• Fisheries and Aquatic Sciences
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• 제27권1호
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• pp.1-6
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• 2024

In this study, the swimming behavior of a small box jellyfish (Carybdea brevipedalia), which consists of inhaling external seawater and expelling it through its mouth to generate forward thrust, was characterized using particle image velocimetry (PIV). The flow rate and structure during the suction and discharge process were quantitatively analyzed. During swimming, there was a change in the ratio of the internal area during inhalation and expulsion. Specifically, there was a 1.10-fold difference between the maximum area after inhalation and the minimum area after discharge. The maximum distance traveled after discharge was inversely proportional to the size of the inner area, with a 2.48-fold difference in the minimum distance traveled after suction. Depending on the propulsion stage, the inner area decreased and then increased in proportion to the moving distance and speed. The moving distance of the small box jellyfish was measured for each period. The speed for each swimming stage increased and then decreased at intervals of 0.15 to 0.2 seconds, and the suction and discharge cycle period was measured at approximately 0.5 seconds. Collectively, our findings provide a methodological basis for studying the swimming behavior of small and highly active trailing jet jellyfish, as well as the biological mechanisms that determine this behavior.

• 한국산업보건학회지
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• 제20권3호
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• pp.203-215
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• 2010

This study is an overview of toxicities and measurement techniques of ultrafine particles (UFPs), and their exposure controls. UFPs are ubiquitous in many working situations. Exposure to UFPs is possibly causing adverse health symptoms including cardio-respiratory disease to humans. In order to measure exposure levels of airborne UFPs, there are current available measurement guidelines, instruments and other techniques (i.e. contour mapping, control banding). However, these risk assessment techniques including measurement techniques, controls and guidelines are dependent on background levels, metrics (e.g. size, mass, number, surface area, composition), environmental conditions and controls. There are no standardized measurement methods available and no generic and specific occupational exposure standards for UFPs. It is thought that there needs to be more effort to develop Regulations and Exposure Standards for generic UFPs should be based on more exposure data, health surveys, toxicological data and epidemiological data. A carefully considered hierarchy of controls can also reduce the maximum amount of airborne UFPs being emitted from diverse sources in industries.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.449-452
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• 2003

The objective of this study is to investigate the basic properties of polyester mortars using ground calcium carbonate(GCC), blast furance slag(BFS), fly ash(FA), ordinary portland cement(OPC) as fillers. Particle size distribution, particle shape and resin absorption of GCC, BFS, FA and OPC are checked. Polyester mortars with GCC, BFS, FA and OPC are prepared with various MEKPO content and tested for working life. The flexural and compressive strengths of the polyester mortars with MEKPO content of 0.5phr are evaluated. As a test result, the average sizes of GCC, BFS, FA and OPC are 9.7$\mu\textrm{m}$, 11.6$\mu\textrm{m}$, 21.2$\mu\textrm{m}$, 29.9$\mu\textrm{m}$. Resin absorption of FA is 1.5times larger than other fillers. The polyester mortar with FA at a MEKPO content of 0.5phr has the longest working life and the maximum flexural and compressive strengths.

• Journal of Electrical Engineering and Technology
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• 제1권1호
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• pp.98-100
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• 2006

ZnO thin films were deposited at different repetition rates of 5 Hz and 10 Hz by pulsed laser deposition. X-ray diffraction (XRD) full widths at half maximum (FWHMs) of (002) ZnO peak in ZnO thin film deposited at 5 Hz and 10 Hz was 0.22 and $0.26^{\circ}$, respectively. The grain size of ZnO thin film deposited at 5 Hz was larger than that of 10 Hz. The variation of repetition rates did not have an effect on the optical property of ZnO thin films. The degradation of the crystalline quality and surface morphology in ZnO thin film deposited at 10 Hz resulted from supersaturation effect by decrease of time interval between a ZnO particle arriving on a substrate by laser shot and a ZnO particle arriving on a substrate by next laser shot.

• 소성∙가공
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• 제18권5호
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• pp.401-409
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• 2009

The change of the thermal properties of exothermic and insulating materials with the mixing condition of raw materials which is the most important factor for exothermic & insulating materials was investigated by using the evaluation system of the thermal properties of exothermic and insulating materials. In this study, the effect of the thermal properties of the exothermic & insulating materials such as exothermic properties, endothermic properties, insulating properties, maximum temperature of molten metal, ignition time of exothermic & insulating materials and temperature recovery time on the mixing ratio of reductant and oxidant, types of reductant, and particle sizes of reductants was examined. It could be expected to design the mixing condition of raw materials for various exothermic and insulating materials.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.118-126
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• 2009

The change of the thermal properties of exothermic & insulating materials with mixing condition of raw materials which is the most important factor for exothermic & insulating materials was investigated by using the evaluation system of the thermal properties of exothermic & insulating materials. In this study, the effect of the thermal properties of the exothermic & insulating materials such as exothermic properties, endothermic properties, insulating properties, maximum temperature of molten metal, ignition time of exothermic & insulating materials and temperature recovery time on the mixing ratio of reductant and oxidant, types of reductant, and particle sizes of reductants was examined. It could be expected to design the mixing condition of raw materials for various exothermic & insulating materials.

• 한국세라믹학회지
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• 제33권9호
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• pp.995-1002
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• 1996

The TiC-(Ni/Ti) composites were prepared by reaction bonding between TiC preforms and the melted mixture of Ni/Ti metal the atomic ratio of which were the ranges of 0.3 to 3. And their microstructures phase composi-tions and mechanical properties were investigated. During reaction bonding Ni/Ti metal mixture had a good wettability an permeability with TiC preforms and pore-free and fully dense sintered bodies were fabricated. TiC particle shape changed from spherical to angular platelet-like and grain size was grown with Ni/Ti atomic ratio increasing from 0.3 to 1. whereas grain growth of TiC particle was restrained and its shape changed gain from angular platelet-like to spherical when Ni/Ti atomic ratio was more than 2. Maximum bending strength and fracture toughness were obtained at the Ni/Ti atomic ratio being 1 their values were 582 MPa and 11.1 MPa.m1/2 respectively.

• Computers and Concrete
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• 제16권3호
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• pp.487-502
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• 2015

This study investigated particle expansion in basic oxygen furnace slag (BOF) and desulfurization slag (DSS) after heat curing by using the volume method. Concrete hydration was accelerated by heat curing. The compressive strength, ultrasonic pulse velocity, and resistivity of the concrete were analyzed. Maximum expansion occurred in the BOF and DSS samples containing 0.30-0.60 mm and 0.60-1.18 mm particles, respectively. Deterioration was more severe in the BOF samples. In the slag aggregates for the complete replacement of fine aggregate, severe fractures occurred in both the BOF and DSS samples. Scanning electron microscopy revealed excess CH after curing, which caused peripheral hydration products to become extruded, resulting in fracture.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.657-664
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• 2002

This study presents the influence of blasting-induced vibration on the adjacent structures in rocks of various RMR values. 3D finite element analysis was performed to simulate the behaviour of tunnel and adjacent structures during rock excavation. The blast loadings were evaluated from the blasting pressure which is depending on the type and amount of explosive charges. Influencing factors for the stability of adjacent structures and ground conditions were reviewed in terms of structural dimensions and RMR values. The stiffness and load of adjacent structures are modeled in the numerical analysis to Investigate blasting effects of the size of adjacent structures. The vibration velocity and maximum particle velocity was increase sharply when the RMR value changed from 30 to 50. The effect of particle velocity was minimized at the width of structure become 2 times of tunnel diameter.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권8호
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• pp.401-406
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• 2004

In this experimentation, we investigated the characteristics of electromagnetic wave absorption of ferroxplana powder and silicone rubber composite. Ferroxplana was prepared by flux method at low temperature. The crystallization, magnetic properties and particle morphology of the obtained ferroxplana powder were investigated by using XRD, VSM and SEM. The particle size of ferroxplana powder was 2∼4$\mu\textrm{m}$ at the ratio of R=26, The coercivity and saturation magnetization of ferroxplana powder increased slightly with increase of temperature, The magnetic loss was the main factor of electromagnetic wave absorption of ferroxplana powder and silicone rubber composite, The maximum reflection loss of composite was about -l5dB below 4GHz.