• Journal of the Korean GEO-environmental Society
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• v.19 no.4
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• pp.5-16
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• 2018

In the current study, the engineering behaviour of prebored and precast steel pipe piles was examined from a series of full-scale field measurements by conducting static pile load tests, dynamic pile load tests (EOID and restrike tests) and Class-A and Class-C1 type numerical analysis. The study includes the pile load - settlement relations, allowable pile capacity and shear stress transfer mechanism. Compared to the allowable pile capacity obtained from the static pile load tests, the dynamic pile load tests and the numerical simulation showed surprisingly large variations. Overall among these the restrike tests displayed the best results, however the reliability of the predictions from the numerical analysis was lower than those estimated from the dynamic pile load tests. The allowable pile capacity obtained from the EOID tests and the restrike tests indicated 20.0%-181.0% (avg: 69.3%) and 48.2%-181.1% (avg: 92.1%) of the corresponding measured values from the static pile loading tests, respectively. Furthermore, the computed results from the Class-A type analysis showed the largest scatters (37.1%-210.5%, avg: 121.2%). In the EOID tests, a majority of the external load were carried by the end bearing pile capacity, however, similar skin friction and end bearing capacity in magnitude were mobilised in the restrike tests. The measured end bearing pile capacity from the restrike tests were smaller than was measured from the EOID tests. The present study has revealed that if the impact energy is not sufficient in a restrike test, the end bearing pile capacity most likely will be underestimated. The shear stresses computed from the numerical analysis deviated substantially from the measured pile force distributions. It can be concluded that the engineering behaviour of the pile is heavily affected if a slime layer exists near the pile tip, and that the smaller the stiffness of the slime and the thicker the slime, the greater the settlement of the pile.

• Journal of Pharmacopuncture
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• v.18 no.1
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• pp.79-85
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• 2015

Objectives: A vertebral compression fracture (VCF) is characterized by back pain and fracture of a vertebral body on spinal radiography. VCFs of the thoraco lumbar spine are common in the elderly. In general, appropriate analgesics should be prescribed to reduce pain and, thus, promote early mobilization. The ideal treatment approach for VCFs has not been determined. In Korea, acupuncture and herbal medication have been used to treat VCFs for many years. There is empirical evidence that acupuncture might benefit patients with a VCF. However, no randomized, controlled, clinical trials evaluating the efficacy and the safety of acupuncture for treating a VCF have been published. Therefore, we designed a randomized, controlled, pilot, clinical trial to obtain information for the design of a further full scale trial. Methods: A five week protocol for a randomized, controlled, pilot, clinical trial is presented. Fourteen patients will be recruited and randomly allocated to two groups: a control group receiving interlaminar epidural steroid injections once a week for three weeks, and an experimental group receiving interlaminar epidural steroid injections plus acupuncture treatment (three acupuncture sessions per week for three weeks, nine sessions in total). The primary outcomes will be the pain intensity (visual analogue scale and PainVision$^{TM}$ system). The secondary outcome measurements will be the answers on the short form McGill pain questionnaire and the oswestry disability index. Assessments will be made at baseline and at one, three, and five weeks. The last assessment (week five) will take place two weeks after treatment cessation. This study will provide both an indication of feasibility and a clinical foundation for a future large scale trial. The outcomes will provide additional resources for incorporating acupuncture into existing treatments, such as nonsteroidal anti-inflammatory medications, narcotics and vertebral augmentation. This article describes the protocol.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.445-453
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• 2010

Recently, the remodeling projects of old low-rise buildings were launched in Korea. However, most of them were not satisfied with the value set forth by the KBC2005. Even though there are some research studies on how to improve the seismic performance of such buildings as newly constructed buildings, there is little research in measuring the actual vibrations on low old buildings to prove the effect of retrofit. There also has not been any in-depth research on the dynamic characteristics of full-scale structures using vibration measurements of the building that was damaged to failure. Using an actuator, the dynamic characteristics of reinforced three-storey concrete buildings were evaluated before and after they were damaged. After an 80-mm horizontal displacement by the actuator, frequency in the long and short directions were reduced to 20.85% and 5.77% respectively ; damping ratio was also reduced to 53.9% and 23.15% respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.76.1-76.1
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• 2015

Optical resonances of metallic or dielectric nanoantennas enable to effectively convert free-propagating electromagnetic waves to localized electromagnetic fields and vice versa. Plasmonic resonances of metal nanoantennas extremely modify the local density of optical states beyond the optical diffraction limit and thus facilitate highly-efficient light-emitting, nonlinear signal conversion, photovoltaics, and optical trapping. The leaky-mode resonances, or termed Mie resonances, allow dielectric nanoantennas to have a compact size even less than the wavelength scale. The dielectric nanoantennas exhibiting low optical losses and supporting both electric and magnetic resonances provide an alternative to their metallic counterparts. To extend the utility of metal and dielectric nanoantennas in further applications, e.g. metasurfaces and metamaterials, it is required to understand and engineer their scattering characteristics. At first, we characterize resonant plasmonic antenna radiations of a single-crystalline Ag nanowire over a wide spectral range from visible to near infrared regions. Dark-field optical microscope and direct far-field scanning measurements successfully identify the FP resonances and mode matching conditions of the antenna radiation, and reveal the mutual relation between the SPP dispersion and the far-field antenna radiation. Secondly, we perform a systematical study on resonant scattering properties of high-refractive-index dielectric nanoantennas. In this research, we examined Si nanoblock and electron-beam induced deposition (EBID) carbonaceous nanorod structures. Scattering spectra of the transverse-electric (TE) and transverse-magnetic (TM) leaky-mode resonances are measured by dark-field microscope spectroscopy. The leaky-mode resonances result a large scattering cross section approaching the theoretical single-channel scattering limit, and their wide tuning ranges enable vivid structural color generation over the full visible spectrum range from blue to green, yellow, and red. In particular, the lowest-order TM01 mode overcomes the diffraction limit. The finite-difference time-domain method and modal dispersion model successfully reproduce the experimental results.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.1
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• pp.23-26
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• 2000

We have fabricated by metal organic chemical vapor deposition (MOCVD) In$\_$0.13/Ga$\_$0.87/N/GaN multiple quantum well (MQW) with thickness as thin as 10 A and barriers also of th same width on (0001) sapphire substrate. We have investigated this thin MQW by steady-state and time-resolved photoluminescence(PL) in picosecond time scale in a wide temperature range from 10 to 290 K. In the PL at 10 K, we observed a broad peak at 3.134 eV which was attributed to the quantum well emission of InGaN. The full width at half maximum (FWHM) of this peak was 129 meV at 10 K and its broadening at low temperatures was considered to be due to compositional fluctuations and interfacial disorder in the alloy. The narrow width of the quantum well was mainly responsible for the broadening of the emission linewidth. We also observed an intense and sharp peak at 3.471 eV of GaN barrier. From the temperature dependent PL measurements, the activation energy of the InGaN quantum well emision peak was estimated to be 69 meV. The lifetime of the quantum well emission was found to be 720 ps at 10 K, which was explained in terms of the exciton localization arising from potential fluctuations.

• Geomechanics and Engineering
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• v.3 no.4
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• pp.291-321
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• 2011

The paper describes a simple numerical FLAC model that was developed to simulate the dynamic response of two instrumented reduced-scale model reinforced soil walls constructed on a 1-g shaking table. The models were 1 m high by 1.4 m wide by 2.4 m long and were constructed with a uniform size sand backfill, a polymeric geogrid reinforcement material with appropriately scaled stiffness, and a structural full-height rigid panel facing. The wall toe was constructed to simulate a perfectly hinged toe (i.e. toe allowed to rotate only) in one model and an idealized sliding toe (i.e. toe allowed to rotate and slide horizontally) in the other. Physical and numerical models were subjected to the same stepped amplitude sinusoidal base acceleration record. The material properties of the component materials (e.g. backfill and reinforcement) were determined from independent laboratory testing (reinforcement) and by back-fitting results of a numerical FLAC model for direct shear box testing to the corresponding physical test results. A simple elastic-plastic model with Mohr-Coulomb failure criterion for the sand was judged to give satisfactory agreement with measured wall results. The numerical results are also compared to closed-form solutions for reinforcement loads. In most cases predicted and closed-form solutions fall within the accuracy of measured loads based on ${\pm}1$ standard deviation applied to physical measurements. The paper summarizes important lessons learned and implications to the seismic design and performance of geosynthetic reinforced soil walls.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.237-247
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• 2002

A total of 18 stress measurements were performed in the rock and rock-like blocks in the laboratory to estimate the influence of anisotropy in rock. Full scale overcoring equipment, which consists of a coring machine and a biaxial loading system by flat jacks, was developed to simulate the in-situ rock stress condition in the laboratory By comparing the isotropic analysis with the anisotropic analysis in measuring the stress, conclusions have been drawn as to the influence of anisotropy. The maximum difference between the isotropic and the anisotropic analysis was 34% and it was shown that the stress measurement considering the anisotropy was needed. To confirm the validity of the observed data, a diagnostic analysis of stress relief curve by overcoring was conducted using the three dimensional finite difference program, FLAC 3D.

• Aerospace Engineering and Technology
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• v.3 no.2
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• pp.217-228
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• 2004

This paper presents the rotating test techniques and the results of the roating test of the small-scaled hingeless rotor system with composite paddle blades in hover and forward flight conditions. The small-scaled rotor system was designed using froude-scaled properties of full scale rotor system. Metal flexures and composite flexures were made as hub flexures by the same dynamic properties of rotor system. The rotating tests of hingeless rotor system installed in GSRTS at KARI were carried out to get lead-lag damping ratios and aerodynamic loads of the hingeless rotor system. MBA(Moving Block Analysis) technique was used for the estimation of lead-lag damping ratio. 6-components balance was installed between hub and main shaft and straingauges on blades were instrumented for the measurements of aerodynamic loads of rotor system. Tests were performed on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively.

• Fire Science and Engineering
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• v.24 no.5
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• pp.128-135
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• 2010

In this study, a mixture fraction analysis was performed to investigate the characteristics of chemical species production in compartment fires burning hydrocarbon fuels such as methane, heptane, and toluene. A series of fire experiments was conducted in the ISO 9705 standard room, and gas species concentration and soot fraction were measured at two locations in the upper layer of the compartment. The mass fractions of measured chemical species, such as unburned hydrocarbons (UHC), carbon monoxide (CO), carbon dioxide ($CO_2$), oxygen ($O_2$), and soot were presented as a function of mixture fraction and compared with state relationships based on the idealized reaction of hydrocarbon fuels. The mixture fraction analysis made it possible to rearrange hundreds of species measurements, which were done under various fire conditions and at two locations of the upper layer, in term of the unified parameter, i.e. the mixture fraction. The results also showed that inclusion of soot in the mixture fraction calculation could improve the performance of analysis, especially for the sooty fuels such as heptane and toluene.

• Structural Monitoring and Maintenance
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• v.1 no.1
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• pp.131-157
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• 2014

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.