• Membrane Journal
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• v.21 no.1
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• pp.1-12
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• 2011

Partially fluorinated poly(arylene ether sulfone) block ionomer membranes with different branch degree for fuel cell applications were investigated. A sulfonable monomer, a non-sulfonable monomer and a trifunctional branching agent were synthesized and the sulfonable monomer was oligomerized to obtain block structures. The oligomer was then further polymerized with the non-sulfonable monomer and the branching agent. The mole ratio of oligomer : non-sulfonable monomer was fixed at 4:6 and the content of the branching agent was varied from 0 to 2 mol% (BBC-40Bx). Post-sulfonation of BBC-40Bx was carried out using chlorosulfonic acid (CSA) (SBBC-40Bx). All the synthesized compounds were characterized by $^1H$-NMR, $^{19}F$-NMR and FT-IR. It was confirmed that the ion exchange capacity (IEC), water uptake and ion conductivity of SBBC-40Bx increased with the increment of branching agent content.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.251-260
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• 2002

Geotextile tribes are made of sewn geotextile sheet and hydraulically or mechanically filled with dredged materials. They have been applied in hydraulic and coastal engineering in recent years(shore protection structure, detached breakwater, groins, and jetty). Therefore, it is composed of geotextile and confined fill material. Recently, new preliminary design criteria supported by model and prototype tests, and some stability analysis calculations have been studied. The stability analysis of geotextile tube is composed of geotechnical and hydrodynamic analysis. The stability check points are sliding failure, overturning, bearing capacity failure against the wave attack. In this paper are presented the stability analysis method by empirical equation and 2-D equilibrium analysis for geotextile tube. Also, the hydraulic model tests were performed to verify the theoretical stability analysis with geotextile tube shape, filling ratio, significant wave height, and so on. The results of this study show that the stability of geotextile tube depends on the tube shape, contact area, projection area. The theoretical analysis and hydraulic model test show almost the same results.

• Journal of the Korean Geotechnical Society
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• v.32 no.9
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• pp.17-27
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• 2016

Parial drainage characteristics of clayey silt with low plasticity from the west coast (Incheon and Hwaseong) was analyzed using CPTU based existing correlation equations and compulsory replacement method. Generally, the estimated $OCRs={\kappa}{\cdot}((q_t-{\sigma}_{vo})/{\sigma}^{\prime}_{vo})$ using Powell and Quartman(1988) were higher than those obtained by the oeodometer tests. These trends were noticeable for the layers containing a lot of silty and sand soils. The assessment of partial drainage conditions was performed through Schnaid et al. (2004)'s equation; it is based on plotting the normalized cone resistance, $Q_t$ versus the pore pressure parameter, $B_q$ in combination with the strength incremental ratio, $s_u/{\sigma}^{\prime}_{vo}$ to the CPTU data. It is evident that more than half of the data fall in the range where $B_q$ < 0.3, corresponding to the domain in which the partial drainage prevails when testing normally consolidated soils at a standard rate of penetration (2 cm/s). To estimate the replacement depth of clayey silt with low plasticity, back analysis was carried out to evaluate the internal friction angle based on where the design depths are equal to the checked depths using bearing capacity equation. The internal friction angels obtained from the back analysis tended to increase as the plasticity index decreases, which is ranged approximately from ${\varphi}^{\prime}=2^{\circ}$ to ${\varphi}^{\prime}=7^{\circ}$.

• Journal of Ecology and Environment
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• v.29 no.6
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• pp.521-529
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• 2006

This study was carried out to classify all forest vegetation types in Ulleung Island, Korea using the methodology of the Z.-M. school's phytosociology, and map out the spatial distribution patterns of those vegetation types. The forest vegetation was classified into the mountain forest type (Acer okamotoanum community group) and maritime forest type (Artemisia scoparia community group). Vegetation units at the community level were divided into three categories; six communities, sixteen groups, and seven subgroups, giving a total of 22 communities. Total area for mapping was 5,544.9 ha, of which Fagus engleriana community accounted for 1,952 ha (35.2%), Hedera rhambea community ror 1,196 ha (21.6%), Camellia japonica community for 1,104 ha (19.9%), Sambucus sieboldiana var. pendula community for 612 ha (11.0%), Aster spathulifolius community for 506 ha (9.1%), and Tsuga sieboldii - Pinus parviflora community for 174 ha (3.1%). According to canonical correspondence analysis (CCA), variables such as $Mg^{2+}$, pH, $Ca^{2+}$ were positively correlated in maritime vegetation types, and variables such as total nitrogen, carbon content, C/N ratio and ration exchange capacity (CEC) were highly correlated in mountain vegetation types, respectively. The sea level and the slope direction were not showing regular trend as a factor to decide on species diversity, evenness and richness in this research area. But it seems to be affected by topography, slope degree and dominance vegetation.

• Journal of the Korea Institute of Building Construction
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• v.17 no.1
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• pp.47-54
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• 2017

Cement industry is typical carbon-emission industry. If the industrial by-products(granulated blast-furnace slag (GGBFS), fly ash, etc.) are used a large amount, it might be able to reduce cement consumption and mitigate carbon emissions. In this case, however, decrease of early strength is relatively large. Therefore, there is a limitation in increase of the amount of substitute. Considering these circumstances, it would be a good solution to reduce carbon emissions in cement industry to improve the performances of mixed cement through proper alkali-activation in Portland blended cement using GGBFS or fly ash. Therefore, this study prepared concrete in ready-mixed concrete manufacturing facilities with an addition of a binder which used 2.0% modified alkali sulfate activator after mixing Portland cement, GGBFS and fly ash in the ratio of 4:4:2 and assessed its basic properties. The results found the followings: The use of modified alkali-sulfate activator slightly reduced slump and shortened setting time. As a result, bleeding capacity decreased while early strength improved. In addition, there is no big difference in carbonation resistance. It appears that there should be continued experiments and analyses on the related long-term aged specimens.

• Korean Chemical Engineering Research
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• v.43 no.3
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• pp.425-431
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• 2005

New type of supercapacitor using high surface area activated carbons mixed with high conductivity polypyrrole (Ppy) has been prepared in order to achieve low impedance and high energy density. Mixed carbons of BP-20 and MSP-20 were used as the active electrode material, and polypyrrole doped with 2-naphthalenesulfonic acid (2-NSA) and carbon black (Super P) as conducting agents were added to activated carbons in order to enhance good electric conductivity. Electrodes prepared with the activated electrode materials and the conducting agents were added to a solution of organic binder [P(VdF-co-HFP) / NMP]. The ratio of optimum electrode composition was 78 : 17 : 5 wt.％ of (MSP20 : BP-20=1 : 1), (Super P : Ppy=10 : 7) and P(VdF-co-HFP) respectively. The performance of unit cell with addition of 7 wt％ Ppy have shown specific capacitance of 28.02 F/g, DC-ESR of $1.34{\Omega}$, AC-ESR of $0.36{\Omega}$, specific energy of 19.87 Wh/kg and specific power of 9.77 kW/kg. With addition of Ppy, quick charge-discharge of unit cell was possible because of low ESR, low charge transfer resistance and quick reaction rate. And good stability up to 500 chargedischarge cycles were retained about 80％ of their original capacity. It was concluded that the specific capacitance originated highly from compound phenomena of the pseudocapacitance by oxidation-reduction of polypyrrole and the nonfaradaic capacitance by adsorption-desorption of activated carbons.

• Korean Journal of Construction Engineering and Management
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• v.14 no.3
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• pp.78-87
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• 2013

The modern society has been drastically changed from the industrial economic society to the knowledge based society, to catch up with the knowledge and the change of technology required for the modern people, the people can not live in the modern society without the continued study or education. In case of architectural design firm, it is concentrating on the productivity of enterprise by cultivating the working level through the self education focused on the improvement of inner capacity. In connection with this, the efficiency of enterprises are analyzed by carrying out the Data Envelopment Analysis(DEA) utilizing the financial ratio index in the various field of industries recently, the analysis study for the efficiency utilizing DEA is increased in the construction industries as well. However, in case of construction industries, the study focused on the efficiency of administration only has been progressed, it is the real situation that the approach for the analysis of education efficiency of each enterprise is very insufficient. Therefore, this study analyzed the education efficiency of architectural design firm after the selection of input and output variables by utilizing the DEA model and utilizing the AHP analysis technique by deducting the variables through the preceding study in relation to the education efficiency and the interview with the specialists.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3A
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• pp.129-139
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• 2003

CAC is a very important issue in CDMA system in order to protect the required QoS(quality of service) and increase the system's capacity. In this paper, we proposed and analyzed a call admission control scheme using multiple thresholds, which can provide quick processing time and better performance. There are two effective thresholds used to decide call admission. One is the number of active users, and the other is the signal to interference ratio(SIR). If the threshold of active users are lower than the low number of users threshold, we accept the new call without any other conditions. Otherwise, we check the current SIR to guarantee the quality of our service. System then accepts the new call when the SIR satisfies system requirement. Otherwise, the call will be rejected. Multiple threshold schemes are investigated and their performance is compared with the number of user and power based CAC's. simulation results are provided to evaluate the performance.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.162-168
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• 2013

$Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn) nano-composite is a promising cathode material for xEV application due to its high theoretic capacity. However high voltage operating system of $Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn) has worked as a hurdle in its application because of the inherent demerits, such as cycle life degradation and gas evolution. In order to enhance cell performance of $Li_2MnO_3-LiMO_2$(M=Ni, Co, Mn)/graphite cell, we examined electrolyte mainly composed of FEC, fluroalkyl ether and $LiPF_6$ (F-based EL). F-based EL showed much better discharging retention ratio than 1.3 M $LiPF_6$ EC/EMC/DMC (3/4/3, v/v/v) (STD). Furthermore gas evolution, especially CO and $CO_2$ during $60^{\circ}C$ storage for 30 days was dramatically reduced owing to thermal stable SEI formation effect of F-based EL.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.4
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• pp.263-270
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• 2017

The shipbuilding industry uses large stationary tanks to store low-pressure air, which is used to open and close large shut-off valves. However, when supplying air from the tank to a distant valve, there are problems related to the need for supplementary pipes and the pressure drop during transportation. In this study, a portable welded vessel for storing high-pressure nitrogen (11 kg, 10 L, and 50 bar) was designed to prevent air leakage and improve the convenience of workers. This pressure vessel was elliptical to reduce the number of welded parts, which are structurally weak. The thickness and ratio of the major and minor axes of the pressure vessel were calculated to verify its structure stability at the working pressure (50 bar), and that the proposed weight and capacity were satisfactory. The residual stress caused by the welding process was calculated by performing a transient thermal-structural coupled field analysis using the ANSYS parametric design language (APDL), and the fatigue life of the vessel was verified based on the Goodman criterion.