• 대한기계학회논문집B
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• 제32권8호
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• pp.604-611
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• 2008

Detailed analysis of NO formation routes and its contributions with strain rate in hydrogen/air flames were numerically investigated. LiG detailed reaction mechanism has been used for calculation, which is compared with experimental data in literature. It shows good agreement with experiment for both temperature and NO mole fraction. Three routes have been found important for NO formation in hydrogen flames. These are the Thermal route, NNH route and $N_2O$ route. Strain rate were varied to discuss the $EI_{NO}$ reduction trend in hydrogen nonpremixed flames, which are analyzed by each NO formation routes. As a result, as the strain rate increase, $EI_{NO}$ decrease sharply until strain rate $100s^{-1}$ and decrease slowly until strain rate $310s^{-1}$ again, after that $EI_{NO}$ keeps nearly constant. It can be identified that $EI_{NO}$ trend with the strain rate is well explained by a combination of variation of production rate of above Thermal, NNH and $N_2O$ route. Also result of Thermal-Mech. that includes only thermal NO reaction is compared with those of Full-Mech. As a result, It can be identified that there was difference between the two results of calculation. It is attributed to result that Thermal-mech did not consider contributions of NNH and $N_2O$ route. From these result, we can conclude that NOx emission characteristics of hydrogen nonpremixed flames should consider contributions of above three routes simultaneously.

• International Journal of Railway
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• 제8권2호
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• pp.50-54
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• 2015

The primary function of the trackbed in a conventional railway track system is to decrease the stresses in the subgrade to be in an acceptable level. A properly designed trackbed layer performs this task adequately. Many design procedures have used assumed and/or are based on critical stiffness values of the layers obtained mostly in the field to calculate an appropriate thickness of the sublayers of the trackbed foundation. However, those stiffness values do not consider strain levels clearly and precisely in the layers. This study proposes a method of computation of stiffness that can handle with strain level in the layers of the trackbed foundation in order to provide properly selected design values of the stiffness of the layers. The shear modulus values are dependent on shear strain level so that the strain levels generated in the subgrade in the trackbed under wheel loading and below plate of Repeated Plate Bearing Test (RPBT) are investigated by finite element analysis program ABAQUS and PLAXIS programs. The strain levels generated in the subgrade from RPBT are compared to those values from RC (Resonant Column) test after some consideration of strain levels and stress consideration. For comparison of shear modulus G obtained from RC test and stiffness moduli $E_{v2}$ obtained from RPBT in the field, many numbers of mid-size RC tests in laboratory and RPBT in field were performed extensively. It was found in this study that there is a big difference in stiffness modulus when the converted $E_{v2}$ values were compared to those values of RC test. It is verified in this study that it is necessary to use precise and increased loading steps to construct nonlinear curves from RPBT in order to get correct $E_{v2}$ values in proper strain levels.

• Safety and Health at Work
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• 제5권4호
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• pp.186-190
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• 2014

Background: Physical exercise during leisure time is known to increase physical capacity; however, the long-term effects on work ability and work strain are inconclusive. The aim of this study was to investigate the effects of a 6-month physical exercise program on work ability and work strain after 6 months and 30 months, among women with menopausal symptoms at baseline. Methods: A questionnaire including questions on work ability and work strain was mailed in the beginning, at 6 months and after 30 months after the intervention to occupationally active women participating in a randomized controlled study on physical exercise and quality of life. The intervention included aerobic exercise training 4 times per week, 50 minutes per session. Work ability was measured with the Work Ability Index (WAI) and with questions about physical and mental work strain. Results: Women aged 47-62 years (N=89) who were occupationally active at baseline were included in the analyses. The increase in WAI from baseline to the end of the exercise intervention (6 months) was statistically significantly greater among the intervention group than among the control group (regression coefficient 2.08; 95% confidence interval 0.71-3.46). The difference between the groups persisted for 30 months. No significant short- or long-term effects on physical and mental work strain were found. Conclusion: A 6-month physical exercise intervention among symptomatic menopausal women had positive short-term as well as long-term effects on work ability.

• Computers and Concrete
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• 제29권1호
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• pp.15-29
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• 2022

Concrete-filled steel tubes (CFSTs) are increasingly used as composite sections in structures owing to their excellent load bearing capacity. Therefore, predicting the mechanical behavior of CFST sections under axial compression loading is vital for design purposes. This paper presents the first study on the nonlinear analysis of heated CFSTs with high-strength concrete core containing steel fiber and waste tire rubber under axial compression loading. CFSTs had steel fibers with 0, 1, and 1.5% volume fractions and 0, 5, and 10% rubber particles as sand alternative material. They were subjected to 20, 250, 500, and 750℃ temperatures. Using flow rule and analytical analysis, a model is developed to predict the load bearing capacity of steel tube, and hoop strain-axial strain relationship, and axial stress-volumetric strain relationship of CFSTs. An elastic-plastic analysis method is applied to determine the axial and hoop stresses of the steel tube, considering elastic, yield, and strain hardening stages of steel in its stress-strain curve. The axial stress in the concrete core is determined as the difference between the total experimental axial stress and the axial stress of steel tube obtained from modeling. The results show that steel tube in CFSTs under 750℃ exhibits a higher load bearing contribution compared to those under 20, 250, and 500℃. It is also found that the ratio of load bearing capacity of steel tube at peak point to the load bearing capacity of CFST at peak load is noticeable such that this ratio is in the ranges of 0.21-0.33 and 0.31-0.38 for the CFST specimens with a steel tube thickness of 2 and 3.5 mm, respectively. In addition, after the steel tube yielding, the load bearing capacity of the tube decreases due to the reduction of its axial stiffness and the increase of hoop strain rate, which is in the range of about 20 to 40%.

• Journal of Hydrospace Technology
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• 제2권2호
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• pp.80-87
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• 1996

A creep-buckling analysis is studied for a simply-supported viscoelastic column. The fluid-type four-parameter model is employed because of its general applicability to creep materials. Using the imperfection-based incremental approach, a nonlinear load deflection equation is derived. Safe load and critical (or life) time which characterize the stability of the viscoelastic column are obtained mathematically and interpreted physically. A finite difference algorithm is applied to solve the second-order differential equation of the viscoelastic stress-strain relation. Numerical calculation has been made and discussed far a SUS316 stainless steel column.

• 농업과학연구
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• 제14권2호
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• pp.329-344
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• 1987

과압밀비(過壓密比)와 전단속도(剪斷速度) 및 다짐율(率)이 점성토(粘性土)의 응력변형특성(應力變形特性)에 미치는 영향(影響)을 검토(檢討)하기 위해서 반부극하(反復戟荷)에 의(依)한 삼축압축시험(三軸壓縮試驗)을 한 결과(結果)를 요약(要約)하면 다음과 같다. 1. 반부재하(反復載荷)를 했을 때 같은 변형(變形)에서 축차응력의 차(差)는 큰 변형(變形)에서 반부재하(反復載荷)했을 때 더욱 크게 나타났고 공극수압(空隙水壓)은 제하시(除荷時)에는 감소(減少)하다가 다시 증가(增加)하며 재재하(再載荷)되면서 급격히 증가하는 현상(現象)을 나타냈다. 2. 과압밀비(過壓密比)가 클수록 변형(變形)의 증가(增加)에 따라 회복되는 탄성변형률은 감소(減少)하였으며 제일재하계수(除一載荷係數)는 과압밀비가 증가(增加)할수록 감소(減少)하였다. 3. 전단속도(剪斷速度)가 증가(增加)함에 따라 탄성변형율(彈性變形率)은 증가(增加)하였고 변형(變形)의 증가(增加)에 따라 탄성변형율(彈性變形率)은 감소(減少)하였다. 제일재하계수(除一載荷係數)는 변형(變形)이 증가(增加)함에 따라 감소(減少)하였고 전단속도(剪斷速度)가 빠른 경우에 큰 값을 나타냈다. 4. 회복되는 탄성변형율(彈性變形率)은 다짐율이 증가(增加)함에 따라 크게 나타났고 또 변형(變形)이 증가(增加)함에 따라 탄성변형율(彈性變形率)은 약간 감소(減少)하는 경향(傾向)을 나타냈다. 제일재하계수(除一載荷係數)는 다짐율(率)의 증가(增加)에 따라 뚜렷한 경향(傾向)은 보이지 않았으나 일반적(一般的)으로 변형(變形)이 증가(增加)함에 따라 감소(減少)하는 경향(傾向)을 나타냈다.

• 한국초전도ㆍ저온공학회논문지
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• 제18권3호
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• pp.6-9
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• 2016

The enhancement of mechanical properties of coated conductor (CC) tapes in practical application are usually achieved by reinforcing through lamination or electroplating metal layers on either sides of the CC tape. Mechanical or electromechanical properties of the CC tapes have been largely affected by the lamination structure under various loading modes such as tension, bending or even cyclic. In this study, the influence of brass laminate volume fraction on electromechanical properties of RCE-DR processed Gadolinium-barium-copper-oxide (GdBCO) CC tapes was investigated. The samples used were composed of single-side and both-side laminate of brass layer to the Cu-stabilized CC tape and their $I_c$ behaviors were compared to those of the Cu-stabilized CC tape without external lamination. The stress/strain dependences of $I_c$ in laminated CC tapes under uniaxial tension were analyzed and the irreversible stress/strain limits were determined. As a result, the increase of brass laminate volume fraction initially increased the irreversible strain limit and became gradual. The corresponding irreversible stress limit, however, showed no difference even though the brass laminate volume fraction increased to 3.4. But the irreversible load limit linearly increased with the brass laminate volume fraction.

• 한국미생물·생명공학회지
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• 제17권4호
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• pp.307-312
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• 1989

77-AG-567 균주는 Pyricularia oryzae와 Sphasrotheca fuliginea에 대한 항균활성을 나타냈다. 활성 물질을 정제해 가는 과정에서 이 균주는 blasticidin S와 또 다른 항생물질을 동시에 생산한다는 사실을 알았다. 이 화합물은 UV 및 $^1$H NMR 스펙트럼에 의해 E-73이라고도 일컬어지는 acetoxycycloheximide로 밝혀졌다. 균주를 동정해본 결과 77-AG-567균주는 Streptomyces atbutus로 판단되며 지금까지 blasticidin S와 acetoxycycloheximide를 동시에 생산하는 것으로 알려져 온 S. albulus와는 다른 특성을 나타냈다. 특히 주목할만한 차이점은 포자의 표면이였다. 또한 acetoxycycloheximide는 지금까지 효모와 종양세포에만 생리활성을 나타내는 것으로 알려져 왔으나 본 실험결과 Pyricularia oryzae와 Sphasrotheca fuliginea에도 항균활성을 가진다는 사실을 알았다.

• 한국지반공학회지:지반
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• 제13권3호
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• pp.5-20
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• 1997

본 연구에서는 유한변형률 이론에 근거하여 3차원 압밀 지배 방정식을 유도하였다. 이 방정식은 비교적 압밀층의 두께가 두꺼운 경우, 비선형 물성치, 공극비에 따른 비선형 투수계수를 갖는 지반에 적합하다. 기존의 유한차분 수치해석 기법(FTCS)은 지배 방정식이 비선형 이며 복잡한 경우 안정된 해를 얻을 수 없기 때문에 본 연구에서는 특수 유한 차분 기법을 도입하였다. 이 수치해석 기법을 지배 방정식에 적용하면 시간에 따른 압밀량을 예측할 수 있다. 본 해석기법에 의해 구해진 값들을 윅드레인을 설치한 여러 가지 고압축성 토질에서의 실험 결과와 비교한 결과, 최종 압밀량과 시간에 따른 압말량이 잘 일치하고 있다.

• Journal of Microbiology and Biotechnology
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• 제13권1호
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• pp.85-89
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• 2003

The difference in the thermotolerance between Saccharomyces cerevisiae KNU5377 and ATCC24858 was compared by assaying the amounts of trehalose accumulated under growth and heat shock conditions. Both strains exhibited similar trehalose accumulation during the growth period, but an intrinsic thermotolerance was much higher in KNU5377 than in the control strain. This result implied that some strain-specific characteristics of KNU5377, other than trehalose accumulation, primarily were responsible fur its higher intrinsic thermotolerance. Heat shock at $43^{\circ}C$ for 90 min to the exponentially growing cells resulted in the maximum level of trehalose In both strains. Trehalose accumulated at least twice more in KNU5377 by the heat shock than in the control, due to the maintenance of its neutral trehalase activity even after the heat shock. Consequently, the Increase of acquired thermotolerance in both strains correlated with an increase in the trehalose content in each strain. In conclusion, KNU5377 exhibited a well-modulated trehalose-related mechanism to accumulate more trehalose by means of maintaining neutral trehalase activity after heat shock than the control strain, thereby contributing to its acquired thermotolerance.