• Geomechanics and Engineering
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• v.10 no.6
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• pp.827-836
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• 2016

The rate of softening is an important factor to determine whether the failure occurs along localized shear band or in a more diffused manner. In this paper, strength loss and softening rate effect depending on sensitivity are investigated for weakly cemented clays, for both artificially cemented high plasticity San Francisco Bay Mud and low plasticity Yolo Loam. Destructuration and softening behavior for weakly cemented sensitive clays are demonstrated and discussed through multiple vane shear tests. Artificial sensitive clays are prepared in the laboratory for physical modeling or constitutive modeling using a small amount of cement (2 to 5%) with controlled initial water content and curing period. Through test results, shear band thickness is theoretically computed and the rate of softening is represented as a newly introduced parameter, ${\omega}_{80%}$. Consequently, it is found that the softening rate increases with sensitivity for weakly cemented sensitive clays. Increased softening rate represents faster strength loss to residual state and faster minimizing of shear band thickness. Uncemented clay has very low softening rate to 80% strength drop. Also, it is found that higher brittleness index ($I_b$) relatively shows faster softening rate. The result would be beneficial to study of physical modeling for sensitive clays in that artificially constructed high sensitivity (up to $S_t=23$) clay exhibits faster strain softening, which results in localized shear band failure once it is remolded.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.713-723
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• 2016

Shear wave velocities of three selected sandy soils subject to drained triaxial compression test were continuously measured using the bender elements. The shear wave velocity during isotropic compression, as widely recognized, increased as confining pressure increased and they were correlated well. However, during drained shearing, the mean effective stress could no further provide a suitable correlation. The shear wave velocity during this stage was almost constant with respect to the mean effective stress. The vertical stress was found to be more favorable at this stage (since confining stress was kept constant). When sample was attained its peak stress, the shear wave velocity reduced and deviated from the previously existed trend line. This was probably caused by the non-uniformity induced by the formation of shear band. Subsequently, void ratios computed based on external measurements could not provide reasonable fitting to the initial stage of post-peak shear wave velocity. At very large strain levels after shear band formation, the digital images revealed that sample may internally re-arrange itself to be in a more uniform loose stage. This final stage void ratio estimated based on the proposed correlation derived during pre-peak state was close to the value of the maximum void ratio.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.10
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• pp.857-863
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• 2005

A yeast strain utilizing styrene epoxide as a sole carbon and energy source was isolated from soil samples for the production of enantiopure of styrene epoxide by kinetic resolution. The strain, identified as a Rhodosporidium toruloides SJ-4, expressed an epoxide hydrolase which preferentially converted (R)-styrene epoxide into the corresponding diol. A maximum activity of 135 U/L was observed when biomass (dry cell mass) reached 6.7 g/L at 21 h of batch culture. Under the partially optimized reaction conditions ($35^{\circ}C$ and pH 8.0), the optically pure (S)-styrene epoxide was obtained with the yield of 21% when the initial substrate concentration was 100 mM. The reaction was completed at 9 h.

• Korean Journal of Microbiology
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• v.26 no.4
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• pp.355-361
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• 1988

The aims of the present studies were to understand the physiolosical and genetic characters of Streptomyces sp. isolated from soil. It revealed that Streptomyces sp. SMF301 had very fast growth rate and produced extracellular protease and heavily sporulated on rich media. It also showed $\beta$-lactamase activity and pigment production. Nonsporulating mutants were isolated after NTG or acriflavin treatment and their characters were compared with the parent strain. It was found that the mutants obtained by acriflavin treatment and ghier characters were compared with the parent strain. It was found that the mutants obtained by acriflavin treatment lost the pigment formation and $\beta$-lactamase production. Protease actibity of the mutant was lowered and the pH optimum was changed toward neutral. It was found that the changes were resulted from the reduction of alkaline protease biosynthesis in the bald mutant. Therefore it is considered that sporulation, pigment formation, $\beta$-lactamase production, and alkaline protease production in Streptomyces sp. might be controlled with a closely related relationship.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.189-197
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• 2003

In this paper, deformation characteristics of fiber-mixed-soils were studied at small strain range(0.0001%～1%) using resonant column test and triaxial test, and reinforcement effect was evaluated by the measure of maximum shear moduli. The effects of the major parameters such as fiber content, aspect ratio and fiber type on reinforcement were comparatively assessed. The specimens were remolded from Jumunjin Sand randomly mixed with discrete polypropylene staple fibers. Maximum shear moduli of fiber-mixed-soils increased by up to 30% and modulus reduction was also restrained in nonlinear range. Shear moduli increased as the aspect ratio increases. The reinforcement was more effective with fibrillated fiber than with monofilament fiber. The most effective reinforcement was achieved with the specimen of 0.3 % fiber content.

• Journal of the Korean Society of Food Science and Nutrition
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• v.35 no.1
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• pp.109-114
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• 2006

For the purpose of oligosaccharide production from alginate, the main component in cell walls of brown algae, the alginate degrading bacteria have been screened from the seaweeds and soil. Among the isolated 69 strains, one strain showing the highest degrading activity was selected and identified as Bacillus licheniformis strain. The adequate sodium alginate concentration for growing the Bacillus licheniformis was $2.0\%$. The effective nitrogen source is nutrient broth $(0.1\%)$, and optimum initial pH, NaCl concentration, temperature and incubation time to produce the alginate degrading enzyme were 7.5, $2\%,\;30{\pm}2^{\circ}C$, and 144 hrs, respectively.

• Geomechanics and Engineering
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• v.6 no.6
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• pp.561-575
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• 2014

Estimating seismic displacements has a great importance for foundations on or adjacent to slope surfaces. However, dynamic solution of the problem has received little attention by previous researchers. This paper presents a new analytical model to determine seismic displacements of the shallow foundations adjacent to slopes. For this purpose, a dynamic equilibrium equation is written for the foundation with failure wedge. Stiffness and damping at the sliding surface are considered variable and a simple method is proposed for its estimation. Finally, for different failure surfaces, the calculated dynamic displacement and the surfaces with maximum strain are selected as the critical failure surface. Analysis results are presented as curves for different slope angles and different foundation distances from edge of the slope and are then compared with the experimental studies and software results. The comparison shows that the proposed model is capable of estimating seismic displacement of the shallow foundations adjacent to slopes. Also, the results demonstrate that, with increased slope angle and decreased foundation distances from the slope edge, seismic displacement increases in a non-linear trend. With increasing the slope angle and failure wedge angle, maximum strain of failure wedge increases. In addition, effect of slope on foundation settlement could be neglected for the foundation distances over 3B to 5B.

• Microbiology and Biotechnology Letters
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• v.22 no.3
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• pp.271-276
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• 1994

The strain S4-14 which produced alkaline lipase and had resistance against linear alkylbenzene sulfonate was isolated from soil or water samples. The isolated strain S4-14 was identified a species belong to Pseudomonas. Alkalin lipase secreted by Pseudomonas sp. S4-14 was purified by ammonium sulfate precipitation procedure follwed by DEAE-Cellulose, DEAE-Sepharose and gel filtration chromatohraphies with 995.15 U/mg protein and 16.1% yield. The molecular weight of the enzyme was estimated to be 65,000 dalton by SDS-PAGE. The optimum pH and temperature of the purified enzyme was 10.5 and 45$\circ $C, respectively. The emzyme was stable at 45$\circ $C for 1 hr and in a pH range from 8.0 to 12.0 for 24 hr at 4$\circ $C. The activity of lipase was enhanced by Ca$^{2+}$ while inhibited strongly by Pb$^{2+}$, Zn$^{2+}$ or Fe$^{3+}$. The activity of lipase was inactivated about 50~60% in the presence of 50 mg/l linear alkylbenzene sulfonate, $\alpha $-olefin sulfonate, alcohol ethoxylate or perborate.

• Journal of Microbiology and Biotechnology
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• v.7 no.2
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• pp.121-126
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• 1997

A bacterial strain LC-413, producing an extracellular inulin fructotransferase (depolymerizing) which converts inulin into di-D-fructofuranose dianhydride (DFAIII), was isolated from soil. Inulin fructotransferase from the isolate identified as a strain Flabobacterium sp. was purified from the culture broth by ammonium sulfate precipitation, followed by column chromatograpies on DEAE-Toyopearl 650 M and phenyl-Toyopearl 650 M. The purified enzyme gave a single band on an electrophoretic disc-gel. The molecular weight of the enzyme was estimated to be 44, 000 Da by SDS-polyacrylamide gel electrophoresis, and 45, 000 Da by gel filtration, suggesting the monomeric state of the enzyme. The isoelectric point of the enzyme was about pH 4.5. The optimal pH and temperature for the enzyme reaction were 6.0 and $50^{\circ}C$, respectively. The purified enzyme digested inulin into di-D-fructofuranose-l, 2': 2, 3'-dianhydride, confirming the enzyme was an inulin fructotransferase (inulinase II).

• Korean Journal of Microbiology
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• v.29 no.4
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• pp.250-257
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• 1991

An obligate methanol-oxidizing bacterium, Methylobacillus sp. strain SK1, which grows only on methanol was isolated from soil. The isolate was nonmotile Gram-negtive rod. It does not have internal membrane system. The colonies were small, whitish-yellow, and smooth. The guanine plus cytosine content of the DNA was 48 mol%. Cellular fatty acids consisted predominantly of large amounts of straight-chain saturated $C_{16:0}$ acid and unsaturated $C_{16:1}$ acid. The major ubiquinone was Q-8, and Q-10 was present as minor component. The cell was obligately aerobic and exhibited catalase, but no oxidase, activity. Poly-.betha.-hydroxybutyrate, endospores, or cysts were not observed. the isolate could grow only on methanol in mineral medium. Growth factors were not required. The isolate was unable to use methane, formaldehyde, formate, methylamine, and several other organic compounds tested as a sole source of carbon and energy. Growth was optimal at 35.deg.C and pH 7.5. It could not grow at 42.deg.C. The doubling time was 1.2h at 30.deg.C when grown with 1.0%(v/v) methanol. The growth was not affected by antibiotics inhibiting cell wall synthesis and carbon monoxide but was completely suppressed by those inhibiting protein synthesis. Methanol was found to be assimilated through the ribulose monophosphate pathway. Cytochromes of b-, c-, and o- types were found. Cell-free extracts contained a phenazine methosulfate-linked methanol dehydrogenase activity, which required ammonium ions as an activator. Cells harvested after the late exponential phase seemed to contain blue protein.ein.