• Steel and Composite Structures
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• 제19권6호
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• pp.1549-1560
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• 2015

This paper presents the characterization of fatigue crack in the A283 Grade C steel using the MMM method by identifying the effects of magnetic flux leakage towards the crack growth rate, da/dN, and crack length. The previous and current research on the relation between MMM parameters and fatigue crack effect is still unclear and requires specific analysis to validate that. This method is considered to be a passive magnetic method among other Non-Destructive Testing (NDT) methods. The tension-tension fatigue test was conducted with a testing frequency of 10 Hz with 4 kN loaded, meanwhile the MMM response signals were captured using a MMM instrument. A correlation between the crack growth rate and magnetic flux leakage produces a sigmoid shape curve with a constant values which present the gradient, m value is in the ranges of 1.4357 to 4.0506, and the y-intercept, log C in the ranges of $4{\times}10^{-7}$ to 0.0303. Moreover, a linear relation was obtained between the crack length and magnetic flux leakage which present the R-Squared values is at 0.830 to 0.978. Therefore, MMM method has their own capability to investigate and characterize the fatigue crack effects as a main source of fracture mechanism for ferrous-based materials.

• 한국재료학회지
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• 제27권1호
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• pp.32-38
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• 2017

Insulating $TaN_x$ films were grown by plasma enhanced atomic layer deposition using butylimido tris dimethylamido tantalum and $N_2+H_2$ mixed gas as metalorganic source and reactance gas, respectively. Crossbar devices having a $Pt/TaN_x/Pt$ stack were fabricated and their electrical properties were examined. The crossbar devices exhibited temperature-dependent nonlinear I (current) - V (voltage) characteristics in the temperature range of 90-300 K. Various electrical conduction mechanisms were adopted to understand the governing electrical conduction mechanism in the device. Among them, the PooleFrenkel emission model, which uses a bulk-limited conduction mechanism, may successfully fit with the I - V characteristics of the devices with 5- and 18-nm-thick $TaN_x$ films. Values of ~0.4 eV of trap energy and ~20 of dielectric constant were extracted from the fitting. These results can be well explained by the amorphous micro-structure and point defects, such as oxygen substitution ($O_N$) and interstitial nitrogen ($N_i$) in the $TaN_x$ films, which were revealed by transmission electron microscopy and UV-Visible spectroscopy. The nonlinear conduction characteristics of $TaN_x$ film can make this film useful as a selector device for a crossbar array of a resistive switching random access memory or a synaptic device.

• Journal of electromagnetic engineering and science
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• 제11권3호
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• pp.166-173
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• 2011

In this paper, we implemented and analyzed a wireless power transfer (WPT) system with a CSPR topology. CSPR refers to constant current source, series resonance circuit topology of a transmitting coil, parallel resonance circuit topology of a receiving coil, and pure resistive loading. The transmitting coil is coupled by a magnetic field to the receiving coil without wire. Although the electromotive force (emf) is small (about 4.5V), the voltage on load resistor is 148V, because a parallel resonance scheme was adopted for the receiving coil. The implemented WPT system is designed to be able to transfer up to 1 kW power and can operate a LED TV. Before the implementation, the EMF reduction mechanism based on the use of ferrite and a metal shield box was confirmed by an EM simulation and we found that the EMF can be suppressed dramatically by using this shield. The operating frequency of the implemented WPT system is 30.7kHz and the air gap between two coils is 150mm. The power transferred to the load resistor is 147W and the real power transfer efficiency is 66.4 %.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2006년도 춘계종합학술대회
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• pp.693-696
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• 2006

본 연구에서는 생체 임피던스의 변화를 계측하여 혈류량의 변화를 추정하기 위한 시스템을 구현하였다. 구현된 시스템은 인위적인 압력을 가하여 압력의 변화에 따른 임피던스의 변화량을 측정할 수 있도록 구성하였으며, 크게 압력 측정부와 4 전극법을 이용한 임피던스 측정부로 구분할 수 있다. 압력 측정부는 반도체식 압력센서와 센서의 출력신호를 처리하기 위한 전자회로부로 구성하였고, 임피던스 측정부는 교류 정전류원 회로와 임피던스 신호의 검출을 위한 락인 증폭기로 시스템을 구성하였다. 구현된 시스템의 성능평가를 위하여 표준저항을 이용한 임피던스 측정부의 특성조사 실험을 수행 하였다. 그리고 실제 실험군을 대상으로 임피던스의 계측을 통한 혈류량 변화 추정실험을 수행하였고, 혈류량 변화와 평균 동맥압을 이용한 혈류 저항비를 추정하였다 그 결과 혈류저항비와 혈류량의 변화는 반비례관계를 명확하게 보여 주었으며, 상관분석을 수행한 결과 상관계수가 -0.96776으로 강한 음의 상관관계를 나타내었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.597-598
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• 2005

Recently, the performance of portable electric equipment can often improved by a Li-ion battery assisted by a supercapacitor. A supercapacitor can provide high power density as well as a low resistance in the hybrid system. In this study, we have prepared, as the pluse power souce, a commercially supplied Li-ion battery with a capacity of 700mAh and AC resistivity of $60m\Omega$ at 1kHz and nonaqeous asymmetric hybrid capacitor composed of an activated carbon cathode and MCMB anode, and have examined the electrochemical characteristics of hybrid capacitor and the pulse performances of parallel connected battery/hybrid capacitor source. The nonaqueous asymmetric hybrid capacitor, the stacks of 10 pairs of the cathode, the porous separator and the anode electrode were housed in Al-laminated film cell. The hybrid capacitor, which was charged and discharged at a constant current at $0.25mA/cm^2$ between 3 and 4.3V, has exhibited the capacitance of 100F. And the equivalent series resistance was $32m\Omega$ at 1kHz. By combining a Li-ion battery and a hybrid capacitor, the pulse performance of battery can be improved 23% in run time under a pulse discharge of 7C-rate.

• Journal of Korean Neurosurgical Society
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• 제60권5호
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• pp.485-497
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• 2017

Surgical treatment of the degenerative disc disease has evolved from traditional open spine surgery to minimally invasive spine surgery including endoscopic spine surgery. Constant improvement in the imaging modality especially with introduction of the magnetic resonance imaging, it is possible to identify culprit degenerated disc segment and again with the discography it is possible to diagnose the pain generator and pathological degenerated disc very precisely and its treatment with minimally invasive approach. With improvements in the optics, high resolution camera, light source, high speed burr, irrigation pump etc, minimally invasive spine surgeries can be performed with various endoscopic techniques for lumbar, cervical and thoracic regions. Advantages of endoscopic spine surgeries are less tissue dissection and muscle trauma, reduced blood loss, less damage to the epidural blood supply and consequent epidural fibrosis and scarring, reduced hospital stay, early functional recovery and improvement in the quality of life & better cosmesis. With precise indication, proper diagnosis and good training, the endoscopic spine surgery can give equally good result as open spine surgery. Initially, endoscopic technique was restricted to the lumbar region but now it also can be used for cervical and thoracic disc herniations. Previously endoscopy was used for disc herniations which were contained without migration but now days it is used for highly up and down migrated disc herniations as well. Use of endoscopic technique in lumbar region was restricted to disc herniations but gradually it is also used for spinal canal stenosis and endoscopic assisted fusion surgeries. Endoscopic spine surgery can play important role in the treatment of adolescent disc herniations especially for the persons who engage in the competitive sports and the athletes where less tissue trauma, cosmesis and early functional recovery is desirable. From simple chemonucleolysis to current day endoscopic procedures the history of minimally invasive spine surgery is interesting. Appropriate indications, clear imaging prior to surgery and preplanning are keys to successful outcome. In this article basic procedures of percutaneous endoscopic lumbar discectomy through transforaminal and interlaminar routes, percutaneous endoscopic cervical discectomy, percutaneous endoscopic posterior cervical foraminotomy and percutaneous endoscopic thoracic discectomy are discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.58-58
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• 1999

The diamond films which can be applied to SOD (silicon-on-diamond) structure were deposited on Si(100) substrate using CO/H2 CH4/H2 source gases by microwave plasma chemical vapor deposition(MPCVD), and SOD structure have been fabricated by poly-silicon film deposited on the diamond/Si(100) structure y low pressure chemical vapor deposition(LPCVD). The phase of the diamond film, surface morpholog, and diamond/Si(100) interface were confirmed by X-ray diffraction(XRD), scanning electron microscopy(SEM), atomic force microscopy(AFM), and Raman spectroscopy. The dielectric constant, leakage current and resistivity as a function of temperature in films are investigated by C-V and I-V characteristics and four-point probe method. The high quality diamond films without amorphous carbon and non-diamond elements were formed on a Si(100), which could be obtained by CO/H2 and CH4/H2 concentration ratio of 15.3% and 1.5%, respectively. The (111) plane of diamond films was preferentially grown on the Si(100) substrate. The grain size of the films deposited by CO/H2 are gradually increased from 26nm to 36 nm as deposition times increased. The well developed cubo-octahedron 100 structure nd triangle shape 111 are mixed together and make smooth and even film surface. The surface roughness of the diamond films deposited by under the condition of CO/H2 and CH4/H2 concentration ratio of 15.3% and 1.5% were 1.86nm and 3.7 nm, respectively, and the diamond/Si(100) interface was uniform resistivity of the films deposited by CO/H2 concentration ratio of 15.3% are obtained 5.3, 1$\times$10-9 A/cm, 1 MV/cm2, and 7.2$\times$106 $\Omega$cm, respectively. In the case of the films deposited by CH4/H2 resistivity are 5.8, 1$\times$10-9 A/cm, 1 MV/cm, and 8.5$\times$106 $\Omega$cm, respectively. In this study, it is known that the diamond films deposited by using CO/H2 gas mixture as a carbon source are better thane these of CH4/H2 one.

• 한국해양학회지:바다
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• 제24권2호
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• pp.187-207
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• 2019

고성능 해양모델을 개발하기 위하여 적시 컴파일(Just-In-Time) 언어인 줄리아 언어를 사용하였고, 운동량 방정식의 해를 구하기 위해 연속완화법으로 푸아송 방정식을 푸는 코드를 작성하였다. 다음으로, 줄리아 계산 코드를 시험하기 위하여 두 가지의 모델을 구축하였다. 첫 번째로, 일정한 유량의 생성/소멸(source/sink) 조건을 시험하기 위해 단순한 수로 형태를 모델링하였고, 두 번째로, 조석 외력(tidal forcing) 및 전향력(Coriolis force), 난류확산계수로 인한 효과 등을 시험하기 위해 황해(Yellow Sea)를 단순화하여 모델링하였다. 모델은 두 가지 시나리오 안에서 총 8개의 실험안으로 테스트되었다. 테스트 결과, 시나리오 1에서 3가지 실험안의 수심 평균된 유속은 이론 값에 완벽하게 수렴하였고, 해저마찰로 인한 수직적 유속 구배를 잘 보여주었다. 또한 시나리오 2에서는 황해의 무조점과 우리나라 서해 중부와 남부 연안의 조석 특성을 잘 재현하였고, 전향력과 수직 난류확산계수에 따른 결과의 차이를 잘 보여주었다. 따라서, 줄리아 언어를 이용한 해양모델을 개발하는 데에 성공하였다고 판단되며, 이는 해양모델이 고전적인 컴파일 언어에서 적시 컴파일 언어로 성공적으로 넘어가는 단계에 오게 됐다는 것을 시사한다.

• 한국해양학회지:바다
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• 제4권1호
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• pp.71-79
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• 1999

금강에서 외해역으로 전달되는 물질의 수지를 이해하기 위한 연구의 일환으로 금강하구의 영양염의 계절적인 분포를 조사하였다. 1997년에서 1998년간 금강하구의 6개 정점에서 13~24시간동안 연속관측을 통하여 영양염, 부유현탁물질(SPM; Suspended Particulate Matter), 엽록소와 염분을 분석하였으며, 조석자료, 기상자료와 금강 하구언의 담수 방출량 자료도 보조자료로서 사용하였다. 이 연구를 통하여 하구내 영양염의 계절적인 분포의 차이와 이런 현상을 주도하는 요인을 밝히는데 주목적이 있고, 부차적으로 금강하구언 조성 이전과 이후 영양염 분포의 차이를 조사하였다. 금강 배출수내 영양염들의 농도는 계절에 따라 확연히 구별된다. 인산염과 암모니움염은 갈수기에 농도가 높게 나타나는 반면, 풍수기에는 규산염이 높게 나타났고 이때 SPM의 농도도 높게 출현하였다. 그러나 질산염은 연중 일정한 농도를 유지하였다. 이러한 계절적인 차이를 결정하는 주원인은 일차적으로 담수의 유입량이다. 강우에 의한 담수의 희석효과가 이러한 영양염과 SPM의 계절적인 변화를 야기하는 것으로 생각된다. 이러한 과정을 통하여 증가하는 SPM의 농도가 2차적으로 영양염의 분포에 영향을 주는 것으로 생각된다. 조사된 모든 영양염의 주 공급원은 금강에서 유입하는 담수이며 조사된 영양염의 기본적인 분포는 이들이 보존적임을 보인다. 조사를 총괄하여 보면 질산염, 아질산염 그리고 규산염은 계절에 상관없이 거의 보존적인 성격을 나타냈다. 그러나 다른 영양염(인산염, 암모니움염)과 SPM은 계절에 따른 차이가 나타났다. 인산염과 암모니움염은 6월과 10월의 갈수기동안에는 거의 보존적인 성향을 보인 반면, 풍수기와 5월의 조사에서 첨가현상을 보였다. 이러한 첨가현상에 영향을 주는 주 요인은 봄철 대량 번식된 담수성 플랑크톤이 해수와 접촉함에 따라 사멸하고, 이와 동시에 유입된 유기물의 분해와 SPM에 흡착되어잇던 인산염이 용출되는 것으로 생각되며, 저층 플럭스(benthic flux)도 기여하는 것으로 보인다. 하구언 조성 이전과의 비교에서 SPM의 농도가 감소함에 따라 SPM이 하구내 영양염의 재생과정에 미치는 중요성은 현저히 약화되었다. 또한 하구내 영양염의 분포를 결정하는 염분의 분포가 갈수기에는 하구언에서 1~2 km 정도로 근접한 곳에서 염분의 구성이 5~15 psu로 나타나 영양염의 첨가현상등 화학적 변화가 이곳에 집중되고, 풍수기 동안에는 하구 전역에서 이러한 염분분포가 나타난다. 따라서 하구언 조성 이후에 갈수기 동안 하구언에 근접한 일부만이 진정한 하구의 역할을 하고 나머지는 만과 같은 특성을 보이고 있다. 하구언 갑문 폐쇄 이전과 이후의 비교 결과 조석의 차단으로 인한 조류속도의 감소로 인하여 부유현탁물질의 농도가 감소하였으며 영양염류의 농도가 증가하였고, 따라서 식물플랑크톤의 대량번식이 발생할 가능성이 있다.

• Ocean and Polar Research
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• 제30권4호
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• pp.519-536
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• 2008

The relatively tranquil area within the Gogunsan Archipelago was for the first time investigated preliminarily with respect to modern sedimentological processes in association with the emplacement of the Saemangeum Dyke. Basic sedimentological observations, bathymetry and surface sediments were performed twice during 2006-2008 to compare the results and elaborate changes during that period of time. In addition, sediment dynamical observations were carried out with latest measuring equipment along two transects crossing the entrances of the archipelago, including 12-hour onboard measurements of current, suspended sediments, temperature, and salinity. This dataset was used to reveal hydrodynamic characteristics for spring season April-May and to estimate the direction and relative magnitude of the net flux of suspended sediments. There occurred three depositional areas (A to C) within the archipelago, where sediment texture was also changed. In area A, around Yami Island and the dyke, and area B, in the center of the archipelago, surface sediments became coarsened over the two-year period; sand content increased 5% at the expense of silt content in the former, whereas silt content increased 3% at the expense of clay content in the latter. By comparison, area C in the western entrance of the archipelago shows a textural trend of fining with more silt and clay (combined increase of 5%) at the expense of sand content. The accumulation of sediments in areas A and B is attributable to the sand and silt resuspended from the seabed sediments off sector 4 of the dyke during the winter. The origin of the fine materials depositing on area C is uncertain at present, although suspended sediments moving offshore around the archipelago may be one of the most likely candidates for the source. The temperature of seawater increased rapidly from $9-10^{\circ}C$ in April to $14-16^{\circ}C$ in May, whereas salinity remained more or less constant at 31-32%o during the two months. Both of these parameters showed little variations with depth through a tidal cycle, suggesting good mixing of seawater without any help of significant waves. The consistency of salinity during a tidal cycle also indicates no insignificant effects of freshwater from the rivers Mangyung and Donjin emitting through the opening gap near Sinsi Island. The suspended sediment concentrations were higher at the entrance between Sunyu and Sinsi islands than at the entrance between Hoenggyong and Sinsi islands, ranging from 20 and 30 mg/l and from 5 and 15 mg/l, respectively at the sea surface. Although tidal currents were variable across a transect between Sunyu and Sinsi islands, the currents across the entrance between Hoenggyong and Sinsi islands flowed consistently in the same direction all over the transect during a tidal cycle. The estimation of net flux of suspended sediments indicates that suspended sediments are transferred to the Gogunsan Archipelago mainly through a relatively deep trough adjacent to Sinsi Island toward the shallow area around Yami Island and the dyke.