Controllable skyrmion chirality in ferroelectrics.

Chirality, an intrinsic handedness, is one of the most intriguing fundamental phenomena in nature. Materials composed of chiral molecules find broad applications in areas ranging from nonlinear optics and spintronics to biology and pharmaceuticals. However, chirality is usually an invariable inherent property of a given material that cannot be easily changed at will. Here, we demonstrate that ferroelectric nanodots support skyrmions the chirality of which can be controlled and switched. We devise protocols for realizing control and efficient manipulations of the different types of skyrmions. Our findings open the route for controlled chirality with potential applications in ferroelectric-based information technologies.

A new portable device for assessing locomotor performance.

We investigated the validity of a new portable system and the feasibility of the method for gait analysis as the assessment of gait has clinical relevance in the study of locomotor pathologies. This system is composed of a data logger, triaxial accelerometers, and software. Measurements of the pelvis kinematics during gait were performed on five hip osteoarthritic subjects and 15 healthy subjects using the portable system and a reference system (Vicon). The healthy subjects were studied in conditions of normal gait and gait altered by a heelpiece. The studied variables were the vertical amplitude of the sacrum, the time of gait cycle and the vertical trajectories of the spines. The new system corresponded with the reference system for the studied variables. The small differences between the two systems in the vertical amplitude of the sacrum (0.53 +/- 6.39 mm), time of the gait cycle (0.002 +/- 0.05 s), and the vertical trajectories of the spine (coefficient correlation of 0.06 +/- 0.05) confirmed the validity of the portable system data. The results showed a distortion of the pelvis trajectory when the gait was impaired. The portable system provides an objective method to discriminate normal from limping gait and is easy to use outside of the laboratory.

The effect of combined self- and expert-modelling on the performance of the double leg circle on the pommel horse.

In this study, we investigated whether video modelling can enhance gymnasts' performance of the circle on a pommel horse. The procedure associated expert-modelling with self-modelling and quantitative performance analysis. Sixteen gymnasts were randomly assigned to one of two groups: (1) a modelling group, which received expert- and self-modelling, and performance feedback, or (2) a control group, which received no feedback. After five sessions of training, an analysis of variance with repeated measures indicated that the gains in the back, entry, front, and exit phases of the circle were greater for the modelling group than for the control group. During the training sessions, the gymnasts in the modelling group improved their body segmental alignment during the back phase more quickly than during the other phases. As predicted, although both groups performed the same number of circles (300 in 5 days, with 10 sequences of 6 circles), the modelling group improved their body segmental alignment more than the control group. It thus appears that immediate video modelling can help to correct complex sports movements such as the circle performed on the pommel horse. However, its effectiveness seemed to be dependent on the complexity of the phase.

Arm-leg coordination in flat breaststroke: a comparative study between elite and non-elite swimmers.

The aim of this study was to compare the arm-leg coordination in flat breaststroke among four groups of swimmers (elite males, elite females and non-elite males, non-elite females) of two different competitive levels. Using a velocity-video system, both forward acceleration and deceleration phases of the hip were first identified. Based on these phases, four temporal gaps indicated the time duration between arm and leg actions throughout three race paces (200, 100, and 50 m). For both groups, a velocity increase was combined with an increase of stroke rate, a decrease of stroke length, and an increase of the propulsive phases and a decrease of the glide phases. However, when the relative duration of one stroke cycle was considered, the elite swimmers had significant shorter time of the glide phase than lower competitive level swimmers (18.80 % vs. 31.04 % for females and 11.89 % vs. 19.60 % for males) combined with a longer stroke length (respectively 2.05 m vs. 1.73 m and 2.03 m vs. 1.82 m). Furthermore, the temporal gaps of the elite swimmers showed a greater continuity in the arm and leg actions, which indicates a better timing than non-elite swimmers. It was concluded that elite breaststroke swimmers are able to optimise their propulsion by reducing their glide phase and using a more continuous timing between arm and leg coordination.