• Journal of Environmental Health Sciences
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• v.29 no.4
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• pp.10-16
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• 2003

Atmospheric samples were conducted from September 2001 to July 2002 with GPS-l PUF sampler in rural site to concentration distributions of gas/particle PCBs and to calculate dry deposition flux of PCBs. $\Sigma$PCBs concentrations of gas/particle PCBs were 59.29$\pm$48.83, 6.56$\pm$6.59 pg/㎥, respectively. Gas contribution (%) of total PCBs (gas + particle) was 90% which existed gas phase in the atmosphere. The particle contribution (%) of PCB congeners increased relatively more of the less volatile congeners with the highest chlorine number. The correlation coefficients (r) between total PCBs and temperature ($^{\circ}C$) showed negative correlation in - 0.62 (p<0.0l) for particle phase, positive correlation in 0.63 (p<0.01) for gas phase. In other word, particle phase PCBs is enriched in colder weather which could be due to greater in corporation of condensed gas phase at low temperature. The calculated dry deposition of total PCBs (gas + particle) was 0.008, 0.008 $\mu\textrm{g}$ $m^{-2}$ da $y^{-l}$ which showed maximum dry deposition flux in December, minimum data in July Bs in the atmosphere. The calculated dry deposition fluxes of total PCBs were influenced by particle phase PCBs even though PCBs in the atmosphere were present primarily in the gas phase.e.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.467-472
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• 1997

Porous silicon was prepared by an anodic etching. The pore size was about 10 nm at an etching time of 20 sec and a current density of 20 mA/$\textrm{cm}^2$. The porous layer was composed of an micro-porous layer (0.6 ${\mu}{\textrm}{m}$) and a macro-porous layer (10 ${\mu}{\textrm}{m}$). Room temperature PL with maximum peak 6700$\AA$ appeared. The peak disappeared by an oxidation reaction when the porous silicon was heated to 100~20$0^{\circ}C$ in atmosphere. In order to avoid the oxidation a heat treatment was done in H2 atmosphere. The micro-pore and Si column, which formed quantum well, were collapsed by the high temperature. The PL maximum peak of heated sample was gradually red-shifted and showed about 300$\AA$ red-shift at 50$0^{\circ}C$. The intensity of PL was maintained to high temperatures in lower pressures. The porous Si was carbonized in C2H2+H2 gas in order to increase thermal stability. The carbonization of the porous Si prevented red-shift of the maximum PL peak caused by sintering effect at high temperatures, and the carbonized porous Si showed Pl signal at higher temperatures by above 20$0^{\circ}C$ than the sample in H2 atmosphere.

• Journal of the Korean Ceramic Society
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• v.28 no.11
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• pp.935-941
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• 1991

Effects of calcination process and ZrO2 addition on the electrical properties of [(Ba0.82Sr0.08Ca0.1)O]m(Ti1-$\chi$Zr$\chi$)O2 ceramics have been investigated. With the variation of A/B-site ratio m of the dielectric formulations, sintering behavior and the resistivity after sintering in a reducing atmosphere have been affected by the calcination process. When the dielectric formulations of m=1.01 were sintered in a reducing atmosphere, the room-temperature resitivity of 109 {{{{ OMEGA }}.cm was obtained for samples processed with two-step calcination, which was much lower than 1012 {{{{ OMEGA }}.cm of samples calcined once. It was confirmed that high resistivity of Ca-doped BaTiO3 ceramics, after sintering in a reducing atmosphere, is maintained by acceptor-like behavior of CaTi" which is formed by Ca substitution to Ti-site. It was also found out that the critical amount of B-site Ca substitution for reduction inhibition of BaTiO3 is around 0.005 mol. With the increasing amount of ZrO2 addition to dielectric formulations, Curie peak was depressed and Curie temperature was lowered due to the enhanced diffuse phase transition.tion.

• Journal of the Korean Society for Heat Treatment
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• v.16 no.4
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• pp.191-196
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• 2003

For improvement of the wear performance of Ti alloy, vacuum-carburizing technique was tried for the first time using propane atmosphere. During the low pressure carburizing carbide was formed at the surface and carbon transfer was occurred from the carbide to the matrix. It was found that: (i) surface hardness increased with the reduction of operating pressure and time; (ii) optimum hardness distribution could be obtained with the proper choice of temperature and carbon flux control; and, (iii) case depth was largely influenced not by time but by temperature. The two steps process was recommended for obtaining thick case depth and high surface hardness of Ti alloy. For the low oxygen partial pressure, it was necessary to introduce additional CO gas to the atmosphere.Grain boundary oxidation and non-uniformity could be prevented.

• Advances in aircraft and spacecraft science
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• v.8 no.1
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• pp.1-15
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• 2021

Mars exploration demands aerodynamic computations for a proper design of missions of spacecraft carrying instruments and astronauts to Mars. Both Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) method play a key role for this purpose. To the author's knowledge, the altitude separating the fields of applicability of CFD and DSMC in Mars atmosphere entry is not yet clearly defined. The limitations in using DSMC at low altitudes are due to technical limitations of the computer. The limitations in using CFD at high altitudes are due to thermodynamic non-equilibrium. Here, this problem is studied in Mars atmosphere entry, considering the Mars Pathfinder capsule in the altitude interval 40-80 km, by means of a DSMC code. Non-equilibrium is quantified by the relative differences between translational temperature and: rotational (θt-r), vibrational (θt-v), overall (θt-ov) temperatures, anisotropy is quantified by the relative difference between the translational temperature component along x and those along y (θx-y) and along z (θx-z). The results showed that θt-r, θt-v, θx-y, θx-z are almost equivalent. The altitude of 45 km should be the limit altitude for a proper use of a CFD code and the altitude of 40 km should be the limit altitude for a reasonable use of a DSMC code.

• Journal of the korean Society of Automotive Engineers
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• v.4 no.2
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• pp.35-46
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• 1982

This paper deals with residual stress characteristics of ion-nitrided metal which is primarilly concerned with the effects of added carbon content in gas atmosphere. A small optimal amount of carbon content in gas atmosphere increase compound layer thickness, as well as to increase diffusion layer thickness and hardness. The residual stress and deflection of the specimens was measured in various elevated temperature at the surface of ion-nitrided metal and the internal stress distribution was calculated. It is found that compressive residual stress at the compound layer is largest at the compound layer, and decreases as the depth from the surface increases.

• IE interfaces
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• v.6 no.2
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• pp.171-181
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• 1993

In this study, a process management system is designed that can automatically control the heat treating atmosphere, and a managment software is developed to monitor and control continously the heat treating process using a n interface device. Especially, a communication protocol is developed to control and monitor atmosphere condition, temperature, surrounding gas, and time. The developed interface device, called COMPORT SELECTOR is to send and receive information from PID controllers and PLC via RS-232C communication. This system will reduce manufacturing cost and cycle time, and improve the effectiveness of working process and quality.

• Toxicological Research
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• v.5 no.2
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• pp.97-104
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• 1989

A new exposure system was developed to generate p-dinitrobenzene (p-DNB) containing atmosphere. A glass column was filled with small glass beads coated with the chemical. The p-DNB containing medium was heated to a temperature beyond the boiling point of p-DNB. A stream of air flow was forced to pass through the column and let it mixed with fresh air before introducing into an inhalation chamber. The concentration of p-DNB in the chamber air was measured by direct assaying the air directly and by sampling the chemical using a microfilter installed in the chamber.

• Proceedings of the KSRS Conference
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• v.1
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• pp.398-401
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• 2006

Dual channel Radiometer for Earth and Atmospheric Monitoring (DREAM) is the main payload on Science and Technology SATellite-2 (STSAT-2) of Korea. DREAM is two-channel microwave radiometer with linear polarization, and operating at center frequencies of 23.8 GHz and 37 GHz. An equation for DREAM calibration is derived which accounts for losses and re-radiation in the microwave components of the radiometer due to physical temperature. This paper describes the radiometric calibration equation to get antenna temperature ($T_A$) from the measured output data. At lower altitude, the measured deep space temperature is contaminated by middle atmosphere and earth radiation. In this paper, we presented the detail mathematical formulation to find the altitude up to which cold source brightness temperature is not affected by earth and middle atmosphere radiation. The DREAMPFM data is used to calculate the performance parameters (linearity, sensitivity, dynamic range, and etc.) of the system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.11
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• pp.832-840
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• 2008

Ablation occurs at irradiance beyond $10^9\;W/cm^2$ with nanosecond and short laser pulses focused onto any materials. Phenomenologically, the surface temperature is instantaneously heated past its vaporization temperature. Before the surface layer is able to vaporize, underlying material will reach its vaporization temperature. Temperature and pressure of the underlying material are raised beyond their critical values, causing the surface to explode. The pressure over the irradiated surface from the recoil of vaporized material can be as high as $10^5\;MPa$. The interaction of high power nanosecond laser with a thin metal in air has been investigated. The nanosecond pulse laser beam in atmosphere generates intensive explosions of the materials. The explosive ejection of materials make the surrounding gas compressed, which form a shock wave that travels at several thousand meters per second. To understand the laser ablation mechanism including the heating and ionization of the metal after lasing, the temporal evolution of shock waves is captured on an ICCD camera through laser flash shadowgraphy. The expansion of shock wave in atmosphere was found to agree with the Sedov's self-similar spherical blast wave solution.