• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.197-202
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• 2010

A combustion chamber with a branch tube was built to investigate the characteristics of a spontaneous oscillating laminar premixed Bunsen flame. The flame behavior was observed, and the relation between the flame surface area and heat release rate was inspected. The equivalence ratio and mean velocity were fixed at 1.1 and 1.75 m/s, respectively. The amplitude of the pressure fluctuation in the combustion chamber was changed and the flame behavior was affected when the length ratio between the branch tube and combustion chamber (L:R) was varied. The $OH^*$, $CH^*$, and flame chemiluminescence had similar behavior qualitatively. There was linearity between the flame surface area and heat release rate.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.7 no.2
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• pp.13-18
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• 2013

In this paper design a 8 bit Current Steering D/A Converter for stimulating neuron signal. Proposed circuit in paper shows the conversion rate of 10KS/s and the power supply of 3.3V with 0.35um Magna chip CMOS process using full custom layout design. It employes segmented structure which consists of 3bit thermometer decoders and 5bit binary decoder for decreasing glitch noise and increasing resolution. So glitch energy is down by $10nV{\bullet}sec$ rather than binary weighted type DAC. And it makes use of low power current stimulator because of low LSB current. And it can make biphasic signal by connecting with Micro Controller Unit which controls period and amplitude of signal. As result of measurement INL is +0.56/-0.38 LSB and DNL is +0.3/-0.4 LSB. It shows great linearity. Power dissipation is 6mW.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.3055-3060
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• 2012

A simple, rapid and sensitive spectrofluorometric method was developed for the determination of folic acid (FA), based on its quenching effect on the fluorescence intensity of enoxacin (ENX)-europium ($Eu^{3+}$) complex as a fluorescent probe. Fluorometric interaction between ENX-$Eu^{3+}$ complex and FA was studied using UV-visible and fluorescence spectroscopy. The quenched fluorescence intensity at an emission wavelength of 614 nm was proportional to the concentration of FA. Optimum conditions for the determination of FA were investigated. Under optimal conditions, the reduced fluorescence intensity at 614 nm was responded linearly with the concentration of FA. The linearity was maintained in the range of $1.25{\times}10^{-9}$ to $1.50{\times}10^{-7}$ M (R = 0.9986) with the limit of detection ($3S_b/m$) (where $S_b$ is the standard deviation of blank and m is the slop of linear calibration curve) of $6.94{\times}10^{-10}$ M. The relative standard deviation (RSD) for 9 repeated measurements of $1.0{\times}10^{-9}$ M FA was 1.42%. This method was simple, cost effective, and relatively free of interference from coexisting substances. Successful determinations of FA in pharmaceutical formulation and biological samples with the developed method were demonstrated.

• Smart Structures and Systems
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• v.19 no.2
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• pp.181-194
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• 2017

In order to investigate the interface debonding defects detection mechanism between steel tube and concrete core of concrete-filled steel tubes (CFSTs), multi-physical fields coupling finite element models constituted of a surface mounted Piezoceramic Lead Zirconate Titanate (PZT) actuator, an embedded PZT sensor and a circular cross section of CFST column are established. The stress wave initiation and propagation induced by the PZT actuator under sinusoidal and sweep frequency excitations are simulated with a two dimensional (2D) plain strain analysis and the difference of stress wave fields close to the interface debonding defect and within the cross section of the CFST members without and with debonding defects are compared in time domain. The linearity and stability of the embedded PZT response under sinusoidal signals with different frequencies and amplitudes are validated. The relationship between the amplitudes of stress wave and the measurement distances in a healthy CFST cross section is also studied. Meanwhile, the responses of PZT sensor under both sinusoidal and sweep frequency excitations are compared and the influence of debonding defect depth and length on the output voltage is also illustrated. The results show the output voltage signal amplitude and head wave arriving time are affected significantly by debonding defects. Moreover, the measurement of PZT sensor is sensitive to the initiation of interface debonding defects. Furthermore, wavelet packet analysis on the voltage signal under sweep frequency excitations is carried out and a normalized wavelet packet energy index (NWPEI) is defined to identify the interfacial debonding. The value of NWPEI attenuates with the increase in the dimension of debonding defects. The results help understand the debonding defects detection mechanism for circular CFST members with PZT technique.

• Journal of Electrochemical Science and Technology
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• v.10 no.4
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• pp.416-423
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• 2019

A novel non-enzymatic oxalic acid (OA) sensor based on the platinum/carbon black-nickel-reduced graphene oxide (Pt/CBNi-rGO) nanocomposite is reported. The nanocomposites were prepared by the ethylene glycol reduction method. Their morphology and chemical composition were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The results clearly demonstrated the formation of the Pt/CB-Ni-rGO nanocomposite. The electrocatalytic activity of the Pt/CB-Ni-rGO electrode was investigated by cyclic voltammetry. It was determined that the appropriate amount of Pt enhanced the catalytic activity of Pt for oxalic acid electro-oxidation. Moreover, the modified electrode was determined to be highly selective for oxalic acid without interference from compounds commonly found in urine including uric acid and ascorbic acid. The chronoamperometric signal gave a wide linearity range of 20 μM-60 mM and the detection limit (3σ) was found to be 2.35 μM. The proposed method showed high selectivity, stability, and good reproducibility and could be used with micro-volumes of sample for the detection of oxalic acid. Finally, the oxalic acid content in artificial and control urine samples were successfully determined by our proposed electrode.

• Journal of Korean Society for Atmospheric Environment
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• v.32 no.3
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• pp.305-319
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• 2016

This study was carried out to evaluate the performance of two sampling methods, i.e., adsorbent tubes and canisters, for the measurement of ambient volatile organic compounds (VOCs). A total of 24 target VOCs were selected from a list of 48 priority hazardous air pollutants (HAPs) in Korea. The two sampling methods were investigated with a wide range of performance criteria such as repeatability, linearity, and lower detection limits. In addition, mean relative errors (MRE) and mean duplicate precisions (MDP) were estimated by inter-lab comparison studies for duplicate field samples. Precisions for the two methods appeared to be well comparable with the performance criteria recommended by USEPA TO-15 and TO-17 for canister and adsorbent methods, respectively. Correlations and variations between the VOCs concentrations determined by the two methods were generally good in most cases. However, MREs and MDPs for individual VOCs appeared to be widely ranged, depending on each VOC. This implies that the two methods have its own advantages and disadvantages in determining a variety of VOCs in ambient air, and neither of which has absolute superiority. Finally, 9 of 24 VOCs were found to be difficult to determine by either methods due to their unstability in a canister, and lack of appropriate standard materials. Thus, it is suggested that development of measurement methods for such unstable VOCs is an urgent task from a viewpoint of HAPs management.

• Journal of Sensor Science and Technology
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• v.29 no.5
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• pp.360-364
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• 2020

In this study, the colorimetric sensor, polyester (PET) fabric dyed with lead (II) acetate (Pb(C₂H₃O₂)₂), was fabricated and characterized for the detection of the hydrogen sulfide (H₂S). The surface morphology of the fabric was determined using scanning electron microscope and energy-dispersive X-ray spectroscopy. The optical properties of the fabric were evaluated by measuring the variation in the blue value of an RGB sensor. The fabric showed a significant color change, high linearity (R² : 0.98256), and fast response time (< 1.0 s) when exposed to H₂S. This is because the sensor is highly porous and permeable to the gas. The fabric can not only be used as a hydrogen sulfide sensor but also be used to detect and prevent H₂S influx using sticky tape on pipelines.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.137-141
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• 2016

There is a growing demand for non-contact current measurements for efficient use of electrical power and energy saving. In this study, I propose a non-contact current sensor using LC resonance by a resonance circuit composed of a sensor coil and 2 coupling coils for enabling a wireless measurement. The inductance of the sensor coil, which could be changed by applied current, causes the change of resonance frequency of the resonance circuit. A pair of magnet was attached to the ferrite core to apply a bias magnetic field that enabled the determination of the current direction. We obtained an output voltage change of 18 V with the current of -3~3 A. But, the output was nonlinear. In order to realize the non-contact current measuring method proposed in the present study, there is a need for a strict investigation of linearity and resolution for the future study.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.430-433
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• 2017

This paper presents a S/C/X-band LNA MMIC with resistive feedback structure in 0.25 um GaN HEMT process. The GaN devices have advantages as a high output power device having high breakdown voltage, energy band gap and stability at high temperature. Since the receiver using the GaN device with high linearity can be implemented without a limiter, the noise figure of the receiver can be improved and the size of receiver module can be reduced. The proposed GaN LNA MMIC based on 0.25 um GaN HEMT device is achieved the gain of > 15 dB, the noise figure of < 3 dB, the input return loss of > 13 dB, and the output return loss of > 8 dB in the S/C/X-band. The current consumption of GaN LNA MMIC is 70 mA with the drain voltage 20 V and the gate voltage -3 V.

• Journal of Environmental Science International
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• v.23 no.6
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• pp.1037-1047
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• 2014

A highly sensitive analytical method based on stir bar sorptive extraction (SBSE) technique and gas chromatography/tandem mass spectrometry (GC/MS-MS) has been developed, allowing the simultaneous multi-analyte determination of seven UV filters in water samples. The stir bar coated with polydimethylsiloxane (PDMS) was added to 40 mL of water sample at pH 3 and stirred at 1,100 rpm for 120 min. Other SBSE parameters (salt effect and presence of organic solvent) were optimised. The method shows good linearity (coefficients > 0.990) and reproducibility (RSD < 12.9%). The extraction efficiencies were above 84% for all the compounds. The limits of detections (LOD) and limits of quantification (LOQ) were 2.1~8.6 ng/L and 6.8~27.5 ng/L, respectively. The developed method offers the ability to detect 8 UV filters at ultra-low concentration levels with only 40 mL of sample volume. Matrix effects in tap water, river water, wastewater treatment plant (WWTP) final effluent water and seawater were investigated and it was shown that the method is suitable for the analysis of trace level of 7 UV filters except of benzophenone (BP). The method developed in the present study has the advantage of being rapid, simple, high-sensitive and both user and environmentally friendly.