1,272 research outputs found
Place-centred interaction design: situated participation and co-creation in places of heritage
This paper argues that the design of interactive installations for museums and other heritage sites should be concerned with understanding, supporting and augmenting visitors 19 lived experiences in context, thus their ability to actively participate in an exhibition. We use the concept of 18place 19 to refer to the physical environment as it is invested by the qualities of human experience, and to placemaking as the active process of connecting and relating to locations that become meaningful in our lives. We will discuss some of the limitations of existing heritage technologies in considering aspects of active place experience, and will argue how a place-sensitive approach can lead to successful interaction design whereby people establish meaningful and active connections at personal, cultural, social and physical levels to the places of heritage they experience
Twisted-torus configurations with large toroidal magnetic fields in relativistic stars
Understanding the properties of the internal magnetic field of neutron stars
remains a theoretical challenge. Over the last years, twisted-torus geometries
have been considered both in Newtonian and general-relativistic equilibrium
models, as they represent a potentially good description of neutron star
interiors. All of these works have found an apparent intrinsic limitation to
geometries that are poloidal-field-dominated, with a toroidal-to-poloidal
energy ratio inside the star that are <10%, unless surface currents are
included and magnetic fields are allowed to be discontinuous. This limitation
is in stark contrast with the general expectation that much higher toroidal
fields should be present in the stellar interior and casts doubt about the
stability and hence realism of these configurations. We here discuss how to
overcome this limitation by adopting a new prescription for the azimuthal
currents that leads to magnetized equilibria where the toroidal-to-total
magnetic-field energy ratio can be as high as 90%, thus including geometries
that are toroidal-field-dominated. Moreover, our results show that for a fixed
exterior magnetic-field strength, a higher toroidal-field energy implies a much
higher total magnetic energy stored in the star, with a potentially strong
impact on the expected electromagnetic and gravitational-wave emission from
highly magnetized neutron stars.Comment: 5 pages, 3 figures, 1 tabl
Magnetically-induced outflows from binary neutron star merger remnants
Recent observations by the Swift satellite have revealed long-lasting (), "plateau-like" X-ray afterglows in the vast majority
of short gamma-ray bursts events. This has put forward the idea of a long-lived
millisecond magnetar central engine being generated in a binary neutron star
(BNS) merger and being responsible for the sustained energy injection over
these timescales ("magnetar model"). We elaborate here on recent simulations
that investigate the early evolution of such a merger remnant in
general-relativistic magnetohydrodynamics. These simulations reveal very
different conditions than those usually assumed for dipole spin-down emission
in the magnetar model. In particular, the surrounding of the newly formed NS is
polluted by baryons due to a dense, highly magnetized and isotropic wind from
the stellar surface that is induced by magnetic field amplification in the
interior of the star. The timescales and luminosities of this wind are
compatible with early X-ray afterglows, such as the "extended emission". These
isotropic winds are a generic feature of BNS merger remnants and thus represent
an attractive alternative to current models of early X-ray afterglows. Further
implications to BNS mergers and short gamma-ray bursts are discussed.Comment: 4 pages, 2 figures. To appear in proceedings of "Swift: 10 Years of
Discovery
Electromagnetic emission from long-lived binary neutron star merger remnants II: lightcurves and spectra
Recent observations indicate that in a large fraction of binary neutron star
(BNS) mergers a long-lived neutron star (NS) may be formed rather than a black
hole. Unambiguous electromagnetic (EM) signatures of such a scenario would
strongly impact our knowledge on how short gamma-ray bursts (SGRBs) and their
afterglow radiation are generated. Furthermore, such EM signals would have
profound implications for multimessenger astronomy with joint EM and
gravitational-wave (GW) observations of BNS mergers, which will soon become
reality with the ground-based advanced LIGO/Virgo GW detector network starting
its first science run this year. Here we explore such EM signatures based on
the model presented in a companion paper, which provides a self-consistent
evolution of the post-merger system and its EM emission starting from an early
baryonic wind phase and resulting in a final pulsar wind nebula that is
confined by the previously ejected material. Lightcurves and spectra are
computed for a wide range of post-merger physical properties and particular
attention is paid to the emission in the X-ray band. In the context of SGRB
afterglow modeling, we present X-ray lightcurves corresponding to the
'standard' and the recently proposed 'time-reversal' scenario (SGRB prompt
emission produced at the time of merger or at the time of collapse of the
long-lived NS). The resulting afterglow lightcurve morphologies include, in
particular, single and two-plateau features with timescales and luminosities
that are in good agreement with the observations by the Swift satellite.
Furthermore, we compute the X-ray signal that should precede the SGRB in the
time-reversal scenario. If found, such a signal would represent smoking-gun
evidence for this scenario. Finally, we find a bright, highly isotropic EM
transient signal peaking in the X-ray band ...Comment: 20 pages, 16 figure
Magnetic field amplification in hypermassive neutron stars via the magnetorotational instability
Mergers of binary neutron stars likely lead to the formation of a
hypermassive neutron star (HMNS), which is metastable and eventually collapses
to a black hole. This merger scenario is thought to explain the phenomenology
of short gamma-ray bursts (SGRBs). The very high energies observed in SGRBs
have been suggested to stem from neutrino-antineutrino annihilation and/or from
very strong magnetic fields created during or after the merger by mechanisms
like the magnetorotational instability (MRI). Here, we report on results that
show for the first time the development of the MRI in HMNSs in
three-dimensional, fully general-relativistic magnetohydrodynamic simulations.
This instability amplifies magnetic fields exponentially and could be a vital
ingredient in solving the SGRB puzzle.Comment: 6 pages, 3 figures. Proceedings of the Karl Schwarzschild Meeting
201
Electromagnetic emission from long-lived binary neutron star merger remnants I: formulation of the problem
Binary neutron star (BNS) mergers are the leading model to explain the
phenomenology of short gamma-ray bursts (SGRBs), which are among the most
luminous explosions in the universe. Recent observations of long-lasting X-ray
afterglows of SGRBs challenge standard paradigms and indicate that in a large
fraction of events a long-lived neutron star (NS) may be formed rather than a
black hole. Understanding the mechanisms underlying these afterglows is
necessary in order to address the open questions concerning the nature of SGRB
central engines. However, recent theoretical progress has been hampered by the
fact that the timescales of interest for the afterglow emission are
inaccessible to numerical relativity simulations. Here we present a detailed
model to bridge the gap between numerical simulations of the merger process and
the relevant timescales for the afterglows, assuming that the merger results in
a long-lived NS. This model is formulated in terms of a set of coupled
differential equations that follow the evolution of the post-merger system and
predict its electromagnetic (EM) emission in a self-consistent way, starting
from initial data that can be extracted from BNS merger simulations and taking
into account the most relevant radiative processes. Moreover, the model can
accomodate the collapse of the remnant NS at any time during the evolution as
well as different scenarios for the prompt SGRB emission. A second major reason
of interest for BNS mergers is that they are considered the most promising
source of gravitational waves (GWs) for detection with the advanced
ground-based detector network LIGO/Virgo coming online this year.
Multimessenger astronomy with joint EM and GW observations of the merger and
post-merger phase can greatly enhance the scientific output of either type of
observation. However, the actual benefit depends on ...Comment: 27 pages, 3 figures, 4 appendice
Social aspects of place experience in nomadic work/life practices
This chapter examines the importance of “where” mobile work/life practices occur. By discussing excerpts of data collected through in-depth interviews with mobile professionals, we focus on the importance of place for mobility, and highlight the social character of place and the intrinsically social motivations of workers when making decisions regarding where to move. In order to show how the experience of mobility is grounded within place as a socially significant con- struct, we concentrate on three analytical themes: place as an essential component of social/collaborative work, place as expressive of organizational needs and characteristics, and place as facilitating a blending of work/life strategies and relationships
Educate Every Child: Promoting Positive Solutions to School Discipline in Virginia
Explains how suspension and expulsion for minor misbehavior leads to lower achievement, higher dropout rates, and more contact with juvenile justice. Calls for evidence-based alternatives, incentives to reduce school exclusion, and data collection
Poloidal-Field Instability in Magnetized Relativistic Stars
We investigate the instability of purely poloidal magnetic fields in
nonrotating neutron stars by means of three-dimensional general-relativistic
magnetohydrodynamics simulations, extending the work presented in Ciolfi et al.
(2011). Our aim is to draw a clear picture of the dynamics associated with the
instability and to study the final configuration reached by the system, thus
obtaining indications on possible equilibria in a magnetized neutron star.
Furthermore, since the internal rearrangement of magnetic fields is a highly
dynamical process, which has been suggested to be behind magnetar giant flares,
our simulations can provide a realistic estimate of the electromagnetic and
gravitational-wave emission which should accompany the flare event. Our main
findings are the following: (i) the initial development of the instability
meets all the expectations of perturbative studies in terms of the location of
the seed of the instability, the timescale for its growth and the generation of
a toroidal component; (ii) in the subsequent nonlinear reorganization of the
system, ~90% of magnetic energy is lost in few Alfven timescales mainly through
electromagnetic emission, and further decreases on a much longer timescale;
(iii) all stellar models tend to achieve a significant amount of magnetic
helicity and the equipartition of energy between poloidal and toroidal magnetic
fields, and evolve to a new configuration which does not show a subsequent
instability on dynamical or Alfven timescales; (iv) the electromagnetic
emission matches the duration of the initial burst in luminosity observed in
giant flares, giving support to the internal rearrangement scenario; (v) only a
small fraction of the energy released during the process is converted into
f-mode oscillations and in the consequent gravitational-wave emission, thus
resulting in very low chances of detecting this signal with present and..Comment: 13 pages, 11 figures, updated to match the published versio
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