• 한국통신학회논문지
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• 제38A권3호
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• pp.268-276
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• 2013

본 연구에서는 Heterogeneous Network에서의 간섭제어에 관한 기술 동향을 살펴보고, 간섭 제어 기술 중 3GPP release 10에서의 주요 기술 enhanced Inter-Cell Interference Coordination (enhanced ICIC, eICIC)을 택하여 성능을 분석해 보았다. eICIC기술 중 시간영역에서의 간섭 제어인 Almost Blank Subframe (ABS)와 Cell Range Expansion (CRE) 기술에 의한 성능을 분석하였다. Heterogeneous Network에서 macrocell과 femtocell 간의 간섭 제어를 적절히 하기 위해서는 ABS기술과 CRE 기술 간의 조합이 중요할 것으로 보인다. Heterogeneous Network의 전체 성능 평가는 정량적으로는 분석되기 어려워 system level simulation에 의해서 평가하였다. 본 연구에서는 SLS 방식으로 다양한 환경에 대한 성능을 분석함으로써 Heterogeneous Network 운영에 있어 각각의 요소가 미치는 영향을 파악할 수 있도록 하였으며, Heterogeneous Network에서의 ABS와 CRE의 결합에 의한 효과를 분석하였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권8호
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• pp.570-576
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• 1999

$LaCrO_3$-dispersed Cr alloys for metallic interconnector of solid oxide fuel cell have been studied as function of $LaCrO_3$ content in the range of 5 to 25 vol.% in order to examine the electric conductivity, the oxidation property and the thermal expansion behavior of these alloys. The $LaCrO_3$-dispersed Cr alloys showed high electrical conductivities of $3~5\times10^4$ S/cm at room temperature, and as the $LaCrO_3$content increased the conductivity decreased slightly. During the cyclic oxidation test at $1100^{\circ}C$, the weight change of the Cr alloys decreased with increasing number of oxidation cycle except first cycle, which is attributed to the vaporization of the oxide scale. More addition of the $LaCrO_3$ content reduced also the weight change of the Cr alloys. These mean that the oxide scale formed at the surface of the Cr alloy becomes stable with increasing number of oxidation cycle and$LaCrO_3$ content. The measured thermal expansion of the Cr alloy was well fitted to that of 8 mol% $Y_2O_3$-stabilized $ZrO_2$ electrolyte. These results demonstrate that $LaCrO_3$-dispersed Cr alloy is a useful material for metallic interconnector of solid oxide fuel cell.

• 공업화학
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• 제9권7호
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• pp.1090-1097
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• 1998

국부 마취제로 이용되는 lidocaine 화합물들이 마취 효과를 나타내는 과정을 알아보기 위하여 세포벽을 구성하는 지질 이중막의 모사 시스템으로 공기/물 계면에 형성된 지질 단분자 막을 이용하여 lidocaine 화합물들이 지질 단분자 막의 팽창에 미치는 영향을 연구하였다. Lidocaine이 신경 세포와 접하게 되면 세포벽을 구성하는 지질 이중막을 팽창시켜 이중막에 함침된 단백질을 압축하여 이를 통한 이온 통과가 차단되어 신경 전달이 마비된다는 가설과, 단백질 이온 통로에 존재하는 lidocaine receptor에 직접 흡착되어 이온 통로를 막는다는 가설이 구체적 실험 없이 제안되었다. 본 연구에서는 두 가설 타당성을 증명하고자 리피드 단분자 막팽창에 lidocaine이 미치는 영향을 조사하였다. 실험 결과 유용성인 lidocaine은 phosphatidyl choline, sphingomyelin, DS-PL95E, lipoid의 단분자 막을 수축시켰으며 phosphatidyl ethanolamine은 특정 조성 범위에서만 단분자 막을 팽창시켰다. 반면 수용성인 lidocaine-HCl 염은 실험에 사용된 모든 지질의 단분자 막을 팽창시켰다.

• International Journal of Automotive Technology
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• 제8권2호
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• pp.149-154
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• 2007

The engine behavior in a transient condition is important to not only emission regulations but also fuel economy. A fast response gas analyzer can be a useful tool to investigate exhaust gas in a transient operation. It should be designed to analyze gas concentration with a short time constant by a fast sampling module and an appropriate measuring method for each emission element. In this study, a new fast sampling module is introduced and flow analysis is performed by numerical simulation. The analysis has shown the proper operating condition and the sensitivity of the module for practical application. Calculated flow to the sampling module has $0.5{\sim}4%$ error, while backflow toward the expansion tube is expected when pressure in CP (Constant Pressure) chamber is over 0.6 bar. For a stable supply of flow to the optical cell, sample gas pressure should be in the range, $0.35{\sim}1.90$ bar, when the pressure in the CP camber and the optical cell are 0.2 bar and 0.158 bar, respectively.

• Journal of Welding and Joining
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• 제35권1호
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• pp.79-88
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• 2017

The effect of residual metallic sodium on the solidification cracking susceptibility of type 316FR stainless steel was investigated via transverse-Varestraint tests. And a solidification brittle temperature range (BTR) of type 316FR stainless steel was 37 K. However, the BTR expanded from 37 to 67 K, as the amount of metallic sodium at the specimen surface increased from 0 to $7.99mg/cm^2$. Microstructural observation of the weld metal suggested that metallic sodium existed in the weld metal, including in the cell boundaries, during welding solidification. Thermodynamic calculations suggested that sodium expanded the temperature range of solidliquid coexistence during welding solidification of the steel weld metal. Therefore, the increased solidification cracking susceptibility (i.e., expansion of the BTR) in the residual sodium environment was attributed to enhanced segregation of sodium during the welding solidification; this segregation, in turn, resulted in an expanded temperature range of solid-liquid coexistence.

• 한국통신학회논문지
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• 제31권7B호
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• pp.595-601
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• 2006

이 연구는 유비쿼터스 컴퓨팅 환경에서 절대 위치 좌표를 제공할 수 있는 초음파 위치인식 시스템에 관한 것이다. 무선(RF: Radio Frequency) 신호에 의해 동기화된 다수의 고정된 발신기가 순차적으로 초음파를 발신하며, 초음파 신호들을 수신한 수신기에서 TOF를 파악하여 이를 거리로 환산한 다음 위치정보를 계산한다. 초음파의 전파시간(TOF: Time of Flight)은 주기인식 방법을 통해 파악한다. 또한 유비쿼터스 컴퓨팅을 위한 인식 영역의 확장을 위해 셀 매칭 기법과 부호화된 초음파 기법을 제안한다. 초음파 위치인식 시스템인 U-SAT을 사용하여 주기인식 기법의 유용성을 입증하기 위하여 다양한 거리에서 실험을 수행하였다. 또한 셀 매칭 기법에 의한 영역 확장에서도 위치 측정의 정확도를 검증하였으며 부호화된 초음파 기법의 분석으로 그 유용성도 입증하였다. 그 결과로 인해 저가격, 높은 갱신율, 그리고 상대적으로 뛰어난 정밀도의 입장에서 GPS가 적용될 수 없는 환경에서의 유비쿼터스 컴퓨팅의 위치인식 시스템으로서의 가능성을 입증하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권8호
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• pp.3529-3550
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• 2016

In heterogeneous networks (HetNets), energy saving is vital for a sustainable network development. Many techniques, such as spectrum allocation, network planning, etc., are used to improve the network energy efficiency (EE). In this paper, micro BSs utilizing cell range expansion (CRE) and spectrum allocation are considered in multi-channel heterogeneous networks to improve EE. Hotspot region is assumed to be covered by micro BSs which can ensure that the hotspot capacity is greater than the average demand of hotspot users. The expressions of network energy efficiency are derived under shared, orthogonal and hybrid subchannel allocation schemes, respectively. Particle swarm optimization (PSO) algorithm is used to solve the optimal ratio of subchannel allocation in orthogonal and hybrid schemes. Based on the results of the optimal analysis, we propose three service control strategies on the basis of large-scale user behaviors, i.e., adjust micro cell rang expansion (AmCRE), adjust micro BSs density (AmBD) and adjust micro BSs transmit power (AmBTP). Both theoretical and simulation results show that using shared subchannel allocation scheme in AmBD strategies can obtain maximal EE with a very small area ratio. Using orthogonal subchannel allocation scheme in AmCRE strategies can obtain maximal EE when area ratio is larger. Using hybrid subchannel allocation scheme in AmCRE strategies can obtain maximal EE when area ratio is large enough. No matter which service control strategy is used, orthogonal spectrum scheme can obtain the maximal hotspot user rates.

• Journal of Communications and Networks
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• 제15권3호
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• pp.312-320
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• 2013

Home evolved Node-B (HeNB), also called a femtocell or a femto base station, is introduced to provide high data rate to indoor users. However, two main problems arise in femtocell networks: (1) Small coverage area of HeNB, which results in limited cell-splitting gain and ping-pong handover (HO) problems and (2) high inter-femtocell interference because HeNBs may be densely deployed in a small region. In this study, an efficient cooperation mechanism called an HeNB-aided virtual-HO (HaVHO) scheme is proposed to expand the coverage area of femtocells and to reduce inter-femtocell interference. The cooperation among neighbor HeNBs is exploited in HaVHO by enabling an HeNB to relay the data of its neighbor HeNB without an HO. The HaVHO procedure is compatible with the existing long term evolution specification, and the information exchange overhead in HaVHO is relatively low. To estimate the signal to interference plus noise ratio improvement, the area average channel state metric is proposed, and the amount of user throughput enhancement by HaVHO is derived. System-level simulation shows that HaVHO has a better performance than the other four schemes, such as lesser radio link failure, lesser ping-pong handover, lesser short-stay handover, and higher user throughput.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.644-648
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• 2004

In the present study were examined numerically and experimentally the off-design performance characteristics on an axisymmetric plug nozzle with variable throat area. In this nozzle concept, its throat area can be changed by translating the plug into the axial direction. First, a mixed-expansion plug nozzle, in which two expansion parts are arranged both inside and outside, was designed by means of the method of characteristics. Second, the CFD analysis was verified by the cold-flow wind tunnel test. Third, its performance characteristics were evaluated over a wide range of pressure ratio from half to double throat area through the design point, using the CFD code verified by the wind tunnel tests. It was made clear from the study that not so critical thrust efficiency losses were found and the maximum thrust efficiency loss was at most approximately 5 % under off-design conditions without external flow. This result shows that a plug nozzle can give the altitude compensation even under off-design geometry operations. However, shock waves were observed in the inner expansion part under the doubled throat area operation and thus some thermal problems may be caused on the plug surface. Furthermore, collapse of cell structure on the plug surface was observed with external flow (around Mach number 2.0) as it became lower pressure ratio below the design point and the fact may result in big efficiency loss regardless of geometrical configuration.

• 한국물환경학회지
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• 제39권6호
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• pp.451-464
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• 2023

Harmful cyanobacterial monitoring is time-consuming and requires skilled professionals. Recently, Phycocyanin, the accessory pigment unique to freshwater cyanobacteria, has been proposed as an indicator for the presence of cyanobacteria, with the advantage of rapid and simple measurement. The purpose of this research was to evaluate the correlation between the harmful cyanobacterial cell density and the concentration of phycocyanin and to consider how to use the real-time water quality monitoring system for algae bloom monitoring. In the downstream of the Nakdong River, Microcystis spp. showed maximum cell density (99 %) in harmful cyanobacteria (four target genera). A strong correlation between phycocyanin(measured in the laboratory) concentrations and harmful cyanobacterial cell density was observed (r = 0.90, p < 0.001), while a weaker relationship (r = 0.65, p < 0.001) resulted between chlorophyll a concentration and harmful cyanobacterial cell density. As a result of comparing the phycocyanin concentration (measured in submersible fluorescence sensor) and harmful cyanobacterial cell density, the error range increased as the number of cyanobacteria cells increased. Before opening the estuary bank, the diurnal variations of phycocyanin concentrations did not mix by depth, and in the case of the surface layer, a pattern of increase and decrease over time was shown. This study is the result of analysis when Microcystis spp. is dominant in downstream of Nakdong River in summer, therefore the correlation between the harmful cyanobacteria density and phycocyanin concentrations should be more generalized through spatio-temporal expansion.