• Korean Journal of Materials Research
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• v.21 no.12
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• pp.690-696
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• 2011

In this study, nano-sized tin oxide powder with an average particle size of below 50 nm is prepared by the spray pyrolysis process. The influence of air pressure on the properties of the generated powder is examined. Along with the rise of air pressure from $0.1kg/cm^2$ to $3kg/cm^2$, the average size of the droplet-shaped particles decreases, while the particle size distribution becomes more regular. When the air pressure increases from $0.1kg/cm^2$ to $1kg/cm^2$, the average size of the dropletshaped particles, which is around 30-50 nm, shows hardly any change. When the air pressure increases up to $3kg/cm^2$, the average size of the droplet-shaped particles decreases to 30 nm. For the independent generated particles, when the air pressure is at $0.1kg/cm^2$, the average particle size is approximately 100 nm; when the air pressure increases up to $0.5kg/m^2$, the average particle size becomes more than 100 nm, and the surface structure becomes more compact; when the air pressure increases up to $1kg/cm^2$, the surface structure is almost the same as in the case of $0.5kg/cm^2$, and the average particle size is around 80- 100 nm; when the air pressure increases up to $3kg/cm^2$, the surface structure becomes incompact compared to the cases of other air pressures, and the average particle size is around 80-100 nm. Along with the rise of air pressure from $0.1kg/cm^2$ to $0.5kg/cm^2$, the XRD peak intensity slightly decreases, and the specific surface area increases. When the air pressure increases up to $1kg/cm^2$ and $3kg/cm^2$, the XRD peak intensity increases, while the specific surface area also increases.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.181-182
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• 2006

When a water jet is injected on the body surface, the pressure and shear stress on the surface are important physical parameters in determining the body surface wash out and physical stimulus. We used the force plate in order to measure the surface average pressure for different nozzle types and distances between a nozzle and a plate. We used the nozzles with a hole dimeter of 1.8, 2.9, 3.2mm, and the shower heads with 10 holes (hole diameter, 1mm) and 20 holes (hole diameter, 1mm). The distances between a nozzle and a plate was 10, 20, 30, 40cm. The results showed that the surface forces were not affected by the distances between a nozzle and a plate. Further numerical studies will be performed to predict wall shear stress based on the measured pressure data.

• Tribology and Lubricants
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• v.29 no.1
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• pp.27-32
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• 2013

This study examined the effects of surface roughness in the mixed lubrication regime of smooth and rough surfaces for roller bearings. The average flow model was adopted for interaction between the flow rheology of the lubricant and the surface roughness. The average Reynolds equation and related flow factor that describes the coupled effects of surface roughness and flow rheology, the viscosity-pressure and density-pressure equations, the elastic deformation equation, and the force balance equation were solved simultaneously. The results showed that the effects of surface roughness on the film thickness and pressure distribution should be considered, especially in elastohydrodynamic lubrication contact problems.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.134-141
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• 2000

The real area of contacts, average film thickness, mean real pressure, and mean hydrodynamic pressure are investigated numerically in this study, especially for the parallel thrust bearing. Model surface is generated numerically with given autocorrelation function and some surface profile parameters. Then the average Reynolds equation contained flow factors and contact factor is applied to predict the effects of surface roughness in mixed lubrication regimes. In this equation, flow factors are defined as correction terms to smooth out high frequency surface roughness and contact factor is introduced to relieve from obtaining the average film thickness. Therefore the computation time to obtain h can be reduced.

• Tribology and Lubricants
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• v.16 no.6
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• pp.455-460
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• 2000

The real area of contacts, average film thickness, mean real pressure, and mean hydrodynamic pressure are investigated numerically in this study, especially for the parallel thrust bearing. Model surface is generated numerically with given autocorrelation function and some surface profile parameters. Then the average Reynolds equation contained flow factors and contact factor is applied to predict the effects of surface roughness in mixed lubrication regimes. In this equation, flow factors are defined as correction terms to smooth out high frequency surface roughness and contact factor is introduced to relieve from obtaining the average film thickness. Therefore the computation time to obtain barh h can be reduced.

• Journal of The Korean Society of Integrative Medicine
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• v.5 no.4
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• pp.1-9
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• 2017

Purpose : This study was conducted among 195 adults in their 20s. To analyze the impact of the slope types of the scapulae on the plantar surface of the foot, the average pressure (AP), the maximum pressure (MP), the average of local distribution values, and the average movement of the center of pressure (COP) of the different slope types of the scapulae were compared. Method : The anterior-posterior slopes of the scapulae were measured by comparing the slopes of the left and right sides of the scapulae based on the differences in the height and the slope of the coracoid process and the angulus inferior scapulae. Those whose left side of the scapulae had an anterior slope were categorized as type 1, and those whose right side of the scapulae had an anterior slope, as type 2. The average plantar pressure, the center of plantar pressure, the maximum plantar pressure, and local distribution values were analyzed using a plantar pressure analyzer of the FSA. Result : In terms of the AP of the left and right feet, there was no statistically significant difference both in types 1 and 2 on the left and right feet. The comparison results of the MP and the average of local distribution values of the two slope types of the scapulae showed that there was no statistically significant difference on the X-axis both in types 1 and 2 on the left and right feet, but that there was a large statistically significant difference on the Y-axis both in types 1 and 2. That is, the MP of the right foot of the left anterior slope type was located more on the hindfoot than that of the right anterior slope type, and the MP of the left foot of the left anterior slope type was located more on the hindfoot than that of right anterior slope type. Conclusion : This study can be used as fundamental data to predict differences in the location and size of the COP and changes in plantar pressure distribution depending on the slope types of the scapulae, and control the distribution for therapeutic purposes.

• Journal of Powder Materials
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• v.17 no.5
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• pp.379-384
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• 2010

In the present work, bismuth nanopowders with various particle size distributions were synthesized by controlling argon (Ar) gas flow rate and chamber pressure of a gas condensation (GC) apparatus. From the analyses of transmission electron microscopy (TEM) images and nitrogen gas adsorption results, it was found that as Ar gas flow rate increased, the specific surface area of bismuth increased and the average particles size decreased. On the other hand, as the chamber pressure increased, the specific surface area of bismuth decreased and the average particles size increased. The optimum gas flow rate and chamber pressure for the maximized electrochemical active surface area were determined to be 8 L/min and 50 torr, respectively. The bismuth nanopowders synthesized at the above condition exhibit 13.47 $m^2g^{-1}$ of specific surface area and 45.6 nm of average particles diameter.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.1
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• pp.29-39
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• 1993

A model for estimating daily effective rainfall of upland crops was developed. The infiltration process was described by Green-Ampt infiltration model developed by Chu(1978). The model considers delayed surface ponding and surface detention storage under a uniform soil profile. The Green-Ampt parameters, that is, average hydraulic conductivity and average capillary pressure head on a sandy loam soil were determined from field experiment using Air-entry permeameter developed by Bouwer(1966). The model was verified by comparing measured and simulated surface runoff. The ratios of effective rainfall to total rainfall for red pepper, soybean, sesame and Chinese cabbage were evaluated using Borg's root growth model( 1986) respectively. The followings are a summary of this study results; 1.In a sandy loam soil average hydraulic conductivity was 3.28cm/hr and average capillary pressure head was 3.00cm. 2.The root growth of upland crops could be expressed by Borg's root growth model successively. 3.The measured and simulated surface runoff was agreed well with each other. 4.As the rainfall amount was increased, the ratio of effective rainfall to total rainfall was decreased exponentially till a certain growing period.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.34-41
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• 2000

Surface roughness plays a significant role in friction, wear, and lubrication in machine components. Most engineering surfaces have the nongaussian distrubution. So, in this study, contact simulation are conducted for not only gaussian surfaces but also nongaussian surfaces. Nongaussian rough surface censidering the kurtosis is generated numerically, And the effects of kurtosis on real contact area fraction, average gap, and mean asperity contact pressure are studied. It will be shown that the real contact area fraction and the mean asperity contact pressure are sensitive to the characteristics of surface geometry according to kurtosis.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.53-60
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• 2001

Surface roughness plays a significant role in friction, wear, and lubrication in machine components. Most engineering surfaces have the nongaussian height distribution. So, in this study, contact simulations are conducted for not only gaussian surfaces but also nongaussian surfaces. Nongaussian rough surface considering the kurtosis is generated numerically And the effects of kurtosis on real contact area fraction, average gap, and mean asperity contact pressure are studied. It will be shown that the real contact area fraction and the mean asperity contact pressure are sensitive to the characteristics of surface geometry according to kurtosis.