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Jeong, Seung Jin,Kwak, No Woo,Byeon, Pilgyu,Chung, Sung-Yoon,Jung, WooChul American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.7
<P>Stabilized Bi2O3 has gained a considerable amount of attention as a solid electrolyte material for low temperature solid oxide fuel cells due to its superior oxygen ion conductivity at the temperature of relevance (<= 500 degrees C). Despite many research efforts to measure the transport properties of stabilized Bi2O3, the effects of grain boundaries on the electrical conductivity have rarely been reported and their results are even controversial. Here, we attempt quantitatively to assess the grain boundary contribution out of the total ionic conductivity at elevated temperatures (350-500 degrees C) by fabricating epitaxial and nano-polycrystalline thin films of yttrium-stabilized Bi2O3. Surprisingly, both epitaxial and polycrystalline films show nearly identical levels of ionic conductivity, as measured by alternating current impedance spectroscopy and this is the case despite the fact that the polyfilm possesses nanosized columnar grains and thus an extremely high density of the grain boundaries. The highly conductive nature of grain boundaries in stabilized Bi2O3 is discussed in terms of the clean and chemically uniform grain boundary without segregates, and the implications for device application are suggested.</P>
Nguyen Van Thang,Nguyen Minh Y,Yong Tae Yoon 대한전기학회 2013 Journal of Electrical Engineering & Technology Vol.8 No.2
This paper proposes a new method for monitoring local voltage stability using the saddle node bifurcation set or loadability boundary in two dimensional power parameter space. The method includes three main steps. First step is to determine the critical buses and the second step is building the static voltage stability boundary or the saddle node bifurcation set. Final step is monitoring the voltage stability through the distance from current operating point to the boundary. Critical buses are defined through the right eigenvector by direct method. The boundary of the static voltage stability region is a quadratic curve that can be obtained by the proposed method that is combining a variation of standard direct method and Thevenin equivalent model of electric power system. And finally the distance is computed through the Euclid norm of normal vector of the boundary at the closest saddle node bifurcation point. The advantage of the proposed method is that it gets the advantages of both methods, the accuracy of the direct method and simple of Thevenin Equivalent model. Thus, the proposed method holds some promises in terms of performing the real-time voltage stability monitoring of power system. Test results of New England 39 bus system are presented to show the effectiveness of the proposed method.
STABILIZATION OF THE KORTEWEG-DE VRIES-BURGERS EQUATION WITH NON-PERIODIC BOUNDARY FEEDBACKS
Aassila, Mohammed 한국전산응용수학회 2003 Journal of applied mathematics & informatics Vol.11 No.1
We consider the Korteweg-de Vries-Burgers (KdVB) equation on the domain [0,11]. We derive a control law which guarantees $L^2$-global exponential stability, $H^3$-global asymptotic stability, and $H^3$-semiglobal exponential stability.
Stability Analysis of the Karman Boundary-Layer Flow
Lee, Yun-Yong,Hwang, Young-Kyu The Society of Air-Conditioning and Refrigerating 2002 International Journal Of Air-Conditioning and Refr Vol.10 No.1
The Karman boundary-layer has been numerically investigated for the disturbance wave number, wave velocity, azimuth angle and radius (Reynolds number, Re). The disturbed flow over rotating disk can lead to transition at a much lower Re than that of the well-known Type I instability. This early transition is due to the excitation of the Type II. Presented are the neutral stability results concerning these instabilities by solving newly formulated stability equations with consideration of whole convective terms. When the present numerical results are compared with the previously known results, the value of critical Re corresponding to Type I is moved from ${Re}_{c.1}$=285.3 to 270.2 and the value corresponding to Type II from ${Re}_{c.2}$=69.4 to 36.9, respectively. Also, the corresponding wave number is moved fro)m $k_1$=0.378 to 0.386 for Type I; from $k_2$=0.279 to 0.385 for Type II. For Type II, the upped limit of wave number and azimuth angle is $k_u$=0.5872, $\varepsilon_u$=$-17.5^{\circ}$, while its lower limit is near $k_u$=0, $\varepsilon_u$=$-28.4^{\circ}$. This implies that the disturbances will be relatively fast amplified at small Re and within narrow bands of wave number compared with the previous results.
Stability and Constant Boundary-Value Problems of f-Harmonic Maps with Potential
Kacimi, Bouazza,Cherif, Ahmed Mohammed Department of Mathematics 2018 Kyungpook mathematical journal Vol.58 No.3
In this paper, we give some results on the stability of f-harmonic maps with potential from or into spheres and any Riemannian manifold. We study the constant boundary-value problems of such maps defined on a specific Cartan-Hadamard manifolds, and obtain a Liouville-type theorem. It can also be applied to the static Landau-Lifshitz equations. We also prove a Liouville theorem for f-harmonic maps with finite f-energy or slowly divergent f-energy.
Phase Plane Method를 이용한 ESC와 TVD 통합 제어
조진국(Jinkuk Cho),김지환(Jihwan Kim),오승규(Seungkyu Oh),장진희(Jinhee Jang),이형철(Hyeongcheol Lee) 한국자동차공학회 2009 한국자동차공학회 부문종합 학술대회 Vol.2009 No.4
This paper presents a integrated control algorithm for ESC (Electronic Stability Control) and TVD (Torque Vectoring Device). The main concept of integrated chassis control is vehicle stability and performance. β-β phase plane and β-r phase plane analysis is used to guarantee vehicle stability. In those phase plane analysis, control boundaries are got experimentally. Sliding mode control is used to control the stability of the vehicle if the vehicle state is in the control boundaries at β-β and β-r phase plane. The ESC and TVD control is used to stabilize the vehicle motion and improve vehicle performance with distributed corrective yaw moment, when vehicle state is in control boundaries at each phase planes. The developed models and the control algorithm are programmed using Matlab/Simulink. CarSim simulator is used to verify the validity of the integrated control algorithm with comparing integrated system and combined system.
Li Yang,Xue Hongtao,Zhou Xin,Tang Fuling,Li Xiuyan,Ren Junqiang,Lu Xuefeng 한국물리학회 2021 Current Applied Physics Vol.28 No.-
Grain boundaries (GBs) relaxation is a promising and effective strategy to improving GB stability or stabilizing nanocrystalline metals. However, previous studies mainly focused on nanocrystalline pure metals and GB behaviors therein, without considering the role of foreign atoms such as impurity or alloying atoms in GB relaxation. In this work, the shear-strain induced structural relaxation of pure Cu Σ3 [110](112) symmetric tilt GBs (STGBs), and the effects of foreign elements (Fe and Ni) and temperature on the GB relaxation were investigated in detail by molecular dynamics method. The results show that shear strain can trigger the structural relaxation of pure, Fe- and Ni-containing Cu GBs by the emission of Shockley partial dislocations from Cu GBs. Both Fe and Ni have impediment effects on the shear-strain induced GB relaxation, though the content of Fe or Ni atom (0.00165 at.%) is quite low in the GB model. The temperature cannot trigger GB relaxation independently within the considered temperature range, but play a positive role in the shear-strain induced structural relaxations of pure, Fe- and Ni-containing Cu Σ3 [110](112) STGBs. Our work might gain new insights into the mechanically induced GB relaxation in nanocrystalline copper and could be beneficial for improving the stability of Cu GBs.
Theoretical Flow Instability of the Karman Boundary Layer
Hwang, Young-Kyu,Lee, Yun-Yong The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.3
The hydrodynamic stability of the Karman boundary-layer flow due to a rotating disk has been numerically investigated for moving disturbance waves. The disturbed flow over a rotating disk can lead to transition at much lower Re than that of the well-known Type I instability mode. This early transition is due to the excitation of the Type II instability mode of moving disturbances. Presented are the neutral stability results concerning the two instability modes by solving new linear stability equations reformulated not only by considering whole convective terms but by correcting some errors in the previous stability equations. The reformulated stability equations are slightly different with the previous ones. However, the present neutral stability results are considerably different with the previously known ones. It is found that the flow is always stable for a disturbance whose dimensionless wave number k is greater than 0.75.
Grain Boundary Healing of Organic-Inorganic Halide Perovskites for Moisture Stability
Chun, Do Hyung,Kim, Sungsoon,Chai, Sung Uk,Kim, Wook,Kim, Wanjung,Lee, Jung Hwan,Rhee, Ryan,Choi, Dukhyun,Kim, Jung Kyu,Shin, Hyunjung,Park, Jong Hyeok American Chemical Society 2019 NANO LETTERS Vol.19 No.9
<P>Although organic-inorganic halide perovskite (OIHP)-based photovoltaics have high photoconversion efficiency (PCE), their poor humidity stability prevents commercialization. To overcome this critical hurdle, focusing on the grain boundary (GB) of OIHPs, which is the main humidity penetration channel, is crucial. Herein, pressure-induced crystallization of OIHP films prepared with controlled mold geometries is demonstrated as a GB-healing technique to obtain high moisture stability. When exposed to 85% RH at 30 °C, OIHP films fabricated by pressure-induced crystallization have enhanced moisture stability due to the enlarged OIHP grain size and low-angle GBs. The crystallographic and optical properties indicate the effect of applying pressure onto OIHP films in terms of moisture stability. The photovoltaic devices with pressure-induced crystallization exhibited dramatically stabilized performance and sustained over 0.95 normalized PCE after 200 h at 40% RH and 30 °C.</P> [FIG OMISSION]</BR>
A Study of Stability for Field Robot using Energy Stability Level Method
C. T. Nguyen(웬치탄),Q. H. Le(레광환),Y. M. Jeong(정영만),S.Y. Yang(양순용) 유공압건설기계학회 2014 드라이브·컨트롤 Vol.11 No.3
In this research, the energy stability level method is used for examining the stable state of Field Robot under effects of swing motion, at particular postures of manipulator, and terrain conditions. The energy stability level is calculated by using the dynamic models of Field Robot, subjected to the concept of equilibrium plane and support boundary. The results, simulated by using computing program for estimating the potential overturning of Field Robot, supply useful predictions of stability analysis for designers and operators.