72 research outputs found
On the masses of neutron stars
We analyze the currently available observations of X-ray binaries in a
consistent way, to re-determine the masses of the neutron stars in these
systems. In particular, our attention is focussed on a realistic and consistent
assessment of observational uncertainties and sources of systematic error.
Confidence limits for these new mass estimates are generally less optimistic
than previously assumed. The available observations, including data on six
radio pulsars, do not firmly constrain the equation of state of neutron star
matter. In particular, a firm upper mass limit cannot yet be established. An
improvement of the accuracy of optical data holds the key to further progress.Comment: 5 pages of compressed, uuencoded postscript (text+figure). Accepted
for publication in A&A. In case of problems, contact [email protected]
Spectroscopy of HD 77581 and the mass of Vela X-1
We present new high-resolution, high signal-to-noise optical spectra of HD 77581, the optical counterpart of the X-ray source Vela X-1, and determine radial velocities from these spectra, as well as from high-resolution IUE spectra and from digitized photographic spectra. The measured velocities show strong deviations from a pure Keplerian radial-velocity curve, which are autocorrelated within one night, but not from one night to another. Since lines of different ions exhibit very similar changes in profile, these deviations most likely reflect large-scale motions of the stellar surface akin to non-radial pulsations. A possible cause could be that the varying tidal force exerted by the neutron star in its eccentric orbit excites high-order pulsation modes in the optical star which interfere constructively for short time intervals. The effect of such velocity excursions on the orbital solution is estimated by means of a Monte-Carlo simulation technique. We investigate sources of systematic error, due to, e.g., the tidal deformation of the star, and find, in particular, evidence for a systematic perturbation of the radial velocity near the time of velocity minimum. This possible distortion severely compromises the accuracy of the radial-velocity amplitude, leading to a 95\% confidence range of 18.0--28.2\,\kms. The corresponding 95\% confidence limits of the masses are given by \MX=1.9_{-0.5}^{+0.7}\,\Msun and \Mopt=23.5_{-1.5}^{+2.2}\,\Msun
Evolution of Neutron-Star, Carbon-Oxygen White-Dwarf Binaries
At least one, but more likely two or more, eccentric neutron-star,
carbon-oxygen white-dwarf binaries with an unrecycled pulsar have been
observed. According to the standard scenario for evolving neutron stars which
are recycled in common envelope evolution we expect to observe \gsim 50 such
circular neutron star-carbon oxygen white dwarf binaries, since their formation
rate is roughly equal to that of the eccentric binaries and the time over which
they can be observed is two orders of magnitude longer, as we shall outline. We
observe at most one or two such circular binaries and from that we conclude
that the standard scenario must be revised. Introducing hypercritical accretion
into common envelope evolution removes the discrepancy by converting the
neutron star into a black hole which does not emit radio waves, and therefore
would not be observed.Comment: 25 pages, 1 figure, accepted in Ap
On the future of astrostatistics: statistical foundations and statistical practice
This paper summarizes a presentation for a panel discussion on "The Future of
Astrostatistics" held at the Statistical Challenges in Modern Astronomy V
conference at Pennsylvania State University in June 2011. I argue that the
emerging needs of astrostatistics may both motivate and benefit from
fundamental developments in statistics. I highlight some recent work within
statistics on fundamental topics relevant to astrostatistical practice,
including the Bayesian/frequentist debate (and ideas for a synthesis),
multilevel models, and multiple testing. As an important direction for future
work in statistics, I emphasize that astronomers need a statistical framework
that explicitly supports unfolding chains of discovery, with acquisition,
cataloging, and modeling of data not seen as isolated tasks, but rather as
parts of an ongoing, integrated sequence of analyses, with information and
uncertainty propagating forward and backward through the chain. A prototypical
example is surveying of astronomical populations, where source detection,
demographic modeling, and the design of survey instruments and strategies all
interact.Comment: 8 pp, 2 figures. To appear in "Statistical Challenges in Modern
Astronomy V," (Lecture Notes in Statistics, Vol. 209), ed. Eric D. Feigelson
and G. Jogesh Babu; publication planned for Sep 2012; see
http://www.springer.com/statistics/book/978-1-4614-3519-
Generating Sustainable Value from Open Data in a Sharing Society
Part 1: Creating ValueInternational audienceOur societies are in the midst of a paradigm shift that transforms hierarchal markets into an open and networked economy based on digital technology and information. In that context, open data is widely presumed to have a positive effect on social, environmental and economic value; however the evidence to that effect has remained scarce. Subsequently, we address the question how the use of open data can stimulate the generation of sustainable value. We argue that open data sharing and reuse can empower new ways of generating value in the sharing society. Moreover, we propose a model that describes how different mechanisms that take part within an open system generate sustainable value. These mechanisms are enabled by a number of contextual factors that provide individuals with the motivation, opportunity and ability to generate sustainable value
Transcriptional profiling of macaque microglia reveals an evolutionary preserved gene expression program
Microglia are tissue-resident macrophages of the central nervous system (CNS), and important for CNS development and homeostasis. In the adult CNS, microglia monitor environmental changes and react to tissue damage, cellular debris, and pathogens. Here, we present a gene expression profile of purified microglia isolated from the rhesus macaque, a non-human primate, that consists of 666 transcripts. The macaque microglia transcriptome was intersected with the transcriptional programs of microglia from mouse, zebrafish, and human CNS tissues, to determine (dis)similarities. This revealed an extensive overlap of 342 genes between the transcriptional profile of macaque and human microglia, and showed that the gene expression profile of zebrafish is most distant when compared to other species. Furthermore, an evolutionair core based on the overlapping gene expression signature from all four species was identified. This study presents a macaque microglia transcriptomics profile, and identifies a gene expression program in microglia that is preserved across species, underscoring their CNS-tailored tissue macrophage functions as innate immune cells with CNS-surveilling properties
Legal linked data ecosystems and the rule of law
This chapter introduces the notions of meta-rule of law and socio-legal ecosystems to both foster and regulate linked democracy. It explores the way of stimulating innovative regulations and building a regulatory quadrant for the rule of law. The chapter summarises briefly (i) the notions of responsive, better and smart regulation; (ii) requirements for legal interchange languages (legal interoperability); (iii) and cognitive ecology approaches. It shows how the protections of the substantive rule of law can be embedded into the semantic languages of the web of data and reflects on the conditions that make possible their enactment and implementation as a socio-legal ecosystem. The chapter suggests in the end a reusable multi-levelled meta-model and four notions of legal validity: positive, composite, formal, and ecological
Factors influencing user acceptance of public sector big open data
In recent years Government departments and public/private organizations are becoming increasingly transparent with their data to establish the whole new paradigm of big open data. Increasing research interest arises from the claimed usability of big open data in improving public sector reforms, facilitating innovation, improving supplier and distribution networks and creating resilient supply chains that help improve the efficiency of public services. Despite the advantages of big open data for supply chain and operations management, there is severe shortage of empirical analyses in this field, especially with regards to its acceptance. To address this gap, in this paper we use an extended Technology Acceptance Model (TAM) to empirically examine the factors affecting usersâ behavioural intentions towards public sector big open data. We outline the importance of our model for operations and supply chain managers, the limitations of the study, and future research directions
Coupling the Leidenfrost effect and elastic deformations to power sustained bouncing
The Leidenfrost effect occurs when an object near a hot surface vaporizes
rapidly enough to lift itself up and hover. Although well-understood for
liquids and stiff sublimable solids, nothing is known about the effect with
materials whose stiffness lies between these extremes. Here we introduce a new
phenomenon that occurs with vaporizable soft solids: the elastic Leidenfrost
effect. By dropping hydrogel spheres onto hot surfaces we find that, rather
than hovering, they energetically bounce several times their diameter for
minutes at a time. With high-speed video during a single impact, we uncover
high-frequency microscopic gap dynamics at the sphere-substrate interface. We
show how these otherwise-hidden agitations constitute work cycles that harvest
mechanical energy from the vapour and sustain the bouncing. Our findings
unleash a powerful and widely applicable strategy for injecting mechanical
energy into soft materials, with relevance to fields ranging from soft robotics
and metamaterials to microfluidics and active matter
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