• 한국전자파학회논문지
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• 제12권4호
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• pp.600-610
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• 2001

본 논문에서는 초고속 위성통신 시스템의 채널 특성에 대한 성능 분석을 하였다. 고속 데이터 전송의 열화요인으로 작용하는 군지연과 비선형 분석을 통하여 다양한 전송 서비스를 제공하는 Ka 대역의 초고속 전송 시스템의 채널 성능 영향을 고찰하였다. 전송 데이터가 증가할수록 군지연과 비선형에 의한 영향은 증가하며, 군지연 선형 성분과 비선형의 AM-AM 성분이 시스템 성능 열화에 지배적으로 작용하는 것을 알 수 있었다. 고속 데이터에 따른 광대역 전송 대역폭으로 낮은 군지연과 이득 평탄도를 얻기가 어려우므로 주요 열화 요소를 등화하여 수십 Mbps에서부터 수백 Mbps 의 넓은 범위의 서비스를 동일 시스템에서 효과적으로 제공하여야 한다. 분석된 결과는 최적의 동작점을 갖는 초고속 위성통신 시스템을 설계하고 운용하는데 활용될 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권8호
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• pp.4041-4059
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• 2019

Key establishment method based on channel reciprocity for time division duplex (TDD) system has earned a vital consideration in the majority of recent research. While most of the cellular systems rely on frequency division duplex (FDD) systems, especially the 5G network, which is not characterized by the channel reciprocity feature. This paper realizes the generation of a group secret key for multi-terminals communicated through a wireless network in FDD mode, by utilizing the nature of the physical layer for the wireless links between them. I consider a new group key generation approach, which using bitwise XOR with a modified pairwise secret key generation approach not based on the channel reciprocity feature. Precisely, this multi-node secret key agreement technique designed for three wireless network topologies: 1) the triangle topology, 2) the multi-terminal star topology, and 3) the multi-node chain topology. Three multi-node secret key agreement protocols suggest for these wireless communication topologies in FDD mode, respectively. I determine the upper bound for the generation rate of the secret key shared among multi-node, for the three multi-terminals topologies, and give numerical cases to expose the achievement of my offered technique.

• International Journal of Fluid Machinery and Systems
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• 제9권4호
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• pp.370-381
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• 2016

As a single-channel pump is used for wastewater treatment, this particular pump type can prevent performance reduction or damage caused by foreign substances. However, the design methods for single-channel pumps are different and more difficult than those for general pumps. In this study, a design optimization method to improve the hydrodynamic performance of a single-channel pump impeller is implemented. Numerical analysis was carried out by solving three-dimensional steady-state incompressible Reynolds-averaged Navier-Stokes equations using the shear stress transport turbulence model. As a state-of-the-art impeller design method, two design variables related to controlling the internal cross-sectional flow area of a single-channel pump impeller were selected for optimization. Efficiency was used as the objective function and was numerically assessed at twelve design points selected by Latin hypercube sampling in the design space. An optimization process based on a radial basis neural network model was conducted systematically, and the performance of the optimum model was finally evaluated through an experimental test. Consequently, the optimum model showed improved performance compared with the base model, and the unstable flow components previously observed in the base model were suppressed remarkably well.

• 비교문화연구
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• 제19권
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• pp.411-444
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• 2010

This paper explored the academic socialization of a group of Mongolian college students, learning Korean as their L3 (Third Language), by focusing on their uses of an electronic communication channel. From a perspective of the continua of bi-literacy, this case study investigated how Mongolian students who had limited exposure to a Korean learning community overcame academic challenges through the use of a written communication channel as a tool in the socialization process. Data were collected mainly through three methods: written products, interviews, and questionnaires. The results from this study were as follows. Interactional opportunities for these minority students were seriously constrained during the classroom practices in a Korean-speaking classroom. They also described the lack of communicative competence in Korean and the limited roles played by L2 (English) communication as key barriers to classroom practices. However, students' ways of engaging in electronic interactions differed widely in that they were able to broaden interactional circles by communicating their expertise and difficulties with their Korean peers through the electronic channel. More importantly, the communication pattern of "L2-L2/L3-L3" (on a L2-L3 continuum) emerging from data demonstrated how these students used a written channel as a socialization tool to mediate their learning process in a new community of learning. This study argues that a written communication channel should be taken as an essential part of teaching practices especially for foreign students who cannot speak Korean fluently in multi-cultural classes.

• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 1997년도 학술발표회
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• pp.35-35
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• 1997

We model the voltage-gated cation channel on the basis of stochastic process by taking into account transmembrane movement of S4 group interacting electrostatically with permeant ions. It is assumed that the interaction between the ion and S4 group is repulsive harmonic force and the ionic motion is much faster than that of the S4 group.(omitted)

• The Korean Journal of Pain
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• 제24권2호
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• pp.74-80
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• 2011

Background: Lidocaine patch (L5P) has demonstrated short-term efficacy in treating both acute surgical pain and chronic neuropathic pain with tolerable side effects. Percutaneous endoscopic lumbar discectomy (PELD) is the mainstay of minimally invasive spine surgery (MISS). Sufficient analgesia during PELD surgery makes the patient consider it real MISS. This study was performed to evaluate the efficacy and adverse effects of lidocaine patch in patients who underwent PELD under local anesthesia. Methods: L5P (L group) or placebo (P group) was randomly applied on the skin of the back covering the anticipated path of the working channel before 1 hour of surgery in 100 patients who underwent a single level PELD at L4-L5. Efficacy of the lidocaine patch was assessed by patient's numeric rating scale (NRS) of pain at each stage during the surgery and by a 5-scale grading of the satisfaction with the anesthesia of the operator and patients after surgery. Results: Mean NRS scores at the stages of needle insertion, skin incision, serial dilation and insertion of working channel, and subcutaneous suture were significantly lower in the L group than the P group. Postoperative operator's and patients' satisfaction scores were also significantly higher in L group than in the P group. There were subtle adverse effects in both groups. Conclusions: L5P provided better pain relief during PELD, especially at the stage of needle insertion, skin incision, serial dilation and insertion of working channel, and subcutaneous suture. It also provided higher patient and operator postoperative satisfaction, with only subtle adverse effects.

• 정보보호학회논문지
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• 제23권3호
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• pp.561-566
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• 2013

본 논문은 Torus-Based-Cryptosystem 중 $T_2(p)$ 에서 부채널공격을 방지하는 효율적인 지수 연산방법을 제안한다. 제안한 지수 연산방법은 일반적인 지수 연산보다 더 효율적일 뿐만 아니라 제곱과 곱셈 연산의 계산량 차이를 없게하여 SPA 공격에 안전하다. 또한 상군(quotient group)의 특성을 이용하여 지수 연산시 메시지를 난수화하여 제1차 DPA 공격도 방어할 수 있다.

• 디지털산업정보학회논문지
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• 제8권4호
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• pp.99-105
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• 2012

Recently, there are many user selection algorithms in multi user multiple-input multiple-output (MU-MIMO) systems. One of well-known user selection methods is Semi orthogonal user selection (SUS). It is an algorithm maximizing channel capacity. However, it is applicable only when user's antenna is one. We propose a generalized user selection algorithm regardless of the number of user's antennas. In the proposed scheme, Base station (Bs) selects the first user who has the highest determinant of channel and generates a user group that correlation with first user's channel is less than allowance of correlation. Then, each determinant of channels made up of first user's channel and a user's channel in the generated group is calculated and BS selects the next user who has the highest determinant of that. BS selects following users by repeating above procedure. In this paper, we get better performance because of selecting users who have the highest determinant of channel as well as allowance of correlation optimally calculated through matrix operations.

• 한국기계가공학회지
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• 제14권3호
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• pp.9-14
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• 2015

The Direct Metal Tooling (DMT) process is a kind of additive manufacturing processes, which is developed using various commercial steel powders, such as P20, P21, SUS420, and other non-ferrous metal powders. The DMT process is a versatile process that can be applied to various fields, such as the molding industry, the medical industry, and the defense industry. Among them, the application of the DMT process to the molding industry is one of its most attractive and practical applications, since the conformal cooling channel cores of injection molds can be fabricated at a slightly expensive cost by using the hybrid fabrication method of DMT technology compared with parts fabricated with machining technology. The main objectives of this study are to provide various characteristics of the parts made using the DMT process compared with the same parts machined from bulk materials and evaluate the performance of the injection mold equipped with a conformal cooling channel core fabricated using the hybrid method of the DMT process.

• 한국통신학회논문지
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• 제35권2A호
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• pp.186-195
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• 2010

WiMAX에서 핸드오버를 준비하는 단말은 타겟 기지국을 결정하기 위해 스캐닝 동작을 수행한다. 보다 빠른 타겟 기지국 결정을 위해, 기존의 그룹 스캐닝 기법에서는 인접한 단말들 간에 그룹을 구성하여 분산적으로 후보채널들을 스캔하도록 하였다. 그러나 기존의 그룹 스캐닝은 각 단말이 사용 중인 서비스의 QoS 요구조건이 각기 다른 경우, 각 단말이 후보 채널들을 스캔하는 성능에 차이가 있을 수 있음을 고려하지 않았다. 본 논문에서는 그룹 스캐닝을 수행하는 단말들이 각각의 QoS에 적합한 스캔 스케쥴을 갖도록 하는 QoS 기반의 효율적 그룹 스캔 스케쥴링 기법을 제안한다. 제안된 방법은 서빙 기지국이 단말의 QoS를 고려하여, 초기에 그룹을 형성한 단말들과 나중에 그룹에 참여하는 단말들에게 적절한 후보 기지국들을 스캔하도록 할당하며, 각 단말이 QoS를 저해하지 않으면서 효율적으로 그룹 스캐닝을 수행할 수 있도록 한다. 모의 실험 결과, 제안된 방법은 단일의 그룹 내에서 상대적으로 QoS가 높은 단말로 하여금 상대적으로 적은 채널을 스캔하도록 하며, 각 단말의 QoS를 저해하지 않는 범위 내에서 기존의 그룹 스캐닝 보다 빠르게 타겟 기지국을 결정하도록 한다.