Effects of injection parameters on propagation patterns of hydrogen-fueled rotating detonation waves

Two-dimensional rotating detonation waves (RDWs) with separate injections of hydrogen and air are simulated using the Navier–Stokes equations together with a detailed chemical mechanism. The effects of injection stagnation temperature and slot width on the detonation propagation patterns are investigated. Results find that extremely high temperatures can lead to a chaotic mode in which detonation waves are generated and extinguished randomly. Increasing the slot width can reduce the number of detonation waves and finally trigger detonation quenching at a low injection stagnation temperature. But increasing the slot width can change the RDW propagation pattern from a chaotic to a stable mode under high injection temperature. Furthermore, the kinetic parameter τ (representing the chemical reactivity of the mixture) and the kinematic parameter α (representing the mixing efficiency of hydrogen and oxygen) are introduced to distinguish the RDW propagation patterns.     

Physical properties of microwave and solid state synthesized La0.7Na0.3MnO3

We report the structural, magnetic, electrical and broadband microwave absorption in La_0.7Na_0.3MnO₃ sample synthesized by microwave (MW) irradiation (Na_0.3LMO_MW) and compare them to the sample synthesized by solid-state (SS) reaction method (Na_0.3LMO_SS). Single phase Na_0.3LMO_MW was synthesized at 800 °C in 30 min, whereas, Na_0.3LMO_SS sample was obtained by sintering at 1200 °C for 48 h. Although both these samples show ferromagnetic transition at T_C ～324.8 K, the MW-synthesized sample shows distinct physical properties: broad ferromagnetic transition, smaller saturation magnetization, a large difference between the magnetic ordering and metal-insulator transition temperatures, a large high-field magnetoresistance, a table top-like magnetocaloric effect, and a large low-field microwave absorption compared to the solid state synthesized sample. These differences are suggested to arise from magnetic heterogeneity induced by smaller grain size and surface spin disorder in the MW synthesized La_0.7Na_0.3MnO₃.     

Self-optimized and renewable Ni–Co alloy@Co–Co2C catalyst for higher alcohols synthesis from syngas

Higher alcohols synthesis (HAS) from syngas (CO/H₂) has attracted widespread attention, while the low selectivity and poor stability of the catalysts mainly stumbled its industrial application. In the work, Ni–Co alloy nanoparticles (NPs) derived from Co_1-xNi_xAl₂O₄ loaded on the SiO₂ with large specific surface area were prepared; and during reaction, the highly dispersed Ni–Co alloys were self-optimized to Ni–Co alloy@Co–Co₂C. Importantly, Ni–Co alloy@Co–Co₂C can be regenerated through oxidation - reduction - self-optimization process. Characteristic results indicated that the structural liberalization during the reaction process inhibited the loss of Ni, regulated and balanced the dual active sites of the catalyst and the Ni–Co alloys were regenerated after the re-oxidation and re-reduction process. The optimized catalyst exhibited excellent catalytic performance, including a high total selectivity to alcohols of 39.3% and an excellent catalytic stability at 250 °C, 3.5 MPa (H₂/CO = 2) and a space velocity of 6000 mL (g_cat h)^?1. In addition, the Ni–Co alloy@Co–Co₂C catalyst after stability test could recover its original catalytic performance after re-oxidation and re-reduction. The renewable characteristics and superior catalytic performance of Ni–Co alloy@Co–Co₂C made the catalyst to be one of the potential industrial catalysts for HAS.     

Crystallization behavior and density functional theory study of solution combustion synthesized silicon doped calcium phosphates

The influence of heat-treatment temperatures (700 °C, 900°C, 1200 °C) on the phase, physical properties, crystallization rate, and in vitro properties of the solution combustion synthesized silicon-doped calcium phosphates (CaPs) were investigated. The thermodynamic aspects (enthalpy, entropy, and free energy) of the synthesis process and the crystallographic properties of the final samples were first predicted and then confirmed using density functional theory (DFT). Results demonstrated that the crystallization rate was controlled by the fuel(s) type (glycine, citric acid, and urea) and the amounts of Si⁴⁺ ions (0, 0.1, 0.4 mol). The highest calculated crystallization rate values of the un-doped, 0.1, and 0.4 mol Si-doped samples were 64%, 22%, 38%, respectively. The obtained results from the DFT simulation revealed that crystal growth in the direction of c-axis of hydroxyapatite (HAp) structure could change the stability of (001) surface of (HAp). Also, the computational data confirmed the adsorption of Si–OH groups on the (001) surface of HAp during the SCS process with an adsorption energy of 1.53 eV. AFM results in line with DFT simulation showed that the observed change in the surface roughness of Si-doped CaPs from 2 to 8 nm could be related to the doping of Si⁴⁺ ions onto the surface of CaPs. Besides, the theoretical and experimental investigation showed that crystal growth and doping of Si⁴⁺ ions could decrease the activation energy of oxygen reduction reaction (ORR). Furthermore, the results showed that the crystallized HAp structure could have great potential to efficiently reduce oxidative stress in human body.     

Techno-economic-environmental evaluation of a combined tri and dry reforming of methane for methanol synthesis with a high efficiency CO2 utilization

Production of methanol, as a green energy, from syngas is coming into focus. However, natural gas based methanol plants, which are used steam reforming of methane for syngas production, have a high CO₂ emission resulting in the global warming. In this study, a novel process for methanol synthesis is proposed to reduce CO₂ emission. In this regard, natural gas and flue gas are fed to a parallel-series system with tri and dry reforming of methane for syngas production with the optimized stoichiometric number. Then, the produced syngas is converted to methanol in a reactor. Finally, the produced methanol is purified by two distillation towers. The proposed method is compared to a referenced method in the view of technological, economic and environmental metrics. The techno-economic-environmental analysis of the processes reveals that not only the proposed method, as compared to the referenced one, increases CO₂ conversion from 20.93% to 99.22%, but also it is more economical and environmentally friendly. In addition, the global warming potential of the proposed method is almost 60% lower than that for the referenced method due to the lower CO₂ emission. Therefore, the proposed method can save above MUS$ 8 a year by CO₂ capture.     

Feeding behavior parameters and temporal patterns in mid-lactation Holstein cows across a range of residual feed intake values

Residual feed intake (RFI) is a measurement of the difference between actual and predicted feed intake when adjusted for energy sinks; more efficient cows eat less than predicted (low RFI) and inefficient cows eat more than predicted (high RFI). Data evaluating the relationship between RFI and feeding behaviors (FB) are limited in dairy cattle; therefore, the objective of this study was to determine daily and temporal FB in mid-lactation Holstein cows across a range of RFI values. Mid-lactation Holstein cows (n = 592 multiparous; 304 primiparous) were enrolled in 17 cohorts at 97 ± 26 d in milk (± standard deviation), and all cows within a cohort were fed a common diet using automated feeding bins. Cow RFI was calculated as the difference between predicted and observed dry matter intake (DMI) after accounting for parity, days in milk, milk energy, metabolic body weight and change, and experiment. The associations between RFI and FB at the level of meals and daily totals were evaluated using mixed models with the fixed effect of RFI and the random effects of cow and cohort. Daily temporal FB analyses were conducted using 2-h blocks and analyzed using mixed models with the fixed effects of RFI, time, RFI × time, and cohort, and the random effect of cow (cohort). There was a positive linear association between RFI and DMI in multiparous cows and a positive quadratic relationship in primiparous cows, where the rate of increase in DMI was less at higher RFI. Eating rate, DMI per meal, and size of the largest daily meal were positively associated with RFI. Daily temporal analysis of FB revealed an interaction between RFI and time for eating rate in multiparous and primiparous cows. The eating rate increased with greater RFI at 11 of 12 time points throughout the day, and eating rate differed across RFI between multiple time points. There tended to be an interaction between RFI and time for eating time and bin visits in multiparous cows but not primiparous cows. Overall, there was a time effect for all FB variables, where DMI, eating time and rate, and bin visits were greatest after the initial daily feeding at 1200 h, increased slightly after each milking, and reached a nadir at 0600 h (6 h before feeding). Considering the relationship between RFI and eating rate, additional efforts to determine cost-effective methods of quantifying eating rate in group-housed dairy cows is warranted. Further investigation is also warranted to determine if management strategies to alter FB, especially eating rate, can be effective in increasing feed efficiency in lactating dairy cattle.     

Evaluation of back-calculated elastic moduli of unreinforced and geocell-reinforced unbound granular material from full-scale field tests

This paper presents a field-scale experimental track over a poor subgrade with an unreinforced section and a geocell-reinforced section subjected to in-situ performance tests. Plate load tests and Benkelman beam tests were carried out distributed in several unreinforced and reinforced layers. The objective was to: (1) examine the variability of the elastic modulus of unbound granular material (UGM) due the influence of its thickness and the presence of poor subgrade in its base, (2) evaluate the modulus improvement factor (MIF) generated by the geocell reinforcement in the UGM and (3) verify the most appropriate condition to apply the MIF to transport infrastructure design. The results showed that there is a significant influence of the thickness of the UGM layer on its elastic modulus when the layer is supported directly over a soft subgrade. The MIF values obtained in field suggest that its determination is mostly related to the UGM maximum elastic modulus rather than its decreased values (by virtue of poor subgrade or reduced thicknesses), and that the analytical formulation presented for MIF calculation has good predictive capability to be applied to pavement design.     

Formation of single-crystalline BaTiO3 nanorods from glycolate by tuning the supersaturation conditions

We have studied peculiarities in the formation of single-crystalline barium titanate (BaTiO₃) nanorods from a glycolate-mediated complex via a single-step hydrothermal process under different supersaturation (S_R) conditions. X-ray diffraction (XRD) showed the formation of pure BaTiO₃ with an S_R of above 19. The tetragonality for the BaTiO₃ (c/a) reached 1.013 at S_R = 19–29 and dropped to 1.010 for S_R = 39. According to the transmission electron microscopy (TEM) and XRD analyses, the rod-shaped particles exhibited single crystallinity and crystal growth along the [001] plane. With scanning electron microscopy (SEM), the morphological evolution from a plate-shaped intermediate precursor (S_R = 6–9) to a rod-shaped product with an aspect ratio of 6–9 (S_R = 19–29), and to non-polar material with an irregular structure (S_R = 39), was observed. The negative slope, linear dependence of the particles’ width and length on the supersaturation level in the range S_R = 19–39 was established for the first time. The replacement of the prevailing crystallization mechanism from in-situ topotactic transformation into dissolution-precipitation above S_R = 19 was observed. It was shown that with a simple regulation of the S_R, the structural and morphological characteristics of the obtained BaTiO₃ nanoparticle can be effectively tuned.     

Photoluminescence and hydrogen evolution properties of ZnS:Eu quantum dots

In the era of Photonics, design and development of novel rare earth ion-doped quantum dots (QDs) for optoelectronic applications has gained significant interest owing to their outstanding characteristics. Simultaneously, the creation of a new class of photocatalytic materials on the nanoscale is also imperative for environmental purification. Thus, we report on wet chemical synthesis, the structural, morphological, and optical characteristics, fluorescence, and hydrogen evolution of ZnS:Eu (0, 2, 4, and 6 at%) QDs for optoelectronic and photocatalytic applications. Comprehensive structural studies depicted that Eu³⁺ ions were efficiently substituted into the host matrix and altered the original structure of the ZnS compound. The emission spectra of the ZnS:Eu QDs exhibited distinctive red fluorescence owing to the transition of dopant ions in ⁵D₀ - ⁷F₁, ⁵D₀ - ⁷F₂, ⁵D₀ - ⁷F₃, and ⁵D₀ - ⁷F₄ energy levels of the 4f orbital of the Eu³⁺ ions. Moreover, the photocatalytic properties of ZnS:Eu (6 at%) QDs possess better catalytic efficiency toward hydrogen evolution through a water splitting mechanism under simulated sunlight irradiation. The observed photocatalytic phenomenon in the synthesized samples agreed well with the luminescence properties exhibited by the QDs.