• Geomechanics and Engineering
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• v.20 no.1
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• pp.75-86
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• 2020

This study aims to simulate the stabilization process of fibrous peat samples using end-bearing Cement Deep Mixing (CDM) columns by three area improvement ratios of 13.1% (TS-2), 19.6% (TS-3) and 26.2% (TS-3). It also focuses on the determination of approximate stress distribution between CDM columns and untreated fibrous peat soil. First, fibrous peat samples were mechanically stabilized using CDM columns of different area improvement ratio. Further, the ultimate bearing capacity of a rectangular foundation rested on the stabilized peat was calculated in stress-controlled condition. Then, this process was simulated via a FEM-based model using Plaxis 3-D foundation and the numerical modelling results were compared with experimental findings. In the numerical modelling stage, the behaviour of fibrous peat was simulated based on hardening soil (HS) model and Mohr-Coulomb (MC) model, while embedded pile element was utilized for CDM columns. The results indicated that in case of untreated peat HS model could predict the behaviour of fibrous peat better than MC model. The comparison between experimental and numerical investigations showed that the stress distribution between soil (S) and CDM columns (C) were 81%C-19%S (TS-2), 83%C-17%S (TS-3) and 89%C-11%S (TS-4), respectively. This implies that when the area improvement ratio is increased, the share of the CDM columns from final load was increased. Finally, the calculated bearing capacity factors were compared with results on the account of empirical design methods.

• Progress in Medical Physics
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• v.10 no.1
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• pp.55-62
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• 1999

In an effort to study the characteristics of x-rays utilized in radiation therapy, we calculated the energy distribution and the mean energy of x-rays generated from a tungsten target bombarded by 6, 10, and 15 MeV electron beams, using a Monte Carlo technique. The average photon energies calculated as a function of the beam radius lied in 1.4 ∼ 1.6, 2.1 ∼ 2.5 and 2.8 ∼ 3.3 MeV ranges for 4, 10, and 15 MV electron beams, respectively, which turned out to have no strong dependence on the radius. Using the energy distributions of 6,10, and 15 MV x-rays obtained for the target distance of 100 cm, percentage depth doses were determined using Monte Carlo calculations. For the case 10 MV, a comparison was made between our calculation and measurement performed by others. The calculated percentage depth dose appeared somewhat smaller than the measured one except in the surface region. We conclude that this is due to the fact that the beam hardening effect resulting from the flattening filter was not properly allowed for in our Monte Carlo calculations.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.628-634
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• 2016

The cold rolling workability and mechanical properties of two new alloys, designed and cast Al-5.5Mg-2.9Si and Al-7Mg-0.9Zn alloys, were investigated in detail. The two alloy sheets of 4 mm thickness, 30 mm width and 100 mm length were reduced to a thickness of 1 mm by multi-pass rolling at ambient temperature. The rolling workability was better for the Al-7Mg-0.9Zn alloy than for the Al-5.5Mg-2.9Si alloy; in case of the former alloy, edge cracks began to occur at 50% rolling reduction, and their number and length increased with rolling reduction; however, in the latter alloy, the sheets did not have any cracks even at higher rolling reduction. The mechanical properties of tensile strength and elongation were also better in the Al-7Mg-0.9Zn alloy than in Al-5.5Mg-2.9Si alloy. Work hardening ability after cold rolling was also higher in the Al-7Mg-0.9Zn alloy than in the Al-5.5Mg-2.9Si alloy. At the same time, the texture development was very similar for both alloys; typical rolling texture developed in both alloys. These differences in the two alloys can primarily be explained by the existence of precipitates of $Mg_2Si$. It is concluded that the Al-7Mg-0.9Zn alloy is better than the Al-5.5Mg-2.9Si alloy in terms of mechanical properties.

• Archives of Plastic Surgery
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• v.35 no.2
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• pp.219-222
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• 2008

Purpose: The purpose of this study is to develop hydroxyapatite cement simplified procedures for reconstruction of craniofacial deformities. Due to its expense and characteristics of quick hardening time, it may be inappropriate for forehead reconstruction or augmentation. Therefore we hear by introduce a more precise, easy and cheap method. The authors report forehead reconstruction with hydroxyapatite cement for a patient who suffered from craniofacial deformity. Methods: Case report and literature review. Results: A 35 year old man came to us with forehead and temporal area depression. He had a history of brain operations due to traumatic epidural hematoma. A physical exam showed an evidence of right side forehead weakness sign. Authors made RP model of his skull and applied check framework with Kirschner's wires for measuring accurate volume and contour on the depressed right side forehead area on the RP model. After complete exposure of defect area by bicoronary insicion, absorbable plate which applied on skull area was removed. Using three Kirschner's wires, authors made check framework on the right forehead lively and fixed with 2-hole miniplates on the boundary of the defect. After checking asymmetry, hydroxyapatite was applied on check shape framework just above Kirschner's wire. After removing Kirschner's wire, we corrected minimal unbalance and contour with bur. Conclusion: Check framework with Kirschner's wire was very convenient and cost saving methods for forehead reconstruction with hydroxyapatite cement.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.1-15
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• 2004

The development of high-performance shotcrete lining is essential in improving the long-term durability of tunnels and in introducing single-shell tunnelling methods, where shotcrete as well as rockbolts are used as permanent support members. In this paper, new and advanced admixtures to improve shotcrete performance are introduced. In addition, requirements for mechanical properties as well as test items for quality control of shotcrete are summarized. A case study on the application of the pneumatic pin penetration test which can estimate compressive strength of shotcrete more easily and quickly is also illustrated. Previous studies to analyze the behaviors of shotcrete lining by considering its transient hardening and to carry out the sensitivity analysis of the design parameters of shotcrete lining are discussed to give fundamental concepts on rock-support interactions. Representative single-shell tunnelling methods where high-performance shotcrete lining is applied as a permanent support are also introduced.

• International Journal of Korean Welding Society
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• v.1 no.1
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• pp.58-62
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• 2001

The surface of AC8A Ah alloy was modified by adding the Cu powder using a Plasma Transferred Arc (PTA) welding process. Under the optimum fabricating conditions, the modified surface of AC8A Ah alloy was observed to possess the sound microstructure with a minimum porosity. Hardness and wear resistance properties of the as-fabricated alloy were compared with those of the 76 heat-treated one. In case of the as-fabricated alloy, the hardness of the modified layer was twice that of the matrix region. Although significant increase in the hardness of the matrix region was observed after T6 heat treatment, the hardness of the modified layer was not observed to change. The wear resistance of the modified layer was significantly increased compared to that of the matrix region. The microstructure of a weld zone and the matrix region were investigated using the optical microscope, scanning electron microscope (SEM), electron probe microanalysis (EPMA), and transmission electron microscope (TEM). The primary and eutectic silicon in the weld zone were finer and more curved than in the matrix region, while some precipitates has had been found therein. According to the TEM observation, the predominant precipitate present in the weld zone was the $\theta$'phase, which is precipitated during cooling by rapid solidification in PTA welding process. Improvement of hardness and wear properties in the weld zone in the as-fabricated condition can be explained based on the presence of $\theta$’precipitates and fine primary and eutectic silicon distribution.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.305-314
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• 1998

This study has been performed to investigate into some effects of various amounts of $CO_2$ and CO gas added to the $50%NH_3-N_2$ based gas atmosphere on microstructure, hardness, chemical analysis and residual stress in the compound and diffusion layer of AISI H13 treated by gaseous nitrocarburising process. The compound layer formed in the surface is composed of mainly ${\varepsilon}-Fe_3$(N,C) and small amount of ${\gamma}^{\prime}-Fe_4N$ and cementite. The maximum hardness value obtainable from H13 steel is shown to be 1200 Hv and the effecvtive hardening depth increases with increasing CO content from 1% to 4%. In the case of CO content over 4%, however, it decreases with increasing CO content. The composition profiles of nitrogen and carbon are found to be within the ${\varepsilon}$-phase field located above the ${\varepsilon}+{\gamma}^{\prime}$ phase field in the Fe-N-C diagram. It is shown that the maximum value of compressive residual stress of H13 steel treated in atmospheres of $50%NH_3-(2,4)%CO_2-N_2-CO$ gas mixture is $48kg/mm^2$ and the depth to which residual stress is in Compressive state is $90{\mu}m$ for the atmosphere $50%NH_3-45%N_2-4%CO_2-1%CO$ gas mixture. It is consequently important to control the maximum value and size of compressive residual stress region in order to obtain desirable mechanical properties.

• Geotechnical Engineering
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• v.12 no.1
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• pp.73-86
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• 1996

In this study, the possibility of the utilization of coal ash as earthwork materials is investigated. For this purpose, some laboratory experiments were carried out. The samples used in these tests are fly ash(FA), bottom ash(BA), coal ash dropped into ash pond(FA:BA=8:2), and mixed coal ash(FA:BA=5:5), which were discharged as a by-product at Yong-Yeul thermoelectric power plant, and general road filling materials. And for the deformation analysis of coal ash reclamation ground, several hyperbolic model parameters were determined by triaxial compression test. As a result of this study, coal ash has excellent engineering properties such as strength parameters comparing with general soils of the same grain size, especially in case of being used as backfill materials and reclamation materials on soft ground, and coal ash is superior to general earthwork materials in engineering properties becasuse of self hardening behaveiour, light weight property, etc.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1325-1348
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• 2015

Real-time hybrid testing (RTHT) involves virtual splitting of the structure into two parts: physical substructure that contains the key region of interest which is tested in a laboratory and numerical substructure that contains the remaining part of the structure in the form of a numerical model. This paper numerically assesses four step-by-step integration methods (Central difference method (CDM), Operator splitting method (OSM), Rosenbrock based method (RBM) and CR-integration method (CR)) which are widely used in RTHT. The methods have been assessed in terms of stability and accuracy for various realistic damping ratios of the physical substructure. The stability is assessed in terms of the spectral radii of the amplification matrix while the accuracy in terms of numerical damping and period distortion. In order to evaluate the performance of the methods, five carefully chosen examples have been studied - undamped SDOF, damped SDOF, instantaneous softening, instantaneous hardening and hysteretic system. The performance of the methods is measured in terms of a non-dimensional error index for displacement and velocity. Based on the error indices, it is observed that OSM and RBM are robust and performs fairly well in all the cases. CDM performed well for undamped SDOF system. CR method can be used for the system showing softening behaviour. The error indices indicate that accuracy of OSM is more than other method in case of hysteretic system. The accuracy of the results obtained through time integration methods for different damping ratios of the physical substructure is addressed in the present study. In the presence of a number of integration methods, it is preferable to have criteria for the selection of the time integration scheme. As such criteria are not available presently, this paper attempts to fill this gap by numerically assessing the four commonly used step-by-step methods.

• Journal of the Korean Ceramic Society
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• v.44 no.9
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• pp.502-509
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• 2007

This paper investigated how Fine Fly Ash (FFA) with $14,000\;cm^2/g$ of Fineness affects the micro structure and material properties of High-Performance Concrete (HPC) before and after hardening from Material Test of HPC and Cement Paste. FFA is applied as a substitute of Silica Fume which is used necessarily in producing HPC. As a Material Test results, 5% FFA series specimen shows the lower fluidity than SF series specimen. When, however, the Fluidity of 10% FFA series specimen is increased reversely to the similar value of SF series specimen. The Porosity of FFA series specimen of 3 day age is displayed to $21{\sim}24%$, which is higher than $19{\sim}20%$ porosity of SF series specimen, while that of 28 day age is reached to $8{\sim}9%$, which is improved compared with 10% fo SF series specimen. It can be thought that FFA has better influence on the porosity of HPC in case of long term age. The Compressive strength of FFA series specimen shows the similar result with the property of porosity. The compressive strength of 28 day age FFA series specimen is $98{\sim}106%$ of SF series specimen and 107% of plain specimen to reveal better strength development.