The role of functional surfaces in the locomotion of snakes

Snakes are one of the world’s most versatile organisms, at ease slithering through rubble or climbing vertical tree trunks. Their adaptations for conquering complex terrain thus serve naturally as inspirations for search and rescue robotics. In a combined experimental and theoretical investigation, we elucidate the propulsion mechanisms of snakes on both hard and granular substrates. The focus of this study is on physics of snake interactions with its environment. Snakes use one of several modes of locomotion, such as slithering on flat surfaces, sidewinding on sand, or accordion-like concertina and worm-like rectilinear motion to traverse crevices. We present a series of experiments and supporting mathematical models demonstrating how snakes optimize their speed and efficiency by adjusting their frictional properties as a function of position and time. Particular attention is paid to a novel paradigm in locomotion, a snake’s active control of its scales, which enables it to modify its frictional interactions with the ground. We use this discovery to build bio-inspired limbless robots that have improved sensitivity to the current state of the art: Scalybot has individually controlled sets of belly scales enabling it to climb slopes of 55 degrees. These findings will result in developing new functional materials and control algorithms that will guide roboticists as they endeavor towards building more effective all-terrain search and rescue robots.Ph.D

Sidewinding with minimal slip: Snake and robot ascent of sandy slopes

Limbless organisms like snakes can navigate nearly all terrain. In particular, desert-dwelling sidewinder rattlesnakes (C. cerastes) operate effectively on inclined granular media (like sand dunes) that induce failure in field-tested limbless robots through slipping and pitching. Our laboratory experiments reveal that as granular incline angle increases, sidewinder rattlesnakes increase the length of their body in contact with the sand. Implementing this strategy in a physical robot model of the snake enables the device to ascend sandy slopes close to the angle of maximum slope stability. Plate drag experiments demonstrate that granular yield stresses decrease with increasing incline angle. Together these three approaches demonstrate how sidewinding with contact-length control mitigates failure on granular media.This is the author’s version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in the journal Science on 10 October 2014, Volume 346 number 6206, DOI: 10.1126/science.1255718. The published article is copyrighted by the American Association for the Advancement of Science and can be found at: http://www.sciencemag.org/journals

Disturbance effects on plant diversity and invasive species in western oak communities of Iran (Case study: Dalab Forest, Ilam)

Abstract Changed environmental conditions, reactions of biotic factors and increase in invasive species due to anthropogenic or natural disturbances, will change composition and diversity of plant communities over time. Therefore, measurement of species diversity can be useful for disturbance and ecosystem management analysis .Oak stands of Dalab Park is located 25 km north west of Ilam was selected for invasive plant and species diversity studies and their effects on plant vegetation, due to their different disturbance regimes, including "grazing", "fire" and "control". Information of vegetation, soil and other environmental variables were collected from 77 sample plots, using random sampling method at various disturbance classes. Surface area of sample plots was determined, based on minimal area, using Helical Technique and Area-Species Curve. The size of sampling plots was 16×16 m. for tree and shrub species and 1×1 m. for herbaceous species. Whittaker´s nested plot method was used in order to record the herbaceous species. Two-Way Indicator Species Analysis, Indicator Species Analysis, Canonical Correspondence Analysis and Numerical Index method were applied to classify ecological groups, determine indicator species in each class, identify relationship between environmental factors and the studied plant groups and assess species diversity, respectively. Results showed that t disturbance affected composition and diversity of such forests. Grazing, fire, soil and topographical factors were identified as the most influential factors on plant composition. Fire led to an increase in vegetation into annuals and ruderal species of plant vegetation, including Coronilla scorpoides, Torilis leptophylla,Boissiera squarrosa,Taeniatherum crinitum, Onopordon carduchorum, Cirsium spectabile and Carduus pycnocephalus. Grazing increased mostly frequency of non-palatable and resistant species to grazing and soil compaction, including Bromus tectorum, Picnomon acarna, Stellaria media, Rochelia disperma, Holesteum umbellatum,Euphorbia macroclada, Turgenia latifolia, Rhagadiolus angulosus, and Valerianella vesicaria. Highest richness and diversity of the species was recorded in moderate grazing disturbance and control classes, whereas the lowest richness and diversity was recorded in intense and light grazing which is consistent with the theory of intermediate disturbance