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Mixed ion–electron conductors have a wide range of important applications in devices relying on mixed ion–electron transport, mainly including conducting polymer composites and ceramics. Herein, we...

A water stable proton-conducting material (NH4)5[Zr3(OH)3F6(PO4)2(HPO4)] (ZrP) was hydrothermally synthesized. The three-dimensional (3D) framework of ZrP is composed of ZrF2O4 octahedra and HxPO4 phosphate units forming 18-ring channels through sharing oxygen atoms. Ammonium cations charge balance the anionic framework. Alternating current (AC) impedance measurements on ZrP powder samples show that at 25–60 °C and 98% relative humidity (RH), the proton conductivity is around 10−2 S cm−1, and the activation energy (Ea) is 0.33 eV.

In a structural chemistry context, the dense packing and the structure-directing agent (SDA) often play a crucial role in the formation of the desired crystal structure. Herein, we present two isomorphous decavanadate-type polyoxometalates, M2(NH4)4−x[V10−xMoxO28]·10H2O (M = Li and x = 0.13 for 1; M = Na and x = 0.95 for 2), prepared by solution evaporation under ambient conditions and characterized by the techniques of EDS, ICP-MS, TG, XPS, X-band EPR spectroscopy, and X-ray single crystal and powder diffractions. Both 1 and 2 crystallized in the space group P with analogous cell parameters, containing thermodynamically stable [M2(H2O)10]2+ (M = Li or Na) clusters, NH4+ ions and decavanadate-type polyoxoanions with V5+ and Mo6+ ions. The polyoxoanions and {M2(H2O)10}2+ cluster cations, owing to their comparable dimensions, arrange alternately to form dense packing along the a + c, c- and a-axis directions. As earlier reported, however, [(H2O)0.3@K6(H2O)12]H4.45[PV7.45Mo4.55O40]·11H2O (3) crystallizes in a CsCl-type dense packing structure under analogous crystal growth conditions. In 3, the thermodynamically-stable (H2O)0.3@K6(H2O)12 cluster cation and Keggin-type {Mo4.55V7.45PO40}10.45− polyoxoanion have comparable dimensions. This study clearly reveals the structure-directing effect of thermodynamically-stable aqueous alkali metal ion clusters, initially formed in the reaction mixture, on a polyoxoanion configuration in vanadium–molybdenum polyoxometalate solid solutions.

The zero/negative thermal expansion (ZTE/NTE), which is an intriguing physical property of solids, has been observed in a few families of materials. ZTE materials possess practical applications in specific circumstances such as space-related applications, engineering structures and precision instrument. Generally, NTE materials are used as additives to form a composite of the ZTE material with positive thermal expansion material. It is still a tremendous challenge to design new families of ZTE/NTE materials. Herein, we presented a temperature-dependent single crystal structure analysis in 110–300 K for a layered (NH4)2V3O8, which crystallizes in a tetragonal space group P4bm and comprises mixed valence [V3O82−]∞ monolayers and NH4+ residual in the interlayer spaces. Along the c-axis, (NH4)2V3O8 demonstrated uniaxial expansion behaviors, i.e., ZTE with αc = −1.10 × 10−6 K−1 in 110–170 K and NTE with αc = −16.25 × 10−6 K−1 in 170–220 K. Along the a-axis, (NH4)2V3O8 exhibited ZTE with αa = + 2.06 × 10−6 K−1 in 240–300 K. The mechanisms of ZTE and NTE were explored using structural analysis. The conduction of NH4+ ions in the interlayer space was studied, indicating that the conductivity rapidly rises with the expansion of interlayer space at temperatures of >293 K. This study discloses that layered vanadates are promising ZTE/NTE materials.

It has long been found that hyaluronidases exist in a variety of organisms, playing their roles in various biological processes including infection, envenomation and metabolic regulation through degrading hyaluronan. However, exploiting them as a bioresource for specific applications had not been extensively studied until the latest decades. In recent years, new application scenarios have been developed, which extended the field of application, and emphasized the research value of hyaluronidase. This critical review comprehensively summarizes existing studies on hyaluronidase from different source, particularly in their structures, action patterns, and biological functions in human and mammals. Furthermore, we give in-depth insight into the resource mining and protein engineering process of hyaluronidase, as well as strategies for their high-level production, indicating that mixed strategies should be adopted to obtain well-performing hyaluronidase with efficiency. In addition, advances in application of hyaluronidase were summarized and discussed. Finally, prospects for future researches are proposed, highlighting the importance of further investigation into the characteristics of hyaluronidases, and the necessity of investigating their products for the development of their application value.

Zero/negative thermal expansion (ZTE/NTE) materials are significantly desired in many applications; however, it is still a tremendous challenge to theoretically predict and successfully achieve new families of ZTE/NTE materials via rational structural designs. Herein, we present a new low-thermal expansion/NTE material, i.e. a lamellar vanadium oxide hybrid [C3H12N2][V4O10] consisting of mixed-valence {V4O102−}∞ monolayers and propane-1,3-diammonium cations in the interlayers. The inorganic layer is parallel to the (001) plane and comprises edge-sharing VO5 square pyramids linked together via corner-sharing VO4 tetrahedra. The hybrid shows a low thermal expansion coefficient (∼10−6 K−1) in the wide temperature range of 90–250 K and a colossal NTE (∼−600 × 10−6 K−1) between 293 and 330 K. Moreover, a reversible thermal anomaly occurs at ∼328/316 K upon heating/cooling, associated with a structural phase transition, which gives rise to switchable dielectric and ion-conducting properties; this study provides a new method for the exploration of lamellar vanadium oxide hybrids as new low-thermal expansion/NTE, switchable dielectric and ion-conducting multifunctional materials.

As a class of anionic oxoclusters of early transition metals in their highest oxidation states, polyoxometalates (POMs) show considerable structural versatility and unique chemical and physical properties, making them promising multifunctional materials. In this study, a Keggin-type POM has been achieved, with a formula of [(H2O)0.3@K6(H2O)12]H4.45[PV7.45Mo4.55O40]·11H2O (1), and its microcrystals and nanocrystals have been obtained, respectively. This POM was characterized by elemental analysis for C, H and N, ICP-MS, TG, PXRD, SEM, X-band EPR and XPS techniques. Single crystal X-ray diffraction analysis demonstrated that 1 shows a rare extended structure with a high-connected three-dimensional (3D) all inorganic network of a Keggin-type POM, built from {Mo4.55V7.45PO40}10.45− polyoxoanions and {(H2O)0.3@K6(H2O)12}6+ clusters with CsCl-type crystal structure. In addition, to the best of our knowledge, 1 shows the highest ratio of vanadium to molybdenum among Keggin-type POMs reported thus far. Most interestingly, 1 exhibits intrinsic proton conduction below the freezing point of water, with a proton conductivity of 6.90 × 10−7 S cm−1 at 249 K and further reaching 3.36 × 10−6 S cm−1 at 272 K and Ea = 0.44 eV at 249–272 K.

To explore clinical effectiveness and safety of ultrasound-guided closed reduction and K-wires internal fixation in treating of Kilfoyle Ⅱand Ⅲ medial condylar fracture of humerus in children.Clinical data of 32 children with medial condylar fracture of humerus treated with closed reduction and internal fixation with K-wires under the guidance of ultrasound were retrospectively analyzed from January 2014 to August 2019, including 23 males and 9 females, age ranged from 3.2 to 12.8 years old with an average of (8.3±2.1) years old;According to classification of Kilfoyle, 12 patients classified to typeⅡ and 20 patients were type Ⅲ;5 patients combined with elbow dislocation;the time from injury to operation ranged from 1 to 5 days with an average of (3.1±1.3) days. Radiological evaluation of treatment results and complications were observed. At the final follow up, Mayo elbow performance score(MEPS) was used to evaluate elbow function. And humerus-ulna angle on the affect side and healthy side were measured and compared.All patients were followed up from 8 to 26 months with an average of(19.3±5.5) months. All fractures were healed well, the healing time ranged from 4 to 6 weeks with an average of (4.5±0.5) weeks. No infection, vascular and nerve injury, bone nonunion, trochlear necrosis, cubitus varus or valgus deformity were occurred. According to Mayo scoring, all patients were assessed as excellent. There was no significant difference in angle of humerus-ulna between affectedside (9.5±3.6)° and healthy side (9.1±3.5)°, and no difference in MEPS scores between affected side(95.3±2.5) and healthy side(96.3±2.2)(For Kilfoyle typeⅡand Ⅲ medial condylar fracture of humerus in children, closed reduction and internal fixation with K-wire under ultrasound guidance is a safe and effective method, and could promote in further.

The zero/negative thermal expansion (ZTE/NTE), which is an intriguing physical property of solids, has been observed in a few families of materials. ZTE materials possess practical applications in specific circumstances such as space-related applications, engineering structures and precision instrument. Generally, NTE materials are used as additives to form a composite of the ZTE material with positive thermal expansion material. It is still a tremendous challenge to design new families of ZTE/NTE materials. Herein, we presented a temperature-dependent single crystal structure analysis in 110-300 K for a layered (NH4)2V3O8, which crystallizes in a tetragonal space group P4bm and comprises mixed valence [V3O82-]∞ monolayers and NH4+ residual in the interlayer spaces. Along the c-axis, (NH4)2V3O8 demonstrated uniaxial expansion behaviors, i.e., ZTE with αc = -1.10 × 10-6 K-1 in 110-170 K and NTE with αc = -16.25 × 10-6 K-1 in 170-220 K. Along the a-axis, (NH4)2V3O8 exhibited ZTE with αa = + 2.06 × 10-6 K-1 in 240-300 K. The mechanisms of ZTE and NTE were explored using structural analysis. The conduction of NH4+ ions in the interlayer space was studied, indicating that the conductivity rapidly rises with the expansion of interlayer space at temperatures of293 K. This study discloses that layered vanadates are promising ZTE/NTE materials.

The emerging organic ion plastic crystals (OIPCs) are the most promising candidates used as solid-state electrolytes in a range of ionic devices. To endow an OIPC with additional functionality may create a new type of material for multifunctional devices. Herein, we present an ion plastic crystal, [EMIm]­[Ni­(mnt)2] (1; [EMIm]+ = 1-ethyl-3-methylimidazolium and mnt2– = maleonitriledithiolate), and its crystal consists of twin dimeric chains of [Ni­(mnt)2]− anions, embraced by [EMIm]+ cations. A crystal-to-plastic crystal transformation with a large latent heat that occurred at ∼367/337 K on heating/cooling is confirmed by the differential scanning calorimetry (DSC) technique. The plastic crystal phase in 1, characterized by variable temperature powder X-ray diffraction (PXRD) and optical microscopy images, spans a broad temperature range with ΔT ∼123/153 K on heating/cooling (DSC measurement), and the wide ΔT is relevant to an extra stable anion chain owing to the strong antiferromagnetic (AFM) interactions protecting the chain from collapse in the plastic crystal state. 1 is a single-component ion plastic crystal with a record high ion conductivity, 0.21 S·cm–1, at 453 K. The crystal-to-plastic crystal transformation in 1 is coupled to a bistable magnetic transition to give a multi-in-one multifunctional material. This study provides a creative thought for the design of OIPCs with striking thermal, electrical, and magnetic multifunctionality.

The ultrasonic motor is an uncertain time-varying nonlinear system because of the nonlinearity of the piezoelectric material, the friction and the temperature. For example, the operating time of the mechanical switch actuated by the ultrasonic motor in regular stroke is highly dispersed. Unfortunately, it is difficult to establish accurate mathematical model. In this paper, an analytical autoregressive process model (AR) is employed to identify and control the ultrasonic motor. First of all, dispersed operating time of the mechanical switch actuated by the ultrasonic motor is investigated. Then, the AR model is established to predict the operating time of the ultrasonic motor on the basis of the statistical data to reduce the nonlinear behavior of the ultrasonic motor, and to improve the accuracy and obtain a good time response of the switch. The simulation results are agreed with experimental results, confirming the effectiveness of proposed model. Furthermore, we adopt the predicted result of the AR model to control the mechanical switch actuated by the ultrasonic motor. The analytical investigation is fulfilled with two target operating time ranges, namely 12 ms and 24 ms. Comparison of the results obtained from the AR model and the experimentation reveal that the standard deviations are less than 95.3 μs and 102.7 μs with maximum errors equal to 0.41 % and 0.44 % respectively. Thereby, the proposed dispersed operating time control is performed. Findings indicate that the maximum errors for the operating time of the mechanical switch are less than 140 μs and 110 μs with ±0.85 % and ±0.42 % respectively.

Haloplumbate-based perovskites display promising functionalities for advanced photovoltaic, optoelectronic and other applications with high performances and low costs. Herein, we present a study of variable-temperature crystal structures, dielectrics and conductance at 153-513 K, and luminescence at ambient temperature for a one-dimensional organic-inorganic perovskite, [N-methyldabconium]PbI3 (1). Hybrid 1 shows extra thermo- and water-stability (thermal decomposition at ca. 653 K), switchable dielectric behaviour and conductance at around 348 K, owing to symmetry-breaking structure phase transition from the hexagonal space group P63/mmc in the high-temperature phase to the orthogonal space group Pcba in the low-temperature phase, and bright yellow-green emission at room temperature, originating from the electron transition within the semiconducting {PbI3}∞ chains. This study will broaden the scope of lead halide-based hybrid materials for practical application in optical and electrical devices.

In this study, two isomorphic hybrid crystals of iodoargentate, M(en)3Ag2I4 (M = transition metal Mn2+ (1) or main-group metal Mg2+ (2) ion), have been prepared through in situ self-assembly in DMF solution at ambient temperature and characterized by microanalysis, IR spectroscopy, thermogravimetric analysis and powder X-ray diffraction and single crystal X-ray diffraction techniques. The magnetic properties of 1 have been investigated. The crystals of 1 and 2 crystallize in the hexagonal non-centrosymmetric space group P6322 with rather similar lattice parameters. The metal complex M(en)32+ (M = Mn2+ or Mg2+) with the symmetry of D3 point group plays a crucial role in directing the formation of the three-dimensional hexagonal non-centrosymmetric framework of {Ag2I42−}∞. To the best of our knowledge, the hybrid Mg(en)3Ag2I4 is the first example of a main-group metal complex used as a structure directing agent for the formation of a hybrid crystal structure, and this is also the first instance where isomorphic hybrid crystals are obtained using transition and main-group metal complexes. These findings can provide a basis for broadening the utilization of metal coordination cations/anions as structure directing agents in the design and construction of novel hybrid crystal structures in more effective ways.

A supramolecular crystal, built from a 1 : 1 molar ratio of potassium tetraphenylboron (KBPh4) with 1,4,7,10,13,16-hexaoxacyclooctadecane (18-Crown-6), contains an organometallic half-sandwich superstructure unit {K(18-Crown-6)(ηn-C6H5B(C6H5)3)} (1 with n = 1–6), and shows a reversible phase transition at ∼211 K. The analysis of crystal structures at 173 K in the low-temperature phase, and 293 and 423 K in the high-temperature phase revealed that the breaking-symmetry phase transition is associated with the order–disorder transformation of [K(18-Crown-6)]+ and the change of the coordination mode of the phenyl ring to K+. A dielectric anomaly appears at ca. 212 K and dielectric relaxation occurs above 375 K in 1. The dielectric and thermal anomaly temperatures are close to each other, and the dielectric relaxation is relevant to the relative displacement of [K(18-Crown-6)]+ and the tetraphenylboron anion.

The corrosion properties of γ′-strengthened Co-xNi-Al-W-Cr (where x=15, 20, 25, and 30 at.%) superalloys were investigated in the mixture of 75 wt.% Na2SO4+25 wt.% NaCl at 900°C. The results showed that the corrosion behavior is associated with both sulfuration and oxidation processes. It was demonstrated that increasing the addition of Ni effectively promoted the formation of continuous Al2O3 scales, so that the hot corrosion resistance could be improved. When Ni content is more than 20 at.%, a large amount of Ni3S2 precipitates during the corrosion process. Sulfuration can destroy the integrity of the corrosion layer and increase the activity of oxygen. In this way, the internal oxidation of the alloys becomes more serious. Therefore, it is recommended that the optimum Ni addition is about 20 at.% for new type Co-Ni-Al-W-Cr superalloys.

Owing to its outstanding water-retention ability, viscoelasticity, biocompatibility and non-immunogenicity, Hyaluronic acid (HA), a natural linear polymer alternating linked by d-glucuronic acid and N-acetylglucosamine, has been widely employed in cosmetic, medical and clinical applications. With the development of synthetic biology and bioprocessing optimization, HA production via microbial fermentation is an economical and sustainable alternative over traditional animal extraction methods. Indeed, recently Streptococci and other recombinant systems for HA synthesis has received increasing interests due to its technical advantages. This review summarizes the production of HA by microorganisms and demonstrates its synthesis mechanism, focusing on the current status in various production systems, as well as common synthetic biology strategies include driving more carbon flux into HA biosynthesis and regulating the molecular weight (MW), and finally discusses the major challenges and prospects.

The synthesis and physico-chemical characterization of an organic-inorganic hybrid material, (N, N'-bi-n-butyl-4,4′-bipyridinium tetrabromocuprate, has been reported. This hybrid has been characterized using IR, thermogravimetric and single-crystal X-ray diffraction analyses. In the title salt, (C18H26N2)[CuBr4], the CuBr42 − ion shows distorted tetrahedral geometry. The tetrabromocuprate and N, N'-bi-n-butyl-4,4′-bipyridiniums are held together via non-classical C H ⋯ Br hydrogen bond to form a 3-D hybrid structure. The percentages of hydrogen bonding interactions are analyzed by fingerprint plots of Hirshfeld surface. The XPS spectrum exhibits the signals of coexistence of CuI and CuII ions. However, the hybrid shows EPR silent behavior at room temperature and variable-temperature magnetic susceptibility displays an isolation of CuII feature with C = 0.46 emu K mol− 1 and θ approximate to − 0.06 K in 2– K as well. Such a novel nature is further analyzed and discussed.

A bimetallic metal–organic framework (MOF) with the formula [Zn3btc2{Cr3O(isonic)6(H2O)2(OH)}]·(DMF)15.5(H2O)8 (H3btc=1,3,5-benzenetricarboxylic acid; isonic=isonicotinicate) shows a pillar-layered structure. The monolayer consists of hexagon-like rings formed by the [Zn(isonic)2(btc)2] tetrahedral and the consecutive monolayers are pillared by trigonal–prismatic clusters of [Cr3O(isonic)6(H2O)2(OH)]through the remaining binding sites of the Zn2+ ions. DMF and water molecules are confined in the cages and channels. TGA indicates that the lattice DMF and water molecules begin to be released at temperatures above 363 K. Dielectric measurements were carried out in the range of 173–363 K and 1–107 Hz for three successive thermal cycles. The dielectric spectroscopy obtained in the first thermal cycle was different from that observed in the next two thermal cycles, while the dielectric spectra in the last two thermal cycles were almost identical. The dielectric nature of this MOF is discussed in detail for each thermal cycle. Since MOFs are unique host–guest systems in which the structure of the host framework is designable and the guests are exchangeable, it is no doubt those MOFs are materials with a variety of dielectric natures. This study gives a fresh impetus to achieve MOFs–based dielectric materials.

The solid state electrolytes show a wide range of practical applications in a variety of all-solid-state electrochemical devices, and it is highly in demand to explore new types of solid state electrolyte materials. In this study, we have designed and prepared a fluorite-type coordination compound, [Mn(en)3]I2, which has been characterized by microanalysis for C, H and N elements, infrared spectrum in the wavenumber range of 4000–400 cm−1, thermogravimetric analysis and differential scanning calorimetry. The single crystal X-ray diffraction revealed that the bigger size [Mn(en)3]2+ cations build three-dimensional network in the crystal of [Mn(en)3]I2 and the smaller size iodide ions occupy the tetrahedral or octahedral cavities surrounded by the [Mn(en)3]2+ cations, featuring as the fluorite-type compound. The impedance spectra were investigated to reveal the ionic conductivity σ = 3.45 × 10−11 S cm−1 at 303 K, while σ = 1.37 × 10−6 S cm−1 at 423 K, sharply increasing by five orders of magnitude regarding to that at 303 K. The electric modulus analysis further confirmed the conductance contributed from the migration of iodide ions. This study opens a way to design and achieve new coordination compound-based ion conductors.

A novel 3-DOF microgripper driven by Linear Ultrasonic Motors (LUMs), with nanometer positional accuracy and an operational space in the millimeter scale is proposed. A two-fingers design method based on a chopstick-like structure is presented. The operational mechanism is illustrated to demonstrate how the microgripper works. Based on the spatial parallel mechanism with joints formed by right circular multi-axis flexible hinges, the kinematic model as well as the relationship between output and input displacement are derived. The maximum displacement of the manipulation end-effector is calculated and an error analysis is conducted. A series of experimental results indicate that the reachable operational workspace of the microgripper is a 20mm height cylinder with the major-axis of 2.3415mm and the minor-axis of 2.1178mm, while the displacement resolution is 100nm. Successful experiments on gripping a single shrimp embryo demonstrate that the microgripper has good performance in gripping micro-objects. A novel 3-DOF flexible hinge-based spatial parallel micromanipulator is proposed.The micromanipulator has a two fingers design based on the use of chopsticks.We establish the kinematic model and calculate the motion stroke of its end-effector.Driven by linear ultrasonic motors, the workspace of the micromanipulator is enlarged meanwhile the displacement resolution is nano-sized.

As a class of anionic oxoclusters of early transition metals in their highest oxidation states, polyoxometalates (POMs) show considerable structural versatility and unique chemical and physical properties, making them promising multifunctional materials. In this study, a Keggin-type POM has been achieved, with a formula of [(H2O)0.3@K6(H2O)12]H4.45[PV7.45Mo4.55O40]·11H2O (1), and its microcrystals and nanocrystals have been obtained, respectively. This POM was characterized by elemental analysis for C, H and N, ICP-MS, TG, PXRD, SEM, X-band EPR and XPS techniques. Single crystal X-ray diffraction analysis demonstrated that 1 shows a rare extended structure with a high-connected three-dimensional (3D) all inorganic network of a Keggin-type POM, built from {Mo4.55V7.45PO40}10.45- polyoxoanions and {(H2O)0.3@K6(H2O)12}6+ clusters with CsCl-type crystal structure. In addition, to the best of our knowledge, 1 shows the highest ratio of vanadium to molybdenum among Keggin-type POMs reported thus far. Most interestingly, 1 exhibits intrinsic proton conduction below the freezing point of water, with a proton conductivity of 6.90 × 10-7 S cm-1 at 249 K and further reaching 3.36 × 10-6 S cm-1 at 272 K and Ea = 0.44 eV at 249-272 K.

Haloplumbate-based perovskites display promising functionalities for advanced photovoltaic, optoelectronic and other applications with high performances and low costs. Herein, we present a study of variable-temperature crystal structures, dielectrics and conductance at 153-513 K, and luminescence at ambient temperature for a one-dimensional organic-inorganic perovskite, [N-methyldabconium]PbI3 (1). Hybrid 1 shows extra thermo- and water-stability (thermal decomposition at ca. 653 K), switchable dielectric behaviour and conductance at around 348 K, owing to symmetry-breaking structure phase transition from the hexagonal space group P63/mmc in the high-temperature phase to the orthogonal space group Pcba in the low-temperature phase, and bright yellow-green emission at room temperature, originating from the electron transition within the semiconducting {PbI3}∞ chains. This study will broaden the scope of lead halide-based hybrid materials for practical application in optical and electrical devices.

This paper proposes an ultrasonic knife system for MEMS packaging. The ultrasonic knife system is consisted of an ultrasonic transducer, a cutter and a gripper feeder. The ultrasonic transducer engenders high frequency vibration, which lead to the resonance of the structure. Amplitude transformer can magnify the amplitude. By the impact and collision of the cutter, the material can be cut through, and the high temperature created by high-frequency vibration can do the welding. The structure is designed and optimized by the finite element method, and a model machine is produced. According to the experimental results, the ultrasonic knife system has the virtues of high cutting force and better wedding feature, which are suitable for MEMS packaging.

During the experiment of cell poking, it is required that the point of a probe is aimed at the cell with the help of a precision motion platform, and then, controlled by this motion platform, the tip of the probe pokes into the cell. When these operations are done, the driving force of this platform will be removed. But within a certain period (for example, an hour), the platform doesn’t stop moving. This kind of movement, which should be only several microns, is termed in this paper as the mechanical drift of ultrasonic linear motors. Experiments show that the forms used for clamping the stator is one of the factors that affect the mechanical drift. It is studied through experiments the impacts of several clamping forms on mechanical drift, the drift value’s relationship with the slide rail’s damping and the motor’s step size, and how the drift direction is related to the motion direction. The mechanism of mechanical drift of ultrasonic linear motors has also been explored preliminarily. This kind of research will facilitate refinements of the design and control methods for ultrasonic linear motor as well as motion platforms.

Ultrasonic motors (USMs) are driven by friction forces between a stator and rotor. So the output properties and life of USMs are strongly related to the properties, such as the mechanical and tribological properties, of the frictional materials. In this study, the effects of the content of potassium titanate whiskers (PTWs) on the mechanical and tribological properties of polytetrafluoroethylene (PTFE)-based friction materials and the performances of the corresponding USMs were studied. The morphology of worn surfaces of PTFE composites were observed with a scanning electron microscope. The experimental results show that the PTWs not only increased the hardness and elastic modulus of the PTFE composites but also increased the friction coefficient and wear resistance of the PTFE composites. On the whole, the PTFE-based friction materials filled with 5 wt % PTWs were the preferable friction materials for USMs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A 4-year field experiment was conducted to investigate the influence of three rotation systems and three corresponding leguminous green manure (LGM) application methods on wheat yield and soil properties. The rotation patterns were summer fallow--winter wheat (SW), LGM-- winter wheat (LW) and LGM--spring maize--winter wheat (LMW). The three LGM application methods of LW included: early mulch, early incorporation and late incorporation while the three LGM application methods of LMW were: stalk mulch, stalk incorporation and stalk move-away. The results indicated that for LW, LGM consumed more soil water, thus the wheat yield was not stable. The nitrate storage in 0-200 cm soil after wheat harvest was significantly higher than that of the others, indicating an increasing risk of nitrate leaching. Early mulch under LW had the highest soil organic carbon (SOC) content and storage of SOC (SSOC) in 0-20 cm soil. For LMW, wheat yield was comparatively stable among years, because of higher water storage before wheat seeding, and the nitrate storage in 0-200 cm soil after wheat harvest was significantly lower than LW, which decreased the risk of nitrate leaching. Stalk mulch had higher SOC content in 0-20 cm soil after wheat harvest compared with move-away. In addition, compared with the soil when the experiment started, stalk much also increased SSOC in 0-20 cm soil. In conclusion, LMW with stalk mulch could increase soil water storage, stabilize crop yield, improve soil fertility and decrease 0-200 cm soil nitrate storage. This system could be treated as a good alternative for areas with similar climate.