• Advanced Composite Materials
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• v.17 no.3
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• pp.259-275
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• 2008

This study aims to optimize the mechanical and electrical properties of electrically conductive polymer composites (CPCs) for use as a material of bipolar plates for PEM fuel cells. The thin CPCs consisting of conductive fillers and polymer resin were fabricated by a preform molding technique. Expanded graphite (EG), flake-type graphite (FG) and carbon fiber (CF) were used as conductive fillers. This study tested two types of CPCs, EG/FG filled CPCs and EG/CF filled CPCs, to optimize the material properties. First, the characteristics of EG/FG filled CPCs were investigated according to the FG ratio for 7 and $100{\mu}m$ sized FG. CPCs using $100{\mu}m$ FG showed optimal material properties at 60 wt% FG ratio, which were an electrical conductivity of 390 S/cm and flexural strength of 51 MPa. The particle size was an important parameter to change the mechanical and electrical behaviors. The flexural strength was sensitive to the particle size due to the different levels of densification. The electrical conductivity also showed size-dependent behavior because of the different contributions to the conductive network. Meanwhile, the material properties of EG/CF filled CPCs was also optimized according to the CF ratio, and the optimized electrical conductivity and flexural strength were 290 S/cm and 58 MPa, respectively. The electrical conductivity of this case decreased similarly to the EG/FG filled case. On the other hand, the behavior of the flexural strength was more complicated than the EG/FG filled case, and the reason was attributed to the interaction between the strengthening effect of CF and the deterioration of voids.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.4
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• pp.11-19
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• 2015

The important properties of EVA (ethylene vinyl acetate) redispersible polymer was waterproof, densification of internal pore space of concrete and ball bearing and micro filler. Also, the significant role of polypropylene(PP) fiber was crack control and blockade of movement for deterioration factors. The most studies for EVA were limited in the field of mortar and PP fiber reinforced concrete had been studied in the state of being restricted unit water content, rich mix and mixing much of the fiber without considering construction site. Therefore, the control mix design were applied in ready mixed concrete using 10 % fly ash of total cement weight used in batch plant. On the basis of control mix design, EVA contents ranging from 0 % to 10 % of total cement weight and PP fiber contents ranging from 0 % to 0.5 % of EVA concrete volume were used in the mix designs. The results showed the maximum compressive strength value was measured at EVA 5.0 % and PP fiber 0.1 %, the minimum water absorption ratio was at EVA 10 % and PP fiber 0 %, the durability factor for freezing and thawing resistance was at EVA 5.0 % and PP fiber 0.3 % and the minimum weight reduction ratio of resistance to sulfuric acid attack was at EVA 10 % and PP fiber 0.5 % after curing age 42days. Meanwhile, From these results, PP fiber reinforced EVA concrete would be very benefit, if each optimal mix types were used in hydraulic structures, underground utilities and agricultural structures.

• KIEAE Journal
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• v.12 no.1
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• pp.3-10
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• 2012

Recently, the increase of impervious area has been pointed out as a major cause of climate change and biotop area deterioration]. Therefore, quantitative indicators for environmental housing design and planning have been needed especially to control the impervious area. The Biotop Area Ratio(BAR) as the mostly applied environmental planning control instrument in Korea verifying the possibility of utilizing has been used effectively in various aspects. However, the fact that the space types are based on two dimension and ecological functions of spaces are simplified has shown the limitations of this planning instrument in the use as planning and evaluation indicator. In this study, classification criteria and the weighting of the space types in similar indicators Biotopflaechenfaktor (BFF, Berlin), Seattle Green Factor (SGF, Seattle), and Green Area Factor (GAF, Malmo) were analyzed. These indicators are similar in the sense that they apply weights to calculate the area and express a percentage of land area. The findings are as follows: The basic method that can estimate the vegetation volume is proposed to overcome the limitation of the BAR. It also was proven that the introduction of three-dimensional volume rate of biotops area was possible. Finally, the framework of space type classification criteria is proposed through linkages with relevant laws and regulations. With the improvement of the space types, the BAR is expected to be reasonable indicator in outdoor space evaluation in housing project.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.3
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• pp.88-97
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• 2013

This paper presents a robust air-to-fuel ratio (AFR) control algorithm for managing exhaust gas recirculation (EGR) systems. In order to handle production tolerance, deterioration and parameter-varying characteristics of the EGR system, quantitative feedback theory (QFT) is applied for designing the robust AFR control algorithm. A plant model of EGR system is approximated by the first order transfer function plus time-delay (FOPTD) model. EGR valve position and AFR of exhaust gas are used as input/output variables of the plant model. Through engine experiments, parameter uncertainty of the plant model is identified in a fixed engine operating point. Requirement specifications of robust stability and reference tracking performance are defined and these are fulfilled by the following steps: during loop shaping process, a PID controller is designed by using a nominal loop transmission function represented on Nichols chart. Then, the frequency response of closed-loop transfer function is used for designing a prefilter. It is validated that the proposed QFT-based AFR control algorithm successfully satisfy the requirements through experiments of various engine operating points.

• Korean Journal of Exercise Nutrition
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• v.25 no.1
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• pp.16-22
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• 2021

[Purpose] Aerobic exercise training (AT) reverses aging-induced deterioration of arterial stiffness via increased arterial nitric oxide (NO) production. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, was decreased by AT. However, whether AT-induced changes in ADMA levels are related to changes in nitrite/nitrate (NOx) levels remains unclear. Accordingly, we aimed to clarify whether the relationship between plasma ADMA and NOx levels afected the AT-induced reduction of arterial stifness in middle-aged and older adults. [Methods] Thirty-one healthy middle-aged and older male and female subjects (66.4 ± 1.3 years) were randomly divided into two groups: exercise intervention and sedentary controls. Subjects in the training group completed an 8-week AT (60%-70% peak oxygen uptake [${\dot{V}}O_{2peak}$] for 45 min, 3 days/week). [Results] AT signifcantly increased ${\dot{V}}O_{2peak}$ (P < 0.05) and decreased carotid β-stifness (P < 0.01). Moreover, plasma ADMA levels were significantly decreased while plasma NOx levels and NOx/ADMA ratio were significantly increased by AT (P < 0.01). Additionally, no sex diferences in AT-induced changes of circulating ADMA and NOx levels, NOx/ADMA ratio, and carotid β-stifness were observed. Furthermore, the AT-induced increase in circulating ADMA levels was negatively correlated with an increase in circulating NOx levels (r = -0.414, P < 0.05), and the AT-induced increase in NOx/ADMA ratio was negatively correlated with a decrease in carotid β-stifness (r = -0.514, P < 0.01). [Conclusion] These results suggest that the increase in circulating NOx with reduction of ADMA elicited by AT is associated with a decrease in arterial stiffness regardless of sex in middle-aged and older adults.

• Journal of Korean Society of Steel Construction
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• v.11 no.1 s.38
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• pp.69-78
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• 1999

When the lateral forces are applied to a frame, columns in the frame are usually accompanied with sidesway. If this sidesway is large, the frame is subjected to buckling and an early yielding of members which reduces the overall frame stiffness. In this study, numerical analysis of frames were conducted to evaluate the ultimate lateral strength of steel moment resisting frames permitted to sidesway under axial and lateral forces, and develope the procedure for determining the limits of column slenderness ratios. In the numerical analysis, the effects of the relative stiffness ratio between beam and column, deterioration of overall frame stiffness, slenderness ratio and loading conditions were considered. The elasto-plastic analysis method in which the $P-{\Delta}$effect is implemented, presented by the author previously, was adopted in the analysis. Incremental lateral forces were applied to the frame under constant axial loads and the generalized inverse is employed for the post-ultimate behavior.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.128-135
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• 2016

In the current concrete structure of the highway is still the major problem most of concrete deterioration caused by the freeze-thaw and deicing salt, which is of issues that are not completely resolved. In particular, a single freezing event does not cause much harm, durability of concrete under multi-deterioration environment by repeated freeze-thaw and deicing salt is rapidly degraded and reduce its service life. In this study, the exposure environmental condition according the regional highway points were established. The damage condition and chloride content of the concrete at general and severe environmental exposure condition were also investigated. In addition, the experimental test of chloride ion permeability, scaling resistant and freeze-thaw resistance were carried out to improve the durability of the mechanical placing concrete of subsidiary structure. According to the results of this study, in observation of concrete surface condition, the concrete exposed by severe environmental condition showed broad ranges of damage with high chloride contents. Meanwhile, the water-binder(W/B) ratio and the less water content, and fly ash concrete than the specified existing mix proportion is significantly improved the durability. Also, the optimal mix proportion derived for test is satisfied the strength and air contents, water-binder ratio, and durability criteria of concrete specifications, as well as service life seems greatly improved.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.651-662
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• 2022

The electrochemical impedance spectroscopy(EIS) method was used to evaluate the concrete deterioration process related to chloride-induced steel corrosion with various corrosion levels(initiation, rust propagation and acceleration periods). The impressed current technique, with four total current levels of 0C, 13C, 65C and 130C, was used to accelerate steel corrosion in concrete cylinder samples with w/c ratio of 0.4, 0.5, and 0.6, immersed in a 0.5M NaCl solution. A series of EIS measurements was performed to monitor concrete deterioration during the accelerated corrosion test in this study. Some critical parameters of the equivalent circuit were obtained through the EIS analysis. It was observed that the charge transfer resistance(R_c) dropped sharply as the impressed current increased from 0C to 13C, indicating a value of approximately 10kΩcm². However, the sensitivity of R_c significantly decreased when the impressed current was further increased from 13C to 130C after corrosion of steel had been initiated. Meanwhile, the double-layer capacitance value(C_dl) linearly increased from 50×10^-6μF/cm² to 250×10^-6μF/cm² as the impressed current in creased from 0C to 130C. The results in this study showed that monitoring C_dl is an effective measurement parameter for evaluating the progress of internal concrete damages(de-bonding between steel and concrete, micro-cracks, and surface-breaking cracks) induced by steel corrosion. The findings of this study provide a fundamental basis for developing an embedded sensor and signal interpretation method for monitoring concrete deterioration due to steel corrosion at various corrosion levels.

• Journal of Bio-Environment Control
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• v.18 no.4
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• pp.475-480
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• 2009

These studies were carried out to find the effect of packing materials and storage temperature to enhance the storability of Salicornia europaea. The fresh weight loss was less than 2% at below $10^{\circ}C$ and non-perforated package, but $25^{\circ}C$ and perforated package treatment showed more than 4% of fresh weight loss that result to deteriorate quality. The carbon dioxide and oxygen contents remained 1~2% and above 15% in non-perforated package, and these contents were in proportion to gas permeability of packing materials. All the temperature treatments except 25c showed rapidly increasing ethylene concent from 7days after storage, and the highest ethylene content was $2^{\circ}C$ treatment that should appear chilling injury. The off-odor and deterioration ratio were lowest in $5^{\circ}C$ among the temperature treatments and $50{\mu}m$ thickness ceramic film treatment at $5^{\circ}C$ storage, while packing materials did not show any trends among the temperature treatments. The shelf life based on visual quality showed highest in $50{\ss}|$ thickness ceramic film packing and $5^{\circ}C$ treatment, and that was 28days.

• Journal of Korean Society on Water Environment
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• v.23 no.1
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• pp.138-143
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• 2007

This study goes in for the observation of the characteristics of nitrogen removal from swine wastewater by struvite crystallization. In addition, the struvite formation potential in supernatants after struvite crystallization was investigated. In the study for nitrogen removal by struvite crystallization, the effects of pH and molar ratio of magnesium (Mg) injected using bittern as Mg source were investigated. Also, the potential of struvite formation in the supernatant with amount of Mg added was carefully observed. As the results, the optimum pH in the removal of nitrogen was 8.8 and sludge volume was increased as pH was raised from 7 to 12 under the condition that the molar ratio of $Mg^{2+}$ to ${NH_4}^+$-N to ${PO_4}^{3-}$-P was 1:1:1. An optimum removal efficiency of ammonia-N was observed at 1 molar ratio of Mg to ${NH_4}^+$-N, showing no further increase at over 1 molar ratio and dramatical deterioration at under 1 molar ratio. However, the sludge volume was increased by increasing the molar ratio of Mg. In the experiments for the potential of struvite formation in the supernatants, initial -log([$Mg^{2+}$][${NH_4}^+$][${PO_4}^{3-}$]) value was much lower than $pK_{sp}$ and gradually reached $pK_{sp}$ at 2 days, as the molar ratio of Mg increased over 1.2. At 31 days, -log([$Mg^{2+}$][${NH_4}^+$][${PO_4}^{3-}$]) value was returned to the initial value. In addition, the supernatants had a potential precipitation of hydroxylapatite due to calcium contained in bittern, $K_2Mg(SO_4)_3$ and $K_3Na(SO_4)_2$ resulting from the decrease of sodium and potassium in supernatants formed after struvite crystallization as times go by. Based on the results, it appears that some retention time and proper dosage of Mg may be needed for the prevention of scale in pipe line.