• Korean Journal of Materials Research
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• v.11 no.5
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• pp.345-353
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• 2001

The present study was carried out to investigate the effect of zirconium addition to $Al_3$Nb intermetallic on the crystal structural modification and microstructural characterization of $Al_3$Nb intermetallic. Elemental Al, Nb, Zr powders and arc melted $Al_3$Nb and $Al_3$Zr intermetallic mixed powders were used as starting materials. MA was carried out in an attritor rotated with 300 rpm for 20 hours. The behavior of MA between two starting materials was some-what different in which the value of internal strain of the elemental powders was higher than that of the intermetallic powder. The intermetallic powder was much more disintegrated during the MA processing. In the case of the elemental powders, AlNb$_2$ phase were transformed to Al(Nb.Zr)$_2$ as a result of ternary addition of Zr element. With the successive heat treatment at 873K for 2 hours, the Al(Nb.Zr)$_2$ phase was transformed to more stable $Al_3$(Nb.Zr) phase. This transformation was clearly confirmed by the identification of X-ray peak position shift. On the other hand, in the carte of the intermetallic powder, there was no evidence of phase transformation to other ternary intermetallic compounds or amorphous phases, even in the case of additional heat treatment. However, nano-sized intermetallic with $Al_3$Nb and $Al_3$Zr were just well distributed instead of phase transformation.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.300-310
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• 2008

Through this study, a conceptual design for the next generation high-speed EMU has been derived to meet the crash worthiness requirements of the Korean rollingstock safety regulation. The crashworthiness regulations require some performance requirements for two heavy collision accident scenarios; a train-to-train collision at the relative speed of 36 km/h, and a collision against a standard deformable obstacle of 15 ton at 110km/h. The complete train set will be composed of 2TC-6M with 13 ton axle load, which is different from KTX with the power car of 17 ton axle load. Using theoretical and numerical analyses, a crashworthy conceptual design was derived in terms of mean crush forces and energy absorptions for principal crushable structures and devices. The derived conceptual design was evaluated and improved using one dimensional dynamic simulations for the bar-spring-damper-mass model. It is shown from the simulation results that the suggested conceptual design can easily satisfy domestic crashworthiness requirements.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.939-946
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• 2005

The stiffness properties of heterogeneous concrete materials and their degradation were investigated at different-levels of observations with aids of the opportunities and limitations of multi-resolution wavelet analysis. The successive Haw transformations lead to a recursive separation of the stiffness properties and the response into coarse-and fine-scale features. In the limit, this recursive process results in a homogenization parameter which is an average measure of stiffness and strain energy capacity at the coarse scale. The basic concept of multi-resolution analysis is illustrated with one and two-dimensional model problems of a two-phase particulate composite representative of the morphology of concrete materials. The computational studies include the meso-structural features of concrete in the form of a hi-material system of aggregate particles which are immersed in a hardened cement paste taking due to account of the mismatch of the two elastic constituents.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.161-161
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• 2000

Ferromagnetic 3d 전이금속과 paramagnetic 5d 금속으로 이루어지진 Pt-Co 계는 자기이방적 (magnetic anisotropy) 성질로 인하여 많은 관심을 모으고 있는 계로서는 다층박막 및 합금박막에 대한 지기적 성질에 대한 많은 연구가 있어 왔다. 최근 sputtering method 에 의해 제작된 Pt-Co 합금박막에 대해 Ar 기체분압에 따라 보자력 (coercivity)이 변화되고 PMA (perpendicular magnetic anisotropy)를 갖는 것을 관측하였다. PMA의 근원은 주로 계면에서의 anisotropy 에너지와 관련이 있는 것으로 이해되기 때문에 합금박막의 경우는 PMA가 불가능한 것으로 여겨져 왔다. 그럼으로서 PMA에 대한 근원에 대한 명확한 해석이 필요하게 되었다. 또한 보자력(coercivity)은 불순물의 함량이 감소할수록, 그리고 내부적 변형이 제거될수록 감소하기 때문에, 계면 및 결정구조와 관련이 있는 것으로 알려져 있다. 이러한 자기적 특성을 관찰하고자 [Pt(51 )/Co(112 )]4, [Pt(90 )/Co(66 )]4, 그리고 [Pt(121 )/Co(30 )]4, 다층박막과 이들 박막을 80kV Ar+ 이온선 혼합후 박막의 결정성 변화를 관찰하기 위하여 GXRD (glancing x-ray diffraction) 스펙트럼을 얻어보았다. 그 결과 세 system 모두 disordered fcc 합금박막임을 확인하였다. fcc(111) 방향에 대한 평균 격자공간(lattice spacing)의 크기변화는 한층 당의 Co 두께가 두꺼울수록 거의 선형적으로 감소함을 볼수 있었다. MOKE 실험에 의하면, 이들 다층박막이나 합금박막의 경우 모두, in-plane 방향에 대해 자화 용이축(easy magnetization axis)을 가지고 있었다. 그리고 보자력의 크기에 있어서, 다층 박막의 경우에 있어서 Co 층에 두께 두꺼울수록 보자력의 크기가 감소하였지만 그림1에서와 같이 합금박막의 경우는 정반대로 Co층의 두께가 얇을수록 보자력의 크기가 감소함을 관찰하였다.

• Journal of Korean Society of Steel Construction
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• v.9 no.3 s.32
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• pp.431-440
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• 1997

The paper describes a theoretical model for the prediction of bridge temperatures from meteorological data measured at bridge site and local meteorological center together with existing finite element heat transfer theory and solar radiation transfer theory to determine the time dependent temperature distribution of bridge. In this analytical model, the most adequate equation for the calculation of solar radiation on the bridge surface, which is dominant in day time is described based on the results of several experimental studies for the solar energy. The validity of this model is tested against field data obtained from long term experimental program on Sadang Viaduct in Seoul. Also, this paper describes the linear correlation between design variables and meteorological data to establish analytical criteria for the prediction of the average temperature, which are responsible for the longitudinal deformation of the bridges and of the vertical differential temperature profiles. which are responsible for the bending deformations from the long term experimental results.

• Applied Microscopy
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• v.37 no.3
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• pp.147-156
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• 2007

The dorsal lingual papillae of Myotis macrodactylus were investigated morphologically using scanning electron microscopy. Three types of lingual papillae from Myotis macrodactylus were recognized. The filiform(Fi) papillae were distributed over the entire dorsal surface of the tongue, and they could be classified into 5 types of papillae by the shape, size and number of the protrusion. Type I was distributed on dorsal surface of the apex in the anterior region of the tongue, has a crow-like shape with ten to fifteen formed projections. Type II was located in the medial portion of the anterior region of the tongue, has an eight to ten spin-like protrusion. Type III was distributed on the medial portion of the tongue, has a scale-like papille with five to seven protrusion. Type IV was distributed on the both lateral portion of the posterior region of the tongue, has a small conical papillae, does not have needle projection. Type V have not needle projection, a large of conical papillae, on the both lateral portion of the posterior region of the tongue. Most Fu(Fungiform) papillae were distributed the both lateral region or medial portion of the posterior region of the tongue, has a round or oval shape with $40{\sim}45$ papillae. The small $(65{\mu}m)$, meddle $(75{\mu}m)$ and large $(120{\mu}m)$ fungiform papillae were distributed on dorsal surface of the apex in the anterior, the both lateral portions and medial portion of the posterior region of the tongue, respectively. Two large oval vallate (V) papillae are located in the medial portion of the posterior region of the tongue. In conclusion, the morphology of lingual papillae is useful to determine species relationship among Myotis species. It suggests that the difference of types and number of lingual papillae caused by the difference of food habit.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.1
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• pp.35-41
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• 2004

The yeongok stream originates at the natural park, Mt. O-dae and flows to the East Sea of korea, normally maintaining I or II grade of water quality and its average water flux is 352,100 ㎥/d. However, the typhoon 'Rusa', which occured on 31 August 2002, changed its watercourse and configuration, and the ecosystem was deeply damaged. Moreover, the hydrological characteristics were once more transformed, and the ecosystem was secondarily damaged during repair-work of destroyed bridges and elevations. After the flood disaster, the species diversity diminished 17% for attached diatom and 44% for aquatic animals. However, the earth and sand, dug from river bed during intensive repair-work throughout the entire stream, made diversity drop to 32% for the diatom and the aquatic animals were wiped out. Especially, fishes were totally destroyed except for some species such as Moroco oxycephalus in the upper stream. The yeongok stream has little contamination source and short water residence time due to the short length and rapid slope, and consequently a temporary deterioration of water quality caused by repair-work may be rapidly recovered, but it needs a long time to restore the damaged ecosystem.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.2
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• pp.91-97
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• 2014

With Pb-free solder joints containing Sn-Ag-Cu-based ternary alloys (Sn-1.0 wt.%Ag-0.5Cu and Sn-4.0Ag-0.5Cu) and Sn-Ag-Cu-In-based quaternary alloys (Sn-1.0Ag-0.5Cu-1.0In, Sn-1.2Ag-0.5Cu-0.4In, Sn-1.2Ag-0.5Cu-0.6In, and Sn-1.2Ag-0.7Cu-0.4In), fracture-mode change, shear strengths, and fracture energies were observed and measured under a high-speed shear test of 500 mm/s. The samples in each composition were prepared with as-reflowed ones or solid-aged ones at $125^{\circ}C$ to 500 h. As a result, it was observed that ductile or quasi-ductile fracture modes occurs in the most of Sn-Ag-Cu-In samples. The happening frequency of a quasi-ductile fracture mode showed that the Sn-Ag-Cu-In joints possessed ductile fracture properties more than that of Sn-3.0Ag-0.5Cu in the high-speed shear condition. Moreover, the Sn-Ag-Cu-In joints presented averagely fracture energies similar to those of Sn-Ag-Cu joints. While maximum values in the fracture energies were measured after the solid aging for 100 h, clear decreases in the fracture energies were observed after the solid aging for 500 h. This result indicated that reliability degradation of the Sn-Ag-Cu-In solder joints might accelerate from about that time.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.226-233
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• 2008

The nucleation and evolution process of Ge nano-islands on Si(001) surfaces grown by chemical vapor deposition have been explored using atomic force microscopy (AFM). The Ge nano-islands are grown by exposing the substrates to a mixture of gasses GeH4 and H2 at pressure of 0.1-0.5Torr and temperatures of $600-650^{\circ}C$. The effect of growth conditions such as temperature, Ge thickness, annealing time on the shape, size, number density, and surface distribution was investigated. For Ge deposition greater than ${\sim}5$ monolayer (ML) with a growth rate of ${\sim}0.1ML/sec$ at $600^{\circ}C$, we observed island nucleation on the surface indicating the transition from strained layer to island structure. Further deposition of Ge led to shape transition from initial pyramid and hut to dome and superdome structure. The lateral average size of the islands increased from ${\sim}20nm$ to ${\sim}310nm$ while the number density decreased from $4{\times}10^{18}$ to $5{\times}10^8cm^{-2}$ during the shape transition process. In contrast, for the samples grown at a relatively higher temperature of $650^{\circ}C$ the morphology of the islands showed that the dome shape is dominant over the pyramid shape. The further deposition of Ge led to transition from the dome to the superdome shape. The evolution of shape, size, and surface distribution is related to energy minimization of the islands and surface diffusion of Ge adatoms. In particular, we found that the initially nucleated islands did not grow through long-range interaction between whole islands on the surface but via local interaction between the neighbor islands by investigation of the inter-islands distance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.116-122
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• 2021

This study quantitatively evaluated the performance improvement of a circular reinforced concrete pier under dynamic load with strengthening using a steel plate. Various three-dimensional elements were applied using the finite element program ABAQUS. The analytical parameters included the ratios of the steel cover length to the pier's total height and the ratios of the steel cover thickness to the pier diameter for inelastic-nonlinear analysis. The lower part of the pier had fixed boundary conditions, and lateral repetitive loads were applied at the top of the pier. The pier was investigated to evaluate the dynamic performance based on the load-displacement curve, stress-strain curve, ductility, energy absorption capability, and energy ratio. The yield and ultimate loads of piers with steel covers increased by 3.76 times, and the energy absorption capability increased by 4 times due to the confinement effects caused by the steel plate. A plastic hinge part of the column with a steel plate improved the ductility, and the thicker the steel plate was, the greater the energy absorption capacity. This study shows that the reinforced pier should be improved in terms of the seismic performance.