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  • 1
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    Jet-intracluster medium interaction in Hydra A - I. Estimates of jet velocity from inner knots (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-01
    Description: We present the first stage of an investigation of the interactions of the jets in the radio galaxy Hydra A with the intracluster medium. We consider the jet kinetic power, the galaxy and cluster atmosphere and the inner structure of the radio source. Analysing radio observations of the inner lobes of Hydra A by Taylor et al. we confirm the jet power estimates ~10 45 erg s –1 derived by Wise et al. from dynamical analysis of the X-ray cavities. With this result and a model for the galaxy halo, we explore the jet–intracluster medium interactions occurring on a scale of 10 kpc using two-dimensional, axisymmetric, relativistic pure hydrodynamic simulations. A key feature is that we identify the three bright knots in the northern jet as biconical reconfinement shocks, which result when an overpressured jet starts to come into equilibrium with the galactic atmosphere. Through an extensive parameter space study we deduce that the jet velocity is approximately 0.8 c at a distance 0.5 kpc from the black hole. The combined constraints of jet power, the observed jet radius profile along the jet and the estimated jet pressure and jet velocity imply a value of the jet density parameter 13 for the northern jet. We show that for a jet β = 0.8 and = 42°, an intrinsic asymmetry in the emissivity of the northern and southern jet is required for a consistent brightness ratio 7 estimated from the 6-cm Very Large Array image of Hydra A.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Growth Temperature and Genome Size in Bacteria Are Negatively Correlated, Suggesting Genomic Streamlining During Thermal Adaptation (2013)
    Oxford University Press
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    Publication Date: 2013-05-16
    Description: Prokaryotic genomes are small and compact. Either this feature is caused by neutral evolution or by natural selection favoring small genomes—genome streamlining. Three separate prior lines of evidence argue against streamlining for most prokaryotes. We find that the same three lines of evidence argue for streamlining in the genomes of thermophile bacteria. Specifically, with increasing habitat temperature and decreasing genome size, the proportion of genomic DNA in intergenic regions decreases. Furthermore, with increasing habitat temperature, generation time decreases. Genome-wide selective constraints do not decrease as in the reduced genomes of host-associated species. Reduced habitat variability is not a likely explanation for the smaller genomes of thermophiles. Genome size may be an indirect target of selection due to its association with cell volume. We use metabolic modeling to demonstrate that known changes in cell structure and physiology at high temperature can provide a selective advantage to reduce cell volume at high temperatures.
    Electronic ISSN: 1759-6653
    Topics: Biology
    Published by Oxford University Press
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  • 3
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    X-ray spectral studies of TeV {gamma}-ray emitting blazars (2016)
    Oxford University Press
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    Publication Date: 2016-03-06
    Description: This work is a summary of the X-ray spectral studies of 29 TeV (10 12 eV, tera-electron-volt) -ray emitting blazars observed with Swift /XRT, especially focusing on sources for which the X-ray regime allows us to study the low- and the high-energy ends of the particle distribution function. Variability studies require simultaneous coverage, ideally sampling different flux states of each source. This is achieved using X-ray observations by disentangling the high-energy end of the synchrotron emission and the low-energy end of the Compton emission, which are produced by the same electron population. We focused on a sample of 29 TeV -ray emitting blazars with the best signal-to-noise X-ray observations collected with Swift /XRT in the energy range 0.3–10 keV during 10 yr of Swift /XRT operations. We investigate the X-ray spectral shapes and the effects of different corrections for neutral hydrogen absorption and decompose the synchrotron and inverse Compton components. For five sources (3C 66A, S5 0716+714, W Comae, 4C +21.35 and BL Lacertae) a superposition of both components is observed in the X-ray band, permitting simultaneous, time-resolved studies of both ends of the electron distribution. The analysis of multi-epoch observations revealed that the break energy of the X-ray spectrum varies only by a small factor with flux changes. Flux variability is more pronounced in the synchrotron domain (high-energy end of the electron distribution) than in the Compton domain (low-energy end of the electron distribution). The spectral shape of the Compton domain is stable, while the flux of the synchrotron domain is variable. These changes cannot be described by simple variations of the cut-off energy, suggesting that the high-energy end of the electron distribution is not generally well described by cooling only.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Human skeletal muscle xenograft as a new preclinical model for muscle disorders (2014)
    Oxford University Press
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    Publication Date: 2014-05-23
    Description: Development of novel therapeutics requires good animal models of disease. Disorders for which good animal models do not exist have very few drugs in development or clinical trial. Even where there are accepted, albeit imperfect models, the leap from promising preclinical drug results to positive clinical trials commonly fails, including in disorders of skeletal muscle. The main alternative model for early drug development, tissue culture, lacks both the architecture and, usually, the metabolic fidelity of the normal tissue in vivo . Herein, we demonstrate the feasibility and validity of human to mouse xenografts as a preclinical model of myopathy. Human skeletal muscle biopsies transplanted into the anterior tibial compartment of the hindlimbs of NOD- Rag1 null IL2r null immunodeficient host mice regenerate new vascularized and innervated myofibers from human myogenic precursor cells. The grafts exhibit contractile and calcium release behavior, characteristic of functional muscle tissue. The validity of the human graft as a model of facioscapulohumeral muscular dystrophy is demonstrated in disease biomarker studies, showing that gene expression profiles of xenografts mirror those of the fresh donor biopsies. These findings illustrate the value of a new experimental model of muscle disease, the human muscle xenograft in mice, as a feasible and valid preclinical tool to better investigate the pathogenesis of human genetic myopathies and to more accurately predict their response to novel therapeutics.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 5
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    Compressive MIMO Beamforming of Data Collected in a Refractive Environment (2017)
    Wiley
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    Publication Date: 2017-11-10
    Description: The phenomenon of ducting is caused by abnormal atmospheric refractivity patterns, and is known to allow electromagnetic (EM) waves to propagate over the horizon with unusually low propagation loss. It is unknown what effect ducting has on multiple input multiple output (MIMO) channels, particularly its effect on multipath propagation in MIMO channels. A high accuracy angle-of-arrival (AoA) and angle-of-departure (AoD) estimation technique for MIMO communications, which we will refer to as compressive MIMO beamforming, was tested on simulated data, then applied to experimental data taken from an over the horizon (OTH) MIMO testbed located in a known ducting hotspot in southern California. The multipath channel was estimated from the receiver data recorded over a period of 18 days, and an analysis was performed on the recorded data. The goal is to observe the evolution of the MIMO multipath channel as atmospheric ducts form and dissipate to gain some understanding of the behavior of channels in a refractive environment. This work is motivated by the idea that some multipath characteristics of MIMO channels within atmospheric ducts could yield important information about the duct.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Modelling the Milky Way – I. Method and first results fitting the thick disc and halo with DES-Y3 data (2020)
    Oxford University Press
    Details
    Publication Date: 2020-07-09
    Description: We present a technique to fit the stellar components of the Galaxy by comparing Hess Diagrams (HDs) generated from trilegal models to real data. We apply this technique, which we call mwfitting, to photometric data from the first 3 yr of the Dark Energy Survey (DES). After removing regions containing known resolved stellar systems such as globular clusters, dwarf galaxies, nearby galaxies, the Large Magellanic Cloud, and the Sagittarius Stream, our main sample spans a total area of ∼2300 deg2. We further explore a smaller subset (∼1300 deg2) that excludes all regions with known stellar streams and stellar overdensities. Validation tests on synthetic data possessing similar properties to the DES data show that the method is able to recover input parameters with a precision better than 3 per cent. We fit the DES data with an exponential thick disc model and an oblate double power-law halo model. We find that the best-fitting thick disc model has radial and vertical scale heights of 2.67 ± 0.09 kpc and 925 ± 40 pc, respectively. The stellar halo is fit with a broken power-law density profile with an oblateness of 0.75 ± 0.01, an inner index of 1.82 ± 0.08, an outer index of 4.14 ± 0.05, and a break at 18.52 ± 0.27 kpc from the Galactic centre. Several previously discovered stellar overdensities are recovered in the residual stellar density map, showing the reliability of mwfitting in determining the Galactic components. Simulations made with the best-fitting parameters are a promising way to predict Milky Way star counts for surveys such as the LSST and Euclid.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 7
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    Fitness Trade-Offs Determine the Role of the Molecular Chaperonin GroEL in Buffering Mutations (2015)
    Oxford University Press
    Details
    Publication Date: 2015-09-22
    Description: Molecular chaperones fold many proteins and their mutated versions in a cell and can sometimes buffer the phenotypic effect of mutations that affect protein folding. Unanswered questions about this buffering include the nature of its mechanism, its influence on the genetic variation of a population, the fitness trade-offs constraining this mechanism, and its role in expediting evolution. Answering these questions is fundamental to understand the contribution of buffering to increase genetic variation and ecological diversification. Here, we performed experimental evolution, genome resequencing, and computational analyses to determine the trade-offs and evolutionary trajectories of Escherichia coli expressing high levels of the essential chaperonin GroEL. GroEL is abundantly present in bacteria, particularly in bacteria with large loads of deleterious mutations, suggesting its role in mutational buffering. We show that groEL overexpression is costly to large populations evolving in the laboratory, leading to groE expression decline within 66 generations. In contrast, populations evolving under the strong genetic drift characteristic of endosymbiotic bacteria avoid extinction or can be rescued in the presence of abundant GroEL. Genomes resequenced from cells evolved under strong genetic drift exhibited significantly higher tolerance to deleterious mutations at high GroEL levels than at native levels, revealing that GroEL is buffering mutations in these cells. GroEL buffered mutations in a highly diverse set of proteins that interact with the environment, including substrate and ion membrane transporters, hinting at its role in ecological diversification. Our results reveal the fitness trade-offs of mutational buffering and how genetic variation is maintained in populations.
    Print ISSN: 0737-4038
    Electronic ISSN: 1537-1719
    Topics: Biology
    Published by Oxford University Press
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  • 8
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    How Archiving by Freezing Affects the Genome-Scale Diversity of Escherichia coli Populations (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-11
    Description: In the experimental evolution of microbes such as Escherichia coli , many replicate populations are evolved from a common ancestor. Freezing a population sample supplemented with the cryoprotectant glycerol permits later analysis or restarting of an evolution experiment. Typically, each evolving population, and thus each sample archived in this way, consists of many unique genotypes and phenotypes. The effect of archiving on such a heterogeneous population is unknown. Here, we identified optimal archiving conditions for E. coli. We also used genome sequencing of archived samples to study the effects that archiving has on genomic population diversity. We observed no allele substitutions and mostly small changes in allele frequency. Nevertheless, principal component analysis of genome-scale allelic diversity shows that archiving affects diversity across many loci. We showed that this change in diversity is due to selection rather than drift. In addition, ~1% of rare alleles that occurred at low frequencies were lost after treatment. Our observations imply that archived populations may be used to conduct fitness or other phenotypic assays of populations, in which the loss of a rare allele may have negligible effects. However, caution is appropriate when sequencing populations restarted from glycerol stocks, as well as when using glycerol stocks to restart or replay evolution. This is because the loss of rare alleles can alter the future evolutionary trajectory of a population if the lost alleles were strongly beneficial.
    Electronic ISSN: 1759-6653
    Topics: Biology
    Published by Oxford University Press
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  • 9
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    Shale gas: Energy innovation in a (non-)knowledge society: A press discourse analysis (2015)
    Oxford University Press
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    Publication Date: 2015-04-07
    Description: For years, technological innovations have been the cause of controversy. In reaction to this, increasingly often the bodies responsible for implementing these innovations undertake social dialogue with stakeholders. An important environment for this is media discourse, which defines the problems and key actors and disseminates strategies for argumentation. Effective communication on public policies is one of the challenges in deliberative democracy. This paper aims to analyse the role of experts and knowledge in reference to the models of public communication on shale gas. Using a qualitative press analysis, an incoherence was observed in the understanding of knowledge and the profile of experts and the models of communication using them. The communication, which is rather oriented towards persuasion without legitimisation of scientific factual knowledge, fails. Reference in the discourse to the unknown or uncertain directs attention to the issues related to the strategic exploitation of nonknowledge.
    Print ISSN: 0302-3427
    Electronic ISSN: 1471-5430
    Topics: Nature of Science, Research, Systems of Higher Education, Museum Science
    Published by Oxford University Press
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  • 10
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    Digging deeper into the Southern skies: a compact Milky Way companion discovered in first-year Dark Energy Survey data (2016)
    Luque, E., Queiroz, A., Santiago, B., Pieres, A., Balbinot, E., Bechtol, K., Drlica-Wagner, A., Neto, A. F., da Costa, L. N., Maia, M. A. G., Yanny, B., Abbott, T., Allam, S., Benoit-Levy, A., Bertin, E., Brooks, D., Buckley-Geer, E., Burke, D. L., Rosell, A. C., Kind, M. C., Carretero, J., Cunha, C. E., Desai, S., Diehl, H. T., Dietrich, J. P., Eifler, T. F., Finley, D. A., Flaugher, B., Fosalba, P., Frieman, J., Gerdes, D. W., Gruen, D., Gutierrez, G., Honscheid, K., James, D. J., Kuehn, K., Kuropatkin, N., Lahav, O., Li, T. S., March, M., Marshall, J. L., Martini, P., Miquel, R., Neilsen, E., Nichol, R. C., Nord, B., Ogando, R., Plazas, A. A., Romer, A. K., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Soares-Santos, M., Sobreira, F., Suchyta, E., Swanson, M. E. C., Tarle, G., Thaler, J., Tucker, D., Walker, A. R., Zhang, Y.
    Oxford University Press
    Details
    Publication Date: 2016-03-09
    Description: We use the first-year Dark Energy Survey (DES) data down to previously unprobed photometric depths to search for stellar systems in the Galactic halo, therefore complementing the previous analysis of the same data carried out by our group earlier this year. Our search is based on a matched filter algorithm that produces stellar density maps consistent with stellar population models of various ages, metallicities, and distances over the survey area. The most conspicuous density peaks in these maps have been identified automatically and ranked according to their significance and recurrence for different input models. We report the discovery of one additional stellar system besides those previously found by several authors using the same first-year DES data. The object is compact, and consistent with being dominated by an old and metal-poor population. DES 1 is found at high significance and appears in the DES images as a compact concentration of faint blue point sources. Assuming different spatial profile parameterizations, the best-fitting heliocentric distance and total absolute magnitude in the range of 77.6–87.1 kpc and –3.00 M V  –2.21, respectively. The half-light radius of this object, r h  ~ 10 pc and total luminosity are consistent with it being a low-mass halo cluster. It is also found to have a very elongated shape ( ~ 0.57). In addition, our deeper probe of DES first-year data confirms the recently reported satellite galaxy candidate Horologium II as a significant stellar overdensity. We also infer its structural properties and compare them to those reported in the literature.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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