http://bura.brunel.ac.uk/handle/2438/234 2013-05-23T22:30:06Z 2013-05-23T22:30:06Z Stolarski, T A http://bura.brunel.ac.uk/handle/2438/5642 2011-07-25T15:29:11Z 2011-01-01T00:00:00Z

Title: Running characteristics of aerodynamic bearing with self-lifting capability at low rotational speed Authors: Stolarski, T A Abstract: An aerodynamic journal bearing that is capable of self-generating squeeze-film pressure is presented and its dynamic characteristics investigated numerically and experimentally. A numerical method based on a time-marching static model was applied to assess the orbit trajectory path of the rotor upon a perturbation. Experimental results were obtained to validate the effect of the self-generated squeeze-film pressure on the stability of the rotor. Analyzing the Fast Fourier Transform (FFT) responses of the rotor orbits enabled identification of self-excited whirling instabilities. Both numerical and experimental results showed that increasing the squeeze-film effect of the bearing could raise the threshold speed of instability. Description: This article has been made available through the Brunel Open Access Publishing Fund - Copyright @ 2011 Tadeusz Adam Stolarski.

2011-01-01T00:00:00Z Akemann, G Bender, M http://bura.brunel.ac.uk/handle/2438/4263 2013-05-13T11:43:00Z 2010-01-01T00:00:00Z

Title: Interpolation between Airy and Poisson statistics for unitary chiral non-Hermitian random matrix ensembles Authors: Akemann, G; Bender, M Abstract: We consider a family of chiral non-Hermitian Gaussian random matrices in the unitarily invariant symmetry class. The eigenvalue distribution in this model is expressed in terms of Laguerre polynomials in the complex plane. These are orthogonal with respect to a non-Gaussian weight including a modified Bessel function of the second kind, and we give an elementary proof for this. In the large n limit, the eigenvalue statistics at the spectral edge close to the real axis are described by the same family of kernels interpolating between Airy and Poisson that was recently found by one of the authors for the elliptic Ginibre ensemble. We conclude that this scaling limit is universal, appearing for two different non-Hermitian random matrix ensembles with unitary symmetry. As a second result we give an equivalent form for the interpolating Airy kernel in terms of a single real integral, similar to representations for the asymptotic kernel in the bulk and at the hard edge of the spectrum. This makes its structure as a one-parameter deformation of the Airy kernel more transparent.

2010-01-01T00:00:00Z Kujawski, B Holyst, JA Rodgers, GJ http://bura.brunel.ac.uk/handle/2438/4256 2012-02-03T14:20:29Z 2007-01-01T00:00:00Z

Title: Growing Trees in Internet News Groups and Forums Authors: Kujawski, B; Holyst, JA; Rodgers, GJ Abstract: We present an empirical study of the networks created by users within internet news groups and forums and show that they organ- ise themselves into scale-free trees. The structure of these trees depends on the topic under discussion; specialist topics have trees with a short shallow structure whereas more universal topics are discussed widely and have a deeper tree structure. For news groups we find that the distribu- tion of the time intervals between when a message is posted and when it receives a response exhibits a composite power-law behaviour. From our statistics we can see if the news group or forum is free or is overseen by a moderator. The correlation function of activity, the number of messages posted in a given time, shows long range correlations connected with the users’ daily routines. The distribution of distances between each message and its root is exponential for most news groups and power-law for the fo- rums. For both formats we find that the relation between the supremacy ( the total number of nodes that are under the node i, including node i) and the degree is linear s(k) k, in contrast to the analytical relation for Barab´asi-Albert network.

2007-01-01T00:00:00Z Akemann, G Phillips, M J Sommers, H-J http://bura.brunel.ac.uk/handle/2438/3954 2009-12-09T16:18:32Z 2009-01-01T00:00:00Z

Title: The chiral Gaussian two-matrix ensemble of real asymmetric matrices Authors: Akemann, G; Phillips, M J; Sommers, H-J Abstract: We solve a family of Gaussian two-matrix models with rectangular Nx(N+nu) matrices,having real asymmetric matrix elements and depending on a non-Hermiticity parameter mu. Our model can be thought of asxthe chiral extension of the real Ginibre ensemble, relevant for Dirac operators in the same symmetry class. It has the property that its eigenvalues are either real, purely imaginary, or come in complex conjugate eigenvalue pairs. The eigenvalue joint probability distribution for our model is explicitly computed, leading to a non-Gaussian distribution including K-Bessel functions. All n-point density correlation functions are expressed for finite N in terms of a Pfaffian form. This contains a kernel involving Laguerre polynomials in the complex plane as a building block which was previously computed by the authors. This kernel can be expressed in terms of the kernel for complex non-Hermitian matrices, generalising the known relation among ensembles of Hermitian random matrices. Compact expressions are given for the density at finite N as an example, as well as its microscopic large-N limits at the origin for fixed nu at strong and weak non-Hermiticity.

2009-01-01T00:00:00Z