• 한국재료학회지
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• 제26권7호
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• pp.388-392
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• 2016

A cold roll-bonding process was applied to fabricate an AA1050/AA6061/AA1050 laminate complex sheet. Two AA1050 and one AA6061 sheets of 2 mm thickness, 40 mm width and 300 mm length were stacked up after surface treatment that included degreasing and wire brushing; material was then reduced to a thickness of 3 mm by one-pass cold rolling. The laminate sheet bonded by the rolling was further reduced to 1.2 mm in thickness by conventional rolling. The rolling was performed at ambient temperature without lubricant using a 2-high mill with a roll diameter of 210 mm. The rolling speed was 5.0 m/sec. The AA1050/AA6061/AA1050 laminate complex sheet fabricated by roll bonding was then hardened by natural aging T4) and artificial aging (T6) treatments. The microstructures of the as-roll bonded and the age hardened Al complex sheets were revealed by optical microscope observation; the mechanical properties were investigated by tensile testing and hardness testing. The strength of the as-roll bonded complex sheet was found to increase by 2.9 times compared to that value of the starting material. In addition, the hardness of the complex sheets increased with cold rolling for AA1050 and age-hardening treatment for AA6061, respectively. After heat treatment, both AA1050 and AA6061 showed typical recrystallization structures in which the grains were equiaxed; however, the grain size was smaller in AA6061 than in AA1050.

• 한국결정성장학회지
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• 제29권1호
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• pp.24-31
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• 2019

사파이어 단결정을 성장시키는 기존 합성방법들의 원료충진율을 높이기 위한 방법으로 스컬용융법을 사용하여 $Al_2O_3$ 파우더를 용융시켰다. 냉각도가니 크기는 내경 24 cm, 내부 높이 30 cm로서 2.75 MHz 발진주파수에서 15 kg의 $Al_2O_3$ 파우더를 1시간 내에 모두 용융시켰으며, 3시간 동안 융액상태로 유지 후 자연냉각 시켰다. 냉각된 잉곳의 부분별 면밀도 및 성분은 SEM-EDS를 통해 분석하였다. 잉곳의 면밀도 및 $Al_2O_3$ 함량은 고주파유도가열 시 냉각도가니 내부에 형성되는 온도 분포와 관련이 있으며, 온도가 높게 형성되었던 부분이 면밀도 및 순도가 높게 나타나는 경향을 보였다.

• 한국건축시공학회지
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• 제19권2호
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• pp.123-130
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• 2019

환경부하저감 및 동절기 시공의 효율을 위해 환경부하저감형 한중콘크리트 시공기술로서 고로슬래그시멘트와 내한촉진제를 병용한 콘크리트에 있어 열화의 기점이 되는 수축균열에 관해 검토했다. 그 결과, 고로슬래그시멘트 및 내한촉진제를 첨가함으로서 자유수축변형량 및 동일재령에 있어서 균열포텐셜은 증가하는 경향으로 구속조건하에서의 균열의 발생도 빠른 것을 확인할 수 있었다. 이것은, 자유수축변형량의 증가와 함께 크리프에 의한 응력 이완량의 감소나 구속도의 증가 등이 원인으로서 생각할 수 있으며, 동절기 시공에 있어서 고로슬래그 및 내한촉진제를 적용할 때는 수축에 의한 균열발생에 대해 검토할 필요가 있다고 판단된다.

• Smart Structures and Systems
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• 제31권5호
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• pp.485-500
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• 2023

Machine learning-based structural health monitoring (ML-based SHM) methods are researched extensively in the recent decade due to the availability of advanced information and sensing technology. ML methods are well-known for their pattern recognition capability for complex problems. However, the main obstacle of ML-based SHM is that it often requires pre-collected historical data for model training. In most actual scenarios, damage presence can be detected using the unsupervised learning method through anomaly detection, but to further identify the damage types would require prior knowledge or historical events as references. This creates the cold-start problem, especially for new and unobserved structures. Modal-based methods identify damages based on the changes in the structural global properties but often require dense measurements for accurate results. Therefore, a two-stage hybrid modal-machine learning damage detection scheme is proposed. The first stage detects damage presence using Principal Component Analysis-Frequency Response Function (PCA-FRF) in an unsupervised manner, whereas the second stage further identifies the damage. To solve the cold-start problem, mode shape assessment using the first mode is initiated when no trained model is available yet in the second stage. The damage identified by the modal-based method would be stored for future training. This work highlights the performance of the scheme in alleviating the cold-start issue as it transitions through different phases, starting from zero damage sample available. Results showed that single and multiple damages can be identified at an acceptable accuracy level even when training samples are limited.

• Journal of Plant Biotechnology
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• 제33권1호
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• pp.19-25
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• 2006

저온저항성 BN115 gene과 표지유전자로서 kanamycin에 저항성 있는 nptII gene을 가지고 있는 식물발현용 binary vector pBin19/BNl15가 도입된 A. tumefacience MP90을 국화잎과 공동배양 하였다. 또한 particle bombardment를 이용하여 목적으로 하는 유전자가 식물체에 안정적으로 도입되어 발현됨을 PCR 및 Real-Time PCR 검정으로 확인하였다. 국화잎과 공동배양에 사용된 Agrobacterium은 $5.0{\times}1.0{\mu}m$로 non-sporing, motile, rod 형이며, Callus는 pin이나 cork-borer에 의해 상처 난 잎 가장자리로부터 형성되어 식물체가 재분화 되었다. 유전자 도입조건은 Agrobacterium을$O.D._{600}{\approx}0.5$에서 20분간 공동배양 할 때, Particle bombardment는 helium 압력을 1,100 psi, target 거리를 9 cm로 유지했을 때, 가장 효율이 높았다. 5mg/L kanamycin이 들어 있는 배지에서 선발된 형질전환체는 PCR 분석으로 형질전환여부를 판별할 수 있었으며, 선발 10개체 중 9개체에서 purified pBN115와 같은 크기의 밴드가 형성되었다. Taq-Man probe를 이용한 Real-Time PCR 결과 $45{\sim}0.00045ng/{\mu}{\ell}$ 범위에서 pBN115 gene을 10배씩 serial dilution한 amplification plot는 일정한 간격으로 standard curve를 보였으며, slope는 -3.313975, R2는 0.998319이었다. Amplification plots의 형질전환체 $C_T$값은 $20.75{\sim}33.81$범위였으며, 유전자 copy수는 정량분석을 기초로 산출하였다. pBN115의 plasmid DNA를 serial dilution했을 때, standard는 $5.6{\times}10^{10}/45ng{\sim} 5.6{\times}10^5/0.00045ng\;copies/{\mu}{\ell}$이 었으며, 형질전환체는 $3.86{\times}10^8{\sim}12565.71 copies/{\mu}{\ell}$이었다. 따라서 PCR, Real-Time PCR 분석 결과 저온저항성 유전자가 국화의 genome에 안정적으로 도입되었음이 확인되었다.

• 한국표면공학회지
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• 제41권5호
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• pp.205-213
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• 2008

A 3D particle code is developed to analyze electron behavior in a planar magnetron sputtering cathode either in balanced or unbalanced configuration. Three types of collisions are included; electron - neutral elastic, excitation to a metastable state and ionization. Flight path is calculated by a 4-th order Runge-Kutta method with a time step of 10 ps. Effects of electron starting position, magnetic field intensity and configuration were analyzed. For a more efficient and accurate modeling, multithreading technique is considered for multicore CPU computers. Under an assumption of cold ion approach, target erosion profiles are predicted for a flat target surface.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3317-3322
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• 2007

THC(Total Hydrocarbon) emissions during cold start and warm-up phase constitute the majority of THC emissions during the FTP-75 mode. As the basic approach to improve the emission performance of Gasoline engine during transient phase, the effect of spark timing retard from MBT on THC emission characteristics is studied by engine test using a Fast response Flame Ionization Detector(FFID). A cyclic analysis of the combustion process shows that high THC emissions are produced first few cycles during the transient phase. This paper presents the results of engine performance and emission of Gasoline engine with various spark timing. consequently, This paper was focused on the combustion phenomena with various spark timing during transient phase which was analyzed by Fast response Flame Ionization Detector (FFID) equipment to measure the cyclic THC emission characteristics.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.344-352
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• 2006

Evacuation performance, starting transient, and plume blowback at diffuser breakdown of a straight cylindrical supersonic exhaust diffuser with no externally supplied secondary flow are investigated. Pressure records in the transitional periods are measured by a small-scale cold-gas simulator. Flow-fields evolving in the diffuser-type ejector are solved by preconditioned Favre-averaged Navier-Stokes equations with a low-Reynolds number $k-{\varepsilon}$ turbulence model edited for turbulence compressibility effects. The present RANS method is properly validated with measured static wall pressure distributions and evacuation level at steady operation as well as the pressure records during the transition regime.

• 대한기계학회논문집B
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• 제23권1호
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• pp.69-81
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• 1999

In this research computational methods for the droplet atomization and spray wall impingement are studied for the non-evaporating diesel fuel spray. The TAB(Taylor Analogy Breakup) model and Wave model are compared with experiments in order to describe droplet atomization process. The Watkins model and O'Rourke model are compared to simulate the spray wall impingement. As a result, It is found that the application of the Wave model has a good agreement with the experimental data in the case of high pressure injection. With regard to wall Impingement phenomena, it is found that the Watkins model is appropriate to the high temperature cylinder wall condition, while the O'Rourke model is appropriate to cold starting problem.

• 한국세라믹학회지
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• 제27권3호
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• pp.394-400
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• 1990

Mullite and cordierite were prepared by the sol-gel route. Boehmite, fumed silica and Mg(NO3)2$.$6H2O were their starting materials. Mullite and cordierite powder were mixed by various weight percent. These mixed sols were ball-milled for 48hrs, dried at 100$^{\circ}C$, pressed, cold isostatic pressed and sintered at 1490$^{\circ}C$ for 2hrs. Mullite-cordierite composites sintered at 1490$^{\circ}C$ for 2hrs had>98% of theoretical density. Bending strength of the sintered bodies were 329-249MPa, dielectric constant 7.1-6.7 at 1MHz and thermal expansion coefficient at 800$^{\circ}C$ was matched with Si in the range of 30-35wt% cordierite.