• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.25 no.1
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• pp.115-125
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• 1995

Forty-four cases of developmental salivary gland defects in 43 patients were analysed radiologically. The obtained results were as follows ; 1. It occurred more frequently in males(86 ％) than in females(14 ％). The age distribution of patients ranged from 20 to 74 years with the average being 52.7 years. 2. All but one were located between the angle of the mandible and the molar tooth. Only one patient showed bilateral occurrence. 3. The shape of the defect was ovoid(15 cases), round(10 cases), or half-ovoid(5 cases) 4. Their size ranged from 5 x 6 mm to 16 x 30 mm with the average around 9 x 14 mm. 5. Twenty-eight cases appeared to be surrounded partially(1/3 - 2/3) by a hyperostotic border. The thickness of the hyperostotic border varied ; thick(14 cases), moderate(l1 cases), thin(9 cases), or mixed(6 cases) 6. Thirteen cases were in contact with the superior border of the mandibular inferior cortex, 11 cases partially eroded the cortical plate, and 7 cases showed discontinuity of the mandibular inferior cortex. 7. Twenty-three cases were located below the mandibular canal, 13 cases overlapped the mandibular canal, and 2 cases showed slight deviation of the mandibular canal.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.137-146
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• 2001

A robust controller with the sliding mode is proposed for stable dynamic walking of the biped robot in this paper. For the robot system to be controlled, which is modeled as 14 DOF rigid bodies by the method of multi-body dynamics, the joint angle trajectories are determined by the velocity transformation matrix. Also Hertz force model and Hysteresis damping element are utilized for the ground reaction and impact forces during the contact with the ground. The biped robot system becomes unstable since those forces contain highly confused noise components and some discontinuity, and modeling uncertainties such as parameter inaccuracies. The sliding mode control is applied to solve above problems. Under the assumption of the bounded estimation errors on the unknown parameters, the proposed controller provides a successful way to achieve the stability and good performance in spite of the presence of modeling imprecisions of uncertainties.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.12-26
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• 2004

A new treatment of cell-interface flux in AUSM-type methods is introduced to reduce the numerical dissipation. Through analysis of TVD limiters, a criterion for the more accurate prediction of cell-interface state is found out and M-AUSMPW+ is developed by determining the transferred property newly and appropriately within the criterion. The superiority of M-AUSMPW+ is clearly revealed in multi-dimensional flow problems. It can eliminate numerical dissipation effectively in a non-flow aligned grid system. As a result, M-AUSMPW+ is shown to be much more accurate and effective than other previous schemes in multi-dimensional problems. Through a stationary contact discontinuity, a vortex flow, a shock wave/boundary layer interactions and viscous shock tube problems, it is verified that accuracy of M-AUSMPW+ is improved.

• Journal of The Korean Astronomical Society
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• v.34 no.4
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• pp.281-283
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• 2001

As a companion to an adiabatic version developed by Ryu and his coworkers, we have built an isothermal magnetohydrodynamic code for astrophysical flows. It is suited for the dynamical simulations of flows where cooling timescale is much shorter than dynamical timescale, as well as for turbulence and dynamo simulations in which detailed energetics are unimportant. Since a simple isothermal equation of state substitutes the energy conservation equation, the numerical schemes for isothermal flows are simpler (no contact discontinuity) than those for adiabatic flows and the resulting code is faster. Tests for shock tubes and Alfven wave decay have shown that our isothermal code has not only a good shock capturing ability, but also numerical dissipation smaller than its adiabatic analogue. As a real astrophysical application of the code, we have simulated the nonlinear three-dimensional evolution of the Parker instability. A factor of two enhancement in vertical column density has been achieved at most, and the main structures formed are sheet-like and aligned with the mean field direction. We conclude that the Parker instability alone is not a viable formation mechanism of the giant molecular clouds.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.4
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• pp.263-273
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• 2011

The diffuse interface model of Saurel et al. (2008) is used for the computation of compressible cavitating flows around underwater missiles. Such systems use gas injection and natural cavitation to reduce drag effects. Consequently material interfaces appear separating liquid and gas. These interfaces may have a really complex dynamics such that only a few formulations are able to predict their evolution. Contrarily to front tracking or interface reconstruction method the interfaces are computed as diffused numerical zones, that are captured in a routinely manner, as is done usually with gas dynamics solvers for shocks and contact discontinuity. With the present approach, a single set of partial differential equations is solved everywhere, with a single numerical scheme. This leads to very efficient solvers. The algorithm derived in Saurel et al. (2009) is used to compute cavitation pockets around solid bodies. It is first validated against experiments done in cavitation tunnel at CNU. Then it is used to compute flows around high speed underwater systems (Shkval-like missile). Performance data are then computed showing method ability to predict forces acting on the system.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.12
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• pp.1089-1093
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• 2013

Depth extraction using the structured illumination method is popularly applied since it has the benefit of measuring the object without contact. With multiple spatial frequencies and phase-shifting techniques, it is possible to extract the depth of objects with large discontinuity. For applications such as 3D (Three Dimensional) displays, 3D information of the object is required and is useful if corresponding to each view of the display. For this purpose, hypercentric optics is appropriate to measure the depth information of an object with a large field of view that is applicable for a 3D display. By experiment, we present the feasibility for phase-shifting profilometry using hypercentric optics to obtain the depth information of an object with the field of view appropriate for a 3D display.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.2
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• pp.149-157
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• 2004

Implicit finite element analysis of the flat surface-straight edge hemming process is performed by using a commercial code ABAQUS/Standard. Methods of finite element modeling for springback simulation and contact pair definition are discussed. An optimal mesh system is chosen through the error analysis that is based on the smoothing of discontinuity in the state variables. This study has focused on the investigation of the influence of process parameters in flanging, pre-hemming and main hemming on final hem quality, which can be defined by turn-down, warp and roll-in. The parameters adopted in this parametric study are flange length, flange angle, flanging die corner radius, face angle and insertion angle of pre-hemming punch, and over-stroke of pre-hemming and main hemming punches.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.89-94
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• 2008

The problem of interaction between the structures interconnected at discrete points as like composite structures, has a attracted considerable attention for a prolonged period of time. Recently, mixed structures are applied for overcoming structural limits by developed countries. In this paper, advanced connection type of mixed structures are presented by numerical approach. Also it is performed on extensive literature review from theoretical method to numerical analysis. For analysing behaviors of mixed structures according to connection type, 2 different connections and 1 reinforced connection are compared by 3D nonlinear numerical analysis. Nonlinear analysis of mixed structures is carried out by utilizing contact elements of a general purpose structural analysis computer program(ABAQUS). By using 6 criteria, each connections are investigated. From this result, proper reinforcing and well designed connection type are proposed. And results also show that the deflections which are induced by discontinuity on mixed structures, has a linear distribution that should decrease as applying proposed connection type.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.11 no.2
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• pp.11-18
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• 1989

Advancement of surgical techniques has made it necessary to accurately diagnose internal derangements. Arthrography and computerized tomography have been used to diagnose the majority of temporomandibular joint disorders, however, these methods have had their disadvantages. Magnetic resonance imaging utilizing surface coils has greatly improved the ability to diagnose meniscus abnormalities without using intrarticular injections or ionizing radiation. Ninety-two patients (184 joints) were evaluated by means of magnetic resonance imaging(MRI). Thirty-one patients (39 joints) were diagnosed as having meniscus perforation. Retrospective review of fifteen patients (20 joints) with a perforated meniscus diagnosed by magnetic resonance imaging pre-operatively demonstrated a sixty-five percent correlation between the radiographic diagnosis and the surgical findings.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.26 no.2
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• pp.191-196
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• 2000

Purpose This study is to report presurgical magnetic resonance imaging(MRI) findings of the temporomandibular joint which had perforation in the disc or its surrounding tissues and to improve its diagnostic rate using MRI. Patients and Methods The sample consisted of patients who visited the TMJ clinic at Yongdong Severance Hospital, Yonsei University, during the years, 1992 and 1997. They were diagnosed as TMJ internal derangement and received surgical treatment. We divided them into two groups. The first group comprised of 85 joints with perforated disc or its surrounding tissues and which were confirmed surgically. The second group of 62 joints which only had disc displacement without perforation, hyperemia or adhesion served as control. Results The preoperative diagnostic sensitivity of TMJ perforation using MRI was 74.1%. The MRI findings for diagnosis of the TMJ perforation were degenerative change of the condyle head or the articular fossa, bone to bone contact between the condyle head and the articular eminence or the articular fossa, bony spurring or osteophytosis of the condyle head, flattening of articular surface of the condyle head or the articular eminence, discontinuity of the disc and the arthrographic effect due to joint effusion. Conclusion The preoperative diagnostic sensitivity of TMJ perforation using MRI in this study was 74.1% which was lower than the diagnostic rate using the arthrogram. Further investigations are needed to improve the diagnostic accuracy of TMJ perforation using MRI.