High-energy neutrino fluxes from AGN populations inferred from X-ray surveys

High-energy neutrinos and photons are complementary messengers, probing violent astrophysical processes and structural evolution of the Universe. X-ray and neutrino observations jointly constrain conditions in active galactic nuclei (AGN) jets: their baryonic and leptonic contents, and particle production efficiency. Testing two standard neutrino production models for local source Cen A \citep{KT2008,BB2009}, we calculate the high-energy neutrino spectra of single AGN sources and derive the flux of high-energy neutrinos expected for the current epoch. Assuming that accretion determines both X-rays and particle creation, our parametric scaling relations predict neutrino yield in various AGN classes. We derive redshift-dependent number densities of each class, from {\it Chandra} and {\it Swift}/BAT X-ray luminosity functions \citep{SGB2008,ACS2009}. We integrate the neutrino spectrum expected from the cumulative history of AGN (correcting for cosmological and source effects, e.g. jet orientation and beaming). Both emission scenarios yield neutrino fluxes well above limits set by {\it IceCube} (by $\sim 4$--$10^6 \times$ at 1 PeV, depending on the assumed jet models for neutrino production). This implies that: (i) Cen A might not be a typical neutrino source as commonly assumed; (ii) both neutrino production models overestimate the efficiency; (iii) neutrino luminosity scales with accretion power differently among AGN classes and hence does not follow X-ray luminosity universally; (iv) some AGN are neutrino-quiet (e.g. below a power threshold for neutrino production); (v) neutrino and X-ray emission have different duty cycles (e.g. jets alternate between baryonic and leptonic flows); or (vi) some combination of the above.Comment: 16 pages, 6 figures, 3 tables, accepted for publication in MNRA

Should forest regeneration studies have more replications?

When it comes to testing for differences in seedling survival, researchers sometimes make a Type II statistical error (i.e. failure to reject a false null hypothesis) due to the inherent variability associated with survival in tree planting studies. For example, in one trial (with five replications) first-year survival of seedlings planted in October (42%) was not significantly different (alpha = 0.05) from those planted in December (69%). Did planting in a dry October truly have no effect on survival? Authors who make a Type II error might not be aware that as seedling survival decreases (down to an overall average of 50% survival), statistical power declines. As a result, the ability to declare an 8% difference as “significant†is very difficult when survival averages 90% or less.  We estimate that about half of regeneration trials (average survival of pines <90%) cannot declare a 12% difference as statistically significant (alpha = 0.05).  When researchers realize their tree planting trials have low statistical power, they should consider using more replications.  Other ways to increase power include: (1) use a one-tailed test (2) use a potentially more powerful contrast test (instead of an overall treatment F-test) and (3) conduct survival trials under a roof

Gauge covariance and the fermion-photon vertex in three- and four- dimensional, massless quantum electrodynamics

In the quenched approximation, the gauge covariance properties of three vertex Ans\"{a}tze in the Schwinger-Dyson equation for the fermion self energy are analysed in three- and four- dimensional quantum electrodynamics. Based on the Cornwall-Jackiw-Tomboulis effective action, it is inferred that the spectral representation used for the vertex in the gauge technique cannot support dynamical chiral symmetry breaking. A criterion for establishing whether a given Ansatz can confer gauge covariance upon the Schwinger-Dyson equation is presented and the Curtis and Pennington Ansatz is shown to satisfy this constraint. We obtain an analytic solution of the Schwinger-Dyson equation for quenched, massless three-dimensional quantum electrodynamics for arbitrary values of the gauge parameter in the absence of dynamical chiral symmetry breaking.Comment: 17 pages, PHY-7143-TH-93, REVTE

Visual tracking of a GPS target within a FieldLab

The monitoring and videoing of a user’s movement within a “FieldLab” recreational facility is required to study the effectiveness of innovative equipment designed to increase physical activity. A low cost alternative to current tracking systems based around the Global positioning system (GPS) was trialed for use within the Sheffield FieldLab. This low cost tracking system is based around a typical AndroidTM smartphone, which was used as a wearable tracking sensor. The system was combined with a bespoke video surveillance system, which takes positional data and outputs appropriate camera parameters. In pilot work, participants’ GPS positional data was converted in real time to a pan tilt and zoom value. This allowed the targeted participant to be viewed in the centre of the video stream. Positional data was updated every second, allowing the camera to move and track the participant by keeping them at the centre of the video frame as they moved around the site. The effectiveness of the system was gauged and limitations noted. It was found that the Sony Xperia-S gave the most accurate GPS positional data, out of the three smartphones tested in this study. Other potential uses as well as enhancements to the system have also been commented on

Increased Uniformity by Planting Clones Will Likely Have a Minimal Effect on Inventory Costs

When conducting inventories, reducing variability among tree diameters, heights, and ultimately volumes or biomass, can reduce the number of points/plots needed to obtain a desired level of precision. We present a simple analysis examining the potential reduction in discounted inventory costs when stand variability is decreased (via improved genetics and intensive management on a uniform soil). Sampling time might be reduced if the coefficient of variation in point volume/biomass estimates is reduced to 10% (versus 25% for genetically diverse stands). However, if this level of variability could be achieved (and depending on the desired probability and allowable percent error) discounted costs might be only reduced by $0.50 per acre for a single inventory (when a 15$20 to $30 per acre. On some very uniform sites, stands with low variability may only need one inventory plot per 25 acres. Although clones (in theory) might reduce variability, microsite conditions within a plantation will always produce variability among plots/points

National Preferences in Business and Communication Education: A Survey Update

This article discusses the results of a survey in the U.S. regarding national preferences in business and communication education. From the results of this and the previous study, it appears that the skills most valued in the contemporary job-entry market are communication skills. The skills of listening, oral communication (both interpersonal and public), written communication and the trait of enthusiasm are indicated to be the most important. Again, it would appear to follow that university officials wishing to be of the greatest help to their graduates in finding employment would make sure that basic competencies in oral and written communication are developed. Courses in listening, interpersonal, and public communication would form the basis of meeting the oral communication competencies. One way to meet the written communication expectation would be to include courses in rhetorical and business writing. Further, training in interviewing skills would be in order to help university graduates maximize their appearance and personality projection as well as gather information necessary for appropriate decision making