6,083 research outputs found
Cooling nonlinear lattices toward localisation
We describe the energy relaxation process produced by surface damping on
lattices of classical anharmonic oscillators. Spontaneous emergence of
localised vibrations dramatically slows down dissipation and gives rise to
quasi-stationary states where energy is trapped in the form of a gas of weakly
interacting discrete breathers. In one dimension (1D), strong enough on--site
coupling may yield stretched--exponential relaxation which is reminiscent of
glassy dynamics. We illustrate the mechanism generating localised structures
and discuss the crucial role of the boundary conditions. For two--dimensional
(2D) lattices, the existence of a gap in the breather spectrum causes the
localisation process to become activated. A statistical analysis of the
resulting quasi-stationary state through the distribution of breathers'
energies yield information on their effective interactions.Comment: 10 pages, 11 figure
Slow energy relaxation and localization in 1D lattices
We investigate the energy relaxation process produced by thermal baths at
zero temperature acting on the boundary atoms of chains of classical anharmonic
oscillators. Time-dependent perturbation theory allows us to obtain an explicit
solution of the harmonic problem: even in such a simple system nontrivial
features emerge from the interplay of the different decay rates of Fourier
modes. In particular, a crossover from an exponential to an inverse-square-root
law occurs on a time scale proportional to the system size . A further
crossover back to an exponential law is observed only at much longer times (of
the order ). In the nonlinear chain, the relaxation process is initially
equivalent to the harmonic case over a wide time span, as illustrated by
simulations of the Fermi-Pasta-Ulam model. The distinctive feature is
that the second crossover is not observed due to the spontaneous appearance of
breathers, i.e. space-localized time-periodic solutions, that keep a finite
residual energy in the lattice. We discuss the mechanism yielding such
solutions and also explain why it crucially depends on the boundary conditions.Comment: 16 pages, 6 figure
Discrete Breathers in a Realistic Coarse-Grained Model of Proteins
We report the results of molecular dynamics simulations of an off-lattice
protein model featuring a physical force-field and amino-acid sequence. We show
that localized modes of nonlinear origin (discrete breathers) emerge naturally
as continuations of a subset of high-frequency normal modes residing at
specific sites dictated by the native fold. In the case of the small
-barrel structure that we consider, localization occurs on the turns
connecting the strands. At high energies, discrete breathers stabilize the
structure by concentrating energy on few sites, while their collapse marks the
onset of large-amplitude fluctuations of the protein. Furthermore, we show how
breathers develop as energy-accumulating centres following perturbations even
at distant locations, thus mediating efficient and irreversible energy
transfers. Remarkably, due to the presence of angular potentials, the breather
induces a local static distortion of the native fold. Altogether, the
combination of this two nonlinear effects may provide a ready means for
remotely controlling local conformational changes in proteins.Comment: Submitted to Physical Biolog
Multifunctions determined by integrable functions
Integral properties of multifunctions determined by vector valued functions are presented. Such multifunctions quite often serve as examples and counterexamples. In particular it can be observed that the properties of being integrable in the sense of Bochner, McShane or Birkhoff can be transferred to the generated multifunction while Henstock integrability does not guarantee i
Apparatus for time‐resolved measurements of acoustic birefringence in particle dispersions
An apparatus for time‐resolved measurements of the birefringence induced in a particle suspension by an acoustic wave pulse is described. Efficient acoustic coupling is obtained by operating near the transducer resonant frequency and by matching the acoustic impedances of the cell constituents. An almost‐overdamped acoustic configuration can alternatively be employed whenever a faster response is needed. Careful design of the optical setup and of the detection unit minimize diffraction and stress‐birefringence parasitic effects and yields a good responsivity at fairly low acoustic intensities. A test of the apparatus on a colloidal suspension of PTFE rodlike particles is presented and discussed
Energy transfer in nonlinear network models of proteins
We investigate how nonlinearity and topological disorder affect the energy
relaxation of local kicks in coarse-grained network models of proteins. We find
that nonlinearity promotes long-range, coherent transfer of substantial energy
to specific, functional sites, while depressing transfer to generic locations.
Remarkably, transfer can be mediated by the self-localization of discrete
breathers at distant locations from the kick, acting as efficient
energy-accumulating centers.Comment: 4 pages, 3 figure
Calibration of a photomultiplier array spectrometer
A systematic approach to the calibration of a photomultiplier array spectrometer is presented. Through this approach, incident light radiance derivation is made by recognizing and tracing gain characteristics for each photomultiplier tube
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Jeremy Corbyn according to the BBC: ideological representation and identity construction of the Labour Party leader
There have been many complaints that the BBC coverage of the rise of Jeremy Corbyn has been partial and biased. This paper is part of an interdisciplinary project on the television representation of Jeremy Corbyn that brings together scholars in the disciplines of linguistics (critical discourse analysis), journalism and politics. The paper is a small scale case study examining the coverage of Jeremy Corbyn’s speech on the 28th September 2016 after he won the leadership by election for the second time in a year. In the first stage we compared the scripting of the reports for the main national UK TV news programmes and the representation of the Labour leader’s identity offered to viewers. In the second, we also evaluate Newsnight, a BBC programme coverage of a slightly different genre, which constructed Corbyn as a particular kind of leader. In addition to the verbal text of the reports, we considered the interplay between the presenter and political correspondent and their tone. This enabled us to broaden our critical discourse analysis to a multimodal investigation and tease out non-textual, nuanced ways of creating partiality. We concluded that some BBC coverage does demonstrate bias and partiality against Corbyn in subtle modes where tone alters the meaning of the script and visuals and the BBC fared badly compared to other mainstream TV news
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