Hyperon bulk viscosity in the presence of antikaon condensate

We investigate the hyperon bulk viscosity due to the non-leptonic process $n + p \rightleftharpoons p + \Lambda$ in $K^-$ condensed matter and its effect on the r-mode instability in neutron stars. We find that the hyperon bulk viscosity coefficient in the presence of antikaon condensate is suppressed compared with the case without the condensate. The suppressed hyperon bulk viscosity in the superconducting phase is still an efficient mechanism to damp the r-mode instability in neutron stars.Comment: AASTeX; 21 pages including 5 figures; change in the title and replaced by the revised versio

Dynamical Origin of Extrasolar Planet Eccentricity Distribution

We explore the possibility that the observed eccentricity distribution of extrasolar planets arose through planet-planet interactions, after the initial stage of planet formation was complete. Our results are based on ~3250 numerical integrations of ensembles of randomly constructed planetary systems, each lasting 100 Myr. We find that for a remarkably wide range of initial conditions the eccentricity distributions of dynamically active planetary systems relax towards a common final equilibrium distribution, well described by the fitting formula dn ~ e exp[-1/2 (e/0.3)^2] de. This distribution agrees well with the observed eccentricity distribution for e > 0.2, but predicts too few planets at lower eccentricities, even when we exclude planets subject to tidal circularization. These findings suggest that a period of large-scale dynamical instability has occurred in a significant fraction of newly formed planetary systems, lasting 1--2 orders of magnitude longer than the ~1 Myr interval in which gas-giant planets are assembled. This mechanism predicts no (or weak) correlations between semimajor axis, eccentricity, inclination, and mass in dynamically relaxed planetary systems. An additional observational consequence of dynamical relaxation is a significant population of planets (>10%) that are highly inclined (>25deg) with respect to the initial symmetry plane of the protoplanetary disk; this population may be detectable in transiting planets through the Rossiter-McLaughlin effect.Comment: Accepted to ApJ, conclusions updated to reflect the current observational constraint

First excited state calculation using different phonon bases for the two-site Holstein model

The single-electron energy and static charge-lattice deformation correlations have been calculated for the first excited state of a two-site Holstein model within perturbative expansions using different standard phonon bases obtained through Lang-Firsov (LF) transformation, LF with squeezed phonon states, modified LF, modified LF transformation with squeezed phonon states, and also within weak-coupling perturbation approach. Comparisons of the convergence of the perturbative expansions for different phonon bases reveal that modified LF approach works much better than other approaches for major range of the coupling strength.Comment: 11 pages (REVTEX), 4 postscript figure

Solution of a Cauchy singular fractional integro-differential equation in Bernstein polynomial basis

This article proposes a simple method to obtain approximate numerical solution of a singular fractional order integro-differential equation with Cauchy kernel by using Bernstein polynomials as basis. The fractional derivative is described in Caputo sense. The properties of Bernstein polynomials are used to reduce the fractional order integro-differential equation to the solution of algebraic equations. The numerical results obtained by the present method compares favorably with those obtained earlier for the first order integro-differential equation. Also the convergence of the method is established rigorously

Effect of hyperon-hyperon interaction on bulk viscosity and r-mode instability in neutron stars

We investigate the effect of hyperon matter including hyperon-hyperon interaction on bulk viscosity. Equations of state are constructed within the framework of a relativistic field theoretical model where baryon-baryon interaction is mediated by the exchange of scalar and vector mesons. Hyperon-hyperon interaction is also taken into account by the exchange of two strange mesons. This interaction results in a smaller maximum mass neutron star compared with the case without the interaction. The coefficient of bulk viscosity due to the non-leptonic weak process is determined by these equations of state. The interacting hyperon matter reduces the bulk viscosity coefficient in a neutron star interior compared with the no interaction case. The r-mode instability is more effectively suppressed in hyperon-hyperon interaction case than that without the interaction.Comment: 25 pages, 10 figures; two new figures added and results and discussion section revised; final version to appear in PR

Collaboration in museums and health research

This study reflects on the range of collaborations in two distinct but thematically linked UCL research projects which consider the role of culture in health promotion: Museums on Prescription (2014–2017), in partnership with Canterbury Christ Church University, explores the value of heritage encounters in social prescribing for lonely older adults at risk of social isolation; and Not So Grim Up North (2016–2018), in conjunction with Whitworth Art Gallery, University of Manchester and Tyne & Wear Archives & Museums, investigates the health and wellbeing impacts of museum activities for stroke survivors; older adults with dementia; and mental health and addiction recovery service-users. Both projects employ a mixed-methods approach using quantitative and qualitative data. The research projects have been developed and delivered through collaborations between interdisciplinary university researchers, museum practitioners, health and social care professionals and end-users. Collaboration has taken different forms including co-developing evaluation methods, co-disseminating outputs, and through advisory boards. This study reflects on the opportunities and challenges of collaboration, noting the language and practice dissonance across different fields and the importance of finding common ground. It also highlights the considerable amount of time that is required to build genuine collaborative relationships, which is not often acknowledged in research outputs

Nondestructive Evaluation of Flaw Criticality in Graphite-Epoxy Laminates

An analytical and experimental study is conducted to determine criticality of interlaminar disbands by NDE methods. Criticality of such flaws in a shear environment (action of shear near support) is defined in terms of crack propagation and is analyzed by principles and methods of fracture mechanics. Growth of disbands under cyclic loading is also being studied. Fajlure under compressive loading in presence of a disband is defined in terms of buckling and an elastic stability analysis is utilized for assessing criticality. Analytical predictions are compared with experimental results in both cases