28,310 research outputs found
Myoung-Jin Lee, oboe and Ho-Kyung Choi, piano, April 22, 2018
No full textThis is the concert program of the Myoung-Jin Lee, oboe and Ho-Kyung Choi, piano performance on Sunday, April 22, 2018 at 6:30 p.m., at the Marshall Room, 855 Commonwealth Avenue. Works performed were Concerto for Oboe in C minor by Alessandro Marcello, Sonatine for Piano by Maurice Ravel, and Concerto for Oboe by Ralph Vaughan Williams. Digitization for Boston University Concert Programs was supported by the Boston University Humanities Library Endowed Fund
“Coastal Dynamics, Hazards, and Numerical Modelling” in Memory of Prof. Byung Ho Choi
No full textThis Special Issue is dedicated to Prof Byung Ho Choi at SungKyunKwan University, South Korea [...
광결정 광섬유의 모드 특성 연구
No full text학위논문(석사) - 한국과학기술원 : 물리학과, 2006.2, [ vii, 33 p. ]Photonic crystal fibers (PCFs) are a special class of pure-silica optical fibers. They consist of a silica core, surrounded by a periodic array of air-holes running along the entire length of the fiber. These air-holes permit guidance of light through total internal reflection in the case of index-guiding microstructured fibers (IGMF). And a periodic air-silica cladding exhibits a band gap for photons in the radial direction in photonic band gap fibers (PBGF). Diameter, spacing of the air-holes and geometric air-holes distribution determine the optical properties of the fiber, therefore allowing for tailoring of the fiber according to the intended application.
In this thesis, we numerically investigate the propagation modes and dispersion proper-ties of light in several types of PCFs such as regular index-guiding microstructured fibers, photonic band gap fibers and irregularly structured low- and high-birefringent PCFs. Effects of fiber birefringence, effective index of cladding and the number of guided modes are studied in designing two modes birefringent PCFs. Birefringence of the fiber is realized by adjusting the size and geometry of the air holes around the core regions. We present a design for a birefringent two modes IGMF which can be applied to interferometers and optical sensors.한국과학기술원 : 물리학과
펄스형 광펌핑을 이용한 루비듐 원자시계 개발 연구
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2010.08, [ ix, 61 p. ]The atomic clock using a vapor cell is appropriate for many applications because it has simple, compact, and stable characteristics. The atomic clock is realized by the use of the atomic transitions between the ground state hyperfine levels. The two approaches have been used to implement a vapor cell atomic clock. One is the microwave-optical double resonance (MODR) technique and the other is the coherent population trapping (CPT) technique. We propose a pulsed optically pumped Rb atomic clock using a laser absorption in MODR technique and a carrier mode suppression of a phase modulated beam using an optical cavity in CPT technique.
We report an optical detection approach instead of the detection of a microwave decay method in a Rb vapor cell atomic clock for its compact setup. We present the data processing method which transfors the optical transmission signal into the clock transition signal in the optical detection approach. We obtained the FWHM of the clock transition signal which is 293 Hz by this data processing method when the microwave interrogation time is 3 ms and microwave power is -4 dBm. The line broadening of the clock transition signal versus the microwave interrogation time for the respective microwave optimum power was measured. In order to estimate the tolerance of the temperature variation of the temperature stabilization servo, we measured the fractional frequency stability versus temperature variation which is 6.6\times10^{-10} / \degC. The measured frequency stability of our 2 \times10^{-11}\tau_{\frac{-1}{2}}$ and the short-term stability could be improved by employing the more stable laser system and the more precise data processing method. And to enhance the long-term stability, the temperature variations of the laser diode and the components of the electronic systems should be greatly reduced.
We adopted an electro-optic modulator (EOM) approach to produce a phas...한국과학기술원 : 물리학과
OFDM 시스템에서 극한 페이딩 채널 특성에 강인한 향상된 잡음 전력, 신호대 잡음비 추정 기법 연구
No full textThe purpose of this study is to estimate signal to noise power ratio (SNR) in a se-vere fading channels. Signal power and SNR estimation is hard to estimate in a severe fading channels because channel variation occurs more extremely. In this situation, noise power estimates are generally higher than the actual values because of channel estimation errors, channel variations, and multipath delays. Moreover, current communi-cation systems reduce pilot density to increase data rate. As a result, accurate SNR estimation is becoming more difficult. This paper analyses SNR estimation techniques and proposes improved signal and SNR estimation schemes in severe fading channels to reduce estimation error. We analyze representative SNR estimators. The proposed signal power and SNR estimators use a chan-nel estimation filter (CEF) and differential scheme. The simulation results show that the differential scheme SNR estimator provides better performance in severe fading channel. The proposed techniques can reduce error because they select a better condi-tion channel domain. The proposed SNR estimation technique uses OFDM characteristics in multi-dimensional domain. Channel status is different along the time and frequency domain. Choosing a better domain can reduce error in SNR estimation. The proposed SNR estimator uses SNR information of each domain to choose the proper domain. The simulation result shows that the proposed estimation technique can reduce estimation error up to 5dB in a frequency selective or fast fading channel.The study result can be applied to contemporary communication system channel esti-mation such as LTE and WiMax, which provide high data rates with low pilot density with high interference channel or fast fading channel. ⓒ 2013 DGISTⅠ. Introduction 1
--
Ⅱ. System description 5
--
2.1 OFDM system overview 5
--
2.2 Channel model for OFDM systems 8
--
2.3 SNR estimation in OFDM systems 11
--
Ⅲ. Comparisons of SNR estimation algorithms
--
3.1 Maximum likelihood (ML) estimation method in AWGN 12
--
3.2 Minimum mean square error (MMSE) estimation method in AWGN 13
--
3.3 Conventional SNR estimator in fading channel 14
--
Ⅳ. Proposed SNR estimation techniques 16
--
4.1 Noise power estimator using channel estimation filter (CEF) 16
--
4.2 Signal power estimator using CEF 17
--
4.3 Signal power estimator using differential scheme 18
--
4.4 Performance analysis 19
--
Ⅴ. Proposed SNR estimation techniques in multi-dimension domain 26
--
5.1 Noise power estimator using channel estimation filter (CEF) 26
--
5.2 Performance analysis 27
--
Ⅵ. Conclusion and future works 29본 논문은 OFDM 통신 시스템에서 극한 페이딩 채널 환경 하에서 보다 나은 잡음 전력과 신호대 잡음비 (SNR)을 추정하는 기법을 제안한다. 정확한 잡음 전력과 SNR값 추정은 통신 시스템 파라메터 설정과 파일럿 선택에 있어서 중요한 파라메터이다. 하지만 극한 페이딩 채널에서는 채널의 변화, 다중 전파 경로 지연, 채널 추정 오차가 극심하므로 정확한 잡음 전력과 SNR 추정이 힘들다.
이를 해결하기 위해서 본 논문에서는 채널 추정 필터를 이용한 잡음 전력 추정기와 채널 추정 필터, 파일럿 사이의 상관 함수 (correlation)를 이용한 신호 전력 추정기를 이용한 SNR 추정기를 제안한다. 기존의 SNR 추정기의 경우에는 신호 혹은 잡음 전력 추정기 하나만을 사용하고, 페이딩 환경에 대한 고려가 적어 오차가 많았다. 본 논문에서는 신호 전력과 잡음 전력을 따로 추정하여 추정 오차의 전파를 막아 보다 정밀한 측정이 가능하였다. 또한 상관함수를 사용한 추정기가 기존의 SNR 추정기보다 5dB 오차를 줄일 수 있었으며, 신호 추정에 따른 잡음 전력 오차를 고려한 추정기를 이용했을 때 3dB정도의 오차를 줄일 수 있음을 시변 채널 환경과 주파수 선택적 페이딩 환경에서의 시뮬레이션 결과를 통해 알 수 있었다.
또한 OFDM 시스템의 다중 캐리어 특성을 이용하여, 다중 도메인에서의 SNR값을 추정하고, 이를 비교하여, 적합한 도메인 선택을 통한 오차 감소 기법을 제시하였다. 채널의 변화는 채널 추정 필터나 잡음 전력 추정의 증가를 가져와 실제 SNR값보다 낮은 SNR추정치를 만들어 낸다. 이러한 특성을 이용하여 신호, 주파수와 같은 다중 도메인에서 높은 SNR값을 가지는 도메인을 선택하여 추정함으로써 SNR 추정 오차를 줄일 수 있었다.
본 논문의 결과는 현재 광범위하게 사용되는LTE, WiMax등 OFDM 통신시스템에서 적용하여 적합한 SNR 추정을 통한 효율적인 통신 방식에 이용할 수 있다. ⓒ 2013 DGISTMasterdCollectio
MIN-HO CHOI
No full text학위논문(석사)--아주대학교 일반대학원 :의생명과학과,2019. 2Ⅰ. 서론 1
Ⅱ. 실험재료 및 방법 3
1. 실험재료 3
2. PVA 나노섬유의 전기방사 및 제조방법 3
3. RGD-PVA 나노섬유의 전기방사 및 제조방법 4
4. 플루오레세인 나트륨 (Sodium fluorescein) 나노섬유의 제조방법 및 전기방사 4
5. MLE-12 세포 배양방법 4
6. 초대 간세포 (Primary hepatocytes) 분리방법 4
7. 초대 간세포 (Primary hepatocytes) 배양방법 5
8. 면역 형광 염색법 (Immunofluorescence) 5
9. 공초점 레이저 현미경 (confocal laser microscope) 5
10. 주사전자현미경 (scanning electron microscopy, SEM) 6
Ⅲ. 결과 7
1. 다양한 전기방사 조건 및 PAA와 GA 첨가에 따른 PVA 나노섬유 제작 7
2. RGD 펩타이드를 함유한 PVA 나노섬유 제작 10
3. RGD 펩타이드가 함유된 배양액이 MLE-12 세포 부착능에 미치는 영향 12
4. 농도별 RGD-PVA 나노섬유에서 MLE-12 세포의 부착능 실험 14
5. 플루오레세인 나트륨이 함유된 나노섬유 제작방법 및 방출되는 정도 16
6. PVA 나노섬유와 RGD 나노섬유에서 MLE-12 세포의 배양 및 형태 확인 18
7. PVA 나노섬유와 RGD-PVA 나노섬유에서 마우스 초대 간세포의 배양 및 형태 확인 20
8. PVA 나노섬유와 RGD-PVA 나노섬유에서 마우스 초대 간세포의 기능 테스트 23
Ⅳ. 고찰 25
Ⅴ. 결론 27
참고 문헌 28
영문 초록 31MasterRecently, the importance of nanofibers as a three-dimensional cell culture scaffold has been revealed. Research and development on nanofiber production using electrospinning has been actively conducted. Among various polymer polyvinyl alcohol (PVA), a water-soluble polyhydroxy polymer, is widely used due to its unique property of dissolving in a water, biocompatibility, biodegradability and permeability. However, PVA nanofiber is highly soluble in water which lead to low protein affinity and poor cell attachment. In this study, addition of PAA and GA to PVA solution resulted to the insolubility of the PVA nanofiber in water. RGD peptide, a major integrin binding domain, was mixed in PVA/PAA/GA solutions and fabricated using electrospinning. Cell adhesion and cell function were examined in RGD-PVA nanofiber membrane.. Surface morphology of nanofibers was analyzed by scanning electron microscope (SEM). MLE-12 cells and mouse hepatocytes were culture on PVA nanofibers and RGD-PVA nanofibers. The adherence, morphology, viability and proliferation of both cells were examined. As a result, cells cultured on RGD-PVA nanofibers showed better cell adhesion and growth stability then on PVA nanofibers alone. This study provides effective and simple way to confirm the possibility PVA nanofibers to be mixed with cell attaching peptides. Thus, RGD containing can be applied in three-dimensional cell culture
Peptide-catalyzed, bioinspired silicification for single-cell encapsulation in the imidazole-buffered system
No full textInspired by biosilicification of glass sponges, we designed a catalytic peptide, which formed silica structures in the imidazole-buffered solution. The peptide was adsorbed selectively onto the surface of yeast cells, and the bioinspired silicification led to the formation of a cytoprotective silica shell on individual yeast cells
A community recommendation method based on social networks for web 2.0-based IPTV
No full textWeb 2.0-based IPTV is a new Internet Protocol Television (IPTV) infrastructure that allows users to participate in content creation and consumption through Web-based communities that are formed based on user interests. However, there are some limitations in making users actively participate in creating and utilizing communities. First, users need to explicitly create and manage their communities. In addition, it is difficult for users to identify and join communities that meet their needs. This paper proposes a method to identify and recommend potential IPTV communities for users by using their social relationships and preferences. The main goal of this method is to motivate users to actively participate in creating and sharing their contents through recommended communities. We have implemented a prototype of Web 2.0-based IPTV that allows users to share their contents and build relevant knowledge regarding the contents through blogs and Wiki-based communities.This work was supported by the IT R&D program of MKE/IITA. [AI 100-0801-3015, Development of OpenIPTV Technologies for Wired and Wireless Networks
- …
