992 research outputs found
Extraction of gravitational-wave energy in higher dimensional numerical relativity using the Weyl tensor
© 2017 IOP Publishing Ltd. Gravitational waves are one of the most important diagnostic tools in the analysis of strong-gravity dynamics and have been turned into an observational channel with LIGO's detection of GW150914. Aside from their importance in astrophysics, black holes and compact matter distributions have also assumed a central role in many other branches of physics. These applications often involve spacetimes with D > 4 dimensions where the calculation of gravitational waves is more involved than in the four dimensional case, but has now become possible thanks to substantial progress in the theoretical study of general relativity in D > 4. Here, we develop a numerical implementation of the formalism by Godazgar and Reall [1] - based on projections of the Weyl tensor analogous to the Newman-Penrose scalars - that allows for the calculation of gravitational waves in higher dimensional spacetimes with rotational symmetry. We apply and test this method in black-hole head-on collisions from rest in D = 6 spacetime dimensions and find that a fraction of the Arnowitt-Deser-Misner mass is radiated away from the system, in excellent agreement with literature results based on the Kodama-Ishibashi perturbation technique. The method presented here complements the perturbative approach by automatically including contributions from all multipoles rather than computing the energy content of individual multipoles.This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie SkĆodowska-Curie grant agreement No 690904, from H2020-ERC-2014-CoG Grant No. 'MaGRaTh' 646597, from STFC Consolidator Grant No. ST/L000636/1, the SDSC Comet, PSC-Bridges and TACC Stampede clusters through NSF-XSEDE Award Nos. PHY-090003, the Cambridge High Performance Computing Service Supercomputer Darwin using Strategic Research Infrastructure Funding from the HEFCE and the STFC, and DiRAC's Cosmos Shared Memory system through BIS Grant No. ST/J005673/1 and STFC Grant Nos. ST/H008586/1, ST/K00333X/1. WGC is supported by a STFC studentship
Orbiting black-hole binaries and apparent horizons in higher dimensions
We study gravitational wave emission and the structure and formation of
apparent horizons in orbiting black-hole binary systems in higher-dimensional
general relativity. For this purpose we present an apparent horizon finder for
use in higher dimensional numerical simulations and test the finder's accuracy
and consistency in single and binary black-hole spacetimes. The black-hole
binaries we model in dimensions complete up to about one orbit before
merging or scatter off each other without formation of a common horizon. In
agreement with the absence of stable circular geodesic orbits around
higher-dimensional black holes, we do not find binaries completing multiple
orbits without finetuning of the initial data. All binaries radiate about
to of the total mass-energy in gravitational waves, over
an order of magnitude below the radiated energy measured for four-dimensional
binaries. The low radiative efficiency is accompanied by relatively slow
dynamics of the binaries as expected from the more rapid falloff of the binding
gravitational force in higher dimensions
Black-hole head-on collisions in higher dimensions
The collision of black holes and the emission of gravitational radiation in
higher-dimensional spacetimes are of interest in various research areas,
including the gauge-gravity duality, the TeV gravity scenarios evoked for the
explanation of the hierarchy problem, and the large-dimensionality limit of
general relativity. We present numerical simulations of head-on collisions of
nonspinning, unequal-mass black holes starting from rest in general relativity
with spacetime dimensions. We compare the energy and linear
momentum radiated in gravitational waves with perturbative predictions in the
extreme mass ratio limit, demonstrating the strength and limitations of
black-hole perturbation theory in this context
Dimensional reduction in numerical relativity: Modified Cartoon formalism and regularization
We present in detail the Einstein equations in the
Baumgarte-Shapiro-Shibata-Nakamura formulation for the case of dimensional
spacetimes with isometry based on a method originally introduced in
Ref.1. Regularized expressions are given for a numerical implementation of this
method on a vertex centered grid including the origin of the quasi-radial
coordinate that covers the extra dimensions with rotational symmetry.
Axisymmetry, corresponding to the value , represents a special case with
fewer constraints on the vanishing of tensor components and is conveniently
implemented in a variation of the general method. The robustness of the scheme
is demonstrated for the case of a black-hole head-on collision in
spacetime dimensions with symmetry.U.S. is supported by the H2020 ERC Consolidator Grant âMatter and strong-field gravity: New frontiers in Einsteinâs theoryâ grant agreement No. MaGRaThâ646597, the H2020-MSCA-RISE-2015 Grant No. StronGrHEP-690904, the STFC Consolidator Grant No. ST/L000636/1, the SDSC Comet and TACC Stampede clusters through NSF-XSEDE Award Nos. PHY-090003, the Cambridge High Performance Computing Service Supercomputer Darwin using Strategic Research Infrastructure Funding from the HEFCE and the STFC, and DiRACâs Cosmos Shared Memory system through BIS Grant No. ST/J005673/1 and STFC Grant Nos. ST/H008586/1, ST/K00333X/1. P.F. and S.T. are supported by the H2020 ERC Starting Grant âNew frontiers in numerical general relativityâ grant agreement No. NewNGR- 639022. P.F. is also supported by a Royal Society University Research Fellowship. W.G.C. and M.K. are supported by STFC studentships.This is the final version of the article. It first appeared from the World Scientific Publishing Company via http://dx.doi.org/10.1142/S021827181641013
A systematic literature review of the use of social media for business process management
In todayâs expansion of new technologies, innovation is found necessary for organizations to be up to date with the latest management trends. Although organizations are increasingly using new technologies, opportunities still exist to achieve the nowadays essential omnichannel management strategy. More precisely, social media are opening a path for benefiting more from an organizationâs process orientation. However, social media strategies are still an under-investigated field, especially when it comes to the research of social media use for the management and improvement of business processes or the internal way of working in organizations. By classifying a variety of articles, this study explores the evolution of social media implementation within the BPM discipline. We also provide avenues for future research and strategic implications for practitioners to use social media more comprehensively
A web-based simulation of a longitudinal clinic used in a 4-week ambulatory rotation: a cohort study
<p>Abstract</p> <p>Background</p> <p>Residency training takes place primarily on inpatient wards. In the absence of a resident continuity clinic, internal medicine residents rely on block rotations to learn about continuity of care. Alternate methods to introduce continuity of care are needed.</p> <p>Methods</p> <p>A web-based tool, Continuity of Care Online Simulations (COCOS), was designed for use in a one-month, postgraduate clinical rotation in endocrinology. It is an interactive tool that simulates the continuing care of any patient with a chronic endocrine disease. Twenty-three residents in internal medicine participated in a study to investigate the effects of using COCOS during a clinical rotation in endocrinology on pre-post knowledge test scores and self-assessment of confidence.</p> <p>Results</p> <p>Compared to residents who did the rotation alone, residents who used COCOS during the rotation had significantly higher improvements in test scores (% increase in pre-post test scores +21.6 [standard deviation, SD, 8.0] vs. +5.9 [SD 6.8]; p < .001). Test score improvements were most pronounced for less commonly seen conditions. There were no significant differences in changes in confidence. Residents rated COCOS very highly, recommending its use as a standard part of the rotation and throughout residency.</p> <p>Conclusion</p> <p>A stand-alone web-based tool can be incorporated into an existing clinical rotation to help residents learn about continuity of care. It has the most potential to teach residents about topics that are less commonly seen during a clinical rotation. The adaptable, web-based format allows the creation of cases for most chronic medical conditions.</p
Motion in classical field theories and the foundations of the self-force problem
This article serves as a pedagogical introduction to the problem of motion in
classical field theories. The primary focus is on self-interaction: How does an
object's own field affect its motion? General laws governing the self-force and
self-torque are derived using simple, non-perturbative arguments. The relevant
concepts are developed gradually by considering motion in a series of
increasingly complicated theories. Newtonian gravity is discussed first, then
Klein-Gordon theory, electromagnetism, and finally general relativity. Linear
and angular momenta as well as centers of mass are defined in each of these
cases. Multipole expansions for the force and torque are then derived to all
orders for arbitrarily self-interacting extended objects. These expansions are
found to be structurally identical to the laws of motion satisfied by extended
test bodies, except that all relevant fields are replaced by effective versions
which exclude the self-fields in a particular sense. Regularization methods
traditionally associated with self-interacting point particles arise as
straightforward perturbative limits of these (more fundamental) results.
Additionally, generic mechanisms are discussed which dynamically shift ---
i.e., renormalize --- the apparent multipole moments associated with
self-interacting extended bodies. Although this is primarily a synthesis of
earlier work, several new results and interpretations are included as well.Comment: 68 pages, 1 figur
The Effect of Genetic and Environmental Variation on Genital Size in Male Drosophila: Canalized but Developmentally Unstable
The genitalia of most male arthropods scale hypoallometrically with body size, that is they are more or less the same size across large and small individuals in a population. Such scaling is expected to arise when genital traits show less variation than somatic traits in response to factors that generate size variation among individuals in a population. Nevertheless, there have been few studies directly examining the relative sensitivity of genital and somatic traits to factors that affect their size. Such studies are key to understanding genital evolution and the evolution of morphological scaling relationships more generally. Previous studies indicate that the size of genital traits in male Drosophila melanogaster show a relatively low response to variation in environmental factors that affect trait size. Here we show that the size of genital traits in male fruit flies also exhibit a relatively low response to variation in genetic factors that affect trait size. Importantly, however, this low response is only to genetic factors that affect body and organ size systemically, not those that affect organ size autonomously. Further, we show that the genital traits do not show low levels of developmental instability, which is the response to stochastic developmental errors that also influence organ size autonomously. We discuss these results in the context of current hypotheses on the proximate and ultimate mechanisms that generate genital hypoallometry
How the weather affects the pain of citizen scientists using a smartphone app
Patients with chronic pain commonly believe their pain is related to the weather. Scientific evidence to support their beliefs is inconclusive, in part due to difficulties in getting a large dataset of patients frequently recording their pain symptoms during a variety of weather conditions. Smartphones allow the opportunity to collect data to overcome these difficulties. Our study Cloudy with a Chance of Pain analysed daily data from 2658 patients collected over a 15-month period. The analysis demonstrated significant yet modest relationships between pain and relative humidity, pressure and wind speed, with correlations remaining even when accounting for mood and physical activity. This research highlights how citizen-science experiments can collect large datasets on real-world populations to address long-standing health questions. These results will act as a starting point for a future system for patients to better manage their health through pain forecasts
âExcellence R Usâ: university research and the fetishisation of excellence
The rhetoric of âexcellenceâ is pervasive across the academy. It is used to refer to research outputs as well as researchers, theory and education, individuals and organisations, from art history to zoology. But does âexcellenceâ actually mean anything? Does this pervasive narrative of âexcellenceâ do any good? Drawing on a range of sources we interrogate âexcellenceâ as a concept and find that it has no intrinsic meaning in academia. Rather it functions as a linguistic interchange mechanism. To investigate whether this linguistic function is useful we examine how the rhetoric of excellence combines with narratives of scarcity and competition to show that the hypercompetition that arises from the performance of âexcellenceâ is completely at odds with the qualities of good research. We trace the roots of issues in reproducibility, fraud, and homophily to this rhetoric. But we also show that this rhetoric is an internal, and not primarily an external, imposition. We conclude by proposing an alternative rhetoric based on soundness and capacity-building. In the final analysis, it turns out that that âexcellenceâ is not excellent. Used in its current unqualified form it is a pernicious and dangerous rhetoric that undermines the very foundations of good research and scholarship
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