• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.47.2-47.2
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• 2020

The Experiment to Detect the Global EoR Signature (EDGES) has probed the status of the early Universe through the global 21cm observation. The claimed (brightness temperature) of ~ 500 mK absorption dip at z~17 against the continuum background cannot be explained in the standard LambdaCDM framework. In the meantime, the Planck 2018 Legacy Data, especially the E-mode polarization power spectrum, puts rather strong constraints on the high-redshift reionization process. We show how these two observational contraints can be accomodated in a series of reionization scenarios, with a special focus on the strongly self-regulated reionization by first stars.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.77.2-77.2
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• 2015

Recently, metamaterials attracted much attention because of the potential applications for superlens, cloaking and high precision sensors. We developed several dielectric metamaterials for enhancing antireflection or light trapping capability in solar energy harvesting devices. Colloidal lithography and electrochemical anodization process were employed to fabricate self-assembed nano- and microscale dielectric metamaterials in a simple and cost-effective manner. We improved broadband light absorption in c-Si, a-Si, and organic semiconductor layer by employing polystyrene (PS) islands integrated Si conical-frustum arrays, resonant PS nanosphere arrays, and diffusive alumina nanowire arrays, respectively. We also demonstrated thin metal coated alumina nanowire array which is utilized as an efficient light-to-heat conversion layer of solar steam generating devices. The scalable design and adaptable fabrication route to our light management nanostructures will be promising in applications of solar energy harvesting system. On the other hands, broadband invisible cloaks, which continuously work while elastically deforming, are developed using smart metamaterials made of photonic and elastic crystals. A self-adjustable, nearly lossless, and broadband (10-12GHz) smart meatamaterials have great potentials for applications in antenna system and military stealth technology.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.655-658
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• 1989

The characteristics of proton-diffused $LiNbO_3$ optical waveguides with self-aligned $SiO_2$-cladding are reported. When the proton diffusion occurs, the $SiO_2$-cladding limits the lateral diffusion of protons by out-diffusion of protons in unclad region. Proton indiffusion in depth direction is promoted by inhibition of out-diffusion in clad region. Consequently, the mode profile in depth direction can be nealy symmetric. The extent of the proton exchange was observed by measuring the infrared absorption peak at about $3500cm^{-1}$. It is confirmed that proton diffusion with $SiO_2$-cladding has structural excellency.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.323-325
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• 1995

An Inductively Coupled Plasma(ICP) was employed to prepare the Diamond-Like Carbon film with $CH_4$ gas. We observed the changes of mechanical, optical properties and internal stress of the films according to the variation of discharge power and negative-self bias. When weak magnetic field is applied, the properties of film are observed to change drastically. In magnetized case, the micro-hardness and the internal stress increase up to critical point and droped down in marked contrast to unmagnetized case. It suggests that large amount of ion flux exists due to high dissociation rate of the reactive radicals in plasma with magnetic field as reported elsewhere. As a result of FT-IR absorption measurement it could be confirmed that the $CH_x$ bonding and the micro-hardness and the internal stress decreased with the increase of negative-self bias.

• Advances in concrete construction
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• v.5 no.3
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• pp.271-288
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• 2017

This paper aims to investigate the effects of replacing cement with ground granulated blast furnace slag (GGBFS) in self compacting concrete in the fresh and hardened state. The performance of SCC in moderate climate is well investigated but few studies are available on the effect of hot environment. In this paper, the effect of initial water-curing period and curing conditions on the performance of SCC is reported. Cement was substituted by GGBFS by weight at two different levels of substitution (15% and 25%). Concrete specimens were stored either in a standard environment (T=$20^{\circ}C$, RH=100%) or in the open air in North Africa during the summer period (T=35 to $40^{\circ}C$; R.H=50 to 60%) after an initial humid curing period of 0, 3, 7 or 28 days. Compressive strength at 28 and 90 days, capillary absorption, sorptivity, water permeability, porosity and chloride ion penetration were investigated. The results show that the viscosity and yield stress are decreased with increasing dosage of GGBFS. The importance of humid curing in hot climates in particular when GGBFS is used is also proved. The substitution of cement by GGBFS improves SCC durability at long term. The best performances were observed in concrete specimens with 25% GGBFS and for 28 days water curing.

• Structural Engineering and Mechanics
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• v.61 no.6
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• pp.701-709
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• 2017

Seismic dissipation devices can play a crucial role in mitigating earthquake damages, loss of life and post-event repair and downtime costs. This research investigates the use of ring springs with high-force-to-volume (HF2V) dissipaters to create damage-free, recentring connections and structures. HF2V devices are passive rate-dependent extrusion-based devices with high energy absorption characteristics. Ring springs are passive energy dissipation devices with high self-centring capability to reduce the residual displacements. Dynamic behaviour of a system with nonlinear structural stiffness and supplemental hybrid damping via HF2V devices and ring spring dampers is used to investigate the design space and potential. HF2V devices are modelled with design forces equal to 5% and 10% of seismic weight and ring springs are modelled with loading stiffness values of 20% and 40% of initial structural stiffness and respective unloading stiffness of 7% and 14% of structural stiffness (equivalent to 35% of their loading stiffness). Using a suite of 20 design level earthquake ground motions, nonlinear response spectra for 8 different configurations are generated. Results show up to 50% reduction in peak displacements and greater than 80% reduction in residual displacements of augmented structure compared to the baseline structure. These gains come at a cost of a significant rise in the base shear values up to 200% mainly as a result of the force contributed by the supplemental devices.

• International Journal of Concrete Structures and Materials
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• v.10 no.3
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• pp.337-353
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• 2016

The successful completion of the present research would be achieved using ground waste glass (GWG) microparticles in self-consolidating concrete (SCC). Here, the influences of GWG microparticles as cementing material on mechanical and durability response properties of SCC are investigated. The aim of this study is to investigate the hardened mechanical properties, percentage of water absorption, free drying shrinkage, unit weight and Alkali Silica Reaction (ASR) of binary blended concrete with partial replacement of cement by 5, 10, 15, 20, 25 and 30 wt% of GWG microparticles. Besides, slump flow, V-funnel, L-box, J-ring, GTM screen stability, visual stability index (VSI), setting time and air content tests were also performed as workability of fresh concrete indicators. The results show that the workability of fresh concrete was increased by increasing the content of GWG microparticles. The results showed that using GWG microparticles up to maximum replacement of 15 % produces concrete with improved hardened strengths. From the results, when the amount of GWG increased there was a gradual decrease in ASR expansion. Results showed that it is possible to successfully produce SCC with GWG as cementing material in terms of workability, durability and hardened properties.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.328-334
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• 1999

Methylene blue-sensitized photopolymerizable material based on acrylamide is investigated with two-wave energy coupling experiments. Differently from other studies, self-diffraction oscillations are observed and the grating phase is determined without applying external electric fields, moving nonlinear materials, and phase shifting one of two writing beams. The phase grating showed a phase shift of $\pm$50$^{\circ}$ with respect to the intensity grating. Modified Kogelnik's coupled wave equation considering the mixed gratings of phase and absorption gratings and nonzero spatial phase shifts of the gratings with respect to the intensity interference patterns formed during the two-wave energy coupling is discussed in detail to understand these phenomenon.

• Advances in concrete construction
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• v.5 no.1
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• pp.31-48
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• 2017

Supplementary cementitious materials (SCM) have turned out to be a vital portion of extraordinary strength and performance concrete. Metakaolin (MK) is one of SCM material is acquired by calcinations of kaolinite. Universally utilised as pozzolanic material in concrete to enhance mechanical and durability properties. This study investigates the fresh and hardened properties of conventional concrete (CC) and self compacting concrete (SCC) by partially replacing cement with MK in diverse percentages. In CC and SCC, partial replacement of cement with MK varies from 5-20%. Fresh concrete properties of CC are conducted by slump test and compaction factor tests and for SCC, slump flow, T500, J-Ring, L-Box, V-Funnel and U-Box tests. Hardened concrete characteristics are investigated by compressive, split tensile and flexural strengths at age of 7, 28 and 90 days of curing under water. Carbonation depth, water absorption and density of MK based CC and SCC was also computed. Fresh concrete test results indicated that increase in MK replacement increases workability of concrete in a constant w/b ratio. Also, outcomes reveal that concrete integrating MK had greater compressive, flexural and split tensile strengths. Optimum replacement level of MK for cement was 10%, which increased mechanical properties and robustness properties of concrete.

• Journal of radiological science and technology
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• v.45 no.5
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• pp.433-438
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• 2022

Targeted radionuclides treatment (TRT) requires the establishment of treatment plans that consider various factors, such as the type of radionuclides, target organs, and administration methods. For this reason, in this study, the absorption dose of a single cell was analyzed according to the type of radioisotope used to treat target radionuclides. In this study, a simulation was performed on beta rays used in the treatment of target radionuclides at the cell level using MCNPX (ver. 2.5.0). First, according to the calculation formula, the beam path according to the type of radioisotope for treatment was calculated. Second, the amount of self-radiation by beta rays emitted from cell diameters of 5 ㎛ and 10 ㎛ cell nuclei was evaluated. As a result, it showed a high range proportional to the maximum energy of the beta-ray, and the highest self-dose distribution from 177 Lu radiation sources among therapeutic radioisotopes. This was analyzed as a result that is inversely proportional to the maximum energy of the beta-ray, and it suggests that the selection of a nuclide considering the range of the beta-ray is necessary in the treatment of target radionuclides in the future.