8,819 research outputs found
Estimating the weak-lensing rotation signal in radio cosmic shear surveys
Weak lensing has become an increasingly important tool in cosmology and the
use of galaxy shapes to measure cosmic shear has become routine. The
weak-lensing distortion tensor contains two other effects in addition to the
two components of shear: the convergence and rotation. The rotation mode is not
measurable using the standard cosmic shear estimators based on galaxy shapes,
as there is no information on the original shapes of the images before they
were lensed. Due to this, no estimator has been proposed for the rotation mode
in cosmological weak-lensing surveys, and the rotation mode has never been
constrained. Here, we derive an estimator for this quantity, which is based on
the use of radio polarisation measurements of the intrinsic position angles of
galaxies. The rotation mode can be sourced by physics beyond CDM, and
also offers the chance to perform consistency checks of CDM and of
weak-lensing surveys themselves. We present simulations of this estimator and
show that, for the pedagogical example of cosmic string spectra, this estimator
could detect a signal that is consistent with the constraints from Planck. We
examine the connection between the rotation mode and the shear -modes and
thus how this estimator could help control systematics in future radio
weak-lensing surveys
Critical Team Composition Issues for Long-Distance and Long-Duration Space Exploration: A Literature Review, an Operational Assessment, and Recommendations for Practice and Research
Prevailing team effectiveness models suggest that teams are best positioned for success when certain enabling conditions are in place (Hackman, 1987; Hackman, 2012; Mathieu, Maynard, Rapp, & Gilson, 2008; Wageman, Hackman, & Lehman, 2005). Team composition, or the configuration of member attributes, is an enabling structure key to fostering competent teamwork (Hackman, 2002; Wageman et al., 2005). A vast body of research supports the importance of team composition in team design (Bell, 2007). For example, team composition is empirically linked to outcomes such as cooperation (Eby & Dobbins, 1997), social integration (Harrison, Price, Gavin, & Florey, 2002), shared cognition (Fisher, Bell, Dierdorff, & Belohlav, 2012), information sharing (Randall, Resick, & DeChurch, 2011), adaptability (LePine, 2005), and team performance (e.g., Bell, 2007). As such, NASA has identified team composition as a potentially powerful means for mitigating the risk of performance decrements due to inadequate crew cooperation, coordination, communication, and psychosocial adaptation in future space exploration missions. Much of what is known about effective team composition is drawn from research conducted in conventional workplaces (e.g., corporate offices, production plants). Quantitative reviews of the team composition literature (e.g., Bell, 2007; Bell, Villado, Lukasik, Belau, & Briggs, 2011) are based primarily on traditional teams. Less is known about how composition affects teams operating in extreme environments such as those that will be experienced by crews of future space exploration missions. For example, long-distance and long-duration space exploration (LDSE) crews are expected to live and work in isolated and confined environments (ICEs) for up to 30 months. Crews will also experience communication time delays from mission control, which will require crews to work more autonomously (see Appendix A for more detailed information regarding the LDSE context). Given the unique context within which LDSE crews will operate, NASA identified both a gap in knowledge related to the effective composition of autonomous, LDSE crews, and the need to identify psychological and psychosocial factors, measures, and combinations thereof that can be used to compose highly effective crews (Team Gap 8). As an initial step to address Team Gap 8, we conducted a focused literature review and operational assessment related to team composition issues for LDSE. The objectives of our research were to: (1) identify critical team composition issues and their effects on team functioning in LDSE-analogous environments with a focus on key composition factors that will most likely have the strongest influence on team performance and well-being, and 1 Astronaut diary entry in regards to group interaction aboard the ISS (p.22; Stuster, 2010) 2 (2) identify and evaluate methods used to compose teams with a focus on methods used in analogous environments. The remainder of the report includes the following components: (a) literature review methodology, (b) review of team composition theory and research, (c) methods for composing teams, (d) operational assessment results, and (e) recommendations
Fast map-based simulations of systematics in CMB surveys including effects of the scanning strategy
We present approaches to quickly simulate systematics affecting CMB
observations, including the effects of the scanning strategy. Using summary
properties of the scan we capture features of full time ordered data (TOD)
simulations, allowing maps and power spectra to be generated at much improved
speed for a number of systematics - the cases we present experienced speed ups
of 3-4 orders of magnitude when implementing the map-based approaches. We
demonstrate the effectiveness of the approaches at capturing the salient
features of the scan by directly comparing to full TOD simulations - seeing
agreement at sub-percent levels of accuracy. We simulate the effects of
differential gain, pointing, and ellipticity to show the effectiveness of the
approaches, but note that one could extend these techniques to other
systematics. We finally show how to apply these fast map-based simulations of
systematic effects to a full focal plane showing their ability to incorporate
thousands of detectors as seen in modern CMB experiments.Comment: 17 pages, 13 figures, 1 table, prepared for submission to MNRA
Kink-induced transport and segregation in oscillated granular layers
We use experiments and molecular dynamics simulations of vertically
oscillated granular layers to study horizontal particle segregation induced by
a kink (a boundary between domains oscillating out of phase). Counter-rotating
convection rolls carry the larger particles in a bidisperse layer along the
granular surface to a kink, where they become trapped. The convection
originates from avalanches that occur inside the layer, along the interface
between solidified and fluidized grains. The position of a kink can be
controlled by modulation of the container frequency, making possible systematic
harvesting of the larger particles.Comment: 4 pages, 5 figures. to appear in Phys. Rev. Let
Efficient Fully Bayesian Approach to Brain Activity Mapping with Complex-Valued fMRI Data
Functional magnetic resonance imaging (fMRI) enables indirect detection of
brain activity changes via the blood-oxygen-level-dependent (BOLD) signal.
Conventional analysis methods mainly rely on the real-valued magnitude of these
signals. In contrast, research suggests that analyzing both real and imaginary
components of the complex-valued fMRI (cv-fMRI) signal provides a more holistic
approach that can increase power to detect neuronal activation. We propose a
fully Bayesian model for brain activity mapping with cv-fMRI data. Our model
accommodates temporal and spatial dynamics. Additionally, we propose a
computationally efficient sampling algorithm, which enhances processing speed
through image partitioning. Our approach is shown to be computationally
efficient via image partitioning and parallel computation while being
competitive with state-of-the-art methods. We support these claims with both
simulated numerical studies and an application to real cv-fMRI data obtained
from a finger-tapping experiment
Spin characterization of systematics in CMB surveys- A comprehensive formalism
The CMB -mode polarisation signal -- both the primordial gravitational
wave signature and the signal sourced by lensing -- is subject to many
contaminants from systematic effects. Of particular concern are systematics
that result in mixing of signals of different ``spin'', particularly leakage
from the much larger spin-0 intensity signal to the spin-2 polarisation signal.
We present a general formalism, which can be applied to arbitrary focal plane
setups, that characterises signals in terms of their spin. We provide general
expressions to describe how spin-coupled signals observed by the detectors
manifest at map-level, in the harmonic domain, and in the power spectra,
focusing on the polarisation spectra -- the signals of interest for upcoming
CMB surveys. We demonstrate the presence of a previously unidentified
cross-term between the systematic and the intrinsic sky signal in the power
spectrum, which in some cases can be the dominant source of contamination. The
formalism is not restricted to intensity to polarisation leakage but provides a
complete elucidation of all leakage including polarisation mixing, and applies
to both full and partial (masked) sky surveys, thus covering space-based,
balloon-borne, and ground-based experiments. Using a pair-differenced setup, we
demonstrate the formalism by using it to completely characterise the effects of
differential gain and pointing systematics, incorporating both intensity
leakage and polarisation mixing. We validate our results with full time ordered
data simulations. Finally, we show in an Appendix that an extension of simple
binning map-making to include additional spin information is capable of
removing spin-coupled systematics during the map-making process.Comment: Minimal revisions - some additional references added, typos fixed,
etc. 31 pages, 8 figures, 1 table. Accepted by MNRA
- …