JEB desktop wallpaper calendar 2016

JEB desktop wallpaper calendar 2016

The green leafhopper, Cicadella viridis (Hemiptera, Auchenorrhyncha, Cicadellidae), jumps with near-constant acceleration
Gabriella Bonsignori, Cesare Stefanini, Umberto Scarfogliero, Stefano Mintchev, Giovanni Benelli, Paolo Dario

SUMMARY

Jumping insects develop accelerations that can greatly exceed gravitational acceleration. Although several species have been analysed using different tools, ranging from a purely physical to a morpho-physiological approach, instantaneous dynamic and kinematic data concerning the jumping motion are lacking. This is mainly due to the difficulty in observing in detail events that occur in a few milliseconds. In this study, the behaviour of the green leafhopper, Cicadella viridis, was investigated during the take-off phase of the jump, through high-speed video recordings (8000 frames s−1). We demonstrate that C. viridis is able to maintain fairly constant acceleration during overall leg elongation. The force exerted at the foot–ground interface is nearly constant and differs from the force expected from other typical motion models. A biomechanical model was used to highlight that this ability relies on the morphology of C. viridis hind legs, which act as a motion converter with a variable transmission ratio and use the time-dependent musculo-elastic force to generate a nearly constant thrust at the body–ground interface. This modulation mechanism minimizes the risk of breaking the substrate thanks to the absence of force peaks. The results of this study are of broad relevance in different research fields ranging from biomechanics to robotics.

FOOTNOTES

  • LIST OF SYMBOLS

    Embedded Image
    acceleration of a generic body
    d
    distance between the two coxo-trochanteral joints
    E
    femoro-tibial joint
    F
    coxo-trochanteral joint
    Embedded Image
    force generated by the ith body on the jth body
    Gc
    C. viridis centre of mass
    Gi
    generic body centre of mass
    I
    moment of inertia
    Embedded Image
    unit vector perpendicular to the plane where the leg lies during jumping
    la
    tibial length
    lb
    femur length
    m
    mass
    O
    point of contact between the feet and the ground modelled as a rotational joint
    Embedded Image
    reaction force of one leg on the ground
    t0
    the instant of the first movement of the hind leg just before jumping
    tfin
    the instant when the hind legs lose contact with the ground
    (xc,yc)
    C. viridis position coordinates of the centre of mass in the plane of trajectory
    γ
    angle between the tibia and the ground
    θ
    angle between the femur and the longitudinal axis of the C. viridis body
    λ
    estimated transformation parameter in the Box–Cox power transformation
    τ
    torque generated at the coxo-trochanteral joint
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