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Antenna Selection Schemes in Bidirectional Full-Duplex MIMO Systems
Jang, Seokju,Ahn, Minki,Lee, Hoon,Lee, Inkyu IEEE 2016 IEEE Transactions on Vehicular Technology VT Vol.65 No.12
<P>In this paper, we investigate antenna selection (AS) methods for bidirectional (BD) full-duplex multiple-input–multiple-output (MIMO) systems in which antennas at each node can be selected to either transmit or receive. In this configuration, we first analyze the average sum rate of the optimal AS scheme that finds the best antenna set solution by examining all the possible candidates. The result provides insight into which transmit and receive antenna configuration improves the average sum-rate performance of the AS scheme. Then, we present a new AS algorithm that achieves near-optimal sum-rate performance with much reduced complexity compared with the optimal AS scheme. From simulation results, we verify that our sum-rate analysis for the optimal AS scheme matches the numerical results and confirm that, by employing the proposed AS algorithm, a performance gain of 15% is achieved.</P>
Chae Minki,Na Ji Ung,Lee Jang Hee,Shin Dong Hyuk 대한응급의학회 2023 Clinical and Experimental Emergency Medicine Vol.10 No.1
Objective: A cardiothoracic ratio ≥0.50 is widely used as an indicator of cardiomegaly, but associations between the cardiothoracic ratio and left ventricular systolic dysfunction (LVSD) have not been investigated previously. We conducted this study to investigate the relationship between cardiothoracic ratio measured using computed tomography (CT) and left ventricular ejection fraction (LVEF), and to determine the optimal cardiothoracic ratio for predicting left ventricular systolic dysfunction (LVSD). Methods: A retrospective cross-sectional study was performed using data from patients who underwent both chest CT and echocardiography at the emergency department from January 1 to December 31, 2021. The patients were classified as normal, or having mild, moderate, and severe LVSD based on their LVEF, and the cardiothoracic ratios of each group were compared. The receiver operating characteristic (ROC) curve analyses were used to identify the optimal cardiothoracic ratio for prediction of mild, moderate, and severe LVSD. Results: The final study population included 444 patients. The median CT-measured cardiothoracic ratio was 0.54 for patients with normal LVEF, and 0.60 for patients with LVSD (P<0.001). The optimal CT-measured cardiothoracic ratios for predicting mild, moderate, and severe LVSD were 0.56, 0.59, and 0.60, and their areas under the ROC curve were 0.653, 0.690, and 0.680, and negative predictive values were 90%, 94%, and 98%, respectively. Conclusion: The best cutoff value for a CT-measured cardiothoracic ratio suggestive of LVSD was 0.56, which is very different from the 0.50 value typically considered an abnormal cardiothoracic ratio. The CT-measured cardiothoracic ratio ≥0.56 can be used as a rough indicator of mild LVSD, and a ratio <0.60 can exclude severe LVSD with a high degree of confidence.
열분해가 Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) 물성에 미치는 영향
조민기(Minki Jo),장타오(Tao Zhang),장윤재(Yunjae Jang),정민호(Minho Jung),이은혜(Eunhye Lee),강호종(Ho-Jong Kang) 한국고분자학회 2022 폴리머 Vol.46 No.6
Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P(3HB-co-4HB))와 결정성 P(3HB-co-4HB)/비결정성 P(3HB-co-4HB) 혼합물의 용융가공에 의한 열분해가 이들 물성에 미치는 영향을 살펴보았다. P(3HB-co-4HB)와 이들 혼합물은 180℃ 이상의 가공온도에서 4HB 함량이 증가됨에 따라 소량의 열분해가 일어남을 확인하였다. 이러한 적은 양의 열분해는 용융 점도 감소와 tan δ를 증가시켜 P(3HB-co-4HB)의 용융가공 특성이 나빠짐을 알 수 있었다. 반면, 혼합물은 같은 4HB 함량에서 혼합된 비결정성 P(3HB-co-4HB)에 의하여 상대적으로 열분해가 적게 일어나 열분해에 의한 유변 특성 변화가 최소화되어 용융가공 특성 변화가 적음을 확인하였다. 이와 함께 열분해는 P(3HB-co-4HB)의 열적 특성 특히, 결정화 거동에 영향을 미쳐 결정화 온도 증가와 함께 결정화도 감소를 초래한다. 하지만 혼합물은 높은 4HB 함량에도 결정성 P(3HB-co-4HB)와 유사한 결정화 거동을 보이며 이는 상대적으로 높은 혼합물의 열안정성에 의한 결과로 해석할 수 있다. The effects of thermal degradation in melt processing on physical properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P(3HB-co-4HB)) and crystalline P(3HB-co-4HB)/non-crystalline P(3HB-co-4HB) mixtures were studied. It was found that thermal degradation occurred at 180℃ or higher and increased with increasing 4HB content. A small amount of thermal degradation reduces melt viscosity and increases the tanδ. As a result, it may cause a problem with melt processing ability. P(3HB-co-4HB) mixtures having similar 4HB content show a small change in rheological properties due to better thermal stability of non-crystalline P(3HB-co-4HB) in the mixtures. In addition, thermal degradation affects the crystallization behavior of P(3HB-co-4HB) in lowering crystallization temperature and decreasing crystallinity. The mixture shows the crystallization behavior similar to that of crystalline P(3HB-co-4HB), which attributed to the relatively better thermal stability of mixtures.
Failure mechanism for metal cylinder under explosive loading
노동환,서송원,이재근,Minki Jang,윤정환 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.9
This paper presents the numerical study of dynamic fracture for metal cylinder under internal explosive loading. Also, the effects of fracture models and groove designs on fracture behavior are investigated. For the dynamic hardening behavior, the Lim-Huh model including the thermal softening effect is adopted [1, 2]. Also, the Lou-Huh fracture model considering the strain rate dependency is used for fracture prediction [3]. The tensile fracture occurs first at the outer surface, and the shear fracture is observed near the inner surface. In addition, finite element analyses are performed to study the effect of various groove designs on dynamic fracture; single U-groove and V-groove at the outer surface. The tensile and shear fracture lines are predicted near the groove tip and inner surface, respectively. It is concluded that the stress triaxiality parameter is one of the critical factors in the dynamic fracture prediction of the metal cylinder.