• Progress in Medical Physics
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• v.23 no.1
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• pp.42-47
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• 2012

In this paper, Acousto-Optical tomography is modeled by a linear integral equation and an inverse problem involving a diffusion equation in n-spatial dimensions. We make two-step mathematical model. First, we solve a linear integral equation. Assuming the optical energy fluence rate has been recovered from the previous equation, the absorption coefficient ${\mu}$ is then reconstructed by solving an inverse problem. Numerical experiments are presented for the case n=2. The traditional gradient descent method is used for the numerical simulations. The result of the gradient descent method produces the blurring effect. To get rid of the blurring effect, we suggest the total variation regularization for the minimization problem.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6D
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• pp.927-933
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• 2006

The Variable Message Signs (VMS) are useful way to reduce the socio-economic costs due to the traffic congestions and delays by providing the information on traffic condition to drivers. This study provided a methodology to determine the locations of VMS's in terms of the minimization of the delay by applying the genetic algorithm. The optimal number of VMS's was also derived by the economic analysis based on the cost and the benefit. The simulation considered the variation of traffic volume, the frequency and duration of the incident, and the traffic conversion in order to reflect the real situation. I've made a scenario to consider traffic volume and incident, and it can undergo through changing different traffic volume and incident in time and days and seasons. And I've comprised two kinds of result, one is based on empirical studies, the other is based on Genetic Algorithm about optimal allocation VMS. This result of using optimal location VMS, reduce total travel time rather than preceding study based on normal location VMS and we can estimate optimal location VMS each one.

• Journal of Wetlands Research
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• v.13 no.1
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• pp.25-33
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• 2011

Climate change is the variation of long term weather pattern based on statistical diversities in terms of natural and artificial factors. Recent numerous extreme weather phenomena have increasingly obtained people's awareness of climate change. Since water resources field especially has higher vulnerability caused by climate variation, the major part of future preparation should be focused on risk minimization of water resources. However, in reality validation of water resources vulnerability is not well built up. For this research, Delphi Method was applied to evaluate middle/small size rivers in Korea with respect to the degree of vulnerability due to the climate change. Delphi Survey is based on iterative, anonymous characteristics with experts' opinion sharing on the given issues. For this study, three iterative surveys were operated for the degree of vulnerability. First round was for selecting vulnerability indicators in terms of the magnitude of total score, and second and third rounds were for collecting experts' idea with opinion convergence. Per the variance of standard deviation of 2nd and 3rd surveys divergence, we clearly see the achievement of opinion agreement. For the future study, we may need to find an applicable field using delphi indicators with various circumstances.