5,357 research outputs found
Generation of finite wave trains in excitable media
Spatiotemporal control of excitable media is of paramount importance in the
development of new applications, ranging from biology to physics. To this end
we identify and describe a qualitative property of excitable media that enables
us to generate a sequence of traveling pulses of any desired length, using a
one-time initial stimulus. The wave trains are produced by a transient
pacemaker generated by a one-time suitably tailored spatially localized finite
amplitude stimulus, and belong to a family of fast pulse trains. A second
family, of slow pulse trains, is also present. The latter are created through a
clumping instability of a traveling wave state (in an excitable regime) and are
inaccessible to single localized stimuli of the type we use. The results
indicate that the presence of a large multiplicity of stable, accessible,
multi-pulse states is a general property of simple models of excitable media.Comment: 6 pages, 6 figure
Neural Network Model for Apparent Deterministic Chaos in Spontaneously Bursting Hippocampal Slices
A neural network model that exhibits stochastic population bursting is
studied by simulation. First return maps of inter-burst intervals exhibit
recurrent unstable periodic orbit (UPO)-like trajectories similar to those
found in experiments on hippocampal slices. Applications of various control
methods and surrogate analysis for UPO-detection also yield results similar to
those of experiments. Our results question the interpretation of the
experimental data as evidence for deterministic chaos and suggest caution in
the use of UPO-based methods for detecting determinism in time-series data.Comment: 4 pages, 5 .eps figures (included), requires psfrag.sty (included
Controlling Fast Chaos in Delay Dynamical Systems
We introduce a novel approach for controlling fast chaos in time-delay
dynamical systems and use it to control a chaotic photonic device with a
characteristic time scale of ~12 ns. Our approach is a prescription for how to
implement existing chaos control algorithms in a way that exploits the system's
inherent time-delay and allows control even in the presence of substantial
control-loop latency (the finite time it takes signals to propagate through the
components in the controller). This research paves the way for applications
exploiting fast control of chaos, such as chaos-based communication schemes and
stabilizing the behavior of ultrafast lasers.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Front motion and localized states in an asymmetric bistable activator-inhibitor system with saturation
We study the spatiotemporal properties of coherent states (peaks, holes, and
fronts) in a bistable activator-inhibitor system that exhibits biochemical
saturated autocatalysis, and in which fronts do not preserve spatial parity
symmetry. Using the Gierer-Meinhardt prototype model, we find the conditions in
which two distinct pinning regions are formed. The first pinning type is known
in the context of variational systems while the second is structurally
different due to the presence of a heteroclinic bifurcation between two uniform
states. The bifurcation also separates the parameter regions of
counterpropagating fronts, leading in turn to the growth or contraction of
activator domains. These phenomena expand the range of pattern formation theory
and its biomedical applications: activator domain retraction suggests potential
therapeutic strategies for patterned pathologies, such as cardiovascular
calcification.Comment: 4 pages, 3 figure
Diagnosis and Decision-Making in Telemedicine
This article provides an analysis of the skills that health professionals and patients employ in reaching diagnosis and decision-making in telemedicine consultations. As governmental priorities continue to emphasize patient involvement in the management of their disease, there is an increasing need to accurately capture the providerâpatient interactions in clinical encounters. Drawing on conversation analysis of 10 video-mediated consultations in 3 National Health Service settings in England, this study examines the interaction between patients, General Practitioner (GPs), nurses, and consultants during diagnosis and decision-making, with the aim to identify the range of skills that participants use in the process and capture the interprofessional communication and patient involvement in the diagnosis and decision-making phases of telemedicine consultations. The analysis shows that teleconsultations enhance collaborative working among professionals and enable GPs and nurses to develop their skills and actively participate in diagnosis and decision-making by contributing primary careâspecific knowledge to the consultation. However, interprofessional interaction may result in limited patient involvement in decisionmaking. The findings of this study can be used to inform training programs in telemedicine that focus on the development of effective skills for professionals and the provision of information to patients
Contestable adulthood: variability and disparity in markers for negotiating the transition to adulthood
Recent research has identified a discreet set of subjective markers that are seen as characterizing the transition to adulthood. The current study challenges this coherence by examining the disparity and variability in young peopleâs selection of such criteria. Four sentence-completion cues corresponding to four differentcontexts in which adult status might be contested were given to 156 British 16- to 17-year-olds. Their qualitative responses were analyzed to
explore patterns whilst capturing some of their richness and diversity. An astonishing amount of variability emerged, both within and between cued contexts.The implications of this variability for how the transition to adulthood is experienced are explored. The argument is made that markers of the transition to adulthood are not merely reflective of the bioâpsychoâsocial development of
young people. Rather, adulthood here is seen as an essentially contested concept,located within the discursive interactional environment in which young people participate
Size-Dependent Transition to High-Dimensional Chaotic Dynamics in a Two-Dimensional Excitable Medium
The spatiotemporal dynamics of an excitable medium with multiple spiral
defects is shown to vary smoothly with system size from short-lived transients
for small systems to extensive chaos for large systems. A comparison of the
Lyapunov dimension density with the average spiral defect density suggests an
average dimension per spiral defect varying between three and seven. We discuss
some implications of these results for experimental studies of excitable media.Comment: 5 pages, Latex, 4 figure
Child support reform: some analysis of the 1999 white paper
This paper uses a sample of lone mothers (and former lone mothers who are now repartnered) drawn from the 1997 Family Resources Survey to analyse the potential effects of reforming the UK system of Child Support. The main deficiency of the data is that non-resident fathers cannot be matched to the mothers in the data and this is overcome by exploiting information from another dataset which gives the joint distribution of the characteristics of separated parents. The effects of reforming the Child Support system is simulated for the amount of maintenance liabilities, the amount paid and the net incomes of households containing mothers with care and households containing non-resident fathers. The likely effects of the reform are simulated at various levels of compliance. The analysis highlights the need for further research into the incentive effects of Child Support on individual behaviour
Interaction between clients and physiotherapists in group exercise classes in geriatric rehabilitation
The aim of this paper is to explore how older people construct their interaction in group exercise classes in geriatric rehabilitation and what is their contribution to the interaction. Discourse analysis was employed and data, consisting of seven videotaped group-based exercise sessions, were collected from 52 older people (aged 66â93 years) and nine rehabilitation professionals in seven rehabilitation centres. Four discourse categories were found. In âtaciturn exercisingâ, older people remained verbally silent but physically active. In âsubmissive disagreeingâ, older people opposed the professionalsâ agenda by displaying reluctant consent to proposals. In âresilient endeavouringâ, older adults persisted on their course of action, regardless of the disapproval of the professionals. In âlay helpingâ, older people initiated spontaneous encouragement, but also gave verbal and physical assistance to their peers. Older people's meaningful contribution to interaction, whilst it may challenge the institutional flow of activities, can constitute an integral part of the re-ablement process of rehabilitation
Fluctuations in the Site Disordered Traveling Salesman Problem
We extend a previous statistical mechanical treatment of the traveling
salesman problem by defining a discrete "site disordered'' problem in which
fluctuations about saddle points can be computed. The results clarify the basis
of our original treatment, and illuminate but do not resolve the difficulties
of taking the zero temperature limit to obtain minimal path lengths.Comment: 17 pages, 3 eps figures, revte
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