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Search Results: 1 - 10 of 298993 matches for " J. Roberts "
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The role of plant physiology in hydrology: looking backwards and forwards
J. Roberts
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2007,
Abstract: The implementation of plant physiological studies at the Institute of Hydrology focussed both on examining and understanding the physiological controls of transpiration as well as evaluating the value of using physiological methods to measure transpiration. Transpiration measurement by physiological methods would be particularly valuable where this could not be achieved by micrometeorological and soil physics methods. The principal physiological measurements used were determinations of leaf stomatal conductance and leaf water relations to monitor plant water stress. In this paper the value of these approaches is illustrated by describing a few case studies in which plant physiological insight, provided both as new measurements and existing knowledge, would aid in the interpretation of the hydrological behaviour of important vegetation. Woody vegetation figured largely in these studies, conducted in the UK and overseas. Each of these case studies is formulated as a quest to answer a particular question. A collaborative comparison of conifer forest transpiration in Thetford forest using micrometeorological and soil physics techniques exhibited a substantially larger (~1 mm day 1) estimate from the micrometeorological approach. So the question – Why is there a disagreement in the estimates of forest transpiration made using micrometeorological and soil physics approaches? A range of physiological studies followed that suggested that there was no one simple answer but that the larger estimate from the micrometeorology technique might include contributions of water taken up by deep roots, from shallow-rooted vegetation and possibly also from water previously stored in trees. These sources of water were probably not included in the soil physics estimate of transpiration. The annual transpiration from woodlands in NW Europe shows a low magnitude and notable similarity between different sites raising the question – Why is transpiration from European forests low and conservative? An important contribution both to the similar and low transpiration is the likely reduction of stomatal conductance of the foliage associated with increasing air humidity deficit. A greater response is usually found when initial conductances are highest. Also contributing to similarities in transpiration from forest stands would be a compensatory role of understories and that deficits in soil moisture may not come into play until severe soil water deficits occur. Physiological studies have been conducted in many locations overseas. The modest transpiration of tropical rainforest is intriguing – Why is tropical rainforest transpiration so low? In common with temperate trees the reduction of stomatal conductance of tropical trees in association with increasing air humidity deficit will limit transpiration. In addition the high leaf area index of tropical rainforest creates conditions in the lower canopy layers that mean transpiration from those layers is much reduced from what migh
Identifying Protein Function—A Call for Community Action
Richard J. Roberts
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0020042
Abstract:
Multi-objective calibration of the land surface scheme TERRA/LM using LITFASS-2003 data
J. Roberts ,P. Rosier
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2005,
Abstract: The possible effects of broadleaved woodland on recharge to the UK Chalk aquifer have led to a study of evaporation and transpiration from beech woodland (Black Wood) and pasture (Bridgets Farm), growing in shallow soils above chalk in Hampshire. Eddy correlation measurements of energy balance components above both the forest and the grassland enabled calculation of latent heat flux (evaporation and transpiration) as a residual. Comparative measurements of soil water content and soil water potential in 9 m profiles under both forest and grassland found changes in soil water content down to 6 m at both sites; however, the soil water potential measurements showed upward movement of water only above a depth of about 2 m. Below this depth, water continued to drain and the soil water potential measurements showed downward movement of water at both sites, notwithstanding significant negative soil water potentials in the chalk and soil above. Seasonal differences occur in the soil water content profiles under broadleaved woodland and grass. Before the woodland foliage emerges, greater drying beneath the grassland is offset in late spring and early summer by increased drying under the forest. Yet, when the change in soil water profiles is at a maximum, in late summer, the profiles below woodland and grass are very similar. A comparison of soil water balances for Black Wood and Bridgets Farm using changes in soil water contents, local rainfall and evaporation measured by the energy balance approach allowed drainage to be calculated at each site. Although seasonal differences occurred, the difference in cumulative drainage below broadleaved woodland and grass was small.
The impact of broadleaved woodland on water resources in lowland UK: II. Evaporation estimates from sensible heat flux measurements over beech woodland and grass on chalk sites in Hampshire
J. Roberts ,P. Rosier
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2005,
Abstract: In the United Kingdom the planting of broadleaved woodland has led to concerns about the impact on water resources. Comparative studies, typically using soil water measurements, have been established to compare water use of broadleaved woodland and grassland. The diversity of outcomes from these studies makes it difficult to make any consistent prediction of the hydrological impact of afforestation. Most studies have shown greater drying of soils under broadleaved woodland than under grass. However, two studies in a beech wood growing on shallow soils above chalk at Black Wood, Micheldever, Hampshire showed little overall difference between broadleaved woodland and grass, either in soil water abstraction or in evaporation. Two factors are thought to contribute to the different results from Black Wood. It is known that evaporation can be considerably enhanced at the edges of woodlands or in small areas of woodlands. The studies at Black Wood were made well within a large area of fairly uniform woodland. Other studies in which a difference occurred in soil drying between broadleaved woodland and grass used measurements made in small areas of woodlands or at woodland edges. Another important difference between comparison of woodland at Black Wood and grassland growing nearby, also on shallow soils above Chalk, compared to other broadleaved woodland/grass comparisons, growing on other geologies, is the influence of the Chalk. Although vegetation such as grass (and woodland) does not populate the chalk profusely with roots, water can be removed from the Chalk by the roots which proliferate at the soil/chalk interface and which can generate upward water movement within the Chalk. Published work showed that only in a very dry summer did the evaporation from grass growing on shallow soils above chalk fall below potential. In broadleaved woodland/grass comparisons on non-chalky soils it is possible that moisture deficits in the soil below the grass may reach critical levels and reduce evaporation below that of the woodland with which it is being compared.
Natural SUSY Dark Matter: A Window on the GUT Scale
Roberts, J. P.
High Energy Physics - Phenomenology , 2007,
Abstract: One of the key motivations for supersymmetry is that it provides a natural candidate for dark matter. For a long time the density of this candidate particle fell within cosmological bounds across much of the SUSY parameter space. However with the precision results of WMAP, it has become apparent that the majority of the SUSY parameter space no longer fits the observed relic density. This has given rise to claims that supersymmetry no longer provides a natural explanation of dark matter. We address this claim by quantifying the degree of fine-tuning required for the different dark matter regions. We find that the dark matter regions vary widely in the degree of tuning required. This degree of tuning can then be used to provide valuable insights into the structure of SUSY breaking at the GUT scale.
Het Filemon vandag nog iets vir ons te sê?
J.H. Roberts
In die Skriflig , 2011, DOI: 10.4102/ids.v45i2&3.25
Abstract: Does Philemon still have meaning for Christians today? The article purports to show that the main thrust of Philemon lies with orthopraxis, in casu the mutual fellowship of believers in the church, underscored by mutual love and respect, hospitality and missionary enterprise. The letter to Philemon is a very human document, dealing with the very human question of how a Christian should treat his runaway slave who has recently converted to Christianity. Owner and slave have become brothers in Christ. Paul, therefore, makes a request that Philemon should show the same hospitality to Onesimus, who is being sent back to his master, that he would show to Paul himself should he come to visit. The request is made in the body of the letter which is formally framed as an ancient petition, showing the typical features of the form. As to the contextual meaning of the text in a modern church situation, the challenge of this letter (but also that of every book of the Bible), is to stop trying to solve ethical questions by bickering over the interpretation of proof texts and rather concentrate on the message of the book as a whole. This should result in completely new answers to old and seemingly insoluble questions.
Identifying Protein Function—A Call for Community Action
Richard J Roberts
PLOS Biology , 2004, DOI: 10.1371/journal.pbio.0020042
Abstract:
Book Reviews - Managing the Insider Threat: No Dark Corners. By Nick Catranzos.
Mark J. Roberts
Journal of Strategic Security , 2012,
Abstract:
Book Reviews- Pakistan on the Brink: The Future of America, Pakistan, and Afghanistan. By Ahmed Rashid.
Mark J. Roberts
Journal of Strategic Security , 2012,
Abstract:
Book Reviews - "Terrorism and Homeland Security: Perspectives, Thoughts, and Opinions," Edited by Dale L. June
Mark J. Roberts
Journal of Strategic Security , 2011,
Abstract:
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