Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Asteroseismology of red giants: photometric observations of Arcturus by SMEI

We present new results on oscillations of the K1.5 III giant Arcturus (alpha Boo), from analysis of just over 2.5 yr of precise photometric observations made by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. A strong mode of oscillation is uncovered by the analysis, having frequency 3.51+/-0.03 micro-Hertz. By fitting its mode peak, we are able offer a highly constrained direct estimate of the damping time (tau = 24+/-1 days). The data also hint at the possible presence of several radial-mode overtones, and maybe some non-radial modes. We are also able to measure the properties of the granulation on the star, with the characteristic timescale for the granulation estimated to be 0.50+/-0.05 days.Comment: 6 pages, 5 figures; accepted for publication in MNRAS Letter

Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Phase 2 of the Multiple Provider Employment Zones Qualitative Study, DWP Research Report 399

This report presents the findings of a qualitative study of the operation and impact of the Multiple Provider Employment Zone (MPEZ) initiatives that have operated in four cities (London, Birmingham, Liverpool and Glasgow) since 20041. The study builds on earlier work by Cambridge Policy Consultants (Hirst et al. 2006), which concentrated on issues related to the early establishment of the MPEZ initiative and the initial experiences of Providers, Jobcentre Plus districts and customers. The Phase 2 research took place approximately one year on from the Phase 1 study and focused on tracking developments in the operation of MPEZ as the initiative became more established. The study involved interviews with EZ Providers (managers and Advisers), Jobcentre Plus representatives (managers and Advisers) and customers (young people (aged 18-24) claiming Jobseeker’s Allowance (JSA), who would otherwise have returned to New Deal for Young People (NDYP)2, lone parents receiving Income Support and early entrants – see section 1.6 for full details). In order to gain a wider perspective, researchers also spoke to representatives of organisations that have employed MPEZ participants and a number of stakeholder organisations with a broad interest in local labour market policies and programmes in the MPEZ areas. In total, the research involved interviews or group discussions with over 300 individuals, providing a range and depth of qualitative information that allows a detailed picture to be established of the way that MPEZs developed between mid- 2005 and mid-2006, including the experiences of employers and the labour market destinations of MPEZ participants. A central issue addressed in the research and in this report is the ‘multiple’ element of the initiative and the value that is added through the existence of more than one Provider in each MPEZ area. Questions of allocation, choice, specialisation, competition and innovation are considered from the perspectives of Providers, Jobcentre Plus, customers, employers and stakeholders and the final sections present some conclusions and issues for consideration in relation to these topics

Non-abelian dynamics in first-order cosmological phase transitions

Bubble collisions in cosmological phase transitions are explored, taking the non-abelian character of the gauge fields into account. Both the QCD and electroweak phase transitions are considered. Numerical solutions of the field equations in several limits are presented.Comment: 8 pages, 2 figures. Contribution to the CosPA 2003 Cosmology and Particle Astrophysics Symposium. Typos correcte

Role of Charged Gauge Fields in Generating Magnetic Seed Fields in Bubble Collisions during the Cosmological Electroweak Phase Transition

We calculate the magnetic field generated during bubble collisions in a first-order electroweak phase transition that may occur for some choices of parameters in the minimal supersymmetric Standard Model. We show that for sufficiently gentle collisions, where the Higgs field is relatively unperturbed in the bubble overlap region, the equations of motion can be linearized so that in the absence of fermions the charged W fields are the source of the electromagnetic current for generating the seed fields. Solutions of the equations of motion for the charged gauge fields and Maxwell's equations for the magnetic field in O(1,2) space-time symmetry are expressed in closed form by applying boundary conditions at the time of collision. Our results indicate that the magnetic fields generated by charged $W^{\pm}$ fields in the collision are comparable to those found in previous work. The magnetic fields so produced could seed galactic and extra-galactic magnetic fields observed today.Comment: 15 Pages, 7 Figure

Knowledge Representation for Web Navigation

Representations of domain knowledge range from those that are ontologically formal, semantically rich to those that are ontologically informal and semantically weak. Representations of knowledge are important in many tasks, one of which is the support of travel around information spaces through the identification and linking of concepts in a field. In this paper we explore how representations of ontologically informal, semantically weak domain knowledge as captured by the Simple Knowledge Organisation System (SKOS) can enable a system to take advantage of the large number of existing ontological representations to support semantic linking of Web based information and thus facilitate information travel

Document Navigation: Ontology or Knowledge Organization System?

Bioinformatics relies heavily on web resources for information gathering. Ontologies are being developed to fill the background knowledge needed to drive Semantic Web applications. This paper discusses how formal ontologies are not always suited for document navigation on the web. Converting ontologies into a model with looser semantics, allows cheap and rapid generation of useful knowledge systems. The message is that ontologies are not the only knowledge artefact needed; vocabularies and other classification schemes with weaker semantics have their role and are the best solution in certain circumstances

Oscillations in β Ursae Minoris

Aims. From observations of the K4III star β UMi we attempt to determine whether oscillations or any other form of variability is present. Methods. A high-quality photometric time series of ≈1000 days in length obtained from the SMEI instrument on the Coriolis satellite is analysed. Various statistical tests were performed to determine the significance of features seen in the power density spectrum of the light curve. Results. Two oscillations with frequencies 2.44 and 2.92 μHz have been identified. We interpret these oscillations as consecutive overtones of an acoustic spectrum, implying a large frequency spacing of 0.48 μHz. Using derived asteroseismic parameters in combination with known astrophysical parameters, we estimate the mass of β UMi to be 1.3 ± 0.3 M. Peaks of the oscillations in the power density spectrum show width, implying that modes are stochastically excited and damped by convection. The mode lifetime is estimated at 18 ± 9 days