University of Warwick

About: University of Warwick is a education organization based out in Coventry, Warwickshire, United Kingdom. It is known for research contribution in the topics: Population & White dwarf. The organization has 26212 authors who have published 77127 publications receiving 2666552 citations. The organization is also known as: Warwick University & The University of Warwick.

A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b

Abstract: In the ultraviolet spectrum, the Neptune-mass exoplanet GJ 436b is shown to have transit depths far greater than those seen in the optical spectrum, indicating that it is surrounded and trailed by a large cloud composed mainly of hydrogen atoms. Observations of the Neptune-mass exoplanet GJ 436b in the ultraviolet reveal a transit signature that is much deeper and longer than in the optical spectrum, an indication that it is surrounded and trailed by a large cloud of gas escaping from the planetary atmosphere. Numerical simulations indicate that in the ultraviolet GJ 436b looks like a giant comet. The authors propose that the gaseous 'tail' is composed mainly of hydrogen atoms and suggest that the exoplanet may have lost 10% of its atmosphere in its early life. Exoplanets orbiting close to their parent stars may lose some fraction of their atmospheres because of the extreme irradiation1,2,3,4,5,6. Atmospheric mass loss primarily affects low-mass exoplanets, leading to the suggestion that hot rocky planets7,8,9 might have begun as Neptune-like10,11,12,13,14,15,16, but subsequently lost all of their atmospheres; however, no confident measurements have hitherto been available. The signature of this loss could be observed in the ultraviolet spectrum, when the planet and its escaping atmosphere transit the star, giving rise to deeper and longer transit signatures than in the optical spectrum17. Here we report that in the ultraviolet the Neptune-mass exoplanet GJ 436b (also known as Gliese 436b) has transit depths of 56.3 ± 3.5% (1σ), far beyond the 0.69% optical transit depth. The ultraviolet transits repeatedly start about two hours before, and end more than three hours after the approximately one hour optical transit, which is substantially different from one previous claim6 (based on an inaccurate ephemeris). We infer from this that the planet is surrounded and trailed by a large exospheric cloud composed mainly of hydrogen atoms. We estimate a mass-loss rate in the range of about 108–109 grams per second, which is far too small to deplete the atmosphere of a Neptune-like planet in the lifetime of the parent star, but would have been much greater in the past.

Focus group method and methodology: current practice and recent debate

Abstract: This paper considers the contemporary use of focus groups as a method of data collection within qualitative research settings. The authors draw upon their own experiences of using focus groups in educational and 'community' user-group environments in order to provide an overview of recent issues and debates surrounding the deployment of focus group methods and to pick out specific areas of contention in relation to both their epistemological and practical implications. Accordingly, the paper reflects on some of the realities of 'doing' focus groups whilst, at the same time, highlighting common problems and dilemmas which beginning researchers might encounter in their application. In turn, the paper raises a number of related issues around which there appears to have been a lack of academic discussion to date.

Genome sequence of the cyanobacterium Prochlorococcus marinus SS120, a nearly minimal oxyphototrophic genome

Abstract: Prochlorococcus marinus, the dominant photosynthetic organism in the ocean, is found in two main ecological forms: high-light-adapted genotypes in the upper part of the water column and low-light-adapted genotypes at the bottom of the illuminated layer. P. marinus SS120, the complete genome sequence reported here, is an extremely low-light-adapted form. The genome of P. marinus SS120 is composed of a single circular chromosome of 1,751,080 bp with an average G+C content of 36.4%. It contains 1,884 predicted protein-coding genes with an average size of 825 bp, a single rRNA operon, and 40 tRNA genes. Together with the 1.66-Mbp genome of P. marinus MED4, the genome of P. marinus SS120 is one of the two smallest genomes of a photosynthetic organism known to date. It lacks many genes that are involved in photosynthesis, DNA repair, solute uptake, intermediary metabolism, motility, phototaxis, and other functions that are conserved among other cyanobacteria. Systems of signal transduction and environmental stress response show a particularly drastic reduction in the number of components, even taking into account the small size of the SS120 genome. In contrast, housekeeping genes, which encode enzymes of amino acid, nucleotide, cofactor, and cell wall biosynthesis, are all present. Because of its remarkable compactness, the genome of P. marinus SS120 might approximate the minimal gene complement of a photosynthetic organism.

The lux autoinducer regulates the production of exoenzyme virulence determinants in Erwinia carotovora and Pseudomonas aeruginosa.

Abstract: Erwinia carotovora and Pseudomonas aeruginosa secrete exoenzymes that contribute to the pathogenesis of plant and mammalian infections respectively. E.carotovora mutants defective in synthesis of the pectinase, cellulase and protease exoenzymes were isolated and classified into two groups. Group 2 mutants were found to be defective in the production of a small freely diffusible molecule, N-3-(oxohexanoyl)-L-homoserine, lactone (HSL), and were avirulent. Addition of exogenous HSL to these group 2 mutants restores synthesis of the exoenzymes and virulence in planta. Of the exoenzymes of P.aeruginosa the metalloprotease, elastase, is an established virulence determinant. Mutants of P.aeruginosa that are defective in elastase production have been isolated and were again found to fall into two groups. Analogous to the group 2 mutants of E.carotovora, group 2 mutants of P. aeruginosa are defective in the synthesis of HSL and exogenous HSL restores elastase production. HSL has now been linked to the control of bioluminescence in Vibrio fischeri, carbapenem antibiotic production of E.carotovora and the above exoenzyme virulence determinants. This information significantly enhances our understanding of the extent and nature of pheromone mediated gene expression control in prokaryotes.

Handbook of Functional MRI Data Analysis

Abstract: Functional magnetic resonance imaging (fMRI) has become the most popular method for imaging brain function. Handbook of Functional MRI Data Analysis provides a comprehensive and practical introduction to the methods used for fMRI data analysis. Using minimal jargon, this book explains the concepts behind processing fMRI data, focusing on the techniques that are most commonly used in the field. This book provides background about the methods employed by common data analysis packages including FSL, SPM and AFNI. Some of the newest cutting-edge techniques, including pattern classification analysis, connectivity modeling and resting state network analysis, are also discussed. Readers of this book, whether newcomers to the field or experienced researchers, will obtain a deep and effective knowledge of how to employ fMRI analysis to ask scientific questions and become more sophisticated users of fMRI analysis software.