• The Korean Journal of Ceramics
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• 제6권1호
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• pp.37-42
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• 2000

To reduce shrinkage and the possibility of fracture during ambient pressure drying, it is of great importance to increase the strength and stiffness of the wet gels. In this paper is presented the strengthening and stiffening of wet silica gels prepared from sodium silicate (water glass) as well as properties of the corresponding xerogels. By washing gels containing different initial silica contents in water solutions at elevated pH, a maximum in shear modulus of ~4 MPa was obtained. The maximum stiffness enabled xerogels with bulk density of 0.28g/$\textrm{cm}^3$ to be made regardless of silica content and washing conditions. However, by aging the wet gels in a solution providing fresh monomers to the gel network, a shear modulus of 20 MPa was obtained after 27h. By this method monolithic xerogels with a density down to ~0.2g/$\textrm{cm}^3$ was prepared. The results are compared to alkoxide based gels.

• 한국분무공학회지
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• 제5권1호
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• pp.30-40
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• 2000

The characteristics of liquefied butane spray are expected to be different from conventional diesel fuel spray, because a kind of flash boiling spray is expected when the back pressure is below the saturated vapor pressure of the butane(0.23MPa at 298K). The ambient pressure was held at a pressure above(0.37MPa) and below(0.15MPa) the fuel vapor pressure. The axial velocities, radial velocities, and size distributions in butane sprays were measured with PDPA(Phase Doppler Particle Analyzer) system. The PDPA measurement showed a smaller SMD at the 0.15MPa chamber pressure, compared to the 0.37MPa case. Log-hyperbolic density function for the droplets size distribution can be fitted to the experimental results of a liquefied butane spray.

• Steel and Composite Structures
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• 제38권2호
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• pp.177-187
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• 2021

The effect of nanoparticle volume fraction on the elastic properties of a polymer-based nanocomposite was experimentally investigated and the obtained results were compared with various existing theoretical models. The nanocomposite was consisted of high density polyethylene (HDPE) as polymeric matrix and 0, 0.5, 1 and 1.5 wt.% multi walled carbon nanotubes (MWCNTs) prepared using twin screw extruder and injection molding technique. Nanocomposite samples were molded in injection apparatus according to ASTM-D638 standard. Therefore, in addition to morphological investigations of the samples, tensile tests at ambient temperature were performed on each sample and stress-strain plots, elastic moduli, Poisson's ratios, and strain energies of volume units were extracted from primary strain test results. Tensile test results demonstrated that 1 wt.% nanoparticles presented the best reinforcement behavior in HDPE-MWCNT nanocomposites. Due to the agglomeration of nanoparticles at above 1 wt.%, Young's modulus, yielding stress, fracture stress, and fracture energy were decreased and Poisson's ratio and failure strain were increased.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전기물성,응용부문
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• pp.23-25
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• 2001

In this work, the $Ta_2O_5$ thin films were deposited on Pt/n-Si substrate by reactive magnetron sputtering and the RTA treatment at temperatures range from 650 to $750^{\circ}C$ in $O_2$ and vacuum. X-ray diffraction analysis, FE SEM, dielectric properties and leakage current density have been used to study the structural and electrical properties of the $Ta_2O_5$ thin films. XRD result showed that as- deposited films were amorphous and the annealed films crystallized (<$700^{\circ}C$) into ${\beta}-Ta_2O_5$. The crystallinity increased with temperature in terms of an increase in the intensity of the diffracted peaks(${\beta}-Ta_2O_5$) and annealing in oxygen reduced defect dang1ing Ta-O bonds. As deposited $Ta_2O_5$ films show the leakage current density $10^{-7}$ to $10^{-8}$ (A/$cm^2)$ at low electric fields (<200 kV/cm) However, it was found leakage current density of $Ta_2O_5$ thin films decreased with $O_2$ ambient annealing. The dielectric constant of the as deposited $Ta_2O_5$ thin films was ${\varepsilon}_r$ $9{\sim}11$ but the dielectric constant was increased after RTA treatment in $O_2$ ambient more then in vacuum.

• Asian-Australasian Journal of Animal Sciences
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• 제12권1호
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• pp.42-48
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• 1999

Three experiments were conducted to develop and test equations for predicting carcass composition. In the first study using 52 d-old Cobb ${\times}$ Cobb male broilers, twenty four carcasses were selected from 325 processed birds based upon visual appraisal for abdominal fat (low, medium, high) and assayed for specific gravity (SG), dry matter (DM), fat, protein, and ash. In experiment 2, 120 birds were fed rations containing 2 caloric densities (2,880 and $3,200kcal\;ME_n/kg$ diet) and assayed as described above on weeks 2,3,4,5, and 6. Carcass fat was elevated (p < 0.05) with increased caloric density. In both studies predictive variables were significantly correlated with chemically determined carcass fat, protein, and ash contents. Pooled across the 2 studies, data were used to form SG, DM, and or age based equations for predicting carcass composition. Results were tested in experiment 3, where 576 birds reared to 49-d consumed either 2,880, 3,200, or $3,574kcal\;ME_n/kg$ diet while exposed to constant $24^{\circ}C$ or cycling 24 to $35^{\circ}C$ ambient temperatures. Both dietary and environmental effects impacted (p < 0.05) carcass composition. The fat content analyzed chemically was enhanced from 12.4 to 15.7%, and predicted fat was also elevated from 13.4 to 14.8% with increasing caloric density. Heat distress reduced (p < 0.05) analyzed carcass protein (18.9 vs 18.3%) and predicted protein (18.2 vs 17.5%). Predicted equation values for carcass fat, protein, ash, and energy were correlated with the chemically analyzed values at r=0.96, 0.77, 0.86, and 0.79, respectively. Results suggest that prediction equations based on DM and SG may be used to estimate carcass fat, protein, ash, and energy contents of broilers consuming diets that differ in caloric density (2,800 to $3,574kcal\;ME_n/kg$) and for broilers exposed to either constant ($24^{\circ}C$) or cycling high (24 to $35^{\circ}C$) ambient temperatures during 49-d rearing period tested in the present study.

• Journal of Mechanical Science and Technology
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• 제19권11호
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• pp.2040-2052
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• 2005

The present paper centers on the establishment of a quantified relationship between the macroscopic visual parameters of a Diesel spray and its most influential factors. The factors considered are the ambient gas density, as an external condition relative to the injection system, and nozzle hole diameter and injection pressure as internal ones. The main purpose of this work is to validate and extend the different correlations available in the literature to the present state of the Diesel engine, i.e. high injection pressure, small nozzle holes, severe cavitating conditions, etc. Five mono-orifice, axi-symmetrical nozzles with different diameters have been studied in two different test rigs from which one can reproduce solely the real engine in-cylinder air density, and the other, both the density and the pressure. A parametric study was carried out and it enabled the spray tip penetration to be expressed as a function of nozzle hole diameter, injection pressure and environment gas density. The temporal synchronization of the penetration and injection rate data revealed a possible explanation for the discontinuity observed as well by other authors in the spray's penetration law. The experimental results obtained from both test rigs have shown good agreement with the theoretical analysis. There have been observed small but consistent differences between the two test rigs regarding the spray penetration and cone angle, and thus an analysis of the possible causes for these differences has also been included.

• Journal of Biosystems Engineering
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• 제39권1호
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• pp.47-56
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• 2014

Purpose: In protected crop production facilities such as greenhouse and plant factory, farmers should be present and/or visit frequently to the production site for maintaining optimum environmental conditions and better production, which is time and labor consuming. Monitoring of environmental condition is highly important for optimum control of the conditions, and the condition is not uniform within the facility. Objectives of the paper were to investigate spatial and vertical variability in ambient environmental variables and to provide useful information for sensing and control of the environments. Methods: Experiments were conducted in a strawberry-growing greenhouse (greenhouse 1) and a cherry tomato-growing greenhouse (greenhouse 2). Selected ambient environmental variables for experiment in greenhouse 1 were air temperature and humidity, and in greenhouse 2, they were air temperature, humidity, PPFD (Photosynthetic Photon Flux Density), and $CO_2$ concentration. Results: Considerable spatial, vertical, and temporal variability of the ambient environments were observed. In greenhouse 1, overall temperature increased from 12:00 to 14:00 and increased after that, while RH increased continuously during the experiments. Differences between the maximum and minimum temperature and RH values were greater when one of the side windows were open than those when both of the windows were closed. The location and height of the maximum and minimum measurements were also different. In greenhouse 2, differences between the maximum and minimum air temperatures at noon and sunset were greater when both windows were open. The maximum PPFD were observed at a 3-m height, close to the lighting source, and $CO_2$ concentration in the crop growing regions. Conclusions: In this study, spatial, vertical, and temporal variability of ambient crop growing conditions in greenhouses was evaluated. And also the variability was affected by operation conditions such as window opening and heating. Results of the study would provide information for optimum monitoring and control of ambient greenhouse environments.

• 한국재료학회지
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• 제12권5호
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• pp.382-386
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• 2002

We studied growth and characterization of $SrBi_2Ta_2O_9$ (SBT) thin films fabricated by low temperature process under vacuum and/or oxygen ambient. A metal organic decomposition (MOD) method based on a spin-on technique and annealing process using a rapid thermal annealing (RTA) method was used to prepare the SBT films. The crystallinity of a ferroelectric phase of SBT thin films is related to the oxygen partial pressure during RTA process. Under an oxygen partial pressure higher than 30 Torr, the crystallization temperature inducing the ferroelectric SBT phase can be lowered to $650^{\circ}C$. Those films annealed at $650^{\circ}C$ in vacuum and oxygen ambient showed good ferroelectric properties, that is, the memory window of 0.5~0.9 V at applied voltage of 3~7 V and the leakage current density of 1.80{\times}10^{-8}$ A/$\textrm{cm}^2$ at an applied voltage of 5V. In comparison with the SBT thin films prepared at 80$0^{\circ}C$ in $O_2$ ambient by furnace annealing process, the SBT thin films prepared at $650^{\circ}C$ in vacuum and oxygen ambient using the RTA process showed a good crystallization and electrical properties which would be able to apply to the virtul device fabrication precess.

• 전기화학회지
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• 제22권1호
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• pp.1-12
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• 2019

암모니아 생산은 이전부터 비료, 식량과 관련되어 많은 연구가 이루어져 왔는데, 최근 신재생 에너지에 대한 관심이 커짐에 따라 암모니아 또한 에너지로서 내연기관이나 연료전지로 활용이 기대되어 더 많은 연구가 활발히 이루어 지고 있다. 하지만 암모니아를 생성하기 위해서 하버-보쉬법을 사용하는데, 150-300기압과 $350-550^{\circ}C$ 이상의 높은 압력과 온도가 필요하므로 지구 에너지의 1-2%를 사용할 만큼 암모니아 생산에 많은 에너지가 소모되며, 주로 화석연료가 사용된다. 위와 같은 반응에 사용되는 에너지를 줄임으로 이산화탄소 배출량을 줄여 환경문제에도 대응할 수 있기 때문에 반응온도 및 압력을 줄이는 노력이 필요하다. 본 총설에서는 암모니아를 생산하기 위한 방법 중 특히 상온, 상압에서의 전기화학적 질소환원반응 결과들을 소개한다. 실험 결과뿐만 아니라 밀도범함수 계산을 통하여 전기화학적 질소환원반응 메커니즘 연구가 많이 되었으며, 더 많이 전기화학반응에 참여할 수 있도록 하는, 나노 와이어, 다공성 전극과 같은 나노구조화 전극설계에 대한 다양한 연구 결과들 또한 제시한다.

• 한국수산과학회지
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• 제47권6호
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• pp.847-852
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• 2014

The aim of this study was to investigate the effects of stocking density and water temperature in the rearing of the longtooth grouper Epinephelus bruneus. Juvenile fish [mean body weight (BW)=$6.9{\pm}1.1g$] were raised for 6 weeks, in four density groups of 0.25, 0.5, 0.75, and 1 individuals/L. There were no significant differences in weight gain (WG) or specific growth rate (SGR) among the density groups; however, both WG and SGR tended to be higher in the low density group. After 6 weeks of rearing in temperature-controlled water ($23.6{\pm}0.8^{\circ}C$) and ambient temperature water ($19.6{\pm}1.8^{\circ}C$), there were no significant differences in WG or SGR values, but both tended to be higher in the temperature controlled water. The feed efficiency (FE) and daily feed intake (DFI) and WG values were also higher in the temperature-controlled water than in the ambient temperature water. WG values were lower at lower water temperatures. The same pattern was observed for SGR, FE, and FI, all of which exhibited lower values at lower temperatures. In particular, WG, SGR, and FE values all tended to decrease at the $16^{\circ}C$ water temperature. The effects of water temperature on 1-year fish (mean BW = $387.6{\pm}30.2g$) and 3-year fish (mean BW = $1,338.3{\pm}73.8g$) were similar to those of the juvenile fish (0-year fish).