• Journal of Communications and Networks
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• v.11 no.5
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• pp.509-517
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• 2009

This work proposes a new distributed and self-organized authentication scheme for mobile ad-hoc networks (MANETs). Apart from describing all its components, special emphasis is placed on proving that the proposal fulfils most requirements derived from the special characteristics of MANETs, including limited physical protection of broadcast medium, frequent route changes caused by mobility, and lack of structured hierarchy. Interesting conclusions are obtained from an analysis of simulation experiments in different scenarios.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.3
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• pp.263-268
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• 2002

DFDM is a good candidate for beyond-3G high-speed wireless communication application because of the robustness to the intersymbol interference and multipath fading. However. an OFDM signal has a serious problem of the high PAPR, which results in the significant nonlinear distortion when it passes through a nonlinear high power amplifier. We propose a new PAPR reduction method using pre-emphasis and clipping. Via the proposed method, the OFDM output signal can have a low PAPR and BER improvement. Then. de-emphasis process is requisite in OFDM receiver. PAPR is reduced to about 5.7 ㏈ at the CCDF= 10$\^$-3/ when the subcarrier number is 16, QPSK modulation is used. pre-emphasis change point Is 3/9 of the peak amplitude of the IFFT output and clipping level is 11 in the IFFT output amplitude. The required SNR at BER=10$\^$-3/ the proposed system is improved by 2 dB than that of the original OFDM system.

• Advances in aircraft and spacecraft science
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• v.6 no.6
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• pp.443-461
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• 2019

This communication investigates exact and distorted similitudes and the related scaling laws for the analysis of both dynamic response and radiated power of rectangular plates. The response of a given panel in similitude from another one is determined from a generalization of the modal approach, allowing the use of mode shapes, natural frequencies and finally radiation functions in order to establish appropriate scaling laws. Analytical models of simply supported rectangular plates are used to produce both original and replica model responses under point mechanical excitation. Emphasis is then especially put on laboratory experiments which are performed on baffled simply supported aluminum panels under mechanical excitations. All the six possible scaling directions, i.e. predicting a plate vibroacoustic reponse from another plate, are reported. All obtained results show that structural response or radiated sound power of a given plate can be both recovered with satisfactory accuracy by using the related scaling laws, even if parent models are used.

• Ocean Systems Engineering
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• v.13 no.3
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• pp.225-245
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• 2023

In the present paper, a numerical and experimental analysis for a wave energy converter under extreme environmental conditions is carried out. After the definition of design waves, including a 100-year return period stochastic sea state and a deterministic rogue wave condition, a numerical analysis using potential theory and a RANS equations solver are compared with experiments carried out at the Seakeeping Basin at the Technical University of Berlin. Results are discussed with special emphasis on the limits of potential theory methods for the evaluation of extreme wave conditions and the use of the presented methodology for early design stages.

• World Technopolis Review
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• v.1 no.2
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• pp.129-140
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• 2012

This paper presents, from a broad perspective, the manner in which various types of clusters and options for regional development have evolved in Korea over the past decade, with particular emphasis on who have taken initiative in establishing the clusters. Characterized by not only progress but also setbacks, two distinctive patterns have emerged: centralized de-concentration and regionalized concentration. Both the Korean government and numerous localities have continuously extended efforts to create different clusters, technology parks, special districts, etc. In many cases, local or regional governments have competed intensely for clusters to be located in their jurisdictions; in particular, concerted efforts to convince national governments to set up special districts have been witnessed. On the other hand, major localities have made their own efforts to generate large- and small-scale clustering projects. It remains to be seen how different outcomes or effectiveness these two approaches will make in the future. Following the review of relevant literature and practices, I examine the well-known national campaign and projects in the previous administration in Korea in the context of 'de-concentration' of economic values and resources. Thereafter, other cases initiated mostly by local governments are discussed; some of these clustering efforts and regional projects have fared well thus far, but some haven't. In the case of Daegu, the progress of some critical projects, such as the Daegu Technopolis and a Free Economic Zone, is elaborated.

• International Journal of Advanced Culture Technology
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• v.11 no.2
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• pp.82-108
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• 2023

As tension escalates between the US and China, scenarios for maintaining peace in Northeast Asia imply that secondary powers will perceive increasing incentives to reappraise their respective international roles. This analysis proposes that an analysis of France's Cold War role in Europe and the world under President Charles de Gaulle provides insights into conflict management in an increasingly multipolar international political environment. Their respective interests in preventing a so-called new Cold War emerging between the US and China include avoiding its excessive economic costs, if only because China is a massive trade partner. This study engages in theoretical framework-informed process tracing of de Gaulle's role. It explicates the assumptions that functionally underpinned de Gaulle's policy of soft balancing between the US and China. The analysis explores de Gaulle's contribution to the decay of the Cold War. It illuminates de Gaulle's contribution to a regional international environment that made West German Chancellor Willy Brandt's Ostpolitik strategy more feasible politically. This study applies these findings in the formulation of strategy recommendations focusing on Japan. Valid inferences regarding the predominant motivations driving American and Chinese international interaction are necessary for this task. To the extent to which the US and China have entered into a conflict spiral, Japan's hedging towards Washington is further incentivized. Tokyo would necessarily need to convince the Chinese that Japan is no longer Washington's unsinkable aircraft carrier off its coast. Tokyo, like de Gaulle's France, would maintain close relations with Washington, but it would need to project to its interlocutors its commitment to its own strategic autonomy. Tokyo's emphasis on closer relations with liberal democratic Indo-Pacific actors would potentially fit well with a commitment to strategic autonomy to defend the global liberal order.

• Proceedings of the Materials Research Society of Korea Conference
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• 1992.05a
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• pp.17-17
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• 1992

The ceramic high transition temperature superconducting materials present many interesting characteristics that will be analysed from two points of view: physical behavior, and chemical aspects. From the first point of view, these materials display an enormous variety of different physical properties. At low doping levels the normal state shows antiferromagnetism and insulating behavior. At intermediate doping levels, an anomalous metallic state appears and, the optimum Tc in the superconducting state is generated. With increasing doping a normal metallic state develops and superconductivity starts to disappear. Many of the physical phenomena that describe the overall behavior when doping levels are changed will be discussed. From the poing of view of the chemical aspects. we well discuss some of the problems involved in the methods of preparation with particular emphasis on defects, crystal structures, critical currrents, and applications in technology.

• The KIPS Transactions:PartC
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• v.18C no.4
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• pp.237-242
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• 2011

LTE/SAE has presented the handover key management to revoke the compromised keys and to isolate corrupted network devices. In this paper, we identify that the handover key management is vulnerable to so-called de-synchronization attacks, which is jeopardizing the forward secrecy of handover key management. We place an emphasis on periodic root key update to minimize the effect of the de-synchronization attacks. An optimal value for the root key update interval is suggested in order to minimize signaling load and ensure security of user traffic.

• Smart Structures and Systems
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• v.23 no.1
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• pp.15-29
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• 2019

This paper addresses the problem of damage detection in suspension bridge hangers, with an emphasis on the modal flexibility method. It aims at evaluating the capability and the accuracy of the modal flexibility method to detect and locate single and multiple damages in suspension bridge hangers, with different level of severity and various locations. The study is conducted numerically and experimentally on a laboratory suspension bridge mock-up. First, the covariance-driven stochastic subspace identification is used to extract the modal parameters of the bridge from experimental data, using only output measurements data from ambient vibration. Then, the method is demonstrated for several damage scenarios and compared against other classical methods, such as: Coordinate Modal Assurance Criterion (COMAC), Enhanced Coordinate Modal Assurance Criterion (ECOMAC), Mode Shape Curvature (MSC) and Modal Strain Energy (MSE). The paper demonstrates the relative merits and shortcomings of these methods which play a significant role in the damage detection ofsuspension bridges.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.6
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• pp.525-533
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• 2009

Emphasis in the paper is placed on describing guided wave successes and challenges for applications in aircraft and composite materials inspection. Guided wave imaging methods discussed includes line of sight, tomography, guided wave C-scan, phased array, and ultrasonic vibration methods. Applications outlined encircles lap splice, bonded repair patch, fuselage corrosion, water loaded structures, delamination, and ice detection and de-icing of various structures.