• Journal of the Korean Chemical Society
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• v.57 no.6
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• pp.703-711
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• 2013

In the present investigation, kinetic studies of oxidation of formic acid with and without catalyst and promoter in aqueous acid media were studied under the pseudo-first order conditions [formic acid]T ${\gg}[Cr(VI)]_T$ at room temperature. In the 1,10-phenanthroline (phen) promoted path, the cationic Cr(VI) phen complex is the main active oxidant species undergoes a nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition through several steps leading to the products $CO_2$ and $H_2$ along with the Cr(III) phen complex. The anionic surfactant (i.e., sodium dodecyl sulfate, SDS) and neutral surfactant (i.e., Triton X-100, TX-100) act as catalyst and the reaction undergo simultaneously in both aqueous and micellar phase with an enhanced rate of oxidation in the micellar phase. Whereas the cationic surfactant (i.e., N-cetyl pyridinium chloride, CPC) acts as an inhibitor restricts the reaction to aqueous phase. The observed net enhancement of rate effects has been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. The neutral surfactant TX-100 has been observed as the suitable micellar catalyst for the phen promoted chromic acid oxidation of formic acid.

• Computers and Concrete
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• v.27 no.3
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• pp.199-210
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• 2021

The aim of this paper was to examine the continuous and discontinuous contact problems between the functionally graded (FG) layer pressed with a uniformly distributed load and homogeneous half plane using an analytical method and FEM. The FG layer is made of non-homogeneous material with an isotropic stress-strain law with exponentially varying properties. It is assumed that the contact at the FG layer-half plane interface is frictionless, and only the normal tractions can be transmitted along the contacted regions. The body force of the FG layer is considered in the study. The FG layer was positioned on the homogeneous half plane without any bonds. Thus, if the external load was smaller than a certain critical value, the contact between the FG layer and half plane would be continuous. However, when the external load exceeded the critical value, there was a separation between the FG layer and half plane on the finite region, as discontinuous contact. Therefore, there have been some steps taken in this study. Firstly, an analytical solution for continuous and discontinuous contact cases of the problem has been realized using the theory of elasticity and Fourier integral transform techniques. Then, the problem modeled and two-dimensional analysis was carried out by using ANSYS package program based on FEM. Numerical results for initial separation distance and contact stress distributions between the FG layer and homogeneous half plane for continuous contact case; the start and end points of separation and contact stress distributions between the FG layer and homogeneous half plane for discontinuous contact case were provided for various dimensionless quantities including material inhomogeneity, distributed load width, the shear module ratio and load factor for both methods. The results obtained using FEM were compared with the results found using analytical formulation. It was found that the results obtained from analytical formulation were in perfect agreement with the FEM study.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.170-175
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• 2007

The finite volume method for forging simulation is examined to reveal its possibility as well as its problem in this paper. For this study, the finite volume method based MSC/SuperForge and the finite element method based AFDEX are employed. The simulated results of the homogeneous compression obtained by the two softwares are compared to indicate the problems of the finite volume method while several application examples are given to show the possibility of the finite volume method for simulation of upsetter forging processes. It is shown that the finite volume method can not predict the exact solution of the homogeneous compression especially in terms of forming load and deformed shape but that it is helpful to simulate very complex forging processes which can hardly be simulated by the conventional finite element method.

• The Korean Journal of Malacology
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• v.11 no.1
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• pp.70-77
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• 1995

The purpose of this study is to determine the differences of the conchiolin layer, prismatic layer and nacreous layer deposited within the shell of the freshwater family Unionidae. shether they possess species-specific characteristics and differences of the microstructure of these layers, A Scanning electron microscopic obwervations were conducted on seven species. The results indicate that all species possess thin and homogeneous layers within the periostracum. The prismatic layers of these species were composed of ednsely packed prisms. The prismatic layers of the shell in six species were typical shape of prisms. especially Inio douglasiae and Lamprotual gottschei. But, in Unio douglasiae sinuolatus, it was irregular and oblique prism shape.The nacreous layer of weven unionids characterized by possession of three types by lamillae shape: thin and homogeneous on genus Anodonta(0.4 pm size of lamella), Unio(1.3pm) and Lamprotual (1.7pm), homogeneous in shape and irregular in size of lamillae in Lanceolaria(1.0 pm)and irregulat in shape and size in Solenaia(0.2-0.4 pm). The microstructure of the naceous layer may be useful as a taxonomic character at the generic level.

• Korean Journal of Computational Design and Engineering
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• v.15 no.2
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• pp.136-143
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• 2010

Realistic Modeling is to maximize the reality of the environment in which perception is made by virtual environment or remote control using two or more senses of human. Especially, the field of haptic rendering, which provides reality through interaction of visual and tactual sense in realistic model, has brought attention. Haptic rendering calculates the force caused by model deformation during interaction with a virtual model and returns it to the user. Deformable model in the haptic rendering has more complexity than a rigid body because the deformation is calculated inside as well as the outside the model. For this model, Gibson suggested the 3D ChainMail algorithm using volumetric data. However, in case of the deformable model with non-homogeneous materials, there were some discordances between visual and tactual sense information when calculating the force-feedback in real time. Therefore, we propose an algorithm for the Volume Haptic Rendering of non-homogeneous deformable object that reflects the force-feedback consistently in real time, depending on visual information (the amount of deformation), without any post-processing.

• Structural Engineering and Mechanics
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• v.58 no.3
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• pp.423-442
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• 2016

This study considers a functionally graded (FG) elastic layer resting on homogeneous elastic substrate under axisymmetric static loading. The shear modulus of the FG layer is assumed to vary in an exponential form through the thickness. In solution, the FG layer is approximated into a multilayered medium consisting of thin homogeneous sublayers. Stiffness matrices for a typical homogeneous isotropic elastic layer and a half-space are first obtained by solving the axisymmetric elasticity equations with the aid of Hankel's transform. Global stiffness matrix is, then, assembled by considering the continuity conditions at the interfaces. Numerical results for the displacements and the stresses are obtained and compared with those of the classical elasticity and the finite element solutions. According to the results of the study, the approach employed here is accurate and efficient for elasto-static problems of FGMs.

• Journal of the Korean Mathematical Society
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• v.55 no.5
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• pp.1235-1255
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• 2018

We provide definitions for the helicoidal Killing field and the helicoid in arbitrary three-manifolds, and investigate helicoids and ruled minimal surfaces in homogeneous three-manifolds, mainly in $SL_2{\mathbb{R}}$ and Sol(3). In so doing we finish our classification of ruled minimal surfaces in homogeneous three-manifolds with the isometry group of dimension 4.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.324-329
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• 2004

As a new concept in engines and a power source for future automotive applications, the HCCI(Homogeneous Charge Compression Ignition) engine has been introduced. Essentially a combination of spark ignition and compression ignition engines, the HCCI engine exhibits low NO$_x$ and PM emissions as well as high efficiency under part load. In this research, a 4 cylinder diesel engine was converted into a HCCI engine, and propane was used as the fuel. The main parameters for this research are fuel flow rate and the temperature of the intake manifold, and the effects of such on a HCCI engine's performance and exhaust was investigated.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.797-801
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• 2003

One of the largest challenges for quantum chemistry today is to obtain accurate results for large complex molecular systems, and a variety of approaches have been proposed recently toward this goal. We have developed the ONIOM method, an onion skin-like multi-level method, combining different levels of quantum chemical methods as well as molecular mechanics method. We have been applying the method to many different large systems, including thermochemistry, homogeneous catalysis, stereoselectivity in organic synthesis, solution chemistry, fullerenes and nanochemistry, and biomolecular systems. The method has recently been combined with the polarizable continuum model (ONIOM-PCM), and was also extended for molecular dynamics simulation of solution (ONIOM-XS). In the present article the recent progress in various applications of ONIOM and other electronic structure methods to problems of homogeneous catalyses and nanochemistry is reviewed. Topics include 1. bond energies in large molecular systems, 2. organometallic reactions and homogeneous catalysis, 3. structure, reactivity and bond energies of large organic molecules including fullerenes and nanotubes, and 4. biomolecular structure and enzymatic reaction mechanisms.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.575-578
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• 2007

The objective of this study is to analyze the regionalization of point rainfall by statistical methods for regional frequency analysis of the rainfall. The rainfall data used in this study are annual maximum rainfall at 57 stations during the period of more than 30 years for 12 durations(10min, 1, 2, 3, 4, 5, 6, 8, 10, 12, 18, 24hr) in Korea. The Mann-Whitney U test, Kruskal-Wallis one-way analysis of variance of nonparametric test the principal component and the cluster analysis have been performed to analyze the regionalization of rainfall. The results of this study are as follows; (1) The region which hydrological homogeneous is accepted does not exist for whole duration in Korea. (2) The result of nonpametric test shows that hydrological homogeneous regions of point rainfall are divided by 5 regions. (3) In case of cluster analysis hydrological homogeneous regions of point rainfall are divided by 6 regions and 4 other areas.