University of LeedsLeeds

Engineering, United Kingdom

University of LeedsLeeds

Engineering, United Kingdom

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Nederveen J.P.,Canadian Center for Activity and Aging | Nederveen J.P.,University of Western Ontario | Keir D.A.,Canadian Center for Activity and Aging | Keir D.A.,University of Western Ontario | And 6 more authors.
Respiratory Physiology and Neurobiology | Year: 2017

We examined the effect of heavy-intensity ‘priming’ exercise on the rate of adjustment of pulmonary O2 uptake (τV˙O2p) initiated from elevated intensities. Fourteen men (separated into two groups: τV˙O2p ≤ 25s [Fast] or τV˙O2p > 25s [Slow]) completed step-transitions from 20 W to 45% lactate threshold (LT; lower-step, LS) and 45% to 90%LT (upper-step, US) performed (i) without; and (ii) with US preceded by heavy-intensity exercise (HUS). Breath-by-breath V˙O2p and near-infrared spectroscopy-derived muscle deoxygenation ([HHb + Mb]) were measured. Compared to LS, τV˙O2p was greater (p < 0.05) in US in both Fast (LS, 19 ± 4s; US, 30 ± 4s) and Slow (LS, 25 ± 5s; US, 40 ± 11s) with τV˙O2p in US being lower (p < 0.05) in Fast. In HUS, τV˙O2p in Slow was reduced (28 ± 8s, p < 0.05) and was not different (p > 0.05) from LS or Fast group US. In Slow, τ[HHb + Mb] increased (p < 0.05) in US relative to HUS; this finding coupled with a reduced τV˙O2p indicates a priming-induced improvement in matching of muscle O2 delivery-to-O2 utilization during transitions from elevated intensities in those with Slow but not Fast V˙O2p kinetics. © 2016 Elsevier B.V.

PubMed | University of LeedsLeeds, U.S. National Center for Atmospheric Research and University of Colorado at Boulder
Type: Journal Article | Journal: Journal of advances in modeling earth systems | Year: 2016

A sectional aerosol model (CARMA) has been developed and coupled with the Community Earth System Model (CESM1). Aerosol microphysics, radiative properties, and interactions with clouds are simulated in the size-resolving model. The model described here uses 20 particle size bins for each aerosol component including freshly nucleated sulfate particles, as well as mixed particles containing sulfate, primary organics, black carbon, dust, and sea salt. The model also includes five types of bulk secondary organic aerosols with four volatility bins. The overall cost of CESM1-CARMA is approximately 2.6 times as much computer time as the standard three-mode aerosol model in CESM1 (CESM1-MAM3) and twice as much computer time as the seven-mode aerosol model in CESM1 (CESM1-MAM7) using similar gas phase chemistry codes. Aerosol spatial-temporal distributions are simulated and compared with a large set of observations from satellites, ground-based measurements, and airborne field campaigns. Simulated annual average aerosol optical depths are lower than MODIS/MISR satellite observations and AERONET observations by 32%. This difference is within the uncertainty of the satellite observations. CESM1/CARMA reproduces sulfate aerosol mass within 8%, organic aerosol mass within 20%, and black carbon aerosol mass within 50% compared with a multiyear average of the IMPROVE/EPA data over United States, but differences vary considerably at individual locations. Other data sets show similar levels of comparison with model simulations. The model suggests that in addition to sulfate, organic aerosols also significantly contribute to aerosol mass in the tropical UTLS, which is consistent with limited data.

Paton J.,University of LeedsLeeds | Khatir Z.,University of LeedsLeeds | Thompson H.,University of LeedsLeeds | Kapur N.,University of LeedsLeeds | Toropov V.,University of LeedsLeeds
Applied Thermal Engineering | Year: 2013

Energy usage in bread ovens is analysed using a generic methodology applicable to all types of mass-production tunnel ovens. The presented methodology quantifies the energy required to bake the dough, and to conduct a detailed analysis of the breakdown of losses from the oven. In addition, a computational fluid dynamics (CFD) optimisation study is undertaken, resulting in improved operating conditions for bread baking with reduced energy usage and baking time. Overall, by combining the two approaches, the analyses suggest that bake time can be reduced by up to 10% and the specific energy required to bake each loaf by approximately 2%. For UK industry, these savings equate to more than £0.5 million cost and carbon reduction of more than 5000 tonnes CO2 per year. © 2012 Elsevier Ltd.

Chu H.H.,University of California at Berkeley | Chan S.-W.,University of California at Berkeley | Gosling J.P.,University of Leeds | Blanchard N.,University Paul Sabatier | And 5 more authors.
Immunity | Year: 2016

Highly functional CD8+ effector T (Teff) cells can persist in large numbers during controlled persistent infections, as exemplified by rare HIV-infected individuals who control the virus. Here we examined the cellular mechanisms that maintain ongoing T effector responses using a mouse model for persistent Toxoplasma gondii infection. In mice expressing the protective MHC-I molecule, H-2Ld, a dominant T effector response against a single parasite antigen was maintained without a contraction phase, correlating with ongoing presentation of the dominant antigen. Large numbers of short-lived Teff cells were continuously produced via a proliferative, antigen-dependent intermediate (Tint) population with a memory-effector hybrid phenotype. During an acute, resolved infection, decreasing antigen load correlated with a sharp drop in the Tint cell population and subsequent loss of the ongoing effector response. Vaccination approaches aimed at the development of Tint populations might prove effective against pathogens that lead to chronic infection. © 2016 Elsevier Inc.

Thomas M.E.,University of LeedsLeeds | Neuberg J.W.,University of LeedsLeeds
Geochemistry, Geophysics, Geosystems | Year: 2014

The estimation of the magma ascent rate is key to predicting volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. Linking potential changes of such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models Soufrière that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. We show that variability in the rate of low frequency seismicity, assumed to correlate directly with the rate of magma movement, can be used as an indicator for changes in ascent rate and, therefore, eruptive activity. The results indicate that conduit diameter and excess pressure in the magma chamber are amongst the dominant controlling variables, but the single most important parameter is the volatile content (assumed as only water). Modeling this parameter in the range of reported values causes changes in the calculated ascent velocities of up to 800%. © 2014. American Geophysical Union. All Rights Reserved.

Ramirez J.A.,University of LeedsLeeds | Baird A.J.,University of LeedsLeeds | Coulthard T.J.,Environment and Earth SciencesUniversity of HullHull | Waddington J.M.,McMaster University
Water Resources Research | Year: 2015

Bubble dynamics in porous media are of great importance in industrial and natural systems. Of particular significance is the impact that bubble-related emissions (ebullition) of greenhouse gases from porous media could have on global climate (e.g., wetland methane emissions). Thus, predictions of future changes in bubble storage, movement, and ebullition from porous media are needed. Methods exist to predict ebullition using numerical models, but all existing models are limited in scale (spatial and temporal) by high computational demands or represent porous media simplistically. A suitable model is needed to simulate ebullition at scales beyond individual pores or relatively small collections (<10-4 m3) of connected pores. Here we present a cellular automaton model of bubbles in porous media that addresses this need. The model is computationally efficient, and could be applied over large spatial and temporal extent without sacrificing fine-scale detail. We test this cellular automaton model against a physical model and find a good correspondence in bubble storage, bubble size, and ebullition between both models. It was found that porous media heterogeneity alone can have a strong effect on ebullition. Furthermore, results from both models suggest that the frequency distributions of number of ebullition events per time and the magnitude of bubble loss are strongly right skewed, which partly explains the difficulty in interpreting ebullition events from natural systems. © 2015 American Geophysical Union.

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