• ETRI Journal
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• v.36 no.1
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• pp.134-140
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• 2014

Many reports have shown that the access pattern for geospatial tiles follows Zipf's law and that its parameter ${\alpha}$ represents the access characteristics. However, visits to geospatial tiles have temporal and spatial popularities, and the ${\alpha}$-value changes as they change. We construct a mathematical model to simulate the user's access behavior by studying the attributes of frequently visited tile objects to determine parameter estimation algorithms. Because the least squares (LS) method in common use cannot obtain an exact ${\alpha}$-value and does not provide a suitable fit to data for frequently visited tiles, we present a new approach, which uses a moment method of estimation to obtain the value of ${\alpha}$ when ${\alpha}$ is close to 1. When ${\alpha}$ is further away from 1, the method uses the associated cache hit ratio for tile access and uses an LS method based on a critical cache size to estimate the value of ${\alpha}$. The decrease in the estimation error is presented and discussed in the section on experiment results. This new method, which provides a more accurate estimate of ${\alpha}$ than earlier methods, promises more effective prediction of requests for frequently accessed tiles for better caching and load balancing.

• Journal of the Korea Society for Simulation
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• v.21 no.2
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• pp.11-17
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• 2012

The past combats depended often on a number of firepower and manpower. However, integrated decision support viewpoint from communications, surveillance, reconnaissance, intelligence and so forth in combats witnessed in the Gulf, the Middle East, and Afghanistan have changed the trends of combat. That is, the force multipliers which many support systems enhance the combat potential of the fighting forces significantly become big issues to win or not in that combat. According to changing recent combat trend, Lanchester's combat model is being challenged to develop keeping pace with the new trend. We approach this paper as mathematical modeling about how the effect of terrain affects in the combat. Terrain information is invisible, but it is necessary to consider for analysis of warfare. Additionally, tangible or intangible elements affecting to attrition coefficients are continuely reflected to the combat model from decision-makers, then it will be a model closer to the reality and very suggestive to the actual world.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.4
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• pp.53-60
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• 2011

In order to augment the robustness of OFDM system to Rayleigh multipath fading, there exist two smart antenna algorithms, namely, Pre-FFT smart antenna and Post-FFT smart antenna. After the mathematical modeling of both smart antenna algorithms, computer simulations have been carried to compare and analyze the performance of generalized eigen problem based Pre-FFT algorithm and the performance of Wiener solution based Post-FFT algorithm. It has been shown that the Post-FFT smart antenna far outperforms the Pre-FFT smart antenna due to the computational complexities. Especially it is so when the multipath signal arrives at beyond the guard interval and a rich co-channel interferer is introduced. Performance of a subcarrier clustering method proposed to lessen the computing load has been compared to that of a typical Wiener solution based Post-FFT smart antenna. Performance comparison between MRC(Maximum Ratio Combining) diversity based Post-FFT algorithm and typical Post-FFT algorithm has also been carried.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.10
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• pp.29-34
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• 2011

We present a network coding scheme which is designed for improving throughput in multi-hop wireless network with multi-radio multi-channel. The co-channel interference and unreliability of wireless transmissions cause the wireless network to reduce throughput. In wireless network, multi-radio multi-channel technology shows benefit to cut down channel interferences and contentions. And network coding can reduce the complexity of scheduling and improve throughput by increasing usage of links in wireless network. In this paper, we propose a method of channel assignment and transmission scheduling in intra-session network coding that efficiently improve throughput for multi-hop wireless network by using mathematical modeling and linear programming. Moreover, we evaluate the performance of the intra-session network coding scheme by using AMPL with CPLEX. The simulation results show that intra-session network coding can achieve better throughput than traditional routing.

• Journal of the Korean Institute of Gas
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• v.20 no.2
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• pp.66-71
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• 2016

Nowadays, a number of sensors which are placed in industrial complex are monitoring areas involving chemical leak and other faults. However, even in the presence of the sensors, chemical leaks, sometimes involving huge amount of chemicals, continuously led to big losses in the industrial complex. In most industries, sensor installation has been performed using past experience or using senor manufacturers' guideline; which leads to poor performance of the installed sensor grid. Therefore, we investigate an optimal placement methodology of point sensors for rapid detention and response when chemical leaks happen. This research suggests a generalized formulation suitable for the optimized decision making of minimizing number of sensors to be placed and increasing the fraction of covered scenarios under assumption of negligible effect of other structures. The proposed method has been verified for suitable performance for simple leak scenario simulations, by achieving the safety objectives and guaranteeing safe process operations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.11
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• pp.1594-1605
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• 2001

In this study, a numerical simulation was developed which was capable of predicting the characteristics of NO formation in pilot scale combustor adopting the air-staged burner flame. The numerical calculation was constructed by means of establishing the mathematical models fur turbulence, turbulent combustion, radiation and turbulent nitric oxide chemistry. Turbulence was solved with standard k-$\xi$ model and the turbulent combustion model was incorporated using a two step reaction scheme together with an eddy dissipation model. The radiative transfer equation was calculated by means of the discrete ordinates method with the weighted sum of gray gases model for CO$_2$and H$_2$O. In the NO chemistry model, the chemical reaction rates for thermal and prompt NO were statistically averaged using the $\beta$ probability density function. The results were validated by comparison with measurements. For the experiment, a 0.2 MW pilot multi-air staged burner has been designed and fabricated. Only when the radiation was taken into account, the predicted gas temperature was in good agreement with the experimental one, which meant that the inclusion of radiation was indispensable for modeling multi-air staged gas flame. This was also true of the prediction of the NO formation, since it heavily depended on temperature. Subsequently, it was found that the multi-air staged combustion technique might be used as a practical tool in reducing the NO formation by controlling the peak flame temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1133-1140
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• 2013

A computer model is a useful tool that provides solution via physical modeling instead of expensive testing. In reality, however, it often does not agree with the experimental data owing to simplifying assumption and unknown or uncertain input parameters. In this study, a Bayesian approach is proposed to calibrate the computer model in a probabilistic manner using the measured data. The elasto-plastic analysis of a pyrotechnically actuated device (PAD) is employed to demonstrate this approach, which is a component that delivers high power in remote environments by the combustion of a self-contained energy source. A simple mathematical model that quickly evaluates the performance is developed. Unknown input parameters are calibrated conditional on the experimental data using the Markov Chain Monte Carlo algorithm, which is a modern computational statistics method. Finally, the results are applied to determine the reliability of the PAD.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.10
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• pp.5125-5129
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• 2012

Economic decision models are being increasingly used to assess medical interventions. Advances in this field are mainly due to enhanced processing capacity of computers, availability of specific software to perform the necessary tasks, and refined mathematical techniques. We here estimated the incremental cost-effectiveness of ten strategies for colon cancer screening, as well as no screening, incorporating quality of life, noncompliance and data on the costs and profit of chemotherapy in Iran. We used a Markov model to measure the costs and quality-adjusted life expectancy of a 50-year-old average-risk Iranian without screening and with screening by each test. In this paper, we tested the model with data from the Ministry of Health and published literature. We considered costs from the perspective of a health insurance organization, with inflation to 2011, the Iranian Rial being converted into US dollars. We focused on three tests for the 10 strategies considered currently being used for population screening in some Iranians provinces (Kerman, Golestan Mazandaran, Ardabil, and Tehran): low-sensitivity guaiac fecal occult blood test, performed annually; fecal immunochemical test, performed annually; and colonoscopy, performed every 10 years. These strategies reduced the incidence of colorectal cancer by 39%, 60% and 76%, and mortality by 50%, 69% and 78%, respectively, compared with no screening. These approaches generated ICER (incremental cost-effectiveness ratios) of $9067, $654 and $8700 per QALY (quality-adjusted life year), respectively. Sensitivity analyses were conducted to assess the influence of various scales on the economic evaluation of screening. The results were sensitive to probabilistic sensitivity analysis. Colonoscopy every ten years yielded the greatest net health value. Screening for colon cancer is economical and cost-effective over conventional levels of WTP8.

• The Journal of the Korea Contents Association
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• v.2 no.4
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• pp.1-8
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• 2002

In this paper, we propose a novel branch method which improve learning effects of the digital contents using a user-friendly access method by taking any conceptual object as the unit of interface. The conceptual objects may exist as a part of one or more contents pages, and we can access them to repeat, replay or return to the original branch point, that elevates the interactions of the digital contents. This method is useful for all kinds of digital contents, but it is especially effective to make educational contents in the field of science, engineering, and language courses because they contain various conceptual elements such as blocks of modeling, mathematical equations, and memorizing units. In addition, if we realize the blanch method proposed in this paper with the conventional page-branch or title-branch methods in the same contents, user interaction will be maximized and learning effects of the contents maybe beautifully improved.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.580-587
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• 2017

Recently, as the education population of Korea has been rapidly declining, many changes have been taking place in the university environment. Especially, community colleges linked to local communities have responded to these crises through various educational changes, such as three-year study transfers, work-parallelism, and employee commissioned education. However, such changes in the contents of education are causing a new type of classroom allocation problem, in which it is difficult to assign the limited number of classrooms to the major courses. In this paper, we classified the constraints involved in assigning classrooms into absolute constraints and relative constraints, mathematically modeled them, and allocated the classrooms optimally through optimization software. The results were satisfactory and enabled us to obtain superior results in terms of the various performance indices (classroom utilization rate, teacher satisfaction, etc.) than when assigning classrooms in the normal way.