• Journal of Microbiology and Biotechnology
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• v.7 no.4
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• pp.215-222
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• 1997

The regulatory mechanism of the flux of acetyl-CoA in Alcaligenes eutrophus in unbalanced growth conditions was investigated using a PHB-negative mutant and transformants reintroduced PHB-biosynthesis enzymes through the transformation of cloned phbCAB genes. The PHB-negative mutant was defected absolutly in PHB synthase but partially in ${\beta}$-ketothiolase and acetoacetyl-CoA reductase, and excreted substantial amount of pyruvate to culture broth at late growth phase. The excretion was due to the inhibitory effect of acetyl-CoA on the activity of pyruvate dehydrogenase. The cloned phbC and phbCAB genes were transformed to the PHB-negative mutant strain to reintroduce PHB biosythesis enzymes. Pyruvate excretion could be decreased substantially but not completely by transformation of PHB synthase alone, while pyruvate excretion was ceased by transformation of all three PHB biosynthesis enzymes. To identify the most critical PHB biosynthesis enzyme influencing on the flux of acetyl-CoA, the effect of the variation of PHB biosynthesis enzymes on pyruvate dehydrogenase was investigated. ${\beta}$-Ketothiolase influenced the activity of pyruvate dehydrogenase more sensitively than PHB synthase. ${\beta}$-Ketothiolase, the first step enzyme of PHB biosynthesis that condense acetyl-CoA to acetoacetyl-CoA, seems to be the major enzyme determining the flux of acetyl-CoA to PHB biosynthesis or TCA cycle, and the rate of PHB biosynthesis in A. eutrophus.

• Microbiology and Biotechnology Letters
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• v.14 no.3
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• pp.239-244
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• 1986

To develop the potential use as new host strain for gene cloning, alkaline-tolerant isolates from soil were examined for amylase activity, protease activity, antimicrobial activity and transformability by using plasmid pUB 110. Of these strains, one was selected and identified as Bacillus sp. YA-14. in the enzymatic properties of Bacillus sp. YA-14 the optimal conditions for the reaction of amylase and protease were at pH 0.8 and pH 7.5 respectively. The antimicrobial activity of Bacillus sp. YA-14 was also found. For the transformation, Bacillus sp. YA-14 was cultured to late logarithmic growth phase ai 37$^{\circ}C$ in modified SPI medium (pH 8.0) containing 0.4% MgSO$_4$. The presence of pUB 110 plasmid DNA in transformants was confirmed by electrophoresis and stably maintained in the new host.

• Geotechnical Engineering
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• v.12 no.5
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• pp.17-26
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• 1996

The undrained behavior of Asan marine soil was investigated by using an automated triaxial testing device. The stress-strain behavior at the preand postfailure state of marine soil under undrained compression and eatension conditions was compared with the behavior of pure silt, pure clay and the overall behavior of Asan marine soil was predicted with the modified Camflay model and the bounding surface model. The marine soil sampled in Asan bay area was clayey silts with 70oA silt-30% clay content and the testing samples were prepared in both undisturbed and remolded conditions. All samples are normally consolidated with 400 kPa of effective mean confining pressure and each sample is unloaded to 200, 100, 67 kPa, respectively. And then the shear test was performed with different confining pressure. According to experimental results, there exists an unique failure line whose slope is lower than silt's and higher than clay's. It is identified that the undrained shear strength of normally consolidated samples increases after crossing the phase transformation line because of volume dilation tendency which is not seen in clay. Overconsolidated samples show different soil behavior compared with pure silt due to its tendency of change in volume. It is also found that the overall behavior of Asan marine soil cannot be predicted precisely with the modified Cam-clay model and the bounding surface model.

• Journal of Powder Materials
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• v.25 no.3
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• pp.246-250
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• 2018

In this study, we investigate the deformation behavior of $Hf_{44.5}Cu_{27}Ni_{13.5}Nb_5Al_{10}$ metallic glass powder under repeated compressive strain during mechanical milling. High-density (11.0 g/cc) Hf-based metallic glass powders are prepared using a gas atomization process. The relationship between the mechanical alloying time and microstructural change under phase transformation is evaluated for crystallization of the amorphous phase. Planetary mechanical milling is performed for 0, 40, or 90 h at 100 rpm. The amorphous structure of the Hf-based metallic glass powders during mechanical milling is analyzed using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Microstructural analysis of the Hf-based metallic glass powder deformed using mechanical milling reveals a layered structure with vein patterns at the fracture surface, which is observed in the fracture of bulk metallic glasses. We also study the crystallization behavior and the phase and microstructure transformations under isothermal heat treatment of the Hf-based metallic glass.

• Journal of Powder Materials
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• v.26 no.5
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• pp.389-394
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• 2019

In the present study, we have investigated the effect of sintering process conditions on the stability of the austenite phase in the nanocrystalline Fe-5wt.%Mn-0.2wt.%C alloy. The stability and volume fraction of the austenite phase are the key factors that determine the mechanical properties of FeMnC alloys, because strain-induced austenite-martensite transformation occurs under the application of an external stress at room temperature. Nanocrystalline Fe-5wt.%Mn-0.2wt.%C samples are fabricated using the spark plasma sintering method. The stability of the austenite phase in the sintered samples is evaluated by X-ray diffraction analysis and hardness test. The volume fraction of austenite at room temperature increases as the sample is held for 10 min at the sintering temperature, because of carbon diffusion in austenite. Moreover, water quenching effectively prevents the formation of cementite during cooling, resulting in a higher volume fraction of austenite. Furthermore, it is found that the hardness is influenced by both the austenite carbon content and volume fraction.

• Journal of Welding and Joining
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• v.30 no.6
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• pp.120-125
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• 2012

Because ships and offshore structures have very large dimensions and complicated shapes, it is difficult to determine the deformation or internal stress in the structure by simple lab tests. Thus, a rigorous analysis by using the computer simulation technology is essential for obtaining their distortions by considering the entire production process characteristics. The rapid development of computer technology made it possible to analyze the heat transfer phenomena, deformation and phase transformation in the welded joint. For large shell structures, shell elements modeling contributed primarily to this development. But if a welding is done by multi-pass, shell elements whose thickness are unchangeable can hard to describe the local situation. Recently, it was researched how to introduce the imaginary temperature for V grooved multi-layer butt welding in strain-boundary method (a kind of shrinkage methodologies). In the present study, we formulated the imaginary temperature for the double bevel and double V groove by considering the thickness change of each pass through the bead and the thickness directions simultaneously and also demonstrated the feasibility of the formula by applying it to the thermal distortion analysis of the erection process of crane pedestal.

• International Journal of Korean Welding Society
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• v.3 no.1
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• pp.39-44
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• 2003

The welded specimens were made by butt welding of the 2 wires of 50mm length using the pulsed YAG laser. The laser welded wires were tested for investigating the shape memory effect and the ability of super elasticity. The fatigue properties of the welded wires were investigated using the rotary bending fatigue tester specially designed for wires. Moreover, the effect of defocusing distance during laser welding on the static and fatigue properties was Investigated. The shape memory effect and super elasticity of the laser welded wires were approximately identical with that of base metal at the test temperature below 353K. However, the welded wires were broken within elastic limit at the test temperature above 353k. Under the cyclic bending loading conditions, the welded wires could be useful only below the elastic limit, while the base metal had sufficient fatigue life even the stress induced M-phase region. The fatigue strength of the welded wires was about half of that of the base metal. The deterioration of the static and fatigue properties in the welded wires was proven to be from the large difference of the transformation behavior between the base metal and welded part that is caused by vaporization of Ni-content at the welded part during the welding process. The defocusing distance below 3mm acted more largely on lowering the strength of the welded wires than that of 6mm or 8mm.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.60-65
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• 2014

Fe-based amorphous coatings were fabricated on a soda-lime glass substrate by the vacuum kinetic spray method. The effect of the gas flow rate, which determines particle velocity, on the deposition behavior of the particle and microstructure of the resultant films was investigated. The as-fabricated microstructure of the film was studied by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). Although the activation energy for transformation from the amorphous phase to crystalline phase was lowered by severe plastic deformation and particle fracturing under a high strain rate, the crystalline phases could not be found in the coating layer. Incompletely fractured and small fragments 100~300 nm in size, which are smaller than initial feedstock material, were found on the coating surface and inside of the coating. Also, some pores and voids occurred between particle-particle interfaces. In the case of brittle Fe-based amorphous alloy, particles fail in fragmentation fracture mode through initiation and propagation of the numerous small cracks rather than shear fracture mode under compressive stress. It could be deduced that amorphous alloy underwent particle fracturing in a vacuum kinetic spray process. Also, it is considered that surface energy caused by the formation of new surfaces and friction energy contributed to the bonding of fragments.

• Korean Journal of Materials Research
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• v.11 no.2
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• pp.88-93
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• 2001

The thermal behavior and the crystallographic characteristics of an epitaxial $C49-TiSi_2$ island formed in a Si (001) substrate by $N_2$, treatment were investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). It was found from the analyzed results that the epitaxial $C49-TiSi_2$ was thermally stable even at high temperature of $1000^{\circ}C$ therefore did not transform into the C54-stable phase and did not deform morphologically. HRTEM results clearly showed that the epitaxial $TiSi_2$ phase and Si have the orientation relationship of (060)[001]$TiSi_2$//(002)[110]Si, and the lattice strain energy at the interface was mostly relaxed by the formation of misfit dislocations. Furthermore, the mechanism on the formation of the epitaxial $_C49-TiSi2$ in Si and stacking faults lying on the (020) plane of the C49 Phase were discussed through the analysis of the HRTEM image and the atomic modeling.

• Journal of Microbiology
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• v.33 no.4
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• pp.339-343
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• 1995

We isolated a 10 kb Bam HI fragment originated from the chromosome of a $H_2O$$^2$-resistant mutant strain of Streptomyces coelicolor, which confer $H_2O$$^2$-resistance to S. lividance upon transformation. Among various subclones ot 10kb Bam HI fragment tested for their $H_2O$$^2$-resistant phenotype in S. lividans, a subclone containing 5.2 kb Bam HI-BglII fragment was found to be responsible for $H_2O$$^2$-resistance. The plasmid containing this 5.2 kb fragment was then transformed into S. coellicolor A3(2) at early and tested for their phenotype of $H_2O$$^2$-resistance and the change in various enzymes whose activity can be stained in the gel. We found out that the 5.2 kb insert DNA conferred $H_2O$$^2$-resisstance in S. coelicolor A3(2) at early phase of cell growth. The presence of this DNA also resulted in higher level of peroxidase compared with the wild type cell containing parental vector (pIJ702) only. Esterase activity was also higher in this clone. However, alcohol dehydrogenase activity decreased compared with the wild type. These results suggest that the presence of a gene in 5.2 kb BamHI-BglII DNA fragment causes multiple changes in S. coelicolor related to its response against hydrogen peroxide. The result also implies that not only peroxidase but also esterase may function in the defencse meahsnism agianst $H_2O$$^2$-.