• Bulletin of the Korean Chemical Society
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• 제33권5호
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• pp.1722-1728
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• 2012

During the analyzing processes of the compounds, some researchers are puzzled by the analytical signals for some TSNAs (with or without splitting peaks at various pHs and temperatures). In this work, a detailed theoretical study of structural and thermal properties of the $E/Z$ isomers of TSNAs and the corresponding protonated structures was performed using DFT methods. The calculations showed that the $E$ isomers are almost stable than $Z$ isomers, while the $Z$ isomers would be more stable when in protonation. The calculated results predicted the possibility of separation of their $E$ and $Z$ isomer forms and also showed that protonation affects the dipole moment of molecules significantly (0.1-0.5 to 0.7-2.1 Debye). The calculations agreed well with the experiments that the split-up of the HPLC signal for TSNAs into two peaks are very sensitive to the pH and temperature of the mobile-phase.

• Korean Journal of Materials Research
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• 제21권2호
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• pp.73-77
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• 2011

Specific heat of a crystal is the sum of electronic specific heat, which is the specific heat of conduction electrons, and lattice specific heat, which is the specific heat of the lattice. Since properties such as crystal structure and Debye temperature do not change even in the superconducting state, the lattice specific heat may remain unchanged between the normal and the superconducting state. The difference of specific heat between the normal and superconducting state may be caused only by the electronic specific heat difference between the normal and superconducting states. Critical temperature, at which transition occurs, becomes lower than $T_{c0}$ under the influence of a magnetic field. It is well known that specific heat also changes abruptly at this critical temperature, but magnetic field dependence of jump of specific heat has not yet been developed theoretically. In this paper, specific heat jump of superconducting crystals at low temperature is derived as an explicit function of applied magnetic field H by using the thermodynamic relations of A. C. Rose-Innes and E. H. Rhoderick. The derived specific heat jump is compared with experimental data for superconducting crystals of $MgCNi_3$, $LiTi_2O_4$ and $Nd_{0.5}Ca_{0.5}MnO_3$. Our specific heat jump function well explains the jump up or down phenomena of superconducting crystals.

• Korea-Australia Rheology Journal
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• 제16권1호
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• pp.17-26
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• 2004

We examine rigorous computations on microstructural as well as rheological properties of concentrated dispersions of bidisperse colloids. The NVT Monte Carlo simulation is applied to obtain the radial distribution function for the concentrated system. The long-range electrostatic interactions between dissimilar spherical colloids are determined using the singularity method, which provides explicit solutions to the linearized electrostatic field. The increasing trend of osmotic pressure with increasing total particle concentration is reduced as the concentration ratio between large and small particles is increased. From the estimation of total structure factor, we observe the strong correlations developed between dissimilar spheres. As the particle concentration increases at a given ionic strength, the magnitude of the first peak in structure factors increases and also moves to higher wave number values. The increase of electrostatic interaction between same charged particles caused by the Debye screening effect provides an increase in both the osmotic pressure and the shear modulus. The higher volume fraction ratio providing larger interparticle spacing yields decreasing high frequency limit of the shear modulus, due to decreasing the particle interaction energy.

• Progress in Superconductivity
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• 제4권2호
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• pp.148-152
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• 2003

We have observed the temperature dependences of Bi $L_{III}$ edge spectra by extended X-ray absorption spectroscopy for a high quality single crystal and a powder of the $Ba_{0.6}K_{0.4}BiO_3$ superconductor. $Ba_{0.6}K_{0.4}BiO_3$ has the cubic structure and metallic states. The deformation of the $BiO_{6}$ octahedra, which is due to the anomalies of the Bi-O and Bi-Ba bond length, was showed by the double-shell fit. It was clearly found that these anomalies are owing to the difference in the strength of Bi-O bonds. The temperature dependences of both bond lengths and the Debye-Walter factor ${\sigma}^2$ of the Bi-O and Bi-(Ba,K) bond are discussed to illustrate local structural features of the $Ba_{0.6}K_{0.4}BiO_3$

• Transactions of the Korean Society of Mechanical Engineers B
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• 제23권9호
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• pp.1139-1150
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• 1999

The evolution of silica aggregate particles in coflow diffusion flames has been studied experimentally using light scattering and thermophoretic sampling techniques. The measurements of scattering cross section from $90^{\circ}$ light scattering have been utilized to calculate the aggregate number density and volume fraction using with combination of measuring the particle size and morphology through the localized sampling and a TEM image analysis. Aggregate or particle number densities and volume fractions were calculated using Rayleigh-Debye-Gans and Mie theory for fractal aggregates and spherical particles, respectively. Of particular interests are the effects of flame temperature on the evolution of silica aggregate particles. As the flow rate of $H_2$ increases, the primary particle diameters of silica aggregates have been first decreased, but, further increase of $H_2$ flow rate causes the diameter of primary particles to increase and for sufficiently larger flow rates, the fractal aggregates finally become spherical particles. The variation of primary particle size along the upward jet centerline and the effect of burner configuration have also been studied.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 1993년도 추계학술대회 논문집
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• pp.85-89
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• 1993

Silicone oil exhibits the properies of both organic and inorganic substances and, thus, it has many superior properties such as higher thermal resistance and lower thermal oxidation level when compared to other dielectric liquids. In order to investigate the dielectric characteristics, dielectric liquids of viscosity 1 [cSt] is chosen as the specimen and experiment is performed in the temperature range of 20∼65 [$^{\circ}C$] and frequency range of 30∼1${\times}$10$\^$6/ [Hz] respectively. As a result, the observed linear decrease in dissipation factor at the frequency range below 3 [kHz] is due to the influence of frequency, whereas the increase in dissipation factor at higher frequency range is contributed by electrode's resistance. At a fixed frequency of 30 [kHz], increasing temperature results in higher peak value and wide width of the absorption curve. This is due to the increase in dipole and viscosity. As temperature increases, dipole moment is decreased from 0.98 to 0.64 [debye]. The activation energy which causes the relaxation and loss of dielectric is obtained about 15 [kcal/mole].

• Korean Journal of Materials Research
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• 제9권4호
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• pp.345-348
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• 1999

The properties of Fe ions in the $ CdFe_2$$O_4$ and $CdFeAlO_4$ were investigated using the Mossbauer spectroscopy, in the temperature range from 300K to 900K. The calculated Debye temperature, recoil free fraction, mean square displacement and velocity are, 476.5K, 0.835, 3.39$\times$10\ulcorner$\textrm{cm}^2$, and 1.11$\times$10\ulcorner$\textrm{cm}^2$sec$^2$for Fe ions in the $CdFe_2$$O_4$ and 369.0K, 0.741, 5.65$\times$10\ulcorner$\textrm{cm}^2$ and 1.33$\times$10\ulcorner$\textrm{cm}^2$/$sec^2$in the $CeFeAlO_4$. The difference of the properties in the two samples were explained by the variation of the Fe\ulcorner-O\ulcorner bonding length with the substituted Al ions.

• Proceedings of the KIEE Conference
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.356-358
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• 1989

Linear and nonlinear complex permittivities have been measured for an alternating copolymer of vinylidene cyanide(VSCN) with vinyl propionale(VPr). It is found that the third order permittivity ${\varepsilon}_3$ depends upon frequency according to a function V ${\varepsilon}_3$/ ${1+(j{\omega}{\tau}_3)^{\beta}}^3$ while the linear permittivity ${\varepsilon}_1$obeys a Debye type function ${\nabla}{\varepsilon}_1$/ {1+$(j{\omega}{\tau}_1)^{\beta}$}. Experimental results are well fitled by predicted functions except at low frequency where dc conduction dominates. The relaxation times ${\tau}_1$ and ${\tau}_3$ at same teperature are nealy equal and depend upon temperature according to WLF form. The relaxation strengths ${\nabla}{\varepsilon}_1$ and ${\nabla}{\varepsilon}_3$ have a peak at the vicinity of glass transition temperature (Tg). The strength ${\nabla}{\varepsilon}_1$ has a value of -9 order and ${\nabla}{\varepsilon}_3$ has a negative value of -25 order. The analysis of mechanism by combined knowledge about linear and nonlinear permittivities and dipole moment gives us an imformation of the electrical and thermal dipolar motions in this copolymer.

• Journal of the Korean Chemical Society
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• 제56권4호
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• pp.416-423
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• 2012

Using time domain reflectometry, the complex dielectric spectra between 10 MHz to 20 GHz has been measured in the whole composition range at 10, 20, 30 and $40^{\circ}C$ for the binary mixtures of ethylene glycol and dimethyl sulfoxide. For all the mixtures, only one dielectric loss peak was observed in this frequency range. The relaxation in these mixtures can be described by a single relaxation time using the Debye model. A systematic variation is observed in dielectric constant (${\varepsilon}_0$) and relaxation time (${\tau}$). The excess permittivity (${\varepsilon}^E$), excess inverse relaxation time $(1/{\tau})^E$, Kirkwood correlation factor (g) and thermodynamic parameters viz. enthalpy of activation (${\Delta}H$) and Gibbs free energy of activation (${\Delta}G$) have been determined, to confirm the formation of hydrogen bonded homogeneous and heterogeneous cooperative domains, the dynamics of solute - solute interaction and the hindrance to molecular rotation in the hydrogen bonded glass forming ethylene glycol - dimethyl sulphoxide system.

• Bulletin of the Korean Chemical Society
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• 제35권12호
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• pp.3601-3608
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• 2014

RGB light emitting ZnSe based nanocrystals: ZnSe (blue), ZnSe:Cu (green) and ZnSe:Mn (red) were synthesized by capping the surface of the nanocrystals with oleic acid. The obtained nanocrystal powders were characterized by using XRD, HR-TEM, ICP-AES, FT-IR, and FT-Raman spectroscopies. The optical properties were also measured by UV/Vis and photoluminescence (PL) spectroscopies. The PL spectra showed broad emission peaks at 471 nm (ZnSe), 530 nm (ZnSe:Cu) and 665 nm (ZnSe:Mn), with relative PL efficiencies in the range of 0.7% to 5.1% compared to a reference organic dye standard. The measured average particle sizes from the HR-TEM images for those three nanocrystals were 4.5 nm on average, which were also supported well by the Debye-Scherrer calculations. The elemental compositions of the ZnSe based nanocrystals were determined by ICP-AES analyses. Finally, the drawn CIE diagram showed the color coordinates of (0.15, 0.16) for ZnSe, (0.22, 0.57) for ZnSe:Cu, and (0.62, 0.35) for ZnSe:Mn respectively, which were fairly well matched to that of the RGB color standards.