Dr Samuel Johnson BSc MSc PhD

• PhD in Physics (Interplay between Network Topology and Dynamics in Neural Systems), University of Granada, 2011
• Certificate of Teaching Aptitude in Mathematics, University of Granada, 2008.
• MSc in Physics and Mathematics (specialising in mathematical biology), University of Granada, 2008
• BSc in Physics, University of Granada, 2006

Sam Johnson studied Physics and Mathematics at the University of Granada, Spain, where he did a PhD entitled 'Interplay between Network Topology and Dynamics in Neural Systems', under the supervision of Joaquin Torres and Joaquin Marro. He was a postdoc at the University of Oxford working with Nick Jones before taking up a Marie Curie research fellowship at Imperial College London. After a brief period in a joint position between DNV GL and the University of Bath, he became a Warwick Zeeman Lecturer at the University of Warwick in 2014. In 2017 he took up his current position at the University of Birmingham as Lecturer in Applied Mathematics.

Semester 2

LM Advanced Mathematical Biology

Research activity

Sam has many research interests, most of which can be placed under the umbrella of 'complex systems'. Some of the topics he is currently working on are as follows.

Trophic structure of directed networks: Together with colleagues in Granada, Sam recently studied a network property called 'trophic coherence', (Johnson et al., PNAS, 2014). This and subsequent work (with colleagues Miguel Ángel Muñoz, Virginia Dominguez, Janis Klaise and Nick Jones) has shown that trophic coherence is related to many aspects of complex systems, including the prevalence of cycles and feedback loops, ecological stability, motif distributions and spreading processes such as epidemics and neuronal avalanches. It has also opened several questions, such as: Does trophic coherence account for the existence of large, complex ecosystems? Can trophic structure be used to identify node function in systems like gene regulatory networks? Is there a general theory relating feedback and stability in complex, dynamical systems.

Human ecology: Work with Weisi Guo, Xueke Lu and Guillem Mosquera has show that the prevalence of violence around the world is related to the spatial distribution of cities according to a remarkably simple and robust law. We are currently looking into the causes of this effect though a combination of data analysis and agent based modelling and looking for ways in which our results can be applied.

Brain development: The neural network underlying all mental activity comes into being in a curious way: at birth it has a great many synapses (connections between neurons), about half of which are 'pruned' throughout infancy. Recent work with Ana Paula Millán, Joaquin Torres and Joaquin Marro describes a mechanism which could explain this phenomenon with a simple neural network model. We are now studying this process with more realistic neural modelling, looking into its effects in other complex systems. 

Adviser to Polymaths R&D Ltd

Member of the Conflict Research Society