• ETRI Journal
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• 제39권2호
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• pp.213-221
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• 2017

The advent of wireless access in vehicular environments (WAVE) technology has improved the intelligence of transportation systems and enabled generic traffic problems to be solved automatically. Based on the IEEE 802.11p standard for vehicle-to-anything (V2X) communications, WAVE provides wireless links with latencies less than 100 ms to vehicles operating at speeds up to 200 km/h. To date, most research has been based on field test results. In contrast, this paper presents a numerical analysis of the V2X broadcast throughput limit using a path loss model. First, the maximum throughput and minimum delay limit were obtained from the MAC frame format of IEEE 802.11p. Second, the packet error probability was derived for additive white Gaussian noise and fading channel conditions. Finally, the maximum throughput limit of the system was derived from the packet error rate using a two-ray path loss model for a typical highway topology. The throughput was analyzed for each data rate, which allowed the performance at the different data rates to be compared. The analysis method can be easily applied to different topologies by substituting an appropriate target path loss model.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권5호
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• pp.1028-1048
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• 2011

The relation of multicast transmission and directional antennas is an open problem that has been debated for a long period of time. In this paper, we propose a group-aware multicast scheme of efficient multicast communication using the directional antennas for 60GHz millimeter wave wireless networks. For this purpose, we first derive the relation among beamwidth, distance between devices and most suitable data rate in the 60GHz frequency-based wireless network. In addition, for the dynamic beamforming of multicast communication, the x and y coordinates of any point with sender device at the center is generated, and a best-chosen group is deduced based on the Euclidean distance. Then the most suitable data rate for the group is obtained using the law of cosine. Using the Standard IEEE 802.11ad MAC protocol as an example, extensive simulation results demonstrate that the proposed scheme outperforms the existing multicast communication schemes with directional antennas under different situations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권3호
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• pp.1152-1167
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• 2018

In this paper, I propose an application layer cooperative congestion control scheme for safety message broadcast in vehicular networks, called CMS, that adaptively controls a vehicle's safety message rate and transmit timing based on the channel congestion state. Motivated by the fact that all vehicles should transmit and receive an application layer safety message in a periodic manner, I directly exploit the message itself as a means of estimating the channel congestion state. In particular, vehicles can determine wider network conditions by appending their local channel estimation result onto safety message transmissions and sharing them with each other. In result CMS realizes cooperative congestion control without any modification of the existing MAC protocol. I present extensive NS-3 simulation results which show that CMS outperforms conventional congestion control schemes in terms of the packet collision rate and throughput, especially in a high-density traffic environment.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2016년도 춘계학술발표대회
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• pp.239-240
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• 2016

모바일 환경이 발전하면서 다양한 스마트폰 중 안드로이드 기반의 스마트폰이 시장 점유율을 높여가고 있다. 하지만 최근 보안 이슈로 인해 애플사에서 만든 아이폰을 사용하는 사람이 증가하고 있다. 따라서 아이폰에 대한 어플리케이션 시장 역시 증가 추세이다. 하지만 안드로이드 기반 스마트폰은 어느 정도 소스코드가 공개되어있기에 개발 및 분석이 수월하지만, 애플사의 아이폰은 공개된 소스코드가 극히 적어 개발 및 분석이 상대적으로 어렵다. 따라서 아이폰 애플리케이션에서 오류 발생 시 시스템 라이브러리에서 발생하는 오류는 효율적으로 대처하기가 힘들다. 본 논문은 더 효율적으로 애플리케이션들을 개발하고 유지 및 보수 할 수 있도록 Mac OS X에서 LLDB를 이용한 아이폰 애플리케이션 역공학 분석 방법론을 제안한다.

• 정보와 통신
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• 제24권12호
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• pp.65-73
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• 2007

2007년8월 v2.0을 출간하면서 표준화가 완료된 Ultra Mobile Broadband(UMB) 기술은 진보된 안테나 기술과 함께, CDMA, TDM, Layer-superposed OFDM(LS-OFDM), OFDM, OFDMA의 장점들을 하나의 Air Interface로 통합하였으며, 효율적인 자원 관리 기법을 통해 더 많은 VoIP 사용자들을 수용할 수 있게 해준다. 4x4 안테나를 사용시 20MHz의 주파수 대역에 순방향 288 Mbps, 역방향 75 Mbps의 최대 전송률을 제공하며, 양방향에 대한 평균 Network 지연시간은 약 16.8 ms을 지원하고, 10 MHz 주파수 대역에 1000명 이상의 VoIP 사용자를 지원할 수 있다. 본 고에서는 UMB의 표준화 과정 및 현황 그리고 물리 계층과 MAC 계층의 요소 기술들에 대해 고찰한다.

• Carbon letters
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• 제24권
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• pp.90-96
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• 2017

We demonstrated the sensitivity of optically active single-walled carbon nanotubes (SWCNTs) with a diameter below 1 nm that were homogeneously dispersed in cement composites under a mechanical load. Deoxyribonucleic acid (DNA) was selected as the dispersing agent to achieve a homogeneous dispersion of SWCNTs in an aqueous solution, and the dispersion state of the SWCNTs were characterized using various optical tools. It was found that the addition of a large amount of DNA prohibited the structural evolution of calcium hydroxide and calcium silicate hydrate. Based on the in-situ Raman and X-ray diffraction studies, it was evident that hydrophilic functional groups within the DNA strongly retarded the hydration reaction. The optimum amount of DNA with respect to the cement was found to be 0.05 wt%. The strong Raman signals coming from the SWCNTs entrapped in the cement composites enabled us to understand their dispersion state within the cement as well as their interfacial interaction. The G and G' bands of the SWCNTs sensitively varied under mechanical compression. Our results indicate that an extremely small amount of SWCNTs can be used as an optical strain sensor if they are homogeneously dispersed within cement composites.

• Journal of Korean Neurosurgical Society
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• 제43권3호
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• pp.139-142
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• 2008

Objective: The purpose of this study was to evaluate the efficacy of spinal implant removal and to determine the possible mechanisms of pain relief. Methods: Fourteen patient~with an average of 42 years (from 22 to 67 years) were retrospectively evaluated. All patients had posterior spinal instrumentation and fusion, who later developed recurrent back pain or persistent back pain despite a solid fusion mass. Patients' clinical charts, operative notes, and preoperative x-rays were evaluated. Relief of pain was evaluated by the Visual Analog Scale (VAS) pain change after implant removal. Clinical outcome using VAS and modified MacNab's criteria was assessed on before implant removal, 1 month after implant removal and at the last clinical follow-up. Radiological analysis of sagittal alignment was also assessed. Results: Average follow-up period was 18 months (from 12 to 25 months). There were 4 patients who had persistent back pain at the surgical site and 10 patients who had recurrent back pain. The median time after the first fusion operation and the recurrence of pain was 6.5 months (from 3 to 13 months). All patients except one had palpation pain at operative site. The mean blood loss was less than 100ml and there were no major complications. The mean pain score before screw removal and at final follow up was 6.4 and 2.9, respectively (p<0.005). Thirteen of the 14 patients were graded as excellent and good according to modified MacNab's criteria. Overall 5.9 degrees of sagittal correction loss was observed at final follow up, but was not statistically significant. Conclusion: For the patients with persistent or recurrent back pain after spinal instrumentation, removal of the spinal implant may be safe and an efficient procedure for carefully selected patients who have palpation pain and are unresponsive to conservative treatment.

• Corrosion Science and Technology
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• 제7권3호
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• pp.162-167
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• 2008

Degradable implants have been in use for bone surgery for decades. However, degradable metal implants are one of the new research areas of biomaterials science. Magnesium has good biocompatibility due to its low toxicity, and it is a corroding, i.e. dissolvable, metal. Furthermore, magnesium is needed in human body, and naturally found in bone tissue. There have been some published reports also asserting the potential bone cell activation or bone healing effect of high magnesium ion concentrations. The classic method for achieving intertransverse process fusion involves autogenous iliac crest bone graft. Several investigations have been performed to enhance this type of autograft fusion. However, there is no research which has been undertaken to investigate the efficiency of pure magnesium particles in posterolateral spinal fusion. In this study, corrosion behavior of magnesium metal at the bone interface, the possibility of new bone cell formation and the degree of effectiveness in producing intertransverse process lumbar fusion in a sheep model have been investigated. Cortical bone screws were machined from magnesium alloy AZ31 extruded rod and implanted to hip-bones of sheep via surgery. Three months after surgery, the bone segments carrying these screws were removed from the sacrificed animals. Samples were sectioned to reveal Mg/bone interfaces and investigated using optical microscope, SEM-EDS and radiography. Optical and SEM images showed that there was a significant amount of corrosion on the magnesium screw. The elemental mapping results indicate, due to the presence of calcium and phosphorus elements, that there exists new bone formation at the interface. Furthermore, sixteen sheep were subjected to intertransverse process spinal fusions with pedicle screw fixation at various locations along their spines. Each animal was treated with 5cc autograft bone at one fusion level and 1cc magnesium+5cc autograft bone at the other. Six months after surgery, bone formation was evaluated by gross inspection and palpation, and radiological, histological, scanning electron microscopic and x-ray diffraction analyses. It may be stated that the potential for using useful corrosion of magnesium alloys in medical applications is expected to be significant.

• 한국통신학회논문지
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• 제38C권2호
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• pp.165-171
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• 2013

차량 통신 프로토콜은 IEEE 802.11 WG과 P1609에서 진행하고 있는 WAVE(Wireless Access in Vehicular Environments)가 대표적이며, 보안 등을 제외한 MAC과 PHY에 대한 부분은 표준으로 제정되었다. 이러한 차량통신을 이용하여 운전자들의 안전과 전체 교통 흐름의 원활한 통제를 위해 국내외에서 많은 프로젝트가 진행되고 있다. 따라서 본 논문에서는 교차로에서 좌회전 시도 시에 위험 상황이 예상되면 운전자에게 알려주기 위한 차량간 통신 기반 안전서비스 알고리즘을 설계하였고, 이를 실제 구현하였다. 제안하는 알고리즘은 자차와 반대편에서의 접근차량에 대한 모델을 구성하고 충돌 위험이 있을 경우 운전자에게 HMI(Human Machine Interface)를 통해 경고를 주게 된다. 본 안전 서비스의 성능 테스트를 위해 테스트 차량을 이용하여 알고리즘을 시스템에 탑재하였으며, 테스트 케이스를 구성하여 성능 시험장에서 검증하였다. 테스트 결과로써, 우수한 성능을 나타냈으며, 앞으로 차량 통신 인프라가 설치된다면 V2I(Vehicle to Infrastructure) 통신을 이용하여 본 알고리즘을 보다 정밀하게 보완해야 할 것이다.

• Journal of Nutrition and Health
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• 제39권2호
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• pp.133-144
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• 2006

The purpose of this study was to evaluate the nutritional status and to identify related factors in elderly hemodialysis patients. Sixty-four patients who were registered in Asan Medical Center, Seoul, Korea, participated in the study. The data was collected between September and December, 2003. General characteristics were obtained with the use of an interviewer-administered questionnaire. Anthropometric and biochemical data, 3-day dietary records and dietary habits were also obtained. The results of this study were analyzed with t-test or $X^2$-test using SPSS package program. The percentage of elderly hemodialysis patients who were undergoing mild to severe malnutrition (MN group) and were normal nutrition (NN group) by subjective global assessment (SGA) criteria were 46.9% and 53.1 %, respectively. Appetite (p < 0.05) and dietary cholesterol intakes (p < 0.05) were significantly lower in MN group than the NN group. Body mass index (BMI, p < 0.001), lean body mass (LBM, p < 0.05), triceps skinfold thickness (TSF, p < 0.01), mid ann circumference (MAC, p < 0.01) and mid ann muscle circumference (MAMC, p < 0.05) were also lower in the MN group than the NN group. There were also significant differences in blood urea nitrogen (BUN, p < 0.05), creatinine (p < 0.05), prealbumin (p < 0.001) and C-reactive protein (CRP, p < 0.05). SGA was negatively correlated with serum BUN, creatinine and pre albumin, dry weight, BMI, LBM, total body water, TSF, MAC and MAMC, and positively correlated with age. In stepwise multiple regression analysis, SGA was related to BMI, CRP, age and BUN. In conclusion, almost half of the subjects were in malnourished status and had lower values in anthropometric and biochemical data. Our results suggest that SGA is a simple and adequate method for assessing the nutritional status in elderly hemodialysis patients and adequate dietary guidelines based on individual nutritional status are needed in the patients.