• 한국응용과학기술학회지
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• 제32권4호
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• pp.599-606
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• 2015

This study aimed at evaluating the antioxidant activity of raw yam (Dioscorea batatas $D_{ECNE.}$) extracted by n-butanol and ethyl acetate. The antioxidant activities, including ABTS [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt] radical scavenging activity, DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity, reducing power, and ferric reducing antioxidant power as well as total phenol contents were studied in vitro. Results showed ethyl acetate extract ($111.88{\pm}0.66mg\;CAE/g$) possessed higher total phenol content than n-butanol extract ($78.68{\pm}0.58mg\;CAE/g$). Ethyl acetate extract exhibited stronger antioxidant activity compared with n-butanol extract apart from reducing power assay.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.9-16
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• 2001

The lifetime of power train components can be improved dramatically by finding crack initiation points with suitable software tools and optimization of the critical areas. With increasing capacities of computers the prediction of the lifetime for components by numerical methods gets more and more important. This paper discusses some applications of the outstanding fatigue simulation program FEMFAT supporting the assessment of uniaxially and multiaxially loaded components (as well as welding seams and spot joints). The theory applied in FEMFAT differs in some aspects from classical approaches like the nominal stress concept or the local one and can be characterized by the term "influence parameter method". The specimen S/N-curve is locally modified by different influence parameters as stress-gradient to take into account notch effects, mean-stress influence which is quantified by means of a Haigh-diagram, surface roughness and treatments, temperature, technological size, etc. It is possible to consider plastic deformations resulting in mean-stress rearrangements. The dynamic loading of power train components is very often multiaxial, e.g. the stress state at each time is not proportional to one single stress state. Hence, the directions of the principal axes vary with time. We will present the way how such complex load situations can be handled with FEMFAT by the examples of a crank case and a gear box.

• Journal of Biosystems Engineering
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• 제37권6호
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• pp.385-397
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• 2012

Purpose: Drying characteristics of sawdust was studied under batch mode using lab scale microwave dryer. The objective of this study was to investigate the effect of material load and microwave output power on drying characteristics of sawdust. Methods: Material load and microwave output power were varied from 23 to 186 g and 530 to 370 W respectively. Different kinetic models were tested to fit the drying rates of sawdust. Similarly, the activation energy was calculated by employing the Arrhenius equation. Results: The drying efficiency increased considerably, whereas the specific energy consumption significantly decreased with increase in material load and microwave output power. The cumulative energy efficiency increased by 9%, and the specific energy consumption decreased by 8% when the material load was increased from 23 to 186 g. The effective diffusivity increased with decrease in material load and increase in microwave output power. The previously published model gave the best fit for data points with $R^2$ and RMSE values of 0.999 and 0.01, respectively. Conclusions: The data obtained from this study could be used as a basis for modeling of large scale industrial microwave dryers for the pellet production.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.1181-1182
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• 2006

The solar power system comprises a solar battery that directly converts light energy to electrical energy with a photovoltaic effect and a power converter system, that is, inverter that converts direct current power, which is generated from solar battery to common alternating current. In this paper, database was constituted through remote monitoring supervision measurement for the long-time positive operation of 3kW solar power system installed within the solar energy positive research complex of Chosun University. As a result of analyzing the reduction of the efficiency of solar battery and inverter that are compositional components of PV system through an analysis on the acquired data, the PV output was proven over 65% of the total output when insolation intensity exceeded 600W/m2 in 2005, and the array conversion efficiency dropped much more than rating; meanwhile, insolation intensity dropped below 600W/m2. Therefore, it has been demonstrated that approximately 35% of the entire amount of PV output operated under the condition that the inverter efficiency rate dropped rapidly by 60 to 70%.

• Nuclear Engineering and Technology
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• 제32권1호
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• pp.10-16
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• 2000

Preliminary experiment was peformed to investigate the leaching characteristics of paraffin waste forms that had been recently generated in large quantities at domestic nuclear power plants. At first, waste simulants whose compositions were different in mixing ratio of paraffin to boric acid were prepared. Their compressive strengths were measured and ninety-day leaching test of specimen including cobalt was carried out according to ANSI/ANS-16.1 test procedure. Water immersion test was also conducted keeping pace with leaching test and the weight change and the compressive strength of specimen were observed after ninety days. The compressive strength of waste form exhibited 666 psi (4.53 MPa) in the case where mixing ratio of boric acid to paraffin was 78/22, which was adopted in concentrate waste drying system of domestic nuclear power plants. The leaching test resulted in about 50% of the cumulative fraction leached for boric acid and cobalt, respectively. The specific gravity of waste form was 0.87 ［g/g］whose value was less than that of water because the weight loss of about 39% occurred after the water immersion test of ninety days. It was also observed that the waste form which had undergone ninety-day water immersion test exhibited the compressive strength of 203 psi (1.38 MPa).

• Journal of Electrical Engineering and Technology
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• 제8권2호
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• pp.354-358
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• 2013

This paper discusses the analysis of arc conductance in a gas circuit breaker (GCB) during current interruption process and the investigation method of the interruption capability. There are some limitations in the application of the computational fluid dynamics (CFD) for the implementation of an arc model around the current zero, despite the fact that it gives good results for the high-current phase arc. In this study, we improved the accuracy in the analysis of the interruption performance by attempting the method using CFD and a mathematical arc model. The arc conductance at 200 ns before current zero (G-200ns) is selected as the indicator to predict the current interruption of the Short Line Fault (SLF). Finally, the proposed method is verified by applying to the actual circuit breakers which have different interruption performances.

• 한국통신학회논문지
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• 제36권12A호
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• pp.959-965
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• 2011

다양한 서비스의 활성화로 인한 이동 단말의 사용 시간 및 트래픽의 증가로 인해 배터리로 구동되는 이동 단말의 전력 절감 기술이 주목받고 있다. 본 논문은 4G 기술 중의 하나인 Mobile WiMAX라 불리는 IEEE 802.16m의 전력 절감 기술에 대해서 기술한다. 먼저 IEEE 802.16m의 기초가 되는 IEEE 802.16e 전력 절감 방안과의 차이점 및 기술적 특정을 살펴본다. 이동 단말의 효율적인 전력 관리를 위해 패킷들의 도착 분포 정보를 기반으로 동적 수면 사이클 조절 방안을 제안한다. 제안한 방안을 에너지 절감 측면과 패킷 대기 지연 시간 측면에서 살펴본다.

• Journal of Communications and Networks
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• 제18권4호
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• pp.639-648
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• 2016

Next-generation (4G) systems are designed to support universal frequency reuse (UFR) to achieve best use of valuable spectra. However, it leads to undesirable interference level near cell borders. To control this, 4G systems adopt techniques, such as network multiple-input multiple-output (MIMO) and inter-cell interference coordination (ICIC), to improve cell-edge throughput. Network MIMO aims at mitigating inter-cell interference towards cell-edge users (CEUs) through multi-cell cooperation, where each collaborative base station serves both cell-center users (CCUs) and CEUs, including other cells' CEUs, under a power constraint. The present ICIC strategies cannot be directly applied to network MIMO because they were designed in absence of multi-cell coordination. In the presence of network MIMO, this paper investigates antenna orientations in ICIC and the method of power management. Results show that a proper antenna orientation can improve the cell-edge capacity and meantime lower the interference to CCUs. Capacity inconsistency between CCUs and CEUs is detrimental to mobile communications. Simulation results show that the proposed power management for ICIC in network MIMO systems can achieve a uniform data rate regardless users' position.

• 응용통계연구
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• 제11권2호
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• pp.269-285
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• 1998

임상시험연구의 설계에서 적절한 표본수의 결정은 매우 중요한 문제 중의 하나이다. 본 논문에서는 생존분포를 비교하기 위한 여러 가지 방법들을 소개하고, 각 방법에서의 가정들을 고찰하였다. 또한 다양한 상황에서의 표본수와 검정력 등을 비교제시하고 모의실험을 통해 각 방법들의 이론상의 검정력과 실제 검정력을 알아보았다 그 결과로서 의학연구자들이 처한 여러 상황에 적합한 표본수의 결정방법을 제시하였다.

• International journal of advanced smart convergence
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• 제10권3호
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• pp.1-9
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• 2021

In the Internet of Thing (IoT) framework, massive machine-type communications (MMTC) have required large spectral efficiency. For this, non-orthogonal multiple access (NOMA) has emerged as an efficient solution. Recently, a non-successive interference cancellation (SIC) NOMA scheme has been implemented without loss. This lossless NOMA without SIC is achieved via correlated superposition coding (SC), in contrast to conventional independent SC. However, conventional minimum high-correlated SC for only 2-user NOMA schemes was investigated in the lossless 2-user non-SIC NOMA implementation. Thus, this paper investigates a 3-user low-correlated SC scheme, especially for an inflated achievable sum rate, with a design of 3-user low-correlated SC. First, we design the 3-user low-correlated SC scheme by taking the minimum sum rate between 3-user SIC NOMA and 3-user non-SIC NOMA, both with correlated SC. Then, simulations demonstrate that the low correlation in the direction of the first user's power allocation inflates the sum rate in the same direction, compared to that of conventional minimum high-correlated SC NOMA, and such inflation due to low correlation is also observed similarly, in the direction of the second user's power allocation. Moreover, we also show that the two low correlations of the first and second users inflates doubly in the both directions of the first and second users' power allocations. As a result, the proposed 3-user low-correlated SC could be considered as a promising scheme, with the inflated sum rate in the future fifth-generation (5G) NOMA networks.