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Unidirectional (60%, volume fraction) and orthogonal (50%, volume fraction) M40 graphite fibre reinforced AZ91D magnesium alloy matrix composites were fabricated by pressure infiltration method. The coefficients of thermal expansion (in the temperature range of 20–350 °C) and dimensional stability (in the temperature range of 20–150 °C) of the composites and the corresponding AZ91D magnesium alloy matrix were measured. The results show that coefficients of thermal expansion of the composites in longitudinal direction decrease with elevating temperature. The coefficients of thermal expansion (CTE) for unidirectional M40/AZ91D composites and orthogonal M40/AZ91D composites are 1.24×10 −6 °C −1 and 5.71×10 −6 °C −1 at 20 °C, and 0.85×10 −6 °C −1 and 2.75×10 −6 °C −1 at 350 °C, respectively, much lower than those of the AZ91D alloy matrix. Thermal cycling testing demonstrates that the thermal stress plays an important role on residual deformation. Thus, a better dimensional stability is obtained for the AZ91D magnesium alloy matrix composites. More extreme strain hysteresis and residual plastic deformation are observed in orthogonally fabric M40 reinforced AZ91D composite, but its net residual strain after each cycle is similar to that of the unidirectional M40/AZ91D composite.

The carbon fibers and the woven reinforced magnesium matrix composites were fabricated by pressure infiltration method. Effects of fiber species, fiber arrangement, hybrid particles and environment temperature on microstructures and properties of the composite were studied. Results showed that the mechanical properties at ambient temperature were affected by interfacial reaction. The magnesium matrix composites reinforced with graphite fibers showed higher strength and elastic modulus due to less interfacial reaction. During loading, the fibers were pulled out and the load was transferred through the interfaces, then the fiber bundles were fractured, finally the whole specimen failed. The introduction of hybrid SiC particles during fabrication can improve the mechanical properties of the magnesium matrix composites. Moreover, taking orthogonal carbon fiber woven as reinforcement can modify the anisotropy and reliability of materials.

Recyclable Si p /1199Al composites with high volume fraction of Si particles were fabricated by squeeze-casting method. The microstructure was observed and the thermal properties were tested and calculated by theoretical models. Si p /1199Al composites are all dense and macroscopically homogeneous without any particle clustering. The interface of Si p /1199Al is clean, smooth and free from any interfacial reaction products. Si p /1199Al composites have high thermal diffusivity (65.083 mm 2 /s) and thermal conductivity (168.211 W/(m· °C)). The specific heat capacity of Si p /1199Al composites at constant pressure increases while the thermal diffusivity and thermal conductivity decrease with increasing temperature. Annealing treatment could improve the thermal properties. The results of Maxwell model and P.G. model are higher than those of experiment.

An 2024Al matrix composite reinforced with 36%(volume fraction) β -Si 3 N 4 particles was fabricated by pressure infiltration method, and its microstructure and the effect of annealing treatment on thermo-conductivity were discussed. Si 3 N 4 particles distribute uniformly without any particle clustering and no apparent particle porosity or significant casting defects are observed in the composites. The combination of particles and matrix is well. The raw Si 3 N 4 particles are regular cylindrical polyhedron with flat surface and change to serrated surface in composite due to reactions during fabrication. Thermal conductivity of as-cast Si 3 N 4p /2024 composite is 90.125 W/(m·K) at room temperature, and increases to 94.997 W/(m·K) after annealing treatment. The calculated results of thermal conductivity of the Si 3 N 4p /Al composite by Maxwell model, H-S model and PG model are lower than experimental results while that by ROM model is higher.

Si 3 N 4p /2024Al composite was fabricated by squeeze casting method and treated by extrusion deformation. Microstructure analyses indicate that Si 3 N 4 particles in the composite are in cylindrical polyhedron shape. Extrusion deformation is beneficial to uniform distribution of Si 3 N 4 particles and improves the relative density of Si 3 N 4p /2024Al composite. Tensile strength of Si 3 N 4p /2024Al composite increases by 76.6% after T6 treatment, and after extrusion and T6 treatment it is by 57.6% more than T6 treatment only. Elastic modulus of Si 3 N 4p /2024Al composite increases a little after T6 treatment but increases by 33.5% after extrusion deformation.

On-line atom trapping inside a nickel flame furnace using chemical vapor generation for sample introduction was proposed for the determination of trace cadmium by flame atomic absorption spectrometry (AAS). Cadmium volatile species was generated upon reaction with potassium borohydride and then flushed into a flame furnace for on-line trapping by a flow of nitrogen carrier gas. The middle part of the flame furnace, where the carrier gas impacts, is cooled by the gas flow, and this provides a fine strategy for on-line atom trapping for the purpose of preconcentration. A stainless steel plate is put on the top of the flame burner in the middle to form a flame-free zone, which also greatly lowers the temperature of the flame furnace and facilitates the atom-trapping process. Due to the introduction of chemical vapor generation, matrix effect was greatly alleviated compared with direct pneumatic nebulization for on-line atom trapping in flame furnace AAS. With trapping time of 35 s, the current appro...

Gimbals and Fast steering mirrors (FSMs) are commonly used to stabilize the line-of-sight (LOS) of the electro-optical tracking system mounted on moving platforms .The gimbal is used to restrain the vibration of low frequencies, and the FSM is used to restrain the vibration of high frequencies. The restraining performance of the Electro-Optical tracking system is equal to the multiplication of the restraining performance of the gimbal and the FSM. The vibration of high frequencies is mainly restrained by the FSM, and so the performance of the FSM is very important to the Electro-Optical tracking system. There are two ways to improve the stabilization accuracy and bandwidth of the FSM, one way is to improve the accuracy and bandwidth of inertial sensors, and the other way is to use low weight inertial sensors to reduce the load of FSM and increase the mechanical resonance frequency. And so the inertial sensors of high accuracy, high bandwidth and low weight are the key to improve the stabilization accuracy and bandwidth of the FSM.

Atmospheric pressure plasma bullets or ionization waves have been generated in one long (Φ 2 mm × 100 mm) dielectric tube filled with He gas when a sinusoidal AC high-voltage with its frequencies of 9.0 kHz is applied between the tungsten pin electrodes. ICCD measurements show that the propagation of ionization waves in I, U and O tubes is anode-driven electrically, and the spatial and temporal development of ionization waves is strongly dependent on the He flow rate and applied voltage. Three stages are clearly observed during the propagation of ionization waves along the tube, and their propagation process is discussed based on the experimental results. The generation and propagation of ionization waves in the tube are affected by many physical processes, such as the drift motion of He+ ions or excited species, the distribution of plasma potential along the dielectric tube, the surface recombination of charged species, He+-induced electron emission from the pin cathode, and so on.

The aim of this paper is to present a sensor fault-tolerant control (FTC) scheme for a two-axis fast steering mirror (FSM) system with minimum power consumption and without changing the controller structure. In this paper, an adaptive PI-based sliding mode observer (APISMO) is adopted firstly to estimate the fault signal, which does not require any prior knowledge of the fault. The estimation is then used by the fault isolation logic to identify the fault. The redundant sensor would be powered up to replace the faulty one when faults occur. During the backup sensor booting up, for maintaining the normal performance of the closed-loop system approximately, a fault-free estimation of the position provided by the APISMO is used as feedback signal. Experimental studies on a prototype system show that the proposed APISMO can effectively reconstruct the fault signals even when the two primary position sensors are faulty simultaneously. Meanwhile, the effectiveness and performance of the proposed scheme have been verified.

A facile simple hydrothermal method combined with a post-solution reaction is developed to grow interconnected three dimensional (3D) hierarchical Co-Al layered double hydroxides (LDHs) on reduced graphene oxide (rGO). The obtained 3D hierarchical rGO-LDHs are characterized by field emission scanning electron microscopy, X-ray diffraction, and X-ray photo-electron spectroscopy. As LDHs nanosheets directly grow on the surface of rGO via chemical covalent bonding, the rGO could provide facile electron transport paths in the electrode for the fast Faradaic reaction. Moreover, benefiting from the rational 3D hierarchical structural, the rGO-LDHs demonstrate excellent electrochemical properties with a combination of high charge storage capacitance, fast rate capability and stable cycling performance. Remarkably, the 3D hierarchical rGO-LDHs exhibit specific capacitance values of 599 F g(-1) at a constant current density of 4 A g(-1). The rGO-LDHs also show high charge-discharge reversibility with an efficiency of 92.4% after 5000 cycles.

Hexagonal mesoporous silica (HMS), Al-HMS, MCM-41, as well as ZrO2 modified HMS supported cobalt and small amount of MnO promoted cobalt catalysts are investigated by using X-ray diffraction, N2 adsorption, transmission electron microscopy, and temperature programmed reduction techniques, and by testing their catalytic properties in Fischer–Tropsch synthesis. Cobalt oxides are dispersed highly on the surface of these mesoporous supports. However, their BET surface area, pore volume, and pore size decrease, and pore wall thickness increases a little. The main hydrocarbon products obtained over these catalysts are the long chain hydrocarbons (wax). Comparing with MCM-41 and Al-HMS, the HMS supported Co catalyst shows better catalytic activity and C5+ selectivity, which is due to its smaller domain size with shorter channels and larger textural mesoporosity. With increasing Co loading on the HMS support, the reduction temperature of cobalt oxides increases a little, but the activity apparently increases, which is caused by more active sites in the channels of HMS. When Al-HMS is used as a support, the interaction between Co species and Al-HMS support caused by the acid properties on the surface of Al-HMS, leads to a decrease of available Co metal sites and a decrease of activity and C5+ selectivity. The pre-impregnated ZrO2 on the surface of HMS support favors the reduction of cobalt oxides and increases the activity and C5+ selectivity. The addition of small amount of Mn (⩽2 wt.%) to Co/HMS catalyst, high yield of wax (36.2%) is obtained, which might be ascribed to that MnO segregates partially the active Co sites and prevents the formation of methane at high reaction temperature.

A facile process was developed for the synthesis of graphene-supported TiO2 (B) nanosheets (GTBN) composite based on the hydrothermal treatment titanium (III) chloride and graphene oxide in an ethylene glycol. The morphology and microstructure of the composites were examined by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy. The obtained GTBN show a high thermal stability and the phase transformation of TiO2 (B) to anatase can be prevented by graphene after pyrolysis of GTBN at 350 °C for 2 h. Furthermore, GTBN exhibited high rate performance and stability of lithium ion batteries, due to the enhanced conductivity of the electrode and accommodation to volume/strain changes during lithium insertion–extraction.

A facile two step process was developed for the synthesis of porous Co3O4 nanorods-reduced graphene oxide (PCNG) hybrid materials based on the hydrothermal treatment cobalt acetate tetrahydrate and graphene oxide in a glycerol-water mixed solvent, followed by annealing the intermediate of reduced graphene oxide-supported Co(CO3)0.5(OH)·0.11H2O nanorods in a N2 atmosphere. The morphology and microstructure of the composites were examined by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy. It is shown that the obtained PCNG have intrinsic peroxidase-like activity. The PCNG are utilized for the catalytic degradation of methylene blue. The good catalytic performance of the composites could be attributed to the synergy between the functions of porous Co3O4 nanorods and reduced graphene oxide.

A facile method is proposed for the synthesis of three-dimensional (3D) flower-like Co3-xFexO4 ferrite (CF) hollow spheres, using SiO2@FeOOH as precursor. The CF hollow spheres are efficient for the catalytic degradation of methylene blue (MB) in the presence of H2O2 at 80 °C. The obtained CF hollow spheres were characterized using transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction, X-ray photo-electron spectroscopy, and N2 adsorption-desorption isotherm measurements. The formation of 3D hierarchical flower-like superstructure was influenced by the relative amount of urea used. As the mole ratio of CoCl2 and urea decreased, the structure of the products was tailored from yolk-like spheres to hollow spheres with different sized void interiors. Moreover, N2 adsorption-desorption isotherm analysis showed that the CF hollow spheres have a large specific surface area (163 m(2) g(-1)) which provided more activity sites. The CF hollow spheres can catalyze the oxidation of MB efficiently. These results indicate that the designed CF hollow spheres exhibit promising capability for the degradation of dyes.

In the present work, milled carbon fibre with high mechanical properties was used to reinforce silicon carbide, and Csf/SiC multilayer composites were prepared by tape casting and pressureless sintering. The milled C fibres were firstly dispersed in solvents with the aid of dispersant (Triton X-100) and then mixed with SiC slurry to make green Csf/SiC tapes to limit fibre breakage. The average length of C fibres slightly decreased with the increase of mixing time in the present duration, indicating that mixing the SiC slurry with the fibre-predispersed solution is an effective method for adding fibres with limited breakage. Fibres were homogeneously distributed in the tapes and tended to align fairly well along the tape casting direction. The relative density of the composite containing milled C fibres decreased with the fibre amount. The Csf/SiC multilayer composites demonstrated significant anisotropic shrinkage behaviour in different directions, while the addition of short C fibres hindered the shrinkage in the plane containing the fibres during sintering. Elastic modulus and bending strength decreased with increased porosity, which implies that bending properties are affected more significantly by residual porosity rather than fibres' properties.

In the charge-coupled device (CCD)-based tracking control system of fast steering mirrors (FSMs), high control bandwidth is the most effective method to enhance closed-loop performance, which, however, usually suffers a great deal from time delay induced by a low CCD sampling rate. Moreover, mechanical resonances also limit high control bandwidth. Therefore, a tentative approach to implementing a CCD-based tracking control system for an FSM with inertial sensor-based cascade feedback is proposed, which is made up of acceleration feedback, velocity feedback, and position feedback. Accelerometers and gyroscopes are all the inertial sensors, sensing vibrations induced by platforms, in turn, which can contribute to disturbance supersession. In theory, the acceleration open-loop frequency response of the FSM includes a quadratic differential, and it is very difficult to compensate a quadratic differential with a double-integral algorithm. A lag controller is used to solve this problem and accomplish acceleration closed-loop control. The disturbance suppression of the proposed method is the product of the error attenuation of the acceleration loop, the velocity loop, and the position loop. Extensive experimental results show that the improved control mode can effectively enhance the error attenuation performance of the line of sight (LOS) for the CCD-based tracking control system.

Bifunctional, binder-free, and non-precious-metal electrocatalysts with superwetting properties are of great significance for high-performance oxygen evolution reactions (OER) and hydrogen evolution reactions (HER). Herein, the fabrication of copper phosphide (Cu3P) microsheets through the phosphidation of CuCl microsheets deposited onto nickel foam, and the effective catalytic activity of the Cu3P microsheets in the HER and OER is demonstrated. Due to their hierarchical structure, the Cu3P microsheets are superhydrophilic and superaerophobic. A well-defined superhydrophilic surface enhances the electrolyte–electrode contact, and a superaerophobic surface facilitates bubbles extraction and efficiently minimizes the dead area of the electrode induced by bubble coverage. These two features are beneficial for the high activity and stability of the electrocatalysts during the OER and HER. The superhydrophilic and superaerophobic Cu3P microsheets prepared at 450 °C afford a current density of 10 mA cm–2 at an overpotential of 290 mV for the OER and 130 mV for the HER. This work highlights a simple, low-cost approach that can be easily scaled-up to construct high-performance electrocatalysts for the OER and HER.

In this article, we propose a facile one-pot solvothermal route for synthesizing TiO 2 –graphene composite nanosheets (TGCN). In the system, ethylene glycol not only as a reducing agent can convert graphene oxide to reduced graphene oxide nanosheets, but also is employed to control the hydrolysis and condensation rates of tetrabutoxytitanium. The obtained TGCN hybrid materials are characterized by atomic force microscopy, transmission electron microscopy, UV–vis spectroscopy, Raman spectroscopy, X-ray photo-electron spectroscopy, X-ray diffraction, and thermal gravimetric analysis. It is found that the quantity of H 2 O used in the reaction is the key to obtain high-quality product. The photocatalytic activities of the products are evaluated using the photocatalytic degradation of methylene blue (MB) as a probe reaction. The results showed that the obtained TGCN have an enhanced adsorption capacity and remarkable improvements in the photodegradation rate of MB under visible light compared to P25.

Results of angle-dependent X-ray photoelectron spectroscopic studies on the covalent binding of bifunctional reagents to silanized silicon wafer surface are reported. The results show that a dense and multilayer (more than five layers) silane structure was achieved by silanizing the silicon surface with aminoalkylsilane. The nitrogen atoms in the deposited silane molecules were nearer to the air/silane interface than the silicon atoms. After the amidization of the surface, a monolayer of SPDP molecules was bound on the silane surface with their pyridyl disulphide groups accessible for the further reaction. A polymeric form glutaraldehyde was observed when it bound to the silane surface.

Friction effect is a main factor which affects the tracking accuracy of the turntable of optoelectronic tracking system, especially when the system works at a low velocity. Researchers have been endeavoring to explore the characters of the friction, model and compensate it. In this paper, a classical friction model-LuGre model is introduced into the turntable system, and an entire nonlinear turntable system model is presented, according to this model, an identification method and integral feedback compensation strategy is used to estimate and compensate the friction effect, then the tracking stability is analyzed, and it proves that the strategy can achieve the semi-global asymptotic tracking results. And the simulation result is presented in this paper.

This paper studies multi-frequency feedback sampling data system. The paper first proposes that a high sampling controller is designed in the low sampling frequency system. The multi-frequency sampling control system cannot be limited by the low sampling frequency, thus the system bandwidth can be extended, the ripple of the system can be reduced and the response speed of the system can be improved. The output fluctuation appeared during the sampling intermittence can be smoothed by the multi-frequency sampling controller. The stable time of the system, stability and instantaneity of the system can be improved by the controller.

This paper describes a new tracking and measuring control system for optical and electronic theodolite. This control system can provide automatic flying object tracking and measuring in visible and infrared band. It also can provide real-time output of the measured results. Use of the multi- mode measuring methods and the on axis tracking control technique can improve the stability of automatic tracking, tracking accuracy and the comprehensive tracking performance of the theodolite. At the same time the smooth switch over among several tracking modes can be carried out. New tracking techniques have been developed to deal with angular tracking rate that exceed one radian in both velocity and acceleration. At the present the tracking and measuring control system has been successfully applied in the optical and electronic theodolite. This paper covers the design concept for the on axis tracking control, the prediction, filtering and smoothing of target measurement, selection of bandwidth, the techniques of automatic video tracking using visible and infrared sensors and the architecture of the servo control algorithms.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A facile method is proposed for the synthesis of cubic CoFe2O4 ferrite–reduced graphene oxide nanocomposite sheets (rGO–CFs), using poly(N-vinyl-2-pyrrolidone) as the reductant and stabilizer. The rGO–CFs functioned as efficient peroxidase mimetics and were successfully applied for colorimetric assay. The morphology and composition of the rGO–CFs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Significantly, the peroxidase-like activity of the rGO–CFs followed typical Michaelis–Menten kinetics and showed a good affinity to 3,3,5,5-tetramethyl benzidine. Under optimum conditions, the colorimetric assay showed a lower detection limit (S/N = 3) of 0.3 μM when compared with that of other nanoparticle based colorimetric assays. Furthermore, the cubic nanostructured rGO–CFs exhibited better stability than horseradish peroxidase when they were exposed to solutions with different solvents and temperatures. These excellent properties made the cubic nanostructured rGO–CFs an ideal candidate for a wide range of potential applications as peroxidase mimetics.

A facile method is proposed for the synthesis of three-dimensional (3D) flower-like Co3−xFexO4 ferrite (CF) hollow spheres, using SiO2@FeOOH as precursor. The CF hollow spheres are efficient for the catalytic degradation of methylene blue (MB) in the presence of H2O2 at 80 °C. The obtained CF hollow spheres were characterized using transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction, X-ray photo-electron spectroscopy, and N2 adsorption–desorption isotherm measurements. The formation of 3D hierarchical flower-like superstructure was influenced by the relative amount of urea used. As the mole ratio of CoCl2 and urea decreased, the structure of the products was tailored from yolk-like spheres to hollow spheres with different sized void interiors. Moreover, N2 adsorption–desorption isotherm analysis showed that the CF hollow spheres have a large specific surface area (163 m2 g−1) which provided more activity sites. The CF hollow spheres can catalyze the oxidation of MB efficiently. These results indicate that the designed CF hollow spheres exhibit promising capability for the degradation of dyes.

Ag-graphene composite nanosheets (AGCN) with adjustable size and well-controlled densities of Ag nanoparticles (Ag NPs) using Poly(N-vinyl-2-pyrrolidone) (PVP) as a reductant and stabilizer are reported. The obtained AGCN substrate is extremely suitable for surface-enhanced Raman spectroscopy (SERS).

A novel displacement-cloud point extraction approach was developed for the selective determination of trace silver in complicated matrices by thermospray flame furnace atomic absorption spectrometry. This method involves two steps of cloud point extraction, i.e., firstly, copper ion reacts with diethyldithiocarbamate (DDTC) to form Cu-DDTC before it is extracted; secondly, after removing the aqueous phase, a sample or standard solution containing silver ion is added and another cloud point extraction procedure is carried out. Because the stability of Ag-DDTC is larger than that of Cu-DDTC, Ag+ can displace Cu2+ from the pre-extracted Cu-DDTC and thus the preconcentration and separation of Ag+ from complicated sample matrix is achieved. Potential interference from co-existing transition metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu2+ from Cu-DDTC complex. Up to 5000 μg mL−1Ni(II), 2000 μg mL−1 Cd(II), 1000 μg mL−1Fe(III), 2000 μg mL−1Co(II), 5000 μg mL−1Zn(II) and 5000 μg mL−1Mn(II) caused no significant interference with the determination of silver of 5 μg L−1. Compared with conventional cloud point extraction, the tolerance limit for the co-existing transition metal ions was increased by at least two orders of magnitude. Under the optimal chemical and instrumental conditions, the limit of detection was 0.2 μg L−1 for silver with a sample volume of 10 mL, and a sensitivity enhancement factor of 21 was achieved. The proposed method was successfully applied to interference-free determination of trace silver in soil, marine sediment and ore samples with high contents of co-existing heavy metals.