• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5C
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• pp.527-539
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• 2009

In this paper, we propose an asynchonous ICI (Inter-Cell Interference) mitigation techniques for 3GPP LTE MIMO-OFDMA down-link receiver. An increasing in symbol timing misalignments may occur relative to sychronous network as the result of BS (Base Station) timing differences. Such symbol synchronization errors that exceed the guard interval or the cyclic prefix duration may result in MAI (Multiple Access Interference) for other carriers. In particular, at the cell boundary, this MAI becomes a critical factor, leading to degraded channel throughput and severe asynchronous ICI. Hence, many researchers have investigated the interference mitigation method in the presence of asynchronous ICI and it appears that the knowledge of the SCM (Spatial Covariance Matrix) of the asynchronous ICI plus background noise is an important issue. Generally, it is assumed that the SCM estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and training symbol is also not appropriate for MIMO-OFDMA system such as LTE. Therefore, a noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sinc type weighing method which can not only reduce the noise effectively minimizing estimation error caused by the spectral leakage but also implement frequency-domain moving average filter easily. By using computer simulation, we show that the proposed method can provide up to 3dB SIR gain compared with the conventional method.

• Tribology and Lubricants
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• v.27 no.5
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• pp.275-280
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• 2011

Automotive wheel bearing grease helps to reduce stresses and prevent wear of wheel bearings. But it is easily contaminated by water and other contaminants. In this study, we investigated the property change of automotive wheel bearing grease under water contamination. The result showed that some properties such as dropping point, work penetration and oxidation stability were not influenced by water content. However, most of properties such as work stability, water washout characteristics, leakage tendency, oil separation, evaporation loss and rust protection became worse after water was added. This is thought that added water makes the interaction weak between thickener and base oil of grease.

• Journal of Sensor Science and Technology
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• v.27 no.3
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• pp.143-149
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• 2018

In this paper, we introduce an edge-spike modulation method for visible light communication (VLC). This method is effective in preventing LED flicker and 120 Hz noise interference in base-band VLC. In the VLC transmitter, edge-spikes are generated by passing the digital data through a simple RC-high pass filter (HPF). The LED modulation of the edge-spikes does not change the average power of the LED light; thus it prevents LED flicker. In the VLC receiver, the 120 Hz noise from other lighting lamps is easily eliminated by RC-HPF, while the edge-spike signal is detected normally. In our experiment, the message of an air-quality sensor was successfully transmitted using edge-spike modulation. This structure is useful in constructing, e.g., wireless gas monitoring sensor systems to warn and prevent harmful gas leakage accidents in buildings using LED light.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.762-772
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• 2016

This paper studies the problem of precoding and post-coding design for multicell multiuser downlink transmissions in the absence of perfect channel state information (CSI). Using statistical information of imperfect CSI, an iterative multiuser multicell transceiver design is formulated by minimizing the mean squared error (MSE) cost function of signal and leakage interference under per-base station power constraint (PBPC). The convergence of the iterative precoding and postcoding algorithm is verified by analytical and empirical results. The proposed precoding and postcoding algorithm offers a low computational complexity and robustness against CSI imperfection.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.367-371
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• 2004

Bio-degradable hydraulic oil using polyolester base oil is formulated for the applications of heavy duty hydraulic machineries. It has proved quality and market price competitiveness by assessment of reliability test in vehicle manufacturer and specific vehicle related institute. Contribution of bio-degradable oil keep the working environment clean and increase export competitiveness in European market. Leakage or waste of mineral types of hydraulic oils in heavy duty machineries causes pollution of river, ocean, underground water. Drinkable-water pollution is serious problem in Europe. In some European countries, using bio-degradable hydraulic oils become an obligation in heavy duty machineries. New product of bio-degradable oils satisfy the European regulations(OECD 302B) and shows excellent performance in compare with European products.

• Journal of Korean Neurosurgical Society
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• v.44 no.5
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• pp.285-294
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• 2008

Objective: Jugular foramen schwannomas are uncommon pathological conditions. This article is constituted for screening these tumors in a wide perspective. Materials: One-hundred-and-ninty-nine patients published in 19 articles between 1984 to 2007 years was collected from Medline/Index Medicus. Results: The series consist of 83 male and 98 female. The mean age of 199 operated patients was 40.4 years. The lesion located on the right side in 32 patients and on the left side in 60 patients. The most common presenting clinical symptoms were hearing loss, tinnitus, disphagia, ataxia, and hoarseness. Complete tumor removal was achieved in 159 patients. In fourteen patients tumor reappeared unexpectedly. The tumor was thought to originate from the glossopharyngeal nerve in forty seven cases; vagal nerve in twenty six cases; and cranial accessory nerve in eleven cases. The most common postoperative complications were lower cranial nerve palsy and facial nerve palsy. Cerebrospinal fluid leakage, meningitis, aspiration pneumonia and mastoiditis were seen as other complications. Conclusion: This review shows that jugular foramen schwannomas still have prominently high morbidity and those complications caused by postoperative lower cranial nerve injury are life threat.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.853-856
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• 2002

Present. direct method x-ray conversion detector is studied by abroad medical instrument and country with amorphous Selenium. And we search the method for large area x-ray detector. Amorphous-Selenium based photoreceptor is widely used on the X-ray conversion materials. But amorphous-selenium based x-ray conversion detector is broken by high voltage and leakage defect point. In this paper, We investigated top-electrode distance rate to improve defect point and high voltage broken. The result to appoint to made large area x-ray conversion detector with base data.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.151-151
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• 2008

바이폴러 트랜지스터(이하 BJT)의 고온 콜렉터-베이스 역전압 수명시험을 실시하였고, 수영시험 전후의 특성평가를 통해 BJT의 고장모드를 분석하였다. 시험조건은 주위온도 $150^{\circ}C$에서 콜렉터-베이스 정격 역전압의 80%를 인가한 상태에서 실시하였으며, 시료수는 57개이고 최종 목표 시험시간은 2,000시간이다. 중간측정을 통해 BJT의 특성열화를 관찰하였으며, 1,500시간 경과 후 1개 시료에서 제품규격을 벗어나는 데이터가 측정되었다. 해당 시료를 분석한 결과 콜렉터-베이스 누설전류 및 전류이득($\beta$)이 증가하였고, 저주파에서의 junction capacitance 가 정상품 대비 크게 관찰되었다. 측정결과를 통해 누설전류 증가 및 이득이 증가한 원인을 추정하였다.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.11
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• pp.30-36
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• 1997

AlGaAs/GaAs HBTs are developed well enough to be commercialized as an active device in optical transmission system, but there remains the unanswered questions about reliability. In this paper we applied the reverse constant current stress at the high voltage in avalanche region for a long time to find out a new degradation mechanism of junctrion I-V. The unction off-set voltage at which the current vanishes to zero was shifted to the negative direction of applied bias due to the increment of leakage current as the stress time increases. It was identified that the degradation was induced by the hot carriers which were generated at space charge region and trapped at the interface between GaAs base and the passivation nitride enhancing the electric field across the nesa edge.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.328-336
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• 2006

Detailed heat transfer coefficient distributions an two. types of gas turbine blade tip, plane tip and squealer tip, were measured using a hue-detection base transient liquid crystals technique.. The heat transfer coefficients an the shroud and near tip regions of the pressure and suction sides af the blade were also. measured. The heat transfer measurements were taken at the three different tip gap clearances af 1.0%, 1.5%, and 2.5% of blade span. Results shaw the overall heat transfer coefficients on the tip and shroud with squealer tip blade were lower than those with plane tip blade. By using squealer tip, however, the reductions af heat transfer coefficients near the tip regions of the pressure and suction sides were nat remarkable.