[en] The light and heavy rare earth elements are added to the magnesium alloys to improve the strengths and the creep resistance. The age hardening behaviors of the extruded Mg–6Gd–4Y–Nd–0.7Zr alloy aged at 200, 225 and 250 °C were investigated. Tensile tests and creep tests of the extruded and extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr were carried out at 150–300 °C. The relationship between the microstructure and the properties of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy was studied. The result shows that the extruded Mg–6Gd–4Y–Nd–0.7Zr (contained less than 10 wt% Gd) peak aged at 225 °C for 72 h has the excellent creep resistance and high strengths with the UTS more than 350 MPa from room temperature to 200 °C, which are correlative with the precipitates. The high dense and uniform distribution of β′ phase with good heat stability precipitates inhibiting the dislocation motion contributes to age hardening, accelerates the ageing hardening response and increases the creep resistance. The artificially aged (T5) at low temperature further creep tested and tensile tested at higher temperatures decreases the resistance to the dislocation motion and the grain boundary sliding, resulting in the reduction in creep properties and strengths of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy above 225 °C.

[en] In a large class of nonlocal as well as local higher derivative theories minimally coupled to the matter sector, we investigate the exactness of two different classes of homogeneous Gödel-type solutions, which may or may not allow closed time-like curves (CTC). Our analysis is limited to spacetimes solving the Einstein's EoM, thus we can not exclude the presence of other Gödel-type solutions solving the EoM of local and nonlocal higher derivative theories but not the Einstein's EoM. It turns out that the homogeneous Gödel spacetimes without CTC are basically exact solutions for all theories, while the metrics with CTC are not exact solutions of (super-)renormalizable local or nonlocal gravitational theories. Hence, the quantum renormalizability property excludes theories suffering of the Gödel's causality violation. We also comment about nonlocal gravity non-minimally coupled to matter. In this class of theories, all the Gödel's spacetimes, with or without CTC, are exact solutions at classical level. However, the quantum corrections, although perturbative, very likely spoil the exactness of such solutions. Therefore, we can state that the Gödel's Universes with CTC and the super-renormalizability are mutually exclusive.

[en] A bistatic space debris observation system using a radio telescope as the receiving part is introduced. The detection capability of the system at different working frequencies is analyzed based on real instruments. The detection range of targets with a fixed radar cross section and the detection ability of small space debris at a fixed range are discussed. The simulations of this particular observation system at different transmitting powers are also implemented and the detection capability is discussed. The simulated results approximately match the actual experiments. The analysis in this paper provides a theoretical basis for developing a space debris observation system that can be built in China

[en] Highlights: • 3000 μm² defect-free HCP domain was successfully synthesized. • Relative humidity (RH) as well as the first rotational speed (v_a) of the dual-speed procedure was identified as the quality-control parameters in spin coating. • 23% RH and v_a = 1000 rpm were identified as the optimistic spin coating processing parameters for SiO₂ HCP monolayer. • Statistical experimental design was demonstrated as one efficient strategy for multi-factor processing optimization. - Abstract: A large-area hexagonal packed monolayer of silica spheres with consistent defect-free domains of a size larger than 3000 μm² was prepared by spin coating on glass substrates with the assistance of experimental design and statistical analysis. The ratio of the defect-free monolayer area to the square of sphere diameter is nearly two times of the previously reported maximum values. Several parameters involved in the spin coating systems were investigated. The results indicated that the relative humidity and the rotational speed of the first step of the spin coating had the most important impact on the ordering degree of the prepared monolayer. Furthermore, the ordering degree of the obtained monolayer increased with a decreased relative humidity. In addition, it reached an optimal value when the first rotational speed during spin coating reached a value of 1000 rpm. From this study, it can be concluded that statistical experimental design is an efficient strategy, especially for multi-factor phenomenon studies

[en] This paper presents a novel temperature independent current reference based on the theory of mutual compensation of mobility and threshold voltage. It is completely compatible with standard CMOS-technology. The experiment results indicate that the temperature coefficient of this current reference is less than 290 ppm/⁰C over a temperature range from -20 to 110⁰C. (semiconductor integrated circuits)

[en] Highlights: • Three-dimensionally ordered macroporous (3DOM) MnCeTi catalysts synthesized. • The 3DOM catalysts have high surface area to expose more active sites. • The addition of Ti promoted the N₂ selectivity. • The MnCeTi catalysts showed remarkable H₂O tolerance. • In situ DRIFT analysis confirmed the SCR reaction followed the L-H mechanism. A series of 3DOM-Mn_xCe_yTi_z catalysts with three-dimensionally ordered macroporous (3DOM) structure were synthesized by a soft template method. The high SCR activity of the 3DOM-Mn₃Ce₁ catalyst at low temperature was owing to the excellent redox ability and rich Lewis and Brønsted acid sites of the catalysts, which were beneficial to improve the catalytic activity. However, the strong oxidizability of MnO_x resulted in the nonselective oxidation of NH₃ and generation of N₂O, decreasing the N₂ selectivity. After addition of Ti, the redox capacity of the 3DOM-Mn₃Ce₁Ti₁ catalyst decreased, and the NH₃ were strongly adsorbed on the acid sites, which enhanced the N₂ selectivity with a broadened temperature window of 240–440 °C and a high GHSV of 120000 h⁻¹. Furthermore, both the 3DOM-Mn₃Ce₁ and 3DOM-Mn₃Ce₁Ti₁ catalysts showed remarkable tolerance of H₂O. Finally, through in situ DRIFT analysis, the Langmuir-Hinshelwood (L-H) mechanism was confirmed as the dominant reaction pathway over the 3DOM-Mn₃Ce₁Ti₁ catalyst.

[en] We present a new polymer quartz piezoelectric crystal sensor that takes a quartz piezoelectric crystal as the basal material and a nanometer nonmetallic polymer thin film as the surface coating based on the principle of quartz crystal microbalance (QCM). The new sensor can be used to detect the characteristic materials of a volatile liquid. A mechanical model of the new sensor was built, whose structure was a thin circle plate composing of polytef/quartz piezoelectric/polytef. The mechanical model had a diameter of 8 mm and a thickness of 170 μm. The vibration state of the model was simulated by software ANSYS after the physical parameters and the boundary condition of the new sensor were set. According to the results of experiments, we set up a frequency range from 9.995850 MHz to 9.997225 MHz, 17 kinds of frequencies and modes of vibration were obtained within this range. We found a special frequency f_sp of 9.996358 MHz. When the resonant frequency of the new sensor's mechanical model reached the special frequency, a special phenomenon occurred. In this case, the amplitude of the center point O on the mechanical model reached the maximum value. At the same time, the minimum absolute difference between the simulated frequency based on the ANSYS software and the experimental measured stable frequency was reached. The research showed that the design of the new polymer quartz piezoelectric crystal sensor perfectly conforms to the principle of QCM. A special frequency value f_sp was found and subsequently became one of the most important parameters in the new sensor design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

[en] Silicon nitride (Si₃N₄) ceramics are widely used in mechanical and thermal management applications due to their excellent properties. To overcome the difficulties in traditional Si₃N₄ ceramic forming techniques, it is interesting to see the possibility of making complex-shaped silicon nitride ceramic component with novel 3D printing methods. In this study, we aim to study the effect of photo-initiators on the curing behavior of pre-formulated Si₃N₄ ceramic UV resin suspension. To elucidate the potential multi-factor interactions, a statistic experiment design was implemented in a sequence of screening and optimization by using Modde software. It was found that the kinds of photo-initiators, total amount of initiators and the mixture ratio between initiators have a great influence on the curing properties of silicon nitride UV ceramic resin. Based on these results, a formula was selected based on the criterion of using least amount photo-initiator while reaching the highest curing thickness. (paper)

[en] Honeycomb sandwich structures were widely used in lightweight design. However, the difficulties with the fabrication process actually highly limit their practical usage, especially for ceramic materials. In this paper, 3 mol% yttria-stabilized ZrO₂ (3Y-TZP) honeycomb sandwich structures with square and hexagonal cell were prepared successfully by using digital light processing (DLP) printing method. With a base material density of >6.02g/cm³, square/hexagonal honeycomb sandwich structures with structural density of 42.89%-66.24% were achieved by modifying unit cell wall thickness. It can be concluded that square honeycomb cell is preferred for getting higher bending strength at the same structural density. (paper)

[en] Cellular structure has been applied in lightweight engineering application because of its high specific strength, high modulus and low relative density. Here we used 3Y-TZP ceramic to realize two typical cellular structures, Kelvin and Octet-truss, through a novel digital light processing (DLP) 3D printing method. The strut size was changed systematically to generate structures with porosities in the range of 10% ∼ 80% and the bending strength of these structures were investigated and analyzed by three-point bending test. (paper)