Passive oscillation damping in plants
In the race for light some plants have slender and long stems. Although stiff building material is (energy) expensive, they must avoid critical oscillations by all means. We examine the plants' approach towards structural efficiency.
Oscillations in spacecraft
In the absence of a damping atmosphere it is difficult to damp oscillations of booms. It can take up to several hours following a spacecraft turning manoeuvre until the vibration has damped out. The performance of pointing and tracking systems can thus be severely affected by the presence of long mechanical booms. Practical countermeasures include active damping (using piezoelectric materials) or shaping the control command via input or command shaping [1] techniques.
Plant stems, on the other hand, have built in oscillation damping (or keeping, depending on the ecology) mechanisms resulting from a clever arrangement of the skeletal tissue (sclerenchyma). This is due to the fact that they are as well exposed to oscillation, e.g. caused by squally winds, so that well adapted structures evolved during hundreds of millions of years. Such an arrangement, or its working principle, could be mimicked and embedded in the very structure of satellites booms such as magnetometers or of solar panels, to give the overall structure a passive damping capability without introducing a mass penalty or using complex control and actuation devices.
To make this principles evident oscillation of different plants is tested and their cross section analyzed.
Sensing and acting in the root apex
Safe anchoring is crucial for landing vehicles and even larger planetary outposts. Plants use a different approach than technical devices do. However, their anchoring is scalable, adaptive and does not require heavy machinery
The complexity of plant roots is underestimated at the first glance. A reason might be that due to their very nature they lack general visibility. Another reason might be that the actual processes of root growth happen on a longer time scale and that the actual mechanisms guiding and coordinating root growth only recently have seen the light of scientific understanding.
Next to coping with the mechanical properties of the soil (i.e. avoiding stones, cracking rocks,...) growing roots incorporate gravity, light, humidity, mechanical load on the stem and the presence of nutritions into their path planning algorithms. Each root tip incorporates a simple bio-controller deciding on where to go next. In consequence, the whole root system can be considered as a system working with distributed intelligence.
When a seed drops on the ground, it only carries the knowledge and a tiny starter package. The material needed for the growth of the plant, including roots and stem has to be extracted from the environment. The attempt of this study is to examine how the anchoring mechanisms of plant roots can be realized technically.
Can we model roots as swarms?
How are roots formed? Where is the brain that tells each single root-branch where to grow? Or are roots just connected cells where everyone does what feel right?
Considering a plant as a swarm of individuals is not a new concept, as it was firstly described in 1800 by Erasmus Darwin (Darwin, 1800). At that time, plant-philosophers discussed the individual 'minds' of plant apexes (mostly those of the sprout) and their power to turn into an entire plant when cut off and put into soil as joining a greater organism and functioning similar to a swarm of individual animals. In later discussions this swarm concept was dismissed as a philosophical concept but still the absence of a central master mind and the distribution of decision loci led to the formulation of meta-population to characterize plants (White, 1979).
Trying to infer basic operational principles from plants, and in this case root swarms, for implementation on engineering the design of efficient exploration algorithms has the advantage that the exploration strategy’s blueprint is imprinted on the root and directly observable. Contrary to other biological systems for which thousands of experimental trials have to be observed in order to deduce patterns in the exploration strategies, in the case of roots these strategies are available and at our disposal right from the start. Even if the social-insect metaphor is straightforward for implementation on engineering the design of efficient exploration algorithms, it suffers from an inherent disadvantage: the exploration of an unknown terrain (or volume) is done before the discovery of food sites, etc. and hence is very difficult to systematically observe.
In this project we analyse plant roots upon their similarities and dissimilarities to commonly known swarms by modelling root growth and evolving the rule set to determine the most relevant rules.
This work is conducted by Tobias Seidl, Christos Ampatzis and Dario Izzo in cooperation with Luis Simoes, Rita Ribeiro, (both Universidade Nova de Lisboa) Luis Correia and Cristina Cruz (both Universidade de Lisboa) within the Ariadna Framework.
