• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1469-1476
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• 2000

We have to consider the drain current as consisting of two components the vertical electric field and the longitudinal electric field because the drain current is almost totally due to the presence of drift in strong inversion of n-MOS FET. Especially the mobility of electrons in the inversion layer is smaller than the bulk mobility because the vertical electric field component that is generated by the effect of the gate voltage is perpendicular to the direction of normal current flow. By the multi-box segmentation technical method that are proposed in this paper we calculated the inversion layer depth and analyzed the vertical electric field component which has an large influence on mobility model.

• Steel and Composite Structures
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• v.20 no.1
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• pp.147-166
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• 2016

The paper presents comprehensive quasi-static stability analysis results for a real funnel-flow cylindrical steel silo composed of horizontally corrugated sheets strengthened by vertical thin-walled column profiles. Linear buckling and non-linear analyses with geometric and material non-linearity were carried out with a perfect and an imperfect silo by taking into account axisymmetric and non-axisymmetric loads imposed by a bulk solid following Eurocode 1. Finite element simulations were carried out with 3 different numerical models (single column on the elastic foundation, 3D silo model with the equivalent orthotropic shell and full 3D silo model with shell elements). Initial imperfections in the form of a first eigen-mode for different wall loads and from 'in-situ' measurements with horizontal different amplitudes were taken into account. The results were compared with Eurocode 3. Some recommendations for the silo dimensioning were elaborated.

• Computers and Concrete
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• v.19 no.2
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• pp.121-126
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• 2017

This paper presents the effect of aggregate type on high temperature resistance of self-compacting mortars (SCM) produced with normal and lightweight aggregates like expanded perlite and pumice. Silica fume (SF) and fly ash (FA) were used as mineral additives. Totally 13 different mixtures were designed according to the aggregate rates. Mini slump flow, mini V-funnel and viscometer tests were carried out on the fresh mortar. On the other hand, bulk density, porosity, water absorption and high temperature tests were made on the hardened SCM. After being heated to temperatures of 300, 600 and $900^{\circ}C$, respectively, the tensile strength in bending and compressive strength of mortars determined. As a result of the experiments, the increase in the use of lightweight aggregate increased total water absorption and porosity of mortars. It is observed that, the increment in the usage of lightweight aggregate decreased tensile strength in bending and compressive strengths of mortar specimens exposed to high temperatures but the usage of up to 10% expanded perlite in mortar increased the compressive strength of specimens exposed to $300^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.2
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• pp.149-155
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• 2007

The row-by-row heat transfer characteristics of fin-and-tube heat exchangers were experimentally investigated. Three wavy fin samples having different rows (one, two and three) and one plain fin sample (three row) were tested for $600{\leq}Re_{D}{\leq}4,000$. The heat transfer data were obtained for individual rows, and the corresponding heat transfer coefficients were reduced from the data. Results showed that the heat transfer coefficients were strongly dependent on the tube row. The heat transfer coefficient decreased as the tube row increased. However, the row effect was different depending on the fin shape. For the wavy fin, the row effect significantly decreased as the Reynolds number increased, yielding approximately the same heat transfer coefficients at $Re_{D}{\approx}2,500$. For the plain fin, however, the row effect lasted for the whole Reynolds number range. The increased mixing of bulk flow by wavy channels appears to induce high heat transfer coefficient (accordingly diminishing row effect) at downstream rows. The heat transfer coefficients of individual rows were higher for heat exchangers having larger tube rows.

• Journal of Navigation and Port Research
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• v.30 no.5 s.111
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• pp.397-404
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• 2006

Gamcheon harbor was developed as a multipurpose port to mix processing functions of exclusive piers for bulk cargo such as marine products, domestic cargoes. Since the container terminal was opened in 1997, maximum $40,000\sim50,000$ DWT containership have been incoming and outgoing. However, bemuse the breakwater entrance in Gamcheon harbor is narrow and the crossed vessels are ever-present at breakwater front, marine accident danger is high that grasping traffic characteristics is required in reply. Therefore marine traffic characteristics were analyzed for Gamcheon harbor and Gamcheon approaching waters, included the track and traffic volumes of peak hours period in inbound/outbound and front sea area of the harbor in present.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.06b
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• pp.137-146
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• 2006

Gamcheon Harbor was developed as a multipurpose port to mix processing functions of exclusive piers for bulk cargo such as marine products. domestic cargo. Since the container terminal was opened in 1997. maximum $40,000{\sim}50,000$ DWT containership have been incoming and outgoing. However, because [he breakwater entrance in Gamcheon Harbor is narrow and the crossed passing of ship is ever-present at breakwater front, marine accident danger is high that grasping traffic characteristics is required in reply. Therefore marine traffic characteristics were analyzed for Gamcheon Harbor, included the track and traffic volumes of peak hours period in inbound/outbound and front sea area of the harbor in present.

• Journal of the Semiconductor & Display Technology
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• v.8 no.3
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• pp.31-37
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• 2009

This paper presents one and two dimensional simulation results with discontinuous features (shocks) of capacitively coupled rf plasmas. The model consists of the first two and three moments of the Boltzmann equation for the ion and electron fluids respectively, coupled to Poisson's equation for the self-consistent electric field. The local field and drift-diffusion approximations are not employed, and as a result the charged species conservation equations are hyperbolic in nature. Hyperbolic equations may develop discontinuous solutions even if their initial conditions are smooth. Indeed, in this work, secondary electron emission is shown to produce transient electron shock waves. These shocks form at the boundary between the cathodic sheath (CS) and the quasi-neutral (QN) bulk region. In the CS, the electrons emitted from the electrode are accelerated to supersonic velocities due to the large electric field. On the other hand, in the QN the electric field is not significant and electrons have small directed velocities. Therefore, at the transition between these regions, the electron fluid decelerates from a supersonic to a subsonic velocity in the direction of flow and a jump in the electron velocity develops. The presented numerical results are consistent with both experimental observations and kinetic simulations.

• Nuclear Engineering and Technology
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• v.50 no.7
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• pp.1173-1183
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• 2018

Transient fluid velocity and pressure fields in a pressurized water reactor (PWR) steam generator (SG) secondary side during the blowdown period of a feedwater line break (FWLB) accident were numerically simulated employing the saturated water flashing model. This model is based on the assumption that compressed water in the SG is saturated at the beginning and decompresses into the two-phase region where saturated vapor forms, creating a mixture of steam bubbles in water by bulk boiling. The numerical calculations were performed for two cases of which the outflow boundary conditions are different from each other; one is specified as the direct blowdown discharge to the atmosphere and the other is specified as the blowdown discharge to an extended calculation domain with atmospheric pressure on its boundary. The present simulation results obtained using the two different outflow boundary conditions were discussed through a comparison with the predictions using a simple non-flashing model neglecting the effects of phase change. In addition, the applicability of each of the non-flashing water discharge and saturated water flashing models for the confirmatory assessments of new SG designs was examined.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2823-2834
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• 2023

Austenitic stainless steel welds (ASSWs) of nuclear components undergo aging-related degradations caused by high temperature and neutron radiation. Since irradiation leads to the change of material characteristics, relevant quantification is important for long-term operation, but limitations exist. Although ion irradiation is utilized to emulate neutron irradiation, its penetration depth is too shallow to measure bulk properties. In this study, a systematic approach was suggested to estimate mechanical properties of ion irradiated 308 ASSW. First of all, weld specimens were irradiated by 2 MeV proton to 1 and 10 dpa. Microstructure evolutions due to irradiation in δ-ferrite and austenite phases were characterized and micropillar compression tests were performed. In succession, dislocation density based stress-strain (S-S) relationships and quantification models of irradiation defects were adopted to define phases in finite element analyses. Resultant microscopic S-S curves were compared to verify material parameters. Finally, macroscopic behaviors were calculated by multiscale simulations using real microstructure based representative volume element (RVE). Validity of the approach was verified for the unirradiated specimens such that the estimated S-S curves and 0.2% offset yield strengths (YSs) which was 363.14 MPa were in 10% agreement with test. For irradiated specimens, the estimated YS were 917.41 MPa in 9% agreement.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.43.5-44
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• 2021

In the local Universe, the gravitational effects of mass density fluctuations exert perturbations on galaxies' redshifts on top of Hubble's Law, called 'peculiar velocities'. These peculiar velocities provide an excellent way to test the cosmological model in the nearby Universe. In this talk, we present new cosmological constraints using peculiar velocities measured with the 2MASS Tully-Fisher survey (2MTF), 6dFGS peculiar-velocity survey (6dFGSv), the Cosmicflows-3 and Cosmicflows-4TF compilation. Firstly, the dipole and the quadrupole of the peculiar velocity field, commonly named 'bulk flow' and 'shear' respectively, enable us to test whether our cosmological model accurately describes the motion of galaxies in the nearby Universe. We develop and use a new estimators that accurately preserves the error distribution of the measurements to measure these moments. In all cases, our results are consistent with the predictions of the Λ cold dark matter model. Additionally, measurements of the growth rate of structure, fσ8 in the low-redshift Universe allow us to test different gravitational models. We developed a new estimator of the "momentum" (density weighted peculiar velocity) power spectrum and use joint measurements of the galaxy density and momentum power spectra to place new constraints on the growth rate of structure from the combined 2MTF and 6dFGSv data. We recover a constraint of fσ8=0.404+0.082-0.081 at an effective redshift zeff=0.03. This measurement is also fully consistent with the expectations of General Relativity and the Λ Cold Dark Matter cosmological model.