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  • 1
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    Perovskite oxides for visible-light-absorbing ferroelectric and photovoltaic materials (2013)
    Nature Publishing Group (NPG)
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    Publication Date: 2013-11-12
    Description: Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices, and for the coupling of light absorption with other functional properties. In these materials, the strong inversion symmetry breaking that is due to spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the bandgap, which may enable efficiencies beyond the maximum possible in a conventional p-n junction solar cell. Ferroelectric oxides are also stable in a wide range of mechanical, chemical and thermal conditions and can be fabricated using low-cost methods such as sol-gel thin-film deposition and sputtering. Recent work has shown how a decrease in ferroelectric layer thickness and judicious engineering of domain structures and ferroelectric-electrode interfaces can greatly increase the current harvested from ferroelectric absorber materials, increasing the power conversion efficiency from about 10(-4) to about 0.5 per cent. Further improvements in photovoltaic efficiency have been inhibited by the wide bandgaps (2.7-4 electronvolts) of ferroelectric oxides, which allow the use of only 8-20 per cent of the solar spectrum. Here we describe a family of single-phase solid oxide solutions made from low-cost and non-toxic elements using conventional solid-state methods: [KNbO3]1 - x[BaNi1/2Nb1/2O3 - delta]x (KBNNO). These oxides exhibit both ferroelectricity and a wide variation of direct bandgaps in the range 1.1-3.8 electronvolts. In particular, the x = 0.1 composition is polar at room temperature, has a direct bandgap of 1.39 electronvolts and has a photocurrent density approximately 50 times larger than that of the classic ferroelectric (Pb,La)(Zr,Ti)O3 material. The ability of KBNNO to absorb three to six times more solar energy than the current ferroelectric materials suggests a route to viable ferroelectric semiconductor-based cells for solar energy conversion and other applications.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Grinberg, Ilya -- West, D Vincent -- Torres, Maria -- Gou, Gaoyang -- Stein, David M -- Wu, Liyan -- Chen, Guannan -- Gallo, Eric M -- Akbashev, Andrew R -- Davies, Peter K -- Spanier, Jonathan E -- Rappe, Andrew M -- England -- Nature. 2013 Nov 28;503(7477):509-12. doi: 10.1038/nature12622. Epub 2013 Nov 10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉The Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24213630" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Integrin-modulating therapy prevents fibrosis and autoimmunity in mouse models of scleroderma (2013)
    Nature Publishing Group (NPG)
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    Publication Date: 2013-10-11
    Description: In systemic sclerosis (SSc), a common and aetiologically mysterious form of scleroderma (defined as pathological fibrosis of the skin), previously healthy adults acquire fibrosis of the skin and viscera in association with autoantibodies. Familial recurrence is extremely rare and causal genes have not been identified. Although the onset of fibrosis in SSc typically correlates with the production of autoantibodies, whether they contribute to disease pathogenesis or simply serve as a marker of disease remains controversial and the mechanism for their induction is largely unknown. The study of SSc is hindered by a lack of animal models that recapitulate the aetiology of this complex disease. To gain a foothold in the pathogenesis of pathological skin fibrosis, we studied stiff skin syndrome (SSS), a rare but tractable Mendelian disorder leading to childhood onset of diffuse skin fibrosis with autosomal dominant inheritance and complete penetrance. We showed previously that SSS is caused by heterozygous missense mutations in the gene (FBN1) encoding fibrillin-1, the main constituent of extracellular microfibrils. SSS mutations all localize to the only domain in fibrillin-1 that harbours an Arg-Gly-Asp (RGD) motif needed to mediate cell-matrix interactions by binding to cell-surface integrins. Here we show that mouse lines harbouring analogous amino acid substitutions in fibrillin-1 recapitulate aggressive skin fibrosis that is prevented by integrin-modulating therapies and reversed by antagonism of the pro-fibrotic cytokine transforming growth factor beta (TGF-beta). Mutant mice show skin infiltration of pro-inflammatory immune cells including plasmacytoid dendritic cells, T helper cells and plasma cells, and also autoantibody production; these findings are normalized by integrin-modulating therapies or TGF-beta antagonism. These results show that alterations in cell-matrix interactions are sufficient to initiate and sustain inflammatory and pro-fibrotic programmes and highlight new therapeutic strategies.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3992987/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3992987/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gerber, Elizabeth E -- Gallo, Elena M -- Fontana, Stefani C -- Davis, Elaine C -- Wigley, Fredrick M -- Huso, David L -- Dietz, Harry C -- P01 AR049698/AR/NIAMS NIH HHS/ -- P01-AR049698/AR/NIAMS NIH HHS/ -- R01 AR041135/AR/NIAMS NIH HHS/ -- R01-AR41135/AR/NIAMS NIH HHS/ -- Howard Hughes Medical Institute/ -- England -- Nature. 2013 Nov 7;503(7474):126-30. doi: 10.1038/nature12614. Epub 2013 Oct 9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24107997" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Motifs/genetics ; Amino Acid Substitution/genetics ; Animals ; Antibodies, Antinuclear/immunology ; Antibodies, Neutralizing/immunology/pharmacology/therapeutic use ; Autoimmunity/*drug effects/immunology ; Contracture/*drug therapy/immunology/*pathology/prevention & control ; Dendritic Cells/drug effects ; Female ; Fibrosis/drug therapy/pathology/prevention & control ; Integrins/*drug effects/*metabolism ; Male ; Mice ; Microfilament Proteins/chemistry/genetics/metabolism ; Mutation, Missense/genetics ; Plasma Cells/drug effects ; Scleroderma, Systemic/*drug therapy/immunology/*pathology/prevention & control ; Skin Diseases, Genetic/*drug therapy/immunology/*pathology/prevention & control ; T-Lymphocytes, Helper-Inducer/drug effects ; Transforming Growth Factor beta/antagonists & inhibitors/immunology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    Observational constraints on the powering mechanism of transient relativistic jets (2013)
    Oxford University Press
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    Publication Date: 2013-04-03
    Description: We revisit the paradigm of the dependence of jet power on black hole (BH) spin in accreting BH systems. In a previous paper, we showed that the luminosity of compact jets continuously launched due to accretion on to BHs in X-ray binaries (analogous to those that dominate the kinetic feedback from active galactic nuclei) does not appear to correlate with reported BH spin measurements. It is therefore unclear whether extraction of the BH spin energy is the main driver powering compact jets from accreting BHs. Occasionally, BH X-ray binaries produce discrete, transient (ballistic) jets for a brief time over accretion state changes. Here, we quantify the dependence of the power of these transient jets (adopting two methods to infer the jet power) on BH spin, making use of all the available data in the current literature, which include 12 BHs with both measured spin parameters and radio flares over the state transition. In several sources, regular, well-sampled radio monitoring has shown that the peak radio flux differs dramatically depending on the outburst (up to a factor of 1000), whereas the total power required to energize the flare may only differ by a factor of 4 between outbursts. The peak flux is determined by the total energy in the flare and the time over which it is radiated (which can vary considerably between outbursts). Using a Bayesian fitting routine, we rule out a statistically significant positive correlation between transient jet power measured using these methods and current estimates of BH spin. Even when selecting sub-samples of the data that disregard some methods of BH spin measurement or jet power measurement, no correlation is found in all cases.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    A clean sightline to quiescence: multiwavelength observations of the high Galactic latitude black hole X-ray binary Swift J1357.2-0933 (2016)
    Oxford University Press
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    Publication Date: 2016-01-02
    Description: We present coordinated multiwavelength observations of the high Galactic latitude ( b  = +50°) black hole X-ray binary (BHXB) Swift J1357.2–0933 in quiescence. Our broad-band spectrum includes strictly simultaneous radio and X-ray observations, and near-infrared, optical, and ultraviolet data taken 1–2 d later. We detect Swift J1357.2–0933 at all wavebands except for the radio ( f 5 GHz 〈 3.9 μJy beam –1 ; 3 rms ). Given current constraints on the distance (2.3–6.3 kpc), its 0.5–10 keV X-ray flux corresponds to an Eddington ratio L X / L Edd  = 4  x  10 –9 –3  x  10 –8 (assuming a black hole mass of 10 M ). The broad-band spectrum is dominated by synchrotron radiation from a relativistic population of outflowing thermal electrons, which we argue to be a common signature of short-period quiescent BHXBs. Furthermore, we identify the frequency where the synchrotron radiation transitions from optically thick-to-thin ( b 2–5  x  10 14  Hz), which is the most robust determination of a ‘jet break’ for a quiescent BHXB to date. Our interpretation relies on the presence of steep curvature in the ultraviolet spectrum, a frequency window made observable by the low amount of interstellar absorption along the line of sight. High Galactic latitude systems like Swift J1357.2–0933 with clean ultraviolet sightlines are crucial for understanding black hole accretion at low luminosities.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Shell-shocked: the interstellar medium near Cygnus X-1 (2014)
    Oxford University Press
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    Publication Date: 2014-12-10
    Description: We conduct a detailed case study of the interstellar shell near the high-mass X-ray binary, Cygnus X-1. We present new WIYN optical spectroscopic and Chandra X-ray observations of this region, which we compare with detailed mappings iii shock models, to investigate the outflow powering the shell. Our analysis places improved, physically motivated constraints on the nature of the shock wave and the interstellar medium (ISM) it is plowing through. We find that the shock is travelling at less than a few hundred km s –1 through a low-density ISM (〈5 cm –3 ). We calculate a robust, 3 upper limit to the total, time-averaged power needed to drive the shock wave and inflate the bubble, 〈2 10 38  erg s –1 . We then review possible origins of the shock wave. We find that a supernova origin to the shock wave is unlikely and that the black hole jet and/or O-star wind can both be central drivers of the shock wave. We conclude that the source of the Cygnus X-1 shock wave is far from solved.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Constraints on relativistic jets in quiescent black hole X-ray binaries from broad-band spectral modelling (2014)
    Oxford University Press
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    Publication Date: 2014-12-12
    Description: The nature of black hole jets at the lowest detectable luminosities remains an open question, largely due to a dearth of observational constraints. Here, we present a new, nearly simultaneous broad-band spectrum of the black hole X-ray binary (BHXB) XTE J1118+480 at an extremely low Eddington ratio ( L X  ~ 10 –8.5 L Edd ). Our new spectral energy distribution (SED) includes the radio, near-infrared, optical, ultraviolet, and X-ray wavebands. XTE J1118+480 is now the second BHXB at such a low Eddington ratio with a well-sampled SED, thereby providing new constraints on highly sub-Eddington accretion flows and jets, and opening the door to begin comparison studies between systems. We apply a multizone jet model to the new broad-band SED, and we compare our results to previous fits to the same source using the same model at 4–5 decades higher luminosity. We find that after a BHXB transitions to the so-called quiescent spectral state, the jet base becomes more compact (by up to an order of magnitude) and slightly cooler (by at least a factor of 2). Our preferred model fit indicates that jet particle acceleration is much weaker after the transition into quiescence. That is, accelerated non-thermal particles no longer reach high enough Lorentz factors to contribute significant amounts of synchrotron X-ray emission. Instead, the X-ray waveband is dominated by synchrotron self-Compton emission from a population of mildly relativistic electrons with a quasi-thermal velocity distribution that are associated with the jet base. The corresponding (thermal) synchrotron component from the jet base emits primarily in the infrared through ultraviolet wavebands. Our results on XTE J1118+480 are consistent with broad-band modelling for A0620-00 (the only other comparably low Eddington ratio BHXB with a well-sampled SED) and for Sgr A* (the quiescent supermassive black hole at the Galactic centre). The above could therefore represent a canonical baseline geometry for accreting black holes in quiescence. We conclude with suggestions for future studies to further investigate the above scenario.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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