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The reclosing action of the distribution network may cause multi-stage voltage sag in the grid nodes, which leads to more serious losses for sensitive users. In order to more reasonably characterize the disturbance degree of multi-stage voltage sag on sensitive equipment, a frequency evaluation method based on process immune time (PIT) and improved analytic hierarchy process is proposed. Firstly, multi-stage voltage sag waveforms caused by the reclosing corresponding action under transient fault and permanent fault are analyzed, and the PIT characteristic curve of sensitive equipment under multi-stage voltage sag is characterized. Secondly, the weight function method is used to calculate the influence degree of each stage sag. The analytic hierarchy process is improved by utilizing the correlation and influence degree of each stage sag. The weight of each stage sag is determined, and then the amplitude of the multi-stage voltage sag is calculated equivalently. The multi-stage voltage sag frequency evaluation method is proposed in the distribution network. Finally, the IEEE 30-bus system is used for simulation verification. The results show that the proposed method is more accurate and reasonable for the evaluation of multi-stage voltage sag frequency. This method provides a basis for the frequency evaluation and governance of multi-stage voltage sag. [ABSTRACT FROM AUTHOR]

In this paper, the free vibration response of a stiffened functionally graded graphene nanoplatelet (GPL)-reinforced composite multilayer cylindrical shell panel is studied for the first time. The shell is stiffened by both stringers and rings. Additionally, the effect of reinforcing the shell panel, ring and stinger with GPLs is independently studied. Halpin–Tsai relations are employed to evaluate the mechanical properties of the shell panel, rings and stringers. The first-order shear deformation shell theory, accompanied by the Lekhnitsky smeared stiffener model, using the numerical finite element method and Hamilton principle, is employed to develop the governing motion equations of the shell panel. Four different types of GPL patterns, including FG-A, FG-X, FG-O and UD, are assumed across the thickness of the shell panel, rings and stringers. The effects of different factors, including various weight fractions and patterns of GPLs nanofillers, the geometry of the shell panel and stiffeners and two displacement boundary conditions, on the natural frequencies of the shell panel, have been studied. [ABSTRACT FROM AUTHOR]

In order to improve the recognition rate and operational efficiency of the system, a method in which the image features compensation coefficients are optimized by using an improved simulated annealing algorithm is proposed. Firstly, eight computational factors with low computational complexity are given, which can be used to compensate image features. Secondly, the design flow of face recognition algorithm is presented. Thirdly, an improved simulated annealing algorithm is designed to solve the optimal combination of feature compensation coefficients in the face recognition system. Fourthly, the results of the feature compensation coefficients recommended by the improved simulated annealing algorithm are applied to the Efficient Face Recognition Algorithm (EFRA) in this paper, and verified on the simulation platform. Experiments show that the recognition rate can reach 100% when the training images are 6 in ORL. The proposed algorithm also performs well in MU_PIE dataset. [ABSTRACT FROM AUTHOR]

Fluoroalkyl(hetero)arylation of allylic alcohols with perfluoroalkyl iodide or difluoroacetic acid as fluoroalkyl source was developed herein, delivering functionalized ketones containing an α‐quaternary center. Formation of the fluoroalkyl radical was followed by its intermolecular addition to alkenes and the migration of a (hetero)aryl group with the concomitant generation of a ketone group to finish the domino sequence. Mechanistic studies indicated that the aryl migration proceeded through neophyl rearrangement in a radical pathway. Moreover, preliminary antifungal evaluation against Magnaporthe grisea is also described for the first time. [ABSTRACT FROM AUTHOR]

• Stator textures and rotor flexibility were used to reshare stresses and anti-wear. • Frictional stress homogenization is available after surface texturing. • Stress overloading and subsurface damage are released for textured stator. • Directional microtextures assist low-voltage and high-performance driving. • 158 rpm and 73 N·mm were obtained at 80Vp of drive voltage and 40 N of preload. Traveling-wave ultrasonic motors promise widespread applications in precision engineering, medical, and aerospace field due to their high-power density, but suffer from low efficiency and stress gradient. In this case, the synergy effect of surface-functionalized friction regulation and interface coupling interference of wear loss/debris could effectively eliminate these deficiencies. Herein, we report a low-voltage driving rotational piezoelectric motor (PM30) that proceeds through laser-induced microtextured stators coupling with flexible rotors, which enables working at a rotational speed of 158 rpm and torque of 73 N·mm, respectively, under the condition of low-voltage (80V p) and low-preload (40 N). Such operation parameters are far beyond the current reported results. Furthermore, FEM simulation and SEM observation demonstrated that the low-voltage driving and high-performance output are resulting from the combination of surface microtextured stators for friction enhancement and flexible rotors for displacement amplification with contact expansion, which regulates tangential friction and reshares the stresses distribution during the dynamic contact along with the rotary motion of rotors. This work provides a promising strategy to construct friction-stress regulation and energy-transformation enhancement toward energy-saving and high-efficient friction drive for piezoelectric devices. [ABSTRACT FROM AUTHOR]

Friction behavior and serious wear of the stator/slider pair are critical to restrict the development and commercialization of standing-wave linear ultrasonic motors. Owing to the effective friction regulation of laser surface microtextures, a multi-connected vesicle-like microarray consisting of the micropits and microgrooves was prepared on the slider surface. Finite element analysis at the microscale showed the proposed micro-textures were prone to cause the stator tip to sink, resulting in an increase of horizontal impact effect of ultrasonic vibration and the alternately regulating of static-dynamic friction boundary, which enhances the tangential force and improves the driving effect. The experimental results approved that the composite microtextures combining the pits of 100 μm and the grooves of 50 μm are positive for friction drive and output performance enhancement. Specifically, the output power of the low-voltage driving linear piezoelectric motor with the complex texturing array is 66% higher than that of non-textured ones. This study provides a reliable approach to enhancing the friction-driving performance and operation stability of piezoelectric motors or actuators. [Display omitted] [ABSTRACT FROM AUTHOR]

A compact impact two-degree-of-freedom linear-rotary piezoelectric motor is proposed using a single actuator. The proposed piezoelectric actuator has a pair of deformation counteracting helical interdigitated electrodes on its outside surface, which can be divided into two parts. When the two parts of the piezoelectric actuator are driving under the same driving voltage signals, the motor can realize independent linear motion. When the two parts of the piezoelectric actuator are driving under the driving voltage signals with opposite duty cycles, the motor can realize independent rotary motion. The fabricated piezoelectric motor can produce a maximum average linear velocity of 1.9 and −2.3 mm/s with a saw-shaped driving signal of 400 Vp-p (peak-to-peak driving voltage) at 9 kHz. Experiments also show that the fabricated piezoelectric motor can realize a maximum average rotary velocity of 2440 and −2235 mrad/s with a driving signal of 400 Vp-p at 9 kHz. The maximum load force and torque of the prototype are about 0.4 N and 1.5 mN m, respectively. The proposed motor provides a wide driving frequency and realizes high velocity in both linear and rotary motions. [ABSTRACT FROM AUTHOR]

Classical traveling-wave ultrasonic motors (TWUMs) usually generate the elliptical clusters on the stator surface through the bending vibration of the annular stator on the basis of piezoelectric excitation, and the torque output and power transmission are realized by friction coupling under the rational preload. Stable and reliable working characteristics attracted the focus of various applications. High energy consumption and low efficiency are restricted factors for the service performance of motors. Displacement amplification and stress regulation based on flexible design become a possible approach to improve motor performances. In this study, a TWUM30 prototype was proposed with consideration of (sub) structure optimization, i.e., tooth height and backlash of the stator elastomer. The flexible design of the rotor structure was carried out for consideration of the contact area and stress regulation. After integrated bonding of the stator and PZT4, the electrical and vibration characteristics of the stator prototype are measured by an impedance analyzer and high-precision laser micro-displacement sensor. Results showed that the proposed TWUM30 is capable of operation under low-voltage driving (41.9 kHz @ 80 V p), and the extreme mechanical performances presented the stall toque of 64mN∙m and the no-load speed of 153.8 rpm. With the combination of the flexible design and systematic integrated manufacturing of the stator/rotor, low-voltage driving of the TWUM30 motor under ultra-low preload was realized at low cost and the adverse effects of excessive preload were suppressed. This study is expected to provide support for high reliability design and long-life service of the TWUMs. It also provides a realistic possibility for the flexible design and application of energy-saving and high-efficient traveling-wave piezoelectric drivers. [Display omitted] • TWUM30 prototype was proposed with (sub)structures optimization and integrated manufacturing. • Flexible redesign of rotor was conducted for the contact area and stress regulation. • TWUM30 is capable of operation under low preload and low-voltage driving (40 N, 80 V p @41.9 kHz). • Mechanical performances (toque & speed) of TWUM30 were compared and improved. [ABSTRACT FROM AUTHOR]

The application of the friction drive of carbon-fiber-reinforced composites to a standing-wave ultrasonic motor was investigated. Friction drive tests were conducted on carbon-fiber-reinforced epoxy resins (CF/epoxy) by home-made test rig, which was based on plate-rod vibrator. The effects of fiber orientation and ply thickness on dynamic drive and dynamic normal forces were investigated. Fiber orientation angle and ply thickness affected friction drive. Different dynamic drive forces, which varied both in amplitude and period, were observed for CF/epoxy composites with different winding angles. A CF/epoxy composite with a winding angle of 30° showed the largest dynamic drive force (∼0.45 N) and the shortest contact period (∼26 μs). The period of dynamic normal force was uniform (∼65 μs) for various CF/epoxy composites. Wear traces of different composites exhibited different wear modes, such as scuffing, peeling, and shearing. The anisotropic property of CF/epoxy material affected the drive process of standing-wave ultrasonic motor. The current study taking the carbon-fiber-reinforced epoxy resin as an example of anisotropic materials arise more enough attention on inexpensive, biodegradable, and renewable alternatives for the efficient and durative drive of a standing-wave ultrasonic motor. POLYM. COMPOS., 37:2152-2159, 2016. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Coulomb friction model is modified with considering the preliminary distance of rigid bristles and shear stiffness of the contact surface. The degeneration in friction drive and wear behavior induced by nonlinear contact (i.e., impact, intermittent, and fretting) is outlined. Wear tests of LUSMs with V-shape transducers are conducted by a homemade reciprocating apparatus. Results show that chemical inertness, thermotolerance, elasticity as well as surface topography are critical for the contact interface of LUSMs A systematic approach involving, for instance, dynamic contact, friction model, and wear behavior provides new perspectives in improving service performances and promoting practical applications. [ABSTRACT FROM AUTHOR]

Friction materials with favorable mechanical and tribological characteristics are critical to the drivability and reliability of ultrasonic motors. Preliminary screening at atmospheric conditions suggests that filled polymer composites such as poly-tetrafluoroethylene (PTFE), phenol formaldehyde resins (PF), and poly-p-hydroxybenzoic acid (Ekonol ® ) are potential candidates for use as friction materials ultrasonic motors. The wear behavior of these polymers in contact with duralumin (2A12) stators was examined and compared under various environmental conditions: room temperature (RT) and atmospheric pressure, RT and low vacuum (5 Pa), RT and high vacuum (5×10 −3 Pa), and both low temperature and low vacuum. The wear loss of these various polymers was characterized by tracking changes in their surface roughness parameters ( R a and R v ). Wear tracks on the surfaces of different frictional materials were inspected using scanning electron microscopy. Results show that the wear resistance of Ekonol and PF composites is poorer in vacuum than in ambient conditions, whereas that of PTFE composite is not readily susceptible to ambient conditions. Lastly, wear modes and mechanisms at the various conditions are discussed. [ABSTRACT FROM AUTHOR]

While high friction coefficients and good wear resistance are antagonistic properties of most materials, these properties are expected to promote excellent torque-speed characteristics and extend the life span of ultrasonic motors. Blending is an accepted technique for modifying tribological applications. p-Hydroxybenzoic acid polymer (Ekonol) blends with different compositions, and proportions were prepared through mechanical blending. Poly(tetrafluoroethylene) (PTFE), poly(etheretherketone), and poly(phylenesulfide) (PPS) were selected as dispersed phases. The mechanical properties of the blends were investigated, and their tribological performance was tested using a block-on-ring wear meter. The worn surfaces of Ekonol blends were observed using a scanning electron microscope to elucidate the relevant wear mechanisms. Results showed that the dispersed phases have distinct effects on the impact strength and hardness, as well as friction coefficient and wear rate, of the blends. Curves of hardness and friction coefficient versus the dispersed phase content showed apparent similarities, which indicates that hardness influences the friction of polymer blends in contact with carbon steel. Worn tracks on the surfaces of different polymer materials showed that the dominant wear mechanism transforms from fatigue and abrasion into adhesion with the addition of a dispersed phase; delamination was observed in the transfer films, especially those formed by the Ekonol/PTFE and Ekonol/PPS blends. [ABSTRACT FROM AUTHOR]

• A home-made measured simple system for output performances of linear piezoelectric motors were constructed. • A prototype of SWUMs is manufactured and the mechanical characteristics were tested. • A basic measurement approach for service performances of linear ultrasonic motors was presented. • Static and dynamic performances of linear motor can be measured simultaneously in real time. A prototype of the linear standing-wave ultrasonic motors having arc tip is designed and manufactured, and the output performances and mechanical characteristics were tested and evaluated using a home-made measured simple system in this study. Results show that the flexible design of the driving foot is interesting for the performance improvement and simplification design of standing-wave ultrasonic motors. The measured system is simple and is available to evaluate the output performances (thrust and speed) and mechanical characteristics curves of linear motors. The influence trend of preload and driving voltage on output speed is opposite, while the influence trend of thrust is parabola. The peak value of applied voltage is critical for the mechanical characteristic curve of piezoelectric motor. This study also supports a basic measurement approach for service performances of linear ultrasonic motors and the tribological behaviors of motor and/or actuator devices using piezoelectric vibration. [ABSTRACT FROM AUTHOR]

A homemade testing device is used to measure the operating speed of linear piezoelectric motors with different friction couples that consist of ceramic stator tip and slider. The dynamic variations of motor performance are analyzed using a statistical method, and the attenuation mechanism is discussed using the energy method during the periodic contact between the driving tip of the stator and the slider. Study of the operating characteristics of piezoelectric motors can clarify the change and transformation of the stator/slider contact by reflecting the driving process, wear, and service lifespan of the contact interface of friction couples under ultrasonic vibration. This study is significant for the performance evaluation of the operations and alternation of friction materials for standing-wave piezoelectric motors. • The dynamic variations of motor performance are analyzed using a statistical method. • The attenuation mechanism is discussed using the energy method during the periodic contact. • The factors to evaluate the steady-state operations of piezoelectric motors is defined. • Friction characteristics of ceramic couples are compared for SWUM operations. [ABSTRACT FROM AUTHOR]

This study focuses on the wear debris of different friction materials for linear standing-wave ultrasonic motors (SWUMs). Wear debris with different morphology and sizes derive from wear mechanisms and has a critical influence on the contact state. The generation mechanisms of the wear debris are analyzed by using the elastic-plastic indentation mechanics and the typical morphography of the wear debris are discussed by considering of the energy balance. Oxide ceramics with high strength and fracture toughness were used as the friction materials of the driving tips, which are in contact with the carbon steel and oxide ceramic sliders. The wear tests were conducted using a homemade reciprocating apparatus. The worn surfaces and debris of different couples were investigated by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). The statistical results of the debris size analysis were consistent with the results of the theoretical analysis of the indentation fracture mechanics. The wear debris was characterized with regard to size parameters, roundness factor, aspect ratio, and fractal dimension using image processing, and the relationships of the parameters and the wear modes are discussed. The generation mechanisms of the wear debris differ for the different friction couples due to the complex states and the differences in the mechanical properties. The plastic factor (E / H) and brittleness factor (H / K IC) are critical to the maximum dimension of the wear debris for given friction couples. Image 1 • Dimensions of wear debris from friction couples for SWUMs were analyzed based on indentation fracture. • Patterns of wear debris were analyzed by using a general theoretical approach. • Relation between debris dimensions and the plastic factor (H / E) and brittle factor (K C / H) were sketched quantitatively. • Clustering of debris was conducted by the morphology parameters of convex hull and bounding circle. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new method is proposed to synthesize fluorine-containing onion carbon films. • A little fluorine species could manyfold decrease the surface adhesion of films. • The optimized film integrates the merits of fluorine doping and onion carbon. Abstract Coating a thin-layer solid lubricant with low adhesion and friction is desired for silica-based micro/nano electromechanical systems (MEMS/NEMS). Onion carbon is a promising one, especially fluorine-containing onion carbon with low surface adhesion. Herein we report a new route to synthesize fluorine-containing onion carbon (FOC) through carbonizing electrophoresis-deposited organic films. A little fluorine (1.65–3.64 at.%) could manyfold decrease the surface adhesion. The optimized FOC integrates the merits of fluorine doping and onion carbon, presenting ultralow surface adhesion (2.72 nN) and friction coefficient (0.03). These results suggest that this strategy is a promising approach to fabricate the desired solid lubricants for MEMS/NEMS. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) Ti–6Al–2Sn–4Zr–2Mo–0.1Si–(0, 2, 4)W (wt%) alloys were fabricated by thermomechanical consolidation of TiH 2 -based powder compacts and subsequent heat treatments. Samples of the as-fabricated alloys were also heated at 650 °C for 200 h. The addition of 2 or 4 wt%W to the base alloy changed its microstructure of parallel α/β lamellar colonies and grain boundary α (α GB) to an interwoven α/β t microstructure consisting of α GB and a network of interpenetrating α plates with β transformed structure (β t) domains comprising variants of fine α laths and β matrix. The partition of the β stabilizing W between β and α phases and the low diffusivity of W atoms limited the growth of α plates/laths, decreasing the thickness of α plates/laths and increasing the volume fraction of β. The increased hardening of the β phase and enhanced α/β interface strengthening associated with the 4 wt%W addition led to a significant increase in the tensile strength of the alloy from 1281 ± 10–1411 ± 12 MPa. However, the high flow stress and the very fine microstructure caused significant strain localization in the weak α GB , resulting in premature fracture of the α GB (intergranular fracture) and the low ductility (1.4%). Here, premature fracture meant the fracture occurred prior to the alloy reaching its ultimate tensile strength. The heating caused the β interlaths in the W-free alloy to partially dissolve and become β particles distributed along the original lines of β interlaths accompanied by the precipitation of α 2 -Ti 3 Al in the α plates. The addition of W inhibited the dissolution of β interlaths and caused the precipitation of a higher volume fraction of α 2 precipitates during heating. The microstructural changes caused by heating resulted in a slight decrease in strength and a significant decrease in ductility for the W-free alloy, but a significant increase of the yield strength of the 2 W and 4 W alloys with some sacrifice of the tensile ductility. The microstructural reasons for the effects on mechanical properties were analyzed with the assistance of detailed characterization of the dislocations in the deformed specimens. • Effects of W alloying on a PM Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy are investigated. • W refines α plates and enhances formation of β transformed structure domains. • W enhances hardening of the β phase and α/β interface strengthening. • W increases the microstructural stability and prevents the strength reduction from heating. • High W content promotes α 2 precipitation strengthening of the alloy after heating. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) near α Ti−6Al−2Sn−4Zr−2Mo−0.1Si−0.5Y (wt.%) alloy with a low oxygen content and fabricated by thermomechanical powder consolidation of an elemental powder blend with a trace amount of Y addition was subjected to two heat treatments to obtain different microstructures which were free of grain boundary α (α GB) layers. One heat treatment (960°C/1h/AC, AC = air cooling) led to the formation of an α/β t microstructure consisting of 75.3 vol% primary α (α p) domains with globular and platelike morphologies, 21.5 vol% β transformed structure (β t) domains comprising ultrafine secondary α (α s) lamellae in a β matrix and 3.2 vol% thin β strips. The other heat treatment (960°C/1h/WQ+580°C/6h/AC, WQ = water quenching) led to the formation of a microstructure consisting of 38.2 vol% isolated α p plates, slabs, and globules dispersed in a β t matrix comprising nanometer-sized α s lamellae and residual β strips. The first microstructure rendered the alloy with high tensile strength of 1128 MPa and excellent tensile ductility of 15.6%, thanks to the activation of abundant and slips in all α grains and tensile twinning in the "hard" <0001> micro-textured α grains with the c-axis parallel to the tensile force direction which mitigated the strain localization and enhanced strain hardening. On the other hand, the harder nanostructure of the β t matrix in the second microstructure resulted in a significantly increased tensile strength of 1351 MPa while maintaining an excellent tensile ductility of 10.5%. This can be attributed to the activation of abundant and slips in thin α plates and a limited degree of tensile twinning in the "hard" α domains, as well as a large number of statistically stored dislocations (SSDs) within the micron-scaled α slabs/globules. Both microstructures rendered the alloy with favorable ductile fracture. [ABSTRACT FROM AUTHOR]

• A measuring system for electromechanical multi-parameters of linear piezoelectric motors was constructed. • Signal conditioning and measurement circuits were designed for physical signals processing, A/D conversion, and transmission. • The principle and structures of the synchronous testing system were demonstrated based on the virtual instrument. • The calculation principle of the transient characteristic of multi-parameters of piezoelectric motors was proposed. Due to the time-dependent correlations, the measurement and characterization of electronic and mechanical parameters are critical for linear piezoelectric ultrasonic motors (USMs) during the running process. This study constructed a homemade system to measure the electromechanical multi-parameters and kinetics performances agilely, transiently, and synchronously. The principles and structures of the test system were demonstrated based on virtual instrument technology. A signal conditioning circuit is designed and used for physical signal processing, A/D conversion, and transmission. The difference in resonant frequencies was discovered for the synchronization acquisition of mechatronic parameters, and the instantaneous characteristics of electromechanical parameters for SWUM (e.g., driving voltage, input current, thrust force, and speed during the start-up and power-off process) were established based on the experimental data. This study is significant for the measurement/evaluation of the dynamic and transient performances of linear piezoelectric motors and actuators. [ABSTRACT FROM AUTHOR]

Epoxy resin (EP) is prone to brittle fracture during friction due to internal stress after curing, resulting in fatigue wear and cracking. Adding carbon fillers is considered as one of the great potential solutions to solve the serious dry wear of EP. Herein, we develop a novel carbon capsule composite filler (CNC‐IL) filled with ionic liquid (IL) in carbon nanocages (CNC) using the vacuum principle to address these concerns. Compared with pure EP, the friction coefficient (0.10) and wear rate (1.712 × 10−6 mm3 Nm−1) of the optimized CNC‐IL/EP were reduced by 74.62% and 88.14%, respectively. Such excellent tribological properties can be attributed to the solid–liquid lubricating film formed by the IL released from the broken CNC during friction. A low‐shear‐resistance slip layer can be formed between the CNC‐IL in the film due to the repulsion of the isoelectric ions adsorbed on the surface of the CNC; it effectively integrates the self‐lubricating functions of CNC and the liquid lubrication functions of ILs. This work provides a valuable idea for designing C/EP composites with good antifriction properties. [ABSTRACT FROM AUTHOR]

• T-phage-inspired multilegged design for microrobot. • A rotationally asymmetric structure. • Multiple working modes: forward motion, backward motion, steering, climbing, and swimming. • The maximum velocity of 120 mm/s under a driving voltage of 50 V p-p and the maximum carrying weight of 10.6 gs, 6 times more than the weight of the microrobot. • Miniaturization capability and ability to work in various environments, i.e., a narrow tube and water. T-phages use contractile tails to recognize host bacterial and move on the surface of bacterial. This virus demonstrates remarkable locomotive capabilities in recognition and infection progress. The field of microrobotics focuses on achieving these functions in mobile robotic systems of centimeter size. However, owing to the structure size and weight, it has been a challenge to satisfy high robustness, fast motion, adequate carrying capacity, low driving voltage, and versatile environmental adaptability in one robot. In addition, functional microrobots require multimodal locomotive strategies that reconcile the constraints imposed by different applications. Inspired by the unique structure of T-phage in the micro-world, we develop a T-phage Mimic MicroRobot (TMMR), which is composed of a triangular prism core with piezoelectric elements and legs attached on bases, mimicking the core and the tail fibers of the T-phage, respectively. The triangular prism structure avoids rollover while moving, indicating the robustness of the design. TMMR of 2.5 × 2.5 × 2.6 mm3 weighs 1.74 gs and can be easily further miniaturized. It is capable of moving forward, backward, and steering at a low voltage of 25 V. Working mechanisms for each type of motion are analyzed using the finite element method. Results show that TMMR reaches 120 mm/s, 4.8 body lengths per second (BL/s), and carry an object weighing 10.6 gs, 6 times more than its weight. By sealing the body and adding passive flaps, TMMR achieves a "swimming" motion with a velocity of 16 mm/s. TMMR shows potential for versatile applications in a narrow and constrained environment. [Display omitted] [ABSTRACT FROM AUTHOR]

The wear of a traveling wave ultrasonic motor has certain particularities due to its special drive mechanism. In this investigation, the progression of wear of a brass stator against a PTFE–matrix composite friction material is reported. During 200 h of operation, the performances of an ultrasonic motor and the properties of its friction surfaces were examined. Different wear stages were observed. Surface topography and debris characteristics were analyzed to assess the wear mechanisms that operate in different wear stages. Under the imposed operating conditions the running-in wear stage requires 80 h. In early period of running-in wear stage, adhesive wear is the main wear mechanism of the friction material. The debris forms a multi-layered, agglomerate sheet. In the second part of the running-in period, the main wear mechanisms change to delamination wear and adhesive wear. The debris piles up as small particles. In the steady wear stage, the main wear mechanism is delamination wear result from fatigue. The debris forms small flake-like sheet but they are rare. Abrasive wear exist in all stages of wear. By contrast, the main wear mechanism of the brass stator is abrasive wear. [ABSTRACT FROM AUTHOR]

A method combining internal oxidation and thermomechanical consolidation of a composite powder with a trace amount of Y addition was used to fabricate powder metallurgy (PM) near-α Ti–6Al–2Sn–4Zr–2Mo−0.1Si−0.5Y (wt%) alloy, in which submicron Y 2 O 3 particles were in-situ formed and distributed uniformly in the matrix to achieve a low oxygen content and an excellent combination of high tensile strength of 1242 MPa and excellent tensile ductility of 16.2%. The in-situ reaction of uniformly dispersed Y particles in the composite powders prepared by high-energy ball milling with the oxygen in the matrix to form submicron Y 2 O 3 particles during powder consolidation can significantly scavenge oxygen in the matrix and eliminate the coarse grain boundary α layers. The Y 2 O 3 particles also work as nucleants for heterogeneous nucleation of α grains in the prior β grains during cooling, thus promoting the formation of α plates with a larger number of orientation variations and a decrease of their aspect ratios in the interwoven α/β t microstructure consisting of fine α plates and β transformed structure (β t) domains, which is beneficial to suppress the initiation and rapid propagation of cracks during tensile deformation. It is demonstrated that with the high flow stress rendered by the ultrafine interwoven α/β t microstructure and oxygen scavenging effect of Y on the matrix, twinning across α/β t interfaces and decohesion between the submicron Y 2 O 3 particles and matrix occur during tensile deformation. This further suppresses formation and propagation of microcracks often seen in the Y 2 O 3 particle free PM near-α titanium alloy of the same composition in the same situation. It is believed that the twinning and decohesion of the interfaces between Y 2 O 3 particles and matrix are responsible for the mitigation of strain localization needed for formation of microcracks, which is essential to maintain a good tensile ductility and allow the fracture to be totally ductilized. • A submicron Y 2 O 3 particle dispersed PM near α alloy with an interweaven α/β t microstructure. is fabricated. • The in-situ Y 2 O 3 particles cause a decrease of matrix O content and microstructural changes. • The microstructural changes cause clear decrease of strength and significant increase of tensile ductility. • The Y 2 O 3 /matrix decohesion and twinning lead to ductilization of the fracture. [ABSTRACT FROM AUTHOR]

• The effects of laser parameters on the surface temperature field were evaluated. • The phase transition in the processed region was analytically modelled. • The effects of the process parameters on the geometrical features were analyzed. Surface micro-texturing paves the way for surface functionalization of material and engineering parts with abrasion resistance, hydrophilicity, anti-reflectivity, and antimicrobial properties. Nevertheless, the morphological control of micro-textures with high precision and efficiency is still challenging for advanced applications, especially for lightweight design and corrosion resistance in aerospace and transportation. Despite many stumbling blocks in achieving high-precision micro-textures, the serviced surface properties relate to their surface asperities and micro-textures. Laser surface texturing can be used for surface-functionalization and structuration control of counterparts with textured micro-pits and micro-grooves. With the interaction of pulse laser and materials, the influence of the laser process on the geometrical configuration of the alloy's surface micro-textures was investigated by altering the laser processing parameters. We found that the depth and width of micro-textures are positively correlated with the laser power and scanning times, and negatively correlated with the laser frequency and scanning speed. This research is significant in enabling the active design of non-ferrous metal surface micro-textures, regulating surface properties, and enhancing unique applications in mechanics, biology, medicine, and physiochemistry fields. [ABSTRACT FROM AUTHOR]

Fe-based Fischer–Tropsch synthesis (FTS) catalysts, promoted by graphitic carbon (GC) and potassium, were directly prepared by a novel modified sol–gel method without further reduction. The effects of the GC promoter and K contents on the catalyst structures and FTS performance were systematically studied. The significant improvement of FTS performance was attributed to GC, which acted as a reductant for synthesizing metallic Fe0 from Fe3+ in the chelating complexes, and effectively enhanced the strength of SiO2 channels. Meanwhile, an appropriate amount of K ions promoted CO chemisorption and inhibited H2 chemisorption by affecting the electronic properties of iron, resulting in a lower hydrogenation capacity and a higher olefin selectivity. Transmission electron microscopy and CO-TPD characterization proved that FeK@SiO2-GC catalysts had well-defined core–shell structures and higher CO chemisorption. The FTS results indicated that the introduction of a small amount of GC and K (K/Fe/GC, 1.5/100/100) improved the reduction and dispersion of iron during the calcination process, and significantly enhanced the FTS activity. The CO conversion and C2–C4 olefin selectivity of the catalyst increased rapidly from 21.1% and 23.7% to 53.5% and 41.3% after GC and K promotion. The GC and K promoted Fe-based catalysts prepared by a modified sol–gel method, which omits the complex and high energy consumption reduction process, can be used directly for highly efficient FTS and thus will be more promising in the future. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) with abundant oxygen functional groups has been widely studied as friction-reduction additive in lubricating oil or directly as solid lubricant. However, the lubrication mechanisms of these groups in solid GO lubricants have not been well revealed yet. Herein, we report a new strategy to prepare hydroxyl-carboxyl-terminated GO, hydroxyl-terminated GO, less-hydroxyl-terminated GO, and reduced GO (rGO), and then employ them as a frictional research model to address this concern. The results reveal that a little amount of water confined in GO layers dominates the interlayer shearing resistance by confining hydrogen-bond interaction. The strongest confinement effect to hydrogen-bond is achieved in hydroxyl-terminated GO, leading to the lowest shearing resistance between GO layers and then the enhanced friction performances. This finding first reveals the synergistic lubrication mechanism of oxygen functional groups and confined interlayer water molecules, providing us a new design view to fabricate superior graphene-based solid lubrication materials. Unlabelled Image • A new strategy is proposed to optimize the oxygen functional groups on GO. • The optimized hydroxyl-terminated GO shows an ultralow friction coefficient. • The contribution of confined interlayer water is first reveled in GO lubricants. • The friction reduction comes from the weakened hydrogen-bond interaction. [ABSTRACT FROM AUTHOR]

Exposure to fine particulate matter (PM2.5) is associated with adverse health impacts on the population. Satellite observations and machine learning algorithms have been applied to improve the accuracy of the prediction of PM2.5 concentrations. In this study, we developed a PM2.5 retrieval approach using machine-learning methods, based on aerosol products from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the NASA Earth Observation System (EOS) Terra and Aqua polar-orbiting satellites, near-ground meteorological variables from the NASA Goddard Earth Observing System (GEOS), and ground-based PM2.5 observation data. Four models, which are orthogonal regression (OR), regression tree (Rpart), random forests (RF), and support vector machine (SVM), were tested and compared in the Beijing–Tianjin–Hebei (BTH) region of China in 2015. Aerosol products derived from the Terra and Aqua satellite sensors were also compared. The 10-repeat 5-fold cross-validation (10 × 5 CV) method was subsequently used to evaluate the performance of the different aerosol products and the four models. The results show that the performance of the Aqua dataset was better than that of the Terra dataset, and that the RF algorithm has the best predictive performance (Terra: R = 0.77, RMSE = 43.51 μg/m3; Aqua: R = 0.85, RMSE = 33.90 μg/m3). This study shows promise for predicting the spatiotemporal distribution of PM2.5 using the RF model and Aqua aerosol product with the assistance of PM2.5 site data. [ABSTRACT FROM AUTHOR]

Despite good approval for excellent friction regulation, surface texturing seems to be a penalty area for gears mostly because of the traditional cognition of surface (micro-)pitting and structural similarity. Surface micro-textures were applied to the pinion flank to regulate the time-varying meshing stiffness and enhance the meshing characteristics. Results showed the stress regulation and smoothing capability of micro-textures in meshing process, the time-varying meshing stiffness increases by 4.75% and the frictional stability increased by 52%. Experiment results approve that the flank micro-textures can control friction and reduce torque by 26.2%. This study is significant for the systemic design of the dynamic performance and frictional meshing, especially for the gear engagement reliability in space without film lubrication. [Display omitted] • Surface pitting-like micro-textures were preset on flank surfaces of spur gears. • The symmetrical and continuous micro-textures near the pitch line were compared. • The micro-textures are capable to improve the meshing stiffness of gears. • Stress on flanks is rearranged for homogenize distribution after micro-texturing. • Micro-textures regulate the dynamic friction and increase friction stability. [ABSTRACT FROM AUTHOR]

An approach combing ball milling (BM) and thermomechanical consolidation of a TiH 2 based composite powder was used to fabricate powder metallurgy (PM) α+β Ti–4Al–4Mo–4Sn-0.5Si (wt%) alloy. Compared with the coarse-grained alloy with the same composition fabricated by the traditional blended elemental (BE-PM) method, the alloy exhibited a low oxygen content of 0.27 wt% and much-refined β grains with average size of 21 μm owing to the unpassivated and refined powder and fast consolidation process. The fine-grained alloy exhibited an α/β t lamellar microstructure in combination with short grain boundary α (GB α) layers and small GB Widmanstätten α (α WGB) colonies, while the coarse-grained alloy was composed of a similar α/β t lamellar structure in combination with long and continuous GB α plates and large-sized α WGB colonies. β t represented a transformed β structure consisting of fine secondary α laths and residual β layers. It was worth noting that the fine-grained alloy exhibited both higher strength and drastically higher ductility than the coarse-grained alloy (yield strength: 1238 vs 1156 MPa; elongation to fracture: 15.4% vs 4.1%). The enhanced strength was ascribed to the width refinement of α plates and increased fraction of β t domains. The excellent ductility was attributed the refined α WGB colonies and short GB α layers with increased variety of crystal orientations, which relieved strain concentration at GB α phase and thus suppressed the crack nucleation and propagation along it. Therefore, a high density of and dislocations were successfully activated in the thin α plates to accommodate plastic deformation, leading to an excellent ductility. This work provides a new strategy to fabricate high strength PM titanium alloys with excellent ductility. [ABSTRACT FROM AUTHOR]

The adhesion strength of coating is critical to the coating lifetime. Our previous study found a novel volcano-shaped texture enhanced the adhesion of physical vapor deposition (PVD) AlCrN coating. This study aims to further investigate the influence mechanism of this texture. Volcano-shaped textures with different diameters and area ratios were fabricated on DC53 die steel samples by a long-pulse-width laser. By adapting X-ray diffraction (XRD), curvature measurement and cross-sectional observation of textures, chemical compliance of coating and substrates, stress condition of the substrate surfaces and physical bonding of coating and substrates were analyzed. Scratching tests and indentation tests were also conducted to study the adhesion strength under dynamic and static contact. The results showed that textured surfaces boasted better chemical compliance with coating than the untextured one; textures with suitable topographic parameters could reduce inner defects of coating and curb crack propagation, thus inhibiting coating spallation. The most suitable topographic parameters were found to be a diameter of 310 μm and an area ratio of 25 %, of which the critical load of coating failure (L c) has improved 17.5 % from that of the untextured sample. This study will provide guide for design and optimization of surface topography of textured coating. [Display omitted] • A novel volcano-shaped texture for enhancing coating adhesion strength is proposed. • The volcano-shaped textured substrate boasts good chemical compliance with coating. • Volcano-shaped textures inhibit micro-defects and crack propagation in coating. • The optimal topography of the texture with the strongest coating adhesion was found. [ABSTRACT FROM AUTHOR]

This study aims to investigate friction and wear performance of a novel volcano-shaped textured PVD coating, hoping to find the influence mechanism of volcano-shaped texture on the tribological behavior of textured coated surface. The volcano-shaped texture was fabricated on the sample surface by laser, and then PVD coating was deposited. For samples with different texture diameters or texture area ratios, reciprocating pin-on-disk wear tests were conducted to study tribological properties. After tests, wear topographies of samples and counter pins were observed to analyze wear details. The results showed volcano-shaped texture with suitable diameters and area ratios was conducive to lowering friction coefficient and reducing adhesive wear. The optimal texture diameter and area ratio were 310 μm and 25%, respectively. Meanwhile, the texture with large area ratios increased friction. These results indicated this texture's potential for friction control. Finally, the influence mechanism of volcano-shaped texture was proposed. [Display omitted] • The volcano-shaped texture can both decrease and increase friction. • There exists optimal diameter and area ratio of volcano-shaped texture to achieve best friction and wear performance. • Tribo-film formed on the convex area reduced texture wear. • Influence mechanism of volcano-shaped textured PVD coating on the friction and wear performance was studied. [ABSTRACT FROM AUTHOR]

Epoxy resin (EP) as a friction material suffers from serious friction and wear in high temperatures. Adding various carbon fillers into EP to form carbon/EP composites is one of the solutions to this concern. However, the correlation between the filler's dimensionality and their friction properties under high temperature conditions is missing. Herein we construct a comparable dimensional model system of carbon fillers (i.e., one- to three-dimensional carbon nanocage assemblies) to reveal the dimensional effect in high temperature lubrication. Compared with EP, a merely 0.10 wt% of one-dimensional filler can reduce the composite's friction coefficient and wear rate by 36% and 95% at 30 °C, respectively; while for those filled with other dimensionalities, the corresponding decreases are less than 24% and 60%. Even at very close to EP's glass transition temperature of 150 °C, it still maintains a low friction coefficient only with a slight increase in wear. The enhanced high temperature lubrication performance is first attributed to the advantage of one-dimensional fillers to suppress the EP matrix's creep and then easily sliding in the softened transfer film. This study provides a new view for the design of carbon fillers used in EP-based high temperature lubrication composites. [Display omitted] • A comparable dimensional model system for carbon fillers is fist constructed. • The dimensional effect of carbon fillers in EP is demonstrated and explained. • EP filled one-dimensional filler has the best high-temperature lubrication property. • Optimized carbon/EP has a maximum friction application temperature of 150 °C. • The possible high temperature friction mechanism of carbon/EP is revealed. [ABSTRACT FROM AUTHOR]

To elucidate the roles of CD34-positive stromal cells and alpha-smooth muscle actin-positive stromal cells at the tumor border of skin sweat gland neoplasms, we examined expression of stromal cell markers in the tumor capsule of 19 skin sweat gland neoplasms (16 mixed tumors of the skin and three nodular hidradenomas) using monoclonal antibodies to CD34, CD31, cytokeratin 14 (CK14), alpha-smooth muscle actin (ASMA) and high molecular weight caldesmon (HCD). We regarded CD34-positive, CD31-, CK14-, ASMA- and HCD-negative stromal cells to be CD34-positive stromal cells, and ASMA-positive, HCD-, CK14-, CD34- and CD31-negative stromal cells to be ASMA-positive stromal cells. CD34-positive stromal cells were detected in the tumor capsule of all 19 of the tumors examined. In nine of the 16 mixed tumors (56%) and all of the three nodular hidradenomas, ASMA-positive stromal cells were detected at the immediate inner side of the CD34-positive stromal cell layers. These results indicate that cellular components in the tumor capsules of mixed tumors of the skin and nodular hidradenomas are CD34-positive stromal cells and ASMA-positive stromal cells, and suggest that stromal cells of these two cell types are associated with tumor capsule formation of skin sweat gland neoplasms. [ABSTRACT FROM AUTHOR]

• A new filler of carbon nanocage is first proposed for epoxy resin nanocomposite. • Carbon nanocage filler shows prominent physical confinement and self-lubrication. • Relative to neat epoxy, wear rate is reduced by 51.9% for the optimized sample. • Friction coefficient is reduced by 55.6% for the optimized sample. • The performances are attributed to the unique hollow structure of carbon nanocage. Epoxy resin (EP) nanocomposite materials with excellent tribological properties are highly desired for many engineering applications requiring low friction and wear. Adding carbon nanofiller is regarded as one of the most potential solutions to solve the serious dry wear problem of epoxy matrix. Herein, we report a new filler of carbon nanocages (CNC) prepared by the method of MgO templates to improve its dry friction performance through filling epoxy into the internal hollow space of CNC. Relative to neat epoxy, the friction coefficient (0.249) and wear rate (7.98 × 10−7 mm3 Nm−1) are reduced by 55.6% and 51.9% for the optimized CNC/EP nanocomposites, respectively. Even compared to typical graphene/epoxy nanocomposites, the wear rate is also reduced by up to 21.8%, as well as greatly enhancing the mechanical properties, thereby effectively protecting epoxy matrix and improving its dry friction. Such great tribological performance is attributed to unique structure of CNC, enabling the multi-functional collaboration of physical confinement, self-lubrication and wear-debris collection for CNC fillers, and making it the most potential carbon-based nanofiller for EP-based nanocomposite material system. More than that, it also provides insights for designing other advanced carbon-based nanofillers. [ABSTRACT FROM AUTHOR]