• Journal of the Korean Society for Heat Treatment
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• v.36 no.2
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• pp.77-85
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• 2023

In this study, the mechanical properties of the Al-Mg-X (X=Cr, Si) alloy, which clearly showed the influence of the specimen and grain size, were investigated by changing the specimen size extensively. In addition, the effect on the specimen size, grain size and aging condition on the mechanical properties of the grain refining alloy according to the addition of Cr was clarified, and the relationship between these factors was studied. As the specimen size decreased, the yield stress decreased and the fracture elongation increased. This change was evident in alloys with coarse grain sizes. Through FEM analysis, it was confirmed that the plastic deformation was localized in the parallel part of specimen S2. Therefore, when designing a tensile specimen of plate material, the W/L balance should be considered along with the radius of curvature of the shoulder. In the case of under-aged materials of alloys with coarse grain size, the fracture pattern changed from intergranular fracture to transgranular fracture as W/d decreased, and δ increased. This is due to the decrease in the binding force between grains due to the decrease in W. In the specimen with W/d > 40 or more, intergranular fracture occurred, and local elongation did not appear. Under-aged materials of alloys with fine grain size always had transgranular fracture over a wide range of W/d = 70~400. As W/d decreased, δ increased, but the change was not as large as that of alloys with coarse grain sizes. Compared to the under-aged material, the peak-aged material did not show significant dependence on the specimen size of σ_0.2 and δ.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.583-590
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• 2008

Blasting has been applied in newly-built steel structures for cleaning forged surfaces and increasing the adhesive property of applied painting systems. However, the effect of the blast cleaning on fatigue behavior of welded joints is not clear. In this paper, fatigue tests were carried out on out-of-plane gusset welded joints and the effect of the blast cleaning on the fatigue behavior was studied. The curvature radius at the weld toe of the surface-treated specimens by using the blast method is larger than that of as-welded specimens. By the blast cleaning compressive residual stresses were induced into weld toes. The experimental results showed that the fatigue life of surface-treated specimens is longer than that of as-welded specimens, even though the fatigue life of surface-treated specimens and that of as-welded specimens are not clearly different in the high stress range. About a 160% increase in fatigue limit could be realized by using blast cleaning.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.4 s.346
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• pp.23-30
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• 2006

This paper describes the short-channel effect(SCE), corner effect of nano-scale MuGFETs(Multiple-Gate FETs) by three-dimensional simulation. We can extract the equivalent gate number of MuGFETs(Double-gate=2, Tri-gate=3, Pi-gate=3.14, Omega-gate=3.4, GAA=4) by threshold voltage model. Using the extracted gate number(n) we can calculate the natural length for each gate devices. We established a scaling theory for MuGFETs, which gives a optimization to avoid short channel effects for the device structure(silicon thickness, gate oxide thickness). It is observed that the comer effects decrease with the reduction of doping concentration and gate oxide thickness when the radius of curvature is larger than 17 % of the channel width.

• Korean Journal of Human Ecology
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• v.24 no.6
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• pp.847-857
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• 2015

The ratio of small-breasted women occupies over 20% among Korean women in their twenties. However, the commercial brassieres for the small-breasted women were not fitted well to their breast shapes. In this research, the various commercial mold brasseries for small-breasted women were evaluated through the wearing test and the analysis of 3D images which were scanned from their torsos wearing the brassieres. In addition, professional panels performed the appearance evaluation based on the 2D front and side images captured from 3D images taken by 3D measurement systems. As the results, we found that small-breasted women preferred a 3/4 cup brassiere, of which volume is concentrated in the lower cup. The most preferred brassiere in wearing state shows that the characteristic angle between the chest and the upper cup is about 167 degrees, which is smaller than those of another brassieres, and that the ratio of the radius of curvature of the nipple part to that of the lower cup was about 0.78. These results provide important implications regarding the design of mold brassieres for small-breasted women in spite of the fact that these results represent the selected set of commercial brassieres. Therefore, further studies are highly demanded for the most suitable design information of mold cup for small-breasted women.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.4
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• pp.53-61
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• 2017

Turbocharger is a device for increasing the power of a vehicle engine. The control plate is the main component for fixing the vane of the turbocharger. Now, the control plate is made of austenite steel cutting after the casting process. It has excellent corrosion, heat resistance and mechanical characteristics of material. However, present the process is made by cutting after casting. when cutting is processed after casting, so materials, processing time, and processing energy are lost. Therefore, this study proposes a process to powder compact use of stainless steel Deklak2 and to minimize amount of cutting through net shape process. The mechanical properties of Deklak2 were verified by tensile test, hardness test and relative density measurement, and the governed equation was defined. Also, the curvature radius 1, 2 and the density, affects the shape, were selected as the design parameters, and the best process conditions was proposed through the Taguchi method and the evaluation of SN ratio. And then prototype molds were fabricated and compared with the results of the finite element analysis for the verification, and it was found that the tendency of relative density and dimension was coincided. Therefore, it was found that the amount of cutting can be minimized by only the net shape process after the sintering process and it can be applied to mass production.

• Korean Journal of Optics and Photonics
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• v.16 no.4
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• pp.340-344
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• 2005

Microlens cells of Ge-doped BPSG (Boro-Phospho-Silicate Glass) are fabricated by dicing the film produced by FHD (Flame Hydrolysis Deposition). Microlens arrays of $53.4{\mu}m$ square unit are produced by the thermal reflow of the diced unit cells at $1200^{\circ}C$. The gap between the microlenses was about $70{\mu}m,$ and the thickness of the produced lens was about $28.4{\mu}m$. We analyzed the reflowed shape of the microlens cell by an image-process technique, and the focal length was about $62.2{\mu}m$. This method of fabricating a microlens is simple and inexpensive compared to the conventional method using the photolithographic process. Also, the control of the radius of curvature of the microlens is easier and a more precise microlens way of various types can be fabricated using this method.

• Korean Journal of Materials Research
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• v.27 no.12
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• pp.658-663
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• 2017

Urchin-structured zinc oxide(ZnO) nanorod(NR) gas sensors were successfully demonstrated on a polyimide(PI) substrate, using single wall carbon nanotubes(SWCNTs) as the electrode. The ZnO NRs were grown with ZnO shells arranged at regular intervals to form a network structure with maximized surface area. The high surface area and numerous junctions of the NR network structure was the key to excellent gas sensing performance. Moreover, the SWCNTs formed a junction barrier with the ZnO which further improved sensor characteristics. The fabricated urchin-structured ZnO NR gas sensors exhibited superior performance upon $NO_2$ exposure with a stable response of 110, fast rise and decay times of 38 and 24 sec, respectively. Comparative analyses revealed that the high performance of the sensors was due to a combination of high surface area, numerous active junction points, and the use of the SWCNTs electrode. Furthermore, the urchin-structured ZnO NR gas sensors showed sustainable mechanical stability. Although degradation of the devices progressed during repeated flexibility tests, the sensors were still operational even after 10000 cycles of a bending test with a radius of curvature of 5 mm.

• Journal of The Korean Astronomical Society
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• v.35 no.4
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• pp.159-174
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• 2002

Cosmological hydrodynamic simulations of large scale structure in the universe have shown that accretion shocks and merger shocks form due to flow motions associated with the gravitational collapse of nonlinear structures. Estimated speed and curvature radius of these shocks could be as large as a few 1000 km/s and several Mpc, respectively. According to the diffusive shock acceleration theory, populations of cosmic-ray particles can be injected and accelerated to very high energy by astrophysical shocks in tenuous plasmas. In order to explore the cosmic ray acceleration at the cosmic shocks, we have performed nonlinear numerical simulations of cosmic ray (CR) modified shocks with the newly developed CRASH (Cosmic Ray Amr SHock) numerical code. We adopted the Bohm diffusion model for CRs, based on the hypothesis that strong Alfven waves are self-generated by streaming CRs. The shock formation simulation includes a plasma-physics-based 'injection' model that transfers a small proportion of the thermal proton flux through the shock into low energy CRs for acceleration there. We found that, for strong accretion shocks, CRs can absorb most of shock kinetic energy and the accretion shock speed is reduced up to $20\%$, compared to pure gas dynamic shocks. For merger shocks with small Mach numbers, however, the energy transfer to CRs is only about $10-20\%$ with an associated CR particle fraction of $10^{-3}$. Nonlinear feedback due to the CR pressure is insignificant in the latter shocks. Although detailed results depend on models for the particle diffusion and injection, these calculations show that cosmic shocks in large scale structure could provide acceleration sites of extragalactic cosmic rays of the highest energy.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.4
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• pp.382-388
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• 2010

In this work the replacement material for magnesium alloy was investigated and an optimized design was suggested for the horizontal fin of a fighter's external fuel tank. For the replacement of magnesium alloy, Aluminum alloy, AL 2034-T351, was selected by considering material properties and its procurement. The strength and fracture toughness properties of AL 2034-T351 are stronger than those of magnesium alloy, but the specific weight of AL 2034-T351 is heavier than that of magnesium alloy by 65%. To meet the allowable limit of C.G. shift in the tank, the design of horizontal fin was optimized by reducing the original shape by 20% and resizing the maximum thickness to 7 mm. From the results of the static and dynamic stress analysis for improving the safety factor of the joint section and the joint hole, the radius of curvature in the aft joint section of the new fin was designed as 8.5mm.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.6-9
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• 2008

Analyzing the characteristics of blood flow in the blood vessels is very important to diagnose the circulatory diseases. In order to investigate the hemodynamic characteristics in vivo, the measurements of blood flows inside the extraembryonic arterial and venous blood vessels of chicken embryos were carried out using an in vivo micro-PIV technique. The circulatory diseases are closely related with the formation of abnormal hemodynamic shear stress regions, thereby it is important to get blood velocity and vessel's morphological information according to the vessel configuration and the flow conditions. In this study, the flow images of RBCs in blood vessels were obtained using a high-speed CMOS camera with a spatial resolution of approximately 14.6${\mu}$m${\times}$14.6${\mu}$m in the whole circulation network of blood vessels. The blood flows in the veins and arteries show steady laminar and unsteady pulsatile flow characteristics, respectively. The mean blood flows merged (in veins) and bifurcated (in arteries) smoothly into the main blood vessel and branches, respectively, without any flow separation or secondary flow which accompanying large variation of shear stress. Vorticity was high in the inner regions for both types of vessels, where the radius of curvature varied greatly. The instantaneous flows in the arterial blood vessels showed noticeable pulsatility due to the heart beat, and the main features of the velocity waveforms, including pulsatile shape, retrograde flow, mean velocity, maximum velocity and pulsatile frequency, were significantly dependent on the pulsatile condition which dominates the arterial blood flow. In near future, these in vivo experimental results of blood flow measured in various extraembryonic blood vessels would be very useful to understand the hemodynamic characteristics of human blood flows and various blood flow researches for clinically useful hemodynamic discoveries as well.