Numerical methods for the coupling of multispecies kinetic and hydrodynamic equations

Shi, Yingzhe The University of Wisconsin - Madison 2009 해외박사(DDOD)

소속기관이 구독 중이 아닌 경우 오후 4시부터 익일 오전 9시까지 원문보기가 가능합니다.

In this thesis, we aim to develop multiscale numerical methods for the coupling of kinetic and hydrodynamic equations for gas mixtures. Our first work is to develop an asymptotic-preserving (AP) scheme for the multispecies kinetic equation. An AP scheme for kinetic equations is very efficient in the fluid regime because it allows coarse mesh size and large time step in the fluid regime. We extend the micro-macro decomposition based AP scheme for the single-species Boltzmann equation by Bennoune, Lemou and Mieussens to the multispecies problems. The difficulty associated with multispecies problems is that there are no local conservation laws for each species, resulting in extra stiff nonlinear source terms that need to be discretized properly in order (1) to avoid Newton-type solvers for nonlinear algebraic systems and (2) to be asymptotic-preserving. We show that these extra nonlinear source terms can be solved using merely linear system solvers, and the scheme preserves the correct Euler and Navier-Stokes limits. Numerical examples are used to demonstrate the efficiency and applicability of the schemes for both Euler and Navier-Stokes regimes. Our second work is to extend the smooth transition model developed by Degond, Jin and Mieussens to the coupling of multispecies kinetic and hydrodynamic equations. The idea is to use a buffer zone where both hydrodynamic and kinetic equations will be solved. The two different equations are coupled by an artificial connecting function of space, which makes the equation on each domain degenerate at the end of the buffer zone. This model avoids the complicated boundary conditions that are needed in a typical domain decomposition method to couple these two systems. The numerical results show that our coupling model is able to approximate the original kinetic model very well under different scales of the Knudsen numbers.

12-14세기 동아시아의 觀音圖像 연구 : 高麗觀音圖를 中心으로

신시호 성균관대학교 일반대학원 2012 국내석사

Accelerated computer generated hologram for real objects using multi-layered modeling

SHI CHENXIAO 충북대학교 2016 국내석사

This thesis is concerned with the generation of computer generated hologram of the real three-dimensional objects. A new method that uses the depth information of the real objects i.e. point cloud to generated hologram is proposed. In the first step, the point cloud of the real object is obtained by using a depth camera. Then, classify points of the point cloud according to the depth information of each point, the points with the same depth are addressed into an over-sampling grid as known as a sub-layer. The sub-hologram is generated from each sub-layer by using angular spectrum method and Fresnel approximation. The final hologram of the object is generated by superposing the sub-hologram of each sub-layer. The proposed method calculate sub-hologram from sub-layer including the points with the same depth, instead of from each single point, which can reduce the computational complexity obviously. Simulation and experiment results show that the proposed method has a fast computing speed and a good reconstruction quality, and the feasibility of the method is verified. In the case of using graphics processing unit, the proposed method has provided to be at least 600x speedup over the conventional method. In order to improve the quality of the optical reconstruction, the bicubic interpolation is utilized to the processing of each sub-layer. After interpolation processing, optical reconstruction can show a lot of details of the original object.

모바일 인스턴트 메신저 이모티콘의 사용행태 연구 : - 카카오톡과 위챗의 이모티콘 중심으로 -

SHI YANGMENGLIN 경희대학교 디지털콘텐츠학과 대학원 2018 국내석사

뉴 미디어시대, 사람들의 소통 방식에 큰 변화가 찾아왔다. 단순히 문자를 사용하는 방식에서 점차 기호, 이미지, 이모티콘 등을 방식으로 변화하고 있으며 특히 사람들 사이에 사회적 소통의 시작점, 소셜 관계를 연결하고 구성하는 경로, 소셜 컨텐츠 등 여러 방면에서 현저한 변화가 발생했다. 이러한 변화들 중 가장 큰 변화요소는 주된 매체가 컴퓨터에서 모바일로 이동한 것으로, 이로 인해 사회적 현상이 연쇄적으로 발생하였다. 최근 들어 이모티콘은 바디랭귀지 특징을 가진 새로운 인터넷 언어로 부각되고 있으며, 모바일 인스턴트 메신저에서 소통의 도구로 사용되며 가장 생명력을 보여주는 기호가 되었다. 본 연구는 한국과 중국에서 소셜 활동으로 가장 많이 활용되고 있는 모바일 인스턴트 메신저인 한국의 카카오톡과 중국의 위챗을 연구대상으로 하였으며, 두 어플리케이션에서 활용되고 있는 이모티콘을 사용자가 어떻게 사용하는지에 대한 사용행태를 주된 연구과제로 삼았다. 본 연구는 먼저, 문헌연구를 통해 위챗과 카카오톡을 기초로 하는 한중 양국의 이모티콘의 표현 형식과 내용을 분류하고 분석하였다. 다음으로, 양국 사용자들의 비교 연구를 통해 위챗과 카카오톡에서 사용하는 다양한 이모티콘의 표현 형식, 내용별 사용빈도에 관하여 분석하였다. 한중 양국 사용자들은 이모티콘의 표현 형식, 내용, 형태 및 사용빈도에서 유사점과 차이점을 나타냈는데, 이모티콘 형식의 경우 컬러, 2D, 애니메이션 형식의 이모티콘 사용빈도가 유사하였으며, 이모티콘 내용의 경우 동물 모양의 이모티콘, 현재 유행하는 문화 내용의 이모티콘 사용빈도가 유사하였다. 반면 한국 사용자들은 그림 위주의 이모티콘과 표정기호 이모티콘을 선호하였고, 중국 사용자들은 문자와 그림이 혼용된 이모티콘을 선호하는 경향을 보였으며 명절과 관련된 이모티콘을 더 빈번하게 사용하는 경향을 보였다. 한국과 중국의 이모티콘 사용행태 분석을 통해 양국의 정서와 문화가 이모티콘 사용에도 반영되고 있음을 알 수 있었다. 따라서 특정 국가의 이모티콘 디자인을 위해서는 디자인적인 요소 뿐만 아니라 그 나라의 문화와 정서를 이해하고 반영하는 것이 필요할 것이다. In the era of new media, people's communication has undergone tremendous changes, from the simple use of text to the gradual transition use of symbols, pictures, animation and other exchanges. The starting point of social interaction between people, the establishment of social relations chain channels, social interaction and other aspects of content logic have undergone significant changes. In these changes, due to the shift from PCs to mobile terminals, the series of chain changes have brought the most significant influences. Especially in recent years, the emoticon has appeared as a new type of network language in people's network communication and demonstrated its strong vitality. This study draws on the mobile instant messaging between South Korea and China. Firstly, classifies and analyzes the expressions forms and contents of emoticon based on WeChat and Kakao Talk. Secondly, the paper analyzes the correlation between the forms, content and use frequency of various emoticon used in WeChat and Kakao Talk, as well as the similarity shown in the correlation. The expression forms of emoticon are similar in the use frequency of colors, 2D and animation aspects. The content of the emoticon is similar in the use of animals emoticon and popular culture-related emoticon. On the contrary, users in the two countries differ in the frequency of using emoticon. Korean users prefer photo-oriented emoticon and Emoji, while Chinese users prefer emoticon with pictures and words, and use them more frequently in holiday-related emoticon. In order to design emoticon suitable for different countries, not only should we pay attention to the design elements themselves, but also understand and reflect the culture and emotion of the country.

A Study on Improving Tool Life of Automotive Axle using Direct Metal Deposition Technology

HAICHUAN SHI 한국대학교 대학원 2018 국내박사

The working condition of hot forging die is very terrible, such as high temperature, high load, repeated thermal and loads. The life of hot forging die is generally lower than cold forging die, the cost of the workpieces and the economic efficiency of the manufactory are affected directly. Expecially for developing counties, average life of hot forging die is far lower than developed countries. It is essential to enhance the service life of hot forging die and to reduce cost of the pieces for hot forging industry. The hot forging die simultaneously withstands the repetitive thermal load and the mechanical load, which can cause thermal stress and mechanical stress respectively. The thermal load is the main reason to cause damage of hot forging die. It is of great social and economic significance to study the surface hardening of tools and reduce the thermal stress precess. This dissertation focuses on the early failure of the hot forging die for automotive axles, mainly by increasing the high-temperature strength of die to prevent thermal softening of tool surface. The surface hardening technology used in this study is direct metal deposition technology to deposit a high-performance metal on the surface of the traditional die that is easy for wear. However, thermal cracks are frequently generated on the deposited areas due to thermal stress from different material properties. A thermal stress control layer (TSCL) is designed to reduce thermal stress and increase fatigue life as a buffer in the vicinity of the joining region between the hardfacing layer and the base metal. TSCL and hardfacing layer are deposited through layer-by-layer way on the substrate using direct metal deposition technology. The TSCL to be produced by mixing of Stellite21 and SKD61 is designed with thicknesses of 0 mm, 1 mm, 1.5 mm, and 2 mm separately. The effect of thermal stress in the transition regions is investigated after adding TSCL. The optimal design of TSCL is selected by the change of thickness and composition proportion. Stellite21 superalloy deposited on the hot forging die must undergo effects of repetitive thermal stress and mechanical stress during forging process. The hardening mechanism of Stellite21 is studied by microhardness tester. The etched Stellite21 samples are observed under the optical microscope. The microstructure analyses of Stellite21 are carried out on a TESCAN MIRA3 scanning electron microscope (SEM) with energy dispersive X-ray (EDX) spectrum. The phases present in the specimens are examined with an X-ray technique, using Cu K_radiation. So that the evolution microstructure and properties of Stellite21 are explained through before and after forging.

The Role of Nocturnal Irrigation during Supplemental Lighting on Shoot Growth and Physiological Responses of Cut Rose ‘Charming Black’

Liyun Shi 서울시립대학교 일반대학원 2014 국내박사

This study was conducted to better understand the importance of regular irrigation on shoot growth and flower quality, and the co-effect of irrigation and supplemental lighting on the flower production of Rosa hybrida ‘Charming Black’. The rose plants were grown under no-supplemental lighting treatment group (0 µmol•m-2•s-1 PAR) and supplemental lighting treatment group (90 µmol•m-2•s-1 PAR) with only two hours of dark period (16:00 - 24:00 h and 02:00 - 10:00 h). Two irrigation regimes (no irrigation regime: 40 - 45% in water content of rockwool slab, TSL×NI and irrigation regime: 70 - 75% in water content of rockwool slab, TSL×I) were applied under nocturnal supplemental lighting. Rose plants treated with nocturnal supplemental lighting showed better growth rate and flowered earlier by one week compared to no-supplemental lighting treatment group. 31% of the shoots became blind shoots and then disappeared under supplemental lighting. Also nocturnal supplemental lighting contributed substantially to photosynthetic rate during night, followed by an increase in shoot length, shoot weight, stem diameter, and leaf area. The rose plant started to experience drought stress when the water content in slab was below 42%. Without irrigation under nocturnal supplemental lighting, the water content in slab dropped below the critical water content, and drought stress could be observed under no-irrigation regime. Rose plants grown without irrigation under nocturnal supplemental lighting demonstrated a decline in shoot growth rate, shoot length, and shoot weight. Besides the shoot growth rate, height of petal and well-formed flower also decreased significantly. Also, leaf area and leaf weight were unfavorably affected by the water deficit. Reduction in total chlorophyll and carotenoid content accompanied by the lowest FV / FM and highest NPQ in the stressed leaves were observed under no-irrigation regime. Meanwhile, drought stress caused the negative effect on photosynthesis including the diurnal photosynthesis. Severe midday depression of photosynthesis occurred under no-irrigation regime. Nevertheless, the irrigation during supplemental lighting in a manner could compensate for this negative effect in terms of increase in both shoot growth and photosynthesis. The results of this study provided information on the importance of regular irrigation during nocturnal supplemental lighting. It indicated that regular irrigation applied under nocturnal irrigation could avoid stress. The co-effect of irrigation and supplemental lighting are beneficial to promote shoot growth, flower quality, and physiological response of Rosa hybrida ‘Charming Black’. 본 논문은 절화 장미 ‘Charming Black’ 의 신초생장과 절화품질에 관한 야간 보광과 관수와의 상호 보완기작을 구명하고자 수행되었다. 대조구(0 µmol.m-2.s-1 PAR)와 보광처리구(90 µmol.m-2.s-1 PAR; 16:00-24:00, 2:00-10:00)로 구분하였고, 보광처리구는 다시 관수처리구(암면 수분함량 75%, TSL×I)와 무관수처리구(암면 수분함량 40-45%, TSL×NI)로 구분하였다. 야간 보광한 장미는 대조구와 비교하여 신초생장이 우수하고 개화가 일주일 촉진되었으며 31%에 달하던 블라인드율이 해소되었다. 또한 야간보광은 광합성을 통해 신초길이와 무게, 줄기직경, 엽면적 등을 증가시켰다. 한편 보광 시 관수를 하지 않은 경우 암면배지의 수분함량은 임계함수율(42%) 이하로 떨어졌고, 결국 수분스트레스에 의한 건조 피해가 관찰되었다. 식물 생장속도, 신초 길이와 무게, 꽃의 크기가 현저히 감소하였다. 또한 잎에서는 FV/FM감소 와 NPQ 증가로 클로로필과 카로티노이드 함량이 감소되었다. 하루 중 광합성을 포함하여 광합성 효율이 전반적으로 감소하였고, 낮잠증상(midday depression of photosynthesis) 또한 발생하였다. 이러한 부정적인 영향은 관수처리를 통해 회복되었다. 신초의 생장은 물론 광합성효율도 수분스트레스 이전 수준으로 향상되었다. 초기 화아발달 단계에서는 수분스트레스를 받게 되면 수분손실을 감소시키기 위해 신초 길이와 엽면적을 감소시켜 적응해 나가지만 화아출현 이후 단계에서는 수분스트레스에 매우 민감하여 기형화 등 다양한 화아 발육억제 현상으로 인해 회복이 불가능해졌다. 따라서 본 연구는 야간 보광시기에 건조에 의한 수분스트레스가 발생할 수 있으며 관수의 필요성에 관한 정보를 제공하였다.

High pressure adsorption and desorption behaviors of CH4 and CO2/CH4 mixture on coal

Shi Yao Graduate School, Yonsei University 2010 국내석사

The recovery of coalbed methane can be enhanced by injecting carbon dioxide in the coal seams at supercritical conditions. Though this process, displaced methane is not only released but also adsorbed carbon dioxide is captured and stored. In this context, studies on the adsorption and desorption of methane on dry and wetted coal (Kyungdong coal, South Korea) were carried out by a static volumetric method, the CO2/CH4 mixture selective adsorption was observed too. The adsorption isotherms were measured at 318.15 K and 338.15 K over a wide pressure range from 0 to 120 atm on dry and wetted coal, respectively. In addition, desorption isotherms of supercritical condition were also investigated correspond to every adsorption situation. Desorption hysteresis phenomenon was observed at the same time. The excess adsorbed amounts of methane obtained directly from experiment were fitted by Modified Dubinin-Radushkevich (DR) and M-DR+k isotherm models under all conditions. Though taking into consideration adsorbed phase volume, absolute adsorbed amount was introduced to display the true supercritical adsorption behavior. Furthermore, the comparison of excess and absolute adsorbed was represented. Moist coal had a significantly lower sorption capacity for methane than dry coal in this study. The thermodynamic calculations of methane absorption and water vaporization were considered in order to explain and modify the wet coal isotherms. The calculation results also indicated changes of water vapor amount in gas phase and methane dissolved into aqueous phase with the increasing equilibrium pressure, respectively. As expected from pure adsorption data, the CO2/CH4 mixture adsorption clearly confirmed that CO2 was preferentially adsorbed on coal. These studies aim on the one hand at providing data to analyze and predict the behavior of ECBM operations, and on the other hand to play an important role in directing in choosing appropriate coal seams for ECBM.

Crystal growth and excited-state dynamics of Eu2+ Luminescence in Eu-doped LiBaF3 single crystals

SHI LIANG 부경대학교 2008 국내석사

The pure and europium doped LiBaF3 single crystals were grown by the Czochralski method. The details of the reagent preparation and the crystal growth were investigated. The different concentrations of Eu-doped powder were checked by XRD. The Eu2+ ion substitutes for Ba2+ ion in the LiBaF3 crystal. The reaction conditions were investigated to get pure LiBaF3 powder. The emission spectra showed the 4f-4f line emission peak at 359 nm and the 5d-4f emission band at around 410 nm. The spectra of Eu2+-doped crystals with different concentrates were compared and the concentration quenching was not observed up to the Eu-concentration of 2 mol%. The luminescent lifetime of 359 nm and 410 nm emissions were measured in the temperature range from 15 K to 300 K. The non-exponential decay curves at 410 nm were discussed in relation with the interaction between the excited 4f and 4f5d levels. A practical method was introduced to calculate the 4f-5d activation energy (ΔE) and the value of this energy gap was 950 cm-1. The configurational coordinate model of the LiBaF3: Eu2+ was introduced to explain the results. The mechanism of the nonradiative transitions between the excited 4f and 4f5d states was discussed.

Physiological effects of the VDU & HMD in virtual environments

Park Shi-Hyun 동의대학교 대학원 2002 국내석사

이 연구의 목적은 개인용 디스플레이 시스템인 VDU(Visual Display Unit)와 HMD(Head Mounted Display)를 통한 가상환경 체험이 인체에 미치는 생리학적 영향에 대해 조사하고, 그 결과에 대한 VDU와 HMD간의 영향 정도를 비교?평가하는 것이다. 이에 따라, 본 연구에서는 정신적 스트레스나 cybersickness를 분석함에 있어서 신체의 각종 생리학적 데이터를 분석함으로써 영향정도를 평가하였다. 이 실험을 위하여 일곱 명의 피실험자들은 VDU 시청 및 HMD 착용과 함께 30분 동안 가상 비행 시뮬레이션 게임을 수행하였다. 생리학적 변수로는, 자율 신경계 측정(심박수, 혈압)과 면역세포(백혈구, 호중구, 림프구), 그리고 호르몬(카테콜라민)을 선정하였으며, 이들은 게임수행 전?후에 각각 측정되었고 이러한 데이터들은 VDU와 HMD상에서의 정신적 스트레스 수준을 비교하기 위하여 측정되었다. 혈압(수축기, 이완기)과 호중구, 노르에피네프린(카테콜라민) 수치에 있어서, HMD를 사용한 집단이 VDU를 사용한 집단보다 실험 전?후간에 유의한 차이를 보였다. 그러나, 심박수는 두 집단 간에 유의한 차이는 없었지만, 두 집단 간의 변화도는 VDU 집단에 비하여 HMD 집단이 더욱 유의하게 높았다. 다른 데이터들의 경우 유의하진 않았지만 VDU에 비하여 HMD 사용시 생리학적 수치의 변화도가 다소 높았다. 그러므로, 우리는 이러한 생리학적 측정(자율신경, 면역세포, 호르몬)을 통하여 HMD 착용 시 받는 자극(정신적 스트레스)이 VDU 사용에서 보다 더욱 높다는 결론을 내릴 수 있었다. The focus of this study is to investigate how personal display systems - a VDU (Visual Display Unit) and an HMD (Head Mounted Display) physiologically affect the body in virtual environments, and to evaluate differential effects of using the VDU and the HMD on physiological responses to mental stressful tasks (virtual reality flight simulation). Seven subjects played the VR flight simulation game for a half-hour while wearing an HMD or monitoring a VDU. The physiological variables, the autonomic measures (heart rate, blood pressure), the immune cells (leukocyte, neutrophil, lymphocyte), the hormones (catecholamine), were measured before and after playing the games. The physiological data were measured in order to compare a level of mental stress on the VDU and the HMD. The increments in blood pressure (systolic (p<0.05), diastolic (p<0.1)), norepinephrin (catecholamine) (p<0.005), and neutrophils (p<0.2) of the group using the HMD showed a significant difference with the group using the VDU. Although, heart rate were not statistically significant between two environments, the differences of them quietly increased on the HMD more than on the VDU. The other data were a little increased on the both conditions, and the differences of the HMD were higher than the VDU. Therefore, we can conclude that mental stress on the HMD is higher than on the VDU through the physiological measures (autonomic, endocrine, and immune cell).lso, this study suggests the quantitative analysis by physiological data on the mental stress or cybersickness.

Examining the Effect of Live Streamers’ Expertise on Sales : An Empirical Study of Douyin

SHI KAI 경희대학교 대학원 2022 국내석사

Since live streaming services have grown rapidly around all over the world, there are lot of studies discussing about the elements that could enhance sales in live streaming. However, the study focusing on the leading role of live streaming – live streamers, still lags. By collecting data records of 499 streamers from Douyin, we employed an empirical approach to explore how live streamers’ expertise affect live streaming sales and what is the interaction effect between word-of-mouth variables and expertise. In addition, what is the interaction effect between different product types and expertise. Through empirical analysis, we find that live streamers’ expertise has a significant and positive effect on sales. Also, live streamers’ expertise will positively moderate the effect of comments and ratings’ effect on sales and will negatively moderate the effect of shares’ effect on sales. However, this study found that the number of likes of streamers will neither have a direct impact on sales, nor will expertise have a moderation effect on it. Finally, we found that moderation effect between Expertise and Tech (product type) is significantly positive. For theoretical contribution, this study explored the function of live streamers’ expertise in live streaming and found the moderation effect of expertise in word-of-mouth variables and different product types. This study also has some managerial implications for companies and live streamers. Firstly, they need to keep their eye on the expertise. And for higher sales, it is significant to understand the relationship among expertise, word of mouth and product type. 전 세계적으로 라이브 스트리밍 서비스가 빠르게 성장하고 있다. 이에 라이브 스트리밍이 판매량에 미치는 요인들에 대한 실증 연구가 증가하고 있으나, 라이브 스트리밍의 주체인 라이브 스트리머에 대한 연구는 아직 미비하다. 틱톡의 중국 버전인 더우인에서 라이브 스트리밍을 하는 스트리머 499명의 데이터를 파이썬을 이용해 수집한 후, 실증 분석을 통해 라이브 스트리머의 전문성이 라이브 스트리밍 판매에 미치는 영향과 입소문 효과와 전문성 간의 상호작용 효과, 다른 제품과 전문성 간의 상호작용 효과에 대해 살펴보았다. 실증 분석 결과, 라이브 스트리머의 전문성이 매출량에 긍정적인 영향을 미치는 것으로 나타났다. 또한 라이브 스트리머의 전문성은 댓글과 평점이 매출에 미치는 영향에 긍정적인 조절 효과를 미치고 ‘공유’ 수가 매출에 미치는 영향을 강화한다. 그러나 본 연구에서 스트리머의 ‘좋아요’ 수가 판매에 직접적인 영향을 미치지 않고 전문성이 ‘좋아요’ 수와 판매 간의 영향력을 조절하지 못하는 것으로 나타났다. 마지막으로 전문성이 테크 상품(제품 유형)과 매출량 간의 통계적으로 유의미한 조절 효과를 나타냈다. 본 연구는 라이브 스트리밍에서 라이브 스트리머 전문성이 미치는 영향을 탐구하고 입소문 효과 변수 및 다양한 제품 유형에서 전문성의 조절 효과를 발견했다. 이러한 연구 결과는 매출을 올리기 위해 라이브 스트리머의 전문성을 더 중시해야 하고, 전문성과 입소문 효과, 제품 유형 간의 관계를 이해하는 것이 중요하다. 화사와 라이브 스트리머에게 시사할 수 있다.