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Aiming at the discharge problem of inductively coupled plasma (ICP), a closed wave-transmitting cavi-ty configuration is designed, the fluid mechanics model of ICP is established, and the multi physical simulation software COMSOL is used for three-dimensional simulation research. The variation laws of typical parameters such as electron density, electron temperature and plasma potential with time in the discharge process are analyzed. On this basis, the power of radio frequency power supply, the air pressure in the cavity and other conditions are changed to obtain the parameter range and spatial gradient distribution of ICP. The results show that the discharge power mainly affects the numerical range of plasma parameters, and the change of air pressure has an effect on the numerical value and spatial distribution of plasma parameters. When the power of radio frequency power supply increases from 100 W to 300 W, the peak electron density increases from 2.54×1017 m-3 to 5.68×1017 m-3, and the electric potential induced in the heating zone and the corresponding electron temperature decrease slightly after the reaction is stable. Increasing the air pressure in the cavity within a certain range will significantly increase the electron density. The air pressure increases from 10 Pa to 30 Pa, and the electron density increases from 9.12×1017 m-3 to 3.62×1018 m-3. However, the uniformity of plasma parameter distribution will deteriorate if the air pressure is too high.

Nanograined materials possess ultrahigh strength, while their processing and technological applications are constrained by inherent thermal and mechanical instability. Existing experiments show that the stability of Cu nanograins can be enhanced by performing a rapid heating pretreatment that reduces the grain boundary (GB) energy by changing the GB structure. The variation in the GB structure inevitably affects the migration mechanism of GBs. However, the effect of the pretreatment-induced variation in migration mechanisms on stability remains unclear. Here, the shear deformation of a series of ⟨ 100 ⟩ symmetrical tilt GBs after rapid heating pretreatment is systematically investigated by molecular dynamics simulations. The simulations of unheated GBs are also included for comparison. Our results show that the rapid heating pretreatment does not improve the mechanical stability of GBs with tilt angles larger than 36.87° but rather enhances the mechanical stability of those with tilt angles less than 36.87° by the transformation of migration behavior from the normal ⟨ 110 ⟩ mode to (i) a ⟨ 100 ⟩ mode; (ii) an inhomogeneous mixed one that reconciles the ⟨ 110 ⟩ and ⟨ 100 ⟩ modes; and (iii) an inhomogeneous ⟨ 110 ⟩ mode. The former leads to an increase in the critical shear stress that is required to initiate the migration, whereas the latter two result in a decrease in the migration distance. The variation in the GB migration mechanism is attributed to the change in the GB structure from an ordered kite structure to a disordered one. The research gives an atomic insight into the stabilizing mechanism of nanocrystalline materials with rapid heating pretreatment. [ABSTRACT FROM AUTHOR]

In sports practices, the intensity and type of forces exerted on the human body are totally different from everyday living. Harsh movements and impact loadings are very common in sports and sometimes cause severe injuries to both muscles and bones. In a specific case, in volleyball games, the lower arm of the player is continuously exposed to heavy impacts by the ball. The main part of the body enduring these impact loads are the two ulna and radius bones in the lower arm. Therefore, in this type of ball impacts it is important to investigate the effect of ball movement and condition on the stress-induced in bones. In the present study, using numerical finite element and generalized differential quadrature (GDQ) methods, stability conditions in the ulna and radius bones in volleyball players under several static and harmonic loading types are investigated. Furthermore, change in the ball mass in the standard range is also considered in analyses. The bone structure is modeled as a cylindrical shell with classical elasticity theory and for inhomogeneous material properties. The results obtained using the numerical method are presented with a focus on the state of stability of the both ulna and radius bones. [ABSTRACT FROM AUTHOR]

The accurate perception of external environment information through the robot foot is crucial for the mobile robot to evaluate its ability to traverse terrain. Adequate foot-end contact signals can provide robust support for robot motion control and decision-making processes. The shape and uncertain rotation of the wheel-legged robot foot end represent a significant challenge to sensing the robot foot-end contact state, which current foot-end sensing schemes cannot solve. This paper presents a sensing method for the tire stress field of wheel-legged robots. A finite element analysis was conducted to study the deformation characteristics of the foot-end tire under force. Based on this analysis, a heuristic contact position estimator was designed that utilizes symmetrical deformation characteristics. Strain sensors, arranged in an array, extract the deformation information on the inner surface of the tire at a frequency of 200 Hz. The contact position estimator reduces the dimensionality of the data and fits the eigenvalues to the estimated contact position. Using support vector regression, the force estimator utilizes the estimated contact position and sensor signal to estimate the normal reaction force, designated as FZ. The sensing system is capable of detecting the contact position on the wheel circumference (with a root mean square error of 1.150°), as well as the normal force of 160 N on the Z axis (with a root mean square error of 6.04%). To validate the efficacy of the sensor detection method, a series of randomized and repeated experiments were conducted on a self-constructed test platform. This novel approach offers a promising avenue for perceiving contact states in wheel-legged robots. [ABSTRACT FROM AUTHOR]

This study investigates the performance of a 4-MIX engine utilizing hydrogen combustion in pure oxygen, water injection, and the application of the early-intake valve closure (EIVC) Miller cycle. Transitioning from a standard petrol–oil mix to hydrogen fuel with pure oxygen combustion aims to reduce emissions. Performance comparisons between baseline and oxyhydrogen engines showed proportional growth in the energy input rate with increasing rotational speed. The oxyhydrogen engine exhibited smoother reductions in brake torque and thermal efficiency as rotational speed increased compared to the baseline, attributed to hydrogen's higher heating value. Water injection targeted cylinder and exhaust temperature reduction while maintaining a consistent injected mass. The results indicated a threshold of around 2.5 kg/h for the optimal water injection rate, beyond which positive effects on engine performance emerged. Investigation into the EIVC Miller cycle revealed improvements in brake torque, thermal efficiency, and brake specific fuel consumption as early-intake valve closure increased. Overall, the EIVC model exhibited superior energy efficiency, torque output, and thermal efficiency compared to alternative models, effectively addressing emissions and cylinder temperature concerns. [ABSTRACT FROM AUTHOR]

At present, the valence state (connectivity) of most covalent organic frameworks (COFs) building units is low, mostly trivalent and tetravalent, making only 18 types of topological structures of COFs materials. On the contrary, the valence states of MOFs building blocks vary from 3 to 24, making them have more than 2 000 topological structure types. If a higher valence COFs building block can be designed, it will greatly enrich its topological structure type and material number. To this end, a hexahedral boron-phosphorus unit (-B4 P4 O12-) and five linear organic linkers (phenyl, fluorophenyl, toluene, naphthalene, biphenyl) were selected, and five high-valent boron-phosphorus covalent organic frameworks (BP-COFs) with lta topology were theoretically designed by molecular mechanics methods. The results show that the five materials have structural characteristics that are conducive to hydrogen storage applications, such as low density (0.52 ~ 1.17 g⋅cm-3), large specific surface area (1 274.12 ~ 4 033. 95 m² ⋅g-1) and high porosity (0. 55% ~ 0.78%). The Grand Canonical Monte Carlo (GCMC) method was used to predict the physical adsorption properties of hydrogen molecules on five materials at 298 and 77 K, and the structure-activity relationship between material structure and hydrogen adsorption properties was analyzed. The results show that the five BP-COFs materials have strong hydrogen adsorption capacity. Especially at 77 K, BP-COF-10 and BP-COF-11 have the best performance in hydrogen storage performance. BP-COF-10 has the highest volumetric hydrogen storage capacity at 77 K, reaching 52.86 g⋅L-1. BP-COF-11 has a large accessible specific surface area and high porosity. It has a good hydrogen storage capacity at 77 K and a gravimetric hydrogen storage capacity of 9.90% at 5 000 kPa. With the increase of pressure, the hydrogen storage capacity of BP-COF-11 still maintains a good upward trend. BP-COF-7 has the largest hydrogen storage capacity at 298 K, and the hydrogen storage capacity reaches 4.83 g⋅L-1 at 5 000 kPa. This indicates that the designed material has good hydrogen storage potential. This study will provide a theoretical reference for the experimental development of new high-performance hydrogen storage materials. [ABSTRACT FROM AUTHOR]

This paper investigated the effects of exhaust gas recirculation (EGR) on homogeneous charge compression ignition (HCCI) combustion in internal combustion engines. The exhaust valve closing (EVC) timings were scanned to obtain a set of baseline operating points for HCCI, and the coupling control of the internal and external EGR was explored. The results indicate that external EGR delays HCCI ignition timing and slows down the combustion speed. As the internal EGR rate increases, the maximum external EGR ratio that can be tolerated decreases. For HCCI detonation operating points with low internal EGR rates, the addition of up to 10% of external EGR can control the pressure rise rate peak to less than 10 bar/°CA, resulting in reduced fuel consumption and increased indicated mean effective pressure (IMEP). However, for HCCI operating points with high internal EGR rates, the effect of external EGR is mainly observed in the control of the pressure rise rate, with limited increase in IMEP. Additionally, an increasing external EGR rate leads to a significant decrease in nitrogen oxide (NOx) emissions, while carbon monoxide (CO) and hydrocarbon (HC) emissions slightly increase before engine misfire occurs. These findings suggest that the coupling control of internal and external EGR should be explored further, particularly in relation to reducing the negative valve overlap (NVO) angle and improving combustion efficiency. [ABSTRACT FROM AUTHOR]