• 한국물환경학회지
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• 제26권1호
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• pp.104-110
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• 2010

Eutrophication is a well-known phenomenon in lentic habitats, however it is receiving increasing attention in shallow streams of Korea due to the increase of periphyton to a nuisance level. In this study temporal and spatial variation in periphyton standing crop and nutrient concentrations were surveyed in the upper reach of the Han River (the Inbuk Stream) that used to be a pristine rural stream until 1980s. Chlorophyll-a concentration per unit surface area of bottom substrate was examined monthly for one year period at nine sites along the Inbuk Stream together with environmental factors such as phosphorus, nitrogen, and water velocity. The standing crop of periphytic algae ranged from $4{\sim}242mgChl.a/m^2$ with a median of $55mgChl.a/m^2$, often exceeding the nuisance level criterion. Along the stream periphyton increased significantly from $39{\pm}48mgChl.a/m^2$ to $94{\pm}49mgChl.a/m^2$ after merging of a tributary in an intensive agricultural basin with high phosphorus concentrations. Seasonally periphyton biomass was highest in autumn (median $171{\pm}76mgChl.a/m^2$) from October through December when water flow velocity was low (median $0.4{\pm}0.3m/s$), while it was higher in flood season (median $1.2{\pm}0.4m/s$) and freezing season (median $0.2{\pm}0.3m/s$) was lower. The result shows that this rural stream often shows characteristics of eutrophication according to periphyton standing crop and it may be regulated by phosphorus and water velocity.

• 한국동물생명공학회지
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• 제37권2호
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• pp.113-120
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• 2022

Sperm cryopreservation is a fundamental process for the long-term conservation of livestock genetic resources. Yet, the packaging method has been shown, among other factors, to affect the frozen-thawed (FT) sperm quality. This study aimed to develop a new mini-straw for sperm cryopreservation. In addition, the kinematic patterns, viability, acrosome integrity, and mitochondrial membrane potential (MMP) of boar spermatozoa frozen in the developed 0.25 mL straw, 0.25 mL (minitube, Germany), or 0.5 mL (IMV technologies, France) straws were assessed. Post-thaw kinematic parameters were not different (experiment 1: total motility (33.89%, 32.42%), progressive motility (19.13%, 19.09%), curvilinear velocity (42.32, 42.86), and average path velocity (33.40, 33.62) for minitube and the developed straws, respectively. Further, the viability (38.56%, 34.03%), acrosome integrity (53.38%, 48.88%), MMP (42.32%, 36.71%) of spermatozoa frozen using both straw were not differ statistically (p > 0.05). In experiment two, the quality parameters for semen frozen in the developed straw were compared with the 0.5 mL IMV straw. The total motility (41.26%, 39.1%), progressive motility (24.62%, 23.25%), curvilinear velocity (46.44, 48.25), and average path velocity (37.98, 39.12), respectively, for IMV and the developed straw, did not differ statistically. Additionally, there was no significant difference in the viability (39.60%, 33.17%), acrosome integrity (46.23%, 43.23%), and MMP (39.66, 32.51) for IMV and the developed straw, respectively. These results validate the safety and efficiency of the developed straw and highlight its great potential for clinical application. Moreover, both 0.25 mL and 0.5 mL straws fit the present protocol for cryopreservation of boar spermatozoa.

• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.520-527
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• 2020

황토는 국내 토양의 약 15.0%를 차지하는 풍부한 자원이며, 고온소성 후 급랭하여 활성화시키면 포졸란 특성을 갖는 콘크리트 결합재로서 사용할 수 있다. 본 연구에서는 시중에서 판매되는 경계석 배합을 기반으로 하여 활성 황토 혼입 모르타르 경계석 시편을 제작하였다. 활성 황토의 혼입율은 10.0% 및 25.0%를 고려하였으며, 시험 항목으로는 압축 및 휨 강도 시험, 동결융해 저항 성능 평가, 촉진 탄산화 시험, 촉진 염화물 확산 시험을 설정하였다. 역학적 성능 평가 결과 OPC 배합에서 가장 높은 강도가 평가되었으며, 재령일의 증가에 따른 강도 증가가 적게 나타났는데 이는 3일간 증기 양생을 통해 대부분의 강도가 발현되었기 때문으로 사료된다. 재령 28일에 해당하는 시편을 대상으로 동결융해 저항성능 평가 결과, 모든 배합에서 85.0% 이상의 강도 저하율을 나타내어 제시된 기준에 만족하였다. 촉진 탄산화 시험은 재령 28일 시편을 대상으로 수행되었으며 활성 황토 혼입 배합에서 OPC 배합 대비 다소 저하된 탄산화 저항성능을 나타내었다. 재령 28일 및 91일에 ASTM C 1202에 준하여 각 배합의 통과 전하량을 평가하였다. OPC 배합의 경우 "Low" 등급을, 활성 황토 혼입 배합의 경우 "Moderate" 등급을 나타내어 활성 황토 혼입 배합에서도 적절한 염해 저항성능을 나타내는 것으로 보인다.

• 한국자동차공학회논문집
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• 제22권5호
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• pp.13-19
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• 2014

Urea-SCR system is the selective catalytic reduction to reduce nitrogen oxides ($NO_x$) emitted from diesel vehicles. The objective of this study is numerical analysis of 3-dimensional unsteady melting problems of frozen urea by using an electric heater. It can be applied to determine capacity of power with respect to time and the location of the urea suction pipe in urea storage tank. The study includes the change of liquid volume fraction, temperature profiles and a influence of natural convection by using the commercial software STAR-CCM+(v7.06). The accuracy of the numerical analysis is estimated by comparisons with experimental data. After validation, a numerical analysis for freezing urea is conducted with four different heating power. From the results, it was found that relation of velocity of phase interface and amount of melting urea by increasing heating power in a container. There is also a difference in trend between velocity of phase interface and amounts of melting urea because of effect of natural convection.

• Journal of Biosystems Engineering
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• 제33권5호
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• pp.303-308
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• 2008

The freezing characteristics of two kinds of phase change materials (PCM) encapsulated in a spherical container were investigated with various cooling air temperatures and velocities. The super cooling and solidification time of PCM were highly affected by cooling air temperature and velocity. The experimental equations are derived to express total solidification time of the PCM in terms of Nusselt number and dimensionless temperature.

• 농업과학연구
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• 제31권1호
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• pp.9-14
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• 2004

This study was carried out for deresinning the larch boards dried in a conventional kiln. Prior to heat treatment they were steamed in an autoclave for 5 hours or frozen for 24 hours at a temperature of $-35^{\circ}C$. The velocities of ultrasound transmitted through the specimens were measured to examine the correlation with their resin contents. It was found that the specimens heated at $100^{\circ}C$ for 5 hours contained less resin that those heated at $200^{\circ}C$ for an hour. Both treatments of steaming and freezing were effective for deresinning and the former was better than the latter. The ultrasonic velocities measured before the heat treatment showed a negative correlation to the resin contents of the specimens, but those measured after the heat treatment a positive correlation. This difference may be attributed to the viscosity of resin.

• 자원리싸이클링
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• 제20권3호
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• pp.40-47
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• 2011

본 논문에서는 시멘트를 전혀 사용하지 않고 결합재로서 고로슬래그를 단독으로 사용한 배합과 고로슬래그와 플라이애쉬를 혼합한 배합의 강도, 수축 및 내구성에 대해 검토하였다. 그리고 비교를 위해 보통포틀랜드시멘트를 사용한 일반 모르타르에 대해서도 동일한 실험을 수행하였다. 그 결과, 알칼리 활성 모르타르는 일반 시멘트 모르타르에 비해 강도발현, 수축 및 동결융해 저항성 측면에서 우수한 것으로 나타났다. 특히 고로슬래그와 플라이애쉬를 혼합사용한 경우에는 압축강도 60 MPa 이상 달성이 가능하고, 일반 시멘트 모르타르에 비하여 수축량은 40% 정도 감소하고 동결융해 저항성은 20% 정도 향상되나, 탄산화 속도는 2~3배 촉진되는 것으로 나타났다.

• 한국농공학회지
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• 제32권3호
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• pp.39-46
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• 1990

This paper was analized the thermal conductivity of polystylene (TENSAR- GEOGRID) embeding into the subbase through frost penetration depth, frost heave, change of bearing capacity, and soil moisture movement due to freezing, thawing and icing actions, and their results were as follows : 1.The change of temperature into the sub-base was much increased by the Tensar-Geogrid insertion, and the frost penetration and frost heave were decreased as the thinner of the insulation thickness but the thawing velocity of melting period was appeared to be faster in case of non-insulated. 2.The frost heave had a close relationship with the thickness of insulations which was reasonably included anti-frost effects. 3.The moisture content during the freezing period of upper layer of the insulation insertion was increased by 15 per cent but it was returned to initial state of the thawing period, and at the down layer temporarily increased by 10 per cent and returned to the original state at once. 4.The insulation was acted as a function of distribution of surcharge, and the settlement of the sub-base was about 1.5 mm under 15 tonnage of load and which was included within the allowable limits. 5.The sliding resistance due to the icing which was induced by the insulation insertion into the sub-base was appeared as more 40 per cent than noninsulation area, so that the insulations should be restricted on the place such as mountains, curved and cross area which were required the braking power under the traffics.

• 한국건설순환자원학회논문집
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• 제1권1호
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• pp.35-41
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• 2013

본 논문에서는 시멘트를 전혀 사용하지 않은 지오폴리머 콘크리트를 개발할 목적으로 시멘트 대신에 결합재로 고로슬래그 미분말 또는 고로슬래그 미분말과 플라이애시를 혼합 사용한 지오폴리머 모르타르의 강도발현과 탄산화 및 동결융해 저항성에 대해 검토하였다. 그리고 비교를 위해 보통포틀랜드 시멘트를 사용한 일반 모르타르에 대해서도 동일한 실험을 수행하였다. 그 결과, 지오폴리머 모르타르는 일반 시멘트 모르타르에 비해 강도발현, 동결융해 저항성 측면에서 우수한 것으로 나타났다. 특히 고로슬래그와 플라이애시를 혼합사용한 지오폴리머 모르타르는 압축강도 60MPa 이상 달성이 가능하고, 일반 시멘트 모르타르에 비하여 동결융해 저항성은 20% 정도 향상되나, 탄산화 속도는 2.2~3.5배 촉진되는 것으로 나타났다.

• Computers and Concrete
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• 제30권6호
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• pp.421-432
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• 2022

Recently, the interminable ozone depletion and the global warming concerns has led to construction industries to seek for construction materials which are eco-friendly. Regarding this, Geopolymer Concrete (GPC) is getting great interest from researchers and scientists, since it can operate by-product waste to replace cement which can lead to the reduction of greenhouse gas emission through its production. Also, compared to ordinary concrete, geopolymer concrete belongs improved mechanical and durability properties. In spite of its positive properties, the practical use of geopolymer concrete is currently limited. This is primarily owing to the scarce structural, design and application knowledge. This study investigates the Mechanical and Durability of Geopolymer Concrete Containing Fibers and Recycled Aggregate. Mixtures of elastoplastic fiber reinforced geopolymer concrete with partial replacement of recycled coarse aggregate in different proportions of 10, 20, 30, and 40% with natural aggregate were fabricated. On the other hand, geopolymer concrete of 100% natural aggregate was prepared as a control specimen. To consider both strength and durability properties and to evaluate the combined effect of recycled coarse aggregate and elastoplastic fiber, an elastoplastic fiber with the ratio of 0.4% and 0.8% were incorporated. The highest compressive strength achieved was 35 MPa when the incorporation of recycled aggregates was 10% with the inclusion of 0.4% elastoplastic fiber. From the result, it was noticed that incorporation of 10% recycled aggregate with 0.8% of the elastoplastic fiber is the perfect combination that can give a GPC having enhanced tensile strength. When specimens exposed to freezing-thawing condition, the physical appearance, compressive strength, weight loss, and ultrasonic pulse velocity of the samples was investigated. In general, all specimens tested performed resistance to freezing thawing. the obtained results indicated that combination of recycled aggregate and elastoplastic fiber up to some extent could be achieved a geopolymer concrete that can replace conventional concrete.