This paper investigates analog beamforming with large-scale antenna arrays for single-group multicast transmission. We focus on the max-min fair (MMF) problem and aim to design the analog beamformer with infinite and finite resolution phase shifters (PSs), respectively, to maximize the minimum signal-to-noise ratio (SNR) over all users subject to a transmit power constraint. However, the constant magnitude and infinite/ finite phase constraints imposed by PSs frustrate the access of an optimal solution of analog beamformer. We thus formulate a sub-optimal MMF problem alternatively and propose a low-complexity algorithm, which iteratively determines each element of analog beamformer to conditionally maximize the minimum SNR among users. The computational complexities of our proposed algorithms are linear in the number of antennas. Simulation results illustrate that our proposed analog beamformer design can achieve satisfactory performance which is close to the full-digital case and outperform the other state-of- the-art schemes.
At present, the internet of things has no standard system architecture. According to the requirements of universal sensing, reliable transmission, intelligent processing and the realization of human, human and the material, real-time communication between objects and things, the internet needs the open, hierarchical, extensible network architecture as the framework. The sensation equipment safe examination platform supports the platform through the open style scene examination to measure the equipment and provides the movement simulated environment, including each kind of movement and network environment and safety management center, turning on application gateway supports. It examines the knowledge library. Under this inspiration, this article proposes the novel security model based on the sparse neural network and wavelet analysis. The experiment indicates that the proposed model performs better compared with the other state-of-the-art algorithms.
Two exchangeable LSPR modes with different coupling field are observed in calculating magnetic field intensity in accordance with adjusting geometrical parameters. Compared with planar nanostructures, three-dimensional windmills show stronger optical activity, and the maximum value of the asymmetry g-factor was 0.6. The numerical simulation results in this paper also contain the optimal geometrical parameters to achieve the best circular dichroism effect at different resonance modes. The results give a contribution to the design of novel chiral optical nanostructures.
There are many functional applications based on hydrogel material, including tissue engineering, energy storage, and flexible devices. The main structure was constructed by polyvinyl alcohol, chitosan and agarose. Hydroxyethyl cellulose was added to enhance plasticity and maintain moisture. Carbon quantum dots were added to bring fluorescent property. The multi-network hydrogel had excellent self-healing properties and excellent tensile strength up to 33 MPa and the self-healing could take place quickly in a variety of media. The self-healing efficiency in air reached up to 93% in just 60 s. The result show that the fluorescence intensity of the hydrogel is negatively correlated with the pressure on the surface, and is positively correlated with its tensile elongation. The data fitting confirmation that the tensile elongation can be monitored by detecting the fluorescence intensity of the hydrogel, and combine composite hydrogel with gecko-like structure to form a pressure detector that can adhere to various surfaces. The liquid pressure is confirmed to be monitored by detecting the fluorescence intensity of the device. This research expands the application of fluorescent hydrogel materials and expects to be used for pressure detection under liquid and engineering structure failure monitoring.
The corrosion behaviour of sintered high purity alpha-Al2O3 refractory composition in contact with soda-lime-silicate (SLS) glass has been investigated using a dynamic corrosion test designed to simulate industrial conditions. Experiments were conducted as function of rotation speed, contact time duration and temperature. The results of dynamic corrosion tests are in excellent agreement with those obtained from static crucible test at 1370 degrees C for 72 h which is a standard industrial testing practice. The phase composition and microstructures of the glass refractory interface of these samples were studied by X-ray Diffraction (XRD) and combined Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy (SEM-EDS), respectively. Elemental mapping was also carried out on the glass-refractory interface.
As one of the few single-phase multiferroic materials with both antiferromagnetic and ferroelectric properties, LaFeO3 has attracted much attention, especially film and ceramic. In this work, LaFeO3 particles were prepared by thermal decomposition of Metal Organic Frameworks (MOFs) precursor La [Fe(CN)(6)]center dot 5H(2)O, and the dielectric and ferroelectric properties of particles were studied for the first time. The effect of annealing temperature and time on the dielectric and ferroelectric performance were investigated in detail. The results indicate that the LaFeO3 particles annealed at 600 degrees C for 5 h achieve dielectric constant of 201, remnant polarization 2P(r) of 0.064 mu C/cm(2) with coercive electric field 2E(c) of 39.16 kV/cm, higher than those of other annealing time. In addition, the LaFeO3 particles annealed at 700 degrees C for 3 h exhibit dielectric constant of 178 and remnant polarization 2P(r) of 0.072 mu C/cm(2) which are higher compared with other annealing temperatures. Our results provide useful information to study LaFeO3 particles.
Directionally solidified (DS) LaB6 (001)-ZrB2 eutectic composite is successfully prepared by optical zone melting technique. The effect of the solidification rate on the microstructure and properties is systemically investigated. With the increase in the solidification rate from 20 to 100 mm/h, the eutectic rods present a homogeneous eutectic microstructure. The relationship between the average eutectic spacing and the solidification rate is established. The fracture toughness shows an obvious anisotropy. Crack deflection and crack bridging play important roles in improving the fracture toughness of the material. As the solidification rate is increased from 20 to 300 mm/h, the fracture toughness, bending strength and current density firstly increase and then decrease. The highest fracture toughness of 5.16 MPa.rn(1/2), bending strength of 809.04 MPa and current density of 36.24 A/cm(2) at 1873 K belong to the DS LaB6 (001)-ZrB2 eutectic composite obtained at V = 100 mm/h.
To evaluate the effect of biochar on soil characteristics and maize yields in meadow soil, a three-year field experiment was performed using different amounts of biochar (0, 10, 20, 40, and 80 t/ha). The soil pH decreased over time when biochar was applied to weakly basic soil. Single biochar applications increased the organic carbon, total nitrogen, available K, and cation exchange capacity for three continuous years, in proportion to the amount of biochar applied. However, as time progressed, the soil organic carbon, total nitrogen, available K, and cation exchange capacity began to decrease. The biochar stimulated the availability of soil phosphorus in the meadow soil and stably increased the available P content in the soil for three years. For maize, the biochar application decreased the occurrence of barren ear tips and increased the ear length, grain number per row, 100-kernel weight, and yield. When the single applications of biochar were greater than 40 t/ha, the soil characteristics showed continuous improvements and the maize yields stably increased for three years.
In2O3 nanoparticles with uniform particle size (10-25 nm) were obtained using the facile precipitation strategy at room temperature with following calcined treatment. The gas-sensing performance of In2O3 nanoparticles with different calcined temperatures was investigated. The results demonstrated that the In2O3 nanoparticles calcined at 500 degrees C exhibited highest sensing response (R-a/R-g = 68.1) to 10 ppm HCHO at 100 degrees C with good selectivity, stability, reproducibility, and ultra-low limit of detection (1 ppm). The results of XPS, UV, and other characterizations indicated that In2O3-500 possessed the most absorbed oxygen species, the highest carrier mobility, and lowest band gap energies. Our work offers new insights into the development of sensing materials to the detection of volatile organic compounds (VOCs).
Significant advances have been made in the development of self-healing synthetic polymer materials in recent years. This review article discusses the recent progress in preparation, characterization and properties of different kinds of intrinsic self-healing elastomers based on reversible covalent bonds and dynamic supramolecular chemistry. Healing conditions, mechanical property recovery and healing efficiency are the main discussion topics. Potential applications, challenges and future prospects in self-healing elastomer fields are also discussed in the last part of this review.
Porous MAX compound combines the advantages of metals and ceramics, and has great filtration application prospects in harsh environments. In this work, porous Ti-3(Si,Al)C-2 was prepared by reaction synthesis of elemental powders, and its cyclic oxidation resistance at 800 degrees C for 100 h was studied. The synthesized Ti-3(Si,Al)C-2 has the MAX phase purity above 99 vol% with the maximum aperture, open porosity and permeability of 5.3 mu m, 42.9% and 16.27 m(3).m(-2).kPa(-1).h(-1), respectively. The oxidation kinetics of porous Ti-3(Si,Al)C-2 is divided into two stages, which includes the linear law for the initial period within the first 10 h and the parabolic law for the subsequent stable period with their oxidation rate constants of 1.37 x 10(-2) h(-1) and 4.76 x 10(-4) h(-1), respectively. The final oxide layer is composed of rutile TiO2 and Al3Ti5O2 phases. In the stable stage, the maximum aperture and open porosity remain nearly constant with slight linear reduction rates of 4.32 x 10(-3) mu m.h(-1) and 5.58 x 10(-2%).h(-1), which are 2.1% and 3.6% of those in the initial stage, respectively. In the last oxidation procedure of 40 h, the permeability decreases by 2.8%, showing a high stability. The high-temperature oxidation process for porous Ti-3(Si,Al)C-2 maintains a high and stable permeability and enhances the filtration accuracy by 96.3%, which improves the filtration performance.
WC-Co cemented carbide tools offer better cutting performance when cutting difficult-to-machine materials, such as high-temperature alloys, titanium alloys, and high-strength steels. In this paper, high performance WC-8 wt.% Co cemented carbide materials with cBN and VC were prepared by spark plasma sintering. The effects of cBN and VC content on mechanical properties and microstructure of WC-8 wt.% Co-VC-cBN cemented carbide materials were studied. The results show that the relative density, Vickers hardness, and fracture toughness of WC-based cemented carbide materials decreased significantly as the content of cBN and VC increased. WC-8 wt.% Co-0.2 wt%VC-1 wt.% cBN (named as YG8V2B10) cemented carbide material had the optimal properties when sintered at 1250 degrees C. Its Vickers hardness, fracture toughness, and flexural strength are 20.81 GPa, 13.01 MPa m(1/2), and 1630 MPa, respectively. High-temperature flexural strength of YG8V2B10 was also investigated. The flexural strength of YG8V2B10 cemented carbide materials decreased as the temperature increased. When the temperature of YG8V2B10 cemented carbide material exceeded 400 degrees C in air, matrix at the surface of YG8V2B10 was oxidized, which leads to a significant decrease in the flexural strength.
Horizontal well production technology gradually occupies a dominant position in the petroleum field. With the rise in water production in the later stage of exploitation, slug flow phenomena will exist in horizontal, inclined and even vertical sections of gas wells. To grasp the flow law of slug flow and guide engineering practice, the flow law of slug flow at various inclination angles (30 degrees similar to 90 degrees) is studied by means of the combination of laboratory experiments (including high frequency pressure data acquisition system) and finite element numerical simulation. The results reveal that because of the delay of pressure variation at the corresponding position of pipeline resulting from gas expansion, the highest point of pressure change curve corresponds not to the highest point of liquid holdup curve (pressure change lags behind 0.125 s of liquid holdup change). Thus, the delay of pressure should be highlighted in predicting slug flow using pressure parameter change; otherwise the accuracy of prediction will be affected when slug flow occurs. It is generally known that liquid holdup and pressure drop are the major factors affecting the pressure variation and stable operation of pipelines. Accordingly, the results of finite element numerical simulation and Beggs-Brill model calculation are compared with those of laboratory experiments. The numerical simulation method is applicable to predicting the pressure drop of the pipeline, while the Beggs-Brill model is more suitable for predicting the liquid holdup variation of the pipeline. The research conclusion helps reveal the slug flow law, and it is of a scientific guiding implication to the prediction method of flow parameters under slug flow pattern in the process of gas well exploitation.
Acoustic metasurface (AMS) is an important branch of metamaterials which has important applications in various fields such as earthquake protection, noise reduction, acoustic hiding, architectural acoustics, particle manipulation, and medical ultrasound and therapy. The AMS with subwavelength thickness can manipulate the acoustic wave by controlling the wavefront phase based on the generalized acoustic Snell's law. In this review, the research and application progresses of AMS in China were introduced, and the further development trends of AMS were analyzed and remarked.