A Three-dimensional Deviation Analysis by the Coordinate Registration of Randomly Positioned Objects

Hyerim Kim Graduate School of UNIST 2018 국내석사

It is very important to accurately inspect machining errors, assembly tolerances of product in manufacturing industry. Recently, a three-dimensional measurement system is widely used for industrial inspection. Typical three-dimensional measurement methods include a coordinate measuring machine (CMM), a line laser scanning method, and a structured light system comprising a camera and light source for generating a pattern. In general, the inspection system applying the three-dimensional measurement method require the physical calibration processing using special device to place object at home position with desired pose. However, such a process requires a considerable time for measurement, and it inhibits the flexibility of measurement spatially. Therefore, to solve this problem, this thesis proposed a methodology to measurement of randomly positioned objects by coordinate recognition. It is assumed that the position and pose of object is varied at every measurement. Coordinate of CAD model must be brought to the coordinate of measured data to calculate deviation of object. Transformation parameters of two coordinates are derived by following procedure. reference plane selection is preceded before measurement as preprocessing. The first step is rough registration based on principal component analysis and iterative closest point algorithm. The second step is main methodology of this thesis, which is coordinate adjustment to calibrate transformation parameters. Coordinate adjustment is composed of two stages, which are reference plane matching for calibrating rotation parameters and edge matching for translation parameters. Then, deviation is calculated by comparison to the CAD model.

Mechanisms for the Decadal Change of the MJO Teleconnection over the Northern Hemisphere in Boreal Winter

Hyerim Kim Graduate School of UNIST 2020 국내박사

This thesis suggests dynamical mechanisms for the decadal change of the MJO teleconnection pattern over the Northern Hemisphere during boreal winter by investigating the influence of the decadal change of background states in the mid-latitude and tropical forcing on MJO teleconnection pattern and interpreting this relationship. Thus, it is important to understand how these changes influence on MJO teleconnection pattern to represent the MJO teleconnection pattern caused by changes of background states and MJO activities over the tropics. In boreal winter, OLR variance with intraseasonal variability variance is strengthened over the Maritime Continent and weakened over the southern Indian Ocean and the western Pacific. This is consistent with the results of the MJO amplitude at each MJO phase based on OMI. These changes of MJO activity are associated with the La Nina-like change of background states in tropics. There is wet and warm anomaly over the Maritime Continent and the western Pacific, and ascending motion over the Maritime Continent, whereas dry, cold and descending anomaly over the central and the eastern Pacific. The location of MJO teleconnection patterns can be determined by seasonal mean upper-level zonal wind acted as a waveguide. The obvious change of the jet stream is found, especially over the eastern Pacific. Over this region, stationary Rossby wavenumber is expanded east and northward in the recent period than that in the past period. This change modifies the location and intensity of the teleconnection patterns based on the analysis of zonal wavenumber. Based on the model experiments, the decadal change in the background states, especially zonal wind at the upper level, leads to strengthening the intensity of the MJO teleconnection pattern over the jet exit region but does not modify the pattern itself. On the other hand, the tropical heating modifies the teleconnection patterns over the North Pacific and North America, and these changes are similar to the observed difference maps between the two periods. Thus, the results indicate that the decadal change of the MJO teleconnection pattern is caused by the change of tropical diabatic heating rather than the change of zonal wind in the mid-latitude as background states. These changes are associated with the background states are changed into La Nina-like pattern in the recent period. This leads to moisture and SST increase over the warm pool region. In addition, the ascending motion of the vertical circulation in the background states strengthens over the eastern region of Maritime Continent, and then the convective anomaly becomes stronger over this region in the recent period than in the past period. It is thought that these background changes including the intensification of the vertical circulation lead to the enhancement of the MJO teleconnection pattern and its teleconnectivity over the upstream regions. Furthermore, there is close relationship of the MJO teleconnection patterns between P1 and El Nino years or P2 and La Nina years.

Photoactiviated Smart Materials using TiO2 complex and BiVO4 for Solar Fuels application

HyeRim Kim DGIST 2020 국내박사

The Expansion of Science Production at Korean Universities, 1970–2017

Kim, Hyerim The Pennsylvania State University ProQuest Dissert 2019 해외박사(DDOD)

Since 1970, when Korean researchers published the first journal article from their country to be cataloged in the Science Citation Index Expanded (SCIE), science production has exponentially expanded among Korean universities. This rapid growth was not driven by a few specific institutions. Rather, it was possible because virtually all universities with STEM programs, regardless of their institutional mission, participated in scholarly publishing. Meanwhile, the Korean government implemented a special research funding initiative, Brain Korea 21, in 1999 to stimulate science production among universities. Using multilevel linear regression models, this dissertation examines the effect of the BK 21 program; it finds that BK 21 had a positive effect on publications, but that its effect turned insignificant when more comparable groups of universities were examined. This research also demonstrates that the scientific collaboration network in Korea has moved from one strongly dominated by a few specific actors to one with more actors participating more equally and significantly. By using an exclusive longitudinal data set of publications—a data set that had not previously been examined—the research reflected in this dissertation contributes to an understanding of the expansion of science production in Korea, changes in publication characteristics, the role of a government-funded project in enhancing science productivity, and the formation of a scientific collaboration network among Korean universities and other countries. Given the relatively short history of the Korean higher education system, this study provides a landscape of how science production has been developed in Korea since its beginning.

A study on the synthesis of MXenes with controlled surface properties and their thin film applications

Hyerim Kim 고려대학교 KU-KIST융합대학원 2023 국내박사

Two-dimensional materials have a layered structure composed of one atomic layer and can be classified into conductors, semiconductors, and insulators according to their electrical properties. Moreover, due to its optical properties from its thin thickness, active research has been conducted to apply it to various industrial fields such as the Internet of Things, flexible devices, and next-generation batteries. Among them, MXenes, first discovered in 2011, are a family of a two-dimensional planar structure composed of transition metal carbides, carbonitrides, and/or nitrides with an atomic thickness of several nanometers. MXene can be synthesized through selective etching of three-phase crystals called MAX phase with a hydrofluoric acid-based etchant. Due to the layer of transition metal MXene can acquire high electrical conductivity, and stable aqueous solution dispersion property from surface functional groups obtained by the aqueous solution-based synthesis method simultaneously. The surface functional group of MXene acts as an important factor in determining the surface properties of MXene and controlling the surface properties through surface group control is a good strategy to control the physical properties of MXene. First, the quality of MAX and the surface properties of MXene were controlled by controlling the surface properties and impurities of raw materials used in the manufacture of MAX in the synthesis step. In order to lower the unit price of MXene, high-quality titanium carbide was produced using recycled titanium dioxide and graphite, and then MAX was synthesized after sintering MAX. In particular, in order to remove vacancy and oxygen solutes, the size of the particles was made small through high-energy ball-milling, and MAX with minimized oxygen impurities was produced through milling for 20 hours. It was confirmed that the MXene synthesized the improved electrical conductivity and electromagnetic shielding value as the oxygen impurity content of MAX decreased. Second, the surface properties of MXene were controlled by controlling the synthesis method in the MXene synthesis step. The surface group of MXene could be controlled according to the type of etchant and intercalant used in the synthesis of MXene. In particular, as the in-situ hydrofluoric acid used as an etchant and the concentration of hydrofluoric acid increased, it was confirmed that the hydrophilic properties of the surface decreased, and the work function was improved. In addition, in the case of MXene using lithium fluoride as an intercalant, the concentration of fluorine could be adjusted complexly. In particular, it was confirmed that the MXene film had the higher hydrophobicity and the higher electrical conductivity value when the larger amount of fluorine functional groups on the surface exists. Finally, MXene thin films were fabricated using interfacial self-assembly. In particular, the surface was controlled through heat treatment of the layered MXene thin film, which the electrical conductivity was improved by increasing the charge mobility and carrier density of the surface as the water and hydroxyl groups on the surface of the MXene was reduced, and the hydrophobic property of the surface was improved. In addition, in the case of MXene thin films whose surface characteristics were controlled through annealing, it was found that the electromagnetic interference shielding performance had higher values than that of two-dimensional material thin films of a few nanometer thicknesses. Especially, absolute electromagnetic interference shielding performance showed the highest value so far. 2차원 소재는 하나의 원자 층으로 이루어진 층상 구조로, 전기적 특성에 따라 도체, 반도체, 부도체로 분류될 수 있으며 이러한 다양한 전기적 특성과 얇은 두께로 인한 광학적 특성 때문에, 사물 인터넷, 유연 소자, 차세대 배터리 등 다양한 산업분야에 적용하기 위한 활발한 연구가 진행되고 있다. 그 중에서도 2011년 처음 발견된 맥신 소재는 전이금속 탄화물, 탄화질화물, 질화물로 구성된 수나노미터의 원자 두께로 구성된 2차원 평면 구조를 갖는 물질이다. 맥스로 불리는 삼상계 결정질을 불화수소 기반의 에천트로 선택적 식각을 통하여 맥신을 합성할 수 있으며, 전이금속의 금속 층으로 인한 고 전기 전도성과 수용액 기반의 합성법으로 인해 얻은 표면 관능기의 친수성으로 수용액 분산 안정성을 동시에 갖는 신물질이다. 맥신의 표면 관능기는 맥신의 표면 특성을 결정짓는 중요한 요인으로 작용하는데, 표면기 제어를 통해 표면 특성을 조절하는 것은 맥신의 물성을 제어할 수 있는 좋은 전략이라 할 수 있다. 먼저, 맥스의 합성 단계에서 맥스 제조 시 사용되는 원료의 표면 특성과 불순물을 제어함으로써 맥스의 품질 및 맥신의 표면 특성을 제어하였다. 맥신의 단가를 낮추기 위해 재활용 이산화 타이타늄과 흑연을 이용하여 결점이 제어된 고품질의 탄화 티탄을 제작 후 맥스를 제작한 뒤 맥신을 합성하였다. 특히, 결정질의 정공과 산소 불순물을 제거하기 위하여 고에너지 밀링을 통하여 입자의 크기를 작게 만들고 20시간 밀링을 통하여 산소 불순물이 최소화된 맥스를 제작하였고, 이렇게 이산화 타이타늄과 흑연 표면 특성을 제어하여 제작한 맥스로 합성한 맥신은 맥스의 산소 불순물 함량이 적어질 수록 전기전도성과 전자파 차폐 값이 향상됨을 확인하였다. 두번째로, 맥신의 합성 단계에서 합성 방법을 제어함으로써 맥신의 표면 특성을 제어하였다. 맥신의 합성에 사용되는 에천트의 종류와 박리제에 따라서 맥신의 표면기를 제어할 수 있었다. 특히, 에천트로 사용된 불산의 직접도가 낮고 불산의 농도가 높아짐에 따라 표면의 친수 특성이 감소하는 것을 확인할 수 있었고, 일함수를 향상시킬 수 있었다. 또한, 단순히 불산의 직접도와 농도뿐만 아니라, 박리제인 플루오린화 리튬을 이용한 맥신의 경우, 에천트의 농도와 복합적으로 불소 농도를 조절할 수 있었다. 특히, 표면의 불소 기능기가 가장 많은 경우 맥신 필름의 소수 특성이 가장 높았으며, 가장 높은 전기전도도 값을 갖는 것을 확인하였다. 마지막으로, 계면 자가 조립을 이용하여 맥신 박막을 제조하였다. 특히, 층층이 쌓아 올린 맥신 박막의 열처리를 통하여 표면을 제어하였는데, 맥신 표면의 수분 및 수산화 기를 감소시키면서 표면의 전하 이동도 및 캐리어 밀도를 높여 전기 전도성을 향상시켰으며, 표면의 소수성 특성을 높였다. 또한, 열처리를 통해 표면 특성을 제어한 맥신 박막의 경우 전자파 차폐 성능이 향상된 것을 알 수 있었고, 다양한 나노미터 두께의 2차원 소재 박막의 전자파 차폐 성능보다 높은 값을 지니며, 특히 단위 두께 및 중량에서 현재까지 보고된 절대 차폐 효과 중 가장 높은 값을 보여줬다.

(The) bank of Korea watch

김혜림 Graduate School, Korea University 2021 국내석사

Traders closely watch the Bank of Korea (BOK) base rate decisions as the short rate is the primary factor in bond and currency valuations. The survey of professional forecast (SPF) has been considered as the most reliable forecaster of the BOK base rate decision. In this paper, we investigate whether it is possible to further improve the prediction ability of the SPF. To do this, we use a predictive dynamic multinomial ordered probit model of the BOK base rate with a large number of predictors. By applying a Bayesian machine learning, we choose relevant predictors that maximize the predictive accuracy. According to our empirical exercise, our predictive model substantially outperforms the SPF in terms of out-of-sample prediction. The key predictors are found to be the SPF, short-term bond yield, lagged base rate, and text data based on newspapers. Further, allowing for their prediction abilities to change over time is essential for improving the predictive accuracy.

Effective operation strategy of ventilation system with low energy consumption for office building

김혜림 Graduate School, Korea University 2018 국내석사

Recent changes in the Korean climate have been leading to the increase in ventilation load and building energy consumptions. Effective use of ventilation systems is important to reduce building energy and CO2 emissions. This study focuses on the operation of the ventilation system with Energy Recovery Ventilator (ERV) and hybrid desiccant system, economizer control, and outdoor airflow rate control in an attempt to save energy consumption in buildings under Korean climate. Measurement and energy simulation using EnergyPlus 8.7 was performed. The energy performance of ERV was measured and simulated. ERV was evaluated to save 23% of heating energy, and ERV & hybrid desiccant system was evaluated to save 22.3% of cooling energy. The economizer controlled by enthalpy was analyzed to be more energy efficient than the economizer controlled by dry-bulb temperature in cooling season. Differential enthalpy economizer control saved average 4% of cooling energy during May to October. CO2 demand-controlled ventilation (CO2 DCV) saved average 46% and 28% of ventilation system heating and cooling energy of the ventilation system while keeping the indoor CO2 concentration below 1000ppm. ERV, hybrid desiccant system, differential enthalpy control, CO2 DCV annually reduces ventilation energy use by 50% and total HVAC energy use by 30%