(The) convectional heat transfer along the metal-coated carbon fiber in high vacuum

Dang, Xuan Dang Sungkyunkwan University 2022 국내석사

In vacuum science and technology, we used different types of vacuum gauges depending on the pressure. For instance, in high and ultrahigh vacuum, we use ionization gauges that detect the ion current that is produced by ionizing gas molecular using hot filament. In the medium vacuum range, the thermal vacuum gauges are working, which measures the pressure by monitoring the filament temperature. In the gauge, the hot filament loses the heat to the residual gases in the chamber, and its temperature changes. Pirani gauge is one of the heat conduction gauges. It employs a metal filament that is usually gold-coated tungsten or thin platinum wires. Currently, the detection limit of the Pirani gauge is approximately 10-3 Torr, around which the conductive heat flow along the filament is larger than the conventional heat flow to the residual gases. To enhance the detection range, the filament with low thermal conductivity and small diameter is strongly demanded to reduce the amount of heat loss via conduction along the filament. In this thesis, we survey the thermal conductivity of the filament and select carbon fiber (CF) as a backbone material because of low thermal conductivity ranging from 3~5 W·m-1·K-1. However, CF is electrically insulating. To implant electrical conductivity, we coated CF with the Cu layer as a conducting layer, and we covered Cu with Au to prevent oxidation. We control the thickness of the metal layer and optimize electroplating conditions to reduce the thermal conductivity but enhance electrical conductivity and temperature coefficient of resistance (TCR) of metal-coated carbon fiber (MCF). After numerous characterizations of MCF, we find the optimum resistance of MCF is about 167.5 x 10-6 Ω·cm, whose TCR is about 10-3 K-1 . With the applied current of 200 A, the filament reaches the temperature of 355 K. At the pressure of 2 x 10-8 torr, the heat loss rates of the filament via the conduction, convection, and radiation are estimated to be 5.8 W, 6.0 W, and 1 W, respectively. Therefore, the designed MCF shows comparable conductional heat loss to a conventional one. So, MCF offers the resistance change by the convection at the pressure of 3.5 x 10-7 torr. Considering the detection range of the present heat conduction vacuum gauge, ranging about 10-3 torr, we improve the detection limit by four orders of magnitude. In addition, the power consumption of our MCF filament is less than the mW scale, which can run on portable batteries.

한류의 한국제품 및 기업에 대한 이미지와 구매행동과의 관계에 관한 연구 : 중국 단동지역 중심으로

Dang, Young-Bin 강원대학교 2006 국내석사

본 연구의 목적은 2000년대 문화의 확산 이론의 관점에 있어서 중국에 한류의 현상, 즉 일련의 사회적 문화적 현상을 재검토하고 이러한 문화확산 현상이 한 국가의 기업이미지와 제품이미지 그리고 이러한 이미지가 고객의 구매행동에 어떠한 영향을 주는지 그 효과에 대하여 분석 해 보고자 하는데 있다. 본 논문에 있어서 한류현상은 1990년대 후반 한국의 대중문화 즉 TV 드라마, 팝송, 패선, 영화, 게임, 광고 등과 같은 한국의 대중문화에 대한 아시아 국가 국민들의 열정과 같은 현상을 의미 한다고 볼 수 있다. 본 연구에 있어 한류현상에 대하여 정성적, 정량적 분석의 두 가지 방법에 의하여 분석 되었다. 정성적 방법에 있어서는 기존의 여러 가지 논문자료와 한류에 대한 시청각 자료, 신문, 잡지, 방송 프로그램, 인터넷을 통한 자료를 수집하여 설문지 및 이론적 근거를 마련하였으며, 정량적 연구방법으로서는 이러한 연구 자료를 토대로 중국 단동지역의 250명의 시민들을 무작위 표본 추출하여 한류와 기업이미지, 제품이미지, 고객들의 구매행동에 관한 설문지를 배포하여 조사하였고, 수집된 자료를 이용하여 SPSS 10.0과 AMOS 4.0 통계프로 그램으로 신뢰성분석, 타당성분석, 요인분석을 하여 한류에 대한 2개의 요인과 각 각 1개씩의 기업, 제품이미지와 구매행동에 대한 요인을 추출 하였다. 이러한 정성적, 정량적 분석 결과로서 다음과 같은 결론을 얻었다 한류에 대한 두 가지 요인 즉, Contents, 인적요인에 있어서 첫 번째 요인 Contents 요인은 한국기업과 제품이미지, 구매행동에 대하여 직접적, 간접적으로 긍정적인 영향을 주고 있는 것으로 나타났으며 두 번째 요인인 인적요인은 한국기업과 제품이미지, 구매행동에 대하여 직접, 간접적으로 영향을 주지 못하고 있는 것으로 나타났다. 본 연구의 결과는 중국에 있어서 한류의 영향은 매우 높은 것으로 나타났으며 기업이미지, 제품이미지, 구매행동에 있어서 영화배우나 가수와 같은 인적요인 보다는 한국 대중문화의 내용면에 있어서 보다 큰 영향을 받는 것으로 나타났다. 그러므로 우리는 한국기업들이 어떠한 연예인이나 배우, 가수 등과 같은 인적요인에 대한 개발과 투자보다는 한류의 주류를 이루는 Contents적인 부분에 보다 많은 질적, 양적 개발과 투자가 이루어지는 것이 중장기적으로 한류문화가 지속화 될 수 있고 성공을 이루어 나갈 수 있으리 제언하고자 한다. The purpose of this thesis is to review Hanliu phenomenon, a kind of social and cultural phenomenon , in china around A. D. 2000 in the view of the culture-diffusion theory, and analyze its effect to the Product Image, Corporate Image of Korea and the Purchase Action. In this thesis, Hanliu phenomenon means the enthusiasm of Asian people for Korean mass cultures such as Korean TV dramas, pop songs, fashions, cinemas, games, advertisements from late 1990's. This research adopts two kinds of methods for analyzing Hanliu phenomenon: a qualitative research method and a quantitative one. As a qualitative research method, We analyzed Hanliu phenomenon with several sources of documentaries and audio-visual materials on it: articles from newspapers and magazines, special Tv programs and documentary movie files from Internet. As a quantitative research method, We conducted a survey of a random sample of 230 citizens in Dan Dong for how they feel of Korean wave(contents, person factors), the Product Image, Corporate Image and how these factors influences Purchase Action. The collected data were analysed by statistics software SPSS 10.0 and AMOS 4.0. The two factors of Korean wave(contents, person factor), one factor of corporation image, one factor of product image, one factor of purchase action were extracted through the reliability, validity analysis and factor analysis. Then Korea wave's factors influence on corporate image of Korea, Korea product image, the customer's purchase action was analyzed through AMOS 4.0. The results of this study are as follow: In the two factors of Korean wave(contents, person factor), first factor, contents factor affects the customer's purchase action directly, and also affects the customer's purchase action indirectly through corporation image, product image at the same. But second factor, person factor doesn't affects the customer's purchase action directly, and also doesn't affects the customer's purchase action indirectly through corporation image, product image. The results of this study revels that Korea wave is popular in China, in the corporation image, product image, Chinese are largely affected by more contents factor than person factor. Therefore we suggest that Korea corporations more invest and develop to contents factor than invest and develop to actor factor.

Design and Implementation of Browser-based Multimedia Sharing Network

MAI VAN DANG KHOA Graduate School of Soongsil University 2014 국내석사

The introduction of DLNA helped solve the problem of sharing multimedia content over a home network. However, DLNA does not meet consumer demands for sharing content with friends as well as for accessing content from other devices outside the home. Although some studies have tried to extend the DLNA architecture to overcome this limitation, the proposed methods still have some issues that have not yet been solved. To this end, this thesis proposes a novel browser-based architecture that includes procedures for control and sharing of multimedia content from any device, regardless of its location on the Internet. We also take into account interworking between the proposed network and DLNA networks by designing a gateway and the necessary procedures. A prototype is implemented to illustrate the feasibility and to evaluate the efficiency of the proposed architecture. DLNA는 홈네트워크에서 멀티미디어 컨텐츠를 공유하기 위해 제안된 프로토콜이다. 그러나 DLNA는 홈네트워크 밖에 있는 장치와 연동하는 것 뿐만 아니라 외부 네트워크에 있는 유저와의 컨텐츠를 공유하는 것을 원하는 소비자의 요구에 맞는 서비스를 제공하지 못한다. 몇몇 논문에서는 DLNA 구조의 확장을 통해 위에서 언급한 네트워크의 제한사항을 극복하려고 했으나 확장 구조에서도 몇가지 문제를 해결하지 못했다. 따라서 본 논문에서는 디바이스와 상관없이 멀티미디어 컨텐츠를 공유할수 있는 방법과 컨트롤 할 수 있는 방법을 제공하는 브라우져 기반의 구조를 제안한다. 또한, 게이트 웨이와 필요한 절차를 디자인 하여 DLNA와 제안된 구조와의 연동 구조 또한 제안한다. 본 구조의 타당성과 효율성을 평가하기 위해 제안된 구조의 프로토타입을 통해 비교 분석 하였다.

Numerical study of free surface effects on compressible supercavitating flows

Dang SonTung 부산대학교 대학원 2016 국내석사

In this thesis, we focus on applying the volume of fluid (VOF) method coupled with an interface reconstruction technique to capture the free surface between liquid and gas. The governing equation is the compressible Navier-Stokes equations based on the homogeneous mixture model. To achieve efficient and accurate computations over a wide range of Mach numbers, a pseudo-time derivative is introduced to the multiphase system of equations, which allows the system eigenvalues to be rescaled and the disparity in speed waves for each phase to be reduced as much as possible. All equations are discretized on a general structured grid using a high-resolution implicit upwind shock-capturing scheme to prevent the generation of spurious solutions near shock waves or discontinuities. For evaluation, the present results have been compared with experiments and other numerical results. A fairly good agreement with the experimental data and other numerical results has been obtained. Finally, the simulation of natural supercavitating flows over a flat plate hydrofoil was conducted to investigate the effect of free surface on characteristic length of supercavity. 본 연구는 액체와 기체 사이의 자유 표면에 대해서 VOF 방식을 적용한 전산해석에 관한 연구이다. 지배 방정식은 균일혼상류 모델을 기초로 한 압축성 Navier-Stokes 방정식을 사용하였다. 해의 수렴성과 넓은 마하수 범위에 대해 전산해석적 적합하도록 의사 시간 항을 적용하였다. 모든 방정식은 정렬격자 구조에 대해 고정도 implicit upwind shock-capturing 기법을 사용하여 이산화 되었으며, 이는 충격파 또는 불연속 지점에서의 비정상 해를 방지해 주었다. 본 연구의 전산해석 결과는 선행연구자들의 해석 및 실험 결과와 비교하고 검증하였으며, 상당히 일치함을 보였다. 최종적으로 익형에 대한 자연공동에 의한 초공동 유동에 대한 전산해석을 수행하여 자유수면 영향을 반영한 초공동 유동의 특성에 대한 연구를 수행하였다.

한국 SNS 관광정보가 베트남인의 관광행동에 미치는 영향

DANG THI HIEP 경희대학교 대학원 2022 국내석사

With the development of information and communication technology and the spread of the Internet and smartphones, it has become the information age, and in line with these changes, online PR media is a powerful online communication medium for the tourism industry, which is highly information-intensive because it brings greater flexibility than other media. SNS has recently been used as an important tourist information tool. In addition, modern tourists no longer serve as receivers of information, but also play active roles as producers and providers of information by using SNS. It has become a selection criterion and is leading to visit intention, visit behavior, and information sharing. On the other hand, the number of Vietnamese tourists visiting Korea is currently increasing significantly, and it is necessary to understand the potential customers, Vietnamese consumers. Therefore, it can be seen that strengthening SNS tourism information and effective marketing methods are very important for this purpose. Therefore, the purpose of this study is to verify the details of the type of SNS and the media most exposed to Korean tourism information, and to understand the whole process from the tourist behavior of Vietnamese who came in contact with Korean tourism information through SNS. To explain this, the AISAS (Attention-Interest-Search-Action-Share) model, which has been widely applied in the advertising field with proven effectiveness, was used as a theoretical basis. As the main result of this study, first, it was found that the SNS medium that received the most tourist information was Facebook. It can be seen that Facebook is the most effective approach when targeting Vietnamese tourists. Second, it can be seen that when more attention is paid to Korean tourism information, both cognitive involvement and emotional involvement in Korean tourism information are increased. In particular, it was found that emotional involvement had a greater effect on interest in Korean tourism than cognitive involvement. Third, it can be seen that as the cognitive involvement in Korean tourism increases, the behavior of searching for more information on Korean tourism increases too. On the other hand, it was found that emotional involvement in Korean tourism information did not affect the search for tourism information. That is, objective information obtained through information viewing rather than emotional involvement affects actual behavior. Fourth, it is interpreted that the more information is searched, the greater the influence on visiting behavior. It can be analyzed that information retrieval has a great influence on behavioral variables and is an important factor in the decision-making process. Fifth, visit behavior was found to have an effect on sharing tourism information or tourism experience. People have a lot of desire to share information with those around them. In other words, it can be seen that the ripple effect of the word of mouth effect is not small. It can be assumed that the expectations for Korean tourism are high enough for tourists to provide and share their tourism information and experiences through online SNS. Finally, it was confirmed that the AISAS model presented in this study is suitable for explaining the effect of Korean tourism information on tourist behavior through SNS. Therefore, this study identifies the most popular social media media in each country in order to shape the behavior of visiting Korea, prepares publicity measures so that viewers can access information in the language of the country as much as possible, and builds content that can lead to interest and provides up-to-date information. It is necessary to recognize the necessity of revitalizing tourism information, such as information update and provision of objective and curious information, and the importance of the quality of tourism information content, and develop a plan to expand it. 정보통신의 발달과 인터넷, 스마트폰 보급화로 인해 정보시대가 되었으며 이러한 시대 변화에 맞춰 온라인 홍보매체는 다른 매체들보다 큰 유연성을 가져오기 때문에 정보 집약도가 매우 높은 관광산업에 강력한 온라인 소통의 매체인 SNS가 최근 중요한 관광정보 수단으로 사용되고 있다. 더불어 현대의 관광객들은 더 이상 정보의 수용자 역할뿐만 아니라 SNS를 활용해서 적극적인 정보의 생산자 및 제공자 역할도 하게 되며 방문결정을 내리기 전에 SNS 정보 조사를 통해 관광지에 대한 이미지와 태도가 형성되고 이러한 정보들이 관광지 선택기준이 되고 방문의도, 방문행동, 정보공유까지 이끌어 나가고 있다. 한편, 현재 한국을 방문한 베트남 관광객이 대폭 증가하고 있고 앞으로도 계속 증가할 추세를 보여주며 잠재 고객인 베트남 소비자에 대하여 파악할 필요가 있다. 따라서 이를 대상으로 SNS 관광정보의 강화 및 효과적인 마케팅 방법이 매우 중요하다는 것을 알 수 있다. 이에 본 연구의 목적은 SNS 종류에서 한국 관광정보를 가장 많이 접한 매체는 무엇인지에 대해 세부적인 검증을 하고 SNS를 통해 한국 관광정보를 접한 베트남인의 관광 행동까지 이르는 전체의 과정을 파악하고자 한다. 이를 설명하는데 실효성이 입증된 광고 분야에서 많이 적용되어 있는 AISAS(Attention-Interest-SearchAction- Share) 모델을 이론적 근거로 이용하였다. vi 본 연구의 주요 결과로는 첫째, 관광정보를 가장 많이 접한 SNS 매체는 Facebook인 것으로 나타났다. 이는 베트남 관광객을 대상으로 삼을 때 가장 효과적인 접근방법이 Facebook인것으로 알 수 있다. 둘째, 한국 관광정보에 주의를 더욱 기울이게 되면 한국 관광정보에 대한 인지적 관여와 정서적 관여 모두 상승하는 것을 알 수 있다. 특히 인지적 관여보다 정서적 관여가 한국관광 관심에 더 크게 영향을 미치는 것으로 나타났다. 셋째, 한국관광에 대한 인지적 관여가 증가하게 되면, 한국 관광에 대한 정보를 더 검색하는 행동이 높아진다는 것을 알 수 있다. 반면, 한국 관광정보에 대한 정서적 관여는 관광정보를 검색하는데 영향을 미치지 않는 것으로 나타났다. 즉, 정서적 관여보다는 정보 시청을 통해 얻은 객관적인 정보들이 실제 행동에 영향을 미친다는 것이다. 넷째, 정보 검색을 많이 하면 할수록 방문행동에 더 큰 영향을 주는 것으로 해석된다. 이는 정보 검색이 행동변수에 큰 영향을 미치고, 의사결정 과정에서 중요한 요인이라고 분석될 수 있다. 다섯째, 방문 행동은 관광정보나 경험을 공유하는데 영향을 미치는 것으로 나타났다. 사람들이 주변사람들과 정보를 공유하고 싶은 욕망 즉 구전효과의 파급력이 적지 않다는 것을 알 수 있다. 관광객들에게 있어서 온라인 SNS를 통해 본인의 관광정보나 경험을 제공하고 공유할 정도로 한국의 관광에 대한 기대감은 높을 것이라고 추측할 수 있다. 마지막으로 본 연구에서 제시된 AISAS모델은 SNS를 통해 한국 관광정보가 관광객 행동에 미치는 영향을 설명하는데 적합하다는 사실을 확인해 주었다. 따라서 본 연구는 한국 방문 행동을 형성하기 위하여 각국에서 가장 인기가 많은 SNS매체를 파악하고 그 국가의 언어로 시청자를 최대한 정보를 접근할 수 있게끔 홍보대책을 마련해야 하며 관심을 이끌 수 있는 콘텐츠 구축, 최신 정보 업데이트, 객관적이면서 호기심을 유발하는 정보 제공 등 관광정보 활성화의 필요성과 관광정보의 콘텐츠 질의 중요성을 인식하고 확대 방안 개발할 필요가 있다

Role of mitochondrial ATP-sensitive K^(+) channels and nitric oxide on ischemic preconditioning cardioprotective mechanism : 허혈전처치의 심장보호기전에 대한 미토콘드리아 ATP-민감성 칼륨-통로와 산화질소의 역할

Dang Van Cuong Graduate School of Inje University 2004 국내박사

목적: 허혈전처치는 허혈-재관류 손상으로부터 심장을 보호하는 현상으로 잘 알려져 왔다. ATP-민감성 칼륨-통로의 활성과 산화질소의 유리는 허혈전처치의 심장보호기전에서 trigger 또는 mediator로서 그 중요성이 인식되고 있다. 본 연구에서는 미토콘드리아 내막에 존재하는 ATP-민감성 칼륨-통로의 분자생물학적 구조와 산화질소와 관련된 심장보호기전을 규명하고자 하였다. 방법: ATP-민감성 칼륨-통로의 분자생물학적 구조와 관련된 연구는 confocal microscope fluorescence-based immunoassay 그리고 Western blotting 방법을 이용하여 규명하였다. 또한 ATP-민감성 칼륨-통로의 활성 및 산화질소의 유리가 허혈-재관류 동안의 DNA 및 산화적 손상을 약화시킬 수 있다는 가설을 검증하기 위해 single cell gel electrophoresis (comet assay)와 Western blotting 방법을 이용하여 DNA와 조직의 손상정도 그리고 산화질소의 유리 정도를 비교 분석하였다. 결과: 단일심실근세포에서 BODIPY-FL glibenclamide 녹색 형광신호가 미토콘드리아 탐침지표인 Mitrotracker Red CMXRos의 적색 형광신호와 잘 일치되었으며, 이는 미토콘드리아에 sulfonylurea receptor가 존재함을 제시한다. 분리한 단일 미토콘드리아의 면역형광법 실험에서 Kir6.1, Kir6.2 그리고 SUR2 형광신호는 미토콘드리아 형광신호와 일치된 결과를 통해 미토콘드리아에 Kir6.1, Kir6.2 그리고 SUR2의 분자생물학적 구조가 존재함을 확인하였다. Single cell gel electrophoresis (comet assay) 실험방법을 이용한 허혈 (30분)-재관류 (60분) 실험모델에서 심장세포의 DNA의 손상이 현저히 증가되었다. 하지만 anoxia, diazoxide (100 μM), SNAP (300μM) 그리고 8-(4-Chlorophenylthio)-guanosine-3',5'-cyclic monophosphate (8-pCPT-cGMP) (100 μM) 등을 5분간 3회 반복 처치하면 허혈-재관류에 의한 심장세포의 DNA 손상이 감소되었다. 이러한 심장보호효과는 glibenclamide (50 μM), 5-hydroxydecanoate (5-HD) (100 μM) 그리고 8-(4-Chlorophenylthio)-guanosine-3',5'-cyclic monophosphate, Rp-isomer (Rp-8-pCPT-cGMP) (100 μM) 등이 존재할 때에는 관찰되지 않았다. 한편, 허혈전처치 실험군에서는 대조군 및 허혈-재관류 실험군에 비하여 iNOS의 발현이 현저히 증가하였다. 결론: 본 연구결과로부터 쥐 심장 미토콘드리아 내막에 존재하는 ATP-민감성 칼륨-통로는 Kir6.1, Kir6.2 그리고 SUR2로 구성되어 있으며, NO-cGMP-PKG 생체신호전달기전은 ATP-민감성 칼륨-통로의 심장보호기전에 중요한 역할을 담당할 것으로 사료된다. The activation of ATP-sensitive potassium (K_(ATP)) channels and the release of myocardial nitric oxide (NO) induced by ischemic preconditioning (IPC) were demonstrated as the triggers or mediators of IPC, thus protect heart against ischemia and reperfusion (I/R) injury. A common action mechanism of NO is increase cGMP, thus PKG in tissue, leading to K_(ATP) channels activation, protect the heart against oxidative stress induction by I/R. Few studies have tried to identify the mitoK_(ATP) channels, but their subunit composition remains unclear. Therefore, we investigated the subunit composition of mitoK_(ATP) channels in rat hearts by confocal microscope, fluorescence-based immunoassay and western blotting. Taken together, we also tested the hypothesis that K_(ATP) channels attenuate DNA strand breaks and oxidative damage. We estimated DNA strand breaks and oxidative damage by mean of single cell gel electrophoresis with Endonuclease Ⅲ cutting sites (comet assay). Enzymatic NO production during I/R was detected by Western blotting. The results showed that sulfonylurea receptors (SUR)-binding BODIBY-FL glibenclamide fluorescence was co-localized with the mitochondrial marker Mitrotracker Red CMXRos in isolated ventricular myocytes and the mitochondria. Immunofluorescence of Anti-Kir6.1, anti-Kir6.2 and anti-SUR2 were co-localized with the Mitotracker in isolated mitochondria. Similarly, Kir6.1 (~46 kDa), Kir6.2 (~46, ~44, and ~30 kDa) and SUR2 (~140 kDa) proteins were found in the mitochondria by western blot. In contrast, SUR1 was not present in the mitochondria by western blots and immunofluorescent confocal imaging. We also found that DNA damage increased massively in the I/R. Preconditioning with three times 5-min anoxia, Diazoxide (100 μM), SNAP (300 μM) and 8-(4-Chlorophenylthio)-guanosine-3',5'-cyclic monophosphate (8-pCPT-cGMP) (100 μM) reduced DNA damage induction by 30 min anoxia and 60 min reoxygenation. These protective effects were blocked by the concomitant presence of Glibenclamide (50 μM),5-hydroxydecanoate (5-HD, 100 μM) and 8-(4-Chlorophenylthio)-guanosine-3',5'-cyclic monophosphate, Rp-isomer (Rp-8-pCPT-cGMP, 100 μM). Endothelial NOS highly expressed in both IPC and I/R but inducible NOS expression were significantly higher compared with either Control or I/R indicating the important NO source to NO-PKG-K_(ATP) channels pathways. In conclusion, the results indicate that mitoK_(ATP) channels may be a combination of Kir6.1, Kir6.2 and SUR2 subunits in rat hearts. It also gave the evidence that NO-cGMP-PKG pathways may contributes to cardioprotective effect of K_(ATP) channels in rat ventricular myocytes.

Reduction of Graphene Oxide by Atomic Hydrogen Dissociated over Pt and Pt/Al2O3 Catalyst

DANG THANH TRUONG 울산대학교 2011 국내석사

Chemically converted graphene has been a promising route to achieve mass production of graphene-like material. So far, the chemical reduction of graphene oxide (GO) has used of hydrogen sulphide, hydrazine monohydrate, sodium borohydride (NaBH4), dimethyl-hydrazine, hydroquinone, NaBH4 and H2SO4, aluminium powder, hydriodic acid with acetic acid (HI-AcOH), phenyl-hydrazine, alcohols, pyrrole. In general, strong reductants such as hydrazine hydrate, hydrazine derivatives or sodium borohydride are the most widely used reducing agent. However, these reducing agents are very toxic and these methodologies are achieving limited extents of reduction. Furthermore, hydrazine hydrate and hydrazine derivatives are used in this work as a control to reduce GO in both the solution and gas phases but they give rise to high sheet resistance because of the nitrogen impurities incorporated during reduction process. Hence, a simple, high level reduction to reduce graphene oxide by non-toxicity reductant is imperative task for producing and controlling high-quality reduced graphene oxide (RGO) for mass production. In this thesis, the synthesis of high quality reduced graphene oxide (hRGO) and high quality reduced graphene oxide platinum hybrid by reducing graphene oxide by atomic hydrogen formed via H2 dissociation on Pt particles decorated on graphene oxide sheets and atomic hydrogen over the platinum on alumina system (Pt/ɤ-Al2O3) has been studied. Reduce graphene oxide by atomic hydrogen decorated on graphene oxide sheets showed the highest reduction level ever reported for graphene oxide reduction (C/O reach to 22). The Pt nanoparticles were decorated well on the reduced graphene oxide sheets effectively. The Pt particles sizes were in the range 2.3-5 nm, uniformly distributed on the graphene sheets. The electrical conductivity of hRGO-Pt pellet was over 8,000 S/m. Graphene/Platinum hybrid nanomaterials have numerous applications that include catalysts, electrocatalysts, gas sensors, and fuel cells. The reduction method of the graphene oxide by atomic hydrogen over Pt/ɤ-Al2O3 was thought to be a possible solution for recycling Pt catalyst after reduction. The C/O hydrogen reduced graphene oxide (hRGO) was reached to 8.6, indicating high degree of reduction in comparison with other chemical reduction methods. The effect of temperature on the reduction level and the different GO/Pt ratio for reduction has been studied. The reaction would be faster when reacted at higher temperature. The saturation of temperature effect appeared after 24 hours reduction. At lower GO/Pt ratio, the reduction was faster due to higher amount of Pt catalyst. The saturation appeared after 12 hours reduction. Reduced graphene oxide is a very promising candidate for many applications such as electronic devices, polymer composites, energy conversion, storage materials and sensors.

3-APTES에 의한 나노기공 실리카의 표면개질 및 효소 고정화에 관한 연구

Dang, Huu Tuan 한양대학교 대학원 2010 국내석사

Abstract In this work, amino-functionalized silicas (AF-NPS) have been successfully synthesized by grafting an organosilane precursor, 3-aminopropyl triethoxysilane (3-APTES), onto the silica surface. The aim of this work is to thoroughly study the effect of the factors such as pH, organosilane precursor concentration, temperature, and reaction time on aqueous silanization of silicas. The study also demonstrates detailed description of the procedure for the preparation of nanoporous silica (NPS), functionalization, and subsequent enzyme immobilization. Sulfuric acid and sodium silicate were used as precursors to synthesize NPS via sol-gel method. The synthesized NPS, which has specific surface area of 133 m2/g, pore size of 36.9 nm, and pore volume of 1.23 cm3/g, is sequentially used as a host material. The performance of the final product was examined by the immobilization of enzyme GL-7-ACA acylase on the activated silicas (AF-NPS-G) obtained by crosslinking of AF-NPS with glutaraldehyde. Nanoporous silicas (before and after modification by 3-APTES and crosslinking by glutaraldehyde) are characterized by Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Nitrogen adsorption/desorption methods. The optimal conditions for silanization were found to be pH of 9, 3-APTES concentration of 10 % (dissolved in 25 ml of distilled water for 1 g of silica), temperature of 80 0C, and the reaction time of 2 h.

Removal of Cobalt, Strontium, and Cesium from Nuclear Wastewater : Polyelectrolyte와 막 사용 방사성 폐수에서 Cobalt, Strontium 및 Cesium 제거

Dang, Thi thu hien 경북대학교 대학원 2010 국내석사

저농도 방사성 폐수(LLRW)는 방사성으로 특별한 관심을 받고 있으며 체적이 방사성 폐수의 총 체적에 85%까지 차지한다. 본 학문은 각 농도와 pH 수준에서 polyelectroly 형태를 연구하는 목적이다. Sr, Co, Cs를 가진 1ppm, EDTA, PAA 및 PEI의 수준인 인공의 방사성 폐수는 chelating agent로 사용된다. Polyaminde로 구성한 RO 막은 소금 여과력이 96%에 이루었다. Regererated cellulose로 구성한 UF막은 cut-off 원자량이 100-10,000Da이다. 실험에 사용한 Stirred cell 설비가 교반속도 150rpm에서의 체적이 150ml이다. 결과를 통해서 UF막을 사용할 때 금속 제거 효과가 RO막을 사용할 때와 같다. 단, RO막은 Polyelectrolyte 농도가 지속 상승할 때 금속 제거 효과가 거의 번화하지 않은 반면에 UF막의 제거 효과는 주로 Polyelectrolyte 농도에 달려 있다. chelating agents의 금속 제거 효과 차이가 일정한 실험요소에 달려 있다. 측, 금속 제거 효과는 PAA polyeletrolyte 사용 시 pH농도에 달려 있으며 PEI 사용 시 이는 그 금속의 특성에 달려 있다. 또한 EDTA 사용 시 Donna exclusion에 달려 있다. Low-level radioactive wastes (LLRW) are of great concern due to the induced radioactivity of the waste, the existence of some fission products, and especially the occupying volume of more than 85% compared to all radioactive wastes. Thus, the purpose of this study was to investigate the performance of the various kinds of membrane with different types of polyelectrolyte at different polyelectrolyte dosages and pH levels. Artificial wastewater containing target metal species, such as Sr2+, Co2+, and Cs+was prepared using CsNO3, Sr(NO)2 and Co(NO3)2 salts with >99.99% purity (Sigma-Aldrich). The solution pH was adjusted by using 0.5 N HCl and NaOH solutions. EDTA, PAA and PEI had a molecular weight of 265 Da to 750,000 Da, respectively, were added as chelating agents. The UF membrane (Millipore) used were made of regenerated cellulose, and had a molecular weight cut-off of 1000 Da to 100,000 Da. A stirred cell membrane unit with a working volume of 150 mL was used and agitated using a magnetic stirrer at a stirring speed of 150 rpm during filtration. UF experiments were performed under a constant pressure using compressed nitrogen gas, while the permeate flux was calculated with the measurement of permeate mass using an electronic balance. Five permeate samples with a volume of 20 mL each were collected for each batch run. It was found that metal removal efficiency by the UF membrane was as high as that of using RO membrane. In which, the metal rejection efficiency by the RO membrane was nearly constant in the polyelectrolyte dosages tested, while that of UF was highly dependent on polyelectrolyte dosages. The difference in metal removal mechanisms of each chelating agent contributed into the varying relies on experimental factors. In particular, metal removal critically depended on pH level of using PAA polyelectrolyte, metals characteristic of using PEI, and Donna exclusion of using EDTA.

Buck Converter Design to Enhance Efficiency of Power Amplifier in Low Power Mode

Dang Trung Sinh 경희대학교 2010 국내석사

Radio-frequency (RF) power amplifiers (PAs) are often the most power-consuming blocks in portable wireless systems. Therefore it is critical to maintain high efficiency of the PA for extending battery life time. It is well-known that the mobile device is usually used in the low power region so that lower the supply voltage helps improving efficiency when the PA is operating in the low power region. The typical operation current of a mobile PA is around 300 mA. So we have to use an adjustable regulator with very high efficiency to supply voltage for PAs. There are tow types of regulator, linearity and switching regulator. Switching Regulator having many advantages was selected to study. We present the buck converter, a kind of switching regulator, to control the supply voltage of a power amplifier. The purpose of the buck converter is enhancing the efficiency of the power amplifier operating in the low power region. In this dissertation a buck converter was designed. The buck converter can generate the output voltage from 0.3 V to 3.4 V. The maximum efficiency of the buck converter is 95% at the output voltage of 3.4 V with the load current of 600 mA. The ripple of the output voltage is less than 12 mV.