• Tribology and Lubricants
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• v.40 no.3
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• pp.84-90
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• 2024

This study investigates the effect of the surface microstructure on the tribological characteristics of glass substrates. Chemical etching using hydrofluoric acid and ammonium hydrogen fluoride was employed to create controlled asperity structures on glass surfaces. By varying the etching time from 10 to 50 min, different surface morphologies were obtained and characterized using optical microscopy, surface roughness measurements, and water contact angle analysis. Friction tests were performed using a stainless steel ball as the counter surface to evaluate the tribological behavior of the etched specimens. The results showed that the specimen etched for 20 min exhibited the lowest and most stable friction coefficient, which was attributed to the formation of a uniform and dense asperity structure that effectively reduced the stress concentration and wear at the contact interface. In contrast, specimens etched for shorter (10 min) or longer (30-50 min) durations displayed higher friction coefficients and accelerated wear owing to nonuniform asperity structures that led to local stress concentration. Optical microscopy of the wear tracks further confirmed the superior wear resistance of the 20-minute etched specimen. These findings highlight the importance of optimizing the etching process parameters to achieve the desired surface morphology for enhanced tribological performance, suggesting the potential of chemical etching as a surface modification technique for various materials in tribological applications.

• Geomechanics and Engineering
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• v.23 no.2
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• pp.151-163
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• 2020

Grouting method is an effective way of reinforcing cracked rock masses and plugging water gushing. Current grouting diffusion models are generally developed for horizontal cracks, which is contradictory to the fact that the crack generally occurs in rock masses with irregular spatial distribution characteristics in real underground environments. To solve this problem, this study selected a cement-sodium silicate slurry (C-S slurry) generally used in engineering as a fast-curing grouting material and regarded the C-S slurry as a Bingham fluid with time-varying viscosity for analysis. Based on the theory of fluid mechanics, and by simultaneously considering the deadweight of slurry and characteristics of non-uniform spatial distribution of viscosity of fast-curing grouts, a theoretical model of slurry diffusion in an oblique crack in rock masses at constant grouting rate was established. Moreover, the viscosity and pressure distribution equations in the slurry diffusion zone were deduced, thus quantifying the relationship between grouting pressure, grouting time, and slurry diffusion distance. On this basis, by using a 3-d finite element program in multi-field coupled software Comsol, the numerical simulation results were compared with theoretical calculation values, further verifying the effectiveness of the theoretical model. In addition, through the analysis of two engineering case studies, the theoretical calculations and measured slurry diffusion radius were compared, to evaluate the application effects of the model in engineering practice. Finally, by using the established theoretical model, the influence of cracking in rock masses on the diffusion characteristics of slurry was analysed. The results demonstrate that the inclination angle of the crack in rock masses and azimuth angle of slurry diffusion affect slurry diffusion characteristics. More attention should be paid to the actual grouting process. The results can provide references for determining grouting parameters of fast-curing grouts in engineering practice.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.7
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• pp.946-953
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• 2018

Photo-plethysmography (PPG), which measures changes in the peripheral blood flow of a human body using difference in absorption rate of light, is a measurement method that is studied and used in clinical and various applications due to its simple circuit configuration and measurement convenience. Magneto-plethysmography (MPG), which is newly developed by our team, is a method of measuring changes in the conductivity of biological tissues by using a eddy current induced by a time-varying magnetic field, and is not subject to optical interference. In this study, we investigated the detection characteristics of MPG according to the change of the conductivity of the object and fluid to be measured by simultaneously measuring PPG and MPG. In order to control the speed of fluid known in advance, a blood flow simulator was implemented and used. The fluid used in the experiment was general mineral water and physiological saline (0.9% NaCl) solution. Experimental results show that the amplitude change of the measured PPG was 0.3% in normal water and saline solution, and that of MPG was 77.3%. Therefore, it is considered that the magneto-plethysmography (MPG) has a strong correlation with the conductivity of the fluid.

• Journal of Soil and Groundwater Environment
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• v.20 no.5
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• pp.16-25
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• 2015

The City of Boulder is located at an average elevation of 1,655 m (5,430 feet), the foothills of the Rocky Mountains in Colorado. Its daily air temperature is much varying and snow is very frequent and heavy even in spring. This paper examines characteristics of shallow (surface and depth = 10 cm) soil temperatures measured from January to May 2015 in the high elevation city Boulder, Colorado. The surface soil temperature quickly responded to the air temperature with the strongest periodicity of 1 day while the subsurface soil temperatures showed a less correlation and delayed response with that. The short-time Fourier of the soil temperatures uncovered their very low frequencies characteristics in heavy snow days while it revealed high frequencies of their variations in warm spring season. The daily minimum air temperature exhibited high cross-correlations with the soil temperatures without lags unlike the maximum air temperature, which is derived from its higher and longer auto-correlation and stronger spectrums of low frequencies than the maximum air temperature. The snow depth showed an inverse relationship with the soil temperature variations due to snow's low thermal conductivity and high albedo. Multiple regression for the soil temperatures using the air temperature and snow depth presented its predicting possibility of them even though the multiple r² of the regression is not that much satisfactory (r² = 0.35-0.64).

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.78-85
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• 2007

Recently, diesel vehicles have been increased and their emission standards have been getting strict. The emission of diesel vehicles contains numerous dangerous compounds, especially particulate matters cause a serious environmental pollutant and affect to human health seriously. Thousands of studies have already reported that particulate matters are associated with respiratory and cardiovascular diseases, and death. Due to these, it is necessary to measure the soot concentration and soot particle size in laboratory flames or practical engines to recognize the soot formation, and develop the control strategies for soot emission. In this study, the characteristics of exhausted soot particle size and volume fraction from 2.0L CRDI diesel engine have been investigated as varying engine speed and load. Laser induced incandescence has been used to measure soot concentration. Time-resolved laser induced incandescence has been used to determine soot particle size in the engine. The soot volume fraction is increased as increasing engine load but soot volume fraction is decreased as increasing engine speed. The primary particle size is distributed about $35nm{\sim}60nm$ at each experimental conditions.

• Asian-Australasian Journal of Animal Sciences
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• v.20 no.6
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• pp.887-893
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• 2007

Influences of forage DM and addition of cane molasses on silage characteristics of berseem (Trifolium alexandrium) and lucerne (Medicago sativa) and their ruminal digestion kinetics in Nili buffaloes were studied. Berseem and lucerne fodders (at one tenth bloom) were ensiled with wheat straw in laboratory silos to achieve 20, 30, 40% forage DM and without wheat straw (control); each forage DM level was supplemented with 2, 4 and 6% of cane molasses at ensiling. The pH and lactic acid contents of berseem and lucerne silages were affected by both forage DM and addition of molasses. Dry matter, CP and true protein (TP) of berseem and lucerne silages were affected by forage DM at ensiling but were not affected by the addition of cane molasses. Higher DM, CP and TP losses were observed when berseem and lucerne fodders were ensiled either without wheat straw or with wheat straw to achieve 20% and 40% forage DM at ensiling compared with 30% DM at ensiling. Fiber fractions (NDF, ADF, hemicellulose and cellulose) of berseem silage and lucerne silage were significantly increased with increasing forage DM at ensiling. Addition of cane molasses did not affect the DM, CP, TP and fiber fractions of both berseem and lucerne silages. Berseem and lucerne ensiled at 30% DM with 2% cane molasses were screened for comparative ruminal digestion kinetics with their respective fodders. Addition of wheat straw to berseem or lucerne fodder at ensiling depressed DM and NDF ruminal degradability. However, ruminal lag time, rate of degradation and extent of digestion of silages were similar to their respective fodders. In conclusion, berseem and lucerne could be ensiled with wheat straw to increase their DM to 30% along with 2% molasses for buffaloes.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.68-75
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• 2015

In this paper, unsteady characteristics of pressure in solid rocket motor were analyzed by using response of pintle actuation, pressure and thrust data from ground test. Pressure and thrust in solid rocket motor can be controlled in real time by varying nozzle throat area with pintle, installed in the valve. Unsteady characteristics of pressure can be observed in this system occurred by various reasons. Two critical reasons, error of pintle actuation and ablation of center tube, are found and effects of each reason can be analyzed individually by re-prediction of pressure with response of pintle actuation and analyzing thrust to pressure ratio.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.4
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• pp.18-24
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• 2010

This paper presents the improvement of the field uniformity in a reverberation chamber which can be substitute an anechoic chamber for the electromagnetic interference (EMI) and immunity test. Nowadays, there are many EMI issues due to the increasing use of wireless local area network (LAN), digital multimedia broadcasting (DMB), and mobile internet. With this reason, this paper studied the field characteristics in a reverberation chamber for 2.3 GHz band. In this paper, the finite difference time domain (FDTD) method is used to analyze the field characteristics in a reverberation chamber. To improve the field uniformity in the reverberation chamber, this paper adopted a 2D cubical residue diffuser (CRD) with varying the disposition and number of CRD. For each case, the tolerance and standard deviation of the electric field strength are evaluated. In comparison with the reverberation chamber without any CRD, the reverberation chamber with two CRDs showed improved results; 1.98 dB improvement in standard deviation and 3.6 dB improvement in tolerance.

• Applied Chemistry for Engineering
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• v.29 no.4
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• pp.388-394
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• 2018

The removal of 2,4-dichlorophenol (2,4-dichlorophenol, 2,4-DCP) in aqueous solution was studied using the magnetic activated carbon (MAC) prepared from waste citrus peel. The adsorption characteristics of 2,4-DCP by MAC were investigated by varying the contact time, MAC dose, solution temperature, pH and 2,4-DCP concentration. The isothermal adsorption data were well explained by the Langmuir isotherm model equation and the maximum adsorption capacity calculated from the Langmuir isotherm equation was 312.5 mg/g. The adsorption kinetic data were well described by the pseudo-second-order reaction equation. The intraparticle diffusion model data indicated that both the film and intraparticle diffusion occur simultaneously during the adsorption process. The thermodynamic parameters of ${\Delta}H^o$ and ${\Delta}G^o$ have positive and negative values, respectively, indicating that the adsorption of 2,4-DCP by MAC is a spontaneous endothermic reaction. After the adsorption experiment was completed, the used MAC could be easily separated by an external magnet.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.139-139
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• 2010

Ionic Transition Metal Complex based (iTMC) Light-emitting electrochemical cells (LEECs) have been drawn attention for cheap and easy-to-fabricate light-emitting device. LEEC is one of the promising candidate for next generation display and solid-state lighting applications which can cover the defects of current commercial OLEDs like complicated fabrication process and strong work-function dependent sturucture. We have investigated the performance characteristics of LEECs based on poly (3, 4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS)-incorporated transition metal complex, which is tris(2, 2'-bipyridyl)ruthenium(II) hexafluorophosphate in this study. There are advantages using conductive polymer-incorporated luminous layer to prevent light disturbance and absorbance while light-emitting process between light-emitting layer and transparent electrode like ITO. The devices were fabricated as sandwiched structure and light-emitting layer was deposited approximately 40nm thickness by spin coating and aluminum electrode was deposited using thermal evaporation process under the vacuum condition (10-3Pa). Current density and light intensity were measured using optical spectrometer, and surface morphology changes of the luminous layer were observed using XRD and AFM varying contents of PEDOT:PSS in the Ruthenium(II) complex solution. To observe enhanced ionic conductivity of PEDOT:PSS and luminous layer, space-charge-limited-currents model was introduced and it showed that the performances and stability of LEECs were improved. Main discussions are the followings. First, relationship between film thickness and performance characteristics of device was considered. Secondly, light-emitting behavior when PEDOT:PSS layer on the ITO, as a buffer, was introduced to iTMC LEECs. Finally, electrical properties including carrier mobility, current density-voltage, light intensity-voltage, response time and turn-on voltages were investigated.