• Korean Journal of Environmental Biology
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• v.40 no.4
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• pp.413-422
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• 2022

Barnea manilensis is a bivalve which bores soft rocks, such as, limestone or mudstone in the low intertidal zone. They make burrows which have narrow entrances and wide interiors and live in these burrows for a lifetime. In this study, the morphology and the microstructure of the valve of rock-boring clam B. manilensis were observed using a stereoscopic microscope and FE-SEM, respectively. The chemical composition of specific part of the valve was assessed by energy dispersive X-ray spectroscopy (EDS) analysis. 3D modeling and structural dynamic analysis were used to simulate the boring behavior of B. manilensis. Microscopy results showed that the valve was asymmetric with plow-like spikes which were located on the anterior surface of the valve and were distributed in a specific direction. The anterior parts of the valve were thicker than the posterior parts. EDS results indicated that the valve mainly consisted of calcium carbonate, while metal elements, such as, Al, Si, Mn, Fe, and Mg were detected on the outer surface of the anterior spikes. It was assumed that the metal elements increased the strength of the valve, thus helping the B. manilensis to bore sediment. The simulation showed that spikes located on the anterior part of the valve received a load at all angles. It was suggested that the anterior part of the shell received the load while drilling rocks. The boring mechanism using the amorphous valve of B. manilensis is expected to be used as basic data to devise an efficient drilling mechanism.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.97-106
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• 2020

Swelling properties and shear strength behavior of MgO-Sand mixtures with hydration procese of MgO are compared according to different MgO contents (W_MgO/W_Total=0, 30, 50, 70, 100%) in this study. The specimens are prepared by mixing with crushed MgO refractory bricks and silica sand. After hydration, the particle size and the specific gravity of MgO were decreases. Through microstructure observation and X-ray diffraction analysis, it is confirmed that MgO changes from the cubic structure of Periclase to the hexagonal cubic structure of Brucite after hydration. As the MgO content increases, both swelling rate and swelling pressure of the mixtures increase. W_MgO/W_Total=30% specimen shows relatively low swelling pressure and swelling rate because produced Mg(OH)₂ mainly fills the pores between sand particles. However, in the case of MgO more than 50%, swelling pressure and swelling rate increase significantly because Mg(OH)₂ fills the pores of sand particles at first and then either pushes out sand particles or Mg(OH)₂ particles after filling the pores. As a result of the direct shear test, before hydration, the mixtures show a dilative behavior on high MgO contents and a contractive behavior on low MgO contents. However, after hydration, the behavior of all mixtures changes to contractive behavior. The threshold fraction of fine (i.e., Mg(OH)₂) contents of the hydrated MgO-Sand mixtures reveals approximately 60% compared with normalized shear strength.

• Applied Microscopy
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• v.38 no.4
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• pp.279-284
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• 2008

The phase change materials have been extensively used as an optical rewritable data storage media utilizing their phase change properties. Recently, the phase change materials have been spotlighted for the application of non-volatile memory device, such as the phase change random access memory. In this work, we have investigated the crystallization behavior and microstructure analysis of In-Sb-Te (IST) thin films deposited by RF magnetron sputtering. Transmission electron microscopy measurement was carried out after the annealing at $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$ and $450^{\circ}C$ for 5 min. It was observed that InSb phases change into $In_3SbTe_2$ phases and InTe phases as the temperature increases. It was found that the thickness of thin films was decreased and the grain size was increased by the bright field transmission electron microscopy (BF TEM) images and the selected area electron diffraction (SAED) patterns. In a high resolution transmission electron microscopy (HRTEM) study, it shows that $350^{\circ}C$-annealed InSb phases have {111} facet because the surface energy of a {111} close-packed plane is the lowest in FCC crystals. When the film was heated up to $400^{\circ}C$, $In_3SbTe_2$ grains have coherent micro-twins with {111} mirror plane, and they are healed annealing at $450^{\circ}C$. From the HRTEM, InTe phase separation was occurred in this stage. It can be found that $In_3SbTe_2$ forms in the crystallization process as composition of the film near stoichiometric composition, while InTe phase separation may take place as the composition deviates from $In_3SbTe_2$.

• The Korean Journal of Financial Management
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• v.22 no.1
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• pp.71-91
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• 2005

The object or this paper is to analyze the rollover effect on KOSPI 200 index option prices. Especially we analyze the implied volatilities of the options that became the near maturity options as the old one expired. For this analysis, a panel data of KOSPI 200 Index Option Prices from year 1999 to year 2001 were used, and following results were obtained. First, after controlling for the underlying index returns, strike prices and other pricing factors, the call option prices tend to decrease while the put option prices tend to increase during the week of expiry. Second, if one concentrates on the daily price changes, call option prices tend to go up on Thursday (as the old options expire), and then experience a price decrease on the following day, while the reverse is true for the put options. These results imply that the option prices are affected by some of the market micro-structure effects such as whether the option is the near maturity option. We conjecture that the reason for this is related to the undervaluation of KOSPI 200 futures. The results from this paper have implications on the timing of option trades. If one wants to buy put options, and/or sell call options, he has better off by executing his intended trades before the old options expire. On the other hand, if one wants to buy call options, and/or sell put options, hi has better off by executing his intended trades after the expiry.

• Korean Journal of Dental Materials
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• v.44 no.2
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• pp.171-178
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• 2017

The purpose of this study is to investigate the effect of number of times dipped in coloring liquid and sintering temperature on the flexural strength of zirconia ceramic. In this study, using a zirconia block having improved transparency, specimens with size of $25mm{\times}2mm{\times}1.5mm$ were fabricated. The zirconia ceramic specimens were divided into three groups according to the number of times dipped in coloring liquid by 0, 2 and 4 times, and dyed in the coloring liquid to give color to each specimen. Then, after sintering them at the final temperature of $1,450^{\circ}C$ and $1,600^{\circ}C$, flexural strength was measured using a universal testing machine (total 6 group, n=10 for each group). Also, a scanning electron microscopy (SEM) was performed to observe its microstructure, and the data obtained through the experiment were analyzed with two-way ANOVA. The results of the flexural strength analysis show that the highest value was measured $762.3{\pm}42.3MPa$ in EKL2 group, while the lowest value was $516.4{\pm}77.1MPa$ in EKH4 group. According to the results of the two-way ANOVAs, flexural strength was not related with interaction between sintering temperature and number of times dipped in coloring liquid ($R^2=0.737$). However, there were statistically significant differences in flexural strength depending on sintering temperature (P<0.001). The flexural strength of zirconia ceramics having improved transparency was dependent on sintering temperature. The number of times dipped in the coloring liquid did not affect flexural strength of the zirconia ceramic having improved transparency.