• Applied Chemistry for Engineering
• /
• v.27 no.4
• /
• pp.380-385
• /
• 2016

Nanocelluloses, mainly cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC, i.e., defect-free, rod-like crystalline residues after acid hydrolysis of fibers), have been the subject of recent interest. Due to the presence of hydroxyl groups on the surface of nanocelluloses, their surfaces are reactive, making them suitable candidates for reinforcing materials for manufacturing polymer composites. In this study, CNF was used as a reinforcing material for manufacturing cement composites. CNF was prepared by TEMPO (2,2,6,6,-tetramethyl piperidine-1-oxyl radical) oxidation procedure combined with extensive homogenization and ultrasonication. Transmission electron microscopy (TEM) analysis of the suspension showed the width of CNF between 10 and 15 nm. The compressive strength of cement composites containing 0.5% CNF was comparable to that of conventional cement composites. On the other hand, the tensile and flexural strength were improved by 49.7% and 38.8%, respectively, compared to those of conventional cement composites. Also, at an ambient condition, the degree of self-shrinkage reduction reached to 18.9% in one day, followed by 5.9% in 28 days after molding.

• Applied Chemistry for Engineering
• /
• v.10 no.5
• /
• pp.789-795
• /
• 1999

In this study, carbon fiber reinforced cement composites(CFRCs) reinforced with short noncircular type carbon fibers were fabricated and properties(drying shrinkage, resistance to freezing and thawing, and fracture toughness) were compared with those of the CFRCs reinforced with circular type carbon fibers. It was found that these properties greatly depended on the shape and length of carbon fibers. The drying shrinkage of CFRCs reinforced with C-type carbon fiber was superior to other CFRCs. This effect was increased with a high aspect ratio of fiber. The resistance to freezing and thawing was increased with the fiber length and fiber volume percent, but there was on remarkable effect to fiber shape. Fracture toughness and resistance to crack propagation of CFRCs reinforced with C-CFs were improved compared with other CFRCs. It was believed that the more absorption of fracture energy into the larger interface caused an increase in fracture toughness and resistance to crack propagation.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.3
• /
• pp.235-242
• /
• 2016

As for a possibility of using high volume of recycled aggregate in concrete mixture, recycled fine one which is known to be worse in quality and hard to control was selected and investigated in terms of performance of mortar as the replacement ratio to natural fine aggregate was changed. As a result of test, it is found that grade of recycled fine aggregate was beyond standard one and fineness modulus of that itself was increased in compare to natural one. In case of making mortar with recycled fine aggregate, disadvantageous results such as less fluidity and air content including the increase of dry shrinkage were shown but strengths of mortar were comparable to the one making with natural aggregate, which means that planned strength of common concrete structure can be achieved by controlling W/C and the amount of chemical admixture, and also that large amount of recycled fine aggregate is applicable to the precast concrete products generally free to the amount of water.

• Applied Chemistry for Engineering
• /
• v.16 no.3
• /
• pp.422-426
• /
• 2005

Visible-light activated polymer nanocomposites (PNC) were designed to be used for dental restoration. Hybrid-filler composed of barium silicate and nano-sized silica was adopted as a filler system. To improve the interfacial be havior of the resin matrix of bisphenol A glycerolate methacrylate/triethyleneglycol dimethacrylate, the surface of filler was hydrophobically treated with a silane coupling agent. Mechanical properties of PNC were investigated by measuring the abrasion resistance, and it was discovered that PNC showed excellent properties with an increase of nanofiller content. However, the polymerization shrinkage was consistently maintained under 3 vol% and the shrinkage continued even after photo-polymerization. In addition, a slight color difference between PNC specimens was observed with increase of nanofiller content.

• Magazine of the Korea Concrete Institute
• /
• v.9 no.1
• /
• pp.115-121
• /
• 1997

This study deals with the suppressing characteristics of alkali-silica reaction by ground granulated blast-furnace slag(GGBS) in NaCl solution. NaCl contents used in the experiment ranges over 0%, 2.8% and 20%. Reactive aggregate used is Japanese andesite. Also, three GGBSs of about 4.000. 6, 000 and $8, 000cm^2/g$ were used in the experiment. The replacement proportions of portland cement by GGBSs were 40%. 60%, 70% and 80%. respectively. The specimens with GGBS were severely contracted according to the increasing replacement ratio in NaCl solution. The contraction rate increases according to the increasing in NaCl content. Also. it does with increasing the blaine fineness of GGRS. It is concluded that the suppression of alkali-silica reaction by GGBS in NaCl solution is complished by contraction of GGBS due to chloride ion induced chemical shrinkage.

• Korean Journal of Acupuncture
• /
• v.23 no.3
• /
• pp.73-80
• /
• 2006

목 적 : 씨클로포스파미드(Cyclophosphamide, CP)는 많은 종양 질환에서 단독 혹은 다른 화학요법과 함께 사용되는 항암제이다. CP의 독성과 부작용으로 출혈성 방광염이 많은 문제를 일으키고 있다. CP로 유도된 방광염 모델은 하부요로의 통증질환을 이해하기 위한 내장성 통증의 주요한 모델로 사용되고 있다. 본 연구는 암컷 백서에서 CP로 유도된 방광의 과활동성에 대한 침의 효과를 관찰하기 위해 요류역학검사를 수행하였다. 방 법 : CP (200 mg/kg) 투여 18시간 후에, 지속적 생리식염수 관류 (분당 0.04 ml) 로 방광내압 측정을 통해 방광기능을 평가하였다. 관류 2시간 이후부터, 위중/곤륜 100 Hz, 위중/곤륜 2 Hz, 족삼리/삼음교 100 Hz, 족삼리/삼음교 2Hz 전침 자극을 하여 자침 전후의 방광수축간격(intercontraction interval, ICI)을 비교하였다. 결 과 : 방광내압 측정하는 동안, 방광수축간격은 CP로 유도된 방광염 모델에서 정상군에서 보다 유의하게 짧았다. CP로 유도된 방광염 모델에서, 위중/곤륜 100Hz 전침 자극은 자침 전보다 통계적으로 유의하게 $40.6\;{\pm}\;10.9\;%$ 증가시켰고, 2Hz 전침 자극은 자침 전보다 현저하게 $22.1\;{\pm}\;13.7\;%$ 증가시켰다. 반면에, 족삼리/삼음교 전침 자극은 100Hz, 강 2Hz 전침 자극 각각 $13.7\;{\pm}\;8.1\;%,\;8.7\;{\pm}\;4.5\;%$ 약간 증가시켰다. 결 론 : 족태양방광경의 경혈에 100Hz 전칩 자극을 하여 CP로 유도된 방광의 과활동성을 억제하였다. 이러한 결과는 침 자극으로 CP로 유도된 혹은 다른 종류의 방광염을 치료하는데 효과적일 것임을 시사한다. 또한, 특정 경락의 경혈과 해당 장부의 질환의 치료에 연관성을 보여준다.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.6
• /
• pp.176-181
• /
• 2018

Concrete structures are degraded physically and chemically due to various reasons after construction. Because the deterioration of concrete structure reduces the service life, reasonable repair and maintenance techniques are needed. Recently, in order to efficiently repair concrete structures, many researches on hybrid repair materials having improved adhesion performance have been carried out actively. In this study, we developed a hybrid repair material containing rapid hardening cement, PVA powder, nylon fiber, and latex to improve adhesion and water-tightness of existing concrete. The compressive strength, drying shrinkage and the adhesion strength test were carried out to evaluate the performance of the repair material. In addition, the flexure bond performance was evaluated before and after repair. From the results, the bending strength was 110% ~ 150% in all specimens except for the specimen containing only the rapid hardening cement, and all the specimens behaved with the existing concrete in the crack pattern generated by the bending strength.

• Polymer(Korea)
• /
• v.36 no.1
• /
• pp.93-97
• /
• 2012

Heat treatment effect of polyethylene (PE) separators was investigated after storage at 80, 100 and $120^{\circ}C$ for 1 h. All the samples showed enhanced tensile strength and modulus after heat treatment, but thermal shrinkage up to 15% was observed in PE films having newly formed dimple structure on the surface of fiber after annealed at 100 and $120^{\circ}C$. Although there was 5% of thermal shrinkage after annealing at $80^{\circ}C$, no such serious changes in PE fiber was observed. Furthermore, the separator was found to have enhanced cell performance with 1.3 and 2.3 times higher tensile strength and modulus after heat treatment at $80^{\circ}C$ for 1 h.

• Tuberculosis and Respiratory Diseases
• /
• v.46 no.5
• /
• pp.697-708
• /
• 1999

Background : Leukotriene (LT) $C_4$, $D_4$, and $E_4$, the main components of slow-reacting substance of anaphylaxis (SRS-A), have been suggested to play an important role in bronchial asthma such as antigen-induced bronchoconstriction, airway hyperreactivity, and pulmonary eosinophil accumulation. The purpose of this study was to evaluate the effects of treatment with the cysteinyl-LTs (cys-LTs) antagonist, pranlukast on allergen-induced guinea pig asthma model. Methods : Guinea pigs of treatment and placebo groups were sensitized by subcutaneous injection of ovalbumin(OVA) and challenged by inhalation of aerosolized OVA (1% weight/volume OVA). Normal control group did not sensitize with OVA. Oral ingestion of pranlukast and normal saline to the treatment and placebo groups was performed. In the treatment and placebo groups, airway resistance was measured before and after oral ingestion. Serum $LTC_4$ and eosinophilic infiltration of the bronchiolar and peribronchiolar tissues were measured after ingestion in the treatment and placebo groups. Results : Allergen-induced airway constriction developed in 20 (8 in treatment group, 12 in placebo group) among 35 guinea pigs. Airway resistance was significantly decreased at 3 and 6 minutes after OVA challenge in the pranlukast treatment group. In the placebo group, there was no difference of airway resistance between before and after saline ingestion. Serum $LTC_4$ levels showed 348.4 pg/ml in the treatment group, 373.9 pg/ml in the placebo group, and 364.4 pg/ml in the control group. There were no statistically significant difference between treatment and placebo group (p=0.232), and treatment and control group (p=0.501). Eosinophilic infiltrations in the peribronchiolar region per one-microscopic field ($\times$400 high power fields) demonstrated 7.06 in the treatment group, 19.2 in the placebo group, and 4.50 in the control group. There was significant decrement of eosinophilic infiltration in the treatment group which was compared with placebo group (p=0.001). Conclusion : These results demonstrate that pranlukast, a cys-LTs receptor antagonist, can attenuate allergen induced early-phase bronchoconstriction and eosinophilic infiltration in the bronchiolar tissues.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.11
• /
• pp.65-73
• /
• 2005

The compressible flow of reactive fluid is investigated by using the transonic small-disturbance (TSD) model and the one-step first-order Arrhenuis chemical reaction. The fluid flow is restricted to dilute premixed reactions with small heat release. The effects of channel shape and Mach number on transonic combustion are studied by numerical analysis. The results show that the channel divergence increases the chemical reaction within the given channel length whereas the channel convergence inhibits the chemical reaction near the outlet and that increasing the inlet flow Mach number at a fixed reaction rate causes the flow acceleration in a diverging channel and the appearance of weak shock waves which do not show in the inert flow case. It also helps to increase the pressure and temperature near the diverging channel outlet and to consume the reactant within the given channel length.