Laguerre-Gaussian laser filamentation for the control of electric discharges in air.

We study the use of Laguerre-Gaussian (LG) femtosecond laser filament with multi GW peak power to guide electric sparks in the atmosphere. We demonstrate that an LG beam with a vortex phase or with 6 azimuthal phase steps generates a filamentation regime, where a longer and more uniform energy deposition is produced compared to a normal beam with a flat phase. Such filaments can guide electric discharges over much longer distances. This technique could significantly extend the guiding range of laser filaments for lightning control and other long-range atmospheric experiments involving filamentation.

Effects of compression running pants and treadmill running stages on knee proprioception and fatigue-related physiological responses in half-marathon runners.

Background: Knee injury is common in half-marathon runners, however, the effect of compression running pants on fatigue and knee proprioception remains unclear. Objectives: The study aims to investigate whether wearing compression running pants (CRP) and treadmill running stages affect knee proprioception and fatigue-related physiological responses during half-marathon running. Methods: Eighteen half-marathon runners completed two self-paced 21 km treadmill running trials, once wearing CRP and once wearing loose running shorts (LRS). For each 21 km run, RPE, heart rate, blood lactic acid, and knee flexion proprioception were assessed before starting, and after each 7 km stage. Results: Data analysis revealed no difference between CRP and LRS conditions in heart rate, RPE, or blood lactic acid. Repeated measures ANOVA showed a significant garment condition main effect whereby wearing CRP was associated with higher knee proprioceptive acuity (p = 0.006). Polynomial trend analysis showed a significant linear downwards trend in proprioceptive acuity across the four measurement occasions (p = 0.048). Stage analysis showed that wearing CRP was associated with better knee proprioception at running distances of 14 km (p = 0.007, 95%CI = -0.054, -0.010) and 21 km (p = 0.016, 95%CI = -0.051, -0.006). Conclusion: Compression running pants provide an overall positive effect on knee proprioception, particularly after 14 km and 21km, which may reduce the probability of knee injury. CRP had no significant effect on physiological measures in half-marathon running.

Femtosecond filamentation of optical vortices for the generation of optical air waveguides.

We study the filamentation in air of multi-millijoule optical vortices and compare them with the classical filamentation regime. The femtosecond vortex beam generates multiple plasma filaments organized in a cylindrical geometry. This plasma configuration evolves into a meter-scale tubular neutral gas column that can be used as a waveguide for nanosecond laser pulses at 532 nm. It appears that optical vortices produce a more uniform heating along the propagation axis, when compared with Gaussian or super-Gaussian beams, and that the resulting low-density channel is poorly sensitive to the laser input power thanks to the combination of filamentation intensity clamping and phase vorticity.

Effects of graduated compression socks on ankle inversion proprioception of half-marathon runners at different running distances.

OBJECTIVES: To determine the effect of graduated compression socks on ankle proprioception and the relationship between fatigue and ankle proprioception measures in half-marathon runners at successive 7 km intervals during a 21-km run. DESIGN: Repeated measures study. METHODS: Twenty well-trained half-marathon runners (mean ±â€¯SD: age 38.6 ±â€¯11.3 y, weekly volume 42.3 ±â€¯21.1 km, training experience 4.7 ±â€¯3.5 y) performed two 21 km running trials on a treadmill wearing either graduated compression socks or looser, standard non-compression running socks. Each running trial was divided into three self-paced 7 km blocks, repeated at the same pace for each trial, heart rate was not controlled, but after each block, heart rate, blood lactate, rating of perceived exertion, and ankle inversion proprioception were measured, the latter by using the active movement extent discrimination apparatus. RESULTS: There was no differences between the graduated compression sock and non-compression running sock conditions in rating of perceived exertion scores (F = 0.524, p = 0.478), heart rate (F = 0.001, p = 0.975) and blood lactate (F = 0.004, p = 0.951). Overall, wearing graduated compression socks was associated with significantly better ankle proprioception after 21 km of running (p = 0.024, 95% CI = -0.066, -0.005). Heart rate, rating of perceived exertion and blood lactate were not correlated with ankle proprioception sensitivity in the graduated compression sock and non-compression running sock conditions at any point during the run (all p > 0.05). CONCLUSIONS: Wearing graduated compression socks provides a positive effect on proprioceptive control of the ankle joint only after 21 km and may therefore reduce the possibility of injury associated with proprioceptive ability diminishing over time during exercise.

A redshift mechanism of high-order harmonics: Change of ionization energy.

We theoretically study the high-order harmonic generation of H2+ and its isotopes beyond the Born-Oppenheimer dynamics. It is surprising that the spectral redshift can still be observed in high harmonic spectra of H2+ driven by a sinusoidal laser pulse in which the trailing (leading) edge of the laser pulse is nonexistent. The results confirm that this spectral redshift originates from the reduction in ionization energy between recombination time and ionization time, which is obviously different from the nonadiabatic spectral redshift induced by the falling edge of the laser pulse. Additionally, the improved instantaneous frequency of harmonics by considering the changeable ionization energy can deeply verify our results. Therefore, this new mechanism must be taken into account when one uses the nonadiabatic spectral redshift to retrieve the nuclear motion.