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Search Results: 1 - 10 of 422749 matches for " D. W. C. Johnston "
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A renormalized expression for the turbulent energy dissipation rate
C. Johnston,W. D. McComb
Physics , 2000, DOI: 10.1103/PhysRevE.63.015304
Abstract: Conditional elimination of degrees of freedom is shown to lead to an exact expression for the rate of turbulent energy dissipation in terms of a renormalized viscosity and a correction. The correction is neglected on the basis of a previous hypothesis [W.D. McComb and C. Johnston, J.Phys.A v33 L15 (2000)] that there is a range of parameters for which a quasi-stochastic estimate is a good approximation to the exact conditional average. This hypothesis was tested by a perturbative calculation to second order in the local Reynolds number, and the Kolmogorov prefactor (taken as a measure of the renormalized dissipation rate) was found to reach a fixed point which was insensitive to initial values of the kinematic viscosity and to values of the spatial rescaling factor h in the range 0.4 <= h <= 0.8.
Barriers and facilitators to an outreach rehabilitation program delivered in nursing homes after hip fracture surgical repair  [PDF]
Donna M. Wilson, Sandra L. Robertson, C. Allyson Jones, D. W. C. Johnston, Lauren A. Beaupre
Advances in Aging Research (AAR) , 2013, DOI: 10.4236/aar.2013.21006

Objective: To identify and understand facilitators and barriers to implementing an Outreach rehabilitation program designed to improve post-operative recovery following hip fracture in long-term care residents. Residents of nursing home facilities are at considerable risk of hip fracture and minimal recovery following a hip fracture. Methods: Data were gathered over June-August, 2012 through semi-structured interviews or focus groups. Fifteen persons (n = 15) who were members of the Outreach rehabilitation team (n = 8) or relevant nursing home staff (n = 7) were interviewed. Data analysis was guided by principles of grounded theory method. Findings: Three major themes that contributed to or hindered the Outreach rehabilitation program emerged, namely, 1) the division, the separate operation and delivery of rehabilitation services; 2) building bridges, or negotiating ways to communicate and work together, and 3) strength in the structure, the acceptance of the program and the perceived benefits of the program. One main challenge to program implementation con- cerned coordinating additional rehabilitation with the rehabilitation provided within the nursing homes. Facility staff was largely unaware of the program and were unprepared to work with Outreach team members. As the program progressed, the facility staff and Outreach team were able to collaborate to overcome resident health issues impeding recovery such as cognitive impairment, language barriers and post-surgical pain control needs. Facilitators included the consistency of Outreach team members and accessible facility staff, which contributed to effective communication and trust between the Outreach team and facility staff. Facilitators also included support for the program by the Outreach team and facility staff, as well

Scaling in Steiner Random Surfaces
C. F. Baillie,A. Irback,W. Janke,D. A. Johnston
Physics , 1993, DOI: 10.1016/0370-2693(94)90069-8
Abstract: It has been suggested that the modified Steiner action functional has desirable properties for a random surface action. In this paper we investigate the scaling of the string tension and massgap in a variant of this action on dynamically triangulated random surfaces and compare the results with the gaussian plus extrinsic curvature actions that have been used previously.
Softening Transitions with Quenched 2D Gravity
C. F. Baillie,W. Janke,D. A. Johnston
Physics , 1996, DOI: 10.1016/S0920-5632(96)00767-0
Abstract: We perform extensive Monte Carlo simulations of the 10-state Potts model on quenched two-dimensional $\Phi^3$ gravity graphs to study the effect of quenched connectivity disorder on the phase transition, which is strongly first order on regular lattices. The numerical data provides strong evidence that, due to the quenched randomness, the discontinuous first-order phase transition of the pure model is softened to a continuous transition.
Spin Glasses on Thin Graphs
C. F. Baillie,W. Janke,D. A. Johnston,P. Plechac
Physics , 1995, DOI: 10.1016/0550-3213(95)00328-P
Abstract: In a recent paper we found strong evidence from simulations that the Isingantiferromagnet on ``thin'' random graphs - Feynman diagrams - displayed amean-field spin glass transition. The intrinsic interest of considering such random graphs is that they give mean field results without long range interactions or the drawbacks, arising from boundary problems, of the Bethe lattice. In this paper we reprise the saddle point calculations for the Ising and Potts ferromagnet, antiferromagnet and spin glass on Feynman diagrams. We use standard results from bifurcation theory that enable us to treat an arbitrary number of replicas and any quenched bond distribution. We note the agreement between the ferromagnetic and spin glass transition temperatures thus calculated and those derived by analogy with the Bethe lattice, or in previous replica calculations. We then investigate numerically spin glasses with a plus or minus J bond distribution for the Ising and Q=3,4,10,50 state Potts models, paying particular attention to the independence of the spin glass transition from the fraction of positive and negative bonds in the Ising case and the qualitative form of the overlap distribution in all the models. The parallels with infinite range spin glass models in both the analytical calculations and simulations are pointed out.
Dgsos on DTRS
C. F. Baillie,W. Janke,D. A. Johnston
Physics , 1993, DOI: 10.1016/0370-2693(93)91535-U
Abstract: We perform simulations of a discrete gaussian solid on solid (DGSOS) model on dynamical $\phi^3$ graphs, which is equivalent to coupling the model to 2d quantum gravity, using the cluster algorithms recently developed by Evertz et.al.for use on fixed lattices. We find evidence from the growth of the width-squared in the rough phase of KT-like behaviour, which is consistent with theoretical expectations. We also investigate the cluster statistics, dynamical critical exponent and lattice properties, and compare these with the dual XY model.
Magnetic and thermal properties of the S = 1/2 zig-zag spin-chain compound In2VO5
Yogesh Singh,R. W. McCallum,D. C. Johnston
Physics , 2007, DOI: 10.1103/PhysRevB.76.174402
Abstract: Static magnetic susceptibility \chi, ac susceptibility \chi_{ac} and specific heat C versus temperature T measurements on polycrystalline samples of In2VO5 and \chi and C versus T measurements on the isostructural, nonmagnetic compound In2TiO5 are reported. A Curie-Wiess fit to the \chi(T) data above 175 K for In2VO5 indicates ferromagnetic exchange between V^{4+} (S = 1/2) moments. Below 150 K the \chi(T) data deviate from the Curie-Weiss behavior but there is no signature of any long range magnetic order down to 1.8 K. There is a cusp at 2.8 K in the zero field cooled (ZFC) \chi(T) data measured in a magnetic field of 100 Oe and the ZFC and field cooled (FC) data show a bifurcation below this temperature. The frequency dependence of the \chi_{ac}(T) data indicate that below 3 K the system is in a spin-glass state. The difference \Delta C between the heat capacity of In2VO5 and In2TiO5 shows a broad anomaly peaked at 130 K. The entropy upto 300 K is more than what is expected for S = 1/2 moments. The anomaly in \Delta C and the extra entropy suggests that there may be a structural change below 130 K in In2VO5.
Softening of First-Order Phase Transition on Quenched Random Gravity Graphs
C. F. Baillie,W. Janke,D. A. Johnston
Physics , 1996, DOI: 10.1016/0370-2693(96)01144-6
Abstract: We perform extensive Monte Carlo simulations of the 10-state Potts model on quenched two-dimensional $\Phi^3$ gravity graphs to study the effect of quenched coordination number randomness on the nature of the phase transition, which is strongly first order on regular lattices. The numerical data provides strong evidence that, due to the quenched randomness, the discontinuous first-order phase transition of the pure model is softened to a continuous transition, representing presumably a new universality class. This result is in striking contrast to a recent Monte Carlo study of the 8-state Potts model on two-dimensional Poissonian random lattices of Voronoi/Delaunay type, where the phase transition clearly stayed of first order, but is in qualitative agreement with results for quenched bond randomness on regular lattices. A precedent for such softening with connectivity disorder is known: in the 10-state Potts model on annealed Phi3 gravity graphs a continuous transition is also observed.
Thin Absolute Villains
C. F. Baillie,N. Dorey,W. Janke,D. A. Johnston
Physics , 1995, DOI: 10.1016/0370-2693(95)01526-4
Abstract: We perform simulations of an absolute value version of the Villain model on phi3 and phi4 Feynman diagrams, ``thin'' 3-regular and 4-regular random graphs. The phi4 results are in excellent quantitative agreement with the exact calculations by Dorey and Kurzepa for an annealed ensemble of thin graphs, in spite of simulating only a single graph of each size. We also derive exact results for an annealed ensemble of phi3 graphs and again find excellent agreement with the numerical data for single phi3 graphs. The simulations confirm the picture of a mean field vortex transition which is suggested by the analytical results. Further simulations on phi5 and phi6 graphs and of the standard XY model on phi3 graphs confirm the universality of these results. The calculations of Dorey and Kurzepa were based on reinterpreting the large orders behaviour of the anharmonic oscillator in a statistical mechanical context so we also discuss briefly the interpretation of singularities in the large orders behaviour in other models as phase transitions.
The Information Geometry of the Ising Model on Planar Random Graphs
W. Janke,D. A. Johnston,Ranasinghe P. K. C. Malmini
Physics , 2002, DOI: 10.1103/PhysRevE.66.056119
Abstract: It has been suggested that an information geometric view of statistical mechanics in which a metric is introduced onto the space of parameters provides an interesting alternative characterisation of the phase structure, particularly in the case where there are two such parameters -- such as the Ising model with inverse temperature $\beta$ and external field $h$. In various two parameter calculable models the scalar curvature ${\cal R}$ of the information metric has been found to diverge at the phase transition point $\beta_c$ and a plausible scaling relation postulated: ${\cal R} \sim |\beta- \beta_c|^{\alpha - 2}$. For spin models the necessity of calculating in non-zero field has limited analytic consideration to 1D, mean-field and Bethe lattice Ising models. In this letter we use the solution in field of the Ising model on an ensemble of planar random graphs (where $\alpha=-1, \beta=1/2, \gamma=2$) to evaluate the scaling behaviour of the scalar curvature, and find ${\cal R} \sim | \beta- \beta_c |^{-2}$. The apparent discrepancy is traced back to the effect of a negative $\alpha$.
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