Complex Systems

One project aimed to understand the complex couplings between living systems and the physical environment, in particular, the effects of climate change and environmental effects on ecological systems, inter-species interactions, effects of anthropogenic activities on wildlife movement and aspects governing human-environment coupling. This was one of three components of an IRHPA scheme SERB project undertaken at NIAS on human-environment interactions. The following directions of work were pursued by the Complex Systems Programme under this project.

A major outcome of this project published in Nature Scientific Reports was the construction of a model of animal movement that not only explains an animal's strategies in trying to move across its home range in search of  resources such as food, but also captures the way in which anthropogenic activities and man-made landscape features affect animal movement.

Effects of human intervention (afforestation, deforestation, vegetative cover changes, etc.) on population cycles in ecological systems were modelled. The results are in agreement with observations recorded over 310 years.

A focus of the project was on the coal mining region around Ramagundam in Telangana state and the growth of atmospheric pollutants in and around this region and effects if any on the vegetation. The outcome was our formulation of a predictive dynamical growth model to understand the growth of PM 2.5, PM10, SOx, NOx from the Singareni open cast coal mines and thermal power plant. The predictions made were shown to be in close agreement with recorded data which was obtained subsequently. 

Studying impact of atmospheric pollutants on the vegetation cover in the coal mining region:  

The vegetation cover in the study region was studied for the period 2012-2019 to estimate the impact if any, of the air-pollution, using data from MODIS, and from the Forest Survey of  India. 

Climate change impact on marine ecosystems was investigated by constructing different predictive models – one which explains increased jellyfish numbers observed in India and elsewhere, and another which explains regime shifts in sardine and mackerel populations observed along Indian coasts after 1985.

This project broadly aims to elucidate the dynamical mechanisms underlying the diverse kinds of nonlinear oscillations observed in different mechanical systems under different types of forcing. These studies are expected to help in giving better insights into the dynamics underlying certain physical and biological systems such as models of neurons. This is a MATRICS research grant obtained by Prof. Janaki Balakrishnan for investigating the complex dynamics of simple nonlinear mechanical systems.

Focussing on the dynamics of biological sensory systems including neurons, this project formed the subject of a third direction of research, funded by a SERB (EMR scheme) grant to Prof. Janaki Balakrishnan. Earlier work by this  programme member explained experimentally observed behaviour of the sound-detecting inner hair cell of the ear, as well as features of the ear’s spontaneous otoacoustic emission spectrum. Several important and inadequately understood issues in hearing research -– multi-tone detection, two-tone interference, pitch perception, etc. are some of the active areas of research. These have practical medical applications. 

Modelling bursting oscillations in neurons is important as this is conjectured to play a key role in information processing, in associative memory, etc. A recent contribution of the Programme is a paper which identifies the dynamical mechanisms governing different types of bursting oscillations observed when neurons having different excitability mechanisms are coupled via electrical gap junctions under different coupling schemes. A unique bifurcation mechanism underlying bursting in bidirectionally coupled neurons is reported. This work has applications in understanding the process of information transfer from the hippocampus to the neocortex, memory consolidation, development of epilepsy.

An important contribution of the Programme is the discovery of a new type (bow-tie shape) of periodic bursting oscillation observed both in coupled Josephson junctions and in a nonlinear mechanical system, and explanations for the distinct complex bifurcation mechanisms underlying this behaviour in the two systems. Bursts similar to these have been observed in certain neuronal activity patterns in the brain.

In a work published in Nature Scientific Reports, we resolved the puzzle of the occurrence, absence & collapse of pest outbreak cycles by incorporating climate parameters for the first time in a mathematical model.  

In a different work we showed that the mere presence of a new species in an ecological system can lead to widely divergent dynamics depending upon the choice of initial conditions. It was shown that this can also lead to cessation of population cycles or unexpected species extinction. It was also demonstrated that introduction of a new species changes periodicity of pest outbreak cycles, as is also experimentally observed.

Here a systematic method is developed to determine the climatic tipping points from global fossil fuel emission data.

Significant contributions have been made by the Programme to acoustic cavitation studies of charged microbubbles imploding in fluids. The nonlinear, forced oscillations of a bubble in a fluid due to an external pressure field were studied theoretically. In the presence of a constant charge on the bubble, the bubble oscillator’s behaviour changes markedly. Ours are the first studies of pressure and charge thresholds worldwide and have enormous applications for medical diagnostics and damage control of industrial machinery in fluids.