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Dispersed raindrop energy harvesting has recently attracted extensive interest owing to the huge amount of energy contained in the water. However, most raindrop-based electromagnetic generators (EMGs) and triboelectric generators (TEGs) are unable to efficiently convert raindrop energy into electricity due to the rigid, bulky, and complex structures of EMGs with low output voltage, as well as the unstable and low current output of TEGs. Herein, we developed a flexible droplet-based triboelectric-electromagnetic hybrid generator (D-TEHG) including a droplet-based electromagnetic generator (D-EMG) and a droplet-based triboelectric generator (D-TEG) for efficiently harvesting raindrop energy. A flexible magnetically responsive hydrophobic film (MRHF) fabricated by a simple spray coating method was used in a hybrid power output system for raindrop energy conversion, serving as a "spring-like" structure for contacting and separating the electrodes in the D-TEG part, and as an excitation structure for moving the coil in the D-EMG part. When the D-TEHG was excited by a water droplet, the vibration of the elastic film induced the contact and separation of the two electrodes in the D-TEG part and the magnetic flux change through the coil in the D-EMG part, thus generating a dual electrical signal. When a 58.2 µL droplet was dropped from a height of 50 cm and impacted the D-TEHG, the D-TEG generated a peak open-circuit voltage (V OC) of ∼3.01 V and the D-EMG output a peak short-circuit current (I SC) of ∼11.21 mA. The integrated D-TEHG could generate high-performance power for charging capacitors and driving "DUT" LED arrays. By employing advanced flexible materials and structures, the hybrid generator might open up an avenue that makes efficient collection and utilization of large-area raindrop energy a reality. [Display omitted] • A flexible droplet-based triboelectric-electromagnetic hybrid generator (D-TEHG) is proposed. • The D-TEHG achieved dual electrical output through a single tiny water droplet impact. • The paralleling array-integrated D-THEGs can realize high-performance electricity conversion from multiple raindrops. [ABSTRACT FROM AUTHOR]

The unique microstructures of bulk metallic glasses (BMGs) provide them with excellent mechanical, physical, and chemical properties, having important applications in the fields of medical devices, military equipment, aerospace, etc. However, the superb mechanical properties also contribute to poor machinability of the BMGs. Currently, researchers have proposed to improve the machinability by single-point diamond turning, laser-assisted machining and ultrasonic vibration-assisted machining, but their plasticity and viscous flow remain unchanged, thus restraining further enhancement of surface quality. Atmospheric pressure cold plasma jet (APCPJ), which is rich in active particles, can effectively ameliorate material machinability by modulating material properties. In this paper, we propose to use the APCPJ to regulate the properties of BMGs, and carry out nanoindentation, nanoscratching, and micro-milling experiments to investigate the influence mechanisms of APCPJ on the material properties and cutting process. The results demonstrate that after modified by APCPJ, plastic deformability of the BMGs is improved due to the increase of free volume content; meanwhile, the viscous flow is inhibited. The micro-milling experiments indicate that under the conditions of feed rate V f = 500 μm/s, spindle speed n = 30,000 rpm, and cutting depth a p = 5 μm, the improvement effect of APCPJ on the cutting process is relatively optimum. The surface roughness Ra of the Zr-based BMG and Ti-based BMG obtained by APCPJ are respectively 0.076 μm and 0.081 μm, which can be reduced by 37.7 % and 38.2 % compared with dry micro-milling. The cutting forces F z in the direction of cutting depth are also reduced by 30.9 % and 23.3 %, respectively. The APCPJ-assisted micro-milling method proposed in this work may ameliorate the machining quality of BMGs and promote the application of BMGs and APCPJ-assisted machining technology in aerospace and precision machining. [ABSTRACT FROM AUTHOR]

Al-Li alloy has excellent overall performance and great development potential, which has been considered as a very ideal structural material for aerospace applications. However, the high ductility causes material adhesion to the tool surface, giving rise to severe tool wear, tool breakage, and other machining problems, which restrict the machining quality and practical application of Al-Li alloy structural parts. The multi-filed coupling of cold plasma and nano-lubricant minimum quantity lubrication (CPNMQL) may provide new enlightenment to break this bottleneck. Effects of the multi-field on the micro-milling process were characterized by tool wear, micro-milling force, three-dimensional surface roughness (Sa), and micromorphology. The research results demonstrated that cold plasma (CP) could not only increase the permeability of nano-lubricant on the Al-Li alloy surface but also enhance the material removal efficiency. When the micro-milling distance was 2 m, the average V B value (3.7 µm) of the three tool teeth under CPNMQL condition was reduced by 80.7 %, 54.9 %, and 51.3 %, while micro-milling edge radius (4.4 µm) decreased by 73.2 %, 24.1 %, and 44.3 % compared to dry, nano-lubricant minimum quantity lubrication (NMQL), and CP conditions, respectively. [Display omitted] • The cold plasma and bio-oil-based nano-lubricant coupling-assisted micro-milling Al-Li alloy. • The mechanism of CPNMQL on material machinability was systematically analyzed. • It is proven the CP could promote permeation of NMQL and fracture of Al-Li alloy. • It is proven the CPNMQL could restrain tool wear and improve surface quality. • The optimum Sa of 17 nm was obtained under CPNMQL condition with 6 mL/h. [ABSTRACT FROM AUTHOR]

• The proposed laser processing method is green and maskless. • This method is applicable for various metal substrates. • Some applications were achieved on the prepared patterned surfaces with grooves. • The patterned superhydrophobic surface has higher fog collection efficiency. Superhydrophobic surfaces with hydrophilic patterns are widely used in liquid transport, water collection, and cell screening. However, the preparation process of these patterned surfaces tends to be time-consuming and complicated. Here, we apply a simple, efficient and versatile laser processing method. Superhydrophobic substrates are firstly constructed by laser treatment and fluoroalkylsilane (FAS) solution; then superhydrophilic patterns such as dot-shaped or linear grooves are processed by secondary laser treatment. The dot-shaped grooves have strong adhesive force to droplets, and the linear grooves show obvious anisotropic adhesion behavior. On the basis of these features, applications like liquid transport, droplets grabbing and mixing, and fog collection are successfully achieved. The proposed laser processing method is applicable for various metal substrates including aluminum, copper, steel and titanium, and is expected to have promising application prospects in lab-on-a-chip system and chemical analysis domains. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the position and yaw angle trajectory tracking control problem is studied for unmanned helicopters subject to both matched and mismatched disturbances. To achieve the trajectory tracking goal, a feedforward-feedback composite control scheme is proposed based on the combination of the generalized proportional integral observer and the block backstepping control techniques. The controller design process mainly consists of two stages. In the first stage, some generalized proportional integral observers are developed for the helicopter system to estimate the mismatched, matched disturbances and their (higher-order) derivatives. In the second stage, the composite controller is designed by integrating the block backstepping control method and the disturbance estimates together. The proposed composite scheme guarantees asymptotic tracking performances for the position and yaw angle of the helicopter to the desired trajectories even in the presence of fast time-varying disturbances. Numerical simulations demonstrate the effectiveness of the proposed composite control scheme. [ABSTRACT FROM AUTHOR]

Polytetrafluoroethylene (PTFE) has excellent properties and has been widely used in various fields. However, the PTFE surfaces have relatively poor wettability and adhesive property, which restrains their widespread applications. Although atmospheric-pressure plasma jets have been employed to treat the PTFE surfaces, hydrophilization effect and processing efficiency still need to be further improved. In this paper, we propose to add ammonia water into the working gas of the atmospheric-pressure plasma jets to better modify the PTFE surfaces. The influences of ammonia water contents on surface wettability and adhesive property of the PTFE surfaces were investigated by water contact angle (WCA) measurement and peel strength experiments, respectively. When the ammonia water-mixed ratio was 1%, a WCA of ∼19° was obtained after 120 s plasma treatment, which was much lower than that treated by pure helium plasma jet (∼29°) and untreated surface (∼101°). In addition, the adhesive property was also well improved by the ammonia water-mixed plasma jets: peel strength of the sample treated by the ammonia water-mixed plasma jet was respectively 119 N/m and 446 N/m larger than that of the sample treated by pure helium plasma jet and the untreated sample. • Ammonia water is added into working gas of plasma jets to better modify PTFE. • The ammonia-mixed plasma jets show much better hydrophilization effect than others. • Water contact angle decreases from ∼101° to ∼19° after 120s plasma treatment. • Peel strength with epoxy glue is improved by 431% after the treatment. [ABSTRACT FROM AUTHOR]