369 research outputs found
Intermittency and non-Gaussian fluctuations of the global energy transfer in fully developed turbulence
We address the experimentally observed non-Gaussian fluctuations for the
energy injected into a closed turbulent flow at fixed Reynolds number. We
propose that the power fluctuations mirror the internal kinetic energy
fluctuations. Using a stochastic cascade model, we construct the excess kinetic
energy as the sum over the energy transfers at different levels of the cascade.
We find an asymmetric distribution that strongly resembles the experimental
data. The asymmetry is an explicit consequence of intermittency and the global
measure is dominated by small scale events correlated over the entire system.
Our calculation is consistent with the statistical analogy recently made
between a confined turbulent flow and a critical system of finite size.Comment: To appear in Physical Review Letter
Canonical Generations and the British Left: The Narrative Construction of the Miners’ Strike 1984–85
‘Generations’ have been invoked to describe a variety of social and cultural relationships, and to understand the development of self-conscious group identity. Equally, the term can be an applied label and politically useful construct; generations can be retrospectively produced. Drawing on the concept of ‘canonical generations’ – those whose experiences come to epitomise an event of historic and symbolic importance – this article examines the narrative creation and functions of ‘generations’ as collective memory shapes and re-shapes the desire for social change. Building a case study of the canonical role of the miners’ strike of 1984–85 in the narrative history of the British left, it examines the selective appropriation and transmission of the past in the development of political consciousness. It foregrounds the autobiographical narratives of activists who, in examining and legitimising their own actions and prospects, (re)produce a ‘generation’ in order to create a relatable and useful historical understanding
Relevance of soft modes for order parameter fluctuations in the Two-Dimensional XY model
We analyse the spin wave approximation for the 2D-XY model, directly in
reciprocal space. In this limit the model is diagonal and the normal modes are
statistically independent. Despite this simplicity non-trivial critical
properties are observed and exploited. We confirm that the observed asymmetry
for the probability density function for order parameter fluctuations comes
from the divergence of the mode amplitudes across the Brillouin zone. We show
that the asymmetry is a many body effect despite the importance played by the
zone centre. The precise form of the function is dependent on the details of
the Gibbs measure, giving weight to the idea that an effective Gibbs measure
should exist in non-equilibrium systems, if a similar distribution is observed.Comment: 12 pages, 9 figure
Universal Fluctuations of the Danube Water Level: a Link with Turbulence, Criticality and Company Growth
A global quantity, regardless of its precise nature, will often fluctuate
according to a Gaussian limit distribution. However, in highly correlated
systems, other limit distributions are possible. We have previously calculated
one such distribution and have argued that this function should apply
specifically, and in many instances, to global quantities that define a steady
state. Here we demonstrate, for the first time, the relevance of this
prediction to natural phenomena. The river level fluctuations of the Danube are
observed to obey our prediction, which immediately establishes a generic
statistical connection between turbulence, criticality and company growth
statistics.Comment: 5 pages, 1 figur
Statistics of extremal intensities for Gaussian interfaces
The extremal Fourier intensities are studied for stationary
Edwards-Wilkinson-type, Gaussian, interfaces with power-law dispersion. We
calculate the probability distribution of the maximal intensity and find that,
generically, it does not coincide with the distribution of the integrated power
spectrum (i.e. roughness of the surface), nor does it obey any of the known
extreme statistics limit distributions. The Fisher-Tippett-Gumbel limit
distribution is, however, recovered in three cases: (i) in the non-dispersive
(white noise) limit, (ii) for high dimensions, and (iii) when only
short-wavelength modes are kept. In the last two cases the limit distribution
emerges in novel scenarios.Comment: 15 pages, including 7 ps figure
Universal Magnetic Fluctuations with a Field Induced Length Scale
We calculate the probability density function for the order parameter
fluctuations in the low temperature phase of the 2D-XY model of magnetism near
the line of critical points. A finite correlation length, \xi, is introduced
with a small magnetic field, h, and an accurate expression for \xi(h) is
developed by treating non-linear contributions to the field energy using a
Hartree approximation. We find analytically a series of universal non-Gaussian
distributions with a finite size scaling form and present a Gumbel-like
function that gives the PDF to an excellent approximation. We propose the
Gumbel exponent, a(h), as an indirect measure of the length scale of
correlations in a wide range of complex systems.Comment: 7 pages, 4 figures, 1 table. To appear in Phys. Rev.
Domain wall QCD with physical quark masses
We present results for several light hadronic quantities (, ,
, , , , ) obtained from simulations of 2+1
flavor domain wall lattice QCD with large physical volumes and nearly-physical
pion masses at two lattice spacings. We perform a short, O(3)%, extrapolation
in pion mass to the physical values by combining our new data in a simultaneous
chiral/continuum `global fit' with a number of other ensembles with heavier
pion masses. We use the physical values of , and to
determine the two quark masses and the scale - all other quantities are outputs
from our simulations. We obtain results with sub-percent statistical errors and
negligible chiral and finite-volume systematics for these light hadronic
quantities, including: = 130.2(9) MeV; = 155.5(8) MeV; the
average up/down quark mass and strange quark mass in the scheme
at 3 GeV, 2.997(49) and 81.64(1.17) MeV respectively; and the neutral kaon
mixing parameter, , in the RGI scheme, 0.750(15) and the
scheme at 3 GeV, 0.530(11).Comment: 131 pages, 30 figures. Updated to match published versio
Light Hadron Masses from Lattice QCD
This article reviews lattice QCD results for the light hadron spectrum. We
give an overview of different formulations of lattice QCD, with discussions on
the fermion doubling problem and improvement programs. We summarize recent
developments in algorithms and analysis techniques, that render calculations
with light, dynamical quarks feasible on present day computer resources.
Finally, we summarize spectrum results for ground state hadrons and resonances
using various actions.Comment: 53 pages, 24 figures, one table; Rev.Mod.Phys. (published version);
v2: corrected typ
Magnetic fluctuations in the classical XY model: the origin of an exponential tail in a complex system
We study the probability density function for the fluctuations of the
magnetic order parameter in the low temperature phase of the XY model of finite
size. In two-dimensions this system is critical over the whole of the low
temperature phase. It is shown analytically and without recourse to the scaling
hypothesis that, in this case, the distribution is non-Gaussian and of
universal form, independent of both system size and critical exponent .
An exact expression for the generating function of the distribution is
obtained, which is transformed and compared with numerical data from high
resolution molecular dynamics and Monte Carlo simulations. The calculation is
extended to general dimension and an exponential tail is found in all
dimensions less than four, despite the fact that critical fluctuations are
limited to D=2. These results are discussed in the light of similar behaviour
observed in models of interface growth and for dissipative systems driven into
a non-equilibrium steady state.Comment: 32 pages, 13 figures, 1 table. Few changes. To appear in Phys. Rev.
- …