• 동력기계공학회지
• /
• 제4권2호
• /
• pp.40-45
• /
• 2000

Some engineering materials are often known to have considerable spatial variation in their resisting strength and other properties. The objective of this study is to investigate the averaging effect and the applicability of extremal statistic for the statistical size effect. In the present study, it is assumed that the material property is a stationary random process in space. The theoretical autocorrelation function of the material strength are discussed for several correlation lengths. And, in order to investigate the statistical size effect, the material properties was simulated by using the non-Gaussian random process method. The material properties were plotted on the Weibull probability papers. The main results are summarized as follows: The autocorrelation function of the material properties are almost independent of the averaging length. The variance decreases with increasing the averaging length. As correlation length is smaller, the slope is larger. And also, it was found that Weibull statistics based on the weakest-link model could not explain the spatial variation of material properties with respect to the size effect satisfactory.

• 수산해양교육연구
• /
• 제19권1호
• /
• pp.1-7
• /
• 2007

The purpose of this study was to investigate geochemical characteristics of surface sediments in the Keum river estuary adjacent to coastal area. For this study we collected the 21 surface sediments samples. Mean size of surface samples was $3.24{\sim}6.65{\phi}$ on inner estuary and was $2.15{\sim}3.42{\phi}$ on outside estuary. Surface samples were composed of silt on inner estuary and were composed of sand which was more larger than $4{\phi}$ on outside estuary. Most major elements except CaO, $Na_2O$ showed good relationships between variation of contents and grain size. Contents of $Al_2O_3$, $Fe_2O_3$, MgO, $K_2O$, $TiO_2$, $P_2O_5$ and $M_nO$ were increased predominately owing to the variation of mean size of surface samples. Contents of Co, Cr, Cu, Li, Sr, Zn, La, Ce, Pb, Rb, Nd have a good relationships with grain size but Ba, Th, Sm have not. All of major and minor elements contents except $K_2O$ and Ba were less than world mean contents of shallow surface sediments but apprehend a high pollution possibility on silt sediments in the estuaries.

• Journal of Advanced Marine Engineering and Technology
• /
• 제15권2호
• /
• pp.53-63
• /
• 1991

This study suggests a new type shaft generator driven by hydraulic power suitable for small size vessels. Since the shaft generator system is very easy to be affected by disturbances such as speed variation of main engine and load variation of the generator, a robust servo control must be implemented to obtain stable electric power with constant frequency. Thus, in this study two types of controller design method-the reference following optimal control method and robust servo control method-are adopted to the controller design. In the experiment, static and dynamic characteristics of the shaft generator system according to the variation of input frequency setting, the speed variation of the pump and the load variation of the generator are investigated. From the considerations on the computer simulation results and experimental results, it is ascertained that the shaft generator system proposed in this study has good control performances.

• 한국작물학회지
• /
• 제26권4호
• /
• pp.293-297
• /
• 1981

맥류시험에 있어서 표본추출 체계를 확립하기 위하여 1979/80년 맥류연구소의 포장에서 실시한 몇가지 소맥재배양식에 대한 표본단위의 크기 및 주어진 정도를 위한 표본수 결정을 시도하였던 바 그 결과를 요약하면 다음과 같다. 1. 소맥의 수수에 대한 변이계수는 휴입광철파를 제외하고는 맥류수량의 평균변이계수와 거의 같았다. 2. 수수의 변이계수와 표본단위의 크기에 대한 회귀계수는 유입광철파를 제외하고 모두 1% 수준에서 유의성을 보였다. 3. 표본단위의 크기는 재배양식에 따라 차이가 크며 변이계수 15%를 허용한다면 협폭파, 관행 및 Drill 파는 각각 0.40, 0.17 및 0.11$m^2$, 로 추정되며 답리작의 유입광철파는 0.55$m^2$, 로 추정되었다. 4. 표본단위간 변이가 심하여 시험오차의 분산성분이 영인 조건하에서 CV=12%를 위해서 2반복인 경우는 구당 2개의 표본단위, 4반복민 경우는 구당 1개의 표본단위로 충분한 것으로 추정되었다.

• 정보과학회 컴퓨팅의 실제 논문지
• /
• 제22권5호
• /
• pp.201-208
• /
• 2016

실시간으로 여러 시계열 데이터를 수집, 저장하는 데는 많은 저장 공간을 요구하게 된다. 이러한 공간 문제를 해결하는 방안으로, 이산 코사인 변환 압축에서 가변 샘플 크기를 사용하는 방안을 제안하였다. 시계열 데이터 셋은 값의 변화가 작을수록, 그리고 변화의 빈도가 낮을수록 압축률이 높아지는 특성을 가지고 있으며 이러한 특성을 잘 반영할 수 있는 척도로 변동 계수와 인접 요소 간 변동성 계수를 사용하여 가변 샘플 크기를 결정하는 데 사용하였다. 여러 실제 데이터 셋을 대상으로 시험한 결과, 두 방식 모두 양호한 압축률을 보이고 있다. 그러나 인접 요소간 변동성 계수 기반 압축 방식이 변동 계수 기반 방식 보다 샘플 크기 결정 방식이 훨씬 간단할 뿐만 아니라 보다 나은 압축률을 보임을 확인하였다.

• 한국광물학회지
• /
• 제11권2호
• /
• pp.126-134
• /
• 1998

Surface site and areas of particles are geometrically calculated for the cubic structures to investigate how the surface sites vary with the variation of morphology and particle size. The numbers of surface site and area become smaller when the particles become equi-dimensional shape. The ratios of surface site to surface area are almost constant except the case of anion of fluorite structure. The ratios of the number of surface site to area are almost constant regardless of particle size except the size of up to 5 to 10 times of the unit cell dimension. This quantification method can be used to obtain data related to the surface reaction.

• 콘크리트학회논문집
• /
• 제12권6호
• /
• pp.99-108
• /
• 2000

The size effect on axial compressive strength in notched concrete specimens was experimentally investigated. Based on the concept of the fracture mechanics and size effect law, theoretical studies for axial compressive failure of concrete were reviewed, and two failure modes of concrete specimens under compression were discussed. In this study, experiments of axial compressive failure, which is one of the two failure modes, was carried out by using cylindrical specimens. Adequate notch length was taken from the experimental result of strength variation based on the notch length. And, by taking various sizes of specimens the size effect on axial compressive strength of concrete was investigated. Also, model equations were suggested by modified size effect law (MSEL). The test results show that size effect appears conspicuously for all series of specimens. Additionally, the effect of initial notch length on axial compressive strength was also apparent.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
• /
• pp.267.2-267.2
• /
• 2013

In the citrate reduction method of gold nanoparticle (AuNP) synthesis, pH of the reaction mixture can have a considerable impact on the size and size distribution of AuNPs. In this work, effects of pH variation upon the size and its distribution were examined systematically. As the initial pH was change from 5.5 to 10.5, it showed an optimal pH around 7.5. At this pH, both of the size and the size distribution showed their minimum values, which was verified by transmission electron microscopy and UV-vis spectroscopy. This occurrence of optimal pH was discussed with the results of in situ monitoring pH during the reaction of AuNP synthesis.

• 한국산림과학회지
• /
• 제80권4호
• /
• pp.379-382
• /
• 1991

난괴법 3반복(反復)으로 배치(配置)한 잣나무 10년생(年生) 반형매차대검정림(半兄妹次代檢定林)에서 plot당(當) 임의(任意)로 2-10본(本)의 표본목(標本木)을 선정(選定)한 후(後), 분산분석(分散分析)을 통하여 가계평균(家系平均) 수고(樹高)의 오차(誤差)를 나타내는 C.V. 값을 각(各) sampling size 별(別)로 추정(推定), 비교(比較)하였다. plot당(當) 표본목수(標本木數)를 증가(增加)시킴에 따라 C.V.값은 점차 감소(減少)되었으며, plot당(當) 4본(本)부터 안정(安定)된 C.V. 값(6.97%)을 나타내었으나, plot당(當) 7본(本)부터는 실험오차(實驗誤差)가 증가(增加)됨을 알 수 있었다. 이들 두 변량간(變量間)에 ${\hat{Y}}=10.425e-^{0.073x}$ ($R^2$=0.840)의 관계식(關係式)을 추정(推定)할 수 있었다.

• 한국콘텐츠학회논문지
• /
• 제9권4호
• /
• pp.347-354
• /
• 2009

석탑들은 일반적으로 석탑 내부에 사리공과 같은 작은 내부 공간이 존재하며 이 내부 공간의 크기가 석탑문화재 보전에 영향을 줄 수 있다. 또한 석탑의 기울기 역시 석탑 보전을 위해 고려해야할 중요한 인자이다. 본 논문에서는 자중을 받고 있는 정혜사지 십삼층석탑에 대하여 유한요소법을 이용한 전산해석을 실시하여 석탑의 최대취약부위를 조사하고 내부 공간 및 기울기 변화에 따라 최대취약부위에 어떻게 영향을 주는지 연구하였다. 그리고 탑의 파손위험성을 판단할 수 있는 변형 및 음력의 관점에서 석탑의 내부 공간 및 기울기 변화에 의한 안전진단기준이 제시되었다.