• Journal of the Korean Ceramic Society
• /
• v.40 no.12
• /
• pp.1202-1207
• /
• 2003

Using a recently developed Hybric Plasma-Particle Accelerating Impact Deposition (HP-PAID) process, synthesis of nanostructured silicon coatings has been investigated by injecting vapor-phase TEOS (tetraethosysilane, (C$_2$H$\_$5/O)$_4$Si) into an Ar hybrid plasma. The plasma jet with reactants was expanded through nozzle into a deposition chamber, with the pressure dropping from 700 to 10 torr. Ultrafine particles accelerated in the free jet downstream of the nozzle, deposited by an inertial impaction onto a temperature controlled substrate. By using this process, nanostructured amorphous silicon coatings with grain size smaller than 10 nm could be synthesized. These samples were annealed in an Ar and crystallized at 900$^{\circ}C$ for 30 min. TEM analysis showed that the annealed coatings were also composed of nanoparticles smaller than 10 nm, which showed a good consistency that the average grain size of 7 nm was also estimated from a peak shift of 2.39 cm$\^$-1/ and Full Width at Half Maximum (FWHM) 5.92 cm$\^$-1/ of Raman analysis. The noteworthy is that a strong PL peak at 398 nm was also obtained for this sample, which indicates that the deposited coatings also contained 3∼4 nm nanostructured grains.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.9
• /
• pp.536-542
• /
• 2018

Tin dioxide, $SnO_2$, is a well-known n-type semiconductor that shows change in resistance in the presence of gas molecules, such as $H_2$, CO, and $CO_2$. Considerable research has been done on $SnO_2$ semiconductors for gas sensor applications due to their noble property. The nanomaterials exhibit a high surface to volume ratio, which means it has an advantage in the sensing of gas molecules. In this study, SnO nanoplatelets were grown densely on Si substrates using a thermal CVD process. The SnO nanostructures grown by the vapor transport method were post annealed to a $SnO_2$ phase by thermal CVD in an oxygen atmosphere at $830^{\circ}C$ and $1030^{\circ}C$. The pressure of the furnace chamber was maintained at 4.2 Torr. The crystallographic properties of the post-annealed SnO nanostructures were investigated by Raman spectroscopy and XRD. The change in morphology was confirmed by scanning electron microscopy. As a result, the SnO nanostructures were transformed to a $SnO_2$ phase by a post-annealing process.

• Journal of Biosystems Engineering
• /
• v.8 no.1
• /
• pp.17-29
• /
• 1983

The milling process is considered as causing one of the greatest grain losses among all the processes in rice post-production. Major source of grain losses in the rice milling is considered as the whitening process. This study was attempted to develop an abrasive-type whitener, the whitening chamber of which being supplied by jet-air evenly and continuously. To investigate the milling performance by the new whitener, three kind of emery-stone grit(#36, #41, and #46), and three levels of rotational speed of emery stone roller (950, 1070, and 1200 rpm) were tested. The jet-air abrasive-type whitener was also compared with the conventional abrasive-type having no jet-air blower in terms of their milling performance. In addition, the effect of different combinations of sequential uses of the abrasive- and friction-type whiteners on the milling performance was also experimentally evaluated. The results of this study are summarized as follows; 1. In general, the whitening system combined with the abrasive type whitener with jet-air supply, which was newly designed, and the existing jet-air friction type whiteners produces more milled- and head-rice by about 0.3% points and 2.8% points, respectively than the system combined with the existing abrasive type without the jet-air supply under the same operational conditions. The former also consumed less electricity by 0.024 KwH per 100kg of milled rice production and gave more milling capacity by about 35 kg/hr. As compared with the conventional whitening system consisting of jet-air friction type whiteners only, the former yielded more milled- and head-rice by 1.5% points and 4.4% points, respectively. 2. The abrasive roller having 46 grit emery was better than the roller having 36 grit in aspects of milling performance and machine efficiency, in general. 3. With regard to the effect of combination method of abrasive type and friction type whiteners, one pass in abrasive type plus three passes in friction type gave better milling performance and energy efficiency than the two passes in abrasive type plus two passes in friction type regardless of the designs of the emery stone rollers. 4. The increase in rotational speed of the emery stone roller from 950 rpm to 1200 rpm presented negative effects on milled and head-rice yields and machine efficiency, but slightly positive effect on milling capacity.

• Korean Chemical Engineering Research
• /
• v.46 no.5
• /
• pp.958-964
• /
• 2008

In this work, micro-sized dextran particles, which have recently been focused as one of the candidate materials for the Drug Delivery System(DDS), were prepared by means of the Supercritical Antisolvent (SAS) process with $CO_2$. With dimethyl sulfoxide(DMSO) as the solvent, effects of the operating variables such as temperature (308.15~323.15 K), pressure(90~130 bar), solute concentration(10~20 mg/ml), and the molecular weight of the solute(Mw=37,500, 450,000) on the size and morphology of the resulting particles were thoroughly observed. The higher solute concentration led to the larger particles, however, the injection velocity of the solution and pressure did not show significant effects on the resulting particle size. With dextran of the lower molecular weight, the smallest particles were obtained at 313.15 K. On the other hand, the size of the particles from the high molecular weight dextran ranged between $0.1{\sim}0.5{\mu}m$ with an incremental effect of the temperature and pressure. For the solute concentration of 5 mg/ml, the lower molecular weight dextran did not form discrete particles while aggregation of the particles appeared when the solute concentration exceeded 15 mg/ml for the higher molecular weight dextran. It is believed that if the solute concentration is too low, the degree of the supersaturation in the recrystallization chamber would not be sufficient for initiation of the nucleation and growth mechanism. Instead, the spinodal decomposition mechanism leads to formation of the island-like phase separation which appears similar to aggregation of the discrete particles. This effect would be more pronounced for the smaller molecular weight polymer system due to the narrower phase-splitting region.

• Journal of the Korean Wood Science and Technology
• /
• v.48 no.5
• /
• pp.732-744
• /
• 2020

In this study, a torrefaction of Quercus serrata to manufacture a molded charcoal was performed, investigated material properties, fuel characteristics, and performed a quantitative analysis of hazardous gases which occur during a combustion process. In addition, a molded charcoal in market was selected as a control group, and a comparative analysis was performed. As a result, the higher heating value (HHV) of the torrefied specimen was about 14% higher than that of molded charcoal, and its ash content was about 51 times lower. Moreover, after performing a quantitative assessment of hazardous gases (carbon monoxide, nitrogen oxide, and sulfur dioxide) which were produced when each specimen was combusted for 900 seconds in an enclosed chamber, it was confirmed that the maximum value of generated amount of carbon monoxide on the torrefied specimen was about 50 times lower than that of the existing molded charcoal. Therefore, it was shown that the torrefied specimen produced in this study had a higher heating value than the molded charcoal in the market, and a very low amount of carbon monoxide generated during the combustion process.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.221-221
• /
• 2013

Vertical LED (VLED) has been recognized as a way to obtain the high-power LED due to their advantages [1]. However, approximately 4% of the light generated from the active region is extracted, if the light extraction from side walls and back side is neglected because of Fresnel reflection (FR) and total internal reflection (TIR) [2,3]. In this study, the optical simulation of the VLED with the various microstructures was performed. Among them, the microlens having the diameter of 3 ${\mu}m$ and the height of 1.5 ${\mu}m$ shown the best result was chosen, and then, optimized microlens was formed on a GaN template using conventional semiconductor process. Various microstructures were proposed to improve the light extraction efficiency (LEE) of the VLED for the simulation. The LEE was simulated using LightTools based on a Monte Carlo ray tracing. The microstructures with hemisphere, cone, truncated and cylinder pattern having diameter of 3 ${\mu}m$ were employed on the top layer of the VLED respectively. The improvement of the LEE by using the microstructure is 87% for the hemisphere, 77% for the cone, 53% for the truncated, 21% for the cylinder, compared with the LEE of the flat surface at the reflectance of 85%. The LEE was increased by 88% at the height of 1.5 ${\mu}m$, compared with the LEE of the flat surface. We found that the microlens on the top layer is the most suitable for increasing the LEE. In order to apply the proposed microlens on n-GaN surface, we fabricated microlens on a GaN template. A photoresist array having hexagonal-closed packed microlens was fabricated on the GaN template. Then, optimization of etching the GaN template was performed using a dry etching process with ICP-RIE. The dry etching carried out using a gas mixture of Cl2 and Ar, each having a flow rate of 16 sccm and 10 sccm, respectively with RF power of 50 W, ICP power of 900 W and chamber pressure of 2 mTorr was the optimum etching condition as shown in Fig. 2(a).

• Korean Journal of Heritage: History & Science
• /
• v.41 no.1
• /
• pp.57-78
• /
• 2008

According to the previous studies about Shilla's cremate grave, in the process of importing the cremate grave, there has been correlation with Chinese Buddhism, and there have been a lot of mentions about the change of the grave, Yinwha(Stamp) patterns and its existence, and about the characteristics of the vessels to contain the bones. The cremate grave is categorized into two-parts type and mono-type, depending on the dead person. The cremate graves that are in local areas such as Wang-Gyeong, show difference in types. The typical vessel to contain the bones, called "Yeongyeol Gori Yoogaeho" is again proved to have existed from A.D 8c. ~ A.D 9c., judging from the Yinwha pattern stamp's existence. Yet, the Yeongyeol Gori Yoogaeho from 9th century used the patternless pottery, also seen from the Won-wha 10 yeon-myeong cremate grave. Due to the prosperity of Buddhism, when the "Mukuchonggwang Taranikyong(Sutra)", translated into Han language in 704 at Dang, was imported into Shilla, the funeral ceremonies of Shilla people changed from making cremate graves with vessels or scattering the bones in oceans, into building stupas in temples with hopes and wishes to bring oneself and family's fortune and the next life of the dead. As a result, the meaning of "Grave" disappeared for the cremate graves, and rather the ceremony changed into scattering bones and wishing fortunes for the dead person. In other words, the ancestor-worship ceremony which was focused on the tomb changed into commemorating the ancestors and wishing individual fortunes by the religious assembly in temples and the building process of stupas. In conclusion, this social change was the cause of the extinction of stone chamber with tunnel entrance and the tombs such as cremate grave.

• Journal of Radiation Protection and Research
• /
• v.47 no.1
• /
• pp.16-21
• /
• 2022

Background: Epidemiological observations such as mental retardation, physical deformities, etc., in children besides different types of cancer in the adult population of the Malwa region have been reported. The present study is designed to get insight into the role of naturally occurring radioactive material (NORM) in causing detrimental health effects observed in the general population of this region. Materials and Methods: Deep soil samples were collected from different locations in the Malwa region. Their activity concentrations were determined using low-level background gammaray spectrometry. High efficiency and high purity germanium detector capped in a lead-shielded chamber having a resolution of 1.8 keV at 1,173 keV and 2.0 keV at the 1,332 keV line of ⁶⁰Co was used in the present work. Data were evaluated with Genie-2000 software. Results and Discussion: Mean activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K in deep soil were found to be 101.3 Bq/kg, 65.8 Bq/kg, and 688.6 Bq/kg, respectively. The mean activity concentration of ²³⁸U was found to be three and half times higher than the global average prescribed by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). It was further observed that the activity concentration of ²³²Th and ⁴⁰K has a magnitude that is nearly one and half times higher than the global average prescribed by UNSCEAR. In addition, the radioisotope ¹³⁷Cs which is likely to have its origin in radiation fallout was also observed. It is postulated that the NORM present in high quantity in deep soil somehow get mobilized into the water aquifers used by the general population and thereby causing harmful health problems. Conclusion: It can be stated that the present work has been able to demonstrate the use of low background gamma-ray spectrometry to understand the role of NORM in causing health-related effects in a general population of the Malwa region of Punjab, India.

• Journal of the Korean Geotechnical Society
• /
• v.38 no.12
• /
• pp.125-134
• /
• 2022

The Global Expansion Roadmap published by the International Space Exploration Coordination Group, which is organized by space agencies around the world, presents future lunar exploration guidance and stresses a lunar habitat program to utilize lunar resources. The Moon attracts attention as an outpost for deep space exploration. Simulating lunar surface environments is required to evaluate the performances of various equipment for future lunar surface missions. In this paper, an experimental study was conducted to simulate high vacuum pressure and cryogenic temperature of the permanent shadow regions in the lunar south pole, which is a promising candidate for landing and outpost construction. The establishment of an efficient dirty thermal vacuum chamber (DTVC) operation process has never been presented. One-dimensional ground cooling tests were conducted with various vacuum pressures with the Korean Lunar Simulant type-1 (KLS-1) in DTVC. The most advantageous vacuum pressure was found to be 30-80 mbar, considering the cooling efficiency and equipment stability. However, peripheral cooling is also required to simulate a cryogenic for not sublimating ice in a high vacuum pressure. In this study, an efficient peripheral cooling operation process was proposed by applying the frost ratio concept.

• Journal of the Korean Vacuum Society
• /
• v.18 no.3
• /
• pp.197-202
• /
• 2009

The long term stability of ion current of QMS has been one of key parameters for monitoring gas process in vacuum. The time dependence of ionic current was monitored while the pressure of nitrogen gas was kept at a fixed pressure by introducing the gas into vacuum chamber. The chamber was evacuated to ${\sim}3{\times}10^{-9}\;Torr$ to reduce background signals before the measurement. Two ion sources were tested; one had brownish or black color due to gas contamination and the other one was new, i.e. cleaner. At a nitrogen pressure of $1{\times}10^{-5}\;Torr$, the ionic currents measured by the contaminated ion source decreased faster with time. The decrease rate was respectively ${\sim}46%$ for cleaner one and ${\sim}84%$ for contaminated one after ${\sim}5.5%$ hours. In order to test the effect of filament material on the ion current decrease, we fabricated a tungsten(W) filament which consisted of two parts; one half was made of W and the other was coated with yttria. The similar decrease of ionic currents were shown for the two types of filaments, indicating that slight change of temperature of filament due to material difference i.e. baking effect could not improve the origin of ionic current decrease. Overall the decreasing rate of ionic current is more closely associated with contaminated ion source of QMS rather than its filament materials.