Doctor of Philosophy

dissertationThe partial nitritation/anammox (PN/A) process, although found to be an energy and cost-effective process, is not well understood yet. This study was carried out to provide a better understanding of PN/A reactors with suspended and attached growth configurations for treating different waste streams that have potential stress factors. Two PN/A reactors with different configurations were successfully initiated to investigate the difference of suspended growth reactor (SR) and attached growth reactor (AR) in nitrogen removal and the overall microbial composition. During the 300 days of operation, both reactors showed a similar nitrogen removal rate at 35°C and 21°C, and harbored similar communities dominated mainly by three phyla: Chloroflexi, Planctomycetes, and Proteobacteria. To further study the external stress effect on the PN/A performance, the suspended growth reactor was kept at 35°C to 21°C and finally at 13°C.. It was confirmed that lower temperature or sulfide content as low as 5 mgS L-1 could eliminate both Nitrosomonas europaea related ammonium oxidizing bacteria (AOB) and Ca. Brocadia sp. affiliated anammox bacteria (AMX). The activity of AOB was inversely correlated with amoA gene expressions. Just the opposite was found with the hzsA gene expression since it correlated well with the activity of AMX. Additionally, anammox process was applied to treat poststruvite precipitated urine in two-stage and single-stage systems. It was found that coupling the struvite precipitation and PN/A process, 99% recovery of phosphorus and up to 80% removal of nitrogen could be achieved. Compared to the two-stage system, the single-stage reactor had a lower nitrogen removal rate. Also, a pilot-scale PN/A reactor was designed and fabricated to treat reject water in a 300 gal sequencing batch reactor at room temperature. The reactor was successfully started and was able to remove 0.164±0.086 kgNkgVSS-1d-1, indicating a relatively high bacterial activity at room temperature. In conclusion, this study evaluated the feasibility and sustainability of the PN/A system in treating different waste streams containing high ammonium. It provided a better understanding of startup and operation strategies for the full-scale installations of anammox in wastewater treatment plants

Triggering waves in nonlinear lattices: Quest for anharmonic phonons and corresponding mean free paths

Guided by a stylized experiment we develop a self-consistent anharmonic phonon concept for nonlinear lattices which allows for explicit "visualization." The idea uses a small external driving force which excites the front particles in a nonlinear lattice slab and subsequently one monitors the excited wave evolution using molecular dynamics simulations. This allows for a simultaneous, direct determination of the existence of the phonon mean free path with its corresponding anharmonic phonon wavenumber as a function of temperature. The concept for the mean free path is very distinct from known prior approaches: the latter evaluate the mean free path only indirectly, via using both, a scale for the phonon relaxation time and yet another one for the phonon velocity. Notably, the concept here is neither limited to small lattice nonlinearities nor to small frequencies. The scheme is tested for three strongly nonlinear lattices of timely current interest which either exhibit normal or anomalous heat transport

Maxwell-Hydrodynamic Model for Simulating Nonlinear Terahertz Generation from Plasmonic Metasurfaces

The interaction between the electromagnetic field and plasmonic nanostructures leads to both the strong linear response and inherent nonlinear behavior. In this paper, a time-domain hydrodynamic model for describing the motion of electrons in plasmonic nanostructures is presented, in which both surface and bulk contributions of nonlinearity are considered. A coupled Maxwell-hydrodynamic system capturing full-wave physics and free electron dynamics is numerically solved with the parallel finite-difference time-domain (FDTD) method. The validation of the proposed method is presented to simulate linear and nonlinear responses from a plasmonic metasurface. The linear response is compared with the Drude dispersion model and the nonlinear terahertz emission from a difference-frequency generation process is validated with theoretical analyses. The proposed scheme is fundamentally important to design nonlinear plasmonic nanodevices, especially for efficient and broadband THz emitters.Comment: 8 pages, 7 figures, IEEE Journal on Multiscale and Multiphysics Computational Techniques, 201

The transformation and influence of overseas commerce of Mingzhou port-city in Tang and Song Dynasties（821-1279）——Concentrated on the historical relics

Known as Mingzhou in the Tang and Song Dynasties, Ningbo was one of the largest port-cities in ancient China. As a local city that combined both port and waterside characteristics, the urban planning was not only limited by its waterside property, but also guided by the development of port trade. At the same time, it possessed the flexibility of a local city beyond the ancient capital under the central system. Furthermore, the most typical feature of Ningbo lied in the characteristic of being a port-city among the three points mentioned above. Ningbo was one of ancient China’s rare cities characterized by being open to overseas commerce. Through overseas commerce acting as the main goal and developmental motivation, its urban planning distinguished itself from that of most political and military type cities. Research on the changes to urban planning under Ningbo’s economic and political competitions can supplement case studies of China’s ancient urban planning. Additionally, it can provide a reference for research on urban planning of ancient port cities around the world. Overseas commerce of ancient Ningbo was developed since the late Tang Dynasty, and reached its peak in the Song and Yuan Dynasties. Later it transformed into domestic commerce due to a ban on maritime trade in Ming and Qing dynasties. This thesis takes historical relics as the breakthrough point to research the transformation of overseas commerce in Mingzhou port-city from the Tang to the Song Dynasty, and on this basis, to discuss the effect on the city. The author considers the overseas commerce as characteristics of Mingzhou port-city that influenced its planning management system, spatial pattern, and its form of open concept.By comparing the historical relics and archaeological information of “Heyi Gate-Yupu Gate District” and “Dongdu Gate-Lingqiao Gate District”, which are the port areas of the Tang and Song dynasties respectively, this thesis explains that the core port region in Mingzhou shifted from Tang to Song Dynasty. Additionally, the port’s function transformed from that of a single port to that of a comprehensive port. This shift reflects a process in which management of overseas-related institutions in the sub-city scaled up and spilled over, then completely separated. Finally, the author suggests that a function of the port-city was it transformed the port region into the earliest street market, which caused the relaxation and disintegration of the "system of workshops and stores"; the nature of a port-city established an asymmetric spatial pattern in which “the western city is residential and the eastern city is commercial”; the orientation of the port-city gives birth to a “window” of overseas commerce and the city’s open culture

PALS/PRISM Software Design Description (SDD): Ver. 0.51

This Software Design Description (SDD) provides detailed information on the architecture and coding for the PRISM C++ library (version 0.51). The PRISM C++ library supports consistent information sharing and in- teractions between distributed components of networked embedded systems, e.g. avionics. It is designed to reduce the complexity of the networked sys- tem by employing synchronous semantics provided by the architectural pat- tern called a Physically-Asynchronous Logically-Synchronous (PALS) system.unpublishednot peer reviewe

Optimized operator-splitting methods in numerical integration of Maxwell's equations

Optimized operator splitting methods for numerical integration of the time domain Maxwell's equations in computational electromagnetics (CEM) are proposed for the first time. The methods are based on splitting the time domain evolution operator of Maxwell's equations into suboperators, and corresponding time coefficients are obtained by reducing the norm of truncation terms to a minimum. The general high-order staggered finite difference is introduced for discretizing the three-dimensional curl operator in the spatial domain. The detail of the schemes and explicit iterated formulas are also included. Furthermore, new high-order Padé approximations are adopted to improve the efficiency of the proposed methods. Theoretical proof of the stability is also included. Numerical results are presented to demonstrate the effectiveness and efficiency of the schemes. It is found that the optimized schemes with coarse discretized grid and large Courant-Friedrichs-Lewy (CFL) number can obtain satisfactory numerical results, which in turn proves to be a promising method, with advantages of high accuracy, low computational resources and facility of large domain and long-time simulation. In addition, due to the generality, our optimized schemes can be extended to other science and engineering areas directly. © 2012 Z. X. Huang et al.published_or_final_versio

Full Hydrodynamic Model of Nonlinear Electromagnetic Response in Metallic Metamaterials

Applications of metallic metamaterials have generated significant interest in recent years. Electromagnetic behavior of metamaterials in the optical range is usually characterized by a local-linear response. In this article, we develop a finite-difference time-domain (FDTD) solution of the hydrodynamic model that describes a free electron gas in metals. Extending beyond the local-linear response, the hydrodynamic model enables numerical investigation of nonlocal and nonlinear interactions between electromagnetic waves and metallic metamaterials. By explicitly imposing the current continuity constraint, the proposed model is solved in a self-consistent manner. Charge, energy and angular momentum conservation laws of high-order harmonic generation have been demonstrated for the first time by the Maxwell-hydrodynamic FDTD model. The model yields nonlinear optical responses for complex metallic metamaterials irradiated by a variety of waveforms. Consequently, the multiphysics model opens up unique opportunities for characterizing and designing nonlinear nanodevices.Comment: 11 pages, 14 figure