• Journal of Life Science
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• v.26 no.3
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• pp.353-358
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• 2016

Thiolase is an enzyme that catalyzes condensation reactions between two acetyl-CoA molecules to produce acetoacetyl-CoA. As thiolase catalyzes is the first reaction in the production of n-butanol, knowledge of the molecular and regulatory mechanism of the enzyme is crucial for synthesizing high-value biofuel. Thiolase from Clostridium butyricum (CbTHL) was expressed, purified, and crystallized. X-ray diffraction data were collected from the crystals, and the 3-dimentional structure of the enzyme was determined at 2.0 Å. The overall structure of thiolase was similar to that of type II biosynthetic thiolases, such as thiolase from C. acetobutylicum (CaTHL). The superposition of this structure with that of CaTHL complexed with CoA revealed the residues that comprise the catalytic and substrate binding sites of CbTHL. The catalytic site of CbTHL contains three conserved residues, Cys88, His349, and Cys379, which may function as a covalent nucleophile, general base, and second nucleophile, respectively. For substrate binding, the way in which CbTHL stabilized the ADP moiety of CoA was unlike that of other thiolases, whereas the stabilization of β-mercaptoethyamine and pantothenic acid moieties of CoA was quite similar to that of other enzymes. The most interesting observation in the CbTHL structure was that the enzyme was regulated through redox-switch modulation, using a reversible disulfide bond.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.393-400
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• 2005

Steel encased composite columns have been used for buildings and piers of bridges. Since the column section for the pier is relatively larger than that of building columns, economical steel ratio needs to be investigated for the required performance. Composite action between concrete and embedded steel sections can be obtained by bond and friction. However, the behavior of the column depends on the load introduction mechanism. Compression can be applied to concrete section, steel section and composite section. In this paper, experiments on shear strength of the steel encased composite column were performed to study the effect of confinement by transverse reinforcements, mechanical interlock by holes, and shear connectors. Bond strength obtained from the tests showed considerably higher value than the design value. Confinement, mechanical interlock and stud connectors Increased the shear strength and these values can be used effectively to obtain composite action of Steel Reinforced Concrete(SRC) columns.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.12
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• pp.1262-1267
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• 2008

Reductive discolorization studies were conducted. Azo-dyes usually have biological toxicity and it is known that the dyes are hardly removed by biological treatments. One of the simplest way to remove the color is to break the azo-bond and it is possible to break the bond with zero-valent metals. Three types of azo-dyes (Cibacron Briliant Yellow 3G-P (CBY3G-P), Benzopurpurin 4b (B-4B), Chicago sky blue 6b (CSB6B)) were tested. All tested azo-dyes were highly pH dependent and lower pH was preferred. The reaction mechanism was reductive cleavage and amines were expected as products. The dissolved iron ions from zero-valent iron can also remove the color through coagulation and precipitation and a set of experiments were conducted to evaluate the contribution by the dissolved iron. The results indicated that the contribution were also dependent on the type of dyes. This study showed that the reductive cleavage using zero-valent iron could be an alternative for the azo-dye waste water.

• Korean Journal of Materials Research
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• v.8 no.6
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• pp.538-544
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• 1998

The spallation of a thermal barrier coating layer depends on the formation of brittle spinels. thermal expansion mismatch between ceramic and metal. the phase transformation of a ceramic layer and residual stress of coating layer. In this work. the formation mechanism of oxide scale formed by oxidation treatment at 90$0^{\circ}C$ was investigated in order to verify oxidation behavior at the interface between E-beam coated $Zr0_2$-7wt.% $Y_20_3$ and plasma sprayed CoNiCrAIY. Some elements distributed in the bond coating layer were selectively oxidized after oxidation. At the initial time of oxidation. AI-depletion zone and $\alpha$-$Al_O_3$,O, were formed at the bond coating layer by the AI-outward diffusion. After layer grew until critical thickness. spinels. $Cr_20$, and $C0_2CrO_4$ by outward diffusion of Co. Cr, Ni were formed. It was found that the formation of spinels may be related to the spallation of $Zr0_2$-7wt.% $Y_20_3$ during isothermal oxidation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.149-156
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• 2021

FRP has been proposed to replace the steel as a reinforcement in the concrete structures for addressing the corrosion issue. However, FRP-Rebar does not behave in the same manner as steel because the properties of FRP are different. For example, FRP-Rebar has a high tensile strength, low stiffness, and linear elastic behavior which results in a difference bonding mechanism to transfer the load between the reinforcement and the surrounding concrete. Therefore, bonding behavior between FRP-Rebar and concrete has to be investigated using the bonding test. So, Pull-out test has been used to estimate bond behavior because it is simple. However, the results of pull-out test have a difference with flexural-boding behavior of FRP-Rebar concrete member. So, it is needed to evaluate the real fleuxral-bonding behavior. In this study, the evaluation method to flexural-bonding behavior of FRP-Rebar concrete member was reviewed and compared. It was found that the most accurate evaluation method for the fleuxral-bonding behavior of FRP-Rebar concrete member was splice beam test, however, the size and length of specimen have to increase than other test method and the design and analysis of splice beam is complex. Meanwhile, characteristics of concrete could be reflected by using arched beam test, unlike hinged beam test which is based on the ignored change of moment arm length in equilibrium equation. However, the possibility of shear failure exists before the flexural-bonding failure occur.

• Korean Journal of Soil Science and Fertilizer
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• v.28 no.2
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• pp.105-113
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• 1995

Adsorption experiments of heavy metal cations by Fe- and Al-hydroxides was conducted to obtain clear information on their adsorption mechanisms. The adsorption isothermal curves of heavy metal cations by Fe- and Al-hydroxides conformed to Langmuir's equation. Increasing the crystallinity degree of Fe- and Al-hydroxides tended to decrease the adsorption capacity and binding energy of heavy metal cations. At the same crystallinity degree, Al-hydroxide showed higher adsorption capacity and energy for the heavy metal cations than Fe-hydroxide. The adsorption capacity and energy of heavy metal cations were directly related to CEC, specific surface area and charge density of hydroxides, and the sequence was in the order of $Cu^{+{+}}$ > $Zn^{+{+}}$ > $Cd^{+{+}}$. The adsorption mechanism of $M^{+{+}}$ form of heavy metal could be presumed as the specific adsorption of $M^{+{+}}$ and the desorption of two $H^+$ from the surface aquo($OH_2$) and/or hydroxo(-OH) group for each mole of $M^{+{+}}$ adsorbed. A ring structure between $M^{+{+}}$ and two surface aquo and/or hydroxo groups was postulated. Nonspecific adsorption involved the adsorption of $MCl^+$ and the desorption of one H+ from the surface aquo and/or hydroxo groups for each mole of $M^{+{+}}$ adsorbed. A single bond structure in which $MCl^+$ replaced one $H^+$ from the surface aquo and/or hydroxo groups was postulated. The ratio of specific to nonspecific adsorption increased with increasing pH.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.6
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• pp.707-714
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• 2015

In this paper, an experimental program has been conducted to investigate transfer length in high strength concrete members pretensioned through a seven-wire strand with FBG sensors. To measure transfer length, five members were fabricated, which had a length of 3 m and a cross-section of $150{\times}150mm$. It was measured that the concrete compressive strength was 58MPa at pretensioning. Test results indicated that more precise and reliable measurement on the transfer length was attained with FBG sensors than conventional gauges attached on concrete surface. Through comparing the measured transfer length and predictions, applicability of several transfer length models in literature was investigated. This paper can be useful for relevant research field such as investigation on the bond mechanism of a seven-wire strand in concrete members.

• Journal of the Korean Chemical Society
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• v.23 no.6
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• pp.358-367
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• 1979

EHT and CNDO/2 calculations have been performed to determine conformations of acetamides and diacetamides, and of their protonated forms. Results show that: protonation is always favored on the cis position with respect to N due to greater attractive potential between $H^+$ and N; the trans-trans conformer of diacetamides gives the most preferred protonated form although the cis-trans conformer is the most stable one for the unprotonated diacetamides. Protonation on a carbonyl oxygen is predicted to increase both charge and orbital controlled $S_N$SN reactivities of the protonated carbonyl carbon due to increases in positive charge and AO coefficient of ${\pi}$-LUMO of the carbon atom. In the acid catalyzed hydrolysis of diacetamides therefore it appears highly probable that the rate determining attack by a water molecule occurs at the carbon of the protonated carbonyl group and the carbonyl carbon-nitrogen bond scission follows subsequently. This mechanism is consistent with that generally accepted for the hydrolysis of amides in dilute acid solution but disagrees with that proposed by Laureut et al., for acid hydrolysis of N-acetyl-lactams.

• Journal of Korean Society of Water and Wastewater
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• v.32 no.3
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• pp.279-289
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• 2018

N-nitrosodimethylamine (NDMA) is a class of disinfection byproducts and a frequently detected nitrosamine with carcinogenic potentials. This review summarizes NDMA precursors, their formation mechanisms in chloraminated water, and mitigation strategies. Understanding the formation mechanism and characteristics of precursors is essential for developing a mitigation strategy. Dimethylamine (DMA), the most widely studied NDMA precursor, has an NDMA molar yield up to 3%. In comparison, a subset of tertiary amines, e.g., pharmaceuticals, generate up to 90% upon chloramination. Potent NDMA precursors, are characterized by their negative partial charge, low planarity values and molecular weight, and high bond length and $pK_a$ values. A nucleophilic substitution of tertiary amine on chloramine is a key reason for the high NDMA yield from the most potent NDMA precursors. The distribution and fate of NDMA in surface water, aquifers, and its formation in the distribution system can be mitigated through two strategies: (1) degrading or/removing NDMA after its formation and (2) pre-treatment of its precursor's prior chloramination.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.721-725
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• 2016

This work focuses on the electrical conduction mechanism in a lead free ($Na_{0.5}K_{0.5}NbO_3$ ; NKN) ceramics system with $LiNbO_3$ content of approximately critical concentration $x{\geq}0.2$. Lead free $(1-x)(Na_{0.5}K_{0.5})NbO_3-x(LiNbO_3)$, $NKN-LN_x$ (x = 0.1, 0.2) ceramics were synthesized by solid-state reaction method. Crystal structures are confirmed by X-ray diffraction. The electric-mechanical bond coefficient $k_p$ decreases and the phase transition temperature $T_c$ increases with increasing x content, as determined by dielectric and piezoelectric measurements. The value of the real dielectric constants ${\varepsilon}^{\prime}$ and $k_BT{\varepsilon}^{\prime\prime}$ showed anomalies around $T_c$ ($462^{\circ}C$ in the NKN-LN0.1 and $500^{\circ}C$ in the NKN-LN0.2). For the ionic conduction of mobile ions, the activation energies are obtained as $E_I=1.76eV$ (NKN-LN0.1) and $E_I=1.55eV$ (NKN-LN0.2), above $T_c$, and $E_{II}=0.78$ (NKNL-N0.1) and $E_{II}=0.81$ (NKN-LN0.2) below $T_c$. It is believed that the conduction mechanisms of NKN-LNx ceramics are related to ionic hopping conduction, which may arise mainly due to the jumping of $Li^+$ ions.