• Korean Journal of Animal Reproduction
• /
• v.25 no.1
• /
• pp.19-28
• /
• 2001

The present study was undertaken to investigate the effects of cooling rate and equilibration time on the survival, in vitro maturation and development to embryos of frozen-thawed bovine immature oocytes(Germinal Vesicle Stage). The cryoprotectants are used 10% ethylene glycol(EG) as permeating cryoprotectant and 0.05M soc.ose(S) or trehalose(T) as low molecular weight nonpermeating cryoprotectants and 5% ficoll(F) or polyvinylpyrrolidone(PVP) as high molecular weight nonpermeating cryoprotectants. Four freezing solution were uysed in this experiment(EFT: 10% EG + 5% F + 0.05M T, EFS: 10% EG + 5% F + 0.05M S, EPT: 10% EG + 5% P + 0.05M T, EPS: 10% EG + 5% P + 0.05M S). The best equilibration time and freezing solution was 15 min in EPT(83% survival rate of frozen-thawed bovine immature oocytes). When frozen-thawed bovine oocytes were cultured following IVM and IVF, there was no significant difference in cleavage and development rates among the EFT, EFS, EPT and EPS solutions. When 9 blastocysts derived from frozen bovine oocytes were transferred to 6 recipients, two recipients were pregnant. And one was aborted at 45 days of pregnancy and the other had a stillbirth.

• International Journal of Highway Engineering
• /
• v.11 no.3
• /
• pp.51-60
• /
• 2009

This study investigates the fresh state characteristics, strength, chloride ion penetration resistance and freeze-thaw resistance of the suggested high strength-high durability cement concrete pavement. The required workability and air content could be achieved by using an appropriate admixtures. However its dosage should be carefully determined through field trial batches. Compressive strength increased with the increased cement content and, in particular, high cement volume concrete continuously developed strength up to 90 days. No clear relationship, however, existed between flexural strength and cement content. Chloride penetration resistance seemed as a function of curing age rather than the cement content. Freeze-thaw resistance test was conducted using two different coolants, tap water and 4% NaCl solution. When the tap water was used no severe damage was observed up to 300 cycles regardless the air content. Under 4% NaCl solution, specimens of 326kg/$m^3$ cement content showed severe damage with surface scaling. Based on the experimental investigations herein, it is highly recommended that the cement content be greater than 400kg/$m^3$ for strength-high durability cement concrete pavement structures.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.5
• /
• pp.161-168
• /
• 2008

The freeze-thaw deterioration and chloride attack, which are the typical degradation factors for durability of marine concrete, are significantly affected by pore structures in terms of penetration and diffusion. These pore structures of concrete are closely related to the types and amount of AE agent, used to guarantee the resistance of freeze-thaw deterioration, and the elapsed time before concrete pouring. This paper evaluates the durability of concrete based on the results of tests on cylinder specimens and core specimens from mock-up members with different air content of 4~6% and 8~10%, respectively. According to the test results, the air content of hardened concrete is 2.5~5.2% at 7 days and 2.4~5.1% at 28 days. These air contents are about half of the initial values just after the concrete mixing. Judging from the amount of scale after the freeze-thaw test completed, air content of 8~10% is slightly more beneficial against the deterioration of concrete than air content of 4~6%. Meanwhile, the core specimens from mock-up members exhibit somewhat unfavorable freeze-thaw deterioration and chloride migration characteristic compared with the cylinder specimens tested in the laboratory under the same mixing condition, as to show 106% in freeze-thaw test and 160% in chloride diffusion coefficient test, respectively.

• Journal of Embryo Transfer
• /
• v.18 no.1
• /
• pp.51-59
• /
• 2003

This study was carried out to evaluate the effect of different freezing and thawing rates on the viability, motility and acrosomal changes of frozen canine spermatozoa. The ejaculated semen was extended with Tris-egg yolk buffer containing 8% glycerol and equilibrated for 60 min after cooled to 4$^{\circ}C$ for 58 min. The straws were cryopreserved gradually by slow-cooling at different distance(6, 10 and 17 cm, respectively) from the liquid nitrogen (L$N_2$) to achieve temperature rate of 3, 8.9 and 19$^{\circ}C$ /min. Thawing of the straws was performed in a water bath fur 2 min at 37$^{\circ}C$ and 55$^{\circ}C$ , respectively. The motility of frozen-thawed spermatozoa was assessed by phase-contrast microscopy. To assess their viability and acrosome content, spermatozoa were stained with a vital stain and Fluorescence conjugated lectin Pisum Savitum Agglutinin (FITC/PAS), respectively. Concentration of the ejaculated fresh semen was normal range of 3.44 $\times$ 10$^{8}$ /ml. Freezing temperature were reduced to -110, -70 and -35$^{\circ}C$, as higher distance from liquid nitrogen, 6, 10 and 17 cm, respectively. Freezing at 3$^{\circ}C$/min in distance of 17 cm from liquid nitrogen yielded better motility, viability and rate of intact acrosome than 8.9 or 19$^{\circ}C$/min and the optimal thawing was 37$^{\circ}C$ for 2 min.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.7 no.4
• /
• pp.438-444
• /
• 2019

In this study, the effect of polypropylene fiber on the freeze-thaw damage of mortar was evaluated experimentally. The effects of the reinforcing of polypropylene fiber on the compressive and bending performance of mortar after 300 cycles of freeze-thaw test were evaluated by comparing the normal mortar and the mortar with polyvinyl alcohol fiber. In addition, the mass loss, relative dynamic elastic modulus, and cumulated pore volume of mortar were measured by each cycle of freeze-thaw test. As a result, it was confirmed that the fiber reinforced mortar, regardless of the fiber type, was effective not only in maintaining the performance of the compressive strength and the bending strength but also suppressing the mass loss after the freeze-thaw test of 300 cycles. Meanwhile, it was confirmed that not only polyvinyl alcohol fibers but also polypropylene fibers can effectively act to suppress the damage of the mortar by freeze-thaw. However, in order to improve the freeze-thaw resistance of mortar mixed with polypropylene fiber, it is necessary to increase the bonding performance with the cement matrix which can be expected from polyvinyl alcohol fiber.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.35 no.5
• /
• pp.487-490
• /
• 2011

We used X-ray tomography to carry out an experimental study to visualize the effect of freeze and thaw cycles on the gas diffusion layer (GDL) in a polymer electrolyte membrane fuel cell (PEMFC). A PEMFC has freeze and thaw cycles if the fuel cell is operating at a below-freezing ambient temperature. The cycle permanently deforms the fuel-cell capillary structures and reduces the ability of the cell to generate electric power and also reduces its service life. The GDL is the thickest capillary layer in the fuel cell, so it experiences the most deformation. The X-ray tomography facility at the Pohang Accelerator Laboratory was used to observe the structural changes in GDLs induced by a freeze and thaw cycle. We discuss the effects of these structural changes on the power production and service life of PEMFCs.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.211-212
• /
• 2010

This study is aimed to investigate effects of water-cement ratio on the freeze thaw resistance of fly ash concrete. Assess the effects of physical properties of fly ash concrete by measure the length change, weight change, dynamic modulus of elasticity.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2010.04a
• /
• pp.766-769
• /
• 2010

본 논문은 콘크리트 구조물 중 원전구조물에서 열화요인에 따른 미세구조적 변화에 대해서 평가하였다. 이는 원전구조물의 경우 열화현상이 발생하게 되면 일반 구조물에 비해 심각한 영향을 초래하기 때문에 기존의 열화 평가 방법에 의존하기 보다는 미세구조적 관점에서 콘크리트의 열화를 재평가해야 한다. 그에 일환으로 열화 요인 중 동결 융해와 황산염에 대한 미세구조 평가를 실시하였다. 동결융해의 경우, 미세구조적 관점에서의 미세공극의 양이 증가하는 것을 확인하였으나 그 증가 폭이 크지 않음을 알 수 있었으며, 물리적 실험에서도 그 변화가 매우 작음을 확인할 수 있다. 그리고 황산염에서는 초지 침지 구간에서는 플라이 애쉬를 사용한 원전 콘크리트 배합이 콘크리트에 더 유리하게 작용함을 알 수 있다.

• The Journal of Engineering Geology
• /
• v.23 no.3
• /
• pp.271-281
• /
• 2013

Freeze-thaw experiments were conducted to evaluate changes in surface roughness and physical properties in samples of granite from Ilgwang and Imki mines, Korea. The temperature range in the experiments was $-20^{\circ}C$ to $40^{\circ}C$, based on typical summer and winter temperatures in Korea, and the surface was observed every 20 cycles. One cycle comprised 1 hour of heating or cooling of the samples and 1 hour during which the target temperature was maintained. With increasing repetitions of the freeze-thaw experiment, porosity increased by 0.05%-0.15% in the two samples and the dry weight increased, whereas the volume of the soil and saturation weight decreased. Observations by confocal laser scanning microscope (CLSM) revealed that line and surface roughness parameters showed a tendency to increase and decrease, respectively, with elapsed time. Changes in surface roughness were apparent on the CLSM images.

• Korean Journal of Animal Reproduction
• /
• v.22 no.4
• /
• pp.307-317
• /
• 1998

This study was to investigate the vitrification method for cryopreservation technique of bovine in vitro fertilization(IVF) embryos. The morphological appearance and viability following vitrification of IVF bovine blastocysts and expanded blastocysts were examined. Embryos obtained 6, 7, 8 or 9 days after IVF were vitrified in both 40% ethylene glycoI(EG) plus 0.3M trehalose and 20% polyvinylpyrrolidone(PVP) in DPBS(ETP, Exp. 1) and ETP solution added 0.375M dextrose (ETPD, Exp. 2). The viability of Days 6, 7, 8 and 9 vitrified /thawed embryos at 24∼48 h culture after thawing was 11.9%, 19.8%, 23.4% and 15.3% in ETP(Exp. 1), and 34.6%, 54.5%, 37.9% and 13.0% in ETPD(Exp. 2), respectively. The viability of vitrified embryos produced from the culture days after IVF did not differ in Exp. 1, but significantly differ in Exp. 2(P＜0.05). The viability of blastocysts and expanded blastocysts significantly differed(P＜0.05) in 15.2% and 23.3%(Exp. 1), and 25.0% and 45.8%(Exp. 2). The result of Exp. 1 was similar to that of Exp. 2 on the viability of embryo according to developmental stages, but ETP solution plus sugar(dextrose) was increased the viability of vitrified embryos. In Experiment 3, The viability of vitrified embryos was not different between 12% and 20% PVP concentrations in ETP solution according to culture days or developmental stages. To investigate the effect of addition of sugar, two type of carbohydrates and a mixture of cryoprotectants for vitrification on the survival of bovine IVF embryos, bovine Days 7 to 9 blastocysts and expanded blastocysts were cryopreserved in either 20% glycerol plus 20% EG, 0.375M sucrose and 0.375M dextrose (GESD, Exp. 4) or 20% glycerol plus 20% EG, 0.3M trehalose and 20% PVP(GETP, Exp. 5) in DPBS. Survival rates of Day 7, 8 and 9 embryos at 24∼48h culture after thawing were 71.4%, 94.6% and 40.5% in GESD, and 59.5%, 81.5% and 62.5% in GETP, respectively. Hatching rates of Day 7, 8 and 9 embryos after thawing were 28.6%, 35.1% and 16.2% in GESD, and 27.0%, 33.3% and 18.8% in GETP, respectively. These results indicates that a mixture of cryoprotectants(glycerol and EG) and addition of sugar can improve the survival rates of the bovine IVF embryos(Day 7 or 8) vitrified, and the expanded blastocyst embryos are more suitable for vitrification than early blastocysts stage.