• Journal of the Korean GEO-environmental Society
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• v.14 no.1
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• pp.53-60
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• 2013

On this study, engineering properties of SGR method and SMI method, which are typical sodium silicate methods, were compared through the laboratory test and durability, strength, waterproof characteristic and environmental effects were compared and analyzed with period and condition of curing on each case. As a result of durability test, volume change of SGR is approximately 23-times greater than SMI and the effects on environment are appeared safe on all method. In case of waterproof characteristic test, permeability coefficient is decreased about 24% on SMI, whereas on SGR permeability coefficient is showed to increase because rapid volume change make wider void. Strength characteristics of SMI are appeared higher about 11-times in case of homogel and 3.9-times in case of sandgel than SGR. Which is because volume change of SMI, caused by leaching, is smaller than SGR.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.9 no.2
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• pp.47-58
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• 2003

To closely examine the effects of the massage treatment as one method of curing hypertension by exploring the effects that one-time circulation-centered massage has on a hypertensive's blood pressure, this study selected as the subject ten among fifty-year-old essential hypertensives visiting N clinic, and measured and compared their blood pressures before and after I gave them massage. After stabilizing them, I measured their blood pressures. In their prone and supine postures, I gave them rubbing massage for twenty minutes from positions proximal to their hearts to ones distal from their hearts to help their artery circulation and circulation-centered stroking massage for ten minutes from positions distal from their hearts to ones proximal to their hearts to help their vein circulation. After the massage, I had them rest for five minutes and measured their blood pressures. Regarding each item analyzed, I calculated the mean and standard deviation before and after the massage. The difference before and after the massage was tested by corresponding t-test and the level of significance was made p<0.05. The findings are as follows. First, systolic pressure was $157.70{\pm}7.48$ before the massage and $143.00{\pm}9.39$, which is less than before the massage, after the massage, showing statistically significant difference (p<.05). Secondly, diastolic pressure was $97.80{\pm}6.56$before the massage and $95.20{\pm}5.18$, which is less than before the massage, after the massage, not showing statistically significant difference (p<.05).

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.734-738
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• 2008

Ettringite$(3CaO{\cdot}Al_2O_3{\cdot}3CaSO_4{\cdot}32H_2O)$, one of the hydrated phase of Portland cement is usually formed in the early stage of hydration by the reaction of tricalciumaluminate$(C_3A)$ and gypsum. The rapid and strong crystal growth of separated rod-shaped ettringite have been utilized for the preparation of special cements of rapid setting, high strength and non-shrinking properties. The ettringite also has been noticed as a promising materials for the immobilization of various waste ions because of its unique crystal structure which has abundant channels and exchangeable ionic compounds. In this study, the formation and growth behavior of the ettringite was investigated in the system $C_3A-CaSO_4-H_2O$ using $C_3A$ clinker and gypsum to obtain a microporous body for waste ion immobilization. Ettringite was revealed to form by the dissolution-precipitation mechanism and the bulk body was by the entangled growth of rod-shaped ettringite crystals. The hardened body was composed of nearly pure rod-shaped ettringite interlocked each other with adequate mechanical strength. The homogeneity of structure, pore size, specific surface area and porosity of the hardened body were influenced by reaction temperature, water/powder ratio and the curing time. The hardened body prepared with water/powder ratio of 1 at $24^{\circ}C$ for one day showed excellent morphological properties for the purposed materials.

• Korean Journal of Materials Research
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• v.30 no.9
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• pp.489-494
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• 2020

SiC is a material with excellent strength, heat resistance, and corrosion resistance. It is generally used as a material for SiC invertors, semiconductor susceptors, edge rings, MOCVD susceptors, and mechanical bearings. Recently, SiC single crystals for LED are expected to be a new market application. In addition, SiC is also used as a heating element applied directly to electrical energy. Research in this study has focused on the manufacture of heating elements that can raise the temperature in a short time by irradiating SiC-I₂ with microwaves with polarization difference, instead of applying electric energy directly to increase the convenience and efficiency. In this experiment, Polydimethylsilane (PDMS) with 1,2 wt% of iodine is synthesized under high temperature and pressure using an autoclave. The synthesized Polycarbosilane (PCS) is heat treated in an argon gas atmosphere after curing process. The experimental results obtain resonance peaks using FT-IR and UV-Visible, and the crystal structure is measured by XRD. Also, the heat-generating characteristics are determined in the frequency band of 2.45 GHz after heat treatment in an air atmosphere furnace.

• Polymer(Korea)
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• v.25 no.2
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• pp.177-185
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• 2001

In this work, the cure kinetics and rheological properties of difunctional epoxy(diglycidylether of bisphenol A, DGEBA)/polysulfone (PSF) blends were investigated using differential scanning calorimeter and rheometer. From the DSC results of the blends, the temperature of the exothermic peak and cure activation energy (E) using a half-width method were increased with increasing the PSF content to neat epoxy resin up to 30 wt%. However, a marginal decrease in the blend system was shown in E. The conversion ($\alpha$) and conversion rate (d$\alpha$/dt) were decreased as the content of PSF increases. Rheological properties of the blend system were investigated under isothermal condition using a rheometer. Cross-linking activation energy (E$_{c}$) was determined from the Arrhenius equation based on gel time and curing temperature. As a result, the E$_{c}$ showed a similar behavior with E which could be resulted from high viscosity of PSF and the phase separation between DGEBA and PSF.PSF.f PSF and the phase separation between DGEBA and PSF.PSF.

• Polymer(Korea)
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• v.26 no.6
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• pp.767-777
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• 2002

In this work, biodegradable modified aliphatic polyester (MAP) in tetrafunctional epoxy (4EP) resin was investigated in terms of cure kinetics, thermal stabilities, rheological properties, and mechanical interfacial properties. DSC results of the blends show that the cure activation energies (E$\_$a/) were increased in 10 wt% of MAP compared with neat 4EP, due to the increasing intermolecular interaction between 4EP and MAP. The decomposed activation energies (E$\_$t/) derived from Coats-Redfern method, were increased within the 10∼30 wt% composition range of MAP contents, resulting from increasing the cross-linking density of the blend system. Rheological properties of the blend system were investigated under isothermal condition using a rheometer. Cross-linking activation energies (E$\_$c/) were determined from the Arrhenius equation based on gel time and curing temperature. As a result, the E$\_$c/ showed a similar behavior with E$\_$a/. The fracture toughness (K$\_$IC/) of the mechanical interfacial properties was discussed in semi-IPN behaviors of the casting specimen.

• Environmental Engineering Research
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• v.21 no.1
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• pp.15-21
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• 2016

Magnesium potassium phosphate cement (MKPC) is an effective agent for solidification/stabilization (S/S) technology. To further explore the mechanism of the S/S by MKPC, two kinds of Cd including $Cd(NO_3)_2$ solution (L-Cd) and municipal solid waste incineration fly ash (MSWI FA) adsorbed Cd (S-Cd), were used to compare the effects of the form of heavy metal on S/S. The results showed that all the MKPC pastes had a high unconfined compressive strength (UCS) above 11 MPa. For L-Cd pastes, Cd leaching concentration increased with the increase of Cd content, and decreased with the increase of curing time. With the percentage of MSWI FA below 20%, S-Cd pastes exhibited similar Cd leaching concentrations as those of L-Cd pastes, while when the content of MSWI FA come up to 30%, the Cd leaching concentration increased significantly. To meet the standard GB5085.3-2007, the highest addition of S-Cd was 30% MSWI FA (6% Cd contained), with the Cd leaching concentration of 0.817 mg/L. The S/S of L-Cd is mainly due to chemical fixation, and the hydration compound of Cd was $NaCdPO_4$, while the S/S of S-Cd is due to physical encapsulation, which is dependent on the pore/crack size and porosity of the MKPC pastes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.57-67
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• 2007

The service life of concrete structure is to a great extent influenced by crack developed at early ages of concrete material. Especially, hydration heat is a main cause of thermal cracking at mass concrete structures. The thermal cracking of massive structure is analyzed of the thermal cracking index which was presented Concrete Standard Specifications. The thesis analyzed the thermal cracking index which considered various variable (cement type, height of casting, curing condition, concrete mixing temperature, the unit cement content) at internal restricted mass concrete. The analysis result is denoted increase and decrease rate of thermal cracking index whenever the variables change. The results is helped to understand thermal cracking every time structures is designed and constructed. And I think that it is useful economic and stable design of mass concrete structures.

• Composites Research
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• v.26 no.3
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• pp.182-188
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• 2013

The purpose of this study was to measure the volumetric polymerization shrinkage kinetics and stress of a silorane-based dental restorative composite and compare it with those of conventional methacrylate-based dental composites. Two methacrylate-based composites (Z250, Z350 flowable) and one silorane-based composite (P90) were investigated. The volumetric polymerization shrinkage of the composites during light curing was measured using a laboratory-made volume shrinkage measurement instrument based on the Archimedes' principle, and the polymerization stress was also determined with the strain gage method. The shrinkage of silorane-based composites (P90) was the lowest, and that of Z350 flowable was the highest. Peak polymerization shrinkage rate was the lowest in P90 and the highest in Z350 flowable. The time to reach peak shrinkage rate of P90 was longer than those of the methacrylate-based composites. The polymerization shrinkage stress of P90 was lower than those of the methacrylate-based composites.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.1011-1018
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• 2005

The influence of liquid shotcrete accelerators(alkali aluminate, two types of alkali-free) was investigated. Comparing to the existing alkali aluminate accelerator, new alkali-free accelerator, AF2, shortened initial and final setting of cement system, and after curing for 1 day compressive strength was analogous with others. On the other hand, compressive strength of specimen cured for 12 hour was the highest by the addition of alkali aluminate accelerator, but final strength was the lowest by that. But compressive strengths of AF1, AF2 were similar to Plain up to 28day. Further from XRD(X-Ray Diffractometer) and DSC(Differential Scanning Calorimeter) analyses, we confirmed that setting promoted by alkali aluminate was mainly because of Ca(OH)2(calcium hydroxide), but the accelerating behavior of alkali-free was influenced by the needle-like ettringite$(6CaO{\cdot}Al_2O_3{\cdot}3SO_3{\cdot}32H_2O)$ crystal.