Pair creation enhancement due to combined external fields

We study the creation of electron-positron pairs from the vacuum induced by a combination of a static electric field and an alternating field. We find that the overall pair production can be increased by two orders of magnitude compared to the yields associated with each field individually. We examine the interesting case where both fields are spatially localized, permitting us to examine the time evolution of the spatial density for the created particle pairs. We find that there are a variety of competing mechanisms that contribute to the total yield

Electron-positron pair creation induced by quantum-mechanical tunneling

We study the creation of electron-positron pairs from the vacuum induced by two spatially displaced static electric fields. The strength and spatial width of each localized field is less than required for pair creation. If, however, the separation between the fields is less than the quantum-mechanical tunneling length associated with the corresponding quantum scattering system, the system produces a steady flux of electron-positron pairs. We compute the time dependence of the pair-creation probability by solving the Dirac equation numerically for various external field sequences. For the special case of two very narrow fields we provide an analytical expression for the pair-creation rate in the long-time limit

Effect of additives on microstructure of coal-based graphite

The Taixi anthracite was used as the raw materials, and mixed with different masses of additives, namely silicon oxide, titanium oxide, and iron oxide, to prepare the coal-based graphite by high temperature graphitization. The microstructure of coal-based graphite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal Raman spectroscopy (Raman) and Specific surface area and porosity analyzer.The results show that the graphitization degree of the coal-based graphite can reach over 89% after high temperature heat treatment at 2800 °C , which significantly improves the microcrystalline structure of anthracite and achieves orderly rearrangement of sp2 hybrid carbon atoms in the coal. Under the same additive mixing level, the graphitization degree and stacking height of coal-based graphite with titanium dioxide as additive are relatively high, the difference between the layer spacing and the ideal graphite layer spacing is the smallest, and the degree of ordering of carbon materials is the highest. The Raman spectroscopy results showed that the order degree of coal -based graphite prepared under different additives was significantly different, and the order degree of TXSC3, TXTC2 and TXIC3 coal-based graphite was the highest among the additives. Under the electron microscope, it is found that under the conditions of three additives, the scales, spherical and two shapes of coal-based graphite can be prepared separately. It can be seen from the specific surface area and pore size distribution data of coal-based graphite that they have similar low-temperature nitrogen adsorption-desorption isotherms

Design, Dynamics, and Optimization of a 3-DoF Nonlinear Micro-Gyroscope by Considering the Influence of the Coriolis Force

In this paper, we use the nonlinear hardening stiffness of drive mode deal with the contradiction between gain and bandwidth of the linear micro-gyroscope, to improve the bandwidth and gain in sense direction. Firstly, in order to adjust the distance between two resonant peaks, we changed an incomplete two-degree-of-freedom(2-DoF) sense mode system of the micro-gyroscope into a complete 2-DoF system. Afterward, according to the given nonlinear coefficient of stiffness of drive mode, the structure size of driving micro-beams was designed to obtain a nonlinear micro-gyroscope with controllable stiffness. Finally, we investigated the effects of peaks spacing, damping, and driving nonlinearity on gain and bandwidth, and the nonlinear micro-gyroscope was optimized by orthogonal experiment method and response surface method. The results reveal that the peaks spacing has a great influence on the gain and bandwidth of both linear and nonlinear micro-gyroscopes. The larger the peaks spacing, the lower the gain, but higher gain can be achieved when the resonant frequency of the drive mode is close to the lower-order resonant frequency of the sense mode. Driving nonlinearity leads to the response peak of the Coriolis force to have a hardening characteristic, thus forming a wide platform in the sense direction. Hardening of the response peak of the Coriolis force allows the micro-gyroscope to obtain a higher gain while the bandwidth of the sense mode is also greatly improved. In addition, parameter optimization can make the gain and bandwidth of the micro-gyroscope optimal. When the peaks spacing is small and the nonlinear stiffness coefficient is about 1012.2, under the premise that the gain is basically constant, the bandwidth of the sense mode increases about 1.76 times compared with the linear gyroscope. Damping can suppress the influence of nonlinearity in a micro-gyroscope system. Within a certain range, the frequency response of the nonlinear micro-gyroscope tends to be a linear system with the increase in damping, resulting in narrower bandwidth and lower gain

How Do Substrates Affect the Friction on Graphene at the Nanoscale?

Substrates supporting two-dimensional materials are omnipresent in micro/nano electromechanical systems. Moreover, substrates are indispensable to all nanotribological experimental systems. However, substrates have rarely been taken into account in first-principles simulations of nanotribological systems. In this work, we investigate the effects of substrates on nanofriction by carrying out first-principles simulations of two systems: (a) one graphene monolayer sliding on another one supported by a metal substrate, denoted as the Gr-Gr/Metal system; and (b) a diatomic tip sliding on a graphene monolayer supported by a metal substrate, named the Tip-Gr/Metal system. Each substrate is made of triatomic layers constituting the minimum period and obtained by cutting a metal through its (111) surface. By varying metal substrates and analyzing the results of the first-principles simulations, it follows that (i) the fluctuation in the sliding energy barriers of the two systems can be modified by changing substrates; (ii) the adsorption type and the pressure affect friction; (iii) the presence of a substrate varies the interfacial binding strength; and (iv) the modulation of friction by substrates lies in altering the interface electron density. These results provide an answer to the important question of how substrates affect the friction on graphene at the nanoscale

A Comparative Study on Loadings of the Lower Extremity during Deep Squat in Asian and Caucasian Individuals via OpenSim Musculoskeletal Modelling

Populations of different ethnicities may present different movement capacities and muscular function adaptations. The purpose of this study was to investigate the differences of motion and loading in the lower extremity during dynamic deep squats between Asian and Caucasian individuals using OpenSim modelling technique with a customized squat-specific musculoskeletal model. Twenty-four participants joined the test performing the step-squat test, with right foot stepping side, squatting, and returning. The one-dimensional statistical parametric mapping package was used for statistical analysis. The main findings of the current study were as follows: (1) significant lower squat depth was observed in the Asian individuals, (2) the greater knee range of motion and contact forces were found in the Asian individuals, and (3) the greater ankle contact forces in the Caucasian individuals were notable while performing the deep squat compared to the Asian group. Knowledge found in the current study may provide implication for exercise practitioners and physiotherapists while designing schemes for the prevention of loading accumulation in the lower extremity

Improvement of leaching efficiency of cathode material of spent LiNixCoyMnzO2LiNi_xCo_yMn_zO_2 lithium-ion battery by the in-situ thermal reduction

Green cars and electronic products consume lots of lithium-ion batteries (LIBs), and massive spent LIBs are yielded due to performance degradation. This paper provides an economical and environmentally friendly approach to recover valuable metals from cathode materials of the spent LIBs. It combines the in-situ thermal reduction (self-reduction by polyvinylidene fluoride (PVDF) and residual electrolyte in cathode material) and sulfuric acid leaching. Elements of high valent are reduced by the binder (PVDF) and the residual electrolyte on the surface of $NCM(LiNi_xCo_yMn_{1-x-y}O_2)$ material at high temperatures. Moreover, the changes in substance type, element valency, and contents of cathode materials reduced with various terminal temperatures and retention time are analyzed by Xray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Results show that the optimal terminal temperature for in-situ thermal reduction is 600 °C, and the optimum retention time is 120 min. Under the best in-situ thermal reduction conditions, the results from XRD confirm that part of $Ni^{2+}$ is converted to simple substance $Ni$, $Co^{3+}$ is reduced to $Co$, and $Mn^{4+}$ is reduced to $Mn^{2+}$ and elemental $Mn$, which are confirmed by XRD. Analyzed results by XPS indicate that the content of $Ni^{2+}$ decreases to 67.05%, and $Co^{3+}$ is completely reduced to $Co$. $Mn^{4+}$ is reduced to 91.41% of $Mn^{2+}$ and 8.59% of simple substance $Mn$. In-situ thermal reduction benefits the leaching processes of cathode materials. The leaching efficiencies of $Ni$, $Co$, and $Mn$ increase from 53.39%, 51.95%, and 0.71% to 99.04%, 96.98%, and 97.52%, respectively

High-Proportion Blue Light Irradiation at the End-of-Production Stage Promotes the Biosynthesis and Recycling of Ascorbate in Lettuce

Ascorbate (AsA), an essential antioxidant for both plants and the human body, plays a vital role in maintaining proper functionality. Light plays an important role in metabolism of AsA in horticultural plants. Our previous research has revealed that subjecting lettuce to high light irradiation (HLI) (500 μmol·m−2·s−1) at the end-of-production (EOP) stage effectively enhances AsA levels, while the optimal light quality for AsA accumulation is still unknown. In this study, four combinations of red (R) and blue (B) light spectra with the ratio of 1:1 (1R1B), 2:1 (2R1B), 3:1 (3R1B), and 4:1 (4R1B) were applied to investigate the biosynthesis and recycling of AsA in lettuce. The results demonstrated that the AsA/total-AsA content in lettuce leaves was notably augmented upon exposure to 1R1B and 2R1B. Interestingly, AsA levels across all treatments increased rapidly at the early stage (2–8 h) of irradiation, while they increased slowly at the late stage (8–16 h). The activity of L-galactono-1,4-lactone dehydrogenase was augmented under 1R1B treatment, which is pivotal to AsA production. Additionally, the activities of enzymes key to AsA cycling were enhanced by 1R1B and 2R1B treatments, including ascorbate peroxidase, dehydroascorbate reductase, and monodehydroascorbate reductase. Notably, hydrogen peroxide and malondialdehyde accumulation increased dramatically following 16 h of 1R1B and 2R1B treatments. In addition, although soluble sugar and starch contents were enhanced by EOP-HLI, this effect was comparatively subdued under the 1R1B treatment. Overall, these results indicated that AsA accumulation was improved by irradiation with a blue light proportion of over 50% in lettuce, aligning with the heightened activities of key enzymes responsible for AsA synthesis, as well as the accrual of hydrogen peroxide. The effective strategy holds the potential to enhance the nutritional quality of lettuce while bolstering its antioxidant defenses