• Journal of the Korean Applied Science and Technology
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• v.20 no.1
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• pp.27-32
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• 2003

The core-shell latex particles were prepared by sequential emulsion polymerization of alkyl methacrylate and styrene(ST) by using an water-soluble initiator(APS) after preparing monomer pre-emulsion in the presence of an anionic surfactant(SDBS). In organic/organic core-shell polymerization, the pre-emulsion method, which minimized required quantity of sulfactant, has been used to increase the conversion rate and the stability of core-shell latex particles as well as to reduce the formation of secondary particle that cause problems of soap-free emulsion during shell polymerization. We used several methods to observe the core-shell structure. The core-shell structure was studied by measuring pH change during hydrolysis by NaOH, glass transition temperature($T_g$) by differential scanning calorimeter(DSC), morphology of latex by transmission electron microscope(TEM) and change of particle size and distribution by a particle analyzer.

• Proceedings of the KIEE Conference
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• 2005.04a
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• pp.172-175
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• 2005

Recently international regulations governing the amount of harmonic currents(e.g IEC 61000-3-2) became mandatory and active Power factor correction (PFC) pre-regulator circuit became inevitable for the AC/DC converters. Among these topologies, the boost topology represents an optimum solution for a PFC pre-regulation in a high power application. This paper propose improved ZVT(Zero Voltage Transition) AC/DC PFC Boost using the average current control employing a soft-switching technique of the auxiliary switch with a minimum number of components. The conventional ZVT PFC Boost Converter has a disadvantage that the auxiliary switch turns off hard, which influences the overall efficiency and the EMI problem. In this paper, an improved ZVT PFC Boost converter using active snubber is proposed to minimize the switching loss of the auxiliary. The prototype of 100kHz, 640W system was implemented to show the improved performance.

• Journal of Korea Technology Innovation Society
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• v.19 no.1
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• pp.1-28
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• 2016

Current Korean innovation system is facing a new turning point while the growth-oriented and S&T provide-oriented development strategy. Accordingly, there are needs for not only system transition in various area, such as sustainable energy, agriculture, and rural area but also STI policy paradigm shift to create a new innovative pathway. Living lab is being discussed in European country as a new innovative model based on user participation and as a niche experiments for sustainable system transition. This study attempts to analyze the living lab cases which are for the purpose of energy transition, agriculture rural areas system transition, and STI policy paradigm shift. Based on this analysis, the implications were derived in Korea. European Suslab project, C@R project, and Taiwan living lab, promoted diverse transitional experiments successfully by collecting users' background and experiences from pre-planning stage and by maintaining the user-driven innovative actions within the whole development process. This result provides various suggestions to current Korean situation that central government and local governments are considering the introduction of living lab. Living lab can also be utilized as a strategic niche experiments for socio-technical system transition in region or country, as a mean of policy integration, and as a new regional innovation model. In addition, it can be an important platform to realize the policy integration reflecting the user and demand-side which are highlighted in recent innovative policy paradigm.

• Asian-Australasian Journal of Animal Sciences
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• v.31 no.11
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• pp.1756-1765
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• 2018

Objective: The purpose of this study was to evaluate the influence of body condition score (BCS) at calving on the metabolic status of female Murrah buffaloes in the transition period. Methods: Thirty-seven pregnant buffaloes (multiparous) were selected and monitored during the transition period based on their body condition score and on the estimated calving date. Two groups were formed: i) buffaloes with a BCS>3.5 (n = 17); this group was classified and named 'high BCS at calving' (HBCS); and ii) buffaloes with a $BCS{\leq}3.5$ (n = 20); this group was classified and named 'low BCS at calving' (LBCS). All animals were monitored during the last 30 days of pregnancy and the first 70 days post-calving and kept in the same environment and under the same feeding and management conditions. Mean values for BCS at calving were $2.98{\pm}0.9$ (mean${\pm}$standard error of the mean [SEM]) and $4.21{\pm}0.9$ (mean${\pm}$SEM) for the HBCS and LBCS groups, respectively. Results: The HBCS group showed higher milk fat content (p = 0.007) and milk fat yield (p = 0.027) and a higher concentration of milk urea nitrogen (p = 0.001) than LBCS buffaloes, which in turn had a lower urine pH value (p = 0.033) than HBCS buffaloes in the pre-calving period (7.86 for HBCS vs 7.76 for LBCS). The HBCS animals had a higher concentration of erythrocytes (p = 0.001) and hematocrit (p = 0.012) post-calving and a higher hemoglobin concentration (p = 0.004) pre-calving. Conclusion: Buffaloes during the transition period exhibited some variations in the oxidative stress related to their metabolic status. After calving, buffaloes with a high BCS at calving and greater lipid mobilization have a more marked alteration in oxidative status, but improved production performance.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.5
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• pp.581-588
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• 2014

Extensive researches toward pool boiling characteristics have been widely investigated. However, the correct understanding of its boiling crisis by Critical Heat Flux (CHF) phenomenon during steady and transient heat transfer as a fundamental database for designing heat generation systems is still need to be clarified. The pool boiling CHFs were investigated to clarify the generalized phenomena of transition to film boiling at transient condition. The CHFs were measured on 1.0 mm diameter horizontal cylinder of platinum for exponential heat generation rates with various periods for saturated liquids at atmospheric pressure. The incipience of boiling processes was completely different depending on pre-pressurization. Also, the dependence of pre-pressure in transient CHFs changed due to the wettability of boiling liquids. The trend of typical CHFs were clearly divided into the first, second and third groups for long, short and intermediate periods, respectively. By the effect of pre-pressurization, the boiling incipience mechanism was replaced from that by active cavities entraining vapor to that by the HSN in originally flooded cavies.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.49.1-49.1
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• 2019

Giant radio relics in the outskirts of galaxy clusters have been observed and they are interpreted as synchrotron emission from relativistic electrons accelerated via diffusive shock acceleration (DSA) in weak shocks of Ms < 3.0. In the DSA theory, the particle momentum should be greater than a few times the momentum of thermal protons to cross the shock transition and participate in the Fermi acceleration process. In the equilibrium, the momentum of thermal electrons is much smaller than the momentum of thermal protons, so electrons need to be pre-accelerated before they can go through DSA. To investigate such electron injection process, we study the electron pre-acceleration in weak quasi-perpendicular shocks (Ms = 2.0 - 3.0) in an ICM plasma (kT = 8.6 keV, beta = 100) through 2D particle-in-cell simulations. It is known that in quasi-perpendicular shocks, a substantial fraction of electrons could be reflected upstream, gain energy via shock drift acceleration (SDA), and generate oblique waves via the electron firehose instability (EFI), leading the energization of electrons through wave-particle interactions. We find that such kinetic processes are effective only in supercritical shocks above a critical Mach number, $Ms{\ast}{\sim}2.3$. In addition, even in shocks with Ms > 2.3, energized electrons may not reach high energies to be injected to DSA, because the oblique EFI alone fails to generate long-wavelength waves. Our results should have implications for the origin and nature of radio relics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.303-310
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• 2000

Fracture toughness of five different reactor pressure vessel steels was characterized in the transition temperature region by the ASTM E1921-97 standard method using Charpy-sized small specimens. T he predominant fracture mode of the tested steels was transgranular cleavage in the test conditions. A statistical analysis based on the Weibull distribution was applied to the interpretation of the scattered fracture toughness data. The size-dependence of the measured fracture toughness values was also well predicted by means of the Weibull probabilistic analysis. The measured fracture toughness transition curves followed the temperature-dependence of the ASTM master curve within the expected scatter bands. Therefore, the fracture toughness characteristics in the transition region could be described by a single parameter, so-called the reference temperature (T。), for a given steel. The determined reference temperatures of the tested materials could not be correlated with the conventional index temperatures from Charpy impact tests.

• Bulletin of the Korean Chemical Society
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• v.25 no.5
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• pp.694-698
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• 2004

A new method for the simultaneous determination of seven transition metal ions in water and food by microcolumn high-performance liquid chromatography has been developed. The lead, cadmium, mercury, nickel, cobalt, silver and tin ions were pre-column derivatized with tetra-(4-aminophenyl)-porphyrin ($T_4$-APP) to form the colored chelates which were then enriched by solid phase extraction with $C_{18}$ cartridge. The enrichment factor of 50 was achieved by eluted the retained chelates from the cartridge with tetrahydrofuran (THF). The chelates were separated on a ZORBAX Stable Bound microcolumn ($2.0{\times}50\;mm,\;1.8\;{\mu}m$)with methanol-tetrahydrofuran (95 : 5, v/v, containing 0.05 mol/L pyrrolidine-acetic acid buffer salt, pH = 10.0) as mobile phase at a flow rate of 0.5 mL/min and detected with a photodiode array detector from 350-600 nm. The seven chelates were separated completely within 2.0 min. The detection limits of lead, cadmium, mercury, nickel, cobalt, silver and tin are 4 ng/L, 3 ng/L, 6 ng/L, 5 ng/L, 5 ng/L, 6 ng/L, 4 ng/L respectively in the original samples. This method was applied to the determination of the seven transition metal in water and food samples with good results.

• Asian-Australasian Journal of Animal Sciences
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• v.22 no.11
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• pp.1513-1520
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• 2009

Forty-six Holstein heifers were used in a completely randomized design and assigned to 1 of 2 treatments to evaluate the effects of 2 diets varying in ruminal fermentable carbohydrate sources, namely ground corn (GC) and rolled wheat (RW), on metabolism and performance of primiparous cows in the periparturient period. The heifers were fed diets as a total mixed ration (TMR) with similar energy and crude protein content including i) 18.57% GC, or ii) 18.57% RW from -24.13${\pm}$7.73 d relative to expected calving until calving. After calving, all animals received the same lactation diet until 28 d. Animals were group fed from the beginning of the study to -7 d relative to expected calving, fed individually from d -7 to 7 days in milk (DIM), and again group fed to 28 DIM. The pre-partum diets affected (p<0.05) dry matter intake (DMI), energy intake, energy balance (EB) and urinary pH during the last week pre-partum. There was no effect of pre-partum carbohydrate source on overall plasma concentration of glucose, nonesterified fatty acid (NEFA), $\beta$-hydroxybutyrate (BHBA), albumin, triglyceride (TG), cholesterol, aspartate aminotransferase (AST), insulin, and cortisol during the periparturient period. Cows fed the RW diet during the pre-partum period had greater calcium for the first week (p<0.05) and during 28 d (p = 0.08) of lactation compared with heifers fed the GC diet. Primiparous cows fed the RW diet produced greater milk protein content and yield (p<0.05). Primiparous cows fed the RW diet had lower milk urea nitrogen (MUN) and somatic cell count (SCC) than cows fed the GC diet (p<0.05). The results of this study show that feeding pre-partum diets with a rapidly fermentable source of starch but low energy content can improve animal metabolism and performance and smooth the transition of primiparous Holstein cows from gestation to lactation.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.34.2-35
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• 2018

Galaxy transition from star-forming to quiescent, accompanied with morphology transformation, is one of the key unresolved issues in extragalactic astronomy. Although several environmental mechanisms have been proposed, a deeper understanding of the impact of environment on galaxy transition still requires much exploration. My Ph.D. thesis focuses on which environmental mechanisms are primarily responsible for galaxy transition in different environments and looks at what happens during the transition phase using multi-wavelength photometric/spectroscopic data, from UV to mid-infrared (MIR), derived from several large surveys (GALEX, SDSS, and WISE) and our GMOS-North IFU observations. Our multi-wavelength approach provides new insights into the *late* stages of galaxy transition with a definition of the MIR green valley different from the optical green valley. I will present highlights from three areas in my thesis. First, through an in-depth study of environmental dependence of various properties of galaxies in a nearby supercluster A2199 (Lee et al. 2015), we found that the star formation of galaxies is quenched before the galaxies enter the MIR green valley, which is driven mainly by strangulation. Then, the morphological transformation from late- to early-type galaxies occurs in the MIR green valley. The main environmental mechanisms for the morphological transformation are galaxy-galaxy mergers and interactions that are likely to happen in high-density regions such as galaxy groups/clusters. After the transformation, early-type MIR green valley galaxies keep the memory of their last star formation for several Gyr until they move on to the next stage for completely quiescent galaxies. Second, compact groups (CGs) of galaxies are the most favorable environments for galaxy interactions. We studied MIR properties of galaxies in CGs and their environmental dependence (Lee et al. 2017), using a sample of 670 CGs identified using a friends-of-friends algorithms. We found that MIR [3.4]-[12] colors of CG galaxies are, on average, bluer than those of cluster galaxies. As CGs are located in denser regions, they tend to have larger early-type galaxy fractions and bluer MIR color galaxies. These trends can also be seen for neighboring galaxies around CGs. However, CG members always have larger early-type fractions and bluer MIR colors than their neighboring galaxies. These results suggest that galaxy evolution is faster in CGs than in other environments and that CGs are likely to be the best place for pre-processing. Third, post-starburst galaxies (PSBs) are an ideal laboratory to investigate the details of the transition phase. Their spectra reveal a phase of vigorous star formation activity, which is abruptly ended within the last 1 Gyr. Numerical simulations predict that the starburst, and thus the current A-type stellar population, should be localized within the galaxy's center (< kpc). Yet our GMOS IFU observations show otherwise; all five PSBs in our sample have Hdelta absorption line profiles that extend well beyond the central kpc. Most interestingly, we found a negative correlation between the Hdelta gradient slopes and the fractions of the stellar mass produced during the starburst, suggesting that stronger starbursts are more centrally-concentrated. I will discuss the results in relation with the origin of PSBs.