Strong convergence rate of a kind of Pickandstype estimator

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Effects of the hierarchical pyrolysis polyaniline on reversible hydrogen storage of LiBH4

In this work,LiBH_4–20 wt%PP composite was prepared by ball-milling with as-synthesized hierarchical pyrolysis polyaniline(PP)and LiBH_4,and the hydrogen sorption performance as well as catalytic mechanism of the composite was studied.It is found that the onset desorption temperature of the composite decreases to 75°C,almost 235°C lower than that of the milled LiBH_4.Moreover,the composite could release 4.1 wt%H_2and rehydrogenate a total of 4.4 wt%H_2when the temperature raiseds up to 400°C,showing an outstanding reversibility,which even 3.9 wt%H_2can be kept after five cycles.Through scanning electron microscopy(SEM)observation and X-ray diffraction(XRD)analysis,we found that the PP surface forms some nanoholes after hydrogenation-dehydrogenation cycles,which leads to the confinement of some LiBH_4in the PP nanoporous structure,therefore,the hydrogen sorption kinetics and reversibility are significantly enhanced.In addition,we also found the oxygenic groups of the PP can react with LiBH_4forming LiBO_2and Li_3BO_3,where the containing Li–B–O bonds loaded in the porous structure of the PP catalyze the hydrogenation reaction of LiBH_4.     

Silicone oil-based solar-thermal fluids dispersed with PDMS-modified Fe3O4@graphene hybrid nanoparticles

One of the most challenging problems that limit the practical application of carbon-based photothermal nanofluids is their poor dispersion stability and tendency to form aggregation. Herein, by using Fe_3O_4@graphene hybrid nanoparticles as a model system, we proposed a new method to prepare stably dispersed silicone oilbased solar-thermal nanofluids that can operate at high temperatures than water-based fluids. The introduction of Fe_3O_4 nanoparticles between graphene nanosheets not only physically increases the inter-plane distance of the graphene nanosheet but also provides numerous anchoring points for surface modification. Phosphate-terminated polydimethylsiloxane chains, which have high compatibility with the silicone oil base fluids and hightemperature stability, were synthesized and utilized to modify the Fe_3 O_4 nanoparticle surfaces. The attached chains create steric hindrance and effectively screen the strong inter-plane van der Waals attraction between graphene sheets. Dispersion stability of the nanofluids with different concentrations of surface-modified hybrid nanoparticles and heated under different temperatures was investigated. We have demonstrated that such fluids could maintain stable dispersion under a heating temperature up to 150 °C depending on the concentration of the hybrid nanoparticles. The resultant nanofluids maintained stable dispersion after repeated heating and were employed for consistent direct solar-thermal energy harvesting at 100 °C.     

Backstepping sliding mode control with self recurrent wavelet neural network observer for a novel coaxial twelve-rotor UAV

The robust attitude control for a novel coaxial twelve-rotor UAV which has much greater payload capacity,higher drive capability and damage tolerance than a quad-rotor UAV is studied. Firstly,a dynamical and kinematical model for the coaxial twelve-rotor UAV is designed. Considering model uncertainties and external disturbances,a robust backstepping sliding mode control( BSMC) with self recurrent wavelet neural network( SRWNN) method is proposed as the attitude controller for the coaxial twelve-rotor. A combinative algorithm of backstepping control and sliding mode control has simplified design procedures with much stronger robustness benefiting from advantages of both controllers. SRWNN as the uncertainty observer is able to estimate the lumped uncertainties effectively.Then the uniformly ultimate stability of the twelve-rotor system is proved by Lyapunov stability theorem. Finally,the validity of the proposed robust control method adopted in the twelve-rotor UAV under model uncertainties and external disturbances are demonstrated via numerical simulations and twelve-rotor prototype experiments.     

Characteristics and implications of stress state in a gold mine in Ludong area,China

In this study, we obtained information from twenty-one measurement points on the stress magnitudes and orientations of a gold mine in the Ludong area. We used the overcoring technique with an improved hollow inclusion strain gauge and then analyzed the distribution characteristics of the in situ stress field. The results indicate that the stress field is characterized by σ_H > σ_h > σ_v and σ_H > σ_v > σ_h (where σ_H, σ_h, and σ_v are the maximum horizontal, minimum horizontal, and vertical principal stresses, respectively). The regional stress field is dominated by horizontal principal stress. The σ_H, σ_h, and σ_v values show a gradual increasing trend with depth. The σ_H is predominantly oriented in the NWW-SEE or near-EW direction. We also confirmed the correspondence between the measured stress field and the regional geological structure. In addition, based on the measured stress data, we discuss the implications of the in situ stress with respect to fault activity in the mine area.     

Lead-bismuth-free piezoceramics （Na0.5K0.44Li0.06）Nb0.95Sb0.05O3-Na5.6Cu1.2Sb10O29

Newly developed sintering aid Na5.6Cu1.2Sb10O29 (NCS) and lead-bismuth-free piezoceramics (Na0.5K0.44Li0.06) Nb0.95Sb0.05O3 (NKLNS) were prepared by the conventional solid state reaction. The effects of sintering aid NCS on the electrical properties of NKLNS were investigated. It was found that the addition of a proper amount of sintering aid NCS to NKLNS is effective not only on improving the density and the piezoelectric activity, but also on reducing the dielectric loss of NKLNS. The NKLNS doped with 0.4 mol% NCS has a piezoelectric constant d33 as high as 261pC/N and an electromechanical coupling factor k33 above 60%. These results show that NCS-doped NKLNS is a promising and practicable candidate for lead-bismuth-free piezoceramics.     

Dispersion stability of thermal nanofluids

Thermal nanofluids, the engineered fluids with dispersed functional nanoparticles, have exhibited extraordinary thermophysical properties and added functionalities, and thus have enabled a broad range of important applications. The poor dispersion stability of thermal nanofluids, however, has been considered as a longexisting issue that limits their further development and practical application. This review overviews the recent efforts and progresses in improving the dispersion stability of thermal nanofluids such as mechanistic understanding of dispersion behavior of nanofluids, examples of both water-based and oil-based nanofluids, strategies to stabilize nanofluids, and characterization techniques for dispersion behavior of nanofluids. Finally, on-going research needs, and possible solutions to research challenges and future research directions in exploring stably dispersed thermal nanofluids are discussed.     

Precipitation of spherical boehmite from concentrated sodium aluminate solution by adding gibbsite as seed

The precipitation of spherical boehmite was studied by surface energy calculations, measurements of precipitation ratios, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The surface energy calculation results show that the (001) and (112) planes of gibbsite surfaces are remarkably stable because of their low surface energies. In addition, the (010) plane of boehmite grows preferentially during precipitation because of its low surface energy. Thus, we propose a method to precipitate spherical boehmite from a supersaturated sodium aluminate solution by adding gibbsite as seed in a heterogeneous system. In this method, gibbsite acts as the preliminary seed and saturation modifier. The results show that the fine boehmite first nucleates on the (001) and (112) planes of gibbsite and then grows vertically on the (001) and (112) basal planes of gibbsite via self-assembly, thereby forming spherical boehmite. Simultaneously, gibbsite is dissolved into the aluminate solution to maintain the saturation for the precipitation of boehmite. The precipitation ratio fluctuates (forming an M-shaped curve) because of gibbsite dissolution and boehmite precipitation. The mechanism of boehmite precipitation was further discussed on the basis of the differences in surface energy and solubility between gibbsite and boehmite. This study provides an environmentally friendly and economical method to prepare specific boehmite in a heterogeneous system.     

Design of a 6 DOF Input Device in Telerobotics and Virtual Reality

The principle of a 6 DOF (degrees of freedom) input device using ultrasonic distance measurement is presented in this paper. The system employs the method of measuring the time of flight. In addition, some techniques, including automatic gain control, self-adaptive variable threshold and temperature compensation, are also used to improve precision. Then, the positions and orientations of the input device can be calculated by the method of spatial analytic geometry. Meanwhile, commands from the 3-D input device are detected and carried out. The validity and precision of the input device are verified by the experiment in a robot system. The proposed device not only can be used for end-effector position and orientation measurement in telerobotics, but also can be an interactive device in virtual reality systems, such as helmet tracking, viewpoint navigation and object manipulation.     

Electronic structures and optical properties of two anthracene derivatives

People have paid extensive attention to the investi- gation of the organic π-conjugated materials with elec- troluminescent (EL) properties during the last two dec- ades. Up to date, the organic luminescent electronicdevice is heading for the promising applications of flat panel displays[1―5]. As well known, the full-color dis- plays require the particular combination of red, green, and blue (named RGB) light emitters. Therefore, it is the principal task for the experimental researchers to…