Ultrasonic Tomography of Immersion Circular Array by Hyperbola Algorithm

This paper presents a development and research of a non-invasive ultrasonic tomography for imaging gas/liquid two-phase flow. Ultrasonic transmitting and receiving are implemented using a circular array model that consists of 36 transducers. COMSOL Multiphysics® software is adopted for the simulation of the ultrasonic propagation in the detecting zone. Various two-phase flows with different gas distributions are radiated by ultrasonic waves and the reflection mode approach is utilized for detecting the scattering waves after the generation of fan-shaped beam. Ultrasonic attenuation and sound speed are both taken into consideration while reconstructing the two-phase flow images under the inhomogeneous medium conditions. The inversion procedure of the image reconstruction is realized using the hyperbola algorithm, which in return demonstrates the feasibility and validity of the proposed circular array model

Yb3+ doping effects on thermal conductivity and thermal expansion of Yttrium aluminium garnet

Yttrium Aluminium Garnet (YAG) is an attractive candidate as thermal barrier material used for turbine blade in aero engines, due to its relatively low thermal conductivity, low oxygen diffusivity and good phase stability at high temperature. YAG has a complex crystal structure, in which Y3+ ions locate in dodecahedron and Al3+ ions in octahedron and tetrahedron. Replacing the host cations with rare earth elements can cause the structure change which influences the thermal properties of YAG. Because the space inside the octahedron is relatively small, Yb3+ ions which have the smallest ionic radial size in the lanthanide series, have been selected and attempted to be doped on dodecahedral and octahedral sites to investigate the effects on thermal conductivity and thermal expansion. The variation of lattice constant indicates that Yb3+ ions are located on the dodecahedron or octahedron. In addition, when Yb3+ ions replace Al3+ ions on octahedral sites, the thermal conductivity at room temperature is dramatically reduced and the coefficient of thermal expansion is over 10×10−6 K−1 at high temperature, which results from the expansion of octahedron due to the much larger radius of Yb3+ ion compared with the host cation (Al3+ ion). On the contrary, replacing Y3+ ions with Yb3+ ions in dodecahedron, the thermal conductivity also gradually reduces to the similar value but the coefficient of thermal expansion is getting smaller, due to the relatively small ionic radius of Yb3+ causing the contraction of the dodecahedron. Therefore, a dopant with much larger radius would be preferred in both dodecahedron and octahedron to significant reduce thermal conductivity as well as increase coefficient of thermal expansion of YAG, by introducing large radial difference between the dopant and the host cations

Some Existence Results of Positive Solutions for φ

We study the existence of positive solutions for the homogeneous Dirichlet boundary value problem of φ-Laplacian systems with a singular weight which may not be in L1

Investigation of Microstructure Evolution and Phase Selection of Peritectic Cuce Alloy During High-Temperature Gradient Directional Solidification

In this work, a CuCe alloy was prepared using a directional solidification method at a series of withdrawal rates of 100, 25, 10, 8, and 5 μm/s. We found that the primary phase microstructure transforms from cellular crystals to cellular peritectic coupled growth and eventually, changes into dendrites as the withdrawal rate increases. The phase constituents in the directionally solidified samples were confirmed to be Cu2Ce, CuCe, and CuCe + Ce eutectics. The primary dendrite spacing was significantly refined with an increasing withdrawal rate, resulting in higher compressive strength and strain. Moreover, the cellular peritectic coupled growth at 10 μm/s further strengthened the alloy, with its compressive property reaching the maximum value of 266 MPa. Directional solidification was proven to be an impactful method to enhance the mechanical properties and produce well-aligned in situ composites in peritectic systems

One-step fabrication of superhydrophobic P(VDF-co-HFP) nanofibre membranes using electrospinning technique

© 2019 Wiley Periodicals, Inc. In this study, superhydrophobic electrospun P(VDF-co-HFP) membranes were fabricated in a one-step electrospinning process. The effects of the key parameters of electrospinning (solution concentration, electrical potential, flow rate, and solvent) on the surface roughness, fiber formation, and hydrophobicity of the membranes were evaluated using Taguchi method. A 4 × 3 orthogonal array was utilized, and the results indicated that the solvent played the critical role in producing the superhydrophobic nanofibre membranes. It was demonstrated that it is possible to produce superhydrophobic membranes with P(VDF-co-HFP) without additional functionalisation and fillers. The highest water contact angle and the lowest contact angle hysteresis obtained were 156° and 5°, respectively, and the roughness values varied from 0.15 to 5.74 μm for the produced P(VDF-co-HFP) nanofibre membranes. The surface superhydrophobicity of the membranes was attributed to the specific structures consisting of a combination of beads and nanofibres. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48817

Highly ordered BN ⊥ –BN ⊥ stacking structure for improved thermally conductive polymer composites

The substantial heat generation in modern electronic devices is one of the major issues requiring efficient thermal management. This work demonstrates a novel concept for the design of thermally conducting networks inside a polymer matrix for the development of highly thermally conductive composites. Highly ordered hexagonal boron nitride (hBN) structures are obtained utilizing a freeze-casting method. These structures are then thermally sintered to get a continuous network of BN⊥–BN⊥ of high thermal conductivity in which a polymer matrix can be impregnated, enabling a directional and thermally conducting composite. The highest achieved thermal conductivity (K) is 4.38 W m−1 K−1 with a BN loading of 32 vol%. The effect of sintering temperatures on the K of the composite is investigated to optimize connectivity and thermal pathways while maintaining an open structure (porosity ≈ 2.7%). The composites also maintain good electrical insulation (volume resistivity ≈ 1014 Ω cm). This new approach of thermally sintering BN⊥–BN⊥ aligned structures opens up a new avenue for the design and preparation of filler alignment in polymer-based composites for improving the thermal conductivity while maintaining high electrical resistance, which is a topic of interest in electronic packaging and power electronics applications

Application of multiple InSAR techniques and SAR data from multi-sources to landslide deformation monitoring: A case study of the Zhixincun landslide in Jilin Province

In order to realize effective monitoring of Zhixincun landslide, this paper selected 27 sentinel-1A data in 2017, and conducted deformation monitoring of Zhixincun landslide based on small baseline radar interferometry technology (SBAS-InSAR), and analyzed its temporal evolution situation. Using ALOS-2 data from 2016 and 2017, differential radar interferometry (D-InSAR) was used to monitor the characteristics of the landslide variant. SBAS-InSAR monitors the temporal evolution situation of landslide deformation, while D-InSAR mainly monitors the deformation of specific landslide shape and variation. Moreover, the penetration of L-band ALOS-2 data is stronger than that of C-band sentinel-1A data, which can obtain more complete interference information. The monitoring results of both can be cross-verified. Improve the reliability of the results. The SBAS-InSAR monitoring results showed that the slope end of the landslide catchment area in Zhixincun had subsidence during the monitoring period, and the surface subsidence at the landslide end reached 12.47mm from July 5 to July 29, with an average subsidence rate of 2.88mm/a during the monitoring period. Uplift occurred in the threatened residential areas in the valley, with an average cumulative uplift of 19.59mm on December 8 and an average uplift rate of 19.99mm/a during the monitoring period. The D-InSAR results showed that there were five major deformations on the slope of Zhixincun landslide catchment area. The largest deformations with an area of 17 973m2 were located on the west side of the slope, and the most unstable deformations were located on the east side of the slope. The average cumulative shape variable reached 49.9mm during the monitoring period. Both monitoring methods showed that the threat of landslide disaster mainly came from the west slope with poor vegetation cover, and the rainy season was the key period of landslide disaster prevention and control in Zhixincun

Boron-doped rutile TiO2/ anatase TiO2/ ZrTiO4 ternary heterojunction photocatalyst with optimized phase interface and band structure

To improve the photocatalytic performance of TiO2-based heterostructures, Z-scheme/Ⅱ-type rutile TiO2 (R)/anatase TiO2 (A)/ZrTiO4 ternary heterojunction photocatalyst was designed and prepared via a facile one-step calcining strategy. Phase interface and band structure of the materials were controlled and optimized by regulating R–TiO2/A–TiO2 mass ratio in the TiO2 (A, R)/ZrTiO4 structures using boron doping. The highest photocatalytic performance and excellent catalytic stability of Rhodamine B removal was observed from the heterojunction with a low R–TiO2/A–TiO2 mass ratio of 0.066, even after five testing cycles, accompanying with low photoluminescence intensity and electrochemical impedance, high photocurrent and charge carrier density (5.12 × 1022 cm−3), and a positive shift of valence band position (from +2.06 to + 2.16 eV). The increased photodegradation behaviour was due to the remarkably enhanced separation efficiency and improved redox ability of the photo-induced charge carriers as a result of the high content of oxygen vacancies and the formed anatase TiO2/rutile TiO2 Z-scheme heterojunction