• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.4
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• pp.33-45
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• 1983

In the course of transportation of ready mixed concrete, it sometimes happens that time of haul from mixing at a batching plant to placing of the concrete at a job site is prolonged too much. When it does happen, improvement in the concrete workability needs to be made by proper measures. It is proposed, therefore, to discuss the quality of concrete modified by time of haul and to search for methods for improvement of the quality by means of adding cement and water or superplasticizer. It was found in this experiment that retempering concrete with superplasticizer is useful in coping with the quality deterioration.

• Current Research on Agriculture and Life Sciences
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• v.25
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• pp.25-31
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• 2007

The several enzymes reaction which involve the quality change of fresh vegetables, such as chlorophylase, polyphenol oxidase, lypoxygenase, C-S-lyase, myrosinase and enzymes related lignification were reviewed. Numerous enzyme reaction continuously proceeds to the deterioration of vegetables after harvest due to the respiration and biochemical metabolism reaction, especially in case of physical injuring. It is extremely important to inhibit and to control these enzyme reaction in order to maintain the organoleptic and nutritional quality of fresh vegetables.

• Preventive Nutrition and Food Science
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• v.11 no.3
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• pp.257-260
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• 2006

The correlation between microbiological and sensory quality indexes was investigated for Korean seasoned side dishes stored under chilled conditions, by using both published data and experimental evaluation. Aerobic bacterial counts on the perishable Korean side dishes showed high inverse correlation with sensory quality and could also be regarded as a main cause of sensory quality deterioration. Therefore, monitoring or estimating the microbial growth on these products should be an effective means for estimating and extending their shelf life.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.11a
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• pp.56-57
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• 2019

Recently, the risk of fine dust is emerging in Korea. According to the OECD report, the incidence of hospitalization and mortality from lung disease is increased, and the incidence of lung cancer and mortality from ischemic heart disease with prolonged exposure are increased. In addition, indoor air quality has become an important factor affecting the human body as indoor life has increased due to the Industrial Revolution. Air pollutants that cause indoor air deterioration typically include particulate dusts as described above, formaldehyde and VOCs released in gaseous form from adhesive wood products used in building materials and furniture. May cause breathing problems. In this study, we analyzed the properties of adsorption matrix for improving indoor air quality using cork.

• Journal of Korean Institute of Industrial Engineers
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• v.34 no.1
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• pp.108-121
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• 2008

Dispatching rule for parallel machines with multi product is proposed in this paper, In current market,customer's request for higher quality is increasing, In accordance with such demand, manufacturers are focusingon improving the quality of the products. Such shift in production objective is risky. The possibility ofneglecting another important factor in customer satisfaction increases, namely due dates. From the aspect ofimproving quality, frequency of product assignment to limited number of high performance machines willincrease. This will lead to increased waiting time which can incur delays, In the case of due date orientedproduct dispatch, Products are assigned to machines without consideration for quality. Overall deterioration ofproduct quality is inevitable, In addition, Poor products will undergo rework process which can increase delays.The objective of this research is dispatching products to minimize due date delays while improving overallquality. Quality index is introduced to provide means of standardizing product quality. The index is used toassure predetermined quality level while minimizing product delays when dispatching products. Qualitystandardization method and dispatching algorithm is presented. And performance evaluation is performed withcomparison to various dispatching methods.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.77-91
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• 2006

Domestic practices in shotcrete use have developed in many respects even now, but it still has issues about material, construction, quality standard and so on. In overseas, the construction using high strength shotcrete with $39.2{\sim}58.8 MPa$ of compressive strength is becoming common based on the shotcrete technology of high strength and durability. However, domestic shotcrete design strength is low at around 20.6 MPa of compressive strength and a long term durability is also insufficient. In this paper, field tests using high-quality additives and accelerators were performed to obtain the improvement of shotcrete strength and EFNARC standard was used to evaluate the field test results. In addition, deterioration test combined with the freezing-thawing and carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of the field test, the promotion ratio of early strength was $90{\sim}97%$ in case of using alkali-free accelerators. And the compressive strength of the shotcrete using Micro-silica fume was $45.2{\sim}55.8MPa$ and flexible strength was $5.01{\sim}6.66MPa$, so the promotion ratio of strength was $37{\sim}79%$ and $17{\sim}61%$ respectively. The promotion effect of strength by silica fine additives ratio of $7.5{\sim}10%$ for cement mass was much superior to the other cases. It was especially examined that using Micro-silica fume reduced deterioration due to mixed steel fiber and improved a long-term durability of shotcrete.

• Water Engineering Research
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• v.3 no.2
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• pp.143-153
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• 2002

As the natural flows in rivers dramatically decrease during drought season in Korea, a deterioration of river water quality is accelerated. Thus, consideration of downstream water quality responding to changes in reservoir release is essential for an integrated watershed management with regards to water quantity and quality. In this study, water quality models based on artificial neural networks (ANNs) method were developed using historical downstream water quality (rm $\NH_3$-N) data obtained from a water treatment plant in Geum river and reservoir release data from Daechung dam. A nonlinear multiple regression model was developed and compared with the ANN models. In the models, the rm NH$_3$-N concentration for next time step is dependent on dam outflow, river water quality data such as pH, alkalinity, temperature, and rm $\NH_3$-N of previous time step. The model parameters were estimated using monthly data from Jan. 1993 to Dec. 1998, then another set of monthly data between Jan. 1999 and Dec. 2000 were used for verification. The predictive performance of the models was evaluated by comparing the statistical characteristics of predicted data with those of observed data. According to the results, the ANN models showed a better performance than the regression model in the applied cases.

• Food Science and Preservation
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• v.5 no.1
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• pp.23-28
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• 1998

The objective of this study was to investigate the methods of quality maintenance using modified atmosphere packaging with various quality preservatives at ambient and low temperatures. Ethylene(<1.0ppm) accumulated during modified atmosphere storage of Chinese cabbage using polyethylene film(60$\mu\textrm{m}$) caused quality deterioration such as yellowing and abscission. The addition of potassium permanganate reduced ethylene level and thus extended storage life of l00% at 20$^{\circ}C$ and 140% at 0$^{\circ}C$. To establish the storage conditions of minimally processed sit and vegetables, the experiment was conducted with various quality preservatives and packaging materials. Ceramic film(Zeolite 7%, 60$\mu\textrm{m}$) showed increasing storage life of 50%, reducing total microbial counts of 50% and keeping high appearance quality of minimally processed pears stored at 20$^{\circ}C$ and 0$^{\circ}C$. Minimally processed Chinese cabbage treated with l% CaCl2 at 20$^{\circ}C$, and 1% CaCl2 and 1% NaCl at 0$^{\circ}C$ has a longer storage life of 90% with good maketable quality. Treatment of 1% NaCl for cut Asian penis appeared increased storage life of 100%, decreased cut surface browning and the best overall acceptability by a sensory panel.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.5 s.347
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• pp.113-120
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• 2006

This thesis deals with solutions such as coverage area extension, reduction of the shadow region and performance enhancement of handover caused by structural modification of WiBro network. The More far the distance of RAS(Radio Access Station) and SS(Subscriber Station) is in micro cell, the more bad the quality of channel environment becomes owing to radio interference. Consequently, it causes the deterioration of the throughput and also the deterioration of communication quality in many sides. In fact, most users of WiBro are located in the region, the QPSK region which is bad in point of channel quality. It brings the service complaint by user. We select RS(relay station) to solve the matter caused by channel environment in this cell, and extend coverage and improve the performance of handover call blocking.

• Journal of the Korean Society of Safety
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• v.32 no.3
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• pp.117-122
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• 2017

In this study, we studied the ride quality considering the deterioration effects of the three type couplers (single, double, and ring types) for EMUs. In order to know the impact occurred when an urban transit vehicle is under breaking, we tested the conditions of the service brake and the emergency brake. Normal coupler models without any slack showed similar dynamic performance results under all breaking conditions. But if the couplers become old, the initial pre-stresses are removed because of permanent compressive deformation in rubber. For three types of the old coupler models without the initial pre-stress, we evaluated dynamic performances of each type. As the results, the maximum and average acceleration levels of the double type and the ring type were similarly low in all conditions. But the accelerations of the single type coupler was high when compared to those of the double and ring types. In addition, Jerk value of the single type model associated with ride quality was high up to 15 times to the ring type in condition of the service braking in empty vehicle weight. Jerk value of the double type model was high up to 6 times to the ring type.