• Maxillofacial Plastic and Reconstructive Surgery
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• v.23 no.4
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• pp.338-347
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• 2001

Purpose: This is to review the cases of posterior maxillary segmental osteotomies to regain the interarch spaces for dental implants in the posterior mandible. Materials & Methods: Seven patients who presented with alveolar extrusion of upper posterior molars underwent segmental osteotomies by single-stage Kufner's buccal approach under the intravenous sedation and local anesthesia. The posterior maxillary cento-alveolar segments were repositioned upward using pre-fabricated palato-occlusal resin splints and immobilized with osteosynthesis microplates and screws. Dental implants were installated simultaneously. The regained spaces, tooth vitality, periodontal healing, relapse, tenderness on function, and complications including maxillary sinus involvements were evaluated periodically for over one year after the surgeries. Results: The single-tage procedures were completed within 80 minutes without any surgical complications. The posterior maxillary segments were repositioned upward to regain the interarch spaces ranging from 2.5 to 5.5mm. All teeth involved in the procedures keep their vitalities. The repositioned segments were maintained showing neither evidence of periodontal break-down nor tenderness to function. One patient whose segments had not been immobilized by osteosynthesis plate resulted in 2mm down-ward relapse in post-operative 8 months. A case of postoperative nasal bleeding from the posterior-lateral wall resulted in oroantral fistula and chronic maxillary sinusitis later. Conclusion: The extruded dento-alveolar segments of the posterior maxilla were repositioned properly by Kufner's one-stage segmental osteotomies. One microplate can be of help to keep the position until the osseous healing enough to support the masticatory force.

• Journal of the Korean Ceramic Society
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• v.54 no.4
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• pp.261-271
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• 2017

Environment-friendly $(K,Na)NbO_3-based$ (KNN) lead-free piezoelectric materials have been studied extensively in the past decade. Significant progress has been made in this field, manifesting competitive piezoelectric performance with that of lead-based, for specific application scenarios. Further understanding of the relationship between high piezoelectricity and microstructure or more precisely, ferroelectric domain structure, domain wall pinning effect, domain wall conduction and local polarization switching underpins the continuous advancement of piezoelectric properties, with the help of piezoresponse force microscopy (PFM). In this review, we will present the fundamentals of scanning probe microscopy (SPM) and its cardinal derivative in piezoelectric and ferroelectric world, PFM. Some representative operational modes and a variety of recent applications in KNN-based piezoelectric materials are presented. We expect that PFM and its combination with some newly developed technology will continue to provide great insight into piezoelectric materials and structures, and will play a valuable role in promoting the performance to a new level.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.783-790
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• 2004

In this study, a newly modified soil nailing technology named as the PSN(pretensioned soil nailing) system, is developed to reduce both facing displacements and ground surface settlements in top-down excavation process as well as to increase the global stability. Up to now, the PSN system has been investigated mainly focusing on an establishment of the design procedure. In the present study, the analytical procedure and design technique are proposed to evaluate maximum pretension force and stability of the PSN system. Also proposed arc techniques to determine the required thickness of a shotcrete facing and to estimate probability of a failure against the punching shear. Based on the proposed procedure and technique, effects of the radius of a influence circle and dilatancy angle on the thickness of a shotcrete facing, bonded length and safety factors arc analyzed. In addition, effects of the reduction of deformations expected by pretensioning of the soil nails are examined in detail throughout an illustrative example and $FLAC^{2D}$ program analysis. And a numerical approach is further made to determine a postulated failure surface as well as a minimum safety factor of the proposed PSN system using the shear strength reduction technique with the $FLAC^{2D}$ program. Global minimum safety factors and local safety factors at various excavation stages computed in case of the PSN system arc analyzed throughout comparisons with the results expected in case of the general soil nailing system. The efficiency of the PSN system is also dealt with by analyzing the wall-facing deformations and the adjacent ground surface settlements.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.544-550
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• 2006

Next-generation wireless/mobile networks are envisioned to have an IP-based infrastructure. One of the research challenges for next-generation all IP-based networks is the design of intelligent mobility management technologies that have a seamless mobility and minimal signaling overhead. Recently, HMIPv6 was proposed by the IETF for efficient mobility management. HMIPv6 reduces the amount of signaling and improves the performance of MIPv6 in terms of handover latency. However the MAP can be a single point of performance bottleneck when there are a lot of local movements. HMIPv6 can cause signaling overhead due to the unnecessary location update of idle mobile nodes. Therefore, in this paper, we propose the dynamic paging Mobile IPv6 that reduces the signaling cost of the unnecessary location updates using IP paging and organizes dynamically optimal MAP area according to user's mobility and traffic. We show performance results that are obtained from the average total location update cost and packet delivery cost.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1407-1413
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• 2011

In this paper, the structural design for composite blade was performed and full scale structural test was conducted to verify the structural design and integrity of composite blade. Firstly, FE analysis was performed using commercial software ABAQUS under conditions of rated wind speed and Case H in IEC 61400-2. Lay-up sequence and ply thickness were designed based on FE results. And to verify the structural design, full scale structural test was conducted according to IEC 61400-2 under identical loading conditions of FE analysis. Finally, the force-deflection and local strain behavior of composite blade were evaluated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.828-836
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• 1987

The inclusion of thermophoresis in particle deposition studies has often been treated separately from deposition due to flow characteristics. Also previously reported experimental results on thermophoresis have been studied in the regions of relatively small temperature gradients. In this study, using real-time laser light reflectivity method, we measured the angular dependence of the deposition rates of particles of the cylindrical collector surface, which immerged in laminar flow of a hot gas suspension of small particles. And we extended the previous narrowband results of thermophoretic deposition rates to the regions of large temperature gradients between the hot gas stream and the collector surface. Based on the obtained data, the cylinder's forward stagnation-point region is considerably enriched in particle 'phase' density owing to the compressibility effect, which leads to locally enhanced deposition while the downstream region from the stagnation point inertial force acts in the opposite direction, which tends to centrifuge particles away from the wall, thus the local deposition rates by thermophoresis are reduced.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.590-598
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• 2005

The present study has been conducted to investigate the effect of discrete ribs and rotation on heat/mass transfer characteristics in a two-pass square duct with $90^{\circ}-rib$ turbulators. The rib turbulator has a square cross section of 1.5 mm. The rib height-to-hydraulic diameter ratio $({e/D_{h})$ is 0.056, and the rib pitch-to-rib height ratio (p/e) is 10. The gap width is the same as the rib height. The rotation number ranges from 0.0 to 0.2 while Reynolds number is fixed to 10,000. In a stationary duct, the heat/mass transfer on the surfaces with discrete ribs is enhanced because the gap flow promotes local turbulence and flow mixing near the ribbed surface. In a rotating duct, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, heat/mass transfer is increased due to the gap flow. On the trailing surface of the first pass, however, heat/mass transfer is decreased because the gap flow disturbs reattachment of main flow. The phenomenon, that is, the difference of heat transfer between the leading and the trailing surfaces is distinctly presented by rotation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.911-920
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• 2005

The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter ($D_h$) of 26.67 mm. Rib turbulators are attached in the parallel arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of 2 m (e) $\times$ 3 m (w) and an attack angle of $70^{\circ}$. The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio (e/$D_h$) is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The results show that a pair of vortex cells are generated due to the symmetric geometry of the rib arrangement, and heat/mass transfer is augmented up to $Sh/Sh_0=2.9$ averagely, which is higher than that of the cross-ribbed case presented in the previous study for the stationary case. With the passage rotation, the main flow in the first-pass deflects toward the trailing surface and the heat transfer is enhanced on the trailing surface. In the second-pass, the flow enlarges the vortex cell close to the leading surface, and the small vortex cell on the trailing surface side contracts to disappear as the passage rotates faster. At the highest rotation number ($R_O=0.20$), the turn-induced single vortex cell becomes identical regardless of the rib configuration so that similar local heat/mass transfer distributions are observed in the fuming region for the cross- and parallel-ribbed case.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.499-504
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• 2001

A validation of a 3D CFD model for predicting local subcooling of moderator in the vicinity of calandria tubes in a CANDU reactor is performed. The small scale moderator experiments performed at Sheridan Park Experimental Laboratory(SPEL) in Ontario, Canada[1] is used for the validation. Also a comparison is made between previous CFD analyses based on 2DMOTH and PHOENICS, and the current model analysis for the same SPEL experiment. For the current model, a set of grid structures for the same geometry as the experimental test section is generated and the momentum, heat and continuity equations are solved by CFX-4.3, a CFD code developed by AEA technology. The matrix of calandria tubes is simplified by the porous media approach. The standard $k-\varepsilon$ turbulence model associated with logarithmic wall treatment and SIMPLEC algorithm on the body fitted grid are used and buoyancy effects are accounted for by the Boussinesq approximation. For the test conditions simulated in this study, the flow pattern identified is a buoyancy-dominated flow, which is generated by the interaction between the dominant buoyancy force by heating and inertial momentum forces by the inlet jets. As a result, the current CFD moderator analysis model predicts the moderator temperature reasonably, and the maximum error against the experimental data is kept at less than $2.0^{\circ}C$ over the whole domain. The simulated velocity field matches with the visualization of SPEL experiments quite well.

• Bulletin of the Korean Chemical Society
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• v.23 no.11
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• pp.1595-1603
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• 2002

In this paper we have presented the results of diffusion behavior of model systems for eight liquid n-alkanes ($C_{12}$-$C_{44}$) in a canonical (NVT) ensemble at several temperatures using molecular dynamics simulations. For these n-alkanes of small chain length n, the chains are clearly <$R_{ee}^2$>/6<$R_g^2$>>1 and non-Gaussian. This result implies that the liquid n-alkanes over the whole temperatures considered are far away from the Rouse regime, though the ratio becomes close to the unity as n increases. Calculated self-diffusion constants $D_{self}$ are comparable with experimental results and the Arrhenius plot of self-diffusion constants versus inverse temperature shows a different temperature dependence of diffusion on the chain length. The global rotational motion of n-alkanes is examined by characterizing the orientation relaxation of the end-to-end vector and it is found that the ratio ${\tau}1/{\tau}2$ is less than 3, the value expected for a isotropically diffusive rotational process. The friction constants ${\xi}$of the whole molecules of n-alkanes are calculated directly from the force auto-correlation (FAC) functions and compared with the monomeric friction constants ${\xi}_D$ extracted from $D_{self}$. Both the friction constants give a correct qualitative trends: decrease with increasing temperature and increase with increasing chain length. The friction constant calculated from the FAC's decreases very slowly with increasing temperature, while the monomeric friction constant varies rapidly with temperature. By considering the orientation relaxation of local vectors and diffusion of each site, it is found that rotational and translational diffusions of the ends are faster than those of the center.