• Structural Engineering and Mechanics
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• 제63권6호
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• pp.751-760
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• 2017

In recent years, multifractal-based analysis methods have been widely applied in engineering. Among these methods, multifractal detrended cross-correlation analysis (MFDXA), a branch of fractal analysis, has been successfully applied in the fields of finance and biomedicine. For its great potential in reflecting the subtle characteristic among signals, a structural health monitoring (SHM) system based on MFDXA is proposed. In this system, damage assessment is conducted by exploiting the concept of multifractal theory to quantify the complexity of the vibration signal measured from a structure. According to the proposed algorithm, the damage condition is first distinguished by multifractal detrended fluctuation analysis. Subsequently, the relationship between the q-order, q-order detrended covariance, and length of segment is further explored. The dissimilarity between damaged and undamaged cases is visualized on contour diagrams, and the damage location can thus be detected using signals measured from different floors. Moreover, a damage index is proposed to efficiently enhance the SHM process. A seven-story benchmark structure, located at the National Center for Research on Earthquake Engineering (NCREE), was employed for an experimental verification to demonstrate the performance of the proposed SHM algorithm. According to the results, the damage condition and orientation could be correctly identified using the MFDXA algorithm and the proposed damage index. Since only the ambient vibration signal is required along with a set of initial reference measurements, the proposed SHM system can provide a lower cost, efficient, and reliable monitoring process.

• 한국항행학회논문지
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• 제14권1호
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• pp.41-48
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• 2010

침입 탐지는 인터넷 보안에 반드시 필요한 구성 요소이다. 발전하고 있는 추세에 뒤지지 않고 따라가기 위해 싱글 레이어 탐지 기술을 멀티 레이어 탐지 기술에 적용 할 수 있는 방법이 필요하다. 다른 타입의 서비스 거부 공격(DoS)은 인가된 사용자의 네트워크 접근을 방해하므로 서비스 거부 공격의 취약한 점을 찾아 피해를 최소화 하기위해 노력했다. 우리는 악의적인 노드를 발견하기 위한 새로운 크로스 레이어 침입 탐지 아키텍처를 제안한다. 프로토콜 스텍에서 서로 다른 레이어를 가로지를 수 있는 정보는 탐색의 정확성을 향상시키기 위하여 제안하였다. 제안한 프로토콜의 아키텍처를 강화하기 위해 데어터 마이닝을 사용하여 조합과 분배의 변칙적인 침입탐지 시스템을 사용했다. 제안하고 있는 구조의 시뮬레이션은 OPNET 시뮬레이터를 사용하여 결과 분석을 하였다.

• Structural Engineering and Mechanics
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• 제35권2호
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• pp.141-173
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• 2010

In this paper a boundary element method is developed for the general flexural-torsional buckling analysis of Timoshenko beams of arbitrarily shaped cross section. The beam is subjected to a compressive centrally applied concentrated axial load together with arbitrarily axial, transverse and torsional distributed loading, while its edges are restrained by the most general linear boundary conditions. The resulting boundary value problem, described by three coupled ordinary differential equations, is solved employing a boundary integral equation approach. All basic equations are formulated with respect to the principal shear axes coordinate system, which does not coincide with the principal bending one in a nonsymmetric cross section. To account for shear deformations, the concept of shear deformation coefficients is used. Six coupled boundary value problems are formulated with respect to the transverse displacements, to the angle of twist, to the primary warping function and to two stress functions and solved using the Analog Equation Method, a BEM based method. Several beams are analysed to illustrate the method and demonstrate its efficiency and wherever possible its accuracy. The range of applicability of the thin-walled theory and the significant influence of the boundary conditions and the shear deformation effect on the buckling load are investigated through examples with great practical interest.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 춘계학술대회 논문집
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• pp.158-163
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• 2008

In inverse synthetic aperture radar (ISAR) imaging, An ISAR autofocusing algorithm is essential to obtain well-focused ISAR images. Traditional methods have relied on the approximation that the phase error due to target motion is a function of the cross-range dimension only. However, in the stepped-frequency radar system, it tends to become a two-dimensional function of both down-range and cross-range, especially when target's movement is very fast and the pulse repetition frequency (PRF) is low. In order to remove the phase error along down-range, this paper proposes a method called SAEM (subarray averaging and entropy minimization) [1] that uses a subarray averaging concept in conjunction with the entropy cost function in order to find target motion parameters, and a novel 2-D optimization technique with the inherent properties of the proposed entropy-based cost function. A well-focused ISAR image can be obtained from the combination of the proposed method and a traditional autofocus algorithm that removes the phase error along the cross-range dimension. The effectiveness of this method is illustrated and analyzed with simulated targets comprised of point scatters.

• Nuclear Engineering and Technology
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• 제48권5호
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• pp.1264-1272
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• 2016

The accurate estimation of leak rate through cracks is crucial in applying the leak before break (LBB) concept to pipeline design in nuclear power plants. Because of its importance, several programs were developed based on the several proposed flow models, and used in nuclear power industries. As the flow models were developed for a homogeneous pipe material, however, some difficulties were encountered in estimating leak rates for bimaterial pipes. In this paper, a flow model is proposed to estimate leak rate in bimaterial pipes based on the modified Henry-Fauske flow model. In the new flow model, different crack morphology parameters can be considered in two parts of a flow path. In addition, based on the proposed flow model, a program was developed to estimate leak rate for a crack with linearly varying cross-sectional area. Using the program, leak rates were calculated for through-thickness cracks with constant or linearly varying cross-sectional areas in a bimaterial pipe. The leak rate results were then compared and discussed in comparison with the results for a homogeneous pipe. The effects of the crack morphology parameters and the variation in cross-sectional area on the leak rate were examined and discussed.

• 설비공학논문집
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• 제23권8호
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• pp.543-548
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• 2011

New concept of wind energy conversion system is proposed to increase the energy density at a given working space. The quality of wind for wind power generation is depend on its direction and speed. However, the quality is not good on land because wind direction is changeable all the time and the speed as well. The most popularly operated wind turbine system is an axial-flow free turbine. But its conversion efficiency is less than 30% and even less than 20% considering the operating time. In this research, a cross-flow type wind turbine system is proposed with a convergent-divergent duct system to accelerate the low speed wind at the inlet of the wind turbine. Inlet guide vane is also introduced to the wind turbine system to have continuous power generation under the change of wind direction. In here, the availability of wind energy generation is evaluated with the change of the size of the inlet guide vane and the optimum geometry of the turbine impeller blade was found for the innovative wind power generation system.

• Journal of the Optical Society of Korea
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• 제20권5호
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• pp.601-606
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• 2016

In this study, in order to analyze the low-temperature sintering process of silver and copper nanoparticles, we calculate their melting temperatures and surface melting temperatures with respect to particle size. For this calculation, we introduce the concept of mean-squared displacement of the atom proposed by Shi (1994). Using a parameter defined by the vibrational component of melting entropy, we readily obtained the surface and bulk melting temperatures of copper and silver nanoparticles. We also calculated the absorption cross-section of nanoparticles for variation in the wavelength of light. By using the calculated absorption cross-section of the nanoparticles at the melting temperature, we obtained the laser threshold energy for the sintering process with respect to particle size and wavelength of laser. We found that the absorption cross-section of silver nanoparticles has a resonant peak at a wavelength of close to 350 nm, yielding the lowest threshold energy. We calculated the intensity distribution around the nanoparticles using the finite-difference time-domain method and confirmed the resonant excitation of silver nanoparticles near the wavelength of the resonant peak.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권6호
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• pp.1849-1876
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• 2022

Wireless Sensor Network (WSN) is considered as an integral part of the Internet of Things (IoT) for collecting real-time data from the site having many applications in industry 4.0 and smart cities. The task of nodes is to sense the environment and send the relevant information over the internet. Though this task seems very straightforward but it is vulnerable to certain issues like energy consumption, delay, throughput, etc. To efficiently address these issues, this work develops a cross-layer model for the optimization between MAC and the Network layer of the OSI model for WSN. A high value of duty cycle for nodes is selected to control the delay and further enhances data transmission reliability. A node measurement prediction system based on the Kalman filter has been introduced, which uses the constraint based on covariance value to decide the scheduling scheme of the nodes. The concept of duty cycle for node scheduling is employed with a greedy data forwarding scheme. The proposed Duty Cycle-based Greedy Routing (DCGR) scheme aims to minimize the hop count, thereby mitigating the energy consumption rate. The proposed algorithm is tested using a real-world wastewater treatment dataset. The proposed method marks an 87.5% increase in the energy efficiency and reduction in the network latency by 61% when validated with other similar pre-existing schemes.

• Asian Journal of Innovation and Policy
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• 제10권2호
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• pp.236-248
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• 2021

The objective of this study is to introduce the urban utility concept that combines urban growth and urban disasters in the aspect of a conceptual theory. While many studies focused on the dollar amount damaged from a disaster, it requires adding not just building damages or human body losses but also the quality of life satisfaction. An issue in measuring the quality of life satisfaction needs to introduce a proper mode quantifying it. This study introduces the urban utility change in measuring the negative impacts of a disaster on urban life, which has been rarely investigated. To identify urban utility, urban flooding that is a cross-sectoral agenda and important to both developed and developing countries was adopted to respond to its increased frequency and damages, encouraging governments to focus on flood control policies. By combining a literature review on urban utility and urban growth, this study defined the urban utility concept as a net benefit of a resident with earnings subtracting housing and commuting costs. The theoretical study also explained that urban utility and its components dynamically change as per urban growth and disasters that even reversely affect urban growth. Because the urban utility can be one of the useful indices to appreciate the relationship between a disaster and urban growth, it is highly expected to apply for similar disaster impacts on urban areas, including COVID-19 and various global warming issues.

• 중환자간호학회지
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• 제12권2호
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• pp.61-72
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• 2019

Purpose : The aim of this study was to explore the attributes, antecedents, and consequences of patient-centered care (PCC) for older adults with multimorbidity in acute care hospitals. Methods : The concept analysis performed by Walker and Avant was used to analyze PCC. Fifteen studies from the literature related to PCC appear in systematic literature reviews in the fields of theology, medicine, psychology, and nursing. Results : PCC in acute care hospitals was defined according to the five attributes of 'maintaining patient autonomy', 'empowering self-care', 'individualized and relationship-based care', 'shared decision-making', and 'creating a homelike environment'. Antecedents of PCC were found to be a respect for patients' preferences, qualifications of the nursing staff, care coordination and integration, and organizational support. Consequences of effective PCC were a functional status; health-related quality of life; satisfaction with care, mortality, and medical costs from the perspective of the patient and family; and quality of care and therapeutic relationships from nurses' viewpoints. Conclusion : PCC as defined by the results of this study will contribute to the foundation of institutionalization and the creation of a safe and healthy acute care hospital culture focused on patients' preferences and values.