• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2006년도 춘계학술대회논문집
• /
• pp.1360-1365
• /
• 2006

In this paper the vibration analysis of cantilever beams having a concentrated tip mass and an open crack are performed. The influences of a concentrated tip mass, the crack depth, and the crack position on the natural frequencies of the cracked cantilever beam are investigated by a numerical method. The cracked cantilever beam is modeled based on the Euler-Bernoulli beam theory. The flexibility due to crack is calculated using a fracture mechanics theory. The crack is assumed to be opened during the vibrations. The results obtained by the present method were compared with experimental results to verify the theory. As inspected, as the crack depth and the concentrated tip mass increase, the natural frequencies of the beam decrease. In general, the natural frequencies of the cantilever beam are more sensitive to the depth of the crack than the position of the crack.

• 환경생물
• /
• 제19권1호
• /
• pp.1-6
• /
• 2001

Many researchers have been studied with guard cell protoplasts and detached epidermis as they think that properly stabilized protoplasts and detached epidermis retain many of the properties of intact guard cells. However, some studies have shown that stomata in detached epidermis behave differently, both quantitatively and qualitatively, from those in the intact leaf. Stomata in the intact leaf are very sensitive to environmental factors such as light, $CO_2$ and osmotic stress, but stomata in detached epidermis are less sensitive to these factors than those in the intact leaf. The clearest evidence to suggest the different response between detached epidermis and intact leaf obtained from the experiments with heavy metal, cadmium. 3-weeks old Commelina. communis was transferred to and grown in Hoagland solution in the presence or absence of 5 mM $Cd^{2+}$ for 4 days. The application of $Cd^{2+}$ showed about 70% inhibition of stomatal conductance when measured at various light intensity (100-1,000 $\mu$mole $m^{-2}s^{-1}). However, stomata in detached epidermis floated on an incubation medium containing 100 $\mu$M $Cd^{2+}$ opened to a degree of about 8.38 fm, but the stomata treated with no cadmium opened to 3.74 ${\mu}{\textrm}{m}$. These results were unexpected as the intact leaf grown in a Hoagland solution containing cadmium showed very negative physiological responses. These results showed that stomata in detached epidermis and in the intact leaf could respond reversely. Therefore, it is possible that we now misunderstand how stomata open in real natural condition.

• 한국안전학회지
• /
• 제20권1호
• /
• pp.62-67
• /
• 2005

An eccentrically-loaded single edge crack tension specimen (ESET) is similar to a compact tension(CT) specimen loaded in tension-tension. The standard ESET specimen exhibits advantages over other types of cracked specimen, such as n, single-edge crack, and middle-crack tension specimen. The details of ESET specimen configuration, test procedure, and calculations are described in ASTM E647 standard. However, a difficulty in attaching COD gage to the knife-edge on the front foe of the specimen can be found when the size of ESET specimen is small for rapid cooling and heating in thermal fatigue testing. The finite element analysis is performed for the ESET specimen with projected knife-edge on the front foe and a crack-length-compliance equation is suggested for the new specimen configuration. Calibration test are conducted with 347 stainless steel to compare the measured crack length with the calculated crack length from the suggested compliance expression. The test results showed good agreements with those of analysis.

• Reproductive and Developmental Biology
• /
• 제36권1호
• /
• pp.49-53
• /
• 2012

The present study was conducted to examine the generation of reactive oxygen species (ROS) during micromanipulation procedures in bovine somatic cell nuclear transfer (SCNT) embryos. Bovine enucleated oocytes were electrofused with donor cells, activated by a combination of Ca-ionophore and 6-dimethylaminopurine culture. Oocytes and embryos were stained in dichlorodihydrofluorescein diacetate or 3'-(p-hydroxyphenyl) fluorescein dye and the $H_2O_2$ or $^.OH$ radical levels were measured. $In$ $vitro$ fertilization (IVF) was performed for controls. The samples were examined with a fluorescent microscope, and fluorescence intensity was analyzed in each oocyte and embryo. The $H_2O_2$ and $^.OH$ radical levels of reconstituted oocytes were increased during manipulation (37.2~49.7 and 51.0~55.2 pixels, respectively) as compared to those of mature oocytes ($p$<0.05). During early $In$ $vitro$ culture, the ROS levels of SCNT embryos were significantly higher than those of IVF embryos ($p$<0.05). These results suggest that the cellular stress during micromanipulation procedures can generate the ROS in bovine SCNT embryos.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
• /
• pp.127-128
• /
• 2012

ZnO nanostructures were grown by the hydrothermal method on ZnO seed layers post-heated in the range $350-500^{\circ}C$. The effects of the post-heated ZnO seed layers on the structural and optical properties of the ZnO nanostructures were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and photoluminescence (PL) spectroscopy. The average grain sizes in the ZnO seed layers increased with increasing post-heating temperature, and nano-fibrous structures were observed on the surface of the ZnO seed layers post-heated at $450^{\circ}C$. The ZnO seed layers post-heated in the range $350-500^{\circ}C$ affected the residual stress, lattice distortion in the ZnO nanostructures and the intensity, positions, and full widths at half maximum of the 2-theta and PL peaks in the XRD and PL spectra for the ZnO nanostructures.

• 대한조선학회논문집
• /
• 제33권4호
• /
• pp.75-86
• /
• 1996

최근 선박, 해양구조물, 항공기 및 원자력 플랜트 등 대형구조물의 사용조건이 극도로 가혹해짐에 따라 이들에 대한 신뢰성 및 안전성 보장이 심각한 문제로 대두되고 있다. 이들 대형구조물에 있어, 파손사례의 대부분은 어떤 형태로든 피로현상과 관련된 것으로서 수명 및 잔여수명의 예측과 함께 안정성 평가기술의 확립이 절실히 요구되고 있다. 그러나, 실제 대다수의 결함은 복수표면 균열 상태로 존재하며, 이들은 단일균열의 경우와는 달리 급속히 합체, 성장할 가능성이 높고 따라서, 관통수명 또한 짧아지며, 관통시 표면균열의 길이가 상대적으로 커져 불안정 파괴의 위험성도 그만큼 높아지게 된다. 본 연구에서는 평판 및 필릿 용접부에 존재하는 복수의 직렬표면균열을 대상으로 인접균열간 간섭효과, 합체현상을 고찰하여 피로균열 진전거동 및 피로수명 예측프로그램을 개발하고, 이를 기존의 실험결과와 비교, 평가하여 그 정도 및 실용성을 확인하였다.

• 생명과학회지
• /
• 제14권4호
• /
• pp.573-576
• /
• 2004

The purpose of the present study is to investigate the lipid peroxidation, creatine kinase activity and cortisol hormone levels following the training intensity in elite judo players. Six elite Judo players participated in the experiments (3h repetition judo program), which include stretching, judo skill practice and cool down without recess. Blood sampling were taken at the judo gymnasium at the time of resting, 1h training, 2h training, 3h training, 2h recovery, and 24h recovery time and this were analyzed for CK, MDA and Cortisol levels. The results obtained were analyzed via repeated measures of ANOVA using SPSS package program (ver.10.0) and a value of p<.05 was considered statistically significant. The results from this study were as follows. In the CK levels, which reflect the contribution of creatine phosphate and muscle damage degree, there was a significant difference (p<.05) after judo training in every period. Recovery 24h showed the highest level. In the MDA levels, which reflect lipid peroxidation, there was a significant difference (p<.05) after judo training. Recovery 2h showed the lowest level. In the cortisol hormone levels, which reflect stress status, there was a significant difference (p<.05). In this study, we can conclude that For the trained athletes, MDA level was lower at the time of exercise compare to the other period, this is caused by the increased antioxidant defence mechanism.

• 생명과학회지
• /
• 제18권3호
• /
• pp.311-317
• /
• 2008

Pathophysiological oxidative stress results in neuronal cell death mainly due to the generation reactive oxygen species (ROS). In low oxygen situation such as hypoxia and ischemia, excessive ROS is generated. Coptidis Rhizoma (CR) is a traditional medicine used for the incipient stroke. In this report we show that CR water extracts $(1\;{\mu}g/ml)$ exhibited protective effects of neuronal cell death in a hypoxic model (2% $O_2/5%\;CO_2,\;37^{\circ}C,$ 3 hr) of cultured rat cortical cells. We further show that CR water extracts significantly reduced the intensity of green fluorescence after staining with $H_2DCF-DA$ on one hour and three days after hypoxic shock and in normoxia as well. Our results indicate that CR water extracts prevent neuronal death by suppressing ROS generation.

• 대한기계학회논문집
• /
• 제12권1호
• /
• pp.116-122
• /
• 1988

본 연구에서는 공기와 물을 매질로 사용하여 3차원 계면파가 존재하는 근사수평 반류성층유동에서의 계면전단응력과 마찰계수를 결정하였다. 기상과 액상의 유량조건에 따라 3차원 계면파의 특성을 needle contact법에 의하여 측정 하였으며, 기상의 압력강하와 속도분포를 구하여 계면전단응력을 구하였다. 또 공학적인 응용을 위하여 3차원과 영역에서의 계면마찰계수에 관한 실험식을 개발하였다. 그리고 거칠은 고체표면에서의 마찰계수를 표현한 Nikuradse식을 이용하여 계면의 등가조도(equivalent roughness)를 계산하였으며 이것을 계면의 파고교란강도와 비교분석하여 계면전단응력에 영향을 미치는 인자들을 규명하였다.

• Journal of Mechanical Science and Technology
• /
• 제19권8호
• /
• pp.1621-1631
• /
• 2005

In this paper, making the best use of the features of the electro-rheological (ER) valve, a two-port pressure control valve using ER fluids is proposed and manufactured. The ER-Valve characteristics are evaluated by changing the intensity of the electric field and the number of electrode. As only with electrical signal change to the ER-Valve in which ER fluid flowing, ER fluid flow is controlled, so development of simple ER-Valves have been tried. The ER-Valves and pressure drop check method are considered to be applied to the fluid power industry. Using the manufactured pressure control valve, a one-link manipulator with FHA (Flexible Hydraulic Actuator) is driven. As a result, it is experimentally confirmed that the pressure control valve using ER fluids is applicable to use in driving actuator. If it applies characteristics of the ER fluids, it will be able to apply in the control system for the ER Valve which occurs from industrial controller. After having durability test, shear stress increased regularly because of starch particles crushed by pump and particle size that was almost the same. Moreover, Ra of copper electrode increased about 1.56 times rather than before those of performing durability test, and Rz increased about 2.2 times.