• Transactions of Materials Processing
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• v.4 no.2
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• pp.131-140
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• 1995

In this paper damage propagation of a material during forming is investigated with the concept of continuum damage mechanics. An isotropic damage model based on the theory of materials of type N is adopted to describe the damage process of a ductile material with large elasto-viscoplastic deformation. The stiffness degradation of the loaded material is chosen as a damage measure. The highly nonlinear equilibrium equations are reduced to the incremental weak form and approximated by the total Lagrangian finite element method. To simulate contact condition, extended interior penalty method with modified coulomb friction law is adopted. The displacement control method along with the modified Riks' continuation technique is used to solve the incremental iterative equations. As numerical examples, upsetting problem and backward extrusion problem are simulated and the results of damage propagation and $J_2$ stress contours with and without friction are presented.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.82-85
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• 2004

This paper proposes the development of delay compensator to minimize performance degradation caused by time delays in network-based real-time control systems. The delay compensator uses the time-stamp method as a direct delay measuring method to measure time delays generated between network nodes. The delay compensator predicts the network time delays of next period in the views point of time delays and minimizes performance degradation from network through considering predicted time delays. Control output considering network time delays is generated by the defuzzification of probable time delays of next period. The time delays considered in the delay compensator are modeled by using a timed Petri net model. The proposed delay prediction mechanism for the delay compensator is evaluated through some simulation tests by measuring deviation of the predicted delays from simulated delays.

• Tunnel and Underground Space
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• v.7 no.1
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• pp.20-30
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• 1997

A discrete joint finite element with joint surface degradation was developed to investigate the shear behavior of rough rock joint. Isoparametric formulation was used for facilitating the implementation of the element in existing Finite Element Codes. The elasto-plastic joint deformation model with the discontinuity constitutive law proposed by Plesha was applied to the element. The reliability of the developed finite element code was successfully testified through numerical direct shear tests conducted under both constant normal stress and constant normal displacement conditions. The result of the numerical direct shear test showed that the code can capture characteristic deformation features envisaged in the direct shear test of rough rock joint.

• Preventive Nutrition and Food Science
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• v.12 no.3
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• pp.131-134
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• 2007

The kinetic analyses for thermal products of alpha-, gamma- and delta-tocopherols during heating as functions of temperature and time were studied. Alpha-, gamma- and delta-tocopherols dissolved in glycerol were heated at $100{\sim}200^{\circ}C$ for $5{\sim}60$ min. The thermal products were separated by hexane extraction and analyzed by HPLC using a reversed phase ${\mu}-Bondapak$ $C_{18}-column$ with two kinds of elution solvents in a gradient mode. The formation kinetics of thermal products of tocopherols followed a first-order kinetic model. The formation rate of thermal products of tocopherols was dependent on heating temperatures and heating times. The activation energy and enthalpy for the thermal products of ${\gamma}-and$ ${\delta}-tocopherols$ were higher than those for ${\alpha}-tocopherol$ as in the case of the oxidative degradation kinetics of tocopherol. The magnitude order of the activation energy was ${\gamma}->{\delta}->{\alpha}-tocopherol$.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.218-222
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• 2004

Batch slurry experiments were conducted to develop cement/slag/Fe(II) system that could treat hazardous liquid wastes containing halogenated organic solvents. Portland cement in combination with Fe(II) was reported to reductively dechlorinate chlorinated organics in a modified solidification/stabilization process. TCE (trichloroethylene) was used a model halogenated organic solvent. The objectives of this study were to assess the feasibility of using cement and steel converter slag amended with Fe(II) as a low cost abiotic reductive dechlorination and to investigate the kinetics of TCE dechlorination over a wide range of TCE concentration. From the result of screening experiments, cement/slag/Fe(II) system was identified as a potentially effective system to treat halogenated organic solvent. Kinetic studies were carried out to further investigate degradation reaction of TCE NAPL (Non Aqueous Phase Liquids) in cement/slag/Fe(II) systems by using batch slurry reactors. Degradation rate of TCE solution in this system can be explained by pseudo-first-order rate law because the prediction with the rate law is in good agreement with the observed data.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.334-335
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• 2006

Solid insulation exposed to voltage is degraded by electrical tree process. And the degradation of the insulation is accelerated by voltage application. For this experimental, specimen of electrical tree model is made by XLPE (cross-linked polyethylene). And the size of the specimen is 7*5*7 $mm^3$. Distance of needle and plane is 2 mm. Voltages applied for acceleration test are 12 kV to 15 kV. And distribution characteristic of degraded stage is studied too. As a PD detecting and data process, discharge data acquire from PD detecting system (Biddle instrument). The system presents statistical distribution as phase resolved. Moreover the processing time of electrical tree is recorded to know the speed of degradation according to voltage.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.1
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• pp.93-102
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• 1994

This paper, presents SECRET(SEC REliability Tool), which predicts reliability problems related to the hot-carrier and electromigration effects on the submicron MOSFETs and interconnections. To simulate DC and AC lifetime for hot-carrier damaged devices, we have developed an accurate substrate current model with the geometric sensitivity, which has been verified over the wide ranges of transistor geometries. A guideline can be provided to design hot-carrier resistant circuits by the analysis of HOREL(HOT-carrier RFsistant Logic) effect, and circuit degradation with respect to physical parameter degradation such as the threshold voltage and the mobility can also be expected. In SECRET, DC and AC MTTF values of metal lines are calculated based on lossy transmission line analysis, and parasitic resistances, inductances and capacitances of metal lines are accurately considered when they operate in the condition of high speed. Also, circuit-level reliability simulation can be applied to the determination of metal line width and-that of optimal capacitor size in substrate bias generation circuit. Experimental results obtained from the several real circuits show that SECERT is very useful to estimate and analyze reliability problems.

• The Journal of the Acoustical Society of Korea
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• v.8 no.4
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• pp.39-43
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• 1989

In this paper, the concept of ultrasonic transmission imaging system with crossed -arrays is Introduced. The crossed-array system is simulated by angular spectrum method In the operating frequency of 12MHz. A theoritical development of a system transfer function matrix 1M is presented. Using this matrix, a priori knowledge on the physical properties of the system is understood. It proves to be a block Toeplitz matrix with Toeplitz entries. Using the Inversion procedure, the spatial degradations of the measured image can be removed.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.12
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• pp.91-99
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• 1994

We used CMOS current mirror and differenial amplifier to find out how the degradation of each devices in circuit affect total circuit performance. The devices in circuit wer degraded by hot-carrier generated during circuit operation and total circuit performance were changed according to the change of each device parameters. To examine the circuit performance phenomena of current mirror, we analyzed three diffent kinds of current mirrors and made correlation model between circuit performance and stressed device parameters, and compare hot-carrier immunity of these circuits. Also we analyzed how the performance of differential amplifier degraded from the initial value after hot-carrier stress incircuit operations.

• MALSORI
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• no.53
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• pp.119-127
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• 2005

Speech recognition is one of the user interface technologies in commanding and controlling any terminal such as a TV, PC, cellular phone etc. in a ubiquitous environment. In controlling a terminal, the mismatch between training and testing causes rapid performance degradation. That is, the mismatch decreases not only the performance of the recognition system but also the reliability of that. Therefore, the performance degradation due to the mismatch caused by the change of the environment should be necessarily compensated. Whenever the environment changes, environment adaptation is performed using the user's speech and the background noise of the changed environment and the performance is increased by employing the models appropriately transformed to the changed environment. So far, the research on the environment compensation has been done actively. However, the compensation method for the effect of distant-talking speech has not been developed yet. Thus, in this paper we apply MLLR-based environment adaptation to compensate for the effect of distant-talking speech and the performance is improved.