Bio-inspired swing leg control for spring-mass robots running on ground with unexpected height disturbance

We proposed three swing leg control policies for spring-mass running robots, inspired by experimental data from our recent collaborative work on ground running birds. Previous investigations suggest that animals may prioritize injury avoidance and/or efficiency as their objective function during running rather than maintaining limit-cycle stability. Therefore, in this study we targeted structural capacity (maximum leg force to avoid damage) and efficiency as the main goals for our control policies, since these objective functions are crucial to reduce motor size and structure weight. Each proposed policy controls the leg angle as a function of time during flight phase such that its objective function during the subsequent stance phase is regulated. The three objective functions that are regulated in the control policies are (i) the leg peak force, (ii) the axial impulse, and (iii) the leg actuator work. It should be noted that each control policy regulates one single objective function. Surprisingly, all three swing leg control policies result in nearly identical subsequent stance phase dynamics. This implies that the implementation of any of the proposed control policies would satisfy both goals (damage avoidance and efficiency) at once. Furthermore, all three control policies require a surprisingly simple leg angle adjustment: leg retraction with constant angular acceleration

The role of moral identity and regret on cheating in sport

Cheating in sport can have adverse interpersonal consequences and violate the ideal of fair play, which involves abiding by the rules when competing. To help develop effective methods to prevent cheating in sport, research is needed that identifies the psychological factors underpinning an athlete’s decision to cheat. The purpose of this multi-study research was to examine the role of moral identity and regret on cheating in sport. In Study 1, we used a cross-sectional design to examine relationships between moral identity, regret, and cheating attitudes. In Study 2, we used a field design to examine relationships between moral identity, regret, and cheating attitudes during competitive running races to win prize money. After awarding the prize money to the winners, we asked participants whether they would change their decision to cheat if given the opportunity. In Study 1, moral identity was directly and indirectly (via regret) related to cheating attitudes. In Study 2, participants who cheated reported lower moral identity, greater regret, and more favourable cheating attitudes than those who did not cheat. After the prizes were awarded to winners, those who did not cheat, but wanted to change their decision to cheat, reported greater feelings of regret compared to those not wanting to change their decision. In conclusion, cheating in sport elicits regret, which could modify future cheating behaviour. However, athletes may be more likely to cheat in future if they had chosen not to cheat and foregone a benefit

RELIABILITY OF ACUTE STATIC STRETCH IMPACT ON VERTICAL JUMP HEIGHT

The purpose of this study was to examine the reliability of the acute effect of stretch on vertical jump performance. Twenty-four subjects completed eight trials. In each trial warm-up, three pre-stretch jumps, stretching, and three post-stretch jumps were completed. Intraclass correlation coefficients (ICC) were used to evaluate the reliability of the stretch impact on vertical jumping across trials. While pre-stretch and post-stretch jumps were highly reliable (ICC=0.99), the difference from pre-stretch to post-stretch was not (ICC=0.07). The stretch impact on vertical jump may not be reliable for subjects across trials

Don't break a leg: Running birds from quail to ostrich prioritise leg safety and economy in uneven terrain

Cursorial ground birds are paragons of bipedal running that span a 500-fold mass range from quail to ostrich. Here we investigate the task-level control priorities of cursorial birds by analysing how they negotiate single-step obstacles that create a conflict between body stability (attenuating deviations in body motion) and consistent leg force–length dynamics (for economy and leg safety). We also test the hypothesis that control priorities shift between body stability and leg safety with increasing body size, reflecting use of active control to overcome size-related challenges. Weight-support demands lead to a shift towards straighter legs and stiffer steady gait with increasing body size, but it remains unknown whether non-steady locomotor priorities diverge with size. We found that all measured species used a consistent obstacle negotiation strategy, involving unsteady body dynamics to minimise fluctuations in leg posture and loading across multiple steps, not directly prioritising body stability. Peak leg forces remained remarkably consistent across obstacle terrain, within 0.35 body weights of level running for obstacle heights from 0.1 to 0.5 times leg length. All species used similar stance leg actuation patterns, involving asymmetric force–length trajectories and posture-dependent actuation to add or remove energy depending on landing conditions. We present a simple stance leg model that explains key features of avian bipedal locomotion, and suggests economy as a key priority on both level and uneven terrain. We suggest that running ground birds target the closely coupled priorities of economy and leg safety as the direct imperatives of control, with adequate stability achieved through appropriately tuned intrinsic dynamics

Cellular automaton rules conserving the number of active sites

This paper shows how to determine all the unidimensional two-state cellular automaton rules of a given number of inputs which conserve the number of active sites. These rules have to satisfy a necessary and sufficient condition. If the active sites are viewed as cells occupied by identical particles, these cellular automaton rules represent evolution operators of systems of identical interacting particles whose total number is conserved. Some of these rules, which allow motion in both directions, mimic ensembles of one-dimensional pseudo-random walkers. Numerical evidence indicates that the corresponding stochastic processes might be non-Gaussian.Comment: 14 pages, 5 figure

Long-distance Spore Transport: Vertical Sections of Spore Clouds over the Sea

RESP-566

The 6-vertex model of hydrogen-bonded crystals with bond defects

It is shown that the percolation model of hydrogen-bonded crystals, which is a 6-vertex model with bond defects, is completely equivalent with an 8-vertex model in an external electric field. Using this equivalence we solve exactly a particular 6-vertex model with bond defects. The general solution for the Bethe-like lattice is also analyzed.Comment: 13 pages, 6 figures; added references for section

Improving measurements of SF6 for the study of atmospheric transport and emissions

Sulfur hexafluoride (SF6) is a potent greenhouse gas and useful atmospheric tracer. Measurements of SF6 on global and regional scales are necessary to estimate emissions and to verify or examine the performance of atmospheric transport models. Typical precision for common gas chromatographic methods with electron capture detection (GC-ECD) is 1–2%. We have modified a common GC-ECD method to achieve measurement precision of 0.5% or better. Global mean SF6 measurements were used to examine changes in the growth rate of SF6 and corresponding SF6 emissions. Global emissions and mixing ratios from 2000–2008 are consistent with recently published work. More recent observations show a 10% decline in SF6 emissions in 2008–2009, which seems to coincide with a decrease in world economic output. This decline was short-lived, as the global SF6 growth rate has recently increased to near its 2007–2008 maximum value of 0.30±0.03 pmol mol−1 (ppt) yr−1 (95% C.L.)