• Journal of the Korean Society for Heat Treatment
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• v.27 no.4
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• pp.180-184
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• 2014

In order to make clear relationship between high temperature tensile properties and fine microstructure of rapidly solidified cast-type Ni-base superalloys without heat treatment required for consolidation process, tensile test was carried out by changing strain rate from $5{\times}10^{-5}s^{-1}$ to $2{\times}10^{-2}s^{-1}$ and test temperature from $900^{\circ}C$ to $1050^{\circ}C$ using IN738LC and Rene'80 melt-spinning ribbons by twin roll process which were superior to ribbons by single roll process from the viewpoint of structure homogeneity. The dependence of tensile strength on strain rate and test temperature was studied and strain rate sensitivity, m, were estimated from tensile test results. From this study, it was found that tensile strength was influenced by ${\gamma}^{\prime}$ particle diameter, test temperature and strain rate, and m of ribbons exhibited above 0.3 over $950^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.750-754
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• 2008

The artificial aggregates with dense surface layer (shell) was fabricated and the dependence of water emission rate upon the shell structures was studied. The EAF dust containing many flux components and waste white clay with ignition loss of above 48% were used as for liquid phase and gas forming agents during a sintering process respectively. In addition, the shell structure was modified with various processes and the modification effect on water emission rate was analyzed. The pores under $10{\mu}m$ were found in the sintered artificial light aggregates and disappeared by incorporating to a bigger pore during re-sintering. The water emission rate in an initial step depended on a void content of aggregates filled in a bottle rather than a shell structure. But, after 7 days where the water emission of the aggregate with a shell is above 40%, the shell of aggregates suppressed the water emission. The core of aggregates was exposed and most shell was lost when crushed to smaller size so, the ability for suppressing water emission of the crushed aggregates decreased. The activation energy for the water emission was $3.46{\pm}0.25{\times}10^{-1}$J/mol for the most specimens showing that the activation energy is irrelevant to the pore size distribution and shell structure.

• Bulletin of the Korean Chemical Society
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• v.15 no.8
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• pp.663-669
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• 1994

Decay kinetics of Ga(5s), Ga(5p) and Ga(4d) atoms in Ar were studied by laser induced fluorescence technique. Theground state gallium atoms in the gas phase were generated by pulsed dc discharge of trimethyl gallium and argon mixtures. Both pulsed discharge and YAG-DYE laser system were controlled by a dual channel pulse generator and the delay time between the end of discharge and laser pulses was set 3.0-6.0 ms. The Ga(5s) and Ga(4d) atoms were generated by single photon excitation from the ground state Ga atoms and radiative lifetimes as well as the total quenching rate constants in Ar were obtained from the pressure dependence of the fluorescence decay rates. The Ga(5p) atoms were populated by a two-photon excitation method and the cascade fluorescence from Ga(5s) atoms were analyzed to extract quenching rate constant of Ga(5p) atoms by Ar in addition to radiative lifetimes of Ga(5p) state. The magnitudes of the quenching rate constants by Ar for the low-lying excited states of Ga atoms are 1.6-3$ {\times}10^{-11}cm^3$ molecul$e^{-1}s^{-1}$, which are much larger than those for alkali, alkaline earth and Group 12 metals. Based on the measured rate constants, kinetic simulations were done to assign state-to-state rate constants.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.48.2-48.2
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• 2019

Tidal disruption events (TDEs) provide evidence for quiescent supermassive black holes (SMBHs) in the centers of inactive galaxies. TDEs occur when a star on a parabolic orbit approaches close enough to a SMBH to be disrupted by the tidal force of the SMBH. The subsequent super-Eddington accretion of stellar debris falling back to the SMBH produces a characteristic flare lasting several months. It is theoretically expected that the bolometric light curve decays with time as proportional to $t^{-5/3}$. However, some of the observed X-ray light curves deviate from the $t^{-5/3}$ decay rate, while some of them are overall in good agreement with the $t^{-5/3}$ law. Therefore, it is required to construct the theoretical model for explaining these light curve variations consistently. In this paper, we revisit the mass fallback rates semi-analytically by taking account of the stellar internal structure, orbital eccentricity and penetration factor. We find that the mass fallback rate is shallower than the standard $t^{-5/3}$ decay rate independently of the polytropic index, and the orbital eccentricity only changes the magnitude of the mass fallback rate. Furthermore, the penetration factor significantly can modify the magnitude and variation of mass fallback rate. We confirm these results by performing the computational hydrodynamic simulations. We also discuss the relevance of our model by comparing these results with the observed light curves.

• The Journal of Korean Society for Radiation Therapy
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• v.22 no.2
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• pp.123-129
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• 2010

Purpose: The purpose of this study was to evaluate dosimetric characteristics of Optically stimulated luminescent dosimeters (OSLD) for dosimetry Materials and Methods: InLight/OSL $NanoDot^{TM}$ dosimeters was used including $Inlight^{TM}MicroStar$ Reader, Solid Water Phantom, and Linear accelerator ($TRYLOGY^{(R)}$) OSLDs were placed at a Dmax in a solid water phantom and were irradiated with 100 cGy of 6 MV X-rays. Most irradiations were carried out using an SSD set up 100 cm, $10{\times}10\;cm^2$ field and 300 MU/min. The time dependence were measured at 10 minute intervals. The dose dependence were measured from 50 cGy to 600 cGy. The energy dependence was measured for nominal photon beam energies of 6, 15 MV and electron beam energies of 4-20 MeV. The dose rate dependence were also measured for dose rates of 100-1,000 MU/min. Finally, the PDD was measured by OSLDs and Ion-chamber. Results: The reproducibility of OSLD according to the Time flow was evaluated within ${\pm}2.5%$. The result of Linearity of OSLD, the dose was increased linearly up to about the 300 cGy and increased supralinearly above the 300 cGy. Energy and dose rate dependence of the response of OSL detectors were evaluated within ${\pm}2%$ and ${\pm}3%$. $PDD_{10}$ and PDD20 which were measured by OSLD was 66.7%, 38.4% and $PDD_{10}$ and $PDD_{20}$ which were measured by Ion-chamber was 66.6%, 38.3% Conclusion: As a result of analyzing characteration of OSLD, OSLD was evaluated within ${\pm}3%$ according to the change of the time, enregy and dose rate. The $PDD_{10}$ and $PDD_{20}$ are measured by OSLD and ion-chamber were evaluated within 0.3%. The OSL response is linear with a dose in the range 50~300 cGy. It was possible to repeat measurement many times and progress of the measurement of reading is easy. So the stability of the system and linear dose response relationship make it a good for dosimetry.

• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.244-260
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• 2018

Issues in the electrical characterization of semiconducting photoanodes in a photoelectrochemical (PEC) cell, such as the cell geometry dependence, scan rate dependence in DC measurements, and the frequency dependence in AC measurements, are addressed, using the example of a $TiO_2$ photoanode. Contrary to conventional constant phase element (CPE) modeling, the capacitive behavior associated with Mott-Schottky (MS) response was successfully modeled by a Havriliak-Negami (HN) capacitance function-which allowed the determination of frequency-independent Schottky capacitance parameters to be explained by a trapping mechanism. Additional polarization can be successfully described by the parallel connection of a Bisquert transmission line (TL) model for the diffusion-recombination process in the nanostructured $TiO_2$ electrode. Instead of shunt CPEs generally employed for the non-ideal TL feature, TL models with ideal shunt capacitors can describe the experimental data in the presence of an infinite-length Warburg element as internal interfacial impedance - a characteristic suggested to be a generic feature of many electrochemical cells. Fully parametrized impedance spectra finally allow in-depth physicochemical interpretations.

• Analytical Science and Technology
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• v.5 no.1
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• pp.63-71
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• 1992

Liquid chromatographic behavior of Pd(II), Ni(II) and Co(III) in N-Alkylisonitrosoacetylacetone imine(HIAA-NR) chelates was investigated by reversed phase high perfomance liquid chromatography. The optimum conditions for the separation of IAA-NR-metal chelates were examined respect to the flow rate and mobile phase strength. The metal-N-Alkylisonitrosoacetylacetone imine chelates in solution were successfully separated on Novapak $C_{18}$ column using acetonitrile/water mixture as mobile phase. The elution order of chelates is methyl>ethyl>propyl>butyl as N-alkyl group for ligand is varied. It was found that all IAA-NR-metal chelates were eluted in an acceptable range of capacity factor value($0{\leq}log\;k^{\prime}{\leq}1$). The dependence of log k' on the volume fraction of water in the binary mobile phase was examined. Also, the dependence of k' on the liquid-liquid extraction distribution ratio(Dc) in acetonitrile-water-alkane extraction system was investigated for IAA-NR-metal chelate. Both kinds of dependence are linear, which suggests that the retention of the electroneutral metal chelates on Novapak $C_{18}$ column is largely due to the hydrophobic effect.

• Journal of Microbiology and Biotechnology
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• v.25 no.12
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• pp.2058-2071
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• 2015

A comparative study was conducted to evaluate precision and accuracy in controlling the temperature dependence of encapsulated microbial time-temperature integrators (TTIs) developed using two different emulsification techniques. Weissela cibaria CIFP 009 cells, immobilized within 2% Na-alginate gel microbeads using homogenization (5,000, 7,000, and 10,000 rpm) and Shirasu porous glass (SPG) membrane technologies (10 μm), were applied to microbial TTIs. The prepared micobeads were characterized with respect to their size, size distribution, shape and morphology, entrapment efficiency, and bead production yield. Additionally, fermentation process parameters including growth rate were investigated. The TTI responses (changes in pH and titratable acidity (TA)) were evaluated as a function of temperature (20℃, 25℃, and 30℃). In comparison with conventional methods, SPG membrane technology was able not only to produce highly uniform, small-sized beads with the narrowest size distribution, but also the bead production yield was found to be nearly 3.0 to 4.5 times higher. However, among the TTIs produced using the homogenization technique, poor linearity (R²) in terms of TA was observed for the 5,000 and 7,000 rpm treatments. Consequently, microbeads produced by the SPG membrane and by homogenization at 10,000 rpm were selected for adjusting the temperature dependence. The E_a values of TTIs containing 0.5, 1.0, and 1.5 g microbeads, prepared by SPG membrane and conventional methods, were estimated to be 86.0, 83.5, and 76.6 kJ/mol, and 85.5, 73.5, and 62.2 kJ/mol, respectively. Therefore, microbial TTIs developed using SPG membrane technology are much more efficient in controlling temperature dependence.

• Progress in Medical Physics
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• v.18 no.1
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• pp.48-54
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• 2007

This study is to develope a phantom for MOSFET (Metal Oxide Semiconductors Field Effect Transistors) dosimetry and compare the dosimetric properties of standard MOSFET and microMOSFET with the phantom. In this study, the developed phantom have two shape: one is the shape of semi-sphere with 10cm diameters and the other one is the flat slab of $30{\times}30cm$with 1 cm thickness. The slab phantom was used for calibration and characterization measurements of reproducibility, linearity and dose rate dependency. The semi-sphere phantom was used for angular and directional dependence on the types of MOSFETs. The measurements were conducted under $10{\times}10cm^2$ fields at 100cm SSD with 6MV photon of Clinac (21EX, Varian, USA). For calibration and reproducibility, five standard MOSFETS and microMOSFETs were repeatedly Irradiated by 200cGy five times. The average calibration factor was a range of $1.09{\pm}0.01{\sim}1.12{\pm}0.02mV/cGy$ for standard MOSFETS and $2.81{\pm}0.03{\sim}2.85{\pm}0.04 mV/cGy$ for microMOSFETs. The response of reproducibility in the two types of MOSFETS was found to be maximum 2% variation. Dose linearity was evaluated In the range of 5 to 600 cGy and showed good linear response with $R^2$ value of 0.997 and 0.999. The dose rate dependence of standard MOSFET and microMOSFET was within 1% for 200 cGy from 100 to 500MU/min. For linearity, reproducibility and calibration factor, two types of MOSFETS showed similar results. On the other hand, the standard MOSFET and microMOSFET were found to be remarkable difference in angular and directional dependence. The measured angular dependence of standard MOSFET and microMOSFET was also found to be the variation of 13%, 10% and standard deviation of ${\pm}4.4%,\;{\pm}2.1%$. The directional dependence was found to be the variation of 5%, 2% and standard deviation of ${\pm}2.1%,\;{\pm}1.5%$. Therefore, dose verification of radiation therapy used multidirectional X-ray beam treatments allows for better the use of microMOSFET which has a reduced angular and directional dependence than that of standard MOSFET.

• Nuclear Engineering and Technology
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• v.41 no.2
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• pp.171-178
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• 2009

The rate of delayed hydride cracking (DHC), V, has been measured in cold-worked and stress-relieved Zircaloy-4 fuel cladding using the Pin-Loading Tension technique. At $250^{\circ}C$ the mean value of V from 69 specimens was $3.3({\pm}0.8)x10^{-8}$ m/s while the temperature dependence up to $275^{\circ}C$ was described by Aexp(-Q/RT), where Q is 48.3 kJ/mol. No cracking or cracking at very low rates was observed at higher temperatures. The fracture surface consisted of flat fracture with no striations. The results are compared with previous results on fuel cladding and pressure tubes.