Bumps and rings in a two-dimensional neural field: splitting and rotational instabilities

In this paper we consider instabilities of localised solutions in planar neural field firing rate models of Wilson-Cowan or Amari type. Importantly we show that angular perturbations can destabilise spatially localised solutions. For a scalar model with Heaviside firing rate function we calculate symmetric one-bump and ring solutions explicitly and use an Evans function approach to predict the point of instability and the shapes of the dominant growing modes. Our predictions are shown to be in excellent agreement with direct numerical simulations. Moreover, beyond the instability our simulations demonstrate the emergence of multi-bump and labyrinthine patterns. With the addition of spike-frequency adaptation, numerical simulations of the resulting vector model show that it is possible for structures without rotational symmetry, and in particular multi-bumps, to undergo an instability to a rotating wave. We use a general argument, valid for smooth firing rate functions, to establish the conditions necessary to generate such a rotational instability. Numerical continuation of the rotating wave is used to quantify the emergent angular velocity as a bifurcation parameter is varied. Wave stability is found via the numerical evaluation of an associated eigenvalue problem

Robustness and Enhancement of Neural Synchronization by Activity-Dependent Coupling

We study the synchronization of two model neurons coupled through a synapse having an activity-dependent strength. Our synapse follows the rules of Spike-Timing Dependent Plasticity (STDP). We show that this plasticity of the coupling between neurons produces enlarged frequency locking zones and results in synchronization that is more rapid and much more robust against noise than classical synchronization arising from connections with constant strength. We also present a simple discrete map model that demonstrates the generality of the phenomenon.Comment: 4 pages, accepted for publication in PR

Pattern recognition in lymphoid malignancies using CytoGPS and Mercator

BACKGROUND: There have been many recent breakthroughs in processing and analyzing large-scale data sets in biomedical informatics. For example, the CytoGPS algorithm has enabled the use of text-based karyotypes by transforming them into a binary model. However, such advances are accompanied by new problems of data sparsity, heterogeneity, and noisiness that are magnified by the large-scale multidimensional nature of the data. To address these problems, we developed the Mercator R package, which processes and visualizes binary biomedical data. We use Mercator to address biomedical questions of cytogenetic patterns relating to lymphoid hematologic malignancies, which include a broad set of leukemias and lymphomas. Karyotype data are one of the most common form of genetic data collected on lymphoid malignancies, because karyotyping is part of the standard of care in these cancers. RESULTS: In this paper we combine the analytic power of CytoGPS and Mercator to perform a large-scale multidimensional pattern recognition study on 22,741 karyotype samples in 47 different hematologic malignancies obtained from the public Mitelman database. CONCLUSION: Our findings indicate that Mercator was able to identify both known and novel cytogenetic patterns across different lymphoid malignancies, furthering our understanding of the genetics of these diseases

Derivation of the Statistical Distribution of the Mass Peak Centroids of Mass Spectrometers Employing Analog-to-Digital Converters and Electron Multipliers

The statistical distribution of mass peak centroids recorded on mass spectrometers employing analog-to-digital converters (ADCs) and electron multipliers is derived from the first principles of the data generation process. The resulting Gaussian model is discussed and is validated with experimental data and with Monte Carlo simulations

Optical Guidance System /OGS/ for rendezvous and docking Final report

Optical guidance system for Apollo rendezvous and dockin

Limits and dynamics of stochastic neuronal networks with random heterogeneous delays

Realistic networks display heterogeneous transmission delays. We analyze here the limits of large stochastic multi-populations networks with stochastic coupling and random interconnection delays. We show that depending on the nature of the delays distributions, a quenched or averaged propagation of chaos takes place in these networks, and that the network equations converge towards a delayed McKean-Vlasov equation with distributed delays. Our approach is mostly fitted to neuroscience applications. We instantiate in particular a classical neuronal model, the Wilson and Cowan system, and show that the obtained limit equations have Gaussian solutions whose mean and standard deviation satisfy a closed set of coupled delay differential equations in which the distribution of delays and the noise levels appear as parameters. This allows to uncover precisely the effects of noise, delays and coupling on the dynamics of such heterogeneous networks, in particular their role in the emergence of synchronized oscillations. We show in several examples that not only the averaged delay, but also the dispersion, govern the dynamics of such networks.Comment: Corrected misprint (useless stopping time) in proof of Lemma 1 and clarified a regularity hypothesis (remark 1

Ironbark: Developing a healthy community program for older Aboriginal people

Issue addressed: Programs by, with and for Aboriginal older people must be culturally safe and relevant. Successful elements include being Aboriginal specific and group based. Co-design with Aboriginal people and stakeholders is essential. We describe the co-design process of developing the Ironbark: Healthy Community program. Methods: Aboriginal ways of knowing, being and doing and yarning conversational methods guided the development process, during 2018. A desktop review provided details of current group characteristics and key community stakeholders. Stakeholder engagement regarding views about group operations, participants and benefits also occurred. Aboriginal Elders views of their groups were gathered through yarning circles in New South Wales (NSW). Grounded theory approach was used to ascertain key themes. Results: Initial engagement occurred with 13 different community stakeholders and organisations in three Australian states (NSW, South Australia (SA), Western Australia (WA)). Three yarning circles occurred with Elders from urban (N = 10), regional coastal (N = 10) and regional country (N = 4) groups. Six key themes were organised in three groups according to an Aboriginal ontology. 1. Knowing: groups provide opportunities to share knowledge and connect socially. Adequate program resourcing and sustainability are valued. 2. Being: groups strengthen culture, providing important social, emotional and other forms of support to age well. 3. Doing: previous program experiences inform perceptions for new program operations. Group venues and operational aspects should be culturally safe, acknowledging diversity among Elders, their preferences and community control. Themes were used to develop the program and its resource manual that were finalised with stakeholders, including steering committee approval. Conclusions: Stakeholder feedback at multiple stages and Aboriginal Elders’ perspectives resulted in a new co-designed community program involving weekly yarning circles and social activities. So what?: Co-design, guided by Aboriginal ways of knowing, being and doing, can develop programs relevant for Aboriginal people