텐츠로의 유기적인 변환이 필요한 실정이다. 본 논문에서는 이러한 유기적인 변환을 실현 가능하게 할 수 있는 비균등 선형 마이크로폰 어레이 기반의 음원분리 기법을 제안한다. 제안된 기법은 주어진 어레이 배치에 따라 채널간의 시간차를 분석하고, 분석된 시간차에 따라 주파수별로 특정 방위각에 위치한 입력 오디오 신호의 spectral magnitude를 예측한다. 이후, azimuth와 width 파라메타를 조정함으로써 객체 오디오 생성을 위한 음원을 분리한다. 제안된 음원분리 기법의 성능을 평가하기 위하여 객관적 음원분리 지표 및 분리정확도를 측정하였고, 최소 분산 무손실 응답 빔형성기와 독립 성분 분석 기법 등 기존 음원분리 기법과의 그 성능을 비교하였다. 비교 결과, 제안된 기법이 기존 음원분리 기법들에 비하여 우수한 음원분리 성능을 보이는 것을 알 수 있었다.

• Radiation Oncology Journal
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• 제33권1호
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• pp.42-49
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• 2015

Purpose: In order to keep the acceptable level of the radiation oncology linear accelerators, it is necessary to apply a reliable quality assurance (QA) program. Materials and Methods: The QA protocols, published by authoritative organizations, such as the American Association of Physicists in Medicine (AAPM), determine the quality control (QC) tests which should be performed on the medical linear accelerators and the threshold levels for each test. The purpose of this study is to increase the accuracy and precision of the selected QC tests in order to increase the quality of treatment and also increase the speed of the tests to convince the crowded centers to start a reliable QA program. A new method has been developed for two of the QC tests; optical distance indicator (ODI) QC test as a daily test and gantry angle QC test as a monthly test. This method uses an image processing approach utilizing the snapshots taken by the CCD camera to measure the source to surface distance (SSD) and gantry angle. Results: The new method of ODI QC test has an accuracy of 99.95% with a standard deviation of 0.061 cm and the new method for gantry angle QC has a precision of $0.43^{\circ}$. The automated proposed method which is used for both ODI and gantry angle QC tests, contains highly accurate and precise results which are objective and the human-caused errors have no effect on the results. Conclusion: The results show that they are in the acceptable range for both of the QC tests, according to AAPM task group 142.

• Journal of Electrical Engineering and Technology
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• 제7권1호
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• pp.1-8
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• 2012

The current paper presents a novel control strategy of a three-phase, four-wire Unified Power Quality (UPQC) to improve power quality. The UPQC is realized by the integration of series and shunt active power filters (APF) sharing a common dc bus capacitor. The realization of shunt APF is carried out using a three-phase, four-leg Voltage Source Inverter (VSI), and the series APF is realized using a three-phase, three-leg VSI. To extract the fundamental source voltages as reference signals for series APF, a zero-crossing detector and sample-and-hold circuits are used. For the control of shunt APF, a simple scheme based on the real component of fundamental load current (I $Cos{\Phi}$) with reduced numbers of current sensors is applied. The performance of the applied control algorithm is evaluated in terms of power-factor correction, source neutral current mitigation, load balancing, and mitigation of voltage and current harmonics in a three-phase, four-wire distribution system for different combinations of linear and non-linear loads. The reference signals and sensed signals are used in a hysteresis controller to generate switching signals for shunt and series APFs. In this proposed UPQC control scheme, the current/voltage control is applied to the fundamental supply currents/voltages instead of fast-changing APF currents/voltages, thus reducing the computational delay and the required sensors. MATLAB/Simulink-based simulations that support the functionality of the UPQC are obtained.

• 한국음향학회지
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• 제16권5호
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• pp.76-82
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• 1997

본 논문은 음원의 절대위치를 정확하게 추정할 수 있는 음향홀로그래픽법에 관하여 계산기상의 시뮬레이션 및 측정시스템을 이용한 실험과결과에 대하여 서술한다. 이 연구에서는 원거리 음장을 만족하도록 측정면을 설정하여 7개의 마이크로폰을 직선으로 배열한다. 음원의 측정은 음원면에 근접한 위치에 한 개의 기준 마이크로폰을 설치하고 측정면의 마이크로폰들을 등간격으로 스캐닝하면서 각지점의 음을 동시 기록한다. 수음한 기준음과 측정음간의 크로스 스펙트럼 알고리즘에 의하여 음원의 절대위치를 측정한다. 그리고 각 마이크로폰의 위상차는 기준 마이크로폰을 대상으로 위상보상 하였으며, 측정시의 시간지연은 제 1열 측정시점을 기준으로 시간보상을 행하였다. 측정면에 설정한 마이크로폰들의 최적 간격은 수치 시뮬레이션에 의하여 정한다. 음원신호는 정현파를 이용하고 S/N비를 30dB의 조건하에서 각각 실험을 행하였다. 시뮬레이션과 실험에서 결정한 최적 마이크로폰 간격은 2KHz인 정현파 음원을 기준으로 하여 공간상의 나이키스트 조건을 만족하도록 설정하였다. 무향실에서 측정한 실험결고, 500Hz 와 1KHz의 신호원에 대한 음원이 2KHz인 경우의 추정된 3차원 홀로그램의 주극폭이 각각 87%와 30%씩 감소하였고, 그 결과 수치 시뮬레이션의 타당성을 확인할 수 있었다. 그러므로 본 연구에서 제안하는 3차원 음향 홀로그래픽법을 이용한 음원위치 추정에 관한 연구의 유용성을 검증하였다.

• 한국병원경영학회지
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• 제22권1호
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• pp.1-9
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• 2017

Purpose : Many studies showed that having a usual source of care improved the efficient access of healthcare service. However in Korea there have been few studies on the usual source of care. So this study aims to find whether having a usual source of care affect the medical utilization and expense. Methodology/Approach : We used the Korean Health Panel data in 2012, 2013 to examine the change of utilization and expenses in ambulatory care affected by having a usual source of care. We selected 1,215 hypertension patients without usual source of care in 2012 and performed linear regression analysis to identify the difference between treatment group(with usual source of care in 2013) and control group(without usual source of care in 2013). Then we performed analysis again separated by the age group. Findings : Among study population, 711(58.5%) reported that they have a usual source of care in 2013. Treatment group reported 1.85 less increase in outpatient visits and 69,234 won less increase in expense than control group with weak significance(visit ${\beta}$ -1.85 p-value 0.0807, expense ${\beta}$ -69,234 p-value 0.0541). People under the age of 65 showed significant change in outpatient visits for tertiary hospital (visit ${\beta}$ -0.78 p-value 0.0154, expense ${\beta}$ -91,462 p-value 0.0168). The analysis which focused outpatient for mild disease showed similar trend. Practical Implications : This study supports the positive effect of having usual source of care which decrease inefficient outpatient utilization. Promoting physician-patient relationships is important for efficiency of healthcare service.

• Journal of Mechanical Science and Technology
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• 제14권10호
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• pp.1061-1071
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• 2000

Linear cyclic systems (LCS's) are a class of systems whose dynamic behavior changes periodically. Such a cyclic behavior is ubiquitous in systems with fundamentally repetitive motion. Yet, the knowledge of the noise and vibration transmission paths in LCS's is quite limited due to the time-varying nature of their dynamics. The first part of this two-part paper derives a generic expression that describes how the noise and/or vibration are transmitted between two (or multiple) points in the LCS's. In Part II, experimental validation of the theoretical development of Part I is provided. The noise and vibration transmission paths of the scroll and rotary compressors (two typical LCS's) are examined to show that the LCS's indeed generate a series of amplitude modulated input signals at the output, where the carrier frequencies are harmonic multiples of the LCS' fundamental frequency. The criterion proposed in Part I to determine how well a given LCS can be approximated as a linear time-invariant systems (LTIS) is applied to the noise and vibration transmission paths of the two compressors. Furthermore, the implications of the experimental validations/applications are discussed in order to assess the applicability of the noise/vibration source and transmission path identification techniques based on the assumption that the system under consideration is linear and time-invariant.

• 한국대기환경학회지
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• 제13권5호
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• pp.383-396
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• 1997

Numerical prediction of the pollutant dispersion over a two-dimensional hilly terrain is presented. The dispersion model used in the present work is based on the gradient diffusion theory and the finite-volume method on a non-orthogonal boundary-fitted grid system. The numerical model is validated by comparing the results with the available experimental data for the flat-floor dispersion within a turbulent boundary-layer. The numerical error analysis is performed based on the guideline of Kasibhatla et al.(1988) for the elevated-source dispersion in the flat-floor boundary layer having a power-law velocity and linear eddy-diffusivity profile. The influences of the two-dimensional hilly terrain on the dispersion from a continuously released source are numerically investigated by changing the emission locations and heights. It is found that the distributions of ground-level concentration are strongly influenced by the source location and the emission height. Hence, the terrain amplification factor is greatly enhanced when the pollutant source is located within a flow separation region. Dispersion from a source of short duration is also simulated and the duration time of the pollutant is compared at several downstream locations on a hilly terrain. The results of the numerical prediction are applied to the evaluation of environmental impacts due to the automobile exhausts at the seashore highway with a parallel mountain range.

• 동력기계공학회지
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• 제10권4호
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• pp.25-30
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• 2006

This paper represents the numerical analysis in unsteady state on the variation of diameter and environmental velocity of carbon heating source. In general heating system, the oil and sheath heater is widely used, but these systems have many problems. So, the heating source with carbon ingredient has been researched in many country about manufacture, thermal and electrical properties. In this research, the carbon heating source was studied through numerical analysis on several conditions of unsteady state, heat generation, diameter and environmental velocity. The temperature distributions at steady state are appeared as a non-proportional linear pattern with variations of environmental velocity due to the Nesselt number with convective heat flux is proportioned to 0.805 of Reynolds number. As the radius is increasing, the temperature distributions is appeared the minus tilt because of the environmental condition is cooling by constant temperature. So, the correlation equation between temperature at steady state and environmental velocity was obtained.