• 응용통계연구
• /
• 제27권3호
• /
• pp.445-459
• /
• 2014

일반적으로 특정한 작업에 익숙해진다는 것은 그 작업에 투입되는 노력에 비해 산출되는 성과가 보다 뚜렷해진다는 것을 의미한다. 동일한 양이나 정도의 노력을 들여 특정한 작업을 반복적으로 수행하게 되면 초기 시점보다 원하는 성과를 기대 이상으로 얻게 된다는 것을 의미한다. 이를 학습곡선효과(learning-curve effects)'라고 한다. 본 연구에서는 특정한 작업을 반복시행한 결과가 개수형인 형태로 측정되는 변수에 대해 (역)S자 형태를 가지는 통계적 모형을 적용하고자 한다. 다양한 모의실험 하에서의 모형의 성능을 평가하고 특정질환으로 인한 사망자 자료에 적합하였다.

• Biomolecules & Therapeutics
• /
• 제4권3호
• /
• pp.265-270
• /
• 1996

The purpose of this study was to determine pharmacokinetic parameters and tissue distribution patters of urinary trypsin inhibitor(UTI) in Sprague-Dawley rats. $Na^{125}$I was conjugated to UTI to make $^{125}I-UTI$ and the concentrations were determined by $\gamma$-counter. With the aid of nonlinear least-square regression analysis for i.v bolus injection of 1,000 unit UTI including $^{125}I-UTI$, the temporal concentration curves were best fitted by 2-compartment open model. The distribution phase half-life was 0.39$\pm$0.02 hours whereas the elimination half-life was 12.99$\pm$1.05 hours in male rats. The volume of distribution and total body clearance in male rats were 0.28$\pm$0.01 1/kg and 83.16$\pm$1.15 ml/kg/h, respectively. We could not find any difference of pharmacokinetic parameters of UTI between male and female rats. UTI were distributed widely in rat organs. In both male and female rats, the kidney was the highest distributed organ. Amount of UTI in 24 hour cumulative urine in male rats was 36.22$\pm$8.74% and that in 48 hours was 43.32$\pm$10.55%. Excretion via feces was very scanty, with the 24 hours cumulative amount being only 2.76$\pm$0.97%. This data suggest the main excretion route of UTI is urine.

• 대한기계학회논문집A
• /
• 제20권12호
• /
• pp.3892-3898
• /
• 1996

In this study, the prediction of the fatigue life as well as the extimation of the characteristics of fatigue cumulative damage on GFRP under random loading were performed. The constant amplitude tests and the ramdom loading test were carried on notched GFRP specimens with a circular hole. Random waves were generated with a micro-computer and had wide band spectra. Since it is useful that the prediction of fatigue life ot the given load sequences is based on S-N curves under constant amplitude loading, the estimation of equivalent stress is done on every random waves. The equivalent stress wasat first estimated by Miner's rule and then by the proposed model which was based on Hashin-Rotem's comulative damage theory regarding nonlinear fatigue cumulative damage behavior. The fatigue lives were predicted from each equivalent stress evaluated. And each predicted fatigue llife was compared with experimental results. The number of cycles of random loads were counted by mean-cross counting method. The reuslts showed that the fatigue life predicted by proposed model was correlated well with the experimental results in comparison with Miner's model.

• 품질경영학회지
• /
• 제25권2호
• /
• pp.1-14
• /
• 1997

This paper considers maximum likelihood (ML) estimation of lifetime distribution under stress bounded ramp tests in which the stress is increased linearly from used condition stress to the stress u, pp.r bound. The following assumptions are used: exponential lifetime distribution under a constant stress, an inverse power law relationship between stress and mean of exponential lifetime distribution, and a cumulative exposure model for the effect of changing stress. Likelihood equations for the parameters involved in the model and asymptotic distribution of the estimators are obtained, and a numerical example is given.

• Journal of Welding and Joining
• /
• 제9권1호
• /
• pp.40-47
• /
• 1991

The most fatigue tests carried out under the either stress or strain control, but machines and structures had taken variable stress. This variable stress was treated as statistics based on p-type distributions. In this paper, the cumulative fatigue damage of SM45C round bar specimens having a center hole resulting from block loading with p-distributions in rotating bending conditions, is presented. The value of p was changed in the range from 0.25 to 1; 0.25, 0.5, 0.75, 1. The following conclusions were obtained through the constant stress amplitude experiments and the block loading experiments. (1) In constant loading test, fatigue life was affected by cyclic rate. From experimental data, N$_{f}$ (100cpm)/N$_{f}$(3000cpm)equal to 0.56. (2) In case of the cyclic rate 100cpm and 3000cpm, at the high stress amplitude level the crack propagation life N$_{*}$f is longer than the low stress amplitude level. (3) Miner's hypothesis may be valid for p=0.75 and prediction of fatigue life by Haibach's method agree with experimental data well for the case p=0.5, while the modified Miner's method agree with experimental data well for the case p=0.25.5.

• 대한기계학회논문집A
• /
• 제20권4호
• /
• pp.1241-1250
• /
• 1996

The characteristics of fatigue cumulative damage and fatigue life of 8-harness satin woven CFRP composites with a circular hole under constant amplitude and 2-level block loading are estimated by Stochastic Makov chain model. It is found in this study that the fatigue damage accumulation behavior is very random and the fatigue damage is accumulated as two regions under constant amplitude fatigue loading. In constant amplitude fatigue loading the predicted mean number of cycles to a specified damage state by Markov chain model shows a good agreement with the test result. The predicted distribution of the fatigue cumulative damage by Markov chain model is similar to the test result. The fatigue life predictions under 2-level block loading by Markov chain model revised are good fitted to the test result more than by 2-parameter Weibull distribution function using percent failure rule.

• 대한토목학회논문집
• /
• 제26권5B호
• /
• pp.519-528
• /
• 2006

수공구조물 설계에서 가장 중요한 일은 설계홍수량을 결정하는 것이다. 따라서 설계홍수량 산정에 영향을 미치는 여러 가지 요소 중 적절한 설계 강우의 시간분포 방법을 선택하는 것은 중요한 일이다. 설계 강우의 시간분포 방법에는 여러 가지 방법들이 있으며, 그 중에서 최근 첨두홍수량 산정을 위한 설계 강우의 시간분포 방법에 많이 이용하고 있는 Huff의 4분위법은 6시간 이상의 무강우시간을 갖는 강우사상을 자료로 이용, 분석하여 설계 강우의 시간분포 방법을 제시한 방법이다. 본 연구에서는 Huff의 4분위법에서 이용한 자료와 달리 1961년부터 2004년까지 서울지역 강우 관측자료 중 지속기간별 연 최대치 강우자료를 이용하여 강우의 시간분포 특성을 분석하고 이전의 연구 결과와 비교하였다. 각각의 결과에 대하여 비교한 결과 서울지역의 경우 연 최대치 강우의 지속기간이 짧을 경우 무차원 누가곡선이 Huff의 4분위법 결과에 비하여 비교적 완만하게 나타났으며, 지속기간이 점점 증대될수록 무차원 누가곡선은 Huff의 4분위법 결과와 유사하게 나타났다.

• Computers and Concrete
• /
• 제8권2호
• /
• pp.163-176
• /
• 2011

By virtue of chord-length density function from the field of statistical physics, this paper introduced a quantitative approach to estimate the distribution of cement paste thickness between aggregates in concrete. Dynamics mixing method based on molecular dynamics was employed to generate one model structure, then image analysis algorithm was used to obtain the distribution of thickness of cement paste in model structure for the purpose of verification. By comparison of probability density curves and cumulative probability curves of the cement paste thickness among neighboring aggregates, it is found that the theoretical results are consistent with the simulation. Furthermore, for the model mortar and concrete mixtures with practical volume fraction of Fuller-type aggregate, this analytical formula was employed to predict the influence of aggregate volume fraction and aggregate fineness. And evolution of its mean values were also investigated with the variation of volume fraction of aggregate as well as the fineness of aggregates in model mortars and concretes.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.445-450
• /
• 2003

This study was performed 10 develop the accelerated life test method using Weibull-IPL(Inverse Power Law) model for mechanical components. Weibull-IPL model is concerned with determining the assurance life with confidence level and the accelerated life test time From the relation of weibull distribution factors and confidence limit, the testing times on the no number of failure acceptance criteria arc determined. The mechanical components generally represent wear and fatigue characteristics as a failure mode. IPL based on the cumulative damage theory is applied effectively the mechanical components to reduce the testing time and to achieve the accelerating test conditions. As the actual application example, accelerated life test method of agricultural tractor transmission was described. Life distribution of agricultural tractor transmission was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 3,000 hours and 90% confidence level for one test sample. According to IPL, because test time call be shorten in case increase test load test time could be reduced by 482 hours when we put the load 1.1 times of rated load than 0.73 times of rated load that is equivalent load calculated by load spectrum of the agricultural tractor. This time, acceleration coefficient was 11.7.

• 한국항행학회논문지
• /
• 제15권2호
• /
• pp.234-240
• /
• 2011

본 논문에서는 다수의 지상국을 이용하여 얻은 FDOA(Frequency Difference of Arrival) 측정값을 통해서 UAV(Unmanned Aerial Vehicle; 무인항공기) 추적 알고리즘의 이론적 경계인 CRLB(Cram$\acute{e}$r-Rao Lower Bound)를 분석하였다. 첫째로 FDOA 측정값을 시간을 두고 모았을 때 CRLB에 주는 영향을 관찰하였고, 둘째로 지상국이 일정한 범위 안에서 무작위적 위치를 가질 때 그 범위에 따른 FDOA의 측정값이 어떤 특성을 갖는지 확인할 수 있었다. 또한 CRLB의 크기를 측정하여 CCDF(Complementary Cumulative Distribution Function)로 나타내어 성능을 비교, 분석하였다.