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The present work focuses on enhancing thermo-acoustics energy conversion performance and nonlinear dynamics of heat-driven acoustics oscillations in standing-wave thermoacoustic engines (SWTAE) in the presence of externally forcing perturbations. Such perturbations could be applied in either pressure or velocity fluctuations. 2D numerical SWTAE models are developed and validated, and then applied to examine the effects of 1) the forcing perturbation frequencies, 2) its amplitudes, and 3) the inlet diameter of applying such perturbations on heat-driven acoustics behavior. Our results show that pressure perturbations attenuate heat-driven acoustic limit cycles, while forcing velocity perturbations at a specific frequency range can enhance the thermo-acoustics conversion in the SWTAEs. Our results also show that frequency lock-in is observed, when the ratio of the forcing velocity perturbations' energy to the self-excited acoustical energy is ranged from 0.11 to 0.66. Furthermore, Hopf supercritical bifurcations are observed, resulting in transitions from steady state to quasi-periodic and limit cycle oscillations. As the forcing perturbation frequency is approaching to that of the self-excited heat-driven acoustic oscillations (i.e. the ratio of the forcing frequency to that of self-excited oscillations is ranged from 0.89 to 1.11), apparent improvements are observed on the output heat-driven acoustic power and thermo-acoustic energy conversion efficiency, especially when the two frequencies are coincided (i.e. ∼180 Hz). Increasing the forcing perturbation's energy or enlarging the inlet diameter of applying such perturbations further enhances these improvements. Overall, the developed numerical model may serve as a valuable tool for predicting the heat-driven acoustic power output from a SWTAE in the presence of externally forcing perturbations. • The 2D/3D TAE numerical model with externally forcing periodic oscillations is established. • Inlet diameter of applying perturbations linearly impacts heat-driven acoustic performances. • Forcing velocity at a specific frequency range enhances TAE's thermo-acoustics conversion. • Varying forcing velocities triggers bifurcations and mode transitions in TAE's oscillations. • Thermal efficiency improves at forcing frequency close to TAE's natural frequency. [ABSTRACT FROM AUTHOR]

Polyurea (PU) elastomers have become increasingly popular in recent years due to their exceptional blast mitigation, ballistic protection, and wear resistance properties. However, their applications as protective materials are often limited as a result of their high flammability. In this study, aromatic dianhydrides (ArDAs) were employed to capture the thermal decomposing products of PU during combustion and facilitate the generation of highly heat-resistant aromatic polyimides (i.e., end group capturing effect), thus enhancing the material's char-forming ability and improving its flame retardancy. The ArDAs were found to significantly reduce the peak heat release rate (PHRR), total heat release (THR), total smoke release (TSR), and total CO release (TCO) of PU, and meanwhile increased the amount of char residue. At 20 wt% content of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), PHRR, THR, TSR and TCO of PU were reduced by 70.6%, 32.5%, 44.7% and 58.8%, respectively, the char residue was increased by 405%, and the mechanical properties of PU were well maintained (88.5% tensile strength and 91.0% elongation at break of pure PU). These findings demonstrate that ArDAs could serve as a new kind of halogen/phosphorus-free flame retardant for PU elastomers. [Display omitted] • Novel halogen/phosphorus-free flame retardants were designed for PU elastomers. • The flame retardant mechanism is end group capturing by aromatic dianhydrides (ArDAs). • PHRR, THR, TSR and TCO were simultaneously reduced, and char residue was improved. • Both excellent flame retardant property and high mechanical property were achieved. [ABSTRACT FROM AUTHOR]

The study presented in this paper aims to simulate a standing-wave thermoacoustic engine (SWTAE) system by capturing its nonlinear thermoacoustic features with three-dimensional (3D) unsteady Reynolds-Averaged Navier-Stokes (URANS) and hybrid URANS/LES (Large Eddy Simulation) models such as Detached-Eddy Simulations (DES) and Stress-blended Eddy Simulation (SBES) models. For comparison, LES is also conducted as a reference case to examine the turbulence model effect on capturing the nonlinear features of heat-driven acoustics in the SWTAE system. The 3D model is validated against numerical results available in the literature, along with mesh- and time-independence studies. The comparison studies show that the computation time required for modeling SWTAE using SBES and DES is 28.4% and 36.5% less than LES, respectively. It is also shown that the prediction of the acoustic power of SWTAE using URANS is about 21.0% lower than that using LES, while the results from SBES and DES are in relatively good agreement with LES. Comparative studies of nonlinear hydrodynamics in the flow fields show that the results from SBES are closer to LES than DES, which can be attributed to the SBES model providing a faster transition to an explicit LES model outside the wall boundary layer. Furthermore, the heat transfer characteristics are compared by analyzing heat leaks and transversal heat flux, and it is found that the URANS model overestimates the heat transfer characteristics, while the results of the other three models are smaller than those obtained by URANS. In conclusion, the SBES model has great potential to be applied in simulating thermoacoustic nonlinear and flow behaviors of SWTAEs. It has the attractive features of delivering relatively accurate predictions and a significant reduction in computational times and costs compared to LES. • 4 numerical models of the 3D standing-wave thermoacoustic engine (TAE) are developed and compared. • Unsteady heat-fluid interaction and nonlinear acoustic behaviors are examined in details. • The popular low-cost unsteady RANS model over-estimated the heat transfer characteristics. • Mass streaming characterizing complex transport phenomena in thermoacoustics is well captured. • SBES model has great potential to capture heat-to-sound energy conversion in thermoacoustic engines. [ABSTRACT FROM AUTHOR]

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccine enables quick upgrade of antigen sequence to combat emerging new variants. In an observer-blinded, randomized, placebo-controlled phase 2 trial, immunologically naïve 300 adults and 150 older participants were enrolled and randomized (1:1:1) to receive two doses of 20 µg or 30 µg of a SARS-CoV-2 mRNA vaccine (SYS6006) or placebo. Adverse events (AEs) were recorded through 30 days after the second dose. Live virus neutralizing antibody (Nab), S1 protein-specific binding antibody (S1-IgG) and cellular immunity were tested. Results showed that robust wild-type Nab response was elicited with geometric mean titers of 91.3 and 84.9 in the adults, and 74.0 and 115.9 in the elders, 14 days following the second dose (Day 35) in the 20-µg and 30-µg groups, respectively. All seroconverted for wild-type Nab except two participants. Nab against Omicron BA.5 was mild. Robust wild-type S1-IgG response was induced with geometric mean concentrations of 2751.0 and 3142.2 BAU/mL in adults, and 2474.1 and 2993.5 BAU/mL in elders at Day 35 in the 20-µg and 30-µg groups, respectively. S1-IgG against Omicron BA.2 was induced. Cellular immunity was elicited, particularly in enzyme-linked immunospot assay. The most frequent AEs were injection-site pain and fever. Most reported AEs were grade 1 or grade 2. The AE incidences were similar following the first dose and second dose. No vaccination-associated serious AE was reported. In conclusion, two-dose vaccination with SYS6006 demonstrated good safety, tolerability and immunogenicity in immunologically naïve healthy participants aged 18 years or more. [ABSTRACT FROM AUTHOR]

Fungal laccases play important roles in matrix degradation. Eleven laccase genes, including three novel ones (designated lac1 , lac2 and lac4 ) were identified after sequencing the entire genome of the edible, white-rot fungus Flammulina velutipes . Analysis using bioinformatics revealed that all of the laccases, except lac3 , possess a signal peptide. These laccase proteins consist of 502–670 amino acids and have predicted molecular weights ranging from 55 kDa to 74 kDa. These proteins each contain four copper-binding sites, except for Lac10. Transcriptomes were sequenced at different developmental stages and in different fruiting body tissues to analyze if there was differential expression of laccase genes. The novel laccase gene lac4 exhibited the highest expression levels among all of the observed laccases at every developmental stage and in all fruiting body tissues examined. We conclude that laccases in F. velutipes play a role not only in lignin degradation, but also in fruiting body formation and development. [ABSTRACT FROM AUTHOR]