<p> The nematic phases of liquid crystals have been the most thoroughly investigated since the founding of the liquid crystal field in the early 1900&rsquo;s. The resulting technologies, most notably the liquid crystal display, have changed our world and spawned an entire industry. Consequently, the recent identification of a new type of nematic &ndash; the twist-bend nematic &ndash; was met with as much surprise as excitement, as it melds the fluid properties and environmental responsiveness of conventional nematics with the intrinsic polarization and complex ordering of bent-core liquid crystals. I summarize the history of the twist-bend nematic phase, charting the development of our understanding from its first identification to the present day. Furthermore, I enumerate and highlight my own efforts in the field to characterize the behavior and nanoscale organization of the twist-bend phase.</p><p>

<p>Advances in technology and instrumentation open new windows for observing astrophysical objects. The first half of my dissertation involves the development of atomic layer deposition (ALD) coatings to create high reflectivity UV mirrors for future satellite astronomical telescopes. Aluminum (Al) has intrinsic reflectance greater than 80% from 90 ? 2,000 nm, but develops a native aluminum oxide (Al2O3) layer upon exposure to air that readily absorbs light below 250 nm. Thus, Al based UV mirrors must be protected by a transmissive overcoat. Traditionally, metal-fluoride overcoats such as MgF2 and LiF are used to mitigate oxidation but with caveats. We utilize a new metal fluoride (AlF3) to protect Al mirrors deposited by ALD. ALD allows for precise thickness control, conformal and near stoichiometric thin films. We prove that depositing ultra-thin (~3 nm) ALD ALF3 to protect Al mirrors after removing the native oxide layer via atomic layer etching (ALE) enhances the reflectance near 90 nm from ~5% to ~30%. X-ray detector technology with high readout rates are necessary for the relatively bright Sun, particularly during large flares. The hot plasma in the solar corona generates X-rays, which yield information on the physical conditions of the plasma. The second half of my dissertation includes detector testing, characterization and solar science with the Miniature X-ray Solar Spectrometer (MinXSS) CubeSats. The MinXSS CubeSats employ Silicon Drift Diode (SDD) detectors called X123, which generate full sun spectrally resolved (~0.15 FWHM at 5.9 keV) measurements of the sparsely measured, 0.5 ? 12 keV range. The absolute radiometric calibration of the MinXSS instrument suite was performed at the National Institute for Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility (SURF) and spectral resolution determined from radioactive sources. I used MinXSS along with data from the Geostationary Operational Environmental Satellites (GOES), Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Hinode X-ray Telescope (XRT), Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) and Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) to study the solar corona. This resulted in new insights on the coronal temperature distribution and elemental abundance variations for quiescence, active regions and during solar flares.

<p> Magnetic nanoparticles (NPs) have the potential to be useful in a variety of applications such as biomedical instruments, catalysis, sensing, recording information, etc. These nanoparticles exhibit remarkably different properties compared to their bulk counter parts. Synthesis of magnetic NPs with the right morphology, phase, size and surface functionality, as well as their usage for specific applications are challenging in terms of efficiency and safety. Morphology wise, there have been numerous reports on magnetic nanoparticles where morphologies such as core/shell, hollow, solid, etc., have been explored. It has been shown that morphology affects the magnetic response. Achieving the right crystal structure with required morphology and the magnetic behavior of the nanoparticle phases determines the magnetic response of the structure. For example, in the case of core/shell NPs various ferromagnetic (FM), ferrimagnetic (FiM), and antiferromagnetic (AFM) core and shell combinations have been reported. In these cases, interesting and strikingly different features, such as unusually high spin glass transition temperature, large exchange bias, finite size effects, magnetic proximity effects, unusual trend of blocking temperature as function of average crystal size, etc., have been reported.</p><p> More specifically, the morphology of core/shell nanoparticles provides added degrees of freedom compared to conventional solid magnetic nanoparticles, including variations in the size, phase and material of the core and shell of the particle, etc. which helps enhance their magnetic properties. Similar to traditional core/shell nanoparticles, inverted core/shell having a FiM or FM order above the Curie temperature (T_C) of the shell has been reported where the N&eacute;el temperature (T_N) is comparable with the bulk value and there is nonmonotonic dependence of the coercive field (H_C) and exchange bias (H_EB) on the core diameter. </p><p> In addition to the core/shell morphology, nanoparticles with hollow morphology are also of interest to the scientific community. For such cases, surface spin glass transition enhancements have been reported due to the presence of the additional inner surface. CoFe₂O₄, NiFe₂O₄ and &gamma;-Fe₂O₃ hollow nanoparticles exhibit strikingly contrasting magnetic behavior compared to bulk and conventional solid particles; similar behavior was also observed in core/shell nanoparticles. Structurally, hollow polycrystalline nanoparticles are composed of multiple crystallographic domains. This random orientation of the crystallographic domains also causes randomization of the local anisotropy axes. Hence the overall effect of this morphology on the magnetic properties is exhibited through the high coercivity, relatively high temperature magnetic irreversibility, lack of magnetic saturation, high blocking temperature, etc.</p><p> Over the years, extensive work on core/shell nanoparticles have been carried out to understand their exchange bias phenomenon and the effect on coercivity. Recently, focus has been given to hollow polycrystalline nanoparticles for the reason mentioned above. This thesis investigates the root cause for the above-mentioned effects on the coercivity and exchange bias. Since hollow nanoparticles with polycrystalline structure have shown to exhibit different and improved magnetic behavior compared to bulk and other conventional solid particles, they will be the focus of our investigation. First, extensive field and temperature dependent magnetic study on polycrystalline hollow nickel ferrite (NiFe₂O₄) have revealed the effect of the presence of inner surface in a single oxide nanoparticle. Second, the effect of having multiple oxides with different magnetic properties (i.e. FM and AFM) in a single nanoparticle, while maintaining a hollow morphology was investigated by studying polycrystalline hollow &gamma;-Mn₂O₃ and MnO nanoparticles. Studies on various conventional solid manganese oxide nanoparticles have already been reported. Therefore, focus was only made on the fabrication and magnetic study of hollow polycrystalline manganese oxide, with a comparison of the results to those from solid nanoparticles already available in literature. A conclusion was drawn to the importance of the coupling of different magnetic phases (i.e. FM and AFM, FiM and AFM, or SG and AFM), in contrast to just having one single oxide in the hollow nanoparticles. Finally, the importance of this coupling as compared to the increase of surface-to-volume ratio was evaluated in CoO/Co₃O₄/CoFe₂O₄ polycrystalline hollow nanoparticles by varying the AFM phase (CoO/Co₃O₄) in the nanoparticles and observing how the magnetic properties varied. This system helped address the effect of the coupling between different magnetic phases, super-exchange interaction, and proximity effect. </p><p>

To study stratospheric water vapor, a new trajectory model was created. The model is built from first principles specific to stratospheric motion and can run on any gridded dataset, making it more versatile than current solutions. The design of a new model was motivated by measurements of elevated stratospheric water vapor, which in situ isotopic measurements have determined to be tropospheric in origin. A moist stratosphere has substantial feedbacks in the climate system including radiative, chemical, and biological effects. Additionally, elevated stratospheric water vapor is theorized as an important coupling in the historical transition to the Eocene, 56 million years ago, as well as emergence from the Eocene 40 million years ago. This transition mirrors modern climate change, both in surface temperature and carbon dioxide increase. However, the historical transition became much more extreme and settled to a state of warm temperatures from the equator to the poles with little variation in between. The lack of latitudinal gradient in temperature is associated with a moist stratosphere, which provides additional motivation for thoroughly understanding the effects of adding water vapor to the stratosphere in a climatological context. The time evolution of water vapor enhancements from convective injection is analyzed by initializing trajectories over satellite-measured water vapor enhancements. The model runs show water vapor concentrations that remain elevated over the background concentrations for several days and often over a week, which is of the timescale that warrants concern over increased halogen catalyzed ozone loss and the subsequent risk to public health. By analyzing stratospheric winds during the summer months over North America using normalized angular momentum, a pattern of frequent stratospheric anticyclonic activity over North America emerges as a unique feature of the region. This provides a mechanism for the modeled persistent elevated water vapor and validates observations. In a climate like today's with increasing surface radiative forcing, the magnitude and frequency of convective injection may increase, with dramatic consequences on the climate system and human health. / Physics

The historical climate record is analyzed to determine trends and variability to develop possible scenarios for future climates. The study area is the Prescott-Russell United Counties and Stormont, Dundas and Glengarry United Counties of Eastern Ontario. Three data sets were used: the Canadian monthly climate data, the Historical Canadian Database Version 2: Monthly Rehabilitated Precipitation and Homogenized Temperature Data Sets and the Eastern Canada daily dataset. The ten warmest years of the past century occurred at the beginning and at the end of the century. However, the last decade (1990--1998) experienced four of the ten warmest years of the century, including the warmest year on record (1998), which was a full degree warmer than the second warmest (1953). Unlike the warmest year, the ten coldest years occurred in the early part of the century, between 1904--1943. The 1990s, although warm in the mean, had fewer extreme heat waves and fewer cold snaps. There is no clear relation between temperature and precipitation, suggesting that future climates may be wet or dry. From the mid 1960s to the present the growing season has started earlier, and since 1984 has been ending later than the long-term average. (Abstract shortened by UMI.)

This thesis examines the concentrations of persistent organic pollutants (POPs) in air and in selected lakes of the Canadian Rocky Mountains. Water was sampled from seven lakes spanning an elevation of 1430 meters from the Interior Plains to the Western Range of the Canadian Rocky Mountains. Air samples were taken at four of these sites, encompassing an altitudinal gradient of 1205 meters. Air and water samples were used to determine net air-water gas exchange fluxes of six POPs at these four sites. This study revealed that air and water concentrations of several persistent organic pollutants did not change significantly with elevation. However, spring pulses of hexachlorocyclohexanes (HCHs) in the lakes were found to coincide with snowmelt, and concentrations of POPs were highest at Bow Lake during the year with the highest snow pack. It was observed that temperature differences with altitude had little impact on the magnitude and direction of air-water gas exchange, indicating net fluxes of POPs were most sensitive to fluctuations in relative air and water concentrations. Air-water gas exchange was compared with the total lake inventory and with estimated losses by outflow. In general, it was revealed that deposition by air-water gas exchanges was an important source of POPs with lower Henry's law constants, such as alpha and gamma-HCH, and net volatilisation was an important loss for the compounds with higher Henry's law constants, (e.g. hexachlorobenzene (HCB) and dieldrin).

No description available.

In the Canadian High Arctic general patterns of temperature are poorly resolved at the meso-scale. This project addressed this issue in three stages. In the first stage a data set of non-standard weather observations was assembled and quality controlled The data set possessed approximately 58000 observations, including dry-bulb temperature, wind, visibility and cloud cover, from the spring and summer seasons of the years 1974--1993. Up to 10% of the data were unusable due to erroneous station information. The second part of the project consisted of a principal components analysis (PCA) of daily temperature data in the Canadian Arctic Archipelago (CAA). The PCA (1) demonstrated how the timing and extent of synoptic events could be tracked, (2) identified the major regional controls of temperature in the CAA, and (3) showed that the non-standard data exhibited general coherency with regional patterns yet were able to reveal zones of coherency at the meso-scale in temperature patterns. In the third stage of the project a model to estimate surface air temperature at the meso-scale was constructed, It was based on a 1 km resolution digital elevation model of the CAA. The effects on temperature due to site elevation and coastal proximity were selected for parameterization. The change in temperature with elevation was implemented in the model using derived environmental lapse rates. Advection effects were handled using resultant winds combined with air temperature above the ocean. Lapse rates and resultant wind estimates were obtained from upper air ascents. Model results for 14-day runs were compared to observed data. Residuals (n = 385) possessed a mean absolute error of 1.5&deg;C. The model was sensitive to steep surface inversions and to low-level warming. Sensitivity analyses were performed on the model to determine response to alterations in lapse rate calculation, sea surface temperature, and wind field generation. The model was most sensitive to lapse rate calculation. The lowest mean absolute error (0.2) was obtained using a moderate lapse rate calculation, moderate wind field and variable sea-surface temperature.

The evaluation of the model CANBEIS that allows the estimation of biogenic VOC emissions has been performed through various sensitivity analyses. Numerous simulations involving the variation of key parameters such as meteorological conditions were conducted and analyzed in comparison with the results from existing literature. Most of the time, there were similarities in the comparisons although in some cases, divergence brought up the consideration of re-assessment of some methodologies in the model. The impact of the terrain elevation on temperature and consequently on emissions, was also evaluated to determine its potential role in the model. This analysis, performed for the lower Fraser Valley in British Columbia, has confirmed that when terrain elevation was involved in the calculation of emissions, the latter indicated significant variations.

No description available.