Master of Science

thesisEcosystems provide many beneficial services to society, but their ability to provide these services will be influenced by climate change. Terrestrial vegetation sequesters significant amounts of carbon, but currently, human activity affects this storage. This research examines changes in vegetation and carbon flux patterns in the northwest United States and southwest Canada using the dynamic global vegetation model LPJ-GUESS. Regional and local simulations were conducted for modern and end-of-century 2.6 and 8.5 RCP scenarios. The results include estimates of changes in net ecosystem exchange and variations in different components of the carbon cycle, including fire activity. Regional net ecosystem exchange remained fairly consistent across the three scenarios, though the northern portion exhibited marked spatial heterogeneity of sink and source locations and the southern portion was highly homogeneous. Local simulations showed the effect of changing vegetation on fire activity. One site with consistent woody vegetation experienced little change in fire activity, while the other site experienced a shift from grass- to tree-dominant vegetation with simultaneous changes in fire. The results have implications for land management as they suggest which areas may release or sequester carbon under future climates due to changes in vegetation and other carbon flux components

High-Contrast 3.8 Micron Imaging Of The Brown Dwarf/Planet-Mass Companion to GJ 758

We present L' band (3.8 $\mu m$) MMT/Clio high-contrast imaging data for the nearby star GJ 758, which was recently reported by Thalmann et al. (2009) to have one -- possibly two-- faint comoving companions (GJ 758B and ``C", respectively). GJ 758B is detected in two distinct datasets. Additionally, we report a \textit{possible} detection of the object identified by Thalmann et al as ``GJ 758C" in our more sensitive dataset, though it is likely a residual speckle. However, if it is the same object as that reported by Thalmann et al. it cannot be a companion in a bound orbit. GJ 758B has a H-L' color redder than nearly all known L--T8 dwarfs. Based on comparisons with the COND evolutionary models, GJ 758B has T$_{e}$ $\sim$ 560 K$^{^{+150 K}_{-90K}}$ and a mass ranging from $\sim$ 10--20 M$_{J}$ if it is $\sim$ 1 Gyr old to $\sim$ 25--40 M$_{J}$ if it is 8.7 Gyr old. GJ 758B is likely in a highly eccentric orbit, e $\sim$ 0.73$^{^{+0.12}_{-0.21}}$, with a semimajor axis of $\sim$ 44 AU$^{^{+32 AU}_{-14 AU}}$. Though GJ 758B is sometimes discussed within the context of exoplanet direct imaging, its mass is likely greater than the deuterium-burning limit and its formation may resemble that of binary stars rather than that of jovian-mass planets.Comment: 14 pages, 3 figures. Accepted for publication in The Astrophysical Journal Letter

The Organizational Efficiency of Multiple Missions for Community Colleges

Community colleges are complex institutions serving a multitude of constituencies with dozens of programs and activities. Comprehensiveness has flourished since the 1970s, as the colleges steadily adopted more missions, and many community college advocates argue that the constant expansion of activities is a natural outcome of the community-based function of the colleges. But during the past two decades, academics and researchers have almost universally condemned the comprehensive model. Even some community college insiders have suggested that these institutions cannot accomplish their goals by trying to be all things to all people. Despite this backdrop of criticism, the accretion of activities continues unabated. The list of community college missions now goes well beyond the core degree-granting programs. Activities now include developmental education, adult basic education, English as a second language, education and training for welfare recipients and others facing barriers to employment, customized training for specific companies, preparation of students for industry certification exams, noncredit instruction in a bewildering plethora of areas (including purely avocational interests), small business development, and even economic forecasting

A Multiple Testing Approach to the Regularisation of Large Sample Correlation Matrices

This paper proposes a novel regularisation method for the estimation of large covariance matrices, which makes use of insights from the multiple testing literature. The method tests the statistical significance of individual pair-wise correlations and sets to zero those elements that are not statistically significant, taking account of the multiple testing nature of the problem. The procedure is straightforward to implement, and does not require cross validation. By using the inverse of the normal distribution at a predetermined significance level, it circumvents the challenge of evaluating the theoretical constant arising in the rate of convergence of existing thresholding estimators. We compare the performance of our multiple testing (MT) estimator to a number of thresholding and shrinkage estimators in the literature in a detailed Monte Carlo simulation study. Results show that our MT estimator performs well in a number of different settings and tends to outperform other estimators, particularly when the cross-sectional dimension, N, is larger than the time series dimension, T: If the inverse covariance matrix is of interest then we recommend a shrinkage version of the MT estimator that ensures positive definiteness

Intraclonal mating occurs during tsetse transmission of Trypanosoma brucei

<p>Abstract</p> <p>Background</p> <p>Mating in <it>Trypanosoma brucei </it>is a non-obligatory event, triggered by the co-occurrence of different strains in the salivary glands of the vector. Recombinants that result from intra- rather than interclonal mating have been detected, but only in crosses of two different trypanosome strains. This has led to the hypothesis that when trypanosomes recognize a different strain, they release a diffusible factor or pheromone that triggers mating in any cell in the vicinity whether it is of the same or a different strain. This idea assumes that the trypanosome can recognize self and non-self, although there is as yet no evidence for the existence of mating types in <it>T. brucei</it>.</p> <p>Results</p> <p>We investigated intraclonal mating in <it>T. b. brucei </it>by crossing red and green fluorescent lines of a single strain, so that recombinant progeny can be detected in the fly by yellow fluorescence. For strain 1738, seven flies had both red and green trypanosomes in the salivary glands and, in three, yellow trypanosomes were also observed, although they could not be recovered for subsequent analysis. Nonetheless, both red and non-fluorescent clones from these flies had recombinant genotypes as judged by microsatellite and karyotype analyses, and some also had raised DNA contents, suggesting recombination or genome duplication. Strain J10 produced similar results indicative of intraclonal mating. In contrast, trypanosome clones recovered from other flies showed that genotypes can be transmitted with fidelity. When a yellow hybrid clone expressing both red and green fluorescent protein genes was transmitted, the salivary glands contained a mixture of fluorescent-coloured trypanosomes, but only yellow and red clones were recovered. While loss of the <it>GFP </it>gene in the red clones could have resulted from gene conversion, some of these clones showed loss of heterozygosity and raised DNA contents as in the other single strain transmissions. Our observations suggest that many recombinants are non-viable after intraclonal mating.</p> <p>Conclusion</p> <p>We have demonstrated intraclonal mating during fly transmission of <it>T. b. brucei</it>, contrary to previous findings that recombination occurs only when another strain is present. It is thus no longer possible to assume that <it>T. b. brucei </it>remains genetically unaltered after fly transmission.</p

Design for sustainable behaviour: a quick fix for slower consumption?

The continuous replacement of durable consumer goods and disposal of functioning or repairable products into UK landfills or, increasingly, to developing countries, has resulted in global environmental and social consequences. Small appliances, which are easily disposed of in household waste, typically end up in UK landfills, are shipped to developing countries or otherwise ‘lost’. Very few are recycled or repaired, yet many are still functioning when disposed of. Consumers’ willingness, opportunity and ability to carry out repairs have historically been hampered by a range of complex factors. Design for Sustainable Behaviour (DfSB) aims to reduce the environmental and social impacts of products by moderating users’ interaction with them. This paper explores how DfSB strategies can be used to encourage a behavioural shift towards repair of small electrical household appliances by overcoming identified barriers. The paper pulls together literature on repair practice, highlighting gaps in current knowledge and outlines the findings of an extensive UK household survey focused on both product breakage rates and consumer mending behaviour. Three mending typologies and associated personas resulting from the analysis are combined with three DfSB strategies to develop conceptual design interventions to encourage repair. The paper concludes with a discussion of the potential efficacy of the design outcomes from a consumer perspective and the potential ramifications for design practice, whilst considering the wider influences on repair practices beyond design and how these may be addressed

The use of yellow fluorescent hybrids to indicate mating in Trypanosoma brucei

<p>Abstract</p> <p>Background</p> <p><it>Trypanosoma brucei </it>undergoes genetic exchange in its insect vector, the tsetse fly, by an unknown mechanism. The difficulties of working with this experimental system of genetic exchange have hampered investigation, particularly because the trypanosome life cycle stages involved cannot be cultured in vitro and therefore must be examined in the insect. Searching for small numbers of hybrid trypanosomes directly in the fly has become possible through the incorporation of fluorescent reporter genes, and we have previously carried out a successful cross using a reporter-repressor strategy. However, we could not be certain that all fluorescent trypanosomes observed in that cross were hybrids, due to mutations of the repressor leading to spontaneous fluorescence, and we have therefore developed an alternative strategy.</p> <p>Results</p> <p>To visualize the production of hybrids in the fly, parental trypanosome clones were transfected with a gene encoding Green Fluorescent Protein (GFP) or Red Fluorescent Protein (RFP). Co-infection of flies with red and green fluorescent parental trypanosomes produced yellow fluorescent hybrids, which were easily visualized in the fly salivary glands. Yellow trypanosomes were not seen in midgut or proventricular samples and first appeared in the glands as epimastigotes as early as 13 days after fly infection. Cloned progeny originating from individual salivary glands had yellow, red, green or no fluorescence and were confirmed as hybrids by microsatellite, molecular karyotype and kinetoplast (mitochondrial) DNA analyses. Hybrid clones showed biparental inheritance of both nuclear and kinetoplast genomes. While segregation and reassortment of the reporter genes and microsatellite alleles were consistent with Mendelian inheritance, flow cytometry measurement of DNA content revealed both diploid and polyploid trypanosomes among the hybrid progeny clones.</p> <p>Conclusion</p> <p>The strategy of using production of yellow hybrids to indicate mating in trypanosomes provides a robust and unequivocal system for analysis of genetic exchange. Mating occurred with high frequency in these experimental crosses, limited only by the ability of both parental trypanosomes to invade the salivary glands. Yellow hybrids appeared as soon as trypanosomes invaded the salivary glands, implicating the short, unattached epimastigote as the sexual stage. The recovery of diploid, triploid and tetraploid hybrids in these crosses was surprising as genetic markers appeared to have been inherited according to Mendelian rules. As the polyploid hybrids could have been produced from fusion of unreduced gametes, there is no fundamental conflict with a model of genetic exchange involving meiosis.</p