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Search Results: 1 - 10 of 93786 matches for " Matthew W. Turnbull "
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Quantitative analysis of hemocyte morphological abnormalities associated with Campoletis sonorensis parasitization
Matthew W. Turnbull,Stacy B. Martin,Bruce A. Webb
Journal of Insect Science , 2004,
Abstract: Endoparasitoids of arthropods evoke host cellular immune responses that result in hemocytic encapsulation of the endoparasitoid, unless these responses are disrupted by the parasite. Our interest has focused on mutualistic viruses found in some hymenopteran endoparasitoids that disrupt hemocyte function and prevent encapsulation. Specifically, the Campoletis sonorensis polydnavirus interacts with wasp factors to suppress immunity via expression of intracellular and secreted viral proteins. To study the roles of specific parasitization-associated factors on immunocyte morphology, fluorescence microscopy was used to visualize the actin cytoskeleton in infected and uninfected cells, or after treatment with C. sonorensis ovarian proteins or plasma from infected larvae. The titer and distribution of F- and G-actin were altered in hemocytes from parasitized insects relative to control cells, with plasma from parasitized larvae having an intermediate effect. This suggests that intracellular and secreted factors contribute to suppression of cellular immune responses in C. sonorensis.
Benzyne arylation of oxathiane glycosyl donors
Martin A. Fascione,W. Bruce Turnbull
Beilstein Journal of Organic Chemistry , 2010, DOI: 10.3762/bjoc.6.19
Abstract: The arylation of bicyclic oxathiane glycosyl donors has been achieved using benzyne generated in situ from 1-aminobenzotriazole (1-ABT) and lead tetraacetate. Following sulfur arylation, glycosylation of acetate ions proceeded with high levels of stereoselectivity to afford α-glycosyl acetates in a ‘one-pot’ reaction, even in the presence of alternative acceptor alcohols.
Utilising polyphenylene oxide for high exposure solar UVA dosimetry
D. J. Turnbull,P. W. Schouten
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: Researchers at the University of Southern Queensland have developed a personal UV dosimeter that can quantitatively assess high exposure solar UVA exposures. The chemical polyphenylene oxide has been previously reported on its ability to measure high UVB exposures. This current research has found that polyphenylene oxide, cast in thin film form, is responsive to both the UVA and UVB parts of the solar spectrum. Further to this, the UVB wavelengths were filtered out with the use of mylar. This combined system responded to the UVA wavelengths only and underwent a change in optical absorbance as a result of UVA exposure. Preliminary results indicate that this UVA dosimeter saturates steadily when exposed to sunlight and can measure exposures of more than 20 MJ/m2 of solar UVA radiation with an uncertainty level of no more than ±5%.
Utilising polyphenylene oxide for high exposure solar UVA dosimetry
D. J. Turnbull,P. W. Schouten
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: A personal UV dosimeter that can quantitatively assess high exposure solar UVA exposures has been developed. The chemical polyphenylene oxide has been previously reported on its ability to measure high UVB exposures. This current research has found that polyphenylene oxide, cast in thin film form, is responsive to both the UVA and UVB parts of the solar spectrum. Further to this, the UVB wavelengths were filtered out with the use of mylar. This combined system responded to the UVA wavelengths only and underwent a change in optical absorbance as a result of UVA exposure. Preliminary results indicate that this UVA dosimeter saturates steadily when exposed to sunlight and can measure exposures of more than 20 MJ/m2 of solar UVA radiation with an uncertainty level of no more than ±5%.
Bias of the Random Forest Out-of-Bag (OOB) Error for Certain Input Parameters  [PDF]
Matthew W. Mitchell
Open Journal of Statistics (OJS) , 2011, DOI: 10.4236/ojs.2011.13024
Abstract: Random Forest is an excellent classification tool, especially in the –omics sciences such as metabolomics, where the number of variables is much greater than the number of subjects, i.e., “n << p.” However, the choices for the arguments for the random forest implementation are very important. Simulation studies are performed to compare the effect of the input parameters on the predictive ability of the random forest. The number of variables sampled, m-try, has the largest impact on the true prediction error. It is often claimed that the out-of-bag error (OOB) is an unbiased estimate of the true prediction error. However, for the case where n << p, with the default arguments, the out-of-bag (OOB) error overestimates the true error, i.e., the random forest actually performs better than indicated by the OOB error. This bias is greatly reduced by subsampling without replacement and choosing the same number of observations from each group. However, even after these adjustments, there is a low amount of bias. The remaining bias occurs because when there are trees with equal predictive ability, the one that performs better on the in-bag samples will perform worse on the out-of-bag samples. Cross-validation can be performed to reduce the remaining bias.
Quantification of drought tolerance in Ethiopian common bean varieties  [PDF]
Asrat Asfaw, Matthew W. Blair
Agricultural Sciences (AS) , 2014, DOI: 10.4236/as.2014.52016
Abstract:

Understanding the level of drought tolerance of the varieties available in each country is of paramount importance for breeding common bean for drought adaptation. The goal of this study was to evaluate 25 common bean genotypes of which 24 were released/recommended varieties for production by farmers and one was a drought tolerant check. The genotypes were planted at two sites in Ethiopia, Hawasssa and Amaro, using variable sowing dates, one that was early to avoid drought and one that was late to expose the crop to drought. The experiments were repeated over two years in Hawassa and one year in Amaro. This resulted in treatments with high and low total seasonal rainfall and six environments for analysis. The impact of drought stress on the trait expression of the varieties was not uniform across traits assessed and varieties tested. The effect of drought on photosynthate translocation and partitioning traits was much greater than on yield component traits in the varieties studied. This indicating less breeding efforts has been made in improving the varieties ability to mobilize photosynthate to the developing grain as compared to the yield component traits. Drought tolerant varieties like Hawassa Dume maintained better photosynthate translocation and partitioning than the drought sensitive varieties like Brown Speckled bean. Hawassa Dume also showed better yield stability and performed well under both drought stress and nonstress conditions. Our results indicate the relevance of high levels of photosynthate translocation and partitioning as an effective selection objective for improving drought tolerance in common bean. The information generated on the drought tolerance of the available varieties should help in the design of a breeding strategy that incorporates adaptation traits with commercial characteristics preferred by common bean farmers for varieties to be grown in diverse environments.

Gene pyramiding as a Bt resistance management strategy: How sustainable is this strategy?
W Manyangarirwa, M Turnbull, GS McCutcheon, JP Smith
African Journal of Biotechnology , 2006,
Abstract: Reports on the emergence of insect resistance to Bacillus thuringiensis delta endotoxins have raised doubts on the sustainability of Bt-toxin based pest management technologies. Corporate industry has responded to this challenge with innovations that include gene pyramiding among others. Pyramiding entails stacking multiple genes leading to the simultaneous expression of more than one toxin in a transgenic variety. Questions have been raised on the sustainability of gene pyramiding since the use of insecticide mixtures has shown that cross resistance and/or multiple resistance can render such strategies to be less effective in the long term. Current theoretical and practical evidence in insect population genetics suggest that gene pyramiding cannot be sustained as a resistance management strategy per se. Pyramiding is useful as a strategy to broaden the range of insect pests controlled in each transgenic variety, and it still has to be deployed in tandem with Bt resistance management strategies such as crop refugia, biological pest control, temporal and spatial crop rotations among others
Leaders as Distinction Generators  [PDF]
Wiley W. Souba, Matthew H. Souba
Open Journal of Leadership (OJL) , 2018, DOI: 10.4236/ojl.2018.72008
Abstract: In this article, we describe and illustrate, by way of examples, an important, though often underappreciated, role of leaders: a distinction generator. In the context of leadership, the idea of a distinction is to be understood as something someone says (spoken) or does that uncovers (discloses) for others a way of “seeing” an issue or a challenge that was previously imperceptible or unavailable. Distinctions, which are linguistic in nature, are crucial communication vehicles because they can evoke new ways of sense-making, thereby motivating others to change the way in which they talk, behave, and work together. In doing so, distinctions, by virtue of enabling us to see things in another light, become framing lenses (contexts) from and through which we live our lives differently. Distinctions, which are especially powerful during times of change and uncertainty, need not be grandiose inspirational elocutions; in fact, most are little “d” distinctions but this in no way lessens their potential for opening up and making available a new prospects for being and acting. In this sense, everyone, whether they have titular authority or not, can, simply by what they say, inspire others to put their best foot forward.
A Comparison of Various Normalization Methods for LC/MS Metabolomics Data  [PDF]
Jacob E. Wulff, Matthew W. Mitchell
Advances in Bioscience and Biotechnology (ABB) , 2018, DOI: 10.4236/abb.2018.98022
Abstract: In metabolomics data, like other -omics data, normalization is an important part of the data processing. The goal of normalization is to reduce the variation from non-biological sources (such as instrument batch effects), while maintaining the biological variation. Many normalization techniques make adjustments to each sample. One common method is to adjust each sample by its Total Ion Current (TIC), i.e. for each feature in the sample, divide its intensity value by the total for the sample. Because many of the assumptions of these methods are dubious in metabolomics data sets, we compare these methods to two methods that make adjustments separately for each metabolite, rather than for each sample. These two methods are the following: 1) for each metabolite, divide its value by the median level in bridge samples (BRDG); 2) for each metabolite divide its value by the median across the experimental samples (MED). These methods were assessed by comparing the correlation of the normalized values to the values from targeted assays for a subset of metabolites in a large human plasma data set. The BRDG and MED normalization techniques greatly outperformed the other methods, which often performed worse than performing no normalization at all.
The Latent Stem Cell Population Is Retained in the Hippocampus of Transgenic Huntington's Disease Mice but Not Wild-Type Mice
Tara L. Walker,Geoff W. Turnbull,Eirinn W. Mackay,Anthony J. Hannan,Perry F. Bartlett
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0018153
Abstract: The demonstration of the brain's ability to initiate repair in response to disease or injury has sparked considerable interest in therapeutic strategies to stimulate adult neurogenesis. In this study we examined the effect of a progressive neurodegenerative condition on neural precursor activity in the subventricular zone (SVZ) and hippocampus of the R6/1 transgenic mouse model of Huntington's disease (HD). Our results revealed an age-related decline in SVZ precursor numbers in both wild-type (WT) and HD mice. Interestingly, hippocampal precursor numbers declined with age in WT mice, although we observed maintenance in hippocampal precursor number in the HD animals in response to advancement of the disease. This maintenance was consistent with activation of a recently identified latent hippocampal precursor population. We found that the small latent stem cell population was also maintained in the HD hippocampus at 33 weeks, whereas it was not present in the WT. Our findings demonstrate that, despite a loss of neurogenesis in the HD hippocampus in vivo, there is a unique maintenance of the precursor and stem cells, which may potentially be activated to ameliorate disease symptoms.
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