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Resonators and resonator-based oscillators are used in most electronics systems and they are classified as either mechanical or electrical, with fixed or difficult-to-tune resonant frequencies. Here, we propose an electro-superlubric spring, whose restoring force between two contacting sliding solid surfaces in the structural superlubric state is linearly dependent on the sliding displacement from the balanced position. We use theoretical analysis and finite element methods to study the restoring force and stability. The stiffness of this electro-superlubric spring is proportional to the square of the applied electric bias, facilitating continuous tuning from zero to several megahertz or gigahertz for the microscale or nanoscale resonators, respectively. Furthermore, we propose an electro-superlubric oscillator that is easily operated by varying a pair of harmonic voltages. The resonant frequency, resonant amplitude, quality factor, and maximum resonant speed can be continuously tuned via the applied voltage and bias. These results indicate significant potential in the applications of electro-superlubric resonators and oscillators. Microscale resonators are widely used in modern technology and achieving large tunability of their resonant frequency is highly desirable. Here, a design for electro-superlubric springs, based on a restoring force between sliding solid surfaces, is predicted to have continuously tunable resonant frequencies from zero to several GHz.

Miniaturized or microscale generators that can effectively convert weak and random mechanical energy into electricity have significant potential to provide solutions for the power supply problem of distributed devices. However, owing to the common occurrence of friction and wear, all such generators developed so far have failed to simultaneously achieve sufficiently high current density and sufficiently long lifetime, which are crucial for real-world applications. To address this issue, we invent a microscale Schottky superlubric generator (S-SLG), such that the sliding contact between microsized graphite flakes and n-type silicon is in a structural superlubric state (an ultra-low friction and wearless state). The S-SLG not only generates high current (~210 Am−2) and power (~7 Wm−2) densities, but also achieves a long lifetime of at least 5,000 cycles, while maintaining stable high electrical current density (~119 Am−2). No current decay and wear are observed during the experiment, indicating that the actual persistence of the S-SLG is enduring or virtually unlimited. By excluding the mechanism of friction-induced excitation in the S-SLG, we further demonstrate an electronic drift process during relative sliding using a quasi-static semiconductor finite element simulation. Our work may guide and accelerate the future use of S-SLGs in real-world applications., It is difficult to achieve high current density and long lifetime for micro generators owing to the common friction and wear. Here the authors invent a microscale Schottky superlubric generator to tackle this issue, reporting not only high current and power densities but also long lifetime of at least 5,000 cycles.

In extended-reach and directional drilling, cuttings transport is a key issue associated with the efficiency of hole-cleaning and drilling operation. If the cuttings cannot be returned to the surface in time, many technical difficulties may arise such as excessive torque and drag, stuck pipe, and loss of well control. In this study, a computational fluid dynamics (CFD) approach with Eulerian–Eulerian (EE) multiphase model was employed to comprehensively understand and analyze the effect of several drilling operation parameters, mud rheological properties, and specularity coefficient (representing various wellbore wall conditions) on the cuttings transport performance. A commercial CFD software (ANSYS FLUENT™ 19.1) was used to implement all simulations, and a sensitivity analysis was executed with an error of less than 5%. Furthermore, the motion patterns of cuttings were observed and analyzed under various factors. The results show that the cuttings transport performance is sensitive to the wellbore wall condition. In the lower side of annuli, the volume fraction of cuttings increases significantly by 28% with increasing specularity coefficients. Additionally, the combined influence of critical shear rate and flow rate on the cuttings distribution was investigated. The relative reduction rate of cuttings concentration decreased by 30% with increasing critical shear rate at the fluid velocity of 0.4 m/s, while that didn't change so obviously at the fluid velocity of 0.8 m/s.

Currently, industries seek to optimize the development of technology from energy-saving, economic, and environmental perspectives. Dissolved air flotation (DAF) is one of the most effective wastewater treatment systems. However, it requires considerable energy and causes significant operating costs. A recently emerged application of using fluidic oscillators (FOs) to generate microbubbles has attracted extensive attention, as it consumes much less energy and has proven to be a more energy-efficient technique. In this article, a microbubble generator based on FOs is introduced into the flotation tank, and an energy-saving water treatment system, namely fluidic air flotation (FAF), is presented. Using the computational fluid dynamics (CFD) method, the flow pattern of the FAF is investigated. It is observed that FAF generates a dynamic flow pattern, which is beneficial for bubble removal. At the upper part of the separation zone, the flow pattern exhibits a wavy shape. The flow pattern at the lower part switches between clockwise and counterclockwise. The air distribution of the separation zone is also studied. It is found that the height of the “white water” zone almost linearly decreases with the increase in bubble diameter and diffuser size. FAF consumes almost no energy and occupies a small area, and it is expected to provide a promising solution to develop a new generation of the wastewater treatment system.

In this paper, a new method based on SBR method is proposed to calculate the electromagnetic scattering problem of electrically large target. In traditional SBR method, the split size is usually less than 0.4 wavelength to ensure the accuracy. In this paper, the split size which could describe the shape of the target is enough. So the calculating memory and time can be reduced greatly. And the parallel technology is utilized to further accelerate the speed of the program.