• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.3
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• pp.419-430
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• 2000

The purpose of this study was to compare the microleakage pattern of preventive resin restoration using conventional composite resin and flowable composite resin that recently developed. 60 sound premolar teeth were allocated to three groups. Flowable composite resin was used for the experimental groups(Group I and II) and conventional resin for the control group(Group III). After composite filling and sealant application, all teeth were thermocycled and evaluated for microleakage under light microscope. Additionally, a variety of voids formed inside restorations were also evaluated. Data were analyzed statistically using Kruskal-Wallis test and/or Mann-Whitney U-test. The results of the present study were as follows. 1. Microleakage found in all samples was only limited to the interface of restoration margin and enamel. 2. The flowable composite resin groups (Group I, II) generally showed less microleakage than control groups (conventional preventive resin restoration) (p<0.05) 3. Various types of voids were observed in most specimens. Especially, there was a tendency for more and larger voids to be found in group I, II than group III (p<0.05).

• Journal of Energy Engineering
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• v.11 no.2
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• pp.149-159
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• 2002

In the entrained flow gasifiers, the slag viscosity is an important parameter determining the operation conditions. The slag viscosities of 9 coals, which were selected and tested as possible gasification feedstock in Korea, were measured in a high temperature slag viscometer under gasification conditions. The type and size of crystalline phases that were known to affect the slag viscosity behavior were also determined. The slag samples were obtained from the IEA dry-feed gasifier. The slags of Alaska Usibelli, Curragh, Kideco, Adaro, Denisovsky, Baiduri and Drayton coals showed the behavior of crystalline slags, while those of Datong and Cypurus glassy slags. When a recommended minimum operating temperature was arbitrarily defined as $T_{1000}$poise/+$50^{\circ}C$ for glassy slags and $T_{cv}$ +$50^{\circ}C$ for crystalline slags, the Drayton slag required the lowest temperature, while Denisovsky slag required the highest. All the slags contained C $r_2$ $O_3$ from the refractory. The crystalline slags with $T_{cv}$ at around 132$0^{\circ}C$ contained large anorthites as the major crystalline phase that would have caused the rapid inrease in viscosity. Denisovsky slag contained many pores which were formed by $O_2$ from F $e_{x}$O reduction..

• Journal of the Mineralogical Society of Korea
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• v.20 no.3
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• pp.181-191
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• 2007

The gemological charateristics of Gwangdong tektites and Baikdusan obsidians were investigated, using microscopy, density and refractive index measurements, X-ray fluorescence spectrometry, Inductively Coupled Plasma Mass spectrometry, X-ray powder diffraction, and electron microprobe analysis. The Gwangdong tektites and Baikdusan obsidians are both black in colour and slightly trans-lucent with various shades of brown when cut into a few mm thick. Both the materials yield conchoidal fracture on broken surface. The tektites occur as tear-drop shapes, ranging from 4 to 10 cm long, and in spheres, from 3 to 5 cm in diameter. On the surface numerous shallow pits up to 3 mm in diameter are present. Mohs' hardness and specific gravity are 5 to 5.5 and 2.66, respectively. The tektites are singly refractive, with an refractive index of 1.51. Numerous spherical air bubbles are randomly scattered throughout the tektites, and silica-rich glass inclusions are occasionally seen. X-ray powder diffraction analysis verifies that they are non-crystalline. The Baikdusan obsidians show very similar properties to those of the Gwangdong tektites, especially in hardness, amorphous nature and fracture. Nevertheless, the Baikdusan obsidian can readily be distinguished from the Gwangdong tektites by refractive index ($1.49{\sim}1.50$), specific gravity (2.67 to 2.68), and inclusions (absence of bubbles and presence of sanidine and magnetite crystals).

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.481-487
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• 2009

In this of study, effects of input air velocity(0.05~0.22 m/sec) and molten carbonate salt temperature ($870{\sim}970^{\circ}C$) on flow regime transition have been studied by adopting a drift-flux model of air holdup and a stochastic analysis of differential pressure fluctuations in an air-molten sodium carbonate salt two-phase system(molten salt oxidation process). Air holdup where the flow regime transition begins was determined by air holdup-drift flux plot. The air holdup value which the flow regime transition begins was increased with increasing molten carbonate salt temperature due to the decrease of viscosity and surface tension of molten carbonate salt. To characterize the flow regime transition more quantitatively, differential pressure fluctuation signals have been analyzed by adopting the stochastic method such as phase space portraits and Kolmogorov entropy, The Kolmogorov entropy decreased with an increasing of molten carbonate salt temperature but increased gradually with an increase in an air velocity, however, it exhibited different tendency with the flow regime and the air velocity value which flow regime transition begins was same to the results of drift-flux analysis.

• Korean Journal of Heritage: History & Science
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• v.41 no.1
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• pp.5-19
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• 2008

Thirty six samples of Western asia glass vessel shards which were excavated from South Mound of Hwangnamdaechong were each measured for thickness, pore size and specific gravity and analyzed for ten major compositions and thirteen trace elements. The glass samples with colorless, greenish blue and dark purple blue were well classified by principal component analysis(PCA). All glass shards of Hwangnamdaechong belonged to Soda glass system ($Na_2O-CaO-SiO_2$) which have the range of 14~17% $Na_2O$ and 5~6% CaO. The corelation coefficients of (MgO, $K_2O$) and (MnO, CuO) showed above 0.90. The concentrations of thirteen trace elements apparently differentiated from colorless, greenish blue and dark blue glasses. We found that thirteen trace elements were very important indices for studying raw material of glass and the origin of glass making. Colorless glass : The specific gravity is $1.50{\pm}0.04$. Circle or oval circle pores are observed with regular direction in internal zone and the longest one is about 0.35 mm. The raw material of sodium must be the plant ash because sodium glasses contain HCLA(High CaO, Low $Al_2O_3$) and HMK(high MgO, high $K_2O$) and suggested to Sasanian glass. The total amount of coloring agent of colorless glass is below 1 % which is too small to attribute to the color. Greenish blue glass : The specific gravity is $1.58{\pm}0.04$. The fine pores which are 0.1~0.2mm are dispersed in internal zone. Sodium glasses are distributed to HCLA and HMK. Therefore the greenish blue glass also have used plant ash for raw material of sodium with the same as colorless glass. It was also suggested to the glass of Sasanian. The total amount of coloring agent of greenish blue glass is about 4% under the influence of working MnO, $Fe_2O_3$ and CuO. Dark purple blue glass : The specific gravity is $1.48{\pm}0.19$. There are rarely pores in internal zone. They are distributed to HCLA and LMK(Low MgO, Low $K_2O$) and suggested to Roman glass. The raw material of sodium is estimated to natron. The total amount of coloring agents of greenish blue is about 3% by $Fe_2O_3$ and CuO. These studies for western asia glass shards from South Mound of Hwangnamdaechong could be used in the future as the standard data which could be compared with those of other several graves in Korea and dispersed in foreign areas.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2001.11a
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• pp.21-21
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• 2001

자원재활용과 원가절감를 위해 고지재활용율이 크게 상승하고 있으며, 이와 아울러 고 지원료로부터 고품질의 제품을 생산할 수 있는 기술에 대한 관심이 증대되고 있는 실 정이다. 저급 고지로부터 고품질의 탈묵펄프를 얻기 위해서는 고지재활용공정의 핵심 공정인 부유부상 공정의 효율화가 가장 중요하다고 믿어진다. 이를 위해서는 부유부상 공정에 가장 큰 영향을 미치는 고형입자의 표면 화학적 특성에 따른 공정의 분리효율 평가와 이에 근거한 공정해석과 개선이 요청된다. 이러한 부유부상 공정을 표면화학적 측면에서 구명하기 위해 마이크로 크리스탈린 셀룰로오스(Microcrystalline cellulose: M MCC)를 모댈 물질로 사용하여 표면화학적 특성은 다르나 입자의 크기와 형태는 동일 한 시료를 준비하였다. 친수성의 표면 특성을 나타내는 MCC의 표면 특성을 바꾸기 위 하여 AKD(alkyl ketene dimer)로 처리비율을 달리하여 솔벤트 사이징 처리를 실시하 였다. 이렇게 준비된 MCC의 표면화학적 특성을 IGC를 이용하여 평가하였다 .. IGC는 G GC를 응용한 표면분석 기술로 고체의 물리화학적 특성과 흡착성을 분석하기 위해서 사용되며 이로부터 흡착제의 표면특성을 평가할 수 있다. 본 실험에서는 AKD로 소수화 정도가 다르도록 소수화시킨 MCC 시료를 이용하여 I IGC 칼럼을 준비하고 n-알칸과 몇가지 극성 용매률 이용하여 이들의 칼럼 내 체류시 간을 측정함으로써 흡착특성을 평가하고 이로부터 흡착현상을 열역학적으로 분석하였다. IGC 분석 시에는 칼럼의 온도를 $30^{\circ}C$, $35^{\circ}C$, $40^{\circ}C$의 3수준으로 변화시켰다. 측정결 과로부터 MCC 표면의 흡착자유에너지와 엔탈피, 엔트로피의 변화량을 평가하였으며, 또한 MCC 표면의 극성에너지와 산염기적 성질을 평가하였다. 실험결과 MCC의 소수화도에 따른 열역학적 흡착현상의 차이가 명백하였다. 이는 소 수화 수준에 따라 소수성 및 친수성 물질의 흡착성이 변화된다는 것을 보여준다. 따라서 탈묵 시 진행되는 기포에의 부착현상을 평가할 수 있는 기초자료로 활용될 수 있다 고 사료되었다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.61-69
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• 2015

The objective of this study is to experimentally investigate the mixed flow behaviors and oxygen transfer characteristics of a vertical orifice ejector. The experimental apparatus consisted of an electric motor-pump, an orifice ejector, a circulation water tank, an air compressor, a high speed camera unit and control or measurement accessories. The mass ratio was calculated using the measured primary flow rate and suction air flow rate with experimental parameters. The visualization images of vertically injected mixed jet issuing from the orifice ejector were qualitatively analyzed. The volumetric oxygen transfer coefficient was calculated using the measured dissolved oxygen concentration. At a constant primary flow rate, the mass ratio and oxygen transfer coefficient increase with the air pressure of compressor. At a constant air pressure of the compressor, the mass ratio decreases and the oxygen transfer coefficient increases as the primary flow rate increases. The residence time and dispersion of fine air bubbles and the penetration of mixed flow were found to be important parameters for the oxygen transfer rate owing to the contact area and time of two phases.

• Journal of Energy Engineering
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• v.12 no.4
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• pp.289-301
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• 2003

To develop a chemical-looping combustion technology, conceptual design of 50 kW thermal chemical-looping combustor, which is composed of two interconnected pressurized circulating fluidized beds, was performed by means of mass and energy balance calculations. A riser type fast fluidized bed was selected as an oxidizer and a bubbling fluidized bed was selected as a reducer by mass balance for the chemical-looping combustor. Calculated values of bed mass, solid circulation flux, and reactor dimension by mass and energy balance calculations were suitable for construction and operation of chemical-looping combustor. It is concluded from the comparison of the design results and operating values of commercial circulating fluidized bed that the process outline is realistic. Moreover, the previous results support that oxygen carrier particle, NiO/bentonite, fulfills the conversion rates needed for the proposed design. The effects of system capacity, metal oxide content in a oxygen carrier particle, amount of steam input, gas velocity, and solid depth on design values were investigated and the changes in the system performance can be estimated by proposed design tool.

• Journal of Energy Engineering
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• v.7 no.1
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• pp.57-64
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• 1998

A neutralized fabric filter of which major raw materials were polyester and stainless steel fibers was developed and its physiochemical properties and basic filter characteristics were investigated. Four finds of dusts generated in the typical domestic industry were used, which were coke dust from a steel manufacturing process, cement dust from a cement manufacturing process, flu ash from a fluidized-bed combustor, and incinerator ash from a waste plastics incinerator. The physicochemical properties of the neutralized fabric filter were analyzed in terms of changes in tensile strength and initial elastic modulus under $SO_2$ and $NO_2$ atmospheres, mean flow pore pressure, bubble point pore diameter, mean flow pore diameter, and pore size distribution. In addition, the pressure drop, dust penetration, and figure of merit for the fabric filter were investigated in a bench-scale filter testing unit. The pressure drop increased as the filtration velocity and dust loading increased, and its increasing shape depended on the type of dust. The dust penetration rapidly decreased as the dust loading increased irrespective of the type of dust. The figures of merit for the fabric filters increased in the early stage of filtration and then showed rapid decreases followed maintaining a constant level.

• Journal of Energy Engineering
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• v.7 no.1
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• pp.103-112
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• 1998

A high temperature fabric filter was developed and characterized in order to solve the various problems encountered in the operation of industrial fabric filters. Four kinds of dusts generated in the typical domestic industry were used for its characterization, coke dust from a steel manufacturing process, cement dust from a cement manufacturing process, fly ash from a fluidized-bed combustor, and incinerator ash from a waste plastics incinerator. The physical and chemical properties of the high temperature fabric filter were analyzed in terms of mean flow pore pressure, bubble point pore diameter, mean flow pore diameter, pore size distribution, and the changes in tensile strength and initial elastic modulus under $SO_2$ and $NO_2$ atmospheres. Pressure drop, dust penetration, and figure of merit for the fabric filter were also investigated in a bench-scale filter testing unit. The fabric filter developed in this study had good physical and chemical filter properties and showed a very applicability to typical industrial dusts treatments.