Multi-path combined linear power amplifier and its application for audio amplifier

학위논문(석사) - 한국과학기술원 : 전기및전자공학전공, 2000.2, [ iii, 94 p. ]한국과학기술원 : 전기및전자공학전공

다이나믹핵자기 공명 영상법과 그의 응용에 관한 연구 -BULK 유속 및 미세 유곡 영상 기법

학위논문(박사) - 한국과학기술원 : 전기 및 전자공학과, 1990.8, [ viii, 105 p. ]In this thesis, the effects of flow on NMR images are studied. The effects of flow appear as a change of phase as well as signal intensity. Since the flows of blood and cerebrospinal fluid (CSF) of human body are pulsatile due to heart pumping, their velocities are not constant during NMR imaging. This type of velocity fluctuation induces irregular flow-dependent phase shifts which have been the main causes of flow artifacts in NMR imaging. In order to reduce the flow artifacts, two kinds of flow artifact reduction schemes are proposed and studied in this thesis. One is the flowinduced phase compensating technique. This technique utilizes back-to-back symmetric gradient waveforms which can remove flow-induced phase shift. The flow compensating pulse sequence for double spin echo is also proposed for the simultaneous acquisition of spin density and heavily $T_2$-weighted images. The technique seems to be promising for the reduction of eyeball and respiratory motion artifacts. The other approach is the cardiac cycle ordered phase encoding method. This technique utilizes the cardiac cycle as a precursor for the phase encoding gradients in such a way as does the respiratory ordered phase encoding (ROPE) technique which has been used for respiratory motion artifact reduction. This approach seems to be advantageous in the sense that the method is easy to implement in any pulse sequences without additional hardware requirements. Both of the proposed techniques were verified by the experimental results obtained with human vounteers using the KAIS 2.0 tesla whole-body NMR imaging system. The effects of diffusion which can be regarded as a kind of microscopic flows are also studied. In particular, the signal attenuation due to the diffusion in the fast steady state free precession (SSFP) sequence is theoretically analyzed and it is shown that the signal attenuation is dependent on spin-spin relaxation time $T_2$ and flip angle. Finally, a new fast diffusion coefficient m...한국과학기술원 : 전기 및 전자공학과

죄수의 딜레마 게임에서 지능형 에이전트의 상호작용

학위논문(석사) - 한국과학기술원 : 바이오시스템학과, 2007.2, [ vii, 53 p. ]A model of an intelligent agent based on recurrent neural network is presented and assessed in prisoner``s dilemma game. This method is superior than classical reinforcement learning especially for the ability of searching continuous action and continuous state space. Through experiments, we show that the agent has good adaptation ability to fixed strategies. In the both learning case, it is not guaranteed that they find optimal solution. To overcome this problem, we introduce personality to each agent. This is an attempt to build an agent retaining high adaptation capability to various environment by imitating the inherent property in human. Through evolutionary simulation, we show that the community of agents with personality evolves to bring social prosperity. In addition, the extension to a model of a stockmarket is presented in which independent adaptive agents can buy and sell stock on a central market.한국과학기술원 : 바이오시스템학과

Inversion recovery 핵자기 공명 영상에 있어서의 위상 보정과 시간 Multiplexing Multislice 영상법에 관한 연구

학위논문(석사) - 한국과학기술원 : 전기 및 전자공학과, 1985.2, [ iii, 36, [11] p. ]A new technique for real value representation in inversion recovery (IR) imaging is proposed. In this scheme, a new phase correction method is used to compensate the phase error of measured nuclear signal without eliminating the polarity information thereby representing the real value of physical properties of nuclei in IR imaging. By use of this scheme, a consistent IR image set as a function of several inversion times $T_I$ can be obtained. On the other hand, two kinds of pulse sequences for more efficient time multiplexing multislice IR imaging are developed. These sequences can utilize maximally the repetition time $T_R$ and the inversion time $T_I$. Some experimental results to confirm these proposed methods are presented.한국과학기술원 : 전기 및 전자공학과

Three-Dimensional Nanostructure Metal Catalyst for Carbon Dioxide Reduction and manufacturing method thereof

본 발명은 이산화탄소 환원을 위한 3차원 나노 구조 금속 촉매 및 이의 제조방법에 관한 것이다. 본 발명의 이산화탄소 환원을 위한 3차원 나노 구조 금속 촉매는 정렬된 금속 나노선이 적층된 구조로, 적층된 촉매 두께에 의해 국소 pH를 높게 조절하여 CO 선택성을 높일 수 있다. 또한, 금속 나노선의 작은 입자 크기 덕분에 높은 CO 선택성을 갖는 고차 결정면을 촉매 활성부위에 포함하여 CO 선택성을 현저하게 증가시키고, 수소 발생 반응을 억제시킴으로써 이산화탄소 환원 반응속도를 높일 수 있다. 3차원 나노 구조 금속 촉매를 이루는 금속 나노선 사이의 공간은 촉매 층 내부에서 반응물 및 생성물의 이동을 원활하게 하여 이산화탄소 환원 반응 속도를 높인다. 또한, 본 발명의 3차원 나노 구조를 가지는 촉매는 나노 구조의 제어를 통해 높은 안정성을 가질 수 있고 이산화탄소 환원을 위한 촉매 전극에 활용될 수 있다