Direct numerical simulations of spatially developing high-enthalpy hypersonic turbulent boundary layers are performed under non-catalytic wall-cooling conditions. Two distinct levels of chemical reactivity are considered, together with a chemically frozen case for reference. The main objective is to elucidate the underlying mechanisms of high-enthalpy turbulence–chemistry interactions and to develop reliable closure models for high-enthalpy hypersonic turbulent boundary layers. It is well established that high-enthalpy reactions have a negligible influence on the turbulent velocity statistics, and it is further shown here that this behaviour arises from the compensating effects. Specifically, the mean temperature is reduced by endothermic reactions, accompanied by a decrease in mixture molar mass, leading to an approximately unchanged mean density. Furthermore, the chemical time scale is found to be much larger than the large-eddy turnover time, resulting in strong linear correlations between the temperature and species mass fraction fluctuations. Consequently, the refined strong Reynolds analogy (RSRA) can be effectively extended from enthalpy to temperature and species mass fraction fluctuations in high-enthalpy hypersonic turbulent boundary layers. A correlation correction for RSRA is proposed, which corrects the breakdown of the original RSRA in the region near the mean temperature peak, while retaining good performance in the outer layer. An isobaric presumed probability density function model incorporating the correlation-corrected RSRA is further developed, which extends the applicability of the temperature-based presumed probability density function approach to stronger high-enthalpy conditions. This work contributes to the development of engineering models for turbulence–chemistry interactions in high-enthalpy hypersonic turbulent boundary layers.

Comprehension of wh-questions often poses challenges for children with autism spectrum disorder (ASD) in wh-movement languages like English. However, it remains unclear whether wh-in situ languages like Mandarin present similar difficulties. Moreover, the present study explores potential differences in comprehension between Mandarin subject and object wh-questions. We hypothesize a subject wh-question advantage, given that Mandarin object wh-questions exhibit a longer dependency than subject wh-questions. If confirmed, it would support that Mandarin wh-questions involve covert movement. Using eye-movement measures of the intermodal preferential looking (IPL) paradigm, this study investigates the comprehension of matrix subject and object wh-questions in Mandarin-speaking children with ASD (N = 35, mean age = 60.94 months) compared to their typically developing (TD) peers (N = 38, mean age = 29.66 months), matched on expressive vocabulary levels. The results showed that children in the TD group comprehended both subject and object wh-questions. However, in the ASD group, children comprehended only subject wh-questions. Overall, Mandarin-speaking children with ASD exhibited weaker comprehension of wh-questions than their TD counterparts, with particular difficulty processing object wh-questions. The subject-over-object advantage in wh-questions among Mandarin-speaking children with ASD suggests that they were sensitive to the longer dependency involved in object wh-questions. These findings support the involvement of covert movement in Mandarin wh-questions.

The utilization of carbon dioxide (CO2) has garnered significant attention as a strategy to mitigate anthropogenic emissions. Within this field, the conversion processes of CO2 through photocatalytic systems have emerged as a particularly noteworthy area of research. This approach leverages solar energy for the reaction and is considered a promising and environmentally friendly alternative to traditional thermally driven catalytic systems. This article aims to summarize recent advancements in several key photo-conversion pathways, including the synthesis of methane, methanol, C2 hydrocarbons, dimethyl carbonate, and glycerol carbonate. Additionally, potential configurations for the development of processes aimed at producing various chemicals will be proposed. Current insights indicate that the photocatalytic conversion of CO2 could be effectively integrated with chemical absorption methods, provided that appropriate separation and process intensification strategies are developed. From an economic perspective, the photocatalytic reduction of CO2 minimizes the reliance on green hydrogen as a hydrogen source, thereby significantly improving overall economic viability. Environmentally, it is essential to enhance the reaction conversion and product selectivity of the photocatalytic conversion processes to maximize their decarbonization potential. Overall, this paper is particularly suited for readers who are new to this field and are interested in transitioning from experimental work to process development.

In compressible turbulent boundary layers (CTBLs), the strong Reynolds analogy (SRA) refers to a set of quantitative relationships between temperature and velocity fluctuations. The essence of the SRA is the linear relationship between these fluctuations in large-scale motions. We investigate the transport processes of the second-order statistical moments associated with temperature and velocity fluctuations to reveal the physical mechanisms underlying this linear correlation. An important finding is that there exists a strong linear mechanism between the turbulent production of velocity and temperature fluctuations. Nonlinear mechanisms, such as the viscous-thermal dissipation, the work contribution, and particularly the pressure term, lead to the failure of the existing SRAs in the outer layer. Based on the above findings, a refined SRA (RSRA) is proposed, which better describes the quantitative relation between the temperature and velocity fluctuation intensities. An approximate expression for the turbulent Prandtl number under different Mach numbers and wall-cooling conditions is derived with the newly proposed RSRA. The relations proposed in this paper are validated through the direct numerical simulation data of flat-plate zero-pressure-gradient CTBLs at different Mach numbers and wall temperatures.

We undertake a comprehensive investigation into the distribution of in situ stars within Milky Way-like galaxies, leveraging TNG50 simulations and comparing their predictions with data from the H3 survey. Our analysis reveals that 28% of galaxies demonstrate reasonable agreement with H3, while only 12% exhibit excellent alignment in their profiles, regardless of the specific spatial cut employed to define in situ stars. To uncover the underlying factors contributing to deviations between TNG50 and H3 distributions, we scrutinise correlation coefficients among internal drivers (e.g. virial radius, star formation rate [SFR]) and merger-related parameters (such as the effective mass-ratio, mean distance, average redshift, total number of mergers, average spin-ratio, and maximum spin alignment between merging galaxies). Notably, we identify significant correlations between deviations from observational data and key parameters such as the median slope of virial radius, mean SFR values, and the rate of SFR change across different redshift scans. Furthermore, positive correlations emerge between deviations from observational data and parameters related to galaxy mergers. We validate these correlations using the Random Forest Regression method. Our findings underscore the invaluable insights provided by the H3 survey in unravelling the cosmic history of galaxies akin to the Milky Way, thereby advancing our understanding of galactic evolution and shedding light on the formation and evolution of Milky Way-like galaxies in cosmological simulations.

Turbulent emulsions are ubiquitous in chemical engineering, food processing, pharmaceuticals and other fields. However, our experimental understanding of this area remains limited due to the multiscale nature of turbulent flow and the presence of extensive interfaces, which pose significant challenges to optical measurements. In this study, we address these challenges by precisely matching the refractive indices of the continuous and dispersed phases, enabling us to measure local velocity information at high volume fractions. The emulsion is generated in a turbulent Taylor–Couette flow, with velocity measured at two radial locations: near the inner cylinder (boundary layer) and in the middle gap (bulk region). Near the inner cylinder, the presence of droplets suppresses the emission of angular velocity plumes, which reduces the mean azimuthal velocity and its root mean squared fluctuation. The former effect leads to a higher angular velocity gradient in the boundary layer, resulting in greater global drag on the system. In the bulk region, although droplets suppress turbulence fluctuations, they enhance the cross-correlation between azimuthal and radial velocities, leaving the angular velocity flux contributed by the turbulent flow nearly unchanged. In both locations, droplets suppress turbulence at scales larger than the average droplet diameter and increase the intermittency of velocity increments. However, the effects of the droplets are more pronounced near the inner cylinder than in the bulk, likely because droplets fragment in the boundary layer but are less prone to break up in the bulk. Our study provides experimental insights into how dispersed droplets modulate global drag, coherent structures and the multiscale characteristics of turbulent flow.

Kawasaki disease is a leading cause of acquired heart disease in children in the developed world, characterised by acute systemic vasculitis, with a complex aetiology that remains poorly understood. Recent studies have highlighted the potential anti-inflammatory effects of Interleukin-35 in various proinflammatory and cardiovascular conditions. However, the relationship between Interleukin-35 gene polymorphisms and Kawasaki disease susceptibility, particularly in Chinese children, has not been well-explored.

In this study, we investigated the association between five Interleukin-35 single-nucleotide polymorphisms—rs2243115, rs2243123, rs583911, rs353698, and rs2302164—and Kawasaki disease in a cohort of Chinese children. A total of ninety-four Kawasaki disease patients and one hundred healthy controls were enrolled, with the Kawasaki disease patients further divided into subgroups based on the presence or absence of coronary artery lesions and incomplete or complete Kawasaki disease. Genotyping of Interleukin-35 polymorphisms was performed using the MassARRAY system.

The results showed the GT + GG genotypes and G allele of rs2243115 (T > G) were significantly more prevalent in Kawasaki disease patients with coronary artery lesions than in those without coronary artery lesions, suggesting a possible association with the development of coronary artery lesions. Additionally, the G allele of rs353698 (A > G) was more frequently observed in the incomplete Kawasaki disease group compared to the complete Kawasaki disease group, suggesting a possible association with the risk of incomplete Kawasaki disease.

We present an experimental study on the drag reduction by polymers in Taylor–Couette turbulence at Reynolds numbers ($Re$) ranging from $4\times 10^3$ to $2.5\times 10^4$. In this $Re$ regime, the Taylor vortex is present and accounts for more than 50 % of the total angular velocity flux. Polyacrylamide polymers with two different average molecular weights are used. It is found that the drag reduction rate increases with polymer concentration and approaches the maximum drag reduction (MDR) limit. At MDR, the friction factor follows the $-0.58$ scaling, i.e. $C_f \sim Re^{-0.58}$, similar to channel/pipe flows. However, the drag reduction rate is about $20\,\%$ at MDR, which is much lower than that in channel/pipe flows at comparable $Re$. We also find that the Reynolds shear stress does not vanish and the slope of the mean azimuthal velocity profile in the logarithmic layer remains unchanged at MDR. These behaviours are reminiscent of the low drag reduction regime reported in channel flow (Warholic et al., Exp. Fluids, vol. 27, no. 5, 1999, pp. 461–472). We reveal that the lower drag reduction rate originates from the fact that polymers strongly suppress the turbulent flow while only slightly weaken the mean Taylor vortex. We further show that polymers steady the velocity boundary layer and suppress the small-scale Görtler vortices in the near-wall region. The former effect reduces the emission rate of both intense fast and slow plumes detached from the boundary layer, resulting in less flux transport from the inner cylinder to the outer one and reduces energy input into the bulk turbulent flow. Our results suggest that in turbulent flows, where secondary flow structures are statistically persistent and dominate the global transport properties of the system, the drag reduction efficiency of polymer additives is significantly diminished.

The presence of dispersed-phase droplets can result in a notable increase in a system's drag. However, our understanding of the mechanism underlying this phenomenon remains limited. In this study, we use three-dimensional direct numerical simulations with a modified multi-marker volume-of-fluid method to investigate liquid–liquid two-phase turbulence in a Taylor–Couette geometry. The dispersed phase has the same density and viscosity as the continuous phase. The Reynolds number $Re\equiv r_i\omega _i d/\nu$ is fixed at 5200, the volume fraction of the dispersed phase is up to $40\,\%$, and the Weber number $We\equiv \rho u^2_\tau d/\sigma$ is approximately 8. It is found that the increase in the system's drag originates from the contribution of interfacial tension. Specifically, droplets experience significant deformation and stretching in the streamwise direction due to shear near the inner cylinder. Consequently, the rear end of the droplets lags behind the fore head. This causes opposing interfacial tension effects on the fore head and rear end of the droplets. For the fore head of the droplets, the effect of interfacial tension appears to act against the flow direction. For the rear end, the effect appears to act in the flow direction. The increase in the system's drag is attributed primarily to the effect of interfacial tension on the fore head of the droplets which leads to the hindering effect of the droplets on the surrounding continuous phase. This hindering effect disrupts the formation of high-speed streaks, favouring the formation of low-speed ones, which are generally associated with higher viscous stress and drag of the system. This study provides new insights into the mechanism of drag enhancement reported in our previous experiments.

We investigate the coupling effects of the two-phase interface, viscosity ratio and density ratio of the dispersed phase to the continuous phase on the flow statistics in two-phase Taylor–Couette turbulence at a system Reynolds number of $6\times 10^3$ and a system Weber number of 10 using interface-resolved three-dimensional direct numerical simulations with the volume-of-fluid method. Our study focuses on four different scenarios: neutral droplets, low-viscosity droplets, light droplets and low-viscosity light droplets. We find that neutral droplets and low-viscosity droplets primarily contribute to drag enhancement through the two-phase interface, whereas light droplets reduce the system's drag by explicitly reducing Reynolds stress due to the density dependence of Reynolds stress. In addition, low-viscosity light droplets contribute to greater drag reduction by further reducing momentum transport near the inner cylinder and implicitly reducing Reynolds stress. While interfacial tension enhances turbulent kinetic energy (TKE) transport, drag enhancement is not strongly correlated with TKE transport for both neutral droplets and low-viscosity droplets. Light droplets primarily reduce the production term by diminishing Reynolds stress, whereas the density contrast between the phases boosts TKE transport near the inner wall. Therefore, the reduction in the dissipation rate is predominantly attributed to decreased turbulence production, causing drag reduction. For low-viscosity light droplets, the production term diminishes further, primarily due to their greater reduction in Reynolds stress, while reduced viscosity weakens the density difference's contribution to TKE transport near the inner cylinder, resulting in a more pronounced reduction in the dissipation rate and consequently stronger drag reduction. Our findings provide new insights into the physics of turbulence modulation by the dispersed phase in two-phase turbulence systems.

The presence of a dispersed phase can significantly modulate the drag in turbulent systems. We derived a conserved quantity that characterizes the radial transport of azimuthal momentum in the fluid–fluid two-phase Taylor–Couette turbulence. This quantity consists of contributions from advection, diffusion and two-phase interface, which are closely related to density, viscosity and interfacial tension, respectively. We found from interface-resolved direct numerical simulations that the presence of the two-phase interface consistently produces a positive contribution to the momentum transport and leads to drag enhancement, while decreasing the density and viscosity ratios of the dispersed phase to the continuous phase reduces the contribution of local advection and diffusion terms to the momentum transport, respectively, resulting in drag reduction. Therefore, we concluded that the decreased density ratio and the decreased viscosity ratio work together to compete with the presence of a two-phase interface for achieving drag modulation in fluid–fluid two-phase turbulence.