Vortex corrections to universal scaling of magnetic fluctuations in 2D XY model

The vortex contribution to the probability density function of longitudinal magnetization fluctuations is examined in finite 2D XY systems close to the Kosterlitz-Thouless-Berezinskii transition temperature. Within the temperature range studied their relevance is limited to rare fluctuations, where they increase the probability of events exceeding four standard deviations below the mean magnetization.Comment: 6 pages, 4 figures. Refs adde

Generalised Longitudinal Susceptibility for Magnetic Monopoles in Spin Ice

The generalised longitudinal susceptibility $\chi({\bf q}, \omega)$ affords a sensitive measure of the spatial and temporal correlations of magnetic monopoles in spin ice. Starting with the monopole model, a mean field expression for $\chi({\bf q}, \omega)$ is derived as well as expressions for the mean square longitudinal field and induction at a point. Monopole motion is shown to be strongly correlated, and both spatial and temporal correlations are controlled by the dimensionless monopole density $x$ which defines the ratio of the magnetization relaxation rate and the monopole hop rate. Thermal effects and spin lattice relaxation are also considered. The derived equations are applicable in the temperature range where the Wien effect for magnetic monopoles is negligible. They are discussed in the context of existing theories of spin ice and the following experimental techniques: dc and ac-magnetization, neutron scattering, neutron spin echo, and longitudinal and transverse field $\mu$SR. The monopole theory is found to unify diverse experimental results, but several discrepancies between theory and experiment are identified. One of these, concerning the neutron scattering line shape, is explained by means of a phenomenological modification to the theory.Comment: 29 pages, 4 figures; to be published in Phil. Trans A, special issue for Royal Society Theo Murphy Meeting on Magnetic Monopoles in Spin Ice (Nov. 2011, UK). Second version, significantly revised after helpful referee comments. Many typos correcte

Mapping metaphors of wealth and want: a digital approach

The AHRC-funded Mapping Metaphor with the Historical Thesaurus project aims to provide data on the extent and development of metaphor across the history of English. It uses the full database of the Historical Thesaurus of English, which extensively categorises and classifies the recorded vocabulary of the English language from Old English to the present day. By using this database to map semantic categories onto one another, and thus showing lexical overlap in different conceptual fields, we aim in the project to provide results which will demonstrate the widespread, systematic and far-reaching impact of metaphor on English.<p></p> This paper outlines the digital and linguistic methodologies used by the project, and presents a case study of the semantic categories of wealth and poverty, demonstrating the metaphorical links between these categories and the rest of the language. In addition, we discuss the nature of lexical overlap as we use it in the project, and discuss both the quantitative and diachronic dimensions of the data we are manipulating and their implications for projects of this type.<p></p&gt

Power fluctuations in stochastic models of dissipative systems

We consider different models of stochastic dissipative equations and theoretically compute the probability distribution functions (actually the associated large deviation functions) of the time averaged injected power required to sustain a nontrivial stationary state. We discuss the results and in particular draw from our results some general features shared by these distributions in realistic dissipative systems

Football goal distributions and extremal statistics

We analyse the distributions of the number of goals scored by home teams, away teams, and the total scored in the match, in domestic football games from 169 countries between 1999 and 2001. The probability density functions (PDFs) of goals scored are too heavy-tailed to be fitted over their entire ranges by Poisson or negative binomial distributions which would be expected for uncorrelated processes. Log-normal distributions cannot include zero scores and here we find that the PDFs are consistent with those arising from extremal statistics. In addition, we show that it is sufficient to model English top division and FA Cup matches in the seasons of 1970/71–2000/01 on Poisson or negative binomial distributions, as reported in analyses of earlier seasons, and that these are not consistent with extremal statistics

Mapping Metaphor with the Historical Thesaurus: a new resource for investigating metaphor in names

The AHRC-funded ‘Mapping Metaphor with the Historical Thesaurus’ project has traced the development of metaphor in English from Anglo-Saxon times to the present day using the unique evidence base of the Historical Thesaurus of the Oxford English Dictionary. The Historical Thesaurus organises the contents of the OED semantically, making it possible to see how vocabulary for any given concept has developed over time. One of the major outputs of the Mapping Metaphor project is the online Metaphor Map, which can be used to investigate metaphor in names and is freely available at: http://mappingmetaphor.arts.gla.ac.uk/

Universal Fluctuations of AEX index

We compute the analytic expression of the probability distributions F{AEX,+} and F{AEX,-} of the normalized positive and negative AEX (Netherlands) index daily returns r(t). Furthermore, we define the \alpha re-scaled AEX daily index positive returns r(t)^\alpha and negative returns (-r(t))^\alpha that we call, after normalization, the \alpha positive fluctuations and \alpha negative fluctuations. We use the Kolmogorov-Smirnov statistical test, as a method, to find the values of \alpha that optimize the data collapse of the histogram of the \alpha fluctuations with the Bramwell-Holdsworth-Pinton (BHP) probability density function. The optimal parameters that we found are \alpha+=0.46 and \alpha-=0.43. Since the BHP probability density function appears in several other dissimilar phenomena, our results reveal universality in the stock exchange markets.Comment: 16 pages, 12 figure

Non-Gaussian Resistance Noise near Electrical Breakdown in Granular Materials

The distribution of resistance fluctuations of conducting thin films with granular structure near electrical breakdown is studied by numerical simulations. The film is modeled as a resistor network in a steady state determined by the competition between two biased processes, breaking and recovery. Systems of different sizes and with different levels of internal disorder are considered. Sharp deviations from a Gaussian distribution are found near breakdown and the effect increases with the degree of internal disorder. However, we show that in general this non-Gaussianity is related to the finite size of the system and vanishes in the large size limit. Nevertheless, near the critical point of the conductor-insulator transition, deviations from Gaussianity persist when the size is increased and the distribution of resistance fluctuations is well fitted by the universal Bramwell-Holdsworth-Pinton distribution.Comment: 8 pages, 6 figures; accepted for publication on Physica