Now showing items 1-20 of 90

  • 3D PiC code investigations of Auroral Kilometric Radiation mechanisms 

    Gillespie, K. M.; McConville, S. L.; Speirs, D. C.; Ronald, K.; Phelps, A. D. R.; Bingham, R.; Cross, A. W.; Robertson, C. W.; Whyte, C. G.; He, W.; Vorgul, I.; Cairns, R. A.; Kellett, B. J. (IOP PUBLISHING LTD, 2014) - Conference item
    Efficient (similar to 1%) electron cyclotron radio emissions are known to originate in the X mode from regions of locally depleted plasma in the Earths polar magnetosphere. These emissions are commonly referred to as the ...
  • Assouad type dimensions and homogeneity of fractals 

    Fraser, Jonathan M. (2014-12) - Journal article
    We investigate several aspects of the Assouad dimension and the lower dimension, which together form a natural 'dimension pair'. In particular, we compute these dimensions for certain classes of self-affine sets and ...
  • Attractors of directed graph IFSs that are not standard IFS attractors and their Hausdorff measure 

    Boore, Graeme; Falconer, Kenneth John (2013) - Journal article
    For directed graph iterated function systems (IFSs) defined on R, we prove that a class of 2-vertex directed graph IFSs have attractors that cannot be the attractors of standard (1-vertex directed graph) IFSs, with or ...
  • Automatic presentations and semigroup constructions 

    Cain, Alan J.; Oliver, Graham; Ruskuc, Nik; Thomas, Richard M. (2010-08) - Journal article
    An automatic presentation for a relational structure is, informally, an abstract representation of the elements of that structure by means of a regular language such that the relations can all be recognized by finite ...
  • Automatic presentations for semigroups 

    Cain, Alan James; Oliver, Graham; Ruskuc, Nik; Thomas, Richard M. (2009-11) - Journal article
    This paper applies the concept of FA-presentable structures to semigroups. We give a complete classification of the finitely generated FA-presentable cancellative semigroups: namely, a finitely generated cancellative ...
  • Backward wave cyclotron-maser emission in the auroral magnetosphere 

    Speirs, D. C.; Bingham, R.; Cairns, R. A.; Vorgul, I.; Kellett, B. J.; Phelps, A. D. R.; Ronald, K. (2014-10-07) - Journal article
    In this Letter, we present theory and particle-in-cell simulations describing cyclotron radio emission from Earth's auroral region and similar phenomena in other astrophysical environments. In particular, we find that the ...
  • The Bergman property for semigroups 

    Maltcev, V.; Mitchell, J. D.; Ruskuc, N. (2009-08) - Journal article
    In this article, we study the Bergman property for semigroups and the associated notions of cofinality and strong cofinality. A large part of the paper is devoted to determining when the Bergman property, and the values ...
  • Beyond sum-free sets in the natural numbers 

    Huczynska, Sophie (2014-02-07) - Journal article
    For an interval [1,N]⊆N, sets S⊆[1,N] with the property that |{(x,y)∈S2:x+y∈S}|=0, known as sum-free sets, have attracted considerable attention. In this paper, we generalize this notion by considering r(S)=|{(x,y)∈S2:x+y∈S}|, ...
  • Cancellative and Malcev presentations for finite Rees index subsemigroups and extensions 

    Cain, Alan James; Robertson, Edmund Frederick; Ruskuc, Nik (2008-02) - Journal article
    It is known that, for semigroups, the property of admitting a finite presentation is preserved on passing to subsemigroups and extensions of finite Rees index. The present paper shows that the same holds true for Malcev, ...
  • Catastrophe versus instability for the eruption of a toroidal solar magnetic flux rope 

    Kliem, B.; Lin, J.; Forbes, T. G.; Priest, E. R.; Toeroek, T. (2014-07-01) - Journal article
    The onset of a solar eruption is formulated here as either a magnetic catastrophe or as an instability. Both start with the same equation of force balance governing the underlying equilibria. Using a toroidal flux rope in ...
  • Codimension formulae for the intersection of fractal subsets of Cantor spaces 

    Donoven, Casey; Falconer, Kenneth John (2016-02) - Journal article
    We examine the dimensions of the intersection of a subset E of an m-ary Cantor space Cm with the image of a subset F under a random isometry with respect to a natural metric. We obtain almost sure upper bounds for the ...
  • Computing in matrix groups without memory 

    Cameron, Peter Jephson; Fairbairn, Ben; Gadouleau, Maximilien (2014-11-02) - Journal article
    Memoryless computation is a novel means of computing any function of a set of registers by updating one register at a time while using no memory. We aim to emulate how computations are performed on modern cores, since they ...
  • Computing in permutation groups without memory 

    Cameron, Peter Jephson; Fairbairn, Ben; Gadouleau, Maximilien (2014-11-02) - Journal article
    Memoryless computation is a new technique to compute any function of a set of registers by updating one register at a time while using no memory. Its aim is to emulate how computations are performed in modern cores, since ...
  • Constructing flag-transitive, point-imprimitive designs 

    Cameron, Peter Jephson; Praeger, Cheryl E. (2016-05-04) - Journal article
    We give a construction of a family of designs with a specified point-partition and determine the subgroup of automorphisms leaving invariant the point-partition. We give necessary and sufficient conditions for a design in ...
  • Coprime invariable generation and minimal-exponent groups 

    Detomi, Eloisa; Lucchini, Andrea; Roney-Dougal, C.M. (2015-08) - Journal article
    A finite group G is coprimely invariably generated if there exists a set of generators {g1,. .,gu} of G with the property that the orders |g1|,. .,|gu| are pairwise coprime and that for all x1,. .,xu∈G the set {g1x1,. ...
  • Copulae on products of compact Riemannian manifolds 

    Jupp, P.E. (2015-09) - Journal article
    Abstract One standard way of considering a probability distribution on the unit n -cube, [0 , 1]n , due to Sklar (1959), is to decompose it into its marginal distributions and a copula, i.e. a probability distribution on ...
  • Digit frequencies and Bernoulli convolutions 

    Kempton, Thomas Michael William (2014-06-27) - Journal article
    It is well known that when β is a Pisot number, the corresponding Bernoulli convolution ν(β) has Hausdorff dimension less than 1, i.e. that there exists a set A(β) with (ν(β))(A(β))=1 and dim_H(A(β))<1. We show explicitly ...
  • Dimension and measure for generic continuous images 

    Balka, Richard; Farkas, Abel; Fraser, Jonathan M.; Hyde, James T. (2013) - Journal article
    We consider the Banach space consisting of continuous functions from an arbitrary uncountable compact metric space, X, into R-n. The key question is 'what is the generic dimension of f(X)?' and we consider two different ...
  • Effect of collisions on amplification of laser beams by Brillouin scattering in plasmas 

    Humphrey, K. A.; Trines, R. M. G. M.; Fiuza, F.; Speirs, D. C.; Norreys, P.; Cairns, R. A.; Silva, L. O.; Bingham, R. (2013-10) - Journal article
    We report on particle in cell simulations of energy transfer between a laser pump beam and a counter-propagating seed beam using the Brillouin scattering process in uniform plasma including collisions. The results presented ...
  • The effect of slip length on vortex rebound from a rigid boundary 

    Sutherland, D.; Macaskill, C.; Dritschel, D.G. (2013-09-23) - Journal article
    The problem of a dipole incident normally on a rigid boundary, for moderate to large Reynolds numbers, has recently been treated numerically using a volume penalisation method by Nguyen van yen, Farge, and Schneider [Phys. ...