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Search Results: 1 - 10 of 386104 matches for " D. V. O'Donnell "
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Exploring the sensitivity of soil carbon dynamics to climate change, fire disturbance and permafrost thaw in a black spruce ecosystem
J. A. O'Donnell, J. W. Harden, A. D. McGuire,V. E. Romanovsky
Biogeosciences (BG) & Discussions (BGD) , 2011,
Abstract: In the boreal region, soil organic carbon (OC) dynamics are strongly governed by the interaction between wildfire and permafrost. Using a combination of field measurements, numerical modeling of soil thermal dynamics, and mass-balance modeling of OC dynamics, we tested the sensitivity of soil OC storage to a suite of individual climate factors (air temperature, soil moisture, and snow depth) and fire severity. We also conducted sensitivity analyses to explore the combined effects of fire-soil moisture interactions and snow seasonality on OC storage. OC losses were calculated as the difference in OC stocks after three fire cycles (~500 yr) following a prescribed step-change in climate and/or fire. Across single-factor scenarios, our findings indicate that warmer air temperatures resulted in the largest relative soil OC losses (~5.3 kg C m 2), whereas dry soil conditions alone (in the absence of wildfire) resulted in the smallest carbon losses (~0.1 kg C m 2). Increased fire severity resulted in carbon loss of ~3.3 kg C m 2, whereas changes in snow depth resulted in smaller OC losses (2.1–2.2 kg C m 2). Across multiple climate factors, we observed larger OC losses than for single-factor scenarios. For instance, high fire severity regime associated with warmer and drier conditions resulted in OC losses of ~6.1 kg C m 2, whereas a low fire severity regime associated with warmer and wetter conditions resulted in OC losses of ~5.6 kg C m 2. A longer snow-free season associated with future warming resulted in OC losses of ~5.4 kg C m 2. Soil climate was the dominant control on soil OC loss, governing the sensitivity of microbial decomposers to fluctuations in temperature and soil moisture; this control, in turn, is governed by interannual changes in active layer depth. Transitional responses of the active layer depth to fire regimes also contributed to OC losses, primarily by determining the proportion of OC into frozen and unfrozen soil layers.
Exploring the sensitivity of soil carbon dynamics to climate change, fire disturbance and permafrost thaw in a black spruce ecosystem
J. A. O'Donnell,J. W. Harden,A. D. McGuire,V. E. Romanovsky
Biogeosciences Discussions , 2010, DOI: 10.5194/bgd-7-8853-2010
Abstract: In the boreal region, soil organic carbon (OC) dynamics are strongly governed by the interaction between wildfire and permafrost. Using a combination of field measurements, numerical modeling of soil thermal dynamics, and process-based modeling of OC dynamics, we tested the sensitivity of soil OC storage to a suite of individual climate factors (air temperature, soil moisture, and snow depth) and fire severity. We also conducted sensitivity analyses to explore the combined effects of fire-moisture interactions and snow seasonality on OC storage. OC losses were calculated as the difference in OC stocks after three fire cycles (~450 years) following a prescribed step-change in climate and/or fire. Across single-factor scenarios, our findings indicate that warmer air temperatures resulted in the largest soil OC losses (5.3 kg C m 2), whereas dry soil conditions alone (in the absence of wildfire) resulted in the smallest carbon losses (0.1 kg C m 2). Increased fire severity resulted in carbon loss of 3.3 kg C m 2, whereas changes in snow depth resulted in smaller OC losses (2.1–2.2 kg C m 2). Across multiple climate factors, we observed larger OC losses than for single-factor scenarios. For instance, high fire severity regime associated with warmer and drier conditions resulted in OC losses of 6.1 kg C m 2, whereas a low fire severity regime associated with warmer and wetter conditions resulted in OC losses of 5.6 kg C m 2. A longer snow-free season associated with future warming resulted in OC losses of 5.4 kg C m 2. Soil climate was the dominant control on soil OC loss, governing the sensitivity of microbial decomposers to fluctuations in temperature and soil moisture; this control, in turn, is governed by interannual changes in active layer depth. Transitional responses of the active layer depth to fire regimes also contributed to OC losses, primarily by determining the proportion of OC into frozen and unfrozen soil layers. Carbon cycle feedbacks from the boreal region to the climate system will clearly depend upon these interactions among climate drivers, fire regime characteristics, and permafrost dynamics.
Impacting patient-centred outcomes in COPD: breathlessness and exercise tolerance
D. E. O'Donnell
European Respiratory Review , 2006,
Abstract: The physiological hallmark of chronic obstructive pulmonary disease (COPD) is expiratory flow limitation. However, it is the resultant air trapping and associated increases in lung volume (hyperinflation) that provide a mechanistic link between the physiological impairment and the characteristic symptoms of COPD, such as dyspnoea (breathlessness), exercise intolerance and reduced health-related quality of life (HRQoL). During exercise, the negative consequences of hyperinflation are particularly apparent. Delayed lung emptying and increased end-expiratory lung volume are aggravated, and tidal volume cannot rise to meet the increased ventilatory demands. Dyspnoea intensity rises abruptly to intolerable levels, and further increases in ventilation can only be achieved by rapid breathing. This rebounds to cause greater hyperinflation in a vicious cycle. As a result, patients with COPD often prematurely stop or avoid activity, leading to deconditioning, increased dyspnoea, worsening of disease and, ultimately, reduced HRQoL. The Global Initiative for Chronic Obstructive Lung Disease guidelines recommend long-acting bronchodilators as first-line maintenance treatment in COPD. Once-daily tiotropium 18 μg, a long-acting anticholinergic agent with 24-h efficacy, has been consistently shown to relieve dyspnoea and improve exercise tolerance and health status. These improvements may allow patients with chronic obstructive pulmonary disease to increase their daily activities, thereby reversing the cycle of chronic inactivity and muscle deconditioning.
A near-infrared excess in the continuum of high-redshift galaxies: a tracer of star formation and circumstellar disks?
E. Mentuch,R. G. Abraham,K. Glazebrook,P. J. McCarthy,H. Yan,D. V. O'Donnell,D. Le Borgne,S. Savaglio,D. Crampton,R. Murowinski,S. Juneau,R. G. Carlberg,I. Jorgensen,K. Roth,H. Chen,R. O. Marzke
Physics , 2009, DOI: 10.1088/0004-637X/706/2/1020
Abstract: A broad continuum excess in the near-infrared, peaking in the rest-frame at 2-5 micron, is detected in a spectroscopic sample of 88 galaxies at 0.5
Nuclear and Coulomb Interaction in the 8B to 7Be + p Breakup Reaction at sub-Coulomb Energies
V. Guimaraes,J. J. Kolata,D. Peterson,P. Santi,R. H. White-Stevens,S. M. Vincent,F. D. Becchetti,M. Y. Lee,T. W. O'Donnell,D. A. Roberts,J. A. Zimmerman
Physics , 1999, DOI: 10.1103/PhysRevLett.84.1862
Abstract: The angular distribution for the breakup of 8B into 7Be+p on a 58Ni target has been measured at an incident energy of 25.75 MeV. The data are inconsistent with first-order theories but are remarkably well described by calculations including higher-order effects. The comparison with theory illustrates the importance of the exotic proton halo structure of 8B in accounting for the observed breakup angular distribution.
An Open Access Database of Genome-wide Association Results
Andrew D Johnson, Christopher J O'Donnell
BMC Medical Genetics , 2009, DOI: 10.1186/1471-2350-10-6
Abstract: We collected available results from 118 GWAS articles into a database of 56,411 significant SNP-phenotype associations and accompanying information, making this database freely available here. In doing so, we met and describe here a number of challenges to creating an open access database of GWAS results. Through preliminary analyses and characterization of available GWAS, we demonstrate the potential to gain new insights by querying a database across GWAS.Using a genomic bin-based density analysis to search for highly associated regions of the genome, positive control loci (e.g., MHC loci) were detected with high sensitivity. Likewise, an analysis of highly repeated SNPs across GWAS identified replicated loci (e.g., APOE, LPL). At the same time we identified novel, highly suggestive loci for a variety of traits that did not meet genome-wide significant thresholds in prior analyses, in some cases with strong support from the primary medical genetics literature (SLC16A7, CSMD1, OAS1), suggesting these genes merit further study. Additional adjustment for linkage disequilibrium within most regions with a high density of GWAS associations did not materially alter our findings. Having a centralized database with standardized gene annotation also allowed us to examine the representation of functional gene categories (gene ontologies) containing one or more associations among top GWAS results. Genes relating to cell adhesion functions were highly over-represented among significant associations (p < 4.6 × 10-14), a finding which was not perturbed by a sensitivity analysis.We provide access to a full gene-annotated GWAS database which could be used for further querying, analyses or integration with other genomic information. We make a number of general observations. Of reported associated SNPs, 40% lie within the boundaries of a RefSeq gene and 68% are within 60 kb of one, indicating a bias toward gene-centricity in the findings. We found considerable heterogeneity in inform
Estimating the direct and indirect effects of secondary organic aerosols using ECHAM5-HAM
D. O'Donnell,K. Tsigaridis,J. Feichter
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011, DOI: 10.5194/acp-11-8635-2011
Abstract: Secondary organic aerosol (SOA) has been introduced into the global climate-aerosol model ECHAM5/HAM. The SOA module handles aerosols originating from both biogenic and anthropogenic sources. The model simulates the emission of precursor gases, their chemical conversion into condensable gases, the partitioning of semi-volatile condenable species into the gas and aerosol phases. As ECHAM5/HAM is a size-resolved model, a new method that permits the calculation of partitioning of semi-volatile species between different size classes is introduced. We compare results of modelled organic aerosol concentrations against measurements from extensive measurement networks in Europe and the United States, running the model with and without SOA. We also compare modelled aerosol optical depth against measurements from the AERONET network of grond stations. We find that SOA improves agreement between model and measurements in both organic aerosol mass and aerosol optical depth, but does not fully correct the low bias that is present in the model for both of these quantities. Although many models now include SOA, any overall estimate of the direct and indirect effects of these aerosols is still lacking. This paper makes a first step in that direction. The model is applied to estimate the direct and indirect effects of SOA under simulated year 2000 conditions. The modelled SOA spatial distribution indicates that SOA is likely to be an important source of free and upper tropospheric aerosol. We find a negative shortwave (SW) forcing from the direct effect, amounting to 0.31 Wm 2 on the global annual mean. In contrast, the model indicates a positive indirect effect of SOA of +0.23 Wm 2, arising from the enlargement of particles due to condensation of SOA, together with an enhanced coagulation sink of small particles. In the longwave, model results are a direct effect of +0.02 Wm 2 and an indirect effect of 0.03 Wm 2.
Physiology and consequences of lung hyperinflation in COPD
D. E. O'Donnell,P. Laveneziana
European Respiratory Review , 2006,
Abstract: Lung hyperinflation commonly accompanies expiratory flow limitation in patients with chronic obstructive pulmonary disease (COPD) and contributes importantly to morbidity and an impoverished quality of life. It is not surprising, therefore, that lung hyperinflation has become an important therapeutic target in symptomatic COPD patients. Acute dynamic increases in lung hyperinflation under conditions of worsening expiratory flow limitation and increased ventilatory demand (or both) can seriously stress cardiopulmonary reserves in patients with more advanced disease. The present understanding of the physiological mechanisms of dynamic hyperinflation during exacerbations of COPD and during physical activity continues to grow, together with an appreciation of its negative mechanical and sensory consequences. In this brief overview, definitions and measurement of lung hyperinflation during rest and exercise will be discussed and its potential clinical importance will be considered. The focus will mainly be on current concepts of the mechanisms of air trapping and its role in inducing respiratory discomfort and activity limitation in COPD.
Lung hyperinflation in COPD: the impact of pharmacotherapy
D. E. O'Donnell,P. Laveneziana
European Respiratory Review , 2006,
Abstract: Improvement in airway function in response to bronchodilator therapy is generally confirmed by simple spirometry. However, improvements in maximal expiratory flow rates have been shown to correlate poorly with important patient-centred outcomes, such as reduced exertional dyspnoea and improved exercise performance. Recent studies have suggested that attendant reductions in end-expiratory lung volume as a result of bronchodilator-induced improvements in lung emptying may be more closely associated with symptom relief and increased exercise capacity than traditional spirometric indices. To the extent that chronic lung hyperinflation and the superimposition of acute dynamic hyperinflation (in response to increased ventilation or expiratory flow limitation) result in excessive loading and weakening of the inspiratory muscles, then pharmacological lung volume reduction should have important mechanical and sensory benefits for the patient. The present article will examine the mechanisms of lung deflation following short-term bronchodilator therapy. The physiological links between reduced hyperinflation, improved dyspnoea and exercise endurance will be examined, and the emerging evidence for the additive effects of combining various modern pharmacological therapies will be reviewed.
Respiratory Consequences of Mild-to-Moderate Obesity: Impact on Exercise Performance in Health and in Chronic Obstructive Pulmonary Disease
Denis E. O'Donnell,Conor D. J. O'Donnell,Katherine A. Webb,Jordan A. Guenette
Pulmonary Medicine , 2012, DOI: 10.1155/2012/818925
Abstract: In many parts of the world, the prevalence of obesity is increasing at an alarming rate. The association between obesity, multiple comorbidities, and increased mortality is now firmly established in many epidemiological studies. However, the link between obesity and exercise intolerance is less well studied and is the focus of this paper. Although exercise limitation is likely to be multifactorial in obesity, it is widely believed that the respiratory mechanical constraints and the attendant dyspnea are important contributors. In this paper, we examined the evidence that critical ventilatory constraint is a proximate source of exercise limitation in individuals with mild-to-moderate obesity. We first reviewed existing information on exercise performance, including ventilatory and perceptual response patterns, in obese individuals who are otherwise healthy. We then considered the impact of obesity in patients with preexisting respiratory mechanical abnormalities due to chronic obstructive pulmonary disease (COPD), with particular reference to the effect on dyspnea and exercise performance. Our main conclusion, based on the existing and rather sparse literature on the subject, is that abnormalities of dynamic respiratory mechanics are not likely to be the dominant source of dyspnea and exercise intolerance in otherwise healthy individuals or in patients with COPD with mild-to-moderate obesity. 1. Introduction The prevalence of obesity is increasing at a remarkable rate in the Western world and this has major negative health and economic ramifications [1, 2]. Obesity is clearly linked to multiple comorbidities and is an independent risk factor for reduced survival [3, 4]. Obesity is also associated with reduced activity levels [5] and this, in turn, is associated with increased risk for comorbidities which include skeletal muscle deconditioning, insulin resistance, and cardiovascular disease [6, 7]. Of interest, obese individuals who remain active appear to have lower morbidity and mortality than normal weight individuals who are sedentary [8]. A better understanding of the nature and source of exercise intolerance in obesity is required if we are to offer more effective treatment for this increasingly common health problem. The mechanisms of activity restriction in obesity are likely to be multifactorial but the role of respiratory impairment and the associated respiratory discomfort is thought to be important. This paper will focus on the respiratory factors that may influence exercise capacity in individuals with mild-to-moderate obesity based on body
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