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•The protonation treatment facilitates the production of g-C3N4 nanosheets with uniform size.•g-C3N4 nanosheets were employed to improve the gas sensing properties of ...graphene.•Optimal composite sensor containing 15% of g-C3N4 exhibited the best sensing performance.•g-C3N4 nanosheets play as an active adsorption site and graphene provides a charge pathway.
In this work, graphitic carbon nitride (g-C3N4) nanosheets were prepared and employed to improve the gas sensitivity performance of graphene. g-C3N4 nanosheets (NS-CN) were exfoliated from bulk powder using a proton-enhanced liquid-phase exfoliation method, where the co-ordinate bonds between nitrogen of g-C3N4 and proton H+ of HCl benefit the swelling of bulk and improve the delamination process. The thickness and size of the exfoliated nanosheets were about ∼4nm and 1–2μm, respectively. A slight increment of the bandgap of g-C3N4 was observed after exfoliation. It was found that the proton functionalization of g-C3N4 powder before exfoliation facilitates the production of uniform nanosheets. A certain amount ranging from 0% to 90% of as-prepared g-C3N4 was added to a graphene solution and ultrasonically mixed to prepare a graphene/g-C3N4 nanocomposite (G/NS-CN). The performances of pure graphene-based and nanocomposite-based sensors in sensing NO2 gas were systematically investigated and compared. We found compositing g-C3N4 with graphene significantly enhanced the sensing performance of the graphene sensor. A trade-off effect on sensing response was observed as the weight ratio of NS-CN to graphene in the nanocomposite sensor was changed, suggesting the specific roles of g-C3N4 and graphene in sensing behavior. It was found that the nanocomposite sensor with 15wt% of NS-CN exhibited the best sensing response. The sensor in this optimized composition presented a linear and stable response as well as good recovery toward NO2 gas. The sensing mechanism of the nanocomposite sensor was also proposed.
Graphene nanosheets (GNSs) reinforced pure copper matrix composites were prepared by ball-milling and hot-press sintering. The morphologies and structures of GNSs-Cu powders were studied after ...ball-milling for different time. The effects of the GNSs content on the microstructures, mechanical properties and fracture mechanisms of the composites were also investigated. It is indicated that the GNSs are gradually dispersed into the copper matrix with increasing the ball-milling time and a uniform dispersion is achieved after ball-milling for 5 h. When the content of GNSs in the composite is 0.5 wt%, GNSs distribute randomly in the composite and the interface bonding is good which is benefit to enhance the mechanical properties of composite. With increasing the GNSs contents, the aggregation of GNSs in the composite is apparent, which seriously separates the matrix and results in low mechanical properties. The fracture mechanism of the composites changes from ductile to brittle.
•Graphene reinforced copper matrix composites were prepared by ball-milling and hot-press sintering.•Graphene is uniformly dispersed into copper matrix after ball-milling and the structure of graphene is relatively complete.•Graphene contents significantly affect mechanical properties and fracture mechanisms of the composites.•The UTS and δ of the composites increase initially and decrease later with increasing the graphene contents.
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•Quasi-static compression behaviours of Miura-ori based 3D printed stainless steel metamaterial are experimentally and numerically investigated.•The graded metamaterials reduce the ...decreasing amplitude of the loading after the peak force and improve the SEA substantially.•The energy absorption increases with the gradient interval size.•The metamaterial with a negative gradient from the top and bottom to the middle layer has better energy absorption capacity.
Origami structures have been widely used for impact energy absorption in lightweight structures. Recently, Miura-ori metamaterial structures have been attractively investigated due to their unique geometric properties, adjustable stiffness and excellent energy absorption performance. In this study, the quasi-static compression characteristics of a Miura-ori based 3D printed stainless steel metamaterial are investigated. It is a graded metamaterial composed of multiple Miura-ori layers with different acute angles. The effects of different gradients on structural deformation and energy absorption were investigated by experiment and numerical simulation. The results show that the graded metamaterials have higher specific energy absorption (SEA) than the uniform ones. In addition, the graded metamaterials effectively reduce the decreasing amplitude of the compression loading after the peak force and improve the SEA compared with the uniform metamaterials. When the volume of the metamaterials remains the same, the energy absorption increases with the gradient interval size. The metamaterial with a negative gradient from the top and bottom to the middle layer has better energy absorption capacity.
To achieve high-quality machining of the 2195 aluminum-lithium alloy, this paper presents an experimental study on the effect of milling processing parameters on milling forces and surface ...topography, during which conventional milling and longitudinal-torsional ultrasonic vibration milling of the 2195 Al-Li alloy were performed. The characterization of the tool tip trajectory illustrates some of the advantages of ultrasonic machining, which include variable depth of cut and tool chip pulling. The differences in milling forces between conventional milling and longitudinal-torsional ultrasonic vibration machining were compared using orthogonal tests, and the effect of ultrasonic vibration on milling forces was investigated in detail. The maximum reduction of milling force
in the feed direction under the influence of torsional vibration is 62% and 54% for larger feed per tooth and cutting depth, respectively. The high-frequency impact generated by the longitudinal vibration not only reduces the chip accumulation on the surface, but also smooths out the tool-tooth scratches and creates a regular surface profile. In addition, the characteristics of the milling force signals of the two machining methods were analyzed, and the analysis of the spectrum of the collected milling forces revealed that the ultrasonic vibration caused the high-frequency components of the milling forces
and
. The orthogonal result analysis and single-factor result analysis verified the superiority of ultrasonic machining, provided parameter selection for subsequent aluminum-lithium alloy machining, and bridged the gap of longitudinal torsional ultrasonic vibration machining of 2195 aluminum-lithium alloy in the study of milling force.
The shaft misalignment under mixed lubrication is an important factor affecting the running performance of the bearing, which can occur under heavy load and unsatisfactory assembly. This paper ...presents a misaligned journal mixed lubrication model coupling for the asperity contact effect, elastic deformation, viscosity–temperature, and viscosity–pressure effect. The finite difference method was employed to calculate the model, and an experimental apparatus designed in this paper was used to test the friction and temperature characteristics of the specimens. The results show that the pressure field, film thickness, and elastic deformation of the bearing conformed to asymmetric distribution along the axial direction under misalignment conditions and there was a notable end side effect. In addition, the frictional force and side leakage flow were evidently enhanced with the increase in the inclination angle in a certain range. The experimental results showed that there was a visible wear phenomenon on the end sides of the bush and shaft. The research results are beneficial for understanding the mixed lubrication mechanism of misaligned journal bearing.
The gate-type carbon nanotubes cathodes exhibit advantages in long-term stable emission owing to the uniformity of electrical field on the carbon nanotubes, but the gate inevitably reduces the ...transmittance of electron beam, posing challenges for system stabilities. In this work, we introduce electron beam focusing technique using the self-charging SiN
/Au/Si gate. The potential of SiN
is measured to be approximately -60 V quickly after the cathode turning on, the negative potential can be maintained as the emission goes on. The charged surface generates rebounding electrostatic forces on the following electrons, significantly focusing the electron beam on the center of gate hole and allowing them to pass through gate with minimal interceptions. An average transmittance of 96.17% is observed during 550 hours prototype test, the transmittance above 95% is recorded for the cathode current from 2.14 μA to 3.25 mA with the current density up to 17.54 mA cm
.
Vibration procedures significantly affect the performances of cement-based materials. However, studies on the distribution of certain particles within cement-based materials are limited due to the ...complexity and difficulty of identifying each specific particle. This paper presents a new method for simulating and quantifying the movements of particles within cement paste through the use of "tagged materials". By separating the tagged particles from the cement paste after vibration, the distribution of the particles in the cement paste can be calculated statistically. The effect of the vibration time and frequency, fresh behavior, and powder characteristics of cement paste on particle motions are investigated. The results demonstrate that when the vibration exceeds 1800 s, it induces a significant uneven dispersion of microparticles. This effect is more pronounced at low viscosities (<1 Pa·s) of cement paste or high vibration frequencies (>200 Hz). Larger and denser particles exhibit greater dispersion. This method provides a valuable tool for investigating the theory of particle motion in cement paste, which is crucial for understanding the influence of vibration on the properties of cement-based materials.
The proposed lubrication theory of textured journal bearing is a major innovation in the study of the tribological properties of surface morphology. When it comes to the study of surface topography, ...it is essential to consider the effect of surface roughness when analyzing the characteristics of journal bearing. In this paper, a Reynolds equation containing longitudinal roughness is established for journal bearing and solved by the finite difference principle to obtain the bearing load and friction characteristics. Subsequently, a combination of laser etching and ultrasonic vibration milling processes was used to prepare 5 µm, 20 µm, and 40 µm bearing friction subsets with square micro-texture surfaces. The analysis of the results shows that the surface roughness distributed in the non-texture region can substantially increase the oil film pressure. When the roughness profile and the surface weave work together, the presence of a surface texture with an optimum depth of 5 µm within a roughness range of less than 1.6 µm can improve the load-bearing characteristics by a maximum of 43%. In the study of the preparation of textured bearing friction substrate, it was found that laser etching can ablate the surface of the friction substrate to a depth greater than 20 µm with the ideal effect, while the surface texturing to a depth of 5 µm is more suitable using an ultrasonic vibration processing process. In the simplified journal bearing operating condition, the frictional wear test shows that if the effect of roughness is considered, the frictional force of the depth of 20 µm and 40 µm is significantly reduced and changes less with increasing load, while the frictional force of the textured frictional pair with a depth of 5 µm is improved but significantly affected by the load carrying capacity. Therefore, when the difference between the roughness profile and the depth of the texture is of a small order of magnitude, it indicates that the effect caused by the roughness factor is not negligible.
Among the Rosaceae species, the gametophytic self-incompatibility (GSI) is controlled by a single multi-allelic S locus, which is composed of the pistil-S and pollen-S genes. The pistil-S gene ...encodes a polymorphic ribonuclease (S-RNase), which is essential for identifying self-pollen. However, the S-RNase system has not been fully characterized. In this study, the self-S-RNase inhibited the Ca
-permeable channel activity at pollen tube apices and the selectively decreased phospholipase C (
) activity in the plasma membrane of
pollen tubes. Self-S-RNase decreased the Ca
influx through a
-mediated signaling pathway. Phosphatidylinositol-specific
has a 26-amino acid insertion in pollen tubes of the 'Jinzhuili' cultivar, which is a spontaneous self-compatible mutant of the 'Yali' cultivar. 'Yali' plants exhibit a typical S-RNase-based GSI. Upon self-pollination,
gene expression is significantly higher in 'Jinzhuili' pollen tubes than that in 'Yali' pollen tubes. Moreover, the
in pollen tubes can only interact with one of the two types of S-RNase from the style. In the
Rehd, the
directly interacted with the S
-RNase in the pollen tube, but not with the S
-RNase. Collectively, our results reveal that the effects of S-RNase on
activity are required for S-specific pollen rejection, and that
-IP
participates in the self-incompatibility reaction of
species.
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