• Bulletin of the Korean Chemical Society
• /
• v.16 no.12
• /
• pp.1203-1208
• /
• 1995

Theoretical studies of the effect of the nonleaving group (RY) on the breakdown mechanism of the tetrahedral anionic intermediate, T-, formed by the addition of a less basic phenoxide nucleophile (X) to phenyl benzoates with a more basic phenoxide leaving group (Z) have been carried out using the PM3 MO method. The identity acyl transfer reactions (X=Z) are facilitated by an electron-withdrawing RY whereas they are inhibited by an electron-donating RY group. The results of non-identity acyl transfer reactions indicate that a more electron-donating RY group leads to a greater lowering of the higher barrier, TS2, with a greater degree of bond cleavage, and a greater negative charge development on the phenoxide oxygen atom, whereas the opposite is true for a more electron-withdrawing RY group, i.e., leads to a greater lowering of the lower barrier, TS1. The results provide theoretical basis for the signs of ρXY(>0) and ρYZ(<0) observations.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.6
• /
• pp.1985-1992
• /
• 2011

The stable conformers of glycine and the inter-conversions between them were studied theoretically at various levels of theory, B3LYP, MP2, CCSD and CCSD(T), in the gas phase and in aqueous solution. In aqueous solution, the structures examined by use of the conductor-like polarizable continuum model (CPCM) with various cavity models, UA0, UAHF, UAKS, UFF, BONDI and PAULING, and by use of a discrete/continuum solvation model with eight water clusters. The Gibbs free energy differences between the neutral (NE) and zwitterionic conformers (ZW), ${\Delta}G_{Z-N}[=G_{ZW}-G_{NE}]$, in aqueous solution were well reproduced by using the BONDI and PAULING cavity models. However the ${\Delta}G_{Z-N}$ values were underestimated in other cavity models, although the ZW conformers existed as stable species in aqueous solution. In the studies of a discrete/continuum solvation model with eight water clusters, gas phase results are still insufficient to reproduce the experimental findings. However the ${\Delta}G_{Z-N}$ values calculated by use of CPCM method in aqueous solution agreed well with the experimental ones.

• Proceedings of the KIEE Conference
• /
• 1992.07b
• /
• pp.649-652
• /
• 1992

ECR(Electron Cyclotron Resonance) occure at ${\omega}_c$=${\omega}$, ${\omega}_c$:electron cycltron frequency, ${\omega}$:electromagnetic wave frequency. ECR system have several merit, 1) power transefer efficiency 2) low neutral gas pressure (below 1 mTorr) 3) high plasma density($10^{12}$ $cm^{-3}$). It is applicated variously in the field of semiconductor and new materials as the manufacturing equipment. Magnetic field in ECR system contruct resonance layer (${\omega}$=2.45GHz, $B_z$=875 Gauss) and control plasma. Plasma is almost generated at resonance layer. If the distance between substrate and resonance layer is short, uniformity of plasma is related with profile of resonance layer. Plasma have the property "Cold in Field", so directonality of magnetic field is one of the control factors of anisotropic etching. In this study, we calculate B field and flux line distribution, optimize geometry and submagnet current and improve of magnetic field directionality (99.9%) near substrate. For the purpose of calculation, vector potential A(r,z) and magnetic field B(r,z), green function and numerical integration is used. Object function for submagnet optimization is magnetic field directionality on the substrate and Powell method is used as optimization skim.

• Asian-Australasian Journal of Animal Sciences
• /
• v.14 no.1
• /
• pp.41-47
• /
• 2001

Ruminal degradation characteristics of dry matter (DM), neutral detergent fiber (NDF) and crude protein (CP) in fresh leaves of two Japanese native grasses (Zoysia japonica and Miscanthus sinensis) and one sown temperate grass (Dactylis glomerata) were investigated by an in sacco method in spring (mid-May), summer (mid-July) and autumn (mid-September). Japanese native grasses had higher NDF and lower CP concentrations than D. glomerata, and the CP concentration in native grasses decreased in autumn. Ruminal degradability of DM, NDF and CP was lower in native grasses than in D. glomerata (p<0.05) in all seasons. DM and NDF degradability decreased in summer for Z. japonica and D. glomerata, while it decreased in autumn for M. sinensis. CP degradability in Z. japonica was constant throughout the seasons, whereas that in M. sinensis greatly decreased in summer and autumn (p<0.05). It was concluded that Z. japonica could stably supply ruminally digestible nutrients for grazing animals in Japanese native pasture. However, the degradation characteristics of freshly chopped native grasses did not fit the exponential model of $D=a+b(1-e^{-ct})$ proposed by Ørskov and McDonald.

• Computers and Concrete
• /
• v.16 no.4
• /
• pp.625-642
• /
• 2015

Prestressed concrete bridges with corrugated steel webs have emerged as one of the promising bridge forms. This structural form provides excellent structural efficiency with the concrete flanges primarily taking bending and the corrugated steel webs primarily taking shear. In the design of this type of bridges, the flexural ductility and deformability as well as strength need to be carefully examined. Evaluation of these safety-related attributes requires the estimation of full-range behaviour. In this study, the full-range behaviour of beam sections with corrugated steel webs is evaluated by means of a nonlinear analytical method which uses the actual stress-strain curves of the materials and considers the path-dependence of materials. In view of the different behaviour of components and the large shear deformation of corrugated steel webs with negligible longitudinal stiffness, the assumption that plane sections remain plane may no longer be valid. The interaction between shear deformation and local bending of flanges may cause additional stress in flanges, which is considered in this study. The numerical results obtained are compared with experimental results for verification. A parametric study is undertaken to clarify the effects of various parameters on ductility, deformability and strength.

• The Journal of Korean Academy of Prosthodontics
• /
• v.45 no.1
• /
• pp.21-33
• /
• 2007

Statement of problem: The esthetic component of dental care has become increasingly more important, while new tooth-colored materials are continually marketed. Various new indirect composite materials have been developed with required advantages. The most recent development in the indirect composites has been the introduction of the second-generation laboratory composite or poly-glass materials. They are processed by different laboratory techniques based on combinations of heat, pressure, vacuum and light polymerization. Although, second generation products became available in 1995, their characteristics and clinical performance have not been adequately investigated. Purpose: The aim of this study was to measure the mechanical properties of the second generation indirect resin system and compare these with an existing universal direct composite resin. Material and method: In this study four indirect composite material (Adoro LC, BelleGlass HP, Tescera, Synfony) were tested for flexural strength, wear resistance, hardness and their degree of conversion against Z250, a light cure direct composite. Results: Within the limitations of this study, the following conclusions were drawn: 1. From the abrasion wear result, Adoro showed the least volume loss while Synfony showed the greatest volume loss. Z250 and BelleGlass HP didn't show significant difference (p>0.05), but they showed significant difference with other groups (p<0.05). From the attrition wear, BelleGlass HP showed the least volume loss and it didn’t show significant difference with Tescera (p>0.05). While Synfony showed the greatest volume loss that it showed significant difference with other groups (p>0.05). 2. Mean values of flexural strength by means of three point bending test was in the order of Z250, Adoro, Belleglass HP, Tescera and Synfony. Mean elastic modulus was in the order of Z250, BelleGlass HP, Tescera, Adoro and Synfony. 3. The result of Vicker‘s microhardness value showed that significantly higher value in Z250 (p<0.05), and is in the order of BelleGlass HP, Tescera, Adoro and Synfony. 4. The degree of conversion measured by FT-IR showed significantly higher value in BelleGlass HP (p<0.05), and is in the order of Adoro, Synfony, Tescera and Z250. Conclusion: Significant differences were found in the flexural strength, wear resistance, hardness and their degree of conversion.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2005.07b
• /
• pp.1012-1015
• /
• 2005

We have developed the technique of fabricating triode structure with simple stacking method using a polymer insulator that is suitable for large panel and the activation method after the fabrication. By the techniques, a test panel was manufactured and proves good emission property and uniformity.

• Journal of the Speleological Society of Korea
• /
• no.71
• /
• pp.13-17
• /
• 2006

New methods of nano sized material and composite coating preparations have been considered on the base of mathematical model of abrasion reaction interaction of milling and grinding bodies in planetary centrifugal mill. The essence of the method is the abrasive and oxidative wear of the milling bodies and amorphous (better inert) additives. Interactions between them has been supplied the necessary impulse of pressure and temperature on the impact frictional contacts and promoted chemical processes. The offered method can find application for such processing as sintering and geological minerals opening.

• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.1
• /
• pp.135-142
• /
• 2002

Input shaping is a method for reducing residual vibration in computer controlled machines. Vibration is eliminated by convolving a sequence of impulses, an input shaper, with a desired system command to produce a shaped input. This paper shows the shape of sensitivity curve of input shaper as impulse interval T and analysis of robustness for input shaper on the z-plane. And a method is presented for designing equivalent input shaper considering sampling time $T_s$. And then we applied equivalent input shaper to crane system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.3
• /
• pp.421-434
• /
• 1995

A new instantaneous flowmeter for hydraulics by means or cylindrical chokes is developed. In this method the instantaneous flowrate through chokes is predicted in real time from measurement of pressure difference on both sides of cylindrical choke. The experimental study for the flowrate of pulsating flow in a pipe is carried out to measure differential pressure drop by using a strain gauge pressure transducer with data acquisition and processing system. A pulsating flow is verified by a visualization method. In the present study, the flow characteristic variables of laminar pulsating flow are investigated analytically and experimentally in a circular pipe. Characteristic parameters of ratio of inertia term to pressure term($\phi_{t.1}$) and ratio of viscous term to pressure term($\phi_{z.1}$) are introduced to describe the flow pattern of laminar pulsating flow.