• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.53.2-53.2
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• 2015

Fiber Bragg gratings (FBGs) are the most compact and reliable method of suppressing atmospheric emission lines in the infrared for ground-based telescopes. It has been proved that real FBGs based filters were able to eliminate 63 bright sky lines with minimal interline losses in 2011 (GNOSIS). Inscribing FBGs on multi-core fibers offers advantages. Compared to arrays of individual SMFs, the multi-core fiber Bragg grating (MCFBG) is greatly reduced in size, resistant to damage, simple to fabricate, and easy to taper into a photonics lantern (PRAXIS). Multi-mode fibers should be used and the number of modes has to be large enough to capture a sufficient amount of light from the telescope. However, the fiber Bragg gratings can only be inscribed in the single-mode fiber. A photonic lantern bi-directionally converts multi-mode to single-mode. The number of cores in MCFBGs corresponds to the mode. For a writing system consisting of a single ultra-violet (UV) laser and phase mask, the standard writing method is insufficient to produce uniform MCFBGs due to the spatial variations of the field at each core within the fiber. Most significant technical challenges are consequences of the side-on illumination of the fiber. Firstly, the fiber cladding acts as a cylindrical lens, narrowing the incident beam as it passes through the air-cladding interface. Consequently, cores receive reduced or zero illumination, while the focusing induces variations in the power at those that are exposed. The second effect is the shadowing of the furthest cores by the cores nearest to the light source. Due to a higher refractive index of cores than the cladding, diffraction occurs at each core-cladding interface as well as cores absorb the light. As a result, any core that is located directly behind another in the beam path is underexposed or exposed to a distorted interference pattern from what phase mask originally generates. Technologies are discussed to overcome the problems and recent experimental results are presented as well as simulation results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.379-387
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• 2012

This study investigates free vibration characteristics of new energy harvesting multi-layer block structures with different geometrical shapes using solid and shell finite elements and evaluate their piezoelectric effect on experiments. The two and three-dimensional finite element (FE) delamination models for block structures described in this paper is attractive not only because it shows excellent accuracy in analysis but also it shows the entire vibration mode shape. The FE model using ABAQUS is used for studying free vibrations of multi-layer block structures for various tip mass and PZT. In particular, new results reported in this paper are focused on the significant effects of the global and local vibration modes for various parameters, such as size of block shape, existence of tip mass and hole, and location of tip mass and PZT. In addition, we evaluate the power generation capacity of developed energy block structures through a laboratory-scale experiment.

• Steel and Composite Structures
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• v.27 no.3
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• pp.389-399
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• 2018

A perforated shear connector group is commonly used to transfer shear in steel-concrete composite structures when the traditional shear stud connection is not strong enough. The multi-hole perforated shear connector demonstrates a more complicated behavior than the single connector. The internal force distribution in a specific multi-hole perforated shear connector group has not been thoroughly studied. This study focuses on the load-carrying capacity and shear force distribution of multi-hole perforated shear connectors in steel-concrete composite structures. ANSYS is used to develop a three-dimensional finite element model to simulate the behavior of multi-hole perforated connectors. Material and geometric nonlinearities are considered in the model to identify the failure modes, ultimate strength, and load-slip behavior of the connection. A three-layer model is introduced and a closed-form solution for the shear force distribution is developed to facilitate design calculations. The shear force distribution curve of the multi-hole shear connector is catenary, and the efficiency coefficient must be considered in different limit states.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.10
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• pp.59-65
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• 2008

We have proposed a UHF/HF multi-band RFID reader, and have implemented it into a system in a package(SiP). The proposed SiP RFID reader has been designed to support both for EPCgloabal Class1 Generation2 protocol of UHF band, and 13.56MHz RFID protocols of ISO14443 A/B type, and ISO15693 standards. The operating mode is controlled by embedded RISC core, and the mode can be selected by users. The area of implemented SiP is $40mm{\times}40mm$ with 4 metal layers. The implemented reader SiP operates at single supply voltage of 3.3V. The maximum current consumption is 210mA. The operating distances are 5cm for 13.56MHz modes, and 20cm for UHF mode.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.56-61
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• 2001

This paper presents the real-time implementation of an AMR (Adaptive Multi Rate) vocoder which is included in the asynchronous International Mobile Telecommunication (IMT)-2000 mobile ASIC. The implemented AMR vocoder is a multi-rate coder with 8 modes operating at bit rates from 12.2kbps down to 4.75kbps. Not only the encoder and the decoder as basic functions of the vocoder are implemented, but VAD (Voice Activity Detection), SCR (Source Controlled Rate) operation and frame structuring blocks for the system interface are also implemented in this vocoder. The DSP for AMR vocoder implementation is a 16bit fixed-point DSP which is based on the TeakLite core and consists of memory block, serial interface block, register files for the parallel interface with CPU, and interrupt control logic. Through the implementation, we reduce the maximum operating complexity to 24MIPS by efficiently managing the memory structure. The AMR vocoder is verified throughout all the test vectors provided by 3GPP, and stable operation in the real-time testing board is also proved.

• Steel and Composite Structures
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• v.41 no.5
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• pp.663-679
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• 2021

To elucidate the differences in the collapse behavior between a single-story beam-column assembly and multi-story frame, two 1/3-scale two-bay composite frames, including a single-story composite beam-column assembly and a three-story composite sub-frame, were designed and quasi-statically tested. The load-displacement responses, failure modes, and internal force development of the two frames were analyzed and compared in detail. Furthermore, the resistance mechanisms of the two specimens were explored, and the respective contributions of different load-resisting mechanisms to the total resistances were quantitatively separated to gain deeper insights. The experimental tests indicated that Vierendeel action was present in the two-dimensional multi-story frames, which led to an uneven internal force distribution among the three stories. The collapse resistance of TSDWA-3S in the flexural stage was not significantly increased by the structural redundancy provided by the additional story, as compared to that of TSDWA-1S. Although the development of the load response was similar in the two specimens at flexural stage, the collapse mechanisms of the multi-story composite frame were much more complicated than those of the single-story beam-column assembly, and the combined action between stories was critical in determining the internal force redistribution and rebalancing of the remaining structure.

• Structural Engineering and Mechanics
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• v.84 no.4
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• pp.489-502
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• 2022

This paper is aimed at developing an optimization-based Finite Element model updating approach for structural damage identification and quantification. A modal flexibility-based error function is introduced, which uses modal assurance criterion to formulate the updating problem as an optimization problem. Because of the inexplicit input/output relationship between the candidate solutions and the error function's output, a robust and efficient optimization algorithm should be employed to evaluate the solution domain and find the global extremum with high speed and accuracy. This paper proposes a new multi-stage Selective Particle Swarm Optimization (SPSO) algorithm to solve the optimization problem. The proposed multi-stage strategy not only fixes the premature convergence of the original Particle Swarm Optimization (PSO) algorithm, but also increases the speed of the search stage and reduces the corresponding computational costs, without changing or adding extra terms to the algorithm's formulation. Solving the introduced objective function with the proposed multi-stage SPSO leads to a smart feedback-wise and self-adjusting damage detection method, which can effectively assess the health of the structural systems. The performance and precision of the proposed method are verified and benchmarked against the original PSO and some of its most popular variants, including SPSO, DPSO, APSO, and MSPSO. For this purpose, two numerical examples of complex civil engineering structures under different damage patterns are studied. Comparative studies are also carried out to evaluate the performance of the proposed method in the presence of measurement errors. Moreover, the robustness and accuracy of the method are validated by assessing the health of a six-story shear-type building structure tested on a shake table. The obtained results introduced the proposed method as an effective and robust damage detection method even if the first few vibration modes are utilized to form the objective function.

• Journal of Intelligence and Information Systems
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• v.14 no.2
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• pp.83-102
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• 2008

Ubiquitous computing requires timely supply of contextual information in order to upgrade decision quality. In this sense, this study is aimed at proposing a multi-dynamic decision support system for highly ill-structured problems. Especially, it is very important for decision makers in the ubiquitous computing to coordinate conflicts among local goals and global goal harmoniously. The proposed Multi-Dynamic Decision Support System (MDDSS) is basically composed of both central structure and distributed structure, in which central structure supports multi objects decision making and distributed structure supports individual decision making. Its hybrid architecture consists of decision processor, multi-agent controller and intelligent knowledge management processor. Decision processor provides decision support using contexts which come from individual agents. Multi-agent controller coordinates tension among multi agents to resolve conflicts among them. Meanwhile, intelligent knowledge management processor manages knowledge to support decision making such as rules, knowledge, cases and so on. To prove the validity of the proposed MDDSS, we applied it to an u-fulfillment problem system in which many kinds of decision makers exist trying to satisfy their own objectives, and timely adjustment of action strategy is required. Therefore, the u-fulfillment problem is a highly ill-structured problem. We proved its effectiveness with the aid of multi-agent simulation comprising 60 customers and 10 vehicles under three experimental modes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.1
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• pp.135-140
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• 2020

Recently, due to the rapid diffusion of intelligent systems and IoT technologies, power saving techniques in real-time embedded systems has become important. In this paper, we propose P-GA (Parallel Genetic Algorithm), a scheduling algorithm aims at reducing the power consumption of real-time systems in multi-core hybrid memory environments. P-GA improves the Proportional-Fairness (PF) algorithm devised for multi-core environments by combining the dynamic voltage/frequency scaling of the processor with the nonvolatile memory technologies. Specifically, P-GA applies genetic algorithms for optimizing the voltage and frequency modes of processors and the memory types, thereby minimizing the power consumptions of the task set. Simulation experiments show that the power consumption of P-GA is reduced by 2.85 times compared to the conventional schemes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.997-1005
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• 2005

The extinction characteristics of low strain rate normal gravity (1-g) nonpremixed methane-air flames were studied numerically and experimentally. A time-dependent axisymmetric two-dimensional (2D) model considering buoyancy effects and radiative heat transfer was developed to capture the structure and extinction limits of 1-g flames. One-dimensional (1D) computations were also conducted to provide information on 0-g flames. A 3-step global reaction mechanism was used in both the 1D and 2D computations to predict the measured extinction limit and flame temperature. A specific maximum heat release rate was introduced to quantify the local flame strength and to elucidate the extinction mechanism. Overall fractional contribution by each term in the energy equation to the heat release was evaluated to investigate the multi-dimensional structure and radiative extinction of 1-g flames. Images of flames were taken for comparison with the model calculation undergoing extinction. The two-dimensional numerical model was validated by comparing flame temperature profiles and extinction limits with experiments and ID computation results. The 2D computations yielded insight into the extinction mode and flame structure of 1-g flames. Two combustion regimes depending on the extinction mode were identified. Lateral heat loss effects and multi-dimensional flame structure were also found. At low strain rates of 1-g flame ('Regime A'), the flame is extinguished from the weak outer flame edge, which is attributed to multi-dimensional flame structure and flow field. At high strain rates, ('Regime B'), the flame extinction initiates near the flame centerline due to an increased diluent concentration in reaction zone, which is the same as the extinction mode of 1D flame. These two extinction modes could be clearly explained with the specific maximum heat release rate.