6,258 research outputs found
Providing structural modules with self-integrity monitoring
With the advent of complex space structures (i.e., U.S. Space Station), the need for methods for remotely detecting structural damage will become greater. Some of these structures will have hundreds of individual structural elements (i.e., strut members). Should some of them become damaged, it could be virtually impossible to detect it using visual or similar inspection techniques. The damage of only a few individual members may or may not be a serious problem. However, should a significant number of the members be damaged, a significant problem could be created. The implementation of an appropriate remote damage detection scheme would greatly reduce the likelihood of a serious problem related to structural damage ever occurring. This report presents the results of the research conducted on remote structural damage detection approaches and the related mathematical algorithms. The research was conducted for the Small Business Innovation and Research (SBIR) Phase 2 National Aeronautics and Space Administration (NASA) Contract NAS7-961
Aircraft and satellite measurement of ocean wave directional spectra using scanning-beam microwave radars
A microwave radar technique for remotely measuring the vector wave number spectrum of the ocean surface is described. The technique, which employs short-pulse, noncoherent radars in a conical scan mode near vertical incidence, is shown to be suitable for both aircraft and satellite application, the technique was validated at 10 km aircraft altitude, where we have found excellent agreement between buoy and radar-inferred absolute wave height spectra
A low-luminosity soft state in the short period black hole X-ray binary Swift J1753.5-0127
We present results from the spectral fitting of the candidate black hole
X-ray binary Swift J1753.5-0127 in an accretion state previously unseen in this
source. We fit the 0.7-78 keV spectrum with a number of models, however the
preferred model is one of a multi-temperature disk with an inner disk
temperature keV scattered into a steep
power-law with photon index and an additional
hard power law tail (). We report on the emergence of a
strong disk-dominated component in the X-ray spectrum and we conclude that the
source has entered the soft state for the first time in its ~10 year prolonged
outburst. Using reasonable estimates for the distance to the source ( kpc)
and black hole mass (), we find the unabsorbed luminosity (0.1-100
keV) to be % of the Eddington luminosity, making this one of the
lowest luminosity soft states recorded in X-ray binaries. We also find that the
accretion disk extended towards the compact object during its transition from
hard to soft, with the inner radius estimated to be
or ~, dependent on the boundary
condition chosen, assuming the above distance and mass, a spectral hardening
factor and a binary inclination .Comment: 10 pages, 5 figures, accepted for publication in MNRA
Evidence for a Variable Ultrafast Outflow in the Newly Discovered Ultraluminous Pulsar NGC 300 ULX-1
Ultraluminous pulsars are a definite proof that persistent super-Eddington
accretion occurs in nature. They support the scenario according to which most
Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar
mass rather than sub-Eddington intermediate mass black holes. An important
prediction of theories of supercritical accretion is the existence of powerful
outflows of moderately ionized gas at mildly relativistic speeds. In practice,
the spectral resolution of X-ray gratings such as RGS onboard XMM-Newton is
required to resolve their observational signatures in ULXs. Using RGS, outflows
have been discovered in the spectra of 3 ULXs (none of which are currently
known to be pulsars). Most recently, the fourth ultraluminous pulsar was
discovered in NGC 300. Here we report detection of an ultrafast outflow (UFO)
in the X-ray spectrum of the object, with a significance of more than
3{\sigma}, during one of the two simultaneous observations of the source by
XMM-Newton and NuSTAR in December 2016. The outflow has a projected velocity of
65000 km/s (0.22c) and a high ionisation factor with a log value of 3.9. This
is the first direct evidence for a UFO in a neutron star ULX and also the first
time that this its evidence in a ULX spectrum is seen in both soft and hard
X-ray data simultaneously. We find no evidence of the UFO during the other
observation of the object, which could be explained by either clumpy nature of
the absorber or a slight change in our viewing angle of the accretion flow.Comment: 10 pages, 4 figures. Accepted to MNRA
Heavy X-ray obscuration in the most-luminous galaxies discovered by WISE
Hot Dust-Obscured Galaxies (Hot DOGs) are hyperluminous
() infrared galaxies with
extremely high (up to hundreds of K) dust temperatures. The sources powering
both their extremely high luminosities and dust temperatures are thought to be
deeply buried and rapidly accreting supermassive black holes (SMBHs). Hot DOGs
could therefore represent a key evolutionary phase in which the SMBH growth
peaks. X-ray observations can be used to study their obscuration levels and
luminosities. In this work, we present the X-ray properties of the 20
most-luminous () known Hot DOGs at
. Five of them are covered by long-exposure ( ks) Chandra and
XMM-Newton observations, with three being X-ray detected, and we study their
individual properties. One of these sources (W01160505) is a Compton-thick
candidate, with column density
derived from X-ray spectral fitting. The remaining 15 Hot DOGs have been
targeted by a Chandra snapshot (3.1 ks) survey. None of these 15 is
individually detected; therefore we applied a stacking analysis to investigate
their average emission. From hardness-ratio analysis, we constrained the
average obscuring column density and intrinsic luminosity to be
log and
, which are consistent with
results for individually detected sources. We also investigated the
and relations, finding hints that Hot
DOGs are typically X-ray weaker than expected, although larger samples of
luminous obscured QSOs are needed to derive solid conclusions.Comment: MNRAS, accepted 2017 November 29 . Received 2017 November 29 ; in
original form 2017 October 11. 15 pages, 6 figure
56Ni dredge-up in the type IIp Supernova 1995V
We present contemporary infrared and optical spectra of the plateau type II
SN 1995V in NGC 1087 covering four epochs, approximately 22 to 84 days after
shock breakout. The data show, for the first time, the infrared spectroscopic
evolution during the plateau phase of a typical type II event. In the optical
region P Cygni lines of the Balmer series and of metals lines were identified.
The infrared (IR) spectra were largely dominated by the continuum, but P Cygni
Paschen lines and Brackett gamma lines were also clearly seen. The other
prominent IR features are confined to wavelengths blueward of 11000 \AA and
include Sr II 10327, Fe II 10547, C I 10695 and He I 10830 \AA. We demonstrate
the presence of He I 10830 \AA on days 69 and 85. The presence of this line at
such late times implies re-ionisation. A likely re-ionising mechanism is
gamma-ray deposition following the radioactive decay of 56Ni. We examine this
mechanism by constructing a spectral model for the He I 10830 \AA line based on
explosion model s15s7b2f of Weaver & Woosley (1993). We find that this does not
generate the observed line owing to the confinement of the 56Ni to the central
zones of the ejecta. In order to reproduce the He I line, it was necessary to
introduce additional upward mixing of the 56Ni, with 10^{-5} of the total
nickel mass reaching above the helium photosphere. In addition, we argue that
the He I line-formation region is likely to have been in the form of pure
helium clumps in the hydrogen envelope.Comment: Accepted for publication in MNRAS, 32 pages including 11 figures
(uses psfig.sty - included
Mathematical modelling of radiation-induced cancer risk from breast screening by mammography
Objectives: Establish a method to determine and convey lifetime radiation risk from FFDM screening.
Methods: Radiation risk from screening mammography was quantified using effective risk (number of radiation-induced cancer cases/million). For effective risk calculations, organ doses and examined breast MGD were used. Screening mammography was simulated by exposing a breast phantom for cranio-caudal and medio-lateral oblique for each breast using 16 FFDM machines. An ATOM phantom loaded with TLD dosimeters was positioned in contact with the breast phantom to simulate the client’s body. Effective risk data were analysed using SPSS software to establish a regression model to predict the effective risk of any screening programme. Graphs were generated to extrapolate the effective risk of all screening programmes for a range of commencement ages and time intervals between screens.
Results: The most important parameters controlling clients’ total effective risk within breast screening are the screening commencement age and number of screens (correlation coefficients were -0.865 and 0.714, respectively). Since the tissue radio-sensitivity reduces with age, the end age of screening does not result in noteworthy effect on total effective risk.
Conclusions: The regression model can be used to predict the total effective risk for clients within breast screening but it cannot be used for exact assessment of total effective risk. Graphical representation of risk could be an easy way to represent risk in a fashion which might be helpful to clients and clinicians
An investigation of angular stiffness and damping coefficients of an axial spline coupling in high-speed rotating machinery
This paper provided an opportunity to quantify the angular stiffness and equivalent viscous damping coefficients of an axial spline coupling used in high-speed turbomachinery. A unique test methodology and data reduction procedures were developed. The bending moments and angular deflections transmitted across an axial spline coupling were measured while a nonrotating shaft was excited by an external shaker. A rotor dynamics computer program was used to simulate the test conditions and to correlate the angular stiffness and damping coefficients. In addition, sensitivity analyses were performed to show that the accuracy of the dynamic coefficients do not rely on the accuracy of the data reduction procedures
NuSTAR Reveals the Comptonizing Corona of the Broad-Line Radio Galaxy 3C 382
Broad-line radio galaxies (BLRGs) are active galactic nuclei that produce
powerful, large-scale radio jets, but appear as Seyfert 1 galaxies in their
optical spectra. In the X-ray band, BLRGs also appear like Seyfert galaxies,
but with flatter spectra and weaker reflection features. One explanation for
these properties is that the X-ray continuum is diluted by emission from the
jet. Here, we present two NuSTAR observations of the BLRG 3C 382 that show
clear evidence that the continuum of this source is dominated by thermal
Comptonization, as in Seyfert 1 galaxies. The two observations were separated
by over a year and found 3C 382 in different states separated by a factor of
1.7 in flux. The lower flux spectrum has a photon-index of
, while the photon-index of the higher flux
spectrum is . Thermal and anisotropic
Comptonization models provide an excellent fit to both spectra and show that
the coronal plasma cooled from keV in the low flux data to
keV in the high flux observation. This cooling behavior is
typical of Comptonizing corona in Seyfert galaxies and is distinct from the
variations observed in jet-dominated sources. In the high flux observation,
simultaneous Swift data are leveraged to obtain a broadband spectral energy
distribution and indicates that the corona intercepts % of the optical
and ultraviolet emitting accretion disk. 3C 382 exhibits very weak reflection
features, with no detectable relativistic Fe K line, that may be best
explained by an outflowing corona combined with an ionized inner accretion
disk.Comment: 8 pages, 8 figures, accepted by Ap
Optical and Infrared Spectroscopy of the type IIn SN 1998S : Days 3-127
We present contemporary infrared and optical spectroscopic observations of
the type IIn SN 1998S for the period between 3 and 127 days after discovery. In
the first week the spectra are characterised by prominent broad emission lines
with narrow peaks superimposed on a very blue continuum(T~24000K). In the
following two weeks broad, blueshifted absorption components appeared in the
spectra and the temperature dropped. By day 44, broad emission components in H
and He reappeared in the spectra. These persisted to 100-130d, becoming
increasingly asymmetric. We agree with Leonard et al. (2000) that the broad
emission lines indicate interaction between the ejecta and circumstellar
material (CSM) and deduce that progenitor of SN 1998S appears to have gone
through at least two phases of mass loss, giving rise to two CSM zones.
Examination of the spectra indicates that the inner zone extended to <90AU,
while the outer CSM extended from 185AU to over 1800AU. Analysis of high
resolution spectra shows that the outer CSM had a velocity of 40-50 km/s.
Assuming a constant velocity, we can infer that the outer CSM wind commenced
more than 170 years ago, and ceased about 20 years ago, while the inner CSM
wind may have commenced less than 9 years ago. During the era of the outer CSM
wind the outflow was high, >2x10^{-5}M_{\odot}/yr corresponding to a mass loss
of at least 0.003M_{\odot} and suggesting a massive progenitor. We also model
the CO emission observed in SN 1998S. We deduce a CO mass of ~10^{-3} M_{\odot}
moving at ~2200km/s, and infer a mixed metal/He core of ~4M_{\odot}, again
indicating a massive progenitor.Comment: 22 pages, 14 figures, accepted in MNRA
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