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Ferroelectric materials are widely used in different applications which are related to their dielectric properties. While dielectric properties of ferroelectric materials at radio frequencies are largely explored, only a few attempts have been made to use THz radiation to research ferroelectrics to understand their high frequency dielectric behaviour and to accelerate the discovery of new applications of ferroelectrics. Here, ferroelectrics with different structures and applications are selected to research their dielectric behaviour at THz band. The selected materials are Bi0.5Na0.5TiO3; Aurivillius phase ABi2Nb2O9 (A=Ca or Ba), Dion Jacobson phase RbBi2Ti2NbO10 and La2Ti2O7, which are good for energy storage, memory application, photocatalytic and piezoelectric sensors, respectively. In particular, high intensity THz pump and low intensity THz probe were used to study the polarization dynamics Bi0.5Na0.5TiO3 ceramic. The high-energy THz pulses induced an ultrafast field-induced phase transition from a weakly polar phase (Cc) to a strongly polar phase (R3c) within 20 ps at 200 K in Bi0.5Na0.5TiO3, which opens a possibility to develop devices with ultrafast switching behaviour. Dielectric properties of unpoled and poled ABi2Nb2O9 show that the dynamics of domain walls are different at kHz and THz frequencies. At low frequencies, domain walls work as a group to increase dielectric permittivity. At THz frequencies, the defective nature of domain walls serves to lower the overall dielectric permittivity, which directly leads a demonstration on dielectric switching memory concept at THz. The similar physical mechanism of domain walls was further confirmed in RbBi2Ti2NbO10 which shows interesting photocatalytic behaviour due to its ferroelectric nature and incorporated tungsten carbide (WC) co-catalyst. Dielectric properties of La2Ti2O7 single crystal were also characterized from 1 kHz to 1 THz along one single direction. The decrease in dielectric permittivity with increasing frequency is related to dielectric relaxation from radio frequency to microwave then to terahertz band.

Temperate tree species exhibit seasonal growth cycling, and the timing of such transition varies with local climate. Under anthropogenic climate change, the local pattern of growth and dormancy in tree populations is expected to become uncoupled with shifting seasonal environmental signals, particularly temperature. Thus, an understanding of the genetic underpinnings of local adaptation is key to predicting the fate of tree populations in the future. In this thesis, we coupled sampling of range-wide natural accessions of P. trichocarpa with adaptive trait phenotyping and genome-wide genotyping to uncover relationships between genotype, phenotype, and environment. We detected strong correlations between adaptive phenotypes, climate, and geography, which suggested climatic selection driving adaptation of these populations to local environments. We subsequently combined genotype-phenotype association tests with sliding window analysis and identified regions strongly associated with these adaptive traits. We also compared adaptive markers identified in two independent GWAS on samples across latitude and altitude transects and found a set of associated variants shared across both transects. We further scanned the genome with three selection tests to identify regions showing evidence of recent positive and divergent selection. By comparing candidate selection regions across altitude and latitude, we detected a set of overlapping regions showing differentiation across gradients of the same climate variables. We validated the functional imortance of these selection regions by combining GWAS and showed that selection regions contain a strong signature of phenotypic associations. We also studied the distribution of deleterious allels across genome and natural populations, and found that deleterious alleles preferentially accumulate in regions of low recombination and hithihking regions. Finally, marginal populations contained more deleterious alleles compared with central populations, which is likely due to ineffective selection in small populations and recent bottlenecks associated with postglacial recolonization. These findings provide new insights into the genomic architecture underlying climatic adaptation and how selection drives adaptive evolution of tree species.

Chlorinated solvents, such as trichloroethylene (TCE), are potent carcinogens and have been found in soil and groundwater at thousands of National Priorities List sites in the U.S. To facilitate in-situ chlorinated solvents remediation, a new class of stabilized zero valent iron nanoparticles was prepared using carboxymethyl cellulose (CMC) as a stabilizer. This study reported that CMC stabilized Fe-Pd nanoparticles could effectively degrade TCE sorbed on two model soils. Soil sorption can limit the rate and extent of the dechlorination reaction especially for organic matter-rich soils. Dissolved orgaic matter (DOM) can inhibit the degradation rate. Anionic surfactant SDS could aid in overcoming these limitations, however, its effectiveness would depend on soil type and dosage. The transport behavior of CMC-stabilized ZVI was investigated. CMC-stabilized ZVI nanoparticles can be delivered into porous media even with 200 mg/L Ca2+. The presence of 40~80 mg/L DOM as total organic carbon (TOC) had insignificant effect on breakthrough profiles of the nanoparticles, whereas metal oxides on sand grains (4.1 mg-Fe/g and 3.6 mg-Al/g) increased particle deposition by approximately 10%. A revised transport model was developed to simulate the breakthrough profiles and to evaluate the respective effects of adsorption and filtration on transport of ZVI nanoparticles. A field test of the in-situ remediation technology was conducted at the Hill Air Force Base site in Utah. The results confirmed the soil deliverability and dechlorination reactivity of CMC-stabilized Fe-Pd nanoparticles. The nanoparticles were able to be delivered at least five feet down-gradient of the injection well. Following the nanoparticles injection, rapid TCE degradation and elevated degradation products, such as ethane and ethene, were observed in the groundwater. To facilitate application of nanoscale Pd catalysts for water treatment uses, we developed and characterized a new class of supported Pd catalyst by immobilizing CMC-stabilized Pd nanoparticles on three support materials (alumina, Ambersorb 572 and Titanium-Silicalite (TS-1)). The alumina-supported Pd nanoparticles could facilitate rapid and complete hydrodechlorination of TCE. The strong adsorption of TCE and carbon contamination on Ambersorb-572 resulted in much diminished activity. TS-1 could offer superior catalytic performance, suggesting that a support of modest hydrophobicity is in favor of TCE hydrodechlorination.

This work includes biochemistry studies on yeast FMO and structure analysis on a prokaryotic protein disulphide isomerase - H. influenzae DsbC. The yeast FMO (yFMO) gene was cloned, expressed and characterized in this lab previously. Deletion experiments suggested that yFMO was involved in folding proteins with disulfide bonds. In continuation of study on yeast FMO, we detected two nucleotide errors in the GenBank sequences of the yFMO gene. These errors had been incorporated into the initial gene engineering, and as a consequence, the protein studied initially is a truncated version of yFMO. To be consistent with previous work, the N-terminal his-tagged full-length yFMO was compared to the truncated enzyme in vitro. Using an oxygen uptake assay, the full-length and the truncated FMOs showed similar pH profiles, Km, Kcat and Vmax values using glutathione as a substrate, indicating that they share similar enzymatic character. Therefore, we conclude that the hypotheses proposed earlier concerning the enzyme’s functions are likely to be still valid for the full-length yeast FMO. The second project aimed for determining the structures of DsbC from several species using X-ray crystallography to improve our knowledge on the structure-function relationship of DsbC, and subsequently provide guidance for engineering DsbC to improve E. coli as a better protein expression system for proteins with multiple disulphide bonds. DsbC proteins from Haemophilus influenzae, Pseudomonas aeruginosa, Erwinia chrysanthemi, Vibrio cholerae and Yersinia pseudotuberculosis were subjected to crystallization efforts, but only crystals of DsbC from H. inf and Y.pse have been obtained. A data set at the resolution of 2.5 Å was collected from a single H. inf DsbC crystal. Molecular replacement strategy was applied, using the known structure of E. coli DsbC, to solve the structure of H. inf DsbC. Due to a flexible protein conformation, many residue side chains in the N-terminal domain of the current structural model are missing. Comparison between the current H. inf DsbC model and E. coli DsbC structure shows that the H. inf DsbC has a similar catalytic domain and a larger, more open cleft within the V-shaped dimer.