• Korean Journal of Materials Research
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• v.4 no.1
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• pp.9-23
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• 1994

Epitaxial $CoSi_2$ layer has been grown on NaCl(100) substrate at low deposition temperature($200^{\circ}C$) by multitarget bias cosputter deposition(MBCD). The phase sequence and crystallinity of deposited silicide as a function of deposition temperature and substrate bias voltage were studied by X-ray diffraction(XRD) and transmission electron microscopy(TEM) analysis. Crystalline Si was grown at $200^{\circ}C$ by metal induced crystallization(M1C) and self bias effect. In addition to, the MIC was analyzed both theoretically and experimentally. The observed phase sequence was $Co_2Si \to CoSi \to Cosi_2$ and was in good agreement with that predicted by effective heat of formation rule. The phase sequence, the CoSi(l11) preferred orientation, and the crystallinity had stronger dependence on the substrate bias voltage than the deposition temperature due to the collisional cascade mixing, the in-situ cleaning, and the increase in the number of nucleation sites by ion bombardment of growing surface. Grain growth induced by ion bombardment was observed with increasing substrate bias voltage at $200^{\circ}C$ and was interpreted with ion bombardment dissociation model. The parameters of $E_{Ar}\;and \alpha(V_s)$ were chosen to properly quantify the ion bombardment effect on the variation in crystallinty at $200^{\circ}C$ with increasing substrate bias voltage using Langmuir probe.

• Korean Journal of Microbiology
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• v.47 no.1
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• pp.14-21
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• 2011

Riboflavin synthase catalyzes the formation of one molecule of each riboflavin and 5-amino-6-ribitylamino-2,4-pyrimidinedione by the transfer of a 4-carbon moiety between two molecules of the substrates, 6,7-dimetyl-8-ribityllumazine. The most remarkable feature is the sequence similarity between the N-terminal half (1-97) and the C-terminal half domain (99-213). To investigate the structure and fluorescent characteristics of the N-terminal half of riboflavin synthase (N-RS) in Escherichia coli, more than 10 mutant genes coding for the mutated N-terminal domain of riboflavin synthase were generated by polymerase chain reaction. The genes coding for the proteins were inserted into pQE vector designed for easy purification of protein by 6X-His tagging system, expressed, and the proteins were purified. Almost all mutated N-terminal domain of riboflavin synthases bind to 6,7-dimethyl-8-ribityllumazine and riboflavin as fluorescent ligands. However, N-RS C47D and N-RS ET66,67DQ mutant proteins show colorless, indicating that fluorescent ligands were dissociated during purification. In addition, most mutated proteins show low fluorescent intensity comparing to N-RS wild type, whereas N-RS C48S posses stronger fluorescent intensity than that of wild type protein. Based on this result, N-RS C48S can be used as the tool for high throughput screening system for searching for the compound with inhibitory effect for the riboflavin synthase.

• Biomedical Science Letters
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• v.6 no.3
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• pp.201-208
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• 2000

The vancomycin, one of the family of glycopeptide antibiotics, inhibits the synthesis of bacterial cell wall peptidoglycan and has been widely used against gram-positive bacterial infections, especially for a treatment of methicillin resistant S. aureus infection. However, clinical isolate which was intermediately resistant to vancomycin (Mu50: MIC 8 $\mu\textrm{g}$/ml) was isolated in recent years. In this study we performed vancomycin susceptibility test with the increment method and population analysis with clinical isolates S. aureus. Also we did several kinds of tests with three selected isolates (s129: MIC 7 $\mu\textrm{g}$/ml, s134: MIC 7 $\mu\textrm{g}$/ml, s135: MIC 8 $\mu\textrm{g}$/ml) to find out possible mechanism of vancomycin resistance. As a result, the prevalence of vancomycin resistant S. aureus isolates among S. aureus strains resistant to methicillin was 23.3% (25/107). The vancomycin resistances of isolated strains of S. aureus were between those of Mu5O and Mu3 strains. By PCR analysis, none of the isolates with decreased vancomycin susceptibility contained known vancomycin resistant genes such as vanA, vanB, vanC1, vanC2, and vanH. Major bands of 81 kDa, 58 kDa, 33 kDa, 28 kDa were demonstrable in whole cell lysates by SDS-PAGE from all three isolates as well as reference strains. And especially,45 kDa protein was overproduced in Mu50 strains. Among them increased production of NAD$^{+}$-linked-$_{D}$-lactate dehydrogenase (dnLDH) were detected from one clinical strain (s135) and Mu5O strain. From these data, we suggest that the mechanism of vancomycin resistance in these isolates are distinct from that in enterococci.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.4
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• pp.531-538
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• 2009

Xylitol has the ability to reduce the adherence of Streptococcus mutans(S. mutans), which can make it easier to remove plaque, decrease acid production and inhibit dental caries. There are few reports on the effects of xylitol on the expression of the virulence related genes in S. mutans. This study examined the inhibitory effect of chewing gum containing xylitol on glucan synthesis related gene expression of S. mutans. Participants were voluntarily recruited for a women's oral health prevention program, classified into two groups(a control and a xylitol group), and then followed for 2 years. Twenty salivary samples were randomly selected from each group. Colony count and real-time reverse transcription polymerase chain reaction were used to analyze the characteristics of S. mutans. The following results were obtained: The S. mutans counts decreased steadily in the xylitol group over the study period(p<0.05). The expression of the virulence related genes (gtfB, gtfC and gtfD) was significantly lower in the xylitol group than in the control groups (p<0.05). In conclusion, these results suggest that chewing xylitol gum for a long period of time may reduce the expression of the genes associated with S. mutans virulence, which can result in a decrease growth of S. mutans colonies as a result.

• Korean Journal of Microbiology
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• v.48 no.1
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• pp.52-56
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• 2012

The aim of this study was to evaluate the antimicrobial effect of carvacrol against periodontopathic and cariogenic bacteria and its cytotoxicity in human oral tissue cells. We tested their antibacterial properties against mutans streptococci and five major periodontopathic bacterial species involved in periodontal disease. The antimicrobial activity was evaluated by the minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The cell viability of carvacrol on normal human gingival fibroblast (NHGF) cells was tested by metyl thiazolyl tetrazolium assay. The data showed that carvacrol had remarkable antimicrobial effect on tested bacteria with a MIC and MBC values ranged from 16 to $128{\mu}g/ml$ and from 32 to $128{\mu}g/ml$, respectively. In cell toxicity studies, carvacrol had significantly decreased cell viability when NHGF cells were treated at $128{\mu}g/ml$. These findings suggest that carvacrol has a strong antimicrobial activity against periodontopathic and cariogenic bacteria. However, in order to use it as a component of gargling solution or toothpaste, its concentration should be below $64{\mu}g/ml$ and other compounds having an antimicrobial activity against periodontopathic and cariogenic bacteria should be used together.

• Korean Journal of Clinical Laboratory Science
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• v.49 no.4
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• pp.345-349
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• 2017

Diabetes mellitus is associated with a variety of adverse health outcomes, including metabolic syndrome and cardiovascular diseases. Recently, diabetes has been receiving increased scientific attention because of the rapid increase in the diabetic population. One of the features of type-2 diabetes mellitus is an elevated glucose level in blood. Fasting glucose level, which is the most basic test, is widely used as a diagnostic indicator of diabetes. Several previous studies reported that TLR4 expression is relatively high in the heart. However, few studies have investigated the association between TLR4 variants and fasting blood glucose to date. Thus, this study tested the association between single nucleotide polymorphisms (SNPs) in the TLR4 gene and fasting glucose in the Korean population. A total of 994 subjects recruited from Seoul were used for the present study. When compared to fasting blood glucose, the TLR4 gene region was shown as a linkage disequilibrium owing to the relatively large gene range. This region also presented as several LD blocks. We found that specific SNPs in the TLR4 gene were associated with the mean fasting glucose (p<0.01). The minor allele frequency of rs1329067 was 16.4%, and individuals with the AA genotype had a higher fasting blood glucose level than those with the GG genotype, suggesting that genetic variants in TLR4 influence glucose levels in Korean adults.

• Korean Journal of Clinical Laboratory Science
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• v.49 no.4
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• pp.323-328
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• 2017

Angiogenesis is a process including members of the angiogenic factors. In particular, fibroblast growth factor 2 (FGF2) is considered the most potent angiogenic factor because it promotes cell proliferation and tube formation. A recent study reported that fucoidan derived from marine plant potentiated FGF-2 induced tube formation in human endothelial cells. On the other hand, the molecular mechanisms involved in the angiogenic activity of fucoidan and FGF2 are unknown. In this study, a fucoidan treatment promoted angiogenesis induced by FGF2. The effects of fucoidan on FGF2-induced angiogenesis were confirmed by a proliferation assay using a CellTiter96 Aqueous One solution after a treatment with fucoidan and FGF2. The tube formation and wound healing assay for the angiogenic activity were also confirmed. Reverse transcription PCR showed a change in the mRNA of vascular endothelial growth factor-A (VEGF-A), intercellular adhesion molecule-1 (ICAM-1), matrix metallopeptidase9 (MMP9), and the signal transducer and activator of transcription3 (STAT3). In summary, the Fucoidan/FGF2 treatment induced an increase in cell proliferation, improved the tube formation and wound healing activity, and altered the STAT3, VEGF-A, ICAM-1, and MMP9 mRNA expression levels. Further research will be needed to provide a scientific explanation in terms of cell-signaling and confirm the present findings.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.299-309
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• 2014

HSA800 is a new high strength steel (HSS) plate for building structures developed by POSCO and RIST in 2011. It has upper and lower bounds for yield ($F_y$) and tensile ($F_u$) strength as of 650-770MPa and 800-950MPa, respectively, with yield ratio ($F_y/F_u$) limit as of 0.85 which make steel quality more reliable and enhance the seismic resistance of structures. As made by TMCP, it has a good weldability without increasing carbon percentage. The objective of this study is to provide alternative design of mega-structural members of the Lotte World Tower (555m, 123 story), a first super-tall building in Korea, using HSS considering structural safety, constructability, and cost-effectiveness. Steel outrigger trusses, belt-trusses and steel exterior columns were selected and analyzed to evaluate the structural performance between original and alternative designs using HSS. The results show that HSS can be applied to the members which do not affect lateral stiffness of a building and, in this study, approximately 1100tons of steel were saved. It implies that HSS can save overall construction costs - manufacturing, delivery, and erection costs - by reducing mega structural member size. HSA800 was very first applied to the Lotte World Tower based on the results of this study.

• Journal of Life Science
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• v.25 no.6
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• pp.715-723
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• 2015

Insects represent the largest class within the animal kingdom in terms of species number. Humans had been utilized insect in the broad area, including food, agriculture, industry, pharmaceuticals and so on. At present, insects are emerging as a leading group for identifying and extracting novel bioactive substances due to enormous number and a high nutritional value. Insects rely on a suite of systemic response to resist infection such as immune cells, hemocytes, activation of enzymes cascades, and antimicrobial peptide/protein. Among the substances, antimicrobial peptides (AMPs) are main components of potent antimircrobial innate defense system into the insect hemolymph. AMPs raise influential candidate as avenue to resolve the development of antibiotic-resistant microbial organism. Insect AMPs are classified into four main classes: cecropins, insect defensins, glycine/proline-rich peptides. Insect AMPs have been purified, over 150. In this review, AMPs derived from several insects were summarized including honey bee, dung beetle, butterfly and longicorn beetle. These peptides almost exhibited potent antimicrobial activities against human microbial pathogens without causing remarkable hemolysis to erythrocytes excluding melittin, and their mode of action(s) are based on disruption of the plasma membrane or fungal apoptosis. Therefore, study of insect AMPs is expected to be useful for designing novel therapeutic antimicrobial applications.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.311-352
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• 1996

Peltier 효과를 이용한 열전소자는 열응담 감도가 좋고 선택적 냉각이 가능하며 무소음, 무진동 및 소형화의 장점으로 각종 전자부품의 국부냉각소자로 응용되고 있다. 또한 최근 냉매의 사용없이 냉각이 가능한 열전재료를 이용한 자동차나 가정용 에어컨 및 냉장고 등의 각종 냉방시스템의 개발도 크게 주목을 받고 있다. 기존의 Bi2Te3계 단결정 열전재료는 성능지수는 우수하나, 기계적 취약성에 기인하여 소자가공시 수율 저하가 가장 큰 문제점으로 지적되고 있다. 이와 같은 문제점을 해결하기 위해 최근 단결정에 비해 기계적 강도가 우수한 다결정 열전재료의 제조공정에 관한 연구가 활발히 이루어지고 있으며, 그 일환으로 기계적 합금화법을 이용한 열전재료의 제조공정이 연구되고 있다. 원료금속이 고 에너지 볼-밀 내에서의 연쇄적인 파괴와 압접에 의해 합금분말로 변화되는 기계적 합금화 공정은 상온공정으로 이를 사용하여 다결정 열전재료를 제조시 기존의 다결정 열전재료의 제조공정인 "용해 및 분쇄법'과 비교하여 제조단가를 낮출 수 있는 장점이 있다. 본 연구에서는 전자냉각소자용 열전재료로서 상온부근에서 성능지수가 가장 우수한 p형 (Bi,Sb)2Te3 및 n형 Bi2(Te,Se)3 합금분말을 기계적 합금화 공정으로 제조하여 분말 특성을 분석하였으며, 가압소결 후 열전특성의 변화거동을 연구하였다. 순도 99.99% 이상인 Bi, Sb, Te, Se granule을 (Bi1-xSbx)2Te3 및 Bi2(Te1-ySey)3 조성에 맞게 칭량하여 불과 분말의 무게비 5:1로 강구와 함께 공구강 vial에 장입 후, Spex mixer/mill을 이용하여 기계적 합금화 하였다. 기계적 합금화 공정으로 제조한 분말에 대한 X-선 회절분석과 시차 열분석으로 합금화 정도를 분석하였다. (Bi1-xSbx)2Te3 및 Bi2(Te1-ySey)3 합금분말을 10-5 torr의 진공중에서 300℃∼550℃의 온도로 30분간 가압소결하였다. 가압소결체의 파단면에서의 미세구조를 주사전자현미경으로 관찰하였으며, 상온에서 가압소결체의 열전특성을 측정하였다. (Bi1-xSbx)2Te3의 기계적 합금화에 요구되는 공정시간은 Sb2Te3 함량에 따라 증가하여 x=0.5 조성에서는 4 시간 45분, x=0.75 조성에서는 5 시간, x=1 조성에서는 6 시간 45분의 vibro 밀링이 요구되었다. n형 Bi2(Te1-ySey)3 합금분말의 제조에 요구되는 밀링시간 역시 Bi2Se3 함량 증가에 따라 증가하였으며 Bi2(Te0.95Se0.05)3 합금분말의 제조에는 2시간, Bi2(Te0.9Se0.1)3 및 Bi2(Te0.85Se0.15)3 합금분말의 형성에는 3시간의 bivro 밀링이 요구되었다. 기계적 합금화로 제조한 p형 (Bi0.2Sb0.8)2Te3 및 n형 Bi2(Te0.9Se0.1)3 가압 소결체는 각기 2.9x10-3/K 및 2.1x10-3/K 의 우수한 성능지수를 나타내었다.