Eu2O3–Cu/NC nanocomposite catalyst with improved oxygen reduction reaction activity for Zn-air batteries

Rare earth oxide promoted transition metal composite catalyst Eu₂O₃–Cu/NC with outstanding oxygen reduction reaction (ORR) performance, is constructed by hydrothermal and subsequent high-temperature calcination, considering replacing Pt/C. This synthesis method yields Eu₂O₃–Cu nanoparticles with uniform distribution, improved oxygen vacancies and increased content of N-doping. And the strong synergistic effect was created between promoter Eu₂O₃ and chief Cu. In addition, the accommodate adsorption and transfer of O species endow Eu₂O₃–Cu/NC the improved ORR activity than Eu₂O₃/NC and Cu/NC. Meanwhile, the stability of Eu₂O₃–Cu/NC is also strengthened compared to Cu/NC on account of the interaction of active sites, and the H₂O₂ yield of Eu₂O₃–Cu/NC is very low. For practical application, a rechargeable Zn-air battery with an air cathode of Eu₂O₃–Cu/NC displays a larger power density, excellent charge-discharge cycle stability and good rate capability. The designed composite shows potential application prospects in the fields of energy conversion.     

Scientific mapping to identify competencies required by industry 4.0

The objective of this study was to identify what competencies are identified in the literature as necessary for Industry 4.0 by conducting a survey of the literature and a scientific mapping of the evolution of the issues related to the qualification of professionals for Industry 4.0 and possible paths for research and education. A search was conducted on the Scopus, Web of Science and Science Direct databases for the interval from 2010 to 2018. This systematic review revealed topics and authors currently specialized in the field and allowed mapping the field of study. The identification of journals and keywords useful in future studies was also an object of this study. SciMAT software was used for the systematic literature review. The results are highlighted by the set of competencies (knowledge and skills) that must be developed in professional education to accompany the new industrial revolution, as well as the importance of integrating efforts by companies, governments and universities. These efforts should focus on creating “learning factories”, which are understood to be environments that provide practical experiences to these professionals, preparing them in the best way possible for the requirements of Industry 4.0. This conceptual map showed that the main competencies needed include skills: (leadership, strategic vision of knowledge, self-organization, giving and receiving feedback, pro-activity, creativity, problem solving, interdisciplinarity, teamwork, collaborative work, initiative, communication, innovation, adaptability, flexibility and self-management) and knowledge of contemporary fields (information and communication technology, algorithms, automation, software development and security, data analysis, general systems theory and sustainable development theory).     

Photoluminescence enhancement in a Na5Y(MoO4)4:Dy3+ white-emitting phosphor by partial replacement of MoO42− with WO42− or VO43−

A series of Na₅Y(MoO₄)_4-yA_y:Dy³⁺ (A = WO₄^2?, VO₄^3?; y = 0–0.05) phosphors were synthesized by the combustion method. Some of the MoO₄^2? sites were occupied by WO₄^2? and VO₄^3? anions, which enhanced the luminescence property of Dy³⁺-doped Na₅Y(MoO₄)₄. XRD results show that the crystal structures of the samples were consistent with the standard Na₅Y(MoO₄)₄ phase. Under excitation at 352 nm, the Na₅Y(MoO₄)_4-yA_y:Dy³⁺ phosphors exhibited a characteristic blue emission at 485 nm and a yellow emission at 577 nm, which originated from the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions of Dy³⁺ ions, respectively. White light can be achieved by combining these blue and yellow emissions. After replacing MoO₄^2? with WO₄^2? and VO₄^3? anions in Na₅Y(MoO₄)₄:Dy³⁺, the luminescence intensity of Dy³⁺ was significantly improved due to the crystal field effect. The results indicate that Na₅Y(MoO₄)_3.97(WO₄)_0.03:Dy³⁺ and Na₅Y(MoO₄)_3.97(VO₄)_0.03:Dy³⁺ phosphors have good prospects for application in n-UV-excited w-LEDs.     

Synthesis and luminescence enhancement of red-emitting Sr9Y(PO4)7:Eu3+ phosphor through Gd3+ co-doping for white light-emitting diodes

A series of Sr₉Y(PO₄)₇:Eu³⁺ and Sr₉Y(PO₄)₇:Eu³⁺, Gd³⁺ red-emitting phosphors were prepared via a high-temperature solid-state method, Gd³⁺ ion was co-doped in Sr₉Y(PO₄)₇:Eu³⁺ as sensitizer to enhance the luminescence property. The X-ray diffraction results verify that the structure of the as-prepared samples is consistent with the standard Sr₉Y(PO₄)₇ phase. All the Sr₉Y(PO₄)₇:Eu³⁺ samples show both characteristic emission peaks at 594 nm and 614 nm under near-ultraviolet excitation of 394 nm. The co-doping of Gd³⁺ significantly improves the luminescence intensity of the Sr₉Y(PO₄)₇:Eu³⁺ phosphors due to the crystal field environment effect and energy transfer of Gd³⁺→Eu³⁺ caused by the introduction of Gd³⁺, especially Sr₉Y(PO₄)₇:0.11Eu³⁺, 0.05Gd³⁺, which emission intensity is higher than that of Sr₉Y(PO₄)₇:0.11Eu³⁺ by 1.21 times. The color purity and lifetime of Sr₉Y(PO₄)₇:0.11Eu³⁺, 0.05Gd³⁺ phosphor are 88.26% and 3.7615 ms, respectively. A w-LED device was packaged via coating the as-prepared phosphor on n-UV chip of 395 nm with commercial phosphors. These results exhibit that the Sr₉Y(PO₄)₇:Eu³⁺, Gd³⁺ red-emitting phosphor can be used as a red component in the w-LEDs application.     

Hydrogen evolution reaction activity and stability of sintered porous Ni-Cu-Ti-La2O3 cathodes in a wide pH range

Finding a low-cost, efficient, stable, and workable electrode for the production of hydrogen based on the hydrogen evolution reaction (HER) is particularly critical. At present, the use of Pt/C electrodes is under development, but the expensive cost hinders its wide application in the HER field. Herein, a novel porous Ni-Cu-Ti-La₂O₃ cathode with a porosity of 29.07% was proved to be an excellent substitute for the HER, which was fabricated by vacuum sintering based on powder metallurgy. The hydrogen evolution efficiency is superior to that of commercial 20% Pt/C under pH = 14.1 condition (2.67 mol/L KOH). The HER activity is also close to commercial 20% Pt/C under pH = 0.1 (1 mol/L HCl) and pH = 8.1 (3.34% simulated seawater) conditions and exceeds it after reaching a high potential. Meanwhile, it can achieve good HER stability within 48 h and maintain its HER activity after 1000 continuous cycle electrolysis.     

Highly porous (La1/5Nd1/5Sm1/5Gd1/5Yb1/5)2Zr2O7 ceramics with ultra-low thermal conductivity

The high-entropy rare earth zirconate (La_1/5Nd_1/5Sm_1/5Gd_1/5Yb_1/5)₂Zr₂O₇ porous ceramics ((5RE_1/5)₂Zr₂O₇ PCs) were prepared using a foam-gel casting-freeze drying method combined with segmented calcination process. The results of SEM, TEM, and XRD analyses of the (5RE_1/5)₂Zr₂O₇ PCs indicated the formation of a defective fluorite crystal structure, with the rare earth elements homogeneously distributed. Meanwhile, the as-prepared (5RE_1/5)₂Zr₂O₇ PCs exhibited high porosity, low bulk density, low thermal conductivity, and relatively high compressive strength. Moreover, the high-temperature thermal conductivity of the samples was evaluated, and the results showed that the (5RE_1/5)₂Zr₂O₇ PCs maintain a thermal conductivity of 0.150 ± 0.002 W m^?1 K^?1 even at 1000 °C. The strategy used in this paper can be extended to the synthesis of other high-entropy porous ceramics with high porosity and low thermal conductivity, which is suitable for applications as thermal insulation materials.     

Shock/expansion fan interaction with real gas effects for Earth and Mars atmospheric conditions

Numerical simulations are performed to investigate the real gas effects on shock/expansion fan interaction. Initial perfect gas simulations at low enthalpy capture the flow structures efficiently and outcomes are found to have excellent agreement with the analytical calculations. Furthermore, the simulations with the real gas solver for different enthalpies showed that the variation in enthalpy significantly changes the flow structures. It is observed that an increase in enthalpy leads to a decrease and increase in the postshock and postexpansion fan Mach numbers, respectively. Another important observation is the decrement in the peak pressure ratio with an increment in the enthalpy. These effects are noted to be more pronounced for Mars's environment due to the higher dependency of specific heat on temperature.     

Estimating of the Dry Unit Weight of Compacted Soils Using General Linear Model and Multi-layer Perceptron Neural Networks

Compaction of earth fill is a very important stage of construction projects. Degree of compaction is defined by relative compaction. The relative compaction of a compacted earth fill is calculated by dividing the dry unit weight obtained from in situ tests by-into the maximum dry unit weight obtained from laboratory compaction tests. This rate represents compaction quality in the field. Numerous test methods such as sand cone, rubber balloon, nuclear measurements, etc., are available to determine the maximum dry unit weight of soils in the field. It is well known that these methods have disadvantages as well as advantages. This study focused on estimation of dry unit weight of soils depending on water contents and P-wave velocities of compacted soils. The multi-layer perceptron (MLP) neural networks and general linear model (GLM) were used in this study to estimate the dry unit weight of different types of soils. Results of the MLP neural networks were compared with the GLM results. Based on the comparisons, it is found that the MLP generally gives better dry unit weight estimates than the GLM technique. The laboratory experiments and modeling studies showed that a new method for compaction control can be developed depending on P-wave velocity to estimate of the dry unit weight of compacted soils.     

Improving the Mechanical Properties of Mg-Gd-Y-Ag-Zr Alloy via Pre-Strain and Two-Stage Ageing

In this study, we investigated the effects of single-stage ageing (SSA), two-stage ageing (TSA), 2% pre-strain + single-stage ageing (P2%SSA) and 2% pre-strain + two-stage ageing (P2%TSA) on the mechanical properties of as-extruded Mg–8Gd–3Y–0.5Ag–0.5Zr alloy (E alloy). Compared with the SSA treatment, the TSA treatment increased the number density of $\beta ^{\prime}$ phase. The P2%SSA and P2%TSA treatments generated the $\gamma ^{\prime}$ phase and chain-like precipitates in addition to the $\beta ^{\prime}$ phase. The contributions of these ageing treatments to the alloy strengthening can be ranked as P2%TSA > P2%SSA > TSA > SSA, because the increments in the tensile yield strength were estimated to be 199 MPa > 148 MPa > 144 MPa > 110 MPa. Different from the traditional strengthening of $\beta ^{\prime}$ phase in the E + SSA and E + TSA alloys, the composite precipitates comprising the $\beta ^{\prime}$ phase, $\gamma ^{\prime}$ phase and chain-like precipitates in the E + P2%SSA and E + P2%TSA alloys provided better combined strengthening effect. The $\beta ^{\prime}$ phase was still dominated in the strengthening effect of the composite precipitates. Owing to the higher number density of $\beta ^{\prime}$ phase in the composite precipitates, the E + P2%TSA alloy exhibited the better mechanical performance as compared with the E + P2%SSA alloy. Finally, the E + P2%TSA alloy had the ultimate tensile strength of 452 MPa, the tensile yield strength of 401 MPa and elongation to failure of 3.3%.     

Bearing capacity of composite ground with soil-cement columns under earth fills: Physical and numerical modeling

Soil-cement columns are widely used to improve soft ground, and the bearing capacity of the formed composite ground is a key design parameter. The currently employed design method was developed for composite grounds under rigid footings, whilst the bearing capacity behavior of composite grounds under earth fills with different degrees of stiffness has rarely been investigated. Hence, the present study attempts to fill this gap. In this investigation, 1-g laboratory model tests are conducted to compare the bearing capacity behavior of composite grounds under a rigid footing and under embankment fill, based on which a numerical model that can capture the strain-softening behavior of soil-cement columns is established. The calibrated numerical model is further employed to perform 144 analyses. The results indicate that the failure mode of composite grounds differs for different types of earth fills: soil failure occurs prior to column failure under soft clay and dredged slurry, whereas column failure is the primary failure mode for composite grounds under embankment fill. This difference in failure mode of composite grounds can be explained using soil arching theories. For different failure modes, different bearing capacity efficiency factors should be used in design.