• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.822-829
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• 2005

In this paper, a processing time and trafnc capacity analysis algorithm for RFID system using LBT-Random Searching scheme is proposed. Service time, carrier sensing time, additional delay time required for contiguous frequency channel occupancy, and additional delay time required for the contiguous using the same frequency channel are considered and the processing delay and frequency channel capacity are analyzed for the steady state operation of the system. The simulation results showing maximum capacity of the system and explaining the accuracy of the algorithm are provided.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.374-379
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• 2001

The satellite electronic equipment is exposed to high level random vibration environment during the launch of spacecraft. The random vibration can cause damage of electronic equipment. Thus very careful consideration on the launch environment, especially for high level random vibration, is required in the design stage of transponder equipments of communication satellite. For the structural integrity of the communication satellite transponder equipment under qualification level random vibration, Finite Element analysis was carried out using the commercial code, MSC/Nastran and ANSYS and stress levels are presented. In order to validate the femodel, modal test was also performed and compared with numerical results.

• Korean Journal of Organic Agriculture
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• v.23 no.1
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• pp.31-42
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• 2015

This thesis has analyzed the determination factor for the crop insurance of rice focused on paddy rice. The analysis on each farmer has been used with integrated probit model & random effects probit model. It has shown in the analysis result of determination factor for buying the crop insurance of paddy rice farmer through integrated probit model & random effects probit model that the higher age, degree of education, cultivated area, and amount of received insurance money and the lower in a number of family member have revealed the higher possibility to buy the crop insurance in the integrated probit model. While the random effects probit model has shown a higher possibility to buy the crop insurance as the higher age, cultivated area, and amount of received insurance money.

• International Journal of Aerospace System Engineering
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• v.6 no.2
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• pp.1-10
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• 2019

In this paper, the probabilistic free vibration analysis of a geometrically coupled cantilever wing with uncertain material properties is carried out using stochastic finite element (SFEM) based on first order perturbation technique. Here, both stiffness and damping of the system are considered as random parameters. The bending and torsional rigidities are assumed as spatially varying second order Gaussian random fields and represented by Karhunen Loeve (K-L) expansion. Here, the expected value, standard deviation, and probability distribution of random natural frequencies and damping ratios are computed. The results obtained from the present approach are also compared with Monte Carlo simulations (MCS). The results show that the uncertain bending rigidity has more influence on the damping ratio and frequency of modes 1 and 3 while uncertain torsional rigidity has more influence on the damping ratio and frequency of modes 2 and 3.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.403-407
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• 2003

This paper studies the error of pressure, particle velocity, and intensity which are distributed in a space. Errors may be amplified when other sound field variables are predicted. We theoretically derive their bias error and random error. The analysis shows that many samples do not always guarantee good results. Random error of the velocity and intensity are increased when many samples are used. The characteristics of the amplification of the random error are analyzed in terms of the sample spacing. The amplification was found to be related to the spatial differential of random noise. The numerical simulations are performed to verify theoretical results.

• Computational Structural Engineering
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• v.10 no.1
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• pp.173-183
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• 1997

In this paper a method is suggested for the probabilistic analysis of impact buckling failure time of cylinder with random axisymmetric geometric imperfection under axial impact. Failure is assumed as axisymmetric radial deformation exceeds the given criteria for the first time. For the generation of random geometric initial imperfection, random field theory by mean function and autocorrelation function of geometric imperfection is used. Suggested method is useful for the treatment of the randomness of realistic geometric imperfection and can be used for the structural safety analysis of cylinder considering its effect.

• Proceedings of the Korean Reliability Society Conference
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• 2006.05a
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• pp.181-191
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• 2006

As an alternative to traditional life testing, degradation tests can be effective in assessing product reliability when measurements of degradation leading to failure can be observed. This article proposes a new model to describe the nonlinear degradation paths caused by nano-contamination for plasma display panels (PDPs) : a bi-exponential model with random coefficients. A sequential likelihood ratio test was executed to select random effects in the nonlinear model. Analysis results indicate that the reliability estimation can be improved substantially by using the nonlinear random-coefficients model to incorporate both inherent degradation characteristics and contamination effects of impurities for PDP degradation paths.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.194-200
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• 2002

A method for simulating flow of extremely low Reynolds number in a vortex-in-cell (VIC) was studied. The viscous diffusion was represented by the random walk method. The validity of this method was proven by applying it to the flows passing over a fence placed vertically at an extremely low Reynolds number. The effects of parameters of the VIC method on the random walk method, such as the number of point vortices, the mesh density and the time increment, were investigated by numerical analysis using a one-dimensional diffusion equation. Changes in the relative error of vorticity depending on those parameters were clarified.

• IEMEK Journal of Embedded Systems and Applications
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• v.17 no.4
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• pp.249-255
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• 2022

The COVID-19 virus appeared in 2019 and is extremely contagious. Because it is very infectious and has a huge impact on people's mobility. In this paper, multiple linear regression and random forest models are used to predict the number of COVID-19 cases using COVID-19 infection status data (open source data provided by the Ministry of health and welfare) and Google Mobility Data, which can check the liquidity of various categories. The data has been divided into two sets. The first dataset is COVID-19 infection status data and all six variables of Google Mobility Data. The second dataset is COVID-19 infection status data and only two variables of Google Mobility Data: (1) Retail stores and leisure facilities (2) Grocery stores and pharmacies. The models' performance has been compared using the mean absolute error indicator. We also a correlation analysis of the random forest model and the multiple linear regression model.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.331-338
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• 1999

In the present study, a searching technique for critical slip surface in two dimensional slope stability analysis is proposed. The failure surface generation and analysis has been usually limited to simple geometric shapes. However, more random surfaces need to be examined for some particular ground conditions. For this purpose, random searching technique is developed using genetic algorithm. The generalized limit equilibrium method is employed as the method of stability analysis. Using this technique, the factor of safety is compared with the result by using simplified Bishop's method. In addition, the convergent trend of fitness value is analyzed.