• 한국물환경학회지
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• 제21권2호
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• pp.176-183
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• 2005

Chlorination of wastewater is recently practiced in Korea. While many researchers have studied the kinetics of aqueous chlorine(HOCl) with nitrogeneous compounds and other organic/inorganic contaminants in drinking water, the researches of wastewater chlorination are relatively few. The purpose of this study was to investigate the chlorine decay kinetics and parameters on wastewater chlorination. Chlorine decay rate increased with increasing initial chlorine concentration. The parameters affecting chlorine decay rate were different in each wastewater treatment plant. One of the most important parameters affecting chlorine decay was initial chlorine concentration, and other parameters such as $NH_3-N$, total coliform, $UV_{254}$ and Fe were also affected. The decay ratio of chlorine was decreased with increasing initial chlorine concentration, and the disinfection efficiency showed good correlation with the decay ratio.

• 한국주거학회논문집
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• 제20권2호
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• pp.109-118
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• 2009

In general, the decay of the residential district has been considered a phenomenon of old towns. But now it has become a problem of new development areas too, which have been a cause of the decay of old town. This study aims to investigate the decay of the residential district in the new development area. The survey site was Dunsan, a town-intown of Daejeon metropolitan city. The findings were as follows (:) 1) even in the new development area, a high level of vacancy ratio was evident. ; 2) among the buildings above ground, 1st floor showed the highest vacancy ratio, which means the 1st floor was allotted to too many commercial facilities relative to the buying power size in this district. ; 3) there were many conversions in response to the decay of the district, from residential to commercial, and commercial to residential. ; and 4) the allocation of each type of conversion showed a spatial pattern.

• 대한치과기공학회지
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• 제42권2호
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• pp.163-171
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• 2020

Purpose: The purpose of this study is the tooth decay ratio of the children and adolescents in four rural areas of Kyrgyzstan. Methods: Oral examinations were conducted 2,677 children and adolescents in Nizhniy chuy, Bokonbayevo, Chon Tash and Arashan from March 2017 to November 2019. It was investigated decayed tooth ratio(DT), decay permanent tooth ratio(DPT) and missing permanent tooth ratio(DMT) according to ages and areas by direct observation of the oral cavity. Results: In all areas, the rate of all children and adolescents aged 6 to 14 had very high DT of more than 94 percent overall. Furthermore, it was showed that high DPT rates above 78% on average and DMT over 8 years old in Chon Tash and Arashan. Conclusion: These results are higher than the average of DT, DPT and DMT in OECD countries. In order to promote oral health of children and adolescents, increased interest in oral health and policy measures at the Kyrgyzstan government level are considered urgent.

• 해양환경안전학회지
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• 제21권5호
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• pp.538-542
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• 2015

선체의 횡관성모멘트는 선박의 횡운동 특성을 다루는 경우 제외될 수 없는 요소로서 그 크기의 적정성은 선체 동특성 해석의 결과와 신뢰성에 큰 영향을 미친다. 그러나 선박은 질량분포와 형상이 복잡하므로 이를 직접적인 계산을 통해 값을 구하기에는 과정이 매우 복잡하고 대상 선박의 구체적인 관련 자료를 얻기도 어렵다는 점에서 실용적으로는 선체 질량의 등가적 관성반경을 선체폭의 일정비율로 계산하는 간접적인 방법이 통용되고 있다. 한편, 어느 선체의 자유 횡운동이 나타내는 횡요 주기와 감쇠형태는 관성모멘트에 의해 영향을 받기 마련이고 따라서 이러한 응답의 결과적인 모양으로부터 역으로 해당 선박의 관성모멘트를 구하는 일반식의 도출이 가능할 것으로 유추될 수 있다. 본 연구에서는 관찰에 의한 선체의 횡요 주기는 경사각의 진폭 감쇠비에 의해서도 달라지는 관계를 해석하여 횡요 주기와 경사각 진폭 감쇠비 모두를 함수 인자로 포함하는 일반식에 의해 횡관성모멘트 크기가 구해질 수 있음을 나타내었다. 또한 이러한 일반식에 횡요 관찰 선박의 주요 제원을 적용하였을 때 나타나는 특성 그래프들을 분석한 결과 횡요주기뿐 아니라 진폭감쇠비가 함께 검토될 때 얻어지는 관성모멘트 값이 보다 정확해진다는 것을 확인하였다.

• 한국세라믹학회지
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• 제32권1호
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• pp.131-139
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• 1995

In order to improve transmittance and response properties, various compositions of light controllable films were prepared by phase separation method. The optical and response properties were measured with the variation of PMMA/suspension ratio and block copolymer/light polarizing particles. According to the increase of the PMMA/suspension ratio, the separated droplets of suspension were interconnected in the film. Decay time was 2.6 sec when PMMA/suspension ratio was 0.5 : 1 and ΔT(difference of the transmittance at OFF/ON states) was reduced with increasing of the ratio of PMMA/suspension. On block copolymer/light polarizing particles ratio variation, the highest transmittance of the film was 67.4% when its ratio was 0.6 : 1 and decay time was varied from 2.15 to 46.6 sec as block copolymer content increased 0.2 : 1 to 1 : 1.

• Structural Engineering and Mechanics
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• 제38권3호
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• pp.349-359
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• 2011

Input excitation and output response of structure are needed in conventional modal analysis methods. However, input excitation is often difficult to be obtained in the dynamic load test of bridge structures. Therefore, what attracts engineers' attention is how to get dynamic parameters from the output response. In this paper, a structural experimental modal analysis method is introduced, which can be used to conveniently obtain dynamic parameters of the structure from the free decay response. With known damping coefficients, this analysis method can be used to identify the natural frequencies and the mode shapes of MDOF structures. Based on the modal analysis theory, the mathematical relationship of damping ratio and frequency is obtained. By using this mathematical relationship to improve the previous method, an improved experimental modal analysis method is proposed in this paper. This improved method can overcome the deficiencies of the previous method, which can not identify damping ratios and requires damping coefficients in advance. Additionally, this improved method can also identify the natural frequencies, mode shapes and damping ratios of the bridge only from the free decay response, and ensure the stability of identification process by using modern mathematical means. Finally, the feasibility and effectiveness of this method are demonstrated by a numerical example of a simply supported reinforced concrete beam.

• Journal of Photoscience
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• 제4권1호
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• pp.11-16
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• 1997

We measured, using femtosecond pump-probe experiment, the time evolution of transient absorption in aqueous CdS colloids. The signal rises within the time resolution (= 0.5 ps) of the experiment and decays with two exponential time constants, 4.8 ps and 132 ps. The ultrafast rise of the transient absorption is considered to be for shallowly trapped conduction band electrons after photoexcitation. The amplitude ratio of the two decaying components varies with the pump intensity and the decay times increase in the presence of hole scavengers. Even though a biexponential function fits the decay well, we object hat two independent first order processes (geminate and nongeminate recombinations) are responsible for the decay. A function with an integrated rate equation for second order nongeminate recombination plus a long background fits the decay well. The long background is considered to be for deeply trapped charges at the CdS particle.

• Korean Chemical Engineering Research
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• 제57권3호
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• pp.368-371
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• 2019

Using first principles calculations we investigated the thermomechanical stability of spent nuclear fuels (SNF), especially how mechanical properties of $UO_2$, such as, bulk, shear and Young's moduli and Poisson's ratio vary through alpha-decay of U into Th with generation of He gas. Our results indicate that substitution of U by Th through alpha decay ($U_{1-x}Th_xO_2$) does not significantly affect the stability of the grain in a fuel matrix. In addition, we studied the transport properties of He in and boundaries of the $U_{1-x}Th_xO_2$ grain. Helium preferentially resides at the grain boundaries through diffusion. Our study can contribute to substantial reduction of environmentally risk and enhancement of our sustainability by safe control of radioactive materials.

• 한국식품저장유통학회지
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• 제7권1호
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• pp.8-11
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• 2000

The antimicrobial extracts of rheum palmatum and coptis chinensis root as well as grapefruit seed extract(GFSE) were applied to dipping treatment for keeping qualities of cucumbers, respectively, which were then packed in low density polyethylene(LDPE) films incorporated with 1 % antimicrobial extracts and stored $10^{\circ}C$. Dipping and packaging in the antimicrobial agents suppressed the growth of putrefactive microorgani는 and the decay ratio of cucumbers. In addition, the loss ratio of ascortic acid content and their weight was decreased during the sotrage of cucumbers. Consequently, the combined method of dippinf and packaging in antimicrobial agents turned out to be superior to dipping treatment or film-packaging in the view point of decay ratio and the keeping qualities of cucumbers.

• Applied Biological Chemistry
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• 제40권2호
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• pp.117-122
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• 1997

제주산 궁천조생의 저장조건에 따른 저온저장 특성을 검토하였다. 상온저장에 비해 저온저장 감귤은 저장기간 중 가용성 고형물, 총당, 비타민 C의 변화가 매우 적었으며, 부패율과 중량감소가 각각 10% 이내 수준에서 비교적 신선도를 유지한 상태에서 3월 하순까지 저장이 가능한 것으로 보였다. 또한, 중량감소, 경도의 저하, 당함량의 감소는 저장기간 중에 계속하여 서서히 일어났다. 필름포장과 wax-coating은 중량감소와 외관향상에는 도움을 주었으나 장기간 저장에는 부패율이 증가하였다. 습도조절을 하지 않은 저온저장은 습도조절한 경우와 비교하였을 때 부패율과 중량감소가 컸다. 증산작용으로 인한 껍질수분의 감소에 따라 과육으로부터 수분이동이 발생하여 저장기간 중 과육율이 감소하였으며, 저장 60일 후부터 경도저하가 많이 일어나 조직이 연화됨을 알 수 있었다. 조기수확한 감귤에 비하여 완숙한 감귤이 부패율과 중량감소가 적어 저장 100일간을 기준하여 출하하는 것이 바람직하였다. 상온저장한 감귤에 비해 저온저장한 감귤은 저장 4개월 이후 출고하였을 경우 외관 및 맛에 비교적 우수하였으며, 출고후 필름포장한 감귤의 부패율은 급속히 증가하여 취급에 주의가 필요하였다. 조생온주의 경우 저온에서 장기간 저장이 어려움을 알 수 있어서 저장용 감귤의 특성을 고려하여 저장조건을 설정할 필요가 있었다.