• Nuclear Engineering and Technology
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• 제33권3호
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• pp.298-306
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• 2001

As fuel burnup proceeds, thermal gradients, differential swelling, and inter-assembly loading may induce assembly duct bowing. Since duct bowing affects the reactivity, such as long or short term power-reactivity-decrement variations, handling problem, caused by top end deflection of the bowed assembly duct, and the integrity of the assembly duct itself. Assembly duct bowing were first observed at EBR-ll in 1965, and then several designs of assembly ducts and core restraint system were used to accommodate this problem. In this study, NUBOW-2D KMOD was used to analyze the bowing behavior of the assembly duct under the KALIMER(Korea Advanced Liquid MEtal Reactor) core restraint system conditions. The mechanical behavior of assembly ducts related to several design parameters are evaluated. ACLP(Above Core Load Pad) positions, the gap distance between the ducts, and the gap distance between the duct and restraint ring were selected as the sensitivity parameter for the evaluation of duct deflection.

• 한국식품영양과학회지
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• 제32권7호
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• pp.1046-1052
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• 2003

Viscoelastic behavior of oxidized starch gel, modified with sodium hypochlorite (NaOCl) and the adding effects of protein in oxidized starch gel was studied by dynamic viscoelastic measurement. The storage modulus(G′) of starch gel increased with the increase of starch concentration. They showed higher value when starch suspension was treated to 95$^{\circ}C$ rather than 85$^{\circ}C$. Consistency of starch gel was decreased over 1.0% active Cl/g starch when heated to 95$^{\circ}C$, which means that the swelling of starch granules increased with concentration of NaOCl and showed more sensitive against shear. As the extent of oxidation increased, starch granules were easily destroyed. Therefore, it is hard to separate between compartment of leached-out amylose and that of amylopectin, which means that the ability of gel formation was reduced. When oxidized starches were gelatinized in presence of soy protein and sodium caseinate, it was found that G′ decreased, and frequency dependence of G′ and G" increased with the increased degree of oxidation in starch. The reduce of starch-protein interaction was thought to be through the dissociation of the branched amylopectin, which playa leading role in protein interaction, with the oxidation of starch.

• Structural Engineering and Mechanics
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• 제50권5호
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• pp.605-616
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• 2014

When the periodic cellular structure is loaded or swelling beyond the critical value, the structure may undergo a pattern transformation owing to the local elastic instabilities, thus leading to structural collapse and the structure changing to a new configuration. Based on this deformation-triggered pattern, we have proposed the novel composite gel materials. This designed material is a type of architectural material possessing special mechanical properties. In this study, the mechanical behavior of the composite gel periodic structure with various gel inclusions is studied further through numerical simulations. When pattern transformation occurs, it results in a different elastic relationship compared with the material at untransformed state. Based on the obtained nominal stress versus nominal strain behavior, the Poisson's ratio and corresponding deformed structure patterns, we investigate the performance of designed composite materials and the effects of the uniformly distributed gel inclusions on composite materials. A better understanding of the characteristics of these composite gel materials is a key to develop its potential applications on new soft machines.

• 폴리머
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• 제26권4호
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• pp.523-534
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• 2002

약 60-$130^{\circ}C$의 온도범위에서 cholesteric 반사색깔을 나타내는 새로운 히드록시프로필셀룰로오스 (HPC)와 에스테르화도 (DE)가 1-3 범위의 값을 갖는 HPC의 아크릴산 에스테르들 (ESs)을 제조하였다. 또한 DE가 2 이상인 ESs가 $50^{\circ}C$에서 나타내는 열방성 cholesteric 상에 UV광을 조사시킴에 의해 광학 pitch ($\lambda_m$)가 전 가시광 파장영역에 존재하는 ES 가교필름들을 제조하였다. 미가교와 가교시료들에 대한 열 및 광학 특성과 아세톤 중에서의 가교필름의 팽윤거동을 검토 하였다. HPC 자체와 동일하게 ESs의 $\lambda_m$은 온도가 증가함에 따라 증가하였다. 그러나 동일한 온도에서 나타내는 $\lambda_m$은 ES가 HPC에 비해 크며 ES의 $\lambda_m$은 DE가 증가함에 따라 감소하였다. 가교시료들의 $\lambda_m$의 온도의존성은 ESs에 비해 대단히 약하였다. 또한, ESs는 DE가 증가함에 따라 낮은 액정상에서 등방상의 액체로의 전이온도를 나타내는 것과는 판이하게, 가교물질들은 액체상으로의 전이를 일으키지 않으며 약 $210^{\circ}C$에서 분해가 일어나는 것으로 나타났다. 가교필름들은 이방성 팽윤을 나타내었으며, 이러한 사실은 ES분자들간에 2차원적인 가교가 우선적으로 일어남을 시사한다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제6권4호
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• pp.274-278
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• 2001

Polymer membranes composed of N, N-dimethylaminoethyl methaccrylate(DMAEMA) and acrylamide(AAm)(or ethyl acrylamide(EAAm) were prepared to demonstrated the thermo-control of solute permeation. Poly DMEMA has a lower critical solution temperature(LCST) at around 50$\^{C}$ in water, With the copolymerization of DMAEMA with AAm (or EAAm) a shift in the LCST to a lowere temperature was observed, probably due to the formation of hydrogen bonds between the amide and N-N-dimethylamino groups. However, the temperature-induced phase transition of poly(DMAEMA-co-EAAm) did not show a similar trend to that of poly(DMAEMA- co-AAm) in the gel state. The hydrogen bonds in poly(DMAEMA-co-EAAm) were significantly disrupted with the formation a gel network, which led to a difference in the swilling behavior of polymer gels in response to temperature. To apply these polymers to temperature-sensitive sol-ute permeation, polymer membranes were prepared. The permeation pattern of hydrocortisone, used as the model solute, was explained based on the temperature-sensitive swelling behavior of the polymer membranes.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.1156-1167
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• 2010

The constant rate of strain (CRS) consolidation test has been widely used to evaluate consolidation characteristics of soils instead of the standard Incremental Loading Test. In practical problems, after the ground improvement, the condition of the soil is over-consolidated. Therefore, it is important to determine the recompression indices and the coefficient of consolidation(or the coefficient of swelling) of unloading-reloading cycle to predict the settlement behavior. However, since standard testing procedures or studies related with strain rate are insufficient especially in unloading-reloading cycle, it is difficult to predict the settlement field behavior accurately from the CRS consolidation test results in spite of its lots of strengths. The several CRS consolidation tests were performed changing the unloading strain rate from 0.2%/hr to 20%/hr with vertical drainage condition using the reconstituted kaolinite sample. For the reconstituted kaolinite sample in CRS consolidation test, the recompression indices are insensitive to the strain rate. It is revealed that the coefficient of consolidation of reloading is affected by the developed pore pressure during unloading. Additionally, the test should be conducted in the positive pore pressure ratio range (3~15%) to obtain the reasonable coefficient of consolidation in the whole range(loading, unloading and reloading).

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.51.2-51.2
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• 2011

A novel electrospun nanofiber membrane was fabricated using combined poly (vinylphosphonic acid) (PVPA) and polyvinyl alcohol (PVA) intended for bone tissue engineering applications. PVPA is a proton-conducting polymer used as primer for bone implants and dental cements to prevent corrosion and brush abrasion. The phosphonate groups of PVPA have the ability to crosslink and attach itself to the hydroxyapatite surface facilitating faster integration of the biomaterial to the bone matrix. PVA was combined with PVPA to provide hydrophilicity, biocompatibility and improve its spinnability. To improve its mechanical strength, PVPA/PVA and neat PVA mixtures were combined to produce a multilayer scaffold. The physical and chemical properties of the of the fabricated matrix was investigated by SEM and TEM morphological analyses, tensile strength test, XRD, FT-IR spectra, swelling behavior and biodegradation rates, porosity and contact angle measurements. Biocompatibility was also examined in vitro by cytotoxicity and cell proliferation studies with MTT assay and cell adhesion behavior by SEM and confocal microscopy.

• Carbon letters
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• 제13권3호
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• pp.173-177
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• 2012

A drug delivery system (DDS) was prepared with a temperature and pH-responsive hydrogel. Poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAAc)/poly(N-isopropylacrylamide) (PNIPAAm)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by radical polymerization for the temperature and pH-responsive hydrogels. MWCNTs were employed to improve both the thermal conductivity and mechanical properties of the PVA/PAAc/PNIPAAm/MWCNT nanocomposite hydrogels. Various amounts of MWCNTs (0, 0.5, 1 and 3 wt%) were added to the nanocomposite hydrogels. PVA/PAAc/PNIPAAm/MWCNT nanocomposite hydrogels were characterized with a scanning electron microscope. The mechanical properties were measured with a universal testing machine. Swelling and releasing properties of nanocomposite hydrogels were investigated at various temperatures and pHs. Temperature and pH-responsive release behavior was found to be dependent on the content of MWCNTs in nanocomposite hydrogels.

• 대한의용생체공학회:의공학회지
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• 제41권1호
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• pp.1-7
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• 2020

Polyvinyl alcohol (PVA)/gelatin hydrogels were prepared by repeating freezing/thawing three times to evaluate the influence of PVA concentration on the strength and the cell growth behavior of the PVA/gelatin hydrogels. The swelling rate of the PVA/gelatin hydrogels decreased with raising the PVA content from 6 wt% to 12 wt% due to the formation of 3-D network inside the hydrogel. No appreciable degradation of the hydrogels was detected. As the PVA content increased from 6 wt% to 12 wt%, the strength of the PVA/gelatin hydrogels increased drastically from 6.4±0.9 kPa to 46.6±9.0 kPa. The PVA/gelatin hydrogels did not show any evidence of causing cell lysis or toxicity, implying that the hydrogels are clinically safe and effective. Although the strength increased with increasing the PVA content, the PVA/gelatin hydrogels containing 8 wt% exhibited the fastest cell growth, which is highly suitable for wound dressing requiring fast healing regeneration.

• Preventive Nutrition and Food Science
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• 제13권3호
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• pp.249-252
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• 2008

Flow behaviors of sweet potato starch (SPS) pastes (5% w/w) were studied in the presence of various sugars (xylose, glucose, fructose and sucrose) and sugar alcohols (xylitol and sorbitol). The flow properties of SPS-sugar mixtures were determined from the rheological parameters of power law model. The vane method was also employed for determining yield stresses of SPS-sugar mixtures directly under a controlled low shear rate. At $25^{\circ}C$ all the samples showed shear-thinning behaviors ($n=0.35{\sim}0.44$) with yield stress. The consistency index (K) values of SPS-sugar mixtures increased in the following order: sorbitol> xylitol> control (no sugar)> sucrose> fructose> glucose> xylose, showing that the addition of sugar alcohols enhanced the K values. The yield stress values were reduced in the presence of ugars and sugar alcohols and they also increased with an increase in swelling power of starch granules in the SPS-sugar mixture systems.