Towards a theoretical determination of the geographical probability distribution of meteoroid impacts on Earth

Tunguska and Chelyabinsk impact events occurred inside a geographical area of only 3.4\% of the Earth's surface. Although two events hardly constitute a statistically significant demonstration of a geographical pattern of impacts, their spatial coincidence is at least tantalizing. To understand if this concurrence reflects an underlying geographical and/or temporal pattern, we must aim at predicting the spatio-temporal distribution of meteoroid impacts on Earth. For this purpose we designed, implemented and tested a novel numerical technique, the "Gravitational Ray Tracing" (GRT) designed to compute the relative impact probability (RIP) on the surface of any planet. GRT is inspired by the so-called ray-casting techniques used to render realistic images of complex 3D scenes. In this paper we describe the method and the results of testing it at the time of large impact events. Our findings suggest a non-trivial pattern of impact probabilities at any given time on Earth. Locations at $60-90\deg$ from the apex are more prone to impacts, especially at midnight. Counterintuitively, sites close to apex direction have the lowest RIP, while in the antapex RIP are slightly larger than average. We present here preliminary maps of RIP at the time of Tunguska and Chelyabinsk events and found no evidence of a spatial or temporal pattern, suggesting that their coincidence was fortuitous. We apply the GRT method to compute theoretical RIP at the location and time of 394 large fireballs. Although the predicted spatio-temporal impact distribution matches marginally the observed events, we successfully predict their impact speed distribution.Comment: 16 pages, 11 figures. Accepted for publication in MNRA

Spatially Continuous Strain Monitoring using Distributed Fiber Optic Sensors Embedded in Carbon Fiber Composites

A distributed fiber optic strain sensor based on Rayleigh backscattering, embedded in a fiber-reinforced polymer composite, has been demonstrated. The optical frequency domain reflectometry technique is used to analyze the backscattered signal. The shift in the Rayleigh backscattered spectrum is observed to be linearly related to the change in strain of the composite material. The sensor (standard single-mode fiber) is embedded between the layers of the composite laminate. A series of tensile loads is applied to the laminate using an Instron testing machine, and the corresponding strain distribution of the laminate is measured. The results show a linear response indicating a seamless integration of the optical fiber in the composite material and a good correlation with the electrical-resistance strain gauge results. The sensor is also used to evaluate the strain response of a composite-laminate-based cantilever beam. Distributed strain measurements in a composite laminate are successfully obtained using an embedded fiber optic sensor

Expanding CWD Disease Surveillance Options Using Environmental Contamination at Deer Signposts

1. Environmental surveillance can allow early detection of diseases, which increases management options and can improve disease trajectories. Chronic wasting disease (CWD) in cervids is a significant prion disease that has been spreading across North America since the 1960s, leading to cervid population declines and concern from hunters and state wildlife agencies. White-tailed deer have a unique breeding season behavior called scraping, where they deposit urine and saliva at shared sites. Since both these fluids can contain CWD prions, scrape sites have the potential to serve as sentinel sites for environmental surveillance of CWD.2. To examine this potential, we used camera traps to monitor deer behavior and collected environmental samples from 105 scrape sites. The 48 km2 study site was located at the center of the CWD zone in southwestern Tennessee (United States), where CWD prevalence is ~50%. We also sampled scrapes in northern Mississippi at the leading edge of the same CWD distribution to test the potential for early CWD detection using scrape sampling.3. From camera data, we identified 218 unique bucks visiting 105 scrapes, with a mean of 12.2 ± 7.5 bucks per scrape (mean ± SD, range 1–39) and individual bucks visiting a mean of 5.9 ± 4.6 monitored scrapes each (range 1–23).4. Using real-time quaking-induced conversion (RT-QuIC), we detected prion seeding activity in 20% of the soil and 41% of the licking branches of the scrape sites within the CWD study area, and in 25% of the soil and 11% of the licking branches of scrape sites sampled at the edge of the known CWD distribution.5. Our data show there is environmental prion contamination at scrape sites. This supports the idea that scrapes could serve as early warning sentinel sites for CWD surveillance through testing soil and licking branches for prion seeding ac-tivity, especially in areas with limited access to harvested deer samples

Genome wide association mapping of grain arsenic, copper, molybdenum and zinc in rice (Oryza sativa L.) grown at four international field sites

Peer reviewedPublisher PD

Formalising the Continuous/Discrete Modeling Step

Formally capturing the transition from a continuous model to a discrete model is investigated using model based refinement techniques. A very simple model for stopping (eg. of a train) is developed in both the continuous and discrete domains. The difference between the two is quantified using generic results from ODE theory, and these estimates can be compared with the exact solutions. Such results do not fit well into a conventional model based refinement framework; however they can be accommodated into a model based retrenchment. The retrenchment is described, and the way it can interface to refinement development on both the continuous and discrete sides is outlined. The approach is compared to what can be achieved using hybrid systems techniques.Comment: In Proceedings Refine 2011, arXiv:1106.348

Galaxy and Mass Assembly (GAMA): merging galaxies and their properties

We derive the close pair fractions and volume merger rates for galaxies in the Galaxy and Mass Assembly (GAMA) survey with −23 < Mr < −17 (ΩM = 0.27, ΩΛ = 0.73, H0 = 100 km s−1 Mpc−1) at 0.01 < z < 0.22 (look-back time of <2 Gyr). The merger fraction is approximately 1.5 per cent Gyr−1 at all luminosities (assuming 50 per cent of pairs merge) and the volume merger rate is ≈3.5 × 10−4 Mpc−3 Gyr−1. We examine how the merger rate varies by luminosity and morphology. Dry mergers (between red/spheroidal galaxies) are found to be uncommon and to decrease with decreasing luminosity. Fainter mergers are wet, between blue/discy galaxies. Damp mergers (one of each type) follow the average of dry and wet mergers. In the brighter luminosity bin (−23 < Mr < −20), the merger rate evolution is flat, irrespective of colour or morphology, out to z ∼ 0.2. The makeup of the merging population does not appear to change over this redshift range. Galaxy growth by major mergers appears comparatively unimportant and dry mergers are unlikely to be significant in the buildup of the red sequence over the past 2 Gyr. We compare the colour, morphology, environmental density and degree of activity (BPT class, Baldwin, Phillips & Terlevich) of galaxies in pairs to those of more isolated objects in the same volume. Galaxies in close pairs tend to be both redder and slightly more spheroid dominated than the comparison sample. We suggest that this may be due to ‘harassment’ in multiple previous passes prior to the current close interaction. Galaxy pairs do not appear to prefer significantly denser environments. There is no evidence of an enhancement in the AGN fraction in pairs, compared to other galaxies in the same volume

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg$^2$ of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the LCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. Adding the new data to planck temperature data tightens the limits on damping tail parameters, for example reducing the joint uncertainty on the number of neutrino species and the primordial helium fraction by 20%.Comment: 23 pages, 25 figure

Variability of protein level and phosphorylation status caused by biopsy protocol design in human skeletal muscle analyses

<p>Abstract</p> <p>Background</p> <p>Bergström needle biopsy is widely used to sample skeletal muscle in order to study cell signaling directly in human tissue. Consequences of the biopsy protocol design on muscle protein quantity and quality remain unclear. The aim of the present study was to assess the impact of different events surrounding biopsy protocol on the stability of the Western blot signal of eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), Akt, glycogen synthase kinase-3β (GSK-3β), muscle RING finger protein 1 (MuRF1) and p70 S6 kinase (p70 S6K). Six healthy subjects underwent four biopsies of the <it>vastus lateralis</it>, distributed into two distinct visits spaced by 48 hrs. At visit 1, a basal biopsy in the right leg was performed in the morning (R1) followed by a second in the left leg in the afternoon (AF). At visit 2, a second basal biopsy (R2) was collected from the right leg. Low intensity mobilization (3 × 20 right leg extensions) was performed and a final biopsy (Mob) was collected using the same incision site as R2.</p> <p>Results</p> <p>Akt and p70 S6K phosphorylation levels were increased by 83% when AF biopsy was compared to R1. Mob condition induced important phosphorylation of p70 S6K when compared to R2. Comparison of R1 and R2 biopsies revealed a relative stability of the signal for both total and phosphorylated proteins.</p> <p>Conclusions</p> <p>This study highlights the importance to standardize muscle biopsy protocols in order to minimize the method-induced variation when analyzing Western blot signals.</p