Open Access Repositories: Recent submissions

Now showing items 861-880 of 4204

  • Large-scale stability and astronomical constraints for coupled dark-energy models 

    Yang, W; Pan, S; Barrow, John David (American Physical SocietyPhysical Review D, 2018-02-26)
    The physics of the dark energy and the dark matter is still an open issue in cosmology. The dark energy occupies about 68.5% of the total energy density of the universe today [1], and is believed to accelerate its observed ...

  • APIC: A method for automated pattern identification and classification 

    Goss, Ryan Gavin (University of Cape TownFaculty of ScienceDepartment of Computer Science, 2017)
    Machine Learning (ML) is a transformative technology at the forefront of many modern research endeavours. The technology is generating a tremendous amount of attention from researchers and practitioners, providing new ...

  • Improving Pan-African research and education networks through traffic engineering: A LISP/SDN approach 

    Chavula, Josiah (University of Cape TownFaculty of ScienceFaculty Science: ICTC4D, 2017)
    The UbuntuNet Alliance, a consortium of National Research and Education Networks (NRENs) runs an exclusive data network for education and research in east and southern Africa. Despite a high degree of route redundancy in ...

  • Enhancing digital heritage archives using gamified annotations 

    Maina, Job King'ori (University of Cape TownFaculty of ScienceDepartment of Computer Science, 2017)
    In the context of digital heritage archives, we find heritage objects having intrinsic contextual and historical information. Capturing all that information is difficult, especially if that effort is left only to the ...

  • Privacy and Security Risks for National Health Records Systems 

    Unknown author (2018-01-24)
    A review of national health records (NEHR) systems shows that privacy and security risks have a profound impact on the success of such projects. Countries have different approaches when dealing with privacy and security ...

  • Testing linear marginal stability in stratified shear layers 

    Howland, Christopher; Taylor, John Ryan; Caulfield, Colm-cille Patrick
    We use two-dimensional direct numerical simulations of Boussinesq stratified shear layers to investigate the influence of the minimum gradient Richardson number Rim on the early time evolution of Kelvin–Helmholtz instability ...

  • On nonrelativistic 3D spin-1 theories 

    Townsend, Paul Kingsley; Bergshoeff, Eric A; Rosseel, Jan
    We describe non-relativistic limits of the 3D Proca and $\sqrt{\rm Proca}$ theories that yield spin-1 Schroedinger equations. Analogous results are found by generalized null reduction of the 4D Maxwell or complex self-dual ...

  • Horizontal locomotion of a vertically flapping oblate spheroid 

    Deng, J; Caulfield, Colm-cille Patrick (Cambridge University PressJournal of Fluid Mechanics, 2018-04-10)
    We consider the self-induced motions of three-dimensional oblate spheroids of density $\rho_s$ with varying aspect ratios $AR=b/c \leq 1$, where $b$ and $c$ are the spheroids' centre-pole radius and centre-equator radius ...

  • Seven lessons from manyfield inflation in random potentials 

    Dias, Mafalda; Frazer, Jonathan; Marsh, Carl Marc (IoPJOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 2018-01)
    We study inflation in models with many interacting fields subject to randomly generated scalar potentials. We use methods from non-equilibrium random matrix theory to construct the potentials and an adaption of the ‘transport ...

  • Connection between nonlinear energy optimization and instantons. 

    Lecoanet, Daniel; Kerswell, Richard Rodney (American Physical SocietyPhysical review. E, 2018-01)
    How systems transit between different stable states under external perturbation is an important practical issue. We discuss here how a recently developed energy optimization method for identifying the minimal disturbance ...

  • Interaction between the Blasius boundary layer and a free surface 

    Tsang, Jonathan; Dalziel, Stuart Bruce; Vriend, Nathalie Maria (Cambridge University PressJournal of Fluid Mechanics, 2018-03-25)
    We consider the steady, supercritical flow of a fluid layer. The layer is bounded above by a free surface and below by a rigid no-slip base. The base is in two parts: the downstream part of the base is stationary, while ...

  • New integrable models and analytical solutions in f(R) cosmology with an ideal gas 

    Papagiannopoulos, Giannis; Basilakos, Spyros; Barrow, John David; Paliathanasis, Andronikos (American Physical SocietyPhysical Review D - Particles, Fields, Gravitation and Cosmology, 2018-01-23)
    In the context of f(R)-gravity with a spatially flat FLRW metric containing an ideal fluid, we use the method of invariant transformations to specify families of models which are integrable. We find three families of f(R) ...

  • Twistor description of spinning particles in AdS 

    Arvanitakis, AS; Barns-Graham, AE; Townsend, Paul Kingsley (Springer NatureJournal of High Energy Physics, 2018-01-01)
    The two-twistor formulation of particle mechanics in D-dimensional anti-de Sitter space for D=4,5,7, which linearises invariance under the AdS isometry group Sp(4;K) for K=R,C,H,, is generalized to the massless N-extended ...

  • A possible failure of determinism in general relativity 

    Reall, Harvey Stephen (American Physical SocietyPhysics, 2018-01-17)
    Is the future predictable? If we know the initial state of a system exactly, then do the laws of physics determine its state arbitrarily far into the future? In Newtonian mechanics, the answer is yes. Similarly in ...

  • Generating Component-based Supervised Learning Programs From Crowdsourced Examples 

    Unknown author (2017-12-21)
    We present CrowdLearn, a new system that processes an existing corpus of crowdsourced machine learning programs to learn how to generate effective pipelines for solving supervised machine learning problems. CrowdLearn uses ...

  • A lower bound on the positive semidefinite rank of convex bodies 

    Fawzi, Hamza; Din, Mohab Safey El
    The positive semidefinite rank of a convex body $C$ is the size of its smallest positive semidefinite formulation. We show that the positive semidefinite rank of any convex body $C$ is at least $\sqrt{\log d}$ where $d$ is ...

  • Arctic Sea Ice Loss in Different Regions Leads to Contrasting Northern Hemisphere Impacts 

    McKenna, Christine; Bracegirdle, TJ; Shuckburgh, EF; Haynes, Peter Howard; Joshi, MM (Wiley-BlackwellGeophysical Research Letters, 2018-01-28)
    To explore the mechanisms linking Arctic sea-ice loss to changes in mid-latitude surface temperatures, we conduct idealized modeling experiments using an intermediate general circulation model and with sea-ice loss confined ...

  • A gluing operator for the ambitwistor string 

    Roehrig, KA; Skinner, David Benjamin
    We present a new operator in the ambitwistor string which glues together correlators with fewer points or of lower genus. It underpins the recursive construction of tree-level CHY scattering amplitudes by Dolan & Goddard, ...

  • Evolution of cyclic mixmaster universes with noncomoving radiation 

    Ganguly, C; Barrow, John David (American Physical SocietyPhysical Review D, 2017-12-15)
    We study a model of a cyclic, spatially homogeneous, anisotropic mixmaster universe of Bianchi type IX 'mixmaster' universe, containing the a radiation field with non-comoving ('tilted' with respect to the tetrad frame of ...

  • Evolution of cyclic mixmaster universes with noncomoving radiation 

    Barrow, John David; Ganguly, Chandrima
    We study a model of a cyclic, spatially homogeneous, anisotropic mixmaster universe of Bianchi type IX 'mixmaster' universe, containing the a radiation field with non-comoving ('tilted' with respect to the tetrad frame of ...