Quasiparticle undressing in a dynamic Hubbard model: exact diagonalization study

Dynamic Hubbard models have been proposed as extensions of the conventional Hubbard model to describe the orbital relaxation that occurs upon double occupancy of an atomic orbital. These models give rise to pairing of holes and superconductivity in certain parameter ranges. Here we explore the changes in carrier effective mass and quasiparticle weight and in one- and two-particle spectral functions that occur in a dynamic Hubbard model upon pairing, by exact diagonalization of small systems. It is found that pairing is associated with lowering of effective mass and increase of quasiparticle weight, manifested in transfer of spectral weight from high to low frequencies in one- and two-particle spectral functions. This 'undressing' phenomenology resembles observations in transport, photoemission and optical experiments in high T_c cuprates. This behavior is contrasted with that of a conventional electron-hole symmetric Holstein-like model with attractive on-site interaction, where pairing is associated with 'dressing' instead of 'undressing'

The use of algorithms to predict surface seawater dimethyl sulphide concentrations in the SE Pacific, a region of steep gradients in primary productivity, biomass and mixed layer depth

Dimethyl sulphide (DMS) is an important precursor of cloud condensation nuclei (CCN), particularly in the remote marine atmosphere. The SE Pacific is consistently covered with a persistent stratocumulus layer that increases the albedo over this large area. It is not certain whether the source of CCN to these clouds is natural and oceanic or anthropogenic and terrestrial. This unknown currently limits our ability to reliably model either the cloud behaviour or the oceanic heat budget of the region. In order to better constrain the marine source of CCN, it is necessary to have an improved understanding of the sea-air flux of DMS. Of the factors that govern the magnitude of this flux, the greatest unknown is the surface seawater DMS concentration. In the study area, there is a paucity of such data, although previous measurements suggest that the concentration can be substantially variable. In order to overcome such data scarcity, a number of climatologies and algorithms have been devised in the last decade to predict seawater DMS. Here we test some of these in the SE Pacific by comparing predictions with measurements of surface seawater made during the Vamos Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in October and November of 2008. We conclude that none of the existing algorithms reproduce local variability in seawater DMS in this region very well. From these findings, we recommend the best algorithm choice for the SE Pacific and suggest lines of investigation for future work

Climate change and the Great Barrier Reef: a vulnerability assessment

The combination of sensitivity and exposure to climate change render the GBR ecosystem highly vulnerable to climate change. While the components and processes that comprise the ecosystem vary in their vulnerability, the implications of climate change are far-reaching and, in many cases, severe. Overall, the GBR ecosystem has features that will afford it some protection from climate change compared with tropical marine reef ecosystems. These features include its immense size, its location adjacent to a relatively sparsely populated and developed country, and its protection under a management regime that is recognised as the best in the world. However, coral reefs are one of the most vulnerable of all of the earth’s ecosystems to climate change, and the GBR will continue to be affected. Even under the most optimistic climate change scenarios, the GBR is destined for significant change over this century; under pessimistic scenarios, catastrophic impacts are possible. In this section, we provide an overview of the exposure of the GBR to climate factors, including a summary of predicted changes to the GBR climate, followed by a review of the reasons for the sensitivity of the GBR to climate change. We then provide a synopsis of current and emerging knowledge about the vulnerability of GBR species groups and habitats to climate change.This is Chapter 24 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/137 ID: 7

Effect of restoration thinning on mycorrhizal fungal propagules in a northern Arizona ponderosa pine forest: Preliminary results

The inoculum potential for arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi were investigated in thinned and uncut control stands in a northern Arizona ponderosa pine forest. A corn bioassay was used to determine the relative amount of infective propagules of AM fungi, and a ponderosa pine (Pinus ponderosa) bioassay was used to determine the relative amount of infective propagules of EM fungi. Three stands of each treatment were sampled by collecting soil cores along 10 randomly chosen transects within each stand. The relative amount of infective propagules of AM fungi was significantly higher in samples collected from the thinned stands than controls. Conversely, there was a slight decrease in the relative amount of infective propagules of EM fungi in samples collected from thinned stands in comparison to the controls; however, this difference was not significant. These preliminary results indicate that population densities of AM fungi can rapidly increase following restoration thinning in northern Arizona ponderosa pine forests. This may have important implications for restoring the herbaceous understory of these forests because most understory plants depend upon AM associations for normal growth

Climate change and the Great Barrier Reef: a vulnerability assessment

The Great Barrier Reef is renowned internationally for its ecological importance and the beauty of its seascapes and landscapes. These natural values also provide important ecosystem services, which underpin Australian $6.9 billion worth of economic activity and incalculable social values. In combination, the social-ecological system centred on the reef is extraordinary in its importance, and in its complexity. Understanding the vulnerability of such a large and intricate system to climate change is a particularly difficult challenge. A first step in meeting this challenge is to describe the general characteristics of the system and the environment in which they interact. Toward this end, this chapter introduces the Great Barrier Reef and the human systems that interact with it, providing a context for the detailed chapters that follow.This is Chapter 1 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13

Chapter 17: Vulnerability of coral reefs of the Great Barrier Reef to climate change

The Great Barrier Reef (GBR) contains the most extensive coral reef ecosystem on earth. It consists of 2900 coral reefs and 900 coral cays that cover approximately 20,000 km2 of the total 345,000 km2 area of the GBR Marine Park. As a consequence of unusually high summer sea surface temperatures, between 42 to 60 percent of the reefs of the GBR experienced mass coral bleaching in 19988. Bleaching was also reported from 31 other nations around the world during 1997–1998. For example, about 50 percent of reefs in the Indian Ocean and south Asia lost much of their coral cover, and an estimated 16 percent of the world’s area of coral reefs was severely damaged. The event coincided with the strongest recorded El Niño-Southern Oscillation event (ENSO) and one of the warmest years on record.This is Chapter 17 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13

Annulus Amplitudes in the Minimal Superstring

We study the annulus amplitudes in the (2,4) minimal superstring theory using the continuum worldsheet approach. Our results reproduce the semiclassical behavior of the wavefunctions of FZZT-branes recently studied in hep-th/0412315 using the dual matrix model. We also study the multi-point functions of neutral FZZT-branes and find the agreement between their semiclassical limit and the worldsheet annulus calculation.Comment: 15 pages, lanlma

Changes in epidemiological patterns of sea lice infestation on farmed Atlantic salmon, Salmo salar L., in Scotland between 1996 and 2006

Analyses of a unique database containing sea lice records over an 11 year period provide evidence of changing infestation patterns in Scotland. The data, collected from more than 50 commercial Atlantic salmon farms, indicate that both species of sea lice commonly found in Scotland, Lepeophtheirus salmonis and Caligus elongatus, have declined on farms over the past decade. Reductions for both species have been particularly marked since 2001 when more effective veterinary medicines became available. Treatment data were also available in the database and these show a growing trend towards the use of the in feed medication emamectin benzoate (Slice), particularly in the first year of the salmon production cycle. However, this trend to wards single product use has not been sustained in 2006, the latest year for which data are available. There is some evidence of region to region variation within Scotland with the Western Isles experiencing higher levels of infestation. However, compared to the levels observed between 1996 and 2000, all regions have benefited from reduced lice infestation, with the overall pattern showing a particular reduction in the second and third quarters of the second year of production

Biophysical assessment of reefs in Keppel Bay: a baseline study (April 2007)

The Keppel Islands are a group of 16 continental islands lying 18 km off the coastal town of Yeppoon in the southern Great Barrier Reef. Located in the shallow basin to the north of Keppel Bay, the islands are host to a patchwork of fringing reefs in various forms of development. Coral communities are abundant in some locations, and coral cover is high (60 to 70%) relative to the average at sites surveyed by the Australian Institute of Marine Science’s Long-Term Monitoring Program (~35%), and are often dominated by extensive stands of branching Acropora that extend into shallow water. These ‘staghorn’ corals are vulnerable to impacts caused by environmental stresses such as elevated sea temperature (causing coral bleaching events), degraded water quality (associated with hyposaline floods events) and physical damage (from cyclones, storms and anchoring). The Fitzroy River, one of the largest catchments in Queensland, is about 40 km to the south of the Keppel Islands. Large flood plumes occur approximately every 10 years, and the soft riverine sediments are regularly re-suspended in the shallow bay by wind and tide action causing high turbidity. Heavy rainfall also affects the shallow reef flat habitats, with reported incidences of coral mortality caused by heavy rain at times of extreme low tidesID: 176