abstract: In the upcoming decade, powerful new astronomical facilities such as the James Webb Space Telescope (JWST), the Square Kilometer Array (SKA), and ground-based 30-meter telescopes will open up the epoch of reionization to direct astronomical observation. One of the primary tools used to understand the bulk astrophysical properties of the high-redshift universe are empirically-derived star-forming laws, which relate observed luminosity to fundamental astrophysical quantities such as star formation rate. The radio/infrared relation is one of the more mysterious of these relations: despite its somewhat uncertain astrophysical origins, this relation is extremely tight and linear, with 0.3 dex of scatter over five orders of magnitude in galaxy luminosity. The effects of primordial metallicities on canonical star-forming laws is an open question: a growing body of evidence suggests that the current empirical star forming laws may not be valid in the unenriched, metal-poor environment of the very early universe. In the modern universe, nearby dwarf galaxies with less than 1/10th the Solar metal abundance provide an opportunity to recalibrate our star formation laws and study the astrophysics of extremely metal-deficient (XMD) environments in detail. I assemble a sample of nearby dwarf galaxies, all within 100 megaparsecs, with nebular oxygen abundances between 1/5th and 1/50th Solar. I identify the subsample of these galaxies with space-based mid- and far-infrared data, and investigate the effects of extreme metallicities on the infrared-radio relationship. For ten of these galaxies, I have acquired 40 hours of observations with the Jansky Very Large Array (JVLA). C-band (4-8 GHz) radio continuum emission is detected from all 10 of these galaxies. These represent the first radio continuum detections from seven galaxies in this sample: Leo A, UGC 4704, HS 0822+3542, SBS 0940+544, and SBS 1129+476. The radio continuum in these galaxies is strongly associated with the presence of optical H-alpha emission, with spectral slopes suggesting a mix of thermal and non-thermal sources. I use the ratio of the radio and far-infrared emission to investigate behavior of the C-band (4-8 GHz) radio/infrared relation at metallicities below 1/10th Solar. I compare the low metallicity sample with the 4.8 GHz radio/infrared relationship from the KINGFISHER nearby galaxy sample Tabatabaei et al. 2017 and to the 1.4 GHz radio/infrared relationship from the blue compact dwarf galaxy sample of Wu et al. 2008. The infrared/radio ratio q of the low metallicity galaxies is below the average q of star forming galaxies in the modern universe. I compare these galaxies' infrared and radio luminosities to their corresponding Halpha luminosities, and find that both the infrared/Halpha and the radio/H-alpha ratios are reduced by nearly 1 dex in the low metallicity sample vs. higher metallicity galaxies; however the deficit is not straightforwardly interpreted as a metallicity effect. / Dissertation/Thesis / Doctoral Dissertation Astrophysics 2019

No study has been done in the western United States concerning dispersal of dwarf mistletoe by mammals. At the outset of the study it was determined that the red squirrel, the yellow pine chipmunk (Eutamias amoenus), the northern flying squirrel, and the bushy-tailed wood rat (Neotaoma cinerea), were all potential vectors of seeds. The red squirrel was chosen as the main object of study because it is diurnal and is closely associated with ponderosa pine (Pinus ponderosa), a heavily infected species. The study was undertaken to determine whether small mammals play a significant role in transporting mistletoe seeds to uninfected areas. Understanding their role can be helpful both in further understanding of the biology of dwarf mistletoe and in evaluating current control practices.

Cytokinin levels were determined by bioassay on a seasonal basis, for two species of dwarf mistletoes (Arceuthobium douglasii and Arceuthobium tsugense) and their respective hosts, Douglas-fir (pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). The highest cytokinin levels occurred in early Spring for all of the samples studied. However, with the exception of the first growth segments of Douglas-fir, the levels of cytokinins detected were significantly greater in infected tissue and aerial shoots of the mistletoe than in the healthy tissue. Further studies were carried out on Spring and Winter samples to determine the kinds of cytokinins present. High performance thin layer chromatography and gas liquid chromatography results showed that zeatin riboside (ZR) was the only detectable cytokinin in Winter samples. ZR was also detected in all Spring samples excepting the aerial shoots of A. douglasii. Two other cytokinins were also detectable in Spring samples. Zeatin was present in aerial shoots from both dwarf mistletoes and in the infected fifth growth segments from Douglas-fir and in infected western hemlock tissue. Zeatin occurred in the healthy tissue only in first growth segments of Douglas-fir. The 2iPA was detectable in the aerial shoots of the dwarf mistletoe, in the fifth grmvth segments of Douglas-fir, and in the infected tissue from western hemlock. These results are discussed with particular reference to the role of cytokinins in the physiological interactions between the host and the parasite.

Germination, respiration, and photosynthesis in seeds of dwarf mistletoe (Arcenthobium) were studied. The effects of 1 hour soakings of seeds in aqueous solutions of 1, 2, or 3% H2O2 or 1, 2, 3, 4, or 5% Chlorox on germination of seeds were tested. Germination rates for seeds from three consecutive years (1975-1977) were obtained. Germination rates varied widely. This variance transcended subtle changes in treatment. Pretreatment of seeds with Chlorox resulted in significantly lower germination rates than those of the control. Chlorophyll concentrations were determined for seeds and aerial shoot tissue of four species. Seeds of A. douglasii had the highest chlorophyll concentration (0.39 mg/g fresh weight) while seeds of A. tsugense had the lowest concentration (0.25 mg/g fresh weight). Net O2 uptake by seeds of A. campylopodum in dark and in light was measured by manometric and polarographic methods. The mean values were 353 μl O2 g-1 h-1 in the dark and 201 O2 g-1 h-1 in the light. The difference between these rates is apparently due to O2 evolution during photosynthesis. In light the seeds can fix 43% of the CO2 produced by respiration. Experiments in which seeds were exposed to 14CO2 in light confirmed that the seeds are able to fix CO2. Extraction of seeds with ethanol showed that 97-99% of the incorporated 14C was ethanol soluble. Ten to sixteen percent of the ethanol fraction was chloroform soluble while the rest was H2o soluble. Ion exchange separation of the H2o phase showed that 11-25% of 14C activity was cationic, 15-29% anionic, and 53-67% neutral.

The goal of this investigation was to determine the potential of birds as vectors for the movement of dwarf mistletoe seeds and the means by which such movement could occur. Birds would greatly speed the rate at which these parasites move horizontally or vertically through the forest. Five areas in Oregon, heavily infected by six species of Arceuthobium were studied. Observations of avian behavior point to 13 species whose general behavior make them potential vectors in the distribution of these parasites. More specifically, the roosting and subsequent bathing behavior of most forest birds proves a very important means of potential seed transport. Additionally, an examination of nesting materials revealed that birds bring viable dwarf mistletoe seeds to infectible portions of host trees during the construction of their nests. Nesting, however, seems the least important of the vector mechanisms discussed. I observed no evidence of birds feeding on the seeds of dwarf mistletoe or of seeds being present in their droppings. The more probably means of seed transport is one of epizoochory.

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<p> The radiation balance of a dwarf apple orchard was evaluated. Results compared favourably with those for a single apple tree in an earlier investigation. Reflection, heating and longwave exchange coefficients were analysed. </p> <p> Transmitted global radiation was measured with moving and stationary sensors. Coefficients for the partitioning of incident global radiation were calculated. A relationship between photosynthetically active radiation and global radiation was established. Coefficients for the partitioning of incident photosynthetically active radiation were obtained and compared to the global radiation components. A problem associated with the measurement of transmitted radiation is discussed briefly. </p> / Thesis / Master of Science (MSc)

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No description available.