• Water for future
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• v.26 no.3
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• pp.113-124
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• 1993

This study aims at the evaluation of the stationary distribution and the emptiness passage time for the effectiveness of water utility in the Keumgang estuary reservoir by two-step transition model. It was taken discrete Markovian correlated inflows for the joint probability of inflows and storage, and was used binomial distribution for inflows distribution. As the results, it was decreased from 0.952 to 0.904 the emptiness probability of the reservoir stationary distribution during 1952-1980, and from 0.900 to 0.829 during 1981-1989, and the average emptiness passage time was increased from 23 days to 37 days during 1952-1980, and from 29 days to 61 days during 1981-1989 at low state of storage. From this, it is found that the emptiness passage time is varied with the increase of the inflows auto-correlation coefficient in the Keumgang estuary reservoir. Therefore, it is understood that auto-correlation coefficient must be taken into consideration for the evaluation of water utility in a small reservoir at drought time.

• Journal of Korean Society of Transportation
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• v.32 no.6
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• pp.662-674
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• 2014

In this study, accident frequency prediction models were constructed by collecting variables such as geometric structures, safety facilities, traffic volume and weather conditions, land use, highway design-satisfaction criteria along 780km (4,372 sections) of 4 lane-highways over 8 areas. As for models, a fixed parameter model and a random parameter model were employed. In the random parameter model, some influences were reversed as the range was expressed based on specific probability in the case of no fixed coefficients. In the fixed parameter model, the influences of independent variables on accident frequency were interpreted by using one coefficient, but in the random parameter model, more various interpretations were took place. In particular, curve radius, securement of shoulder lane, vertical grade design criteria satisfaction showed both positive and negative influence, according to specific probability. This means that there could be a reverse effect depending on the behavioral characteristics of drivers and the characteristics of highway sections. Rather, they influence the increase of accident frequency through the all sections.

• Korean Journal of Health Education and Promotion
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• v.21 no.4
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• pp.15-33
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• 2004

With growing significance of psychological well-being in the worksite, the purpose of this analysis was to overview the empirical studies on worksite stress management and to identity the overall effect of worksite health promotion programs on stress management through meta-analysis. Literature retrieval was conducted on-line first in MEDLINE, EBSCOhost Academic Search Premier, and PSYCHINFO databases in public health, psychology, sociology, and human resource management areas. All studies written in English and published in the peer-reviewed journals during 1990 and 2002 were recruited. Key words used in literature retrieval were 'worksite,' 'intervention,' 'program,' 'work stress,' 'strain,' 'burnout,' 'management,' 'prevention,' 'education,' and 'health promotion.' A total of 18 worksite intervention studies with 48 effect sizes were analyzed and the results were as follows. Approximately 60％ of the studies had quasi-experimental design and were conducted in manufacturing company and public sector. General psychological strains and burnout were frequently used measures of psychological stress. The lecturing and discussion typed intervention and the participatory problem-solving typed intervention were employed more than others in the studies. The average effect (r: pearson's simple correlation coefficient) weighted by sampling error was -0.14 (-0.32 to 0.05). In the conventional category of effects this is a small effect ranging from -0.59 to 0.05. Binomial effect size showed that success rates increased from 43％ without intervention to 57％ after an intervention. Sampling error explained 47.14％ of the observed variance and its effectiveness on stress management were heterogeneous. In regression analysis with suspected moderating factors affecting the worksite interventions, research design was the only significant moderating factor. The studies with quasi-experimental design had greater effects than the studies with experimental design.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.1
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• pp.185-190
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• 2019

This study aims to apply the mathematical method of fractional order derivatives to the controller that controls the system response. In general, the Laplace transform of the PID controller has an exponent of the integer order of s. The derivative of the fractional order has a fractional exponent of s when it is transformed by Laplace transform. Therefore, this controller proposes a design method with the result of discrete time conversion. Because controllers with fractional exponents of s are not easy to design. This controller is applied to a standard secondary system and its performance is examined. Then, it applies to solenoid valve which is widely used in industrial field. A Luenberger's observer was designed to estimate the disturbance state and the observed state was applied to the fractional order controller. As a result, uniform and precise control performance was obtained. It was confirmed that the position error of the steady state is within 0.1 [%] and the rising time is within about 0.03 [s].

• Korean journal of applied entomology
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• v.24 no.1 s.62
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• pp.1-6
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• 1985

The data on the striped rice, borer populations, collected in the four years from 1973 to 1976, was reanalyzed to study the characteristics in the aggregation pattern of the insect larvae in the paddy fields. The distribution pattern of the larvae was well fitted to the negative binomial model in both the first and the second generation. With reference to the Green's coefficient of dispersion estimated, the aggregation of the larvae was categorized into three phases: initial high aggregation, changing, and dispersed stable phase. Except the changing phase, each phase in each generation could be defined by a common k. The phase-change was initiated by the larval dispersal between hills of the rice plants: the larvae of the third stage and those of the fifth stage, for the first and second generation, respectively. The characteristics of the aggregation pattern were stable in the second generation. In the first genaration, the pattern was more or less variable, indicating that the life system of the insect in the first generation was more susceptible to the variations of the external physical factors than that in the second generation.

• Journal of Korean Society of Transportation
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• v.21 no.3
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• pp.15-22
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• 2003

In general, the linear regression model has been used to estimate trip generation in the travel demand forecasting procedure. However, the model suffers from several methodological limitations. First, trips as a dependent variable with non-negative integer show discrete distribution but the model assumes that the dependent variable is continuously distributed between -$\infty$ and +$\infty$. Second, the model may produce negative estimates. Third, even if estimated trips are within the valid range, the model offers only forecasted trips without discrete probability distribution of them. To overcome these limitations, a poisson model with a assumption of equidispersion has frequently been used to analyze count data such as trip frequencies. However, if the variance of data is greater than the mean. the poisson model tends to underestimate errors, resulting in unreliable estimates. Using overdispersion test, this study proved that the poisson model is not appropriate and by using Vuong test, zero inflated negative binomial model is optimal. Model reliability was checked by likelihood test and the accuracy of model by Theil inequality coefficient as well. Finally, marginal effect of the change of socio-demographic characteristics of households on trips was analyzed.