노치재의 균열닫힘현상과 피로균열성장거동에 관한 연구

우홍식,한지원 東國大學校 1993 東國論叢 Vol.32 No.-

Crack length and closure are monitored simultaneously and countinuously in terms of the testing by a PC-aided unloading elastic compliance technique. The relation between the crack opening stress intensity factor and crack length is determined from the experimental results. The crack opening stress intensity factor of short cracks, K_op, can be predicted from the crack opening stress intensity factor of near threshold of long crack, K_op.L. The growth rate of short cracks at notch root can be predicted from the crack opening stress intensity factor of short cracks, K_op, and the growth equation of long cracks in region Ⅱ.

부식환경에서의 용접재의 피로균열성장거동에 관한 연구

우홍식 동국대학교 경주대학 1993 東國論集 Vol.12 No.-

The objective of this paper is to investigate the effect of residual stress on the fatigue crack growth behavior in corrosion environments. For this purpose, transverse butt submerged arc welding was performed on SM50A steel plate and CT(compact tension) specimens which loading directions are perpendicular to weld bead were selected. And the environments under which the experiments performed were in air, in pure water and 3.5% NaCl solution. From the experimental results and discussin, in region I, the value of ΔK_th, CF in pure water in similiar to that of 3.5% NaCl solution but they are about 1.6-2.1 times that of air environment. In region Ⅱ, also the fatigue crack growth behavior in pure water is similiar to that of 3.5% NaCl solution. But their behaviors were slower than that of air environment. So it is assumed that the fatigue crack growth behavior was affected by more crack closure phenomenon due to corrosion products than the residual stress.

이축연신폴리프로필렌 필름의 Co^(60)-γ선 조사에 따른 전기전도 특성 변화

류부형,우흥식 동국대학교 경주대학 1996 東國論集 Vol.15 No.-

In order to investigate the CO60-γray irradiation effects on DC electrical conduction characteristics of the biaxially-oriented polypropylene(OPP) films, DC current on the 15㎛ thick OPP films before and after irradiation were observed in the temterature range of 25~55℃ and in the electric field of 10 ~250MV/m. The electrical conduction characteristics of OPP films were devided into the four regions having different mechanisms as the hopping, space charge limiting, Schottky emission and Fowler-Nordheim's tunneling effects with the increase of the electric field. The conduction current through the OPP film were concluded as the ohmic current on the fields below 55MV/m, the space charge limited current(SCLC) on the field range from 55 to 90MV/m, the Schottky current on the mid fields from 90 to 175MV/m and the tunneling current on the high fields above 175MV/m. The conduction current on the all regions increases in proportion to the increase of the irradiated dose and temperature, but the transition points from ohmic current to SCLC and from Schottky current to tunneling current are shifted towared a lower field as the irradiated dose and temperature increase. The crystallinity of OPP film increased with increase of the irradiated dose, which caused the boundary fields of conduction regions to shift toward a higher fields.

CORBA 기반의 Application Service System을 위한 부하 공유 서비스의 설계 및 구현

임주혁,박세명,강흥식 인제대학교 2001 仁濟論叢 Vol.16 No.1

근간 분산된 객체에 대한 부하분산의 목적으로 OMG의 CORBA를 많이 이용하고 있지만 CORBA의 일반적인 기본 서비스는 특정 시스템에서 최적의 기능을 발휘하지 못한다. 이에 본 논문에서는 화상 회의를 하는 특정 시스템의 분산된 이미지 처리 객체(IPO)에 대해 CORBA를 기반으로 하여 어떻게 작업 반환 시간을 최소화 할 수 있는가에 대한 방법을 제시하였다. 이는 동일한 처리를 하는 IPO가 여러 개 존재할 경우 어떤 IPO를 선택하여 이미지 처리를 시키는 것이 가장 적합한지에 대한 것이다. 즉, Client의 이미지 처리 요청이 있을 때 Object Manager는 작업 반환 시간을 최소화 할 수 있는 IPO를 선택하여 작업을 의뢰하기 위해 Object Manager는 IPO가 탑재된 머신의 하드웨어적 성능, 실행되고 있는 IPO의 개수, 해당 IPO가 현재 처리 가능한지의 여부 그리고 처리할 이미지와 처리 후의 이미지의 크기를 고려하여 최적의 성능을 낼 수 있는 IPO를 선택하였다. 결과적으로, IPO의 상태를 고려한 경우가 CORBA의 기본 기능만을 사용한 경우보다 작업 반환 시간에 대해 9∼22% 정도 성능이 개선되었다. Recently, CORBA by OMG is widely adopted as a middleware for constructing distributed object system, but the basic services on CORBA do not appropriate for the operations on a specific distributed object system. particularly in managing the distributed image processing objects on MICS(Medical-Image Conference System). In this paper, We propose and implemented Object Manager with the load distributing policy for CORBA-based MICS to minimize the response time for a particular image processing requests. Object Manager collects and manages the informations such as the processing speed on a particular system, number of IPOs currently executing on a particular system, availability of IPO, and the size of image being requested to be processed, and returns most appropriate IPO with the minimum job response time expected on a given image. We showed with experiments that the improved MICS with the proposed Object Manager has much more shorter job response time about 9 ∼ 22 % than the system using CORBA basic services.

Anticandidal Effect of Polygonum cuspidatum on C. albicans Biofilm Formation

Heung-Shick Lee,Younhee Kim 한의병리학회 2012 동의생리병리학회지 Vol.26 No.1

Aucklandia lappa Causes Cell Wall Damage in Candida albicans by Reducing Chitin and (1,3)-β-D-Glucan

( Heung-shick Lee ),( Younhee Kim ) 한국미생물 · 생명공학회 2020 Journal of microbiology and biotechnology Vol.30 No.7

The fungal cell wall is a major target of antifungals. In this study, we report the antifungal activity of an ethanol extract from Aucklandia lappa against Candida albicans. We found that the extract caused cell wall injury by decreasing chitin synthesis or assembly and (1,3)-β-D-glucan synthesis. A sorbitol protection assay demonstrated that the minimum inhibitory concentration (MIC) of the A. lappa extract against C. albicans cells increased eight-fold from 0.78 to 6.24 mg/ml in 72 h. Cell aggregates, which indicate damage to the cell wall or membrane, were commonly observed in the A. lappatreated C. albicans cells through microscopic analysis. In addition, the relative fluorescence intensities of the C. albicans cells incubated with the A. lappa extract for 3, 5, and 6 h were 92.1, 84.6, and 79.8%, respectively, compared to the controls, estimated by Calcofluor White binding assay. This result indicates that chitin content was reduced by the A. lappa treatment. Furthermore, synthesis of (1,3)-β-D-glucan polymers was inhibited to 84.3, 79.7, and 70.2% of that of the control treatment following incubation of C. albicans microsomes with the A. lappa extract at a final concentration equal to its MIC, 2× MIC, and 4× MIC, respectively. These findings suggest that the A. lappa ethanol extract may aid the development of a new antifungal to successfully control Candidaassociated disease.

In Vitro Proliferation Model of Helicobacter pylori Required for Large - Scale Cultivation

(Heung Il Oh),(Heung Shick Lee),(Kyung Hyun Kim),(Se Hwang Paek) 한국미생물생명공학회 2000 Journal of microbiology and biotechnology Vol.10 No.3

N/A N/A

Aucklandia lappa Causes Membrane Permeation of Candida albicans

( Heung-shick Lee ),( Younhee Kim ) 한국미생물생명공학회(구 한국산업미생물학회) 2020 Journal of microbiology and biotechnology Vol.30 No.12

Candida albicans is a major fungal pathogen in humans. In our previous study, we reported that an ethanol extract from Aucklandia lappa weakens C. albicans cell wall by inhibiting synthesis or assembly of both (1,3)-β-D-glucan polymers and chitin. In the current study, we found that the extract is involved in permeabilization of C. albicans cell membranes. While uptake of ethidium bromide (EtBr) was 3.0% in control cells, it increased to 7.4% for 30 min in the presence of the A. lappa ethanol extract at its minimal inhibitory concentration (MIC), 0.78 mg/ml, compared to uptake by heat-killed cells. Besides, leakage of DNA and proteins was observed in A. lappa-treated C. albicans cells. The increased uptake of EtBr and leakage of cellular materials suggest that A. lappa ethanol extract induced functional changes in C. albicans cell membranes. Incorporation of diphenylhexatriene (DPH) into membranes in the A. lappa-treated C. albicans cells at its MIC decreased to 84.8%, after 60 min of incubation, compared with that of the controls, indicate that there was a change in membrane dynamics. Moreover, the anticandidal effect of the A. lappa ethanol extract was enhanced at a growth temperature of 40°C compared to that at 35°C. The above data suggest that the antifungal activity of the A. lappa ethanol extract against C. albicans is associated with synergistic action of membrane permeabilization due to changes in membrane dynamics and cell wall damage caused by reduced formation of (1,3)-β-D-glucan and chitin.

Development of Candida albicans Biofilms Is Diminished by Paeonia lactiflora via Obstruction of Cell Adhesion and Cell Lysis

( Heung-shick Lee ),( Younhee Kim ) 한국미생물생명공학회(구 한국산업미생물학회) 2018 Journal of microbiology and biotechnology Vol.28 No.3

Candida albicans infections are often problematic to treat owing to antifungal resistance, as such infections are mostly associated with biofilms. The ability of C. albicans to switch from a budding yeast to filamentous hyphae and to adhere to host cells or various surfaces supports biofilm formation. Previously, the ethanol extract from Paeonia lactiflora was reported to inhibit cell wall synthesis and cause depolarization and permeabilization of the cell membrane in C. albicans. In this study, the P. lactiflora extract was found to significantly reduce the initial stage of C. albicans biofilms from 12 clinical isolates by 38.4%. Thus, to assess the action mechanism, the effect of the P. lactiflora extract on the adhesion of C. albicans cells to polystyrene and germ tube formation was investigated using a microscopic analysis. The density of the adherent cells was diminished following incubation with the P. lactiflora extract in an acidic medium. Additionally, the P. lactiflora-treated C. albicans cells were mostly composed of less virulent pseudohyphae, and ruptured debris was found in the serumcontaining medium. A quantitative real-time PCR analysis indicated that P. lactiflora downregulated the expression of C. albicans hypha-specific genes: ALS3 by 65% (p = 0.004), ECE1 by 34.9% (p = 0.001), HWP1 by 29.2% (p = 0.002), and SAP1 by 37.5% (p = 0.001), matching the microscopic analysis of the P. lactiflora action on biofilm formation. Therefore, the current findings demonstrate that the P. lactiflora ethanol extract is effective in inhibiting C. albicans biofilms in vitro, suggesting its therapeutic potential for the treatment of biofilmassociated infections.

Paeonia lactiflora Inhibits Cell Wall Synthesis and Triggers Membrane Depolarization in Candida albicans

( Heung-shick Lee ),( Younhee Kim ) 한국미생물 · 생명공학회 2017 Journal of microbiology and biotechnology Vol.27 No.2

Fungal cell walls and cell membranes are the main targets of antifungals. In this study, we report on the antifungal activity of an ethanol extract from Paeonia lactiflora against Candida albicans, showing that the antifungal activity is associated with the synergistic actions of preventing cell wall synthesis, enabling membrane depolarization, and compromising permeability. First, it was shown that the ethanol extract from P. lactiflora was involved in damaging the integrity of cell walls in C. albicans. In isotonic media, cell bursts of C. albicans by the P. lactiflora ethanol extract could be restored, and the minimum inhibitory concentration (MIC) of the P. lactiflora ethanol extract against C. albicans cells increased 4-fold. In addition, synthesis of (1,3)-β-D-glucan polymer was inhibited by 87% and 83% following treatment of C. albicans microsomes with the P. lactiflora ethanol extract at their 1× MIC and 2× MIC, respectively. Second, the ethanol extract from P. lactiflora influenced the function of C. albicans cell membranes. C. albicans cells treated with the P. lactiflora ethanol extract formed red aggregates by staining with a membrane-impermeable dye, propidium iodide. Membrane depolarization manifested as increased fluorescence intensity by staining P. lactiflora-treated C. albicans cells with a membrane-potential marker, DiBAC4(3) ((bis-1,3-dibutylbarbituric acid) trimethine oxonol). Membrane permeability was assessed by crystal violet assay, and C. albicans cells treated with the P. lactiflora ethanol extract exhibited significant uptake of crystal violet in a concentration-dependent manner. The findings suggest that P. lactiflora ethanol extract is a viable and effective candidate for the development of new antifungal agents to treat Candida-associated diseases.