• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.65-73
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• 1992

The effect of grain size on the time-dependent piezoelectrice degradation of a poled PZT of MPB composition Pb0.988Sr0.012 (Zr0.52Ti0.48)O3 with 2.4 mol% of Nb2O5 was studied, and the degradation mechanism was discussed. Changes in the internal bias field and the internal stress both responsible for the time-dependent degradation of poled PZT were examined by the polarization reveral technique, XRD and Vickers indentation, respectively. The piezoelectric degradation increased with increasing time and grain size, and the internal bias field due to space charge diffusion decreased with increasing grain size of poled PZT. The internal bias field, however, was almost insensitive to the degradation time regardless of the grain size. On the other hand, both the x-ray diffraction peak intensity ratio of (002) to (200) and the fracture behavior including the crack propagation support that the ferroelectric domain rearrangement of larger grain size showed rapid relaxation of the internal stress compared with smaller one, which is thought the origin of the larger piezoelectric degradation in the former. In conclusion, the contribution of space charge diffusion on the piezoelectric degradation of PZT is strongly dependent on both the grain size and the composition. Thus, the relaxation of internal stress due to the ferroelectric domain rearrangement as well as the amount and time-dependence of the internal bias field due to space charge diffusion should be considered simultaneously in the degradation mechanism of PZT.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.5
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• pp.808-813
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• 2021

The diet composition of Spanish mackerel Scomberomorus niphonius, was investigated using 853 specimens collected using two-boat trawl, stow net, gill net and set net from January to December 2019 from the South Sea of Korea. The size of the specimens ranged from 25.2 to 114.8 cm in fork length. S. niphonius fed mostly on fishes. Its diets also included small quantities of shrimps, cephalopods, crabs, stomatopods, etc. Among them, Engraulis japonicus was the dominant species. The dietary composition of S. niphonius exhibited significant differences based on their size. The proportion of Trichiurus japonicus increased as body size of S. niphonius increased, whereas the proportion of E. japonicus decreased gradually. As the body size of S. niphonius increased, the mean weight of prey per the stomach (mW/ST) tended to increase significantly (one-way ANOVA, P<0.05).

• The Korean Journal of Ceramics
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• v.3 no.2
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• pp.116-123
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• 1997

A chemically stabilized $\beta$-cristobalite, which is stabilized by stuffing cations of $Ca^{2+}$ and $Al^{3+}$, was prepared by a solution-polymerization route employing Pechini resin or PVA solution as a polymeric carrier. The polymeric carrier affected the crystallization temperature, morphology of calicined powder, and particle size distribution. In case of the polyvinyl alcohol (PVA) solution process, a fine $\beta$-cristobalite powder with a narrow particle size distribution (average particle size : 0.3$\mu\textrm{m}$) and a BET specific surface area of 72 $\m^2$/g was prepared by an attrition-milling for 1 h after calcination at 110$0^{\circ}C$ for 1h. Wider particle size distribution and higher specific surface area were observed for the $\beta$-cristobalite powder derived from Pechini resin. The cubie(P1-to-tetraganalb) phase transformation in polynystalline $\beta$-cristobalite was induced at approximately 18$0^{\circ}C$. Like other materials showing transformation toughening, a critical size effect controlled the $\beta$-to-$\alpha$ transformation. Densifed cristobalite sample had some cracks in its internal texture after annealing. The cracks, occurred spontaneoulsy on cooling, were observed in the sample with an average grain sizes of 4.0 $\mu\textrm{m}$ or above. In case of the sintered cristobalite having a composition of CaO.$2Al_2O_3$.40SiO$_2$, small amount of amorphous phase and slow grain growth during annealing were observed. Shear stress-induced transformation was also observed in ground specimen. Cristobalite having a composition of CaO.2Al2O3.80SiO2 showed a more sensitive response to shear stress than the CaO.$2Al_2O_3$.40SiO$_2$ type cristobalite. Shear-induced transformation resulted in an increase of volume about 13% in $\alpha$-cristobalite phase on annealing for above 10 h in the case of the former composition.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.50 no.4
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• pp.530-541
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• 2014

The dredge gear is dragged along the bottom of the sea to catch targeted edible bottom dwelling species. Species composition and ecological index of the catches of dredge were estimated around Gangneung coastal fishing ground by dredge with different mesh size and tooth space from July to December 2013. Eight different types of dredge including four different tooth space (24.7 mm, 29.9 mm, 34.9 mm, 40.1 mm) and four different mesh size(15.5 mm, 32.7 mm, 51.1 mm, 60.0 mm) were used in the experiment. During the experiment, total catches were collected 31 species as sipunculida 1 species, mollusca 13 species, annelida 3 species, arthropoda 8 species, echinodermata 4 species and others 2 species. The dominant genus were mollusca and echinodermata while the dominant species were Megangulus venulosus, Pseudocardium sachalinensis, Schaphechinus brevis. The richness index was ranged 1.29-1.72, evenness index was 0.6-0.65 and diversity index was 1.65-1.83 according to the tooth space and mesh size of dredge. Richness index, diversity index were high at tooth space 34.9 mm dredge and ecological index showed decreasing tendency with the increasing of mesh size of dredge. Cluster and MDS analysis, based on a Bray-Curtis and similarity matrix of fourth root transformed data of number of species and wet weight, showed division into four different groups as four different tooth space (Group A), four different mesh size Group B (51.1 mm, 60.0 mm), Group C (32.7 mm) and Group D (15.5 mm).

• Toxicological Research
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• v.30 no.1
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• pp.55-63
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• 2014

Objectives: The use of indium compounds, especially those of small size, for the production of semiconductors, liquid-crystal panels, etc., has increased recently. However, the role of particle size or the chemical composition of indium compounds in their toxicity and distribution in the body has not been sufficiently investigated. Therefore, the aim of this study was to examine the effects of particle size and the chemical composition of indium compounds on their toxicity and distribution. Methods: Male Sprague-Dawley rats were exposed to two different-sized indium oxides (average particle sizes under 4,000 nm [IO_4000] and 100 nm [IO_100]) and one nano-sized indium-tin oxide (ITO; average particle size less than 50 nm) by inhalation for 6 hr daily, 5 days per week, for 4 weeks at approximately $1mg/m^3$ of indium by mass concentration. Results: We observed differences in lung weights and histopathological findings, differential cell counts, and cell damage indicators in the bronchoalveolar lavage fluid between the normal control group and IO- or ITO-exposed groups. However, only ITO affected respiratory functions in exposed rats. Overall, the toxicity of ITO was much higher than that of IOs; the toxicity of IO_4000 was higher than that of IO_100. A 4-week recovery period was not sufficient to alleviate the toxic effects of IO and ITO exposure. Inhaled indium was mainly deposited in the lungs. ITO in the lungs was removed more slowly than IOs; IO_4000 was removed faster than IO_100. IOs were not distributed to other organs (i.e., the brain, liver, and spleen), whereas ITO was. Concentrations of indium in the blood and organ tissues were higher at 4 weeks after exposure. Conclusions: The effect of particle size on the toxicity of indium compounds was not clear, whereas chemical composition clearly affected toxicity; ITO showed much higher toxicity than that of IO.

• Journal of the Korean Institute of Educational Facilities
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• v.18 no.6
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• pp.33-43
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• 2011

The Korean academics of classical learning, Seowon which from the middle of Joseon Dynasty was complexly reflected in "the illustration of Taiji(太極圖說)" Five-Elements school(陰陽五行說), "Zhou Yi(周易)" and a theory on spherical heaven and square ground(天圓地方) which based on orientalism. Also the theory of Xiangshu Xue(象數學) was a significant factor to decide the size(number of facade module) of Seowon architecture. So, in this study, how the oriental thought was adopted and reflected in existing 21 Seowon in South Korea. The size of Seowon architecture was adopted a theory of combination with heaven, earth and human(天地人三合論) that based on the theory of Xiangshu Xue on "the illustration of Taiji" and "Zhou Yi". "Zhou Yi" was the central thought of Confucian culture in Joseon Dynasty, with which Seowon space was divided into two, ancestral rites space and lecture space. It coincides with balance of yin(陰) and yang(陽), Five-Elements(五行) and four seasons(四季節). In lecture space, lecture hall is relevant with the water(水) and winter, and front tower structure or outer three-door is the fire(火) and summer. Also, central garden means the soil(土) and center. Thus, the size and spatial composition was planned with the philosophy, "the illustration of Taiji", Five-Elements school and a theory on spherical heaven and square ground. Yin and yang has an idea of the heaven and earth, and Five-Elements has an idea of direction and season with which spatial composition of Seowon could be set. And the numeral meaning on the theory of Xiangshu Xue established an ideal background for spatial composition of Seowon architecture.

• Journal of the Korean Ceramic Society
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• v.21 no.4
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• pp.366-372
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• 1984

Unstabilized Zirconia was added to basic composition under 44$mu extrm{m}$ of 57.80wt% Clay-22.20wt% Chamotte-20.00wt% Agalmatolite system. Here the amount and the particle size of Zirconia were 5-25wt% and -20${\mu}{\textrm}{m}$ respectively and the body of these composition was first at 135$0^{\circ}C$. The results obtained from examining the properties of sintered body were as follows. 1. Firing linear shrinkage apparent density and bulk density apparent porosity and water absorption of the samples had the tend to increase according as the particle size of zirconia became larger and the amount of zirconia increased. 2. Modulus of rupture was inversely proportional to the particle size and the additive amount of zirconia, . Especially in case that the particle size of zirconia over 5${\mu}{\textrm}{m}$ and the additive amount of zirconia was 25wt% the modulus of rupture had shrunk drastically. 3. The maximum value of KIC was obtained at 20wt% additive amount of zirconia according to the each particle size of zirconia. Especially the highest value of KIC is 2, 173 M. Pa. M1/2 when the particle size of zirconia is 5~10${\mu}{\textrm}{m}$ and the additive amount is 20wt%.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.1
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• pp.80-89
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• 2021

In Korea, marine fish landed at ports are randomly sampled on a periodic basis (e.g., daily or weekly), and body sizes (e.g., lengths and weights) of those sampled fish are measured. The motivation for our study is whether or not such measurements reflect the size distribution, especially the length distribution of fish landed (= a population), because such length measurements are key data for a length-based assessment model. The current sampling method is to sample fish landed at ports by body size group (e.g., very small, small, medium, large, very large), using the sampling weights as the number of boxes by body size group. In this study, we showed that length composition data about fish sampled by the current method did not represent the length frequency distribution of the fish landed, and suggested that an alternative sampling method should be applied of using the sampling weights as the number of fish landed by body size group. We also introduced a method for determining an appropriate sample size.

• Geomechanics and Engineering
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• v.28 no.2
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• pp.135-143
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• 2022

Soils are natural granular materials whose mechanical properties differ according to the size and composition of the particles, so soils exhibit an obvious scale effect. Traditional soil mechanics is based on continuum mechanics, which can not reflect the impact of particle size on soil mechanics. On that basis, a matrix-reinforcing-particle cell model is established in which the reinforcing particles are larger-diameter sand particles and the matrix comprises smaller-diameter bentonite particles. Since these two types of particles deform differently under shear stress, a new shear-strength theory under direct shear that considers the stress concentration and bypass phenomena of the matrix is established. In order to verify the rationality of this theory, a series of direct shear tests with different reinforcing particle diameter and volume fraction ratio are carried out. Theoretical analysis and experimental results showed that the interaction among particles of differing size and composition is the basic reason for the size effect of soils. Furthermore, the stress concentration and bypass phenomena of the matrix enhance the shear strength of a soil, and the volume ratio of reinforcing particles has an obvious impact on the shear strength. In addition, the newly proposed shear-strength theory agrees well with experimental values.

• Journal of the Korean housing association
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• v.16 no.1
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• pp.97-104
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• 2005

The purpose of this study is to understand changes of the population and family composition in apartment houses. The main contents of this study is to find the way of housing planning through the analysis of the population and family composition by the unit types. The population and family composition were studied by computer data base program to 11,000 residents of selection 4 apartments houses. The structure of the family types proved to be constant by the result of analyzing the 10 family types. If the family types of certain resident's groups are given, this study will be able to estimate population structure to them. The transition of the population and the family composition changes to the unit types proved to be constant by the time. The distribution of manhood and matured children is tend to change according to how large the size of house is, and to change the structure of family composition.