• The Korean Journal of Applied Statistics
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• v.30 no.2
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• pp.301-309
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• 2017

It is often possible to test for differences in population means when two or more samples are extracted from each N population. However, it is not possible to test for the mean difference if one sample is extracted from each population since a sample mean does not exist. But, by dividing a group of samples extracted one by one into two groups and generating a sample mean, we can identify a heterogeneity that may exist within the group by comparing the differences of the groups' mean. Therefore, we propose a minimum combination t-test method that can test the mean difference by the number of combinations that can be divided into two groups. In this paper, we proposed a method to test differences between means to check heterogeneity in a group of extracted samples. We verified the performance of the method by simulation study and obtained the results through real data analysis.

• Korean Journal of Soil Science and Fertilizer
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• v.17 no.3
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• pp.212-217
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• 1984

Spatial variabilities of particle size distribution of 96 samples from Hwadong SiCL and Jungdong Sl were studied by using geostatistical concepts. The measurement was made at the nodes of the regular grid consisting of 12 rows and 8 columns. Sample spacing within rows and columns was 3 and 2 meters, respectively. The results are summarized as follows. 1. Variograms of Hwadong SiCL were fitted for the linear model and those of Jungdong SL for the spherical model. 2. Variograms of properties for Hwadong and clay for Jungdong showed the pure nugget effect. Those of silt and clay for Jungdong, however, appeared the nugget effect. 3. The minimum number of samples necessary to reproduce results similar to the true mean of the 96 measured values was approximately estimated. The minimum sample sizes of silt, clay, and sand in Hwadong SiCL were 27, 13, and 6, respectively. And the minimum sample size of clay in Jungdong SL was 17. 4. The approximate number of samples required to detect the difference of 5% of the true mean with 0.95 confidence level was estimated. The resulting number of samples for silt and sand in Jungdong was 14, and 26, respectively.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.13 no.6
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• pp.25-33
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• 2014

This study investigates the reliability of DSRC-based traffic information system on the typical urban arterial with the minimum sample size method. VISSIM has been employed to calculate the required sample size. After comparing the number of hi-pass vehicles recorded from DSRC and the required sample size, this study found that the interrupted traffic state tends to generate more outliers than the uninterrupted one, the lack of the number of vehicles completely passing links with multiple driveways makes it difficult to estimate the reliable traffic information, the traffic information during peak hour is relatively more reliable than that during off-peak hour, and the reliability of DSRC-based traffic information system depends on the significance level in calculating the sample size. The driveway density and traffic signal operation due to the individual link length significantly affects the required sample size, resulting in determining the reliability of the DSRC-based traffic information system.

• Communications for Statistical Applications and Methods
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• v.12 no.1
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• pp.11-18
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• 2005

Assume that the life times of the units under test follow the Rayleigh distribution and the test is terminated at a pre assigned time. Acceptance sampling plans are developed for this situation. The minimum sample size necessary to ensure the specified average life are obtained and the operating characteristic values of the sampling plans and producer's risk are given. An example is given to illustrate the methodology.

• Journal of Magnetics
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• v.22 no.2
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• pp.188-195
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• 2017

The ferromagnetic resonance and other magnetic properties dependence on $Ni^{2+}/Fe^{3+}$ ratio and crystallite size were investigated for nano nickel ferrite ($NiFe_2O_4$). The crystallite size was controlled by controlling the nickel content in the starting material solution. The XRD and TEM were utilized to measure the crystallite size through Scherrer formula and particle size respectively. The most frequent particle sizes were lower than crystallite size, which ranged from 16.5 to 44.65 nm. The general behavior of M-H loop shapes and parameters showed superparamagnetic one. The saturation magnetization had a maximum value at $Ni^{2+}/Fe^{3+}$ molar ratio equal to 0.186. The FMR signals showed, generally, broad linewidths, where the maximum width and minimum resonance field were for the sample of the lowest crystalline size. Furthermore, FMR resonance field shows linear dependence on crystalline size. The fitting relation was estimated to express this linear dependency on the base of behavior coincidence between particle size and the inverse of saturation magnetization. The given interpretations to understand the intercept and the slope meanings of the fitted relation were based on Larmor equation, and inhomogeneous in the anisotropy constant.

• International Journal of Safety
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• v.1 no.1
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• pp.47-51
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• 2002

This study was performed by measuring the minimum ignition temperature of polyurethane form recovered from the recycling process of the end-of-life home appliances. The critical ignition temperature of polyurethane form was lower as the size of the sample vessel was increased, and that of polyurethane form using cyclopentane as the forming agent was relatively lower than the polyurethane form using CFC and the combustion of cyclopentane-polyurethane form occurred fiercely. It is considered that the recycling process of end-of-life home appliances using cyclopentane-polyurethane form as the insulator would require a special fire and dust explosion prevention measures since there exists a high potential hazard of fire and dust explosion during crushing and storage processes.

• Journal of the Korean Statistical Society
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• v.22 no.1
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• pp.71-81
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• 1993

Among k independent normal populations with unknown means and a common unknown variance, the problem of detecting the population with the largest absolute value of mean is considered. This problem is formulated in a manner close to the framework of testing hypotheses, and the maximum error probability and the minimum power are considered. The power charts necessary to determine the sample size are provided. The problem of detecting the population with the smallest absolute value of mean is also considered.

• Journal of the Korean Society of Safety
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• v.4 no.1
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• pp.5-14
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• 1989

Deterioration induced by partial discharge was investigated for low-density polyethylene samples. Under an electrical field, a cold-drawn PE film was stretched perpendicularly to the direction of the original drawing. The starting voltage of the discharge shows a minimum at the draw ratio of 1.2 to 1.8. Around the same draw ratio, the elastic modulus and mechanical loss factor (tan S) of the sample exhibit a minimum and a maximum, respectively. According to the X-ray analysis, the size itf microcrystals decreases with increasing draw ratios. Reorientation of the ru01ecular chains was observed above a draw ratio of 1.5 by the IR method.

• Journal of Soil and Groundwater Environment
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• v.21 no.6
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• pp.179-191
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• 2016

In addition to the measurement of the concentration of soil contaminants, the new idea of indicative parameters was proposed to validate the remedial works through the monitoring for the changes of soil characteristics after applying the clean up technologies. The parameters like CFU (colony forming unit), pH and soil texture were recommended as indicative parameters for land farming. In case of soil washing, water content and the particle size distribution of the sludge were recommended as indicative parameters. The sludge is produced through the particle separation process in soil washing and it is usually treated as a waste. The parameters like water content, organic matter content, CEC (cation exchange capacity) and CFU were recommended as indicative parameters for the low temperature thermal desorption method. Besides the indicative parameter, sampling methods in stock pile and the optimal minimum amount of composite soil sample were proposed. The rates of sampling error in regular grid, zigzag, four bearing, random grid methods were 17.3%, 17.6%, 17.2% and 16.5% respectively. The random grid method showed the minimum sampling error among the 4 kinds of sampling methods although the differences in sampling errors were very little. Therefore the random grid method was recommended as an appropriate sampling method in stock pile. It was not possible to propose a value of optimal minimum amount of composite soil sample based on the real analytical data due to the dynamic variation of $CV_{fund{\cdot}error}$. Instead of this, 355 g of soil was recommended for the optimal minimum amount of composite soil sample under the assumption of ISO 10381-8.

• Geomechanics and Engineering
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• v.31 no.5
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• pp.461-476
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• 2022

Research studies on the scale effect on triaxial strength of intact rocks are scarce, being more common those in uniaxial strength. In this paper, the authors present and briefly interpret the peak and residual strength trends on a series of triaxial tests on different size specimens (30 mm to 84 mm diameter) of an intact granitic rock at confinements ranging from 0 to 15 MPa. Peak strength tends to grow from smaller to standard-size samples (54 mm) and then diminishes for larger values at low confinement. However, a slight change in strength is observed at higher confinements. Residual strength is observed to be much less size-dependent. Additionally, this study introduces preliminary modelling approaches of these laboratory observations with the help of three-dimensional particle flow code (PFC3D) simulations based on bonded particle models (BPM). Based on previous studies, two modelling approaches have been followed. In the first one, the maximum and minimum particle diameter (D_max and D_min) are kept constant irrespective of the sample size, whereas in the second one, the resolution (number of particles within the sample or ϕ_v) was kept constant. Neither of these approaches properly represent the observations in actual laboratory tests, even if both of them show some interesting capabilities reported in this document. Eventually, some suggestions are provided to proceed towards improving modelling approaches to represent observed scale effects.