957 research outputs found
The fitness of persons in the landscape: isolation, belonging and emergent subjects in rural Ireland
The concept of isolation has dogged anthropological studies of rural Ireland. This paper re‐conceptualises isolation through ethnographic work undertaken on the minibuses run by Rural Transport projects in five counties of Ireland. Instead of seeing isolation as an embedded characteristic of Irish landscapes, histories or of the ageing body, the paper describes dynamic, shifting expectations of belonging and community. On the Rural Transport buses, characteristic moments of witnessing ‘figures in the landscape’ during predictable and routinised journeys produce strikingly new negotiations of alterity and sameness among the passengers. The paper argues for the significance of these moments in developing a socialised, inscribed landscape and new senses of generative agency
Optimal Taylor-Couette flow: direct numerical simulations
We numerically simulate turbulent Taylor-Couette flow for independently
rotating inner and outer cylinders, focusing on the analogy with turbulent
Rayleigh-B\'enard flow. Reynolds numbers of and
of the inner and outer cylinders, respectively, are
reached, corresponding to Taylor numbers Ta up to . Effective scaling
laws for the torque and other system responses are found. Recent experiments
with the Twente turbulent Taylor-Couette () setup and with a similar
facility in Maryland at very high Reynolds numbers have revealed an optimum
transport at a certain non-zero rotation rate ratio
of about . For large enough in the numerically
accessible range we also find such an optimum transport at non-zero
counter-rotation. The position of this maximum is found to shift with the
driving, reaching a maximum of for . An
explanation for this shift is elucidated, consistent with the experimental
result that becomes approximately independent of the driving strength
for large enough Reynolds numbers. We furthermore numerically calculate the
angular velocity profiles and visualize the different flow structures for the
various regimes. By writing the equations in a frame co-rotating with the outer
cylinder a link is found between the local angular velocity profiles and the
global transport quantities.Comment: Under consideration for publication in JFM, 31 pages, 25 figure
Discrete breathers at the interface between a diatomic and monoatomic granular chain
In the present work, we develop a systematic examination of the existence,
stability and dynamical properties of a discrete breather at the interface
between a diatomic and a monoatomic granular chain. We remarkably find that
such an "interface breather" is more robust than its bulk diatomic counterpart
throughout the gap of the linear spectrum. The latter linear spectral gap needs
to exist for the breather state to arise and the relevant spectral conditions
are discussed. We illustrate the minimal excitation conditions under which such
an interface breather can be "nucleated" and analyze its apparently weak
interaction with regular highly nonlinear solitary waveforms.Comment: 11 pages, 10 figure
The Universal Gaussian in Soliton Tails
We show that in a large class of equations, solitons formed from generic
initial conditions do not have infinitely long exponential tails, but are
truncated by a region of Gaussian decay. This phenomenon makes it possible to
treat solitons as localized, individual objects. For the case of the KdV
equation, we show how the Gaussian decay emerges in the inverse scattering
formalism.Comment: 4 pages, 2 figures, revtex with eps
New solution of the Supersymmetric KdV equation via Hirota methods
We consider the resolution of the supersymmetric KdV equation
with () from the Hirota formalism. For the first time, a
bilinear form of the equation is constructed. We construct
multisoliton solutions and rational similarity solutions.Comment: 7 pages, 9 figures. arXiv admin note: significant text overlap with
arXiv:1104.059
Von Neumann Regular Cellular Automata
For any group and any set , a cellular automaton (CA) is a
transformation of the configuration space defined via a finite memory set
and a local function. Let be the monoid of all CA over .
In this paper, we investigate a generalisation of the inverse of a CA from the
semigroup-theoretic perspective. An element is von
Neumann regular (or simply regular) if there exists
such that and , where is the composition of functions. Such an
element is called a generalised inverse of . The monoid
itself is regular if all its elements are regular. We
establish that is regular if and only if
or , and we characterise all regular elements in
when and are both finite. Furthermore, we study
regular linear CA when is a vector space over a field ; in
particular, we show that every regular linear CA is invertible when is
torsion-free elementary amenable (e.g. when ) and , and that every linear CA is regular when
is finite-dimensional and is locally finite with for all .Comment: 10 pages. Theorem 5 corrected from previous versions, in A.
Dennunzio, E. Formenti, L. Manzoni, A.E. Porreca (Eds.): Cellular Automata
and Discrete Complex Systems, AUTOMATA 2017, LNCS 10248, pp. 44-55, Springer,
201
Radiation tolerance of nanocrystalline ceramics: insights from Yttria Stabilized Zirconia.
Materials for applications in hostile environments, such as nuclear reactors or radioactive waste immobilization, require extremely high resistance to radiation damage, such as resistance to amorphization or volume swelling. Nanocrystalline materials have been reported to present exceptionally high radiation-tolerance to amorphization. In principle, grain boundaries that are prevalent in nanomaterials could act as sinks for point-defects, enhancing defect recombination. In this paper we present evidence for this mechanism in nanograined Yttria Stabilized Zirconia (YSZ), associated with the observation that the concentration of defects after irradiation using heavy ions (Kr(+), 400 keV) is inversely proportional to the grain size. HAADF images suggest the short migration distances in nanograined YSZ allow radiation induced interstitials to reach the grain boundaries on the irradiation time scale, leaving behind only vacancy clusters distributed within the grain. Because of the relatively low temperature of the irradiations and the fact that interstitials diffuse thermally more slowly than vacancies, this result indicates that the interstitials must reach the boundaries directly in the collision cascade, consistent with previous simulation results. Concomitant radiation-induced grain growth was observed which, as a consequence of the non-uniform implantation, caused cracking of the nano-samples induced by local stresses at the irradiated/non-irradiated interfaces
Rapidly rotating plane layer convection with zonal flow
The onset of convection in a rapidly rotating layer in which a thermal wind
is present is studied. Diffusive effects are included. The main motivation is
from convection in planetary interiors, where thermal winds are expected due to
temperature variations on the core-mantle boundary. The system admits both
convective instability and baroclinic instability. We find a smooth transition
between the two types of modes, and investigate where the transition region
between the two types of instability occurs in parameter space. The thermal
wind helps to destabilise the convective modes. Baroclinic instability can
occur when the applied vertical temperature gradient is stable, and the
critical Rayleigh number is then negative. Long wavelength modes are the first
to become unstable. Asymptotic analysis is possible for the transition region
and also for long wavelength instabilities, and the results agree well with our
numerical solutions. We also investigate how the instabilities in this system
relate to the classical baroclinic instability in the Eady problem. We conclude
by noting that baroclinic instabilities in the Earth's core arising from
heterogeneity in the lower mantle could possibly drive a dynamo even if the
Earth's core were stably stratified and so not convecting.Comment: 20 pages, 7 figure
A pulsed atomic soliton laser
It is shown that simultaneously changing the scattering length of an
elongated, harmonically trapped Bose-Einstein condensate from positive to
negative and inverting the axial portion of the trap, so that it becomes
expulsive, results in a train of self-coherent solitonic pulses. Each pulse is
itself a non-dispersive attractive Bose-Einstein condensate that rapidly
self-cools. The axial trap functions as a waveguide. The solitons can be made
robustly stable with the right choice of trap geometry, number of atoms, and
interaction strength. Theoretical and numerical evidence suggests that such a
pulsed atomic soliton laser can be made in present experiments.Comment: 11 pages, 4 figure
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