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Search Results: 1 - 10 of 1626 matches for " Terry Done "
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Ecological States and the Resilience of Coral Reefs
Tim McClanahan,Nicholas Polunin,Terry Done
Ecology and Society , 2002,
Abstract: We review the evidence for multiple ecological states and the factors that create ecological resilience in coral reef ecosystems. There are natural differences among benthic communities along gradients of water temperature, light, nutrients, and organic matter associated with upwelling-downwelling and onshore-offshore systems. Along gradients from oligotrophy to eutrophy, plant-animal symbioses tend to decrease, and the abundance of algae and heterotrophic suspension feeders and the ratio of organic to inorganic carbon production tend to increase. Human influences such as fishing, increased organic matter and nutrients, sediments, warm water, and transportation of xenobiotics and diseases are common causes of a large number of recently reported ecological shifts. It is often the interaction of persistent and multiple synergistic disturbances that causes permanent ecological transitions, rather than the succession of individual short-term disturbances. For example, fishing can remove top-level predators, resulting in the ecological release of prey such as sea urchins and coral-eating invertebrates. When sea urchins are not common because of unsuitable habitat, recruitment limitations, and diseases, and when overfishing removes herbivorous fish, frondose brown algae can dominate. Terrigenous sediments carried onto reefs as a result of increased soil erosion largely promote the dominance of turf or articulated green algae. Elevated nutrients and organic matter can increase internal eroders of reef substratum and a mixture of filamentous algae. Local conservation actions that attempt to reduce fishing and terrestrial influences promote the high production of inorganic carbon that is necessary for reef growth. However, global climate change threatens to undermine such actions because of increased bleaching and mortality caused by warm-water anomalies, weakened coral skeletons caused by reduced aragonite availability in reef waters, and increased incidence of diseases in coral reef species. Consequently, many coral reefs, including those that are heavily managed, have experienced net losses in accumulated inorganic carbon in recent decades and appear likely to continue this trend in coming decades. Reefs urgently need to be managed with a view to strengthening their resilience to the increased frequency and intensity of these pressures. Ecological targets must include the restoration or maintenance of species diversity, keystone species, spatial heterogeneity, refugia, and connectivity. Achieving these goals will require unprecedented cooperative synergy betw
Predicting the Location and Spatial Extent of Submerged Coral Reef Habitat in the Great Barrier Reef World Heritage Area, Australia
Tom Bridge, Robin Beaman, Terry Done, Jody Webster
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0048203
Abstract: Aim Coral reef communities occurring in deeper waters have received little research effort compared to their shallow-water counterparts, and even such basic information as their location and extent are currently unknown throughout most of the world. Using the Great Barrier Reef as a case study, habitat suitability modelling is used to predict the distribution of deep-water coral reef communities on the Great Barrier Reef, Australia. We test the effectiveness of a range of geophysical and environmental variables for predicting the location of deep-water coral reef communities on the Great Barrier Reef. Location Great Barrier Reef, Australia. Methods Maximum entropy modelling is used to identify the spatial extent of two broad communities of habitat-forming megabenthos phototrophs and heterotrophs. Models were generated using combinations of geophysical substrate properties derived from multibeam bathymetry and environmental data derived from Bio-ORACLE, combined with georeferenced occurrence records of mesophotic coral communities from autonomous underwater vehicle, remotely operated vehicle and SCUBA surveys. Model results are used to estimate the total amount of mesophotic coral reef habitat on the GBR. Results Our models predict extensive but previously undocumented coral communities occurring both along the continental shelf-edge of the Great Barrier Reef and also on submerged reefs inside the lagoon. Habitat suitability for phototrophs is highest on submerged reefs along the outer-shelf and the deeper flanks of emergent reefs inside the GBR lagoon, while suitability for heterotrophs is highest in the deep waters along the shelf-edge. Models using only geophysical variables consistently outperformed models incorporating environmental data for both phototrophs and heterotrophs. Main Conclusion Extensive submerged coral reef communities that are currently undocumented are likely to occur throughout the Great Barrier Reef. High-quality bathymetry data can be used to identify these reefs, which may play an important role in resilience of the GBR ecosystem to climate change.
Revista Romana de Economie , 2005,
Abstract: The parties involved in negotiating collective labour contracts define and follow their objectives from the perspective of interests that determine their existence. After 1989, in Romania, due to privatisation, at the companies’ level substantial changes have occurred with respect to the hierarchy coefficients. As a result, companies endowed with modern technologies and producing for export have motivational policies for their personnel, so that these are concerned with respect to the performance increase. Trade unions almost gave up direct involvement in determining and executing the incomes and expenditures budget, being concerned lately with achieving safe labour conditions, increasing professional training, and maintaining and raising the actual wage. The responsibility for optimising the relationship between labour and capital is with employers and trade unions, and the efficient solving of labour market issues cannot be done but through government, employers’ organisations and trade union.
Revista Romana de Economie , 2005,
Abstract: The functional market economy, characterised firstly by competitiveness cannot be achieved but with the immediate involvement of elite within all structures and all levels. This appreciation is largely confirmed by the economic-social successes of several states, called more and more meritocracy states.The road from chances to realities is strewn in all cases with difficulties and lacks, and each time the success is for individuals who are simultaneously aware and motivated. Romania has a high potential of elite’s generation, the share of over-endowed of total population being double in comparison to the world average. For our country a development strategy built on promoting elite and ensuring the conditions for reforms and professional achievement is necessary.
Revista Romana de Economie , 2006,
Abstract: For Romania’s success in the intrepid attempt to join within the new coordinates of competitiveness it is indisputable and indispensable to massively and swiftly absorb direct foreign investments. Maintaining and increasing the attractiveness of foreign investments in Romania shall both face in the following period very difficult problems. We envisage, first of all, the dramatic decrease of amounts that shall be cashed from privatisation, and secondly the need of treating with more responsibility the elements that limit the attraction of foreigners to invest in Romania and, thirdly, the accession to the European Union which shall have as core issue the question of competitiveness based not that much on comparative advantages, but on the levels of the economic efficiency.
Observational characteristics of accretion onto black holes
Chris Done
Physics , 2010,
Abstract: These notes resulted from a series of lectures at the IAC winter school. They are designed to help students, especially those just starting in subject, to get hold of the fundamental tools used to study accretion powered sources. As such, the references give a place to start reading, rather than representing a complete survey of work done in the field. I outline Compton scattering and blackbody radiation as the two predominant radiation mechanisms for accreting black holes, producing the hard X-ray tail and disc spectral components, respectively. The interaction of this radiation with matter can result in photo-electric absorption and/or reflection. While the basic processes can be found in any textbook, here I focus on how these can be used as a toolkit to interpret the spectra and variability of black hole binaries (hereafter BHB) and Active Galactic Nuclei (AGN). I also discuss how to use these to physically interpret real data using the publicly available XSPEC spectral fitting package (Arnaud et al 1996), and how this has led to current models (and controversies) of the accretion flow in both BHB and AGN.
Accretion Flows in X-ray Binaries
Chris Done
Physics , 2002, DOI: 10.1098/rsta.2002.1047
Abstract: I review the X-ray observations of Galactic accreting black holes and neutron stars, and interpretions of these in terms of solutions of the accretion flow equations.
Accretion Flows in X--Ray Binaries and Active Galactic Nuclei
Chris Done
Physics , 2001,
Abstract: Hard X-ray emission is ubiquitous in accreting black holes, both in Galactic binary systems and in Active Galactic Nuclei. I review the different spectra which can be seen from these systems, and possible ways of producing this emission. X-ray reflection should give an observational test of these scenarios, but we need better models before this can give an unambiguous diagnostic of the accretion geometry.
Scaling accretion flow models from BHB to AGN - Why doesn't it work?
Chris Done
Physics , 2014,
Abstract: Black holes depend only on mass and spin, while what we see from the accretion flow in steady state depends also on mass accretion rate and (weakly) inclination. Hence we should be able to scale the accretion flow properties from the stellar to the supermassive black holes. But the data show significant differences between these two types of systems, suggesting that we are missing some crucial physics in AGN. One of these differences is the soft X-ray excess which is seen ubiquitously in bright AGN, but only occasionally in BHB. Another is the much faster variability seen in the high energy tail of high mass accretion rate AGN compared to that seen in the tail of BHB. We show that while this variability is not understood, it can be used via the new spectral-timing techniques to constrain the nature of the soft X-ray excess. The coherence, lag-frequency and lag-energy results strongly support this being an additional low temperature Comptonisation component rather than extreme relativistically smeared reflection in the 'simple' Narrow Line Seyfert 1 PG1244+026.
Galactic Black HOle Binary Systems
C. Done
Physics , 2000, DOI: 10.1016/S0273-1177(01)00404-5
Abstract: I review observations of the X-ray spectra of Galactic Black Hole Candidates, and theoretical ideas as to how these can be produced. X-ray reflection should enable different source geometries to be distinguished, but the ionisation instability of X-ray irradiated material in hydrostatic equilibrium gives rise to large ambiguities in interpretation. It is not currently possible to determine whether the underlying emission mechanism in the low state is an advective flow or magnetic reconnection above the disk, but more detailed modelling of the ionisation instability {\it may} allow us to distinguish between these scenarios.
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