• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.15-18
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• 2001

Sixty natural springs and wells used as community facilities for drinking water are developed along mountain climbing way of suburban area and residential area in Daejeon City. In this study, the seasonal variation of their water quality and hydrochemical characteristics were investigated. Some natural springs are vulnerable to bacilli contamination because of their short residence time and shallow circulation in subsurface environment. The waters show hydrochemical types of Ca-HCO$_3$ and Na-HCO$_3$, and are characterized by low electrical conductance and weak acidic pH.

• Journal of Environmental Science International
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• v.29 no.3
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• pp.273-282
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• 2020

Residence time is defined as the time taken for a material in a system to leave the system. The residence time characteristics in shellfish aquaculture determine the dispersion of excretion from aquaculture farms, along with the supply of food by seawater exchange. In this study, we estimated the spatial distribution of average residence time in the shellfish farming area using a particle tracking model. As a result, a relatively short average residence time of about 20 days or less was calculated in most areas, but an average residence time of more than 40 days was calculated in the inner areas. Relatively long average residence times were calculated along the west coast compared to the east coast, with the longest average residence time of more than 50 days in the northwestern areas. It can be inferred that the disturbance of the benthic ecosystem caused by shellfish farms is likely to be large because of the relatively weak dispersion of excrement from shellfish farms located on the west coast, especially in the northwest region. This distribution of average residence time is important for understanding the potential effects of seawater exchange on the environmental sustainability of shellfish farms, along with the seawater circulation characteristics of Jaran Bay.

• Korean Journal of Environmental Agriculture
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• v.24 no.1
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• pp.6-11
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• 2005

A prototype surface flow constructed wetland was built in the upstream area of reclaimed tidal lands to improve the water quality of Lake Sihwa by treating severely polluted stream water. In this study, a tracer test using rhodamine-WT was performed to investigate the flow characteristics and to quantify the observed hydraulic residence time (HRT) for a high-lying cell in the Banwol wetland of the Sihwa constructed wetland. The tracer test indicated that even if flow was mainly observed in the open water area of the Banwol wetland, water flowed continuously in the vegetative area and there was no dead zone. The calculated HRT (51.3 hrs), calculated by dividing the wetland volume by the wetland inflow, exceeded the observed HRT (38.7 hrs), since the short-circuiting of flux resulting from irregular topography and vegetation was not reflected in the calculated HRT. The exit tracer concentration curves were reproduced well by both the plug flow with dispersion and tanks-in-series models, indicating that the performance of the Banwol wetland can be estimated accurately using these models.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.514-517
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• 2008

Water gas shift(WGS) is an important step in fuel process for fuel cells, and improperness of commercial WGS catalysts for use in fuel cell systems has prompted numerous researches on noble metal catalysts. A selected noble metal catalyst for water gas shift reaction(WGS) was prepared with various metal loadings. The prepared catalysts were tested under two feeding conditions. At moderate residence time, carbon monoxide conversion was much higher on the noble metal catalysts as compared to commercial high-temperature shift catalyst. Effects of metal loading were examined by activity tests at short residence time. Higher metal loading effected higher reaction rate. The kinetic data was fitted to simple reaction equations and effectiveness factor was estimated. The results suggest the necessity of a structural design for the highly active noble metal catalysts.

• Journal of the Korean Institute of Rural Architecture
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• v.9 no.3
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• pp.33-45
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• 2007

Recently, large scale disasters have been occurred in rural areas. Most people suffering from the disaster live in the temporary containers. These could not provide the fundamental occupancy performances such as thermal insulation, ventilation and heating system. It is very important to rebuild the residence for sufferers quickly and safely. Because modular building system has some advantages such as short construction time, mobility, light-weight structure, modularity, flexibility and economical efficiency, it is expected that it could be easily applied to the disaster restoration. So, this research aims at developing the design model of modular building system for disaster restorations in fishing and agrarian villages. For this purpose, current counterplan for restoration was firstly investigated. Also the basic guideline was established through the investigation of current status of residence in fishing and agrarian villages. Finally, 2 types of design model such as single story residence and temporary accommodation facility were proposed. We could see that we could make the flexible building plan when applying the modular building system to the temporary housing for the sufferers.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.4
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• pp.76-90
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• 2000

The estimation of material cycle of pollutants is necessary for the environment management in coastal zone. Model for material budgets are useful tools to understand the phenomena of natural system and to provide an insight into the complex processes including physical, chemical and biological processes occuring in natural system. Budgets of fresh water, salt and nutrients were estimated in order to clarify the characteristics of seasonal material cycle in Keum river estuary. Inflow volumes of freshwater into system was approximately 1.014×10/sup 8/～12.565×10/sup 8/m³/month and discharge in Keum river has occupied 99.7% of total freshwater. Seasonal variations of freshwater volume in the system were found to be very high in the range of about 4 ～ 14 times due to rainfall in summer season. Existing water mass of freshwater in system calculated by salt budget was approximately 0.339×10/sup 8/～0.652×10/sup 8/m³. Mean residence time of freshwater was calculated to be about 1.6～10.0day, and exchange time was calculated to be about 2.2～11.9day. Mean residence time was short as 1.6day in summer due to precipitation, and long as 10.1day in winter due to a drought. Inflow masses of DIP and DIN were approximately 5.57～32.68ton/month and 234.93～2,373.39ton/month, respectively. Seasonal inflow mass of DIP was larger than the outflow mass except for summer season. Thus, we postulate that accumulation of DIP in the system will happen. Residence times of DIP and DIN were calculated to be 1.1～6.4day and 1.8～10.9day, respectively. The ratio of water residence time versus DIP, DIN residence time was calculated to be 0.39～2.31 times and 0.83～1.13 times, respectively.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.245-248
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• 2005

SCRamjet is the key technology for hypersonic flight over mach number 6. It is characterized by very short residence time in combustor because its internal flow is supersonic. In this short time, the whole process of combustion must be done. Especially numerical study of combustor is important because air-fuel mixing rate influences the performance of combustor. Various methods of air-fuel mixing enhancement are proposed. Among these, cavity injection method is selected to study in this paper. The numerical study is conducted with the variation of the cavity length at the fixed height of unit and jet injection on the downstream of cavity.

• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.3
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• pp.163-170
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• 2002

This report describes the use of a transtubular bioreactor to study the relative effects of diffusion versus perfusion of medium on antibody production by a hybridoma cell line. The study was performed with a high-density cell culture maintained in a serum-free, low-protein medium for 77 days. It was determined that the reactor possessed a macro-mixing pattern residence time distribution similar to a continuous stirred tank reactor (CSTR), However, due to the arrangement of the medium lines in the reactor, the flow patterns for nutrient distribution consist of largely independent medium path lengths ranging from short to long. When operated with cyclic, reversing, transtubular medium flow, some regions of the reactor (with short residence times) are more accessible to medium than others (with long residence times). From this standpoint, the reactor can be divided into three regions: a captive volume, which consists of medium primarily delivered via diffusion; a lapped volume, which provides nutrients through unilateral convection; and a swept volume, which operates through bilateral convection. The relative sizes of these three volumes were modified experimentally by changing the period over which the direction of medium flow was reversed from 15 min (larger captive volume) to 9 h (larger swept volume). The results suggest that antibody concentration increases as the size of the diffusion-limited (captive) volume is increased to a maximum at around 30 min with a sharp decrease thereafter. As reflected by changes in measured consumption of glucose and production of lactate, no significant difference in cellular metabolism occurred as the reactor was moved between these different states. These results indicate that the mode of operation of the transtubular bioreactor may influence antibody productivity under serum-free, low-protein conditions with minimal effects on cellular metabolism.

• KSBB Journal
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• v.6 no.2
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• pp.129-133
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• 1991

This study is to investigate the kinetics of anaerobic process, the effect of mass transfer on process, and the characteristics of the conventional anaerobic bioreactor, and develop new high efficiency bioreactor. In the new bioreactor wastewater containing highly concentrated organic materials, was treated without diluting wastewater. In this experiment the high COD removal rate (about 88%) and gas production(about 200l/d) was showed with short residence time(1.5 day). This performance is about 10 times as large as the conventional reactor.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.9
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• pp.727-735
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• 2003

The determination of completion time constitutes an important step in developing algorithms for short-term production scheduling. Existing completion time algorithms of multi-product batch processes often assume that intermediate storage tanks are always available when it is needed. In this paper, we consider a serial multi-product batch plants with ZW and NIS policy intermediate storge tank. We limit storage residence time and allocated products in the intermediate storage tank to minimize the quality change of the stored material as well as to reduce the clearing time during product change. A set of recurrence relations is suggested to calculate the completion times for the given batch sequence of products on all processing units. Also analytic solution for the suggested model is solved by a graphical method. The effectiveness of these results is proved by a few illustrative examples.