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  • 1
    Publikationsdatum: 2016-07-29
    Beschreibung: 1RXS J180408.9–342058 is a transient neutron star low-mass X-ray binary that exhibited a bright accretion outburst in 2015. We present NuSTAR , Swift , and Chandra observations obtained around the peak brightness of this outburst. The source was in a soft X-ray spectral state and displayed an X-ray luminosity of L X ~= (2–3)  x  10 37 ( D /5.8 kpc) 2 erg s –1 (0.5–10 keV). The NuSTAR data reveal a broad Fe–K emission line that we model as relativistically broadened reflection to constrain the accretion geometry. We found that the accretion disc is viewed at an inclination of i ~= 27°–35° and extended close to the neutron star, down to R in ~= 5–7.5 gravitational radii (~=11–17 km). This inner disc radius suggests that the neutron star magnetic field strength is B 2  x  10 8  G. We find a narrow absorption line in the Chandra /HEG data at an energy of ~=7.64 keV with a significance of ~=4.8. This feature could correspond to blueshifted Fe  xxvi and arise from an accretion disc wind, which would imply an outflow velocity of v out ~= 0.086 c (~=25 800 km s –1 ). However, this would be extreme for an X-ray binary and it is unclear if a disc wind should be visible at the low inclination angle that we infer from our reflection analysis. Finally, we discuss how the X-ray and optical properties of 1RXS J180408.9–342058 are consistent with a relatively small ( P orb 3 h) binary orbit.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2016-06-21
    Beschreibung: Mitochondrial DNA (mtDNA) rearrangements are an important cause of mitochondrial disease and age related mitochondrial dysfunction in tissues including brain and skeletal muscle. It is known that different mtDNA deletions accumulate in single cells, but the detailed nature of these rearrangements is still unknown. To evaluate this we used a complementary set of sensitive assays to explore the mtDNA rearrangements in individual cells from patients with sporadic inclusion body myositis, a late-onset inflammatory myopathy with prominent mitochondrial changes. We identified large-scale mtDNA deletions in individual muscle fibres with 20% of cytochrome c oxidase-deficient myofibres accumulating two or more mtDNA deletions. The majority of deletions removed only the major arc but ~10% of all deletions extended into the minor arc removing the origin of light strand replication (O L ) and a variable number of genes. Some mtDNA molecules contained two deletion sites. Additionally, we found evidence of mitochondrial genome duplications allowing replication and clonal expansion of these complex rearranged molecules. The extended spectrum of mtDNA rearrangements in single cells provides insight into the process of clonal expansion which is fundamental to our understanding of the role of mtDNA mutations in ageing and disease.
    Print ISSN: 0305-1048
    Digitale ISSN: 1362-4962
    Thema: Biologie
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2015-04-07
    Print ISSN: 0302-3427
    Digitale ISSN: 1471-5430
    Thema: Wissenschaftskunde und Wissenschaftsorganisation, Hochschul- und Universitätswesen, Museumswissenschaft
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2015-07-07
    Beschreibung: Developmental changes in the temporal and spatial regulation of gene expression drive the emergence of normal mature brain function, while disruptions in these processes underlie many neurodevelopmental abnormalities. To solidify our foundational knowledge of such changes in a primate brain with an extended period of postnatal maturation like in human, we investigated the whole-genome transcriptional profiles of rhesus monkey brains from birth to adulthood. We found that gene expression dynamics are largest from birth through infancy, after which gene expression profiles transition to a relatively stable state by young adulthood. Biological pathway enrichment analysis revealed that genes more highly expressed at birth are associated with cell adhesion and neuron differentiation, while genes more highly expressed in juveniles and adults are associated with cell death. Neocortex showed significantly greater differential expression over time than subcortical structures, and this trend likely reflects the protracted postnatal development of the cortex. Using network analysis, we identified 27 co-expression modules containing genes with highly correlated expression patterns that are associated with specific brain regions, ages or both. In particular, one module with high expression in neonatal cortex and striatum that decreases during infancy and juvenile development was significantly enriched for autism spectrum disorder (ASD)-related genes. This network was enriched for genes associated with axon guidance and interneuron differentiation, consistent with a disruption in the formation of functional cortical circuitry in ASD.
    Print ISSN: 0964-6906
    Digitale ISSN: 1460-2083
    Thema: Biologie , Medizin
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2016-01-16
    Beschreibung: Observational evidence has been accumulating that thermonuclear X-ray bursts ignited on the surface of neutron stars influence the surrounding accretion flow. Here, we exploit the excellent sensitivity of NuSTAR up to 79 keV to analyse the impact of an X-ray burst on the accretion emission of the neutron star LMXB 4U 1608–52. The ~=200 s long X-ray burst occurred during a hard X-ray spectral state, and had a peak intensity of ~=30–50 per cent of the Eddington limit with no signs of photospheric radius expansion. Spectral analysis suggests that the accretion emission was enhanced up to a factor of ~=5 during the X-ray burst. We also applied a linear unsupervised decomposition method, namely non-negative matrix factorization (NMF), to study this X-ray burst. We find that the NMF performs well in characterizing the evolution of the burst emission and is a promising technique to study changes in the underlying accretion emission in more detail than is possible through conventional spectral fitting. For the burst of 4U 1608–52, the NMF suggests a possible softening of the accretion spectrum during the X-ray burst, which could potentially be ascribed to cooling of a corona. Finally, we report a small (~=3 per cent) but significant rise in the accretion emission ~=0.5 h before the X-ray burst, although it is unclear whether this was related to the X-ray burst ignition.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2015-03-11
    Beschreibung: The purpose of this note is to clarify some details in McDuff and Segal's proof of the group-completion theorem in McDuff and Segal [Homology fibrations and the ‘group-completion’ theorem, Invent. Math. 31 (1975/76), 279–284] and generalize this and the homology fibration criterion of McDuff [Configuration spaces of positive and negative particles, Topology 14 (1975), 91–107] to homology with twisted coefficients. This will be used in Miller and Palmer [Scanning for oriented configuration spaces, preprint, 2014] to identify the limiting homology of ‘oriented’ configuration spaces, which doubly cover the classical configuration spaces of distinct unordered points in a manifold.
    Print ISSN: 0033-5606
    Digitale ISSN: 1464-3847
    Thema: Mathematik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2015-01-16
    Beschreibung: The Arabidopsis Information Portal ( https://www.araport.org ) is a new online resource for plant biology research. It houses the Arabidopsis thaliana genome sequence and associated annotation. It was conceived as a framework that allows the research community to develop and release ‘modules’ that integrate, analyze and visualize Arabidopsis data that may reside at remote sites. The current implementation provides an indexed database of core genomic information. These data are made available through feature-rich web applications that provide search, data mining, and genome browser functionality, and also by bulk download and web services. Araport uses software from the InterMine and JBrowse projects to expose curated data from TAIR, GO, BAR, EBI, UniProt, PubMed and EPIC CoGe. The site also hosts ‘science apps,’ developed as prototypes for community modules that use dynamic web pages to present data obtained on-demand from third-party servers via RESTful web services. Designed for sustainability, the Arabidopsis Information Portal strategy exploits existing scientific computing infrastructure, adopts a practical mixture of data integration technologies and encourages collaborative enhancement of the resource by its user community.
    Print ISSN: 0305-1048
    Digitale ISSN: 1362-4962
    Thema: Biologie
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2016-09-02
    Beschreibung: Periodic pulsations have been found in emission from the ultraluminous X-ray source M82 X-2, strongly suggesting that the emitter is a rotating neutron star rather than a black hole. However, the radiation mechanisms and accretion mode involved have not yet been clearly established. In this paper, we examine the applicability to this object of standard accretion modes for high mass X-ray binaries (HMXBs). We find that spherical wind accretion, which drives OB-type HMXBs, cannot apply here but that there is a natural explanation in terms of an extension of the picture for standard Be-type HMXBs. We show that a neutron star with a moderately strong magnetic field, accreting from a disc-shaped wind emitted by a Be-companion, could be compatible with the observed relation between spin and orbital period. A Roche lobe overflow picture is also possible under certain conditions.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2016-10-17
    Beschreibung: Due to observational challenges, our knowledge of low-level accretion flows around neutron stars is limited. We present NuSTAR , Swift and Chandra observations of the low-mass X-ray binary IGR J17062-6143, which has been persistently accreting at ~=0.1 per cent of the Eddington limit since 2006. Our simultaneous NuSTAR / Swift observations show that the 0.5–79 keV spectrum can be described by a combination of a power law with a photon index of ~= 2, a blackbody with a temperature of kT bb ~= 0.5 keV (presumably arising from the neutron star surface) and disc reflection. Modelling the reflection spectrum suggests that the inner accretion disc was located at R in 100 GM / c 2 (225 km) from the neutron star. The apparent truncation may be due to evaporation of the inner disc into a radiatively-inefficient accretion flow, or due to the pressure of the neutron star magnetic field. Our Chandra gratings data reveal possible narrow emission lines near 1 keV that can be modelled as reflection or collisionally ionized gas, and possible low-energy absorption features that could point to the presence of an outflow. We consider a scenario in which this neutron star has been able to sustain its low accretion rate through magnetic inhibition of the accretion flow, which gives some constraints on its magnetic field strength and spin period. In this configuration, IGR J17062-6143 could exhibit a strong radio jet as well as a (propeller-driven) wind-like outflow.
    Print ISSN: 0035-8711
    Digitale ISSN: 1365-2966
    Thema: Physik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2015-07-25
    Beschreibung: We study the number of changes of the initial segment Z s n for computable approximations of a Martin-Löf random $${\Delta }_{2}^{0}$$ set Z . We establish connections between this number of changes and various notions of computability theoretic lowness, as well as the fundamental thesis that, among random sets, randomness is antithetical to computational power. We introduce a new randomness notion, called balanced randomness, which implies that for each computable approximation and each constant c , there are infinitely many n such that Z s n changes more than c 2 n times. We establish various connections with -c.e. tracing and omega; -c.e. jump domination, a new lowness property. We also examine some relationships to randomness theoretic notions of highness, and give applications to the study of (weak) Demuth cuppability.
    Print ISSN: 0955-792X
    Digitale ISSN: 1465-363X
    Thema: Informatik , Mathematik
    Publiziert von Oxford University Press
    Standort Signatur Erwartet Verfügbarkeit
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