• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.671-681
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• 2006

This study focuses on the development of numerical procedure to analyze the nonlinear combustion instabilities in liquid rocket engine. Nonlinear behaviors of acoustic instabilities are characterized by the existence of limit cycle in linearly unstable engines and nonlinear or triggering instability in linearly stable engines. To discretize convective fluxes with high accuracy and robustness, approximated Riemann solver based on characteristics and Euler-characteristic boundary conditions are employed. The present procedure predicts well the transition processes from initial harmonic pressure disturbance to N-like steep-fronted shock wave in a resonant pipe. Longitudinal pressure oscillations within the SSME(Space Shuttle Main Engine) engine have been analyzed using the pressure-sensitive time lag model to account for unsteady combustion response. It is observed that the pressure oscillations reach a limit cycle which is independent of the characteristics of the initial disturbances and depends only on combustion parameters and operating conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.9
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• pp.699-705
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• 2002

The present study discusses the deviation from the pure dead-time model of passive scalars such as temperature and concentration in the Poiseulle flow Even in the case of no thermal diffusion, there exists a substantial amount of damping and large deviation of phase lag from that computed by the traditional dead-time model after only 10 diameter downstream. These are caused by the phase difference of temperature in the radial direction due to the nonuniform velocity distribution. In the presence of thermal diffusion, damping is more pronounced.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.4
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• pp.93-102
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• 1989

A runoff model is estabilished for the direct runoff hydrograph at the watershed outlet. The watershed is divided into subareas bounded by watershed lines of stream segment. Different storage elements are used to represent the subareas which simply translate rain-fall excess to runoff and transmit flow from an upstream areas. For transmit, the relationship between flowsection and runoff is expressed by the exponential function to represent the nonlinearity of lag time, and the relationship between flowsection and stream length is expressed by the 1st order equation to represent the effect of the travel length. The parameters of lag time can be obtained by stream magnitude and the effective rain fall is routed through the main stream. Application of the model to the Bochung river basin gives accurate results, especially for the peak runoff and peak time, and is approved to be used for the prediction by stream magnitude of small watershed having no runoff records.

• Journal of Food Hygiene and Safety
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• v.16 no.2
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• pp.103-110
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• 2001

Predictive food microbiology(PFM) is an emerging area of food microbiology since the later 1980’s. It does apply mathematical models to predict the responses of microorganism to specified environmental variables. Although, at present, PFM models do not completely developed, models can provide very useful information for microbiological responses in HACCP(Hazard Analysis Critical Control Point) system and Risk Assessment. This study illustrates the possible use of PFM models(PMP: Pathogen Modeling Program win5.1) with milk in several elements in the HACCP system, such as conduction of hazard analysis and determination of CCP(Critical Control Points) and CL(Critical Limits). The factors likely to affect the growth of the pathogens in milk involved storage fixed factors were pH 6.7, Aw 0.993 and NaCl 1.3%. PMPwin5.1 calculated generation time, lag phase duration, time to level of infective dose for pathogens across a range of storage (Critical Control Points) and CL(Critical Limits). The factors likely to affect the growth of the pathogens in milk involved storage temperature, pH, Aw and NaCl content. The factors likely to affect the growth of the pathogens in milk involved storage temperature, pH, Aw and NaCl content. The variable factor was storage temperature at the range of 4~15$^{\circ}C$ and the fixed factors were pH 6.7, Aw 0.993 and NaC 1.3%. PMPwin5.1 calculated generation time, lag phase duration, time to level of infective dose for pathogens across a range of storage temperature.

• Journal of Technology Innovation
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• v.7 no.2
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• pp.1-20
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• 1999

This paper investigates the effects of various R&D investments on economic growth empirically. To this end, the relationships between various R&D investments and economic growth are analysed, and the rates of return of R&D investments are estimated. Furthermore, the effect of government R&D investment on private sector R&D investment, and the effect of social factors, which affect the relationship between the R&D inputs and economic growth, are analysed. Based on the results of this analysis, a simulation model is developed, which shows the relationship between R&D investments and economic growth rate; this model is verified by analysing the correlation between the actual and the estimated economic growth rate, using the data between 1981 and 1995 of eight selected countries. The validation results show that the simulation model has sufficient accuracy to be used for evaluating and proposing R&D policies for the countries for which appropriate data is available. However, the time-lag effect, which is naturally believed to exist between the R&D input and the economic growth, could not be analysed in a mathematical form, because of the lack of the data to establish this relationship. Thus, when estimating the relationship between them, the time-lag effect in this relationship was included implicitly by using the data of fifteen years.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.114-117
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• 2002

Sorption and desorption studies were conducted to evaluate several media as a potential biobarrier for the remediation of groundwater contaminated with hydrophobic organic compounds (HOCs). Pahokee and Bion peats, Devonian Ohio shale, vermicompost, and 50% HDTMA-montmorillonite were used as model sorbents. Sorption and desorption isotherms were determined using the radiolabeled phenanthrene (Phe). Sorption capacity of Phe on several sorbents was in the order Ohio shale > 50% HDTMA-montmorillonite > vermicompost > Pahokee peat. Mineralization kinetics was investigated for Phe-sorbed sorbents using Pseudomonas putida 17484. Among the tested sorbents, active biodegradation of Phe was observed in shale and vermicompost: degradation in shale exhibited little lag time while that in shale showed a significant lag time. Results of this study indicate that sorbents used in this work can be utilized as permeable reactive biobarrier media for the remediation of HOC-contaminated groundwater.

• Food Science and Biotechnology
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• v.15 no.5
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• pp.715-720
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• 2006

This study was performed to develop a predictive model for the growth kinetics of Listeria monocytogenes in tryptic soy broth (TSB) using a response surface model with a combination of potassium lactate (PL), temperature, and pH. The growth parameters, specific growth rate (SGR), and lag time (LT) were obtained by fitting the data into the Gompertz equation and showed high fitness with a correlation coefficient of $R^2{\geq}0.9192$. The polynomial model was identified as an appropriate secondary model for SGR and LT based on the coefficient of determination for the developed model ($R^2\;=\;0.97$ for SGR and $R^2\;=\;0.86$ for LT). The induced values that were calculated using the developed secondary model indicated that the growth kinetics of L. monocytogenes were dependent on storage temperature, pH, and PL. Finally, the predicted model was validated using statistical indicators, such as coefficient of determination, mean square error, bias factor, and accuracy factor. Validation of the model demonstrates that the overall prediction agreed well with the observed data. However, the model developed for SGR showed better predictive ability than the model developed for LT, which can be seen from its statistical validation indices, with the exception of the bias factor ($B_f$ was 0.6 for SGR and 0.97 for LT).

• Journal of Korea Water Resources Association
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• v.33 no.1
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• pp.51-59
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• 2000

A dynamic model, which combined time series model with distributed-lag model, is applied to understand the relationship between rainfall and groundwater level. In the model, rainfall with distribution lags and past groundwater level as a dependent variables were used to estimate present groundwater level. The distribution of the lagged rainfall effects for groundwater levels was modeled by Almon polynomials. The model was applied to Banglim and Tanbu groundwater stations in Pyungchang river and Bocheong stream watershed which are representative basins for International Hydrological Program (IHP). The dynamic model represents observed groundwater levels very well and can be used to predict the levels. The model parameters reflect hydraulic characteristics of aquifer. In addition, from the parameters it appears that the increase in groundwater level due to rainfall takes place significantly within first two days of the rainfall event. The rainfall of the order of 18mm/day and 30mm/day at Banglim and Tanbu, respectively, had no significant effect on the groundwater levels.

• Biotechnology and Bioprocess Engineering:BBE
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• v.5 no.5
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• pp.382-385
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• 2000

A mathematical model was developed, based on the time dependent changes of the specific growth rate, for prediction of the typical microbial cell growth in batch cultures. This model could predict both the lag growth phase and the stationary growth phase of batch cultures, and it was tested with the batch growth of Trichoderma reesei and Lactobacillus delbrueckii.

• Journal of Korea Water Resources Association
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• v.38 no.10 s.159
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• pp.801-810
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• 2005

The lag time is one of the most important factors for estimating a flood runoff from streams. It is well known to be under the influence of the morphometric properties of basins which could be expressed by catchment shape descriptors. In this paper, the notion of the geometric characteristics of an equivalent ellipse proposed by Moussa(2003) is applied for calculating the lag time of geomorphological instantaneous unit hydrograph(GIUH) at the basin outlet. The lag time is obtained from the observed data of rainfall and runoff by using the method of moments suggested by Nash(1957), and the procedure based on geomorphology is used for GIUH. The relationships between the basin morphometric properties and the hydrological response are discussed as applied to 3 catchments In Korea. Additionally, the shapes of equivalent ellipse are examined how then are transformed from upstream area to downstream one. As a result, the relationship between the hydrological response and descriptors is shown to be comparatively good, and the shape of ellipse is presented to approach a circle along the river downwards. These results may be expanded to the estimation of hydrological response of ungauged catchment.