• Journal of the Korean Geotechnical Society
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• v.29 no.6
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• pp.77-86
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• 2013

Embankments on soft ground experience significant deformation during time-dependent consolidation settlement, as well as an initial undrained settlement. Since infinitesimal strain theory assumes no configuration change and minute strain during deformation, finite strain analysis is required for better prediction of geotechnical problems involving large strain and geometric change induced by imposed loadings. Updated Lagrangian formulation is developed for time-dependent consolidation combining both force equilibrium and mass conservation of fluid, and mechanical constitutive equation is written in Janumann stress rate. Numerical convergence during Newton's iteration in large deformation analysis is improved by Nagtegaal's approach of considering the effect of rotation in mechanical constitutive relationship. Numerical simulations are conducted to discuss numerical reliability and applicability of developed numerical code: deformation of cantilever beam, two-dimensional consolidation. The numerical results show that developed formulation can efficiently describe large deformation problems. Proposed formulation is expected to facilitate the upgrading of a numerical code based on infinitesimal strain theory to that based on finite strain analysis.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.114-114
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• 2014

We present our activities linking to planning of possible forms of large program to study on circumstellar H2O and SiO maser sources with KaVA. A great advantage of KaVA for the stellar maser observations is the combination of the unique capability of the multi-frequency phase referencing technique of KVN and the dual-beam astrometry of VERA with the KaVA's relative dense antenna configuration. We have demonstrated this advantage through the test observations conducted by the KaVA Evolved Stars Sub-working Group since 2012 March. Snapshot KaVA imaging is confirmed to be possible in integration time of 0.5 hour at the 22 GHz band and 1.0 hour at the 43 GHz band in typical cases. This implies that large snapshot imaging surveys towards many H2O and SiO stellar masers are possible within a reasonable machine time (e.g., scans on ~100 maser sources within 200 hours). This possibility enables us to select the maser sources, which are suitable for future long-term (10 years) intensive (biweekly-monthly) monitoring observations, from 1000 potential target candidates selected from dual-frequency band (K/Q-bands) KVN single-dish observations. The output of the survey programs will be used for statistical analysis of the structures of individual stellar maser clumps and the spatio-kinematical structures of circumstellar envelopes with accelerating outflows. The combination of astrometry in milliarcsecond(mas) level and the multi-phase referencing technique yields not only trigonometric parallax distances to the masers but also precise position reference for registration of different maser lines. The accuracy of the map registration affects interpretation of the excitation mechanism of the SiO maser lines and the origin of the variety of the maser actions, which are expected to reflect periodic behaviors of the circumstellar envelope with stellar pulsation. Currently we are checking the technical feasibility of KaVA operations for this combination. After this feasibility test, the long-term monitoring campaign program will run as one of KaVA's legacy projects.

• Asian Pacific Journal of Cancer Prevention
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• v.17 no.3
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• pp.985-992
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• 2016

Objective of the study is to evaluate volumetric and dosimetric alterations taking place during radiotherapy for locally advanced head and neck cancer (LAHNC) and to assess benefit of replanning in them. Materials and Methods: Thirty patients with LAHNC fulfilling the inclusion and exclusion criteria were enrolled in a prospective study. Planning scans were acquired both pre-treatment and after 20 fractions (mid-course) of radiotherapy. Single plan (OPLAN) based on initial CT scan was generated and executed for entire treatment course. Beam configuration of OPLAN was applied to anatomy of interim scan and a hybrid plan (HPLAN30) was generated. Adaptive replanning (RPLAN30) for remaining fractions was done and dose distribution with and without replanning compared for remaining fractions. Results: Substantial shrinkage of target volume (TV) and parotids after 4 weeks of radiotherapy was reported (p<0.05). No significant difference between planned and delivered doses was seen for remaining fractions. Hybrid plans showed increase in delivered dose to spinal cord and parotids for remaining fractions. Interim replanning improved homogeneity of treatment plan and significantly reduced doses to cord (Dmax, D2% and D1%) and ipsilateral parotid (D33%, D50% and D66%) (p<0.05). Conclusions: Use of one or two mid-treatment CT scans and replanning provides greater normal tissue sparing along with improved TV coverage.

• Nuclear Engineering and Technology
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• v.48 no.3
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• pp.785-794
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• 2016

The Argonne National Laboratory of the United States and the Kharkov Institute of Physics and Technology of the Ukraine have been collaborating on the design, development and construction of a neutron source facility at Kharkov Institute of Physics and Technology utilizing an electron-accelerator-driven subcritical assembly. The electron beam power is 100 kW using 100-MeV electrons. The facility was designed to perform basic and applied nuclear research, produce medical isotopes, and train nuclear specialists. The biological shield of the accelerator building was designed to reduce the biological dose to less than 5.0e-03 mSv/h during operation. The main source of the biological dose for the accelerator building is the photons and neutrons generated from different interactions of leaked electrons from the electron gun and the accelerator sections with the surrounding components and materials. The Monte Carlo N-particle extended code (MCNPX) was used for the shielding calculations because of its capability to perform electron-, photon-, and neutron-coupled transport simulations. The photon dose was tallied using the MCNPX calculation, starting with the leaked electrons. However, it is difficult to accurately tally the neutron dose directly from the leaked electrons. The neutron yield per electron from the interactions with the surrounding components is very small, ~0.01 neutron for 100-MeV electron and even smaller for lower-energy electrons. This causes difficulties for the Monte Carlo analyses and consumes tremendous computation resources for tallying the neutron dose outside the shield boundary with an acceptable accuracy. To avoid these difficulties, the SOURCE and TALLYX user subroutines of MCNPX were utilized for this study. The generated neutrons were banked, together with all related parameters, for a subsequent MCNPX calculation to obtain the neutron dose. The weight windows variance reduction technique was also utilized for both neutron and photon dose calculations. Two shielding materials, heavy concrete and ordinary concrete, were considered for the shield design. The main goal is to maintain the total dose outside the shield boundary less than 5.0e-03 mSv/h during operation. The shield configuration and parameters of the accelerator building were determined and are presented in this paper.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.11
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• pp.937-950
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• 2015

Microstrip reflectarray is an antenna which controls its radiation pattern with a number of reflective elements. Conventionally, the reflectarray has been researched to replace curved reflector antennas. In this paper, design theories of reflectarray is briefly introduced, and research trends of high gain and broadband reflectarrays are reviewed. To improve the gain of the reflectarrays, it is required that the reflection phase errors on the reflectarray surface be minimized. For this purpose, sufficiently wide reflection phase range and low phase sensitivity should be realized with the designed element. For bandwidth improvement, the reflection phase of the element should be linear with the frequency variation. In this paper, various researches to improve the reflection phase characteristics of the element for high gain and broadband reflectarrays, such as multi-layer and single-layer multi-resonant structures, are reviewed. Also, dual-reflectarray configuration for compact antenna design is reviewed. Finally, various applications of reflectarrays such as contoured beam, near-field focusing, and RCS reduction are reviewed.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1297-1300
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• 2008

A conventional linear accelerator system requires a flat-topped pulse with less than ${\pm}$ 0.5% ripple to meet the beam energy spread requirements and to improve pulse efficiency of RF systems. A pulse transformer is one of main determinants on the output pulse voltage shape. The pulse transformer was investigated and analyzed with the pulse response characteristics using a simplified equivalent circuit model. The damping factor ${\sigma}$ must be >0.86 to limit the overshoot to less than 0.5% during the flat-top phase. The low leakage inductance and distributed capacitance are often limiting factors to obtain a fast rise time. These parameters are largely controlled by the physical geometry and winding configuration of the transformer. A rise time can be improved by reducing the number of turns, but it produces larger pulse droop and requires a larger core size. By tradeoffs among these parameters, the high-voltage pulse transformer with a pulse width of 10 ${\mu}s$, a rise time of 0.84 ${\mu}s$, and a pulse droop of 2.9% has been designed and fabricated to drive a klystron which has an output voltage of 284 kV, 30-MW peak and 60-kW average RF output power. This paper describes design optimization of a high-voltage pulse transformer for high-power pulsed applications. The experimental results were analyzed and compared with the design. The design and optimal tuning parameter of the system was identified using the model simulation.

• Steel and Composite Structures
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• v.26 no.6
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• pp.745-757
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• 2018

The inclusion of a ductile steel bracing as means of repairing an earthquake-damaged bridge bent is evaluated and experimentally assessed for the purposes of restoring the damaged bent's strength and stiffness and further improving the energy dissipation capacity. The study is focused on substandard reinforced concrete multi-column bridge bents constructed in the 1950 to mid-1970 in the United States. These types of bents have numerous deficiencies making them susceptible to seismic damage. Large-scale experiments were used on a two-column reinforced concrete bent to impose considerable damage of the bent through increasing amplitude cyclic deformations. The damaged bent was then repaired by installing a ductile fuse steel brace in the form of a buckling-restrained brace in a diagonal configuration between the columns and using post-tensioned rods to strengthen the cap beam. The brace was secured to the bent using steel gusset plate brackets and post-installed adhesive anchors. The repaired bent was then subjected to increasing amplitude cyclic deformations to reassess the bent performance. A subassemblage test of a nominally identical steel brace was also conducted in an effort to quantify and isolate the ductile fuse behavior. The experimental data from these large-scale experiments were analyzed in terms of the hysteretic response, observed damage, internal member loads, as well as the overall stiffness and energy dissipation characteristics. The results of this study demonstrated the effectiveness of utilizing ductile steel bracing for restoring the bent and preventing further damage to the columns and cap beams while also improving the stiffness and energy dissipation characteristics.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.259-259
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• 2010

Periodically polarity inverted (PPI) ZnO structures on (0001) Al2O3 substrates are demonstrated by plasmas assisted molecular beam epitaxy. The patterning and re-growth methods are used to realize the PPI ZnO by employing the polarity controlling method. For the in-situ polarity controlling of ZnO films, Cr-compound buffer layers are used.[1, 2] The region with the CrN intermediate layer and the region with the Cr2O3 and Al2O3 substrate were used to grow the Zn- and O-polar ZnO films, respectively. The growth behaviors with anisotropic properties of PPI ZnO heterostructures are investigated. The periodical polarity inversion is evaluated by contrast images of piezo-response microscopy. Structural and optical interface properties of PPI ZnO are investigated by the transmission electron microcopy (TEM) and micro photoluminescence ($\mu$-PL). The inversion domain boundaries (IDBs) between the Zn and the O-polar ZnO regions were clearly observed by TEM. Moreover, the investigation of spatially resolved local photoluminescence characteristics of PPI ZnO revealed stronger excitonic emission at the interfacial region with the IDBs compared to the Zn-polar or the O-polar ZnO region. The possible mechanisms will be discussed with the consideration of the atomic configuration, carrier life time, and geometrical effects. The successful realization of PPI structures with nanometer scale period indicates the possibility for the application to the photonic band-gap structures or waveguide fabrication. The details of application and results will be discussed.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.656-661
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• 2016

4H- and 6H-SiC grown by physical vapor transport method were investigated by transmission electron microscopy (TEM). From the TEM diffraction patterns observed along the [11-20] zone axis, 4H- and 6H-SiC were identified due to their additional diffraction spots, indicating atomic stacking sequences. However, identification was not possible in the [10-10] zone axis due to the absence of additional diffraction spots. Basal plane dislocations (BPDs) were investigated in the TEM specimen prepared along the [10-10] zone axis using the two-beam technique. BPDs were two Shockley partial dislocations with a stacking fault (SF) between them. Shockley partial BPDs arrayed along the [0001] growth direction were observed in the investigated 4H-SiC. This arrayed configuration of Shockley partial BPDs cannot be recognized from the plan view TEM with the [0001] zone axis. The evaluated distances between the two Shockley partial dislocations for the investigated samples were similar to the equilibrium distance, with values of several hundreds of nanometers or even values as large as over a few micrometers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.109-117
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• 2002

An off-surface flow visualization experiments have been performed to investigate the flow field over a delta wing with the leading edge extension(LEX). The model is a flat wing with $65^{\circ}$ sweepback angle. The free stream velocity is 6.2 m/s, which corresponds to Reynolds number of $4.4\times10^5$ based on the wing root chord. The angle of attack and sideslip angle range from $16^{\circ}\sim28^{\circ}$ and $0^{\circ}\sim-15^{\circ}$, respectively. The visualization technique of using the micro water-droplet and the laser beam sheet enabled to observe the vortical flow structures, which can not be obtained by 5-hole probe measurements. With sideslip angle, the interaction and breakdown of the LEX and wing vortices was promoted in the windward side, whereas, it was suppressed in the leeward side.