• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.114-121
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• 1998

Using Hebb-Wagner's asymmetric cell, partial conductivities of holes and electrons in yttria stabilized zirconia doped with 10 mol% TiO2 have been estimated by a dc polarization measurement. The current interrruption method and ac impedance measurements have been also made to evaluate the ionic conductivity and to examine the consistency of the partial conductivities. Partial conductivities of electrons(σn) and holes (σp) were found to be pro-peortional to -1/4 and 1/4 power of partial pressure of oxygen gas, respectively, except for σn at reducing conditions. In comparison with 5 mol% doped YSZ, σn was found to increase with the increase of TiO2 concentration, but σp stayed at almost a constant value.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.1
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• pp.9-18
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• 2007

This study shows an implementation of partial holes in an initial design domain in order to improve convergences of topology optimization algorithms. The method is associated with a bubble method as introduced by Eschenauer et al. to overcome slow convergence of boundary-based shape optimization methods. However, contrary to the bubble method, initial holes are only implemented for initializations of optimization algorithm in this approach, and there is no need to consider a characteristic function which defines hole's deposition during every optimization procedure. In addition, solid and void regions within the initial design domain are not fixed but merged or split during optimization Procedures. Since this phenomenon activates finite changes of design parameters without numerically calculating movements and positions of holes, convergences of topology optimization algorithm can be improved. In the present study, material topology optimization designs of Michell-type beam utilizing the initial design domain with initial holes of varied sizes and shapes is carried out by using SIMP like a density distribution method. Numerical examples demonstrate the efficiency and simplicity of the present method.

• The Korean Journal of Ceramics
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• v.6 no.2
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• pp.150-154
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• 2000

Mobilities of electrons ($\mu_p$) and holes ($\mu_p$) in 2, 5, and 10 mol% $TiO_2$-doped yttria stabilized zirconia (TD-YSZ) have been estimated by a non-steady state gas permeation method using models proposed by Weppner and Maruyama. Values of $\mu_n$ and $\mu_p$ were found to be closed to those in non-doped YSZ reported earlier. The concentration of electrons and holes were calculated from $\mu_n$ and $\mu_p$ values and the partial conductivities of electrons and holes measured by a dc-polarization method. The concentration of electrons at unit oxygen partial pressure increased with increasing $TiO_2$concentration, while the hole concentration was almost independent of $TiO_2$concentration.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.271-279
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• 2000

5 m/o Yb-doped SrCeO3 proton conductor was prepared by a solid state reaction method and its total electriccal conductivity measured as a function of both oxygen partial pressure and water vapor partial pressure in the temperature range of 500~100$0^{\circ}C$. From the total conductivity have been deconvoluted the partial conductivities of oxide ions, protons, and holes, respectively, on the basis of the defect model proposed. The equilibrium constant of hydrogen-dissolution reaction, proton concentration, and mobilities of oxygen vacancies and protons have subsequently been evaluated. It is verified that SrCe1-xYbxO3 is a mixed conductor of holes, protons and oxide ions and the proton conduction prevails as temperature decreases and water vapor pressure increases. The heat of water dissolution takes a representative value of $\Delta$HoH=-(140$\pm$20) kJ/mol-H2O, but tends to be less negative with increasing temperature. Migration enthalpies of proton and oxygen vacancy are extracted as 0.83$\pm$0.10 eV and 0.81$\pm$0.01 eV, respectively.

• Steel and Composite Structures
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• v.38 no.4
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• pp.399-414
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• 2021

This paper aims to verify the feasibility of rubber rings to mitigate the shear concentration in perfobond connector (PBL) groups. Firstly, modified push-out tests for five specimens with four holes were conducted to investigate the effects of rubber rings on the shear mechanism of PBL groups. The test results showed that by employing rubber rings on partial holes, more shear forces were distributed to the holes without rubber rings. The rubber rings significantly improved the slip ability of the specimens, and the ductility of PBL groups is dependent on the number and thickness of rubber rings. Subsequently, three-dimensional numerical models were established and validated by the experimental results. According to the plastic strain distribution in concrete dowels, the action principle of rubber rings in PBL groups was explained. Furthermore, the parametric study was conducted to investigate the influential factors on shear distributions, including the width of steel plates, the hole spacing, the number of holes, the rubber ring thickness, and the positions of rubber rings. The parametric analysis results showed that the redistribution of shear forces is significantly affected by the rubber rings with the smallest thickness. By properly employing rubber rings in PBL groups, the shear forces of holes are more even. Finally, an analytical model for PBL groups with rubber rings was proposed to predict the shear distribution at the serviceability stage.

• Journal of the Korean Institute of Gas
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• v.24 no.4
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• pp.25-31
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• 2020

Experimental investigations were conducted to examine the combustion characteristics of a swirl-stabilized double cone premixed burner nozzle used for industrial gas turbines for power generation. Several variants with different fuel injection patterns are tested to compare the combustion characteristics such as NOx and CO emissions, stability, and wall temperature distributions. Main results show that NOx emissions and stability are decreased either when the fuel hole diameter is decreased with the same number of fuel holes, or when the number of fuel holes is reduced with the same total area of fuel holes, both of which are due to a higher penetration of fuel into the air stream. Not only is NOx reduced but also stability is enhanced when the fuel hole diameter varies in an alternating manner with the same total area of fuel holes, showing that NOx reduction is due to a higher penetration of mean fuel injection path while stability enhancement is due to a lowered penetration of minimum fuel injection path.

• Journal of the Korean Ceramic Society
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• v.52 no.5
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• pp.299-303
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• 2015

The electrolyte is an important component in determining the performance of Fuel Cells. Especially, investigation of the conduction properties of electrolytes plays a key role in determining the performance of the electrolyte. The electrochemical properties of Yttrium stabilized zirconia (YSZ) were measured to allow the use of this material as an electrolyte for solid oxide fuel cells (SOFC) in the temperature range of $700-1000^{\circ}C$ and in $0.21{\leq}pO_2/atm{\leq}10^{-23}$. A Hebb-Wagner polarization experimental cell was optimally manufactured; here we discuss typical problems associated with making cells. The partial conductivities due to electrons and holes for 8YSZ, which is known as a superior oxygen conductor, were obtained using I-V characteristics based on the Hebb-Wagner polarization method. Activation energies for holes and electrons are $3.99{\pm}0.17eV$ and $1.70{\pm}0.06eV$ respectively. Further, we calculated the oxygen ion conductivity with electron, hole, and total conductivity, which was obtained by DC four probe conductivity measurements. The oxygen ion conductivity was dependent on the temperature; the activation energy was $0.80{\pm}0.10eV$. The electrolyte domain was determined from the top limit, bottom limit, and boundary (p=n) of the oxygen partial pressure. As a result, the electrolyte domain was widely presented in an extensive range of oxygen partial pressures and temperatures.

• ETRI Journal
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• v.42 no.2
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• pp.282-291
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• 2020

The study reports on the design and performance of two air-filled and two partial ethanol-filled photonic crystal fiber (PCF) structures with a tetra core for supercontinuum generation. The PCFs are nonlinear with ultra-flattened zero dispersion. Holes with smaller areas are used to create a tetra-core PCF structure. Ethanol is filled in the holes of smaller area while the larger holes of cladding region are airfilled. Optical properties including dispersion, effective mode area, confinement loss, normalized frequency, and nonlinear coefficient of the designed PCF structures are investigated via full vector finite difference time domain (FDTD) method. A PCF structure with lead silicate as wafer exhibits significantly better results than a PCF structure with silica as wafer. However, both structures report dispersion at a telecommunication wavelength corresponding to 1.55 ㎛. Furthermore, the PCF structure with lead silicate as wafer exhibits a very high nonlinear coefficient corresponding to 1375 W^-1 km^-1 at the same wavelength. This scheme can be used for optical communication systems and in optical devices by exploiting the principle of nonlinearity.

• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.288-295
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• 1999

Partial conductivities contributed by electron holes, oxygen ions, and protons were caluclated in $SrZr_{0.95}Y_{0.05}O_{2.975}$, using the reported formulae derived from the defect chemistry of HTPCs. Required parameters were obtained from the graphical analysis of total conductivity variation against partial pressure of water vapor and oxygen. Predicted overall conductivities showed a reasonable agreement with experimental measurements. The conductivity of the material showed a linear increase with square root of the water vapor pressure. This increase was due to proton conduction in an almost pure ionic conductivity. The calculation of partial conductivities at $800^{\circ}C$ resulted in an almost pure ionic conductivity at $P_{02}=10^{-10}$ atm and a predominant hole conductivity at $P_{02}=10^{-10}$ atm. Pure proton conduction was not expected at this temperature, contrary to the earlier reports. Discussions were made in relation with reported thermodynamic data and defect structure of the material. It was shown that from the total conductivity dependence on water vapor pressure, the pure ionic conductivity at low oxygen partial pressures could be separated into protonic and oxygen ionic conductivity in $ZrO_2$-based HTPCs.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.223-227
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• 2003

The method of flame hole dynamics is demonstrated as a mean to simulate turbulent flame extinction. The core of the flame hole dynamics involves derivation of a random walk mapping for the flame holes, created by local quenching, between the burning and quenched states provided that the dynamic characteristics of flame edges is known. Then, the random walk mapping is projected to a background turbulent field. The numerical simulations are carried out with the further simplifications of flame string and unconditioned scalar dissipation rate. The simulation results show how the chance of partial quenching is influenced by the crossover scalar dissipation rate. Finally, a list of improvements, necessary to achieve more realistic turbulent flame quenching simulation, are discussed.