2,935 research outputs found
Stickiness in Chaos
We distinguish two types of stickiness in systems of two degrees of freedom
(a) stickiness around an island of stability and (b) stickiness in chaos, along
the unstable asymptotic curves of unstable periodic orbits. We studied these
effects in the standard map with a rather large nonlinearity K=5, and we
emphasized the role of the asymptotic curves U, S from the central orbit O and
the asymptotic curves U+U-S+S- from the simplest unstable orbit around the
island O1. We calculated the escape times (initial stickiness times) for many
initial points outside but close to the island O1. The lines that separate the
regions of the fast from the slow escape time follow the shape of the
asymptotic curves S+,S-. We explained this phenomenon by noting that lines
close to S+ on its inner side (closer to O1) approach a point of the orbit 4/9,
say P1, and then follow the oscillations of the asymptotic curve U+, and escape
after a rather long time, while the curves outside S+ after their approach to
P1 follow the shape of the asymptotic curves U- and escape fast into the
chaotic sea. All these curves return near the original arcs of U+,U- and
contribute to the overall stickiness close to U+,U-. The isodensity curves
follow the shape of the curves U+,U- and the maxima of density are along U+,U-.
For a rather long time the stickiness effects along U+,U- are very pronounced.
However after much longer times (about 1000 iterations) the overall stickiness
effects are reduced and the distribution of points in the chaotic sea outside
the islands tends to be uniform.Comment: 28 pages, 12 figure
Highest weight Macdonald and Jack Polynomials
Fractional quantum Hall states of particles in the lowest Landau levels are
described by multivariate polynomials. The incompressible liquid states when
described on a sphere are fully invariant under the rotation group. Excited
quasiparticle/quasihole states are member of multiplets under the rotation
group and generically there is a nontrivial highest weight member of the
multiplet from which all states can be constructed. Some of the trial states
proposed in the literature belong to classical families of symmetric
polynomials. In this paper we study Macdonald and Jack polynomials that are
highest weight states. For Macdonald polynomials it is a (q,t)-deformation of
the raising angular momentum operator that defines the highest weight
condition. By specialization of the parameters we obtain a classification of
the highest weight Jack polynomials. Our results are valid in the case of
staircase and rectangular partition indexing the polynomials.Comment: 17 pages, published versio
Advance telephone calls ahead of reminder questionnaires increase response rate in non-responders compared to questionnaire reminders only : The RECORD phone trial
Peer reviewedPublisher PD
The study of metaphor as part of Critical Discourse Analysis
This article discusses how the study of metaphoric and more generally, figurative language use contributes to critical discourse analysis (CDA). It shows how cognitive linguistsâ recognition of metaphor as a fundamental means of concept- and argument-building can add to CDA's account of meaning constitution in the social context. It then discusses discrepancies between the early model of conceptual metaphor theory and empirical data and argues that discursive-pragmatic factors as well as sociolinguistic variation have to be taken into account in order to make cognitive analyses more empirically and socially relevant. In conclusion, we sketch a modified cognitive approach informed by Relevance Theory within CDA
Chaos and Noise in a Truncated Toda Potential
Results are reported from a numerical investigation of orbits in a truncated
Toda potential which is perturbed by weak friction and noise. Two significant
conclusions are shown to emerge: (1) Despite other nontrivial behaviour,
configuration, velocity, and energy space moments associated with these
perturbations exhibit a simple scaling in the amplitude of the friction and
noise. (2) Even very weak friction and noise can induce an extrinsic diffusion
through cantori on a time scale much shorter than that associated with
intrinsic diffusion in the unperturbed system.Comment: 10 pages uuencoded PostScript (figures included), (A trivial
mathematical error leading to an erroneous conclusion is corrected
Chaotic mixing in noisy Hamiltonian systems
This paper summarises an investigation of the effects of low amplitude noise
and periodic driving on phase space transport in 3-D Hamiltonian systems, a
problem directly applicable to systems like galaxies, where such perturbations
reflect internal irregularities and.or a surrounding environment. A new
diagnsotic tool is exploited to quantify how, over long times, different
segments of the same chaotic orbit can exhibit very different amounts of chaos.
First passage time experiments are used to study how small perturbations of an
individual orbit can dramatically accelerate phase space transport, allowing
`sticky' chaotic orbits trapped near regular islands to become unstuck on
suprisingly short time scales. Small perturbations are also studied in the
context of orbit ensembles with the aim of understanding how such
irregularities can increase the efficacy of chaotic mixing. For both noise and
periodic driving, the effect of the perturbation scales roughly in amplitude.
For white noise, the details are unimportant: additive and multiplicative noise
tend to have similar effects and the presence or absence of a friction related
to the noise by a Fluctuation- Dissipation Theorem is largely irrelevant.
Allowing for coloured noise can significantly decrease the efficacy of the
perturbation, but only when the autocorrelation time, which vanishes for white
noise, becomes so large that t here is little power at frequencies comparable
to the natural frequencies of the unperturbed orbit. This suggests strongly
that noise-induced extrinsic diffusion, like modulational diffusion associated
with periodic driving, is a resonance phenomenon. Potential implications for
galaxies are discussed.Comment: 15 pages including 18 figures, uses MNRAS LaTeX macro
Noise-Induced Phase Space Transport in Two-Dimensional Hamiltonian Systems
First passage time experiments were used to explore the effects of low
amplitude noise as a source of accelerated phase space diffusion in
two-dimensional Hamiltonian systems, and these effects were then compared with
the effects of periodic driving. The objective was to quantify and understand
the manner in which ``sticky'' chaotic orbits that, in the absence of
perturbations, are confined near regular islands for very long times, can
become ``unstuck'' much more quickly when subjected to even very weak
perturbations. For both noise and periodic driving, the typical escape time
scales logarithmically with the amplitude of the perturbation. For white noise,
the details seem unimportant: Additive and multiplicative noise typically have
very similar effects, and the presence or absence of a friction related to the
noise by a Fluctuation-Dissipation Theorem is also largely irrelevant. Allowing
for colored noise can significantly decrease the efficacy of the perturbation,
but only when the autocorrelation time becomes so large that there is little
power at frequencies comparable to the natural frequencies of the unperturbed
orbit. Similarly, periodic driving is relatively inefficient when the driving
frequency is not comparable to these natural frequencies. This suggests
strongly that noise-induced extrinsic diffusion, like modulational diffusion
associated with periodic driving, is a resonance phenomenon. The logarithmic
dependence of the escape time on amplitude reflects the fact that the time
required for perturbed and unperturbed orbits to diverge a given distance
scales logarithmically in the amplitude of the perturbation.Comment: 15 pages, including 13 Figures and 1 Table, uses Phys. Rev. macro
Enabling recruitment success in bariatric surgical trials: pilot phase of the By-Band-Sleeve study
This is the final version. Available on open access from Springer Nature via the DOI in this recordData availability:
The data (transcripts) that support the findings of this study are available on request from the corresponding author. The data are not publicly available because of them containing information that could compromise privacy/consent, but the authors will be able to consider specific requests on a case-by-case basis.BACKGROUND: Randomized controlled trials (RCTs) involving surgical procedures are challenging for recruitment and infrequent in the specialty of bariatrics. The pilot phase of the By-Band-Sleeve study (gastric bypass versus gastric band versus sleeve gastrectomy) provided the opportunity for an investigation of recruitment using a qualitative research integrated in trials (QuinteT) recruitment intervention (QRI). PATIENTS/METHODS: The QRI investigated recruitment in two centers in the pilot phase comparing bypass and banding, through the analysis of 12 in-depth staff interviews, 84 audio recordings of patient consultations, 19 non-participant observations of consultations and patient screening data. QRI findings were developed into a plan of action and fed back to centers to improve information provision and recruitment organization. RESULTS: Recruitment proved to be extremely difficult with only two patients recruited during the first 2 months. The pivotal issue in Center A was that an effective and established clinical service could not easily adapt to the needs of the RCT. There was little scope to present RCT details or ensure efficient eligibility assessment, and recruiters struggled to convey equipoise. Following presentation of QRI findings, recruitment in Center A increased from 9% in the first 2 months (2/22) to 40% (26/65) in the 4 months thereafter. Center B, commencing recruitment 3 months after Center A, learnt from the emerging issues in Center A and set up a special clinic for trial recruitment. The trial successfully completed pilot recruitment and progressed to the main phase across 11 centers. CONCLUSIONS: The QRI identified key issues that enabled the integration of the trial into the clinical setting. This contributed to successful recruitment in the By-Band-Sleeve trial-currently the largest in bariatric practice-and offers opportunities to optimize recruitment in other trials in bariatrics.National Institute for Health Research Health Technology Assessment ProgrammeMedical Research Council (MRC
Chaos and Noise in Galactic Potentials
ABBREVIATED ABSTRACT: This paper summarises an investigation of the effects
of weak friction and noise in time-independent, nonintegrable potentials which
admit both regular and stochastic orbits. The aim is to understand the
qualitative effects of internal and external irregularities associated, e.g.,
with discreteness effects or couplings to an external environment, which stars
in any real galaxy must experience. The two principal conclusions are: (1)
These irregularities can be important on time scales much shorter than the
natural relaxation time scale t_R associated with the friction and noise. For
stochastic orbits friction and noise induce an average exponential divergence
from the unperturbed Hamiltonian trajectory at a rate set by the value of the
local Lyapunov exponent. Even weak noise can make a pointwise interpretation of
orbits suspect already on time scales much shorter than t_R. (2) The friction
and noise can also have significant effects on the statistical properties of
ensembles of stochastic orbits, these also occurring on time scales much
shorter than t_R. Potential implications for galactic dynamics are discussed,
including the problem of shadowing.Comment: 45 pages, uuencoded PostScript (figures included), LA-UR-94-282
- âŠ