• 동력기계공학회지
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• 제12권2호
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• pp.5-11
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• 2008

An analytical study was performed to have temperature and thermal stress distribution on a piston with the change of the 2nd land length of a piston and the existence of knocking in a cylinder. The result showed that the temperature on the skirt region was about $4\sim10^{\circ}C$ higher than that on the pin region. However the thermal stress on the skirt region was about 4MPa lower than on the pin region. It may be due to the higher heat release rate on the pin boss than on the skirt. The result regarding the variation of the 2nd land length of the piston showed that the temperature distribution on the piston was getting lower and the thermal stress distribution was getting higher as the 2nd land length of the piston was shorter.

• International Journal of Aeronautical and Space Sciences
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• 제12권1호
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• pp.57-62
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• 2011

The effects of swirl chamber's diameter and length on injector's dynamic characteristics were investigated through an experimental study. A mechanical pulsator was installed in front of the manifold of a swirl injector which produces pressure oscillations in the feed line. Pressure in the manifold, liquid film thickness in the orifice and the pressure in the orifice were measured in order to understand the dynamic characteristic of the simplex swirl injector with varying geometry. A direct pressure measuring method (DPMM) was used to calculate the axial velocity of the propellant in the orifice and the mass flow rate through the orifice. These measured and calculated values were analyzed to observe the amplitude and phase differences between the input value in the manifold and the output values in the orifice. As a result, a phase-amplitude diagram was obtained which exhibits the injector's response to certain pressure fluctuation inputs. The mass flow rate was calculated by the DPMM and measured directly through the actual injection. The effect of mean manifold pressure change was insignificant with the frequency range of manifold pressure oscillation used in this experiment. Mass flow rate was measured with the variation of injector's geometries and amplitude of the mass flow rate was observed with geometry and pulsation frequency variation. It was confirmed that the swirl chamber diameter and length affect an injector's dynamic characteristics. Furthermore, the direction of geometry change for achieving dynamic stability in the injector was suggested.

• 한국식품영양학회지
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• 제7권4호
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• pp.267-273
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• 1994

To provide the effective application scheme and basic information of buckwheat (Fagopyrum esculentum Moench), buckwheat was germinated at 10$^{\circ}C$ for 7 days and 100 kernels weight, germination rate, root length, chemical composition and mineral contents were examined at 24 hour Intervals. During the germination period, the 100 kernels weight increased approximately 0.3g per day. The germination rate increased sharply after 2 days and the root length increased greatly after 4 days. The crude protein contents increased with germination time, whereas the carbohydrate contents decreased. The crude ash and fat contents did not differ significantly during the germination period. The Ca contents Increased for the 4th day of gemination, but gradually decreased afterwords. The Na contents increased in the initial stage of germination, but then gradually decreased. However, there were no significant change In the Mg, K. Fe. Mn and Zn contents.

• 생물환경조절학회지
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• 제22권2호
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• pp.131-137
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• 2013

본 연구는 자생 덩굴식물인 마삭줄과 후추등의 실내 광도차에 따른 생육특성의 변화를 알아보고자 광도 처리 조합을 3처리구를 만들어 환경 조절 생육상에서 조사하였다. 사용된 광원은 형광등이고, 광 처리를 각각 100lux, 1,000lux, 2,500lux로 달리하여 5개월간 생육특성 변화를 조사하였다. 자생 마삭줄은 저광도인 100lux에서 처리 2개월 이후 생존율이 약 16.7%로 식물체 대부분이 고사하였고, 1,000lux와 2,500lux에서는 처리 5개월까지도 생존율이 83.3%로 높게 유지되었다. 실내광도가 높아짐에 따라 초장, 엽수, 분지수, 엽장 및 엽폭은 증가하는 경향을 보였고 고광도인 2,500lux에서 가장 우세한 생육 및 생장을 보였다. 자생 후추등은 저광도인 100lux에서는 처리 4개월 후 생존율이 50%로 생육이 불량하였으나 1,000lux와 2,500lux에서는 처리 5개월까지도 100%의 높은 생존율을 보였다. 1,000lux 조건에서 엽록소 함량이 증가되는 경향을 보였고, 엽장과 엽폭이 약간 넓어지는 경향은 보였다. 상록성 덩굴식물인 자생 마삭줄과 후추등을 실내 광조건을 달리하여 처리한 결과 두 식물 모두 1,000lux 이상의 광조건에서 생육이 양호하였고 특히 후추등의 경우 마삭줄에 비해 1,000lux의 낮은 광도에서도 생육이 양호하고 잎이 넓어지고 엽색도 짙은 녹색으로 유지되어 실내식물로서 활용성이 높을 것으로 판단되었으나 광도가 지나치게 낮아질 경우 생육이 저조한 것으로 나타나 내 음성이 높다고 할지라도 정상적인 생육을 위해서는 적당한 광조건이 필요함을 알 수 있었다.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.57-63
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• 2003

An eigenvalue design sensitivity formulation of a general nonsymmetric-matrix rotor-bearing system is devised. using the DDM (direct differential method). Then, investigations on the design sensitivities of critical speeds are carried out for an APU turbogenerator with a spline shaft connection. Results show that the dependence of the rate of change of the critical speed on the stiffness changes of bearing models of spline shaft connection points is negligible, and thereby their modeling uncertainty does not present any problem. And the passing critical speeds up to the 4th critical speed are not sensitive to the design stiffness coefficients of four main bearings. Further, the dependence of the rate of change of the critical speed on the shaft-element length changes shows quantitatively that the spline shaft has some limited influence on the 4th critical speed but no influence on the 1st to 3rd critical speeds. With no adverse effect from the spline shaft, the APU system achieves a critical speed separation margin of more than 40% at a rated speed of 60,000 rpm.

• 대한치과보철학회지
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• 제29권1호
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• pp.281-287
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• 1991

This study was designed to investigate the influence of the clasp arm length on the change of retentive force with repeated placement or removal. The author measured the retentive force of Akers clasp and I-bar clasp in the depth of undercut 0.5mm, 0.25mm, respectively, varying the length of clasp arm, that is, 10mm, 14mm, 17mm in Akers clasp and 16mm, 18mm, 20mm in I-bar clasp. The retentive force was measured just before the placement of removal, after 100 times repeated placement or removal, after 300 times repeated placement or removal. The obtained results were as follows : 1. The shorter the clasp arm, the greater retention in Akers clasp and I-bar clasp(p<0.05). 2. There was decreased retentive force of Akers clasp and I-bar clasp after 300 times repeated placement or removal(p.<0.005). 3. The decreasing rate of retentive force in Akers clasp with 10mm was higher than that with 17mm, after 300 times repeated placement or removal, but there was no statistica difference(p>0.05).

• 한국전문물리치료학회지
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• 제11권3호
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• pp.85-90
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• 2004

The purpose of this study was to find the difference in muscle firing rate between each muscle according to the knee angle with the quadriceps femoris which is a representative action muscle of the lower extremity. Seven normal healthy subjects were recruited. The median frequency (MDF) of muscle contraction was recorded from vastus lateralis, vastus medialis, and rectus femoris muscles using the surface EMG, in 5 seconds, during maximal isometric knee extension. The data were analyzed by the two-way repeated ANOVA. The results of the study were as follows: 1) median frequency of muscle contraction was significantly higher at the vastus lateralis, vastus medialis, and rectus femoris in descending order. 2) median frequency of muscle contraction was significantly higher at the $30^{\circ}$, $60^{\circ}$, and $90^{\circ}$ in descending order. Consequently, muscle recruitment at the knee decreases the EMG activity of the lengthened muscle. This study suggests that the change in EMG activity at different muscle lengths resulted in affecting the muscle firing rate during the knee extension.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.397-403
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• 2000

In the present study, flow characteristics of turbulent pulsating flow in a square-sectional $180^{\circ}$ curved duct were experimentally investigated. Experimental studies for air flows were conducted to measure axial velocity and wall shear stress distributions and entrance length in a square-sectional $180^{\circ}$ curved duct by using the LDV with the data acquisition and the processing system. The experiment was conducted in seven sections from the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) at $30^{\circ}$ intervals of the duct. The results obtained from the experimentation were summarized as follows ; (1) When the ratio of velocity amplitude ($A_1$) was less than one, there was hardly any velocity change in the section except near the wall and any change in axial velocity distributions along the phase. When the ratio of velocity amplitude ($A_1$) was 0.6, the change rate of velocity was slow. (2) Wall shear stress distributions of turbulent pulsating flow were similar to those of turbulent steady flow. The value of the wall shear stress became minimum in the inner wall aid gradually increased toward the outer wall where it became maximum. (3) The entrance length of turbulent pulsating flow reached near the region of bend angle of $90^{\circ}$, like that of turbulent steady flow. The entrance length was changed by the dimensionless angular frequency (${\omega}^+$).

• 한국산업보건학회지
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• 제11권1호
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• pp.34-41
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• 2001

Passive samplers have been used for personal, indoor, and outdoor air monitoring of VOCs at ppb concentrations in community and office environments. The path length of modified passive sampler was shortened, so it was intended to increase an uptake rate. The performance of the modified 3M 3500 organic vapor monitor(OVM) as a tool for assessing exposures to toxic air pollutants in nonoccupational community environments was evaluated using combined controlled test atmospheres of six selected target volatile organic compounds(VOCs): benzene, methyl tert-butyl ether(MTBE), chloroform, 1,4-dichlorobenzene, tetrachloroethylene, and toluene. The experiments were conducted by exposing the dosimeters to concentrations of $50{\sim}100{\mu}g/m^3$ on six face velocity(0.00, 0.02, 0.06, 0.12, 0.20, 0.30 m/sec) for 24 hours. If the uptake rate was increased, that means that we could use the passive sampler more effectively. The uptake rates were increased linearly according to reduce the path length. Although the diffusion path length was shortened, the change of uptake rate was within ${\pm}25%$ of theoretical value, indicating that the modified passive sampler(TM) can be effectively used over the range of concentrations and environmental conditions tested with a 24-h sampling period if the face velocities were over 0.12 m/s for 6 components of VOCs. But when the face velocities were less than 0.12 m/s, uptake rates were reduced more than expected values. So, the passive sampler with the shortened path length should be used at indoor or outdoor environment where the face velocity should be over about 0.10 m/s. If the path length was shortened more, the uptake rate was more effected by starvation.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.113-114
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• 2016

In this study, various fats and oils were soaked in low-strength mortar to experiment what kind of fats and oils had the worst effect on low-strength mortar; it went as follows. For rate of change in length of fat and oil soaking, there was an increase in the order of pig fat, bio-diesel, grape seed oil, and water; in the case of olive oil it was destroyed within 56 days. For rate of change in mass, there was an increase in the order of bio-diesel, water, pig fat, grape seed oil, and olive oil. For relative motion elastic coefficient, there was a decrease in the order of olive oil, grape seed oil, and water. On the whole, pig fat, bio-diesel, and olive oil were shown to have the worst effect on low-strength mortar.