• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.720-724
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• 2003

Aluminum nitride (AlN) powders were synthesized by using a mixture of an aluminum nitrate or sulfate salt and carbon (mole ratio of $Al^{3+}$ to carbon=L : 30). The AlN was obtained by calcining the mixture under a flow of nitrogen in the temperature range 1100-1$600^{\circ}C$ and then burning out the residual carbon. The process of conversion of the salt to AlN was monitored by XRD and $^{27}$ Al magic-angle spinning (MAS) NMR spectroscopy. The salt decomposed to ${\gamma}$-alumina and then converted to AlN without phase transition from ${\gamma}$-to-$\alpha$-alumina. $^{27}$ Al MAS NMR spectroscopy shows that the formation of AlN commenced at 110$0^{\circ}C$. AlN powders obtained from the sulfate salt were superior to those from the nitrate salt in terms of homogeneity and crystallinity. A very small amount of AlN whiskers was obtained by calcining a mixture of an aluminum sulfate salt and carbon at 115$0^{\circ}C$ for 40 h, and the growth of the whiskers is well explained by the particle-to-particle self-assembly mechanism.

• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.3
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• pp.83-95
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• 1997

This study was conducted to derive optimal design floods by Gamma distribution models of the annual maximum series at eight watersheds along Geum , Yeong San and Seom Jin river Systems, Design floods obtained by different methods for evaluation of parameters and for plotting positions in the Gamma distribution models were compared by the relative mean errors and graphical fit along with 95% confidence interval plotted on Gamma probability paper. The results were analyzed and summarized as follows. 1.Adequacy for the analysis of flood flow data used in this study was confirmed by the tests of Independence, Homogeneity and detection of Outliers. 2.Basic statistics and parameters were calculated by Gamma distribution models using Methods of Moments and Maximum Likelihood. 3.It was found that design floods derived by the method of maximum likelihood and Hazen plotting position formular of two parameter Gamma distribution are much closer to those of the observed data in comparison with those obtained by other methods for parameters and for plotting positions from the viewpoint of relative mean errors. 4.Reliability of derived design floods by both maximum likelihood and method of moments with two parameter Gamma distribution was acknowledged within 95% confidence interval.

• Journal of Korea Foundry Society
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• v.31 no.5
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• pp.288-292
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• 2011

In order to complement the drawbacks of quartz crucible such as fragile-like break and melt-leakage through open slit nozzle, a new PFC system has been developed using a common graphite crucible and plugging system. The u melt is fed on to the rotating a roll through slit nozzle by self-gravity. The new equipment was designed and manufactured successfully. An effort for optimizing all related parameter has been made. Then using the optimized parameters about 10 meters u foil having very thin thickness, which meets the target thickness of 130 ${\mu}m$ and enough width more than 60 mm could be made. The thickness homogeneity set improved, due to the lower eddy flowing of the melt flow the self-gravity feeding system.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.37 no.4
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• pp.323-329
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• 2004

In situ particle size and volume concentration of suspended sediment was measured at the mouth of Seomjin River Estuary In February 2001, using an optical instrument, 'LISST-100'. Time variation of in situ particle size and concentration shows: (1) during ebb tide, Seomjin River supplies relatively fine-grained particles with less-fluctuated, compared to during flood tide, and well-behaved concentrations following the tidal cycle; and (2) during flood tide, relatively coarse-grained particles with highly variable in size distribution and concentration flow upstream from Kwangyang Bay. This explains a poor correlation $(r^{2}=0.10)$ between sediment concentration and beam attenuation coefficient during flood and a high degree of correlation $(r^{2}=0.80)$ during ebb tide. Relatively fine grained and well defined, monotonous size distribution may promote the correlation between concentration and beam attenuation coefficient due to optical homogeneity of particles during ebb tide. Abundance of large aggregates with time-varying size and shape distributions may be mainly responsible for variations in optical properties of the sediment during flood tide, and thus may confound the relationship between the two variables. The difference in particle sizes and shapes between flood and ebb tides can also be observed on SEM images.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.365-368
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• 2008

This research is related to 240MPa ultra-high strength concrete(UHSC) with extremely loss W/B ratio. For this development, High flow cement is mainly used which has a short reaction rate due to the high blaine and high early strength, which can make greater fluidity in case of very low W/C ratio. It made the best mixture using the mineral admixtures silica fume, slag powder and special admixture. For dispersibility and homogeneity of cement binder, cement of premix type is produced using omni-mixer. Moreover, it ensures the fluidity of ultra-high strength concrete(UHSC). For having a good fire performance, we made an experiment special coarse aggregate. As a result, we got 180MPa in case of water curing, 200MPa in case of steam curing and uniform UHSC of 240MPa in case of a special curing method.

• Journal of the Korean Ceramic Society
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• v.48 no.3
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• pp.236-240
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• 2011

In order to deposit a homogeneous and uniform ${\beta}$-SiC films by chemical vapor deposition, we demonstrated the phase stability of ${\beta}$-SiC over graphite and silicon via computational thermodynamic calculation considering pressure, temperature and gas composition as variables. The ${\beta}$-SiC predominant region over other solid phases like carbon and silicon was changed gradually and consistently with temperature and pressure. Practically these maps provide necessary conditions for homogeneous ${\beta}$-SiC deposition of single phase. With the thermodynamic analyses, the CVD apparatus for uniform coating was modeled and simulated with computational fluid dynamics to obtain temperature and flow distribution in the CVD chamber. It gave an inspiration for the uniform temperature distribution and low local flow velocity over the deposition chamber. These calculation and model simulation could provide milestones for improving the thickness uniformity and phase homogeneity.

• Journal of Soil and Groundwater Environment
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• v.14 no.1
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• pp.51-60
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• 2009

A series of experiments was performed to develop an optimized analytical procedure for the analysis of explosives in soil by HPLC with soil samples collected at two live-fire military shooting ranges. The minimum amount of soil to be collected, Wmin, for the analysis of explosive compounds was 125g, based on the segregation and homogeneity constants that account for soil heterogeneity and non-homogeneous distribution of target explosive compounds. The optimization of extraction and HPLC analytical conditions were also studied based on analytes CV values. The most effective soil/ extractant ratio was estimated to be 10g-pretreated soil/20 mL acetonitrile as extractant. The optimized HPLC elution conditions for the separation of US EPA designated 14 explosive compounds, were column temperature 30${\circ}C$, eluents ratio of isopropanol: acetonitrile: water = 18 : 12: 70, and flow rate of 0.8 mUmin at 230 nm. However, UV wavelength 254 nm was better for the analysis of NB, 2,4-DNT, 2NT, 4NT, and 3NT.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.205-217
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• 2006

Rock and discontinuities are main factors consisting of a rock mass and the physical properties of each factor have direct effects on the mechanical stability of artificial structures in the rock mass. Because physical properties of the rock and discontinuities change a lot according to the size of test materials, a close attention is needed when the physical properties, obtained from laboratory tests, are used for the design of field structures. In this study, change of physical properties of intact materials due to the change of their size are studied. Six kinds of artificial materials including crystal, instead of an intact rock, are adopted for the study to guarantee the homogeneity of specimen materials even with relatively large size. Uniaxial strength and Young's modulus of each artificial material are checked out for a size effect and compared with the predicted values by Buckingham's theorem - dimensional analysis. A numerical analysis using PFC (Particle Flow Code) is also applied and primary factors influencing on the size effect are investigated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.144-149
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• 2020

Bubble reduction devices are intended to solve problems related to the quantitative supply of oil. Therefore, in this study, numerical analysis was conducted to verify the flow characteristics of bubble particles during the operation of a bubble reduction device. As a result of the basic analysis, the area where the rise and fall of bubbles were most active was found, and numerical calculations were performed focusing on the points. Before the numerical calculations, a non-dimensional derivation was performed to secure homogeneity among the variables. Based on the data obtained from non-dimension derivation, 25 variable conditions for each particle size and fluid velocity were set. Through separate calculations, the equation for bubble rise and fall was derived. By calculating the ratio of drag and buoyancy for each variable, if the drag force acting on the bubble was greater than buoyancy, the bubble falls, and bubbles are not reduced. If the buoyancy is larger than drag, the bubble rises, and the bubble is reduced. Through the analysis, the rise and fall of the bubble were confirmed, and the results were consistent with the separate numerical calculations.

• Parasites, Hosts and Diseases
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• v.56 no.2
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• pp.153-165
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• 2018

Development of an effective vaccine is critically needed for the prevention of malaria. One of the key antigens for malaria vaccines is the apical membrane antigen 1 (AMA-1) of the human malaria parasite Plasmodium falciparum, the surface protein for erythrocyte invasion of the parasite. The gene encoding AMA-1 has been sequenced from populations of P. falciparum worldwide, but the haplotype diversity of the gene in P. falciparum populations in the Greater Mekong Subregion (GMS), including Thailand, remains to be characterized. In the present study, the AMA-1 gene was PCR amplified and sequenced from the genomic DNA of 65 P. falciparum isolates from 5 endemic areas in Thailand. The nearly full-length 1,848 nucleotide sequence of AMA-1 was subjected to molecular analyses, including nucleotide sequence diversity, haplotype diversity and deduced amino acid sequence diversity and neutrality tests. Phylogenetic analysis and pair-wise population differentiation ($F_{st}$ indices) were performed to infer the population structure. The analyses identified 60 single nucleotide polymorphic loci, predominately located in domain I of AMA-1. A total of 31 unique AMA-1 haplotypes were identified, which included 11 novel ones. The phylogenetic tree of the AMA-1 haplotypes revealed multiple clades of AMA-1, each of which contained parasites of multiple geographical origins, consistent with the $F_{st}$ indices indicating genetic homogeneity or gene flow among geographically distinct populations of P. falciparum in Thailand's borders with Myanmar, Laos and Cambodia. In summary, the study revealed novel haplotypes and population structure needed for the further advancement of AMA-1-based malaria vaccines in the GMS.