• Journal of Institute of Convergence Technology
• /
• v.5 no.1
• /
• pp.27-31
• /
• 2015

A Pin-fin array is widely used to enhance the heat transfer in the internal cooling passage. The heat transfer distribution around the pin-fin is varied by the horseshoe vortex and flow separation. The difference of heat transfer coefficient induces the large thermal stress, which is one of the major reasons to break of hot components. So, it is required to enhance the heat transfer on the back side of pin-fin to solve the thermal stress problem. This study suggests the pin-fin with inclined jet hole and complex pin-fin/dimple array to enhance the heat transfer on the back side of pin-fin. The heat transfer coefficient is predicted by the numerical analysis, which is performed by CFX 14.0. The numerical results are obtained at Reynolds number, 10,000. The results show that the heat transfer on the back side of pin-fin is increased in both cases. Beside, the wake, which comes from dimple and jet, helps to develop the horseshoe vortex and increase the heat transfer on the next row pin-fin.

• Journal of Periodontal and Implant Science
• /
• v.53 no.3
• /
• pp.233-244
• /
• 2023

Purpose: An implant-supported prosthesis consists of an implant fixture, an abutment, an internal screw that connects the abutment to the implant fixture, and the upper prosthesis. Numerous studies have investigated the microorganisms present on the implant surface, surrounding tissues, and the subgingival microflora associated with peri-implantitis. However, there is limited information regarding the microbiome within the internal screw space. In this study, microbial samples were collected from the supragingival surfaces of natural teeth, the peri-implant sulcus, and the implant-abutment screw hole, in order to characterize the microbiome of the internal screw space in healthy subjects. Methods: Samples were obtained from the supragingival region of natural teeth, the peri-implant sulcus, and the implant screw hole in 20 healthy subjects. DNA was extracted, and the V3-V4 region of the 16S ribosomal RNA was sequenced for microbiome analysis. Alpha diversity, beta diversity, linear discriminant analysis effect size (LEfSe), and network analysis were employed to compare the characteristics of the microbiomes. Results: We observed significant differences in beta diversity among the samples. Upon analyzing the significant taxa using LEfSe, the microbial composition of the implant-abutment screw hole's microbiome was found to be similar to that of the other sampling sites' microbiomes. Moreover, the microbiome network analysis revealed a unique network complexity in samples obtained from the implant screw hole compared to those from the other sampling sites. Conclusions: The bacterial composition of the biofilm collected from the implant-abutment screw hole exhibited significant differences compared to the supra-structure of the implant. Therefore, long-term monitoring and management of not only the peri-implant tissue but also the implant screw are necessary.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.17 no.6
• /
• pp.653-664
• /
• 2015

When the structural analysis is performed for the concrete lining of the water pressure tunnel, many parameters are considered such as relaxed ground loads, internal water pressure, external water pressure, the shrinkage of the concrete lining, grouting pressure, etc. But, there are no standards and manuals for the structural analysis for the concrete lining of the water pressure tunnel. Above all, the external water pressure has an much effect on the stability of tunnel. So, in case that permeability of ground is large, the external water pressure should be decreased by installation of weep hole, or reinforced ground by ground improvement grouting should be pressed by the external water pressure instead. But, when weep hole is installed to reduce the external water pressure, the many problems may me occurred. Thus, reasonable approach for treatment of the external water pressure is necessary if weep hole is not installed. Therefore, the purpose of this study is to analyze design cases and studies for treatment of the external water pressure in performing structural analysis for the concrete lining of the water pressure tunnel, and to find reasonable method for tunnel lining modeling which is the treatment of the external water pressure according to permeability of ground and consequently the design of ground improvement grouting.

• Journal of Korean Society for Quality Management
• /
• v.25 no.1
• /
• pp.135-141
• /
• 1997

The Copper-Clad Laminate (CCL) is a main electronic component of specialtype printed circuit boards (PCBs) such as Silver Through Hole PCB. This CCL should have high reliability under the aging test, and usually the test is done at a higher temperature (110-$150^{\circ}C$) than the normal. Then, this test condition of high temperature may cause such quality problems as hole eccentricity and reduction of distance between part holes. After measuring the CCL shrinkage affected by temperature, the correction factor of a press mold was a, pp.ied to solve these problems. The results showed that the tolerance of hole pitch(${\pm}$$100{\mu}m$) was satisfactory and the internal and external failure costs were reduced by 55%.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.12
• /
• pp.1984-1991
• /
• 1997

Recently burr technology is rising in the fields of the precision manufacturing and the high quality machining, deburring has treated as a difficult problem on going to the high efficiency, automation in the FMS. Removal of burr with various shapes, dimensions and properties couldn't be standardized and has depended on manual treatment. Especially, deburring for cross hole inside owing to passing through out perpendicular to a main hole is more difficult, the electrochemical method is proper as its solution at practical aspects. Burr elimination in the cross hole drilling of governor shaft used in the automobile engine so far has been worked by a manual post-processing by a skillful worker, which becomes a factor of productivity-down and cost-up so that improvement of machining process is needed. Therefore, for the high efficiency and automation of internal deburring in the cross hole, development of electrochemical deburring technology is needed. So, the new process in the burr treatment is supposed. In this study, characteristics of electrochemical deburring through experiments were identified and factors such as electrolytic gap and electorlytic fluid contributed to removal burr height were analyzed. Also, deburring efficiency and electrolytic performance for cross hole were examined according to electrolytic current and electrochemical deburring condition corresponding to acquired edge quality was found out.

• Archives of Craniofacial Surgery
• /
• v.12 no.1
• /
• pp.12-16
• /
• 2011

Purpose: This study examined the biomechanical stability of four different plating techniques in the experimental model of mandibular subcondyle fracture. Methods: Twenty standardized bovine tibia bone samples ($7{\times}1.5{\times}1.0cm$) were used for this study. Each of the four sets of tibia bone was cut to mimic a perpendicular subcondyle fracture in the center area. The osteotomized tibia bone was fixed using one of four different fixation groups (A,B,C,D). The fixation systems included single 2.0 mm 4 hole mini adaption plate (A), single 2.0 mm 4 hole dynamic compression miniplate (B), double fixation with 2.0 mm 4 hole mini adaption plate (C), double fixation with a 2.0 mm 4 hole mini adaption plate and 2.0 mm 4 hole dynamic compression miniplate (D). A bending force was applied to the experimental model using a pressure machine (858 table top system, $MTS^{(R)}$) until failure occurred. The load for permanent deformation, maximum load of failure were measured in the load displacement curve with the chart recorder. Results: Double fixation with a 2.0 mm 4 hole mini adaption plate and a 2.0 mm 4 hole dynamic compression miniplate (D) applied to the anterior and posterior regions of the subcondyle experimental model showed the highest load to failure. Conclusion: From this study, double fixation with an adaption plate and dynamic compression miniplate fixation technique produced the greatest biomechanical stability. This technique may be considered a useful means of fixation to reduce the postoperative internal maxillary fixation period and achieve early mobility of the jaw.

• Journal of the Korean Physical Society
• /
• v.73 no.10
• /
• pp.1420-1430
• /
• 2018

We investigate an entangled system, which is analogous to a composite system of a black hole and Hawking radiation. If Hawking radiation is well approximated by an outgoing particle generated from pair creation around the black hole, such a pair creation increases the total number of states. There should be a unitary mechanism to reduce the number of states inside the horizon for black hole evaporation. Because the infalling antiparticle has negative energy, as long as the infalling antiparticle finds its partner such that the two particles form a separable state, one can trace out such a zero energy system by maintaining unitarity. In this paper, based on some toy model calculations, we show that such a unitary tracing-out process is only possible before the Page time while it is impossible after the Page time. Hence, after the Page time, if we assume that the process is unitary and the Hawking pair forms a separable state, the internal number of states will monotonically increase, which is supported by the Almheiri-Marolf-Polchinski-Sully (AMPS) argument. In addition, the Hawking particles cannot generate randomness of the entire system; hence, the entanglement entropy cannot reach its maximum. Based on these results, we modify the correct form of the Page curve for the remnant picture. The most important conclusion is this: if we assume unitarity, semi-classical quantum field theory, and general relativity, then the black hole should violate the Bekenstein-Hawking entropy bound around the Page time at the latest; hence, the infinite production arguments for remnants might be applied for semi-classical black holes, which seems very problematic.

• Journal of the Korean Society for Precision Engineering
• /
• v.14 no.9
• /
• pp.30-36
• /
• 1997

In this study, the development of an aluminum forged piston was tried to substitute the cast piston, in which there were internal defects such as blow hole and shrink pipe. A gasoline engine piston was chosen as an example for developing the forged piston. Before aluminum forging, model, material (plasticine) test was carried out to investigate the forgeability and internal flow pattern of the forged piston at room temperature. From the result of model material test, an aluminum piston to be forged was redesigned. The aluminum pistion was forged in hot process. The quality of a forged piston was compared with that of a cast piston in the point of mechanical properties, internal defect and microstructure. It was proved that the forged piston was superior to the cast piston.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1995.10a
• /
• pp.102-108
• /
• 1995

Internal contact scheme between two free surfaces on one deforming body has been proposed by using the penalty method. It has been imposed to be internal boundary condition on two-dimensional thermo-viscoplastic finite element method so as to analyze one deforming body, which has two free surfaces penetrating each others. Analysis of side pressing with a circular void and a inclined elliptic hole have been carried out in order to verity the proposed contact scheme. A finite element code imposed internal boundary condition has been applied to two-dimensional analysis of free forging of large ingot with a void. Through the analysis, effects of working parameters in order to consolidate voids have been investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1853-1856
• /
• 2003

Multi-layer printed circuit board(PCB) is being used widely for the product with relatively complex circuits such as TV, VTR and FAX. With the rapid enlargement of electronic and IT industry, the hole machining technology on multi-layer PCB is increasingly required to improve. Thus, the micro drilling with ultrasonic vibration can be a good method for hole machining. Unlike conventional drilling, ultrasonic vibration applied drilling introduces less wear and fracture of not only tool but also internal surface of workpiece due to little cutting resistance, thus, machinability can be improved. The experiment is conducted through the comparison between the results of conventional drilling and ultrasonic micro drilling as well as among each results by the variation according to not only feed rate of drill but also amplitude and frequency of ultrasonic vibration. The multi-layer PCB consists of 6 layers and ${\Phi}$0.3 diameter drill was used. As a result, it was found that the state of internal surfaces of holes on multiple layer PCBs is improved by the application of ultrasonic vibration.