• BMB Reports
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• 제31권3호
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• pp.254-257
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• 1998

The gshI gene from the Escherichia coli K-12 strain codes for ${\gamma}-glutamylcysteine$ synthetase which mediates the rate-limiting step of glutathione biosynthesis. The isolated gshI gene from E. coli K-12 has an unusual translation initiation codon, UUG. The 494th amino acid is Ala rather than Gly which was found in a mutant strain E. coli B. In order to improve the translational rate of the gshI gene of E. coli K-12, the initiation codon, UUG, was changed to the usual AUG codon by the site-specific mutagenesis. This change has resulted in a 53% increase of ${\gamma}-glutamylcysteine$ synthetase activity. The enzyme activity was also improved by replacing $Ala^{494}$ with Val (A494V) or Leu (A494L). The replacement of $Ser^{495}$ with Thr (S495T) also resulted in a 62% increase of the enzyme activity. Therefore, the specific activity of ${\gamma}-glutamylcysteine$ synthetase was increased with the increasing chain length of the aliphathic amino acid at the site of the 494th amino acid (Ala<$Val{\leq}Leu$).

• 한국결정학회지
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• 제5권1호
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• pp.20-23
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• 1994

대장균의 IciA 단백질은 DnaA 단백질의 작용장소에 결합하여 DNA의 복제가 개시되는 것을 막는다. 따라 서 IciA단백질은 세포주기의 주요 단계에서 결정적인 역할을 한다. 이러한 IciA 단백질의 구조와 기능간의 관 계를 연구하기 위하여 X-선 결정학을 이용하여 삼차원 구조를 결정하고자 한다. 그 첫 단계로 IciA단백질 결정화를 시도하였다. sodium formate를 침전제로 이용하여 결정을 얻을 수 있었다.

• 대한기계학회논문집
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• 제19권3호
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• pp.688-696
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• 1995

Cemented carbides, best known for their superior mechanical properties such as high strength, high hardness and high wear resistance, have a wide range of industrial applications including metal working tools, mining tools, and wear resistance components. The cobalt has been used as a binder in the WC-based hard composites due to its outstanding wetting and adhesion characteristics even though its expensiveness. Therefore many studies attempted to find a better substitute for cobalt as binder to decrease production costs. This investigation is a pre-step to study dynamic fracture characteristic evaluation of a WC-Co hardmetal were evaluated by using the instrumented Charpy impact testing procedures. It was found that the dynamic characteristics of used strain amplifier were very important experimental factors to extract valid dynamic fracturing data in WC-Co specimens. It was suggested by showing some experimental examples that when we wished to evaluate dynamic fracture toughness for cemented carbide composites by using the instrumented Charpy impact testing procedure, a careful attention must be given to obtain valid results.

• 한국해양공학회지
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• 제4권1호
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• pp.88-100
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• 1990

Among the test methods to evaluate stress-corrosion cracking(SCC) on the basis of fracture mechanics, constant displacement(bolt) loading method using modified-WOL specimen is practically convenient. In this test method, compliance formula is generally required to calculate load(consequently $K_{ISCC}$). There are many problems in using the analytic compliance formula to calculate $K_{ISCC}$, so we had proposed the experimental $K_{ISCC}$ evaluation technique in the previous report. This study has employed the slightly altered configuration of modified-WOL specimen made of weldable structural stee(BS360-50D). With these specimens, stress-corrosion tests have been performed in $H_2S$ gas saturated 20% HCl solution. Through the test, the problems as mentioned earlier have been discussed again, and the proposed evaluation technique has been verified. And the stress-corrosion cracks and hydrogen blisters have been investigated in the initiation step with the aids of metallurgical micrographs, SEM fractographs, and EPMA analysis. The inclusions segregated in the mid-thickness region traps hydrogen to produce the hydrogen blistering. The applied or residual stress does not contribute the occurrence of the blister. Hydrogen absorbed into the mid-thickness region is consumed to produce the blistering so that stress-corrosion crack could hardly be detected at that region. The stress-corrosion cracks initiate from the inclusions and propagate in radial pattern. And the initiation site is remote from the crack tip and is inclined from the crack plane, which is assumed to be caused by the triaxial stress and the amount of the absorbed hydrogen.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.244-251
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• 2003

A two-dimensional BEM code, $FRACOD^{2D}$, was applied to simulate fracture initiation and propagation processes in a rock pillar during an in situ heater test of a rock pillar planned at the $\"{A}sp\"{o}$ Underground Rock laboratory of SKB, in Southern Sweden. To take the advantage of conventional BEM for simulating fracturing processes, but without efforts for domain integral transformation, a hybrid approach is developed to simulate the fracturing processes in rock pillar under coupled thermo-mechanical loading. The code FRACOD was used for simulating the fracture initiation and propagation processes with its boundary tractions reflecting the effects of the initial and redistributed thermomechanical stresses in the domain of interest at multiple excavation and heating steps were produced by a special algorithm of stress inversion, based on resultant thermo-mechanical stress fields at each excavation and heat loading step by a FEM code without considering fracturing processes. This hybrid approach can take the advantages of both types of numerical methods and avoids their shortcomings for fracturing process simulation and domain effects, respectively. In this paper, we present the hybrid approach for the stress, displacements, and fracturing processes at sequential excavation and heating steps of the in situ heater test as a predictive modelling, the formulation of the fracturing models and the predictive results. Two sections of borehole depth, 0.5 m and 1.5 m below the tunnel floor are considered. The pillar area is modelled with the FRACOD and the stress field produced by excavation and heating is transferred with corresponding boundary stresses. From the modelling results, the degree of fracturing and damage are evaluated for 120 days of heating. Dominated shear fracturing in the vicinity of the central pillar was observed from the models at both sections, but spalled area appears to be limited. Based on the modelling results, a sensitivity study for the effect of pre-existing fractures in the vicinity of the holes is also conducted, and the initiation and evolution of EDZ around the deposition holes are investigated using this particular numerical technique.

• 대한기계학회논문집
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• 제16권8호
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• pp.1519-1529
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• 1992

본 연구에서는 단열 전단 밴드의 특성 규명을 위하여 특별히 고안된 계단 형 상 시편(stepped specimen)의 수치해석을 통하여 단열 전단 밴드의 형성과 성장(init- iation and growth of adiabatic shear band)에 관한 체계적 해석을 시도해 보았다. 금번 논문에서는 우선 격자 크기(mesh size)와 충격 속도(impact velocity)가 단열 전 단 밴드의 형성 및 성장에 미치는 영향과 제반 특성을 규명할 계획이며 차후 재료의 기하학적 형상 등이 단열 전단 밴드의 형성 및 성장에 미치는 영향에 대해서도 단계적 연구를 시도할 계획이다. 해석을 위하여 가공경화효과, 변형률 속도 경화효과(stra- in rate hardening effect), 열적연화효과 등을 고려할 수 있는 구성 방정식(constit- utive equation)을 갖춘 엑스플리시트 시간적분 유한요소 코드(explicit time integr- ation finite element code)를 사용하였으며 기존의 연구 결과와는 달리 어떠한 인위 적 결함도 해석에 사용하지 않았다.

• 한국지반공학회논문집
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• 제34권12호
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• pp.29-42
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• 2018

대구경북지역 셰일 및 이암은 다른 암석에 비해 강도가 낮고 풍화에 약하므로 이러한 암석의 포화상태나 균열 발달 정도가 강도에 미치는 영향에 대해 분석할 필요가 있다. 이에 본 연구에서는 대구경북지역 토목공사 현장에서 셰일 및 이암을 채취한 다음 흡수율, SEM, 화학성분, 내구성시험과 같은 기본 물성시험을 실시하였으며, 셰일에 비해 이암의 공극률(흡수율)은 31%(25%) 정도로 6(8)배 정도 높은 값을 보였다. 물에 쉽게 풀리는 이암의 경우 활성도가 높은 스멕타이트 군의 점토광물이 많이 포함되어 있는 것으로 나타났다. 채취한 암석을 소형 정육면체로 가공한 다음 일축압축시험을 실시하여 암석의 건조 및 포화 상태에 따른 일축압축강도를 비교하였다. 또한, 전자레인지를 이용하여 암석 공극 내 물을 가열시켜 내부에서 균열이 발생하도록 유도하였으며, 작동시간을 달리하여 내부 균열의 발생 정도에 따른 강도를 비교하였다. 건조된 셰일과 이암의 일축압축강도는 평균 62MPa, 11MPa이며, 이를 포화시키면 일축압축강도는 셰일은 평균 33MPa, 이암은 4MPa로 47% 및 64% 정도 감소하였다. 전자레인지로 15초 작동시켜 균열을 유발할 경우 포화 상태보다 셰일은 49%, 이암은 52% 정도 강도가 감소하였다. 20초 정도 작동 시 대부분의 암석이 여러 조각으로 파쇄되었으며, 이때 소형 암석 내부의 온도는 200도 정도였다.

• Annals of Rehabilitation Medicine
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• 제39권6호
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• pp.897-904
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• 2015

Objective To investigate differences in plantar pressure distribution between a normal gait and unpredictable slip events to predict the initiation of the slipping process. Methods Eleven male participants were enrolled. Subjects walked onto a wooden tile, and two layers of oily vinyl sheet were placed on the expected spot of the 4th step to induce a slip. An insole pressure-measuring system was used to monitor plantar pressure distribution. This system measured plantar pressure in four regions (the toes, metatarsal head, arch, and heel) for three events: the step during normal gait; the recovered step, when the subject recovered from a slip; and the uncorrected, harmful slipped step. Four variables were analyzed: peak pressure (PP), contact time (CT), the pressure-time integral (PTI), and the instant of peak pressure (IPP). Results The plantar pressure pattern in the heel was unique, as compared with other parts of the sole. In the heel, PP, CT, and PTI values were high in slipped and recovered steps compared with normal steps. The IPP differed markedly among the three steps. The IPPs in the heel for the three events were, in descending order (from latest to earliest), slipped, recovered, and normal steps, whereas in the other regions the order was normal, recovered, and slipped steps. Finally, the metatarsal head-to-heel IPP ratios for the normal, recovered, and slipped steps were $6.1{\pm}2.9$, $3.1{\pm}3.0$, and $2.2{\pm}2.5$, respectively. Conclusion A distinctive plantar pressure pattern in the heel might be useful for early detection of a slip event to prevent slip-related injuries.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.269-273
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• 2003

There is a growing interest to replace the commercial steels with non-heat treated steels, which does not involve the spheroidization and quenching-tempering treatment. However, Non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, Dual-Phase Steels were studied as candidate materials for non-heat treated steels, which have different martensite morphologies and volume fractions obtained through heat-treatment of intercritical quenching (IcQ), intermediate quenching (ImQ) and step quenching (SQ). The mechanical properties of DP steels were measured by tension and compression tests. Also, the cold formability of three DP steels which have similar tensile strength value was investigated by estimating the deformation resistance and the forming limit. The deformation resistance which is important factor in determining die life was estimated by calculating the deformation energy. And the forming limit was estimated by measuring the critical strain revealing crack initiation at the notch tip of the specimens.

• Journal of Electrical Engineering and Technology
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• 제10권6호
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• pp.2376-2383
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• 2015

Assistance of the operator’s walking ability while carrying a load is a challenging area in lower limb exoskeletons. We implement an exoskeleton called the Unmanned Technology Research Center Exoskeleton (UTRCEXO), which enables the operator to walk with a load more comfortably. The UTRCEXO makes use of two types of DC motor to assist the hip and knee joints. The UTRCEXO detects the operator’s walking intention including step initiation with insole-type FSRs faster without using any bio-signals and precedes the operator’s step with a reference torque. It not only reduces interaction forces between the operator and the UTRCEXO, but also allows the operator to walk with a load more comfortably. In this paper, we present the UTRCEXO implementing the walking assistance mechanism with interaction force reduction during walking.