• Carbon letters
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• v.14 no.1
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• pp.45-50
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• 2013

Polyacrylonitrile (PAN) copolymers of different molecular weights were synthesized by a suspension polymerization and precipitation polymerization method. The rheology behaviors of the synthesized PAN copolymers were investigated in relation to their molecular weight, solid content and melting temperature. The influence of "historical effects" on the spinning solution of PAN was studied by analyzing the laws of viscosity considering the diversification time and temperature. The viscosity disciplines of each spinning solution conformed well to the rheological universal laws in a comparison of the suspension polymerization product with that of precipitation polymerization. Viscosity changes in the swelling process of dissolution were gentler in the suspension polymerization product; a small amount of water will quickly debase the solution viscosity, and high-speed mixing can greatly shorten the time required by the spinning solution to reach the final viscosity.

• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.993-999
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• 1998

Acid catalyzed hydrolysis of 1-phenoxyethyl propionate, Ⅰ, has been studied using the PM3 method in the gas phase. The first step of the reaction is the protonation of basic sites, three different oxygens in Ⅰ, producing three protonated species Ⅱ, Ⅲ and Ⅳ. All possible reaction pathways have been studied from each protonated structure. Changes in the reaction mechanisms have also been discussed from the results obtained by varying a nucleophile from a water monomer to a water dimer to a complex between one water molecule and an intermediate product (propionic acid or phenol) produced in the preceding unimolecular dissociation processes. Minimum energy reaction pathway is 2-W among the possible pathways, in which water dimer acts as an active catalyst and therefore facilitates the formation of a six-membered cyclic transition state. Lower barrier of 2-W is ascribed to an efficient bifunctional catalytic effect of water molecules. PM3-SM3.1 single point calculations have been done at the gas-phase optimized structure (SM3.1/PM3//PM3) to compare theoretical results to those of experimental work.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.265-269
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• 2017

Because of abrupt changes for velocity in water, transient flow is occurred in practical life. To reduce and avoid the high or low pressure of pipe network system, various surge protection facilities are used to prevent the risk in pipe network system. Especially, we focused on study not only preventing positive and negative pressure but also selecting adequate equipment for high pressurized pipelines. Several critical cases were considered by undertaking a steady state hydraulic study and transient dynamic simulation and we suggested that the surge vessel of various surge protection system was recommended to control high and low pressures on pipeline system in perspective.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.3
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• pp.86-94
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• 2015

A series of injection and drainage test were conducted on an circular acrylic tube to investigate the pressure generated by the accumulated fill materials inside a circular acrylic tube structure. The acrylic tube was filled by means of gravity filling with a slurry material having an average water content of 700%. The water head during the filling process was 1.8m and the bottom pressure during initial filling was 20.18kPa. The recorded stress at the sides of the acrylic tube was 17.89kPa during the filling process and was reduced to 13.58kPa during the leaving process. Continuous drainage of the acrylic tube has greatly influenced the stresses around the tube structure. As the water is gradually allowed to overflow, the generated pressure at the topmost pressure sensor of the tube was reduced further to 2.17kPa. Eventually, the initially liquid state slurry material transforms into plastic state after water has dissipated and substantial soil particles are deposited in the acrylic tube. The final water content of the deposited silt inside the acrylic tube after the test was 42%. It was found that the state of stresses(geo-static earth pressures) in the acrylic tube was anisotropic rather than isotropic.

• Geomechanics and Engineering
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• v.18 no.2
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• pp.189-203
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• 2019

Brine leakage is a common phenomenon during construction facilitated by artificial freezing technique, threatening the stability of frozen wall due to the continual thawing of already frozen domain. This paper takes the frequently encountered soft clay in Wujiang District as the study object, and remolded specimens were prepared by mixing calcium chloride solutions at five levels of concentration. Both the deformation and pore water pressure of frozen specimens during thawing were investigated by two-stage loading tests. Three sections were noted from the changes in the strain rate of specimens during thawing at the first-stage load, i.e., instantaneous, attenuated, and quasi-stable sections. During the second-stage loading, the deformation of post-thawed soils is closely correlated with the dissipation of pore water pressure. Two characteristic indexes were obtained including thaw-settlement coefficient and critical water content. The critical water content increases positively with salt content. The higher water content of soil leads to a larger thaw-settlement coefficient, especially at higher salt contents, based on which an empirical equation was proposed and verified. The normalized pore water pressure during thawing was found to dissipate slower at higher salt contents, with a longer duration to stabilize. Three physical indexes were experimentally determined such as freezing point, heat conductivity and water permeability. The freezing point decreases at higher salt contents, especially as more water is involved, like the changes in heat conductivity. The water permeability maintains within the same order at the considered range of salt contents, like the development of the coefficient of consolidation. The variation of the pore volume distribution also accounts for this.

• Korean Journal of Ecology and Environment
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• v.50 no.1
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• pp.169-185
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• 2017

Physicochemical properties of water quality were analyzed to understand the long-term variations in Lake Youngrang from 1998 to 2015. Nonparametric statistical methods were applied to deduct correlation among water quality parameters and water quality trend. In total observations(N=64), the Secchi depth (SD) transparency showed significant positive correlation with salinity (r=0.458) and highly significant negative correlation with chlorophyll-a (r= -0.649) for p<0.0001 in two-tailed test of Spearman's rank correlation. Significant negative correlations of SD were observed with chemical oxygen demand (COD), total phosphorus (TP) and total nitrogen (TN). These correlation patterns were very similar in rainy (N=25) and non-rainy (N=39) periods too. Chlorophyll-a (Chl-a) had significant correlation with COD. Sen's slope test was performed along with Mann-Kendall trend test (significance ${\alpha}=0.05$, two-tailed) to find water quality trend. Positive trends were observed for SD and salinity with Sen's slopes 0.012 and 0.385, respectively (p<0.0001). Negative significant trends were observed for total nitrogen (TN) and Chl-a with Sen's slopes -0.02 (p<0.0001) and -0.346 (p=0.0010), respectively. Temperature, COD and phosphorus components had no trends. Carlson's trophic state index (TSI) for SD, TP and Chl-a were obtained in the ranges of 46~80, 37~82 and 39~82, respectively. Trophic index values suggest that Lake Youngrang was mesoeutrophic to eutrophic and there could be possibility of anoxia during the summer and dominance of blue-green algae. Excess nutrient inputs from external and internal sources were the causes of eutrophication in this lake. The findings of this study would be helpful to recognize water quality variables to manage the water body.

• Applied Microscopy
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• v.27 no.4
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• pp.433-452
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• 1997

Mongolian gerbil (Meriones unguiculatus) has been as an animal model for studing the neurological diseases such as stroke and epilepsy because of the congenital incompleteries in Willis circle, as well as the investigation of water metabolism because of the long time-survival in the condition of water-deprived desert condition, compared with other species animals. In order to accomplish the this research, first of all another divided the laboratory animals 5 groups of which each group include the 5 animals. In this study were investigated the histological structure in the kidney, measured the plasma osmolalities at the time of sacrifice of indivisual animals, and the body weights every day during water-deprived. The results obtained in this study were summarized as followings: 1. The body weights and decreasing rates of the body weight in water-deprived mongolian gerbil groups were continuosly decreased. 2. The plasma osmolalities were increased from the 5th water-deprived day, after then the gradually increasing reached nearly its equilibrium state at the 10th water-deprived day. 3. The urine volumes were abruptly decreased from the 2th water-deprived day, after then the gradually decreasing patterns were reached nearly its equilibrium state at the 10th day, and stopped the 11th day. 4. In the light microscopical observation of the kidney, glomerular capillary loop thickening, mesangial matrix increasing, sclerosis, glomerular cystic atrophy, interstitial fibrosis, tubular dilatation, mononuclear interstitial inflammation, interstitial mineralization, and hyperplasia of the collecting duct epithelium in the cortex area, were observed from the 10th water deprived day, and the lesions were gradually severe changed as the time lapse. 5. In the electron microscopical findings of the kidney, the degenerative changes of endothelial cell, podocyte and mesangial cell in glomeruli were initially observed on the 10th water-deprived day as well as the degeneration of microvilli and intracellular organelle in the renal tubules.

• Computers and Concrete
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• v.21 no.6
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• pp.697-703
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• 2018

Compressive strength is one of the most important engineering properties of concrete, and testing of the compressive strength of concrete specimens is often costly and time consuming. In order to provide the time for concrete form removal, re-shoring to slab, project scheduling and quality control, it is necessary to predict the concrete strength based upon the early strength data. However, concrete compressive strength is affected by many factors, such as quality of raw materials, water cement ratio, ratio of fine aggregate to coarse aggregate, age of concrete, compaction of concrete, temperature, relative humidity and curing of concrete. The concrete compressive strength is a quite nonlinear function that changes depend on the materials used in the concrete and the time. This paper presents an adaptive neuro-fuzzy inference system (ANFIS) for the prediction of concrete compressive strength. The training of fuzzy system was performed by a hybrid method of gradient descent method and least squares algorithm, and the subtractive clustering algorithm (SCA) was utilized for optimizing the number of fuzzy rules. Experimental data on concrete compressive strength in the literature were used to validate and evaluate the performance of the proposed ANFIS model. Further, predictions from three models (the back propagation neural network model, the statistics model, and the ANFIS model) were compared with the experimental data. The results show that the proposed ANFIS model is a feasible, efficient, and accurate tool for predicting the concrete compressive strength.

• Geomechanics and Engineering
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• v.19 no.1
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• pp.1-9
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• 2019

Shallow failures occur frequently in both engineered and natural slopes in expansive soils. Rainfall infiltration is the most predominant triggering factor that contributes to slope failures in both expansive soils and clayey soils. However, slope failures in expansive soils have some distinct characteristics in comparison to slopes in conventional clayey soils. They typically undergo shallow failures with gentle sliding retrogression characteristics. The shallow sliding mass near the slope surface is typically in a state of unsaturated condition and will exhibit significant volume changes with increasing water content during rainfall periods. Many other properties or characteristics change such as the shear strength, matric suction including stress distribution change with respect to depth and time. All these parameters have a significant contribution to the expansive soil slopes instability and are difficult to take into consideration in slope stability analysis using traditional slope stability analysis methods based on principles of saturated soil mechanics. In this paper, commercial software VADOSE/W that can account for climatic factors is used to predict variation of matric suction with respect to time for an expansive soil cut slope in China, which is reported in the literature. The variation of factor of safety with respect to time for this slope is computed using SLOPE/W by taking account of shear strength reduction associated with loss of matric suction extending state-of-the art understanding of the mechanics of unsaturated soils.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.63-67
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• 2002

The induced chemical and salt solution in water or admixture are originated to the corrosion process of the steeo rebar. These liquids penetrate into concrete as the accompanied by the chemical reaction and cause to attack the steel rebar in concrete. Concrete surfaces which it exposed to deicing, water and sea water is allowed to enter the chlorides in the structures. To prevent from the source of corrosion and deterioration Is subjected to put an end to corrode or reduce to contaminate on the steel rebar. As this reason the MCI 2022 products are applied to the surface of concrete and steel rebar. The concrete samples were made of to the kind of four, i.e. RF, MR, MS, and MM. Corrosion inhibitor is applied to coat on the surface of concrete after it had been cured for 28days. Specimen were immersed in a 3.5％ sodium chloride solution. Concrete specimen were tested to determine the changes of the resistance polarization, Rp, over a 22 weeks period. MCI 2022 is significantly shown the corrosion inhibition of steel rebar in 3.5% NaCl solution. In the each different concrete sample, MS and MM is seemed to be better than others. The results are proofed that MCI 2022 is promised to maintain the inhibition of corrosion with high resistance polarization of the steel rebar in concrete.