• Journal of Microbiology and Biotechnology
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• v.17 no.9
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• pp.1538-1545
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• 2007

Clavulanic acid (CA) is an inhibitor of ${\beta}$-lactamase that is produced from Streptomyces clavuligerus NRRL3585 and is used in combination with other antibiotics in clinical treatments. In order to increase the production of CA, the replicative and integrative expressions of ccaR (encoding for a specific regulator of the CA biosynthetic operon) and cas2 (encoding for the rate-limiting enzyme in the CA biosynthetic pathway) were applied. Six recombinant plasmids were designed for this study. The pIBRHL1, pIBRHL3, and pIBRHL13 were constructed for overexpression, whereas pNQ3, pNQ2, and pNQ1 were constructed for chromosomal integration with ccaR, cas2, and ccaR-cas2, respectively. All of these plasmids were transformed into S. clavuligerus NRRL3585. CA production in transformants resulted in a significantly enhanced amount greater than that of the wild type, a 2.25-fold increase with pIBRHLl, a 9.28-fold increase with pNQ3, a 5.06-fold increase with pIBRHL3, a 2.93-fold increase with pNQ2 integration, a 5.79-fold increase with pIBRHLl3, and a 23.8-fold increase with pNQ1. The integrative pNQl strain has been successfully applied to enhance production.

• Journal of Microbiology and Biotechnology
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• v.19 no.1
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• pp.23-36
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• 2009

In the present work, the metabolic network of primary metabolism of the slow-growing myxobacterium Sorangium cellulosum was reconstructed from the annotated genome sequence of the type strain So ce56. During growth on glucose as the carbon source and asparagine as the nitrogen source, So ce56 showed a very low growth rate of $0.23\;d^{-1}$, equivalent to a doubling time of 3 days. Based on a complete stoichiometric and isotopomer model of the central metabolism, $^{13}C$ metabolic flux analysis was carried out for growth with glucose as carbon and asparagine as nitrogen sources. Normalized to the uptake flux for glucose (100%), cells recruited glycolysis (51%) and the pentose phosphate pathway (48%) as major catabolic pathways. The Entner-Doudoroff pathway and glyoxylate shunt were not active. A high flux through the TCA cycle (118%) enabled a strong formation of ATP, but cells revealed a rather low yield for biomass. Inspection of fluxes linked to energy metabolism revealed that S. cellulosum utilized only 10% of the ATP formed for growth, whereas 90% is required for maintenance. This explains the apparent discrepancy between the relatively low biomass yield and the high flux through the energy-delivering TCA cycle. The total flux of NADPH supply (216%) was higher than the demand for anabolism (156%), indicating additional reactions for balancing of NADPH. The cells further exhibited a highly active metabolic cycle, interconverting $C_3$ and $C_4$ metabolites of glycolysis and the TCA cycle. The present work provides the first insight into fluxes of the primary metabolism of myxobacteria, especially for future investigation on the supply of cofactors, building blocks, and energy in myxobacteria, producing natural compounds of biotechnological interest.

• Journal of Microbiology and Biotechnology
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• v.19 no.1
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• pp.72-77
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• 2009

Here, we demonstrate that the overexpression of the GroELS chaperone system, which assists the folding of intracellular proteins and prevents aggregation of its biological targets, can enhance the thermotolerance of Escherichia coli strains and facilitate the production of recombinant protein under thermal stress. The overexpression of GroELS led to an about 2-fold higher growth rate of E. coli XL-1 blue than control at $45^{\circ}C$ and induced the growth of the strain even at $50^{\circ}C$, although the growth was not sustained in the second-round culture. The effect of GroELS overexpression was also effective on other E. coli strains such as JM109, $DH5{\alpha}$, and BL21. Finally, we have shown that coexpression of GroELS allows us to produce recombinant protein even at $50^{\circ}C$, a temperature at which the protein production based on E. coli is not efficient. This study indicates that the employment of the GroELS overexpression system can expand the range of environmental conditions for E. coli.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.4
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• pp.1130-1147
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• 2014

Large size ships have a very flexible construction resulting in low resonance frequencies of the structural eigen-modes. This feature increases the dynamic response of the structure on short period waves (springing) and on impulsive wave loads (whipping). This dynamic response in its turn increases both the fatigue damage and the ultimate load on the structure; these aspects illustrate the importance of including the dynamic response into the design loads for these ship types. Experiments have been carried out using a segmented scaled model of a container ship in a Seakeeping Basin. This paper describes the development of the model for these experiments; the choice was made to divide the hull into six rigid segments connected with a flexible beam. In order to model the typical feature of the open structure of the containership that the shear center is well below the keel line of the vessel, the beam was built into the model as low as possible. The model was instrumented with accelerometers and rotation rate gyroscopes on each segment, relative wave height meters and pressure gauges in the bow area. The beam was instrumented with strain gauges to measure the internal loads at the position of each of the cuts. Experiments have been carried out in regular waves at different amplitudes for the same wave period and in long crested irregular waves for a matrix of wave heights and periods. The results of the experiments are compared to results of calculations with a linear model based on potential flow theory that includes the effects of the flexural modes. Some of the tests were repeated with additional links between the segments to increase the model rigidity by several orders of magnitude, in order to compare the loads between a rigid and a flexible model.

• Mycobiology
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• v.42 no.4
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• pp.346-352
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• 2014

Recently, the Q biotype of tobacco whitefly has been recognized as the most hazardous strain of Bemisia tabaci worldwide, because of its increased resistance to some insecticide groups. As an alternative control agent, we selected an Isaria javanica isolate as a candidate for the development of a mycopesticide against the Q biotype of sweet potato whitefly. To select optimal mass production media for solid-state fermentation, we compared the production yield and virulence of conidia between 2 substrates (barley and brown rice), and we also compared the effects of various additives on conidia production and virulence. Barley was a better substrate for conidia production, producing $3.43{\times}10^{10}$ conidia/g, compared with $3.05{\times}10^{10}$ conidia/g for brown rice. The addition of 2% $CaCO_3+2%$ $CaSO_4$ to barley significantly increased conidia production. Addition of yeast extract, casein, or gluten also improved conidia production on barley. Gluten addition (3% and 1.32%) to brown rice improved conidia production by 14 and 6 times, respectively, relative to brown rice without additives. Conidia cultivated on barley produced a mortality rate of 62% in the sweet potato whitefly after 4-day treatment, compared with 53% for conidia cultivated on brown rice. The amendment of solid substrate cultivation with additives changed the virulence of the conidia produced; the median lethal time ($LT_{50}$) was shorter for conidia produced on barley and brown rice with added yeast extract (1.32% and 3%, respectively), $KNO_3$ (0.6% and 1%), or gluten (1.32% and 3%) compared with conidia produced on substrates without additives.

• Journal of Magnetics
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• v.21 no.1
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• pp.12-19
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• 2016

The <100> oriented $Fe_{83}Ga_{17}$ alloys with various contents of NbC or B were prepared by directionally solidification method at the growth rate of $720mm{\cdot}h^{-1}$. With a small amount of precipitates, the columnar grains grew with cellular mode during directional solidification process, while like-dendrite mode of grains growth was observed in the alloys with higher contents of 0.5 at% due to the dragging effect of precipitates on the boundaries. The NbC precipitates disperse both inside grains and along the boundaries of $Fe_{83}Ga_{17}$ alloys with NbC addition, and the Fe2B secondary phase particles preferentially distribute along the grain boundaries in B-doped alloys. Precipitates could affect grain growth and improved the <100> orientation during directional solidification process. Small amount of precipitate element addition slightly increased the magnetostrictive strain, and a high value of 335 ppm under pre-stress of 15 MPa was achieved in the alloys with 0.1 at% NbC. Despite the fact that the effect on magnetic induction density of small amount of precipitates could be negligible, the coercivity markedly increased with addition of precipitate element for $Fe_{83}Ga_{17}$ alloy due to the retarded domain motion resulted by precipitates.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.44 no.6
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• pp.658-664
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• 2011

Rotifers of the genus Brachionus are commonly used as a live food for larval fish, and rotifers of different sizes are preferred according the mouth size of the fish. Rotifer species vary in size, and individual size can depend on the temperature and salinity of the rearing environment. We investigated the effects of temperature and salinity for two species, B. plicatilis (250-300 ${\mu}m$) and B. rotundiformis (100-220 ${\mu}m$). Two strains of B. plicatilis (CCUMP 36 and 48) and two strains of B. rotundiformis (CCUMP 51 and 56) were received from the Culture Collection of Useful Marine Plankton (CCUMP) at Pukyong National University and cultured with the green alga, Nannochloris oculata (KMMCC 16) from the Korea Marine Microalgal Culture Center (KMMCC). The growth and size of rotifers were examined at three water temperatures ($16^{\circ}C$, $24^{\circ}C$, $32^{\circ}C$) and four salinities (20 psu, 25 psu, 30 psu, 35 psu) under continuous light (40 ${\mu}molm^{-2}s^{-1}$). The maximum density and growth rate of B. rotundiformis were greater than those of B. plicatilis. The lorica length of B. plicatilis ranged from 215.4 to 269.7 ${\mu}m$ and from 154.9 to 206.6 ${\mu}m$ for B. rotundiformis, depending on strain, temperature and salinity. Rotifers were smaller when cultured at high temperatures, regardless of salinity. B. rotundiformis preferred higher salinity than B. plicatilis. The results demonstrated that the size of rotifers could be controlled to some extent by temperature and salinity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1562-1570
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• 2003

The prediction of the inelastic behavior of the structure is an essential part of reliability assessment procedure, because most of the failures are induced by the inelastic deformation, such as creep and plastic deformation. During decades, there has been much progress in understanding of the inelastic behavior of the materials and a lot of inelastic constitutive equations have been developed. The complexity of these constitutive equations generally requires a stable and accurate numerical method. The radial return mapping is one of the most robust integration scheme currently used. Nonlinear kinematic hardening model of Armstrong-Fredrick type has recovery term and the direction of kinematic hardening increment is not parallel to that of plastic strain increment. In this case, The conventional radial return mapping method cannot be applied directly. In this investigation, we expanded the radial return mapping method to consider the nonlinear kinematic hardening model and implemented this integration scheme into ABAQUS by means of UMAT subroutine. The solution of the non-linear system of algebraic equations arising from time discretization with the generalized midpoint rule is determined using Newton method and bisection method. Using dynamic yield condition derived from linearization of flow rule, the integration scheme for elastoplastic and viscoplastic constitutive model was unified. Several numerical examples are considered to demonstrate the efficiency and applicability of the present method.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.671-677
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• 2014

In this research, flow experiments and simulation of highly flowable concrete has been attempted using a viscoplastic particle method varying with dosages of SP admixture and water-cement (W/C) ratios. Rheological and flow characteristics of flowable concrete manufactured in domestic products of cement, aggregates, and SP admixtures were investigated by experimental programs varying with mix proportions. From experiment, the predictive model of rheological characteristics of flowable concrete has been newly proposed considering with the effects of the W/C ratio and the dosage of SP admixture, and the effect of mixing proportion has also been incorporated into shear stress and strain rate curve of flowable concrete in the current method. A series of L-box flow test of highly flowable concrete varying with dosages of SP admixture and W/C ratios was compared with the proposed model.

• Journal of Veterinary Science
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• v.23 no.5
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• pp.63.1-63.14
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• 2022

Background: Chicken anemia virus (CAV) causes chicken infectious anemia, which results in immunosuppression; the virus has spread widely in chicken flocks in China. Objectives: The aim of this study was to understand recent CAV genetic evolution in chicken flocks in Guangxi Province, southern China. Methods: In total, 350 liver samples were collected from eight commercial broiler chicken farms in Guangxi Province in southern China from 2018 to 2020. CAV was detected by conventional PCR, and twenty CAV complete genomes were amplified and used for the phylogenetic analysis and recombination analysis. Results: The overall CAV-positive rate was 17.1%. The genetic analysis revealed that 84 CAVs were distributed in groups A, B, C (subgroups C1-C3) and D. In total, 30 of 47 Chinese CAV sequences from 2005-2020 belong to subgroup C3, including 15 CAVs from this study. There were some specific mutation sites among the intergenotypes in the VP1 protein. The amino acids at position 394Q in the VP1 protein of 20 CAV strains were consistent with the characteristics of a highly pathogenic strain. GX1904B was a putative recombinant. Conclusions: Subgroup C3 was the dominant genotype in Guangxi Province from 2018-2020. The 20 CAV strains in this study might be virulent according to the amino acid residue analysis. These data help improve our understanding of the epidemiological trends of CAV in southern China.