• Tribology and Lubricants
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• v.23 no.6
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• pp.298-300
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• 2007

Frictional characteristics of mesoporous $SiO_2$ thin films were evaluated with different pore sizes. The films were manufactured by sol-gel and self-assembly methods to have a porous structure. The pores on the surface may play as the outlet of wear particle and the storage of lubricant so that the surface interactions could be improved. The pores were exposed on the surface by chemical mechanical polishing (CMP) or plasma-etching after forming the porous films. The ball-on-disk tests with mesoporous $SiO_2$ thin films on glass specimen were conducted at sliding speed of 15 rpm and a load of 0.26 N. The results show considerable dependency of friction on pore size of mesoporous $SiO_2$ thin films. The friction coefficient decreased as increasing the pore size. CMP process was very useful to expose the pores on the surface.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.39.1-39.1
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• 2016

We report the discovery of a kiloparsec-size supershell in the outskirts of the Milky Way with the compact high-velocity cloud, HVC 040+01-282 (hereafter, CHVC040), at its geometrical center using the "Inner-Galaxy Arecibo L-band Feed Array" HI 21 cm survey data. Supershells are large gaseous shells, which could be produced by one of most energetic activities with an explosion energy more than $3{\times}1052erg$. The most promising origin is the explosion of multiple supernovae in OB associations, or alternatively, the impact of HVCs falling into the Galactic disk. We found the association between CHVC040 and the Galactic supershell by analysis of their morphological and physical properties. Our results imply that some compact HVCs can survive their trip through the Galactic halo and inject energy and momentum into the Milky Way disk.

• The Korean Journal of Ceramics
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• v.3 no.1
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• pp.47-51
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• 1997

The dense sintered bodies of Si/SiC composite with various Si contents could be fabricated by changing the green density in the forming process. The Si/SiC/graphite composites with various graphite contents could be also fabricated by changing a graphite content in the starting composition. Their mechanical and tribological properties were characterized and wear mechanism was also studided. The hardness and strength of the Si/SiC and the Si/SiC/graphite were decreased with increasing the contents of free Si and graphite, respectively. However, the friction coefficient and specific wear rate had no specific relations to their hardness and strength. Adhesion of free Si was a main factor to determine a wear resistance of the Si/SiC composite. In the case of the Si/SiC/graphite, solid lubricationl and liquid reservoir of the graphite particles played the main role of the reduction of the friction force. In the torque test to estimate the possibility of practical of practical applications, the value of torque between the Al2O3 disk and Si/SiC/graphite disk was 1/6 lower compared with two $Al_2O_3$ disks on the basis of 100,000 cycles.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.73.2-73.2
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• 2019

The physical origin of low escape fractions of ionizing radiation derived from Lyman-break galaxies (LBGs) at z ~ 3 - 4 is a puzzle in the theory of reionization. We perform idealized disk galaxy simulations to investigate how galactic properties, such as metallicity and gas mass, affect the escape of Lyman continuum (LyC) photons using radiation-hydrodynamic code RAMSES-RT, with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor (Z=0.002) galaxy embedded in a halo of mass M_h ~ 10¹¹ M_⊙ is 〈f^3D_esc〉 ~ 8%. However, when the gas metallicity is increased to Z=0.02, the escape fraction is significantly reduced to 〈f^3D_esc〉 ~ 1%, as young stars are enshrouded by their birth clouds for a longer period of time. On the other hand, increasing the gas mass by a factor of 5 leads to 〈f^3D_esc〉 ~ 4%, as LyC photons are only moderately absorbed by the thicker disk. Our experiments seem to suggest that high metallicity is primarily responsible for the low escape fractions observed from LBGs, supporting the scenario in which the escape fraction has a negative correlation with halo mass. Indeed, our simulated galaxy with the typical metallicity of LBGs (Z=0.006) shows the relative escape fraction of 8%, consistent with recent observations of galaxies with M₁₅₀₀ = -20.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.3
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• pp.335-342
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• 2003

In this study, the effects of oxide layer formed on the contact parts of TiN coated ball and steel disk in sliding are investigated. Also wear mechanism to from the oxide layer and the characteristics of the oxide layer formation are investigated. AISI 52100 steel ball is used for the substrate of coated ball specimens. Two types of coated ball specimens were prepared by depositing TiN coating with 1 and 4 ${\mu}{\textrm}{m}$ in coating thickness. AISI 1045 steel is used for the disk type counter-body. To investigate the effect of oxide layer on the contact parts of the two materials, the tests were performed both in air for forming oxide layer on the contact parts and in nitrogen environment to avoid oxidation. And to study the effects of surface roughness of counter-body, TiN coating thickness and contact load of sliding test on the characteristics of oxide layer formation on counter-body, various tests were carried out. From the results, the friction characteristics between the two materials was predominated by iron oxide layer that formed on wear track on counter-body and this layer caused the high friction. And the formation rate of the oxide layer on wear track increased as the real contact area between the two materials increased as the contact load increased, the TiN coating thickness decreased and the surface of counter-body smoothened.

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.74-81
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• 2013

A numerical design analysis is conducted to search for an optimal shape of outlet in a rotating-disk CVD reactor. The goal is to suppress flow recirculation that has been found in a reactor having a sudden expansion of flow passage outside of the rotating disk. In order to streamline gas flow, the sidewall at which the flow in the Ekman layer is impinged, is tilted. The axisymmetric laminar flow and heat transfer in the reactor are simulated using the incompressible ideal gas model. For the conventional vertical sidewall, the flow recirculation forming in the corner region could be expanded into the interior to distort the upstream flow. The numerical results show that this unfavorable phenomenon inducing back flow could be dramatically suppressed by tilting the sidewall at a certain range of angle. The assessment of deviation in deposition rate based on the characteristic isotherm illustrates that the sidewall tilting may expand the domain of stable plug-like flow regime toward higher pressure. A physical interpretation is attempted to explain the mechanism to suppress flow recirculation.

• Laser Solutions
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• v.17 no.2
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• pp.11-18
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• 2014

This research was conducted as a fundamental study to apply tailored blank welding technique into automotive production process. Specially we tried to apply the TWB technique to exhaust system. The materials used in this work were ferritic 439 stainless steel sheet with a thickness of 1.2mm and 0.8mm. Welding tests were conducted for BOP test and dissimilar thickness (0.8 to 1.2t) cases. Major process parameters were position of focus, travel speed, shielding gas and joint (gap) condition. As a result, there are nothing significant welding characteristic compare with TWB of carbon steel. Stainless steel shows the good weldability and mechanical properties (tensile, hardness and forming strength) also shows high level. Just problem is gap condition. However, also in this case, it shows not only good forming strength but also base metal fracture after tensile test. And to conclude, it is good opportunity to make lightweight design muffler using TB welding technique.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.75.1-75.1
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• 2017

Ram pressure due to the intracluster medium (ICM) is known to play a crucial role in removing the cool gas content of a galaxy on a short timescale, potentially driving a star forming galaxy to evolve into a red passive population. Although many HI imaging studies find clear evidence of diffuse atomic gas stripping from cluster galaxies, it is still debatable whether the ram pressure can also strip dense molecular gas. NGC 4522, a Virgo spiral, undergoing strong ram pressure stripping, is one of the few cases where extraplanar CO emission together with stripped HI gas and $H{\alpha}$ knots has been identified, providing an ideal laboratory to study the molecular gas stripping event and the extraplanar star formation activity. The aim of this work is to investigate the origin of extraplanar molecular clouds near NGC 4522 (e.g. stripped or forming in situ), and to probe a relation between the molecular gas surface density and the star formation rate (i.e. the Kennicutt-Schmidt law) at sub-kpc scale, especially in the extraplanar space, using ALMA Cycle 3 CO data and $H{\alpha}$ data of NGC 4522. We present the results from our ALMA observations, and discuss possible scenarios for the origin of extraplanar molecular clouds and to characterize the star formation activity associated with stripped gas outside the galactic disk.

• The Journal of the Korean dental association
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• v.58 no.1
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• pp.19-26
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• 2019

Purpose: The purpose of this study is to compare the adhesion of Candida albicans according to build angle in 3D printing denture base resin. Methods: The 3D printing was performed by setting the build angle of the disk type specimen designed by CAD program at 0 degree, 30 degrees, 60 degrees, and 90 degrees. Surface roughness was measured using a non-contact 3D microsurface profiler. The specimens were incubated in Candida albicans suspension for 24 hours. The attached Candida albicans were detached by cell scraper. The suspension of detached C. albicans was serially diluted and plated on Trypticase soy broth. After 48 hours of incubation, total colony forming unit was counted. Results: There was no significant difference in surface roughness(Sa) between the test groups, but the interlayer boundary was observed. There was no statistically significant difference in total colony forming units of Candida albicans between the test groups. Conclusion: There was no difference in the average surface roughness and adhesion of Candida albicans between the specimens. It is considered that the setting of the build angle should be set considering the accuracy or strength rather than the roughness of the surface.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.35.2-35.2
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• 2018

Using the K-band Multi-object Spectrograph (KMOS) at the Very Large Telescope (VLT), the KMOS Redshift One Spectroscopic Survey (KROSS) has gathered integral-field data for ~800 star-forming galaxies at a redshift z~1, when the universe was roughly half its current age and forming the bulk of its stars. With spatially-resolved observations, KROSS reveals galaxies that are both gas-rich and highly turbulent. It is possible to derive the observed and baryonic Tully-Fisher (luminosity - rotation velocity) relations, thus constraining the mass-to-light ratios and total (luminous + dark) masses of the galaxies. This in turn highlights the dependence of the relation zero-point on the degree of rotational support of the galaxies (rotational velocity to velocity dispersion ratio). By degrading and analogously analysing integral-field data of hundreds of local galaxies from the Sydney-AAO Multi-object Integral-field Spectrograph (SAMI) survey, a robust comparison z=0 Tully-Fisher relation can also be derived, thus further constraining the luminous and dark mass growth of disk galaxies over the last 7 billions years. This unique comparison also reveals that systematic effects associated with sample selection and analysis methods are as large as the effects expected from cosmological evolution, and thus that most other comparisons employing heterogeneous data and/or methods can safely be ignored.