Bone defects have become a challenging health issue after extensive trauma, osteoporosis, and tumor extirpation worldwide. To enhance bone healing, bone grafts have been employed in clinical treatment for many years. Autologous grafts have been considered as the “gold standard” for the bone graft material, but their application is limited by the donor site morbidity. Demineralized bone matrix (DBM), one of the alternations of autologous graft, has been widely used for craniofacial bone repair. However, the application of DBM is compromised due to its rapid dispersion after the implantation and low osteoinductivity. In order to deliver and localize DBM, carriers with high bioactivity are in need to be developed.

Chitosan has been proved to be attractive for researchers in the field of tissue bioengineering due to its high biocompatibility, biodegradability, and low immunogenicity. Besides, heparin, a highly sulfated polysaccharide in the extracellular matrix, possesses the typical structure which can interact with multiple osteoinductive factors to enhance and stabilize the biological activities of growth factors. Therefore, we synthesized a chitosan-based hydrogel with heparinized conjugation (Hep-MeGC), which can not only deliver DBM but also enhance its osteogenic activity. Moreover, upon the stimulation of BMPs (major osteogenic factors in DBM), BMP efficacy is significantly reduced due to increased expression of BMP antagonists like Noggin. Thus, the potency of BMPs in DBM may be enhanced through Noggin suppression. This study aims to investigate the new method by using Noggin suppression and Hep-MeGC hydrogel to enhance DBM-mediated bone repair.

To suppress Noggin, human bone marrow stem cells (hBMSCs) were transfected with lentiviral particles that encode Noggin-shRNA. The methacrylate glycol chitosan (MeGC) and heparinized chitosan hydrogel (Hep-MeGC) hydrogel, were then prepared to deliver DBM and BMSCs with Noggin-suppression. The effect of DBM and Noggin suppression on osteogenesis was evaluated in vitro, and the ability of DBM and Noggin suppression in Hep-MeGC hydrogels to bone regeneration was investigated through in vivo study.

Noggin suppression + DBM greatly enhanced the osteogenesis of BMSCs in Hep-MeGC hydrogels, as shown by the increased ALP production, calcium deposition, and expression of osteogenic genes. The mechanistic study showed that Noggin suppression enhanced the DBM-based osteoinductivity through the stimulation of BMP-Smad signals. Detected by microCT and histological/immunohistochemical analysis, the combinational treatment further displayed a robust bone healing capacity in the critical-sized mouse calvarial defect model. To conclude, the incorporation of DBM and Noggin suppression in the Hep-MeGC hydrogel significantly promoted bone healing.

Plasmonic nanostructures with tunable localized surface plasmon resonance (LSPR) have attracted much attention due to their broad applications in chemical sensing, photothermal therapy, and colorimetric detection. Because LSPR is related to particle morphology, controlling their size and shape is crucial for tailoring and tuning their optical resonance properties. Compared with conventional synthesis methods, space-confined seed-mediated growth is more reproducible and scalable and offers more opportunities to design hybrid and thermodynamically unstable structures. This dissertation discusses the seed-mediated growth of various plasmonic nanostructures within polymer confinement and explores their applications for colorimetric devices.We first investigate the confined seeded growth process of plasmonic nanostructures, which involves the deposition of various metal atoms, including Au, Ag, and Pt, onto the pre-formed seeds confined within polymer nanoshells. The key parameters affecting the growth are systematically studied, including the surfactants, reductants, and some kinetics factors. Different metals are found to exhibit diverse behaviors during the seeded growth process, producing plasmonic-polymeric hybrid nanostructures with different chemical and physical properties. In particular, we highlight the seeded growth of Pt within the confined space, which has not been achieved previously. These plasmonic nanostructures are promising building blocks for designing various colorimetric devices. The seeded growth process is coupled with a plasmonic decoupling mechanism to design a colorimetric pressure sensor that can respond to applied pressure with instant color changes. The sensor consists of a thin film of stacked uniform nanoshells of resorcinol formaldehyde resin, with their inner surfaces functionalized with Ag nanoparticles. Upon compression, the flexible polymer nanoshells expand laterally, inducing plasmonic decoupling between neighboring Ag nanoparticles and a subsequent blueshift. The initial color of the sensor is determined by the extent of plasmonic coupling, which can be controlled by tuning the interparticle distance through a seeded growth process. The sensing range can be conveniently customized by controlling the polymer shell thickness or incorporating the hybrid nanoshells into various polymer matrices. We further demonstrate that the controlled growth of plasmonic nanoparticles within polymer nanoshells offers an excellent opportunity for tuning their refractive index. Such tunability is employed to design novel colloidal photonic crystal films. Theoretical simulations coupled with experimental observations confirm the strong interaction between Au and resorcinol formaldehyde, which results in a notable decrease in the refractive index and a subsequent blueshift in the photonic bandgap. The photonic crystal films fabricated using such nanoshells exhibit brilliant structural colors, which can be conveniently controlled by the amount of Au loading through the seeded growth process. The tuning range of diffraction colors can be tailored by adjusting the diameter and thickness of the polymer nanoshells. This high spectral tunability enables the design of unique colorimetric refractive index sensors capable of distinguishing various polar solvents. Plasmonic nanoparticles can efficiently convert light of their resonance wavelength into heat. This photothermal effect is utilized to induce photoresponsive expansion of hollow polymer nanoshells, resulting in a color response in two-dimensional (2D) arrays assembled on a substrate using these nanoshells. When exposed to light, the liquid inside the polymer shells vaporizes quickly, creating high pressure that causes the shells to expand. The expansion can be controlled by adjusting light intensity, shell thickness, and void size. This expansion allows the nanoshells to reposition themselves, improving the order of the 2D arrays and, consequently, the optical diffraction. Additionally, the expansion causes a redshift in the structural color, enabling the development of a light-responsive writing technique.

Understanding of the electronic properties of new materials is of central importance for science and technology. In particular, low-dimensional nano-materials exhibit exotic properties that are determined by quantum mechanics. Rapid development of reticular chemistry has enabled the syntheses of a variety of low-dimensional condensed matter systems that are formed by linking up molecular building blocks. This dissertation focuses on the on-surface synthesis of such materials and consequent characterization of their local electronic structure with scanning tunneling microscopy (STM).

The structure － property relationship of two low-dimensional nano-materials will be described: quasi-one-dimensional (1D) graphene nanoribbons (GNRs) and two-dimensional (2D) covalent organic frameworks (COFs). In the case of GNRs, we first show that two compatible molecular precursors with different sizes lead to GNR heterojunctions with atomically precise interfaces. In order to test predictions for how doped GNRs should behave, we synthesized B-doped GNRs with different doping concentrations on Au(111). Characterization of their electronic properties revealed a symmetry-dependent hybridization between the dopant states and the underlying Au substrate. We also describe our efforts to synthesize N=11 armchair GNRs through sp3-to-sp2 conversion of carbon atoms. In the case of 2D COFs, we first show that formation of imine linkages within COF366-OMe causes a downshift in the frontier orbital energy of porphyrin cores due to the electron-withdrawing characteristics of imine bonds. We then demonstrate the ability to achieve a 2D lattice of type II heterojunctions through judicious choice of molecular precursors that result in an asymmetrical bonding scheme within a 2D COF.

Our studies show that on-surface synthesis can lead to the realization of target nanostructures that are unreachable via solution-based methods, as demonstrated by intra-molecular reactions that lead to new “nano-graphene” species.

In the field of solar thermochemical energy storage, ammonia synthesis/dissociation is feasible for practical use in the concentrating solar power industry. In ammonia-based solar thermochemical energy storage systems, the stored energy is released when the hydrogen (H2) and nitrogen (N2) react exothermically to synthesize ammonia (NH3), providing thermal energy to a power block for electricity generation. But ammonia synthesis has not yet been shown to reach temperatures consistent with the highest performance modern power blocks (~650 °C). The following dissertation addresses an ongoing investigation into the field of ammonia based thermochemical energy storage.

In the first part of the dissertation, the state of the art of Concentrating Solar Power (CSP) and Thermochemical Energy Storage (TCES) are reviewed. In the second part, a two-dimensional model is proposed to simulate heating supercritical steam in an ammonia synthesis reactor. Thirdly, the model is validated as the model predicted temperature profiles match with experimental measured results well. A sensitivity analysis is carried out for the model to study the effects of six input parameters on heat transfer and reaction kinetics. The results show the process is “heat-transfer-limited” and most sensitive to activation energy. The process is also very sensitive to inlet ammonia mass fraction. Improving heat transfer and decreasing inlet ammonia mass fraction are crucial to improve the capability of the reactor to heat steam. In the fourth part, some preliminary designs for ammonia synthesis systems are proposed. Parametric studies are made with the model for each component in the proposed systems. The systems are optimized and investigated to minimize the total tube wall volume per unit power. The result shows that improving heat transfer by small dimensions and subdividing the reactor into different sections for different steam temperature ranges are good for minimizing the tube wall volume for the system. Also, it is necessary to optimize the entire system simultaneously since the wall volume for each component is comparable. At last, a future study plan for model improvement and system optimization is proposed.

The overarching goal of this study was to systematically investigate how engineered particles behave in engineered filters under a range of relevant solution chemistry conditions. Specifically, the approach was to conduct a combination of fundamental and applied experiments, looking at engineered particles transport in idealized conditions, followed by those simulating actual scenarios in the filtration stage of drinking water treatment. It was confirmed that the leading factors in engineered particles destabilization which leads to their removal include the type and concentrations of salts in solution, and the process operating conditions (ionic strength and coagulant residual). Ultimately, through the systematic variation of these parameters in the proposed micromodel experiments described below, the conditions for optimal engineered particles destabilization and removal was determined.

This dissertation work has allowed for the following observations. In the 2D micromodel, the removal efficiency of latex nanoparticles and food grade TiO2 in filtration is sensitive to the particle aggregate size, surface charge, and surface composition. The model was built to show single collector removal efficiency as a function of particle size and ionic strength, as well as predict the behavior or deposition location on collector of any nanoparticles entering the filtration system in order to improve the field of environmental nanotechnology. Furthermore, the predictions generated from the present work parallel those of the constricted 3D model, for instance, the collector size and average velocity. Ultimately, this research could be applied in place of 3D columns when designing filters for water and wastewater treatment.

Finally, the role of coagulant residual, TiO2 structure, and solution chemistry on the removal efficiency were studied as well in simulated water (AGW and ASW). Results from this study indicate that for all TiO2 suspensions, the greater coagulant residual concentrations increased the removal efficiency up until 0.5 mg/L alum, above that threshold the effect of coagulant residual were negligible. This collection of studies provides critical insights into the importance of understanding particles size and coagulant residual concentrations more impactful and in realistic environments. These studies demonstrate the need to update more tests such that they more

accurately reflect real exposure scenarios simulating environmental conditions.

This dissertation is concerned with the design of branch-and-cut algorithms for a variety of nonconvex nonlinear problems pertaining to power systems operations and planning. By understanding the structure of specific problems, we can leverage powerful commercial optimization solvers designed for convex optimization and mixed-integer programs. The bulk of the work concerns the Alternating Current Optimal Power Flow (ACOPF) problem. The ACOPF problem is to find a minimum cost generation dispatch that will yield flows that can satisfy demand as well as various engineering constraints. A standard formulation can be posed as a nonconvex Quadratically Constrained Quadratic Program with complex variables. We develop a novel spatial branch-and-bound algorithm for generic nonconvex QCQP with bounded complex variables that relies on a semidefinite programming (SDP) relaxation strengthened with linear valid inequalities. ACOPF-specific domain reduction or bound tightening techniques are also introduced to improve the algorithm's convergence rate. We also introduce second-order conic valid inequalities so that any SDP can be outer-approximated with conic quadratic cuts and test the technique on ACOPF. Another application is the incorporation of convex quadratic costs in unit commitment, which is a multi-period electric generation scheduling problem. We show that conic reformulation can both theoretically and practically improve performance on this mixed-integer nonlinear problem. We conclude with methods for approximating a mixed-integer convex exponential constraint. Applications include capital budgeting, the system reliability redundancy problem, and feature subset selection for logistic regression.

Rural-urban migration in China has long been recognized as circular migration. However, few studies have systematically reviewed when rural workers migrate, what factors affect the length of migration, when they return, if they migrate again, how often they circulate over their life cycle, or how circularity has changed in the past 30 years. This dissertation investigates these questions using a longitudinal dataset from two counties in Anhui province.

The empirical analysis shows that over the past 30 years, more and more rural workers have participated in rural-urban migration. Although migrants have circulated less often since 2000, circular migration has long been and continues to be a major form of rural-urban migration in China. Age, gender, generation, education level and marital status all affect the frequency of circularity and the direction of migration. Frequency of circularity at first increases by age, then decreases. Male workers are less likely to circulate and they tend to spend more time away from their home towns (“outside”) than female workers. Mid and new-generation rural workers are more likely to move and spend more time outside, and they circulate less often than the old-generation rural workers. The location of family members affects men and women differently. Although having more children in the home town (“inside”) reduces the probability of moving outside for both men and women, women are affected more than men. Once a man has moved outside, the more children he has inside, the less likely he will return. However, having more children inside encourages a female migrant to return. Having parents inside reduces the frequency of circulation and encourages migrants to stay outside longer. It also increases the probability that women will initiate migration.

Regression models show that having a high quality house encourages migrants to return, and this effect exists across generations, despite the fact that younger generations of migrants now spend more time in cities than in the countryside. I use a case study of a village (“Y1”) to understand why rural houses are important to migrant workers and their families, and thus to further interpret the relationship between migration, circularity, and settlement. I find that demographic changes caused by migration and the state birth planning policy have contributed to migrant workers’ enthusiasm for building large houses in the countryside. Although new-generation migrant workers do not have agricultural work experience and are not interested in agriculture, rural areas are still important to this generation because these areas provide affordable housing, family support, and future development opportunities. As a result, circular migration can be expected to continue in China.

In the context of China’s rural-urban geography and socioeconomic structure, circulation allows migrant workers to take advantage of different opportunities and resources in both cities and the countryside. Thus, for rural-urban migrants, permanent migration to a city may not be optimal or inevitable. These findings have implications for policy makers, especially policy makers concerned with hukou reforms.