The expression of the coupler curve of a spherical five-bar mechanism is established using Fourier series theory. An analysis of the harmonic component of the trajectory output showed that it has an ...internal relation with the mechanism size. On this basis, a characteristic parameter database containing 4,804,800 groups of basic size coupler curve positions is established. The theoretical formulas for calculating the actual size and the installation position parameters of the spherical five-bar mechanism are derived. The path synthesis problem of the spherical five-bar mechanism is solved by establishing characteristic parameter database and theoretical formula. Finally, the effectiveness of this method is proved by the given example.
•A new vibration assisted nanoimprinting method is proposed for face-to-face imprinting.•Vibration assisted-nanoimprinting can improve the filling rate of photoresist.•Vibration ...assisted-nanoimprinting can improve the hydrophobicity of microstructure surface.•Vibration assisted-nanoimprinting can improve the photovoltaic conversion efficiency of solar cells.
To effectively improve the power conversion efficiency (PCE) of Si solar cells, vibration-assisted UV nanoimprint lithography based on piezoelectric driving is proposed to fabricate grating on Si solar cells. By applying piezoelectric vibration under the photoresist layer, vibration causes micro-displacement and micro-impact force, increasing the contact area between the photoresist and the grating's side wall and reducing surface tension. Meanwhile, the photoresist filling rate is increased by 25%. The effect of grating parameters on reflection is determined using Finite Difference Time Domain (FDTD), and grating with the best optical performance is optimized. In addition, the rationality of vibration introduction is verified by establishing a motion model, the influence of frequency and amplitude on the filling rate is analyzed using the finite element method, and a reasonable range of vibration parameters required by the experiment is obtained. Vibration-assisted UV nanoimprint is used to fabricate the periodic grating structures. PCE is increased by 25% when compared to bare Si solar cells. PCE of grating fabricated by vibration-assisted UV nanoimprint is increased by 4% when compared to traditional nanoimprint. The results show that vibration-assisted nanoimprint can efficiently and accurately fabricate periodic grating structures, resulting in improved Si solar cells performance.
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•There is a significant difference in NEE between two adjacent years in a wetland.•Higher precipitation redistribution in the fast growth stage promoted NEE.•Higher precipitation ...redistribution in the middle growth stage suppressed NEE.•Precipitation redistribution affected the light and temperature responses of NEE.•Precipitation redistribution regulated NEE during the growing season in a wetland.
Hydrological regime is crucial in determining the carbon dioxide (CO2) exchange between the atmosphere and wetlands. Seasonal redistribution of precipitation is one featured hydrological regime shift, but its impacts on ecosystem CO2 exchange in coastal wetlands remain unclear. Here, based on the eddy-covariance technique, we examined how the net ecosystem CO2 exchange (NEE) in a coastal wetland of Yellow River Delta in China differed between two years (2012 and 2013) with contrasting seasonal distribution of precipitation. The ecosystem absorbed more CO2 during the growing stage in 2013 (−268.5gCm−2) than 2012 (−174.7gCm−2). This difference resulted from higher NEE in the fast and middle growth stages with different reasons. In the fast growth stage, the higher mean daily NEE occurred due to more precipitation coupled with lower salt stress in 2013 (−6.3g CO2m−2day−1) compared to that in 2012 (−2.2g CO2m−2day−1). During the middle growth stage, the mean daily NEE in 2013 (−4.2g CO2m−2day−1) was significantly higher than that in 2012 (−1.1g CO2m−2day−1) because the ecosystem in 2012 suffered more waterlogged stress. This dual effect of precipitation distribution on vegetation photosynthesis was also observed in a field manipulation experiment at the same site. Our results indicated that the redistribution of precipitation among seasons would play a critical role in regulating ecosystem CO2 exchange in the coastal wetland. More research on the associated changes between dynamics of soil hydrology and salinity could promote the accuracy of the carbon-budget estimates in coastal wetlands.
The acetabular cups used in total hip arthroplasty are mostly made of dense metal materials with an elastic moduli much higher than that of human bone. This leads to stress shielding after ...implantation, which may cause aseptic loosening of the implant. Selective laser melting (SLM) technology allows us to produce tiny and complex porous structures and to reduce the elastic moduli of dense metals, thereby avoiding stress shielding. In the present study, rhombic dodecahedron porous structures with cell sizes of 1 mm, 1.5 mm, and 2 mm were designed. The strut diameter was changed to ensure that the porosity and pore size would meet the bone ingrowth requirements. Then, porous Ti6Al4V alloy specimens were printed using SLM, and compressive tests were carried out. The results showed that the compressive strength and elastic modulus values of the specimens with a cell size of 1.5 mm were in the range of 78.16–242.94 MPa and 1.74–4.17 GPa, respectively, which are in line with the mechanical properties of human cortical bone. Finite element analysis of a total hip joint model was carried out to simulate gait, and the surface of the trabecular acetabular cup was divided into 10 regions according to the stress distribution, with the stress interval in the range of 37.44–219.24 MPa. According to the compression test results, the gradient structure of Ti6Al4V alloy with different porosity was designed for trabecular coating. The gradient porous structure meets the mechanical requirements and is closer to the natural structure of human bone than the uniformly distributed porous structure.
The advancement of Li-metal batteries is significantly impeded by the presence of unstable solid electrolyte interphase and Li dendrites upon cycling. Herein, we present an innovative approach to ...address these issues through the synergetic regulation of solid electrolyte interphase mechanics and Li crystallography using yttrium fluoride/polymethyl methacrylate composite layer. Specifically, we demonstrate the in-situ generation of Y-doped lithium metal through the reaction of composite layer with Li metal, which reduces the surface energy of the (200) plane, and tunes the preferential crystallographic orientation to (200) plane from conventional (110) plane during Li plating. These changes effectively passivate Li metal, thereby significantly reducing undesired side reactions between Li and electrolytes by 4 times. Meanwhile, the composite layer with suitable modulus (~1.02 GPa) can enhance mechanical stability and maintain structural stability of SEI. Consequently, a 4.2 Ah pouch cell with high energy density of 468 Wh kg
and remarkable capacity stability of 0.08% decay/cycle is demonstrated under harsh condition, such as high-areal-capacity cathode (6 mAh cm
), lean electrolyte (1.98 g Ah
), and high current density (3 mA cm
). Our findings highlight the potential of reactive composite layer as a promising strategy for the development of stable Li-metal batteries.
The ZL205A aluminum alloy is mostly used in automobiles, aircraft, aerospace, and other mechanical components, but now, it focuses on the study of its casting performance, and there is still a lack ...of research on its cutting performance. In this paper, the milling ZL205A aluminum alloy was milled for testing and simulation analysis. The milling test showed that the impact of the axial cutting depth, radial cutting depth, feed, and cutting speed on the milling force was successively reduced. A thermodynamic analysis model is proposed to evaluate the cutting force and tool design in milling. The model considers the front angle and friction angle of the tool, in which the friction angle is adjusted by the friction coefficient, the variable is the cutting parameter, the constant is fitted through the milling experiment, and the effectiveness of the model is verified to predict the milling force. The pre-grinding test was carried out before the experiment, and the stability of the test was proved by observing the macroscopic shape of the chip and the wear of the cutting edge. The model comprehensively considers the tool angle and quickly calculates the minimum load on the milling cutter based on the optimal geometric parameters, which can be used to optimize the milling cutter structure and provide a theoretical basis for the preparation of ZL205A aluminum alloy mechanical components.
The article presents output expressions of linkage mechanism in general mathematical form. The harmonic components of the mathematical expressions are analyzed by using the Fourier series theory. The ...relationship between the harmonic component and the harmonic characteristic parameters of coupler rotation-angle operator is discovered. Based on this relationship, a unified approach to establish the numerical atlas database is given. The unified derivation process of formula, which can compute the actual dimensions and installation parameters of linkage mechanism, is presented. The concepts of the coupler rotation-angle operator, the harmonic output characteristic parameters of dimensional type, the mechanism’s basic dimensional types and the harmonic dimension characteristic parameters of dimensional type are defined. Based on these definitions and the concrete steps of harmonic characteristic parameter method, the unified model is set up for the dimensional synthesis of linkage mechanism from planar, spherical to spatial motion.
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