Geometrically-controlled polarisation processing in an integrated photonic platform

The polarisation of light is a powerful and widely used degree of freedom to encode information, both in classical and quantum applications. In particular, quantum information technologies based on photons are being revolutionised by the use of integrated photonic circuits. It is therefore very important to be able to manipulate the polarisation of photons in such circuits. We experimentally demonstrate the fabrication by femtosecond laser micromachining of components such as polarisation insensitive or polarising directional couplers, operating at 1550 nm wavelength, where the two opposite behaviours are achieved just by controlling the geometric layout of the photonic circuits, being the waveguides fabricated with the same irradiation recipe. We expect to employ this approach in complex integrated photonic devices, capable of a full control of the photons polarisation for quantum cryptography, quantum computation and quantum teleportation experiments.Comment: 9 pages, 7 figure

Dynamic Stall on Pitching Cambered Airfoil with Phase Offset Trailing Edge Flap

Dynamic stall on wind turbine blades often leads to severe fatigue that tends to decrease the lifespan of the blades. To mitigate cyclic loading on the blades, trailing edge flaps (TEF) may be used to control the energy captured by the blades. In this study the influence of a TEF on a pitching S833 cambered airfoil is investigated at a Reynolds number of 170,000 and reduced frequencies of k = 0.06 and 0.1. The lift and moment hysteresis cycles are presented for mean pitch angles of 0 deg and 10 deg to represent stall onset and deep stall. The flap, hinged at 0.8 chord, is pitching with different phase lags to study the influence of flap motion. Coefficient of pressure contour plots presented here, clearly indicate the leading edge vortex (LEV) formation and convection. It is concluded that even though the TEF was not capable of controlling the formation of the LEV, it was however capable of reducing the LEV magnitude and more importantly, a reduction in cyclic loading. It is recommended to dynamically pitch the flap out-of-phase with the airfoil motion to reduce the min/max of the lift and moment cycles and reduce negative damping that can lead to stall flutter

Deep Dynamic Stall and Active Aerodynamic Modification on a S833 Airfoil using Pitching Trailing Edge Flap

Natural Sciences and Engineering Research Council of CanadaDue to the dynamic nature of the wind resource, wind turbine blades are subjected to significant variation in flow parameters such as angle of attack. In some cases, the occurrence of dynamic stall on wind turbine blades causes load fluctuation which leads to material fatigue that tend to decrease the lifespan of the blades. In this study, the influence of a trailing edge flap (TEF) on dynamic stall effects is investigated at high angle of attack typical of wind turbines but atypical elsewhere. Pitching of the TEF was found to have a significant impact on the dynamic stall hysteresis loops responsible for the load fluctuation. Frequency analysis showed that the TEF was capable of reducing the cyclic fluctuation in the coefficient of lift and root bending moment by at least 26% and 24% respectively. These results are a significant contribution towards understanding the advantages of using TEFs and how implementing them will reduce wind turbine blade load fluctuations

Entanglement swapping between independent and asynchronous integrated photon-pair sources

Integrated photonics represents a technology that could greatly improve quantum communication networks in terms of cost, size, scaling, and robustness. A key benchmark for this is to demonstrate their performance in complex quantum networking protocols, such as entanglement swapping between independent photon-pair sources. Here, using time-resolved detection, and two independent and integrated Si$_3$N$_4$ microring resonator photon-pair sources, operating in the CW regime at telecom wavelengths, we obtained spectral purities up to $0.97 \pm 0.02$ and a HOM interference visibility between the two sources of $V_{\rm HOM}=93.2 \pm 1.6\,\%$. This results in entanglement swapping visibility as high as $91.2 \pm 3.4\,\%

Heralded distribution of single-photon path entanglement

We report the experimental realization of heralded distribution of single-photon path entanglement at telecommunication wavelengths in a repeater-like architecture. The entanglement is established upon detection of a single photon, originating from one of two spontaneous parametric down conversion photon pair sources, after erasing the photon's which-path information. In order to certify the entanglement, we use an entanglement witness which does not rely on post-selection. We herald entanglement between two locations, separated by a total distance of 2 km of optical fiber, at a rate of 1.6 kHz. This work paves the way towards high-rate and practical quantum repeater architectures.Comment: 5+9 pages, 7 figure

Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

Background Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI <18·5 kg/m2) and obesity (BMI ≥30 kg/m2). For schoolaged children and adolescents, we report thinness (BMI <2 SD below the median of the WHO growth reference) and obesity (BMI >2 SD above the median). Findings From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining underweight or thinness. Interpretation The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesit

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Integrated Si3N4 Microring Resonator: A Photon-Pair Source for Quantum Communication

Integrated photonics is emerging as a key technology for use in quantum information and communication. Driven by classical communication, which already has a swathe of scalable, efficient, and robust components, integrated photonics promises to transfer quantum science from a mere lab curiosity into a commercial reality. Chip-based quantum light sources are increasingly being recognized as a practical and high-performance alternative to bulky and power-hungry, table-top photon-pair sources. In particular, photon-pair sources based on spontaneous four-wave mixing in microring resonators (MRR) have emerged as a viable integrated photonic solution for quantum information and communication. This thesis relies on silicon nitride (Si3N4) MRR to realize narrowband, telecom photonpair sources. High quality factor MRRs are enabled by the low propagation losses in the Si3N4 platform; in this thesis, they are exploited to realize bright photon-pair sources with heralded spectral purity up to 0.98. Low quality factor MRRs are exploited for a proof-of-concept high-rate sequential time-bin entanglement with net visibilities up to 99.96 ± 0.03 %. For the goal of practical, real-world deployment of integrated photon-pair sources, it is not enough to demonstrate the performance of a single source. One also needs to demonstrate their high-performance operation in complex quantum networking protocols, such as entanglement swapping between genuinely independent sources. Here, for the first time, we demonstrate entanglement swapping between two independent, spatially separated, and asynchronously-pumped MRR photon-pair sources. Our sources operate in the continuous-wave regime, and time-resolved detection results in high Hong-Ou-Mandel (93.2 ±1.6 %) and entanglement swapping (91.2 ± 3.4 %) visibilities. Finally, to further improve our rates while maintaining high visibilities in multi-source interference scenarios, the origin of an on-chip-generated noise must be identified and mitigated. Here, we present our first efforts in the quest for tackling this notorious noise problem

Active Aerodynamic Modification of Wind Turbine Blades to Reduce Load Fluctuation

Wind turbines operate predominantly in relatively unsteady flow conditions and are typically misaligned with the incoming wind. Moreover, as wind turbines increase in size, the loading on the blades becomes more problematic and obstructs the development of larger and more efficient wind turbines. In this project, a trailing edge flap (TEF) is used to develop an active control strategy to attenuate load fluctuation on the blades in normal environmental conditions. Wind turbine load fluctuation reduction techniques could increase the power produced by the turbine, reduce the capital and maintenance cost while prolonging the life span of not just the blades but the drivetrain and tower. An experimental 3.5 m diameter wind turbine rig was designed and tested in a large scale wind generation facility operating at different tip speed ratios, blade pitch angles and yaw angles. The instrumentation of the compact blade was capable of measuring rotor torque, flapwise/edgewise blade root bending moment, and normal force coefficient at r/R=0.66 and 0.82. Two custom-built actuation systems were capable of oscillating the pitch and flap independently to create an active control strategy. The blade is of constant pitch and chord of 178 mm while the TEF covers 20% of the chord and 22% of the 1.47 m aerodynamic blade span. First, a 2D experimental campaign showed how the TEF is fully capable of controlling the airfoil aerodynamics statically and during dynamic stall. It is concluded that even though the TEF was not capable of controlling the formation of the leading edge vortex (LEV), it was however capable of reducing its magnitude and more importantly, a reduction in cyclic loading. Second, a comprehensive and a detailed set of results showed how the rotor torque, flapwise/edgewise blade root bending moment, and normal force coefficient at multiple r/R locations change under different yaw angles, pitch angles, tip speed ratio and TEF angles. When possible the results were compared to numerical models such as the NREL OpenFast code to increase confidence in the results and provide essential conclusions to improve the models. It was found that in non-yawed conditions, OpenFast predictions were accurate but discrepancies start to emerge when the turbine is yawed and operating in dynamic stall conditions. Finally, the pitch and TEF were continuously actuated in separate tests to determine the effectiveness of each system at reducing load fluctuation on a yawed wind turbine. The reduction in load fluctuation due to the TEF and the pitch systems were found to be between 45%-65% and 65%-80% respectively. The data presented throughout this thesis provides a methodical and comprehensive argument to support the use of TEF on a utility-scale turbines to reduce load fluctuation and fatigue levels at the blade root. It also provides insight on the effects of dynamic stall, stall delay and 3D flow induced by the blade rotation on an operating wind turbine