• Journal of ILASS-Korea
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• v.1 no.3
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• pp.20-28
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• 1996

It is well known that drag reduction in single phase liquid flow is affected by polymer material, molecular weight, polymer concentration, pipe diameter, and flow velocity. Drag reduction in two phase flow can be applied to the transport of crude oil, phase change system such as chemical reactor, pool and boiling flow, and to present cavitation which occurs in pump impellers. But the research of drag reduction in two phase flow is not sufficient. The purpose of the present work is to evaluate the drag reduction by measuring pressure drop, void fraction whether polymer is added in the horizontal two phase system or not. Experiment has been conducted in a test section with 24 m of the inner diameter and 1,500 mm of the length. The used polymer materials are two kinds of polyacrylamide[PAAM] and co-polymer[A611P]. The polymer concentration was varied with 50, 100 and 200 ppm under the same experimental conditions. Experimental results were shown that the drag is higher reduced by co-polymer rather than polyanylamide.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.753-759
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• 1996

The artificial construction of well-defined low-dimensional (low-D) quantum structures, such as quantum wire (QWR) still attracts attention of many researchers due to their applications in room-temperature optoelectronic devices. In this work, the migration enhanced epitaxial growth (MEE) and the analysis of InAs/ AlAs QWR are reported. On the vicinal semi-insulating InP substrate of $3^o$ tilted cut from (100) surface towards (010) direction, InAs/ AlAs QWR superlattices have been successfully grown by MEE with the introduction of growth interruption at each shutter operation of MBE cell. The in-situ RHEED analyses show that MEE gives superior step-flow growth (SFG) and sharper interface formation over a conventional MBE growth. We have grown 4 samples in series varying the growth temperature. The QWR samples are analyzed by photoluminescence (PL) and atomic force microscopy (AFM). From the AFM images, we can get the definitely resolved 1-D structures. This structure is believed to be due to the MEE method and its separation is better than any other data from others. We are now studying the dependence of the structure on the growth temperature.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.261-263
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• 2004

We present a progress report on HCN(1-0) line observations toward starless cores to probe inward motions. We have made a single pointing survey toward the central regions of 85 starless cores and performed mapping observations of 6 infall candidate starless cores. The distributions of the velocity difference between HCN(1-0) hyperfine lines and the optically thin tracer $N_2H^+$(1-0) are significantly skewed to the blue, meaning that HCN(1-0) frequently detects inward motions. Their skewness to the blue is even greater than that of CS(2-1) Lee et al., possibly implying more infall occurrence than CS(1-0). We identify 19 infall candidates by using several characteristics illustrating spectral infall asymmetry seen in HCN(1-0) hyperfine lines, CS(3-2), CS(2-1), $DCO^+(2-1)$ and $N_2H^+$ observations. The HCN(1-0) F(O-l) with the least optical depth usually shows a similar intensity distribution to that of $N_2H^+$ which closely traces the density distribution of the cores, indicating that HCN(1-0) is less chemically affected and so believed to reflect kinematics occurring in rather inner regions of the cores. Detailed radiative transfer model fits of the spectra are underway to analyze central infall kinematics in starless cores.

• Current Optics and Photonics
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• v.1 no.4
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• pp.402-411
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• 2017

Combined LIBS-Raman spectroscopy has been widely studied, due to its complementary capabilities as an elemental analyzer that can acquire signals of atoms, ions, and molecules. In this study, the classification of polymorphs was performed by laser-induced breakdown spectroscopy (LIBS) to overcome the limitation in molecular analysis; the results were verified by Raman spectroscopy. LIBS signals of the $CaCO_3$ polymorphs calcite and aragonite, and $CaSO_4{\cdot}2H_2O$ (gypsum) and $CaSO_4$ (anhydrite), were acquired using a Nd:YAG laser (532 nm, 6 ns). While the molecular study was performed using Raman spectroscopy, LIBS could also provide sufficient key data for classifying samples containing different molecular densities and structures, using the peculiar signal ratio of $5s{\rightarrow}4p$ for the orbital transition of two polymorphs that contain Ca. The basic principle was analyzed by electronic motion in plasma and electronic transition in atoms or ions. The key factors for the classification of polymorphs were the different electron quantities in the unit-cell volume of each sample, and the selection rule in electric-dipole transitions. The present work has extended the capabilities of LIBS in molecular analysis, as well as in atomic and ionic analysis.

• Macromolecular Research
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• v.14 no.3
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• pp.300-305
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• 2006

The chemical structure of a semi-aromatic polyimide-I, which was prepared by the chemical imidization of cyclopentanetetracarboxylic dianhydride and 2,2-bis(4-aminophenyl)hexafluoropropane, was characterized by $^{13}C-NMR$ spectroscopy. The chemically imidized polyimide-I was used for the preparation of a photosensitive polyimide (PSPI) through the addition of benzophenone and benzophenone oxime hexamethylene diurethane (BOHD), a photobase generator containing oxime-urethane groups. The polyimide-I film containing benzophenone and BOHD was not soluble in 2.38 wt% tetrabutylammonium hydroxide solution in $H_2O$. However, it became soluble following irradiation with 310 nm UV light. A positive tone image with a resolution of $5{\mu}m$ was obtained with this PSPI, having sensitivity($D_c$) of $1.2J/cm^2$ and contrast(${\gamma}_p$) of 1.08. Thus, a polyimide, which is not intrinsically photosensitive, can become photosensitive through the addition of a photobase generator containing oxime-urethane groups as a photosensitive compound.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1717-1722
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• 2021

This study is devoted to the ability of carbon fiber material samples impregnated with various amounts of barium iodide and triethylenediamine to remove radioactive methyliodide from air streams. The main sorption characteristics of impregnated UVIS® carbon fiber were determined and the use of this material for purifying of technological gas flows at nuclear power plants was evaluated. The methyliodide trapping efficiency by samples impregnated with barium iodide, TEDA, and their mixture was 83.4 ± 0.8%; 93.1 ± 0.6% and 93.5 ± 0.7% respectively, under the same conditions. The study established a significantly higher capacity (8.3 ± 0.07 mg/cm²) of samples impregnated simultaneously with both chemical compounds toward methyliodide. Under the same test conditions, the values of this parameter for the samples impregnated separately with TEDA and BaI₂ were 2.85 ± 0.05 mg/cm² and 0.86 ± 0.04 mg/cm², respectively.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1885-1891
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• 2023

The present work aims to fabricate Na_1+xZr₂Si_xP_3-xO₁₂ compound at various calcination temperatures based on the zircon mineral. The fabricated compound was calcinated at 250, 500, and 1000℃. The effect of calcination temperature on the structure, crystal phase, and radiation shielding properties was studied for the fabricated compound. The X-ray diffraction diffractometer demonstrates that, the monoclinic crystal phase appeared at a calcination temperature of 250℃ and 500℃ is totally transformed to a high-symmetry hexagonal crystal phase under a calcination temperature of 1000℃. The radiation shielding capacity was also qualified for the fabricated compounds using the Monte Carlo N-Particle transport code in the g-photons energy interval between 15keV and 122keV. The impacts of calcination temperature on the g-ray shielding behavior were clarified in the present study, where the linear attenuation coefficient was enhanced by 218% at energy of 122keV, when the calcination temperature increased from 250 to 1000℃, respectively.

• Progress in Superconductivity and Cryogenics
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• v.26 no.1
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• pp.14-19
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• 2024

In this study, we explore the anisotropy of electron-phonon coupling (EPC) constant in epitaxially grown MgB₂ films on c-axis oriented Al₂O₃, examining its correlation with the critical temperature (T_c) and local structural disorder assessed through polarized Raman scattering. Analysis of the polarized Raman spectra reveals angle-dependent variations in the intensity of the phonon spectra. The Raman active mode originating from the boron plane, along with two additional phonon modes from the phonon density of states (PDOS) induced by lattice distortion, was distinctly observed. Persistent impurity scattering, likely attributed to oxygen diffusion, was noted at consistent frequencies across all measurement angles. The EPC values derived from the primary Raman active phonon do not significantly vary with changing observation angles, followed by that the T_c values calculated using the Allen and Dynes formula remain relatively constant across all polarization angles. Although the E_2g phonon mode plays a crucial role in the EPC mechanism, the determination of T_c values in MgB₂ involves not only electron-E_2g coupling but also contributions from other phonon modes.

• Corrosion Science and Technology
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• v.23 no.1
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• pp.64-71
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• 2024

The objective of this study was to investigate corrosion and cavitation-erosion characteristics of the electroless nickel plating layer with heat treatment. The crystallization temperature of the electroless nickel plating layer was about 410 ℃. The phase transformation energy was confirmed to be 12.66 J/g. With increasing heat treatment temperature, the amorphous electroless nickel plating layer gradually changed to crystalline Ni and Ni₃P. At the same time, the crystal grain size was also increased. Additionally, when heat treatment was performed at a temperature above 400 ℃, NiO phase was observed due to oxidation phenomenon. As a result of the electrochemical polarization experiment, the corrosion resistance of the heat-treated electroless nickel plating layers was superior to that of the as-deposited plating layer. This was because crystal grains became larger and grain boundaries decreased during heat treatment. The cavitation-erosion resistance of heat-treated plating layers tended to be superior to that of as-deposited plating layers due to increased microhardness.

• Korean Journal of Weed Science
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• v.8 no.2
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• pp.199-207
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• 1988

The study was intended to know any relations between the rice tolerance to oxyfluorfen and varietal speciation in seed protein composition or any enzymatical allelies with or without chemical treatment. Rice varieties used were Chokoto, Aichiasahi, Agabyeo, IR 3941 and Tablei as the tolerant group, and Mushakdanti, Weld Pally, HP 1033, HP 857, and HP 907 as the susceptible, respectively. Electrophoretic methods used were SDS-PAGE for seed protein, 7% PAGE for isozymes (acid phosphatase and peroxidase from rice seedling) and changes in isoenzyme activity (malate dehydrogenase, peroxidase and esterase) as affected by oxyfluorfen treatment ($10^{-4}M$) was also studied. The results are summarized as follows. -Among 19 bands separated in seed proteins, two different rice groups selected in terms of tolerance were clustered in dissimilarity. This was based on 2 facts in that G band was not present in susceptible varieties and that less activity of H, N, O, P, Q, Rand S band was shown. -Among 4 bands separated in acid phosphatase, the presence of (band and lower activity of B band was specific for tolerant varieties. For 4 minor bands separated in peroxidase, the tolerant varieties had no activity in B band and higher activity in A, C, D bands. -Time-course study of isozymes as affected by $10^{-4}M$ oxyfluorfen showed that Chokoto, the tolerant varieties, had little activity in A band and consistently higher activities in Band C bands for malate dehydrogenase. For 5 bands separated in peroxidase, B band was not found in Chokoto while A, C, D, and E bands were consistently present. Esterase was separated into about 4 bands in which Chokoto had maintained higher activities in A, C and D bands.