218 research outputs found
IR thermography applied to flash experiments of semitransparent TBCs
Abstract Thermal Barrier Coatings (TBC) are applied to protect components of gas turbines from high temperature of combustion gases. ZrO 2 , the material mainly used in TBCs, is semitransparent to near IR radiation that is typically delivered by the laser in the laser flash equipment and also radiated at working temperatures that are grater than 1000 °C. Thermography and radiometers are utilized to measure thermal diffusivity of TBCs. Discussion is done on the countermeasures to obtain correct results in case of semitransparency
Virological rebound in human immunodeficiency virus-infected patients with or without residual viraemia: results from an extended follow-up
AbstractHuman immunodeficiency virus (HIV) -infected patients with HIV RNA loads of < 50 copies/mL were followed-up for a median (interquartile range) of 30.8 (11.7–32.9) months to study the effect of residual viraemia (RV) on virological rebound (VR). At baseline, 446 (60.3%) patients had undetectable HIV RNA (group A) and 293 (39.7%) had RV (1–49 HIV RNA copies/mL, group B) by kinetic PCR. VR occurred in 4 (0.9%) patients in group A and in 12 (4.1%) patients in group B (p 0.007). Time to VR was shorter among patients of group B (Log-rank test: p 0.003). However, the proportion of VR was extremely low also among patients with RV
Optical and Infrared Analysis of Type II SN 2006BC
We present nebular phase optical imaging and spectroscopy and near/mid-IR
imaging of the Type II SN 2006bc. Observations reveal the central wavelength of
the symmetric H line profile to be red-shifted with respect to the host
galaxy H emission by day 325. Such an phenomenon has been argued to
result from an asymmetric explosion in the iron-peak elements resulting in a
larger mass of Ni and higher excitation of hydrogen on the far side of
the SN explosion. We also observe a gradual blue-shifting of this H
peak which is indicative of dust formation in the ejecta. Although showing a
normal peak brightness, V -17.2, for a core-collapse SN, 2006bc fades by
6 mag during the first 400 days suggesting either a relatively low
Ni yield, an increase in extinction due to new dust, or both. A short
duration flattening of the light curve is observed from day 416 to day 541
suggesting an optical light echo. Based on the narrow time window of this echo,
we discuss implications on the location and geometry of the reflecting ISM.
With our radiative transfer models, we find an upper limit of 2 x 10
M of dust around SN 2006bc. In the event that all of this dust were
formed during the SN explosion, this quantity of dust is still several orders
of magnitude lower than that needed to explain the large quantities of dust
observed in the early universe.Comment: 6 pages, 10 figures, accepted for publication in Ap
On the source of the late-time infrared luminosity of SN 1998S and other type II supernovae
We present late-time near-infrared (NIR) and optical observations of the type
IIn SN 1998S. The NIR photometry spans 333-1242 days after explosion, while the
NIR and optical spectra cover 333-1191 days and 305-1093 days respectively. The
NIR photometry extends to the M'-band (4.7 mu), making SN 1998S only the second
ever supernova for which such a long IR wavelength has been detected. The shape
and evolution of the H alpha and HeI 1.083 mu line profiles indicate a powerful
interaction with a progenitor wind, as well as providing evidence of dust
condensation within the ejecta. The latest optical spectrum suggests that the
wind had been flowing for at least 430 years. The intensity and rise of the HK
continuum towards longer wavelengths together with the relatively bright L' and
M' magnitudes shows that the NIR emission was due to hot dust newly-formed in
supernovae may provide the ejecta and/or pre-existing dust in the progenitor
circumstellar medium (CSM). [ABRIDGED] Possible origins for the NIR emission
are considered. Significant radioactive heating of ejecta dust is ruled out, as
is shock/X-ray-precursor heating of CSM dust. More plausible sources are (a) an
IR-echo from CSM dust driven by the UV/optical peak luminosity, and (b)
emission from newly-condensed dust which formed within a cool, dense shell
produced by the ejecta shock/CSM interaction. We argue that the evidence
favours the condensing dust hypothesis, although an IR-echo is not ruled out.
Within the condensing-dust scenario, the IR luminosity indicates the presence
of at least 0.001 solar masses of dust in the ejecta, and probably considerably
more. Finally, we show that the late-time intrinsic (K-L') evolution of type II
supernovae may provide a useful tool for determining the presence or absence of
a massive CSM around their progenitor stars.Comment: 23 pages, 15 figures, to be published in MNRA
Stellar structure and compact objects before 1940: Towards relativistic astrophysics
Since the mid-1920s, different strands of research used stars as "physics
laboratories" for investigating the nature of matter under extreme densities
and pressures, impossible to realize on Earth. To trace this process this paper
is following the evolution of the concept of a dense core in stars, which was
important both for an understanding of stellar evolution and as a testing
ground for the fast-evolving field of nuclear physics. In spite of the divide
between physicists and astrophysicists, some key actors working in the
cross-fertilized soil of overlapping but different scientific cultures
formulated models and tentative theories that gradually evolved into more
realistic and structured astrophysical objects. These investigations culminated
in the first contact with general relativity in 1939, when J. Robert
Oppenheimer and his students George Volkoff and Hartland Snyder systematically
applied the theory to the dense core of a collapsing neutron star. This
pioneering application of Einstein's theory to an astrophysical compact object
can be regarded as a milestone in the path eventually leading to the emergence
of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal
Integration of terrestrial and UAV photogrammetry for the assessment of collapse risk in Alpine glaciers
The application of Structure-from-Motion photogrammetry with ground-based and UAV-based camera stations can be effectively exploited for modeling the topographic surface of Alpine glaciers. Multi-temporal repeated surveys may lead to geometric models that may be applied to analyze the glacier retreat under global warming conditions. Here the case study of Forni Glacier in the Italian Alps is presented. Thanks to the integration of point clouds obtained from the independent photogrammetric processing of ground-based and UAV blocks of images (captured on 2016), a complete 3D reconstruction also including vertical and sub-vertical surfaces has been achieved. This 3D model, compared to a second model obtained from a ground-based photogrammetric survey on September 2017, has been exploited to understand the precursory signal of a big collapse that might have involved tourists and hikers visiting the glacier ice tongue during summer. In addition to some technical aspects related to the acquisition and processing of photogrammetric data of glaciers, this paper highlights how Structure-from-Motion photogrammetry may help evaluate the risk of collapse in Alpine glaciers
Dust and the type II-plateau supernova 2004et
We present mid-infrared (MIR) observations of the Type II-plateau supernova
(SN) 2004et, obtained with the {\it Spitzer Space Telescope} between days 64
and 1406 past explosion. Late-time optical spectra are also presented. For the
period 300-795 days past explosion, we argue that the spectral energy
distribution of SN 2004et comprises (a) a hot component due to emission from
optically thick gas, as well as free-bound radiation, (b) a warm component due
to newly formed, radioactively heated dust in the ejecta, and (c) a cold
component due to an IR echo from the interstellar-medium dust of the host
galaxy, NGC 6946. There may also have been a small contribution to the IR SED
due to free-free emission from ionised gas in the ejecta. We reveal the
first-ever spectroscopic evidence for silicate dust formed in the ejecta of a
supernova. This is supported by our detection of a large, but progressively
declining, mass of SiO. However, we conclude that the mass of directly detected
ejecta dust grew to no more than a few times 10^(-4)Msun. We also provide
evidence that the ejecta dust formed in comoving clumps of fixed size. We argue
that, after about two years past explosion, the appearance of wide, box-shaped
optical line profiles was due to the impact of the ejecta on the progenitor
circumstellar medium and that the subsequent formation of a cool, dense shell
was responsible for a later rise in the MIR flux. This study demonstrates the
rich, multi-faceted ways in which a typical core-collapse supernova and its
progenitor can produce and/or interact with dust grains. The work presented
here adds to the growing number of studies which do not support the contention
that SNe are responsible for the large mass of observed dust in high-redshift
galaxies.Comment: (ApJ; in press
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