The VLT-FLAMES Tarantula Survey XXII. Multiplicity properties of the B-type stars

<p>We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal absorption lines for each of our targets. Objects with significant radial-velocity variations (and with an amplitude larger than 16 km s<sup&gt;-1</sup&gt;) are classified as spectroscopic binaries. We find an observed spectroscopic binary fraction (defined by periods of <10<sup&gt;3.5</sup&gt; d and mass ratios >0.1) for the B-type stars, f<inf>B</inf>(obs) = 0.25 ± 0.02, which appears constant across the field of view, except for the two older clusters (Hodge 301 and SL 639). These two clusters have significantly lower binary fractions of 0.08 ± 0.08 and 0.10 ± 0.09, respectively. Using synthetic populations and a model of our observed epochs and their potential biases, we constrain the intrinsic multiplicity properties of the dwarf and giant (i.e. relatively unevolved) B-type stars in 30 Dor. We obtain a present-day binary fraction f<inf>B</inf>(true) = 0.58 ± 0.11, with a flat period distribution. Within the uncertainties, the multiplicity properties of the B-type stars agree with those for the O stars in 30 Dor from the VFTS.p>

Thiol isomerases negatively regulate the cellular shedding activity of ADAM17

<p>ADAM17 (where ADAM is 'a disintegrin and metalloproteinase') can rapidly modulate cell-surface signalling events by the proteolytic release of soluble forms of proligands for cellular receptors. Many regulatory pathways affect the ADAM17 sheddase activity, but the mechanisms for the activation are still not clear. We have utilized a cell-based ADAM17 assay to show that thiol isomerases, specifically PDI (protein disulfide isomerase), could be responsible for maintaining ADAM17 in an inactive form. Down-regulation of thiol isomerases, by changes in the redox environment (for instance as elicited by phorbol ester modulation of mitochondrial reactive oxygen species) markedly enhanced ADAM17 activation. On the basis of ELISA binding studies with novel fragment antibodies against ADAM17 we propose that isomerization of the disulfide bonds in ADAM17, and the subsequent conformational changes, form the basis for the modulation of ADAM17 activity. The shuffling of disulfide bond patterns in ADAMs has been suggested by a number of recent adamalysin crystal structures, with distinct disulfide bond patterns altering the relative orientations of the domains. Such a mechanism is rapid and reversible, and the role of thiol isomerases should be investigated further as a potential factor in the redox regulation of ADAM17.p>

Learning from the QUEST multicentre feasibility randomization trials in breast reconstruction after mastectomy

<p>BACKGROUND: Breast reconstruction aims to improve health-related quality of life after mastectomy. However, evidence guiding patients and surgeons in shared decision-making concerning the optimal type or timing of surgery is lacking.p><p>METHODS: QUEST comprised two parallel feasibility phase III randomized multicentre trials to assess the impact of the type and timing of latissimus dorsi breast reconstruction on health-related quality of life when postmastectomy radiotherapy is unlikely (QUEST A) or highly probable (QUEST B). The primary endpoint for the feasibility phase was the proportion of women who accepted randomization, and it would be considered feasible if patient acceptability rates exceeded 25 per cent of women approached. A companion QUEST Perspectives Study (QPS) of patients (both accepting and declining trial participation) and healthcare professionals assessed trial acceptability.p><p>RESULTS: The QUEST trials opened in 15 UK centres. After 18 months of recruitment, 17 patients were randomized to QUEST A and eight to QUEST B, with overall acceptance rates of 19 per cent (17 of 88) and 22 per cent (8 of 36) respectively. The QPS recruited 56 patients and 51 healthcare professionals. Patient preference was the predominant reason for declining trial entry, given by 47 (53 per cent) of the 88 patients approached for QUEST A and 22 (61 per cent) of the 36 approached for QUEST B. Both trials closed to recruitment in December 2012, acknowledging the challenges of achieving satisfactory patient accrual.p><p>CONCLUSION: Despite extensive efforts to overcome recruitment barriers, it was not feasible to reach timely recruitment targets within a feasibility study. Patient preferences for breast reconstruction types and timings were common, rendering patients unwilling to enter the trial.p>

Alzheimer's disease-like pathology has transient effects on the brain and blood metabolome

The pathogenesis of Alzheimer's disease (AD) is complex involving multiple contributing factors. The extent to which AD pathology impacts upon the metabolome is still not understood, nor is it known how disturbances change as the disease progresses. For the first time we have profiled longitudinally (6, 8, 10, 12 and 18 months) both the brain and plasma metabolome of APP/PS1 double transgenic and wild type (WT) mice. A total of 187 metabolites were quantified using a targeted metabolomics methodology. Multivariate statistical analysis produced models that distinguished APP/PS1 from WT mice at 8, 10 and 12 months.Metabolic pathway analysis found perturbed polyamine metabolism in both brain and blood plasma. There were other disturbances in essential amino acids,branched chain amino acids and also in the neurotransmitter serotonin.Pronounced imbalances in phospholipid and acylcarnitine homeostasis was evident in two age groups. AD-like pathology therefore impacts greatly on both the brain and blood metabolomes, although there appears to be a clear temporal sequence whereby changes to brain metabolites precede those in blood.

Laboratory measurements of resistivity in warm dense plasmas relevant to the microphysics of brown dwarfs

<p>Since the observation of the first brown dwarf in 1995, numerous studies have led to a better understanding of the structures of these objects. Here we present a method for studying material resistivity in warm dense plasmas in the laboratory, which we relate to the microphysics of brown dwarfs through viscosity and electron collisions. Here we use X-ray polarimetry to determine the resistivity of a sulphur-doped plastic target heated to Brown Dwarf conditions by an ultra-intense laser. The resistivity is determined by matching the plasma physics model to the atomic physics calculations of the measured large, positive, polarization. The inferred resistivity is larger than predicted using standard resistivity models, suggesting that these commonly used models will not adequately describe the resistivity of warm dense plasma related to the viscosity of brown dwarfs.p>

The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 au heliocentric distance range inbound

Context. The ESA Rosetta spacecraft, currently orbiting around comet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments,particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution.
Aims. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014.
Methods. A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately.
Results. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is α = −3, instead of α = −2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 AU, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 AU. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment.

Introducing the CTA concept

The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. © 2013 Elsevier B.V. All rights reserved.

Beamed neutron emission driven by laser accelerated light ions

Highly anisotropic, beam-like neutron emission with peak flux of the order of 10^9 n/sr was obtained from light nuclei reactions in a pitcher–catcher scenario, by employing MeV ions driven by subpetawatt laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHMdivergence angle of ~70 deg, with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher–catcher materials indicates the dominant reactions being d(p, n+p)1Hand d(d,n)3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons’ spatial and spectral profiles are most likely related to the directionality and high energy of the projectile ions.

Guided post-acceleration of laser-driven ions by a miniature modular structure

All-optical approaches to particle acceleration are currently attracting a significant research effort internationally. Although characterized by exceptional transverse and longitudinal emittance, laser-driven ion beams currently have limitations in terms of peak ion energy, bandwidth of the energy spectrum and beam divergence. Here we introduce the concept of a versatile, miniature linear accelerating module, which, by employing laser-excited electromagnetic pulses directed along a helical path surrounding the laser-accelerated ion beams, addresses these shortcomings simultaneously. In a proof-of-principle experiment on a university-scale system, we demonstrate post-acceleration of laser-driven protons from a flat foil at a rate of 0.5 GeVm^-1, already beyond what can be sustained by conventional accelerator technologies, with dynamic beam collimation and energy selection. These results open up new opportunities for the development of extremely compact and cost-effective ion accelerators for both established and innovative applications.

Magnetic collimation of petawatt driven fast electron beam for prospective fast ignition studies

Collimated transport of fast electron beam through solid density matter is one of the key issues behind the success of the fast ignition scheme by means of which the required amount of ignition energy can be delivered to the hot spot region of the compressed fuel. Here we report on a hot electron beam collimation scheme in solids by tactfully using the strong magnetic fields generated by an electrical resistivity gradient according to Faraday's law. This was accomplished by appropriately fabricating the targets in such a way that the electron beam is directed to flow in a metal which is embedded in a much lower resistivity and atomic number metal. Experimental results showed guided transport of hot electron beam over hundreds of microns length inside solid density plasma, which were obtained from two experiments examining the scheme for petawatt laser driven hot electron beam while employing various target configurations.