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Search Results: 1 - 10 of 415972 matches for " E. J. Burke "
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Simulation of permafrost and seasonal thaw depth in the JULES land surface scheme
R. Dankers,E. J. Burke,J. Price
The Cryosphere Discussions , 2011, DOI: 10.5194/tcd-5-1263-2011
Abstract: Land surface models (LSMs) need to be able to simulate realistically the dynamics of permafrost and frozen ground. In this paper we evaluate the performance of the LSM JULES (Joint UK Land Environment Simulator), the stand-alone version of the land surface scheme used in Hadley Centre climate models, in simulating the large-scale distribution of surface permafrost. In particular we look at how well the model is able to simulate the seasonal thaw depth or active layer thickness (ALT). We performed a number of experiments driven by observation-based climate datasets. Visually there is a very good agreement between areas with permafrost in JULES and known permafrost distribution in the Northern Hemisphere, and the model captures 97% of the area where the permafrost coverage is at least 50% of the grid cell. However, the model overestimates the total extent as it also simulates permafrost where it occurs sporadically or only in isolated patches. Consistent with this we find a cold bias in the simulated soil temperatures, especially in winter. However, when compared with observations on end-of-season thaw depth from around the Arctic, the ALT in JULES is generally too deep. Additional runs at three sites in Alaska demonstrate how uncertainties in the precipitation input affect the simulation of soil temperatures by affecting the thickness of the snowpack and therefore the thermal insulation in winter. In addition, changes in soil moisture content influence the thermodynamics of soil layers close to freezing. We also present results from three experiments in which the standard model setup was modified to improve physical realism of the simulations in permafrost regions. Extending the soil column to a depth of 60 m and adjusting the soil parameters for organic content had relatively little effect on the simulation of permafrost and ALT. A higher vertical resolution improves the simulation of ALT, although a considerable bias still remains. Future model development in JULES should focus on a dynamic coupling of soil organic carbon content and soil thermal and hydraulic properties, as well as allowing for sub-grid variability in soil types.
Simulation of permafrost and seasonal thaw depth in the JULES land surface scheme
R. Dankers,E. J. Burke,J. Price
The Cryosphere , 2011, DOI: 10.5194/tc-5-773-2011
Abstract: Land surface models (LSMs) need to be able to simulate realistically the dynamics of permafrost and frozen ground. In this paper we evaluate the performance of the LSM JULES (Joint UK Land Environment Simulator), the stand-alone version of the land surface scheme used in Hadley Centre climate models, in simulating the large-scale distribution of surface permafrost. In particular we look at how well the model is able to simulate the seasonal thaw depth or active layer thickness (ALT). We performed a number of experiments driven by observation-based climate datasets. Visually there is a very good agreement between areas with permafrost in JULES and known permafrost distribution in the Northern Hemisphere, and the model captures 97% of the area where the spatial coverage of the permafrost is at least 50%. However, the model overestimates the total extent as it also simulates permafrost where it occurs sporadically or only in isolated patches. Consistent with this we find a cold bias in the simulated soil temperatures, especially in winter. However, when compared with observations on end-of-season thaw depth from around the Arctic, the ALT in JULES is generally too deep. Additional runs at three sites in Alaska demonstrate how uncertainties in the precipitation input affect the simulation of soil temperatures by affecting the thickness of the snowpack and therefore the thermal insulation in winter. In addition, changes in soil moisture content influence the thermodynamics of soil layers close to freezing. We also present results from three experiments in which the standard model setup was modified to improve physical realism of the simulations in permafrost regions. Extending the soil column to a depth of 60 m and adjusting the soil parameters for organic content had relatively little effect on the simulation of permafrost and ALT. A higher vertical resolution improves the simulation of ALT, although a considerable bias still remains. Future model development in JULES should focus on a dynamic coupling of soil organic carbon content and soil thermal and hydraulic properties, as well as allowing for sub-grid variability in soil types.
Application of a coupled microwave, energy and water transfer model to relate passive microwave emission from bare soils to near-surface water content and evaporation
L. P. Simmonds,E. J. Burke
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 1999,
Abstract: The paper examines the stability of the relation between microwave emission from the soil and the average near-surface water content in the case of relatively smooth, bare soils, and then considers the extent to which microwave radiometry can be used to estimate the effective surface resistance to vapour transfer, which is also related to the near-surface water status. The analysis is based on the use of a model (MICRO-SWEAT) which couples a microwave radiative transfer model with a SVAT scheme that describes the exchanges of water vapour, energy and sensible heat at the land surface. Verification of MICRO-SWEAT showed good agreement (about 3K RMSE) between predicted L band (1.4 GHz) brightness temperature over soils with contrasting texture during a multi-day drydown, and those measured using a truck-mounted radiometer. There was good agreement between the measured and predicted relations between the average water content of the upper 2 cm of the soil profile and the brightness temperature normalised with respect to the radiometric surface temperature. Some of the scatter in this relationship was attributable to diurnal variation in the magnitude of near-surface gradients in temperature and water content, and could be accounted for by using the physically-based simulation model. The influence of soil texture on this relationship was well-simulated using MICRO-SWEAT. The paper concludes by demonstrating how MICRO-SWEAT can be used to establish a relationship between the normalised brightness temperature and the surface resistance for use in the prediction of evaporation using the Penman-Montheith equation.
A simple parameterisation for retrieving soil moisture from passive microwave data
E. J. Burke,L. P. Simmonds
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2001,
Abstract: MICRO-SWEAT, a physically based soil water and energy balance model coupled with a microwave emission model, was used to investigate the relationship between near surface soil moisture (θ0-5) and L-band microwave brightness temperature (TB) under a wide range of conditions. The effects of soil texture, look angle and vegetation on this relationship were parameterised and combined into a simple summary model relating θ0-5 to TB. This model retains much of the physical basis of MICRO-SWEAT but can be used in more data limiting circumstances. It was tested using a variety of truck-based L-band data sets collected between 1980 and 1982. This paper emphasises the need to have an accurate estimate of the vegetation optical depth (a parameter that describes the degree of influence of the vegetation on the microwave emission from the soil surface) in order to retrieve correctly the soil water content. Keywords: passive microwave, soil moisture, remote sensing, vegetation, retrieval algorithm
Local anaesthesia using Articaine and Lidocaine in oral and dental surgery: A comparative meta-analysis  [PDF]
M. K. Saggu, H. Aga, J. S. Saggu, G. A. E. Burke
Open Journal of Stomatology (OJST) , 2014, DOI: 10.4236/ojst.2014.42014
Abstract:

Background: Articaine is an amide local anaesthetic, which is gaining popularity for use in dental and oral surgical anaesthesia in the United Kingdom. Hitherto there has been insufficient evidence to recommend articaine above the more commonly used lidocaine for dental procedures. The aim of this study is to compare the efficacy of 4% articaine with 1:100,000 adrenaline (4AA) with that of 2% lidocaine with 1:100,000 adrenaline (2LA) administered as buccal infiltrations for anaesthesia in mandibular permanent first molar teeth. Any significant advantage noted may obviate the need for regional blockage of the inferior dental nerve in dental or minor oral surgical procedure under local anaesthesia. Objectives: To review the published literature comparing the efficacies of 4AA and 2LA for achieving pulpal anaesthesia in human mandibular permanent first molar teeth. Null Hypothesis: 4AA and 2LA are of equal efficacy when used to anaesthetize mandibular permanent first molar teeth by buccal infiltration. Method: An electronic search encompassing Ovid MEDLINE?, PubMed (National Center for Biotechnology Information, US National Library of Medicine), SCOPUS?, SCIRUS?, EMBASE? databases and the Cochrane Library was performed to identify trials relating to the efficacy of 4AA and 2LA local anaesthetic solutions on mandibular first molars in adult participants. Study characteristics and outcome data were extracted as a basis for meta-analysis. Results: Three randomised controlled trials were identified for this meta-analysis. The relative efficacy of 4AA over 2LA in anesthetizing permanent first mandibular molars was calculated at 1.57 (95% CI = 1.27 to 1.95). Conclusion: Despite the promising results shown in the meta-analysis it is difficult to say from the evidence presented that 4AA should be used clinically in preference over 2LA.

Research Note: Bird-Resistant Pollination Bags for Sorghum Breeding and Germplasm Maintenance  [PDF]
Dennis C. Gitz III, Jeffrey T. Baker, Zhanguo Xin, Robert J. Lascano, John J. Burke, Sara E. Duke
American Journal of Plant Sciences (AJPS) , 2013, DOI: 10.4236/ajps.2013.43074
Abstract: Bird damage is a problem in sorghum breeding and germplasm maintenance operations. Paper pollination bags are damaged by rain and provide only a minimal deterrent to birds. To overcome these limitations we fabricated pollination bags from spun polyethylene fiber sheeting. No seed yield difference was found between plants bagged with either spun polyethylene or paper. Seed loss by bird damage was nearly eliminated under the polyethylene bags. In areas where bird damage is problematic bird resistant pollination bags can allow for a reduction in the plot size required for breeding and germplasm maintenance operations, increase the productivity of such operations as genetic diversity per unit land area, and make direct measurement of seed yield possible in agronomic field experiments.
Research Note:The comparison of two models that determine the effects of a vegetation canopy on passive microwave emission
E. J. Burke,J.-P. Wigneron,R. J. Gurney
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 1999,
Abstract: Two contrasting models are used to account for the effects of vegetation on microwave emission from the soil. These are: a simple model which requires two empirically derived parameters as input data (optical depth and single scattering albedo); and a complex discrete model which requires a detailed description of all of the components of the vegetation canopy. Both models account effectively for the vegetation, although the simple model takes a fraction of the computation time compared to the discrete model. However, the simple model was fitted to the data, whereas the discrete model used measured parameters as input. In addition to predicting the microwave brightness temperature, the discrete model also calculates the optical depth and single scattering albedo. These calculated values were in agreement with those fitted using the simple model. Therefore, it is suggested that the discrete model could be used to calculate the input parameters for the simple model.
Genetic Diversity in the Environmental Conditioning of Gossypium hirsutum and Gossypium barbadense Cultivars  [PDF]
John J. Burke
American Journal of Plant Sciences (AJPS) , 2017, DOI: 10.4236/ajps.2017.83036
Abstract: Enzyme adaptations to temperature occur constantly as temperature patterns modulate diurnally and seasonally. These adaptations entail qualitative and/or quantitative metabolic changes that often provide a competitive advantage, impact adjustment to new environments, and effect the survival of the species. Changes in isozymes or allozymes, changes in enzyme concentration, modification by substrate and effectors, and metabolic regulation of enzyme function without changing enzyme composition are all possible strategies for adaptation to changes in temperature. The degree of adaptation among cotton cultivars to a specific thermal regime may be difficult to determine from phenotypic responses of the plants. The present study evaluated the thermal sensitivity of Gossypium hirsutum L. and Gossypium barbadense L. cultivars following growth under distinct thermal environments. The metabolic fitness of Gossypium hirsutum L. and Gossypium barbadense L. cultivars showed that the Gossypium hirsutum L. cultivars grown in a 28°C/20°C day/night cycle tended to be better equipped to cope with a 16 h - 38°C treatment than the same cultivars grown in a 38°C/32°C day/night cycle. The Gossypium barbadense L. cultivars, on the other hand, grown in a 38°C/32°C day/night cycle tended to be equipped to cope with a 16 h - 38°C treatment than the same cultivars grown in a 28°C/20°C day/night cycle. The Gossypium hirsutum L. line TX 303 is an exception to these general trends as its responses were similar to the Gossypium barbadense L. St. Vincent and Pima S-7 cottons.
A procedure to correct the effects of a relative delay between the quadrature components of radar signals at base band
E. V. Mishin, W. J. Burke,T. Pedersen
Annales Geophysicae (ANGEO) , 2005,
Abstract: Observations of airglow at 630nm (red line) and 557.7nm (green line) during HF modification experiments at the High Frequency Active Auroral Research Program (HAARP) heating facility are analyzed. We propose a theoretical framework for understanding the generation of Langmuir and ion acoustic waves during magnetic zenith injections. We show that observations of HF-induced airglow in an underdense ionosphere as well as a decrease in the height of the emitting volume are consistent with this scenario.
Uncertainties in the global temperature change caused by carbon release from permafrost thawing
E. J. Burke,I. P. Hartley,C. D. Jones
The Cryosphere , 2012, DOI: 10.5194/tc-6-1063-2012
Abstract: Under climate change thawing permafrost will cause old carbon which is currently frozen and inert to become vulnerable to decomposition and release into the climate system. This paper develops a simple framework for estimating the impact of this permafrost carbon release on the global mean temperature (P-GMT). The analysis is based on simulations made with the Hadley Centre climate model (HadGEM2-ES) for a range of representative CO2 concentration pathways. Results using the high concentration pathway (RCP 8.5) suggest that by 2100 the annual methane (CH4) emission rate is 2–59 Tg CH4 yr 1 and 50–270 Pg C has been released as CO2 with an associated P-GMT of 0.08–0.36 °C (all 5th–95th percentile ranges). P-GMT is considerably lower – between 0.02 and 0.11 °C – for the low concentration pathway (RCP2.6). The uncertainty in climate model scenario causes about 50% of the spread in P-GMT by the end of the 21st century. The distribution of soil carbon, in particular how it varies with depth, contributes to about half of the remaining spread, with quality of soil carbon and decomposition processes contributing a further quarter each. These latter uncertainties could be reduced through additional observations. Over the next 20–30 yr, whilst scenario uncertainty is small, improving our knowledge of the quality of soil carbon will contribute significantly to reducing the spread in the, albeit relatively small, P-GMT.
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