70 research outputs found
Fractography, elastic modulus and oxidation resistance of novel metal-intermetallic Ni/Ni 3Al multilayer films
Novel metal–intermetallic Ni/Ni3Al multilayer films are synthesized by a magnetron sputtering technique. The fractography, elastic modulus, and the oxidation resistance of the multilayer films are studied by a series of experimental tests. The scanning electron microscopy fractography of the films shows that both Ni and Ni3Al layers fracture with the appearance of ductile metal failure. No metal–intermetallic delamination appears in the multilayered films. Fluted dimpling in each Ni and Ni3Al layer is
evident and continuous, layer through layer, illustrating very good adherence among the constituent layers. Such adherence makes the toughness of the Ni layers capable of transferring into the Ni3Al layers. Young’s modulus of the Ni/Ni3Al film is found to be 226 and 253 ± 10 GPa by nanoindentation and laser acoustic techniques, respectively. The continuity of elastic modulus between the two phases is revealed by nanoindentation test. The modulus continuity indicates an excellent integration of the
constituent layers with similar crystal structure and close lattice constants. This integration makes the multilayers unsurpassed in comprehensive mechanical properties. Sheet resistance measurements show a good protective ability of the Ni/Ni3Al
multilayers during high temperature oxidation. X-ray photoelectron spectroscopy spectra suggest that crystallized Al2O3 /Ni scales formed during the deposition and subsequent annealing processes are apparently responsible for the stability of these
films under oxidative conditions. The appearance of the crystallized Al2O3 /Ni thin scales on the top of Ni3Al layers provides the Ni/Ni3Al multilayers good thermal oxidation resistance without lowering the fracture toughness.published_or_final_versio
Mid-infrared interferometry of massive young stellar objects
The very inner structure of massive young stellar objects (YSOs) is difficult
to trace. With conventional observational methods we identify structures still
several hundreds of AU in size. However, the (proto-)stellar growth takes place
at the innermost regions (<100 AU) where the actual mass transfer onto the
forming high-mass star occurs. We present results from our programme toward
massive YSOs at the VLTI, utilising the two-element interferometer MIDI. To
date, we observed 10 well-known massive YSOs down to scales of 20 mas
(typically corresponding to 20 - 40 AU for our targets) in the 8-13 micron
region. We clearly resolve these objects which results in low visibilities and
sizes in the order of 30-50 mas. For two objects, we show results of our
modelling. We demonstrate that the MIDI data can reveal decisive structure
information for massive YSOs. They are often pivotal in order to resolve
ambiguities still immanent in model parameters derived from sole SED fitting.Comment: 6 pages, 5 figures, necessary style files iopams.sty, jpconf11.clo,
and jpconf.cls included; contribution for the conference "The Universe under
the Microscope" (AHAR 2008), held in Bad Honnef (Germany) in April 2008, to
be published in Journal of Physics: Conference Series by Institute of Physics
Publishing, R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.
Mid-infrared interferometry of the massive young stellar object NGC3603 - IRS 9A
We present observations and models for one of these MYSO candidates, NGC3603
IRS 9A. Our goal is to investigate with infrared interferometry the structure
of IRS 9A on scales as small as 200AU, exploiting the fact that a cluster of O
and B stars has blown away much of the obscuring foreground dust and gas.
Observations in the N-band were carried out with the MIDI beam combiner
attached to the VLTI. Additional interferometric observations which probe the
structure of IRS 9A on larger scales were performed with an aperture mask
installed in the T-ReCS instrument of Gemini South. The spectral energy
distribution (SED) is constrained by the MIDI N-band spectrum and by data from
the Spitzer Space Telescope. Our efforts to model the structure and SED of IRS
9A range from simple geometrical models of the brightness distribution to one-
and two-dimensional radiative transfer computations. The target is resolved by
T-ReCS, with an equivalent (elliptical) Gaussian width of 330mas by 280mas
(2300 AU by 2000 AU). Despite this fact, a warm compact unresolved component
was detected by MIDI which is possibly associated with the inner regions of a
flattened dust distribution. Based on our interferometric data, no sign of
multiplicity was found on scales between about 200AU and 700AU projected
separation. A geometric model consisting of a warm (1000 K) ring (400 AU
diameter) and a cool (140 K) large envelope provides a good fit to the data. No
single model fitting all visibility and photometric data could be found, with
disk models performing better than spherical models. While the data are clearly
inconsistent with a spherical dust distribution they are insufficient to prove
the existence of a disk but rather hint at a more complex dust distribution.Comment: 8 pages, 11 figures. Accepted for publication in A&
Probing the envelopes of massive young stellar objects with diffraction limited mid-infrared imaging
Massive stars form whilst they are still embedded in dense envelopes. As a
result, the roles of rotation, mass loss and accretion in massive star
formation are not well understood. This study evaluates the source of the
Q-band, lambda=19.5 microns, emission of massive young stellar objects (MYSOs).
This allows us to determine the relative importance of rotation and outflow
activity in shaping the circumstellar environments of MYSOs on 1000 AU scales.
We obtained diffraction limited mid-infrared images of a sample of 20 MYSOs
using the VLT/VISIR and Subaru/COMICS instruments. For these 8 m class
telescopes and the sample selected, the diffraction limit, ~0.6", corresponds
to approximately 1000 AU. We compare the images and the spectral energy
distributions (SEDs) observed to a 2D, axis-symmetric dust radiative transfer
model that reproduces VLTI/MIDI observations of the MYSO W33A. We vary the
inclination, mass infall rate, and outflow opening angle to simultaneously
recreate the behaviour of the sample of MYSOs in the spatial and spectral
domains. The mid-IR emission of 70 percent of the MYSOs is spatially resolved.
In the majority of cases, the spatial extent of their emission and their SEDs
can be reproduced by the W33A model featuring an in-falling, rotating dusty
envelope with outflow cavities. There is independent evidence that most of the
sources which are not fit by the model are associated with ultracompact HII
regions and are thus more evolved. We find that, in general, the diverse 20
micron morphology of MYSOs can be attributed to warm dust in the walls of
outflow cavities seen at different inclinations. This implies that the warm
dust in the outflow cavity walls dominates the Q-band emission of MYSOs. In
turn, this emphasises that outflows are an ubiquitous feature of massive star
formation.Comment: Accepted for publication in A&A. The images in this version have been
compressed. A high resolution version is available on reques
The Swiss Multiple Sclerosis Cohort-Study (SMSC): A Prospective Swiss Wide Investigation of Key Phases in Disease Evolution and New Treatment Options.
The mechanisms leading to disability and the long-term efficacy and safety of disease modifying drugs (DMDs) in multiple sclerosis (MS) are unclear. We aimed at building a prospective cohort of MS patients with standardized collection of demographic, clinical, MRI data and body fluids that can be used to develop prognostic indicators and biomarkers of disease evolution and therapeutic response. The Swiss MS Cohort (SMSC) is a prospective observational study performed across seven Swiss MS centers including patients with MS, clinically isolated syndrome (CIS), radiologically isolated syndrome or neuromyelitis optica. Neurological and radiological assessments and biological samples are collected every 6-12 months. We recruited 872 patients (clinically isolated syndrome [CIS] 5.5%, relapsing-remitting MS [RRMS] 85.8%, primary progressive MS [PPMS] 3.5%, secondary progressive MS [SPMS] 5.2%) between June 2012 and July 2015. We performed 2,286 visits (median follow-up 398 days) and collected 2,274 serum, plasma and blood samples, 152 cerebrospinal fluid samples and 1,276 brain MRI scans. 158 relapses occurred and expanded disability status scale (EDSS) scores increased in PPMS, SPMS and RRMS patients experiencing relapses. Most RRMS patients were treated with fingolimod (33.4%), natalizumab (24.5%) or injectable DMDs (13.6%). The SMSC will provide relevant information regarding DMDs efficacy and safety and will serve as a comprehensive infrastructure available for nested research projects
Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
We present a review of the interplay between the evolution of circumstellar
disks and the formation of planets, both from the perspective of theoretical
models and dedicated observations. Based on this, we identify and discuss
fundamental questions concerning the formation and evolution of circumstellar
disks and planets which can be addressed in the near future with optical and
infrared long-baseline interferometers. Furthermore, the importance of
complementary observations with long-baseline (sub)millimeter interferometers
and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics
Review"; The final publication is available at http://www.springerlink.co
Serum neurofilament light chain for individual prognostication of disease activity in people with multiple sclerosis: a retrospective modelling and validation study
Background: Serum neurofilament light chain (sNfL) is a biomarker of neuronal damage that is used not only to monitor disease activity and response to drugs and to prognosticate disease course in people with multiple sclerosis on the group level. The absence of representative reference values to correct for physiological age-dependent increases in sNfL has limited the diagnostic use of this biomarker at an individual level. We aimed to assess the applicability of sNfL for identification of people at risk for future disease activity by establishing a reference database to derive reference values corrected for age and body-mass index (BMI). Furthermore, we used the reference database to test the suitability of sNfL as an endpoint for group-level comparison of effectiveness across disease-modifying therapies. Methods: For derivation of a reference database of sNfL values, a control group was created, comprising participants with no evidence of CNS disease taking part in four cohort studies in Europe and North America. We modelled the distribution of sNfL concentrations in function of physiological age-related increase and BMI-dependent modulation, to derive percentile and Z score values from this reference database, via a generalised additive model for location, scale, and shape. We tested the reference database in participants with multiple sclerosis in the Swiss Multiple Sclerosis Cohort (SMSC). We compared the association of sNfL Z scores with clinical and MRI characteristics recorded longitudinally to ascertain their respective disease prognostic capacity. We validated these findings in an independent sample of individuals with multiple sclerosis who were followed up in the Swedish Multiple Sclerosis registry. Findings: We obtained 10 133 blood samples from 5390 people (median samples per patient 1 [IQR 1–2] in the control group). In the control group, sNfL concentrations rose exponentially with age and at a steeper increased rate after approximately 50 years of age. We obtained 7769 samples from 1313 people (median samples per person 6·0 [IQR 3·0–8·0]). In people with multiple sclerosis from the SMSC, sNfL percentiles and Z scores indicated a gradually increased risk for future acute (eg, relapse and lesion formation) and chronic (disability worsening) disease activity. A sNfL Z score above 1·5 was associated with an increased risk of future clinical or MRI disease activity in all people with multiple sclerosis (odds ratio 3·15, 95% CI 2·35–4·23; p<0·0001) and in people considered stable with no evidence of disease activity (2·66, 1·08–6·55; p=0·034). Increased Z scores outperformed absolute raw sNfL cutoff values for diagnostic accuracy. At the group level, the longitudinal course of sNfL Z score values in people with multiple sclerosis from the SMSC decreased to those seen in the control group with use of monoclonal antibodies (ie, alemtuzumab, natalizumab, ocrelizumab, and rituximab) and, to a lesser extent, oral therapies (ie, dimethyl fumarate, fingolimod, siponimod, and teriflunomide). However, longitudinal sNfL Z scores remained elevated with platform compounds (interferons and glatiramer acetate; p<0·0001 for the interaction term between treatment category and treatment duration). Results were fully supported in the validation cohort (n=4341) from the Swedish Multiple Sclerosis registry. Interpretation: The use of sNfL percentiles and Z scores allows for identification of individual people with multiple sclerosis at risk for a detrimental disease course and suboptimal therapy response beyond clinical and MRI measures, specifically in people with disease activity-free status. Additionally, sNfL might be used as an endpoint for comparing effectiveness across drug classes in pragmatic trials. Funding: Swiss National Science Foundation, Progressive Multiple Sclerosis Alliance, Biogen, Celgene, Novartis, Roche
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