• Smart Structures and Systems
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• v.25 no.5
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• pp.543-557
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• 2020

This paper presents a series of experimental and numerical investigations on a vertical isolation system with quasi-zero stiffness (QZS) property. The isolation system comprises a linear helical spring and disk spring. The disk spring is designed to provide variable stiffness to the system. Orthogonal static tests with different design parameters are conducted to verify the mathematical and mechanical models of the isolation system. The deviations between theoretical and test results influenced by the design parameters are summarized. Then, the dynamic tests for the systems with different under-load degrees are performed, including the fast sweeping tests, harmonic excitation tests, and half-sine impact tests. The displacement transmissibility, vibration reduction rate, and free vibration response are calculated. Based on the test results, the variation of the transmission rule is evaluated and the damping magnitudes and types are identified. In addition, the relevant numerical time history responses are calculated considering the nonlinear behavior of the system. The results indicate that the QZS isolation system has a satisfactory isolation effect, while a higher damping level can potentially promote the isolation performance in the low-frequency range. It is also proved that the numerical calculation method accurately predicts the transmission character of the isolation system.

• Nuclear Engineering and Technology
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• v.46 no.5
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• pp.605-618
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• 2014

The effects of variability of the mechanical properties of lead rubber bearings on the response of a seismic isolation system are investigated. Material variability in manufacturing, aging, and operation temperature is assumed, and two variation models of an isolation system are considered. To evaluate the effect of ground motion characteristics on the response, 27 earthquake record sets with different peak A/V ratios were selected, and three components of ground motions were used for a seismic response analysis. The response in an isolation system and a superstructure increases significantly for ground motions with low A/V ratios. The variation in the mechanical properties of isolators results in a significant influence on the shear strains of the isolators and the acceleration response of the superstructure. The variation provisions in the ASCE-4 are reasonable, but more strict variation limits should be given to isolation systems subjected to ground motions having low A/V ratios. For application of seismic isolation systems to safety-related nuclear structures, the variation in the material and mechanical properties of the isolation system should be properly controlled during the manufacturing and aging processes. In addition, special consideration should be given to minimize the accidental torsion caused by the dissimilarity in the stiffness variations of the isolators.

• Earthquakes and Structures
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• v.26 no.1
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• pp.1-15
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• 2024

Isolation technology has been proven effective in reducing the seismic response of superstructures, where most of the deformation is concentrated in the isolation layer. However, in cases of earthquakes with intensities surpassing the fortification level of the area, or severe near-fault earthquakes, the isolation layer may experience excessive deformation, resulting in damage to the isolation bearings or collisions with the retaining wall or surrounding buildings. In this study, a finite element model using ABAQUS is established and compared with experimental test results to deeply investigate the influence of limit devices on the isolation layer and its response to the superstructure. The findings reveal that a larger limiter stiffness and a smaller reserved gap can achieve a more effective limiting effect. Nevertheless, a smaller reserved gap and a larger limiter stiffness may result in increased response of the superstructure. Therefore, rational selection of the reserved gap and limiter stiffness is crucial to reduce the acceleration response.

• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.691-703
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• 2022

To obtain the seismic response of lead-cored rubber, shape memory alloy (SMA)-rubber isolation Plate-shell Integrated Concrete Liquid-Storage Structure (PSICLSS), based on a PSICLSS in a water treatment plant, built a scale experimental model, and a shaking table test was conducted. Discussed the seismic responses of rubber isolation, SMA-rubber isolation PSICLSS. Combined with numerical model analysis, the vibration characteristics of rubber isolation PSICLSS are studied. The results showed that the acceleration, liquid sloshing height, hydrodynamic pressure of rubber and SMA-rubber isolation PSICLSS are amplified when the frequency of seismic excitation is close to the main frequency of the isolation PSICLSS. The earthquake causes a significant leakage of liquid, at the same time, the external liquid sloshing height is significantly higher than internal liquid sloshing height. Numerical analysis showed that the low-frequency acceleration excitation causes a more significant dynamic response of PSICLSS. The sinusoidal excitation with first-order sloshing frequency of internal liquid causes a more significant sloshing height of the internal liquid, but has little effect on the structural principal stresses. The sinusoidal excitation with first-order sloshing frequency of external liquid causes the most enormous structural principal stress, and a more significant external liquid sloshing height. In particular, the principal stress of PSICLSSS with long isolation period will be significantly enlarged. Therefore, the stiffness of the isolation layer should be properly adjusted in the design of rubber and SMA-rubber isolation PSICLSS.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.424-431
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• 2000

After the Kobe earthquake(1995) in Japan, the Izmit earthquake(1997) in Turkey and the Chi-chi earthquake(1999) in Taiwan, the small-to-medium-sized earthquakes occurred in the Koreans peninsula and this shows the fact that Korea is not located in the safety zone of earthquake. The main concept of base isolation system is to reduce the member forces by decreasing the earthquake forces transmitted to superstructure instead of the conventional techniques of strengthening the structural members. This study investigates the effect of seismic response attenuation of computer floors using base isolation systems

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.10
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• pp.20-26
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• 1993

The base-collector capacitance of an npn bipolar transistor in bipolar or BiCMOS technology has significant influence on the switching performances, and comprises pnjunction component and MOS component. Both components have complicated dependences on the isolation oxide structure, epitaxial doping density, and bias voltage. Analytical/empirical formulas for both components are derived in this paper for a generic isolation structure as a function of epitaxial doping density and bias voltage based on some theoretical understanding and two-dimensional device simulations. These formulas are useful in estimating the effect of device isoation schemes on the switching speed of bipolar transistors.

• Bulletin of the Korean Chemical Society
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• v.13 no.2
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• pp.119-122
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• 1992

The affinity chromatographic technique was applied to the isolation of Thromboxane Synthase, with a variety of imidazolyl alkanoic acids coupled Sepharose 2B including a gel (G in Table 4) which has one free COOH group in the bound affinity ligand. The effect of ligand structure on the "affinity" and "selectivity" for thromboxane synthase isolation is described.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.1
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• pp.17-22
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• 2009

A switch or circulator is used for distinguishing between the paths of transmitter and receiver in TDD systems. If the isolation between Tx and Rx paths is low in TDD systems, the output signal of the ransmitter acts as an interferer to the receiver even if the transceiver operates on the receiver mode. In this paper we propose a method to get high isolation characteristics between transmitting and receiving paths in TDD systems. We implement the module with a proposed improving method to verify the effect of the isolation improvement and the experimental results are presented. The isolation improvement of above 44.8 dB over the frequency bandwidth of 30 MHz is obtained from the implemented isolation improvement module.

• Earthquakes and Structures
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• v.11 no.6
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• pp.1101-1121
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• 2016

Base isolation, one of the popular seismic protection approaches proven to be effective in practical applications, has been widely applied worldwide during the past few decades. As the techniques mature, it has been recognised that, the biggest issue faced in base isolation technique is the challenge of great base displacement demand, which leads to the potential of overturning of the structure, instability and permanent damage of the isolators. Meanwhile, drain, ventilation and regular maintenance at the base isolation level are quite difficult and rather time- and fund- consuming, especially in the highly populated areas. To address these challenges, a number of efforts have been dedicated to propose new isolation systems, including segmental building, additional storey isolation (ASI) and mid-storey isolation system, etc. However, such techniques have their own flaws, among which whipping effect is the most obvious one. Moreover, due to their inherent passive nature, all these techniques, including traditional base isolation system, show incapability to cope with the unpredictable and diverse nature of earthquakes. The solution for the aforementioned challenge is to develop an innovative vibration isolation system to realise variable structural stiffness to maximise the adaptability and controllability of the system. Recently, advances on the development of an adaptive magneto-rheological elastomer (MRE) vibration isolator has enlightened the development of adaptive base isolation systems due to its ability to alter stiffness by changing applied electrical current. In this study, an innovative semi-active storey isolation system inserting such novel MRE isolators between each floor is proposed. The stiffness of each level in the proposed isolation system can thus be changed according to characteristics of the MRE isolators. Non-dominated sorting genetic algorithm type II (NSGA-II) with dynamic crowding distance (DCD) is utilised for the optimisation of the parameters at isolation level in the system. Extensive comparative simulation studies have been conducted using 5-storey benchmark model to evaluate the performance of the proposed isolation system under different earthquake excitations. Simulation results compare the seismic responses of bare building, building with passive controlled MRE base isolation system, building with passive-controlled MRE storey isolation system and building with optimised storey isolation system.

• The Journal of the Korea Contents Association
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• v.12 no.5
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• pp.525-540
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• 2012

The purpose of the present study is to examine the causal relationship and invest the difference among isolation, interaction, content satisfaction, achievement and persistence in cyber university education by employment status. For this study, 104 students at A cyber university in Korea completed surveys in the fall semester of 2011. The result of this study indicated that there was a meaningful effect of interaction on isolation. Secondly, there was a meaningful effect of interaction on content satisfaction. Thirdly there was a meaningful effect of interaction on achievement. Lastly there were meaningful effects of isolation and interaction on persistence. In addition, according to multi-group analysis, there were no significant differences of structural path coefficients between two groups. Based on these results, this study suggests instructional design methods and management strategies to improve the quality of learning in cyber universities.