Management of red rice (Oryza sativa) and barnyardgrass (Echinochloa crus-galli) grown with sorghum with reduced rate of atrazine and mechanical methods.

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Quantum threshold for optomechanical self-structuring in a Bose-Einstein condensate

Theoretical analysis of the optomechanics of degenerate bosonic atoms with a single feedback mirror shows that self-structuring occurs only above an input threshold that is quantum mechanical in origin. This threshold also implies a lower limit to the size (period) of patterns that can be produced in a condensate for a given pump intensity. These thresholds are interpreted as due to the quantum rigidity of Bose-Einstein condensates, which has no classical counterpart. Above the threshold, the condensate self-organizes into an ordered supersolid state with a spatial period self-selected by optical diffraction

Combined study of segmental movements and motion of the centre of mass during adaptation on a split-belt treadmill

BACKGROUND AND AIM: Walking on a split-belt treadmill (each of the two belts running at different speed) has been proposed as an experimental paradigm to investigate the flexibility of the neural control of gait and as a form of therapeutic exercise for hemi-paretic patients[1]. However the scarcity of dynamic investigations both for segmental aspects and for the entire body system, represented by the Centre of Mass (CoM), challenges the validity of the available findings on split-gait. Thus, the aim of the present study is to describe the dynamic adaptation of healthy subjects in terms of segmental and CoM motion, using Gait Analysis on Force Treadmill [2]. The study intends to clarify the effect of "split-gait", underlining its differences with pathologic claudication. METHODS: Ten healthy adults walked on a split-belt treadmill mounted on force sensors, with belts running either at the same speed ('Tied Condition', TC) or at different speeds ('Split Condition', SC, 0.4 vs 0.8 m/s). For the study of segmental motion, the surface Electromyography (sEMG), sagittal power and work provided by ankle, the main engine of body propulsion, were simultaneously recorded. For the study of the CoM motion, the Total Energy (Etot) and the percentage of Recovery (%R), the index of efficiency of the pendulum-like mechanism, were simultaneously analyzed. Various tied/split walking sequences were requested. The study was approved by the Local Ethic Committee. RESULTS: In the SC, the segmental motion analysis revealed a marked asymmetry between the two sides. The work provided by the ankle was 4.8 times higher (in the 0.4 vs 0.8 m/s conditions, respectively) compared with the slower side, and 1.2 times higher compared with the same speed in the TC (0.6 m/s) [3]. Paradoxically, the analysis of the CoM revealed an increased efficiency of the pendulum mechanism, with a higher %R in SC with respect to the TC at the same speed. CONCLUSIONS: Split gait entails its own pattern of locomotion, very different from pathologic claudication. The faster leg mimics the paretic limb temporally, but the unimpaired limb from the spatial and dynamic point of view[3]. This must be considered when a therapeutic application is designed. REFERENCES:1. Helm et al. Phys Med Rehabil Clin N Am. 2015;26(4):703-13. 2. Tesio et al. Am J Phys Med Rehabil. 2008;87(7):515-26. 3. Tesio et al. Int J Rehabil Res. 2018;41(4):304-315

Split-belt walking does not reproduce hemiparetic claudication: a study on the power output at the ankle and at the body centre of mass

Walking on a split-belt treadmill (with each of two belts running at a different velocity) has been claimed, based on kinematic findings, to mimic pathologic claudication by imposing a shorter stance (“escape” limp) on the faster belt. However, the anterior step decreases, contrary to what is usually observed in hemiparesis. This paradigm has been claimed to be a useful therapeutic exercise. Nevertheless, it leads to contradictory findings: spatial symmetry can be forced by placing the hemiparetic lower limb on the faster belt, but this entails exaggeration of the temporal asymmetry (vice-versa if belts are exchanged). Some light can be shed onto this contradiction if one considers the dynamics of gait. In the present study, the muscle power subtending the sagittal rotation of the joints of the lower limbs and the translation of the body Centre of Mass (CoM) were analyzed. METHODS Ten healthy adults (5 women), mean age (SD) 26 (2.81) years, height (SD) 1.71 (0.12) m, body mass (SD) 63.67 (11.13) kg walked on a split-belt treadmill mounted on force sensors providing 3D ground reaction forces. The belts ran either at the same (‘tied’ condition, TC) or at different velocities (‘split’ condition, SC) [2]. Lower limb joint rotations were recorded through a wireless optoelectronic system. The spatiotemporal synchronization of sagittal ground reactions and joint rotations allowed measuring the muscle power in the sagittal plane at the ankle, which provides about 70% of the muscle power needed to keep the body in motion during normal waking [3]. Subjects walked in TC at 0.6 m s-1 and in SC at 0.4 vs. 0.8 m s-1, with the dominant lower limb placed on the faster belt. By summing vectorially the ground reactions from both belts, the 3D mechanical energy changes of the body CoM could be computed, according to the “double integration” method (Cavagna’s algorithms, [3]). The total mechanical energy (Etot) and the efficiency of its pendulum-like transfer (saving of muscle work, percentage of energy Recovery, %R), were analyzed. A 30-180-30 s tied/split/tied walking sequence was requested. RESULTS In the SC, it has already been demonstrated that healthy adults show a marked asymmetry in the peak joint power provided by the trailing ankle at push-off: this was 2.5 times higher compared with the slower side, and 1.2 times higher compared to the one observed at the intermediate speed in TC [4]. In the present study, the analysis of the CoM unexpectedly revealed an increased efficiency of the pendulum mechanism during the whole stride (hence, per unit distance). %R was 58% in SC and 40% in TC. The reasons still need to be clarified. DISCUSSION Walking on a split-belt does not reproduce pathologic claudication but is an original form of gait instead. %R is higher than that recorded during TC at intermediate velocity. The step performed on the faster belt mimics the paretic step temporally but neither spatially nor, which is the original finding here, dynamically. Split-belt walking cannot be proposed as an established therapeutic paradigm until the choice for forcing dynamic (at joint and/or CoM level) vs. temporal vs. spatial symmetry is motivated