• Computers and Concrete
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• 제26권6호
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• pp.505-513
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• 2020

Grading of aggregate influences significantly almost all of the concrete performances. The purpose of this paper is to propose practicable equations that express the optimized total aggregate gradation, by weight or by number of particles in a concrete mix. The principle is based on the fractal feature of the grading of combined aggregate in a solid skeleton of concrete. Therefore, equations are derived based on the so-called fractal dimension of the grain size distribution of aggregates. Obtained model was then applied in such a way a correlation between some properties of the dry concrete mix and the fractal dimension of the aggregate gradation has been built. This demonstrates that the parameter fractal dimension is an efficacious tool to establish a unified model to study the solid phase of concrete in order to design aggregate gradation to meet certain requirements or even to predict some characteristics of the dry concrete mixture.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2141-2147
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• 1996

The strength of material is scattered owing to the inhomogenity of microstructure, in spite of the same material. Therefore, in order to design the mechanical structure with the reliability engineering, it is important to grasp the statistical nature of material strength. In this paper, effects of grain sezes for the statistical nature of the fatigue crack growth was discussed. And the statistical nature of mechanical properties was compared with the statistical nature of the fatigue crack growth rate.

• Ocean Science Journal
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• 제42권2호
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• pp.69-79
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• 2007

A vertical transect with 4 km length was established for the macrofaunal survey on the Chokchon macrotidal flat in Kyeonggi Bay, Incheon, Korea, 1994. Tidal elevation (m) and sediment mean grain size $(\phi)$ were inversely predicted by the transfer functions from the faunal assemblages. Three methods: weighted average using optimum value (WA), tolerance weighted version of the weighted average (WAT) and maximum likelihood calibration (MLC) were employed. Estimates of tidal elevation and mean grain size obtained by using the three different methods showed positively corresponding trends with the observations. The estimates of MLC were found to have the minimum value of sum of squares due to errors (SSE). When applied to the previous data $(1990\sim1992)$, each of three inference models exhibited high predictive power. This result implied there are visible relationships between species composition and faunas' critical environmental factors. Although a potential significance of the two major abiotic factors was re-affirmed, a weak tendency of biological interaction was detected from faunal distribution patterns across the flat. In comparison to the spatial and temporal patterns of the estimates, it was suggested that sediment characteristics were the primary factors regulating the distribution of macrofaunal assemblages, rather than tidal elevation, and the species composition may be sensitively determined by minute changes in substratum properties on a tidal flat.

• 한국주조공학회지
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• 제4권1호
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• pp.5-11
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• 1984

Green compressive strength, permeability, deformation, flowability, compactability and green hardness values at room temperature are dependable on the grain distribution and grain shape. The results obtained under constant moisture (4% for sand) and bentonite (8% for sand) were as follows; 1. With decreasing grain size, surface area of sand grain was increased. 2. With decreasing grain size, coefficient of angularity was increased. 3. As surface area increased from $8926.43cm^2$ to $21211.16cm^2$ , green compressive strength was increased from $210.93\;g/cm^2$ to $449.98\;g/cm^2$, hardness was increased from 76.7 to 82.3, but permeability was decreased from $411.7\;{\frac{\;cc\;{\cdot}\;cm\;}{atm\;{\cdot}\;cm^2\;{\cdot}\;min.}}$ to $113.7\;{\frac{\;cc\;{\cdot}\;mm\;}{atm\;{\cdot}\;cm^2\;{\cdot}\;min.}}$ 4. As surface area increased from $8926.43\;cm^2$ to $21211.16\;cm^2$, flowability was decreased from 82.3% to 80.8%, deformation was decreased from $67.1\;cm\;{\times}\;10^{-3}$ to $54.6\;cm\;{\times}\;10^{-3}$, but compactability was increased from 44.8% to 54.3%. 5. Room temperature properties of molding sand were affected by variation of surface area.

• 열처리공학회지
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• 제35권2호
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• pp.57-65
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• 2022

In this study, the effect of the initial particle size distribution (PSD) of (K_0.5Na_0.5)NbO₃ powders on the microstructure of sintered ceramics was investigated. (K_0.5Na_0.5)NbO₃ powders with uni-, bi-, tri-, and quad-modal PSDs were obtained through a planetary ball-mill. For the specimens sintered at 1080℃, the growth of abnormal grains was promoted from the powders exhibiting quad- and tri-modal PSDs with a high content of large particles, resulting in a microstructure in which huge abnormal grains were predominant. However, as the number of peaks in PSD and the overall particle size decreased, the abnormal grain growth was suppressed and the grain growth of small particles started, resulting in a microstructure with a uniform grain size. For the specimens sintered at 1100℃, huge abnormal grains were not observed due to the decrease in the critical driving force for 2D nucleation even when powders with quad- and tri-modal PSDs were used. It was confirmed that when powder with unimodal PSD was used, a uniform microstructure that was not significantly affected by the sintering temperature could be obtained. The results of this study demonstrate that the microstructure of (K_0.5Na_0.5)NbO₃-based ceramics can be controlled by controlling the particle size of the initial powder.

• 자원환경지질
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• 제33권3호
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• pp.195-204
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• 2000

order to investigate physical characteristics and element concentrations of sediments, coastal bottom sediments were collected at 20 stations in the vicinity of Youngkwang Nuclear Power Plant. After air drying of samples in the laboratory. article size distribution was examined by Master sizer (X-350F), radio-activity by HPGe ${\gamma}$-spectrphotometer, and element concentrations by ICP-AES and AAS. According to particle size analysis , sediments are mainly composed of silt fraction weith 23% of sand, 65% of silt and 12% of clay on average. Most sediments are derived from muddy environment that silt dominates with the characteristics of 5.3${\varsigma}$ mean particle size, poorly sorted, very fine skewed and lepto-kurtic. Only two sediments are well sorted with sandy silt owing to wind, winnowing action, tide and current andits complex reactions. Element concentrations in the coastal bottom sediments are relatively high at finer sediment and show significant relationship with grain size. Index of geoaccumulation by heavy metals at every sampling station is classified as practically unpolluted. The radioactivities of the sediments were measured for 15 isotope elements, and 2 elements of K-40 and Cs-137 were detected in most sediments. The K-40 is the natural nuclide and the artificial nuclide of Cs-137 was thought to be derived from the fallout of past nuclear weapon test. The results of correlation coefficient between grain size and radioactivity shows that the activity of Cs-137 significantly increases in finer grain.

• 한국세라믹학회지
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• 제35권5호
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• pp.499-504
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• 1998

Pechini 방법으로 98.0 mol% ZnO, 1.0mol% $Bi_2O_3$, 0.5mol% CaO, 그리고 0.5mol% $MnO_2$ 조성의 ZnO 바리스터를 제조하여 소결거동과 전기적 특성을 관찰하였다. Pechini 방법으로 제조된 ZnO 바리스터 분말은 평균 입자크기가 $1.5\mu$m 정도이며 좁은 입도 분포를 보였다. $1100^{\circ}C$의 소결온도에서 전형적인 액상소결 과정에서 나타나는 입자성장 거동을 보였으며, 균일한 입자크기와 입계를 따라 Bi가 풍부한 액상이 고르게 분포된ZnO 바리스터를 제조할 수 있었다. 본 실험에서 비직선계수는 40~60 정도의 비교적 높은 값을 보였으며, 항복전압의 역수는 입자크기에 거의 비례하였다. 이것은 Pechini 방법으로 제조한 ZnO 바리스터가 균일한 입자크기와 균일한 액상의 분포를 갖는 바람직한 미세구조를 갖는 것을 보여 주는 것으로, Pechini 방법을 이용함으로서 ZnO 바리스터의 미세구조를 효과적으로 조절할 수 있으므로, 그 전기적 특성의 제어가 가능할 것으로 사료된다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.225-228
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• 2007

This paper presents a geostatistical methodology to model local uncertainty in spatial estimation of sediment grain size with high-resolution remote sensing imagery. Within a multi-Gaussian framework, the IKONOS imagery is used as local means both to estimate the grain size values and to model local uncertainty at unsample locations. A conditional cumulative distribution function (ccdf) at any locations is defined by mean and variance values which can be estimated by multi-Gaussian kriging with local means. Two ccdf statistics including condition variance and interquartile range are used here as measures of local uncertainty and are compared through a cross validation analysis. In addition to local uncertainty measures, the probabilities of not exceeding or exceeding any grain size value at any locations are retrieved and mapped from the local ccdf models. A case study of Baramarae beach, Korea is carried out to illustrate the potential of geostatistical uncertainty modeling.

• 한국환경과학회지
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• 제17권11호
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• pp.1203-1210
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• 2008

Flow resistance in a natural stream is caused by complex factors, such as the grains on the bed, vegetation, and bed-form, reach profile. Flow resistance in a generally stable gravel bed stream is due to protrudent grains from bed. Therefore, the flow resistance can be calculated by equivalent roughness in gravel bed stream, but estimation of equivalent roughness is difficult because nonuniform size and irregular arrangement of distributed grain on natural stream bed. In previous study, equivalent roughness is empirically estimated using characteristic grain size. However, application of empirical equation have uncertainty in stream that stream bed characteristic differs. In this study, we developed a model using an analytical method considering grain diameter distribution characteristics of grains on the bed and also taking into account flow resistance acting on each grain. Also, the model consider the protrusion height of grain.

• 한국농공학회논문집
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• 제60권4호
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• pp.83-91
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• 2018

Land reclamation, coastal construction, coastline extension and port construction, all of which involve dredging, are increasingly required to meet the growing economic and societal demands in the coastal zone. During the land reclamation, a portion of landfills are lost from the desired location due to a variety of causes, and therefore prediction of sediment transport is very important for economical and efficient land reclamation management. In this study, laboratory disposal tests were performed using an open channel, and suspended sediment transport was analyzed according to flow velocity and grain size. The relationships between the average and standard deviation of the deposition distance and the flow velocity were almost linear, and the relationships between the average and standard deviation of deposition distance and the grain size were found to have high non-linearity in the form of power law. The deposition distribution of sediments was demonstrated to have log-normal distributions regardless of the flow velocity. Based on the experimental results, modeling of suspended sediment transport was performed using deep neural network, one of deep learning techniques, and the deposition distribution was reproduced through log-normal distribution.