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Distributed simulation and the grid: Position statements
The Grid provides a new and unrivaled technology for large scale distributed simulation as it enables collaboration and the use of distributed computing resources. This panel paper presents the views of four researchers in the area of Distributed Simulation and the Grid. Together we try to identify the main research issues involved in applying Grid technology to distributed simulation and the key future challenges that need to be solved to achieve this goal. Such challenges include not only technical challenges, but also political ones such as management methodology for the Grid and the development of standards. The benefits of the Grid to end-user simulation modelers also are discussed
X-ray variability analysis of a large series of XMM-Newton + NuSTAR observations of NGC 3227
We present a series of X-ray variability results from a long XMM-Newton +
NuSTAR campaign on the bright, variable AGN NGC 3227. We present an analysis of
the lightcurves, showing that the source displays typically
softer-when-brighter behaviour, although also undergoes significant spectral
hardening during one observation which we interpret as due to an occultation
event by a cloud of absorbing gas. We spectrally decompose the data and show
that the bulk of the variability is continuum-driven and, through rms
variability analysis, strongly enhanced in the soft band. We show that the
source largely conforms to linear rms-flux behaviour and we compute X-ray power
spectra, detecting moderate evidence for a bend in the power spectrum,
consistent with existing scaling relations. Additionally, we compute X-ray
Fourier time lags using both the XMM-Newton and - through maximum-likelihood
methods - NuSTAR data, revealing a strong low-frequency hard lag and evidence
for a soft lag at higher frequencies, which we discuss in terms of
reverberation models.Comment: Accepted for publication in MNRAS; 19 pages, 13 figures, 4 tables;
minor typographical errors corrected and reference list update
Photometric Variability in Earthshine Observations
The identification of an extrasolar planet as Earth-like will depend on the
detection of atmospheric signatures or surface non-uniformities. In this paper
we present spatially unresolved flux light curves of Earth for the purpose of
studying a prototype extrasolar terrestrial planet. Our monitoring of the
photometric variability of earthshine revealed changes of up to 23 % per hour
in the brightness of Earth's scattered light at around 600 nm, due to the
removal of specular reflection from the view of the Moon. This variability is
accompanied by reddening of the spectrum, and results from a change in surface
properties across the continental boundary between the Indian Ocean and
Africa's east coast. Our results based on earthshine monitoring indicate that
specular reflection should provide a useful tool in determining the presence of
liquid water on extrasolar planets via photometric observations.Comment: To appear in Astrobiology 9(3). 17 pages, 3 figures, 1 tabl
Suspended liminality: Vacillating affects in cyberbullying/research
This paper develops a concept of liminal hotspots in the context of i) a secondary analysis of a cyberbullying case involving a group of school children from a Danish school, and ii) an altered auto-ethnography in which the authors âentangleâ their own experiences with the case analysis. These two sources are used to build an account of a liminal hotspot conceived as an occasion of troubled and suspended transformative transition in which a liminal phase is extended and remains unresolved. The altered auto-ethnography is used to explore the affectivity at play in liminal hotspots, and this liminal affectivity is characterised in terms of volatility, vacillation, suggestibility and paradox
Evidence for a Truncated Accretion Disc in the Low Luminosity Seyfert Galaxy, NGC 7213?
We present the broad-band 0.6-150 keV Suzaku and Swift BAT spectra of the low
luminosity Seyfert galaxy, NGC 7213. The time-averaged continuum emission is
well fitted by a single powerlaw of photon index Gamma = 1.75 and from
consideration of the Fermi flux limit we constrain the high energy cutoff to be
350 keV < E < 25 MeV. Line emission from both near-neutral iron K_alpha at 6.39
keV and highly ionised iron, from Fe_(xxv) and Fe_(xxvi), is strongly detected
in the Suzaku spectrum, further confirming the results of previous observations
with Chandra and XMM-Newton. We find the centroid energies for the Fe_(xxv) and
Fe_(xxvi) emission to be 6.60 keV and 6.95 keV respectively, with the latter
appearing to be resolved in the Suzaku spectrum. We show that the Fe_(xxv) and
Fe_(xxvi) emission can result from a highly photo-ionised plasma of column
density N_(H) ~ 3 x 10^(23) cm^(-2). A Compton reflection component, e.g.,
originating from an optically-thick accretion disc or a Compton-thick torus,
appears either very weak or absent in this AGN, subtending < 1 sr to the X-ray
source, consistent with previous findings. Indeed the absence of either neutral
or ionised Compton reflection coupled with the lack of any relativistic Fe K
signatures in the spectrum suggests that an inner, optically-thick accretion
disc is absent in this source. Instead, the accretion disc could be truncated
with the inner regions perhaps replaced by a Compton-thin Radiatively
Inefficient Accretion Flow. Thus, the Fe_(xxv) and Fe_(xxvi) emission could
both originate in ionised material perhaps at the transition region between the
hot, inner flow and the cold, truncated accretion disc on the order of 10^(3) -
10^(4) gravitational radii from the black hole. The origin for the unresolved
neutral Fe K_alpha emission is then likely to be further out, perhaps
originating in the optical BLR or a Compton-thin pc-scale torus.Comment: 15 pages, 11 figures, accepted for publication by MNRA
Significant X-ray Line Emission in the 5-6 keV band of NGC 4051
A Suzaku X-ray observation of NGC 4051 taken during 2005 Nov reveals line
emission at 5.44 keV in the rest-frame of the galaxy which does not have an
obvious origin in known rest-frame atomic transitions. The improvement to the
fit statistic when this line is accounted for establishes its reality at >99.9%
confidence: we have also verified that the line is detected in the three XIS
units independently. Comparison between the data and Monte Carlo simulations
shows that the probability of the line being a statistical fluctuation is p <
3.3 x 10^-4. Consideration of three independent line detections in Suzaku data
taken at different epochs yields a probability p< 3 x 10^-11 and thus
conclusively demonstrates that it cannot be a statistical fluctuation in the
data. The new line and a strong component of Fe Ka emission from neutral
material are prominent when the source flux is low, during 2005. Spectra from
2008 show evidence for a line consistent with having the same flux and energy
as that observed during 2005, but inconsistent with having a constant
equivalent width against the observed continuum. The stability of the line flux
and energy suggests that it may not arise in transient hotspots, as has been
suggested for similar lines in other sources, but could arise from a special
location in the reprocessor, such as the inner edge of the accretion disk.
Alternatively, the line energy may be explained by spallation of Fe into Cr, as
discussed in a companion paper.Comment: 18 pages, accepted for publication by Ap
A Machian Model of Dark Energy
Einstein believed that Mach's principle should play a major role in finding a
meaningful spacetime geometry, though it was discovered later that his field
equations gave some solutions which were not Machian. It is shown, in this
essay, that the kinematical models, which are invoked to solve the
cosmological constant problem, are in fact consistent with Mach's ideas. One
particular model in this category is described which results from the
microstructure of spacetime and seems to explain the current observations
successfully and also has some benefits over the conventional models. This
forces one to think whether the Mach's ideas and the cosmological constant are
interrelated in some way.Comment: Received an Honorable mention in the Essay Contest-2002 sponsored by
the Gravity Research Foundation; A paragraph added on how the model can
explain the CMB anisotropy observations; To appear in the Classical and
Quantum Gravit
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