Search

As people have higher and higher requirements for water-air detection and communication, the research of aquatic-aerial unmanned vehicles with high flexibility and maneuverability has become more and more in-depth. In this paper, the aquatic-aerial unmanned vehicles is classified according to their driving modes and constructions, and the aquatic-aerial unmanned vehicles is divided into multi-rotor vehicles, fixed-wing vehicles and bionic principle driven vehicles. This paper will give the readers a detailed and comprehensive introduction to the aquatic-aerial unmanned vehicles. In this paper, the aquatic-aerial unmanned vehicles is classified according to their driving modes and constructions, and the aquatic-aerial unmanned vehicles is divided into multi-rotor vehicles, fixed-wing vehicles and bionic principle driven vehicles, and the driving principle and operation mode of each type of aquatic-aerial unmanned vehicles are introduced. At the same time, the application of aquatic-aerial unmanned vehicles in different scenarios is analyzed, so that readers can have some reference when they need to buy or develop aquatic-aerial unmanned vehicles.

Multiple-point statistics (MPS) is a useful approach to reconstruct three-dimensional models in the macroscopic or microscopic field. Extracting spatial features for three-dimensional reconstruction from two-dimensional training images (TIs), and characterizing non-stationary features with directional ductility are two key issues in MPS simulation. This study presents a step-wise MPS-based three-dimensional structures reconstruction algorithm with the sequential process and hierarchical strategy based on two-dimensional images. An extension method is proposed to construct three-dimensional TIs. With a sequential simulation process, an initial guess at the coarsest scale is simulated, in which hierarchical strategy is used according to the characteristics of TIs. To obtain a more refined realization, an expectation-maximization like iterative process with global optimization is implemented. A concrete example of chondrite micro-structure simulation, in which one scanning electron microscopy (SEM) image of the Heyetang meteorite is used as TI, shows that the presented algorithm can simulate complex non-stationary structures.

Intrinsic broadband photoluminescence (PL) of self-trapped excitons (STEs) are systematically studied in lead-free double perovskite nanocrystals (NCs). It is clarified that bandgap (direct/indirect) has important influence on the PL properties of STEs: indirect bandgap NCs exhibit strong exciton-phonon coupling which results in non-radiative STEs, while direct bandgap NCs exhibit moderate exciton-phonon coupling, inducing bright STE PL. Furthermore, by alloying K+ and Li+ ions in Cs2AgInCl6 NCs, the NCs exhibit broadband white-light emission. Charge-carrier dynamics study indicates that the efficient white-light emission originates from the further suppressed non-radiative processes of the STEs in the direct bandgap structure. This work may deepen the understanding of STEs and guide the design of high-performance lead-free perovskites.

For inorganic semiconductor nanostructure, excitons in the triplet states are known as the "dark exciton" with poor emitting properties, because of the spin-forbidden transition. Herein, we report a design principle to boost triplet excitons photoluminescence (PL) in all-inorganic lead-free double-perovskite nanocrystals (NCs). Our experimental data reveal that singlet self-trapped excitons (STEs) experience fast intersystem crossing (80 ps) to triplet states. These triplet STEs give bright green color emission with unity PL quantum yield (PLQY). Furthermore, efficient energy transfer from triplet STEs to dopants (Mn2+) can be achieved, which leads to white-light emitting with 87% PLQY in both colloidal and solid thin film NCs. These findings illustrate a fundamental principle to design efficient white-light emitting inorganic phosphors, propelling the development of illumination-related applications.

Random lasing from a polydimethylsiloxane substrate prepared from abalone shell by soft lithography was investigated. The substrate has better scattering efficiency than abalone shell and its groove structure can support both incoherent and coherent random lasing when covered with a layer of dye solution. When employing rhodamine 640 dye as gain medium, a dual-band random laser signal based on the mechanism of optical feedback intensity and mode competition can be observed, where the signals of the two bands are shown as incoherent and coherent random lasing regimes respectively. Speckle-free imaging is achieved by using incoherent and coherent random lasers as illumination sources and imaging effects are compared. This research shall promote the development of random lasers in the fields of illumination and imaging.

In this work, Random laser (RL) and stimulated Raman scattering (SRS) are investigated using Rhodamine 6G ethanol solution in poly (melamine formaldehyde) foam with micro/nano-sized porous structures. At low dye concentration, the RL containing multiple discrete narrow peaks is observed in both its natural and compressed state of foam. It is found that the cavity length in the compressed state is significantly shorter through the power Fourier transform of the spectra. At high dye concentration, in the natural state of the foam, the coexistence of the RL and SRS is observed, while only the SRS peaks appear in the compressed state. It may provide a novel approach to achieving mode-controllable RL emission.

The burst pressures of large diameter-to-thickness ratio thin-walled cylinders constructed of steel exhibiting a yield plateau were evaluated experimentally, by finite element analyses (FEA), and by existing predictive equations. The good agreement between the predicted and experimentally measured burst pressures of three thin-walled tanks with a large diameter-to-thickness ratio of 342, demonstrates that the proposed FEA model and failure criterion can evaluate the burst pressure of a thin-walled cylinder accurately. In contrast, a conventional elastic-strain hardening plasticity material model may overestimate the burst pressure of a cylinder. The results indicate that a nonlinear stabilization technique in ANSYS is a useful way to overcome the convergence difficulty caused by material softening when the FEA model includes the steel yield plateau. Comparisons of existing predictive models and experimental values reveal that most of the equations have a prediction deviation less than 10%, and that the Faupel equation can predict the burst pressure of a thin cylinder with high diameter-to-thickness ratio, with high precision.

Here we reported on a tunable and stable random laser based on the abalone shell. The groove structure on the inner surface of abalone shell can support coherent random lasing when covered with a layer of dye doped film. By changing the pump position, the emission spectrum wavelength can be tuned by 12.10 nm due to the random distribution of the groove structure on the inner surface of abalone shell. The random laser can also be tuned by 13.85 nm using different concentrations of dye solutions. Furthermore, several different kinds of dyes were used to extent the emission wavelength range of the random laser. The normalized scattering efficiency spectrum confirms the experimental results. The excellent mechanical properties of the abalone shell endow the random laser with good stability. The random laser has potential applications in speckle-free imaging and probing nanoscale structural alterations.

In this work, single cylindrical lens, an extreme of the astigmatic case, is used to study Stimulated Raman scattering (SRS) in CH4 gas. In comparison with the conventional spherical optics case, single cylindrical lens focusing has three obvious advantages: (1) an increase of the dimension of the focus will decrease pump power density, and the laser-induced breakdown is suppressed. (2) It will efficiently disperse the heat generated in the SRS process, and benefit for the heat management for SRS. Consequently, SRS with cylindrical lens focusing configuration shows stronger resistance to thermal defocusing effect. (3) The forward high-order Stokes and backward SRS are suppressed. Therefore, the utilization of cylindrical lens has improved forward first Stokes in CH4, acquiring the maximum photon conversion efficiency of 67.1% at 188.5 mJ pump energy and 1Hz, and 44.9% at 109.4 mJ pump energy and 10 Hz, for the condition of 3 Mpa pressure. This effect has great potential for the gaseous SRS with high repetition rates and high pressure.

We prepared a new size-stable UV-cured material by loading a radical scavenger, 4-methoxyphenol (MEHQ), into halloysite nanotubes (HNTs) to improve the size-stability of UV-cured products. Loading the MEHQ into halloysite nanotubes was intended to protect the curing reaction from the typical inhibitive influence of a radical scavenger. After the curing process, heating treatment was performed on the cured products to accelerate the release of MEHQ from the halloysite lumen. The Brunauer-Emmett-Teller tests and transmission electron micrographs showed that MEHQ was successfully loaded into the halloysite lumen. The photopolymerization kinetic curves of composites revealed that adding the MEHQ-loaded halloysite nanotubes (HNTs-M) into UV-cured materials enabled faster photopolymerization rate than adding a simple mixture of HNTs and MEHQ. With MEHQ loaded in HNTs, the inhibition influence of MEHQ could be reduced. The results of the size-stability test showed that composites with HNTs-M underwent lower deformation during daily use than neat cured materials. In particular, the volume shrinkage of the composites with 8 wt% HNTs-M in daily use was decreased by 51.3%. The results of the release experiment showed that the release rate of MEHQ could be increased through heating treatment. This method may be used to improve the size-stability of UV-curable materials in the future.

Novel flame-resistant UV-curable epoxy (EP) composites were prepared using the organophosphorous flame retardant dimethyl methylphosphonate (DMMP) which was loaded into halloysite nanotubes (HNTs). We used a cone calorimeter to investigate the flame retardancy of the UV-curable epoxy resin containing DMMP-loaded halloysite nanotubes (HNT-D). It was found that compared with the neat epoxy resin the EP/HNT-D system exhibited better flame retardancy with an obvious decrease in the heat release rate (HRR), total heat release (THR), total smoke release (TSR), mass loss rate (MLR) and smoke production rate (SPR). Exploring the flame retardant mechanism revealed two reaction steps in the process of the flame retardant: DMMP gasification followed by a polyphosphoric-HNT carbon layer generating on the condensed phase. It was revealed through measuring the dynamic mechanical properties and tensile properties of the UV-cured EP materials that adding DMMP-loaded halloysite nanotubes (HNT-D) into EP obtained better mechanical properties than adding a simple mixture of halloysite clay and DMMP. With DMMP loaded in HNTs, the HNT-D could reduce the softening influence of DMMP. This method may potentially be applied to improve the flame retardancy of UV-curable epoxy resin in the future.

The halloysite nanotubes (HNT) were loaded with pentaerythritol (PER). The as-prepared composite (HNT-P) and ammonium polyphosphate (APP) was subsequently added to the UV-curable epoxy resins, giving a new flame-resistant system. Loading of the hydrophilic PER into HNT can reduce the moisture absorption in the UV-curable epoxy resins. The flame retardancy was evaluated by means of the cone calorimeter and limit oxygen index test. The results showed that the flame retardancy of the modified epoxy resin was greatly improved with an obvious decrease in both the heat release and smoke release. Moreover, it was revealed that HNT could catalyze the reaction of APP and PER, and the burning surface of the epoxy resin should be covered by the polyphosphoric-HNT intumescent char layer. We have measured the moisture sorption and dynamic mechanical properties of the UV-cured epoxy resins. As compared to the use of the simple mixture of PER and HNT, the use of the HNT-P nearly kept the storage modulus at about 1809 Mpa and reduced the moisture absorption by 58.2 wt % at 40 °C. The results proved that the addition of the HNT-P obtained lower moisture absorption and higher stability of the mechanical properties than adding the simple mixture. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45045.

In the paper, the ARIMA model is used for analyzing and forecasting the short-term dynamic characteristics of rain-induced attenuation. In this way, an ARIMA (Autoregressive Integrated Moving Average) model to forecast real-time dynamic rain-induced attenuation is established. The paper also analyses, evaluates and does the spectrum inspection to the model as well as the forecasting results.

The mutual coupling which has great effect on the performance of the multi-input multi-output communication system is particularly analysed. In this work, the mutual impedance of the dipole array is calculated and the effect of mutual coupling on the correlation and capacity of N×N MIMO system in i.i.d. channel is investigated. The results show that mutual coupling reduces the correlation between the antennas and the simulations show that mutual coupling results in degradation of the capacity of MIMO communication system.