• Natural Product Sciences
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• v.25 no.3
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• pp.222-227
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• 2019

Quantitative nuclear magnetic resonance (qNMR) is a well-established method adopted by international pharmacopoeia for quantitative and purity analyses. Emodin is a type of anthraquinone, well known as the main active component of Fabaceae, Polygonaceae and Rhamnaceae. Purity analysis of emodin is usually performed by using the high-performance liquid chromatography (HPLC)-UV method. However, it cannot detect impurities such as salts, volatile matter, and trace elements. Using the qNMR method, it is possible to determine the compound content as well as the nature of the impurities. Several experimental parameters were optimized for the quantification, such as relaxation delay, spectral width, number of scans, temperature, pulse width, and acquisition time. The method was validated, and the results of the qNMR method were compared with those obtained by the HPLC and mass balance analysis methods. The qNMR method is specific, rapid, simple, and therefore, a valuable and reliable method for the purity analysis of emodin.

• Journal of IKEEE
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• v.23 no.1
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• pp.53-57
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• 2019

In this paper, we propose a new Z-source inverter structure to reduce switching elements and PWM pulse control method. Z-network is connected between the inverter backplane and ground, rather than between the DC voltage and the inverter in an improved Z-source inverter. And the improved Z-source inverter has the advantages of limiting the capacitor inrush current and reducing the capacitor voltage stress. We have proposed a topology of a new type of switch-reduced improved Z-source inverter that reduces the number of switches from six to four in an improved Z-source inverter and developed a PWM control method suitable for the proposed topology. The characteristics and the performance of the proposed method were verified by using PSIM simulation.

• Journal of Astronomy and Space Sciences
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• v.36 no.2
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• pp.97-103
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• 2019

An automated signal-acquisition method for the NASA's space geodesy satellite laser ranging (SGSLR) system is described as a selection of two system parameters with specified probabilities. These parameters are the correlation parameter: the minimum received pulse number for a signal-acquisition and the frame time: the minimum time for the correlation parameter. The probabilities specified are the signal-detection and false-acquisition probabilities to distinguish signals from background noise. The steps of parameter selection are finding the minimum set of values by fitting a curve and performing a graph-domain approximation. However, this selection method is inefficient, not only because of repetition of the entire process if any performance values change, such as the signal and noise count rate, but also because this method is dependent upon system specifications and environmental conditions. Moreover, computation is complicated and graph-domain approximation can introduce inaccuracy. In this study, a new method is proposed to select the parameters via a conditional equation derived from characteristics of the signal-detection and false-acquisition probabilities. The results show that this method yields better efficiency and robustness against changing performance values with simplicity and accuracy and can be easily applied to other satellite laser ranging (SLR) systems.

• Korean Journal of Materials Research
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• v.29 no.5
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• pp.288-296
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• 2019

The passivation of AZ91D Mg alloys through plasma anodization depends on several process parameters, such as power mode and electrolyte composition. In this work, we study the dependence of the thickness, composition, pore formation, surface roughness, and corrosion resistance of formed films on the electrolyte temperature at which anodization is performed. The higher the electrolyte temperature, the lower is the surface roughness, the smaller is the oxide thickness, and the better is the corrosion resistance. More specifically, as the electrolyte temperature increases from 10 to $50^{\circ}C$, the surface roughness (Ra) decreases from 0.7 to $0.15{\mu}m$ and the corrosion resistance increases from 3.5 to 9 in terms of rating number in a salt spray test. The temperature increase from 10 to $50^{\circ}C$ also causes an increase in magnesium content in the film from 25 to 63 wt% and a decrease in oxygen from 66 to 21 wt%, indicating dehydration of the film.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.1
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• pp.37-44
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• 2021

This study is implemented as a sensor-less position controller capable of multi-turn detection to replace the expensive absolute encoder used in the turret servo system. For sensor-less control, the position information of the rotor is essential. For this, a magnetic flux estimator was implemented from the mathematical model of IPMSM used in the turret servo system. The position of the rotor and the angular velocity of the rotor were obtained using the rotor magnetic flux calculated from the magnetic flux estimator. Using the zero-crossing technique, one pulse was generated for each rotation of the estimated rotor magnetic flux to measure the number of multi-turns. Simulation and experiment results confirmed the usefulness of the proposed method.

• Journal of ILASS-Korea
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• v.25 no.4
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• pp.188-195
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• 2020

To meet stringent emission regulations of automotive engines, fuel injection control techniques have advanced based on reliable and fast computing prediction models. This study aims to develop a reliable lightweight prediction model of fuel injection rates using a small number of input parameters and based on simple fluid dynamic theories. The prediction model uses the geometry of the injector nozzle, needle motion data, injection conditions and the fuel properties. A commercial diesel injector and US No. 2 diesel were used as the test injector and fuel, respectively. The needle motion data were measured using X-ray phase-contrast imaging technique under various fuel injection pressures and injection pulse durations. The actual injector rate profiles were measured using an injection rate meter for the validation of the model prediction results. In the case of long injection durations with the steady-state operation, the model prediction results showed over 99 % consistency with the measurement results. However, in the case of short injection cases with the transient operation, the prediction model overestimated the injection rate that needs to be further improved.

• International Journal of Advanced Culture Technology
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• v.10 no.3
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• pp.339-345
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• 2022

In this paper, the effect of porosity on the acoustic phase velocity of the 3D printed Kelvin closed-cell structure was investigated using the spectral phase analysis. Since Kelvin cells bring about the large amount of scattering, acoustic pulses in ultrasonic measurements undergoes a distortion of waveforms due to the dispersion effect. In order to take account on the dispersion, mathematical expressions for calculating the phase velocity of longitudinal waves propagating normal to the plane of the Kelvin structure are suggested by introducing a complex wave number based on Fourier transform. 3D Kelvin structure composed of identical unit-cells, a polyhedron of 14 faces with 6 quadrilateral and 8 hexagonal faces, was developed and fabricated by 3D CAD and 3D printer to represent the micro-structure of porous materials such as aluminum foam and cancellous bone. Total nine samples of 3D Kelvin structure with different porosity were made by changing the thickness of polyhedron. Ultrasonic pulse of 1MHz center frequency was applied to the Kelvin structures for the measurement of the phase velocity of ultrasound using the TOF(time-of-flight) and the phase spectral method. From the experimental results, it was found that the acoustic phase velocity decreased linearly with the porosity.

• Geomechanics and Engineering
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• v.25 no.4
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• pp.317-330
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• 2021

This paper reports the results of advanced data analysis involving artificial neural networks for the prediction of the unconfined compressive strength of granite using only two non-destructive test indexes. A data-independent site-independent unbiased database comprising 182 datasets from non-destructive tests reported in the literature was compiled and used to train and develop artificial neural networks for the prediction of the unconfined compressive strength of granite. The results show that the optimum artificial network developed in this research predicts the unconfined compressive strength of weak to very strong granites (20.3-198.15 MPa) with less than ±20% deviation from the experimental data for 70% of the specimen and significantly outperforms a number of available models available in the literature. The results also raise interesting questions with regards to the suitability of the Pearson correlation coefficient in assessing the prediction accuracy of models.

• Journal of the Semiconductor & Display Technology
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• v.21 no.1
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• pp.50-55
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• 2022

Due to the wavelength shift problem of micro LED caused by the change of current density, the active matrix driving pixel circuit that is used in OLED cannot be applied to micro LED displays. Therefore, we need a gray scale method based on modulation of duration time of light emission. In this study, we propose the PWM-controlled micro LED pixel circuit based on CMOS thin film transistors (TFTs). By adopting CMOS inverter structure, we can reduce the number of storage capacitors from the circuit and make the operating speed of the circuit faster. Most of all, our circuit is designed to make operating speed of PWM circuit faster by adopting feedback effect through double gate TFT structure. As a result, it takes about 4.7ns to turn on the LED and about 5.6ns to turn it off. This operating time is short enough to avoid the color distortion and help the precise control of the gray scale.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.28-33
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• 2022

The heating roller of an actual pulse output device (POD) production facility is composed of a steel roller and a rubber roller. The time to reach a specific temperature and the temperature distribution on the roller surface were analyzed and compared according to the change in the number of cartridge heaters inside the heating roller. In this analysis, a steady-state thermal analysis of a steel roller was performed for the cases of a 5-cartridge heater and 9-cartridge heater. Finite element analysis was applied with reference to the surface temperature data of the heating roller during operation and the calorific value of the cartridge heater. Using the 9-cartridge heater, faster target temperature achievement and more uniform temperature distribution were confirmed than for the 5-cartridge heater.