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Lee, Yonghee,Kim, Somang,Kim, Hyo Seok,Shin, Jeong Bin,Choi, Wonseok,Cho, Hyunjin,Kim, Kyungmok,Lee, Taeyang,Kim, Jinwuk,Kang, In-Byeong,Choi, Kyung Cheol,Kim, Yong-Hoon,Jeon, Duk Young The Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.8
<P>We demonstrate for the first time highly luminescent blue-emitting CdZnS/ZnS wurtzite core/shell nanorods (NRs) that show electric-field-induced fluorescence switching properties. Uniform CdZnS NRs were rapidly synthesized by injecting sulfur powder dissolved in 1-octadecene into a flask containing phosphonic acid ligands, and subsequently ZnS shells were coated using reagents consisting of sulfur powder, zinc sulfate heptahydrate, and oleylamine. The growth of high-quality ZnS shells resulted in a dramatically increased photoluminescence (PL) quantum yield (QY) of ∼40% with a minimal red-shift of the blue PL peak, which indicates that the combination of reagents successfully controlled a large number of defects appearing on the surface of the NR cores. By pre-annealing CdZnS cores before growing ZnS shells, we could achieve an additional increase in the maximum PL QY to 50%, decreases in both the full width at half maximum (FWHM) and the red-shift of the PL peak, and improved electric-field-induced fluorescence switching performance. Density functional theory calculations reveal that the effective relaxation of strain accumulating on the NR core during shell growth is the key to our successful synthesis of blue-emitting NRs, and that the additional improvement in performance obtained through the pre-annealing process results from the elimination of sulfur vacancies appearing at the surface of the NR core.</P>
Verification of 1-g Shaking Table Test Using Laminar Shear Box by Numerical Modeling
( Yonghee Lee ),( Hak-sung Kim ),( Weon-hack Choi ),( Seok-chul Kim ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
The most accurate results on soil amplification can be obtained from full-scale model. However, it is often impractical because of the cost of full scale model and the natural uncertainty of earthquake occurrence. Therefore, lab-scale physical modeling such as 1-g shaking table and centrifuge tests are widely performed to determine the effect of ground motion during earthquake. Meanwhile, the boundary effect is one of the major limitation in lab-scale physical model. In this study, laminar shear box (LSB) to minimize the boundary effect was developed, and the capacity of developed LSB was evaluated using preliminary 1-g shaking table test. LSB is composed of a stack of aluminum frames. Ball bearings between the aluminum frames allow the lateral displacement of the box corresponding soil deformation during the dynamic loading time. The height, length, and width of LSB are 2,000, 600 and 600 mm, respectively. Sine sweep test (from 2 Hz to 30 Hz) was conducted to determine the response characteristic of LSB. Furthermore, numerical modeling was performed using the DEEPSOIL version 7.1, and FLAC 2D software. LSB shaking table test results on center and boundary area of LSB are well matched with the numerical analyses results. However, response of boundary area is slightly larger than that of center area. It seems that this phenomenon is induced by the inevitable partial reflection of the seismic wave at the boundary. The test results show that LSB greatly mitigate the boundary effect of the lab-scale physical modeling in comparison to conventional rigid box (RB).
Applicability Evaluation of Fault Characteristic Analysis using Terrestrial LiDAR
( Yonghee Lee ),( Weon-hack Choi ),( Hak-sung Kim ),( Seok-chul Kim ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
It is common that the geometric information of faults is obtained directly by field investigation. However, there are several limitations to obtain the quantitative geometric information from the field investigation when investigator is difficult to access. When the fault is located on the steep slope, fault displacements have been measured with naked eye or indirectly method. The indirect measurement can lead the intervention of subjectivity which can cause a large range of epistemic uncertainty. Recently, the terrestrial LiDAR (light detection and ranging) technique has been introduced in the geological investigation to obtain quantitative geometric information of geological structures including faults. Since LiDAR technique provides full three-dimension (3-D) model of geological outcrop, fault geometric information can be measured accurately. LiDAR uses pulsed laser light to measure distance to the target and relative coordinates of the targets are calculated from flight time or phase difference of reflected laser pulses from targets. A 3-D model of the terrain feature can be obtained using position information data (i.e., point clouds) of reflection points. In this study, the applicability of terrestrial LiDAR technique for fault characteristic analysis was evaluated based on the field-test results. The study area is located in the road construction site near Hwa-gok reservoir in Kyoung-ju, south-eastern part of Korea. 3-D outcrop point clouds including fault were built using the terrestrial LiDAR device. Color mapping, reflectance, and echo amplitude of obtained point cloud data were analyzed. Analyses results show that the terrestrial LiDAR technique is effective for geologic structures.
New Approach for Slope Deformation Measurement Using Terrestrial LiDAR in Nuclear Power Plant Site
( Yonghee Lee ),( Weon-hack Choi ),( Hak-sung Kim ),( Seok-chul Kim ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
Recently, slope failures are frequently occurred in Korea due to localized torrential rainfalls induced by the world climate change. Therefore, the stability of slopes in nuclear power plant sites has become a major geotechnical issue in the nuclear industry. The slope monitoring using slope-mounted sensors (e.g., inclinometer, tension-wire, and precipitation gauge) are the most accurate and reliable motioning method for slopes. However, slope-mounted sensor systems are ineffective to evaluate the overall deformation of large slopes because measured data from the each slope-mounted sensor represent the single cross-area of the slope. In this study, terrestrial light detection and ranging system (LiDAR) was used to evaluate the overall slope deformation without slope-mounted sensor system. The testbed slope is located in ○○ nuclear power plant site. The length, height, and slope angle of the slope is 1,700 m, 80 m and 34°, respectively. The measurement and analysis procedure are as follows: (1) point cloud data acquisition using terrestrial LiDAR, (2) station adjustment using global navigation satellite system (GNSS), (3) noise filtering to remove unnecessary data (e.g., trees and transmission towers), and (4) slope digital elevation model (DEM) generation. The terrestrial LiDAR data that obtained in 2015 (53 scan positions) and in 2016 (91 scan positions) were compared in this study. There was no significant deformation on the testbed slope, however, slight sediment-scouring which has no impact on the slope stability was observed. Deformation analysis using terrestrial LiDAR data obtained periodically is cost-effective and reliable to monitor the overall deformation of the large slopes.
Spontaneous Self-Formation of 3D Plasmonic Optical Structures
Choi, Inhee,Shin, Yonghee,Song, Jihwan,Hong, SoonGweon,Park, Younggeun,Kim, Dongchoul,Kang, Taewook,Lee, Luke P. American Chemical Society 2016 ACS NANO Vol.10 No.8
<P>Self-formation of colloidal oil droplets in water or water droplets in oil not only has been regarded as fascinating fundamental science but also has been utilized in an enormous number of applications in everyday life. However, the creation of three-dimensional (3D) architectures by a liquid droplet and an immiscible liquid interface has been less investigated than other applications. Here, we report interfacial energy-driven spontaneous self-formation of a 3D plasmonic optical structure at room temperature without an external force. Based on the densities and interfacial energies of two liquids, we simulated the spontaneous formation of a plasmonic optical structure when a water droplet containing metal ions meets an immiscible liquid polydimethylsiloxane (PDMS) interface. At the interface, the metal ions in the droplet are automatically reduced to form an interfacial plasmonic layer as the liquid PDMS cures. The self-formation of both an optical cavity and integrated plasmonic nanostructure significantly enhances the fluorescence by a magnitude of 1000. Our findings will have a huge impact on the development of various photonic and plasmonic materials as well as metamaterials and devices.</P>
Seismic Input Motion Generation for Nuclear Power Plants
( Yonghee Lee ),( Seok-chul Kim ),( Hak-sung Kim ),( Weon-hack Choi ),( Young-tae Ju ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
Time histories which correspond to the design requirement are required to perform a seismic analysis on safety-related structures of nuclear power plants (NPPs). The requirement for evaluating the adequacy of calculated response spectrum and corresponding artificial seismic time histories are presented in the US NRC NUREG-0800 and standard review plan (SRP) 3.7.1 Revision 4. SRP 3.7.1 requirement is composed with option 1 (single set of time history) and option 2 (multiple sets of time histories). The option 1 is subdivided into approach 1 and approach 2. Approach 1 requires that calculated response spectrum (CRS) envelops required response spectrum (RRS). In addition, it is required that the power spectrum density (PSD) calculated from the artificial seismic time histories encompasses the target power spectrum function to show that the artificial seismic time history has sufficient energy in all frequency ranges. Meanwhile, in approach 2, the average ratio of spectral acceleration calculated from the time histories to the target, where the ratio is calculated frequency by frequency, is only slightly greater than 1. It is remarkable that there is no requirement for PSD in approach 2. Instead, response spectrum for 5% damping ratio of the artificial time history must be lower than 130% of the RRS for the entire frequency range of interest. In this study, time history for seismic analysis of NPP structures was successfully generated with approach 1 & 2 method.