• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.10-18
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• 2018

The primary purposes of this study are to understand a fundamental aspect of current uniformity around a reinforcing bar (rebar) in cement mortar, and to develop an accurate monitoring method in a wet-dry cycling process with the alternative current (AC) impedance method. Three cement mortar specimens with two embedded rebars were prepared in the laboratory. As a main variable, the distance between two rebars was designed to be 10, 20 and 30 mm with the same thickness of 20 mm. To simulate the corrosion of rebars in concrete structures in a marine environment, three cement mortar specimens were exposed to 15 wet-drying cycles (24-hour-immersion in seawater and 48-hour-drying in a room temperature) in the laboratory. It was observed that the potential level shifted to a noble value during corrosion potential monitoring, which is attributed to acceleration of dissolved oxygen diffusion at the drying process. AC impedance was measured in a frequency range from 100 kHz to 1 mHz on a wet-drying process. A theoretical model was proposed to explain the interface condition between the rebars and cement mortar by using the equivalent circuit consisting of a solution resistance, a charge transfer resistance and a CPE (constant phase element). It was observed that the diffusion impedance appeared in a low frequency range as corrosion of rebars progresses. At the drying stage of the wet-drying cycles, the currents line for monitoring tended to be non-uniform at the interface of rebar/mortar, being phase shift, ${\theta}$, close to $-45^{\circ}$.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.1
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• pp.9-18
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• 2016

The slender structures such as high rise building or marine riser are highly susceptible to dynamic force exerted by fluid-structure interactions among which vortex-induced vibration(VIV) is the main cause of dynamic unstability of the structural system. If VIV occurs in natural frequency regime of the structure, fatigue failure likely happens by so-called lock-in phenomenon. This study presents the numerical analysis of dynamic behavior of both structure and fluid in the lock-in regimes and investigates the subjacent phenomena to hold the resonance frequency in spite of the change of flow condition. Unsteady and laminar flow was considered for a two-dimensional circular cylinder which was assumed to move freely in 1 degree of freedom in the direction orthogonal to the uniform inflow. Fluid-structure interaction was implemented by solving both unsteady flow and dynamic motion of the structure sequentially in each time step where the fluid domain was remeshed considering the movement of the body. The results show reasonable agreements with previous studies and reveal characteristic features of the lock-in phenomena. Not only the lift force but also drag force are drastically increasing during the lock-in regime, the vertical displacement of the cylinder reaches up to 20% of the diameter of the cylinder. The correlation analysis between lift and vertical displacement clearly show the dramatic change of the phase difference from in-phase to out-of-phase when the cylinder experiences lock-in. From the results, it can be postulated that the change of phase difference and flow condition is responsible for the resonating behavior of the structure during lock-in.

• Journal of Microbiology and Biotechnology
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• v.20 no.12
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• pp.1735-1743
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• 2010

The full-length genes gyrB (2,415 bp), parC (2,277 bp), and parE (1,896 bp) in Edwardsiella tarda were cloned by PCR with degenerate primers based on the sequence of the respective quinolone resistance-determining region (QRDR), followed by elongation of 5' and 3' ends using cassette ligation-mediated PCR (CLMP). Analysis of the cloned genes revealed open reading frames (ORFs) encoding proteins of 804 (GyrB), 758 (ParC), and 631 (ParE) amino acids with conserved gyrase/topoisomerase features and motifs important for enzymatic function. The ORFs were preceded by putative promoters, ribosome binding sites, and inverted repeats with the potential to form cruciform structures for binding of DNA-binding proteins. When comparing the deduced amino acid sequences of E. tarda GyrB, ParC, and ParE with those of the corresponding proteins in other bacteria, they were found to be most closely related to Escherichia coli GyrB (87.6% identity), Klebsiella pneumoniae ParC (78.8% identity), and Salmonella Typhimurium ParE (89.5% identity), respectively. The two topoisomerase genes, parC and parE, were found to be contiguous on the E. tarda chromosome. All 18 quinolone-resistant isolates obtained from Korea thus far did not contain subunit alternations apart from a substitution in GyrA (Ser83$\rightarrow$Arg). However, an alteration in the QRDR of ParC (Ser84$\rightarrow$Ile) following an amino acid substitution in GyrA (Asp87$\rightarrow$Gly) was detected in E. tarda mutants selected in vitro at $8{\mu}g/ml$ ciprofloxacin (CIP). A mutant with a GyrB (Ser464$\rightarrow$Leu) and GyrA (Asp87$\rightarrow$Gly) substitution did not show a significant increase in the minimum inhibitory concentration (MIC) of CIP. None of the in vitro mutants exhibited mutations in parE. Thus, gyrA and parC should be considered to be the primary and secondary targets, respectively, of quinolones in E. tarda.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.3
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• pp.279-284
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• 2001

This paper reports the purification of myomodulin A (MMA) and myomodulin E (MME) from the sea hare. The central nervous systems of 500 sea hare were extracted in an acidified solvent, after which four HPLC column systems were used to obtain pure peptides, The phasic contraction bioassay using a Mytilus edulis anterior byssus retractor muscle (ABRW) was applied to monitor all collected fractions. The pure peptides were submitted to Edman degradation based automated microsequencing. Mass spectrometry and chemical synthesis confirmed the sequence. The primary structures of MMA and MME were Pro-Met-Ser-Met-Leu-Arg-Leu-$NH_2$, (847.41 Da) and Cly-Leu-Gln-Met-Leu-Arg-Leu-$NH_2$, (830.50 Da), respectively. Synthetic peptides showed a modulating activity of phasic contraction in the ABRM of Mrtilus edulis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.4
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• pp.18-24
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• 2012

In this study, hybrid method using polyvinyl acetate (PVAc) which has a strong adhesion and flexibility in which acrylic copolymer chemical-reaction reacts with cement, and is eco-friendly, is to improve the watertightness. The hybrid method is applied applied primarily waterproof stuff comprising silicate system and secondary mortar mixed with PVAc on the concrete surface. And then, in order to evaluate the performance, the properties of bond strength and amount of water absorption were measured. Based on the above experiments, mock-up specimens for field application were fabricated, and then the properties were evaluated as laboratory experiments. As the results, specimens cast from hybrid method using PVAc showed the best results on watertightness and bond strength. And also, with respect to experiment of mock-up specimens, the properties were in agreement with laboratory results. Especially, it could know that PVAc has strengthening effect from the results of the compressive strength. Due to outstanding results of carbonation depth and resistance to chloride ion penetration, it may be applied in weak areas such as underground and marine structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.23-30
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• 2012

For cracked concrete, it is obvious that cracks should be preferential channel for the penetration of aggressive substances such as chloride ions according to the previous researches. In order to extend the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of surface coating system, which can be able to seal the concrete and the cracks to aggressive substances-induced corrosion in particular. In this study, it is excuted to examine the effect of surfaced treated systems on chloride penetration and carbonation through compressive stress induced cracks. Experimental results have showed conclusively that critical stress linked with deterioration, should be existed in compressive stress ratio 50 ~ 70% for chloride penetration and 70 ~ 80% for carbonation, respectively. When the critical stress is exceeded in concrete, a comparatively large deterioration was measured where the critical stress in concrete, the increase in the mass transportation is marginal in spite of the large increase in micro-cracks. As for the effect of surface coating system on crack-sealing, it can be seen conclusively that cracks can be healed.

• Journal of the Korean Society of Food Science and Nutrition
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• v.20 no.6
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• pp.629-636
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• 1991

Yellowtail fishes(Seriola quinqueeradiata) were submitted to the storages using ice-cooling($0^{\circ}C$), partial freezing($-3^{\circ}C$) and freezing $-20^{\circ}C$) method. Changes in the structures of muscle during storage at different temperatures were investigated. The ice-cooling and partial freezing storage caused early decomposition of glycogen granules and mitochondrial inner membrane, but it was accorded to much slower manner comparing with that of ice-cooling storage. The scars of ice crystals were appeared after three days of storage. The number and size of the crystal increased as progressing of the storage. They were circular and mostly located between fibers. When using the freezing storage, glycogen granules were mostly found from the muscle cell even after fourteen days of storage. Mitochonidral inner membrane maintained their integrity. The scars of ice crystals were also found, however, different from those of partial freezing storage. Their existing sites were random and their shapes were irregular. In many cases, they located in the fiber and had keen edges. Fibers were broken mostly at the Z-lines on fourteen days of storage. From these results, it was concluded that partial freezing storage can repress autolytic enzymic action and can reduce the physical damage from ice crystals which is caused by freezing.

• Journal of the Korean earth science society
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• v.24 no.4
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• pp.361-368
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• 2003

We have investigated the electric resistivity structure of the fault zone located in the Hongseong area where a big earthquake with M 5.0 occurred in 1978. Usually, Electric and Electromagnetic methods are broadly operated in the field of engineering works since these methods are effective to understand the distribution of geological weak zones - fault or fracture zones. We have conducted the dipole-dipole array resistivity method and MT(magnetotelluric) method and interpreted the resistivity distribution of the fault zone with the aid of various inversion methods. An MT survey was performed at 18 points along a 2.9 km survey line perpendicular to the fault line and a magnetic dipole source was used to enhance the S/N ratio in the high frequency. A Electric dipole-dipole array resistivity survey with the dipole length of 50 meters was carried out perpendicular to the fault. In view of two survey results, the fault marks the boundary between two opposite resistivity structures, especially the low resistivity zone is exhibited deeply through the prospective fault line. The result that the low resistivity zone is located at the center of the fault zone corresponds with the fact that the fault zone of the Hongseong area is active. We expect these results to provide basic information about the physical properties of fault zones in Korea.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1077-1080
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• 2008

Material parameters such as surface chloride content, water permeability coefficient, chloride diffusivity and critical chloride content are a substantial key parameter for understanding the durability performance of concrete and its micro-structural densification. Over the past few decades, a considerable number of studies on the durability design for marine concrete structures have been carried out. However, the results are different to each other. In order to establish a consistent durability design system of concrete, it is a precondition to define material parameters, which affect deterioration of concrete due to chloride penetration. Such parameters are surface chloride content, chloride diffusivity, and critical chloride content. Usually these parameters are assumed as temporary constant values or obtained from the experimental results for short term. However, it is necessary to define these parameters reasonably, because these significantly influence the calculation of service life of concrete. In this paper, it is introduced to define material parameters of concrete for chloride diffusion, such as surface chloride content $[Cl]_s$, water permeability coefficient K, chloride diffusivity $D_{Cl}$, critical chloride content $[Cl]_{cr}$. These are expressed as time function considering hydration evolution of hardened cement paste. The definition of the material parameters is a prerequisite to simulate chloride penetration into concrete as time elapsed.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.581-584
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• 2008

Generally, durability of concrete structures under marine environment is grossly declined by detrimental ions such as chlorides, which penetrate concrete and was diffused to corrode reinforcing rod. Therefore, chloride diffusion properties in concrete are important for durability evaluation and design of concrete structure. For estimation of chloride diffusion coefficient in concrete, both evaluation methods are used for steady state and non-steady state derived from Fick's 1st and 2nd law, respectively. However, as it is very difficult to evaluate diffusion coefficient for non-steady state like service environment where concrete is actually exposed, indirect evaluation method by laboratory accelerated test is generally used. In this study, comparison of chloride diffusion behavior was investigated for fixed mix proportion and age of concrete using four accelerated test methods based on domestic and foreign standards. From test results, only relative comparison between concrete mixtures was possible using ASTM C 1202 test, and diffusion coefficient for steady state was estimated as low as 1/10 of that for non-steady state. In addition, diffusion coefficient estimated by immersion test was similar to result by NT build 492 test.