• 설비공학논문집
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• 제5권1호
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• pp.10-17
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• 1993

This paper describes the boiling heat transfer phenomena to be divided into three regions, nonboiling, nucleate boiling and burn-out in the impinging subcooled water jet system. In the nonboiling region, Nusselt number is a function of Prandtl number, Reynolds number and ${\Delta}T_{sub}/T_{ast}$ In the nucleate boiling region, the heat flux increases with increment of the nozzle exit velocity. But the degree of liquid subcooling does not affect the shape of the nucleate boilng curve. The dimensionless correlations can be expressed in the form of $q{\ell}/K_f{\Delta}T_{ast}=C(Bo{\cdot}C_p{\cdot}{\Delta}T_{sat}/Vo^2)^m{\cdot}(Re/We)^n$. The burn-out heat flux increases linearly with increment of the nozzle exit velocity, but independs of degree of subcooling and the supplementary water height.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.39-42
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• 2002

In the current study, characteristics of the laser-induced plasma were investigated in a gas filled chamber or in a gas jet by using a relatively low intensity laser $(I\;\leq\;5\;\times\;10^{12}\;W/cm^2)$. Temporal evolutions of the produced plasma were measured using the shadow visualization and the shock wave propagation as well as the electron density profiles in the plasma channel was measured using the Mach-Zehnder interferometry. Experimental results such as the structure of the produced plasma, shock propagation speed $(V_s)$, electron density profiles $(n_e)$, and the electron temperature $(T_e)$ are discussed in this study. Since the diagnostic laser pulse occurs over short time intervals compared to the hydrodynamic time scales of expanding plasma or a gas jet, all the transient motion occurring during the measurement is assumed to be essentially frozen. Therefore, temporally well-resolved quantitative measurements were possible in this study.

• The Journal of Advanced Prosthodontics
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• 제10권5호
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• pp.367-373
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• 2018

PURPOSE. To evaluate the fit of a crown produced based on a 3D printed model and to investigate its clinical applicability. MATERIALS AND METHODS. A master die was fabricated with epoxy. Stone dies were fabricated from conventional impressions (Conventional stone die group: CS, n=10). Digital virtual dies were fabricated by making digital impressions (Digital Virtual die group: VD, n=10). 3D data obtained from the digital impression was used to fabricate 3D printed models (DLP die group: DD, n=10, PolyJet die group: PD, n=10). A total of 40 crowns were fabricated with a milling machine, based on CS, VD, DD and PD. The inner surface of all crowns was superimposed with the master die files by the "Best-fit alignment" method using the analysis software. One-way and 2-way ANOVA were performed to identify significant differences among the groups and areas and their interactive effects (${\alpha}=.05$). Tukey's HSD was used for post-hoc analysis. RESULTS. One-way ANOVA results revealed a significantly higher RMS value in the 3D printed models (DD and PD) than in the CS and DV. The RMS values of PD were the largest among the four groups. Statistically significant differences among groups (P<.001) and between areas (P<.001) were further revealed by 2-way ANOVA. CONCLUSION. Although the fit of crowns fabricated based on the 3D printed models (DD and PD) was inferior to that of crowns prepared with CS and DV, the values of all four groups were within the clinically acceptable range (<$120{\mu}m$).

• 한국결정학회지
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• 제8권1호
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• pp.1-5
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• 1997

표제화합물의 결정구조는 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium, $C_{16}H_{19}N_2$와 tosylate, $C_7H_7SO_3$의 불연속한 이분자체로 구성되어 있다. 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium 분자는 중간에 있는 C=C double bond에서 trans conformation을 가지고 있으며 phenyl 및 pyridyl ring들간의 이면각은 $5.7(2)^{\circ}$을 이루어 전분자는 $0.138(8){\AA}$ 내에서 평면을 이루고 있다. Tosylate 분자들은 거리가 각각 2.855(9) and $2.899(8){\AA}$인 O-H...O 수소결합으로 연결된 이분자체를 나타내고 있다. 이 두 분자간의 가장 가까운 거리는 O(3)와 C(16) 원자간의 $3.10(1){\AA}$이다.

• 한국염색가공학회지
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• 제14권2호
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• pp.109-109
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• 2002

A study has been made of the dry-jet-wet spinning of PAN copolymer fibers using 60% aqueous zinc chloride solution as solvent and 25∼40% aqueous zinc chloride solution as non-solvent. The technological characteristics of this method were that small streams of dope were extruded from the die and allowed to pass through a short distance of air gap(about 10mm) before entering the spinning bath for full coagulation. This work showed the importances which coagulation condition, stretch ratio and fiber tenacity up to 10.5 g/d could be obtained with elongation of 11∼16%. Individual fibers were evaluated on the basis of density and mechanical properties such as tenacity and elongation etc.

• 한국재료학회지
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• 제21권2호
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• pp.106-110
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• 2011

A high thermal conductive AlN composite coating is attractive in thermal management applications. In this study, AlN-YAG composite coatings were manufactured by atmospheric plasma spraying from two different powders: spray-dried and plasma-treated. The mixture of both AlN and YAG was first mechanically alloyed and then spray-dried to obtain an agglomerated powder. The spray-dried powder was primarily spherical in shape and composed of an agglomerate of primary particles. The decomposition of AlN was pronounced at elevated temperatures due to the porous nature of the spray-dried powder, and was completely eliminated in nitrogen environment. A highly spherical, dense AlN-YAG composite powder was synthesized by plasma alloying and spheroidization (PAS) in an inert gas environment. The AlN-YAG coatings consisted of irregular-shaped, crystalline AlN particles embedded in amorphous YAG phase, indicating solid deposition of AlN and liquid deposition of YAG. The PAS-processed powder produced a lower-porosity and higher-hardness AlN-YAG coating due to a greater degree of melting in the plasma jet, compared to that of the spray-dried powder. The amorphization of the YAG matrix was evidence of melting degree of feedstock powder in flight because a fully molten YAG droplet formed an amorphous phase during splat quenching.

• 한국세라믹학회지
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• 제33권3호
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• pp.321-326
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• 1996

Thermal fatigue test and stress analysis of Si3N4 and metal swirl chamber were carried out to investigate the reliability of the swirl chambers. Conditions of the thermal fatigue test were severer than those in real engine and FEM was used to analize the stress distribution in the swirl chambers. Fatigue cracks of the maximum length 2.4 mm and deformation were occurred at the corner of the jet in metal swirl chamber but not observed in Si3N4 swirl chamber. Maximum tensile stress in Si3N4 swirl chamber calculated by FEM was 300 MPa.

• 한국안전학회지
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• 제27권5호
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• pp.9-15
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• 2012

The ignition characteristics in a confined axisymmetric coflow $CH_4$ jet were investigated numerically with the Fire Dynamics Simulator(FDS). The $CH_4$ fuel stream was diluted with main combustion product gases, such as $O_2$, $N_2$, CO, $CO_2$, and $H_2O$, and the mixed fuel stream was heated up to the sufficient temperature where a supplying fuel stream can be ignited. For the calculation of chemical reaction in the simulation, a 2-step global finite chemistry model was considered. Boundary condition for confined wall was optimized by investigating the effects of wall temperature on the ignition characteristics of fuel stream. In addition, the effects of composition of diluents in the fuel stream and fuel stream temperature on the ignition of fuel steam were investigated. The ignition characteristics of $CH_4$ stream with diluents were very sensitive to the wall temperature, composition of diluents in the fuel stream and fuel stream temperature.

• 한국해양학회지
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• 제20권2호
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• pp.28-39
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• 1985

저층 jet와 야간 최대 연안표층풍의 유도 mechanism을 텍사스주의 Port Aransas 와 Victoria지역에서 1976년 6월부터 1980년 8월까지 관측된 바람자료를 사용하여 경압모델에 의해 연구되었다. 이모델은 forcing function인 종관 및 중기압 경도, 마찰력과 대기안정도를 고려하여 개발된다. 연구결과는 야간최대 연안표층풍 에 대해 저층 jet가 95%의 출현빈도를 보여준다. 여름철에는 경사지형에 의한 경압 성이 thermal field의 일변화를 초래한다. 이 온도풍이 낮에는 탁월한 남풍의 풍속을 감소시키고 밤에는 증가시킨 다. 야간대기안정도는 마찰력 유리를 유도하므로 야간 저층 jet를 강화한다. 해안에서는 중립안정도가 지배적이고 또 저층 jet로부터 운동 량의 연직전이는 야간 최대연안표층풍을 형성한다. 저층 jet의 출현고도는 역전층과 의 뚜렷한 관계를 보여주지 않으며, 이 모델에 의한 계산결과는 관측치와 잘 일치 한다.

• 대한치과교정학회지
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• 제53권3호
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• pp.139-149
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• 2023

Objective: To assess the color stability and translucency of full cubic stabilized zirconia (FSZ) following orthodontic bonding with different surface treatments and coffee thermocycling (CTC). Methods: This in vitro study was conducted on 120 disc-shaped specimens of FSZ. Thirty specimens were selected as the control group and remained intact. The remaining specimens were randomly divided into three groups based on the type of surface treatment (n = 30): airborne particle abrasion (APA), silica-coating (CoJet), and carbon dioxide (CO₂) laser. After metal bracket bonding in the test groups, debonding and polishing were performed. Subsequently, all specimens underwent CTC (10,000 cycles). Color parameters, color difference (ΔE₀₀), and translucency parameter (TP) were measured three times at baseline (t0), after debonding and polishing (t1), and after CTC (t2). Data were statistically analyzed (α = 0.05). Results: Significant difference existed among the groups regarding ΔE₀₀t0t2 (p < 0.001). The APA group showed minimum (ΔE₀₀ = 1.15 ± 0.53) and the control group showed maximum (ΔE₀₀ = 0.19 ± 0.02) color stability, with no significant difference between the laser and CoJet groups (p = 0.511). The four groups were significantly different regarding ΔTPt0t2 (p < 0.001). Maximal increases in TP were noted in the CoJet (1.00 ± 0.18) and APA (1.04 ± 0.38) groups while minimal increase was recorded in the control group (0.1 ± 0.02). Conclusions: Orthodontic treatment makes zirconia restorations susceptible to discoloration and increased translucency. Nonetheless, the recorded ΔE₀₀ and ΔTP did not exceed the acceptability threshold.