• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.05a
• /
• pp.258-262
• /
• 2008

Micro forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). In this study, the micro forming property was studied, using Al5083 superplastic alloy with micro grain, suitable for the micro forming process and Zr-BMG amorphous with pseudo-superplastic phenomena in the supercooled liquid state. Micro forming experiments under stastic load status showed that distortion by slip and spin of the grain system and slip inside the grain was observed in the Al5083 superplastic alloy. In case of Zr-BMG, because there is no grain, the distribution of the forming property was similar to the load distribution between punch and metal.

• Bulletin of the Korean Chemical Society
• /
• v.18 no.9
• /
• pp.985-994
• /
• 1997

The reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on Fe(110) surface is studied by use of classical trajectory procedures. Flow of energy between the reaction zone and bulk solid phase has been treated in the generalized Langevin equation approach. A London-Eyring-Polanyi-Sato energy surface is used for the reaction zone interaction. Most reactive events are found to occur in strong single-impact collisions on a subpicosecond scale via the Eley-Rideal mechanism. The extent of reaction is large and a major fraction of the available energy goes into the vibrational excitation of H2, exhibiting a vibrational population inversion. Dissipation of reaction energy to the heat bath can be adequately described using a seven-atom chain with the chain end bound to the rest of solid. The extent of reaction is not sensitive to the variation of surface temperature in the range of Ts=0-300 K in the fixed gas temperature, but it shows a minimum near 1000 K over the Tg=300-2500 K.

• Journal of The Korean Astronomical Society
• /
• v.52 no.5
• /
• pp.173-180
• /
• 2019

We present IR flux density measurements, models of the broadband SED, and results of SED modeling for the Pulsar Wind Nebula (PWN) 3C 58. We find that the Herschel flux density seems to be slightly lower than suggested by interpolation of previous measurements in nearby wavebands, implying that there may be multiple electron populations in 3C 58. We model the SED using a simple stationary one-zone and a more realistic time-evolving multi-zone scenario. The latter includes variations of flow properties in the PWN (injected energy, magnetic field, and bulk speed), radiative energy losses, adiabatic expansion, and diffusion, similar to previous PWN models. From the modeling, we find that a PWN age of 2900-5400 yrs is preferred and that there may be excess emission at ${\sim}10^{11}Hz$. The latter may imply multiple populations of electrons in the PWN.

• Wind and Structures
• /
• v.5 no.5
• /
• pp.393-406
• /
• 2002

Aerodynamic pressures and forces were measured on a model of a solar panel containing six slender, parallel modules. Of particular importance to system design is the aerodynamically induced torque. The peak system torque was generally observed to occur at approach wind angles near the diagonals of the panel ($45^{\circ}$, $135^{\circ}$, $225^{\circ}$ and $315^{\circ}$) although large loads also occurred at $270^{\circ}$, where wind is in the plane of the panel, perpendicular to the individual modules. In this case, there was strong vortex shedding from the in-line modules, due to the observation that the module spacing was near the critical value for wake buffeting. The largest loads, however, occurred at a wind angle where there was limited vortex shedding ($330^{\circ}$). In this case, the bulk of the fluctuating torque came from turbulent velocity fluctuations, which acted in a quasi-steady sense, in the oncoming flow. A simple, quasi-steady, model for determining the peak system torque coefficient was developed.

• Journal of the Korean Society for Precision Engineering
• /
• v.12 no.8
• /
• pp.122-130
• /
• 1995

To reduce the shock in shifting, the clutches and the brakes in automatic transmission have to be connected smoothly and disconnected rapidly. It is PCSV(Pressure Control Solenoid Valve) that paly this role of automatic transmission. In this paper, there were two steps in the analysis of the PCSV. The first step was modeling the elctromagnet by the permeance method. The second step was modeling the hydraulic circuit by the pressure differential equa- tion. In addition to this modeling, a experiment was performed and the commercial package program was used in order to justify modeling. The result of modeling coincide with the result of experiment and commercial package program. As a result, this modeling is usable in analysis of dynamic characteristics of the PCSV.

• Journal of the Korean Society for Precision Engineering
• /
• v.13 no.8
• /
• pp.120-127
• /
• 1996

Anti-lock Brake System has been developed to reduce tendency for wheel lock and improve vehicle control during sudden braking on slippery road surfaces. This is achieved by controlling the braking pressure, avoiding wheel lock, while retaining handling and brake performance. This paper is concerned about pressurecharacteristics of hydraulic modulator. Experimental sets which is consists of hydraulic modulator, duty controller, pressure regulator, pressure senset is consuructed. System modelling and computer simulation are performed for comparison with experimental results. Brake wheel pressure are measured under various driving pulse. The result of experiment show fairly agreement with the simulation. As a result, it is known that wheel pressure is affected by duty ratio, orifice diameter through computer simulation.

• Asian Journal of Turfgrass Science
• /
• v.6 no.1
• /
• pp.11-22
• /
• 1992

To determine the use of waste materials as root zone soil mixtures for turfgrass culture, the effects of paper mill sludge and briquet ash on physical and chemical properties of soil and growth of turfgrasses were examined. Three turfgrass species of zoysiagrass(Zoysia japonicaSteud.). kentycky bluegrass(Poa pratensis L. 'Ram I') and creeping bentgrass(Agrostis panistris Huds 'Persucross') were cultured in 32cm diameter plastic pots containing various soil mixtures. The basic ingredients used for mixtures included sand(SD), field soil(SL), paper mill sludge(PS), sphagnum peat moss(PM) and briquet ash(BA). Seven combinations using these ingreients were mixed in different percentage by volume as follows: SD+SL+PM(80:10.10), SH+SL+PS(80:10:10), SD-PM(80:20), SD+PS (80:20), SD+BA(80:20), SD+BA+PM(60:20:20) and SD+BA+PS(60:20:20). 1. Paper mill sludge showed pH of 6.6, more than 30% of organic matter content, and higher concentrations of total N, P, k, Ca, Mg and CEC. Bulk density, fild moisture capacity and electrical conductivity of soil mixtures were increased by the comimation of 10~20% PS by volume. 2. Briquet ash showed pH of 8.0, and higher levels of P, k, Ca and Mg than those of field soiks. Bulk density, field moisture capacity and hardenss of soil mixtures were increased but vertical water flow rate and electrical conductivity were decreased by the combination of 20% BA by volume. 3. Phytotoxic effects of PS and BA on growth of turfgrasses were not found. Shoot growth of all three species was higher in soil combination of SD+BA+PS than that of SD+SL+PM added with fertilizer. However, root growth was better in soil mixtures combined with PM. Soil mixtureomposed of 60% SD, 20% BA and 20% PS by volume was most effective on growth of all three species. 4. Paper mill sludge resulted in higher N level in the leaf tissue. The contents of heavy metals such as Cd and Ph did not vary significantly among soil mixtures and species. However, the Mn level was 2~3 times higher in plants growh in mixtures containing PM compared with others, and especially it was higher in creeping bentgrass than other species.

• Journal of Korea Soil Environment Society
• /
• v.2 no.2
• /
• pp.35-51
• /
• 1997

To clarify the effect of forest environmental changes (forest type difference and clearcut) on water storage capacity in soil and stream flow, watershed had been investigated in Pyungchang, Kangwon-Do during 1983∼1993. Hydrological datas such as runoff, monthly ratio of runoff to precipitation, runoff-duration, monthly runoff(by plenty, ordinary, low and scanty duration), total runoff, direct runoff by runoff components, bulk density, porosity, coarse pore, fine pore, permeability and effective water storage were obtained from Backokpo and Yimokjong watersheds. The monthly ratio of runoff to precipitation, runoff and runoff-duration were higher in Yimokiong than in Backokpo due to forest type difference. On compararing pre-treatment with trement period in two experimental watersheds, pre-treatment period was lower than treatment period. Physical properties of soil such as bulk density, porosity, permeability, and effective water storage capacity conditions were better during the pre-trement period than treatment period in the two experiment plots.

• Tribology and Lubricants
• /
• v.30 no.2
• /
• pp.108-115
• /
• 2014

The friction behaviors of bulk amorphous thermal spray coating (BAC) and second phase-reinforced composite coatings using a high velocity oxy-fuel spraying process were investigated using a ball-on-disk test rig that slides against a ceramic ball in an atmospheric environment. The surface temperatures were measured using an infrared thermometer installed 50 mm from the contact surface. The crystallinities of the coating layers were determined using X-ray diffraction. The morphologies of the coating layers and worn surfaces were observed using a scanning electron microscope and energy-dispersive spectroscopy. The results show that the friction behavior of the monolithic amorphous coating was sensitive to the testing conditions. Under lower than normal loads, a low and stable friction coefficient of about 0.1 was observed, whereas under a higher relative load, a high and unstable friction coefficient of greater than 0.3 was obtained with an instant temperature increase. For the composite coatings, a sudden increase in friction coefficient did not occur, i.e., the transition region did not exist and during the friction test, a gradual increase occurred only after a significant delay. The BAC morphology observations indicate that viscous plastic flow was generated with low loads, but severe surface damage (i.e., tearing) occurred at high loads. For composite coatings, a relatively smooth surface was observed on the worn surface for all applied loads.

• Journal of Wetlands Research
• /
• v.12 no.3
• /
• pp.57-65
• /
• 2010

This study was conducted to present primary data on the change of the physical characteristics of reservoir sediments for understanding the sedimentation. The records of the annual summation of the precipitation of >50mm per day (AP50) were compared with changes of bulk density, organic matter, mean grain-size, and sand ratio in sediment cores sampled from three reservoirs without dredging record. Reservoir sediments, characterized by mineral soil, contained organic matters originated from the debris of terrestrial plants, and changes of organic matter were related to changes of grain-size flowing into reservoirs when sediments of fine sandy loam showed 10% of organic matter contents. Rapid changes of grain-size and sand ratio in the sediment cores were associated with the increase and decrease of precipitation, and fluctuation of water level and water flow in reservoirs might have influenced on the formation of sediments in reservoirs. Records of AP50 suggested that sediments could accumulate more than about 30 within the short period of 10 years. The accumulated sediments in a short time can reflect the effect of natural and anthropogenic events on the physical characteristics of sediments.