• Polymer(Korea)
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• v.36 no.3
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• pp.281-286
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• 2012

Experimental study was performed regarding the effects of disc-like filler orientation and contents on the coefficient of thermal expansion (CTE) of polypropylene composites using the three dimensional ellipsoids ($a_1$ > $a_2$ > $a_3$) analyzed by two aspect ratios(${\rho}_{\alpha}=a_1/a_3$and ${\rho}_{\beta}=a_1/a_2$). Measured data were compared with the theoretical approaches proposed by Lee et al. Mica and talc were useed as disk-like fillers in the composites. As experimental results, ${\alpha}_{11}/{\alpha}_m$ decreased down to ca. 0.56 with mica content of 20 wt% and the aspect ratios, ${\rho}_{\alpha}=13.5$, ${\rho}_{\beta}=1.8$. However, ${\alpha}_{33}/{\alpha}_m$ increased to more than 1. In the case of talc, ${\alpha}_{11}/{\alpha}_m$ decreased to ca. 0.63 with 20 wt% and ${\rho}_{\alpha}=3.7$, ${\rho}_{\beta}=1.4$. Finally, the longitudinal CTEs (${\alpha}_{11}$) of polypropylene composites decreased as filler contents increased, but normal CTE (${\alpha}_{33}$) increased in the low filler contents like the theory.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2708-2712
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• 2010

Amines, ammonia or 3-methoxypropylamine (MPA), are used to maintain the optimized pH for the prevention of corrosion in the secondary side of Pressurized Water Reactors (PWRs). They are differently dissociated as a function of temperature which is not same in each location of the water-steam cycle. pH at the operation temperature depends on temperature of fluid and equilibrium constants of water and amines. Thus, every amine provides the different pH in the entire secondary side so that pH is not only the sufficient parameter in corrosion control. The secondary parameter, i.e., buffer intensity, is the ability to maintain a stable pH when $H^+$ are added or removed due to the ingress of impurities or the reaction of corrosion. The buffer intensity is necessary to provide the selection criteria for the best pH control agent for secondary side and the basic understanding of the reason why the flow-accelerated corrosion(FAC) rate may demonstrate the bell-shape curve over temperature. The buffer intensities of ammonia and MPA were reviewed over the entire operation temperature of PWRs. The sufficient buffer intensity is provided for the inhibition of corrosion by ammonia in low temperature $(25{\sim}100^{\circ}C)$ and by DMA in high temperature $(150{\sim}250^{\circ}C)$. In terms of buffer intensity, i) the best pH control agent is an amine with $pK_a(T)$ range of pH(T)- $1{\leq}pK_a(T){\leq}pH(T)$ + 0.5 and ii) the amine solution should have sufficient buffer intensity, ${\beta}$ to inhibit corrosion, and iii) FAC rate may be maximum at the temperature, where ${\beta}_B/{\beta}$ ratio is lowest.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.848-854
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• 2012

We have studied the oligomerization of a fibril-forming segment of ${\alpha}$-Synulcein using a replica exchange molecular dynamics (REMD) simulation. The simulation was performed with trimers and tetramers of a 12 amino acid residue stretch (residues 71-82) of ${\alpha}$-Synulcein. From extensive REMD simulations, we observed the spontaneous formation of both trimer and tetramer, demonstrating the self-aggregating and fibril-forming properties of the peptides. Secondary structure profile and clustering analysis illustrated that antiparallel ${\beta}$-sheet structures are major species corresponding to the global free energy minimum. As the size of the oligomer increases from a dimer to a tetramer, conformational stability is increased. We examined the evolution of simple order parameters and their free energy profiles to identify the process of aggregation. It was found that the degree of aggregation increased as time passed. Tetramer formation was slower than trimer formation and a transition in order parameters was observed, indicating the full development of tetramer conformation which is more stable than that of the trimer. The shape of free energy surface and change of order parameter distributions indicate that the oligomer formation follows a dock-and-lock process.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.784-794
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• 1994

Though spodumene have a law theraml expension and good thermal shock resistance, its sintering temperature is too close to its melting point in the application for industral purpose. Solving the problems, impurities within the silicate minerals act as a frit during firing, so its densification is expected through enlargement of sintering temperature range. By the heat treatment of starting materials, mixtures of silicate mineral, lithium carbonate, if necessary SiO2 or Al2O3 were added for stoichiometric correction, in the range of 1000~125$0^{\circ}C$ for 10 hrs, $\beta$-spodumene single phase was synthesized. Mixtures with sillimanite group minerals, $\beta$-spodumene was formed at 120$0^{\circ}C$ or 125$0^{\circ}C$ via intermediate phases of petalite, Li2SiO3 and LiAlO2. For the case of kaolin group minerals, synthesis were completed at 110$0^{\circ}C$ for Hadon pink kaolin, 120$0^{\circ}C$ for New Zealand white kaolin, When pyrophyllite group minerals were used, those were at the range of 1000~125$0^{\circ}C$. Spodumene was completed at lowest temperature, 100$0^{\circ}C$ from the mixture of Wando pyrophyllite among them. Microstructure of synthesized powders showed the inrregular lump shape such as densed crystallines.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.668-673
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• 2000

Spud angle( ${\alpha}$ ) and fuel injection angle ( ${\beta}$ ) have strong influence on spud type gas burner combustion. A wide range of flame stability is shown at ${\alpha}=60^{\circ}$, but at ${\alpha}=30^{\circ}$ is narrow. Optimum condition of flame stability swirl angle( ${\gamma}$ ) is $40^{\circ}$. At condition of ${\alpha}=30^{\circ}$ flame shape is relatively narrow and long, on the other hand, at ${\alpha}=60^{\circ}$ flame is wide and short. Regardless of spud angle, maximum flame temperature shows in the range of Z=200mm and R=0mm. Flame temperature, on the whole, is high at ${\alpha}=45^{\circ}$. At ${\alpha}=45^{\circ}$, NOx emission is higher than other conditions that may be concerned with flame temperature. At ${\beta}=60^{\circ}$ and ${\gamma}=40^{\circ}$, NOx emission is reduced due to fuel injection angle.

• 한국해양학회지
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• v.28 no.1
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• pp.17-23
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• 1993

A right cylindrical tank with sloping bottom and top (${\beta}-effect$) is filled with two-layered fluid and is put on the rotating table. External fluid of same density as the lower-layer fluid is continuously injected to drive the lower-layer current. By minimizing the interfacial stress between two layers the motion in the lower-layer deformed the shape of interface such that the upper-layer adjust itself to the variations of the interface in terms of its direction of flow patterns .The most significant parameter is the internal Froude Number($F_1$) and when $F_1$ is greater than 6 two-cellular circulation of the upper-layer changes its direction, there by creates a separation of Western boundary current. The separation position moves to the most northward when $F_1$ equals to 6.

• Journal of Magnetics
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• v.9 no.4
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• pp.105-108
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• 2004

The attempt for the addition of double-phase nanocomposite $Nd_2Fe_{14}BFe_3B$ powders, respectively, into several $RE_2Fe_{14}B$(RE=Pr, Nd) powders with high magnetic properties was carried out. The powders were compounded and compressed to take shape bonded magnets. By means of investigating the variation of compound magnet $B_r$, the interaction between magnetic powders was revealed. The result shows that not chemical just but physical interaction exists between elements. The compound effect of $Nd_2Fe_{14}BFe_3B$-ferrite bonded magnets was detailed studied. The functional relation was revealed between magnetic properties and ferrite content. That is $Y = 5.42 x^2 -11.34x + 6.62$. The variation of $_iH_c$ temperature coefficient ${\beta}_{iHc}$ with ferrite content was investigated. Following the ferrite content increased, ${\beta}_{iHc}$ and $h_{irr}$ were obviously decreased, compression-resistant strength was enhanced.

• The korean journal of orthodontics
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• v.18 no.1 s.25
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• pp.155-163
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• 1988

The purpose of this study was to evaluate and compare frictional forces generated between orthodontic brackets and arch wires. Independent variables were chosen for study: arch wire size and shape, arch wire material, bracket width, and second-order angulation between bracket and arch wire. Kinetic frictional forces of stainless steel (0.014', 0.016', 0.018', 0.016' ${\times}$ 0.022', 0.018' ${\times}$ 0.022'), $\beta-titanium$ (0.016' ${\times}}$ 0.022') arch wires were measured on wide and junior edgewise twin brackets (0.018' ${\times}$ 0.022' slot). Instron was used to pull arch wires while $0^{\circ},\;3^{\circ},\;6^{\circ},\;or\;9^{\circ}$ angulation between and wire and bracket was given. The results were as follows: 1. The frictional force of $\beta-titanium$ wire was larger than that of stainless steel wire. 2. The frictional force was generally increased as the size of wire is increased. 3. The frictional force of rectangular wire was larger than that of round wire. 4. As second order angulation was increased, the frictional force was also increased. 5. The frictional force was larger on a wide bracket than on a junior bracket.

• Journal of ILASS-Korea
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• v.13 no.1
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• pp.34-41
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• 2008

Molecular dynamic simulations have been carried out to study the effect of the nano-structure substrate and its temperature on cluster laminating. The interaction between substrate molecules and liquid molecules was modeled in the molecular scale and simulated by the molecular dynamics method in order to understand behaviors of the liquid cluster on nano-structure substrate. In the present model, the Lennard-Jones potential is applied to mono-atomic molecules of argon as liquid and platinum as nano-structure substrate to perform simulations of molecular dynamics. The effect of wettability on a substrate was investigated for the various beta of Lennard-Jones potential. The behavior of the liquid cluster and nano-structure substrate depends on interface wettability and function of molecules force, such as attraction and repulsion, in the collision progress. Furthermore, nano-structure substrate temperature and beta of Lennard-Jones potential have effect on the accumulation ratio. These results of simulation will be the foundation of coating application technology for micro fabrication manufacturing.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4015-4022
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• 2012

Manganese(III) 5-(4-carboxyphenyl)-10,15,20-triphenyl porphyrin chloride (Mn(TCPP)Cl) was grafted through amide bond on silica zeolite Y (HY), zeolite beta ($H{\beta}$) and hexagonal mesoporous silica (HMS). XRD, ICP-AES, $N_2$ physisorption, SEM, TEM, FTIR and thermal analysis were employed to analyse these novel heterogeneous materials. These silica supported catalysts were shown to be used for epoxidation and good shape selectivity was observed. The effect of support structure on catalytic performance was also discussed. The catalytic activity remained when the catalysts were recycled five times. The energy changes about epoxidation of alkenes by $NaIO_4$ and $H_2O_2$ were also computationally calculated to explain the different catalytic efficiency.