• Journal of the Korean Society of Food Science and Nutrition
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• v.26 no.6
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• pp.1028-1032
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• 1997

Low-temperature crystallization method silver nitrate-impregnated silicic acid column chromatography were applied for the isolation of pure $\alpha$-linolenic acid(ALA) from perilla seed oil. ALA or 78% in purity(HALA; yield, 83%) was obtained from the fatty acid mixture(ALA, 65.7%) derived from perilla oil by the low-temperature crystallization method, when the mixture was frozen at -8$0^{\circ}C$ for 210min. ALA over 90% in purity(yield, 71%) was also obtained from HALA ethyl esters(ALA, 78%) by the silver nitrate-impregnated silicic acid column(100cm$\times$10cm, i.d.) chromatography. In addition, the silver nitrate-impregnated silicic acid could be semipermanently used for isolation of ALA, because $Ag^{+}$ ion was not dissociated from the stationary phase.

• Bulletin of the Korean Chemical Society
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• v.18 no.11
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• pp.1186-1191
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• 1997

Solvolyses of methanesulfonyl chloride (CH3SO2Cl) in water and methanol have been studied theoretically using ab initio self-consistent reaction field (SCRF) molecular orbital method. All stationary structures including transition state on the potential energy surface in solution have been found and compared with the gas phase structures. The overall reaction occurs via a concerted SN2 mechanism with a non-cyclic trigonal bipyramidal transition state, and the activation barrier is lowered significantly in solution. The transition state for the hydrolysis reaction is looser than that for the methanolysis reaction, and this is in accord with the experimental findings that an SN2 type mechanism, which is shifted toward an SN1 process or an SAN process in the hydrolysis and alcoholysis reaction, respectively, takes place. The catalytic role of additional solvent molecules appears to be a purely general-base catalysis based on the linear transition structures. Experimental barrier can be estimated by taking into account the desolvation energy of nucleophile in the reaction of methanesulfonyl chloride with bulk solvent cluster as a nucleophile.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.1
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• pp.25-32
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• 2019

Recent high-end treadmills are demanding stable performance at lower speeds. In this study, a slip control-based induction motor sensorless algorithm for treadmills, which have heavy load variations, is proposed. A modified Gopinath flux estimator is used to evaluate the rotor flux. Results indicate that a good speed regulation performance is achieved even at a low speed of approximately 3 Hz with a nominal exercise load of 90 kg body weight. The slip calculation method in the stationary coordinate system is adopted to improve the control stability. The proposed algorithm is verified throughout the simulation study using PSIM, and the experimental test consists of a commercial treadmill system.

• Microbiology and Biotechnology Letters
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• v.48 no.4
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• pp.423-428
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• 2020

In vitro evolution is a powerful technique for the engineering of yeast strains to study cellular mechanisms associated with evolutionary adaptation; strains with desirable traits for industrial processes can also be generated. There are two distinct approaches to generate evolved strains in vitro: the sequential transfer of cells in the stationary phase into fresh medium or the continuous growth of cells in a chemostat bioreactor via the constant supply of fresh medium. In culture, evolutionary forces drive diverse adaptive mechanisms within the cell to overcome environmental or intracellular stressors. Especially, this engineering strategy has expanded to the field of human cell lines; the understanding of such adaptive mechanisms provides promising targets for the treatment of human genetic diseases and cancer. Therefore, this technology has the potential to generate numerous industrial, medical, and academic applications.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.346-351
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• 1998

In design of a digital current controller for a 3-phase (3 ) voltage-source (VS) PWM converter, its conventional model, i.e., stationary or synchronous reference frame model, is used in obtaining its discretized version. It introduces, however, inherent errors since the following practical problems are not taken into consideration: the characteristics of the space vector-based pulse-width modulation (SVPWM) and the time delays in the process of sampling and computation. In this paper, the new hybrid reference frame model of the 3 VS PWM converter is proposed considering these problems. In addition, the direct digital current controller based on this model is designed without any prediction or extrapolation algorithm to compensate the time delay. So the control algorithm is made very simple. It represents no steady-state error in input current control and has the optimized transient responses. The validity of the proposed algorithm is proved by the computer simulation and experimental results.

• Analytical Science and Technology
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• v.36 no.6
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• pp.259-266
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• 2023

The demand for rare-earth elements (REEs) is increasing owing to their significance as prominent materials in electronics, high-tech industries, geological research, nuclear forensics, and environmental monitoring. In general, the utilization of REEs in various applications requires the use of chromatographic techniques to separate individual elements. However, REEs have similar physicochemical properties, which makes them difficult to separate. Recently, several studies have examined the separation of REEs using LN resin as the stationary phase and aqueous nitric acid and hydrochloric acid solutions as eluents. Using this method, light REEs have been separated using dilute acid solutions as the eluent, whereas heavy REEs are separated using solutions with high acid concentrations. To increase the separation resolution between different REEs, either the column length or resin size is changed. In addition, the suggested methods are implemented to decrease the analysis time. This review presents technical information on the chromatographic separation of REEs using the LN resin and discusses the optimal experimental conditions.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.185-192
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• 2004

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 30000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall sound power level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental blade passing frequency (BPF) is reduced by about 6 dB (A) and the 2$\^$nd/ BPF is reduced about 20 dB (A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.

• Journal of the Korea Furniture Society
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• v.17 no.3
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• pp.95-111
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• 2006

These series articles were written in order to understand rockers of today and to provide basic data of their designs and manufacture studying pattern changes in the West. In the first article of the series reports we already described the theoretical background of rockers and the Windsor and the Boston style among the American classic rockers from the eighteenth to the twentieth century. This article contained the characteristics of the styles of the Shaker rocker, the Wicker rocker, and the Platform rocker. The three periods associated with furnituremaking in the Shaker sect are; the Primitive Era, which lasted from 1790 to 1820; the Classical Era, from 1820 to 1860; and the Final Phase, from 1860 to 1935. The important skills the Shaker needed to make the Shaker rocker are woodturning joinery, seat braid weaving and steam bending for the slats. The Wicker rocker continues to be extremely popular furniture style as the wicker proved equally effective for translating the ornate vine-like motifs popular among Art Nouveau proponents. The Wicker rockers were developed for child's, gentleman's and lady's, and it represents the most diverse forms among the above mentioned styles. However the rocker skates were often clumsy and took up too much room, preventing the chair from being shoved close to the wall and out of the way. These problems were overcome by the Platform rocker. The most important innovation was the technical development of a stationary base, which allowed the chair to rock noiselessly, without skating along the floor. The Modernism of the modern furnitures in America and Europe were affected by the characteristics of the Shaker rocker, the Wicker rocker, and the Platform rocker.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.83-90
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• 2001

The Talbot effect for periodic objects with the spatial period p illuminated by expanded coherent light is analyzed by Fresnel diffraction theory, and the Talbot distance (Zr) at which we can observe 1: 1 imaging without any lenses can be defined. We confmned experimentally the Talbot imaging of line, circular, X -type and '||'&'||'copy;-type 2 dimensional alTay gratings at ZT. At the same time, we observed phase reversed Talbot imaging at Zr/2 and Talbot subimage with p/2 at Zr/4 and 3Zr/4. The visibility of Talbot images as a function of the number of slits of the input grating was measured by the FFf (Fast Fourier Transform) results of these images. As a result stationary maximum visibility of V = 0.25 was obtained from grating numbers with more than 15 slit pairs.

• Wind and Structures
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• v.34 no.1
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• pp.81-90
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• 2022

To better understand the vortex-induced vibration (VIV) characteristics of a 5:1 rectangular cylinder, the distribution of aerodynamic force and the non-dimensional power spectral density (PSD) of fluctuating pressure on the side surface were studied in different VIV development stages, and their differences in the stationary state and vibration stages were analyzed. The spanwise and streamwise correlations of surface pressures were studied, and the flow field structure partitions on the side surface were defined based on the streamwise correlation analysis. The results show that the variation tendencies of mean and root mean square (RMS) pressure coefficients are similar in different VIV development stages. The RMS values during amplitude growth are larger than those at peak amplitude, and the smallest RMS values are observed in the stationary state. The spanwise correlation coefficients of aerodynamic lifts increase with increase of the peak amplitude. However, for the lock-in region, the maximum spanwise correlation coefficient for aerodynamic lifts occurs in the VIV rising stage rather than in the peak amplitude stage, probably due to the interaction of vortex shedding force (VSF) and self-excited force (SEF). The streamwise correlation results show that the demarcation point positions between the recirculation region and the main vortex region remain almost constant in different VIV development stages, and the reattachment points gradually move to the tailing edge with increasing amplitude. This study provides a reference to estimate the demarcation point and reattachment point positions through streamwise correlation and phase angle analysis from wind tunnel tests.