Enhancing Robotic Tactile Perception through Biomimetic Approaches : From Neuron Modeling to Spiking Neural Networks

Jaehun Kim Ulsan National Institute of Science and Technology 2024 국내박사

LASER WELDING OF ZINC-COATED AND UNCOATED STEEL SHEETS AT ATMOSPHERIC AND SUBATMOSPHERIC PRESSURES

Jaehun Kim Graduate School of UNIST 2017 국내박사

In the automotive industry, zinc-coated steel is widely used because of its high corrosion resistance. Many automotive industry companies have tried to employ laser welding because of its many benefits, such as low heat input, high-intensity heat source, minimal distortion in heat affected zones, and high productivity. In lap joint laser welding of zinc-coated steel sheets, a proper gap needs to be maintained to avoid weld defects in weldment because the zinc vaporization temperature (1180 K) is lower than the steel melting temperature (1809 K). However, in this case, additional processes are required for application to actual industrial production lines, and it is difficult to precisely control the gap. Furthermore, although many researchers have investigated ways to mitigate the influence of high zinc vaporization pressure, it remains an issue because of erratic and unstable keyhole motion and melt pool behavior. Therefore, the purpose of this dissertation is to investigate the keyhole behavior and weldability of zero-gap laser welding of zinc-coated and uncoated steel sheets at atmospheric and subatmospheric pressures according to process parameters to develop the gap insensitive lap joint laser welding of zinc-coated steel. In this dissertation, firstly, a scaling law for predicting penetration depth was proposed, because the determination of penetration depth is the first consideration before the welding process. Moreover, then precisely observation method and analysis method were developed to observe clearly keyhole behavior, and effect of relative configuration of the laser beam and keyhole geometry on weldability for zero-gap lap laser welding of zinc-coated steel sheets. Also, the influence of ambient pressure on keyhole behavior and weldability were investigated to find solutions and possibilities for obtaining good welds for zero-gap lap laser welding of zinc-coated steel sheets by adjusting processing parameters (i.e. laser intensity and welding speed and ambient pressures).These studies can be summarized as follows. Firstly, a scaling law for predicting penetration depth was proposed that can be applied to both conduction mode and keyhole mode laser welding. The proposed scaling law was formulated based on a simple one-dimensional heat conduction model, and the effect of multiple reflections was accounted for. Because the scaling law was obtained from a laser heating problem, its physical meaning and why it needs to be formulated that way can be clearly explained. Experiments were conducted, and the obtained results were found to be in good agreement with the proposed scaling law. Secondly, in order to observe the keyhole behavior and reconstruct the keyhole geometry, a coaxial observation method was developed using a high-speed camera. A coaxial observation is a more useful and precise method to observe keyhole behavior than other lateral observation methods, and it was possible to study how the keyhole shape changes as the process parameters are varied. This chapter investigated the overall differences in the keyhole geometry between the zinc-coated and uncoated steels over a large process parameter space. Thirdly, using the obtained keyhole geometry data, the effect of keyhole geometry and dynamics on weldability was investigated by defining several key factors. It was found that the relative configuration of the keyhole and the laser beam is the most influential factor for obtaining good welds. For the zinc-coated steel, good welds were obtained at low welding speeds even zero-gap lap joint laser welding of zinc-coated steel sheets. Finally, based on the observation and analysis method from previous chapters, we investigated the laser welding of zinc-coated steel at subatmospheric pressures in order to compare between laser welding at atmospheric pressure and subatmospheric pressure. The purpose of this work is because the pressures inside the keyhole play a major role in weldability during zero-gap lap joint laser welding of the zinc-coated steel sheets. In this chapter, the main focus was to reconstruct time-averaged 3-D keyhole shapes and studying the influence of ambient pressures on keyhole behavior and weldability.

(The) relationship of the maxillary molar and sinus on cone beam computed tomographic images in Korean population

Kim, Jaehun Graduate School, Yonsei University 2019 국내박사

목적: 본 연구의 목적은 콘 빔 씨티(CBCT)를 이용해 한국인의 상악 구치부와 상악동 바닥과의 관계를 조사하고 둘 사이의 수직적 거리를 측정하는 것이다. 도구 및 방법: 상악 대구치가 완전 맹출된 17세 이상인 188 명의 환자의 CBCT 영상을 선택했다. 상악 제1대구치와 제2대구치 총 756개의 치아가 CBCT 단면영상에서 상악동으로의 함입관계에 따라 4개의 타입으로 분류되었다. 두 명의 관찰자가 소프트웨어를 이용하여 상악 제 1 대구치와 제 2 대구치의 치근 분지부 중간 점에서 상악동 최하연의 수평연장선까지의 최단 거리를 측정하였다. 각 타입의 빈도가 분석되었고 단면 영상에서 관찰자 간 및 내적 신뢰도에 대한 상관 분석이 이루어졌다. 남성과 여성, 좌 우측 사이의 수직거리 측정값의 차이를 분석하기 위해 independent t-test가 시행되었다. 결과: 상악 제1대구치에서 가장 빈번한 타입은 상악동으로 적어도 하나의 치근이 함입된 TYPE 3이고 그 다음이 상악동을 둘러싸고 있는 타입2였다. 상악 제2대구치는 타입3와 타입1의 순서였다. 상악 제1,2 대구치에서 타입1의 평균 수직거리는 각각 9.51±3.68 mm, 8.07±2.73 mm였다. 타입3에서 수직거리는 3.70±1.52 mm, 4.03±1.53 mm 였다. 전체 평균 수직거리 값은 5.48±3.02 mm and 5.62±2.56 mm 로 측정되었다. 상악 제2대구치에서 수직거리는 통계적으로 유의하게 남성보다 여성이 더 높게 나타났다. 결론: 한국인은 타입3가 상악 구치부에서 가장 빈번하게 관찰되고 타입3의 치조골의 높이가 가장 낮았다. 제1대구치의 치조골의 높이가 제2대구치보다 짧았다. 이 결과는 상악 구치의 치료계획을 세우고 즉시 식립 임플란트를 위한 사용 가능한 골량을 예측하여 상악동과 관련한 부작용을 예방하는 데 도움을 줄 것이다. Objective: The aim of this study was to investigate the relationship and the available alveolar bone height between the maxillary molars and the sinus floor using cone beam computed tomographic (CBCT) images in Korean population. Materials and Methods: The CBCT scans of 188 patients older than 17 years with four molars fully erupted maxillary first and second molars were selected. A total 756 of maxillary first (M1) and second molars (M2) were categorized into 4 types according to the relationship of the molar root and the maxillary sinus floor on CBCT images. And the shortest vertical distance (VD) from the furcation midpoints of the roots to the lowest point of the sinus floor was measured using software by two observers. The frequency distribution of each type were analyzed. Correlation analyses in the mean values of VD measurements were calculated for inter- and intra-observer reliability. The independent ttest was performed for the analysis of the difference in vertical distance measurements between male and female, and right and left side. Results: For M1, type 3 which was at least one root protruding into the maxillary sinus was the most frequent and type 2 which was enveloped the sinus followed. Meanwhile the frequency was higher in the order of type 3 and type 1 for M2. VD measurements of type 1 were 9.51±3.68 mm and 8.07±2.73 mm for M1 and M2, and those of type 3 were 3.70±1.52 mm, 4.03±1.53 mm for M1 and M2, respectively. Total mean value of VD measurements was found as 5.48±3.02 mm and 5.62±2.56 mm in M1 and M2, respectively. In VD measurements of M2, female showed higher than male with the statistically significant differences. Conclusion: In Korean population, the type 3 was the most frequent in the maxillary molars, and the alveolar bone height of type 3 was the least among other types. Alveolar bone height of the first molar are shorter than those of the second molar. This data will help the clinician to prevent the complication related with the maxillary sinus during maxillary molar treatment and to predict the available bone height for immediate implant planning.

Why Should Marketers be Interested in Online Games? The Influence of BIRFing (Basking in Reflected Failure) on Self-Congruity of Sports Fans

김재훈 부산대학교 대학원 2020 국내박사

This study aims to examine the role of online games in the sports marketing environment by exploring the mechanisms by which sports fans experience psychological changes from BIRFing (Basking in Reflected Failure) to BIRGing (Basking in Reflected Glory) through online games. Just as game users feel vicarious satisfaction through games that cannot be achieved in reality, sports fans also enjoy online games to feel greater sense of achievement, regardless of the results of the team they support in reality. BIRFing is generally regarded as the behavior of fans who are loyal to a certain team. However, no matter how loyal customers are, they buy better products when they come out. Likewise, sports fans may be loyal to the team they support for the time being, but if the team's performance is not good, it may be difficult to maintain the support of their fans. This study was conducted with research questions in order to determine whether psychological awakening can occur through online games in the virtual world, even if the performance of the team a fan supports is not good. To examine the psychological mechanism of sports fans, psychological variables such as BIRFing, BIRGing, self-congruity, and psychological well-being were used as mediators. The survey was conducted using a structured questionnaire for users who enjoy online games as well as for fans who are loyal to sports teams. The reliability and validity of the collected data were reviewed and the hypotheses was verified through structural equation model analysis. The results of the study show that sports fans can experience self-congruity through the tool of online games and the emotional change of BIRFing to BIRGing, which shows stronger loyalty to a team. This study is meaningful in providing a new theoretical perspective on BIRFing behavior of sports fans and suggesting implications for finding ways for sports teams to maintain and improve marketing strategies. 본 연구는 스포츠 팬들이 온라인 게임을 매개로 BIRFing에서 BIRGing 의 심리적 변화를 겪는 매커니즘을 탐색해 봄으로써, 스포츠 마케팅 환경에서 온라인게임의 역할에 대해 검토해보고자 한다. 게임 유저들은 현실에서 이룰 수 없는 것들을 게임을 통해 대리만족을 느끼듯이, 스포츠팬들 역시 현실에서 본인들이 응원하는 팀의 결과와 상관없이 더 큰 성취를 즐기기 위해 온라인 게임을 즐긴다. BIRFing은 일반적으로 팀에 충성도가 높은 팬들의 행동이다. 그러나 아무리 제품 충성도가 높은 고객이라 할지라도 더 좋은 제품이 나오면 구매를 하듯이, 스포츠팬이 현재 응원하는 팀에 충성도가 높다 할지라고, 팀의 성적이 좋지 않다면 팬의 이탈을 피할 수 없을 것이다. 스포츠에서 승리는 최고의 마케팅이자 팬을 확보하는 가장 확실한 방법이다. 그러나 어느 팀도 계속 이길 수는 없다. 따라서, 스포츠 구단이나 기업은 BIRFing 팬들이 BIRGing 팬들이 될 수 있는 방법이나 수단을 개발해야 한다. 본 연구에서는 스포츠팬들이 현실에서 응원하는 팀의 성적이 좋지 않을지라도 가상세계 속 온라인 게임을 통해 심리적 각성이 일어날 수 있을지에 대한 연구문제를 갖고 연구를 진행하였다. 스포츠팬들의 심리적 매커니즘을 검토하기 위해, BIRFing, BIRGing, 자아일치, 심리적 Well-Being이라는 심리적 변수를 매개로 사용하였다. 현재 응원하는 스포츠 구단에 충성도가 높은 팬들을 대상으로 온라인 게임을 즐기는 유저들을 대상으로 구조화된 설문지를 사용하여 설문조사를 실시하였다. 수집된 자료의 신뢰도와 타당도를 검토하고 구조방정식 모형분석을 통해 가설을 검증하였다. 연구결과 스포츠팬들은 온라인 게임이라는 도구를 통해서 현실의 자아를 투영하며, BIRFing의 행동에서 BIRGing의 감정 변화가 일어나며 이는 팀에 대한 더욱 강한 충성도를 보이는 것으로 나타났다. 본 연구는 스포츠팬들의 BIRFing 행동에 관한 새로운 이론적 시각을 제공하고 스포츠 팀이 마케팅을 유지 할 수 있는 방안 모색에 대한 시사점을 제시하는데 그 의의가 있다.

Laser interaction with grass tissues

김재훈 UNIST 2012 국내석사

This thesis has three chapters as first chapter: UV, Visible and IR light interaction with grass-tissues, second chapter: IR light with different water absorption coefficient interaction with grass-tissues and third chapter: laser lawn mowing system. Fist chapter, we investigated how UV, Visible and IR light affectgrass tissues. Grass tissues are composed mainly of pigments and water. Chlorophyll plays the role of the photosynthesis and it is not only the green pigment but it also absorbs visible light(blue and red) well. The water content of grass tissues helps the photosynthesis with carbondioxide and it can react well with absorbed IR light. UV light canbreak the chemical bonding of materials more easily than longerwavelengths (i.e. Visible and IR regimes), since the shorter wavelengths have higher electrical potential than longer wavelengths. 355nm (UV), 532nm (Visible) and 1064nm (NIR) wavelengths generated by a picosecond pulsed laser were used in the experiment. Thus, we made a process map of each wavelength and we analyzed the difference between the three wavelength regimes by using a scanning electron microscope and an optical microscope.From a process map of each wavelength, we found that the 355nm is most effective energy transfer to grass-tissues than 532nm and 1064nm wavelength and 1064nm (IR) light can reduce the damage of grass-tissues because of water absorption coefficient dominant. Therefore, we believed that chlorophyll dominant case and water dominant case have difference interaction mechanism. The chlorophyll dominant case makes directly energy of light transfer to grass-tissues then grass-tissues ablated directly. However, the water dominant case makes responses (carbonization, through-cut, partial-cut and decoloration) by heat of around absorbed area from water evaporation in grass-tissue or on surface of grass. In chapter II,Er:YAG (2.94μm) and CO2 (10.6μm) laser interaction with grass tissues had investigated. 2.94μm and 10.6μm light, Infrared (IR) regimes, laser have high water absorption coefficient as 12000 and 860 respectively. The sample thickness (grass thickness) is around 110μm. Since we can believe that the water content can reduce damage to grass-tissues from results previous Chapter I, the effect of water content in grass tissues had investigated in this chapter as how differently affect grass tissues as different water absorption coefficient at 2.94μm and 10.6μm wavelength cases. Plus, we investigated beam size effect and how seasonally affect grass-tissues (water concentration). Therefore, some results were found. Even though same intensity and interaction time, response is different as large beam size makes only carbonization response. 2.94μm with high water absorption coefficient light made faster response change than 10.6μmlight at using same beam size (1mm). Chapter III, Typical lawn mower is cut the lawn by contact method such as rotate blade and its equipment used foil fuel engine. From these reason, typical lawn mower can make noise seriously and dangerous and some pollution. However, laser lawn mower is using non-contact method and electrical power. Thus, it can be more quite, safety and little pollution. Furthermore, from previous results Chapter I and II, developed process maps of each laser can be used to manufacturing laser lawn mowing system. In this chapter, we will introduce concept of laser lawn mowing system and suggest optical-setups to cut-well and advantage and disadvantage of each wavelengths.