Ab initio R-matrix calculations of e+-molecule scattering

The adaptation of the molecular R-matrix method, originally developed for electron-molecule collision studies, to positron scattering is discussed. Ab initio R-matrix calculations are presented for collisions of low energy positrons with a number of diatomic systems including H2, HF and N2. Differential elastic cross sections for positron-H2 show a minimum at about 45 deg for collision energies between 0.3 and 0.5 Ryd. The calculations predict a bound state of positronHF. Calculations on inelastic processes in N2 and O2 are also discussed

Talk in activity during young children’s use of digital technologies at home

This article establishes ways that family members engage and disengage in talk so as to manage their individual activity with mobile devices and accomplish interaction with each other.AbstractInternet-connected tablets and smart phones are being used increasingly by young children. Little is known, however, about their social interactions with family members when engaged with these technologies. This article examines video-recorded interactions between a father and his two young children, one aged 18 months using an iPhone and one aged three years accessing an iPad. Drawing on Ethnomethodology and Conversation Analysis, analysis establishes ways the family members engage and disengage in talk so as to manage their individual activity with mobile devices and accomplish interaction with each other. Findings are relevant for understanding children’s everyday practices with mobile technologies.Authored by Susan Danby, Christina Davidson, Maryanne Theobald, Brooke Scriven, Charlotte Cobb-Moore, Sandra Houen, Sandra Grant, Lisa M. Given, and Karen Thorpe

How terrestrial planets traverse spin-orbit resonances: A camel goes through a needle's eye

The dynamical evolution of terrestrial planets resembling Mercury in the vicinity of spin-orbit resonances is investigated using comprehensive harmonic expansions of the tidal torque taking into account the frequency-dependent quality factors and Love numbers. The torque equations are integrated numerically with a small step in time, includng the oscillating triaxial torque components but neglecting the layered structure of the planet and assuming a zero obliquity. We find that a Mercury-like planet with its current value of orbital eccentricity (0.2056) is always captured in the 3:2 resonance. The probability of capture in the higher 2:1 resonance is approximately 0.23. These results are confirmed by a semi-analytical estimation of capture probabilities as functions of eccentricity for both prograde and retrograde evolution of spin rate. As follows from analysis of equilibrium torques, entrapment in the 3:2 resonance is inevitable at eccentricities between 0.2 and 0.41. Considering the phase space parameters at the times of periastron, the range of spin rates and phase angles, for which an immediate resonance passage is triggered, is very narrow, and yet, a planet like Mercury rarely fails to align itself into this state of unstable equilibrium before it traverses the 2:1 resonance.Comment: 10 figures. Fig. 8 may be corrupted when printed on some printers but shows fine in the PDF file. Submitted in ApJ v. 2: the probabilities of capture of Mercury in 2:1 resonance are re-evaluated; a general formula for capture probability derived. v3: accepted in ApJ under a different title: Conditions of passage and entrapment of terrestrial planets in spin-orbit resonance

Resonance Behavior and Partial Averaging in a Three-Body System with Gravitational Radiation Damping

In a previous investigation, a model of three-body motion was developed which included the effects of gravitational radiation reaction. The aim was to describe the motion of a relativistic binary pulsar that is perturbed by a third mass and look for resonances between the binary and third mass orbits. Numerical integration of an equation of relative motion that approximates the binary gives evidence of such resonances. These $(m:n)$ resonances are defined for the present purposes by the resonance condition, $m\omega=2n\Omega$, where $m$ and $n$ are relatively prime integers and $\omega$ and $\Omega$ are the angular frequencies of the binary orbit and third mass orbit, respectively. The resonance condition consequently fixes a value for the semimajor axis $a$ of the binary orbit for the duration of the resonance because of the Kepler relationship $\omega=a^{-3/2}$. This paper outlines a method of averaging developed by Chicone, Mashhoon, and Retzloff which renders a nonlinear system that undergoes resonance capture into a mathematically amenable form. This method is applied to the present system and one arrives at an analytical solution that describes the average motion during resonance. Furthermore, prominent features of the full nonlinear system, such as the frequency of oscillation and antidamping, accord with their analytically derived formulae.Comment: 19 pages, 4 Postscript figure

Limelight: Cardiff Contemporary & Llangattock Lime Kiln

Limelight (2016-20) aims to establish terms through which limestone as a geological material with industrial application, presents and holds agency. It aims to determine how exposures of limestone’s material agency are intrinsic to understanding the representations and experiences of its landscapes. It considers this in relation to the transforming phases of industrial limestone landscapes in the UK. Limelight (Cardiff Contemporary & Llangattock Lime Kiln) was one of ten commissioned exhibitions for Cardiff Contemporary, a biennial of contemporary art. It was funded by PEAK and Cardiff Contemporary, and developed and delivered in partnership with the BBC and Arts Alive Wales through a Digital Innovation Fund For Arts In Wales and NESTA grant. A limelight illumination, at a restored lime kiln at Llangattock in the Black Mountains Welsh National Park, using an apparatus developed by the artists, was broadcast by the BBC through the internet and into an exhibition space in Cardiff. The duration of the limelight illumination at Llangattock was contingent to the material behaviour of quicklime as it was heated to temperatures in excess of 2000ºc emitting a bright white light. The limelight illumination in Llangattock provided a real-time base for a performance event in Cardiff. The two artists live-mixed pre-recorded video and sound from extraction and industrial infrastructure limestone sites in the Black Mountains, and two performers projected and moved these images around the space and through the audience through rehearsed choreography. A film work of the live event was presented for the remainder of the exhibition

Education Bill: Committee Stage Report. Research paper 11/37

"This is an account of the House of Commons Committee Stage of the Education Bill. It complements Research Paper 11/14, prepared for the Commons Second Reading debate... The Bill, as amended in Public Bill Committee, was published as Bill 180.

Dust Grain Orbital Behavior Around Ceres

Many asteroids show indications they have undergone impacts with meteoroid particles having radii between 0.01 m and 1 m. During such impacts, small dust grains will be ejected at the impact site. The possibility of these dust grains (with radii greater than 2.2x10-6 m) forming a halo around a spherical asteroid (such as Ceres) is investigated using standard numerical integration techniques. The orbital elements, positions, and velocities are determined for particles with varying radii taking into account both the influence of gravity, radiation pressure, and the interplanetary magnetic field (for charged particles). Under the influence of these forces it is found that dust grains (under the appropriate conditions) can be injected into orbits with lifetimes in excess of one year. The lifetime of the orbits is shown to be highly dependent on the location of the ejection point as well as the angle between the surface normal and the ejection path. It is also shown that only particles ejected within 10 degrees relative to the surface tangential survive more than a few hours and that the longest-lived particles originate along a line perpendicular to the Ceres-Sun line.Comment: 8 pages, Presented at COSPAR '0