13,052 research outputs found
Evidence from Rb–Sr mineral ages for multiple orogenic events in the Caledonides of Shetland, Scotland
Shetland occupies a unique central location within the North Atlantic Caledonides. Thirty-three new high-precision Rb–Sr mineral ages indicate a polyorogenic history. Ages of 723–702 Ma obtained from the vicinity of the Wester Keolka Shear Zone indicate a Neoproterozoic (Knoydartian) age and preclude its correlation with the Silurian Moine Thrust. Ordovician ages of c. 480–443 Ma obtained from the Yell Sound Group and the East Mainland Succession constrain deformation fabrics and metamorphic assemblages to have formed during Grampian accretionary orogenic events, broadly contemporaneously with orogenesis of the Dalradian Supergroup in Ireland and mainland Scotland. The relative paucity of Silurian ages is attributed to a likely location at a high structural level in the Scandian nappe pile relative to mainland Scotland. Ages of c. 416 and c. 411 Ma for the Uyea Shear Zone suggest a late orogenic evolution that has more in common with East Greenland and Norway than with northern mainland Scotland
Towards a portable and future-proof particle-in-cell plasma physics code
We present the first reported OpenCL implementation of EPOCH3D, an extensible particle-in-cell plasma physics code developed at the University of Warwick. We document the challenges and successes of this porting effort, and compare the performance of our implementation executing on a wide variety of hardware from multiple vendors. The focus of our work is on understanding the suitability of existing algorithms for future accelerator-based architectures, and identifying the changes necessary to achieve performance portability for particle-in-cell plasma physics codes.
We achieve good levels of performance with limited changes to the algorithmic behaviour of the code. However, our results suggest that a fundamental change to EPOCH3D’s current accumulation step (and its dependency on atomic operations) is necessary in order to fully utilise the massive levels of parallelism supported by emerging parallel architectures
Hard X-ray selected giant radio galaxies - I. The X-ray properties and radio connection
We present the first broad-band X-ray study of the nuclei of 14 hard X-ray
selected giant radio galaxies, based both on the literature and on the analysis
of archival X-ray data from NuSTAR, XMM-Newton, Swift and INTEGRAL. The X-ray
properties of the sources are consistent with an accretion-related X-ray
emission, likely originating from an X-ray corona coupled to a radiatively
efficient accretion flow. We find a correlation between the X-ray luminosity
and the radio core luminosity, consistent with that expected for AGNs powered
by efficient accretion. In most sources, the luminosity of the radio lobes and
the estimated jet power are relatively low compared with the nuclear X-ray
emission. This indicates that either the nucleus is more powerful than in the
past, consistent with a restarting of the central engine, or that the giant
lobes are dimmer due to expansion losses.Comment: 11 pages, 3 figures. Accepted for publication in MNRA
Establishing the boundaries: the hippocampal contribution to imagining scenes
When we visualize scenes, either from our own past or invented, we impose a viewpoint for our “mind's eye” and we experience the resulting image as spatially coherent from that viewpoint. The hippocampus has been implicated in this process, but its precise contribution is unknown. We tested a specific hypothesis based on the spatial firing properties of neurons in the hippocampal formation of rats, that this region supports the construction of spatially coherent mental images by representing the locations of the environmental boundaries surrounding our viewpoint. Using functional magnetic resonance imaging, we show that hippocampal activation increases parametrically with the number of enclosing boundaries in the imagined scene. In contrast, hippocampal activity is not modulated by a nonspatial manipulation of scene complexity nor to increasing difficulty of imagining the scenes in general. Our findings identify a specific computational role for the hippocampus in mental imagery and episodic recollection
INTEGRAL high energy behaviour of 4U 1812-12
The low mass X-ray binary system 4U 1812-12 was monitored with the INTEGRAL
observatory in the period 2003-2004 and with BeppoSAX on April 20, 2000. We
report here on the spectral and temporal analysis of both persistent and burst
emission. The full data set confirms the persistent nature of this burster, and
reveals the presence of emission up to 200 keV. The persistent spectrum is well
described by a comptonization (CompTT) model plus a soft blackbody component.
The source was observed in a hard spectral state with a 1-200 keV luminosity of
2*10^(36) ergs/s and L/LEdd~1% and no meaningful flux variation has been
revealed, as also confirmed by a 2004 RXTE observation. We have also detected 4
bursts showing double peaked profiles and blackbody spectra with temperatures
ranging from 1.9 to 3.1 keV.Comment: 6 pages, 4 figures. Accepted for publication by A&
A Population-Based Ultra-Widefield Digital Image Grading Study for Age-Related Macular Degeneration-Like Lesions at the Peripheral Retina.
Our understanding of the relevance of peripheral retinal abnormalities to disease in general and in age-related macular degeneration (AMD) in particular is limited by the lack of detailed peripheral imaging studies. The purpose of this study was to develop image grading protocols suited to ultra-widefield imaging (UWFI) in an aged population
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