• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.2
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• pp.245-256
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• 2000

A moment-curvature relationship to simulate the behavior of reinforced concrete beam under cyclic loading is introduced. Unlike previous moment-curvature models and the layered section approach, the proposed model takes into consideration the bond-slip effect by using monotonic moment-curvature relationship constructed on the basis of the bond-slip relation and corresponding equilibrium equation at each nodal point. In addition, the use of curved unloading and reloading branches inferred from the stress-strain relation of steel gives more exact numerical result. The advantages of the proposed model, comparing to layered section approach, may be on the reduction in calculation time and memory space in case of its application to large structures. The modification of the moment-curvature relation to reflect the fixed-end rotation and pinching effect is also introduced. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.2
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• pp.119-129
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• 2004

A three dimensional (3D) method of analysis is presented for determining the free vibration frequencies and mode shapes of thick, circular and annular plates with nonlinear thickness variation along the radial direction. Unlike conventional plate theories, which are mathematically two dimensional (2D), the present method is based upon the 3D dynamic equations of elasticity. Displacement components u/sub s/, u/sub z/, and u/sub θ/ in the radial, thickness, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the s and z directions. Potential (strain) and kinetic energies of the plates are formulated, and the Ritz method is used to solve the eigenvalue problem thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four digit exactitude is demonstrated for the first five frequencies of the plates. Numerical results we presented for completely free, annular and circular plates with uniform linear, and quadratic variations in thickness. Comparisons are also made between results obtained from the present 3D and previously published thin plate (2D) data.

• Journal of Life Science
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• v.23 no.7
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• pp.904-912
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• 2013

This study aimed to evaluate the protective effect of cordycepin-increased Cordyceps militaris strain on carbon tetrachloride ($CCl_4$)-induced hepatotoxicity and oxidative stress in rats. Male Sprague-Dawley rats were randomly divided into five groups (n=6) based on six dietary categories: normal (N), $CCl_4$ control (C), $CCl_4$ plus Paecilomyces japonica (CPJ) (3%, w/w), $CCl_4$ plus C. militaris (CCM) (3%, w/w), and $CCl_4$ plus cordycepin-increased C. militaris ($CCM{\alpha}$) (3%, w/w). The activities of the liver marker enzymes ALT, AST, and LDH and the levels of lipid peroxidation were increased in the $CCl_4$-treated groups, but these parameters were significantly decreased in the $CCM{\alpha}$ group. The TBARS content in the liver homogenate, microsome, and mitochondrial fractions of the C group was significantly elevated compared with the N group. However, in the $CCl_4$-treated groups, $CCM{\alpha}$ group was significantly lowered in the TBARS levels of hepatic homogenate and microsomal fractions. The C group showed a significant decrease in the levels of plasma and hepatic glutathione, whereas they were significantly increased in the $CCM{\alpha}$ group. Accordingly, cordycepin-increased C. militaris may be an ideal animal model for studying hepatoprotective effects.

• Journal of Life Science
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• v.26 no.10
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• pp.1202-1206
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• 2016

Unicellular cyanobacterial strains of Subsections I and II and filamentous cyanobacterial strains of Subsection III have been shown to be polyphyletic, heterocystous strains of Subsections IV and V, both of which were previously reported to be monophyletic. In this study, the small subunit ribosomal RNA (16S rRNA) sequences of 13 strains of cyanobacteria - one strain, Oscillatoria nigro-viridis PCC7112, of the Subsection III, 6 strains including genus Anabaena, Nostoc, Tolypothrix, Calothrix and Scytonema of the Subsection IV, and 6 strains including genus Hapalosiphon, Fischerella and Chlorogloeopsis of the Subsection V - were determined. The phylogenetic analysis of cyanobacteria was carried out using the 16S rRNA sequences. The results of the phylogenetic analyses of 16S rRNA sequences, based on Neighbour-joining, maximum-parsimony, and maximum-likelihood methods, indicated that the members of Subsection IV were not monophyletic but polyphyletic. In addition, the phylogenetic results strongly indicated that the genus Scytonema in Subsection IV could be a common ancestor of heterocystous cyanobacteria in Subsection IV and V. Furthermore, the phylogenetic analyses revealed that the genus Anabaena could be phylogenetically diverse and that cyanobacterial strains in Subsection IV might be polyphyletic, whereas those in Subsection V could be monophyletic, as reported before. The results for the genus Anabaena indicate that it should be reclassified.

• Journal of the Korean Wood Science and Technology
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• v.37 no.4
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• pp.364-371
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• 2009

This study was carried out to investigate the bending strength of the Larix glulam beams which were reinforced with CFRP (Carbon fiber reinforced plastic) of which the reinforcement ratios were 0.7% and 2.1% by volume. In the bending test, the rupture shape of the reinforced glulam shows that the reinforced glulam broke firstly in the lowest bottom layer on which tension was loaded, but did not in the upper part reinforced with the CFRP layer. The upper part of the reinforced layer kept strength and did not break when the reinforced glulam broke firstly at the bottom part of the reinforced layer, but broke secondly as loading was increased. In the glulam beams reinforced with CFRP of which the reinforcement ratio was 0.7% by volume, the bending strength of the reinforced beams was increased by 28% at the first break. When beams broke up to the upper part of the reinforced layer, the bending strength of the reinforced beams was increased by 55%, compared to those of control glulam beams. When the glulam beams were reinforced with CFRP of which the reinforcement ratio was 2.1% by volume, the bending strength of the reinforced beams was increased by 77%, compared to those of control glulam beams. The ratio of the height of calculated neutral axis using failure mode recommended by Romani and the height of actual neutral axis using strain gauge was 1.03 and agreed well.

• Food Science of Animal Resources
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• v.33 no.4
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• pp.522-530
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• 2013

The ability of probiotics to adhere to the intestinal epithelium likely plays an important role in their colonization of the gastrointestinal tract. Here, we performed high-throughput screening (HTS) for suitable characteristics of potential probiotic bacteria using attachment and colonization ability through a C. elegans surrogate in vivo model. A total of 100 strains of lactic acid bacteria (LAB) isolated from infant feces were subjected to the colonization assay using C. elegans intestine. Based on colonization ability, we showed that nine isolates have a high attachment ability during whole experimental periods (up to 168 h), compared to Lactobacillus rhamnosus strain GG as a control. Also, through the use of an in vitro cell attachment model, nine isolates revealed highly binding activity to the mucus layer. Next, the selected 9 isolates were assayed for their survival ability when exposed to acidic and bile conditions as well as cholesterol reduction and the utilization of prebiotic substrates. As a result, the isolated nine strains were determined to be highly resistant to acid and bile conditions. In addition, they have significant activity for the reduction of cholesterol and utilization of several prebiotic substrates as a carbon source. Finally, the selected nine strains were identified by either L. rhamnosus or L. plantarum (4 strains for L. rhamnosus and 5 strains for L. plantarum, respectively). Taken together, we propose that the direct colonization of probiotics using C. elegans may be applicable to the rapid screening of valuable probiotic strains in vivo.

• Journal of Microbiology and Biotechnology
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• v.23 no.2
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• pp.225-236
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• 2013

Among several bacteria examined, an antibacterial-producing Lactobacillus strain with probiotic characteristics was selected and identified based on 16S rRNA gene sequencing. Subsequent purification and mode of action of the antibacterial compounds on target cells including E. coli were investigated. Maximum production of the antibacterial compound was recorded at 18 h incubation at $30^{\circ}C$. Interestingly, antibacterial activity remained unchanged after heating at $121^{\circ}C$ for 45 min, 24 h storage in temperature range of $70^{\circ}C$ to room temperature, and 15 min exposure to UV light, and it was stable in the pH of range 2-10. The active compounds were inactivated by proteolytic enzymes, indicating their proteinaceous nature, and, therefore, referred to as bacteriocin-like inhibitory substances. Isolation and partial purification of the effective agent was done by performing ammonium sulfate precipitation and gel filtration chromatography. The molecular mass of the GFC-purified active compound (~3 kDa) was determined by Tris-Tricine SDS-PAGE. To predict the mechanisms of action, transmission electron microscopy (TEM) analysis of ultrathin sections of E. coli before and after antibacterial treatment was carried out. TEM analysis of antibacterial compounds-treated E. coli demonstrated that the completely altered bacteria appear much darker compared with the less altered bacteria, suggesting a change in the cytoplasmic composition. There were also some membrane-bound convoluted structures visible within the completely altered bacteria, which could be attributed to the response of the E. coli to the treatment with the antibacterial compound. According to the in vivo experiments oral administration of L. plantarum HKN01 resulted in recovery of infected BALB/c mice with Salmonella enterica ser. Typhimurium.

• Journal of Microbiology and Biotechnology
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• v.23 no.2
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• pp.211-217
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• 2013

Corynebacterium glutamicum is one of the well-studied industrial strain that is used for the production of nucleotides and amino acids. Recently, it has also been studied as a possible producer of organic acids such as succinic acid, based on its ability to produce organic acids under an oxygen deprivation condition. In this study, we conducted the optimization of medium components for improved succinate production from C. glutamicum under an oxygen deprivation condition by Plackett-Burman design and applied a response surface methodology. A Plackett-Burman design for ten factors such as glucose, ammonium sulfate, magnesium sulfate, potassium phosphate ($K_2HPO_4$ and $KH_2PO_4$), iron sulfate, manganese sulfate, biotin, thiamine, and sodium bicarbonate was applied to evaluate the effects on succinate production. Glucose, ammonium sulfate, magnesium sulfate, and dipotassium phosphate were found to have significant influence on succinate production, and the optimal concentrations of these four factors were sequentially investigated by the response surface methodology using a Box-Behnken design. The optimal medium components obtained for achieving maximum concentration of succinic acid were as follows: glucose 10 g/l, magnesium sulfate 0.5 g/l, dipotassium phosphate ($K_2HPO_4$) 0.75 g/l, potassium dihydrogen phosphate ($KH_2PO_4$) 0.5 g/l, iron sulfate 6 mg/l, manganese sulfate 4.2 mg/l, biotin 0.2 mg/l, thiamine 0.2 mg/l, and sodium bicarbonate 100 mM. The parameters that differed from a normal BT medium were glucose changed from 40 g/l to 10 g/l, dipotassium phosphate ($K_2HPO_4$) 0.5 g/l changed to 0.75 g/l, and ammonium sulfate ($(NH_4)_2SO_4$) 7 g/l changed to 0 g/l. Under these conditions, the final succinic acid concentration was 16.3 mM, which is about 1.46 fold higher than the original medium (11.1 mM) at 24 h. This work showed the improvement of succinate production by a simple change of media components deduced from sequential optimization.

• Journal of Microbiology and Biotechnology
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• v.27 no.7
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• pp.1249-1256
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• 2017

In our search for new sources of bioactive secondary metabolites from Streptomyces sp., the ethyl acetate extracts from endophytic Streptomyces SUK 25 afforded five active diketopiperazine (DKP) compounds. The aim of this study was to characterize the bioactive compounds isolated from endophytic Streptomyces SUK 25 and evaluate their bioactivity against multiple drug resistance (MDR) bacteria such as Enterococcus raffinosus, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, and Enterobacter spp., and their cytotoxic activities against the human hepatoma (HepaRG) cell line. The production of secondary metabolites by this strain was optimized through Thornton's medium. Isolation, purification, and identification of the bioactive compounds were carried out using high-performance liquid chromatography, high-resolution mass liquid chromatography-mass spectrometry, Fourier transform infrared spectroscopy, and nuclear magnetic resonance, and cryopreserved HepaRG cells were selected to test the cytotoxicity. The results showed that endophytic Streptomyces SUK 25 produces four active DKP compounds and an acetamide derivative, which were elucidated as $cyclo-({\text\tiny{L}}-Val-{\text\tiny{L}}-Pro)$, $cyclo-({\text\tiny{L}}-Leu-{\text\tiny{L}}-Pro)$, $cyclo-({\text\tiny{L}}-Phe-{\text\tiny{L}}-Pro)$, $cyclo-({\text\tiny{L}}-Val-{\text\tiny{L}}-Phe)$, and N-(7-hydroxy-6-methyl-octyl)-acetamide. These active compounds exhibited activity against methicillin-resistant S. aureus ATCC 43300 and Enterococcus raffinosus, with low toxicity against human hepatoma HepaRG cells. Endophytic Streptomyces SUK 25 has the ability to produce DKP derivatives biologically active against some MDR bacteria with relatively low toxicity against HepaRG cells line.

• Journal of the Korean Society of Food Science and Nutrition
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• v.40 no.3
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• pp.466-469
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• 2011

The purpose of this study was to obtain the fatty acid composition and the antibacterial activity against pathogen of acne in various parts including seed, flesh and fruit from ripened black raspberry. In fatty acid analysis of lyophilized black raspberry, total fat of dried seed (11.047%) was much higher than in other parts. Moreover, linoleic acid (5.577%) and linolenic acid (2.317%) identified as the major fatty acids in the seed. By contrast, highest fatty acid of dried flesh was palmitic acid (0.323%) but it was remarkably low level compared with fatty acid composition of dried seed. Total polyphenol content in seed extract and flesh extract were 123.64 mg/g and 55.43 mg/g, respectively. DPPH radical scavenging ability of seed extract was higher than flesh and fruit extract. In antibacterial activity experiment against strains related acne such as Propionibacterium acne and Staphylococcus epidermidis, antibacterial activity of flesh extract was stronger than seed extract. However, seed extract showed antibacterial activity of 76.96~89.08% against each strain compared to activity of flesh extract. Based on these results, we concluded that seed of black raspberry can be useful in related field.