• Korean Chemical Engineering Research
• /
• v.53 no.6
• /
• pp.717-722
• /
• 2015

D-limonene included in citrus fruits is obtainable to extract essential oil as well as separate the oil ingredient. Soxhlet extraction, a type of SDE (Simultaneous steam Distillation and solvent Extraction), was used to extract limonene from tangerine peel. HPLC analysis was performed to quantify extracted d-limonene by using reversed-phase HPLC column. Results of HPLC analysis showed that the optimal extraction time was 2 hours in any solvent, and the extracted amounts of d-limonene in tangerine peel (per g tangerine peel) were 7.77 mg, 0.49 mg, and 0.28 mg in ethyl alcohol, n-hexane, and ether. Because yield was the highest in using ethyl alcohol as a solvent, polarity is stronger factor to effect on yield of extraction than boiling point.

• Journal of rehabilitation welfare engineering & assistive technology
• /
• v.8 no.4
• /
• pp.305-312
• /
• 2014

In this study, in order to quantitatively confirm walking rehabilitation degree, we analyzed EMG pattern simulated abnormal gait and normal gait by applying a curve fitting. We calculated the suitable high-order function for EMG signal, and classified them into 5 groups by using cluster analysis. Depending on the distance from normal pattern group, we listed the pattern group and then the distribution of each variables were confirmed. The amplitude-decreased pattern was the most similar to the normal pattern, but the reversed pattern showed the lowest similarity. Due to the smaller overlapping range, the distribution of the groups were possible to classify using the value of variable. The standard deviation of each term coefficient was compared to indicate the quantitative rehabilitation extent, and the higher value was confirmed as the pattern is close to the normal pattern. Consequently, the representation of quantitative rehabilitation extent is expected to contribute to the more effective rehabilitation method study.

• The Journal of the Acoustical Society of Korea
• /
• v.20 no.6
• /
• pp.87-93
• /
• 2001

As a new type of a linear decorrelating receiver, the Pseudo-Decorrelator was presented for asynchronous code division multiple access systems by the author. In this paper, the concept of the Pseudo-Decorrelator is extended to derive a receiver for WCDMA uplink systems over an additive white Gaussian noise channel. Starting with the analysis of the multiple access components of the decision statistics, a non-square cross-correlation matrix for each bit is obtained. This cross-correlation matrix is then inverted, and the inverted matrix is applied to the decision statistics obtained from a conventional receiver. In this receiver, the detection process can be started after the first three consecutive bits are received. Simulation results are presented for K-user systems over an additive white Gaussian noise channel under the circumstances in which synchronization errors, including time delay errors and carrier phase errors exist. It is shown that the proposed receiver performs better than a conventional receiver and parallel interference canceller.

• Korean Journal of Medicinal Crop Science
• /
• v.9 no.1
• /
• pp.21-25
• /
• 2001

Major saponins in ginseng were analysed using reverse phase high performance liquid chromatography with binary mobile phase gradient control system instead of normal phase column. The optimum condition were as following : reverse phase column; ${\mu}{\beta}ondapak\;C_{18}$ column (Waters, $3.9mm{\times}300\;mm,\;5{\mu}m$), methyl cyanaide/water binary mobile phase gradient control system, solvent flow rate; 1.5 ml/min, and UV($203{\mu}m$ ) detector. The complete separation of ginsenoside $Rb_1,\;Rb_2,\;Rc,\;Rd,\;Re,\;Rf\;and\;Rg_1$ was achieved within 55 min. The Regression coefficients of the calibration curves for seven ginsenosides were 0.99.

• Applied Chemistry for Engineering
• /
• v.8 no.2
• /
• pp.315-319
• /
• 1997

In this study, the optimum analytical conditions for determination of distribution of propylene oxide in a nonionic surfactant and separation of fatty alcohols were investigated by Reversed Phase High Performance Liquid Chromatography. To analyse the distribution of propylene oxide (PO) and carbon chain length of a fatty alcohol, we derivatized samples for the purpose of using a UV detector. Also, we studied the influences of columns and mobile phase composition to obtain the optimum separation conditions. In our experiment, Waters Symmetry $C_8(3.9{\times}150mm)$ column was used. And the optimum condition were obtained by gradient elution with methanol and water as the mobile phase. In the plot of log k' vs composition of water in the binary phase, the linerality was very good. We ploted the calibration curve to conform the quality of fatty alcohol, a good linerality was obtained.

• Analytical Science and Technology
• /
• v.10 no.6
• /
• pp.408-417
• /
• 1997

Normal phase or reversed phase liquid chromatographic separation of some structural isomers of functionalized heterocyclic compounds has been carried out by using several different columns and various mobile phases. The optimal experimental conditions for separation of structural isomers were found on a ternary solvent system including alcohol as a modifier. This polar modifier is preferentially adsorbed onto strong adsorption site, leaving a more uniform population of weaker site that then serve to retain the sample. This 'deactivation' of the adsorbent leads to a number of improvements in subsequent separations. The optimal mobile phase system of separation were found on normal phase on structural isomers. Retention mechanism of normal phase system was also studied depending on adsorption strength between solute and stationary phase of column. However, retention factors of reversed phase system were found on hydrophobic interaction with solvophobic effect.

• Polymer(Korea)
• /
• v.25 no.4
• /
• pp.460-467
• /
• 2001

Inverse suspension polymerization of acrylamide (AM) in cyclohexane was carried out to study the effects of concentrations of sorbitan ester (Span) stabilizers and 2,2'-azobis (2-methyl propionamidine) dihydrochloride (AIBA) initiator, amount of monomer, shaking speed, and polymerization temperature on the particle size of the resulting poly (acrylamide) (PAM) beads and their molecular weights. It was found that the particle diameter. in general, decreased with increasing concentration of stabilizer, shaking speed, and water content in the aqueous phase, and with decreasing concentration of initiator and polymerization temperature. The average molecular weight of the resulting PAM beads was also found to increase with increasing concentrations of monomer and stabilizer, and also with decreasing concentration of initiator, polymerization temperature, and water content in the aqueous phase. In this study, PAM beads ranging 2 ~ 50 ${\mu}$m in diameter, with 8000000 ~ 12000000 in the weight average molecular weight were successfully prepared in almost 100% conversion.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.4
• /
• pp.301-305
• /
• 2012

In this work the mechanical behaviors of GaN nanowires are analyzed during tension, compression, and unloading deformations. The thermal conductivity of the nanowires at each deformed state is evaluated using an equilibrium Green-Kubo approach. Under tensile loading, the [0001]-oriented nanowires with hexagonal cross-sections undergo a phase transformation from wurtzite to a tetragonal structure. The phase transformation is not observed under compressive loading. The thermal conductivity decreases on going from compressive strains to tensile strains. The strain dependence of the thermal conductivity results from the relaxation time of phonon. A reverse transformation from the tetragonal structure to the wurtzite structure is observed during unloading. The thermal conductivities in the intermediate states are lower than the conductivity in the wurtzite structure at same strain. Such differences in the thermal conductivity between different atomic structures are mainly due to changes in the group velocity of phonon.

• Journal of the Korean Chemical Society
• /
• v.32 no.3
• /
• pp.211-226
• /
• 1988

Liquid chromatographic behavior of several metal ions in dithiocarbamate(DTC) chelates were investigated by reversed phase high performance liquid chromatography on Novapak $C_{18}$ and ${\mu}$-Bondapak $C_{18}$ columns. The optimum conditions for the separation of DTC-metal chelate were examined with respect to the pH, shaking time, flow rate, extraction solvent, and mobile phase strength. The metal ions in mixtures at trace level, chelated with some dithiocarbamate derivatives were separated successfully on Novapak $C_{18}$ column using acetonitrile/methanol/water or acetonitril/water mixtures as mobile phases. It was found that all DTC metal chelates studied were eluted in an acceptable range of capacity factor values ($0{\leqq}log\;k'{\leqq}1$). Although several foreign metal ions were coexisted, high recovery and good precision were attained ; 97.0-106.7 % for the recovery and 0.98-3.41% for the coefficient of variation. Under the optimum analytical conditions, trace metal ions in the composite water samples were determined sucessfully with in relative error of about {\pm}$6.7 %.

• Journal of the Korean Chemical Society
• /
• v.42 no.4
• /
• pp.416-421
• /
• 1998

In the reversed-phase ion-pair high performance liquid chromatographic (RPIP-HPLC) elution behavior of noble metal-thiacrown ether complexes, the effects of the concentration of ion-pairing reagent and kind of ligands were studied. It was found that the less the number of atoms in the ring of the thiacrown ether molecule was, the larger the selectivity was, and the elution mechanism of the complexes was explained due to the formation of ion-pair when the concentration of sodium dodecyl sulfate (SDS) in mobile phase was lower than 10 mM and due to the formation of micelle when the SDS concentration was higher than 10 mM. As a conclusion, separations of the noble metal-thiacrown ether complexes in an optimum separation condition were accomplished successfully and the method was proved to be an useful one for the separation and determination of Ag (Ⅰ) ion in a black-white photographic fixing solution.