• International Journal of Industrial Entomology and Biomaterials
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• 제23권1호
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• pp.175-178
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• 2011

Yeonnokjam is a newly bred high yield special silkworm strain for spring rearing, bred from Japanese originated green cocoon spinning strain Jam 315 and Chinese originated white cocoon spinning strain Jam 316. This strain showed high hatching ratio of 96% and high healthiness of 96.7% of pupatin ratio. And its spins heavier cocoon with somewhat shorter fiber length but thicker fineness. The merits of these_strains are short larval period and labor saving, and its breeding goals are producing polish green silk and use for education.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.777-780
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• 2010

실린더 중앙 원주방향 변형률을 바탕으로 킥모터의 연소 압력을 계산하는 방법을 제안하였다. 지상연소시험으로부터 연소시간 동안의 변형률-압력 비(strain ratio)를 근사하는 다항식을 계산하였다. 이 다항식에 비행 중 측정한 변형률을 대입하여 비행 중 연소압력으로 변환하였다. 실제 비행 중에 측정한 압력과 비교한 결과 전체적인 변화 양상이 일치함을 확인하였으며 최대 약 10psi 수준의 차이가 나타난 것을 볼 수 있었다.

• Metals and materials international
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• 제24권6호
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• pp.1221-1231
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• 2018

The effect of strain aging on tensile behavior and properties of API X60, X70, and X80 pipeline steels was investigated in this study. The API X60, X70, and X80 pipeline steels were fabricated by varying alloying elements and thermomechanical processing conditions. Although all the steels exhibited complex microstructure consisting of polygonal ferrite (PF), acicular ferrite, granular bainite (GB), bainitic ferrite (BF), and secondary phases, they had different fractions of microstructures depending on the alloying elements and thermomechanical processing conditions. The tensile test results revealed that yielding behavior steadily changed from continuous-type to discontinuous-type as aging temperature increases after 1% pre-strain. After pre-strain and thermal aging treatment in all the steels, the yield and tensile strengths, and yield ratio were increased, while the uniform elongation and work hardening exponent were decreased. In the case of the X80 steel, particularly, the decrease in uniform elongation was relatively small due to many mobile dislocations in PF, and the increase in yield ratio was the lowest because a large amount of harder microstructures such as GB, BF, and coarse secondary phases effectively enhanced work hardening.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.1071-1084
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• 2022

The present study aims to investigate the dynamic properties of a novel isolation system composed of separate rubber and wire isolators. The testing program comprised pure compressive, pure-shear, compressive-stress dependence, and shear-strain dependence tests that used full-scale test specimens according to ISO 22762-1. A total of 22 test specimens were fabricated and investigated. Among the tests, the pure compressive test was a destructive test that reached up to the failure stage, whereas the others were nondestructive tests before the failure stage. Similar to the pure-shear test, at each compressive-stress level in the compressive dependence test or at each shear-strain level in the shear-strain dependence test, the cyclic loading was conducted for three cycles. In the nondestructive tests, examination of the dynamic shear properties in the X-direction was independent of the Y-direction. The test results revealed that the increase in the shear strain increased the energy dissipation but decreased the damping ratio, whereas the increase in the compressive stress increased the damping ratio. In addition, a macro model was developed to simulate the load-displacement response of the isolation systems, and the prediction results were consistent with the experimental results.

• Journal of Preventive Medicine and Public Health
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• 제32권4호
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• pp.505-512
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• 1999

Objectives : The purpose of this study was to assess the relationship between job strains and absenteeism from work. Methods : The study design was cross-sectional, and the study subjects consisted of 1,166 workers who were employed in the small-sized industries. A self administered questionnaire was used to measure the general characteristics, job characteristics(job demand, job control), and social support(coworker support, supervisor support) at work. The Job Content Questionnaire(JCQ) was used to assess job demand(2 items) and decision lattitude(10 items). Social support at work (10 items) was measured using JCQ. Sick absence was collected using self-report and were rechecked by the attendance record of their company. Odds ratios and 95% confidence intervals for the association between job strain and sick absence were estimated. The modifying effect of social support was evaluated by stratification. Logistic regression was used to estimate the relationship between job strain and sick absence. Results : In the bivariate analysis, the variables related to sick absence were age, marital status, occupation, job demand. Four distinctly different kinds of level of job strain were generated by the combination of job demand and job control: low strain group, high strain group, active group, and passive group. The crude odds ratio of high job strain was 1.78(95% CI: 1.26-2.53), and those of active group and passive group were 1.33(95% CI: 1.07-1.66) and 1.13 (95% CI: 0.88-1.47), respectively. The odds ratio of high job strain after adjusting for age and occupation were still significant The odds ratio of high job strain in low social support was 5.96(95% CI: 2.45-14.51), but that in high social support was 0.73(95% CI: 0.26-2.01). Conclusions : Job strain was associated with increased risk of absenteeism from work, and social support at work modified the association between job strain and sick absence.

• 한국지반공학회지:지반
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• 제14권4호
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• pp.47-60
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• 1998

본 연구에서는 남해안 해성점토의 일정변형률 압밀특성을 파악하기 위해 표준압밀시첩과 변형률 속도가 다른 일정변형율 압밀시험을 수행하고 이들 결과를 비교.분석하였다. 표준압밀시험 및 일정변형율 시험에서 선행압밀하중을 산정하기 위하여 여러 제안된 방법을 사용하였으며 각 방법의 적용성을 검토하였다. 또한, 변형률 속도가 응력-변형뮬 관계, 간극수압, 그리고 선행압밀 하중에 미치는 영향을 분석하였다. 해석결과에 의하면 압밀곡선의 분포와 선행압밀하중비($a_2=\sigma'_{pCRS}/\sigma'_{pConv}$)는 변형률 속도의 영향을 받지만, 정규압 밀구간의 압축지수는 상대적으로 변형률 속도의 크기와 무관한 것으로 나타났다. 해성점토의 선행압밀하중비는 변형률 속도의 대수축척에 비례하여 증가하는 것으로의 변형률 속도에서 평균적으로 1.11~1.30의 분포를 보였다. 일정변형률 압밀시험에서 간극수압비는 변형플 속도가$6.67\times10^{-4}$ %sec일 때를 제외하고는 6.0%를 초과하지 않는 것으로 나타났다. 정규압밀구간의 압축지수, 압밀계수와 투수계수는 각각 0.59~0.95, $0.56\times10^{-3}~3.0\times10^{-3} cm^2/sec,\; 그리고 \;2.0\times10^4~7.0\times10^{-4} cm/sec$의 분포를 보였다.

• 대한환경공학회지
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• 제36권1호
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• pp.42-48
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• 2014

본 연구에서는 단일반응조에서 포기/비포기 시간에 따른 하수 내 유기물질 및 질소화합물을 변화양상을 살펴보고자 하였다. 실험 결과 C/N비 3 : 1, 포기/비포기 20/40 min 구간에서부터 90% 이상의 안정적인 유기물 및 질소 제거가 이루어짐을 알 수 있었다. 포기/비포기 구간의 비율을 길게 유지하는 것이 탈질에 더욱 효과적이었으며 이는 비포기 구간을 유지하는 동안 반응조 내 미생물의 군집변화에 기인하는 것으로 판단하였다. PCR-DGGE를 한 결과, 유기물 및 질소화합물의 산화에 관여하는 미생물로 Dysgonomonas mossii strain Melo40, Eubacterium sp. oral clone JN088, Uncultured bacterium clone SPESB2_718과 Bacterium enrichment culture clone LE이 관찰되었고 탈질에 관여하는 미생물은 Uncultured Acidobacteria bacterium clone AKYG487, Lactobacillus harbinensis strain FQ003, Erythrobacter litoralis strain Gi-3, Phytobacter diazotrophicus strain Ls8, Mycobacterium sp. enrichment culture clone GE10037biofNNA로 나타났다.

• 한국표면공학회지
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• 제41권3호
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• pp.121-128
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• 2008

High strength 7xxx aluminum alloys have been applied to automotive bump back beam of the some limited model for light weight vehicle. The aluminum bump back beam is manufactured through extrusion, bending and welding. The residual stress given on these processes combines with the corrosive atmosphere on the road spreaded with corrosive chemicals to melt snow to occur the stress corrosion cracking. The composition of commercial 7xxx aluminum has Zn/Mg ratio about 3 and Cu over 2 wt% for better strength and stress corrosion cracking resistivity. But this composition isn't adequate for appling to the automotive bump back beam with high resistance to extrusion and bad weldability. In this study the composition of 7xxx aluminum alloy was modified to high Zn/Mg ratio and low Cu content for better extrusion and weldability. To estimate the resistivity against stress corrosion cracking of this aluminum alloy by slow strain rate test, the corrosion atmosphere and strain rate separate the stress corrosion cracking from conventional corrosion must be investigated. Using 0.6 Mol NaCl solution on slow strain rate test the stress corrosion cracking induced fracture was not observed. By adding 0.3% $H_2O_2$ and 0.6M $Na_2SO_4$ to 1M NaCl solution, the corrosion potential and current density of polarization curve moved to active potential and larger current density, and on the slow strain rate test the fracture energy in solution was lower than that in pre-exposure. These mean the stress corrosion cracking induced fracture can be estimated in this 1M NaCl + 0.3% $H_2O_2$ + 0.6M $Na_2SO_4$ solution. When the strain rate was below $2{\times}10^{-6}$, the stress corrosion cracking induced fracture start to be observed.

• Geomechanics and Engineering
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• 제34권5호
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• pp.481-489
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• 2023

Drained cyclic triaxial tests were conducted on a saturated sand to examine its deformation characteristics under either axial or lateral cyclic loading condition. To apply lateral cyclic loading, the cell pressure was cycled while maintaining a constant vertical stress. The strain accumulations and flow direction in the soil were presented and discussed considering various initial stress ratios (η₀), cyclic stress amplitudes and cyclic stress paths. The results indicate that axial strain accumulation shows an exponential increase with the maximum stress ratio (η^max). The initial deviatoric stress has comparable effects with lateral cyclic stress amplitude on the accumulated axial strain. In contrast, the accumulated volumetric strain is directly proportional to the lateral cyclic stress amplitude but not much affected by η₀ values. Due to the anisotropy of the soil, the accumulated axial and lateral bulging strains are greater in lateral cyclic loading when compared to axial cyclic loading even though η^max is the same. It is also found that η^max affects soil's lateral deformation and increasing the ratio could change the lateral deformation from contraction to bulging. The flow direction depends on η^max in the sand under lateral cyclic loading, regardless of η₀ values and the cyclic stress amplitudes, and a large η^max could lead to great deviatoric strain but a little volumetric strain accumulation.

• Geomechanics and Engineering
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• 제34권5호
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• pp.577-595
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• 2023

A dynamic triaxial discrete element numerical model of lightweight soil was established using the discrete element method to study the microscopic mechanism of expanded polystyrene (EPS) particles in the soil under cyclic loading. The microscopic parameters of the discrete element model of the lightweight soil were calibrated depending on the dynamic triaxial test hysteresis curves. Based on the calibration results, the effects of the EPS particles volume ratio and amplitude on the contact force, displacement field, and velocity field of the lightweight soil under different accumulated strains were studied. The results showed that the hysteresis curves of lightweight soil exhibit nonlinearity, hysteresis, and strain accumulation. The strain accumulated in remolded soil is mainly tensile strain, and that in lightweight soil is mainly compressive strain. As the volume ratio of EPS particles increased, the contact force first increased and then decreased, and the displacement and velocity of the particles increased accordingly. With an increase in amplitude, the dynamic stress of the particle system increased, and the accumulation rate of the dynamic strain of the samples also increased. At 5% compressive strain, the contact force of the particles changed significantly and the number of particles deflected in the direction of velocity also increased considerably. These results indicated that the cemented structure of the lightweight soil began to fail at a compressive strain of 5%. Thus, a compressive strain of 5% is more reasonable than the dynamic strength failure standard of lightweight soil.