• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.47-56
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• 2021

The cryosuction (negative pore pressure) in freezing soils causes groundwater migration from the frozen fringe to freezing front for ice lens formation. Frost heave and heaving pressure by ice lens cause damage to ground infrastructure. In order to prevent damage by the frost heave, various frost susceptibility criteria have been proposed. The SP (Segregation Potential) is the most widely used classification criterion for frost susceptibility in cold regions. The expansion of the ice lens by the migration of the groundwater is a key role in frost heave mechanism, and thus it is necessary to evaluate the hydraulic conductivity. In this paper, soil mixtures of coarse-fines (sand-silt) were prepared in various weight fractions and used for frost heave and column permeability test. For each case, the SP and the hydraulic conductivity were derived and correlations were analyzed. As a results, the transition threshold of the SP and the hydraulic conductivity were shown at 20% and 50% of the silt weight fraction, respectively. Although there are difference between these transition thresholds, these two coefficients show a specific correlation. In the future, additional study should be conducted for detailed analysis of the threshold transition values between SP and hydraulic conductivity.

• Journal of the Korean Wood Science and Technology
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• v.28 no.4
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• pp.41-50
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• 2000

Cement-bonded particleboard is being used as outdoor siding material all over the world, because this composite particularly bears a light weight, high resistance against fire, decay, and crack by cyclic freezing and thawing, anti-shock property, and strength enhancement. Construction systems are currently changing into a frame-building style and wooden houses are being constructed with prefabrication type. Therefore, they require a more durability at outdoor-exposed sides. In this study, the cement hydration property for Korean pine particle, Japanese larch particle and face- and middle layer particles (designated as PB particle below) used in Korean particleboard-manufacturing company was investigated, and the rapid manufacturing characteristics of cement-bonded particleboard by supercritical $CO_2$ curing was evaluated. Korean pine flour showed a good hydration property, however, larch flour showed a bad one. PB particle had a better hydration property than larch flour. The addition of $Na_2SiO_3$ indicated a negative effect on hydration, however, $MgCl_2$ had a positive one. Curing by supercritical $CO_2$ fluid gave a conspicuous enhancement in the performances of cement-bonded particleboards compared to conventional curing. $MgCl_2$ 3%-added PB particle had the highest properties, and $MgCl_2$ 1%-added Korean pine particle had the second class with the conditions of cement/wood ratio of 2.7, a small fraction-screened particle and supercritical curing. On the contrary, the composition of non-hammermilled or large fraction-screened particle at cement/wood ratio of 2.2 was poorer. Also, the feasibility for actual use of 3%-added, small PB particle-screened fraction was greatest of all the conventional curing treatments. Relative superiority of supercritical curing vs. conventional curing at dimensional stability was not so apparent as in strength properties. Through the thermogravimetric analysis, it was ascertained that the peak of a component $CaCO_3$ was highest, and the two weak peaks of calcium silicate hydrate and ettringite and $Ca(OH)_2$ were present in supercritical treatment. Accordingly, it was inferred that the increased formation of carbonates in board contributes to strength enhancement.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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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.

• Tunnel and Underground Space
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• v.14 no.4
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• pp.287-294
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• 2004

To predict the temperature distribution around a underground rock storage cavern, two- and three- dimensional numerical analysis using FLAC was conducted. The effects of groundwater and latent heat on thermal properties were considered in numerical calculation. The temperature estimated by FLAC are compared with the temperature measured for 5-year operation at Gonjiam storage cavern. Estimated and measured temperatures showed great discrepancy when thermal properties from laboratory tests were used and showed good agreement when the effects from 20% of volumetric water fraction and latent heat were considered. However, the discrepancy still increased with operation time due to the heat flow from ground surface. Three-dimensional numerical models were established to closely approximate the boundary condition of the test site, and numerical results better agreement when groundwater and latent heat effects were considered.

• Journal of Korea Foundry Society
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• v.32 no.5
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• pp.219-224
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• 2012

The effects of Mg and Si contents on the microstructure and mechanical properties in Al-Mg alloy (ALDC6) were investigated. The results showed that phase fraction and size of $Mg_2Si$ and $Al_{15}(Fe,Mn)_3Si_2$ phase in the microstructure of Al-Mg alloy were increased as the Mg and Si contents were raised from 2.5 to 3.5 wt%. With Si content of 1.5 wt%, freezing range of the alloy was significantly reduced and solidification became more complex during the final stage of solidification. While there was no significant influence of Mg contents on mechanical properties, Si contents up to 1.5 wt%, strongly affected the mechanical properties. Especially elongation was reduced by about a half with more than 1.0 wt%Si in the alloy. The bending and impact strength were decreased with increased amount of Si in the alloy, as well. The lowered mechanical properties are because of the growth of particle shaped coarse $Mg_2Si$ phase and precipitation of the needle like $\beta$-AlFeSi in the microstructure at the last region to solidify due to presence of excess amount of Si in the alloy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.4
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• pp.336-342
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• 2012

Large-scale active solar heat systems are generally using heat exchanger between collector and storage tank loops to prevent damage by freezing. It is difficult to maintain stratification in a storage tank in the system owing to greater flow rate enhancing heat transfer. In the previous study, we introduced a spiral-jacketed storage tank and obtained good results to keep system performance of general level without better stratification. We added a scroll-shaped heat exchanger coil on the upper part in the spiral-jacketed storage tank. As a result of the experiment, it was verified that degree of stratification of the new type storage tank is higher than that of the previous one with a possibility of better collector efficiency and solar fraction.

• Geomechanics and Engineering
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• v.30 no.4
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• pp.393-399
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• 2022

The Segregation Potential (SP) is one of the most widely used predictors of frost heave in cold regions. Laboratory step-freezing tests determining a representative SP at the onset of the formation of the last ice lens (near the thermal steady state condition) can predict susceptibility to frost heave. Previous work has proposed empirical semi-log fitting for determination of the representative SP and applied it to several fine-grained soils, but considering only frost-susceptible soils. The presence of fines in coarse-grained soil affects frost susceptibility. Therefore, it is required to evaluate the applicability of the empirical semi-log fitting for both frost-susceptible and non-frost-susceptible soils with fines content. This paper reports laboratory frost heave tests for fines contents of 5%-70%. The frost susceptibility of soil mixtures composed of sand and silt was classified by the representative SP, and the suitability of the empirical semi-log fitting method was assessed. Combining semi-log fitting with simple laboratory frost heave testing using a temperature-controllable cell is shown to be suitable for both frost-susceptible and non-frost-susceptible soils. In addition, initially non-frost-susceptible soil became frost susceptible at a 10%-20% weight fraction of fines. This threshold fines content matched well with transitions in the engineering characteristics of both the unfrozen and frozen soil mixtures.

• Journal of Sericultural and Entomological Science
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• v.44 no.1
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• pp.4-8
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• 2002

We conducted this study to investigate the morphological characteristics and physiological effects of mulberry leaves and fruits with wild varieties. Morphologically sampling materials were showed Morus bombycis type and Morus alba type characteristics. Water contents of mulberry fruits were higher than that of mulberry leaves. Sugar degree of sampling materials was 5.1∼22.7 Brix %. The yield of 85% MeOH extract from freezing dried Mulberry Fruits was 60.2% and Hexane, BuOH and H$_2$O fraction from MeOH extract were 2.8%, 4.6%, 92.3% respectively. In the cholesterol-induced hyperlipidemia rats administered with subfraction of mulberry fruit extract, total cholesterol and serum triglyceride were decreased in the MeOH extract group and H$_2$O soluble fraction group. Also H$_2$O soluble fraction group decreased GPT, GOT and LDH level. Therefore, the above results suggested that mulberry fruit with wild varieties can help to maintain normal liver functions and to protect hyperlipidemia.

• The Journal of Engineering Geology
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• v.25 no.1
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• pp.93-102
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• 2015

The characteristics of frozen soils are one of most important factors for foundation design in cold region. The objective of this study is to evaluate the shear strength and stiffness of frozen soils according to the confining conditions during the freezing and shearing phase. A direct shear box is constructed for the frozen specimens and bender elements are mounted on the wall of the shear box to measure shear wave velocities. Specimens are prepared by mixing sand and silt with a silt fraction of 30% in weight and the degree of saturation of 10%, giving a relative density of 60% for all tests. The temperature of the specimens in the freezer is allowed to fall below -5℃, and then direct shear tests are performed. A series of vertical stresses are applied during the freezing and shearing phase. Shear stress, vertical displacement, and shear wave along the horizontal displacement are measured. Experimental results show that in all the tests, shear strength increases with increasing vertical stress applied during the freezing and shearing phases. The magnitude of the increase in shear strength with increasing vertical stress during shearing under fixed vertical stress in the frozen state is smaller than the magnitude of the increase in vertical stress during freezing and shearing. In addition, the change in shear wave velocities varies with the position of the bender elements. In the case of shear waves passing through the shear plane, the shear wave velocities decrease with increasing horizontal displacement. This study provides an evaluation of the properties of shear strength and stiffness of frozen soils under varied confining condition.

• Journal of Embryo Transfer
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• v.16 no.1
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• pp.53-60
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• 2001

This study was conducted to evaluate whether \"Royal jelly\" (RJ) added to Tris-buffer dilute contributed to supporting post-thaw viability and longevity of frozen canine spermatozoa. Two Japanese spitzs (2 to 4 years of age) were used as a semen donor. Semen was collected by manual masturbation and separated into 3 fractions. Only the sperm-rich fraction having sperm motility of more than 70%, containing sperm concentration of 2~4$\times$10$^{8}$ cells/ml and having dead or abnormal spermatozoa of less than 15% was used for the experiment. Each ejaculated semen was centrifuged at 400 $\times$ g for 5 min and then diluted in a Tris-buffer supplemented with 20 ml egg yolk (Ext I), 4% glycero1 and 1% Equex STM Paste (Ext II) or g1ycero1, Equex STM paste and RJ of various concentrations (Ext II-RJ). After freezing and thawing, viability of spermatozoa in Ext II -RJ containing 1% RJ immediately after thawing (67.5$\pm$9.6) was significantly lower than that of Ext II , Ext II -RJ containing 0.01 or 0.1% RJ (77.5$\pm$12.5, 78.7$\pm$8.2 and 80.0$\pm$6.3). However, Ext II-RJ containing 0.1% RJ yielded higher viability than Ext II, Ext II-RJ containing 0.01% at or 1% 1 h after thawing (69.5$\pm$8.1 vs. 55.0$\pm$12.9, 57.5$\pm$9.6 and 41.5$\pm$12.6; P<0.05). At 1 h after thawing, the viability of spermatozoa thawed in 7$0^{\circ}C$ (68.8$\pm$12.5) was significantly higher than that of spermatozoa thawed in 38$^{\circ}C$ (48.8$\pm$16.3), although there was no difference in the viability between both groups immediately after thawing (77.5$\pm$9.6 and 81.3$\pm$8.1). Post-thaw viability and longevity of post-thaw spermatozoa in Ext II-RJ containing 0.1% RJ was higher in those in Ext II at 1 h (65.0$\pm$12.9 vs. 42.5$\pm$12.6), 2 h (52.5$\pm$12.6 vs. 27.5$\pm$17.1) and 3 h (40.0$\pm$14.1 vs. 20.0$\pm$12.1) after thawing. These results indicated that addition of 0.1% af to Tris-buffer enhanced post-thaw viability and longevity of canine spermatozoa and this additive can be used for increasing the possibility of collision between spermatozoa and ova during insemination.emination.