Droplet sizing in atomizing sprays using polarization ratio with structured laser illumination planar imaging.

Previous research has shown that the polarization ratio technique allows the characterization of the surface mean diameter, D21, of droplets forming dilute sprays. However, its application to optically dense sprays has posed significant challenges due to the presence of multiple light scattering. Additionally, errors in measurement can arise from the angular dependence of the signal. In this Letter, we present a novel, to the best of our knowledge, method that addresses these challenges. Our approach combines the use of a telecentric objective with structured laser illumination, to both optimize light detection and suppress the unwanted intensity from multiple scattering. This approach enables the utilization of the polarization ratio technique for measuring the droplet size of challenging atomizing sprays. The method offers a promising solution for accurate and comprehensive spray characterization. It is applied, here, to a hollow-cone water spray running at 30, 50, and 70 bar injection pressure, reaching an optical depth up to three.

Comparison of landing kinematics and kinetics between experienced and novice volleyball players during block and spike jumps.

BACKGROUND: The practice of volleyball requires many jumps. During landing, anterior cruciate ligament injuries may occur with high-risk lower limb kinematics and kinetics. Differences in landing strategies between experienced and novice volleyball players have not been fully explored. The purpose of the study was to compare lower limb kinematics and kinetics in experienced and novice volleyball players when performing volleyball specific jumps. METHODS: A total of 30 healthy males, 15 experienced and 15 novice volleyball players, participated in the study. Participants performed block and spike jumps at a controlled jump height. Hip, knee and ankle joints angles at initial ground contact and ranges of motion in the sagittal plane, knee joint angles and moments in the frontal plane, vertical ground reaction force peak and loading rate were analyzed to investigate the expertise effect. RESULTS: Experienced volleyball players landed with larger ankle dorsiflexion range of motion compared to novices. For the spike jump, experienced players landed with larger ankle plantarflexion angles at initial contact and larger ankle dorsiflexion ranges of motion, and for the block jump, they landed with larger knee flexion ranges of motion. Experienced players jumped significantly higher than novices. No difference was found in vertical ground reaction force peaks and loading rates. CONCLUSIONS: Although the experienced group jumped higher than the novice group, no difference was found in ground reaction force parameters. These findings highlight that the experience of volleyball players acquired during regular trainings and competitions may play an important role in landing kinematics and kinetics to reduce the injury risk.

Overlapping two standing waves in a microcavity for a multi-atom photon interface.

We develop a light-matter interface enabling strong and uniform coupling between a chain of cold atoms and photons of an optical cavity. This interface is a fiber Fabry-Perot cavity, doubly resonant for both the wavelength of the atomic transition and for a geometrically commensurate red-detuned intracavity trapping lattice. Fulfilling the condition of a strong and uniform atom-photon coupling requires optimization of the spatial overlap between the two standing waves in the cavity. In a strong-coupling cavity, where the mode waists and Rayleigh range are small, we derive the expression of the optimal trapping wavelength, taking into account the Gouy phase. The main parameter controlling the overlap of the standing waves is the relative phase shift at the reflection on the cavity mirrors between the two wavelengths, for which we derive the optimal value. We have built a microcavity optimized according to these results, employing custom-made mirrors with engineered reflection phase for both wavelengths. We present a method to measure with high precision the relative phase shift at reflection, which allows us to determine the spatial overlap of the two modes in this cavity.

Mapping optical standing-waves of an open-access Fabry-Perot cavity with a tapered fiber.

We describe a method to map the standing-wave pattern inside an open-access Fabry-Perot optical cavity with sub-wavelength resolution by perturbing it with a commercially available tapered fiber. The method is applied to a fiber Fabry-Perot microcavity. We demonstrate its use in determining the relative position of the antinodes at two different wavelengths. In addition, we use the tapered optical fiber as a point-like source, allowing precise positioning of a microscope objective with respect to the cavity mode.

Manipulating cold atoms through a high-resolution compact system based on a multimode fiber.

We show that a standard multimode optical fiber can act as a high-resolution ultra-compact tool to manipulate cold atoms in setups with limited optical access. Spatial light modulators allow us to generate control beams at the in-vacuum fiber end by digital optical phase conjugation. With no additional in-vacuum optics, this system reaches a $ \sim 1\;{\unicode{x00B5}{\rm m}} $∼1µm resolution for a transverse size of only 225 µm. As a demonstration, we use it to optically transport cold atoms towards the in-vacuum fiber end, to load them in optical microtraps, and to re-cool them in optical molasses. This work shows that the rapid progress of optics in complex media opens new, to the best of our knowledge, perspectives for spatially constrained quantum technology platforms combining cold atoms with other optical, electronic, or opto-mechanical systems.

Epidemiological factors and mitigation measures influencing production losses in cattle due to bovine viral diarrhoea virus infection: A meta-analysis.

Infection with bovine viral diarrhoea virus (BVDV) is associated with a loss in productivity in cattle farms. Determining which factors influence monetary losses due to BVDV could facilitate the implementation of mitigation measures to reduce the burden of BVDV. Mixed-effect meta-analysis models were performed to estimate the extent to which the costs of mean annual BVDV production losses per animal may be influenced by epidemiological factors such as BVDV introduction risk, initial prevalence, viral circulation intensity and circulation duration (trial 1). Additionally, changes in mean annual BVDV production losses per animal due to specific mitigation measures (i.e., biosecurity, vaccination, testing and culling, cattle introduction or contact with neighbouring cattle herds) were analysed (trial 2). In total, 19 studies were included in the meta-analysis to assess mean annual BVDV production losses. The mean annual direct losses were determined to be €42.14 per animal (trial 1). The multivariate meta-regression showed that four of the previously mentioned epidemiological factors significantly influenced the mean annual BVDV production losses per animal. Indeed, the per animal costs increased to €67.19 when these four factors (trial 1) were considered as "high or moderate" compared to "low". The meta-regression analysis revealed that implementation of vaccination and biosecurity measures were associated with an 8%-12% and 28%-29% decrease in BVDV production losses on average, respectively, when simulated herds were compared with or without such mitigation measures (trial 2). This reduction of mean annual BVDV production losses per animal due to mitigation measures was partially counteracted when farmers brought new cattle on to farm or allowed contact with neighbouring cattle herds. The influencing mitigation factors presented here could help to guide farmers in their decision to implement mitigation strategies for the control of BVDV at farm level.

Dual-wavelength fiber Fabry-Perot cavities with engineered birefringence.

We present a method to engineer the frequency splitting of polarization eigenmodes in fiber Fabry-Perot (FFP) cavities. Using specific patterns of multiple CO2 laser pulses, we machine paraboloidal micromirrors with controlled elliptical shape in a large range of radii of curvature. This method is versatile and can be used to produce cavities with maximized or near-zero polarization mode splitting. In addition, we realize dual-wavelength FFP cavities with finesse exceeding 40 000 at 780 nm and at 1559 nm in the telecom range. We provide direct evidence that the birefringent frequency splitting in FFP cavities is governed only by the geometrical shape of the mirrors, and that the astigmatism of the cavity modes needs to be taken into account for specific cavities.

Millimeter-long fiber Fabry-Perot cavities.

We demonstrate fiber Fabry-Perot (FFP) cavities with concave mirrors that can be operated at cavity lengths as large as 1.5 mm without significant deterioration of the finesse. This is achieved by using a laser dot machining technique to shape spherical mirrors with ultralow roughness and employing single-mode fibers with large mode area for good mode matching to the cavity. Additionally, in contrast to previous FFPs, these cavities can be used over an octave-spanning frequency range with adequate coatings. We also show directly that shape deviations caused by the fiber's index profile lead to a finesse decrease as observed in earlier attempts to build long FFP cavities, and show a way to overcome this problem.