• Interaction and multiscale mechanics
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• 제6권2호
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• pp.127-136
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• 2013

In this study, atomistic simulations are performed to study the effect of Al solute on the behaviour of edge dislocation in Mg alloys. After the dissociation of an Mg basal edge dislocation into two Shockley partials using molecular mechanics, the interaction between the dislocation and Al solute at different temperatures is studied using molecular dynamics. It appears from the simulations that the critical shear stress increases with the Al solute concentration. Comparing with the solute effect at T = 0 K, however, the critical shear stress at a finite temperature is lower since the kinetic energy of the atoms can help the dislocation conquer the energy barriers created by the Al atoms. The velocity of the edge dislocation decreases as the Al concentration increases when the external shear stress is relatively small regardless of temperature. The Al concentration effect on the dislocation velocity is not significant at very high shear stress level when the solute concentration is below 4.0 at%. Drag coefficient B increases with the Al concentration when the stress to temperature ratio is below 0.3 MPa/K, although the effect is more significant at low temperatures.

• 한국전기전자재료학회논문지
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• 제27권12호
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• pp.847-851
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• 2014

The characteristics of dielectric constant and $tan{\delta}$ of low viscosity silicone oils with changing degree of polymerization were investigated. The result shows dipole loss mechanism at low temperature range. The dielectric loss in the range of low frequencies are predominantly of ionic nature with temperature increase. The peak of dielectric loss is the detrapping of the electrons which is were trapped in the localized level of the silicone oils at the frequency of 30 kHz. The increase of ionic conduction is attributed to the presence of ionizable oxidation products and their increased dissociation feature. The activation energy ${\Delta}H$ and dipole moment ${\mu}_d$ were increased whit increasing degree of polymerization.

• Bulletin of the Korean Chemical Society
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• 제9권6호
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• pp.388-393
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• 1988

The chemisorption of CO molecules on polycrystalline nickel surface has been studied by investigating the resulting chemisorbed species with the X-ray photoelectron spectroscopy at temperatures between 300K through 433K. It is found that the adsorbed CO molecules are dissociated by the simple C-O bond cleavage as well as by the disproportionation reaction at temperatures above 373K. The former type dissociation is more favored at low coverages and at elevated temperatures. The isotherms of CO chemisorption are obtained from the xps intensities of C 1s peaks, and then the activation energy of the dissociative adsorption is estimated as a function of the CO exposure. These activation energies are extrapolated to zero coverage to obtain the activation energy of chemisorption in which thermal C-O bond cleavage takes place. The value obtained is 38.1 kJ/mol.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.529-536
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• 1991

In this paper, the question whether the curvature of the minimum energy path can affect the dynamic threshold was tested using the boundary trajectory method developed by Chesnavich and coworkers. For nonreactive system, the MO EXP model potential surface was used with modified equilibrium distance to control the curvature. The results showed that there is no relation between the curvature and the dynamic threshold. In order to study the reactive system, a generalization of the boundary trajectory method was achieved to apply on the nonsymmetric system. We have found no correspondence between the curvature and the dynamic threshold of the system. It was also shown that the fate of the trajectories strongly depends on the shape of potential surface around the turning points along the symmetric stretch line.

• Bulletin of the Korean Chemical Society
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• 제35권9호
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• pp.2774-2780
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• 2014

A dynamics study of relaxation and fragmentation of icosahedral argon cluster with a vibrationally excited $Ar_2^+$ (${\nu}$) is presented. Local translation is shown to be responsible for inducing energy flow from the embedded ion to host atoms and fragmentation of the cluster consisting of various low frequency modes. The total potential energy of $(Ar_2^+)Ar_{12}$ is formulated using a building-up procedure of host-guest and host-host interactions. The time dependence of ion-to-host energy transfer is found to be tri-exponential, with the short-time process of ~100 ps contributing most to the overall relaxation process. Relaxation timescales are weakly dependent on both temperature (50-300 K) and initial vibrational excitation (${\nu}$ = 1-4). Nearly 27% of host atoms in the cluster with $Ar_2^+$ (${\nu}$ = 1) fragment immediately after energy flow, the extent increasing to ~43% for ${\nu}$ = 4. The distribution of fragmentation products of $(Ar_2^+)Ar_{12}{\rightarrow}(Ar_2^+)Ar_n+(12-n)Ar$ are peaked around $(Ar_2^+)Ar_8$. The distribution of dissociation times reveals fragmentation from one hemisphere dominates that from the other. This effect is attributed to the initial fragmentation causing a sequential perturbation of adjacent atoms on the same icosahedral five-atom layer.

• 전기학회논문지P
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• 제56권1호
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• pp.1-5
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• 2007

Study on the electron transport coefficient in mixtures of CF4 and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for $CF_4$ and Ar, were used. The differences of the transport coefficients of electrons in $CF_4$ mixtures of Ar, have been explained by the deduced energy distribution functions for electrons and the complete collision cross-sections for electrons. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in $CF_4-Ar$ mixtures shows the Maxwellian distribution for energy. That is, $f({\varepsilon})$ has the symmetrical shape whose axis of symmetry is a most probably energy. The proposed theoretical simulation techniques in this work will be useful to predict the fundamental process of charged particles and the breakdown properties of gas mixtures. A two-term approximation of the Boltzmann equation analysis and Monte Carlo simulation have been used to study electron transport coefficients.

• Bulletin of the Korean Chemical Society
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• 제20권12호
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• pp.1493-1500
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• 1999

The electronic transitions from the ground state to low-lying excited states of CF₃OH have been investigated using high level ab initio quantum mechanical techniques. Also the possible photodissociation procedures of CF₃OH have been considered. The highest level employed in this study is TZP CCSD(T) level of theory. The possible four low-lying excited states can result by the excitation of the lone pair electron (n) in oxygen to σ$^*$ molecular orbital in C-O or O-H bond. The vertical transition (n → σ$^*$) energy is predicted to be 220.5 kcal/mol (130 nm) at TZ2P CISD level to theory. The bond dissociation energies of CF₃OH to CF₃O +H and CF₃+OH have been predicted to be 119.5 kcal/mol and 114.1 kcal/mol, respectively, at TZP CCSD level of theory. In addition, the transition state for the unimolecular decomposition of CF₃OH into CF₂O + HF has been examined. The activation energy and energy separation for this decomposition have been computed to be 43.6kcal/mol and 5.0 kcal/mol including zero-point vibrational energy corrections at TZP CCSD(T) level of theory.ed phenols were also estimated.

• 대한방사성의약품학회지
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• 제4권2호
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• pp.90-94
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• 2018

The potential health risk from inhalational exposure of diesel exhaust particulates (DEP) has gained considerable scientific interests. However, the long-term in vivo behavior of DEP have not been clearly understood due to the difficulty of accurate analysis of these substances in a living subject. We herein demonstrate a detail protocol for the preparation of radiolabeled DEP using a radioactive-iodine-tagged pyrene analog. The purified $^{125}I$-labeled pyrene ($[^{125}I]1$) was obtained with a good radiochemical yield ($32{\pm}4%$, n=3) and high radiochemical purity (>99%) from the stannylated precursor 2. Next, the purified $[^{125}I]1$ was successfully assembled into the DEP suspension in an efficient manner. The radiolabeled DEP was highly stable in a mouse serum for 7 days without significant deiodination or dissociation of $[^{125}I]1$. These results clearly indicate that the present radiolabeling method will be useful for biodistribution study of carbonaceous particulates in vivo.

• 한국수소및신에너지학회논문집
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• 제13권1호
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• pp.74-82
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• 2002

Ni nanoparticles이 표면에 분산된 mutiwall carbon nanotubes (MWNTs)의 수소저장 특성을 분석하였다. Metal nanoparticles의 분산 방법은 incipient wetness impregnation procedure을 사용하였는데, 이러한 Ni catalysts의 역할은 기존에 알려진 Li, K doping과 같은 개념으로 기상의 수소를 분해하여 carbon 표면에 chemical adsorption 시키는 역할을 하게 된다. 실제로 Ni nanoparticles이 6wt% loading된 경우에는 thermal desorption spectra를 분석한 결과 ~2.8wt% hydrogen이 ~340-520K의 온도범위에서 방출되는 것을 관찰할 수 있었다. Kissingers plot을 통해서 MWNTs와 hydrogen과 interaction energy를 구한 결과 ${\sim}31kJ/molH_2$를 얻을 수 있었으며 이 값은 기존의 SWNTs에 hydrogen이 physi-sorption에서 실험적으로 얻을 수 있었던 값보다 1.5배 큰 값이라고 할 수 있다. 자세한 수소저장 기구를 분석하기 위해서 FT-IR분석을 한 결과 C-Hn stretching vibrations이 관찰되었으며 mono-hydride와 weak di-hydride $sp^3$가 형성된 것으로 해석 될 수 있었다. 이와 같은 결과는 Ni nanoparticle들이 예상과 같이 hydrogen molecules을 dissociation하는 역할을 하는 것을 의미한다. 연속적인 thermal desorption 실험을 통해 가역성도 평가하였다.

• 전기학회논문지P
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• 제61권1호
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• pp.13-17
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• 2012

Ionization and Attachment Coefficients in pure $CH_4$, $CF_4$ and mixtures of $CF_4$ and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for $CH_4$, $CF_4$ and Ar, were used. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in $CF_4$-Ar mixtures shows the Maxwellian distribution for energy. That is, f(${\varepsilon}$) has the symmetrical shape whose axis of symmetry is a most probably energy. The proposed theoretical simulation techniques in this work will be useful to predict the fundamental process of charged particles and the breakdown properties of gas mixtures.