• Geomechanics and Engineering
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• v.33 no.1
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• pp.91-99
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• 2023

To test the effect of various pile tip shape series of model scale loading tests were carried out on test piles with special pile tips. Special pile tips were made using the 3D printer and were attached to the bottom end of the test pile for loading tests. The pile tips were made to have 30°, 45°, 60° inclined tips, as well as a rounded tip. The main objective of the test was to observe the effect of various pile tip shapes on settlement and penetrability of the pile. Moreover, a numerical model simulating the pile loading test carried out in this study was established and verified based on the loading test results. From this, the stress concentration around the pile tip was investigated. This will allow us to analyze the decrease of stress concentration around the pile tip which is the main cause of the pile tip damage during pile installation. However, modifying the pile tip shape will eventually increase the settlement of the pile. By estimating the degree of increase in pile settlement, the viability and the efficiency of the pile shape modification was judged. In addition, case studies on the effect of different pile tip shape and ground conditions on pile settlement and stress dispersion was conducted.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.12-17
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• 2017

We construct 3D SV-wave velocity structure of the crust and the upper mantle beneath East Asia from Rayleighwave group-velocity measurements. For the construction of the SV-wave velocity model at 10 ~ 100 km depth, we used seismic data recorded at 321 broadband stations in Korea, Japan, and China. Rayleigh-wave group-velocity dispersion curves were obtained by using the multiple filtering technique in the period range from 3 to 150 s. High SV-velocity anomalies are imaged beneath the East Sea from 10 km depth to deeper depth, implying that the Moho beneath the East Sea is between at 10 ~ 20 km depth. We estimated the Moho beneath the Korean peninsula to be around 35 km based on the depth where a high-velocity anomaly is observed. The SV-wave velocity model shows prominent fast S-velocity anomalies near northeastern Japan, associated with the subducting Pacific plate. Low-velocity anomalies are found beneath the east coast of the Korean peninsula at 100 km depth, which may play a role in the formation of the Ulleungdo and the Ulleung basin. We observed low-velocity anomalies beneath the Yamato basin at 100 km depth as well, which may indicate the upwelling of fluid from the Pacific plate via dehydration at deeper depth.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.69-79
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• 2008

Prediction of ground condition ahead of tunnel face might be the most important factor to prevent collapse during tunnel excavation. In this study, a non-destructive method to evaluate the phase velocity in model rock mass using wavelet transform of surface wave was proposed aiming at ground condition assessment ahead of tunnel face. Model tests using gypsum as a rocklike material composed of two layers were performed. A Piezoelectric actuator with frequencies ranging from 150 Hz to 5 kHz was selected as a harmonic source. The acceleration history was measured with two accelerometers. Wavelet transform analysis was used to obtain the dispersion curves from the measured data. The experimental results showed that the near-field effects can be neglected if the distance between two receivers is chosen to be three times the wavelength. A simple inversion method using weighted factor based on the normal distribution was proposed. The inversion results showed that the predicted phase velocity agreed reasonably well with the measured one when the wavelength influence factor was 0.2. The depth of propagation of surface wave was from 0.42 to 0.63 times the wavelength. The range of wavelength varying with phase velocity in dispersion curve matched well with that estimated by inversion technique.

• Journal of Soil and Groundwater Environment
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• v.12 no.6
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• pp.17-25
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• 2007

Convergent flow tracer test for 2 m (IW-1 well) and 5 m (IW-2 well) of test scale was conducted at the alluvial aquifer with high permeability and storativity. Pumping rate for convergent flow tracer test were $2,500m^3/day$, and the chloride tracer of 5 kg was instantaneously injected into IW-1 and IW-2 wells. Differences of first arrival time and peak concentration were analyzed by using the concentration breakthrough curves of chloride. Recovered chloride mass were analyzed by recovered cumulative mass curves. And, increment and decrement for chloride concentration were analyzed through chloride concentration versus recovered cumulative mass ratio graphs. Also, increment and decrement ratios of chloride concentration were estimated through linear regression analyses for increment and decrement intervals of chloride concentration. Longitudinal dispersivities were estimated by quot;Converging Radial Flow With Instantaneous Injectionquot; method using CATTI code. Longitudinal dispersivities estimated by CATTI code were 0.4152 m between pumping well and IW-1 well, and 3.2665 m between pumping well and IW-2 well. Longitudinal dispersivity was increased according to far distance from the pumping well. The longitudinal dispersivity according to distance were estimated as 0.21 between pumping well and IW-1 well, and 0.65 between pumping well and IW-2 well.

• Polymer(Korea)
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• v.30 no.1
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• pp.85-89
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• 2006

The effect of vapor grown carbon fiber (VGCF) contents on electrical and rheological properties of VGCF filled polyphenylene sulfide (PPS) composites prepared through melt mixing using a twin screw exruder was studied. This method was proved to be quite effective to produce good dispersion of VGCF in the matrix even for highly filled PPS. From the dependence of the electrical conductivity on VGCF content, the percolation phenomena began to occur above $10\;wt\%$. While there is only a marginal increase of viscosity for 1 and $5\;wt\%$ VGCF filled PPS, the composites containing $10\;wt\%$. While VGCF showed abrupt increase in viscosity as well as flattening of frequency vs modulus curve, indicating a transition from a liquid-like to a solid-like behavior due to the creation of VGCF network. This result agrees well to the fact that the network formation in the composite can be composite by rheological property dependence on filler content as well as by electrical conductivity measurement.

• Korean Journal of Veterinary Research
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• v.36 no.3
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• pp.541-550
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• 1996

Tetracycline antibiotics have been widely used not only therapeutics but feed additives. There are many methods for the isolation and determination of tetracycline antibiotics in animal muscle tissue. But those methods take much time and labor, so it is difficult to analyse many samples simultaneously. A rapid isolation method and liquid chromatographic determination of tetracycline antibiotics in animal muscle tissue (bovine, porcine, chicken) is presented. Blank control and tetracyclines fortified samples (0.5g) were blended with $C_{18}$ containing 0.05g each of oxalic acid and disodium ethylenediaminetetraacetate. After homogenize, homogenate was transferred to glass column made from 10ml glass syringe and compressed to 4~4.5ml volume. A column made from the $C_{18}$/meat matrix was washed with hexane (8ml) and dichloromethane (8ml, if needed), following which the tetracyclines were eluted,vith methanol or 0.01M methanolic oxalic acid (8ml). The eluates containing tetracyclines analytes were free from interfering compounds when analysed by HPLC with UV detection (photodiode array at 360nm). Standard curve for each tetracycline showed a linear response at the range of $0.05{\sim}1.0{\mu}g/ml$ and tetracycline antibiotics were eluted within 4ml of eluted volume. All tetracycline antibiotics except tetracycline were stable during the concentration process at $40^{\circ}C$ and time required for concentration was 3~4 hours. Fortified samples containing oxalic aicd and EDTA represented more good recoveries than those of not-contained sample. Recoveries were 91.8~110.1% (oxytetracycline; OTC), 57.7~79.5% (tetracycline; TC), 78.1~88.6% (chlortetracyclines; CTC) and 88.4~100.6% (doxycycline; DC) in pork tissue, 101.1~126.8% (OTC), 66.4~75.4% (TC), 79.2~88.1% (CTC) and 69.3~86.7% (DC) in beef tissue, and 90.8~95.6% (OTC), 66.2~84.4% (TC), 75.7~77.2% (CTC) and 55.6~80.7% (DC) in chicken muscle tissue. The detection limits validated in muscle tissue by this method were $0.05{\mu}g/g$ for OTC and TC, and $0.1{\mu}g/g$ for CTC and DC.

• Archives of Pharmacal Research
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• v.28 no.5
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• pp.604-611
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• 2005

Polyethylene glycol (PEG) 6000-based solid dispersions (SDs), by incorporating various pharmaceutical excipients or microemulsion systems, were prepared using a fusion method, t o compare the dissolution rates and bioavailabilities in rats. The amorphous structure of the drug in SDs was also characterized by powder X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The ketoconazole (KT), as an antifungal agent, was selected as a model drug. The dissolution rate of KT increased when solubilizing excipients were incorporated into the PEG-based SDs. When hydrophilic and lipophilic excipients were combined and incorporated into PEG-based SDs, a remarkable enhancement of the dissolution rate was observed. The PEG-based SDs, incorporating a self microemulsifying drug delivery system (SMEDDS) or microemulsion (ME), were also useful at improving the dissolution rate by forming a microemulsion or dispersible particles within the aqueous medium. However, due to the limited solubilization capacity, these PEG-based SDs showed dissolution rates, below 50% in this study, under sink conditions. The PEG-based SD, with no pharmaceutical excipients incorporated, increased the maximum plasma concentration (C$_{max}$) and area under the plasma concentration curve (AUC$_{0-6h}$) two-fold compared to the drug only. The bioavailability was more pronounced in the cases of solubilizing and microemulsifying PEG-based SDs. The thermograms of the PEG-based SDs showed the characteristic peak of the carrier matrix around 60$^{\circ}C$, without a drug peak, indicating that the drug had changed into an amorphous structure. The diffraction pattern of the pure drug showed the drug to be highly crystalline in nature, as indicated by numerous distinctive peaks. The lack of the numerous distinctive peaks of the drug in the PEG-based SDs demonstrated that a high concentration of the drug molecules was dissolved in the solid-state carrier matrix of the amorphous structure. The utilization of oils, fatty acid and surfactant, or their mixtures, in PEG-based SD could be a useful tool to enhance the dissolution and bioavailability of poorly water-soluble drugs by forming solubilizing and microemulsifying systems when exposed to gastrointestinal fluid.

• Journal of the Korean Institute of Gas
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• v.20 no.6
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• pp.50-57
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• 2016

Pipeline is one of the most abundant components in petrochemical plant. It plays a critical role in transporting fluids. Some pipelines are thermally insulated by wrapping them with insulating materials to prevent the loss of energy. However, when corrosion begins under insulation, it cannot be easily seen without unwrapping the cover, and thus corrossion should be detected using a non-destructive ways such as ultrasound guided wave. In this paper, the piping where the CUI (Corrosion Under Insulation) which occurs in the insulation parts guided waves effectively the optimum condition which is theoretical for selected guided waves phase velocity dispersion curve and wave-structure. The results of this study are expected to be directly utilized for onsite inspection of pipeline's CUI in many petrochemical plants.

• Korean Chemical Engineering Research
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• v.59 no.2
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• pp.281-295
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• 2021

In this study, the direct amination of ethanol was performed over impregnated Ni on SiO2-Al2O3 mixed oxide catalysts prepared by varying Si/(Si + Al) molar ratio to 30 mol%. To characterize the physico-chemical properties of the catalysts used, X-ray diffraction (XRD), N2-physisorption, temperature-programmed desorption of iso-propyl alcohol (IPA-TPD), temperature-programmed desorption of ethanol (EtOH-TPD), temperature-programmed reduction with H2 (H2-TPR), H2-chemisorption and transmission electron microscopy (TEM) were used. The acidic property was continuously increased until Si/(Si + Al) = 30 mol% in SiO2-Al2O3 mixed oxides used. The dispersion of Ni metal and surface area, acid characteristics of the supported Ni catalyst have a complex effect on the catalytic reaction activity. The low reduction temperature of nickel oxide and acidic properties were beneficial to the formation of acetonitrile. In terms of conversion of ethanol, Ni/SiO2-Al2O3 catalyst with a molar ratio of 10 mol% Si/(Si+Al) showed the highest activity and a volcanic curve based on it. The tendency of results were consistent in the metal dispersion and catalytic activity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4C
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• pp.231-238
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• 2008

A column testing device capable of measuring the electrical resistivity of soil at 3 different locations was developed to verify applicability of bulk electrical conductivity (BEC) breakthrough curves in monitoring contaminant transport. Tracer injection tests were conducted with three different types of saturated sands to obtain average linear velocities and longitudinal hydrodynamic dispersion coefficients based on BEC breakthrough curves and effluent solute breakthrough curves. Comparative analysis of transport parameters obtained from curve fitting the results into the analytical solutions confirmed the validity of resistance measurements in estimating time-continuous resident solute concentration. Under the assumption that a linear relationship exists between ${\sigma}_{sat}-{\sigma}_w-C$, the BEC breakthrough curves are able to effectively reduce the laborious and time-consuming processes involved in the conventional method of sampling and analysis. In order to reduce possible uncertainties in analyzing the BEC breakthrough curves, it was recommended that resistance measurements take place nearby the effluent boundary. In addition, a sufficient electrical contrast or difference in the electrical conductivity of the influent and the saturating solution is required to conduct reliable analysis.