28,297 research outputs found
The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum?
An inflationary gravitational wave background consistent with BICEP2 is
difficult to reconcile with a simple power-law spectrum of primordial scalar
perturbations. Tensor modes contribute to the temperature anisotropies at
multipoles with , and this effect --- together with a prior on
the form of the scalar perturbations --- was the source of previous bounds on
the tensor-to-scalar ratio. We compute Bayesian evidence for combined fits to
BICEP2 and Planck for three nontrivial primordial spectra: a) a running
spectral index, b) a cutoff at fixed wavenumber, and c) a spectrum described by
a linear spline with a single internal knot. We find no evidence for a cutoff,
weak evidence for a running index, and significant evidence for a "broken"
spectrum. Taken at face-value, the BICEP2 results require two new inflationary
parameters in order to describe both the broken scale invariance in the
perturbation spectrum and the observed tensor-to-scalar ratio. Alternatively,
this tension may be resolved by additional data and more detailed analyses.Comment: 14 pages, 5 figures, 4 tables; v2: references added, discussion
updated, matches published versio
The Knotted Sky I: Planck constraints on the primordial power spectrum
Using the temperature data from Planck we search for departures from a
power-law primordial power spectrum, employing Bayesian model-selection and
posterior probabilities. We parametrize the spectrum with knots located at
arbitrary values of , with both linear and cubic splines. This
formulation recovers both slow modulations and sharp transitions in the
primordial spectrum. The power spectrum is well-fit by a featureless, power-law
at wavenumbers . A modulated primordial
spectrum yields a better fit relative to CDM at large scales, but
there is no strong evidence for a departure from a power-law spectrum.
Moreover, using simulated maps we show that a local feature at can mimic the suppression of large-scale power. With
multi-knot spectra we see only small changes in the posterior distributions for
the other free parameters in the standard CDM universe. Lastly, we
investigate whether the hemispherical power asymmetry is explained by
independent features in the primordial power spectrum in each ecliptic
hemisphere, but find no significant differences between them.Comment: 24 pages, 9 figures, 4 tables, 1 appendix; v2: references added,
discussion updated, matches published versio
Testing for New Physics: Neutrinos and the Primordial Power Spectrum
We test the sensitivity of neutrino parameter constraints from combinations
of CMB and LSS data sets to the assumed form of the primordial power spectrum
(PPS) using Bayesian model selection. Significantly, none of the tested
combinations, including recent high-precision local measurements of
and cluster abundances, indicate a signal for massive neutrinos
or extra relativistic degrees of freedom. For PPS models with a large, but
fixed number of degrees of freedom, neutrino parameter constraints do not
change significantly if the location of any features in the PPS are allowed to
vary, although neutrino constraints are more sensitive to PPS features if they
are known a priori to exist at fixed intervals in . Although there is
no support for a non-standard neutrino sector from constraints on both neutrino
mass and relativistic energy density, we see surprisingly strong evidence for
features in the PPS when it is constrained with data from Planck 2015, SZ
cluster counts, and recent high-precision local measurements of .
Conversely combining Planck with matter power spectrum and BAO measurements
yields a much weaker constraint. Given that this result is sensitive to the
choice of data this tension between SZ cluster counts, Planck and
measurements is likely an indication of unmodeled systematic
bias that mimics PPS features, rather than new physics in the PPS or neutrino
sector.Comment: 23 pages, 9 figures, 8 tables; matches version published in JCA
Becoming in touch with industrial robots through ethnography
Touch is central to communication and social interaction. For both humans and robots touch is a mode through which they sense the world. A second wave of industrial robots is reshaping how touch operates within the labor process. Recent studies have turned their attention to the role of touch in Human-Robot Interaction (HRI). While these studies have produced useful knowledge in relation to the affective capacities of robotic touch, methods remain restrictive. This paper contributes to expanding research methods for the study of robotic touch. It reports on the design of an ongoing ethnography that forms part of the InTouch project. The interdisciplinary project takes forward a socially orientated stance and is concerned with how technologies shape the semiotic and sensory dimensions of touch in the 'real world'. We contend that these dimensions are key factors in shaping how humans and robots interact, yet are currently overlooked in the HRI community. This multi-sited sensory ethnography research has been designed to explore the social implications of robotic touch within industrial settings (e.g. manufacturing and construction)
Making sense of digitally remediated touch in virtual reality experiences
Touch, often called the âfirst senseâ, is fundamental to how we experience and know ourselves, others and the world. Increasingly, touch is being brought into the digital landscape. This paper explores this shifting landscape to understand the ways in which touch is re-mediated in the context of virtual reality. With attention to the sensoriality and sociality of touch, it asks what âcountsâ as touch in VR, how is touch experienced and how is it incorporated into meaning making. We present and discuss findings from a multimodal and multisensory study of 16 participants interacting in two VR experiences to describe: the participantsâ material encounters with the virtual through a focus on touch practices, expectations and norms; the ways in which participants made meaning of (and with) virtual touch through their dynamic selection and orchestration of the range of semiotic and experiential resources available; and how these virtual touch experiences translated into discourses of touch in VR to emphasize continuities and change between the past, present and futures. The paper comments on the methodological challenges of researching touch in the emergent landscape of VR and asks how multimodality might engage newly with touch, perhaps the most under-rated and neglected of modes and senses, and its digital remediation
Taking an Extended Embodied Perspective of Touch: Connection-Disconnection in iVR
Bringing touch into VR experiences through haptics is considered increasingly important for user engagement and fostering feelings of presence and immersion, yet few qualitative studies have explored users' iVR touch experiences. This paper takes an embodied approachâbringing attention to the tactile-kinaesthetic bodyâto explore users' wholistic experiences of touch in iVR, moving beyond the cutaneous and tactile elements of âfeelingâ to elaborate upon themes of movement and kinetics. Our findings show how both touch connections and disconnections emerged though material forms of tactility (the controller, body positioning, tactile expectations) and through âfelt proximitiesâ and the tactile-kinaesthetic experience thus shaping the sense of presence. The analysis shows three key factors that influence connection and disconnection, and how connection is re-navigated or sought at moments of experienced disconnection: a sense of control or agency; identity; and bridging between the material and virtual. This extended notion of touch deepens our understanding of its role in feelings of presence by providing insight into a range of factors related to notions of touch â both physical and virtualâthat come into play in creating a sense of connection or presence (e.g., histories, expectations), and highlights the potential for iVR interaction to attend to the body beyond the hands in terms of touch
Electrical switching of magnetic polarity in a multiferroic BiFeO3 device at room temperature
We have directly imaged reversible electrical switching of the cycloidal
rotation direction (magnetic polarity) in a (111)-BiFeO3 epitaxial-film device
at room temperature by non-resonant x-ray magnetic scattering. Consistent with
previous reports, fully relaxed (111)-BiFeO3 epitaxial films consisting of a
single ferroelectric domain were found to comprise a sub-micron-scale mosaic of
magneto-elastic domains, all sharing a common direction of the magnetic
polarity, which was found to switch reversibly upon reversal of the
ferroelectric polarization without any measurable change of the magneto-elastic
domain population. A real-space polarimetry map of our device clearly
distinguished between regions of the sample electrically addressed into the two
magnetic states with a resolution of a few tens of micron. Contrary to the
general belief that the magneto-electric coupling in BiFeO3 is weak, we find
that electrical switching has a dramatic effect on the magnetic structure, with
the magnetic moments rotating on average by 90 degrees at every cycle.Comment: 6 pages, 5 figures; corrected figure
Accurate Liability Estimation Improves Power in Ascertained Case Control Studies
Linear mixed models (LMMs) have emerged as the method of choice for
confounded genome-wide association studies. However, the performance of LMMs in
non-randomly ascertained case-control studies deteriorates with increasing
sample size. We propose a framework called LEAP (Liability Estimator As a
Phenotype, https://github.com/omerwe/LEAP) that tests for association with
estimated latent values corresponding to severity of phenotype, and demonstrate
that this can lead to a substantial power increase
Image Coaddition with Temporally Varying Kernels
Large, multi-frequency imaging surveys, such as the Large Synaptic Survey
Telescope (LSST), need to do near-real time analysis of very large datasets.
This raises a host of statistical and computational problems where standard
methods do not work. In this paper, we study a proposed method for combining
stacks of images into a single summary image, sometimes referred to as a
template. This task is commonly referred to as image coaddition. In part, we
focus on a method proposed in previous work, which outlines a procedure for
combining stacks of images in an online fashion in the Fourier domain. We
evaluate this method by comparing it to two straightforward methods through the
use of various criteria and simulations. Note that the goal is not to propose
these comparison methods for use in their own right, but to ensure that
additional complexity also provides substantially improved performance
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