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Search Results: 1 - 10 of 44980 matches for " Michael McDowell "
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Meta-analysis of the Effects of Insect Vector Saliva on Host Immune Responses and Infection of Vector-Transmitted Pathogens: A Focus on Leishmaniasis
Brittany Ockenfels,Edwin Michael,Mary Ann McDowell
PLOS Neglected Tropical Diseases , 2014, DOI: 10.1371/journal.pntd.0003197
Abstract: A meta-analysis of the effects of vector saliva on the immune response and progression of vector-transmitted disease, specifically with regard to pathology, infection level, and host cytokine levels was conducted. Infection in the absence or presence of saliva in na?ve mice was compared. In addition, infection in mice pre-exposed to uninfected vector saliva was compared to infection in unexposed mice. To control for differences in vector and pathogen species, mouse strain, and experimental design, a random effects model was used to compare the ratio of the natural log of the experimental to the control means of the studies. Saliva was demonstrated to enhance pathology, infection level, and the production of Th2 cytokines (IL-4 and IL-10) in na?ve mice. This effect was observed across vector/pathogen pairings, whether natural or unnatural, and with single salivary proteins used as a proxy for whole saliva. Saliva pre-exposure was determined to result in less severe leishmaniasis pathology when compared with unexposed mice infected either in the presence or absence of sand fly saliva. The results of further analyses were not significant, but demonstrated trends toward protection and IFN-γ elevation for pre-exposed mice.
Characterization and Transport of Contaminated Sediments in the Southern Central Lake Superior  [PDF]
Jaebong Jeong, S. Douglas McDowell
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2003, DOI: 10.4236/jmmce.2003.22010
Abstract: Three major source sediments were characterized and classified in terms of mineralogical and chemical composition in the west coastal area of the Keweenaw Peninsula. Bulk chemical analysis reveals that concentrations of Cu, Ag, Co, and As were enriched in metal rich mine tailings. SEM-EDS analysis indicates that the Ontonagon River sediments have high P and S concentrations. X-ray diffraction analysis of clay fraction shows that the mine tailings (chlorite rich) could be distinguished from the other two sources, Ontonagon River sediments (low chlorite and high illite) and Wisconsin red clay (low illite and high expandable phase). Local environmental conditions, including currents, bathymetry, weather conditions, and sediments texture, are important factors for cross-margin and longshore transport of contaminated sediments. The Keweenaw Current is responsible for the longshore transport of fine fraction of tailings, whereas wave action causes the lateral transport of the coarse deposits along the shore.
John McDowell
Philósophos : Revista de Filosofia , 2008, DOI: 10.5216/phi.v10i2.2829
Capacidades conceituais na percep o
John McDowell
DoisPontos , 2006,
Abstract: A sound empiricism must attribute a rational meaning to our perceptual experience lest this experience be severed from the universe of our beliefs. On the other hand, perceptual experiences cannot be treated as creations of our own. They must be considered as contributions coming from the world around us. These two requirements can only be met if we conceive our perception as an exercise of our conceptual capacities within the range of our sensorial consciousness.
Toward a Mechanistic Modeling of Nitrogen Limitation on Vegetation Dynamics
Chonggang Xu, Rosie Fisher, Stan D. Wullschleger, Cathy J. Wilson, Michael Cai, Nate G. McDowell
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0037914
Abstract: Nitrogen is a dominant regulator of vegetation dynamics, net primary production, and terrestrial carbon cycles; however, most ecosystem models use a rather simplistic relationship between leaf nitrogen content and photosynthetic capacity. Such an approach does not consider how patterns of nitrogen allocation may change with differences in light intensity, growing-season temperature and CO2 concentration. To account for this known variability in nitrogen-photosynthesis relationships, we develop a mechanistic nitrogen allocation model based on a trade-off of nitrogen allocated between growth and storage, and an optimization of nitrogen allocated among light capture, electron transport, carboxylation, and respiration. The developed model is able to predict the acclimation of photosynthetic capacity to changes in CO2 concentration, temperature, and radiation when evaluated against published data of Vc,max (maximum carboxylation rate) and Jmax (maximum electron transport rate). A sensitivity analysis of the model for herbaceous plants, deciduous and evergreen trees implies that elevated CO2 concentrations lead to lower allocation of nitrogen to carboxylation but higher allocation to storage. Higher growing-season temperatures cause lower allocation of nitrogen to carboxylation, due to higher nitrogen requirements for light capture pigments and for storage. Lower levels of radiation have a much stronger effect on allocation of nitrogen to carboxylation for herbaceous plants than for trees, resulting from higher nitrogen requirements for light capture for herbaceous plants. As far as we know, this is the first model of complete nitrogen allocation that simultaneously considers nitrogen allocation to light capture, electron transport, carboxylation, respiration and storage, and the responses of each to altered environmental conditions. We expect this model could potentially improve our confidence in simulations of carbon-nitrogen interactions and the vegetation feedbacks to climate in Earth system models.
Depressive symptoms in people with chronic physical conditions: prevalence and risk factors in a Hong Kong community sample
Hairong Nan, Paul H Lee, Ian McDowell, Michael Y Ni, Sunita M Stewart, Tai Lam
BMC Psychiatry , 2012, DOI: 10.1186/1471-244x-12-198
Abstract: Data were obtained from the Hong Kong Jockey Club FAMILY Project cohort study in 2009–2011, which included 6,195 participants (age ≥15) with self-reported chronic conditions. Depressive symptoms were recorded using the Patient Health Questionnaire-9 (PHQ-9). Demographic and lifestyle variables, stressful life events, perceived family support and neighborhood cohesion were assessed. Factors associated with a non-somatic (PHQ-6) depression score were also examined.The prevalence of depressive symptoms (PHQ-9 scores ≥5) was 17% in those with one or more chronic conditions, and was more prevalent in women than in men (19.7% vs. 13.9%; p?<?0.001). In multilevel analyses, life stress, number of chronic conditions and satisfaction with family support explained 43% of the variance in PHQ-9 scores (standardized regression coefficients of 0.46, 0.15, and ?0.12 respectively, all p <0.001). Body mass index, problem alcohol drinking, physical activity, and unmarried status were significantly associated with PHQ-9 scores, although these associations were weak. Variables associated with depression explained 35% of the variance in non-somatic (PHQ-6) depression scores. Satisfaction with family support played a stronger protective role against depressive symptoms (both PHQ-9 and PHQ-6 scores) among women than men (p?<?0.05).Acute life stress and the number of chronic conditions, together with socio-demographic factors, explain most variance in depressive symptoms among chronically ill Chinese individuals. Somatic items in the PHQ-9 increased the depression scores but they did not alter the pattern of predictors. Family support appears to be an important protective factor in Chinese cultures for individuals with chronic conditions.Chronic physical conditions have been associated with an increased risk for depression in a range of cultural settings [1-4], and the risk has been shown to increase with the number of conditions [5]. Mainland China, Hong Kong and Taiwan have been undergoin
CodY-mediated regulation of Streptococcus pyogenes exoproteins
Emily J McDowell, Eduardo A Callegari, Horst Malke, Michael S Chaussee
BMC Microbiology , 2012, DOI: 10.1186/1471-2180-12-114
Abstract: We compared the secreted proteins produced by wild-type S. pyogenes to a codY mutant in the post-exponential phase of growth. We used both one and two-dimensional gel electrophoresis to separate exoproteins. Proteins that were significantly different in abundance upon repeated analysis were identified with tandem mass spectrometry. The production of the secreted cysteine protease SpeB, a secreted chromosomally encoded nuclease (SdaB), and a putative adhesion factor (Spy49_0549) were more abundant in supernatant fluids obtained from the codY mutant. In addition, hyaluronidase (HylA), CAMP factor (Cfa), a prophage encoded nuclease (Spd-3), and an uncharacterized extracellular protein (Spy49_0015) were less abundant in supernatant fluids obtained from the codY mutant strain. Enzymatic assays showed greater DNase activity in culture supernatants isolated in the post-exponential phase of growth from the codY mutant strain compared to the wild-type strain. Because extracellular nucleases and proteases can influence biofilm formation, we also measured the ability of the strains to form biofilms during growth with both rich medium (Todd Hewitt yeast extract; THY) and chemically defined media (CDM). No difference was observed with rich media but with CDM the biofilms formed by the codY mutant strain had less biomass compared to the wild-type strain.Overall, the results indicate that CodY alters the abundance of a select group of S. pyogenes exoproteins, including DNases, a protease, and hylauronidase, which together may alleviate starvation by promoting dissemination of the pathogen to nutrient rich environments and by hydrolysis of host macromolecules.
Loss of the Arabidopsis thaliana P4-ATPase ALA3 Reduces Adaptability to Temperature Stresses and Impairs Vegetative, Pollen, and Ovule Development
Stephen C. McDowell, Rosa L. López-Marqués, Lisbeth R. Poulsen, Michael G. Palmgren, Jeffrey F. Harper
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0062577
Abstract: Members of the P4 subfamily of P-type ATPases are thought to help create asymmetry in lipid bilayers by flipping specific lipids between the leaflets of a membrane. This asymmetry is believed to be central to the formation of vesicles in the secretory and endocytic pathways. In Arabidopsis thaliana, a P4-ATPase associated with the trans-Golgi network (ALA3) was previously reported to be important for vegetative growth and reproductive success. Here we show that multiple phenotypes for ala3 knockouts are sensitive to growth conditions. For example, ala3 rosette size was observed to be dependent upon both temperature and soil, and varied between 40% and 80% that of wild-type under different conditions. We also demonstrate that ala3 mutants have reduced fecundity resulting from a combination of decreased ovule production and pollen tube growth defects. In-vitro pollen tube growth assays showed that ala3 pollen germinated ~2 h slower than wild-type and had approximately 2-fold reductions in both maximal growth rate and overall length. In genetic crosses under conditions of hot days and cold nights, pollen fitness was reduced by at least 90-fold; from ~18% transmission efficiency (unstressed) to less than 0.2% (stressed). Together, these results support a model in which ALA3 functions to modify endomembranes in multiple cell types, enabling structural changes, or signaling functions that are critical in plants for normal development and adaptation to varied growth environments.
The Redshift of the Optical Transient Associated with GRB 010222
Saurabh Jha,Michael A. Pahre,Peter M. Garnavich,Michael L. Calkins,Roy E. Kilgard,Thomas Matheson,Jonathan C. McDowell,John B. Roll,Krzysztof Z. Stanek
Physics , 2001, DOI: 10.1086/321709
Abstract: The gamma-ray burst (GRB) 010222 is the brightest GRB detected to date by the BeppoSAX satellite. Prompt identification of the associated optical transient (OT) allowed for spectroscopy with the Tillinghast 1.5m telescope at F. L. Whipple Observatory while the source was still relatively bright (R ~ 18.6 mag), within five hours of the burst. The OT shows a blue continuum with many superimposed absorption features corresponding to metal lines at z = 1.477, 1.157, and possibly also at 0.928. The redshift of GRB 010222 is therefore unambiguously placed at z >= 1.477. The high number of Mg II absorbers and especially the large equivalent widths of the Mg II, Mg I, and Fe II absorption lines in the z = 1.477 system further argue either for a very small impact parameter or that the z = 1.477 system is the GRB host galaxy itself. The spectral index of the OT is relatively steep, beta = 0.89 +/- 0.03, and this cannot be caused by dust with a standard Galactic extinction law in the z = 1.477 absorption system. This spectroscopic identification of the redshift of GRB 010222 shows that prompt and well-coordinated followup of bright GRBs can be successful even with telescopes of modest aperture.
Neural Oscillators Programming Simplified
Patrick McDowell,Theresa Beaubouef
Applied Computational Intelligence and Soft Computing , 2012, DOI: 10.1155/2012/963917
Abstract: The neurological mechanism used for generating rhythmic patterns for functions such as swallowing, walking, and chewing has been modeled computationally by the neural oscillator. It has been widely studied by biologists to model various aspects of organisms and by computer scientists and robotics engineers as a method for controlling and coordinating the gaits of walking robots. Although there has been significant study in this area, it is difficult to find basic guidelines for programming neural oscillators. In this paper, the authors approach neural oscillators from a programmer’s point of view, providing background and examples for developing neural oscillators to generate rhythmic patterns that can be used in biological modeling and robotics applications. 1. Introduction Scientists have long employed neural oscillators as a method to study neuron/ganglia-based processes that serve as central pattern generators for various organisms and as a method to generate control and coordination signals for various robotic mechanisms. For example, significant work has been done in trying to understand the functions of various neurons and components of such biological neural networks [1, 2], developing properties general to all networks of neural oscillators [3], and the modeling of processes such as locomotion in simple animals [4–8]. Associative neural network models with behavior similar to central path generators have also been developed [9]. Computer scientists have researched and developed several varieties of artificial neural networks that model natural neural networks to some extent. Artificial neural network is a well-developed field, and the literature in this general area is quite vast; however, literature related to neural oscillators and central pattern generators using these computerized neural network models, such as in [10], is not so prevalent. Even so, the use of such models in controlling the motion of robots has been well established [11–13]. For researchers wanting to apply the techniques of neural oscillators and/or central path generators for the programming robotic controls, modeling rhythmic patterns, and so forth, without the necessity of understanding complex theoretical mathematical models or learning how simple invertebrates swim, there appears to be no single source of basic information available. Many articles provide basic diagrams of oscillators and occasionally some tuning parameters, but most do not provide discussions concerning the general nature of the mechanism, conceptual overviews, or implementation information. To help
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