• 대한전자공학회논문지TC
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• 제46권7호
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• pp.52-60
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• 2009

본 논문에서는 십자형 슬롯 급전방식을 이용한 다층 CP-DRA(Circularly Polarized Dielectric Resonator Antenna)의 이득 및 축비대역폭 증대에 관하여 연구한다. CP-DRA의 이득 및 축비대역폭 증대를 위하여 단층 CP-DRA에 대하여 분석하고, 이를 바탕으로 다층 CP-DRA의 구조를 제안하여 동작특성을 연구한다. 또한, 안테나의 이득 증대를 위하여 다층 CP-DRA 사이의 간격을 0.7$\lambda_0$ 및 1.2$\lambda_0$로 2$\times$2 평면 배열한 안테나의 방사특성을 CST사의 MWS을 이용하여 시뮬레이션을 통해 검토한다. 제안한 다층 CP-DRA를 제작하여 측정한 결과, 이득 및 대역폭이 단층 CP-DRA에 비하여 약 2배 개선됨을 알 수 있다. 그리고, 다층 CP-DRA를 1.2$\lambda_0$ 간격으로 배열한 안테나에서 일반적인 배열안테나와 달리 grating lobe가 크게 감소하며, 이득은 13.4dBi, 축비대역폭은 0.8GHz으로 증가하였다.

• 한국터널지하공간학회 논문집
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• 제3권1호
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• pp.51-62
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• 2001

AE와 DRA를 이용한 초기응력 측정법은 실험실 시험을 통해 초기응력을 측정하는 방법 중의 하나이다. 이 방법은 시추와 실험실 시험간에 지연시간이 발생하며 시료에 축방향 반복하중을 가하여 초기응력을 결정하기 때문에 지하 암반의 응력 상태와는 다른 결과를 얻을 수도 있다. 이 연구에서는 지연시간을 다르게 하여 지연시간이 선행응력 결정에 미치는 영향을 살펴보았다. 그리고 축방향 선행응력만을 가한 시료와 축방향 선행응력과 봉압을 모두 가한 시료에 대해 AE와 DRA를 이용하여 선행응력을 결정하여 봉압이 축방향 선행응력 결정에 미치는 영향을 살펴보았다. 지연시간이 길어질수록 오차가 약간씩 증가하는 경향이 나타났으나 지연시간이 1개월인 시료라 할지라도 AE와 DRA를 이용한 경우 각각 16%와 12%의 오차범위 내에서 선행응력을 결정할 수 있었다. 축방향 선행응력만을 가한 경우 AE를 이용하면 9%, DRA를 이용하면 4%의 오차범위 내에서 축방향 선행응력을 결정할 수 있었으나 축방향 선행응력과 봉압을 모두 가한 경우는 각각 17%와 14%의 오차범위 내에서 축방향 선행응력을 결정할 수 있었다. 터널현장에서 시추한 코어를 이용하여 초기응력을 측정한 결과 AE와 DRA는 유사한 결과를 나타내었으나 수압파쇄법에 의한 결과보다는 작은 값을 갖는 것으로 나타났다.

• Corrosion Science and Technology
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• 제7권5호
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• pp.283-287
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• 2008

The drag reduction agency (DRA) for gas pipeline, a novel method used for reducing friction or drag on a gas flowing to increase the transmission efficiency of gas pipeline, is a more flexible and economical technology than internal flow efficient coatings. In this paper, an effective DRA has been developed in Authors' Institute by analyzing the hydrodynamic friction resistance on internal gas pipeline and then studying the work mechanism and molecular structure of DRA. In the meantime, a group of property test for selecting DRA material has been determined, including viscosity, contact angle, volatility, corrosion, slab extending, and flow behavior in horizontal tube. The inhibition efficiency and drag reduction efficiency of the developed DRA have been investigated finally based on the relevant test methods. Results of corrosion test show that the developed DRA has very good inhibition effect on mild steel by brushing a thin layer of DRA on steel specimens, giving inhibition efficiency of 91.2% and 73.1% in 3%NaCl solution and standard salt fog environment respectively. Results of drag-reducing test also show that the Colebrook formula could be used to calculate friction factors on internal pipes with DRA as the Reynolds number is in the range of $0.75\times10^5\sim2.0\times10^5$. By comparing with normal industrial pipes, the friction resistance coefficient of the steel pipe with DRA on internal wall decreases by 13% and the gas flux increases by 7.3% in testing condition with Reynolds number of $2.0\times10^5$.

• 한국임상약학회지
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• 제17권1호
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• pp.46-51
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• 2007

This study was aimed to provide the controlled terminology for adverse drug reactions by selecting an appropriate internationally standardized classifications (WHO-ART or MedDRA). We collected the relevant information on ADR terminology systems including WHO-ART and MedDRA by online searching and visiting pharmaceutical companies and WHO UMC (Uppsala Monitoring Centre, Uppsala, Sweden). For MedDRA, project leader directly communicated with the officer of MSSO (Maintenance and Support Services Organization). Collecting all the pertinent information, two possible terminology classifications or systems (WHO-ART and MedDRA) were compared in the views of acceptability, cost-effectiveness and international feasibility and reviewed by the consultation committee and finally WHO-ART was selected.

• Journal of Communications and Networks
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• 제11권1호
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• pp.26-35
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• 2009

In this paper, we investigate how to do resource allocation to guarantee a minimum user data rate at low signaling overhead in multi-cell orthogonal frequency division multiple access (OFDMA) wireless systems. We devise dynamic resource allocation (DRA) algorithms that can minimize the QoS violation ratio (i.e., the ratio of the number of users who fail to get the requested data rate to the total number of users in the overall network). We assume an OFDMA system that allows dynamic control of frequency reuse factor (FRF) of each sub-carrier. The proposed DRA algorithms determine the FRFs of the sub-carriers and allocate them to the users adaptively based on inter-cell interference and load distribution. In order to reduce the signaling overhead, we adopt a hierarchical resource allocation architecture which divides the resource allocation decision into the inter-cell coordinator (ICC) and the base station (BS) levels. We limit the information available at the ICC only to the load of each cell, that is, the total number of sub-carriers required for supporting the data rate requirement of all the users. We then present the DRA with limited coordination (DRA-LC) algorithm where the ICC performs load-adaptive inter-cell resource allocation with the limited information while the BS performs intra-cell resource allocation with full information about its own cell. For performance comparison, we design a centralized algorithm called DRA with full coordination (DRA-FC). Simulation results reveal that the DRA-LC algorithm can perform close to the DRA-FC algorithm at very low signaling overhead. In addition, it turns out to improve the QoS performance of the cell-boundary users, and achieve a better fairness among neighboring cells under non-uniform load distribution.

• 천문학회지
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• 제53권2호
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• pp.43-48
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• 2020

We report an analysis of two poorly studied eclipsing binary stars, GSC 04396-00605 and GSC 04395-00485 (recently named V455 Dra and V454 Dra, respectively). Photometric data of the two stars were obtained using the 1-m Korean telescope of the LOAO operated by KASI while monitoring the cataclysmic variable DO Dra in the frame of the Inter-Longitude Astronomy (ILA) project. We derived periods of 0.434914 and 0.376833 days as well as initial epochs JD 2456480.04281 and JD 2456479.0523, respectively, more accurate than previously published values by factors 9 and 6. The phenomenological characteristics of the mean light curves were determined using the New Algol Variable (NAV) algorithm. The individual times of maxima/minima (ToM) were determined using the newly developed software MAVKA, which outputs accurate parameters using "asymptotic parabola" approximations. The light curves were approximated using phenomenological and physical models. In the NAV algorithm, the phenomenological parameters are well determined. We derived physical parameters using the Wilson-Devinney model. In this model, the best-fit parameters are highly correlated, thus some of them were fixed to reasonable values. For both systems, we find evidence for the presence of a cool spot and estimate its parameters. Both systems can be classified as overcontact binaries of EW type.

• 전자공학회논문지
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• 제50권10호
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• pp.41-49
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• 2013

본 논문에서는 차량 충돌 방지용 밀리미터파 레이더 시스템용 안테나에 적용 가능한 LTCC(low temperature co-fired ceramic) 공정을 사용한 유전체 공진기 안테나(DRA, dielectric resonator antenna)를 제안한다. 76-77 GHz에서 공진하는 DRA를 설계하며, LTCC 공정을 사용하여 유전체 공진기 내부에 SRR(split ring resonator)을 넣은 구조와 모노폴을 넣은 구조를 제안한다. 또한 모노폴을 넣은 구조는 선형 편파를 제공하는 안테나와 원형편파를 제공하는 두 가지 구조로 설계한다. 유전체 공진기 내부 구조 및 편파, 급전 마이크로스트립 선로 길이 및 마이크로스트립 구조에 따라 총 3가지 모델의 DRA를 설계하고, EM 해석 소프트웨어인 CST를 사용하여 각 안테나의 반사손실 특성 및 방사 패턴을 계산한다. 설계된 안테나를 실제 제작하여 특성을 측정하고 계산치와 비교한다. 제작된 DRA 측정결과 원하는 대역인 76-77GHz 대역에서 공진 특성을 나타내고, 8.15 dBi에서 10.82 dBi의 안테나 이득을 획득하였다.

• Journal of Korean Neurosurgical Society
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• 제64권5호
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• pp.726-731
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• 2021

Objective : Distinguishing between an infundibulum and a true aneurysm is clinically important. This study aimed to evaluate whether using source image based new three-dimensional rotational angiography (S-n3DRA) can increase the rate of aneurysm detection and improve distinction between a true aneurysm and an infundibulum. Methods : Twenty-two consecutive patients with 23 lesions, were evaluated by time-of-flight (TOF) magnetic resonance angiography (MRA), S-n3DRA, and digital subtraction angiography (DSA). The data were retrospectively and independently reviewed by two neurointerventionists, and the diagnoses based on TOF MRA, S-n3DRA, and DSA were compared. The diagnostic efficacy (interobserver agreement and diagnostic performance) of S-n3DRA was compared with that of TOF MRA. Results : S-n3DRA showed higher interobserver agreement (κ=0.923) than TOF MRA (κ=0.465) and significantly higher accuracy than MRA in distinguishing an aneurysm from an infundibulum (p=0.0039). Conclusion : Compared to MRA, S-n3DRA could provide better screening accuracy and information for distinguishing an aneurysm from an infundibulum. Therefore, S-n3DRA has the potential to reduce the need for DSA.

• 한국통신학회논문지
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• 제30권11A호
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• pp.1035-1046
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• 2005

본 논문은 On Board Processing(OBP) 위성종신 중계기시스템에 대한 채널할당방식과 그 성능에 대하여 분석하였으며 채널할당의 효율을 개선하기 위한 CRA와 DRA에 대한 개선방식을 제시하였다. 수학적 분석과 시뮬레이션을 통해서 시스템의 성능을 평가한다. 실시간과 비실시간 서비스를 구분하였으며 음성, 화상과 같은 실시간 서비스는 지연민감성을 고려하여 우선순위를 높게 고려하였다. 탑재교환기는 CRA와 DRA의 두가지 할당방식을 역동적으로 활용한 알고리즘을 사용하여 채널 효율을 높이는 우수한 기법을 소개한다.

• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2157-2165
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• 2017

This study deals with the design of the mechanism in which demand response (DR) resources are traded in the power generation market. In general, a DR aggregator (DRA), which extends DR resources and provides technical support, is central to this mechanism. In this study, power users, called DR customer (DRC), participate in load reduction and are also modeled to participate directly in DR-related bidding. The DRA provides incentives to the DRC, indirectly impacting the market, and the DRC use the bid parameters strategically. We present the conditions for finding Nash Equilibrium (NE) in game problems of various participants including market operators, and analyze the characteristics of DRA and DRC related models. It also analyzes the impact of the participants on the market according to various types of competition and coalitions between DRA and DRC.