Ge Guo Qin. / "April 18, 2001." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (p. 129-143). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Recently, Coherent Optical Orthogonal Frequency-division Multiplexing (CO-OFDM) has been considered as a promising technology for high-speed optical transmission due to its easiness of dispersion compensation, high optical spectral efficiency and superior scalability over the channel dispersion and data rate. In this thesis, we conduct analysis on the transceiver nonlinearity impact on a coherent optical Orthogonal Frequency-division Multiplexing (OFDM) system and the feasibility of transmitting up to 1 Tb/s per channel data rate over CO-OFDM WDM systems. / We investigate the optimum design for a CO-OFDM transmitter using an optical In-phase/Quadrature (I/Q) modulator and show by simulation that in contrast to the direct-detected system, the optimal modulator bias point for the coherent system is π, or the null point of the modulator. We also propose and demonstrate through simulation a transmitter side digital signal processing technique including digital clipping and digital pre-distortion to compensate the nonlinearity induced by the OFDM peak-to-average power ratio effect and Mach–Zehnder modulator (MZM). Furthermore, we conduct analysis on the study of nonlinearity and dynamic range for a CO-OFDM receiver induced by the imbalance between the two ports of a balanced receiver. The input power dynamic range and tolerance to the relative-intensity-noise (RIN) are analyzed for the coherent balanced-receiver. / We then explore the transmission performance for high speed wavelength-division multiplexing (WDM) CO-OFDM systems with up to 1Tb/s per channel data rate under the impact of fiber nonlinearity. We find that the optimum fiber launch power increases almost linearly with the increase of data rate. A 7 dB optimum launch power difference is observed between 107-Gb/s and 1.07-Tb/s CO-OFDM systems. We also investigate the dispersion compensation fiber impact and filter concatenation effect issues when upgrading the 10-Gb/s to the future 100-Gb/s CO-OFDM systems. We identify three contributions to the Q degradation for the inline dispersion compensated WDM systems. We show that due to the high spectral efficiency, 100-Gb/s CO-OFDM signals have very high tolerance to the filter narrowing effect, and are resilient to the group ripples from the filter concatenation effect.

Coherent transmission system has been extensively studied in recent years, and it can use different modulation formats and different detection techniques. The modulation formats are ASK (Amplitude shift keying), PSK (Phase shift keying), and FSK (Frequency shift keying). The detection techniques are Homodyne detection and Heterodyne detection, and they need a laser in the receiver called as the LO (Local oscillator). In the previous study, the BPSK (Binary phase shift keying) modulation format was investigated, and the pilot carrier method realized the Homodyne Detection. The merit of the pilot carrier is that it do not need the LO in the receiver. In this master thesis, the QPSK (Quadrature phase shift keying) modulation format is investigated using the pilot carrier method, The BER is calculated using the matlab program. The performance of 20G bit/s, 50 km transmission system using the BPSK and the QPSK is compared to clarify the merits and demerits of the QPSK modulation.

High-resolution particle image velocimetry (PIV) is employed to resolve the velocity fields within a Mach 4.9 mechanically distorted turbulent boundary layer (Reθ ≈ 40,000). The goal of this study is to directly observe the mechanisms responsible for the modified turbulent stresses present in mechanically distorted boundary layers. This is achieved by measuring the effects of the mechanical distortions upon the distribution, population, size, orientation, and energy content of the turbulent structures, and how the perturbed state of these structures is manifested within the ensemble-averaged turbulent stresses. The two mechanical distortions under investigation are 1) streamline curvature-induced favorable pressure gradients (Ip = {-0.08; -0.49}), and 2) periodic arrays of diamond roughness elements (k/δ ≈ 0.07). A smooth-wall, flat-plate boundary layer is also included to establish the unperturbed state of the turbulent structures. The response of the mean turbulence statistics is investigated through ensemble-averaged profiles of Reynolds stresses, indicating the respective influences of pressure gradient effects and surface roughness upon the turbulent statistics. The distortion and reorientation of the large-scale coherent motions is quantified through the determination of the integral length scale and local structure angle from two-point correlations. Detection of individual vortices through the swirling strength criterion λci allows the population distribution of the turbulent eddies to be examined, along with the conditionally averaged hairpin structure. The baseline and rough-wall stresses showed good agreement when scaled by the smooth-wall friction velocity. Two-point correlations indicate that the reorientation of the large-scale [i.e. O(δ)] coherent structures, coupled with the modified wall-normal fluctuations, is primarily responsible for the modification of the rough-wall Reynolds stresses. The reduced Reynolds stresses observed in the favorable pressure gradients is partially due to the attenuation of the local flowfield around the near-wall hairpin structures, mitigating the mechanism for “producing” turbulence. The rotational rate of the hairpin vortices, measured through the mean prograde swirling strength, was reduced for the favorable pressure gradient models.

Typescript. Includes vita and abstract. Includes bibliographical references (leaves 84-85) Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

This thesis examines the statistics and dynamics of turbulent flow structures generated by towing a grid through a tank of water. The structures were made visible by recording the paths of aluminum tracers moving with the water surface. Flow patterns recorded using a time-exposure method were manually analyzed to extract information on the structure statistics. This two-dimensional flow field was found to be composed of closed rotating 'surface eddies', open and largely translational 'river' motion and stagnant regions. Energy distributions of the eddies and rivers were obtained and characterized by Boltzmann type distributions. A newly developed computer-automated structure identification and flow field analysis system was used to study the structure dynamics. The system analyzes digital images obtained from video recordings of the tracer motion. The predominant evolution processes of initial vortex production, eddy pairing, viscous decay and the omega decay were examined. Flow Reynolds numbers, based on bar spacing, of about 10,000 were examined. The structure statistics and dynamics study was performed in order to examine the validity and viability of a new model for turbulence. The model predicts the evolution of a population of structures using rate equations where the rate coefficients are determined by the individual structure dynamics. A summary of the model is presented and contrasted with models based the the Reynolds stresses as well as computational models. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Understanding cellular heterogeneity has been a challenge in biology. Current bio-analytical methods such as mass spectrometry or fluorescence-based detection would destruct the sample or perturb the functions of targeted molecules. In situ imaging of bio-molecules at single cell level resolves the phenotypes at metabolomics domain, which can address the challenges in studying cellular heterogeneity. Stimulated Raman scattering (SRS) microscopy provides a label-free approach to identify molecules based on the signature of molecular vibrations. However, there are several challenges to overcome in order to use SRS as a single-cell analysis platform with high throughput, high content, and high sensitivity. My thesis work aims to overcome above-mentioned difficulties. To fulfill the first unmet need of single cell metabolic analysis, we developed an SRS flow cytometry, and demonstrated the discrimination of particles at a throughput of up to 11,000 particles per second, which is a four orders of magnitude improvement compared to conventional spontaneous Raman flow cytometry. Next, we addressed the second unmet need of single-cell metabolic analysis through the development of SRS imaging cytometry. Using this platform, we studied the response of human pancreatic cancer to drug-induced and starvation-induced stress, and discovered lipid-facilitated protrusion as a metabolic biomarker for stress-resistant cancer cells. Lastly, to probe low-concentration bio-molecules using fingerprint Raman bands, we utilized pre-resonance enhancement to increase the SRS signal by two orders of magnitude, and demonstrated ultra-sensitive imaging of retinoids in cells. We demonstrated in situ imaging of retinoid level in cancer cells and during neuronal development. Collectively, these efforts demonstrate SRS cytometry as a high-throughput, high-content, and high-sensitivity single-cell analysis platform with broad applications. / 2022-01-28T00:00:00Z

Yes / A quantum system with variables in Z(d) is considered. Coherent density matrices and coherent projectors of rank n are introduced, and their properties (e.g., the resolution of the identity) are discussed. Cooperative game theory and in particular the Shapley methodology, is used to renormalize coherent states, into a particular type of coherent density matrices (dressed coherent states). The Q-function of a Hermitian operator, is then renormalized into a physical analogue of the Shapley values. Both the Q-function and the Shapley values, are used to study the relocation of a Hamiltonian in phase space as the coupling constant varies, and its effect on the ground state of the system. The formalism is also generalized for any total set of states, for which we have no resolution of the identity. The dressing formalism leads to density matrices that resolve the identity, and makes them practically useful.

Yes

Efficient mixing can be achieved in flows where turbulence is absent, if the trajectories of passively advected particles in the flow are chaotic. The chaotic nature of particle trajectories results in exponential stretching of material lines in the flow. Thus the interface along which diffusion occurs is stretched exponentially leading to efficient mixing. It has been demonstrated recently that regions in flow fields that exhibit poor mixing and non-chaotic particle trajectories can have an important bearing on the overall dynamics and transport of the entire domain. The space-time trajectories of physical stirrers or elliptic points in two dimensional flows can be classified according to braid groups. One can predict a lower bound on the topological entropy (i.e. exponential rate of stretching of material lines) of flows (h_f) by applying the Thurston-Nielsen classification theorems to these braids. This gives a reduced order model for the dynamics of transport of the entire flow field using just a few points. Recent work has shown that this methodology can be used to estimate a lower bound on h_f using the braids formed by Almost Cyclic Sets (ACS) in certain periodic Stokes' flows. These ACS are closely related to Almost Invariant Sets (AIS) which are identified using a probabilistic set oriented method that makes use of the descritised Perron-Frobenius operator of the flow map. This work extends this approach to flows at non-zero Reynolds numbers, which take into account the effects of inertia. The role of Finite Time Coherent Structures (FTCS) in the dynamics of flow fields is also investigated. Unlike ACS, the FTCS approach is more general as it can be applied to aperiodic flow fields. Further, the relationship between mixing efficiency and the topological entropy of flow fields at non-zero Reynolds numbers is also studied. / Ph. D.