• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.618-626
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• 2011

Recent development of related technologies and efficient utilization of the entire country for the purpose of railway construction, and plans are being accelerated. the railway noise has been improved by increasing the high speed railway station, and accelerating the existing trains. Nord2000 which is an overseas noise prediction equation could not be applied directly to the domestic railway vehicles. So the specific vehicles in the Nordic countries which is a similar specification to domestic trains should be selected. Nord2000's accuracy was compared to Schall03, CRN's. Prediction of Ground impedance and Roughness class were carried out at different. In this paper, the result of selected vehicles for Nord2000 was as follows. S-1aX2 was for express trains, N-$^*2c$-3b was for Mugunghwa, S-Pass/wood was for Saemaul, N-4a was for freight trains, N-3a was for subway, the calculation time for Nord2000 took longer than others, in addition, Ground absorption was indispensable to calculate a noise map for Nord2000. As a result, CRN's prediction noise levels at Wonju-si was closest to the measurements. However, the predicted noise levels of Nord2000 was the most accurate.

• Journal of Korean Academy of Nursing Administration
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• v.16 no.3
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• pp.348-359
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• 2010

Purpose: This study aimed to evaluate the performance of Clinical Research Nurses (CRNs) and the importance of their roles at the Regional Clinical Trial Centers (RCTCs). Method: A questionnaire focused on the role of CRNs was crafted by a researcher and the content validity was verified by a panel of experts on clinical research. The subjects of this study were 91 CRNs and Clinical Research Coordinators (CRCs), who were Korean registered nurses working at nine RCTCs. 77 subjects yielded valid data were analyzed using descriptive analysis, the Mann-Whitney U test, Spearman's rank order correlation coefficient, and Kruskal-Wallis test. Results: The performance of CRNs and the recognition in the importance of their roles were statistically significant different in age, education, CRN careers, positions, employment status and the phase of clinical trial. The role of direct caregiver was performed most often by CRNs. The role of coordinator of care and research (pre-study) was considered the most important role but performed the least frequent. Conclusions: The role of CRNs can easily be differentiated from CRCs who are not registered nurses. The domains of CRNs should be clearly identified and established. Moreover, research should be carried out on CRN training programs to cultivate competence in CRNs.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.5
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• pp.223-228
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• 2017

Aluminum nitride (AlN) powder was successfully synthesized at low temperature via carbothermal reduction and nitridation (CRN) assisted by microwave heating. The synthesis processes of AlN powder were investigated with X-ray diffraction, FE-SEM, FT-IR and TGA/DSC. Aluminum nitrate was used as an oxidizer and aluminum source, urea as fuel, and glucose as carbon source. These starting materials were mixed with D.I water and reacted in a flask at $100^{\circ}C$ for 20 minutes. After the reaction was finished, black foamy intermediate product was formed, which was considered to be an amorphous $Al_2O_3$ particles through intermediate product obtained by solution combustion synthesis (SCS) at the results of X-ray diffraction patterns and FT-IR. This intermediate product was nitridated at temperatures of $1300^{\circ}C$ and $1400^{\circ}C$ in $N_2$ atmosphere by a microwave heating furnace and then decarbonated at $600^{\circ}C$ for 2 hours in air. It should be noticed from FE-SEM images that as nitridated particles, identified as AlN from X-ray diffraction patterns, are covered with carbon residues. After decarbonating the nitridated powders, the spherical pure AlN powders were obtained without alumina and their particle sizes were dependent on the nitridating temperature with high temperature of $1400^{\circ}C$ giving large particles of around 70~100 nm.

• Journal of Communications and Networks
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• v.17 no.4
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• pp.406-418
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• 2015

Cognitive radio networks (CRNs) have emerged as a promising solution to the problem of spectrum under utilization and artificial radio spectrum scarcity. The paradigm of dynamic spectrum access allows a secondary network comprising of secondary users (SUs) to coexist with a primary network comprising of licensed primary users (PUs) subject to the condition that SUs do not cause any interference to the primary network. Since it is necessary for SUs to avoid any interference to the primary network, PU activity precludes attempts of SUs to access the licensed spectrum and forces frequent channel switching for SUs. This dynamic nature of CRNs, coupled with the possibility that an SU may not share a common channel with all its neighbors, makes the task of multicast routing especially challenging. In this work, we have proposed a novel multipath on-demand multicast routing protocol for CRNs. The approach of multipath routing, although commonly used in unicast routing, has not been explored for multicasting earlier. Motivated by the fact that CRNs have highly dynamic conditions, whose parameters are often unknown, the multicast routing problem is modeled in the reinforcement learning based framework of learning automata. Simulation results demonstrate that the approach of multipath multicasting is feasible, with our proposed protocol showing a superior performance to a baseline state-of-the-art CRN multicasting protocol.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.12
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• pp.3037-3054
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• 2013

Interference between primary user (PU) and secondary user (SU) transceivers should be mitigated in order to implement underlay spectrum sharing in cognitive radio networks (CRN). Considering this scenario, an improved joint subcarrier and bit allocation scheme for cognitive user with primary users' cooperation (PU Coop) in CRN is proposed. In this scheme, the optimization problem is formulated to minimize the average interference power level at the PU receiver via PU Coop, which guarantees a higher primary signal to interference plus noise ratio (SINR) while maintaining the secondary user total rate constraint. The joint optimal scheme is separated into subcarrier allocation and bit assignment in each subcarrier via arith-metric geo-metric (AM-GM) inequality with asymptotical optimization solution. Moreover, the joint subcarrier and bit optimization scheme, which is evaluated by the available SU subcarriers and the allocated bits, is analyzed in the proposed PU Coop model. The performance of cognitive spectral efficiency and the average interference power level are investigated. Numerical analysis indicates that the SU's spectral efficiency increases significantly compared with the PU non-cooperation scenario. Moreover, the interference power level decreases dramatically for the proposed scheme compared with the traditional Hughes-Hartogs bit allocation scheme.

• Journal of Communications and Networks
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• v.18 no.1
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• pp.112-122
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• 2016

Cognitive radio (CR) is considered an attractive technology to deal with the spectrum scarcity problem. Multi-radio access technology (multi-RAT) can improve network capacity because data are transmitted by multiple RANs (radio access networks) concurrently. Thus, multi-RAT embedded in a cognitive radio network (CRN) is a promising paradigm for developing spectrum efficiency and network capacity in future wireless networks. In this study, we consider a new CRN model in which the primary user networks consist of heterogeneous primary users (PUs). Specifically, we focus on the energy-efficient resource allocation (EERA) problem for CR users with a special location coverage overlapping region in which heterogeneous PUs operate simultaneously via multi-RAT. We propose a two-tier crossover genetic algorithm-based search scheme to obtain an optimal solution in terms of the power and bandwidth. In addition, we introduce a radio environment map to manage the resource allocation and network synchronization. The simulation results show the proposed algorithm is stable and has faster convergence. Our proposal can significantly increase the energy efficiency.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3313-3315
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• 1999

Si direct bonding(SDB) technology is very attractive for both Si-on-insulator(SOI) electric devices and MEMS applications because of its stress free structure and stability. This paper presents on pre-bonding according to HF pre-treatment conditions in Si wafer direct bonding. The characteristics of bonded sample were measured under different bonding conditions of HF concentration, and applied pressure. The bonding strength was evaluated by tensile strength method. The bonded interface and the void were analyzed by using SEM and IR camera respectively. A bond characteristic on the interface was analyzed by using IT- IR. Si-F bonds on Si surface after HF pre-treatment are replaced by Si-OH during a DI water rinse. Consequently, hydrophobic wafer was bonded by hydrogen bonding of Si $OH{\cdots}(HOH{\cdots}HOH{\cdots}HOH){\cdots}OH-Si$. The bond strength depends on the HF pre-treatment condition before pre- bonding (Min:$2.4kgf/crn^2{\sim}Max:14.9kgf/crn^2$)

• ETRI Journal
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• v.44 no.3
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• pp.400-412
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• 2022

In cognitive radio networks (CRNs), the computational complexity of resource allocation algorithms is a significant problem that must be addressed. However, the high computational complexity of the optimal solution for tackling resource allocation in CRNs makes it inappropriate for use in practical applications. Therefore, this study proposes a power-based pricing algorithm (PPA) primarily to reduce the computational complexity in downlink CRN scenarios while restricting the interference to primary users to permissible levels. A two-stage approach reduces the computational complexity of the proposed mathematical model. Stage 1 assigns subcarriers to the CRN's users, while the utility function in Stage 2 incorporates a pricing method to provide a power algorithm with enhanced reliability. The PPA's performance is simulated and tested for orthogonal frequency-division multiplexing-based CRNs. The results confirm that the proposed algorithm's performance is close to that of the optimal algorithm, albeit with lower computational complexity of O(M log(M)).

• The Journal of the Korea Contents Association
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• v.16 no.4
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• pp.347-358
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• 2016

ICT sector has been made a great deal of achievements for past 20 or more years in the aspects of the industrial promotion and the efficiency improvement under the strong leadership by the government for the informatization and still leads the Korean industries. However, the previous studies are mostly on how the quantitative growth of patents impacts a company's management achievements while being insufficient on the qualitative level. In this study, an analysis is attempted on the impact from the qualitative level of patents held by a ICT company leading Korean industry to its management achievements. In other words, if the concentration of technological innovation activities, a scale to measure the qualitative level of possessed patents is influential to the growth and the profit of a company is analyzed. The analysis result shows that the current time technological superiority index, RTA and the concentration index, CRn of the technological innovation activities significantly impact to the growth and the profit of company. This study demonstrates the positive impact from a highly qualitative level of patents to the growth and the profit of a company in ICT sector in the current circumstance of insufficient researches on the qualitative level of patents. Therefore, this study is expected to present a new start point for the future studies.

• Proceedings of the Korean Vacuum Society Conference
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• 2004.02a
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• pp.64-64
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• 2004