• 대한조선학회논문집
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• 제45권6호
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• pp.669-678
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• 2008

The fatigue life of ship structure under cyclic loading condition is made up of initiation and propagation stages. In this study, crack growth test is carried out on large scale structure test specimens and fracture mechanical analysis is performed. The fatigue lives measured from fatigue tests are compared with DNV, Matsuoka and BS 5400 S-N curve. And to predict the crack initiation life, S-N curve, corresponding to crack length 20mm at welded joint, is developed based on hot spot stress range. Also crack propagation life is calculated using crack growth equation. Consequently, computed crack propagation life is compared with experiment results.

• 한국결정성장학회지
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• 제10권4호
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• pp.324-329
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• 2000

상온에서 $Cs^+$ ion sputtering에 의해 발생된 탄소 음이온 빔과 Kaufmann type ion source를 이용하여 발생된 수소 양이온 빔을 Si기판 위에 동시에 증착함으로써 얻어지는 DLC 박막의 특성을 분석하여 DLC 박막의 증착에 미치는 수소 이온의 영향을 관찰하였다. 수소 가스의 flow rate을 0 sccm부터 12 sccm까지 변화 시킴에 따라 박막 내에 포함되는 수소의 양이 증가하였으며, 수소의 증가에 따라 박막 내에 $sp^2$구조가 증가하는 것을 알 수 있었다. 수소에 의한 $sp^2$결합이 증가되는 현상은 증착시 박막 내에 주입되는 수소의 양이 CVD에 비해 매우 적은 양이지만, 상대적으로 높은 에너지를 지니고 기판에 충돌하기 때문에 물리적 에너지 전달 효과가 DLC 박막의 형성에 크게 작용하였음을 알 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.119-119
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• 2010

We report strong exciton transition and exciton-phonon couplings in photoluminescence (PL) of ZnO thin films grown on MgO/sapphire (buffer/substrate) by plasma-assisted molecular beam epitaxy. The PL spectra at 10 K showed the intensity of the dominant emission, donor-bound exciton transition of front surface (top surface, the latter part in growth) is found to be about 100 times higher than that of back surface (in-depth bottom area, the initial part), while the room temperature PL spectra showed dominant contributions from the free exciton emissions and phonon-replicas of free excitons for front surface and back surface, respectively, It could be attributed to the strong contributions of exciton-phonon coupling. Time resolved PL spectra reveal that the life time of exciton recombination from the front surface are longer than those from back surface. This is most probably due to the fact that reduction of non-radiative recombination in the front surface. This investigation indicates that the existence of native defects or trap centers which can be reduced by the proper initial condition in growth and the exciton-phonon interaction couplings play an important role in optical properties and crystal quality of ZnO thin films.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.327.1-327.1
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• 2014

Nitrides-on-silicon structures are considered to be an excellent candidate for unique design architectures and creating devices for high-power applications. Therefore, a lot of effort has been concentrating on growing high-quality III-nitrides on Si substrates, mostly Si(111) and Si(001) substrates. However, there are several fundamental problems in the growth of nitride compound semiconductors on silicon. First, the large difference in lattice constants and thermal expansion coefficients will lead to misfit dislocation and stress in the epitaxial films. Second, the growth of polar compounds on a non-polar substrate can lead to antiphase domains or other defective structures. Even though the lattice mismatches are reached to 16.9 % to GaN and 19 % to AlN and a number of dislocations are originated, Si(111) has been selected as the substrate for the epitaxial growth of nitrides because it is always favored due to its three-fold symmetry at the surface, which gives a good rotational matching for the six-fold symmetry of the wurtzite structure of nitrides. Also, Si(001) has been used for the growth of nitrides due to a possible integration of nitride devices with silicon technology despite a four-fold symmetry and a surface reconstruction. Moreover, Si(110), one of surface orientations used in the silicon technology, begins to attract attention as a substrate for the epitaxial growth of nitrides due to an interesting interface structure. In this system, the close lattice match along the [-1100]AlN/[001]Si direction promotes the faster growth along a particular crystal orientation. However, there are insufficient until now on the studies for the growth of nitride compound semiconductors on Si(110) substrate from a microstructural point of view. In this work, the microstructural properties of nitride thin layers grown on Si(110) have been characterized using various TEM techniques. The main purpose of this study was to understand the atomic structure and the strain behavior of III-nitrides grown on Si(110) substrate by molecular beam epitaxy (MBE). Insight gained at the microscopic level regarding how thin layer grows at the interface is essential for the growth of high quality thin films for various applications.

• KSBB Journal
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• 제19권5호
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• pp.358-362
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• 2004

Characteristics of cell growth and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] synthesis was investigated through flask and batch cultures of Alcaligenes latus and Comamonas acidovorans. The specific growth rate of C. acidovorans increased with yeast extract concentration and decreased with 1,4-butanediol concentration. Optimum glucose concentration for growth of C. acidovorans was 20 g/L. In one-step flask cultures of C. acidovorans, final dry cell weight and PHA content decreased with the ratio of 1,4-butanediol to glucose, while the 4HB fraction in copolymers gradually increased to 100 $mol\%$ with an initial 1,4-butanediol concentration of 20 g/L as single carbon source. The specific growth rate of A. latus decreased with v-butyrolactone concentration and optimum sucrose concentration for growth was 10 g/L. In batch cultures of A. latus, 4HB fraction increased with initial v-butyrolactone concentration. P(3HB-co-4HB) with 19 $mol\%$ 4HB was obtained when the initial ratio of v-butyloractone (g/L) to sucrose (g/L) was 10 : 10.

• 한국전기전자재료학회논문지
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• 제26권6호
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• pp.446-450
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• 2013

Growth mechanism of GS-MBE(Gas source-Molecular Beam Epitaxy) has been investigated. We observed that the growth rate of GaN films is changing from 520 nm/h to 440 nm/h by the variation of V/III ratio under nitrogen-rich growth condition. It was explained that the amount of hydrogen on the growth front varies by the ammonia flow, and gallium hydrides are generated on the surface by a reaction of hydrogen and gallium, resultantly the amount of gallium supplying is changing along with the $NH_3$ flow. Reflection high energy electron diffraction (RHEED) observation was used to confirm the N-rich condition. The crystal quality of GaN was estimated by photoluminescence (PL) and X-ray diffraction (XRD).

• 열처리공학회지
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• 제31권5호
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• pp.237-243
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• 2018

In-rich InGaN epilayers were grown on (0001) sapphire substrates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). InGaN epilayers grown at various growth condition were observed by SEM, XRD, and RHEED. When plasma power of nitrogen increased from 290 to 350 W, surface morphology and crystal quality became worse according to more active nitrogen on the surface of InGaN at N-rich growth condition. As In composition was reduced from 89 to 71% by changing the incoming flux of In and Ga, surface morphology and crystal quality became worse. In addition, weak peaks of cubic InGaN phase was observed from InGaN layer with 71% In composition by XRD ${\Phi}$ scan measurement. When growth temperature decreased from 500 to $400^{\circ}C$, RHEED diffraction pattern was changed to be from streaky to spotty which means atomically rough surface, and spotty pattern showed cubic symmetry of InGaN clearly. XRD ${\Phi}$ scan measurement gave clear evidence that more cubic InGaN phase was formed at low growth temperature. All these results indicates that extremely low surface mobility of Ga adatom caused inferior crystal quality and cubic InGaN phase.

• 대한원격탐사학회지
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• 제16권2호
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• pp.109-116
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• 2000

This study was carried out to assess the use of RADARSAT data which is C-band with HH polarization for the rice growth monitoring in Korea. Nine time-series data were taken by shallow incidence angle (standard beam mode 5 or 6) during rice growing season. And then, backscattering coefficients ($\sigma$$^{\circ}$) were extracted by calibration process for comparing with rice growth parameters such as plant height, leaf area index(LAI), and fresh and dry biomass. Field experimental data concerned with rice growth were collected 8 times for the ground truth at the study area, Tangjin, Chungnam, Korea. At the beginning of rice growth, backscattering coefficients were ranged from -l6~-l3dB when rice fields were not covered with rice canopy and flooded. At the maximum vegetative stage of rice, backscattering coefficients of the rice field were the highest ranging from -4.4dB~-3.1dB. The temporal variation of backscattering coefficient($\sigma$$^{\circ}$) in rice field was significant in this study. Backscattering coefficient ($\sigma$$^{\circ}$) of rice field was a little bit lower again after heading stage than before. This results show RADARSAT data is promising for rice monitoring.

• Steel and Composite Structures
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• 제21권2호
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• pp.343-356
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• 2016

As the common cast-in-place construction works fails to meet the enormous construction demand under rapid economic growth, the development of prefabricated structure instead becomes increasingly promising in China. For the prefabricated structure, its load carrying connection joint play a key role in maintaining the structural integrity. Therefore, a novel end plate bolt connecting joint between fully prefabricated pre-stressed concrete beam and high-strength reinforcement-confined concrete column was proposed. Under action of low cycle repeated horizontal loadings, comparative tests are conducted on 6 prefabricated pre-stressed intermediate joint specimens and 1 cast-in-place joint specimen to obtain the specimen failure modes, hysteresis curves, skeleton curves, ductility factor, stiffness degradation and energy dissipation capacity and other seismic indicators, and the seismic characteristics of the new-type prefabricated beam-column connecting joint are determined. The test results show that all the specimens for end plate bolt connecting joint between fully prefabricated pre-stressed concrete beam and high-strength reinforcement-confined concrete column have realized the design objectives of strong column weak beam. The hysteretic curves for specimens are good, indicating desirable ductility and energy dissipation capacity and seismic performances, and the research results provide theoretical basis and technical support for the promotion and application of prefabricated assembly frames in the earthquake zone.

• 한국축산식품학회지
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• 제22권4호
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• pp.316-321
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• 2002

본 실험 결과를 종합하여 볼 때 전자선의 처리는 돈육의 냉장, 냉동 중 일반세균과 중온균의 증식 억제에 효과가 있는 것으로 밝혀졌으며 전자선의 조사량이 증가할 수록(1.5에서 3.0 kGy로) 그 효과는 더욱 커지는 것으로 나타났다. 본 실험에서 사용한 전자선 1.5와 3.0 kGy는 그 조사량이 매우 낮은 수준이므로 조사량을 증가시키면 살균효과는 증대될 것으로 예상된다. 반면 전자선의 처리가 지방의 산패를 촉진한다는 결과는 충분히 예상한 결과였고 본 실험에서도 전자 건의 조사량이 증가할수록(1.5에서 3.0 kCy로) 산패는 더욱 촉진되었다. 따라서 전자선 처리의 살균 효과를 극대화하기 위하여는 전자선을 조사하여도 돈육의 산패도는 전자선을 조사하지 않은 돈육의 수준으로 유지시킬 수 있는 방법이 필수적으로 연구되어야 할 것이다. 이러한 방법으로는 전자선의 조사 속도를 조절한다든지 공기조절 포장 방법($N_2$, $CO_2$) 과의 병용 등을 들 수 있을 것이다. 전자선을 식품에 활용하는 작업은 그 유용성이 무궁 무진 할 수 있으므로 앞으로도 그 활용이 기대되며 우선적으로 해결해야 할 문제는 전자선 조사에 의 한 지방의 산패를 억제 할 수 있는 방법을 강구하는 것이다.