• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.605-609
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• 2006

In this study, two kinds of smart accelerometers are investigated for the application of smart sensors to the structural health monitoring of infrastructures. Smart optical Fiber Bragg Grating (FBG) type and Micro-Electo-Mechanical System (MEMS) type accelerometers are selected for this study and the high sensitive ICP type accelerometer is used for the reference sensor. Small size shaking table tests were performed with 3-story shear building model using random input ground motions. The output only modal identification was carried out using stochastic subspace identification and the performances of sensors are compared in modal domain indirectly. The modal sensitivity method was applied to update the story stiffness of numerical model and the updated results were verified using the additional experiments for the same structure with additional mass.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.195-206
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• 2024

Shenzhen Innovation Light source Facility (SILF) is a 3.0 GeV fourth generation diffraction limited synchrotron light source currently under construction in Shenzhen. The SILF storage ring is proposed to use two 500 MHz single cell superconducting radio frequency (SRF) cavities to provide 2.4 MV RF voltage. In this study, we examined the geometric structure of mature CESR superconducting cavities and adopted a beam-pipe-type extraction scheme for high-order modes (HOM). One of the objectives of SRF cavity design and optimization in this study is to reduce E_p/E_acc and B_p/E_acc as much as possible to reduce power loss and ensure stable operation of the cavity. To reduce the risk of beam instability and thermal breakdown, the HOM and Multipacting (MP) are simulated. Moreover, the mechanical properties of the cavity are analyzed, including frequency sensitivity from pressure of liquid helium (LHe), stress, tuning, Lorentz force detuning (LFD), the microphone effect, and buckling. By comprehensive design and optimization of 500 MHz single-cell SRF cavities, a superconducting cavity for SILF storage ring was developed. This paper will detailed present the design and simulation.

• Journal of Radiation Protection and Research
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• v.49 no.1
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• pp.29-39
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• 2024

Background: The gamma emission tomography (GET) device has been reported a reliable technique to inspect partial defects within spent nuclear fuel (SNF) of pin-by-pin level. However, the existing GET devices have low accuracy owing to the high attenuation and scatter probability for SNF inspection condition. The purpose of this study is to design and optimize a Yonsei single-photon emission computed tomography version 2 (YSECT.v.2) for fast inspection of SNF in water storage by acquisition of high-quality tomographic images. Materials and Methods: Using Geant4 (Geant4 Collaboration) and DETECT-2000 (Glenn F. Knoll et al.) Monte Carlo simulation, the geometrical structure of the proposed device was determined and its performance was evaluated for the ¹³⁷Cs source in water. In a Geant4-based assessment, proposed device was compared with the International Atomic Energy Agency (IAEA)-authenticated device for the quality of tomographic images obtained for 12 fuel sources in a 14 × 14 Westinghouse-type fuel assembly. Results and Discussion: According to the results, the length, slit width, and septal width of the collimator were determined to be 65, 2.1, and 1.5 mm, respectively, and the material and length of the trapezoidal-shaped scintillator were determined to be gadolinium aluminum gallium garnet and 45 mm, respectively. Based on the results of performance comparison between the YSECT.v.2 and IAEA's device, the proposed device showed 200 times higher performance in gamma-detection sensitivity and similar source discrimination probability. Conclusion: In this study, we optimally designed the GET device for improving the SNF inspection accuracy and evaluated its performance. Our results show that the YSECT.v.2 device could be employed for SNF inspection.

• Computers and Concrete
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• v.34 no.2
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• pp.151-168
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• 2024

This research aimed to appraise the effectiveness of four optimization approaches - cuckoo optimization algorithm (COA), multi-verse optimization (MVO), particle swarm optimization (PSO), and teaching-learning-based optimization (TLBO) - that were enhanced with an artificial neural network (ANN) in predicting the bearing capacity of shallow foundations located on cohesionless soils. The study utilized a database of 97 laboratory experiments, with 68 experiments for training data sets and 29 for testing data sets. The ANN algorithms were optimized by adjusting various variables, such as population size and number of neurons in each hidden layer, through trial-and-error techniques. Input parameters used for analysis included width, depth, geometry, unit weight, and angle of shearing resistance. After performing sensitivity analysis, it was determined that the optimized architecture for the ANN structure was 5×5×1. The study found that all four models demonstrated exceptional prediction performance: COA-MLP, MVO-MLP, PSO-MLP, and TLBO-MLP. It is worth noting that the MVO-MLP model exhibited superior accuracy in generating network outputs for predicting measured values compared to the other models. The training data sets showed R² and RMSE values of (0.07184 and 0.9819), (0.04536 and 0.9928), (0.09194 and 0.9702), and (0.04714 and 0.9923) for COA-MLP, MVO-MLP, PSO-MLP, and TLBO-MLP methods respectively. Similarly, the testing data sets produced R² and RMSE values of (0.08126 and 0.07218), (0.07218 and 0.9814), (0.10827 and 0.95764), and (0.09886 and 0.96481) for COA-MLP, MVO-MLP, PSO-MLP, and TLBO-MLP methods respectively.

• Journal of Forest and Environmental Science
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• v.40 no.3
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• pp.210-226
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• 2024

Old-growth mixed-conifer forests in Bhutan are characterized by remarkable tree species compositional heterogeneity. However, our knowledge of tree species assemblages and their structural attributes in these forests has been limited. Therefore, forest classification has been reliant on a single dominant species. This study aimed to distinguish tree species assemblages in an old-growth mixed conifer forest in Western Bhutan and to describe their natural compositional and stand structural characteristics. Furthermore, the regeneration status of species was investigated and the quantity and quality of accumulated coarse woody debris were assessed. Ninety simple random sampling plots were surveyed in the study site between 3,000 and 3,600 meters above sea level. Tree, standing deadwood, regeneration, and coarse woody debris data were collected. Seven tree species assemblages were distinguished by Hierarchical Cluster Analysis and Indicator Species Analysis, representing five previously undescribed tree species associations with unique set of consistent species. Principal Component Analysis revealed two transitional pathways of species dominance along an altitudinal gradient, highly determined by relative topographic position. The level of stand stratification varied within a very wide range, corresponding to physiognomic composition. Rotated-sigmoid and negative exponential diameter distributions were formed by overstorey species with modal, and understorey species with negative exponential distribution. Overstorey dominant species showed extreme nurse log dependence during regeneration, which supports the formation of their modal distribution by an early natural selection process. This allows the coexistence of overstorey and understorey dominant species, increasing the sensitivity of these primary ecosystems to forest management.

• The Journal of the Korea Contents Association
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• v.18 no.2
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• pp.553-568
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• 2018

Popular music is a spce where intrinsic desires and values of young people are well exposed in its process of production and consumption. Previous discussions of Korean youth and youth culture have been proceeding mainly in the sense of their resistances to older generation. However, this is limited in that it neglects the inherent microscopic characteristics of youth culture. The purpose of this study is to investigate what the signs and discourses of youth generation make and share in popular music, and how it relates to social context through the 'Mimesis' theory. As a result, the songs of the 1990s remarkably showed the resistance to the old generation in its narrative structure and have signs which expresses repression and uniformity. On the other hand, the songs of the 2010s have many fragmented signs which has been reconstructed into individualized discourse structure. It is assumed that the songs have been able to gain a lot of empathy and popularity from the young generation by visualizing emotions and desires experienced by themselves in the social context. Through this study, it suggests to pay attention to the sensitivity, desire and creativity of young people in music in the social and cultural context of the time.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.508-517
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• 2004

We described a near-field scanning microwave microscope which uses a high-quality dielectric resonator with a tunable screw. The operating frequency is f=4.5 5GHz. The probe tip is mounted in a cylindrical resonant cavity coupled to a dielectric resonator We developed a hybrid tip combining a reduced length of the tapered part with a small apex. In order to understand the function of the probe, we fabricated three different tips using a conventional chemical etching technique and observed three different NSMM images for patterened Cr films on glass substrates. We measured the reflection coefficient of different metal thin film samples with the same thickness of 300m and compared with theoretical impedance respectly. By tuning the tunable screw coming through the top cover, we could improve sensitivity, signal-to-noise ratio, and spatial resolution to better than $1{\mu}m$. To demonstrate the ability of local microwave characterization, the surface resistance of metallic thin films has been mapped.

• Fire Science and Engineering
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• v.30 no.4
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• pp.1-5
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• 2016

This research performed tests of Video Fire Detector and criteria of installation to make suggestions regarding the criteria that must be reflected in NFSC 203 by comparing the standards of FM Approvals, UL, ISO7240 and NFPA 72. FM Standard related to Video Fire Detector test has been classified as Smoke, Flame type, but the UL Standard has classified only as a Smoke type. This research examined 6 cases of fire phenomenon detection case in ISO 7240 and 3 cases in NFPA 72, respectively. There are 15 items required for the installation standard of a Video Fire Detector and each field standard is presented as a per installation method. To apply a Video Fire Detector, the pertinent items (the definition of term, detector's classification, structure and function among its test item) must be inserted. In addition, 7 items of the fire test, i.e., the sensitivity adjustment, prevent false alarm, ambient temperature test, the effective sensitivity and detection distance and viewing angle, aging test, flood test, must be applied to the actual test. For installation in the field, the operation environment and levels of illumination, and NFSC 203 must be set, and standards relevant to the sound system, indicators' installation distance, etc. need to be inserted.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.103-111
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• 2014

In this study, the probabilistic internal pressure fragility analysis was performed by using the non-linear finite element analysis method. The target structure is one of the containment buildings of typical domestic pressurized water reactors(PWRs). The 3-dimensional finite element model of the containment building was developed with considering the large equipment hatches. To consider uncertainties in the material properties and structural capacities, we performed the sensitivity analysis of the ultimate pressure capacity with respect to the variation of four important uncertain parameters. The results of the sensitivity analysis were used to the selection of the probabilistic variables and the determination of their probabilistic parameters. To reflect the present condition of the tendon pre-stressing force, the data of the pre-stressing force acquired from the in-service inspections of tendon forces were used for the determination of the median value. Two failure modes(leak, rupture) were considered and their limit states were defined to assess the internal pressure fragility of target containment building. The internal pressure fragilities for each failure mode were evaluated in terms of median internal pressure capacity, high confidence low probability of failure(HCLPF) capacity, and fragility curves with respect to the confidence levels. The HCLPF capacity was 115.9 psig for leak failure mode, and 125.0 psig for rupture failure mode.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.604-609
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• 2019

In this study, we fabricated a capacitive humidity sensor with interdigitated (IDT) electrodes using a thermosetting polyimide as a humidifying material. First, the number of electrodes, thickness, and spacing of the polyimide film were optimized, and a mask was designed and fabricated. The sensor was fabricated on a silicon substrate using semiconductor processing equipment. The area of the sensor was $1.56{\times}1.66mm^2$, and the width of the electrode and the gap between the electrodes were each $3{\mu}m$. The number of electrodes was 166, and the length of an electrode was 1.294 mm for the sensitivity of the sensor. The sensor was then packaged on a PCB for measurement. The sensor was inserted into a chamber environment with a temperature of $25^{\circ}C$ and connected to an LCR meter to measure the change in capacitance at relative humidity (RH) of 20% to 90%, 1 V, and 20 kHz. The results showed a sensitivity of 26fF/%RH, linearity of < ${\pm}2%RH$, and hysteresis of < ${\pm}2.5%RH$.