Resolved Imaging of the HD191089 Debris Disc

Two thirds of the F star members of the 12 Myr old Beta Pictoris Moving Group (BPMG) show significant excess emission in the mid-infrared, several million years after the expected dispersal of the protoplanetary disc. Theoretical models of planet formation suggest that this peak in the mid-infrared emission could be due to the formation of Pluto-sized bodies in the disc, which ignite the collisional cascade and enhance the production of small dust. Here we present resolved mid-infrared imaging of the disc of HD191089 (F5V in the BPMG) and consider its implications for the state of planet formation in this system. HD191089 was observed at 18.3 microns using T-ReCS on Gemini South and the images were compared to models of the disc to constrain the radial distribution of the dust. The emission observed at 18.3 microns is shown to be significantly extended beyond the PSF at a position angle of 80 degrees. This is the first time dust emission has been resolved around HD191089. Modelling indicates that the emission arises from a dust belt from 28-90 AU, inclined at 35 degrees from edge on with very little emission from the inner 28AU of the disc, indicating the presence of an inner cavity. The steep slope of the inner edge is more consistent with truncation by a planet than with ongoing stirring. A tentative brightness asymmetry F(W)/F(E)=0.80+/-0.12 (1.8 sigma) between the two sides of the disc could be evidence for perturbations from a massive body on an eccentric orbit in the system.Comment: 11 Pages Accepted to MNRA

Extinct equids from Limeworks Cave and Cave of Hearths, Makapansgat, Northern Province, and a consideration of variation in the cheek teeth of Equus capensis Broom

Dental specimens of Hipparion libycum from Limeworks Cave, and Equus capensis from Cave of the Horse’s Mandible in the Limeworks Cave entrance and from Cave of Hearths on the farm Makapansgat in the Makapansgat Valley are described. The concept of restricted local formations within each cave is discussed. Qualitative variation in the cheek teeth of E. capensis, based on a sample of 40 upper and 60 lower permanent premolars and molars from Cave of Hearths, demonstrates that there appears to be no correlation in the occurrence of one enamel feature with another between teeth of presumed different individuals. Teeth within a molar row show similar development of features between teeth, whether premolar or molar, as shown by plis, progressive migration of the protocone isthmus along the row, and penetration of the buccal valley to between the enamel loops of the metaconid and metastylid. Consequently, earlier descriptions of species of large Pleistocene Equus in Southern Africa founded on isolated teeth and, using such qualitative variation, are inept, unsuitable and inappropriate, and modem taxonomies synonymising them under E. capensis are supported. The Cave of Hearths ‘loose breccia’ (Beds 1-3 of Mason, 1988) containing earlier Stone Age/Later Acheulean artifacts, is circumstantially dated between 300 000 and 200 000 years BP.THE COUNCIL’S RESEARCH COMMITTEE, UNIVERSITY OF THE WITWATERSRAND; NATIONAL RESEARCH FOUNDATION (NRF

A generic template for the evaluation of dialogue management systems

We present a generic template for spoken dialogue systems integrating speech recognition and synthesis with 'higher-level' natural language dialogue modelling components. The generic model is abstracted from a number of real application systems targetted at very different domains. Our research aim in developing this generic template is to investigate a new approach to the evaluation of Dialogue Management Systems. Rather than attempting to measure accuracy/speed of output, we propose principles for the evaluation of the underlying theoretical linguistic model of Dialogue Management in a given system, in terms of how well it fits our generic template for Dialogue Management Systems. This is a measure of 'genericness' or 'application-independence' of a given system, which can be used to moderate accuracy/speed scores in comparisons of very unlike DMSs serving different domains. This relates to (but is orthogonal to) Dialogue Management Systems evaluation in terms of naturalness and like measurable metrics (eg. Dybkjaer et al 1995, Vilnat 1996, EAGLES 1994, Fraser 1995); it follows more closely emerging qualitative evaluation techniques for NL grammatical parsing schemes (Leech et al 1996, Atwell 1996)

Reducing Plasmodium falciparum malaria transmission in Africa: a model-based evaluation of intervention strategies.

BACKGROUND: Over the past decade malaria intervention coverage has been scaled up across Africa. However, it remains unclear what overall reduction in transmission is achievable using currently available tools. METHODS AND FINDINGS: We developed an individual-based simulation model for Plasmodium falciparum transmission in an African context incorporating the three major vector species (Anopheles gambiae s.s., An. arabiensis, and An. funestus) with parameters obtained by fitting to parasite prevalence data from 34 transmission settings across Africa. We incorporated the effect of the switch to artemisinin-combination therapy (ACT) and increasing coverage of long-lasting insecticide treated nets (LLINs) from the year 2000 onwards. We then explored the impact on transmission of continued roll-out of LLINs, additional rounds of indoor residual spraying (IRS), mass screening and treatment (MSAT), and a future RTS,S/AS01 vaccine in six representative settings with varying transmission intensity (as summarized by the annual entomological inoculation rate, EIR: 1 setting with low, 3 with moderate, and 2 with high EIRs), vector-species combinations, and patterns of seasonality. In all settings we considered a realistic target of 80% coverage of interventions. In the low-transmission setting (EIR approximately 3 ibppy [infectious bites per person per year]), LLINs have the potential to reduce malaria transmission to low levels (90%) or novel tools and/or substantial social improvements will be required, although considerable reductions in prevalence can be achieved with existing tools and realistic coverage levels. CONCLUSIONS: Interventions using current tools can result in major reductions in P. falciparum malaria transmission and the associated disease burden in Africa. Reduction to the 1% parasite prevalence threshold is possible in low- to moderate-transmission settings when vectors are primarily endophilic (indoor-resting), provided a comprehensive and sustained intervention program is achieved through roll-out of interventions. In high-transmission settings and those in which vectors are mainly exophilic (outdoor-resting), additional new tools that target exophagic (outdoor-biting), exophilic, and partly zoophagic mosquitoes will be required

Using a commercial speech recogniser within the domain of air traffic control

We have taken an off-the-shelf, commercial continuous speech recogniser and conducted tests using three syntaxes for the domain of Air Traffic Control. The syntaxes are based on a corpus of transmissions between the ATC and pilots and reflect three differing levels of "linguistic" knowledge. The first represented the system where, in effect, there would be no syntax but a lexicon of all words in the corpus. The second took a partial look at syntactic information by using a key phrase spotting mechanism. The third represented the entire syntax of the corpus. Initial experiments show that key phrase spotting is insignificantly more accurate than no syntax at all, whilst use of a complete syntax can improve performance, to a point. The benefits of a discourse grammar are briefly discussed

Dialogue management systems: a survey and overview

This report provides an overview of the current issues and techniques for the modelling of dialogues using a computer. A dialogue management system can manage a dialogue between two or more agents, be they human or computer. Recently, increasingly complex dialogues are being modelled which allow a range of discourse phenomena including ellipsis and anaphoric reference. Such dialogues are thought to be similar to those between two humans, and accurate modelling of these phenomena leads to "pleasant", i.e. easy to talk to, and natural human-computer dialogues. Dialogue management can be classified into three often overlapping approaches: discourse grammars, plan-based and collaborative approaches. The design of a system often begins by eliciting the language used initially between two humans and later by Wizard of Oz experiments. Special issues relating to dialogue management systems are discussed including recovery strategies from different types of errors and the coding of dialogue in corpora. Lastly, approaches to evaluation are briefly discussed from the qualitative and quantitative viewpoints, recognising the importance and size of this sub-field

Developing a corpus-based grammar model within a continuous commercial speech recognition package

This paper is derived from experiments with a commercial ’off-the-shelf’ continuous speech recognition system, applied to the apparently restricted domain of Air Traffic Control (ATC) for light aircraft. The system is required to transcribe key sub-phrases in a transmission by the ATC to a particular aircraft, the commercial speech recognition system providing the main recognition component. After the development of a corpus of transmissions, it was realised that key information is often interspersed with unconstrained English. Initial attempts focused on using a wildcard mechanism for the non-key sub- phrases. The mechanism, however, proved to be valuable only in simplistic grammars due to its overgenerative nature. The speech recognition system showed us that whilst useful mechanisms are provided, such as the wildcard mechanism, they tend to make over-simplistic assumptions about English grammar and dialogue structure

Predicting mosquito infection from Plasmodium falciparum gametocyte density and estimating the reservoir of infection

Transmission reduction is a key component of global efforts to control and eliminate malaria; yet, it is unclear how the density of transmission stages (gametocytes) influences infection (proportion of mosquitoes infected). Human to mosquito transmission was assessed using 171 direct mosquito feeding assays conducted in Burkina Faso and Kenya. Plasmodium falciparum infects Anopheles gambiae efficiently at low densities (4% mosquitoes at 1/µl blood), although substantially more (>200/µl) are required to increase infection further. In a site in Burkina Faso, children harbour more gametocytes than adults though the non-linear relationship between gametocyte density and mosquito infection means that (per person) they only contribute slightly more to transmission. This method can be used to determine the reservoir of infection in different endemic settings. Interventions reducing gametocyte density need to be highly effective in order to halt human-mosquito transmission, although their use can be optimised by targeting those contributing the most to transmission. DOI:http://dx.doi.org/10.7554/eLife.00626.001

Asymmetric Heating of the HR 4796A Dust Ring Due to Pericenter Glow

We have obtained new resolved images of the well-studied HR 4796A dust ring at 18 and 25 microns with the 8-meter Gemini telescopes. These images confirm the previously observed spatial extent seen in mid-IR, near-IR, and optical images of the source. We detect brightness and temperature asymmetries such that dust on the NE side is both brighter and warmer than dust in the SW. We show that models of so-called pericenter glow account for these asymmetries, thus both confirming and extending our previous analyses. In this scenario, the center of the dust ring is offset from the star due to gravitational perturbations of a body with an eccentric orbit that has induced a forced eccentricity on the dust particle orbits. Models with 2-micron silicate dust particles and a forced eccentricity of 0.06 simultaneously fit the observations at both wavelengths. We also show that parameters used to characterize the thermal-emission properties of the disk can also account for the disk asymmetry observed in shorter-wavelength scattered-light images.Comment: accepted for publication in A&A; 7 pages, 4 figure

Meningococcal genetic variation mechanisms viewed through comparative analysis of Serogroup C strain FAM18

Copyright @ 2007 Public Library of ScienceThe bacterium Neisseria meningitidis is commonly found harmlessly colonising the mucosal surfaces of the human nasopharynx. Occasionally strains can invade host tissues causing septicaemia and meningitis, making the bacterium a major cause of morbidity and mortality in both the developed and developing world. The species is known to be diverse in many ways, as a product of its natural transformability and of a range of recombination and mutation-based systems. Previous work on pathogenic Neisseria has identified several mechanisms for the generation of diversity of surface structures, including phase variation based on slippage-like mechanisms and sequence conversion of expressed genes using information from silent loci. Comparison of the genome sequences of two N. meningitidis strains, serogroup B MC58 and serogroup A Z2491, suggested further mechanisms of variation, including C-terminal exchange in specific genes and enhanced localised recombination and variation related to repeat arrays. We have sequenced the genome of N. meningitidis strain FAM18, a representative of the ST-11/ET-37 complex, providing the first genome sequence for the disease-causing serogroup C meningococci; it has 1,976 predicted genes, of which 60 do not have orthologues in the previously sequenced serogroup A or B strains. Through genome comparison with Z2491 and MC58 we have further characterised specific mechanisms of genetic variation in N. meningitidis, describing specialised loci for generation of cell surface protein variants and measuring the association between noncoding repeat arrays and sequence variation in flanking genes. Here we provide a detailed view of novel genetic diversification mechanisms in N. meningitidis. Our analysis provides evidence for the hypothesis that the noncoding repeat arrays in neisserial genomes (neisserial intergenic mosaic elements) provide a crucial mechanism for the generation of surface antigen variants. Such variation will have an impact on the interaction with the host tissues, and understanding these mechanisms is important to aid our understanding of the intimate and complex relationship between the human nasopharynx and the meningococcus.This work was supported by the Wellcome Trust through the Beowulf Genomics Initiative