• Journal of Korean Society of Steel Construction
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• v.24 no.1
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• pp.35-46
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• 2012

With the increase in the demand for high-rise buildings, the use of high-strength steel has likewise increased. Thus, it has become more necessary to study the resistance force of the high-strength hollow structural section (HSS) joint of 600MPa. Additionally, the current design equation in Korea limits maximum yield stress at 360MPa in the case of HSS. In other words, since the current specification does not apply to HSS of 600MPa, this study aims to investigate the applicability of design equations as well as examine the behavior of the connection through the experiment and finite element analysis (FEA) of the plate-tube connection of 600MPa. In particular, this paper presents the behavior of joints with the gusset plates welded in the longitudinal direction of the circular hollow section (CHS) when the joints are subjected to lateral force. Comparing design equations with the results of FEA and the test, existing design equations are underestimated to be 56~79% in the case of high-strength materials.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.3
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• pp.14-21
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• 1998

In this paper, the measurements of ELF electric and magnetic fields due to double circuit 345[kV} transmission lines are made using planar-type electric field sensor and multitum loop-type magnetic field sensor, and the magnitudes of electric and magnetic fields are illustrated by a three-dimensional plot. Also, in order to predict the magnetic field strength with lad variation, a typical daily load current curves of the transmission lines are displayed because the magnetic field is changed with load current. experimental results of ELF electric and magnetic fields along center line versus lateral distance are compared with the theoretical values computed by using the FIELDS program. The electric field intensity in and around a transmission tower is lowered, and the greatest point of the magnetic field is shifted to the heavy load line but generally is given the trend that the peak value appear at the central part of the transmission tower. The magnitudes of the maximum electric and magnetic fields in the vicinity of a transmission tower are less than 3.5[kV/m] and $20[{\mu}T]$, respectively. The measured electric and magnetic fields are satisfied with limits and guidelines recommended by various authorized international institutes.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.12
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• pp.761-767
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• 1999

Poly-Si TFTs(polycrystalline silicon thin film transistors) fabricated on a low cost glass substrate have attracted a considerable amount of attention for pixel elements and peripheral driving circuits in AMLCS(active matrix liquid crystal display). In order to apply poly-Si TFTs for high resolution AMLCD, a high operating frequency and reliable circuit performances are desired. A new poly-Si TFT with CLBT(counter doped lateral body terminal) is proposed and fabricated to suppress kink effects and to improve the device stability. And this proposed device with BC(buried channel) is fabricated to increase ON-current and operating frequency. Although the troublesome LDD structure is not used in the proposed device, a low OFF-current is successfully obtained by removing the minority carrier through the CLBT. We have measured the dynamic properties of the poly-Si TFT device and its circuit. The reliability of the TFTs and their circuits after AC stress are also discussed in our paper. Our experimental results show that the BC enables the device to have high mobility and switching frequency (33MHz at $V_{DD}$ = 15 V). The minority carrier elimination of the CLBT suppresses kink effects and makes for superb dynamic reliability of the CMOS circuit. We have analyzed the mechanism in order to see why the ring oscillators do not operate by analyzing AC stressed device characteristics.

• Nuclear Engineering and Technology
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• v.44 no.7
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• pp.735-744
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• 2012

In order to quantify the flow distribution characteristics of APR+ reactor, a test was performed on a test facility, ACOP ($\underline{A}$PR+ $\underline{C}$ore Flow & $\underline{P}$ressure Test Facility), having a length scale of 1/5 referring to the prototype plant. The major parameters are core inlet flow and outlet pressure distribution and sectional pressure drops along the major flow path inside reactor vessel. To preserve the flow characteristics of prototype plant, the test facility was designed based on a preservation of major flow path geometry. An Euler number is considered as primary dimensionless parameter, which is conserved with a 1/40.9 of Reynolds number scaling ratio. ACOP simplifies each fuel assembly into a hydraulic simulator having the same axial flow resistance and lateral cross flow characteristics. In order to supply boundary condition to estimate thermal margins of the reactor, the distribution of inlet core flow and core exit pressure were measured in each of 257 fuel assembly simulators. In total, 584 points of static pressure and differential pressures were measured with a limited number of differential pressure transmitters by developing a sequential operation system of valves. In the current study, reactor flow characteristics under the balanced four-cold leg flow conditions at each of the cold legs were quantified, which is a part of the test matrix composing the APR+ flow distribution test program. The final identification of the reactor flow distribution was obtained by ensemble averaging 15 independent test data. The details of the design of the test facility, experiment, and data analysis are included in the current paper.

• Water for future
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• v.27 no.2
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• pp.73-83
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• 1994

The unproper development of the nearshore zone can enhance the diffusion of pollutant in the nearshore zone resulting in unbalanced sediment budget of beach which causes alteration of beach topography. Therefore, it is required to predict the effects of the envirnmental change quantitatively. In this paper, the depth-averaged and time-averaged energy balance equation is selected to acount for the wave transformation such as refraction, shoaling effect, the surf zone energy disipation, wave breaking index and bore, due to wave breaking in the shore region.(Numerical solutions are obtained by a finite difference method, ADI and Upwind. For the calculation of the wave-induced current, the unsteady nonlinear depth-averaged and time-averaged governing equation is derived based on the continuity and momentum equation for imcompressible fluid.) Numerical solutions are obtained by finite difference method considering influences of factors such as lateral mixing coefficient, bed shear stress, wave direction angle, wave steepness, wave period and bottom slope. The model is applied to the computation of wave transformation, wave-induced current and variation of mean water leel on a uniformly sloping beach.

• Computational Structural Engineering
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• v.10 no.4
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• pp.281-290
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• 1997

Current seismic design code is based on the assumption that the designed structures would be behaved inelastically during a severe earthquake ground motion. For this reason, seismic design forces calculated by seismic codes are much lower than the forces generated by design earthquakes which makes structures responding elastically. Present procedures for calculating seismic design forces are based on the use of elastic spectra reduced by a strength reduction factors known as "response modificaion factor". Because these factors were determined empirically, it is difficult to know how much inelastic behaviors of the structures exhibit. In this study, lateral strength required to maintain target ductility ratio was first calculated from nonlinear dynamic analysis of the single degree of freedom system. At the following step, base shear foeces specified in seismic design code compare with above results. If the base shear force required to maintain target ductility ratio was higher than the code specified one, the lack of required strength should be filled by overstrength and/or redundancy. Therefore, overstrength of moment resisting frame structure will be estimated from the results of push-over analysis.

• Steel and Composite Structures
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• v.33 no.4
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• pp.595-614
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• 2019

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.230-232
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• 2019

Light Triggerd Thyristor (LTT)는 HVDC 및 산업용 스위치 등에 사용되는 대전력 반도체소자이다. 일반적인 Thyristor가 전기적 신호에 의해 trigger 되는 것과는 다르게 LTT는 광신호에 의해 동작하는 소자이다. 본 논문에서는 5,000V, 2,200A 급의 4인치 LTT 소자의 제작 및 전기적인 특성평가 결과를 기술하였다. 4인치 LTT의 구조적인 특징은 전면부 중앙에 광신호가 주입되는 수광부가 위치해 있으며 입력 전류 증폭을 위한 4-단계 증폭 게이트 (gate) 구조를 가지도록 설계하였다. $400{\Omega}{\cdot}cm$ 비저항을 갖는 1mm 두께의 n-형 실리콘 웨이퍼에 boron 이온주입과 열처리 공정으로 약 $30{\mu}m$ 깊이의 p-base를 형성하였으며, 고내압 저지를 위한 edge termination은 VLD (variable lateral doping) 기술을 적용하였다. 제작된 4인치 LTT는 6,500 V의 순방향 항복전압 ($V_{DRM}$) 특성을 나타내었으며, 100V의 어노드전압 ($V_A$)과 20 mA의 게이트전류 ($I_G$)에 의하여 thyristor가 trigger 됨을 확인하였다. 제작한 LTT 소자는 disk형 press-pack 패키지를 진행한 후, LTT의 수광부에 $10{\mu}s$, 50 mW의 900 nm 광 펄스를 조사하여 전류 특성을 평가하였다. LTT 패키지 샘플에 60 Hz 주파수의 광 펄스를 조사한 경우 2,460 A의 순방향 평균전류 ($I_T$)와 $336A/{\mu}s$의 반복전류상승기울기 (repetitive di/dt)에 안정적으로 동작함을 확인하였다. 또한, 펄스 전류 시험의 경우 61.6 kA의 최대 통전 전류 (ITSM, surge current)와 $1,050A/{\mu}s$의 펄스전류 상승 기울기 (di/dt of on-state pulse current)에도 LTT의 손상 없이 동작함을 확인하였다.

• Structural Engineering and Mechanics
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• v.24 no.4
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• pp.463-478
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• 2006

The design of structural frameworks for buildings is constantly evolving and is dependent on regional issues such as loading and constructability. One of the most promising recent developments for low to medium rise construction in terms of efficiency of construction, robustness and aesthetic appearance utilises concrete-filled steel tubular sections as the columns in a moment-resisting frame. These are coupled to rigid or semi-rigid connections to composite steel-concrete beams. This paper includes the results of a pilot experimental programme leading towards the development of economical, reliable connections that are easily constructed for this type of frame. The connections must provide the requisite strength, stiffness and ductility to suit gravity loading conditions as well as gravity combined with the governing lateral wind or earthquake loading. The aim is to develop connections that are stiffer, less expensive and easier to construct than those in current use. A proposed fabricated T-stub connection is to be used to connect the beam flanges and the column. These T-stubs are connected to the column using "blind bolts" with extensions, allowing installation from the outside of the tube. In general, the use of the extensions results in a dramatic increase in the strength and stiffness of the T-stub to column connection in tension, since the load is shared between membrane action in the tube wall and the anchorage of the bolts through the extensions into the concrete.

• Annals of Clinical Neurophysiology
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• v.13 no.1
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• pp.1-12
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• 2011

Transcranial magnetic stimulation (TMS) is a non-invasive tool used to study aspects of human brain physiology, including motor function and the pathophysiology of various brain disorders. A brief electric current passed through a magnetic coil produces a high-intensity magnetic field, which can excite or inhibit the cerebral cortex. Although various brain regions can be evaluated by TMS, most studies have focused on the motor cortex where motor evoked potentials (MEPs) are produced. Single-pulse and paired-pulse TMS can be used to measure the excitability of the motor cortex via various parameters, while repetitive TMS induces cortical plasticity via long-term potentiation or long-term depression-like mechanisms. Therefore, TMS is useful in the evaluation of physiological mechanisms of various neurological diseases, including movement disorders and epilepsy. In addition, it has diagnostic utility in spinal cord diseases, amyotrophic lateral sclerosis and demyelinating diseases. The therapeutic effects of repetitive TMS on stroke, Parkinson disease and focal hand dystonia are limited since the duration and clinical benefits seem to be temporary. New TMS techniques, which may improve clinical utility, are being developed to enhance clinical utilities in various neurological diseases.