• Polymer(Korea)
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• v.29 no.2
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• pp.211-215
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• 2005

Stabilization process is absolutely necessary to convert the precursor fibers into chemically, physically, thermally and structurally stable carbon fibers. Especially, it is critically important for rayon fibers experiencing severe weight loss and thermal shrinkage occurring at the stabilization stage below $400^{\circ}C$. The stabilization of rayon fibers strongly depends not only on stabilization temperature but also on heating rate, chemical pre-treatment, atmosphere, and so on. In the present study, the weight loss, fiber diameter change occurred in the furnace during the stabilization process for rayon fibers produced with various heating rates and in the absence and presence of phosphorous-based flame retardants and the thermal stability of the stabilized fibers were investigated. The result indicates that the weight, diameter and thermal stability of the rayon fibers are significantly affected by the type and amount of the flame retardant used. It is also suggested that the pre-treatment of rayon fibers with a concentration lower than $3\;vol\%$ of phosphoric acid is most desirable for further carbonization process of stabilized rayon fibers.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.2
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• pp.97-104
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• 2012

A porous $TiO_2$ pellet was electrochemically converted to the metallic titanium by using a $CaCl_2$ molten salt system at $850^{\circ}C$. Ni-$TiO_2$ and graphite electrodes were used as cathode and anode, respectively. The electrochemical behaviour of $TiO_2$ pellet was determined by a constant voltage control electrolysis. Various reaction intermediates such as $CaTiO_3$, $Ti_2O$ and $Ti_6O$ were observed by XRD analysis during electrolysis of the pellet. Once $TiO_2$ pellet was converted to a porous metallic structure, the porous structure disappeared by sintering and shrinking with increasing the reaction time at high temperature.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.684-691
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• 2015

A sudden increase in combustion pressure is observed in the ducted rocket combustion test equipped with pipe shaped and converging nozzle exhaust tubes. This study aims to understand the physical mechanism of abrupt change in combustion pressure using thermal choking in the exhaust tube. Results confirmed that the thermal choking of the flow inside the exhaust tube was responsible for the sudden increase in combustion pressure. Also, high pressure exponent of solid propellants is critical sensitive to the occurrence of thermal choking exhaust pipe. Additionally, numerical simulation showed that the sudden increase in combustion pressure was less possible in diverging pipe because thermal choking is more reluctant to occur.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.846-850
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• 2011

Nanocomposite anodes for rechargeable lithium battery are prepared by mixing tin and nickel nanoparticles via wet method and their electrochemical properties are examined. The Sn-Ni nanocomposite anode shows a maximum discharge capacity of 700 mAh $g^{-1}$ at the first cycle but very poor cycle performance. This means that the electrode porosity and the Ni component formed by the simple mixing of nanoparticles no longer play the role of buffering the volume expansion/contraction of Sn component during charge-discharge. To solve the cycle performance problem, a novel nanostructured Sn-Ni anode should be designed and tested.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.641-647
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• 2017

In order to meet the stricter emission regulations, the proportion of after-treatments for vehicles and vessels has been increasing gradually. The objective of this study is to investigate the physicochemical properties according to ash cleaning agents of CDPF for Diesel Engines. Penetrating agents with strong penetration into ash and a surfactant component to mix water and oil were prepared properly. The cleaning characteristics of S1 sample were good. Washcoat loss rate of S1 sample was lower by about 2.2% because of less KOH component and lower Na2SiO3 content. Washcoat loss rate of S4 sample with an added KOH and Na2SiO3 components by penetration agents was increased by about 13%. In terms of less than about 13% of CDPF's washcoat loss rate, it was able to reduce the harmful gas components.

• Resources Recycling
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• v.28 no.1
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• pp.32-39
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• 2019

The present study investigated hydration of alkali activated slag incorporating sulfate as a form of anhydrite by employing thermodynamic modeling using the Gibbs free energy minimization approach. Various parameters were evaluated in the thermodynamic calculations, such as presence of sulfide, precipitation/dissolution of AFt/AFm phase, and the effect of oxic condition on the predicted reaction. The calculations suggested no significant difference in the void volume and chemical shrinkage, which might influence the performance of the mixtures, in spite of various changes of the parameters. Although the types of hydration products and their amount varied according to the input conditions, their variations were smaller range than that induced by water-to-binder ratio. Moreover, it did not affect the amount of C-(N-)A-S-H which was the most important hydration product.

• Biomedical Science Letters
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• v.2 no.1
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• pp.91-108
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• 1996

The present study was designed to examine effect of short term treadmill and weight-training on aging arophy in the rat skeletal muscle. Male rats of 24 months old were used. Each groups included control, treadmill and weight-training for 4 weeks by using treadmill apparatus and body press apparatus. The histo and cytochemical, ultrastructural and stereological changes in senile skeletal muscles of the rat were observed in the present study. During the training period the body weight and muscular weight in all groups remained constant. The volume density of muscle fiber type IIC and IIB were increased, that of type IIA was decreased, but type I remained constant in treadmill-training group. In weight-training rat, the density of type IIA and IIB were increased, both those of type IIC was decreased. But, all changes of muscle fiber type is not significant. Senile control group some usual formation of mild contraction band, liposuscin pigment and muscular splitting were observed. After treadmill-training, histological and ultrastructural changes occurred in the muscle fiber, such as irregularity of the sarcolemma, interfibrillar vacuolization, longitudinal splitting, and widened I-bond. After weight-training, the changes occurred in the trained muscle fiber, such as appearances of many lysosomes and autophagic vacuoles, severe contraction band, and breakup of myofibrils. Histo and cytochemical studies showed that the activities of succinic dehydrogenase and acid phosphatase remained constant, activities of $Mg^{++}$-ATPase decrease with training. Stereological changes were not observed in the volume and numerical density of all subject component, but the surface density of mitochondrial inner membrane was increased with treadmill-training. These experimental results suggested that endurance training during short-term may result in the adaptible response in senile skeletal muscles. On the other side, weight-training is bad for senile skeletal muscle.

• The Journal of Korean Medicine Ophthalmology and Otolaryngology and Dermatology
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• v.19 no.1
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• pp.115-122
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• 2006

기관지 천식은 가역적 기도 폐색, 호산구에 의한 만성기관지 염증 및 기관지 수축 물질에 대한 기관지 평활근의 과민반응 등 3가지 주 증상을 갖는 만성 염증성 호흡기 질환의 일종으로서 천식은 항원에 대한 노출이 과민반응으로 이어져 기도 내 염증 유발로 이어지면 조직 내 백혈구 침윤이 일어나게 되어 기도 상피세포의 손상 및 기도 폐색이 일어나게 된다. 이 때 백혈구를 혈액에서 조직으로 끌어오는 것이 chemotactic cytokine, 즉 chemokine이다. 본 실험은 사람의 폐 상피세포를 이용하여 염증유발 매개물질인 $TNF-{\alpha}$와 IL-4를 단독 혹은 병용 투여하여, 폐 상피세포에서 chemokine 중 호중구의 화학주성에 관여하는 TARC, eotaxin, RANTES의 생성을 유도하였고, 이러한 chemokine의 생성과정에서 청열소독음(淸熱消毒飮)이 미치는 영향에 대하여 연구하였다. 본 연구를 통하여 청열소독음(淸熱消毒飮)이 사람의 폐 상피세포에서 $TNF-{\alpha}$와 IL-4로 유발시킨 TARC, exotain, RANTES의 생성을 농도 의존적으로 억제하는 효과를 볼 수 있었다. 따라서 청열소독음(淸熱消毒飮)은 TARC, eotaxin, RANTES와 같은 chemokine 생성을 억제함으로써 천식을 포함한 알레르기 질환 치료 전반에 유의적인 효과를 보일 것으로 사려 된다.

• Korean Journal of Materials Research
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• v.13 no.5
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• pp.297-302
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• 2003

The effects of risering design and alloying element on the formation of defects such as external depression, primary and secondary shrinkage cavity in gray cast iron were investigated. Two types of risering design for the cylindrically step-wise specimen, No. 1(progressive solidification) and No. 2(directional solidification) risering designs, were prepared and five different alloy compositions were casted. In the No. 1 risering design, external depression or primary shrinkage cavity due to liquid contraction was observed in all the specimens from ISO 150 to ISO 350. The primary shrinkage cavity was located right under the top surface or connected to the top surface, and was characterized by smooth surface. Its size increased with an increase in ISO number. However, neither secondary shrinkage cavity nor swollen surface was observed in all the castings. In the No.2 risering design, neither primary shrinkage cavity nor secondary shrinkage cavity was observed in all the specimens due to proper risering design. A swollen surface was also not observed in all the castings with the application of pep-set mold.

• Membrane Journal
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• v.25 no.2
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• pp.171-179
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• 2015

Perfluorinated sulfonic acid ionomers (PFSAs) have been widely as solid electrolyte materials for polymer electrolyte membrane fuel cells, since they exhibit excellent chemical durability under their harsh application conditions as well as good proton conductivity. Even PFSA materials, however, suffer from physical failures associated with repeated membrane swelling and deswelling, resulting in fairly reduced electrochemical lifetime. In this study, pore-filling membranes are prepared by impregnating a Nafion ionomer into the pore of a porous PTFE support film and their fundamental characteristics are evaluated. The developed pore-filling membranes exhibit extremely high proton conductivity of about $0.5S\;cm^{-1}@90^{\circ}C$ in liquid water.