• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.3
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• pp.122-130
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• 2013

To examine floc characteristics of cohesive bed sediment of the Yeongsan River estuary, a floc camera system has been developed and utilized to observe flocs under varying conditions. In order to validate the floc camera system, sand particles were passed through 88-125 and $63-88{\mu}m$ sieves and observed within the laboratory. Mean grain size and settling velocities were found to be 102 and $56.2{\mu}m$ and 6.7 and 5.9 mm/s, respectively. Artifacts of particles estimated outside of the sieve range are attributed to being imaged out of the depth of focus. However, as mean grain size and settling velocity of each size class were within the confidence interval, the floc camera system was confidently used to examine cohesive bed sediments of Yeongsan River estuary. The bed sediment sample was prepared with a concentration of 0.1 g/L in 0 psu deionized water. The mean grain size, settling velocity and fractal dimension of flocs were $40.6{\pm}0.66{\mu}m$, 14 mm/s, and 2.86, respectively. Experiments were also conducted using different salinities (10 and 34 psu) and sediment concentrations (0.1 and 0.3 g/L). Despite changing these parameters, the mean observed grain size and settling velocities were found to be the same within the error range of the system. The relatively higher values of settling velocity and fractal dimension are considered a result of the sediment containing relatively small concentrations of organic matter. Moreover, consistent floc size over various grain sizes and concentrations may be the result of insufficient turbulence to aggregate flocs.

• Carbon letters
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• v.28
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• pp.47-54
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• 2018

High surface carbon aerogels with hierarchical and tunable pore structure were prepared using ionic liquid as carbon precursor via a simple salt templating method. The as-prepared carbon aerogels were characterized by nitrogen sorption measurement and scanning electron microscopy. Through instant visual observation experiments, it was found that salt eutectics not only serve as solvents, porogens, and templates, but also play an important role of foaming agents in the preparation of carbon aerogels. When the pyrolyzing temperature rises from 800 to $1000^{\circ}C$, the higher temperature deepens the carbonization reaction further to form a nanoporous interconnected fractal structure and increase the contribution of super-micropores and small mesopores and improve the specific surface area and pore volume, while having few effects on the macropores. As the mass ratio of ionic liquid to salt eutectics drops from 55% to 15%, that is, the content of salt eutectics increases, the salt eutectics gradually aggregate from ion pairs, to clusters with minimal free energy, and finally to a continuous salt phase, leading to the formation of micropores, uniform mesopores, and macropores, respectively; these processes cause BET specific surface area initially to increase but subsequently to decrease. With the mass ratio of ionic liquids to salts at 35% and carbonization temperature at $900^{\circ}C$, the specific surface area of the resultant carbon aerogels reached $2309m^2g^{-1}$. By controlling the carbonization temperature and mass ratio of the raw materials, the hierarchically porous architecture of carbon aerogels can be tuned; this advantage will promote their use in the fields of electrodes and adsorption.

• Journal of The Korean Astronomical Society
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• v.41 no.3
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• pp.65-76
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• 2008

We have investigated the optical properties of the global haze on Titan from spectra recorded between 7100 and $9200{\AA}$, where $CH_4$ absorption bands of various intensities occur. The Titan spectra were obtained on Feb. 23, 2005 (UT), near the times of the Cassini T3 flyby and Huygens probe, using an optical echelle spectrograph (BOES) on the 1.8-m telescope at Bohyunsan Observatory in Korea. In order to derive the optical properties of the haze as a function of altitude, we developed an inversion radiative-transfer program using an atmospheric model of Titan and laboratory $CH_4$ absorption coefficients available from the literature. The derived extinction coefficients of the haze increase toward the surface, and the coefficients at shorter wavelengths are greater than those at longer wavelengths for the 30 - 120 km altitude range, indicating that the Titanian haze becomes optically thin toward the longer wavelength range. Total optical depths of the haze are estimated to be 1.4 and 1.2 for the 7270 - $7360{\AA}$ and 8940 - $9150{\AA}$ ranges, respectively. Based on the Huygens/DISR data set, Tomasko et al. (2005) reported total optical depths of 2.5 - 3.5 at $8290{\AA}$, depending on the assumed fractal aggregate particle model. The total optical depths based on our results are smaller than those of Tomasko et al., but they partially overlap with their results if we consider a large uncertainty from possible variations of the $CH_4$ mixing ratio over Titan's disk. We also derived the single scattering albedo of the haze particles as a function of altitude: it is less than 0.5 at altitudes higher than ${\sim}150\;km$, and approaches 1.0 toward the surface. This behavior suggests that, at altitudes above ${\sim}150\;km$, the average particle radius is smaller than the wavelengths, whereas near the surface, it becomes comparable or greater.