• 한국환경과학회지
• /
• 제11권5호
• /
• pp.419-436
• /
• 2002

The current paper reports on the enhancement of O$_3$, CO, NO$_2$, and aerosols during the Asian dust event that occurred over Korea on 1 May 1999. To confirm the origin and net flux of the O$_3$, CO, NO$_2$, and aerosols, the meteorological parameters of the weather conditions were investigated using Mesoscale Meteorological Model 5(MM5) and the TOMS total ozone and aerosol index, the back trajectory was identified using the Hybrid Single-Particle Lagrangian Integrated Trajectory Model(HYSPLIT), and the ozone and ozone precursor concentrations were determined using the Urban Ashed Model(UAM). In the presence of sufficiently large concentrations of NO$\sub$x/, the oxidation of CO led to O$_3$ formation with OH, HO$_2$, NO, and NO$_2$ acting as catalysts. The sudden enhancement of O$_3$, CO, NO$_2$ and aerosols was also found to be associated with a deepening cut-off low connected with a surface cyclone and surface anticyclone located to the south of Korea during the Asian dust event. The wave pattern of the upper trough/cut-off low and total ozone level remained stationary when they came into contact with a surface cyclone during the Asian dust event. A typical example of a stratosphere-troposphere exchange(STE) of ozone was demonstrated by tropopause folding due to the jet stream. As such, the secondary maxima of ozone above 80 ppbv that occurred at night in Busan, Korea on 1 May 2001 were considered to result from vertical mixing and advection from a free troposphere-boundary layer exchange in connection with an STE in the upper troposphere. Whereas the sudden enhancement of ozone above 100 ppbv during the day was explained by the catalytic reaction of ozone precursors and transport of ozone from a slow-moving anticyclone area that included a high level of ozone and its precursors coming from China to the south of Korea. The aerosols identified in the free troposphere over Busan, Korea on 1 May 1999 originated from the Taklamakan and Gobi deserts across the Yellow River. In particular, the 1000m profile indicated that the source of the air parcels was from an anticyclone located to the south of Korea. The net flux due to the first invasion of ozone between 0000 LST and 0600 LST on 1 May 1999 agreed with the observed ground-based background concentration of ozone. From 0600 LST to 1200 LST, the net flux of the second invasion of ozone was twice as much as the day before. In this case, a change in the horizontal wind direction may have been responsible for the ozone increase.

• 한국세라믹학회지
• /
• 제23권5호
• /
• pp.93-101
• /
• 1986

Microporous glasses were prepared from the 50 $SiO_2-44$ $B_2O_3-6$ $Na_2O$(wt%) parent glass by the phase eparation technique and were characterized by SEM, BET, and Gas Adsorption methods to investigate the possiblity of their use as salt-rejection membranes for reverse osmosis. The conditions of the phase separation for the possible glass membranes were optimized for the given parent glass. The temperature and duration of heat-treatment were desired to be lower(853K) and shorter (1/2~1 hr) respectively. The specific surface areas of porous glasses prepared in this study were about 80~120$m^2$/g and their pore size distribution had a unimodal shape(peak pore radius less than 15$\AA$) It was suggested that the porous glass obtained in this work could be effective for salt-rejection in point of pore size distributions but the way to increase its surface area for the high flux must be studied.

• 한국세라믹학회지
• /
• 제43권6호
• /
• pp.333-337
• /
• 2006

In this study, the $Sr_{1-x}Ba_{x}Al_{2}O_{4}:Eu^{2+},Dy^{3+}$ phosphor were prepared by the solid-state reaction method and its photoluminescence properties were investigated. Starting powders of $SrCO_3,\;BaCO_3,\;and\;Al_{2}O_3$ were mixed with $Eu_{2}O_3$ as activator, $Dy_{2}O_3$ as co-activator and $B_{2}O_3$ as flux. Then, the mixed powders were heated at the temperature of $1100{\sim}1400^{\circ}C$ for 3 h under the reducing ambient atmosphere of $95%Ar+5%H_2$. The effect of Ba addition from 0.0 to 1.0 mol on photoluminescence was investigated. As the amount of Ba increased, the intensity of emission increased and the optimum long phosphorescence occurred at the amount of 0.1 mol Ba. The optimum sintering condition for long phosphorescent phosphor of $Sr_{1-x}Ba_{x}Al_{2}O_{4}:Eu^{2+},Dy^{3+}$($x=0{\sim}1.0mol$) was found at $1400^{\circ}C$. The excitation spectra showed a broad band of $250{\sim}450nm$ with maximum peak at 360 nm. The maximum peak intensity of emission spectra occurred at the range of $480{\sim}520nm$, depending on Ba content.

• 대한기계학회논문집B
• /
• 제25권2호
• /
• pp.180-186
• /
• 2001

The condensation heat transfer coefficients of pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube were investigated. The experiment apparatus consists of a refrigerant loop and a water loop. The main components of the refrigerant loop consist of a variable-speed pump, a mass flowmeter, an evaporator, and a condenser(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flowmeter. The condenser is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. The test section consists of smooth, horizontal copper tube of 3.38mm outer diameter and 1.77mm inner diameter. The length of test section is 1220mm. The refrigerant mass fluxes varied from 450 to 1050kg/(㎡$.$s) and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main results were summarized as follows ; in the case of single-phase flow, the heat transfer coefficients increase with increasing mass flux. The heat transfer coefficient of R-410A was higher than that of R-22 and R-134a, and the heat transfer for small diameter tubes were about 20% to 27% higher than those predicted by Gnielinski. In the case of two-phase flow, the heat transfer coefficients also increase with increasing mass flux and quality. The condensation heat transfer coefficient of R-410A was slightly higher than that of R-22 and R-134a. Most of correlations proposed in the large diameter tube showed significant deviations with experimental data except for the ranges of low quality and low mass flux.

• 한국방사선학회논문지
• /
• 제10권5호
• /
• pp.337-341
• /
• 2016

중성자에너지 영역 0.003 eV에서 10 eV에 대해 천연 Sm의 Sm(n,${\gamma}$) 반응에 대한 중성자 포획단면적을 측정하였다. 교토대학교 원자로실험소의 46-MeV 전자선형가속기에서 발생되는 전자의 광핵반응에 의한 중성자를 사용하였고 TOF 방법으로 측정하였다. 사용한 검출기는 12개의 BGO($Bi_4Ge_3O_{12}$) 섬광체로 구성되었고 이 검출장치로 Sm(n,${\gamma}$) 반응으로부터 나오는 즉발감마선을 측정하였다. 검출장치는 중성자 생성 위치로부터 $12.7{\pm}0.02m$ 위치에 설치되었으며 $^{10}B(n,{\alpha}{\gamma})^7Li$ 반응을 이용해 Sm 시료에 입사되는 중성자 선속을 구하였다. 또한 중성자 선속의 변화를 확인하기 위해 $BF_3$ 검출기로 모니터링 하였다. Sm(n,${\gamma}$) 반응단면적 측정결과는 BROND 2.2에 의한 평가결과와 J. C. Chou 및 V. N. Kononov 의 측정값과 비교하였다.

• 대한금속재료학회지
• /
• 제49권4호
• /
• pp.348-354
• /
• 2011

Long-lasting brightness $Sr_{4}Al_{14}O_{25}$ : $Eu^{2+}$, $Dy^{3+}$, $Ag^{+}$ phosphor was synthesized by modified solid state reaction and its photoluminescence was investigated. $Sr(NO_3)_{2}$ and $Al(NO_3)_3{\cdot}9H_{2}O$ as starting materials, and $B_{2}O_{3}$ as a flux were mixed with $Eu_{2}O_{3}$ as an activator, $Dy_{2}O_{3}$ as a coactivator, and $AgNO_{3}$ as a charge compensator. The crystalline of target powder showed a single-phase $Sr_{4}Al_{14}O_{25}$ by the XRD characterization and the average particle size was about 20-30 ${\mu}m$ from the FE-SEM observation. $Ag^{+}$ ion doping effects (0-0.06 mol) on $Sr_{4}Al_{14}O_{25}:Eu^{2+},\;Dy^{3+},\;Ag^{+}$ phosphor were measured by photoluminescence spectrometer and luminescence meter. The of photoluminescence intensity of the $Sr_{3.64}Al_{14}O_{25}:Eu_{0.11},\;Dy_{0.22},\;Ag_{0.03}$ phosphor was higher than other compositions and afterglow brightness was 0.186 $cd/m^{2}$.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
• /
• pp.1087-1090
• /
• 2004

Samples of yttrium oxide doped with trivalent europium have been prepared by ceramic techniques, under different synthesis conditions; barium chloride ($BaCl_2$) and sodium tetraborate ($Na_2B_4O_7$) were tested as flux. The improvement of luminescence properties in dependence on substitution of $Eu^{3+}$ for $Y^{3+}$ in the host lattice, under electron and UV excitations is demonstrated The obtained results are discussed with respect to the employed processing method.

• 한국주조공학회지
• /
• 제30권3호
• /
• pp.94-99
• /
• 2010

When the returned scrap of bulk amorphous alloy is remelted, impurities such as oxides and intermetallic compounds increase. Glass forming ability of its scrap is deteriorated remarkably. Melt fluxing technique is introduced to enhance the glass forming ability during melting and freezing of bulk amorphous alloys. Cu and Zr based alloys are chosen. Small pieces of these alloy scraps and $B_2O_3$ flux are put together in a quartz tube. Cyclic heating and cooling are done by induction heating and water quenching or air cooling. Melting fluxing was effective for both Cu-based and Zr-based alloy, and their glass forming abilities were improved with increasing the number of fluxing.

• Journal of Radiation Protection and Research
• /
• 제45권3호
• /
• pp.130-141
• /
• 2020

Background: Concrete activation in cyclotron vaults is a major concern associated with their decommissioning because a considerable amount of activated concrete is generated by secondary neutrons during the operation of cyclotrons. Reducing the amount of activated concrete is important because of the high cost associated with radioactive waste management. This study aims to investigate the capability of the neutron absorbing materials to reduce concrete activation. Materials and Methods: The Particle and Heavy Ion Transport code System (PHITS) code was used to simulate a cyclotron target and room. The dimensions of the room were 457 cm (length), 470 cm (width), and 320 cm (height). Gd₂O₃, B₄C, polyethylene (PE), and borated (5 wt% ^natB) PE with thicknesses of 5, 10, and 15 cm and their different combinations were selected as neutron absorbing materials. They were placed on the concrete walls to determine their effects on thermal neutrons. Thin B₄C and Gd₂O₃ were placed between the concrete wall and additional PE shield separately to decrease the required thickness of the additional shield, and the thermal neutron flux at certain depths inside the concrete was calculated for each condition. Subsequently, the optimum combination was determined with respect to radioactive waste reduction, price, and availability, and the total reduced radioactive concrete waste was estimated. Results and Discussion: In the specific conditions considered in this study, the front wall with respect to the proton beam contained radioactive waste with a depth of up to 64 cm without any additional shield. A single layer of additional shield was inefficient because a thick shield was required. Two-layer combinations comprising 0.1- or 0.4-cm-thick B₄C or Gd₂O₃ behind 10 cm-thick PE were studied to verify whether the appropriate thickness of the additional shield could be maintained. The number of transmitted thermal neutrons reduced to 30% in case of 0.1 cm-thick Gd₂O₃+10 cm-thick PE or 0.1 cm-thick B₄C+10 cm-thick PE. Thus, the thickness of the radioactive waste in the front wall was reduced from 64 to 48 cm. Conclusion: Based on price and availability, the combination of the 10 cm-thick PE+0.1 cmthick B₄C was reasonable and could effectively reduce the number of thermal neutrons. The amount of radioactive concrete waste was reduced by factor of two when considering whole concrete walls of the PET cyclotron vault.

• Progress in Superconductivity
• /
• 제2권2호
• /
• pp.76-80
• /
• 2001

We have fabricated YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) ramp-edge Josephson junctions by modifying ramp edges of the base electrodes without depositing any artificial barrier layer. YBa$_2$Cu$_3$O/7-x//SrTiO$_3$ (YBCO/STO) films were deposited on SrTiO$_3$(100) by on-axis KrF laser deposition. After patterning the bottom YBCO/STO layer, the ramp edge was cleaned by ion-beam and then reacted with deionized water under various conditions prior to the deposition of counter-electrode layers. The top YBCO/STO layer was deposited and patterned by photolithography and ion milling. We measured current-voltage (I-V) characteristics, magnetic field modulation of the critical current at 77 K. Some showed resistively shunted junction (RSJ)-type I-V characteristics, while others exhibited flux-flow behaviors, depending on the dipping time of the ramp edge in deionized water. Junctions fabricated using optimized conditions showed fairly uniform distribution of junction parameters such as I$_{c}$R$_{n}$ values, which were about 0.16 mV at 77 K with 1$\sigma$~ 24%. We made a dc SQUID with the same deionized water treated junctions, and it showed the sinusoidal modulation under applied magnetic field at 77 K. 77 K.