• Corrosion Science and Technology
• /
• 제2권5호
• /
• pp.212-218
• /
• 2003

Electronic properties of passive films formed on Ti at film formation potentials $(E_f)V_{SCE}$ in pH 8.5 buffer solution and in an artificial seawater were examined through the photocurrent measurement and Mott-Schottky analysis. The passive films formed on Ti in pH 8.5 buffer solution exhibited a n-type semiconductor with a band gap energys $(E_g);E_g^{n=2}=3.4$ eV for nondirect electron transition, and $E_g^{n=0.5}=3.7$ eV for direct electron transition. These band gap values were almost same as those for the passive films formed in artificial seawater, indicating that chloride ion ($Cl^-$ in solution did not affect the electronic structure of the passive film on Ti. $E_g$ for passive films formed on Ti were found to be greater than those ($E_g^{n=0.5}=3.1$ eV, $E_g^{n=2}=3.4$) for a thermal oxide film formed on Ti in air at $400^{\circ}C$. The disorder energy of passive film, determined from the absorption tail of photocurrent spectrum, was much greater than that for the thermal oxide film farmed on Ti in air at $400^{\circ}C$. The greater $E_g$ and the higher disorder energy for the passive film compared with those for the thermal oxide fIlm suggest that the passive film on Ti exhibited more disorded structure than the thermal oxide film. The donor density (about $2.4{\times}10^{20}cm^{-3}$) for the passive film formed in artificial seawater was greater than that (about $20{\times}10^{20}cm^{-3}$) formed in pH 8.5 buffer solution, indicating that $Cl^-$ increased the donor density for the passive film on Ti.

• 한국컴퓨터정보학회논문지
• /
• 제10권2호
• /
• pp.49-57
• /
• 2005

본 논문은 상관관계(trade-off)에 의한 CLB구조의 CPLD 저전력 기술 매핑 알고리즘을 제안하였다. 제안한 저전력 기술 매핑 알고리즘은 주어진 불린 네트워크를 DAG로 구성하여 소모전력 계산을 위한 TD(Transition Density) 계산 단계와 매핑 가능 클러스터 생성, CLB 패킹의 단계로 구성하였다. TD 계산 단계는 DAG를 구성하고 있는 각 노드들에 대한 스위칭 동작을 계산하여 전체 소모 전력을 계산하는 단계이다. 매핑 가능 클러스터 생성 단계는 주어진 CPLD의 CLB에 대한 입출력의 수와 OR 텀수를 고려하여 매핑 가능 클러스터를 생성하는 단계이다. 매핑 가능 클러스터를 생성하기 위하여 공통 노드 클러스터 병합과 노드 분할, 노드 복제의 방법을 이용한다. 제안된 알고리즘을 SIS에서 제공되는 벤치마크에 적용하여 실험한 결과 OR 텀수를 5로 했을 경우 기존의 CPLD 기술 매핑 알고리즘인 TEMPLA에 비해 30.73$\%$의 소모전력이 감소되었으며, PLAmap에 비해 17.11$\%$감소되었다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2010년도 제39회 하계학술대회 초록집
• /
• pp.139-139
• /
• 2010

Ionic Transition Metal Complex based (iTMC) Light-emitting electrochemical cells (LEECs) have been drawn attention for cheap and easy-to-fabricate light-emitting device. LEEC is one of the promising candidate for next generation display and solid-state lighting applications which can cover the defects of current commercial OLEDs like complicated fabrication process and strong work-function dependent sturucture. We have investigated the performance characteristics of LEECs based on poly (3, 4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS)-incorporated transition metal complex, which is tris(2, 2'-bipyridyl)ruthenium(II) hexafluorophosphate in this study. There are advantages using conductive polymer-incorporated luminous layer to prevent light disturbance and absorbance while light-emitting process between light-emitting layer and transparent electrode like ITO. The devices were fabricated as sandwiched structure and light-emitting layer was deposited approximately 40nm thickness by spin coating and aluminum electrode was deposited using thermal evaporation process under the vacuum condition (10-3Pa). Current density and light intensity were measured using optical spectrometer, and surface morphology changes of the luminous layer were observed using XRD and AFM varying contents of PEDOT:PSS in the Ruthenium(II) complex solution. To observe enhanced ionic conductivity of PEDOT:PSS and luminous layer, space-charge-limited-currents model was introduced and it showed that the performances and stability of LEECs were improved. Main discussions are the followings. First, relationship between film thickness and performance characteristics of device was considered. Secondly, light-emitting behavior when PEDOT:PSS layer on the ITO, as a buffer, was introduced to iTMC LEECs. Finally, electrical properties including carrier mobility, current density-voltage, light intensity-voltage, response time and turn-on voltages were investigated.

• Progress in Superconductivity
• /
• 제3권2호
• /
• pp.135-139
• /
• 2002

We have fabricated high-quality c-axis-oriented $MgB_2$ thin films by using a pulsed laser deposition technique. The thin films grown on (1 1 0 2) $Al_2$$O_3$ substrates show an onset transition temperature of 39.2 K with a sharp transition width of ~0.15 K. X-ray diffraction patterns indicate a c-axis-oriented crystal structure perpendicular to the substrate surface. We observed high critical current densities ($J_{c}$) of ~ 16 $MA/\textrm{cm}^2$ at 15 K and under self-field, which is comparable to or exceeds those of cuprate high-temperature superconductors. The extrapolation $J_{c}$ at 5 K was estimated to be ~ 40 MA/$\textrm{cm}^2$, which is the highest record for $MgB_2$ compounds. At a magnetic field of 5 T, the $J_{c}$ of~ 0.1 $MA/\textrm{cm}^2$ was detected at 15 K, suggesting that this compound is very promising candidate for the practical applications at high temperature with lower power consumption. As a possible explanation for the high current-carving capability, the vortex-glass phase will be discussed.d.d.d.

• Elastomers and Composites
• /
• 제39권2호
• /
• pp.142-152
• /
• 2004

서로 다른 두 종류의 폴리스타일렌(PS)을 injection 기계를 이용하여 인장 시편을 만들고, 온도와 인장 속도에 따른 crazing 거동 특성을 연구하기 위하여 다양한 시험을 하였다. 기계적물성은 craze 형성뿐만 아니라 다양한 시험 변수에 의해 영향을 받으며, brittle-ductile transition 이하의 온도에서의 인장 응력 및 최대 신율은 분자량, 인장 속도의 증가 및 온도의 감소에 따라 증가하며 craze의 수와 평균 길이 또한 증가한다. Crazing 응력도 동일한 형태로 증가함을 보여준다. 그러나, 이러한 특성은 인장 강도에 미치는 영향과 비교했을 때 보다 의존도는 상대적으로 낮다. Craze 형성과 성장에 필요한 시간으로 설명할 수 있는 crazing 응력과 인장 응력간의 차이는 분자량, 인장 속도에 따라 비례적으로 그리고, 온도가 감소함에 따라 증가함을 보여 준다. Crazing 은 ${\beta}$-relaxation 온도 근처에서 활성화된다. 이 온도에서는 crazing 응력이 급격하게 감소함을 나타낸다. 인장 평가시 craze 밀도가 적용된 응력에 따라 기하 급수적으로 증가되는데, 개시 단계에서는 craze는 서서히 형성되며, 일단 일정한 수만큼의 craze가 형성이 되면 craze 밀도가 급속도로 증가했다.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제8권4호
• /
• pp.330-343
• /
• 2016

This paper presents results of an experimental investigation of vortex-induced vibration (VIV) of a flexibly mounted and rigid cylinder with two-degrees-of-freedom with respect to varying ratio of in-line natural frequency to cross-flow natural frequency, $f^*$, at a fixed low mass ratio. Combined in-line and cross-flow motion was observed in a sub-critical Reynolds number range. Three-dimensional displacement meter and tension meter were used to measure dynamic responses of the model. To validate the results and the experiment system, x and y response amplitudes and ratio of oscillation frequency to cross-flow natural frequency were compared with other experimental results. It has been found that the higher harmonics, such as third and more vibration components, can occur on a certain part of steel catenary riser under a condition of dual resonance mode. In the present work, however, due to the limitation of a size of circulating water channel, the whole test of a whole configuration of the riser at an adequate scale for VIV phenomenon was not able to be conducted. Instead, we have modeled a rigid cylinder and assumed that the cylinder is a part of steel catenary riser where the higher harmonic motions could occur. Through the experiment, we have found that even though the cylinder was assumed to be rigid, the occurrence of the higher harmonic motions was observed in a small reduced velocity ($V_r$) range, where the influence of the in-line response is relatively large. The transition of the vortex shedding mode from one to another was examined by using time history of x and y directional displacement over all experimental cases. We also observed the influence of in-line restoring force power spectral density with $f^*$.

• 한국결정성장학회지
• /
• 제8권3호
• /
• pp.498-502
• /
• 1998

순수 스피넬$(MgAl_2O_4)$에 대하여 $1400^{\circ}C$에서 $1700^{\circ}C$까지에 내화온도 범위에서 입자크기(G), 밀도($\rho$), 활성에너지(Q)를 구하고 다른 실험값과 비교 분석하였다. 스피넬에 대한 입자크기와 상대밀도는 매우 유사한 경향을 나타내었다. 이들은 두 개의 뚜렷한 영역을 나타내었는데 상대밀도가 약 85~90%까지의 중간소결단계와 전이-밀도 수준 이상의 마지막 단계, 소결영역으로 나타난다. 입자크기(G)와 밀도($\rho$)의 관계에서 활성화에너지 값은 670-48kJ/mol이었으며 다른 스피넬에서는 넓은 온도 범위에서 약 590kJ/mol이었다. 이 값은 기존의 360~580kJ/mol의 값은 근접하였다.

• 한국수소및신에너지학회논문집
• /
• 제16권1호
• /
• pp.1-8
• /
• 2005

Transition of momentum-controlling hydrogen jet to buoyant jet is experimentally investigated in order to develop a prediction model for the moving trajectory of hydrogen leaked from hydrogen devices. In the experiments, room-temperature helium, that has a similar density to the hydrogen leaked from high pressure tank, is horizontally injected through a 4mm tube and its moving trajectory is visualized by the shadowgraph method. The moving trajectories are found to be parabolic, thereby exhibiting increasing influence of the buoyancy. In analyzing the experimental results, the vertical movement is assumed to be controlled by the buoyancy while the horizontal movement is controlled by the air entrainment caused by the initial momentum. The resealing based on this assumption yields a single curve fitting to the all experimental results.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
• /
• pp.378-382
• /
• 1999

We evaluated the effect of joining process such as contact method, shape of joined area and pressure on the electrical property of Bi-2223 superconducting tape. It was observed that the current capacity was reduced at the transition area of the joined tape and was significantly dependent on the uniaxial pressure. The lap-joined tape, fabricated with a pressure of 1,000-1,600 MPa, show the highest value of current capacity(80-90%) of the tape itself. It is believed the highest value of current capacity results from improvement in core density, contacting area and grain alignment, etc. In addition, the irreversible strain( ${\varepsilon}$ irrev) for the joined tape· was measured to be 0.1%, smaller than that of enjoined tape( ${\varepsilon}$ irrev = 0.3%). The decrease in the strength and irreversible strain for joined tape is believed to be due to the irregular geometry/morphology of the transition area of the tape.

• 한국자기학회지
• /
• 제3권1호
• /
• pp.1-6
• /
• 1993

희토류-전이금속 화합물, $LaCo_{13}$에 대한 자체충족적 국제밀도함수근사 LMTO (Linearized Muffin-Tin Orbital) 에너지 띠 전자구조 계산을 토대로 하여 이물질의 상자성, 강자성상에서 자성을 포함한 전기적, 자기적 물성을 고찰하였다. 강자성상에서의 CoI, CoII원자들의 자기모멘트는 각각 $1.34,\;1.65{\mu}_{B}$로 계산되었으며 이는 Co 원자당 평균 자기모멘트 $1.60{\mu}_{B}$에 해당하여 실험치 $1.56~1.68{\mu}_{B}$와 근사한 결과를 얻었다.