• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.11
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• pp.71-78
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• 1995

Based on the popular 4-transistor SRAM cell, an analytical expression of the minimum cell ratio was derived by modeling the static read operation. By analyzing the relatively simple expression for the minimum cell ratio, which was derived assuming the ideal transistor characteristics, effects of the changes in supply voltage and process parameters on the minimum cell ratio was predicted, and the minimum power supply voltage for read operation was determined. The results were verified by simulations utilizing the suggested simulation method, which is suitable for monitoring the lower limit of supply voltage for proper cell operation. From the analysis, it was shown that the worst condition for cell operation is low temperature and low supply voltage, and that the operation margin can be effectively improved by reducing the threshold voltage of the cell transistors.

• Journal of applied mathematics & informatics
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• v.29 no.5_6
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• pp.1097-1115
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• 2011

We consider the global stability of a general tuberculosis model with two differential infectivity, n classes of latent individuals and mass action incidence. This system exhibits the traditional threshold behavior. There is always a globally asymptotically stable equilibrium state. Depending on the value of the basic reproduction ratio $\mathcal{R}_0$, this state can be either endemic ($\mathcal{R}_0$ > 1), or infection-free ($\mathcal{R}_0{\leq}1$). The global stability of this model is derived through the use of Lyapunov stability theory and LaSalle's invariant set theorem. Both the analytical results and numerical simulations suggest that patients should be strongly encouraged to complete their treatment and sputum examination.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.45-50
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• 2005

Electro-osmotic flow (EOF) instability in a microchannel has been experimentally investigated using a micro-PIV system. The micro-PIV system consisting of a two-head Nd:Yag laser and cooled CCD camera was used to measure instantaneous velocity fields and vorticity contours of the EOF instability in a T-shape glass microchannel. The electrokinetic flow instability occurs in the presence of electric conductivity gradients. Charge accumulation at the interface of conductivity gradients leads to electric body forces, driving the coupled flow and electric field into an unstable dynamics. The threshold electric field above which the flow becomes unstable and rapid mixing occurs is about 1000V/cm. As the electric field increases, the flow pattern becomes unstable and vortical motion is enhanced. This kind of instability is a key factor limiting the robust performance of complex electrokinetic bio-analytical devices, but can also be used for rapid mixing and effective flow control fer micro-scale bio-chips.

• Journal of the Korean Operations Research and Management Science Society
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• v.27 no.3
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• pp.59-74
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• 2002

This study investigates two basic operations of mobility management of PCNs (Personal Communication Networks), i.e., the location update and the paging of the mobile terminal. From the realistic consideration that a user either moves through several cells consecutively or stays in a cell with long time, we model the mobility pattern by introducing two types of CRT (Cell Residence Time). Mobility patterns of the mobile terminal are classified Into various ways by using the ratios of two types of CRT. Cost analysis is performed for distance-based and movement-based location update schemes combined with blanket polling paging and selective paging scheme. It is demonstrated that in a certain condition of mobility pattern and call arrival pattern, 2-state CRT model produces different optimal threshold and so, is more effective than IID ( Independently-Identically-Distributed) CRT model. An analytical model for the new CRT model is compact and easily extendable to the other location update schemes.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.41 no.2
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• pp.163-169
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• 1992

A new analytical expression for the temperature variation characteristics of hydrogenerated amorphous silicon thin film transistors(a-si:H TFT), between 223K and 433K, is presented and experimentally verified. The results show that the experimental transfer and output characteristics at several temperatures are easily modeled between -5$0^{\circ}C$ and 9$0^{\circ}C$. The model is based on three functions obtained from the experimental data of IS1DT versus VS1GT. Theoretical results confirm the simple form of the model in terms of the device geometry. It was determined that as the temperature increased, the saturated drain current increased and, at a fixed gate voltage, the device saturated at increasingly larger drain voltages while the threshold voltages decreased.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.11
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• pp.1290-1298
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• 1992

In this paper, the Poisson's equation is solved two-dimensionally without employing any fitting parameters, and the model formulation of a short-channel MOSFET is accomplished fully analytically. It automatically derives a very accurate drain current expression that can be used simultaneously for strong inversion, subthreshold, and saturation regions. Furthermore, this model gives a unified explanation for the short-channel effect, the body effect, the DIBL effect, and even the variation of the effective carrier mobility. The obtained expression of the threshold voltage also includes the dependence on the oxide thickness, the n+ junction depth, and temperature.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1315-1317
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• 1998

We have investigated the effects of electrical stress on poly-Si TFTs with different hydrogen passivation conditions. The amounts of threshold voltage shift of hydrogen passivated poly-Si TFTs are much larger than those of as-fabricated devices both under the gate bias stressing and under the gate and drain bias stressing. Also, we have quantitatively analized the degradation phenomena using by analytical method. we have suggested that the electron trapping in the gate dielectric is the dominant degradation mechanism in only gate bias stressed poly-Si TFT while the creation of defects in the poly-Si is prevalent in gate and drain bias stressed device.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.11a
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• pp.3-6
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• 1992

A new analytical expression for the saturated I-V characteristics of hydrogenerated amorphous silicon thin film transistors(a-si:H TFT) is presented and experimentally verified. The results show that the experimental transfer and output characteristics at several temperatures are easily modeled. The model is based on three functions obtained from the experimental data of $I_D$ versus $V_G$. Theoretical results confirm the simple form of the model in terms of the device geometry. It was determined that the saturated drain current increased at a fixed gate voltage and the device saturated at increasingly larger drain voltages while the threshold voltages decreased.

• Computers and Concrete
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• v.12 no.1
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• pp.91-107
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• 2013

Corrosion of RC bridge decks eventually leads to delamination, severe cracking and spalling of the concrete cover. This is a prevalent deterioration mechanism and demands for the most costly repair interventions during the service life of bridges worldwide. On the other hand, decisions for repairs are usually made whenever the extent of a limit crack width, reported in routine visual inspections, exceeds an acceptable threshold level. In this paper, while random fields are applied to account for spatial variation of governing parameters of the corrosion process, an analytical model is used to simulate the corrosion induced crack width. However when dealing with random fields, the Monte Carlo simulation is apparently an inefficient and time consuming method, hence the utility of neural networks as a surrogate in simulation is investigated and found very promising. The proposed method can be regarded as an invaluable tool in decision making concerning maintenance of bridges.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.117-122
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• 2002

This study assesses the wear process of particle impingement erosion which is a major source of erosion among fluid power components. First, Bitter's theory was modified to simplify engineering calculations. Second, actual experiments were conducted to validate the modified equation. And the effect of concentration and size distribution of impinging particles was tested. Little deviation from the prediction of the modified equation was observed. To develop complete analytical approach to the erosion mechanism, further experimental data are required to establish a correlation with other engineering parameters.