• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.187-197
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• 2013

PURPOSE. The purpose of this study was to evaluate various core designs on stress distribution within zirconia crowns. MATERIALS AND METHODS. Three-dimensional finite element models, representing mandibular molars, comprising a prepared tooth, cement layer, zirconia core, and veneer porcelain were designed by computer software. The shoulder (1 mm in width) variations in core were incremental increases of 1 mm, 2 mm and 3 mm in proximal and lingual height, and buccal height respectively. To simulate masticatory force, loads of 280 N were applied from three directions (vertical, at a $45^{\circ}$ angle, and horizontal). To simulate maximum bite force, a load of 700 N was applied vertically to the crowns. Maximum principal stress (MPS) was determined for each model, loading condition, and position. RESULTS. In the maximum bite force simulation test, the MPSs on all crowns observed around the shoulder region and loading points. The compressive stresses were located in the shoulder region of the veneer-zirconia interface and at the occlusal region. In the test simulating masticatory force, the MPS was concentrated around the loading points, and the compressive stresses were located at the 3 mm height lingual shoulder region, when the load was applied horizontally. MPS increased in the shoulder region as the shoulder height increased. CONCLUSION. This study suggested that reinforced shoulder play an essential role in the success of the zirconia restoration, and veneer fracture due to occlusal loading can be prevented by proper core design, such as shoulder.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.1
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• pp.19-27
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• 2007

Analytical investigation on the performance of a two stage twin rotary compressor for $CO_2$ heat pump water heater system has been carried out. A computer simulation program was made based on analytical models for gas compression in control volumes, leakages among neighboring volumes, and dynamics of moving elements of the compressor. Calculated cooling capacity, compressor input, and COP were well compared to those of experiments over the compressor speeds tested. For the operating condition of suction pressure of 3 MPa, and discharge pressure of 9 MPa, and compressor inlet temperature of $35^{\circ}C$, the compressor efficiency was calculated to be 80.2%: volumetric, adiabatic, and mechanical efficiencies were 88.3%, 93.2%, and 92.7%, respectively. For the present compressor model, volumetric and adiabatic efficiencies of the second stage cylinder were lower by about $6{\sim}7%$ than those of the first stage mainly due to the smaller discharge port at the second stage. Parametric study on the discharge port size showed that the compressor performance could be improved by 3.5% just by increasing the discharge port diameter by 20%.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.207-214
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• 2001

Silica glass is a core material for optical fiber in optical telecommunications, but its centrosymmetry eliminates the second order nonlinearity. But it is experimentally well known that the space charge polarization induces the Second Harmonic Generation (SHG) when a strong DC voltage is applied to silica glass for a long period of time with metal blocking electrodes. In this report, the results of a theoretical calculation of the nonlinear optical property caused by the space charge polarization, and a model of a numerical analysis to predict the small chance in nonlinear optical property as functions of time and space are provided. Assuming that amorphous silica is a solid state electrolyte and sodium ion is the only mobile charge carrier, 'Finite Difference Method' was employed for modeling of numerical analysis. The distributions of the concentration of sodium ion and electric field as functions of a normalized length of the specimen and a normalized applied voltage were simulated.

• Journal of Communications and Networks
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• v.18 no.4
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• pp.559-566
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• 2016

Software defined network (SDN) can effectively improve the performance of traffic engineering and will be widely used in backbone networks. Therefore, new energy-saving schemes must take SDN into consideration; this action is extremely important owing to the rapidly increasing energy consumption in telecom and Internet service provider (ISP) networks. Meanwhile, the introduction of SDN in current networks must be incremental in most cases, for technical and economic reasons. During this period, operators must manage hybrid networks in which SDN and traditional protocols coexist. In this study, we investigate the energy-efficient traffic engineering problem in hybrid SDN/Internet protocol (IP) networks. First, we formulate the mathematical optimization model considering the SDN/IP hybrid routing mode. The problem is NP-hard; therefore, we propose a fast heuristic algorithm named hybrid energy-aware traffic engineering (HEATE) as a solution. In our proposed HEATE algorithm, the IP routers perform shortest-path routing by using distributed open shortest path first (OSPF) link weight optimization. The SDNs perform multipath routing with traffic-flow splitting managed by the global SDN controller. The HEATE algorithm determines the optimal setting for the OSPF link weight and the splitting ratio of SDNs. Thus, the traffic flow is aggregated onto partial links, and the underutilized links can be turned off to save energy. Based on computer simulation results, we demonstrate that our algorithm achieves a significant improvement in energy efficiency in hybrid SDN/IP networks.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.8
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• pp.1811-1819
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• 2013

In this paper, we carried out a study on how to find an appropriate helper node for cooperative communications, the role of which is very import to enhance system throughput of wireless communication system. The busy tone cooperative MAC (BT-COMAC) protocol proposed in this paper is a new cooperative MAC protocol with a reactive helper node scheme and maximizes the benefits of existing schemes while making up for their shortcomings. We conducted performance evaluation of this new protocol using computer simulation experiment. System throughput in bps and channel access delay are utilized as performance measures. We used a random way point mobility model where every communication node moves independently one another, and slow fading channel where every communication node decided its transmission rate with received power basis. Numerical results show that the new MAC protocol enhances system throughput as much as 15% of the existing scheme.

• The Journal of Engineering Geology
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• v.12 no.2
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• pp.179-188
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• 2002

With improving computer penormance and advancing simulation techniques, a growing number of softwares are being developed for visualization of investigation results in geotechnical problems. It is a very important subject for geological site investigation to understand or predict if there would be any hazardous geological conclition that might cause any increase of construction costs or an extension of construction period. A 3-D (three-climensional) visualization technique may be one of the powerful tools to overcome an uncertainty problem of geologica] site investigatior. The paper describes an overview of a newly developed geotechnical 3-D interpretation system for the purpose of applying the 3-D visualization technique, GIS (geographic information system) and D/B (database) to tunnel design and construction. VR (virtual reality) and 3-D visualization techniques are applied in order to develope the 3-D model of characteristics and structures of rock mass. D/B system for all the materials related to site investigation and tunnel construction is developed using GIS technique. This system is very useful for civil engineers to make a plan of tunnel construction at the design stage and also during construction with the advantage of improving the economy and safety of tunnels.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.4
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• pp.404-412
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• 1994

On July 12. 1993 at 22 : 17 local time (-9h. KST). an earthquake of surface magnitude (MS) 7.6 occurred on the west coast of the Hokkaido and small of offshore island of Okushiri in the East Sea. A major tsumani was generated and within 2 to 5 minutes, extremely large tsunami waves engulfed the Okushiri coastal area and the central west roast of the Hokkaido. This tsunami caused tremendous casualities and damage. A giant tsunami runup of more than 30 m in height was recorded. The tsunami crossed the East Sea and feeled at 27 sites of the eastern Korean coast during the survey on 17-19, July, 1993. The observed tsunami runup at southern part of the eastern Korean coast were generally weaker than the 1993 Japan Sea Central Earthquake tsunami and varied from 0.8 m to 2.6 m. The Present Paper intends to understand the propagation on this tsunami with the aid of numerical computation model andd computer graphic aided video animation.

• Journal of Korea Foundry Society
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• v.27 no.1
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• pp.31-35
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• 2007

In order to develop the semi-solid forming technology for magnesium alloy the rheological and thixotropic behavior of Mg alloy slurry with varying shear rates and cooling rates was investigated and simulated with considering the viscosity based on microstructures and processing variables. The viscosity of slurry of Mg alloy (AZ91D) in semi-solid region was exponentially increased with a solid fraction, and was decreased with increasing a shear rate. In order to analyze precisely the rheological behavior, the ANYCAST program modified with the Carreau model and the different heat transfer coefficient between the cast and mold was used to simulate the flow behavior of Mg semi-solid slurry during the injection into a casting mold in a high pressure diecasting machine. The simulated rheological behavior of Mg alloy slurry was matched well with the experimental results.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.4
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• pp.239-246
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• 2009

In this study, we analyze the mean waiting time on the nested open queueing network, where the population within each subnetwork is controlled by a semaphore queue. The queueing network can be transformed into a simpler queueing network in terms of customers waiting time. A major characteristic of this model is that the lower layer flow is halted by the state of higher layer. Since this type of queueing network does not have exact solutions for performance measure, the lower bound and upper bound on the mean waiting time are checked by comparing them with the mean waiting time in the transformed nested queueing network. Simulation estimates are obtained assuming Poisson arrivals and other phase-type arrival process, i.e., Erlang and hyper-exponential distributions. The bounds obtained can be applied to get more close approximation using the suitable approach.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.11
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• pp.2021-2026
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• 2016

In this paper, a system model for transmission of 3-dimensional (3-D) signals is presented and its performance is analyzed. Unlike 2-D signals, no quadrature form expression for the 3-D signals is available. Exploiting a set of orthogonal basis functions, the 3-D signals are transmitted. As a result of computer simulation using very higher-level signal constellations, the 3-D transmission system has significantly improved error performance as compared with the 2-D system. It is considered that the principal reason for such performance improvement is much increased minimum Euclidean distance (MED) of the 3-D lattice constellations compared with the corresponding 2-D ones. When the MEDs of 2-D and 3-D lattice constellation are compared to confirm the analysis, the MED of 3-D 1024-ary constellation is around 2.6 times larger than that of the quadrature amplitude modulation (QAM). Expanding the constellation size to 4096, the MED of 3-D lattice constellation is increased by 3.2 times of the QAM.