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A major challenge is the synergistic regulation of porous carbon materials' dielectric and magnetic loss to produce lightweight and broadband absorption performance. This study used bamboo powders as a carbon source during hydrothermal and pyrolysis processes to create MCeOx/PC (M = Fe, Ni, and Co) composites. The NiCeOx/PC composites demonstrate outstanding microwave absorption (MA) performance with a minimum reflection loss (RLmin) of −58.21 dB at a thickness of 1.9 mm, and an effective absorption bandwidth (EAB) of 4.74 GHz (covering 13.26–18.00 GHz) at a matched thickness of 1.6 mm, which is attributed to the synergistic effect of their excellent impedance matching, dielectric and magnetic loss. Furthermore, the highest radar cross-section (RCS) attenuation of 16.55 dB m2 is achieved by the RCS in comparison to the perfect electric conductor (PEC) plate, suggesting a potential practical use. This work offers a theoretical foundation for the production of carbon-based MA materials obtained from sustainable biomass. [ABSTRACT FROM AUTHOR]

High efficiency thermal insulation materials are highly desirable in aerospace industry, whereas combining low density and low thermal conductivity of thermal insulation materials still remains a challenge. In this work, a series of fluorinated polyimide foams (PIFs) based on 4,4‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) were successfully prepared by microwave‐assisted powder foaming. The modification of fluorination decreased the melt strength while simultaneously enhanced the thermal properties of fluorinated PIFs through the high bonding energy of CF bond. Thus, fluorinated PIFs exhibited one of the lowest densities of reported PIFs, among them, the density of PIF6FDA‐DMBZ was as low as 9.34 kg m−3. The glass transition temperature of all fluorinated PIFs was greater than 295°C. Microwave‐assisted foaming optimized the cell structure effectively, resulting in the thermal conductivity of PIF6FDA‐ODA as low as 0.029 W m−1 K−1. The incorporation of hexafluoroisopropylidene groups reduced the polarization and enhanced the free volume of fluorinated PIFs, leading to hydrophobic characteristics (CA >105°) and ultra‐low dielectric loss properties (tan δ <0.001 at 20 GHz). PIF6FDA‐ODA demonstrated the most excellent comprehensive performance. The excellent comprehensive performance of fluorinated PIFs indicated their potential application as thermal insulation and wave‐transparent materials in aerospace, railway, and shipbuilding industries. [ABSTRACT FROM AUTHOR]

The development of economical, high-efficiency synthesis approaches is the primary field of concern for research on microwave-absorbing materials (MAMs). In this work, we used the hydrothermal approach to effectively manufacture CeO2 nanoparticles/porous carbon composites enriched with oxygen vacancies under urea-assisted conditions. The carbon source for these composites was the porous carbon generated from bamboo powders. We adjusted the electromagnetic characteristics of the composites to optimize their electromagnetic wave (EMW) attenuation mechanisms and impedance matching properties by altering the heat treatment temperatures and the extra quantity of cerium salts. The creation of many defects and heterostructures as a result of the nitrogen/oxygen doping and oxygen vacancy-rich CeO2 leads to better EMW attenuation, conductivity loss, and increased polarization effects. The remarkable microwave absorption ability of the C2-500 composite is attributed to good impedance matching and interfacial polarization as well as dipole polarization induced by a significant number of heterogeneous interfaces and oxygen vacancies, particularly from N/O heterogeneous elements. At a filler loading of 10 wt %, C2-500 exhibits a minimum reflection loss (RLmin) of −44.94 dB at 16.16 GHz, accompanied by an effective absorption bandwidth (EAB) of 4.72 GHz. In comparison, the C3-500 composites demonstrate an EAB of 4.88 GHz and an RLmin of −46.81 dB at 9.28 GHz. This study is expected to be instrumental in the design of high-performance biomass-derived porous carbon-based MAMs, providing valuable insights for future research in this field. [ABSTRACT FROM AUTHOR]

Wearable fiber flexible sensors for sports motion monitoring have recently received attention. However, wearable flexible sensors still face limitations in material and device design. Here, we proposed a thermoplastic polyurethane (TPU)/polyvinylidene fluoride (PVDF) film as triboelectric material to manufacture triboelectric nanogenerator (TP-TENG) for harvesting mechanical energy and athlete step rate monitoring. The TPU/PVDF fiber film can be fabricated by using electrospinning technology. In addition, the role of negative triboelectric materials is played by TPU/PVDF film, and the nylon film acts as a positive triboelectric material. The TP-TENG device follows a single-electrode working mode, and it is easy to integrate into human clothing. The TP-TENG electrical output can achieve the maximum output when the content of PVDF in TPU/PVDF film reaches 15%. The TP-TENG can acquire the maximum output power of 699 µW under a 7 MΩ load. Also, the TP-TENG can be used as an electronic skin to achieve self-powered pressure sensing, and the sensitivity of the pressure sensor based on TP-TENG can reach 14.08 V N−1. By integrating it inside the shoes, TP-TENG can obtain the pace rate of runners for sports motion monitoring. This research reports an effective method for monitoring step rate in running and has potential application value. [ABSTRACT FROM AUTHOR]

This paper explores the feasibility of using the coupled smooth particle hydrodynamics–finite element method (SPH–FEM) to study the gear rack and meshing impact problem. Firstly, a numerical model containing both SPH and FEM units is established, and its accuracy is verified. Then, the principle of gear rack meshing impact is analyzed from the perspective of impact dynamics theory, and the formula of maximum meshing impact force is derived. Finally, the meshing impact process of the rack and pinion is simulated using the coupled SPH–FEM method, and experiments are designed to verify it. The analysis results show that the SPH–FEM coupling method can simulate the meshing impact behavior of the gear mechanism more accurately. On the other hand, the severity of the impact in each operating section was obtained. It is also found that the impact stress has reached the material's tensile limit, revealing the mechanism of tooth surface wear caused by the impact. The results of the study provide a choice of research methods for gear mechanism meshing impact and also provide some reference for gear rack tooth shape optimization. [ABSTRACT FROM AUTHOR]

Participation in a health promotion program for 192 overweight and obese adults with mental retardation was associated with behavior change resulting in reduction of body mass index--BMI (weight in kg, divided by height in meters, squared) by the end of the program. We analyzed the mediating and intermediate factors contributing to weight reduction and found knowledge and exercise to be the primary contributing factors. The curriculum emphasized exercise, nutritional choices, and stress reduction. Participation in the program was associated with a reduction of 0.8 BMI or approximately 2.3 kg for 26% of the participants. Increased knowledge about healthy diet and exercise was the most significant mediator of program impact on BMI.

Biomass porous carbon has attracted significant attention in wave absorption for its ultra-light, low cost and easy availability. Herein, lychee-like MoS2-doped rice husk-derived porous carbon (RPC@MoS2) composites were successfully prepared for electromagnetic wave absorption (EMA). The unique crocodile skin-like porous structure of rice husks and the lychee-like structure of MoS2 microspheres significantly develop numerous heterogeneous interfaces and increase the transmission path of electromagnetic waves (EMWs), which play an essential role in the dissipation of EMWs. The suitable dielectric constant of the composite can be got by simply changing the heat treatment temperature. RPC@MoS2-600 shows good EMA performance with a minimum reflection loss (RLmin) of −50.69 dB at 2.2 mm and an exceptionally wide effective absorption bandwidth (EAB) of 6.375 GHz at 2.0 mm. This work provides a new idea for the design of novel, low-cost, high-performance EMW absorbing materials. [ABSTRACT FROM AUTHOR]