• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.7
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• pp.533-538
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• 2001

The barrier height is found to increase from 0.25 to 0.690 eV for Schottky contacts on n-InGaAs using deposition of Ag on a substrate cooled to 77K(LT). Surface analysis leads to an interface model for the LT diode in which there are oxide compounds of In:O and As:O between the metal and semiconductor, leading to behavior as a metal-insulator-semiconductor diode. The metal film deposited t LT has a finer and more uniform structure, as revealed by scanning electron microscopy and in situ metal layer resistance measurement. This increased uniformity is an additional reason for the barrier height improvement. In contrast, the diodes formed at room temperature exhibit poorer performance due to an unpassivated surface and non-uniform metal coverage on a microscopic level.

• Journal of Environmental Science International
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• v.24 no.12
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• pp.1591-1600
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• 2015

The response of the freshwater microalga, Chlorella vulgaris, to heavy metal stress was examined based on chlorophyll fluorescence analysis to assess the toxic effects of heavy metals in freshwater ecosystems. When toxic effects were analyzed using regular chlorophyll fluorescence analysis, photosystem II activity($F_v/F_m$) decreased significantly when exposed to $Cu^{2+}$ and $Hg^{2+}$ for 12 h, and decreased in the order of $Hg^{2+}>Cu^{2+}>Cd^{2+}>Ni^{2+}$ when exposed for 24h. The effective photochemical quantum yield(${\phi}{\prime}_{PSII}$), chlorophyll fluorescence decrease ratio($R_{Fd}$), minimal fluorescence yield($F_o$), and non-photochemical quenching(NPQ), but not photochemical quenching(qP), responded sensitively to $Hg^{2+}$, $Cu^{2+}$, and $Cd^{2+}$. These results suggest that $F_v/F_m$, as well as ${\phi}{\prime}_{PSII}$, $R_{Fd}$, $F_o$, and NPQ could be used to assess the effects of heavy metal ions in freshwater ecosystems. However, because many types of heavy metal ions and toxic compounds co-occur under natural conditions, it is difficult to assess heavy metal toxicity in freshwater ecosystems. When Chlorella was exposed to heavy metal ions for 12 or 24h, $F_v/F_m$ and maximal fluorescence yield($F_m$) changed in response to $Hg^{2+}$ and $Cu^{2+}$ based on image analysis. However, assessing quantitatively the toxic effects of several heavy metal ions is challenging.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.245-248
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• 1999

Explicit dynamic finite element analysis has been used widely in the field of sheet metal forming. However in using the analysis technique there are some parameters which are not clearly defined so that engineers may obtain inaccurate solutions In the present study parameters such as time step damping ratio penalty constant and punch speed were investigated on their influence to the solution behavior. Considered forming processes are plane stain bending by a punch and axisymmetric deep drawing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.552-556
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• 1997

The Direct Metal Prototyping(DMP), one of the rapid prototyping technologies, allows the manufacturing of three-dimensional metallic parts using metal powders directly from the CAD data. Laser power and scanning speed are the most important variables of the process. The objective of this study is to obtain the design data for laser power and scanning speed to bond metal powders effectively using the finite element method. To obtain the design values, a numerical analysis considering two-dimensional heat transfer during the sintering of metal powder layers of the process was performed. The laser beam has been modeled to have directionality in its heat flux distribution, i. e., in the scanning direction a Gaussian beam mode distribution has been assumed and in the thickness direction a square beam mode distribution. The three-dimensional irregular distribution of metal powders of the powder layer is idealized as two-dimensional distribution in which metal powders are located regularly and periodically on the plate. In this study the design values of laser power vs scanning speed have been obtained. Temperature distribution and temperature variation of the powder layers with respect to time have been predicted. The commputed dsign data will be useful in determining the initial conditions of the process.

• Journal of Technologic Dentistry
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• v.22 no.1
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• pp.79-88
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• 2000

The objective of this finite element method study was to analyze the stress distribution induced in a maxillary central incisor Ni-Cr base metal coping ceramic crowns with various margin design. Margin designs of crown in this experiment were knife-edge metal margin on chamfer finishing line of tooth preparation(M1), butt metal margin on shoulder finishing line(M2), reinforced butt metal margin on shoulder finishing line(M3), beveled metal margin on bevelde shoulder finishing line(M4). Two- dimensional finite element models of crown designs were subjected to a simulated biting force of 100N which was forced over porcelain near the lingual incisal edge. Base on plane stress analysis, the maxium von Miss stresses(Mpa) in porcelain venner was 0.432, in metal coping was 0.579, in dentin abutment was 0.324 for M1 model, and M2 model revealed in porcelain was 0.556, in metal coping was 0.511, in dentin was 0.339, and M3 model revealed in porcelain was 0.556, in metal coping was 0.794, in dentin was 0.383 for M4 model. All values of each material in metal-ceramic crown were much below the critical failure values.

• Nuclear Engineering and Technology
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• v.32 no.1
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• pp.34-45
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• 2000

This study is concerned with the experimental test and numerical analysis of the heat transfer and solidification of the molten metal pool with overlying coolant with boiling. In the test, the metal pool is heated from the bottom surface and coolant is injected onto the molten metal pool. Experiments were performed by changing the test section bottom surface temperature of the metal layer and the coolant injection rate. The two-phase boiling coolant experimental results are compared against the dry test data without coolant or solidification of the molten metal pool, and against the crust formation experiment with subcooled coolant. Also, a numerical analysis is performed to check on the measured data. The numerical program is developed using the enthalpy method, the finite volume method and the SIMPLER algorithm. The experimental results of the heat transfer show general agreement with the calculated values. The present empirical test and numerical results of the heat transfer on the molten metal pool are apparently higher than those without coolant boiling. This is probably because this experiment was performed in concurrence of solidification in the molten metal pool and the rapid boiling of the coolant. The other experiments were performed without coolant boiling and the correlation was developed for the pure molten metal without phase change.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.963-970
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• 2015

Laminate structures are used in the automobile, aerospace, and display industries. The advantages of fiber metal laminates are well known. Fiber metal laminates are useful for reducing the weight and improving impact resistance . However, currently, the mechanical properties of fiber metal laminates are not derived. In this paper, we use thickness as a factor for comparing the properties of laminates of various thickness combinations. The properties fiber metal laminates are analyzed using design of experiments. In addition, the finite element method is used to analyze elastic and plastic strains of fiber metal laminates and aluminum plates. The final goal of this paper is to find a suitable finite element model of fiber metal laminates under bending.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.100-105
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• 2001

The manufacturing of metal bellows consists of the four main forming processes, deep-drawing, ironing, tube bulging and folding. Among these, the bulging and folding processes are critically important because the quality of metal bellows is greatly influenced by the forming conditions of these processes. In the present study, the finite element analysis technique is applied to the bulging and folding processes to obtain information about the design parameters of a metal bellows.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1569-1572
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• 2003

Meshfree approximations exhibit significant potential to solve partial differential equations. Meshfree methods have been successfully applied to various problems which the traditional finite element methods have difficulties to handle, including the quasi-static and dynamic fracture. large deformation problems, contact problems, and strain localization problems. A meshfree method based on the reproducing kernel particle approximation(RKPM) is applied to sheet metal forming analysis in this research. Metal forming examples, such as stretch forming and flanging operation, are analyzed to demonstrate the performance of the proposed meshfree method for largely deformed elasto-plastic material.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.46-49
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• 1997

During sheet metal forming on a double-action press, drawbeads on the blankholder supply a restraining force which controls the flow of metal into the die. The sheet formability can be improved by the optimum drawbeads installation when the punch enters into the die opening. Experiments on the various drawbeads, circular, step, double circular, and circular-step drawbead, have been performed under various working conditions.