• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.231-240
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• 2006

The crustal structure of the Korean Peninsula was investigated by analyzing phase velocity dispersion data of Rayleigh waves. Earthquakes recorded by three component broad-band velocity seismographs during 1999-2004 in South Korea were used in this study. The fundamental mode Rayleigh waves were extracted from vertical components of seismograms by multiple filter technique and phase match filter method. Phase velocity dispersion curves of the fundamental mode signal pairs for 14 surface wave propagation paths on the great circle in the range 10 to 80 sec were computed by two-station method. Treating the shear velocity of each layer as an independent parameter, phase velocity data of Rayleigh wave were inverted. All the result models can be explained by a rather homogeneous crust of shear-wave velocity increasing from 2.8 to 3.25 km/sec from top to about 33 km depth without any distinctive crustal discontinuities and an uppermost mantle of shear-wave velocity between 4.55 and 4.67 km/sec. Our results turn out to agree well with recent study of Cho et al. (2006 b) based on the analysis of seismic background noises to recover short-period (0.5-20 sec) Rayleigh- and Love-wave group velocity dispersion characteristics.

• The Korean Journal of Food And Nutrition
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• v.32 no.4
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• pp.304-311
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• 2019

Ohmic heating is a heating method based on the principle when an electrical current passes through food. Since this method is internal, electrical current damage occurred during heating treatment. The results of ohmic heated starch's external structure, X-ray diffraction, DSC analysis and RVA were differed from those of conventional heating at the same temperature. Several starches changed more rigid by structure re-aggregation. This change in starch was caused by change of physical, chemical, rheological property. The rheology of ohmic heated potato and corn starch of different heated methods were compared with chemically modified starch. After gelatinization, sample starch suspension (2%, 3%) measured flow curves by rheometer. Cross-linked chemically modified starch's shear stress was decreased with degree of substitution reversibly. Ohmic heated more dramatic, at $60^{\circ}C$. Potato starch's shear stress was less than commercial high cross-linked modified starch. Flow curves of potato starches measured at $4^{\circ}C$, $10^{\circ}C$, $20^{\circ}C$. Showed that Ohmic heated potato starch's shear stress ranging between $4^{\circ}C$ and $20^{\circ}C$ was narrower than modified starch. According to this study, ohmic heated potato starch can be used by decreasing viscosity agent like cross-linked modified starch.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.154-164
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• 2019

A rotor dynamic analysis is mandatory for stability and design optimization of submerged propellers and turbines. An accurate simulation requires a proper consideration of fluid-induced reaction forces. This paper presents a bi-directional coupling of a bond graph method solver and an unsteady vortex lattice method solver where the former is used to model the rotor dynamics of the power train and the latter is used to predict transient hydrodynamic forces. Due to solver coupling, determination of hydrodynamic coefficients is obsolete and added mass effects are considered automatically. Additionally, power grid and structural faults like grid fluctuations, eccentricity or failure could be investigated using the same model. In this research work a fast, time resolved dynamic simulation of the complete power train is conducted. As an example, the rotor dynamics of a tidal stream turbine is investigated under two inflow conditions: I - shear flow, II - shear flow + water waves.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.1-8
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• 2019

To analyze the dynamic behavior and the structure of the gaseous methane-gaseous oxygen diffusion flame formed by a swirl/shear-coaxial injector, combustion experiments were carried out under different propellant injection conditions. As a result, the OH radical emission intensity of the diffusion flame visualized through chemiluminescence was observed to increase as the propellant mass flow and the momentum flux ratio increased. And flames with swirl showed a more high radical emission intensity than those without swirl.

• Earthquakes and Structures
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• v.24 no.1
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• pp.53-64
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• 2023

Earth fissures with several kilometers will inevitably approach or cross the metro line, significantly threatening the safety of the underground structure in the earth fissure site. However, the influence of the earth fissure site's amplification effect on the metro station's dynamic response is still unclear. A representative earth fissure in Xi'an was taken as an example to establish a numerical model of a metro station in the earth fissure site. The dynamic response characteristics of the metro stations at different distances from the earth fissure under various seismic waves were calculated. The results show that the existence of the earth fissure significantly amplifies the dynamic response of the nearby underground structures. The responses of the axial force, shear force, bending moment, normal stress, horizontal displacement, inter-story drift, and relative slip of the metro station were all amplified within a specific influence range. The amplification effect increases with the seismic wave intensity. The amplification effect caused by the earth fissure has relatively weak impacts on the axial shear, shear force, bending movement, normal stress, and horizontal movement; slightly larger impacts on the inter-story drift and acceleration; and a significant impact on the relative slip. The influence ranges of the axial force and normal stress are approximately 20 m. The influence ranges of the acceleration and inter-story drift can reach 30 m. Therefore, the seismic fortification level of the underground structure in the earth fissure site needs to be improved.

• Computers and Concrete
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• v.32 no.3
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• pp.313-326
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• 2023

The seismic safety of the shear wall structure can be assessed through seismic fragility analysis, which requires high computational costs in estimating seismic demands. Accordingly, machine learning methods have been applied to such fragility analyses in recent years to reduce the numerical analysis cost, but it still remains a challenging task. Therefore, this study uses the ensemble machine learning method to present an improved framework for developing a more accurate seismic demand model than the existing ones. To this end, a rank-based selection method that enables determining an excellent model among several single machine learning models is presented. In addition, an index that can evaluate the degree of overfitting/underfitting of each model for the selection of an excellent single model is suggested. Furthermore, based on the selected single machine learning model, we propose a method to derive a more accurate ensemble model based on the bagging method. As a result, the seismic demand model for which the proposed framework is applied shows about 3-17% better prediction performance than the existing single machine learning models. Finally, the seismic fragility obtained from the proposed framework shows better accuracy than the existing fragility methods.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.6
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• pp.111-119
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• 2019

The purpose of this study is to investigate the shear strength of reinforced concrete beam according to beam section size and shear reinforcement ratio. A total of nine specimens were tested and designed concrete compressive strength is 24 MPa. The main variables are shear reinforcement ratio and beam section size fixed with shear span to depth ratio (a/d = 2.5), the tensile reinforcement ratio (${\rho}=0.013$) and width to depth ratio (h/b = 1.5). The test specimens were divided into three series of S1 ($225{\times}338mm$), S2 ($270{\times}405mm$) and S3 ($315{\times}473mm$), respectively. The experimental results show that all specimens represent diagonal tensile failure. For $S^*-1$ specimens (d/s=0), the shear strength decreased by 33% and 46% with increasing the beam effective depth, 26% and 33% for $S^*-2$ specimens (d/s=1.5) and 16% and 20% for $S^*-3$ specimens (d/s=2.0) respectively. As the shear reinforcement ratio increases, the decrease range in shear strength decreases. In other words, this means that as the shear reinforcement ratio increases, the size effect of concrete decreases. In the S1 series, the shear strength increased by 39% and 41% as the shear reinforcement ratio increased, 54% and 76% in the S2 series and 66% and 100% in the S3 series, respectively. As the effective depth of beam increases, the increase range of shear strength increases. This means that the effect of shear reinforcement increases as the beam effective depth increases. As a result of comparing experimental values with theoretical values by standard equation and proposed equation, the ratio by Zsutty and Bazant's equation is 1.30 ~ 1.36 and the ratio by KBC1 and KBC2 is 1.55~.163, respectively. Therefore, Zsutty and Bazant's proposed equation is more likely to reflect the experimental data. The current standard for shear reinforcement ratio (i.e., $S_{max}=d/2$) is expected to be somewhat relaxed because the ratio of experimental values to theoretical values was found to be 1.01 ~ 1.44 for most specimens.

• Steel and Composite Structures
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• v.33 no.6
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• pp.891-906
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• 2019

This study considers the instability behavior of sandwich plates considering magnetorheological (MR) fluid core and piezoelectric reinforced facesheets. As facesheets at the top and bottom of structure have piezoelectric properties they are subjected to 3D electric field therefore they can be used as actuator and sensor, respectively and in order to control the vibration responses and loss factor of the structure a proportional-derivative (PD) controller is applied. Furthermore, Halpin-Tsai model is used to determine the material properties of facesheets which are reinforced by graphene platelets (GPLs). Moreover, because the core has magnetic property, it is exposed to magnetic field. In addition, Kelvin-Voigt theory is applied to calculate the structural damping of the piezoelectric layers. In order to consider environmental forces applied to structure, the visco-Pasternak model is assumed. In order to consider the mechanical behavior of structure, sinusoidal shear deformation theory (SSDT) is assumed and Hamilton's principle according to piezoelasticity theory is employed to calculate motion equations and these equations are solved based on differential cubature method (DCM) to obtain the vibration and modal loss factor of the structure subsequently. The effect of different factors such as GPLs distribution, dimensions of structure, electro-magnetic field, damping of structure, viscoelastic environment and boundary conditions of the structure on the vibration and loss factor of the system are considered. In order to indicate the accuracy of the obtained results, the results are validated with other published work. It is concluded from results that exposing magnetic field to the MR fluid core has positive effect on the behavior of the system.

• Coupled systems mechanics
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• v.13 no.4
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• pp.293-310
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• 2024

This paper investigates the dynamic response of structures during earthquakes and provides a clear understanding of soil-structure interaction phenomena. It analyses various parameters, comprising ground shear wave velocity and structure properties. The effect of soil impedance function form on the structural response of the system through the use of springs and dashpots with two frequency cases: independent and dependent frequencies. The superstructure and the ground were modeled linearly. Using the substructure method, two different approaches are used in this study. The first is an analytical formulation based on the dynamic equilibrium of the soil-structure system modeled by an analog model with three degrees of freedom. The second is a numerical analysis generated with 2D finite element modeling using ABAQUS software. The superstructure is represented as a SDOF system in all the SSI models assessed. This analysis establishes the key parameters affecting the soil-structure interaction and their effects. The different results obtained from the analysis are compared for each studied case (frequency-independent and frequency-dependent impedance functions). The achieved results confirm the sensitivity of buildings to soil-structure interaction and highlight the various factors and effects, such as soil and structure properties, specifically the shear wave velocity, the height and mass of the structure. Excitation frequency, and the foundation anchoring height, also has a significant impact on the fundamental parameters and the response of the coupled system at the same time. On the other hand, it have been demonstrated that the impedance function forms play a critical role in the accurate evaluation of structural behavior during seismic excitation. As a result, the evaluation of SSI effects on structural response must take into account the dynamic properties of the structure and soil accordingly.

• Journal of Pharmaceutical Investigation
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• v.39 no.3
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• pp.185-199
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• 2009

Using a strain-controlled rheometer [Advanced Rheometric Expansion System (ARES)], the steady shear flow properties and the dynamic viscoelastic properties of $Antiphlamine-S^{(R)}$ lotion have been measured at $20^{\circ}C$ (storage temperature) and $37^{\circ}C$ (body temperature). In this article, the temperature dependence of the linear viscoelastic behavior was firstly reported from the experimental data obtained from a temperature-sweep test. The steady shear flow behavior was secondly reported and then the effect of shear rate on this behavior was discussed in detail. In addition, several inelastic-viscoplastic flow models including a yield stress parameter were employed to make a quantitative evaluation of the steady shear flow behavior, and then the applicability of these models was examined by calculating the various material parameters. The angular frequency dependence of the linear viscoelastic behavior was nextly explained and quantitatively predicted using a fractional derivative model. Finally, the strain amplitude dependence of the dynamic viscoelastic behavior was discussed in full to elucidate a nonlinear rheological behavior in large amplitude oscillatory shear flow fields. Main findings obtained from this study can be summarized as follows : (1) The linear viscoelastic behavior is almostly independent of temperature over a temperature range of $15{\sim}40^{circ}C$. (2) The steady shear viscosity is sharply decreased as an increase in shear rate, demonstrating a pronounced Non-Newtonian shear-thinning flow behavior. (3) The shear stress tends to approach a limiting constant value as a decrease in shear rate, exhibiting an existence of a yield stress. (4) The Herschel-Bulkley, Mizrahi-Berk and Heinz-Casson models are all applicable and have an equivalent validity to quantitatively describe the steady shear flow behavior of $Antiphlamine-S^{(R)}$ lotion whereas both the Bingham and Casson models do not give a good applicability. (5) In small amplitude oscillatory shear flow fields, the storage modulus is always greater than the loss modulus over an entire range of angular frequencies tested and both moduli show a slight dependence on angular frequency. This means that the linear viscoelastic behavior of $Antiphlamine-S^{(R)}$ lotion is dominated by an elastic nature rather than a viscous feature and that a gel-like structure is present in this system. (6) In large amplitude oscillatory shear flow fields, the storage modulus shows a nonlinear strain-thinning behavior at strain amplitude range larger than 10 % while the loss modulus exhibits a weak strain-overshoot behavior up to a strain amplitude of 50 % beyond which followed by a decrease in loss modulus with an increase in strain amplitude. (7) At sufficiently large strain amplitude range (${\gamma}_0$>100 %), the loss modulus is found to be greater than the storage modulus, indicating that a viscous property becomes superior to an elastic character in large shear deformations.