• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.600-610
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• 2001

The effects of group delay and non-linear characteristics on high data rate(HDR) satellite channel are presented in this paper Based on the modeling of group delay and non-linear characteristics the system performances which provide various data rate services were analyzed in Ka-band satellite channel. As the transmission data rate is increased, the degradation due to these channel characteristics is severely increased. The linear component of group delay and the AM-AM component of non-linear characteristics severely affect the system performance. To efficiently provide the various service via the same transmission system it is necessary to equalize the primary impairment factors. The optimum operating points of HDR satellite transmission system are implemented by considering the analyzed results on channel characteristics.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.8
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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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• v.9 no.4
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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.

• Cross-Cultural Studies
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• v.19
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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.

• Proceedings of the Korean Biophysical Society Conference
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• 1997.07a
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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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• v.24 no.2
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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.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.23 no.3
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• pp.561-566
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• 2013

We propose an efficient exponentiation method which is resistant against some side channel attacks in $T_2(p)$, Torus-Based-Cryptosystem. It is more efficient than the general exponentiation method in $T_2(p)$ and is resistant against SPA by using that the difference of squaring and multiplication costs is negligible. Moreover, we can randomize a message in exponentiation step using the characteristic of quotient group which naturally protects against the first DPA.

• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.4
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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.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.3
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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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2A
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• pp.186-195
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• 2010

For the fast target base station channel decision in WiMAX networks, fast group scanning scheme was suggested, in which mobile stations in proximity of each other form a group and scan the candidate channels dispersively. However, the previous group scanning scheme does not consider the different QoS requirements of each MS in a group. In this paper we propose the enhanced group scanning scheme, so-called QoS-aware group scan scheduling scheme, that makes mobile stations in a group scan the candidate channels without deteriorating the QoS requirements. We introduce the QoS-aware channel scanning concept of a individual mobile station and show the different scanning latencies due to the different QoS requirements. With the help of the efficient channel allocation by the serving BS, in the proposed scanning scheme, a mobile station with relatively higher QoS in a group scans less amount of candidate channels than the others with relatively lower QoS, while the mobile stations in a group still guarantees the fast target base station decision. The performance results show that our proposed scanning scheme results in the fast target base station decision while considering the QoS requirements of each MS.