• Journal of the Microelectronics and Packaging Society
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• v.19 no.4
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• pp.57-64
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• 2012

Ball shear test was performed by test variables such as loading speed and annealing time in order to investigate the effect of surface finishes on the bonding strength of Sn-1.2Ag-0.7Cu-0.4In Pb-free solder. The shear strength increased and the ductility decreased with increasing shear speed. With increasing shear speed, the electroless nickel immersion gold (ENIG) finish showed dominant brittle fracture mode, while organic solderability preservative (OSP) finish showed pad open fracture mode. The shear strength and toughness for both surface finishes decreased with increasing annealing time under the high-speed shear test of 500 mm/s. Typically, the thickness of intermetallic compound increased with increasing annealing time, which means that exposure of brittle fracture became much easier. With increasing annealing time, the both ENIG and OSP finishes exhibited the pad open fracture mode. Overall, ENIG finish showed higher shear strength rather than OSP finish due to its superior barrier stability.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.4
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• pp.309-322
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• 2002

The purpose of this study was to investigate the cytotoxicity and mutagenicity of denture base resins. According to manufacturer's instructions, resin specimens were made. Group 1 : heat-polymerizing acrylic resin (Luciton $199^{(R)}$) Group 2 : heat-polymerizing acrylic resin containing polyhedraloligosilsesquioxane(POSS resin) Group 3 : auto-polymerizing acrylic resin (Repair $Acrylic^{(R)}$) Group 4 : direct relining auto-polymerizing acrylic resin (Tokuso $Rebase^{(R)}$). Fresh specimens 24 hrs. and 72 hrs. soaked specimens in distil)ed water were made. Responses with metabolic assay and mutagenesis assay to eluates from resin specimens were measured. Cultures with medium alone provided controls. Cytotoxicity was assessed with agar overlay test. The results were as follows; 1. Group 4 showed higher cytotoxicity than Group 1, Group 2 and Group 3 in fresh, 24-an4 72-hour immersion caries (p<.05). Group 3 showed higher cytotoxicity than Group 2 in fresh cases and showed higher cytotoxicity than Group 1 and Group 2 in 24-and 72-hour immersion cases (p<.05) . Group 1 and Group 2 showed no significant difference. 2. All acrylic denture base resins skewed significant increase of cell activity as immersion time increased (p<.05). 3. Auto-polymerizing acrylic denture base resins skewed higher cytotoxicity than heat-polymerizing acrylic denture base resins (p<.05). 4. All acrylic denture base resins showed lower mutagenicity than controls (p<.05).

• The Journal of the Korea Contents Association
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• v.8 no.3
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• pp.182-189
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• 2008

The purpose of this study were to investigate 1) present condition of children's usage of computer game, 2) difference in extent of immersing in computer game according to grade, and 3) difference in extent of immersing in computer game according to conditions of computer game usage. A total of 239 children from 1st to 3rd grade in an elementary school in Busan were surveyed with two kinds of questionnaires about usage of and immersion in computer game. The collected data were analyzed using SPSS 12.0 program. It was revealed that the 1st graders showed higher scores on experience of computer game, frequency of computer game per week, and amount of time for each computer game than the 3rd graders. However, there were no significant differences in extent of immersing in computer game according to grade and to conditions of computer game usage. The findings of this study implies that the age of using computer game is going down rapidly. Discussions and suggestions for further study were provided.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.30-32
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• 2006

The interfacial reaction and reliability of eutectic Sn-Pb and Pb-free eutectic Sn-Ag ball-grid-array (BGA) solders with an immersion Ag-plated Cu substrate were evaluated following isothermal aging at $150^{\circ}C$. During reflowing, the topmost Ag layer was dissolved completely into the molten solder, leaving the Cu layer exposed to the molten solder for both solder systems. A typical scallop-type Cu-Sn intermetallic compound (IMC) layer was formed at both of the solder/Cu interfaces during reflowing. The thickness of the Cu-Sn IMCs for both solders was found to increase linearly with the square root of isothermal aging time. The growth of the $Cu_3Sn$ layer for the Sn-37Pb solder was faster than that for the Sn-3.5Ag solder, In the case of the Sn-37Pb solder, the formation of the Pb-rich layer on the Cu-Sn IMC layer retarded the growth of the $Cu_6Sn_5$ IMC layer, and thereby increased the growth rate of the $Cu_3Sn$ IMC layer. In the ball shear test conducted on the Sn-37Pb/Ag-plated Cu joint after aging for 500h, fracturing occurred at the solder/$Cu_6Sn_5$ interface. The shear failure was significantly related to the interfacial adhesion strength between the Pb-rich and $Cu_6Sn_5$ IMC layers. On the other hand, all fracturing occurred in the bulk solder for the Sn-3.5Ag/Ag-plated Cu joint, which confirmed its desirable joint reliability.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.400-403
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• 2018

The VR / AR market has grown significantly due to the development of Virtual Reality and Augmented Reality, the core technologies of the Fourth Industrial Revolution. According to a report released by the Korea Science and Engineering Corporation (KISTEP), the global VR / AR market will grow to $ 105 billion by 2022. An important key to the growth of the VR / AR market is user immersion. VR is dependent on technology of hardware such as display and sensor for biometric signal recognition. In order to improve user's immersion feeling, it is important to transmit sensor data to display device more accurately and quickly. In this paper, we consider various sensor hardware dependencies of VR, and compare various correction methods and filtering methods to lower the Motion to Photon (MTP) time that user movement is fully reflected on the display using sensor devices.

• Corrosion Science and Technology
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• v.9 no.2
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• pp.92-97
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• 2010

Many kinds of alternative fuels such as biodiesel, ethanol, methanol, and natural gas have been developed in order to overcome the limited deposits in fossil fuels. In some cases, the alternative fuels have been reported to cause degrade materials. The corrosion rates of metals were measured by immersion test, a kind of time consuming test because low conductivity of these fuels was not allowed to employ electrochemical tests. With twin two-electrode cell newly designed for the study, however, electrochemical impedance spectroscopy (EIS) test was successfully applied to evaluation of the corrosion resistance ($R_p$) of zinc, iron, aluminum, and its alloys in an oxidized biodiesel and gasoline/ethanol solutions and the corrosion resistance from EIS was compared with the corrosion rate from immersion test. In biodiesel, $R_p$ increased in the order of zinc, iron, and aluminum, which agreed with the corrosion resistance measured from immersion test. In addition, on aluminum showing the best corrosion resistance ($R_p$), the effect of magnesium as an alloying element was evaluated in gasoline/ethanol solutions as well as the oxidized biodiesel. $R_p$ increased with addition of magnesium in gasoline/ethanol solutions containing chloride and the oxidized biodiesel. In the mean while, in gasoline/ethanol solutions containing formic acid, Al-Mg alloy added 1% magnesium had the highest $R_p$ and the further addition of magnesium decreased $R_p$. It can be explained with the fact that the addition of more than 1% magnesium increases the passive current density of Al-Mg alloys.

• KIEE International Transactions on Power Engineering
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• v.4A no.4
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• pp.171-177
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• 2004

In the current age of the information oriented society in which we live, many people use PCs and are dependant on the databases provided by the network server. However, online data can be missed during the occurrence of a blackout and furthermore, power failure can greatly effect Power Quality. This has resulted in the trend of using interruption-free live-line work when trouble occurs in a power system. However, 83% of the population receives an electric shock experience when a laborer is performing interruption-free live-line work. In the interruption-free method, education and training problems have been pinpointed. However, there are few instructors to implement the necessary training. Furthermore, the trainees undergo only a short training period of just 4 weeks. In this paper, to develop a method with no restrictions on time and place and to ensure a reduction in the misuse of materials, immersion type virtual reality (or environment) technology is used. The users of a 3D immersion type VR training system can interact with the system by performing the equivalent action in a safe environment. Thus, it can be valuable to apply this training system to such dangerous work as 'Interruption-free live-line work exchanging COS (Cut-Out-Switch)'. In this program, the user carries out work according to instructions displayed through the window and speaker and cannot perform other tasks until each part of the task is completed in the proper sequence. The workers using this system can utilize their hands and viewpoint movement since they are in a real environment but the trainee cannot use all parts and senses of a real body with the current VR technology. Despite these weak points, when we consider the trends of improvement in electrical devices and communication technology, we can say that 3D graphic VR application has high potentiality.

• Journal of Information Processing Systems
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• v.14 no.4
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• pp.1049-1061
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• 2018

As mobile devices such as smartphones and tablet PCs become more popular, users are becoming accustomed to consuming a massive amount of multimedia content every day without time or space limitations. From the industry, the need for user satisfaction investigation has consequently emerged. Conventional methods to investigate user satisfaction usually employ user feedback surveys or interviews, which are considered manual, subjective, and inefficient. Therefore, the authors focus on a more objective method of investigating users' brainwaves to measure how much they enjoy their content. Particularly for multimedia content, it is natural that users will be immersed in the played content if they are satisfied with it. In this paper, the authors propose a method of using a portable and dry electroencephalogram (EEG) sensor device to overcome the limitations of the existing conventional methods and to further advance existing EEG-based studies. The proposed method uses a portable EEG sensor device that has a small, dry (i.e., not wet or adhesive), and simple sensor using a single channel, because the authors assume mobile device environments where users consider the features of portability and usability to be important. This paper presents how to measure attention, gauge and compute a score of user's content immersion level after addressing some technical details related to adopting the portable EEG sensor device. Lastly, via an experiment, the authors verified a meaningful correlation between the computed scores and the actual user satisfaction scores.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.2
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• pp.68-76
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• 2022

This study was performed to investigate the mechanism of the change in compressive strength of autoclave cured geopolymers. Specimens were immerged in distilled water, 2M, 8M, and 14M alkaline solutions for 3, 7, and 21 days. The change in the specimens immersed in a short period of time was not significant, but the compressive strength of the specimens immersed in the distilled water and 8M alkali solution) for 21 days increased more than twice as much as before immersion because of additional geopolymerization. However, compressive strength decreased due to the alkaline aggregate reaction when alkaline solution was supplied more than a certain level of concentration. Therefore, immersing the specimens for more than 21 days in the distilled water or 8M alkaline solution would be desirable for the improvement of compressive strength of autoclave cured specimens.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.178-178
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• 2016

Every display is equipped with a cover glass to protect the underneath displaying devices from mechanical and environmental impact during its use. The strengthened glass such as Gorilla glass.$^{TM}$ has been exclusively adopted as a cover glass in many displays. Conventionally, the strengthened glass has been manufactured via ion-exchange process in wet salt bath at high temperature of around $500^{\circ}C$ for hours of treatment time. During ion-exchange process, Na ions with smaller diameter are substituted with larger-diameter K ions, resulting in high compressive stress in near-surface region and making the treated glass very resistant to scratch or impact during its use. In this study, PIIID (plasma immersion ion implantation and deposition) technique was used to implant metal ions into the glass surface for strengthening. In addition, due to the plasmonic effect of the implanted metal ions, the metal-ion implanted glass samples got colored. To implant metal ions, plasma immersion ion implantation technique combined with HiPIMS method was adopted. The HiPIMS pulse voltage of up to 1.4 kV was applied to the 3" magnetron sputtering targets (Cu, Ag, Au, Al). At the same time, the sample stage with glass samples was synchronously pulse-biased via -50 kV high voltage pulse modulator. The frequency and pulse width of 100 Hz and 15 usec, respectively, were used during metal ion implantation. In addition, nitrogen ions were implanted to study the strengthening effect of gas ion implantation. The mechanical and optical properties of implanted glass samples were investigated using micro-hardness tester and UV-Vis spectrometer. The implanted ion distribution and the chemical states along depth was studied with XPS (X-ray photo-electron spectroscopy). A cross-sectional TEM study was also conducted to investigate the nature of implanted metal ions. The ion-implanted glass samples showed increased hardness of ~1.5 times at short implantation times. However, with increasing the implantation time, the surface hardness was decreased due to the accumulation of implantation damage.