• Current Optics and Photonics
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• v.5 no.3
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• pp.250-260
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• 2021

A tapered As₂S₃ photonic crystal fiber (PCF) with four layers of air holes in a hexagonal array around the core is designed in this paper. Numerical simulation shows that the dispersion D decreases and the nonlinearity coefficient γ increases from the thick to the thin end along the tapered PCF. We simulate the midinfrared pulse compression in the tapered As₂S₃ PCF using the adaptive split-step Fourier method. Initial Gaussian pulses of 4.4 ps and a central wavelength of 2.5 ㎛ propagating in the tapered PCF are located in the anomalous dispersion region. With an average power of assumed input pulses at 3 mW and a repetition frequency of 81.0 MHz, we theoretically obtain a pulse duration of 56 fs and a compression factor of 78 when the pulse propagates from the thick end to the thin end of the tapered PCF. When confinement loss in the tapered PCF is included in the simulation, the minimum pulse duration reaches 72 fs; correspondingly, the maximum compression factor reaches 61. The results show that in the anomalous-dispersion region, midinfrared pulses can be efficiently compressed in a dispersion-decreasing and nonlinearity-increasing tapered As₂S₃ PCF. Due to confinement loss in the tapered fiber, the efficiency of pulse compression is suppressed.

• Applied Chemistry for Engineering
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• v.33 no.6
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• pp.618-623
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• 2022

The bipolar plate is a key component of the polymer electrolyte membrane fuel cell (PEMFC) that transfers reactants and electrons, discharges water and heat as by-products, and serves as a mechanical support for the membrane electrode assembly (MEA). Therefore, the flow field structure of the bipolar plate plays an important role in improving fuel cell performance. In this study, PEMFC performance was investigated with copper foams with different compressibility ratios applied to cathode bipolar plates using a 25 cm² unit cell. The total resistance decreased as the compressibility ratio of the metal foams increased, and, in particular, the charge transfer and mass transfer resistance were significantly improved compared to the serpentine flow field, lowering voltage loss in medium and high current density region. In the case of pressurized air reactant flow with serpentine structure, fuel cell performance was similar to that of a compressed metal foam flow field (S3) up to the medium current density region, but low performance appeared in the high current density region due to flow field structure limitations.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.47 no.2
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• pp.10-20
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• 2024

In recent automated manufacturing systems, compressed air-based pneumatic cylinders have been widely used for basic perpetration including picking up and moving a target object. They are relatively categorized as small machines, but many linear or rotary cylinders play an important role in discrete manufacturing systems. Therefore, sudden operation stop or interruption due to a fault occurrence in pneumatic cylinders leads to a decrease in repair costs and production and even threatens the safety of workers. In this regard, this study proposed a fault detection technique by developing a time-variant deep learning model from multivariate sensor data analysis for estimating a current health state as four levels. In addition, it aims to establish a real-time fault detection system that allows workers to immediately identify and manage the cylinder's status in either an actual shop floor or a remote management situation. To validate and verify the performance of the proposed system, we collected multivariate sensor signals from a rotary cylinder and it was successful in detecting the health state of the pneumatic cylinder with four severity levels. Furthermore, the optimal sensor location and signal type were analyzed through statistical inferences.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.421-431
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• 2007

The main purpose of this study is to develop a sprayed FRP repair and strengthening method, which is a new technique for strengthening the existing concrete structures by mixing one of the carbon or glass chopped fibers and one of the epoxy or vinyl ester resins with high-speed compressed air in open air and randomly spraying the mixture onto the concrete surface. At present, the sprayed FRP repair and strengthening method using the epoxy resin has not been fully discussed. In order to investigate the material property of the sprayed FRP, this study carried out tensile tests of the material specimens, which were changed with the combinations of various variables including the length of chopped fiber and the mixture ratio of chopped fiber and resin. These variables were set to have the equal material strength, compared with that of one layer of the FRP sheet. As a result, the optimal length of glass and carbon chopped fibers was fumed out to be 38 mm, and the optimal mixture ratio between chopped fiber and resin was also turned out to be 1 : 2 from each variable. And also, the thickness of the sprayed FRP to have the equal strength to one layer of the FRP sheet was finally calculated. In is study, a series of experiments were carried out to evaluate the strengthening effects of flexural beams, shear beams and damaged beams strengthened with the sprayed FRP method, respectively. The results revealed that the strengthening effects of the flexural and shear specimens were reasonably similar to those of the FRP sheet, and the developed Sprayed FRP technique is able to be used as a strengthening scheme of existing RC building.

• Journal of the Korean Chemical Society
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• v.64 no.6
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• pp.327-333
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• 2020

Performance of a portable GC that can be utilized for the real time determination of volatile organic compounds in air was evaluated. It employs purified/compressed ambient air as the carrier gas eliminating the need for high pressure gas tanks. The compact system with dimensions of 35 × 26 × 15 ㎤ and weight of 5 kg is powered by either a 24 V DC external adapter or battery pack. Chromatograms of the mixture sample including benzene, toluene, ethylbenzene, and oxylene at concentrations of 1 ppmv and 20 ppmv represent a good reproducibility: 3.79% and 0.48% relative standard deviations (RSDs) for peak area variations; 0.40% and 0.08% RSDs for retention times. The method detection limit was 0.09 ppmv. A 30 m long, 0.28 mm I.D. column operated at an optimal condition yielded a peak capacity of 61 with good resolution for a 10 min isothermal analysis. The relative standard deviations (RSD) of the peak area variations and retention times during consecutive measurements over 27 h were less than 2.4%RSD and 0.5%RSD, respectively. Thus, this instrument makes it suitable for continuous and field analysis of low-concentration VOC mixtures in the indoor/outdoor environment as well as the spillage accident of hazardous chemicals.

• The Journal of the Convergence on Culture Technology
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• v.10 no.4
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• pp.693-700
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• 2024

As of the end of March 2022, the total area of domestic industrial complexes is 606 km2, which is only about 0.6% of the total land area. However, as of 2018, the annual energy consumption of domestic industrial complexes is 110,866.1 thousand TOE, accounting for 53.5% of the country's total energy consumption and 83.1% of the entire industrial sector energy consumption. In addition, industrial complexes have a significant impact on the environment, accounting for 45.1% of the country's total greenhouse gas emissions and 76.8% of industrial sector greenhouse gas emissions. Under this background, in this study, in order to contribute to the energy efficiency of industrial complexes, a prediction study on energy demand and supply for an industrial complex in Korea using machine learning was conducted. In addition, a simulator UI screen was designed to more efficiently convey information on energy demand/supply prediction results and energy consumption status. Among the machine learning algorithms, Multi-Layer Perceptron (MLP) was used, and Bayesian Optimization was applied as an optimization technique for the prediction model. The energy prediction model for the industrial complex built in this study showed a prediction accuracy of 87.90% for compressed air demand and 99.54% for the flow rate available for the public air compressor.

• Tunnel and Underground Space
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• v.24 no.6
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• pp.449-463
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• 2014

There are many case studies and application cases in abandoned mines for hydraulic filling method filled by slurry or paste form, but research on the pneumatic filling is not applied in Korea. The damage of steel pipe is occurred by wear due to the flow of filling material in the bent area of steel pipe in traditional pneumatic filling method. In this study, the new pneumatic filling method was developed using a newly devised improved nozzle to improve the above problem. The model test for mine filling was performed in the laboratory for the simulated accessible or inaccessible mine cavities, and the filling efficiency by the results obtained from the test was calculated. The filling efficiency was analyzed from the variation of outlet angle, feed rate and grain size of sand in model test of simulated accessible mine cavity. The superiority of improved pneumatic filling method was proved through the analysis of filling efficiency by the results obtained from each model tests of gravitational, traditional, and improved filling method in simulated inaccessible mine cavity.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.571-576
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• 2011

Characteristics of bubble driven wakes were investigated in a simulated GTL process(0.102 m ${\times}$ 1.5 m in height) with viscous liquid medium. Effects of gas velocity(0.04 ~ 0.12 m/s) and liquid viscosity(0.001 ~ 0.050 $Pa{\cdot}s$) on the wake characteristics such as rising velocity, frequency, size and holdup were determined by employing a resistivity probe method. The wake phase formed behind the rising multi-bubbles as well as single bubbles were detected effectively from the conductivity fluctuations measured by the probe. Compressed, filtered and regulated air and aqueous solutions of Carboxy Methyl Cellulose(CMC) were used as a dispersed gas phase and a continuous liquid medium, respectively. It was found that the rising velocity and size of wake phase increased with an increase in gas velocity or liquid viscosity. The holdup and frequency of wake phase increased with increasing gas velocity due to the increase of gas input into the process with increasing gas velocity. However, the values of holdup and frequency of wake phase decreased with increasing liquid viscosity, since the size of bubbles and thus that of wakes increased with increasing liquid viscosity. The ratio of wake holdup to that of gas phase, which was in the range of 0.25 ~ 0.48, increased with an increase in liquid viscosity but decreased with gas velocity. The wake characteristics were well correlated in terms of operating variables within this experimental conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.167-175
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• 2018

Natural gas is a clean fuel that discharges almost no air-contaminating substances. This study examined the simultaneous reduction of $CH_4$ and NOx of NGOC/LNT catalysts for CNG buses related to the improvement of the $de-CH_4/NOx$ performance, focusing mainly on identifying the additive catalysts, loading of the washcoat, stirring time, and types of substrates. The 3wt. % Ni-loaded NGOC generally exhibited superior $CH_4$ reduction performance through $CH_4$ conversion, because Ni is an alkaline, toxic oxide, and exerts a reducing effect on $CH_4$. A excessively small loading resulted in insufficient adsorption capacity of harmful gases, whereasa too high loading of washcoat caused clogging of the substrate cells. In addition, with the economic feasibility of catalysts considered, the appropriate amount of catalyst washcoat loading was estimated to be 124g/L. The NOx conversion rate of the NGOC/LNT catalysts stirred from $200^{\circ}C$ to $550^{\circ}C$ for 5 hours showed 10-15% better performance than the NGOC/LNT catalysts mixed for 2 hours over the entire temperature range. The NGOC/LNT catalysts exhibitedapproximately 20% higher $de-CH_4$ performance on the ceramic substrates than on the metal substrates.

• Journal of Radiation Protection and Research
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• v.20 no.2
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• pp.79-83
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• 1995

A number of investigators have reported formation of radiolytic ultrafine particles produced by the interaction of ionizing radiation with atmospheric trace gases. Previous studies have suggested that a very high localized concentration of the hydroxyl radical produced by the radiolysis of water can react with atmospheric trace gases such as $SO_2$ and produce lower vapor pressure compounds that can subsequently nucleate. To determine the trace gas and water vapor concentration dependence of the active, positively charged, first decayt product of radon (Po-218), a well-controlled radon chamber was used in this research. The mobility spectrum of the decay products in the range of $0.07-5.0cm^2/V\;sec$ from the radon chamber was measured using alpha track detector installed inside a specially-designed electrostatic spectrometer. Measurements were taken for different concentrations (0.5ppm to 5ppm) of $SO_2$ in Purified, Compressed air. A kinetics Study following the clustering of $SO_2$ around the $PoO_x^+$ ion in an excess of $SO_2$ for interpretation of the reaction processes was performed.