• Journal of Korea Foundry Society
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• v.23 no.3
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• pp.130-136
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• 2003

Rheocasting of AZ91D magnesium alloys yielded the microstructure consisted of the spherical primary particles in the matrix which is different from conventional casting. Rheocast ingots were produced under various processing conditions using batch type rheocaster. Morphology of primary particles was changed from rosette-shape to spherical shape with increasing stirring rate$(V_s)$ and decreasing isothermal stirring temperature$(T_s)$. With increasing $V_s$, more effective shearing between the particles occurred rather than the agglomeration and clustering, so the primary particle size decreased. But with decreasing $T_s$, primary particle size increased mainly due to sintering and partially Ostwald ripening. The sphericity of primary particles increased with increasing $V_s$ and decreasing $T_s$ due to enhanced abrasion among the primary particles. The uniformity of primary particle size increased with increasing Vs and $T_s$.

• KIEAE Journal
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• v.12 no.1
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• pp.29-34
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• 2012

As a series of studies about natural ventilation driven by wind in basement parking lots of apartment, the influence of opening size and surrounding buildings on ventilation rate was analyzed. Natural ventilation in underground parking lots almost rely on wind than temperature difference. To investigate natural ventilation driven by wind, wind tunnel tests by using scale model and tracer gas method were conducted. $CO_2$-gas concentration was measured, natural ventilation rates were calculated. The experimental results showed that the natural ventilation rate is more reliable to wind direction and surrounding building than opening size and distance between buildings. It was verified that surrounding buildings play a principal role in increasing air flow rate by accelerating wind speed, and growing turbulence intensity. And it showed that ventilation performance is able to be increased by oblique wind to entrance ramp than head on wind in underground parking lots with surrounding buildings.

• Journal of Biosystems Engineering
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• v.24 no.4
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• pp.359-364
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• 1999

A theoretical model was developed to evaluate the influence of control variables on the composting performance in a bin composting system. The model was verified using pilot scale composting system. Simulation of the composting temperature according to air flow rate and composting bin size was conducted using the mathematical model. High composting temperature above 55$^{\circ}C$ needed to kill a pathogen was maintained for longer periods as the air flow rate was lower and the bin size was larger. Optimum air flow rate was 0.77L/min/kg.DM for the experimental pilot scale bin system. The size of composting bin should be large enough to maintain the higher composting temperature for required periods.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.914-916
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• 2009

Using gelatin and acacia as wall and electronic ink as core substance, microcapsules were prepared by complex coacervation to fabricate a flexible electronic paper display. In order to obtain the microcapsules in a narrow dispersed distribution, we focus on the interfacial tension between the hydrophobic electrophoretic ink and an aqueous polyelectrolyte solution, through controlling sodium dodecyl sulphate (SDS) concentration and stirring rate. The existence of anionic surfactant of SDS not only decreases the droplet diameters, but also reduces the diameter size distribution. And, as the stirring rate is increased, the average size of microcapsule is also decreased.

• Korean Journal of Social Welfare
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• v.66 no.1
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• pp.251-276
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• 2014

This study scrutinizes the common sense in the field of disability employment that the bigger the size of a firm, the lower the employment rate of people with disabilities. This common sense has been established by conventional cross-tabulation and multiple regression analyses without taking into account possible interactions between the sizes of firms and the industries in which they operate. This study shows that the distribution of the disability employment rate violates the linearity and homoscedasticity assumptions of the OLS. In an effort to find models that explain the data better, this study fits the OLS model, the weighted linear regression model, and the multinomial logit model as well as the path analysis which is meant to examine the relationships between firm size and other variables relevant to disability employment. The result shows that, when an interaction term between firm size and industry is added to the model, firm size does not have any significant effect on disability employment rate for those firms with 100 or more regular employees, to the contrary of the findings of prior studies. It also demonstrates that other factors such as job setting, the extent of helpfulness of disability employment employers perceive, employers' care for disability, and employers' awareness of disability policies may matter more than does firm size. This study proposes that future research and policy implementation for disability employment should pay no less attention to industry and other factors mentioned above than to firm size.

• Korean Journal of Materials Research
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• v.29 no.4
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• pp.233-240
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• 2019

This study analyzes the mechanical properties, including the attrition rate, of $50{\mu}m$ size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grain-boundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of $50{\mu}m$ YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than $BaTiO_3$ powder (Hv ~315).

• Korean Journal of Human Ecology
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• v.11 no.4
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• pp.401-413
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• 2002

The purpose of this study was to survey the high school girls' alteration of school uniforms concerned about both size satisfaction and dissatisfaction and to improve the size of school uniforms. The subjects were 1,007 girls attending high schools in Cheju. The questionnaire survey was done from July 8th to Sep. 21th, 2001. According to the survey, 67.3 percentile of the interviewed girls alterated their uniforms. It was appeared that they alterated skirts more than blouses as a way of shortening. The main reason of alteration is ill-fitting uniforms, most of girls had a positive idea to alterate uniforms. Dissatisfaction of uniforms is mainly caused by the large size not by the small size. It was appeared that dissatisfaction rate of skirt was higher than that of blouse. The large part of dissatisfaction was appeared on waist circumference of blouse and hem circumference of skirt. The girls who experienced alterating the part of uniforms such as waist circumference of skirt, skirt length and hem circumference had high satisfaction rate. And a result of analyzing the level of satisfaction with uniforms-size-satisfaction/dissatisfaction showed the significant differences in fashion, factors-aesthetics and factors-activity of skirt and blouse.

• Journal of Embryo Transfer
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• v.26 no.1
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• pp.1-7
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• 2011

The purpose of this study was to determine the relationship between conception rate and other parameters (body condition score; BCS, progesterone concentrations and follicle size) before estrus induction with CIDR(intravaginal progesterone-releasing controlled internal drug release). The conception rate in cows with < 2.75, 2.75 to 3.25, and 3.25 <, BCS regardless of AI (artificial insemination) time was 46.6%, 63.3%, and 46.6% at CIDR insertion, respectively. The conception rate regardless of BCS was 54.9% in cows inseminated based on detected estrus, and 48.7% in cows inseminated at 72 to 80 hours (timed artificial insemination, TAI) after removal of CIDR. The conception rate regardless of AI time was 40.0% in cows with low progesterone concentrations (less than 1.0 ng/ml), and 56.6% in cows with high progesterone concentrations (more than 1.0 ng/ml) at CIDR injection. The conception rate regardless of progesterone concentrations was 53.8% in cows inseminated based on detected estrus, and 38.0% in cows of TAI after removal of CIDR. The conception rate regardless of AI time was 43.3% in cows with small follicle (less than 5 mm), 53.3% in cows between 5 mm to 10 mm of follicle, and 63.3% in cows with large folliclc (more than 10 mm) at CIDR injection, respectively. The conception rate regardless of follicle size was 58.4% in cows inseminated based on detected estrus, and 45.9% in cows of TAI after removal of CIDR. These results indicated that if the cows with BCS 2.75 to 3.25, active corpus luteum, and/or large dominant follicle (more than 10 mm) are used for estrus induction, the conception rate will be greater.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.19-20
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• 2021

In order to reduce the emission of harmful substances that degrade indoor air quality, the Ministry of Environment strengthened the standards for the content of VOCs in paints to supply and sell eco-friendly paints. In this related study, an eco-friendly paint mixed with a powder-type absorbent material was prepared and its characteristics were reviewed. As the amount of powder-type absorbent material increased, the workability (viscosity, peeling, etc) decreased. Accordingly, this study aims to examine which particle size is suitable according to the particle size of the granular adsorbent while improving the problem of the powdery adsorbent by using the granular adsorbent. As an experimental plan, the particle size of granular activated clay is selected to be 0.250, 0.425, 0.710(mm), and the decrease rate of VOCs concentration and impact resistance are reviewed. As a result of the experiment, as the particle size of the granular activated clay increased, the decrease rate of the VOCs concentration increased and the impact resistance improved. Therefore, considering the problems that occur after actual painting, the particle size of granular activated clay of 0.425mm is suitable.

• Journal of Korea Foundry Society
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• v.10 no.6
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• pp.528-537
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• 1990

7XXX aluminum alloy powders produced by the self-manufactured rotating disc atomizer were investigated to determine the influence of the atomization parameters on the particle size distributions in air atmosphere. The particle size distributions are almost always bimodal with the dominant mode on the large particle size. Average powder size of 7XXX aluminum alloy is $74/{\mu}m~125/{\mu}m$ when melt is poured with the rate of 9g /sec at 730$^{\circ}C$ on a rotating disc of 30㎜ diameter at 6300rad/sec. The mass of finer particle increased when disc diameter, angular velocity, pouring temperature increased and pouring rate decreased. The powder shapes of bimodal change from acicular to tear-drop and from tear-drop to ligament with increasing powder size. Powder shape was determined by the atomization mechanism and oxidation in liquid state. Microstructure of powders appeared to be cell and cellular dendrite. The SDAS of Al-7.9wt%Zn-2.4wt%Mg-1.5wt%Cu-0.9wt%Ni Powders is $0.8{\mu}m~1.0{\mu}m$ for the powders of $size＋44{\mu}m~53{\mu}m$ and $1.6{\mu}m∼1.8{\mu}m$ for the powders of $size＋105{\mu}m~125{\mu}m$, repectively.