• 방송공학회논문지
• /
• 제14권3호
• /
• pp.357-365
• /
• 2009

OFDM 시스템에서 송수신단의 샘플링 주파수가 정확하지 않을 경우 샘플링 주파수 옵셋으로 인한 ICI(Inter-Carrier Interference) 현상이 발생하여 수신 성능의 열화를 초래한다. 일반적으로 샘플링 주파수 옵셋은 주파수 영역에서 2개의 인접한 OFDM 심볼의 동일한 파일럿 위치에서의 부반송파간 상관을 통해 추정하게 되는데, 본 논문에서는 인접한 심볼뿐만 아니라 더 많은 연속된 심볼들 간의 다양한 조합을 통한 상관을 이용하여 샘플링 주파수 옵셋을 추정하는 기법을 제안한다. 제안된 방법을 DVB-T(2K 모드) 시스템에 적용하여 모의실험을 진행하고, 이를 통해 AWGN 채널 환경에서 심볼들 사이의 잡음의 영향을 줄임으로써 샘플링 주파수 옵셋 추정 성능을 향상시킬 수 있음을 확인한다.

• 한국지진공학회논문집
• /
• 제22권2호
• /
• pp.63-75
• /
• 2018

This paper proposes extension of Latin Hypercube Sampling (LHS) to avoid the necessity of using intervals with the same probability area where intervals with different probability areas are used. This method is called Weighted Latin Hypercube Sampling (WLHS). This paper describes equations and detail procedure necessary to apply weight function to WLHS. WLHS is verified through numerical examples by comparing the estimated distribution parameters with those from other methods such as Random Sampling and Latin Hypercube Sampling. WLHS provides more flexible way on selecting samples than LHS. Accuracy of WLHS estimation on distribution parameters is depending on the selection of weight function. The proposed WLHS is applied to seismically isolated structures in nuclear power plants. In this application, clearance-to-stops (CSs) calculated using LHS proposed by Huang et al. [1] and WLHS proposed in this paper, respectively, are compared to investigate the effect of choosing different sampling techniques.

• 한국산업보건학회지
• /
• 제18권1호
• /
• pp.20-31
• /
• 2008

A respirator is useful to protect a worker from the harmful gases and vapors in the workplace, and the evaluation of respirator cartridge service life is important for the worker's health and safety. The performance of cartridge is effected by several factors such as concentration of gas and vapor, humidity, temperature, adsorbents and cartridge packing density. Adsorption model was applied to both sampling tube and respirator cartridge to predict the service life for organic vapors. The variables of the adsorption model were measured from the experiment with the sampling tube, and it was used to predict the service life of respirator cartridge. In the experiment, we used carbon tetrachloride as a organic vapor and activated carbon take out respirator cartridge as activated carbon. As a result, it was possible to predict the service life of respirator cartridge and predicted service life was quite correct. Breakthrough time decreased with increase of CCl4 concentration. In case of sampling tube, adsorbed amount of CCl4 was larger than respirator cartridge due to linear velocity. Also, rate constant of sampling tube was larger than respirator cartridge, because of, effect of flow rate, packing density. In the prediction of service life of respirator cartridge by using sampling tube, the time required for 50% contaminant breakthrough(${\tau}$) is more effective than the rate constant(k').

• The Journal of Asian Finance, Economics and Business
• /
• 제8권7호
• /
• pp.79-90
• /
• 2021

The purpose of this research is to identify factors affecting the acceptance and use of e-tax services among medium taxpayers in Phnom Penh, Cambodia. The researcher conducted the study based on a quantitative approach by using multi-stage sampling method, which selects a sample size by two or more stages. The first stage sampling was the stratified random sampling and the subsequent stage was purposive sampling. In this study, the stratified random sampling was first used, followed by purposive sampling. The data were collected from 450 medium taxpayers who experienced using e-tax services located in three tax branches in Phnom Penh. This study adapted the confirmatory factor analysis (CFA) and structural equation model (SEM) to analyze the model accuracy, reliability and influence of various variables. The primary result showed that behavioral intention has a significant effect on user behavior of e-tax services among medium taxpayers in Phnom Penh, Cambodia. Moreover, the results revealed that performance expectancy, effort expectancy, social influence, and anxiety have significant impact on behavioral intention. In addition, social influence has the strongest impact on behavioral intention, followed by anxiety, performance expectancy and effort expectancy. Conversely, facilitating conditions, trust in government, and trust in internet do not influence behavioral intention.

• 한국전자파학회논문지
• /
• 제22권5호
• /
• pp.501-509
• /
• 2011

Software Defined Radio(SDR)에서는 ADC를 안테나 가까이에 위치시키는 것을 목표로 하고 있다. 하지만 실제 RF 대역의 신호를 ADC를 이용해 디지털화 하는 방법은 아직 어렵다. 그래서 RF 대역의 신호를 IF 대역으로 하향 변환 후 샘플링을 하는 방법이 연구되고 있다. 이런 방법의 하나로, Sub-Sampling 방식은 발진기 없이 RF 대역의 신호를 IF로 변환할 수 있는 방법이다. Sub-Sampling 방법을 이용한다면 2개 이상의 밴드를 하향 변환할 수 있지만, RF 필터의 성능으로 인해 하향 변환된 신호간에 간섭이 작용할 수 있어 성능을 저하시킨다. 본 논문에서는 time division multiplexing(TDM) 방식을 이용해 2개 이상의 신호를 시간적으로 분리시킴으로써 RF 필터의 좋지 않은 성능으로 인해 발생할 수 있는 신호간 간섭을 피할 수 있는 방법을 제안한다. 이 방식은 샘플앤홀더에서 두 신호에 대한 시간적 분리와 Sub-Sampling을 동시에 구현함으로써 하드웨어적인 큰 변화 없이 신호를 수신할 수 있다.

• The Journal of Asian Finance, Economics and Business
• /
• 제8권3호
• /
• pp.695-704
• /
• 2021

This study aims to determine the effect of changes in learning systems and its effects on students' learning outcomes amid the Covid-19 pandemic. The sample of this study are the students who are in Jakarta, Indonesia. "Non-probability random sampling" technique has been used to select the samples while the sampling method used is "purposive sampling", where criteria are used to select samples. The samples in this study are 200 people taken randomly using Google Form. Concentration ability and learning interest can affect learning outcomes with the mediation of learning comfort and a good learning environment. As well as physical distancing can moderate the effect of concentration ability and learning interest on learning outcomes. The ability to concentrate on improving learning outcomes requires psychomotor improvement. Whereas interest in learning with indicators of learning awareness can improve learning outcomes. A clean environment is a strength in the learning comfort and the community environment can be recommended in the learning environment. The implementation of the restriction of gathering becomes an important point of physical distancing. The other novelties are the learning comfort and the learning environment as mediating variables and physical distancing as moderating variables in one study at a time.

• The Journal of Asian Finance, Economics and Business
• /
• 제8권2호
• /
• pp.1215-1224
• /
• 2021

This research aims to discuss the relationship between the courage, anticipation, and satisfaction comprehensively. This study will be complemented by gratitude as a variable that moderates the relationship between courage and anticipation, as well as the relationship between the courage and satisfaction. The large area as survey location is the reason for sampling conducted in 2 stages: (1) taking 15 districts through judgement sampling, (2) allocated sub-districts sample through proportional random sampling. The sample used in this study were 155 sub-districts in East Java. Respondents in each sub-district consisted of 1 farmer and 1 field extension officer to get a total of 310 respondents. The analysis method used to test the hypothesis was Structural Equation Modeling (SEM). The findings of this research are: (1) The courage of field extension officers' have a positive but non-significant direct effect on farmers' anticipation, however, the effect significantly strengthen with religiosity as moderation; (2) The courage of field extension officers' and farmers' anticipation have a significant and positive effect on satisfaction. This study will be complemented by gratitude as a variable that moderates the relationship between the courage and anticipation, as well as the relationship between courage and satisfaction.

• The Journal of Asian Finance, Economics and Business
• /
• 제8권4호
• /
• pp.959-969
• /
• 2021

This study aims to develop new constructs and indicators for sharia destination image, and then examine its effects on perceived value, tourist satisfaction, and post-visit behaviour. Furthermore, it analyses the mediating role of perceived value and tourist satisfaction on relationship between sharia destination image and post-visit behaviour. The population were domestic and Malaysian Muslim tourists who visited Aceh during the study period. The sampling was carried out in two stages. The first stage involved selecting most visited districts. The second stage involved randomly selecting tourists who visit during the study period in the districts. Data was collected using a structured questionnaire with a Likert scale. Also, a total of 270 questionnaires were distributed to domestic and Malaysian tourists in Aceh. Cluster sampling was used to determine the sample area, and purposive sampling technique was used to determine the study sample. Furthermore, the data analysis technique is Structural Equation Modelling. The results showed that the sharia destination image has a significant effect on perceived value. Meanwhile, the perceived value significantly influenced tourist satisfaction and post-visit behaviour. In addition, the perceived value and tourist satisfaction can mediate the effects of sharia destination image, which has no direct effect on post-visit behaviour.

• International journal of advanced smart convergence
• /
• 제10권2호
• /
• pp.194-200
• /
• 2021

The purpose of this study is to analyze the structural relationship among self-leadership, grit, and performance.Specifically, self-leadership was selected as an independent variable, two dimensions of grit were selected as mediator variables, and performance was selected as a dependent variable. This structural equation model is based on previous studies.The subjects of this study were middle and high school Taekwondo players, and the survey was collected using the online survey system KSDC (Korean Social-Science Data Center). The sampling method was a non-probability sampling method, convenience sampling method.A total of 367 copies were collected through this process, and 355 copies were used as the final valid samples after excluding the insincere data.Data processing was done with SPSS 23 for frequency analysis, exploratory factor analysis and reliability analysis. Also, AMOS 21 was used for confirmatory factor analysis and structural equation model analysis. The results of the analysis are as follows: First, self-leadership had a positive effect on bothi interest consistency grit and effort persistence grit. Second, it was found that both interest consistency grit and effort persistence grit have a positive effect on performance.Third,self-leadership had a positive effect on performance.

• 한국산업보건학회지
• /
• 제6권1호
• /
• pp.125-137
• /
• 1996

This study was designed to investigate effects of relative humidity on the breakthrough of charcoal tubes at a fixed vapor concentration and sampling time during mixed organic vapor sampling. A vapor generator was used to generate three different concentrations of mixed organic vapor and a stainless steel chamber was fabricated and utilized to maintain three different percentages of relative humidity while maintaining a constant temperature. The results were as follows; 1. At high relative humidity, breakthrough of mixed organic vapor occurred quickly at low vapor concentration than at high vapor concentration because of the reduced adsorption volume of charcoal tube due to humidity. 2. Breakthrough by competitive adsorption of vapors onto charcoal tube was observed at first from n-hexane having the lowest boiling point and highest vapor pressure among the three organic vapors investigated, followed by TCE. No breakthrough was observed from toluene under all experimental conditions. 3. For n-hexane, breakthrough was observed after 2 hours of sampling and breakthrough rates were increased as relative humidity increased. For TCE, breakthrough was found after 3 hours of sampling and breakthrough rates by sampling time were increased as vapor concentration increased. 4. The adsorbed amount of mixed organic vapor at breakthrough was shown to have statistically significant correlations with sampling time, relative humidity, and vapor concentration in descending order of correlation. Relative humidity and sampling time for n-hexane and sampling time and concentration for TCE were both statistically significantly correlated. 5. Relative humidity was found to affect the amount of breakthrough of mixed organic vapor and n-hexane. Among three percentages of relative humidity investigated, the amount of breakthrough at 85 % relative humidity was significantly larger than those of at lower percentages of relative humidity. No statistically significant difference was found between 25 % and 55 % relative humidity. 6. The results of multiple regression analysis between breakthrough and relative humidity, vapor concentrations showed that the coefficient of determination of mixed organic vapor was 0.263 and those of n-hexane and TCE were 0.275 and 0.189, respectively. 7. Flow rates of sampling pumps used were found to be affected by relative humidity present. At 25 %, 55 %, and 85 % relative humidity, the relative errors of sampling pump were 1.4 %, 13.4 %, and 18.6 %, respectively. In conclusion, the results of this study showed that high relative humidity could reduce the adsorption volume of charcoal tubes and subsequently increase breakthrough rates. Therefore, to prevent breakthrough when sampling mixed organic vapors, it is suggested that either sampling volume be reduced on the flow rate be lowered so as to minimize breakthrough of the most volatile organic vapor in the mixture. In addition, since the flow rates of a sampling pump can be adversely affected by high relative humidity, it is recommended to use a constant flow mode pump when sampling in the highly humid environment.