Cosmogenic neutron production at the Sudbury Neutrino Observatory

Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of geant4 physics models. In addition, the cosmogenic neutron yield, in units of 10-4 cm2/(g·μ), is measured to be 7.28±0.09(stat)-1.12+1.59(syst) in pure heavy water and 7.30±0.07(stat)-1.02+1.40(syst) in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB

UV-Green Iridescence Predicts Male Quality during Jumping Spider Contests

10.1371/journal.pone.0059774PLoS ONE84

Chromatic Illumination Discrimination Ability Reveals that Human Colour Constancy Is Optimised for Blue Daylight Illuminations

The phenomenon of colour constancy in human visual perception keeps surface colours constant, despite changes in their reflected light due to changing illumination. Although colour constancy has evolved under a constrained subset of illuminations, it is unknown whether its underlying mechanisms, thought to involve multiple components from retina to cortex, are optimised for particular environmental variations. Here we demonstrate a new method for investigating colour constancy using illumination matching in real scenes which, unlike previous methods using surface matching and simulated scenes, allows testing of multiple, real illuminations. We use real scenes consisting of solid familiar or unfamiliar objects against uniform or variegated backgrounds and compare discrimination performance for typical illuminations from the daylight chromaticity locus (approximately blue-yellow) and atypical spectra from an orthogonal locus (approximately red-green, at correlated colour temperature 6700 K), all produced in real time by a 10-channel LED illuminator. We find that discrimination of illumination changes is poorer along the daylight locus than the atypical locus, and is poorest particularly for bluer illumination changes, demonstrating conversely that surface colour constancy is best for blue daylight illuminations. Illumination discrimination is also enhanced, and therefore colour constancy diminished, for uniform backgrounds, irrespective of the object type. These results are not explained by statistical properties of the scene signal changes at the retinal level. We conclude that high-level mechanisms of colour constancy are biased for the blue daylight illuminations and variegated backgrounds to which the human visual system has typically been exposed

Combining eye and hand in search is suboptimal

When performing everyday tasks, we often move our eyes and hand together: we look where we are reaching in order to better guide the hand. This coordinated pattern with the eye leading the hand is presumably optimal behaviour. But eyes and hands can move to different locations if they are involved in different tasks. To find out whether this leads to optimal performance, we studied the combination of visual and haptic search. We asked ten participants to perform a combined visual and haptic search for a target that was present in both modalities and compared their search times to those on visual only and haptic only search tasks. Without distractors, search times were faster for visual search than for haptic search. With many visual distractors, search times were longer for visual than for haptic search. For the combined search, performance was poorer than the optimal strategy whereby each modality searched a different part of the display. The results are consistent with several alternative accounts, for instance with vision and touch searching independently at the same time

Exploiting Anopheles responses to thermal, odour and visual stimuli to improve surveillance and control of malaria

Mosquito surveillance and control are at the heart of efforts to eliminate malaria, however, there remain significant gaps in our understanding of mosquito behaviour that impede innovation. We hypothesised that a combination of human-associated stimuli could be used to attract and kill malaria vectors more successfully than individual stimuli, and at least as well as a real human. To test this in the field, we quantified Anopheles responses to olfactory, visual and thermal stimuli in Burkina Faso using a simple adhesive trap. Traps baited with human odour plus high contrast visual stimuli caught more Anopheles than traps with odour alone, showing that despite their nocturnal habit, malaria vectors make use of visual cues in host-seeking. The best performing traps, however, combined odour and visual stimuli with a thermal signature in the range equivalent to human body temperature. When tested against a human landing catch during peak mosquito abundance, this “host decoy” trap caught nearly ten times the number of Anopheles mosquitoes caught by a human collector. Exploiting the behavioural responses of mosquitoes to the entire suite of host stimuli promises to revolutionise vector surveillance and provide new paradigms in disease control

Patterns of nucleotide diversity at the regions encompassing the Drosophila insulin-like peptide (dilp) genes: demography vs positive selection in Drosophila melanogaster.

In Drosophila, the insulin-signaling pathway controls some life history traits, such as fertility and lifespan, and it is considered to be the main metabolic pathway involved in establishing adult body size. Several observations concerning variation in body size in the Drosophila genus are suggestive of its adaptive character. Genes encoding proteins in this pathway are, therefore, good candidates to have experienced adaptive changes and to reveal the footprint of positive selection. The Drosophila insulin-like peptides (DILPs) are the ligands that trigger the insulin-signaling cascade. In Drosophila melanogaster, there are several peptides that are structurally similar to the single mammalian insulin peptide. The footprint of recent adaptive changes on nucleotide variation can be unveiled through the analysis of polymorphism and divergence. With this aim, we have surveyed nucleotide sequence variation at the dilp1-7 genes in a natural population of D. melanogaster. The comparison of polymorphism in D. melanogaster and divergence from D. simulans at different functional classes of the dilp genes provided no evidence of adaptive protein evolution after the split of the D. melanogaster and D. simulans lineages. However, our survey of polymorphism at the dilp gene regions of D. melanogaster has provided some evidence for the action of positive selection at or near these genes. The regions encompassing the dilp1-4 genes and the dilp6 gene stand out as likely affected by recent adaptive events

Measurement of neutron production in atmospheric neutrino interactions at the Sudbury Neutrino Observatory

Neutron production in GeV-scale neutrino interactions is a poorly studied process. We have measured the neutron multiplicities in atmospheric neutrino interactions in the Sudbury Neutrino Observatory experiment and compared them to the prediction of a Monte Carlo simulation using GENIE and a minimally modified version of GEANT4. We analyzed 837 days of exposure corresponding to Phase I, using pure heavy water, and Phase II, using a mixture of Cl in heavy water. Neutrons produced in atmospheric neutrino interactions were identified with an efficiency of $15.3\%$ and $44.3\%$, for Phase I and II respectively. The neutron production is measured as a function of the visible energy of the neutrino interaction and, for charged current quasi-elastic interaction candidates, also as a function of the neutrino energy. This study is also performed classifying the complete sample into two pairs of event categories: charged current quasi-elastic and non charged current quasi-elastic, and $\nu_{\mu}$ and $\nu_e$. Results show good overall agreement between data and Monte Carlo for both phases, with some small tension with a statistical significance below $2\sigma$ for some intermediate energies

The use of open data as a material for learning

Open data has potential value as a material for use in learning activities. However, approaches to harnessing this are not well understood or in mainstream use in education. In this research, early adopters from a diverse range of educational projects and teaching settings were interviewed to explore their rationale for using open data in teaching, how suitable activity designs could be achieved, and the practical challenges of using open data. A thematic analysis was conducted to identify patterns and relationships in these open data-based practices that have already emerged. A document analysis of teaching materials and other related artefacts was used to augment and validate the findings. Drawing on this, common approaches and issues are identified, and a conceptual framework to support greater use of open data by educators is described. This paper also highlights where existing concepts in education and educational technology research, including inquiry-based learning, authenticity, motivation, dialogue, and personalisation can help us to understand the value and challenges of using open data in education

Acquisition vs. Memorization Trade-Offs Are Modulated by Walking Distance and Pattern Complexity in a Large-Scale Copying Paradigm

In a “block-copying paradigm”, subjects were required to copy a configuration of colored blocks from a model area to a distant work area, using additional blocks provided at an equally distant resource area. Experimental conditions varied between the inter-area separation (walking distance) and the complexity of the block patterns to be copied. Two major behavioral strategies were identified: in the memory-intensive strategy, subjects memorize large parts of the pattern and rebuild them without intermediate visits at the model area. In the acquisition-intensive strategy, subjects memorize one block at a time and return to the model after having placed this block. Results show that the frequency of the memory-intensive strategy is increased for larger inter-area separations (larger walking distances) and for simpler block patterns. This strategy-shift can be interpreted as the result of an optimization process or trade-off, minimizing combined, condition-dependent costs of the two strategies. Combined costs correlate with overall response time. We present evidence that for the memory-intensive strategy, costs correlate with model visit duration, while for the acquisition-intensive strategy, costs correlate with inter-area transition (i.e., walking) times