189,388 research outputs found
New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
No full textXMM–Newton observations of the supergiant fast X-ray transient IGR J17544?2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272?±?0.0004?d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM–Newton observations (each lasting ?15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544?2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033?erg?s?1 (0.5–10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544?2619 dropped to ?4?×?1032?erg?s?1 (0.5–10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544?2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544?2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the ‘quasi-spherical accretion’ model provides a good description of the behaviour of IGR J17544?2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Demography of obscured and unobscured AGN: prospects for a Wide Field X-ray Telescope
No full textWe discuss some of the main open issues in the evolution of Active Galactic Nuclei which can be solved by the sensitive, wide area surveys to be performed by the proposed Wide Field X-ray Telescope mission
Experimental Measurements and Computer Simulation of Fission Product Gamma-Ray Spectra
No full textAirborne gamma ray spectrometry using high volume scintillation detectors, optionally in conjunction with Ge detectors, has potential for making rapid environmental measurements in response to nuclear accidents. An experimental investigation and computer simulation have been used to characterise the response of such detectors to short lived fission products. Small samples of 235U were irradiated in a research reactor for short periods, to generate fission product sources. Gamma ray spectra were recorded over a period of one year using both high volume scintillation detectors and semiconductor detectors. The main gamma emitting nuclides have been identified, and their associated signals in each detector defined. Simulation work has been used to calculate the corresponding spectra which would have been observed at airborne survey heights, or from fission product sources irradiated for a prolonged period. While Ge detectors can record a fuller range of isotopes, of interest in characterising release terms, the NaI spectra also have potential for providing data on a range of radiologically important isotopes at all stages
The high-redshift Universe with the International X-ray Observatory
No full textWe discuss some of the main open issues related to the light-up and evolution of the first accreting sources powering high redshift luminous quasars. We discuss the perspectives of future deep X-ray surveys with the International X-ray Observatory and possible synergies with the Wide Field X-ray Telescope
Time Resolved Two Dimensional X-Ray Densitometry of a Two Phase Flow Downstream of a Ventilated Cavity
No full textTo measure the void fraction distribution in gas-liquid flows, a two-dimensional x-ray densitometry system was developed. This system is capable of acquiring a two-dimensional projection with a 225 cm2 area of measurement through 21 cm of water. The images can be acquired at rates on the order of 1 kHz. Common sources of error in x-ray imaging, such as x-ray scatter, image distortion, veiling glare, and beam hardening were considered, and mitigated. The measured average void fraction was compared success fully to that of a phantom target and found to be within 1%. To evaluate the performance of the new system, the flow in and downstream of a ventilated nominally two-dimensional partial cavity was investigated and compared to measurements from dual tip fiber optical probes and high speed video. The measurements were found to have satisfactory agreement for void fractions above 5% of the selected void fraction measurement range.Office of Naval Research under grant N00014-10-1-097
Ray P. Holland to Horace Kephart, December 31, 1928
No full textIn a letter to Horace Kephart on December 21, 1928, Ray P. Holland, Editor of “Field & Stream” writes to tell Kephart that his article “Afoot and Awing in the Great Smokies” was chosen as one of the ten best stories of the month by a committee of judges of the Franklin Square Agency.RAY P. HOLLAND
EDITOR
ELTINGE F. WARNER
PUBLISHER
578 Madison Avenue
at fifty-seventh street
New York City
Field & Stream's
CONSERVATION
COUNCIL
D. R. ANTHONY, JR.
Congressman; joint Introducer of the Game Refuge Bill.
HORACE M.ALBRIGHT
Superintendent of Yellowstone National Park.
BROOKE ANDERSON
Member of the Federal
Advisory Board of the
Migratory Bird Treaty
Act.
J. B. HARKIN
Commissioner of the
Canadian National Parks.
GEORGE A. LAWYER
Former Chief United
States Game Warden.
WM. B. MERSHON
Sportsman — Author —
Conservationist.
E. W. NELSON
Ex-Chief of the U. S.
Biological Survey.
HARRY S. NEW
U. S. Postmaster General;
joint Introducer of the
Game Refuge Bill in the
United States. Senate.
T. GILBERT PEARSON
President of the National
Association of Audubon
Societies.
THEO. ROOSEVELT
First Executive Chairman
of the National Conference on Outdoor Recreation.
December 31, 1928
Mr. Horace Kephart,
Bryson City, N. C.
Dear Mr. Kephart:
I thought you would be interested
in knowing that your story "Afoot and Awing in
the Great Smokies", published in the January
issue, was chosen by a committee of judges of
the Franklin Square Agency, which is owned by
Harper Brothers, as one of the ten best stories
of the month.
With the best of the holiday greetings,
I am
Sincerely yours,
RPHsFTC
Edito
GPU-accelerated depth map generation for X-ray simulations of complex CAD geometries
No full textInteractive x-ray simulations of complex computer-aided design (CAD) models can provide valuable insights for better interpretation of the defect signatures such as porosity from x-ray CT images. Generating the depth map along a particular direction for the given CAD geometry is the most compute-intensive step in x-ray simulations. We have developed a GPU-accelerated method for real-time generation of depth maps of complex CAD geometries. We preprocess complex components designed using commercial CAD systems using a custom CAD module and convert them into a fine user-defined surface tessellation. Our CAD module can be used by different simulators as well as handle complex geometries, including those that arise from complex castings and composite structures. We then make use of a parallel algorithm that runs on a graphics processing unit (GPU) to convert the finely-tessellated CAD model to a voxelized representation. The voxelized representation can enable heterogeneous modeling of the volume enclosed by the CAD model by assigning heterogeneous material properties in specific regions. The depth maps are generated from this voxelized representation with the help of a GPU-accelerated ray-casting algorithm. The GPU-accelerated ray-casting method enables interactive (> 60 frames-per-second) generation of the depth maps of complex CAD geometries. This enables arbitrarily rotation and slicing of the CAD model, leading to better interpretation of the x-ray images by the user. In addition, the depth maps can be used to aid directly in CT reconstruction algorithms.This proceeding may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This proceeding appeared in Grandin, Robert J., Gavin Young, Stephen D. Holland, and Adarsh Krishnamurthy. "GPU-accelerated depth map generation for X-ray simulations of complex CAD geometries." In AIP Conference Proceedings, vol. 1949, no. 1, p. 190002. AIP Publishing LLC, 2018, and may be found at
DOI: 10.1063/1.5031636.
Copyright 2018 Author(s).
Posted with permission
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