• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.103-110
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• 2014

Sisal fiber, an agricultural resource abundantly available in china, has been used as raw material to prepare activated carbon with high surface area and huge pore volume by chemical activation with zinc chloride. The orthogonal test was designed to investigate the influence of zinc chloride concentration, impregnation ratio, activation temperature and activation time on preparation of activated carbon. Scanning electron micrograph, Thermo-gravimetric, $N_2$-adsorption isotherm, mathematical models such as t-plot, H-K equation, D-R equation and BJH methods were used to characterize the properties of the prepared carbons and the activation mechanism was discussed. The results showed that $ZnCl_2$ changed the pyrolysis process of sisal fiber. Characteristics of activated carbon are: BET surface area was $1628m^2/g$, total pore volume was $1.316m^3/g$ and ratio of mesopore volume to total pore volume up to 94.3%. These results suggest that sisal fiber is an attractive source to prepare mesoporous high-capacity activated carbon by chemical activation with zinc chloride.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1001-1010
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• 2009

The study that unconfined compression strength of intact rock which is the most important factor to determine the bearing capacity effects discontinuities in rock mass has been carried out actively so far. However, the study which is related to lithological characters such as vesicle which is one of the primary characteristics of Basalt has barely been conducted. On this study, We have analyzed the correlation-ship between vesicle and unconfined compression strength and the effect on the bearing capacity, based on the reviewing on the changes of unconfined compression strength as the amount of vesicle of Basalt. It is impossible to analyze the amount of vesicle of Basalt as measuring unit. So it was analyzed by the ratio of the core sample's surface area and another area that vesicle takes up. Also, unconfined compression strength was calculated by point load test and unconfined compression strength test. The analysis shows that vesicle area ratio and unconfined compression strength have the exponential relationship and vesicle area ration is the factor to determine the bearing capacity of Basalt. It is considered that the reliability of calculating of the bearing capacity of Basalt will be improved as we study the correlation-ship between the vesicle area ratio and rock mass grade hereafter.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.880-885
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• 2008

Spray pyrolysis was applied to prepare spherical silica particles with mesopores of a regular structure. The physical properties such as surface area, pore size, pore structure, particle size, and morphology were studied by BET, SEM, SAXS, and DLS analysis. At a fixed gas flow rate, the BET surface area changed from 200 to $1,290m^2/g$ as changing the CTAB/TEOS molar ratio from 0.05 to 0.3. At a fixed CTAB/TEOS ratio, the surface area of silica particles was varied from 1,062 to $1,305m^2/g$ with changing the gas flow rate from 10 to 40 l/min. The average pore size measured by BJH desorption was about $21{\sim}23{\AA}$ and not significantly influenced by the CTAB/TEOS ratio and the gas flow rate. Finally, the highest surface area which was $1,305m^2/g$ were obtained when the CTAB/TEOS ratio and the gas flow rate were 0.2 and 20 l/min, respectively. According to SAXS analysis, the prepared silica particles showed a strong peak at $2{\theta}=2.6^{\circ}$ and two minor peaks around $2{\theta}=4.4^{\circ}$ and $5.1^{\circ}$, which are due to regular mesopores of hexagonal structure. The morphology of silica particles prepared were spherical shape and the average particle size was $1.0{\mu}m$.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.156-161
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• 2006

The rivulet is a narrow stream of liquid flowing down a solid surface. Heat transfer of rivulet flow over on inclined heated surface has been investigated experimentally. This problem is of particular interest in the understanding of fundamental mechanism on rivulet heat transfer as well as in the design of a regenerative evaporative cooler. The rivulet is seem to be meandering flow, single wide flat flow. and film flow as rivulet flow rate is increased. Even though the wetted surface area is increased with an increase in the rivulet flow rate, the absorbed heat transfer of rivulet flow from a heated surface strongly depends on the flow pattern of rivulet.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.1
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• pp.33-44
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• 1994

This work studies for boiling and condensation heat transfer performance of trapezoidally shaped integral-fin tubes having fin densities from 748fpm to 1654fpm. For comparison, tests are made using a plain tube having the same inside and outside diameter as that of the root of fins of finned tubes. Hahne's theoretical model and Webb's theoretical model are used to predict the R-11 boiling heat transfer coefficient and condensing heat transfer coefficient respectively for plain tube and all integral-fin tubes. Experiments are carried out using R-11 as working fluid. This work is limited to film-wise condensation and pool boiling on the outside surface of plain tube and 4 low integral-fin tubes. In case of condensation, the refrigerant condenses at saturation state of 32$^{\circ}C$ on the outside tube surface cooled by coolant and in case of boiling. the refrigerant evaporates at saturation state of 1bar on the outside tube surface. The amount of non-con-densable gases in the test loop is reduced to a negligible value by repeated purging. The actual boiling and condensing processes occur on the outside tube surfaces. Hence the nature of this surface geometry affects the heat transfer performances of condenser and evaporator in refrigerating system. The condensation heat transfer coefficient of integral-fin tube is enhanced by both extended tube surface area and surface tension. The ratio of the condensation heat transfer coefficients of finned to plain tubes is greater than that of surface area of finned to plain tubes, while ratio of the boiling heat transfer coefficient of finned to plain tubes shows reverse result. As a result, low integral-fin tube can be used in condenser more effectively than used in evaporator.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.4
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• pp.13-23
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• 2003

Organic carbon and nitrogen contents in suspended particulate matter (SPM) and surface sediments in seawater were measured in the Northern East China Sea in summer. The distribution of particulate organic carbon(POC) and particulate organic nitrogen(PON) were in the ranges of 54~481㎍/ℓ and 6~85㎍/ℓ, respectively, with relatively high level of concentrations in the western and southern sides of the study area. Also, there has been a significantly positive correlation between POC and PON, gradually increasing toward the deeper range of depth. Average C:N ratios of POC and PON of SPM were 6 in study area. The ratios of POC to PON of SPM increased as the range of depth increased, indicating nitrogen decomposes more rapidly than carbon and is considered to be influenced by the input of detritus from surface sediments. The distribution of total organic matter(TOM), total organic carbon(TOC) and total organic nitrogen(TON) in surface sediments were in the ranges of 3.1~9.6%, 0.282~0.635% and 0.022~0.069%, respectively, with relatively low range in the western and northern sides of the study area. The ratio of TOC to TON of surface sediments were in the range of 9.8~17.4(average of 13), strongly indicating the active role of the input from the terrestrial organic pollutants.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1444-1451
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• 2018

The surface-to-volume ratio of one-dimensional (1D) semiconductor metal-oxide sensors is an important factor for achieving good gas sensing properties because it offers a wide response area. To exploit this effect, in this study, we determined the optimal calcination temperature to maximize the specific surface area and thereby the sensitivity of the sensor. The $In_2O_3$ nanorods were synthesized by using vapor-liquid-solid growth of $In_2O_3$ powders and were decorated with the Pt nanoparticles by using a sol-gel method. Subsequently, the Pt nanoparticle-decorated $In_2O_3$ nanorods were calcined at different temperatures to determine the optimal calcination temperature. The $NO_2$ gas sensing properties of five different samples (pristine uncalcined $In_2O_3$ nanorods, Pt-decorated uncalcined $In_2O_3$ nanorods, and Pt-decorated $In_2O_3$ nanorods calcined at 400, 600, and $800^{\circ}C$) were determined and compared. The Pt-decorated $In_2O_3$ nanorods calcined at $600^{\circ}C$ showed the highest surface-to-volume ratio and the strongest response to $NO_2$ gas. Moreover, these nanorods showed the shortest response/recovery times toward $NO_2$. These enhanced sensing properties are attributed to a combination of increased surface-to-volume ratio (achieved through the optimal calcination) and increased electrical/chemical sensitization (provided by the noble-metal decoration).

• KCID journal
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• v.19 no.1
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• pp.19-29
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• 2012

The data of the agricultural water quality survey network was analyzed between from 1990 to 2010 in order to propose effective plans for water quality management by analyzing the characteristics of agricultural lakes and the change of water quality. The result of the analysis shows that there is a correlation between water quality and items that can be a function of water depth such as dam height, dam length, dam height/dam length ratio and active storage/surface area of lake ratio. This means that, Korean agricultural lakes, there is a correlation between water quality and water depth. Water quality of the lakes that have lower than 5m of active storage/surface area of lake ratio (effective water depth) especially tends to get worse rapidly. The Chl-a and COD concentration of Korean agricultural lakes have a tendency to increase between June and September. Therefore, we recommend first taking a water quality improvement project for the lakes preformed watershed management project, and taking a preventive short-term water quality improvement project for the unperformed lakes before June among lakes that have lower than 5m of effective water depth.

• Restorative Dentistry and Endodontics
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• v.38 no.2
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• pp.59-64
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• 2013

Apical surgery cuts off the apical root and the crown-to-root ratio becomes unfavorable. Crown-to-root ratio has been applied to periodontally compromised teeth. Apical root resection is a different matter from periodontal bone loss. The purpose of this paper is to review the validity of crown-to-root ratio in the apically resected teeth. Most roots have conical shape and the root surface area of coronal part is wider than apical part of the same length. Therefore loss of alveolar bone support from apical resection is much less than its linear length.The maximum stress from mastication concentrates on the cervical area and the minimum stress was found on the apical 1/3 area. Therefore apical root resection is not so harmful as periodontal bone loss. Osteotomy for apical resection reduces longitudinal width of the buccal bone and increases the risk of endo-perio communication which leads to failure. Endodontic microsurgery is able to realize 0 degree or shallow bevel and precise length of root resection, and minimize the longitudinal width of osteotomy. The crown-to-root ratio is not valid in evaluating the prosthodontic prognosis of the apically resected teeth. Accurate execution of endodontic microsurgery to preserve the buccal bone is essential to avoid endo-perio communication.

• Carbon letters
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• v.9 no.1
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• pp.23-27
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• 2008

The adsorption and reduction of Cr (VI) to Cr (III) by surface modified activated carbon (AC) in an aqueous solution was studied. The effects of surface modifications on the properties of the carbons were investigated by the analysis of specific surface area, carbon surface pH, acid/base surface values and functional groups. In order to understand the Cr(VI) adsorption and reduction ratio from Cr(VI) to Cr(III), the Cr adsorption capacity of AC was also measured and discussed by using inductively coupled plasma and UV spectrophotometer. The modifications bring about substantial variation in the chemical properties whereas the physical properties such as specific surface area, pore volume and pore size distribution nearly were not changed. Total Cr adsorption efficiency of as-received activated carbon (R-AC) and nitric acid treated activated carbon (N1-AC and N2-AC) were recorded on 98.2, 99.7 and 100%. Cr(III) reduction efficiency of R-AC increased largely from 0.4% to 28.3% compared to N1-AC and N2-AC.