• Proceedings of the KOSOMBE Conference
• /
• v.1995 no.11
• /
• pp.124-127
• /
• 1995

Due to the self-diffusion of nuclear spins, the edge of phantoms is enhanced in the magnetic resonance imaging (MRI), especially in the case of microscopy [1]. According to several published works, theory has been established that the edge enhancement is caused by the motion narrowing around bounded regions due to diffusions of nuclear spins during data acquisition. It is found, however, that the signal decreases due to the diffusion attenuation and image is distorted as edge of the image is sharpened. In this paper, we wilt investigate this signal loss during data acquisition and its effects on image, i.e., image edge enhancement due to the diffusion phenomenon. This result is new and different from the previously discussed edge enhancement due to the diffusion, namely, by motion narrowing effect or spin bouncing effect at the boundary.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.32A no.2
• /
• pp.31-37
• /
• 1995

A ray-based approach is developed to calculate the scattering from inhomogeneous dielectric objects. This approach is a natural extension of the "shooting and bouncing ray(SBR)" technique developed earlier for calculating the radar cross section of cavity structures and complex targets. In this formulation, a dense grid of rays representing the incident field is shot toward the scatterer. The curved trajectory, amplitude, phase and polarization of the ray fields inside the inhomogeneous object are computed numerically based on the laws of geometrical optics. The contributions of the exting rays to the exterior scattered field are then calculated by using the equivalence principle in conjunction with " a ray-tube integration" scheme. The ray-based approach is applied for the effect of an arcjet plasma plume on satellite reflector performance and backscattering from inhomogeneous objects.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.320-323
• /
• 2008

In this study the effect of collision model was evaluated in spray field by CFD. A collision is basically the interaction between droplets and criteria of collision is determined by drop Weber number, impact parameter, and drop-size ratio. Early developed collision model considered coalescence and grazing collision with the exchange of momentum. However in experimental research there were bouncing, coalescence, reflexive separating and stretching separating in interaction between droplets. In this study the collision considering such complex phenomena is modeled and was compared with the basic collision model.

• Journal of Information Display
• /
• v.3 no.3
• /
• pp.35-43
• /
• 2002

Silicon-based 0.69-inch AMOEL microdisplay with integrated driver and timing controller circuits for microdisplay applications has been developed using 0.35 ${\mu}m$ l-poly 4-metal standard CMOS process with 5 V CMOS devices and CMP (Chemical Mechanical Polishing) technology. To reduce the large data programming time consumed in a conventional current programming pixel circuit technique and to achieve uniform display, de-amplifying current mirror pixel circuit and the current-mode data driver circuit with threshold roltage compensation are proposed. The proposed current-mode data driver circuit is inherently immune to the ground-bouncing effect. The Monte-Carlo simulation results show that the proposed current-mode data driver circuit has channel-to-channel non-uniformity of less than ${\pm}$0.6 LSB under ${\pm}$70 mV threshold voltage variaions for both NMOS and PMOS transistors, which gives very good display uniformity.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2000.10a
• /
• pp.273-280
• /
• 2000

Building structures which are in need of large open space make the damping effect of the structures decrease greatly. Assembly and office buildings with a lower natural frequency have a higher possibility of experiencing excessive vibration induced by human activities. These excessive vibration make the residents uncomfortable and the serviceability deterioration. The loads induced by human activities were classified into two types. First type is in place loads as like jumping, foot stamping and body bouncing. The other type is moving loads as like walking, running and dancing. A series of laboratories experiments had been conducted to study the dynamic loads induced by human activities, The earlier works were mainly concerned to parameters study of dynamic loads as like activity type, weight, sex, surface condition of structure and etc. In this paper, we have measured directly the walking loads by using the platform. And we have evaluated and analyzed load-time history of walking loads. One of the most important parameter is pacing rate (walking speed) in the walking loads. The difference between the maximum value and minimum value of walking loads depends on the walking speed.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.52-52
• /
• 2010

Amorphous carbon films have a variety of potential applications. In most such applications film properties are crucial and highly dependent on the film growth conditions. We here investigate the atomic structure of the films, which is generated at various incidence angles, using the classical molecular dynamics. Varying incidence angle of the deposited carbon atoms, different level of sp hybridization and porosity of the film are captured in our model. As the incidence angle becomes glancing, subplantation of the deposited carbon in vertical direction is significantly reduced, rather bouncing back of the incident carbon with slight modification of surface structure is mainly occurred at the early stage of the film growth. As the surface becomes rougher, shadowing effect at these glancing incidences also becomes more significant, which tends to cause asymmetrical and columnar structure. We describe incidence angle dependence of the evolution of the atomic structure of the film and its corresponding properties.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.25 no.2
• /
• pp.236-241
• /
• 2017

Electrohydraulic forming is a high-speed forming process that deforms a blank using electric discharge in liquid. When high voltage is discharged in the water, a shock wave is propagated from the tip of the electrodes to the blank, causing the blank to be deformed into the die. Electrohydraulic forming has many advantages including improved formability and reduced bouncing effect and springback. The objective of this paper was to conduct a feasibility study to identify the electrohydraulic effect. An electrohydraulic forming apparatus was developed and experiments were carried out. The results of the experiment showed that the developed apparatus had sufficient energy to deform the blank into the die. Using the hole to emit residual air in the die was more effective than using the vacuum pump in terms of saving on experiment time.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.2
• /
• pp.307-313
• /
• 2022

As the development of renewable energy expands internationally to cope with global warming and climate change, the share of wind power generation has been gradually increasing. Although wind farms can produce electric power for 24 h a day compared to solar power plants, Their interfere with the operation of nearby radars or communication equipment must be analyzed because large-scale wind power turbines are installed. This study analyzed whether a land radio station can receive sufficient signals when a ship sailing outside the offshore wind farm transmits distress signals on the VHF band. Based on the geographic information system digital map around the target area, wind turbine CAD model, and wind farm layout, the area of interest and wind farm were modeled to enable numerical analysis. Among the high frequency analysis techniques suitable for radio wave analysis in a wide area, a dedicated program applying physical optics (PO) and shooting and bouncing ray (SBR) techniques were used. Consequently, the land radio station could receive the electromagnetic field above the threshold of the VHF receiver when a ship outside the offshore wind farm transmitted a distress communication signal. When the line of sight between the ships and the land station are completely blocked, the strength of the received field decreases, but it is still above the threshold. Hence, although a wind farm is a huge complex, a land station can receive the electromagnetic field from the ship's VHF transmitter because the wave length of the VHF band is sufficiently long to have effects such as diffraction or reflection.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.559-564
• /
• 2008

A prediction of binary droplets collision is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter and drop-size ratio have influence on the interaction of the droplets. By the effect of these parameter, the collision processes are generated with the complicated phenomena. The droplet collision can be classified into four interactions such as the bouncing, coalescence, reflexive separation and stretching separation. In this study, the two-phase flow of the droplet collision was simulated numerically by using the Level Set method. 2D axi-symmetric simulations on the head-on collisions in the coalescence and reflexive separation, and 3D simulation on the off-center collisions in the coalescence and stretching separation were performed. These numerical results showed good agreements with the experimental and analytical results. For tracking the identity of droplets after the collision, transport equation for the volume fraction of the each initial droplet were used. From this, the identities of droplets were analyzed on the collision of droplets having different size.

• Journal of Advanced Research in Ocean Engineering
• /
• v.4 no.4
• /
• pp.146-162
• /
• 2018

The unsteady problem of a rigid body impact onto a floating plate is studied. Both the plate and the water are at rest before impact. The plate motion is caused by the impact force transmitted to the plate through an elastic layer with viscous damping on the top of the plate. The hydrodynamic force is calculated by using the second-order model of plate impact by Iafrati and Korobkin (2011). The present study is concerned with the deceleration experienced by a rigid body during its collision with a floating object. The problem is studied also by a fully-nonlinear computational-fluid-dynamics method. The elastic layer is treated with a moving body-fitted grid, the impacting body with an immersed boundary method, and a discrete-element method is used for the contact-force model. The presence of the elastic layer between the impacting bod- ies may lead to multiple bouncing of them, if the bodies are relatively light, before their interaction is settled and they continue to penetrate together into the water. The present study is motivated by ship slamming in icy waters, and by the effect of ice conditions on conventional free-fall lifeboats.