• 유통과학연구
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• 제11권4호
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• pp.5-11
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• 2013

Purpose - The aim of this work is to study the reorientation that the export industrial sectors in Costa Rica have experienced during the last 20 years. Research design, data, methodology - The study employs the Cluster Analysis with the export data (20 years of cut-off period) from Costa Rica to the U.S-market. To make the predictions, the technique of the time series was used, with official data (from 2001 to 2010) from the U.S. Department of Commerce and the U.S. International Trade Commission. Results - The Cluster Analysis, show how the economic sectors of traditional products exports of Costa Rica have progressively become in exporters of non-traditional products, meanwhile,the time series confirms that this trend will continue, at least during the next five years. Conclusions - The industry of traditional products exports of Costa Rica (dressmaking, vegetables, coffee, mate, species, etc.) will progressively become in exporters of non- traditional products with a high-tech component (i.e., mechanical equipment and devices, electronic devices and medical equipment),as a consequence of the Chinese (Costa Rica's main competitor) economy's presence in the Organization for Economic Co-operation and Development (OCDE). This fact has enabled the potential improvement of Costa Rica's international competitiveness in the U.S. market.

• 한국측량학회지
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• 제32권3호
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• pp.225-231
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• 2014

When a spatial regression model that uses kernel density values as a dependent variable is applied to retail business data, a unique model cannot be selected because kernel density values change following kernel bandwidths. To overcome this problem, this paper suggests how to use the point pattern analysis, especially the L-index to select a unique spatial regression model. In this study, kernel density values of retail business are computed by the bandwidth, the distance of the maximum L-index and used as the dependent variable of spatial regression model. To test this procedure, we apply it to meeting room business data in Seoul, Korea. As a result, a spatial error model (SEM) is selected between two popular spatial regression models, a spatial lag model and a spatial error model. Also, a unique SEM based on the real distribution of retail business is selected. We confirm that there is a trade-off between the goodness of fit of the SEM and the real distribution of meeting room business over the bandwidth of maximum L-index.

• Journal of Communications and Networks
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• 제16권2호
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• pp.193-201
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• 2014

In cognitive radio networks, the packet transmissions of the secondary users (SUs) can be interrupted randomly by the primary users (PUs). That is to say, the PU packets have preemptive priority over the SU packets. In order to enhance the quality of service (QoS) for the SUs, we propose a spectrum access strategy with an ${\alpha}$-Retry policy. A buffer is deployed for the SU packets. An interrupted SU packet will return to the buffer with probability ${\alpha}$ for later retrial, or leave the system with probability (1-${\alpha}$). For mathematical analysis, we build a preemptive priority queue and model the spectrum access strategy with an ${\alpha}$-Retry policy as a two-dimensional discrete-time Markov chain (DTMC).We give the transition probability matrix of the Markov chain and obtain the steady-state distribution. Accordingly, we derive the formulas for the blocked rate, the forced dropping rate, the throughput and the average delay of the SU packets. With numerical results, we show the influence of the retrial probability for the strategy proposed in this paper on different performance measures. Finally, based on the trade-off between different performance measures, we construct a cost function and optimize the retrial probabilities with respect to different system parameters by employing an iterative algorithm.

• 동력기계공학회지
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• 제3권1호
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• pp.55-59
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• 1999

Generally, T.G(Tacho-generator, Tachometer) sensor is used widely for sensing the angular velocity in rotary machine. By limitation of T.G sensor's structure, the sensed angular velocity include a periodic noise, and the noise is called "ripple" as an electrical term. To reduce the effecting of the ripple, many kinds of filters are designed and installed, but there is necessary a trade off between response time and adapted frequency band. In this paper, we propose a generalized observer to estimate an angular velocity from the output signal of T.G sensor. The generalized observer is proposed firstly for continue systems, and it is applied to DC servo motor with T.G sensor. For simulation, we measure T.G signals at 60, 400, 570 rpm respectively, and analysis those to obtain the resonance frequency of ripple by FFT method. To verify the effectiveness of the proposed algorithm, we compare the results with those of a RC low frequency band filter.

• 한국산업융합학회 논문집
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• 제24권4_2호
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• pp.467-474
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• 2021

The renewable energy is known as eco-friendly energy to reduce the use of fossil fuel and decrease the environmental pollution due to exhaust gas. Targets of solar collector in domestic are usually acquisitions of hot water and hot air. System of air-heating collector is one of the technologies for obtaining hot air in cases of especially heating room and drying agricultural product. The purpose of this study is to investigate the characteristics of thermal flow such as relative pressure, velocity, outlet temperature and buoyancy effect in air-heating collector using solar heat. The flow field of air-heating collector was simulated using ANSYS-CFX program and the behaviour of hot air was evaluated with SST turbulence model. As the results, The streamline in air-heating collector showed several circular shapes in case of condition of buoyancy. Temperature difference in cross section of outlet of air-heating collector did not almost show in cases of buoyancy and small inlet velocity. Furthermore merit of air-heating collector was not observed in cases of inlet velocities. Even though it was useful to select condition of buoyancy for obtaining high temperature, however, it was confirmed that the trade off between high temperature of room and rapid injection of hot air to room could be needed through this numerical analysis.

• Earthquakes and Structures
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• 제22권2호
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• pp.109-120
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• 2022

Older or damaged structures can require significant retrofit to ensure they perform well in subsequent earthquakes. Supplemental damping devices are used to achieve this goal, but increase base shear forces, foundation demand, and cost. Displacement reduction without increasing base shear is possible using novel semi-active and recently-created passive devices, which offer energy dissipation in selected quadrants of the force-displacement response. Combining these devices with large, strictly passive energy dissipation devices can offer greater, yet customized response reductions. Supplemental damping to reduce response without increasing base shear enables a net-zero base shear approach. This study evaluates this concept using two incremental dynamic analyses (IDAs) to show displacement reductions up to 40% without increasing base shear, more than would be achieved for either device alone, significantly reducing the risk of response exceeding the unaltered structural case. IDA results lead to direct calculation of reductions in risk and annualized economic cost for adding these devices using this net-zero concept, thus quantifying the trade-off. The overall device assessment and risk analysis method presented provides a generalizable proof-of-concept approach, and provides a framework for assessing the impact and economic cost-benefit of using modern supplemental energy dissipation devices.

• 한국식생활문화학회지
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• 제39권2호
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• pp.96-105
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• 2024

The domestic artificially sweetened beverage market has grown rapidly in recent years, and sodas have led this growth. This study investigated consumer food purchasing behavior of artificially sweetened sodas in terms of the food health stereotypes of "vice" and "virtue"; used to denote unhealthy and healthy food purchases, respectively. The study was conducted using consumer panel data collected by the Rural Development Administration from 2017 to 2020. Given the semi-continuous nature of artificially sweetened soda purchases, Cragg's two-part model was used for the analysis. The probability of purchasing artificially sweetened sodas increased as expenditure on snacks (a vice food category) increased. However, of those panelists who purchased artificially sweetened sodas, expenditure on artificially sweetened sodas decreased with expenditure on snacks and increased with expenditure on fruits (a virtue food category). These results suggest that vicious-lifestyle consumers choose artificially sweetened sodas when they regulate eating habits, whereas virtuous-lifestyle consumers increase artificially sweetened soda expenditure for hedonic consumption to reduce guilt based on a sensible trade-off effect.

• 국제지역연구
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• 제14권3호
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• pp.157-177
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• 2010

본 연구는 중국의 1985년부터 2008년까지의 각 성 시에 관한 패널데이터를 활용해서 재정분권화가 경제성장에 미치는 영향을 실증분석한다. 재정분권화를 위해 최근에 개발된 지표를 사용하고 지방정부의 자율재량권을 계량화해서 모형에 반영하여 다음의 결론을 얻는다. 인플레이션율의 증가는 중국경제에 긍정적인 영향을 미치는 것으로 나타났는데 이는 필립스커브에 의하면 고용량의 증가로 대변되는 중국경제성장과 상충되는 개념으로서 향후 중국경제의 불안정성을 암시하고 있다. 중국의 WTO가입은 중국경제에 긍정적인 역할을 해온 것으로 나타났는데 이는 고전학파의 자유무역이론을 뒷받침하는 실증결과로 해석할 수 있다. 지출분권화는 중국경제성장에 긍정적인 영향을 미치고, 또한 세입분권화도 지출분권화만큼 크지는 않지만 경제성장에 긍정적인 영향을 끼쳤다. 국세나 지방세를 많이 부과하면 경제성장에 부정적인 영향을 미치는 것으로 나타났고, 기대와는 달리 지방정부의 자율재량권을 계량화해서 반영한 지표는 경제성장과 관련이 없는 것으로 나타났다.

• 한국인터넷방송통신학회논문지
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• 제19권6호
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• pp.57-63
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• 2019

EMI 차폐막의 높이가 회로에 어떤 영향을 끼치는지를 S파라미터를 통해 분석하였다. S파라미터 중에서 회로의 기능에 끼치는 영향을 판단할 수 있는 요소로서 S11, S21, S22, S31이 있다. 시뮬레이션은 그래파이트와 페라이트로 이루어진 차폐막을 이용하였고, 주파수는 100 MHz ~ 1 GHz에서 진행하였다. 차폐막의 높이가 증가함에 따라 S21값이 0 dB에 점점 가까워지는 모습을 보였다. 또한 SE(Shielding Effectiveness)값은 특정한 주파수 대역에서만 절연층의 두께에 따른 차폐성능의 향상을 확인할 수 있었다. 이산화규소(Silicon dioxide)의 두께가 가장 두꺼운 800 um 경우를 기준으로 FG(Ferrite-Graphite) 구조는 100 MHz ~ 300 MHz의 좁은 주파수 대역에서 평균 -1 dB를 보이며 -2 dB의 평균을 보이는 GF(Graphite-Ferrite)보다 뛰어난 효율을 보인다. GF 구조는 높은 효율을 보이지는 못하지만 넓은 범위에서 흔들리는 FG 구조보다 100 MHz ~ 1 GHz의 주파수 대역에서 -3 dB의 평균적인 성능을 보인다. 즉, FG 구조와 GF 구조는 트레이드-오프(trade-off)의 구조를 갖는다. 따라서 용도에 따라 적절한 구조를 선택해야 한다.

• 방사성폐기물학회지
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• 제11권3호
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• pp.207-212
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• 2013

2011년 3월 발생한 일본의 후쿠시마 원전 사고는 원전의 안전성 문제를 넘어 경제성까지 논란을 불러일으키고 있으며, 이러한 문제는 원전 확대에 대한 비판적 시각을 전 세계적으로 확대시키고 있다. 따라서 원전이 안전성을 충분히 유지하면서도 타 전원에 비해 경제성이 있다는 것을 입증한다면 현재는 물론 지속가능한 전원으로서의 원전의 역할을 기대할 수 있을 것이다. 후쿠시마 원전사고 이후 국민들이 실제로 느끼는 '사회적 안전성' 정도를 알아보기 위해 안전성 대신 일반국민의 수용성을 지표로 삼아 안전에 대한 비용을 얼마나 지불할 수 있느냐를 알아보기 위해 비용편익분석의 하나인 조건부가치측정법(CVM: contingent valuation method)을 이용하였다. 경제성과 안전성의 trade-off값을 설문조사를 통해 알아본 결과 발전원가 4.75원/kWh 인상효과를 가져왔다. 이를 현재 원전발전단가 39.11 원/kWh에 반영하면 43.86 원/kWh으로 석탄화력 발전원가 67 원/kWh과 비교해 여전히 경쟁력이 있는 것으로 나타났다. 이러한 결과는 2013년 말 수립예정인 제2차 에너지기본계획[1] 등에 기초자료로 중요한 정책적 시사점을 가져다 줄 것이다.