• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1373-1378
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• 2000

Vibration caused by railroad vehicle including subway train running raises a lot of problems to the neighboring buildings. Therefore lots of methods to isolate the railway vibration have been studied and practically applied to sites. As one of them, specially designed vibration isolation device was installed in the some section of Seoul subway. This device is installed between the rail and track slab. Because the process of installation is relatively simple, this method can be applied to the existing railways in servicing. We measured the vibration and noise to check the effectiveness of this device before and after the installation. The result showed that the vibration level of the slab and platform was reduced to 7 - 10 dB. Expecially high frequency component was reduced to a large amount. From this result, we can conclude that these kind of devices are useful to the reduction of the railroad vibration, expecially the high frequency vibration which can cause structure born noise.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.556-560
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• 2017

A hemoglobin/silver nanoparticle heterolayer was fabricated for bioelectronic device with electrochemical signal-enhancement effect. As a device element, a hemoglobin, the metalloprotein, contained the heme group that showed the redox property was introduced for charge storage element. For electron transfer facilitation, a silver nanoparticle was introduced for electrochemical signal facilitation, the hemoglobin was immobilized onto Au substrate using chemical linker 6-mercaptohexanoic acid (6-MHA). Then, the silver nanoparticle was immobilized onto fabricated hemoglobin/6-MHA heterolayers by layer-by-layer (LbL) method. The surface morphology and surface roughness of fabricated heterolayer were investigated by atomic force microscopy (AFM). The redox property of hemoglobin/silver nanoparticle heterolayer was investigated by a cyclic voltammetry (CV) experiment for obtaining an oxidation potential and reduction potential. Moreover, for the assessing charge storage function, a chronoamperometry (CA) experiment was conducted to hemoglobin/silver nanoparticle-modified heterolayer electrode using oxidation and reduction potentials, respectively. Based on the results, the fabricated hemoglobin/silver nanoparticle heterolayer showed that an increased charge storage effect compared to hemoglobin monolayer-modified electrode.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.1-8
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• 1999

Extensive resistance tests for a passenger boat(now in service at Chung-Ju lake) have been performed in a towing tank to investigate the effect of an artificial air cavity attached to the hull bottom on the reduction of the ship resistance. The attached air cavity has been observed at various air sully rates, from which we have determined a proper shape of an air supply device. In order to prevent the supplied air from leaking near the bilge of the ship, longitudinal barrier strips have been attached to both sides of the device. The investigation on their effectiveness reveals that a cascade system of the air supply device reduces the resistance of the ship furthermore. Energy saving of more than 10% is achieved at the design speed in spite of the additional power necessary for the air supply.

• Journal of the Korean Vacuum Society
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• v.17 no.6
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• pp.523-527
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• 2008

GaAs/AlGaAs based quantum cascade lasers were fabricated with two different types of i) the shallow mesa type which was etched up to above active region and ii) the deep mesa type which was etched through active region. While the threshold current density of shallow mesa type was $26-32\;kA/cm^2$, the one of deep mesa type was reduced drastically up to $13\;kA/cm^2$. Such lowered threshold current density at deep mesa type attributed to the reduction of current loss to the lateral directions.

• Journal of radiological science and technology
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• v.44 no.3
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• pp.189-194
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• 2021

This study was conducted to reduce the exposure dose to the breast and adjacent organs as the number of Mammography increased. Therefore, it has been designed a shield in lead, bismuth + tungsten, and bismuth that does not require to be equipped by the patient, in which each type of shield was compared and analyzed of radiation exposure dose to breast, thyroid, and eye. Using a mammography machine, optically stimulated luminescent dosimeter(OSLD) was inserted to bilateral breast, thyroid, and eye of a dosimetry phantom to measure dose radiated onto the phantom. Shielding device was made in different thickness of 2mm, 3mm, and 5mm and dose evaluation was performed by measuring the dose while using lead, bismuth, and bismuth + tungsten prosthesis. When each shields combined with shielding device, were compared of dose, all showed similar does reduction in the dose to breast, thyroid, and eye in both cranialcaudal and mediolateraloblique view. Based on the current study, bismuth and bismuth + tungsten can replace conventional lead shield and it is anticipated to safely and conveniently reduce radiation exposure to breast, thyroid, and eye with the shield that does not require to be equipped.

• Structural Engineering and Mechanics
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• v.24 no.3
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• pp.375-393
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• 2006

Under high velocity, pulse type near source earthquakes semi-active control systems are very effective in reducing seismic response base isolated structures. Semi-active control systems can be classified as: 1) independently variable stiffness, 2) independently variable damping, and 3) combined variable stiffness and damping systems. Several researchers have studied the effectiveness of independently varying damping systems for seismic response reduction of base isolated structures. In this study effectiveness of a combined system consisting of a semi-active independently variable stiffness (SAIVS) device and a magnetorheological (MR) damper in reducing seismic response of base isolated structures is analytically investigated. The SAIVS device can vary the stiffness, and hence the period, of the isolation system; whereas, the MR damper enhances the energy dissipation characteristics of the isolation system. Two separate control algorithms, i.e., a nonlinear tangential stiffness moving average control algorithm for smooth switching of the SAIVS device and a Lyapunov based control algorithm for damping variation of MR damper, are developed. Single and multi degree of freedom systems consisting of sliding base isolation system and both the SAIVS device and MR damper are considered. Results are presented in the form of nonlinear response spectra, and effectiveness of combined variable stiffness and variable damping system in reducing seismic response of sliding base isolated structures is evaluated. It is shown that the combined variable stiffness and variable damping system leads to significant response reduction over cases with variable stiffness or variable damping systems acting independently, over a broad period range.

• Smart Structures and Systems
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• v.15 no.3
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• pp.627-643
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• 2015

Negative stiffness, previously emulated by active or semi-active control for cable vibration mitigation, is realized passively using a self-contained highly compressed spring, the negative stiffness device (NSD).The NSD installed in parallel with a viscous damper (VD) in the vicinity of cable anchorage, enables increment of damper deformation during cable vibrations and hence increases the attainable cable damping. Considering the small cable displacement at the damper location, even with the weakening device, the force provided by the NSD-VD assembly is approximately linear. Complex frequency analysis has thus been conducted to evaluate the damping effect of the assembly on the cable; the displacement-dependent negative stiffness is further accounted by numerical analysis, validating the accuracy of the linear approximation for practical ranges of cable and NSD configurations. The NSD is confirmed to be a practical and cost-effective solution to improve the modal damping of a cable provided by an external damper, especially for super-long cables where the damper location is particularly limited. Moreover, mathematically, a linear negative stiffness and viscous damping assembly has proven capability to represent active or semi-active control for simplified cable vibration analysis as reported in the literature, while in these studies only the assembly located near cable anchorage has been addressed. It is of considerable interest to understand the general characteristics of a cable with the assembly relieving the location restriction, since it is quite practical to have an active controller installed at arbitrary location along the cable span such as by hanging an active tuned mass damper. In this paper the cable frequency variations and damping evolutions with respect to the arbitrary assembly location are then evaluated and compared to those of a taut cable with a viscous damper at arbitrary location, and novel frequency shifts are observed. The characterized complex frequencies presented in this paper can be used for preliminary damping effect evaluation of an adaptive passive or semi-active or active device for cable vibration control.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.419-426
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• 2018

Recently, in an effort to reduce the energy efficiency design index (EEDI), studies on energy saving devices (ESDs) have been conducted. In this study, we designed a post-device suitable for a KRISO container ship (KCS) using computational fluid dynamics (CFD). In order to increase the efficiency of the post-device, a twisted rudder was used, which has a proven performance (showing a 1.34% reduction in DHP compared to the bare hull at 24 knots) in previous research at Pusan National University. In addition, an increase in efficiency was expected by the use of a rudder bulb, including the discontinuous section of the twisted rudder and a divergent propeller cap to prevent the contraction of the wake. The optimization criterion was the case where the delivery power was the least compared with the bare hull. We analyzed the cause of the efficiency increase through an analysis of the self-propulsion factor. The case study for optimization was divided into 4 types (1. clearance of the bulb and cap, 2. shape of the bulb, 3. size of the bulb and cap, and 4. asymmetric bulb). Finally, with a clearance of 50 mm from the ship, a spherical bulb with the cap having an angle of $5^{\circ}$, and an asymmetric rudder bulb with a bulb diameter of 1.2HH/1.4H (horizontal/vertical) showed a 2.05% reduction in DHP compared to the bare hull at 24 knots. We will fabricate a post-device that will be optimized in the future and verify the performance of the post-device through model tests.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.372-377
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• 2005

EMC(Electromagnetic Compatibility) is the ability of an electronic device that operates properly in its intended electromagnetic environment and not be a source of pollution to that environment. The designer anticipates EMC problems at beginning of the process and finds remaining problems in early prototype stages, and tests the final prototypes for EMC as thoroughly as possible. This is a more cost-effective method. In this paper, it analyzes EMC problems that were appeared in actual measurement of electric power control device and presents reduction technique of these problems.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.480-483
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• 2000

We developed a home electric panel board with surge protection device to protect home electric appliances from transient overvoltages and electromagnetic(EM) noise. In this paper, electrical characteristics of the home electric panel board are described. From the performance test using a combination surge generator standardized in IEC 610004-5, it is confirmed that the proposed home panel board has an excellent surge protection performance. Also, EM noise reduction characteristics of the panel board in ranges from 150 kHz to 30 MHz is estimated by using a network analyser, and the results showed that the panel board has an over 20 45 noise reduction performance.