• Journal of Advanced Marine Engineering and Technology
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• 제29권8호
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• pp.891-898
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• 2005

Inertia welding is a solid-state welding process in which butt welds in materials are made in bar and in ring form at the joint race, and energy required lot welding is obtained from a rotating flywheel. The stored energy is converted to frictional heat at the interface under axial load. The quality of the welded joint depends on many parameters, including axial force, initial revolution speed and energy amount of upset. working time, and residual stresses in the joint. Inertia welding was conducted to make the large exhaust valve spindle for low speed marine diesel engine. superalloy Nimonic 80A for valve head of 540mm and high alloy SNCrW for valve stem of 115mm. Due to different material characteristics such as, thermal conductivity and flow stress. on the two sides of the weld interface, modeling is crucial in determining the optimal weld geometry and Parameters. FE simulation was performed by the commercial code DEFORM-2D. A good agreement between the Predicted and actual welded shape is observed. It is expected that modeling will significantly reduce the number of experimental trials needed to determine the weld parameters. especially for welds for which are very expensive materials or large shaft. Many kinds of tests, including macro and microstructure observation, chemical composition tensile , hardness and fatigue test , are conducted to evaluate the qualify of welded joints. Based on the results of the tests it can be concluded that the inertia welding joints of the superalloy exhaust valve spindle are better properties than the material specification of SNCrW.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 추계학술대회
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• pp.50-53
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• 2006

Regional geophysical surveys and geological cal studies on natural gas hydrate (NGH) in the East Sea were carried out by the Korea Institute of Geoscience and Mineral Resources (KIGAM) from 2000 to 2004. 16 piston cores, 2270 L-km of multi-channel reflection seismic (MCRS) data and 730 L-km of 3.5kHz Chirp data obtained from the southwestern part of the deep-water Ulleung Basin were analyzed in this study. In piston cores, cracks generally developed parallel to bedding suggest significant gas content. The core analyses showed high total organic carbon (TOC) content, sedimentation rate and heat flow of sediments. These are in favor of the general ion of substantial biogenic methane, which can form the NGH within the stability zone of the near seafloor sediments in the study area. The cores generally show also high residual hydrocarbon gas concentrations for the formation of natural gas hydrates The geophysical indicators of the presence of gas and/or NGH such as bottom simulating reflectors (BSRs), seismic blank Bones, pockmarks and gas seeping features were well defined on the MCRS and Chirp data.

• Journal of Chest Surgery
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• 제29권4호
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• pp.440-443
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• 1996

삼첨 판막 심내막염은 감수성이 있는 항생제에 효과적으로 치료될 수 있다. 그러나 패혈증이 지속되거 나, 중증의 심부전, 다발성 폐 색전증 그리고 실 초음파상 증식증 (vegetation)이 있는 경우는 수술이 필요 하다. . 19세횝 남자환자가 감염성심내막염으로 입원하였다. 환자는 9년전에 perimembranous type의 VSD로 수술받은 병 력 이 있다. 심초음파상 삼첨판의 전엽부에 커다란 증식증의 소견이 보였고,과거에 VSD를 봉합했던 부위에 누 출 (leakage)을 통한 좌우단락이 관찰되었다. 항생제치료와 함께 인공판막치 환술을 시행하였다. St. Jude Medical 양엽판막 (size 33 mm으로 삼첨 판막 대 치술을 시 행하였고 잔여 VSD는 단순봉합으 로 폐쇄하였다. 술후 시행한 심초음파검사에서 치환된 삼첨 판막의 기능은 좋았고, 증식증과 좌우단락의 소견은 보이지 않았다. 환자는 합병증없이 술후 25일째에 퇴원하였다. 저자들이 경험한 본 증례는 잔여 VSD로 인해 생긴 감염성심내막염을 초기에 적극적인 수술을 시행 하여 좋은결과를 얻었음을 보여준다. 이 에 문헌고찰과 더불어 보고하는 바이다.

• 대한환경공학회지
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• 제32권5호
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• pp.427-436
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• 2010

본 연구는 마산만 특별관리해역 관리범위에 속해있는 총 18개 지점을 선정하여 표층 퇴적물 내 폴리브롬화디페닐에테르(PBDEs)의 공간적 농도분포와 오염경로를 조사하였다. 22개의 PBDE 이성질체가 검출되었으며, BDE-209는 가장 주된 이성질체로 검출되었다. BDE-209와 ${\Sigma}_{21}$PBDEs (BDE-209를 제외한 나머지 이성질체의 합)의 농도범위는 각각 2.32~64.2 ng/g, 0.72~8.24 ng/g이었다. 마산만에서 BDE~209 및 ${\Sigma}_{21}$PBDEs의 공간적 농도분포는 내만에서 외만으로 갈수록 감소하였다. PBDEs의 주오염원은 내만의 유입하천수과 하수처리장 방류수이었다. 마산만에서 PBDEs의 오염 수준을 결정하는 주요 인자는 육상기인 오염원 거리와 해수의 유동에 따른 퇴적물의 이동성 및 특성으로 나타났다.

• Geomechanics and Engineering
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• 제11권3호
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• pp.439-455
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• 2016

This paper presented solutions of displacement and stress for a circular opening which is reinforced with grouted rock bolt. It satisfies the Mohr-Coulomb (M-C) or generalized Hoek-Brown (H-B) failure criterion, and exhibits elastic-brittle-plastic or strain-softening behavior. The numerical stepwise produce for strain-softening rock mass reinforced with grouted rock bolt was developed with non-associative flow rules and two segments piecewise linear functions related to a principle strain-dependent plastic parameter, to model the transition from peak to residual strength. Three models of the interaction mechanism between grouted rock bolt and surrounding rock proposed by Fahimifar and Soroush (2005) were adopted. Based on the axial symmetrical plane strain assumption, the theoretical solution of the displacement and stress were proposed for a circular tunnel excavated in elastic-brittle-plastic and strain-softening rock mass compatible with M-C or generalized H-B failure criterion, which is reinforced with grouted rock bolt. It showed that Fahimifar and Soroush's (2005) solution is a special case of the proposed solution for n = 0.5. Further, the proposed method is validated through example comparison calculated by MATLAB programming. Meanwhile, some particular examples for M-C or generalized H-B failure criterion have been conducted, and parametric studies were carried out to highlight the influence of different parameters (e.g., the very good, average and very poor rock mass). The results showed that, stress field in plastic region of surrounding rock with considering the supporting effectiveness of the grouted rock bolt is more than that without considering the effectiveness of the grouted rock bolt, and the convergence and plastic radius are reduced.

• Geomechanics and Engineering
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• 제3권1호
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• pp.1-16
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• 2011

Piles passing through sloping liquefiable deposits are prone to lateral loading if these deposits liquefy and flow during earthquakes. These lateral loads caused by the relative soil-pile movement will induce bending in the piles and may result in failure of the piles or excessive pile-head displacement. Whilst the weak nature of the flowing liquefied soil would suggest that only small loads would be exerted on the piles, it is known from case histories that piles do fail owing to the influence of laterally spreading soils. It will be shown, based on dynamic centrifuge test data, that dilatant behaviour of soil close to the pile is the major cause of these considerable transient lateral loads which are transferred to the pile. This paper reports the results of geotechnical centrifuge tests in which models of gently sloping liquefiable sand with pile foundations passing through them were subjected to earthquake excitation. The soil close to the pile was instrumented with pore-pressure transducers and contact stress cells in order to monitor the interaction between soil and pile and to track the soil stress state both upslope and downslope of the pile. The presence of instrumentation measuring pore-pressure and lateral stress close to the pile in the research described in this paper gives the opportunity to better study the soil stress state close to the pile and to compare the loads measured as being applied to the piles by the laterally spreading soils with those suggested by the JRA design code. This test data shows that lateral stresses much greater than one might expect from calculations based on the residual strength of liquefied soil may be applied to piles in flowing liquefied slopes owing to the dilative behaviour of the liquefied soil. It is shown at least for the particular geometry studied that the current JRA design code can be un-conservative by a factor of three for these dilation-affected transient lateral loads.

• Advances in nano research
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• 제5권3호
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• pp.261-279
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• 2017

Spectroscopic investigation of Si quantum dots (Si-QDs) embedded in silicon nitride was performed over a broad stoichiometry range to optimize light emission. Plasma-enhanced chemical vapor deposition was used to grow the $SiN_x$ films on Si (001) substrates. The film composition was controlled via the flow ratio of silane ($SiH_4$) and ammonia ($NH_3$) in the range of R = 0.45-1.0 allowed to vary the Si excess in the range of 21-62 at.%. The films were submitted to annealing at $1100^{\circ}C$ for 30 min in nitrogen to form the Si-QDs. The properties of as-deposited and annealed films were investigated using spectroscopic ellipsometry, Fourier transform infrared spectroscopy, Raman scattering and photoluminescence (PL) methods. Si-QDs were detected in $SiN_x$ films demonstrating the increase of sizes with Si excess. The residual amorphous Si clusters were found to be present in the films grown with Si excess higher than 50 at.%. Multi-component PL spectra at 300 K in the range of 1.5-3.5 eV were detected and nonmonotonous varying total PL peak versus Si excess was revealed. To identify the different PL components, the temperature dependence of PL spectra was investigated in the range of 20-300 K. The analysis allowed concluding that the "blue-orange" emission is due to the radiative defects in a $SiN_x$ matrix, whereas the "red" and "infrared" PL bands are caused by the exciton recombination in crystalline Si-QDs and amorphous Si clusters. The nature of radiative and no radiative defects in $SiN_x$ films is discussed. The ways to control the dominant PL emission mechanisms are proposed.

• Journal of Korean Neurosurgical Society
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• 제42권4호
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• pp.281-285
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• 2007

Objective : Distal anterior cerebral artery (DACA) aneurysms are fragile and known to have high risks for intraoperative premature rupture and a relatively high associated morbidity. To improve surgical outcomes of DACA aneurysms, we reviewed our surgical strategy and its results postoperatively. Methods : A total of 845 patients with ruptured cerebral aneurysms were operated in our hospital from January 1991 to December 2005. Twenty-three of 845 patients had ruptured DACA aneurysms which were operated on according to our surgical strategy. Our surgical strategy was as follows; early surgery, appropriate releasing of CSF, appropriate surgical approach, using neuronavigating system, securing the bridging veins, using temporary clipping and/or tentative clipping, meticulous manipulation of aneurysm, and using micro-Doppler flow probe. Twenty of 23 patients who had complete medical records were studied retrospectively. We observed the postoperative radiographic findings and checked Glasgow Outcome Scale score sixth months after the operation. Results : Nineteen DACA aneurysms were clipped through a unilateral interhemispheric approach and one DACA aneurysm was clipped through a pterional approach. Postoperative radiographic findings revealed complete clipping of aneurysmal neck without stenosis or occlusion of parent arteries. In two patients, a residual neck of aneurysm was visualized. Seventeen patients showed good recovery, one patient resulted in moderate disability, while 2 patients died. Conclusion : With our surgical strategy it was possible to achieve acceptable surgical morbidity and mortality rates in patients with DACA aneurysms. Appropriate use of tentative clipping, temporary clipping and neuro-navigating systems can give great help for safe approach and clipping of DACA aneurysm.

• 한국방재학회 논문집
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• 제10권4호
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• pp.81-88
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• 2010

최근 들어 기상 이변에 따라 단시간 동안에 특정 소유역에 집중하는 호우 또는 초과우량에 의한 국지성 돌발홍수가 빈번히 발생함에 따라, 이로 인한 인명과 재산의 상당한 위험과 손실은 전 세계적인 것으로서 우리나라도 증가일로에 있다. 돌발홍수는 일반적으로 급경사 소유역에서 집중적인 강우에 의해 발생하여 빠른 유출과 토석류를 동반하기 때문에, 홍수피해를 대비하기 위한 사전 홍수예보시간이 부족할 정도로 급격히 빠른 홍수의 특성을 보인다. 본 연구의 목적은 대상유역의 확률강우량으로부터 돌발홍수지수(flash flood index, FFI)를 산정하여 돌발홍수의 심각성 정도를 정량적으로 분석하고자 한다. 특히 미계측 유역하천에서의 지역 홍수예 경보를 위한 기초자료를 제공할 수 있도록, 대상유역에 대하여 상대적인 돌발홍수심도를 제시할 수 있는 FFI-D-F(돌발홍수지수-지속시간-빈도) 관계곡선을 개발하였다. 또한 FFI-D-F 관계곡선은 현존 및 계획 방재시설물의 돌발홍수 대응능력 및 잔여홍수위험 평가에 활용될 수 있을 것으로 기대된다.

• 한국항해항만학회지
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• 제31권6호
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• pp.515-521
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• 2007

컨테이너 화물의 복합운송시스템 중에서 체화현상은 항만에서 가장 심각하다. 이러한 문제를 해결하기 위해 해상과 육상의 경계선에서 체선체화 문제를 발생시키는 컨테이너 크레인의 직업효율을 향상시키는 방법을 생각할 수 있다. 이를 위해 본 연구에서는 가능한 범위에서 트롤리를 목표지점까지 빠르게 이동시키는 동시에 목표위치에서의 흔들림도 짧은 시간 내에 제어하는 문제를 다루고 있다. 제어 전략으로 설계된 구간에서 최적의 성능과 강인성이 보장되는 LQ 제어와 제약조건에서 최적화가 가능한 실수코딩 유전알고리즘을 결합한다. 컴퓨터 시뮬레이션을 통해 제안한 제어기가 설정한 설계사양을 완벽하게 만족하는 것을 보임으로 그 유효성을 증명한다.