Alternating steady state in one-dimensional flocking

We study flocking in one dimension, introducing a lattice model in which particles can move either left or right. We find that the model exhibits a continuous nonequilibrium phase transition from a condensed phase, in which a single `flock' contains a finite fraction of the particles, to a homogeneous phase; we study the transition using numerical finite-size scaling. Surprisingly, in the condensed phase the steady state is alternating, with the mean direction of motion of particles reversing stochastically on a timescale proportional to the logarithm of the system size. We present a simple argument to explain this logarithmic dependence. We argue that the reversals are essential to the survival of the condensate. Thus, the discrete directional symmetry is not spontaneously broken.Comment: 8 pages LaTeX2e, 5 figures. Uses epsfig and IOP style. Submitted to J. Phys. A (Math. Gen.

Post-injection normal closure of fractures as a mechanism for induced seismicity

Understanding the controlling mechanisms underlying injection-induced seismicity is important for optimizing reservoir productivity and addressing seismicity-related concerns related to hydraulic stimulation in Enhanced Geothermal Systems. Hydraulic stimulation enhances permeability through elevated pressures, which cause normal deformations, and the shear slip of pre-existing fractures. Previous experiments indicate that fracture deformation in the normal direction reverses as the pressure decreases, e.g., at the end of stimulation. We hypothesize that this normal closure of fractures enhances pressure propagation away from the injection region and significantly increases the potential for post-injection seismicity. To test this hypothesis, hydraulic stimulation is modeled by numerically coupling fracture deformation, pressure diffusion and stress alterations for a synthetic geothermal reservoir in which the flow and mechanics are strongly affected by a complex three-dimensional fracture network. The role of the normal closure of fractures is verified by comparing simulations conducted with and without the normal closure effect

Condensation Transitions in a One-Dimensional Zero-Range Process with a Single Defect Site

Condensation occurs in nonequilibrium steady states when a finite fraction of particles in the system occupies a single lattice site. We study condensation transitions in a one-dimensional zero-range process with a single defect site. The system is analysed in the grand canonical and canonical ensembles and the two are contrasted. Two distinct condensation mechanisms are found in the grand canonical ensemble. Discrepancies between the infinite and large but finite systems' particle current versus particle density diagrams are investigated and an explanation for how the finite current goes above a maximum value predicted for infinite systems is found in the canonical ensemble.Comment: 18 pages, 4 figures, revtex

Spontaneous Jamming in One-Dimensional Systems

We study the phenomenon of jamming in driven diffusive systems. We introduce a simple microscopic model in which jamming of a conserved driven species is mediated by the presence of a non-conserved quantity, causing an effective long range interaction of the driven species. We study the model analytically and numerically, providing strong evidence that jamming occurs; however, this proceeds via a strict phase transition (with spontaneous symmetry breaking) only in a prescribed limit. Outside this limit, the nearby transition (characterised by an essential singularity) induces sharp crossovers and transient coarsening phenomena. We discuss the relevance of the model to two physical situations: the clustering of buses, and the clogging of a suspension forced along a pipe.Comment: 8 pages, 4 figures, uses epsfig. Submitted to Europhysics Letter

Spray drag effect of fluidized sand for a supersonic vehicle

This paper deals with fluidized sand simulation in order to estimate the impact of sand particle motion on the BLOODHOUND SuperSonic Car (SSC) drag forces, such phenomenon is known as a spray drag effect. A gas-particle model is used to simulate the sand particles that rise from the ground because of the strong shockwave-desert surface interaction. A finite volume scheme is used to discretise the continuous model with a special treatment of the solid phase equations. An indefinitely differentiable and anisotropic limiter to reinforce the method stability and reduce any excessive smearing is applied. To estimate the area where sand particles are detached from the ground, a criterion based on pressure change is proposed. The model is first validated on a curved 90 bend test case with comparison to experimental results and then applied to the supersonic car

Enhanced Ductility of PEEK thin film with self-assembled fibre-like crystals

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Poly Ether Ether Ketone (PEEK) is a high temperature polymer material known for its excellent chemical resistance, high strength and toughness. As a semi-crystalline polymer, PEEK can become very brittle during long crystallisation times and temperatures helped as well by its high content of rigid benzene rings within its chemical structure. This paper presents a simple quench crystallization method for preparation of PEEK thin films with the formation of a novel fibre-like crystal structure on the surface of the films. These quenched crystallised films show higher elongation at break when compared with conventional melt crystallised thin films incorporating spherulitic crystals, while the tensile strength of both types of films (quenched crystallised and conventional melt) remained the same. The fracture analysis carried out using microscopy revealed an interesting microstructure which evolves as a function of annealing time. Based on these results, a crystal growth mechanism describing the development of the fibre-like crystals on the surface of the quenched crystallised films is proposed.This work is supported by the UK Engineering and Physical Science Research Council (EPSRC Grant No EP/L017318/1-Particle Shape and Flow behaviour in Laser Sintering: from modelling to experimental validation)

A Primary Study into Graphene/Polyether Ether Ketone (PEEK) Nanocomposite for Laser Sintering

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.This paper proposes two methods of preparation of graphene/PEEK powders for Laser Sintering (LS) and investigates their behaviour in relation to their microstructure, the powder bed process and their properties. Thin composite films were fabricated in an attempt to replicate the thin layer formation of the powder bed process. Both methods of composite powder preparation (wet and dry) led to enhanced mechanical performance of the composite films at 0.1 and 0.5% graphene nano-platelets (GNP) concentrations. The TEM images show that the GNP act as a nucleation point in crystallisation of PEEK, being at the centre of the spherulites. The hot stage microscopy revealed a 20 second delay in the onset of GNP/PEEK nanocomposite coalescence in comparison with plain PEEK. This is a very important observation for laser sintering, as it will influence the build strategy and specific parameters (e.g. time between layers deposition, multiple exposures). The excellent electrical conductivity properties of graphene were noticeable in the nanocomposite films at concentrations above 1 wt% GNP.The authors would like to thank the UK Engineering and Physical Science Research Council for its funding (EPSRC grant no EP/L017318/1-Particle Shape and Flow behaviour in Laser Sintering: from modelling to experimental validation), 2D-Tech for providing the graphene and John Benson for his help with the Raman evaluation

Qualitative evidence syntheses : assessing the relative contributions of multi‐context and single‐context reviews

Aims To examine the strengths and weaknesses of multi‐context (international) qualitative evidence syntheses in comparison with single‐context (typically single‐country) reviews. We compare a multi‐country synthesis with single‐context syntheses on facility‐based delivery in Nigeria and Kenya. Design Discussion Paper. Background Qualitative evidence increasingly contributes to decision‐making. International organisations commission multi‐context reviews of qualitative evidence to gain a comprehensive picture of similarities and differences across comparable (e.g. low‐ and middle‐income) countries. Such syntheses privilege breadth over contextual detail, risking inappropriate interpretation and application of review findings. Decision‐makers value single‐context syntheses that account for the contexts of their populations and health services. We explore how findings from multi‐ and single‐context syntheses contribute against a conceptual framework (adequacy, coherence, methodological limitations and relevance) that underpins the GRADE Confidence in Evidence of Reviews of Qualitative Evidence approach. Data sources Included studies and findings from a multi‐context qualitative evidence synthesis (2001‐2013) and two single‐context syntheses (Nigeria, 2006‐2017; and Kenya, 2002‐2016; subsequently, updated and revised). Findings Single‐context reviews contribute cultural, ethnic and religious nuances as well as specific health system factors (e.g. use of a voucher system). Multi‐context reviews contribute to universal health concerns and to generic health system concerns (e.g. access and availability). Implications for nursing: Nurse decision‐makers require relevant, timely and context‐sensitive evidence to inform clinical and managerial decision‐making. This discussion paper informs future commissioning and use of multi‐ and single‐context qualitative evidence syntheses. Conclusion Multi‐ and single‐context syntheses fulfil complementary functions. Single‐context syntheses add nuances not identifiable within the remit and timescales of a multi‐context review

Hybrid Variation for Yield, Crude Protein, Feed Value and Percent Lysine of Corn Grown in the 1991 Kentucky Hybrid Corn Performance Test

These data are the results from the second year of protein analyses of corn hybrids grown at three locations in the Kentucky Hybrid Corn Performance Test. These analyses were supported. by a grant from the Kentucky Corn Growers Association

Crude Protein, and other Chemical Constituents of Corn Hybrids Evaluated in the 1994 Kentucky Hybrid Corn Performance Tests

Grain samples have been collected each year since 1990 from three locations of the Kentucky Hybrid Corn Performance Test and analyzed for crude protein (CP). The objective was to provide an unbiased comparative evaluation of the CP concentration of com hybrids sold in Kentucky. The results indicate that while management and environment at each test location may have significant influences, CP does differ among hybrid genotypes. The feeding value of specific hybrid genotypes based on their protein concentration may have significant influence in diet formulation for non-ruminant animals due to the amount of supplement needed to properly balance the diet, and may be an important economic factor in animal production. Previous summaries of annual results have been published (I, 2, 3). CP data for hybrids tested in 1994 plus multiple year means derived from data collected in three previous years are included in this report. Annual data are averaged over locations