The COVID lockdown and its effects on soft tissue injuries in Premier League Athletes.

BACKGROUND: During the COVID impacted 2020-2021 season of the English soccer league, there was an appreciable number of injuries experienced by players. These injuries, however, have not been quantified against previous seasons to highlight the altered season as a causative factor. METHODS: A review of an online database was conducted to search for injuries to football players in the Premier League across three seasons; 2018-2019, 2019-2020, and 2020-2021, to compare for difference in injury rates across the years and assess for higher rates in this current season, where athletes have had less play time due to COVID-19. Injury number and injury characteristics were abstracted from the online database Transfermarkt, with the provided information allowing for the sorting of the data into muscular and ligamentous injuries and skeletal injuries. RESULTS: Overall 226, 260, and 289 muscular and ligamentous injuries were observed across the 2018/2019, 2019/2020, and 2020/2021 seasons, respectively. There were 495 minutes on average played leading up to first injury in the 2020/2021 season, compared with 521 minutes in the 2019/2020 season and 536 minutes in the 2018/2019. There was an average of games played to injury of 5.6 games in the 2020/2021 year, with 6.0 in the 2019/2020 year and 6.1 in the 2018/2019 year. Additionally, there was a significantly shorter time in between games was noted during the COVID-affected season with a mean time of 6.8 days in-between games played during the 2020-2021 season as compared to the previous years of 9.12 and 7.12 days. CONCLUSION: Our study found that there were more injuries and a decreased time to first injury observed during the COVID-impacted 2020-2021 season than the two preceding seasons, perhaps demonstrating a link between fixture congestion and athlete injuries as evidenced by the significantly shorter time between games. It is therefore prudent to retain fixture spacing for athlete recovery even against the backdrop of an overall shortened season.

High-resolution microscopy through optically opaque media using ultrafast photoacoustics.

We present a high-resolution microscope capable of imaging buried structures through optically opaque materials with micrometer transverse resolution and a nanometer-scale depth sensitivity. The ability to image through such materials is made possible by the use of laser ultrasonic techniques, where an ultrafast laser pulse launches acoustic waves inside an opaque layer and subsequent acoustic echoes from buried interfaces are detected optically by a time-delayed probe pulse. We show that the high frequency of the generated ultrasound waves enables imaging with a transverse resolution only limited by the optical detection system. We present the imaging system and signal analysis and demonstrate its imaging capability on complex microstructured objects through 200 nm thick metal layers and gratings through 500 nm thickness. Furthermore, we characterize the obtained imaging performance, achieving a diffraction-limited transverse resolution of 1.2 µm and a depth sensitivity better than 10 nm.

Role of scattering by surface roughness in the photoacoustic detection of hidden micro-structures.

We present an experimental study in which we compare two different pump-probe setups to generate and detect high-frequency laser-induced ultrasound for the detection of gratings buried underneath optically opaque metal layers. One system is built around a high-fluence, low-repetition-rate femtosecond laser (1 kHz) and the other around a low-fluence, high-repetition-rate femtosecond laser (5.1 MHz). We find that the signal diffracted by the acoustic replica of the grating as a function of pump-probe time delay is very different for the two setups used. We attribute this difference to the presence of a constant background field due to optical scattering by interface roughness. In the low-fluence setup, the optical field diffracted by the acoustic replica is significantly weaker than the background optical field, with which it can destructively or constructively interfere. For the right phase difference between the optical fields, this can lead to a significant "amplification" of the weak field diffracted off the grating-shaped acoustic waves. For the high-fluence system, the situation is reversed because the field diffracted off the acoustic-wave-induced grating is significantly larger than the background optical field. Our measurements show that optical scattering by interface roughness must be taken into account to properly explain experiments on laser-induced ultrasound performed with high-repetition-rate laser systems and can be used to enhance signal strength.

Optimal Control of Shigellosis with Cost-Effective Strategies.

In this paper, we apply optimal control theory to the model for shigellosis. It is assumed that education campaign, sanitation, and treatment are the main controls for this disease. The aim is to minimize the number of infections resulting from contact with careers, infectious population, and contaminated environments while keeping the cost of associated controls minimum. We achieve this aim through the application of Pontryagin's Maximum Principle. Numerical simulations are carried out by using both forward and backward in time fourth-order Runge-Kutta schemes. We simulate the model under different strategies to investigate which option could yield the best results. The findings show that the strategy combining all three control efforts (treatment, sanitation, and education campaign) proves to be more beneficial in containing shigellosis than the rest. On the other hand, cost-effectiveness analysis is performed via incremental cost-effectiveness ratio (ICER). The findings from the ICER show that a strategy incorporating all three controls (treatment, sanitation, and education campaign) is the most cost-effective of all strategies considered in the study.

Laser-induced ultrasonics for detection of low-amplitude grating through metal layers with finite roughness.

We report on the use of laser-induced ultrasonics for the detection of gratings with amplitudes as small as 0.5 nm, buried underneath an optically opaque nickel layer. In our experiments, we use gratings fabricated on top of a nickel layer on glass, and we optically pump and probe the sample from the glass side. The diffraction of the probe pulse from the acoustic echo from the buried grating is measured as a function of time. We use a numerical model to show how the various physical phenomena such as interface displacement, strain-optic effects, thermo-optic effects, and surface roughness influence the shape and strength of the time-dependent diffraction signal. More importantly, we use a Rayleigh-Rice scattering theory to quantify the amount of light scattering, which is then used as in input parameter in our numerical model to predict the time-dependent diffracted signal.